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Metalic Ores and Iron Ores
Introduction:Co mp o n e n t s o f the Harth:
Earth is divided into three layers main sections which are as below in sequence from top to bottom:
1 - the earth’s c ru st: variable thickness ranges from 60 kilometers deep under the mountains and between 40-45 kilometers in continent areas It is possible that the thickness of up to 5 kilometers below the ocean.
2 - Mantle: a second layer is formed in general of iron and magnesium silicates and continue to a depth of 2900 km and divided to three sections each of which is:
- Upper Mantle.
- Transition Zone.
- Lower Mantle.
3 - The Core: a thickness of 3370 kilometers and is divided into the inner core is solid-state thickness of 1370 kilometers surrounded the outside a thickness of 2000 km and both of iron and nickel, but the elements in it is as metallic due to the high temperature in excess of 4000 degrees Celsius and a high pressure .
Components of the earth's crust
More Components of the earth's crust is followed by an oxygen element silicon and then aluminum, iron, calcium, magnesium, sodium, potassium, these eight elements formed 98.5% and the rest of all the ingredients formed only 1.5%.
■ O xygen 46 .5
■ S ilicon 27.7
■ Al 8
■ Fe 5
■ Ca 3.5
□ M g 2.8
□ K 2.6
□ M g 2
□ O th e rs 1.5
Ores Minerals
Ore: commercial term means any metal aggregates have economic value lead to extract.And so is the metal must have (Value) economic and depends on four factors, as below:
1 - The amount of ore existing and ability to extraction .
2 - The amount of (Mineral) found in the ore.
3 - The amount of (Metal) to be extract.
4 - The total production costs.
Ores in nature
Di v i ded into two tvpcs:
1 - Native Elements
These elements are free as a result of their persistence and resistance to the natural conditions of reduction and other interactions and remains as metals or non-metals not united.
The most important types:
A - Gold (Au)
B - Silver (Ag)
C - Platinum (Pt).
D - Diamond & Graphite (C )
2 - chemical compounds include:
A - oxides, which are divided to two types of water and non-water:
Hydrated Oxides: It consists of oxides containing water
molecules and the most important:
Opal Si02
Limonize HFe02. nH2o
Manganite MnO. OH
Bauxite consist of aluminum hydrated Oxides
1- unhydrated oxides(S iO > )
(Fe, 0 , )
(FeO . T i 0 2) or (FeTiO, )
(Fe3 0 4 ) or (FeFe2 0 4 )
(FeO . Cr2 ) or (FeCr2 0 4 )
(Cu2 O)
( A l 2 0 3)
( MgO . A 1, 0 3) or < Mg A 1, 0 4 )
( M n O , )
<U02)
( T iO , )
( S n 0 2)
( ZnO)
U U l
j jL J I
1! l^ jl
B-sulphides :
(Ag,S)
<Cu2S)
(Cu, FeS<)
(Pbs)
( ZnS)
(CuFeS2)
(FeS)
(HgS)
(AgS)
( As 2S 3 )
1
c^-»Lw*JLA-l
O jU j y S 1
U l i l
j Aj
j I S L J I
C - Halides
Some of the various metal halides arise either united between the direct halogen and metal at high-temperature or chemical reactions as a metal fluorite, which arises from the interaction of hydrogen fluoride with calcium carbonate.
The most important of these raw materials:
Halite NaCL or so-called sodium chlorite
Slivite KCL and consists of potassium chloride crystals
There are other types of halides, such as:
Fluorite CaF,
Ceraggrite AgCl f
Cryolite Na_» A lFb *
Atacamite Cu, S I ( O H ) , c - jUISI'V*
Cranallite <KC1 ■ M g C K 6 H ; 0 )
Or (KMg C\ . 6 H ; O)
D- CarbonatesThere are three types in the nature:
Unhydrated C a r b o n a t e s I O
Hydrated Carbonates i J l i l o Ljj j IS'
Hydroxyl Carbonates i j J U A I o \jym j l S
E - sulfatesAnd also are found in the nature in the form of three types,
_A group of sulfate Unhydrated
_A group Hydrated sulphates
_A group of sulfate hydroxide
F- Phosphatesincludes a wide range of raw phosphate which have high economic importance to production of some phosphate fertilizers or to obtain some rare m etals, and divided into two types of metals and ores phosphate hydrated and anhydrous ,and most important in the field
of metal is a metal Monazite, which consists of phosphate some metals rare earth such as ( cerium Ce Agliatriom Y )as well as lanthanum La, as there may be some where metal thorium Th has some concentrations up to 20% is possible that contain the metal Kairotal and zircon.
There are other oresas natriate and Borate salts and sulfur but its importance because of other material not metals .
Lee. 2 Introduction to Iron and steel making
Introduction:
Fe (Iron) of the cheapest metals in the world and the least expensive and most widely used and best work. Hardened steel products used high-power endurance, in thousands of industry products used in everyday life, and these products ranging from screws to cars, ships and many others. It also is made from iron and steel machines that contribute to the production of almost everything we use in our lives including clothing, food and homes.
The word ferrous metal came from the Latin word ferrum, which means iron, which took the chemical symbol for iron ore Fe and now used for the expression of iron and its alloys.
And use the word iron in general to express every element of a number of iron and alloys (mixtures) iron with a number of metallic elements.
Iron represents one of the most well-known chemical elements prevalent in the earth's crust, but it does not exist in a single image, but in the form of pure compounds called iron ore. It uses industrial iron alloy in the manufacture and production of all what is known as steel products.
And produces (Steel) purified iron and alloyed different metallic elements. That is the iron raw material for the production of steel, as steel can be considered an image of pure iron. And looks like it just the fact that petroleum products from the purification (refining) oil, and that despite the fact that the properties and uses of iron and steel vary greatly differing extent the use of oil and petroleum.
And (Iron ores) deposition of metal or rock focus where iron during the formation of the earth's crust. The makers of steel breaks down these raw materials and processed for the production of iron ores in
which the degree of concentration of iron is higher than the degree of concentration in the raw materials, then turned to the resulting concentrates iron ore through heated with other raw materials in large
furnaces. It uses most of the output of the iron ore extraction operations in the steel industry, albeit a small part of it is used in the manufacture of other iron products.
The makers of steel to convert iron ore into steel liquid purification process in special furnaces, where it also heats steel products as well as recycled steel scrap. After the production of liquid steel is machined in different forms of panels and bars, columns, bars, wires, pipes and any other form of appropriate forms for use. The most modern factories for the production of steel undertake various steps starting from the steel industry and the smelting reduction of iron ore to steel production processes, and then forming processes different images useful for use.
Historical Overview:
Start using iron since ancient times, and believed that people have used it before Birth about four thousand years, and was the beginning of use using iron meteorites.
Iron meteorites have been made in several forms, including artifacts, weapons, tools and household items. Despite the beginnings developed for the use of iron, but it is not known precisely where and when began extracting iron from ores.
Believes that operations have begun to draw iron and grew, and then evolved in different parts of the world are independent from each other, particularly in the areas now known as the Middle East, China and India. And which then quickly spread to different parts of the world.
By the tenth century BC iron industry flourished and became very much in reach of most civilizations known at that time.
The steel industry has begun in small quantities and limited in poor quality. The steel industry continued in this period, this picture can not be manufactured at affordable prices. It was not produced in large
quantities available only at the end of the nineteenth century. Then the steel industry has developed technology very quickly through the end of the second half of the twentieth century
Typ es of iron ore:
. Iron is found in nature on a permanent basis in the form of chemical compounds, where iron combined with other elements, and in particular elements of oxygen and carbon, sulfur and silicon.
It contains a lot of iron ore on the chemical compounds composed of iron, and one or more of the other elements.
Include iron ore, the main draw, including iron:
1 - Hematite
2 - magnetite.
3 - limonite.
4 - pyrite
5 - Alsedric.
6 - Altcconnet.
Is both hematite and magnetite iron ore richest. The two types of iron oxides, both of which contain about 70% iron, and there hematite crystals in the form of shiny rocks or granular materials or non-coherent ground. Hematite and can be black or red color tinged with gray, and the magnetite is black in color and magnetic properties.
The percentage of iron in the limonite ore to about 60%. Limonite ore yellowish brown iron oxide which is watery.
Pyrite is composed of 50% iron and 50% sulfur. It is a glossy metallic appearance and looks like gold in its external appearance to a great extent.
Alsedric is composite color brown unblemished gray contains about 50% iron in addition to carbon and oxygen. Alsedric has been in the past an important source of iron in both Austria and Britain. Has consumed ail
of the two reserves of this crude, leaving him any stock.
Altcconnet are hard rock contains about 30% iron. There are in this iron ore in the form of magnetite Bakaat minutes, in some cases, be in the form of hematite iron. It has become Altcconnet of the most important deposits of iron ore.
At the present time the production of iron and steel is one of the most vibrant industries in the world. And working in these industries millions of workers in factories and production units around the world. In addition to the workers in the factories, there are millions of other works in the development and manufacture of machinery, raw materials, and energy companies needed to iron and steel industry, or in the industry and the formation and the production of consumer products of iron and steel
W o rld crude steel p ro d u c tio n 1950 to 20 0 4(million metric tons)
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t*j> Worm1M0 7701 « b m1M0 Wli»7V NiJw o mirws Cjf-
tw o U tIV..S« * » 190
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Properties of iron and its chemical composition:
Properties of iron depends largely on the degree of purity as that of iron much of the properties of silver and have (Ductility) and (Hardness) and good (Corrosion resistance) as well as the coefficient of connecting electric (Electrical conductivity) in addition to the fundamental property characteristic of iron which (Magnatibility).
It can be said that the carbon content of great importance, since it has hot metal produced from the reduction of iron ore in the blast furnace of 2 to 5.7% carbon can be melted easily and pouring into molds, but it is not malleable or rolling or pressing is not subject to any process of forming a mechanical or rolling Ali Hot or cold, and the so- called (Pig Iron).
There are two types of pig iron:
1 - white pig iron.
2 - Gray pig iron
And (Cast Iron) General contains 2-4% carbon and from 0.3-3% silicon and 0.2 to 1.2% manganese and must contain only a very small proportion of sulfur because the phosphorus makes iron easy liquidity,
but it makes it brittle and sulfur makes iron brittle at temperatures at which the composition of the hot.
It has wrought iron, which can be can be a means of manual or automated or rolled on the carbon less than pig iron or cast iron between 2% - 0.01%, and this means the steel where it can be defined hard as iron, which contains a proportion of carbon is less than 2% .
The steel can be divided as follows:
1 -carbon steel contains
A low-carbon steel: a percentage of its carbon to 0.25% and is adding some elements to improve the mechanical properties, such as copper, nickel and vanadium.
Uses: This is used in the manufacture of steel bridge beams and columns and pressure vessels.
Lovrcarbon AISI/SAE1010 Steel
(B) meduim carbon Steel: contains carbon from 0.25% to 0.6% is
handling this kind of hard work fast cooling where it will lead to improvement also add to it some of the elements of the composition of
different alloys with good mechanical properties of these elements chromium and molybdenum.
Uses: used in the manufacture of gears in the transmission industry columns and wheels rail trains
\
Medium-carbon AISI/SAE 1040 Steel
c - high carbonsteel : carbon ratio ranging from a 0.6% to 1.4%
carbon has been added to some of the elements such as chromium and vanadium and tingustin increases its resistance to corrosion and wear. It is a high hardness and weak ductility .
Uses: used in the manufacture of cutting tools and various industry number that is used in operating machines.
High-carbon AISI/SAE 1095 Steel
D - stainless steel "stainless steel" contains carbon ratio of 0.1% to
0.4% carbon and contains 11% chromium and 8% nickel in addition to some elements such as nickel and molybdenum
Uses: enters this type of steel in various industries, but is used primarily for industries that need a very high resistance to rust.
2 -steel high temperatures:
Boilers, which makes it resilient because it keeps in constant temperatures of 500-600 degrees C and molybdenum alloy is the main element in this steel.
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y j j S S J i j J j j £ j J! j ju h f l 4-lx.jL// >/ ■ >■ ^ v
Burden preparation agglomeration sintering and
pelle tiz ing o f iron ore
:Prepara t ion o f iron ore -
After extracting the iron ore from the mines soon convey crude from the factory and there are processes
Prepare raw where it is disposed of silica and alumina operations called Benefaction process and the aim of this operation is also to increase the concentration component of iron oxide in the ore
There are three ways of fracture and separation of component iron ore a volumetric components1.1.1 milling and dry processing
Using 65% of the Hematite oxide is generally used for Hematite ores Where raw iron crushes multiple stages and screen at each stage where the crusher With a diameter up to 40 mm are sent to the treated of the high furnace .and the sizes from 10-18 send to manufacture of sponge iron , below flowchart represent of dry processing
/ t C ; J Lw V
2.1.1 Milling and dry-wet processingThere ore crusher of sizes less than 10 mm produced when dryprocessing is added
Mechanic clacifire or spiral Hydrostatic so isolated particles larger than0.15 mm to the size of 10 mm to be sent to the sintering stage but Smaller volume less than 0.15 mm is called fines which alumina ratio which is high and not favors where discarded as waste
3. /. 1 Milling and w et ProcessingThis method is used for materials that contain less iron than the proportion (60-62% iron)
The process involves multiple stages of crushing, washing and sieving and the interest of the big advantageFrom this process compared to the above methods are separated and disposed of most of the alumina and silica of the same dimensions of the particles 10-40 mm which send to high furnace as well as the size of Particles from 0.15-10 mm sent directly to the sintering and the least of them go as tailing
ROM Of«i
After milling process which is known as the washing process and classification include volumetric Milling after milling process Or qualitative classification has been reported in the volumetric three methods above but Classification Qualitative are a number of ways, including classification by flotation or by weighted focus or The following is a way to explain Agglomeration magnetic separation and thus clustering process.Below Simplified the process for each of them :
On the whole, all the raw preparation operations include three final components A-Concentrate: It is the raw material high concentration of iron B- Middling: or raw material and low iron concentration C-Tailing (waste)
1.2 Magnetic Separation ^^aULJf J ^ J lThe process involves shedding a magnetic field on the crusher of the ore to separate materials which have ability to magnetize.There are two types of this method:
(2.1-(Low intensity magnetic saparation) which field strength Magnetic ranging from 1,000 to 3,000 (gauss) and in this way Can easily capture high lumps such as magnetization ore (Magnetite) And in general are not expensive way economical.
(2.2-(High intensity): magnetic separation and the field strength up Magnetic to 20,000 gauss, and used this method for the separation and low magnetization components such as (Hematite) Which can not be supported first way to disconnect it
In general, the separation has been done by passing the lumps on the conveyor belt near Magnet and the ocean is wet or dry, but in most cases it is wet ocean
And magnetic separation process is divided into three phases:The first phase, called Cobbing include passing on the magnet to separate the relatively large or larger lumps of (3/8 inch) and thus about 40% of the remaining waste product is due to the second
phase, which is called Cleaners or Scavengers
And working to separate the granules with networking dimension 48 mich keeps from 10 to 15% as waste to the final stage, which is called the phase FinishersAnd working to separate the granules with measurement of at least lOOmich measure and thus keep the 5% or so-called waste product (gangue)
3
Magnetic separation using permanent magnets equip
2.2 Flotationtechnique used by preference for suspension to a metal powder within the raw bubbles Air without other metals. This is achieved through the use of chemical agents are added Preferentially react with some metals to increase the adhesion property with air. In order to achieve the principle of flotation must provide several factors, namely:
-Ensure the convergence of granular size of the grains of the material
-The use of solvents compatible with the metal to be separated.
-Water quality should not react against Assistant flotation lotion or bubbles between the metal and aerobic
H
The flotation process complementary to the process of magnetic separation and fifty percent of the iron ore is Treated this way.
For the metals iron, there are two types of interaction between the
additive and the powder metal cationic and anionic. The difference between these two method depends on the nature of the components such as Article Value material or gangue whichever floats and whichever is deposited in the basin. On the whole, it is being experimentally measured the weight ratio of the materia! Floating or deposited and see the iron concentration in each.
Anionic flotation method crystals of iron oxide soft as hematite
And Al-siderat float and leave waste or other silicate at deposition.
The cationic flotation method will float value of mineral deposition and materials will benefit them later
The table below shows some of the names of the chemicals used to separate and float components and manufacturers have .
Reagent Type Chemical Composition Producing Company
Fro th e rs
M eth v l iso b u tv l C 'a rb inol M e th y l isobu ty l C a rb iu o l Shell
TX-4733 C -t - iS a lcoho ls , a ld eh y d es , an d esters : b u ty r ic acid: 2 -
e tl iy lh ex au e
N a j c o
D P - S C - 7 9 - 139 M ix e d a ld e h y d es , a lco h o ls , and e s te rs
S h e re x
Col lec to rs /A m in e s
A rc s u r f M G 83 A 1.3 -p ro p e n d ia m in e . N -[3 - b ra n c h e d t r id ecv lo x y l p ropy l] d e r iv a t iv e s ; ace tic a c id
S h e re x
M G -5 S 0 1.3 -p ro p e n d ia m in e . N -[3 - b ran c l ied t r id e cv lo x y l p ropy l] d e r iv a t iv e s
S h e re x
A n t i fo a m s
10 P o ly g ly co l ester> in h y d ro c a rb o n so lven t
N a lc o
9
The figure below is a chart showing the working principle of separation device to float and a picture of a flotation Multi-cells can be seen pumping air mixing above engines.
Upper portion of rotor draws air down the standpipe tor thorough mixing with puip
Larger notation units include taise bottom to aid pump now
There are other ways to separate them by gravity separation and sedimentation basins by .filter will not be Addressed
3.2- AgglomerationAfter completing the process of separation granules are grouped into considering where granules are recycled Imps Iron with heating rotary cylinders to clump according to the desired shape and in most cases The final shape is a spherical shape.
The aim of Agglomeration process is to get a high-capacity for interaction between them and gas blocks Entered during the blast furnace, which reduces the consumption of coal added.
4.2 Pelletizing operationsGive pelleting process lumps granular or spherical moist and non- hardened burned through Thermal treatment later. Be relatively large diameters ranging from (3/8 -1/2 inch) And containing not less than 60% of the iron. This should be a strong pellets Some thing to be able to maintain its shape when handling or transport and thermal treatment furnace. Components of this material pellets Bentonite clay additive To act as a binding agent.
As well as add other materials limiston an dolomite limestone and called (Fluxing) The pellets was directly in the former is added directly in the Higher furnace, which increases the efficiency of the furnace.
The first step of pelleting of iron ore is the composition of the pellets. This is achieved by Sequential stages as these pellets are formed inside the rotary cylinder automatically. There are Three systems followed for pelletizing, as follows
1-Travelling - Grate
used for the production of pellets by Magnetic field that already exists in the ore components. Where he leads the field Magnetic combines raw components magnatite a humid air and then passes Gradually to dry the pellets heating With all magnetite turns to iron oxide hematite, which is then cooled pellets these currents pregnancy
1
2 - shaft-furnacecsj^^'ore pellets are formed from the top of the furnace by moving on a conveyor belt and then pass vertically downward from the top to the
bottom of the oven. During that dry pellets warmly up to 1000 ° C and two-thirds of the The bottom of the furnace is used for the process of cooling the pellets.
2 Grate-kilnThis method includes the barrier technique with the rotary kiln. There is mixed with any fuel or pellets during this process. Dried pellets And the movement of the barrier to another and then hardened by heating the furnace at high temperatures. Gas Hot product of the individual spins again to take advantage of it in the drying process.
2
Iron makingIron making is the process of converting iron ore (solid, oxidized iron) into molten iron.
Iron ore is reduced to iron by heating them with coke in blast furnace.
Blast Furnace• The blast furnace is the first step in producing steel from iron oxides.• The purpose of a blast furnace is to chemically reduce and physically
convert iron oxides into liquid iron called "hot metal" or pig iron.• The blast furnace is a huge, steel stack lined with refractory brick,
where iron ore, coke and limestone are dumped into the top, and preheated air is blown into the bottom
Raw Materials:The essential raw materials required for the present practice of pig iron
production are;• Iron ore
Coal^estone
mmercial forms of iron ore are; hematite (Fe20 3), A limonite (Fe20 3.H20).
'ire of coals.+he volatile matter such as oil and tar
\
‘bonization, the "cooked coal, called
chemical reactions and
for the reduction of iron
oxides.• It provides an open permeable bed through which slag and metal
pass down into the hearth and hot reducing gases pass upwards..Flux
• Limestone (CaC03) and dolomite ((Ca,M g)C03) are the common fluxes used in iron making.
• The primary function of the flux is to combine with the gangue in the ore, sulfur, and ash in the coke.
Air• The hot air used in the furnace at an average temperature of 1200 °C
provides oxygen for burning the coke.• Hot air enters the furnace through tuyeres placed around the furnace
just above the hearth.
Gas uptakes
Small bell
Large bell
Skip bridge {or conveyor) for charging furnace with ore, coke, and limestone
Downcomer
Charge hopper
Blast furnace gas to cleaning plant
'■H
Layers of iron ore, coke, and limestone
__ - Hot blast air
Slag-— iron notch (for trapping)
— Hot iron troughHot iron ladle car
CO
Cross-section of iron-making blast furnace showing majorcomponents
Blast furnace process
In the furnace, iron ore, coke and limestone are dumped into the top, and preheated air is blown into the bottom.The raw materials descend to the bottom of the furnace where they become the final product of liquid slag and liquid iron.The liquid products are drained from the furnace at regular intervals.Liquid slag also collects in the bottom of the blast furnace over the liquid metal pool in the hearth. The hot air that was blown into the bottom of the furnace ascends to the top.
The blast furnace subdivided into various zones (generally divided into 5 zones) according to the physical and chemical state of the feed materials and products.
1. Throat: the burden surface at the top of the blast furnace.2. Shaft: where the ores are heated and reduction reactions start3. Belly: the short vertical section4. Bosh: where the ore reduction completes, and the ores are melting
down.5. Hearth: where the molten materials (slag and hot metal) are
collected and tapped via the tap-holes.
Chemical Reactions in the Blast Furnace:
The coke descends to the bottom of the furnace to the level where the preheated air or hot blast enters the blast furnace.
The coke is ignited by this l iot blast and immediately reacts to generate heat as follows:
C + 0 2 -> C 0 2 + Heat
The temperature in front of the tuyeres exceeds 2000 °C when high
exothermic heat is generated by carbon combustion.
Since the reaction takes place in the presence of excess carbon at a high temperature the carbon dioxide is reduced to carbon monoxide as follows:
C 0 2+ C -» 2CO
The product of this reaction, carbon monoxide, is necessary to reduce the iron ore.The raw materials, that charged into the furnace top, go through numerous chemical and physical reactions while descending to the bottom of the furnace.The iron ore, pellets and sinter are reduced which simply means the oxygen in the iron oxides is removed by a series of chemical reactions. These reactions occur as follows:
At the same time the iron oxides are going through these purifying reactions, they are also beginning to soften then melt and finally trickle as liquid iron through the coke to the bottom of the furnace.
The reduction of iron oxide by carbon monoxide can occur in three steps at temperatures over 600 °C , where Fe20 3 successively reduces to Fe30 4, FeO, and finally iron.
In addition to reducing the oxides of iron, carbon monoxide reduces the oxides of manganese, silicon, and phosphorus present in the gangue of the ore and ash of the coke:
MnO +CO M n+C02
1) 3 Fe20 3 + CO -> C 0 2 + 2 Fe30 4
2) Fe30 4 + CO -> C 0 2 + 3 FeO
3) FeO + CO -> C 0 2 + Feor
FeO + C -> CO + Fe
S i0 2+2CO -> Si +2C02 P205+ 5CO -> 2P+ 5 C 0 2
The water vapor in the hot blast also plays an important role in the reduction, as hydrogen gas produced by the reduction of water by carbon. Hydrogen gas serves as an efficient reductant, particularly at lower temperatures in the furnace:
H20 + C ^ H 2+C0
Slag Chemistry
Slag is the fusible material formed by the chemical reaction of a flux with gangue of an ore, with the ash from a fuel, or with the impurities oxidized during the refining metal.The limestone descends in the blast furnace and remains a solid while going through its first reaction as follows:
CaC03 ->CaO + C 0 2
The CaO formed from this reaction is used to remove sulfur from the iron which is necessary before the hot metal becomes steel. This sulfur removing reaction is:
FeS + CaO + C CaS + FeO + CO
The CaS becomes part of the slag. The slag is also formed from any remaining Silica (S i0 2), Alumina (Al20 3), Magnesia (MgO) or Calcia (CaO) that entered with the iron ore, pellets, sinter or coke.
The liquid slag then trickles through the coke bed to the bottom of the furnace where it floats on top of the liquid iron since it is less dense.
Composition of Pig Iron
The primary impurities in molten pig iron or hot metal are carbon, sulfur, manganese, silicon, and phosphorus.
While manganese, silicon, and phosphorus are present in the ore as oxides, carbon and sulfur are in the coke of the burden. Silica is also present in the ash of the coke. A typical hot metal has;
• 1.0 to 2 .0% Si• 0.1 to 0.5% P,• 0.04 to 0.07% S,
• 0.75 to 1.25% Mn, and• up to 4.5% C. Carbon is usually dissolved in molten iron close to the
solubility limit at the temperature.
Basic interaction compounds:-
Ferrous iron oxide FeO binary oxide - does not exist in nature to the lack of Thbati
Ferric oxide Fe203 (hematite) iron oxide trio - RAW
Black iron oxide Fe304 (Almagntait) - RAW
CaC03 limestone limestone
Calcium silicate CaSi03 - slag
Calcium phosphate Ca3 (P04) 2 - Slag
Chemical reactions inside the oven
Fe203 + 3CO -> 2Fe + 3C02
Alternative Sources of Iron Direct-Reduced Iron (DRI)The need to employ low-grade ores and types of fuel unsuitable for blast furnaces has been driving the search for alternative sources of iron.
Direct reduction (DR), an alternative route of iron making, is the process of converting iron ore (iron oxide) into metallic iron without melting.
Direct-reduced iron (DRI), also called sponge iron, is produced from direct reduction of iron ore (in the form of lumps, pellets or fines) by a reducing gas produced from natural gas or coal.
The reducing gas is a mixture majority of Hydrogen (H2) and Carbon Monoxide (CO) which acts as reducing agent.The metallic iron product is used as a high quality feed material in steelmaking.
Direct Reduction P ro cesses
The sponge ironmaking or DR processes can be conveniently classified into a few categories depending upon the type of reductant used.
A. Gas Based Process; using hydrogen or carbon monoxide or mixture of both as reductant.
o Shaft processes (MIDREX, HYL process) o Fluidized processes ( FiNMET, Circored).
B. Solid Reducant or Coal Based ProcessThis process utilizes non-coking coal as reducing agent along with lumpy rich grade iron ore.
o Rotary kiln processes (SL/RN, DRC, and ACCAR/OSIL)o Retort processes (Kinglor Metor)o Rotary hearth processes (Inmetco, FASTMET)
The main reduction reactions are :
Reduction by CO:3Fe203 + C 0 ^ 2 F e 304 + C02 F03O4 + CO 3FeO + CO2 FeO + CO Fe + CO;
Reduction by Hydrogen:Reduction by Hydrogen occurs in three stages as follows:
3Fe20 3 + H2 2Fe30 4 + H2 Fe304 + H2 -> 3 FeO + H20 FeO + H2 -» Fe + H20
Reduction by Carbon:For solid carbon in a DR process, the following three reduction reactions can be written:
3Fe20 3 + C 2Fe304 + CO Fe30 4 + C 3FeO + CO FeO + C —> Fe + CO
The direct reduction process is intrinsically more energy efficient than the blast furnace because it operates at a lower temperature, and there are several other factors which make it economical, such as:
• Direct-reduced iron is richer in iron than pig iron, typically 90-94% total iron (depending on the quality of the raw ore) as opposed to about 93% for molten pig iron.
. Hot-briquetted iron (HBI) is a compacted form of DRI designed for ease of shipping, handling, and storage.
• The direct reduction process uses pelletized iron ore or natural "lump” ore.
• In most cases the DRI plant is located near natural gas source as it is more cost effective to ship the ore rather than the gas.
2
j j .^*1 -x. j i 11
1 - Krupp Renn process- developed in the 1930's
- Treat high silica ore with a basicity ratio as low as 0.2 to 0.3
- The maximum temperature of kiln is kept at 1230 to 1260oC
- Recovery o f iron in the luppen varies between 94% to 97.5%.
2 - Krupp - CODIR process
- The process operates at a lower temperature then the Krupp - Renn thus producing a standard DR1 product.
- Furthermore, limestone or dolomite in the furnace charge absorb a substantial part o f the sulfur introduced with fuel.
- started operation 1973
- The reduction kiln in this plant is about 4.0 meter (13 feet) inside diameter and 74 meters
RecyleConcentrate
Krupp-RENN Process Flow Diagram
- The energy consumption is about 15.9 million kilojoules per metric ton.
In this process lump ore or oxide pellets, solid reductant, dolomite or limestone as flux is needed.
Primary heat is supplied to the kiln by the combustion of pulverized coal injected at the solids discharge end of the kiln
Secondary heat is supplied by in injecting air into the kiln gas space through tubes spaced along the entire length of the kiln
a uniform charge temperature profile between 950 and 1050°C is achieved in the reaction zone o f the kiln
lim estone reductan t o r raw
pellets coal dolomite cokei__ __j__ __ I
\ya ir" Q
ro ta r y kiln > coal
w ater-coo ledro ta ry c o o le r-c r
kilndischarge
♦5mm sponge iron - ^ screen-5 m m
magnetic j separa to rlime-coke-ash m ixture
sponge ir o n ------ ^
„ _ __ -3 m m !’̂ 7
screen 1 screening an<3 1 gravity separation
sconce , r o n “ J Driquetting
i recycle coke tailings
lime and ash
Krupp-CODIR Process Flow Diagram
3 - SL / RN Process (Outcompu)
product
SL/RN Process Flow Diagram
- began operating in 1975
- The reduction kiln in this plant is 6 meters (19.7 feet) inside diameter and 125 meters (410 feet) long.
- The energy consumption at this plant is about 22 million kilojoules per metric ton.
- This relatively high consumption occurs because most o f the volatile matter in the reductant coal leaves the kiln and is not recovered.
- process consists of lump ore or pellets, coal, recycle char, and flux need to scavenge sulphur from the coal.
- In the kiln preheat zone, the charge is heated to about 980°C (1800°F) by counter flowing hot freeboard gases.
- For high kiln efficiency the reheated zone is made as short as possible usually 40 to 50% of kiln length
- Reduction begins when the charge reaches temperature in excess o f 900°C (1650°F) when the carbon gassification reaction starts generating carbon monoxide.
- Air is introduced axially in to the kiln.
- The solids are discharged forms the rotary kiln via transfer chute ( J jLo into a sealed rotary cooler.
- Water sprays on the cooler shell reduces the temperature of solids to about 95°C in a non-oxidizing atmosphere.
4 - ACCAR Process
- The Allis Chalamers Controlled Atmosphere Reactor (ACCAR) produces highly metabolized DRI in a rotary kiln.
- Liquid, solid and gaseous fuels singly or in combination are used directly in the kiln with an external reformer or gasifying plan..
- development work started in the late 1960.
- The reduction kiln is 5 meter (16.4 feet) inside diameter and 50 meters (164 feet) long and is claimed to be capable o f producing 233,000 metric ton (257,000 net tons) of DRI per year with a
6
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Lec/6-10
Steel Making process,Chemistry of steel making
Steelmaking
Steelmaking can be broadly classified into two steps:• primary steelmaking in a converter or furnace
secondary steelmaking in a ladle.The two most important primary steelmaking processes are:
• the Electric-Arc Furnace (EAF) process• the Basic Oxygen Furnace (BOF) process or LD (Linz-Donawitz) process.
Basic Oxygen FurnaceThe basic oxygen furnace or LD converter (originating from the Linz-Donawitz
process started in 1956) is based on oxygen injection by a lance into the melt of hot metal.
Scrap and lime are charged into the converter to cool the melt and remove phosphorus, silicon and manganese.The converter is lined with dolomite or magnesite refractory which best resists erosion by slag and heat during oxygen blowing.There are many process types of BOF depending on oxygen blowing ;
Types of converter steelmaking• In converter steelmaking pure oxygen is blown from top through a water cooled lance fitted with multi-hole nozzles. This technology of refining of hot metal is called top blown steelmaking.• In another version of converter steelmaking oxygen is blown from top and bath is gas stirred through the bottom. These are called combined top blowing and bottom stirred processes.
1
• In some converters, 0 2 is blown from top and bottom and these processes are called top and bottom blowing, Duplex blowing or hybrid blowing.
• In some converters oxygen is blown through the bottom and the process is bottom blown converter.
I f ) I !
Lec/6-10
I . \
I I
iB iOTypes of converter steelmaking {a)Top blown steelmaking (b) Combined top/ and bottom blowing, and (c) Bottom blowing
Top blowing is the most common form of oxygen steelmaking, in the top-bfowing process, oxygen is blown at supersonic velocity with the help of a water-cooled lance inserted through the mouth of the vessel.
Basic oxygen furnace showing BOF vessel during processing of a heat.
Charge ConstituentsOxygen steelmaking uses gaseous oxygen as the primary agent for autothermic
generation of heat as a result of the oxidation of dissolved impurities present in hot metal and scrap, such as carbon, silicon, manganese, sulfur and phosphorus.The charge consists of steel scrap, hot metal, and flux .Process Description,
o The converter is tilted approximately 30 to 40', and the scrap is charged into the vessel using charging buckets,
o Hot metai (liquid iron) is then poured on the scrap. The vessel is then tilted back to an upright position for blowing oxygen,
o A water-cooled oxygen lance is gradually lowered to a specified distance from the bath surface, and oxygen is started simultaneously,
o Within the first five minutes, all the lime is added through mechanized hoppers to flux the oxides of silicon, manganese, and iron,
o The lime silicate slag formed essentially contains CaO, SiO, FeO, MnO, and P2Os. o After specified periods the lance is gradually lowered to the lowest position
where carbon is oxidized to carbon monoxide and carbon dioxide, o Total blowing time varies between 17 and 22 min, depending on the impurity
content and the lance design, o The lance is raised it the end of the blow.o Steel is tapped into a ladle between 1650 and 1700 °C and the slag is removed by
tilting the converter.
C h a rg in g s tra p in to furnace
A d d iln m r>f h u rm lim e
3B ln w in fi w ith oxvgeri
Tapp ing the furnace
Pouringthe
Lec/6 10
BOF sequence : (a) charging of scrap, pig iron, and lime(b) blowing,(c) tapping the molten steel and pouring off the slag.
Principle chemical reactionsHot metal contains C ~ 3.5 to 4%, Si ~ 0.6 to 1%, Mn~ 0.6 to 0.8% and P ~ 0.1 to 0.2%. Oxygen is blown from top and the following reactions occur:[Fe]+[0]= (FeO) -------1
[C]+[0]= {CO} -------2
[Si]+2[0]= (S i O 2) -------3
[Mn]+[0]= (MnO) -------- 4
2[P]+5[0]= (P205) -------- 5
[C]+(FeO)= {CO}+[Fe] - ....... 6
(Fe)+ (MnO)= (FeO)+[Mn] -------- 7
Note the following:• No heat is supplied from outside. The heat produced due to chemical reactions is
sufficient enough to raise the temperature of hot metal from around 1250°C to 1300°C to molten steel tapping temperature of 1600°C to 1650°C .
• Except carbon which is removed as a gaseous phase rest al! other elements form slag.
• Typically converter steelmaking technology allows to tap liquid steel in approximately every 50 to 60 minutes with specified steel chemistry.
• Typically oxygen blowing time is independent of converter capacity i.e. 0 2 is blown for 15 to 20 minutes irrespective of the converter capacity.
4
Lec/6-10
Electric-Arc FurnaceEAF steelmaking uses electric arcs to heat a charge. Heat is supplied from electricity
that arcs from graphite electrodes to the metal bath.EAF steelmaking can use a wide range of scrap types, as well as direct reduced iron (DRI) and pig iron.
E lectrodes
A schematic cross section of an EAF
Burden PreparationSegregation of scrap is an important function in burden preparation for electric
furnaces. Grade-wise separation of scrap is done:(1) to conserve the valuable alloy content of steel scrap,
(2) to use virgin alloys economically, and(3) to ensure that only the desired alloying elements end up in the finished steel product.
5
Lec/6-10
o Separation of scrap on the basis of size and bulk density is also performed to blend the charge properly.
c Exclusive use of light scrap (bundles, turnings, punchings, etc.) lowers the productivity by occupying a large volume in the furnace,
o Light scrap is also prone to oxidation.o Light scrap as the initial charge can damage the hearth as the arc can bore through
the metallic charge.o A charge comprising all heavy scrap (ingots, butts, crops, etc.) is also not suitable as
the roof and walls of the furnace are not shielded causing refractory damage, o Essentially, the scrap charge is mixed for optimum melting, power utilization, and
electrode consumption at minimum operating costs, o Direct-reduced iron can be used to partially or fully replace the scrap in an electric
furnace charge. Usually a 30% DRI and 70% scrap charge mix is used depending on the price of the two materials.
Process DescriptionThe process of making steel in the basic-lined EAF can be divided into
1. The melt-down period,Once the charging is complete, the electrodes are lowered to about an inch above the charge material and arcs are struck. Power and electrode consumption are highest during the melt-down period. Melting occurs by direct arcing as well as through radiation from the molten pool of metal collecting in the hearth. Burned or calcined lime as the flux is added toward the end of the melting of the first load of scrap charge.
2. The oxidizing period,The oxidizing period begins front the time the molten metal forms until the entire charge is in solution. During this period, phosphorus, silicon, manganese, carbon, and iron are oxidized. The sources of oxygen are the injected oxygen, furnace atmosphere, oxides of added alloying elements, and the ore added to
6
Lec/6-10
the charge.
3. The composition and temperature adjustment period,The steel is finished by adjusting the composition and temperature to thedesired value followed by tapping.
4. The tapping period.The electrodes are raised to allow tilting of the furnace for tapping. Stream oxidation is prevented during tapping of steel into ladles. Slag is removed from the furnace before, during, or after steel tapping depending on the practice used.
The main advantage of the arc furnace are;o Flexibility in accepting charge materials in any proportion, that is, scrap, molten
iron, DRI, and pellets, o The control of electric power can be well regulated to impart heat to the bath at
different desired rates, o Oxygen can be blown to speed up the melt-down refining processes, o The EAF offers a wide range of possibilities in controlled production of ordinary
as well as high-quality special steels, o The process is best suited for the production of higher alloy steel grades, such as
tool steels and stainless steels, o Small-capacity EAF can be put into service, whereas small oxygen furnaces are
usually uneconomical.
Lec/6-10
Cupola Furnace
Cupola are vertical shaft furnace used for melting cast iron.How the cupola furnace operate:
■ Metal, coke, and flux, are charged into the top of the furnace■ Air, often preheated and/or enriched with oxygen, is blown in at the bottom
through tuyeres.■ The coke burns in the air, melting the metal that trickles down to the bottom of
the furnace or well, where it is tapped.
Cupolas, despite their inherent simplicity and energy efficiency are used only by the largest foundries which require a high tonnage of molten iron in operation.
As requirements on cast iron tighten, the cupola is used more and more as a bulk melter to provide metal for subsequent refining and treatment operations, usually carried out in induction furnaces or special treatment ladles, and less as a method of providing iron ready to he poured into molds.
Charging Cupola FurnaceThe charge used in cupola furnace consists of alternate layers of;• metal (iron),• flux and• coke.
❖ The metallic part of the charge is made up of;o Foundry returnes; Gates, risers, and internally generated foundry scrap
generally constitute 30 to 50% of the charge, o Pig iron and cast iron; Cast iron scrap is also used, and pig iron is added
to adjust the quality of the iron. Pig iron has a low level of tramp elements, and thus it can be used to bring melts contaminated by tramp elements from the scrap charge into specification.
8
• The flux also melts and reacts with the impurities of the molten metal forming a slag.
• The iron and slag formed tn the melting operation flow from a tap hole in the wall of the furnace well.
• The metal is usually tapped into induction-heated holding and/or treatment furnaces.
• The slag that is formed is lighter than the iron, it floats and separated from the iron.
Zones Of Cupola Furnace• Well zone; The molten metal is occupied in this zone.• Combustion Zone ; It is in this zone where rapid combustion of coke takes place
due to which a lot of heat is generated in the furnace.• Reducing Zone ; Reduction of C02 to CO occurs in this zone.• Melting Zone;The metal starts melting in this zone and trickles down through the *
coke bed to the well zone.• Preheating zone ; The hot gases rising upwards from the combustion and reducing
zone gives its heat to the charge before passing out of the furnace. Thus, the charge is preheated before descending downwards.
Lec/6-10
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Lec/6-10
Induction Furnace• In induction furnace the crucible (refractory lining) is surrounded by several turns
of water cooled copper tubing which carries the high frequency primary current.
• A.C. current is passed into copper coil. The copper coil acts as a primary circuit
and introduced an eddy current in the charge inside the crucible which acts as
secondary current.
• The eddy current raises the temperature of charge very high which start melting.
• The size of the furnace, that is that of the crucible vary from a few kilo to several
tonnes.
• The furnace is generally charged manually but simple mechanical charging
devices are not uncommon.
• The operation is quite simple. Light scrap is charged at the bottom and heavy at
the top to prevent atmospheric oxidation of the scrap, as far as possible.
• The charge must be of accurately known composition, the bath analysis is
controlled by the charge composition.
• After melting, necessary alloy additions are made to meet the specifications.
• As the temperature reaches the required value it is tapped in a teeming ladle or
directly in moulds to produce castings.
• Since usually no oxidation is carried out, the steel bath is not deoxidised to any
appreciable extent.
• The process is equally suited to produce any type of alloy steels and cast irons.
10
The crucible can be enclosed in a vacuum chamber and thereby better quality
steels of ^in, m̂ a wide specifications can
be produced ' ' r : on a small scale. This is
Lec/6-10
known as
melting.
vacuum induction
Induction furnace
Crucible furnaces
Crucible furnaces are those in which the stock to be melted is placed in a crucible and
heated externally by oil, gas or cock via heat conduction through the walls of crucible.
The amount of the metal melted is limited by the low thermal efficiency of the process
and thus a small batch melting is the usual practice.
• Metal is melted without direct contact with burning fuel mixture• Sometimes called indirect fuel-fired furnaces• Container (crucible) is made of refractory material or high-temperature steel
alloy• Used for nonferrous metals such as bronze, brass, and alloys of zinc and
aluminum• Three types used in foundries: (a) lift-out type, (b) stationary, (c) tilting
11
Lec/6-10
Cover------ — C o v e r ------
S u ppo rt b iock
Fuei
Refractory lining
(b;
P o uring
spout
Steel shelt
Crucible furnace
Fram e
/*~s\ i T:|tin9 M f i tHndieW
Fuel
Three types of crucible furnaces:(a) tift-out crucible,(b) stationary pot, from which molten metal must be ladled,(c) tiiting-pot furnace.
Reverberatory furnaces
• A furnace or kiln in which the material under treatment is heated indirectly by means of a fiame deflected downward from the roof.
• Reverberatory furnaces are used in copper, tin, and nickel production, and in aluminum.• Reverberatory furnaces heat the metal to melting temperatures with direct fired wall-
mounted burners.
• The advantages provided by reverberatory melters is the high volume processing rate, and low operating and maintenance costs.
• The disadvantages of the reverberatory melters are the high metal oxidation rates, low efficiencies, and large floor space requirements
Charge Chute
Stag Layer
Burnet -
12
Molten Metal
Metal Well and Tap
Secondary SteelmakingOverview
Secondary steelmakings (also called ; ladle metallurgy, Secondary Refining or
Secondary M etallurgy) is a critical step in the steel production process between the
prim ary processes (Basic Oxygen Furnace or Electric Arc Furnace) and casting.
Some elements are added and some have to be removed during secondary
steelmaking in order to fine-tune the com position of the steel to meet the
specification and the custom er's requirem ents.
The tem perature, internal quality and the inclusion content o f the steel also have to
be carefully contro lled during secondary steelmaking.
The objectives (^secondary steelmaking can be summarized as follows:
• Im provem ent in physical quality o f the product in term s o f surface quality and
internal homogeneity.
• M ore close and homogeneous chemistry
• Lower level o f im pu ritie s ./tra m p
• Effective tem perature contro l
• Deeper carburization
• desulphurization to very tow levels # 0# A
• dephosphorization to extra low P w
• degassing (e.g. hydrogen removal ^ very low levels by vacuum treatm ent)
• deoxidation
• m odification o f m orphology / chem istry o f inclusion
• im provem ent of cleanless
• control o f solid ification structure
• m icro-alloying
'J,
25
Secondary steelmaking involves some of the follow ing processes:
❖ Stirring treatment
o Lance
c Bottom porous plug
o Electromagnetic Stirring (EMS)
❖ Ladle injection (injection metallurgy)
o Powder injection
o Cored w ire injection
❖ Ladle furnace
❖ Degassing (Vacuum ladie degassing)
o Recirculation Degassing (RH Degasser)
c Recirculation Degassing w ith oxygen top lance (RH-OB)
o Ladle Degassing (VD, Tank Degassing)
o Stream Degasser
o DH Degasser
o Vacuum Oxygen Decarburization (VOD)
Stirring & Homogenization
Stirring treatment w ith argon gas, also known as online argon rinsing, can be done
to homogenize the bath and to prom ote decarbunzation,
Argon rinsing also helps in lowering the nitrogen and hydrogen content, as well as
enhancing alloy dissolution and slag -m e ta l reaction due to stirring effects.
Ladle stirring is an essentia! operation during secondary steelmaking in order to:
❖ homogenize bath composition;❖ homogenize bath temperature;
; • fac ilita te slag-metal interactions essential fo r processes such as
desulfurization;
❖ accelerate the removal of inclusions in the steei
26
In practice, stirring is achieved by:
♦> Argon bubbling through the liquid steel, e ither via a sumberged lance, o r by
porous plugs in the bo ttom of the ladle;
❖ Electromagnetic Stirring - EMS
♦> Top Lance Injection of Argon
Top Lance Injection of Argon
Advantages
■ simple
■ good slag-metal contact, the re fore good
sulfur and phosphorus removal
■ safe ladle lining
■ low er capital and running costs than EMS
Disadvantages
■ tu rbu le n t surface
* nitrogen and hydrogen pickup
■ alloy oxidation and loss
■ reduced alloy cleanness
■ stirring only at stir station
Lance s tirr in g and in|ect»on
Basal Injection of Argon
Nowadays, most ladles are fitte d w ith bo ttom (or 'basal') plugs fo r argon bubbling.
B o t t o m s t i r r in g
27
Advantages
■ un iform dispersed stirring action
■ excellent siag-metai contact, the re fo re good sulfur and phosphorus
removal
■ m oderate nitrogen and hydrogen pickup
■ cleaner steel
■ ability to stir ladle com inously anywhere
■ low er capital and running costs than EMS
Disadvantages
® heavy localized re fractory wear
® more rigorous bricking regime
® danger o f'b re a ko u t'
Injection treatment
• Injection of desulfurizing agents (Ca, Mg, CaSi, CaC2, CaF2+CaO) to a m olten
steel is the most effective m ethod o f sulfur removal.
• in jection methods usually combine supply o f a disperse desulfurizing agent
(powder) w ith stirring by argon blowing.
• When the desulfurizing agents are injected into m olten
steel in fo rm of a cored w ire containing powder of
desulfurizing agent, stirring by argon bubbling from the porous plug m ounted in
the ladle bottom is used.
• Desulfurization agents are injected in argon stream.
Argon bubbles produce stirring o f the m olten steel and
the slag prom oting desulfurization.
• Stirring also provides therm al and chemical
homogenization o f the melt.
28
Benefits of Ladle desulfurization by injection of active agents:
Deep sulfur removal (desulfurization);
- Tem perature and chemical homogenizing;
■ Non-metailic inclusions removal.
• the boiling po in t o f Ca (1491°C) is below the bath tem perature.
Wire feeding is also useful for additions that:
• are less dense than m olten steel and m ight otherw ise floa t to the surface;
• have lim ited solubility;
• have a high vapor pressure;
• have a high a ffin ity fo r oxygen;
• are very expensive and/or added in very small quantities;
• are toxic;
A lum inum is o ften added by w irefeeding to im prove recovery rate, contro l o f Al
content and improve steel cleanness.
Ladle Furnace (LF)
• The ladle furnace is used to heat and refining a w ide variety o f steels.
• During the trea tm ent process argon is blown through
the bottom porous plug to homogenize the steel
com position and tem perature.
• Heating up is achieved by a set o f graphite electrodes,
which are lowering into the slag tayer, just above the
m olten steel surface.
• Alloying elements and /o r slag components may be\
added through the addition hopper.
If deep desulfurization is required active desulfurizing
agents are injected in to the m elt through the injection
lance or in form of cored w ire.
29
Benefits of Ladle Furnace (LF):
• Deep sulfur removal (desulfurization);
- Controllable reheating by electric power;
■ Alloying;
• Temperature and chemical homogenizing;
Non-meta!!ic inclusions removal.
Vacuum ladle degassing
Degassing
Liquid steel absorbs gases from the atm osphere and from the materials used in
steelmaking and can cause em brittlem en t, voids, inclusions, etc., in the steel when
solidified.
The m ajor gases to be elim inated are oxygen, hydrogen, and nitrogen.
Oxygen is the principal refining agent in steelmaking and plays a role in de
term in ing the final com position and properties of steel and influences the
consum ption o f deoxidizers.
Hydrogen is usually picked up from the m oisture in the charge and the
environm ent.
Hydrogen causes bleeding ingots, em brittlem ent, low ductility; and b low
holes.
Nitrogen is particularly harm ful fo r low-carbon steels intended fo r draw ing
applications and should be lowered as much as possible. Primary control o f
nitrogen is a ttem pted during steelmaking practices.,-J s
M ethods of vacuum ladle degassing utilize the reaction of deoxidation by carbon
dissolved in steel according to the equation:
C + O = CO
• Bubbles of carbon monoxide form in the liquid steel, floa t up and then they are
removed by the vacuum system.
30
• In addition to deoxidation vacuum trea tm en t helps to remove Hydrogen
dissolved in liquid steel. Hydrogen diffuses into the CO bubbles and the gas is
then evacuated by the vacuum pump.
• CO bubbles also favor the process of floating and removal o f nitride inclusions
and gaseous Nitrogen.
• Steels refined in vacuum are characterized by homogeneous structure, low
content o f non-m etaflic inclusions and low gas porosity.
• Vacuum degassing methods are used fo r manufacturing large steel ingots, rails,
ball bearings and o ther high quality steels.
Vacuum ladle degassing methods:
• Recirculation Degassing (RH)
o The recirculation (RH) degasser is used fo r the removal umrcuijition <km»*sin» unit
o f carbon and o ther im purity elements.
o Recirculation degassing unit uses a vacuum chamber __p;• V ' ■' : „
having tw o snorkels which are lowered into liquid steel. v
c The recirculation degassing vacuum chambers are
usually equipped w ith addition hoppers, through which alloying elements or/and
desulfurization slag may be added.
Benefits of Recirculation Degassing (RH):
■ Hydrogen removal (degassing);
■ Oxygen removal (deoxidation);
■ Carbon removal (decarburization);
■ Sulfur removal (desulfurization);
■ Precise alloying;
■ Non-m etallic inclusions removal;
Argon is injected through tuyers in one of the snorkels,
facing the steel up into the unit and out again through
other snorkel.
31
Recirculation Degassing w ith oxygen top lance (RH-OB)In this m ethod a conventional Recirculation degassing
(RH) vessel (chamber) is equipped w ith a vertical water
cooled lance fo r blowing oxygen on the m olten steel
surface.
i
Oxygen intensifies the reaction [C] + [O] = {CO} resulting in j i i ' ' ’j * H
fast and effective decarburization. ^ ["71 (J~ ^ u i i i j rOxygen also oxidizes phosphorus like in Basic Oxygen , i JUUUM
i 1 iProcess (BOP) or in oxidizing slag stage in Electric-arc I i
furnace.
Oxidation reactions have also heating effect there fore the treated metal may be
heated to a required tem perature w itho u t any additional energy source.
Ladle Degassing (Tank Degassing)
• The tank degasser is used to remove gaseous elements and sulfur from the steel.
• The removal of sulfur is achieved through slag-metal reactions, which are
prom oted by strong argon 'flushing' (bubbling) w ith in the vacuum envelope.
• The ladle is equipped w ith a porous re fractory plug m ounted in the ladle bottom .
Through the plug argon is supplied during vacuum treatm ent.
• There is an addition hopper w ith vacuum lock on the
chamber cover. The hopper is used fo r adding alloying
elements and /o r slag components.
• The reaction [C] + [O] = {CO} starting in the steel under
vacuum conditions causes stirring, which is additionally
intensified by argon blown through the bo ttom porous
plug.
• Intensive stirring of the m elt and the slag results in deep
desulfurization o f the steel.
Vacuum Oxygen Decarburization (VOD)
• Vacuum Oxygen Decarburization (VOD) m ethod is used fo r m anufacturing
Stainless steels.
• Oxygen blow on the molten steei surface by water cooled lance.
m inor chrom ium losses. s ^
• Oxidation reactions have also heating effect ......x
there fore the treated meta! may be heated to a required tem perature w itho u t
any additional energy source.
• A fte r having the decarburization (oxidation) stage com pleted deoxidizers are
added to the steel in order to remove excessive oxygen.
• Then a Desulfurizing slag is added to the m olten steel surface.
• Stirring of the m elt and the slag caused by argon blown through the porous
bo ttom plug results in deep desulfurization o f the steel.
Benefits of Vacuum Oxygen Decarburization (VOD):
■ Deep carbon removal (decarburization);
■ Low losses o f chrom ium in trea tm en t of stainless steels;
■ Hydrogen removal (degassing);
• Sulfur removal (desulfurization);
■*. Non-m etallic inclusions (oxides and nitrides) removai;
■ Tem perature and chemical homogenizing.
• Oxidation of liquid steel under vacuum differs from
tha t at normal pressure:
oxygen is consumed mainly by the reaction
[C] + [O] = {CO}
• rather than by oxidation o f chrom ium , which is the
main constituent of stainless steels. \ him>mv h . i i t i l n I
• VOD process allows to decarburize the steei w ith
Deoxidation of steel
The main sources of Oxygen in steel are as fo llows:
• Oxygen blow ing (example: Basic Oxygen Furnace (BOF));
• Oxidizing slags used in steel making processes(exampie: Electric-arc furnace);
. A tm ospheric oxygen dissolving in liquid steel during pouring operation;
• Oxidizing refractories (lining of furnaces and ladles);
• Rusted and wet scrap,
■ Solubility o f oxygen in m olten steel is 0.23% at 170CTC. However it decreases
during cooling down and then drops sharply in Solidification reaching 0.003%
in solid steel.
■ Oxygen liberated from the solid solution oxidizes the steel components (C,
Fe, alloying elements) fo rm ing gas pores (blowholes) and non-m etallic
inclusions entrapped w ith in the ingot structure.
■ Both blowholes and inclusions adversely affect the steel quality.
■ In order to prevent oxidizing of steel com ponents during solid ifica tion the
oxygen content should be reduced.
Deoxidation of steel is a steel making technological operation, in which
concentration (activity) o f oxygen dissolved in m olten steel is reduced to a required
level. There are three principal deoxidation methods:
• Deoxidation by m etallic deoxidizers
• Deoxidation by vacuum
• Diffusion deoxidation.
Deoxidation by metallic deoxidizers
This is the most popular deoxidation m ethod, it uses elements form ing strong and
stable oxides. Manganese (Mn), silicone (Si), alum inum (Al), cerium (Ce), calcium
(Ca) are com m only used as deoxidizers.
34
The table presents parameters o f the deoxidation reactions fo r some m etallic
oxidizers:
Deoxidizer Reaction
Manganese [M n] + [0 ] = (MnO)
Silicone [Si] + 2 [0 ] = (S i 0 2)
A lum inum 2 [A!] + 3 [0 ] = (Al?0 ?)
According to the degree of deoxidation Carbon steels may be subdivided into
three groups:
• Killed steels - com pletely deoxidized steels; solid ification of which does not
cause fo rm ation of carbon monoxide (CO). Ingots and castings of killed steel
have homogeneous structure and no gas porosity (blowholes).
! y , ; ' • Semi-killed steels - incom pletely deoxidized steels containing some am ount of
J excess oxygen, which form s carbon monoxide during last stages of
solid ification.
• Rimmed steels - partia lly deoxidized or non-deoxidized low carbon steels
,, V ; evolving suffic ient am ount o f carbon monoxide during solid ification. Ingots of)rimmed steels are characterized by good surface quality and considerable
quantity o f blowholes.
Teeming Methods
Teeming means pouring o f liquid steel in an ingot mould. The m ethod of teem ing
affects the ingot quality. Three d iffe ren t methods are used fo r teem ing to produce
ingots.
35
1-Direct pouring:-
• The metal is teemed from the iadle
directly in the mould.Lao* e
• The rate of pouring can be controlled by
the used of d iffe ren t sizes and designs of
nozzle. | Mo Id
• The size of the nozzle em ployed varies . . | ig i....;. 00 i
w ith the type of the steel to be teemed.
• Since the metai stream directly hits the bottom plate o f the mold, the wear o f
the bo ttom plate is quite sever in the direct teeming.
• This is used fo r teem ing ro lling ingots.
2-Tundish Teeming
• The ingot should be teemed by a pipe like metal stream at a un iform rate to
m inim ise ingot defects.
• A tundish is, therefore , inserted between the ladle and the ingot mould to ensure
un iform metal stream while teem ing from top.
• The tundish has its own nozzle to regulate the flow . A stopper may be provided
in the tundish to fu rth e r regulate the flow .
• Tundished w ith one or more, up to eight, nozzles are employed to d is tribute the
metal evenly in tha t many moulds at a tim e. This reduces the to ta l teem ing tim e
of a ladle and, the available superheat in the metal can be fu lly utilized. This is
not possible in the direct teeming.
• Tundish is used fo r teem ing forging ingots and special alloy steel ingots.
I
36
3-Bottom teeming: -
• Steei is teem ed into a vertical runner which is connected at the bo ttom to a
horizontal through runner, the end of which w ith an elbow shape, open up in the
bo ttom of the mould.
• The top of the vertical runner is shaped like a trum pe t or beli to make teem ing
easy.
• The height o f the vertical runner is more than that o f the mould to ensure
com plete filling o f the mould.
• In general one vertical runner is meant to feed at least tw o and as many as
tw elve moulds at a tim e, w ith four as a more popular figure.
• All the moulds are set on the same bo ttom plate having required num ber of
through runner channels.
• The quality of bo ttom teem ed ingot is much superior and the bottom plate wear
is much less as compared to top teemed ingots.
• Use of bottom teem ing is econom ically justifiab le only if the superior quality of
the ingot is necessarily required.
Bottom pour mg
-4 Runner Bricks
37
Ingot casting and continuous casting
In the conventional production of w rought steel products, the steel is cast into a
large tapered cast iron vessel to form an ingot.
The ingot is subsequently rolled into slabs or billets, which may be used fo r the
production o f standard product form s such as plate, sheet, pipe, rod, and w ire.
A lternatively, slabs or billets can be cast d irectly during the prim ary casting
operation in process called continuous casting.
Conventional ingots
■ A fter the final ladle treatm ents are made and the chem istry o f the steel is
satisfactory, the ladle is tapped from the bo ttom by lifting the internal
stopper-rod, perm itting the flow of m olten metal.
■ The steel is poured or teemed into the ingot molds, where it begins to cool
and solidify.
■ Ideally, the ingot would cool uniform ly, resulting in a chemically homogenous
equiaxed structure, free from voids, cracks, and nonm etallic inclusions.
■ In fact, the center of the ingot typica lly is still m olten when the ingot mold is
removed or stripped from the ingot.
■ A fte r stripping, ingots are places in a furnace called a soaking pit, where the
tem perature o f the ingot is contro lled to prom ote homogenization o f the
steel.
■ The nonuniform cooling tha t occurs in an ingot coupled w ith the many
dissolved im purities and gasses, gives ride to various chemical segregation
phenomena tha t generate defect structures in the ingot and u ltim ate ly affect
the downstream properties or process ability.
38
The principle of continuous casting:-
a) M olten metai from steel ladte flow continuously through tundish into m ater
cooied copper mould.
b) Before casting beings a starting bar equal in cross section to the mould bo ttom .
c) As the m olten metal contact the mould bo ttom and walls it beings to crystallized
d) W hen the metal solidifies to a high of (300_400) mm above the starting bar, the
bar draw ing mechanism is started and fu rth e r pouring the whole of the mould is
tilled w ith the metal
e) The ingot w ithdraw al speed and the pouring rate are so adjusted tha t the metal
is maintained at a constant level in the mould and the solid ify ingot is
continuously drawn out of the mould by ro ta ting rolls
f) A fter leaving the mould the blank whose core is still liquid blank, passes through
secondary cooling zone. W here its subjected to intensive o f cooling by atomized
w ater which accelerate the crystallization of the ingot core.
g) The cooled blank is cut by torch, and standared length are transferred to rolling
plants.
M o lte n m e ta l
Horizontal continuous casting
41
CAST IRONOverview of cast iron
• Wide range of iron-carbon -silicon alloys containing upto 4.5% carbon and upto
about 3.5% silicon, in combination with varying percentages of manganese, sulphur
and phosphorus as impurities.
Cast iron are produced by pouring the molten alioy into moulds (sand or metal) to make
castings.
Lower melting point and more fluid than steel (better castability)
Low cost material usually produced by sand casting
• A wide range of properties, depending on composition & cooling rate
- Strength- Hardness- Ductility- Thermal conductivity- Damping capacity
Production of cast iron• Raw materials; Pig iron, scrap steel, limestone and carbon (coke)
• Furnaces used; Cupola, Reverberatory furnaces, Crucible furnaces, Electric arc furnaces or Electric induction furnaces.
• Melting Practice; The essential purpose of melting is to produce molten iron of the desired composition and temperature.
• Casting; Usually sand cast, but can be gravity die cast in reusable graphite moulds
• Forming; Not formed, finished by machining
Iron carbon diagram
] GOO
1400
1?(W
1000
800
600
400
C om position {at% C)
10 If) 98T
Liquid
- LL iq u id
+G raphite
11 S3 ::vLAuMemte) \ ' 4.2 wt%C
? . \ w l% C
y t Graphite;
/40'C
o sr. wt no c
(Tf-intc:-) i t + G ra p h ite 1
I______ I1 ? 3 4C o m position (w t% C)
90
2100
?0(X)
IbOO
100
Graphite; T
Microstructures of Cast IronsCast irons can exhibit a wide range of microstructural constituents depending upon
their composition and heat treatment. This wide spectrum of properties is controlled by
three main factors:
(i) the chemical composition of the iron;
(ii) the rate of cooling of the casting in the mould (which depends in part on the
section
thicknesses in the casting);
(iii) the type of graphite formed (if any).
Effect of cooling rate• Slow cooling favours the formation of graphite & low hardness
• Rapid cooling promotes carbides with high hardness
• Thick sections cool slowly, while thin sections cool quickly
• Sand moulds cool slowly, but metal chills can be used to increase cooling rate &
promote white iron
Commercial cast iron range
Reheat: hold at ~700°C for 30 + h
■j Mg/Ce
Fast cool Moderate Slow cool Moderate Slow coolP + Fe3C P+ Gf or + Gf P + Gp a + Gp
Fast cool Slow coolP + Gf cx + Gf
Pearlitic Ferritic malleable malleable
White Pearlitic gray Ferritic gray Pearlitic Ferritic cast iron cast iron cast iron ductile ductile
cast iron cast iron
Inoculation
Inoculation is the means of controlling structures and properties of cast iron by
minimizing undercooling and increasing the number of nucleation sites during
solidification. An inoculants is a material added to the liquid iron just prior to casting that
will provide suitable sites for nucleation of graphite during the subsequent cooling.
Traditionally, inoculants have been based on graphite, ferrosilicon or calcium silicide.
The purpose of inoculation is to assist in providing sufficient nucleation sites for dissolved
carbon to precipitate as graphite rather than iron carbide (cementite, Fe3C). This is done
by preventing undercooling below the metastable eutectic temperature where carbidic (white) structures are formed.
Addition Methods.
Inoculants may be added to the melt in a number of different ways.
Ladle inoculation is common; in this, the alloy is added to the stream of metal as it flows
from the transfer ladle to the pouring ladle.
Stream inoculation is the addition of the inoculant to the pouring stream as the metal
enters the mold.
Mold inoculation involves placing the inoculant in the mold, usually at the base of the
sprue.
Inoculation and Cast Iron Properties Inoculation and StrengthInoculation increases the number of eutectic cells (or nodules) which leads to a finer
structure of the iron, and in particular, this will cause an increase in tensile strength in
hypoeutectic irons.
Inoculation and MachinabilityInoculation increases the number of potent nuclei that will promote graphite nucleation at
low undercooling.Improved machinability is achieved by inoculation suppressing the formation of hard un-
machinable white iron structures. Inoculation also reduces section sensitivity.
While uninoculated irons will show a wide variation in hardness, inoculated grey or nodular
cast irons will show more consistent hardness values over a wide range of sections.
Grey cast ironGeneral Characteristics of Grey Cast Irons
• Gray Cast Irons contain silicon, in addition to carbon, as a primary alloy (Most gray
irons are produced with 2.5 to 4.0% carbon levels and 1.0 to 3.0% silicon levels).
• Amounts of manganese are also added to yield the desired microstructure.
• Graphite morphology and matrix characteristics affect the physical and mechanical
properties of gray cast iron.
• Grey cast iron forms wheno Cooling is slow, as in heavy sections c High silicon or carbon (High carbon equivalence)
• Graphite flakes surrounded by a matrix of either Pearlite or Ferrite.
• Exhibits gray fracture surface due to fracture occurring along Graphite plates.
• Considerable strength,
• Weak & brittle under tension due to its microstructure; the graphite flakes have tips
which serve as points of stress concentration.
• Stronger under compression
• Excellent vibrational dampening (Damping capacity high)
• Machineability is excellent
• Thermal conductivity high
• Low ductility - elongation 0.6%
Micrographs of gray cast iron.
Carbon Equivalent (CE):
■ A measure of the equivalency of carbon coupled with other alloying elements to that
of just carbon.
■ The three constituents of cast iron which most affect strength and hardness are
total carbon, silicon and phosphorus. Carbon equivalent combines the effects of
these elements.
^ 0 /() _|_ po/Carbon equivalent ( E = C ’% + —-----
3
The grey iron eutectic occurs at a carbon content of 4.3% in the binary Fe-C system.
• A (CE) over 4.3 (hypereutectic) leads to carbide or graphite solidifying first &
promotes grey cast iron
• A (CE) less than 4.3 (hypoeutectic) leads to austenite solidifying first & promotes
white iron
Since the structure (and hence the strength) of flake irons is a function of composition,
a knowledge of the CEV of an iron can give an approximate indication of the strength to be
expected in any sound section.
AlloyingAlloying elements may be added to cast iron to obtain specific properties that are not
obtainable without alloy additions.
Alloying and inoculation are not the same process and should not be confused, although
alloying can affect choice of inoculation practice.
Common alloying elements for gray iron include chromium, copper, nickel, molybdenum,
and tin. The effects of these additions are as follows:
• Chromium additions of 0.5 to 0.75% increase the strength of gray iron by increasing
the pearlite content. Chromium is also a chill promoter.
• Copper additions in the range of 0.25 to 0.5% increase tensile properties, again by
promoting the formation of a pearlite matrix. Copper also acts as a graphitizes.
• Nickel additions of up to 2% cause a minor increase in properties. Nickel is also a
graphitizer.
• Molybdenum in additions of 0.25 to 0.75% has a significant impact on the strength
of gray iron as a matrix strengthener and a graphite flake refiner.
• Tin in the range of 0.025 to 0.1 % stabilizes pearlite.
When higher amounts of alloying elements are added, the product is known as "alloyed
cast iron" or "high-alloy cast iron."
Ductile ironGeneral Characteristics of Ductile Irons
• Ductile (Nodular) Iron: Graphite nodules surrounded by a matrix of either Ferrite, Pearlite, or Austenite. Exhibits substantial ductility in its as cast form.
• As a liquid, Ductile Iron has a high fluidity, excellent castability.• Inoculation with Ce or Mg or both causes graphite to form as spherulites, rather
than flakes• Also known as spheroidal graphite (SG), and nodular graphite iron• Ductility up to 6 % as cast or 20% annealed• Low cost• Machineability better than steel. Because the graphite lowers the melting point from
that of steel, ductile iron is, in many ways, a low-cost, lower melting point steel.
Production• Composition similar to grey cast iron except for higher purity.
• To achieve the spherical shape of the graphite, a nodulizing treatment is necessary.
This is carried out by adding magnesium to the melt. Rare earth elements such as
cerium can also be used, but magnesium is used most commonly.
Magnesium as wire, ingots or pellets is added to ladle before adding hot iron.
• The sulfur content must be reduced below 0.02% before attempting the nodulizing
treatment.
• The melt is usually inoculated just before or during casting with a silicon-containing
alloy.
Magnesium TreatmentTo achieve the spherical shape of the graphite, a nodulizing treatment is necessary. This
is carried out by adding magnesium to the melt. Rare earth elements such as cerium can
also be used, but magnesium is used most commonly. Magnesium may be introduced as
pure magnesium metal or alloyed in ferrosilicon containing 3 to 10% Mg or nickel-base
nodulizers containing 4 to 16% Mg. The magnesium additions can be added to the ladle
during filling or by plunging.
Microstructure• Graphite spheres surrounded by ferrite
Usually some pearliteMay be some cementite
• Can be hardened to martensite by heat treatment
Micrographs of nodular cast iron.
Effect of composition on properties:Carbon: During solidification, Carbon precipitates to Graphite, which offsets
shrinkage.
Silicon: Graphitizing agent. Increasing amount of Silicon also increases amount
of Ferrite. Can improve resistance to scaling at high temperature
Manganese: Acts as a Pearlite stabilizer and increases strength, but decreases
ductility and machinability.
Nickel: Increases strength by promoting formation of fine Pearlite. Increases
hardenibility.
Copper: Used to form Pearlite upon solidification with high strength and good
toughness and machinability.
Molybdenum: Used to stabilize structures at high temperatures.
• Chromium: Promote carbides formation
Special properties, such as resistance to heat, corrosion, or oxidation, can be
achieved by alloying with nickel (20%), chromium (up to 5%), and silicon (up to 6 %).
Applications■ Automotive industry
■ Crankshafts, front wheel spindle supports, steering knuckles, disc brake callipers
■ Pipe and pipe fittings
■ Used for a variety of applications, specifically those requiring strength and
toughness along with good machinability and low cost
■ Other important applications are: Papermaking machinery; Farm equipment;
Construction machinery and equipment; Power transmission components (gears);
Oilfield equipment£ *1
Malleable iron• Malleable Iron: Produced by first casting the Iron as a White Iron, then heat treating to
transform the Carbide into Graphite in the form of irregularly shaped nodules
(sometimes called tempered graphite).
• Heat treatment carried out in a neutral atmosphere (to prevent oxidation) causes a
decomposition of the cementite, forming graphite, which exists in the form of clusters or
rosettes surrounded by a ferrite or pearlite matrix, depending on cooling rate.
• Carbon and silicon content limited to levels below those used for gray or ductile iron.
• Posses’ considerable ductility and toughness due to the combination of nodular
graphite and low carbon matrix.
• Categorized into 3 categories: Ferritic, Pearlitic, and Martensitic Malleable Cast Iron.
• Two types of Ferritic malleable irons: Blackheart and Whiteheart, these names are
derived from the color of fracture of annealed material.
* W n
Microstructure• Uniformly dispersed graphite
Ferrite, pearlite or tempered martensite matrix
• Ferritic castings require 2 stage anneal.
Pearlitic castings - 1st stage only
r W ? .'A JN - Graphite
s s
Micrographs of ferritic malleable cast iron.
Properties• Similar to ductile iron
• Good shock resistance
• Good ductility
• Good machineability
■if'
White iron• White Iron: With a lower silicon content and faster cooling, large amount of carbide
phases(Fe3C) are precipitates instead of graphite, surrounded by a matrix of either
Pearlite or Martensite.
• Has a white crystalline fracture surface because fracture occurs along the iron
carbide plates. Considerable strength, insignificant ductility.
• Abrasion resistant
• Often alloyed ; White Cast Irons contain Chromium to prevent formation of Graphite
upon solidification and to ensure stability of the carbide phase. Usually, Nickel,
Molybdenum, and/or Copper are alloyed to prevent to the formation of Pearlite
when a matrix of Martensite is desired.
Application• Exceptionally hard, but brittle and almost impossible to machine used in very few
applications e.g. rollers in rolling mills • Used as intermediary in production of malleable iron.
Micrographs of white cast iron.
White cast iron Fall into three major groups:• Nickel Chromium White Irons: containing 3-5%Ni, 1-4%Cr. Identified by
the name Ni-Hard 1-4
• The chromium-molybdenum irons (high chromium irons): 11-23%Cr,
3%Mo, and sometimes additionally alloyed w/ Ni or Cu.
• 25-28%Cr White Irons: contain other alloying additions of Molybdenum
and/or Nickel up to 1.5%
Compacted Graphite Cast Iron• Consists of a microstructure similar to that of Gray Iron, except that the Graphite
cells are coarser and more rounded, i.e. graphite in the cast structures having a
shape which represent a transition (intermediate) from between flake and
spheroidal graphite.
• Magnesium and/or cerium is also added, but concentrations are lower than for
ductile iron.
• Compacted Graphite Cast Iron consists of a microstructure having both
characteristics of Gray and Ductile Irons. Furthermore, depending on heat
treatment, the matrix phase will be pearlite and/or ferrite.
• An increase in degree of nodularity of the graphite particles leads to enhancements
of both strength and ductility.
Properties
• Tensile and yield strengths for compacted graphite irons are comparable to values for ductile and malleable irons.
• Ductilities for CGIs are intermediate between values for gray and ductile irons• Compared to the other cast iron types, desirable characteristics of CGIs include
the following: o Higher thermal conductivityo Better resistance to thermal shock (i.e., fracture resulting from rapid
temperature changes) o Lower oxidation at elevated temperatures
ApplicationsCompacted graphite irons are now being used in a number of important applications,
these include: diesel engine blocks, exhaust manifolds, gearbox housings, brake discs for high-speed trains, and flywheels.
Alloyed Cast IronsThe alloy Cast iron is produced by adding alloying elements like nickel, chromium ,
molybdenum, copper, silicon and manganese. These alloying elements give more strength and result in improvement of properties.
PropertiesThe alloy Cast iron has special properties like increased strength, high wear
resistance, corrosion resistance or heat resistance.
ApplicationThe alloy Cast iron are mostly used for automobile parts like cylinder, pistons, piston
rings, crank case, brake drums, parts of crushing and grinding machines.
Nonferrous Metals
■ The common nonferrous metals: Aluminum (Al), copper (Cu), magnesium
(Mg), zinc (Zn), titanium (Ti), etc.
■ The melting points of principal nonferrous metals that are cast vary from 327
to 1438 °C.
■ Non-ferrous can be categorized into:
o Light metals: Density (p) < 4.5 g cm-3, e.g. Li, Be, Al, Mg.
o Heavy metals: (p) > 4.5 g cm-3, e.g. Cu, Pb, Mn, Co.
■ Non-ferrous metals are better if combined with small amount of other elements
(alloys).
■ Higher cost than ferrous metals but have good properties such as:
• Corrosion resistance
• High thermal and electrical conductivity
• Low density and ease of fabrication
Aluminum
Aluminum occurrence:
Abundant element of 8% on earth crust and normally found in oxide forms
(ALO.O, i.e., Bauxite; A l2Ov2H20. Kaolinite, Nepheline and Alunite.
Aluminum Production:
1. Bayer Process: obtain Alumina ( A L O 3 ) from Bauxite.
A. Extraction: dissolve oxides with hot solution of NaOH.
Al (OH); + Na“ + OH" -— > Al (OH)i' + Na’
1
B. Precipitation: reverse of above, but controlling crystal formation.
Al (OH)4 + Na" — > Al (OH); + Na + OH'
C. Calcination: water is driven off Al(OH);, to form alumina (aluminum
oxide).
Al(OH)3 — > A120 3 + 3 H20
2. Hall-Heroult Process (Electrolytic Reaction).
Aluminium is produced by electrolytic reduction of its molten oxide with cryolite
(Na^^AlFft) as an electrolyte. Cryolite is added to lower electrolytic temperature to
~ 950 °C (T /77 of alumina ~ 2030°C)
A. AI2O3 is dissolved in molten cryolite (Na^AlFfJ
B. As the current passes through this mixture, (4-5 volts, and 50,000-280,000
amperes) aluminum ions reduce to molten aluminum at the cathode, and
oxygen is produce at the anode reacting with carbon to produce C 0 2.
Carboncathode
2 A120 3 + 3 C — > 4 Al + 3 CO,
Carbon anodes
Alumina/cryolite
Hall-Heroult electrolvtic cell.
The electrolytic cell consists of1) Carbon as anode — consumed2) M olten cryolite-alum ina e lectro lyte3) Liquid a lum inium pool.
Condition:Temp: 950°C Current: 250 kA Voltage: 4.5 V
2
Purifying aluminium by Cl2
• Aluminium produced by electrolytic process normally contains impurity such as
powder of coal or electrolyte and hydrogen gas.
• Cl2 is blown through a graphite tube to purify aluminium. This reaction produces
bubbles of aluminium chloride A 1C 13 which floats away and helps carrying impurity
out from aluminium.
2A1 + 3CI2 — > 2 AICI3
• In the case of ultra-pure aluminium, i.e., for use as conductors, the electrolytic
process is again used to purify aluminium.
• Aluminium obtained from the first process is now anode and the electrolyte used is
60% BaCl2, 17% NaF, 23% A1F3 and 5% NaCl. (T - 760-800°C.)
Melting aluminium alloys
The successful melting and casting of aluminium alloys requires attention to a
number of special factors, such as impurities, hydrogen pick up, oxidation, structure
modifying, feeding problems.
Impurities in Aluminium melts
Impurities in Aluminium melts can be divided into “solid impurities” and
“dissolved impurities”.Solid impurities in Aluminium have different sources. The exogenous inclusions
may come from the melt environment as the refractory linings of furnaces, ladles, or
reactors etc. Mainly these are simple oxides as ALO3 and MgO, ..etc.
The endogenous inclusions for e.g. AI3C4, AIN or A1B2 are formed in the melt
during production, e.g. in the electrolysis cell.
Dissolved impurities may be foreign metals and dissolved gas (Flydrogen).
Foreign metals such as Na, Li, and Ca coming from the electrolyte.
Remelted metal may contain Fe, Si, and Cu as impurities.
3
Hydrogen
Molten aluminium readily picks up hydrogen from the atmosphere or from
moisture-containing refractories, the solubility of hydrogen in solid aluminium is
very low, so that as the alloy freezes hydrogen gas is expelled, causing micro- or
macro-porosity in the casting( porosity defects). To achieve high integrity castings,
aluminium alloy melts must be degassed before casting.
Oxidation
Molten aluminium and its alloys immediately oxidise when exposed to air forming
a skin of aluminium oxide (AUO^ The oxide skin has a protective effect, preventing
catastrophic oxidation of the melt but it causes problems during melting and also
during casting. An oxide film can form even as the metal is filling the mould and can
give rise to entrained oxide in the casting harming the physical properties of the
casting.
Oxide inclusions in aluminium alloys are of A120^ which have a density only 5%
less than that of liquid aluminium so flotation of oxide inclusions takes place slowly.
For inclusion-free castings it is advisable to use metal filters to clean the metal as it
enters the mould.
Fluxes are used during melting to protect the metal from oxidation and to trap oxides
as they float out of the melt.
Structure Modification
The microstructure, and therefore the mechanical properties, of Al-Si alloys can be
modified and improved by appropriate metal treatment. “Modifiers” and/or grain
refiners are usually added to the alloy before casting to control the structure and
grain size of the solidifying metal.
4
Feeding
Aluminium alloys shrink on freezing so that castings must be correctly fed to
achieve soundness. To avoid the above problems, great care must be taken at all
stages of melting, treatment and casting of aluminium alloys.
Melting furnaces
A wide range of furnace types is used by aluminium foundries. Small foundries
may use lift-out crucible furnaces in which the metal is melted and treated in a
crucible which is then lifted out of the furnace for pouring.
Large foundries usually melt aluminium alloy ingot and foundry returns in a bulk
melting furnace, then transfer the metal to smaller holding furnaces near to the
casting area. Degassing and metal treatment are usually carried out in the transfer
ladle. The bulk melting furnaces can be coreless electric induction furnaces or, more
commonly, gas-fired reverberatory or shaft furnaces. The tilting crucible furnace,
which may be electric or gas, is also popular as a bulk melter. Holding furnaces may
be electric or gas.
Fluxes
Chemical fluxes for aluminium have a number of functions:
• Covering fluxes which form a molten layer to protect the melt from oxidation
and hydrogen pick-up.
• Cleaning fluxes which remove non-metallics from the melt by trapping the
oxide particles as they float out.
• Fluxes which ^modify” the alloy, by introducing sodium, improving its
microstructure
• Exothermic fluxes which ensure that aluminium liquid trapped in the dross
layer is returned to the melt
• Fluxes for reclaiming swarf, skimmings and turnings, giving a high metal yield
• Fluxes for the removal of oxide build-up from furnace walls
• Some fluxes combine several of these functions.
5
Processing o f molten aluminium
For treatment of Aluminium melts a variety of methods are in use industrially.
The cleaning of Aluminium melts stalls with a simple ladle treatment, before the melt
is transferred into the casting furnace. There the alloying is conducted and a further
settling operation may take place.
A cheap and simple settling procedure in the casting furnace is an easy but ineffective
method to clean an Aluminium melt.
Solid inclusions settle down depending on size, form and density.
From the casting furnace the molten metal is fed via a launder to the degassing unit
for the removal of hydrogen.
Grain refining is carried out by wire injection between the gas purging unit and the
filtration station.
Melt filtration is used extensively for the separation of solid particles.
Sometimes gas purging is combined with a filter in one unit.
After the melt treatment the liquid metal is cast in a DC casting unit.
Casting of aluminium
Direct-chill casting process
• Uniform ingot structure is obtained by direct-chill (DC) casting most common in
vertical than horizontal process.
• Molten alloy is poured into water-cooled moulds having retractable bases.
• During the solidification process, metal solidifies at the bottom block with
subsequent solidification of the rest occurs rapidly by means of chill water.
6
MOl'LDH I Dl K
DISTKIMTION
Direct-chill casting process (vertical)
Continuous casting process
• The process produces continuous thin slabs and sheets with sizes to those required
in final products, — reducing great amount of investment cost required to reduce in
sizes from large ingot.
• Continuous casting of aluminium alloys involves complex surface cooling patterns,
due to the alternation of rolls and spray zones.
• Sets of water-cooled rolls are rotated continuously to produce slab.
Cost bar
Spray bo* for' beH cooling
incomingmetal
WOter cooled roll ft
Liquid merol lourider
Continuous casting process
Continuous casting of aluminum based
bearing alloys in water-cooled mold
H olding furnace o r tundish W ithdraw al
Prjmar> Sccondar> unit
cooling cooling
7
fu rn aceH uldin^
furnace
L i n e f o r c o n t i n u o u s c a s t i n g s t r i p s o f a l u m i n u m
b a s e d b e a r i n g al loys
Sources o f defects
When aluminium alloys are cast, there are many potential sources of defects which
can harm the quality of the cast part. All aluminium alloys are subject to:
• Shrinkage defects
Al alloys shrink by 3.5-6.0% during solidification (depending on alloy type).
• Gas porosity
Molten aluminium readily picks up hydrogen which is expelled during
solidification giving rise to porosity.
• Oxide inclusions
Molten Al exposed to air immediately oxidizes forming a skin of oxide which
may be entrained into the casting.
8
Primary copper production starts with the extraction of copper-bearing ores. There
arc three basic ways of copper mining:
• surface,
• underground mining and
• leaching.
Open-pit mining is the predominant mining method in the world.
Extraction o f copper from ores '
• Copper ores are normally associated with sulphur in which copper can be extracted
from chalcocite Cu2S, chalcopyrite CuFeS2 and cuprite Cu20.
Extraction processes:
Pyrometallurgical- for copper sulphide basedores.
Hydrometallurgical- for oxide or carbonate ores.
Pyrometallurgical process
Copper sulphide concentrates are produced through different ore dressing
processes (crushing— washing—screening-roasting).
• The concentrates are smelted in a reverberatory furnace to produce matte (mixture
of copper& iron sulphides, and slag (waste).
• Matte is then converted into blister copper (elemental copper with impurities) by
blowing air through the matte in a copper converter.
2 C u 2 S + 2 Q 2 — > 4C u + 2S02
^per and Copper Alloys
l9
Copper sulphide concentrate*
Process
R everter? to ry furnace
Copper convertor
Jough pitch copper
(99.5% Cij) E lectro iytic refinery
slag
slag
slag
Mud(treated for Au and Ag)
Electrolytic tough pitch copper (99.9% Cu) |
Ingots Billets
Production o f Copper
Refining o f blister copper
• Blister copper is fire-refined in the process called poling to produce tough pitch
copper, which can be used for some applications other than electrical applications.
• Most impurities are oxidized and slagged off.
M +Cu,0 — > MO + 2Cu
• The remained copper oxide CU2O is reduced using coke or charcoal and green tree
trunks until the copper oxide content is about 0.5% then stop.
10
Electrolytic refining o f tough pitch copper
• Further refining of copper to about 99.95% is for electronics applications.
• Electrolytic refining converts fire-refined copper at anode into high-purity copper at
cathode.
• Electrolyte used is CuS04 + H2S04
• This high-purity copper is subsequently melted and cast into shapes.
Electro refining of impure copper
C opper Alloys —Melting and Casting
COPPER is alloyed with other elements because pure copper is extremely difficult
to cast as well as being prone to surface cracking, porosity problems, and to the
formation of internal cavities.
The casting characteristics of copper can be improved by the addition of small
amounts of elements including beryllium, silicon, nickel, tin, zinc, chromium, and
silver.
When casting copper and its alloys, the lowest possible pouring temperature needed
to suit the size and form of the solid metal should be adopted to encourage as small a
grain size as possible as well as to create a minimum of turbulence of the metal
during pouring.
11
Copper alloys are poured into many types of castings such as sand, shell, investment,
permanent mold, chemical sand, centrifugal, and die.
The copper-base casting alloy family can be subdivided into three groups according
to solidification (freezing range between the liquidus and solidus ). The three Major
Copper-Base Alloy Ranges as follows:
The alloys in group I (with narrow solidification temperature range of 50 °C, or
less), are the yellow brasses, manganese and aluminum bronzes, nickel bronze,
manganese bronze alloys, chromium copper, and copper.
The alloys in group II (intermediate solidification temperature range of 50 to 110
°C), are the beryllium coppers, silicon bronzes, silicon brass, and cupro-nickel
alloys.
The alloys in group III (wide solidification temperature range of over 1 10 °C), are
the leaded red and semired brasses, tin and leaded tin bronzes, and high leaded tin
bronze alloys.
Melting Practice - Furnaces
Fuel-Fired Furnaces. Copper-base alloys are melted in oil- and gas-fired crucible
and open-flame furnaces.
Electric Induction Furnaces. Induction melting is increasingly used for the
production of nonferrous metals and alloys.
The production of high-purity copper having less than 2 ppm O can be accomplished
only in a vacuum induction furnace.
Types of Copper Alloys
12
Metal treatment
Gas porosity is a problem in the casting of copper and copper alloys. The
dissolved gas that is most important is hydrogen. However, gaseous compounds such
as water vapor, carbon monixide, and sulfur dioxide can also evolve during
solidification.
Hydrogen Solubility and Reactions.
Hydrogen dissolves in copper and copper alloys as hydrogen atoms.
Different copper alloys and alloy systems have varying tendencies toward gas
absorption and subsequent problems.
The most common alloying element for copper is tin, which it decreases the solubility
of hydrogen. On the other hand, nickel increases the solubility of hydrogen.
Hydrogen can enter the copper directly from the hydrogen in the atmosphere.
The main cause of porosity in the casting results from the evolution of hydrogen or
water vapor during solidification.
Oxygen also presents a potential problem in most copper alloys.
O ther gases that can cause porosity are sulfur dioxide and carbon monoxide, which
also form during solidification.
The type and amount of gas absorbed by a copper alloy melt and retained in a casting
depend on a number of conditions, such as melt temperature, raw materials, atmosphere, pouring conditions, and mold materials.
Degassing o f Copper Alloys
The two primary methods of removing dissolved gases from copper alloys are
oxidation-reduction and inert gas flushing.
Oxidation-reduction
The first step is to remove the hydrogen by oxidation using an oxidizing slag or
oxygen-rich copper. Then, just prior to pouring, the melt is deoxidized by adding
phosphorus or other deoxidizers. Calcium boride, boron carbide, and lithium have
13
also been used for deoxidation. A charcoal cover is often used for deoxidation and
protection of the melt from reoxidation.
Inert Gas Fluxing
With gas fluxing, an inert collector or sparger gas such as argon or nitrogen is
injected into the melt with a graphite fluxing tube. The bubbling action collects the
hydrogen gas that diffuses to the bubble surface, and the hydrogen is removed as the
inert gas bubbles rise to the melt surface.
Deoxidation of Copper Alloys
All copper alloys are subject to oxidation during most melting operations. Oxygen
reacts with copper to form cuprous oxide, which is completely miscible with the
molten metal.
Cuprous oxide exists within the melt cause discontinuous solidification during
casting, resulting in considerable porosity and low mechanical strength.
Thus, some type of deoxidation process is required. In addition, proper deoxidation of
all melts enhances fluidity and therefore castability.
Grain Refining of C opper Alloys
In general, the grain refinement of copper alloys is not practiced as a specific molten
metal processing step per se, because a certain degree of refinement can be achieved
through normal casting processes.
As with aluminum alloys, grain refinement in copper alloys can be achieved by rapid
cooling, mechanical vibration, or the addition of nucleating or grain growth
restricting agents.
14
Fluxing practice in copper alloy melting and casting encompasses a variety of
different fluxing materials and functions.
Fluxes are specifically used to remove gas or prevent its absorption into the melt, to
reduce metal loss, to remove specific impurities and nonmetallic inclusions, to refine
metallic constituents, or to lubricate and control surface structure in the
semicontinuous casting of mill alloys.
Types o f Fluxes. Fluxes for copper alloys fall into five basic categories: oxidizing
fluxes, neutral cover fluxes, reducing fluxes (usually graphite or charcoal), refining
fluxes, and semicontinuous casting mold fluxes.
Oxidizing fluxes are used in the oxidation-deoxidation process; the principal function
here is control of hydrogen gas content.
Neutral cover fluxes are used to reduce metal loss by providing a fluid cover. Fluxes
of this type are usually based on borax, boric acid, or glass, which melts at copper
alloy melting temperatures to provide a fluid slag cover.
Reducing fluxes containing carbonaceous materials such as charcoal or graphite are
used on higher-copper lower-zinc alloys. Their principal advantage lies in reducing
oxygen absorption of the copper and reducing melt loss
Mold fluxes . Certain mo Id-lubricating fluxes have been used in the direct chill
semicontinuous casting of brass and copper alloys into semifinished wrought shapes.
These fluxes serve to protect the metal from oxidation during casting.
They also act as lubricants so that the solidifying skin separates easily from the mold
wall as the solidifying billet or slab moves downward from the mold during casting.
Fluxing of Copper Alloys
15
Inclusions arise from many sources, such as charge materials, furnace tools
excessive temperatures, grain-refiner additions , intermetallic compound
precipitation and refractory Inclusions .
In addition to the usual inclusions arising from oxides, fluxing salts, and
intermetallics, copper oxide inclusions and phosphorus pentoxide (from deoxidation)
may be present in copper alloys if the melt is not allowed to settle or if it is
inadequately skimmed before pouring and casting.
Molten Metal Filtration
The most significant modern development in nonferrous molten metal processing
involves the application of filtration. The filtration process consists of passing the
molten metal through a porous device (a filter) in which the inclusions contained in
the flowing metal are trapped or captured by one or more filtration mechanisms. The
filter material itself must have sufficient integrity (strength, refractoriness, thermal
shock resistance, and corrosion resistance) so that it is not destroyed by the molten
metal before its task is accomplished.
Inspection o f Copper and Copper Alloy Castings
Inspection of copper and copper alloy castings is generally limited to visual and
liquid penetrant inspection of the surface, along with radiographic inspection for
internal discontinuities.
In specific cases, electrical conductivity tests and ultrasonic inspection can be
applied.
Visual inspection is simple yet informative. A visual inspection would include
significant dimensional measurements as well as general appearance.
For the detection of internal defects, radiographic inspection is recommended.
Inclusions in Copper Alloys
16
Magnesium
• Found 2.8% in sea water and other forms, i.e., Dolomite (CaMg(C002),
Magnesite (MgCOjt) and Carnallite (KMgCh.6H20).
• M agnesium with 99.8% purity are readily available but rarely used in this stage
for engineering applications.
Production o f magnesium alloys
Extraction of magnesium
• Calcination
Heating MgCO^ to produce MgO and mix with petroleum coke and then heat
to separate (O) from Mg.
• Pidgeon process (Thermal reduction method)
Powdered ferrosilicon and magnesium oxide are charged in a retort and heated
under vacuum at T~1200°C, giving Mg vapour, which is then condensed into
crystals.
• Dow process (Electrolysis process)
Precipitate dolomite and seawater and treated with HC1 to give MgCF and put
in electrolytic cell to give Mg metal at cathode.
Calcination Process
• MgCO;, is calcined to produce MgO.
• MgO is then mixed with petroleum coke and pressed into solid block, called
briquette.
• Briquette is heated to -2500°C to give Mg gas and cooled down to -120 °C to
give Mg solid.
MgO + coke— > Mg + CO
17
Calcination*
Mixed with petroleum coke and press
Heated at ~2500°C in H2 atmosphere
*Fast cooled to T-120 °C
Extraction o f magnesium - Calcination
Melting o f magnesium alloys
Magnesium is normally melt in mild steel crucibles for the alloying, refining or
cleaning stage due to very slow reaction with the steels.
• Magnesium and its alloys are highly reactive with oxygen and can oxidized and
burn in air.
• Magnesium alloys form a loose, permeable oxide coating on the molten metal
surface. This allows oxygen to pass through and support burning below the oxide
at the surface.
• Protection of the molten alloy using either a flux or a protective gas cover to
exclude oxygen is therefore necessary.
• Melting stage: Using fluxes containing a mixture of chlorides such as MgCl2, KCl
or NaCl. Removal of chlorides is essential prior to pouring due to corrosive effect.
• Alloying and refining stage: Using flux containing a mixture of CaF2, MgFi, and
MgO to form a coherent, viscous cake which excludes air.
• Sulphur hexafluoride SF6 protection is also used, which lowers oxidation melt
losses and operating cost.
Casting o f magnesium alloys
Magnesium alloy castings can be produced by nearly all of the conventional casting
methods, namely, sand, permanent, and semipermanent mold and shell, investment,
and die casting.
The choice of a casting method for a particular part depends upon factors such as:
18
• the configuration of the proposed design,
• the application,
• the properties required,
• the total number of castings required, and the properties of the alloy.
casting methods
• Sand casting - cheap
• Investment or Permanent Mold Castings
• High pressure dies casting
Most widely used for magnesium alloy components, Hot chamber and Cold
chamber
• Squeeze casting
Vertical arrangement of casting unit and molding direction
- Direct squeeze casting
- Indirect squeeze casting
• Thixocasting
Relatively new method based on the thixotropic properties of the semi liquid
alloys.
• Squeezed while ‘'mushy”
• More uniform microstructures
• Better properties (lower porosity
Com m ercial magnesium alloys
• Mg-Al casting alloys
• Mg-Al-Zn casting alloys
• Mg-Zn and Mg-Zn-Cu casting alloys
• High temperature Mg casting alloys
• Wrought Mg alloys
19
Refractory metals
Refractory metals (titanium, Ti, zirconium, Zr, and hafnium, Hf , vanadium, V,
niobium, Nb, and tantalum, Ta , chromium, Cr, molybdenum. Mo, and tungsten, W
,and rhenium, Re) vary in relative abundance in the Earth’s crust. A major part of
these metals occurs as oxides and complex oxides (Ti, V, Cr, Nb, Ta, W), two as
sulfides (Mo, Re), and the remaining two (Zr, Hf) as silicates.
All these Refractory metals have high melting points, mechanical strength, hardness,
and electrical resistance.
Production of refractory metals
- Most of refractory metals, are obtained from ore concentrates or industrially
produced oxides by aluminothermic method in the form of ferroalloys used in
alloying steel (Aluminothermic reactions are exothermic chemical reactions
using aluminium as the reducing agent at high temperature).
Pure refractory metals are produced from ore concentrates by a complex three-
stage process: breaking up the concentrate, separating and purifying the chemical
compounds, and reducing and refining the metal.
- Production of massive Nb, Ta, Mo, and W and of these metals’ alloys is based on
powder metallurgy, which also figures in the production of other refractory
metals.
Melting of refractory metals
• Melting of refractory metals is carried out either in a protective atmosphere or
under vacuum so as to prevent oxidation.
• The melting of these metals in ceramic or graphite crucibles is difficult
in practice, and sometimes even impossible.
• From experiments it appears, for example, that zirconium can be melted only
in thorium oxide crucibles.
20
• When melted in beryllium oxide crucibles, the metal becomes brittle. Melts in
graphite result in carbon contamination up to 0.25%.
• Therefore, zirconium melting in induction or resistance furnaces by ordinary
methods is very difficult.
• Arc, electron-beam, and plasma melting are finding increasing use in the
metallurgy of all the refractory metals
o A '"
■ The essence of arc melting consists in the ignition of an arc
between the specimen placed in an intensively cooled copper
crucible, and the electrode.
■ The current is applied to the crucible and the electrode.
■ The specimen maintains a thin unmelted skin in contact with the
crucible.
■ Due to this interface there is no reaction between the melted
specimen and the crucible.
o Alectron beam jnelting
■ electron beam melting is distinguished by its superior refining
capacity and offers a high degree of flexibility of the heat source.
■ Thus, it is ideal for remelting and refining of metals and alloys
under high vacuum in water-cooled copper molds.
■ Today the process is mainly employed for the production of
refractory and reactive metals (tantalum, niobium, molybdenum,
tungsten, vanadium, hafnium, zirconium, titanium) and their
alloys.
■ It plays an important role in manufacturing of ultra-pure
sputtering target materials and electronic alloys and the recycling
of titanium scrap.
Titanium and its alloys
21
7
Titanium is the forth abundant metal on earth crust 0.86%) after aluminium, iron
and magnesium.
• Not found in its free, pure metal form in nature but as oxides, i.e., ilmenite (FeTiO^)
and rutile (Ti02).
Because of high reactivity of titanium, it requires complex methods and high energy
input to win the metal from the oxide ores. The required energy per ton is - 1.7 times
that of aluminum and - 16 times that of steel.
• Have similar strength as steel but with a weight nearly half of steel.
Used mainly in aerospace, marine, chemical, biomedical applications and sports.
Production of titanium alloys
Extraction o f titanium- KroII process
Titanium ore - rutile (TiO?) is converted into titanium sponge by
1) Passing Cl2 gas through charge the ore, resulting in colourless,
titanium tetrachloride TiCl4.
T i02 + 2C12 + C --- TiCl4 + C 0 2
2) TiCl4 is purified by fractional distillation.
3) The liquid form of TiCl4 is reacted with either Mg or Na under an inert
(Ar) atmosphere to obtain titanium sponge while Mg or Na is recycled.
2Mg + TiC14 --- MgCl2 + Ti
titaniim sponge
Melting processes
- Rlectroslag Refining (ESR)
- Vacuum Arc Remelting (VAR)
- Electron Beam Melting (EBM)22
- Plasma Arc Melting (PAM)
- Induction Skull Melting
Induction Skull Melting
• A water-cooled copper crucible is used to avoid contamination of reactive
materials.
• Metal is charged inside the crucible by induction power source applied by
magnetic field.
• The charge is melted and freeze along the bottom and wall,
• producing a shell or skull with molten metal in it.
• Revert or scrap can be used.
• Low cost, high quality titanium alloy production.
M'jl'OA CuL>p*rrisers*
Coc! nc; Out
U Hirr-uMklrU
indurlinn coil
Induction skull melting schematic
N alrr*n>olc<l
copper Tinner*
W jMmvoolcri fuse
Classification o f titanium alloys
• Commercially pure (CP) titanium alpha and near alpha titanium alloys
- Generally non-heat treatable and weldable
- Medium strength, good creep strength, good corrosion resistance
• Alpha-beta titanium alloys
23
- I leat treatable, good forming properties
- Medium to high strength, good creep strength
• Beta titanium alloys
- Heat treatable and readily formable
- Very high strength, low ductility
Casting of titanium alloys
Titanium castings contribute to small amount of titanium products recently used.
There are several methods as follows;
Conventional casting
• Investment casting
• Vacuum casting
Conventional casting
• Rammed graphite is used as the mould rather than sand due to its minimal tendency
to react with molten titanium.
• Produce intricate shapes with good surface finish condition
Investment casting
This process begins with
1) Duplicating a wax part from engineering drawing of the specific part.
2) Dipping in ceramic slurry until a shell is formed.
3) The wax is then melted out and the fired shell is filled with molten
metal to form a part near to the net shape of the drawing.
• Most widely used for titanium castings
• Cost effective
• Precise dimensional control
24
U icd for structural applications requiring, metallurgical integrity and sports
applications such as golf heads.
Vacuum die casting
• Reduce porosity in the castings
• Provide high quality parts
Vacuum is applied for die casting to reduce gas entrapment during metal injection
and to decrease porosity in the casting.
Vacuum die casting
Tin and Tin alloys
fin is found in the form of oxide (SnO^) as vein tin or stream tin. Its colour is in
white and grey.
• Easily extracted because it is already in its oxide form.
Tin - Extraction
25