5steel making

7/31/2019 5Steel Making

1/5

Steel Making

What is Steel ?

Steel is an alloy of iron (Fe), carbon (C) and alloying elements which are addedintentionally to develop certain properties in final product based on end

use/requirement.

In engineering, Fe-C alloys are classed into iron,steel, and pig iron according to the C content Iron : 0.01 - 0.025% CarbonSteel : 0.025 - 2.06% CarbonPig Iron : >2.06% Carbon

It also contain certain other elements, such as Mn, P,S, Si, Cr, Mo,Ni, Al etc.

Steel Making Process :Steelmaking is an oxidising process. It refines and oxidises the impurities in hot

metal like C, Si, Mn and removes S & P to a desired level Fluxes are added toform basic slag to fix S & P.Hot metal supplies the necessary heat in BasicOxygen Furnace (BOF)/Twin Hearth steelmaking & Electrical Power in ElectricArc Furnace(EAF)/Induction Furnace.

Classification of Steel :Carbon Steels:

Variations in properties are obtained by varying the Carbon content.

Class C % Mn %

Low C steel : upto 0.25% 0.25 - 0.50

Medium C steel : 0.25 - 0.60 0.5 0 - 0.90

High C steel : 0.61 - 2.06 0.30 - 0.90


2/5

Alloy Steels:

Special purpose steels that contains alloying elements ( such as Cr, Ni, Mo, V, B, Wetc.) apart from carbon steels to improve mechanical and other properties

- Stainless Steel (High Cr, Ni, Mn etc)- Non-Stainless Steel

Devolopment of Steelmaking :

Crucible process was available till 1855. Acid Bessemer developed in 1855 by Henry Bessemer of Great Britain. Basic Bessemer process was developed by Sydney Thomas in 1878.

Open- Hearth process developed by Siemens and Pierre Martin in 1856. Electric Arc Furnace steel making started in 1906 at New York and gained

momentum after second worldwar. LD process of steelmaking ( BOF) developed in 1950 where pure oxygen is

blown from the top of the converter. Induction Furnace steel making started around 1950. Open- Hearth furnace has been modified to Twin Hearth Furnace ( THF ) in

late seventies.

Raw Materiasl in Steelmaking : Hot Metal Scrap / Sponge Iron / DRI Fluxes

Lime / Dolomitic LimeRaw Dolomite/ Burnt DolomiteIron Ore / Mill ScaleBauxite / FluorsparBOF SlagOxygen / Air

Stages of Steelmaking :

Primary Steelmaking :Basic oxygen steelmaking is a method of primary steelmaking in which

carbon-rich molten pig iron is made into steel. Blowing oxygen through
http://en.wikipedia.org/wiki/Pig_ironhttp://en.wikipedia.org/wiki/Pig_iron


3/5

molten pig iron lowers the carbon content of the alloy and changes it intolow-carbon steel. The process is known as basic due to the pH of therefractoriescalcium oxide and magnesium oxidethat line the vessel towithstand the high temperature of molten metal.

The process was developed in 1948 by Robert Durrer and

commercialized in 19521953 by Austrian VOEST and AMG. The LDconverter, named after the Austrian towns Linz and Donawitz (a district ofLeoben) is a refined version of the Bessemer converter where blowing ofair is replaced with blowing oxygen. It reduced capital cost of the plants,time of smelting, and increased labor productivity. Between 1920 and2000, labor requirements in the industry decreased by a factor of 1,000,from more than 3 worker-hours per tonne to just 0.003. The vast majorityof steel manufactured in the world is produced using the basic oxygenfurnace; in 2000, it accounted for 60% of global steel output. Modern

furnaces will take a charge of iron of up to 350 tons and convert it intosteel in less than 40 minutes, compared to 1012 hours in an open hearthfurnace.

Secondary Refining of Steel :1. Molten pig iron (sometimes referred to as "hot metal") from a

blast furnace is poured into a large refractory-lined container calleda ladle.

2. The metal in the ladle is sent directly for basic oxygensteelmaking or to a pretreatment stage. Pretreatment of the blast

furnace metal is used to reduce the refining load of sulfur,silicon,and phosphorus. In desulfurising pretreatment, a lance is loweredinto the molten iron in the ladle and several hundred kilograms ofpowdered magnesium are added. Sulfur impurities are reduced tomagnesium sulfide in a violent exothermic reaction. The sulfide isthen raked off. Similar pretreatment is possible for desiliconisationand dephosphorisation using mill scale (iron oxide) and lime asreagents. The decision to pretreat depends on the quality of theblast furnace metal and the required final quality of the BOS steel.

3. Filling the furnace with the ingredients is called charging. The

BOS process is autogenous: the required thermal energy isproduced during the process. Maintaining the proper chargebalance, the ratio of hotmetal to scrap, is therefore very important.The BOS vessel is one-fifth filled with steel scrap. Molten iron fromthe ladle is added as required by the charge balance. A typicalchemistry of hotmetal charged into the BOS vessel is: 4% C, 0.20.8% Si, 0.08%0.18% P, and 0.010.04% S.
http://en.wikipedia.org/wiki/Alloyhttp://en.wikipedia.org/wiki/Low-carbon_steelhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Refractoryhttp://en.wikipedia.org/wiki/Calcium_oxidehttp://en.wikipedia.org/wiki/Magnesium_oxidehttp://en.wikipedia.org/wiki/Robert_Durrerhttp://en.wikipedia.org/wiki/Voestalpinehttp://en.wikipedia.org/wiki/Austriahttp://en.wikipedia.org/wiki/Linzhttp://en.wikipedia.org/wiki/Leobenhttp://en.wikipedia.org/wiki/Bessemer_converterhttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Open_hearth_furnacehttp://en.wikipedia.org/wiki/Open_hearth_furnacehttp://en.wikipedia.org/wiki/Blast_furnacehttp://en.wikipedia.org/wiki/Ladle_%28metallurgy%29http://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/w/index.php?title=Lance_%28metallurgy%29&action=edit&redlink=1http://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Magnesiumhttp://en.wikipedia.org/wiki/Magnesium_sulfidehttp://en.wikipedia.org/wiki/Exothermichttp://en.wikipedia.org/wiki/Mill_scalehttp://en.wikipedia.org/wiki/Furnacehttp://en.wikipedia.org/wiki/Furnacehttp://en.wikipedia.org/wiki/Mill_scalehttp://en.wikipedia.org/wiki/Exothermichttp://en.wikipedia.org/wiki/Magnesium_sulfidehttp://en.wikipedia.org/wiki/Magnesiumhttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/w/index.php?title=Lance_%28metallurgy%29&action=edit&redlink=1http://en.wikipedia.org/wiki/Siliconhttp://en.wikipedia.org/wiki/Sulfurhttp://en.wikipedia.org/wiki/Ladle_%28metallurgy%29http://en.wikipedia.org/wiki/Blast_furnacehttp://en.wikipedia.org/wiki/Open_hearth_furnacehttp://en.wikipedia.org/wiki/Open_hearth_furnacehttp://en.wikipedia.org/wiki/Oxygenhttp://en.wikipedia.org/wiki/Bessemer_converterhttp://en.wikipedia.org/wiki/Leobenhttp://en.wikipedia.org/wiki/Linzhttp://en.wikipedia.org/wiki/Austriahttp://en.wikipedia.org/wiki/Voestalpinehttp://en.wikipedia.org/wiki/Robert_Durrerhttp://en.wikipedia.org/wiki/Magnesium_oxidehttp://en.wikipedia.org/wiki/Calcium_oxidehttp://en.wikipedia.org/wiki/Refractoryhttp://en.wikipedia.org/wiki/PHhttp://en.wikipedia.org/wiki/Low-carbon_steelhttp://en.wikipedia.org/wiki/Alloy


4/5

4. The vessel is then set upright and a water-cooled lance islowered down into it. The lance blows 99% pure oxygen onto thesteel and iron, igniting the carbon dissolved in the steel and burningit to form carbon monoxide and carbon dioxide, causing thetemperature to rise to about 1700C. This melts the scrap, lowers

the carbon content of the molten iron and helps remove unwantedchemical elements. It is this use of oxygen instead of air thatimproves upon the Bessemer process, for the nitrogen (and othergases) in air do not react with the charge as oxygen does. Highpurity oxygen is blown into the furnace or BOS vessel through avertically oriented water-cooled lance with velocities faster thanMach 1.

5. Fluxes (burnt lime or dolomite) are fed into the vessel to formslag, which absorbs impurities of the steelmaking process. During

blowing the metal in the vessel forms an emulsion with the slag,facilitating the refining process. Near the end of the blowing cycle,which takes about 20 minutes, the temperature is measured andsamples are taken. The samples are tested and a computeranalysis of the steel given within six minutes. A typical chemistry ofthe blown metal is 0.30.6% C, 0.050.1% Mn, 0.010.03% Si,0.010.03% S and P.

6. The BOS vessel is tilted again and the steel is poured into agiant ladle. This process is called tapping the steel. The steel isfurther refined in the ladle furnace, by adding alloying materials to

give the steel special properties required by the customer.Sometimes argon or nitrogen gas is bubbled into the ladle to makesure the alloys mix correctly. The steel now contains 0.11%carbon. The more carbon in the steel, the harder it is, but it is alsomore brittle and less flexible.

7. After the steel is removed from the BOS vessel, the slag, filledwith impurities, is poured off and cooled.

Secondary Refining of Steel :Secondary steelmaking is most commonly performed in an Electric Arc Furnace(EAF).

Precise control of temperature through ELECTRICAL POWER INPUT /CHEMICAL HEATING.

DE-OXIDATION and adjustment of chemical composition through alloyadditions and inert gas stirring.
http://en.wikipedia.org/wiki/Carbon_monoxidehttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Chemical_elementhttp://en.wikipedia.org/wiki/Bessemer_processhttp://en.wikipedia.org/wiki/Flux_%28metallurgy%29http://en.wikipedia.org/wiki/Lime_%28mineral%29http://en.wikipedia.org/wiki/Dolomitehttp://en.wikipedia.org/wiki/Slaghttp://en.wikipedia.org/wiki/Argonhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Nitrogenhttp://en.wikipedia.org/wiki/Argonhttp://en.wikipedia.org/wiki/Slaghttp://en.wikipedia.org/wiki/Dolomitehttp://en.wikipedia.org/wiki/Lime_%28mineral%29http://en.wikipedia.org/wiki/Flux_%28metallurgy%29http://en.wikipedia.org/wiki/Bessemer_processhttp://en.wikipedia.org/wiki/Chemical_elementhttp://en.wikipedia.org/wiki/Carbonhttp://en.wikipedia.org/wiki/Carbon_dioxidehttp://en.wikipedia.org/wiki/Carbon_monoxide


5/5

Flotation/removal/modification of inclusion from liquid steel by inert GASSTIRRING.

Refining under basic and reducing SLAG for de-sulphurisation. Removal of gases from steel by VACUUM DEGASSING. Maintains inert atmosphere during processing.

Secondary Refining Units : Argon Rinsing Unit (ARU) / LRS Ladle Furnace (LF) Vacuum Arc Degassing & Refining (VADR) Ruhrstahl Heraeus Degasser (R-H / R-H OB) Argon Oxygen Decarburisation (AOD) Vacuum Oxygen De-carburisation (VOD)

5steel making

Documents