TOPIC 2FERROUS METAL

INTRODUCTION

• There are a lot of metals used in engineering, however those based on iron are the most important and widely used. Steel is a ferrous metal because its main constituent is iron. A quick and easy way to tell if metal is ferrous or not, is to use magnet.

2.1 METAL PRODUCTION2.1.1 CONTENT OF IRON ORE

Iron ore Composition Colour

Magnetite (Fe3o4)

Contain 70% of iron

Dark grey, black

Hematite (Fe2o3)

Contain 40% - 65% of iron

Rusty red

limonite Contain 20% - 55% of iron

Rusty brown

carbonate Contain 30% of iron

grey

2.1.2 PROCESS OF IRON PRODUCTION USING BLAST FURNACEThe iron itself is chemically combined with oxygen and is called iron oxide in order to remove all of the impurities the iron ore has to be smelted, and this is done using a Blast furnace

2.1 METAL PRODUCTION

2.1.2 PROCESS OF IRON PRODUCTION USING BLAST FURNACE

The blast furnace process:1. The iron ore, coke and limestone(the charge), is conveyed

to the top of the furnace.2. Hot air is then blown through pipes called tuyeres, to fire

the mixture.3. The coke burns to increase the temperature in the furnace4. The limestone attracts the impurities in the iron ore and

form slag. The slag is lighter than the molten iron and so floats on top of it.

5. As the furnace fills, the molten iron is tapped off. The slag is also tapped off at regular intervals.

6. Most iron is taken straight from the blast furnace to the steel mill, but some is poured into buckets called pigs. The iron is called pig iron and is used to make cast iron.

2.1 METAL PRODUCTION

2.2.1 PROCESS OF STEEL PRODUCTIONSteel is made from iron mixed with carbon. The two methods of producing steel from iron are;

a. Basic Oxygen furnace

2.2 STEEL PRODUCTION

There are six steps in the production of steel using the Basic Oxygen Furnace process. During each stage, the furnace is turned in different directions. This is shown clearly in the accompanying diagram

2.2 STEEL PRODUCTIONBasic Oxygen Furnace process

2.2.1 PROCESS OF STEEL PRODUCTIONb. Electric Arc Furnace

2.2 STEEL PRODUCTION

The Electric arc furnace is heated by electricity, similar to arc welding and so large amount of electricity are needed.

Tapping

2.2 STEEL PRODUCTIONElectric Arc Furnace process

2.3 PLAIN CARBON STEEL2.3.1 EQUILIBRIUM PHASE DIAGRAM UP TO 1.7% CARBON

2.3.1 EQUILIBRIUM PHASE DIAGRAM UP TO 1.7% CARBONPhase in Iron Carbon Phase Diagram

2.3 PLAIN CARBON STEEL

a. Ferrite( iron)

At 0% carbon is pure iron. BCC crystal structure. The maximum solubility of carbon is 0.02% carbon at 723C

b. Austenite( iron)

FCC crystal structure. High solubility for carbon compared to ferrite. The solubility reaches a maximum of 2.0% carbon at 1147C.

c. Pearlite( + Fe3C)

It is eutectoid mixture containing 0.8% carbon and is form at 723C. A lamellar structure of ferrite and cementite

d. Cementite(Fe3C)

Unlike ferrite and austenite, cementite is a very hard intermetallic compound consisting of 6.7% carbon and the remainder iron.

Classification composition Properties Application

Low Carbon steel and Mild steel

0.02 - 0.3 %C Low carbon steel contains approximately 0.05–0.15% carbon and mild steel contains 0.16–0.3%. has a relatively low tensile strength, but it is cheap and malleable; surface hardness can be increased through carburizing

Sheets, wires, pipes, car body and etc.

Medium Carbon steel

0.3 - 0.6 %C. Approximately 0.30–0.6% carbon content. ductility and strength and has good wear resistance

Used for large parts, forging and automotive components.

High Carbon steel

0.6 - 1.7 %C. Approximately 0.6–1.7% carbon content. Steels that can be tempered to great hardness

Used for special purposes like (non-industrial-purpose) knives, axles or punches and spring.

2.3 PLAIN CARBON STEELCarbon steel, also called plain-carbon steel, is steel where the main interstitial alloying constituent is carbon

2.4.1 Define term and purpose of alloy steelAlloy steel is steel alloyed with a variety of elements in total amounts of between 1.0% and 50% by weight to improve its mechanical propertiesEffect of alloying element to steel properties1. Increase hardenability2. Formation of new carbides3. Solubility of solid solution4. Improvement in corrosion resistance5. Stability of austenite and ferrite Alloy element of steel and how this element effecting metal properties

2.4 ALLOY STEEL

Alloy material Composition Effect

Manganese 1-1.5% -Increases hardenability

Sulfur 0.08 – 0.15% - Improve machinability

Nickel 2-5% or 12 – 20% -increase touhgness and improve corrosion resistance

Chromium < 2% - Improve Heat resistance and strenght

2.4.3 Identify the characteristic of alloy steel.

2.4 ALLOY STEEL

Type of steel alloy Characteristics

1. Structural steel Structural steel is steel construction material, a profile, formed with a specific shape or cross section and certain standards of chemical composition and mechanical properties.Application: I-beam

2. Corrosion Resistance steel or stainless steel

Steel alloy with minimum of 10% chromiumWhy is it stainless?The Cr react with oxygen to form a tough , adherent, invisible and passive layer of Cr2O3 film.Application: Household utensils, automotive exhaust, kitchen sink and etc

3. Heat resistance steel or High speed steel

Capable of cutting metal at much higher rate than carbon steel. Used to cut other metals/alloys and continues to cut and retain its hardness even when the point of the tool is heated to a low red temperature.Application: Milling tool, tool bits and etc

4. Tool and mould steel.

Wear resistance, capable of holding sharp cutting edge and very hard.Application: Concrete drill, drawing dies and etc.

2.4.3 Identify the characteristic of alloy steel.

2.4 ALLOY STEEL

2.5.1 Explain cast iron position in iron-carbon phase diagram.

• Family of ferrous alloy• Typical compositions: 2-4% of carbon and 1-3% silicon

2.5.2 Explain the effect of each factor below on cast iron properties:

a. Cooling rate- Rapid cooling discourages the nucleation graphite and

encourages the formation of metastable iron carbide. Longer holding times at higher temperatures and slower cooling and the addition of certain alloying elements encourage the formation of stable iron-graphite phase.

b. Carbon content- High carbon content metals can, under controlled

conditions, solidify as stable iron-graphite systems or metastable iron-carbide systems.

2.5 CAST IRON

2.5.2 Explain the effect of each factor below on cast iron properties:

c. Element content- Cast iron contains significant amounts of silicon in

addition to the high carbon content. Cast irons are therefore really iron-carbon-silicon alloys. The presence of silicon in iron carbon alloys promotes the formation of graphite

2.5 CAST IRON

2.5.3 Expain the characteristic and applications of the cast iron:

Grey cast iron

a. Named as a Grey cast iron because its fracture has a grey appearance.

b. Carbon content: 2.5 – 4.0% carbon and 1-3% siliconc. Microstructure: Graphite presence in the form of flake

or rossete

d. Properties: High compressive strength, hardness and moderate machinability.

e. Application: Engine block, cylinder block, clutch plate and gear boxes

2.5 CAST IRON

2.5.3 Expain the characteristic and applications of the cast iron:

White cast iron

a. Named as a Grey cast iron because its fracture has a white/silver appearance.

b. Carbon content: < 4.3% of carbon and presence of manganese and silicon

c. Microstructure: Carbon + Fe presence in the form of cementite

d. Properties: High wear and abrasion resistance. e. Application: Brake shoes, ball mills and extrusion nozzle

2.5 CAST IRON

2.5.3 Expain the characteristic and applications of the cast iron:

Malleable cast iron

a. Produced by annealing White cast iron at 900-1060C for 50 -80 hour (Slow cooling to room temperature)

b. Two groups of malleable cast iron are specified,( black and white) differentiated by chemical composition, temperature and time cycles of the annealing process, the annealing atmosphere and the properties and microstructure resulting there from. Microstructure: Carbon + Fe presence in the form of cementite.

c. Properties: increase ductilty of white cast iron d. Casting mould, railroad and pipe fitting

2.5 CAST IRON

2.5.3 Expain the characteristic and applications of the cast iron:

Malleable cast iron(Black)

a. The microstructure of blackheart malleable cast iron has a matrix essentially of ferrite

Malleable cast iron(Black)a. Cast iron, which has a pearlite matrix. By adding

manganese to the structure, carbon is retained in the form of cementite.

2.5 CAST IRON

2.5.3 Expain the characteristic and applications of the cast iron:

Ductile Cast Iron (Nodular Cast Iron):

This structure is developed from the melt. The carbon forms into spheres when cerium, magnesium, sodium, or other elements are added to a melt of iron with a very low sulfur content that will inhibit carbon from forming. The control of the heat-treating process can yield pearlitic, ferritic, martensitic matrices into which the carbon spheres are embedded.

Figure 6. Photomicrograph of Nodular Cast iron

2.5 CAST IRON