Ferrous Metals and Alloys: Production,

General Properties, and Applications

IntroductionGeneral catagories of ferrous metals and alloys:

1. Carbon and alloy steels2. Stainless steels3. Tool and die steels4. Cast irons5. Cast steels

Produced as1. Sheet2. Plates3. Structural members4. Gears5. Music wires6. Fasteners

Production of Iron and SteelRaw MaterialsThree basic materials used in iron & steel

making:1. Iron ore2. Limestone3. Coke

Principal iron ores: Taconite: black rock Hematite: iron oxide mineral Limonite: iron oxide containing water

Limestone (calcium carbonate) is used to remove impurities from the molten iron by chemically reacting with impurities to form a slag

Production of Iron and SteelRaw MaterialsAfter it is mined, the ore is:

1. crushed into fine particles2. Impurities are removed3. The ore is formed into pellets

Coke is obtained from special grades of bituminous coal, which are heated in vertical ovens @ 1150 ⁰C and then cooled with water in quenching towers.

Functions of coke:1. Generate high level of heat required for the

chemical reaction2. Produce CO, which is used to reduce iron oxide to

iron

Production of Iron and SteelIron MakingThe three raw materials are carried to the top of

the blast furnace and dumped into it.The charge mixture is melted in a reaction at

°1650 C with air pre-heated to about 1100 °C and blasted into the furnace through nozzles.

The molten metal accumulates at the bottom of the furnace while the impurities float to the top of the metal as slag

Molten metal is drawn off into ladle cars (pig iron).Pig iron composition: 4% C, 1.5% Si, 1%Mn, 0.04%

S, 0.4% P

Production of Iron and SteelSteel Making – Electric FurnacesRefining of pig iron

Electric Furnaces

Casting of IngotsDepending on the amount of gas evolved

during solidification, three types of steel ingots can be produced:1. Killed steel2. Semi-Killed steel3. Rimmed steel

Casting of IngotsKilled SteelFully deoxidized steel, oxygen is removed and

porosity is eliminated. The dissolved oxygen reacts with Al, Mn, and Vn.

The chemical and mechanical properties are uniform

Because of shrinkage during solidification, a pipe (funnel-like) is developed at the top of the ingot

Casting of IngotsSemi-Killed SteelPartially deoxidized steel with some porosity

in the upper central section of the ingotLittle or no pipeEconomical to produce

Casting of IngotsRimmed SteelLow carbon content (<0.15%)Evolved gases are killed partially using Al.Little or no pipingDuctile skin with good surface finishImpurities and inclusions tend to segregate

toward the center of the ingot

Continuous Casting

Carbon and Alloy SteelsEffects of various elements in steelBoron: improves hardenability without loss of

machinability and formability.Calcium: deoxidizes steels, improves tougness and may

improve machineablity and formablityCarbon: improves hardenability, strength, hardness,

and wear resistanceCerium or mangnese or Zirconium: controls the

shape of inclusions and improves toughness in high strength alloy steels, it deoxidizes steel

Chromium: improves toughness, hardenability, wear and corrosion resistance, and high-temperature strength. It increases the depth of hardness penetration in HT by promoting carbonization.

Carbon and Alloy SteelsResidual elements in steelAntimony and Arsenic: cause temper

embrittlementHydrogen: embrittle steelNitrogen: improves strength, hardness, and

machinability. In Al deoxidized steels, it controls the size of inclusions and improves strength and toughness. It decreases ductility and toughness

Oxygen: increases strength of rimmes steel. It reduces tougness

Lead: causes hot shortness and temper embrittlement

Carbon and Alloy SteelsDesignations for steelsAISI and SAE: 4 digits1st two digits: %weight of alloying elements2nd two digits: %weight of carbonTable 5-2

Alloy steels: steels containing significant amounts of alloying elements

Carbon and Alloy SteelsHigh strength alloy steelsLow carbon content: <0.30%Microstructure consists of fine grain ferrite as

one phase and a hard 2nd phase of martensite and austenite

Designation: Table 5-3Structural quality (S): C, Mn, P, NLow Alloys (X): Nb,Cr, Cu, Mn, Ni, Si, Ti, V, ZrWeathering steels (W): environmental corrosion

resistance; Si, P, Cu, Ni, CrFormability: F(excelemt), K (good), O (fair)

Stainless SteelsMain alloying element:: Cr (10-12% min)Other alloying elements: Ni, Mo, Cu, Ti, Si, Mn,

Al, N, SHigher C content reduces corrosion resistance 5 types:

1. Austenstic (200 and 300 series)2. Ferretic (400 series)3. Martenstic (400 and 500 series)4. Preciptation hardening (PH)5. Duplex structure

Tool and die steelsDesigned for high strength, impact

toughness, and wear resistance at room and elevated temperatures

Used in forming and machining of metalsBasic types (see table 5-5)