Ferrous Alloys (l.u. 10/1/10)

Ferrous Metals and Alloys

Contain IRON as their base metal.second most abundant element in Earth’s crust

(5%).Relatively inexpensive.

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Relative cost per unit Volume (Kalpakjian & Schmid, 2006)

Carbon Steel

Copper Nickel Silver Gold

1 5-6X 35X 600X 60,000X

Three materials used in Steel: 1. Iron ore - pelletized metal

2. Coke - for heat & producing carbon monoxide which reduces iron-oxide to iron (removes oxygen)

3. Limestone - combines with impurities which floats to surface (slag)

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Common Terms

Pig Iron- hot metal, molten metal used in making iron and steels

Ingot- molten metal to solid form – ready for rolling/forging = Inefficient!

Continuous Casting become most popular steel-making technique

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Three Types of Steel Ingots:

1) Killed Steel- steel is fully deoxidized: oxygen is removed and porosity is eliminated (consistent mechanical and chemical properties)

2) Semi-Killed Steel- partially deoxidized steel: contains some porosity (economical)

3) Rimmed Steel- low carbon content, porosity (blowholes), lower quality steel (requires inspection)

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Refining

Removal of impurities (Trace Elements)

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Tin Hot shortness & temper embrittlement (melting)

Oxygen Reduces toughness

Hydrogen Causes embrittlement

Nitrogen Decreases ductility and toughness

Antimony & Arsenic

Cause temper embrittlement

Refining:

Used to create higher quality steels

Improves uniformity and consistency in composition

Removing impurities, inclusions, other elements

Adding various elements

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Inclusions? Good or bad?

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“Free-machining steels are basically carbon steels that have been modified by an addition of sulfur, lead, bismuth, selenium, tellurium, or phosphorous plus sulfur to enhance machinability. Sulfur combines with manganese to form soft manganese sulfide inclusions. These, in turn, serve as chip-breaking discontinuities within the structure. The inclusions also provide a build-in lubricant that prevents formation of a build-up edge on the cutting tool and imparts an improved geometry” (Black & Kohser, 2008, p. 130).

Alloy Steels

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(Black & Kohser, 2008, p. 125)

Iron - Carbon Alloys

Pure Iron - less than 0.008% C

Steel - up to 2.11% C

Cast Iron - up to 6.67% C*

typically less than 4.5% C

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Carbon Steels Classification

Low-Carbon (mild steel): 0.30% or less

Medium-Carbon: 0.30-0.60%

High-Carbon: more than 0.60%

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Bolts, nuts, sheet, tubes, plate, low strength machine components

Machinery and automotive parts, gears, axles, connecting rods, etc.

Cutting tools, cables, springs, cutlery

Carbon Effects

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(Black & Kohser, 2008, p. 124)

Common Designations for Steel:

AISI - The American Iron and Steel Institute

SAE - Society of Automotive Engineers

ASTM - American Society for Testing Materials

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Carbon and Alloy Steels

AISI and SAE designate a four-digit numbering

system for the classification of steels.

first two digits indicate alloying elements.

last two digits percentage of carbon.

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1020

Plain Carbon .2% Carbon Content

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(Black & Kohser, 2008, p. 126)

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(Black & Kohser, 2008, p. 123-4)

Sample Question

What makes up a “forty-three forty” 4340 steel?

43 = Mo, Cr, Ni

40 = .40% C

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Sample Question

Why is aircraft landing gear made of 4140 or 4340 steel?

Mo = imparts temperature strength, toughness, hardness, dimensional stability

C = imparts hardness, wear resistance, reduces ductility

Ni/Cr = hardness and oxidation resistance

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Stainless Steels

Characterized by their corrosion resistance, high strength and ductility, and high chromium content.

In the presence of air (oxygen) they develop a thin and hard adherent film of chromium oxide which protects the metal from corrosion Passivation

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(Black & Kohser, 2008, p. 134)

(Black & Kohser, 2008, p. 132)

Stainless Steels Classifications

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• Nonmagnetic• Most ductile of all stainless steels• Susceptible to stress-corrosion cracking

Austenitic(200-300 series)

•High chromium content•Lower ductility•Not heat-treatable

Ferritic (400 series)

• Magnetic.• Moderate corrosion resistance.• High strength, hardness, fatigue resistance, good

ductility

Martensitic (400 and 500 series)

• Chromium and nickel (along with copper, aluminum, titanium, or molybdenum.

• Good corrosion resistance, ductility, and high strength at elevated temperatures

Precipitation Hardening (PH)

• Austenite and ferrite.• Higher resistance to corrosion and stress corrosion

than 300 seriesDuplex Structure

Kitchenware, fittings, welded construction,Heat/chemical resistant environments

Non-structural applications, automotive trim, kitchenware

Cutlery, surgical tools, springs, valves

Aircraft & aerospace applications

Heat exchangers

Tool and Die Steels

Special alloys designed for high strength, impact toughness, and wear resistance at room or elevated temperatures.

For forming and machining of metalsHigh-Speed Steels

○ maintain strengths at elevated temperatures.○ molybdenum (95% of all HSS) and tungsten

series.

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Tool and Die Steels (Cont.) – (See text table)

Hot Work Steels○ designed for use at elevated temperatures○ high toughness, resistance to wear and cracking.

Cold Work Steels○ designed for cold working operations.

Shock-resistant○ designed for impact toughness.○ For dies, punches, chisels

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