Introduction to Manufacturing 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. Relative cost per unit Volume (Kalpakjian & Schmid, 2006) Carbon Steel Copper Nickel Silver Gold 1 5-6X 35X 600X 60,000X Engr 241

Three materials used in Steel: Iron ore - pelletized metal Coke - for heat & producing carbon monoxide which reduces iron-oxide to iron (removes oxygen) Limestone - combines with impurities which floats to surface (slag) Engr 241

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 Engr 241

Three Types of Steel Ingots: Killed Steel- steel is fully deoxidized: oxygen is removed and porosity is eliminated (consistent mechanical and chemical properties) Semi-Killed Steel- partially deoxidized steel: contains some porosity (economical) Rimmed Steel- low carbon content, porosity (blowholes), lower quality steel (requires inspection) Engr 241

Refining Removal of impurities (Trace Elements) Tin Hot shortness & temper embrittlement (melting) Oxygen Reduces toughness Hydrogen Causes embrittlement Nitrogen Decreases ductility and toughness Antimony & Arsenic Cause temper embrittlement Engr 241

Refining: Used to create higher quality steels Improves uniformity and consistency in composition Removing impurities, inclusions, other elements Adding various elements Engr 241

Inclusions? Good or bad? “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). Engr 241

Alloy Steels (Black & Kohser, 2008, p. 125) Engr 241

Iron - Carbon Alloys  typically less than 4.5% C 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 Engr 241

Carbon Steels Classification Low-Carbon (mild steel): 0.30% or less Medium-Carbon: 0.30-0.60% High-Carbon: more than 0.60% Bolts, nuts, sheet, tubes, plate, low strength machine components Machinery and automotive parts, gears, axles, connecting rods, etc. Cutting tools, cables, springs, cutlery Engr 241

Carbon Effects (Black & Kohser, 2008, p. 124) Engr 241

Common Designations for Steel: AISI - The American Iron and Steel Institute SAE - Society of Automotive Engineers ASTM - American Society for Testing Materials Engr 241

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. Plain Carbon .2% Carbon Content 1020 Engr 241

(Black & Kohser, 2008, p. 126) Engr 241

(Black & Kohser, 2008, p. 123-4) Engr 241

Sample Question What makes up a “forty-three forty” 4340 steel? 43 = Mo, Cr, Ni 40 = .40% C Engr 241

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 Engr 241

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 Engr 241

(Black & Kohser, 2008, p. 132) (Black & Kohser, 2008, p. 134) Engr 241

Stainless Steels Classifications Austenitic (200-300 series) Kitchenware, fittings, welded construction, Heat/chemical resistant environments Nonmagnetic Most ductile of all stainless steels Susceptible to stress-corrosion cracking Ferritic (400 series) Non-structural applications, automotive trim, kitchenware High chromium content Lower ductility Not heat-treatable Martensitic (400 and 500 series) Cutlery, surgical tools, springs, valves Magnetic. Moderate corrosion resistance. High strength, hardness, fatigue resistance, good ductility Precipitation Hardening (PH) Aircraft & aerospace applications Chromium and nickel (along with copper, aluminum, titanium, or molybdenum. Good corrosion resistance, ductility, and high strength at elevated temperatures Duplex Structure Heat exchangers Austenite and ferrite. Higher resistance to corrosion and stress corrosion than 300 series Engr 241

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 metals High-Speed Steels maintain strengths at elevated temperatures. molybdenum (95% of all HSS) and tungsten series. Engr 241

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 Engr 241