Types of Metal Alloys Metal alloys Ferrous Nonferrous Steels Cast iron 257 Uses low carbon <0.25wt%C auto struc. sheet bridges towers press. vessels Steels Low Alloy med carbon 0.25-0.6wt%C crank shafts bolts hammers blades pistons gears wear applic. high carbon 0.6-1.4wt%C wear applic. drills saws s High Alloy Name plain HSLA plain heat treatable plain tool austentitic stainless Additions none Cr,V Ni, Mo none Cr, Ni Cr, V, none Mo Mo, W Cr, Ni, Mo Example 1010 4310 1040 4340 1095 4190 304 Hardenability 0 + + ++ ++ +++ 0 TS - 0 + ++ + ++ 0 EL + + 0 - - -- ++ increasing strength, cost, decreasing ductility high T applic. turbines furnaces V. corros. resistant 258
259 Cast Irons Gray Iron Nodular Iron White Iron Malleable Iron 260
Cu Alloys Brass: Zn is subst. impurity (costume jewelry, coins, corrosion resistant) Bronze: Sn, Al, Si, Ni are subst. impurity (bushings, landing gear) Cu-Be: precip. hardened for strength Ti Alloys -lower ρ: 4.5g/cm 3 vs 7.9 for steel -reactive at high T -space applic. Nonferrous Alloys NonFerrous Alloys Noble metals -Ag, Au, Pt -oxid./corr. resistant Al Alloys -lower ρ: 2.7g/cm 3 -Cu, Mg, Si, Mn, Zn additions -solid sol. or precip. strengthened (struct. aircraft parts & packaging) Mg Alloys -very low ρ: 1.7g/cm 3 -ignites easily -aircraft, missles Refractory metals -high melting T -Nb, Mo, W, Ta 261 Coke Iron Ore Limestone Refinement of Steel from Ore gas refractory vessel layers of coke and iron ore slag air Molten iron BLAST FURNACE heat generation C+O2 CO2 reduction of iron ore to metal CO2+C 2CO 3CO+Fe2O3 2Fe+3CO2 purification CaCO3 CaO+CO2 CaO + SiO2 +Al2O3 slag 262
FORMING Forging (wrenches, crankshafts) blank Ad Drawing (rods, wire, tubing) CASTING often at elev. T Metal Fabrication Methods (I) Ad tensile JOINING Rolling (I-beams, rails) Extrusion (rods, tubing) roll roll container ram billet container Ad holder extrusion Ad 263 Metal Fabrication Methods-II FORMING Sand Casting (large parts, e.g., auto engine blocks) CASTING JOINING Die Casting (high volume, low T alloys) Sand Sand molten metal Investment Casting (low volume, complex shapes e.g., jewelry, turbine blades) plaster formed wax around wax prototype Continuous Casting (simple slab shapes) molten solidified 264
Metal Fabrication Methods-III FORMING Powder Processing (materials w/low ductility) point contact at low T pressure densify heat area contact densification by diffusion at higher T JOINING CASTING Welding (when one large part is impractical) filler metal (melted) base metal (melted) fused base metal heat affected zone unaffected unaffected piece 1 piece 2 Heat affected zone: (region in which the microstructure has been changed). 265 Thermal Processing of Metals Annealing: Heat to Tanneal, then cool slowly. Stress Relief : Reduce stress caused by: -plastic deformation -nonuniform cooling -phase transform. Process Anneal : Negate effect of cold working by (recovery/ recrystallization) Types of Annealing Spheroidize (steels): Make very soft steels for good machining. Heat just below T E & hold for 15-25h. Full Anneal (steels): Make soft steels for good forming by heating to get γ, then cool in furnace to get coarse P. Normalize (steels): Deform steel with large grains, then normalize to make grains small. 266
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