Types of Metal Alloys

Transcription

1 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 wt%C crank shafts bolts hammers blades pistons gears wear applic. high carbon wt%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 Hardenability TS EL increasing strength, cost, decreasing ductility high T applic. turbines furnaces V. corros. resistant 258

2 259 Cast Irons Gray Iron Nodular Iron White Iron Malleable Iron 260

3 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

4 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

5 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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