Transcript Chapter 11
10 for plain carbon steels, and 40 for 0.4 wt% C STEELS High Strength, Low Alloy Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister 6e. Chapter 11- 3 NONFERROUS ALLOYS • Cu Alloys • Al Alloys Brass: Zn is subst. impurity -lower : 2.7g/cm3 (costume jewelry, coins, -Cu, Mg, Si, Mn, Zn additions corrosion resistant) -solid sol. or precip. Bronze: Sn, Al, Si, Ni are strengthened (struct. subst. impurity aircraft parts (bushings, landing & packaging) gear) • Mg Alloys NonFerrous Cu-Be: -very low : 1.7g/cm3 Alloys precip. hardened -ignites easily for strength -aircraft, missles • Ti Alloys -lower : 4.5g/cm3 • Refractory metals -high melting T vs 7.9 for steel • Noble metals -Nb, Mo, W, Ta -reactive at high T -Ag, Au, Pt -oxid./corr. resistant -space applic. Based on discussion and data provided in Section 11.3, Callister 6e. Chapter 11- 4 REFINEMENT OF STEEL FROM ORE Coke (coal residue) Limestone Iron Ore gas refractory vessel layers of coke and iron ore air slag Molten iron BLAST FURNACE heat generation C+O2CO2 reduction of iron ore to metal CO2+C2CO 3CO+Fe2O32Fe+3CO2 purification CaCO3CaO+CO2 CaO + SiO2 +Al 2O3slag Chapter 11- 5 METAL FABRICATION METHODS-I FORMING • Forging (wrenches, crankshafts) force die Ao blank • Rolling (I-beams, rails) Ad often at elev. T • Drawing force • Extrusion (rods, wire, tubing) die Ao die Ad Adapted from Fig. 11.7, Callister 6e. (rods, tubing) tensile force Chapter 11- 6 FORMING TEMPERATURE • Hot working --recrystallization • Cold working -- no recrystallization --less energy to deform --oxidation: poor finish --lower strength -- more energy to deform -- no oxidation: good finish -- higher strength • Cold worked microstructures --generally are very anisotropic! --Forged (a) --Swaged (b) --Fracture resistant! (c) Reprinted w/ permission from R.W. Hertzberg, "Deformation and Fracture Mechanics of Engineering Materials", (4th ed.), John Wiley and Sons, Inc., 1996. (a) Fig. 10.5, p. 410 (micrograph courtesy of G. Vander Voort, Car Tech Corp.); (b) Fig. 10.6(b), p. 411 (Orig. source: J.F. Peck and D.A. Thomas, Trans. Metall. Soc. AIME, 1961, p. 1240); (c) Fig. 10.10, p. 415 (Orig. source: A.J. McEvily, Jr. and R.H. Bush, Trans. ASM 55, 1962, p. 654.) Chapter 11- 7 METAL FABRICATION METHODS-II CASTING • Sand Casting (large parts, e.g., auto engine blocks) • Investment Casting • Die Casting (high volume, low T alloys) • Continuous Casting (simple slab shapes) (low volume, complex shapes e.g., jewelry, turbine blades) plaster die formed around wax prototype Chapter 11- 8 METAL FABRICATION METHODS-III FORMING • Powder Processing (materials w/low ductility) CASTING JOINING • Welding (when one large part is impractical) filler metal (melted) base metal (melted) fused base metal unaffected piece 1 heat affected zone unaffected Adapted from Fig. piece 2 11.8, Callister 6e. (Fig. 11.8 from • Heat affected zone: Iron Castings Handbook, C.F. Walton and T.J. (region in which the Opar (Ed.), 1981.) microstructure has been changed). Chapter 11- 9 THERMAL PROCESSING OF METALS Annealing: Heat to Tanneal, then cool slowly. Based on discussion in Section 11.7, Callister 6e. Chapter 11- 10 THERMAL PROCESSING OF METALS Based on discussion in Section 11.7, Callister 6e. Chapter 11- 10 HARDENABILITY--STEELS • Ability to form martensite • Jominy end quench test to measure hardenability. 1” specimen (heated to phase field) 24°C water flat ground 4” Adapted from Fig. 11.10, Callister 6e. (Fig. 11.10 adapted from A.G. Guy, Essentials of Materials Science, McGraw-Hill Book Company, New York, 1978.) • Hardness versus distance from the quenched end. Adapted from Fig. 11.11, Callister 6e. Chapter 11- 11 WHY HARDNESS CHANGES W/POSITION • The cooling rate varies with position. Adapted from Fig. 11.12, Callister 6e. (Fig. 11.12 adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.) Chapter 11- 12 HARDENABILITY VS ALLOY CONTENT • Jominy end quench results, C = 0.4wt%C Adapted from Fig. 11.13, Callister 6e. (Fig. 11.13 adapted from figure furnished courtesy Republic Steel Corporation.) • "Alloy Steels" (4140, 4340, 5140, 8640) --contain Ni, Cr, Mo (0.2 to 2wt%) --these elements shift the "nose". --martensite is easier to form. Chapter 11- 13 QUENCHING MEDIUM & GEOMETRY • Effect of quenching medium: Medium air oil water Severity of Quench small moderate large Hardness small moderate large • Effect of geometry: When surface-to-volume ratio increases: --cooling rate increases --hardness increases Position Cooling rate center small surface large Hardness small large Chapter 11- 14 PREDICTING HARDNESS PROFILES • Ex: Round bar, 1040 steel, water quenched, 2" diam. Adapted from Fig. 11.18, Callister 6e. Chapter 11- 15