Chapter 11: Applications and Processing of Metal Alloys ISSUES TO ADDRESS... • How are metal alloys classified and what are their common applications? • What are some of the common fabrication techniques for metals? • What heat treatment procedures are used to improve the mechanical properties of both ferrous and nonferrous alloys? Chapter 11 - 1 Classification of Metal Alloys Metal Alloys Ferrous Steels Steels <1.4wt%C <1.4 wt% C Nonferrous Cast Irons Cast Irons 3-4.5 wt%C 3-4.5 wt% C microstructure: ferrite, graphite/cementite T(ºC) 1600 d L 1400 1200 g austenite g+L a800 ferrite 600 0 (Fe) L+Fe3C 1148ºC 4.30 1000 400 Adapted from Fig. 11.1, Callister & Rethwisch 8e. 727ºC Eutectoid: 0.76 1 2 Eutectic: g+Fe3C Fe3C cementite a+Fe3C 3 4 Adapted from Fig. 9.24, Callister & Rethwisch 8e. (Fig. 9.24 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), ASM International, Materials Park, OH, 1990.) 5 6 Co , wt% C 6.7 Chapter 11 - 2 Steels High Alloy Low Alloy low carbon Med carbon <0.25 wt% C 0.25-0.6wt% C high carbon 0.6-1.4wt% C heat plain treatable Cr,V Cr, Ni Additions none none none Ni, Mo Mo Example 1010 4310 1040 4340 1095 Hardenability 0 + + ++ ++ TS 0 + ++ + EL + + 0 Name plain Uses auto struc. sheet HSLA bridges towers press. vessels plain crank shafts bolts hammers blades pistons gears wear applic. wear applic. tool Cr, V, Mo, W 4190 +++ ++ -drills saws dies increasing strength, cost, decreasing ductility Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister & Rethwisch 8e. stainless Cr, Ni, Mo 304, 409 varies varies ++ high T applic. turbines furnaces Very corros. resistant Chapter 11 - 3 Refinement of Steel from Ore Coke Iron Ore gas refractory vessel layers of coke and iron ore air slag Molten iron Limestone 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 Chapter 11 - 4 Ferrous Alloys Iron-based alloys • Steels • Cast Irons Nomenclature for steels (AISI/SAE) 10xx Plain Carbon Steels 11xx Plain Carbon Steels (resulfurized for machinability) 15xx Mn (1.00 - 1.65%) 40xx Mo (0.20 ~ 0.30%) 43xx Ni (1.65 - 2.00%), Cr (0.40 - 0.90%), Mo (0.20 - 0.30%) 44xx Mo (0.5%) where xx is wt% C x 100 example: 1060 steel – plain carbon steel with 0.60 wt% C Stainless Steel >11% Cr Chapter 11 - 5 Cast Irons • Ferrous alloys with > 2.1 wt% C – more commonly 3 - 4.5 wt% C • Low melting – relatively easy to cast • Generally brittle • Cementite decomposes to ferrite + graphite Fe3C 3 Fe (a) + C (graphite) – generally a slow process Chapter 11 - 6 Fe-C True Equilibrium Diagram T(ºC) 1600 Graphite formation promoted by 1400 • Si > 1 wt% 1200 • slow cooling L g Austenite Liquid + Graphite g +L 1153ºC 4.2 wt% C 1000 g + Graphite a+g 800 0.65 740ºC 600 Adapted from Fig. 11.2, Callister & Rethwisch 8e. [Fig. 11.2 adapted from Binary Alloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.in-Chief), ASM International, Materials Park, OH, 1990.] 400 (Fe) a + Graphite 0 1 2 3 4 90 C, wt% C Chapter 11 - 7 100 Types of Cast Iron Adapted from Fig. 11.3(a) & (b), Callister & Rethwisch 8e. Gray iron • graphite flakes • weak & brittle in tension • stronger in compression • excellent vibrational dampening • wear resistant Ductile iron • add Mg and/or Ce • graphite as nodules not flakes • matrix often pearlite – stronger but less ductile Chapter 11 - 8 Types of Cast Iron (cont.) White iron • < 1 wt% Si • pearlite + cementite • very hard and brittle Adapted from Fig. 11.3(c) & (d), Callister & Rethwisch 8e. Malleable iron • heat treat white iron at 800-900ºC • graphite in rosettes • reasonably strong and ductile Chapter 11 - 9 Types of Cast Iron (cont.) Compacted graphite iron • relatively high thermal conductivity • good resistance to thermal shock • lower oxidation at elevated temperatures Adapted from Fig. 11.3(e), Callister & Rethwisch 8e. Chapter 11 - 10 Chapter 11 - 11 Chapter 11 - 12 Chapter 11 - 13 Production of Cast Irons Adapted from Fig.11.5, Callister & Rethwisch 8e. Chapter 11 - 14 Limitations of Ferrous Alloys 1) Relatively high densities 2) Relatively low electrical conductivities 3) Generally poor corrosion resistance Chapter 11 - 15 Nonferrous Alloys • Cu Alloys • Al Alloys -low r: 2.7 g/cm3 Brass: Zn is subst. impurity (costume jewelry, coins, -Cu, Mg, Si, Mn, Zn additions corrosion resistant) -solid sol. or precip. Bronze : Sn, Al, Si, Ni are strengthened (struct. subst. impurities aircraft parts (bushings, landing & packaging) gear) • Mg Alloys NonFerrous Cu-Be: -very low r: 1.7g/cm3 Alloys precip. hardened -ignites easily for strength -aircraft, missiles • Ti Alloys • Refractory metals -relatively low r: 4.5 g/cm3 -high melting T’s vs 7.9 for steel • Noble metals -Nb, Mo, W, Ta -reactive at high T’s -Ag, Au, Pt -oxid./corr. resistant -space applic. Based on discussion and data provided in Section 11.3, Callister & Rethwisch 3e. Chapter 11 - 16 Metal Fabrication • How do we fabricate metals? – Blacksmith - hammer (forged) – Cast molten metal into mold • Forming Operations – Rough stock formed to final shape Hot working vs. • Deformation temperature high enough for recrystallization • Large deformations Cold working • Deformation below recrystallization temperature • Strain hardening occurs • Small deformations Chapter 11 - 17 Metal Fabrication Methods (i) FORMING CASTING MISCELLANEOUS • Forging (Hammering; Stamping) • Rolling (Hot or Cold Rolling) (wrenches, crankshafts) force (I-beams, rails, sheet & plate) roll die A o blank A d often at elev. T • Drawing force Ao Ad roll • Extrusion (rods, wire, tubing) die Ao (rods, tubing) Ao tensile force die die must be well lubricated & clean Ad force container ram billet Adapted from Fig. 11.8, Callister & Rethwisch 8e. die holder Ad extrusion die ductile metals, e.g. Cu, Al (hot) Chapter 11 container 18 Metal Fabrication Methods (ii) FORMING CASTING MISCELLANEOUS • Casting- mold is filled with molten metal – metal melted in furnace, perhaps alloying elements added, then cast in a mold – common and inexpensive – gives good production of shapes – weaker products, internal defects – good option for brittle materials Chapter 11 - 19 Metal Fabrication Methods (iii) FORMING CASTING MISCELLANEOUS • Sand Casting (large parts, e.g., auto engine blocks) • What material will withstand T >1600ºC and is inexpensive and easy to mold? • Answer: sand!!! Sand Sand molten metal • To create mold, pack sand around form (pattern) of desired shape Chapter 11 - 20 Metal Fabrication Methods (iv) FORMING CASTING MISCELLANEOUS • Investment Casting (low volume, complex shapes e.g., jewelry, turbine blades) • Stage I — Mold formed by pouring plaster of paris around wax pattern. Plaster allowed to harden. wax I • Stage II — Wax is melted and then poured from mold—hollow mold cavity remains. II • Stage III — Molten metal is poured into mold and allowed to solidify. III Chapter 11 - 21 Metal Fabrication Methods (v) FORMING CASTING • Die Casting -- high volume -- for alloys having low melting temperatures MISCELLANEOUS • Continuous Casting -- simple shapes (e.g., rectangular slabs, cylinders) molten solidified Chapter 11 - 22 Chapter 11 - 23 Chapter 11 - 24 Metal Fabrication Methods (vi) FORMING CASTING • Powder Metallurgy (metals w/low ductilities) MISCELLANEOUS • Welding (when fabrication of one large part is impractical) pressure filler metal (melted) base metal (melted) fused base metal heat area contact densify unaffected piece 1 heat-affected zone unaffected Adapted from Fig. piece 2 11.9, Callister & • Heat-affected zone: point contact at low T densification by diffusion at higher T (region in which the microstructure has been changed). Rethwisch 8e. (Fig. 11.9 from Iron Castings Handbook, C.F. Walton and T.J. Opar (Ed.), 1981.) Chapter 11 - 25 Thermal Processing of Metals Annealing: Heat to Tanneal, then cool slowly. • Stress Relief: Reduce • Spheroidize (steels): stresses resulting from: - plastic deformation - nonuniform cooling - phase transform. Make very soft steels for good machining. Heat just below Teutectoid & hold for 15-25 h. Types of Annealing • Process Anneal: Negate effects of cold working by (recovery/ recrystallization) Based on discussion in Section 11.7, Callister & Rethwisch 8e. • Full Anneal (steels): Make soft steels for good forming. Heat to get g, then furnace-cool to obtain coarse pearlite. • Normalize (steels): Deform steel with large grains. Then heat treat to allow recrystallization and formation of smaller grains. Chapter 11 - 26 Heat Treatment Temperature-Time Paths a) Full Annealing A b) Quenching c) Tempering (Tempered Martensite) P A B Fig. 10.25, Callister & Rethwisch 8e. b) a) c) Chapter 11 - 27 Hardenability -- Steels • Hardenability – measure of the ability to form martensite • Jominy end quench test used to measure hardenability. specimen (heated to g phase field) 24ºC water flat ground Rockwell C hardness tests Adapted from Fig. 11.11, Callister & Rethwisch 8e. (Fig. 11.11 adapted from A.G. Guy, Essentials of Materials Science, McGraw-Hill Book Company, New York, 1978.) Hardness, HRC • Plot hardness versus distance from the quenched end. Adapted from Fig. 11.12, Callister & Rethwisch 8e. Distance from quenched end Chapter 11 - 28 Reason Why Hardness Changes with Distance Hardness, HRC • The cooling rate decreases with distance from quenched end. 60 40 20 0 1 2 3 distance from quenched end (in) T(ºC) 0% 100% 600 Adapted from Fig. 11.13, Callister & Rethwisch 8e. (Fig. 11.13 adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.) 400 200 M(start) AM 0 M(finish) 0.1 1 10 100 1000 Time (s) Chapter 11 - 29 Hardenability vs Alloy Composition 100 10 3 60 Hardness, HRC • Hardenability curves for five alloys each with, C = 0.4 wt% C 100 • "Alloy Steels" (4140, 4340, 5140, 8640) -- contain Ni, Cr, Mo (0.2 to 2 wt%) -- these elements shift the "nose" to longer times (from A to B) -- martensite is easier to form 80 %M 4340 50 40 Adapted from Fig. 11.14, Callister & Rethwisch 8e. (Fig. 11.14 adapted from figure furnished courtesy Republic Steel Corporation.) 2 Cooling rate (ºC/s) 4140 8640 20 5140 0 10 20 30 40 50 Distance from quenched end (mm) 800 T(ºC) TE 600 A B 400 200 0 -1 10 10 M(start) M(90%) 103 105 Time (s) Chapter 11 - 30 Influences of Quenching Medium & Specimen Geometry • Effect of quenching medium: Medium air oil water Severity of Quench low moderate high Hardness low moderate high • Effect of specimen geometry: When surface area-to-volume ratio increases: -- cooling rate throughout interior increases -- hardness throughout interior increases Position center surface Cooling rate low high Hardness low high Chapter 11 - 31 Precipitation Hardening • Particles impede dislocation motion. 700 • Ex: Al-Cu system T(ºC) • Procedure: 600 a+L -- Pt A: solution heat treat (get a solid solution) -- Pt B: quench to room temp. (retain a solid solution) -- Pt C: reheat to nucleate small q particles within a phase. a 500 400 • Other alloys that precipitation harden: Temp. • Cu-Be • Cu-Sn • Mg-Al Adapted from Fig. 11.22, Callister & Rethwisch 8e. Pt A (sol’n heat treat) q+L A q a+q C 300 0 B 10 (Al) CuAl2 L 20 30 40 50 wt% Cu composition range available for precipitation hardening Adapted from Fig. 11.24, Callister & Rethwisch 8e. (Fig. 11.24 adapted from J.L. Murray, International Metals Review 30, p.5, 1985.) Pt C (precipitate q) Pt B Time Chapter 11 - 32 Influence of Precipitation Heat Treatment on TS, %EL • 2014 Al Alloy: 400 300 200 100 149ºC 204ºC 1min 1h 1day 1mo 1yr precipitation heat treat time • Minima on %EL curves. %EL (2 in sample) tensile strength (MPa) • Maxima on TS curves. • Increasing T accelerates process. 30 20 10 204ºC 0 149ºC 1min 1h 1day 1mo 1yr precipitation heat treat time Adapted from Fig. 11.27, Callister & Rethwisch 8e. (Fig. 11.27 adapted from Metals Handbook: Properties and Selection: Nonferrous Alloys and Pure Metals, Vol. 2, 9th ed., H. Baker (Managing Ed.), American Society for Metals, 1979. p. 41.) Chapter 11 - 33 Summary • Ferrous alloys: steels and cast irons • Non-ferrous alloys: -- Cu, Al, Ti, and Mg alloys; refractory alloys; and noble metals. • Metal fabrication techniques: -- forming, casting, miscellaneous. • Hardenability of metals -- measure of ability of a steel to be heat treated. -- increases with alloy content. • Precipitation hardening --hardening, strengthening due to formation of precipitate particles. --Al, Mg alloys precipitation hardenable. Chapter 11 - 34 ANNOUNCEMENTS Reading: Core Problems: Self-help Problems: Chapter 11 - 35