Chapter 11 Applications and Processing of Metal Alloys

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 Ferrous Steels <1. 4 wt%C <1. 4 wt% C Nonferrous Cast Irons 3 -4. 5 wt%C 3 -4. 5 wt% C microstructure: ferrite, graphite/cementite T(ºC) 1600 d L 1400 1200 austenite +L 4. 30 + 600 400 L+Fe 3 C 1148ºC 1000 800 ferrite Adapted from Fig. 11. 1, Callister & Rethwisch 8 e. 0 (Fe) 727ºC Eutectoid: 0. 76 1 2 Eutectic: +Fe 3 C cementite +Fe 3 C 3 4 Adapted from Fig. 9. 24, Callister & Rethwisch 8 e. (Fig. 9. 24 adapted from Binary Alloy Phase Diagrams, 2 nd 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. 6 wt% C high carbon 0. 6 -1. 4 wt% C heat plain treatable Cr, V Cr, Ni Additions 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. 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 8 e. stainless Cr, Ni, Mo 304, 409 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+O 2 ®CO 2 reduction of iron ore to metal CO 2 + C ® 2 CO 3 CO + Fe 2 O 3 ® 2 Fe+3 CO 2 purification Ca. CO 3 ® Ca. O+CO 2 Ca. O + Si. O 2 + Al 2 O 3 ® slag Chapter 11 - 4

Ferrous Alloys Iron-based alloys • Steels • Cast Irons Nomenclature for steels (AISI/SAE) 10 xx Plain Carbon Steels 11 xx Plain Carbon Steels (resulfurized for machinability) 15 xx Mn (1. 00 - 1. 65%) 40 xx Mo (0. 20 ~ 0. 30%) 43 xx Ni (1. 65 - 2. 00%), Cr (0. 40 - 0. 90%), Mo (0. 20 - 0. 30%) 44 xx 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 Fe 3 C 3 Fe ( ) + 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 Austenite Liquid + Graphite +L 1153ºC 4. 2 wt% C 1000 + Graphite 800 740ºC 0. 65 + 600 Adapted from Fig. 11. 2, Callister & Rethwisch 8 e. [Fig. 11. 2 adapted from Binary Alloy Phase Diagrams, 2 nd ed. , Vol. 1, T. B. Massalski (Ed. -in -Chief), ASM International, Materials Park, OH, 1990. ] L 400 (Fe) + 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 8 e. 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 8 e. 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 8 e. Chapter 11 - 10

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Production of Cast Irons Adapted from Fig. 11. 5, Callister & Rethwisch 8 e. 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/cm 3 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 Non. Ferrous Cu-Be: -very low r: 1. 7 g/cm 3 Alloys precip. hardened -ignites easily for strength -aircraft, missiles • Ti Alloys • Refractory metals -relatively low r: 4. 5 g/cm 3 -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 3 e. 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 die Ad roll • Extrusion (rods, wire, tubing) die Ao (rods, tubing) Ao tensile force die must be well lubricated & clean Ad force container ram billet Adapted from Fig. 11. 8, Callister & Rethwisch 8 e. 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) Sand molten metal • What material will withstand T >1600ºC and is inexpensive and easy to mold? • Answer: sand!!! • 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. • Stage II — Wax is melted and then poured from mold—hollow mold cavity remains. • Stage III — Molten metal is poured into mold and allowed to solidify. wax I II 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

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Metal Fabrication Methods (vi) FORMING CASTING • Powder Metallurgy (metals w/low ductilities) pressure MISCELLANEOUS • Welding (when fabrication of one large part is impractical) 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 8 e. (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 8 e. • Full Anneal (steels): Make soft steels for good forming. Heat to get , 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 b) Quenching c) Tempering (Tempered Martensite) A P B A 10 0% 50 0% % Fig. 10. 25, Callister & Rethwisch 8 e. 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 phase field) 24ºC water flat ground Rockwell C hardness tests Adapted from Fig. 11, Callister & Rethwisch 8 e. (Fig. 11 adapted from A. G. Guy, Essentials of Materials Science, Mc. Graw -Hill Book Company, New York, 1978. ) Hardness, HRC • Plot hardness versus distance from the quenched end. Adapted from Fig. 11. 12, Callister & Rethwisch 8 e. 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) 600 A ® 0% 100% P Adapted from Fig. 11. 13, Callister & Rethwisch 8 e. (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) A®M 1 li te ar rli Pe lite ea + ar P ite Pe ine ens F t ar ite M ens t ar 0. 1 M 0 M(finish) 10 1000 te 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 50 8640 20 40 (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 4140 10 • "Alloy Steels" 80 %M 4340 40 Adapted from Fig. 11. 14, Callister & Rethwisch 8 e. (Fig. 11. 14 adapted from figure furnished courtesy Republic Steel Corporation. ) 2 Cooling rate (ºC/s) 5140 0 10 20 30 40 50 Distance from quenched end (mm) 800 T(ºC) 600 TE A 400 200 0 -1 10 10 B 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 +L -- Pt A: solution heat treat (get solid solution) -- Pt B: quench to room temp. (retain solid solution) -- Pt C: reheat to nucleate small particles within phase. 500 400 • Other alloys that precipitation harden: Temp. • Cu-Be • Cu-Sn • Mg-Al Adapted from Fig. 11. 22, Callister & Rethwisch 8 e. Pt A (sol’n heat treat) +L A + C 300 0 B 10 (Al) Cu. Al 2 L 20 30 40 50 wt% Cu composition range available for precipitation hardening Adapted from Fig. 11. 24, Callister & Rethwisch 8 e. (Fig. 11. 24 adapted from J. L. Murray, International Metals Review 30, p. 5, 1985. ) Pt C (precipitate ) Pt B Time Chapter 11 - 32

Influence of Precipitation Heat Treatment on TS, %EL • 2014 Al Alloy: 300 200 100 204ºC 149ºC 1 min 1 h 1 day 1 mo 1 yr precipitation heat treat time %EL (2 in sample) 400 • Minima on %EL curves. fe pre wer “ov cip lar era ita ge ge tes d” ma pre ny s cip ma ita ll “ag tes ed ” no so n-eq lid uil so. lut ion tensile strength (MPa) • Maxima on TS curves. • Increasing T accelerates process. 30 20 10 0 204ºC 149ºC 1 min 1 h 1 day 1 mo 1 yr precipitation heat treat time Adapted from Fig. 11. 27, Callister & Rethwisch 8 e. (Fig. 11. 27 adapted from Metals Handbook: Properties and Selection: Nonferrous Alloys and Pure Metals, Vol. 2, 9 th 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