10/11/2014. Chapter 6: Applications and Processing of Metal Alloys. Classification of Metal Alloys. Steels. Refinement of Steel from Ore

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1 Chapter 6: pplications and Processing of Metal lloys Classification of Metal lloys Metal lloys ISSUES TO DDRESS... 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? Ferrous Steels <1.4 <1.4wt%C wt% C 1 d 1 Cast Irons wt%c C Nonferrous microstructure: ferrite, graphite/cementite 11.1, g , g +Fe 3C 10 (Fig adapted from 1148ºC austenite Eutectic: Binary lloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.-in-Chief), SM International, Materials Park, OH, g +Fe 3C 1990.) 800 a Fe 3 C 727ºC ferrite Eutectoid: cementite 0.76 a +Fe 3C Chapter 11-1 (Fe) C o, wt% C Chapter 11-2 Name dditions none Uses Steels ow lloy carbon Med carbon <0.25 wt% C wt% C plain HS plain auto struc. sheet Cr,V Ni, Mo bridges towers press. vessels none crank shafts bolts hammers blades heat treatable Cr, Ni Mo pistons gears wear carbon wt% C none wear drills saws s Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Cr, V, Mo, W High lloy plain tool stainless Cr, Ni, Mo Example , 409 Hardenability varies TS varies E increasing strength, cost, decreasing ductility T turbines furnaces Very corros. resistant Chapter 11-3 Refinement of Steel from Ore gas refractory vessel layers of coke and iron ore air slag Molten iron Coke Iron Ore imestone BST FURNCE heat generation C + O 2 CO 2 reduction of iron ore to metal CO 2 + C 2CO 3CO + Fe 2 O 3 2Fe +3CO 2 purification CaCO 3 CaO+CO 2 CaO + SiO 2 + l 2 O 3 slag Chapter 11-4 Iron-based alloys Steels Cast Irons Ferrous lloys Nomenclature for steels (ISI/SE) 10xx Plain Carbon Steels 11xx Plain Carbon Steels (resulfurized for machinability) 15xx Mn ( %) 40xx Mo (0. ~ 0.30%) 43xx Ni ( %), Cr ( %), Mo ( %) 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 wt% C ow melting relatively easy to cast Generally brittle Cementite decomposes to ferrite + graphite Fe 3 C 3 Fe (a) + C (graphite) generally a s process Chapter

2 0.65 Fe-C True Equilibrium Diagram Graphite formation promoted by Si > 1 wt% s cooling 11.2, [Fig adapted from Binary lloy Phase Diagrams, 2nd ed., Vol. 1, T.B. Massalski (Ed.- in-chief), SM International, Materials Park, OH, 1990.] a + g g ustenite g ºC (Fe) C, wt% C 4.2 wt% C g + Graphite a + Graphite iquid + Graphite 740ºC Chapter 11-7 Types of Cast Iron 11.3(a) & (b), 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 11.3(c) & (d), Types of Cast Iron (cont.) Compacted graphite iron relatively thermal conductivity good resistance to thermal shock er oxidation at elevated temperatures Malleable iron heat treat white iron at ºC graphite in rosettes reasonably strong and ductile 11.3(e), Chapter 11-9 Chapter Production of Cast Irons imitations of Ferrous lloys 11.5, 1) Relatively densities 2) Relatively electrical conductivities 3) Generally poor corrosion resistance Chapter Chapter

3 Cu lloys Brass: Zn is subst. impurity (costume jewelry, coins, corrosion resistant) Bronze : Sn, l, Si, Ni are subst. impurities (bushings, landing gear) Cu-Be : precip. hardened for strength Ti lloys -relatively r: 4.5 g/cm 3 vs 7.9 for steel -reactive at T s - space Nonferrous lloys NonFerrous lloys l lloys - r: 2.7 g/cm 3 -Cu, Mg, Si, Mn, Zn additions -solid sol. or precip. strengthened (struct. aircraft parts & packaging) Mg lloys -very r : 1.7g/cm 3 -ignites easily - aircraft, missiles Refractory metals - melting T s Noble metals -Nb, Mo, W, Ta -g, u, Pt - oxid./corr. resistant 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. Cold working Deformation temperature enough for recrystallization arge deformations Deformation be recrystallization temperature Strain hardening occurs Small deformations Based on discussion and data provided in Section 11.3, Rethwisch 3e. Chapter Chapter Metal Fabrication Methods (i) Metal Fabrication Methods (ii) Forging (Hammering; Stamping) (wrenches, crankshafts) o blank d Drawing (rods, wire, tubing) o d tensile often at elev. T must be well lubricated & clean CSTING MISCENEOUS Rolling (Hot or Cold Rolling) (I-beams, rails, sheet & plate) roll d o roll dapted from Fig. 11.8, Extrusion (rods, tubing) o container holder ram billet extrusion d container ductile metals, e.g. Cu, l (hot) Chapter CSTING MISCENEOUS 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 Metal Fabrication Methods (iii) Metal Fabrication Methods (iv) CSTING MISCENEOUS Sand Casting (large parts, e.g., What material will withstand T >1ºC auto engine blocks) and is inexpensive and easy to mold? Sand Sand molten metal nswer: sand!!! To create mold, pack sand around form (pattern) of desired shape CSTING MISCENEOUS Investment Casting ( volume, complex shapes e.g., jewelry, turbine blades) Stage I Mold formed by pouring plaster of paris around wax pattern. Plaster aled to harden. Stage II Wax is melted and then poured from mold hol mold cavity remains. Stage III Molten metal is poured into mold and aled to solidify. wax I II III Chapter Chapter

4 Hardness, HRC Hardness, HRC Metal Fabrication Methods (v) Metal Fabrication Methods (vi) CSTING MISCENEOUS Die Casting -- volume -- for alloys having melting temperatures Continuous Casting -- simple shapes (e.g., rectangular slabs, cylinders) molten solidified Chapter Powder Metallurgy (metals w/ ductilities) point contact at T densify pressure heat area contact densification by diffusion at er T CSTING MISCENEOUS Welding (when fabrication of one large part is impractical) filler metal (melted) base metal (melted) fused base metal heat-affected zone unaffected unaffected piece 1 piece , (Fig from Iron Castings Handbook, C.F. Walton and T.J. Opar (Ed.), 1981.) Heat-affected zone: (region in which the microstructure has been changed). Chapter 11 - Thermal Processing of Metals nnealing: Heat to Tanneal, then cool sly. Stress Relief: Reduce stresses resulting from: - plastic deformation - nonuniform cooling - phase transform. Process nneal: Negate effects of cold working by (recovery/ recrystallization) Types of nnealing Based on discussion in Section 11.7, Spheroidize (steels): Make very soft steels for good machining. Heat just be T eutectoid & hold for h. Full nneal (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 al recrystallization and formation of smaller grains. Chapter Heat Treatment Temperature-Time Paths a) Full nnealing b) Quenching c) Tempering (Tempered Martensite) Fig , b) B P a) Chapter c) 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 11.11, flat ground (Fig adapted from.g. Guy, Essentials of Materials Science, Rockwell C McGraw-Hill Book Company, New York, hardness tests 1978.) Plot hardness versus distance from the quenched end. Reason Why Hardness Changes with Distance The cooling rate decreases with distance from quenched end M(start) 0 M 0 M(finish) distance from quenched end (in) 0% 100% 11.13, (Fig adapted from H. Boyer (Ed.) tlas of Isothermal Transformation and Cooling Transformation Diagrams, merican Society for Metals, 1977, p. 376.) Distance from quenched end 11.12, Chapter Time (s) Chapter

5 Hardness, HRC tensile strength (MPa) %E (2 in sample) Hardenability vs lloy Composition Hardenability curves for five alloys each with, C = 0.4 wt% C 11.14, (Fig adapted from figure furnished courtesy Republic Steel Corporation.) "lloy Steels" (4140, 4340, 5140, 8640) -- contain Ni, Cr, Mo (0.2 to 2 wt%) -- these elements shift the "nose" to longer times (from to B) -- martensite is easier to form Cooling rate (ºC/s) %M Distance from quenched end (mm) B T E M(start) M(90%) Time (s) Chapter Influences of Quenching Medium & Specimen Geometry Effect of quenching medium: Medium air oil water Severity of Quench moderate 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 Hardness moderate Hardness Chapter , Precipitation Hardening Particles impede dislocation motion. Ex: l-cu system 700 Procedure: Cul 2 a a+ -- Pt : solution heat treat q+ (get a solid solution) 500 q -- Pt B: quench to room temp. a+q C (retain a solid solution) -- Pt C: reheat to nucleate 300 small q particles within 0 B (l) wt% Cu a phase. composition range available for precipitation hardening Other alloys that precipitation harden: Cu-Be Cu-Sn Mg-l Temp. Pt (sol n heat treat) Pt B Pt C (precipitate q) 11.24, (Fig adapted from J.. Murray, International Metals Review 30, p.5, 1985.) Time Chapter l lloy: Influence of Precipitation Heat Treatment on TS, %E Maxima on TS curves. Increasing T accelerates process ºC 0 4ºC 100 1min 1h 1day 1mo 1yr precipitation heat treat time Minima on %E curves , (Fig adapted from Metals Handbook: Properties and Selection: Nonferrous lloys and Pure Metals, Vol. 2, 9th ed., H. Baker (Managing Ed.), merican Society for Metals, p. 41.) ºC 149ºC 0 1min 1h 1day 1mo 1yr precipitation heat treat time Chapter Summary Ferrous alloys: steels and cast irons Non-ferrous alloys: -- Cu, l, 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. --l, Mg alloys precipitation hardenable. Reading: Core Problems: Self-help Problems: NNOUNCEMENTS Chapter Chapter