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Chapter 11 - 1 ISSUES TO ADDRESS... How are metal alloys classified and how are they used? What are some of the common fabrication techniques? How do properties.

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Presentation on theme: "Chapter 11 - 1 ISSUES TO ADDRESS... How are metal alloys classified and how are they used? What are some of the common fabrication techniques? How do properties."— Presentation transcript:

1 Chapter 11 - 1 ISSUES TO ADDRESS... How are metal alloys classified and how are they used? What are some of the common fabrication techniques? How do properties vary throughout a piece of material that has been quenched, for example? How can properties be modified by post heat treatment? Chapter 11: Metal Alloys Applications and Processing

2 Chapter 11 - 2 Adapted from Fig. 9.24,Callister 7e. (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.) Adapted from Fig. 11.1, Callister 7e. Taxonomy of Metals Metal Alloys Steels FerrousNonferrous Cast Irons CuAlMgTi <1.4wt%C3-4.5wt%C Steels <1.4 wt% C Cast Irons 3-4.5 wt% C Fe 3 C cementite 1600 1400 1200 1000 800 600 400 0 1234566.7 L  austenite  +L+L  +Fe 3 C  ferrite  +Fe 3 C  +  L+Fe 3 C  (Fe) C o, wt% C Eutectic: Eutectoid: 0.76 4.30 727°C 1148°C T(°C) microstructure: ferrite, graphite cementite

3 Chapter 11 - 3 Based on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister 7e. Steels Low Alloy High Alloy low carbon <0.25 wt% C Med carbon 0.25-0.6 wt% C high carbon 0.6-1.4 wt% C Usesauto struc. sheet bridges towers press. vessels crank shafts bolts hammers blades pistons gears wear applic. wear applic. drills saws dies high T applic. turbines furnaces V. corros. resistant Example101043101040434010954190304 Additionsnone Cr,V Ni, Mo none Cr, Ni Mo none Cr, V, Mo, W Cr, Ni, Mo plainHSLAplain heat treatable plaintool austenitic stainless Name Hardenability 0++++ +++0 TS -0++++ 0 EL ++0----++ increasing strength, cost, decreasing ductility

4 Chapter 11 - 4 Refinement of Steel from Ore Iron Ore Coke Limestone 3CO +Fe 2 O 3  2Fe+3CO 2 C+O2O2  CO 2 +C  2CO CaCO 3  CaO+CO 2 CaO + SiO 2 + Al 2 O 3  slag purification reduction of iron ore to metal heat generation Molten iron BLAST FURNACE slag air layers of coke and iron ore gas refractory vessel

5 Chapter 11 - 5 Ferrous Alloys Iron containing – Steels - cast irons Nomenclature AISI & SAE 10xxPlain Carbon Steels 11xxPlain Carbon Steels (resulfurized for machinability) 15xxMn (10 ~ 20%) 40xxMo (0.20 ~ 0.30%) 43xxNi (1.65 - 2.00%), Cr (0.4 - 0.90%), Mo (0.2 - 0.3%) 44xxMo (0.5%) where xx is wt% C x 100 example: 1060 steel – plain carbon steel with 0.60 wt% C Stainless Steel -- >11% Cr

6 Chapter 11 - 6 Cast Iron Ferrous alloys with > 2.1 wt% C –more commonly 3 - 4.5 wt%C low melting (also brittle) so easiest to cast Cementite decomposes to ferrite + graphite Fe 3 C  3 Fe (  ) + C (graphite) –generally a slow process

7 Chapter 11 - 7 Fe-C True Equilibrium Diagram Graphite formation promoted by Si > 1 wt% slow cooling Adapted from Fig. 11.2,Callister 7e. (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.) 1600 1400 1200 1000 800 600 400 0 1234 90 L  +L +L  + Graphite Liquid + Graphite (Fe) C o, wt% C 0.65 740°C T(°C)  + Graphite 100 1153°C  Austenite 4.2 wt% C 

8 Chapter 11 - 8 Types of Cast Iron Gray iron graphite flakes weak & brittle under tension stronger under compression excellent vibrational dampening wear resistant Ductile iron add Mg or Ce graphite in nodules not flakes matrix often pearlite - better ductility Adapted from Fig. 11.3(a) & (b), Callister 7e.

9 Chapter 11 - 9 Types of Cast Iron White iron <1wt% Si so harder but brittle more cementite Malleable iron heat treat at 800-900ºC graphite in rosettes more ductile Adapted from Fig. 11.3(c) & (d), Callister 7e.

10 Chapter 11 - 10 Production of Cast Iron Adapted from Fig.11.5, Callister 7e.

11 Chapter 11 - 11 Limitations of Ferrous Alloys 1)Relatively high density 2)Relatively low conductivity 3)Poor corrosion resistance

12 Chapter 11 - 12 Based on discussion and data provided in Section 11.3, Callister 7e. Nonferrous Alloys NonFerrous Alloys Al Alloys -lower  : 2.7g/cm 3 -Cu, Mg, Si, Mn, Zn additions -solid sol. or precip. strengthened (struct. aircraft parts & packaging) Mg Alloys -very low  : 1.7g/cm 3 -ignites easily -aircraft, missiles Refractory metals -high melting T -Nb, Mo, W, Ta Noble metals -Ag, Au, Pt -oxid./corr. resistant Ti Alloys -lower  : 4.5g/cm 3 vs 7.9 for steel -reactive at high T -space applic. 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

13 Chapter 11 - 13 Metal Fabrication How do we fabricate metals? –Blacksmith - hammer (forged) –Molding - cast Forming Operations –Rough stock formed to final shape Hot working vs. Cold working T high enough for well below T m recrystallization work hardening Larger deformations smaller deformations

14 Chapter 11 - 14 FORMING roll A o A d Rolling (Hot or Cold Rolling) (I-beams, rails, sheet & plate) A o A d force die blank force Forging (Hammering; Stamping) (wrenches, crankshafts) often at elev. T Adapted from Fig. 11.8, Callister 7e. Metal Fabrication Methods - I ram billet container force die holder die A o A d extrusion Extrusion (rods, tubing) ductile metals, e.g. Cu, Al (hot) tensile force A o A d die Drawing (rods, wire, tubing) die must be well lubricated & clean CASTINGJOINING

15 Chapter 11 - 15 FORMINGCASTINGJOINING Metal Fabrication Methods - II Casting- mold is filled with metal –metal melted in furnace, perhaps alloying elements added. Then cast in a mold –most common, cheapest method –gives good production of shapes –weaker products, internal defects –good option for brittle materials

16 Chapter 11 - 16 Sand Casting (large parts, e.g., auto engine blocks) Metal Fabrication Methods - II trying to hold something that is hot what will withstand >1600ºC? cheap - easy to mold => sand!!! pack sand around form (pattern) of desired shape Sand molten metal FORMINGCASTINGJOINING

17 Chapter 11 - 17 plaster die formed around wax prototype Sand Casting (large parts, e.g., auto engine blocks) Investment Casting (low volume, complex shapes e.g., jewelry, turbine blades) Metal Fabrication Methods - II Investment Casting pattern is made from paraffin. mold made by encasing in plaster of paris melt the wax & the hollow mold is left pour in metal wax FORMINGCASTINGJOINING Sand molten metal

18 Chapter 11 - 18 plaster die formed around wax prototype Sand Casting (large parts, e.g., auto engine blocks) Investment Casting (low volume, complex shapes e.g., jewelry, turbine blades) Metal Fabrication Methods - II wax Die Casting (high volume, low T alloys) Continuous Casting (simple slab shapes) molten solidified FORMINGCASTINGJOINING Sand molten metal

19 Chapter 11 - 19 CASTINGJOINING Metal Fabrication Methods - III Powder Metallurgy (materials w/low ductility) pressure heat point contact at low T densification by diffusion at higher T area contact densify Welding (when one large part is impractical) Heat affected zone: (region in which the microstructure has been changed). Adapted from Fig. 11.9, Callister 7e. (Fig. 11.9 from Iron Castings Handbook, C.F. Walton and T.J. Opar (Ed.), 1981.) piece 1piece 2 fused base metal filler metal (melted) base metal (melted) unaffected heat affected zone FORMING

20 Chapter 11 - 20 Annealing: Heat to T anneal, then cool slowly. Based on discussion in Section 11.7, Callister 7e. Thermal Processing of Metals Types of Annealing Process Anneal: Negate effect of cold working by (recovery/ recrystallization) Stress Relief: Reduce stress caused by: -plastic deformation -nonuniform cooling -phase transform. Normalize (steels): Deform steel with large grains, then normalize to make grains small. Full Anneal (steels): Make soft steels for good forming by heating to get , then cool in furnace to get coarse P. Spheroidize (steels): Make very soft steels for good machining. Heat just below T E & hold for 15-25 h.

21 Chapter 11 - 21 a)Annealing b)Quenching Heat Treatments c) c)Tempered Martensite Adapted from Fig. 10.22, Callister 7e. time (s) 10 3 5 400 600 800 T(°C) Austenite (stable) 200 P B TETE 0% 100% 50% A A M + A 0% 50% 90% a) b)

22 Chapter 11 - 22 Hardenability--Steels Ability to form martensite Jominy end quench test to measure hardenability. Hardness versus distance from the quenched end. Adapted from Fig. 11.11, Callister 7e. (Fig. 11.11 adapted from A.G. Guy, Essentials of Materials Science, McGraw-Hill Book Company, New York, 1978.) Adapted from Fig. 11.12, Callister 7e. 24°C water specimen (heated to  phase field) flat ground Rockwell C hardness tests Hardness, HRC Distance from quenched end

23 Chapter 11 - 23 The cooling rate varies with position. Adapted from Fig. 11.13, Callister 7e. (Fig. 11.13 adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.) Why Hardness Changes W/Position distance from quenched end (in) Hardness, HRC 20 40 60 0123 600 400 200 A  M A  P 0.11101001000 T(°C) M(start) Time (s) 0 0% 100% M(finish) Martensite Martensite + Pearlite Fine Pearlite Pearlite

24 Chapter 11 - 24 Hardenability vs Alloy Composition Jominy end quench results, C = 0.4 wt% C "Alloy Steels" (4140, 4340, 5140, 8640) --contain Ni, Cr, Mo (0.2 to 2wt%) --these elements shift the "nose". --martensite is easier to form. Adapted from Fig. 11.14, Callister 7e. (Fig. 11.14 adapted from figure furnished courtesy Republic Steel Corporation.) Cooling rate (°C/s) Hardness, HRC 20 40 60 10020304050 Distance from quenched end (mm) 2101003 4140 8640 5140 1040 50 80 100 %M%M 4340 T(°C) 10 10 3 5 0 200 400 600 800 Time (s) M(start) M(90%) shift from A to B due to alloying B A TETE

25 Chapter 11 - 25 Effect of quenching medium: Medium air oil water Severity of Quench low moderate high Hardness low moderate high Effect of geometry: When surface-to-volume ratio increases: --cooling rate increases --hardness increases Position center surface Cooling rate low high Hardness low high Quenching Medium & Geometry

26 Chapter 11 - 26 01020304050 wt% Cu L +L+L    +L+L 300 400 500 600 700 (Al) T(°C) composition range needed for precipitation hardening CuAl 2 A Adapted from Fig. 11.24, Callister 7e. (Fig. 11.24 adapted from J.L. Murray, International Metals Review 30, p.5, 1985.) Precipitation Hardening Particles impede dislocations. Ex: Al-Cu system Procedure: Adapted from Fig. 11.22, Callister 7e. --Pt B: quench to room temp. --Pt C: reheat to nucleate small  crystals within  crystals. Other precipitation systems: Cu-Be Cu-Sn Mg-Al Temp. Time --Pt A: solution heat treat (get  solid solution) Pt A (sol’n heat treat) B Pt B C Pt C (precipitate 

27 Chapter 11 - 27 2014 Al Alloy: TS peaks with precipitation time. Increasing T accelerates process. Adapted from Fig. 11.27 (a) and (b), Callister 7e. (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.) Precipitate Effect on TS, %EL precipitation heat treat time tensile strength (MPa) 200 300 400 100 1min1h1day1mo1yr 204°C non-equil. solid solution many small precipitates “aged” fewer large precipitates “overaged” 149°C %EL reaches minimum with precipitation time. %EL (2 in sample) 10 20 30 0 1min1h1day1mo1yr 204°C 149°C precipitation heat treat time

28 Chapter 11 - 28 Metal Alloy Crystal Stucture Alloys substitutional alloys –can be ordered or disordered –disordered solid solution –ordered - periodic substitution example: CuAu FCC Cu Au

29 Chapter 11 - 29 Interstitial alloys (compounds) –one metal much larger than the other –smaller metal goes in ordered way into interstitial “holes” in the structure of larger metal –Ex: Cementite – Fe 3 C Metal Alloy Crystal Stucture

30 Chapter 11 - 30 Metal Alloy Crystal Stucture Consider FCC structure --- what types of holes are there? Octahedron - octahedral site = O H Tetrahedron - tetrahedral site = T D

31 Chapter 11 - 31 Metal Alloy Crystal Stucture Interstitials such as H, N, B, C FCC has 4 atoms per unit cell metal atoms T D sites 8 T D sites O H sites 4 O H sites

32 Chapter 11 - 32 Steels: increase TS, Hardness (and cost) by adding --C (low alloy steels) --Cr, V, Ni, Mo, W (high alloy steels) --ductility usually decreases w/additions. Non-ferrous: --Cu, Al, Ti, Mg, Refractory, and noble metals. Fabrication techniques: --forming, casting, joining. Hardenability --increases with alloy content. Precipitation hardening --effective means to increase strength in Al, Cu, and Mg alloys. Summary

33 Chapter 11 - 33 Core Problems: Self-help Problems: ANNOUNCEMENTS Reading:

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