8Steels Low Alloy High Alloy low carbon <0.25 wt% C Med carbon high carbonwt% CplainHSLAheattreatabletoolausteniticstainlessNameAdditionsnoneCr,VNi, MoCr, NiMoCr, V,Mo, WCr, Ni, MoExample101043101040434010954190304Hardenability++++++TS-+++EL++----++Usesautobridgescrankpistonsweardrillshigh Tstruc.towersshaftsgearsapplic.sawsapplic.sheetpress.boltsweardiesturbinesvesselshammersapplic.furnacesincreasing strength, cost, decreasing ductilitybladesV. corros.resistantBased on data provided in Tables 11.1(b), 11.2(b), 11.3, and 11.4, Callister 7e.
9LOW-CARBON STEEL ~<0.25%C High Strength Low Alloy Steel Unresponsive to heat treatmentConsist of ferrites and pearliteRelatively soft and weakRelatively ductile and toughWeldable and machinableEconomical amongst all steelHigh Strength Low Alloy SteelAlloying up to 10%Increase corrosion propertiesHigher strengthSAE – Society of Automotive engineersAISI- American Iron and Steel InstituteASTM- American Society for Testingand MaterialsUNS- Unified Numbering System
10MEDIUM CARBON STEELS – 0.25-0.6 wt%C Heat treated by austenizing, quenching, and then tempering to improve their mechanical properties. Most often utilized in tempered condition with tempered martensite microsture.Low hardenability can be heat treated only in very thin sections and with rapid quenching
11High Carbon steels: 0.60-1.4 wt%C – hardest, strongest, least ductile Always used in hardened/tempered condition – wear and indentation resistantTool/die steels contain high Carbon and Chromium, Vanadium, tungsten and molybdenum Carbides
16Types of Cast Iron Gray iron Ductile iron graphite flakes weak & brittle under tensionstronger under compressionexcellent vibrational dampeningwear resistantDuctile ironadd Mg or Cegraphite in nodules not flakesmatrix often pearlite - better ductilityAdapted from Fig. 11.3(a) & (b), Callister 7e.
17Types of Cast Iron White iron <1wt% Si so harder but brittle more cementiteMalleable ironheat treat at ºCgraphite in rosettesmore ductileAdapted from Fig. 11.3(c) & (d), Callister 7e.
18Production of Cast Iron Adapted from Fig.11.5, Callister 7e.
19Nonferrous Alloys NonFerrous Alloys • Cu Alloys • Al Alloys Brass: Zn is subst. impurity(costume jewelry, coins,corrosion resistant)Bronze: Sn, Al, Si, Ni aresubst. impurity(bushings, landinggear)Cu-Be:precip. hardenedfor strength• Al Alloys-lowerr: 2.7g/cm3-Cu, Mg, Si, Mn, Zn additions-solid sol. or precip.strengthened (struct.aircraft parts& packaging)NonFerrousAlloys• Mg Alloys-very lowr: 1.7g/cm3-ignites easily-aircraft, missiles• Ti Alloys-lowerr: 4.5g/cm3vs 7.9 for steel-reactive at high T-space applic.• Refractory metals-high melting T-Nb, Mo, W, Ta• Noble metals-Ag, Au, Pt-oxid./corr. resistantBased on discussion and data provided in Section 11.3, Callister 7e.
22Additions to Cu and Al alloy Designations Temper designation scheme for alloys: a letter and possibly a one- to three-digit number:F, H, and O represent, respectively, the as-fabricated, strain hardened, and annealed states.T3 means that the alloy was solution heat treated, cold worked, and then naturally aged (age hardened).T6 means that the alloy was solution heat treated followed by artificial aging.
25Metal Fabrication How do we fabricate metals? Forming Operations Blacksmith - hammer (forged)Molding - castForming OperationsRough stock formed to final shapeHot working vs Cold working• T high enough for • well below Tm recrystallization • work hardening• Larger deformations • smaller deformations
26Metal Fabrication Methods - I FORMINGCASTINGJOININGAodforcedieblank• Forging (Hammering; Stamping)(wrenches, crankshafts)often atelev. TAdapted from Fig. 11.8, Callister 7e.rollAod• Rolling (Hot or Cold Rolling)(I-beams, rails, sheet & plate)tensileforceAoddie• Drawing(rods, wire, tubing)die must be well lubricated & cleanrambilletcontainerforcedie holderdieAodextrusion• Extrusion(rods, tubing)ductile metals, e.g. Cu, Al (hot)
27Metal Fabrication Methods - II FORMINGCASTINGJOININGCasting- mold is filled with liquid metalmetal melted in furnace, perhaps alloying elements added. Then cast in a moldmost common, cheapest methodgives good reproduction of shapesweaker products, internal defectsgood option for brittle materials or microstructures that are cooling rate sensitive
29Metal Fabrication Methods - III FORMINGCASTINGJOINING• Powder Metallurgy(materials w/low ductility)• Welding(when one large part isimpractical)• Heat affected zone:(region in which themicrostructure has beenchanged).Adapted from Fig. 11.9, Callister 7e.(Fig from Iron Castings Handbook, C.F. Walton and T.J. Opar (Ed.), 1981.)piece 1piece 2fused base metalfiller metal (melted)basemetal (melted)unaffectedheat affected zonepressureheatpoint contactat low Tdensificationby diffusion athigher Tareacontactdensify
30Thermal Processing of Metals Annealing: Heat to Tanneal, then cool slowly.Types ofAnnealing•Stress Relief: Reducestress caused by:-plastic deformation-nonuniform cooling-phase transform.•Spheroidize(steels):Make very soft steels forgood machining. Heat justbelow TE & hold for15-25 h.•Full Anneal(steels):Make soft steels forgood forming by heatingto getg, then cool infurnace to get coarse P.•Process Anneal:Negate effect ofcold working by(recovery/recrystallization)•Normalize(steels):Deform steel with largegrains, then normalizeto make grains small.Based on discussion in Section 11.7, Callister 7e.
31Heat Treatments Annealing Quenching Tempered Martensite a) b) c) TE 800Austenite (stable)a)b)TET(°C)AAnnealingP600QuenchingTempered MartensiteB400A100%Adapted from Fig , Callister 7e.50%0%c)0%200M + A50%M + A90%-13510101010time (s)
32Hardenability--Steels • Ability to form martensite• Jominy end quench test to measure hardenability.24°C waterspecimen(heated to gphase field)flat groundRockwell C hardness testsAdapted from Fig , Callister 7e. (Fig adapted from A.G. Guy, Essentials of Materials Science, McGraw-Hill Book Company, New York, 1978.)• Hardness versus distance from the quenched end.Hardness, HRCDistance from quenched endAdapted from Fig , Callister 7e.
33Why Hardness Changes W/Position • The cooling rate varies with position.60MartensiteMartensite + PearliteFine PearlitePearliteHardness, HRC4020distance from quenched end (in)123600400200AMP0.11101001000T(°C)M(start)Time (s)0%100%M(finish)Adapted from Fig , Callister 7e.(Fig adapted from H. Boyer (Ed.) Atlas of Isothermal Transformation and Cooling Transformation Diagrams, American Society for Metals, 1977, p. 376.)
34Hardenability vs Alloy Composition Cooling rate (°C/s)Hardness, HRC204060103050Distance from quenched end (mm)21003414086405140104080%M4340• Jominy end quenchresults, C = 0.4 wt% CAdapted from Fig , Callister 7e.(Fig adapted from figure furnished courtesy Republic Steel Corporation.)• "Alloy Steels"(4140, 4340, 5140, 8640)--contain Ni, Cr, Mo(0.2 to 2wt%)--these elements shiftthe "nose".--martensite is easierto form.T(°C)10-135200400600800Time (s)M(start)M(90%)shift fromA to B dueto alloyingBATE
35Quenching Medium & Geometry • Effect of quenching medium:MediumairoilwaterSeverity of QuenchlowmoderatehighHardnesslowmoderatehigh• Effect of geometry:When surface-to-volume ratio increases:--cooling rate increases--hardness increasesPositioncentersurfaceCooling ratelowhighHardness
36Precipitation Hardening • Particles impede dislocations.• Ex: Al-Cu system• Procedure:1020304050wt% CuL+Laa+qq+L300400500600700(Al)T(°C)composition rangeneeded for precipitation hardeningCuAl2A--Pt A: solution heat treat (get a solid solution)BPt B--Pt B: quench to room temp.C--Pt C: reheat to nucleate small q crystals within a crystals.Other precipitation systems: • Cu-Be • Cu-Sn • Mg-AlAdapted from Fig , Callister 7e. (Fig adapted from J.L. Murray, International Metals Review 30, p.5, 1985.)Temp.TimePt A (sol’n heat treat)Consider: 17-4 PH St. Steel and Ni-Superalloys too!Pt C (precipitate )Adapted from Fig , Callister 7e.
37Effect of time at Temperature during Precipitation Hardening