Last class - Improving hardenability - shift TTT curves to right Tempering for toughness stress relief carbide and FE formation Today - Austenitization & tempering Types of steels & irons

But first - a little more on the MAR transformation ms mf T MAR formation starts here 50% MAR - 50% AUS MAR formation finishes here Only changing temperature gives more MAR Time at temperature doesn't help

Austenitizing Hypoeutectoid steels: about 25°C above a3 no FE

Austenitizing Hypereutectoid steels: betwn a3 & acm undissolved carbides present - not particularly detrimental

Tempering temperature/time Depend upon desired props, application Low T gives high hardness, low toughness - wear resistance Hi T gives high toughness, reduced hardness

Plain carbon steels alloy steels Low carbon steels high carbon steels Types of steels Plain carbon steels alloy steels Low carbon steels high carbon steels Stainless steels 420 13Cr-0.15C 230ksi(ht treated) 440A 17Cr-0.5Ni-0.7C 260ksi(ht treated) 440C 17Cr-0.5Ni-1.2C 285ksi(ht treated) 405 13Cr-0.5Ni-0.08C 60ksi(annealed) 430 16Cr-0.5Ni-0.12C 65ksi(annealed) 304 19Cr-10Ni-0.08C 85ksi(annealed) 304L 19Cr-10Ni-0.03C 80ksi(annealed) 316 17Cr-12Ni-0.08C 85ksi(annealed) 420 13Cr-0.15C cutlery 440A 17Cr-0.5Ni-0.7C cutlery 440C 17Cr-0.5Ni-1.2C ball bearings 405 13Cr-0.5Ni-0.08C machine parts 430 16Cr-0.5Ni-0.12C acid tanks 304 19Cr-10Ni-0.08C food equipment 304L 19Cr-10Ni-0.03C food equipment 316 17Cr-12Ni-0.08C chemical tanks 420 440A 440C 405 430 304 304L 316 420 13Cr-0.15C 440A 17Cr-0.5Ni-0.7C 440C 17Cr-0.5Ni-1.2C 405 13Cr-0.5Ni-0.08C 430 16Cr-0.5Ni-0.12C 304 19Cr-10Ni-0.08C 304L 19Cr-10Ni-0.03C 316 17Cr-12Ni-0.08C

Types of steels Stainless steels

Stainless steels 420 13Cr-0.15C 230ksi(ht treated) 440A 17Cr-0.5Ni-0.7C 260ksi(ht treated) 440C 17Cr-0.5Ni-1.2C 285ksi(ht treated) 405 13Cr-0.5Ni-0.08C 60ksi(annealed) 430 16Cr-0.5Ni-0.12C 65ksi(annealed) 304 19Cr-10Ni-0.08C 85ksi(annealed) 304L 19Cr-10Ni-0.03C 80ksi(annealed) 316 17Cr-12Ni-0.08C 85ksi(annealed)

Stainless steels hardenable! not hardenable!

austenitic SSs ----- ≥ 18% Cr & ≥ 8% Ni not hardenable Stainless steels sufficient amt of Ni ––> AUS at rm temp austenitic SSs ----- ≥ 18% Cr & ≥ 8% Ni not hardenable

Types of steels Plain carbon steels alloy steels Low carbon steels high carbon steels Stainless steels Tool steels

Some types of tool steels W1, W2..... water hardening 0.60-1.40C S2, S2...... shock resisting 0.5C-Cr, W, Mo O1, O2..... oil hardening 0.9C-Mn, Ni, W A2, A3..... air hardening 1.25C-5Cr, V, Mo H10, H11..... hot work 0.4C-0.4V-3-5Cr T1, T2..... high-speed 0.8C-4Cr-18W-1-2V Compositions not exact - higher grades have different compositions

Speaking of tools….. What about "carbide" tools? Most are WC fragments imbedded in Co matrix angular WC fragments Co matrix phase - the "glue"

Speaking of tools….. OK, then, what about "ceramic" tools? Most from Al2O3 - pressed to near-net shape & sintered at 1600-1700° C - ground on diamond wheels At high temps, high hardness, wear resistance Can use for mat'ls w/ up to RC66 Very brittle Cost ≈ 2X that of carbide tools

Cast irons Types White - C is all in CM Grey - C as graphite flakes Ductile (nodular) - C as graphite nodules

Cast irons

Cast irons White - C is all in CM very brittle, wear resistant, not machinable, limited use Grey - C as graphite ("corn") flakes Si added to graphitize, brittle cuz of flake stress raisers - cheap, widely used, vibration damping Ductile (nodular) - C as graphite nodules "inoculated" w/ Mg or Ce to get nodules - up to 40% EL

Case hardening Gear tooth Carburizing - pack & gas - add C from CO gas