Most people would rather die than think; in fact, they do so. –Bertrand Russell
Tempering Fresh MAR too brittle - infrequently used Brittle materials can be used in compression Ex: fresh MAR in ball bearings
Martensite (MAR)
Tempering Tempering conditions 200°C < T < 700°C days sec What happens? carbide formation starts - very fine closely spaced (makes material harder) carbon depletion in MAR (makes material softer) net change about 0
Tempering Tempering does not form P - get discontinuous particles
Tempering What else can happen? stress relief carbide formation transition Fe carbides (not Fe3C) alloy carbides (ex: Cr7C3, Mo6C, VC) start FE formation
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
Review today's notes a. what is martensite b. why is martensite c. martensite structure & properties Read text: pp 277-290; 302-314 Do problems in text: 9.55, 9.57, 10.14, 10.16 4. Do second set of problems on website