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Hardenability

Hardenability. center cools slowly. surface cools rapidly. Problem: Suppose want to full harden a shaft – i.e., make MAR all the way through shaft. Hardenability. So - this could happen:. Hardenability. Solution to problem: increase quench rate.

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Hardenability

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  1. Hardenability center cools slowly surface cools rapidly Problem: Suppose want to full harden a shaft – i.e., make MAR all the way through shaft

  2. Hardenability So - this could happen:

  3. Hardenability Solution to problem: increase quench rate But rapid quenching leads to distortion & cracking Generally quench as gently as possible

  4. Hardenability So….is there a solution?? OK, how to do that? What controls position of TTT curves?

  5. Hardenability So….is there a solution?? OK, how to do that? What controls position of TTT curves? a. % C – more C to move…slower P growth b. add alloy elements…slows C diffusion c. increase AUS grain size. P nucleates on AUS grain boundaries. Increases diffusion distance

  6. Hardenability

  7. Hardenability

  8. Hardenability Shift curves to right: Mn Mo Cr V Nb Si Ni W

  9. Tempering Fresh MAR too brittle - infrequently used Brittle materials can be used in compression Ex: fresh MAR in ball bearings

  10. Martensite (MAR)

  11. 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

  12. Tempering Tempering does not form P - get discontinuous particles

  13. Tempering • What else can happen? stress relief carbide formation transition Fe carbides (not Fe3C) alloy carbides (ex: Cr7C3, Mo6C, VC) • start FE formation

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

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

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

  17. Types of steels Plain carbon steels alloy steels Low carbon steels high carbon steels Stainless steels 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 420 440A 440C 405 430 304 304L 316 420 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 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)

  18. Types of steels Stainless steels

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