Hypoeutectoid steels - strength vs P content

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Presentation transcript:

Hypoeutectoid steels - strength vs P content The Fe-C system

Martensite (MAR) Quenching suppresses diffusion AUS ––> P rxn doesn't go! But something has to happen - a. too much carbon for FE b. AUS needs to change structure AUS ––> MAR (very fine structure)

Martensite (MAR) MAR is metastable…… C is trapped in wrong structure MAR comes from AUS AUS wants to exsolve C & change atom arrangement

Transformation to MAR is time independent ….but temperature dependent Martensite (MAR) Transformation to MAR is time independent ….but temperature dependent martensite start martensite finish

Martensite (MAR) TTT curves & MAR formation

Martensite (MAR) Very hard, very strong due to: solution hardening by xs carbon residual internal strain But……

Martensite (MAR) Toughness = ??

Hardenability Definitions - For steels: harden = make MAR hardenability = ability to make MAR