Time-Temperature-Transformation Diagram of Successive γ → ε′ → α′ Martensitic Transformation in SUS304L Stainless Steel

We have investigated the kinetics of successive gamma -> epsilon' -> alpha' martensitic transformation in a SUS304L stainless steel by isothermal holding experiments. An in-situ optical micrograph observation suggests that the gamma -> epsilon' martensitic transformation has so-called isothermal kinetics while the epsilon' -> alpha' martensitic transformation has so-called athermal kinetics. The TTT diagram corresponding to the formation of 0.5 vol% of alpha'-martensite via epsilon'-martensite front gamma-phase shows a C-curve with a nose temperature located at about 103 K, due to the isothermal kinetics of the gamma -> epsilon' transformation. [doi: 10.2320/matertrans.MAW200814]