Martensite transformation of sub-micron retained austenite in ultra-fine grained manganese transformation-induced plasticity steel

The influence of the chemical composition and the grain size of retained austenite in an ultra-fine grained medium manganese steel on the martensite transformation kinetics was investigated by means of dilatometry. A modified Koistinen-Marburger type exponential function was developed for the martensite transformation kinetics, which includes the influence of the size and the composition of the austenite. Whereas the ultra-fine grained retained austenite had a remarkably low M-s temperature, the kinetics of its transformation to martensite was accelerated.