Microstructural heterogeneity and its relationship to the strength of martensite

The complex microstructure of ferrous martensite is reflected in its complex mechanical response. In an attempt to highlight how carbon redistribution during quenching and/or low temperature tempering can affect mechanical response, a set of controlled experiments were performed. By rapidly quenching samples it was possible to limit autotempering allowing the evolution of mechanical response and microstructure to be followed with low temperature tempering. This was compared to a situation where the material was more slowly quenched, leading to a highly autotempered state. The gradual transition from elastic to plastic deformation is interpreted based on possible sources of microstructural heterogeneity. Lath-to-lath variations of dislocation density are discussed as a contributor to the development of microstructural heterogeneity during tempering. These results shed light on the possible origins of the continuous-composite like mechanical response of lath martensite proposed in recent work.