Austenite grain size and the martensite-start temperature

New experimental evidence confirms the dependence of the martensite-start temperature on the austenite grain size. The Fisher model for the geometrical partitioning of austenite grains by plates of martensite is used here to develop a theory to explain the observations, based on the ability to detect transformation as a function of the austenite grain size. The relationship derived has been tested on a range of published data.