The mean size of plate martensite: influence of austenite grain size,partitioning, and transformation heterogeneity

The evolution of transformation microstructure during martensite transformation is revisited. The influence of “spread” heterogeneity on current partitioning concepts is assessed. Following that, a method to infer details of martensite transformation in an average austenite grain is described. The results indicate that the mean martensite plate size may remain constant up to a significant extent of grain transformation. Moreover, it is found that the mean martensite plate volume in fine grain austenite is proportionally larger than that observed with coarse grain austenite, and these effects are ascribed to autocatalysis. Finally, a transformation model is derived which accurately describes the data up to V_v = 0.65, irrespective of austenite grain size.