Quantitative geometric characterization of high carbon martensite

Quantitative stereology was applied to study the transformation behavior and the microgeometry of athermally transformed martensite for two austenite grain sizes in Fe-1.4 wt pct C-0.02 wt pct P alloy and commercial 01 tool steel. The effects of prior austenite grain boundaries and the existing martensite plates on the nucleation of martensite were studied and each was found to play different roles during the transformation. Autocatalytic nucleation was found to be less than that for a burst transformation. Prior austenite grain boundaries were found to have a strong influence on the initial nucleation of martensite. Plate thickness was constant during the transformation except for coarsegrained 01 tool steel after ～60 pct transformation. The plate radius decreased slowly with fraction transformed and was found to be independent of the mean free path in austenite initially, but decreases with the decreasing mean free path in the later stages.