Correlation Between Crystal Structure Change and Transformation Strain for Multiphase Transformations

Transformation strains measured via dilatometry and phase fractions measured by optical metallography were used to develop a two-stage, conversional model to accurately determine phase fraction directly and continuously from measured dilation strains for multiphase transformations. The multiphase ferrite + pearlite to austenite transformation was analyzed here, but the two-stage conversional model developed may also be applied to other multiphase transformations. It was found that the lever rule provides accurate results for single-phase to single-phase transformations; the use of a conversional model is not necessary in this case.