Prediction of martensite volume fraction in Fe-Cr-Ni alloys

An analytical model for predicting the volume fraction of martensite from a dilation curve by considering the effect of alloying elements in Fe-Cr-Ni stainless steel alloys was investigated. Four dilation curves of Fe-Cr-Ni stainless steel alloys that have different chemical compositions were selected to verify the analytical model. In each case the cooling rates were high enough to obtain full martensite without other diffusion-controlled transformational products above the M_s temperature. The martensite transformations of the S3 and S4 curves were completed above room temperature, while the martensite transformation was not completed at room temperature for the S1 and S2 curves. A constant amount of each alloying element was considered in order to determine the effect of that individual element on the martensite transformation strain. By comparing with the calculation of pure iron, the addition of Ni produces expansion and the additions of Mn and Cr produce contraction.