Thermodynamical calculation of martensite start temperatures in the systemFeCrMnNiC

A thermodynamic model recently developed by the authors considers martensit ic iron-carbon alloys to be a mixture of body centred tetragonal Fe:C and b ody centred cubic Fe:Va groups (Va = vacant interstitial site). In this inv estigation, the model has been extended to multi-component carbon containin g alloys. From thermodynamic T-o and experimental M-s temperatures of FeCr, FeCrC, and FeMn alloys, driving forces were derived which were near 2100 J /mol when plate martensite was formed, and proportional to the concentratio n of the alloying elements when lath martensite was formed. Using the equat ions describing the dependence of the driving forces on the concentration o f alloying elements, a very good correspondence between M-s temperatures re ported in TTT diagrams for alloys in the system FeCrMnC and calculated ones was achieved. For FeNi alloys, T-o temperatures calculated by means of SGT E data were at high Ni concentrations more negative than measured M-s tempe ratures. By a fitting procedure, suitable solution parameters for the bcc p hase were derived. Using these parameters, correct T-o and M-s temperatures in binary FeNi as well as in FeCrNiC and FeNiC alloys were obtained.