CALCULATION OF THE EFFECT OF ALLOYING ELEMENTS ON THE M(S) TEMPERATURE IN STEELS

A thermodynamic calculation was carried out to predict the effect of alloying elements on the M(s) temperature in iron-base alloys. It is shown that changes in M(s) temperature by alloy addition are due to both chemical and mechanical effects. Magnetic and non-magnetic contributions to the Gibbs energy constitute the chemical part, while the mechanical effect arises mainly as a result of the change in friction stress required to move transformation dislocations, which in turn is related to solid solution hardening in the parent austenite. In this paper the chemical contributions to Gibbs free energy are evaluated quantitatively from thermodynamic data. These data are used in combination with mechanical data to calculate the M(s) temperature. Calculated M(s) temperatures are compared with results obtained using previously reported empirical formulae.