MODELING OF AUSTENITE STABILITY IN LOW-ALLOY TRIPLE-PHASE STEELS

A model for the stability of dispersed austenite in low alloy triple-p hase steels has been developed. The model was based on the dislocation dissociation model for classical heterogeneous martensitic nucleation by considering stress effects on the nucleation site potency distribu tion. The driving force for martensitic transformation has been calcul ated with the aid of computational thermodynamics. The model allows fo r the effects of chemical composition of austenite, mean austenite par ticle size, yield strength of the steel and stress state on austenite stability. Chemical enrichment in C and Mn, as well as size refinement of the austenite particles lead to stabilization. On the contrary, th e increase in the yield strength of the steel and triaxiality of the s tress state lead to destabilization. The model can be used to determin e the microstructural characteristics of the austenite dispersion, i.e . chemical composition and size, for optimum transformation plasticity interactions at the particular stress state of interest and can then be useful in the design of low-alloy triple-phase steels.