Finite Element Modelling of Concurrent Deformation and Transformation in Metastable Steels

Abstract: Metastable austenitic stainless steels are designed to be thermodynamically unstable so that plastic deformations even at ambient temperatures can cause the austenite to transform to martensite. It improves the formability of these steels, since necking is delayed. This is a solid-state phase transformation where concurrently there is a latent heat of transformation and an adiabatic heat is generated due to plastic deformation. Since the lattice structure of the polycrystal changes, the thermo-physical properties of the metal also change during this process as a function of strain, strain rate and temperature. Such a transformation is believed to be initiated by either a local concentration of stresses or strain induced stacking faults in the polycrystal. It is a diffusionless shear transformation at the lattice level and the in-situ state of stress affects the amount and kinetics of the phase transformed. Therefore a Finite Element Model is developed for a specific Cr-Ni maraging stainless steel to study the influence of deformation on phase transformation