Deep drawing ability of TRIP-aided DP steel under a non-isothermal warm deep drawing process

Abstract

The formability of transformation-induced plasticity-assisted steels is significantly influenced by the transformation-induced plasticity transformation mechanism (transformation of retained austenite to martensite) that occurs during deformation. However, the additional strain hardening that develops in the flange regions during the deep drawing process adversely affects their deep drawability. Therefore, an advanced method is required to enhance the deep drawing performance of transformation-induced plasticity-assisted steels. In this study, a novel non-isothermal warm deep drawing process has been developed to enable controlled transformation-induced plasticity during forming. In this process, the flange region of the sheet metal is heated to elevated temperatures (50 °C, 100 °C and 150 °C), while the centre and wall regions are continuously cooled by liquid nitrogen throughout deformation. This thermal gradient is designed to suppress the transformation-induced plasticity effect in the flange region while activating it in the centre and wall regions of the sheet during forming. Furthermore, a simplified version of this setup was modelled using finite element analysis, employing the Modified Mohr–Coulomb damage model as a failure criterion to predict the limiting drawing ratio. Experimental results demonstrated a 12.67% improvement in the limiting drawing ratio at 150 °C using the proposed non-isothermal approach. The simulation results closely matched the experimental findings, confirming the predictive accuracy of the finite element analysis model.