A MULTISCALE CRYSTAL PLASTICITY ANALYSIS OF DEFORMATION IN A TWO-PHASE STEEL

A rate-and lengthscale-dependent crystal plasticity model is employed with a representative volume element for a two-phase austenitic steel under hot-forming conditions to investigate the role of austenite and MnS particle crystallographic orientation on local stress and slip conditions at austenite-MnS interfaces. It was found that austenite-MnS particle interfacial stress magnifications are determined largely by the crystallographic orientation of the MnS and not significantly by the austenite orientations. However, the crystallographic orientation of an austenite grain neighboring a MnS particle has a dramatic effect on slip localization and slip magnitude in the absence of any significant change in interfacial stress magnitude. The results suggest that it is the crystallographic orientation of the MnS rather than that of the austenite which determines the onset and rapidity of void nucleation. The results also show that there are very particular combinations of austenite-MnS particle orientations which lead to the highest interfacial stresses, and that the peak stress magnification arises not from the properties of the second phase particles but from their orientation. Micromechanical models based on isotropic plasticity will not capture correctly the interfacial stresses.