Effects of Cold Rolling Reduction on Retained Austenite Fraction and Mechanical Properties of High-Si TRIP Steel

Abstract

Transformation-induced plasticity-aided steel [TRIP steel (0. 4C-1. 5Si-1. 5Mn)] was rolled at room temperature to different thickness reductions (0, 4%, 10%, 20%, 40%, and 60%). The mechanical properties, microstructure and austenite fractions of the rolled samples were measured by tensile test, electron back scattered diffraction (EBSD) and X-ray diffraction (XRD) for each rolling. The deformation behavior was studied based on the analysis of the mechanical properties and microstructure of steel after tensile deformation, aiming at understanding the effects of cold rolling reduction on the decay behavior of the austenite and the change of mechanical properties of the TRIP steels. It was found that increasing rolling reduction increases the yield stress gradually but decreases the total elongation significantly. It is very interesting that after 10% rolling reduction the yield stress is about 1000 MPa but still with 20% total elongation, which gives an excellent combination of yield strength and ductility. Based on the XRD results, it was revealed that in both rolling and tension the austenite volume fraction monotonically decayed with the increase of rolling strain, but the decaying rate is faster in tension than in rolling, which may be ascribed to the higher temperature in rolled specimens than in the tensioned ones during deformation. Experimental results and theoretical reasoning indicate that the decreasing trend of austenite volume fraction with strain can be formulated by a unique equation.