Effect of deformation processes in austenite region on microstructure and mechanical properties in a Si-Mn hot-rolled TRIP steel

A Si-Mn hot-rolled TRIP steel was subjected to different deformation in austenite recrystallization and non-recrystallization regions during thermo-mechanical processes. The microstructural characteristics were analyzed using optical microscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD), and its effects on mechanical properties were investigated. The results show that a bigger reduction in deformation in the austenite non-recrystallization region results in a more remarkable pancaking of the austenite grain. This austenite condition strongly promotes proeutectoid ferrite formation, which causes an increase in the amount of retained austenite (RA). Compared with the case of smaller reduction in austenite non-recrystallization region, the steel with bigger reduction exhibits higher elongation and excellent combination of strength and ductility because of higher fractions of proeutectoid ferrite and RA particles with different sizes that provide sustained transformation-induced plasticity (TRIP) effect over a significantly wide strain range. The untransformed RA in the fractured tensile specimen has a much smaller grain size and higher carbon content than the case before the fracture.