Effect of temperature and heat generation on martensitic phase transformation in DH steels

Abstract

Transformation induced plasticity (TRIP) phenomenon and mechanical behavior of TRIP-aided steels are influenced by the ambient as well as local temperature which raises due to plastic deformation and latent heat of transformation. In order to study this effect, tensile tests with samples made of DH800 steel were carried out at various temperatures, while the temperature rise was monitored during the test. In parallel, a physically-based model was applied to predict the change in material behavior as a consequence of the TRIP effect. In this model, martensitic transformation is mainly stress-driven, and the self-consistent scheme was adopted to achieve a homogenized material behavior. In addition, temperature rise as a result of plastic energy dissipation and latent heat of mechanically-induced retained austenite-martensite transformation was taken into account. Empirical flow curves at various temperatures indicated that at sub-zero values, the hardening of material due to the TRIP effect is much more pronounced. It was observed that a temperature change between +80 °C and −40 °C increases the flow stress by 200 MPa. Measured temperature rise, especially at sub-zero levels, showed an initial sharp increase at low strain stages due to phase transformation that flattens afterward. The numerical results are in agreement with experimental measurements of material flow curves and retained austenite fraction.