Effect of temperature on flow and work hardening behavior of high bainite dual phase (HBDP) steels

High bainite dual phase steel has been subjected to tension test at different temperatures from 25 to 500 °C with strain rate of 4.6 × 10−4 s−1 to investigate the effect of temperature on its mechanical properties. Stress–strain curves of steels showed serration flow at temperature range of 200–350 °C and smooth flow at the other temperatures. In agreement with previous studies on some steels, peaks in the variations of yield strength (YS) and ultimate tensile strength (UTS) and minima in ductility were observed at temperature range of 200–350 °C which are various manifestations of dynamic strain aging (DSA). It has been also found that ferrite volume fraction has no effect on the temperature range of serrated flow but work hardening decreased slightly with increasing ferrite volume fraction.The tensile test data were also analyzed in term of Hollomon equation and it was found that this steel has two work hardening stages. In this study the effects of temperature on Hollomon equation parameters and onset strain of stage II hardening were investigated. The observed peaks/plateaus in the variation of Hollomon equation parameters with temperature at the intermediate temperature range have been identified as the other manifestation of dynamic strain aging. The work hardening analysis of flow stress data revealed that, in the DSA region, the onset strain of stage II work hardening is athermal.