Abstract

In the direct quenching and partitioning (DQ&P) process to develop tough, ultrahigh-strength steel, the hot rolling stage involving deformation and recrystallization between successive passes affects the state of the austenite prior to the quenching and partitioning step. Therefore, in order to design appropriate thermo-mechanically controlled rolling processes, the recrystallization characteristics of two experimental high-Si DQ&P steels, with compositions (in wt.%) 0.3C-1Si-2Mn-1Cr and 0.25C-1.5Si-3Mn, were determined using the stress relaxation technique on a Gleeble thermomechanical simulator and modelled in terms of the effects of temperature, strain, strain rate and initial grain size. Data analysis resulted in the estimation of the powers of strain (-2.8 and -2.4) and strain rate (-0.23 and -0.14) and the recrystallization activation energies (303 and 289 kJ/mol) for the 0.3C-1Si-2Mn-1Cr and 0.25C-1.5Si-3Mn steels, respectively. This suggests that increasing the contents of Mn and Si made the recrystallization kinetics less sensitive to strain, strain rate and temperature. New regression equations derived to describe the recrystallization kinetics can be used in the design of the rough rolling part of thermomechanical processing.