Flow stress-strain curves and dynamic recrystallization behavior of high carbon low alloy steels during hot deformation

The stress-strain curves and dynamic recrystallization (DRX) behavior of high carbon low alloy (HCLA) steels were investigated by hot deformation at a wide range of temperatures (900–1150 °C) and strain rates (0.01–10 s−1). Based on the dislocation density theory, this paper established the stress-strain curve equation and analyzed in detail the critical stresses for nucleation and growth of DRX in relation to the stress-strain curve. The main DRX mechanism of the HCLA steel is discontinuous dynamic recrystallization (dDRX). When deformed at high strain rates, the DRX grains nucleated non-uniformly, preferentially at the trigonal grain boundaries. Conversely, at low strain rates, both serrated and bulged grain boundaries can simultaneously be the nucleation sites of DRX grains in a uniform manner. In the DRX type curve, when the strain rate reduced from 0.1 s−1 to 0.01 s−1, the inoculation temperature for the rapid growth of DRX grains in HCLA steel was reduced from 1050 °C to 1000 °C. Compared to the initial microstructure, the average grain size at 1050 oC-0.1 s−1 decreased by 79.4%, while the aspect ratio of the grain shape increased by only 9.1%. Considering the variation of temperature and strain rate in industrial production, the optimal deformation parameters of the HCLA steel to obtain the equiaxial DRX grains are the deformation temperature of 1000–1050 °C, and the strain rate of 0.1–1 s−1.