Evaluation of the deformation behaviors and hot workability of a high-strength low-alloy steel

Abstract

Abstract The flow behaviors of 300M steel are studied by hot compression experiments at the deformation temperatures of 1173~1423 K and strain rates of 0.01~10 s−1. The flow stress curves are corrected to eliminate the effects of adiabatic heating and friction on the flow stress. Based on the corrected flow stress curves, a modified constitutive model is established to quantify the flow behaviors of 300M steel accurately. It is found that the apparent activation energy is a function of deformation temperature and strain rate, and the stress exponent is a function of deformation temperature. The dynamic recrystallization (DRX) map is constructed to analyze the microstructure evolution mechanism, which is made up of four parts including dynamic recovery (DRV), partial DRX (P-DRX), full DRX (F-DRX), and grain coarsening (GC). Besides, the average grain size maps for DRX grains and all grains are constructed to analyze the effects of the DRX process on the microstructure and optimize the microstructure of the alloy. The 3D instability map and 3D power dissipation map are constructed to evaluate the hot workability. The instability region corresponds to high strain rates and low deformation temperatures. The peak domain of power dissipation efficiency varies with the increaseing strain, which can be ascribed to the development of the DRX process and microstructure evolution. There are two suitable processing regions according to the processing map. Combining with the degree of DRX, and the size and distribution of austenite grains, the deformation parameters are optimized. The optimized deformation parameters are the strain rate of 0.36~10 s−1 and deformation temperature of 1382~1423 K, and the strain rate of 0.01~0.07 s−1 and deformation temperature of 1243~1323 K. The power dissipation efficiency is an important index to evaluate the DRX degree and flow instability. When the power dissipation efficiency is below 25%, the flow instability of 300M steel occurs easily and the DRX develops inadequately.