Processing Map and Hot Deformation Characteristics of 21Cr-11Ni-N-RE Lean Austenitic Heat-Resistant Steel

Hot deformation behavior of 21Cr-11Ni-N-RE lean austenitic heat-resistant steel is investigated within the temperature of 1173-1473 K and the strain rate of 0.01-10 s(-1). Hot deformation equation and prediction modeling of peak stress and strain are obtained. Based on the dynamic material model (DMM) theories, the processing maps are developed. The results show that at lower strain (0.3), the efficiency of power dissipation (eta) increases with increasing temperature and decreasing strain rate; however at the strain of 1.0, eta exhibits an obvious decrease at 1373-1473 K and 0.01 s(-1), in which significant coarsening of grains is found. At large strain (1.0), the optimum hot working domain of test steel should be at 1423-1473 K and strain rate of 1-10 s(-1), in which more uniform and finer microstructure is formed due to the complete dynamic recrystallization (DRX). The average grain diameter of recrystallized grains shows a power law relationship with Z. The larger the Z-value is, the finer the grains are. Besides, the unstable hot working regions are delineated in the processing maps using Prasad instability criterion. As predicted, twinning bands of flow localization and localized kinking observed at 1173-1223 K and 1-10 s(-1) should be responsible for the flow instability.