Thermomechanical processing model and abnormal microstructure evolution of high-nitrogen stainless steel X30CrMoN15-1

Abstract

The high temperature deformation behavior of a X30CrMoN15-1 high-nitrogen stainless steel has been investigated using uniaxial compression test in the temperature range of 850–1250 ℃ and strain rate of 0.001–10 s−1. An Arrhenius-based hyperbolic sine equation was used to establish the flow stress constitutive model of the alloy at high temperatures, and the activation energy was 385.5 kJ/mol. Processing maps based on the dynamic material model were developed for true strains of 0.2, 0.4, 0.6 and 0.8. The domain of the safe region was in two parts: first, a strain rate range of 1–10 s−1 and temperature range of 1000–1100 ℃, and second, a strain rate range of 0.3–0.001 s−1 and temperature range of 1100–1250 ℃. The deformed microstructure at 1050 °C was characterized at different strain rates, strong< 100 >fiber textures parallel to the compression axis developed during high temperature deformation, and the strength gradually increased and became more concentrated with decreasing strain rate. The maximum dynamic recrystallization fraction and geometrically necessary dislocation densities were recorded at a medium strain rate (ε̇=0.1s−1), which was more conducive than a low strain rate to the continuous dynamic recrystallization process. Discontinuous and continuous dynamic recrystallization both contributed to the microstructural evolution of the columnar grains studied in this research, but discontinuous dynamic recrystallization was the dominant mechanism.