Dynamic recrystallization behaviors and cracking mechanism for the hot deformation of new-generation high nitrogen bearing steel

Abstract

In this work, the hot deformation behaviors of the high-nitrogen steel X30CrMoN15-1 from 900 °C to 1200 °C have been investigated. The microstructure observation indicates that the maximum DRXed grain size reaches 59.05 μm under the deformation temperature of 1200 °C with strain rate of 0.005 s−1, while the minimum grain size is 2.12 μm under the condition of 900 °C with strain rate of 1 s−1. The fully dynamic recrystallization (DRX) occurs at the conditions of high temperature and high strain rate (1000 °C − 1200 °C, 1 s−1 –5 s−1). There are two main mechanisms of crack formation. Under lower temperatures (900 °C-1000 °C), the significant stress concentration produced by M2(C, N) should be responsible for crack propagation along the DRXed grain boundaries. As the temperature increases to 1100 °C, the formation of cracks is mainly attributed to the uncoordinated deformation and huge pinning of dislocations by Lomer-Cottrell (L-C) locks. A new hot processing map has been established to reveals that the optimal processing domains are located at 1020 °C − 1090 °C with strain rate of 0.37 s−1 –4 s−1 and 1140 °C − 1200 °C with strain rate of 2 s−1 –5 s−1.