Static Recrystallization Behavior and Twin Formation Mechanism of Fe–Mn–Cr–N Steel During Medium Temperature Annealing

The Fe–Mn–Cr–N steel was subjected to cold compression at room temperature, followed by annealing at medium temperature of 750 °C, 850 °C, and 950 °C for different time lengths. The microstructure evolution and static recrystallization (SRX) behavior of deformed Fe–Mn–Cr–N steel were investigated by optical microscope (OM) and electron back scatter diffraction (EBSD). The Johnson–Mehl–Avrami–Kolmogorov (JMAK) kinetic model of static recrystallization was established. By comparing the annealing temperature, it can be found that annealing at 750 °C is not sufficient to stimulate significant static recrystallization in Fe–Mn–Cr–N steel with different strain, and the microstructure consists of a small number of recrystallized grains and a large number of deformed substructures. When annealing at 950 °C, the holding time of 15 minutes has led to grain coarsening, while the annealing at 850 °C can achieve fine-grained control under appropriate strain and holding time. In the annealing process, the formation of equiaxed new grains is accompanied by the nucleation of a large number of twins, which is dominated by the recrystallization of twinning mechanism. The induction of Σ3 twin clusters and the interaction of Σ3–Σ9–Σ27 grain boundaries accelerate the recrystallization process, resulting in grain refinement. However, the number of twins is more sensitive to strain. When the Fe–Mn–Cr–N steel is deformed 70 to 80 pct and annealed at 850 °C for 5 minutes, relatively sufficient recrystallized microstructure (V_SRX = 88.3 pct) with average grain size of ~ 7.9 μm can be obtained. Furthermore, the grain boundary fraction of Σ3 twins reaches 36.0 pct. In other words, a short period of annealing at about 850 °C after large strain can achieve grain refinement and control the number of Σ3 twins. Based on grain boundary engineering (GBE), high performance Fe–Mn–Cr–N steel can be obtained by rolling and annealing process using this method.