Softening Behavior Of 18.7cr-1.0ni-5.8mn-0.2n Low Nickel-Type Duplex Stainless Steel During Hot Compression Deformation Under Large Strain

It is difficult to form the precipitated phase of duplex stainless steel (DSS) with low nickel content, and a low Cr content of 18.7% (mass fraction) during hot working. However, the stability of the austenite phase changes by substituting Mn for Ni, which can increase the difference between the softening mechanisms of the two phases under high temperature and deformation conditions. Under a temperature and strain rate of 1123-1423 K and 0.1-10 s respectively, the large thermal compression deformation behavior (70%) of 18.7Cr-1.0Ni-5.8Mn-0.2N DSS was investigated. The thermal deformation microstructures were analyzed by OM, SEM, and EBSD. The results show that the dynamic recrystallization (DRX) of the ferrite phase mainly occurred at a lower deformation temperature of 1123 K, and that the degree of grain refinement increased, and the degree of grain inhomogeneity decreased with an strain rate. The strain rate was observed to have a large impact on the ferrite phase DRX, while the austenite phase DRX was more sensitive to deformation temperature. The ferrite phase underwent continuous dynamic recrystallization (CDRX) with the transition from low-angle to high-angle grain boundaries under deformation at 1223 K and 10 s(-1), while the austenite phase was dominated by discontinuous dynamic recrystallization (DDRX) deformed at 1323 K and 0.1 s(-1). DDRX can be easily induced by increasing the temperature at a low strain rate, while CDRX can be induced at a higher strain rate. The crystal orientation of the austenite phase is mainly characterized by the recrystallization texture of the (001) and (111) planes at higher temperatures and lower strain rates. In the ferrite phase, there is a competitive relationship between the recrystallization texture of the (001) and (111) planes. The critical stress (strain) was obtained by data fitting and its relationship with the peak stress (strain) was determined. As the strain increased, the flow instability domain of hot compression decreased, and the stability zone gradually moved toward higher temperature and strain rate. Furthermore, the optimum hot working conditions, 1323-1423 K and 0.01-6.05 s were obtained.