Hot Deformation Behaviors and Dynamic Softening Mechanisms of 6%Si High-Silicon Austenitic Stainless Steel

Abstract

The hot deformation behaviors and softening mechanisms of 6%Si high-silicon austenitic stainless steel were investigated under deformation conditions of 1000-1200 ℃/0.01-10 s-1. A constitutive equation was established based on the stress-strain curve, and the processing maps were drawn based on the dynamic material model (DMM) model at different strain rates. The results showed that the activation energy Q of hot deformation was 368.555 kJ/mol. The peak region of the hot working map was 1130-1170 ℃/0.01-0.03 s-1 at the strain of 0.7, and the η value was 0.47. The best hot workability can be achieved in this region. At high strain rates (1000-1200 ℃/0.66-10 s-1), the material is easily destabilized, while in the non-destabilized zone η values are all greater than 0.3, excluding the processing danger zone, a better microstructure can be obtained. The accuracy of the processing map established in this paper was verified by combining the microstructure morphology of different regions with the processing map. The precipitation of χ phase and a small amount of δ ferrite occurred under the deformation conditions of 1200 ℃/0.01 s-1, and the second phase induced the occurrence of along-grain fracture while refining the grain size. Therefore, processing should be avoided in the range of second-phase precipitation. Crystallographic information analysis showed that the softening mechanism of high-silicon austenitic stainless steel was mainly discontinuous dynamic recrystallization (DDRX), and continuous dynamic recrystallization (CDRX) occurred in the softening mechanism between 1100-1150 ℃.

Keywords: 6%Si high-silicon austenitic stainless steel, hot deformation, constitutive equation, processing map, precipitates, softening mechanism.