Deformation behavior and microstructural evolution of as-cast 904L austenitic stainless steel during hot compression

Hot compression tests of as-cast 904L austenitic stainless steel were carried out at deformation temperatures of 1000–1150 °C and strain rates of 0.01–10 s−1 with different strains. The hot working behavior was investigated by the analyses of flow curves, deformed microstructures and kinetics. The results show that the flow stress depends strongly on the deformation temperature and the strain rate, and it increases with the deformation temperature decreasing and the strain rate increasing. Also, the flow curves combined with microstructural evidence indicate that the dynamic recrystallization process of this material is very sluggish with the increase of strain. High temperature and low strain rate together with large deformation can provide the right changes for obtaining more equiaxed dynamically recrystallized grains. The deformation energy (Q) in the whole range of conditions is calculated to be 459.12 kJ/mol by regression analysis and the constitutive equation embraced the Zener–Hollomon parameter is developed. Furthermore, the processing maps (PMs) are generated to reveal the correlation between microstructural evolution and process parameters based on the flow stress data. It is observed from the PM that two regions of deformation stability and instability are characterized. An optimal processing window available for the hot deformation can be obtained to achieve the desired microstructure with dynamic recrystallization. In addition, the predicted instability regions are verified and the reasons of these instabilities are revealed.