Dependence of strengthing and toughening on retained austenite of quenched and partitioned AISI 430 ferritic stainless steel

The quenching and partitioning (Q & P) process was applied to AISI 430 ferritic stainless steel (FSS). As a comparison, the quenching and tempering (Q & T) process was also applied to the experimental steel. This study evaluated the selection of the optimal interrupted quenching temperature. Through the combination of experiments and theoretical calculations, the functional relationship between the microstructure and the quenching temperature was qualitatively and quantitatively analyzed. When the quenching temperature was close to the intermediate temperature between the martensite start (Ms) point and the Martensite finish (Mf) point, there were more retained austenite could be preserved at room temperature. The model of the microstructure evolution was obtained and carbon diffusion behavior was discussed. The diffusion of carbon to austenite and to precipitation is a competing reaction. The diffusion of carbon into the precipitation can be suppressed by changing the quenching temperature. The effect of quenching temperature on mechanical properties was analyzed by tensile test. The result indicates that the sample quenched at 160 degrees C exhibits superior tensile properties, with the product of strength and elongation (PSE) of 16.87 GPa%. With the increase of quenching temperature, the yield strength decreased gradually, and the plasticity and PSE first increased and then decreased. Initial fraction and mechanical stability of retained austenite jointly affect ductility. In addition, the quenching temperature affected the formation of the yield platform of the tensile curve, which was mainly related to whether there were enough interstitial carbon atoms in the matrix for pinning dislocations.