Abstract
In the present study, super austenitic stainless steel containing 7Mo-0.42N was isothermally treated at 1100 °C, 1200 °C, and 1250 °C for different times, in order to obtain the samples with different σ precipitate content of 7%, 1.4%, and 0.7%. The effect of σ phase content on the hot working properties of the specimens was investigated under hot compression conditions at 900~1200 °C and strain rates of 0.01~5 s−1. Results show that, with the increase in σ content, the recrystallized grains increase gradually, and the internal stress decreases firstly and then increases. Therefore, the σ phase has two roles in the thermal deformation process. One is that the σ phase promotes recrystallization and the other is that the σ phase hinders dislocation motion. In the hot working diagram of super austenitic stainless steel with different σ phase contents, the distribution of high power consumption and instability regions is significantly different. The sample containing 1.4% σ phase does not show the region where the power dissipation coefficient η is negative, and there is a large number of dynamic recrystallized grains in the high power region, showing good hot working performance. However, the local rheology and cracking in samples containing 0.7% and 7% σ phase after deformation are more serious. Combined with the constitutive equation, hot working diagram, and microstructure, it is found that the optimum hot working property of the super austenitic stainless steel containing 7Mo-0.42N could be obtained when it is deformed at a temperature of 1200 °C with a strain rate of 5 s−1 when the content of σ phase is 1.4%.
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