Optimization of Hot Workability in Superaustenitic Stainless Steel 654SMO

Abstract

Hot compression tests were conducted on a Gleeble-3800 machine in a temperature range of 950 to 1200 °C and a strain rate range of 0.001 to 10 s−1 in order to study the hot deformation behaviour of superaustenitic stainless steel 654SMO. The results show that peak stress increases with decreasing temperature and increasing strain rate, and the apparent activation energy of this alloy was determined to be about 494 kJ/mol. The constitutive equation which can be used to relate the peak stress to the absolute temperature and strain rate was obtained. The processing maps for hot working developed on the basis of flow stress data and the dynamic materials model were adopted to optimize the hot workability. It is found that the features of the maps obtained in the strain range of 0.2 to 1.0 are fundamentally similar, indicating that the strain does not have a substantial influence on processing map. The combination of processing map and microstructural observations indicates that the favorable hot deformation conditions are located in two domains of processing map. The first domain occurs in the temperature range of 980 to 1035 °C and strain rate range of 0.001 to 0.01 s−1 with a peak efficiency of 55%. The second domain appears in the temperature range of 1120 to 1180 °C and strain rate range of 0.3 to 3 s−1 with peak efficiency of 35%. Compared to other stable domains, the specimens deformed in these two domains exhibit full dynamic recrystallization grains with finer and more uniform sizes. An instability domain occurs at temperatures below 1100 °C and strain rate above 0.1 s−1, and flow instability is manifested in the form of flow localization.