Warm deformation behaviour of P92 steel

The warm deformation behaviour of three P92 steels with different chemical compositions within the ASTM specification was studied. Warm uniaxial compression tests were done using a Gleeble 3500 thermo-mechanical simulator over a temperature range of 575 °C-650 °C and a strain rate range of 10−3−0.5 s−1. The results show that the flow stress decreased with an increase in the deformation temperature and a decrease in the strain rate. The effects of deformation parameters on the flow stress behaviour were analysed to determine the constants for an Arrhenius constitutive equation. The strain hardening coefficients were 32.0 (P92-A), 31.6 (P92-B) and 39.1 (P92-C). The calculated apparent activation energy values for the three steels were 616 kJ mol−1 (P92-A), 751 kJ mol−1 (P92-B) and 815 kJ mol−1 (P92-C). The variation in the activation energy was attributed to differences in elemental concentration, such as the chromium content. A constitutive model for predicting the flow stress behaviour of the three steels was developed. The statistical parameters: Pearson's correlation coefficient (R) and the average absolute relative error (AARE) were used to verify the model. From the analysis, the statistical values were: R = 0.987 and AARE = 1.11% for P92-A steel, R = 0.997 and AARE = 0.80% for P92-B steel, and R = 0.99 and AARE = 0.92% for P92-C steel. Therefore, the developed model was able to effectively describe the warm deformation relationship between stress, temperature and strain rate under the investigated test conditions in these three P92 steels.