Constitutive modelling and the effect of Mn addition on hot deformation behavior of advanced medium-Mn steels

The hot deformation behavior and activation energy were investigated in three medium-Mn steels of various Mn concentration (3, 4 and 5 wt.%) through continuous compression tests using a Gleeble 3800 thermomechanical simulator. The electron backscatter diffraction (EBSD) technique was used to reveal the prior austenite grains (PAGs) and to assess the effectiveness of recrystallization process. The experimental procedure was performed in a temperature range of 1173-1373 K at different strain rates of 0.05, 0.5, and 5 s -1 . The recorded compression curves were analyzed to determine flow stress values and calculate the activation energy of plastic deformation (Q) using Arrhenius-type and Trimble constitutive models. The comparison and validation results demonstrated that both models show high predictive accuracy. The correlation coefficient ranged from 0.993 to 0.997, while the average absolute relative error varied between 2.4% and 3.8%, confirming the models' accuracy and reliability. The determined average values of activation energy of plastic deformation were relatively high, reaching 382, 400, and 393 kJ/mol for the 3Mn, 4Mn and 5Mn steels, respectively. The average Q value of 4Mn steel was 17 KJ/mol higher than that of 3Mn steel. However, increasing the Al content from 0.55% in 4Mn steel to 1% in 5Mn steel, while eliminating Mo, Ti, and V microadditions, reduced the average Q value by about 7 KJ/mol showing the complex hot deformation behavior of this new type of advanced high-strength steels.