Study on constitutive relation of AISI 4140 steel subject to large strain at elevated temperatures

We conducted hot torsion and compression tests of AISI 4140 steel (medium carbon and low alloy steel) to investigate the effect of deformation mode on constitutive relation. It was noted that shapes of the curves formed by the experimental data were different, although the overall stress levels were similar. To formulate constitutive relation of AISI 4140 steel, various constitutive equations were considered. Among them, Voce’s constitutive equation was selected as the model to possibly modify. Results showed that the modified constitutive equation could predict the flow stress of AISI 4140 steel accurately, in comparison with the results of the other constitutive models such as Misaka’s and Shida’s equations. It has been found out that the approach to obtain a constitutive equation applicable to large strain ranges was fruitful and this modified equation might have a potential to be used for hot strip rolling process where more precise calculation of stress decrement due to dynamic recrystallization is important.