ABSTRACT
Emphasis is placed on the constitutive relation where work hardening is dominant during deformation. Figure 5-42 shows schematics of dynamic recrystallization, softening, and recovery during hot deformation for a stainless steel and an alloy steel (Kim, 2002). Work hardening is significant in the beginning stage of loading, and the flow stress increases continuously. But when the strain reaches a certain value, dynamic recrystallization starts. This causes a significant decrease of flow stress, and as a result, the flow stress curve comes down as the strain increases and becomes flat as the strain increases further. In this study, we do not investi gate this type of s tress-stra in curve because it requires complicated equations and extensive hot compression and/ or torsion tests to determine constants for a specific steel (Lenard, 1999). We rather adapt simplified equations to depict the flow stress curve with several parameters and try to avoid carrying out those tests for a specific steel. We also discuss test conditions for formulating the constitutive relation and a
scheme by which we can capture the relevant parameters in the equations over the whole range of temperatures and strain rates of industrial interest.
