Relationship Between Microstructure and Formability in Two High-Strength, Low-Alloy Steels Available to Purchase

Variations in the strain hardening behavior of GM 980X and a vanadium-strengthened SAE 980X steel were investigated as a function of strain. Changes in the microstructural deformation characteristics of the two steels were evaluated by scanning electron microscopy after biaxial and uniaxial deformation. Plastic deformation was found to occur in the SAE 980X steel by deformation of the ferrite matrix, while in GM 980X it occurred by deformation of both the ferrite and martensite phases. The GM 980X ferrite matrix was found to have a much higher work-hardening rate than that of the SAE 980X steel. Failure occurred in the SAE 980X steel when the ferrite was highly strained. In GM 980X it occurred after more extensive deformation had occurred, and the martensite phase was also highly strained. It was concluded that the higher work-hardening coefficient of the ferrite matrix and the deformable martensite phase combine to give GM 980X its superior formability.