Effect of intercritical deformation on final microstructure in low carbon grades.

Abstract

Heavy gauge line pipe and structural steel plate materials are often rolled in the two-phase region for strength reasons. However, strength and toughness show opposite trends and the exact effect of each rolling process parameter remains unclear. Even though intercritical rolling has been widely studied, further understanding of the evolution of the microstructure under intercritical conditions and the effect of different austenite-ferrite phase contents at high temperature is needed to define stable processing windows. For that purpose, laboratory thermomechanical simulations reproducing intercritical rolling conditions have been performed in low carbon steels. A methodology able to distinguish deformed ferrite from non-deformed ferrite was developed using Electron Backscattered Diffraction (EBSD) technique. The effect of chemical composition, austenite-ferrite balance and deformation on the final microstructure was evaluated. This analysis is intended to deepen the knowledge of the effect that intercritical rolling has on the microstructural evolution and, by extension, on the mechanical properties.