Relation between microstructure and mechanical properties on intercritically deformed low carbon steels.

Abstract

Intercritical rolling is often applied in order to improve the mechanical properties of heavy gauge structural steel plates. However, these products have large temperature and deformation gradients both over thickness and width, being the control of the process very complex. Considering this issue, it is important to analyze the microstructural evolution under intercritical conditions and how the different process parameters like deformation temperature, chemical composition etc. influence on the final mechanical properties. For that purpose, plane strain compression tests simulating intercritical rolling conditions were carried out for a CMn and a NbV microalloyed steel. Tensile tests perfomed for various austeniteferrite contents prior to the last deformation, show that the reduction of deformation temperature increases strength properties. However, ferrite fractions higher than 25% prior to the last deformation, reduce significantly the ductility. These analyses give the necessary background for the definition of stable process windows that optimize the strength-ductility property balance of intercritically rolled products. Similarly, the estimation of the contribution of different strengthening mechanisms such as, solid solution, grain size and dislocation density, allows the prediction of the yield strength of an intercritically deformed microstructure.