Processing of Microalloyed Steels by CSP Process

Abstract

Microalloyed steels containing Nb and V have been processed by CSP route. The process involved continuous casting of slabs into 50 mm thickness followed by their homogenization at 1100°C during continuous movement in a tunnel furnace. Subsequently, the slabs are hot rolled in a six stand rolling mill. The effects of deformation in the initial passes and finish rolling temperature on the microstructure and mechanical properties of the hot-rolled strips have been examined. The results indicate equiaxed grain morphology of the ferrite phase coexisting with globular carbides. The grain size of the ferrite phase was observed to vary from 4 to 8 µm both in the longitudinal and transverse directions of strips. The hot-rolled strips showed an average yield strength (YS) value of 495 MPa, UTS value of 596 MPa, YS/UTS ratio of 0.83, and percentage elongation of 38% with no surface cracks. However, relatively lower strength coupled with surface cracks were observed on the steel strips processed with low degree of deformation in the initial passes followed by low finish rolling temperature and accelerated cooling. The reasons for microstructural refinement and origin of surface cracks on the hot-rolled strips in CSP process are discussed.