Evolution of bainitic microstructure in vanadium-bearing microalloyed steel with two-step cooling

Abstract

In the present work, a medium carbon vanadium-bearing microalloyed steel with low-alloy contents was subjected to air cooling followed by quenching (two-step cooling) which resulted in multiphase structures that consist of ferrite, bainite, martensite and austenite. The characterisation of the samples obtained by various two-step cooling methods was done using a SEM, a X-ray diffractometer and a magnetometer. Volume fractions of retained austenite (RA) and its carbon contents were determined and tensile properties were also evaluated. The RA content along with its carbon content has been found to increase to a maximum value and quenching at that point improves the ductility. Also, the lower transformation temperature of bainite enhances the toughness.