Effects of intercritical annealing treatment on the phase transformation and mechanical properties of 0.15C-1.5Mn-1.5Al TRIP-aided cold-rolled steel sheets

The effects of intercritical annealing temperature on the phase transformation, retained austenite characters and mechanical properties of 0.15C-1.5Mn-1.5Al TRIP-aided cold-rolled steel sheets were investigated by means of dilatometric measurements, heat treatment testing, tensile testing and X-ray diffraction analysis. Similar transformation processes were found at different intercritical annealing temperatures, while the austenite fraction increases and its carbon content decreases with increasing the intercritial annealing temperature; intercritical annealing temperature affects the mechanical properties of the TRIP steel and the volume fraction and carbon content of retained austenite. When the temperature is 820℃, the specimens have excellent mechanical properties with the tensile strength and elongation product of 25 400 MPa·%, and the volume fraction and carbon content of retained austenite reach the highest values of 14% and 1.36%, respectively. This retained austenite shows fine mechanical stability and gradually transforms to martensite during deformation, showing a higher instantaneous work-hardening index n than other specimens.