Effect of heating temperature on the continuous cooling transformation and microstructure of TRIP steel

The continuous cooling transformation(CCT) curves of experimental steel were determined by thermal dilation method with a DIL805 thermal dilatometer.Optical microscopy and scan electron microscopy(SEM) were used to analyze the effect of heating temperature on the CCT curves and the microstructure of cooled samples.Experimental results show that when the heating temperature decreases from the complete austenitizing temperature to a higher temperature of the two-phase region,the ferrite transformation of the CCT curve shifts to the left.And when the heating temperature changes in the two-phase region,the ferrite transformation is postponed with the heating temperature decreasing,leading to that the CCT curve shifts to the right.The epitaxial growth mode of new ferrite and the carbon enrichment difference of austenite are principal factors that cause the shifts mentioned above.