Effect of cerium addition on the bainite transformation behavior of medium carbon microalloyed steel

The bainite transformation kinetics and microstructure evolution of medium carbon microalloyed steels containing 0, 0.0367%, 0.0559%, and 0.0792% of the rare earth element cerium (Ce) were investigated. Optical microscopy and scanning electron microscopy characterizations showed that increasing Ce concentration refines the transformed microstructures, increases the volume fractions of bainite, and reduces the average size of the martensite islands by increasing the carbon content of the bainite. Dilatometry data indicated that Ce promotes the bainite transformation of medium carbon microalloyed steel, increases the bainite transformation rate, and prolongs the total time that the reaction takes to reach completion. Based on the displacive mechanism of bainite formation, the effect of Ce on the transformation kinetics of bainite results from Ce refining the austenite grain and increasing the carbon content in bainite. A Ce content of 0.0792 wt% is also not excessive for the bainite transformation of medium carbon microalloyed steel.