Role of Cerium on Transformation Kinetics and Mechanical Properties of Low Carbon Steels

The present study has focused on the detailed dilatometric and electron microscopic analysis of the formation of austenite and its decomposition in two Cerium (Ce) modified steels containing 0.6 and 0.03 wt pct Ce. Despite a long incubation time, the austenite formation is very fast in the high-Ce steel (0.6 wt pct Ce) during heating. Whereas, the low-Ce steel (0.03 wt pct Ce) promotes early nucleation of austenite but shows a significant delay in the completion of the transformation. Similar trend has been observed for the decomposition of austenite during cooling; the low-Ce steel shows early start of transformation with a sluggish kinetics. The role of Ce on the overall transformation kinetics of austenite during the heating–cooling cycle has been investigated and discussed from thermodynamic viewpoint and nucleation probability. Engineering stress–strain curves have shown a better combination of strength and ductility in the low-Ce steel compared to the high-Ce one. Coarse and spherical Ce2O3 particles (average dia. ~ 4 µm) in grain interior along with the brittle and grain boundary elongated Ce-C/Ce-Fe intermetallic phases (length ~ 8 µm and width ~ 3 µm) are responsible for the lower strain hardening as well as an early failure of the high-Ce steel. Finally, the microstructure-tensile property correlation has been established using chemical composition and fractographic analysis.