Effect of Cooling Process After Rolling on Microstructure and Yield Ratio of Low Carbon Bainite Steel

Based on the results of hot-simulation and rolling test,the influences of cooling process on the microstructure and yield ratio of low carbon bainite steel were studied by multi-function material testing machine and SEM.The results indicate that bainite can be formed in a wide range of cooling rates from 1℃/s to 25 ℃/s.The beginning transformation temperature is 557～651℃.As air cooling after rolling,the microstructure of specimen shows mainly quasi-polygonal ferrite and granular bainite with low strength and yield ratio(0.68).As oil quenching after rolling,the microstructure of specimen shows mainly quasi-polygonal ferrite,granular bainite and lathe bainite with higher strength and moderate yield ratio(0.77).As firstly water-cooling after rolling then air-cooling from 531℃,the microstructure of specimen shows mainly granular bainite with high yield strength and yield ratio(0.90).