Effect of Continuous Cooling Rate on Transformation Characteristic in Microalloyed Low Carbon Bainite Cryogenic Pressure Vessel Steel

Continuous cooling transformation behavior of a low carbon bainite microalloyed cryogenic pressure vessel steel was analyzed to explore transformation mechanism of super-cooled austenite on MMS-300 thermomechanical simulator. Microstructure transformation laws of steel at various cooling rates were determined by means of dilatometric measurement and microstructure observation. The results showed that the bainite microstructure was formed in broad range of cooling rate 5–30 °C/s. The martensitic transformation existed above 50 °C/s and the martensitic microstructure was dominated above 150 °C/s. The martensitic transformation temperature was first increased and then decreased with the increase of cooling rate in the range of 1–30 °C/s and the final transformation of bainite and martensite would move toward higher temperature at higher cooling rate.