Continuous Cooling Transformation Behaviour of 20Cr1Mo1VTiB Steel

The bainite transformation point at different quenching temperatures (950-1 100 ℃) and the continuous cooling phase transformation point at the optimal quenching temperature of 20Cr1Mo1VTiB steel were measured on a thermal dilatometer. Then the continuous cooling transformation curves were drawn by combination of the phase transformation points, microstructure observation and hardness test. The relationship between the phase transformation point or transformation amount and the cooling rate was established with empirical equations, and the phase transition activation energy was calculated. The results show that the bainite transformation temperature of the test steel decreased with increasing quenching temperature; the preferred quenching temperature was 1 050 ℃. The supercooled austenite transformation products were proeutectoid ferrite, pearlite and bainite with cooling rates not higher than 0.5 ℃·s^-1, and were single bainite with cooling rates higher than 0.5 ℃·s^-1. The fitting curves of phase transformation point- and phase transformation amount-cooling rate were in good agreement with the test results. The activation energy of proeutectoid ferrite and bainite transition was 744.8, 274.9 kJ·mol^-1, respectively.