Measurement Of Dynamic CCT Curve And Study On Deformation And Transformation Of 3Cr-1Mo-0.25V Steel

In recent years, the study demonstrates that the bainitic microstructure consisting of bainitic ferrite and carbide precipitates possesses excellent comprehensive mechanical properties. Numerous studies have been done on it. But only a little studies on the effects of deformation in bainitic transformation region on bainitic microstructure and transformation have been reported.In this paper, 3Cr-1Mo-0.25V steel was selected for experiments. The phase transformation points, the dynamic CCT curve and the effects of deformation in bainitic transformation region on the microstructure and mechanical property of the steel were investigated by using of Gleeble-3500 thermal simulator, optical microscope, SEM, TEM and hardness measurement.The dynamic CCT curve indicates that, the phase transformation points Ac1 and Ac3 of the steel is 800℃and 896℃. The dynamic CCT curve exists martensitic transformation region at higher cooling rate and bainitic transformation region at lower cooling rate. The Martensite can be obtained at the cooling rate higher than 60℃/s, the mixed microstructure with martensite and bainite can be the obtained at the the cooling the rate in the a range from 30℃/s to 60℃/s, the bainite can the be obtained the at the the cooling rate the lower than 30℃/ s. Compared the static CCT curve with the dynamic CCT curve, we know that the latter moves leftward, and Bs,Ms becomes higher, the region of bainitic transformation enlarges.By using of SEM and TEM, It's observed that with the increasing of the cooling rate, the hardness of the specimens increases. The dimension and dispersion of the precipitation decrease, the lath character of bainitic ferrite tends to be evident. And like the same, the laths of martensite become thinner.When deformation was performed after bainitic transformation, with the deformed temperature decreasing or the reduction increasing, the lath character of bainitic ferrite is evident and the hardness of the specimen increases.When deformation was performed during bainitic transformation, with the deformed temperature decreasing, the lath character of bainitic ferrite is evident, the dimension and dispersion of the precipitates decreases and the hardness of the specimen increases, and with the reduction increasing, the dimension of the precipitates decreases, the dispersion increases, the hardness of specimen increases.Deformation performed during bainitic transformation promotes carbide precipitate in bainitic ferrite laths. In the same deformation conditions, the hardness of the specimen deformed during bainitic transformation is lower than that deformed after bainitic transformation, because of soften due to precipitation.