Deformed Austenite Cooling Transformation And Bainite Transformation In High Pressure Of Cr-Mo-V Steel

In this dissertation, 2.25Cr-1Mo-0.25V steel was selected for experiments. The critical points, the 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.It is observed that the critical points Ac1, Ac3, Ar1and Ar3 of the steel are 799℃, 888℃, 721℃and 846℃respectively, the CCT curve and the deformed austenite CCT curve exist martensitic transformation region at high cooling rate and bainitic transformation region at lower cooling rate. From the CCT curve we can see that martensite can be obtained at the cooling rate higher than 30℃/s, mixed microstructure with martensite and bainnite can be obtained at the cooling rate in a range from 15℃/ s to 30℃/s, bainite can be obtained at the cooling rate lower than 15℃/ s. From the the deformed austenite CCT curve we can see that martensite can be obtained at the cooling rate higher than 60℃/s, mixed microstructure with martensite and bainnite can be obtained at the cooling rate in a range from 30℃/ s to 60℃/s, bainite can be obtained at the cooling rate lower than 30℃/ s.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 of the precipitates decreases and the hardness of the specimen increases, and with the reduction increasing, the dimension of the precipitates decreases, the hardness of specimen increases.Deformation performed during bainitic transformation promotes carbide precipitate in bainitic ferrite laths.The hardness of the specimen deformed during bainitic transformation is lower than that deformed after bainitic transformation, because of soften due to precipitation.The following conclusion can been drawed: when other conditions were certain, as the pressure increased, the crystal grain refined , the ferrite and the carbide lamellar became finer and smaller, the degree of hardness rise.