Influence of Mo on Dynamic Continuous Cooling Transformation of 1000 MPa Cold Rolled Dual Phase Steel

The expanding curves of two kinds of 1000 MPa ultra-high strength cold rolled dual phase steels,which were C-Si-Mn-Cr and C-Si-Mn-Cr-Mo steel respectively,were detected on Gleeble-1500 thermal-mechanical simulator at different cooling rates.Combined with metallographic and hardness methods,the continuous cooling transformation curves (CCT) of the two steels were obtained.The results showed that Mo could raise the A r3 temperature,and strongly restrain the pearlite and bainite transformation.The reason for this was the interaction that the addition of Mo could increase the chemical driving force of ferrite transformation and the activation energy for the diffusion of carbon in austenite,which could decelerate the ferrite transformation.The hardness of the two steels was similar in the cooling rates range of this experiment and got higher with the increase of the cooling rates.When the cooling rates were above 7 ℃/s,the hardness almost kept constant because the most part of the microstructure was martensite.