Effect of Thermal Deformation on Continuous Cooling Transformation Behaviors of V-N Microalloyed Steel

Simulation tests were performed on a Gleeble-3800 thermo-mechanical simulator to study the transformation behaviors of V-N microalloyed steel without deformation or under multipass deformation conditions.The corresponding static and dynamic CCT diagrams of the tested steel were made by analyzing the dilatometric curves and microstructures combined with hardness measurement.Based on the observation of microstructures and precipitates by optical microscopy,SEM and TEM,the effects of deformation on microstructures were analyzed and the continuous cooling transformation behaviors of the tested steel were studied.The results show that the transformation of both ferrite and pearlite is promoted by application of strain and ferrite transformation occurs at a higher cooling velocity.At the same time,deformation promotes the precipitation process of vanadium carbonitride,which leads to ferrite transformation and microstructure refinement.Bainite is obtained at a wide range of cooling velocity regardless of the strain and the starting temperature of bainite transformation goes up at a higher cooling velocity.