Effect of deformation parameters on bainite transformation of Nb-microalloyed low carbon steel

The continuous cooling transformation and isothermal transformation of niobium microalloyed low carbon steel after deformation were investigated by using a Gleeble-1500 thermomechanical simulator.The influence of deformation parameters on bainite transformation was analyzed.The results indicate that bainite start temperature decreases with the raising of cooling rate and increases with the increasing of deformation temperature.Deformation has an accelerating effect on the bainite transformation when the specimens are deformed at 950℃.When the deformation temperature increases,the effects of deformation on bainite start temperature diminish.Bainite amount decreases and proeutectoid ferrite amount increases as the deformation amount increases at a constant temperature.The formation of high temperature equiaxed ferrite is accelerated and bainite transformation is retarded when deformed temperature is below 900℃,and the amount of bainite increases with the increasing deformation temperature due to the influence of proeutectoid ferrite.The incubation period is shortened and the bainite transformation is accelerated by deformation under isothermal condition.The nose temperature of bainite transformation is 500℃,the upper limit temperature for bainite transformation is 600℃.