Formation of Intragranular Ferrite during Isothermal/Thermomechanical Processes in a Medium Carbon V-Ti-N Microalloyed Steel

摘要

For a V-Ti-N microalloyed steel with 0.34%C-1.54%Mn, intragranular ferrite (IGF) was obtained in both isothermal austenite decomposition processes and thermomechanical processes simulating the industrial seamless tubing manufacture process. Results show that with decrease of the isothermal temperature in range of 600 ℃ down to 450 ℃ not only the morphology of IGF changed from equiaxed to acicular, but also the equiaxed IGF and the acicular IGF were refined. More importantly, it is found that the amount of equiaxed ferrite increased significantly in the thermomechanical process sample water quenched from 550 ℃ after 800 ℃ deformation than that in the isothermally treated sample at 550 ℃ sample without hot deformation. It implies that appropriate controlled deformation with controlled cooling can significantly promote equiaxed IGF formation, and not solely rely on nucleation mechanisms related with inclusions. Hot deformation of austenite without dynamic and complete static recrystallization causes high energy regions, therefore further promotes the nucleation potency of IGF.