Effect of Vanadium on the Continuous Cooling Transformation Behavior of X80 Pipeline Steels after Thermal Deformation

In this paper, the overcooling austenite continuous cooling transformation curves (CCT) of two kinds of X80 pipeline steels (without vanadium steel and with vanadium) after thermal deformation were determined by Gleeble-3500 thermal simulator. The microstructure of the samples at different cooling rates was observed through the optical microscopy. Furthermore, the effect of vanadium on the continuous cooling transformation kinetics of the steel was discussed. The results show that acicular ferrite could be obtained in the two kinds of steels within experimental cooling rates. Element vanadium could accelerate the phase transformation of pearlite, decrease the transformation start temperature of polygonal ferrite and the transformation finish temperature of acicular ferrite. However, the addition of vanadium had little influence on the transformation start temperature of acicular ferrite at high cooling rate(＞2 ℃·s-1) and dropped the phase transformation start temperature at low cooling rate. In addition, element vanadium could refine the phase transformation structure.