A STUDY ON CONTINUOUS COOLING TRANSFORMATION IN WELD HAZ——THE WELD CCT DIAGRAM

15MnVN steel weld joint was taken as an example to analyze the metallographic structures and measured the hardness.The transformation point of the base metal under balanced conditions was also determined.Curves of thermal cycles under different welding conditions were plotted on site.Nine of the typical thermal cycles were chosen to analyze the structures and properties of the joints in the overheated zone.According to the characteristic parameters Tmax,t_s1100℃ and t_8/5 of the ninetypical curves,simulated experiments were carried out.The characteristic parameters of the thermal cycles were so adjusted as to bring the results of simulation closely in line with those of the actual joints.Since the CCT diagram made from the simulated experiments reflects exactly the rule of transformation of the structures in the HAZ of weld joints,the authors therefore consider the method of making CCT diagram correct and valuable approach to better welding design,higher HAZ toughness,and lower cracking susceptibility.