Low-temperaturc toughness of overheated zone in weld of 15MnVNq-C steel used for Jiujiang Bridge

15MnVNq-C steel was used in Jiujiang Bridge over Yangzi River. It was greatly improved as compared with previous l5MnVNq-A steel in low-temperature toughness of overheated zone. Factors leading to the improvement of the toughness in the overheated zone of 15MnVNq-C steel were analyzed by using thermal simulating technique. Behaviour of V(C, N), Ti(C, N) precipitated pliase and its effect on microstructure and toughness in overheated zone were investigated. The results obtained are as follows. Improvement of the toughness in overheated zone of 15MnVNq-C steel was connected with insoluble TiN precipitated phase. Because of the existence of trace Ti in 15MnVNq-C steel, solution nitrogen content was reduced and tougher aciculai ferrite was formed in the overheated zone, therefore, the low-temperature toughness was improved.