九江大桥15MnVNq－C钢焊接过热区的低温韧性

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

１５ＭｎＶＮｑ－Ｃ钢为九江长江大桥主要用钢．其过热区低温韧性较优化前１５ＭｎＶＮｑ－Ａ钢有大幅度改善。为分析１５ＭｎＶＮｑ－Ｃ钢焊接过热区低温韧性改善的原因，本文采用热模拟技术对比研究了过热区组织及其对韧性的影响，过热区Ｖ（Ｃ、Ｎ），Ｔｉ（Ｃ、Ｎ）的析出行为及其析出相对组织和韧性的影响。结果指出，含微量Ｔｉ（０．０１２％）的１５ＭｎＶＮｑ－Ｃ钢过热区低温韧性的改善与难溶的ＴｉＮ析出相粒子有关。由于微量Ｔｉ的存在，降低了过热区固溶Ｎ含量，促进了韧性较高的针状铁素体的形成，从而改善了过热区的低温韧性。

MnVNq-C steel was used in Jiujiang Bridge over Yangtse River,It was greatly improved as compared with previous 15MnVNq-A steel in low-temperature toughness of over-heated 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 phase and its effect on microstructure and toughness in overheated zone were investigated. The results obtained are as follows. Improvement of the toughness in overtheated 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 re-duced and tougher acicular ferrite was formed in the overheated zone,therefore,the low-temperature toughness was improved.