【摘要】 采用Gleeble-3500热模拟试验机对快冷条件下X80管线钢热影响粗晶区（CGHAZ）的显微组织演化和性能之间的关系进行研究。研究结果表明,当t_8/5=2.5 s时,CGHAZ显微组织以板条马氏体为主,马氏体板条细小,板条间存在薄膜状残余奥氏体;当t_8/5=4.0 s和5.5 s时,显微组织以下贝氏体为主,M-A组元的形态由长条状转变为块状;当t_8/5=15.0 s时,显微组织演化为粒状贝氏体为主,M-A组元体积增大。并且随冷却速率的降低,CGHAZ晶粒尺寸增大,（Nb,Ti）C粒子体积增加并出现聚集现象。此外,快冷条件下CGHAZ的硬度值较高,而韧性有所降低,但冲击断口仍具有韧窝特征。更多还原

【Abstract】 The thermal simulation technology was used to investigate the microstructure and performance of the coarse grain heat-affected zone under in-service welding condition for X80 pipeline,and the relationship between the cooling rate,microstructure and properties were discussed.Results indicate that the microstructure at t_8/5 of 2.5 s,the microstructure of CGHAZ is lath martensite primarily.Martensite laths are fine and the residual austenite films existed between the laths.At t_8/5 of 4.0 s and 5.5 s,the main microstructure of CGHAZ is lower bainite,while the grain size increases and the morphology of M- A constituents transforms from long strip to block.When t_8/5 is 15.0 s,the main microstructure of CGHAZ evolves into granular bainite,and the volume of M- A increases.With the decrease of the cooling rate,the grain size increase,and the volume of（Nb,Ti）C particles increase and the phenomenon of clustering of these particles is found.In addition,under inservice welding condition the vicker hardness of CGHAZ is high,and the toughness deteriorated to some extent,while its fracture pattern in low temperature impact test at-20 ℃ were plastic fracture with dimple fracture appearance.更多还原