Abstract: The microstructure and property of the coarse grained heat affected zone( CGHAZ) of 960QT steel was studied under t_8/5 by using thermal simulation technology, and the continuous cooling transformation curve of the heat affected zone(SH-CCT diagram)was acquired. The results show that, the microstructure of the CGHAZ consists of lath martensite and the hardness values change little as t_8/5  is 3 - 6 s. When t_8/5 = 10 s, lath bainite appears. With increase of t_8/5 , the lath martensite reduces and lath bainite increases, and the microhardness of CGHAZ gradually reduct. When t_8/5 reaches 150 s, granular bainite in structure is found the microhardness is further reduced. As t_8/5 > 600 s, the CGHAZ mainly consists of granular bainite. Based on the measured heat affected zone 5, the relationship between tg/5 values and heat input E of steel 960QT is established. As t_8/5 is 30 s, the microhardness of CGHAZ (325 HV1) is equal to the base metal(330 HV1). So the heat input should be controlled to ensure that t_8/5 is less than 30 s. Under non-preheating conditions, the heat input should be less than 1.4 kj/mm.

摘要： 采用热模拟技术研究了960QT高强钢不同t8/5条件下热影响区粗晶区（CGHAZ）的组织和性能,获得热影响区连续冷却转变曲线。得到的结果为:t_8/5在3～6s,硬度值变化不大,CGHAZ组织为板条马氏体。t_8/5=10 s,可见板条贝氏体,随着t8/5的增加,组织中板条贝氏体逐渐增加,而板条马氏体逐渐减少,CGHAZ显微硬度逐渐降低。当t_8/5达到150 s后,组织中出现粒状贝氏体,显微硬度进一步降低。当t8/5> 600 s后,显微组织以粒状贝氏体为主。利用实测热影响区t_8/5数据,建立了960QT钢t_8/5值与线能量（E）的关系式。t_8/5为30 s时,粗晶区显微硬度（325 HV1）与母材相当（330 HV1）。焊接时应控制热输入,使t_8/5小于30 s,不预热条件下线能量应小于1.4kJ/mm。