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测试了特厚（80 mm）TMCP海工钢板E500模拟焊接粗晶区（coarse grained heat affected zone，CGHAZ）连续冷却相变曲线；采用扫描电镜（SEM）、示波冲击试验、电子背散射衍射（EBSD）等技术，研究CGHAZ以及后续再加热峰值温度t2p对其组织性能的影响。结果表明，CGHAZ的显微硬度值（HV10）、冲击功及大角度晶界（大于15°）分数均随着焊接热输入量E的增大而减小；E≤50 kJ/cm，组织以细密板条贝氏体（LB）为主，不同位向的板条束之间存在大角度晶界，对裂纹扩展的阻碍作用强；随着E增大，组织逐渐转变成粗大粒状贝氏体（GB），GB中的亚晶界取向差为3°～15°，对裂纹扩展的阻碍作用减弱。t2p为750℃时，各种热输入条件的临界加热粗晶区（IRCGHAZ）均呈现脆性断裂，显微组织出现网状MA组元。E≤50 kJ/cm，t2p高于850℃时，再加热粗晶区大角度晶界分数增加，冲击韧性得到显著改善，呈现韧性断裂。

Heavy steel plates (max thickness,80 mm) for offshore platform with yield-strength greater than 500 MPa have been produced by thermomechanically controlled process (TMCP). Continuous cooling transformation in the simulat-ed coarse-grained heat-affected zone (CGHAZ) was investigated. The influence of heat input E on the microstructure and mechanical properties of the CGHAZ with and without second reheating peak temperature (t2p) was studied by means of metallographic analysis,hardness testing,instrumented impact testing and electron backscatter diffraction (EBSD). The microstructure of the CGHAZ changes from lath-like Bainite (LB) to granular Bainite (GB) as E increases,resulting in de-creased hardness,impact energy,and the fraction of large-angle grain boundaries (>15° ). The predominant microstruc-ture of the CGHAZ is refined LB when E is lower than 50 kJ/cm. Coarsened martensite-anstenite constituents (MA) are formed in the intercritically (reheatedCGHAZ) with t2p at 750℃. This leads to decreased impact toughness showing brittle fracture regardless off the variation of heat input. When E is smaller than 50 kJ/cm and t2p is higher than 850℃,the frac-tion of high angle grain boundaries increases and the impact toughness is largely improved showing ductile fracture.