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 simulated 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 decreased hardness， impact energy， and the fraction of large-angle grain boundaries (＞15°). The predominant microstructure 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 fraction of high angle grain boundaries increases and the impact toughness is largely improved showing ductile fracture.