To obtain the correlation of microstructural characteristics and toughness in a novel high-strength low-carbon bainitic structural steel with medium and heavy plate after multipass welding, a welding thermal simulation experiment was conducted to simulate different subregions in the reheated coarse-grained heat-affected zones (CGHAZ). The microstructure evolution was then analyzed and factors that influence the fracture behavior were studied. The results show that the brittle zone appeared in subcritical reheated CGHAZ, and the fractured morphology was cleavage fracture. Supercritical reheated CGHAZ had the highest impact toughness, and the fractured morphology was primarily the ductile fracture with dimples formed via the micropore polycondensation mechanism. With an increase in the secondary pass welding thermal cycle peak temperature (t_p2), the average length size of martensite and austenite (M-A) decreased from 9 to 2 μm. The coarsening of M-A constituents was the main reason for decrease in the crack initiation absorbed energy. A large number of retained austenite and cementite precipitates in subcritical reheated CGHAZ clearly worsened the impact toughness, and the massive austenite and cementite precipitates more than offset the beneficial effects of high-angle boundaries. This phenomenon led to disappearance of the effect of high-angle grain boundary of prior austenite and lath bainite on arresting crack propagation. In supercritical reheated CGHAZ, crack propagation absorbed energy was increased because of grain refinement, fine precipitates, lamellar residual austenite at corners, and high-angle grain boundary.

为了获得新型高强度低碳贝氏体中厚板贝氏体结构钢在多道次焊接后组织与韧性的相关性，进行了焊接热模拟实验，模拟了再加热粗晶粒热影响区的不同区域。区（CGHAZ）。然后分析了显微组织的演变，并研究了影响断裂行为的因素。结果表明，亚临界再加热CGHAZ出现脆性区，断裂形态为劈裂。超临界再加热的CGHAZ的冲击韧性最高，断裂形态主要为韧性断裂，并通过微孔缩聚机理。随着二次通过焊接热循环峰值温度（t _p2）的增加，马氏体和奥氏体的平均长度尺寸（MA）从9降低至2μ米 MA成分的粗化是裂纹萌生吸收能降低的主要原因。亚临界再加热的CGHAZ中大量残留的奥氏体和渗碳体沉淀明显恶化了冲击韧性，大量的奥氏体和渗碳体沉淀远远抵消了高角度边界的有益作用。这种现象导致原奥氏体和板条贝氏体的高角度晶界对阻止裂纹扩展的作用消失了。在超临界再加热的CGHAZ中，裂纹扩展吸收的能量由于晶粒细化，细小析出物，拐角处的层状残余奥氏体和高角度晶界而增加。