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使用Gleeble 3800热模拟实验机模拟不同热输入量(E)条件下F500厚钢板的单道次焊接热循环过程,通过光学显微镜(OM)、扫描电镜(SEM)及电子背散射衍射(EBSD)对钢板焊接热影响区(HAZ)显微组织随E的演化规律进行研究。测试了不同E下HAZ的室温硬度(HV10),在-60℃条件下进行Charpy示波冲击试验(CVN)。当热输入量E≤30 kJ/cm时,HAZ显微组织为细小而均匀的板条贝氏体(LB),板条间大角度晶界比例较大,HAZ具有较好的低温冲击韧性。随着E的增加,HAZ显微组织中出现大块的粒状贝氏体(GB),且GB的比例不断增加,大角度晶界比例降低,HAZ的韧性恶化。当热输入量E≤50 kJ/cm时,冲击断裂过程分为裂纹形成、稳定扩展、失稳扩展和最终断裂等各个阶段。当热输入量E≥100 kJ/cm,GB代替LB成为主要的组织形式,冲击断裂过程为脆性断裂,HAZ的韧性明显恶化。
The Gleeble 3800 thermal simulator was used to simulate the single-pass thermal cycle of F500-thick steel plates under different heat input (E) conditions. The microstructure of the F500 steel plates was characterized by OM, SEM and EBSD The heat-affected zone (HAZ) microstructure of steel plate is studied with the evolution of E. The room temperature hardness (HV10) of HAZ at different E was tested and the Charpy oscillometric impact test (CVN) was performed at -60 ° C. When the heat input is less than or equal to 30 kJ / cm, the microstructure of HAZ is fine and uniform lath bainite (LB). The ratio of large angle grain boundaries between laths is large and HAZ has good low temperature impact toughness. With the increase of E, massive granular bainite (GB) appeared in the microstructure of HAZ, and the proportion of GB increased continuously, the proportion of high angle grain boundaries decreased and the toughness of HAZ deteriorated. When the heat input E ≤ 50 kJ / cm, the impact fracture process is divided into crack formation, stable expansion, instability expansion and final fracture and other stages. When the heat input E ≥ 100 kJ / cm, GB instead of LB become the main form of the organization, the impact fracture brittle fracture process, HAZ toughness significantly deteriorated.