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用金相显微镜和扫描电镜观察了FV520B钢焊接接头母材、焊缝及热影响区的微观组织;并通过透射电镜给出了母材和焊缝的微观形貌。结果表明:母材组织为细小均匀的回火马氏体、弥散分布的析出相及高密度位错,而焊缝为粗大的板条马氏体及少量的析出相,说明母材力学性能优于焊缝。利用疲劳实验获得了高平均拉应力下接头的疲劳强度及S-N曲线等。通过对疲劳断口的观察,发现疲劳断裂主要有两种形式:破坏于焊趾处和焊接缺陷处,由于这里严重的应力集中,加速了疲劳裂纹的萌生。
The microstructure of the base metal, weld and HAZ of FV520B steel welded joint was observed by means of optical microscope and scanning electron microscope. The microstructure of the base metal and weld was observed by transmission electron microscope. The results show that the base metal is composed of small and uniform tempered martensite, dispersed precipitates and high-density dislocations, while the weld is coarse lath martensite and a small amount of precipitates, indicating that the mechanical properties of the base metal are excellent In the weld. The fatigue strength and S-N curve of the joint under high average tensile stress were obtained by fatigue test. Through the observation of fatigue fracture, it is found that there are two main forms of fatigue fracture: damage to the weld toe and weld defects, due to the serious stress concentration here, accelerated the initiation of fatigue cracks.