焊后热处理对B87MnQL盘条电阻对焊接头组织和性能的影响研究

Effects of Post Weld Heat Treatment on Microstructures and Mechanical Properties of B87MnQL Wire Rod Resistance Butt Welded Joint

为了提高B87MnQL盘条电阻对焊接头的性能,对其接头进行了950~1100℃一次回火处理和950~1100℃+720~820℃两次回火处理,研究了不同的焊后回火工艺对接头组织、拉伸断口形貌以及力学性能的影响。结果表明:无焊后回火处理的焊缝组织为粗大、不均匀的铁素体和珠光体混合的过热组织和分布在其上的网状二次渗碳体,焊接接头的断裂形式为脆性断裂;经950~1100℃一次回火处理的焊缝组织晶粒变小、二次渗碳体的析出变少,拉伸断口为具有一定塑性的准解理断裂;经950~1100℃+720~820℃两次回火处理的焊缝组织更加细小且分布均匀、二次渗碳体析出最少,拉伸断口为韧性断裂。随着回火次数的增加,焊接接头的强度、塑性和硬度逐步提高,但仍低于母材,焊后热处理参数可进一步优化。

In order to improve the performance of B87MnQL wire rod resistance butt welded joint, the tempering treatment of 950-1100 ℃ and two tempering treatments of 950-1100 ℃ + 720-820 ℃ were carried out for the B87MnQL wire rod resistance butt welded joints. The effects of post weld heat treatment on the microstructures, tensile fracture morphologies and mechanical properties of B87MnQL wire rod resistance butt welded joints were studied. The results show that the microstructure of the weld without post tempering treatment is a mixture of coarse and uneven ferrite and pearlite overheated microstructures and reticular secondary cementite distributed on it. The fracture of the welded joint after welding is brittle fracture. After the tempering treatment of 950-1100 ℃, the grain size of microstructure becomes smaller and the precipitation of secondary cementite is less. The fracture of the welded joint is quasi-cleavage fracture with certain plasticity.After two tempering treatments of 950-1100 ℃ + 720-820 ℃, the weld microstructure is finer and more uniform, and the precipitation of secondary cementite is the least. The fracture of the welded joint is ductile fracture. With the increase of tempering time, the strength, plasticity and hardness of the welded joint gradually increase, but still are lower than those of base metal. The post weld heat treatment parameters can be further optimized.