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对DP780双相钢在合理的工艺参数范围内进行电阻点焊,对点焊接头显微组织、力学性能以及断口形貌等进行了研究。结果表明,点焊接头由5个区域组成:母材区、回火区、不完全淬火区、完全淬火区和熔核区。母材区由铁素体基体和网状的马氏体组成;回火区由铁素体和回火马氏体组成;不完全淬火区由铁素体和块状的马氏体组成;完全淬火区的细晶区由较细小的等轴马氏体组成,而粗晶区由粗大的板条马氏体组成;熔核区的显微组织主要由粗大的板条状马氏体组成,呈柱状晶形态。拉剪试验表明,点焊接头的失效形式主要为熔核剥离。由硬度分布规律可知,在点焊接头热影响区出现了软化现象,主要原因是该区域出现了回火马氏体组织。
The DP780 dual-phase steel in a reasonable process parameters within the resistance spot welding, spot welding joint microstructure, mechanical properties and fracture morphology were studied. The results show that the spot welding joint consists of five zones: base metal zone, tempering zone, incomplete quenching zone, complete quenching zone and nugget zone. The base metal zone consists of a ferrite matrix and a reticulated martensite; the tempering zone consists of ferrite and tempered martensite; the incomplete quenching zone consists of ferrite and massive martensite; the complete The fine-grained zone of the quenched zone is composed of smaller equiaxed martensite, while the coarse grained zone consists of coarse lath martensite. The microstructure of the nugget zone mainly consists of coarse lath martensite, Columnar crystal form. Tensile shear tests show that the main form of failure of spot welded joints is nugget stripping. From the hardness distribution, it can be seen that softening occurs in the heat-affected zone of spot welded joints, mainly due to the presence of tempered martensite in the region.