DP780双相钢电阻点焊接头组织及性能研究

Research on Resistance Spot Welding Microstructure and Performance of DP780 Dual Phase Steel

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 resistance spot welding of 780 MPa grade dual phase steel with reasonable process parameters was carried out. The microstructure and mechanical properties of the weld seam and the fracture morphology were analyzed. The results show that the resistance spot welding joint can be divided into five zones： base metal zone, tempering zone, partial-quenched zone,completely quenched zone and nugget zone. The base metal zone is composed of ferrite matrix and mesh martensite; the tempering zone is composed of ferrite and tempering martensite. The partial-quenched zone is composed of ferrite and massive martensite. The free-grained zone of the completely quenched zone is composed of fine equiaxed martensite and the coarse-grained zone consists of thick lath martensite. The nugget microstructures which were founded to be the columnar crystals, mainly contained thick lath martensite. The tests show that the failure mode of the spot-welded joints are mainly nugget stripping. The softening was investigated along the heat-affected zone in welded joint from the distribution of hardness, mainly due to the emergence of tempering martensite.