材料期刊网

采用不同的点焊工艺参数对研发的1700MPa级Si-Mn系热成形淬火钢板与低碳钢板DC04进行异种材料之间点焊，并对焊接接头的拉伸性能、显微硬度分布及微观组织特征等进行了分析。结果表明，焊接电流对点焊接头熔核直径和抗剪强度具有显著的影响，而焊接时间的影响相对较小。超高强度钢板侧的热影响区存在两个明显的软化区和硬化区，即在靠近母材处存在一个硬度明显低于母材的软化区，其组织为回火马氏体；在靠近熔核处存在一个硬度明显高于母材的硬化区，其组织为细小的马氏体。点焊接头熔核部位为柱状粗大马氏体组织，其硬度明显低于超高强度钢板母材且远高于低碳钢板母材。低碳钢板热影响区低的硬度和明显粗化的铁素体组织，使得点焊接头单向拉伸时均从低碳钢板的热影响区一侧破断。

Spot welding properties of a new Si-Mn type ultrahigh strength hot stamping quenched steel sheet with low carbon steel sheet DC04 in different welding processing parameters was investigated. The tensile property, microhardness distribution and microstructure of welded joints were analyzed. The results show that welding current has a significant effect on nugget diameter and tensile shear stress of the joints, whereas the effect of welding time is a little smaller. There exist two kinds of region of the heat affected zone (HAZ) of the parent metal of ultrahigh strength steel sheet, namely, a soft region with its microhardness much lower than that of the parent metal and its microstructure is tempered martensite, and a hardened region with its microhardness higher than that of the parent metal and its microstructure is fine martensite. The microstructure of nugget is coarse martensite and its harness is lower than that of the parent metal of ultrahigh strength steel sheet and much higher than that of the parent metal of low carbon steel sheet. In the one-dimension tension test, the fracture of welded joints always occurred at the side of low carbon steel sheet owing to its rather coarse microstructure and low hardness of HAZ.