热成形钢电阻点焊断裂模式与失效力预测研究

A Predictive Study on Fracture Mode and Failure of Resistance Spot Welding of Hot-Formed Steel

本文研究了1500HS热成形钢两层板电阻点焊接头的组织演变和变形行为。通过金相组织分析、热输入分布图以及合金材料性质图,分析了点焊接头在不同热输入量位置的组织演变。随着距焊核中心区域距离增加,点焊接头组织可以分为柱状晶马氏体、粗晶马氏体、细晶马氏体、铁素体-马氏体双相组织和回火马氏体组织。结合维氏硬度分析,明确了不同组织特征下的硬度差异,结果表明在铁素体-马氏体双相组织和回火马氏体区域的硬度下降较为明显,是焊点的薄弱区域。基于不同板厚组合下的熔核尺寸、最大失效载荷、断口宏观形貌、初始断裂位置和维氏硬度等实验结果,阐明了板材厚度和板材强度两类因素对于焊点断裂模式、初始断裂位置和最大失效载荷的影响规律。

The microstructure evolution and deformation behavior of resistance spot-welded joints of the two layer plates of 1500HS hot-formed steel sheets are studied in this paper.Through metallographic analysis,heat input distribution map,and alloy material property map,the microstructural changes at various positions relative to the weld nugget are analyzed.As the distance from the center area of the weld nugget increases,the microstructure of the welded joint can be divided into columnar crystal martensite,coarse-grained martensite,fine-grained mar-tensite,ferrite-martensite dual phase microstructure and tempered martensite microstructure.Combined with Vick-ers hardness analysis,the differences in hardness under different organizational characteristics are clarified.The re-sults show that the hardness decreases significantly in the ferrite martensite dual phase structure and tempered mar-tensite region,which are the weak areas of the welding joints.Based on the experimental results of fusion size,maxi-mum failure load,fracture surface macro-morphology,initial fracture location,and Vickers hardness of different plate thickness combinations,the influence of plate thickness and plate strength on the fracture mode,initial frac-ture location,and maximum failure load of the spot welded joints is explained.