马氏体含量对双相钢焊点拉拉疲劳性能的影响

焊点的疲劳性能是决定车身安全性和可靠性的重要因素. 对不同强度的DP780,DP980和DP1180双相钢焊点进行了检验，在疲劳试验机上进行了拉剪疲劳试验，获得了焊点的疲劳寿命曲线，分析了焊点显微组织、硬度与疲劳性能的关系. 并对焊点的疲劳失效进行了分析. 结果表明：母材性能对其焊点的疲劳性能有较大影响. 母材强度越高即马氏体含量越多，其疲劳性能越优异，三种材料的失效模式均是沿着焊点圆周断裂，裂纹在熔核与母材交界的热影响区萌生，且先贯穿板厚，贯穿板厚的裂纹作为二次裂纹源向板宽方向扩展直至断裂.

Influence of martensite content on tension-compression fatigue life of spot-weld joints of dual-phase steels

The fatigue performance of spot-weld joints is an important factor to determine the safety and reliability of the car body. The welded joints of DP780, DP980 and DP1180 were inspected. Load-life curves of the welded joints were obtained by the fatigue test on fatigue test machine. The relationship between microstructure, micro-hardness distribution of spot welds and fatigue properties of spot-weld joints was analyzed. And then, the fatigue failure of solder joint was analyzed. The results showed that spot-weld joints fatigue performance was affected by base material properties. The higher martensite content, the better fatigue property. All of the three fatigue failure modes were fracture along the circumference. It was found that the fatigue cracks mainly initiated at the heat affected zone between the fusion zone and the base material, and firstly penetrated through the sheets along thickness. Finally, the through-thickness cracks could be considered as the secondary fatigue crack source, which grew into the base material along the direction of width up to the fracture of weld joints.