超高强度钢点焊结构疲劳试验分析

Fatigue test analysis of ultra-high strength steel spot welded structure

以超高强度淬火钢22Mn B5为母体的点焊结构为研究对象,分别通过恒压和锻压工艺,利用光学显微镜,运用成组法进行了疲劳试验测试分析.结果表明,锻压和恒压二种工艺的p-S-N曲线显示出前者比后者工艺的疲劳寿命分散性略大及两种工艺的断裂模式基本相同,裂纹在焊核与热影响区交界处发生,并进一步向两侧较对称扩展至母材区,成为裂纹起裂点.异种母材与同种母材的试样发生疲劳断裂的位置相同,均为焊核与内层热影响区的交界处,异种母材的试样在裂纹扩展形态具有不对称性,疲劳失效均发生在低碳钢焊核处,得到3种应力等级下焊点的疲劳寿命变化曲线.

Fatigue test of 22 MnB 5 ultra-high strength quenched steel spot welded structure was conducted with constant pressure and forging technology,respectively,by means of optical microscope and grouping approach. the p-s-n curves in forging and constant pressure processes display that the dispersion of former fatigue life was slightly larger than the latter one,and the fracture mode for two processes were basically the same. Cracking occurred at the junction of weld and heat-affected zone,and further propagated from both sides symmetrically to the substrate,becoming the origin of failure. The fatigue fracture position located at the junction of inner heat-affected zone and weld for both heterogeneous substrates and homogeneous substrates. However,the crack propagation in heterogeneous specimens was asymmetric,fatigue failure occurred in the low carbon steel weld,and fatigue life curves of solder joints in three stress levels.