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

Fatigue test of 22MnB5 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.