Dependence of strength and fracture behavior on chemical compositions in spot-welded L-type joints

In order to achieve lighter and stronger car bodies by applying high strength steel sheets, one of key technologies is enhancement of joints strength. In this study, we investigated dependence of strength and fracture behavior on chemical compositions of the steels in spot-welded L-type joints in detail. Consequently, the following experimental results were obtained: 1) Maximum load of the joint decreased with increase of carbon (C) and phosphorous (P). The maximum load was decreased by 0.4 to 0.7kN with increase of 0.1% in C, with C content ranging from 0.03% to 0.5%, and 0.5kN with increase of 0.01% in P, with P content ranging from 0% to 0.03%, 2) Fracture portion changed from the outside to the inside of weld metal with increase of C and P. 3) Fracture path was estimated to accord with solidification segregation site in the weld metal, in case of a steel of 0.2%C-0.03%P. 4) By implementation of an appropriate post heat during spot welding process for the steel of 0.2%C-0.03%P, the degree of solidification segregation was clearly reduced and the maximum load of the joins was improved by 70%.