Improvement of Crashworthiness in a Hat-Shaped Component Made of 0.44%-Carbon Steel through Arc Spot Welding

To reduce the weight of automobile bodies, application of high-strength steel sheets is expanding. Furthermore, middle and high carbon steels are expected to be used to lower the environmental impact and cost in the automobile steel sheet industry. However, it is necessary to enhance the joint strength of the steel sheets. In this study, hat-shaped components were made using resistance spot (RS) welding or arc spot (AS) welding on S45C steel sheets (including 0.44% carbon), 1.4 mm thickness and strength of 1180 MPa grade. A dynamic three-point bending test was conducted on the components and their crashworthiness was compared. Some RS welds fractured (separated) during the three-point bending test even though the diameter of the weld metal was increased to 5√t (t means thickness of the sheet); however, AS welds did not fracture. The absorbed energy of the AS-welded component was higher than that of the RS-spot-welded one by approximately 25%, when both welds had the same diameter of 5√t. The AS welding is therefore seemed to be effective to improve the strength of the weld and crashworthiness of the component for middle and high carbon steel sheets.