Determination of cracking susceptibility of resistance spot welded advanced high strength steels

In order to respond to the challenges of reducing pollutant emissions and fuel consumption, e.g., by weight reduction, as well as for enhancement of passenger safety, new materials are being applied in automotive industry. These modern materials, namely advanced high strength steels, show superior mechanical properties and a good weldability in general. But despite their qualities, the complex microstructure of these steel types leads to an increased cracking susceptibility, especially during resistance spot welding. Because the potential influences of the occurring imperfections on spot welded joints are not investigated finally, avoiding them is still an important issue in industrial practice. Therefore, a simple and manufacture-oriented method was developed, which enables even small companies to determine the cracking susceptibility of the material combinations which they process. The method is based on the forced and reproducible generation of cracks and uses a simple setup. Samples are being welded under tensile loading, which is applied to basically-shaped samples by a hydraulic frame. The resulting crack lengths can be evaluated optically, and conclusions regarding the cracking susceptibility in industrial environments can be drawn. This way, a material ranking of susceptibility to crack during resistance spot welding of advanced high strength steel combinations can be established.