Cold spot joining of high-strength steel sheets

A novel solid-state joining method, called cold spot joining (CSJ), has been successfully developed. In this method, the material near the joining interface undergoes plastic deformation under high pressure, forming a joining interface, while oxide layers at the interface are fragmented and expelled to the exterior. High-strength steel sheets (HSS) with strengths of 780 MPa were joined under various conditions. The joining temperature can be adjusted by applying pressure during CSJ. Applying suitable pressure results in solid-state joining, and microstructural observations, alongside fracture morphology, indicate that the formation of a brittle structure was effectively prevented. Furthermore, cross-tensile strength measurements were conducted on steel sheets of varying strength grades, ranging from 270 to 1180 MPa and exhibited that the cross-tensile strength increased with increasing tensile strength.