Development of a cold spot joining method that enables sound joining of carbon steel below the A1 temperature

A novel solid-state joining method, which we call cold spot joining (CSJ), was successfully developed. In this joining concept, the material in the vicinity of the interface is plastically deformed using high pressure to form the joining interface, and impurities at the interface are expelled to the outside. Medium-carbon steel sheets were joined using the CSJ method under various process conditions. The joining temperature can be modified by the pressure applied during CSJ. Microstructural observations and hardness distributions revealed that proper pressurisation led to a joining temperature below the A1 point and prevented the formation of brittle martensitic phase. A sound S45C joint showing plug rupture at the base metal under both tensile shear and cross-tension tests was successfully fabricated by providing appropriate applied pressure and energising conditions.