Correlation between Microstructure and Macro-Instrumented Indentation properties of Solid-state Capacitor Discharge Welded CP1200 steel Joints

CP1200 is an ultrahigh-resistant structural steel used in the automotive industry for safety parts. Many attempts have been made to join this steel with other lower-resistant steels by using conventional resistance spot welding (RSW). Frequently it resulted in several issues, such as pores, cracks, over-hardened weld nuggets, vert sensitivity to crack HAZ, and the like. In this work Capacity Discharge Welding (CDW) has been proposed as an alternate solid-state welding method aimed at preventing the aforementioned RWD issues while forming a peculiar Electric Current Activated Region (ECAR) rather than a typical HAZ with relevant features, say, much smaller, finer and mechanically tougher than HAZ. The fine microstructure of the ECAR is promoted by the very short electric currents pulse and the very fast cooling. The results are given in terms of relevant microstructure and macro-indentation properties across the welded zone. A final correlation between microstructure and macro-indentation properties has been attempted. The role of residual stresses after CDW of CP1200 is also discussed.