Optimizing Advanced High-Strength Steel Joints via Regional Rapid Cooling in Resistance Spot Welding

During resistance spot welding (RSW), the thermal cycles that occur cause microstructural differentiations in the heat-affected zones of martensitic steels, leading to internal stresses. In this context, a new and innovative methodology has been developed to minimize the adverse effects of heterogeneous hardness changes in the welding area on joint durability. This methodology utilizes a unique prototype setup based on the regional rapid cooling (RRC) process, which is integrated into the welding machine and operates in synchronization with the machine during the process. Through this setup, the aim is to effectively control the microstructure and hardness values in the welding area. This innovative approach presents potential improvements in the field of welding technology by aiming to optimize material performance during the welding process. According to microstructure results, the RRC process has narrowed the heat-affected zone to 1.27 mm, increased the hardness values by 9.2%, showed a 3% increase in tensile-shear strength, a 9% increase in cross-tension strength, and based on fatigue strength results, no fractures occurred in all specimens subjected to a force of 0.3 kN.