Properties and Tempering Stability of Friction-welded Joints of 700-MPa-grade Fine-grained Steel

Friction welding (FRW) was used to weld 700-MPa-grade fine-grained steel and the changes in the microstructure state of the joints after low-temperature tempering treatment were analyzed. The results of testing show that it is advantageous to adopt a high current for welding to reduce the width of the heat-affected zone (HAZ) and minimize the size of the grain growth. The microstructures of the weld zone (HZ) and HAZ were finer than those of the base metal (BM), and the size of the grain in the HAZ was 9–11 μm. As the thermal stability of the friction-welded joints of ultrafine-grained (UFG) welding steel is low, if it is necessary to release the residual stress of joints by tempering after welding, the temperature should not exceed 300 ℃.