Post-Weld Heat Treatment-Induced Microstructural Evolution and Mechanical Property Enhancement in Rotary Friction-Welded low carbon steel to stainless steel

This study aims to investigate the combined effects of friction time and post-weld heat treatment on the microstructural evolution and mechanical properties of rotary friction-welded AISI 1015/AISI 304 joints. The welding process was performed at friction times of 3 and 5 s, and the sample welded at 5 s was subjected to PWHT. PWHT was conducted on the joints at temperatures of 300 °C, 400 °C, and 500 °C for 1 hour, followed by air cooling. The tensile and microhardness tests were employed to assess the mechanical properties of the joints. Optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were utilized for microstructural characterization and fractography. Results depicted a residual stress reduction at elevated temperatures. The joint strength increased with increasing welding time (up to 5 s) and the PWHT temperature (up to 400 °C). The maximum joint strength was achieved at a friction time of 5 s (440.5 MPa), which was followed by PWHT at 400 °C and then yielded a maximum tensile strength of 449.9 MPa and efficiency of 107.3%. Furthermore, maximum elongation was observed in the PWHT500 sample (8.32%). The weld zone hardness of the sample welded at 5 s equals 275 HV, which decreased to 250 HV after PWHT at 500 °C. Microstructural analysis confirmed the formation of recrystallized grains and annealing twins as well as delta ferrite. At the same time, the fractography indicated increased brittleness with increasing welding time and softening at higher PWHT temperatures.