Rotational speed effects on fatigue performance and microstructural characteristics of friction-welded 316 L stainless steel

The purpose of the research is to determine the fatigue life of friction-welded 316L stainless steel joints. This was done by means of experimental testing and the stress-life method. Specimens were welded using a rotary friction welding process. Parameters such as friction pressure, forging pressure, forging time, and burn-off were kept constant, while rotational speed was varied (1500 rpm, 1800 rpm, 2100 rpm). After the specimens were welded, a flash was removed using a CNC lathe machine. An Amsler RBM 12 bending fatigue machine was used to determine the fatigue life of 316L stainless steel specimens. These specimens were subjected to a stress of 286.981MPa, 229.585 MPa, 172.189 MPa, and 133.925 MPa. The results obtained were plotted on the stress-life (S-N) curve. A microstructure and chemical element analysis was carried out on the three samples which were welded with a speed of 1500 rpm, 1800 rpm, and 2100 rpm. Fracture surface analysis was carried out using Olympus DSX500 and SEM JSM-IT100 microscopy. From the results obtained, it was discovered that all the specimens welded with a speed of 1500 rpm fractured when they were subjected to four different bending stresses. However, specimens welded at 1800 rpm and 2100 rpm fractured only at the highest applied stress of 286.981 MPa, while tests conducted at 229.585 MPa, 172.189 MPa, and 133.925 MPa resulted in run-out conditions exceeding two million cycles, indicating operation predominantly in the high-cycle fatigue regime. The fracture surface of the specimens revealed three regions: crack initiation, crack propagation, and final fracture. Some of these regions showed striation and chevron markings which they pointed out where the crack initiated. Through the use of microscopy, it was discovered that the specimen welded with a speed of 1500 and 1800 rpm had a lot of voids compared with the specimen welded with a speed of 2100 rpm. The results indicate that increasing the rotational speed improves the fatigue resistance of friction-welded 316L stainless steel joints under the tested loading conditions, although further finite-life data would be required for a complete S–N characterization.