Influence of Ultrasonic Surface Rolling on the Tensile and Fatigue Properties of Laser-Cladding-Repaired 300M Steel Components

Herein, to address the issue of decreased tensile and fatigue performances observed in 300M steel scratched parts after laser-cladding repairing, an ultrasonic surface rolling process (USRP) was employed to enhance the strength of the laser-cladding-repaired (LCR) samples. Results indicated that USRP led to the formation of a strengthening layer on the surface of the samples. In the parent material area, the thickness of the strengthening layer was 180 μm, while in the cladding area, it was 35 μm. The superficial microhardness increased by 11.6% in the parent material area and by 5.0% in the cladding area. Furthermore, the surface residual stress transitioned from tensile to compressive stress, reaching a maximum of 1169.9 MPa. Improvements were observed in the tensile performance, as evidenced by a reduction in the length of the tearing ridge in the fracture morphology. In addition, the fatigue life considerably increased, initially increasing and then decreasing as the number of rolling passes increased. After four cycles of USRP, the fatigue life of the samples was the highest, which was about 18.4 times that of an unprocessed sample. The origin location of cracks shifted from the surface to the interior of the samples. This shift was accompanied by a decrease in the instantaneous fracture area and the emergence of additional secondary cracks. These experimental results demonstrate that USRP is an effective technique for improving the tensile and fatigue performances of LCR 300M steel samples.