The high-cycle fatigue behavior of carburized M50NiL steel with high-energy modification and compound infiltration: A comparative study

Abstract

In this study, ultrasonic rolling (C + USRP) and plasma nitriding (C + N) is performed on the surface of M50NiL steel after carburizing， the tension-compression fatigue test of R = −1 on different samples. The results show that the maximum fatigue limit of C + N, C + USRP, and single carburizing are 770 MPa, 676 MPa, and 412 MPa, respectively. The residual stress relaxation in the fatigue process of C + N and C + USRP is tested and found that the initial residual compressive stress of C + N is lower than that of C + USRP, but its attenuation value is considerably smaller. The microscopic characterization of samples is conducted after the fatigue tests. The nanometer nitrogen compounds in the composite permeability layer showed a strong pinning effect, however, microplastic deformation limits the fatigue process. The C + N demonstrates a much lower residual compressive stress relaxation, consequently, the C + N short crack propagation effective driving force ΔKeff value decreases. As a result, due to the higher crack closure effect, the C + N fatigue limit is observed higher than the C + USRP.