Effect of pulsed magnetic field + N ion implantation on the rolling contact fatigue performance of 8Cr4Mo4V steel

In this study, 8Cr4Mo4V steel was strengthened by the combined treatment of pulse magnetic field treatment (PMT) and N plasma immersion ion implantation (N-PIII). The elemental concentration, phase composition, microstructure, residual stress, surface hardness and rolling contact fatigue performance of 8Cr4Mo4V steel under different treatment conditions were analyzed and tested. The results show that PMT can reduce the surface roughness and make the dislocation distribution more uniform, thereby narrowing the range of residual compressive stress, and these provide a better sample basis for N-PIII. N-PIII can modify the surface defects after machining, and increase the surface hardness and residual compressive stress. Therefore, PMT + N-PIII combined treatment integrates the advantages of both. It effectively improves the surface morphology and residual stress distribution of 8Cr4Mo4V steel, as well as further enhancing the surface hardness. This significantly reducing the probability of “surface-initiated spalling” and transforming it into a “sub-surface and surface mixed-initiated spalling” with a longer fatigue life. The PMT + N-PIII combined treatment significantly extends the fatigue life under high reliability of 8Cr4Mo4V steel and reducing the life dispersion, increasing its L ₁₀ life to 25.7 times that of the untreated state, and the slope of the RCF life Weibull curve also significantly increased.