Improving fatigue properties of 18CrNiMo7-6 steel by surface strengthening

Surface gradient structures with small to large grain sizes were obtained on 18CrNiMo7-6 steel by ultrasonic surface rolling processing (USRP). Both tensile properties and fatigue resistance have been enhanced. Based on the gradient layer generated after USRP, the fatigue strengthening mechanism was discussed. After USRP, the reduction of the ratcheting strain reduced the fatigue damage of the material under the same stress level and prolonged the fatigue life. Meanwhile, USRP changed the grain orientation of the surface layer, the initiation mode of the fatigue crack was transformed from the surface to the interior at a low stress level.

Automated summary

The ultrasonic surface rolling processing (USRP) can generate surface gradient structures with different grain sizes on 18CrNiMo7-6 steel, improving its tensile properties and fatigue resistance. USRP reduces ratcheting strain, decreases fatigue damage under the same stress level, and prolongs fatigue life. Additionally, USRP changes the grain orientation of the surface layer, transforming the initiation mode of fatigue cracks from the surface to the interior at lower stress levels.