Very high cycle fatigue properties of Cr-Mo low alloy steel containing V-rich MC type carbides

The present study was attempted to investigate the very high cycle fatigue (VHCF) properties of Cr-Mo low alloy steel containing V-rich MC carbides by using ultrasonic fatigue testing machine. All the specimens were quenched and tempered at 500 °C and 600 °C and part of them were electrochemical hydrogen charged. Mainly owing to the precipitation of fine V-rich MC particles at 600 °C, the introduced hydrogen content of the 600 °C tempered specimen is much higher than that of the 500 °C tempered specimen. Both the hydrogen-charged and uncharged specimens revealed internal fractures in the long-life region and no notable fracture surface difference were observed. Both fatigue strength and fatigue strength ratio increase with increasing tempering temperature from 500 °C to 600 °C for both the hydrogen-charged and uncharged specimens, though the 600 °C tempered specimen possessed higher hydrogen content. Increasing hydrogen content was definitely detrimental to the fatigue properties. However, compared to other high strength steels investigated previously, the detrimental effect of hydrogen on fatigue properties of the tested steel was comparatively small, which was ascribed mainly to the presence of fine V-rich MC carbides acting as hydrogen trapping sites. In is concluded that appropriate controlling of fine V-rich MC carbides is a promising way to alleviate the detrimental effect of hydrogen on VHCF properties of high strength steels.