Effects of Crack Size, Stress Ratio and Hydogen on the Near Threshold Fatigue Crack Propagation of High Strength Steel
Kazutoshi YANAGIHARA, Satoshi OHYANAGI,Masanobu KUBOTA, Chu SAKAE and Yoshiyuki KONDO
Abstract:The effects of crack size, stress ratio and absorbed hydrogen on the fatigue crack propagation characteristics of high strength steel were studied near threshold regime. The test material was SCM440H low alloy steel. The material was quenched in vacuum and tempered at low temperature to achieve high strength and to lower the initial content of hydrogen of the material. The effects of crack size and stress ratio on the fatigue crack propagation rate and threshold stress intensity factor were investigated in air at first. These data offered a baseline as a reference. The effect of absorbed hydrogen was examined using a material in which hydrogen was introduced by cathodic charging. It was verified that the absorbed hydrogen in high strength steel affected the high cycle fatigue crack propagation characteristics. The fatigue crack propagation rate near threshold region was accelerated and DKth was lowered. The concentration of about 1ppm hydrogen caused 20% reduction of DKth. Since absorbed hydrogen has an influence even on high cycle fatigue crack propagation, it should be taken into account in the evaluation of defect of hydrogen utilization machine. Key Words:Fatigue, Short crack, Fatigue crack propagation, Hydrogen, Stress ratio, Threshold stress intensity factor