OVERLOADING BEHAVIOUR OF CORROSION FATIGUE CRACK INITIATION FOR 300M STEEL
300M钢腐蚀疲劳裂纹萌生的超载特性

The periodic and simple overloading behaviours of fatigue crack initiation inair and in 3.5% NaCl solution were experimentally studied and theoretically analyzed for300M (40CrMnSiNiMoV) steel. Retardation intensity of retardating crack initiation of corro-sion fatigue of simple overloading is significantly smaller than the corresponding value of pe-riodic overloading in 3.5% NaCl solution. The overloading retardation intensity increaseswith the increase of overloading ratio or level of equivalent stress amplitude value in air and in3.5% NaCl solution without exception. The physical essential resulting in the above-men-tioned results was also explored theoretically from several respects of residual stress, stress re-laxation and environment effect. If only the simple overloading retardation law is consideredin corrosion fatigue crack initiation life prediction, the very conservative life prediction wouldbe obtained. Only if the retardation laws of simple overloading and periodic overloading arecomprehensively considered, the comparatively higher precision life prediction can be ob-tained.