Enhancement of fatigue crack initiation life in low carbon steels by solid solution strengthening element addition

To investigate the effects of solid solution strengthening elements (Si, Cu, Cr, and Ni) on the fatigue properties, fatigue tests were conducted on low-carbon steels using smooth plate specimens. The results indicate that the addition of Si and Cu is particularly effective in improving the fatigue limit ratio. Transmission electron microscopy observations revealed that these elements suppress the formation of cell structures, which are regarded as precursors to fatigue crack initiation. A fatigue-resistant steel was developed by optimizing the combined addition of these solid solution strengthening elements. In the developed steel, fatigue crack initiation was significantly delayed, resulting in an improvement in crack initiation life compared with a conventional 490 MPa class steel of comparable strength. Fatigue tests using full-thickness specimens demonstrated that the developed steel exhibits superior fatigue performance relative to the conventional steel, with the fatigue strength at ten million cycles improved by approximately 36%.