Fatigue properties of Ti microalloyed high-strength steel by CSP process

The fatigue properties of 2 mm-thick Ti-microalloyed high-strength steel produced in a CSP line was studied by the up-down method. It is found that the tensile strength of the steel is 830 MPa, the fatigue strength is 685 MPa, about 0.83 times as large as the tensile strength, and the elongation is 18.8%. The S-N curve of the steel was drawn out and the relationship between the maximum stress and fatigue life was fitted. The cracking mechanism was analyzed by scanning electron microscopy. The crack source, expansion region, and eventual failure region appears significantly in the microscopic structure. Fatigue cracks initiate from microcracks on the strip surface. Microcosmic fatigue striations, secondary cracks, and macroscopic fatigue bay ridges are observed in the fatigue extension region. The eventual failure region meets the characteristics of tear edge morphology along with dimples.