In order to evaluate the amount of bending fatigue damage in an austenitic stainless steel (SUS304), we are investigating the relationship between plane bending fatigue damage and martensite induced by plane bending fatigue using the perpendicular residual magnetization method. The sample is excited in a constant external magnetic field perpendicularly. The Z component of the leakage magnetic flux density caused by perpendicular residual magnetization at 1 mm above a specimen is measured by using a thin-film flux-gate (FG) magnetic sensor. Residual magnetization is caused by partial martensite in an austenitic stainless steel. From our experiments, we clarified that the maximum leakage magnetic flux density obviously depends on the plane bending stress and the number of stress cycles and we evaluated martensitic volume ratio in a damaged austenitic stainless steel when the martensitic volume ratio is 0.9% or less.
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