The effect of supper rapid induction quenching to fatigue property of steel

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In this study, for the purpose of making clear the fatigue property of surface hardened steel by super rapid induction quenching, measurement of hardness, residual stress and fatique test on plane and notched specimen consisted of 0.45 C steel given hardening layr by super repid quenching were carried out.Significant ant remarkable results were obtained. The summary of those results is as below.1. A high compressive residual stress (more than-1000MPa on plane specimen and-3000MPa on notched specimen) was observed on the surface of specimen and easy control of hardening depth has become possible. As a results of a fatigue strength of those quenched specimen became higher compared with non-quenched specimen. Especially, fatigue strength of notched specimen with 1.0mm depth hardening layr was over 2000MPa.2. These exists a residual concentration at a notch root which is similar to an ordinary stress concentration at the notch root in the specimen subjected to an axial loading. The degree of a residual stress concentration depends on the notch sharpness.3. The release of residual stress occurs in the fatigue process of super rapid induction hardened steel depending on the magnitude of stress amplitude. At a higher stress amplitude, the release of a residual stress becomes more remarkable.4. High compresive residual stress has an effect of restraining the separation of the non-metallic inclusion from surrounding steel. This means that a high residual compressive stress can suppress a fatigue from an inclusion which results in the fatigue fracture with a fish eye pattern.