軸受鋼の回転曲げ疲れについて

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In relation to fatigue phenomenon of JIS SUJ2 bearing steel, it has been well known that fatigue cracks start at non-metallic inclusions present in the steel and that the resultant fracture is of so called fish-eye type.This time, a series of rotating bending fatigue test was conducted on SUJ2 bearing steel specimens heat-treated to different hardness. From this test the following were confirmed:(1) The fish-eye type fracture was not observed with hardness lower than HRC 44.4 although it appeared on hardness range of HRC 63.8∼53.4.(2) With hardness range of HRC 63.8∼57.2 eventually 100% of specimens had fatigue cracks starting at non-metallic inclusions, whereas it diminished with reduction of hardness. Namely, approximately 50% of HRC 56.0∼53.4 specimens and only 20% of HRC 44.4 or lower specimens had fatigue cracks starting at non-metallic inclusions. It was also found that the size of non-metallic inclusions at which fatigue cracks started was as large as approximately 11∼40μ.
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