801 高強度鋼の高サイクル疲労破壊挙動に及ぼす非金属介在物の影響 : 各種介在物の疲労寿命と粒状領域の生成過程

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The primary aim of present study is to clarify the fatigue fracture mechanism of high strength steel at the high cycle region. Oil-tempered high strength steel wire (SWOSC-B) is prepared for fatigue test by using monopodium fatigue testing machine at frequencies of 1kHz. The S-N diagram has a knee point at about 2×(10)^6 cycle. From scanning electron microscopy (SEM) observation of the fracture surface at the long cycle fatigue range, nonmetallic inclusion is identified at the origin of fracture and optically dark area (ODA) is formed around the inclusion. On the other hand, a constitution of the nonmetallic inclusion is measured by using electron probe micro analyzer (EPMA). As a result, the inclusions are decided as Al_2O_3-CaO and TiN. Fatigue fracture from Al_2O_3-CaO is occurred earlier than that of TiN. Based on these results, finite element analysis (FEA) is conducted for analyzing the stress field in vicinity nonmetallic inclusion. Then, the effect of mechanical property of inclusion on fatigue failure behavior and ODA are discussed.
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