高強度鋼の疲労強度と靭性,介在物寸法の関係

概要

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Rotating bending fatigue tests and the measurement of inclusion size distribution using the quantitative metallography technique were carried out on a quenched and tempered SAE9254 steel, and discussions were made on the relationship among the fatigue limit, inclusion size and toughness. Results showed that the high fatigue limit over 1000 MPa is easily obtained when the induction-hardened SAE9254 steel is tempered at the temperature just below the temper brittleness zone, indicating that such a condition of tempering gives the combination of hardness and toughness preferable for high fatigue resistance. Existence of an inclusion having maximum size (〜30 μm in dia. for present material) below the specimen surface is a primary cause for the occurrence of subsurface fracture associated with a fish eye on the fatigue fracture surface. The role of the inclusion with extraordinarily large size in the fatigue behavior of high-strength steel has also been discussed on the basis of the results of the fatigue test of the specimen having a surface micropit artificially introduced to simulate a surface inclusion.
1988-10-25