Abstract
Effects of the cooling method after tufftriding and of the temperature rise due to the internal friction during the fatigue test on the fatigue strength of tufftrided mild steel (S15CK) were investigated. Ono-type rotating bending fatigue test specimens tufftrided at 570°C for 120 min and cooled with water, oil or air were used. Temperatures of the specimen surfaces were measured by the infrared radiation thermometer.The results obtained are as follows:(1) The fatigue strength of S15CK tufftrided specimens varies with the cooling method after tufftriding, that is, the fatigue limits of the tufftrided specimens cooled with water, oil and air are about 43 kg/mm2, 42 kg/mm2 and 39 kg/mm2 respectively, while that of the untufftrided is about 24 kg/mm2.(2) The surface temperature of the fatigue test specimens rises with an increase of the stress applied and a decrease of the dissolved nitrogen. The maximum temperature of the water cooled test specimen during the fatigue test reached about 250°C under a stress of 55 kg/mm2.(3) It is expected that the fatigue strength can be increased by cooling the specimen during the fatigue test.
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