The present paper proposes a relation between the
intrinsic defect size affecting the
fatigue strength of high strength
steel and the mechanical properties.The results of checking a lot of published data for high strength steel indicate that the calculated values are in good agreement with the measured ones, basically within±10%.For the high strength steel its lower
limit of fatigue strength is determined by the intrinsic defect size,while its upper limit is dominated by the slip hand cracking dimension.For the high strength steel, the higher the hardness or the hardenig exponent, and the
larger the intrinsic defect size, the smaller the lower limit of the fatigue strength. It is proposed that the intrinsic fatigue stress concentration factor is equal to the ratio of the slip band cracking fatigue strength to the measuring fatigue strength. For the steels of low and middle strength, the intrinsic fatigue stress concentration factor is near to 1, while for high strength steel, this factor is larger than 1. The larger this factor is, the more sensitive the material is to notch.