Fatigue Strength of 18% Ni Managing Steel and the Effect of Distributed Inclusions

概要

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Rotating bending fatigue tests were conducted on 18% Ni maraging steel with in 10^8 cycles to failure. Solution treated specimens and five kinds of aged ones having the same hardness level were tested to investigate their effects on fatigue lives. SEM observations were made on the fractured surfaces, and the distribution of fatigue lives was theoretically analyzed. The major conclusions are as follows: (1) The fatigue strength of aged 18% Ni maraging steel was higher than that of solution treated one by at least 14kg/mm^2. (2) A large scatter of the fatigue lives was observed for the aged specimens, but the effect of different aging treatments was not recognized. (3) It was confirmed that the fatigue cracks were almost initiated from the inclusions near the surface, and that the scatter of fatigue lives was mainly caused by the distribution of inclusions. (4) Based on several assumptions concerning the distribution of inclusions and stress concentrations around them, the distribution of fatigue lives was theoretically derived, which showed a good agreement with the experimental distribution of lives.
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