Abstract
The influence of aging condition on fatigue strength of the 300 grade 18Ni maraging steel has been investigated in relation to the behavior of age hardening and the formation of reversion austenite. In this study, rotating bending fatigue tests were performed for three series of specimens with different aging condition; as solution-treated without aging, aged for various time at 753K which is the temperature applied for the industrial aging treatment, and overaged to form a small amount of reversion austenite. Effect of reversion austenite on fatigue strength was examined using specimens with the same static strength which had been controlled by varying aging temperature and time, namely under-aging or over-aging. The main results obtained are as follows.(1) In the case of 753K aging, the fatigue limits of specimens aged for 11ks to 48ks were nearly the same value, although an under-aged (2.8ks) specimen has as much lower value as a solution-treated specimen without aging treatment.(2) A small amount of reversion austenite is effective for increasing fatigue resistance. For instance, 2vol% of austenite was enough for improving fatigue limit of the maraging steel used, from 580MPa to 640MPa at the same hardness level of Hv 610.
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