Abstract
In order to clarify the fatigue strength characteristics of lowalloy steels tempered at low temperature (150-200°C) or carburized in generated gas, rotating bending fatigue tests were conducted in laboratory air and dry air. The influence of moisture in air was only observed for the carburized steel. The low- temperature-tempered steel revealed two knees on the S-N diagram, and no fatigue limit was found up to 109cycles (9 months). The carburized steel revealed three knees and the fatigue limit was found over lO8 cycles. When the fatigue test of carburized steel was carried out in dry air or the surface structure anomalies were removed, the fatigue strengths were improved, but neither knees nor fatigue limits were found up to 109 cycles. The reasons for this were discovered from the results of fractography and the equations proposed by Murakami et al. for the prediction of the fatigue limit of steel with microdefects.
