Effects of retained austenite on the fatigue properties of carburized steels

The effects of a large amount of retained austenite on the fatigue strength of carburized or carbonitrided and shotpeened steels have been studied for 0.8% Mo Steel and 0.8% Mo-4% Ni Steel. The results suggest that approximately 20-30% of retained austenite after shotpeening did not have any deteriorating effect on fatigue strength even with the presence of detrimental factors. Based upon consideration of both the beneficial and harmful effects of retained austenite, an improved treatment which produces a suitable profile of retained austenite has been developed. As a result, improved fatigue property has been obtained, although the exact mechanism which gives rise to fatigue life improvement has not yet been clarified.