Study of the relationship among total oxygen, inclusions and fatigue properties of gear steel

In order to control non-metallic inclusions and improve fatigue performance of gear steel, the relationship among total oxygen, inclusion size and fatigue properties of gear steel was investigated. In the work, Mn–Cr system gear steels with different total oxygen contents were selected as the research objects. Inclusions and fatigue properties of gear steels with different total oxygen contents were studied by using traditional metallographic method, extreme value method and fatigue test. The experimental results demonstrates that with the decrease of total oxygen content(i.e., 0.0013%→0.0010%→0.0005%), the number of small-size oxide inclusions in the range of 5–10 μm decreases greatly, whereas the number of large-size oxide inclusions over 10 μm has relatively little change. Meanwhile, it is found that the change of total oxygen content in different ranges has different influences on the size of maximum size oxide inclusion and fatigue properties. Reducing the total oxygen content of gear steel from 0.0013% to 0.0010% decreases the inclusion size of maximum oxide inclusion and improves fatigue resistance of materials, but these benefits do not extend to a total oxygen level of 0.0005%. Accordingly, we can conclude that no evident linear correlation exists between total oxygen content and maximum inclusion size or between the total oxygen content and the fatigue performance.