Bending fatigue strength of aerospace quality gear steels at ambient and elevated temperatures

Gear bending fatigue testing was conducted on six commercial aerospace quality steels, in the carburised, shot-peened and super finished condition, establishing S-N curves at ambient and elevated temperatures, providing evidence of higher than predicted strength established in accordance with ISO 6336:2006. At elevated temperatures, a systematic drop in mean strength was experienced for all candidate steels. Detailed fractography established the fracture initiation site, unique to each steel, illustrating a propensity for surface initiation in the finite life region and subsurface beyond the knee point, whilst certain grades displayed a distinct change in the location of fracture initiation at elevated temperatures.