Resistance to contact fatigue of heavy-duty gear wheels made of steel 20KhN3A and hardened by thermochemical treatment

1. When the surface layers of steel 20KhN3A are saturated in nitriding with nitrogen to 0.6–0.8; 0.4–0.5, and 0.3–0.4% at a distance from the surface of 0.05, 0.3, and 0.6 mm, respectively, a structure forms with high strength, increased amount of residual nitrogen austenite, stability of the martensite to loss of strength and of the residual austenite to γ → αM transformation both in the surface zones of the case and in the region of action of the reversed tangential contact stresses. 2. Strengthening heavy-duty driving pinions of steel 20KhN3A of the final reduction gear of tractors by nitriding with increased nitrogen potential and immediate quenching increases considerably the resistance to contact fatigue, regardless of the fact that the case is thinner than a case obtained by case-hardening with repeated quenching.