Effect of structure on the fatigue limit of carburized steel 20Kh2N4A

Abstract

1. When the excess carbides in the case of steel 20Kh2N4A are in the form of fine spheroids, an increase of the carbon concentration in the surface zone from 0.8 to 1.5% does not reduce the fatigue limit. 2. After heat treatment (quenching from carburizing temperature and repeated quenching from 800°C) the fatigue limit of steel 20Kh2N4A is higher than after the commercial treatment, No. 6 (carburizing+high-temperature tempering+quenching+low-temperature tempering). 3. With quenching from the carburizing temperature without high-temperature tempering before quenching and quenching in a hot medium the fatigue limit is lower than after treatment 6. 4. Cold treatment after quenching results in the lowest fatigue limit. 5. At the higher low-temperature tempering temperatures the brittleness of the case is reduced and also the residual compressive stresses. The fatigue limit for carburized steel 20Kh2N4A is highest after tempering at 140°C. An increase of the tempering time at 140°C from 1 to 4 h has no effect on the fatigue limit.