Corrosion failure analysis of 20CrMnTi gear in gearbox after oil pressure test

Abstract The causes of corrosion failure of 20CrMnTi rusted gear were analyzed by quantitative analysis of the composition, observation of the microstructure, hardness test and electrochemical test. The microstructure characterization showed that the proportion of retained austenite in the rusted gear was slightly higher and the length‐width ratio of martensite on the surface of addendum of rusted gear was slightly larger than that of the normal gear. However, the corrosion resistance of the rusted gear surface was similar to that of the normal gear. The lubricating oil of the gear was detected to contain water molecules. Further investigation showed that continuous rainy days during the period from installation to disassembly led to a relatively high humidity environment and also the block cover was not installed at that time. Therefore, the corrosive medium continuously entered the gearbox through the block cover hole and destroyed the protection of lubricating oil film, resulting in serious erosion of the gear near the block cover hole. After securing the problem, the block cover was kept installed all the time and no such corrosion failure occurred again.