Abstract: Fracture occurred during the operation of the reducer high speed shaft in certain power plant. Through macroscopic examination, chemical composition analysis, surface energy spectrum analysis, hardness testing, metallographic examination and mechanical performance test, this paper makes an analysis combining with the operating conditions of the reducer. The results show that the manufacturing quality of the reducer high speed shaft was unqualified. Since there are plenty of micro-cracks and acicular tissues in the surface of the nitriding layer, the micro-cracks spread during operation, which results in surface metal peeling and stress concentration. Finally, this leads to fatigue fracture of the high speed shaft. Aiming at the fracture causes, the paper presents some corresponding improvement suggestions.

Key words: high speed shaft, nitriding layer, micro-crack, fatigue fracture