Fracture Reason Analysis of Last Stage Blade of Steam Turbine

The low pressure last stage blade of certain unit fractured during operation. The fracture reason was analyzed by means of the test methods for chemical composition,mechaniced performance and metallurgical structure of blade steel. The results showed that the fatigue crack initiated. from a mechanical gap. Analysis on residual stress in X-ray showed that the residual stress was very high at crack origin area. The crack origin growed to fatigue fracture forced by alternating stress and residual stress together.