Damage causes and failure analysis of a steam turbine blade made of martensitic stainless steel after 72,000 h of working

Abstract The harsh operating environment, and the extreme working condition, of the steam turbine blades have led to the use of alloys with special characteristics. Of these properties are high corrosion resistance and excellent rupture strength. The most widely used alloys in this category are heat treatable martensitic stainless steels. They provide a wide range of mechanical properties. In that sense, this research is focused on one of the most commonly used alloys of these series; i.e. 410 alloy. In this study, a turbine blade made of 410 stainless steel was under operation for 72,000 h, and its possible damage mechanisms were explored. To define the damage causes, microstructural analyses were performed by Optical Microscopy (OM), and a Field Emission Scanning Electron Microscopy (FESEM) instrument equipped with Energy Dispersive Spectroscopy (EDS) detector. As well, mechanical properties evaluation was performed using hardness testing. Results showed that the existence of foreign particles in the environment of the turbine has led to the initiation of damage in the blade through the erosion mechanism. Alternatively, such a damage was intensified by corrosion attack due to the presence of the fuel impurities. Such damages eventually led to the formation of fatigue cracks on the trailing edge of the blade. The latest phenomenon substantially reduced the fatigue strength of the blade. Finally, it is predicted that the reduced fatigue strength would ensue shortened service life for the blade.