Crack investigation of martensitic stainless steel turbine blade in thermal power plant

Turbine blade is one of the key parts in thermal power plant, its failure will bring the power plant out of operation. Premature failure of turbine blade in thermal power plant was reported frequently. The crack was detected on the top of the last stage turbine blade in a thermal power plant. The failure causes of turbine blade were determined based on the testing and analysis by different methods. The macro morphology of the crack was observed by optical light microscope (OLM) method. The fracture surface of crack was observed by scanning electron microscopy (SEM) method and the mechanical property of the failure turbine blade was analyzed by different mechanical testing methods. The analysis results showed that the high level microstructure stress existed in the heat affected zone in the part of the blade, which was the directly factor to cause the failure. The uneven distribution fine and course martensitic due to the unqualified heat treatment in the heat affected zone and the high-frequency hardening zone was the root cause of the failure. Suggestions were proposed to prevent the failure about turbine blade according to the testing and analysis results as well.