Fretting wear fatigue fracture failure occurred at the beginning of service of the second stage moving blade of feedwater pump turbine in an ultra supercritical 600 MW unit. Field investigation was performed to analyze the material and fracture morphology of the fractured blade. Moreover

finite element calculation was carried out to study the centrifugal stress of the blade. Through comprehensive analysis on vibration characteristics of the impeller blade system

the failure characteristics and causes of fretting wear were obtained. The results show that

the fretting wear fatigue fracture originated from the first working face of blade root. There existed wear marks such as tire mark

wear spot

surface brightness and small crack on the surface of the first tooth working face and blade top side. There were many cracks with mechanical fatigue which were delamination cracking in the section of the first tooth working face. The microstructure and hardness of the source area were obviously abnormal compared with the matrix. The reason of fretting wear fatigue fracture of the second stage moving blade was poor assembly quality.