Failure study of steam turbine Last-Stage rotor blades under a High-Speed wet steam environment

•The causes of pits and cracks in the last-stage rotor blades in a high-speed wet steam environment were investigated.•The pits were generated by the water hammer pressure of the secondary water droplets and the cavitation jet.•Crack initiation was induced by the combined action of the stress concentration and the alternating stress.•Crack propagation was accelerated by the combined action of stress corrosion and corrosion fatigue.