Abstract
Crack-induced failure of 17-4PH steel was observed in the fir-tree root section of the blades in a wet-typed top gas energy recovery turbine (TRT) operated in a steelmaking plant. In order to determine failure behaviors and mechanisms, the chemical composition, microstructure and mechanical properties of a typical cracked 2nd stage blade root were analyzed in details. The crack was found in the middle contact surface of the first root groove, and the results indicated that the failure behaviors were due to corrosion fatigue. Actually, the corrosion and fatigue played different roles in the distinct failure stages. With the assistance of fretting, cracks initiated from corrosion pits on the steeple surface between the blade root serration and the shaft groove, suggesting that the cracks were initiated through corrosion. In addition, results of laboratory SEM analysis revealed that the high-cycle fatigue (HCF) loaded with visible presence of beach, striation marks, and transgranular feature played a key role in the crack propagation, which eventually led to the abnormal vibration and the shut-down of the TRT.
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