Failure analysis of an AISI 410 stainless steel airfoil in a steam turbine

A failure analysis was performed to determine the occurrence of cracking in an AISI 410 stainless steel airfoil from a steam turbine. The failure was detected arising from a reinforcing lacing bar located at the upper part of the blade. Failure resulted from nucleation and growth of a crack running transversally to the length of the airfoil. Poor surface preparation of both blade and lacing bar, previous to brazing, resulted in excessive oxide formation at the interface; also, an inadequate gap between both components resulted in incomplete penetration of the brazing material leading to deprived localized bonding. SEM evaluation revealed that crack propagation was promoted by fatigue. Vibration and stress distribution analyses performed by FEM demonstrated that the operating conditions of the blade were within stress permissible limits, suggesting that failure was effectively associated to a deficient brazing procedure.