The influence of corrosion pits on the fatigue life of 17-4PH steam turbine blade steel

Fatigue life tests on smooth and pre-pitted specimens and near threshold fatigue crack growth rate measurements are performed on 17-4PH steam turbine blade steel. The influence of environment and stress ratio is investigated. A decrease in the fatigue life and a slowdown of the crack growth rate in the near threshold regime is found in salt solution compared to air. The latter can be explained by oxide-induced crack closure. The critical stresses for fatigue failure in the presence of corrosion pits can be calculated using a methodology that was already successfully applied to 12% Cr steam turbine blade steel.