A Strain-Control Technique for Assessing the Corrosion-Fatigue Sensitivity of Stainless Steels

Recent studies have clearly shown the effect of mechanical depassivation on the behavior of stainless steels subject to stress corrosion. When these steels are cyclically deformed, the passive film can be locally perturbed by cyclic modifications of the topography of the underlying metal. Under these conditions the sensitivity of a stainless steel to fatigue in a corrosive medium depends, to a large extent, on the respective kinetics of mechanical depassivation and electrochemical repassivation. From a study conducted on different stainless steels, a method is proposed for evaluating the sensitivity of stainless steels to corrosion fatigue. Low-cycle fatigue tests under strain control have been carried out in a chloride solution. Evaluation of transient electrochemical parameters recorded during the tests enables us to give a coherent explanation of the behavior of these materials during long-life fatigue tests and of the fatigue crack growth rates. The experimental apparatus and methods used to interpret the mechanical and electrochemical results are discussed.