Modelling of corrosion fatigue crack initiation on martensitic stainless steel in high cycle fatigue regime

Highlights: • Corrosion fatigue tests are carried out in high cycle regime (10⁷ cycles) at 10 and 120 Hz. • In situ electrochemical measurements were carried out during corrosion fatigue tests. • Behaviour of the passive film was studied during corrosion fatigue tests in aqueous solution. • A model of corrosion fatigue crack initiation is proposed based on physical evidences. • The experimental results are compared to the proposed model taking into account mechanical and electrochemical material parameters. - Abstract: This paper presents an analytical model for assessing the corrosion fatigue crack initiation life on a martensitic stainless steel X12CrNiMoV12-3 in high cycle fatigue regime (between 10⁵ and 10⁷ cycles). Based on in-situ electrochemical measurements during corrosion fatigue tests in NaCl aqueous solution, the corrosion fatigue crack initiation mechanism was identified. Two main stages were investigated: (i) the fracture of the passive film by slip bands and (ii) the free dissolution of the metal developing fatigue crack initiation from a critical corrosion defect. The depassivation stress threshold corresponds to the median fatigue strength at 10⁷ cycles for fatigue corrosion tests. For an applied stress range less than this threshold, the depassivation phenomenon was not observed at 10⁷ cycles and no crack initiation occurred. The proposed model takes into account the depassivation process induced by the slip bands emergence at the specimen surface and the corrosion rate under cyclic loading. The experimental results are compared to the proposed model taking into account mechanical and electrochemical material parameters.