Stress Corrosion Cracks Initiation Process Model Involving Repetition of Growth and Breaking of Oxide Passive Film or Hydride Layer on Stainless Alloy

The surface of stainless alloy is covered with oxide film such as Cr2O3 and is passivated in neutral aqueous solution. This film attains a thickness that may be expressed in micro meter units(μm) and may undergo partial rupture physically in a high-temperature oxygen enriched water environment. Crack propagation occurs through repeated growth and rupture of the oxide film; the rupturing process is designated as tarnish rupture type SCC. Individual cracks are initiated randomly for film of uniform thickness and this process may be described by the stochastic model. Hydride layer formation occurs on the alloy surface under the proper conditions, using titanium in a reducing neutral water environment. Crack initiation may thus also be described by a model similar to that for film rupture. (authors)