Semiconductor electrochemistry approach to passivity and stress corrosion cracking susceptibility of stainless steels

The susceptibility of AISI 304 type stainless steel to stress corrosion cracking (SCC) in boiling concentrated boric acid-chloride aqueous solutions, appears to be closely linked to the formation of a chromium rich passive oxide film presenting p-type semiconductivity. Furthermore, the flat band potential of the oxide, which separates potential regions of predominant ionic conduction from regions of predominant electronic conduction, can be considered a critical potential. A band structure model is proposed, in which the SCC phenomenon can be described as being the consequence of a localised change of the semiconductivity properties of the passive film, in the potential region situated near the flat band potential. The relationship between SCC and the electronic structure of the passive film on stainless steel is discussed.