Effect of Selective Dissolution on Stress Corrosion Cracking Susceptibility of Austenitic and Duplex Stainless Steels in Alkaline Solutions

The formation of nickel layers on austenitic stainless steel in strong caustic solutions has been reported in 1979. Recently, a detailed study was reported clarifying the nature of the de-alloying process and establishing firm links with other metal-environment systems that show de-alloying and associated stress corrosion cracking (SCC) in strong caustic environments. In this study, role of de-alloying in SCC of the austenitic and duplex stainless steels AISI304 (EN1.4301), S32101 (EN1.4162), S32304 (EN1.4362), S322205 (EN1.4462) and S32750 (EN1.4410) has been evaluated in 10% and 50% NaOH and sulphide-containing caustic environments (pulping liquors) at 413K (140ºC) and 463K (190ºC).

The results show that selective dissolution of alloying elements occurs at the crack tip and strain induces selective dissolution. It is proposed that rate determining step in SCC is generation of vacancies by selective dissolution at the crack tip. Chromium is dissolved and/or precipitated during the process. The process has effects on corrosion and SCC susceptibility and depends on the alloy composition and microstructure of the steel. FEG-SEM examination shows that the de-alloyed layer has extremely fine nanoporosity.  

Keywords:  selective dissolution, de-alloying, duplex stainless steel, austenitic stainless steel, stress corrosion cracking, caustic