Effect of Alloy Composition on Stress Corrosion Cracking Susceptibility of Duplex Stainless Steels in Hot Alkaline Sulfide Solution

摘要

Stress corrosion cracking (SCC) susceptibility of the duplex stainless steels E 1.4162 (U S S32101) and E 1.4462 (U S S32205) was evaluated with U-bend specimens in the alkaline sulfide solution containing 100 g/l aOH and 55 g/l a_2S. Complementary potentiodynamic measurements were used to evaluate the effect of alloy composition on corrosion and on passivation behavior of the duplex stainless steels. The reference material in the study was the austenitic stainless steel E 1.4301 (U S S30400). Based on separate potentiodynamic curves and the free corrosion potential measurements of the alloys during the SCC tests, it is evident that Cr and i as the main alloying elements in duplex stainless steels raised the corrosion potential and lowered the critical current density of the steel, thus improving SCC resistance. Based on the potentiodynamic curves the alloying elements Mo and Mn were highly active in the hot caustic solution. SCC in the austenitic reference stainless steel was severe penetrating in the unaffected material but in the duplex stainless steels cracking was observed only inside the affected surface layer. Selective dissolution of Fe, Cr, Mn and Mo and/or enrichment of i and Cr as well as a, S and O took place in the affected surface layers of the duplex stainless steels depending on the steel grade.