Effect of tungsten and nickel addition on the repassivation behavior of stainless steel

Abstract

This study examines the effect of alloying elements of Ni and Won the repassivation properties of stainless steel (SS) as evaluated by a rapid scratching electrode technique and stress corrosion cracking (SCC) test. The SS specimens were grouped into two different grades according to Ni content (22Cr-5Ni duplex, Type 317LMN [UNS S31726] austenitic SS). Major considerations regarding alloy design were Ni content and the substitution of W for Mo. However, a similar pitting resistance equivalent number (PREN) of 35 to 36 was maintained for all specimens. The main factors for evaluation of repassivation properties are the peak current for the scratched surface and repassivation rate. In 1 M magnesium chloride (MgCl2) and 1 N sulfuric acid containing chloride ions (H2SO4 + 3.5% Cl-) solution, repassivation test results showed that repassivation properties decreased as Ni content increased. However, W substitution was effective on the repassivation process and increased the resistance of SCC property for alloys containing high Ni content.