Effect of Ni Additions Upon the Stress Corrosion of Ferritic Steels in a Chloride Environment Available to Purchase

Although mild steels will not fail by stress corrosion cracking (SCC) in a boiling MgCl₂ solution, the addition of only 1% Ni to such steels will promote a susceptibility that becomes more marked at higher Ni contents. Constant strain rate stress corrosion tests, together with fractographic examination of failed specimens and the determination of relevant polarization curves, have been employed in order to ascertain the roles of both Ni and Cl⁻ in the cracking mechanism. It seems that failures of Ni containing "mild steels" in concentrated chloride solutions are most readily explicable in terms of Ni promoting Cl adsorption which subsequently inhibits anodic dissolution. The mechanism of crack propagation is thought to be dependent on dissolution processes, possibly aided by mechanical tearing.