Influence of Sulfur on the Corrosion Resistance of Austenitic Stainless Steel

Abstract

The influence of sulfur in the range 80 to 1700 ppm on the corrosion resistance of a 14 wt % Cr-14 wt % Ni-balance Fe alloy has been determined in various media. In general, high purity alloys containing sulfur are shown to have excellent general corrosion resistance to oxidizing and nonoxidizing acids when compared with equivalent alloys of commercial purity. Susceptibility to stress corrosion cracking in boiling magnesium chloride is low compared with commercial purity materials and an increase in sulfur content does not affect this susceptibility. High purity alloys containing sulfur are susceptible to attack in aqueous ferric chloride. Severity of attack increases with increased sulfur content. Pitting attack initiates at sulfide inclusions in all high purity alloys studied. A sevenfold increase in the anodic dissolution rate in 1.0N¯ H2SO4 was found when the sulfur content was increased from 80 to 1700 ppm. Analysis of electrochemical polarization data indicates that an increase in sulfur content increases the exchange current density for metal dissolution and is responsible for the accelerated anodic dissolution rate. Anodic dissolution rates in the passive and transpassive region of the polarization curve are independent of the sulfur content of the allloys.