Effect of Mo and Cu on stress corrosion cracking of ferritic stainless steel in chloride media

Abstract

Stress corrosion cracking behaviour of ferritic stainless steels with copper and molybdenum additions in 42 wt-% boiling magnesium chloride at 143¡18C has been determined. The nature of the corrosion products was analysed by X-ray photoelectron spectroscopy (XPS). XPS results show that the presence of Fe(0), Cr(0) and Mo(0) unoxidised states on the crack tips of (copper þ molybdenum) addition ferritic stainless steel cannot form the stable passive film and causes the further corrosion in the chloride solution. The addition of both copper and molybdenum to 19% Cr ferritic stainless steel causes stress corrosion cracking. The susceptibility to stress corrosion cracking increases with the growth of 1-copper precipitates, and the fracture mode changes from transgranular to intergranular with the increasing aging time. Stress corrosion cracking initiates from pitting of 1-copper phases, then propagates to molybdenum atoms, and finally propagates to the other 1-copper precipitations perpendicular to the direction of maximum strain.

Influence of surface grinding on corrosion behavior of ferritic stainless steels in boiling magnesium chloride solution

“…In FSSs, the presence of microstructural features that reduce the ductility tend to make them more prone to chloride induced SCC in chloride media . The addition of both copper and molybdenum to 19% Cr FSSs has been shown to cause SCC and the SCC initiated from pitting of ɛ‐copper phases; the SCC susceptibility was observed to increase with the growth of ɛ‐copper precipitates . Similarly, copper and nickel contents have been shown to introduce SCC in boiling magnesium chloride tests in welded Fe‐18Cr‐2Mo alloy …”

Corrosion Resistance of Cu-modified 3Cr Low-alloy Steel in 3.5%NaCl Solution

“…Obviously, Cu precipitates in the microstructure resulted from the addition of 0.6% Cu. Because the solubility of Cu in ferrite is low (~0.2%), 11) 0.6% Cu added in 3Cr steel was sufficient for the precipitation of the Cu precipitates during the heat treatment process.…”