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 ± 1°C 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+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 ε-copper precipitates, and the fracture mode changes from transgranular to intergranular with the increasing aging time. Stress corrosion cracking initiates from pitting of ε-copper phases, then propagates to molybdenum atoms, and finally propagates to the other ε-copper precipitations perpendicular to the direction of maximum strain.

Keywords

Stainless steel TEM XPS Inclusion Stress corrosion

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