Cracking susceptibility and characteristics were investigated on non-sensitized UNS $31603 stainless steel by slow strain rate tests in supercritical and sub-critical water containing 0.01mol/kg-H2SO4 at 400°C/25MPa, 400°C/60MPa, and 360°C/25MPa with two levels of oxygen concentration, 8ppm and 800ppm. The stainless steel had excellent corrosion resistance in 0.01mol/kg-H2SO4 at 400°C when oxygen level was as high as 800ppm and this was attributed to a thin and compact scale of Fe-Cr spinel and γ-Fe2O3 formed on the alloy. However, sever intergranular cracking occurred even under the 0.01 mol/kg-H2SO4 + 800ppm O2 environment, where the alloy showed excellent corrosion resistance. Cracking severity was higher for the supercritical conditions at 400°C than in the sub-critical condition at 360°C. The fact that sever cracking occurred even in the "gas-like" supercritical water at 400°C/25MPa, where dielectric constant of water is low and solubility of metal oxide is very limited, may suggest that dissolution mechanism would not be very likely for the cracking in this material-environment system.

Subject
Environmental cracking, Supercritical water, Water, Corrosion resistant alloys, Stainless alloys, Nickel based alloys, Oxide formation, Aqueous environments, Intergranular cracking, Oxide scales, Oxygen, Corrosion resistance, Stainless steel
Keywords:
supercritical water, corrosion, stress corrosion cracking, stainless steel, sulfuric acid, oxygen concentration, slow strain rate test, intergranular crack
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2004
Association for Materials Protection and Performance (AMPP)
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