KCl-Induced Corrosion of a 304-type Austenitic Stainless Steel in O-2 and in O-2 + H2O Environment: The Influence of Temperature

• The oxidation of the 304-type (Fe18Cr10Ni) austenitic stainless steel was investigated in the temperature range 400-600 A degrees C in 5% O-2 and 5% O-2 + 40% H2O. Exposure time was up to 1 week. Prior to exposure, the polished samples were coated with 0.1 mg/cm(2) KCl. Uncoated samples were also exposed and used as references. The oxidized samples were analyzed by gravimetry and by ESEM/EDX, XRD, IC and AES. The results show that KCl is strongly corrosive. Corrosion is initiated by the reaction of KCl with the chromia-containing oxide that normally forms a protective layer on the alloy. This reaction produces potassium chromate particles, leaving a chromium-depleted oxide on the alloy surface. At 500 and 600 A degrees C this results in rapid oxidation, resulting in the formation of a thick scale consisting of a mixture of hematite, spinel oxide ((Fe,Cr,Ni)(3)O-4) and K2CrO4. The thick scale is poorly protective and permeable to e.g. chloride ions. The KCl-induced corrosion of alloy 304L in dry O-2 and in an O-2 + H2O mixture increases strongly with temperature in the range 400-600 A degrees C. The strong temperature dependence is explained partly by the temperature dependence of the chromate-formation reaction and partly by the ability of the chromium-depleted oxide to protect the alloy at low temperature. At 400 A degrees C, the oxide was still protective after 168 h.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

Nyckelord

600-degrees-c

304L

KCl

Breakaway Corrosion

304l

chloride

water-vapor

Deposit

oxidation

Oxidation

oxide hydroxide evaporation

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art (ämneskategori)

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