KCl induced corrosion of a 304-type austenitic stainless steel at 600 degrees C; The role of potassium

• Published in: Oxidation of metals Vol. 64; no. 1-2; p. 23
• Main Authors: Pettersson, Jesper, Asteman, Henrik, Svensson, Jan-Erik, Johansson, Lars-Gunnar
• Format: Journal Article
• Language: English
• Published: 01-08-2005
• Subjects: 11-percent; 304L; alloys; breakaway corrosion; chloride; chromate; chromium steel; deposit; deposits; fired boilers; flow-rate; high-temperature corrosion; KCl; oxidation; oxide hydroxide evaporation; water-vapor
• ISSN: 1573-4889; 0030-770X
• DOI: 10.1007/s11085-005-5704-3

The influence of KCl on the oxidation of the 304-type (Fe18Cr10Ni) austenitic stainless steel at 600 degrees C in 5% O-2 and in 5% O-2 + 40%H2O is investigated in the laboratory. The samples are coated with 0.1 mg/cm(2) KCl prior to exposure. Exposure time is 1-168 h. Uncoated samples are exposed for reference. The oxidized samples are analyzed by ESEM/EDX, XRD and AES. The results show that small additions of potassium chloride strongly accelerate high temperature corrosion, the oxide thickness being up to two orders of magnitude greater after exposure in the presence of KCl. The rapid corrosion is initiated by the formation of potassium chromate through the reaction of KCl with the protective oxide. Chromate formation is a sink for chromium in the oxide and leads to a loss of its protective properties. The resulting rapidly growing scale consists of an outer hematite layer with embedded K2CrO4 particles and an inner layer consisting of spinel oxide, (Fe,Cr,Ni)(3)O-4. Little or no chlorine is found in the scale or at the scale/metal interface.