St. Petersburg State Polytechnic University (St. Petersburg, Russia):

Yurkinskiy V. P., Dr. Chem., Prof., e-mail: jurkinskij@rambler.ru
Baturova L. P., Cand. Chem., Associate Prof.
Firsova E. G., Cand. Tech., Associate Prof.

The research results of the corrosion resistance of stainless steels (AISI) SS 316, 254 and 354 in deaerated sodium hydroxide melt at temperatures of 400–600 ^oC are presented. Corrosion rate of the stainless steels was determined by the gravimetric method in the gas phase and sodium hydroxide melt. Microstructure and phase composition of corrosion products forming on the steel samples during corrosion testing were determined by the X-ray phase analysis and microscopic studies. It was found that SS 316 steel has low corrosion resistance in deaerated sodium hydroxide melt within preset temperature range. As temperature rises to 500–600 ^oC, chrome oxides Cr₃O₄ and Cr₂O₅ appear in the corrosion products resulting in formation of denser corrosion product film with good adhesion to the sample surface (especially at 500 ^oC) which leads to reducing the dissolution rate. Increase in molybdenum and nickel content in stainless chromium-nickel steels to 6.0–6.5% and 17.5–18.0% correspondingly results in reducing the corrosion rate of SS 254 and 354 stainless steels in deaerated sodium hydroxide melt at temperatures not higher than 500 ^oC. The under lying reason for this is as follows. The internal steel/corrosion product fi lm interface becomes molybdenum-enriched during steel corrosion which results in inhibiting the dissolution rate. It is shown that though the phase composition of the corrosion products is practically the same for all steels under study (SS 254, 354 и 316), their corrosion rates differ remarkably.

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