ELECTROCHEMICAL BEHAVIOR OF SILICON MODIFIED STAINLESS STEELS IN HIGH TEMPERATURE WATER

摘要

Austenitic stainless steels are used extensively in commercial nuclear power plants. Under irradiation some of the materials may undergo grain boundary enrichment in some of the minor alloying elements or impurities. The objective of this research project was to characterize the electrochemical behavior of stainless steels with different amount of chromium, nickel and silicon. The amount of Si in the alloys were varied from ~1% to 5%, the amount of Cr varied from 12% to 19% and the amount of Ni from 8 to 15%. The electrochemical studies were performed using non-irradiated materials. The tests were carried out at 288°C in water contaminated with chloride, fluoride or sulfate in the order of 100 ppm. Typical electrochemical techniques such as polarization resistance, potentiodynamic polarization, and electrochemical impedance spectroscopy were used. Little or no effect was found on the effect of Si and Cr on the electrochemical behavior in high temperature water of the several types of stainless steel tested. That is, electrochemical tests could not explain why a material containing 12%Cr + 15%Ni + 5%Si was highly susceptible to environmental cracking in high temperature water while a material containing 19%Cr + 10% Ni + 2%Si was not susceptible to cracking under the same conditions.