Hiroo Numata1, Naotsugu Yamanouchi2, Keiji Nunomura2, Manabu Tamura2, Iwao Matsushima2 and Shiro Haruyama1
1Department of Metallurgical Engineering, Faculty of Engineering, Tokyo Institute of Technology, Tokyo
Corrosion of iron, nickel, chromium, stainless steels and Cr-Mo alloy in (Na, K)2SO4-Fe2(SO4)3 melt has been studied with the electrochemical polarization technique at 923 and 973 K under SO2-O2-CO2 atmosphere. The rate of corrosion estimated from polarization resistance was consistent with that obtained from mass loss. With the increase in chromium content of the alloys, the rate of corrosion decreases shifting the corrosion potential to anodic direction. This behavior was well explained by the superposition of the partial anodic and cathodic polarization curves. The partial cathodic reaction is the cathodic reduction of ferric ion in the melt, which was independent of the composition of the alloys. The anodic polarization curves exhibit a passive region. Both the currents at the peak and the passive state decrease with the increase in chromium content of the alloys. Therefore, high chromium alloys are highly corrosion resistant in molten sulfate. The result is well consistent with that obtained by Salt-coating test.
electrochemical study, hot corrosion, alkali ferricsulfate, polarization resistance method, stainless steel, chromium-molybdenum steel, polarization measurement, effect of chromium content
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