Niobium addition effect in Fe-17%Cr on its corrosion resistance in sulfuric acid

Abstract

The aim of present work was to investigate the influence of Nb upon the corrosion resistance to 0,5M H2SO4 cf 17%Cr ferritic stainless steels, to which it was added in amounts larger than those necessary for the stabilization of interstitial elements. The performance of Fe -17%Cr alloys containing 0,31%, 0,58%, 1,12%, and 1,62% Nb was compared to that of two other Fe -17% Cr alloys, one without additions and another containing 0,93%Mo. Through weight and electrochemical measurements and through morphologic examination of corroded surface it was found that in 0,5M H2SO4 solution the corrosion of these alloys, with the exception of that containing molybdenum, proceeds in two different stages. In the first stage (up to about 60 minutes) the corrosion rate practically does not change with time, the lower rates being displayed by alloys containing larger amounts of Nb. In the second stage (for immersion times larger than 60 minutes) the corrosion rate increases with time. The corrosion rate of Mo containing alloy is constant with time so that for longer immersion times this alloy becomes the most resistant. The first stage was discussed in terms of electrochemical properties of Nb and its ability to combine with steel impurities, while the second stage was considered as affected by corrosion products formed on the surface of these alloys after certain time of immersion.


Reference
ALONSO, N & WOLYNEC, S. Efeito da adição de nióbio à liga de Fe-17%Cr sobre a resistência à corrosão generalizada em ácido sulfúrico. In: SEMINÁRIO NACIONAL DE CORROSÃO, 3., 1992, Rio de Janeiro. Anais… Rio de Janeiro: ABRACO, 1992.

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