Review of the Stress Corrosion Cracking of Inconel 600

Abstract

Abstract Intergranular stress corrosion cracking (SCC) of Inconel 600 is of concern to the nuclear power industry. Heat exchangers in commercial nuclear systems have shown SCC in only a fraction of a percent of the tubes in high temperature water, but laboratory SCC of Ni-containing alloys have been demonstrated by several research groups. This review revolves around French data, which show a reversal of the usual sensitizing effect in the case of SCC in high temperature, deaerated water. There is no cracking reported in material first heated so as to precipitate carbides at the grain boundaries, whereas high temperature annealed conditions lead to intergranular SCC in the same laboratory experiments. Electrochemically, SCC and also grain boundary corrosion are related to the potential level of a given test; however, it is not yet understood how the different grain boundary zones in Inconel 600 corrode (with and without applied stress) so that the mechanism of cracking remains speculative. Cr-depletion is sufficient to explain only some cases of intergranular corrosion. Grain boundary segregation seems to be of equal or greater importance in high temperature water, especially when the attack involves SCC. Grain boundaries may become cleaned when segregated elements dissolve in chromium carbide precipitates. Physically, precipitates at grain boundaries could possibly influence the manner in which the metal undergoes strain. Hydrogen as a cause of SCC has not been ruled out. The relationship between surface films formed and SCC of Alloy 600 in high temperature aqueous environments requires more work.