1992 Volume 41 Issue 7 Pages 461-469
In order to clarify the reason why the caustic IGSCC resistance of nickel base alloy 600 is improved by the precipitation of chromium carbides at the grain boundaries, the author investigated the role of grain boundary chromium carbides on the caustic IGSCC resistance of nickel base alloy 600 in high temperature NaOH solution. The results obtained were as follows: The author made clear that the dominant contribution factor of grain boundary chromium carbides to the caustic IGSCC resistance is to be attributable to the cleansing of the grain boundaries by the trapping of grain boundary segregated elements such as C, B, P by the chromium carbides. The formation of corrosion resistant film due to CrO2- ions caused by the chromium carbides dissolution at the crack tip may be also contributable to the caustic IGSCC resistance apart from the extent of contribution. However, inhabitant effect of IGSCC propagation by the insolubility of carbide itseif, improving effect of the caustic IGSCC resistance by the formation of grain boundary chromium depleted zones, electro-chemical protection effect by the precipitation of chromium carbides from the interface boundaries of alloy 600 which have large difference of the corrosion potential and grain boundary strengthening due to the alternative coherent precipitation of chromium carbides along the grain boundaries seem to be not contributed to the caustic IGSCC resistance of alloy 600.
