1981 Volume 30 Issue 12 Pages 692-698
Carbide precipitation behavior and intergranular stress corrosion cracking (IGSCC) of Ni-base Alloy 600 were studied under various aging treatments. IGSCC test was performed on stressed double U-bend specimens in non-deaerated water containing 500ppm Cl- at 300°C. The relationship between the IGSCC sensitivity and intergranular corrosion (IGC) sensitivity in boiling 40% HNO3 solution was also examined. The carbide precipitation during aging was much affected by the prior metallurgical conditions or the annealed conditions. Undissolved carbides in annealed material accelerated the carbide precipitation within the grains and thus acted to depress the grain boundary precipitation. The chromium carbides found in Alloy 600 were Cr7C3 and Cr23C6. The former existed as undissolved carbides in annealed material, and the latter precipitated at aging stage. The sensitivities to both IGSCC and IGC increased, reached the maximum and then decreased with aging time. This result supports that these intergranular attacks are caused by the formation of chromium depleted areas along grain boundaries. But the IGSCC sensitivity was much higher than the IGC sensitivity at early stage of aging duration. This difference in the sensitivity between IGSCC and IGC is also discussed.
