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Creep tests were performed to compare the creep behavior of commercial nickel-base alloys as a function of s!ress, temperature, and the environment. Alloy 600 (nominal and low carbon) and the precipitation strengthened Alloys 625 and X-750 in the AH and HTH conditions were tested at constant load in &aerated primary water containing 40-60cc/kg hydrogen. The stress dependence of Alloy 600 in the mill-annealed (MA) condition was obtained at 337°C and 360"C. 'Ihe stress exponent was determined to be between 3 and 9. The activation energy of creep was 64 kcal/mole. Both results support a dislocation climb controlled mechanism of creep in commercial Alloy 600. The creep twults were compared to the known stress corrosion cracking (SCC) performance of these alloys. The creep rates of the low carbon (LC) alloy are higher on average than those with nominal carbon level. Intergranular (IG) cracking occurred only in the X-750 AH alloy and the precipitation treated LC A600 alloy. These results support earlier work that showed that low carbon alloys are more susceptible to creep and IG cxacking than are high carbon alloys. However, these results also show a smaller influence of a water environment on the creep rate of commercial, creep-resistant alloys compared to high purity alloys.
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