Stress Corrosion of Age-Hardenable NiFeCr Alloys

Abstract Stress corrosion cracking (SCC) tests have been conducted on the age-hardenable NiFeCr Alloys X-750, 718, and A-286 in flowing pressurized water reactor (PWR) primary coolant water at 360 C. The effect of Zr additions to Alloy X-750 and the effect of heat treatment on all of the alloys were studied. The test specimens were U-bends and precracked 1/2 T-CT fracture mechanics specimens. The total exposure was 6000 h, with inspections at 500, 1500, and 3000 h. No initiation was observed on the U-bend specimens, but crack growth was observed on all of the precracked samples. The cracking was intergranular on all of the specimens, with only a few grains of transgranular cracking occurring on one. Zr additions to Alloy X-750 had no significant effect on SCC growth. The 1107 C solution anneal plus the overaged conditions provided the greatest resistance to SCC growth. Alloy 718 exhibited the least resistance.