The EFFECT OF STRAIN-HARDENING ON PWSCC OF NICKEL-BASE ALLOYS 600 AND 690

摘要

Stress corrosion cracking (SCC) behavior of base metals, cold-worked base metals and heat-affected zones (HAZs) in Alloy 600MA/Alloy 182 and Alloy 690TT/Alloy 52 welds in simulated PWR primary water environments is investigated. Hardness measurements and electron backscatter diffraction measurements show a hardened area in the heat-affected zones. Grain boundary chemistries and carbide precipitations were analyzed by Auger Electron Spectroscopy of the exposed intergranular fracture surface. Alloy 690TT base metal and Alloy 690TT HAZ show high SCC resistance. Extensive IGSCC was found in the Alloy 600MA HAZ, 8% and 20% cross-rolled (2DCR) Alloy 600MA materials, while mixed intergranular/transgranular SCC was found in the 40% CR Alloy 600MA specimens. The crack growth rate in the Alloy 600MA HAZ is close to that in the 8% 2DCR base metal, which is significantly lower than that in the 20% 2DCR base metal, but significantly higher than that in the as-received Alloy 600MA base metal.