%0 Journal Article
%T Experimental and Theoretical Investigation of Three Alloy 690 Mockup Components: Base Metal and Welding Induced Changes
%A Rickard R. Shen
%A Bartek Kaplan
%A P£¿l Efsing
%J International Journal of Nuclear Energy
%D 2014
%R 10.1155/2014/504927
%X The stress corrosion cracking (SCC) resistance of cold deformed thermally treated (TT) Alloy 690 has been questioned in recent years. As a step towards understanding its relevancy for weld deformed Alloy 690 in operating plants, Alloy 690 base metal and heat affected zone (HAZ) microstructures of three mockup components have been studied. All mockups were manufactured using commercial heats and welding procedures in order to attain results relevant to the materials in the field. Thermodynamic calculations were performed to add confidence in phase identification as well as understanding of the evolution of the microstructure with temperature. Ti(C,N) banding was found in all materials. Bands with few large Ti(C,N) precipitates had negligible effect on the microstructure, whereas bands consisting of numerous small precipitates were associated with locally finer grains and coarser grain boundary carbides. The Ti(C,N) remained unaffected in the HAZ while the carbides were fully dissolved close to the fusion line. Cold deformed solution annealed Alloy 690 is believed to be a better representation of this region than cold deformed TT Alloy 690. 1. Introduction Many components in pressurized water reactors (PWRs) today are made of Ni-base alloys, for example, control rod drive mechanism (CRDM) nozzles, steam generator (SG) tubing, and SG divider plates. These components were previously made of Alloy 600 since it had exhibited good corrosion resistance in many aggressive environments in combination with having a coefficient of thermal expansion close to that of steel. Unfortunately, Alloy 600 soon turned out to be susceptible to stress corrosion cracking (SCC) in primary water, having a case reported in field in 1971 after only two years in service [1]. Alloy 690 was developed as a remedy to the SCC in Alloy 600, essentially being a high Cr version of Alloy 600 containing nominally 30% Cr instead of around 15-16%. Since the SCC resistance of Alloy 600 was found to significantly increase after being thermally treated (TT) [2¨C4], that is, heat treated for precipitation of a semicontinuous carbide network along the grain boundaries, Alloy 690 has also been used in the TT state. TT Alloy 690 has been used in operating plants since 1989, and no cracking due to SCC has been reported to date. From both operational experience and laboratory experiments, it is evident that Alloy 690 has considerably higher SCC initiation resistance than its predecessor [2¨C4]. Experiments in recent years have however shown that it is possible to induce high SCC crack propagation rates in
%U http://www.hindawi.com/journals/ijne/2014/504927/