报告：The SCC initiation behavior of alloy 690 in simulated pressurized water reactor primary environment
内容简介：Alloy 690 is an important structure material in modern light water reactor. Initiation of stress corrosion cracks in Alloy 690 in high temperature water is a rare occurrence and depends on the method by which the sample is loaded. Only in dynamic straining experiments is crack initiation consistently observed. The investigation on the oxidation behavior of alloy 690 shows that this material is prone to penetrative internal oxidation along closely packed lattice planes. However, the grain boundary forms a protective Chromia layer on the surface with the fast diffusion of Cr along the grain boundary. The surface oxide film would be breached under dynamic straining and the chromium depleted grain boundary is open to the inwards diffusing oxygen, resulting in formation and rupture of oxides down the grain boundary. Microstructure study of the SCC cracks indicates that grain boundary migration and intergranular oxidation are two fundamental precursors in SCC propagation. Cold work can significantly change the grain boundary structure and extends the SCC propagation path.