Role of Heat Treating on the Intergranular Stress Corrosion Cracking of Alloy 600
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Role of Heat Treating on the Intergranular Stress Corrosion Cracking of Alloy 600 A. Aguilar1, A. García-Ruiz2, A. Escobedo1 and R. Pérez3 1
Instituto de Ciencias Físicas, UNAM. A.P. 48-3, C.P. 62251, Cuernavaca, Morelos, México. 2 UPIICSA-COFAA, Instituto Politécnico Nacional (IPN). Té 950, Col. Granjas-México, Iztacalco, 08400, México, D. 3 Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, P. O. Box 1-1010, C.P. 76230, Boulevard Juriquilla 3001, Santiago de Querétaro, Qro. México. Email: [email protected] ABSTRACT It has been recognized in Ni-base alloys that the grain boundary chemistry and its microestructural heterogeneities are important factors in the material environmental degradation. Therefore, in this study, we investigated the role of the heat treatments and the obtained microstructure in the IGSCC susceptibility of alloy 600 in environments of pressurized water reactors (PWR). The role of microstructure on the intergranular cracking resistance (IGC) of alloy 600 was also investigated using a modified wedge opening loading specimens which were annealed at 930, 800 and 600°C and also exposed to high purity water pressurized with hydrogen at 300°C. It was found the microstructure induce relatively low crack growth rates associated with the development of significant plastic deformation at the crack tip. In addition, some common features were found between the IGSCC performance and the pre-fatigue cracking conditions. For this purpose, the fatigue crack growth properties of this alloy were also evaluated using the ASTM E 606-92.
Keywords: Corrosion, Fatigue, Fracture, Microstructure, Grain Boundaries
INTRODUCTION Extensive word worldwide has been devoted to disclosing the mechanisms involved during the intergranular stress corrosion cracking (IGSCC) of pressurized water reactor (PWR) made of Inconel alloys [1]. From these works, it is well known that Inconel alloy 600 is susceptible to stress corrosion cracking (SCC) under hydrogen supersaturated steam at temperatures above 300oC. Yet, the mechanistic aspects involved in the SCC of these alloys are far being resolved [2]. In general, it has been found that heat treating can lead to Cr depletion of the grain boundaries in precipitation hardened Ni-base alloys as a result of grain boundary chromium carbide precipitation [3]. This condition should be highly susceptible to SCC, in contrast with the experimental reports [2]. Yet, these alloys become increasingly susceptible in the milled annealed condition [1, 2]. Moreover, it has been found that crack propagation occurs preferentially along grain boundaries [4]. In addition, grain boundary segregation which can reduce the cohesive strength of the grained structure is not able to account for the IGSCC susceptibility for the present amounts of segregated impurities [3]. The role of molecular hydrogen dissolved in primary water in pressurized water reactor (PWR) on intergranular stress
Mater. Res. Soc. Symp. Proc. Vol. 1275 © Materials Research Society
corrosion crack
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