| Inconel alloys which have good high temperature mechanical properties and corrosion resistance have been used extensively as steam generator tube of nuclear power plants. There have been some reports on the intergranular stress corrosion cracking (IGSCC) failure problems in steam generator tubes of nuclear reactors. In order to evaluate the effects of heat treatment and composition on the IGSCC behavior of Inconel alloys in simulated nuclear reactor environment, four different specimens(Inconel 600 MA, 600TT, 690 MA and 690 TT) were prepared and tested by electrochemical method. Static potential tests for stressed C-ring type Inconel specimens were carried out in 10% NaOH solution at 300℃(75atm). It was found that IGSCC was initiated in Inconel 600 MA specimen, but the other three specimens were not cracked. Based on the gradients of corrosion current density of the four specimens as a function of test time, thermally treated alloys show better IGSCC resistance than mill-annealed alloys, and Inconel 690TT has better passivation characteristic than Inconel 600 MA. Inconel 690 TT shows clear periodic passivation that indicates good SCC resistance. The good IGSCC resistance of Inconel 690TT is due to periodic passivation characteristics of surface layer. |
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