Strain rate dependence of iodine-induced stress corrosion cracking of Zircaloy-4 under internal pressurization tests

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Pressurization tests were run on unirradiated Zircaloy-4 tubing in the pressure range of 400 to 550 MPa and temperature, 330 to 400 ° C. The effects of the mechanical factor on the susceptibility of Zircaloy to iodine-induced stress corrosion cracking (ISCC) were studied in terms of both time-to-failure and failure strain. The time-to-failure was related to thenth power of stress, and the failure strain was a parabolic function of the strain rate in the limited range of 10−7 to 10−4 sec−1. The ISCC susceptibility was determined by the strain rate rather than the stress, and decreased with increasing test temperature. The results suggest that the film rupture step should be involved in the Zircaloy ISCC and that gas adsorption process is an important step in the overall ISCC.