Influence of mechanical properties induced by hydrogen absorption on the stress corrosion cracking initiation of Zircaloy-4

The mechanical properties of Zircaloy-4 alloy having different hydrogen contents comprised between 100 and 350 ppm, established by tensile tests, were correlated with the SCC susceptibility in iodine vapors at 320 deg. C. The maximum values of stress and strain from C-rings, induced by a Zircaloy-4 block of 18 mm length was estimated by means of ANSYS code. Using metallographic method and SEM it was emphasized the transgranular character of SCC cracks. The following conclusions are pointed out: 1. No major difference resulted between the values of yield stress and ultimate tensile stress in samples with hydrogen contents within the range (100-350) ppm; The presence of zirconium hydrides resulted in brittleness of zirconium alloy; 3. In the case of pre-cracked and non-hydrided samples, the applied stress threshold for propagation mechanism of SCC cracks is 300 MPa; in these testing conditions the deformation value is 2.7%; 4. By means of optic and scanning electron microscopy it was emphasized the transgranular character of SCC cracks obtained in the pre-cracked samples tested in these conditions. (authors)