The Effects of Texture and Surface Condition on the Iodine Stress Corrosion Cracking Susceptibility of Unirradiated Zircaloy-2

Abstract

Four lots of stress-relieved Zircaloy-2 tubing were prepared from a single heat of the alloy. Tube reduction parameters were controlled so that each lot had a different crystallographic texture. The tubing with the most radial (least tangential) basal pole intensity was shown to have a Kearns texture number in the radial direction of 0.61, whereas the equivalent value for the tubing with the least radial texture was 0.48. Each lot of tubing was given one of three surface treatments: etched, etched and grit blasted, or lightly etched and shot blasted. The iodine stress corrosion cracking (SCC) susceptibility of the unirradiated tubing was determined by measuring the time to failure in a standard tube pressurization test at about 593 K in which 6 mg of iodine was present for each square centimetre of exposed Zircaloy surface. The results showed that texture has a large effect on SCC susceptibility and that surface condition has a significant but lesser effect. The SCC resistance was lowest in the material with the most tangential basal pole intensity and increased as the texture became more radial. The lightly etched and shot-blasted surface resulted in times to failure that were shorter than the times for the othermore » two surface conditions. However, it seems likely that the influence of surface treatment is quite complex and that SCC susceptibility can change significantly with a seemingly minor change in the surface treatment technique. The effect of texture was interpreted in terms of its influence on strength, on deformation characteristics, and on orientation of SCC susceptible planes with respect to the dominant tensile (hoop) stress. The effect of surface condition was interpreted in terms of its influence on residual stresses, on local texture changes, on local stress concentration, and on chemical activity.« less