Iodine stress corrosion cracking resistance of high anisotropy zircaloy-4 sheet processed by cross-rolling and heat treatment

Mechanical properties and iodine-stress-corrosion-cracking resistance of Zircaloy-4 sheet processed by cross rolling and heat treatment were studied to improve the materials quality for nuclear fuel cladding application.The stress-corrosion-cracking tests were conducted at 300deg C under gaseous iodine atmosphere in which the rate of crack propagation as a function of stress intensity factor was determined. The room temperature yield strength, elongation and the critical stress intensity factor under the 300deg C iodine atmosphere varied sensitively with the methods of rolling and heat treatment, which was related to the distribution characteristics of basal poles. The density of basal poles along the sheet normal increased by a cross rolling followed by beta-phase heat treatment and furnace cooling, which resulted in an improvement in the stress-corrosion-cracking resistance of the alloy. The appearance of stress-corrosion-cracking fracture surface was predominantly brittle, in which transgranular fracture was dominant when a beta-phase heat treatment followed by furnace cooling was conducted, whereas intergranular fracture was dominant when the finishing process was either alpha-phase recrystallization heat treatment or cross rolling. (Author)