Strain-hardening influence on iodine induced stress corrosion cracking of Zircaloy-4

The iodine induced stress corrosion cracking (SCC) of recrystallized Zircaloy-4 is first intergranular, and then turns to transgranular propagation, before leading to final ductile rupture. In order to progress in the identification of the factors enhancing transgranular propagation of SCC cracks, the effect of strain-hardening on SCC propagation modes is studied. Fractographic observations by SEM of as-received or pre-strained specimens, submitted to iodine methanol under constant load until rupture, show that strain-hardening enhances transgranular propagation of SCC cracks. This propagation mode is associated with a significant acoustic emission. On the base of these results and metallographic observations and texture measurements, the mechanisms associated with strain-hardening at grain scale and their potential consequences on transgranular initiation and propagation of SCC cracks are discussed.