Effects of iodine concentration, stress, and strain rate on stress corrosion cracking (SCC) of stress-relieved zircaloy-4 tube in iodine vapor were investigated by an internal pressurization method and by a constant strain-rate method at temperature ranging from 573 to 673˚K. Stress corrosion cracking was observed when iodine concentration exceeded a critical value of 0.2 mg/㎠ at 603˚K. The failure time was found to decrease with increasing stress. At iodine concentration of 0.8 mg/㎠ and at temperature at 603˚K, the following relationship was found between the failure time (tf) and the hoop stress(σ) at stresses above the threshold level of 380MPa.
$tf=8.84\times10^8\exp(-0.045\sigma)$
Using specimens with internal surface flaws, the relationship between crack growth rate (da/dt) and stress intensity factor (K) was established as follows.
$da/dt=3.8\times10^{-9}K^{6.3}(mm/\sec)$
The SCC resistivity was found to be minimum at a certain strain rate. The strain rate corresponding to this minimum resistivity increased as the temperature increased. This phenomenon is considered to be related to the rate of formation of protective film on zircaloy surface.
