Threshold stress intensity factor for delayed hydride cracking of a recrystallized N18 alloy plate along the rolling direction

The objective of this study is to obtain the threshold stress intensity factor, KIH, for an initiation of delayed hydride cracking (DHC) in a recrystallized N18 (Zr-1.05Sn-0.27Nb) alloy plate which was manufactured in China, gaseously charged with 60ppm of hydrogen by weight. By using both the load increasing method (LIM) and load drop method (LDM), the KIH’s along the rolling direction were investigated over a temperature range of 150–255°C. The results showed that KIH along the rolling direction was found to be higher in the LIM than that in the LDM. In the LIM, KIH’s of the N18 alloy plate appeared to be in the range of 31–32.5 Mpa·m1/2, and KIH in the LDM appeared to be in the range of 27.5–28.6 Mpa·m1/2. This means that the N18 alloy plate has high tolerance for DHC initiation along the rolling direction. The texture of a N18 alloy plate was investigated using an X-ray diffraction (XRD) and the KIH was discussed based on texture and analytically as a function of the tilting angle of hydride habit planes to the cracking plane.