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, K_IH, 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 K_IH’s along the rolling direction were investigated over a temperature range of 150–255°C. The results showed that K_IH along the rolling direction was found to be higher in the LIM than that in the LDM. In the LIM, K_IH’s of the N18 alloy plate appeared to be in the range of 31–32.5 Mpa·m^1/2, and K_IH in the LDM appeared to be in the range of 27.5–28.6 Mpa·m^1/2. 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 K_IH was discussed based on texture and analytically as a function of the tilting angle of hydride habit planes to the cracking plane.