Effect of metallurgical variables on hydride precipitation behavior in Zr-2.5Nb micro pressure tubes

The effect of manufacturing routes (heat treatment done by a conventional β-quenching (BQ), or slow cooling (SC) prior to hot extrusion), and location along the tube (front end (FE) and back end (BE) emerging from the press) on hydride precipitation behavior in Zr-2.5Nb micro pressure tubes were evaluated. After being hydrided to 100 wppm H, stepped micro pressure tube samples with three kinds of microstructure (BQ-BE, SC-FE, SC-BE) were pressurized to obtain nominal hoop stresses ranging from 65 MPa to 350 MPa. All the samples were heated to 350°C to dissolve all of the hydrogen, followed by cooling under stress to allow hydride reorientation to occur. Almost complete reorientation was observed in the BQ-BE sample at stress levels of above 100MPa, while the SC-FE and BE samples showed stronger resistance to reorientation. After subsequent reheating to 350°C for 1 hour or 24 hours and cooling without stress, little memory effect was found for the re-orientated hydrides in the BQ-BE sample. However, a clear memory effect was observed in the SC-FE and SC-BE sample in the range of angles where hydrides were naturally present.