The α-Zr with a hexagonal close-packed structure at room temperature is likely to form texture during cold deformation. The texture of silicon zirconium has an important influence on its strength, creep performance, hydride orientation, and irradiation growth. The Zr-4 alloy cladding tube used in the reactor usually requires a near radial base texture (that is, the C axis of the hexagonal lattice is substantially parallel to the diameter of the tube). Generally, when the ratio of the wall thickness reduction ratio to the diameter shrinkage ratio in the final cold working process is greater than 1, such a texture orientation is easily obtained. In the production of Zr-2.5Nb pressure tube, the texture is controlled by controlling the extrusion process parameters and the structure of the extrusion blank. In the Zr-2.5Nb alloy, the flake hydride is randomly oriented. Controlling the pressure tube addition process can make the flake hydride tangentially distributed to obtain the desired texture.
After recrystallization annealing (about 650℃), the texture of the cold-worked material changes, and the orientation of the hydride becomes chaotic (see preferred orientation). Annealing of cold processed materials must be carried out in a vacuum furnace, the degree of vacuum should be higher than 10-4 Torr. The intermediate annealing temperature is about 700°C. Finished product annealing is determined according to performance requirements. The requirements on the surface of the fuel cladding tube are very strict, and generally need to be pickled. The pickling solution is an aqueous solution of hydrofluoric acid and nitric acid. After pickling, the fluoride ion on the surface of the part must be completely removed, otherwise the corrosion resistance of the material will be reduced. The finished tube must be straightened. If the straightening process is not suitable, it will cause uneven mechanical properties, low blast ductility and unfavorable hydride orientation.
