Creep strength of Zircaloy tubing at 4000C as dependent on metallurgical structure and texture

Zircaloy tubes were cold worked 50 or 80 percent to a series of textures and annealed at 475 to 575°C. Tube specimens were creep tested under internal pressure at 400°C with the transverse creep stress 152 MPa for 240 h, after which the transverse strain was measured. Annealing at 510 to 520°C in the temperature range of partial recrystallization gives maximum transverse creep strength. The creep strength maximum is higher the lower the degree of cold work. The high creep strength is caused by an optimum dislocation structure which is reached through recovery without copious recrystallization. Complementary creep tests under tensile load showed that the creep strength is lower transversely than longitudinally. This creep anisotropy may be explained in relation to texture by the action of <1123> dislocations. The transverse creep strength dependence on texture variations indicates that more radial basal poles give lower creep strength than more tangential basal poles. However, this texture effect is smaller than the effect of cold work, within the ranges of practical interest.