Abstract: Effect of final annealing process on microstructure and mechanical properties of Zr-4 alloy cladding tubes were studied by means of metallographic experiments, room temperature tensile experiments, room temperature blasting experiments, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results show that the Zr-4 alloy is in an intermediate state between stress reliefing and recrystallization, and the recrystallization degree of the Zr-4 alloy increases with the increase of annealing temperature or the extension of annealing time within the temperature range of 480 ℃ to 525 ℃. The maximum grain size increases from rolling deformed structure to basic recrystallization structure, but the variation pattern of average grain size is not significant. Two types of second phase particles, Zr(Fe, Cr)₂ with dense hexagonal structure and ZrFe₂ with cubic structure, are precipitated from matrix under different annealing processes. Zr(Fe, Cr)₂ particles have a significant difference in size and a relatively large proportion in quantity, while the ZrFe₂ particles have a smaller size and a relatively small proportion in quantity. The size of the second phase particles gradually increases with increase of annealing temperature or extension of holding time, but the second phase structure has not changed. The strength of burst test and tensile test decrease with the increase of annealing temperature or the extension of holding time, elongation after tensile fracture and circumferential elongation after blasting increase and show nonlinear change, the change trend gradually show down with the increase of recrystallization degree of tubes.

Key words: final annealing process, Zr-4 alloy tube, microstructure, mechanical properties, second phase particles