The stress relief annealing temperature of cold-processed (97% deformation rate) pure zirconium is about 300℃. In order to reduce its corrosion and oxygen absorption rate and stable structure, stress annealing is generally carried out after cold-processed. After stress relief annealing, the strength of zirconium alloy does not change much, but the plasticity increases obviously.
Recrystallization temperature is related to the amount of deformation and annealing time during cold processing.
It was determined that recrystallization had occurred in Zr-2 alloy with a cold processing capacity of 52% after annealing at 545℃ for 1 hour, and recrystallization was completed after annealing at 570℃ for 1 hour. When annealed at 700℃, the grain growth tendency was obvious. However, in order to further cold work, from the processing practice of Zr-2 and Zr-4 alloy, the recrystallization annealing temperature should be 700 ~ 750℃. For finished pipes, annealing at 580~600℃ is recommended to maintain good texture and hydride orientation.
The solution treatment temperature of Zr-2.5 Nb alloy is usually 880°C (+ → conversion temperature paper is 40°C). The holding time is generally 0.5 hours, and then quenching. The hardened Vickers hardness value is 245 LBS 5 kg/mm2.
The aging temperature is usually 500°C, and the hardness of the alloy increases for the first 3 ~ 6 hours, and then remains at a maximum of 265 ± 7 kg/mm2 (Vickers hardness). The aging time reaches 72 hours and still maintains the same hardness value. At lower ages of 300°C and 400°C, peak hardness will be reached slowly.
For ternary alloy Zr-2.5 Nb-0.5Cu, the conversion temperature decreases due to the addition of Cu. The conversion temperature of → + is about 880°C, which is generally quenched at 825 ~ 850°C and aged for 6 hours at 530°C.
Between the quenching and aging of Zr-2.5Nb alloy, a certain degree of cold deformation (generally less than 20%) is often carried out, which is beneficial to the corrosion properties, but also has the disadvantage of increasing the creep rate of the alloy.
The microstructure of ternary and binary alloys is similar, and their hardness increase depends on the quenching speed, which indicates that the performance improvement is related to Martensitic phase transition, and the hardness increases further after aging due to "nebula" -like Nb phase precipitation. Zr-2.5Nb alloy is a kind of high strength zirconium alloy because it has both solid solution strengthening and dispersion strengthening after quenching and aging.
