Effects of Final Heat Treatment on Corrosion and Mechanical Properties of Zr Alloy Strip Incorporating Nb

The effects of final heat treatment on the mechanical and corrosion properties of a Zr alloy strip incorporating Nb were investigated. The chemical composition of the strip was Zr-1.49Nb-0.38Sn-0.20Fe-0.11Cr, and strip specimens were subjected to final heat treatment in a temperature range of 580 similar to 700 degrees C. Tensile tests at room temperature and 316 degrees C, along with corrosion tests in a simulated PWR loop and a 70 ppm LiOH solution environment at 360 degrees C, were performed on the specimens. The mechanical properties of the strip were saturated when the specimens received final heat treatment at an elevated temperature of more than 640 degrees C. However, the corrosion resistance of the strip in the simulated PWR loop and in the 70 ppm LiOH solution environment was improved with a decrease of the final annealing temperature. It is recommended that the alloy strip be finally heat-treated at a temperature of less than 620 degrees C for longer than 10 minutes in order to obtain fully recrystallized microstructures, and thereby attain enlarged tensile elongation, and to prevent the precipitation of beta-Zr, which is known to deteriorate the corrosion resistance.