The effect of annealing parameter on corrosion resistance of Zircaloy-2

The effects of equal ΣAi for different combinations of the annealing temperature and annealing time on corrosion resistance and evolution of precipitates of Zircaloy-2 were investigated. Nodular corrosion resistance in the out-of-pile corrosion test was degraded with increasing ΣAi only when it was increased by extending the annealing time at 894 K but did not depend on ΣAi which was increased by raising the annealing temperature for a constant annealing time of 2.5 h. Extensive observation and micro-analysis of precipitates by analytical electron microscope (AEM) suggested the cause of degradation of nodular corrosion resistance to be the remarkable increase in volume fraction of Si-containing precipitates such as Zr3Si and Zr2Si, which were observed more frequently in large ΣAi only when it was increased by extending the annealing time at 894 K. On the other hand, uniform corrosion resistance was improved with increasing ΣAi irrespective of the annealing conditions, but was slightly better when ΣAi was increased by extending the annealing time under constant annealing temperature at 894 K. This behavior can be understood from the reduction in content of alloying elements such as Fe, Cr and Ni which remained as solutes in the matrix at large ΣAi. (author)