Influence of final recrystallization heat treatment on Zircaloy-4 strip corrosion

Abstract

Zircaloy-4 strip material was processed to the final size using standard fabrication techniques. The final size material was subjected to many different recrystallization heat treatments. The temperatures covered a range from 550 to 775°C, and post-beta-quench thermal processing, represented by the cumulative A parameter, ranged from 1.4 × 10 −20 to 2.9 × 10 −17 h . The uniform and nodular corrosion behavior was characterized using 400 and 500 °C autoclave tests. The results show that maximum uniform and nodular corrosion resistance may be obtained by control of the final recrystallization anneal. Maximum uniform and nodular corrosion resistance was obtained when the cumulative A parameter was in the range of 4 × 10 −19 to 7 × 10 −18 h . Selected samples were examined using transmission electron microscopy. A relationship was observed between the mean diameter of the second phase particles and the corrosion behavior. The diameter increased with increasing cumulative A parameter. The particle structure changed from fcc to hexagonal as a result of alpha thermal processing after beta-quenching and may be related to the onset of uniform and nodular corrosion.