Nodular Corrosion of Zr–0.85Sn–0.16Nb–0.37Fe–0.18Cr Alloy in 500 °C Steam Caused by High-temperature Processing

Zr–0.85Sn–0.16Nb–0.37Fe–0.18Cr alloy samples prepared by low-temperature process (LTP) and high-temperature process (HTP) show different corrosion behaviors in 500 °C steam. The former exhibits uniform corrosion, while the latter exhibits nodular corrosion casually. The occurrence of nodular corrosion on HTP samples is attributed to the formation of local alloying elements depletion region in the Zr matrix. During hot rolling at 800 °C, transformation of zirconium from α-phase to β-phase happens locally. Alloying elements migrate to β-phase from its neighboring α-phase. The local β-phase dissolves in the subsequent cold rolling and final annealing, leaving the microstructure with agglomeration of precipitate particles and neighboring alloying elements depletion regions in Zr matrix. And the undesirable microstructure becomes the causation of nodular corrosion.