Effect of Sn content on corrosion resistance of Zr-Sn-Nb alloys in steam

The corrosion behaviors of Zr-xSn-1Nb-0.3Fe (x=0~1.5wt%) alloys have been investigated in the superheated steam of 400°C/10.3 MPa for 270 days. Results show that the corrosion weight distinctly decreased with the decreasing of Sn content from 1.5wt% to 0.8wt%. However, the corrosion weight was hardly changed when the Sn content was 0~0.8wt%. The characteristics of grains and second phase particles were analyzed by optical microscope (OM) and scanning electron microscope (SEM), respectively, and the crystal structure of oxide films formed on specimens after corrosion test were characterized by X-ray diffraction (XRD) method. The microstructural characteristics indicated that some Sn promoted the recrystallization of Zr-1Nb-0.3Fe alloy, and the area fraction of precipitates in the alloy was increased with the Sn content decreased when all the samples were the same heat treatment condition. It was found that, the higher the fraction of the tetragonal ZrO2 in the oxide films was, the lower the corrosion rate of specimens, and it can be concluded that the tetragonal ZrO2 in the oxide films makes for the corrosion resistance.