Effect of Impurity Elements (C, Si) on Microstructure and Corrosion Resistance of Zircaloy-4 Sheet

In the range of ASTM, the effect of impurity elements on microstructure and corrosion resistance of Zr-4 alloy was studied by using sheet samples. The results show that reducing carbon content and increasing silicon content are beneficial to improve uniform corrosion resistance of Zr-4 alloy at 400 degrees C steam. Microscopic analysis shows that carbon is easily enriched in the form of Zr-C on the matrix phase, and it mainly affects the corrosion resistance by influencing the precipitation of second phase particles. The lower its content is, the easier it is to form the parallel plate (PP) structure during quenching, and the higher its content is, the more likely it is to form basket weave (BW) structure, while the second phase particles are easier to precipitate along the grain boundary of PP structure. When quenching temperature is lower than 1200 degrees C, silicon content has no obvious effect on the formation of PP structure. Meanwhile, three-dimensional atom probe (3DAP) analysis shows that silicon tends to agglomerate in the form of SiO2 around the second phase particles, and delays or weakens the oxidation of second phase particles, thus improving the corrosion resistance of Zr-4 alloy.