ジルカロイ‐４材の耐食性に及ぼす金属組織の影響

Abstract

The high temperature steam (500°C, 10.3MPa) test and observation of microstructure were conducted in order to investigate the effect of the solid solutional alloying elements on the nodular corrosion resistance of Zircaloy-4.Needle-like structure, which resulted from rapid cooling from β- and α+β-temperature range, contained martensite produced by diffusionless transformation. The content of solid solutional Fe and Cr in the matrix increases with the increasing of quenching temperature and cooling rate. A good correlation between the weight gain after the steam test and the volume fraction of precipitates (fvol) was obtained. Nodular corrosion did not occur on the heat-treated specimens, in which fvol was less than 3×10-5.In the β-furnace cooled specimen, nodular oxides were observed in the α-grain near the grain boundary, where the precipitation of intermetallic compound Zr(Cr, Fe)2 was remarkable. From these results, it is considered that nodular corrosion initiates at the solid solutional Fe and Cr depleted zone.