STP1245: Corrosion Behavior of Zircaloy-4 Sheets Produced Under Various Hot-Rolling and Annealing Conditions

    Anada, H
    Research engineers and general manager, Advanced Technology Research Laboratories, Sumitomo Metal Industries, Ltd., Hyogo,

    Nomoto, K
    Research engineers and general manager, Advanced Technology Research Laboratories, Sumitomo Metal Industries, Ltd., Hyogo,

    Shida, Y
    Research engineers and general manager, Advanced Technology Research Laboratories, Sumitomo Metal Industries, Ltd., Hyogo,

    Pages: 21    Published: Jan 1994


    Abstract

    The uniform corrosion resistance of Zircaloy-4 sheets produced under various hot-rolling and annealing conditions was investigated. The uniform corrosion resistance in static steam at 673 K improved with an increasing cumulative annealing parameter (ΣA). However, to clarify the physical meaning of the annealing parameter and the different combinations of various heating stages, the effects of individual manufacturing conditions that influence the corrosion behavior and ripening behavior of the precipitates were investigated. As a result, the annealing temperature after hot-rolling influenced the uniform corrosion more significantly than the intermediate annealing and the final annealing temperatures. Size distributions of the intermetallic compound precipitates that were observed by means of a scanning electron microscope (SEM) with an image analyzer were examined for a correlation with weight gain. The percentage of small precipitates below 100 nm in size was important in determining corrosion resistance and had a good correlation with the annealing parameter; that is, if the percentage was lower than 30%, the corrosion resistance was satisfactory. Also, the frequency of precipitates under 100 nm in size decreased sharply with increasing annealing temperature after hot-rolling. The intermetallic compounds that were incorporated into the ZrOst oxide scale and the scale/metal interface were observed by a transmission electron microscope (TEM). The incorporated intermetallic precipitates were observed to have changed their composition; that is, the iron content decreased and the iron/chromium (Fe/Cr) ratio for the zirconium-chromiumiron intermetallic precipitate was approximately 1 compared to approximately 2 in the Zircaloy matrix. During oxidation, iron from the intermetallic compound precipitates scattered more into the oxide than chromium. These results suggest that the iron that diffused into the oxide from the incorporated intermetallic precipitates may play an important role in the corrosion process. It was observed that a stress-relieved microstructure of the Zircaloy-4 just beneath the growing front of the oxide was transformed into a recrystallized microstructure. This was especially clear in a high ΣA material compared to a low ΣA material. This seems to be one of the reasons that a higher ΣA Zircaloy-4 is more corrosion resistant under uniform corrosion conditions.

    Keywords:

    zirconium alloys, zirconium, uniform corrosion, intermetallic compounds, manufacturing conditions, cumulative annealing parameter, oxide scale, transmission electron microscopy, autoclave tests, nuclear materials, nuclear applications, radiation effects


    Paper ID: STP15196S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP15196S


    CrossRef ASTM International is a member of CrossRef.