12%Crフェライト系耐熱鋼のクリープに伴うアノード分極特性の変化

概要

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In order to investigate the possibility of electrochemical material characterization method as a procedure for remaining-life prediction of 12%Cr ferritic steels, this method was applied to three kinds of 12%Cr ferritic steels used in boiler and steam turbine and the changes in their anodic polarization behavior due to creep were measured. Experimental results revealed that the peak current densities “Ip1” and “Ip2” appeared at specific potentials during anodic polarization curve measurement in 1M-KOH solution. These peak current densities corresponded to the preferential dissolutions of several kinds of precipitates, respectively. The Ip2, which corresponded to the selective dissolution of M23C6 and Laves phase, increased more significantly with creep than thermal aging in all three steels. On the other hand, the effect of applied stress was not clearly reflected on the change in Ip1 corresponding to the selective dissolution of copper precipitate in the boiler steel, although it increased with thermal aging and creep as well as the Ip2. Therefore, it was expected that these peak current densities were useful indicators for estimating a temperature and applied stress working in high-temperature components of 12%Cr ferritic steels. Additionally, it was also revealed that the ΔIp2, which was increment of Ip2 from the as-tempered, increased with increasing creep life fraction and its variation showed almost no steel dependence.