INFLUENCE OF EXPOSURE TO PB-LI ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF 9CRODS AND CLAM STEELS

摘要

In this work, corrosion experiments on 9Cr-ODS and CLAM steels were carried out in static Pb-Li at 873 K for 250 h. Both steels showed weight loss and softening near the surface after the exposure. Tensile properties did not change and creep properties degraded slightly for 9Cr-ODS steel. In contrast, CLAM steel showed hardening by increase in tensile strength and creep rupture time, and decrease in minimum creep rate and reduction of area. The metallurgical analyses showed that the both steels were non-uniformly corroded by preferential corrosion at grain and sub-grain boundaries. Near the surface, carbides were lost and Cr was depleted to several tens of μm depth. The depletion was heavier for 9Cr-ODS than for CLAM. The corrosion mechanism was proposed to be a loss of protective oxide layer followed by dissolution of Cr in matrix into liquid Pb-Li. The more pronounced corrosion effect on 9Cr-ODS than on CLAM may be due to finer grain and sub-grain size enhancing preferential attack by Pb-Li at the boundaries, or lack of Mn in 9Cr-ODS, which conform protective layers for CLAM.