Corrosion behavior of a ferritic/martensitic steel HCM12A exposed to harsh environments

The corrosion behavior of a 12%Cr ferritic/martensitic steel, HCM12A, exposed separately in supercritical water (SCW) and lead–bismuth eutectic (LBE) was evaluated focusing on the microstructure of the corrosion products that develops in the first 333–1000 h. The effect of an yttrium-coating layer on the corrosion resistance of the steel was also studied. Detailed comparison of the corrosion results, including oxide scale layer structure, oxide grain morphology, texture development, and distribution of phases and alloying elements, between as-heat treated and Y-coated samples, and between SCW- and LBE-exposed environments, are reported. Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS), X-ray diffractometry (XRD), and electron backscatter diffraction (EBSD) were employed for these analyses. The outer oxide scale, magnetite, was detached/dissolved into LBE but not in SCW. Exposure results indicate that the Y-coating improved the corrosion resistance, as represented by a smaller weight gain, thinner oxide scale, and prevention of the oxide scale from detachment into LBE compared as compared to that which occurred on the non-Y treated samples.