Microstructural Characterization and Pitting Corrosion Behavior of UNS S30466 Borated Stainless Steel

For the last few years, new alloys are being developed to increase the storage capacity of spent-fuel pools. Boron-strengthened austenitic stainless steel (SS) alloys are now replacing AISI 304 SS (UNS S30400), as their capacity to absorb neutron is higher. The effect of boron on susceptibility to pitting corrosion has not been studied in depth until now. In this paper, the microstructure of a boron-strengthened austenitic SS in an as-received and heat-treated state is analyzed. Chromium boride particles ([Cr2Fe]7.66 [B,C]6) that follow the rolling direction on an austenitic matrix belonging to a facecentered cubic system are observed. Pitting corrosion behavior in the presence of chloride anions and chloride with a higher sulfide content has been determined. The morphology of corrosion pits produced in both solutions for both states has been analyzed by two different types of microscopes: an optical and a scanning electron microscope. For the chloride medium, there is a greater number of pits; for the sulfide medium, the pits are not as deep but are more extended. The pitting potentials in the sulfide medium are higher than those obtained in the chloride medium.