Corrosion behavior and mechanisms of rare-earth ferrite/martensite steel weldment in liquid lead-bismuth eutectic

Abstract

With the increasing operating temperatures in fast neutron nuclear reactor designs, the incorporation of Cr, Si, and rare earth elements into the ferrite/martensite (F/M) steels has become common practice to bolster high-temperature mechanical properties and corrosion resistance. Nonetheless, weld joints often emerge as critical positions limiting the steel service life. Research on the service performances of weld joints in novel F/M steels enriched with Cr, Si, and especially rare earth elements remains lacking. Here, by studying a rare earth F/M steel and its weld joints, we systematically evaluated the corrosion resistance and degradation mechanism of laser-weld joints of the steels in liquid lead-bismuth eutectic alloy. Atomic-scale structural and chemical characterizations revealed that the welding process leads to a loss of solute Y and hence hinders the formation of the crucial Cr₂O₃-rich anti-oxidation layer. Without the protection, oxygen diffusion zone develops in the coarse columnar crystals in the weldment, which further undermines the density of the oxide scale. These findings provide critical fundamental information with insights for enhancing the service performance of weldments in advanced F/M steels.