Novel Hafnium-Containing Steels for Power Generation

Research has demonstrated that creep damage in power plant steels is directly linked to grain boundary precipitates, which serve as nucleation sites for cavities and micro-cracks. The formation of M₂₃C₆ carbides along grain boundaries creates chromium-depleted zones vulnerable to corrosion and significantly reduces creep life due to rapid coarsening. Through combined Monte Carlo grain boundary precipitation kinetics and continuum creep damage modeling, researchers have predicted that increasing the proportion of MX-type particles could enhance creep performance. This hypothesis was tested using hafnium-containing steel, which showed improved creep and corrosion properties in 9% Cr steels. Ion implantation of Hafnium into thin foils of 9 wt% Cr ferritic steel resulted in two new types of precipitates: hafnium carbide (MX-type) and a Cr-V rich nitride (M₂N). The hafnium carbide particles, identified through convergent beam diffraction and microanalysis, appeared in significantly higher volume fractions compared to VN in conventional ferritic steels. Additionally, Hafnium was found to eliminate M₂₃C₆ grain boundary precipitates, resulting in increased matrix chromium concentration, reduced grain boundary chromium depletion, and enhanced resistance to intergranular corrosion cracking.