Precipitation behavior of oxide in 9Cr-ODS steel prepared by three melting routes: A comparative study

Melting routes provide a viable pathway for the large-scale fabrication of oxide dispersion strengthened (ODS) steels. In this work, three processing routes, FeO precursor powder method, Y₂O₃ precursor powder method, and controlled oxygen atmosphere method, were systematically compared to clarify their effects on oxide precipitation behavior in 9Cr-ODS steels. For the FeO precursor powder method, the fabricated steel contained 200 ppm yttrium and 110 ppm total oxygen, resulting in the formation of submicron Y-rich oxides (∼479 nm, ∼3.2 × 1015 m−3) and Y₂TiO₅ nano-oxides (∼8.2 nm, ∼2.5 × 1021 m−3), which formed through reactions between dissolved oxygen and solute Y and Ti during aging. The Y₂O₃ precursor powder method increased the yttrium and oxygen contents to 300 ppm and 130 ppm, respectively, while retaining Y-O clusters in the as-cast microstructure, which provided additional nucleation sites and led to a slightly higher nano-oxide number density (∼2.8 × 1021 m−3). In contrast, the controlled oxygen atmosphere method supplied continuous external oxygen, raising the dissolved oxygen concentration, thereby significantly increasing the chemical driving force for nano-oxide nucleation. As a result, the O₂-ODS sample exhibited a nearly doubled nano-oxide number density, giving rise to a superior strength-ductility synergy with an elongation of 11.7%. This study elucidates the intrinsic link between yttrium and oxygen states, nucleation mechanism, and oxide precipitation, providing guidance for melting routes of ODS steel.