Microstructure and tensile properties of oxide dispersion strengthened Fe–14Cr– 0.3Y₂O₃ and Fe–14Cr–2W–0.3Ti–0.3Y₂O₃

Abstract

Two ODS ferritic steels with nominal compositions (wt.%): Fe–14Cr–0.3Y2O3 and Fe–14Cr–2W–0.3Ti–0.3Y2O3 have been produced by mechanical alloying and consolidation by hot isostatic pressing. The microstructure and tensile properties of these materials after being forged and heat treated at 1123 K have been investigated to clarify the interrelation between composition, microstructure and mechanical properties. The second phase precipitates in these alloys have been analyzed by high angle annular dark field imaging in scanning TEM mode and electron diffraction. Fe–14Cr–2W–0.3Ti–0.3Y2O3 exhibits a duplex microstructure consisting of large recrystallized grains, as large as 1.5 μm, and unrecovered regions containing submicron equiaxed grains. In addition, three types of secondary phase particles have been found: large M₂₃C₆ particles containing W and Cr, (Cr + Ti) rich spherical particles with diameters between 50 and 500 nm, and fine (Y + Ti) oxide particles with sizes below 30 nm. In contrast, Fe14CrY shows a uniform structure of equiaxed grains, with sizes in the range 0.5 3 μm, containing a fine disper sion of Y oxide particles (<30 nm) homogeneously distributed inside the grains, as well as large carbide and oxide particles. Tensile tests performed over the temperature range 273 973 K have revealed that the alloy containing W and Ti has lower yield and tensile strengths than Fe–14Cr–0.3Y2O3 at tempera tures up to 773 K, but the opposite appears to occur beyond this temperature.