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 1123K 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 1.5μm, 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 500nm, and fine (Y+Ti) oxide particles with sizes below 30nm. In contrast, Fe14CrY shows a uniform structure of equiaxed grains, with sizes in the range 0.5–3μm, containing a fine dispersion of Y oxide particles (<30nm) homogeneously distributed inside the grains, as well as large carbide and oxide particles. Tensile tests performed over the temperature range 273–973K have revealed that the alloy containing W and Ti has lower yield and tensile strengths than Fe–14Cr–0.3Y2O3 at temperatures up to 773K, but the opposite appears to occur beyond this temperature.