Microstructure and mechanical properties of an ODS RAF steel fabricated by hot extrusion or hot isostatic pressing

Abstract

a b s t r a c tIngots of an oxide dispersion strengthened reduced activation ferritic steel with the Fe-14Cr-2W-0.3Ti-0.3Y 2 O 3 chemical composition (in wt.%) were synthesized by mechanical alloying of elemental powders with 0.3 wt.% Y 2 O 3 particles in a planetary ball mill, in a hydrogen atmosphere, and compacted by either hot extrusion or hot isostatic pressing. The microstructures of the obtained materials were characterized by means of light microscopy, transmission electron microscopy and chemical analyses. The mechanical properties were evaluated by means of Vickers microhardness measurements and tensile tests. It was found that the microstructure of both materials is composed of ferritic grains having a submicron size and containing nanometric Y-Ti-O oxide particles with a mean size of about 10 nm, uniformly distributed in the matrix. The oxide particles in the hot extruded steel were identified as YTiO 3 phase. In larger (>10 nm) oxide particles Cr was found next to Ti, Y and O. The steel produced by hot extrusion exhibits much higher tensile strength and hardness at low to moderate temperatures, as compared to the steel fabricated by hot isostatic pressing, which was mainly attributed to smaller pores but also to more severe work hardening in the case of the hot extruded steel.

Behaviour of new ODS alloys under single and multiple deformation

“…In the consolidation step the processing temperatures are critical in order to retain the nanocrystalline structure generated during the mechanical alloying and to impede particle coarsening and grain growth. [11][12][13][14] The Ni-and Fe-based ODS alloys rely on the formation of slowly growing and strongly adherent chromium and aluminium scales for their high-temperature oxidation/corrosion resistance. Because of the lower diffusion coefficient, austenitic ODS alloys show a better creep resistance for the same oxide volume fraction and contain some minimum chromium/ aluminium content to guarantee sufficient oxidation resistance.…”

Development of a Novel Melt Spinning-Based Processing Route for Oxide Dispersion-Strengthened Steels

“…However, annealed Fe-1Y-1Ti had only approximately half the hardness of a mechanically alloyed 14YWT ODS steel. [43][44][45][46] Although the dispersion of oxide particle diameters of 20 to 300 nm produced by melt spinning and internal oxidation route were coarser than the 1-to 5-nm-diameter oxides achievable by mechanical alloying under optimum conditions, there is sufficient encouragement to suggest future work might focus on melt spinning of more standard Fe-14Cr-3W-based alloys, with lower concentrations of Y and Ti, and that with further optimization of heat treatment conditions, an alloy that provides useful performance with improved availability in bulk might be developed.…”

Influence of thermomechanical treatment on the grain-growth behaviour of new Fe-Al based alloys with fine Al2O3 precipitates

“…Tests in group A were carried out to investigate the thermomechanical behaviour of different materials (1)(2)(3)(4)(5)(6)(7)(8) at different temperatures, looking at a single tensile and compression loading with a constant strain rate of 1 s -1 (Figure 7). In order to give a clearer comparison of the results, only the results at room temperature (RT), (800, 1000 and 1200)°C are presented.…”

“…[5][6][7][8][9] The Ni-and F-based ODS alloys rely on the formation of slowly growing and strongly adherent chromium and aluminium scales for their high temperature oxidation/corrosion resistance. In the present study, the ODS alloys consist of a ferritic Fe-Al matrix strengthened with about 4 % volume fraction of Al 2 O 3 particles.…”