Direct consolidation of an oxide dispersion strengthened alloy by hot rotary swaging Direkte Verfestigung einer oxiddispersionsgehärteten Legierung durch Warmdrehkneten

Abstract

Steels strengthened by alloying elements and precipitates typically maintain their enhanced properties up to the ferrite-austenite transformation. However, oxide dispersion strengthened ferritic steels are creep resistant even at much higher temperatures given by dispersions of nanosized oxides. To ensure homogeneous dispersion of the oxides, powder metallurgy is used for preparation of the original material. The presented study investigates the effects of direct consolidation of powder of ferritic steel strengthened with yttrium oxide nanoparticles. The powders were mechanically alloyed and sealed into evacuated steel containers, which were subjected to gradual hot consolidation via the industrially applicable intensive plastic deformation method of rotary swaging. Investigations assessing the effects of several reduction ratios showed that the direct consolidation of the oxide dispersion strengthened steel was successful – in the macroscale – at the swaging ratio of 1.03; the quality of consolidation further increased with increasing swaging ratio. At the swaging ratio of 1.83, the consolidated bulk material featured ultra-fine grains characterized with high angle grain boundaries, homogeneous dispersion of oxide precipitates, and the average Vickers microhardness of 706.6 HV 1.