Manganese effect on the microstructural transformation and mechanical properties of oxide dispersion strengthened steels fabricated with pre-alloyed powders

Abstract

The effect of Mn on the microstructure and mechanical properties of oxide dispersion strengthened (ODS) steels prepared with pre-alloyed powders were evaluated. Two sets of ODS steels with nominal compositions (wt. %) of Fe-2.9Cr-0.25Ti-0.1Y-0.3Y(2)O(3)-0.2C (labeled as PA0) and Fe-25Mn-2.9Cr-0.25Ti-0.1Y-0.3Y(2)O(3)-0.2C (labeled as PA25) were fabricated. The microstructures were systematically investigated using X-ray powder diffraction, electron backscatter diffraction, and transmission electron microscopy. Fine oxide nanoparticles (NPs) were observed in the matrices of both PA0 and PA25. However, few agglomerates of Y2Ti2O7 and TiMn2O4 were observed in PA25. Tensile and Charpy impact properties at room, subzero, and high temperatures were also examined. Tensile test results showed that the yield and ultimate strengths were higher in PA0 due to its finer oxide NPs. Conversely, PA25 showed a higher ductility and work hardening rate ascribed to the high number of mechanical twins in its austenitic matrix. Similarly, Charpy impact energies at both room and subzero temperatures were higher in PA25, which could be explained by the high number of mechanical twins and strain-induced epsilon(hcp)-martensite transformation in PA25. We suggest that to prevent the formation of agglomerates and improve the mechanical properties of Mn-added ODS steel, Mn should be introduced not in the pre-mixed state, as was done here, but in the pre-alloyed state, which will be the focus of future studies.