Effect of radio-frequency plasma spheroidization on the microstructure and mechanical properties of 10Cr ferritic oxide dispersion-strengthened steel

Abstract

Reducing the porosity of irregularly shaped mechanically alloyed oxide dispersion-strengthened (ODS) steel powders is critical for their application at cryogenic temperatures. Although the plasma rotating electrode process has been widely used as a suitable method for producing spherical powders, its high cost and low powder yield impede its application. Thus, we investigated the feasibility of applying plasma spheroidization on ODS steel particles, to reduce their porosity, by investigating the influence of radio-frequency plasma spheroidization on the microstructure and mechanical properties of 10-Cr ODS steel. The ODS steel powder was ball-milled and then spheroidized prior to consolidation. The prepared samples were analyzed using X-ray diffraction, electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) as well as subjected to tensile and impact tests. The EBSD analysis revealed that the grains in the plasma-spheroidized sample were coarser than those in the non-spheroidized sample, and thus, the room- and cryogenic-temperature Charpy impact strengths of the latter were superior to those of the former sample. TEM analysis showed that the average particle size of plasma-spheroidized ODS steel was slightly higher than that of the non-plasma-spheroidized ODS steel. Furthermore, the room-temperature yield strength of the non-spheroidized ODS was higher than that of the spheroidized ODS because of the finer grains of the former. In the future, plasma spheroidization can be combined with other techniques to obtain completely dense ODS steel with increased upper shelf energies for various advanced and military applications.