Developing a Novel Ods Steel to Tailoring Mechanical Properties and Microstructure by Addition of Vn and Y2o3 Powders

Abstract

There are several approaches to increase the high-temperature performance and upper service temperature of reduced activation ferritic/martensitic (RAFM) steels for application in fusion reactors, which mainly involve optimizing MX carbonitrides or introducing oxides into matrix. In this work, a novel steel is proposed, which is synergistically strengthened by MX nitrides and oxides via addition of 0.2% VN and 0.35% Y2O3 powders together during the mechanical milling. In addition, the steels with an addition of 0.35% Y2O3 or 0.2% VN powder alone were also prepared for comparison. As a result, fine gains less than about 1 µm accompanied by a large number of dislocations and nanoprecipitates were obtained in these steels. Fine VN precipitates were formed in the steel with the addition of 0.2% VN powder. Its elongation reached about 40% at 700 ℃, which is even superior to those of RAFM and castable nanostructured alloys (CNAs) fabricated by melting method. In the steel with 0.35% Y2O3 powder added, dispersed Y2O3 oxides were formed and the tensile strength is comparable to that of 9Cr-ODS steel. On the contrary, after the addition of 0.2% VN and 0.35% Y2O3 powders together, the complex Y-V-N-O precipitates with structure of Y2O3 were formed to have a finest average diameter of 6.4 nm and highest number density of 7.9×1022 m-3. Consequently, it exhibited improved tensile strength and almost without impairing elongation at room temperature and 700 ℃, compared with those of RAFM, CNAs and 9Cr-ODS steels. The proposed idea could be extended to other alloys.

Keywords: Oxide dispersion strengthened (ODS) steels, Nano-oxides, VN precipitates, Powder metallurgy.