Casting technology for ODS steels - the internal oxidation approach

Abstract

View the article online for updates and enhancements. Related contentCasting technology for ODS steelsdispersion of nanoparticles in liquid metals M Sarma, I Grants, I Kaldre et al. Abstract. The formation of stainless ODS steel by internal oxidation of as-cast steel has been investigated. An alloy (Fe-16Cr-0.2Al-0.05Y, wt.%) was embedded in a (VO/V 2 O 3 ) powder mixture serving as an oxygen activity buffer and heat treated at 1450°C for 20 h. After this procedure no oxide scale was present on the surface of the sample but a zone of internal oxidation with a depth of about 2000 µm was formed in its interior. The precipitates within this zone consisted of two types of oxides. Discrete aluminium oxide particles with a size of a few micrometres were formed in outer regions of the specimen. Finer aluminium-yttrium oxides with a size of some hundred nanometres were mainly precipitated in inner regions of the sample. The results can be considered as a promising step towards an alternative production route for ODS steels. IntroductionReduced activation ferritic-martensitic (RAFM) steels are promising candidate materials for structural applications in fusion reactors. These steels have been developed based on massive industrial experiences of ferritic/martensitic steel [1]. RAFM steels have interesting properties such as low sensitivity to irradiation-induced swelling and helium embrittlement [2].RAFM steels are very attractive structural materials but their high-temperature strength is limited and one of the effective approaches to solve this issue is oxide dispersion strengthening (ODS) method [3]. The nano-sized oxide particles with high number density can act as pinning points to dislocation movement [4]. Dispersed nano-sized oxides may provide a large number of trap sites for transmutant helium and radiation-induced defects [5]. The improved creep resistance and fatigue strength at high temperatures is another advantage of ODS steels [6].The typical procedure for manufacturing ODS steels is the powder metallurgy route in which steel powders and Y 2 O 3 powders are mechanically alloyed by high energy milling. The input oxides remain unmixed but they are dispersed throughout the microstructure of the alloy [7]. This technique was first developed by J. S. Benjamin and published in 1970 [8].The next step in this route is hot isostatic pressing (HIP). In HIP process, the simultaneous application of a high pressure at elevated temperatures in a constructed vessel is planned for hot compaction of the powders. The pressure inside HIP chamber is generated usually by applying purified argon gas. In the later steps after HIP, the deformed powders are hot extruded or rolled for the desired shape.

Effect of hot cross rolling on the microstructure and mechanical properties of an Fe-14Cr ODS ferritic steel

“…Although these days there are some advances, it is really difficult and complex to produce ODS steels by common and economical fabrication techniques such as casting. 81,82 For example, if the oxide powders were directly introduced to a metallic melt, there would be some critical issues such as the limited wettability and flotation of the oxide particles and their tendency to form agglomeration before introduction in the melt. In addition, as important volumes of nanoparticles would have to be managed in a foundry environment, there would be practical difficulties and possible health and safety issues due to the manipulation of the nanoparticles.…”

A Novel Processing Route in the Mechano-Synthesis of Austenitic 58Fe25Ni17Cr Oxide Dispersion Strengthened Cast Alloy through Y₂O₃ Pre-Linking

“…Research on high-temperature steel has been carried out for a few years, both by powder metallurgy (P/M) [2], casting [3,4,5] and its combination [6] methods. However, the researchers have encountered many problems in homogenizing the reinforcing oxide dispersing into the ODS alloy.…”