Microstructures and Mechanical Properties of Alumina and/or Yttrium Oxides Strengthened 9Cr Steel Fabricated by Vacuum Casting

Abstract

High-Cr (9-12 wt%) ferritic/martensitic (F/M) steels are considered to be the most promising structural materials for advanced nuclear reactors because of their excellent performance in strength as well as high thermal conductivity and superior radiation resistance compared with austenitic stainless steels. [1,2] Even that, the upper operating temperature for the F/M steels was limited to about 550 °C due to the aging embrittlement and insufficient strength at higher temperatures. [3][4][5][6][7] One way to overcome this limitation is to introduce oxide dispersoids in the matrix, and the corresponding steels are called oxide dispersion strengthened (ODS) F/M steels. These steels contain a high density of small oxide particles dispersed in the matrix that significantly improve creep strength and maintain other favorable properties of the conventional F/M steels, pushing the operating temperatures to 650 °C and beyond. [4,[8][9][10] The well-established and default process for the production of ODS F/M steels is based on the powder metallurgy route, which consists of mechanical alloying, degassing & canning, hot powder consolidation, and heat treatment. [11][12][13] However, this fabrication process is expensive, and results in anisotropic microstructure and mechanical properties, [14,15] and fitness for scaling up to the industrial scale is limited. [16] More recently, the casting (or liquid metal) route, which simply adds fine oxide powder directly to liquid steel, is suggested to be a promising approach to producing low-cost ODS steels with larger volumes and higher throughput. [17] Using the casting route, many researchers mainly focused on the investigation of Y-containing oxides for ODS F/M steels, such as Y 2 O 3 , [18,19] Y-Ti-O, [20][21][22][23] and Y-Zr-O [23][24][25][26] To the authors' knowledge, other types of oxides are rarely introduced into the ODS F/M steels fabricated through the casting route.Al is generally used for the deoxidation of steel in the smelting process and Al 2 O 3 inclusions inevitably appear in the steel after solidification. Furthermore, Al 2 O 3 , as an oxide dispersion strengthened phase, has been successfully introduced in carbon structural steel [27] and martensite stainless steel [28] by casting route. The Al 2 O 3 -containing particles can act as heterogeneous nucleates that play an important role in grain refinement and dispersion strengthening for the steels, and thus effectively improve the mechanical properties of these steels. In this work, to broaden the types of oxide particles used in ODS F/M steels as well as improve their mechanical properties, Al 2 O 3 -containing particles were introduced into the F/M steel with 9 wt% Cr content (9Cr steel) by casting route under the help of master alloying

Effect of addition of alumina and rare-earth oxide particles on the corrosion resistance and mechanism of low carbon low alloy steel

“…This ingot was used as master alloy 20 wt% master alloy nuggets and pure metal pieces were prepared, melted in the vacuum induction furnace, and cast into the NHAl steel ingot. More details about the experiment could be found in [29,30,39]. The RE oxide particles were introduced into the NHRE ingot by directly adding pure RE pieces (La and Ce) to the molten steel during the final smelting stage.…”