A new method for preparing 9Cr-ODS steel using elemental yttrium and Fe2O3 oxygen carrier

Progress toward controllable nuclear fusion operations largely relies on the high performance of advanced nuclear structural materials. [1][2][3][4][5][6] Attributed to the extremely harsh environments where fusion reactors work, the components suffer from both high level of heat flux and high dose of neutron radiation. Oxide-dispersion-strengthened (ODS) steel is one of the most promising candidate structural materials for the next-generation fusion reactors due to its excellent resistance to high-temperature creep, corrosion, and neutron radiation. [7][8][9][10][11][12] ODS steels are mainly based on the reduced activated alloys such as Fe-Cr-W system. These alloys can be divided as reduced activated ferritic martensitic (RAFM) steels with a lower Cr (9-12 wt%) content and reduced activated ferritic (RAF) ones with a higher Cr (>12 wt%) content. Unlike RAFM steels, the RAF steels do not experience a γ-α transformation at elevated temperatures. Therefore, they can be operated at a higher temperature and have a better resistance to radiation swelling. [13][14][15] ODS steels possess a huge number of nano-oxides that are thermally stabilized in the matrix. These nanoparticles can not only hinder the movement of dislocations, but also absorb the point defects induced by irradiation, enhancing the pore expansion resistance and preventing void swelling of the materials under neutron irradiation. [16][17][18][19][20][21] For these reasons, a higher number density, a finer size, and a better distribution of the oxides are always pursued.Mechanical alloying (MA) is one of the most widely used methods to prepare ODS steels, where Y 2 O 3 powder is often added to the steel powder for long-term high-energy ball-milling. During MA, a large amount of lattice defects (e.g., vacancies and dislocations), along with the supersaturated dissolved Y and O atoms that are decomposed from the Y 2 O 3 powder, can be gradually restored in the powders. Then, powder metallurgy is conducted to this non-equilibrious MA powders to build the components with proper sizes and shapes. [22] In this step, one of the following densification strategies, that is, hot extrusion (HE), hot isostatic pressing (HIP), or spark plasma sintering (SPS), is usually carried out. [23][24][25] Assisted by the subsequent heat treatment, a huge number of Y 2 O 3 nanoparticles win the chance to simultaneously precipitate from the supersaturated matrix. In the earlier procedures, MA is definitely a timeconsuming stage. It takes an extremely long period, usually longer than 50 h, for the complete decomposition and dissolution of Y 2 O 3 through ball-milling since it has the highest bonding energy among most of the common oxides. [24][25][26] If MA process can be accelerated by a faster decomposition of the oxide

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

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Fabrication of Oxide‐Dispersion‐Strengthened Ferritic Alloys by Mechanical Alloying Using Pre‐Alloyed Powder

Zhang

Zhao

et al. 2022

“…Hong et al developed an ODS alloy via VIM using dissolved Y in liquid metal and Fe 2 O 3 as an oxygen carrier. [ 15 ] Particles bearing Y and measuring 0.2–1.1 μm in size (e.g., Y 2 O 3 , Y 2 O 2 S, Y 2 S 3 , YN, and YC 2 ) were achieved in the steel matrix, and the ODS steel obtained exhibited higher ultimate tensile and yield strengths and slightly lower elongation compared with 9Cr steel prepared by the same method. Studies on the characterization of Y‐rich particles in ODS steels prepared by the liquid‐metal method and mechanical property tests demonstrated that introducing Y oxides to the steel matrix via the traditional steelmaking process is feasible.…”

Section: Introductionmentioning

confidence: 99%

Strengthening Effect of Multiscale Second Phases in Reduced Activation Ferrite/Martensitic Steel

Qiu

et al. 2021

Owing to their excellent resistance to irradiation, good creep property, and extraordinary structural and chemical stability in harsh, high-temperature environments, oxide dispersionstrengthened (ODS) reduced activation ferritic martensitic (RAFM) steels are considered prime candidates for advanced structures, including nuclear fusion reactors. [1,2] The excellent properties of ODS RAFM steel can be attributed to the fine grain size of the steel and the dispersed nano strengthening phases, such as Y 2 O 3 , MX (M ¼ Ta, V, X ¼ C, N), and M 23 C 6 (M ¼ Fe, Cr). [3,4] Dispersed Y 2 O 3 particles can not only effectively block dislocation movements but also absorb the vacancies produced by irradiation and the helium generated by transmutation in the nuclear fusion reactor, thereby improving the radiation resistance of the alloy. [5] Y 2 O 3 particles could be refined by the addition of Ti and Zr to the Fe matrix to form Y-Ti-O and Y-Zr-O clusters. [6,7] Ti and Zr elements could also form TiC, (Ti, W) C, (Ti, Ta) C, and V 3 Zr 3 C, which have strengthening effects similar to that of MX with Ta/V, to improve the high-temperature mechanical properties of steel alloys. [8,9] Ti and Zr are important alloying elements often used to prepare ODS steel. ODS RAFM alloys are commonly manufactured via powder metallurgy (PM), which involves mechanical alloying, hot powder consolidation (e.g., hot isostatic pressure, hot extrusion, or sparking-plasma sintering), and heat treatment. However, PM presents several inherent defects for the preparation of ODS alloys; for example, the technique could introduce impurities (e.g., O 2 ) to its complex processes, thereby inducing anisotropy in the microstructure and mechanical properties of the resulting alloys. [10] The technology also requires large amounts of energy and, at present, cannot be scaled up to industrial production.A demonstration nuclear fusion reactor requires over 11 000 tons of ODS RAFM steel as its structural material, [11] but PM technology for fabricating large-scale ODS steels has not yet been developed. This shortcoming is a basic defect of ODS RAFM steel production. Research on alternative preparation technologies for ODS steel is ongoing globally.Shi and Han directly added micron Y 2 O 3 powders to molten Fe alloy to prepare ODS steel by vacuum casting, forging, and heat treatment. [12] Analysis of the resulting alloys revealed complicated oxides containing Cr, Ti, Ta, Mn, V, Y, and O, which could prevent dislocations from gliding to improve the yield strength of the steel. Zhan et al. prepared 9Cr-ODS alloys by adding Y and Ti alloys to 9Cr steel through vacuum induction melting (VIM). [13] A large number of Y-Ti-O particles smaller than 0.5 μm were found in the steel, and the density of these particles reached 2.69 Â 10 19 m À3 ; this value is close to the density reported for 9Cr-ODS steel prepared by chemical reduction and mechanical milling (i.e., 5.7-8.1 Â 10 20 m À3 ). Oxygen carrier casting technology has been adopted to prepare ODS RAFM alloys by introducin...

“…[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.…”

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confidence: 99%

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

Xiao

Yang

et al. 2023

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