Effect of Yttrium and Titanium on Inclusions and the Mechanical Properties of 9Cr RAFM Steel Fabricated by Vacuum Melting

Zhan, Dongping; Qiu, Guoxing; Zhang, Huishu

doi:10.1002/srin.201700159

Cited by 16 publications

(9 citation statements)

References 30 publications

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“…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 × 10 19 m −3 ; 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 × 10 20 m −3 ). Oxygen carrier casting technology has been adopted to prepare ODS RAFM alloys by introducing Y oxides to the steel matrix using elemental Y and TiO 2 as an oxygen carrier.…”

Section: Introductionsupporting

confidence: 69%

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

Qiu

et al. 2021

steel research int.

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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...

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Section: Introductionsupporting

confidence: 69%

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

Qiu

et al. 2021

steel research int.

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“…It is well known that MX precipitates play a significant role in determining the mechanical properties of steel. More MX can be observed in the Ti-RAFM steels [8][9]12]. The carbides in the C2 alloy were much finer than those in the other alloys.…”

Section: Microstructure and Precipitatesmentioning

confidence: 93%

“…However, the aforementioned studies only dealt with a single element (Y or Ti). Only few reports exist on RAFM steel with Y and Ti and the formation mechanism of the inclusions during the smelting process [8,9,12]. Hence, understanding the role of Y and Ti in the evolution of inclusions as well as the microstructure and properties of the RAFM steel is necessary.…”

Section: Introductionmentioning

confidence: 99%

Influence of Inclusions on the Mechanical Properties of RAFM Steels Via Y and Ti Addition

Qiu

Zhan

et al. 2019

Metals

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The effects of the Y- and Ti-containing inclusions on the tensile and impact properties of reduced activation ferritic martensitic (RAFM) steels were evaluated. Four steels with different Y and Ti contents were produced via vacuum induction melting. The size and quantity of inclusions in the steels were analyzed using scanning electron microscopy, and the oxide particle formation mechanism was clarified. These inclusions helped to enhance the pinning effect of the austenite grain boundaries based on the Zener pinning force. The average prior austenite grain sizes, measured via the linear intercept method, were 12.34 (0 wt.% Ti), 9.35 (0.010 wt.% Ti), 10.22 (0.030 wt.% Ti), and 11.83 (0.050 wt.% Ti) μm for the four steels, in order of increasing Ti content, respectively. Transmission electron microscopy was conducted to observe the fine carbides. The strength and impact properties of the steel containing 0.010 wt.% Ti were improved, and the ductile-to-brittle-transition temperature was reduced to −70.5 °C. The tensile strength and impact toughness of the steel with 0.050 wt.% Ti were significantly reduced due to the coarsening of both the inclusions and grain size, as well as the precipitation of large TiN inclusions. The RAFM steel with approximately 0.015 wt.% Y and 0.010 wt.% Ti exhibited an optimized combination of microstructures, tensile properties, and impact properties among the four steels.

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“…Yttrium, as a reactive element, has stronger thermodynamic affinity with oxygen than Al element does [35,36]. With decreasing temperature, the solubility of yttrium in steel matrix would decrease [37].…”

Section: Interfacial Reaction Between Inclusions and Steel Matrixmentioning

confidence: 99%

Transformation of Oxide Inclusions in Stainless Steel Containing Yttrium during Isothermal Heating at 1473 K

Zhang

Yang

et al. 2019

Metals

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To provide fundamental information on the control of rare earth inclusions in solid steel, two 18 mass% Cr-8 mass% Ni stainless steels with different yttrium additions were prepared using an electric resistance furnace and the evolution of yttrium-based oxide inclusions during heat treatment of the steels at 1473 K was investigated. In both as-cast steels, homogeneous spherical Al-Y-Si(-Mn-Cr) oxide inclusions were observed; however, the steel with larger yttrium additions also had some heterogeneous oxide inclusions with double phases. After heating, a new oxide phase with higher yttrium content precipitated from the original inclusions and resulted in partitioning to Y-rich and Al-rich parts in both steels. The average size and number density of inclusions slightly increased, and the morphology of inclusions changed from spherical to irregular. The transformation mechanism during isothermal heating was proposed to be the mutual effects of (i) internal transformation of the yttrium-based inclusions owing to crystallization of glassy oxide and (ii) interfacial reaction between inclusions and the steel matrix.Metals 2019, 9, 961 2 of 15 morphology of inclusions changed from dendritic to globular. A similar result was also observed by Katsumata et al. in 25 mass% Cr-6 mass% Ni stainless steel [8]. Kwon et al. [9,10] investigated the evolution of inclusions in Al-killed stainless steel with Ce addition at 1873 K. Mn(Cr)-silicates were found to be the primary inclusions before Al addition. When Al was added without Ce addition, the initial Mn(Cr)-silicate changed to Al 2 O 3 -rich inclusions. Then, Al-Ce complex inclusions were formed in the steel after Ce addition due to the reaction between Ce and Al 2 O 3 particles. Jönsson et al. [11,12] investigated the three-dimensional characteristics of clusters in REM-alloyed (Ce, La, Pr, and Nd) stainless steel through an electrolytic extraction method. It was found that most of the REM cluster consisted of regular and irregular REM-oxides, and the size of these clusters varied in the range of 2 to 23 µm. Moreover, turbulent collisions were determined to be the dominant form for the growth of REM clusters. With increasing the size of clusters, the growth rate of REM clusters increased.The changing behavior of rare earth inclusions in molten steel is relatively clear now; however, less attention has been paid to the possible transformation of rare earth inclusions in solid steel during heat treatment. This is practically important because steel quality significantly depends on the final state of inclusions after different thermal and mechanical treatments [13]. Many researchers have reported that some inclusions would change during heat treatment [14][15][16][17][18][19][20][21]. In 18 mass% Cr-8 mass% Ni austenitic stainless steel, MnO-SiO 2 oxide inclusions changed to finer MnO-Cr 2 O 3 spinel during heat treatment at 1473 K due to the interfacial reaction between inclusions and steel matrix [14][15][16][17][18]. Grain growth during heat treatment was also suppressed effec...

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Effect of Yttrium and Titanium on Inclusions and the Mechanical Properties of 9Cr RAFM Steel Fabricated by Vacuum Melting

Cited by 16 publications

References 30 publications

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

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

Influence of Inclusions on the Mechanical Properties of RAFM Steels Via Y and Ti Addition

Transformation of Oxide Inclusions in Stainless Steel Containing Yttrium during Isothermal Heating at 1473 K

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