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High-speed steels (HSSs) are widely used in making cutting tools due to their high hardness and good wear resistance even at high temperature. These excellent properties can be attributed to the carbides uniformly distributed in the matrix, such as MC, M 6 C, etc [1,2] . As for W-Mo HSSs, the as-cast structure at room temperature mainly contains M 2 C eutectic carbides and a small number of large-size primary MC carbides (stable phase) directly precipitate from the liquid phase [3] . Among them, M 2 C is a metastable phase, and could totally decompose into smaller MC and M 6 C secondary carbides after a series of processing [4][5][6] . Even though MC carbides have the highest hardness (around 3,000 HV) and contribute high wear resistance [7] , these

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

Abstract：The microstructure evolution of Ti-47Al-2Cr-2Nb alloy was investigated on liquid metal cooling type directional solidified apparatus at high temperature gradient. The analysis shows that it is solidified with primary β cells/dendrites, and then α phase is formed through peritectic reaction. Once the columnar grains grow into the steady state, the lamellar orientation inclined with the angle of 45° to the withdrawal direction is more favored than that with parallel to the withdrawal direction. In addition, α phase grain nucleates from β-interdendrite regions, and grows up to the dendritic trunk. If no other α grain hinders its growth, it would occupy the whole dendrite, or it would stop at the dendritic trunk for the weakened motivating drive in the β dendritic core.