Evolutions of Micro- and Macrostructure by Cerium Treatment in As-Cast AISI M42 High-Speed Steel
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AISI M42, a molybdenum-series high-speed steel (HSS) with an additional 8 wt pct cobalt, has been extensively employed in cutting tools manufacturing owing to its harmonious combination of high hardness, superior hot hardness, excellent wear resistance and good toughness.[1,2] Traditionally, M42 HSS is produced in the route as follows: ingot casting fi hot forging and hot rolling fi heat treatment.[3,4] However, due to the low cooling rate and the severe segregation of alloying elements (C, Mo, Cr, W, V, etc.) during solidification, the as-cast structure of M42 HSS inevitably contains comparably high proportion of coarse eutectic carbides WEI-CHAO JIAO, HAO FENG, LING-FENG XIA, SHU-CAI ZHANG, and HONG-CHUN ZHU are with the School of Metallurgy, Northeastern University, No. 3-11, Wenhua Road, Heping District, Shenyang 110819, P.R. China. HUA-BING LI and ZHOU-HUA JIANG are with the School of Metallurgy, Northeastern University and also with the State Key Laboratory of Rolling and Automation, Northeastern University, No. 3-11, Wenhua Road, Heping District, Shenyang, 110819, P.R. China. Contact e-mail: [email protected] WEI WU is with the Metallurgical Technology Institute, Central Iron & Steel Research Institute, No. 76, Xueyuan Nanlu, Haidian District, Beijing, 100081, P.R. China. Manuscript submitted February 27, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
(including MC, M2C and M6C) heterogeneously distributed along the interdendritic regions.[1–6] These coarse eutectic carbides significantly decrease the hot workability of steel, thus leading to increased forging scrap rate.[3,7] Meanwhile, they are apt to form large-size and uneven carbide bands even after a substantial amount of hot plastic deformation, deteriorating the toughness and isotropic properties of steel.[2,8–11] In addition, the difference in the cooling rate from the center to the edge of the cast ingot results in a serious non-uniform distribution of M6C eutectic carbides at the macroscopic scale.[1,12] Therefore, improving the as-cast structure is of significance for M42 HSS to obtain the superior overall performance. In order to solve above-mentioned problems, an idea option is to use the rapid solidification technologies like powder metallurgy and spray forming, which can enormously eliminate the segregation of alloying elements and achieve fine and uniformly distributed eutectic carbides.[13–15] However, complicated process and high costs restrict their wide application and large-scale industrial production.[7,16,17] Under such condition, ingot casting modification by adding some amounts of modifying agents (different chemical elements) into the molten steel becomes the first selected option. Several recent studies have shown that adding rare earth metals like cerium (Ce) and lanthanum (La)
can produce some beneficial effects on the microstructures and properties of HSS. Li et al.[18] and Zhou et al.[19] reported that introducing Ce to M2 HSS can refine the dendritic structure and the plate-like M2C eutectic carbide and alleviate the segregation
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