A Novel Method for Improving Cast Structure of M42 High Speed Steel by Pressurized Metallurgy Technology

Abstract

In this paper, a novel method of pressurized metallurgy technology was proposed to improve cast structure of M42 high speed steel (HSS). The effect of solidification pressure (0.1, 1 and 2 MPa) on the cast structure of M42 HSS was investigated by means of experimental analysis and calculation of Thermo-Calc and DICTRA software. Increasing solidification pressure can obviously enhance cooling rate by improving interfacial heat transfer coefficient, which results in some remarkable improvement of the cast structure of M42 HSS. Firstly, the primary/secondary dendrite arm spacing and the average thickness of eutectic ledeburite reduce, which means dendrite structure is refined and eutectic ledeburite more homogeneously distributes with smaller size. Secondly, increasing solidification pressure, the volume fraction of M 6 C carbides decreases obviously and that of M 2 C increases correspondingly. And the morphology of M 2 C carbide changes from larger size lamellar and straight-rod shape into smaller size curved-rod morphology under higher solidification pressure due to larger nucleation number and overgrowth of γ, indicating that carbides are refined and distribute more uniformly. At last, higher solidification pressure is beneficial to reduce the lamellar spacing of M 2 C carbide and make compositions distribute more homogeneously.

Evolutions of Micro- and Macrostructure by Cerium Treatment in As-Cast AISI M42 High-Speed Steel

“…This morphological characteristic is called fishbone morphology by previous researchers. [1,13] Therefore, the addition of Ce can significantly change the morphology of M 2 C carbides, but it has little influence on the morphology of M 6 C carbides. Figure 9 shows the as-cast macrostructure on the cross section of M42 cast ingots with different Ce contents.…”

“…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 (including MC, M 2 C and M 6 C) heterogeneously distributed along the interdendritic regions. [1][2][3][4][5][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][9][10][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 M 6 C 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.…”

Fabrication of Ultrafine Grained High Speed Steel with Satisfactory Carbide Dissolution by Electropulsing Treatment

“…High speed steels (HSSs) are complex alloy tool steels with high carbon and high alloying elements, such as W, Mo, Cr, V, or Co. 1,2) Because of their high wear resistance, good red hardness and reasonable toughness when treated correctly, 3) HSSs grab over 30% of the global cutting tool market. 1) The mechanical properties of HSSs are greatly influenced by carbides in this material, such as carbide type, volume percent, shape, and size and distribution.…”