Effect of SiC Addition on the Compatibility and Sintering Behavior of M2 High Speed Steel Powder
Year: 2026
Type: article
Abstract: Effect of SiC Addition on the Compatibility and Sintering Behavior of M2 High Speed Steel PowderAuthors: M. Khakbiz; A. SimchiPublished in: P/M Science & Technology Briefs, 2003, 5(4), 23–32Full-text transcription of the published article, including the original tables and all five figure captions. The original figures are available in the PDF or illustrated HTML uploaded as record files.AbstractHigh speed steels are used for applications that require strength and hardness combined with the ability to withstand high temperatures. On the other hand, addition of ceramic particles, which are easily incorporated by powder metallurgy route, has the potential to increase the wear resistance of these materials for the mass production of automotive parts. However, these alloys are difficult to process by standard P/M route on an industrial scale because it needs sintering at relatively high temperature, with a very narrow sintering window. The present work was undertaken to improve the overall performance of P/M M2 grade high speed steel by reinforcing it with SiC. As a reference material M2 grade HSS with and without additions of copper was chosen. Microstructural analysis of sintered microstructure and identification of phases were made using optical microscopy, SEM and EDX-analysis. It was found that during the processing of the composite, the M2 matrix interacts strongly with the SiC at around 1100 °C resulting in the formation of low melting Fe-Si-C phase. An attempt to process M2/SiC composite above 1120 °C resulted in complete melting of the compact. By varying the composition of the mixture and sintering condition, the structure, density, and properties such wear resistance, resistance to hot crating and hot hardness may be optimized for a given application.1. IntroductionHigh speed steels (HSS) are high alloy, high strength tool steels being used for various types of cutting tools, including drills, saws, milling tools, treating tools, etc., but also for demanding cold work applications such as fine blanking tools and dies [1]. These materials have been produced by conventional steelmaking methods for several years. However, powder metallurgy high speed steels have opened up new possibilities in tool making and tool usage and they have contributed to dramatic cost reductions e.g. in automotive transportation plants as well as in aerospace components [2-4]. Indeed, during the couple of last decades the process has been satisfactorily developed, allowing producing tools with improved properties and lower production costs than the conventional methods.The main advantage of P/M route for manufacturing HSS refers to the ability of obtaining a fine and uniform microstructure in which segregation is reduced to insignificant levels [5]. Accordingly, better strength and grinding characteristics as well as higher hardness and resistance to wear can be achieved. However, it is known that application of the supersolidus sintering process of HSS requires keeping a close interval of temperature of liquid phase formation [6]. This problem suggests an important field of study of densification by formation of a secondary liquid phase using several additives [e.g. 7]. For instance, introduction ofcopper phosphide is successful in lowering the sintering temperature and fully dense parts can be produced using continuous mesh belt furnaces [8]. The vacuum sintering of systems based on HSS M2 powder chemically coated with Cu and graphite additions was successfully implemented [6]. The positive influence of FeB powder on the densification of HSS was also studied [9].However, attentions have been recently focused on developing new wear resistant materials to be used in components for the automotive industry [10]. One of the main fields of the study is about investigating the effects of ceramic particles on the hardness, bend strength, and fracture toughness of HSS composites, as compared to the base material. Unfortunately, introduction of ceramic particles results in lower green density and it also reduces sintering activity of the composite compacts [8]. Therefore, high amounts of additives such as copper phosphide and graphite have to be added to the mixture to counterbalance the influence of ceramic particles. This consequently leads to a decrease in the fracture toughness and the bending strength of the composite [11]. The aim of this paper is to report on the matrix reinforcement interaction that occurs during processing of M2 grade high speed steel composite with one such reinforcement, namely SiC.2. Experimental ProcedureThe starting powders used for manufacturing the sintered materials were water atomized M2 grade HSS powder from Hoganas, Belgium; SiC powders with mean powder particle size of 600, 800, and 1000 mesh from Zamin Tavana Co., Iran; water atomized copper powders from MPM Co., Iran. The composition and some characteristics of HSS powder used were summarized in Table 1.A small batch of the HSS powder was modified by coating of particles with copper by a cementation reaction in an aqueous CuSO4 solution as cited in [12]. The copper content was adjusted to 2 wt-% by controlling the powder mass. Moreover, some runs were made by 2 wt-% elemental Cu additions. The chemical composition of the composite compacts was fixed on M2-5 wt-% SiC with and without copper coating / addition.Powders were uniaxially cold compacted to cylindrical (25 mm diameter and 6 mm high) compacts at 550 MPa without lubricant. Sintering was performed in a laboratory tube furnace in a vacuum of the order of 10-2 torr at 1120 °C for 20 and 60 min. The specimens were furnace cooled to ambient temperature. The mean cooling rate was around 10 K/min in the range from 800 to 580 °C. The density of the sintered samples was measured by the water displacement method. The hardness of the samples was evaluated by using the Vickers method under 0.05 and 30 kg force. Microstructural analysis of sintered microstructure and identification of phases were made using optical microscopy, SEM and EDX-analysis. Some specimens were also hardened and tempered with austenitisation being carried out at 950 °C for 30 min followed by oil quenching. The specimens were subsequently single tempered in air at temperature within the range of 400-550 °C for 60 min.Table 1 (original). Composition of M2 grade high-speed steel powder.ElementCCrWMoVMnSiO+NComposition (wt.%)0.834.196.134.081.9250.270.19*Table 1 (continued). Powder sieve analysis.Powder sieve range<45 µm45–53 µm53–75 µm75–106 µmPowder fraction (wt.%)35.611.921.817.8Table 1 (continued). Powder properties.Apparent density (g cm⁻³)Hall flow (s/50 g)2.5529.73. Results and Discussion3.1 DensityThe green density of the investigated material systems compacted at 550 MPa is illustrated in Fig. 1. One can see that the copper coating decreases the green density. However, addition of elemental copper powder has a positive influence on the densification. The advantage of blending hard high speed steel particles with tough and highly compressible powders to enhance the compressibility has been already established [4]. On the other hand, Strobl and Danninger [13] have shown that Cu-coated M2 powders were more difficult to compact in comparison to the base powders, and the green bodies being comparatively fragile. Similar results were found in this study. It may due to surface condition of the coated powder, which influences friction, interlocking, and cold welding between particles.From Fig. 1, it is also visible that additions of SiC particles to the M2 base powder adversely affect the compressibility. The SiC particles are rigid bodies that do not deform to fill in the voids. On the other hand, the M2 particles are comparatively more ductile plastic bodies. On the base of the percolation theory [14, 15], which analyzes the connectivity of a two-body system, it can be concluded that the amount of SiC added to the base powder should be above the percolation threshold. It means that the SiC particles are not distributed predominantly as isolated grains spanning M2 particles, i.e. larger SiC clusters are formed. This leads to lower green density and reduces the green strength. When the M2/SiC composite is accompanied by Cu coating, the green density is reduced further. It seems that the adverse effect of adding SiC and Cu coating was superimposed.Figure 1. The green density of the investigated material systems compacted at 550 MPa; Cu-C: copper coated; Cu-E: elemental Cu addition; SiC-XXX denotes mesh size.The effect of sintering on the density of the investigated material systems is given in Table 1. It is known that the optimum vacuum sintering temperature of cold compacted M2 HSS was established as 1243-1255 °C, but also about 1330 °C [16]. For ultra-fine M2 powders full density could be achieved at approximately 1200 °C [9]. So, sintering at a temperature as low as 1120 °C does not impact the density of M2 base powder. On the other hand, the Cu content does not markedly affect the optimum sintering temperature which is well comparable to that of the plain HSS used as basic powder.However, the results show that additions of SiC particles strongly influence the densification of M2 base composite compacts. The effect also markedly depends on the particle size of the ceramic particles as well as sintering time (Fig. 2). It is well known that adding inert, rigid inclusions to a powder system retards sintering [17, 18]. The inert particles not only reduce the volume of densifying material, they also create a hydrostatic tensile stress in the matrix which opposes the sintering stress This cause de-sintering and crack-like void formation [19]. In the case of HSS/TiC/TiN composites Bolton and Oliveira [11] have found that additions of the ceramic particles reduce the sintering rate. They have also shown the sintering rate is greater for the composites containing coarser TiC particles at low temperatures of Ts < 1160 °C. However
Source: Figshare
Author: Mehrdad Khakbiz
Language: English
Subfield: Mechanical Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7225594754