High Speed Steel Carbide Research Articles

Effect of Alloying and Microalloying Elements on Carbides of High-Speed Steel: An Overview

In high-speed steel, carbides are essential phase constituents, which have a direct impact on engineering performance and qualities of high-speed steel. The formation, morphology, and distribution of carbides are dictated by alloying elements. In this paper, various types of carbides in high-speed steel are presented. The effects of different alloying elements such as C, W, Mo, Cr, and V on the formation of carbides in high-speed steel are discussed. Research progresses on carbide improvement by microalloying elements such as N, B, Mg, and rare earth (RE) elements are reviewed. It is reported that Cr promotes the precipitation of M2C, N enhances the formation of fibrous M2C, Mg effectively shatters the large-size carbide grid, Nb refines granular carbide MC, and rare earth elements encourage the formation of M6C, resulting in irregular M2C lamellae. The incorporation of microalloying elements improves the distribution and size of carbides and also refines the solidification structure of high-speed steel.

Precipitation Behaviors of Carbides in High Speed Steel during ESR and Heat Treatment

The microstructure and carbides evolution of high-speed steel after electroslag remelting and solution treatment were studied. The thermodynamic precipitation mechanism of carbides in solid phase was discussed and the characteristic parameters of carbides in different processes were also investigated. The results show that there were large lamellar and fibrous Mo2C and a small amount of VC in the ESR ingot. Mo2C are metastable carbides, which can be decomposed into VC and Fe2Mo4C during the solution treatment. The average diameter of the carbides is reduced to 1.28 μm and the space distance is reduced to 3.23 μm after forging and hot rolling, which means carbides are completely spheroidal and dispersed in matrix.

Determination of Martensite Start Temperature of High‐Speed Steels Based on Thermodynamic Calculations

High‐speed steels (HSS) exhibit a microstructure that comprises a martensitic matrix with carbides. Due to the generally high thermal stability of carbides, it is necessary to perform hardening at very high austenitizing temperatures. Nevertheless, there are certain carbides in HSS that are not dissolved. Therefore, the composition of the austenite, which can be transformed into martensite, is significantly different from the alloys’ nominal composition. Consequently, commonly applied formulae for the calculation of martensite start temperature cannot be used for HSS. The current study demonstrates how empirical formulae, which are basically applied for low‐alloyed steels, where no carbides are present at austenitizing temperature, can be modified for high‐alloyed HSS by applying thermodynamic calculations. Thermo‐Calc software is utilized to calculate the composition of the austenite at two different austenitizing temperatures, and with these compositions are calculated subsequently. For experimental verification, of four alloys, which are quenched from these austenitizing temperatures, are determined using dilatometry. The experimental results show good agreement with the corresponding thermodynamic equilibrium calculations. Furthermore, the results reveal that Co does not raise as predicted by the commonly applied empirical formulae. Therefore, adapted formulae for HSS in a wide composition range are proposed.

Condition of Carbides in High-Speed Steels after Multidirectional Forging

Although heat treatment of high-speed steels has been covered in numerous treatises, their microstructure before treatment still receives insufficient attention. This article therefore explores the relationship between the initial microstructure and resultant properties in heat treated steels for cutting tools and sonotrodes (special tools for ultrasonic welding). As shown in experiments, the size of fragments of primary carbides affects the properties of the matrix after heat treatment and the precipitation of secondary carbides. Hence, the decisive factor is the method by which the initial stock is mechanically worked, as it may produce primary carbides with more uniform distribution and size. In contrast, the article lists some cases where clusters of carbides caused cracking after heat treatment. The article also covers multidirectional forging by which the desired initial microstructure is obtained.

Effect of Nitrogen on Carbonitride in High Speed Steel

The vanadium-nitrogen alloying technology was used to investigate the effect of vanadium-nitrogen alloy on the carbides in high-speed steel after replacing vanadium-iron alloy. The morphology, composition and quantity of carbides in steel were analyzed in detail, and the replacement of some carbon with nitrogen was verified. The theoretical basis and experimental data for the application of vanadium-nitrogen alloys in high-speed steel is provided by this theory in this paper.

Effect of Alloying on the Nature of Eutectic Carbides in High-Speed Steels

We studied the nature of formation of eutectic carbides in economically alloyed high-speed steels after additional introduction of niobium and titanium. We analyzed the changes in the chemical composition of the matrix and carbides depending on the stages of heat treatment. It is shown that their operating properties are on a satisfactory level. The experimental steel is recommended as a substitute for the classical R6M5 steel.

Effects of carbides on abrasive wear properties and failure behaviours of high speed steels with different alloy element content

High speed steels (HSSs) are effective materials applied in aggressive environments where abrasion resistances are required because they have hard carbides and relatively ductile matrix to bind carbides. But there are many kinds of carbides in HSSs, which lead to different effect on wear properties of HSSs. In this paper, three kinds of casting HSSs with VC, M6C or M2C type carbide were prepared respectively through the reasonable design of alloy elements, and then the effects of carbide type on wear behaviours were researched under different abrasive particle size and load using abrasive wear testing machine. The microstructures and failure behaviours of HSSs were analyzed by electron microscopy. The results showed the abrasive particle size and load had obvious effect on wear weight loss of high speed steel (HSS), but the carbide type decided the relative wear resistance of HSS. As the abrasive particle size or load increased, the wear weight loss of any HSS increased obviously. For the fine abrasive wear, the HSS with M6C had higher relative wear resistance than HSS with M2C. But the contrary was the case for the coarse abrasive wear. For any abrasive particle size and load, the HSS with VC had more excellent wear resistance than HSS with M6C or M2C type carbide. The relative wear resistance of HSS with VC was three times higher than that of HSS with M6C or M2C. The excellent wear resistance of HSS with VC was mainly attributed to VC characteristics, such as high hardness and good morphology, which can resist micro-cutting of abrasive particles efficiently.

Morphology, microstructure and decomposition behavior of M2C carbides in high speed steel

The morphology, microstructure and decomposition behavior of M2C carbides in high speed steels with different chemical compositions have been investigated by scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction and X-ray diffraction. The results show that the morphology and substructure of M2C carbides are very sensitive to chemical compositions of high speed steels. M2C carbides present the plate-like shape in tungsten-molybdenum steel and present the polycrystal orientation in the eutectic cell. In contrast, they show the fibrous shape in molybdenum-base steel and exhibit the monocrystal orientation. Plate-like and fibrous M2C carbides are both metastable and decompose into M6C together with MC at high temperatures. MC nucleates inside the plate-like M2C while it is formed at the fibrous M2C/matrix interface during the decomposition process. Such differences are expected to arise from different compositions of plate-like and fibrous M2C carbides.

Precipitation of Secondary Carbides in M2 High-Speed Steel Modified with Titanium diboride

The precipitation of the secondary carbides in high-speed steel of AISI M2 type modified with titanium diboride has been investigated for both the cast and the heat-treated states. The primary focus was on the effect of austenitizing temperatures on the secondary carbide precipitation during tempering. Some differences in origin of the secondary carbides, as well as in their shape and size distribution, were found in the tempered microstructure for the different austenitizing temperatures. After austenitization at 1180 °C and triple tempering at 560 °C, the secondary carbide particles of a spherical shape up to 200 nm in size were identified by selected area electron diffraction as M23C6. After austenitization at 1220 °C, two types of the secondary carbides were found in the tempered microstructure, M23C6 with a size up to 200 nm and M6C with a size up to 400 nm. In both the cases, the carbide particles were slightly angular. After austenitization at 1260 °C, only M6C secondary carbides were revealed in the tempered microstructure, which occurred as the angular particles up to 350 nm in size. In addition, considerably finer M23C6 carbide particles with a size of 10-40 nm were found to precipitate in the tempered microstructure.

Influence of rare earths on eutectic carbides in AISI M2 high speed steel

The effect of rare earths on the morphology and microstructure of eutectic carbides in M2 high speed steel was studied. The results showed that rare earths promoted the formation of fishbone-like M6C eutectic carbides, compared to plate-like M2C carbides in ingots without modification. The formation of M6C was expected to be caused by rare earth inclusions which acted effectively as the substrate for nucleation of M6C carbides during solidification. M2C and M6C eutectic carbides exhibited different stability during heating. M2C eutectic carbides were much less stable than M6C carbides, and decomposed at high temperatures, favoring the spheroidization and refinement of carbides in high speed steels.

Thermocyclic regulation of the morphology and size distribution of eutectic carbides in high-speed steel

The influence of the temperature and time of softening thermocyclic annealing on the morphology and size distribution of carbides in high-speed steel is investigated. It is established that hot plasticity is facilitated by globular microstructure, when round carbides are uniformly distributed throughout the ferrite matrix. Thermocyclic treatment of high-speed steel creates a structural state with desirable carbide morphology. For maximum effectiveness, thermocyclic treatment is combined with holding at maximum and minimum temperatures. Research permits the development of thermocyclic treatment of hot-rolled high-speed steel bar in industrial chamber furnaces.

Diffusion and Secondary Carbide Precipitation in High-Speed Steels

Besides primary carbides, so-called secondary carbides are usually observed in high-speed steel (HSS) microstructure, which precipitate from the oversaturated solid solution upon its cooling. Some of the secondary carbides precipitate from an oversaturated austenite at cooling during solidification or quenching, in both cases, in the form of the relatively big particles in the bulk of a matrix. Considerably finer secondary carbides precipitate in martensitic condition during tempering inducing secondary hardening in HSSs. In general, secondary carbides of both types have obvious effect on the fracture mode of HSSs. The precipitation of secondary carbides in HSSs in solidified and heat-treated conditions has been investigated. The microstructures of HSSs have been examined using light and electron microscopy (both scanning and transmission), X-ray diffraction analysis, and energy dispersive X-ray spectrometry. Results indicate that diffusion of both carbon and alloying elements plays an important role in the secondary carbide precipitation in HSSs.

Diffusion in MC Carbides in High-Speed Steels during High-Temperature Treatments

The microstructure and chemical composition of MC carbides in the modified variants of AISI M2 type high-speed steel after casting, annealing, carburising and subsequent final heat treatment (quenching and tempering) have been studied by focusing on diffusion processes in these carbides and their stability during high-temperature treatments. Significant changes in both the microstructure and chemical composition of the MC carbides as well as in their volume fraction shown to occur in the high-speed steels studied were attributed to decomposition, coagulation and dissolution of these carbides during heat treatments caused by strong diffusion of alloying elements and carbon. It was also shown that boron, in general, strongly suppressed the diffusion of carbon during carburising.

Diffusion and Transformation of Eutectic Carbides in High-Speed Steels during Heat Treatment

The structure and phase composition of high-speed steels of different grades after casting, annealing, and subsequent final heat treatment (quenching and tempering) have been studied focusing on diffusion processes. In order to investigate kinetics of both the structure and phase transformations in eutectic carbides upon heat treatments, different techniques of optical microscopy, electron microscopy (both scanning and transmission ones), X-ray diffraction, and energy dispersive X-ray analysis have been used.

On the evolution of secondary hardening carbides in a high-speed steel characterised by APFIM and SANS

Abstract Secondary hardening carbides in high-speed steels are very important microstructural constituents, responsible for the excellent properties of this type of steel. Therefore, detailed knowledge about their precipitation behaviour with respect to type, size and chemical composition is of paramount interest. Atom probe field ion microscopy and small-angle neutron scattering have emerged to be important techniques for the characterisation of nanometre-sized precipitates, such as secondary hardening carbides. In this paper, the precipitation behaviour of the high-speed steel HS6-5-2 with the nominal composition (in wt.%) Fe-0.9C-4.1Cr-6.4W-5Mo-1.8V was investigated. Differently tempered specimens were analysed to determine size, volume fraction and chemical composition of the secondary hardening carbides using a three-dimensional tomographic atom probe and small-angle neutron scattering. The results obtained from both techniques were compared with emphasis on the chemical composition of the precipitates.

Carbides in high-speed steels containing silicon

The effects of silicon additions up to 3.5 wt pct on the as-cast carbides, as-quenched carbides, and as-tempered carbides of high-speed steels W3Mo2Cr4V, W6Mo5Cr4V2, and W9Mo3Cr4V were investigated. In order to further understand these effects, a Fe-16Mo-0.9C alloy was also studied. The results show that a critical content of silicon exists for the effects of silicon on the types and amount of eutectic carbides in the high-speed steels, which is about 3, 2, and 1 wt pct for W3Mo2Cr4V, W6Mo5Cr4V2, and W9Mo3Cr4V, respectively. When the silicon content exceeds the critical value, the M2C eutectic carbide almost disappears in the tested high-speed steels. Silicon additions were found to raise the precipitate temperature of primary MC carbide in the melt of high-speed steels that contained d-ferrite, and hence increased the size of primary MC carbide. The precipitate temperature of primary MC carbide in the high-speed steels without d-ferrite, however, was almost not affected by the addition of silicon. It is found that silicon additions increase the amount of undis-solved M6C carbide very obviously. The higher the tungsten content in the high-speed steels, the more apparent is the effect of silicon additions on the undissolved M6C carbides. The amount of MC and M2C temper precipitates is decreased in the W6Mo5Cr4V and W9Mo3Cr4V steels by the addition of silicon, but in the W3Mo2Cr4V steel, it rises to about 2.3 wt pct.

Primary and secondary carbides in high-speed steels after conventional heat treatment and laser modification

Complex structure examinations were performed on high-speed steels of different grades obtained using conventional metallurgy and produced by application of powder metallurgy. Hot hardness measurements were focused on the secondary carbide precipitation. Transmission electron microscopy and X-ray diffraction studies established the type of primary carbides and the amount of retained austenite. Scanning electron microscopy examinations were used to calculate the volume fraction of primary carbides. The contribution of the applied heat treatment and laser modification by diode laser remelting to the residual stress state was studied. Energy filtering was used to study the secondary carbides of nanometer size.

Accelerated investigation of carbothermal reactions : K.Wetzig et al. (Inst. of Solid State and Materials Research, Dresden, Germany.) Int. J. Refract. Metals Hard Mater., vol 17, no 1/3, 1999, 227–234

The morphology, microstructure and decomposition behavior of M2C carbides in high speed steels with different chemical compositions have been investigated by scanning electron microscopy, transmission electron microscopy, electron backscatter diffraction and X-ray diffraction. The results show that the morphology and substructure of M2C carbides are very sensitive to chemical compositions of high speed steels. M2C carbides present the plate-like shape in tungsten-molybdenum steel and present the polycrystal orientation in the eutectic cell. In contrast, they show the fibrous shape in molybdenum-base steel and exhibit the monocrystal orientation. Plate-like and fibrous M2C carbides are both metastable and decompose into M6C together with MC at high temperatures. MC nucleates inside the plate-like M2C while it is formed at the fibrous M2C/matrix interface during the decomposition process. Such differences are expected to arise from different compositions of plate-like and fibrous M2C carbides.

Investigations of precipitated phases in liquid phase sintered tungsten alloys: G.L.Zu (Central Iron and Steel Research Inst., Beijing, China.)

The effect of rare earths on the morphology and microstructure of eutectic carbides in M2 high speed steel was studied. The results showed that rare earths promoted the formation of fishbone-like M6C eutectic carbides, compared to plate-like M2C carbides in ingots without modification. The formation of M6C was expected to be caused by rare earth inclusions which acted effectively as the substrate for nucleation of M6C carbides during solidification. M2C and M6C eutectic carbides exhibited different stability during heating. M2C eutectic carbides were much less stable than M6C carbides, and decomposed at high temperatures, favoring the spheroidization and refinement of carbides in high speed steels.

REM-Untersuchungen zur quantitativen Metallographie von Karbiden in Schnellarbeitsstählen / SEM-Investigations into the Quantitative Metallographical Determination of Carbides in High Speed Steels

When examining carbides in high speed steels using the scanning electron microscope, the contrast obtained with the polished specimen in the unetched condition is often inadequate. High speed steels were examined, each of which contained two different types of carbides. With the MC-carbides present in the S 11-2-5-8 steel formed by powder metallurgical route, it was found that by reducing the accelerating voltage from the usual 15 kV down to 3 kV their contrast in the matrix was improved to such an extent that automatic quantitative image analysis became possible. The determination of M 2 C- and M 6 C-carbides in S 2-9-1-8 steel proved to be more difficult as, having the same back scattering coefficient, they both exhibited the same degree of contrast. A clear discrimination between these two carbides was however achieved chemically by element mapping. A difference in contrast, and thus reliable identification, was however also obtained by the more simple method of selective deposition, achieved using a Murakami etchant. Investigations in a scanning electron microscope equipped with a field emission cathode showed also that contrast reversal could be achieved at a voltage of 1 kV which affected only the M 2 C-carbides