FI72753B - SLITSTARK KROPP AV EN STAOL-HAORDKARBIDKOMPOSIT, FOERFARANDE FOER FRAMSTAELLNING AV DENSAMMA SAMT STAOL-HAORDKARBIDVERKTYG MED MAKROSTRUKTUR. - Google Patents

Description

1 72753

Wear-resistant steel-hard carbide combination piece, method for its production and macrostructured steel-hard carbide tools

Since 1940, wear-resistant tools and equipment have been manufactured from carbide alloys consisting of a fine-grained carbide phase based on metals selected from Groups IVB, VB and VIB of the Periodic Table and cemented with cobalt or nickel or both. When cemented carbide alloys are prepared by compression of finely ground powders followed by liquid phase sintering to provide compaction, these alloys have microstructures characterized by hard carbide granules, typically 1-15 microns in size.

The use of iron or steel as binders has proved difficult because the fine state and high specific surface area of the hard phases promote the formation of relatively brittle double intermediates containing tungsten and iron together with carbon, which reduces the free binder volume fraction and makes the sintered body more or less dependent. the accuracy of the sintering parameters and the additions of free carbon made to satisfy the affinity between iron and carbon.

In contrast to cobalt and nickel, iron forms a stable carbide, Fe 2 Crn, and has a greater tendency to form brittle double carbides than cobalt or nickel binders. The transition of carbon from the hard carbide phase or phases to iron is facilitated by the presence of a liquid or plastic state of the iron or steel binder during liquid state sintering performed at temperatures close to or above the melting point of the binder.

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Recently, useful wear parts have been made by casting running steel or cast iron melt into a finished layer consisting of a relatively coarse, particulate, e.g., 3.12-4.76 mm sintered, cemented carbide.

The present invention can be distinguished from the molten metal casting process of U.S. Patents 4,024,902 and 4,140,170 and the molten cast iron process of U.S. Patent 4,119,459 by two main factors: (1) steel or iron and graphite powder extrudate containing dispersed, sintered, cemented carbide particles; a plurality of sized, sintered, cemented carbide pieces or primary, unmilled, macrocrystalline carbide crystals are sintered at a temperature below the melting point of steel or cast iron, and (2) instead of using a melting temperature of after preventing deterioration of the dispersed hard phase particle surfaces by decomposition, melting or carbon diffusion reactions.

Casting methods also lack the known economic advantages of powder metallurgy methods, especially when multiple wear parts with small or thin cuts have to be made. Indeed, due to the relatively high processing temperatures and fluidity, too large amounts of harmful double carbides can also be formed despite the use of relatively coarse, small surface area carbide particles.

Since both the conventional powder metallurgy process in which finely ground steel-cemented carbide powders are compressed and sintered and the processes in which liquid steel or liquid cast iron is cast into a particulate, cemented, preformed carbide of the invention 3 have the problems described above, , which can be used to produce a steel-cemented hard carbide alloy which is substantially free of double intermediates of iron and tungsten with carbon and in which the dispersed hard carbide phase does not show boundary decomposition, melting or thermal cracking and is firmly bonded to the steel matrix.

It is also an object of the present invention to provide a wear-resistant composite body in which a dispersed hard carbide material is firmly and adherently bonded to a metal matrix by a powder metallurgy method comprising compression and high temperature and a high-pressure diffusion bond, and to provide a method of making such a wear-resistant composite body.

Another object of the present invention is to provide tools with hard carbide wear or cutting inserts embedded and bonded in a sealed steel powder matrix or wear-resistant composite body according to the present invention.

It is a further object of the present invention to provide parts which are hardly machinable and which have sufficient impact strength to be suitable for use as safety plates and padlock components.

According to the present invention, there is provided a wear-resistant steel-hard carbide composite body containing 30 to 80% by weight of a carbide material having a size greater than 37 microns, which carbide material is a hard carbide consisting of tungsten carbide, titanium carbide, tantalum carbide, niobium carbide, niobium carbide, , vanadium carbide, hafnium carbide, molybdenum carbide, chromium carbide, boron carbide, silicon carbide, their alloys, their solid solutions or cemented combinations thereof, and 20 to 70 4 72753% by weight of copper, a matrix wave consisting of steel and steel, , or steel and nickel, the body being characterized in that the carbide material is embedded and bonded to the matrix by compression and solid diffusion methods, and that there is an interface between the carbide material and the matrix having a thickness of up to 50.

According to a preferred embodiment, the carbide material has a metal coating which forms a tough and adhesive bond between the carbide material and the matrix.

The process according to the invention for the production of wear-resistant steel-hard carbide composites is characterized in that 20-70% by weight of steel molding powders are mixed with 30-80% by weight of hard carbide particles with a particle size between 8 mm and 37 [mu] m to form a mixture. to produce a preform, and the extruded preform is compacted by a high temperature and high pressure diffusion bonding and sintering process, and that said high temperature is below the melting temperature of the steel.

In the process according to the invention, sintered, cemented tungsten carbide particles or primary, unground, macrocrystalline (i.e. greater than 37 μm) tungsten carbide crystals are mixed with iron and graphite powder or steel powder in a pre-molded, cold-extruded mixture. at a relatively low temperature, especially below the melting point of steel, preferably at 1038-1232 ° C, and the sintered body is then hot-pressed isostatically (HIP) at a temperature well below the melting point of steel to provide final sealing. A diffusion bond is formed between the hard carbide particles and the surrounding steel powder, which holds the wear-resistant hard carbide particles in place.

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The invention further relates to a tool made by the method according to the invention, comprising a machining head with a hard-wearing, cobalt-cemented carbide insert and a steel body, characterized in that the insert is powder metallurgically bonded to the body in a diffusion zone formed at high temperatures. below the melting point of steel, and that the diffusion zone contains iron and cobalt.

Finally, the invention relates to the use of a method according to the invention for forming such a cemented carbide tool by immersing a pre-sized cobalt-cemented carbide insert at a predetermined location in a steel forming powder whereby at the same time a metallurgical bond is formed between the insert and the steel under high pressure.

A critical aspect of the present invention is high pressure sealing, both cold and hot, which avoids process temperatures that cause the fluidity of the steel binder phase and thus promote the aforementioned undesired reactions between the steel binder and the hard dispersed phase. The method is improved in this respect by the use of a hard dispersed particle or particles with a low specific surface area. The process also significantly enhances production efficiency in the manufacture of steel carbide wear parts having a relatively small size or thin cut or complex structure compared to the methods disclosed in the U.S. patents listed above, in which molten steel or molten cast iron is cast into a mold pre-filled with cemented carbide particles.

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In addition, both the chemical control and the flexibility of the composition of the matrix mixture are vastly better than in melt-stable casting methods. Avoiding the high process temperatures required for melting and casting steel or cast iron improves the economics of the molds, allowing the molds to be reused, and the economy of the matrix metals, as they do not cause casting wastes or reuse costs. The method of the present invention is well suited for forming parts that must withstand highly abrasive, abrasive forces as well as impact forces.

The method is ideally suited for forming wear-resistant parts and cutting blades used in agricultural machinery, road construction and road maintenance, roughing, grinding, excavation and machining. Because the products made by this method have such good wear resistance that they can hardly be machined, they are also ideally suited for use as security plates for safes. Due to this abrasion resistance and impact resistance, these alloys are also suitable for use in padlocks.

The precise nature of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings, in which: Figure 1 is a 1500x magnification photomicrograph of a cemented carbide particle in which a cobalt binder is embedded and bonded to a pressed steel powder cross-section; a wear plate in which the cemented carbide inserts are embedded and bonded in a pressed steel powder matrix, and Fig. 3 is a cross-sectional view of a portion of a cutting tool in which a carbide knob is embedded and bonded in a pressed steel powder matrix.

The premixed steel matrix powder or a mixture of iron powder and graphite powder containing 20-70% by weight of the final mixture is mixed with 30-80% by weight of W, Ti, Ta,

To hard carbide particles of Nb or Zr, V, Hf, Mo, B, Si, Cr or mixtures thereof, either as sintered, cemented carbide particles or as primary, uncemented tower, unsintered, unground carbide crystals .

About 3% naphtha or other liquid hydrocarbon is added to the powder mixture during mixing to prevent the separation of higher density carbide particles during mixing and mold filling, especially when the dispersed hard phase consists of hard carbide particles coarser than about 250 microns.

For dispersed hard phase particles finer than about 250 mesh, a paraffin wax or solid lubricant such as zinc stearate can be used, as the possibility of separation of the component particles during mixing is reduced.

Next, the matrix powder containing the dispersed hard carbide phase is packaged in a preforming mold made of polyurethane or other elastomeric plastic. Steel powders having different kamique compositions (such as carbon, alloy or stainless steel powders) of elemental powder such as iron, copper or nickel can also be packaged in the same mold with the main steel powder-carbide mixture located at any point in the around the body or around a dimensioned, sintered, cemented carbide insert. The packaged mold, on which a suitable lid is fitted, is then sealed and placed in a rubber bag or ball, which is then evacuated, sealed and compressed isostatically, preferably at a pressure of about 241.317 MPa, but at least 68.948 MPa.

The compressed powder preform is then removed from the mold and heated under vacuum or in a shielding or reducing gas atmosphere, e.g. a hydrogen atmosphere, to a temperature below the melting temperature of the steel matrix, preferably 1038-1149 ° C, for 20-90 minutes.

In an alternative preforming process, a composite mixture preferably containing a liquid hydrocarbon, e.g. naphtha, preferably 7% by weight, and methylcellulose, preferably 0.5% by weight, as a compression lubricant and a sintered state binder, respectively, is packaged in a steel preforming mold. The crude preform is then air dried at room temperature in a mold and then removed from the mold and placed in a rubber bag, which is then evacuated and sealed ready for isostatic cold pressing as described above.

72753 The portions thus sintered in the solid state have some porosity left; shrinkage during sintering does not exceed 1%. However, it has been found that the compaction achieved by isostatic high pressure compression followed by sintering, as described herein, is sufficient to remove any interconnected pores and that the sintered bodies are therefore suitable for efficient final compaction by known isostatic hot compression (HIP) methods.

The isostatic hot pressing used for the purposes of this invention is carried out in an inert atmosphere, preferably at 871 ° C to 1260 ° C or at any temperature below the melting point of the steel for 20-90 minutes at a minimum pressure of 68.948 MPa, but preferably at a pressure of about 103.421 MPa for 60 minutes. Equally important, the alloy layer is formed at the interfaces of the cemented carbide particles and the steel matrix. This interfacial alloy bond, which is first formed during sintering and which subsequently improves during isostatic hot pressing, consists of a thin boundary region between, for example, 0.75% of a carbon steel matrix and dispersed cobalt-cemented carbide particles ranging in size from 3.175 to 4.763 mm. The bond is typically less than 40 microns thick and no thicker than 50 microns. The interface idosle jeer Inki under these conditions consists mainly of cobalt and iron. Bond formation becomes especially important when the hard dispersed phase contains relatively coarse particles, as these tend to retract if they are not firmly attached to the matrix alloy.

The sizes of the cemented tungsten micarbide particles forming the dispersed hard phase are selected from the general size range of 8-0.149 mm (2.5-100 mesh in the U.S. screen series), with preferred size ranges being 0.84-1.53 mm (+20 to -12 mesh). , 1.53-3.36 mm (+12 - -6 mesh) and 3.36-4.76 mm (+6 - -4 mesh). Certain selected size ranges can be made by known methods for grinding and sizing sintered, cemented carbide tool components. These alloys are more commonly based on cobalt or nickel cemented tungsten carbide (WC) / which sometimes also contains TiC, TaC or NbC or combinations of these hard carbides.

Another useful aspect of the method of the present invention is to apply an alloy or metal coating, preferably a Corson bronze or nickel coating, to the surfaces of a dimensioned, sintered, cemented tungsten carbide insert of a particular shape and size, or to a plurality of such inserts. The inserts are then embedded in steel or iron-graphite matrix powder at selected locations in the preform before the filled mold is compressed from the isostatic. The Corson bronze coating used may be either of the two nominal alloys shown in Table 1.

Table I

Corson bronze alloys

A D

2.5% by weight Ni 10% by weight Mn 0.6% by weight Si 4% by weight Co 0.25% by weight Mn 86% by weight Cu remainder Cu

After isostatic cold pressing and subsequent sintering and isostatic hot pressing of the carbide steel extrudate, the coating on the cemented carbide body autogenously forms a diffusion bond to increase the bond strength with which the sized, cemented carbide bodies are held in the matrix. By this method, a cemented carbide body or a plurality of such bodies having a certain shape and size can replace a fluffy, dispersed hard carbide phase and thus form a wear-resistant body or tool for cutting and drilling metal or rock.

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It will be appreciated that the relatively low process temperatures used in the process of this invention may result in insufficient bond strength at the interface between the matrix and the carbide particles when steel matrix powder mixtures are used which do not bind to properly dispersed hard carbide phase particles. In these cases, for example, when using steel alloy powders which are known to be less sinterable at the relatively low solid state sintering temperatures disclosed in the process of this invention, it has been found advantageous to pre-coat the hard carbide particles with nickel or copper, e.g. Nickel coatings applied to the hard carbide fraction thus dispersed prior to mixing have been found to improve the bond strength of carbide particles. Such pre-coating of hard carbide particles would also be advantageous when using stainless steel powders.

Another and useful part of the present invention is to include a hard carbide phase dispersed in a steel or iron-graphite powder compact consisting of a mill tower, macrocrystalline carbide crystals having size fractions of 0.037 to 0.250 mm (400 to 60 mesh) and preferred size ranges of e.g. 0.149. -0.250 mm (+100 to -60 mesh), 0.074-0.177 mm (+200 to -80 mesh) or 0.044-0.099 mm (+325 to -150 mesh) instead of cemented carbide particles. The process of the present invention for forming macrostructured cemented carbide blends is exactly as described above.

The relatively low process temperatures used result in a macrostructure substantially free of brittle iron and tungsten double carbides (eta phase) and coarse porosity. Liquid-phase sintered, microstructured, cemented tungsten carbide alloys using a steel binder instead of, for example, the usual cobalt binder, are known to develop 1 2 7275 3 brittle eta-type phases. It is believed that avoiding liquid phase sintering and thus avoiding the carbon transition promoted by such a practice, as well as the uniquely small specific surface area of the dispersed hard phase-forming, unmilled macrocrystalline carbide particles, are essential for the successful formation of biphasic steel carbide produced by this process. It is clear that the liquid phase sintering mentioned here means sintering at a temperature at which the steel binder is at least partially liquid. The prohibition of liquid phase sintering in the present invention therefore does not apply to any lower melting point metals or alloys (e.g. copper or Corson bronze) which may be added as a powder or coating to improve bonding or sealing and which may intentionally become liquid by sintering or sintering. during hot pressing.

The use of unground macrocrystalline hard carbide crystals as a dispersed hard phase is a preferred embodiment of the process of this invention because it is an effective means of maintaining a hard phase having a low specific surface area. However, it will be appreciated that substantially unbound, hard aggregates of finer or ground hard carbides may also be used.

An important feature of the above-mentioned macrostructured bodies is that the matrix-carbide powder mixtures or both of these two substances separately do not need to be ground in a ball mill or otherwise comminuted before isostatic cold pressing, sintering and HIP. Previous practice, which has been widely regarded as essential for commercial cemented carbide structures, promotes the reaction between carbides and iron-based matrix powders to form brittle double carbides. The omission of powder grinding also lowers costs.

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Any macrocrystalline carbides or combinations of their solid solutions can be used in the process of the invention, in particular WC, TiC, TaC or NbC, all of which have the low specific surface area and angular, ingot-like shapes typical of these mono- and double carbides. It is known that primary macrocrystalline carbide materials can be finely ground together with cobalt and nickel to form cemented carbide microstructures by liquid phase incorporation in the temperature range of 1316-1538 ° C, with the resulting dispersed hard carbide phases typically being between 1 and about 10. The process according to the invention, on the other hand, results in dispersed, simple, macrocrystalline carbide granules with size ranges within the much rougher limits of 250 to about 40.

The invention is further illustrated by the following examples:

Example 1

Wear-resistant cutting tips were made for rotary sugar cane cutters. A uniformly mixed mixture was prepared containing about 55% by weight of cobalt-cemented 3.175-4.763 mm tungsten carbide granules, about 44.67% by weight of iron powder comminuted to a particle size of less than 0.149 mm (-100 mesh), and 0.33% by weight of % by weight of graphite powder having a particle size of less than 0.044 mm (-325 mesh). During mixing, 5% by weight of naphtha was added to minimize the separation of higher density cemented carbide particles. The wet mixture was manually pressed into an elastomeric polyurethane mold roll having the desired tool shape and sized to allow isostatic cold pressing of the powder as well as 1% sintering shrinkage. After isostatic cold pressing, the preform pressed at 241.317 MPa was removed from the mold and vacuum sintered at 1093 ° C for 60 minutes, after which the sintered body was isostatically pressed at 1232 ° C for 60 minutes at 103.421 MPa in a helium atmosphere.

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Metallographic examination showed a matrix structure consisting mostly of perlite and a small amount of ferrite, which is typical of conventional, slowly cooled 0.75% carbon steel with low porosity. The interfaces of the cemented carbide and the matrix had bands about 5 μm wide, consisting of an alloy thought to consist mainly of iron and cobalt. It was found that thermal cracking did not degrade the dispersed particles of the cemented carbide and no dissolution, melting or decomposition of the dispersed carbide phase was observed at or near the interfaces, these boundaries being sharp except for the iron-cobalt alloy diffusion zone mentioned above. No potentially harmful concentrations of the eta phase were observed. The specimens were bent by hand over the mandrel by hammering at room temperature and were found to have good resistance to impact loading and showed little brittle fracture.

Figure 1 is a photomicrograph of a typical range of the combination prepared according to Example 1 except that sintering was performed at 1149 ° C. The cobalt-cemented tungsten carbide dira 40 is shown metallurgically bonded to ordinary carbon steel having a predominantly perlite structure 50 in a diffusion zone 45 containing iron and cobalt. The diffusion zone 45 is about 3 microns thick.

Example 2 - 2

A wear-resistant, 12.9 cm pxnta-alam and 9.5 mm thick plate consisting of 60% by weight of unground macrocrystalline toilet with a particle size of 0.149-0.250 mm (+100 - -60 mesh) was prepared. was cemented with 40% by weight of 0.75% C steel containing 2% by weight of Cu. Uniformly dry mixed mixture of macrocrystalline toilet crystals with a particle size of 0.1490.250 mm (+100 to -60 mesh), graphite powder with a particle size of less than 0.044 mm (-325 mesh), iron powder with a particle size of was less than 0.149 mm (-100 mesh) and copper powder having a particle size of less than 0.044 mm (-325 mesh) was dry blended as a ground mat to a uniform mixture.

72 72753 was then moistened by mixing liquid naphtha and methylcellulose in amounts of 7% by weight and 0.5% by weight of the dry mixture, respectively, and then packed in a steel preforming mold into a solid, sintered sheet form measuring approximately 102% of the desired final size. size.

After air drying in the mold at room temperature, the extrudate was removed from the mold, placed in a rubber bag and further treated with isostatic cold pressing, sintering and HIP as described in Example 1. Metallographic examination revealed a macrocrystalline toilet macrostructure uniformly dispersed throughout the steel matrix. A 5 μm thick bonding layer of unknown composition was observed at the toilet steel interfaces. There were no brittle binary carbide phases or cracks at these interfaces.

Example 3 - 3

A 55.31 cm wear-resistant steel body was made surrounding a sintered, 5 wt% cobalt cemented tungsten carbide sized sheet, the sized sheet being intentionally embedded in a sintered, cemented carbide in the crude powder prior to co-extrusion so that its outer surface with. A dry unground mixture was prepared containing 97.25% by weight of iron powder comminuted to a particle size of less than 0.149 mm (-100 mesh), 2% by weight

Cu powder having a particle size of less than 0.044 mm (-325 mesh) and 0.75% by weight of graphite, followed by mixing naphtha and methylcellulose in amounts of 5% by weight and 0.3% by weight of the dry mixture, respectively. This was packed, 2 then into an elastomeric mold, after which a 6.54 cm square and 6.35 mm thick sintered cemented carbide sheet was pressed down into the iron powder mixture so that the outer surfaces were aligned.

After sealing, the mold was placed in a rubber bag, evacuated, sealed, and currently isostatically compressed, removed from the mold, sintered, and hot-pressed asostatically as in Example 1. Metallographic examination revealed that the pre-positioned sintered carbide plate was bound to the 5 micron boundary. to the steel matrix surrounding it on three sides and that the whole structure looked flawless and distortion-free.

Figure 2 shows a wear plate 20 made as described in this example except that three cemented carbide inserts 30 are embedded in the plate 20 instead of one and that the surface 45 of each insert 30 is substantially aligned with the tool machining head 40. It is found that the interface bond 35 is substantially flat and uniform and forms a tough and adhesive bond between the cemented carbide and the compacted carbon steel and copper matrix 25.

In some wear applications, depending on the corrosive nature of the environment in which the wear plate will be used, stainless steel or steel alloy powders may be advantageously used in place of the iron, carbon and copper powders used in this example.

Figure 3 shows a cross-sectional view of another embodiment of a tool according to the present invention. The tool 1 can be manufactured mainly as described in Example 3, except that the machining head 2 of the cemented carbide insert 5 protrudes: outwards and over the steel body 10 of the tool 1. As shown in this figure, the insert 5 is bonded to the steel body 10 by a diffusion zone 15 formed by mutual diffusion from the cobalt insert 5 and the iron steel body 10 during the high temperature and high pressure sintering steps.

The invention may be modified within the scope of the appended claims.

Claims (14)

72753 A wear-resistant steel-hard carbide composite body containing 30 to 80% by weight of a carbide material having a size greater than 37 μm, which carbide material is a hard carbide consisting of tungsten carbide, titanium carbide, tantalum carbide, niobicarbide, zirconium carbide, zirconium carbide, hafnium carbide, molybdenum carbide, chromium carbide, boron carbide, silicon carbide, mixtures thereof, solid solutions thereof or cemented combinations thereof, and 20 to 70% by weight of a matrix material consisting of steel, steel and iron, steel and copper, steel and that the carbide material is embedded and bonded to the matrix by compression and solid diffusion methods, and that there is an interface between the carbide material and the matrix having a thickness of up to 50 μm. Body according to Claim 1, characterized in that the interface has a thickness of 0 to 40 μm. Body according to Claim 1, characterized in that the carbide material is a cemented composite material with a cobalt binder and that the interface contains iron and cobalt and has a thickness of 0 to 40 μm. Body according to Claim 3, characterized in that the cemented composite contains tungsten carbide. Body according to Claim 1, characterized in that the hard carbide is tungsten carbide. A body according to claim 1, characterized in that it is moldable at room temperature. 18 72753 Body according to Claim 1, 3 or 5, characterized in that the steel is an alloy steel. Body according to Claim 1, 3 or 5, characterized in that the steel is stainless steel. Body according to one of the preceding claims, characterized in that the carbide wave has a metal coating which forms a tough and adhesive bond between the carbide material and the matrix. A process for the production of wear-resistant steel-hard carbide composites, characterized in that 20-70% by weight of steel molding powders are mixed with 30-80% by weight of hard carbide particles with a particle size between 8 mm and 37 μm to form a mixture. cold-pressed to produce a pressed pre-press, and the pressed pre-press is compacted by a high-temperature and high-pressure diffusion bonding and sintering process, and that said high temperature is below the melting temperature of the steel. Method for producing wear-resistant steel-hard carbide composite bodies according to Claim 10, characterized in that the hard carbide particles are coated with a metal coating before mixing with the steel molding powders. A method of manufacturing wear-resistant steel hard carbide composite bodies according to claim 10 or 11, wherein the compression of the extruded preform is performed by diffusion bonding, characterized in that the extruded preform is sintered at a temperature above 1038 C 3a below the solidification temperature of the steel. isostostatically pressed at a pressure above 68.95 MPa and at a temperature between 871 ° C and the melting point of steel. 72753 A tool made by the method of claim 10, 11 or 12, comprising a machining head having a hard-wearing, cobalt-cemented carbide insert and a steel body, characterized in that the insert is powder metallurgically bonded to the body in a diffusion zone which is formed during high temperature sintering below the melting point of steel, and that the diffusion zone contains iron and cobalt. Use of a method according to claim 10, 11 or 12 for forming a cemented carbide tool according to claim 13, characterized in that a pre-dimensioned cobalt-cemented carbide insert is immersed in a predetermined position in the steel molding powder mixture, the powder is compacted around the insert and adjacent to the insert at a high temperature below the melting point of the steel, thereby simultaneously forming a metallurgical bond between the insert and the steel under high pressure.