EP1364732A2 - Hard metal part with graded structure - Google Patents

Abstract

Structural component comprises cemented carbide alloy containing carbonized material, mixed carbonized material or carbonitride of tungsten, titanium, tantalum, vanadium, molybdenum, zirconium, hafnium, niobium and/or chromium, additive(s) and binder (1-20 wt.%) of cobalt, nickel and/or iron. Additive suppresses crystal growth of vanadium, chromium, titanium, tantalum, niobium or their compounds. An Independent claim is included for manufacture of structural component.

Description

The invention relates to a powder metallurgically produced component of a Hard metal alloy with a binder content of 0.1 to 20 wt.%, The contains at least one grain growth inhibiting additive and a method for its production.

By hard metal is meant a composite material consisting essentially of a carbide component and a binder. Among the most important Carbide components include the carbides or mixed carbides of the metals W, Ti, Zr, Hf, V, Nb, Ta, Mo and Cr. Typical binder metals are Co, Ni and Fe. Also additives of other hard materials, such as carbonitrides, come to the application.

The properties of hard metals are determined by the ratio of carbide content to binder content, chemical composition, carbide grain size and carbide grain size distribution. This opens up many possibilities to adapt the properties of carbide to the respective field of application.
Thus, increasing binder content improves fracture toughness and flexural strength while reducing hardness, stiffness and compressive strength. A reduction in the carbide grain size leads to an increase in hardness, compressive and flexural strength, with reduced impact and fracture toughness.

Adapted to the particular application, carbide powders in the particle size range 0.2 μm to 15 μm are used today for the production of carbide components. In order to reduce the grain coarsening during the sintering process when using fine-grained carbide powder, grain growth inhibitors are added. The most effective grain growth inhibiting additives are vanadium carbide, chromium carbide, titanium carbide, tantalum carbide and niobium carbide. In many cases, two or more additives are used, such as mixtures of VC and Cr ₃ C ₂ or TaC, NbC and TiC. The grain growth-inhibiting additive can be finely distributed in the main component before or during the carburization. However, the effectiveness is also present when the grain growth inhibitor is added to the hard metal powder or individual constituents of the hard metal powder before, during or after the grinding.

Hard metal components can be locally loaded very differently. Therefore are early solutions have been known or implemented on a Composite of two or more carbide alloys based. So describes the US 5,543,235 a hard metal composite material, which by powder metallurgical composite pressing is produced, wherein the individual material areas by their composition or microstructure differ. A rotating compound tool that consists of two Hard metal alloys is constructed, is also in PCT / US00 / 33644 described. The preparation is also preferably via composite presses.

Another process technique for producing a hard metal composite body is shown in US Pat. No. 5,594,931. On a green body is a slip applied, consisting of a powder mixture, a solvent, a binder and a plasticizer. The composite green product thus produced is compressed by sintering.

A disadvantage of the material composites described here, however, is that in the areas of the composite where materials with different Properties meet, stress concentrations arise. Furthermore, it has to be considered that every material component has its own Having sintering behavior. This can cause a distortion of the component during the Trigger sintering.

However, if you make the transition between two material areas in the Composition graded, so spikes can largely be avoided. Under one, in composition, graded construction it is understood that the composition is gradual over a range of continuously changes. Especially with coated carbide are graded Finishes in the area of the layer, in the area of the transition Layer / base material and in the neighboring base material for a long time known. This grading is achieved, for example, by the addition of Carbonitrides. During sintering, the nitrogen is broken down in the edge zone of the carbide body. The metallic carbide or nitride forming elements diffuse towards the center of the Carbide body. This achieves a binder enrichment in the field of Edge zone and a graded transition to the matrix composition. So are indexable inserts with a binder-rich edge zone, adjacent the hard material layer, long used for steel cutting. The However, grading is limited to a small, near-surface area.

For highly stressed components, it is advantageous to have a, over a wide range, to adjust the graded structure. It can be so clear Stand time improvements are achieved, especially when the mechanical requirements for the carbide in the edge and core area differ.

Since the usual binder metals, such as cobalt, at sintering temperature show a high diffusivity, it is possible to balance the concentration in the transition zone between two hard metal alloys, the one have different cobalt content, via diffusion processes to reach. This allows a continuous transition to be set. One Processes for this purpose are described for example in EP 0 871 556. One Composite body consisting of at least two areas that are in binder content distinguish, is produced by composite presses. When sintering is the Adjust temperature so that the binder metal from the composite area with the higher binder content in the composite area with lower Binder content diffused. The disadvantage here is that the sintering temperature is very high is to be set exactly, so as not to complete a concentration adjustment and thus to achieve loss of different material properties. Another disadvantage is that the composite presses with higher Manufacturing costs associated with this than in the production of a monolithic greenlings is the case.

In EP 0247985 and EP 0498 781 are also carbide body with a gradient of the binder phase and a method of preparation described. It is first using a carburized Starting powder mixture by means of conventional process steps a sintered body with evenly distributed η-phase produced. About a subsequent Treatment in a carburizing atmosphere achieves a dissolution of the η-phase in the area of the edge zone. Towards the center of the carbide body As the proportion of η-phase gradually increases, the binder metal content gradually decreases. The disadvantage, however, is that the η phase has an embrittling effect. In addition, the additional carburizing step time and energy consuming.

In EP 0 111 600 is a highly stressed tool for the Rockwork described. This consists of an inner and an outer area, with a continuous transition of mechanical properties between these areas. When Process engineering is proposed a complex powder feed, with the it is possible during the filling process, the concentration of the powder to change continuously. Such a powder feed is expensive in terms of apparatus and technically difficult to master.

It is therefore an object of this invention, a hard metal component with gradiertem To provide construction that does not overcome the disadvantages of the prior art having. It is a further object of the invention to provide a method for this Specify production.

This object is achieved by a component made of a hard metal alloy and a method for its production, wherein the hard metal alloy at least a carbide, mixed carbide or carbonitride of the metals of group W, Ti, Ta, Mo, Zr, Hf, V, Nb, Cr and V, at least one grain growth inhibiting additive the group V, Cr, Ti, Ta and Nb or a compound of these metals and contains at least one metallic binder of the group Co, Ni and Fe, wherein at least one of the grain growth inhibiting additives at least locally Has graded concentration curve.

The graded concentration course of the grain growth inhibiting additive leads to a graded course of the carbide grain size. Subsequently, the mechanical properties also show a graded course. This is advantageous, for example, where a high level of wear resistance and bending strength at the surface and at the same time a high level of toughness in the core is required, for example in the case of forming tools or tools for diamond production. If now the concentration profile of the grain growth-inhibiting additive is adjusted so that the concentration values are higher in the region of the edge zone and they decrease in the direction of the center of the component, the edge zone is fine-grained, with a graded transition to the coarse-grained center. As a result, components with excellent wear resistance and bending strength in the region of the edge zone, combined with a high toughness of the center can be produced. These have improved tool life. At high cyclic or impact stress, in turn, a high fracture toughness in the region of the edge zone may be advantageous. This is achieved by a reduced content of grain growth inhibiting additive in the region of the edge zone. By a graded course of the grain size and a finer-grained center, the compressive and flexural strength properties are improved in the core of the component. This version is also favorable for coated parts. The effect of the invention is also given if the hard metal alloy contains other non-carbide hard material phases, as long as the mechanical properties are not appreciably affected unfavorably.
Advantageous grain growth inhibiting additives are vanadium and chromium compounds, the maximum concentration being 2% by weight. Higher levels lead to embrittlement effects. A particularly advantageous process is the superficial application of a dispersion or solution on a green body. The dispersion contains the grain growth inhibiting additive in very finely divided form. The green compact can be in the as-pressed state. If the green compact contains waxing or plasticizing agent additives, it can also be present in the dewaxed or partially dewaxed state, in accordance with an advantageous embodiment of the present invention. The dispersion or solution can be applied, for example, by dipping, spraying or brushing on. Subsequently, the dispersion or solution penetrates into the interior of the green body along open pore channels. The reaction time and the content of the dispersion or solution of grain growth inhibiting additive essentially determine the amount introduced or the penetration depth. It is therefore possible, depending on the requirement profile, to set a grading which extends only on the micrometer scale. However, it is also possible to perform the grading so that it extends to the center of the component. Furthermore, the process can also be carried out so that initially the green compact is completely soaked with the dispersion. This is then removed again by appropriate solvents or by thermal processes from the near-surface areas. Furthermore, the dispersion can be applied over the entire surface or even only locally. Specifically, the local application allows the production of components or tools that only have a high hardness where wear resistance is required. The remaining areas have a coarser texture with high fracture toughness. Furthermore, it proves to be advantageous if the carbide component of the green body has a mean particle size of less than 2 microns.
In the following production examples are given, which are intended to illustrate the embodiment of the invention by way of example. To illustrate the results of Examples 1 to 3, FIGS. 1 to 5 are used.
Fig. 1 shows the vanadium content over the sample cross-section. In Figure 2, in addition to the vanadium content and the carbide grain size is indicated. 3 and 5 each show the hardness profile over the sample cross-section. Fig. 4 shows schematically the cross section of a drawing tool. FIG. 1 and FIG. 2 relate to example 1, FIG. 3 to example 2, FIG. 4 and FIG. 5 to example 3.

example 1

A hard metal batch with 94 wt.% WC with a mean particle size of 1 .mu.m, remainder Co, was produced according to the methods customary in the hard metal industry. By means of die pressing with a pressing pressure of 50 kN, green compacts were produced in the form of indexable inserts. The greenlings were subjected to a usual eviscerating process. Further, a dispersion of distilled water and V ₂ O _{5 was} prepared, the solid content being 2% by weight and the average V ₂ O ₅ particle size being less than 50 nm. Subsequently, the green compacts were immersed for 5 seconds in the above-described dispersion and then dried in air at 50 ° C. These samples were sintered with reference green sheets that were not aftertreated at a temperature of 1400 ° C under vacuum. The analysis of the samples was carried out by means of electron microprobe, the microstructural and mechanical characterization by light microscopic examination or hardness testing, respectively on cross sections. Fig. 1 shows that the vanadium content in the region of the edge zone is 0.24% by weight and this value decreases gradually over the cross section of the sample towards the inside. The vanadium content at a distance of 3.8 mm from the sample edge is 0.08 wt.%. For the reference sample, the corresponding vanadium concentrations were below the detection limit of the microprobe. The graded vanadium distribution results in a graded grain stabilization effect, as documented by the WC grain size values in FIG. As the average grain size increases from the edge zone toward the center, the corresponding hardness values decrease, as shown in FIG.

Example 2

A cemented carbide approach with 89.5 wt.% WC micron a mean grain size of 0.8, 0.5 wt.% Cr ₃ C _2, balance Co was prepared according to the usual method in the hard metal industry. By means of die pressing with a pressing pressure of 50 kN, green compacts were produced in the form of indexable inserts. The greenlings were subjected to a usual eviscerating process. Further, a dispersion of distilled water and V ₂ O _{5 was} prepared, the solid content being 2% by weight and the average V ₂ O ₅ particle size being less than 50 nm. Subsequently, the green compacts were immersed for 5 seconds in the above-described dispersion and then dried in air at 50 ° C. These samples were sintered with reference green sheets that were not aftertreated at a temperature of 1400 ° C under vacuum. The analysis of the samples was carried out by means of electron microprobe, the microstructural and mechanical characterization by a light microscopic examination or hardness testing. The samples according to the invention again show a graded vanadium concentration course, with a marginal zone value of 0.21 wt.% V and a center value of 0.03 wt.% V. The corresponding hardness values are 1698 HV30 or 1648 HV30. The hardness profile is reproduced in FIG. The reference sample shows a uniform hardness profile over the cross section with an average value of 1605 HV30. The samples according to the invention and the reference samples were also subjected to a bending test. The mean value of ten measurements is 3950 MPa for the samples according to the invention and 3500 MPa for the comparative samples.

Example 3

A hard metal batch with 93.4 wt.% WC with an average particle size of 2.0 .mu.m, 0.2 wt.% TiC, 0.4 wt.% TaC / NbC, remainder Co was prepared according to the methods customary in the hard metal industry. Cylindrical green compacts were produced by isostatic pressing with a compacting pressure of 100 MPa, which were formed by mechanical machining into a hard metal drawing tool. The greenlings were subjected to a usual eviscerating process. In turn, a dispersion of distilled water and V ₂ O _{5 was} prepared, wherein the solids content was 2 wt.%, With a particle size of dispersed V ₂ O ₅ particles of less than 50 nm. Subsequently, the dispersion was selectively in the inlet and Applied drilling area. The drying was again carried out at 50 ° C in air. These samples were sintered at a temperature of 1400 ° C in vacuum. By metallographic sample preparation, a cross-section was made, as shown in Fig. 4. Figure 4 also shows the area where the characterization was done by electron beam microprobe and hardness testing. The vanadium content in the edge zone is 0.18 wt.%, At a distance of 2 mm from the sample edge only 0.11 wt.%. Fig. 5 shows the gradual hardness curve.

Claims (13)

Component of a hard metal alloy containing at least one carbide, mixed carbide or carbonitride of the metals of the group W, Ti, Ta, Mo, Zr, Hf, V, Nb, Cr and V, at least one grain growth inhibiting additive of group V, Cr, Ti, Ta and Nb or a compound of these metals, and at least one metallic binder of the group Co, Ni and Fe, wherein the binder content is 0.1 to 20 weight percent, characterized in that at least one of the grain growth inhibiting additives at least locally has a graded concentration curve. Component made of a hard metal alloy according to claim 1, characterized in that this at least locally has a graded course of the grain size. Component made of a hard metal alloy according to claim 1 or 2, characterized in that this at least locally has a graded hardness curve. Component made of a hard metal alloy according to one of claims 1 to 3, characterized in that the grain growth-inhibiting additive from the edge zone of the component in the direction of the center of the component decreases in gradient. Component made of a hard metal alloy according to claim 4, characterized in that the carbide grain size of the edge zone of the component increases in the direction of the center of the component graded. Component made of a hard metal alloy according to one of claims 1 to 3, characterized in that the grain growth-inhibiting additive from the edge zone of the component increases in the direction of the center of the component graded. Component made of a hard metal alloy according to claim 6, characterized in that the carbide grain size decreases graded from the edge zone of the component in the direction of the center of the component. Component of a hard metal alloy according to one of claims 1 to 7, characterized in that the grain growth inhibiting additive consists of Cr and / or V or a compound of these metals and the maximum content based on the hard metal alloy 2 wt.% And this gradually to a value x decreases, with 0 <x <1.0 wt%. Method for producing a component according to claim 1, characterized in that the production thereof comprises at least the following method steps: Producing a green compact from a hard metal alloy, comprising at least one carbide, mixed carbide or carbonitride of the metals of the group W, Ti, Ta, Mo, Zr, Hf, V, Nb, Cr and V, at least one metallic binder from the group Co, Ni and Fe and optionally a wax additive or a plasticizer, according to the usual powder metallurgical compaction or molding process; Preparing a dispersion or solution containing at least one grain growth inhibiting additive from the group V, Cr, Ti, Ta and Nb or a compound of these metals in finely divided or dissolved form; Applying and this dispersion or solution to the surface of the green body by, for example, dipping, spraying or brushing; Targeted exposure to adjust the concentration gradient Warm consolidation. Method for producing a component according to claim 1, characterized in that the production thereof comprises at least the following method steps: Producing a green compact from a hard metal alloy, comprising at least one carbide, mixed carbide or carbonitride of the metals of the group W, Ti, Ta, Mo, Zr, Hf, V, Nb, Cr and V, at least one metallic binder from the group Co, Ni and Fe and optionally a wax additive or a plasticizer, according to the usual powder metallurgical compaction or molding process; Preparing a solution containing at least one grain growth inhibiting additive from the group V, Cr, Ti, Ta and Nb or a compound of these metals; Applying this solution to the surface of the green body by, for example, dipping, spraying or brushing; Targeted exposure to the setting of a concentration gradient or full penetration; Gradual degradation of the grain growth inhibitor from near-surface areas by a thermal treatment and / or a solvent; Warm consolidation. A method for producing a component according to claim 9 or 10, characterized in that the dispersion or solution is applied only to a portion of the component surface. A method for producing a component according to claim 9 or 10, characterized in that the carbide powder component of the green compact has an average particle size of <2 microns. A method for producing a component according to claim 9 or 10, characterized in that the green compact is at least partially dewaxed by a heat treatment step.

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