EP2066821B9 - Metal powder - Google Patents

Description

Hard metals as a sintered and composite material consist of at least two phases, including a metallic binder phase, and one or more hard material phases. Due to the respective proportion of the metallic or hard phases, their different properties can be weighted and thus the desired properties of the hard metal, such as strength, hardness, modulus of elasticity, etc., can be set. The hard material phase usually consists of tungsten carbide, and depending on the application of the carbide tool also cubic carbides such as vanadium carbide, zirconium, tantalum or niobium carbide, their mixed carbides with each other or with tungsten carbide, as well as chromium carbide or molybdenum carbide. It is also possible to use nitrogen-containing cubic carbides ("carbonitrides") in order, for example, to influence the phase relationships of the edge zones during sintering. Typical binder contents for cemented carbides are between 5 and 15% by weight, but in special applications they may be up to 3% and more up to 40% by weight.

The metallic binder phase consists of predominantly cobalt in the classic carbide. Due to the liquid phase sintering and the consequent dissolution and deposition processes of the carbide phase, the metallic phase contains, after sintering, dissolved tungsten and carbon fractions, often also Cr - if e.g. Chromium carbide is used as an additive -, and for corrosion-resistant carbides also molybdenum. Very rarely, rhenium or ruthenium is used as an additive. The proportions of such metals in the binder which form cubic carbides are considerably lower because of their very low solubility.

The metallic binder phase in the sintered state comprises the hard material phase, forms a continuous network and is therefore often referred to as a "metallic binder" or as a "binder". It is crucial for the strength of the carbide.

For the production of hard metal, cobalt metal powder is usually mixed-milled with hard-material powders in ball mills or atres in liquids such as water, alcohols or acetone. In this case, a deforming stress of the cobalt metal powder takes place. The resulting liquid suspension is dried, the resulting granules or powder ("hard metal mixture") pressed into compacts, and then sintered with at least partial melting of the metallic binder, subsequently ground if necessary to final gauge and / or provided with coatings.

Grinding operations require some technical effort, because it produces fine, harmful dusts or generated grinding sludge, which represent a loss and their environmentally friendly handling costs. Therefore, it is desirable to control the size change of the compact during sintering so that grinding operations omitted as possible.

In powder metallurgy as well as in ceramics, the size change of the compact during sintering is referred to as shrinkage or shrinkage. Calculated is the linear shrinkage (S _l ) of a dimension due to the sintered dimensional change divided by the original dimension of the compact. Typical values for this so-called linear shrinkage in the hard metal industry are between 15 and 23%. This value is dependent on numerous parameters, such as added organic auxiliaries (such as paraffin, low molecular weight polyethylenes or esters or amides of long-chain fatty acids as pressing aids, a film-forming agent for stabilizing granules after spray drying, such as polyethylene glycol or polyvinyl alcohol, or antioxidants such as hydroxylamine or Ascorbic acid). These organic aids are also referred to as organic additives. Other influencing factors which influence the shrinkage and its isotropy are, for example, the particle size and size distribution of the hard material powders, the mixed grinding conditions and the geometry of the compact. The deeper reason is that these parameters and additives affect the compaction process when pressing the hard metal mixture to the compact. Furthermore, to control the carbon balance during sintering, elemental carbon or refractory metal powders are used as further additives (inorganic additives), which can likewise influence the shrinkage and its isotropy.

In the case of axially pressed compacts of the industrial standard, anisotropies of the pressed density occur due to internal friction and wall friction during compaction, which can not be eliminated even by varying the parameters in the previous paragraph. These density anisotropies lead to different shrinkages in two or even three spatial axes (anisotropic shrinkage), thus to tensions or even cracks in the sintered piece and must therefore be minimized as possible. In principle, the empirical value is that the lower the shrinkage, ie the better the compactability during pressing, the better the shrinkage can be controlled within the desired tolerances, and the anisotropy of the shrinkage can be reduced. Together with a suitable design of the pressing tools, eridkonturnahe or accurate sintered parts can be produced. In the latter case, grinding operations are eliminated.

In axial pressing, experience has shown that there is a difference in shrinkage perpendicular and parallel to the pressing direction. In simple geometries, eg cubes or plates with a square surface perpendicular to the pressing direction, however, no significant differences occur in the two directions perpendicular to the pressing direction that it is sufficient to determine the shrinkage only in one of the two directions perpendicular to the pressing direction.

EP 0 937 781 B1 describes how the undesirable shrinkage anisotropy in the production of cobalt-bonded tungsten carbide hard metals below 1 μm can be influenced by uniaxial pressing by means of the grain size of the cobalt metal powder used as binder. The aim is a shrinkage that is completely equal in the pressing direction and perpendicular thereto (= isotropic shrinkage), which corresponds to a value for the parameter K of one. The further the value of K is less than one, the more anisotropic is the shrinkage. The value for K should be at least 0.988 to avoid reworking by grinding operations. For hard metals with 20% cobalt, a K value of 0.960 is given. From the present shrinkages S (in%), the K value can be calculated according to the following formula, the indices "s" being perpendicular to the pressing direction, "p" being parallel to the pressing direction: $$K=\frac{\left({}^{\mathrm{ss}}{/}_{100}\right)+1}{\left({}^{\mathrm{sp}}{/}_{100}\right)+1}$$

The global shrinkage S _g in percent can be calculated from the compactness and the sintered density according to the following formula: $$\mathrm{sg}=100\left(1-{\left(\frac{\mathrm{pr}\mathit{essdichte}}{\mathit{SIntedichte}}\right)}^{⅓}\right)$$

The global shrinkage does not consider possible differences in the 3 dimensions and is to be regarded as the average of the shrinkages in the three spatial axes. It enables a forecast of shrinkage based on the press density.

Due to the harmful effect of dust-like composite tungsten carbide with cobalt, as occurs for example when grinding sintered cemented carbide, and the often poor availability of cobalt as co-product of nickel or copper extraction, there is considerable interest in the substitution of cobalt as binder phase.

As a potential replacement for cobalt-based metallic binders, nickel-based binders are already being used, for example, for corrosion-resistant or non-magnetic carbide grades. by virtue of However, the low hardness and high ductility at higher temperatures such carbide types are not used for metal cutting.

Iron- and cobalt-containing metallic binder systems are therefore in the center of interest and are already available on a commercial basis. As feedstocks in the mixed grinding with the hard material powders usually either element powder such as cobalt, nickel or iron metal powder or prealloyed powders are used. The latter already represent the desired composition of the FeCoNi portion of the binder after sintering as a pre-alloyed powder.

Out EP-B-1007751 Carbides are known with up to 36% Fe for carbide applications. Performance advantages are achieved over cobalt bonded hardmetals since the sintered cemented carbide has a stable face centered cubic (fcc) binder phase as opposed to a cobalt bonded cemented carbide having an fcc binder phase after sintering. However, this converts in use in the stable at lower temperatures hexagonal phase. This phase transformation leads to a microstructural change, which is also referred to as case hardening, and a poorer fatigue behavior, which can not occur in a stable fcc binder phase.

In EPA 1346074 describes a cobalt-free FeNi-based binder type for coated carbide cutting tools. In this case, the case hardening can not occur due to the stable stability of the fcc binder phase over a wide temperature range from room temperature to the sintering temperature. The lack of cobalt suggests that the high temperature properties (hot hardness) of the ductile binder are not sufficient for certain applications such as turning metal.

Out DE-U-29617040 and the dissertation by Leo Prakash (TH Karlsruhe, 1979) has long been known that carbide with FeCoNi-based binder phases, which have a martensite-induced phase transformation after sintering, particularly high thermal hardness and a generally higher wear resistance and better chemical corrosion resistance exhibit. From the phase diagram of the three-component system Fe-Co-Ni it is possible to estimate the range in which martensite can occur, but in the sintered hard metal the content of tungsten, carbon or chromium dissolved in the metallic binder after sintering results in a shift of the two-phase region because these elements stabilize the fcc lattice type. For some hard metal applications, a metallic binder phase with about 70% iron, 10% cobalt and 20% nickel has proven to be particularly resistant to wear Characterized by a martensitic transformation on cooling. (B. Wittman, W.-D. Schubert, B. Lux, Euro PM 2002, Lausanne).

From a metallurgical point of view, it is advantageous to use the FeCoNi portion of the metallic binder phase pre-alloyed as a powder, because experience shows that the use of elemental powders (eg Fe, Co and Ni powders) leads to locally different temperature and compositional layers of the melt eutectics Co-WC or Ni-WC or Fe-WC, thus premature local shrinkage, inhomogeneities of the sintered structure and mechanical stresses. The sintering process is thus superimposed chemical compensation processes.

In EP-A-1079950 Production processes for pre-alloyed metal powders from the FeCoNi alloy system are described. Here coprecipitated metal compounds or mixed oxides are reduced with hydrogen at temperatures between 300 ° C and 600 ° C to the metal powder. Alternatively, pre-alloyed metal powders may also be made by other methods in which there is a possibility that the metal components will be mixed by diffusion, such as mixing and annealing of oxides. If the equilibrium phase content of these powders given by the gross composition is biphasic at room temperature, these powders frequently already contain portions of excreted ferritic phase (cubic-body-centered, bcc) after production, the fcc portion still remaining (cubic face-centered , fcc) may be completely or partially metastable. Thus, the alloy powders may be supersaturated at room temperature with respect to bcc fractions to be precipitated, and the excretion of bcc fractions may be promoted by mechanical activation of the powders even at room temperature. Owing to the known poor deformability of bcc phases and their finely distributed presence due to their precipitation, the bcc-containing cemented carbide powder obtained after the mixing milling and drying can be pressed poorly. This results in low green densities, high and anisotropic shrinkages, and a greater dependence of compacted density on compacting pressure compared to elemental metal powders. Despite the pronounced homogeneity, pre-alloyed FeCoNi powders, which tend to biphase, could not be used as feedstock for carbide production due to process engineering reasons. Since the tungsten carbide is not deformed during pressing and only the metallic binder powder ensures the ductility required during pressing, the abovementioned problems with reduced binder content occur more frequently. Hard metals with a martensitic binder state - which require a pre-alloyed binder powder with very high iron contents and therefore high bcc contents - and low binder contents such as 6% are therefore only possible to produce under great process engineering effort.

Uhrenius at.al. in "Int J of Refractory & Hard Materials", 15 (1997), pages 139-149 , the use of alternative binders in hard metals. The hardness of the Ni-Fe-Co-WC, Ni-Fe-WC and Co-WC alloys with different carbon contents are investigated and the hardness of the sintered alloys is compared. It has been found that the hardness of the Fe-Ni-Co-WC alloys decreased with increasing carbon contents.

In Metal Powder Report, Vol. 58, March 2003, pp. 28-29 the pre-alloyed 60Co / 20Ni / 20Fe powders are described. These powders are characterized by a uniform structure and high sintering activity.

It is an object of the present invention to provide a sintered cemented carbide having FeCoNi-based metallic binder with improved pressing performance before sintering and having an acceptable shrinkage performance using prealloyed FeCoNi alloy powder, and a method of manufacturing and a metallic powder mixture suitable therefor.

(mit Fe: Eisengehalt in Gew.-%, %Co: Cobaltgehalt in Gew.-%, %Ni: Nickelgehalt in Gew.-%) genügt, wobei mindestens zwei Binderpulver a) und b) verwendet werden, wobei ein Binderpulver eisenärmer ist als die Bruttozusammensetzung des Binders und das andere Binderpulver eisenreicher ist als die Bruttozusammensetzung des Binders und wobei mindestens ein Binderpulver vorlegiert ist aus mindestens zwei Elementen ausgewählt aus der Gruppe bestehend aus Eisen, Nickel und Kobalt verwendet wird.This object is achieved by the method according to claim 7 for producing a hard metal mixture by using a) at least one prealloyed powder selected from the group consisting of iron / nickel, iron / cobalt, iron / nickel / cobalt and nickel / cobalt; b) at least one element powder selected from the group consisting of iron, nickel and cobalt or a prealloyed powder selected from the group consisting of iron / nickel, iron / cobalt, iron / nickel / cobalt and nickel / cobalt, which is derived from component a) is different; c) hard material powder, wherein the gross composition of components a) and b) together contains a maximum of 90% cobalt and a maximum of 70 wt .-% nickel. The iron content is advantageously at least 10 wt .-%. In the embodiment of the invention, this is a method for producing a hard metal mixture according to claim 7, wherein the gross composition of the binder of Co max. 90% by weight, Ni max. 70 wt .-% and Fe is at least 10 wt .-%, wherein the iron content of the inequality $$\mathit{Fe}\ge 100\%-\frac{\%\mathit{Co}•90\%}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}-\frac{\%\mathit{Ni}•70\%}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}$$

(with Fe: iron content in% by weight,% Co: cobalt content in% by weight,% Ni: nickel content in% by weight) is sufficient, with at least two binder powders a) and b) being used, with one binder powder having less iron as the gross composition of the binder and the other binder powder is more ferrous than the gross composition of the binder and wherein at least one binder powder is pre-alloyed of at least two elements selected from the group consisting of iron, nickel and cobalt is used.

It was surprisingly found that not the actual proportion of the bcc phase of the metallic binder powder is responsible for the use of prealloyed powders for the poor compression behavior, but expected from theoretical considerations, stable at room temperature bcc content, as apparently in the Mixtures mechanically induced phase transformations of pre-alloyed binder powders which still have metastable phase portions at room temperature (resulting in conversion hardening) for which poor compaction behavior is responsible. Decisive for a favorable compression and shrinkage behavior is therefore the stable fcc fraction which can be expected at room temperature out of theoretical considerations. Component a) is a prealloyed metal powder and component b) is an element powder or a prealloyed powder having a different composition, wherein one of the components a) or b) in particular advantageously has a greater proportion of a fcc phase which is stable at room temperature than the gross composition of Binders, this would be completely pre-alloyed. Particularly advantageous is one of the components a) or b) lower in iron than the gross composition of the binder powder.

Accordingly, the respective other component is more iron-rich, with the contents of iron, nickel and cobalt complementing the desired overall composition of the binder (the composition of components a) and b) together).

Since the densities and molecular weights of the elements iron, cobalt and nickel are very similar, in this disclosure, volume percent (vol.), Mol percent (mol.%) And weight percent (wt.%) Are used interchangeably.

The nickel content of the components is collectively 70% by weight of the powder mixture or less.

Advantageously, the nickel content of components a) and b) together amount to 45% by weight of the powder mixture or less if the cobalt content is less than 5% by weight.

In a further embodiment of the invention, the nickel content of both components a) and b) together is 45% by weight of the powder mixture or less if the cobalt content is less than 5% by weight.

In an advantageous embodiment of the invention, a) a prealloyed powder consisting of iron / nickel and b) an iron powder. In a further embodiment of the invention, component a) is a prealloyed powder such as FeNi 50/50, FeCo 50/50 or FeCoNi 40/20/40. The present invention also relates to a hard metal mixture obtainable by the method described above.

This hard metal mixture according to the invention can be used for the production of shaped articles, preferably by pressing and sintering.

• Bereitstellen eines ersten vorlegierten Metallpulvers,
• Bereitstellen eines Elementpulvers oder eines zweiten vorlegierten Metallpulvers,
• Mischmahlen beider Komponenten mit einen Hartstoffpulver um eine Hartmetallmischung zu erhalten
• Pressen und Sintern der Hartmetallmischung, wobei ein geformter Gegenstand aus einem Hartmetall erhalten wird.

The present invention also relates to the process according to claim 17 for the production of shaped articles, comprising the steps:

• Providing a first prealloyed metal powder,
• Providing an element powder or a second pre-alloyed metal powder,
• Mixing of both components with a hard powder to obtain a hard metal mixture
• Pressing and sintering the cemented carbide mixture, whereby a molded article is obtained from a cemented carbide.

The process for producing shaped articles is schematically shown in FIG FIG. 6 shown. The components a) and b), which are collectively referred to as binder powder 10, and the hard material powder 20 (component c) are mixed with a customary Mahlfüssigkeit 30, for example water, hexane, ethanol, acetone and optionally other organic and / or inorganic additives (additives 40) subjected to a Mischmahlung 100, for example in a ball mill or an attritor. The resulting suspension 50 is dried, removing the grinding fluid 90 and obtaining a hard metal mixture 60. This cemented carbide mixture is pressed by a press 120 into the desired shape, whereby a compact 70 is obtained. This is sintered by a conventional method, as described in detail below (sintering 130). Here, a molded article 90 is obtained, which consists of a hard metal.

It may also contain conventional auxiliaries. These are in particular organic and inorganic additives.

Organic additives are e.g. Paraffin, low molecular weight polyethylene or esters or amides of long-chain fatty acids, which are used as pressing aids; a film-forming agent for stabilizing granules after spray-drying, such as e.g. Polyethylene glycol or polyvinyl alcohol, or antioxidants such as hydroxylamine or ascorbic acid. In particular, low molecular weight organic compounds are suitable as organic additives. When polymers are used, polymers having a low ceiling temperature of preferably below 250 ° C., for example polyacrylates and polymethacrylates such as polymethyl methacrylate, polyethyl methacrylate, polymethyl acrylate, polyethyl acrylate or even polyvinyl acetate or polyacetal homo- or copolymers are suitable. These are generally used in amounts of from 1% by weight to 5% by weight, based on the total amount of components a, b and c.

Inorganic additives are, for example, elemental carbon or refractory metal powder added to control the carbon balance of sintering, which may also affect shrinkage and its isotropy. For example, tungsten, chromium or molybdenum metal powders can be used as the refractory metal powder. In general, they are used in amounts of less than 1: 5, in particular less than 1:10 in a weight ratio to the total binder content of the hard metal.

As carbon, carbon black or graphite can be used. Suitable graphite powders generally have BET surface areas of 10 to 30 m ² / g, in particular 15 to 25 m ² / g, advantageously 15 to 20 m ² / g. The particle size distributions have a d50 value of usually 2 to 10 .mu.m, advantageously from 3 to 7 .mu.m, the d90 value is generally from 5 to 15 .mu.m.

The basic feature of the invention is to have the lowest possible proportion of room-temperature-stable bcc phase in pressing on such binder compositions, which, if they were completely prealloyed, would be in the two-phase region bcc / fcc at room temperature. This is achieved by adjusting the gross composition of the binder to at least two different powders, one of which is stable at room temperature (eg, iron powder or an iron-rich composition which is stable at room temperature and single-phase bcc), and another stable at room temperature fcc or at room temperature has a higher stable fcc content than the gross composition would have been, it would be completely prealloyed.

Another aspect of the invention is that when pressed, the least amount of bcc phase is present on such binder compositions, as compared to those which would have been produced entirely from elemental powders.

This is accomplished by adjusting the gross composition to at least two different powders, one of which has a higher stable fcc content at room temperature, compared to using elemental powders to make the cemented carbide blend.

Thus, the invention is preferably relevant to the composition range FeCoNi of the binder (gross composition) which is pre-alloyed at room temperature (it is assumed that the temperature prevailing in the mixed grinding is between room temperature and a maximum of 80 ° C) according to the phase diagram in the two-phase region bcc (cubic-body centered ) / fcc (face-centered cubic), which is the prerequisite for the mechanically activated excretion of bcc phases. Since the fcc phases are more stable at high temperatures or their area of existence is larger, the general rule is that pre-alloyed metal powders in the FeCoNi system - provided the composition is in the two-phase region at room temperature - due to the usual manufacturing temperatures between 400 and 900 ° C. , are generally supersaturated at room temperature with respect to the content of fcc phase, and therefore tend to excrete bcc phase upon mechanical activation. This preferred range is thus defined by the boundary of the two-phase region fcc / bcc to the fcc region. Preferably, therefore, the gross composition of the binder of one or more of the group of prealloyed FeCoNi, FeNi, CoNi and Ni powders, on the one hand (with higher stable room temperature fcc phase than the gross composition, or even 100% at room temperature, is stable Ni powder or FeNi 15/85) and one from the group of stable single-phase bcc powder or those with a higher proportion of stable at room temperature bcc content on the other hand, for. As iron powder, FeCo powder with up to 90% Co, FeNi 82/18 or FeCoNi 90/5/5, constructed.

Surprisingly, in a pre-alloyed powder of composition FeCoNi 40/20/40, cubic face-centered phase is already found by X-ray diffraction at room temperature, although published phase diagrams for this composition alone show the face-centered cubic phase to be stable. Furthermore, the very high proportion of cubic face-centered phase after the mixed grinding of Example 1 is a further indication that the boundary line of the biph / fcc two-phase region to the fcc phase must be at far lower iron values than indicated in the literature.

Considering the binary phase diagrams FeNi (shown in Fig. 1 ) and FeCo (shown in Fig. 2 ), which represent two edge systems of the ternary system, it can be seen that the published phase diagram FeCoNi (shown in Fig. 3 , out Bradley, Bragg et al., J. Iron, Steel Inst. 1940, (142), pp. 109-110 ) coincides with that of the FeCo on the Ni-free side (boundary line two-phase region to the fcc region at about 10% Fe), but that there are very large discrepancies on the Co-free side. Whereas, according to the ternary diagram, the boundary line two-phase region / fcc in the edge system FeNi is about 26% Ni, it is in the edge system FeNi at 70% Ni. If you connect these two points on the edge systems (FeNi 30/70 and FeCo 10/90) in the ternary system, you can draw the approximate course of the boundary line two-phase area / fcc at room temperature as a line and thus obtains its approximate course in the ternary system.

This is in FIG. 4 shown. In the diagram, the dashed line A shows the boundary, the hatched area to the left of the dashed line A represents the gross composition area according to the invention. The determined line also provides a means to obtain binder powder having the highest possible room temperature stable fcc Share.

Hiermit ist die Grenzlinie A in Figur 4 mathematisch beschrieben.Interestingly, it now appears that according to the limit line thus obtained, the composition FeCoNi 40/20/40 must be biphasic. Preferably, therefore, the invention is carried out in such gross compositions FeCoNi of the binder, which satisfies the conditions Co a maximum of 90% and Ni a maximum of 70%, with the additional condition $$\mathit{Fe}\ge 100\%-\frac{\%\mathit{Co}•90\%}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}-\frac{\%\mathit{Ni}•70\%}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}$$

Herewith the boundary line A is in FIG. 4 described mathematically.

Preferably, iron powder is used as the element powder in component b), but it is also possible to use an iron-rich alloy powder. You can get out of the Phase diagrams show that this preferred range for the bcc powder stable at room temperature satisfies the conditions "Ni max 10%" and "Co max 70%". In addition, any iron-rich prealloyed powder having a higher bcc stable at room temperature than the gross pre-alloyed powder composition may be used.

The gross composition of the binder, which is calculated from the chemical compositions of the element or alloy powders used, takes into account only the metal content of the powders used. The content of oxygen, nitrogen, carbon or any passivating organic nature (for example, waxes, polymers or antioxidants such as ascorbic acid) is not taken into account. This must be taken into account, in particular, in the commercially available iron carbonyl powders, which may well have carbon and nitrogen of more than one percent by weight. Nevertheless, they are called element powder. According to the invention, the elements copper, zinc or tin are preferably present at most in the trace range, ie in amounts of at most 1000 ppm.

Surprisingly, there is no statement in the literature as to how the shrinkage or its anisotropy can be controlled in the case of FeCoN bonded hard metals, although these are important parameters for the controllability of the industrial production, which is as close to final contour as possible or appropriate.

Component a) are so-called pre-alloyed powders. The preparation of pre-alloyed powders is known in principle to a person skilled in the art and is described, for example, in US Pat EP-A-1079950 and EP-A-865 511 described, to which reference is made. These pre-alloyed powders can be prepared by reduction of coprecipitated metal compounds or mixed oxides with hydrogen at temperatures between 300 ° C and 600 ° C to the metal powder. Alternatively, pre-alloyed metal powders may also be made by other methods in which there is a possibility that the metal components will be mixed by diffusion, such as mixing and annealing of oxides. The reduction can also be achieved in other reducing gases at a corresponding temperature. Such methods are known to the person skilled in the art or can be achieved by a small number of corresponding experiments.

In the literature, sometimes powders obtained by mixing and melting elemental powders and then atomizing the melt are also erroneously referred to as pre-alloyed powders (eg atomised pre-alloy). Such powders are expressly excluded from the term of pre-alloyed powders used herein and differ greatly in their properties.

For the preparation of pre-alloyed metal powders used according to the invention, an aqueous solution containing metal salts of the desired metals in the appropriate proportions to each other, with an aqueous solution, for. a carboxylic acid, a hydroxide, carbonate or basic carbonate mixed. The metal salts may advantageously be nitrates, sulfates or halides (especially chlorides) of iron, cobalt or nickel. This forms insoluble compounds of the metals, which precipitate from the solution and can be filtered off. The precipitate is hydroxides, carbonates, or oxalates of the metals. This precipitation product may optionally be subjected to thermal decomposition at a temperature of 200 to 1000 ° C in an oxygen-containing atmosphere (calcination). The precipitate can be reduced to the prealloyed metal powder after precipitation and drying or after a calcination step in a hydrogen atmosphere at a temperature of 300 ° C to 1000 ° C. Component a), the prealloyed powder, contains at least two metals selected from the group consisting of iron, nickel and cobalt. Examples of pre-alloyed powders in component a) are: pre-alloyed CoNi powders with any ratio Co: Ni between 0 and 200 also pre-alloyed with up to 10% Fe, FeNi powder with up to 30% Fe, FeNi 50/50. Examples of component b) are FeCo 50/50, FeCo 20/80, FeCoNi 90/5/5, FeNi 95/5.

Component b) is an element powder selected from the group consisting of iron, nickel and cobalt, alternatively another prealloyed powder.

In one embodiment of the invention, component b) is a prealloyed powder selected from the group consisting of iron / nickel, iron / cobalt, iron / nickel / cobalt and nickel / cobalt, which is different from component a).

Preferably, the gross composition of components a) and b) together contains at least 10% by weight of iron and not more than 70% by weight of nickel. More preferably, the proportion of room-temperature-stable fcc phase of both components a) and b) is different from each other, and is higher than that of components a) and b), if they were completely pre-alloyed together to the desired gross composition of the binder. Also advantageous is a content of not more than 90% cobalt.

In turn, components a) or b) can in turn also be made up of components having different compositions, so that theoretically the number of binder powders used is not limited. The choice of binder powder is also here according to the invention, i. the proportion of fcc phase stable at room temperature is greater than that of the gross composition as prealloyed powder.

In a further embodiment of the invention, the component b) according to the invention is a conventional iron powder, or the component b) is a conventional one Nickel metal powder, for example for powder metallurgical applications, or component b) is a conventional cobalt powder. In this case, component b) is a conventional iron or nickel powder.

These are powders that have a substantially spherical, chapped or fractured shape of the particles, such as in FIG. 1 of the PCT / EP / 2004/00736 shown, have. These metal powders are elemental powders, that is, these powders consist essentially of one, advantageously pure, metal. The powder may contain common impurities. These powders are known to those skilled in the art and are commercially available. For their preparation, numerous metallurgical or chemical processes are known. If fine powders are to be produced, the known methods often begin with the melting of a metal. The mechanical coarse and fine comminution of metals or alloys is also often used for the production of "conventional powders", but results in a non-spherical morphology of the powder particles. Provided that it works in principle, it represents a very simple and efficient method of powder production. ( W. Schatt, K.-P. Wieters in "Powder Metallurgy - Processing and Materials", EPMA European Powder Metallurgy Association, 1997, 5-10 ). The morphology of the particles is also determined by the type of atomization.

Pre-alloyed powders are powders which consist of punctually sintered primary grains and therefore have an internal porosity and can therefore be comminuted in the case of mixed grinding, as in WO 00/23631 A1 , P.1, lines 26-30. In contrast, melted metal powders are not suitable for the disclosed process since they have no internal porosity. In the described mixed grinding for the production of the hard metal mixture occurs in the case of the use of atomized metal powders not for comminution, but for the ductile deformation of the powder particles, which causes microstructural defects in the sintered cemented carbide. Known are so-called binder pools ("binder pools"), which contain no hard material, as well as elongated pores, which are formed by the fact that deformed metal particles melt with high aspect ratio in the liquid phase sintering and absorbed by the surrounding hard material powder via capillary forces, then leaving a pore which has the shape of the deformed metal particle. For these reasons, in cemented carbide production, it is preferable to use a point sintered cobalt metal powder produced by hydrogen reduction of oxides or oxalates. Sputtered cobalt metal powders, although easier to produce, have not been able to assert themselves from the problems described above for producing hard metal blends.

In addition to the production of conventional element powders for powder metallurgical applications by atomization, other single-stage melt metallurgical processes are often used, such as the so-called "melt-spinning", ie Pouring a melt onto a cooled roll to form a thin, generally easily shredded strip or so-called "crucible-melt-extraction", ie immersing a cooled, profiled, high-speed roll into a molten metal, whereby particles or fibers are recovered become.

A suitable variant of the production of conventional powder element powders for powder metallurgy, which are suitable for the production of the hard metal mixture according to the invention, is the chemical route via reduction of metal oxides or metal salts (US Pat. W. Schatt, K.-P. Wieters in "Powder Metallurgy - Processing and Materials", EPMA European Powder Metallurgy Association, 1997, 23-30 ), so that the procedure (apart from the use of the starting metal) is identical to the preparation of component a). Extremely fine particles having particle sizes below one micrometer can also be produced by the combination of vaporization and condensation processes of metals as well as by gas phase reactions (US Pat. W. Schatt, K.-P. Wieters in "Powder Metallurgy - Processing and Materials", EPMA European Powder Metallurgy Association, 1997, 39-41 ).

One known industrial process for the production of iron, nickel and FeNi powders is the so-called carbonyl process, in which metal carbonyls are thermally decomposed. The particle sizes here are between 0.3 and 10 .mu.m, with powders having particle sizes of less than 5 .mu.m being often suitable for hard metal production, such as, for example, the commercially available CM-type carbonyl iron powders from BASF AG, Germany.

Component c), the hard material powder, is known in principle to the person skilled in the art and is commercially available. These hard material powders are powders of, for example, carbides, borides, nitrides, metals of groups 4, 5 and 6 of the Periodic Table of the Elements. Advantageously, the hard powder in the powder mixture according to the invention, in particular carbides, borides and nitrides of the elements of Groups 4, 5 and 6 of the Periodic Table; in particular carbides, borides and nitrides of the elements molybdenum, tungsten, chromium, hafnium, vanadium, tantalum, niobium, zirconium. Advantageous hard materials are in particular titanium nitride, titanium boride, boron nitride, titanium carbide, chromium carbide or tungsten carbide. As hard material powder, one or more of the compounds mentioned above can be used.

In general, component c), the hard material powder, in ratios of component a) and b): component c) in the ratio of 1: 100 to 100: 1 or of 1:10 to 10: 1 or of 1: 2 to 2 : 1 or 1: 1 used. In the case of tungsten carbide, boron nitride or titanium nitride, these are advantageously used in amounts of from 3: 1 to 1: 100 or from 1: 1 to 1:10 or from 1: 2 to 1: 7 or from 1: 3 to 1: 6.3 used.

In a further embodiment of the invention, the hard material is advantageously used in amounts of from 3: 1 to 1: 100 or from 1: 1 to 1:10 or from 1: 2 to 1: 7 or from 1: 3 to 1: 6.3 ,

In a further embodiment of the invention, the hard metal mixture is a mixture of components a) and b) and component c) with the proviso that the ratio of component I to component III at 3: 1 to 1: 100, or from 1: 1 to 1:10, or from 1: 2 to 1: 7, or from 1: 3 to 1: 6.3. The mean particle sizes before use in the process according to the invention are generally between 0.1 μm to 100 μm

As further components, the hard metal mixture according to the invention may contain conventional organic and inorganic additives, such as organic film-forming binders, as already described above.

(mit Fe: Eisengehalt in Gew.-%, %Co: Cobaltgehalt in Gew.-%, %Ni: Nickelgehalt in Gew.-%.)Component a), the pre-alloyed powder, and component b), the element powder or the further pre-alloyed powder, complement the desired composition of the binder metal ("gross composition") for the component c), the hard material. Here, the components a) and b) together contain at least 10 wt .-% iron, the nickel content is not more than 70 wt .-%, advantageously, the maximum cobalt content is 90%. In addition, the proviso that the iron content of the gross composition of both components a) and b) together satisfies the following inequality is particularly advantageous: $$\mathit{Fe}\ge 100-\frac{\%\mathit{Co}•90}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}-\frac{\%\mathit{Ni}•70}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}$$

(with Fe: iron content in wt%,% Co: cobalt content in wt%,% Ni: nickel content in wt%)

The nickel content of components a) and b) together is advantageously 70% by weight or less.

In a further embodiment of the invention, the nickel content of both components a) and b) together is 45% by weight of the powder mixture or less if the cobalt content is less than 5% by weight.

In a further embodiment of the invention, component a) is a prealloyed powder consisting of iron and nickel and component b) is a conventional elemental powder of iron.

In a further embodiment of the invention, component a) is a prealloyed powder selected from the group consisting of FeNi 50/50 and FeCoNi 40/20/40 or a nickel metal powder. Here, the components of the pre-alloyed powder are indicated by the element abbreviations and the numbers indicate the amount of the corresponding metal in weight percent. In this case, component b) is a conventional one Iron powder, or a prealloyed powder of the composition FeCo 50/50, FeCoNi 90/5/5 or FeNi 90/10.

The hard metal mixture is used according to the invention for the production of shaped articles by sintering. For this purpose, the hard metal mixture is pressed and sintered. The cemented carbide composition according to the invention can be made into green bodies by known powder metallurgical processing methods, and is then sintered at a temperature of 1220 ° C to 1600 ° C for a period of 0.1 hour to 20 hours to form a liquid metal binder phase. Before sintering, the green body must be debinded in the presence of an organic additive, which is achieved for example by heating to a temperature of 200 to 450 ° C, but is also possible by other methods.

The sintering takes place advantageously in an inert or reducing atmosphere or in a vacuum. As an inert gas can be noble gases such as helium or argon, in some cases also use nitrogen, as reducing gases hydrogen or its mixtures with nitrogen, noble gases. In some cases, hydrocarbons are also used.

The design of the entire sintering cycle has great significance for the mechanical properties of the cemented carbides, but not for the shrinkage, provided the densification during sintering is close to the theoretical one.

The invention will be further described by the following examples. All examples describe a cemented carbide having the same nominal composition and gross composition of the binder. The sintered densities at 20% binder content were 13.1 +/- 0.1 g / cm ³ , so that it was reasonable to use this average to calculate the global shrinkage so that the examples are more comparable. Individual sintered pieces were metallographically prepared for control, the porosity being better than A02 B02 according to ISO 4505.

Comparative Example 1

• Eisen 69.7 Gew.-%, Kobalt 10.3 Gew.-%, Nickel 19.5 Gew.-%, Sauerstoff 0.51 Gew.-%, Kohlenstoff 0.0242 Gew.-%, FSSS 2.86 µm

As a metallic binder powder was after EP-A-1079950 manufactured, pre-alloyed metal powder FeCoNi 70/10/20 Amperit® MAP HM from the company HC Starck GmbH, Germany with the following properties:

• Iron 69.7% by weight, cobalt 10.3% by weight, nickel 19.5% by weight, oxygen 0.51% by weight, carbon 0.0242% by weight, FSSS 2.86 μm

The powder was examined by X-ray diffraction analysis. The height ratio of the main reflexes fcc and bcc was bcc / fcc = 3.45. From this it can be estimated that the bcc content is about 78% by volume.

100 g of the binder metal powder was mixed with 400 g of WC (FSSS 0.6 (ASTM B330), type WC DS 60, manufacturer: HC Starck GmbH) and 2.13 g of carbon black (specific surface area: 9.6 m ² / g) with 570 ml of spirit and 30 ml of water a ball mill (content 2 l) with 5 kg of 15 mm diameter hard metal balls at 63 rpm for 14 h mixed milled. The hard metal balls were mechanically separated, and the suspension obtained in a glass flask at 65 ° C and 175 mbar absolute pressure heated under rotation to separate the grinding liquid by distillation. Was obtained a hard metal powder, which was sieved over 400 microns. The height ratio of the main reflections bcc / fcc was determined by X-ray diffraction analysis to be 14.3, ie the bcc content is about 94% by volume and the fcc content is about 6% by volume. Based on this result, it can be assumed that the fcc phase stable at room temperature for a FeCoNi 70/10/20 is at most 6% by volume.

The cemented carbide powder was pressed uniaxially with a firm punch at 100, 150 and 200 MPa, determined the densities of the compacts, and sintered in vacuo at 1400 ° C for 1 h. The following table shows the results thus obtained: Pressing pressure (MPa) 100 150 200 Press density (g / cm ³ ) 6.01 6.25 6.45 Global shrinkage (calculated from pressed density and sintered density, in%) 22.87 21.86 21,04

The change in phase balance is presumably due to supersaturation of the fully prealloyed binder powder at room temperature with respect to the face centered cubic content, and acceleration of the conversion rate from fcc to bcc due to the mechanical activation in the mixed grinding.

Comparative Example 2

Example 1) was repeated, but instead of the pre-alloyed binder powder, the following elemental metal powders were used: amount element Manufacturer FSSS * Phase inventory according to X-ray diffraction analysis 70 g iron BASF, D 2.47 Pure bcc 10g cobalt Umicore, B 0.9 Hexagonal: fcc 1:25 20 g nickel Inco Specialties, UK 2.8 Pure fcc * ASTM B330

Due to the carbon content of the element powders, the amount of carbon black added had to be reduced to 0.84 g to achieve the same carbon content of the formulation as in Example 1. Since only the Ni powder is stable at room temperature fcc and the co-powder is predominantly hexagonal , results for the binder powder used On the other hand, the fcc portion stable at room temperature is 20% since the fcc portion in the cobalt metal powder is metastable at room temperature while iron is stably hexagonal at room temperature bcc and cobalt.

The following results were obtained: Pressing pressure (MPa) 100 150 200 Press density (g / cm ³ ) 6.28 6.47 6.59 Global shrinkage (calculated from pressed density and sintered density, in%) 21.74 20.95 20.47

Comparative Example 3

a) Example 1) was repeated, except that 0.71 g of graphite powder having a BET surface area of 20 m ² / g, a d50 of 3.3 μm and d90 of 6.5 μm were added as internal lubricant and the amount of carbon black added was reduced by the same amount , The results obtained are shown in the following table: Pressing pressure (MPa) 100 150 200 Press density (g / cm ³ ) 6.27 6.49 6.68 Global shrinkage (calculated from pressed density and sintered density, in%) 21.78 20.87 20.11

Comparison with Examples 1 and 2 shows that the green density obtained with fully prealloyed binder powder is comparable to that obtained using the single powders.

b) In the following Comparative Example 3b, the procedure was identical to that in 3a, but using a graphite powder having a BET surface area of 14.2 m ² / g, a d50 of 6 μm and a d90 of 12 μm: Pressing pressure (MPa) 100 150 200 Press density (g / cm ³ ) 6.52 6.8 6.94 Global shrinkage (calculated from pressed density and sintered density, in%) 20.83 19.72 19.17

Example 4

Example 1 was repeated, but the following amounts of prealloyed binder powder or Fe metal powder were added instead of the prealloyed binder powder: amount Manufacturer FSSS * Phase inventory according to X-ray diffraction analysis 40 g FeNi 50/50 HC Starck 2.01 Pure fcc 20 g FeCo 50/50 HC Starck 1.26 Pure bcc 40 g Fe powder BASF 2.47 Pure bcc • ASTM B330

The addition of carbon black was 1.94 g to set the same carbon content in the formulation as in Example 1. The fcc content to be assumed at room temperature should be about, and is calculated as follows: according to the phase diagram FeNi, a FeNi 50/50 is unstable at room temperature and separates into FeNi 90/10 and FeNi 30/70. The proportions of the two segregation products are 1/3 for the FeNi 90/10 and 2/3 for the FeNi 30/70. This means that the FeNi 50/50 has a 2/3 room temperature stable fcc phase. FeCo 50/50 and Fe are stable at room temperature bcc. The proportion of fcc phase stable at room temperature relative to the gross composition is therefore 2/3 x 40% = 26.7%.

The results are summarized in the following table: Pressing pressure (MPa) 100 150 200 Press density (g / cm ³ ) 7.19 7.33 7.44 Global shrinkage (calculated from pressed density and sintered density, in%) 18.12 17.6 17.19

Example 5

Example 1 was repeated, but instead of the pre-alloyed binder powder, the following quantities of pre-mixed binder powder or Fe powder were added: amount Manufacturer FSSS * Phase inventory according to X-ray diffraction analysis 50 g FeCoNi 40/20/40 HC Starck 0.96 Bcc / fcc = 0.77, fcc = 56.5 wt% 50 g Fe powder BASF 2.47 Pure bcc * ASTM B330

The carbon black addition was 2.03 g to adjust the same carbon content in the formulation as in Example 1. The total fcc phase fraction is 0.5 x 56.3% = 28.3%. The proportion of stable at room temperature fcc phase after the Mixed grinding in the pre-alloyed binder content is difficult to estimate, since the phase diagram FeCoNi is not known in this alloy composition at room temperature, but should be well below 50%, since the starting powder FeCoNi 40/20/40 precipitates below about 500 ° C already bcc phase , Thus, the stable at room temperature fcc content of the binder would be less than 25%.

The results obtained are summarized in the following table: Pressing pressure (MPa) 100 150 200 Press density (g / cm ³ ) 6.76 6.93 7.06 Global shrinkage (calculated from pressed density and sintered density, in%) 19,79 19,12 18.62

The results of Examples 1 to 5 are in Fig.1 shown. It can be seen that the green density is the highest or the global shrinkage is lowest for the case in which all the metal powders used are stable in a single phase and the fcc content stable at room temperature is as high as possible.

Comparative Example 6

Example 2 was repeated. A portion of the hard metal powder was pressed directly after drying, another part was according to WO 2004 014586 with 2 parts by weight of paraffin infiltrated to 98 parts by weight of hard metal powder to achieve a homogeneous wax distribution. The results "waxed" and "unwaxed" are compared in the following table. At the values for the density "waxed" the measured value for the density was multiplied by the factor 0.98, because the wax is expelled during sintering.

It can be deduced from the results that the use of pressing aids is neutral with regard to the pressed density and the resulting gobal shrinkage, but that the differences in the observed shrinkage, measured vertically and parallel to the pressing direction, are from about 1% point in the unwaxed case to 0.6 reduced to 0.8% points in the waxed case. The undesirable shrinkage anisotropy can therefore only be mitigated with a pressing aid agent. The disadvantages of using elemental powders in sintering remain. Pressing pressure (MPa) 100 150 200 Press density g / cm ³ waxed 6.47 6.64 6.76 unwaxed 6.48 6.63 6.74 Global shrinkage (calculated from press density and sintered density,%) waxed 20.95 20.27 19,79 unwaxed 20.92 20.31 19,87 Measured shrinkages (%) Perpendicular to the pressing direction waxed 20.29 19.77 19.15 unwaxed 20.56 20,04 19.64 Parallel to the pressing direction waxed 20.88 20.39 19,95 unwaxed 21,50 21.10 20.59 K value waxed 0.995 0.995 0.993 unwaxed 0.992 0.994 0.992

Comparative Example 7

The hard metal powder from Example 1 was infiltrated with paraffin wax to give a content of 2%. Press densities corrected for wax content were 5.99 (100 MPa), 6.39 (150 MPa), and 6.61 (200 MPa). Comparison with Example 1 shows that there is only a slight improvement in the green density due to the added wax.

It can be concluded from Examples 6 and 7 that the global compaction behavior during pressing is dominated by the phase state of the binder metal powder after the mixed grinding, and only secondarily by the lubricant additive.

Example 8 (a) according to the invention)

1. a) bestehend aus FeCo 50/50, FeNi 50/50 und Fe-Pulver in den Gewichtsverhältnissen 1:2:2
2. b) bestehend aus vollständig vorlegiertem FeCoNi 70/10/20
3. c) bestehend aus den Elementpulvern

3 hard metal batches with 6% by weight of a FeCoNi 70/10/20 binder were prepared analogously to the preceding examples, pressed and sintered. The sintering temperature was 1500 ° C. The wording of the binder was varied:

1. a) consisting of FeCo 50/50, FeNi 50/50 and Fe powder in the weight ratios 1: 2: 2
2. b) consisting of fully pre-alloyed FeCoNi 70/10/20
3. c) consisting of the elemental powders

The sintering density was 14.80 g / cm3 +/- 0.03, but variant b) showed porosity and therefore reached only 14.54 g / cm3.

The differences in green density and shrinkage are not as pronounced in the three variants with 6% binder as at 20%, since the proportion of the binder in the pressing forces is of course less heavily weighted.

The variant a) shows a lower anisotropy of the shrinkage compared to the variant c).

Variant b) could not be densely sintered, which is an indication of a poor homogeneity of the green density and an indication of very high internal friction during pressing. The values for the shrinkage can therefore not be evaluated.

The results are summarized in the following table (a to c among each other): Pressing pressure (MPa) 100 150 200 Green density g / cm ³ a) 7.50 7.63 7.79 b) 7.35 7.63 7.79 c) 7.31 7.51 7.66 Global shrinkage (calculated from press density and sintered density,%) a) 20.27 19.82 19.26 b) 20.81 20.13 19.64 c) 20.95 20.24 19.71 Measured shrinkages (%) Perpendicular to the pressing direction a) 20.59 19.82 19.26 b) 20.20 * 20.13 * 19.64 * c) 20.53 20.24 19.71 Parallel to the pressing direction a) 20.36 19,79 19.42 b) 20.45 * 19.93 * 19.57 * c) 21,25 20.52 19.97 K values a) 1,002 1,000 0.999 b) 0.998 * 1,002 * 1.001 * c) 0.994 0.998 0.998 * not evaluable due to porosity

Examples 9 to 12 (partially according to the invention)

The cemented carbide powders of Comparative Examples 1 and 2 and Examples 4 and 5 (Comparative Examples 9 and 10, Examples 11 and 12) were pressed again, the pellets were measured and sintered in vacuo at 1410 ° C. The sintered pieces were measured, by determining the dimensions parallel and perpendicular to the pressing direction, and then calculating the shrinkages in the two directions with the help of the dimensions in the pressed state. Pressing pressure: 100 MPa 150 MPa 200 MPa Carbide powder: from Example 1 (not according to the invention) Shrinkage vertical (%) 19.64 18.76 17.94 Shrinkage in parallel (%) 27.23 26.24 24.93 K value 0.940 0.941 0.944 from Example 2 (not according to the invention) Shrinkage vertical (%) 20.56 20,04 19.64 Shrinkage in parallel (%) 21.5 21.1 20.59 K value 0.992 0.991 0.992 from Example 4 (according to the invention) Shrinkage vertical (%) 18.3 17.9 17.31 Shrinkage in parallel (%) 19.1 18.6 18,32 K value 0.993 0.994 0.992 from Example 5 (according to the invention) Shrinkage vertical (%) 20 19.21 18.8 Shrinkage in parallel (%) 20,23 19.81 19.46 K value 0.998 0.995 0.994

The results of Examples 9 to 12 illustrate the essence of the invention particularly clearly. The two embodiments of the invention show in comparison to the use of elemental powders a significantly lower shrinkage at the same time higher K value. The fully pre-alloyed powder causes a much smaller K value at high shrinkages, which is even below the K value for 20% cobalt cemented carbides. The K values which were obtained according to the invention and with elemental powders are above the value of 0.988 EP 0 937 781 B1 and it is therefore believed that these three cemented carbide mixtures are suitable for the production of sintered hard metal parts without post-processing. The two embodiments of the invention provide in Compared to the use of pure element powders additionally the advantage of an overall lower shrinkage, which additionally facilitates the production of final contour sintering and the advantages of pre-alloyed powders in the sintering.

If a conclusion is drawn from the results of the examples, it becomes clear first of all that, surprisingly, the paraffin wax commonly used as a lubricant in the hard metal industry improves the green density and the shrinkage, but does not increase the K value. This is explained by the fact that the lubricant facilitates the rotation or displacement of particles occurring during pressing against each other, but of course not the equally necessary deformation of metallic binder particles.

The examples also show that the alloy state of the binder is the largest major factor influencing shrinkage and K value. This is even more true, the higher the binder content. In the case of 6% binder, the influence decreases significantly, which confirms the assumption that the role of the binder is crucial. Thus, the deformability of the binder particles would be crucial.

It also becomes clear that phase transformations or precipitates, presumably caused by mechanical activation of precipitation processes or phase transformations of pre-alloyed powders in the mixed grinding with tungsten carbide, lead to an aggravation of compaction during pressing, by deteriorating the deformability. As the proportion of cubic-body-centered phase increases, it can be assumed that a mechanically activated precipitation hardening occurs. In addition, it is known that cubic body-centered metal alloys are less deformable than face-centered cubic because they have less crystallographic slip planes. The green density increases disproportionately with the stable at room temperature fraction of fcc phase. This is in FIG. 5 shown.

Example 13

1. a) unter Verwendung von reinem Eisen und Nickelpulver (nicht erfindungsgemäß, Anteil an bei Raumtemperatur stabiler fcc Phase 15%, da nur Nickel bei Raumtemperatur stabil fcc ist)
2. b) unter Verwendung eines vollständig vorlegierten Legierungspulvers (nicht erfindungsgemäß), mit praktisch vollständiger bcc-Phase
3. c) unter Verwendung von vorlegiertem FeNi 50/50 und Eisenpulver (erfindungsgemäß). Der Anteil an bei Raumtemperatur stabiler Phase wird hier wie folgt abgeschätzt: nach der Hebelregel kann man für FeNi 50/50 aus Figur 4 abschätzen, dass das Verhältnis an bei Raumtemperatur stabiler fcc-Phase zur bcc-Phase 2,5 : 1 betragen muss, daraus errechnet sich ein Anteil von 71,4%. Da andererseits 30% FeNi 50/50-Pulver in der Bindemetallformulierung enthalten sind, errechnet sich der bei Raumtemperatur stabile Anteil an fcc-Phase zu 0,3 x 71,4% = 21,4%.

Analogous to the previous examples, three different binder metal powders of the same gross composition (Fe 85 wt.%, Ni 15 wt.%) Were used together with a tungsten carbide powder (WC) having an FSSS value of 0.6 .mu.m for the production of three hard metal powders 90% by weight of tungsten carbide used without further organic or inorganic additives:

1. a) using pure iron and nickel powder (not according to the invention, proportion of room-temperature-stable fcc phase 15%, since only nickel is stable at room temperature fcc)
2. b) using a fully pre-alloyed alloy powder (not according to the invention), with practically complete bcc phase
3. c) using prealloyed FeNi 50/50 and iron powder (according to the invention). The proportion of stable at room temperature phase is estimated here as follows: according to the rule of leverage can be for FeNi 50/50 off FIG. 4 estimate that the ratio of room-temperature-stable fcc phase to bcc phase must be 2.5: 1, resulting in a ratio of 71.4%. On the other hand, since 30% FeNi 50/50 powder is contained in the binder metal formulation, the fcc phase stable portion at room temperature is calculated to be 0.3 × 71.4% = 21.4%.

The further procedure was as in the previous examples, however, the sintering was carried out at 1420 ° C for 45 minutes in vacuo. The resulting hard metal powders were used without addition of wax.

FIG. 7 shows the results obtained for the dependence of the shrinkage on the pressing pressure, the alloy state of the binding metal powder and in the direction perpendicular and parallel to the pressing direction. In the case of the use of elemental powders results in a virtually complete isotropy, the lines are practically superimposed. In the case of fully prealloyed binder powder, the expected, very high anisotropy of shrinkage results, in the direction parallel to the pressing direction a much higher shrinkage is found. In the case c) according to the invention ("FeNi 50/50 + Fe"), a very significant reduction in the shrinkage compared to a) results, with an anisotropy which is acceptable for industrial production (K value of 0.9937 at 150 MPa).

Claims (17)

1. Metallic powder mixture comprising a) at least one prealloyed powder selected from the group consisting of iron/nickel, iron/cobalt, iron/nickel/cobalt and nickel/cobalt; b) at least one element powder selected from the group consisting of iron, nickel and cobalt or a prealloyed powder selected from the group consisting of iron/nickel, iron/cobalt, iron/nickel/cobalt and nickel/cobalt which is different from component a).
2. Metallic powder mixture according to Claim 1, wherein the overall composition of the components a) and b) together contains not more than 90% by weight of cobalt and not more than 70% by weight of nickel and the iron content satisfies the inequality $$\mathit{Fe}\ge 100\%-\frac{\%\mathit{Co}•90\%}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}-\frac{\%\mathit{Ni}•70\%}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}\mathrm{.}$$

   
3. Metallic powder mixture according to one or more of Claims 1 to 2 containing organic and/or inorganic additives.
4. Metallic powder mixture according to one or more of Claims 1 to 3 containing a component c) which is a hard material.
5. Metallic powder mixture according to one or more of Claims 1 to 4 which is a metallic binder mixture.
6. Use of a metallic powder mixture according to one or more of Claims 1 to 5 for producing metallic binders for hard metals.
7. Process for producing a hard metal mixture using a) at least one prealloyed powder selected from the group consisting of iron/nickel, iron/cobalt, iron/nickel/cobalt and nickel/cobalt; b) at least one element powder selected from the group consisting of iron, nickel and cobalt or a prealloyed powder selected from the group consisting of iron/nickel, iron/cobalt, iron/nickel/cobalt and nickel/cobalt which is different from component a); c) hard material powder, wherein the overall composition of the components a) and b) together contains not more than 90% by weight of cobalt and not more than 70% by weight of nickel and the iron content satisfies the inequality $$\mathit{Fe}\ge 100\%-\frac{\%\mathit{Co}•90\%}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}-\frac{\%\mathit{Ni}•70\%}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}\mathrm{.}$$

   
8. Process for producing a hard metal mixture according to Claim 7, wherein the overall composition of the binder comprises not more than 70% by weight of Ni and at least 10% by weight of Fe, wherein the iron content satisfies the inequality $$\mathit{Fe}\ge 100\%-\frac{\%\mathit{Co}•90\%}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}-\frac{\%\mathit{Ni}•70\%}{\left(\%\mathit{Co}+\%\mathit{Ni}\right)}$$

   

   
   and at least two binder powders a) and b) are used, the first binder powder is lower in iron than the overall composition of the binder and the second binder powder is richer in iron than the overall composition of the binder and at least one binder powder is prealloyed from at least two elements selected from the group consisting of iron, nickel and cobalt.
9. Process according to either of Claims 7 or 8, wherein the nickel content of the components together makes up 60% by weight or less of the powder mixture.
10. Process according to any of Claims 7 to 9, wherein the iron content of the two components together makes up 5% by weight or more of the powder mixture.
11. Process according to one or more of the preceding process claims, wherein the nickel content of the two components together makes up 45% by weight or less of the powder mixture when the cobalt content is less than 5% by weight.
12. Process according to one or more of the preceding process claims, wherein component a) is a prealloyed metal powder and component b) is an element powder and the contents of iron, nickel and cobalt add up to the desired total composition of the binder powder.
13. Process according to one or more of the preceding process claims, wherein a) is a prealloyed powder consisting of iron/nickel and b) is an iron powder.
14. Process according to one or more of the preceding process claims, wherein component a) is a prealloyed powder FeNi 50/50, FeCo 50/50 or FeCoNi 40/20/40.
15. Hard metal mixture obtainable according to one or more of the preceding process claims.
16. Use of a hard metal mixture according to Claim 15 for producing shaped articles, preferably by sintering.
17. Process for producing shaped articles from a hard metal mixture as defined in one or more of Claims 7-14, which comprises the following steps:

    - provision of a first prealloyed metal powder,

    - provision of an element powder or a second prealloyed metal powder,

    - mix-milling of the two components with a hard material powder to give a hard metal mixture

    - pressing and sintering of the hard metal mixture, giving a shaped article composed of a hard metal.

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