NL1016112C2 - Gradually hard metal body such as punching tools and method for producing them. - Google Patents

Description

Title: Body of graduated hard metal such as punching tools and method for producing them.

The invention relates to a body of graduated hard metal such as punching tools and a method for producing them. According to the invention, the use of per se known static and dynamic compaction techniques for the manufacture of new hard metal bodies such as tools with a hard first end and a tough second end, for example cutting and forming tools such as punching tools, plays an essential role. Before discussing the invention in detail, an explanation first follows regarding the terms used in this description and claims or the techniques used according to the present invention.

Tungsten carbide bodies 15

Hard metal bodies are understood to mean products that contain a hard compound such as a metal carbide and a metallic binder and that have been subjected to sintering or hot isostatic pressing. Their relatively large amount of carbide makes the hard metal rigid, hard and durable. The binder gives the assembly the necessary toughness and strength.

In the present description and claims, the hard compound is indicated by A and the metallic binder by B.

The hard compounds A are, for example, carbides, borides, nitrides and diamonds.

The hard compounds A have the following properties: high hardness, low toughness, high compressive strength, low tensile strength and a high melting point. In addition, they are not or very little ferromagnetic. Tungsten carbide is the most commonly used hard metallic compound in hard metal products.

The tough compounds B are, for example, metals such as Co, Cr, Ni, Fe (stainless steel) and alloys thereof.

Much information can be found in the general technical literature and in the patent literature on hard metal products, the methods for their manufacture including sintering and hot isostatic pressing. For a general overview of mifii 12 I 1 2 "cemented carbides" reference can be made to the ASM Metals Handbook, 9th edition, Vol. 16, "Machining", pp. 71-83, published in 1989. The content of this publication is to be considered here.

For the production, properties and testing methods of tungsten carbide-based carbide products, reference can also be made to the book Cemented Tungsten Carbides, Production, Properties, and Testing, 1998, by Gopal S. Upad-hyaya, published by Noyes Publications, USA. Special reference is made to the information about sintering and hot isostatic pressing (HIP) including sinter HIP. The relevant text of pages 110-130 of this publication of 10 Upadhyaya should be considered as inserted here.

Static and dynamic compaction techniques

Static and dynamic compaction techniques are known per se for the compaction of powdered materials.

Static compaction techniques that can be used in the context of the present invention are therefore generally known and do not appear to require further explanation. For an overview of static compaction techniques, which can play a role in the context of the present invention, reference can be made to J.S. Already Principles of ceramic processing, 2 ed., J. Wiley & Sons, New York (1995).

For dynamic compaction techniques, which can play a role in the context of the present invention, reference can be made to the publication "The Dynamic Compaction of Powdered Materials" by S. Clyens and W. Johnson in Materials Science and Engineering, 30 ( 1977) 121-139. In this publication four main areas are indicated, in which powder compaction processes are used: the powder metallurgy, fuel, ceramic and pharmaceutical industries. With regard to these industries, the following is stated: "Powder metallurgy fabrication techniques have been developed for three principal reasons. 30 Firstly, because for some components and materials established methods of forming are not suitable, eg, refractory metals have long been fabricated by powder metallurgy because of the difficulties encountered in melting and casting Secondly, in some cases powder metallurgy processes are more economical; many iron-base alloys are factories 1n1R1 3 cated from powders into finished components because the savings in materials and machining make it worthwhile. Thirdly, the greater control of both grain size and component distribution afforded by the processes often results in a more homogeneous metallurgical structure.

5 For many years the ceramic industry has employed compaction techniques to form dry or slightly moist ceramic powders into a wide range of products. The dry pressing technique has two main advantages; unlike the law-forming methods, dry pressing may be fully automated with high rates of production and one operator may take charge or several presses. Also, if the powder is pressed dry, the expense of filter 10 pressing and drying is avoided, so that dimensional tolerances of better than 1% in the fired product may be achieved.

The pharmaceutical industry employs powder compaction processes to form medicinal powders into tablets. Tabletting has been used mainly as a convenient and simple form of dosage and there are now few countries in which tablets are not manu-15 invoiced.

In the fuel industries many processes lead to the production of powdered fuels which cannot be conveniently or re-used. Such powders often have been disposed of or as waste representing an economic loss to industry and, in some instances, a major cause of pollution. Compaction processes have been used to form these powders 20 into briquettes which may be handled easily and used again. "

It is noted that the above information does not relate to relatively strong compaction. The compacting technique used in the ceramic industry concerns, for example, the pre-pressing of ceramic powders before being sintered, so that the "dimensional tolerance is better than 1%". This is in fact a compaction that is used as a possible pre-compaction (not compulsory) in the method according to the invention, as will be further described below.

The publication of Clyens et al., After the introduction of the static compaction methods conventional in 1977, pays attention to the dynamic compaction methods. Regarding the difference with the previously used compaction methods, it is said: "These methods differ from the more conventional consolidation techniques in respect of the compacting pressure and the speed or rate of compaction used. There is now some evidence to suggest that increasing the rate or compaction results in more uniform density distribution, improved green strength, and in the case of those com- paction 10161 12 é 1 4 paction, lower compact ejection forces. " In the sense that runs from biz. 121 to biz. 122 the following is said: "In the powder metallurgy and ceramic industries efforts have concentrated mainly upon developing methods capable of producing high-density components or complex shape or large, semi-finished articles, whereas, in the pharma-5 ceutical and fuel industry , interest has concentrated on increasing production rates. "

The compaction, which is mentioned in the literature mentioned above, naturally entails a reduction in porosity. This means that the pore volume is reduced and therefore the density increases. In the present context - also that of the invention discussed below - the density is not shown as an absolute value (in g / cm 3), but as a relative density (RD) relative to the density of the pore-free solid, or the Theoretical Maximum Density (TMD) of the substance. It is clear that with the known compaction discussed above in the field of hard metal production, a relatively small compaction takes place, whereby the RD of the relevant materials is never increased to a value that is above approximately 65% TMD, which will immediately be clear to the experts. to be.

For the dynamic compaction techniques and the underlying mechanisms, reference is made to the aforementioned publication by Clyens et al., The contents of which are incorporated herein by reference.

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The problem underlying the present invention

As indicated in the first paragraph of this description, the invention relates to solid carbide bodies and their production. The problem underlying the present invention is elucidated on the basis of punching tools, but similar problems are encountered with all kinds of tools made from hard metal and which (must) have different mechanical properties at different locations.

Punching tools must be hard (wear-resistant) on the punching side and impact-resistant (tough) on the back-impact side. So far these properties cannot be combined within one material, so that punching tools are generally made up of two materials. The rebound side is generally made of high-speed steel (a wear-resistant steel type) while the die-cutting side consists of hard metal (tungsten carbide with cobalt, WC / Co). These 1016112 5 materials are mechanically connected to each other. As a result, there is play in the connection during use of the tool, which leads to a reduction in product quality. This limits the punching time of the punching tool (such as punching stamps), as a result of which this tool must be replaced at an early stage, which increases costs and whereby the production process must be frequently interrupted. That is why it would be desirable to have punching tools that are entirely made of hard metal, but in which, due to the gradual course of the composition, there is nevertheless an impact-resistant (tough) edge and a wear-resistant (hard) punching edge. With regard to this problem, reference is made, for example, to U.S. Pat. Nos. 4,820,482 and 5,543,235.

For example, in U.S. Pat. No. 4,820,482 it is described in the introduction that diffusion of the binder phase takes place during the sintering of hard metal bodies, which leads to sintered bodies with a substantially uniform binder phase. The technique is also discussed in which starting materials with different particle sizes are used or in which the hard metal body is subdivided into zones with different particle sizes. These techniques also fail to produce bodies with impact-resistant locations on the one hand and wear-resistant locations on the other. In this patent a solution is given for this problem by using "carburizing" of the sintered body to such an extent that thereby completely removing the so-called eta phase. This creates a body with two zones: a core with a relatively high binder content and a surface zone with a relatively low binder content (and possibly small amounts of free graphite). It is true that with this technique a body can be obtained whose core has other properties than the surface, but bodies with an impact-resistant side and a hard punching side, in which a gradual transition of the binder content is present, cannot be manufactured according to this technique .

More recently, (1996), the aforementioned U.S. Patent No. 5,543,235 discloses "multiple grade" hard metal products and a process for their manufacture. Also in the introduction of this patent specification 30 (column 1, lines 56-64) mention is made of "cemented carbide articles are invariably fabricated having a substantially uniform composition and microstructure .... and substantially uniform properties throughout the volume of the article. Many such substantially homogeneous compositions exist in the prior art. " According to this American patent specification, the starting materials for the hard metal body are introduced into a mold which can be subdivided into different compartments, whereby the partitions can be removed from those compartments. The compartments are filled with different mixtures, after which the partitions are removed and the powder is compressed into a "single compact" with the desired shape. After this, sintering.

The problem is also addressed in the recent (1998) aforementioned book Cemented Tungsten Carbides by G. Upadhyaya, in particular biz. 365/366, where "Functionally Graded Cemented Carbides" states the following: "Com-10 position gradient cemented carbide tools are expected to offer a number of advantages for specific engineering applications. For example, a tough bulk and a hard surface would be interesting in the case of cutting picks used in the mining industry, which are subject to shocks.

The first attempt to study a model or such a type or structure was done'by Cooper 15 et al. In order to explain the migration of cobalt from the coarse grained to fine grained layers or a hard metal composite. The driving force for migration was the higher capillary forces existing in the fine grained layer during liquid phase sintering.

Coling et al. Investigated multilayer graded structures in WC-Co cemented carbides with cobalt content ranging from 10-30 wt% from one side of the structure to the other 20, prepared by solid state or liquid phase sintering routes. In the case of solid state sintering, the graded structure remained after sintering, as there was no risk of homogenization during such sintering. In the case of liquid phase sintering, the sintering time had to be much shorter because densification occurred much faster with the liquid phase. This required precise control or sintering time, which had to be as short as 25 possible in order to avoid homogenization of the structure. In the former case, to obtain dense material, post-sintering HIP treatment became necessary. "

According to the invention, the problem of undesired mass transport, leading to homogenization, is solved by providing a method which makes it possible to produce bodies which consist almost entirely of hard metal with a minor amount of binder in which the composition of A and B has a gradual course .

ln 1K11 o.

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The invention therefore relates to a method for producing a hard metal body consisting of a hard compound A and a binder B, wherein selected amounts of powdered A and B or an object, whether or not pre-compacted, that A and B in selected amounts contains and places the A and B containing material in one or more steps to increase the relative density (RD) to a value that is above 70% of the Theoretical Maximum Density (TMD) with formation of a carbide body, in which on the one hand at least one zone (Za) with a relatively large amount of B and on the other hand at least one zone (Zb) with a relatively small amount of B are present and the amount of B from at least one zone Za gradually towards minus 15 a zone Zb takes off, after which this body may be subjected to sintering, hot isostatic pressing (HIP) or sinter-HIP.

When "compaction" is used in the present description and claims, this does not mean the compaction (consolidation) that occurs during a temperature treatment such as sintering, HIP or sinter-HIP.

The method according to the invention makes it possible to immobilize B in a desired and controlled manner with respect to A. With immobilization of B with respect to A it is meant that no complete or substantially no mass transport of B occurs during sintering or hot isostatic pressing ( HIP). The invention is based on the insight that the desired immobilisation of B, i.e. the incomplete occurrence of mass transport during sintering or HIP, can be achieved by adjusting the pore volume of the powdered starting material A and B to a suitable value. Reduce. This reduction in the pore volume goes beyond the prior compaction known from the prior art, which precedes sintering or HIP of precursors. As already stated above, the pre-compaction according to the state of the art is in the order of a maximum of 65% TMD.

1016112 8 *

In order to achieve the desired immobilization of B during sintering or HIP, it is preferable to effect a compaction of the starting material above 80% TMD, in particular above 90% TMD.

The stronger the compaction, the smaller the transport of B during sintering or HIP 5. The transport or immobilization of binder B can be controlled via the T, t effect. A large compaction (even up to 100% TMD) ensures a very substantial or even complete immobilisation of B against A according to the invention if the compacted product is subjected to sintering or HIP. Thus, a too long sintering time and / or a too high sintering temperature will nevertheless (ultimately) lead to a hard metal with a homogeneous composition. On the other hand, a too short sintering time and / or too low temperature will cause insufficient diffusion of B, as a result of which the (too) steep B gradient will continue to exist in the end product.

The problem with conventional hard metal production is that the T, t combination required for removing the porosity (a prerequisite for strong products) already brings about homogenization of the binder B. The compaction according to the invention makes it possible to sinter gradually hard metal before homogenization occurs to a large or complete extent.

No particular requirements are imposed on the grain sizes of A and B in the method according to the invention. Reference can be made here to the values for the grain sizes as used in the conventional hard metal production.

The compaction according to the invention can be carried out in one go or in various steps. It is often expedient to subject the powder of A and B, which is introduced into a container in a controlled manner, to a pre-compaction, so that the subsequent final compaction step or steps are more effective. The invention according to a preferred embodiment therefore relates to a method as described above, wherein the compaction is carried out in two steps: a) a first compaction (pre-compaction) for increasing the RD to a value of a maximum of 70% TMD; b) a second compaction wherein the RD of the pre-compacted powder or article of step a) is further increased to a value above 70% TMD, preferably above 80% TMD, in particular to above 90% TMD.

The method according to the invention makes it possible for mechanical bonds, which are often used in tools such as punching tools, to be eliminated because, according to the invention, tools can be manufactured entirely from hard metal (with a varying percentage of binder). Because the composition of A and B is gradual, there is nevertheless an impact-resistant (tough) side and a wear-resistant (hard) punching side. Therefore, the invention also relates to a method as described above, wherein different mixtures of A and B are introduced into two or more zones of the container, wherein the weight ratio A: B in the two or more zones have different values.

For the manufacture of punching tools, for example, a method is used according to the invention, wherein the holder has an elongated shape and the holder is filled with different mixtures of A and B such that the amount of binder at one end of the shape H is smaller than at the other end of the form T. Possible embodiments are explained in more detail later in this description with reference to drawings.

Thus, in the method according to the invention, use will generally be made of varying amounts of A and B, wherein the amount of B at the hard end is of course small and the amount of B at the tough end is relatively high. It is preferred here that the amount of B at the end H of the mold is at least 1% by weight, and the amount of B at the end T of the mold is at most 50% by weight, the amount being based on the weight of the total Mixture. The invention makes it possible to gradually increase the amount of weight B from end H to end T. If "end H" and "end T" are used in this description, zone Zb and zone Za are also meant. By choosing the "geometry" of the starting materials (arrangement), objects with all kinds of conceivable zones of hard and tough areas can be set, also "inside" in the objects.

Suitable starting materials A and B are the known hard compounds on the one hand and the known metallic binders on the other. Reference is made to the literature mentioned in the introduction to this description. Preferably A is selected from the group consisting of diamonds or carbides such as SiC, WC, TiC, TaC, NbC, ZrC, HfC, Cr3 C2, MO2 C, nitrides such as TiN, HfN and BN and borides such as TiB2 and ZrB2. in particular tungsten carbide, and B is selected from the group consisting of the metals Co, Cr, Ni, Fe (e.g. stainless steel) and alloys thereof, in particular cobalt.

1016Π2 10

The compaction according to the invention is preferably carried out at a temperature at which no mass transport of one component into the other component occurs, i.e. that both diffusion of B and A is avoided. This means that no special measures have to be taken regarding the temperature. It is preferable to work at ambient temperature. This contributes to a simple implementation of the method according to the invention.

It will be appreciated that the pore volume reduction of powdered A and B forms the core of the present invention. This pore volume reduction can be achieved by methods known per se. In the method according to the invention, static or dynamic compaction techniques are generally used for compaction, preferably (iso) dynamic compaction techniques such as pneumomechanical uniaxial compaction, ballistic compaction, explosive compaction including shock (wave) compaction ( "shock compaction") and magnetic compaction. For the compaction techniques, reference is made to the information and literature given in the introduction to this description.

The invention also relates to hard metal bodies obtainable according to the above-mentioned methods according to the invention, as well as hard metal bodies comprising a hard compound A and a binder B wherein the weight ratio A: B changes over a cross-section of the body in order to impart various mechanical properties such as toughness in at least one zone Za or at least one end (T) and hardness in at least one zone Zb or at least one other end (H) to that body, the change in the ratio A: B is gradual.

The invention furthermore relates to the use of dynamic compaction techniques as mentioned in claim 10 for the manufacture of one-piece hard metal bodies with at least one hard zone (Zb) or hard end (H) and at least one tough zone (Za ) or tough end (T). It is not known from the prior art to use compaction techniques as mentioned above for the strong pore volume reduction according to the invention (i.e. up to more than 70% TMD) of powdered mixtures or materials that serve as starting material for hard metal bodies.

An important field of application of bodies according to the invention is punching tools.

1016112 I

11

Examples of gradual embodiments according to the invention are shown in Figures 1-4.

In the figures, the concentration differences of components A and B are represented by shades of gray. Here, white means a relatively low amount of hard compound (relatively much binder) and black means a relatively large amount of hard compound (relatively little binder).

In figure 1 it can be seen that due to the very steep concentration gradient in the pressing surface after pre-compaction (middle between T and H) HIP still has (some) transport of B, which smoothes the gradient in concentration of B and spontaneously smoothes a gradually hard metal is being formed.

In figures 2-4, where each time a different arrangement of A and B is assumed, it appears that a slight gradient produces too little driving force for diffusion of B, whereby the gradual composition is retained during HIP.

It is thus clear from the above examples that gradual patterns of various types can be set.

Examples

According to these examples, hard metal is made from a large fraction of tungsten carbide and a small fraction of cobalt. The starting materials are Grade 8 and WC / Co 70/30, known to those skilled in the art, with 8 and 30 m% Co respectively. To make gradually hard metal, these starting materials are mixed together in different proportions, as shown in the table below; see also the "stacking method" in Fig. 5 ..

Fraction Fraction Co-fraction Hardness final TMD mixture

Grade 8 WC / Co 70/30 in product mixture [GPa] [g / cm3] ÏÖÖ Ö 8 Ï25Ö 14.74 75 25 333312124/8 50 50 19 ÏÖIÖ 13 ^ 67 25 75 24/5 900 Ï3J9 Ö ÏÖÖ 3Ö 8IÖ 12/74 25 1016112 12 *

The compositions (powder compacts) indicated in the table above are pre-compacted to approximately 50% TMD by cold uniaxial pressing. This pre-pressing is carried out with the aid of a stainless steel tube with an inner diameter of 20 mm and a wall thickness of 1.5 mm, which is closed unilaterally with a stainless steel stopper (see also figure 5, which is further discussed below) . The lower half of the tube is then each time filled with a hard metal powder in the WC / Co mass ratio as indicated in the table above. The upper half of the tube is filled with hard metal powder with a Co-fraction as indicated in the table above. The powder is always uni-axially pressed after applying a small amount of powder with a pressure of approximately 100 MPa. After this filling and pre-compaction process, the pipe is sealed at the top with a stainless steel stopper.

An alternative version of the pre-compacting of the powder is to use a Cold Isostatic Press (CIP). The powder (or the various powder mixtures) is herein poured into a cylindrical rubber container, after which the container is closed with a rubber stopper, too. The powder-containing container is placed in the liquid-filled CIP, after which the CIP is hermetically sealed. The liquid is pressurized (3000 bar) via a pump, the powder in the rubber container being pre-compacted isostatically. With this method an initial density of the powder of 64% TMD has been achieved. After removal of the cylindrical powder compact from the rubber container, it is wrapped with a metal foil (copper foil with a thickness of 0.1 mm), so that the diameter of the compact can be adjusted to the inside diameter of a slightly larger metal tube. The tube is then closed again at both ends with metal plugs.

Dynamic compaction

For dynamic (explosive) compacting of the powder, the tube is glued centered in a PVC cylinder with a length of 175 mm, an inner diameter of 76 mm and a wall thickness of 4 mm. The intermediate space remaining is filled with an explosive powder on an ammonium nitrate basis. The detonation speed of the explosive powder is 3.6 km / s. When detonating the explosive, the metal tube is (mainly) reduced in diameter, thereby compacting the hard metal powder to a relative density of approximately 90% TMD. A mifii 1? Fig. 13 schematically shows such an arrangement for explosive compacting is shown in Fig. 5, in which the reference numerals have the following meaning: 1. = detonator; 2. = powder explosive; 3. = PVC pipe; 4. = metal tube; 5. = hard metal powder; 6. = metal stopper; 7. = substrate.

In 1 «1 io

Claims (14)

Method for producing a hard metal body consisting of a hard compound A and a binder B, wherein selected amounts of powdered A and B or an object, whether or not pre-compacted, containing A and B in selected amounts, in a container and subject the A and B containing material to compaction in one or more steps to increase the relative density (RD) to a value that is above 70% of the Theoretical Maximum Density (TMD) to form a hard metal body, in which on the one hand at least one zone (Za) with a relatively large amount of B and on the other hand at least one zone (Zb) with a relatively small amount B are present and the amount B from at least one zone Za gradually to at least one zone Zb, after which this body may be subjected to sintering, hot isostatic pressing (HIP) or sinter-HIP. Method according to claim 1, wherein the material containing A and B is reduced to an RD value above 80% TMD, preferably above 90% TMD. Method according to claim 1 or 2, wherein the compaction is carried out in two steps: a) a first compaction (pre-compaction) to increase the RD to a value of a maximum of 70% TMD; b) a second compaction wherein the RD of the pre-compacted powder or article of step a) is further increased to a value above 70% TMD, preferably above 80% TMD, in particular to above 90% TMD. 4. Method as claimed in one or more of the foregoing claims, wherein different mixtures of A and B are introduced into two or more zones of the container, wherein the weight ratio A: B in the two or more zones have different values. Method according to one or more of the preceding claims, wherein the container has an elongated shape and the container is filled with different mixtures 1016112 tt of A and B such that the amount of binder at one end of the shape (H) is less than at the other end of the mold (T). Method according to one or more of the preceding claims, wherein the amount of B in Zone Zb is at least 1% by weight, and the amount of B in zone Za is a maximum of 50% by weight, the amount being based on the weight of the total mixture. Method according to one of the preceding claims, in which the amount by weight B gradually increases from zone Zb to zone Za, whether or not gradually. 8. Method according to one or more of the preceding claims, wherein A is selected from the group consisting of diamond or carbides such as SiC, WC, TiC, TaC, NbC, ZrC, HfC, Cr 3 C 2, M02 C, nitrides such as TiN, HfN and BN and borides such as T1B2 and ZrB2, preferably tungsten carbide, and wherein B is selected from the group consisting of the metals Co, Cr, Ni, Fe (e.g. stainless steel) and alloys thereof, preferably cobalt. 9. Method according to one or more of the preceding claims, wherein the densification is carried out at a temperature at which no or substantially no mass transport of B or A occurs, preferably ambient temperature. 10. Method as claimed in one or more of the foregoing claims, wherein static or (iso) dynamic compaction techniques are used for compaction, preferably dynamic compaction techniques such as pneumomechanical uniaxial compaction; ballistic compaction; explosive compaction including shock (wave) compaction ("shock compaction") and magnetic compaction. Body obtainable according to the method of one or more of the preceding claims. 12. Tungsten carbide body comprising a hard compound A and a binder B wherein the weight ratio A: B changes over a cross section of the body in order to have different mechanical properties such as toughness in at least one zone Za or at least one end (T) and, on the other hand, impart hardness in at least one zone Zb or at least one other end (H) to that body, wherein the change in the ratio A: B is gradual. 1016112 »* Tungsten carbide body according to claim 11 or 12, comprising punching tool. Use of dynamic compaction techniques as claimed in claim 10 for the manufacture of one-piece bodies with at least one hard zone (Zb) or hard end (H) and at least one tough zone (Za) or tough end (T). 1016112