EP2082072A2

EP2082072A2 - Prealloyed metal powder, process for obtaining it, and cutting tools produced with it

Info

Publication number: EP2082072A2
Application number: EP07848318A
Authority: EP
Inventors: Mario Molteni; Sophie Marcon; Hervé SENILLOU; Bartolomeo Maretto
Original assignee: Eurotungstene Poudres SA
Current assignee: Eurotungstene Poudres SA
Priority date: 2006-10-04
Filing date: 2007-10-04
Publication date: 2009-07-29
Anticipated expiration: 2027-10-04
Also published as: FR2906739B1; PT2082072T; EP2082072B1; CN101541990B; HUE036676T2; DK2082072T3; WO2008040885A2; WO2008040885A3; KR20090060330A; CN101541990A; FR2906739A1; PL2082072T3; ES2663267T3

Abstract

Prealloyed metal powder, especially for the manufacture of cutting tools by sintering, characterized in that its composition, in percentages by weight, is: 48 - 52% Fe; 14 - 19% Co; 32 - 37% Cu; ≤ 1 % O, the balance being impurities resulting from its manufacture. Process for obtaining this powder and diamond saws and cutting wires produced with this powder.

Description

Pre-metallized metal powder, its production process, and cutting tools made with it.

The invention relates to the field of pre-alloyed metal powders, from which diamond cutting tools such as saw segments and beads for the production of yarns for cutting hard materials such as granite are produced.

The metal powders used to make diamond beads are usually made from granules containing about 20% tungsten carbide and about 80% cobalt. These granules are mixed with diamonds and compressed in the form of rings, and the green parts are sintered according to two possibilities.

In the first case, graphite molds are filled with the green parts, each equipped with a steel sheath, and pressure sintering is carried out in conventional hot presses. But because of the particular shape of the diamond beads:

- Graphite molds have a complex geometry and are expensive to buy, especially since it is necessary to renew them periodically;

the filling of the molds with the green parts and the rings being delicate, it must be done manually, which entails significant labor costs;

- To obtain sintered diamond beads homogeneously, the number of sintered beads in each mold is limited to a few dozen parts, which implies low productivity. In a second case, a natural sintering, also called "free sintering", (without mold) of the raw parts with their steel sheaths is carried out in a static or scrolling oven. But after this sintering, the cobalt and tungsten carbide beads are not sufficiently densified. A second heat treatment is essential, which must be carried out in a furnace operating at a high pressure of between 1500 and 2000 bar, to achieve hot isostatic pressing of the beads. This oven is expensive to buy and maintain. These processes are therefore in any case very expensive, both in terms of raw materials and production process.

The object of the invention is above all to provide pre-alloyed metal powders whose cost would be relatively moderate, and which would be compatible with processes for manufacturing diamond beads substantially less expensive than existing processes, in particular because natural sintering , realized without mold, would nevertheless make it possible to obtain sufficiently powerful products, in particular for the cut of the granite. Also, these powders should be compatible with the manufacture of other types of cutting tools for less demanding applications.

To this end, the subject of the invention is a pre-alloyed metal powder, in particular for the manufacture of sintering cutting tools, characterized in that its composition in weight percentages is:

Fe = 48 - 52% * Co = 14 - 19%

* Cu = 32 - 37% * O ≤ 1.2% the remainder being impurities resulting from its manufacture. Preferably, the Fisher diameter of its particles is 1 to 3 μm. It is preferably constituted by a mixture of such a powder and of at least one sintering aid additive in a proportion of 80 to 90% by weight of powder and 10 to 20% by weight of additive.

The sintering aid additive is preferably a phosphide of iron, nickel, copper or cobalt, or a mixture of at least two of these phosphides, or a mixed phosphide of at least two of these metals.

The powder is preferably obtained by mixing a first powder and a second powder, and a possible sintering additive, said first and second powders having the respective characteristics:

- for the first powder * Fe = 27 -32%

* Co = 24 - 28%

^* Cu = 42 - 47%

* O <1% the rest being impurities resulting from its manufacture - for the second powder

* Fe = 75 - 80%

* Co <5% * Cu = 17 - 22%

* O <1% the rest being impurities resulting from its manufacture.

Preferably, the Fisher diameter of the particles of the first powder is 0.8 to 1.5 μm, the Fisher diameter of the particles of the second powder is 3.0 to 4.0 μm, and the Fisher diameter of the powder. obtained after mixing is 1 to 3 μm.

The subject of the invention is also a process for manufacturing a diamond cutting tool, comprising in particular a step of mixing a pre-alloyed metal powder and diamonds, a cold pressing step of the mixture and a sintering step to said mixture. tablet, characterized in that said metal powder is of the preceding type.

Sintering is preferably natural sintering. Said tool can be a cutting segment for diamond saw. Said tool can be a diamond bead for cutting wire. Said powder may be of the aforementioned type.

The invention also relates to a diamond saw of the type comprising cutting segments fixed on the periphery of a metal disk, characterized in that said segments were obtained by the above method. The invention also relates to a cutting wire of the type comprising diamond beads threaded on a cable, characterized in that said beads were obtained by the above method.

As will be understood, the invention is based on the use of a prealloyed powder of precise composition, based on iron, cobalt and copper. It turns out that this powder, which does not implement very expensive elements in high proportions, allows for diamond cutting tools (saws and beads) high performance by simple natural sintering, so by an economical process and can be run with high productivity. A process for obtaining the powder, making it possible to obtain sintered products of particularly high characteristics from said powder, is also proposed.

The invention will be better understood on reading the description which follows. The prealloyed powder according to the invention must in particular meet the following requirements.

The relative density of the raw parts obtained with it must be at least 60% for a maximum cold pressure of 700 MPa.

It should preferably be easily granular in the particle size fraction between 63 and 450 microns which is best suited for filling cold compression molds made of steel, intended for the manufacture of beads for diamond threads.

After free sintering at 850-1100 ^° C. in a scroll oven (for continuous production) or in a static oven (for batch production), the relative density of the part obtained must preferably be at least 97 %.

The powder must be able to be used to manufacture parts whose hardness after sintering would be at least 220 HB, so that they can be used for cutting the granite. It appears that these objectives, as well as those previously expressed, are achieved, according to the invention, using a prealloyed powder having the following characteristics.

Its composition is (in percentages by weight):

- Fe = 48 - 52% - Co = 14 - 19%

- Cu = 32 - 37%

- O <1, 2% the rest being impurities resulting from its manufacture.

The mean Fisher diameter of the particles (measured according to standard 150 10070 by determination of the envelope surface area from the measurement of the air permeability of a powder bed under steady-state conditions) is preferably from 1 to 3 μm.

Its typical theoretical density is preferably 8.4 g / cm ³ . The ratio between the iron and cobalt contents is deliberately adjusted so as to avoid forming a hard and weak α 'phase, which is formed when the mass ratio Fe / (Fe + Co) is between 30 and 70%. According to the invention, this ratio is between 72 and 78%, and the α 'phase is avoided. The amount of copper added is that which is sufficient to provide good sintering.

The oxygen content is maintained at a maximum of 1.2% to avoid the presence of oxides which would not be reduced entirely by hydrogen during natural sintering. Such unreduced oxides would reduce the sinterability of the green parts, cause heterogeneities in the structures of the sintered parts, increase the hardness, therefore the fragility of the parts and react with the diamonds by destroying them at least on the surface. This would reduce the cutting performance of the tools.

This powder can be obtained in particular in two different ways.

According to a first embodiment, a powder having the desired composition and morphology characteristics is prepared directly by the conventional hydrometallurgical route.

This hydrometallurgical route consists in first producing metal hydroxides by sodium hydroxide precipitation of a mixture of metal chlorides according to the reaction: x CuCl ₂ + y FeCl ₃ + z CoCl ₂ + (2 + t) NaOH -> Cu _x Fe _y Co ₂ (OH) ₂ + 2

NaCl + t NaOH, with x + y + z = 1, and t being the level of NaOH in excess of stoichiometry. x, y and z are in ratios corresponding to the atomic ratios which one wishes to find on the final powder between the respective contents in Cu, Fe, Co.

Solid-liquid separation is then carried out followed by washing the hydroxide cake with deionized water to remove NaCl. The cake is then passed through a dryer to obtain a co-precipitated hydroxide powder with a residual water content of a few%.

Then the hydroxide powder is reduced, in order to be transformed into a pre-alloyed metal powder. This reduction is preferably carried out in a scroll oven and under H ₂ according to: Cu _x Fe _y Co _z (OH) + H ₂ -> Cu _x + Fe _y + Co ₂ + H ₂ O.

After reduction, the pre-alloyed powder is ground under an inert gas in a mill, then sieved at 90 μm.

According to a second embodiment, the powder according to the invention is produced by mixing two powders of different compositions, also obtained separately by hydrometallurgy. Table 1 shows the compositions of the two powders to be used:

Table 1: characteristics of the powders I and II used.

Surprisingly, as will be seen, during sintering, better results are obtained from several points of view when the powder according to the invention is produced by mixing these two powders I and II, in such proportions that we obtain overall a powder having the specified characteristics, that when using a powder obtained directly by a hydrometallurgical process according to the first embodiment described.

In general, a mixture of the powders I and II in relative proportions of 60 - 40% by weight approximately makes it possible to manufacture the powder according to the invention.

After obtaining the powder according to the invention, it can be used directly or granulated by a conventional method that will now be described. These granules can then be used to make specific diamond tools, such as diamond threads and thin diamond segments.

The prealloyed powder to be granulated is mixed with an organic binder powder at 2 to 3% by weight of the amount of powder to be granulated and an organic solvent in a high shear granulator. After the granulation step, the solvent is removed by evaporation.

Finally, the granules are sieved continuously on vibrating screens comprising two superposed canvases, openings of different mesh (450 microns for the first, 63 microns for the second for example). The fraction of diameter between 63 μm and 450 μm is thus selected. The finer and coarser granules are recycled during the next granulation operation.

It is also advisable to add to the powder one or more additives to increase the hardness of the sintered parts. Conventional additives known for this purpose, such as tungsten carbide, have proved to be ineffective in the context of the invention because they decreased the densification during sintering, and thus the hardness of the parts, the opposite result of what was desired. It turns out that the tungsten carbide is insoluble in the powder according to the invention and therefore does not metallurgically bind to the metal matrix. On the other hand, it turns out that iron phosphide makes it possible to obtain remarkable results from this point of view; the phosphides of nickel, copper and cobalt are also interesting.

Natural sintering tests of powders according to the invention which have demonstrated the superiority of the powders obtained by a mixture of powders have been carried out.

I and II described above on the powders obtained directly by a single hydrometallurgical treatment. The powder obtained directly ("direct powder") was prepared by the hydrometallurgical process described above, that is to say by adding NaOH to a mixture of chlorides of Co and Fe, drying the hydroxide thus obtained in a dryer microniser, reduction at 66O ⁰ C and grinding in a nitrogen jet mill. Its composition was Fe = 48.8%; Co = 16.0%; Cu = 34.4%; O = 0.8%. Its Fisher diameter was 1.3 μm.

The powder obtained by mixing ("powder mixture") was in a blender previously put under CO ₂ , from 60% of powder I and 40% of powder II, these powders having been previously prepared separately by hydrometallurgy. The mixing operation lasted 50 minutes. The resulting powder had the composition: Fe = 49.1%; Co = 16.0%; Cu = 34.4%; O = 0.6%. Its Fisher diameter was 1.74 μm.

The "direct" and "mixing" powders were then compressed to 200 MPa in order to produce PS 21 pieces, whose raw density was calculated from their dimensions and their weight. The direct powder had a density equal to 58.0% of the theoretical density, the powder mixes a density equal to

55.2% of its theoretical density.

It is recalled that, conventionally, the PS21 parts are parallelepipedal pieces obtained by cold compression at 200 MPa of 6 g of powder in a steel matrix of dimensions 24.48 x 7.97 mm. The height of the green part obtained depends on the compressibility of the powder, and is generally of the order of 5 to 6 mm.

Then sintering was carried out in a static laboratory furnace under H ₂ at temperatures ranging from 850 to 1000 ⁰ C. In all cases, the rate of rise in temperature was 150 ° C / h, the bearing at the sintering temperature was 1 h and the cooling was natural for about one night. The density of the sintered pieces as a% of the theoretical value was measured

(8.35g / cm ³ ), their HB hardness and their HRB hardness. The results are summarized in Table 2.

Table 2: results of the sintering of direct powders and mixing. The test results show that the direct powder has better cold compressibility than the mixed powder. It will therefore be the easiest of the two to form before sintering.

On the other hand, the mixed powder has the best sintering densification and the best hardness after sintering.

Similar tests were carried out on direct powders and mixtures to which, prior to sintering, iron phosphide at 10% by weight of P supplied by BASF was added. The mixing took place in a Gericke mixer under CO ₂ for 50 min at 85% powder and 15% FeP (% by weight).

Cold compression tests were carried out under the same conditions as above. It has been found that the FeP additive direct powder has a density equal to 59.1% of the theoretical density and the powder mixes a density equal to 53.1% of its theoretical density.

Sintering of these powders was then carried out, under the same conditions as above, and the densities and hardnesses HB and HRB of the parts obtained were measured. The results are summarized in Table 3.

Table 3: results of the sintering of direct powders and mixture additive to FeP.

The hierarchy of performances between the direct powders and additive mix with FeP is the same as for pure powders (not additive). The mixed powder has the best results after sintering. The additivation makes it possible to obtain sintered pieces having a hardness substantially higher than that of the parts obtained under the same conditions from non-additive powders, as can be seen by comparing the results of Tables 2 and 3.

As an indication, a powder according to the invention to which one would add FeP at a rate of 85% of powder and 15% of FeP would end up with approximately the following characteristics:

typical theoretical density 8.21 g / cm ³ Fe = 54 - 58%

- Co = 12 - 16% - Cu = 27 - 31%

- P = 1 - 2% - O <1.5%

Fisher = 2 - 5 μm.

Sintering tests were also carried out on a Ni-phosphide-additive mixed powder containing 8.8% by weight of P, at a rate of 85% of mixed powder and 15% of NiP. The results are summarized in Table 4.

Table 4: results of the sintering of the mixed powder additive with NiP.

The additive NiP under the conditions that have been said also provides outstanding results in terms of density and hardness sintered parts. As a guide, a powder according to the invention to which NiP would be added at a rate of 85% of powder and 15% of NiP would have approximately the following characteristics:

- typical theoretical density 8.37 g / cm ³ - Fe = 40 - 44%

. Co = 1 1 - 17%

- Cu = 27 - 31% - Ni = 13 - 15%

- P = 1 - 2% - 0 ≤ 1, 5%

- 0 Fisher 1 - 4 μm

The additivation can also be carried out using copper phosphide or cobalt. Also, a mixture of at least two of iron, nickel, copper and cobalt phosphides or a mixed phosphide of at least two of these metals can be used.

Granite cutting tests carried out with parts made with the aid of powders according to the invention and with a reference powder gave the following results.

Granite cutting tests were carried out with 500 mm diameter diamond saws whose cutting segments were made by natural sintering, using to make the segments:

a reference powder known in the prior art (Cobalite® CNF) of composition (mass percentages): Co = 0%; Cu = 26%; Fe = 68.4%; Ni = 0%; Sn = 3%; W = 2%; Y ₂ O ₃ = 0.6% - the powder according to the invention additive of FeP (85% - 15%) as previously described.

Both powders were used to manufacture diamond segments forming the toothing of the saws. These segments were of the "sandwich segment" type, that is, they had a larger diamond concentration at their periphery (1.1 carat / cm ³ of segment) than at their center (0.8 carat / cm ³ segment). Standard diamonds and diamonds coated with titanium were used. This type of segment was chosen because they are particularly complex and expensive to achieve by the conventional method of hot pressing in graphite molds.

The segments made with the reference powder and with the powder of the invention were sintered by natural sintering in a rolling oven at 940 ^° C. for the powder of the invention and 980 ^° C. for the reference powder, and then brazed. on 500 mm diameter steel discs to form the saws. Granites of different categories were then cut with saws. For each type of powder, three types of diamond mixtures were tested, made from diamonds of the company ELEMENT SIX whose references will be indicated.

After each cutting test, the cutting speed (in cm ² of granite cut per minute) and saw life (in m ² of granite cut per mm of segment height) were calculated. The higher these values are, the better the quality of the saw. Using a blend of diamonds SDB VB 40 to 50 mesh (30%) and

SDB LBW 50 to 60 mesh (70%), the results were as follows:

The reference saw had a service life of 4.4 m ² / mm and a cutting speed of 520 cnrYmin).

The saw of the invention had a service life of 4.8 m ² / mm and a cutting speed of 620 cnfVmin.

Using a blend of VB 30 to 40 mesh (10%) SDB, 40 to 50 mesh (40%) SDB and 50 to 60 mesh LBW (50%) SDB diamonds, the results were as follows.

The reference saw was unable to cut the granite. The saw of the invention had a life of 3 m ² / mm and a cutting speed of 620 cm ² / min.

Using a blend of SDB VB 30 to 40 mesh (10%), SDB TMF 40 to 50 mesh (40%), and SDB TMF 50 to 60 mesh (50%) diamonds, the results were as follows. TMF are coated with titanium). The reference saw had a service life of 4.1 m ² / mm and a cutting speed of 600 cm ² / min.

The saw of the invention had a service life of 6.7 m ² / mm and a cutting speed of 900 cm ² / min. The results of tests of the saws of the invention are excellent in absolute value, and systematically better in every respect than those of the reference saws. The method of manufacturing the saw segments of the invention, coupling a natural sintering segments with a precise composition of the prealloyed powder used, thus gives satisfactory results for a very low cost compared to known methods using molds.

It has also been verified that the powder according to the invention lends itself well to the production of diamond beads which can be used for the manufacture of cutting threads for granite cutting, which are the preferred application envisaged for the invention.

These beads had outer diameters of 7.2 mm (beads for multi-thread machines) and 11 mm (beads for single-thread machines) and were manufactured by the following process:

- Manufacture of granules by the method described above, from a powder according to the invention additive FeP (85% / 15%);

- mixing the granules with standard diamonds or coated with titanium according to the tests;

- cold compression of the mixture granules / diamonds, providing a density of green parts of about 65% of the theoretical density; elimination of the granulation binder at 590 ^° C.

sintering at 900 ^° C.

brazing at 900 ° C. using a solder containing 72% of Ag and 28% of Cu to ensure sufficient bonding on the steel sheath which serves as a support. The debinding, sintering and brazing operations were carried out in an oven under H ₂ .

The beads obtained were threaded onto steel cables at the rate of 37 beads / linear meter, then the assembly was plasticized to stiffen it.

The yarns have been tested on different machines for the cutting of various granites. The test results are summarized in Table 5.

Table 5: results of the tests carried out on cutting son (pearls made from powder according to the invention additive of FeP).

These results are quite satisfactory, and show that the invention makes it possible to produce high-performance diamond beads at a substantially lower cost than by conventional methods. For comparison, the life of usual son, using diamond-coated titanium, is of the order of 28 m ^z / m linear. In general, the powder according to the invention, used pure, has a good cold compressibility and densifies very correctly from 900 ^° C. (97% of its theoretical density), in particular when it is obtained by mixing the powders I and II as previously defined. The hardness obtained after sintering can be considered as insufficient for the cutting of the granite, but would be sufficient for the cutting of marble. But the addition of 15% iron phosphide or nickel increases the densification and hardness of the sintered parts in a manner that makes them perfectly suitable for cutting the granite.

By way of comparison, in order to show that the invention requires the use of a prealloyed powder or a mixture of such powders for obtaining the desired results, the following tests were carried out.

A "mixture 1" mixture under CO _{2 was} prepared for 50 min from commercial Fe, Co and Cu powders as shown in Table 6:

Table 6: Characteristics of the mixture 1

The weight percentages of metals are expressed excluding oxygen content.

This composition is in the middle of the range of the prealloyed powder according to the invention.

At 85% by weight of this mixture, 15% of iron phosphide FeP 10% of BASF, of the same quality as that of the tests mentioned above, were added (according to the same protocol as above). The composition of this Mixture 2 is then (Table 7):

Table 7: Composition of the mixture 2

The weight percentages of metals and phosphorus are expressed excluding oxygen content.

For both mixtures, PS21-type parts were compressed at 200 MPa.

The average raw material density, calculated from the ratings and weight, was (Table 8):

Table 8: Percentages of theoretical densities of raw parts

These green parts are then sintered at 850, 900, 950 and 1000 ^° C. On these parts, their density was measured in% of the theoretical density, their HB hardness and their hardness HRB, according to the protocol described above for the parts produced. according to the invention.

After sintering, the following results were obtained (Tables 9 and 10)

Table 9: Sintering results of the mixture 1.

Table 10: Sintering results of the mixture 2.

All the results show that these two mixtures of commercial metal powders, in comparison with the pre-alloyed powders according to the invention of comparable compositions, have:

- a very similar particle size

- better cold compressibility - densification after sintering significantly worse and lower HB and HRB hardnesses

- A structure of sintered parts significantly coarser because of the large initial grain size of the constituents. In these conditions :

- diamond tools made from these commercial metal powder mixes will have a lower diamond retention (that is to say, a lower bonding of diamonds in the metal matrix), due in part to their high porosity; - This will result in tool performance (cutting speed and life) significantly lower than that of the pre-alloyed powder (pure or additive of iron phosphide) according to the invention, of comparable composition and particle size.

The powder according to the invention, in particular in its additive version, is easily granular, which makes it possible to produce thin segments and diamond threads by inexpensive methods. It is easily sinterable in the presence of diamonds, whether in a static oven or in a scrolling oven, both in powder form and in the form of granules. It responds very well to the problems posed. Of course, the powder according to the invention could also be used with advantage for making cutting tools by methods other than those described.

Claims

1. Pre-metallized metal powder, especially for the manufacture of sintering cutting tools, characterized in that its composition in percent by weight is: * Fe = 48 - 52%

* Co = 14 - 19%

* Cu = 32 - 37% * 0 <1.2% the rest being impurities resulting from its manufacture.

2. prealloyed metal powder according to claim 1, characterized in that the Fisher diameter of its particles is 1 to 3 microns.

3. Pre-alloyed metal powder, characterized in that it consists of a mixture of a powder according to claim 1 or 2 and at least one sintering aid additive at a rate of 80 to 90% by weight of powder. and 10 to 20% by weight of additive.

Pre-metallized metal powder according to claim 3, characterized in that the sintering aid additive is an iron, nickel, copper or cobalt phosphide, or a mixture of at least two of these phosphides, or a mixed phosphide of at least two of these metals.

5. prealloyed metal powder according to one of claims 1 to 4 characterized in that it is obtained by mixing a first powder and a second powder, and a possible sintering additive, said first and second powders having the respective characteristics: - for the first powder * Fe = 27 -32%

* Co = 24 - 28%

* Cu = 42 - 47%

* O <1% the remainder being impurities resulting from its manufacture - for the second powder

* Fe = 75 - 80%

* Co <5%

* Cu = 17 - 22% * O <1% the rest being impurities resulting from its manufacture.

Pre-metallized metal powder according to claim 5, characterized in that the Fisher diameter of the particles of the first powder is 0.8 to 1.5 μm, in that the Fisher diameter of the particles of the second powder is 3, 0 to 4.0 microns, and in that the Fisher diameter of the powder obtained after mixing is 1 to 3 microns.

7. A method of manufacturing a diamond cutting tool, comprising in particular a step of mixing a prealloyed metal powder and diamonds, a cold pressing step of the mixture and a sintering step of said compressed mixture, characterized in that said metal powder is of the type according to one of claims 1 to 6.

8. Process according to claim 7, characterized in that the sintering is a natural sintering.

9. The method of claim 7 or 8, characterized in that said tool is a cutting segment for diamond saw.

10. The method of claim 7 or 8, characterized in that said tool is a diamond bead for cutting wire.

11. Method according to one of claims 7 to 10, characterized in that said powder is of the type according to claim 5 or 6.

Diamond saw of the type comprising cutting segments fixed on the periphery of a metal disc, characterized in that said segments have been obtained by the method according to claim 9.

13. Cutting wire of the type comprising diamond beads threaded on a cable, characterized in that said beads were obtained by the process according to claim 10.