EP1948838A1

EP1948838A1 - Multi-metal powder and a sintered compact produced therefrom

Info

Publication number: EP1948838A1
Application number: EP06831061A
Authority: EP
Inventors: Maxime Bonneau; Jean-François LARTIGUE; Thierry Commeau; Christian Huet
Original assignee: Eurotungstene Poudres SA
Current assignee: Umicore Specialty Powders France
Priority date: 2005-11-09
Filing date: 2006-11-03
Publication date: 2008-07-30
Anticipated expiration: 2026-11-03
Also published as: US20090188171A1; FR2892957A1; KR101363968B1; KR20080077148A; WO2007057533A1; JP2009515051A; FR2892957B1; US7998230B2; EP1948838B1; PL1948838T3

Abstract

A multi-metal powder, in particular for producing diamond tools comprises iron copper, cobalt and molybdenum whose contents are expressed in the following mass percentages: Fe + Cu + Co + Mo = 98 mass %, the rest being oxygen and production impurities, wherein 15 % = Cu = 35 %, 0,03 = Mo / (Co + Fe + Mo) = 0,10, - Fe / Co = 2. A sintered compact is obtained by hot compaction of said multi-metal powder, for example, in the form of a diamond cutting tool.

Description

Polymetallic powder and sintered part made from this powder.

The invention relates to the field of metal powders known as "pre-alloyed powders" or "polymetallic powders", used in powder metallurgy, in particular for the manufacture of diamond tools.

To produce diamond tools intended especially for cutting stone, building materials or asphalt, the most common method is to mix diamonds with a metal binder in the form of a mixture of powders, to compress the diamond mixture in a cold press, to transfer the piece thus compressed in a graphite compression tool, and finally consolidate by sintering the tablet in a hot press. The parameters to consider when manufacturing these tools are as follows, a) Binder composition.

Depending on the nature of the material to be cut, particularly its hardness and abrasiveness, the binder composition is chosen to adjust the hardness, impact resistance and wear resistance of the tool. The goal is to optimize either cutting speed or tool life, while minimizing the power required for cutting.

The most commonly used materials are micron powders of cobalt, iron, nickel, copper, and atomized powders (typically 5 to 100 μm) of bronze, copper, tin. These base binders can be additive micronic WC tungsten carbide, fused carbide (typically 50 to 500 microns), or micron tungsten to increase the wear resistance. b) Cold compression at 150 to 500 MPa.

The pressure is adjusted to obtain a tablet whose holding raw is sufficient to allow its handling. To facilitate automatic feeding of the presses, the binder + diamond mixture is most often granulated using an organic additive. The size of the granules is typically 50 to 700 μm. c) Hot compression. The purpose of this step is to crimp the diamond in a binder matrix whose relative density is greater than 95% of its theoretical density. For this, pressures of the order of 25 to 50 MPa, and temperatures of the order of 700 to 1100 ⁰ C are used. The sintering stage at maximum temperature lasts 2 to 10 minutes. The temperature is chosen according to the nature of the binder, to optimize its properties of hardness, impact resistance, wear resistance, diamond retention. It must be minimized to avoid degrading diamonds by graphitization. The use of diamonds coated with titanium, chromium, silicon or nickel improves the resistance of diamonds to graphitization, and improves the chemical bond between diamond and metal binder.

The parts thus obtained are mounted on a steel support of different shapes to produce tools such as circular saws, corers, polishing heads, diamond threads, etc. The attachment is by soldering or laser welding. Historically, the basis of binders used for cutting the most resistant materials such as granite, sandstone, concrete, asphalt, is pure cobalt in the form of very fine powders (0.8 to 5 microns). Cobalt achieves an excellent compromise between the hardness (95 to 110 HRB on the Rockwell B scale according to ISO 6508-1), the impact resistance (20 to 50 J / cm ² of rupture energy in CHARPY test according to ISO 5754), resistance to corrosion, resistance to oxidation in powder form (initial oxygen content less than 1%, and evolution in atmosphere at 35 ° C and 80% relative humidity not exceeding 0.6% in 48 hours). The major disadvantage of cobalt is its relative rarity in nature, which is accompanied by a high price which is also subject to rapid and large fluctuations.

In recent years, the use of polymetallic powders, made by co-precipitation of metal salts followed by reduction by hydrogen, has developed as a substitute for pure cobalt for the manufacture of diamond tools intended mainly for the cutting of metals. natural stone. In particular, the first generation of Cu-Fe-Co products developed by the Applicant, in addition to its price advantages (lower and more stable than that pure cobalt), has improved the performance of cutting tools. In particular, the ease of cutting has been increased: higher cutting speeds have become possible without increasing the power consumed and maintaining the life of the tool at a high level. WO-A-00/23630, WO-A-00/23631, WO-A-98/49361,

WO-A-03/083150 are representative of what may be polymetallic powders usable in this context.

However, for certain applications in the field of construction such as high-power sawing, sawing fresh concrete, cutting asphalt ... the mechanical properties of tools made from these known powders have proved insufficient. In these applications, the required impact and hardness levels are higher than what can be achieved, for example, from Cu-Fe-Co powders. As a result, this market segment continues to use pure cobalt as the base of its binders. The first-generation Cu-Fe-Co powders do not exceed a hardness of 107 HRB coupled with a fracture energy of 15 J / cm ² CHARPY whereas the desired characteristics for this market are a hardness greater than 108 HRB and an energy of rupture greater than 20 J / cm ² CHARPY.

The object of the invention is to provide a polymetallic powder suitable in particular for the manufacture of diamond tools meeting these stringent requirements, while being less expensive than the commonly used cobalt powders.

For this purpose, the subject of the invention is a polymetallic powder, in particular for the manufacture of diamond tools, characterized in that it contains iron, copper, cobalt and molybdenum in contents, in mass percentages, such as than :

- Fe + Cu + Co + Mo> 98%, the rest being oxygen and impurities resulting from the manufacture;

- 15% <Cu <35% - 0.03 <Mo / (Co + Fe + Mo) <0.10

- Fe / Co> 2. Preferably, Co + Mo <30%. Preferably:

- Fe + Cu + Co + Mo> 98%, the rest being oxygen and impurities resulting from the manufacture - 40.5% <Fe ≤ 46.5%

- 29% <Cu <35% - 17% <Co <21%

- 5% <Mo <6%.

This polymetallic powder may have been additivated by at least one abrasive additive.

Said abrasive additive may be chosen from oxides and carbides. This polymetallic powder may have been additivated by at least one softening additive.

The softening additive may be selected from copper and bronze. The invention also relates to a sintered part by hot pressing of a polymetallic powder, characterized in that said polymetallic powder is a polymetallic powder of the above type.

Said polymetallic powder may have been mixed with a diamond powder. Said sintered part may be a diamond cutting tool.

As will be understood, the invention is based on a polymetallic powder using copper, iron, cobalt and molybdenum. Compared with conventional Cu-Fe-Co powders, the addition of molybdenum and the precise balancing of the composition as proposed make it possible to produce diamond tools whose cutting performance, under the most demanding conditions, prove to be equal. and even often superior to those commonly used cobalt tools. On the other hand, these powders have a cost price that remains lower than that of pure cobalt powders.

The invention will be better understood on reading the description which follows. It was known that Cu-Fe-Co polymetallic powders are necessarily biphasic. A first phase is very rich in Cu, a second phase is very rich in Fe and Co, and these two phases have only a very low reciprocal solubility.

It was also known that elements such as W and Mo tend to harden the Fe-Co phase. However, since the corresponding quaternary phase diagrams are very poorly known, it was not possible without extensive research to quantitatively and accurately estimate the influences that such elements might have on the properties of the Cu-Fe-2 powders. Co.

Thanks to such researches, the inventors have been able to demonstrate a narrow composition range for a Cu-Fe-Co-Mo powder making it possible to obtain the excellent compromise sought between the various properties, while preserving the powder, by compared to Co-based powders, an attractive cost price and not too dependent on fluctuations in commodity prices.

These powders offer remarkable ductility and impact resistance coupled with a level of hardness compatible with the most demanding applications of diamond tools.

The composition range of the powders according to the invention is defined by the following criteria. The contents are given in percentages by mass.

The sum of the contents Cu, Co, Fe and Mo is at least 98%, the rest being oxygen and impurities resulting from the manufacture. No element other than Cu, Co, Fe and Mo shall be present at a level of more than 0.5%. This is particularly the case of Sn, which at a higher content, would have a weakening effect by generating hard and fragile phases during cooling.

The Cu content, which determines the relative importance of the Cu-rich phase with respect to the Fe-Co-Mo rich phase, is between 15 and 35% to ensure densification of the sintering without greatly reducing the hardness.

The ratio Mo / (Co + Fe + Mo) must be between 0.03 and 0.10 to obtain an effective cure without risking undesirable embrittlement.

The Fe / Co ratio must be greater than or equal to 2 so that the composition of the Fe-Co-Mo phase makes it possible to obtain the desired hardness / resilience compromise. Preferably, for economic reasons, the total Co + Mo does not exceed 30% of the total composition.

A preferred composition range of the polymetallic powder according to the invention is: Fe + Cu + Co + Mo> 98%

- 40.5 <Fe <46.5%

- 29% <Cu <35% - 17% ≤ Co ≤ 21%

- 5% <Mo <6% An example of a process for preparing the polymetallic powder according to the invention consists, in a conventional manner, in first making a mixture of aqueous solutions of metal chlorides of Cu, Fe and Co, these elements Metals in the mixture in relative proportions corresponding to those referred to the final powder. The metals are then precipitated by addition of sodium hydroxide with vigorous stirring. A precipitate of polymetallic hydroxide is obtained, which is filtered and washed to obtain an Na content of less than 0.04% relative to the sum Co + Cu + Fe. It is dried and reduced to powder. coarse less than 100μm. This powder is then impregnated with an aqueous solution of ammonium molybdate prepared from a soluble molybdenum salt, the proportion of Mo relative to other metals corresponding to that referred to the final powder.

The impregnated powder is reduced under hydrogen in a passage oven at a temperature of 750-850 ^° C. for 2 to 10 hours. This makes it possible to obtain the metal in the form of agglomerated micron powder.

A grinding step makes it possible to obtain the polymetallic powder that is ready to be sintered, with typically a particle size of 3 μm Fisher (defined by the ISO10070 standard) and an oxygen content of less than 0.8%. The documents of the prior art cited above describe processes for the preparation of polymetallic powders analogous to the process just described, and reference may be made for more details.

The polymetallic powder according to the invention exhibits remarkably high oxidation resistance compared to pure Co-based powders and conventional Cu-Fe-Co powders. A powder according to the invention, initially containing 0.3% oxygen, captures only 0.1% additional oxygen in an atmosphere at 80% relative humidity at 35 ° C. for 48 hours. Under the same conditions, the oxygen uptake of a pure Co-base powder would be 0.5% and that of a Cu-Fe-Co powder at 50% Cu, 25% Fe, and 25% Co. would be of the order of 2%. This ensures excellent stability of the properties of the parts and tools that will be subsequently produced by sintering the powders according to the invention.

On the other hand, the oxides present during hot compression, even if they are partially reduced during sintering, cause weakening structural defects. The low sensitivity to oxidation of the powder according to the invention ensures that such defects will not occur too much, even if the storage conditions of the powder prior to hot compression have not been optimal. Finally, this low sensitivity to oxidation is a safety criterion: it ensures that despite the relatively high presence of Fe, the powder will not warm up dangerously in contact with moist air.

The pressure and temperature range during the sintering of the powders according to the invention in a hot press making it possible to obtain parts whose density is greater than or equal to 95% of the theoretical density has been determined.

For a temperature of 900 ^° C., the minimum pressure is 45 MPa for a period of 3 minutes.

To a temperature of 950 ⁰ C ₁ the minimum pressure is 37,5MPa, for a period of 3 minutes.

For a temperature of 975 ^° C., and more, the minimum pressure is 35 MPa for a period of 3 minutes. A temperature of 975 ° C, a pressure of 35 MPa and a duration of 3 minutes are recommended. The high temperature favors the development of the hardness brought by the Mo.

Table 1 shows the properties of Rockwell B hardness, impact resistance and breaking strength of hot-sintered non-diamond samples by hot pressing, under specified conditions, of a powder according to the invention of Fe = 43 composition. , 5%, Cu = 32.0%, Co = 19.0%, Mo = 5.5%. They are compared to those of sets of reference samples of compositions:

reference 1: Fe = 58.0%, Cu = 16.0%, Co = 26.0%; it differs from the invention essentially in that it does not include Mo;

reference 2: Fe = 25.0%, Cu = 50.0%, Co = 25.0%; it corresponds to Cu-Fe-Co products of the prior art;

- Reference 3: Co = 100% grains of average size 1, 8μm.

- Reference 4: Co = 100% fine grain size 0.9μm.

The breaking force was measured by 3-point bending tests. It is considered as an indicator of the good retention of diamonds, in the case where the powder tested would be used for the manufacture of diamond tools.

reference 470 ⁰ C / 35 MPa 108 - 110 HRB 25 - 35 J / cm 2 3800 - 4000 N

Table 1: Sintering conditions and mechanical properties of the samples tested.

It is seen that the samples according to the invention have a slightly higher hardness than those of reference sample sets 1 and 2 made from other types of polymetallic powders. In particular, compared to reference 1 the addition of Mo actually brings an increase in hardness. Compared to the pure Co samples, the hardness of the sample according to the invention is comparable to that of the very fine grain Co-based sample and higher than that of the Co-based sample. average grains.

The addition of Mo does not impair impact strength, which remains comparable to that of medium grain Co samples and may be greater than that of fine grain Co samples.

As for the breaking force, that of the samples according to the invention still surpasses those of the Co-based samples which were already superior to those of the other references.

The polymetallic powders according to the invention can be used in various ways, as can the polymetallic powders of the prior art. In particular they can be mixed with one or more abrasive additives (carbides, oxides) or with one or more softening additives (Cu, bronze, etc.) to modulate the properties of the tools. In this way it is preferred to reduce the speed of wear or increase the cutting speed. From the powder according to the invention which has just been described, diamond saws have been made, the performances of which have been compared during cutting tests of various materials with those of industrial saws based on Co which in each case , were considered the best available in their category. On some of these saws, the binder was used pure. On others it was used additive by micron tungsten carbide, or by molten carbide (eutectic WC-W ₂ C melted then crushed into grains of 0.05-1 mm). In most cases, the diamonds were in the uncoated state. In one case the diamonds were coated with Si to prevent their graphitization, according to a known practice. Except when a more precise value is given, the diamond concentrations of the various saws described are typically between 0.7 and 1.5 carat / cm ³ .

Dry sawing of asphalt - Saws with a diameter of 300 mm, depth 5.5 cm, binder according to the invention + 7% WC;

- Uncoated diamonds.

The wear of the tool is reduced (10.3 m ² cut per mm used compared to 9.1 m ² / mm used for the saw base Co), and the cutting speed is increased (620 cm ² / min against 580 cπrYmn for the saw with base Co).

Wet sawing of concrete walls

Saws diameter 700 mm, depth 25 cm, binder according to the invention pure;

- Machine power 14 kW; - Uncoated diamonds.

The wear of the tool is considerably reduced (7.5 m ² cut per mm, compared to 5.1 m ² / mm for the Co-based saw) at the cost of an acceptable reduction in cutting speed (295 cm ² / min, against 360 cm / min for the Co-based saw).

Wet sawing of reinforced concrete floors - saws with a diameter of 400 mm, depth 14 mm, binder according to the invention, pure or reinforced with 6% molten carbide;

- Machine power 9.8 kW;

- Uncoated diamonds, concentration 1.1 carat / cm ³ , size 50% 30/40 MESH + 50% 40-50 MESH. The wear of the tool is considerably reduced (2.6 or 2.9 m ² cut per mm, against 1.9 m ² / mm) and the cutting speed increased (600 or 590 cm ² / min, against 480 cm ² / min for the saw based on Co).

Wet sawing of reinforced concrete blocks - saws with a diameter of 400 mm, depth of passage 50 mm, binder according to the invention;

- Machine power 23 kW;

- Uncoated diamonds or diamonds coated with silicon; concentration 1.1 carat / cm ³ . The wear of the tool is considerably reduced (11.6 m ² cut per mm against 3.3 m ² / mm for the Co-based saw) with a cutting speed of 500 cm ² / min. By using silicon-coated diamonds, the wear can be maintained at 8.5 m ² / mm for an average power of the apparatus of the order of 6 kW identical to that required for the cobalt-based saw. In both cases, there was no stoppage related to a peak power of more than 23 kW, while the reference binder Co based caused two stops: the ease of cutting has been increased.

In use, the saws made with the binder according to the invention, in the pure state or additive to micron tungsten carbide or molten carbide, behave therefore at least as well, and often quite frankly better, than the best saws at Base Co.

Of course, if the manufacture of diamond cutting tools is a preferred application of the polymetallic powders according to the invention, it is not exclusive. Other types of sintered parts for which similar qualities are required can advantageously be made using these powders.

Claims

1. Polymetallic powder, especially for the manufacture of diamond tools, characterized in that it contains iron, copper, cobalt and molybdenum in contents, in percentages by weight, such as: Fe + Cu + Co + Mo> 98%, the rest being oxygen and impurities resulting from the manufacture;

- 15% <Cu <35%

- 0.03 <Mo / (Co + Fe + Mo) <0.10

- Fe / Co> 2.

2. The polymetallic powder according to claim 1, characterized in that Co + Mo <30%.

3. The polymetallic powder according to claim 2, characterized in that

- Fe + Cu + Co + Mo> 98%, the rest being oxygen and impurities resulting from the manufacture

- 40.5% <Fe <46.5%

- 29% <Cu <35% - 17% <Co <21%

- 5% <Mo <6%.

4. polymetallic powder according to one of claims 1 to 3, characterized in that it has been additivated by at least one abrasive additive.

5. Polymetallic powder according to claim 4, characterized in that said abrasive additive is selected from oxides and carbides.

6. polymetallic powder according to one of claims 1 to 3, characterized in that said powder has been additivated by at least one softening additive.

7. polymetallic powder according to claim 6, characterized in that said softening additive is selected from copper and bronze.

8. Sintered part by hot compression of a polymetallic powder, characterized in that said polymetallic powder is a polymetallic powder according to one of claims 1 to 7.

9. Sintered part according to claim 8, characterized in that said polymetallic powder has been mixed with a diamond powder.

10. Sintered part according to claim 9, characterized in that it is a diamond cutting tool.