MXPA98004600A - Powder previously allocated and its use in the manufacture of diamond tools - Google Patents

Abstract

The powder has a particle size of less than 8æm and a loss of mass by reduction in hydrogen of less than 3% and contains 10-80% Fe, up to 40% Co, up to 60% Ni and up to 15% M N is present, at least partially, in the oxidized state and represents one or more of the elements Mn, Cr, V, Al, Mo and Ti, the rest with unavoidable impurities. This powder can be sintered at 650-1000 ° C to provide a matrix that has a high hardness

Description

POWDER ALLOYED PREVIOUSLY AND ITS USE IN THE MANUFACTURE OF DIAMOND TOOLS DESCRIPTION OF THE INVENTION The present invention relates to the use of a pre-alloyed powder containing iron as a binder in the manufacture of diamond tools by hot sintering. In the manufacture of diamond tools by hot sintering, with or without pressure, of an intimate mixture of diamond and binder, use is made, for the binder, of what is called the matrix-forming material of the tool at the end of the sintering operation, either fine cobalt powders (1-6 μm) or mixtures of fine powders, such as a mixture of fine cobalt, nickel and iron powders, or coarse powders previously alloyed (less than 44 μm), such as steel powder obtained by atomization. The use of fine cobalt powder has very good results from a technical point of view; its only drawback is based on the high price of dust. When using mixtures of fine powders, matrices are obtained whose hardness and, consequently resistance to wear, is relatively low.

The use of coarse powders previously alloyed requires a sintering temperature of approximately 1100-1300 ° C, a temperature at which the degradation of the diamond, called grafitation, becomes appreciable. The object of the present invention is to provide a pre-alloyed powder containing iron, whose use as a binder in the manufacture of diamond tools by hot sintering avoids the drawbacks mentioned above. For this purpose, the powder used according to the invention has an average particle size of less than 8 μm measured with the Fisher Sub Sizer, and a mass loss by reduction in hydrogen of less than 3%, measured in accordance with the ISO 4491-2: 1989 standard; This powder contains in% by weight, 10-80% of iron, up to 40% of cobalt, up to 60% of nickel and up to 15% of M, M is present, at least partially, in the oxidized state and represents one or more of the elements Mn, Cr, V, Al, Mo and Ti, the other components in the powder consist of unavoidable impurities. In fact, it has been found that such a powder, which in this way contains at most only 40% cobalt, can be sintered at moderate temperatures (650-1000 ° C) to provide a matrix having a high hardness and which, In addition, this hardness can be easily adapted to the particular requirements of diamond tool users, by varying the composition of the powder. It is necessary that the particle size is less than 8 μm in order that the powder is sinterable at moderate temperatures; advantageously, it is less than 5 μm. The loss of mass by reduction in hydrogen must be less than 3%; otherwise, there is a risk of producing, when sintering the powder mixed with diamonds in a reducing atmosphere, such a large production of gas that they resemble porosities in the sintered product and / or the graficación of the diamond becomes too large; the mass loss preferably is less than 2%. The contents mentioned before Fe, Co, Ni and M are necessary in order that the matrix has an adequate hardness and in order that this hardness is able to adapt to the requirements of the users of diamond tools. Preference is given to an Fe content of at least 30%, a Co content, which varies up to 30%, a Ni content of 10-30% and an M content that varies up to 10%, these contents lead to very high hardness. The most preferred Fe content is at least 50% and that of M is equal to or less than 5%. The present invention also relates to a previously alloyed powder, defined above, which contains iron, therefore this powder is characterized in that it has an average particle size of less than 8 μm, as measured by the Fisher Sub sieve sizer, and a loss of mass by reduction in hydrogen less than 3%, measured in accordance with the ISO standard 4491-2: 1989 and containing, in% by weight, 10-80% iron, up to 40% cobalt, up to 60% nickel and up to 15% M, M is present, at least partially, in the oxidized state and represents one or more of the elements Mn, Cr, V, Al, Mo and Ti, The other components in the powder consist of unavoidable impurities. The powder of the invention can be prepared by heating, in a reducing atmosphere, a hydroxide, oxide, carbonate or basic carbonate (mixture of hydroxide and carbonate) or mixed organic salt of the constituents of the alloy so that a powdery product is obtained whose mass loss by reduction in hydrogen is less than 3%, and by grinding this product (the expression "constituents of the alloy" is used herein to indicate that all the elements present in the composition of the alloy, in addition to the oxygen: as, for example, Fe, Ni, Co and Mn should be considered as constituents of the Fe-Ni-Co-Mn-O alloy). The hydroxide, carbonate, basic carbonate and organic salt can be prepared by adding an aqueous solution of the constituents of the alloy to an aqueous solution of, respectively, a base, a carbonate, a base and a carbonate and a carboxylic acid, separating the precipitate obtained in this way from the aqueous phase and dry the precipitate.

The solution of the constituents of the alloy can be a chloride solution, a sulphate solution, a nitrate solution or a mixed solution of these salts. It may be useful to add a small amount of carbon, for example, 0.05-3% in the form of an organic compound to the previously alloyed powder in order to reduce the risk of graphing, this risk is low at moderate temperatures used for sintering.

Example 1 This example relates to the preparation of a powder according to the invention by the precipitation of a mixed oxalate and the subsequent decomposition of this oxalate. 2.47 liters of a chloride solution containing 39 g / 1 of Co, 25 g / 1 of Ni, 85 g / 1 of Fe and 11 g / 1 of Mn, at room temperature and with stirring, are added to 13.64 liters of an aqueous solution of oxalic acid containing 65 g / 1 of C2H204 «2H20. Therefore, 94% Co, 85% Ni, 81% Fe and 48% Mn precipitate in the form of a mixed oxalate. This precipitate is separated by filtration, washed in water and dried at 100 ° C. The dry precipitate contains 9.2% Co, 5.3% Ni, 17.2% Fe and 1.3% Mn. The precipitate is heated at 520 ° C in a stream of hydrogen for 6 hours. In this way a pulverulent metal product is obtained. Grinding this product in a mortar provides a previously alloyed powder that has a mass loss by reduction in hydrogen of 2% and that contains 27.1% Co, 15.7% Ni, 50.8% Fe and 3.9% Mn, and the particles of which have an average diameter of 2.1 μm, measured with the Fisher Sub sieve sizer. Examination of the powder using X-ray diffraction shows that virtually all of Mn is present in the oxidized state.

Example 2 This example relates to the preparation of a powder according to the invention by the precipitation of a mixed hydroxide and the subsequent reduction of this hydroxide. Add 9.4 liters of a chloride solution containing 24.4 g / 1 of Co, 13.5 g / 1 of Ni, 58.6 g / 1 of Fe and 2.3 g / 1 of Mn, at 80 ° C and with agitation, to 36.7 liters of an aqueous solution of caustic soda containing 45 g / 1 of NaOH. Virtually all these elements are precipitated in this way in the form of a mixed hydroxide. This precipitate is separated by filtration, washed in water, re-formed in pulp at 80 ° C in a solution of 45 g / 1 NaOH, separated once again by filtration, washed in water and dried at 100 ° C. ° C. The dry precipitate contains 14.8% Co, 8.2% Ni, 35.6% Fe and 1.4% Mn.

The precipitate is heated at 510 ° C in a stream of hydrogen for 7.5 hours. The pulverulent metal product obtained in this way provides, after grinding in a mortar, a previously alloyed powder having a mass loss by reduction in hydrogen of 1.65% and containing 24.2% Co, 13.4% Ni, 58% Fe and 2.3% of Mn, and the particles of which have an average diameter of 2.1 μm. Examination of the dust Using X-ray diffraction shows that virtually all the Mn is present in the oxidized state.

Example 3 This example relates to a series of tests comparing the sintering capacity of two powders according to the invention, hereinafter referred to as powder A and powder B of a fine Co-powder (powder C) and of a CO powder obtained by atomization (powder D). The powder A is that obtained according to Example 1 and the powder B is that obtained according to Example 2. The powder C is a commercially available Co powder (1.5 μm) obtained via the oxalate route. Dust consists of particles having an average diameter of 9.7 μm. A cylindrical pill, having a diameter of 4 mm and a length of 4 mm, is produced from each of the powders to be tested by cold pressing. These cylinders are heated at a rate of 5 ° C per minute and the change in length is measured as a function of temperature. The variation of the change (in%) in the length of the cylinders as a function of the temperature is given in the figure appended to the present. The densities (in g / cm3) of the cylinders before and after heating and the ratio between these densities are given in the following table: The sintering capacity of the powders according to the invention (A and B) is superior to that of the fine Co-powder (C) and much higher than that of the coarse D powder. 4 In this example, the mechanical properties of sintered parts made of cobalt powder, nickel powder, iron powder, various mixtures of Co, Fe, Ni and Mn powders and various powders according to the invention were compared. The following powders were used: extra-fine cobalt powder from Union Minére, which has an average diameter (Fisher) of 1.50 μm and which has a mass loss by reduction in hydrogen (LMRH) of 0.55%; ex-carbonyl nickel powder a Fisher of 2.06 μm and having an LMRH of 0.35%; ex-carbonyl iron powder having a Fisher of 4.00 μm and having an LMRH of 0.23%; manganese electrolytic powder having a Fisher of 2.80 μm and having an LMRH of 0.23%, mixture of powders, manufactured from the above powders and the content of Co, Ni, Fe and Mn of which are given in the Table I, below, - powders according to the invention, the composition of which is given in Table II below, when these powders are prepared via the oxalate route, and in table III below, when these powders are prepared via the route hydroxide; these powders have a Fisher of 1.8-2.2 μm; their LMRH are less than 2.5%. The powders are sintered by pressing for 3 minutes 5 to 650, 700, 750, 800, 850 or 900 ° C under a pressure of 35 MPa in a graphite mold. The Vickers density and hardness of all the sintered parts was measured. A large number of parts was also subjected to the cross-joint test in accordance with DIN / ISO 10 3325: the sintered bar of 45 x 10 x 6 mm is placed so that it rests freely on two 25 mm separate supports and the load It is applied in the middle part of this separation by means of a punch until the piece fractures. The results are given in tables I, II and III, below, the first table 15 refers to the elemental powders (Co, Ni, Fe) and to the powder mixtures, the second table relates to powders of ex-oxalate of the invention and the third table relates to the ex-hydroxide powders of the invention.

Table I Properties of sintered parts made of elemental powders and powder mixtures * the total of the elements of Co, Ni, Fe and Mn is considered as 100%.

Table II Properties of sintered parts obtained from powders of the invention: oxalate root * the total of the elements of Co, Ni, Fe and Mn is considered as 100%.

Table III Properties of sintered parts obtained from the powder of the invention: hydroxide guide * the total of the elements of Co, Ni, Fe and Mn is considered as 100%.

These results show that, after sintering, superior mechanical properties are obtained with the powders previously alloyed according to the invention in comparison with the mixtures of elemental powders. For comparable compositions (see, for example, test No. 14, versus test No. 57), the hardness obtained with the powders of the invention is 2 to 3 times higher than that obtained with powder mixtures. With respect to the failure load, higher values are measured with the previously alloyed powders compared to the mixed powders within the range of 25-35% Co, 50 Ni and 45-55% Fe, - out of this interval, the loads in fault are comparable.

This example relates to the use of a powder according to the invention in the manufacture of diamond tools. The powder obtained in Example 1 is mixed with 1% synthetic diamonds. This mixture is sintered by pressing under vacuum at 800 ° C and 35 MPa.

The microscopic examination of the sintered material shows that the manganese oxide is finely dispersed in the metal matrix, that the diamonds remain intact and that they are firmly embedded in the metal matrix. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following:

Claims (11)

1. The use of a pre-alloyed powder containing iron as a binder in the manufacture of diamond tools by hot sintering, the use is characterized in that the powder has an average particle size of less than 8 μm, measured with the Fisher Sub-sizer. , and a loss of mass by reduction in hydrogen of less than 3% measured according to the standard ISO 4491-2: 1989 and in which it contains, in% by weight, 10-80% of iron, up to 40% of cobalt, up to 60% nickel and up to 15% M, M is present, at least partially, in the oxidized state and represents 1 or more of the elements Mn, Cr, V, Al, Mo and Ti, the other components in the powder They consist of unavoidable impurities.

2. The use according to claim 1, characterized in that the powder has an average particle size of less than 5 μm.

3. The use according to claim 1 or 2, characterized in that the powder contains at least 30% Fe and preferably at least 50%.

4. The use according to claim 1, 2 or 3, characterized in that the powder contains up to 30% Co.

5. The use according to claim 1, 2, 3 or 4, characterized in that the powder contains 10-30% Ni.

6. The use according to any of claims 1 to 5, characterized in that the powder contains up to 10% M, preferably up to 5%.

7. The use according to any of claims 1 to 6, characterized in that the mass loss is less than 2%.

8. The use according to any of claims 1 to 7, characterized in that the powder is prepared by heating, in a reducing atmosphere, a clear hydroxide or a mixed oxalate, of its constituents.

9. The use according to claim 8, characterized in that 0.05-3% carbon is added to the powder in the form of an organic compound.

10. The use according to any of claims 1 to 9, characterized in that the sintering is carried out at 650-1000 ° C.

11. A pre-alloyed powder containing iron, characterized in that the use thereof forms the objective of claims 1 a.