DE2415553C3 - Process for the production of a hard metal powder - Google Patents

Description

55

The invention relates to a method for producing a hard metal powder for producing hard alloys containing binder metals based on nitride in the presence of transition metals Group VI of the periodic table.

The constructive application of new high-temperature materials is compared to those used for their processing Cutting materials constantly increasing demands, which are met by new hard material alloys seeks to encounter. The development tends towards harder and harder alloys, but theirs comparatively low elasticity is still a major problem. In this context Attempts have become known instead of those usually used as hard material components Carbides of metals of group IVa, Va and VIa of the periodic table of their nitrides and carbonitrides to use. It was found that the nitrides of the metals mentioned did not have the hardness of the corresponding Reach carbides, but exceed them in terms of elasticity. In addition, the nitrides exhibit their use as a cutting tool has a slight tendency to weld with the running chip. It was also known that carbonitrides with a certain ratio of nitrogen to Carbon show a favorable combination of hardness and elasticity.

The carbonitrides and nitrides, however, have the disadvantage, at least superficially, as oxycarbonitrides or oxynitrides, which are very stable and of the alloys used as the binder metal phase are very poorly wetted, which results in brittle sintered hard metal bodies.

Therefore, great efforts have been made to improve the wettability of the nitride-containing hard materials to improve. A well-known method aimed in this direction (DT-AS 2005 707) attempts the To improve the wettability of hard material powders by enveloping the powder particles with a metal carbide layer which is easily wettable by binding metals will.

According to a known method (DT-OS 2043 411) of the type mentioned, is already oxygen-poor nitrides and carbonitrides assumed. Low-oxygen nitrides are obtained on best from the pure metal components or the corresponding metal hydrides and purified Nitrogen. The temperatures required for the technical production of the nitrides are between 1400 and 1800 ° C. Oxygen firing produces carbonitride from the nitrides and vacuum-cleaned carbides obtained in this way, again with temperatures of the same order of magnitude are necessary.

However, the nitridic and carbonitridic raw materials obtained in this way contain still remains of oxygen and must therefore be followed by a refined annealing treatment in the presence of metals of the chromium group, which have a deoxidizing effect will.

Only these nitridic and carbonitridic end products result together with binder metal alloys from metals of the iron group and metals of the chromium group a satisfactory hard metal approach. The known method described has the disadvantage that to produce a useful Hard material component at least two high-temperature reactions are necessary, which is what the process makes costly. It has therefore, as well as the mentioned method of coating nitrides, not yet found broad technical application.

The object of the invention is therefore to provide a method for producing a hard metal powder based on nitride indicate which one is easier and cheaper to carry out.

Based on the surprising and inventive knowledge that in the present of a metal of the iron group, the nitridation of refractory metals even at low temperatures and short reaction times leads to nitrides with an almost theoretical nitrogen content and the like

Nitrides will show good wettability during sintering This object is achieved in that in a method of the type mentioned above, a powdery Transition metal of group IV and / or V of the periodic table or a mixture of these substances in Presence of transition metals of group VI of the periodic table and a powder mixture of finely divided Binding metals of the iron group nitrided by reaction with a nitrogen-containing gas will.

The reaction here is preferably at one temperature carried out between 600 and 1250 ° C. The low temperature compared to the known process means not only a reduction in the technical effort, it also biotet for the first time Completely new possibility to use the hard material component in the presence of the binding metal component from metals of the Iron groups that melt in the vicinity of 1500 ° C. Compared with the conclusion of With the known method of simple nitriding reaction, the finished hard metal powder is thus already in place before. All in all, the method according to the invention is suitable for hard material alloys containing binder metal more than before for technical recycling.

Nitriding can be carried out at normal and overpressure in a fixed bed, fluidized bed or fluidized bed process as well as under reduced pressure in a suitable foot or fixed bed process will.

According to a preferred embodiment of the process according to the invention, the reaction is carried out in a first step over a period of between 1 and 6 hours, preferably 2 and 4 hours, at a temperature between 600 and 900 ° C., preferably 700 to 800 ° C., and in a subsequent step second step over a period between 1 and 12 hours, preferably 2 to 6 hours, at a temperature between 900 ° and 1250 ° C, preferably 1000 to HOO ⁰ C is performed. It is particularly advantageous in the first step to use a nitrogen-containing gas, for example NH ₃ , which disproportionates under the catalytic effect of the finely divided binding metal of the iron group, and in the second step, nitrogen under a pressure of between 1 and 20 atmospheres. By using a nitrogen-containing gas, such as NH, which disproportionates due to the catalytic effect of the binding metal, in the presence of any oxides-reducing hydrogen, an increased amount of nitrogen is obtained in statu nascendi.

Since wettability and certain other physical properties, such as e.g. B. Melting point, electrical Conductivity, wear resistance, of the nitrides due to the inclusion of carbon, d. H. through Formation of a nitride-carbide mixed crystal, further improved, proposes the invention for the production These carbonitrides are preferred before that a carbon-containing gas, before, during or after is fed to the nitriding. The desired ratio between N and C in the carbonitrides can on the composition of the gas phase or on the duration of action of the N or C releasing components being controlled. On the other hand, particles made of pure nitride are obtained with a good wettability outer layer of a carbonitride by first carrying out the two nitriding process steps described above and then the nitrogen-containing gas is replaced by a carbon-containing gas, causing partial degradation of the gas in the outermost layer of bound nitrogen and an incorporation of carbon This process is much easier than the well-known coating of nitrides with a metal carbide.

In another advantageous embodiment of the invention, a gas phase can be used to generate the gas phase Gas containing nitrogen and carbon, e.g. B.

ίο methylamine, can be used. Methylamine has here the advantage of being easy to disintegrate, the same amount of carbon and nitrogen and less in terms of atomic percentage Containing hydrogen as other amino hydrocarbons.

Came with an advantage? the inventive method can also be carried out in such a way that the powdery metal batch is still powdery bimetallic carbides Transition metals of group V and / or VI of the periodic table and / or monometal carbides of

ao contains transition metals of group V and / or VI of the periodic table.

The dimetallic carbides react through the action of nitrogen or nitrogenous gases N incorporation to carbonitrides with a C / N ratio

a5 nis of at least 50 ⁰ Zo C.

The presence of small amounts of free carbides also increases the hardness of the carbonitrides.

The hard metal powder, which according to the invention Procedures produced can be processed using known methods of powder metallurgy by either sintering them as they are or by adding more to them beforehand Powders of any binding metals and / or hard materials mixed or mixed.

Instead of the powder batches according to the invention in loosely agglomerated or granulated form of nitriding and / or to be subjected to carbon nitridation, the powder batches can also be pressed into shaped bodies and then treated and sintered by the method according to the invention.

The invention is to be explained further with the examples given below.

example 1

A powder mixture of 85 parts of Ti, 15 parts of Mo and 15 parts of Ni is heated to 800 ° C. in a high vacuum. While maintaining this temperature, purified NH ₃ is passed through the sieve bottom of the reaction vessel at normal pressure for 2 hours.

The temperature is then increased to 1100 ° C. over 4 hours and a mixture of N ₂ / CH ₄ in a ratio of 5: 1 is introduced under an overpressure of 5 atm. The chemical analysis of the powder showed 12.5 _{% N 2} and 3.4%> C. After the

pressing the powder was pre-sintered at 900 ° C for 30 minutes under NH ₃ and sintered in a vacuum of 10 " ¹ Torr for 2 hours at 1350 ° C. The hardness of the polished body was 1450 to 1500 HV 2 with a bending strength of 100 to 120 kp / mm ² .

Example 2

In a planetary ball mill, 24 parts of Ti, 34.8 parts of TiC, 14.4 parts of Ni, 18.8 parts of Mo, 2 parts of Cr and 10 parts of Ta are mixed and processed with an organic solvent to give free-flowing granules. The granulate is heated to 750 ° C. _{under purified N 2} in an inductively heated fluidized bed furnace. After a hold time of

The mixture is heated to 1100 ° C. for 1 hour at a rate of 5 deg / min and held for 3 hours while maintaining the fluidized bed. After cooling below N «, the granules are pressed in the usual way and sintered under 1 atm N, overpressure at 1450 ° C. for 45 minutes. A hardness of 1400 HV 2 \ ind a flexural strength of 120 to 130 kp / mm ^{i was} determined on the test specimens.

Example 3

As described, 33 parts of Ti, 14 parts of Ta, 5.6 parts of Hf, 5 parts of W, 1 part of Cr ₃ C ₂ , 12 parts of Mo, 12 parts of Ni and 5 parts of Co are mixed, ground and granulated. The granulate is placed in a _{rotary kiln heated to 850 ° C. and through which N 2} flows, the average usage time being 4 hours. The hard metal powder pre-nitrided in this way is briefly ground and pressed to form shaped bodies. The molded bodies are heated in a vacuum furnace at 1100 ⁰ C and reacted for 3 hours by 400 Torr methylamine to react ίο After pumping of the reaction gas is sintered 1 hour in a vacuum at 10 Torr at a temperature of ² ° C 140UE.

Claims (7)

Patent claims: 1. Process for the production of a hard metal powder for the production of binder metal-containing Hard material alloys based on nitride in the presence of transition metals of group VI des Periodic table, characterized in that a powdery transition metal of group IV and / or V of the periodic table or a mixture of these substances in the presence the transition metals of group VI of the periodic table and a powder mixture of finely divided Binding metals of the iron group by reaction with a nitrogen-containing gas is nitrided. 2. The method according to claim 1, characterized in that the reaction is carried out at a Temperarur 600-1250 ⁰ C. 3. The method according to claim 2, characterized ge ao indicates that the reaction in a first step for 1 to 6 hours, preferably 2 to 4 hours, at a temperature of 600 to 900 ° C, preferably 700 to 800 ° C, and in a subsequent second step for 1 to 12 hours, preferably 2 to 6 hours, at a temperature of 900 to 1250 ° C, is carried out preferably 1000-1100 ⁰ C.. 4. The method according to claim 3, characterized in that in the first step a gas containing disproOOrtionierendes nitrogen under the catalytic effect of the finely divided binding metal of the iron group, for example NH ₃ , and that in the second step nitrogen is supplied under a pressure between 1 and 20 atm. 5. The method according to any one of the preceding claims, characterized in that a carbon containing gas is supplied before, during or after the nitriding. 6. Procedure according to one of the preceding 4 » claims, characterized in that a nitrogen and carbon to generate the gas phase containing gas such as methylamine is supplied. 7. The method according to any one of the preceding claims, characterized in that the powdery Metal base still powdered bimetal carbides of transition metals of group V and / or VI of the periodic table and / or monometal carbides of transition metals of groups IV, V and VI of the periodic table can be added.