DE2115999B2 - USE OF TUNGSTEN POWDER FOR SINTER HARD METAL HIGH BENDING STRENGTH AND HARDNESS - Google Patents

Description

tion of the corresponding metal halides in the gas - low flexural strengths of hard metals phase with a defect in the hard metal structure consisting essentially of hydrogen, standing reducing gas, in which the metal - being a primary cause of the low flexural strength halide, the reducing gas and possibly pores in the hard metal are. It is also known other gases, before they enter a reaction chamber, are contaminated hard metal merges that are difficult to melt in one or more lines with each other carbides tend to be a larger number of are mixed, which is characterized by pores during the sintering process as that the gases or the gas mixture before their (his) if with pure, hard-to-melt hard metal entry is worked in the reaction chamber to a temperature of 30 carbides. In particular, step overhead brought the reaction temperature and the-like pores then when the carbides with oxides Particle size of the resulting metal powder are contaminated by, e.g. B. silica, which ge control one or more parameters of the gas shared with carbon at elevated temperatures mixture, such as its mixing ratio, its gaseous products. Furthermore one has Flow velocity and its temperature, so found that carbide grains of too large a grain like possibly by means of the temperature within size in a non-homogeneous structure as a crack generator the reaction chamber is regulated. That work in the and therefore low flexural strength values Process described in the main patent will cause preferential treatment.

wisely carried out in such a way that the re-The purity of

The gas mixture introduced into the action chamber of a temperature-generated tungsten carbide can be significantly improved in order to achieve a good temperature of at least 300, preferably of a minimum, flexural strength values. For this purpose, at least 350 ° C, whereby according to further preferred but cost-increasing additional process configurations, the temperature of the gas mixture is required in the carburizing process, either by heating or cooling the gas in the post-treatment of the tungsten carbide gas lines, for example, or by adding gas after generation in hydrogen gas with increased form halogen during the reaction, the temperature is increased, optionally in combination with the. The reducing gas used can use a vacuum. When using this with hydrogen chloride gas, gaseous nitrogen or process, it is possible, in the case of coarse-grained, another inert gas to be diluted, and the Tempe-hard metal alloys with about 10% binding nature adjustment can be made so that they metal within 50, e.g. B. cobalt, flexural strength values of up to the reaction chamber in the direction of flow of the reaction to 350 kg / mm ² and hardness values of about 1200 to gas increases. 1250 kg / mm ² to be achieved. The application of such

The invention now represents a further embodiment of additional and special process stages in the Verdes However, the course of the carburization process described in the cited main patent entails a process insofar as the various disadvantages associated with this process, quite apart from the ren manufacturable tungsten powder then on the already mentioned cost increase. So come together known way carburized and shared with, for example, difficulties as a result of breaking or Binding metals and possibly other hard grinding of the carbide cake during preparation metal compounds is sintered (see »Journal of the Sintering Process in such a way that during the für Metallkunde «, 48, pp. 615 to 624, [1957]), under 60 sintering process the carbides generally form a grain formation of a cemented carbide with a high bending growth, which leads to a non-uniform strength and hardness. Microstructure leads, which in turn cause a

The recent development of modern technology, deterioration in the flexural strength and hardness of the i \ e , has resulted in the properties of the work-preserved cemented carbide.

fabrics and construction materials, e.g. B. Schnell- 65 Commonly known cemented carbides, made from Turning steels and high-strength alloys, elevated tungsten carbide powders, produced from tungsten, the Orders are placed. The consequence of this is, again, due to the reduction of tungsten trioxide The works holdings also have to meet increasingly stringent requirements, often not having a

3 4

granular microstructure, which is based on the fact that the grain system with a high thermodynamic «! Stability growth of the carbide grains is obtained strongly from the sintering. No temperature is affected within this system. So it has been shown that or at most only a slight congrowth. A high sintering temperature generally leads to a This effect is based on the fact that, due to the narrow • considerable increase in grain growth, which has very little or no particle size distribution, the hard metals obtained have fine grains available, which dissolve only a few Have flexural strength. In order to avoid small and larger grains, as is the case with flexural strength, it is therefore necessary to precisely control the sintering temperature using conventional tungsten carbide powders with a wide range. In addition, the particle size distribution is the case. Sintering tests, the construction of the furnace must be such that only low temperature gradients can occur at temperatures of 1300 to 1500 ° C. At shows that Wolf use of batch furnaces produced by conventional methods, for example, in ram carbide powder can tend to have a considerable grain growth in most cases only part of the furnace space at elevated temperature while the furnace is being used. In summary, the tungsten carbide powder used according to the invention thus shows that the known method shows no or no substantial core growth and has some serious disadvantages. _{although also} ^ _n j _c ij _t ^ increased sintering temperature.

_{It is also known that tungsten powder can be produced by the tungsten ride (WCl 8} ) generated by the process according to the main patent plasma hydrogen reduction of tungsten hexachloride registration via the halide. Such tungsten powder powder is particularly advantageous because it has no practical interest, and 20 technical scale in very high purity is not obtained because this powder can be. The consequence of this is that during the extp-m small particle sizes are characterized, the sintering process practically no pore-forming activities, for example, significantly below 0.1 μm, actions can occur.

can. According to the invention, for example, the sintering task of the invention is to produce cemented carbides based on tungsten carbide, e.g. with 13%> tungsten carbide, the improved physical cobalt as the binding phase, with flexural strength values, and in particular a high flexural strength of over 350 kg / mm ² and have hardness values of approximately strength and hardness. "Use 1400 kg / mm ^2. These values are exceptional. It has now been shown that this task can be achieved in a fairly high manner compared to flexural strength by using about 300 kg / mm ² and hardness values from driving according to the main application P 20 23 958.1-24 about 1150 kg / mm ² , the tungsten powder available with conventional hard metals for the production of the same carbide content and the same binder cemented carbide with a high flexural strength and phase and practically the same average hardness In practice one proceeds in such a way that it has been shown that, depending on the particle size, an increase in the flexural strength according to the method mentioned at the beginning and according to the main application P 20 23 958.1-24 obtained Wolf hardness of 10 to 25% compared to the remaining powder, which is achieved through a narrow particle size borrowed known hard metals It has also surprisingly been found that, within the technically important range of we- 40, high flexural strength values of over 350 kg / mm ^{2 are} less than 0.1 up to several microns (e.g. B. up to 2 in combination with high hardness values of over or 3 μηι) can be easily regulated, in itself 1400 kg / mm ² can be achieved, in particular in a known manner carburized to tungsten carbide, wor- if for the production of carbides with very fine Teilaus then by sintering a cemented carbide with a particle size, e.g. B. tungsten carbide with a particle particularly advantageous combination of high 45 size of less than 1 μm, in particular of weni hardness and high flexural strength are obtained ger than 0.5 μm. As a result of her can. It has been shown that sintered carbides produced in this way are suitable for excellent mechanical properties, in addition to the advantageous mechanical properties mentioned, which can be produced according to the invention, have an extremely homogeneous microstructure for machining special high-speed materials, which steel and which are particularly largely insensitive to cutting others compared to hard materials.

change in the sintering temperature. The sintered hard-

for example, e shown that within a range of metals are also common cemented carbides above-

around 1300 to 1500 ° C no or at most only a place that is created by a recarburization process

very little grain growth occurs. 55 were begotten. While in certain cases by

Particularly narrow particle size distributions mean that cemented carbides produced by recarburization have good bending properties.

can be achieved by having the fine-grained, from may have strength values, they have

tungsten powder obtained from the halide with a hardness value that does not have the advantageous hardness values

Particle size of less than about 1 μm, in particular sintered carbides that can be produced

which have less than about 0.5 μm, at temperatures above ⁶ °. The difference in hardness values is included

half 1400 ° C with gaseous hydrogen carburizes about 10 to 25 ° / o and is of fundamental importance.

(The particle sizes given here were, if used for cemented carbides used there,

nothing else is specified, by means of an elec-

electron microscope). That z. B. when turning metals. An essential one The tungsten carbide powder obtained can now be, for example, the factor of even greater importance

wisely mixed with cobalt and used to reduce production costs incurred by

of a carbide with the desired properties this application is made possible,

be subjected to the sintering process, with a Das for the subsequent carburization to tungsten

Tungsten powder required for carbide can be, for example, The method is preferably carried out in such a way that

prepare as follows: that the metal halide, preferably the chloride,

In a nickel tube that connects to the chamber one with the reducing gas. in a line verauf 1000 ⁰ C heated reactor was connected, was is mixed oObei the metal halide gas and a stream of 22 kg WCl _e gas per hour with a 5 reducing gas having such a temperature, current of 961 H ₂ per minute ( based on room - that the temperature of the mixture is mixed above the retemperature). The tungsten chloride gas action temperature of the mixture is that the buttocks have a temperature of 400 ° C and the water mix from the line in a reaction chamber material gas emc temperature of 525 ° C. This results in the particle size of the nickel tube being produced Before entering the metal powder, the mixture had a temperature of about 440 ° C in the line by adjusting the mixing ratio in the reactor chamber, the flow rate taking into account the heat transfer to the speed of the mixture in the line and / or the environment. The rate of introduction of the gas temperature of the mixture regulated in the line into the reactor was about 25 m / sec. The reaction is that the mixture of tungsten powder formed in the reaction chamber had a chlorine content of 15% and that the metal formed of about 0.25%, a particle size of 0.2 μm and powder from the gaseous reaction products has a bulk weight of about 1.32. is separated.

In the nickel tube, a gas Ar. By means of preliminary tests, it is really possible to produce a shaped mixture in which the minimum temperature can be determined at one temperature at which the temperature takes place above the reaction temperature of the Mi-reaction. So you can, for example, the schung, for example at a temperature of tungsten halide in a quartz tube ol'en below about 440 ^? Heat a slow stream of hydrogen gas towards the approximate reaction temperature. The temperature of the reaction components from 300 to the resulting metal powder is collected in a 350 ° C, the reaction components practically quartz wool plug. Traces of tungsten had not yet reacted, whereupon after the introduction of metal, a spontaneous reduction of 300 to 330 C could be determined within a temperature range of the mixture in the reactor, whereby the formation of HCl could also be detected from the tungsten halide to tungsten powder,
narrow particle size range took place. The minimum reaction temperature between the desired particle sizes can thus be achieved by ramchloride and hydrogen gas, so that initially as homogeneous a mixture as possible in the temperature range from 330 to 330 ° C. is produced, in which the reaction particles lie. However, it is not expedient to produce a gas component premixing in a predetermined ratio with the minimum temperature, and by setting certain temperatures, but rather the mixing temperature of the gas in the and feed speeds. Mixing tube by, for example, 20 to 150 C above

In this process, the Woiframhalo- 35 can raise the minimum reaction temperature. These

genid, especially tungsten chloride, and the redu- Temperatures are also applicable to other halides than

ornamental gas can be used in an advantageous manner before their one tungsten chloride.

enters the reactor in one or more tube- After the process, a metal powder can be used

lines are mixed with each other, the most expedient for industrial use

Mixing takes place at a temperature that is above the particle size range by adjusting the vari-

half of the reaction temperature of the gas mixture. Easily produce ablcn of the gas mixture, e.g. B. can-

It is clear that the reaction conditions already nen metal powder with a particle size of 0.05

present in this or these mixing lines until 10 μΐη are obtained.

and that the reaction in this or these already The mixing ratio of reducing gas

begins. However, the reaction should not in too large a 45 to halide gas affects the particle size in the

Circumstances in the mixing line take place because we know that with increasing content of reduced

The goal of this mixing is, first, to make a generating gas less. Also is for the little ones

to obtain a very homogeneous mixture and, secondly, particle sizes a relatively small excess

in making a mixture, their mixed-breed shot of reducing gas, usually not

The ratio of which the temperature and temperature of the mixture are more than twice that required for the reaction

speed are such that a powder with a definite stoichiometric amount is required. There-

ned particle size is obtained. It is therefore very economical through the process.

Of course, the flow rate affects the particle size in temperature

of the gas in proportion to the length of the mixture in such a way that it tends to increase with increasing temperature

pipe must be chosen so high that the gas mixture is reduced within 55,
of the mixing pipe before the gas enters

only a minor reaction occurs in the reactor. example 1
After the gas mixture has entered the reactor

are then all necessary for a continuous reaction. A batch of 5 kg of tungsten powder, which is produced in the lordeilichen conditions, and this begins very quickly and is completely produced via tungsten chloride. As a result, with a particle size of around 0.23 microns in many fillings, it is not necessary to additionally increase the temperature in your (BET = determined according to the Brunauer-Emmet-Teller In some cases, however, it may be useful, the reaction of technical chemistry, Vol. 211, 1961, p. 758) was mixed by maintaining a higher reactor 65 with 6.27% carbon and at a hydrogen temperature, for example of more than 600 ⁰ C to gas IV carburized at 1650 ⁰ C for _{2 hours.} The tungsten carbide to be kept at a maximum temperature of 1600 ° C with a particle size of accelerate. _about χ ^ μτη (BET, corresponding to 2.2 um Fisher)

was ground in a ball mill for 35 hours together with 13%> cobalt and 2% wax. The powder mixture was then pressed at a pressure of 945 to 1100 kg / cm ² into flexible bars (6 mm high, 4 mm wide, held by 20 m spaced carriers), whereupon the strips or rods for 1 hour at 950 ° C in one Hydrogen atmosphere were presintered. The actual sintering then took place in a vacuum by heating to 1420 "C for 15 minutes.

For comparison purposes, test strips were used in the same way Way, but this time using tungsten carbide produced in the usual way which has practically the same particle size as the tungsten carbide used in the present invention owned.

The test strips or test sticks produced were tested for their microgel (1500x magnification), Porosity (determined according to ASTM method B 276-54), its hardness and flexural strength checked.

The values given in Table 1 below were obtained:

Tabel

Test sticks according to 1 iMikrogcAddc Porosity *) H _V 3 kg,
kg'mm ⁵ Flexural strength
kg / mm ² invention
State of the art .. uniform
not uniform Al
A3 1398
1248 364 + 18
289 ± 36

*) determined according to the ASTM B 276-54 method

From the measurement results obtained, it is clear that the one used in the present invention Carbide has the greater hardness and the greater flexural strength, with the hardness values and the Flexural strength values are about 12 and 26% greater than the values of the cemented carbide after the Prior art method was generated.

Example 2

In order to illustrate the influence of the sintering temperature on the microstructure and the mechanical properties of hard metals, a test with 5 kg of tungsten carbide, made from tungsten powder with a particle size of 1.8 μm (Fisher) and a corresponding formulation of tungsten carbide, was made according to carried out according to the state of the art. The carbides were each ground in a ball mill together with 13% cobalt and 2% wax for 35 hours, whereupon test bars were produced from the mixtures obtained by pressing at a pressure of 945 to 1100 kg / cm ² . Pre-sintering was carried out by heating in hydrogen gas for 1 hour. to a temperature of 950 "C.

The actual sintering was carried out by 1 '/'hours' heating under vacuum to temperatures of 1350, 1400 and 146O ⁰ C.

The test bars were then described as in Example 1 tested. The following results were obtained:

Table 2 Sinter inventive Micro addc // ₍ , 3 kg'mm ² after this Flexural strength kg mm ² after this temperature used inventive was standing invention was standing no grain According to the state of the art gcmüß of the technique according to of the technique 1350 growth used 1135 used 300 + 10 no grain Grain growth increases with it 1370 343 + 10 1400 growth increased temperature 1130 303 ± IS no grain Grain growth increases with it 1350 360 + 16 1460 growth rising temperature 1030 272 ± 12 Grain growth increases with it 1350 348 ± 12 rising temperature

Example 3

Tested as described in Example 1 The following results were obtained:

55

To illustrate the properties of a finely ground hard metal carbide, a finely ground tungsten powder (0.2 μρ) was produced. The powder was then carburized in the usual way in a carbon tube furnace at 1450 ° C. The particle size of the carbide was 0.4 μm. About 5 kg of the carbide powder were then ground together with 13% cobalt and 2% wax in a ball mill for 35 hours. The preliminary sintering was carried out by heating under hydrogen lstündiges to 950 ⁰ C. The subsequent sintering was carried out by lVsstündiges heating in vacuum at 1380 ⁰ C. The test strips obtained were then

Microstructure porosity ff "3 kg
kg / mm ² Bend
strength
kg / mm ⁵ Uniform
Tungsten carbide
grains
(<0.5 mm) Al 1480 364 + 17

This example shows that carbide grains are very uniform through the use of the present invention can be obtained in a simple and economical manner, the grains being compared to

known more complicated and expensive processes are of high quality.

Particularly advantageous results are obtained when at a temperature of about 1350 is sintered up to 1460 ° C.

According to the invention, hard metal systems can be produced in which the binding metal consists of a metal from the iron group, namely iron, nickel or cobalt, this metal or its alloys preferably being 2 to 30 ⁿ / o, based on the hard metal, ie the hard metals preferably consist of about 2 to 30 ¹ Vo of one or more of the specified metals and the remainder of tungsten carbide. Cobalt has proven to be particularly advantageous as a binding metal. Particularly advantageous hard metals are those arrival of tungsten carbide with about 2.5 to 6.5 ⁰ Zo cobalt, or 6.5 to 15 "Zo cobalt or even 15 to 30 ⁰ Zn cobalt Optionally, minor amounts

whose carbides are present, for example TiC and / or TaC, ie if a hard metal ^{consists of 2 to 30 0} Zo of one of the specified binding metals and the remainder of tungsten carbide, this means that such carbides are included in the remaining ⁽ ) 8 to 70 ⁰ zo carbide may be included.

Typical examples of advantageous tungsten carbide-cobalt sleeves used according to the invention are those of the following composition:

⁰ Ai cobalt

5 rest toilet

10 rest toilet

15 rest toilet

20 rest toilet

25 rest toilet

30 rest toilet

In addition to tungsten carbide, the carbide content can also contain smaller amounts of other carbides.

Claims (1)

witnesses for the processing of these materials and construction claims: structural materials are provided, d. H. the materials, the z. B. for cutting, processing and using the according to the method according to form the workpieces and construction materials Patent application P 20 23 958.1-24 produced 5 are required. The research and development of tungsten powder for the production of sintering work in the field of hard metals metal of high flexural strength and hardness. primarily aimed at the physical properties the hard metals, especially the hardness and Flexural strength, to increase. However, since it has been known ίο is that with an increase in the hardness of the cemented carbides is associated with a reduction in flexural strength, The invention relates to the use of the, after it has become common practice, a comprodem Process according to the main patent application is inappropriate with regard to these two properties P 20 23 958.1-24 manufactured tungsten powder for close. the production of cemented carbide of high 15 In practice it is not uncommon to produce cemented carbides with flexural strength and hardness. Hardness values of up to 1800 kg / mm ² (H _v 3 to 30 kg The subject of the main patent mentioned is a load) and flexural strengths of about 150 kg / mm ² . In the case of hardness values around powder of the metals tungsten, molybdenum, tantalum, 1000 kg / mm- ', the corresponding flexural strength niobium, rhenium and chromium and the alloys 20 are up to 300 kg / mm ² . It has been known for several decades that the