HRP20220467A1 - HARD METAL COMPOSITION WC-1.0Cr3C2-0.2Co AND ITS APPLICATION - Google Patents

Abstract

The subject invention discloses a process for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr<SUB>3</SUB>C<SUB>2) and cobalt (Co) powders. The composition was chosen to be WC - 98.8%. wt. with an average grain size of about 150 nm, Cr3C2 – 1.0% wt. which is used in the mixture as a grain growth inhibitor, and Co – 0.2% by weight. The mentioned process produces hard metal with composition WC-1.0Cr<SUB>3</SUB>C<SUB>2</SUB>-0.2Co<B> </B>mainly<B> </B>without pores, density 15.55 g/cm<SUP>3</SUP>, hardness 2590 according to the Vickers method, by sintering by hot isostatic pressing at a temperature of 1600°C, which is approximately 200°C lower sintering temperature than is usual in the state of the art. This material is extremely suitable for the production of nozzles used for water jet cutting. The related invention discloses a process for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr<SUB>3</SUB>C<SUB >2</SUB>) and cobalt (Co) powders. The composition was chosen to be WC - 98.8%. wt. with an average grain size of about 150 nm, Cr3C2 – 1.0% wt. which is used in the mixture as a grain growth inhibitor, and Co – 0.2% wt. The mentioned process produces a hard metal with composition WC-1.0Cr<SUB>3</SUB>C<SUB>2</SUB>-0.2Co, mostly without pores, density 15.55 g/cm<SUP>3</SUP >, hardness 2590 according to the Vickers method, by sintering by hot isostatic pressing at a temperature of 1600°C, which is approximately 200°C lower sintering temperature than is usual in the state of the art. This material is extremely suitable for the production of nozzles used for water jet cutting.

Description

The field of technology

This invention discloses a specific process for obtaining hard metal composition WC-1.0Cr3C2-0.2Co as well as its specific use. Considering the composition of this hard metal where the main constituent is tungsten carbide (WC), this invention belongs to the field of alloys based on carbides, especially tungsten carbide. With regard to the specific method of obtaining, the subject invention belongs to the field of powder metallurgy, where all the materials used are initially in powder form, and which are consolidated into the desired hard metal by the sintering process.

Technical problem

The production of tungsten carbide dates back to the early 1920s when the German electric light bulb company Osram was looking for a replacement for the expensive diamond nozzles (tools) used in the production of tungsten wire. Efforts to replace diamond led to the invention of carbide, which many companies soon began producing and marketing for multiple applications. Its high wear resistance was crucial for its wide application.

The first compositions based on tungsten carbide and cobalt were soon used as materials in the production of tools for cutting and grinding cast iron. In the early 1930s, pioneering hard metal production companies introduced hard metal compositions into steel mills, where these then new and revolutionary materials, in addition to cobalt and tungsten carbide, also contained tantalum and titanium carbides. This was followed by special carbide tipped mining tools that extended the life of rock drills by a factor of at least 10 compared to conventional steel-based drilling tools.

Over time, other applications followed, such as, for example, the application for making nozzles for water cutting. Water jet cutting is one of the non-standard methods of processing metals and hard materials, which are based on the process of mechanical material removal. Abrasive water jet is a thin jet of a mixture of water and flint sand under high pressure, which acts on the work piece being processed and removes the base material by erosion, thus making a cut on the mentioned material. Waterjet cutting is used for cutting metals (stainless steel, aluminum alloys, hardened steel, copper and brass - up to 150 mm thick), hard metal, glass, stone (e.g. granite), polymer, rubber, wood, etc. Water cutting does not heat the material, which is especially useful for steels that are intended for subsequent heat treatment. It is clear to the average expert in the field that the nozzle, which is sometimes called a mixing tube, must be resistant to wear in order to perform its job efficiently for a certain period of use, after which it is of course replaced due to wear and tear.

The basic technical problem that is solved by the present invention relates to the consolidation of hard metal composition WC-1.0Cr3C2-0.2Co, so called. sinter-HIP process (sintering via Hot Isostatic Pressure) in one cycle, where the sintering temperature is about 200°C lower than the usual sintering temperature of materials of similar composition, and with a technological result which is at least as good as the one at elevated temperature, and is manifested in hard metal - a product without pores. Namely, it is known that the sinter-HIP process is used mainly to obtain carbides with little or almost no porosity and with a density that is close to the theoretical density for the given composition. The procedure in question has been proven, as we will see, to give the same result with a significantly lower temperature of the procedure.

The second technical problem, which is solved simultaneously with the first problem, relates to the actual application of the thus obtained material WC-1.0Cr3C2-0.2Co for the formation of nozzles for water cutting. The solution to the mentioned technical problems is found in the preparation of the sintering mixture, as we will see in the detailed description of this invention that follows below.

State of the art

In the state of the art, materials close to the composition specified in this document are known.

The Chinese patent application published as CN113061764A for the invention TUNGSTEN CARBIDE-BASED HARD ALLOY AND PREPARATION METHOD THEREOF teaches the preparation of a material where tungsten carbide (WC) is added from 0-1.5% by weight. chromium carbide (Cr3C2), 0.0-2.0% by weight. vanadium carbide (VC) or titanium carbide (TiC) and between 0-1.5% by weight. cobalt (Co) or nickel (Ni). In example 6 of the document of the same name, the composition WC-0.8Cr3C2-0.5VC-0.2Co is specified, where a mixture of Cr3C2 and VC is used as a grain growth inhibitor, and n-hexane or acetone is used in the homogenization process. This document shows that sintering is performed in two steps, the first up to 1540°C and the second at about 1800°C, with a pressure of 240 MPa. The difference between the subject invention and CN113061764A is in the sintering temperature, although the materials are of very similar composition with the already mentioned 0.2% by weight. Co.

The US patent application published as US2014072469A1 for the invention INERT HIGH HARDNESS MATERIAL FOR TOOL LENS PRODUCTION teaches about a material whose composition can be written as WC-0.16%Co-0.95%Cr, and the mixture contains carbon in the range of 5.85-6.13 % wt. The amount of Co is close to that of the invention where the cobalt content is specified as 0.2% by weight. As written in the description of the mentioned state of the art document, typical sintering temperatures for the mentioned materials range from 1300°C-1850°C, but quality densification is obtained only in the range of 1600°C-1700°C. Basically, this document specifies, for a given weight composition, temperatures that are generally substantially above 1600°C.

2017 paper, Ma, R., Ju, S., Chen, H., & Shu, C.: “Effect of Cobalt Content on Microstructures and Wear Resistance of Tungsten Carbide–Cobalt-Cemented Carbides Fabricated by Spark Plasma Sintering ", IOP Conference Series; Materials Science and Engineering, 207, 012019. doi:10.1088/1757-899x/207/1/012019; teaches about WC-Co carbides with little or no binder in the form of cobalt (Co), i.e. 0% wt., 0.2% wt., 0.5% wt. and 0.8% by weight, and equivalent sintering procedures, especially through SPS (spark plasma sintering). In the mentioned document in table 2 there are process parameters which for the composition of WC-0.2 % wt. Co still show a temperature that is higher than 1600 °C, specifically by 5%, and is around 1680 °C. This work is significant because it indicates the fact that increasing the proportion of Co in WC-Co materials reduces the required sintering temperature. However, this document does not talk about densification and the absence of pores in the obtained samples according to the disclosed procedure, which is an extremely important characteristic if the mentioned material is to be used to form nozzles for water jet cutting.

Paper from 2012, Poetschke, J., Richter, V., & Holke, R.: "Influence and effectiveness of VC and Cr3C2 grain growth inhibitors on sintering of binderless tungsten carbide." International Journal of Refractory Metals and Hard Materials", 31, 218–223. doi:10.1016/j.ijrmhm.2011.11.006; examines the influence of VC or Cr3C2 as a grain growth inhibitor on the microstructural characteristics of WC materials. From table 1 of the same work, it can be deduced that the preferred proportion of Cr3C2 of 1% by weight. gives 100% desnification, without abnormal grains in the product, which makes it suitable for various applications.

2020 paper by Lay, S., Antoni-Zdziobek, A., Pötschke, J., & Herrmann, M.: "Microstructural investigations in binderless tungsten carbide with grain growth inhibitors", International Journal of Refractory Metals and Hard Materials, 93, 105340. doi:10.1016/j.ijrmhm.2020.105340; describes WC without Co content, but with 1% wt. Cr3C2. It should be said that in the description of the method, especially in the process of grinding the ingredients, contamination of powders with cobalt (Co) of about 0.05% by weight was subsequently found. which comes from used ball mills. Such a "contaminated" mixture with a proportion of Co which is four times lower than that according to the invention, was sintered at temperatures of around 1900°C and 100% densified samples were obtained.

None of the above-mentioned state-of-the-art documents explicitly discloses the WC-1.0Cr3C2-0.2Co material, which is sintered at a relatively low temperature of 1600°C, and which is completely pore-free. The solution to this technical problem will be given in detail in the description of the invention.

The essence of invention

The present invention relates to a new process for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr3C2) and cobalt (Co) powders. The composition was chosen to be WC - 98.8%. wt. with an average grain size of about 150 nm, Cr3C2 – 1.0% wt. which is used in the mixture as a grain growth inhibitor, and the rest is Co – 0.2% by weight. This procedure consists of the following steps:

A. preparation of the mixture of starting powders,

B. mixing and homogenization without contamination in order to create a homogeneous microstructure, with the addition of heptane (CH3(CH2)5CH3) and optionally paraffin wax up to a maximum of 0.5% by weight. mixture ratio, in a ball mill,

C. drying the mixture in order to eliminate the liquid phase of heptane by vacuum distillation,

D. granulation using a sieve, which aims to bring the mixture of powders into a flowable state, and

E. molding by pressing or extrusion, which defines the final shape of the product, and is carried out at a temperature of 15-30°C.

F. pre-sintering – removal of previously optionally additional paraffin wax, and the step of heating the product up to 800°C in a vacuum or hydrogen atmosphere,

The product formed in this way is subjected to the sintering process in several steps:

G. heating the product up to 1200°C in a vacuum,

H. heating from 1200°C to 1600°C in an atmosphere of argon (Ar) at a pressure of 10 mbar for 30 minutes, and

I. sintering by hot isostatic pressing at a temperature of 1600°C and a pressure of 80-100 bar for at least 45 minutes.

As a result of the process, a hard metal of composition WC-1.0Cr3C2-0.2Co is obtained, mostly without pores, density 15.55 g/cm3 and hardness of about 2590 HV determined according to the Vickers method.

It is preferable that step B. is carried out for at least 72 hours. Furthermore, it is preferable that step C. is carried out at a temperature of about 80°C, and step D with a sieve of approximately 315 μm. Step E. is carried out at room temperature under a pressure of about 200 MPa if it is about pressing.

The product obtained according to the process in question can, among other things, be shaped as a nozzle used for cutting with a water jet in step E. of the process itself.

Description of the drawing

Figure 1 shows the microstructure of sample PL38-02, a sample of composition WC-1.0Cr3C2-0.2Co obtained by the process according to the subject invention with a sintering temperature of 1600°C, where the characterization was carried out using the FESEM technique.

Figure 1A shows the sample PL38-02 obtained by the process according to the subject invention with a sintering temperature of 1600°C, where the characterization was carried out with an optical microscope, and where the absence of pores on the sample can be seen.

Figure 2 shows the PK109-01 sample obtained with a sintering temperature of 1600°C, where the characterization was performed with an optical microscope, and where the presence of pores on the sample is clearly visible. The sample's input composition is identical to that of sample PL38-02, but the procedure in step B. took about 3 times less time, about 24 hours.

Figure 3 shows the sample PK111-01 obtained with a sintering temperature of 1600°C, where the characterization was carried out with an optical microscope, and where one can see an even greater presence of pores on the sample compared to the samples PL38-02 and PK109-01. The sample's input composition is identical to that of sample PL38-02, but the procedure in step B. lasted about 3x shorter, about 24 hours, and the powder used in the WC batch was initially of smaller particle size and larger specific surface area.

Figures 4, 4A; 5, 5A and 6 and 6A show samples PL38-01, PK109-02 and PK111-02, the same composition as in Figures 1-3, the same powders and the same procedure/treatment in step B. However, the sintering temperature of this control group was 1800°C. The images clearly show the absence of pores - Figures 4A, 5A and 6A, and the quality densification of the samples additionally characterized by the FESEM technique, Figures 4, 5 and 6.

Detailed description of the invention

As already mentioned before, the basic technical problem that is solved by the present invention relates to the formation of a hard metal with the composition WC-1.0Cr3C2-0.2Co, the so-called sinter-HIP process (sintering via Hot Isostatic Pressure) in which the sintering temperature used is about 200°C lower than the usual sintering temperature of the same or similar samples, which, according to the state of the art, is about 1800°C. The technological result according to the process in question performed at 1600°C is as good as that at the elevated sintering temperature of 1800°C and is manifested in obtaining hard metal as a product without pores.

According to the attached state-of-the-art documents, the sintering of powders with the initial composition of WC-1.0Cr3C2-0.2Co at 1600°C does not give sufficient densification, i.e. products that are without pores, which is unusually important if it is intended to produce products such as cutting nozzles water jet. In the practice of powder metallurgy, this problem can be approached from two sides; one is certainly raising the sintering temperature to approx. 1800°C which is well known in the state of the art, and the other inventive - to pay more attention to the input parameters of the preparation of the mixture, for example to increase the time of homogenization in the mill and increase its speed - about which there is no information in the state of the art.

Experiments related to the present invention are designed in such a way that certain process parameters are varied, and that two batches of three samples are formed that will undergo the same consolidation/sintering procedure at different temperatures; once at 1600°C and the second time at 1800°C. The common composition of all samples is WC-1.0Cr3C2-0.2Co with the alternation of input powders for WC – DN2.5 and/or DN3, as shown in Table 1:

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A. Preparation of the mixture

In this part, we will describe the powders used. As can be seen from Table 1, tungsten carbide (WC) powders were used for the samples, average WC grain size approximately 150 nm, powder designation WC DN 2.5 and WC DN3.0, manufacturer, H.C. Starck Tungsten GmbH, Germany. These powders are characterized by an extremely low content of impurities, where the powders are of nano- to ultrafine grain sizes, from 90 nm to 200 nm, with a different BET specific surface area, for DN 2.5 of 2.4-2.7 m2/g, and for the powder marks DN 3.0 of 2.8-3.2 m2/year.

More detailed information can be obtained at the link:

https://www.hcstarck.com/wp-content/uploads/2021/12/PD-1406_5-WC-DN.pdf

As a grain growth inhibitor, chromium carbide (Cr3C2) powder of 1% by weight was used in the mixture. In addition to the above, cobalt (Co) powder, 0.2% by weight, brand name HMP Co, particle size 0.5 μm, from the Belgian manufacturer Umicore was also used. In all the mentioned samples from Table 1, the mixture of constituents WC-1.0Cr3C2-0.2Co was weighed in such a way as to obtain a mixture of powders weighing 200 g.

B. Mixing and homogenization

The preparation of the starting powder mixture was carried out in a horizontal ball mill in a stainless steel container with hard metal balls. The primary goal of the procedure is to mix and homogenize the powders. As already mentioned, 200 g of the powder mixture was put into the mill, paraffin was optionally added up to a maximum proportion of 0.5% by weight, and the balls used were 4.5 mm in diameter with a ratio of the mass of the balls to the mass of the powder mixture of 10: 1, that is, the total mass of the balls was 2 kg. The volume of the mill chamber where the mixing was carried out was approximately 1 dm3, and the laboratory ball mill of the company ZOZ GmbH, Germany, was used. It should be noted that the hard metal balls used in the ball mill itself must be such that they do not contaminate or only minimally contaminate the mixture in the mixing and homogenization process, as described in the state of the art section, in the work by Lay, S. and others. where cobalt (Co) appeared in a mixture that was initially conceived without cobalt.

In the mixture itself, as is usual in the state of the art, a medium for mixing and homogenization was added - heptane (CH3(CH2)5CH3), in an amount of approximately 200 mL, which with a density of 0.683 g/cm3 gives about 135 g of new liquid stages in the mill, along with all other listed constituents.

Table 1 shows the process times and speeds of the ball mill used in the process itself. Samples PK109 and PK111 were treated for 24 hours at 70 revolutions per minute (rpm - rotation per minute). PL38 samples were treated for 72 hours at 90 rpm. During the formation of samples from the PL38 series, paraffin was omitted from the mixture, but subsequent tests and repetitions of these experiments showed that the addition of paraffin almost does not produce a measurable effect, if it is added in amounts of 0.5% by weight. Of course, the addition of paraffin requires its subsequent removal by the pre-sintering process as described below in step F

C. Drying of the mixture

After step B. and mixing and homogenization, it is necessary to remove the liquid phase from the mixture, i.e. remove heptane. The removal of heptane is done by vacuum distillation, i.e. by heating the mixture to a temperature above the boiling temperature in a vacuum, which is around 80°C. For reference, we state that the boiling point of heptane at normal pressure is about 98°C. The procedure is carried out as long as there is a "pressure" that indicates the evaporation of heptane from the mixture, or else through an empirically determined time of the drying process, for example through 8 hours of drying in the case in question.

D. Granulation

The granulation process is carried out using a sieve. The purpose of the granulation process is to separate the grinding balls from the powder mixture and bring the powder mixture into a flowable state. For the granulation process according to the subject invention, a sieve with a mesh diameter of about 315 μm was used, which achieved the uniformity of the size of the granules in the mixture and the previously mentioned flow property.

E. Shaping

Forming the mixture into the form of the desired product is done by pressing, where the mixture is compacted into a mold that defines the shape of the product. Compacting is usually carried out at a temperature of 15-30°C and a pressure of 150-350 MPa, preferably at room temperature and a pressure of approximately 200 MPa.

For the purposes of the experiment and the measurements carried out in this patent application, molds with dimensions of 60.8 mm x 8.8 mm were used with a thickness of the compacted layer of about 7.5 mm, which gave samples weighing about 35 g. The compaction carried out was uniaxial.

Samples from the PL38 series, in which paraffin was not used, showed marked brittleness - which was to be expected due to the lack of paraffin wax added to the initial mixtures due to better formability and flow when filling the mold. Due to fragility, it was not possible to check the so-called mean density of the green phase, which we believe was above 50% of the theoretical density, comparing the other tested samples where paraffin wax was used.

Of course, producing nozzles for waterjet cutting in the manner described above would be impractical. The extrusion process, which is a frequently used process in the state of the art, meets all the needs for forming more complex object shapes before the final presintering and sintering processes described below. It is usual in practice to use standard available extruders for the purpose of shaping the product.

This phase, regardless of whether it is an extrusion process or a simple compacting process, results in a material that in practice is called raw material. It is common to have several raw materials at the same time in the processing process, which makes the production of a unit product cheaper.

F. Pre-sintering

If the sample was formed with the use of paraffin wax, before the actual sintering process, the wax must be removed by the pre-sintering process. The procedure known as "debindering" or "vacuum dewax for hardmetals" was carried out in such a way that at a low vacuum of approximately 30 mbar in a hydrogen atmosphere and a temperature of approx. 800°C for 60 minutes samples "drain" and "evaporate" the wax.

For the procedure itself, it is good to see the reference: https://vacuum-furnaces.com/images/debindingand%20sinteringofmetalsceramics_062001.pdf

Alternatively, the raw material can be heated to approx. 400°C in a hydrogen (H2) atmosphere, heating rate 1°C/min (approximately 7 hours) and subsequent heating up to 800°C with a higher heating rate in a vacuum, with a retention time for the raw materials in these conditions for 60 minutes, which achieves the same or similar technical effect as in the procedures described above.

G. - I. Sintering

After that, the wax-free product from step F. or molded in step E. is subjected to a sintering procedure in several steps:

G. heating the product up to 1200°C in a vacuum,

H. heating from 1200°C to 1600°C in an atmosphere of argon (Ar) at a pressure of 10 mbar for 30 minutes, and

I. sintering by hot isostatic pressing at a temperature of 1600°C and a pressure of 80-100 bar for at least 45 minutes.

At the end of step I, a hard metal of the desired shape and composition WC-1.0Cr3C2-0.2Co was obtained, the characterization of which will be discussed further below.

Characterization of the sample

The samples listed in Table 1 were characterized by methods that are standard in the field. Determination of the density of the consolidated samples was carried out immediately after the obtaining procedure. The density of the test samples was determined by weighing the test samples in air and in liquid in accordance with HRN EN ISO 3369:2016, and the results are shown in the already mentioned Table 1.

In order to carry out the analysis of determination of porosity and unbound carbon, the surfaces of the obtained samples were polished, cleaned and etched in accordance with the current standard HRN EN ISO 4499-1:2011. The characterization of the microstructure was based on different reactions of Murakami's solution with different phases of the microstructure. Etching research so far has led to the classification of constituent etching reactions using the Murakami solution. Murakami's solution consists of 10 g of K3Fe(CN)6, 10 g of KOH and 100 ml of H2O in accordance with ISO 4499-4:2016. Usually, several cycles of etching, rinsing with water and cleaning the surface using a 96% ethanol solution are carried out. As is known in the state of the art, such a procedure makes the microstructure more visible under an optical microscope.

The microstructures of the obtained samples were analyzed on an optical microscope, as well as on an electron microscope with field emission FESEM.

The surfaces prepared in this way were photographed with an optical microscope and the results are visible in Figures 1A, 2, 3, 4A, 5A and 6A.

In Figure 1A, we can see that the polished surface of sample PL38-02, sintered at 1600°C, is completely free of porosity. The degree of porosity can be classified as less than A02 or A00, no unbound carbon or any other irregularities. It is also evident that there are no large pores or cracks, as well as no unbound carbon, and therefore the sample is also marked as B00 and C00, in accordance with the above-mentioned norm. Figures 2 and 3 show samples PK109-01 and PK111-01, of the same composition and sintered at 1600°C, with possibly 3x shorter treatment in step B. - but with evidently significantly pronounced porosity of the samples.

Figures 4A, 5A and 6A are images of the control group for the samples (PL38-01, PK109-02, PK111-02). These pictures were also made with an optical microscope, where the mentioned samples were previously sintered at 1800°C. It is observed that the control group does not have pronounced pores of the samples, regardless of the duration of the treatment carried out in step B. of this procedure.

Figure 1 shows the surface of sample PL38-02 taken with a Field Emission Scanning Electron Microscopy (FESEM). The other two samples were not fully densified after sintering at a temperature of 1600°C (PK109-01, PK111-02), so no FESEM image was taken of them. Figures 4, 5, 6 show the FESEM surface characterization of the control group for samples (PL38-01, PK109-02, PK111-02) that were adequately densified throughout.

The analysis of these images indicates an unexpected impact of the duration of the procedure in step B, which directly affects the quality of the samples and the lowering of the sintering temperature by about 200°C, which is certainly not an expected result for an expert in the field.

The determination of other mechanical properties was carried out on all samples in order to examine the influence of the selected parameters and applied powder metallurgy procedures, especially the sintering temperature.

Determination of mechanical properties consisted of hardness and toughness measurements. The hardness test was carried out according to the Vickers method, which consists of pressing a diamond indenter in the shape of a regular four-sided pyramid into the surface of the test samples by applying the prescribed force F (N) in accordance with HRN EN ISO 6507-1:2018.

In order to determine the toughness, the method according to Palmqvist was applied, by which it is possible to simultaneously determine the value of the hardness and toughness of the sample based on the analysis of the indentation impression.

The measurement was carried out in accordance with ISO 28079:2009. The toughness values were determined by measuring the length of the cracks - l1, l2, l3 and l4 - formed at the tips of the Vickers imprint. The results are summarized in Table 2 below:

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From the above data from Table 2, it is easy to conclude that the mechanical properties of the product sintered at 1600°C (sample PL38-02) are comparable to the control group (PL38-01, PK109-02, PK111-02) within the errors of the method, where the control a group of samples sintered at 1800°C – which shows that the technical problem in question has been completely solved. The measured hardness of samples PK109-1 and PK111-01, where 100% density was not achieved and with a higher degree of porosity, the measured hardness values are slightly lower compared to the hardness of samples PL38-01, PK109-02, PK111-02.

Industrial applicability

The subject invention discloses a process for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr3C2) and cobalt (Co) powders. The composition was chosen to be WC - 98.8%. wt. with an average grain size of about 150 nm, Cr3C2 – 1.0% by weight, which is used in the mixture as a grain growth inhibitor, and Co – 0.2% by weight. The mentioned process produces a hard metal with composition WC-1.0Cr3C2-0.2Co, mostly without pores, density 15.55 g/cm3, hardness approximately 2590 HV. Due to its characteristics and excellent wear resistance, this material is extremely suitable for the production of nozzles used for water jet cutting. Therefore, the industrial applicability of this procedure and the products resulting from it is obvious.

Claims (7)

1. The process of obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr3C2) and cobalt (Co) powders, in such a way that the composition is chosen to be WC - 98.8%. wt. with an average grain size of about 150 nm, Cr3C2 – 1.0% by weight used in the mixture as a grain growth inhibitor, and Co – 0.2% by weight, indicating that the procedure consists of the following steps: A. preparation of the mixture of starting powders, B. mixing and homogenization without contamination in order to create a homogeneous microstructure, with the addition of heptane (CH3(CH2)5CH3) as a liquid medium and optionally paraffin wax up to 0.5% by weight. mixture ratio, in a ball mill, C. drying the mixture in order to eliminate the liquid phase of heptane by vacuum distillation, D. granulation using a sieve, which aims to bring the mixture of powders into a flowable state, E. molding by pressing, where the mixture is compacted into a mold that defines the shape of the product, or by extrusion into the desired shape, carried out at a temperature of 15-30°C, and the product formed in this way is subjected to the sintering process in several steps: F. pre-sintering with the removal of the optional paraffin wax if it was used, G. heating the product up to 1200°C in a vacuum, H. heating from 1200°C to 1600°C in an atmosphere of argon (Ar) at a pressure of 10 mbar for 30 minutes, and I. sintering by hot isostatic pressing at a temperature of 1600°C and a pressure of 80-100 bar for at least 45 minutes, whereby a hard metal of composition WC-1.0Cr3C2-0.2Co is obtained, mostly without pores, density 15.55 g/cm3, hardness about 2590 HV according to the Vickers method. 2. Process for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr3C2) and cobalt (Co) powders, according to claim 1, characterized in that step B. is carried out for at least 72 hours. 3. The process of obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr3C2) and cobalt (Co) powders, according to claim 2, characterized by the fact that step C. is carried out at a temperature of about 80 °C. 4. The process of obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr3C2) and cobalt (Co) powders, according to claim 3, characterized by the fact that step D. is carried out with a mesh size of about 315 μm. 5. The procedure for obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr3C2) and cobalt (Co) powders, according to 4, indicated by the fact that step E. is carried out at room temperature and under a pressure of 150-350 MPa, preferably 200 MPa. 6. The process of obtaining hard metal products based on tungsten carbide (WC), chromium carbide (Cr3C2) and cobalt (Co) powders, according to any of patent claims 1-5, characterized in that the obtained product is a nozzle used for water jet cutting. 7. The product, characterized by the fact that it was obtained according to any of patent claims 1-5.