DE3100266A1 - Process for preparing a hard mixed-crystal solution containing molybdenum - Google Patents

Abstract

The invention relates to a process for preparing a solid solution containing at least one hard phase which has a simple hexagonal crystal structure and is selected from the group comprising mixed carbides or carbonitrides of molybdenum and tungsten. This process involves preparing an alloy powder which consists of a solid solution of molybdenum and tungsten. This alloy powder is then admixed with carbon in such an amount that (Mo, W)2C and/or (Mo, W)2(CN) is formed. The mixture is heated to a temperature at which (Mo, W)2C and/or (Mo, W)2(CN) is stable. Then (Mo, W)2C and/or (Mo, W)2(CN) is admixed with carbon in such an amount that (Mo, W)C and/or (Mo, W)(CN) is formed, possibly together with an iron-group metal. Then the mixture is heated to a temperature at which (Mo, W)C and/or (Mo, W)(CN) is stable. <IMAGE>

Description

Process for the production of a molybdenum containing

Hard mixed crystal solution The invention relates to a method for Production of a hard mixed crystal carbide (Mo, W) C or carbonitride (Mo, W) (CN), which are used as starting materials for hard metal alloys and in particular the invention is concerned with a process for producing such a carbide or carbonitride, which has a uniform particle size. The invention relates thus on a method according to the preamble of the main claim.

Tungsten carbide has been used as a raw material for hard carbides to date (WC) used as a main ingredient.

However, tungsten is and is only found in a few places on earth therefore very expensive. Recently there is a tendency to use tungsten carbide (WC) To replace molybdenum carbide (MoC), which has the same crystal structure as WC as well as similar ones has mechanical properties like toilet. Since MoC is unstable, MoC is stabilized by that therein toilet with the formation of a hard mixed crystal solution or solid solution of (Mo, W) C is dissolved, which is used as a raw material for hard metal alloys will.

When such a carbide or carbonitride as a raw material for hard metal alloys or hard alloys is used, it is very important the particle size of the Hard phase in the alloys and the strength of the binder phase accordingly to adjust this. This is where the particle size and the uniformity of the Raw material powder like (Mo, W) C or (Mo, W) (CN) the main importance to the particle size and to even out the distribution of the hard phase.

In the production of mixed carbides of groups IVa, Va and VIa of the periodic table are metal oxides, carbides and carbon according to the desired composition mixed and allowed to react over a high temperature brought or the reaction is supported by adding an additive, to increase the rate of diffusion. When a solid solution passes through the However, the solid phase reaction of the powder is generated, but the Degree of reaction depending on the mixing method of the powder, the particle size and the particle size distribution of the powders used. A uniform mixed solution To achieve this, warming is required over a long period of time, as described in Japanese Patent Application No. 146306/1976 is described in which part of Mo in MoC is replaced by W to simplify the (Mo, W) C phase with stabilize hexagonal crystal structure. In making a uniform Solid solution is by diffusion of metal powders, such as Mo and W and carbides it therefore required a long time heating at a high temperature such as 16000C or higher especially for the diffusion and dissolution of the metal powder of Mo and W with a particle size of several Am.

When checking the particle size and the particle size distribution of (Mo, W) C and (Mo, W) (CN) produced by such a known method, a reaction mechanism has emerged which is illustrated in FIG. 1.

In the case of the Japanese Patent Application No. 146306/1976 and 104617/1978 shown method in which predetermined amounts of MoC and WC to form a final carbide (Mo, W) C are mixed beforehand, large amounts of carbon become and an iron group metal such as Co or Ni to stabilize (Mo, W) C added to reaction (a-1). A stable form occurs once during the reaction of (Mo, W) 2C + C (a-2) on. However, if this stable form is converted to (Mo, W) C by a subsequent heat treatment is converted, the particle size or fluctuate the particle diameters (a-3).

On the other hand, if the powder particles are very fine, one results favorable diffusion and there is not a large amount of an iron group metal to support the diffusion required. This gives a high quality carbide. However, it is economically difficult to use metal powder and Obtain carbides having a particle size of 12.7Am (0.1 microns) or less.

In the invention, however, it has surprisingly been found that you get better mixing and a more uniform solid solution on simpler Way at a relatively low temperature compared to combinations of metal powders and / or carbide powders obtained when Mo and W are in the form of ammonium salts of Mo and W in the state their solutions or in the form of their oxides or halides mixes. Here, for example, W and Mo are at the stage of forming their oxides mixed evenly and mixed with hydrogen to form a solid solution of (Mo, W), which then reacts with carbon to form a hard mixed crystal carbide to obtain. This has already been suggested in one method (US Pat. No. 4,216,009).

The invention is based on the object of a method for production a hard mixed crystal solution (a hard solid solution) to create the molybdenum contains, wherein a hard mixed crystal carbide of (Mo, W) C or a hard mixed crystal carbonitride is produced by (Mo, W) (CN) having a uniform particle size, and where a solid solution of (Mo, W) C or (Mo, W) (CN) by a two-stage carburization is produced.

According to the invention, a method for producing a Hard mixed crystal solution with at least one hard phase that is a simple hexagonal Has crystal structure and from the group of mixed carbides or carbonitrides is selected from molybdenum and tungsten, in that an alloy powder is prepared which consists of a solid mixed crystal solution of molybdenum and tungsten, that powdered carbon is added to the alloy in such an amount, that at least one of the compounds (Mo, W) 2C and (Mo, W) 2 (CN) is formed, the Mixture is heated at a temperature at which at least one compound of (Mo, W) 2C and / or (Mo, W) 2 (CN) is stable, that furthermore the mixture contains carbon in is added in such an amount that at least one prevention from (Mo, W) C and (Mo, W) (CN) optionally formed with a metal of the iron group and that the mixture is then heated at a temperature at least at one of the compounds (Mo, W) C and (Mo, W) (CN) is stable.

The invention is described below with reference to the attached Drawing and examples explained in more detail.

In the drawing: FIGS. 1 and 2 show reaction models for clarification the formation process of a solid solution (Mo, W) C, where the model according to Fig. 1 for a previously used method and the model according to FIG. 2 for the method according to the invention is used for explanation, Fig. 3 is a diagram for clarification the relationship between carbon content and strength in alloys according to the invention and with previous comparison alloys, and FIGS. 4 and 5 150 times enlarged micrographs to illustrate the disperse state of (Mo, l7Wo, 3) , C in the alloys according to the invention and in previous alloys.

The invention aims at the particle size in a solid To equalize mixed crystal powder of (Mo, W) C and (Mo, W) (CN), which is finally receives.

The invention therefore provides a method for producing a mixed crystal solution or a solid solution that has at least one hard phase that is a simple one Has a hexagonal crystal structure and consists of mixtures, carbides or carbonitrides chosen from molybdenum and tungsten and solid solutions from tungsten and molybdenum which is characterized in that an alloy powder is prepared that consists of a solid solution of molybdenum and tungsten that to the alloy powder Carbon is added in such an amount that (Mo, W) 2C and / or (Mo, W) 2 (CN) forms that the mixture is heated at a temperature at which (Mo, W) 2C and / or (wo, W) 2 (CN) is stable that (Mo, W) 2C and / or (Mo, W) 2 (CN) carbon is added in such an amount that (Mo, W) C and / or (Mo, W) (CN) are optionally with an iron group metal and that then the mixture forms at a temperature is heated at which (Mo, W) C and / or (Mo, W) (CN) is stable.

In the method according to the invention, a molybdenum and tungsten containing Alloy powder prepared by a mixed powder obtained by that (1) an ammonium salt of tungsten (e.g. ammonium tungstate) and an ammonium salt of molybdenum (e.g. ammonium molybdate) in the form of a solution for deposition or formation of parasalts of tungsten and molybdenum are mixed that (2) W03 and MoO3 with Nitric acid or hydrogen chloride or

Hydrochloric acid is deposited together or that (3) previously prepared Oxides or hydroxides are completely mixed in a mechanical manner. The alloy powder of (Mo, W) is synthesized beforehand, only with carbon in a minimal resp. very small amount mixed that leads to formation of (Mo, W) 2C is sufficient and then subjected to a primary reaction (Fig. 2, b-1). When the reaction temperature is chosen accordingly during the entire time specified below, uniform particle growth is obtained because there is no excess carbon which participates in the particle growth of (Mo, W) 2C. That through this Process created (Mo, W) 2C powder (b-2) is made with carbon in an amount mixed, which is necessary for the final carbide composition and optionally with an iron group metal such as cobalt or nickel (b-3) and then a second or secondary carburization at a temperature at which (Mo, W) C is stable is so that (Mo, W) C powder with a uniform particle size distribution (b-4) receives.

In the production of a carbon nitride (Mo, W) (CN), a similar manner to (Mo, W) C mixed carbon mixture carburizing steps subjected, the carburizing atmosphere is changed so that it is partially N2 or in all procedural steps.

When carrying out the method according to the invention, it is desirable that the amount of carbon added before the primary reaction is in the range of e.g. = 0.4 - 0.6 is added in the form of carbides or carbonitrides, which are derived from (Mo, W) Cz or (Mo, W) (CN) z are formed. When z is less than 4 or 0.4, becomes the carbide is not stabilized as (Mo, W) 2C. But if z is greater than 0.6, is the carbide after the primary reaction is in such a state that at the same time (Mo, W) 2C, (Mo, W) C and (Mo, W) 3C2 present are and that thus no uniform particle growth occurs. In particular, it is desirable that the adjust the amount of carbon added before the secondary reaction such that the final carbide composition in the range of z = 0.9 to 1.0 in terms of shape of (Mo, W) Cz or (Mo, W) (CN) z. When z is less than 0.9, the strength is inadequate in the final alloy. On the other hand, when z is greater than 0.9, becomes difficult to sinter the final alloy.

When the carbod or carbonitride of (MoaWb) Cz or (MoaWb) (CN) e.g. is formed, the temperature is expediently during the first heating to 14000C or greater when a> 0.8 and b = 0.2. When the temperature is lower than 14000C, (Mo, W) 2C is not so stabilized, so it is higher here Temperature is desired. On the contrary, the second reaction becomes preferable carried out at a temperature of 1400 ° C or less.

When au is 0.8 and b is 70.2, the temperature is at the first Heating expediently to 1400C or greater, in particular to 18000C or greater. When the carburizing reaction occurs at a temperature of 1800C or lower is carried out, the carbide is stabilized as (Mo, W) C and at a temperature at 1400 ° C or lower, the carbide is better stabilized. To make the response reliable and to be able to perform within a short period of time, it is further desirable that the Primarily formed carbide is cooled once to standard temperature and then a treatment with a mechanical stress, such as grinding or grinding is subjected.

Examples are given below to illustrate the invention.

Example 1 54 g of Mo powder and 46 g of W powder become 28% aqueous Dissolved ammonium solution and gradually neutralized with hydrochloric acid or hydrochloric acid, to secrete needle crystals. The so separated connections like W03 and MoO3 are mixed well. These oxides are sintered in air at 8000C. The mixed powder is placed in a Ni boat or bath, covered and then reduced at 1000C in a stream of H2 to an alloy powder of 50.8 pm (2 microns).

The alloy powder (NO0.7W0.3) thus obtained was 4.5% by weight Carbon powder mixed and ground in a ball mill for 36 hours. The mixed one Powder then reacted in a temperature range in which the subcarbide (MoO 7Wo 3) 2C was stable, i.e. at 19000C in a stream of hydrogen for 1 hour. The carbide was then cooled once and ball milled for 1 hour.

Measurement of the particle size of the (Mo0.7W0.3) 2C powder showed that a powder with a uniform particle size of 203 µm (8 microns) and a very narrow particle size distribution.

The initially formed carbide powder was made with 4.5% by weight of carbon powder and 1% by weight of Co 2 O 3 powder mixed and again carburizing at one temperature at which the monocarbide was stable, i.e. at 14000C in an H2 stream. When the properties of the carbide thus obtained were examined, it was found that the carbide was a WC-type monocarbide, the bonded carbon in about amount theoretically shown in Table 1.

Table 1 Total Free Bound Reactivity Carbon Carbon Carbon = bound carbon x 10 (theoretical carbon 8.93% 0.02% 8.91% 99.8% Example 2 A solid carbide solution of (Mo0.85W0.15) C was prepared for the sample according to the procedure of Example 1. An alloy powder of (No0.85W0.15) was previously prepared in a manner analogous to that in Example 1 and then sufficiently mixed with 5 wt% & carbon powder. The mixed powder was placed in a graphite boat (graphite bed) to a temperature heated at 1600C for about 3 hours, at the maximum temperature for 1 hour left and then cooled to room temperature for 10 hours. the The amount of carbon in the powder is shown in Table 2. The responsiveness amounted to 50.2%.

The analytical result of X-ray diffraction gave only a peak value for (Mo, W) 2C.

Table 2 Total Free Bound Reactive Carbon Carbon Carbon speed +) 4.91% 0.07% 4.84% 50.2% +) Reactivity = bound Carbon theoretical carbon x 100 The subcarbide powder (No0.85W0.15) 2C was sufficiently mixed with 4 wt% carbon powder and 0.3 wt% Co powder, in placed in a Tammann oven and in a stream of H2 at 1250 ° C for about 40 minutes warmed up. The properties of the carbide thus obtained were checked and found the results shown in Table 3: Table 3 Total Free Bound Reactive Carbon Carbon Carbon 9.57% 0.21% 9.45% 95% The X-ray diffraction revealed that the top of (Mo, W) 2C essentially disappeared and that the carbide had a substantially WC-type crystal structure.

Example 3 An alloy powder obtained in a manner analogous to Example 1 of (No0.7W0.3) was mixed with 4.5 wt% carbon powder and 36 hours long ground in a ball mill. The mixed powder could be used at 18000C in one React N2 stream for 1 hour, was then cooled to room temperature and again Ground for 1 hour using a ball mill. The one analyzed for the powder Carbon content was 0.10%. The obtained carbonitride (Mog 7WO, 3) 2 (CN) was mixed with 4.3% by weight of carbon powder and 0.3% by weight of iron powder and it was carburized at 15000C in an N2 stream.

This gave a carbonitride with the following analysis data: Table 4 Total Free Bound Nitrogen Reaction Carbon Carbon Carbon material capacity 8.60% 0.00% 8.60% 0.15% 97.5% The carbonitride obtained in this way had a particle size of 177 µm (7 microns) by X-ray diffraction analysis revealed essentially a peak value for the toilet type with a negligible one Amount of (Mo, W) 2C.

As can be inferred from these results, the carbides had and carbonitrides have an average particle size according to the process according to the invention from 1o1 plm to 203Am (4 to 8 microns) and was suitable as a raw material for Carbide alloys for hot use.

Example 4 The alloy powder obtained in a manner analogous to Example 1 (Mo0.5W0.5) was mixed with 4 wt% carbon powder and dried in. For 36 hours ground in a ball mill. The mixed powder reacted in a stream of H2 at 17000C For 1 hour and then was cooled to room temperature. The (MoO 5Wo 5) 2C powder was then made with 4.0 wt% carbon powder and 0.3 wt% cobalt powder mixed and subjected to carburization at 14500C in a stream of H2. Here a carbide was obtained with the following analytical data: Table 5 Total suitors Bonded nitrogen reaction carbon carbon carbon capacity 7.87% 0.01 z 7.86% 0.02% 99.5% Example 5 One in example 1 prepared alloy powder was mixed with 8.9 wt% carbon powder, Milled in a ball mill for 36 hours and then reacted in one at 17000C H 2 flow for 1 hour to give (Mo0.7W0.3) C powder (B).

The (MoO 7Wo 3) C powder (A) and (Mo0.7W0.3) C powder (B) were each mixed with 30 wt .-% Co in a mortar, compacted in a mold and at 13000C sintered under a high vacuum of 10 -4 mm Hg or less for 1 hour.

The alloy (C) from the powder (A) and the alloy (D) from the Powders (B) were each made of carbide in terms of their particle size distribution examined using an image analyzer, and those in Table were obtained 6 listed results: Table 6 (vol .-%) d <0.5 µ 0.5 µ # d lr 1 µ # d <3 µ 3) 1-dU5 / u 5μ # d <10μ 10 »- d Le- O 0 0.9 11.1 77.9 10.1 alloy (C) comparative alloy according to the invention 4.5 6.1 16.7 20.3 40.2 12.2 (D) d = particle diameter example 6 The (MoO, 7WO, 3) 0.7 0.3) O powder (A) obtained in Example 1 and that in Example 5 obtained (Mo0.7W0.3) C powders (B) were each mixed with 30% by weight of Co, im Wet process ground in a ball mill, compacted in a mold and at 1300 ° C sintered in a high vacuum of 10-4 mmHg or less for 1 hour, wherein alloys with the following properties were obtained: Table 7 Density used Hardness transverse breaking strength (MoO 7W0.3) C (g / m) (HRA) in N / mm (kg / mm powder he invention according to alloy A 10.2 83.5 2844.9 (290) (E) comparison alloy B 10.2 83.0 2452.5 (2507 (E) Example 7 Head tools for nuts were made from the inventive Alloy (E) and from the comparison alloy (E), prepared according to the example 6 produced and for test purposes as a head tool and the production of a wire-shaped Rod material made of SCr4 is used. The results are in Table 8 with those shown those on the market with the designation WC-25% by weight Co alloy are available.

Table 8 Service life (x 10 10 20 30 40 50 (pieces) according to the invention o Alloy (E) o Comparative x35 alloy (F) x28 x46 WC-25% Co x17 alloy - x17 -xlO x1 1 o: usable x: broken Example 8 The one prepared according to Example 1 (Mo0.7W0.3) C powder (A) and the (Mo0.7W0.3) C powder prepared according to Example 5 (B) were each mixed with 35 cJew.-t Co powder and there were six each Sample alloys with variation of the carbon content in the range of 5.30 up to 5.90% by weight. The properties of these alloys are shown in table 9 shown: Table 9 Density, hardness, cross-fracture analysis values (g / cm ) (HRA) strength total Free N / mm 2 carbon (kg / mm2) material (%) (%) Le alloy of the present invention No. 1 10.0 82.6 1814.8 (185) 5.32 0.00 2 10.0 82.9 2550.6 (260) 5.46 0.00 3 10.0 82.3 3139.2 (320) 5.60 0.00 4 10.0 82.4 2893.9 (295) 5.72 0.00 5 9.9 82.3 2256.3 (230) 5.80 0.06 6 9.9 82.4 1765.8 (180) 5.90 0.15 7 10.0 82.3 1765.8 (180) 5.30 0.00 8 10.0 82.2 1638.3 (167) 5.48 0.00 9 10.0 82.5 2207.2 (225) 5.62 0.00 10 10.0 82.1 2432.9 (248) 5.70 0.00 11 9.9 82.2 2060.1 (210) 5.81 0.06 12 9.9 82.2 1716.7 (175) 5.90 0.14 The alloys made in Example 8 were subjected to a Charpy test to obtain the results shown in FIG obtained (curve A: alloys Nos.% -6 according to the invention; curve B: alloys Nos. 7-12 of the previous type).

The alloys of Example 8 (No. 2 and No. 8) were tested for the dispersed state of (Mog 7WO, 3) C enlarged by the creation of lr3Ofold Compare microstructural images shown in FIGS. 4 and 5.

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Claims (9)

Process for the production of a hard mixed crystal solution containing molybdenum Claims: 1. A method for producing a hard mixed crystal solution with at least one hard phase which has a simple hexagonal crystal structure and from the group of mixed carbides or carbonitrides of molybdenum and tungsten is selected, thereby g e k e n n n -z e i c h n e t that an alloy powder is prepared which consists of a solid mixed crystal solution of molybdenum and tungsten, that powdered carbon is added to the alloy in such an amount, that at least one of the compounds (Mo, W) 2C and (Mo, W) 2 (CN) is formed, the Mixture is heated at a temperature at which at least one compound of (Mo, W) 2C and / or (Mo, W) 2 (CN) is stable, that furthermore the mixture contains carbon in is added in such an amount that at least one compound of (Mo, W) C and (Mo, W) (CN) is optionally formed with an iron group metal, and that then the mixture at a temperature is heated in the at least one of the compounds (Mo, W) C and (Mo, W) (CN) is stable. 2. The method according to claim 1, characterized in that g e k e n n -z e i c h n e t that carbon is added in such a way that the primary carburization reaction in a range of z = 0.4 to 0.6 and the secondary carburization reaction in one Range from z = 0.9 to 1.0 occurs when the solid solution of (Mo, W) Cz or (Mo, W) (CN) z is formed. 3. The method according to claim 1 or 2, characterized in that g e k e n n -z e i c Note that the stable temperature for (Mo, W) 2C - and (Mo, W) 2 (CN) - at least 14000C and that the stable temperature for (Mo, W) C- and (Mo, W) (CN) - is at most 14000c when a> = 0.8 and b # 0.2 and the solid solution of (MoaWb) (CN) is e.g. or (MoaWb) (CN) z is formed. 4. The method according to claim 1 or 2, characterized in that g e k e n n -z e i c Note that the stable temperature for (Mo, W) 2C and (Mo, W) 2 (CN) is at least 14000C and the stable temperature for (Mo, W) C and (Mo, W) (CN) is 1800 C or less when a <0.8 and b 2 0.2 and the solid solution of (MoaWb) Cz or (MoaWb) (CN) z is formed. 5. The method according to any one of claims 1 to 4, characterized g e k e n n notices that the alloy powder is prepared by that molybdenum and tungsten is mixed in the form of compounds from the group are chosen, the oxides, hydroxides, chlorides, sulfates, nitrates, metallic acids and mixtures thereof, and then comprising the mixture with at least one compound selected from the group consisting of hydrogen and ammonium. 6. The method according to claim 5, characterized in that g e k e n n -z e i c h n e t that ammonia-containing solutions of molybdenum and tungsten are mixed. 7. The method according to any one of claims 1 to 6, characterized in that g e k e n n indicates that part or that all of the carburizing steps in a nitrogen containing atmosphere. 8. The method according to any one of claims 1 to 7, characterized g e k e n n notes that the primary carbide is cooled once and then with deposition mechanical stress is treated before the secondary carburization he follows. 9. The method according to any one of claims 1 to 8, characterized g e k e n n shows that the carburization takes place in a hydrogen stream.