A kind of cemented carbide and preparation method thereof

Abstract

The invention belongs to the technical field of powder metallurgy, and specifically relates to a cemented carbide and a preparation method thereof. While a metal bonding phase is doped in a later stage, composite powder is pretreated to ensure controllable components of the composite powder and stability of alloy components and performance. Uniformly dispersed cobalt acetate is converted into elemental cobalt through pretreatment, and a segmented pretreatment method is adopted to ensure thorough conversion in each step. Sintering is performed after the pretreatment, and the prepared cemented carbide has good density and low porosity.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy, and specifically relates to a hard alloy and a preparation method thereof. Background Art

[0002] Cemented carbide is a metal-ceramic composite material made of refractory metal hard compounds as a hard matrix and transition metals as a tough bonding phase through powder metallurgy. Due to the high strength and high toughness of cemented carbide, it has been widely used in oil and gas drilling, geological exploration, mining, rollers, mold materials, cutting tools, wear-resistant parts and other fields, and plays a vital role in promoting national industrial manufacturing and national economic development. With the development of industry, a special type of corrosion-resistant cemented carbide containing a small amount (less than or equal to 0.5%) of metal binders such as Fe, Co, and Ni has been used in many fields because of its superior wear resistance, corrosion resistance, excellent polishing and oxidation resistance compared to traditional cemented carbide, and its demand has greatly increased.

[0003] The distribution of the binder phase in cemented carbide products directly affects the service life of the alloy, especially in cemented carbide with a binder phase content of less than 0.5%, the uniformity of the distribution of the binder phase has a more obvious effect on the cemented carbide. Since the binder metal has good ductility, it is difficult to disperse it evenly by wet grinding directly with WC. Therefore, researchers move the doping of the binder metal forward in the production process of APT or WO3, add the binder metal in the form of a compound to the front-end raw material of WC, and then reduce and carbonize it with the W element to prepare a composite powder. However, it is difficult to accurately control the content of the binder metal in the early stage of doping, which increases the difficulty of quality control and causes large fluctuations in product quality. At the same time, some researchers have also carried out research on the later doping of binder metal salts. However, this method directly sinters after doping. Since the binder metal salt will undergo a series of chemical reactions during the sintering process, the prepared products are often accompanied by Class A or Class B pores and the product density is low. Summary of the invention

[0004] In order to solve the problems existing in the prior art, the main purpose of the present invention is to provide a cemented carbide and a preparation method thereof.

[0005] To solve the above technical problems, according to one aspect of the present invention, the present invention provides the following technical solutions:

[0006] A method for preparing a cemented carbide, wherein the cobalt content of the cemented carbide is ≤0.5wt%, comprising the following steps:

[0007] S1. The raw materials are mixed and ball-milled according to the requirements of cemented carbide products, wherein the cobalt element is added in the form of cobalt acetate, and the mixed powder is prepared by drying and sieving after ball milling;

[0008] S2. The mixed powder is placed in a tubular furnace, a mixed gas is introduced for heating pretreatment, and then cooled with the furnace to prepare a pretreated composite powder;

[0009] S3. Place the pretreated composite powder in a spark plasma sintering furnace for sintering to prepare a cemented carbide.

[0010] As a preferred embodiment of the method for controlling the carbon content of cemented carbide described in the present invention, in step S1, the ball milling speed is 300-400 r / min, the ball milling time is 6-12 h, and the ball-to-material ratio is 8-12:1.

[0011] As a preferred solution of the method for controlling the carbon content of cemented carbide described in the present invention, wherein: in the step S2, the mixed gas includes an inert gas and hydrogen.

[0012] As a preferred solution of the method for controlling the carbon content of cemented carbide described in the present invention, wherein: in the step S2, the volume ratio of hydrogen in the mixed gas is 10-30 vol%.

[0013] As a preferred solution of the method for controlling the carbon content of cemented carbide described in the present invention, wherein: in the step S2, the temperature rise pretreatment adopts a staged temperature rise method.

[0014] As a preferred embodiment of the method for controlling the carbon content of cemented carbide according to the present invention, in step S2, the temperature rise pretreatment is specifically as follows:

[0015] Heat up to 180-220°C at a rate of 10°C / min, keep warm for 20-40 minutes,

[0016] Then heat up to 300-320°C at a rate of 5-10°C / min and keep warm for 40-60 minutes.

[0017] Then heat up to 345-365℃ at a rate of 5-10℃ / min and keep warm for 40-60min.

[0018] Continue to increase the temperature to 450-550°C at a rate of 10°C / min and keep warm for 60-90 minutes.

[0019] As a preferred embodiment of the method for controlling the carbon content of cemented carbide described in the present invention, in step S3, the sintering temperature is 1800-2200° C., the sintering pressure is 30-60 MPa, and the sintering time is 8-15 min.

[0020] To solve the above technical problem, according to another aspect of the present invention, the present invention provides the following technical solution:

[0021] A hard alloy is prepared by adopting the above preparation method.

[0022] As a preferred solution of the cemented carbide described in the present invention, the cobalt content of the cemented carbide is ≤0.5wt%.

[0023] As a preferred solution of the cemented carbide described in the present invention, the density of the cemented carbide is ≥99.95%.

[0024] The beneficial effects of the present invention are as follows:

[0025] The invention provides a cemented carbide and a preparation method thereof. The composite powder is pretreated while a metal bonding phase is doped in the later stage, so that the controllable composition of the composite powder and the stability of the alloy composition and performance are ensured. The uniformly dispersed cobalt acetate is converted into elemental cobalt through the pretreatment, and a segmented pretreatment method is adopted to ensure that each step of the conversion is complete. After the pretreatment, sintering is performed, and the prepared cemented carbide has good density and low porosity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0027] Figure 1 This is a picture of cemented carbide A prepared in Example 1 of the present invention;

[0028] Figure 2 This is a picture of cemented carbide D prepared in Comparative Example 1 of the present invention;

[0029] Figure 3 This is a picture of cemented carbide E prepared in Comparative Example 2 of the present invention;

[0030] Figure 4 This is a picture of cemented carbide G prepared in Comparative Example 4 of the present invention;

[0031] Figure 5 This is a picture of cemented carbide H prepared in comparative example 5 of the present invention. DETAILED DESCRIPTION

[0032] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] The main purpose of the present invention is to provide a cemented carbide and a preparation method thereof, which can at least solve the problem that it is difficult to accurately control the binder metal content in the early stage of doping and the low density of the late stage doping product.

[0034] According to one aspect of the present invention, the present invention provides the following technical solution:

[0035] A method for preparing a cemented carbide, wherein the cobalt content of the cemented carbide is ≤0.5wt%, comprising the following steps:

[0036] S1. The raw materials are mixed and ball-milled according to the requirements of cemented carbide products, wherein the cobalt element is added in the form of cobalt acetate, and the mixed powder is prepared by drying and sieving after ball milling;

[0037] S2. The mixed powder is placed in a tubular furnace, a mixed gas is introduced for heating pretreatment, and then cooled with the furnace to prepare a pretreated composite powder;

[0038] S3. Place the pretreated composite powder in a spark plasma sintering furnace for sintering to prepare a cemented carbide.

[0039] Preferably, in step S1, the ball milling speed is 300-400 r / min, the ball milling time is 6-12 h, and the ball milling ratio is 8-12:1. Specifically, the ball milling speed can be, for example but not limited to, any one of 300 r / min, 310 r / min, 320 r / min, 330 r / min, 340 r / min, 350 r / min, 360 r / min, 370 r / min, 380 r / min, 390 r / min, 400 r / min, or any range between two thereof; the ball milling time can be, for example but not limited to, any one of 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, or any range between two thereof; the ball milling ratio can be, for example but not limited to, any one of 8:1, 9:1, 10:1, 11:1, 12:1, or any range between two thereof;

[0040] Preferably, in step S2, the mixed gas includes an inert gas and hydrogen; the volume ratio of the hydrogen in the mixed gas is 10-30 vol%. Specifically, the volume ratio of the hydrogen in the mixed gas can be, for example but not limited to, any one of 10 vol%, 12 vol%, 15 vol%, 18 vol%, 20 vol%, 23 vol%, 25 vol%, 27 vol%, 30 vol%, or a range between any two thereof;

[0041] Preferably, in step S2, the temperature pretreatment adopts a staged temperature increase method to ensure that the cobalt acetate is completely converted in each stage. The temperature pretreatment is specifically as follows:

[0042] The temperature is raised to 180-220°C at a heating rate of 10°C / min, and kept warm for 20-40min. Specifically, the temperature may be, for example but not limited to, any one of 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, or any range between two thereof; the holding time may be, for example but not limited to, any one of 20min, 23min, 25min, 27min, 30min, 32min, 35min, 38min, 40min, or any range between two thereof;

[0043] Then, the temperature is raised to 300-320°C at a heating rate of 5-10°C / min and kept warm for 40-60min. Specifically, the heating rate can be, for example but not limited to, any one of 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min, 7.5°C / min, 8°C / min, 8.5°C / min, 9°C / min, 9.5°C / min, 10°C / min or any range between two of them; the temperature can be, for example but not limited to The temperature is not limited to any one of 300°C, 302°C, 304°C, 306°C, 308°C, 310°C, 312°C, 314°C, 316°C, 318°C, 320°C, or any range between two thereof; the holding time may be, for example, but not limited to, any one of 40min, 42min, 44min, 46min, 48min, 50min, 52min, 54min, 56min, 58min, 60min, or any range between two thereof;

[0044] Then, the temperature is raised to 345-365°C at a heating rate of 5-10°C / min, and the temperature is kept for 40-60min. Specifically, the heating rate can be, for example, but not limited to, any one of 5°C / min, 5.5°C / min, 6°C / min, 6.5°C / min, 7°C / min, 7.5°C / min, 8°C / min, 8.5°C / min, 9°C / min, 9.5°C / min, and 10°C / min, or a range between any two of them; the temperature can be, for example, but not limited to, any one of 345°C, 348°C, 350°C, 352°C, 355°C, 357°C, 360°C, 363°C, and 365°C, or a range between any two of them; the holding time can be, for example, but not limited to, any one of 40min, 42min, 44min, 46min, 48min, 50min, 52min, 54min, 56min, 58min, and 60min, or a range between any two of them;

[0045] Continue to heat up to 450-550°C at a heating rate of 10°C / min, and keep warm for 60-90min. Specifically, the temperature can be, for example but not limited to, any one of 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, or any range between two thereof; the holding time can be, for example but not limited to, any one of 60min, 65min, 70min, 75min, 80min, 85min, 90min, or any range between two thereof.

[0046] Preferably, in step S3, the sintering temperature is 1800-2200°C, the sintering pressure is 30-60MPa, and the sintering time is 8-15min. Specifically, the sintering temperature can be, for example but not limited to, any one of 1800°C, 1850°C, 1900°C, 1950°C, 2000°C, 2050°C, 2100°C, 2150°C, 2200°C, or any range between two thereof; the sintering pressure can be, for example but not limited to, any one of 30MPa, 35MPa, 40MPa, 45MPa, 50MPa, 55MPa, 60MPa, or any range between two thereof; the sintering time can be, for example but not limited to, any one of 8min, 9min, 10min, 11min, 12min, 13min, 14min, 15min, or any range between two thereof;

[0047] According to another aspect of the present invention, the present invention provides the following technical solution:

[0048] A hard alloy is prepared by the above preparation method, wherein the cobalt content of the hard alloy is ≤0.5wt%; and the density of the hard alloy is ≥99.95%.

[0049] The technical solution of the present invention is further described below in conjunction with specific embodiments.

[0050] Example 1

[0051] A method for preparing cemented carbide comprises the following steps:

[0052] S1. The raw materials were mixed according to the requirements of cemented carbide products (99.70 g of WC and 0.9 g of cobalt acetate) and ball milled at a speed of 350 r / min, a milling time of 8 h, a ball-to-material ratio of 10:1, and the mixed powder was prepared by drying and sieving after ball milling;

[0053] S2. The mixed powder is placed in a tubular furnace, and a mixed gas is introduced for temperature pretreatment, wherein the mixed gas is argon and hydrogen; the volume ratio of hydrogen in the mixed gas is 10 vol%, and the temperature pretreatment is specifically as follows: heating to 200°C at a heating rate of 10°C / min, keeping warm for 30min, then heating to 310°C at a heating rate of 5°C / min, keeping warm for 50min, then heating to 350°C at a heating rate of 5°C / min, keeping warm for 50min, and then heating to 500°C at a heating rate of 10°C / min, keeping warm for 60min; then cooling with the furnace to prepare a pretreated composite powder;

[0054] S3. The pretreated composite powder was placed in a spark plasma sintering furnace for sintering at a sintering temperature of 2000°C, a sintering pressure of 45MPa, and a sintering time of 10min to prepare a cemented carbide A such as Figure 1 As shown, the density is 99.98%, the organizational structure is uniform, the WC grains have not grown abnormally, and there is no cobalt pool in the metallographic structure. The metallographic structure is: A02B00C00E00.

[0055] Example 2

[0056] A method for preparing cemented carbide comprises the following steps:

[0057] S1. The raw material ratio (99.60 g of WC and 1.2 g of cobalt acetate) was ball-milled according to the requirements of cemented carbide products. The ball-milling speed was 300 r / min, the ball-milling time was 12 h, the ball-to-material ratio was 8:1, and the mixed powder was prepared by drying and sieving after ball milling;

[0058] S2. The mixed powder is placed in a tubular furnace, and a mixed gas is introduced for temperature pretreatment, wherein the mixed gas is argon and hydrogen; the volume ratio of hydrogen in the mixed gas is 30 vol%, and the temperature pretreatment is specifically as follows: heating to 220°C at a heating rate of 10°C / min, keeping warm for 20min, then heating to 320°C at a heating rate of 10°C / min, keeping warm for 40min, then heating to 365°C at a heating rate of 10°C / min, keeping warm for 60min, and then heating to 550°C at a heating rate of 10°C / min, keeping warm for 75min; then cooling with the furnace to prepare a pretreated composite powder;

[0059] S3. The pretreated composite powder is placed in a spark plasma sintering furnace for sintering at a sintering temperature of 2200°C, a sintering pressure of 30 MPa, and a sintering time of 15 min to prepare cemented carbide B, which has a density of 99.98%, a uniform microstructure, no abnormal growth of WC grains, and no cobalt pool in the metallographic structure. The metallographic structure is: A02B00C00E00.

[0060] Example 3

[0061] A method for preparing cemented carbide comprises the following steps:

[0062] S1. The raw material ratio (99.50 g of WC and 1.5 g of cobalt acetate) was ball-milled according to the requirements of cemented carbide products. The ball-milling speed was 400 r / min, the ball-milling time was 8 h, the ball-to-material ratio was 12: 1, and the mixed powder was prepared by drying and sieving after ball milling;

[0063] S2. The mixed powder is placed in a tubular furnace, and a mixed gas is introduced for temperature pretreatment, wherein the mixed gas is argon and hydrogen; the volume ratio of hydrogen in the mixed gas is 20 vol%, and the temperature pretreatment is specifically as follows: heating to 180°C at a heating rate of 10°C / min, keeping warm for 40min, then heating to 320°C at a heating rate of 8°C / min, keeping warm for 60min, then heating to 345°C at a heating rate of 8°C / min, keeping warm for 60min, and then heating to 450°C at a heating rate of 10°C / min, keeping warm for 90min; then cooling with the furnace to prepare a pretreated composite powder;

[0064] S3. The pretreated composite powder is placed in a spark plasma sintering furnace for sintering at a sintering temperature of 1800°C, a sintering pressure of 40 MPa, and a sintering time of 8 min to prepare cemented carbide C with a density of 99.97% and a uniform microstructure. The WC grains do not grow abnormally, and there is no cobalt pool in the metallographic structure. The metallographic structure is: A02B00C00E00.

[0065] Comparative Example 1

[0066] Only steps S1 and S4 of Example 1 are performed to prepare sample D as shown in Figure 2 As shown, there are a large number of pores, the density is 99.10%, and the metallographic structure is A08B04C00E00.

[0067] Comparative Example 2

[0068] The difference from Example 1 is that pure argon gas is used in step S2 to prepare sample E such as Figure 3 As shown, it has pores, a density of 98.70%, and a metallographic structure of A08B08C00E00.

[0069] Comparative Example 3

[0070] The difference from Example 1 is that step S2 is: placing the mixed powder in a tubular furnace, introducing a mixed gas for temperature pretreatment, the mixed gas is argon and hydrogen; the volume ratio of hydrogen in the mixed gas is 10 vol%, and the temperature pretreatment is specifically: heating to 500°C at 10°C / min, keeping warm for 60 minutes, and then cooling with the furnace to prepare a pretreated composite powder; sample F is prepared, which has pores, a density of 99.15%, and coarser grains than Example 1, and a metallographic structure of A04B02C00E00.

[0071] Comparative Example 4

[0072] The difference from Example 1 is that the sintering time in step S3 is 30 min. Sample G is prepared as Figure 4 As shown, the density is 99.91%, and a large amount of abnormal growth of WC grains occurs.

[0073] Comparative Example 5

[0074] The difference from Example 1 is that 0.3 g of cobalt powder is used in step S1, and cobalt acetate is not used; and step S2 is not performed. Sample H is prepared as Figure 5 As shown, the density is 98.85%. Due to the uneven distribution of cobalt, the WC grains are coarsely aggregated and unevenly distributed.

[0075] The present invention pre-treats the composite powder while doping the metal bonding phase in the later stage, thereby ensuring the controllable composition of the composite powder and the stability of the alloy composition and performance; the uniformly dispersed cobalt acetate is converted into elemental cobalt by pre-treatment, and the segmented pre-treatment method is adopted to ensure that each step of the conversion is thorough, and the sintering is performed after the pre-treatment, so that the prepared cemented carbide has good density and low porosity. Comparative Examples 1-4 that do not adopt the preparation method of the present invention cannot achieve stable control of the quality of cemented carbide products with a cobalt content of ≤0.5wt%, which is not conducive to large-scale industrial production.

[0076] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for preparing a cemented carbide, characterized in that: The cobalt content of the cemented carbide is ≤0.5wt% and not zero, comprising the following steps: S1. The raw materials are mixed and ball-milled according to the requirements of cemented carbide products, wherein the cobalt element is added in the form of cobalt acetate, and the mixed powder is prepared by drying and sieving after ball milling; S2. The mixed powder is placed in a tubular furnace, a mixed gas is introduced for temperature pretreatment, and then cooled with the furnace to prepare a pretreated composite powder; the mixed gas includes an inert gas and hydrogen; the volume ratio of hydrogen in the mixed gas is 10~30vol%; the temperature pretreatment adopts a staged temperature increase method; The specific heating pretreatment is as follows: heating to 180-220°C at a heating rate of 10°C / min, keeping the temperature for 20-40min, then heating to 300-320°C at a heating rate of 5-10°C / min, keeping the temperature for 40-60min, then heating to 345-365°C at a heating rate of 5-10°C / min, keeping the temperature for 40-60min, then heating to 450-550°C at a heating rate of 10°C / min, keeping the temperature for 60-90min; S3. The pretreated composite powder is placed in a spark plasma sintering furnace for sintering at a sintering temperature of 1800-2200°C, a sintering pressure of 30-60 MPa, and a sintering time of 8-15 min; The hard alloy is prepared, and the density of the hard alloy is ≥99.95%.

2. The method for preparing cemented carbide according to claim 1, characterized in that: In the step S1, the ball milling speed is 300-400 r / min, the ball milling time is 6-12 h, and the ball-to-material ratio is 8-12:

1.

3. A cemented carbide prepared by the method for preparing the cemented carbide according to any one of claims 1 to 2.

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