CN115074568A

CN115074568A - Preparation method of hard alloy with controllable cobalt phase gradient structure

Info

Publication number: CN115074568A
Application number: CN202210763939.8A
Authority: CN
Inventors: 胡兴; 许雄亮; 刘欢; 蒋文镭
Original assignee: Jwe Carbide Co ltd
Current assignee: Jwe Carbide Co ltd
Priority date: 2022-06-29
Filing date: 2022-06-29
Publication date: 2022-09-20
Anticipated expiration: 2042-06-29
Also published as: CN115074568B

Abstract

The invention discloses a preparation method of a hard alloy with a controllable cobalt phase gradient structure, which comprises the steps of mixing tungsten carbide powder and cobalt powder in proportion, adding a forming agent, carrying out ball-milling mixing granulation and compression molding to form a pressed compact, putting the pressed compact into a graphite box, completely coating and sealing the pressed compact by using carbon black, putting the filled graphite box into a low-pressure sintering furnace to carry out carburizing and overpressure integrated sintering, wherein the final temperature of the integrated sintering is 1400-1500 ℃, the carburizing and overpressure integrated sintering also comprises dewaxing, solid-phase carburizing, cobalt phase migration, densification and cooling and discharging, and finally the hard alloy with the controllable cobalt phase gradient structure is obtained. The method adopts carbon black carburization and carburization overpressure integrated sintering treatment, the carburization efficiency is higher, the thickness of the formed hard alloy gradient layer is controllable, and the cost is lower; meanwhile, through process adjustment and pressure sintering, residual carburizing phases and pores can be effectively eliminated, the volume fraction of the decarburized phase is controlled, and the gradient alloy with excellent performance, stability and controllability is obtained.

Description

Preparation method of hard alloy with controllable cobalt phase gradient structure

Technical Field

The invention relates to the technical field of alloy material preparation, in particular to a preparation method of a hard alloy with a controllable cobalt phase gradient structure.

Background

As a tool material, the hard alloy has high hardness, strength, wear resistance, corrosion resistance and other properties, and is widely applied to the fields of military industry, aerospace, machining, metallurgy, oil drilling, mine tools, buildings and the like. The traditional WC-Co hard alloy is generally adapted to different fields by changing the wear resistance and toughness of the alloy by adjusting the cobalt content and the tungsten carbide granularity. Generally, the lower the cobalt content and the finer the tungsten carbide particle size, the higher the hardness, the better the wear resistance and the poor toughness, whereas the higher the cobalt content and the coarser the tungsten carbide particle size, the lower the hardness, the poor wear resistance and the high toughness, which cannot be obtained at the same time. Therefore, the development of a gradient cemented carbide material with high wear resistance and high toughness is a common goal of researchers in the industry.

The traditional gradient alloy is represented by DP alloy of Shantevick company in Sweden, and the typical process comprises the steps of preparing a carbon-poor sintered matrix, and then carburizing the carbon-poor matrix to obtain the gradient alloy with a surface layer poor in cobalt, a middle layer rich in cobalt and a core part containing a carbon-poor eta phase.

Patent CN102031435A discloses a process for preparing a cemented carbide with a gradient cobalt content on the surface, which comprises, under the protection of hydrogen atmosphere, carburizing the cemented carbide to obtain a cemented carbide with a surface layer decarburized and a core part having a normal phase composition, and then carburizing the cemented carbide under the protection of hydrogen to obtain the cemented carbide with a gradient cobalt content. The core of the process is that a hard alloy matrix with a decarburized surface layer is prepared first, then the matrix is carburized, a cobalt phase gradient is formed on the surface layer of the hard alloy due to reaction diffusion, liquid phase flow and the like, and the core part keeps the structure of normal hard alloy, so that a product with excellent mechanical properties is obtained.

Patent CN107267837A discloses a gradient cemented carbide with a gradient change of binding phase and a preparation method thereof, which is characterized by sequentially comprising the following steps: preparing WC-Co powder; adjusting the carbon content of the WC-Co powder, and calculating the upper limit and the lower limit of the carbon content in a sub-stoichiometric manner; adding a forming agent; pressing into a blank; removing the forming agent; vacuum sintering; heating to 900-1200 ℃, introducing gas in a pulse mode, and performing carburizing heat treatment on the vacuum sintered body; heating to 1275-1325 ℃, and carrying out Co phase migration treatment; heating to 1380-1450 ℃, introducing Ar gas, and keeping the pressure at 10-20 mbar; pressure sintering; rapidly cooling to 1270 ℃; then cooling the alloy to room temperature from 1270 ℃, and discharging the alloy to obtain the gradient hard alloy. The method belongs to a one-step treatment method, but the method adopts a gas phase carburization process, and has two obvious defects: the gas phase concentration is not uniform in the furnace and changes along with different positions in the furnace, boat and product placement, so that different carburization degrees of different parts of the product in the furnace and different parts of the product are caused, the alloy performance is unstable, and the structural level of the gradient alloy cannot be accurately regulated; in addition, the method is characterized in that carburizing gas is introduced at high temperature and is in a negative pressure state, hydrogen and methane are combustible gases, potential safety hazards of furnace explosion exist, and carbon black decomposed from the carburizing gas at high temperature can be deposited on components in the furnace to cause furnace failure, so that the safety coefficient of furnace opening is reduced.

In the reports of the prior art, the production efficiency of the gradient hard alloy is not low, or the performance of the prepared gradient alloy is unstable, so that the industrialization is difficult to carry out, which is also the main reason why the cobalt phase gradient alloy is not industrialized for many researches so far. Therefore, there is a need to develop a method for preparing a gradient cemented carbide with high production efficiency, low cost and high safety, and promote the early industrialization of the gradient cemented carbide.

Disclosure of Invention

In order to solve the technical problems, the invention provides the preparation method of the hard alloy with the controllable cobalt phase gradient structure, and the method has the advantages that the carburization mode and the carburization sintering process of the hard alloy are optimized and are matched with each other, so that the preparation method of the gradient hard alloy is simpler and more convenient, the production cost is reduced, the production process is safe, the gradient structure of the prepared gradient hard alloy is controllable, and the industrial popularization and application of the gradient hard alloy are facilitated.

In order to achieve the aim, the invention provides a preparation method of a hard alloy with a controllable cobalt phase gradient structure, which is characterized by comprising the following steps:

s1, preparing an alloy mixture: tungsten carbide powder accounts for 80-97% of the total weight, and cobalt powder accounts for 20-3% of the total weight; adding tungsten powder to adjust the carbon content of the mixture, wherein the theoretical carbon content of the mixture is calculated in a mode of 6.13% xWC, the carbon balance coefficient is-0.1% -0.5%, and adding a forming agent;

s2, ball-milling, mixing and granulating: ball-milling the prepared alloy mixture, and spray-drying the mixture slurry after ball-milling to obtain a granular mixture;

s3, press forming: pressing the mixture obtained after the ball milling, mixing and granulating in the step S2 into a pressed compact;

s4, loading: laying carbon black in a graphite box, completely wrapping the pressed compacts obtained in the step S3 by using the carbon black, spacing the compacts from each other, and finally sealing the graphite box;

s5, carburizing and overpressure integral sintering: putting the graphite box loaded in the step S4 into a low-pressure sintering furnace to perform carburizing and overpressure integrated sintering, wherein the final sintering temperature is 1400-1500 ℃, and the carburizing and overpressure integrated sintering comprises the following steps:

s501, dewaxing: heating the mixture to 350-450 ℃ from room temperature in a hydrogen atmosphere, keeping the temperature, removing the forming agent to obtain a porous pressed blank, and then vacuumizing to discharge hydrogen;

s502, solid-phase carburizing: under the vacuum environment, the temperature is continuously increased to 1350 ℃ and kept, the solid-phase carbon black diffuses inwards through the pores of the pressed compact to gradually form a carbon gradient with high outside and low inside, and a small amount of cobalt phase is migrated at the later stage;

s503, cobalt phase migration and densification: under 40-60 mabr low-pressure argon atmosphere, continuously heating to the final temperature and keeping for 10-60 min, then controlling the argon pressure in the low-pressure sintering furnace to be 50-100 bar, and continuously keeping the final temperature for 30-120 min; at the stage, a liquid phase begins to appear, the pores on the surface of the pressed compact are closed, solid-phase carburization is terminated, and a gradient structure sintered body with a surface layer poor in cobalt, a middle layer rich in cobalt and a core part normal in cobalt content is gradually formed;

s504, cooling and discharging: and after sintering and heat preservation are finished, entering a cooling stage, and obtaining the hard alloy with the controllable cobalt phase gradient structure after cooling is finished.

In step S503, the reverse migration of W and Co in the green compact is performed due to the existence of the surface carbon gradient, and as the migration of Co to the core portion continues, a gradient structure sintered body with a surface layer depleted in cobalt, an intermediate layer enriched in cobalt, and a core portion normal cobalt content (nominal cobalt content) is gradually formed until the surface carbon gradient disappears. And finally, high-pressure argon is introduced in the final temperature heat preservation stage, so that the pores are effectively eliminated while cobalt phase migration is carried out on the sintered body, and finally, a compact gradient alloy sintered body is formed.

Preferably, the forming agent in step S1 is one of rubber, paraffin wax or polyethylene glycol, and the addition amount of the forming agent is 1-3% of the weight of the mixture.

Preferably, the ball milling in the step S2 is performed by using a roller ball mill, the ball milling alcohol coefficient is 0.2-0.4L/KG, the ball-to-material ratio is 1-6: 1, and the ball milling time is 15-50 h.

Preferably, the graphite box loaded with the boat in the step S4 includes a pressed compact, carbon black, a graphite box and a graphite cover plate, the inside of the graphite box is densely filled with the carbon black, the pressed compact is uniformly distributed inside the carbon black, and the graphite cover plate detachably covers the opening of the graphite box to seal the graphite box.

Preferably, the dewaxing retention time after the temperature rise in step S501 is 60 to 180 min.

Preferably, the flow rate of the hydrogen gas in the step S501 is 30-90L/min.

Preferably, the retention time at 1350 ℃ in the step S502 is 60-180 min, and the vacuum degree of the vacuum environment is less than or equal to 0.4 mbar.

Preferably, the core region of the sintered compact in step S503 contains a carbon-depleted region, and the size of the carbon-depleted region is inversely related to the carburizing in step S502 and the sintering time in step S503.

The design principle of the preparation method of the gradient alloy is as follows: placing the alloy pressed compact under the carbon black package, in the same pressure furnace, firstly carrying out solid phase uniform carburization treatment on the porous pressed compact to obtain a surface carbon gradient, promoting the surface carbon gradient to carry out cobalt phase migration after high temperature or liquid phase appears to form a gradient structure, and then completely densifying in a pressure sintering stage to finally obtain the gradient structure alloy with a surface layer being poor in cobalt, a middle layer being rich in cobalt, and a core part being normal in cobalt content but containing a decarbonized phase. The core part retains proper decarburized phases, which is beneficial to the formation of a gradient structure, improves the rigidity of the alloy, and simultaneously forms compressive stress on the surface to delay the failure process of the alloy; the volume percentage of the carbon powder can be controlled by adjusting carbon balance, carburizing and sintering time according to the application requirements of actual products, and even the carbon powder can completely disappear.

The scheme of the invention has the following beneficial effects:

1. according to the preparation method of the hard alloy with the controllable cobalt phase gradient structure, carbon black carburization and carburization overpressure integrated sintering treatment are adopted, the carburization efficiency is high, the thickness of the formed hard alloy gradient layer is controllable, and the cost is low; meanwhile, through process adjustment and pressure sintering, residual carburizing phases and pores can be effectively eliminated, the volume fraction of the decarburized phase is controlled, and the gradient alloy with excellent performance, stability and controllability is obtained.

2. Compared with the conventional preparation method of the gradient hard alloy, the preparation method provided by the invention is simpler and more efficient. The preparation method of the conventional gradient alloy comprises the steps of pre-sintering a blank to obtain a lean carbon matrix, and then performing carburization treatment to obtain the gradient hard alloy; the preparation method of the invention is that the carbon-poor blank is directly carburized in a pressure furnace, the carburization and the overpressure sintering are carried out together, one step is completed, the gradient hard alloy with controllable gradient structure and excellent comprehensive performance can be obtained by controlling the carburization, the production steps are simplified, and the production cost is reduced;

3. according to the invention, the carburizing and sintering are carried out together and then coordinated with the solid-phase carburizing together, the carburizing temperature is optimized to 1350 ℃, carbon gradients with high outside and low inside are gradually formed in the solid-phase carburizing process, and a small amount of cobalt phase migration is accompanied in the later stage of the carburizing process, so that the carbon gradients can be better formed, the subsequent cobalt phase migration is facilitated to form the hard alloy with obvious cobalt gradient difference and uniformly distributed cobalt phases in each gradient, and the composition of the gradient structure area of the prepared hard alloy can be regulated and controlled in real time.

3. The preparation method has the advantages that the preparation process is simple and easy to control, the carburizing efficiency is improved to a greater extent, the hardness difference between the cobalt-poor area and the cobalt-rich area of the prepared cobalt-phase gradient alloy is very large, the performance of the obtained alloy is very stable, the repeatability of the experiment is very high, compared with the process of the conventional gradient hard alloy, the intermediate process is reduced, the production efficiency and the stability of the product quality are obviously improved, the production cost is reduced, and the industrialization of the cobalt-phase gradient alloy is possible; meanwhile, the method adopts solid-phase carburization and sintering in a low-pressure sintering furnace, so that the production safety is effectively guaranteed.

4. Compared with the alloy disclosed in the Chinese patent CN107267837A, the main difference of the method of the invention compared with the disclosed technology is that solid-phase carburization is adopted, and the ideal gradient alloy is prepared by wet grinding and batching, synchronous optimization design of carburization and sintering processes (temperature, atmosphere, heat preservation time and the like), and especially by obviously improving the sintering process on the basis of combining the solid-phase carburization; secondly, the thickness of the cobalt-rich layer can be improved by adjusting carbon balance and sintering heat preservation time, so that the hardness range of the gradient layer reaches more than 200HV3, the thickness of the decarbonization phase is controlled below 1/3 of the size of the product, the superior performances of wear resistance of the alloy surface layer and impact resistance of the middle high cobalt layer are achieved, while the unique superiority of the gradient alloy cannot be reflected when the hardness range of the general gradient alloy is below 200HV 3; thirdly, solid carburization is adopted, the carbon atmosphere around each product is consistent, the carburization degree is consistent, the obtained gradient alloy has stable performance, and the gradient alloy prepared by the patent technology has inconsistent alloy gradient structures at different parts due to non-uniform carbon atmosphere in a furnace, so that the stability of the gradient alloy cannot be guaranteed; fourthly, the process of the invention has no potential safety hazards of negative pressure, combustible gas and furnace failure. Therefore, the invention has obvious industrialization advantages.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.

FIG. 1 is a schematic view showing the overall structure of a cartridge boat for a stone ink cartridge according to example 1 of the present invention;

FIG. 2 is a cross-sectional view of a YG13 cemented carbide product made in example 1 of the present invention;

FIG. 3 is a schematic cross-sectional view of a YG13 cemented carbide product made in example 1 of the present invention;

FIG. 4 is a 1500-fold magnified photomicrograph of a YG13 cemented carbide product made in example 1 of the present invention, where FIG. 4A is a photomicrograph of cobalt-poor areas and FIG. 4B is a photomicrograph of cobalt-rich areas, with white dots indicated as cobalt;

FIG. 5 is a graph showing the results of measuring the cobalt content of YG13 hard alloy prepared in example 1 of the present invention at different distances from the surface layer;

FIG. 6 is a graph showing the results of cobalt content measurements of YG6 cemented carbide prepared in example 2 of the present invention at different distances from the surface layer;

fig. 7 is a diagram of different drill bit products after wear failure of high wind pressure down-the-hole drill in experimental example 1 of the present invention, wherein fig. 7A shows YG6 drill bit 1, fig. 7B shows YG6 drill bit 2, fig. 7C shows control 1, and fig. 7D shows control 2.

Description of reference numerals:

1-compacting; 2-carbon black; 3-a graphite box; 4-graphite cover plate.

Detailed Description

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.

The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention. Modifications or substitutions to methods, procedures, or conditions of the invention may be made without departing from the spirit and scope of the invention.

Example 1

Preparation of hard alloy with controllable cobalt phase gradient structure

1. Preparing a batch of mixed material YG13, wherein the tungsten carbide powder accounts for 87% of the total weight, and the cobalt powder accounts for 13% of the total weight; the theoretical carbon content of the mixed material YG13 is 5.33%, and the carbon balance coefficient value is-0.4%; adding a forming agent paraffin, wherein the addition amount of the paraffin is 2 percent of the weight of the mixture.

2. The prepared mixture YG13 was put into a roller ball mill and mixed uniformly, the alcohol coefficient was 0.28L/KG, the ball-to-feed ratio was 4:1, and the ball milling time was 30 hours.

3. After spray drying and granulation, the powder is pressed into a compact with the diameter (phi) of 18mm and the height (H) of 12 mm.

4. Loading the pressed blank into a boat: as shown in fig. 1, carbon black is laid in a graphite box 3, the green compacts 1 pressed in step S3 are completely wrapped with carbon black 2, the green compacts 1 are spaced apart from each other, and finally the graphite box 3 is sealed; the inside closely knit packing of stone ink horn 3 has carbon black 2, and 1 evenly distributed of pressed compact closes in the inside of carbon black 2, and graphite apron 4 can be dismantled the lid and close at the opening part of graphite box 3, seals stone ink horn 3, prevents that the carbon black from being stirred by the heat wave and flying to the fritting furnace in, influences the stability of fritting furnace.

5. Carburizing and overpressure integral sintering: putting the graphite box after the boat loading into a low-pressure sintering furnace for carburizing and overpressure integrated sintering, wherein the final sintering temperature is 1400 ℃, and the carburizing and overpressure integrated sintering comprises the following steps:

(1) and dewaxing: heating to 450 deg.C from room temperature under hydrogen atmosphere, maintaining for 60min, removing forming agent at hydrogen flow rate of 90L/min to obtain porous compact, and vacuumizing to discharge hydrogen;

(2) solid-phase carburization: under the environment that the vacuum degree is 0.4mbar, the temperature is continuously increased to 1350 ℃ and kept, solid-phase carbon black diffuses inwards through pores of a pressed compact, a carbon gradient with high outside and low inside is gradually formed, and a small amount of cobalt phase migrates in the later stage;

(3) cobalt phase migration and densification: under 40mabr low-pressure argon atmosphere, continuously heating to the final temperature and keeping for 10min, then adjusting and controlling the argon pressure in the low-pressure sintering furnace to be 50bar, and continuously keeping the final temperature for 120 min; at the stage, a liquid phase begins to appear, pores on the surface of a pressed blank are closed, solid-phase carburization is stopped, and a gradient structure sintered body with a surface layer poor in cobalt, a middle layer rich in cobalt and a core part normal in cobalt content is gradually formed;

(4) and cooling and discharging: after the sintering and heat preservation are finished, a cooling stage is carried out, and the YG13 hard alloy product is obtained after the cooling is finished, wherein the sectional view of the YG13 product is shown in fig. 2, the sectional view of the product is shown in fig. 3, and as can be seen from fig. 2 and 3, the YG13 hard alloy has obvious cobalt gradient and is divided into a cobalt-rich area, a cobalt-poor area and a normal area.

Fig. 4 is a 1500-fold magnified photomicrograph of the YG13 cemented carbide, fig. 4A is a photomicrograph of the cobalt-poor region, fig. 4B is a photomicrograph of the cobalt-rich region, the white dots indicate cobalt, and it is evident from fig. 4 that the cobalt content is significantly higher in the cobalt-rich region than in the cobalt-poor region.

Fig. 5 is a diagram illustrating the results of detecting the cobalt content of the YG13 cemented carbide at different distances from the surface layer, and it can be seen from fig. 5 that the average thickness of the YG13 cemented carbide gradient layer reaches 3mm, the average thickness of the cobalt-rich region reaches 1.7mm, and the cobalt content of the cobalt-rich region is uniform, and the cemented carbide product YG13 with uniform gradient distribution of cobalt is prepared in this example.

Vickers hardness tests were performed on different positions of the YG13 cemented carbide product, and the test results are shown in table 1.

TABLE 1 Vickers hardness of YG13 cemented carbide at various positions

From the results in table 1, the maximum gradient layer HV3 in the cobalt-poor region is 1276, the minimum gradient layer HV3 in the cobalt-rich region is 1066, and the maximum range of the YG13 gradient cemented carbide product is 210.

Example 2

Preparation of hard alloy with controllable cobalt phase gradient structure

1. Preparing a batch of mixed material YG6, wherein the tungsten carbide powder accounts for 94% of the total weight, and the cobalt powder accounts for 4% of the total weight; the theoretical carbon content of the mixed material YG6 is 5.76%, and the carbon balance coefficient value is-0.3%; adding a forming agent, wherein the addition amount of the paraffin is 2 percent of the weight of the mixture.

2. The prepared mixture YG6 was put into a roller ball mill and mixed uniformly, the alcohol coefficient was 0.25L/KG, the ball-to-feed ratio was 4:1, and the ball milling time was 28 hours.

3. After drying and granulation, the powder is pressed into a compact with a diameter (phi) of 16mm and a height (H) of 23 mm.

4. The procedure of example 1 was followed for loading.

5. Carburizing and overpressure integral sintering: putting the graphite box after the boat loading into a low-pressure sintering furnace for carburizing and overpressure integrated sintering, wherein the final sintering temperature is 1500 ℃, and the carburizing and overpressure integrated sintering comprises the following steps:

(1) and dewaxing: heating from room temperature to 400 ℃ in hydrogen atmosphere, keeping for 180min, removing the forming agent with hydrogen flow of 30L/min to obtain porous pressed compact, and vacuumizing to discharge hydrogen;

(2) solid-phase carburization: under the environment that the vacuum degree is 0.4mbar, the temperature is continuously increased to 1350 ℃ and kept for 120min, solid-phase carbon black diffuses inwards through pores of a pressed compact, a carbon gradient with high outside and low inside is gradually formed, and a small amount of cobalt phase migrates in the later stage;

(3) cobalt phase migration and densification: under the condition of 60-mabr low-pressure argon atmosphere, continuously heating to the final temperature of 1500 ℃ and keeping for 30min, then controlling the argon pressure in the low-pressure sintering furnace to be 50bar, and continuously keeping the final temperature for 120 min; at the stage, a liquid phase begins to appear, the pores on the surface of the pressed compact are closed, solid-phase carburization is terminated, and a gradient structure sintered body with a surface layer poor in cobalt, a middle layer rich in cobalt and a core part normal in cobalt content is gradually formed;

(4) and cooling and discharging: and after sintering and heat preservation are finished, entering a cooling stage, and obtaining the hard alloy with the controllable cobalt phase gradient structure after cooling is finished.

Fig. 6 is a graph showing the results of measuring the cobalt content of the YG6 cemented carbide at different distances from the surface layer, and it can be seen from fig. 6 that the average thickness of the final YG6 alloy gradient layer reached 3mm, and the average thickness of the cobalt-rich region reached 1.2 mm.

Vickers hardness tests were performed on different positions of the YG13 cemented carbide product, and the test results are shown in table 2.

TABLE 2 Vickers hardness of YG13 cemented carbide at various positions

From the results in table 2, the maximum gradient layer HV3 of the cobalt-poor region is 1695, the minimum gradient layer HV3 of the cobalt-rich region is 1403, and the maximum range of the YG13 gradient cemented carbide product is 292.

Experimental example 1

Application of YG6 gradient hard alloy in high wind pressure down-the-hole drill bit

A batch of YG6 gradient cemented carbide was prepared according to the preparation method of example 2, wherein 14 specimens of alloy with a diameter (Φ) of 16mm and 12 specimens of alloy with a diameter (Φ) of 14 mm; preparing 2 phi 115mm high wind pressure down-the-hole drill YG6 bit 1 and YG6 bit 2 (phi 16mm alloy as side teeth and phi 14mm alloy as middle teeth) by using YG6 gradient alloy product; 2 drill bits (also phi 16mm alloy is used as side teeth, and phi 14mm alloy is used as middle teeth) of the same type of products of certain large-scale enterprises in China are purchased from the market and used as a control group.

Carrying out down-the-hole operation on phi 115 high-wind-pressure down-the-hole drill bits (two YG6 gradient alloy drill bits, comparison 1 and comparison 2 of the same type of drill bits of certain large-scale enterprises in China) on working surfaces (granite f15-16, the hardest part reaches f18) of stone quarries 810 and 840 in Meishan village in Putian city, the use wind pressure reaches 2.0MPa, and the specific experimental data are shown in Table 3:

TABLE 3 service condition recording chart of different drill bit products in high wind pressure down-the-hole drill

The results in Table 3 show that the service life of the grade-f 15-f16 granite high-wind-pressure down-the-hole drill made of the YG6 gradient alloy drill bit of the invention can be improved by 28.5% compared with the average service life of the similar drill bit of a certain large enterprise in China, which also indicates that the gradient hard alloy made by the method of the invention has better wear resistance and toughness.

Fig. 7 is a diagram of different drill bit products after wear failure of high wind pressure down-the-hole drill, fig. 7A and 7B are YG6 drill bits, and fig. 7C and 7D are comparison 1 and comparison 2 drill bits. As can be seen from FIG. 7, the YG6 gradient alloy bit had less wear after wear failure than control 1 and control 2, which further illustrates the better wear resistance and toughness of the gradient cemented carbide made by the method of the present invention.

The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments. It will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit of the invention.

Claims

1. A preparation method of hard alloy with a controllable cobalt phase gradient structure is characterized by comprising the following steps:

s502, solid-phase carburizing: under the vacuum environment, the temperature is continuously increased to 1350 ℃ and kept, solid-phase carbon black diffuses inwards through pores of a pressed blank, so that a carbon gradient with high outside and low inside is gradually formed, and a small amount of cobalt phase is migrated at the later stage;

2. The method for preparing a hard alloy with a controllable cobalt phase gradient structure according to claim 1, wherein the forming agent in step S1 is one of rubber, paraffin wax or polyethylene glycol, and the addition amount of the forming agent is 1-3% of the weight of the mixture.

3. The method for preparing a hard alloy with a controllable cobalt phase gradient structure according to claim 1, wherein a roller ball mill is used for ball milling in the step S2, the ball milling alcohol coefficient is 0.2-0.4L/KG, the ball-to-material ratio is 1-6: 1, and the ball milling time is 15-50 h.

4. The method for preparing a hard alloy with a controllable cobalt phase gradient structure according to claim 1, wherein the graphite box finished by the boat in the step S4 comprises a pressed compact (1), carbon black (2), a graphite box (3) and a graphite cover plate (4), wherein the carbon black (2) is densely filled in the graphite box (1), the pressed compact (1) is uniformly distributed in the carbon black (2), and the graphite cover plate (4) is detachably covered on the opening of the graphite box (3) to seal the graphite box (3).

5. The method for preparing a hard alloy with a controllable cobalt phase gradient structure according to claim 1, wherein the dewaxing retention time after temperature rise in step S501 is 60-180 min.

6. The method for preparing a hard alloy with a controllable cobalt phase gradient structure according to claim 1, wherein the flow rate of hydrogen in step S501 is 30-90L/min.

7. The method for preparing the hard alloy with the controllable cobalt phase gradient structure according to claim 1, wherein the retention time at 1350 ℃ in the step S502 is 60-180 min, and the vacuum degree in the vacuum environment is less than or equal to 0.4 mbar.

8. The method of claim 1, wherein the core region of the sintered compact of step S503 contains carbon-poor regions, and the size of the carbon-poor regions is inversely related to the carburizing time of step S502 and the sintering time of step S503.