CN111206202A

CN111206202A - Method for preparing cobalt phase gradient hard alloy by carburizing treatment

Info

Publication number: CN111206202A
Application number: CN202010101399.8A
Authority: CN
Inventors: 吴建国; 潘思尧
Original assignee: Zhuzhou Kingtal Cemented Carbide Co ltd
Current assignee: Zhuzhou Kingtal Cemented Carbide Co ltd
Priority date: 2020-02-19
Filing date: 2020-02-19
Publication date: 2020-05-29

Abstract

A method for preparing cobalt phase gradient hard alloy by carburizing treatment comprises the steps of respectively placing hard alloy pressed compacts into a plurality of different sealed containers, placing cleavable carburizing gas substances with different weight and mass into each sealed container, enabling the hard alloy pressed compacts in each sealed container to obtain carburizing gas with different amounts during sintering, and carburizing by the carburizing gas with different amounts during the sintering process of the hard alloy, thereby obtaining the hard alloy with different cobalt phase gradients. The invention utilizes the input different amounts of the cleavable carburizing gas substances to cleave out different carburizing gases to carburize the hard alloy pressed blank, and can simultaneously realize the preparation of hard alloy products with different sizes and different gradient thicknesses in the same furnace by controlling and quantitatively adjusting the carburizing gradient difference.

Description

Method for preparing cobalt phase gradient hard alloy by carburizing treatment

Technical Field

The invention relates to a method for changing the surface performance of hard alloy, in particular to a method for preparing cobalt phase gradient hard alloy by carburizing the hard alloy to form a surface gradient structure of the hard alloy by utilizing carbon-containing gas cracked in the sintering process and performing carburization treatment; the method for preparing the cobalt phase gradient hard alloy through carburizing treatment can effectively form surface thickness gradient structures of different hard alloys; meanwhile, the method can also be used for preparing the gradient hard alloy by taking one or a plurality of combinations of cobalt or nickel and iron as a binding phase in the hard alloy mixture, and taking one or a plurality of refractory metal carbides of tungsten, titanium, tantalum, niobium, vanadium, chromium and the like as a hard phase; belongs to the technical field of hard alloy production.

Background

Cemented carbide has high hardness and strength and is widely used in various industries, so that it is called industrial teeth, and the demand for cemented carbide as a tool is increasing with the development of the industry. However, generally, the hardness and the toughness of the alloy are a pair of contradictory indexes, and how to improve the performance of one index on the premise of not reducing the other index so as to improve the service life of the alloy is a cumin target of vast researchers of hard alloys.

The gradient hard alloy adopts a special method or process, so that the components or the performance in the hard alloy are distributed in a gradient manner according to the use requirement, and the local performance of the alloy is combined with the use requirement, thereby achieving the purpose of improving the comprehensive use effect of the hard alloy.

Because of the excellent properties of gradient alloys, there are many reports on related documents, for example, in patent No. CN 101864554A, a uniform powder mixture is prepared by mixing tungsten carbide powder, cobalt powder (Co) and cubic carbonitride or a solid solution additive composed of these cubic compounds, the powder mixture is pressed, and then sintered by a gradient sintering technique (sintering at 1440 ℃ and cooling in a N-removing atmosphere after high-temperature sintering) to form a binder phase enriched surface region on the surface of a cemented carbide substrate and a cubic carbonitride enriched region under the binder phase enriched surface region, the method is generally used for producing cemented carbide coated blade substrates, and requires that the alloy components contain cubic phases, and the thickness of the obtained gradient layer is generally only tens of micrometers, and the method is not suitable for being applied to alloys containing no cubic phase components, at the same time, gradient layers with a thickness of several millimeters cannot be prepared; CN 103817150A discloses a hard alloy roll collar with a gradient structure and a manufacturing process thereof, wherein a composition gradient is formed between an outer layer and a core part of the roll collar, the outer layer and the core part of the roll collar are respectively provided with hard materials, bonding materials and/or additives with different mass contents, the hard materials, the bonding materials and/or the additives are subjected to ball milling and mixing to form a roll collar ball milling and mixing material, the roll collar ball milling and mixing material is dried, doped with wax and dried, the ball milling and mixing material of the outer layer of the roll collar doped with the wax and the ball milling and mixing material of the core part of the roll collar doped with the wax are layered and stacked to form powder, the powder is subjected to cold press molding to form a roll collar blank, the roll collar blank is subjected to sintering dewaxing to form into hard alloy, and the, the powder filling and pressing method by the layering method has the characteristics of low efficiency and even incapability of producing and large product deformation when producing small products or products with complex shapes, and cannot be popularized and applied to small products; patent No. CN 108149183 a describes: putting the hard alloy into a low-pressure sintering furnace with graphite as a heating body, introducing mixed gas of reducing gas, carburizing gas and inert gas, heating to 1000 ℃ at room temperature at the heating rate of 2-10 ℃/min, heating to 1300-1400 ℃ at the heating rate of 2-5 ℃/min, preserving heat for 30-180 min for carburizing treatment, then cooling for diffusion treatment, and finally cooling to room temperature to obtain the hard alloy with the surface layer hardness in gradient distribution. Patent No. CN 107267837B describes a preparation method of gradient hard alloy, which comprises 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; performing carburizing heat treatment, namely heating to 900-1200 ℃, performing carburizing heat treatment on the vacuum sintered body, and introducing gas in a pulse mode; 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. In the methods described in the two patents, carburizing gas is introduced into a hearth, and the thickness of a gradient layer of a product cannot be controlled due to different products with different sizes, different surface areas and different reaction speeds with the gas; meanwhile, when the hearth is large, the gas concentration difference of each part in the hearth is large, and the gradient layer thickness of the same furnace product cannot be accurately controlled.

So far, how to prepare products with gradient thickness more than a few millimeters and capable of accurately controlling the gradient thickness in batches aiming at products with different sizes still remains a problem faced by vast cemented carbide enterprises, and particularly, no good method is found for simply realizing cobalt phase gradient according to needs. There is therefore a great need for improvement.

Disclosure of Invention

The invention aims to provide a novel method for preparing cobalt-phase gradient hard alloy aiming at the defect that the thickness of a gradient layer cannot be accurately controlled in the existing cobalt-phase gradient alloy preparation process. Meanwhile, the method can also be used for preparing the gradient hard alloy by using the hard alloy mixture and using one or more of cobalt, nickel and iron as a binding phase, wherein the hard phase is one or more of tungsten, titanium, tantalum, niobium, vanadium, chromium and other refractory metal carbides.

In order to achieve the purpose, the invention provides a method for preparing cobalt phase gradient hard alloy through carburizing treatment, which comprises the steps of respectively placing hard alloy pressed compacts into a plurality of different sealed containers, placing cleavable carburizing gas substances with different weights into the sealed containers, enabling the hard alloy pressed compacts in the sealed containers to obtain different amounts of carburizing gas during sintering, and carburizing through the carburizing gas with different amounts during the sintering process of the hard alloy, thereby obtaining the hard alloy with different cobalt phase gradients.

Further, the hard alloy pressed compacts are respectively placed into a plurality of different sealed containers, namely the hard alloy pressed compacts to be sintered are respectively placed into different sealed containers with covers according to the cobalt phase gradient expected to be obtained, different amounts of cleavable carburizing gas substances are simultaneously placed when the hard alloy pressed compacts are placed, then the sealed containers are sealed, and the hard alloy pressed compacts are sent into a hard alloy sintering furnace for sintering.

Furthermore, the amount of the cracking carburizing gas substances which are put in unequal amounts is determined according to the cobalt phase gradient, the amount of the cracking carburizing gas which is needed by the unit surface area during sintering is determined, and then the needed cracking carburizing gas substances are determined according to the surface area of the put hard alloy pressed compact, so that the cobalt phase gradient structure of the hard alloy formed through carburizing is ensured.

Furthermore, the cleavable carburizing gas substance is an organic matter block, and the carburizing gas is formed by cracking the organic matter block during sintering.

Further, the organic matter block comprises a rubber block, a paraffin block or a rubber and paraffin composition.

Furthermore, the closed container is a closable container made of high-temperature-resistant materials, and the high-temperature-resistant materials do not react or dissolve with any component in the hard alloy at the sintering temperature, and other harmful impurities cannot be volatilized.

Further, the high-temperature resistant material comprises graphite, dense white corundum or mullite.

Furthermore, the closable container comprises a graphite box with a cover, the graphite box with the cover comprises a graphite box body and a graphite cover, the graphite box body is a container with an upper opening, and the graphite cover is screwed on the opening part of the graphite box body to form the closable container.

Furthermore, a movable valve is additionally arranged on the ink box with the cover stone, and the movable valve ensures that the valve is in a closed state and the carburizing gas is not easy to escape when the carburizing gas is cracked out from the box in the sintering process; however, in the pressure sintering stage, when high-pressure gas is filled into the furnace, the high-pressure gas can open the valve and smoothly enter the graphite box to pressurize the hard alloy pressed compact without damaging the container.

Further, in the carburizing of the hard alloy through different amounts of carburizing gas in the sintering process, organic matter blocks in the closed container are cracked into the carburizing gas, and the carburizing gas can further crack carbon on the surface of the hard alloy pressed compact, so that the carbon content of the surface layer of the hard alloy pressed compact is higher than that of the core part of the hard alloy pressed compact; after the liquid phase appears in the hard alloy pressed compact, as the appearing time and the appearing amount of the liquid phase are related to the carbon content, the higher the carbon content is, the earlier the appearing time of the liquid phase is, and the more the amount of the liquid phase is; in the sintering process, the carbon content of the surface layer of the hard alloy pressed compact is increased under the action of carburizing gas, and a liquid phase of the surface layer of the hard alloy pressed compact appears firstly and flows to the core part of the hard alloy pressed compact; after sintering is finished, a gradient alloy structure with low surface cobalt content and high core cobalt content is formed in the hard alloy pressed compact, and the amount of liquid phase flowing from the surface layer to the core of the hard alloy pressed compact is different due to different carburized gas amounts generated in each container, so that the formed cobalt phase gradient is different, and the purpose of preparing hard alloys with different cobalt phase gradients is achieved.

Furthermore, the hard alloy compact is made of a carbon unsaturated mixture, and alloy components are in a carbon-poor area in a phase diagram.

Further, the hard alloy mixture takes one or a combination of more of cobalt, nickel and iron as a binding phase, and the hard phase is one or more of tungsten, titanium, tantalum, niobium, vanadium, chromium and other refractory metal carbides, wherein the most common hard alloy is tungsten-cobalt hard alloy and tungsten-titanium-cobalt hard alloy.

The invention has the advantages that:

the hard alloy green compacts are filled in different closed containers, a proper amount of rubber blocks are added in the closed containers, and then sintering is carried out in the same sintering furnace under the same sintering environment; in the sintering process, the rubber block placed in the closed container cracks carburizing gas during sintering, the carburizing gas can further crack carbon on the surface of the hard alloy, and the hard alloy is subjected to carburizing strengthening treatment, so that the carbon content of the surface layer of the product is higher than that of the core part of the product, because the hard alloy is liquid phase sintered, the time and the quantity of liquid phases in the sintering process are related to the carbon content, and the higher the carbon content is, the earlier the time of liquid phase occurrence is, and the more the quantity of liquid phases is; the carbide pressed compact of different airtight containers is because the degree of carburization differs, liquid phase will appear in proper order, after appearing the liquid phase in the carbide pressed compact, carbide pressed compact top layer is because carbon content is high, the liquid phase appears earlier and flows to the product core, after the sintering is accomplished, carbide will form the gradient structure that top layer cobalt content is low, core cobalt content is high, and because the degree of carburization is different, the liquid phase that appears also can be different, thereby lead to the cobalt phase gradient that forms also can be different, thereby reach the carbide purpose of preparing different cobalt phase ladders.

Meanwhile, the method can also be used for preparing the gradient hard alloy by using the hard alloy mixture and using one or more of cobalt, nickel and iron as a binding phase, wherein the hard phase is one or more of tungsten, titanium, tantalum, niobium, vanadium, chromium and other refractory metal carbides.

Drawings

FIG. 1 is a schematic diagram of the general principles of the present invention;

FIG. 2 is a schematic structural view of a cemented carbide carburizing containment vessel according to one embodiment of the invention;

FIG. 3 is a schematic view of the opening structure of the movable valve of the cemented carbide carburizing sealing container box according to one embodiment of the invention;

FIG. 4 is a schematic view of a detection site and a direction of a cemented carbide sample according to an embodiment of the present invention;

FIG. 5 is a schematic illustration of a cobalt content profile according to an embodiment of the present invention;

FIG. 6 is a schematic view of a cobalt content distribution according to another embodiment of the present invention;

FIG. 7 is a schematic view of a cobalt content distribution according to another embodiment of the present invention;

FIG. 8 is a schematic diagram of a cobalt content distribution according to another embodiment of the present invention.

Detailed Description

The invention is further illustrated with reference to the following figures and specific examples.

Example one

As shown in attached figure 1, a method for preparing cobalt phase gradient hard alloy by carburization treatment, WC powder and Co powder are mixed into a mixture according to the proportion of WC-6wt% Co, the carbon content of the mixture is controlled at 5.67%, the mixture is pressed into hard alloy button pressed compacts with the diameter of 14mm, each hard alloy button pressed compact 12 with the same grain number is put into two graphite boxes with covers 1 with the same volume and a movable valve 6, and 1.0 g-1.5 g of rubber blocks 15 are put into the graphite boxes with covers 1; 1.5g of rubber is put into one ink box 1 with the covering stone, 1.0g of rubber is put into the other graphite box with the covering stone, the ink box 1 with the covering stone is covered by a covering plate to be sealed and then put into the same sintering furnace 13, and the two ink boxes 1 with the covering stone are vertically overlapped and placed together; dewaxing and sintering are carried out according to a conventional sintering operation process and conditions, the bottom of the graphite box with the cover is supported by a graphite column 14 at a certain distance so as to prevent the graphite box with the cover from being directly pressed on the movable valve 6, meanwhile, high-pressure gas can be ensured to push the movable valve 6 from the bottom to enter the graphite box with the cover 1, after sintering is completed, the hard alloy spherical teeth 12 in the two graphite boxes with the cover 1 are respectively sampled, a sample is cut from a cross section (like figure 4, the same below), and cobalt contents at different positions are detected by using an energy spectrum. Fig. 5 and 6 show the distribution of cobalt content in two cemented carbide button samples with 1.5g and 1.0g rubber in the cartridge with cover stone, respectively, where fig. 5 shows that the gradient layer thickness below the average cobalt content reaches 1.6-1.8mm, while fig. 6 shows that the gradient layer thickness below the average cobalt content is only around 1.2mm, and experiments show that the preparation of products with different gradient layer thicknesses can be achieved in the same furnace.

According to the test, the invention discloses a method for preparing cobalt phase gradient hard alloy button pressed compacts through carburizing treatment, which comprises the steps of respectively placing hard alloy button pressed compacts 12 into a plurality of different graphite boxes 1 with covers and movable valves 6, placing rubber blocks 15 with different weights and masses into the graphite boxes 1 with covers, so that the hard alloy button pressed compacts 12 in the graphite boxes 1 with covers can obtain different amounts of carburizing gas during sintering, and carburizing the hard alloy buttons by the different amounts of carburizing gas during sintering, thereby obtaining the hard alloy button pressed compacts with different cobalt phase gradients.

The hard alloy button pressed compact is respectively placed into a plurality of different ink boxes 1 with covering stones, namely the hard alloy button pressed compact 12 to be sintered is respectively placed into different ink boxes 1 with covering stones according to a desired cobalt phase gradient, different amounts of cleavable carburizing gas substances are simultaneously placed when the hard alloy button pressed compact 12 is placed, then the ink boxes 1 with covering stones are sealed, and the hard alloy button pressed compact is sent into a hard alloy sintering furnace for sintering.

The amount of the cracked carburizing gas substances added in unequal amounts is determined according to the cobalt phase gradient, the amount of the cracked carburizing gas required by the unit surface area during sintering is determined, and the required amount of the cracked carburizing gas substances is determined according to the surface area of the added hard alloy button pressed compact 12, so that the cobalt phase gradient structure of the hard alloy button pressed compact 12 formed through carburizing is ensured.

The graphite box with the cover 1 is a sealable container made of high-temperature-resistant graphite material, and the graphite material does not react or dissolve with any component in the hard alloy button pressed compact 12 at the sintering temperature, and does not volatilize other harmful impurities.

The ink box 1 with the cover is a sealed box (shown in figure 2) with a cover and a movable valve, the graphite box 1 comprises an open box body 2, the upper end face of the open box body 2 is covered with a box cover 3, and the box cover 3 is screwed on the open box body 2 through screwing; a movable valve 5 is arranged at the bottom 4 of the open box body 2, and the hard alloy spherical tooth pressed compact 12 is uniformly prevented from being in the closed inner cavity of the graphite box 1.

The movable valve 5 is an internal and external pressure balance valve arranged at the bottom of the stone ink box, and the movable valve 5 ensures that high-pressure gas can smoothly enter the graphite box to pressurize the hard alloy pressed compact without damaging the stone ink box in the pressure sintering process. The movable valve 5 comprises a movable valve core 6, and the movable valve core 6 is in an I shape; one end of the movable valve core 6 is a movable end 7 of a movable detachable structure, and the other end is a fixed end 9 connected with the middle part 8; the middle part 8 of the movable valve core 6 is sleeved in a movable valve hole 10 at the bottom of the stone ink box in a penetrating manner, after the middle part 8 of the movable valve core 6 passes through the movable valve hole 10 at the bottom of the stone ink box, the movable end 7 of the movable valve core is connected with the middle part 8 to form an I-shaped movable valve core, and a vent groove 11 is arranged at the middle part of the movable valve core; when the atmospheric pressure of stone ink horn 1 is higher than outside atmospheric pressure, block up the graphite box bottom through the one end shutoff of the movable valve element 6 of arranging in stone ink horn 1 in, when outside atmospheric pressure is higher than the inside atmospheric pressure of graphite box 1, will upwards promote movable valve element 6 upward movement through the pressure differential that is located the outside one end of stone ink horn 1 and inner face one end, the air channel 11 of mid portion 8 will communicate the inside and outside (as shown in figure 3) of stone ink horn 1 for outside high-pressure gas gets into the inside of stone ink horn 1, guarantee the inside and outside atmospheric pressure balance of stone ink horn 1, avoid damaging stone ink horn 1.

Example two

The basic principle of the second embodiment is the same as that of the first embodiment, but the adopted materials and products are different, namely a method for carburizing hard alloy by utilizing carbon-containing gas cracked in the sintering process is characterized in that WC and Co powder are mixed according to the proportion of WC-6wt% Co and WC-11wt% Co, wherein the carbon content of the WC-6wt% Co mixture is controlled to be 5.67%, the carbon content of the WC-11wt% Co mixture is controlled to be 5.32%, the WC-6wt% Co mixture is pressed into a spherical tooth pressed blank with the diameter of 12, the WC-11wt% Co mixture is pressed into a spherical tooth pressed blank with the diameter of 16, a plurality of grains of the two spherical tooth pressed blanks are respectively placed into different compact white corundum boxes (or made of mullite), paraffin blocks with different amounts are placed into the compact white corundum boxes, and the compact white corundum boxes are sealed, and putting the compact white corundum box with the button pressed compact and the paraffin block into a hard alloy sintering furnace together for sintering, carburizing the hard alloy button pressed compact by utilizing carbon-containing gas cracked by the paraffin block in the sintering process, and carburizing to form the hard alloy button with the gradient structure, wherein the carbon content of the surface layer of the hard alloy button pressed compact is higher than that of the core part of the hard alloy button. The method comprises the steps of putting 1.0g of paraffin blocks into a compact white corundum box with WC-6wt% of spherical teeth, putting 2.0g of paraffin blocks into a compact white corundum box with WC-11wt% of Co spherical teeth, covering the two compact white corundum boxes, putting the two compact white corundum boxes into the same sintering furnace for dewaxing and sintering, supporting the bottom of the compact white corundum box by using graphite columns at intervals to prevent the compact white corundum box from being directly pressed on a movable valve, simultaneously ensuring that high-pressure gas can push the movable valve open from the bottom to enter the compact white corundum box, respectively sampling products in the two compact white corundum boxes after sintering is finished, cutting the samples from cross sections, and detecting the cobalt content in different positions by using an energy spectrum. FIGS. 7 and 8 show the distribution of cobalt content in two samples, WC-11wt% Co and WC-6wt% Co, respectively, and it can be seen from the graphs that the thickness of the low-cobalt (lower than the average cobalt content) layer of both samples is 1.8-2.0mm, and experiments show that the preparation of the gradient structure cemented carbide button tooth with the same thickness can be realized in the same furnace according to different product sizes.

The structure of the compact white corundum box is similar to that of the embodiment.

Of course, the method can also be used for preparing the gradient hard alloy by using the hard alloy mixture and using one or more of cobalt, nickel and iron as a binding phase, wherein the hard phase is one or more of tungsten, titanium, tantalum, niobium, vanadium, chromium and other refractory metal carbides.

It can be seen from the above examples that the cobalt phase gradient cemented carbide is prepared as follows:

in the sintering process, organic matter blocks in the closed container are cracked to generate carburizing gas, and the carburizing gas can further crack carbon on the surface of the hard alloy pressed compact, so that the carbon content of the surface layer of the hard alloy pressed compact is higher than that of the core part of the hard alloy pressed compact; after the liquid phase appears in the hard alloy pressed compact, as the appearing time and the appearing amount of the liquid phase are related to the carbon content, the higher the carbon content is, the earlier the appearing time of the liquid phase is, and the more the amount of the liquid phase is; in the sintering process, the carbon content of the surface layer of the hard alloy pressed compact is increased under the action of carburizing gas, and a liquid phase of the surface layer of the hard alloy pressed compact appears firstly and flows to the core part of the hard alloy pressed compact; after sintering is finished, a gradient alloy structure with low surface cobalt content and high core cobalt content is formed in the hard alloy pressed compact, and because the carburizing gas amount per unit surface area generated in each container is different, the surface liquid phase of the hard alloy pressed compact is also different, so that the formed cobalt phase gradient is also different, and the purpose of preparing hard alloys with different cobalt phase gradients is achieved.

The above listed embodiments are only for clear and complete description of the technical solution of the present invention with reference to the accompanying drawings; it should be understood that the embodiments described are only a part of the embodiments of the present invention, and not all embodiments, and the terms such as "upper", "lower", "front", "back", "middle", etc. used in this specification are for clarity of description only, and are not intended to limit the scope of the invention, which can be implemented, and the changes or modifications of the relative relationship thereof are also regarded as the scope of the invention without substantial technical changes. Meanwhile, the structures, the proportions, the sizes, and the like shown in the drawings are only used for matching with the contents disclosed in the specification, so as to be understood and read by those skilled in the art, and are not used for limiting the conditions under which the present invention can be implemented, so that the present invention has no technical essence, and any structural modification, changes in proportion relation, or adjustments of the sizes, can still fall within the range covered by the technical contents disclosed in the present invention without affecting the effects and the achievable purposes of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention has the advantages that:

the hard alloy green compacts are filled in different closed containers, a proper amount of rubber blocks are added in the closed containers, and then sintering is carried out in the same sintering furnace under the same sintering environment; in the sintering process, the rubber block placed in the closed container cracks carburizing gas during sintering, the carburizing gas can further crack carbon on the surface of the hard alloy, and the hard alloy is subjected to carburizing strengthening treatment, so that the carbon content of the surface layer of the product is higher than that of the core part of the product, because the hard alloy is liquid phase sintered, the time and the quantity of liquid phases in the sintering process are related to the carbon content, and the higher the carbon content is, the earlier the time of liquid phase occurrence is, and the more the quantity of liquid phases is; the carbide pressed compact of different airtight containers is because the degree of carburization differs, liquid phase will appear in proper order, after appearing the liquid phase in the carbide pressed compact, carbide pressed compact top layer is because carbon content is high, the liquid phase appears earlier and flows to the product core, after the sintering is accomplished, carbide will form the gradient structure that top layer cobalt content is low, core cobalt content is high, and because the degree of carburization is different, the liquid phase that appears also can be different, thereby lead to the cobalt phase gradient that forms also can be different, thereby reach the carbide purpose of preparing different cobalt phase ladders. This has some advantages as follows:

1. when the rubber block and products with the same specification are relatively and uniformly placed in the closed container, the carburizing gas cracked from the rubber block can uniformly react with the products in the closed container, so that gradient structures formed by the products at different positions in the closed container are the same, and the consistency of the products is ensured.

2. When the number of the rubber blocks put into the box is different, the concentration of the carburizing gas cracked from the rubber blocks in the sintering process is different, so that the carbon amount reacted with the surface layer of the product is also different. Aiming at the condition that the surface layers of products with different specifications and sizes have different volumes, the gradient layers with the same thickness can be generated by adjusting the number of the rubber blocks in the closed container.

3. When the quantity of the products in the closed container is different or the gradient thickness of the products needs to be changed, the quantity of the rubber blocks placed in the closed container can be adjusted to realize the purpose. When different products are put into different closed containers and are put into a sintering furnace together, the production of the products with different specifications and different gradient layer thickness requirements can be realized simultaneously.

Claims

1. A method for preparing cobalt phase gradient hard alloy by carburizing treatment is characterized in that: the hard alloy pressed compacts are respectively placed into a plurality of different sealed containers, and the hard alloy pressed compacts in the sealed containers can obtain different amounts of carburizing gas during sintering by placing the cleavable carburizing gas substances with different weight and mass into the sealed containers, and the hard alloys with different cobalt phase gradients are obtained by carburizing the hard alloy pressed compacts with different amounts of carburizing gas during the sintering process of the hard alloys.

2. The method of preparing a cobalt phase gradient cemented carbide by carburization according to claim 1, characterized in that: the hard alloy pressed compacts are respectively placed into a plurality of different sealed containers, namely the hard alloy pressed compacts to be sintered are respectively placed into different sealed containers with covers according to the cobalt phase gradient expected to be obtained, different amounts of cleavable carburizing gas substances are simultaneously placed when the hard alloy pressed compacts are placed into the sealed containers, then the sealed containers are sealed, and the sealed containers are sent into a hard alloy sintering furnace for sintering.

3. The method of preparing a cobalt phase gradient cemented carbide by carburization according to claim 2, characterized in that: the amount of the cracking carburizing gas substances which are put in unequal amounts is determined according to the cobalt phase gradient, the amount of the cracking carburizing gas required by the unit surface area is determined during sintering, and the required cracking carburizing gas substances are determined according to the surface area of the put hard alloy pressed compact so as to ensure the cobalt phase gradient structure of the hard alloy formed by carburizing.

4. A method of preparing a cobalt phase gradient cemented carbide by carburization according to claim 3, characterized in that: the cracking carburizing gas substance is an organic matter block, and the organic matter block is cracked during sintering to form the carburizing gas.

5. A method of preparing a cobalt phase gradient cemented carbide by carburization according to claim 3, characterized in that: the organic matter block comprises a rubber block, a paraffin block or a rubber and paraffin composition.

6. The method of preparing a cobalt phase gradient cemented carbide by carburization according to claim 1, characterized in that: the closed container is a closable container made of high-temperature-resistant materials, and the high-temperature-resistant materials do not react or are mutually soluble with any component in the hard alloy at the sintering temperature, and other harmful impurities cannot be volatilized.

7. The method of preparing a cobalt phase gradient cemented carbide by carburization according to claim 6, characterized in that: the high-temperature resistant material comprises graphite, dense white corundum or mullite.

8. The method of preparing a cobalt phase gradient cemented carbide by carburization according to claim 6, characterized in that: the closable container comprises a graphite box with a cover, the graphite box with the cover comprises a graphite box body and a graphite cover, the graphite box body is a container with an upper opening, and the graphite cover is screwed on the opening part of the graphite box body to form the closable container.

9. The method of preparing a cobalt-phase gradient cemented carbide by carburization according to claim 6, characterized in that: the ink box with the cover stone is additionally provided with a movable valve, and the movable valve ensures that when carburizing gas is cracked out in the box in the sintering process, the valve is in a closed state, and the carburizing gas is not easy to escape; however, in the pressure sintering stage, when high-pressure gas is filled into the furnace, the high-pressure gas can open the valve and smoothly enter the graphite box to pressurize the hard alloy pressed compact without damaging the container.

10. The method of preparing a cobalt phase gradient cemented carbide by carburization according to claim 1, characterized in that: in the hard alloy sintering process, carburizing is carried out by different amounts of carburizing gas, wherein in the sintering process, organic matter blocks in a closed container are cracked to form the carburizing gas, and the carburizing gas can further crack to form carbon on the surface of a hard alloy pressed compact, so that the carbon content of the surface layer of the hard alloy pressed compact is higher than that of the core part of the hard alloy pressed compact; after the liquid phase appears in the hard alloy pressed compact, as the appearing time and the appearing amount of the liquid phase are related to the carbon content, the higher the carbon content is, the earlier the appearing time of the liquid phase is, and the more the amount of the liquid phase is; in the sintering process, the carbon content of the surface layer of the hard alloy pressed compact is increased under the action of carburizing gas, and a liquid phase of the surface layer of the hard alloy pressed compact appears firstly and flows to the core part of the hard alloy pressed compact; after sintering is completed, a gradient alloy structure with high surface carbon content and low core carbon content is formed in the hard alloy pressed compact, and the surface liquid phase of the hard alloy pressed compact is different due to different gas amounts of surface carburization generated in each container, so that the formed cobalt phase gradient is different, and the purpose of preparing hard alloys with different cobalt phase gradients is achieved.