Gradient Structure Coated Cemented Carbide Cutting Tools with Sharp Angle Effect and Preparation Method Thereof

Abstract

The present invention belongs to the technical field of powder metallurgy, and specifically relates to a hard alloy tool with a sharp-corner effect gradient structure coating and a preparation method thereof. While having a β-phase-depleted layer in the surface layer area of the tool, the β-phase is retained at the tool tip, making the tool not only have good toughness but also maintain good wear resistance. In the pressing die of the present invention, a prefabricated groove is provided at the pressing position of the tool tip of the die body and the punch. The existence of this prefabricated groove results in a low-density β-phase migration area at the tool tip of the tool compact. During the sintering process, not only can a β-phase-depleted layer be formed, but also the enrichment of the β-phase can be achieved at the tool tip. By improving the pressing die, the present invention obtains a tool blank with a low-density prefabricated protrusion, and in cooperation with the sandblasting effect, a tool substrate with the β-phase in contact with the tool tip is obtained. This invention can stably obtain a hard alloy tool with a sharp-corner effect gradient structure without a complex sintering process, greatly reducing the production difficulty, improving the product quality, having a high qualified rate, and being easy to industrialize.

Description

Technical Field

[0001] The present invention belongs to the technical field of powder metallurgy, and particularly relates to a cemented carbide cutting tool with a sharp-corner effect gradient structure coating and a preparation method thereof. Background Art

[0002] Cemented carbide is an alloy material made of refractory metal hard compounds (such as WC, TiC, TaC, NbC, Mo2C, etc.) and binder metals (such as Co, Ni, Fe, etc.). Due to a series of excellent properties such as high hardness, wear resistance, good strength and toughness, heat resistance, and corrosion resistance, it is known as the "industrial tooth" and is widely used as a cutting tool material. With the addition of cubic phases such as TiC, TaC, NbC, and their composite carbides, the high-temperature red hardness and wear resistance of cemented carbide are greatly improved, remaining basically unchanged even at a temperature of 500 °C and still having a high hardness at 1000 °C. Therefore, it is often used to prepare cutting tools for non-ferrous metals.

[0003] However, current cemented carbides are difficult to achieve an ideal balance among properties such as yield strength, red hardness, resistance to plastic deformation, and wear resistance, but can only improve one or several of the above properties. For example, while improving the hardness and toughness of cemented carbide, it is often difficult to ensure the yield strength of the alloy and problems such as plastic deformation. Gradient treatment of the cemented carbide surface is carried out to enable different parts to have different functions. For example, for a cemented carbide with a surface decarburized β-layer gradient structure, a tough layer lacking cubic phase and rich in binder phase with a thickness of about 10 - 100 μm is prepared on its surface. The Co content on the surface of its matrix is 1 - 2 times the average Co content of the matrix. The decarburized β-layer has high toughness and can absorb the thermal stress generated during the cooling process due to the difference in thermal expansion coefficients between the coating and the matrix during vapor deposition coating, slowing down the propagation of microcracks into the matrix during tool use, thereby increasing the service life of the tool. However, at the cutting edge of the cutting tool, due to the interaction of the denitrification driving forces on both sides, the absence of a cubic-phase-free and Co-rich structure at the tip of the cutting edge will reduce the yield strength and red hardness of the material. During the cutting process, the cutting edge will bear severe thermal and mechanical loads. The absence of cubic phase and the presence of a rich binder phase at the cutting edge easily lead to plastic deformation of the cutting edge of this type of cemented carbide, reducing the wear resistance of the tool face.

[0004] In order to solve the problems that traditional tool substrates are prone to cracks and the wear resistance of gradient substrates is poor, a gradient substrate in which the β-phase is in contact with the tool tip and contains a β-depleted layer has well solved the above problems. However, at present in the industry, in order to obtain a gradient structure with a sharp-corner effect, a composition sintering process method is generally adopted. For example, Patent CN102002664B discloses a preparation method of a gradient structure cemented carbide. First, a gradient alloy precursor is obtained by decarburizing the surface of the cemented carbide to a certain depth through a surface oxidation method, that is, the standard cemented carbide is buried in a mixed filler of Mg(OH)2 and Al2O3 in a certain proportion and heat-treated in a hydrogen atmosphere at a high temperature for a certain time to locally decarburize the alloy within a certain depth range to generate the η-phase, and then the decarburized sample is subjected to solid carburizing treatment to obtain a gradient structure cemented carbide with a gradient binder phase. Another example is Patent CN113652629A, which discloses a functionally gradient structure cemented carbide, its preparation method and application. Its preparation method adopts a two-step carburizing sintering process of low-temperature deposition + high-temperature carburizing to obtain a functionally gradient structure cemented carbide. Patent CN112846259B discloses a method for preparing a cemented carbide substrate with a cubic-phase-containing gradient structure on the surface layer and its preparation method. However, at the tool tip of the alloy, due to the interaction of the driving forces on both sides, the amount of cubic phase at the tool tip is still insufficient, affecting problems such as high-temperature red hardness. At the same time, in the non-tool tip part, due to the presence of the cubic phase, the overall toughness of the tool will be reduced, thereby reducing the processing range of the tool.

[0005] In summary, in the current preparation methods, there are few reports on the preparation of cemented carbide with a gradient substrate in which the β-phase is in contact with the tool tip and contains a β-depleted layer. How to prepare a gradient structure coated cemented carbide tool with a β-depleted layer on the tool and retaining the β-phase at the tool tip has become a new technical difficulty. Summary of the Invention

[0006] To solve the problems existing in the prior art, the main object of the present invention is to propose a gradient structure coated cemented carbide tool with a sharp-corner effect and its preparation method.

[0007] To solve the above technical problems, according to one aspect of the present invention, the following technical solutions are provided:

[0008] A gradient structure coated cemented carbide tool with a sharp-corner effect, comprising:

[0009] A tool substrate formed of cemented carbide and a coating formed on the substrate;

[0010] The tool substrate has a surface layer region and a homogeneous region located on the side of the surface layer region away from the coating; the surface layer region has a β-depleted layer while retaining the β-phase at the tool tip.

[0011] As a preferred embodiment of the cemented carbide cutting tool with a sharp-corner effect gradient structure coating according to the present invention, wherein: the cemented carbide includes a hard phase and a binder phase. Based on the total mass of the cemented carbide, the mass fraction of the binder phase is 4.5 to 20 wt%, and the mass fraction of the hard phase is 80 to 95.5 wt%.

[0012] As a preferred embodiment of the cemented carbide cutting tool with a sharp-corner effect gradient structure coating according to the present invention, wherein: the hard phase of the cemented carbide includes at least one of tungsten carbide, titanium carbide, tantalum carbide, niobium carbide or their composite carbides; the binder phase of the cemented carbide contains Co, and optionally Fe and Ni.

[0013] As a preferred embodiment of the cemented carbide cutting tool with a sharp-corner effect gradient structure coating according to the present invention, wherein: the particle size range of the hard phase is 0.1 to 10 μm.

[0014] To solve the above technical problems, according to another aspect of the present invention, the present invention provides the following technical solutions:

[0015] A method for preparing a cemented carbide cutting tool with a sharp-corner effect gradient structure coating, comprising the following steps:

[0016] S1. Provide a prefabricated groove at the tip pressing positions of the die body and the punch of the pressing die;

[0017] S2. Ball-mill the cemented carbide raw materials, the inducer for surface decarburization layer, and the molding agent, and after drying, press and mold to obtain a green compact;

[0018] S3. Place the green compact in a vacuum atmosphere and heat up to remove the molding agent;

[0019] S4. Sinter the green compact from which the molding agent has been removed in a slightly pressurized nitrogen atmosphere to obtain a cutting tool blank;

[0020] S5. Perform sandblasting on the cutting tool blank to obtain a cutting tool substrate;

[0021] S6. After cleaning the cutting tool substrate, perform chemical vapor deposition to obtain a coated cemented carbide cutting tool;

[0022] S7. Perform sandblasting on the coated cemented carbide cutting tool to obtain a cemented carbide cutting tool with a sharp-corner effect gradient structure.

[0023] As a preferred embodiment of the preparation method of the cemented carbide cutting tool with a sharp-corner effect gradient structure according to the present invention, wherein: in the step S1, the cross-sectional size of the prefabricated groove is 0.025 - 0.035 mm × 0.015 - 0.025 mm; the size of the prefabricated groove of the die body and the tool tip is the same, and the depth of the prefabricated groove is 2.8 - 3.2 mm; in the present invention, a prefabricated groove is provided at the tool tip pressing position of the die body and the punch of the pressing die. The existence of this prefabricated groove enables a low-density β-phase migration zone at the tool tip of the tool compact. During the sintering process, a β-phase removal layer can be formed, and it can also ensure the existence of the β-phase at the tool tip part. The traditional die does not have this prefabricated groove, and the prepared compact is flat, making it difficult to stably form a sharp-corner effect gradient structure by physical methods.

[0024] As a preferred embodiment of the preparation method of the cemented carbide cutting tool with a sharp-corner effect gradient structure according to the present invention, wherein: in the step S1, the pressing die includes a core rod, a die body, an ejector, a punch and an outer sleeve.

[0025] As a preferred embodiment of the preparation method of the cemented carbide cutting tool with a sharp-corner effect gradient structure according to the present invention, wherein: in the step S2, the inducer of the surface β-phase removal layer is TiCN, and the ratio of C and N in the TiCN is 8:2 - 5:5; the mass of the inducer of the surface β-phase removal layer is 0.5 - 0.7% of the mass of the cemented carbide raw material.

[0026] As a preferred embodiment of the preparation method of the cemented carbide cutting tool with a sharp-corner effect gradient structure according to the present invention, wherein: in the step S4, the sintering process is as follows:

[0027] The first sintering heat preservation stage: when the sintering temperature rises to 1200 - 1250 °C, an inert gas with a pressure of 50 - 200 mbar is introduced, and sintering is carried out under an inert atmosphere with a heating rate of 2 - 5 °C / min;

[0028] The second sintering low-pressure heat preservation stage: when the sintering temperature rises to 1400 - 1470 °C, the furnace pressure is reduced to 30 - 100 mbar, and heat preservation sintering is carried out for 30 - 50 min under the inert atmosphere;

[0029] The third sintering low-pressure heat preservation stage: keep the sintering temperature at 1400 - 1470 °C, and carry out heat preservation sintering under a vacuum atmosphere for 30 - 60 min;

[0030] The fourth sintering high-pressure heat preservation stage: keep the sintering temperature at 1400 - 1470 °C, and carry out heat preservation sintering under a high-pressure argon atmosphere for 30 - 90 min, and the sintering pressure is 2 - 10 MPa;

[0031] The first cooling stage: cooling the green compact to 1150 - 1250 °C in an argon atmosphere;

[0032] The second cooling stage: introducing high-pressure argon and cooling the green compact to room temperature in a high-pressure argon atmosphere.

[0033] As a preferred embodiment of the preparation method of the cemented carbide cutting tool with a gradient structure coating having a sharp corner effect of the present invention, wherein: in the step S7, the sandblasting medium is corundum with a mesh size of 180 - 220, and the sandblasting pressure is 0.3 - 0.4 MPa.

[0034] The beneficial effects of the present invention are as follows:

[0035] The present invention provides a cemented carbide cutting tool with a gradient structure coating having a sharp corner effect and a preparation method thereof. While having a β-phase removal layer in the surface layer area of the cutting tool, the β-phase is retained at the tip of the cutting tool, making the cutting tool not only have good toughness but also maintain good wear resistance; in the pressing die of the present invention, a prefabricated groove is provided at the tip pressing part of the die body and the punch. The existence of this prefabricated groove enables a low-density β-phase migration area at the tip of the cutting tool green compact. During the sintering process, not only can a β-phase removal layer be formed, but also β-phase enrichment can be achieved at the tip of the cutting tool; by improving the pressing die, the present invention obtains a tool blank with low-density prefabricated protrusions, and in cooperation with the sandblasting effect, a tool substrate with β-phase contacting the tip of the cutting tool is obtained. This invention can stably obtain a cemented carbide cutting tool with a gradient structure having a sharp corner effect without a complex sintering process, greatly reducing the production difficulty and improving the product quality; through the combined physical action of the pressing die and sandblasting, the present invention prepares a cemented carbide cutting tool with a gradient structure having a sharp corner effect. The products prepared by this method have stable quality, high qualification rate, and are easy to industrialize. Description of the Drawings

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on the structures shown in these drawings.

[0037] Figure 1 It is a schematic diagram of the mold of the present invention;

[0038] Figure 2 It is an enlarged view of the punch of the mold of the present invention and an enlarged view of the prefabricated groove;

[0039] Figure 3 It is a view of the die body of the mold of the present invention and an enlarged view of the prefabricated groove;

[0040] Figure 4 It is an enlarged view of the ejector of the mold of the present invention and an enlarged view of the prefabricated groove;

[0041] Figure 5 It is the metallographic analysis diagram of sample A prepared in Embodiment 1 of the present invention;

[0042] Figure 6 It is the metallographic analysis diagram of sample E prepared in Comparative Example 1 of the present invention;

[0043] Figure 7 It is the metallographic analysis diagram of sample F prepared in Comparative Example 2 of the present invention;

[0044] Figure 8 It is the metallographic analysis diagram of sample G prepared in Comparative Example 3 of the present invention;

[0045] Figure 9 It is the metallographic analysis diagram of sample H prepared in Comparative Example 4 of the present invention.

[0046] Wherein, 1-core rod, 2-ejector, 3-die body, 4-compact, 5-punch.

[0047] The realization, functional features and advantages of the object of the present invention will be further described with reference to the embodiments and the accompanying drawings. Detailed Embodiments

[0048] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0049] The present invention is made based on the inventor's discovery and recognition of the following facts and problems:

[0050] The inventors have found that it is difficult for current cemented carbides to achieve an ideal balance among properties such as yield strength, hot hardness, resistance to plastic deformation, and wear resistance. This is mainly due to the unreasonable internal structure of the cemented carbide. Specifically, in order to improve the toughness of the cemented carbide, absorb the thermal stress generated during the cooling process due to the different thermal expansion coefficients between the coating and the substrate during vapor deposition coating, and slow down the propagation of microcracks into the substrate during tool use, thereby increasing the service life of the tool, a gradient layer with a certain thickness of cubic-phase-deficient can be formed on the surface layer of the cemented carbide substrate. The cubic-phase-deficient phase does not contain hard and brittle cubic phases, so it has relatively high toughness. However, due to the absence of a cubic-phase-rich cobalt structure on the surface, when this type of cemented carbide substrate with a cobalt-rich cubic-phase-free gradient structure on the surface layer is used as the tool substrate, it will reduce the yield strength and hot hardness of the material. As a result, the cutting edge of the tool made of this type of cemented carbide is prone to plastic deformation, leading to a decrease in the wear resistance of the tool face. The main object of the present invention is to propose a coated cemented carbide tool with a sharp-corner effect gradient structure and a preparation method thereof.

[0051] According to one aspect of the present invention, the present invention provides the following technical solution:

[0052] A coated cemented carbide tool with a sharp-corner effect gradient structure, comprising:

[0053] A tool substrate formed of cemented carbide and a coating formed on the substrate;

[0054] The tool substrate has a surface layer region and a homogeneous region located on the side of the surface layer region away from the coating; the surface layer region has a β-phase-depleted layer while retaining the β-phase at the tool tip.

[0055] Wherein, the average binder phase content in the surface layer region is 1 to 2 times the average cobalt content of the substrate, which can effectively absorb the energy of crack propagation into the substrate during tool service, thereby improving the chipping resistance and coating spalling resistance of the alloy; retaining the β-phase at the tool tip can greatly improve the wear resistance and hot hardness of the alloy, and still have good cutting edge integrity at a relatively high cutting temperature, enabling high-speed, high-efficiency and precision cutting of the tool. The tool combines hardness and toughness, high yield strength and high-temperature hot hardness, and can be applied to various high-speed, high-precision or strong interrupted turning processes. This tool can improve the plastic deformation of the cutting edge, and can also improve the chipping resistance and coating spalling resistance of the tool. In addition, the multi-layer coating on the tool substrate and the tool substrate act synergistically, which can greatly improve the hardness and wear resistance of the tool on the basis of maintaining the toughness of the tool substrate and the ability of the cutting edge to resist plastic deformation.

[0056] Preferably, the cemented carbide comprises a hard phase and a binder phase. Based on the total mass of the cemented carbide, the mass fraction of the binder phase is 4.5 to 20 wt%, and the mass fraction of the hard phase is 80 to 95.5 wt%. Specifically, the mass fraction of the binder phase can be, for example but not limited to, any one of 4.5 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt% or the range between any two of them; the mass fraction of the hard phase can be, for example but not limited to, any one of 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 95.5 wt% or the range between any two of them; The inventors have found that when the composition of the cemented carbide is within the above range, both the hardness and toughness of the tool can be ensured, it is more conducive to the formation of the β-depleted layer during the sintering process, and the enrichment of the β-phase can be achieved at the tool tip, and better effects can be obtained.

[0057] Preferably, the hard phase of the cemented carbide comprises at least one of tungsten carbide, titanium carbide, tantalum carbide, niobium carbide or their composite carbides; the binder phase of the cemented carbide contains Co, and optionally Fe, Ni.

[0058] Preferably, the particle size of the hard phase is 0.1 to 10 μm. Specifically, the particle size of the hard phase can be, for example but not limited to, any one of 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or the range between any two of them;

[0059] According to another aspect of the present invention, the present invention provides the following technical solution:

[0060] A preparation method of a cemented carbide tool with a sharp-corner effect gradient structure coating, comprising the following steps:

[0061] S1. A prefabricated groove is arranged at the tool tip pressing positions of the die body and the punch of the pressing die;

[0062] S2. Ball-mill the cemented carbide raw materials, the inducer for the surface β-depleted layer, and the molding agent, and after drying, press them into a green compact;

[0063] S3. Place the green compact in a vacuum atmosphere and heat it up to remove the molding agent;

[0064] S4. Sinter the green compact from which the forming agent has been removed in a slightly pressurized nitrogen atmosphere to obtain a tool blank;

[0065] S5. Perform sandblasting on the tool blank to obtain a tool substrate;

[0066] S6. After cleaning the tool substrate, perform chemical vapor deposition to obtain a coated cemented carbide tool;

[0067] S7. Perform sandblasting on the coated cemented carbide tool to obtain a coated cemented carbide tool with a sharp-corner effect gradient structure.

[0068] Preferably, in step S1, as Figure 1 shown in the schematic diagram of the mold of the present invention, where Figure 1 (A) is the overall view of the mold, Figure 1 (B) is the enlarged view of the green compact and the sharp corner. The pressing mold includes a core rod 1, a die body 3, an ejector 2, a punch 5 and an outer sleeve; among them, the core rod 1 is placed at the bottom and is connected to the ejector 2. The ejector 2 is connected to the die body 3, and the punch 5 is at the top. During the pressing process: the core rod 1 remains stationary, the punch 5 reciprocates up and down for one round trip, that is, the pressing of the green compact 4 is completed, and the ejector 2 moves upward to eject the green compact 4.

[0069] Preferably, in step S1, as Figure 2 shown in the enlarged view of the punch and the prefabricated groove of the mold of the present invention, where Figure 2 (A) is the overall view of the punch, Figure 2 (B) is the enlarged view of the prefabricated groove, Figure 2 (C) is the enlarged view of the punch; as Figure 3 shown in the die body diagram and the enlarged view of the prefabricated groove of the mold of the present invention, where Figure 3 (A) is the overall view of the die body, Figure 3 (B) is the view of the die cavity, Figure 3 (C) is the enlarged view of the prefabricated groove in the die cavity; as Figure 4 shown in the ejector and the enlarged view of the prefabricated groove of the mold of the present invention, where Figure 4 (A) is the overall view of the ejector, Figure 4 (B) is the left view of the ejector, Figure 4(C) in the figure is an enlarged view of the ejector prefabricated groove; the cross-sectional size of the prefabricated groove is 0.025 - 0.035 mm × 0.015 - 0.025 mm; the size of the prefabricated groove of the die body is the same as that of the cutting edge tip, and the depth of the prefabricated groove is 2.8 - 3.2 mm; the present invention has no other more special limitations on the punch, and the punch well-known to those skilled in the art can be used; the present invention provides a prefabricated groove at the pressing position of the die body and the cutting edge tip of the pressing die. The existence of this prefabricated groove enables a low-density β-phase migration zone to exist at the cutting edge tip of the tool compact. During the sintering process, not only can a β-phase removal layer be formed, but also the existence of the β-phase at the cutting edge tip can be ensured. The traditional die is not provided with this prefabricated groove, and the prepared compact is flat, making it difficult to stably form a gradient structure with a corner effect by physical methods. The applicant's research found that the volume of the prefabricated groove has an important impact on whether a stable cemented carbide tool with a corner effect gradient structure can be formed; the inventor also found that within the above reasonable range of prefabricated groove sizes, it is easier to prepare the cemented carbide tool with the corner effect gradient structure described in the present invention; since the β-phase migration zone is obtained through the prefabricated groove, if the volume of the prefabricated groove is too large, the density of the migration zone will be too low; if the volume of the prefabricated groove is too small, the β-phase migration will be insufficient, resulting in the inability to form a stable cemented carbide tool with a corner effect gradient structure.

[0070] Preferably, in the step S2, the inducer of the surface β-phase removal layer is TiCN, and the ratio of C and N in the TiCN is 8:2 - 5:5. Specifically, the ratio of C and N in the TiCN can be, for example but not limited to, any one or any range between any two of 8:2, 7:3, 6:4, 5:5; the mass of the inducer of the surface β-phase removal layer is 0.5 - 0.7% of the mass of the cemented carbide raw material; the inventor found that when the mass of the inducer of the surface β-phase removal layer is within the above range, the performance of the formed β-phase removal layer is beneficial to improving the service life of the tool and better effects can be obtained. The molding agent can be a conventional molding agent in the art. For example, the molding agent is paraffin.

[0071] Preferably, in the step S4, the sintering process is:

[0072] The first sintering heat preservation stage: When the sintering temperature rises to 1200 - 1250 °C, an inert gas with a pressure of 50 - 200 mbar is introduced, and heating sintering is carried out under an inert atmosphere with a heating rate of 2 - 5 °C / min; specifically, the temperature can be, for example but not limited to, any one of 1200 °C, 1210 °C, 1220 °C, 1230 °C, 1240 °C, 1250 °C or the range between any two of them; the pressure of the inert gas can be, for example but not limited to, any one of 50 mbar, 80 mbar, 100 mbar, 120 mbar, 140 mbar, 160 mbar, 180 mbar, 200 mbar or the range between any two of them; the heating rate can be, for example but not limited to, any one of 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min or the range between any two of them;

[0073] The second sintering low - pressure heat preservation stage: When the sintering temperature rises to 1400 - 1470 °C, the pressure in the furnace is reduced to 30 - 100 mbar, and heat preservation sintering is carried out for 30 - 50 min under the inert atmosphere; specifically, the temperature can be, for example but not limited to, any one of 1400 °C, 1410 °C, 1420 °C, 1430 °C, 1440 °C, 1450 °C, 1460 °C, 1470 °C or the range between any two of them; the pressure in the furnace can be, for example but not limited to, any one of 30 mbar, 40 mbar, 50 mbar, 60 mbar, 70 mbar, 80 mbar, 90 mbar, 100 mbar or the range between any two of them; the time can be, for example but not limited to, any one of 30 min, 35 min, 40 min, 45 min, 50 min or the range between any two of them;

[0074] The third sintering low - pressure heat preservation stage: Keep the sintering temperature at 1400 - 1470 °C, and carry out heat preservation sintering under a vacuum atmosphere for 30 - 60 min; specifically, the temperature can be, for example but not limited to, any one of 1400 °C, 1410 °C, 1420 °C, 1430 °C, 1440 °C, 1450 °C, 1460 °C, 1470 °C or the range between any two of them; the time can be, for example but not limited to, any one of 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min or the range between any two of them;

[0075] Fourth sintering high-pressure heat preservation stage: Keep the sintering temperature at 1400 - 1470 °C, perform heat preservation sintering under a high-pressure argon atmosphere, with a sintering time of 30 - 90 min and a sintering pressure of 2 - 10 MPa; specifically, the temperature can be, for example but not limited to, any one of 1400 °C, 1410 °C, 1420 °C, 1430 °C, 1440 °C, 1450 °C, 1460 °C, 1470 °C or the range between any two of them; the time can be, for example but not limited to, any one of 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min or the range between any two of them; the sintering pressure can be, for example but not limited to, any one of 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, 10 MPa or the range between any two of them;

[0076] First cooling stage: Cool the green compact to 1150 - 1250 °C under an argon atmosphere; specifically, the temperature can be, for example but not limited to, any one of 1150 °C, 1160 °C, 1170 °C, 1180 °C, 1190 °C, 1200 °C, 1210 °C, 1220 °C, 1230 °C, 1240 °C, 1250 °C or the range between any two of them;

[0077] Second cooling stage: Introduce high-pressure argon and cool the green compact to room temperature under a high-pressure argon atmosphere.

[0078] Preferably, in step S7, the sandblasting medium is corundum with a mesh size of 180 - 220, and the sandblasting pressure is 0.3 - 0.4 MPa. The inventor's research found that within the above reasonable range of corundum mesh size and air pressure, it is easier to prepare the cemented carbide cutting tool with a corner effect gradient structure described in the present invention; if the corundum is too coarse, it is easy to damage the tool substrate; if the corundum is too fine, the impact force is insufficient, and it is difficult to obtain a stable cemented carbide cutting tool with a corner effect gradient structure coating; in addition, when the air pressure is lower than 0.3 MPa, the prefabricated protrusions cannot be removed, and when the air pressure is higher than 0.4 MPa, it will affect the roughness of the tool substrate, and it is still difficult to obtain a stable cemented carbide cutting tool with a corner effect gradient structure coating.

[0079] The technical solution of the present invention will be further described below in conjunction with specific embodiments.

[0080] Example 1

[0081] A preparation method of a cemented carbide cutting tool with a corner effect gradient structure coating includes the following steps:

[0082] S1. Set a prefabricated groove at the tip pressing positions of the die body and the punch in the pressing die. The cross-sectional size of the prefabricated groove is 0.03 mm × 0.02 mm, and the depth of the prefabricated groove is 3.0 mm;

[0083] S2. Ball mill the cemented carbide raw materials, the inducer for surface β-phase removal, and the molding agent, and after drying, press them into a green compact; the cemented carbide raw materials include a hard phase and a binder phase, the binder phase is cobalt with a mass fraction of 8 wt%, the hard phase is a composite carbide, among which, the mass fraction of the carbides of tantalum, niobium and titanium is 7 wt%, and the mass fraction of the particle size of tungsten carbide is 85 wt%; the inducer for surface β-phase removal is TiCN, and its mass is 0.6% of the mass of the cemented carbide raw materials, and the ratio of C and N in TiCN is 7:3; the molding agent is paraffin wax.

[0084] S3. Place the green compact under a vacuum atmosphere and raise the temperature to remove the molding agent;

[0085] S4. Sinter the green compact from which the molding agent has been removed under a slightly pressurized nitrogen atmosphere to obtain a tool blank; the sintering process is as follows:

[0086] The first sintering holding stage: When the sintering temperature rises to 1200 °C, introduce an inert gas at 100 mbar, and perform heating and sintering under an inert atmosphere, and the heating rate is 3 °C / min;

[0087] The second sintering low-pressure holding stage: When the sintering temperature rises to 1450 °C, reduce the furnace pressure to 50 mbar under the inert atmosphere and hold for sintering for 30 min;

[0088] The third sintering low-pressure holding stage: Keep the sintering temperature at 1450 °C and perform holding sintering under a vacuum atmosphere for 30 min;

[0089] The fourth sintering high-pressure holding stage: Keep the sintering temperature at 1450 °C and perform holding sintering under a high-pressure argon atmosphere for 30 min, and the sintering pressure is 6 MPa;

[0090] The first cooling stage: Cool the green compact to 1150 °C under an argon atmosphere;

[0091] The second cooling stage: Introduce high-pressure argon and cool the green compact to room temperature under a high-pressure argon atmosphere;

[0092] S5. Perform sandblasting on the tool blank to obtain a tool substrate;

[0093] S6. After cleaning the tool substrate, perform chemical vapor deposition to obtain a coated cemented carbide tool;

[0094] S7. Perform sandblasting on the coated cemented carbide tool, the sandblasting medium is corundum with a mesh size of 200, and the sandblasting pressure is 0.35 MPa to obtain a coated cemented carbide tool sample A with a sharp-corner effect gradient structure. The metallographic analysis diagram of sample A is asFigure 5 As shown, sample A retains the decarburized layer, and the β-phase has good contact with the tool tip.

[0095] Example 2

[0096] A preparation method of a cemented carbide cutting tool with a gradient structure coating having a sharp corner effect includes the following steps:

[0097] S1. A prefabricated groove is set at the tool tip pressing positions of the die body and the punch of the pressing die. The cross-sectional size of the prefabricated groove is 0.0295 mm × 0.015 mm, and the depth of the prefabricated groove is 2.8 mm;

[0098] S2. The cemented carbide raw material, the inducer for the surface decarburized layer, and the forming agent are ball-milled, and after drying, they are pressed into a green compact; the cemented carbide raw material includes a hard phase and a binder phase. The binder phase is cobalt, and its mass fraction is 4.5 wt%. The hard phase is a composite carbide. Among them, the mass fraction of the carbides of tantalum, niobium, and titanium is 5.5 wt%, and the mass fraction of the particle size of tungsten carbide is 90 wt%. The inducer for the surface decarburized layer is TiCN, and its mass is 0.5% of the mass of the cemented carbide raw material. The ratio of C and N in TiCN is 8:2. The forming agent is paraffin.

[0099] S3. The green compact is placed in a vacuum atmosphere and heated to remove the forming agent;

[0100] S4. The green compact after removing the forming agent is sintered in a slightly pressurized nitrogen atmosphere to obtain a tool blank; the sintering process is as follows:

[0101] The first sintering holding stage: When the sintering temperature rises to 1200 °C, an inert gas of 100 mbar is introduced, and sintering is carried out under an inert atmosphere with a heating rate of 3 °C / min;

[0102] The second sintering low-pressure holding stage: When the sintering temperature rises to 1450 °C, the furnace pressure is reduced to 50 mbar under the inert atmosphere, and holding sintering is carried out for 30 min;

[0103] The third sintering low-pressure holding stage: Keep the sintering temperature at 1450 °C, and carry out holding sintering in a vacuum atmosphere for 30 min;

[0104] The fourth sintering high-pressure holding stage: Keep the sintering temperature at 1450 °C, and carry out holding sintering in a high-pressure argon atmosphere for 30 min, and the sintering pressure is 6 MPa;

[0105] The first cooling stage: Cool the green compact to 1150 °C in an argon atmosphere;

[0106] The second cooling stage: Introduce high-pressure argon, and cool the green compact to room temperature in a high-pressure argon atmosphere.

[0107] S5. Sandblast the tool blank to obtain the tool substrate;

[0108] S6. After cleaning the tool substrate, perform chemical vapor deposition to obtain a coated cemented carbide tool;

[0109] S7. Sandblast the coated cemented carbide tool with corundum of 200 mesh as the sandblasting medium and a sandblasting pressure of 0.35 MPa to obtain a coated cemented carbide tool sample B with a sharp-corner effect gradient structure. Sample B retains the β-depleted layer, and the β-phase has good contact with the tool tip.

[0110] Example 3

[0111] A preparation method of a coated cemented carbide tool with a sharp-corner effect gradient structure includes the following steps:

[0112] S1. Set a prefabricated groove at the tool tip pressing positions of the die body and the punch in the pressing die. The cross-sectional size of the prefabricated groove is 0.035 mm × 0.025 mm, and the depth of the prefabricated groove is 3.2 mm;

[0113] S2. Ball-mill the cemented carbide raw material, the inducer for the surface β-depleted layer, and the forming agent, and after drying, press and form to obtain a green compact; The cemented carbide raw material includes a hard phase and a binder phase. The binder phase is cobalt, and its mass fraction is 20 wt%. The hard phase is a composite carbide. Among them, the mass fraction of the carbides of tantalum, niobium, and titanium is 7.5 wt%, and the mass fraction of the grain size of tungsten carbide is 72.5 wt%. The inducer for the surface β-depleted layer is TiCN, and its mass is 0.7% of the mass of the cemented carbide raw material. The ratio of C and N in TiCN is 5:5. The forming agent is paraffin.

[0114] S3. Place the green compact in a vacuum atmosphere and heat up to remove the forming agent;

[0115] S4. Sinter the green compact from which the forming agent has been removed in a slightly pressurized nitrogen atmosphere to obtain a tool blank; The sintering process is as follows:

[0116] The first sintering holding stage: When the sintering temperature rises to 1200 °C, introduce an inert gas of 100 mbar, and perform heating and sintering in an inert atmosphere with a heating rate of 3 °C / min;

[0117] The second sintering low-pressure holding stage: When the sintering temperature rises to 1450 °C, reduce the furnace pressure to 50 mbar in the inert atmosphere and hold for sintering for 30 min;

[0118] The third sintering low-pressure holding stage: Keep the sintering temperature at 1450 °C and perform holding sintering in a vacuum atmosphere for 30 min;

[0119] The fourth sintering high-pressure heat preservation stage: maintain the sintering temperature at 1450 °C, perform heat preservation sintering in a high-pressure argon atmosphere, the sintering time is 30 min, and the sintering pressure is 6 MPa;

[0120] The first cooling stage: cool the green compact to 1150 °C in an argon atmosphere;

[0121] The second cooling stage: introduce high-pressure argon, and cool the green compact to room temperature in a high-pressure argon atmosphere.

[0122] S5. Perform sandblasting on the tool blank to obtain a tool substrate;

[0123] S6. After cleaning the tool substrate, perform chemical vapor deposition to obtain a coated cemented carbide tool;

[0124] S7. Perform sandblasting on the coated cemented carbide tool, the sandblasting medium is corundum with a mesh size of 200, and the sandblasting pressure is 0.35 MPa to obtain a coated cemented carbide tool sample C with a sharp-corner effect gradient structure. Sample C retains the decarburized β layer, and the β phase has good contact with the tool tip.

[0125] Example 4

[0126] A preparation method of a coated cemented carbide tool with a sharp-corner effect gradient structure, comprising the following steps:

[0127] S1. Set a prefabricated groove at the tool tip pressing positions of the die body and the punch in the pressing die. The cross-sectional size of the prefabricated groove is 0.03 mm × 0.02 mm, and the depth of the prefabricated groove is 3.0 mm;

[0128] S2. Ball-mill the cemented carbide raw material, the inducer for the surface decarburized β layer, and the molding agent, and press and mold them after drying to obtain a green compact; the cemented carbide raw material includes a hard phase and a binder phase. The binder phase is cobalt, and its mass fraction is 8 wt%. The hard phase is a composite carbide. Among them, the mass fraction of the carbides of tantalum, niobium, and titanium is 7 wt%, and the mass fraction of the particle size of tungsten carbide is 85 wt%. The inducer for the surface decarburized β layer is TiCN, and its mass is 0.6% of the mass of the cemented carbide raw material. The ratio of C and N in TiCN is 7:3. The molding agent is paraffin.

[0129] S3. Place the green compact in a vacuum atmosphere and heat it up to remove the molding agent;

[0130] S4. Sinter the green compact from which the molding agent has been removed in a slightly pressurized nitrogen atmosphere to obtain a tool blank; the sintering process is as follows:

[0131] The first sintering heat preservation stage: When the sintering temperature rises to 1200 °C, an inert gas of 100 mbar is introduced, and heating sintering is carried out in an inert atmosphere at a heating rate of 3 °C / min;

[0132] The second sintering low-pressure heat preservation stage: When the sintering temperature rises to 1450 °C, the pressure in the furnace is reduced to 50 mbar in the inert atmosphere, and heat preservation sintering is carried out for 30 min;

[0133] The third sintering low-pressure heat preservation stage: Keep the sintering temperature at 1450 °C, and carry out heat preservation sintering in a vacuum atmosphere for 30 min;

[0134] The fourth sintering high-pressure heat preservation stage: Keep the sintering temperature at 1450 °C, and carry out heat preservation sintering in a high-pressure argon atmosphere for 30 min, and the sintering pressure is 6 MPa;

[0135] The first cooling stage: Cool the green compact to 1150 °C in an argon atmosphere;

[0136] The second cooling stage: Introduce high-pressure argon, and cool the green compact to room temperature in a high-pressure argon atmosphere.

[0137] S5. Carry out sandblasting treatment on the tool blank to obtain a tool substrate;

[0138] S6. After cleaning the tool substrate, carry out chemical vapor deposition to obtain a coated cemented carbide tool;

[0139] S7. Carry out sandblasting treatment on the coated cemented carbide tool, the sandblasting medium is corundum with a mesh size of 220, and the sandblasting pressure is 0.4 MPa, to obtain a coated cemented carbide tool sample D with a sharp-corner effect gradient structure. Sample D retains the β-depleted layer, and the β-phase is in good contact with the tool tip.

[0140] Comparative Example 1

[0141] The difference from Example 1 is that a traditional pressing die is used to replace the die described in Example 1 to obtain sample E. The metallographic analysis diagram of sample E is as Figure 6 shown. Sample E has a β-depleted layer, but the β-phase is not in contact with the tool tip.

[0142] Comparative Example 2

[0143] The difference from Example 4 is that in S7. Carry out sandblasting treatment on the coated cemented carbide tool, the sandblasting medium is corundum with a mesh size of 200, and the sandblasting pressure is 0.5 MPa, to obtain a coated cemented carbide tool sample F with a sharp-corner effect gradient structure. The metallographic analysis diagram of sample F is as Figure 7 shown. The β-depleted layer of sample F is damaged, and the surface of the product becomes pitted.

[0144] Comparative Example 3

[0145] The difference from Example 4 is that in S7, the coated cemented carbide cutting tool is subjected to sandblasting treatment. The sandblasting medium is corundum with a size of 200, and the sandblasting pressure is 0.1 MPa, obtaining a coated cemented carbide cutting tool sample G with a gradient structure of cusp effect. The metallographic analysis diagram of sample G is as shown in Figure 8 shown. Due to the too low sandblasting pressure of sample G, the migration zone of the specimen is not completely removed.

[0146] Comparative Example 4

[0147] The difference from Example 4 is that in S1, prefabricated grooves are provided at the tip pressing positions of the die body and the punch of the pressing die. The cross-sectional size of the prefabricated grooves is 0.010 mm × 3.0 mm, and the depth of the prefabricated grooves is 3.0 mm; obtaining a coated cemented carbide cutting tool sample H with a gradient structure of cusp effect. The metallographic analysis diagram of sample H is as shown in Figure 9 shown. The β phase of sample H has a tendency to approach the tip but does not contact it, and the product is unqualified.

[0148] It can be seen from the above embodiments that the pressing die of the present invention is provided with prefabricated grooves with specific dimensions at the tip pressing positions of the die body and the punch. The existence of the prefabricated grooves enables a low-density β phase migration zone to be formed at the tip of the cutting tool blank, which can not only form a β-depleted layer during the sintering process but also achieve the enrichment of the β phase at the tip; by improving the pressing die, the present invention obtains a cutting tool blank with low-density prefabricated protrusions. In cooperation with the sandblasting effect, by setting the sandblasting parameters, a cutting tool substrate with the β phase contacting the tip is obtained. The present invention can stably obtain a cemented carbide cutting tool with a gradient structure of cusp effect without a complex preparation and sintering process, greatly reducing the production difficulty and improving the product quality; through the physical cooperation of the pressing die and sandblasting, the present invention prepares a cemented carbide cutting tool with a gradient structure of cusp effect. The products prepared by this method have stable quality, high qualification rate, and are easy to industrialize.

[0149] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural transformation made using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect application in other related technical fields, is included in the patent protection scope of the present invention.

Claims

1. A cemented carbide cutting tool with a gradient structure coating having a sharp corner effect, characterized in that, Comprising: A tool substrate formed of cemented carbide and a coating formed on the substrate; The tool substrate has a surface layer region and a homogeneous region located on the side of the surface layer region away from the coating; the surface layer region has a β-phase depleted layer while retaining the β-phase at the tool tip; The preparation method of the tool includes the following steps: S1. A prefabricated groove is provided at the tool tip pressing positions of the die body and the punch of the pressing die; the cross-sectional size of the prefabricated groove is 0.025 - 0.035 mm × 0.015 - 0.025 mm, and the depth of the prefabricated groove is 2.8 - 3.2 mm; S2. Cemented carbide raw materials, an inducer for surface β-phase depletion, and a forming agent are ball-milled, and after drying, they are pressed into a green compact; S3. The green compact is placed in a vacuum atmosphere and heated to remove the forming agent; S4. The green compact after removing the forming agent is sintered in a slightly pressurized nitrogen atmosphere to obtain a tool blank; S5. The tool blank is subjected to sandblasting to obtain a tool substrate; S6. After cleaning the tool substrate, chemical vapor deposition is carried out to obtain a coated cemented carbide tool; S7. The coated cemented carbide tool is subjected to sandblasting to obtain a coated cemented carbide tool with a sharp-corner effect gradient structure.

2. The cutting tool according to claim 1, characterized in that, The cemented carbide includes a hard phase and a binder phase. Based on the total mass of the cemented carbide, the mass fraction of the binder phase is 4.5 - 20 wt%, and the mass fraction of the hard phase is 80 - 95.5 wt%.

3. The cutting tool according to claim 2, characterized in that, The hard phase of the cemented carbide includes at least one of tungsten carbide, titanium carbide, tantalum carbide, niobium carbide or their composite carbides; the binder phase of the cemented carbide contains Co, and optionally Fe, Ni.

4. The cutting tool according to claim 2, wherein, The particle size range of the hard phase is 0.1 - 10 μm.

5. A method for preparing the cutting tool according to any one of claims 1-4, characterized in that, Including the following steps: S1. A prefabricated groove is provided at the tool tip pressing positions of the die body and the punch of the pressing die; S2. Cemented carbide raw materials, an inducer for surface β-phase depletion, and a forming agent are ball-milled, and after drying, they are pressed into a green compact; S3. The green compact is placed in a vacuum atmosphere and heated to remove the forming agent; S4. The green compact after removing the forming agent is sintered in a slightly pressurized nitrogen atmosphere to obtain a tool blank; S5. The tool blank is subjected to sandblasting to obtain a tool substrate; S6. After cleaning the tool substrate, chemical vapor deposition is carried out to obtain a coated cemented carbide tool; S7. The coated cemented carbide tool is subjected to sandblasting to obtain a coated cemented carbide tool with a sharp-corner effect gradient structure.

6. The preparation method according to claim 5, wherein In step S1, the pressing die includes a core rod, a die body, an ejector, a punch and an outer sleeve.

7. The preparation method according to claim 5, characterized in that, In step S2, the inducer for surface β-phase depletion is TiCN, and the ratio of C and N in the TiCN is 8:2 - 5:5, and the mass of the inducer for surface β-phase depletion is 0.5 - 0.7% of the mass of the cemented carbide raw materials.

8. The preparation method according to claim 5, characterized in that, In step S4, the sintering process is: The first sintering holding stage: When the sintering temperature rises to 1200 - 1250 °C, an inert gas of 50 - 200 mbar is introduced, and sintering is carried out under an inert atmosphere with a heating rate of 2 - 5 °C / min; The second sintering low-pressure heat preservation stage: When the sintering temperature rises to 1400~1470 °C, the pressure in the furnace drops to 30~100 mbar, and heat preservation and sintering are carried out for 30~50 min under the inert atmosphere; The third sintering low-pressure heat preservation stage: Keep the sintering temperature at 1400~1470 °C, and carry out heat preservation and sintering in a vacuum atmosphere, and the sintering time is 30~60 min; The fourth sintering high-pressure heat preservation stage: Keep the sintering temperature at 1400~1470 °C, and carry out heat preservation and sintering in a high-pressure argon atmosphere, the sintering time is 30~90 min, and the sintering pressure is 2~10 MPa; The first cooling stage: Cool the green compact to 1150~1250 °C in an argon atmosphere; The second cooling stage: Introduce high-pressure argon, and cool the green compact to room temperature in a high-pressure argon atmosphere.

9. The preparation method according to claim 5, characterized in that, In the step S7, the sandblasting medium is corundum with a mesh size of 180~220, and the sandblasting pressure is 0.3~0.4 MPa.

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