PcBN composite sheet for machining quenched steel and preparation method

Abstract

The invention discloses a PcBN composite sheet for processing quenched steel. The formula of the PcBN composite sheet comprises 45-95 parts of titanium-plated cubic boron nitride micro powder, 2-5 parts of aluminum powder, 3-37 parts of nitride or carbide ceramic powder, 0-3 parts of titanium carbonitride and 0-10 parts of aluminum oxide. The PcBN composite sheet has high strength, high red hardness and wear resistance when being used for processing various quenched steel, and is suitable for cutting the quenched steel, various intermittent heavy load processing and continuous finish processing.

Description

Technical Field

[0001] The invention relates to PcBN material technology, in particular to a PcBN composite sheet for machining quenched steel and a preparation method thereof. Background Art

[0002] Cubic boron nitride (cBN) is the second hardest material in the world known to date, and its Vickers hardness can reach 7200~9800. Although its hardness is not as high as diamond, its thermal stability and chemical stability are far superior to diamond. Its hardness does not drop significantly at 1200℃, and it is chemically inert to metal elements such as Fe, Cr, Ni, and Co. Therefore, it has significant advantages in processing ferrous metal materials. Cubic boron nitride polycrystalline (PcBN) composite sheet (hereinafter referred to as PcBN composite sheet) is a tool material synthesized by combining cubic boron nitride powder, binder powder, and cemented carbide matrix at 1300~1900℃ and 4~8GPa high temperature and high pressure. It solves the problems of small size, anisotropy and inability to process cubic boron nitride crystals, and has the characteristics of high strength, high hardness, and good machinability. It is currently the most commonly used cubic boron nitride tool material with significant performance advantages and broad market prospects. PcBN composite sheets can be divided into three categories according to the materials they are used to process: 1. PcBN composite sheet for processing cast iron (including gray cast iron, ductile cast iron, boron-containing wear-resistant cast iron, etc.).

[0003] 2. PcBN composite sheets for processing powder metallurgy (including iron-based alloys, nickel-based alloys, cobalt-based alloys, etc.).

[0004] 3. PcBN composite sheets are used for processing hardened steel (bearing steel with HRC ≥ 55, die steel, 20CrMnTi carburizing steel, etc.).

[0005] In the machinery manufacturing industry, more and more manufacturers use PcBN tools to replace grinding with turning, and milling with grinding to manufacture parts, especially for the processing of hardened steel. Hardened steel is widely used in the automotive and mold industries, such as gears, shafts, bearings, molds, etc.; the market is huge. Due to the high hardness and strength of hardened steel and high processing precision requirements, the PcBN blade is subjected to large shear force, large friction and high temperature (up to 1000°C or above) during cutting. This requires the PcBN composite sheet used for processing hardened steel to have high wear resistance, strength and toughness at high temperatures; that is, it has excellent red hardness, wear resistance and toughness. Since metal binders have low strength and poor wear resistance at high temperatures, in order to ensure the red hardness and wear resistance of composite sheets for processing hardened steel, the formula design is mainly based on ceramic binders. Commonly used binders are: TiN, TiC, TINC, WC, Al2O3, etc.; but ceramics are relatively brittle and are prone to chipping and edge loss during high-speed cutting. Therefore, the red hardness, wear resistance and toughness of composite sheets for processing hardened steel have always been a contradiction and are difficult to coexist. At present, the commonly used solution is to add a small amount of metal binder to the formula, sacrificing some red hardness and wear resistance to improve its toughness. Commonly used metal binders include Co, W, Ni, Ti, etc. Studies have shown that Ti can react with cBN at high temperatures to produce TiN and TiB2, both of which have high hardness, wear resistance and thermal stability. Therefore, adding Ti can not only improve the strength and toughness of the composite sheet, but also ensure its wear resistance, and has a significant effect on improving the comprehensive performance of low-content PcBN composite sheets for processing quenched steel; but there are two problems with the conventional addition of Ti powder: one is that Ti powder is easily oxidized into TiO2 in the air, which is difficult to preserve and control during the production process; the other is that ultrafine metal Ti powder is highly active and easily agglomerated, and it is difficult to ensure uniform distribution during the production process, resulting in uneven organization. These two problems greatly reduce the use effect of Ti powder. Summary of the invention

[0006] The purpose of the present invention is to solve the problem that Ti powder is easily oxidized into TiO2 in the air, which is difficult to store and control during the production process, and ultrafine metal Ti powder is highly active and easily agglomerated, which is difficult to ensure uniform distribution during the production process, resulting in uneven organization. The present invention proposes a PcBN composite sheet for processing hardened steel and a preparation method. The PcBN composite sheet has high strength, high red hardness and wear resistance when processing various hardened steels, and is suitable for cutting hardened steel, various intermittent heavy-load processing and continuous finishing.

[0007] The technical solution for achieving the purpose of the present invention is: A PcBN composite sheet for machining quenched steel, wherein the formula of the PcBN composite sheet comprises: 45-95 parts of titanium-plated cubic boron nitride powder, 2-5 parts of aluminum powder, 3-37 parts of nitride or carbide ceramic powder, 0-3 parts of titanium carbonitride, and 0-10 parts of aluminum oxide.

[0008] The titanium-coated cubic boron nitride powder has a particle size of 0-5 μm and a purity greater than 99.99%, and the aluminum powder has a particle size of 0-2 μm and a purity greater than 99.9%.

[0009] The nitride or carbide is one of titanium nitride, titanium carbide and tungsten carbide, with a particle size of 0-2 μm and a purity greater than 99.8%.

[0010] A method for preparing a PcBN composite sheet for processing quenched steel comprises the following steps: 1) Weigh titanium-coated cubic boron nitride, aluminum, titanium carbonitride, nitride and alumina powders, add carbide balls and wetting agents at a ball-to-material ratio of 12:1 for high-energy ball milling to make the powders evenly mixed; 2) Place the powder obtained in step 1) into a vacuum oven at 0.1 Pa and dry at 60-80°C for 4 hours; 3) Grind the powder obtained in step 2) again and sieve it through a 200-mesh sieve; 4) Put the powder obtained in step 3) into a metal mold cup and perform high temperature vacuum treatment at a temperature above 700°C and a vacuum degree of 10 -3 Pa or above; 5) Put the metal cup and powder after high-temperature vacuum purification into the carbon salt tube, put the carbon salt tube into the pyrophyllite cavity, and then put the titanium sheet and powder ring plug in sequence. Put the assembled pyrophyllite block into a 120℃ oven and dry it for 0.5~2h; 6) The assembly block obtained in step 5) is placed in a six-sided top press for synthesis. The parameters of the six-sided top press are: pressure of 5~5.5GPa, temperature of 1350~1550℃, synthesis time of 3~25min, and finally a PcBN composite sheet is obtained.

[0011] In the step 1), the wetting agent is ethanol or acetone.

[0012] Ti reacts with CBN at high temperature to produce TIN and TiB2, as shown in the following formula: , .

[0013] Beneficial effects of this technical solution: This technical solution makes full use of the titanium coating on the surface of cBN particles to solve the problem of easy oxidation and agglomeration of ultrafine titanium powder, and also plays the role of titanium powder. Titanium powder reacts with cubic boron nitride at high temperature to produce titanium nitride and titanium boride. Both titanium nitride and titanium boride have the characteristics of high hardness, high thermal stability, and stable chemical properties. While improving the strength of cubic boron nitride composite sheets, it also ensures its wear resistance and red hardness. The prepared cubic boron nitride composite sheet has the advantages of high strength, high red hardness and wear resistance when processing various hardened steels. The cubic boron nitride composite sheet of this technical solution is particularly suitable for cutting hardened steel, various intermittent heavy-load processing and continuous finishing. For example, when it is heavy-loaded cutting hardened steel above HRC58, the single-side cutting depth can reach 0.5mm, and when continuously processing hardened steel above HRC58, the line speed can reach 200~250m / min. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The PcBN composite sheet of Example 1 with an average particle size of 4 μm; Figure 2 This is a SEM photo of a cross section of a PcBN composite sheet with an average particle size of 4 μm in Example 1; Figure 3 The PcBN composite sheet of Example 2 has an average particle size of 1.5 μm; Figure 4 This is a SEM photograph of a cross-section of a PcBN composite sheet with an average particle size of 1.5 μm in Example 2. DETAILED DESCRIPTION

[0015] The content of the present invention is further described below in conjunction with the drawings and embodiments, but the present invention is not limited thereto.

[0016] Embodiment 1: 1) Select titanium-coated cubic boron nitride powder with a particle size of 4 μm as the raw material, the mass fraction of titanium-coated cubic boron nitride powder to the raw material powder is 70%; the mass fraction of aluminum powder, titanium carbonitride and titanium nitride to the raw material powder is 30%, among which the mass ratio of titanium nitride to titanium carbonitride is 6:1, and the content of aluminum powder is not more than 5% of the total mass fraction, and then add carbide balls and wetting agents for high-energy ball milling to mix the powders evenly. In this case, the wetting agent is ethanol; 2) Place the powder obtained in step 1) into a vacuum oven at 0.1 Pa and dry at 70°C for 4 h; 3) Grind the powder obtained in step 2) again and sieve it through a 200-mesh sieve; 4) Put the powder obtained in step 3) into a metal mold cup and perform high temperature vacuum treatment at a temperature of 800°C and a vacuum degree of 10 -3 Pa; 5) Put the metal cup and powder after high-temperature vacuum purification into the carbon salt tube, put the carbon salt tube into the pyrophyllite cavity, and then put the titanium sheet and powder ring plug in sequence, and put the assembled pyrophyllite block into a 120℃ oven for drying for 2h; 6) The assembled block obtained in step 5) is placed in a six-sided top press for synthesis. The parameters of the six-sided top press are: pressure of 5 GPa, temperature of 1500°C, and synthesis time of 12 min. Finally, a PcBN composite sheet is obtained, such as Figure 1 , Figure 2 shown.

[0017] The polycrystalline cubic boron nitride tool material prepared by the method of Example 1 has a microhardness of HV3100 and a bending strength of 1250 MPa, and is mainly used for intermittent processing and heavy-load processing of hardened steel.

[0018] Embodiment 2: 1) Select titanium-coated cubic boron nitride powder with a particle size of 1.5 μm as the raw material, the mass fraction ratio of titanium-coated cubic boron nitride powder to raw material powder is 50%; the mass fraction ratio of aluminum powder, titanium carbonitride and titanium nitride to raw material powder is 50%, among which the mass ratio of titanium nitride to titanium carbonitride is 8:1, and the content of aluminum powder is not more than 6% of the total mass fraction, and then add carbide balls and wetting agents for high-energy ball milling to make the powders evenly mixed. In this case, the wetting agent is ethanol; 2) Place the powder obtained in step 1) into a vacuum oven at 0.1 Pa and dry at 70°C for 4 h; 3) Grind the powder obtained in step 2) again and sieve it through a 200-mesh sieve; 4) Put the powder obtained in step 3) into a metal mold cup and perform high temperature vacuum treatment at a temperature of 800°C and a vacuum degree of 10 -3 Pa; 5) Put the metal cup and powder after high-temperature vacuum purification into the carbon salt tube, put the carbon salt tube into the pyrophyllite cavity, and then put the titanium sheet and powder ring plug in sequence, and put the assembled pyrophyllite block into a 120℃ oven for drying for 2h; 6) The assembled block obtained in step 5) is placed in a six-sided top press for synthesis. The parameters of the six-sided top press are: pressure of 5.5 GPa, temperature of 1500°C, synthesis time of 12 min, and finally a PcBN composite sheet is obtained. Figure 3 , Figure 4 shown.

[0019] The polycrystalline cubic boron nitride tool material prepared by the method of Example 2 has a microhardness of HV2800 and a bending strength of 950 MPa, and is mainly used for continuous finishing of hardened steel.

Claims

1. A PcBN composite sheet for machining hardened steel, characterized in that: The formula of the PcBN composite sheet includes: 45-95 parts of titanium-plated cubic boron nitride powder, 2-5 parts of aluminum powder, 3-37 parts of nitride or carbide ceramic powder, 0-3 parts of titanium carbonitride, and 0-10 parts of aluminum oxide.

2. The PcBN composite sheet for hardened steel according to claim 1, characterized in that: The titanium-coated cubic boron nitride powder has a particle size of 0-5 μm and a purity greater than 99.99%, and the aluminum powder has a particle size of 0-2 μm and a purity greater than 99.9%.

3. The PcBN composite sheet for hardened steel according to claim 1, characterized in that: The nitride or carbide is one of titanium nitride, titanium carbide and tungsten carbide, with a particle size of 0-2 μm and a purity greater than 99.8%.

4. A method for preparing a PcBN composite sheet for processing hardened steel, characterized in that: The steps include: 1) Weigh titanium-coated cubic boron nitride, aluminum, titanium carbonitride, nitride and alumina powders, add carbide balls and wetting agents at a ball-to-powder ratio of 12:1, and perform high-energy ball milling to mix the powders evenly; 2) Place the powder obtained in step 1) into a vacuum oven at 0.1 Pa and dry at 60-80°C for 4 hours; 3) Grind the powder obtained in step 2) again and sieve it through a 200-mesh sieve; 4) Put the powder obtained in step 3) into a metal mold cup and perform high temperature vacuum treatment at a temperature above 700°C and a vacuum degree of 10 -3 Pa or above; 5) Put the metal mold cup and powder after high-temperature vacuum purification into the carbon salt tube, put the carbon salt tube into the pyrophyllite cavity, and then put the titanium sheet and powder ring plug in sequence. Put the assembled pyrophyllite block into a 120℃ oven and dry it for 0.5~2h; 6) The assembly block obtained in step 5) is placed in a six-sided top press for synthesis. The parameters of the six-sided top press are: pressure of 5~5.5GPa, temperature of 1350~1550℃, synthesis time of 3~25min, and finally a PcBN composite sheet is obtained.

5. The method for preparing a PcBN composite sheet for machining hardened steel according to claim 4, characterized in that: In the step 1), the wetting agent is ethanol or acetone.

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