A gradient cemented carbide with a varying distribution of grain sizes of the hard phase and a method for producing the same

Abstract

The application discloses a gradient cemented carbide with varied distribution of hard phase particle size and a preparation method thereof. The gradient cemented carbide comprises a first zone, a second zone and a third zone from outside to inside, the first zone comprises WC and Co, the second zone comprises WC, Co and FCC, the third zone comprises WC, Co and FCC, WC1>WC2, WC1>WC3, WC2<WC3, FCC2>FCC3, and the area percentage of FCC in the second zone is greater than that in the third zone. The preparation method comprises preparing raw materials, compression molding and sintering. The gradient cemented carbide can realize the alloy characteristics of 'high-toughness surface layer-high-plastic-deformation-resistance layer-high-bending-strength core', can cope with higher-speed and higher-efficiency processing requirements without changing the alloy matrix component system, and can realize industrialized production with convenient preparation process.

Description

Technical Field

[0001] This invention belongs to the field of CVD coated gradient cemented carbide cutting tool technology, specifically relating to a gradient cemented carbide with varying hard phase particle size distribution and its preparation method. Background Technology

[0002] The WC-Co-(W,Ti,Ta,Nb)CN system cemented carbide matrix has a tough gradient layer (typically 5-50 μm thick) of cobalt-rich, cubic solid solution phase near the surface. This layer effectively prevents the rapid propagation of CVD coating cracks into the matrix during machining, significantly improving the machining life of CVD-coated tools. Therefore, gradient cemented carbide has always been a core technology and research hotspot in the field of steel turning CVD CNC inserts. Here, the (W,Ti,Ta,Nb)CN phase is a cubic solid solution phase formed by refractory carbides such as TaC, NbC, TiC, (W,Ti)C, or (TaNb)C, abbreviated as FCC. In recent years, with the gradual improvement of the properties of machined materials and the increasing complexity of working conditions, market demands have placed higher requirements on the gradient cemented carbide matrix for CVD-coated CNC tools. High-speed machining temperatures are rising, thus the need to improve the high-temperature hardness of the gradient cemented carbide matrix to resist high-temperature plastic deformation is becoming increasingly prominent. Simultaneously achieving low surface hardness and high toughness to effectively prevent CVD coating cracks from propagating into the matrix, and increasing the high-temperature hardness of the gradient cemented carbide matrix to resist high-temperature plastic deformation, have become key technical breakthroughs in the field of cemented carbide cutting tools.

[0003] Based on the Hall-Petch formula and the relationship between fracture toughness and Vickers hardness:

[0004] Hv=A+Bd -1 / 2 ………………………………………(1)

[0005] K 1C =A(F Hv / ΣL) 1 / 2 …………………………………(2)

[0006] In formula (1), A and B are material-related constants, and d is the average grain size. The higher the grain size, the lower the Hv. In formula (2), A is a material-related constant, F is the load, and ΣL is the length of the indentation crack at the top of the material. From formulas (1) and (2), it can be seen that the alloy hardness Hv decreases with the increase of grain size d. Under the same load conditions, when the material Hv decreases, the length of the indentation crack at the top of the material ΣL will decrease significantly, and thus the K of the material will decrease. 1C An increase in hardness, i.e., a decrease in hardness, results in higher fracture toughness in the material.

[0007] The hardness of refractory metal cubic carbide raw materials is typically higher than WC's 1780 N / mm. 2For example, the hardness of TiC, TiN, and NbC is 3200 N / mm². 2 2450N / mm 2 1961 N / mm 2 The hardness (especially hot hardness at high temperatures) of cubic carbonitrides formed by solid solutions of TiC, TaC, and NbC is significantly higher than that of WC. Compared to WC-Co cemented carbides, increasing FCC can significantly improve the high-temperature hardness of the gradient cemented carbide matrix, thereby enhancing the hot hardness of the cutting tool under continuous high-temperature machining conditions. However, FCC is a brittle hard phase, and an excessively high proportion will greatly reduce the bending strength of the alloy, so it needs to be controlled within a suitable range.

[0008] Zhang Weibin disclosed a dual-gradient cemented carbide in Chinese patent document CN106048360A. This method involves adding ZrC / HfC to a conventional gradient cemented carbide formulation. Utilizing the interstitial dissolution between Ti-rich cubic solid solutions and Zr / Hf-rich cubic solid solutions, a dual-gradient structure with different distributions of Co and cubic phases is formed during a denitrification process. However, this patent document does not describe the particle size distribution of the hard phase, and this method requires the addition of ZrC / HfC to the raw materials and a nitrogen removal sintering process to achieve its purpose. ZrC readily forms ZrO2 defects in powder metallurgy, which are distributed throughout the gradient alloy, significantly reducing the alloy's bending strength and shortening the lifespan of CVD CNC tools. Chinese patent document CN109161711B discloses a method for preparing an ultrafine-grained gradient cemented carbide with a dual-gradient structure and a WC particle size of 0.1-0.5μm. The sintering process of this technology involves first forming a dense, non-gradient cemented carbide, and then performing a secondary re-sintering process to form a dual-gradient structure. This process is complex, doubles the cost, and is not suitable for industrial production.

[0009] In summary, in order to meet the increasing demand in the steel market for CVD-coated gradient carbide tools, it is necessary to develop new gradient carbide tools that ensure high bending strength in the core of the material, while possessing the technical characteristics of high toughness in the surface layer and high hardness in the subsurface layer. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a gradient cemented carbide and its preparation method that achieves the mechanical properties of "high toughness surface layer - high hardness sub-surface layer" by controlling the hard phase particle size (including WC grain size, cubic solid solution FCC grain size and FCC particle size) and phase change distribution of the near-surface layer (usually 200 μm) of the gradient cemented carbide, thereby ensuring the material has high core bending strength.

[0011] To solve the above-mentioned technical problems, the present invention adopts the following technical solution.

[0012] A gradient cemented carbide with varying hard phase particle size distribution, comprising a first region, a second region, and a third region from the outside to the inside (i.e., from the outer surface to the core). The first region includes WC and Co, the second region includes WC, Co, and FCC, and the third region is the core region, including WC, Co, and FCC. FCC refers to a cubic solid solution phase composed of refractory compounds, wherein the refractory compounds are one or two of refractory carbonitrides and refractory nitrides combined with refractory carbides, and the refractory carbides include Ti-containing carbides. The Ti-containing carbides include TiC and / or (W,Ti)C, the refractory carbonitrides include TiCN, and the refractory nitrides include TiN; the average grain size of WC in the first region is denoted as WC1, the average grain size of WC in the second region is denoted as WC2, and the average grain size of WC in the third region is denoted as WC3, then WC1 > WC3 > WC2; the average grain size of FCC in the second region is denoted as FCC2, and the average grain size of FCC in the third region is denoted as FCC3, then FCC2 > FCC3.

[0013] For the gradient cemented carbide with the aforementioned hard phase grain size variation distribution, preferably, 1 < WC1:WC2 ≤ 1.5, 1 < WC1:WC3 ≤ 1.3, and 0.8 ≤ WC2:WC3 ≤ 1.5. 3. <1; 1 < FCC2: FCC 3. ≤1.6.

[0014] Preferably, in the gradient cemented carbide with the above-mentioned hard phase grain size variation distribution, the area ratio of FCC in the second region is greater than that in the third region, and the total length L2 of the EBSD grain boundary of FCC in the second region is greater than that of the total length L3 of the EBSD grain boundary of FCC in the third region.

[0015] The gradient cemented carbide with the above-mentioned hard phase particle size variation distribution is preferably 1 < L2 : L3 < 1.3.

[0016] In the gradient cemented carbide with the above-mentioned hard phase particle size variation distribution, preferably, the average particle size of FCC in the second region is denoted as FCCP2, and the average particle size of FCC in the third region is denoted as FCCP3, then FCCP2 > FCCP3, and 1 < FCCP2 : FCCP3 ≤ 1.6.

[0017] In the aforementioned gradient cemented carbide with varying hard phase particle size distribution, preferably, the refractory carbides further include one or more of TaC, NbC, (Ta,Nb)C, Cr3C2, and VC.

[0018] Preferably, in the gradient cemented carbide with the aforementioned hard phase grain size variation distribution, based on the total mass of each region, Co in the first region exhibits a bell-shaped distribution, and the point with the highest mass fraction of Co in the first region is denoted as Co. 1maxThe second region has a uniform distribution of Co, and the average mass fraction of Co in the second region is denoted as Co2. The third region has a uniform distribution of Co, and the average mass fraction of Co in the third region is denoted as Co3. Therefore, Co... 1max In Co2 and Co3, Co 1max For the maximum value, 1.5 ≤ Co 1max ∶Co3≤2.2, Co2<Co3.

[0019] Preferably, in the gradient cemented carbide with varying hard phase particle size distribution, the thickness D1 of the first region is 5 μm to 40 μm, the thickness D2 of the second region is 30 μm to 100 μm, and D2 > D1.

[0020] As a general technical concept, the present invention also provides a method for preparing the above-mentioned gradient cemented carbide with varying hard phase grain size distribution, comprising the following steps:

[0021] (1) Preparation of raw materials: Based on the total mass of raw materials, the following percentages are calculated by mass: Co 5%–12%, Ti 2%–8%, Ta 0%–5%, Nb 0%–5%, Cr 0%–0.3%, V 0%–0.3%, N 0.06%–1%, C 6.2%–6.9%, with the remainder being W;

[0022] (2) Pressing and molding: The above raw materials, molding agent, ball milling rod and alcohol are mixed and wet milled. The resulting slurry is dried and sieved to form a mixed powder, which is then pressed into a green embryo.

[0023] (3) Alloy sintering: The above green sample is heated to 300℃~450℃ for H2 sintering. The forming agent in the sample is removed by Towack process at 400℃~500℃. Then, under vacuum conditions, the sample is heated to 1300℃~1370℃, 20mbar~100mbar N2 is introduced and sintered for 20min~30min. Then, the sample is heated to 1390℃~1420℃ and sintered for 10min~40min. The sample is cooled to 800℃~1200℃ and sintered for 10min~30min. After vacuum sintering for 0.2min~2min, 20mbar~200mbar Ar gas is introduced and the sample is heated to 1420℃~1480℃ and sintered for 30min~60min. Then, 30bar~100bar inert gas Ar is introduced and sintered under pressure for 10min~30min. Finally, the sample is cooled to room temperature to obtain a gradient cemented carbide with varying hard phase particle size distribution.

[0024] In the preferred method for preparing the gradient cemented carbide with varying hard phase particle size distribution described above, in step (1), the following percentages by mass are: Co 5%–12%, Ti 2%–8%, Ta 0.5%–5%, Nb 0.5%–5%, Cr 0%–0.3%, V 0%–0.3%, N 0.06%–1%, C 6.2%–6.9%, with the balance being W.

[0025] In the preferred embodiment of the above-mentioned method for preparing gradient cemented carbide with varying hard phase particle size distribution, in step (1), the raw material sources for the W element include WC powder and / or (W,Ti)C solid solution powder; the raw material sources for the Ti element include one or more of TiC powder, TiCN powder, (W,Ti)C solid solution powder, and TiN powder; the raw material sources for the Ta element include TaC powder and / or (Ta,Nb)C solid solution powder; the raw material sources for the Nb element include NbC powder and / or (Ta,Nb)C solid solution powder; the raw material sources for the N element include TiCN powder and / or TiN powder; the raw material sources for the Co element include Co powder; the raw material sources for the Cr element include Cr3C2 powder; and the raw material sources for the V element include VC powder.

[0026] In the preferred embodiment of the above-mentioned method for preparing gradient cemented carbide with varying hard phase particle size distribution, the Fsss particle size of the Co powder is 1.2 μm to 1.5 μm, the Fsss particle size of the (W,Ti)C solid solution powder is 1.5 μm to 2.0 μm, the Fsss particle size of the TiCN powder is 0.8 μm to 1.5 μm, the Fsss particle size of the (Ta,Nb)C solid solution powder is 1.0 μm to 2 μm, the Fsss particle size of the TiC powder, TiN powder, TaC powder, VC powder, Cr3C2 powder, and NbC powder is 1.0 μm to 2.0 μm, and the Fsss particle size of the WC powder is 3.0 μm to 4.0 μm.

[0027] In the preferred method for preparing the gradient cemented carbide with varying hard phase particle size distribution described above, in step (2), the forming agent is PEG, the mass of the forming agent is 1.5% to 2.5% of the total mass of the raw materials in step (1), the mass of the ball milling rod is 4 to 6 times the total mass of the raw materials in step (1), the amount of alcohol added is 200 mL to 300 mL of alcohol per kilogram of raw materials, and the wet milling time is 25 h to 40 h.

[0028] In the preferred method for preparing gradient cemented carbide with varying hard phase particle size distribution, step (2) involves drying at a temperature of 60°C to 120°C, drying for 2 hours to 3 hours, and sieving through a 60-80 mesh sieve.

[0029] In this invention, WC and FCC in a gradient cemented carbide are polycrystalline materials. The average grain size is the average size of grains with the same growth orientation and crystal boundary. The size is characterized by the equivalent circle diameter of the two-dimensional grain area after the sample is cut and polished. The average particle size of FCC refers to the average size of an agglomerate composed of one or more FCC grains. Each FCC agglomerate is surrounded by other phases and has a clear phase boundary. The size is characterized by the equivalent circle diameter of the two-dimensional FCC particle area after the sample is cut and polished.

[0030] Compared with the prior art, the advantages of the present invention are as follows:

[0031] (1) This invention proposes and realizes a novel gradient cemented carbide through process control. The alloy consists of three regions from the surface to the core. The particle size distribution of the phases and hard phases varies in the three regions. The first layer includes only WC and Co. WC has the largest average grain size and the highest Co content. There is no brittle hard phase FCC, which ensures the high toughness advantage of the gradient cemented carbide surface layer. The second region includes WC, Co and FCC. WC has the finest average grain size and the highest FCC proportion. At the same time, the FCC grain boundary proportion is the highest, which ensures the highest hardness of the sub-surface layer. The core has a uniform distribution of WC-Co-FCC three phases, which ensures the high bending strength advantage of the main body of the alloy matrix, thereby realizing the alloy characteristics of "high toughness surface layer - high hardness sub-surface layer - high bending strength core".

[0032] (2) The gradient cemented carbide in this invention is composed of WC, Co, (W,Ti)C, (Ta,Nb)C, TaC, NbC, TiCN, Cr3C2 or VC, and the particle size system Fsss is 0.8μm-4.0μm. All of these are commonly used raw materials for cemented carbide, which are convenient for production.

[0033] (3) In the preparation method of the present invention, the particle size of the hard phase and the thickness of the first and second regions in the three regions can be controlled by the component ratio and sintering procedure, which helps to meet the requirements of different processing conditions on the tool substrate structure when the substrate technology is applied to CVD coated tools. Attached Figure Description

[0034] Figure 1 This is a bar chart of the average grain size of the hard phase in each region of the gradient cemented carbide with varying hard phase grain size distribution according to Example 1 of the present invention. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. All materials and instruments used in the following embodiments are commercially available.

[0036] In the following examples and comparative examples, the characterization method was as follows: the prepared samples were cut to expose the alloy core cross-section, and the alloy cross-section was metallographically ground and polished using a Struer metallographic sample preparation instrument until it was flat, smooth, and free of obvious scratches. A Zeiss Supra 55 field emission scanning electron microscope and an Oxford X-MAX 50mm energy dispersive spectrometer were used. 2 The microstructure and composition of the alloy core were analyzed. Data acquisition and analysis were performed on the first and second depleted regions and the core of the sample using an Oxford Instruments Nordlys EBSD system. The average grain size of the hard phase, the proportion of FCC to the total phase area, and the FCC grain boundary length were statistically analyzed. The microhardness and fracture toughness (Ki) of the three regions of the sample were measured using an AFFRI microhardness tester. 1C Conduct the test.

[0037] Example 1

[0038] A gradient cemented carbide with varying hard phase particle size distribution according to the present invention comprises a first region, a second region, and a third region from the outside to the inside (from the outer surface to the core). The first region includes WC and Co, the second region includes WC, Co, and FCC, where FCC is a cubic solid solution phase composed of (W,Ti)C, TiCN, (Ta,Nb)C, TaC, Cr3C2, and VC, and the third region is the core region, comprising WC, Co, and FCC. Figure 1 As shown, the average grain size of WC in the first region is denoted as WC1, the average grain size of WC in the second region is denoted as WC2, and the average grain size of WC in the third region is denoted as WC3. The ratios of WC1 to WC2 are 1.19 and 1.13, respectively. 3. =0.95, WC1>WC3>WC2; the average grain size of FCC in the second region is denoted as FCC2, and the average grain size of FCC in the third region is denoted as FCC3, FCC2∶FCC 3. =1.34.

[0039] In this embodiment, the area ratio of FCC in the second region is 25% (based on the total area of ​​the test area), and the area ratio of FCC in the third region is 16%. Furthermore, the total grain boundary length L2 of FCC in the second region is greater than the total grain boundary length L3 of FCC in the third region, with L2:L3 = 1.16.

[0040] In the first region of this embodiment, Co exhibits a bell-shaped distribution, and the point with the highest mass fraction content is denoted as Co1. max In the second region, Co is uniformly distributed, and its average mass fraction is denoted as Co2. In the third region, Co is uniformly distributed, and its average mass fraction is denoted as Co3. 1max =14.7% is the maximum value, Co2=6.3%, Co3=7.46%, Co 1max∶Co 3. =1.97.

[0041] In this embodiment, the thickness D1 of the first region is 36 μm, the thickness D2 of the second region is 55 μm, and D2 > D1.

[0042] In this embodiment, the average granularity of the FCC in the second zone is denoted as FCCP2, and the average granularity of the FCC in the third zone is denoted as FCCP3, with FCCP2:FCCP3 = 1.38.

[0043] A method for preparing a gradient cemented carbide with varying hard phase particle size distribution according to this embodiment includes the following steps:

[0044] (1) Prepare raw materials according to the elements and proportions of gradient cemented carbide: Based on the total mass of the raw materials, the mass percentages are as follows: Co is 7.5%, Ta is 2.5%, Nb is 1.3%, Ti is 3.5%, Cr is 0.2%, V is 0.2%, N is 0.16%, C is 6.45%, and the remainder is W;

[0045] (2) Pressing and molding: The above raw materials, molding agent, ball milling rod and alcohol are mixed and wet milled. The resulting slurry is dried and sieved to obtain a mixture, which is then pressed into a green embryo.

[0046] (3) Alloy sintering: The above green blank is heated to 370℃ for H2 sintering, and the forming agent in the sample is removed by Towack process at 450℃. Then, under vacuum conditions, the temperature is raised to 1340℃, 40mbar N2 is introduced and sintered for 30min, then the temperature is raised to 1410℃ and sintered for 20min, then the temperature is lowered to 1000℃ and sintered for 20min, vacuum sintering for 0.5min, 40mbar Ar gas is introduced and the temperature is raised to 1450℃ and sintered for 50min, 60bar inert gas Ar is introduced and sintered under pressure for 10min, and then the temperature is lowered to room temperature to obtain a gradient cemented carbide with varying hard phase particle size distribution.

[0047] In step (1) of this embodiment, the raw material sources for Co element include Co powder, the raw material sources for W element include WC powder and (W,Ti)C solid solution powder, the raw material sources for Ti element are TiCN powder and (W,Ti)C solid solution powder, the raw material sources for Ta element are (Ta,Nb)C solid solution powder and TaC powder, the raw material sources for Nb element are (Ta,Nb)C solid solution powder, the raw material source for Cr element is Cr3C2 powder, the raw material source for V element is VC powder, the raw material source for N element is TiCN powder, and the C element comes from the carbides of the above elements.

[0048] In this embodiment, the Fsss particle sizes of the raw materials are as follows: Co powder is 1.3 μm, (W,Ti)C solid solution powder is 1.58 μm, TiCN powder is 1.3 μm, (Ta,Nb)C solid solution powder is 1.6 μm, TaC powder is 1.1 μm, VC powder is 1.4 μm, Cr3C2 powder is 1.4 μm, and WC powder is 3.3 μm.

[0049] In step (2) of this embodiment, the molding agent is PEG, the mass of the molding agent is 2% of the total mass of the raw materials in step (1), the mass of the ball milling rod is 5 times the total mass of the raw materials in step (1), the amount of alcohol added is 200 mL of alcohol per kilogram of raw materials, and the wet milling time is 28 h. The drying temperature is 120℃, the drying time is 3 h, and the sieve is 80 mesh.

[0050] The gradient cemented carbide with varying hard phase particle size distribution prepared in this embodiment exhibits high Vickers hardness (HV) and fracture toughness (K) from the surface to the core in the first region. 1C 1320 N / mm 2 and 12.92 MPa.m 1 / 2 Second zone HV and K 1C 1650 N / mm 2 and 10.12 MPa.m 1 / 2 In the core HV and K 1C 1550 N / mm 2 and 10.67 MPa.m 1 / 2 The first zone has the highest fracture toughness, the second zone has the highest Vickers hardness, and the core has intermediate fracture toughness and Vickers hardness.

[0051] Example 2

[0052] A gradient cemented carbide with varying hard phase grain size distribution according to the present invention comprises a first region, a second region, and a third region from the outside to the inside. The first region includes WC and Co; the second region includes WC, Co, and FCC, where FCC is a cubic solid solution phase composed of (W,Ti)C, TiCN, (Ta,Nb)C, TaC, and Cr3C2; and the third region is the core region, comprising WC, Co, and FCC. The average grain size of WC in the first region is denoted as WC1, the average grain size of WC in the second region is denoted as WC2, and the average grain size of WC in the third region is denoted as WC3. The ratios of WC1 to WC2 are 1.10 and 1.05, respectively. 3. =0.96, WC1>WC3>WC2; the average grain size of FCC in the second region is denoted as FCC2, and the average grain size of FCC in the third region is denoted as FCC3, FCC2∶FCC 3. =1.31.

[0053] In this embodiment, the area ratio of FCC in the second region is 28%, and the area ratio of FCC in the third region is 22%. Furthermore, the total grain boundary length L2 of FCC in the second region is greater than the total grain boundary length L3 of FCC in the third region, with L2:L3 = 1.13.

[0054] In this embodiment, Co in the first region exhibits a bell-shaped distribution, and the point with the highest mass fraction content is denoted as Co. 1max In the second region, Co is uniformly distributed, and its average mass fraction is denoted as Co2. In the third region, Co is uniformly distributed, and its average mass fraction is denoted as Co3. 1max =15.4% is the maximum value, Co2=5.91%, Co3=7.43%, Co 1max ∶Co 3. =2.07.

[0055] In this embodiment, the thickness D1 of the first region is 27 μm, the thickness D2 of the second region is 86 μm, and D2 > D1.

[0056] In this embodiment, the average granularity of the FCC in the second zone is denoted as FCCP2, and the average granularity of the FCC in the third zone is denoted as FCCP3, with FCCP2:FCCP3 = 1.29.

[0057] A method for preparing a gradient cemented carbide with varying hard phase particle size distribution according to this embodiment includes the following steps:

[0058] (1) Prepare raw materials according to the elements and proportions of gradient cemented carbide: Based on the total mass of the raw materials, the mass percentages are as follows: Co is 7.5%, Ta is 3%, Nb is 0.8%, Ti is 4.5%, Cr is 0.3%, N is 0.33%, C is 6.37%, and the remainder is W;

[0059] (2) Pressing and molding: The above raw materials, molding agent, ball milling rod and alcohol are mixed and wet milled. The resulting slurry is dried and sieved to obtain a mixture, which is then pressed into a green embryo.

[0060] (3) Alloy sintering: The above green blank is heated to 370℃ for H2 sintering, and the forming agent in the sample is removed by Towack process at 450℃. Then, under vacuum conditions, the temperature is raised to 1340℃, 40mbar N2 is introduced and sintered for 30min, then the temperature is raised to 1410℃ and sintered for 20min, then the temperature is lowered to 1000℃ and sintered for 20min, vacuum sintering for 0.5min, 40mbar Ar gas is introduced and the temperature is raised to 1450℃ and sintered for 50min, 60bar inert gas Ar is introduced and sintered under pressure for 10min, and then the temperature is lowered to room temperature to obtain a gradient cemented carbide with varying hard phase particle size distribution.

[0061] In step (1) of this embodiment, the raw material sources for Co element include Co powder, the raw material sources for W element include WC powder and (W,Ti)C solid solution powder, the raw material sources for Ti element are TiCN powder and (W,Ti)C solid solution powder, the raw material sources for Ta element are (Ta,Nb)C solid solution powder and TaC powder, the raw material source for Nb element is (Ta,Nb)C solid solution powder, the raw material source for Cr element is Cr3C2, the raw material source for N element is TiCN powder, and the C element comes from the carbides of the above elements.

[0062] In this embodiment, the Fsss particle sizes of the raw materials are as follows: Co powder is 1.3 μm, (W,Ti)C solid solution powder is 1.58 μm, TiCN powder is 1.3 μm, (Ta,Nb)C solid solution powder is 1.6 μm, TaC powder is 1.1 μm, Cr3C2 powder is 1.4 μm, and WC powder is 3.3 μm.

[0063] In step (2) of this embodiment, the molding agent is PEG, the mass of the molding agent is 2% of the total mass of the raw materials in step (1), the mass of the ball milling rod is 5 times the total mass of the raw materials in step (1), the amount of alcohol added is 200 mL of alcohol per kilogram of raw materials, and the wet milling time is 28 h. The drying temperature is 120℃, the drying time is 3 h, and the sieve is 80 mesh.

[0064] The gradient cemented carbide with varying hard phase particle size distribution prepared in this embodiment exhibits high Vickers hardness (HV) and fracture toughness (K) from the surface to the core in the first region. 1C 1360 N / mm 2 and 12.31 MPa.m 1 / 2 Second zone HV and K 1C 1685 N / mm 2 and 9.79 MPa.m 1 / 2 In the core HV and K 1C 1550 N / mm 2 and 10.96 MPa.m 1 / 2 The first zone has the highest fracture toughness, the second zone has the highest Vickers hardness, and the core has intermediate fracture toughness and Vickers hardness.

[0065] Comparative Example 1

[0066] To better demonstrate the structural features and performance advantages of the gradient cemented carbide of this invention, a conventional gradient cemented carbide product from our company was selected as a comparative example. The sample, from its surface to its core, only includes the first region and the core region. The first region comprises WC and Co, while the core region comprises WC, Co, and FCC. FCC is a cubic solid solution phase formed from refractory carbides TaC, (W,Ti)C, (TaNb)C, and TiCN. The thickness D1 of the first region is 23 μm.

[0067] In the first region of this comparative example, Co exhibits a bell-shaped distribution, and the point with the highest mass fraction content is denoted as Co. 1max The core has a uniform Co distribution, and the average mass fraction is denoted as Co3. 1max =12.03%, Co3 = 7.52%, Co 1max ∶Co3.=1.61.

[0068] Compared to the embodiments, the comparative sample lacks a second region. To better reveal the advantages of the structural characteristics of different hard phase particle size distributions in this invention, a region in the comparative sample with the same geometric depth as the second region of the embodiments is used as an analog region, and its hardness and fracture toughness are tested. The Vickers hardness HV and fracture toughness K of the first region of the comparative sample are also tested. 1C 1420 N / mm 2 and 11.56 MPa.m 1 / 2 Analog regions HV and K 1C 1570 N / mm 2 and 10.68 MPa.m 1 / 2 In the core HV and K 1C 1565 N / mm 2 and 10.70 MPa.m 1 / 2 Comparative Example 1 cannot achieve the structural and performance characteristics of the present invention, and the resistance to plastic deformation of the present invention is significantly better than that of Comparative Example 1.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the spirit and technical essence of the present invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall still fall within the protection scope of the technical solutions of the present invention.

Claims

1. A gradient cemented carbide with a varying distribution of hard phase particle size, c h a r a c t e r i s e d in that, The gradient cemented carbide comprises a first region, a second region, and a third region from the outside in. The first region includes WC and Co, the second region includes WC, Co, and FCC, and the third region is the core region, including WC, Co, and FCC. FCC refers to a cubic solid solution phase made of refractory compounds. The refractory compounds are one or more of refractory carbonitrides and refractory nitrides combined with refractory carbides. The refractory carbides include Ti-containing carbides, which include TiC and / or (W,Ti)C. The refractory carbonitrides include Ti... CN, the refractory nitride includes TiN; the average grain size of WC in the first region is denoted as WC1, the average grain size of WC in the second region is denoted as WC2, and the average grain size of WC in the third region is denoted as WC3, then WC1 > WC3 > WC2; the average grain size of FCC in the second region is denoted as FCC2, and the average grain size of FCC in the third region is denoted as FCC3, then FCC2 > FCC3; based on the total mass of each region, Co in the first region has a bell-shaped distribution, and the point with the highest mass fraction of Co in the first region is denoted as Co. 1max The second region has a uniform distribution of Co, and the average mass fraction of Co in the second region is denoted as Co2. The third region has a uniform distribution of Co, and the average mass fraction of Co in the third region is denoted as Co3. Therefore, Co... 1max In Co2 and Co3, Co 1max For the maximum value, Co2 < Co3.

2. The gradient cemented carbide with a varying distribution of hard phase particle size according to claim 1, characterized in that, 1<WC1∶WC2≤1.5,1<WC1∶WC3≤1.3,0.8≤WC2∶WC 3. <1;1<FCC2∶FCC 3. ≤1.6。 3. The gradient cemented carbide of varying distribution of hardness phase particle size according to claim 1, characterized in that, The area occupied by FCC in the second region is greater than that occupied by FCC in the third region, and the total length L2 of the EBSD grain boundary of FCC in the second region is greater than that of the total length L3 of the EBSD grain boundary of FCC in the third region.

4. The gradient cemented carbide of varying distribution of hardness phase particle size according to claim 3, characterized in that, 1 < L2 : L3 < 1.

3.

5. The gradient cemented carbide of varying distribution of hardness phase particle size according to any one of claims 1 to 4, characterized in that, The average granularity of the FCC in the second region is denoted as FCCP2, and the average granularity of the FCC in the third region is denoted as FCCP3. Then, FCCP2 > FCCP3, and 1 < FCCP2 : FCCP3 ≤ 1.

6.

6. The gradient cemented carbide of varying distribution of hardness phase particle size according to any one of claims 1 to 4, characterized in that, The refractory carbides also include one or more of TaC, NbC, (Ta,Nb)C, Cr3C2 and VC.

7. The gradient cemented carbide with varying hard phase grain size distribution according to any one of claims 1 to 4, characterized in that, 1.5 < Co 1max : Co3 < 2.

2.

8. The gradient cemented carbide of varying distribution of hardness phase particle size according to any one of claims 1 to 4, characterized in that, The thickness D1 of the first region is 5μm to 40μm, and the thickness D2 of the second region is 30μm to 100μm, with D2 > D1.

9. A method of producing a cemented carbide with a gradient of the distribution of the grain size of the hard phase according to any one of claims 1 to 8, characterized in that Includes the following steps: (1) Preparation of raw materials: Based on the total mass of raw materials, the following percentages are calculated by mass: Co 5% to 12%, Ti 2% to 8%, Ta 0% to 5%, Nb 0% to 5%, Cr 0% to 0.3%, V 0% to 0.3%, N 0.06% to 1%, C 6.2% to 6.9%, with the remainder being W; (2) Pressing and molding: The above raw materials, molding agent, ball milling rod and alcohol are mixed and wet milled. The resulting slurry is dried and sieved to form a mixed powder, which is then pressed into a green embryo. (3) Alloy sintering: The above green blank is heated to 300℃~450℃ for H2 sintering. The forming agent in the sample is removed by Towack process at 400℃~500℃. Then, under vacuum conditions, the temperature is raised to 1300℃~1370℃, 20mbar~100mbar N2 is introduced and sintered for 20min~30min. Then, the temperature is raised to 1390℃~1420℃ and sintered for 10min~40min. The temperature is lowered to 800℃~1200℃ and sintered for 10min~30min. After vacuum sintering for 0.2min~2min, 20mbar~200mbar Ar gas is introduced and the temperature is raised to 1420℃~1480℃. The temperature is sintered for 30min~60min. Then, 30bar~100bar inert gas Ar is introduced and sintered under pressure for 10min~30min. Finally, the temperature is lowered to room temperature to obtain a gradient cemented carbide with varying hard phase particle size distribution.

10. The method of producing a gradient cemented carbide with a varying distribution of hardness phase particle size according to claim 9, characterized in that, In step (1), by mass percentage, Co is 5%–12%, Ti is 2%–8%, Ta is 0.5%–5%, Nb is 0.5%–5%, Cr is 0%–0.3%, V is 0%–0.3%, N is 0.06%–1%, C is 6.2%–6.9%, and the balance is W.

11. A method of producing a gradient cemented carbide with a varying distribution of hardness phase particle size according to claim 9 or 10, characterised in that, In step (1), the raw material sources for the W element include WC powder and / or (W,Ti)C solid solution powder; the raw material sources for the Ti element include one or more of TiC powder, TiCN powder, (W,Ti)C solid solution powder, and TiN powder; the raw material sources for the Ta element include TaC powder and / or (Ta,Nb)C solid solution powder; the raw material sources for the Nb element include NbC powder and / or (Ta,Nb)C solid solution powder; the raw material sources for the N element include TiCN powder and / or TiN powder; the raw material sources for the Co element include Co powder; the raw material sources for the Cr element include Cr3C2 powder; and the raw material sources for the V element include VC powder.

12. The method of producing a gradient cemented carbide with a varying distribution of hardness phase particle size according to claim 11, characterized in that, The Fsss particle size of the Co powder is 1.2 μm to 1.5 μm, the Fsss particle size of the (W,Ti)C solid solution powder is 1.5 μm to 2.0 μm, the Fsss particle size of the TiCN powder is 0.8 μm to 1.5 μm, the Fsss particle size of the (Ta,Nb)C solid solution powder is 1.0 μm to 2 μm, the Fsss particle size of the TiC powder, TiN powder, TaC powder, VC powder, Cr3C2 powder and NbC powder is 1.0 μm to 2.0 μm, and the Fsss particle size of the WC powder is 3.0 μm to 4.0 μm.

13. A method of producing a gradient cemented carbide with a varying distribution of hardness phase particle size according to claim 9 or 10, characterized in that, In step (2), the molding agent is PEG, the mass of the molding agent is 1.5% to 2.5% of the total mass of the raw materials in step (1), the mass of the ball milling rod is 4 to 6 times the total mass of the raw materials in step (1), the amount of alcohol added is 200 mL to 300 mL of alcohol per kilogram of raw materials, and the wet milling time is 25 h to 40 h.

14. The method of producing a gradient cemented carbide of varying distribution of hardness phase particle size according to claim 9 or 10, characterized in that, In step (2), the drying temperature is 60℃~120℃, the drying time is 2h~3h, and the sieving is through a 60-80 mesh sieve.

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