A TiB2-based steel-bonded cemented carbide and its preparation method

Abstract

The present invention relates to a high-performance TiB₂-based steel-bonded cemented carbide and a preparation method thereof, belonging to the field of cemented carbides. The mass percentage composition is as follows: TiB₂: 45% to 55%; Cr₃C₂: 2 to 4%; Mo₂C: 0 to 10%; Ni: 2 to 4%; Fe: 35.0 to 45.0%; C: 0.7%, and the sum of each component is 100%. Take each raw material powder according to the designed group distribution, mix by planetary ball milling, vacuum dry and screen to remove agglomerates, press into shape, and adopt an integrated technology of vacuum reduction-vacuum liquid-phase sintering-dissolution and precipitation to sinter at 1350 °C to 1450 °C to prepare a high-performance TiB₂-based steel-bonded cemented carbide. Its bulk density is 5.62 to 5.69 g / cm³, the hardness is 88.8 to 92.5 HRA, the flexural strength is 1175.25 to 1552.34 MPa, and the fracture toughness is 9.15 to 11.21 MPa·m¹ / ². The TiB₂-based steel-bonded cemented carbide prepared by the present invention has a reasonable component design and a simple preparation process flow, and is suitable for industrial production. It has broad application prospects in various fields such as die materials for stamping, forming, cold heading dies, etc., and machinery, metallurgy, light industry, and navigation, aerospace, missiles, etc.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of steel-bonded cemented carbide materials, and relates to a high-performance TiB2-based steel-bonded cemented carbide and a preparation method thereof. Technical Background

[0002] Steel-bonded cemented carbide is a new engineering material with comprehensive properties between steel and cemented carbide, combining the performance characteristics of both materials. Compared with steel, steel-bonded cemented carbide has higher rigidity, flexural strength, elastic modulus and compressive strength, and has high hardness, high wear resistance and hardenability; at the same time, it has the performance advantages of machinability, heat treatability and weldability comparable to those of steel, and the processed alloy can also be hardened. After hardening treatment, the steel-bonded cemented carbide has higher hardness. Compared with cemented carbide, it has higher toughness, wear resistance equivalent to or even higher than that of high-cobalt cemented carbide, and the strength and impact resistance of the material are better than those of general tungsten-cobalt cemented carbide. These excellent comprehensive properties make it have a very broad application prospect in the fields of mechanical industry, electronic industry, metallurgy, chemistry, instrumentation, geology, building materials industry, light industry, national defense, navigation, aerospace and other fields.

[0003] An important application field of steel-bonded cemented carbide is used as die materials. Compared with traditional tool and die materials, its service life is increased by several times to dozens of times, and it can be competent for large-load dies that general smelted steel cannot handle, and the economic benefits are very significant. It can be applied to manufacture various dies, such as: wire drawing, pipe drawing, blanking, cold heading, extrusion, stretching, embossing, hot heading and die casting dies.

[0004] Steel-bonded cemented carbide has an extremely low friction coefficient and good oxidation and corrosion resistance, so it is a better material for making wear-resistant parts, tools and sealing devices, such as: guide wheels, guide rollers, parts of high-temperature bearings, wire feeding wheels, bearings, threaded sleeves, rotor engine scraping blades, valve parts, sealing rings of various pumps and pipes and other mechanical sealing rings, medical device parts, and piercing mandrels, grinding tools, rolling rolls, rolling tools, drill sleeves, file wire plates, nozzles, key rods, etc.

[0005] The hard phase particles in the steel-bonded cemented carbide are firmly supported by the hardened steel matrix, which is beneficial to maintaining the sharpness of the cutting edge. Steel-bonded cemented carbide can be used to manufacture milling cutters, broaches, hob cutters, drills and other tools, and can be used for machining heat-resistant steel, non-ferrous alloys, stainless steel, etc.

[0006] Currently, the steel-bonded carbides produced domestically are mainly those with TiC, WC, and TiN as the hard phases, while the research and development of steel-bonded carbides with borides as the hard phase lags behind. Compared with other borides, TiB2 has more excellent physical and chemical properties. It has a high melting point (2980 °C), high hardness (HV3000), excellent oxidation resistance (the air oxidation temperature reaches 1000 °C), good chemical stability, acid and alkali corrosion resistance, and low density (4.52 g / cm 3 ), has advantages such as low adhesion and friction coefficient with metals and good anti-adhesive wear resistance, and is an ideal hard phase for preparing steel-bonded carbides. In a vacuum environment, Fe has good wettability to TiB2 ceramic particles; the solubility of TiB2 in Fe is very low, and it forms a eutectic with low melting point with Fe at a relatively low temperature (1340 °C). Therefore, using iron as the binder phase and adding elements such as Mo, Cr, and W can improve the wettability of the binder phase to TiB2 ceramic particles, and high-performance TiB2-based steel-bonded carbides can be prepared.

[0007] Therefore, the present invention uses TiB2 as the hard phase, Fe and Ni as the binder phases, adds hard phase additives such as Cr3C2 / Mo2C, and graphite powder (C) as the carbon source, and prepares a high-performance TiB2-based steel-bonded carbide with a "core-ring" structure strengthening through powder metallurgy liquid-phase sintering technology to promote its application in the fields of machinery, electronics, chemical industry, metallurgy, aerospace, national defense, etc. Summary of the Invention

[0008] The present invention provides a high-performance TiB2-based steel-bonded carbide and a preparation method thereof. This steel-bonded carbide uses TiB2 as the hard phase, Fe and Ni as the binder phases, and Mo2C and Cr3C2 as the hard phase additives. Utilizing the fact that Mo2C and Cr3C2 have a certain saturation solubility in the Fe and Ni binder phases, during the vacuum sintering process, Mo2C and Cr3C2 are preferentially dissolved in the Fe and Ni binder phases rather than TiB2, and through the dissolution-precipitation mechanism, they precipitate on the undissolved TiB2 particles to form a "core-ring" structure with TiB2 as the core and (Ti, Mo, Cr, Fe, Ni)(B, C) as the annular phase, and a TiB2-based steel-bonded carbide with excellent comprehensive mechanical properties is prepared. During the sintering preparation process of the steel-bonded carbide, combined with the TG-DSC-QMS (degassing process) analysis of the mixed powder of TiB2-6wt%Mo2C-3w%Cr3C2-3wt%Ni-38wt%Fe-0.7wt%C steel-bonded carbide during the sintering process from room temperature to 1450 °C (such as Figure 1 and Figure 2As shown in the figure, a reasonable sintering system curve is formulated. Making full use of vacuum sintering is beneficial for gases such as water vapor and oxygen contained in the pores of the green compact to escape during the sintering process by means of dissolution, grain boundary diffusion or through the grains, so that the sintered product is free of pores, thereby improving the density of the product; vacuum is conducive to the reduction of oxides in the raw material powder, improving the purity of the material; vacuum can improve the wettability of the binder phase to the hard phase during the liquid phase sintering process, which is beneficial to shrinkage and improve the structure of the alloy, and improve the mechanical properties of the alloy; vacuum is beneficial to discharging the gases generated during the sintering process and promoting the shrinkage in the later stage of sintering and other advantages. Through the fine control of the sintering process, the adsorbed water and adsorbed oxygen in the raw material powder are removed during the vacuum sintering process, and the oxides on the surface of the raw material powder are reduced by vacuum carbothermal reduction, thereby playing a role in purifying the material and purifying the grain boundary. The interface bonding strength between the "TiB2 core-(Ti,Mo,Cr,Fe,Ni)(B,C) annular phase-FeNi binder phase" in the prepared TiB2-based steel-bonded carbide is higher, thereby improving the comprehensive mechanical properties of the TiB2-based steel-bonded carbide. To achieve the above object, the specific technical solution provided by the present invention is as follows:

[0009] The described TiB2-based steel-bonded carbide is composed of the following components in mass percentages: TiB2: 45-55%, Cr3C2: 2-4%, Mo2C: 0-10%, Ni: 2-4%, Fe: 35.0-45.0%, C: 0.7%, and the sum of the mass percentages of each component is 100%.

[0010] Preferably, the mass percentages of the components of a TiB2-based steel-bonded carbide are: TiB2: 50-55%, Cr3C2: 2.5-3.5%, Mo2C: 1-10%, Ni: 2.5-3.5%, Fe: 35.0-45.0%, C: 0.7%.

[0011] Among the raw materials used for the described TiB2-based steel-bonded carbide, the average particle size of the TiB2 powder is 2.0-4.0 μm, the average particle size of the Cr3C2 powder is 2-5 μm, the average particle size of the Mo2C powder is 3-5 μm, the average particle size of the Ni powder is 3-5 μm, the average particle size of the Fe powder is 3-5 μm, and the average particle size of the C powder is 2-5 μm.

[0012] A preparation method of a TiB2-based steel-bonded carbide includes the following specific steps:

[0013] (1) Preparation of the mixed powder: Weigh TiB2, Cr3C2, Mo2C, Ni, Fe, and C powders according to the above mass percentages, mix them by planetary ball milling or drum ball milling, dry them in a vacuum drying oven at 50-60 °C, and then screen them through an 80-mesh sieve to remove agglomerates to obtain the mixed powder of the TiB2-based steel-bonded carbide;

[0014] (2) Compression molding: The mixed powder is compression-molded into a cuboid green body under a pressure of 100 MPa, and then cold isostatically pressed and kept under pressure at 250 - 300 MPa for 150 - 200 s to further increase the density of the green compact.

[0015] (3) Vacuum sintering: The green body obtained in step (2) is subjected to vacuum sintering, with a vacuum degree of 10 -3 ~10 -1 Pa, a sintering temperature of 1350 - 1450 °C, and an insulation time of 0.5 - 2 h to obtain the TiB2-based steel-bonded carbide.

[0016] The planetary ball milling or drum ball milling described in step (1) is characterized in that: when preparing the mixed powder, alcohol or kerosene is used as the ball milling medium, the ball-to-material ratio is (1 - 5):1, and the ball milling speed is 150 - 200 r / min. First, the TiB2, Cr3C2, Mo2C, and C powders are ball milled and mixed for 12 h, then the Fe and Ni metal powders are added and ball milled together for another 24 h. The mixture is mixed by alternating forward rotation for 1 h and reverse rotation for 1 h to obtain the mixed powder slurry.

[0017] The vacuum sintering described in step (3) is characterized in that: it is heated from room temperature to 136 °C at a rate of 1 - 3 °C / min and kept at this temperature for 1 h to remove the water adsorbed in the raw material powder; then it is heated to 235 °C at a rate of 1 - 3 °C / min and kept at this temperature for 1 h to remove the oxygen adsorbed in the raw material powder; then it is heated to 3,60 °C at a rate of 1 - 3 °C / min and kept at this temperature for 1 h, and then heated to 545 °C at a rate of 1 - 3 °C / min and kept at this temperature for 1 h to vacuum carbothermally reduce the oxides on the surface of the Ni powder; then it is heated to 742 °C at a rate of 1 - 3 °C / min and kept at this temperature for 1 h, and then heated to 834 °C at a rate of 1 - 3 °C / min and kept at this temperature for 1 h to vacuum carbothermally reduce the oxides on the surface of the Fe powder; then it is heated to 1000 °C at a rate of 1 - 3 °C / min and kept at this temperature for 1 h, and then heated to 1122 °C at a rate of 1 - 2 °C / min and kept at this temperature for 1 h to vacuum carbothermally reduce the oxides on the surfaces of TiB2, Mo2C, and Cr3C2; then it is heated to 1145 °C at a rate of 1 - 2 °C / min and kept at this temperature for 1 h; then it is heated to 1350 - 1450 °C at a rate of 1 - 2 °C / min and kept at this temperature for 1 h to fully carry out the vacuum liquid phase sintering. After the heating is completed, a high vacuum is maintained throughout the process, and it is cooled to room temperature with the furnace.

[0018] The TiB2-based steel-bonded carbide prepared by the present invention has a bulk density of 5.62 - 5.69 g / cm 3 , a hardness of 88.8 - 92.5 HRA, a flexural strength of 1175.25 - 1552.34 MPa, and a fracture toughness of 9.15 - 11.21 MPa·m 1 / 2。The steel-bonded cemented carbide mainly includes four phases: TiB2, Fe2B, TiC, and (Fe,Ni). As Figure 4 shown by the SEM-EDS energy spectrum results, a thin layer of (Ti,Mo,Cr,Fe,Ni)(B,C) annular phase grows adherently around the TiB2 ceramic particles. The formation of the "core-ring" structure is beneficial to improving the interfacial bonding strength and enhancing the comprehensive performance of the steel-bonded cemented carbide. Fine TiC ceramic particles are observed in the steel-bonded cemented carbide, indicating that a new TiC phase is generated during the vacuum liquid-phase sintering process. This provides the possibility for subsequent composition optimization to form a "core-ring" structure of "TiC core-(Ti,Mo,Fe,Ni)C annular phase" in the TiB2-based steel-bonded cemented carbide and further regulate the structure and properties of the cermet. Description of the Drawings

[0019] Figure 1 TG-DSC Thermodynamic Analysis of the Mixed Powder of the Steel-Bonded Cemented Carbide in Example 5 of the Present Invention

[0020] Figure 2 Gas Emission during the Sintering Process of the Steel-Bonded Cemented Carbide in Example 5 of the Present Invention

[0021] Figure 3 XRD Phase Analysis of the TiB2-Based Steel-Bonded Cemented Carbide in Examples 1-7 of the Present Invention

[0022] Figure 4 Backscattered Morphology of the TiB2-Based Steel-Bonded Cemented Carbide in Example 6 of the Present Invention. The corresponding energy spectrum point scanning results are shown in Table 1-1

[0023] Figure 5 Backscattered Morphology Diagrams of the TiB2-Based Steel-Bonded Cemented Carbide in Examples 1-6 of the Present Invention Specific Embodiments

[0024] The formulation of the TiB2-based steel-bonded cemented carbide in Example 1 consists of powders with the following mass percentages and average particle sizes: TiB2: 50%, average particle size of 3.0 μm, Mo2C: 0%; Cr3C2: 3.0%, average particle size of 2.5 μm, Ni: 3.0%, average particle size of 3.5 μm, Fe: 43.3%, average particle size of 4.0 μm, C: 0.7%, average particle size of 3 μm. The sum of the mass percentages of each component is 100%.

[0025] The specific steps for preparing the cermet are as follows:

[0026] (1) Preparation of mixed powder: Weigh the TiB2, Cr3C2, Fe, Ni, and C powders according to the above mass percentages, and use planetary ball milling for mixing. Alcohol is used as the ball milling medium, the ball-to-powder ratio is 2:1, and the ball milling speed is 160 r / min. First, perform planetary ball milling on the TiB2, Cr3C2, and C powders for 12 h, and then add the Fe and Ni powders and perform planetary ball milling for 24 h to obtain a mixed powder slurry. Dry the mixed powder slurry in a vacuum drying oven at 55 °C for 15 h, and then screen it through an 80-mesh sieve to remove agglomerates, obtaining the TiB2-based steel-bonded carbide mixed powder.

[0027] (2) Compression molding: First, use die pressing to compress it into a rectangular green compact with dimensions of 25×8×5 mm 3 under a pressure of 100 MPa, and then further improve the density of the green compact by subjecting the rectangular green compact to cold isostatic pressing at a pressure of 270 MPa for 150 s.

[0028] (3) Vacuum sintering: Vacuum sinter the green compact prepared in step (2), and maintain the vacuum degree at 10 -1 ~10 -3 Pa throughout the process. The specific heating and sintering regime is as follows: Heat from room temperature to 136 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 235 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 360 °C at a rate of 1 - 3 °C / min and hold for 1 h; heat to 545 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 742 °C at a rate of 1 - 3 °C / min and hold for 1 h, heat to 834 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 1000 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 1122 °C at a rate of 1 - 2 °C / min and hold for 1 h; then heat to 1145 °C at a rate of 1 - 2 °C / min and hold for 1 h; then heat to 1410 °C at a rate of 1 - 2 °C / min and hold for 1 h. After the heating is completed, maintain a high vacuum throughout the process and cool it to room temperature with the furnace.

[0029] The bulk density of the TiB2-based steel-bonded carbide prepared in this example is 5.63 g / cm 3 , the hardness is 88.8 HRA, the flexural strength is 1175.25 MPa, and the fracture toughness is 9.16 MPa·m 1 / 2 . Its phase composition is as shown in Figure 3 (a), including 4 phases: TiB2, Fe2B, TiC, and (Fe,Ni) binder phase. The backscattered morphology is as shown in Figure 5 (a), the black ones are TiB2 hard phase particles, and the grayish-white area is the (Fe,Ni) binder phase.

[0030] Example 2: The ingredients of the TiB2-based steel-bonded cemented carbide consist of powders with the following mass percentages and average particle sizes: TiB2: 51%, average particle size of 3.5 μm, Mo2C: 1.5%, average particle size of 3.5 μm, Cr3C2: 2.5%, average particle size of 2.5 μm, Ni: 2.5%, average particle size of 3.5 μm, Fe: 41.8%, average particle size of 3.0 μm, C: 0.7%, average particle size of 3 μm. The sum of the mass percentages of each component is 100%.

[0031] The specific steps for preparing the cermet are as follows:

[0032] (1) Preparation of the mixed powder: Weigh the TiB2, Mo2C, Cr3C2, Fe, Ni, and C powders according to the above mass percentages, and use a planetary ball mill for mixing with alcohol as the ball-milling medium, a ball-to-material ratio of 3:1, and a ball-milling speed of 170 r / min. First, ball-mill the TiB2, Mo2C, Cr3C2, and C powders in a planetary ball mill for 12 h, then add the Fe and Ni powders and ball-mill for another 24 h to obtain a mixed powder slurry. Dry the mixed powder slurry in a vacuum drying oven at 56°C for 15 h, and then sieve it through an 80-mesh sieve to remove agglomerates, obtaining the TiB2-based steel-bonded cemented carbide mixed powder.

[0033] (2) Compression molding: First, use die pressing to compress it into a rectangular green compact of 25×8×6 mm 3 under a pressure of 100 MPa, and then use cold isostatic pressing to hold the rectangular green compact at a pressure of 260 MPa for 160 s to further increase the density of the green compact.

[0034] (3) Vacuum sintering: Vacuum sinter the green compact prepared in step (2), and maintain a vacuum degree of 10 -1 ~10 -3 Pa throughout the process. The specific heating and sintering regime is as follows: Heat from room temperature to 136°C at a rate of 1 - 3°C / min and hold for 1 h; then heat to 235°C at a rate of 1 - 3°C / min and hold for 1 h; then heat to 360°C at a rate of 1 - 3°C / min and hold for 1 h; heat to 545°C at a rate of 1 - 3°C / min and hold for 1 h; then heat to 742°C at a rate of 1 - 3°C / min and hold for 1 h, heat to 834°C at a rate of 1 - 3°C / min and hold for 1 h; then heat to 1000°C at a rate of 1 - 3°C / min and hold for 1 h; then heat to 1,122°C at a rate of 1 - 2°C / min and hold for 1 h; then heat to 1,145°C at a rate of 1 - 2°C / min and hold for 1 h; then heat to 1,420°C at a rate of 1 - 2°C / min and hold for 1 h. After the heating is completed, maintain a high vacuum throughout the process and cool to room temperature with the furnace.

[0035] The bulk density of the TiB2-based steel-bonded cemented carbide prepared in this example is 5.62 g / cm 3, with a hardness of 92.0 HRA, a flexural strength of 1277.73 MPa, and a fracture toughness of 9.17 MPa·m 1 / 2 . Its phase composition is as Figure 3 (b) shown, including 4 phases of TiB2, Fe2B, TiC, and (Fe,Ni) binder phase. The backscattered morphology is as Figure 5 (b) shown. The black ones are TiB2 hard phase particles, and the grayish-white area is the (Fe,Ni) binder phase. There is a gray annular phase coating around the TiB2 ceramic particles.

[0036] Example 3 The formulation of the TiB2-based steel-bonded cemented carbide consists of powders with the following mass percentages and average particle sizes: TiB2: 50%, average particle size of 2.5 μm, Mo2C: 3.0%, average particle size of 4.0 μm, Cr3C2: 3.5%, average particle size of 3.0 μm, Ni: 3.0%, average particle size of 4.0 μm, Fe: 39.8%, average particle size of 4.0 μm, C: 0.7%, average particle size of 3 μm. The sum of the mass percentages of each component is 100%.

[0037] The specific steps for preparing the cermet are as follows:

[0038] (1) Preparation of the mixed powder: Weigh the TiB2, Mo2C, Cr3C2, Fe, Ni, and C powders according to the above mass percentages, and use planetary ball milling for mixing with alcohol as the ball milling medium, the ball-to-powder ratio is 2.5:1, and the ball milling speed is 180 r / min. First, planetary ball mill the TiB2, Mo2C, Cr3C2, and C powders for 12 h, and then add the Fe and Ni powders and planetary ball mill for 24 h to obtain a mixed powder slurry. Dry the mixed powder slurry in a vacuum drying oven at 58 °C for 16 h, and then sieve through an 80-mesh sieve to remove agglomerates to obtain the TiB2-based steel-bonded cemented carbide mixed powder.

[0039] (2) Compression molding: First, use die pressing to compress into a cuboid green compact of 25×8×7 mm 3 under a pressure of 100 MPa, and then use cold isostatic pressing to hold the pressure at 270 MPa for 170 s to further increase the density of the green compact.

[0040] (3) Vacuum sintering: Vacuum sinter the green compact prepared in step (2), and keep the vacuum degree at 10 -1 ~10 -3Pa. The specific heating and sintering regime is as follows: starting from room temperature, it is heated at a rate of 1 - 3 °C / min to 136 °C and held for 1 h; then heated at a rate of 1 - 3 °C / min to 235 °C and held for 1 h; then heated at a rate of 1 - 3 °C / min to 360 °C and held for 1 h; heated at a rate of 1 - 3 °C / min to 545 °C and held for 1 h; then heated at a rate of 1 - 3 °C / min to 742 °C and held for 1 h, heated at a rate of 1 - 3 °C / min to 834 °C and held for 1 h; then heated at a rate of 1 - 3 °C / min to 1000 °C and held for 1 h; then heated at a rate of 1 - 2 °C / min to 1122 °C and held for 1 h; then heated at a rate of 1 - 2 °C / min to 1145 °C and held for 1 h; then heated at a rate of 1 - 2 °C / min to 1400 °C and held for 1 h. After the heating is completed, a high vacuum is maintained throughout the process, and it is cooled to room temperature in the furnace.

[0041] The bulk density of the TiB2 - based steel - bonded cemented carbide prepared in this example is 5.65 g / cm 3 , the hardness is 91.58 HRA, the flexural strength is 1307.58 MPa, and the fracture toughness is 10.90 MPa·m 1 / 2 . Its phase composition is as Figure 3 (c) shows, including 4 phases: TiB2, Fe2B, TiC, and (Fe,Ni) binder phase. The backscattered morphology is as Figure 5 (c) shows. The black ones are TiB2 hard - phase particles, the gray - white area is the (Fe,Ni) binder phase, and there is a gray - colored annular phase coating around the TiB2 ceramic particles.

[0042] Example 4: The ingredients of the TiB2 - based steel - bonded cemented carbide are composed of powders with the following mass percentages and average particle sizes: TiB2: 50%, average particle size is 4.0 μm, Mo2C: 4.5%, average particle size is 5.0 μm, Cr3C2: 3.0%, average particle size is 4.0 μm, Ni: 3.0%, average particle size is 5.0 μm, Fe: 38.8%, average particle size is 5.0 μm, C: 0.7%, average particle size is 4 μm. The sum of the mass percentages of each component is 100%.

[0043] The specific steps for preparing the cermet are as follows:

[0044] (1) Preparation of the mixed powder: Weigh the TiB2, Mo2C, Cr3C2, Fe, Ni, and C powders according to the above mass percentages. Use a planetary ball mill for mixing, with alcohol as the ball milling medium, a ball-to-powder ratio of 4:1, and a ball milling speed of 190 r / min. First, ball mill the TiB2, Mo2C, Cr3C2, and C powders in a planetary ball mill for 12 h, then add the Fe and Ni powders and continue ball milling for 24 h to obtain a mixed powder slurry. Dry the mixed powder slurry in a vacuum drying oven at 60 °C for 12 h, and then sieve it through an 80-mesh sieve to remove agglomerates, obtaining the TiB2-based steel-bonded carbide mixed powder.

[0045] (2) Compression molding: First, use die pressing to compress it into a rectangular green compact with dimensions of 25×8×5.5 mm 3 under a pressure of 100 MPa, and then further improve the density of the green compact by cold isostatic pressing at a pressure of 280 MPa for 180 s.

[0046] (3) Vacuum sintering: Sinter the green compact prepared in step (2) under vacuum, maintaining a vacuum degree of 10 -1 ~10 -3 Pa throughout the process. The specific heating and sintering regime is as follows: Heat from room temperature to 136 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 235 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 360 °C at a rate of 1 - 3 °C / min and hold for 1 h; heat to 545 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 742 °C at a rate of 1 - 3 °C / min and hold for 1 h, heat to 834 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 1000 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 1122 °C at a rate of 1 - 2 °C / min and hold for 1 h; then heat to 1145 °C at a rate of 1 - 2 °C / min and hold for 1 h; then heat to 1430 °C at a rate of 1 - 2 °C / min and hold for 1 h. After the heating is completed, maintain a high vacuum throughout and cool to room temperature with the furnace.

[0047] The bulk density of the TiB2-based steel-bonded carbide prepared in this example is 5.66 g / cm 3 , the hardness is 91.82 HRA, the flexural strength is 1456.23 MPa, and the fracture toughness is 10.65 MPa·m 1 / 2 . Its phase composition is as shown in Figure 3 (d), including 4 phases: TiB2, Fe2B, TiC, and (Fe,Ni) binder phase. The backscattered morphology is as shown in Figure 5 (d). The black ones are TiB2 hard phase particles, the grayish-white area is the (Fe,Ni) binder phase, and there is a gray annular phase coating around the TiB2 ceramic particles.

[0048] Example 5: The ingredients of the TiB2-based steel-bonded cemented carbide consist of powders with the following mass percentages and average particle sizes: TiB2: 50%, average particle size of 2.0 μm; Mo2C: 6.0%, average particle size of 3.0 μm; Cr3C2: 3.0%, average particle size of 2.5 μm; Ni: 3.0%, average particle size of 3.0 μm; Fe: 37.3%, average particle size of 3.0 μm; C: 0.7%, average particle size of 2 μm. The sum of the mass percentages of each component is 100%.

[0049] The specific steps for preparing the cermet are as follows:

[0050] (1) Preparation of the mixed powder: Weigh the powders of TiB2, Mo2C, Cr3C2, Fe, Ni, and C according to the above mass percentages, and use a planetary ball mill for mixing. Alcohol is used as the ball-milling medium, the ball-to-material ratio is 1:1, and the ball-milling speed is 200 r / min. First, planetary ball-mill the powders of TiB2, Mo2C, Cr3C2, and C for 12 h, then add the powders of Fe and Ni and planetary ball-mill for 24 h to obtain a mixed powder slurry. Dry the mixed powder slurry in a vacuum drying oven at 55 °C for 15 h, and then screen through an 80-mesh sieve to remove agglomerates to obtain the mixed powder of the TiB2-based steel-bonded cemented carbide.

[0051] (2) Compression molding: First, use die pressing to compress into a rectangular green compact of 25×8×6 mm 3 under a pressure of 100 MPa, and then use cold isostatic pressing to hold the pressure at 300 MPa for 200 s to further increase the density of the green compact.

[0052] (3) Vacuum sintering: Vacuum sinter the green compact prepared in step (2), and maintain the vacuum degree at 10 -1 ~10 -3 Pa throughout the process. The specific heating and sintering regime is as follows: Heat from room temperature to 136 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 235 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 360 °C at a rate of 1 - 3 °C / min and hold for 1 h; heat to 545 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 742 °C at a rate of 1 - 3 °C / min and hold for 1 h, heat to 834 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 1000 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 1122 °C at a rate of 1 - 2 °C / min and hold for 1 h; then heat to 1145 °C at a rate of 1 - 2 °C / min and hold for 1 h; then heat to 1410 °C at a rate of 1 - 2 °C / min and hold for 1 h. After the heating is completed, maintain a high vacuum throughout the process and cool to room temperature with the furnace.

[0053] The bulk density of the TiB2-based steel-bonded cemented carbide prepared in this example is 5.67 g / cm 3, with a hardness of 92.2 HRA, a flexural strength of 1552.34 MPa, and a fracture toughness of 11.21 MPa·m 1 / 2 . Its phase composition is as Figure 3 (e) shows, including 5 phases of TiB2, Fe2B, TiC, (Fe,Ni), and Mo2C binder phase. Its backscattered morphology is as Figure 5 (e) shows, where the black ones are TiB2 hard phase particles, the grayish-white area is the (Fe,Ni) binder phase, and around the TiB2 ceramic particles, there is a layer of gray annular phase growing adherently.

[0054] Figure 1 and Figure 2 are the TG-DSC-QMS comprehensive thermal analysis curves of this example. Using a Netzsch STA449F5 synchronous thermal analyzer, the endothermic, thermogravimetric, and exhaust behaviors of TiB2-6wt% Mo2C-3w% Cr3C2-3wt% Ni-38wt% Fe-0.7wt% C steel-bonded carbide during the process of heating from room temperature to 1450 °C are measured. During the measurement process, high-purity Ar protection is used, the heating rate is 10 °C / min, and the gas flow rate is 20 ml / min. Based on the test results of the comprehensive thermal analysis, fully considering the temperature corresponding to each endothermic peak, the change of the sintering system's thermogravimetry, the dehydration temperature of the adsorbed water in the mixed powder, the reduction temperature of the oxide impurities in the mixed powder, the melting temperature of the metal FeNi in the sintering system, and the dissolution temperature of Mo2C, Cr3C2, and TiB2 ceramic particles in the liquid metal, the sintering system curve of the TiB2-based steel-bonded carbide prepared by the present invention is comprehensively set, and a sufficient holding time is set at each corresponding temperature point to ensure the full progress of each reaction. The setting of this sintering system curve lays a solid foundation for the preparation of high-performance TiB2-based steel-bonded carbide materials.

[0055] Example 6 The ingredients of the TiB2-based steel-bonded carbide are composed of powders with the following mass percentages and average particle sizes: TiB2: 50%, average particle size of 3.5 μm, Mo2C: 7.5%, average particle size of 4.0 μm, Cr3C2: 3.0%, average particle size of 3.0 μm, Ni: 3.0%, average particle size of 3.5 μm, Fe: 35.8%, average particle size of 3.5 μm, C: 0.7%, average particle size of 2.5 μm, and the sum of the mass percentages of each component is 100%.

[0056] The specific steps for preparing the cermet are as follows:

[0057] (1) Preparation of the mixed powder: Weigh the TiB2, Mo2C, Cr3C2, Fe, Ni, and C powders according to the above mass percentages, and use a planetary ball mill for mixing. Alcohol is used as the ball milling medium, the ball-to-powder ratio is 5:1, and the ball milling speed is 190 r / min. First, planetary ball mill the TiB2, Mo2C, Cr3C2, and C powders for 12 h, then add the Fe and Ni powders and planetary ball mill for 24 h to obtain a mixed powder slurry. Dry the mixed powder slurry in a vacuum drying oven at 53 °C for 15 h, and then screen it through an 80-mesh sieve to remove agglomerates, obtaining the TiB2-based steel-bonded carbide mixed powder.

[0058] (2) Compression molding: First, use die pressing to compress it into a rectangular green compact with dimensions of 25×8×6 mm 3 under a pressure of 100 MPa, and then use cold isostatic pressing to hold the pressure at 290 MPa for 190 s to further increase the density of the green compact.

[0059] (3) Vacuum sintering: Vacuum sinter the green compact prepared in step (2), and maintain the vacuum degree at 10 -1 ~10 -3 Pa throughout the process. The specific heating and sintering regime is as follows: heat from room temperature to 136 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 235 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 360 °C at a rate of 1 - 3 °C / min and hold for 1 h; heat to 545 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 742 °C at a rate of 1 - 3 °C / min and hold for 1 h, heat to 834 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 1000 °C at a rate of 1 - 3 °C / min and hold for 1 h; then heat to 1122 °C at a rate of 1 - 2 °C / min and hold for 1 h; then heat to 1145 °C at a rate of 1 - 2 °C / min and hold for 1 h; then heat to 1450 °C at a rate of 1 - 2 °C / min and hold for 1 h. After the heating is completed, maintain a high vacuum throughout the process and cool it to room temperature with the furnace.

[0060] The bulk density of the TiB2-based steel-bonded carbide prepared in this example is 5.68 g / cm 3 , the hardness is 92.3 HRA, the flexural strength is 1454.42 MPa, and the fracture toughness is 10.56 MPa·m 1 / 2 . Its phase composition is as shown in Figure 3 (f), including 5 phases: TiB2, Fe2B, TiC, (Fe,Ni), and Mo2C binder phase. Its backscattered morphology is as shown in Figure 5 (f), mainly observing the black TiB2 hard phase and the grayish-white (Fe,Ni) binder phase. Around the TiB2 ceramic particles, a gray annular phase grows attached.

[0061] Figure 4This is the backscattered morphology of the TiB2-based steel-bonded cemented carbide of this embodiment. The corresponding energy spectrum point scanning results are shown in Table 1-1. The energy spectrum results show that in the TiB2-based steel-bonded cemented carbide, the undissolved Mo2C particles dissolve a relatively high content of Fe elements; a certain amount of Ti, B, C, Cr, Mo and other elements are dissolved in the bonding phase (Fe, Ni), which plays a solution strengthening role for the bonding phase; the annular phase attached to the TiB2 core is mainly composed of Ti, Fe, B, C elements, and at the same time contains a small amount of Mo, Ni, Cr elements, and is a (Ti, Mo, Cr, Fe, Ni)(B, C) solid solution. The gray ceramic particles are mainly composed of Ti and C elements, and at the same time contain a relatively high content of Fe, Mo, Ni elements, and a small amount of B, Cr elements, forming a TiC core-(Ti, Mo, Fe, Ni, Cr)(B, C) annular phase. The formation of the two "core-ring" structures with TiB2 as the core and TiC as the core plays a very important role in improving the interfacial bonding strength between the core, the annular phase and the bonding phase in the cermet, which is beneficial to improving the strength and toughness of the TiB2-based steel-bonded cemented carbide.

[0062] Table 1-1 Figure 4 Energy spectrum point scanning results in

[0063]

[0064] The ingredients of the TiB2-based steel-bonded cemented carbide in Example 7 are composed of powders with the following mass percentages and average particle sizes: TiB2: 50%, average particle size is 4.0 μm, Mo2C: 9.0%, average particle size is 4.5 μm, Cr3C2: 3.0%, average particle size is 2.5 μm, Ni: 3.0%, average particle size is 4.5 μm, Fe: 34.3%, average particle size is 4.5 μm, C: 0.7%, average particle size is 4.0 μm, and the sum of the mass percentages of each component is 100%.

[0065] The specific steps for preparing the cermet are as follows:

[0066] (1) Preparation of the mixed powder: Weigh the TiB2, Mo2C, Cr3C2, Fe, Ni, and C powders according to the above mass percentages, and use planetary ball milling for mixing. Alcohol is used as the ball milling medium, the ball-to-material ratio is 2:1, and the ball milling speed is 160 r / min. First, planetary ball mill the TiB2, Mo2C, Cr3C2, and C powders for 12 h, and then add the Fe and Ni powders and planetary ball mill for 24 h to obtain a mixed powder slurry. Dry the mixed powder slurry in a vacuum drying oven at 57 °C for 15 h, and then sieve through an 80-mesh sieve to remove agglomerates to obtain the TiB2-based steel-bonded cemented carbide mixed powder.

[0067] (2) Compression molding: First, use die pressing to press at a pressure of 100 MPa into a size of 25×8×7.5 mm3 The cuboid green compact is then subjected to cold isostatic pressing at a pressure of 280 MPa for 170 s to further increase the green compact density.

[0068] (3) Vacuum sintering: The green compact prepared in step (2) is subjected to vacuum sintering, and the vacuum degree is maintained at 10 -1 ~10 -3 Pa throughout the process. The specific heating and sintering regime is as follows: from room temperature, it is heated at 1 - 3 °C / min to 136 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 235 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 360 °C and held for 1 h; it is heated at 1 - 3 °C / min to 545 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 742 °C and held for 1 h, and it is heated at 1 - 3 °C / min to 834 °C and held for 1 h; then it is heated at 1 - 3 °C / min to 1000 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1122 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1145 °C and held for 1 h; then it is heated at 1 - 2 °C / min to 1370 °C and held for 1 h. After the heating is completed, high vacuum is maintained throughout the process, and it is cooled to room temperature with the furnace.

[0069] The bulk density of the TiB2 - based steel - bonded carbide prepared in this example is 5.69 g / cm 3 , the hardness is 92.3 HRA, the flexural strength is 1351.46 MPa, and the fracture toughness is 10.15 MPa·m 1 / 2 . Its phase composition is as shown in Figure 3 (g), including 5 phases: TiB2, Fe2B, TiC, (Fe,Ni), and Mo2C binder phase.

Claims

1. A TiB2-based steel-bonded cemented carbide, characterized in that: The mass percentage composition of the TiB2-based steel-bonded cemented carbide is as follows: TiB2: 45-55%, Cr3C2: 2-4%, Mo2C: 0-10%, Ni: 2-4%, Fe: 35.0-45.0%, C: 0.7%, and the sum of the mass percentages of each component is 100%; The preparation process of the TiB2-based steel-bonded cemented carbide includes: mixing, pressing, vacuum reduction and vacuum liquid-phase sintering; the XRD phase composition of the TiB2-based steel-bonded cemented carbide mainly includes four phases: TiB2, Fe2B, TiC and (Fe,Ni); the energy spectrum results of SEM-EDS show that around the TiB2 ceramic particles, a (Ti,Mo,Cr,Fe,Ni)(B,C) annular phase grows adherently.

2. The preparation method of a TiB2-based steel-bonded cemented carbide according to claim 1, characterized in that: It includes the following steps: (1) Preparation of the mixed powder: Weigh the TiB2, Cr3C2, Mo2C, Ni, Fe, and C powders according to the above mass percentages, mix the materials by planetary ball milling or drum ball milling, dry them in a vacuum drying oven at 50-60°C, and then screen them through an 80-mesh sieve to remove agglomerates to obtain the mixed powder of the TiB2-based steel-bonded cemented carbide; (2) Compression molding: Use cold isostatic pressing to press the mixed powder in step (1) under a pressure of 250-300 MPa for 150-200 s to obtain a green body; (3) Vacuum sintering: The green compact obtained in step (2) is subjected to vacuum sintering with a vacuum degree of 10 -3 ~10 -1 Pa, a sintering temperature of 1350 - 1450 °C, and an insulation time of 0.5 - 2 h to obtain TiB2-based steel-bonded cemented carbide with a bulk density of 5.62 - 5.69 g / cm 3 , a hardness of 88.8 - 92.5 HRA, a flexural strength of 1175.25 - 1552.34 MPa, and a fracture toughness of 9.15 - 11.21 MPa·m 1 / 2 .

3. The preparation method of a TiB2-based steel-bonded carbide according to claim 2, characterized in that: The average particle size of the TiB2 powder is 2.0-4.0 μm, the average particle size of the Cr3C2 powder is 2-5 μm, the average particle size of the Mo2C powder is 3-5 μm, the average particle size of the Ni powder is 3-5 μm, the average particle size of the Fe powder is 3-5 μm, and the average particle size of the C powder is 2-5 μm.

4. The preparation method of a TiB2-based steel-bonded cemented carbide according to claim 2, characterized in that: The TiB2 powder is prepared by chemical vapor deposition method, and its surface is coated with a layer of carbon with a thickness of 2-4 nm.

5. The preparation method of a TiB2-based steel-bonded cemented carbide according to claim 2, characterized in that: For the preparation of the mixed powder in step (1), alcohol or kerosene is used as the ball milling medium, the ball-to-material ratio is (1-5):1, and the ball milling speed is 150-200 r / min; first, ball mill and mix the TiB2, Cr3C2, Mo2C, and C powders for 12 h, then add the Fe and Ni powders and ball mill them together for another 24 h, running alternately in forward and reverse directions.

6. The preparation method of a TiB2-based steel-bonded cemented carbide according to claim 2, characterized in that: The vacuum sintering described in step (3) includes the integrated technology of removing adsorbed water vapor and oxygen, vacuum carbothermal reduction, and vacuum liquid-phase sintering dissolution and precipitation. The heating process is as follows: heating from room temperature to 136°C at a rate of 1 - 3°C / min and holding for 1 h to remove the water vapor adsorbed in the raw material powder; then heating to 235°C at a rate of 1 - 3°C / min and holding for 1 h to remove the oxygen adsorbed in the raw material powder; then heating to 360°C at a rate of 1 - 3°C / min and holding for 1 h, and then heating to 545°C at a rate of 1 - 3°C / min and holding for 1 h to reduce the oxides on the surface of Ni powder by vacuum carbothermal reduction; then heating to 742°C at a rate of 1 - 3°C / min and holding for 1 h, and then heating to 834°C at a rate of 1 - 3°C / min and holding for 1 h to reduce the oxides on the surface of Fe powder by vacuum carbothermal reduction; then heating to 1000°C at a rate of 1 - 3°C / min and holding for 1 h, then heating to 1122°C at a rate of 1 - 2°C / min and holding for 1 h to reduce the surface oxides of TiB2, Mo2C, and Cr3C2 by vacuum carbothermal reduction; then heating to 1145°C at a rate of 1 - 2°C / min and holding for 1 h; then heating to 1350°C - 1450°C at a rate of 1 - 2°C / min and holding for 1 h to fully perform vacuum liquid-phase sintering; after the heating is completed, maintain a high vacuum throughout the process and cool to room temperature with the furnace.

7. The preparation method of a TiB2-based steel-bonded cemented carbide according to claim 2, characterized in that: The XRD phase composition of the TiB2-based steel-bonded cemented carbide mainly includes four phases: TiB2, Fe2B, TiC, and (Fe,Ni); the energy spectrum results of SEM-EDS show that around the TiB2 ceramic particles, a (Ti,Mo,Cr,Fe,Ni)(B,C) annular phase grows adherently.

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