CN111876698A - Steel bonded hard alloy and preparation method thereof - Google Patents

Abstract

The invention also discloses a steel bonded hard alloy which comprises 63.9-82.1% of tungsten powder, 2-5% of steel powder, 7-12.6% of graphite powder and 4.8-26.9% of niobium powder or tantalum powder in percentage by mass, wherein the sum of the percentages by mass of the components is 100%; the niobium fiber or tantalum fiber in the alloy is directionally arranged in multiple layers, the fiber arrangement directions in adjacent niobium fiber layers or tantalum fiber layers are different, and the steel powder is carbon steel powder, high-manganese steel powder or alloy steel powder. The invention also discloses a preparation method of the steel bonded hard alloy, and the steel bonded hard alloy prepared by the method contains in-situ formed WC aggregates, NbC (TaC) aggregates, a bonding phase and metal fibers, so that the hard alloy has higher strength and good toughness.

Description

A kind of steel-bonded cemented carbide and preparation method thereof

technical field

The invention belongs to the technical field of hard alloys, and relates to a steel-bonded hard alloy and a preparation method thereof.

Background technique

Traditional WC-Co cemented carbides are used in military, aerospace, machining, metallurgy, oil drilling, mining tools, electronic communications, construction and other fields due to their high hardness and high wear resistance. Co is a rare strategic resource, the preparation cost is relatively high, and Co powder has strong industrial toxicity during the preparation process, especially the WC-Co composite powder will cause permanent damage to human lungs, so the search for alternative materials for Co has become a One of the important development directions of traditional cemented carbide.

Due to its excellent wear resistance, high strength, low cost and good machinability and heat treatment characteristics, steel-bonded cemented carbide has become a potential new type of cemented carbide to replace WC-Co cemented carbide. . In recent years, steel-bonded cemented carbide has been widely used in molds, wear-resistant parts, and geology and mining industries. The boundary between it and traditional WC-Co-based cemented carbide and steel is gradually disappearing, and its market share is increasing. However, both the traditional WC-Co series cemented carbide and the new steel-bonded cemented carbide still have an urgent problem to be solved: when the volume fraction of the hard phase is high, the cemented carbide can meet the actual working conditions. Strength requirements, but can not meet toughness requirements; this leads to failure of cemented carbide during service, reducing service life and increasing the cost of industrial manufacturing. For example, Richter et al., in the paper "On hardness and toughness of ultrafine and nanocrystalline hard materials" published in "International Journal of Refractory Metals and Hard Materials" in 1999, prepared WC-10Co cemented carbide by hot pressing sintering process, Its hardness can reach 1800HV, while the fracture toughness is only 6MPa·m1/2. The patent "High Manganese Steel-Based Cemented Carbide and Its Preparation Method" (CN200610031772.7) discloses a steel-bonded cemented carbide with TiC as the hard phase and high manganese steel as the binder phase, and its hardness is HRC62.1 , the flexural strength is 2000MPa, and the impact toughness is 7.2J/mm2. Due to the ex-situ formation of TiC particles, the wettability between the binder phase Fe and the hard phase TiC is poor, and there are many pores. The existence of pores makes the cemented carbide easy to initiate cracks during service, which reduces the toughness. Compared with WC-Co cemented carbide, although the toughness of steel-bonded cemented carbide has been improved, it still does not meet the needs of actual harsh working conditions, such as drill pieces and cold heading dies that are subjected to high-speed impact loads.

Therefore, in order to meet the needs of actual working conditions, it has become an urgent problem to be solved in the field of materials research to develop a steel-bonded cemented carbide with high strength, high toughness and high wear resistance.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a steel-bonded cemented carbide to solve the problems of low toughness and short service life of the existing cemented carbide.

Another object of the present invention is to provide a method for preparing a steel-bonded cemented carbide.

The first technical solution adopted by the present invention is a steel-bonded cemented carbide, which is characterized in that, according to the mass percentage, it includes the following components: 63.9-82.1% tungsten powder, 2-5% steel powder, and 7-12.6% graphite powder , 4.8-26.9% niobium powder or tantalum powder, the sum of the mass percentages of the above components is 100%; it also includes niobium fibers or tantalum fibers, and the niobium fibers or tantalum fibers in the alloy are oriented in multiple layers, and the adjacent niobium fiber layers Or the fibers in the tantalum fiber layer are arranged in different directions.

The technical feature of the present invention is also that,

The steel powder is carbon steel powder, high manganese steel powder or alloy steel powder.

The second technical solution adopted in the present invention is a preparation method of a steel-bonded cemented carbide, comprising the following steps:

Step 1, respectively weigh the following components according to the mass percentage: 63.9-82.1% tungsten powder, 2-5% steel powder, 7-12.6% graphite powder, 4.8-26.9% niobium powder or tantalum powder, the mass percentage of the above components The sum is 100%;

Step 2, mix the powder weighed in step 1 evenly to make a mixed powder;

Step 3, take the mixed powder and spread a mixed powder layer at the bottom of the mold, arrange a plurality of metal fibers on the mixed powder layer, the metal fibers are niobium fibers or tantalum fibers, fill the gaps between the metal fibers with the mixed powder, and cover the metal fibers , the metal fiber and the mixed powder form a mixed layer, the mixed layer is re-prepared on the mixed layer, and the multi-layer mixed layers are superimposed on each other until the target thickness is reached, that is, a composite preform is formed;

Step 4, using a cold isostatic pressing machine to preform the composite preform to form a green compact;

In step 5, the compact is placed in a pressure sintering furnace for sintering and molding to form a sintered body, and then the sintered body is sequentially quenched and tempered to obtain a steel-bonded cemented carbide.

In step 1, the particle size of the tungsten powder is 20 μm-120 μm, the particle size of the steel powder is 5 μm-20 μm, and the particle size of the niobium powder and the tantalum powder are both 10 μm-100 μm.

In step 2, the tungsten powder, steel powder and graphite powder weighed in step 1 are uniformly mixed by a V-type mixer. During the mixing process, the rotation speed of the V-type mixer is 100-300 r/min, and the mixing time is 6 -24h.

In step 3, the metal fibers in the same mixed layer are parallel to each other, the spacing between adjacent metal fibers is equal, and the metal fibers in the adjacent mixed layers are arranged in different directions.

In step 3, the diameter d ₁ of the metal fiber is 0.2 mm to 3 mm, and the thickness of the mixed layer is 2d ₁ to 10d ₁ .

In step 4, a cold isostatic press is used to hold the pressure under a pressure of 15 MPa to 30 MPa for 1-2 hours to pre-press the composite preform.

Step 5 specifically includes the following:

Step 5.1, placing the compact in a pressure sintering furnace for low temperature pre-burning and dewaxing, the dewaxing temperature is 450-650°C, and the dewaxing time is 0.8-1.5h;

Step 5.2, raising the furnace temperature to 1450-1525 °C for a period of time, then reducing the furnace temperature to 1050-1200 °C for a period of time, and finally cooling to room temperature with the furnace to obtain a cemented carbide sintered body;

Step 5.3, quenching the cemented carbide sintered body, heating the cemented carbide sintered body to 800-1000° C., holding the temperature for 5-120 min, and then quenching to restore the temperature of the cemented carbide sintered body to room temperature;

In step 5.4, the quenched cemented carbide sintered body is tempered, and the cemented carbide sintered body is heated to 150-400° C., kept for 0.5h-12h, and air-cooled to room temperature to obtain a steel-bonded cemented carbide.

In step 5.2, when the furnace temperature is 1450-1525°C, the holding time is 10-30min, and the pressure per unit area of the sintered body is 10-15MPa; when the furnace temperature is 1050-1200°C, the holding time is 4h-20h, and the unit area of the sintered body is 4h-20h. The pressure is 15-30MPa.

The beneficial effects of the present invention are:

① The high-toughness metal Nb(Ta) fibers oriented in the steel-bonded cemented carbide make the cemented carbide show significant anisotropy, which provides a choice for the use of the cemented carbide under different working conditions;

②The mixed distribution of WC aggregates and NbC(TaC) aggregates can significantly change the crack propagation path, thereby toughening the cemented carbide;

(3) The in-situ formation of WC aggregates, NbC(TaC) aggregates, and NbC(TaC) layer on the surface of metallic Nb(Ta) fibers significantly improved the relationship between the hard phase and the binder phase and between the metallic Nb(Ta) fibers and the NbC(TaC) layer. The interface bonding strength, which makes the cemented carbide have higher strength;

④ The use of liquid-solid sintering process can effectively promote the sintering and densification of cemented carbide, and achieve the purpose of reducing porosity, and the reduction of porosity will certainly help to improve the strength and toughness of cemented carbide; in addition, the post-treatment process can Significantly improve the structure of the steel matrix and reduce the residual thermal stress inside the cemented carbide.

The steel-bonded cemented carbide prepared by the invention has high strength, excellent toughness and good wear resistance, the preparation process is simple, the operation is convenient, the controllability of the sintering cycle is strong, the process cost is low, and it can be widely used in industrialization Production, has a very high cost performance, the prepared cemented carbide can provide a good initial microstructure and excellent comprehensive performance matrix for widely used tool materials and devices, is a suitable replacement material, and effectively reduces production costs.

Description of drawings

Fig. 1 is the arrangement schematic diagram of metal fibers in the steel-bonded cemented carbide of the present invention;

Fig. 2 is the low magnification microstructure schematic diagram of the steel-bonded cemented carbide prepared in Example 1 of the present invention;

3 is a schematic diagram of a high-power microstructure of the steel-bonded cemented carbide prepared in Example 1 of the present invention.

In the figure, 1. metal fiber, 2. WC aggregate, 3. NbC (TaC) aggregate, 4. NbC (TaC) layer, 5. binder phase.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

A steel-bonded cemented carbide according to the present invention comprises the following components according to mass percentage: 63.9-82.1% tungsten powder, 2-5% steel powder, 7-12.6% graphite powder, 4.8-26.9% niobium powder or tantalum powder, the above The sum of the mass percentages of each component is 100%; it also includes niobium fibers or tantalum fibers, the niobium fibers or tantalum fibers in the alloy are oriented in multiple layers, and the fibers in adjacent niobium fiber layers or tantalum fiber layers are arranged in different directions. The steel powder is carbon steel powder, high manganese steel powder or alloy steel powder.

A preparation method of a steel-bonded cemented carbide of the present invention specifically comprises the following steps:

Step 1, respectively weigh the following components according to the mass percentage: 63.9-82.1% tungsten powder, 2-5% steel powder, 7-12.6% graphite powder, 4.8-26.9% niobium powder or tantalum powder, the mass percentage of the above components The sum is 100%; wherein, the particle size of the tungsten powder is 20 μm-120 μm, the particle size of the steel powder is 5 μm-20 μm, and the particle size of the niobium powder and the tantalum powder are both 10 μm-100 μm.

In step 2, the powder weighed in step 1 is uniformly mixed by a V-type mixer to form a mixed powder; during the mixing process, the rotation speed of the V-type mixer is 100-300r/min, and the mixing time is 6-24h.

Step 3, referring to Figure 1, take the mixed powder and lay a layer of mixed powder on the bottom of the mold, arrange a plurality of metal fibers on the mixed powder layer, the metal fibers are niobium fibers or tantalum fibers, and fill the gaps between the metal fibers with the mixed powder, And cover the metal fibers, the metal fibers and the mixed powder form a mixed layer, the mixed layer is re-prepared on the mixed layer, and the multi-layer mixed layers are superimposed on each other until the target thickness is reached, that is, a composite preform is formed; the metal fibers in the same mixed layer are parallel to each other , the spacing between adjacent metal fibers is equal, and the metal fibers in the adjacent mixed layers are arranged in different directions. The diameter d ₁ of the metal fibers is 0.2 mm to 3 mm, and the thickness of the mixed layer is 2d ₁ to 10d ₁ .

Step 4, using a cold isostatic press to hold pressure for 1-2 hours at a pressure of 15 MPa to 30 MPa, to pre-compress the composite preform; in the molding process, paraffin is used as a forming agent, and the paraffin accounts for 2-4 wt% of the total mass of the mixed powder;

In step 5, the compact is placed in a pressure sintering furnace for sintering and molding to form a sintered body, and then the sintered body is sequentially quenched and tempered to obtain a steel-bonded cemented carbide.

Step 5 specifically includes the following:

Step 5.1, placing the compact in a pressure sintering furnace for low temperature pre-burning and dewaxing, the dewaxing temperature is 450-650°C, and the dewaxing time is 0.8-1.5h;

In step 5.2, the furnace temperature is raised to 1450-1525°C for 10-30min, and the heating rate is 2-10°C/min. During the heat preservation process, the pressure per unit area of the sintered body is 10-15MPa; then the furnace temperature is lowered to 1050- Heat preservation at 1200°C for 4h-20h, during the heat preservation process, the pressure per unit area of the sintered body is 15-30MPa; finally, it is cooled to room temperature with the furnace to obtain a cemented carbide sintered body;

Step 5.3, quenching the cemented carbide sintered body, heating the cemented carbide sintered body to 800-1000° C., holding the temperature for 5-120 min, and then quenching to restore the temperature of the cemented carbide sintered body to room temperature;

In step 5.4, the quenched cemented carbide sintered body is tempered, and the cemented carbide sintered body is heated to 150-400° C., kept for 0.5h-12h, and air-cooled to room temperature to obtain a steel-bonded cemented carbide.

Example 1

The preparation of a steel-bonded cemented carbide specifically includes the following steps:

Step 1, respectively weigh the following components according to mass percentage: 80.6% tungsten powder, 2% carbon steel powder (T10), 12.6% graphite powder, 4.8% niobium powder, and the sum of the mass percentages of the above components is 100%; wherein , the particle size of tungsten powder is 20 μm, the particle size of carbon steel powder (T10) is 10 μm, and the particle size of niobium powder is 10 μm.

In step 2, the powder weighed in step 1 is uniformly mixed by a V-type mixer to form a mixed powder; during the mixing process, the rotation speed of the V-type mixer is 100 r/min, and the mixing time is 6 hours.

Step 3, take the mixed powder and lay a mixed powder layer with a thickness of 0.4mm on the bottom of the mold, and arrange the metal fibers with equal spacing parallel to each other on the mixed powder layer. The metal fibers are niobium fibers, and the mixed powder is used to fill the gaps between the metal fibers , and cover the metal fibers, the metal fibers and the mixed powder form a mixed layer, the diameter of the metal fibers is 0.2mm, the thickness of the mixed layer is 0.4mm, and the spacing between adjacent metal fibers in the mixed layer is 0.4mm;

Re-preparing the mixed layer on the mixed layer, the metal fibers in the adjacent mixed layers are perpendicular to each other, and the multi-layer mixed layers are superimposed on each other until the target thickness is reached, that is, the total thickness of the mixed powder layer and the mixed layer is 40mm, that is, a composite preform is formed;

Step 4, using a cold isostatic press to hold the pressure for 1 hour at a pressure of 20 MPa, pre-compressing the composite preform, using paraffin as a forming agent in the molding process, and the paraffin accounting for 4wt% of the total mass of the mixed powder;

Step 5, heat treatment after sintering the compact

Step 5.1, place the compact in a pressure sintering furnace for low-temperature pre-burning and dewaxing, the dewaxing temperature is 450°C, and the dewaxing time is 0.8h;

In step 5.2, the furnace temperature was raised to 1450°C for 30 minutes. During the heat preservation process, the pressure per unit area of the sintered body was 15MPa; then the furnace temperature was lowered to 1050°C for 10 hours. During the heat preservation process, the pressure per unit area of the sintered body was 30MPa; finally With the furnace cooled to room temperature, the cemented carbide sintered body was obtained;

During the compact sintering process, carbon atoms diffused to the surface of the metal powder to form WC and NbC aggregates in situ, while carbon atoms diffused to the surface of the high-toughness metal Nb fibers to form a dense NbC layer in situ.

Step 5.3, quenching the cemented carbide sintered body, heating the cemented carbide sintered body to 800° C., holding the temperature for 100 min, and quenching to room temperature, and the quenching medium is water;

In step 5.4, the quenched cemented carbide sintered body is tempered, and the cemented carbide sintered body is heated to 300° C., kept for 2 hours, and air-cooled to room temperature to obtain a steel-bonded cemented carbide.

The steel-bonded cemented carbide prepared in Example 1 was subjected to metallographic treatment, and its internal microstructure was observed. The high-magnification microstructure of the steel-bonded cemented carbide can be seen from Figures 2 and 3 that metal fibers 1, WC aggregates 2 and NbC aggregates 3 are distributed inside the steel-bonded cemented carbide, and the metal fibers 1 are layered. The metal fibers in different layers are arranged in different directions, so that the steel-bonded cemented carbide has good anisotropy, and thus meets the use conditions of various working conditions. Among them, WC aggregates 2 and NbC aggregates 3 are evenly distributed, WC aggregates 2 are composed of aggregated WC grains, NbC aggregates are composed of aggregated NbC grains, and NbC layer 4, WC aggregates 2 and NbC aggregates 3 are formed on the surface of metal fiber 1. There is a binder phase 5 distributed between them, and the binder phase 5 is Fe. The mixed distribution of WC aggregates 2 and NbC aggregates 3 can significantly change the crack propagation path, thereby toughening the cemented carbide; WC aggregates, NbC aggregates and Nb fiber surfaces The in-situ formed NbC layer significantly improves the interfacial bonding strength between the hard phase and the binder phase and the metal Nb fibers and the NbC layer, making the cemented carbide have higher strength.

After measurement, the average particle size of WC grains in WC aggregates in the steel-bonded cemented carbide is about 3 μm, the average particle size of NbC grains in NbC aggregates is about 0.7 μm, and the diameter of metal fibers (niobium fibers) is about 0.16 μm. mm. The fracture toughness of the steel-bonded cemented carbide is about 23.6MPa·m1/2, and the flexural strength is about 1343MPa.

Example 2

The preparation of a steel-bonded cemented carbide specifically includes the following steps:

Step 1, respectively weigh the following components according to mass percentage: 72.7% tungsten powder, 5% high manganese steel powder, 7.8% graphite powder, 14.5% niobium powder, and the sum of the mass percentages of the above components is 100%; The particle size of the powder is 75 μm, the particle size of the high manganese steel powder is 20 μm, and the particle size of the niobium powder is 75 μm.

In step 2, the powder weighed in step 1 is uniformly mixed by a V-type mixer to prepare a mixed powder; during the mixing process, the rotation speed of the V-type mixer is 150r/min, and the mixing time is 8h.

Step 3, take the mixed powder and lay a mixed powder layer with a thickness of 4 mm on the bottom of the mold, and arrange the metal fibers parallel to each other at equal intervals on the mixed powder layer. The metal fibers are niobium fibers, and the mixed powder is used to fill the gap between the metal fibers. And covered with metal fibers, the metal fibers and the mixed powder form a mixed layer, the diameter of the metal fibers is 1.5mm, the thickness of the mixed layer is 4mm, and the spacing between adjacent metal fibers in the mixed layer is 3mm;

Re-preparing the mixed layer on the mixed layer, the metal fibers in the adjacent mixed layers are perpendicular to each other, and the multi-layer mixed layers are superimposed on each other until the target thickness is reached, that is, the total thickness of the mixed powder layer and the mixed layer is 60mm, that is, a composite preform is formed;

Step 4, using a cold isostatic press to hold the pressure for 1.5 hours at a pressure of 20 MPa, pre-compressing the composite preform, using paraffin as a forming agent in the molding process, and the paraffin accounting for 4wt% of the total mass of the mixed powder;

Step 5, heat treatment after sintering the compact

Step 5.1, place the compact in a pressure sintering furnace for low temperature pre-burning and dewaxing, the dewaxing temperature is 450°C, and the dewaxing time is 1h;

In step 5.2, the furnace temperature was raised to 1450°C for 20 minutes, and the heating rate was 6°C/min. During the heat preservation process, the pressure per unit area of the sintered body was 15MPa; then the furnace temperature was lowered to 1150°C for 8 hours. During the heat preservation process, the sintered body was sintered. The unit area pressure of the body is 25MPa; finally, it is cooled to room temperature with the furnace, and the cemented carbide sintered body is obtained;

Step 5.3, quenching the cemented carbide sintered body, heating the cemented carbide sintered body to 900° C., holding the temperature for 90 minutes, and quenching to room temperature, and the quenching medium is water;

In step 5.4, the quenched cemented carbide sintered body is tempered, and the cemented carbide sintered body is heated to 220° C., maintained for 5 hours, and air-cooled to room temperature to obtain a steel-bonded cemented carbide.

The steel-bonded cemented carbide prepared in Example 2 is subjected to metallographic treatment, and its internal microstructure is observed. It can be seen that metal fibers, WC aggregates and NbC aggregates are distributed in the steel-bonded cemented carbide, and the metal fibers 1 are layered. Distribution, the metal fibers in different layers are arranged in different directions, so that the steel-bonded cemented carbide has good anisotropy, WC aggregates and NbC aggregates are uniformly distributed, WC aggregates are composed of aggregated WC grains, and NbC aggregates are composed of aggregated NbC crystals. The NbC layer is formed on the surface of the metal fiber, and the binder phase is distributed between the WC agglomerates and the NbC agglomerates. The interfacial bonding strength between the metallic Nb fibers and the NbC layer makes the cemented carbide have high strength.

After measurement, the average particle size of WC grains in WC aggregates in the steel-bonded cemented carbide is about 5 μm, the average particle size of NbC grains in NbC aggregates is about 0.75 μm, and the diameter of metal fibers (niobium fibers) is about 1.35 μm. mm. The fracture toughness of the steel-bonded cemented carbide is about 17.6MPa·m1/2, and the flexural strength is about 1486MPa.

Example 3

The preparation of a steel-bonded cemented carbide specifically includes the following steps:

Step 1, respectively weigh the following components according to mass percentage: 82.6% tungsten powder, 2.6% stainless steel powder, 6.0% graphite powder, 8.8% tantalum powder, and the sum of the mass percentages of the above components is 100%; The particle size is 120 μm, the particle size of the stainless steel powder is 15 μm, and the particle size of the tantalum powder is 100 μm.

In step 2, the powder weighed in step 1 is uniformly mixed by a V-type mixer to form a mixed powder; during the mixing process, the rotation speed of the V-type mixer is 200 r/min, and the mixing time is 12 hours.

Step 3, take the mixed powder and lay a mixed powder layer with a thickness of 20mm on the bottom of the mold, and arrange the metal fibers with equal spacing in parallel on the mixed powder layer, the metal fibers are tantalum fibers, and the mixed powder is used to fill the gaps between the metal fibers, And covered with metal fibers, the metal fibers and the mixed powder form a mixed layer, the diameter of the metal fibers is 3mm, the thickness of the mixed layer is 20mm, and the distance between adjacent metal fibers in the mixed layer is 6mm;

Re-preparing the mixed layer on the mixed layer, the metal fibers in the adjacent mixed layers are perpendicular to each other, and the multi-layer mixed layers are superimposed on each other until the target thickness is reached, that is, the total thickness of the mixed powder layer and the mixed layer is 100mm, that is, a composite preform is formed;

Step 4, using a cold isostatic press to hold the pressure for 1.5 hours at a pressure of 25 MPa, pre-compressing the composite preform, using paraffin as a forming agent in the molding process, and the paraffin accounting for 4wt% of the total mass of the mixed powder;

Step 5, heat treatment after sintering the compact

Step 5.1, place the compact in a pressure sintering furnace for low temperature pre-burning and dewaxing, the dewaxing temperature is 600°C, and the dewaxing time is 1h;

In step 5.2, the furnace temperature was raised to 1500°C for 5 min, and the heating rate was 7°C/min. During the heat preservation process, the pressure per unit area of the sintered body was 10MPa; then the furnace temperature was lowered to 1200°C for 10 hours, and during the heat preservation process, the sintered body was sintered. The unit area pressure of the body is 20MPa; finally, it is cooled to room temperature with the furnace to obtain a cemented carbide sintered body;

Step 5.3, quenching the cemented carbide sintered body, heating the cemented carbide sintered body to 950° C., keeping the temperature for 60 minutes, and quenching to room temperature, and the quenching medium is water;

In step 5.4, the quenched cemented carbide sintered body is tempered, and the cemented carbide sintered body is heated to 300° C., kept for 2 hours, and air-cooled to room temperature to obtain a steel-bonded cemented carbide.

The steel-bonded cemented carbide prepared in Example 2 is subjected to metallographic treatment, and its internal microstructure is observed. It can be seen that tantalum metal fibers, WC agglomerates and TaC agglomerates, WC agglomerates and TaC agglomerates are distributed inside the steel-bonded cemented carbide. Uniform distribution, WC agglomerates are composed of aggregated WC grains, NbC agglomerates are composed of agglomerated TaC grains, a TaC layer is formed on the surface of the metal fiber, and there are binder phases Fe, WC agglomerates and TaC agglomerates distributed between the WC agglomerates and TaC agglomerates The mixed distribution of WC can significantly change the crack propagation path, thereby toughening the cemented carbide; the TaC layer formed in situ on the surface of the WC aggregates, TaC aggregates and Ta fibers significantly improves the hard phase and the binder phase, as well as the metallic Ta fibers and TaC layers. The interface bonding strength between them makes the cemented carbide have higher strength.

After measurement, the average grain size of WC grains in WC aggregates in the steel-bonded cemented carbide is about 6.5 μm, the average grain size of TaC grains in TaC aggregates is about 0.8 μm, and the diameter of Ta metal fibers is about 2.75 mm. The fracture toughness of the steel-bonded cemented carbide is about 15.5MPa·m1/2, and the flexural strength is about 1651MPa.

Example 4

The preparation of a steel-bonded cemented carbide specifically includes the following steps:

Step 1, respectively weigh the following components according to mass percentage: 68% tungsten powder, 2.6% high manganese steel powder, 7.0% graphite powder, 22.4% tantalum powder, and the sum of the mass percentages of the above components is 100%; The particle size of the powder is 60 μm, the particle size of the high manganese steel powder is 15 μm, and the particle size of the tantalum powder is 50 μm.

In step 2, the powder weighed in step 1 is uniformly mixed by a V-type mixer to prepare a mixed powder; during the mixing process, the rotation speed of the V-type mixer is 100r/min, and the mixing time is 20h.

Step 3, take the mixed powder and lay a mixed powder layer with a thickness of 3 mm on the bottom of the mold, and arrange the metal fibers with equal spacing in parallel on the mixed powder layer, the metal fibers are tantalum fibers, and the mixed powder is used to fill the gaps between the metal fibers, And covered with metal fibers, the metal fibers and the mixed powder form a mixed layer, the diameter of the metal fibers is 1mm, the thickness of the mixed layer is 3mm, and the spacing between adjacent metal fibers in the mixed layer is 2mm;

Re-preparing the mixed layer on the mixed layer, the metal fibers in the adjacent mixed layers are perpendicular to each other, and the multi-layer mixed layers are superimposed on each other until the target thickness is reached, that is, the total thickness of the mixed powder layer and the mixed layer is 60mm, that is, a composite preform is formed;

Step 4, using a cold isostatic press to hold the pressure for 1 hour at a pressure of 10 MPa, pre-compressing the composite preform, using paraffin as a forming agent in the molding process, and the paraffin accounting for 2wt% of the total mass of the mixed powder;

Step 5, heat treatment after sintering the compact

Step 5.1, place the compact in a pressure sintering furnace for low-temperature pre-burning and dewaxing, the dewaxing temperature is 500°C, and the dewaxing time is 0.8h;

In step 5.2, the furnace temperature was raised to 1525°C for 8 minutes, and the heating rate was 6°C/min. During the heat preservation process, the pressure per unit area of the sintered body was 10 MPa; the furnace temperature was then lowered to 1175°C for 6 hours. The unit area pressure of the body is 25MPa; finally, it is cooled to room temperature with the furnace, and the cemented carbide sintered body is obtained;

Step 5.3, quenching the cemented carbide sintered body, heating the cemented carbide sintered body to 1000° C., holding the temperature for 60 minutes, and quenching to room temperature, and the quenching medium is water;

In step 5.4, the quenched cemented carbide sintered body is tempered, and the cemented carbide sintered body is heated to 250° C., maintained for 4 hours, and air-cooled to room temperature to obtain a steel-bonded cemented carbide.

The steel-bonded cemented carbide prepared in Example 2 is subjected to metallographic treatment, and its internal microstructure is observed. It can be seen that tantalum metal fibers, WC agglomerates and TaC agglomerates, WC agglomerates and TaC agglomerates are distributed inside the steel-bonded cemented carbide. Uniform distribution, WC agglomerates are composed of aggregated WC grains, NbC agglomerates are composed of agglomerated TaC grains, a TaC layer is formed on the surface of the metal fiber, and there are binder phases Fe, WC agglomerates and TaC agglomerates distributed between the WC agglomerates and TaC agglomerates The mixed distribution of WC can significantly change the crack propagation path, thereby toughening the cemented carbide; the TaC layer formed in situ on the surface of the WC aggregates, TaC aggregates and Ta fibers significantly improves the hard phase and the binder phase, as well as the metallic Ta fibers and TaC layers. The interface bonding strength between them makes the cemented carbide have higher strength.

After measurement, the average grain size of WC grains in WC aggregates in the steel-bonded cemented carbide is about 7 μm, the average grain size of TaC grains in TaC aggregates is about 0.8 μm, and the diameter of Ta metal fibers is about 0.88 mm. The fracture toughness of the steel-bonded cemented carbide is about 21.5MPa·m1/2, and the flexural strength is about 1508MPa.

Claims (10)

1. The steel bonded hard alloy is characterized by comprising, by mass, 63.9-82.1% of tungsten powder, 2-5% of steel powder, 7-12.6% of graphite powder and 4.8-26.9% of niobium powder or tantalum powder, wherein the sum of the mass percentages of the components is 100%; the niobium fiber or tantalum fiber alloy further comprises niobium fibers or tantalum fibers, wherein the niobium fibers or tantalum fibers in the alloy are arranged in a multi-layer oriented mode, and the fiber arrangement directions in adjacent niobium fiber layers or tantalum fiber layers are different.

2. The steel bonded hard alloy according to claim 1, wherein the steel powder is carbon steel powder, high manganese steel powder or alloy steel powder.

3. The preparation method of the steel bonded hard alloy is characterized by comprising the following steps of:

step 1, respectively weighing 63.9-82.1% of tungsten powder, 2-5% of steel powder, 7-12.6% of graphite powder and 4.8-26.9% of niobium powder or tantalum powder according to the mass percentage, wherein the sum of the mass percentages of the tungsten powder and the steel powder is 100%;

step 2, uniformly mixing the powder weighed in the step 1 to prepare mixed powder;

step 3, taking mixed powder, flatly paving a layer of mixed powder layer at the bottom of the die, distributing a plurality of metal fibers on the mixed powder layer, filling gaps among the metal fibers with the mixed powder, covering the metal fibers, forming a mixed layer by the metal fibers and the mixed powder, preparing the mixed layer again on the mixed layer, and mutually overlapping the mixed layers until the target thickness is reached to form a composite prefabricated body;

step 4, prepressing and molding the composite prefabricated part by using a cold isostatic press to prepare a pressed blank;

and 5, placing the pressed compact in a pressure sintering furnace for sintering and forming to form a sintered body, and then sequentially quenching and tempering the sintered body to obtain the steel-bonded hard alloy.

4. The method for preparing a steel bonded hard alloy according to claim 3, wherein in the step 1, the particle size of the tungsten powder is 20 μm to 120 μm, the particle size of the steel powder is 5 μm to 20 μm, and the particle size of the niobium powder and the tantalum powder is 10 μm to 100 μm.

5. The method for preparing the steel bonded hard alloy according to claim 3, wherein in the step 2, the tungsten powder, the steel powder and the graphite powder weighed in the step 1 are uniformly mixed by using a V-shaped mixer, and in the mixing process, the rotating speed of the V-shaped mixer is 300r/min and the mixing time is 6-24 h.

6. The method for preparing the steel bonded hard alloy according to claim 3, wherein in the step 3, the metal fibers in the same mixed layer are parallel to each other, the spacing between the adjacent metal fibers is equal, and the arrangement directions of the metal fibers in the adjacent mixed layers are different.

7. The method for preparing the steel bonded hard alloy according to the claim 3, wherein the diameter d of the metal fiber in the step 3₁0.2 mm-3 mm, and the thickness of the mixed layer is 2d₁～10d₁。

8. The method for preparing the steel bonded hard alloy according to the claim 3, wherein in the step 4, the composite preform is pre-pressed and formed by a cold isostatic press under the pressure of 15 MPa-30 MPa for 1-2 h.

9. The method for preparing the steel bonded hard alloy according to claim 3, wherein the step 5 specifically comprises the following steps:

step 5.1, placing the pressed compact in a pressure sintering furnace for low-temperature presintering and dewaxing, wherein the dewaxing temperature is 450 ℃ and 650 ℃, and the dewaxing time is 0.8-1.5 h;

step 5.2, raising the furnace temperature to 1450-;

step 5.3, quenching the hard alloy sintered body, heating the hard alloy sintered body to 800-1000 ℃, preserving heat for 5-120min, and then quenching to recover the temperature of the hard alloy sintered body to room temperature;

and 5.4, tempering the quenched hard alloy sintered body, heating the hard alloy sintered body to 400 ℃, preserving the heat for 0.5-12 h, and cooling the hard alloy sintered body to room temperature in air to obtain the steel-bonded hard alloy.

10. The method for preparing the steel bonded hard alloy as claimed in claim 9, wherein in the step 5.2, the holding time is 10-30min when the furnace temperature is 1450-1525 ℃, and the unit area pressure of the sintered body is 10-15 MPa; the furnace temperature is 1050-1200 ℃, the heat preservation time is 4-20 h, and the unit area pressure of the sintered body is 15-30 MPa.

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