CN111876698B - Steel bonded hard alloy and preparation method thereof - Google Patents

Steel bonded hard alloy and preparation method thereof Download PDF

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CN111876698B
CN111876698B CN202010577668.8A CN202010577668A CN111876698B CN 111876698 B CN111876698 B CN 111876698B CN 202010577668 A CN202010577668 A CN 202010577668A CN 111876698 B CN111876698 B CN 111876698B
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hard alloy
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sintered body
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CN111876698A (en
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钟黎声
白海强
吕振林
卢正欣
许云华
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Xian University of Technology
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C49/00—Alloys containing metallic or non-metallic fibres or filaments
    • C22C49/02—Alloys containing metallic or non-metallic fibres or filaments characterised by the matrix material
    • C22C49/10—Refractory metals
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C47/00—Making alloys containing metallic or non-metallic fibres or filaments
    • C22C47/14—Making alloys containing metallic or non-metallic fibres or filaments by powder metallurgy, i.e. by processing mixtures of metal powder and fibres or filaments
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C49/00—Alloys containing metallic or non-metallic fibres or filaments
    • C22C49/14—Alloys containing metallic or non-metallic fibres or filaments characterised by the fibres or filaments
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/002—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working by rapid cooling or quenching; cooling agents used therefor
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C22F1/16—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of other metals or alloys based thereon
    • C22F1/18—High-melting or refractory metals or alloys based thereon

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

Steel bonded hard alloy and preparation method thereof
Technical Field
The invention belongs to the technical field of hard alloy, and relates to steel bonded hard alloy and a preparation method thereof.
Background
The traditional WC-Co series hard alloy has the advantages of high hardness and high wear resistance, and is used in the fields of military industry, aerospace, machining, metallurgy, petroleum drilling, mine tools, electronic communication, buildings and the like, but the binder phase Co belongs to rare strategic resources, the preparation cost is relatively high, the Co powder has strong industrial toxicity in the preparation process, and particularly, the WC-Co composite powder can cause permanent damage to the lung of a human body, so that the search for a Co substitute material becomes one of the important development directions of the traditional hard alloy.
The steel bonded hard alloy is a potential novel hard alloy capable of replacing WC-Co series hard alloy due to excellent wear resistance, high strength, low cost, good processability and good heat treatment characteristics. In recent years, steel bonded cemented carbide has been widely used in the industries of dies, wear-resistant parts and mines, and the boundary between the steel bonded carbide and the conventional WC-Co cemented carbide and the steel gradually disappears, so that the market share is getting larger and larger. However, both the conventional WC-Co cemented carbide and the new steel-bonded cemented carbide still have a problem to be solved: when the volume fraction of the hard phase is high, the hard alloy can meet the strength requirement of the actual working condition but cannot meet the toughness requirement; this results in the hard alloy being prone to failure during service, reducing service life and increasing industrial manufacturing costs. For example, Richter et al, On hardnessand toughnesss of ultra and nanocrystalline hardmaterials, 1999 in International Journal of reflective Metals and Hard Materials, produced WC-10Co cemented carbide using a hot press sintering process with hardness up to 1800HV and fracture toughness of only 6 MPa.m 1/2. The patent "high manganese steel base hard alloy and preparation method thereof" (CN200610031772.7) discloses a steel bond hard alloy with TiC as hard phase and high manganese steel as binding phase, the hardness of the steel bond hard alloy is HRC62.1, the bending strength is 2000MPa, and the impact toughness is 7.2J/mm 2. Due to the ex-situ formation of TiC particles, the wettability between the binding phase Fe and the hard phase TiC is poor, and more pores exist. The existence of the pores leads the hard alloy to be easy to generate cracks in the service process, and reduces the toughness. Compared with WC-Co hard alloy, although the toughness of the steel bond hard alloy is improved, the steel bond hard alloy still does not meet the requirements of practical harsh working conditions, such as a drill plate and a cold heading die for bearing high-speed impact load.
Therefore, in order to meet the requirements of actual working conditions, the development of a steel bonded cemented carbide with high strength, high toughness and high wear resistance has become an urgent problem to be solved in the field of material research.
Disclosure of Invention
The invention aims to provide a steel bonded hard alloy, which solves the problems of low toughness and short service life of the existing hard alloy.
The invention also aims to provide a preparation method of the steel bonded hard alloy.
The first technical scheme adopted by the invention is that the steel bonded hard alloy is characterized by comprising 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 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.
The present invention is also technically characterized in that,
the steel powder is carbon steel powder, high manganese steel powder or alloy steel powder.
The second technical scheme adopted by the invention is that the preparation method of the steel bonded hard alloy comprises the following steps:
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.
In the step 1, the granularity of the tungsten powder is 20-120 mu m, the granularity of the steel powder is 5-20 mu m, and the granularity of the niobium powder and the tantalum powder is 10-100 mu m.
In the step 2, uniformly mixing the tungsten powder, the steel powder and the graphite powder weighed in the step 1 by using a V-shaped mixer, wherein the rotating speed of the V-shaped mixer is 300r/min and the mixing time is 6-24h in the mixing process.
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 arrangement directions of the metal fibers in adjacent mixed layers are different.
In step 3, the diameter d of the metal fiber10.2 mm-3 mm, and the thickness of the mixed layer is 2d1～10d1。
And 4, maintaining the pressure for 1-2 hours by using a cold isostatic press under the pressure of 15-30MPa, and performing prepressing molding on the composite preform.
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.
In step 5.2, when the furnace temperature is 1450-; 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.
The invention has the beneficial effects that:
the high-toughness Nb (Ta) fibers arranged in the steel bonded hard alloy in an oriented manner enable the hard alloy to present obvious anisotropy, so that a choice is provided for the use of the hard alloy under different working conditions;
the mixed distribution of WC granules and NbC (TaC) granules can obviously change crack propagation paths, thereby toughening the hard alloy;
③ the in-situ formation of the WC pellets, NbC (TaC) layer on the surface of the metal Nb (Ta) fibers remarkably improves the interface bonding strength between the hard phase and the binding phase and between the metal Nb (Ta) fibers and the NbC (TaC) layer, thus leading the hard alloy to have higher strength;
fourthly, the liquid-solid sintering process can effectively promote the sintering densification of the hard alloy and realize the purpose of reducing the porosity, and the reduction of the porosity is necessarily beneficial to the improvement of the obdurability of the hard alloy; in addition, the post-treatment process can obviously improve the steel matrix structure and reduce the residual thermal stress in the hard alloy.
The steel bonded hard alloy prepared by the invention has high strength, excellent toughness and good wear resistance, the preparation process is simple and convenient, the operation is convenient, the sintering period controllability is strong, the process cost is low, the steel bonded hard alloy can be widely applied to industrial production, the cost performance is extremely high, the prepared hard alloy can provide a good initial structure state and an excellent comprehensive performance matrix for widely applied cutter materials and devices, and is a suitable replacement material, and the production cost is effectively reduced.
Drawings
FIG. 1 is a schematic view of the arrangement of metal fibers in a steel-bonded cemented carbide according to the present invention;
FIG. 2 is a schematic view of the microstructure of a steel-bonded cemented carbide prepared in example 1 of the present invention;
FIG. 3 is a schematic diagram of the high power microstructure of the steel bonded cemented carbide prepared in example 1 of the present invention.
In the figure, 1. metal fibers, 2.WC pellets, 3.NbC (TaC) pellets, 4.NbC (TaC) layers, 5. binder phase.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention relates to a steel bonded hard alloy, which comprises, 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 above components is 100%; the niobium fiber or tantalum fiber is arranged in multilayer orientation in the alloy, and the fiber arrangement directions in adjacent niobium fiber layers or tantalum fiber layers are different. The steel powder is carbon steel powder, high manganese steel powder or alloy steel powder.
The invention relates to a preparation method of steel bonded hard alloy, which comprises the following steps:
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%; wherein the granularity of the tungsten powder is 20-120 mu m, the granularity of the steel powder is 5-20 mu m, and the granularity of the niobium powder and the tantalum powder is 10-100 mu m.
Step 2, uniformly mixing the powder weighed in the step 1 by adopting a V-shaped mixer to prepare mixed powder; in the mixing process, the rotating speed of the V-shaped mixer is 100-300r/min, and the mixing time is 6-24 h.
Step 3, referring to fig. 1, paving a layer of mixed powder layer on the bottom of the die by taking the mixed powder, distributing a plurality of metal fibers on the mixed powder layer, wherein the metal fibers are niobium fibers or tantalum fibers, 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; the metal fibers in the same mixed layer are parallel to each other, the spacing between adjacent metal fibers is equal, and the arrangement directions of the metal fibers in the adjacent mixed layers are different. Diameter d of the metal fibers10.2 mm-3 mm, and the thickness of the mixed layer is 2d1～10d1。
Step 4, keeping the pressure for 1-2 hours by adopting a cold isostatic press under the pressure of 15-30MPa, and prepressing and molding the composite preform; in the mould pressing process, paraffin is used as a forming agent, and accounts for 2-4 wt% of the total mass of the mixed powder;
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.
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 1450-1525 ℃, and preserving the temperature for 10-30min, wherein the temperature raising rate is 2-10 ℃/min, and the unit area pressure of the sintered body is 10-15 MPa in the heat preservation process; then reducing the furnace temperature to 1050-; finally, cooling to room temperature along with the furnace to obtain a hard alloy sintered body;
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.
Example 1
The preparation method of the steel bonded hard alloy specifically comprises the following steps:
step 1, respectively weighing 80.6 percent of tungsten powder, 2 percent of carbon steel powder (T10), 12.6 percent of graphite powder and 4.8 percent of niobium powder according to the mass percent, wherein the sum of the mass percent of the tungsten powder, the carbon steel powder and the niobium powder is 100 percent; wherein the granularity of the tungsten powder is 20 mu m, the granularity of the carbon steel powder (T10) is 10 mu m, and the granularity of the niobium powder is 10 mu m.
Step 2, uniformly mixing the powder weighed in the step 1 by adopting a V-shaped mixer to prepare mixed powder; in the material mixing process, the rotating speed of the V-shaped material mixer is 100r/min, and the material mixing time is 6 h.
Step 3, spreading a layer of mixed powder with the thickness of 0.4mm on the bottom of the die, arranging parallel equidistant metal fibers on the mixed powder layer, wherein the metal fibers are niobium fibers, 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, the diameter of the metal fibers is 0.2mm, the thickness of the mixed layer is 0.4mm, and the distance between adjacent metal fibers in the mixed layer is 0.4 mm;
preparing mixed layers again on the mixed layers, wherein metal fibers in the adjacent mixed layers are vertical to each other, and the multiple mixed layers are mutually superposed until the target thickness is reached, namely the total thickness of the mixed powder layers and the mixed layers is 40mm, so that a composite prefabricated body is formed;
step 4, maintaining the pressure for 1h under the pressure of 20MPa by using a cold isostatic press, and pre-pressing and forming the composite preform, wherein paraffin is used as a forming agent in the mould pressing process, and accounts for 4 wt% of the total mass of the mixed powder;
step 5, sintering and forming the pressed compact and then carrying out heat treatment
Step 5.1, placing the pressed blank in a pressure sintering furnace for low-temperature presintering and dewaxing, wherein the dewaxing temperature is 450 ℃, and the dewaxing time is 0.8 h;
step 5.2, raising the furnace temperature to 1450 ℃, and preserving the temperature for 30min, wherein the unit area pressure of the sintered body is 15MPa in the heat preservation process; then reducing the furnace temperature to 1050 ℃ and preserving the temperature for 10h, wherein the unit area pressure of the sintered body is 30MPa in the heat preservation process; finally, cooling to room temperature along with the furnace to obtain a hard alloy sintered body;
in the process of green compact sintering, carbon atoms are diffused to the surface of metal powder in situ to form WC and NbC aggregates, and simultaneously, the carbon atoms are diffused to the surface of the high-toughness metal Nb fiber in situ to form a compact NbC layer.
Step 5.3, quenching the hard alloy sintered body, heating the hard alloy sintered body to 800 ℃, preserving heat for 100min, and quenching to room temperature, wherein the quenching medium is water;
and 5.4, tempering the quenched hard alloy sintered body, heating the hard alloy sintered body to 300 ℃, preserving heat for 2 hours, and cooling in air to room temperature to obtain the steel-bonded hard alloy.
The steel-bonded hard alloy prepared in the example 1 is subjected to metallographic treatment, the microstructure of the steel-bonded hard alloy is observed, fig. 2 is a low-power microstructure diagram of the steel-bonded hard alloy prepared in the example 1, fig. 3 is a high-power microstructure diagram of the steel-bonded hard alloy prepared in the example 1, and as can be seen from fig. 2 and fig. 3, metal fibers 1, WC granules 2 and NbC granules 3 are distributed in the steel-bonded hard alloy, the metal fibers 1 are distributed in a layered manner, and the arrangement directions of the metal fibers in different layers are different, so that the steel-bonded hard alloy has good anisotropy, and further meets the use conditions of various working conditions. Wherein, WC granules 2 and NbC granules 3 are uniformly distributed, the WC granules 2 are composed of aggregated WC grains, the NbC granules are composed of aggregated NbC grains, a NbC layer 4 is generated on the surface of the metal fiber 1, a binding phase 5 is distributed between the WC granules 2 and the NbC granules 3, the binding phase 5 is Fe, and the mixed distribution of the WC granules 2 and the NbC granules 3 can obviously change crack propagation paths, thereby toughening the hard alloy; the WC granules, the NbC granules and the NbC layer formed in situ on the surface of the Nb fiber remarkably improve the interface bonding strength between the hard phase and the binding phase and between the metal Nb fiber and the NbC layer, so that the hard alloy has higher strength.
The average grain size of the WC grains in the WC granules in this steel-bonded cemented carbide was measured to be about 3 μm, the average grain size of the NbC grains in the NbC granules was measured to be about 0.7 μm, and the diameter of the metal fibers (niobium fibers) was measured to be about 0.16 mm. The fracture toughness of the steel bond hard alloy is about 23.6 MPa.m 1/2, and the bending strength is about 1343 MPa.
Example 2
The preparation method of the steel bonded hard alloy specifically comprises the following steps:
step 1, weighing 72.7% of tungsten powder, 5% of high manganese steel powder, 7.8% of graphite powder and 14.5% of niobium powder according to the mass percentage, wherein the sum of the mass percentages of the components is 100%; wherein the granularity of the tungsten powder is 75 microns, the granularity of the high manganese steel powder is 20 microns, and the granularity of the niobium powder is 75 microns.
Step 2, uniformly mixing the powder weighed in the step 1 by adopting a V-shaped mixer to prepare mixed powder; in the material mixing process, the rotating speed of the V-shaped material mixer is 150r/min, and the material mixing time is 8 h.
Step 3, paving a layer of mixed powder layer with the thickness of 4mm on the bottom of the die, distributing parallel equidistant metal fibers on the mixed powder layer, wherein the metal fibers are niobium fibers, the gaps among the metal fibers are filled with the mixed powder and covered with the 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 distance between adjacent metal fibers in the mixed layer is 3 mm;
preparing mixed layers again on the mixed layers, wherein metal fibers in the adjacent mixed layers are vertical to each other, and the multiple mixed layers are mutually superposed until the target thickness is reached, namely the total thickness of the mixed powder layers and the mixed layers is 60mm, so that a composite prefabricated body is formed;
step 4, keeping the pressure for 1.5 hours under the pressure of 20MPa by using a cold isostatic press, and pre-pressing and forming the composite preform, wherein paraffin is used as a forming agent in the mould pressing process, and accounts for 4 wt% of the total mass of the mixed powder;
step 5, sintering and forming the pressed compact and then carrying out heat treatment
Step 5.1, placing the pressed blank in a pressure sintering furnace for low-temperature presintering and dewaxing, wherein the dewaxing temperature is 450 ℃, and the dewaxing time is 1 h;
step 5.2, raising the furnace temperature to 1450 ℃, and preserving the temperature for 20min, wherein the temperature raising rate is 6 ℃/min, and the unit area pressure of the sintered body is 15MPa in the heat preservation process; then reducing the furnace temperature to 1150 ℃ and preserving the temperature for 8h, wherein the unit area pressure of the sintered body is 25MPa in the heat preservation process; finally, cooling to room temperature along with the furnace to obtain a hard alloy sintered body;
step 5.3, quenching the hard alloy sintered body, heating the hard alloy sintered body to 900 ℃, preserving heat for 90min, and quenching to room temperature, wherein the quenching medium is water;
and 5.4, tempering the quenched hard alloy sintered body, heating the hard alloy sintered body to 220 ℃, preserving the heat for 5 hours, and cooling the hard alloy sintered body to room temperature in air to obtain the steel-bonded hard alloy.
The steel bond hard alloy prepared in the example 2 is subjected to metallographic treatment, and the microstructure inside the steel bond hard alloy is observed, so that metal fibers, WC granules and NbC granules are distributed in the steel bond hard alloy, the metal fibers 1 are distributed in a layered manner, the arrangement directions of the metal fibers in different layers are different, the steel bond hard alloy has good anisotropy, the WC granules and the NbC granules are uniformly distributed, the WC granules are composed of aggregated WC grains, the NbC granules are composed of aggregated NbC grains, NbC layers are generated on the surfaces of the metal fibers, and bonding phases are distributed between the WC granules and the NbC granules; the WC granules, the NbC granules and the NbC layer formed in situ on the surface of the Nb fiber remarkably improve the interface bonding strength between the hard phase and the binding phase and between the metal Nb fiber and the NbC layer, so that the hard alloy has higher strength.
The mean grain size of the WC grains in the WC granules in this steel-bonded cemented carbide was measured to be about 5 μm, the mean grain size of the NbC grains in the NbC granules was measured to be about 0.75 μm, and the diameter of the metal fibers (niobium fibers) was measured to be about 1.35 mm. The fracture toughness of the steel bond hard alloy is about 17.6 MPa.m 1/2, and the bending strength is about 1486 MPa.
Example 3
The preparation method of the steel bonded hard alloy specifically comprises the following steps:
step 1, weighing 82.6 percent of tungsten powder, 2.6 percent of stainless steel powder, 6.0 percent of graphite powder and 8.8 percent of tantalum powder according to the mass percentage, wherein the sum of the mass percentages of the tungsten powder, the stainless steel powder, the graphite powder and the tantalum powder is 100 percent; wherein the granularity of the tungsten powder is 120 mu m, the granularity of the stainless steel powder is 15 mu m, and the granularity of the tantalum powder is 100 mu m.
Step 2, uniformly mixing the powder weighed in the step 1 by adopting a V-shaped mixer to prepare mixed powder; in the mixing process, the rotating speed of the V-shaped mixer is 200r/min, and the mixing time is 12 h.
Step 3, spreading a layer of mixed powder with the thickness of 20mm on the bottom of the die, distributing parallel equidistant metal fibers on the mixed powder layer, wherein the metal fibers are tantalum fibers, the gaps among the metal fibers are filled with the mixed powder and covered with the 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 6 mm;
preparing mixed layers again on the mixed layers, wherein metal fibers in the adjacent mixed layers are vertical to each other, and the multiple mixed layers are mutually superposed until the target thickness is reached, namely the total thickness of the mixed powder layers and the mixed layers is 100mm, so that a composite prefabricated body is formed;
step 4, keeping the pressure for 1.5 hours under the pressure of 25MPa by using a cold isostatic press, and pre-pressing and forming the composite preform, wherein paraffin is used as a forming agent in the mould pressing process, and accounts for 4 wt% of the total mass of the mixed powder;
step 5, sintering and forming the pressed compact and then carrying out heat treatment
Step 5.1, placing the pressed blank in a pressure sintering furnace for low-temperature presintering and dewaxing, wherein the dewaxing temperature is 600 ℃, and the dewaxing time is 1 h;
step 5.2, raising the furnace temperature to 1500 ℃ and preserving the temperature for 5min, wherein the temperature rise rate is 7 ℃/min, and the unit area pressure of a sintered body is 10MPa in the heat preservation process; then reducing the furnace temperature to 1200 ℃ and preserving the temperature for 10h, wherein the unit area pressure of the sintered body is 20MPa in the heat preservation process; finally, cooling to room temperature along with the furnace to obtain a hard alloy sintered body;
step 5.3, quenching the hard alloy sintered body, heating the hard alloy sintered body to 950 ℃, preserving heat for 60min, and quenching to room temperature, wherein the quenching medium is water;
and 5.4, tempering the quenched hard alloy sintered body, heating the hard alloy sintered body to 300 ℃, preserving heat for 2 hours, and cooling in air to room temperature to obtain the steel-bonded hard alloy.
Metallographic treatment is carried out on the steel bond hard alloy prepared in the example 2, and the microstructure inside the steel bond hard alloy is observed, so that tantalum metal fibers, WC granules and TaC granules are distributed in the steel bond hard alloy, the WC granules and the TaC granules are uniformly distributed, the WC granules consist of aggregated WC grains, the NbC granules consist of aggregated TaC grains, a TaC layer is generated on the surface of the metal fibers, binding phase Fe is distributed between the WC granules and the TaC granules, and the mixed distribution of the WC granules and the TaC granules can remarkably change crack propagation paths, so that the hard alloy is toughened; the WC granules, the TaC granules and the TaC layer formed on the surface of the Ta fiber in situ significantly improve the interface bonding strength between the hard phase and the binding phase and between the metal Ta fiber and the TaC layer, so that the hard alloy has higher strength.
The mean grain size of the WC grains in the WC granules in this steel-bonded cemented carbide was measured to be about 6.5. mu.m, the mean grain size of the TaC grains in the TaC granules was measured to be about 0.8. mu.m, and the diameter of the Ta metal fiber was measured to be about 2.75 mm. The fracture toughness of the steel bond hard alloy is about 15.5 MPa.m 1/2, and the bending strength is about 1651 MPa.
Example 4
The preparation method of the steel bonded hard alloy specifically comprises the following steps:
step 1, respectively weighing the following components, by mass, 68% of tungsten powder, 2.6% of high-manganese steel powder, 7.0% of graphite powder and 22.4% of tantalum powder, wherein the sum of the mass percentages of the components is 100%; wherein the granularity of the tungsten powder is 60 mu m, the granularity of the high manganese steel powder is 15 mu m, and the granularity of the tantalum powder is 50 mu m.
Step 2, uniformly mixing the powder weighed in the step 1 by adopting a V-shaped mixer to prepare mixed powder; in the mixing process, the rotating speed of the V-shaped mixer is 100r/min, and the mixing time is 20 h.
Step 3, paving a layer of mixed powder layer with the thickness of 3mm on the bottom of the die, distributing parallel equidistant metal fibers on the mixed powder layer, wherein the metal fibers are tantalum fibers, the gaps among the metal fibers are filled with the mixed powder and covered with the 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 distance between adjacent metal fibers in the mixed layer is 2 mm;
preparing mixed layers again on the mixed layers, wherein metal fibers in the adjacent mixed layers are vertical to each other, and the multiple mixed layers are mutually superposed until the target thickness is reached, namely the total thickness of the mixed powder layers and the mixed layers is 60mm, so that a composite prefabricated body is formed;
step 4, keeping the pressure for 1 hour under the pressure of 10MPa by using a cold isostatic press, and pre-pressing and forming the composite preform, wherein paraffin is used as a forming agent in the mould pressing process, and accounts for 2 wt% of the total mass of the mixed powder;
step 5, sintering and forming the pressed compact and then carrying out heat treatment
Step 5.1, placing the pressed blank in a pressure sintering furnace for low-temperature presintering and dewaxing, wherein the dewaxing temperature is 500 ℃, and the dewaxing time is 0.8 h;
step 5.2, raising the furnace temperature to 1525 ℃ and preserving the temperature for 8min, wherein the temperature rise rate is 6 ℃/min, and the unit area pressure of a sintered body is 10MPa in the heat preservation process; then reducing the furnace temperature to 1175 ℃ and preserving the temperature for 6 hours, wherein the unit area pressure of the sintered body is 25MPa in the heat preservation process; finally, cooling to room temperature along with the furnace to obtain a hard alloy sintered body;
step 5.3, quenching the hard alloy sintered body, heating the hard alloy sintered body to 1000 ℃, preserving heat for 60min, and quenching to room temperature, wherein the quenching medium is water;
and 5.4, tempering the quenched hard alloy sintered body, heating the hard alloy sintered body to 250 ℃, preserving heat for 4 hours, and cooling in air to room temperature to obtain the steel-bonded hard alloy.
Metallographic treatment is carried out on the steel bond hard alloy prepared in the example 2, and the microstructure inside the steel bond hard alloy is observed, so that tantalum metal fibers, WC granules and TaC granules are distributed in the steel bond hard alloy, the WC granules and the TaC granules are uniformly distributed, the WC granules consist of aggregated WC grains, the NbC granules consist of aggregated TaC grains, a TaC layer is generated on the surface of the metal fibers, binding phase Fe is distributed between the WC granules and the TaC granules, and the mixed distribution of the WC granules and the TaC granules can remarkably change crack propagation paths, so that the hard alloy is toughened; the WC granules, the TaC granules and the TaC layer formed on the surface of the Ta fiber in situ significantly improve the interface bonding strength between the hard phase and the binding phase and between the metal Ta fiber and the TaC layer, so that the hard alloy has higher strength.
The mean grain size of the WC grains in the WC granules in the steel bonded cemented carbide was measured to be about 7 μm, the mean grain size of the TaC grains in the TaC granules was measured to be about 0.8 μm, and the diameter of the Ta metal fiber was measured to be about 0.88 mm. The fracture toughness of the steel bond hard alloy is about 21.5 MPa.m 1/2, and the bending strength is about 1508 MPa.

Claims (5)

1. 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%; the steel powder is carbon steel powder or alloy steel powder;
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; 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;
step 4, prepressing and molding the composite prefabricated part by using a cold isostatic press to prepare a pressed blank;
step 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;
the step 5 specifically includes the following contents:
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.
2. The method for preparing a steel bonded hard alloy according to claim 1, 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.
3. The method for preparing the steel bonded hard alloy according to claim 1, wherein in the step 2, the tungsten powder, the steel powder and the graphite powder weighed in the step 1 are uniformly mixed by 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.
4. The method for preparing a steel bonded hard alloy according to claim 1, wherein in the step 3, the diameter d of the metal fiber10.2 mm-3 mm, and the thickness of the mixed layer is 2d1～10d1。
5. The method for preparing the steel bonded hard alloy according to claim 1, wherein in the step 4, the composite preform is pre-pressed and molded by a cold isostatic press under the pressure of 15 MPa-30 MPa for 1-2 h.
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CN106086575A (en) * 2016-08-26 2016-11-09 洛阳金鹭硬质合金工具有限公司 A kind of steel bonded carbide and preparation method thereof
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CN1228798A (en) * 1996-06-28 1999-09-15 德克萨斯研究协会奥斯丁公司 High density composite material
EP1312467A1 (en) * 2001-11-16 2003-05-21 EADS Deutschland GmbH Metal fibre reinforced composite material and method of making
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