High-strength wear-resistant self-lubricating drill bit for coal mine and preparation method thereof

Abstract

The invention discloses a high-strength wear-resistant self-lubricating drill bit for a coal mine and a preparation method of the high-strength wear-resistant self-lubricating drill bit. The preparation process comprises the steps that a drill bit blank is prepared from low-alloy carbon structural steel, a high-strength and high-toughness matrix is obtained through thermal refining, and then sand blasting activation is conducted to clean and coarsen the surface. After diamond particles are subjected to acid pickling pretreatment, metal modified diamond composite powder is obtained through salt bath metal and reduction prefabrication. The preparation method comprises the following steps: mixing MoS2 with the carbon dioxide, spraying the mixture on the surface of a matrix through high velocity oxy-fuel to form a wear-resistant coating, and then improving the density and interface bonding strength of the coating through high-frequency induction instantaneous remelting, thereby finally obtaining the coal mine drill bit with high hardness, strong bonding force and self-lubricating performance. The metal modified diamond composite coating containing the metal transition layer and the MoS2 lubricating phase is constructed on the steel substrate, and a high-frequency remelting process is combined, so that the wear resistance, the bonding strength and the self-lubricating performance of the drill bit are synergistically improved, and the drill bit has the advantages of high strength and toughness matching and low cost.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, and in particular relates to a high-strength, wear-resistant, self-lubricating drill bit for coal mines and its preparation method. Background Technology

[0002] With the continuous growth of my country's energy demand, shallow coal resources are gradually being depleted, and coal mining is increasingly pushing towards deeper strata. Deep mining faces harsh conditions such as high stress, high ground temperature, highly abrasive rock formations, and complex geological structures, placing higher demands on the performance of drilling tools. In hard rock formations with a drillability grade f≥8, conventional drill bits suffer from severe wear, frequent chipping, and significant thermal fatigue, resulting in a significantly shortened service life, a substantial increase in the frequency of drill bit tripping and replacement, and a marked extension of single-hole operation time; this severely restricts the development efficiency and economic benefits of deep coal mines.

[0003] Currently, coal mine drill bits mainly utilize materials such as cemented carbide, high-speed steel, ceramics, and polycrystalline diamond composite (PDC). However, each material has significant technical limitations in practical applications. While cemented carbide drill bits possess high hardness, their impact toughness is low, making them prone to brittle chipping in conglomerate or fault-bounded formations. Furthermore, their red hardness is poor; when drilling temperatures exceed 600℃, the binder phase softens, leading to a significant decrease in hardness and consequently, reduced wear resistance. High-speed steel drill bits (such as M42 and M35) exhibit good toughness and machinability, with bending strength exceeding 3.5 GPa. However, their room temperature hardness is only around 67 HRC, and at high temperatures, the hardness decreases to 60% of its room temperature value. In hard rock drilling, the cutting edge rapidly dulls, resulting in a high wear rate and requiring frequent resharpening. Moreover, high-speed steel raw materials are expensive, leading to excessively high overall operating costs. Ceramic drill bits possess excellent wear resistance and heat resistance, remaining stable at 1200℃. However, they exhibit low fracture toughness and poor thermal shock resistance, resulting in a high chipping rate in heterogeneous formations. Furthermore, the yield of sintered products with complex structures is insufficient, limiting their widespread application. While PDC and diamond drill bits possess extremely high hardness and wear resistance, their impact resistance is weak, and they are prone to delamination when interfacial shear strength is high. They also pose a risk of abnormal failure in formations containing flint or quartz nodules. In addition, their high manufacturing costs limit their economic applicability.

[0004] Despite the significant advantages of high-speed steel in terms of cost and processability, leading to its widespread application in drilling medium-hard rock formations, its wear resistance and thermal stability under deep hard rock conditions have become key bottlenecks restricting its performance improvement. In recent years, surface modification technology has provided an effective way to improve the performance of high-speed steel drill bits. Preparing ultrahard coatings such as TiAlN and DLC through physical vapor deposition (PVD) or chemical vapor deposition (CVD) can significantly improve surface hardness and wear resistance; laser cladding of composite materials such as WC / Co can form a deep reinforcing layer, enhancing wear resistance; furthermore, constructing microtextures on the surface and introducing solid lubricating phases (such as MoS2 and h-BN) helps reduce the coefficient of friction, achieving self-lubrication and friction reduction, and suppressing temperature rise and adhesive wear during drilling.

[0005] However, existing surface treatment technologies still have many shortcomings: First, the bonding strength between the hardened layer and the substrate is generally low, making it prone to spalling failure under high impact loads; second, increasing the thickness of the reinforced layer is often accompanied by a decrease in overall toughness; and third, traditional self-lubricating structures are prone to depletion of the lubricating phase under high temperature and high pressure environments, failing to achieve long-term lubrication and making it difficult to sustain the friction-reducing effect. Therefore, how to synergistically improve the surface wear resistance, impact resistance, and self-lubricating properties while ensuring the high toughness of the steel substrate has become a significant challenge in the current development of coal mine drill bit technology.

[0006] In summary, existing drill bit materials generally suffer from insufficient wear resistance, poor impact resistance, limited thermal stability, or excessive cost in deep hard rock drilling, making it difficult to meet the engineering requirements of high efficiency, long service life, and low cost. Especially for low-alloy carbon structural steel-based drill bits, there is an urgent need for a novel surface modification technology that combines composite strengthening and self-lubrication to overcome key technical bottlenecks such as weak film-substrate bonding, the contradiction between thickness and toughness, and poor lubrication continuity. Summary of the Invention

[0007] The purpose of this invention is to provide a high-strength, wear-resistant, self-lubricating drill bit for coal mines, so as to achieve high wear resistance, strong impact resistance, and long-term self-lubrication of low-alloy carbon structural steel ordinary quenched carbon steel drill bits in deep hard rock drilling, solving the problems of short life, easy chipping and lubrication failure of existing drill bits, and significantly reducing costs.

[0008] The second objective of this invention is to provide a method for preparing high-strength, wear-resistant, self-lubricating drill bits for coal mines. To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a method for preparing a high-strength, wear-resistant, self-lubricating drill bit for coal mines, comprising the following steps: S1. The drill bit blank made of steel by machining is heated, water quenched and tempered to obtain a drill bit blank with a preset hardness; S2. Use pure alumina abrasive to sandblast the surface of the drill bit blank after step S1 to remove the surface oxide scale and rust products. S3. Metal modification of the surface of diamond particles to obtain metal-modified diamond composite powder; S4. Mix the metal-modified diamond composite powder with MoS2 particles in a preset ratio, and spray it onto the surface of the drill bit blank after step S2 with a preset impact energy to form a coating of a preset thickness. S5. Rotate the coated drill bit at a uniform speed and use a high-frequency induction heating device to heat the coating for a short time. After cooling, a high-strength, wear-resistant, self-lubricating drill bit for coal mines is obtained.

[0009] Furthermore, the specific process of S1 is as follows: the drill bit blank is placed in a heat treatment furnace at 860~920℃ and kept at that temperature for 0.5~1 hour, then water-quenched and cooled to room temperature; subsequently, it is placed in a box-type heat treatment furnace at 550~560℃ and kept at that temperature for 2~3 hours, then air-cooled to room temperature; the hardness of the drill bit blank with the preset hardness is HRC28~32.

[0010] Furthermore, the particle size of the pure alumina abrasive in S2 is 100~200 mesh, the blasting speed is 20~30m / s, and the processing time is 20~30 minutes; the surface roughness Ra value of the drill bit blank surface after blasting is controlled at 6.3~12.5μm.

[0011] Furthermore, the process for obtaining the metal-modified diamond composite powder in S3 is as follows: S301. Take diamond particles of a preset size, and remove surface impurities by acid leaching, cleaning, and drying. S302. The pretreated diamond particles and nano metal powder are mixed and ground in a preset ratio, then combined with molten salt and heated under a protective atmosphere. After cooling, cleaning and drying, metal-modified diamond composite powder is obtained. S303. The metal-modified diamond composite powder is heated and kept at a temperature under a reducing atmosphere, and then cooled to obtain the reduced metal-modified diamond composite powder.

[0012] Furthermore, in S301, the diamond particles have a particle size of 50~200μm; the acid leaching treatment uses a dilute hydrochloric acid solution with a mass fraction of 20%~30%, a stirring rate of 300~400r / min, and a treatment time of 20~30 minutes; the drying treatment is performed at a temperature of 60~80℃ for 100~120 minutes.

[0013] Furthermore, in S302, the molar ratio of diamond particles to nano-metal powder is 1:1, and the grinding time is 30-40 minutes; the molten salt is composed of equal masses of NaCl and KCl, and the mass ratio of the mixed powder to the molten salt is 1:2-1:3; the protective atmosphere is argon, the heating rate is 6-8℃ / min, the heating temperature is 1000-1100℃, and the holding time is 60-120 minutes; the drying temperature is 60-80℃, and the drying time is 50-80 minutes. The nano-metal powder includes one of chromium powder, tungsten powder, molybdenum powder, and titanium powder.

[0014] Furthermore, the reducing atmosphere described in S303 is hydrogen, the heating temperature is 600~700℃, and the holding time is 60~90 minutes; hydrogen is continuously introduced during the heating and holding process to maintain the reducing atmosphere; the thickness of the metal coating on the diamond is 1~5 micrometers.

[0015] Furthermore, in S4, the particle size of the metal-modified diamond composite powder is 100-300 mesh, the particle size of the MoS2 particles is 200-300 mesh, and the mass of the MoS2 particles accounts for 1%-3% of the mass of the metal-modified diamond composite powder; the preset impact energy is 10×10⁻⁶. 6 ~20×10 6 The coating thickness is 0.2~0.5 mm; the supersonic flame spraying uses the power and heat energy of the high-speed combustion flow to melt the metal components in the mixed powder and heat them to the supersonic flame temperature, and sprays them onto the surface of the drill bit blank through the nozzle and bonds them to the substrate.

[0016] Furthermore, the rotational speed of the drill bit in S5 is 600~800rpm, the power of the high-frequency induction heating device is 40~80kW, and the heating time is 1.0~1.5s.

[0017] A high-strength, wear-resistant, self-lubricating drill bit for coal mines, wherein the drill bit is prepared by the above-described preparation method; The drill bit comprises a 45 steel or 40Cr substrate, on which a metal transition layer and a coating are sequentially formed. The coating is composed of metal-modified diamond composite powder, MoS2 particles, and carbon formed by partial diamond graphitization. The thickness of the coating is 0.2~0.5 mm.

[0018] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention achieves synergistic optimization of drill bit performance by constructing a multi-layer functional composite coating on the surface of a 45 steel or 40Cr carbon steel substrate. Firstly, using Cr(W / Mo / Ti) as a transition layer for supersonic flame spraying not only significantly improves the coating bonding strength due to the good metallurgical compatibility between Cr(W / Mo / Ti) and the steel substrate, but also allows it to react with carbon atoms on the diamond surface at high temperatures to generate stable carbides, further enhancing the interfacial bonding between diamond particles and the metal substrate. Furthermore, the Cr(W / Mo / Ti) layer possesses both corrosion resistance and certain self-lubricating properties, contributing to improved service stability of the drill bit under complex working conditions. Selecting larger diamond particles with a particle size of 50–200 μm as the reinforcing phase not only facilitates uniform coating of the metal layer but also significantly reduces overall manufacturing costs due to the lower raw material cost. By introducing 1–3 wt% of a MoS2 solid lubricating phase into the sprayed powder, and combining this with the graphite-like carbon structure generated by the localized graphitization of diamond that may occur during subsequent high-frequency induction instantaneous heating, a multi-layered lubrication mechanism is constructed, endowing the coating with excellent self-lubricating properties. The overall design achieves a strong and tough match between the high-hardness diamond reinforcing phase and the tough steel matrix, ensuring wear resistance while also taking into account impact resistance, significantly extending the service life of the drill bit, and combining process feasibility with economic practicality. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a flowchart illustrating the preparation of a high-strength, wear-resistant, self-lubricating drill bit according to an embodiment of the present invention; Figure 2 These are micrographs of diamond particles before and after Cr plating on the surface of diamond particles in Embodiment 1 of the present invention; wherein, (a) is a low-magnification micrograph of diamond particles before plating, (b) is a high-magnification micrograph of diamond particles before plating, (c) is a low-magnification micrograph of particles after plating, and (c1) is a high-magnification micrograph of particles after plating. Figure 3 The microstructure (tempered sorbite) obtained by quenching and tempering 45 steel in Example 1 of this invention is shown. Figure 4 These are scanning electron microscope (SEM) images of the cross-section and surface of the high-strength, wear-resistant, self-lubricating drill bit prepared in Example 1 of this invention; wherein, (a) is the cross-section and (b) is the surface. Figure 5These are comparative wear curves of the drill bit made in Embodiment 1 of the present invention and drill bits made of other materials; wherein, (a) is a wear amount-time comparison curve, and (b) is a friction coefficient-stroke comparison curve; Figure 6 The microstructure (laminate martensite) obtained by heat treatment of 45 steel in Comparative Example 1 is shown. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This embodiment provides a high-strength, wear-resistant, self-lubricating drill bit for coal mines, the specific process of which is as follows: Figure 1 The preparation method is as follows: S1. Place the drill bit, which has been machined from commercially available low-alloy carbon structural steel (such as 45 steel, 40Cr steel or other low-alloy carbon structural steel), in a heat treatment furnace at a temperature of 860~920℃ and hold it for 0.5~1 hour. Then, quench it in water to room temperature and then temper it in a box-type heat treatment furnace at 550~560℃ for 2~3 hours and air cool it. This is called quenching and tempering treatment, which ensures that the hardness is HRC28~32, and the drill bit blank is obtained.

[0023] In this embodiment, the heat treatment process requires precise control of heating temperature and holding time to achieve the optimal match between material strength and toughness: excessively high austenitizing temperature can easily lead to grain boundary oxidation or overheating, damaging the integrity of the microstructure, while insufficient temperature will prevent complete entry into the austenite phase region, resulting in incomplete phase transformation and affecting the subsequent quenching effect; the holding time needs to be determined comprehensively based on the workpiece size, thermal conductivity characteristics, and diffusion kinetics, if the time is too short, it will lead to uneven temperature field and incomplete austenitizing, while if the time is too long, it will easily cause austenite grain coarsening or even overheating defects; the subsequent tempering process also requires precise control of temperature and time, if the parameters are too high or too long, it will cause carbide coarsening and matrix softening, resulting in decreased strength, if it is too low or too short, the martensite decomposition will be insufficient, the residual stress will not be effectively released, and the toughness will be insufficient.

[0024] S2. Solid sandblasting is performed on the surface of the heat-treated drill bit. Pure alumina abrasive with a particle size of 100~200 mesh is used. The treatment is carried out for 20~30 minutes at a spraying speed of 20~30m / s to thoroughly remove the surface oxide scale and rust products, and obtain a clean and activated substrate surface.

[0025] In some specific embodiments, the surface roughness Ra value of the sandblasting process is controlled within the range of 6.3–12.5 μm. This roughness is introduced to increase the specific surface area of ​​the substrate and form a microstructure conducive to mechanical interlocking, thereby enhancing the interfacial bonding strength between the subsequent thermal spray coating and the substrate. This roughness range in this embodiment promotes the physical anchoring effect between the sprayed particles and the peak-valley structure of the substrate surface during cooling and solidification, improving bonding performance. However, if the surface roughness is too high, it may not only cause fine powder particles to embed in the deep valleys of the substrate surface during deposition without sufficient melting or effective overlap, affecting the density and continuity of the coating, but may also lead to coating peeling or a decrease in surface quality due to uneven thickness distribution or localized weak bonding areas between the coating and the substrate in subsequent processes, thus weakening the functionality and process adaptability of the coating.

[0026] S3, diamond surface coated with metal S301, diamond particle pretreatment The purpose of diamond particle pretreatment is mainly to remove residual catalysts, paraffin wax, and other impurities, exposing the active sites for surface plating. In this embodiment, diamond particles with a particle size of 50-200 μm are placed in a 20%-30% (w / w) dilute hydrochloric acid solution and stirred at 300-400 rpm for 20-30 min using a magnetic stirrer. Afterward, they are thoroughly washed with deionized water until neutral and then placed in an oven at 60-80°C for 100-120 min for later use. In this embodiment, if the diamond particles are too fine, their large specific surface area and high surface energy make them prone to agglomeration, leading to difficulty in dispersion in the plating solution and hindering uniform deposition of the metal layer on the particle surface. This affects the integrity and density of the pre-plated layer, weakening its metallurgical bonding with the substrate. Simultaneously, the presence of agglomerates reduces the effective coating rate and creates bonding defects. Conversely, if the particles are too coarse, they will protrude more than the coating surface during the spraying deposition process, reducing the effective embedment depth and resulting in a relatively small contact area with the substrate or binder phase. This forms a mechanical structure similar to a cantilever beam, which is subjected to greater shear stress and bending moment during service or subsequent processing. This can easily lead to stress concentration, causing early particle fracture or interface debonding, resulting in detachment.

[0027] S302, salt bath plating Pretreated diamond particles are weighed and mixed with nano-chromium powder, nano-tungsten powder, nano-molybdenum powder, or nano-titanium powder at a molar ratio of carbon to chromium, tungsten, molybdenum, or titanium of 1:1. The mixture is then ground in a mortar for 30–40 minutes to achieve uniform dispersion. The resulting powder mixture is placed in an alumina crucible and compacted. Molten salt composed of equal masses of NaCl and KCl is weighed at a mass ratio of powder mixture to molten salt of 1:2–1:3. After grinding and mixing, the molten salt is applied to the surface of the powder mixture and compacted. The crucible is then placed in a tube furnace under an inert gas (preferably argon) protective atmosphere. Salt bath coating is performed by heating to 1000-1100℃ at a rate of 6-8℃ / min and holding at that temperature for 60-120min, followed by furnace cooling to room temperature. If the temperature is too low, the molten salt system cannot be completely melted, making it difficult to form a continuous liquid medium, thus hindering the effective contact and interfacial reaction between the metal particles and the diamond matrix. On the other hand, if the temperature is too high, it will not only increase energy consumption, but also cause the diamond surface to undergo thermodynamic instability transformation, that is, some carbon atoms rearrange to form a graphite phase, which reduces its hardness and structural integrity, thereby weakening the wear resistance of the composite material. The temperature range of this embodiment allows the molten salt to be completely liquefied, forming a molten medium with good fluidity and ionic conductivity. On the one hand, this promotes the activation and diffusion of metal elements, driving them to react with carbon atoms on the diamond surface to form transition metal carbides, thus enhancing the chemical bond between the two phases. On the other hand, the molten salt layer forms a dense liquid phase covering layer on the surface of the diamond particles, effectively isolating oxygen in the air and inhibiting the oxidation and ablation of diamond at high temperatures, thus acting as a protective atmosphere. This ensures the structural stability of the matrix material while achieving interface strengthening. The resulting product is subjected to multiple water bath heating and ultrasonic cleaning to remove residual molten salt, and finally dried in an oven at 60–80°C for 50–80 min to obtain chromium-plated (tungsten / molybdenum / titanium) modified diamond composite powder.

[0028] In this embodiment, the formation of a uniform metal coating relies on the interfacial chemical reaction between metal particles and the diamond surface at high temperatures, generating intermediate phases such as carbides as a bonding layer. However, this reaction is a self-limiting process: once reaction products form in the contact area, they prevent further direct contact between the metal and the diamond substrate, leading to reaction termination and making it difficult to achieve continuous and uniform coating. To address this, a molten salt phase is introduced as a dynamic medium. This not only lowers the diffusion barrier of the system but also promotes relative movement between particles through capillary action and thermal convection, causing the reacted interface to continuously break down and expose new active surfaces. Simultaneously, it drives unreacted metal particles to migrate to new contact positions, re-initiating the interfacial reaction. This dynamic reaction, breakdown, and re-contact process overcomes the reaction self-passivation effect, enabling continuous and uniform growth of the carbide layer on the diamond particle surface, thereby obtaining a dense and uniformly distributed metallized coating that significantly improves its interfacial bonding stability with the subsequent substrate.

[0029] S303, metal-modified diamond composite powder reduction pre-sintering The reduction and pre-calcination of the metal-modified diamond composite powder described in this embodiment aims to eliminate surface oxides that may be generated during salt bath chromium plating, thereby obtaining high-purity, impurity-free metal-modified diamond composite powder. Specifically, the coated powder, after being dried in an oven, is uniformly dispersed in a mortar and then placed in a graphite crucible. This crucible is then placed in a tube furnace with a hydrogen (H2) reducing atmosphere and heated to 600–700°C for 60–90 minutes. This embodiment uses a graphite crucible, which not only utilizes the reducing properties of carbon but also effectively prevents the reaction between carbon and the plating metal to form metal carbides. If the temperature is too low during the reduction process, the reduction reaction kinetics are slow, the oxides decompose incompletely, and the residual oxide layer will hinder effective contact and interfacial reaction between the metal and diamond. This reduces the uniformity and bonding strength of the coating; while excessively high temperatures may cause excessive diffusion of the coating metal, grain coarsening, or even graphitization of carbon atoms on the diamond surface, or promote the excessive growth and embrittlement of the already formed metal-carbon interface reaction layer, thereby damaging the integrity and thermal stability of the coating. Hydrogen gas is continuously introduced throughout the process to maintain the reducing environment and promote the reduction reaction of oxides. After the heat preservation is completed, the heating power is turned off, and the sample is cooled to room temperature in the hydrogen atmosphere with the furnace, finally obtaining chromium-modified diamond composite powder with a clean surface and fully reduced metal layer.

[0030] In some specific embodiments, the thickness of the metal-coated diamond layer is approximately 1-5 micrometers. If the coating is too thin, the metal coverage is insufficient, resulting in a reduced effective bonding area with the substrate and difficulty in forming a continuous carbide transition layer, thereby reducing the interfacial bonding strength. On the other hand, if the coating is too thick, it is easy to cause segregation of chromium during subsequent hot working or sintering. On the one hand, due to the limited solid solubility between chromium and the iron substrate, excessive chromium may precipitate in the form of brittle intermetallic compounds or chromium-rich phases, deteriorating the interfacial toughness. On the other hand, excessive free chromium may also change the composition design and phase structure of the tool's working layer, affecting its hardness, wear resistance, and thermal stability, thereby weakening the overall service performance of the tool.

[0031] S4, Supersonic Flame Spraying In this embodiment, the kinetic and thermal energy carried by the high-speed combustion stream is used to heat the material powder particles to a molten or semi-molten state, and further raise the temperature to the supersonic flame temperature range. Subsequently, the combustion products and the atomized powder phase are thoroughly mixed in the nozzle or nozzle exit area to form a high-speed jet, which is sprayed onto the substrate surface. During this process, the molten particles undergo plastic deformation under high-speed impact and form a physicochemical bond with the substrate surface, thereby forming a dense and continuous thin coating. If the energy input is insufficient, the powder particles will not melt sufficiently and the impact velocity will be too low, resulting in poor wettability between the particles and the substrate, insufficient deformation, and the interface bonding will be mainly mechanical interlocking, significantly reducing the adhesion performance. Conversely, if the energy is too high, although it can increase the degree of particle melting and flight velocity, it may lead to over-embedding, that is, the high-temperature, high-speed particles undergo excessive plastic flow during impact, and may even be locally embedded in the substrate surface, causing damage to the substrate surface or generating residual stress, which weakens the bonding strength and structural integrity of the coating. Therefore, this embodiment achieves precise control of energy input by optimizing the heat source parameters and particle kinetic state to obtain the best deposition interface quality.

[0032] In some specific embodiments, metal-modified diamond composite powder with a particle size of 100-300 mesh and an equal proportion of MoS2 particles with a particle size of approximately 200-300 mesh, comprising approximately 1%-3% of the mass of the metal-modified diamond composite powder, are packaged in a 10×10⁻⁶ ratio. 6 ~20×10 6 Joule impact energy is sprayed onto the surface of a heat-treated drill bit. During the spraying process, the drill bit continues to rotate, with a rotation speed set to 100-200 rad / min. The spraying time is set to 0.5-1.5 min, resulting in a drill bit with a coating thickness of 0.2-0.5 mm. The coating consists of metal-modified diamond composite powder, MoS2 particles, and carbon formed by partial diamond graphitization. In the supersonic flame spraying process of this embodiment, the mixed powder is heated to the supersonic flame temperature by the power and heat energy of the high-speed combustion stream, causing the metal components to melt. This melted metal is then sprayed at high speed through a nozzle onto the surface of the drill bit blank, where it firmly bonds with the substrate. Because diamond has an extremely high melting point, the metal plated on its surface melts during the spraying process, but the diamond itself remains solid, thus effectively preserving its physical properties.

[0033] S5. To improve the density of the coating and the interfacial bonding strength between the coating and the substrate, a high-frequency induction instantaneous remelting treatment is applied to the drill bit after supersonic flame spraying. Specifically, the sprayed drill bit is clamped on a conventional lathe and rotated at a constant speed of 600–800 rpm to ensure uniform interaction between the thermal field and the material surface. A high-frequency induction heating device is used to rapidly heat the circumference of the drill bit, with the heating power controlled at 40–80 kW and the action time precisely controlled at 1.0–1.5 s. This transient thermal process causes local softening or micro-melting of the surface coating material, achieving pore closure and micro-densification through the synergistic effect of centrifugal force and surface tension. At the same time, rapid thermal cycling effectively relaxes the residual stress accumulated during the spraying process due to drastic cooling and thermal gradient, inhibiting the propagation of microcracks. More importantly, the short-term high temperature stimulates atomic diffusion at the coating-substrate interface, promoting the formation of metallurgical bonding and significantly enhancing the interfacial bonding strength.

[0034] Example 1 S1. The 45 steel drill bit is heated in a heating furnace at 890℃ for 0.75h and then water-quenched; then it is heated at 550℃ for 2.5h and air-cooled for tempering. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment until the surface roughness Ra value is 9.4. S301. Place 125μm diamond particles in a 25% dilute hydrochloric acid solution and stir magnetically at 350r / min for 25min. Then wash thoroughly with deionized water until neutral and place in an oven at 70℃ for 110min for later use. S302. The pretreated diamond and nano-chromium powder are mixed at a carbon-chromium molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1050℃ at 7℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 70℃ for 65 min to obtain chromium-modified diamond composite powder with a coating thickness of about 3μm. S303. Chromium-modified diamond composite powder is placed in a tube sintering furnace and heated to 650℃ under a hydrogen atmosphere. After holding at this temperature for 75 minutes, it is cooled with the furnace to obtain chromium-modified diamond composite powder with a clean surface and fully reduced metallic chromium layer. According to... Figure 2 As can be seen from (a) to (c1), the diamond particles have achieved good diamond coating coverage, indicating that the epitaxial growth process is uniform and complete, effectively coating the surface of the original particles.

[0035] S4. Mix equal proportions of chromium-modified diamond composite powder (100-300 mesh) with 2% (by mass of composite powder) MoS2 particles (approximately 250 mesh), and use a 15×10... 6 J-impact energy is sprayed onto the surface of a heat-treated drill bit. During the spraying process, the drill bit continues to rotate, and the rotation speed can be set to 150 rad / min; the spraying time is set to 1 min; resulting in a drill bit with a coating thickness of 0.35 mm.

[0036] S5. The coated drill bit is clamped onto a lathe and rotated at a constant speed of 700 rpm. A high-frequency induction heating device is used to rapidly heat the drill bit's circumference, with the heating power controlled at 60 kW and the heating time precisely adjusted to 1.25 seconds. The drill bit after the coating process is completed is displayed below. Figure 4 In (a) and (b), the bonding between the surface coating and the substrate can be clearly observed. The coating uniformly covers the substrate, with almost no obvious interfaces or defects, indicating good bonding strength and integrity between the coating and the substrate. The sprayed drill bit, high-speed steel quenched drill bit, and carbide drill bit prepared in the examples were subjected to tribological tests under a load of 10 kgf and room temperature air, using silica ceramic as the grinding element. The results are as follows... Figure 5 As shown in (a) and (b), the wear curves indicate that, under the same test conditions, the drill bit prepared in this embodiment exhibits significantly better wear resistance, with a mass loss approximately half that of high-speed steel quenched drill bits and cemented carbide drill bits, demonstrating a significantly enhanced wear resistance. Simultaneously, the friction coefficient test results show that the average friction coefficient of this sprayed drill bit is as low as 0.02, significantly lower than the other two types of drill bits, exhibiting excellent friction-reducing characteristics. The performance comparison between the drill bit prepared in this embodiment and drill bits manufactured using conventional processes after approximately 60–90 minutes of the same rock drilling operation is shown in Table 1. Table 1 Comparison of wear data between the drill bit and high-speed steel prepared in Example 1. Example

[0037] S1. The 40Cr steel drill bit is heated in a heating furnace at 860℃ for 0.5h and then water-quenched; then it is heated at 560℃ for 2h and air-cooled for tempering. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 20 min under the condition of 20 m / s spraying speed, until the surface roughness Ra value is 6.3 μm. S301. Place 50μm diamond particles in a 20% (w / w) dilute hydrochloric acid solution and stir magnetically at 300r / min for 20min. Then wash thoroughly with deionized water until neutral and place in an oven at 60℃ for 80min for later use. S302. The pretreated diamond and nano-chromium powder are mixed at a carbon-chromium molar ratio of 1:1 and ground for 30 min. Then, the mixture is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2 (mixed powder: molten salt). Under argon protection, the temperature is increased to 1000℃ at 6℃ / min and held for 60 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, the mixture is dried in an oven at 60℃ for 50 min to obtain chromium-modified diamond composite powder with a coating thickness of about 1 μm. S303. Chromium-modified diamond composite powder is placed in a tube sintering furnace and heated at 600°C in a hydrogen atmosphere. After holding at the temperature for 60 minutes, it is cooled with the furnace to obtain chromium-modified diamond composite powder with a clean surface and fully reduced metallic chromium layer. S4. Mix equal proportions of chromium-modified diamond composite powder (100-300 mesh) with 1% (by mass of composite powder) MoS2 particles (approximately 200 mesh), using a 10×10⁻⁶ mixing agent. 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 100 rad / min, and the spraying time was set to 0.5 min; a drill bit with a coating thickness of 0.2 mm was obtained. S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 600 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. The heating power is controlled at 40 kW and the action time is precisely controlled at 1.0 s.

[0038] Example 3 S1. After holding the 45 steel drill bit at 920℃ for 1 hour, water quench it; then temper it at 560℃ for 3 hours and air cool it. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 30 min under the condition of 30 m / s spraying speed, until the surface roughness Ra value is 12.5 μm. S301. Place 200μm diamond particles in a 30% dilute hydrochloric acid solution and stir magnetically at 400r / min for 30min. Then wash thoroughly with deionized water until neutral and place in an oven at 80℃ for 50min for later use. S302. The pretreated diamond and nano-chromium powder are mixed at a carbon-chromium molar ratio of 1:1 and ground for 40 min. Then, the mixture is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:3 (mixed powder: molten salt). Under argon protection, the temperature is increased to 1100℃ at 8℃ / min and held for 120 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, the mixture is dried in an oven at 80℃ for 80 min to obtain chromium-modified diamond composite powder with a coating thickness of about 5 μm. S303. Chromium-modified diamond composite powder is placed in a tube sintering furnace and heated at 700°C in a hydrogen atmosphere. After holding at the temperature for 90 minutes, it is cooled with the furnace to obtain chromium-modified diamond composite powder with a clean surface and fully reduced metallic chromium layer. S4. Mix equal proportions of chromium-modified diamond composite powder (100-300 mesh) with 3% (by mass of composite powder) MoS2 particles (approximately 300 mesh), using a 20×10⁻⁶ ppm diaphragm filter. 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 200 rad / min, and the spraying time was set to 1.5 min; a drill bit with a coating thickness of 0.5 mm was obtained. S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 800 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 80 kW and precisely adjust the action time to 1.5 s.

[0039] Example 4 S1. The 40Cr steel drill bit is held at 890℃ for 0.75h and then water-quenched; then tempered at 555℃ for 2.5h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 9.4 μm. S301. Place 125μm diamond particles in a 25% dilute hydrochloric acid solution and stir magnetically at 350r / min for 25min. Then wash thoroughly with deionized water until neutral and place in an oven at 70℃ for 60min for later use. S302. The pretreated diamond and nano-titanium powder are mixed at a carbon-titanium molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1050℃ at 7℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 70℃ for 65 min to obtain titanium-modified diamond composite powder with a coating thickness of about 3μm. S303. The titanium-modified diamond composite powder is placed in a tube sintering furnace and heated at 650°C in a hydrogen atmosphere. After holding at the temperature for 75 minutes, it is cooled with the furnace to obtain titanium-modified diamond composite powder with a clean surface and fully reduced metallic titanium layer. S4. Mix equal proportions of 100-300 mesh titanium-modified diamond composite powder with 2% (by mass of composite powder) MoS2 particles with a particle size of approximately 250 mesh, and then mix using a 15×10... 6J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 150 rad / min, and the spraying time was set to 1 min; a drill bit with a coating thickness of 0.35 mm was obtained; S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 700 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 60 kW and precisely adjust the action time to 1.25 s.

[0040] Example 5 S1. The 45 steel drill bit is held at 860℃ for 0.5h and then water-quenched; then tempered at 550℃ for 2h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 20 min under the condition of 20 m / s spraying speed, until the surface roughness Ra value is 6.3 μm. S301. Place 50μm diamond particles in a 20% (w / w) dilute hydrochloric acid solution and stir magnetically at 300r / min for 20min. Then wash thoroughly with deionized water until neutral and place in an oven at 60℃ for 80min for later use. S302. The pretreated diamond and nano-titanium powder are mixed at a carbon-titanium molar ratio of 1:1 and ground for 30 min. Then, the mixture is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2 (mixed powder: molten salt). Under argon protection, the temperature is increased to 1000℃ at 6℃ / min and held for 60 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, the mixture is dried in an oven at 60℃ for 50 min to obtain titanium-modified diamond composite powder with a coating thickness of about 1 μm. S303. The titanium-modified diamond composite powder is placed in a tube sintering furnace and heated at 600°C in a hydrogen atmosphere. After holding at the temperature for 60 minutes, it is cooled with the furnace to obtain titanium-modified diamond composite powder with a clean surface and fully reduced metallic titanium layer. S4. Mix equal proportions of 100-300 mesh titanium-modified diamond composite powder with 1% (by mass of composite powder) MoS2 particles with a particle size of approximately 200 mesh, using a 10×10... 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 100 rad / min, and the spraying time was set to 0.5 min; a drill bit with a coating thickness of 0.2 mm was obtained. S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 600 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. The heating power is controlled at 40 kW and the action time is precisely controlled at 1.0 s.

[0041] Example 6 S1. After holding the 45 steel drill bit at 920℃ for 1 hour, water quench it; then temper it at 560℃ for 3 hours and air cool it. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 30 min under the condition of 30 m / s spraying speed, until the surface roughness Ra value is 12.5 μm. S301. Place 200μm diamond particles in a 30% dilute hydrochloric acid solution and stir magnetically at 400r / min for 30min. Then wash thoroughly with deionized water until neutral and place in an oven at 80℃ for 50min for later use. S302. The pretreated diamond and nano-titanium powder are mixed at a carbon-titanium molar ratio of 1:1 and ground for 40 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:3 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1100℃ at 8℃ / min and held for 120 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 80℃ for 80 min to obtain titanium-modified diamond composite powder with a coating thickness of about 5μm. S303. The titanium-modified diamond composite powder is placed in a tube sintering furnace and heated at 700°C in a hydrogen atmosphere. After holding at the temperature for 90 minutes, it is cooled with the furnace to obtain titanium-modified diamond composite powder with a clean surface and fully reduced metallic titanium layer. S4. Mix equal proportions of 100-300 mesh titanium-modified diamond composite powder with 3% (by mass of composite powder) MoS2 particles with a particle size of approximately 300 mesh, using a 20×10⁻⁶ ppm diaphragm filter. 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 200 rad / min, and the spraying time was set to 1.5 min; a drill bit with a coating thickness of 0.5 mm was obtained. S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 800 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 80 kW and precisely adjust the action time to 1.5 s.

[0042] Example 7 S1. The 45 steel drill bit is held at 890℃ for 0.75 hours and then water-quenched; then tempered at 555℃ for 2.5 hours and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 9.4 μm. S301. Place 125μm diamond particles in a 25% dilute hydrochloric acid solution and stir magnetically at 350r / min for 25min. Then wash thoroughly with deionized water until neutral and place in an oven at 70℃ for 70min for later use. S302. The pretreated diamond and nano-molybdenum powder are mixed at a carbon-molybdenum molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1050℃ at 7℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 70℃ for 65 min to obtain molybdenum modified diamond composite powder with a coating thickness of about 3μm. S303. The molybdenum-modified diamond composite powder is placed in a tube sintering furnace and heated at 650°C in a hydrogen atmosphere. After holding at the temperature for 75 minutes, it is cooled with the furnace to obtain a molybdenum-modified diamond composite powder with a clean surface and fully reduced metallic molybdenum layer. S4. Mix equal proportions of molybdenum-modified diamond composite powder (100-300 mesh) with 2% (by mass of composite powder) MoS2 particles (approximately 250 mesh). Use a 15×10⁻⁶ ppm diaphragm filter. 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 150 rad / min, and the spraying time was set to 1 min; a drill bit with a coating thickness of 0.35 mm was obtained; S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 700 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 60 kW and precisely adjust the action time to 1.25 s.

[0043] Example 8 S1. The 40Cr steel drill bit is held at 860℃ for 0.5h and then water-quenched; then tempered at 550℃ for 2h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 20 min under the condition of 20 m / s spraying speed, until the surface roughness Ra value is 6.3 μm. S301. Place 50μm diamond particles in a 20% (w / w) dilute hydrochloric acid solution and stir magnetically at 300r / min for 20min. Then wash thoroughly with deionized water until neutral and place in an oven at 60℃ for 80min for later use. S302. The pretreated diamond and nano-molybdenum powder are mixed at a carbon-molybdenum molar ratio of 1:1 and ground for 30 min. Then, the mixture is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2 (mixed powder: molten salt). Under argon protection, the temperature is increased to 1000℃ at 6℃ / min and held for 60 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, the mixture is dried in a 60℃ oven for 50 min to obtain a molybdenum-modified diamond composite powder with a coating thickness of about 1 μm. S303. The molybdenum-modified diamond composite powder is placed in a tube sintering furnace and heated at 600°C in a hydrogen atmosphere. After holding at the temperature for 60 minutes, it is cooled with the furnace to obtain a molybdenum-modified diamond composite powder with a clean surface and fully reduced metallic molybdenum layer. S4. Mix equal proportions of molybdenum-modified diamond composite powder (100-300 mesh) with 1% (by mass of composite powder) MoS2 particles (approximately 200 mesh), using a 10×10⁻⁶ mixing agent. 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 100 rad / min, and the spraying time was set to 0.5 min; a drill bit with a coating thickness of 0.2 mm was obtained. S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 600 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. The heating power is controlled at 40 kW and the action time is precisely controlled at 1.0 s.

[0044] Example 9 S1. The 40Cr steel drill bit is held at 920℃ for 1 hour and then water-quenched; then tempered at 560℃ for 3 hours and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 30 min under the condition of 30 m / s spraying speed, until the surface roughness Ra value is 12.5 μm. S301. Place 200μm diamond particles in a 30% dilute hydrochloric acid solution and stir magnetically at 400r / min for 30min. Then wash thoroughly with deionized water until neutral and place in an oven at 80℃ for 50min for later use. S302. The pretreated diamond and nano-molybdenum powder are mixed at a carbon-molybdenum molar ratio of 1:1 and ground for 40 min. Then, the mixture is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:3 (mixed powder: molten salt). Under argon protection, the temperature is increased to 1100℃ at 8℃ / min and held for 120 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, the mixture is dried in an oven at 80℃ for 80 min to obtain a molybdenum-modified diamond composite powder with a coating thickness of about 5 μm. S303. The molybdenum-modified diamond composite powder is placed in a tube sintering furnace and heated at 700°C in a hydrogen atmosphere. After holding at this temperature for 90 minutes, it is cooled with the furnace to obtain a molybdenum-modified diamond composite powder with a clean surface and fully reduced metallic molybdenum layer. S4. Mix equal proportions of molybdenum-modified diamond composite powder (100-300 mesh) with 3% (by mass of composite powder) MoS2 particles (approximately 300 mesh), using a 20×10⁻⁶ mixing tank. 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 200 rad / min, and the spraying time was set to 1.5 min; a drill bit with a coating thickness of 0.5 mm was obtained. S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 800 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 80 kW and precisely adjust the action time to 1.5 s.

[0045] Example 10 S1. The 40Cr steel drill bit is held at 890℃ for 0.75h and then water-quenched; then tempered at 555℃ for 2.5h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 9.4 μm. S301. Place 125μm diamond particles in a 25% dilute hydrochloric acid solution and stir magnetically at 350r / min for 25min. Then wash thoroughly with deionized water until neutral and place in an oven at 70℃ for 60min for later use. S302. The pretreated diamond and nano-tungsten powder are mixed at a carbon-tungsten molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1050℃ at 7℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 70℃ for 65 min to obtain tungsten-modified diamond composite powder with a coating thickness of about 3μm. S303. Tungsten-modified diamond composite powder is placed in a tube sintering furnace and heated at 650°C in a hydrogen atmosphere. After holding at the temperature for 75 minutes, it is cooled with the furnace to obtain tungsten-modified diamond composite powder with a clean surface and fully reduced metallic tungsten layer. S4. Mix equal proportions of 100-300 mesh tungsten-modified diamond composite powder with 2% (by mass of composite powder) MoS2 particles with a particle size of approximately 250 mesh, using a 15×10⁻⁶ m³ / h tandem powder mixture. 6J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 150 rad / min, and the spraying time was set to 1 min; a drill bit with a coating thickness of 0.35 mm was obtained; S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 700 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 60 kW and precisely adjust the action time to 1.25 s.

[0046] Example 11 S1. The 45 steel drill bit is held at 860℃ for 0.5h and then water-quenched; then tempered at 550℃ for 2h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 20 min under the condition of 20 m / s spraying speed, until the surface roughness Ra value is 6.3 μm. S301. Place 50μm diamond particles in a 20% (w / w) dilute hydrochloric acid solution and stir magnetically at 300r / min for 20min. Then wash thoroughly with deionized water until neutral and place in an oven at 60℃ for 80min for later use. S302. The pretreated diamond and nano-tungsten powder are mixed at a carbon-tungsten element molar ratio of 1:1 and ground for 30 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1000℃ at 6℃ / min and held for 60 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 60℃ for 50 min to obtain tungsten-modified diamond composite powder with a coating thickness of about 1 μm. S303. Tungsten-modified diamond composite powder is placed in a tube sintering furnace and heated at 600°C in a hydrogen atmosphere. After holding at the temperature for 60 minutes, it is cooled with the furnace to obtain tungsten-modified diamond composite powder with a clean surface and fully reduced metallic tungsten layer. S4. Mix equal proportions of tungsten-modified diamond composite powder (100-300 mesh) with 1% (by mass of composite powder) MoS2 particles (approximately 200 mesh), using a 10×10⁻⁶ mixing agent. 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 100 rad / min, and the spraying time was set to 0.5 min; a drill bit with a coating thickness of 0.2 mm was obtained. S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 600 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. The heating power is controlled at 40 kW and the action time is precisely controlled at 1.0 s.

[0047] Example 12 S1. After holding the 45 steel drill bit at 920℃ for 1 hour, water quench it; then temper it at 560℃ for 3 hours and air cool it. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 30 min under the condition of 30 m / s spraying speed, until the surface roughness Ra value is 12.5 μm. S301. Place 200μm diamond particles in a 30% (w / w) dilute hydrochloric acid solution and stir magnetically at 400 rpm for 30 min; then wash thoroughly with deionized water until neutral and place in an oven at 80℃ for 7 minutes. 0min standby; S302. The pretreated diamond and nano-tungsten powder are mixed at a carbon-tungsten molar ratio of 1:1 and ground for 40 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:3 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1100℃ at 8℃ / min and held for 120 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 80℃ for 80 min to obtain tungsten-modified diamond composite powder with a coating thickness of about 5μm. S303. Tungsten-modified diamond composite powder is placed in a tube sintering furnace and heated at 700°C in a hydrogen atmosphere. After holding at this temperature for 90 minutes, it is cooled with the furnace to obtain tungsten-modified diamond composite powder with a clean surface and fully reduced metallic tungsten layer. S4. Mix equal proportions of 100-300 mesh tungsten-modified diamond composite powder with 3% (by mass of composite powder) MoS2 particles with a particle size of approximately 300 mesh, using a 20×10⁻⁶ ppm diaphragm. 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 200 rad / min, and the spraying time was set to 1.5 min; a drill bit with a coating thickness of 0.5 mm was obtained. S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 800 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 80 kW and precisely adjust the action time to 1.5 s.

[0048] Comparative Example 1 S1. The 45 steel drill bit is held at 820℃ (lower than the range of 860~920℃ in this embodiment) for 0.3h (shorter than the range of 0.5~1h in this embodiment) and then water-quenched; then tempered at 520℃ (lower than the range of 550~560℃ in this embodiment) for 1.5h (shorter than the range of 2~3h in this embodiment) and then air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 9.4 μm. S301. Place 125μm diamond particles in a 25% dilute hydrochloric acid solution and stir magnetically at 350r / min for 25min. Then wash thoroughly with deionized water until neutral and place in an oven at 70℃ for 110min for later use. S302. The pretreated diamond and nano-chromium powder are mixed at a carbon-chromium molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1050℃ at 7℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 70℃ for 65 min to obtain chromium-modified diamond composite powder with a coating thickness of about 3μm. S303. Chromium-modified diamond composite powder is placed in a tube sintering furnace and heated at 650°C in a hydrogen atmosphere. After holding at this temperature for 75 minutes, it is cooled with the furnace to obtain chromium-modified diamond composite powder with a clean surface and fully reduced metallic chromium layer. S4. Mix equal proportions of chromium-modified diamond composite powder (100-300 mesh) with 2% (by mass of composite powder) MoS2 particles (approximately 250 mesh), and use a 15×10... 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 150 rad / min, and the spraying time was set to 1 min; a drill bit with a coating thickness of 0.35 mm was obtained; S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 700 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 60 kW and precisely adjust the action time to 1.25 s.

[0049] Comparative Example 2 S1. The 40Cr steel drill bit is held at 890℃ for 0.75h and then water-quenched; then tempered at 555℃ for 2.5h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 15.0 μm (greater than the range of 6.3~12.5 μm in this embodiment). S301. Place 125μm diamond particles in a 25% dilute hydrochloric acid solution and stir magnetically at 350r / min for 25min. Then wash thoroughly with deionized water until neutral and place in an oven at 70℃ for 110min for later use. S302. The pretreated diamond and nano-titanium powder are mixed at a carbon-titanium molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1050℃ at 7℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 70℃ for 65 min to obtain titanium-modified diamond composite powder with a coating thickness of about 3μm. S303. The titanium-modified diamond composite powder is placed in a tube sintering furnace and heated at 650°C in a hydrogen atmosphere. After holding at the temperature for 75 minutes, it is cooled with the furnace to obtain titanium-modified diamond composite powder with a clean surface and fully reduced metallic titanium layer. S4. Mix equal proportions of 100-300 mesh titanium-modified diamond composite powder with 2% (by mass of composite powder) MoS2 particles with a particle size of approximately 250 mesh, and then mix using a 15×10... 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 150 rad / min, and the spraying time was set to 1 min; a drill bit with a coating thickness of 0.35 mm was obtained; S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 700 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 60 kW and precisely adjust the action time to 1.25 s.

[0050] Comparative Example 3 S1. The 45 steel drill bit is held at 890℃ for 0.75h and then water-quenched; then tempered at 555℃ for 2.5h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 9.4 μm. S301. Place 125μm diamond particles in a 15% (lower than 20% to 30% in this embodiment) dilute hydrochloric acid solution and magnetically stir at 250 r / min (lower than 300 to 400 r / min in this embodiment) for 25 min; then wash thoroughly with deionized water until neutral and place in an oven at 70°C for 110 min for later use. S302. The pretreated diamond and nano-molybdenum powder are mixed at a carbon-molybdenum molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1050℃ at 7℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 70℃ for 65 min to obtain molybdenum modified diamond composite powder with a coating thickness of about 3μm. S303. The molybdenum-modified diamond composite powder is placed in a tube sintering furnace and heated at 650°C in a hydrogen atmosphere. After holding at the temperature for 75 minutes, it is cooled with the furnace to obtain a molybdenum-modified diamond composite powder with a clean surface and fully reduced metallic molybdenum layer. S4. Mix equal proportions of molybdenum-modified diamond composite powder (100-300 mesh) with 2% (by mass of composite powder) MoS2 particles (approximately 250 mesh). Use a 15×10⁻⁶ ppm diaphragm filter. 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 150 rad / min, and the spraying time was set to 1 min; a drill bit with a coating thickness of 0.35 mm was obtained; S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 700 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 60 kW and precisely adjust the action time to 1.25 s.

[0051] Comparative Example 4 S1. The 40Cr steel drill bit is held at 890℃ for 0.75h and then water-quenched; then tempered at 555℃ for 2.5h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 9.4 μm. S301. Place 125μm diamond particles in a 25% dilute hydrochloric acid solution and stir magnetically at 350r / min for 25min. Then wash thoroughly with deionized water until neutral and place in an oven at 70℃ for 110min for later use. S302. The pretreated diamond and nano-tungsten powder are mixed at a carbon-tungsten molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1150℃ (higher than the range of 6~8℃ / min in this embodiment) at 10℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in a 70℃ oven for 65 min to obtain tungsten-modified diamond composite powder with a coating thickness of about 3 μm. S303. Tungsten-modified diamond composite powder is placed in a tube sintering furnace and heated at 650°C in a hydrogen atmosphere. After holding at the temperature for 75 minutes, it is cooled with the furnace to obtain tungsten-modified diamond composite powder with a clean surface and fully reduced metallic tungsten layer. S4. Mix equal proportions of 100-300 mesh tungsten-modified diamond composite powder with 2% (by mass of composite powder) MoS2 particles with a particle size of approximately 250 mesh, using a 15×10⁻⁶ m³ / h tandem powder mixture. 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 150 rad / min, and the spraying time was set to 1 min; a drill bit with a coating thickness of 0.35 mm was obtained; S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 700 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 60 kW and precisely adjust the action time to 1.25 s.

[0052] Comparative Example 5 S1. The 45 steel drill bit is held at 890℃ for 0.75h and then water-quenched; then tempered at 555℃ for 2.5h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 9.4 μm. S301. Place 125μm diamond particles in a 25% dilute hydrochloric acid solution and stir magnetically at 350r / min for 25min. Then wash thoroughly with deionized water until neutral and place in an oven at 70℃ for 110min for later use. S302. The pretreated diamond and nano-chromium powder are mixed at a carbon-chromium molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1050℃ at 7℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 70℃ for 65 min to obtain chromium-modified diamond composite powder with a coating thickness of about 3μm. S303. Chromium-modified diamond composite powder is placed in a tube sintering furnace and heated at 650°C in a hydrogen atmosphere. After holding at this temperature for 75 minutes, it is cooled with the furnace to obtain chromium-modified diamond composite powder with a clean surface and fully reduced metallic chromium layer. S4. Mix equal proportions of chromium-modified diamond composite powder (100-300 mesh) with 2% (by mass of composite powder) MoS2 particles (approximately 250 mesh), using an 8×10⁻⁶ mixing tank. 6 J (lower than 10×10 in this embodiment) 6 ~20×10 6 Impact energy (within J range) is sprayed onto the surface of a heat-treated drill bit; during the spraying process, the drill bit is rotated at 150 rad / min, and the spraying time is set to 1 min; a drill bit with a coating thickness of 0.35 mm is obtained; S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 700 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 60 kW and precisely adjust the action time to 1.25 s.

[0053] Comparative Example 6 S1. The 40Cr steel drill bit is held at 890℃ for 0.75h and then water-quenched; then tempered at 555℃ for 2.5h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 9.4 μm. S301. Place 125μm diamond particles in a 25% dilute hydrochloric acid solution and stir magnetically at 350r / min for 25min. Then wash thoroughly with deionized water until neutral and place in an oven at 70℃ for 110min for later use. S302. The pretreated diamond and nano-titanium powder are mixed at a carbon-titanium molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1050℃ at 7℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 70℃ for 65 min to obtain titanium-modified diamond composite powder with a coating thickness of about 3μm. S303. The titanium-modified diamond composite powder is placed in a tube sintering furnace and heated at 650°C in a hydrogen atmosphere. After holding at the temperature for 75 minutes, it is cooled with the furnace to obtain titanium-modified diamond composite powder with a clean surface and fully reduced metallic titanium layer. S4. Mix equal proportions of 100-300 mesh titanium-modified diamond composite powder with 2% (by mass of composite powder) MoS2 particles with a particle size of approximately 250 mesh, and then mix using a 15×10... 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 150 rad / min, and the spraying time was set to 1 min; a drill bit with a coating thickness of 0.35 mm was obtained; S5. The coated drill bit is clamped on a lathe and rotated at a constant speed of 700 rpm. A high-frequency induction heating device is used to rapidly heat the circumference of the drill bit. The heating power is controlled at 90 kW (higher than the range of 40~80 kW in this embodiment), and the action time is precisely controlled at 2.0 s (longer than the range of 1.0~1.5 s in this embodiment).

[0054] Comparative Example 7 S1. The 45 steel drill bit is held at 890℃ for 0.75h and then water-quenched; then tempered at 555℃ for 2.5h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 9.4 μm. S3. Mix equal proportions of pure nano-chromium powder (100-300 mesh) with 2% (by mass of pure nano-chromium powder) MoS2 particles (approximately 250 mesh), using a 15×10... 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 150 rad / min, and the spraying time was set to 1 min; a drill bit with a coating thickness of 0.35 mm was obtained; S4. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 700 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 60 kW and precisely adjust the action time to 1.25 s.

[0055] Comparative Example 8 S1. The 45 steel drill bit is held at 890℃ for 0.75h and then water-quenched; then tempered at 555℃ for 2.5h and air-cooled. S2. Using pure alumina abrasive with a particle size of 100~200 mesh, the surface of the drill bit obtained in S1 is subjected to solid sandblasting treatment for 25 min at a spraying speed of 25 m / s until the surface roughness Ra value is 9.4 μm. S301. Place 125μm diamond particles in a 25% dilute hydrochloric acid solution and stir magnetically at 350r / min for 25min. Then wash thoroughly with deionized water until neutral and place in an oven at 70℃ for 110min for later use. S302. The pretreated diamond and nano-chromium powder are mixed at a carbon-chromium molar ratio of 1:1 and ground for 35 min. Then, it is mixed with molten salt composed of equal masses of NaCl and KCl at a mass ratio of 1:2.5 (mixed powder: molten salt). Under argon protection, the temperature is raised to 1050℃ at 7℃ / min and held for 90 min. The residual molten salt is removed by water bath heating and ultrasonic cleaning. Finally, it is dried in an oven at 70℃ for 65 min to obtain chromium-modified diamond composite powder with a coating thickness of about 3μm. S303. Chromium-modified diamond composite powder is placed in a tube sintering furnace and heated at 650°C in a hydrogen atmosphere. After holding at this temperature for 75 minutes, it is cooled with the furnace to obtain chromium-modified diamond composite powder with a clean surface and fully reduced metallic chromium layer. S4. Equal proportions of chromium-modified diamond composite powder (without MoS2 particles) of 100-300 mesh are processed using a 15×10... 6 J-impact energy was sprayed onto the surface of the heat-treated drill bit; during the spraying process, the drill bit was rotated at 150 rad / min, and the spraying time was set to 1 min; a drill bit with a coating thickness of 0.35 mm was obtained; S5. Mount the coated drill bit onto a lathe and rotate it at a constant speed of 700 rpm. Use a high-frequency induction heating device to rapidly heat the circumference of the drill bit. Control the heating power at 60 kW and precisely adjust the action time to 1.25 s.

[0056] Table 2. Wear resistance properties of the examples and comparative examples

[0057] In Comparative Example 1, the heat treatment parameters for step S1 were significantly lower than those in the examples, with an austenitizing temperature of 820°C and a holding time of only 0.3 hours, failing to achieve sufficient austenitization of the matrix. Figure 6Subsequent tempering at 520℃ for 1.5 hours was insufficient to complete the tempering transformation. The microstructure formed under these conditions was predominantly lath martensite. Due to insufficient carbide precipitation and high dislocation density, the material's toughness was significantly reduced, and the residual stress level was high. In contrast, the example used a tempering treatment of 860~920℃ for 0.5~1 hour followed by 550~560℃ for 2~3 hours, resulting in a uniformly distributed tempered sorbite microstructure. Figure 3 The first example combines high strength with good toughness. However, the suboptimal microstructure resulting from insufficient heat treatment in the comparative example weakens the strength-toughness balance of the substrate and reduces its load-bearing capacity for the coating, easily inducing coating peeling or brittle cracking of the substrate. In Comparative Example 2, the excessively high surface roughness of the substrate and the deep peak-valley structure make it difficult for molten particles to fully overlap during spraying, reducing coating density. The interface bonding is mainly mechanically interlocked, resulting in weak impact load resistance and easy peeling. In Comparative Example 3, incomplete pickling left residual catalyst or organic contaminants on the diamond surface, hindering the uniform deposition of the metal coating and causing discontinuity in the modified composite powder coating. This significantly weakened the interfacial bonding strength between diamond and the substrate, leading to decreased wear resistance. In Comparative Example 4, the excessively high heating rate and temperature during remelting caused irreversible graphitization of the diamond surface, reducing hardness. Simultaneously, the metal coating overgrowth and formed coarse, brittle phases, damaging interfacial integrity, causing the reinforcing phase to fail, and significantly increasing wear. Comparative Example 5 suffered from insufficient energy input during thermal spraying, resulting in incomplete melting of powder particles, low impact velocity, and a coating primarily composed of mechanical interlocking with a lack of metallurgical bonding. This led to high porosity, poor bonding strength, and unsatisfactory density and wear resistance. Comparative Example 6 experienced excessively high heating power and prolonged treatment time during subsequent remelting, causing overall overmelting of the coating. This not only accelerated diamond graphitization and the decomposition of the MoS2 lubricating phase but also expanded the heat-affected zone of the matrix, introducing excessive residual stress, leading to an increased friction coefficient and loss of self-lubricating function. Comparative Example 7 completely omitted the introduction of the diamond reinforcing phase, directly spraying pure nano-chromium powder and MoS2. The resulting coating lacked a high-hardness framework support, with mechanical properties approaching those of ordinary metal coatings, exhibiting the worst wear resistance. Comparative Example 8, lacking the addition of MoS2 solid lubricant, lost its friction-reducing effect during the friction process. It could not synergistically construct a low-shear interface with the carbon generated by diamond graphitization, resulting in a significant increase in the friction coefficient, severe temperature rise during drilling, and a tendency to induce adhesive wear.

[0058] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-strength, wear-resistant, self-lubricating drill bit for coal mines, characterized in that, Includes the following steps: S1. The drill bit blank made of steel by machining is heated, water quenched and tempered to obtain a drill bit blank with a preset hardness; S2. Use pure alumina abrasive to sandblast the surface of the drill bit blank after step S1 to remove the surface oxide scale and rust products. S3. Metal modification of the surface of diamond particles to obtain metal-modified diamond composite powder; S4. Mix the metal-modified diamond composite powder with MoS2 particles in a preset ratio, and spray it onto the surface of the drill bit blank after step S2 with a preset impact energy to form a coating of a preset thickness. S5. Rotate the coated drill bit at a constant speed and heat the coating with a high-frequency induction heating device. After cooling, a high-strength, wear-resistant, self-lubricating drill bit for coal mines is obtained.

2. The method for preparing a high-strength, wear-resistant, self-lubricating drill bit for coal mines according to claim 1, characterized in that, The specific process of S1 is as follows: the drill bit blank is placed in a heat treatment furnace at 860~920℃ and kept at that temperature for 0.5~1 hour, and then water-quenched to room temperature; subsequently, it is placed in a box-type heat treatment furnace at 550~560℃ and kept at that temperature for 2~3 hours, and then air-cooled to room temperature; the hardness of the drill bit blank with the preset hardness is HRC28~32.

3. The method for preparing a high-strength, wear-resistant, self-lubricating drill bit for coal mines according to claim 1, characterized in that, The pure alumina abrasive in S2 has a particle size of 100-200 mesh, a sandblasting speed of 20-30 m / s, and a processing time of 20-30 minutes; the surface roughness Ra value of the drill bit blank after sandblasting is controlled at 6.3-12.5 μm.

4. The method for preparing a high-strength, wear-resistant, self-lubricating drill bit for coal mines according to claim 1, characterized in that, The process for obtaining the metal-modified diamond composite powder in S3 is as follows: S301. Take diamond particles of a preset size, and remove surface impurities by acid leaching, cleaning, and drying. S302. The pretreated diamond particles and nano metal powder are mixed and ground in a preset ratio, then combined with molten salt and heated under a protective atmosphere. After cooling, cleaning and drying, metal-modified diamond composite powder is obtained. S303. The metal-modified diamond composite powder is heated and kept at a temperature under a reducing atmosphere, and then cooled to obtain the reduced metal-modified diamond composite powder.

5. The method for preparing a high-strength, wear-resistant, self-lubricating drill bit for coal mines according to claim 4, characterized in that, The diamond particles described in S301 have a particle size of 50~200μm; the acid leaching treatment uses a dilute hydrochloric acid solution with a mass fraction of 20%~30%, a stirring rate of 300~400r / min, and a treatment time of 20~30 minutes; the drying treatment is performed at a temperature of 60~80℃ for 100~120 minutes.

6. The method for preparing a high-strength, wear-resistant, self-lubricating drill bit for coal mines according to claim 4, characterized in that, In S302, the molar ratio of diamond particles to nano-metal powder is 1:1, and the grinding time is 30-40 minutes; the molten salt is composed of equal masses of NaCl and KCl, and the mass ratio of the mixed powder to the molten salt is 1:2-1:3; the protective atmosphere is argon, the heating rate is 6-8℃ / min, the heating temperature is 1000-1100℃, and the holding time is 60-120 minutes; the drying temperature is 60-80℃, and the drying time is 50-80 minutes. The nano-metal powder includes one of chromium powder, tungsten powder, molybdenum powder, and titanium powder.

7. The method for preparing a high-strength, wear-resistant, self-lubricating drill bit for coal mines according to claim 4, characterized in that, The reducing atmosphere described in S303 is hydrogen, the heating temperature is 600~700℃, and the holding time is 60~90 minutes; hydrogen is continuously introduced during the heating and holding process to maintain the reducing atmosphere; the thickness of the metal coating on the diamond is 1~5 micrometers.

8. The method for preparing a high-strength, wear-resistant, self-lubricating drill bit for coal mines according to claim 1, characterized in that, The metal-modified diamond composite powder in S4 has a particle size of 100-300 mesh, and the MoS2 particles have a particle size of 200-300 mesh. The mass of the MoS2 particles accounts for 1%-3% of the mass of the metal-modified diamond composite powder. The preset impact energy is 10×10⁻⁶. 6 ~20×10 6 The coating thickness is 0.2~0.5 mm; the supersonic flame spraying uses the power and heat energy of the high-speed combustion flow to melt the metal components in the mixed powder and heat them to the supersonic flame temperature, and sprays them onto the surface of the drill bit blank through the nozzle and bonds them to the substrate.

9. The method for preparing a high-strength, wear-resistant, self-lubricating drill bit for coal mines according to claim 1, characterized in that, The drill bit described in S5 has a rotational speed of 600~800rpm, a power of 40~80kW for the high-frequency induction heating device, and a heating time of 1.0~1.5s.

10. A high-strength, wear-resistant, self-lubricating drill bit for coal mines, characterized in that, The drill bit is prepared by the preparation method according to any one of claims 1 to 9; the drill bit includes a 45 steel or 40Cr substrate, and a metal transition layer and a coating are sequentially formed on the surface of the substrate. The coating is composed of metal-modified diamond composite powder, MoS2 particles and carbon formed by partial diamond graphitization, and the thickness of the coating is 0.2 to 0.5 mm.

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