Oxygen lance nozzle laval powder spray tube with wear-resistant coating and preparation method thereof

Abstract

The application provides an oxygen lance nozzle Laval powder injection tube with a wear-resistant coating and a preparation method thereof, and relates to the metallurgy field. The oxygen lance nozzle Laval powder injection tube with the wear-resistant coating comprises an oxygen-free copper Laval tube base body and a ceramic wear-resistant coating arranged on the inner cavity surface of the oxygen-free copper Laval tube base body; and the ceramic wear-resistant coating is formed by vacuum brazing of Al2O3 ceramic powder and AgCuTi4.8 active filler metal powder. The oxygen lance nozzle Laval powder injection tube with the wear-resistant coating provided by the application has a ceramic wear-resistant coating, the ceramic wear-resistant coating takes high-hardness Al2O3 ceramic as a wear-resistant phase and AgCuTi4.8 active filler metal as a bonding phase, can significantly improve the wear resistance, high-temperature erosion resistance and thermal shock resistance of the Laval tube, prolongs the service life of the Laval tube from 50-250 heats to 350-500 heats, and effectively reduces the equipment replacement cost and production interruption time.

Description

Technical Field

[0001] This application relates to the field of metallurgy, and in particular to an oxygen lance nozzle with a wear-resistant coating and a method for preparing the same. Background Technology

[0002] The converter oxygen lance is a core piece of equipment in steelmaking, and the Laval tube inside its nozzle is responsible for mixing and injecting oxygen and powder. This component operates in an extremely harsh environment, not only enduring the continuous scouring of high-temperature flue gas, but also withstanding the intense erosion and wear caused by the high-speed airflow carrying powder, and facing periodic thermal shock.

[0003] Currently, Laval nozzles are mostly made of oxygen-free copper. Oxygen-free copper has excellent thermal conductivity and processing properties, enabling it to quickly dissipate high-temperature heat and effectively prevent nozzle burn-out. However, oxygen-free copper has relatively low hardness, with a hardness value of HV. 0.2 With a wear resistance of no more than 100 mm, the inner surface of the Laval tube is easily eroded by powder, resulting in defects such as grooves and pits. These defects severely affect the stability of the oxygen jet and reduce steelmaking efficiency. Typically, the service life of a Laval tube is only 50-250 heats, requiring frequent shutdowns to replace the nozzles. This not only increases production costs but also prolongs production downtime.

[0004] To improve the wear resistance of Laval tubes, common methods include surface electroplating with hard chrome, plasma spraying with WC-Co coating, and laser cladding with ceramic coating. Among these, hard chrome plating has low hardness and limited wear resistance life, and the electroplating process generates environmental pollution. Plasma spraying forms a mechanical bond between the coating and the oxygen-free copper substrate, resulting in low bonding strength; the coating is prone to peeling off under thermal shock and high-speed erosion. While laser cladding achieves metallurgical bonding, the high-temperature process coarsens the grains of the oxygen-free copper substrate, leading to decreased thermal conductivity and making the cladding layer prone to cracking.

[0005] In summary, the existing wear-resistant strengthening technologies for Laval tubes in converter oxygen lance nozzles all have obvious defects, such as insufficient wear resistance life, low bonding strength, damage to the original properties of the matrix, complex processes, and environmental pollution. They are difficult to meet the core requirements of converter steelmaking for high wear resistance, high bonding, long service life, and low loss of Laval tubes. Summary of the Invention

[0006] The purpose of this application is to provide an oxygen lance nozzle with a wear-resistant coating and a method for preparing the same, in order to solve the above-mentioned problems.

[0007] To achieve the above objectives, this application adopts the following technical solution: An oxygen lance nozzle Laval powder spraying tube with a wear-resistant coating includes an oxygen-free copper Laval tube substrate and a ceramic wear-resistant coating disposed on the inner surface of the oxygen-free copper Laval tube substrate. The ceramic wear-resistant coating is formed by vacuum brazing Al2O3 ceramic powder and AgCuTi4.8 active brazing filler powder; The AgCuTi4.8 active solder powder, calculated by mass fraction, includes Ag: 67.2-69.2%, Cu: 26-28%, and Ti: 4.8%.

[0008] Preferably, the purity of the oxygen-free copper Laval tube substrate is not less than 99.7%, the cone angle of its inner constriction section is 10°-15°, the throat diameter is Φ8-15mm, the cone angle of its expansion section is 6°-12°, and the overall length is 80-110mm; the roughness Ra of the inner surface is ≤1.6μm.

[0009] Preferably, the purity of the Al2O3 ceramic powder is not less than 99.9%, and the particle size is 300-500 mesh.

[0010] This application also provides a method for preparing the Laval powder spraying tube with the wear-resistant coating of the oxygen lance nozzle, comprising: The Al2O3 ceramic powder, the AgCuTi4.8 active solder powder, and the binder are mixed to obtain a slurry; The flexible mandrel is coaxially inserted into the oxygen-free copper Laval tube substrate, forming a gap between them; The slurry is injected into the gap, the oxygen-free copper Laval tube substrate is rotated and subjected to negative pressure adsorption, and after drying, a dry coating film is obtained on the inner surface of the oxygen-free copper Laval tube substrate. The oxygen-free copper Laval tube substrate with the flexible mandrel and the dry film of the coating is vacuum brazed, and then the flexible mandrel is removed. The post-processing yields the oxygen lance nozzle Laval powder spraying tube with the wear-resistant coating.

[0011] Preferably, the method for preparing the Laval powder injection tube of the oxygen lance nozzle with the wear-resistant coating satisfies one or more of the following conditions: (1) The mass ratio of the Al2O3 ceramic powder to the AgCuTi4.8 active solder powder is 2.5-3.5:1; (2) The adhesive comprises anhydrous ethanol and gum arabic, wherein the mass ratio of the anhydrous ethanol to the gum arabic is 8-12:1; (3) The amount of the binder is 10-15% of the total mass of the Al2O3 ceramic powder and the AgCuTi4.8 active solder powder; (4) The viscosity of the slurry is 500-800 mPa·s.

[0012] Preferably, the diameter of the flexible mandrel is 0.5-0.7 mm smaller than the throat diameter of the oxygen-free copper Laval tube substrate.

[0013] Preferably, the raw materials of the flexible core mold, calculated by total mass as 100%, include 64-75% silicone rubber, 2-3% dicumyl peroxide, 15-20% talc, 5-8% zinc stearate, and 3-5% silicon dioxide.

[0014] Preferably, the method for preparing the Laval powder injection tube of the oxygen lance nozzle with the wear-resistant coating satisfies one or more of the following conditions: (1) The rotational speed of the rotation is 5-8 r / min; (2) The vacuum degree of the negative pressure adsorption is not higher than 5×10 -2 Pa; (3) The thickness of the dry film of the coating is 0.3-0.4 mm; (4) The thickness deviation of the dry film coating in the circumferential direction shall not exceed ±0.03 mm; (5) The vacuum degree of the vacuum brazing is not higher than 5×10 -3 Pa; (6) Argon gas is introduced into the vacuum brazing environment at a rate of 5-10 mL / min; (7) The heat preservation procedure for vacuum brazing is as follows: heat up to 600-620℃ at 2-2.5℃ / min and keep for 10-15min, then heat up to 850-880℃ at 1.5-2℃ / min and keep for 30-40min.

[0015] Preferably, the post-processing includes: grinding to remove residual brazing filler metal slag from the coating surface, and testing the coating porosity to be no higher than 5% and the hardness to be no lower than 1200 HV. 0.2 The bonding strength is not less than 15MPa.

[0016] Preferably, the post-processing further includes an inner cavity surface polishing step, wherein the surface roughness of the coating after polishing is Ra≤1.0μm.

[0017] Compared with the prior art, the beneficial effects of this application include: The Laval tube of the converter powder-injected oxygen lance provided in this application has a ceramic wear-resistant coating on its inner surface. High-hardness Al2O3 ceramic is used as the wear-resistant phase, and AgCuTi4.8 active brazing filler metal is used as the bonding phase. This significantly improves the wear resistance, high-temperature erosion resistance, and thermal shock resistance of the Laval tube. The bonding strength is ≥15MPa, far exceeding that of plasma-sprayed coatings, and the coating hardness is ≥1200HV. 0.2Its wear resistance is 10-12 times that of oxygen-free copper matrix, extending its service life from 50-250 heats to 350-500 heats, effectively reducing equipment replacement costs and production downtime, and providing strong support for steelmaking enterprises to reduce production costs.

[0018] The method for preparing the Laval tube of the converter powder injection oxygen lance nozzle provided in this application solves the problem of uniform coating on the complex inner curved surface of the Laval tube by precisely optimizing the brazing process, scientifically matching the coating system, using a flexible mandrel, and employing rotational coating and negative pressure adsorption coating methods. This method successfully prepares a uniform, dense, and extremely firmly bonded ceramic wear-resistant coating on the inner surface of the oxygen-free copper Laval tube. The coating thickness deviation is ≤±0.03mm, ensuring the stability of the powder injection or oxygen jet. The coating preparation process is environmentally friendly and pollution-free, using inexpensive and readily available raw materials, and the process is simple and controllable, making it suitable for industrial mass production. Attached Figure Description

[0019] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation on the scope of this application.

[0020] Figure 1 A schematic diagram of the substrate structure of the Laval powder injection tube of the oxygen lance nozzle with a wear-resistant coating provided in this application; Figure 2 A schematic diagram of the coating mandrel and Laval tube assembly provided in this application; Figure 3 This is a schematic diagram of the cross-sectional structure of the ceramic wear-resistant coating provided in this application; Figure 4 This is a comparison chart of wear rate data between the Laval tube obtained in Example 1 and the oxygen-free copper substrate in Comparative Example 2; Figure 5 The image shows the white light interference wear morphology of the Laval tube obtained in Example 1. Figure 6 The image shows the white light interference wear morphology of the oxygen-free copper substrate in Comparative Example 2.

[0021] Figure label: 1-Oxygen-free copper Laval tube substrate; 2-Contraction section; 3-Throat; 4-Expansion section; 5-Flexible coated mandrel; 6-Slurry filling gap; 7-Interfacial reaction layer; 8-Ceramic wear-resistant coating. Detailed Implementation

[0022] To better illustrate the technical solution provided in this application, the technical solution will be described in its entirety before the embodiments, as follows: A Laval powder spraying tube for an oxygen lance with a wear-resistant coating includes an oxygen-free copper Laval tube substrate and a ceramic wear-resistant coating disposed on the inner surface of the oxygen-free copper Laval tube substrate. The ceramic wear-resistant coating is formed by vacuum brazing Al2O3 ceramic powder and AgCuTi4.8 active brazing filler powder; The AgCuTi4.8 active solder powder, calculated by mass fraction, includes Ag: 67.2-69.2% (which can be any value between 67.5%, 68%, 68.5%, 69%, or 67.2-69.2%), Cu: 26-28% (which can be any value between 26%, 26.5%, 27%, 27.5%, 28%, or 26-28%), and Ti: 4.8%.

[0023] The melting point of AgCuTi4.8 active solder powder (765-805℃) is lower than that of oxygen-free copper matrix, allowing it to melt and wet without damaging the matrix. Ti element, as the active element, can undergo interfacial reaction with Al2O3 ceramic and oxygen-free copper to achieve metallurgical bonding.

[0024] In one optional embodiment, the purity of the oxygen-free copper Laval tube substrate is not less than 99.7%, the cone angle of its inner constriction section is 10°-15°, the throat diameter is Φ8-15mm, the cone angle of its expansion section is 6°-12°, and the overall length is 80-110mm; the roughness Ra of the inner surface is ≤1.6μm.

[0025] Pre-treatment of the Laval tube substrate lays a clean and suitable surface foundation for a strong bond between the coating and the substrate, preventing contaminants and defects from affecting the bonding quality. The inner surface of the Laval tube is ground with a diamond wheel to remove oxide film and burrs, increasing the contact area between the substrate and the coating and creating conditions for slurry spreading and interfacial reaction. The ground Laval tube is then ultrasonically cleaned with anhydrous ethanol to thoroughly remove surface oil and impurities, preventing defects such as porosity and inclusions caused by contaminants during brazing; and residual moisture in the substrate is removed by drying to prevent moisture vaporization during high-temperature brazing, which could damage the coating integrity.

[0026] The preferred internal structure dimensions of the oxygen-free copper Laval tube are a 10° cone angle in the contraction section, a Φ10mm diameter in the throat, an 8° cone angle in the expansion section, and a 100mm length, which can be adapted to the working parameters of mainstream converter powder injection oxygen lances.

[0027] In one optional embodiment, the purity of the Al2O3 ceramic powder is not less than 99.9%, and the particle size is 300-500 mesh.

[0028] Optionally, the particle size of the Al2O3 ceramic powder can be 300 mesh, 400 mesh, 500 mesh, or any value between 300 and 500 mesh.

[0029] 400 mesh is preferred, as it can improve the density and wear resistance uniformity of the coating.

[0030] This application also provides a method for preparing the Laval powder spraying tube of the oxygen lance nozzle with the wear-resistant coating as described above, comprising: The Al2O3 ceramic powder, the AgCuTi4.8 active solder powder, and the binder are mixed to obtain a slurry; The flexible mandrel is coaxially inserted into the oxygen-free copper Laval tube substrate, forming a gap between them; The slurry is injected into the gap, the oxygen-free copper Laval tube substrate is rotated and subjected to negative pressure adsorption, and after drying, a dry coating film is obtained on the inner surface of the oxygen-free copper Laval tube substrate. The oxygen-free copper Laval tube substrate with the flexible mandrel and the dry film of the coating is vacuum brazed, and then the flexible mandrel is removed. The post-processing yields the Laval powder spraying tube with the wear-resistant coating for the oxygen lance nozzle.

[0031] Brazing, as an effective method for achieving metallurgical bonding of dissimilar materials, can firmly bond ceramics and metals at relatively low temperatures with minimal impact on the properties of the substrate. However, existing brazing technologies are mostly applied to coatings on flat plates or simple curved surfaces. For components like the Laval tube of a converter powder-injected oxygen lance nozzle, which has a complex internal curved surface (including a contraction section, throat, and expansion section), achieving uniform coating application, precise control of the interfacial reaction layer thickness, and ensuring the stability of the coating under high-temperature erosion and thermal shock environments remain unsolved technical challenges.

[0032] If a wear-resistant coating technology that can combine ceramics and oxygen-free copper metallurgy can be developed based on brazing and successfully applied, it will not only significantly improve the service life of converter powder injection oxygen lances and reduce production interruption time caused by frequent nozzle replacement, but also effectively reduce steelmaking production costs. It has important engineering application value and broad market promotion prospects in the field of steelmaking production.

[0033] This application achieves this objective through the aforementioned process.

[0034] In one optional embodiment, the mass ratio of the Al2O3 ceramic powder to the AgCuTi4.8 active solder powder is 2.5-3.5:1; A reasonable ratio of ceramic powder to brazing filler metal powder can balance the coating hardness and bonding performance, ensuring sufficient wear-resistant phase content while allowing the brazing filler metal to fully fill the gaps between ceramic particles.

[0035] Optionally, the mass ratio of the Al2O3 ceramic powder to the AgCuTi4.8 active solder powder can be any value between 2.5:1, 3:1, 3.5:1, or 2.5-3.5:1; In an optional embodiment, the adhesive comprises anhydrous ethanol and gum arabic, wherein the mass ratio of the anhydrous ethanol to the gum arabic is 8-12:1; The preferred ratio of anhydrous ethanol to gum arabic in the adhesive is 10:1, which ensures the fluidity of the slurry during application and the molding stability after drying.

[0036] The proper selection and proportioning of the binder can ensure that the slurry has good fluidity and coating properties, which facilitates uniform coating of complex internal cavities. Anhydrous ethanol has high volatility and can quickly disperse gum arabic, accelerating coating drying and leaving little residue. Gum arabic has good film-forming and adhesion properties, which can form a dense protective film on the steel surface, improving wear and corrosion resistance, and is also environmentally friendly.

[0037] The optimal mass ratio of anhydrous ethanol to gum arabic is 8-12:1. This ratio ensures moderate solution viscosity, smooth coating without dripping, and guarantees full cross-linking of the gum, resulting in a high-quality coating with low porosity and strong adhesion.

[0038] Optionally, the mass ratio of the anhydrous ethanol to the gum arabic can be any value between 8:1, 9:1, 10:1, 11:1, 12:1, or 8-12:1. (3) The amount of the binder is 10-15% of the total mass of the Al2O3 ceramic powder and the AgCuTi4.8 active solder powder; Optionally, the amount of the binder can be any value between 10%, 11%, 12%, 13%, 14%, 15% or 10-15% of the total mass of the Al2O3 ceramic powder and the AgCuTi4.8 active solder powder. (4) The viscosity of the slurry is 500-800 mPa·s.

[0039] Optionally, the viscosity of the slurry can be any value between 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, or 500-800 mPa·s.

[0040] In an optional embodiment, the method for preparing the Laval tube of the converter powder injection oxygen lance nozzle satisfies one or more of the following conditions: (1) The diameter of the flexible core mold is 0.5-0.7 mm smaller than the throat diameter of the oxygen-free copper Laval tube substrate (it can be any value between 0.5 mm, 0.6 mm, 0.7 mm or 0.5-0.7 mm). The flexible mandrel is precisely fitted to the inner cavity of the Laval tube, which not only provides support for the slurry, but also ensures that the final shape of the coating is consistent with the inner cavity of the Laval tube, avoiding dimensional deviations after coating. The flexible mandrel can elastically fit the complex inner curved surface of the Laval tube, which can provide a uniform support surface for the coating slurry, ensuring consistent coating thickness and no accumulation voids, and the soft material will not scratch the substrate surface.

[0041] (2) The raw materials of the flexible core mold, calculated by total mass as 100%, include 64-75% silicone rubber (which can be any value between 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75% or 64-75%), 2-3% dicumyl peroxide (which can be any value between 2%, 2.5%, 3% or 2-3%), 15-20% talc (which can be any value between 15%, 16%, 17%, 18%, 19%, 20% or 15-20%), 5-8% zinc stearate (which can be any value between 5%, 6%, 7%, 8% or 5-8%) and 3-5% silicon dioxide (which can be any value between 3%, 4%, 5% or 3-5%).

[0042] The components are mixed thoroughly and poured into a molding die that matches the inner diameter of the Laval tube. After vulcanization and shaping, the die is removed to obtain a flexible mandrel that precisely fits the inner diameter of the Laval tube. The added release agent allows it to easily separate from the dry film coating, preventing damage to the coating integrity during demolding. Simultaneously, it inhibits dry film shrinkage and deformation during the drying stage, providing a precise coating shape for subsequent vacuum brazing.

[0043] In an optional embodiment, the method for preparing the Laval powder injection nozzle with a wear-resistant coating of the powder-injected oxygen lance meets one or more of the following conditions: (1) The rotational speed of the rotation is 5-8 r / min; The rotation speed of the Laval tube is controlled at 5-8 r / min, which can be adapted to the uniform coating of complex inner curved surfaces and prevent local accumulation or gaps in the slurry.

[0044] Optionally, the rotational speed can be any value between 5 r / min, 6 r / min, 7 r / min, 8 r / min or 5-8 r / min; (2) The vacuum degree of the negative pressure adsorption is not higher than 5×10 -2 Pa; The combination of rotary coating and negative pressure adsorption utilizes centrifugal force and adsorption force to evenly spread the slurry on complex curved surfaces such as the shrinkage section, throat, and expansion section, solving the problem that traditional coating methods are difficult to adapt to complex cavities.

[0045] (3) The thickness of the dry film of the coating is 0.3-0.4 mm; If the thickness is too thin, the wear resistance life will be insufficient; if it is too thick, the risk of cracking during thermal shock will increase.

[0046] (4) The thickness deviation of the dry film coating in the circumferential direction shall not exceed ±0.03 mm; After application, allow it to air dry at room temperature for 4 hours to slowly remove the adhesive and prevent rapid drying that could cause the coating to crack or peel. Strictly control the dry film thickness (0.3-0.4mm) and thickness deviation (≤±0.03mm) to ensure wear resistance and prevent uneven thickness from causing thermal stress concentration.

[0047] (5) The vacuum degree of the vacuum brazing is not higher than 5×10 -3 Pa; (6) Argon gas is introduced into the vacuum brazing environment at a rate of 5-10 mL / min (which can be any value between 5 mL / min, 6 mL / min, 7 mL / min, 8 mL / min, 9 mL / min, 10 mL / min or 5-10 mL / min); Introducing a trace amount of argon gas further inhibits the oxidation reaction between the substrate and the coating, improving the quality of interfacial bonding.

[0048] (7) The heat preservation procedure for vacuum brazing is as follows: The temperature is increased to 600-620℃ (which can be any value between 2℃ / min, 2.1℃ / min, 2.2℃ / min, 2.3℃ / min, 2.4℃ / min, 2.5℃ / min or 2-2.5℃ / min) at a rate of 2-2.5℃ / min, and then held for 10-15 minutes (which can be 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes or 10 minutes). (Any value between -15 min), then raise the temperature to 850-880℃ (any value between 1.5℃ / min, 1.6℃ / min, 1.7℃ / min, 1.8℃ / min, 1.9℃ / min, 2℃ / min or 1.5-2℃ / min) at 1.5-2℃ / min and hold for 30-40 min (any value between 30 min, 35 min, 40 min or 30-40 min).

[0049] Optimizing the temperature and holding time of vacuum brazing ensures that the brazing filler metal is fully melted and wetted, avoiding an excessively thick interfacial reaction layer that increases the brittleness of the coating.

[0050] Vacuum brazing forms a strong interfacial bond through metallurgical reactions, controls the thickness of the reaction layer, and avoids oxidation and thermal stress cracking, thus imparting core bonding strength to the coating. The vacuum environment isolates the substrate, ceramic powder, and brazing filler metal from air, preventing oxidation products from affecting the interfacial bonding quality. The segmented heating process reduces the difference in thermal expansion between the substrate and the coating, lowering thermal stress and preventing cracking. Holding at 600℃ further removes residual moisture and binder volatiles. Holding at 860℃ for 30 minutes allows the brazing filler metal to completely melt and fully wet the ceramic powder and substrate surface, promoting Ti diffusion and interfacial reactions to form an ideal reaction layer (Cu3Ti3O, Ti3Cu), achieving a strong metallurgical bond between the coating and the substrate.

[0051] After the heat treatment is completed, the furnace is cooled to room temperature. The Laval tube is then removed and the mandrel is taken out, completing the preparation of the wear-resistant coating. Furnace cooling can slowly release the residual stress generated during brazing, avoiding rapid cooling that could cause the coating to crack or reduce its adhesion. Retaining the mandrel throughout the process can prevent the coating from deforming during cooling. Optimized brazing process parameters ensure strong bonding while avoiding coating cracking caused by excessively thick hard and brittle reaction layers. At the same time, low-temperature brazing does not affect the thermal conductivity of the oxygen-free copper substrate.

[0052] In an optional embodiment, the method for preparing the Laval tube of the converter powder injection oxygen lance nozzle satisfies one or more of the following conditions: (1) The post-processing includes: grinding to remove residual brazing slag from the coating surface, and testing the coating porosity to be no higher than 5% and the hardness to be no lower than 1200 HV. 0.2 The bonding strength is not less than 15 MPa; (2) The post-processing also includes an inner cavity surface polishing step, and the surface roughness of the coating after polishing is Ra≤1.0μm.

[0053] An internal cavity surface polishing step can be added in the post-processing. After polishing, the surface roughness of the coating Ra≤1.0μm, which reduces the frictional resistance during powder delivery and improves the stability of the jet.

[0054] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0055] Example 1 This embodiment provides a Laval powder spraying nozzle for an oxygen lance with a wear-resistant coating, and its preparation method is as follows: First, the oxygen-free copper Laval tube substrate is pretreated by grinding to remove the oxide film and burrs on the inner surface, followed by ultrasonic cleaning to remove oil and impurities, and then drying for later use. Next, Al2O3 ceramic powder and AgCuTi-based active brazing filler powder are mixed in a specific ratio, and a binder is added to form a uniform slurry. Then, a flexible mandrel adapted to the inner cavity of the Laval tube is prepared, and the slurry is uniformly coated onto the interior of the substrate using a combination of spin coating and negative pressure adsorption. After drying, a stable dry film is formed. The substrate with the mandrel is then placed in a vacuum brazing furnace, and brazing is completed using a segmented heating, holding, and furnace cooling process to achieve a metallurgical bond between the coating and the substrate. Finally, the brazed product undergoes surface grinding and cleaning to remove defective parts, and only finished products meeting performance standards are selected.

[0056] like Figure 1 As shown, a 99.97% pure oxygen-free copper Laval tube was selected, with the following internal structural parameters: a 10° cone angle in the contraction section, a throat diameter of Φ10mm, an 8° cone angle in the expansion section, and an overall length of 100mm. The inner surface was first ground with a diamond wheel to Ra=1.0μm to remove the oxide film and machining burrs; then it was immersed in anhydrous ethanol and ultrasonically cleaned at a frequency of 50kHz for 20 minutes; finally, it was dried in a 120℃ oven for 2 hours for later use.

[0057] Al2O3 ceramic powder with a purity of 99.9% and a particle size of 400 mesh was selected and dried at 120℃ for 2 hours to remove moisture. AgCuTi4.8 active brazing filler powder (mass fraction: Ag-68.8%, Cu-26.52%, Ti-4.8%) was selected. Al2O3 ceramic powder and brazing filler powder were mixed at a mass ratio of 3:1, and 12% of the mixed powder mass of binder (anhydrous ethanol and gum arabic mass ratio of 10:1) was added. The mixture was stirred in a ball mill for 30 minutes to prepare a uniform slurry with a viscosity of 650 mPa·s.

[0058] A high-temperature flexible mandrel (mass fraction: 70% silicone rubber, 3% dicumyl peroxide as a high-temperature curing agent, 17% talc as a filler, 7% zinc stearate as a release agent, and 3% silica as a heat-resistant additive) with a diameter 0.7 mm smaller than the throat of the Laval tube is fabricated and coaxially inserted into the inner cavity of the Laval tube (e.g., Figure 2 (As shown). After the slurry is injected, the Laval pipe is driven to rotate at a speed of 6 r / min, while simultaneously moving at a speed of 3 × 10⁻⁶. -2 Vacuum negative pressure adsorption for 15 minutes to ensure uniform spreading of the slurry.

[0059] After coating, the Laval tube along with the mandrel was placed on a rotating support and dried at room temperature for 4 hours. The dry film thickness of the coating was measured to be 0.35 mm, with a circumferential thickness deviation of ±0.02 mm.

[0060] The Laval tube with the mandrel is placed into a ZT-50-22Y vacuum brazing furnace, and a vacuum of 3×10⁻⁶ is applied. -3Pa. The temperature is increased to 600℃ at 2.5℃ / min and held for 10 min; then increased to 860℃ at 1.5℃ / min and held for 30 min. After holding, the furnace is cooled to room temperature, and the core mold is carefully removed. A schematic diagram of the cross-sectional structure of the ceramic wear-resistant coating is shown below. Figure 3 As shown.

[0061] Use 800-grit sandpaper to sand the coated surface to remove residual brazing filler metal.

[0062] Testing revealed that the coating had a porosity of 3.2% and an average hardness of 1350 HV. 0.2 (Tested using an HV-100 microhardness tester under a load of 200gf and a holding time of 10s), the coating-substrate bonding strength was 15.8MPa (tested using a shear strength tester).

[0063] The Laval tube was assembled into a converter oxygen lance for industrial steelmaking tests. After a total of 432 heats, there were no obvious erosion grooves on the inner surface, and the coating did not peel off or crack, so it could still be used normally.

[0064] Example 2 A 99.97% pure oxygen-free copper Laval tube was selected, with the following internal structural parameters: a 12° cone angle in the contraction section, a throat diameter of Φ12mm, a 10° cone angle in the expansion section, and an overall length of 110mm. The inner surface was polished to achieve a surface roughness Ra of 0.7μm, then ultrasonically cleaned in anhydrous ethanol for 20 minutes, and finally dried in a 120℃ oven for 2 hours before use.

[0065] Al2O3 ceramic powder with a purity of 99.9% and a particle size of 300 mesh was selected and dried at 120℃ for 2 hours. AgCuTi4.8 solder powder and Al2O3 ceramic powder were mixed at a mass ratio of 3:1, and 14% of the mixed powder mass of binder was added to prepare a slurry with a viscosity of 720 mPa·s.

[0066] A flexible mandrel (material same as in Example 1) with a diameter 0.7 mm smaller than the throat was used. The rotation speed of the Laval tube was set to 5 r / min, and the negative pressure adsorption vacuum degree was 5 × 10⁻⁶. -2 Pa. After coating and drying for 4 hours, the dry film thickness was measured to be 0.38 mm, with a thickness deviation of ±0.03 mm.

[0067] Set the vacuum level to 4×10. -3 Pa, the segmented heating and heat preservation parameters are consistent with those in Example 1, and the furnace is cooled to room temperature before being taken out.

[0068] After polishing, the coating was tested and found to have a porosity of 3.8% and an average hardness of 1280 HV. 0.2The bonding strength is 15 MPa. After 388 heats of industrial steelmaking trials, the coating remained in good condition with no obvious signs of erosion failure.

[0069] Example 3 Select oxygen-free copper Laval tubes with a purity of 99.97% (cone angle of the contraction section is 10°, throat diameter is Φ10mm, cone angle of the expansion section is 8°, and overall length is 100mm). Grind the inner surface to Ra=0.7μm, ultrasonically clean it with anhydrous ethanol for 20min, and then dry it at 120℃ for 2h for later use.

[0070] 400-mesh Al2O3 ceramic powder and AgCuTi4.8 brazing filler powder were mixed at a mass ratio of 3:1, and 13% of the mass of the mixed powder was added as binder (anhydrous ethanol: gum arabic = 9:1) to prepare a slurry with a viscosity of 700 mPa·s.

[0071] The method of applying the slurry is the same as in Example 1.

[0072] The Laval tube with a mandrel (material as in Example 1) was placed in a vacuum brazing furnace and evacuated to a vacuum level of 4×10⁻⁶. -3 Pa; heat to 640℃ at 2.5℃ / min and hold for 12 min; then heat to 880℃ at 1.5℃ / min and hold for 28 min; after cooling to room temperature in the furnace, remove and remove the core mold.

[0073] Residual brazing filler metal slag was removed by grinding. The coating porosity was 3.6% and the average hardness was 1330 HV. 0.2 The bonding strength is 15.2 MPa; it has been used in 401 heats of industrial steelmaking tests, with no coating peeling, slight erosion marks, and stable performance.

[0074] Comparative Example 1 An oxygen-free copper Laval tube with the same specifications as in Example 1 was selected, and its inner surface was pretreated using the same steps as in Example 1. Subsequently, a WC-Co coating was prepared using conventional plasma spraying equipment according to standard processes, with the coating thickness controlled at 0.35 mm.

[0075] For performance testing, an HV-100 microhardness tester was used to test the coating hardness at 964 HV under a load of 200 gf and a holding time of 10 s. 0.2 The shear strength test device showed that the bonding strength between the coating and the substrate was 8 MPa. The Laval tube was then assembled into an oxygen lance for steelmaking trials. After 112 heats, endoscopic observation revealed localized coating peeling and obvious erosion grooves on the inner surface of the Laval tube, rendering it unusable.

[0076] Comparative Example 2 Similarly, an oxygen-free copper Laval tube with the same specifications as in Example 1 was selected, and only the same substrate pretreatment steps as in Example 1 were performed, without coating preparation. In industrial steelmaking tests, the Laval tube was directly assembled into the converter powder injection oxygen lance. After 61 heats, it was found that the depth of the erosion grooves on the inner surface reached 0.2 mm, which led to a serious decrease in the stability of the oxygen jet, and the Laval tube had to be replaced after shutdown.

[0077] The test specimens were subjected to friction and wear behavior tests simulating actual working conditions using a high-temperature friction and wear testing machine. Then, the wear track contours were characterized in 3D using a white light interferometer, and the wear rate of the specimens was calculated using the wear track contours. Figure 4 This is a comparison chart of wear rate data between the Laval tube obtained in Example 1 and the oxygen-free copper substrate in Comparative Example 2; Figure 5 The image shows the white light interference wear morphology of the Laval tube obtained in Example 1. Figure 6 The image shows the white light interference wear morphology of the oxygen-free copper substrate in Comparative Example 2.

[0078] Based on the wear rate data measured by white light interferometry, the wear rate of the prepared ceramic coating was only 0.00303 mm. 3 / N×m, far lower than the wear rate of oxygen-free copper substrate (0.07048), indicating a significant improvement in wear resistance. From Figure 5 The left image shows deep furrows formed on the surface of oxygen-free copper, while the right image shows the wear morphology after the ceramic coating is prepared. The wear condition is shallow, the wear resistance is excellent, and the service life can be improved.

[0079] Comparative Example 3 Select oxygen-free copper Laval tubes with specifications exactly the same as those in Example 1. Mix Al2O3 ceramic powder and AgCuTi4.8 solder powder at a mass ratio of 3:1. Change the binder to anhydrous ethanol and gum arabic at a mass ratio of 5:1 and add 12% of the mixed powder mass.

[0080] After being prepared into a slurry, the viscosity reached 1200 mPa·s, resulting in extremely poor fluidity. The slurry could not be spread evenly, and severe accumulation occurred at the throat, with gaps in the slurry in the expansion section.

[0081] The coating thickness deviation reached ±0.15mm, and cracks appeared in the local accumulation area due to stress concentration; the porosity was 6.8%, and the bonding strength was 8.7MPa; after 65 heats of use in industrial steelmaking trials, the coating at the accumulation area cracked and fell off first, and then the entire coating failed, requiring the replacement of the Laval tube.

[0082] Comparative Example 4 Oxygen-free copper Laval tubes with specifications identical to those in Example 1 were selected, and the substrate pretreatment was performed using the same method. Only Al2O3 ceramic powder with a purity of 99.9% and a particle size of 400 mesh was used, and 12% of the same specification binder was added to the mixed powder to prepare a slurry with a viscosity of 650 mPa·s. No AgCuTi4.8 brazing filler powder was added. The inner surface coating, vacuum brazing, and post-treatment processes were all completely consistent with those in Example 1.

[0083] The coating adhered only physically to the substrate, without any metallurgical bonding, and the bonding strength was only 2.8 MPa. Local peeling occurred during the grinding process, and the porosity reached 8.6%. After being assembled into an oxygen lance for steelmaking tests, the coating peeled off over a large area after 22 heats, and the inner surface of the Laval tube was severely eroded, rendering it unusable.

[0084] Comparative Example 5 An oxygen-free copper Laval tube with specifications identical to that of Example 1 was selected, and the substrate pretreatment process was the same as in Example 1. Al2O3 ceramic powder and AgCuTi4.8 brazing filler powder were mixed at a mass ratio of 3:1, and the binder was replaced with polyvinyl alcohol (concentration 5%), with the addition amount still being 12% of the mixed powder mass, to prepare a slurry. The inner surface coating, vacuum brazing, and post-treatment processes were the same as in Example 1.

[0085] Polyvinyl alcohol binders have poor high-temperature resistance, and carbonization and decomposition during drying and brazing lead to numerous pores and cracks in the coating, with a porosity of up to 11.2%; the average hardness of the coating is only 930 HV. 0.2 The bonding strength was 5.3 MPa. After 48 heats of use in industrial steelmaking trials, the coating cracked locally due to porosity defects, which led to large-area peeling and made it unusable.

[0086] Comparative Example 6 An oxygen-free copper Laval tube with specifications identical to that of Example 1 was selected, and the substrate pretreatment, coating material preparation, and inner surface coating process were all the same as in Example 1. The tube was evacuated to 4 × 10⁻⁶. -3 After Pa, a uniform heating mode was adopted, and the temperature was directly raised to 860°C at a rate of 2°C / min without segmented heat preservation steps. After the temperature was raised to the target temperature, it was kept at the target temperature for 30 minutes. The subsequent cooling and post-processing were the same as in Example 1.

[0087] Uniform heating caused excessive temperature difference between the substrate and the coating, resulting in concentrated thermal stress. Multiple through cracks appeared in the coating, and the porosity reached 7.9%. The bonding strength dropped to 8.2 MPa, and the hardness fluctuated greatly. After 52 heats in industrial steelmaking tests, the crack propagation caused large-area peeling of the coating, and the Laval tube failed.

[0088] Through performance comparisons of the examples and comparative examples, and verification through industrial trials, the following conclusions can be drawn: The copper-based wear-resistant coatings prepared in the embodiments of the present invention have a porosity of ≤5% and a hardness of ≥1200HV. 0.2 The bonding strength is ≥15MPa, which is significantly better than the plasma spraying coating of Comparative Example 1 (bonding strength is only 8MPa). The core reason is that the present invention achieves metallurgical bonding between the ceramic coating and the oxygen-free copper substrate through brazing, while plasma spraying is only mechanical bonding, resulting in a significant difference in bonding strength.

[0089] In industrial steelmaking trials, the service life of the Laval tube coated with this invention reached 350-500 heats, effectively solving the problems of insufficient wear resistance and frequent replacement of traditional Laval tubes.

[0090] The process of this invention uses a flexible mandrel and employs a coating method of rotational coating and negative pressure adsorption, which successfully achieves uniform coating on complex inner cavity curved surfaces with a coating thickness deviation of ≤±0.03mm, ensuring the stability of powder and oxygen jet. In contrast, existing technologies are difficult to adapt to the composite curved surfaces of Laval tubes and are prone to problems such as uneven coating and performance fluctuations.

[0091] The low-temperature brazing process used in this invention does not result in coarse grains in the oxygen-free copper substrate, and the thermal conductivity of the substrate remains good. It avoids the damage to the substrate performance caused by high-temperature processes such as laser cladding, and retains the substrate performance while strengthening the wear resistance of the coating.

[0092] Example 3 demonstrates that by finely adjusting the vacuum brazing temperature, the coating still maintains excellent performance, indicating that the process of the present invention has good stability within a certain temperature range and can be adapted to the needs of different production scenarios.

[0093] Comparative Example 3 confirms the criticality of the binder ratio. An improper ratio will damage the fluidity of the slurry, causing problems such as uneven coating and stress concentration, and ultimately affecting the service life of the coating.

[0094] Comparative Example 4 demonstrates that the alumina coating alone cannot form a strong bond with the oxygen-free copper substrate, and AgCuTi4.8 solder powder is the core component for achieving metallurgical bonding and ensuring coating strength.

[0095] Comparative Example 5 shows that the type of binder cannot be arbitrarily replaced. The combination of anhydrous ethanol and gum arabic can balance the fluidity of the slurry, high temperature resistance and demolding effect. Replacing it with other binders will lead to an increase in coating defects and a significant decrease in performance.

[0096] Comparative Example 6 illustrates that segmented heating and heat preservation are necessary for vacuum brazing. Uniform heating can lead to thermal stress concentration, causing coating cracking and reducing bonding strength, further highlighting the rationality of the segmented heating process of this invention.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A Laval powder spray nozzle for an oxygen lance with a wear-resistant coating, characterized in that, Includes an oxygen-free copper Laval tube substrate and a ceramic wear-resistant coating disposed on the inner surface of the oxygen-free copper Laval tube substrate; The ceramic wear-resistant coating is formed by vacuum brazing Al2O3 ceramic powder and AgCuTi4.8 active brazing filler powder; The AgCuTi4.8 active solder powder, calculated by mass fraction, includes Ag: 67.2-69.2%, Cu: 26-28%, and Ti: 4.8%.

2. The oxygen lance nozzle with a wear-resistant coating according to claim 1, characterized in that, The purity of the oxygen-free copper Laval tube substrate is not less than 99.7%, and its inner constriction section cone angle is 10°-15°, throat diameter is Φ8-15mm, expansion section cone angle is 6°-12°, and overall length is 80-110mm; the roughness of the inner surface Ra≤1.6μm.

3. The oxygen lance nozzle with a wear-resistant coating according to claim 1 or 2, characterized in that, The purity of the Al2O3 ceramic powder is not less than 99.9%, and the particle size is 300-500 mesh.

4. A method for preparing a Laval powder spraying tube with a wear-resistant coating for an oxygen lance nozzle according to any one of claims 1-3, characterized in that, include: The Al2O3 ceramic powder, the AgCuTi4.8 active solder powder, and the binder are mixed to obtain a slurry; The flexible mandrel is coaxially inserted into the oxygen-free copper Laval tube substrate, forming a gap between them; The slurry is injected into the gap, the oxygen-free copper Laval tube substrate is rotated and subjected to negative pressure adsorption, and after drying, a dry coating film is obtained on the inner surface of the oxygen-free copper Laval tube substrate. The oxygen-free copper Laval tube substrate with the flexible mandrel and the dry film of the coating is vacuum brazed, and then the flexible mandrel is removed. The post-processing yields the oxygen lance nozzle Laval powder spraying tube with the wear-resistant coating.

5. The method for preparing the Laval powder injection tube with wear-resistant coating of the oxygen lance nozzle according to claim 4, characterized in that, One or more of the following conditions must be met: (1) The mass ratio of the Al2O3 ceramic powder to the AgCuTi4.8 active solder powder is 2.5-3.5:1; (2) The adhesive comprises anhydrous ethanol and gum arabic, wherein the mass ratio of the anhydrous ethanol to the gum arabic is 8-12:1; (3) The amount of the binder is 10-15% of the total mass of the Al2O3 ceramic powder and the AgCuTi4.8 active solder powder; (4) The viscosity of the slurry is 500-800 mPa·s.

6. The method for preparing the Laval powder injection tube with wear-resistant coating of the oxygen lance nozzle according to claim 4, characterized in that... The diameter of the flexible mandrel is 0.5-0.7 mm smaller than the throat diameter of the oxygen-free copper Laval tube substrate.

7. The method for preparing the Laval powder injection tube with wear-resistant coating of the oxygen lance nozzle according to claim 4, characterized in that, The raw materials of the flexible core mold, calculated by total mass as 100%, include 64-75% silicone rubber, 2-3% dicumyl peroxide, 15-20% talc, 5-8% zinc stearate, and 3-5% silicon dioxide.

8. The method for preparing the Laval powder injection tube with wear-resistant coating of the oxygen lance nozzle according to claim 4, characterized in that, One or more of the following conditions must be met: (1) The rotational speed of the rotation is 5-8 r / min; (2) The vacuum degree of the negative pressure adsorption is not higher than 5×10 -2 Pa; (3) The thickness of the dry film of the coating is 0.3-0.4 mm; (4) The thickness deviation of the dry film coating in the circumferential direction shall not exceed ±0.03 mm; (5) The vacuum degree of the vacuum brazing is not higher than 5×10 -3 Pa; (6) Argon gas is introduced into the vacuum brazing environment at a rate of 5-10 mL / min; (7) The heat preservation procedure for vacuum brazing is as follows: heat up to 600-620℃ at 2-2.5℃ / min and keep for 10-15min, then heat up to 850-880℃ at 1.5-2℃ / min and keep for 30-40min.

9. The method for preparing the Laval powder injection tube with a wear-resistant coating for an oxygen lance nozzle according to any one of claims 4-8, characterized in that, The post-processing includes: grinding to remove residual brazing slag from the coating surface, and checking that the coating porosity is not higher than 5% and the hardness is not lower than 1200 HV. 0.2 The bonding strength is not less than 15MPa.

10. The method for preparing the Laval powder injection tube with a wear-resistant coating of the oxygen lance nozzle according to claim 9, characterized in that, The post-processing also includes an inner cavity surface polishing step, after which the surface roughness of the coating Ra is ≤1.0μm.

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