A coating for the outer tube of a converter oxygen lance and a method for producing the same

Abstract

The present application relates to a kind of converter oxygen lance outer tube coating and its preparation method, belong to metallurgical equipment surface protection technical field, a kind of converter oxygen lance outer tube coating, including three layers gradient structure, from inside to outside in turn transition layer, intermediate layer and surface layer, transition layer includes 8-25wt% Cr, 5-10wt% Al, 0.3-1.5wt% Y, 60-85wt% Ni and ≤5wt% by substrate diffusion introduced Fe element, intermediate layer includes 85-95wt% ZrO2, 5-15wt% MgO, surface layer includes 65-75wt% ZrO2, 25-35wt% TiO2, the present application solves the existing oxygen lance outer tube high, easy to crack, poor high temperature scouring, coating easy to peel off and other technical problems, realize the multiple protection of oxygen lance outer tube, prolong its service life.

Description

Technical Field

[0001] This invention belongs to the field of surface protection technology for metallurgical equipment, and specifically relates to a coating for the outer tube of a converter oxygen lance and its preparation method. Background Technology

[0002] The oxygen lance is a core piece of equipment in the converter steelmaking process. Its main function is to blow oxygen into the molten pool for decarburization, which directly determines the efficiency and quality of steelmaking. The outer tube of the oxygen lance is directly exposed to the high-temperature furnace environment of 1600℃. It not only bears huge thermal stress and heat radiation, but also faces multiple erosions such as slag splashing, high-temperature oxidation, molten slag erosion and scouring wear. Its service conditions are extremely harsh.

[0003] Traditional converter oxygen lances have no coating on their outer tubes, relying solely on internal cooling water circulation, which presents several technical drawbacks: First, the slag adhesion rate on the outer tubes is extremely high, and the adhesion of steel slag easily leads to poor cooling of the oxygen lance, shortening the lifespan of the outer tubes and nozzles. Second, the steel tubes are exposed in the extremely harsh furnace conditions, making them highly susceptible to cracking and fissures under high temperatures and thermal stress. The oxygen lance scraper further exacerbates the functional failure of the outer tube surface, resulting in longitudinal and transverse cracks, affecting normal smelting safety and efficiency.

[0004] To address the aforementioned issues, existing technologies have attempted simple surface treatments for the oxygen lance outer tube. However, these methods all employ a single coating structure, which cannot simultaneously meet multiple performance requirements such as interface bonding, wear resistance, oxidation resistance, and slag resistance. They suffer from a series of problems, including weak coating adhesion, easy peeling, and limited functionality, making them unsuitable for the extreme working conditions of the oxygen lance outer tube and failing to fundamentally solve the technical defects of traditional oxygen lances.

[0005] Currently, there are also related patents, such as the patent with publication number CN102839254A, entitled "Non-stick Steel Converter Oxygen Lance and its Manufacturing Method". However, the patent document only proposes a vague concept of composite coating layering, without clarifying the functional positioning, composition ratio, microstructure and gradient connection design of each layer, and does not achieve wear resistance and crack prevention functions, and cannot adapt to extreme working conditions such as high temperature of 1600℃ and slag erosion of the converter oxygen lance outer tube.

[0006] Therefore, developing a multi-layered, highly adhesive, high-temperature impact resistant, wear-resistant, and slag-resistant coating and its preparation method has become a technical problem that the metallurgical industry urgently needs to solve. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a coating for the outer tube of a converter oxygen lance and its preparation method, which solves the technical problems of high slag adhesion rate, easy cracking, poor high temperature erosion resistance, and easy peeling of coating in the existing oxygen lance outer tube, so as to achieve multiple protections for the oxygen lance outer tube and extend its service life.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A converter oxygen lance outer tube coating comprises a three-layer gradient structure, consisting of a transition layer, an intermediate layer, and a surface layer from the inside out. The transition layer contains 8-25 wt% Cr, 5-10 wt% Al, 0.3-1.5 wt% Y, 60-85 wt% Ni, and ≤5 wt% Fe element diffused from the matrix. The intermediate layer contains 85-95 wt% ZrO2 and 5-15 wt% MgO. The surface layer contains 65-75 wt% ZrO2 and 25-35 wt% TiO2.

[0009] The intermediate layer also contains 0.3-1.0 wt% Y2O3.

[0010] The surface layer also contains 1-3 wt% SiO2.

[0011] The microstructure of the transition layer is mainly composed of β-NiAl phase, with the remainder containing 0.5-5 vol% AlCr. x Phase, x is 1.0-3.0.

[0012] The microstructure of the intermediate layer is mainly composed of MgO-stabilized tetragonal ZrO2.

[0013] The microstructure of the surface layer is mainly composed of ZrO2-TiO2 solid solution.

[0014] A coating for the outer tube of a converter oxygen lance is tightly adhered to the surface of the oxygen lance outer tube substrate. The total coating thickness is 0.5-0.9 mm, the transition layer thickness is 0.2-0.4 mm, the intermediate layer thickness is 0.1-0.3 mm, and the surface layer thickness is 0.1-0.3 mm.

[0015] A method for preparing a coating for the outer tube of a converter oxygen lance, characterized by comprising the following steps: S1. Pretreatment of oxygen lance outer tube substrate: The seamless steel pipe is processed into shape, and the substrate surface is treated by chemical degreasing and physical rust removal, followed by roughening treatment; S2. Coating material preparation: Prepare powders suitable for atmospheric plasma spraying technology. The transition layer spraying powder consists of Cr powder, Ni powder, Al powder, and Y2O3 powder, with a powder particle size of 200 mesh. The Cr powder content is 9-29 wt%, Ni powder is 63-89 wt%, Al powder is 6-12 wt%, and Y2O3 powder is 0.3-1.5 wt%. The intermediate layer coating powder includes ZrO2 powder and MgO powder, with a particle size of 200 mesh; wherein, the ZrO2 powder content is 85-95 wt%, and the MgO powder content is 5-15 wt%. The surface coating powder includes ZrO2 powder and TiO2 powder, with a particle size of 200 mesh; the content of ZrO2 powder is 65-75 wt%, and the content of TiO2 powder is 25-35 wt%.

[0016] A method for preparing a coating for the outer tube of a converter oxygen lance further includes the following steps: S3. Gradient Coating Spraying: Fix the pretreated substrate to ensure that the substrate is stable and does not shift during the spraying process; spray the substrate surface in the order of transition layer - intermediate layer - surface layer, and control the total coating thickness to 0.5-0.9mm.

[0017] A method for preparing a coating for the outer tube of a converter oxygen lance further includes the following steps: S4. Post-treatment: After spraying, the coating surface is lightly sanded to remove bumps, impurities and splatter particles.

[0018] 1. Transition Layer (Thermal Stress Buffer and Metallurgical Bonding Mechanism): This layer serves as the underlying base, and its core mechanism lies in the gradient transition of thermal expansion coefficients. Due to the significant difference in thermal expansion coefficients between the substrate and the ceramic / alloy coating, direct contact would generate enormous shear stress during high-temperature cycling. The transition layer, through compositional design, ensures its thermal expansion coefficient falls between that of the substrate and the working layer, effectively mitigating thermal mismatch at the interface. Simultaneously, during high-temperature spraying or cladding, transition layer elements diffuse into the substrate, forming micro-regional metallurgical bonding. This fundamentally reduces interfacial thermal stress concentration, preventing catastrophic interfacial delamination under rapid heating and cooling conditions and ensuring the overall structural bonding strength.

[0019] The oxygen lance substrate is steel, and the coating must match the coefficient of thermal expansion of the substrate to avoid thermal stress delamination. The coefficient of thermal expansion of Ni is approximately 13.3 × 10⁻⁻⁻⁴. 6 / K, with the steel matrix (such as low carbon steel 11–13×10⁻ 6 / K) is close, while Cu (16.5×10⁻ 6 / K), Ti (8.6×10⁻ 6 Large differences in metals such as K can easily lead to coating cracking and failure.

[0020] Cr and Al form dense oxide films of Cr2O3 and Al2O3 in situ at high temperatures, forming a metallurgical bond and blocking oxygen diffusion. If replaced with Si or Mn, their oxides (SiO2, MnO) have a loose structure and are easily volatile, failing to effectively protect the matrix.

[0021] Y significantly improves the toughness and thermal shock resistance of coatings by refining grains and strengthening grain boundaries through grain boundary segregation. Conventional strengthening elements (such as Mo and W) can increase hardness, but they cannot improve grain boundary strength, leading to thermal shock brittle fracture.

[0022] 2. Intermediate Layer (Performance Gradient Connection and Toughening Mechanism): This layer plays a crucial role in connecting the upper and lower layers, with its mechanism manifested in the synergistic matching of hardness and toughness. On the one hand, through solid solution strengthening or second-phase strengthening mechanisms, it significantly improves the surface microhardness, wear resistance, and high-temperature oxidation resistance. On the other hand, it constructs a smooth gradient of elastic modulus and hardness from the transition layer to the surface layer, avoiding stress concentration crack initiation caused by abrupt performance changes. This gradient design further alleviates the thermal stress within the coating, significantly improving the overall thermal shock fatigue resistance and mechanical stability against high-speed slag erosion.

[0023] ZrO2 has low thermal conductivity (approximately 2.0 W / (m•K)), effectively insulating against high temperatures. Other materials, such as Al2O3 (thermal conductivity approximately 30 W / (m•K)) and SiC (approximately 80 W / (m•K)), have excessively high thermal conductivity, failing to prevent heat transfer to the steel matrix and causing the matrix to soften and fail.

[0024] MgO stabilizes the tetragonal phase of ZrO2 to room temperature, inhibiting phase transformation volume expansion (pure ZrO2 phase transformation volume expansion is about 5%–8%). Other stabilizers such as CaO are easily hydrated and dissolved in high-temperature alkaline slag, while Y2O3 is effective but expensive, and Y2O3 plays a synergistic role in slag resistance on the surface layer.

[0025] 3. Surface Layer (Wettability Control and Slag Erosion Resistance Mechanism): As a functional defense line directly facing harsh working conditions, the core mechanism of this layer lies in surface energy control and densification barrier. Through specific chemical composition design, the interfacial tension between steel slag droplets and the coating surface is effectively reduced (i.e., wettability is reduced), making it difficult for steel slag to spread and penetrate the surface, thus achieving the core function of preventing steel slag adhesion. At the same time, this layer has excellent high-temperature stability and corrosion resistance, forming a dense physical barrier that blocks the inward diffusion path of oxygen atoms and corrosive media, perfectly adapting to the high-temperature and harsh working conditions of converter steelmaking, and significantly extending the service life of the coating.

[0026] TiO2 and ZrO2 form a low-melting-point solid solution, which improves the spreadability of plasma spray droplets and reduces porosity. Other fluxes (Na2O, K2O) lower the melting point, but they also compromise chemical stability and accelerate slag erosion.

[0027] The converter slag is alkaline (containing CaO and FeO). SiO2 reacts with it at high temperatures to form a high-viscosity silicate glass phase, creating a "self-healing" protection. Other oxides, such as B2O3, can also form a glass phase, but their volatilization at high temperatures leads to the failure of the protection.

[0028] The present invention adopts the above technical solution and has the following advantages: The present invention effectively solves the defects of traditional oxygen lance outer tube technology, significantly extends the service life of oxygen lance, reduces the replacement frequency of oxygen lance, reduces the cost and maintenance cost of steelmaking equipment, and at the same time reduces the occurrence of safety accidents.

[0029] The coating of this invention adopts a three-layer gradient structure design, with each layer's material and function precisely matched. The transition layer alleviates differences in thermal expansion coefficients and prevents coating peeling; the middle layer provides high hardness, wear resistance, and oxidation resistance, serving as the core protective layer; and the surface layer achieves anti-slag adhesion while also possessing high-temperature stability. These layers form a coordinated protective effect, solving the technical problem of traditional single-coating systems having limited functionality, while simultaneously meeting multiple performance requirements such as interfacial bonding, wear resistance, oxidation resistance, anti-slag adhesion, and crack resistance.

[0030] The three-layer gradient structure of this invention achieves triple functional synergy through precise division of functions in each layer and gradient design of composition and microstructure, effectively alleviating thermal stress at the interface and inside the coating, and fundamentally solving the defect of existing fuzzy layering that cannot adapt to extreme working conditions.

[0031] The total coating thickness of this invention is only 0.5-0.9 mm, achieving high-efficiency protection without increasing the weight of the oxygen lance, thus meeting the normal operating requirements of the oxygen lance. Testing shows that this coating can reduce the slag adhesion rate of the oxygen lance outer tube from 28% to approximately 10%, with wear only 5% of the substrate. It can rapidly form a dense oxide film at 1600℃, effectively preventing oxygen diffusion into the substrate, significantly improving the oxygen lance's anti-slag adhesion, impact resistance, and high-temperature oxidation resistance. No cracking, circumferential cracking, or longitudinal cracking occurred on the outer tube. After 2200 heats, the surface remained smooth, with no obvious slag adhesion or cracking, demonstrating excellent coating integrity.

[0032] The present invention will be further described below with reference to specific embodiments. Detailed Implementation

[0033] The embodiments of the present invention will be described in detail below with reference to the examples. Specific conditions not specified in the examples are based on conventional conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased on the market.

[0034] The described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. Example 1

[0035] A coating for the outer tube of a converter oxygen lance, which is tightly adhered to the surface of the oxygen lance outer tube substrate, includes a three-layer gradient structure, consisting of a transition layer, an intermediate layer, and a surface layer from the inside out, with a total coating thickness of 0.5 mm.

[0036] The transition layer comprises 8 wt% Cr, 5 wt% Al, 0.3 wt% Y, 85 wt% Ni and 1.7 wt% Fe element introduced by diffusion from the matrix, and the thickness of the transition layer is 0.2 mm. The microstructure of the transition layer is mainly composed of β-NiAl phase, with the remainder containing 0.5 vol% AlCr. x Phase X is 1.0; phase Y is dissolved in the coating and gradually increases from the substrate side to the outer side of the coating in a gradient distribution. The core function of the transition layer is to improve the interfacial bonding performance between the coating and the substrate, alleviate the difference in thermal expansion coefficients between the substrate and the coating, reduce interfacial thermal stress concentration, and prevent interfacial delamination of the coating under high-temperature conditions.

[0037] The intermediate layer contains 85 wt% ZrO2 and 15 wt% MgO, and the thickness of the intermediate layer is 0.1 mm; The microstructure of the intermediate layer is mainly composed of MgO-stabilized tetragonal ZrO2, with a dense structure free of pores, free of free phases, and crystallization defects. This intermediate layer serves as the main protective layer of the coating, significantly improving the surface hardness of the substrate, enhancing wear resistance and high-temperature oxidation resistance. It also achieves a performance gradient connection between the transition layer and the surface layer, further reducing internal thermal stress, improving the overall thermal shock resistance and slag erosion resistance of the coating, and enhancing coating adhesion.

[0038] The surface layer comprises 65 wt% ZrO2 and 35 wt% TiO2, with a thickness of 0.2 mm. The microstructure of the surface layer is primarily a ZrO2-TiO2 solid solution, exhibiting high-temperature crystal stability without phase transformation or cracking. The surface layer possesses extremely low slag wettability, effectively preventing slag adhesion, while also demonstrating excellent high-temperature stability, wear resistance, and corrosion resistance, making it suitable for the harsh high-temperature conditions of converter steelmaking.

[0039] The oxygen lance outer tube is made of tubing such as 20# steel or 20G seamless steel pipe.

[0040] A method for preparing a coating for the outer tube of a converter oxygen lance includes the following steps: S1. Pretreatment of the oxygen lance outer tube substrate: The seamless steel pipe is processed into shape according to the size requirements of the converter oxygen lance outer tube. The substrate surface is treated by chemical degreasing and physical rust removal methods, followed by roughening treatment to ensure that the substrate surface is clean, free of oil, rust and other impurities, and has a certain roughness, which lays the foundation for the tight bonding between the coating and the substrate.

[0041] S2. Coating Material Preparation: Prepare powders suitable for atmospheric plasma spraying technology, strictly controlling the particle size and uniformity of each powder. The transition layer spraying powder consists of Cr powder, Ni powder, Al powder, and Y2O3 powder, with a powder particle size of 200 mesh. The Cr powder content is 9 wt%, Ni powder is 89 wt%, Al powder is 6 wt%, and Y2O3 powder is 0.3 wt%.

[0042] The intermediate layer spray powder includes ZrO2 powder and MgO powder, with a particle size of 200 mesh; among which, the ZrO2 powder content is 85wt% and the MgO powder content is 15wt%.

[0043] The surface coating powder includes ZrO2 powder and TiO2 powder, with a particle size of 200 mesh; the content of ZrO2 powder is 65wt% and the content of TiO2 powder is 35wt%.

[0044] S3. Gradient Coating Spraying: The pretreated substrate is fixed on the tooling fixture of the atmospheric plasma spraying equipment to ensure that the substrate is stable and does not shift during the spraying process. Atmospheric plasma spraying technology is used to spray the substrate surface in the order of transition layer-intermediate layer-surface layer. Through precise control of the equipment, the thickness of each layer is guaranteed. During the spraying process, the continuous connection of each layer is ensured, without gaps or interlayer peeling, so as to achieve gradient connection between the coating and the substrate and synergistic optimization of the performance of each layer.

[0045] S4. Post-treatment: After spraying, the coating surface is lightly sanded and corrected using sanding equipment to remove protrusions, impurities and splatter particles from the coating surface, ensuring that the coating surface is smooth, uniform in thickness and free of obvious defects. Example 2

[0046] A coating for the outer tube of a converter oxygen lance, which is tightly adhered to the surface of the oxygen lance outer tube substrate, includes a three-layer gradient structure, consisting of a transition layer, an intermediate layer, and a surface layer from the inside out, with a total coating thickness of 0.9 mm.

[0047] The transition layer comprises 25 wt% Cr, 10 wt% Al, 1.5 wt% Y, 60 wt% Ni and 3.5 wt% Fe element introduced by diffusion from the matrix, and the thickness of the transition layer is 0.4 mm. The microstructure of the transition layer is mainly composed of β-NiAl phase, with the remainder containing 5 vol% AlCr. x Phase X is 3.0; Y is dissolved in the coating and gradually increases from the substrate side to the outer side of the coating in a gradient distribution. The core function of the transition layer is to improve the interfacial bonding performance between the coating and the substrate, alleviate the difference in thermal expansion coefficients between the substrate and the coating, reduce interfacial thermal stress concentration, and prevent the coating from peeling off under high-temperature conditions.

[0048] The intermediate layer contains 95 wt% ZrO2 and 5 wt% MgO, and has a thickness of 0.2 mm; The microstructure of the intermediate layer is mainly composed of MgO-stabilized tetragonal ZrO2, with a dense structure free of pores, free of free phases, and crystallization defects. This intermediate layer serves as the main protective layer of the coating, significantly improving the surface hardness of the substrate, enhancing wear resistance and high-temperature oxidation resistance. It also achieves a performance gradient connection between the transition layer and the surface layer, further reducing internal thermal stress, improving the overall thermal shock resistance and slag erosion resistance of the coating, and enhancing coating adhesion.

[0049] The surface layer comprises 75 wt% ZrO2 and 25 wt% TiO2, with a thickness of 0.3 mm. The microstructure of the surface layer is primarily a ZrO2-TiO2 solid solution, exhibiting high-temperature crystal stability without phase transformation or cracking. The surface layer possesses extremely low slag wettability, effectively preventing slag adhesion, while also demonstrating excellent high-temperature stability, wear resistance, and corrosion resistance, making it suitable for the harsh high-temperature conditions of converter steelmaking.

[0050] The oxygen lance outer tube is made of tubing such as 20# steel or 20G seamless steel pipe.

[0051] A method for preparing a coating for the outer tube of a converter oxygen lance includes the following steps: S1. Pretreatment of the oxygen lance outer tube substrate: The seamless steel pipe is processed into shape according to the size requirements of the converter oxygen lance outer tube. The substrate surface is treated by chemical degreasing and physical rust removal methods, followed by roughening treatment to ensure that the substrate surface is clean, free of oil, rust and other impurities, and has a certain roughness, which lays the foundation for the tight bonding between the coating and the substrate.

[0052] S2. Coating Material Preparation: Prepare powders suitable for atmospheric plasma spraying technology, strictly controlling the particle size and uniformity of each powder. The transition layer spraying powder consists of Cr powder, Ni powder, Al powder, and Y2O3 powder, with a powder particle size of 200 mesh. The Cr powder content is 29wt%, Ni powder is 63wt%, Al powder is 12wt%, and Y2O3 powder is 1.5wt%.

[0053] The intermediate layer spray powder includes ZrO2 powder and MgO powder, with a particle size of 200 mesh; among which, the ZrO2 powder content is 95wt% and the MgO powder content is 5wt%.

[0054] The surface coating powder includes ZrO2 powder and TiO2 powder, with a particle size of 200 mesh; the content of ZrO2 powder is 75wt% and the content of TiO2 powder is 25wt%.

[0055] S3. Gradient Coating Spraying: The pretreated substrate is fixed on the tooling fixture of the atmospheric plasma spraying equipment to ensure that the substrate is stable and does not shift during the spraying process. Atmospheric plasma spraying technology is used to spray the substrate surface in the order of transition layer-intermediate layer-surface layer. Through precise control of the equipment, the thickness of each layer is guaranteed. During the spraying process, the continuous connection of each layer is ensured, without gaps or interlayer peeling, so as to achieve gradient connection between the coating and the substrate and synergistic optimization of the performance of each layer.

[0056] S4. Post-treatment: After spraying, the coating surface is lightly sanded and corrected using sanding equipment to remove protrusions, impurities and splatter particles from the coating surface, ensuring that the coating surface is smooth, uniform in thickness and free of obvious defects. Example 3

[0057] A coating for the outer tube of a converter oxygen lance is tightly adhered to the surface of the oxygen lance outer tube substrate. It comprises a three-layer gradient structure, consisting of a transition layer, an intermediate layer, and a surface layer from the inside out, with a total coating thickness of 0.7 mm.

[0058] The transition layer contains 17 wt% Cr, 8 wt% Al, 1 wt% Y, 72 wt% Ni and 2 wt% Fe element introduced by diffusion from the matrix, and the thickness of the transition layer is 0.3 mm. The microstructure of the transition layer is dominated by the β-NiAl phase, with the remainder containing 3 vol% AlCr. x Phase X is 2.0; Y is dissolved in the coating and gradually increases from the substrate side to the outer side of the coating in a gradient distribution. The core function of the transition layer is to improve the interfacial bonding performance between the coating and the substrate, alleviate the difference in thermal expansion coefficients between the substrate and the coating, reduce interfacial thermal stress concentration, and prevent the coating from peeling off under high-temperature conditions.

[0059] The intermediate layer contains 90 wt% ZrO2 and 10 wt% MgO, with a thickness of 0.3 mm; The microstructure of the intermediate layer is mainly composed of MgO-stabilized tetragonal ZrO2, with a dense structure free of pores, free of free phases, and crystallization defects. This intermediate layer serves as the main protective layer of the coating, significantly improving the surface hardness of the substrate, enhancing wear resistance and high-temperature oxidation resistance. It also achieves a performance gradient connection between the transition layer and the surface layer, further reducing internal thermal stress, improving the overall thermal shock resistance and slag erosion resistance of the coating, and enhancing coating adhesion.

[0060] The surface layer comprises 70 wt% ZrO2 and 30 wt% TiO2, with a thickness of 0.1 mm. The microstructure of the surface layer is primarily a ZrO2-TiO2 solid solution, exhibiting high-temperature crystal stability without phase transformation or cracking. The surface layer possesses extremely low slag wettability, effectively preventing slag adhesion, while also demonstrating excellent high-temperature stability, wear resistance, and corrosion resistance, making it suitable for the harsh high-temperature conditions of converter steelmaking.

[0061] The oxygen lance outer tube is made of tubing such as 20# steel or 20G seamless steel pipe.

[0062] A method for preparing a coating for the outer tube of a converter oxygen lance includes the following steps: S1. Pretreatment of the oxygen lance outer tube substrate: The seamless steel pipe is processed into shape according to the size requirements of the converter oxygen lance outer tube. The substrate surface is treated by chemical degreasing and physical rust removal methods, followed by roughening treatment to ensure that the substrate surface is clean, free of oil, rust and other impurities, and has a certain roughness, which lays the foundation for the tight bonding between the coating and the substrate.

[0063] S2. Coating Material Preparation: Prepare powders suitable for atmospheric plasma spraying technology, strictly controlling the particle size and uniformity of each powder. The transition layer spraying powder consists of Cr powder, Ni powder, Al powder, and Y2O3 powder, with a powder particle size of 200 mesh. The Cr powder content is 19wt%, Ni powder is 75wt%, Al powder is 10wt%, and Y2O3 powder is 1wt%.

[0064] The intermediate layer spray powder includes ZrO2 powder and MgO powder, with a particle size of 200 mesh; among which, the ZrO2 powder content is 90wt% and the MgO powder content is 10wt%.

[0065] The surface coating powder includes ZrO2 powder and TiO2 powder, with a particle size of 200 mesh; wherein, the content of ZrO2 powder is 70wt% and the content of TiO2 powder is 30wt%.

[0066] S3. Gradient Coating Spraying: The pretreated substrate is fixed on the tooling fixture of the atmospheric plasma spraying equipment to ensure that the substrate is stable and does not shift during the spraying process. Atmospheric plasma spraying technology is used to spray the substrate surface in the order of transition layer-intermediate layer-surface layer. Through precise control of the equipment, the thickness of each layer is guaranteed. During the spraying process, the continuous connection of each layer is ensured, without gaps or interlayer peeling, so as to achieve gradient connection between the coating and the substrate and synergistic optimization of the performance of each layer.

[0067] S4. Post-treatment: After spraying, the coating surface is lightly sanded and corrected using sanding equipment to remove protrusions, impurities and splatter particles from the coating surface, ensuring that the coating surface is smooth, uniform in thickness and free of obvious defects. Example 4

[0068] A coating for the outer tube of a converter oxygen lance is tightly adhered to the surface of the oxygen lance outer tube substrate. It comprises a three-layer gradient structure, consisting of a transition layer, an intermediate layer, and a surface layer from the inside out, with a total coating thickness of 0.7 mm.

[0069] The transition layer contains 17 wt% Cr, 8 wt% Al, 1 wt% Y, 72 wt% Ni and 2 wt% Fe element introduced by diffusion from the matrix, and the thickness of the transition layer is 0.3 mm. The microstructure of the transition layer is dominated by the β-NiAl phase, with the remainder containing 3 vol% AlCr. x Phase X is 2.0; Y is dissolved in the coating and gradually increases from the substrate side to the outer side of the coating in a gradient distribution. The core function of the transition layer is to improve the interfacial bonding performance between the coating and the substrate, alleviate the difference in thermal expansion coefficients between the substrate and the coating, reduce interfacial thermal stress concentration, and prevent the coating from peeling off under high-temperature conditions.

[0070] The intermediate layer comprises 90 wt% ZrO2, 9.7 wt% MgO, and 0.3 wt% Y2O3, with a thickness of 0.3 mm; The microstructure of the intermediate layer is mainly composed of MgO-stabilized tetragonal ZrO2, with a dense structure free of pores, free of free phases, and crystallization defects. This intermediate layer serves as the main protective layer of the coating, significantly improving the surface hardness of the substrate, enhancing wear resistance and high-temperature oxidation resistance. It also achieves a performance gradient connection between the transition layer and the surface layer, further reducing internal thermal stress, improving the overall thermal shock resistance and slag erosion resistance of the coating, and enhancing coating adhesion.

[0071] The surface layer comprises 70 wt% ZrO2, 29 wt% TiO2, and 1 wt% SiO2, with a thickness of 0.1 mm. The microstructure of the surface layer is primarily a ZrO2-TiO2 solid solution, exhibiting high-temperature crystal stability without phase transformation or cracking. The surface layer possesses extremely low slag wettability, effectively preventing slag adhesion, while also demonstrating excellent high-temperature stability, wear resistance, and corrosion resistance, making it suitable for the harsh high-temperature conditions of converter steelmaking.

[0072] The oxygen lance outer tube is made of tubing such as 20# steel or 20G seamless steel pipe.

[0073] A method for preparing a coating for the outer tube of a converter oxygen lance includes the following steps: S1. Pretreatment of the oxygen lance outer tube substrate: The seamless steel pipe is processed into shape according to the size requirements of the converter oxygen lance outer tube. The substrate surface is treated by chemical degreasing and physical rust removal methods, followed by roughening treatment to ensure that the substrate surface is clean, free of oil, rust and other impurities, and has a certain roughness, which lays the foundation for the tight bonding between the coating and the substrate.

[0074] S2. Coating Material Preparation: Prepare powders suitable for atmospheric plasma spraying technology, strictly controlling the particle size and uniformity of each powder. The transition layer spraying powder consists of Cr powder, Ni powder, Al powder, and Y2O3 powder, with a powder particle size of 200 mesh. The Cr powder content is 19wt%, Ni powder is 75wt%, Al powder is 10wt%, and Y2O3 powder is 1wt%.

[0075] The intermediate layer coating powder includes ZrO2 powder, MgO powder, and Y2O3 powder, with a particle size of 200 mesh; among which, the ZrO2 powder content is 90wt%, the MgO powder content is 9.7wt%, and the Y2O3 powder content is 0.3wt%.

[0076] The surface coating powder includes ZrO2 powder, TiO2 powder, and SiO2 powder, with a particle size of 200 mesh; among which, the content of ZrO2 powder is 70wt%, the content of TiO2 powder is 29wt%, and the content of SiO2 powder is 1wt%.

[0077] S3. Gradient Coating Spraying: The pretreated substrate is fixed on the tooling fixture of the atmospheric plasma spraying equipment to ensure that the substrate is stable and does not shift during the spraying process. Atmospheric plasma spraying technology is used to spray the substrate surface in the order of transition layer-intermediate layer-surface layer. Through precise control of the equipment, the thickness of each layer is guaranteed. During the spraying process, the continuous connection of each layer is ensured, without gaps or interlayer peeling, so as to achieve gradient connection between the coating and the substrate and synergistic optimization of the performance of each layer.

[0078] S4. Post-treatment: After spraying, the coating surface is lightly sanded and corrected using sanding equipment to remove protrusions, impurities and splatter particles from the coating surface, ensuring that the coating surface is smooth, uniform in thickness and free of obvious defects. Example 5

[0079] A coating for the outer tube of a converter oxygen lance is tightly adhered to the surface of the oxygen lance outer tube substrate. It comprises a three-layer gradient structure, consisting of a transition layer, an intermediate layer, and a surface layer from the inside out, with a total coating thickness of 0.7 mm.

[0080] The transition layer contains 17 wt% Cr, 8 wt% Al, 1 wt% Y, 72 wt% Ni and 2 wt% Fe element introduced by diffusion from the matrix, and the thickness of the transition layer is 0.3 mm. The microstructure of the transition layer is dominated by the β-NiAl phase, with the remainder containing 3 vol% AlCr. x Phase X is 2.0; Y is dissolved in the coating and gradually increases from the substrate side to the outer side of the coating in a gradient distribution. The core function of the transition layer is to improve the interfacial bonding performance between the coating and the substrate, alleviate the difference in thermal expansion coefficients between the substrate and the coating, reduce interfacial thermal stress concentration, and prevent the coating from peeling off under high-temperature conditions.

[0081] The intermediate layer comprises 89 wt% ZrO2, 10 wt% MgO, and 1.0 wt% Y2O3, with a thickness of 0.3 mm; The microstructure of the intermediate layer is mainly composed of MgO-stabilized tetragonal ZrO2, with a dense structure free of pores, free of free phases, and crystallization defects. This intermediate layer serves as the main protective layer of the coating, significantly improving the surface hardness of the substrate, enhancing wear resistance and high-temperature oxidation resistance. It also achieves a performance gradient connection between the transition layer and the surface layer, further reducing internal thermal stress, improving the overall thermal shock resistance and slag erosion resistance of the coating, and enhancing coating adhesion.

[0082] The surface layer comprises 67 wt% ZrO2, 30 wt% TiO2, and 3 wt% SiO2, with a thickness of 0.1 mm. The microstructure of the surface layer is primarily a ZrO2-TiO2 solid solution, exhibiting high-temperature crystal stability without phase transformation or cracking. The surface layer possesses extremely low slag wettability, effectively preventing slag adhesion, while also demonstrating excellent high-temperature stability, wear resistance, and corrosion resistance, making it suitable for the harsh high-temperature conditions of converter steelmaking.

[0083] The oxygen lance outer tube is made of tubing such as 20# steel or 20G seamless steel pipe.

[0084] A method for preparing a coating for the outer tube of a converter oxygen lance includes the following steps: S1. Pretreatment of the oxygen lance outer tube substrate: The seamless steel pipe is processed into shape according to the size requirements of the converter oxygen lance outer tube. The substrate surface is treated by chemical degreasing and physical rust removal methods, followed by roughening treatment to ensure that the substrate surface is clean, free of oil, rust and other impurities, and has a certain roughness, which lays the foundation for the tight bonding between the coating and the substrate.

[0085] S2. Coating Material Preparation: Prepare powders suitable for atmospheric plasma spraying technology, strictly controlling the particle size and uniformity of each powder. The transition layer spraying powder consists of Cr powder, Ni powder, Al powder, and Y2O3 powder, with a powder particle size of 200 mesh. The Cr powder content is 19wt%, Ni powder is 75wt%, Al powder is 10wt%, and Y2O3 powder is 1wt%.

[0086] The intermediate layer coating powder includes ZrO2 powder, MgO powder, and Y2O3 powder, with a particle size of 200 mesh; among which, the content of ZrO2 powder is 89wt%, the content of MgO powder is 10wt%, and the content of Y2O3 powder is 1wt%.

[0087] The surface coating powder includes ZrO2 powder, TiO2 powder, and SiO2 powder, with a particle size of 200 mesh; among which, the content of ZrO2 powder is 67wt%, the content of TiO2 powder is 30wt%, and the content of SiO2 powder is 3wt%.

[0088] S3. Gradient Coating Spraying: The pretreated substrate is fixed on the tooling fixture of the atmospheric plasma spraying equipment to ensure that the substrate is stable and does not shift during the spraying process. Atmospheric plasma spraying technology is used to spray the substrate surface in the order of transition layer-intermediate layer-surface layer. Through precise control of the equipment, the thickness of each layer is guaranteed. During the spraying process, the continuous connection of each layer is ensured, without gaps or interlayer peeling, so as to achieve gradient connection between the coating and the substrate and synergistic optimization of the performance of each layer.

[0089] S4. Post-treatment: After spraying, the coating surface is lightly sanded and corrected using sanding equipment to remove protrusions, impurities and splatter particles from the coating surface, ensuring that the coating surface is smooth, uniform in thickness and free of obvious defects. Example 6

[0090] A coating for the outer tube of a converter oxygen lance is tightly adhered to the surface of the oxygen lance outer tube substrate. It comprises a three-layer gradient structure, consisting of a transition layer, an intermediate layer, and a surface layer from the inside out, with a total coating thickness of 0.7 mm.

[0091] The transition layer contains 17 wt% Cr, 8 wt% Al, 1 wt% Y, 72 wt% Ni and 2 wt% Fe element introduced by diffusion from the matrix, and the thickness of the transition layer is 0.3 mm. The microstructure of the transition layer is dominated by the β-NiAl phase, with the remainder containing 3 vol% AlCr. x Phase X is 2.0; Y is dissolved in the coating and gradually increases from the substrate side to the outer side of the coating in a gradient distribution. The core function of the transition layer is to improve the interfacial bonding performance between the coating and the substrate, alleviate the difference in thermal expansion coefficients between the substrate and the coating, reduce interfacial thermal stress concentration, and prevent the coating from peeling off under high-temperature conditions.

[0092] The intermediate layer comprises 89.3 wt% ZrO2, 10 wt% MgO, and 0.7 wt% Y2O3, with a thickness of 0.3 mm; The microstructure of the intermediate layer is mainly composed of MgO-stabilized tetragonal ZrO2, with a dense structure free of pores, free of free phases, and crystallization defects. This intermediate layer serves as the main protective layer of the coating, significantly improving the surface hardness of the substrate, enhancing wear resistance and high-temperature oxidation resistance. It also achieves a performance gradient connection between the transition layer and the surface layer, further reducing internal thermal stress, improving the overall thermal shock resistance and slag erosion resistance of the coating, and enhancing coating adhesion.

[0093] The surface layer comprises 70 wt% ZrO2, 28 wt% TiO2, and 2 wt% SiO2, with a thickness of 0.1 mm. The microstructure of the surface layer is primarily a ZrO2-TiO2 solid solution, exhibiting high-temperature crystal stability without phase transformation or cracking. The surface layer possesses extremely low slag wettability, effectively preventing slag adhesion, while also demonstrating excellent high-temperature stability, wear resistance, and corrosion resistance, making it suitable for the harsh high-temperature conditions of converter steelmaking.

[0094] The oxygen lance outer tube is made of tubing such as 20# steel or 20G seamless steel pipe.

[0095] A method for preparing a coating for the outer tube of a converter oxygen lance includes the following steps: S1. Pretreatment of the oxygen lance outer tube substrate: The seamless steel pipe is processed into shape according to the size requirements of the converter oxygen lance outer tube. The substrate surface is treated by chemical degreasing and physical rust removal methods, followed by roughening treatment to ensure that the substrate surface is clean, free of oil, rust and other impurities, and has a certain roughness, which lays the foundation for the tight bonding between the coating and the substrate.

[0096] S2. Coating Material Preparation: Prepare powders suitable for atmospheric plasma spraying technology, strictly controlling the particle size and uniformity of each powder. The transition layer spraying powder consists of Cr powder, Ni powder, Al powder, and Y2O3 powder, with a powder particle size of 200 mesh. The Cr powder content is 19wt%, Ni powder is 75wt%, Al powder is 10wt%, and Y2O3 powder is 1wt%.

[0097] The intermediate layer coating powder includes ZrO2 powder, MgO powder, and Y2O3 powder, with a particle size of 200 mesh; among which, the ZrO2 powder content is 89.3 wt%, the MgO powder content is 10 wt%, and the Y2O3 powder content is 0.7 wt%.

[0098] The surface coating powder includes ZrO2 powder, TiO2 powder, and SiO2 powder, with a particle size of 200 mesh; among which, the content of ZrO2 powder is 70wt%, the content of TiO2 powder is 28wt%, and the content of SiO2 powder is 2wt%.

[0099] S3. Gradient Coating Spraying: The pretreated substrate is fixed on the tooling fixture of the atmospheric plasma spraying equipment to ensure that the substrate is stable and does not shift during the spraying process. Atmospheric plasma spraying technology is used to spray the substrate surface in the order of transition layer-intermediate layer-surface layer. Through precise control of the equipment, the thickness of each layer is guaranteed. During the spraying process, the continuous connection of each layer is ensured, without gaps or interlayer peeling, so as to achieve gradient connection between the coating and the substrate and synergistic optimization of the performance of each layer.

[0100] S4. Post-treatment: After spraying, the coating surface is lightly sanded and corrected using sanding equipment to remove protrusions, impurities and splatter particles from the coating surface, ensuring that the coating surface is smooth, uniform in thickness and free of obvious defects.

[0101] experiment 1. Base material: 20# high-quality carbon structural steel with an initial wall thickness of 12.00mm is selected as the base material.

[0102] 2. Comparative Example 1: The substrate was coated with a coating using the preparation method of Example 1. The completed coating has a continuous and dense overall structure, which is fully compatible with the variable diameter curved surface structure of the oxygen lance cone tube. There are no coating defects such as cracks, pinholes, peeling, delamination, or detachment. The coating has excellent bonding strength with the substrate.

[0103] 3. Comparative Example 2: No protective coating was applied to the outer surface of the substrate.

[0104] I. High-Temperature Erosion and Wear Resistance Test To verify the effect of the coating of the present invention on the high-temperature erosion wear resistance of the oxygen lance cone tube, an in-situ synchronous service control test of an industrial converter was conducted to compare and verify the oxygen lance cone tube samples using Comparative Example 1 and Comparative Example 2.

[0105] This verification test was conducted in a 150 top-blown converter, with test conditions perfectly matching the actual operating conditions of the oxygen lance cone tube in industrial mass production: the steel grades smelted were mainly high-quality carbon structural steel and oil pipeline steel; the single-furnace smelting cycle was controlled at 33 minutes; the oxygen supply intensity was stable at 3.50 m³ / (t•min); and the peak temperature during the furnace smelting process was maintained at a constant 1680℃. Conical tube samples from Comparative Example 1 and Comparative Example 2 were assembled into oxygen lance equipment of the same specifications and simultaneously conducted service tests within the same furnace service cycle under a completely unified smelting process. The cumulative number of heats in service was tracked and recorded in real time throughout the test. After the test cycle, the oxygen lance assembly was disassembled, and the wall thickness changes of the conical tube samples were accurately detected and quantitatively analyzed.

[0106] Wall thickness was measured using a digital micrometer with an accuracy of ±0.01 mm. Eight fixed test points were evenly set along the circumference of the tapered tube, and the wall thickness was measured at each point. The final result was the arithmetic mean of the eight points. The wall thickness wear rate was used as the core evaluation index for erosion wear resistance. The wear rate calculation formula is as follows:

[0107] The test results of the erosion wear resistance of Comparative Example 1 and Comparative Example 2 are shown in Table 1.

[0108] Table 1

[0109] As shown in Table 1, under the coupled conditions of strong erosion and corrosion in a converter at 1680℃, after 1800 heats of continuous service, the wear rate of the cone tube in Comparative Example 2 reached 28.14%, approaching the safe scrapping threshold for oxygen lance cone tubes; while the wear rate of the cone tube in Comparative Example 1 was only 5.63%, a significant reduction compared to Comparative Example 2. Furthermore, the cone tube in Comparative Example 2 could no longer meet safety production requirements after 1800 heats of service, while the cone tube in Comparative Example 1 retained sufficient safety wall thickness after an extended service life of 3600 heats, allowing it to continue stable service. This completely solves the shortcomings of uncoated substrate oxygen lance cone tubes, such as short service life and insufficient resistance to erosion corrosion under high-temperature conditions, demonstrating extremely excellent high-temperature protection.

[0110] II. Verification of the high-temperature oxidation protection performance of the coating To evaluate the antioxidant protection capability of the coating of the present invention under the high-temperature smelting conditions of the converter, a special equal-weight sample test matching the actual service temperature of the converter was carried out on the samples of Comparative Example 1 and Comparative Example 2. At the same time, the in-situ full-cycle service tracking verification of the industrial converter was carried out.

[0111] The temperature of this experiment was matched to the actual peak smelting temperature of the converter, which was 1680℃. On-site service tracking was conducted in the aforementioned 150t industrial converter, maintaining smelting conditions completely consistent with the erosion and wear resistance test. The high-temperature oxidation behavior of the samples was systematically investigated within 0-1500 heat cycles. An electronic analytical balance with an accuracy of 0.01 mg was used to determine the oxidation weight gain per unit area of ​​the samples, expressed in mg·cm⁻². Three parallel samples were set up for each group of samples, and the final test result was the arithmetic mean of the three parallel samples to eliminate random errors.

[0112] The results of the oxidation weight gain test of Comparative Example 1 and Comparative Example 2 at 1680℃ are shown in Table 2.

[0113] Table 2

[0114] As shown in Table 2, in the early stages of service (within 240 heats), the oxidation weight gain rates of both Comparative Example 1 and Comparative Example 2 were relatively fast. This phenomenon stemmed from the rapid contact and reaction between the sample surface and the high-temperature oxidizing atmosphere inside the furnace, forming an initial oxide film. With the increase in the cumulative number of heats served and the extension of the high-temperature exposure time, the oxidation weight gain rate of Comparative Example 1 gradually slowed down and eventually stabilized, while the oxidation weight gain of Comparative Example 2 showed a continuous linear upward trend. After 1500 heats of continuous service, the oxidation weight gain of Comparative Example 1 was only 5.58 mg·cm⁻², less than 24% of the oxidation weight gain of Comparative Example 2. This fully demonstrates that the coating of the present invention can quickly form a stable and dense passivation protective layer under high-temperature conditions, effectively blocking the contact between the oxidizing atmosphere and the steel substrate, significantly improving the high-temperature oxidation resistance of the oxygen lance cone, and avoiding wall thinning, structural strength deterioration, and sudden service failure caused by continuous oxidation of the substrate.

[0115] III. Verification of the Influence of Coating on the Water-Cooled Heat Transfer Performance of Oxygen Lance To clarify the influence of the coating of this invention on the heat exchange efficiency of the oxygen lance water cooling system, a comparative test of the water cooling heat exchange performance under steady-state conditions was conducted on oxygen lances of the same specifications equipped with conical tubes of Comparative Example 1 and Comparative Example 2.

[0116] This test targeted two sets of 150t converter oxygen lances of identical structure and from the same batch. The two sets of oxygen lances had completely identical conical tube base material, water-cooled flow channel structure, and dimensional parameters, with only the outer surface of the conical tube adopting the technical solutions of Comparative Example 1 and Comparative Example 2, respectively. The test was conducted under stable converter smelting conditions, with the cooling water inlet temperature constantly controlled at 25℃ and the inlet flow rate at 220m³ / h throughout the test. K-type armored thermocouples with an accuracy of ±0.1℃ were used to simultaneously collect the steady-state temperature values ​​of the cooling water inlet and outlet of the two sets of oxygen lances. Each set of conditions was tested 6 times, and the final result was the arithmetic mean of the 6 tests.

[0117] The test results of cooling water temperature parameters for Comparative Example 1 and Comparative Example 2 are shown in Table 3.

[0118] Table 3

[0119] As shown in Table 3, the inlet temperature of the cooling water for both oxygen lances was stably controlled at 25℃. The outlet temperature of the cooling water for Comparative Example 1 was 42℃, resulting in a temperature difference of 17℃ between the inlet and outlet, which was 3℃ higher than that of Comparative Example 2. This result confirms that the coating of this invention did not negatively impact the water-cooling heat exchange performance of the oxygen lance; on the contrary, it effectively improved the heat exchange efficiency of the cooling water and enhanced the water-cooling effect. This is because the coating system of this invention possesses excellent high-temperature thermal conductivity, and the ultra-thin gradient structure design achieves comprehensive protection while fully ensuring the heat exchange efficiency of the oxygen lance cone tube. This overcomes the problem in existing technologies where "protective coatings inevitably reduce the heat exchange performance of the oxygen lance," further ensuring the high-temperature service safety of the oxygen lance while improving the protection performance and service life of the oxygen lance cone tube.

[0120] IV. Coating Forming Compatibility Verification The coating prepared by this invention using atmospheric plasma spraying technology exhibits excellent formability on the variable-diameter curved surface substrate of the oxygen lance cone. The overall structure of the coating is continuous and dense, exhibiting a uniform ceramic morphology. The surface is smooth and flat, free from visible defects such as cracks, pinholes, delamination, and edge curling. The interface between the coating and the substrate is strong, eliminating the risk of poor bonding. It can be fully adapted to the variable-diameter curved surface structure of the oxygen lance cone, meeting the requirements for long-term stable use under the complex operating conditions of converters, including high temperature, high erosion, strong oxidation, and easy slag adhesion.

[0121] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Examples of implementation methods are provided, and any parts not described in detail are common knowledge to those skilled in the art. Those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A coating for the outer tube of a converter oxygen lance, characterized in that: It includes a three-layer gradient structure, consisting of a transition layer, an intermediate layer, and a surface layer from the inside out. The transition layer contains 8-25 wt% Cr, 5-10 wt% Al, 0.3-1.5 wt% Y, 60-85 wt% Ni, and ≤5 wt% Fe elements introduced by diffusion from the matrix. The intermediate layer contains 85-95 wt% ZrO2 and 5-15 wt% MgO. The surface layer contains 65-75 wt% ZrO2 and 25-35 wt% TiO2.

2. The coating for the outer tube of a converter oxygen lance according to claim 1, characterized in that: The intermediate layer also contains 0.3-1.0 wt% Y2O3.

3. The coating for the outer tube of a converter oxygen lance according to claim 1, characterized in that: The surface layer also contains 1-3 wt% SiO2.

4. The coating for the outer tube of a converter oxygen lance according to claim 1, characterized in that: The microstructure of the transition layer is mainly composed of β-NiAl phase, with the remainder containing 0.5-5 vol% AlCr. x Phase, x is 1.0-3.

0.

5. The coating for the outer tube of a converter oxygen lance according to claim 1, characterized in that: The microstructure of the intermediate layer is mainly composed of MgO-stabilized tetragonal ZrO2.

6. The coating for the outer tube of a converter oxygen lance according to claim 1, characterized in that: The microstructure of the surface layer is mainly composed of ZrO2-TiO2 solid solution.

7. The coating for the outer tube of a converter oxygen lance according to claim 1, characterized in that: It is tightly attached to the surface of the oxygen lance outer tube substrate, with a total coating thickness of 0.5-0.9mm, a transition layer thickness of 0.2-0.4mm, an intermediate layer thickness of 0.1-0.3mm, and a surface layer thickness of 0.1-0.3mm.

8. A method for preparing a coating on the outer tube of a converter oxygen lance, characterized in that: Includes the following steps: S1. Pretreatment of oxygen lance outer tube substrate: The seamless steel pipe is processed into shape, and the substrate surface is treated by chemical degreasing and physical rust removal, followed by roughening treatment; S2. Coating material preparation: Prepare powders suitable for atmospheric plasma spraying technology. The transition layer spraying powders include Cr powder, Ni powder, Al powder, and Y2O3 powder, with a powder particle size of 200 mesh. The Cr powder content is 9-29 wt%, Ni powder is 63-89 wt%, Al powder is 6-12 wt%, and Y2O3 powder is 0.3-1.5 wt%. The intermediate layer coating powder includes ZrO2 powder and MgO powder, with a particle size of 200 mesh; wherein, the ZrO2 powder content is 85-95 wt%, and the MgO powder content is 5-15 wt%. The surface coating powder includes ZrO2 powder and TiO2 powder, with a particle size of 200 mesh; the content of ZrO2 powder is 65-75 wt%, and the content of TiO2 powder is 25-35 wt%.

9. The method for preparing a coating for the outer tube of a converter oxygen lance according to claim 8, characterized in that: It also includes the following steps: S3, gradient coating spraying: fix the pretreated substrate to ensure that the substrate is stable and does not shift during the spraying process; spray the substrate surface in sequence according to the order of transition layer-intermediate layer-surface layer, and control the total coating thickness to 0.5-0.9mm.

10. The method for preparing a coating for the outer tube of a converter oxygen lance according to claim 9, characterized in that: It also includes the following steps: S4, Post-treatment: After the spraying is completed, the coating surface is lightly sanded and corrected to remove protrusions, impurities and splatter particles from the coating surface.

Images