A method for laser cladding coating of furnace bottom roller to prevent tumor accumulation

Abstract

The present invention discloses a method for laser cladding of a furnace bottom roller to prevent buildup. This method involves the composite addition of rare earth oxides (Y2O3, CeO2, and La2O3) and a two-dimensional in-situ boron nitride phase to significantly improve the performance of the furnace bottom roller, enhancing its buildup resistance, wear resistance, and self-lubrication properties. A prefabricated layer on the surface of the furnace bottom roller is exposed to a high-power laser beam for laser cladding. After cladding, a uniform and dense coating forms on the surface of the furnace bottom roller, containing dispersed particles of the rare earth oxides (Y2O3, CeO2, and La2O3) and nano-boron nitride phase. The addition of the rare earth oxides significantly increases the density of the coating, while the boron nitride phase enhances the coating's self-lubrication properties. The resulting composite coating significantly improves the hardness, wear resistance, buildup resistance, and self-lubrication properties of the furnace bottom roller, significantly extending its service life and reducing maintenance costs during production. This provides practical value and economic benefits in energy conservation and emission reduction.

Description

Technical Field

[0001] The invention relates to a roller cladding coating method, in particular to a furnace bottom roller anti-tumor laser cladding coating method. Background Art

[0002] The hearth rollers in the continuous annealing furnace are used to transport hot billets, and their operating temperature is between 900 and 1,100°C. During the production process, the oxide scale of the billets will accumulate on the surface of the roller rings. The oxide scale at high temperatures will adhere to the surface of the roller rings, causing nodules on the surface of the roller rings, which will affect the quality of the steel. At present, two types of annealing furnace hearth rollers are used in China, namely cobalt-based materials (Co-based materials) and 50 ) and nickel-based materials (Cr 28 Ni 48 W5). Cobalt-based hearth rollers offer excellent high-temperature oxidation resistance and anti-nodulation properties, but they are relatively expensive. Nickel-based roller rings are less expensive, but they typically experience severe wear, edge collapse, and nodulation within six months of use. To improve the performance and extend the service life of these rollers, researchers employed laser cladding technology to create a coating on the surface of nickel-based hearth roller rings. This coating utilizes high-energy-density laser cladding of a metal-ceramic powder, primarily composed of NiCr-Cr3C, which exhibits excellent heat resistance, oxidation resistance, and wear resistance. Cr3C2, a ceramic phase, exhibits high hardness and excellent hardness stability at high temperatures, while also providing excellent wear resistance. Oxidation in air above 1100°C makes NiCr-Cr3C powder a viable anti-nodulation and high-temperature resistant cladding coating material. However, since NiCr-Cr3C is a carbide phase, the density and wear resistance of laser-clad NiCr-Cr3C coatings still require further improvement.

[0003] Rare earth oxides play multiple roles in the coating microstructure during the laser cladding process. First, their good melting point and thermal stability help reduce the formation of pores and cracks. Second, their dispersion in the coating helps prevent the formation of grain boundaries and improve the coating's density. Furthermore, rare earth oxides form a strengthened interface with the substrate, enhancing the bonding strength between the coating and the substrate. The addition of rare earth oxides can significantly improve the coating's hardness, wear resistance, and corrosion resistance. Boron nitride, with the chemical formula BN, is an important ceramic material. In the field of lubricants, boron nitride is widely used due to its unique properties. Boron nitride has ultra-high hardness similar to that of diamond, maintaining stability under high loads and high pressures, reducing wear. Furthermore, boron nitride has a low coefficient of friction, which can reduce friction and wear by forming an extremely thin boron nitride film. Its high temperature resistance and chemical stability enable it to maintain excellent lubrication properties even in high-temperature and corrosive environments.

[0004] During the laser cladding process, rare earth oxides and boron nitride each play different roles in the laser cladding coating. Rare earth oxides improve the density and chemical stability of the coating, while boron nitride enhances the coating's hardness and wear resistance. Boron nitride's low coefficient of friction allows an extremely thin boron nitride film to form on the coating surface, reducing friction and wear between the coating and the friction surface. This helps improve the coating's lubricity and reduce energy loss and friction and wear. The combined addition of rare earth oxides and boron nitride can enhance the coating's high-temperature stability, allowing it to maintain good performance even in high-temperature environments. Therefore, the use of composite rare earth oxides and in-situ generated boron nitride phases to enhance the performance of furnace bottom roller anti-buildup laser cladding coatings has important technical and economic value. Summary of the Invention

[0005] The object of the present invention is to provide a method for laser cladding coating of furnace bottom rollers to prevent buildup. During the laser cladding process, the method introduces a composite rare earth oxide of Y2O3, CeO2, and La2O3 to further improve the density of the cladding coating, and simultaneously introduces a boron nitride phase in situ. The preparation of boron nitride is completed in one step during the laser cladding process. Ultimately, a uniformly distributed boron nitride nanoparticle phase is generated in the coating material. The low friction coefficient of boron nitride allows an extremely thin boron nitride film to form on the coating surface, thereby reducing friction and wear between the coating and the friction surface. This helps to improve the lubrication properties of the coating and reduce energy loss and friction and wear. Experimental research and analysis have shown that rare earth oxide and boron nitride enhanced laser cladding coatings can significantly improve the wear, collapse, and nodule problems of nickel-based furnace bottom rollers, increase the service life of the furnace bottom rollers, and reduce the cost of spare parts, providing an effective solution for actual production.

[0006] The present invention adopts the following technical solutions:

[0007] A method for laser cladding coating of a furnace bottom roller to prevent buildup, the method is carried out according to the following steps:

[0008] (1) NiCr and Cr3C mixed powder is used as the basic component of the cladding coating;

[0009] (2) uniformly dispersing one or more of Y2O3, CeO2, and La2O3 in the mixed powder of NiCr and Cr3C;

[0010] (3) uniformly dispersing the nano-boron nitride precursor phase in the above-mentioned mixed powder; mixing rare earth oxides Y2O3, CeO2, La2O3, the nano-boron nitride precursor phase, NiCr and Cr3C by spray drying; first dissolving the nano-boron nitride precursor phase in a solvent, the type of solvent being selected according to the characteristics and type of the nano-boron nitride precursor phase; dispersing the dissolved nano-boron nitride precursor with the rare earth oxide mixture, NiCr and Cr3C to form a uniform dispersed phase; and finally performing a spray drying process to obtain a mixed powder;

[0011] (4) NiCr and Cr3C powders mixed with rare earth powder and nano boron nitride precursor phase are sprayed on nickel-based (Cr 28 Ni 48 W5) on the finished hearth roller base material of the roller ring;

[0012] (5) Through laser irradiation, an anti-tumor activation cladding coating is formed on the surface of the Ni-based furnace bottom roller ring.

[0013] In the method for forming a furnace bottom roller anti-tumor laser cladding coating, the mass ratio of the total weight of Y2O3, CeO2, and La2O3 to the mixed powder of NiCr and Cr3C is (0.1~1):100.

[0014] In the method for forming a furnace bottom roller anti-tumor laser cladding coating, the nano-boron nitride precursor phase is a compound that generates two-dimensional boron nitride in situ under laser irradiation, the boron source is one or a mixture of two or more of boric acid, elemental boron, and boron oxide, and the nitrogen source is high-purity nitrogen.

[0015] In the method for forming a furnace bottom roller anti-tumor laser cladding coating, the weight ratio of the total weight of the nano-boron nitride precursor phase to the weight ratio of the mixed powder of NiCr and Cr3C is (0.1-3):100.

[0016] In the method for laser cladding coating of a furnace bottom roller for preventing buildup, the spray drying process is a centrifugal spray or pressure spray drying process, the inlet temperature is 50-350°C, and the outlet temperature is 50-150°C; in the method for laser cladding coating of a furnace bottom roller for preventing buildup, the solvent for dissolving the nano-boron nitride precursor phase is one of water, methanol, and ethanol, or a mixture of two or more thereof;

[0017] The method for laser cladding coating of a furnace bottom roller to prevent buildup is described. During the laser cladding, the laser power is 1000~4000W, the welding speed is 1~10mm / s, the powder feeding rate is 1~6g / min, the spot diameter is 2~8mm, and the defocus amount is: +2~5mm.

[0018] The design concept of this invention is to propose a method for preparing a laser cladding coating for a furnace bottom roller by introducing a composite rare earth oxide of Y2O3, CeO2, and La2O3 to further improve the density of the cladding coating, while also in-situ introducing a boron nitride reinforcement phase. In-situ nano-boron nitride reinforcement refers to the process of uniformly dispersing a boron nitride precursor in NiCr-Cr3C powder through appropriate pretreatment measures during the laser cladding process, followed by uniformly dispersing the composite rare earth oxide within the mixed oxide. A spray drying process is then used to obtain a uniformly mixed particle of the rare earth oxides Y2O3, CeO2, La2O3, a nano-boron nitride precursor phase, and NiCr and Cr3C. Finally, the preparation of the boron nitride nanophase and the doping of the rare earth composite oxide are completed in a single step during the laser cladding process.

[0019] The advantages and beneficial effects of the present invention are:

[0020] 1. The present invention improves the density, wear resistance, high temperature stability and oxidation resistance of the furnace bottom roller laser cladding coating by introducing composite rare earth oxides and in-situ nano-boron nitride phases, reduces the friction coefficient, extends the equipment life, and improves performance and reliability. Before the introduction of appropriate amounts of composite rare earth oxides and in-situ nano-boron nitride phases, the microhardness was 701HV, and after the modification, it was 820HV. The porosity was reduced from 2.77±0.3% to 2.40±0.2

[0021] 2. The NiCr-Cr3C coating, reinforced with composite rare earth oxides and in-situ nano-boron nitride, effectively improves the service life of the hearth rollers. The manufactured product has been in continuous production with a service life exceeding one year. During this period, the hearth roller rings showed no signs of scale buildup or significant wear, and no cracking or flaking of the cladding coating. This more than doubled the service life of the nickel-based hearth rollers compared to the original coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the surface morphology of the NiCr-Cr3C laser cladding coating in Example 1 of the present invention;

[0023] Figure 2 This is the surface morphology of the NiCr-Cr3C-rare earth composite oxide-boron nitride coating in Example 1 of the present invention;

[0024] Figure 3 The surface hardness of the NiCr-Cr3C laser cladding coating and the NiCr-Cr3C-rare earth composite oxide-boron nitride coating in Example 1 of the present invention and Comparative Example 1 is compared;

[0025] Figure 4The porosity comparison between the NiCr-Cr3C laser cladding coating and the NiCr-Cr3C-rare earth composite oxide-boron nitride coating in Example 1 of the present invention and Comparative Example 1 is shown. Implementation Method

[0026] The present invention will be described in detail below with reference to the embodiments shown in the accompanying drawings.

[0027] Figure 1 This is the surface morphology of the NiCr-Cr3C laser cladding coating in Example 1 of the present invention;

[0028] Figure 2 This is the surface morphology of the NiCr-Cr3C-rare earth composite oxide-boron nitride coating in Example 1 of the present invention;

[0029] Comparing the two reveals that during the spraying process, the low-melting-point NiCr particles embed into the high-melting-point, high-hardness Cr3C particles as they rapidly cool and solidify on the substrate surface, creating pores at the coating interface. The addition of the Y2O3-La2O3-CeO2 composite rare earth oxide and the in-situ generated boron nitride phase significantly reduces the grain size of the composite coating, making the NiCr phase more uniformly distributed and, in combination with the Cr3C, denser. The reinforcing phase refines the coating microstructure. During crystallization, it increases the number of crystal nuclei while inhibiting grain growth, resulting in a more uniform coating microstructure.

[0030] Figure 3 This figure compares the surface hardness of a NiCr-Cr3C laser-clad coating and a NiCr-Cr3C-rare earth composite oxide-boron nitride coating in Example 1 and Comparative Example 1. Before introducing the appropriate amount of composite rare earth oxide and in-situ nano-boron nitride phase, the microhardness was 701 HV. After modification, the hardness peaked at 820 HV.

[0031] Figure 4 This figure compares the porosity of the NiCr-Cr3C laser-clad coating and the NiCr-Cr3C-rare earth composite oxide-boron nitride coating in Example 1 and Comparative Example 1. Before the introduction of the appropriate amount of composite rare earth oxide and in-situ nano-boron nitride phase, the porosity was 2.77±0.3%. After the reinforcing phase was added, the porosity decreased to 2.40±0.2.

[0032] In practice, the present invention proposes significantly improving the performance of hearth rollers by utilizing the combined addition of rare earth oxides Y2O3, CeO2, and La2O3, along with a two-dimensional in-situ boron nitride phase, enhancing their anti-buildup, wear resistance, and self-lubricating properties. The experimental methods described in the following examples are conventional unless otherwise noted. Reagents and materials are commercially available unless otherwise specified.

[0033] Example 1

[0034] A method for preparing a Y2O3, CeO2, La2O3-boron nitride modified NiCr-Cr3C laser cladding coating for a furnace bottom roller comprises the following steps:

[0035] Step 1: Weighing and mixing

[0036] (1) Take 10 g of boric acid H3BO3 and dissolve it in 10,000 g of distilled water to form a uniform mixed solution;

[0037] (2) Take 15 g of a mixed oxide of Y2O3, CeO2, and La2O3, with the weight ratio of Y2O3, CeO2, and La2O3 being: Y2O3:CeO2:La2O3=1:1:1, and add it to the above mixed solution;

[0038] (3) Take 2000g of commercial NiCr-Cr3C alloy powder, add it to the above mixed solution, and disperse it by ultrasonication;

[0039] Step 2: Spray Drying

[0040] A mixed solution of NiCr-Cr3C alloy powder, composite rare earth oxide, and boric acid was dried using a spray drying process. The drying process was a centrifugal spray process with an inlet temperature of 220°C and an outlet temperature of 110°C. The resulting powder had a diameter of 10-60 μm.

[0041] Step 3: Laser Cladding

[0042] (1) Use a grinding wheel to remove nickel-based materials (Cr 28 Ni 48 W5) The oxidation layer on the surface of the furnace bottom roller is then polished with gauze. After polishing, the base surface of the furnace bottom roller is cleaned with alcohol. (2) The intersection of the raw material powder and the laser is transferred to the workpiece using a laser to prepare a laser cladding layer. (3) The laser cladding technology is used to adjust the process parameters for surface repair. During laser cladding, the laser power is 2000W, the welding speed is 2mm / s, the powder feed rate is 2g / min, the spot diameter is 4mm, and the defocus is +2mm.

[0043] Step 4: Sample post-processing

[0044] The furnace bottom roller surface is machined and polished using a mechanical automatic grinding and polishing machine until the surface meets the required accuracy for use, obtaining a surface cladding layer with excellent performance. The resulting coating thickness is 500μm. Example 2

[0045] Compared with Example 1, Example 2 increases the proportion of composite rare earth oxide. The proportions are as follows:

[0046] Step 1: Weighing and mixing

[0047] (1) Take 10 g of boric acid and dissolve it in 10,000 g of distilled water to form a uniform mixed solution;

[0048] (2) Take 30 g of a mixed oxide of Y2O3, CeO2, and La2O3, with the weight ratio of Y2O3, CeO2, and La2O3 being: Y2O3:CeO2:La2O3=1:1:1, and add it to the above mixed solution;

[0049] (3) Take 2000g of commercial NiCr-Cr3C alloy powder, add it to the above mixed solution, and disperse it by ultrasonication;

[0050] The remaining steps are the same as those in Example 1. Example 3

[0051] Compared with Example 1, Example 3 increases the proportion of the boron nitride phase. The specific steps are as follows:

[0052] Step 1: Weighing and mixing

[0053] (1) Take 20 g of boric acid and dissolve it in 10,000 g of distilled water to form a uniform mixed solution;

[0054] (2) Take 15 g of a mixed oxide of Y2O3, CeO2, and La2O3, with the weight ratio of Y2O3, CeO2, and La2O3 being: Y2O3:CeO2:La2O3=1:1:1, and add it to the above mixed solution;

[0055] (3) Take 2000g of commercial NiCr-Cr3C alloy powder, add it to the above mixed solution, and disperse it by ultrasonication;

[0056] The remaining steps are the same as those in Example 1.

[0057] Comparative Example 1

[0058] In this comparative example, instead of using composite rare earth oxide and boron nitride phase for reinforcement, only NiCr-Cr3C laser cladding coating was used to modify the nickel-based hearth roller. The steps are as follows:

[0059] Step 1: Laser Cladding

[0060] (1) Use a grinding wheel to remove nickel-based materials (Cr 28 Ni 48W5) The oxide layer on the surface of the furnace bottom roller is then polished with gauze. After polishing, the base surface of the furnace bottom roller is cleaned with alcohol. (2) The intersection of NiCr-Cr3C powder and laser is transferred to the workpiece by laser to prepare the cladding layer. (3) Laser cladding technology is used to adjust the process parameters for surface repair. During laser cladding, the laser power is 2000W, the welding speed is 2mm / s, the powder feed rate is 2g / min, the spot diameter is 4mm, and the defocus amount is +2mm. Step 2: Sample post-processing

[0061] The surface of the furnace bottom roller was machined and polished by a mechanical automatic grinding and polishing machine until the surface met the use accuracy requirements, obtaining a surface cladding layer with excellent performance. The obtained coating thickness was 500 μm. The results showed that the density, wear resistance, high-temperature stability, performance and reliability of the nickel-based furnace bottom roller laser cladding coating of the present invention were significantly improved. Before the introduction of the composite rare earth oxide and in-situ nano-boron nitride phase, the microhardness was 701HV, and after the modification, it was 820HV. The porosity was reduced from 2.77±0.3% to 2.40±0.2. This method is compatible with the traditional laser cladding process and has good economic benefits and operability.

[0062] The surface morphology of the laser-clad coatings was analyzed using a FEI NOVA 430 scanning electron microscope. The hardness of the specimens was measured using an HV-1000 microhardness tester. Fifteen sets of data were measured at different points on the cladding layer, and the average value was calculated as the surface microhardness value. Two test furnace bottom rollers, laser-clad with NiCr-Cr3C and rare earth-boron nitride-modified NiCr-Cr3C coatings, were tested for high-temperature wear resistance, oxidation resistance, and anti-nodulation properties.

[0063] Table 1 shows the inspection results of furnace bottom rollers (NiCr-Cr3C laser cladding coating and NiCr-Cr3C-rare earth oxide-boron nitride coating) after one year of use in the 1050°C high-temperature range. Compared to the uncladding, the addition of rare earth oxide and boron nitride reinforcements showed less wear and stretching on the roller surface, with some minor sticking to the steel, which was easily removed with gentle vibration. The roller dimensions showed slight variations within normal limits. The laser cladding coating texture remained visible on the roller surface, and the cladding remained largely intact. The cladding exhibited a cast structure with strong bonding and no signs of burnout or flaking. Slight oxide scale adhered to certain areas during use, but this was easily removed with vibration. The roller's wear resistance, oxidation resistance, and anti-bulking properties were significantly improved. Uncoated nickel-based rollers showed noticeable wear and flaking after just three months of use.

[0064] Table 1 shows the usage test conditions of the high temperature section of three furnace bottom rollers;

[0065] 。

Claims

1. A method for laser cladding coating of furnace bottom roller to prevent buildup, characterized in that: The method is carried out according to the following steps: (1) NiCr and Cr3C mixed powder is used as the basic component of the cladding coating; (2) uniformly dispersing one or more of Y2O3, CeO2, and La2O3 in a mixed powder of NiCr and Cr3C; (3) uniformly dispersing the nano-boron nitride precursor phase in the above-mentioned mixed powder; the mixed rare earth oxides Y2O3, CeO2, La2O3, the nano-boron nitride precursor phase and NiCr and Cr3C are mixed by spray drying; the total weight ratio of Y2O3, CeO2, La2O3 to the mass ratio of NiCr and Cr3C mixed powder is (0.1~1):100; The nano-boron nitride precursor phase is a mixture of one or more of boric acid, elemental boron, and boron oxide. The nano-boron nitride precursor phase is first dissolved in a solvent, the type of solvent being selected based on the characteristics and type of the nano-boron nitride precursor phase; the dissolved nano-boron nitride precursor is dispersed with a rare earth oxide mixture and NiCr and Cr3C to form a uniform dispersed phase; and finally, a spray drying process is performed to obtain a mixed powder; the weight ratio of the total weight of the nano-boron nitride precursor phase to the weight of the NiCr and Cr3C mixed powder is (0.1-3):100; (4) spraying NiCr and Cr3C powders mixed with rare earth powder and nano-boron nitride precursor phase onto the finished furnace bottom roller substrate of the nickel-based roller ring; (5) Through laser irradiation, an anti-tumor activation cladding coating is formed on the surface of the Ni-based furnace bottom roller ring.

2. The method for laser cladding coating of furnace bottom roller for preventing buildup according to claim 1, characterized in that: The spray drying process is a centrifugal spray or pressure spray drying process, with an inlet temperature of 50-350°C and an outlet temperature of 50-150°C.

3. The method for laser cladding coating of furnace bottom roller for preventing buildup according to claim 1, characterized in that: The solvent is one of water, methanol, and ethanol, or a mixture of two or more thereof.

4. The method for laser cladding coating of furnace bottom roller for preventing buildup according to claim 1, characterized in that: During the laser cladding, the laser power is 1000-4000 W, the welding speed is 1-10 mm / s, the powder feeding amount is 1-6 g / min, the spot diameter is 2-8 mm, and the defocus amount is +2-5 mm.

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