Nickel-based alloys, nickel-based alloy slurries, bimetallic metallurgical composite tube blanks and their preparation methods and applications

Abstract

This invention discloses a nickel-based alloy, a nickel-based alloy slurry, a bimetallic metallurgical composite tube blank, and their preparation methods and applications, relating to the field of metal composite materials technology. The nickel-based alloy mainly comprises the following chemical components: C≤0.08%, Si 0.20%~0.60%, P≤0.025%, S≤0.015%, Al 0.015%~0.035%, Mn 0.40%~0.70%, Cr 20.0%~25.0%, Mo 1.0%~3.0%, Ni 41.0%~45.0%, Nb 0.8%~1.2%. When preparing the bimetallic metallurgical composite tube blank using a metallurgical composite method, this nickel-based alloy serves as an intermediate transition layer, forming an efficient compositional transition zone and a carbon diffusion barrier, effectively preventing carbon migration and interfacial oxidation, completely preventing the formation of brittle chromium-rich carbides at the interface, and improving the interfacial bonding strength.

Description

Technical Field

[0001] This invention relates to the field of metal composite materials technology, and in particular to nickel-based alloys, nickel-based alloy slurries, bimetallic metallurgical composite tube blanks, their preparation methods and applications. Background Technology

[0002] In the harsh environments of industries such as petrochemicals, coal chemicals, and power generation, heat exchanger tube bundles undergo long-term service in high-temperature, high-pressure, and complex corrosive media (such as those containing Cl). - Under conditions such as H2S, CO2, and organic acids, heat exchangers face multiple failure risks, including corrosion, erosion, stress corrosion cracking, and high-temperature creep. The entire heat exchange tube is manufactured using high-grade corrosion-resistant alloys (such as NS1402 (Incoloy 825) iron-nickel-based alloy), resulting in extremely high material costs.

[0003] Using bimetallic composite pipes is an effective way to balance corrosion resistance and economy. Existing technologies, such as mechanical expansion bonding, have low bond strength (typically <100 MPa), posing risks of high interfacial thermal resistance and delamination failure during use. Traditional metallurgical composite methods, such as hot rolling and hot extrusion, when directly bonding dissimilar metals with significantly different physicochemical properties (such as chromium-molybdenum steel and austenitic stainless steel), result in the formation of continuous chromium carbides (such as Cr) at the interface due to the intense diffusion of carbon from the steel side to the stainless steel side during the high-temperature bonding process. 23 C6) A brittle layer leads to a sharp decrease in interfacial toughness, insufficient bonding strength, and is prone to interfacial delamination under thermal cycling conditions.

[0004] Therefore, developing a composite pipe manufacturing technology that can effectively block carbon diffusion, achieve high-strength metallurgical bonding of dissimilar metals, and is applicable to various combinations of heat-resistant steels and corrosion-resistant alloys is of great significance for improving the safety, reliability, and economy of key equipment.

[0005] Therefore, existing technologies still need to be improved and developed. Summary of the Invention

[0006] Based on the shortcomings of the prior art, the purpose of this invention is to provide nickel-based alloys, nickel-based alloy slurries, bimetallic metallurgical composite tube blanks, their preparation methods and applications, aiming to solve the problem of insufficient interfacial bonding strength when directly combining dissimilar metals with large differences in physicochemical properties using existing metallurgical composite methods such as hot rolling and hot extrusion.

[0007] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a nickel-based alloy, wherein, by weight percentage, the nickel-based alloy comprises the following chemical composition: C≤0.08%, Si 0.20%~0.60%, P≤0.025%, S≤0.015%, Al 0.015%~0.035%, Mn0.40%~0.70%, Cr 20.0%~25.0%, Mo 1.0%~3.0%, Ni 41.0%~45.0%, Nb 0.8%~1.2%; balance Fe and unavoidable impurities.

[0008] Optionally, the nickel-based alloy further includes one or more of the following chemical components in weight percentage: V 0.5%~0.8%, Ti 0.3%~0.6%, Cu 0.8%~1.5%.

[0009] In a second aspect, the present invention provides a nickel-based alloy slurry, wherein the nickel-based alloy slurry comprises nickel-based alloy powder and an organic carrier, the organic carrier comprising an organic solvent; The nickel-based alloy powder comprises the chemical composition of the nickel-based alloy described above in this invention.

[0010] Optionally, the mass ratio of the nickel-based alloy powder to the organic carrier is (72-78):(22-28). The organic carrier comprises the following components in parts by weight: The ingredients include 3.5 to 4.5 parts of binder, 1.0 to 1.5 parts of plasticizer, 0.3 to 0.6 parts of rheology modifier, and 93.4 to 95.2 parts of solvent.

[0011] Optionally, the binder comprises polyvinyl butyral, the plasticizer comprises dibutyl phthalate, the rheology modifier comprises ethyl cellulose, and the solvent comprises terpineol.

[0012] A third aspect of the present invention provides a bimetallic metallurgical composite tube blank, wherein the bimetallic metallurgical composite tube blank includes an outer base tube, an intermediate transition layer and an inner liner tube arranged coaxially from the outside to the inside, and the outer base tube and the inner liner tube are metallurgically bonded through the intermediate transition layer. The outer base tube is made of 15CrMoG steel, 12Cr1MoVG steel or 12Cr2MoG steel. The intermediate transition layer comprises the nickel-based alloy described above in this invention; The inner lining tube is made of S30408 ​​(304) austenitic stainless steel, S31603 (316L) austenitic stainless steel or NS1402 (Incoloy 825) corrosion-resistant alloy.

[0013] A fourth aspect of the present invention provides a method for preparing the bimetallic metallurgical composite tube blank as described above, comprising the following steps: S1. Provide an outer base tube, an inner liner tube, and a nickel-based alloy slurry, wherein the nickel-based alloy slurry is the nickel-based alloy slurry of the present invention as described above; S2. The nickel-based alloy slurry is coated on the inner surface of the outer base tube and dried to form a coating, resulting in an outer base tube with a coating on the inner surface. The inner liner is placed in the outer base tube with the coating on the inner surface. Then, the two ends of the inner liner and the outer base tube are sealed and vacuumed to form an assembled tube body. Alternatively, the nickel-based alloy slurry is coated onto the outer surface of the inner liner tube, dried to form a coating, resulting in an inner liner tube with a coated outer surface. The inner liner tube with the coated outer surface is placed in the outer base tube, and then the two ends of the inner liner tube and the outer base tube are sealed and vacuumed to form an assembled tube body. Alternatively, the nickel-based alloy slurry is coated onto the inner surface of the outer base tube and the outer surface of the inner liner tube, respectively. After drying, a coating is formed, resulting in an outer base tube with a coating on the inner surface and an inner liner tube with a coating on the outer surface. The inner liner tube with a coating on the outer surface is placed inside the outer base tube with a coating on the inner surface. Then, the two ends of the inner liner tube and the outer base tube are sealed and vacuumed to form an assembled tube body. S3. Under a protective atmosphere, the assembled tube body is kept at 1150-1250℃ for a first preset time, and then hot-extruded at 1100-1200℃ with an extrusion ratio of (4.5-6.5):1. Then, it is cooled by water spraying, and the cooling rate in the temperature range of 900℃ to 400℃ is not less than 40℃ / s. After being cooled by water spraying to 400℃, it is air-cooled to room temperature to obtain the bimetallic metallurgical composite tube blank.

[0014] Optionally, in step S1, the surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner liner tube is 6.3–10.0 μm; and / or, In step S2, before sealing and welding the two ends of the inner liner tube and the outer base tube and drawing a vacuum, the process also includes baking at 250-300°C for 1-2 hours. The inner liner and the outer base tube are sealed at both ends and a vacuum is drawn to ensure that the vacuum level of the annular cavity formed between the inner liner and the outer base tube is no greater than 5.0 × 10⁻⁶. -3 Pa.

[0015] Optionally, when the unit of the first preset time is min and the unit of the total wall thickness of the assembled tube is mm, the numerical relationship between the first preset time and the total wall thickness of the assembled tube is as follows: First preset time = total wall thickness of assembled tube × (1.5~2.0).

[0016] In a fifth aspect, the present invention provides the application of the bimetallic metallurgical composite tube blank as described above, or the bimetallic metallurgical composite tube blank prepared by the preparation method described above, in the preparation of heat exchange tubes.

[0017] Beneficial Effects: When preparing bimetallic composite tube blanks using metallurgical composite methods such as hot rolling and hot extrusion, the nickel-based alloy provided by this invention can serve as an intermediate transition layer between the outer base tube and the inner liner tube, which have significantly different compositions. This intermediate transition layer, with a high-nickel austenitic structure as its matrix, undergoes superplastic deformation at the high temperature of hot extrusion, filling the microscopic voids at the interface and promoting close contact. The high nickel content exhibits excellent crystal structure compatibility and a low difference in thermal expansion coefficients with the austenitic stainless steel or nickel-based corrosion-resistant alloy of the inner liner tube. Furthermore, the strong carbide-forming elements (such as Nb) in the intermediate transition layer act as efficient carbon traps, preferentially capturing and fixing carbon atoms diffusing from the outer base tube side, forming fine, stable MC-type carbides (such as NbC). This constructs a carbon diffusion barrier within the intermediate transition layer, effectively preventing further migration of carbon atoms to the inner liner tube side, and completely avoiding the formation of embrittlement-causing chromium-rich carbides (Cr) at the interface or inner liner tube side. 23 C6) Continuous layer. Therefore, the nickel-based alloy provided by this invention serves as an intermediate transition layer, forming an efficient compositional transition zone and carbon diffusion barrier, effectively preventing carbon migration and interfacial oxidation, completely preventing the formation of brittle chromium-rich carbides at the interface, improving interfacial bonding strength, and ensuring the toughness and stability of the interface under high temperature and thermal cycling. The interfacial bonding strength of the bimetallic metallurgical composite tube blank prepared using the nickel-based alloy provided by this invention as an intermediate transition layer is higher than 300 MPa. Detailed Implementation

[0018] This invention provides nickel-based alloys, nickel-based alloy slurries, bimetallic metallurgical composite tube blanks, their preparation methods, and applications. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0020] If the embodiments of the present invention involve descriptions such as "first" or "second", such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0021] This invention provides a nickel-based alloy, wherein the nickel-based alloy comprises the following chemical composition by mass percentage: C≤0.08%, Si 0.20%~0.60%, P≤0.025%, S≤0.015%, Al 0.015%~0.035%, Mn0.40%~0.70%, Cr 20.0%~25.0%, Mo 1.0%~3.0%, Ni 41.0%~45.0%, Nb 0.8%~1.2%; balance Fe and unavoidable impurities.

[0022] This invention also provides another nickel-based alloy, which comprises the following chemical composition: C≤0.08%, Si 0.20%~0.60%, P≤0.025%, S≤0.015%, Al 0.015%~0.035%, Mn 0.40%~0.70%, Cr 20.0%~25.0%, Mo 1.0%~3.0%, Ni 41.0%~45.0%, Nb 0.8%~1.2%, with the balance being Fe and unavoidable impurities; and including one or more of the following chemical components in mass percentage: V 0.5%~0.8%, Ti 0.3%~0.6%, Cu 0.8%~1.5%.

[0023] When preparing bimetallic composite tube blanks using metallurgical composite methods such as hot rolling and hot extrusion, the nickel-based alloy provided by this invention can serve as an intermediate transition layer between the outer base tube and the inner liner tube, which have significantly different compositions. This intermediate transition layer, with a high-nickel austenitic structure as its matrix, undergoes superplastic deformation at the high temperature of hot extrusion, filling the microscopic voids at the interface and promoting close contact. The high nickel content exhibits excellent crystal structure compatibility and a low difference in thermal expansion coefficients with the austenitic stainless steel or nickel-based corrosion-resistant alloy of the inner liner tube. Furthermore, the strong carbide-forming elements (such as Nb) in the intermediate transition layer act as efficient carbon traps, preferentially capturing and fixing carbon atoms diffusing from the outer base tube side, forming fine, stable MC-type carbides (such as NbC). This constructs a carbon diffusion barrier within the intermediate transition layer, effectively preventing further migration of carbon atoms to the inner liner tube side and completely avoiding the formation of embrittlement-causing chromium-rich carbides (Cr) at the interface or inner liner tube side. 23 (C6) Continuous layer. Therefore, the nickel-based alloy provided by this invention serves as an intermediate transition layer, forming an efficient compositional transition zone and carbon diffusion barrier, effectively preventing carbon migration and interfacial oxidation, and completely preventing the formation of brittle chromium-rich carbides at the interface, ensuring the toughness and stability of the interface under high temperature and thermal cycling. The interfacial bonding strength of the bimetallic metallurgical composite tube blank prepared using the nickel-based alloy provided by this invention as an intermediate transition layer is higher than 300 MPa.

[0024] The functions of each element are as follows: Nickel (Ni, 41.0%–45.0%): Matrix and core element. Provides excellent plasticity, toughness, and high-temperature structural stability; infinitely miscible with iron (Fe), serving as a crucial bridge connecting the outer base tube (carbon steel) and the inner liner (corrosion-resistant alloy); high nickel content significantly reduces the activity and diffusion rate of carbon in austenite, thus inhibiting carbon migration.

[0025] Chromium (Cr, 20.0%–25.0%): A key functional element. It enhances the oxidation and corrosion resistance of the intermediate transition layer.

[0026] Molybdenum (Mo, 1.0%–3.0%): A solid solution strengthening and corrosion resistance element. Solid solution strengthening significantly improves the high-temperature strength and creep resistance of the intermediate transition layer; enhances the corrosion resistance of the intermediate transition layer in reducing acidic media; and helps to refine the microstructure of the diffusion layer.

[0027] Niobium (Nb, 0.8%–1.2%): A core microalloying element. A strong carbide-forming element (with an extremely strong affinity for carbon), it preferentially forms fine, thermally stable NbC particles. These particles strongly pin grain boundaries and dislocations, effectively preventing grain growth in the diffusion reaction zone at high temperatures, thus contributing to the acquisition of high-strength, highly thermally stable interfaces.

[0028] Aluminum (Al, 0.015%–0.035%): Deoxidizer. It forms an extremely thin Al2O3 film during the initial stages of powder preparation and preheating, protecting the powder surface. Under high pressure during hot extrusion, this film ruptures, exposing a fresh, active metal surface and promoting metallurgical bonding.

[0029] Silicon (Si) and manganese (Mn): Deoxidation and solid solution strengthening elements that improve alloy fluidity and help increase strength.

[0030] Optional elements vanadium (V, 0.5%–0.8%) and titanium (Ti, 0.3%–0.6%): similar to Nb, as complementary strong carbonitride forming elements, providing additional precipitation strengthening and grain refinement effects, and further optimizing interface properties.

[0031] Optional element: Copper (Cu, 0.8%–1.5%): Specific suitable element. Added when the inner liner is NS1402 (a Cu-containing iron-nickel based alloy). The addition of Cu can lower the solidus temperature of the intermediate transition layer alloy, improve its plasticity and fluidity at hot working temperatures, make its thermophysical properties closer to NS1402, reduce interfacial residual stress, and promote homogenization and diffusion of the composition.

[0032] This invention also provides a nickel-based alloy slurry, wherein the nickel-based alloy slurry comprises nickel-based alloy powder and an organic carrier, and the organic carrier comprises an organic solvent; The nickel-based alloy powder comprises the chemical composition of the nickel-based alloy described above. The nickel-based alloy powder is prepared by vacuum induction melting gas atomization (VIGA). The atomizing gas pressure is 4–6 MPa (e.g., 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa, or 6 MPa), and the melt superheat is 200–300°C (e.g., 200°C, 220°C, 250°C, 280°C, or 300°C). The particle size of the prepared nickel-based alloy powder is -150 mesh to +400 mesh (i.e., ≤106 μm and ≥38 μm), wherein the proportion of -200 mesh (≤74 μm) powder is not less than 70%. The oxygen content of the nickel-based alloy powder is not higher than 200 ppm.

[0033] The "-" in -150 mesh indicates that the particles can pass through the sieve of that mesh size, meaning the particle size is smaller than the sieve aperture. The "+" in +400 mesh indicates that the particles cannot pass through the sieve of that mesh size, meaning the particle size is larger than the sieve aperture.

[0034] In some embodiments, the mass ratio of the nickel-based alloy powder to the organic carrier is (72-78):(22-28). The organic carrier comprises the following components in parts by weight: The ingredients include 3.5 to 4.5 parts of binder, 1.0 to 1.5 parts of plasticizer, 0.3 to 0.6 parts of rheology modifier, and 93.4 to 95.2 parts of solvent.

[0035] Specifically, the preparation method of the nickel-based alloy slurry involves mixing the components of the above-mentioned organic carrier and stirring them in a water bath at 60-70°C until completely dissolved to form a uniform, transparent, viscous liquid, i.e., the organic carrier. Then, the nickel-based alloy powder and the organic carrier are mixed according to the above proportions and placed in a planetary ball mill, where they are ball-milled at 150-250 rpm for 3-5 hours to form a uniform, stable, and thixotropic paste, i.e., the nickel-based alloy slurry.

[0036] In some embodiments, the binder comprises polyvinyl butyral, the plasticizer comprises dibutyl phthalate, the rheology modifier comprises ethyl cellulose, and the solvent comprises terpineol.

[0037] This invention also provides a bimetallic metallurgical composite tube blank, wherein the bimetallic metallurgical composite tube blank includes an outer base tube, an intermediate transition layer and an inner liner tube arranged coaxially from the outside to the inside, and the outer base tube and the inner liner tube are metallurgically bonded through the intermediate transition layer; The outer base tube is made of 15CrMoG steel, 12Cr1MoVG steel or 12Cr2MoG steel. The 15CrMoG steel comprises the following chemical composition by mass percentage: C 0.12%~0.18%, Si 0.17%~0.37%, Mn 0.40%~0.70%, P≤0.025%, S≤0.015%, Cr0.80%~1.10%, Mo 0.40%~0.55%, Al 0.015%~0.035%, N≤0.005%, O≤0.002%, H≤0.00015%, with the balance being Fe and unavoidable impurities.

[0038] The 12Cr1MoVG steel comprises the following chemical composition in weight percentages: C 0.08%~0.15%, Si 0.17%~0.37%, Mn 0.40%~0.70%, P≤0.025%, S≤0.010%, Cr0.90%~1.20%, Mo 0.25%~0.35%, V 0.15%~0.30%, Al 0.015%~0.035%, N≤0.005%, O≤0.002%, H≤0.00015%, with the balance being Fe and unavoidable impurities.

[0039] The 12Cr2MoG steel comprises the following chemical composition in weight percentages: C 0.08%~0.15%, Si 0.17%~0.37%, Mn 0.40%~0.60%, P≤0.025%, S≤0.015%, Cr 2.00%~2.50%, Mo 0.90%~1.13%, Al 0.015%~0.035%, N≤0.005%, O≤0.002%, H≤0.00015%, with the balance being Fe and unavoidable impurities.

[0040] The intermediate transition layer comprises the nickel-based alloy described above in this invention; The inner lining tube is made of S30408 ​​(304) austenitic stainless steel, S31603 (316L) austenitic stainless steel or NS1402 (Incoloy 825) corrosion-resistant alloy.

[0041] The S30408 ​​(304) austenitic stainless steel comprises the following chemical composition in weight percentages: C≤0.080%, Cr 18.0%~20.0%, Ni 8.0%~11.0%, Mn≤2.0%, Si≤1.0%, P≤0.025%, S≤0.015%, Al 0.015%~0.035%, N≤0.015%, O≤0.003%, H≤0.0002%, with the balance being Fe and unavoidable impurities.

[0042] The S31603 (316L) austenitic stainless steel comprises the following chemical composition in weight percentages: C≤0.030%, Cr 16.0%~18.0%, Ni 10.0%~14.0%, Mo 2.0%~3.0%, Mn≤2.0%, Si≤1.0%, P≤0.025%, S≤0.015%, Al 0.015%~0.035%, N≤0.015%, O≤0.003%, H≤0.0002%, with the balance being Fe and unavoidable impurities.

[0043] The NS1402 (825) corrosion-resistant alloy comprises the following chemical composition in weight percentages: C≤0.05%, Si≤0.5%, Mn≤1.0%, P≤0.030%, S≤0.030%, Ni 38%~46%, Cr 19.5%~23.5%, Mo 2.5%~3.5%, Cu 1.5%~3.0%, Ti 0.6%~1.2%, Al≤0.20%, N≤0.010%, H≤0.0002%, O≤0.003%, with the balance being Fe and unavoidable impurities.

[0044] The coating formed by the nickel-based alloy powder provided by this invention can effectively prevent carbon migration and interfacial oxidation, and can form a high-quality metallurgical bonding interface with a shear strength ≥300MPa between 15CrMoG, 12Cr1MoVG, and 12Cr2MoG low-alloy heat-resistant steels and S30408 ​​austenitic stainless steel, S31603 austenitic stainless steel, and NS1402 corrosion-resistant alloy materials. This method is particularly suitable for manufacturing high-strength bimetallic metallurgical composite tube blanks for heat exchanger tubes with an outer diameter of 100–510 mm and a wide range of wall thicknesses. The interface bonding is uniform and stable, providing high-quality raw materials for the subsequent production of high-performance bimetallic metallurgical composite heat exchanger tubes.

[0045] This invention also provides a method for preparing the bimetallic metallurgical composite tube blank as described above, comprising the following steps: S1. Provide an outer base tube, an inner liner tube, and a nickel-based alloy slurry, wherein the nickel-based alloy slurry is the nickel-based alloy slurry of the present invention as described above; S2. The nickel-based alloy slurry is coated on the inner surface of the outer base tube and dried to form a coating, resulting in an outer base tube with a coating on the inner surface. The inner liner is placed in the outer base tube with the coating on the inner surface. Then, the two ends of the inner liner and the outer base tube are sealed and vacuumed to form an assembled tube body. Alternatively, the nickel-based alloy slurry is coated onto the outer surface of the inner liner tube, dried to form a coating, resulting in an inner liner tube with a coated outer surface. The inner liner tube with the coated outer surface is placed in the outer base tube, and then the two ends of the inner liner tube and the outer base tube are sealed and vacuumed to form an assembled tube body. Alternatively, the nickel-based alloy slurry is coated onto the inner surface of the outer base tube and the outer surface of the inner liner tube, respectively. After drying, a coating is formed, resulting in an outer base tube with a coating on the inner surface and an inner liner tube with a coating on the outer surface. The inner liner tube with a coating on the outer surface is placed inside the outer base tube with a coating on the inner surface. Then, the two ends of the inner liner tube and the outer base tube are sealed and vacuumed to form an assembled tube body. S3. Under a protective atmosphere, the assembled tube body is kept at 1150-1250℃ (for example, 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃, 1210℃, 1220℃, 1230℃, 1240℃, or 1250℃, etc.) for a first preset time, and then hot-extruded at 1100-1200℃ with an extrusion ratio of (4.5-6). 5):1 (the extrusion ratio can be 4.5:1, 5:1, 5.5:1, 6:1 or 6.5:1, etc.), then spray water for cooling, and the cooling rate in the temperature range of 900℃ to 400℃ is not less than 40℃ / s (for example, it can be 40℃ / s, 45℃ / s, 50℃ / s, 55℃ / s or 60℃ / s, etc.). After spraying water to cool to 400℃, air cool to room temperature to obtain the bimetallic metallurgical composite tube blank.

[0046] This invention achieves high-quality metallurgical bonding of dissimilar metals through the synergy of an optimized nickel-based alloy coating and a vacuum hot extrusion process, with interfacial shear strength consistently above 300 MPa, reaching a maximum of 405 MPa. The nickel-based alloy coating, acting as an efficient compositional transition zone and carbon diffusion barrier, completely prevents the formation of brittle chromium-rich carbides at the interface, ensuring the toughness and stability of the interface under high temperature and thermal cycling. The method and nickel-based alloy composition coating are successfully applicable to various combinations ranging from low-alloy heat-resistant steel to high-alloy nickel-based corrosion-resistant alloys. By fine-tuning the composition of the nickel-based alloy (e.g., adding Cu), the bonding performance with nickel-based alloys such as NS1402 can be particularly optimized. The method provided by this invention can be combined with non-destructive testing methods such as ultrasonic C-scanning to ensure the stability and consistency of product quality, fully meeting the long-cycle, high-reliability operation requirements of petrochemical plants. After the above-mentioned steps, the coating becomes an intermediate transition layer for the metallurgical bonding of the outer base tube and the inner liner.

[0047] In step S1, in some embodiments, the outer diameter (i.e., outer diameter) of the outer base tube is 100-510 mm, for example, it can be 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 450 mm, 500 mm or 510 mm, etc.; the wall thickness of the outer base tube is 15-60 mm, for example, it can be 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm or 60 mm, etc.; the wall thickness of the inner liner tube is 5-30 mm, for example, it can be 5 mm, 10 mm, 15 mm, 20 mm, 25 mm or 30 mm, etc.

[0048] In some embodiments, the steps following the provision of the outer base tube and the inner liner tube specifically include: The outer base tube and inner liner tube are ultrasonically cleaned for 10-15 minutes in an alkaline cleaning solution (containing 2wt%-4wt% Na2CO3, 1wt%-2wt% Na3PO4·12H2O, and 0.5wt%-1wt% surfactant) at 60-70℃ to remove oil stains. The surfactant is a compound of n-hexyl glucoside (APG06), potassium phenol ethoxyphosphate (PPE1040K), and polyoxyethylene-8-octylphenyl ether (X-100) in a mass ratio of 2:2:1.

[0049] Then, using brown corundum sand with a particle size of 80–120 mesh and compressed air with a pressure of 0.6–0.8 MPa, the inner surface of the outer base tube and the outer surface of the inner liner tube are sandblasted to achieve a surface roughness Ra of 6.3–10.0 μm (to increase the actual surface area and provide sufficient mechanical interlocking and diffusion channels for diffusion bonding; this surface exhibits a uniform silver-gray metallic luster without any oxidation color; for example, surface roughness Ra of 6.3 μm, 6.5 μm, 7.0 μm, 8.0 μm, 9.0 μm, or 10.0 μm, etc.).

[0050] Immediately after sandblasting, acid pickling is performed to remove the extremely thin, newly formed oxide film, resulting in a highly activated, fresh metal surface. Specifically: For the outer base tube (carbon steel / low alloy steel): immerse it in an aqueous solution of hydrochloric acid at a temperature of 40-50℃ and a concentration of 10-15wt.% (i.e., mass percentage) for 3-5 minutes.

[0051] For inner lining tubes (stainless steel / corrosion-resistant alloy): Immerse in a mixed acid solution (containing 20-25 wt.% HNO3 and 3-5 wt.% HF, with the balance being water) at room temperature for 2-4 minutes.

[0052] After pickling, rinse immediately with high-pressure deionized water, then dehydrate with anhydrous ethanol, and dry quickly and thoroughly with hot air (≤80℃).

[0053] In step S2, in some embodiments, when the nickel-based alloy slurry is coated onto the inner surface of the outer base tube and dried to form a coating, the thickness of the coating is 0.1–0.5 mm (e.g., 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, or 0.5 mm, etc.); when the nickel-based alloy slurry is coated onto the outer surface of the inner liner tube and dried to form a coating, the thickness of the coating is 0.1–0.5 mm; when the nickel-based alloy slurry is coated onto the inner surface of the outer base tube and the outer surface of the inner liner tube respectively, and dried to form a coating, the total thickness of the coating on the inner surface of the outer base tube and the outer surface of the inner liner tube is 0.1–0.5 mm.

[0054] In step S2, a high-pressure airless spraying device can be used to uniformly spray the nickel-based alloy slurry onto the inner surface of the treated outer base tube and / or the outer surface of the inner liner tube. By controlling the spraying trajectory and number of sprays, the wet film thickness is made to reach 1.8 to 2.2 times the final coating thickness (0.1 to 0.5 mm) to allow for drying and thermal compression. After coating, the tube is placed in a programmable temperature-controlled drying oven and slowly dried according to a stepped temperature increase program of 80℃ for 2 hours, 120℃ for 2 hours, and 160℃ for 1 hour to ensure complete solvent evaporation and the formation of a strong, crack-free coating.

[0055] In some embodiments, before sealing and evacuating the two ends of the inner liner and the outer base tube, the process includes baking at 250-300°C (e.g., 250°C, 260°C, 270°C, 280°C, 290°C, or 300°C) for 1-2 hours (e.g., 1 hour, 1.5 hours, or 2 hours). The inner liner and the outer base tube are sealed at both ends and a vacuum is drawn to ensure that the vacuum level of the annular cavity formed between the inner liner and the outer base tube is no greater than 5.0 × 10⁻⁶. -3 Pa (for example, it can be 5.0 × 10) -3 Pa, 4.0 × 10 - 3 Pa, 3.2 × 10 -3 Pa, 1.0 × 10 -3 Pa, 8.0×10 -4 Pa or 5.0 × 10 -4 Pa, etc.

[0056] Taking the process of placing the inner liner inside the outer base tube with a coating on its inner surface, then sealing and welding the two ends of the inner liner and the outer base tube together and drawing a vacuum to form an assembled tube body as an example, the specific steps include: The inner liner is coaxially placed inside the outer base tube, whose inner surface has a coating. End caps (ring-shaped) of the same material as the inner liner are welded to seal both ends of the inner liner and the outer base tube, forming a closed annular cavity. Welding is performed using pulsed tungsten inert gas welding (GTAW-P) to ensure full penetration and a defect-free weld. A vacuum pipe with a high-vacuum valve is pre-welded to one of the end caps, connected to a high-vacuum unit, and baked at 250–300°C for 1–2 hours to remove gas. Vacuuming continues until the vacuum level of the annular cavity does not exceed 5.0 × 10⁻⁶. -3 Pa. After reaching the vacuum level, use specialized hydraulic clamps to flatten and weld the extraction pipe, achieving a permanent seal.

[0057] In step S3, in some embodiments, when the unit of the first preset time is min and the unit of the total wall thickness of the assembled tube is mm, the numerical relationship between the first preset time and the total wall thickness of the assembled tube (i.e., the outer base tube wall thickness + the inner liner tube wall thickness + the coating thickness) is as follows: First preset time = total wall thickness of assembled tube × (1.5~2.0).

[0058] The total wall thickness of the assembled tube is the sum of the outer base tube wall thickness, the inner liner tube wall thickness, and the coating thickness.

[0059] For example, when the total wall thickness of the assembled tube is 40 mm, the first preset time can be 60 min.

[0060] Step S3 specifically includes placing the assembled tube in a walking beam furnace, and under the protection of high-purity argon gas (Ar≥99.999%) under slight positive pressure, heating it to 600℃ at a rate of ≤100℃ / h, and then heating it to 1150℃~1250℃ at a rate of ≤80℃ / h for a first preset time to ensure uniform core temperature. After the holding time, it is quickly transferred to an extrusion cylinder preheated to 1100~1200℃, and lubricated with glass lubricating pads and glass powder. Hot extrusion molding is performed at 1100~1200℃ on a large horizontal extruder, with an extrusion ratio (i.e., the ratio of cross-sectional area before extrusion to cross-sectional area after extrusion) of (4.5~6.5):1. Under the combined action of high temperature, huge triaxial compressive stress and high vacuum environment, the coating (containing nickel-based alloy) undergoes plastic flow, densification sintering, and sufficient atomic interdiffusion with the surfaces of the two base materials, forming a strong metallurgical bonding interface. After extrusion, forced water cooling is immediately applied to ensure that the cooling rate is not less than 40℃ / s in the temperature range of 900℃ to 400℃, so as to suppress the precipitation of brittle phase.

[0061] This invention also provides an application of the bimetallic metallurgical composite tube blank described above, or the bimetallic metallurgical composite tube blank prepared by the preparation method described above, in the preparation of heat exchange tubes. Specific preparation methods include hot rolling or cold rolling, heat treatment, etc.

[0062] Furthermore, heat exchange tubes can be used to manufacture heat exchangers for high-temperature, high-pressure, and corrosive environments in the petrochemical and coal chemical industries.

[0063] The present invention will be further described below through specific embodiments.

[0064] In the following embodiments, the higher the carbon content and alloy content of the outer base tube, the higher the content of carbon trapping elements (Cr, Nb) in the coating should be, the higher the requirements for alloying degree and corrosion resistance of the inner liner tube, the higher the content of Ni and Mo in the coating should be adjusted accordingly to improve compatibility, and Cu needs to be added for NS1402.

[0065] In the following examples, the alkaline cleaning agent used consists of the following components: 4wt% Na2CO3, 2wt% Na3PO4·12H2O, 1wt% surfactant and 93wt% water.

[0066] Acid solution a (for acid washing of the outer base tube) is hydrochloric acid with a concentration of 12 wt.%.

[0067] Acid solution B (for pickling inner liner tubes) consists of the following components: HNO3 22 wt.%, HF 4 wt.%, balance is water.

[0068] In the following embodiments, the chemical composition and mass percentage of the outer base tube and inner liner tube are shown in Table 1 and Table 2, respectively.

[0069] Table 1. Chemical composition and mass percentage of the outer base tubes used in Examples 1-9

[0070] Table 2. Chemical composition and mass percentage of the inner lining tubes used in Examples 1-9

[0071] Example 1 This embodiment provides a method for preparing a bimetallic metallurgical composite tube blank, including the following steps: (1) Provide outer base tube and inner cover tube.

[0072] The outer base pipe is made of 15CrMoG pipe with an outer diameter of 139.7 mm and a wall thickness of 15 mm. The inner liner pipe is made of S30408 ​​pipe with an outer diameter of 108 mm and a wall thickness of 5 mm.

[0073] The preparation method of the outer base tube includes the following steps: According to the chemical composition and mass percentage of the outer base tube in Example 1 of Table 1, steelmaking and continuous casting are carried out to obtain continuously cast billets. The continuously cast billets are heated to 1230°C, held for 2 hours, and hot piercing is performed. Then, hot continuous rolling is carried out in the temperature range of 1200-950°C (initial rolling temperature is 1200°C, final rolling temperature is 950°C). After rolling, the billets are air-cooled to obtain the outer base tube.

[0074] The preparation method of the inner liner includes the following steps: According to the chemical composition and mass percentage of the inner liner in Example 1 of Table 2, steelmaking and continuous casting were carried out to obtain continuously cast billets. The continuously cast billets were heated to 1200°C and held for 3 hours for hot piercing. Then, they were hot rolled in the temperature range of 1170°C to 950°C (initial rolling temperature of 1170°C and final rolling temperature of 950°C). After that, they were cooled by water spraying to obtain the inner liner.

[0075] (2) Treat the inner surface of the outer base pipe and the outer surface of the inner liner pipe separately, including the following steps: (21) Ultrasonic alkaline cleaning (i.e. degreasing cleaning): The outer base tube and inner liner tube after the above treatment are ultrasonically cleaned in an alkaline cleaning solution at 60°C for 15 minutes.

[0076] (22) Sandblasting roughening: using brown corundum sand with a particle size of 100 mesh and compressed air with a pressure of 0.7 MPa, sandblasting was performed. The surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner cover tube after treatment were 9.2 μm and 8.3 μm, respectively.

[0077] (23) Pickling and activation: Immerse the outer base tube in acid solution a at 45°C for 4 minutes. Immerse the inner liner tube in acid solution b at room temperature for 2.5 minutes.

[0078] (24) Rinsing and drying: After acid washing, rinse immediately with high-pressure deionized water, then dehydrate with anhydrous ethanol, and dry quickly and thoroughly with 80°C hot air.

[0079] (3) Preparation of nickel-based alloy powder and slurry and slurry coating, including the following steps: (31) Preparation of nickel-based alloy powder: Nickel-based alloy powder (spherical) was prepared by vacuum induction melting gas atomization method. The atomizing gas pressure was 5 MPa and the melt superheat was 250℃. Then, it was sieved to obtain nickel-based alloy powder with a particle size of -150~+400 mesh (-200 mesh accounted for 85%) and an oxygen content of 58 ppm.

[0080] Nickel-based alloy powder comprises the following chemical components in weight percentage: C 0.05%, Si 0.37%, P 0.020%, S 0.011%, Al 0.026%, Mn 0.55%, Cr 21.5%, Mo 1.8%, Ni 42.3%, Nb 0.9%, balance Fe and unavoidable impurities.

[0081] (32) Preparation of nickel-based alloy slurry: 4% polyvinyl butyral, 1.5% dibutyl phthalate, 0.5% ethyl cellulose and 94% terpineol were mixed by mass percentage and stirred in a water bath at 65°C until completely dissolved to form a uniform and transparent viscous liquid, thus obtaining an organic carrier.

[0082] Nickel-based alloy powder and organic carrier were placed in a planetary ball mill at a mass ratio of 75:25 and ball milled at 200 rpm for 4 hours to obtain nickel-based alloy slurry.

[0083] (33) Slurry coating and drying: Using a high-pressure airless spraying device, nickel-based alloy slurry is uniformly sprayed onto the inner surface of the treated outer base tube, with a wet film thickness of 0.3 mm. Then, it is placed in a programmable temperature-controlled drying oven and slowly dried according to a step-by-step temperature increase program of 80℃ for 2 hours, 120℃ for 2 hours, and 160℃ for 1 hour to form a coating (thickness of 0.15 mm), thus obtaining an outer base tube with a coating on the inner surface.

[0084] (4) Assembly and vacuuming, including the following steps: The inner liner is coaxially placed inside the outer base tube, whose inner surface has a coating. Tungsten inert gas welding (GTAW, shielding gas: 99.99% Ar) is used, and end caps (ring-shaped) of the same material as the inner liner are welded to seal both ends of the inner and outer base tubes, forming a ring-shaped sealed cavity. A high-vacuum unit is connected via a vacuum valve-equipped extraction pipe pre-welded to the end caps. The tube is baked at 280°C for 1 hour to remove gas, and then evacuated to a vacuum level of 5.0 × 10⁻⁶. -3 After reaching the vacuum level, a special hydraulic clamp is used to flatten and weld the vacuum tube to achieve a permanent seal, resulting in the assembled tube body.

[0085] (5) Thermal processing composite, including the following steps: The assembled tube was placed in a walking beam furnace and heated to 600°C at a rate of 100°C / h under a slightly positive pressure of high-purity argon gas (Ar ≥ 99.999%). The temperature was then increased to 1180°C at a rate of 80°C / h and held for 35 minutes. After holding, it was quickly transferred to the extrusion cylinder of a large horizontal extruder preheated to 1150°C. Hot extrusion molding was performed using glass lubricating pads and glass powder for lubrication at 1150°C and an extrusion ratio of 5:1. Immediately after extrusion, forced water cooling was applied to ensure a cooling rate of 50°C / s within the 900°C to 400°C temperature range to suppress the precipitation of brittle phases, resulting in the bimetallic metallurgical composite tube blank.

[0086] The bimetallic composite tube blank prepared in this embodiment was tested: The interfacial shear strength is 328 MPa; ultrasonic C-scan shows that the interfacial bonding is continuous, uniform, and defect-free.

[0087] Example 2 This embodiment provides a method for preparing a bimetallic metallurgical composite tube blank, including the following steps: (1) Provide outer base tube and inner cover tube.

[0088] The outer base pipe is made of 15CrMoG pipe with an outer diameter of 177.8 mm and a wall thickness of 20 mm. The inner liner pipe is made of S31603 pipe with an outer diameter of 136 mm and a wall thickness of 8 mm.

[0089] The preparation method of the outer base tube includes the following steps: According to the chemical composition and mass percentage of the outer base tube in Example 2 of Table 1, steelmaking and continuous casting are carried out to obtain continuously cast billets. The continuously cast billets are heated to 1230°C, held for 2 hours, and hot piercing is performed. Then, hot continuous rolling is carried out in the temperature range of 1200-950°C (initial rolling temperature is 1200°C, final rolling temperature is 950°C). After rolling, the billets are air-cooled to obtain the outer base tube.

[0090] The preparation method of the inner liner includes the following steps: According to the chemical composition and mass percentage of the inner liner in Example 2 of Table 2, steelmaking and continuous casting were carried out to obtain continuously cast billets. The continuously cast billets were heated to 1230°C, held for 3 hours, and hot pierced. Then, hot continuous rolling was carried out in the temperature range of 1200-950°C (initial rolling temperature of 1200°C and final rolling temperature of 950°C). After that, water was sprayed to cool, and the inner liner was obtained.

[0091] (2) Treat the inner surface of the outer base pipe and the outer surface of the inner liner pipe separately, including the following steps: (21) Ultrasonic alkaline cleaning (i.e. degreasing cleaning): The outer base tube and inner liner tube after the above treatment are ultrasonically cleaned in an alkaline cleaning solution at 60°C for 15 minutes.

[0092] (22) Sandblasting roughening: using brown corundum sand with a particle size of 100 mesh and compressed air with a pressure of 0.7 MPa, sandblasting was performed. The surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner cover tube after treatment were 7.3 μm and 6.5 μm, respectively.

[0093] (23) Pickling and activation: Immerse the outer base tube in acid solution a at 45°C for 4 minutes. Immerse the inner liner tube in acid solution b at room temperature for 2.5 minutes.

[0094] (24) Rinsing and drying: After acid washing, rinse immediately with high-pressure deionized water, then dehydrate with anhydrous ethanol, and dry quickly and thoroughly with 80°C hot air.

[0095] (3) Preparation of nickel-based alloy powder and slurry and slurry coating, including the following steps: (31) Preparation of nickel-based alloy powder: Nickel-based alloy powder (spherical) was prepared by vacuum induction melting gas atomization method. The atomizing gas pressure was 5 MPa and the melt superheat was 250℃. Then, it was sieved to obtain nickel-based alloy powder with a particle size of -150~+400 mesh (-200 mesh accounted for 88%) and an oxygen content of 57 ppm.

[0096] Nickel-based alloy powder comprises the following chemical components in weight percentage: C 0.04%, Si 0.39%, P 0.018%, S 0.012%, Al 0.023%, Mn 0.52%, Cr 22.0%, Mo 2.2%, Ni 42.9%, Nb 1.0%, balance Fe and unavoidable impurities.

[0097] (32) Preparation of nickel-based alloy slurry: 4% polyvinyl butyral, 1.5% dibutyl phthalate, 0.5% ethyl cellulose and 94% terpineol were mixed by mass percentage and stirred in a water bath at 65°C until completely dissolved to form a uniform and transparent viscous liquid, thus obtaining an organic carrier.

[0098] Nickel-based alloy powder and organic carrier were placed in a planetary ball mill at a mass ratio of 75:25 and ball milled at 200 rpm for 4 hours to obtain nickel-based alloy slurry.

[0099] (33) Slurry coating and drying: Using a high-pressure airless spraying device, the nickel-based alloy slurry is uniformly sprayed onto the inner surface of the treated outer base tube, with a wet film thickness of 0.50 mm. Then, it is placed in a programmable temperature-controlled drying oven and slowly dried according to a step-by-step temperature increase program of 80℃ for 2 hours, 120℃ for 2 hours, and 160℃ for 1 hour to form a coating (thickness of 0.25 mm), thus obtaining an outer base tube with a coating on the inner surface.

[0100] (4) Assembly and vacuuming, including the following steps: The inner liner is coaxially placed inside the outer base tube, whose inner surface has a coating. Tungsten inert gas welding (GTAW, shielding gas: 99.99% Ar) is used, and end caps (ring-shaped) of the same material as the inner liner are welded to seal both ends of the inner and outer base tubes, forming a ring-shaped sealed cavity. A high-vacuum unit is connected via a vacuum valve-equipped extraction pipe pre-welded to the end caps. The tube is then baked at 280°C for 1.5 hours to remove gas, and a vacuum of 5.0 × 10⁻⁶ is achieved. -3 After reaching the vacuum level, a special hydraulic clamp is used to flatten and weld the vacuum tube to achieve a permanent seal, resulting in the assembled tube body.

[0101] (5) Thermal processing composite, including the following steps: The assembled tube was placed in a walking beam furnace and heated to 600°C at a rate of 100°C / h under a slightly positive pressure of high-purity argon gas (Ar ≥ 99.999%). The temperature was then increased to 1180°C at a rate of 80°C / h and held for 45 minutes. After holding, it was quickly transferred to the extrusion cylinder of a large horizontal extruder preheated to 1150°C. Hot extrusion molding was performed using glass lubricating pads and glass powder for lubrication. The extrusion temperature was 1150°C, and the extrusion ratio was 5:1. Immediately after extrusion, forced water cooling was applied to ensure a cooling rate of 50°C / s within the 900°C to 400°C temperature range to suppress the precipitation of brittle phases, resulting in the bimetallic metallurgical composite tube blank.

[0102] The bimetallic composite tube blank prepared in this embodiment was tested: The interfacial shear strength is 345 MPa; ultrasonic C-scan shows that the interfacial bonding is continuous, uniform, and defect-free.

[0103] Example 3 This embodiment provides a method for preparing a bimetallic metallurgical composite tube blank, including the following steps: (1) Provide outer base tube and inner cover tube.

[0104] The outer base pipe is made of 15CrMoG pipe with an outer diameter of 244.5 mm and a wall thickness of 25 mm. The inner liner pipe is made of NS1402 pipe with an outer diameter of 193 mm and a wall thickness of 10 mm.

[0105] The preparation method of the outer base tube includes the following steps: According to the chemical composition and mass percentage of the chemical composition of the outer base tube in Example 3 of Table 1, steelmaking and continuous casting are carried out to obtain continuously cast billets. The continuously cast billets are heated to 1230°C, held for 2 hours, and hot piercing is performed. Then, hot continuous rolling is carried out in the temperature range of 1200-950°C (initial rolling temperature is 1200°C, and final rolling temperature is 950°C). After rolling, the billets are air-cooled to obtain the outer base tube.

[0106] The preparation method of the inner liner includes the following steps: According to the chemical composition and mass percentage of the inner liner in Example 3 of Table 2, steelmaking and continuous casting were carried out to obtain continuously cast billets. The continuously cast billets were heated to 1200°C and held for 3 hours for hot piercing. Then, they were hot rolled in the temperature range of 1170°C to 950°C (initial rolling temperature of 1170°C and final rolling temperature of 950°C). After that, they were cooled by water spraying to obtain the inner liner.

[0107] (2) Treat the inner surface of the outer base pipe and the outer surface of the inner liner pipe separately, including the following steps: (21) Ultrasonic alkaline cleaning (i.e. degreasing cleaning): The outer base tube and inner liner tube after the above treatment are ultrasonically cleaned in an alkaline cleaning solution at 60°C for 15 minutes.

[0108] (22) Sandblasting roughening: Brown corundum sand with a particle size of 100 mesh and compressed air with a pressure of 0.7 MPa were used for sandblasting. The surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner cover tube after treatment were 9.1 μm and 8.6 μm, respectively.

[0109] (23) Pickling and activation: Immerse the outer base tube in acid solution a at 45°C for 4 minutes. Immerse the inner liner tube in acid solution b at room temperature for 2.5 minutes.

[0110] (24) Rinsing and drying: After acid washing, rinse immediately with high-pressure deionized water, then dehydrate with anhydrous ethanol, and dry quickly and thoroughly with 80°C hot air.

[0111] (3) Preparation of nickel-based alloy powder and slurry and slurry coating, including the following steps: (31) Preparation of nickel-based alloy powder: Nickel-based alloy powder (spherical) was prepared by vacuum induction melting gas atomization method. The atomizing gas pressure was 5 MPa and the melt superheat was 250℃. Then, it was sieved to obtain nickel-based alloy powder with a particle size of -150~+400 mesh (-200 mesh accounted for 86%) and an oxygen content of 55 ppm.

[0112] Nickel-based alloy powder comprises the following chemical components in weight percentage: C 0.06%, Si 0.40%, P 0.023%, S 0.013%, Al 0.035%, Mn 0.47%, Cr 22.5%, Mo 2.5%, Ni 43.1%, Nb 1.05%, Ti 0.3%, Cu 1.2%, balance Fe and unavoidable impurities.

[0113] (32) Preparation of nickel-based alloy slurry: 4% polyvinyl butyral, 1.5% dibutyl phthalate, 0.5% ethyl cellulose and 94% terpineol were mixed by mass percentage and stirred in a water bath at 65°C until completely dissolved to form a uniform and transparent viscous liquid, thus obtaining an organic carrier.

[0114] Nickel-based alloy powder and organic carrier were placed in a planetary ball mill at a mass ratio of 75:25 and ball milled at 200 rpm for 4 hours to obtain nickel-based alloy slurry.

[0115] (33) Slurry coating and drying: Using a high-pressure airless spraying device, the nickel-based alloy slurry is uniformly sprayed onto the inner surface of the treated outer base tube, with a wet film thickness of 0.6 mm. Then, it is placed in a programmable temperature-controlled drying oven and slowly dried according to a step-by-step temperature increase program of 80℃ for 2 hours, 120℃ for 2 hours, and 160℃ for 1 hour to form a coating (thickness of 0.3 mm), thus obtaining an outer base tube with a coating on the inner surface.

[0116] (4) Assembly and vacuuming, including the following steps: The inner liner is coaxially placed inside the outer base tube, whose inner surface has a coating. Tungsten inert gas welding (GTAW, shielding gas: 99.99% Ar) is used, and end caps (ring-shaped) of the same material as the inner liner are welded to seal both ends of the inner and outer base tubes, forming a ring-shaped sealed cavity. A high-vacuum unit is connected via a vacuum valve-equipped extraction pipe pre-welded to the end caps. The tube is then baked at 280°C for 100 minutes to remove gas, and a vacuum of 5.0 × 10⁻⁶ is achieved. -3 After reaching the vacuum level, a special hydraulic clamp is used to flatten and weld the vacuum tube to achieve a permanent seal, resulting in the assembled tube body.

[0117] (5) Thermal processing composite, including the following steps: The assembled tube was placed in a walking beam furnace and heated to 600°C at a rate of 100°C / h under a slightly positive pressure of high-purity argon gas (Ar ≥ 99.999%). The temperature was then increased to 1180°C at a rate of 80°C / h and held for 60 minutes. After holding, it was quickly transferred to the extrusion cylinder of a large horizontal extruder preheated to 1150°C. Hot extrusion molding was performed using glass lubricating pads and glass powder for lubrication. The extrusion temperature was 1150°C, and the extrusion ratio was 5:1. Immediately after extrusion, forced water cooling was applied to ensure a cooling rate of 50°C / s within the 900°C to 400°C temperature range to suppress the precipitation of brittle phases, resulting in the bimetallic metallurgical composite tube blank.

[0118] The bimetallic composite tube blank prepared in this embodiment was tested: The interfacial shear strength is 358 MPa; ultrasonic C-scan shows that the interfacial bonding is continuous, uniform, and defect-free.

[0119] Example 4 This embodiment provides a method for preparing a bimetallic metallurgical composite tube blank, including the following steps: (1) Provide outer base tube and inner cover tube.

[0120] The outer base pipe is made of 12Cr1MoVG pipe with an outer diameter of 339.7 mm and a wall thickness of 30 mm. The inner liner pipe is made of S30408 ​​pipe with an outer diameter of 278 mm and a wall thickness of 12 mm.

[0121] The preparation method of the outer base tube includes the following steps: According to the chemical composition and mass percentage of the outer base tube in Example 4 of Table 1, steelmaking and continuous casting were carried out to obtain continuously cast billets. The continuously cast billets were heated to 1250°C, held for 2 hours, and hot pierced. Then, hot continuous rolling was carried out in the temperature range of 1200-950°C (initial rolling temperature is 1200°C, final rolling temperature is 950°C). After rolling, the billets were air-cooled to obtain the outer base tube.

[0122] The preparation method of the inner liner includes the following steps: According to the chemical composition and mass percentage of the inner liner in Example 4 of Table 2, steelmaking and continuous casting were carried out to obtain continuously cast billets. The continuously cast billets were heated to 1200°C and held for 3 hours for hot piercing. Then, they were hot rolled in the temperature range of 1170°C to 950°C (initial rolling temperature of 1170°C and final rolling temperature of 950°C). After that, they were cooled by water spraying to obtain the inner liner.

[0123] (2) Treat the inner surface of the outer base pipe and the outer surface of the inner liner pipe separately, including the following steps: (21) Ultrasonic alkaline cleaning (i.e. degreasing cleaning): The outer base tube and inner liner tube after the above treatment are ultrasonically cleaned in an alkaline cleaning solution at 60°C for 15 minutes.

[0124] (22) Sandblasting roughening: Brown corundum sand with a particle size of 100 mesh and compressed air with a pressure of 0.7 MPa were used for sandblasting. The surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner cover tube after treatment were 8.8 μm and 7.9 μm, respectively.

[0125] (23) Pickling and activation: Immerse the outer base tube in acid solution a at 45°C for 4 minutes. Immerse the inner liner tube in acid solution b at room temperature for 2.5 minutes.

[0126] (24) Rinsing and drying: After acid washing, rinse immediately with high-pressure deionized water, then dehydrate with anhydrous ethanol, and dry quickly and thoroughly with 80°C hot air.

[0127] (3) Preparation of nickel-based alloy powder and slurry and slurry coating, including the following steps: (31) Preparation of nickel-based alloy powder: Nickel-based alloy powder (spherical) was prepared by vacuum induction melting gas atomization method. The atomizing gas pressure was 5 MPa and the melt superheat was 250℃. Then, it was sieved to obtain nickel-based alloy powder with a particle size of -150~+400 mesh (-200 mesh accounted for 87%) and an oxygen content of 55 ppm.

[0128] Nickel-based alloy powder comprises the following chemical components in weight percentage: C 0.04%, Si 0.35%, P 0.019%, S 0.010%, Al 0.025%, Mn 0.49%, Cr 22.5%, Mo 2.2%, Ni 41.9%, Nb 1.1%, V 0.6%, balance Fe and unavoidable impurities.

[0129] (32) Preparation of nickel-based alloy slurry: 4% polyvinyl butyral, 1.5% dibutyl phthalate, 0.5% ethyl cellulose and 94% terpineol were mixed by mass percentage and stirred in a water bath at 65°C until completely dissolved to form a uniform and transparent viscous liquid, thus obtaining an organic carrier.

[0130] Nickel-based alloy powder and organic carrier were placed in a planetary ball mill at a mass ratio of 75:25 and ball milled at 200 rpm for 4 hours to obtain nickel-based alloy slurry.

[0131] (33) Slurry coating and drying: Using a high-pressure airless spraying device, the nickel-based alloy slurry is uniformly sprayed onto the inner surface of the treated outer base tube, with a wet film thickness of 0.7 mm. Then, it is placed in a programmable temperature-controlled drying oven and slowly dried according to a step-by-step temperature increase program of 80℃ for 2 hours, 120℃ for 2 hours, and 160℃ for 1 hour to form a coating (thickness of 0.35 mm), thus obtaining an outer base tube with a coating on the inner surface.

[0132] (4) Assembly and vacuuming, including the following steps: The inner liner is coaxially placed inside the outer base tube, whose inner surface has a coating. Tungsten inert gas welding (GTAW, shielding gas: 99.99% Ar) is used, and end caps (ring-shaped) of the same material as the inner liner are welded to seal both ends of the inner and outer base tubes, forming a sealed annular cavity. A high-vacuum unit is connected via a vacuum valve-equipped extraction pipe pre-welded to the end caps. The tube is then baked at 280°C for 110 minutes to remove gas, and a vacuum of 5.0 × 10⁻⁶ is achieved. -3 After reaching the vacuum level, a special hydraulic clamp is used to flatten and weld the vacuum tube to achieve a permanent seal, resulting in the assembled tube body.

[0133] (5) Thermal processing composite, including the following steps: The assembled tube was placed in a walking beam furnace and heated to 600°C at a rate of 100°C / h under a slightly positive pressure of high-purity argon gas (Ar ≥ 99.999%). The temperature was then increased to 1180°C at a rate of 80°C / h and held for 70 minutes. After holding, it was quickly transferred to the extrusion cylinder of a large horizontal extruder preheated to 1150°C. Hot extrusion molding was performed using glass lubricating pads and glass powder for lubrication at 1150°C and an extrusion ratio of 5:1. Immediately after extrusion, forced water cooling was applied to ensure a cooling rate of 50°C / s within the 900°C to 400°C temperature range to suppress the precipitation of brittle phases, resulting in the bimetallic metallurgical composite tube blank.

[0134] The bimetallic composite tube blank prepared in this embodiment was tested: The interfacial shear strength is 352 MPa; ultrasonic C-scan shows that the interfacial bonding is continuous, uniform, and defect-free.

[0135] Example 5 This embodiment provides a method for preparing a bimetallic metallurgical composite tube blank, including the following steps: (1) Provide outer base tube and inner cover tube.

[0136] The outer base pipe is made of 12Cr1MoVG pipe with an outer diameter of 406.4 mm and a wall thickness of 35 mm. The inner liner pipe is made of S31603 pipe with an outer diameter of 335 mm and a wall thickness of 15 mm.

[0137] The preparation method of the outer base tube includes the following steps: According to the chemical composition and mass percentage of the chemical composition of the outer base tube in Example 5 of Table 1, steelmaking and continuous casting are carried out to obtain continuously cast billets. The continuously cast billets are heated to 1250°C, held for 2 hours, and hot piercing is performed. Then, hot continuous rolling is carried out in the temperature range of 1200-950°C (initial rolling temperature is 1200°C, final rolling temperature is 950°C). After rolling, the billets are air-cooled to obtain the outer base tube.

[0138] The preparation method of the inner liner includes the following steps: According to the chemical composition and mass percentage of the inner liner in Example 5 of Table 2, steelmaking and continuous casting were carried out to obtain continuously cast billets. The continuously cast billets were heated to 1230°C, held for 3 hours, and hot pierced. Then, hot continuous rolling was carried out in the temperature range of 1200-950°C (initial rolling temperature is 1200°C, final rolling temperature is 950°C). After that, water was sprayed to cool, and the inner liner was obtained.

[0139] (2) Treat the inner surface of the outer base pipe and the outer surface of the inner liner pipe separately, including the following steps: (21) Ultrasonic alkaline cleaning (i.e. degreasing cleaning): The outer base tube and inner liner tube after the above treatment are ultrasonically cleaned in an alkaline cleaning solution at 60°C for 15 minutes.

[0140] (22) Sandblasting roughening: using brown corundum sand with a particle size of 100 mesh and compressed air with a pressure of 0.7 MPa, sandblasting was performed. The surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner cover tube after treatment were 8.6 μm and 7.7 μm, respectively.

[0141] (23) Pickling and activation: Immerse the outer base tube in acid solution a at 45°C for 4 minutes. Immerse the inner liner tube in acid solution b at room temperature for 2.5 minutes.

[0142] (24) Rinsing and drying: After acid washing, rinse immediately with high-pressure deionized water, then dehydrate with anhydrous ethanol, and dry quickly and thoroughly with 80°C hot air.

[0143] (3) Preparation of nickel-based alloy powder and slurry and slurry coating, including the following steps: (31) Preparation of nickel-based alloy powder: Nickel-based alloy powder (spherical) was prepared by vacuum induction melting gas atomization method. The atomizing gas pressure was 5 MPa and the melt superheat was 250℃. Then, it was sieved to obtain nickel-based alloy powder with a particle size of -150~+400 mesh (-200 mesh accounted for 89%) and an oxygen content of 58 ppm.

[0144] Nickel-based alloy powder comprises the following chemical components in weight percentage: C 0.04%, Si 0.34%, P 0.018%, S 0.009%, Al 0.020%, Mn 0.45%, Cr 23.0%, Mo 2.5%, Ni 43.1%, Nb 1.15%, V 0.6%, balance Fe and unavoidable impurities.

[0145] (32) Preparation of nickel-based alloy slurry: 4% polyvinyl butyral, 1.5% dibutyl phthalate, 0.5% ethyl cellulose and 94% terpineol were mixed by mass percentage and stirred in a water bath at 65°C until completely dissolved to form a uniform and transparent viscous liquid, thus obtaining an organic carrier.

[0146] Nickel-based alloy powder and organic carrier were placed in a planetary ball mill at a mass ratio of 75:25 and ball milled at 200 rpm for 4 hours to obtain nickel-based alloy slurry.

[0147] (33) Slurry coating and drying: Using a high-pressure airless spraying device, the nickel-based alloy slurry is uniformly sprayed onto the inner surface of the treated outer base tube, with a wet film thickness of 0.36 mm. Then, it is placed in a programmable temperature-controlled drying oven and slowly dried according to a step-by-step temperature increase program of 80℃ for 2 hours, 120℃ for 2 hours, and 160℃ for 1 hour to form a coating (thickness of 0.18 mm), thus obtaining an outer base tube with a coating on the inner surface.

[0148] (4) Assembly and vacuuming, including the following steps: The inner liner is coaxially placed inside the outer base tube, which has an inner coating. Tungsten inert gas welding (GTAW, shielding gas 99.99% Ar) is used, and end caps (ring-shaped) of the same material as the inner liner are welded to seal both ends of the inner and outer base tubes, forming a sealed annular cavity. A high-vacuum unit is connected via a vacuum valve-equipped extraction pipe pre-welded to the end caps. The tube is then baked at 280°C for 115 minutes to remove gas, and a vacuum of 5.0 × 10⁻⁶ is achieved. -3 After reaching the vacuum level, a special hydraulic clamp is used to flatten and weld the vacuum tube to achieve a permanent seal, resulting in the assembled tube body.

[0149] (5) Thermal processing composite, including the following steps: The assembled tube was placed in a walking beam furnace and heated to 600°C at a rate of 100°C / h under a slightly positive pressure of high-purity argon gas (Ar ≥ 99.999%). The temperature was then increased to 1180°C at a rate of 80°C / h and held for 90 minutes. After holding, it was quickly transferred to the extrusion cylinder of a large horizontal extruder preheated to 1150°C. Hot extrusion molding was performed using glass lubricating pads and glass powder for lubrication at 1150°C and an extrusion ratio of 5:1. Immediately after extrusion, forced water cooling was applied to ensure a cooling rate of 50°C / s within the 900°C to 400°C temperature range to suppress the precipitation of brittle phases, resulting in the bimetallic metallurgical composite tube blank.

[0150] The bimetallic composite tube blank prepared in this embodiment was tested: The interfacial shear strength is 368 MPa; ultrasonic C-scan shows that the interfacial bonding is continuous, uniform, and defect-free.

[0151] Example 6 This embodiment provides a method for preparing a bimetallic metallurgical composite tube blank, including the following steps: (1) Provide outer base tube and inner cover tube.

[0152] The outer base pipe is made of 12Cr1MoVG pipe with an outer diameter of 457.2 mm and a wall thickness of 40 mm. The inner liner pipe is made of NS1402 pipe with an outer diameter of 375 mm and a wall thickness of 20 mm.

[0153] The preparation method of the outer base tube includes the following steps: According to the chemical composition and mass percentage of the chemical composition of the outer base tube in Example 6 of Table 1, steelmaking and continuous casting are carried out to obtain continuously cast billets. The continuously cast billets are heated to 1250°C, held for 2 hours, and hot piercing is performed. Then, hot continuous rolling is carried out in the temperature range of 1200-950°C (initial rolling temperature is 1200°C, final rolling temperature is 950°C). After rolling, the billets are air-cooled to obtain the outer base tube.

[0154] The preparation method of the inner liner includes the following steps: According to the chemical composition and mass percentage of the inner liner in Example 6 of Table 2, steelmaking and continuous casting were carried out to obtain continuously cast billets. The continuously cast billets were heated to 1200°C, held for 3 hours, and hot pierced. Then, they were hot rolled in the temperature range of 1170°C to 950°C (initial rolling temperature is 1170°C, final rolling temperature is 950°C). After that, they were cooled by water spraying to obtain the inner liner.

[0155] (2) Treat the inner surface of the outer base pipe and the outer surface of the inner liner pipe separately, including the following steps: (21) Ultrasonic alkaline cleaning (i.e. degreasing cleaning): The outer base tube and inner liner tube after the above treatment are ultrasonically cleaned in an alkaline cleaning solution at 60°C for 15 minutes.

[0156] (22) Sandblasting roughening: Brown corundum sand with a particle size of 100 mesh and compressed air with a pressure of 0.7 MPa were used for sandblasting. The surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner cover tube after treatment were 8.8 μm and 7.6 μm, respectively.

[0157] (23) Pickling and activation: Immerse the outer base tube in acid solution a at 45°C for 4 minutes. Immerse the inner liner tube in acid solution b at room temperature for 2.5 minutes.

[0158] (24) Rinsing and drying: After acid washing, rinse immediately with high-pressure deionized water, then dehydrate with anhydrous ethanol, and dry quickly and thoroughly with 80°C hot air.

[0159] (3) Preparation of nickel-based alloy powder and slurry and slurry coating, including the following steps: (31) Preparation of nickel-based alloy powder: Nickel-based alloy powder (spherical) was prepared by vacuum induction melting gas atomization method. The atomizing gas pressure was 5 MPa and the melt superheat was 250℃. Then, it was sieved to obtain nickel-based alloy powder with a particle size of -150~+400 mesh (-200 mesh accounted for 89%) and an oxygen content of 53 ppm.

[0160] Nickel-based alloy powder comprises the following chemical components in weight percentage: C 0.05%, Si 0.32%, P 0.020%, S 0.010%, Al 0.033%, Mn 0.56%, Cr 23.5%, Mo 2.8%, Ni 44.2%, Nb 1.15%, V 0.6%, Ti 0.4%, Cu 1.0%, balance Fe and unavoidable impurities.

[0161] (32) Preparation of nickel-based alloy slurry: 4% polyvinyl butyral, 1.5% dibutyl phthalate, 0.5% ethyl cellulose and 94% terpineol were mixed by mass percentage and stirred in a water bath at 65°C until completely dissolved to form a uniform and transparent viscous liquid, thus obtaining an organic carrier.

[0162] Nickel-based alloy powder and organic carrier were placed in a planetary ball mill at a mass ratio of 75:25 and ball milled at 200 rpm for 4 hours to obtain nickel-based alloy slurry.

[0163] (33) Slurry coating and drying: Using a high-pressure airless spraying device, the nickel-based alloy slurry is uniformly sprayed onto the inner surface of the treated outer base tube, with a wet film thickness of 0.8 mm. Then, it is placed in a programmable temperature-controlled drying oven and slowly dried according to a step-by-step temperature increase program of 80℃ for 2 hours, 120℃ for 2 hours, and 160℃ for 1 hour to form a coating (thickness of 0.4 mm), thus obtaining an outer base tube with a coating on the inner surface.

[0164] (4) Assembly and vacuuming, including the following steps: The inner liner is coaxially placed inside the outer base tube, which has an inner coating. Tungsten inert gas welding (GTAW, shielding gas 99.99% Ar) is used, and end caps (ring-shaped) of the same material as the inner liner are welded to seal both ends of the inner and outer base tubes, forming a sealed annular cavity. A high-vacuum unit is connected via a vacuum valve-equipped extraction pipe pre-welded to the end caps. The tube is then baked at 280°C for 2 hours to remove gas, and a vacuum of 5.0 × 10⁻⁶ is achieved. -3 After reaching the vacuum level, a special hydraulic clamp is used to flatten and weld the vacuum tube to achieve a permanent seal, resulting in the assembled tube body.

[0165] (5) Thermal processing composite, including the following steps: The assembled tube was placed in a walking beam furnace and heated to 600°C at a rate of 100°C / h under a slightly positive pressure of high-purity argon gas (Ar ≥ 99.999%). The temperature was then increased to 1180°C at a rate of 80°C / h and held for 110 minutes. After holding, it was quickly transferred to the extrusion cylinder of a large horizontal extruder preheated to 1150°C. Hot extrusion molding was performed using glass lubricating pads and glass powder for lubrication at 1150°C and an extrusion ratio of 5:1. Immediately after extrusion, forced water cooling was applied to ensure a cooling rate of 50°C / s within the 900°C to 400°C temperature range to suppress the precipitation of brittle phases, resulting in the bimetallic metallurgical composite tube blank.

[0166] The bimetallic composite tube blank prepared in this embodiment was tested: The interfacial shear strength is 382 MPa; ultrasonic C-scan shows that the interfacial bonding is continuous, uniform, and defect-free.

[0167] Example 7 This embodiment provides a method for preparing a bimetallic metallurgical composite tube blank, including the following steps: (1) Provide outer base tube and inner cover tube.

[0168] The outer base pipe is made of 12Cr2MoG pipe with an outer diameter of 508 mm and a wall thickness of 50 mm. The inner liner pipe is made of S30408 ​​pipe with an outer diameter of 406 mm and a wall thickness of 25 mm.

[0169] The preparation method of the outer base tube includes the following steps: According to the chemical composition and mass percentage of the chemical composition of the outer base tube in Example 7 of Table 1, steelmaking and continuous casting are carried out to obtain continuously cast billets; the continuously cast billets are heated to 1250°C, held for 2 hours, and hot piercing is performed. Then, hot continuous rolling is carried out in the temperature range of 1200-950°C (initial rolling temperature is 1200°C, final rolling temperature is 850°C), and air cooling is performed after rolling to obtain the outer base tube.

[0170] The preparation method of the inner liner includes the following steps: According to the chemical composition and mass percentage of the inner liner in Example 7 of Table 2, steelmaking and continuous casting were carried out to obtain continuously cast billets. The continuously cast billets were heated to 1200°C, held for 3 hours, and hot pierced. Then, hot continuous rolling was carried out in the temperature range of 1170°C to 950°C (initial rolling temperature is 1170°C, final rolling temperature is 950°C). After that, water was sprayed to cool, and the inner liner was obtained.

[0171] (2) Treat the inner surface of the outer base pipe and the outer surface of the inner liner pipe separately, including the following steps: (21) Ultrasonic alkaline cleaning (i.e. degreasing cleaning): The outer base tube and inner liner tube after the above treatment are ultrasonically cleaned in an alkaline cleaning solution at 60°C for 15 minutes.

[0172] (22) Sandblasting roughening: using brown corundum sand with a particle size of 100 mesh and compressed air with a pressure of 0.7 MPa, sandblasting was performed. The surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner cover tube after treatment were 8.6 μm and 7.7 μm, respectively.

[0173] (23) Pickling and activation: Immerse the outer base tube in acid solution a at 45°C for 4 minutes. Immerse the inner liner tube in acid solution b at room temperature for 2.5 minutes.

[0174] (24) Rinsing and drying: After acid washing, rinse immediately with high-pressure deionized water, then dehydrate with anhydrous ethanol, and dry quickly and thoroughly with 80°C hot air.

[0175] (3) Preparation of nickel-based alloy powder and slurry and slurry coating, including the following steps: (31) Preparation of nickel-based alloy powder: Nickel-based alloy powder (spherical) was prepared by vacuum induction melting gas atomization method. The atomizing gas pressure was 5 MPa and the melt superheat was 250℃. Then, it was sieved to obtain nickel-based alloy powder with a particle size of -150~+400 mesh (-200 mesh accounted for 84%) and an oxygen content of 57 ppm.

[0176] Nickel-based alloy powder comprises the following chemical components in weight percentage: C 0.05%, Si 0.35%, P 0.018%, S 0.010%, Al 0.021%, Mn 0.51%, Cr 23.5%, Mo 2.5%, Ni 42.5%, Nb 1.15%, balance Fe and unavoidable impurities.

[0177] (32) Preparation of nickel-based alloy slurry: 4% polyvinyl butyral, 1.5% dibutyl phthalate, 0.5% ethyl cellulose and 94% terpineol were mixed by mass percentage and stirred in a water bath at 65°C until completely dissolved to form a uniform and transparent viscous liquid, thus obtaining an organic carrier.

[0178] Nickel-based alloy powder and organic carrier were placed in a planetary ball mill at a mass ratio of 75:25 and ball milled at 200 rpm for 4 hours to obtain nickel-based alloy slurry.

[0179] (33) Slurry coating and drying: Using a high-pressure airless spraying device, the nickel-based alloy slurry is uniformly sprayed onto the inner surface of the treated outer base tube, with a wet film thickness of 0.65 mm. Then, it is placed in a programmable temperature-controlled drying oven and slowly dried according to a step-by-step temperature increase program of 80℃ for 2 hours, 120℃ for 2 hours, and 160℃ for 1 hour to form a coating (thickness of 0.33 mm), thus obtaining an outer base tube with a coating on the inner surface.

[0180] (4) Assembly and vacuuming, including the following steps: The inner liner is coaxially placed inside the outer base tube, which has an inner coating. Tungsten inert gas welding (GTAW, shielding gas 99.99% Ar) is used, and end caps (ring-shaped) of the same material as the inner liner are welded to seal both ends of the inner and outer base tubes, forming a sealed annular cavity. A high-vacuum unit is connected via a vacuum valve-equipped extraction pipe pre-welded to the end caps. The tube is then baked at 280°C for 2 hours to remove gas, and a vacuum of 5.0 × 10⁻⁶ is achieved. -3 After reaching the vacuum level, a special hydraulic clamp is used to flatten and weld the vacuum tube to achieve a permanent seal, resulting in the assembled tube body.

[0181] (5) Thermal processing composite, including the following steps: The assembled tube was placed in a walking beam furnace and heated to 600°C at a rate of 100°C / h under a slightly positive pressure of high-purity argon gas (Ar ≥ 99.999%). The temperature was then increased to 1180°C at a rate of 80°C / h and held for 130 minutes. After holding, it was quickly transferred to the extrusion cylinder of a large horizontal extruder preheated to 1150°C. Hot extrusion molding was performed using glass lubricating pads and glass powder for lubrication at 1150°C and an extrusion ratio of 5:1. Immediately after extrusion, forced water cooling was applied to ensure a cooling rate of 50°C / s within the 900°C to 400°C temperature range to suppress the precipitation of brittle phases, resulting in the bimetallic metallurgical composite tube blank.

[0182] The bimetallic composite tube blank prepared in this embodiment was tested: The interfacial shear strength is 372 MPa; ultrasonic C-scan shows that the interfacial bonding is continuous, uniform, and defect-free.

[0183] Example 8 This embodiment provides a method for preparing a bimetallic metallurgical composite tube blank, including the following steps: (1) Provide outer base tube and inner cover tube.

[0184] The outer base pipe is made of 12Cr2MoG pipe with an outer diameter of 244.5 mm and a wall thickness of 25 mm. The inner liner pipe is made of S31603 pipe with an outer diameter of 193 mm and a wall thickness of 15 mm.

[0185] The preparation method of the outer base tube includes the following steps: According to the chemical composition and mass percentage of the chemical composition of the outer base tube in Example 8 of Table 1, steelmaking and continuous casting are carried out to obtain continuously cast billets; the continuously cast billets are heated to 1250°C, held for 2 hours, and hot piercing is performed. Then, hot continuous rolling is carried out in the temperature range of 1200-950°C (initial rolling temperature is 1200°C, final rolling temperature is 950°C), and air cooling is performed after rolling to obtain the outer base tube.

[0186] The preparation method of the inner liner includes the following steps: According to the chemical composition and mass percentage of the inner liner in Example 8 of Table 2, steelmaking and continuous casting were carried out to obtain continuously cast billets. The continuously cast billets were heated to 1230°C, held for 3 hours, and hot pierced. Then, they were hot rolled in the temperature range of 1200-950°C (initial rolling temperature of 1200°C and final rolling temperature of 950°C). After that, they were cooled by water spraying to obtain the inner liner.

[0187] (2) Treat the inner surface of the outer base pipe and the outer surface of the inner liner pipe separately, including the following steps: (21) Ultrasonic alkaline cleaning (i.e. degreasing cleaning): The outer base tube and inner liner tube after the above treatment are ultrasonically cleaned in an alkaline cleaning solution at 60°C for 15 minutes.

[0188] (22) Sandblasting roughening: using brown corundum sand with a particle size of 100 mesh and compressed air with a pressure of 0.7 MPa, sandblasting was performed. The surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner cover tube after treatment were 9.2 μm and 8.4 μm, respectively.

[0189] (23) Pickling and activation: Immerse the outer base tube in acid solution a at 45°C for 4 minutes. Immerse the inner liner tube in acid solution b at room temperature for 2.5 minutes.

[0190] (24) Rinsing and drying: After acid washing, rinse immediately with high-pressure deionized water, then dehydrate with anhydrous ethanol, and dry quickly and thoroughly with 80°C hot air.

[0191] (3) Preparation of nickel-based alloy powder and slurry and slurry coating, including the following steps: (31) Preparation of nickel-based alloy powder: Nickel-based alloy powder (spherical) was prepared by vacuum induction melting gas atomization method. The atomizing gas pressure was 5 MPa and the melt superheat was 250℃. Then, it was sieved to obtain nickel-based alloy powder with a particle size of -150~+400 mesh (-200 mesh accounted for 81%) and an oxygen content of 60 ppm.

[0192] Nickel-based alloy powder comprises the following chemical components in weight percentage: C 0.04%, Si 0.30%, P 0.021%, S 0.013%, Al 0.023%, Mn 0.59%, Cr 24.0%, Mo 2.8%, Ni 42.8%, Nb 1.18%, balance Fe and unavoidable impurities.

[0193] (32) Preparation of nickel-based alloy slurry: 4% polyvinyl butyral, 1.5% dibutyl phthalate, 0.5% ethyl cellulose and 94% terpineol were mixed by mass percentage and stirred in a water bath at 65°C until completely dissolved to form a uniform and transparent viscous liquid, thus obtaining an organic carrier.

[0194] Nickel-based alloy powder and organic carrier were placed in a planetary ball mill at a mass ratio of 75:25 and ball milled at 200 rpm for 4 hours to obtain nickel-based alloy slurry.

[0195] (33) Slurry coating and drying: Using a high-pressure airless spraying device, the nickel-based alloy slurry is uniformly sprayed onto the inner surface of the treated outer base tube, with a wet film thickness of 0.42 mm. Then, it is placed in a programmable temperature-controlled drying oven and slowly dried in a stepped temperature increase program of 80℃ for 2 hours, 120℃ for 2 hours, and 160℃ for 1 hour to form a coating (thickness of 0.21 mm), thus obtaining an outer base tube with a coating on the inner surface.

[0196] (4) Assembly and vacuuming, including the following steps: The inner liner is coaxially placed inside the outer base tube, whose inner surface has a coating. Tungsten inert gas welding (GTAW, shielding gas: 99.99% Ar) is used, and end caps (ring-shaped) of the same material as the inner liner are welded to seal both ends of the inner and outer base tubes, forming a ring-shaped sealed cavity. A high-vacuum unit is connected via a vacuum valve-equipped extraction pipe pre-welded to the end caps. The tube is then baked at 280°C for 100 minutes to remove gas, and a vacuum of 5.0 × 10⁻⁶ is achieved. -3 After reaching the vacuum level, a special hydraulic clamp is used to flatten and weld the vacuum tube to achieve a permanent seal, resulting in the assembled tube body.

[0197] (5) Thermal processing composite, including the following steps: The assembled tube was placed in a walking beam furnace and heated to 600°C at a rate of 100°C / h under a slightly positive pressure of high-purity argon gas (Ar ≥ 99.999%). The temperature was then increased to 1180°C at a rate of 80°C / h and held for 70 minutes. After holding, it was quickly transferred to the extrusion cylinder of a large horizontal extruder preheated to 1150°C. Hot extrusion molding was performed using glass lubricating pads and glass powder for lubrication. The extrusion temperature was 1150°C, and the extrusion ratio was 5:1. Immediately after extrusion, forced water cooling was applied to ensure a cooling rate of 50°C / s within the 900°C to 400°C temperature range to suppress the precipitation of brittle phases, resulting in the bimetallic metallurgical composite tube blank.

[0198] The bimetallic composite tube blank prepared in this embodiment was tested: The interfacial shear strength is 388 MPa; ultrasonic C-scan shows that the interfacial bonding is continuous, uniform, and defect-free.

[0199] Example 9 This embodiment provides a method for preparing a bimetallic metallurgical composite tube blank, including the following steps: (1) Provide outer base tube and inner cover tube.

[0200] The outer base pipe is made of 12Cr2MoG pipe with an outer diameter of 220 mm and a wall thickness of 45 mm. The inner liner pipe is made of NS1402 pipe with an outer diameter of 128 mm and a wall thickness of 18 mm.

[0201] The preparation method of the outer base tube includes the following steps: According to the chemical composition and mass percentage of the outer base tube in Example 9 of Table 1, steelmaking and continuous casting are carried out to obtain continuously cast billets. The continuously cast billets are heated to 1250°C, held for 2 hours, and hot piercing is performed. Then, hot continuous rolling is carried out in the temperature range of 1200-950°C (initial rolling temperature is 1200°C, final rolling temperature is 950°C). After rolling, the billets are air-cooled to obtain the outer base tube.

[0202] The preparation method of the inner liner includes the following steps: According to the chemical composition and mass percentage of the inner liner in Example 9 of Table 2, steelmaking and continuous casting were carried out to obtain continuously cast billets. The continuously cast billets were heated to 1200°C, held for 3 hours, and hot pierced. Then, they were hot rolled in the temperature range of 1170°C to 950°C (initial rolling temperature is 1170°C, final rolling temperature is 950°C). After that, they were cooled by water spraying to obtain the inner liner.

[0203] (2) Treat the inner surface of the outer base pipe and the outer surface of the inner liner pipe separately, including the following steps: (21) Ultrasonic alkaline cleaning (i.e. degreasing cleaning): The outer base tube and inner liner tube after the above treatment are ultrasonically cleaned in an alkaline cleaning solution at 60°C for 15 minutes.

[0204] (22) Sandblasting roughening: Brown corundum sand with a particle size of 100 mesh and compressed air with a pressure of 0.7 MPa were used for sandblasting. The surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner cover tube after treatment were 8.5 μm and 7.8 μm, respectively.

[0205] (23) Pickling and activation: Immerse the outer base tube in acid solution a at 45°C for 4 minutes. Immerse the inner liner tube in acid solution b at room temperature for 2.5 minutes.

[0206] (24) Rinsing and drying: After acid washing, rinse immediately with high-pressure deionized water, then dehydrate with anhydrous ethanol, and dry quickly and thoroughly with 80°C hot air.

[0207] (3) Preparation of nickel-based alloy powder and slurry and slurry coating, including the following steps: (31) Preparation of nickel-based alloy powder: Nickel-based alloy powder (spherical) was prepared by vacuum induction melting gas atomization method. The atomizing gas pressure was 5 MPa and the melt superheat was 250℃. Then, it was sieved to obtain nickel-based alloy powder with a particle size of -150~+400 mesh (-200 mesh accounted for 83%) and an oxygen content of 65 ppm.

[0208] Nickel-based alloy powder comprises the following chemical components in weight percentage: C 0.05%, Si 0.40%, P 0.020%, S 0.012%, Al 0.025%, Mn 0.63%, Cr 24.0%, Mo 2.9%, Ni 43.5%, Nb 1.2%, Ti 0.5%, Cu 1.5%, balance Fe and unavoidable impurities.

[0209] (32) Preparation of nickel-based alloy slurry: 4% polyvinyl butyral, 1.5% dibutyl phthalate, 0.5% ethyl cellulose and 94% terpineol were mixed by mass percentage and stirred in a water bath at 65°C until completely dissolved to form a uniform and transparent viscous liquid, thus obtaining an organic carrier.

[0210] Nickel-based alloy powder and organic carrier were placed in a planetary ball mill at a mass ratio of 75:25 and ball milled at 200 rpm for 4 hours to obtain nickel-based alloy slurry.

[0211] (33) Slurry coating and drying: Using a high-pressure airless spraying device, the nickel-based alloy slurry is uniformly sprayed onto the inner surface of the treated outer base tube, with a wet film thickness of 0.60 mm. Then, it is placed in a programmable temperature-controlled drying oven and slowly dried according to a step-by-step temperature increase program of 80℃ for 2 hours, 120℃ for 2 hours, and 160℃ for 1 hour to form a coating (thickness of 0.30 mm), thus obtaining an outer base tube with a coating on the inner surface.

[0212] (4) Assembly and vacuuming, including the following steps: The inner liner is coaxially placed inside the outer base tube, which has an inner coating. Tungsten inert gas welding (GTAW, shielding gas 99.99% Ar) is used, and end caps (ring-shaped) of the same material as the inner liner are welded to seal both ends of the inner and outer base tubes, forming a sealed annular cavity. A high-vacuum unit is connected via a vacuum valve-equipped extraction pipe pre-welded to the end caps. The tube is then baked at 280°C for 1.5 hours to remove gas, and a vacuum of 5 × 10⁻⁶ is achieved. -3 After reaching the vacuum level, a special hydraulic clamp is used to flatten and weld the vacuum tube to achieve a permanent seal, resulting in the assembled tube body.

[0213] (5) Thermal processing composite, including the following steps: The assembled tube was placed in a walking beam furnace and heated to 600°C at a rate of 80°C / h under a slightly positive pressure of high-purity argon gas (Ar ≥ 99.999%). The temperature was then increased to 1180°C at a rate of 80°C / h and held for 110 minutes. After holding, it was quickly transferred to the extrusion cylinder of a large horizontal extruder preheated to 1150°C. Hot extrusion molding was performed using glass lubricating pads and glass powder for lubrication at 1150°C and an extrusion ratio of 5:1. Immediately after extrusion, forced water cooling was applied to ensure a cooling rate of 50°C / s within the 900°C to 400°C temperature range to suppress the precipitation of brittle phases, resulting in the bimetallic metallurgical composite tube blank.

[0214] The bimetallic composite tube blank prepared in this embodiment was tested: The interfacial shear strength is 405 MPa; ultrasonic C-scan shows that the interfacial bonding is continuous, uniform, and defect-free.

[0215] Comparative Example 1 This comparative example provides a bimetallic metallurgical composite tube blank, which differs from Example 1 only in that: No vacuuming is performed in step (4); In step (5), air cooling is used in the temperature range of 900℃ to 400℃ (i.e., water spray cooling is replaced by air cooling).

[0216] The remaining processes are the same as in Example 1.

[0217] The bimetallic composite tube blank prepared in this comparative example was tested: The interfacial shear strength is 228 MPa; there are discontinuous oxide inclusions at the interface, and some carbide precipitates at the interface.

[0218] Comparative Example 2 This comparative example provides a bimetallic metallurgical composite tube blank, which differs from Example 6 only in that: Step (31) The nickel-based alloy powder is pure nickel powder (Ni mass percentage ≥ 99.5%).

[0219] No vacuuming is performed in step (4); In step (5), air cooling is used in the temperature range of 900℃ to 400℃ (i.e., water spray cooling is replaced by air cooling).

[0220] The remaining processes are the same as in Example 6.

[0221] The bimetallic composite tube blank prepared in this comparative example was tested: The interfacial shear strength is 185 MPa; the interface is continuous (Fe, Cr, Mo). 23 C6 carbides, with discontinuous oxide inclusions at the interface.

[0222] Comparative Example 3 This comparative example provides a bimetallic metallurgical composite tube blank, which differs from Example 7 only in that: Step (3) is not performed: preparation of nickel-based alloy powder and slurry and slurry coating.

[0223] No vacuuming is performed in step (4).

[0224] The remaining processes are the same as in Example 7.

[0225] The bimetallic composite tube blank prepared in this comparative example was tested: The interfacial shear strength is 162 MPa; the interface is continuous (Fe, Cr, Mo). 23 C6 carbides, with discontinuous oxide inclusions at the interface.

[0226] Comparative Example 4 This comparative example provides a bimetallic metallurgical composite tube blank, which differs from Example 8 only in that: Step (31) The nickel-based alloy powder does not contain Nb.

[0227] No vacuuming is performed in step (4); In step (5), air cooling is used in the temperature range of 900℃ to 400℃ (i.e., water spray cooling is replaced by air cooling).

[0228] The remaining processes are the same as in Example 8.

[0229] The bimetallic composite tube blank prepared in this comparative example was tested: The interfacial shear strength is 265 MPa; the coating has insufficient ability to fix carbon, the diffusion layer grains are relatively coarse, some carbide precipitates are present at the interface, and there are discontinuous oxide inclusions at the interface.

[0230] Comparative Example 5 This comparative example provides a bimetallic metallurgical composite tube blank, which differs from Example 9 only in that: No vacuuming is performed in step (4); In step (5), the temperature is raised to 1080°C in the walking beam furnace; and then air-cooled in the temperature range of 900°C to 400°C (i.e., water spray cooling is replaced by air cooling).

[0231] The remaining processes are the same as in Example 9.

[0232] The bimetallic composite tube blank prepared in this comparative example was tested: The interfacial shear strength is 210 MPa; there are discontinuous oxide inclusions at the interface, and some carbide precipitates at the interface.

[0233] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A nickel-based alloy, characterized by, The nickel-based alloy comprises the following chemical components by weight percentage: C≤0.08%, Si 0.20%~0.60%, P≤0.025%, S≤0.015%, Al 0.015%~0.035%, Mn 0.40%~0.70%, Cr 20.0%~25.0%, Mo 1.0%~3.0%, Ni 41.0%~45.0%, Nb 0.8%~1.2%; balance Fe and unavoidable impurities.

2. The nickel-base alloy of claim 1, wherein, The nickel-based alloy also includes one or more of the following chemical components in weight percentage: V 0.5%~0.8%, Ti 0.3%~0.6%, Cu 0.8%~1.5%.

3. A nickel-based alloy slurry characterized by, The nickel-based alloy slurry comprises nickel-based alloy powder and an organic carrier, wherein the organic carrier comprises an organic solvent; The nickel-based alloy powder comprises the chemical composition of the nickel-based alloy according to any one of claims 1-2.

4. The nickel-based alloy slurry of claim 3, wherein, The mass ratio of the nickel-based alloy powder to the organic carrier is (72-78):(22-28). The organic carrier comprises the following components in parts by weight: The ingredients include 3.5 to 4.5 parts of binder, 1.0 to 1.5 parts of plasticizer, 0.3 to 0.6 parts of rheology modifier, and 93.4 to 95.2 parts of solvent.

5. The nickel-based alloy slurry of claim 4, wherein, The binder comprises polyvinyl butyral, the plasticizer comprises dibutyl phthalate, the rheology modifier comprises ethyl cellulose, and the solvent comprises terpineol.

6. A bimetallic metallurgical composite pipe blank, characterized by The bimetallic composite tube blank includes an outer base tube, an intermediate transition layer, and an inner liner tube arranged coaxially from the outside to the inside. The outer base tube and the inner liner tube are metallurgically bonded through the intermediate transition layer. The outer base tube is made of 15CrMoG steel, 12Cr1MoVG steel or 12Cr2MoG steel. The intermediate transition layer comprises the nickel-based alloy according to any one of claims 1-2; The inner liner is made of S30408 ​​austenitic stainless steel, S31603 austenitic stainless steel or NS1402 corrosion-resistant alloy.

7. A method of producing a bimetallic metallurgical composite pipe blank as claimed in claim 6, characterized in that Includes the following steps: S1. Provide an outer base tube, an inner liner tube, and a nickel-based alloy slurry, wherein the nickel-based alloy slurry is the nickel-based alloy slurry according to any one of claims 3-5; S2. The nickel-based alloy slurry is coated on the inner surface of the outer base tube and dried to form a coating, resulting in an outer base tube with a coating on the inner surface. The inner liner is placed in the outer base tube with the coating on the inner surface. Then, the two ends of the inner liner and the outer base tube are sealed and vacuumed to form an assembled tube body. Alternatively, the nickel-based alloy slurry is coated onto the outer surface of the inner liner tube, dried to form a coating, resulting in an inner liner tube with a coated outer surface. The inner liner tube with the coated outer surface is placed in the outer base tube, and then the two ends of the inner liner tube and the outer base tube are sealed and vacuumed to form an assembled tube body. Alternatively, the nickel-based alloy slurry is coated onto the inner surface of the outer base tube and the outer surface of the inner liner tube, respectively. After drying, a coating is formed, resulting in an outer base tube with a coating on the inner surface and an inner liner tube with a coating on the outer surface. The inner liner tube with a coating on the outer surface is placed inside the outer base tube with a coating on the inner surface. Then, the two ends of the inner liner tube and the outer base tube are sealed and vacuumed to form an assembled tube body. S3. Under a protective atmosphere, the assembled tube body is kept at 1150-1250℃ for a first preset time, and then hot-extruded at 1100-1200℃ with an extrusion ratio of (4.5-6.5):

1. Then, it is cooled by water spraying, and the cooling rate in the temperature range of 900℃ to 400℃ is not less than 40℃ / s. After being cooled by water spraying to 400℃, it is air-cooled to room temperature to obtain the bimetallic metallurgical composite tube blank.

8. The preparation method according to claim 7, characterized in that, In step S1, the surface roughness Ra of the inner surface of the outer base tube and the outer surface of the inner liner tube is 6.3–10.0 μm; and / or, In step S2, before sealing and welding the two ends of the inner liner tube and the outer base tube and drawing a vacuum, the process also includes baking at 250-300°C for 1-2 hours. The end faces of the inner cover tube and the outer base tube are sealed and vacuumized, so that the vacuum degree of the annular cavity formed between the inner cover tube and the outer base tube is not greater than 5.0x10 -3 Pa.

9. The preparation method according to claim 7, characterized in that, When the unit of the first preset time is min and the unit of the total wall thickness of the assembled tube is mm, the numerical relationship between the first preset time and the total wall thickness of the assembled tube is as follows: First preset time = total wall thickness of assembled tube body × (1.5~2.0).

10. The application of the bimetallic metallurgical composite tube blank according to claim 6 or the bimetallic metallurgical composite tube blank prepared by any one of claims 7-9 in the preparation of heat exchange tubes.

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