Bimetal composite pipe and production method thereof

Abstract

The invention discloses a bimetal composite pipe and a production method thereof, and the method comprises the following steps: preparing a high-chromium cast iron inner pipe matrix through centrifugal casting, and preparing a nickel-based alloy transition layer on the outer surface of the high-chromium cast iron inner pipe matrix through laser cladding; the inner wall of the outer pipe is subjected to partitioned sand blasting treatment and coated with a multifunctional binder containing Al-Si alloy powder, nickel powder, Cr powder, Y2O3 and a pore forming agent; the outer pipe is subjected to partitioned gradient heating, meanwhile, the inner pipe is preheated, and hot charging is completed under the temperature gradient; and finally, carrying out in-situ reaction-diffusion composite treatment to form the bimetal tube with the gradient composite interface layer. The interface layer sequentially comprises a nickel-based alloy transition layer, an element mutual diffusion layer and a microcosmic channel strengthening layer containing directional micropores from inside to outside. The problems of interface bonding and stress concentration in long pipe manufacturing are effectively solved, the interface shear strength of the obtained composite pipe is larger than or equal to 280 MPa, the thermal shock cycle life is larger than or equal to 1000 times, and the reliability under the severe working condition is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of metal pipe processing, specifically, it relates to a bimetallic composite pipe and its production method. Background Technology

[0002] As a key component of construction machinery, concrete conveying pipes are subjected to severe erosion and wear from the concrete mixture on their inner walls. To improve wear resistance, bimetallic composite pipes, which use a composite structure of a high-wear-resistant material (such as high-chromium cast iron) as the inner pipe and a high-toughness material (such as carbon steel) as the outer pipe, have become the mainstream technology in this field.

[0003] Among existing technologies, the most widely used is the centrifugal casting composite process. This process involves directly pouring molten wear-resistant metal into a rotating outer tube in a single casting. However, this process has two inherent drawbacks: First, due to the limitations of the fluidity and solidification rate of the molten metal, the length of a single casting is limited, making it difficult to meet the needs of long tubes. Welding is often required for connection, and the weld area inevitably becomes a weak point in terms of wear resistance. Second, and more critically, the composite interface formed by this process is inherently inadequate. Because the inner and outer tube materials differ significantly in their physicochemical properties (such as coefficients of thermal expansion and melting points), direct metallurgical bonding easily leads to the formation of coarse, brittle intermetallic compounds and significant residual stress at the interface. This makes the interface prone to crack initiation and propagation when the composite tube is subjected to harsh conditions such as high pressure, strong impact, and thermal cycling, resulting in interlayer delamination or cracking, severely restricting the reliability and service life of the composite tube.

[0004] To overcome the length limitations of centrifugal casting, an alternative approach of "split manufacturing + thermal assembly" has emerged in existing technologies. This method involves manufacturing long inner and outer tubes separately, then assembling them by heating the outer tube and utilizing its thermal expansion. However, this method also faces significant challenges: its interfacial bonding relies solely on macroscopic mechanical shrinkage stress, resulting in low bonding strength and poor shear and peel resistance. More importantly, for long pipes, traditional uniform heating and cooling methods can create uneven temperature and stress fields along the pipe's axis, easily leading to stress concentration at the pipe ends and causing the composite pipe to fail from the ends early in its service life.

[0005] Therefore, the technical problem that urgently needs to be solved in this field is: how to provide a bimetallic composite pipe and its production method, which can not only realize the manufacturing of long-sized pipes, but more importantly, can build a strong, stable gradient composite interface between dissimilar materials that can effectively alleviate and redistribute stress, thereby fundamentally improving the interface reliability and overall service life of the composite pipe under harsh working conditions. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a bimetallic composite pipe and its manufacturing method, the details of which are as follows: A method for producing a bimetallic composite pipe includes the following steps: (1) Preparation of the inner tube: The high-chromium cast iron alloy melt is centrifugally cast into an inner tube substrate. On the outer surface of the inner tube substrate, a nickel-based alloy transition layer with a thickness of 100~300μm is prepared by laser cladding. The nickel-based alloy contains 3~8% Fe and 1.5~4% B. The inner tube with the transition layer is subjected to two-stage heat treatment: first, it is held at 1000~1050℃ for 1~2 hours, and then held at 520~560℃ for 3~5 hours. The alloy, by mass percentage, comprises: C: 2.0~3.5%, Si: 0.5~1.5%, Mn: 0.5~1.5%, Cr: 25~35%, Mo: 0.8~2.0%, Ni: 0.5~1.5%, W: 0.5~1.8%, V: 0.1~0.5%, Nb: 0.1~0.4%, B: 0.02~0.08%, with the balance being Fe and unavoidable impurities, of which P≤0.04% and S≤0.04%. (2) Preparation of outer tube: Select carbon steel or low alloy steel seamless steel pipe as the outer tube substrate, perform zoned sandblasting on the inner wall of the outer tube to form a rough area with Ra=10~15μm at the pipe end and a smooth area with Ra=6~10μm in the middle area. Coat the inner wall of the sandblasted outer tube with a multifunctional adhesive, and then keep it at 80~120℃ for 10~30 minutes to allow the organic carrier to initially volatilize and solidify. The adhesive is composed of the following components: 50~70% Al-Si alloy powder, 10~20% nickel powder, 5~15% Cr powder, 1~3% rare earth oxide Y2O3, and 2~5% thermal decomposition pore-forming agent. (3) Gradient thermal bonding: The outer tube coated with adhesive is heated in a protective atmosphere to make the temperature of the tube end area reach 650~700℃ and the temperature of the tube middle area reach 600~650℃, forming an axial temperature gradient. At the same time, the inner tube is preheated to 480~520℃. While maintaining the temperature gradient, the inner tube is pushed into the outer tube. During the pushing process, the pushing speed is controlled to be 0.3~1.0m / s. (4) In-situ reaction-diffusion composite: The assembled composite tube is kept at 580~620℃ for 30~90 minutes, then cooled to below 250℃ at a rate of 20~40℃ / hour, and then air-cooled to room temperature.

[0007] Furthermore, in step (1), the parameters of the laser cladding process are: laser power 2~4kW, scanning speed 5~15mm / s, and overlap rate 30~50%. Through this combination of parameters, a dense and defect-free metallurgical bond can be formed between the nickel-based alloy transition layer and the inner tube substrate, while controlling the dilution rate and microstructure of the transition layer.

[0008] Furthermore, in step (2), the particle size of the Al-Si alloy powder, nickel powder, and Cr powder is all between -200 mesh and -400 mesh. This particle size range helps to ensure uniform powder mixing and dense coating, avoids component segregation, and provides a suitable specific surface area for subsequent metallurgical reactions.

[0009] Furthermore, in step (2), the thermally decomposable pore-forming agent is at least one of ammonium carbonate, ammonium bicarbonate, or ammonium oxalate. By selecting a specific ammonium salt thermally decomposable pore-forming agent, it can decompose stably within a set temperature range, generating uniformly distributed micropores, avoiding interface defects caused by concentrated gas release, and ensuring the controllable formation of the microchannel structure.

[0010] Furthermore, the partitioned gradient heating described in step (3) is achieved by setting independently temperature-controlled induction coils in different areas of the outer tube. Using independently temperature-controlled induction coils to achieve partitioned gradient heating has the advantages of rapid heating, precise temperature control, and flexible adjustment of the axial temperature gradient, which can adapt to the process requirements of different specifications of pipe fittings and ensure the stable implementation of the gradient heat fitting composite process.

[0011] This invention also provides a bimetallic composite tube prepared by the above method, comprising an outer tube and an inner tube composited inside the outer tube, with a gradient composite interface layer formed between the inner and outer tubes. This interface layer, from the inside out, comprises: a nickel-based alloy transition layer with a thickness of 100-300 μm; an elemental interdiffusion layer with a thickness of 20-80 μm, rich in Fe, Ni, Cr, Al, and Si elements; and a microchannel reinforcement layer containing 3-15 vol% oriented micropores. This structure achieves a smooth transition of material properties, ensuring interfacial bonding strength while exhibiting excellent thermal shock resistance and impact resistance.

[0012] Furthermore, the micropores in the microchannel reinforcement layer exhibit a gradient distribution, with the porosity near the inner tube region being 1.5 to 3 times that near the outer tube region. This gradient distribution of micropores, with a higher porosity near the inner tube region, aligns with the stress distribution patterns of the composite pipe during service. It effectively alleviates compressive stress on the inner tube side and tensile stress on the outer tube side, further optimizing the stress state at the interface.

[0013] Furthermore, the bimetallic tube exhibits an interfacial shear strength ≥280MPa and a thermal shock cycle life ≥1000 cycles. These performance indicators meet the long-term use requirements under harsh working conditions such as concrete conveying.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: I. This invention establishes a gradient transition of material properties by laser-cladding a nickel-based alloy transition layer on the outer surface of the inner tube, effectively solving the interfacial bonding problem caused by the significant differences in physicochemical properties between high-chromium cast iron and the steel outer tube. This transition layer, as a functionally graded material, forms a good metallurgical bond with the inner tube matrix and is also highly compatible with the binder on the outer tube side, significantly inhibiting the formation of coarse and brittle intermetallic compounds and improving the interfacial strength, toughness, and thermal stability.

[0015] Second, this invention employs a unique process combining zoned gradient heating and zoned sandblasting to specifically address the problem of uneven axial stress distribution in the thermal bonding of long pipe fittings. By setting higher temperatures and greater roughness in the pipe end region, stress concentration in this area is effectively compensated, ensuring uniform and consistent interface bonding quality throughout the entire pipe length. This fundamentally avoids the premature failure of pipe ends in traditional thermal bonding processes.

[0016] Third, this invention constructs a unique micro-channel structure in the interface layer through the design of a multifunctional binder containing a pore-forming agent and a precisely controlled in-situ reaction-diffusion process. These channels not only provide more pathways for element interdiffusion and promote full metallurgical bonding, but also effectively alleviate and redistribute stress during service, significantly improving the interface reliability of the composite pipe under thermal shock and impact loads. Detailed Implementation

[0017] To enable those skilled in the art to understand the features and effects of this application, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art in this application, and in case of conflict, the definitions in this specification shall prevail.

[0018] The present application will be described below with reference to specific embodiments and examples. It should be understood that these specific embodiments and examples are merely illustrative and are not intended to limit the scope or use of the present application.

[0019] Unless otherwise stated, the methods, reagents, and conditions used in the preparation examples, comparative examples, and embodiments described below are conventional methods, reagents, and conditions in the art.

[0020] Unless otherwise specified, in this application, parts by weight represent the relative number of mass parts in the composition, which can be any mass unit, such as, but not limited to, kilograms, grams, etc.

[0021] The specific embodiments are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. Unless otherwise specified, the raw materials and reagents used in the examples are commercially available.

[0022] Example 1 (1) Inner tube preparation: A high-chromium cast iron alloy melt with a total mass of 100 kg was prepared. Its chemical composition (mass percentage) was: C: 2.8%, Si: 1.0%, Mn: 1.0%, Cr: 30%, Mo: 1.4%, Ni: 1.0%, W: 1.2%, V: 0.3%, Nb: 0.25%, B: 0.05%, P: 0.036%, S: 0.036%, with the balance being Fe. The alloy melt was centrifuged at 1420℃ to form the inner tube substrate at a speed of 1200 rpm. After casting, forced cooling was performed using mist cooling. A nickel-based alloy transition layer was prepared by laser cladding on the outer surface of the inner tube substrate. The laser power was 3 kW, the scanning speed was 10 mm / s, the overlap rate was 40%, and the thickness of the transition layer was 200 μm. Its composition was Fe 5%, B 1.0%, and C 1.0%. 2.5% nickel-based alloy; the inner tube with transition layer is subjected to two-stage heat treatment: first, it is held at 1020℃ for 1.5 hours and then oil-quenched to room temperature; then it is held at 540℃ for 4 hours and then air-cooled after being taken out of the furnace.

[0023] (2) Outer tube preparation: 35CrMn low alloy steel seamless steel pipe was selected as the outer tube substrate, with a wall thickness of 7mm and a length of 9 meters; the inner wall of the outer tube was subjected to zoned sandblasting treatment: a rough area with Ra=12μm was formed in the area 250mm away from the pipe end, and a smooth area with Ra=8μm was formed in the middle of the pipe; a multifunctional binder was prepared with a total mass of 500g, the composition (mass percentage) of which was: 60% Al-Si alloy powder (Al:Si=82:18), 15% nickel powder, 10% Cr powder, 2% Y2O3, 3% ammonium bicarbonate, and the balance being an organic carrier. All powder particles were -300 mesh; the binder was coated on the inner wall of the sandblasted outer tube with a coating thickness of 100μm, and then kept at 100℃ for 20 minutes.

[0024] (3) Gradient thermal bonding: The outer tube coated with adhesive is subjected to zoned gradient heating under a nitrogen protective atmosphere (oxygen content <100ppm). Through an independently temperature-controlled induction coil, the temperature of the tube end area reaches 680℃ and the temperature of the tube middle area reaches 630℃, forming an axial temperature gradient. At the same time, the inner tube is preheated to 500℃. While maintaining the temperature gradient, the inner tube is pushed into the outer tube at a pushing speed of 0.6m / s.

[0025] (4) In-situ reaction-diffusion composite: The assembled composite tube was kept at 600℃ for 60 minutes. Then it was cooled to below 250℃ at a controlled rate of 30℃ / hour, and then air-cooled to room temperature.

[0026] Example 2 (1) Inner tube preparation: A high-chromium cast iron alloy melt with a total mass of 100 kg was prepared. Its chemical composition (mass percentage) was: C: 2.0%, Si: 0.5%, Mn: 0.5%, Cr: 25%, Mo: 0.8%, Ni: 0.5%, W: 0.5%, V: 0.1%, Nb: 0.1%, B: 0.02%, P: 0.035%, S: 0.035%, with the balance being Fe. The alloy melt was centrifuged at 1380℃ to form the inner tube substrate at a speed of 800 rpm. After casting, forced cooling was performed using mist cooling. A nickel-based alloy transition layer was prepared by laser cladding on the outer surface of the inner tube substrate. The laser power was 2 kW, the scanning speed was 5 mm / s, the overlap rate was 30%, and the thickness of the transition layer was 100 μm. Its composition was Fe 3%, B 0.035%, and C 0.035%. 1.5% nickel-based alloy; the inner tube with transition layer is subjected to two-stage heat treatment: first, it is held at 1000℃ for 1 hour and then oil-quenched to room temperature; then it is held at 520℃ for 3 hours and then air-cooled after being taken out of the furnace.

[0027] (2) Preparation of outer tube: No. 20 seamless carbon steel pipe was selected as the outer tube substrate, with a wall thickness of 4mm and a length of 6m. The inner wall of the outer tube was subjected to zoned sandblasting treatment: a rough area with Ra=10μm was formed in the area 200mm away from the end of the tube, and a smooth area with Ra=6μm was formed in the middle of the tube. A multifunctional adhesive was prepared with a total mass of 500g. Its composition (mass percentage) was: 50% Al-Si alloy powder (Al:Si=88:12), 10% nickel powder, 15% Cr powder, 1% Y2O3, 2% ammonium carbonate, and the balance was an organic carrier. All powder particles were -200 mesh. The adhesive was coated on the inner wall of the sandblasted outer tube with a coating thickness of 50μm, and then kept at 80℃ for 30 minutes.

[0028] (3) Gradient thermal bonding: The outer tube coated with adhesive is subjected to zoned gradient heating under a nitrogen protective atmosphere (oxygen content <100ppm). Through an independently temperature-controlled induction coil, the temperature of the tube end area reaches 650℃ and the temperature of the tube middle area reaches 600℃, forming an axial temperature gradient. At the same time, the inner tube is preheated to 480℃. While maintaining the temperature gradient, the inner tube is pushed into the outer tube at a pushing speed of 0.3m / s.

[0029] (4) In-situ reaction-diffusion composite: The assembled composite tube is kept at 580℃ for 30 minutes, then cooled to below 250℃ at a rate of 20℃ / hour, and then air-cooled to room temperature.

[0030] Example 3 (1) Inner tube preparation: A high-chromium cast iron alloy melt with a total mass of 100 kg was prepared. Its chemical composition (mass percentage) was: C: 3.5%, Si: 1.5%, Mn: 1.5%, Cr: 35%, Mo: 2.0%, Ni: 1.5%, W: 1.8%, V: 0.5%, Nb: 0.4%, B: 0.08%, P: 0.038%, S: 0.038%, with the balance being Fe. The alloy melt was centrifuged at 1450℃ to form the inner tube substrate at a speed of 1500 rpm. After casting, forced cooling was performed using mist cooling. A nickel-based alloy transition layer was prepared by laser cladding on the outer surface of the inner tube substrate. The laser power was 4 kW, the scanning speed was 15 mm / s, the overlap rate was 50%, and the thickness of the transition layer was 300 μm. Its composition was Fe 8%, B 1.5%, and C 1.5%. 4% nickel-based alloy; the inner tube with transition layer is subjected to two-stage heat treatment: first, it is held at 1050℃ for 2 hours and then oil-quenched to room temperature; then it is held at 560℃ for 5 hours and then air-cooled after being taken out of the furnace.

[0031] (2) Outer tube preparation: 42CrMo low alloy steel seamless steel pipe was selected as the outer tube substrate, with a wall thickness of 10mm and a length of 12m. The inner wall of the outer tube was subjected to zoned sandblasting treatment: a rough area with Ra=15μm was formed in the area 300mm away from the end of the pipe, and a smooth area with Ra=10μm was formed in the middle of the pipe. A multifunctional adhesive was prepared with a total mass of 500g. Its composition (mass percentage) was: 70% Al-Si alloy powder (Al:Si=78:22), 20% nickel powder, 5% Cr powder, 3% Y2O3, 5% ammonium oxalate, and the balance was an organic carrier. All powder particles were -400 mesh. The adhesive was coated on the inner wall of the sandblasted outer tube with a coating thickness of 150μm, and then kept at 120℃ for 10 minutes.

[0032] (3) Gradient thermal bonding: The outer tube coated with adhesive is subjected to zoned gradient heating under an argon protective atmosphere (oxygen content <100ppm). Through an independently temperature-controlled induction coil, the temperature of the tube end area reaches 700℃ and the temperature of the tube middle area reaches 650℃, forming an axial temperature gradient. At the same time, the inner tube is preheated to 520℃. While maintaining the temperature gradient, the inner tube is pushed into the outer tube at a pushing speed of 1.0m / s.

[0033] (4) In-situ reaction-diffusion composite: The assembled composite tube was kept at 620℃ for 90 minutes, then cooled to below 250℃ at a rate of 40℃ / hour, and then air-cooled to room temperature.

[0034] Comparative Example 1 (Traditional Centrifugal Casting Process) The outer tube (35CrMn low alloy steel, 7mm wall thickness, 9m length) with the same material and size as in Example 1 was selected. After preheating the outer tube to 300°C, the high-chromium cast iron alloy melt with the same composition as in Example 1 was directly poured into the rotating outer tube and centrifugally cast at 1200rpm to form an inner lining layer. After pouring, forced cooling was performed using mist cooling, and the composite tube underwent the same two-stage heat treatment as in Example 1.

[0035] Comparative Example 2 (Traditional thermal bonding process) The inner tube was prepared using the same method as in Example 1 (including laser cladding transition layer and heat treatment). Then, the same outer tube substrate as in Example 1 was selected. The inner wall of the outer tube was uniformly sandblasted (Ra=10μm for the whole tube) and coated with ordinary aluminum-silicon adhesive (without nickel powder, Cr powder, Y2O3 and pore-forming agent). The outer tube was uniformly heated to 650°C (without temperature gradient), and the inner tube was preheated to 500°C. The inner tube and outer tube were assembled at a pushing speed of 0.6m / s. The cooling process was controlled in the same way as in Example 1.

[0036] Comparative Example 3 (without microchannel structure) The inner tube was prepared using the same method as in Example 1, and the same outer tube substrate and partition sandblasting treatment were used as in Example 1. After sandblasting, the inner wall of the outer tube was coated with a binder without a pore-forming agent (composition: 63% Al-Si alloy powder, 15% nickel powder, 10% Cr powder, 2% Y2O3). The remaining operations were the same as in Example 1.

[0037] Examples 1-3 and Comparative Examples 1-3 were tested using the following methods: 1. Interfacial shear strength Typically, following ASTM A265 or similar standards, a specimen with the interface is cut from the composite tube and fixed in a special fixture. A shear force is applied on a universal testing machine in a direction parallel to the interface until the interface fails. The maximum load is recorded, and the shear strength is calculated based on the shear area.

[0038] 2. Thermal shock cycle life The composite pipe sample is repeatedly and rapidly transferred between high-temperature (e.g., 200℃) and room-temperature (or low-temperature) media and held for a certain period of time to form a cycle. This process is repeated until cracks, peeling, or significant performance degradation are observed at the interface. The total number of cycles that the sample can withstand is recorded, thereby simulating the drastic temperature changes experienced by the pipeline during service and assessing the interface's resistance to thermal fatigue.

[0039] 3. Interface structural features The sample is cut perpendicular to the interface, and after mounting, grinding, polishing, and etching, a metallographic sample is prepared. The morphology, thickness, continuity, and presence of defects (such as cracks and pores) of each layer of the interface are observed using a metallographic microscope or a scanning electron microscope (SEM) to visually verify whether a gradient composite interface layer has been formed.

[0040] 4. Residual stress Non-destructive testing methods such as X-ray diffraction (XRD) are used to measure the lattice distortion in the region near the interface. The magnitude and distribution of residual stress (tensile stress or compressive stress) are calculated to quantify the internal stress introduced during the process due to the difference in the thermal expansion coefficient of the materials. The lower the stress, the more stable the interface.

[0041] 5. Pipe length limitation For the traditional centrifugal casting process (Comparative Example 1), the maximum single length of composite pipe successfully manufactured in one run using existing equipment and technology is directly recorded. This is compared with the length achievable by the method of the present invention (Example), thus visually demonstrating the ability of the present invention to solve the technical problem of long pipe manufacturing.

[0042] The test data is shown in the table below: Testing items Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Interfacial shear strength (MPa) 300 290 295 185 210 255 Thermal shock cycle life (times) 1100 1050 1080 350 480 680 Interface structural features Complete gradient structure Complete gradient structure Complete gradient structure Brittle compound layer Simple combination layer No microscopic channels Residual stress (MPa) 95 98 97 220 180 150 Pipe length limit Unrestricted Unrestricted Unrestricted 3 meters Unrestricted Unrestricted Analyze the data in the table: 1. Compared with the traditional centrifugal casting process (Comparative Example 1): This invention completely solves the technical problem of limited tube length, realizes the manufacturing of tubes of arbitrary length, increases the interfacial shear strength by 62%, and increases the thermal shock life by 214%, fully demonstrating the superiority of the gradient interface structure. Moreover, it avoids the quality hazards and uneven wear resistance caused by welding.

[0043] 2. Compared with the traditional hot-fitting process (Comparative Example 2): the zoned gradient heating and zoned sandblasting technologies effectively solve the problem of stress concentration at the pipe ends. The design of the multi-functional adhesive increases the interfacial bonding strength by 43%, and the complete three-layer gradient structure provides better stress buffering capacity. 3. Compared with the structure without microchannels (Comparative Example 3): the presence of microchannels further increases the interfacial shear strength by 18%; the thermal shock cycle life is increased by 62%, proving that the microchannels have a significant effect on relieving thermal stress; the interfacial residual stress is reduced by 47%, reflecting the stress redistribution function of the microchannels.

[0044] In summary, this invention achieves significant technological advancements in interfacial bonding strength, thermal shock lifetime, and stress control through the synergistic effects of laser cladding transition layer, zoned gradient heating, multifunctional adhesive, and microchannel structure. It completely overcomes the shortcomings of existing technologies and possesses outstanding substantive features and significant technological progress.

[0045] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. It should not be considered that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for producing a bimetallic composite pipe, characterized in that, Includes the following steps: (1) Preparation of inner tube: The high-chromium cast iron alloy melt is centrifugally cast into an inner tube substrate. On the outer surface of the inner tube substrate, a nickel-based alloy transition layer with a thickness of 100~300μm is prepared by laser cladding process. The nickel-based alloy contains 3~8% Fe and 1.5~4% B. The inner tube with the transition layer is subjected to two-stage heat treatment. First, it is held at 1000~1050℃ for 1~2 hours, and then held at 520~560℃ for 3~5 hours. The high-chromium cast iron alloy, by mass percentage, comprises: C: 2.0~3.5%, Si: 0.5~1.5%, Mn: 0.5~1.5%, Cr: 25~35%, Mo: 0.8~2.0%, Ni: 0.5~1.5%, W: 0.5~1.8%, V: 0.1~0.5%, Nb: 0.1~0.4%, B: 0.02~0.08%, with the balance being Fe and unavoidable impurities, of which P≤0.04% and S≤0.04%. (2) Preparation of outer tube: Select carbon steel or low alloy steel seamless steel pipe as outer tube substrate, perform zoned sandblasting treatment on the inner wall of outer tube, form a rough area with Ra=10~15μm in the pipe end area, and form a smooth area with Ra=6~10μm in the middle area of ​​the pipe, coat the inner wall of the sandblasted outer tube with a multifunctional adhesive, and then keep it at 80~120℃ for 10~30 minutes; The binder is composed of the following components: 50-70% Al-Si alloy powder, 10-20% nickel powder, 5-15% Cr powder, 1-3% rare earth oxide Y2O3, and 2-5% thermally decomposable pore-forming agent; (3) Gradient thermal bonding: The outer tube coated with adhesive is heated in a protective atmosphere to make the temperature of the tube end area reach 650~700℃ and the temperature of the tube middle area reach 600~650℃, forming an axial temperature gradient. At the same time, the inner tube is preheated to 480~520℃. While maintaining the temperature gradient, the inner tube is pushed into the outer tube. During the pushing process, the pushing speed is controlled to be 0.3~1.0m / s. (4) In-situ reaction-diffusion composite: The assembled composite tube is kept at 580~620℃ for 30~90 minutes, then cooled to below 250℃ at a rate of 20~40℃ / hour, and then air-cooled to room temperature.

2. The production method according to claim 1, characterized in that: In step (1), the parameters of the laser cladding process are laser power 2~4kW, scanning speed 5~15mm / s, and overlap rate 30~50%.

3. The production method according to claim 1, characterized in that: In step (2), the particle size of the Al-Si alloy powder, nickel powder and Cr powder is between -200 mesh and -400 mesh.

4. The production method according to claim 1, characterized in that: In step (2), the thermally decomposable pore-forming agent is at least one of ammonium carbonate, ammonium bicarbonate, or ammonium oxalate.

5. The production method according to claim 1, characterized in that: The partitioned gradient heating described in step (3) is achieved by setting up independently temperature-controlled induction coils in different areas of the outer tube.

6. A bimetallic composite tube prepared by any one of claims 1 to 5, characterized in that: It includes an outer tube and an inner tube composite inside the outer tube. A gradient composite interface layer is formed between the inner tube and the outer tube. The interface layer includes, from the inside to the outside: a nickel-based alloy transition layer with a thickness of 100~300μm; an element interdiffusion layer with a thickness of 20~80μm, rich in Fe, Ni, Cr, Al and Si elements; and a microchannel reinforcement layer containing 3~15 vol% directionally distributed micropores.

7. The gradient composite bimetallic tube according to claim 6, characterized in that: The micropores in the microchannel reinforcement layer are distributed in a gradient, and the microporosity near the inner tube region is 1.5 to 3 times that near the outer tube region.

8. The gradient composite bimetallic tube according to claim 6, characterized in that: The bimetallic tube has an interfacial shear strength ≥280MPa and a thermal shock cycle life ≥1000 cycles.