A metal composite pipe interface anti-oxidation pretreatment method based on thermal expansion and cold contraction principle

Abstract

The application discloses a metal composite pipe interface anti-oxidation pretreatment method based on the thermal expansion and cold shrink principle and belongs to the technical field of metal composite rolling process. The method comprises the following steps: removing the oxidation layer on the surface to be compounded, heat-treating the outer metal pipe so that the inner diameter of the outer metal pipe is larger than the outer diameter of the inner metal pipe, sleeving the inner metal pipe and the outer metal pipe together to form a combined pipe blank, and cooling the combined pipe blank to room temperature. The method utilizes the principle of thermal expansion and cold shrink to make the inner and outer metal pipes mutually sleeve and closely adhere to each other, and removes the air at the interface, thereby effectively avoiding the problem that the interface of the combined pipe blank is oxidized in subsequent hot working forming. The method has the advantages of remarkable anti-oxidation effect, simple and stable process, low equipment investment cost and the like, and is suitable for interface anti-oxidation pretreatment in large-scale production of metal pipe rolling compounding.

Description

Technical Field

[0001] This invention belongs to the field of metal composite material rolling technology, specifically relating to a pretreatment method for anti-oxidation of metal composite pipe interface based on the principle of thermal expansion and contraction. Background Technology

[0002] Metal composite pipes combine the superior properties of two or more metallic materials, such as corrosion resistance, high strength, and low cost, and are widely used in petrochemical, municipal water supply, and marine engineering fields. The fabrication of metal composite pipes typically employs a rolling composite process. The quality of the interfacial bonding is a core factor determining the performance of the composite pipe, and interfacial oxidation is one of the key defects affecting the bonding quality. During the rolling composite process, if residual air remains at the interface of the composite pipe blank, the oxygen in the air will react with the surfaces of the inner and outer metal pipes to be laminated during subsequent high-temperature rolling and other hot processing steps, forming an oxide film. This oxide film severely hinders the metallurgical bonding of the inner and outer metal layers, leading to defects such as delamination and peeling at the composite pipe interface, thus reducing the mechanical properties and service life of the composite pipe.

[0003] Existing methods for preventing oxidation at the interface of metal composite pipes mainly include vacuum bonding, inert atmosphere-protected bonding, interface coating with anti-oxidation coatings, and explosive-rolling composite. Among these, vacuum bonding and inert atmosphere-protected bonding require specialized equipment, resulting in high equipment costs, complex operation, low bonding efficiency, and difficulty in large-scale production. Interface coating with anti-oxidation coatings suffers from problems such as difficulty in controlling coating uniformity and easy coating detachment during subsequent rolling, contaminating the interface and affecting composite quality. While explosive-rolling composite can effectively avoid interface oxidation, the process is complex, resulting in poor consistency in interface bonding quality and significant environmental pollution. Although some studies have proposed utilizing the difference in thermal expansion coefficients to achieve a tight bond between inner and outer metal pipes through room temperature bonding followed by high-temperature heat treatment, thus reducing the risk of interface oxidation, this method only applies to metal pipe combinations where the inner layer's thermal expansion coefficient is greater than the outer layer's, and requires strict control over the initial dimensional differences and thermal expansion coefficient differences between the composite metal pipes, limiting its practical application. Therefore, there is an urgent need for a simple, easy-to-operate, low-cost, and highly applicable pretreatment method for preventing oxidation at the interface of metal composite pipes to address the shortcomings of existing technologies. Summary of the Invention

[0004] To address the problems of high equipment cost, complex processes, and difficulty in large-scale application of existing anti-oxidation treatment methods for metal composite pipe interfaces, this invention provides a pretreatment method for anti-oxidation of metal composite pipe interfaces based on the principle of thermal expansion and contraction.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] On the one hand, the present invention provides a method for pre-treatment of the interface of metal composite pipes based on the principle of thermal expansion and contraction, comprising the following steps: S1. Surface treatment to be laminated: Provide two metal tubes to be laminated (metal tube A as the outer layer and metal tube B as the inner layer). Grind the inner surface of metal tube A and the outer surface of metal tube B to remove the surface oxide layer. Then clean and dry metal tube A and metal tube B. S2. Interference fitting: The interference fitting temperature is calculated according to formula (1) using the thermal expansion coefficients of metal tube A and metal tube B and the initial dimensions. After placing metal tube A in a heating furnace and heating it to the interference fitting temperature or above, metal tube B is fitted together with metal tube A to form a combined tube blank. Then, it is cooled to room temperature to obtain the interference-fitted combined tube blank. T c =(D B +KD A ) / (D A ×α Ac )+ T0(1) Among them, T c Interference fitting temperature; T0: Room temperature; D A Initial inner diameter of metal tube A; D B Initial outer diameter of metal tube B; α Ac Metal tube A at room temperature ~ temperature T c The average linear expansion coefficient; K: Interference fitting constant, taken as 0.05mm; α Ac Calculate according to formula (2); α Ac =(α A0 +α Ax ) / 2 (2) α Ac Metal tube A at room temperature ~ temperature T c The average linear expansion coefficient; α A0 : Coefficient of linear expansion of metal tube A at room temperature; α Ax Metal tube A at room temperature ~ temperature T x The average linear expansion coefficient, x is taken as 300℃, 200℃, 100℃.

[0007] Further, in step S1, the initial inner diameter of the metal tube A is less than or equal to the initial outer diameter of the metal tube B; the dimensional error of the metal tube does not exceed ±0.005mm; the grinding method is mechanical grinding, and the roughness of the composite interface after grinding is not greater than 10µm; the method for judging the removal of the oxide layer is to expose the metal's original color; the cleaning method is to rinse the surface of the metal tube with industrial anhydrous alcohol; the drying method is to use a heating furnace for drying, with the temperature difference of the heating furnace not exceeding ±10℃, the heating temperature being 80℃-150℃, the heating rate not exceeding 5℃ / min, the holding time being 30min-120min, and the tube being cooled with the furnace after the holding time is completed.

[0008] Further, in step S2, the interference fit temperature does not exceed the oxidation temperature of metal tube A and metal tube B; the inner diameter of metal tube A at the interference fit temperature is larger than the outer diameter of metal tube B in the cold state; during interference fit, metal tube A is in a hot state and metal tube B is in a cold state; the heating method is to use a heating furnace, the temperature difference of the heating furnace does not exceed ±10℃, the heating temperature is not lower than the interference fit temperature, the heating rate does not exceed 5℃ / min, the holding time is 30min-120min, and the tube is cooled with the furnace after the holding time is completed.

[0009] It should be noted that in order to ensure that the error of the obtained interference fit temperature is ≤5℃, the final interference fit temperature must be obtained after three rounds of iterative correction.

[0010] On the other hand, a metal composite tube prepared by the above method is provided, wherein the metal composite tube has a tightly bonded interface and no oxide layer.

[0011] Compared with the prior art, the present invention has the following advantages and positive effects: 1. This invention utilizes the principle of thermal expansion and contraction of metal tubes. After the outer metal tube of the metal composite tube is expanded by heat treatment, it is fitted with the cold inner metal tube. Then, they are cooled together to room temperature. After the outer metal tube cools and contracts, it fits tightly with the inner metal tube, eliminating air at the interface to be composited. This effectively avoids the risk of interface oxidation during subsequent high-temperature rolling and forming processes of the composite tube. 2. This invention can be completed simply by removing the oxide layer, heat treating the outer layer, fitting, and cooling. It does not require complex vacuum equipment or a continuous inert gas supply system. The operation process is simple, the process parameters are easy to control, the stability is strong, the equipment investment cost is low, and it is suitable for industrial-scale production. 3. The interference-fit composite tube blank obtained by the present invention has a certain mechanical bonding compressive stress formed at the interface before rolling, which is beneficial to the plastic deformation of the interface metal and the interdiffusion of elements in the subsequent high-temperature rolling forming process, thereby enhancing the metallurgical bonding of the interface. 4. This invention is applicable to metal materials where the outer diameter of the inner metal tube is greater than or equal to the inner diameter of the outer metal tube, and has a wide range of applications and strong versatility; In summary, the present invention can effectively prevent oxidation of the metal composite pipe interface, promote metallurgical bonding at the interface, and improve the bonding strength at the interface. Attached Figure Description

[0012] Figure 1 This is a process flow diagram of an anti-oxidation pretreatment method for the interface of a metal composite pipe based on the principle of thermal expansion and contraction according to the present invention. Figure 2 This is a schematic diagram showing the process steps of a pretreatment method for preventing oxidation at the interface of a metal composite pipe based on the principle of thermal expansion and contraction, according to the present invention. Figure 3 This is a schematic diagram of the cross-section of the composite tube blank before and after the treatment of the metal composite tube interface anti-oxidation pretreatment method based on the principle of thermal expansion and contraction according to the present invention.

[0013] Among them, 1-metal tube A, 2-metal tube B, 3-combined tube blank, 4-interference fit combined tube blank, 5-air. Detailed Implementation

[0014] Exemplary embodiments will now be described in detail. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention; rather, they are merely examples of methods or apparatus consistent with some aspects of the present invention as detailed in the appended claims.

[0015] Example This invention provides a pretreatment method for preventing oxidation at the interface of metal composite pipes based on the principle of thermal expansion and contraction: S1. Surface Treatment for Composite Assembly: Two types of metal pipes to be composited (X70 pipeline steel pipe and 316L stainless steel pipe) are provided. The X70 pipeline steel pipe serves as the outer layer of the composite pipe, and the 316L stainless steel pipe serves as the inner layer. The initial inner diameter of the X70 pipeline steel pipe is 30.0 mm, the thickness is 8.0 mm, and the length is 100.0 mm. The initial outer diameter of the 316L stainless steel pipe is 30.0 mm, the thickness is 2.0 mm, and the length is 100.0 mm. The oxide layer on the inner surface of the X70 pipeline steel pipe and the outer surface of the 316L stainless steel pipe is removed by mechanical grinding until the metal is exposed. After rinsing the surface of the metal pipes with industrial anhydrous alcohol, the metal pipes are placed in a heating furnace and kept at 150°C for 30 minutes. Furthermore, the dimensional error of the metal tube shall not exceed ±0.005mm, and the temperature difference of the heating furnace shall not exceed ±10℃; S2. Interference fitting: Using the thermal expansion coefficients of X70 pipeline steel pipe and 316L stainless steel pipe and the initial dimensions, the interference fitting temperature is calculated according to formula (1) to be 100℃. After placing metal pipe A in the heating furnace and heating it to 300℃, the cold 316L stainless steel pipe and the hot X70 pipeline steel pipe are fitted together to form a combined pipe blank. Then, it is cooled to room temperature to obtain the interference-fitted combined pipe blank.

[0016] The initial inner diameter of the X70 pipeline steel pipe is the same as the initial outer diameter of the 316L stainless steel pipe. Neither the X70 pipeline steel pipe nor the 316L stainless steel pipe will oxidize in air at temperatures of 300°C or below. After the cold 316L stainless steel pipe and the 300°C hot X70 pipeline steel pipe are fitted together and cooled to room temperature, the inner surface of the X70 pipeline steel pipe and the outer surface of the 316L stainless steel pipe are tightly bonded, and the interfacial air is eliminated. Furthermore, since the coefficient of thermal expansion of the X70 pipeline steel pipe is less than that of the 316L stainless steel pipe, at the same temperature, the increase in thermal expansion of the X70 pipeline steel pipe is less than that of the 316L stainless steel pipe. Therefore, in subsequent high-temperature hot rolling and other processes, as the temperature rises, the interfacial pressure between the X70 pipeline steel pipe and the 316L stainless steel pipe continues to increase. Thus, this invention effectively avoids the risk of interface oxidation of the X70 / 316L bimetallic composite pipe during high-temperature rolling and other hot processing processes.

Claims

1. A method for pre-treatment of the interface of a metal composite pipe based on the principle of thermal expansion and contraction, characterized in that, Includes the following steps: S1. Surface treatment to be laminated: Provide two metal tubes to be laminated (metal tube A as the outer layer and metal tube B as the inner layer). Grind the inner surface of metal tube A and the outer surface of metal tube B to remove the surface oxide layer. Then clean and dry metal tube A and metal tube B. S2. Interference fitting: The interference fitting temperature is calculated according to formula (1) using the thermal expansion coefficients of metal tube A and metal tube B and the initial dimensions. After placing metal tube A in a heating furnace and heating it to the interference fitting temperature or above, metal tube B is fitted together with metal tube A to form a combined tube blank. Then, it is cooled to room temperature to obtain the interference-fitted combined tube blank. T c =(D B +K-D A ) / (D A ×α Ac )+ T0(1) Among them, T c Interference fitting temperature; T0: Room temperature; D A Initial inner diameter of metal tube A; D B Initial outer diameter of metal tube B; α Ac Metal tube A at room temperature ~ temperature T c The average linear expansion coefficient; K: Interference fitting constant, taken as 0.05mm; α Ac Calculate according to formula (2); α Ac =（α A0 +α Ax ） / 2（2） α Ac Metal tube A at room temperature ~ temperature T c The average linear expansion coefficient; α A0 : Coefficient of linear expansion of metal tube A at room temperature; α Ax Metal tube A at room temperature ~ temperature T x The average linear expansion coefficient, x is taken as 300℃, 200℃, 100℃.

2. The pretreatment method for anti-oxidation of metal composite pipe interface based on thermal expansion and contraction according to claim 1, characterized in that, In step S1, the initial inner diameter of metal tube A is less than or equal to the initial outer diameter of metal tube B, and the dimensional error of the metal tube does not exceed ±0.005mm.

3. The pretreatment method for anti-oxidation of metal composite pipe interface based on thermal expansion and contraction according to claim 1 or 2, characterized in that, In step S1, the polishing method is mechanical polishing, and the roughness of the composite interface after polishing is no more than 10µm. The method for judging the removal of the oxide layer is to expose the metal's original color.

4. The method for pretreatment of metal composite pipe interface for anti-oxidation based on thermal expansion and contraction according to claim 1, 2 or 3, characterized in that, In step S1, the cleaning method is to rinse the surface of the metal pipe with industrial anhydrous alcohol.

5. The method for pretreatment of metal composite pipe interface for anti-oxidation based on thermal expansion and contraction according to claim 1, 2, 3 or 4, characterized in that, In step S1, the drying method is to use a heating furnace for drying, with a temperature difference of no more than ±10℃, a heating temperature of 80℃-150℃, a heating rate of no more than 5℃ / min, a holding time of 30min-120min, and cooling with the furnace after the holding time is completed.

6. The method for pretreatment of metal composite pipe interface for oxidation prevention based on thermal expansion and contraction according to claim 1, characterized in that, In step S2, the interference fit temperature does not exceed the oxidation temperature of metal tube A and metal tube B. The inner diameter of metal tube A at the interference fit temperature is greater than the outer diameter of metal tube B in the cold state. During interference fit, metal tube A is in a hot state and metal tube B is in a cold state.

7. The method for pretreatment of metal composite pipe interface for oxidation prevention based on thermal expansion and contraction according to claim 1, characterized in that, In step S2, the calculation of the interference fit temperature must be corrected through three rounds of iterations to ensure that the error of the obtained interference fit temperature is ≤5℃.

8. The method for pretreatment of metal composite pipe interface for oxidation prevention based on thermal expansion and contraction according to claim 1, characterized in that, In step S2, the heating method is to use a heating furnace, the temperature difference of the heating furnace does not exceed ±10℃, the heating temperature is not lower than the interference fit temperature, the heating rate does not exceed 5℃ / min, the holding time is 30min-120min, and the furnace is cooled after the holding time is completed.

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