Bimetal composite oil casing pipe with pipe opening threads manufactured through laser additive and preparation method of bimetal composite oil casing pipe

Abstract

The invention discloses a bimetal composite oil casing with a pipe opening thread manufactured through laser additive and a preparation method of the bimetal composite oil casing, and belongs to the field of oil and gas field exploitation underground equipment manufacturing. The preparation method mainly aims at preparation of oil casing threads with corrosion-resistant and high-strength requirements, and comprises the following steps: firstly, removing a surface material at a pipe orifice thread part through turning, and processing to remove the depth which is equal to the thread height of the thread, so that the outer surface of a threaded pipe orifice connecting part is smooth and free of threads; according to the method, a thread is directly prepared on the outer surface of a threaded pipe opening through laser cladding, the bottom of the threaded pipe opening is equivalent to a base plate in the additive manufacturing process, the connection strength of the thread and a bimetal composite oil casing pipe opening is enhanced, the additive manufacturing thread is introduced into the end of the bimetal composite oil casing pipe, an additive manufacturing material is directly used as the thread, and the double-metal composite oil casing pipe opening is formed. And meanwhile, the residual stress state of the thread part can be improved, and various properties of the thread are enhanced.

Description

Technical Field

[0001] This invention belongs to the field of downhole equipment manufacturing for oil and gas field development, specifically relating to a bimetallic composite oil casing with laser additive manufacturing of pipe threads and its preparation method. Background Technology

[0002] Laser cladding technology, as a key technology in laser additive manufacturing, has broad application prospects. It is mainly used to prepare coatings with high hardness, wear resistance, and corrosion resistance, and can replace chrome plating and arc welding techniques for preparing special functional coatings on the surface of parts. The surface properties of the laser cladding layer mainly depend on the properties of the metal material used, while the overall strength of the part is ensured by the base material. The prepared special functional coatings have metallurgical bonding characteristics, high bonding strength, and stable mechanical properties, making them suitable for the manufacture of high-end products.

[0003] For highly corrosive operating conditions (including H2S, CO2, Cl) - Oil casing used in high-temperature and high-pressure conditions typically uses nickel-based alloy oil casing, or bimetallic composite oil casing instead. Bimetallic composite oil casing usually has a nickel-based alloy layer applied to the surface of a carbon steel oil casing of the corresponding grade through a special process to improve the corrosion resistance of the casing surface. The threaded parts are usually treated with electroplating, phosphating, or other surface treatments to improve the corrosion resistance of the threaded parts. However, traditional surface treatment processes often result in low coating bonding strength (below 100 MPa) and coating thickness typically 10-30 μm, which cannot effectively improve the corrosion resistance and service life of the threaded parts, and cannot meet the requirement of over 20 years of service life for corrosion-resistant oil casing under high sulfur content conditions.

[0004] Nickel-based alloy cladding layers prepared by laser cladding technology are characterized by low dilution rate and metallurgical bonding between the cladding layer and the substrate. The cladding layer exhibits high strength, hardness, and corrosion resistance. However, the microstructure of the laser cladding layer material is that of cast titanium. When laser cladding is used to prepare threads for bimetallic composite oil casings, a brittle σ phase easily forms at the dissimilar metal interface. The overall mechanical properties of the cladding layer often fail to reach the level of castings or forgings, limiting the application of laser cladding for thread preparation. CN103967425 provides a fully covered composite bimetallic oil pipe, but does not perform corrosion-resistant treatment on the threads. CN112049580A discloses a bimetallic composite oil pipe joint, but only performs corrosion-resistant treatment on the sealing surface cross-section, without mentioning the corrosion-resistant treatment process for the threaded portion.

[0005] In summary, while full-coverage composite treatment of the tubing body and corrosion-resistant treatment of joint sealing surfaces have been achieved, the specific performance requirements of the threaded parts have not been effectively addressed, particularly in areas such as thread geometry accuracy control, interfacial bonding strength enhancement, and stress corrosion resistance optimization. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a bimetallic composite oil casing with laser additive manufacturing of pipe threads and its preparation method, so as to solve the problem that the corrosion resistance and service life of the threaded part of the bimetallic composite oil casing in the prior art are difficult to meet the service requirements.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A method for preparing a bimetallic composite oil casing with laser additive manufacturing of pipe threads includes the following steps: S1, removing the surface material of the threaded portion of the outer surface of the threaded pipe opening by turning; S2, a cladding layer is prepared on the outer and inner surfaces of the threaded pipe opening by laser cladding; S3, threads are prepared on the outer surface of the threaded pipe opening by laser cladding, and ultrasonic vibration is performed simultaneously during the laser cladding process; S4, Laser cladding is performed on the end face ring of the threaded pipe to obtain the end face cladding layer; S5 involves turning the threads of the threaded pipe opening, followed by laser shock peening to strengthen the root of the thread.

[0008] A further improvement of the present invention is that: Preferably, when the composite oil casing is a carbon steel oil casing matrix, the laser cladding material in S3 includes a nickel-based alloy, a nano-TiC reinforcing phase, and a rare earth reinforcing agent.

[0009] Preferably, in S2 and S3, the content of nano-TiC reinforcing phase in the laser cladding material is 0.3 wt%, and the content of rare earth reinforcing agent is 0.1 wt%.

[0010] Preferably, in S3, the thread thickness prepared by laser cladding is greater than the actual maximum thread thickness.

[0011] Preferably, in S3, the laser power is 2.0-3.0KW, the spot size is 3-5mm, the scanning speed is 10-30mm / s, the overlap rate is 40-60%, the thickness of the single-layer additive layer is 0.8-1.5mm, and multi-layer cladding is performed to meet the dimensional requirements of thread processing.

[0012] Preferably, in S3, the ultrasonic vibration frequency is 40-80kHz.

[0013] Preferably, in S4, the thickness of the end face cladding layer is ≥3mm.

[0014] Preferably, in S4, the power density during laser shock is 10. 10 W / cm 2 Shock wave pressure ≥ 5 GPa.

[0015] Preferably, after S5, the dimensional accuracy and sealing performance of the pipe thread are tested.

[0016] A bimetallic composite oil casing with threaded nozzle obtained by any of the above preparation methods using laser additive manufacturing, wherein the threaded portion of the bimetallic composite oil casing has a tensile strength ≥800MPa, a shear strength ≥685MPa, and a corrosion rate ≤0.007mm / a.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing bimetallic composite oil casing with laser additive manufacturing of pipe threads. This method is mainly for preparing oil casing threads with requirements for corrosion resistance and high strength. The method first removes the carbon steel substrate from the surface of the threaded pipe end by turning, making the outer surface of the threaded pipe end connection smooth and threadless. The turning depth is greater than the designed thread height. The method directly prepares the thread by laser cladding on the outer surface of the threaded pipe end. The bottom of the threaded pipe end is equivalent to the substrate in the additive manufacturing process, which enhances the connection strength between the thread and the bimetallic composite oil casing pipe end. The additively manufactured thread is introduced into the end of the bimetallic composite oil casing. The additively manufactured material is directly used as the thread, which enhances the various properties of the thread and improves the residual stress state of the threaded part. This invention combines laser cladding with ultrasonic vibration. During the cladding process, ultrasonic vibration is added to the molten pool, causing the grains to disperse and refine during cooling, thus improving the strength of the cladding layer material. A laser shock peening post-treatment is then applied to the thread surface prepared by laser cladding to further reduce residual stress on the cladding layer surface, changing the tensile stress at the thread root and surface to compressive stress, thereby improving the thread's fatigue life. Furthermore, this manufacturing method can improve the geometric accuracy control of the thread. This laser additive manufacturing method is suitable for materials containing H2S, CO2, and Cl. - Preparation of oil casing threads for high-corrosion oil and gas field well conditions.

[0018] This invention also has the following advantages: 1) The bimetallic composite oil casing thread proposed in this invention is prepared by laser-ultrasonic field composite additive manufacturing technology. It mainly solves the problems of refining the structure and high strength requirements of the cladding layer on the surface of the thread. This method solves the problems of improving the bonding strength between the thread and the matrix and the strength of the cladding layer material itself.

[0019] 2) The end face of the threaded part of the oil casing provided by the present invention is also sealed by laser cladding, which ensures that the pipe end and the inner and outer surfaces are made of highly corrosion-resistant nickel-based alloy, thus solving the corrosion resistance problem of the oil casing thread and sealing part. 3) This invention uses laser shock reinforcement for post-processing of the thread after machining, which changes the residual stress state of the thread and mainly solves the problem of improving the fatigue life of the cladding layer at the root of the thread.

[0020] 4) The material system used in this invention, by adding 0.3wt% nano-TiC and 0.1wt% rare earth reinforcing agent to nickel-based alloy powder, suppresses the problem of easy formation of σ brittle phase at dissimilar metal interfaces and improves the comprehensive mechanical properties of the thread. Attached Figure Description

[0021] Figure 1 This is a flowchart of the present invention; Figure 2 This is a structural diagram of the composite oil casing of the present invention. Detailed Implementation

[0022] The present invention will now be described in further detail with reference to the accompanying drawings: To enable those skilled in the art to understand the features and effects of the present invention, 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 regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0023] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0024] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0025] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0026] When traditional oil casing threads are treated with electroplating or phosphating, the coating bonding strength is insufficient and the thickness is limited, failing to meet the long-term service requirements under highly corrosive conditions. Existing technologies for thread treatment mostly focus on modifying the sealing surface, but this is insufficient to meet the service requirements of corrosion-resistant oil casings.

[0027] This invention relates to the design of a laser additive manufacturing system for bimetallic composite oil sleeve threads, a laser-ultrasonic composite additive manufacturing process, and post-processing techniques for improving part performance, specifically including the following steps: S1, the carbon steel substrate of the threaded part on the outer surface of the threaded pipe is removed by turning; S2, a cladding layer is prepared on the outer and inner surfaces of the threaded pipe opening by laser cladding; S3, threads are prepared on the outer surface of the threaded pipe opening by laser cladding, and ultrasonic vibration is performed simultaneously during the laser cladding process; S4, Laser cladding is performed on the end face ring of the threaded pipe to obtain the end face cladding layer; S5 involves turning the threads of the threaded pipe opening, followed by laser shock peening to strengthen the root of the thread.

[0028] The process includes several steps: Turning to remove the threaded carbon steel substrate involves using a rotary cutting tool to remove the original thread structure, or turning the entire carbon steel substrate at the threaded location to a certain depth. This can be achieved using a CNC lathe with carbide cutting tools, providing a smooth substrate surface for subsequent metallurgical bonding. Laser cladding for thread fabrication involves melting metal powder with a high-energy laser beam and depositing it layer by layer on the substrate surface to form a cladding material for thread fabrication. This can be achieved using a coaxial powder feeding system with path planning software, enabling metallurgical bonding of dissimilar metals. Ultrasonic vibration involves introducing high-frequency mechanical vibration into the molten pool region. This can be achieved using a vibration system composed of a piezoelectric transducer and an amplitude transformer. This technique suppresses the formation of brittle phases through cavitation. The end-face annular cladding layer forms a ring-shaped metal layer on the end face of the pipe. This can be achieved using a ring-shaped scanning path with an adjustable-angle laser head, enhancing the corrosion resistance of the sealing surface. Laser shock strengthening refers to the use of high-power-density lasers to induce shock waves and produce plastic deformation. Specifically, it can be achieved by using a tunable pulsed laser in conjunction with a constraint layer. This treatment forms a residual compressive stress layer at the root of the thread.

[0029] Further analysis shows that the machining of the substrate surface eliminates the geometric features and surface defects of the original thread, providing a uniform contact interface for laser cladding. During the thread cladding forming stage, the synchronously applied ultrasonic vibration causes the molten pool metal to oscillate at high frequency, promoting grain refinement and reducing elemental segregation, effectively suppressing the formation rate of brittle σ phases. Furthermore, this application achieves a metallurgical bonding layer with a thickness of millimeters through laser cladding. The end-face annular cladding layer forms a dense protective layer through continuous scanning, blocking the path of corrosive media intrusion along the end face. When the machined thread undergoes laser shock treatment, the plasma shock wave generated by the high-energy laser causes plastic deformation of the surface metal, forming a gradient-distributed residual compressive stress at the thread root, significantly improving fatigue resistance. The various process steps work synergistically, improving thread performance from multiple dimensions, including interface modification, structural strengthening, and stress regulation.

[0030] The method of the present invention is applicable to bimetallic composite oil casing with carbon steel material base material such as P110 / P125 steel grade.

[0031] In some embodiments of the present invention, in step S2, during the laser cladding process, the cladding layer material is composed of a nickel-based alloy, a nano-TiC reinforcing phase, and a rare earth reinforcing agent; wherein the content of the nano-TiC reinforcing phase is 0.3 wt%, and the content of the rare earth reinforcing agent is 0.1 wt%; the particle size of the nickel-based alloy is 38-75 μm, and the particle size of the nano-TiC reinforcing phase is 50-80 nm. Exemplarily, the rare earth reinforcing agent can be CeO2, La2O3, or Y2O3.

[0032] The materials that can be used in this invention include nickel-based alloy powders such as Inconel 625, Inconel 718, Ni825, and Ni925. The powder specifications are spherical powders with a particle size of 200-400 mesh, and nano-TiC and rare earth reinforcing agents are added to improve the microstructure and properties.

[0033] During laser cladding, a nickel-based alloy, acting as the matrix material, undergoes a metallurgical reaction with the carbon steel matrix to form a continuously transitioning interfacial bonding layer. Nano-TiC particles are uniformly distributed within the molten pool, forming a second-phase strengthening structure. Rare earth elements promote uniform molten pool flow by reducing surface tension. Through the synergistic effect of these three elements, a composite strengthening structure of fine-grained and dispersed strengthening is formed within the cladding layer. The segregation of rare earth elements in the interfacial region reduces the formation of brittle intermetallic compounds, thereby improving the crack propagation resistance of the threaded portion while maintaining metallurgical bonding strength.

[0034] In this invention, during laser cladding on a carbon steel substrate, nano-TiC particles are uniformly dispersed in the molten pool to form dislocation pinning points. When the content is controlled at 0.3% by weight, it ensures the interfacial bonding strength between the reinforcing phase and the matrix while avoiding increased brittleness of the cladding layer due to excessive addition. Rare earth elements preferentially segregate at grain boundaries during solidification, inhibiting carbon diffusion during the ferrite-austenite phase transformation and hindering the nucleation and growth of the σ-brittle phase. The synergistic effect of the two additives reduces the grain size of the cladding layer to below 10 μm, while controlling the thickness of the interfacial brittle phase to within 2 μm.

[0035] In some embodiments of the present invention, the thickness of the thread additive layer is greater than the actual maximum height of the thread, ensuring that the threaded portion after processing is entirely made of nickel-based alloy manufactured by laser additive manufacturing.

[0036] In some embodiments of the present invention, the two sleeves are connected by a coupling, which can be made of nickel-based alloy.

[0037] Thread thickness refers to the actual formed thickness of the thread structure before machining in the laser cladding process. Specifically, it can be achieved by combining layered scanning path planning with molten pool morphology monitoring, forming a thread preform exceeding the design dimensions through layer-by-layer stacking. During the thread preformation stage, laser energy input control and cladding trajectory planning ensure that the cladding layer thickness exceeds the maximum design value of the thread. The machining allowance allows the turning process to completely remove excess cladding material from the surface, ensuring the dimensional integrity of the threaded area. The retained dense cladding layer's internal structure forms a uniform columnar crystal structure through grain refinement, effectively maintaining the tensile strength and corrosion resistance of the thread root region.

[0038] In S2, the specific process parameters for the laser-ultrasonic composite additive manufacturing are as follows: laser power is 2.0-3.0KW, spot size is φ3-5mm, scanning speed is 10-30mm / s, overlap rate is 40-60%, single-layer additive layer thickness is 0.8-1.5mm, protective gas flow rate is 10-20L / min, and during the thread laser cladding process, the inner cavity of the oil casing is cooled to below 50℃ by liquid nitrogen spray cooling.

[0039] In S3, during the laser cladding process, a coaxial powder-feeding laser cladding system combined with ultrasonic vibration composite technology is used for the cladding additive manufacturing of bimetallic composite oil casing threads. The specific process parameters for the laser-ultrasonic composite additive manufacturing are as follows: laser power 2.0-3.0KW, spot size φ3-5mm, scanning speed 10-30mm / s, overlap rate 40-60%, single-layer additive layer thickness 0.8-1.5mm, protective gas flow rate 10-20L / min. During the thread laser cladding process, the inner cavity of the oil casing is cooled to below 50℃ by liquid nitrogen jet cooling.

[0040] By limiting the lower limit of laser power, complete melting of the powder can be ensured to form a metallurgical bond, while the upper limit can prevent the rapid formation of brittle phases at the interface due to matrix overheating. Setting the spot size matches the molten pool size to the thread geometry, ensuring forming accuracy while avoiding localized heat accumulation. A dynamic balance is achieved between scanning speed and laser power, maintaining stable molten pool flow to form a dense cladding layer while shortening the high-temperature dwell time to suppress brittle phase precipitation. Controlling the overlap ratio ensures effective metallurgical bonding between adjacent cladding passes, eliminating interlayer incomplete fusion defects and improving overall structural continuity. The limitation on the thickness of a single additive layer necessitates a multi-layer thin-layer deposition strategy, refining grains and dispersing residual stress through multiple thermal cycles.

[0041] As a preferred option, the laser power is 2.5KW, the spot size is φ4.0mm, the scanning speed is 10-30mm / s, the overlap rate is 50%, the thickness of the single-layer additive layer is 1.2mm, the protective gas flow rate is 15L / min, and the cooling method for the inner cavity of the oil casing is liquid nitrogen spray cooling to below 50℃.

[0042] In some embodiments of the present invention, the ultrasonic vibration frequency is 40-80kHz; the ultrasonic vibration time is linked to the laser cladding system, with the ultrasonic vibration being turned on in advance for 3 seconds and the ultrasonic vibration being turned off after cladding for 10 seconds.

[0043] As a preferred option, the ultrasonic vibration frequency is 55kHz.

[0044] During solidification, the molten metal is subjected to high-frequency mechanical vibration, resulting in periodic pressure fluctuations within the liquid metal. These fluctuations induce turbulence within the molten pool, accelerating the interdiffusion of nickel-based alloying elements and the carbon steel matrix, while inhibiting localized aggregation in chromium-rich regions at the interface. This turbulent flow also disrupts the continuity of dendrite growth, transforming the solidified structure from coarse columnar crystals to fine equiaxed crystals. The rupture of cavitation bubbles generated by the vibration energy forms microjets, promoting secondary melting of unmelted powder within the cladding layer and eliminating interlayer bonding defects. This invention controls the ultrasonic vibration frequency between 40-80 kHz. The cavitation effect generated in this frequency band alters the grain growth pattern during molten pool solidification. The lower frequency limit of 40 kHz ensures the vibration energy penetrates the molten pool to a certain depth, while the upper frequency limit of 80 kHz avoids excessive attenuation of high-frequency signals in the metallic medium. This parameter range allows for effective transmission of vibration energy along the thickness of the cladding layer.

[0045] This invention employs a laser-ultrasonic composite cladding device to perform additive cladding on the threaded portion of the outer wall of the oil casing. The cladding length is 150mm. The laser used is a 6kW fiber laser with a wavelength of 900-1080nm and a spot diameter of 4.0mm. Two layers are clad on the outer wall laser cladding head and the machined portion of the pipe end, ensuring a cladding layer thickness ≥3.0mm. The ultrasonic vibration device is located below the oil casing opposite the cladding head. The ultrasonic vibration device is linked to the laser cladding system, and the ultrasonic vibration function is automatically activated when laser cladding begins.

[0046] The technical solution of this invention simultaneously applies cladding to the end face, ensuring that both the pipe end and the inner and outer surfaces are made of a highly corrosion-resistant nickel-based alloy. The thickness of the end face cladding layer refers to the vertical dimension of the metal protective layer formed on the end face of the threaded pipe through laser cladding. Specifically, it can be achieved by controlling the cumulative thickness of the cladding layer using a layered welding process, with each layer's additive thickness controllable within the range of 0.8-1.5 mm. When the cladding layer thickness reaches 3 mm, the depth of the molten pool formed by the laser energy input is sufficient to penetrate the oxide layer on the substrate surface, promoting a continuous and dense metallurgical bond between the cladding material and the substrate. This thickness range can cover the depth of the heat-affected zone of the substrate material, avoiding residual stress concentration at the interface. Simultaneously, the thickened cladding layer can form multiple grain boundary barrier structures, effectively slowing down the rate of corrosive media diffusion along grain boundaries under high temperature and high pressure conditions. In subsequent thread machining, this thickness also provides sufficient allowance for turning operations, preventing the protective layer from failing due to machining losses.

[0047] In some embodiments of the present invention, after obtaining the thread through laser cladding, a laser post-treatment process is introduced. Specifically, this involves laser shock peening. This post-treatment alters the residual stress state of the threaded portion, addressing the issue of improving the fatigue life of the cladding layer at the thread root. The power density during the treatment is 10. 10 W / cm 2 The shock wave pressure is ≥5 GPa, and a water film confinement layer is used. During laser shock strengthening, a high-power-density laser beam forms a plasma explosion on the material surface, generating a shock wave with an extremely short duration. When the shock wave pressure reaches 5 GPa, its energy is sufficient to penetrate the cladding layer in the thread root region, causing dislocation slip and grain boundary reorganization within the material. This process not only eliminates the residual stress formed during cladding but also forms a dense, fine-grained structure on the surface layer at the thread root, thereby sealing existing microcracks and inhibiting the initiation of new cracks.

[0048] In some embodiments of the present invention, the dimensional accuracy and sealing performance of the pipe thread are tested after fabrication. During laser cladding additive manufacturing, residual stress may occur at the interface of dissimilar metals due to differences in thermal expansion coefficients, leading to dimensional deviations or microcracks at the thread root. A coordinate measuring machine (CMM) can be used to scan the thread height and pitch around the entire circumference, locating localized deformation areas and providing feedback to correct subsequent processing parameters. In the sealing performance testing stage, helium is used as a tracer medium for pressure testing. Its molecular penetration properties are utilized to detect the presence of through-hole defects on the thread meshing surface, thereby verifying the continuity of the metallurgical interface. In some specific embodiments, dimensional accuracy testing can be combined with an optical profilometer to simultaneously analyze the surface roughness of the thread flanks, and sealing performance testing can be performed under simulated operating temperature conditions using cyclic pressure testing.

[0049] The present invention also discloses a bimetallic composite oil casing with a threaded nozzle obtained by the above preparation method using laser additive manufacturing. The threaded portion of the bimetallic composite oil casing has a tensile strength of not less than 800 MPa, a shear strength of not less than 685 MPa, and a corrosion rate of not more than 0.007 mm / a.

[0050] The tensile strength of the bimetallic composite oil casing of this invention, not less than 800 MPa, refers to the load-bearing capacity of the threaded structure under axial tensile load. This is achieved through the synergistic effect of laser cladding metallurgical interface and ultrasonic vibration to eliminate porosity defects. This feature ensures the thread maintains structural integrity under high stress conditions. The shear strength, not less than 685 MPa, refers to the ability of the thread meshing surface to resist shear deformation. This is achieved through the gradient nanocrystalline structure and residual compressive stress field formed by laser shock peening treatment. This feature effectively inhibits plastic deformation of the thread contact surface. The corrosion rate, not higher than 0.007 mm / a, refers to the annual corrosion depth of the material in a corrosive medium environment. This is achieved through the synergistic effect of nano-TiC particle dispersion strengthening and rare earth element grain boundary purification. This feature blocks the penetration channels of corrosive media at grain boundaries.

[0051] The following description, in conjunction with specific embodiments, provides further details.

[0052] Example 1: Preparation of nickel-based alloy threads for φ88.9×6.45, P110 bimetallic composite oil pipes.

[0053] A nickel-based alloy cladding layer was prepared on the threaded portion of a composite oil casing using a laser-ultrasonic field composite cladding technology. The preparation process included: S1, Surface pretreatment of threaded parts For the machining of the outer wall of the oil pipe opening, since the finished threaded outer wall is a tapered thread, the minimum outer diameter of the threaded pipe opening is 4.0mm smaller than the outer diameter of the pipe body, which means a single-sided thickness reduction of 2.0mm. Therefore, the machining dimension of the outer wall opening before cladding is the pipe diameter minus 5.0mm, i.e., a single-sided machining thickness of 2.5mm, with a machining length of 150mm, ensuring that the entire threaded area after machining is coated with nickel-based alloy metal. Before cladding, the machined area is laser-cleaned to remove surface oil, rust, etc.

[0054] S2, as Figure 2 As shown, laser cladding is performed on the outer and inner surfaces of the bimetallic composite oil pipe to form a cladding layer on the outer and inner surfaces; S3, laser cladding on the outer surface of bimetallic composite tubing threads The outer diameter of the threaded part of the oil pipe is laser-ultrasonic composite cladding equipment is used to laser clad the threaded part of the outer surface of the oil pipe. The cladding thickness is 3mm on one side and 4.0mm within 20mm of the threaded end, to ensure the processing of the sealing surface size after the joint is narrowed.

[0055] Cladding material: Nickel-based alloy Inconel718 (particle size 38-75μm) + 0.3wt% nano-TiC reinforcing phase (particle size 50-80nm) + 0.1wt% rare earth reinforcing agent.

[0056] Cladding process parameters: laser power 2500W, spot diameter 4mm, cladding speed 20mm / s, overlap 2mm, powder feeding rate 20g / min, single-layer cladding thickness 1.0mm, ultrasonic vibration pre-start time 3s, ultrasonic vibration shutdown delay time after single-layer cladding 10s. Ultrasonic vibration frequency 55kHz. Interlayer cooling, inner wall liquid nitrogen spray cooling below 50℃. Overall cladding layer thickness 3mm per side.

[0057] S4, end face cladding: The end face ring of the oil pipe is laser clad with nickel-based alloy Inconel718. The cladding process parameters are: laser power 2000W, spot size 4mm, cladding speed 15mm / s, feed 1.5mm, powder feeding 15g / min, and cladding layer thickness ≥3mm, ensuring that the entire surface of the pipe end is made of nickel-based alloy material after processing.

[0058] S5, Pipe thread and seal turning The pipe cladding layer is machined using a CNC lathe for threading and sealing.

[0059] S6, thread post-treatment After thread machining, laser shock peening is used to strengthen the root of the thread. Laser power density: 10 10 W / cm 2The shock wave pressure is ≥5GPa, the overlap rate is 30%, a water film constraint layer is used, and the impact is repeated 3 times.

[0060] S7, Thread accuracy and seal inspection The final machined threads and seals are inspected for dimensional accuracy and sealing performance.

[0061] The bimetallic composite oil casing finally prepared by this invention has the following advantages.

[0062] 1) This invention uses laser-ultrasonic composite energy field cladding to prepare composite oil casing thread parts. The tensile strength of the nickel-based alloy cladding metal in the thread part can reach more than 800 MPa, which meets the strength requirements of oil casing thread. The tensile strength of the cladding layer is more than 50% higher than that of the traditional laser cladding process.

[0063] 2) The cladding material of this invention is a high-strength nickel-based alloy with added nano-ceramic reinforcing phase and rare earth reinforcing agent. The brittle phase at the interface is reduced to less than 0.05%, which has excellent corrosion resistance and mechanical properties. The interfacial shear strength of the composite layer reaches more than 685 MPa, which is 60% higher than that of the traditional process. 3) The cladding material of this invention is a high-strength nickel-based alloy, which has excellent corrosion resistance and the corrosion rate of the composite layer is ≤0.007mm / a; 4) This invention allows for the selection of materials suitable for different operating conditions, based on the usage environment of the oil casing, to meet the requirements of use under harsh conditions. The thread root is strengthened by laser impact, which significantly improves the stress state of the threaded area. The number of threading cycles is increased from ≤4 times to more than 7 times, and the service life is increased by 133%. 5) The composite oil pipe thread of the present invention adopts a fully encapsulated metallurgical bonded nickel-based alloy, and there will be no galvanic corrosion caused by the potential difference between different materials in the cladding layer and the threaded part.

[0064] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a bimetallic composite oil casing with laser additive manufacturing of pipe threads, characterized in that, Includes the following steps: S1, removing the surface material of the threaded portion of the outer surface of the threaded pipe opening by turning; S2, a cladding layer is prepared on the outer and inner surfaces of the threaded pipe opening by laser cladding; S3, threads are prepared on the outer surface of the threaded pipe opening by laser cladding, and ultrasonic vibration is performed simultaneously during the laser cladding process; S4, Laser cladding is performed on the end face ring of the threaded pipe to obtain the end face cladding layer; S5 involves turning the threads of the threaded pipe opening, followed by laser shock peening to strengthen the root of the thread.

2. The method for preparing a bimetallic composite oil casing with laser additive manufacturing of pipe threads according to claim 1, characterized in that, When the composite oil casing is a carbon steel oil casing substrate, the laser cladding material in S3 includes a nickel-based alloy, a nano-TiC reinforcing phase, and a rare earth reinforcing agent.

3. The method for preparing a bimetallic composite oil casing with laser additive manufacturing of pipe threads according to claim 2, characterized in that, In S2 and S3, the content of nano-TiC reinforcing phase in the laser cladding material is 0.3 wt%, and the content of rare earth reinforcing agent is 0.1 wt%.

4. The method for preparing a bimetallic composite oil casing with laser additive manufacturing of pipe threads according to claim 1, characterized in that, In S3, the thread thickness prepared by laser cladding is greater than the actual maximum thread thickness.

5. The method for preparing a bimetallic composite oil casing with laser additive manufacturing of pipe threads according to claim 1, characterized in that, In S3, the laser power is 2.0-3.0KW, the spot size is 3-5mm, the scanning speed is 10-30mm / s, the overlap rate is 40-60%, the thickness of a single additive layer is 0.8-1.5mm, and multi-layer cladding is performed to meet the dimensional requirements of thread processing.

6. The method for preparing a bimetallic composite oil casing with a pipe end thread manufactured by laser additive manufacturing according to claim 1, characterized in that, In S3, the ultrasonic vibration frequency is 40-80kHz.

7. The method for preparing a bimetallic composite oil casing with a pipe end thread manufactured by laser additive manufacturing according to claim 1, characterized in that, In S4, the thickness of the end face cladding layer is ≥3mm.

8. The method for preparing a bimetallic composite oil casing with a pipe end thread manufactured by laser additive manufacturing according to claim 1, characterized in that, In S4, the power density during laser shock is 10. 10 W / cm 2 Shock wave pressure ≥ 5 GPa.

9. A method for preparing a bimetallic composite oil casing with a pipe end thread manufactured by laser additive manufacturing according to any one of claims 1-8, characterized in that, After S5, the dimensional accuracy and sealing performance of the pipe thread are tested.

10. A bimetallic composite oil casing with laser additive manufacturing of pipe end threads, prepared by any one of claims 1-9, characterized in that, The threaded portion of the bimetallic composite oil casing has a tensile strength ≥800MPa, a shear strength ≥685MPa, and a corrosion rate ≤0.007mm / a.

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