Manufacturing method of high-strength cold rolled pipe

Abstract

The invention is applicable to the technical field of cold-rolled tube manufacturing, and provides a high-strength cold-rolled tube manufacturing method which comprises the following steps: designing Fe-Co-Ni-Cr-based metastable-state high-entropy alloy components, and adopting a multi-field coupling asynchronous cold rolling unit integrating ultrahigh-frequency pulse induction heating, a strong pulse magnetic field and an ultrahigh-speed aerial fog copious cooling module, so that the high-strength cold-rolled tube is manufactured. Synchronously applying the physical field in rolling deformation; according to the process, instantaneous conjugation of plastic deformation-phase change-amplitude modulation decomposition is forcibly realized, and a three-dimensional nano interlocking reinforced structure consisting of an ultra-fine grain matrix, a nano sheet layer and nano particles is constructed in the pipe in one step, so that ultrahigh strength and good toughness are synchronously obtained; the cold-rolled tube prepared by the method does not need subsequent aging or tempering, the tensile strength can reach 1600 MPa or above, the ductility is not lower than 8%, and the cold-rolled tube has high uniformity, designable functional gradient and high process integration level.

Description

Technical Field

[0001] This invention belongs to the field of cold-rolled tube manufacturing technology, and particularly relates to a method for manufacturing high-strength cold-rolled tubes. Background Technology

[0002] High-performance cold-rolled tubes are core basic materials in key fields such as energy, aerospace, and marine engineering. As equipment develops towards higher parameters, lighter weight, and longer service life, high requirements are placed on the coordinated strength, toughness, and corrosion resistance of tubes.

[0003] Traditional high-performance cold-rolled tube manufacturing technologies mainly follow two paths: one is to use martensitic aging steel, secondary hardening steel, etc., to obtain high strength through complex thermomechanical processing (TMCP) and long-term aging, but often faces problems such as insufficient toughness, narrow process window and long production cycle; the other is to use severe plastic deformation (SPD) methods such as equal channel angle extrusion (ECAP) to refine grains. Although it can greatly improve strength, it is difficult to process tubular workpieces and has extremely low efficiency, making it impossible to achieve industrial continuous production. Summary of the Invention

[0004] This invention provides a method for manufacturing high-strength cold-rolled tubes. By designing an alloy composition system with specific metastable characteristics, and simultaneously introducing multiple physical fields such as ultra-high frequency thermal shock, strong pulsed electromagnetic field, and millisecond-level deep cryogenic field during single-pass cold rolling deformation, the instantaneous, forced, and synergistic occurrence of "deformation-phase transformation-precipitation" is achieved, constructing a three-dimensional nano-interlocking reinforced structure, and obtaining a combination of high strength and good toughness.

[0005] This invention is implemented as follows: a method for manufacturing high-strength cold-rolled tubes, comprising the following steps: S1. Alloy melting and billet preparation: Alloys with the following chemical composition are prepared by weight percentage: Fe: 40-50%, Co: 15-20%, Ni: 15-20%, Cr: 10-15%, Al: 1.0-2.5%, Ti: 0.3-1.0%, C: 0.08-0.15%, B: 0.005-0.02%, N: 0.05-0.10%, with the balance being unavoidable impurities; wherein the atomic ratio of (Ti content) / (C content) is controlled between 0.8 and 1.2. The prepared raw materials are vacuum induction melted and cast into ingots; the alloy ingots are homogenized at 1150-1200℃ for 2-4 hours, and then hot extrusion or skew rolling is performed to produce rough tubes with an outer diameter of D0 and a wall thickness of T0.

[0006] S2. Solution pretreatment: The rough tube is held at 1100-1180℃ for 0.5-1.5 hours to allow the alloying elements to fully dissolve, and then water-quenched or oil-quenched to obtain a supersaturated solid solution structure.

[0007] S3. Multi-field coupled asynchronous cold rolling: The tube blank, after solution treatment and surface lubrication (surface lubrication is achieved by immersing the solution-treated tube blank in an aqueous graphite emulsion lubricant (solid content approximately 12%), then drying it in an oven at 180°C for 5-10 minutes to form a uniform lubricating film), is fed into a dedicated multi-field coupled asynchronous cold rolling mill for processing; the cold rolling mill includes at least a pair of rolls with speed difference, and three energy field application modules integrated near the rolling deformation zone. A) Ultra-high frequency pulse induction heating module: set 5-30mm before the billet enters the roll bite zone, used to heat the surface layer of the billet (depth about 0.1-0.5mm) to a temperature Th 100-250℃ above the Ac3 phase transformation point in an instant before rolling, with a heating frequency of 50-500 kHz and a heating time of 0.5-3 seconds. B) Strong pulsed magnetic field generating module: Its magnetic poles are symmetrically arranged on both sides of the roll deformation zone. When the billet is subjected to the maximum rolling force, a pulsed magnetic field perpendicular to the rolling direction is applied. The magnetic field strength is 3-15 T and the width of a single pulse is 10-100 milliseconds. C) Ultra-high-speed aerosol cryogenic module: Located at the exit position where the billet just leaves the deformation zone of the roll, it is used to rapidly cool the surface of the rolled tube to below -50°C within 10-100 milliseconds. The cooling medium is liquid nitrogen aerosol or ultra-low temperature compressed gas. The three energy field application modules are synchronously controlled by the rolling mill's main control system. The control logic is as follows: the event starting point (t0) is the arrival of the billet head at the center of the heating module; heating is initiated at time t0. Based on the rolling speed calculation, when the heated area of ​​the billet reaches the center of the roll deformation zone (t1), a strong pulse magnetic field is triggered; when the same area of ​​the billet leaves the roll deformation zone (t2), ultra-high-speed gas mist deep cooling is immediately triggered. This synchronous control ensures that the energy field is precisely applied to the material's deformation process. The rolling process is carried out in 1-3 passes on the unit, with a total diameter reduction rate of 20%-50% and a total wall reduction rate of 15%-40%. The above three energy field application modules are activated simultaneously in each pass, and the ratio of the upper and lower linear speeds of the rolls is controlled between 1.05:1 and 1.30:1.

[0008] S4. Finished Product Processing: After the rolled tubes are straightened, cut, and cleaned, the final high-performance cold-rolled tubes are obtained; no subsequent aging or tempering heat treatment is required.

[0009] This invention achieves a strong coupling and closed-loop causal relationship between component design (S1), multi-field coupling process (S3), and final microstructure.

[0010] The metastable design of the composition (S1) provides the basis for multi-field coupling effects: The Fe-Co-Ni-Cr based high-entropy system designed in this invention has high thermal stability and high work hardening ability; the key is to adjust the system to a kinetically metastable state by precisely introducing microalloying elements such as Al, Ti, C, B, and N. Al promotes the formation of B2 ordered nanophases during subsequent deformation; Ti and C exist in near stoichiometry, ensuring the formation of a large number of tiny TiC prototype cores; Trace amounts of boron agglomerate at grain boundaries, improving interfacial bonding. The combination of N with elements such as Cr lowers the thermodynamic energy barrier for amplitude modulation decomposition in the system.

[0011] This compositional design makes the material exceptionally sensitive and tunable to external energy fields (especially heat and magnetic fields), providing a material basis for the effectiveness of subsequent processes.

[0012] Multi-field coupled asynchronous cold rolling (S3) generates a synergistic effect by applying three energy fields synchronously with mechanical deformation on a second / millisecond scale: Ultra-high frequency thermal shock: Instantly creates an extremely steep temperature gradient (>1000 ℃ / mm) and an extremely high heating / cooling rate on the surface of the tube blank; this leads to instantaneous austenitization of the surface layer, greatly increasing plasticity and reducing rolling force; while the core remains in a low-temperature, high-strength state; this "soft outside, hard inside" state combined with the intense shear strain generated by asynchronous rolling introduces an unprecedented non-uniform, multiaxial strain field in the radial and tangential directions of the tube, providing an extremely high nucleation driving force for subsequent phase transformation.

[0013] Strong pulsed magnetic fields: First, they induce powerful eddy currents and Lorentz forces in conductive, rapidly deforming metals. The superposition of this Lorentz force vector with the rolling force vector produces a magnetic vibration effect at the microscopic level, greatly promoting the cross-slip and multiplication-annihilation processes of dislocations, enabling dynamic recovery and the formation of ultrafine substructures. Second, the magnetic field affects the path and rate of atomic diffusion, directionally guiding the amplitude modulation decomposition process induced by nitrogen, causing its products (Cr-rich and N-poor regions) to grow in alignment along the direction of the magnetic field lines, forming nanoscale composition-modulated lamellae. Finally, the magnetic field can also affect the variant selection of martensitic phase transformation, refining the microstructure.

[0014] Millisecond-level cryogenics: Its function is to "instantly freeze" the non-equilibrium metastable structures (including high-density dislocations, a large number of crystal defects, metastable phases, initial nanomodulation structures, etc.) formed under the above-mentioned thermo-magnetic-mechanical coupling, preventing them from relaxing to the equilibrium state; at the same time, cryogenics induces some residual austenite to transform into martensite and generates more crystal defects, further strengthening them.

[0015] The synchronous coupling of these three fields essentially creates an extremely non-equilibrium physical environment in the deformation zone, forcing the material to undergo multiple processes such as "plastic rheology, solid-state phase transformation, and diffusion-type decomposition" simultaneously at ultra-high strain rates, which cannot be simulated by any stepwise process.

[0016] Formation and Performance Enhancement of Three-Dimensional Nano-Interlocking Structure: As a natural result of the above-mentioned components and processes, a novel microstructure—a three-dimensional nano-interlocking structure—is formed in the final finished pipe. This structure includes: Ultrafine-grained dual-phase matrix: a mixed structure of BCC and FCC with grain sizes of 100-500 nm; One-dimensional nanosheet reinforcement: Compositionally modulated nanosheets parallel to the magnetic field direction generated by amplitude modulation decomposition, with a thickness of 2-10 nm, penetrate the matrix grains like nanobrick walls, strongly hindering the movement of dislocations along the main deformation direction and providing strong anisotropic reinforcement. Zero-dimensional nanoparticle reinforcement: Uniformly dispersed coherent B2-NiAl ordered phase (5-20 nm) and TiC carbide (<10 nm) particles provide classic precipitation reinforcement.

[0017] Strengthened interface: The segregation of B element at grain boundaries and phase boundaries significantly improves the interfacial bonding strength and resistance to crack propagation.

[0018] By using a structure in three-dimensional space where the matrix (0D), lamellae (1D), and particles (0D) are interlocked, dislocation movement and crack propagation are hindered from multiple scales and through multiple mechanisms, while achieving ultra-high strength and high damage tolerance (toughness).

[0019] Preferably, in step S1, by controlling the smelting process, the chemical composition of the obtained rough tube exhibits a continuous gradient distribution in the radial direction: within a depth of about 1 mm from the outer surface inward, the contents of Cr, N, and B elements are 10-20 wt% higher than those in the core region of the tube; within a radius of about 1 mm from the core outward, the contents of Ti and Al elements are 8-15 wt% higher than those in the outer surface region; the main elements such as Fe, Co, and Ni remain uniform in the radial direction; simultaneously, 0.01-0.3 wt% of Ce or Y (rare earth elements) is added to the alloy; this gradient composition design is suitable for rough tubes with a wall thickness (T0) of not less than 2 mm, to ensure that the definition of the core and surface regions is physically valid and can exert their functional gradient effect; enabling the tube blank to generate a "targeted response" in subsequent multi-field coupling processes: the surface layer focuses on corrosion resistance and grain boundary strengthening, the core layer focuses on precipitation strengthening, and the rare earth elements play a role in purifying the melt and microalloying, optimizing the formation of the final nanostructure.

[0020] Preferably, in step S3, two optimizations are performed on the multi-field coupling process: Firstly, the strong pulse magnetic field generating module generates a dynamic rotating magnetic field. During the rolling process, its magnetic poles rotate around the pipe axis at a speed of 50-200 rpm, thereby causing the direction of the applied magnetic field to change continuously relative to the pipe, so as to ensure the circumferential uniformity of the strengthening effect.

[0021] Secondly, an ultrasonic vibration field is simultaneously applied in the roll deformation zone. The ultrasonic vibration is generated by a non-contact transducer close to the tube surface and the vibration energy is transmitted through a coupling medium (such as high-temperature resistant silicone oil). The ultrasonic frequency is 20-40 kHz and the power is 5-15 kW. The dynamic rotating magnetic field causes the direction of the Lorentz force and the amplitude-modulated decomposition to change continuously in the circumferential direction, promoting the formation of more uniform and isotropic nanostructures. The introduction of ultrasonic vibration, with its high-frequency "micro-forging" effect, can assist plastic deformation at the microscale, promote dislocation proliferation and rearrangement, and effectively break or passivate micron-level defects, complementing the macroscopic rolling force. Together, these two factors ensure the high uniformity and integrity of the three-dimensional nano-interlocked structure throughout the entire tube volume, further improving the consistency and reliability of product performance.

[0022] Compared with the prior art, the embodiments of this application have the following main advantages: The high-strength cold-rolled tube manufacturing method of the present invention successfully breaks the traditional inverse relationship between strength and toughness of high-strength metal materials. The prepared cold-rolled tube has a tensile strength of over 1600MPa, while the elongation after fracture can still be maintained at over 8%, achieving a synergistic improvement in strength and toughness.

[0023] The traditional step-by-step "deformation-heat treatment" process has been innovated into an integrated "deformation as treatment" process, which eliminates the time-consuming subsequent aging or tempering process, significantly shortens the production cycle and reduces energy consumption.

[0024] By combining composition gradient design with the synergistic control of multiple physical fields, it is possible to actively construct a composite structure that ranges from macroscopic performance gradients to microscopic nanoscale interlocking, thereby achieving customization of material properties. The introduction of dynamic and ultrasonic fields effectively eliminates performance fluctuations caused by static fields or uneven local deformation, significantly improving the circumferential and radial performance uniformity of the finished pipe.

[0025] Through radial gradient composition design, it achieves an integrated function of high corrosion resistance on the surface and ultra-high strength in the core, perfectly adapting to harsh working conditions such as corrosion-resistant high-pressure pipelines on marine platforms and corrosion-resistant pressure-bearing pipelines in the chemical industry, which require both resistance to harsh environmental corrosion and the ability to withstand extremely high internal pressure. Attached Figure Description

[0026] Figure 1 This is a flowchart of the high-strength cold-rolled tube manufacturing method described in this invention.

[0027] Figure 2 This is a typical transmission electron microscope (TEM) image of the cold-rolled tube prepared in Example 1 of the present invention. Detailed Implementation

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, not to describe a particular order.

[0029] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0030] The alloys involved in the following examples have an Ac1 phase transformation point of approximately 720-780℃ and an Ac3 phase transformation point of approximately 800-880℃. In practice, the specific components can be accurately determined by using a thermal expansion meter or thermodynamic calculation software (such as Thermo-Calc).

[0031] All alloys in all embodiments were prepared by vacuum induction melting, with a melting vacuum degree of less than 5.0 × 10⁻⁶. -2 Pa, refining temperature 1600-1650℃, cast into a cylindrical copper mold preheated to 300℃.

[0032] The multi-field coupled asynchronous cold rolling mill involved in this invention operates on the following principle in its core working area: Along the billet rolling direction, this area sequentially integrates three functional modules: Ultra-high frequency pulse induction heating zone: Located about 10-30mm in front of the roll bite point, a set of induction coils surrounding the billet are located at this position, which can rapidly heat the surface of the billet as it passes through.

[0033] Magnetic-force coupling deformation zone: that is, the roll biting area; a pair of upper and lower work rolls with different linear velocities asynchronously roll the billet here, generating severe shear strain; at the same time, a pair of pulsed magnetic poles (N pole and S pole) symmetrically arranged on both sides of the rolls are directly opposite this area, which can apply a strong pulsed magnetic field perpendicular to the rolling direction at the moment of rolling.

[0034] Ultra-high-speed aerosol cryogenic zone: located immediately behind the roll exit; a row or ring of nozzles are aimed at the surface of the just-deformed tube and spray ultra-low temperature aerosol (such as liquid nitrogen aerosol) to achieve millisecond-level rapid cooling.

[0035] The actions of the three functional modules are precisely time-synchronized by the main control system based on the rolling line speed, ensuring that the energy field and the plastic deformation process are precisely coupled in time and space.

[0036] Example 1 This invention provides a method for manufacturing high-strength cold-rolled tubes, such as... Figure 1 As shown, it includes the following steps: Alloy preparation: Raw materials of Fe: 46.5%, Co: 18%, Ni: 17%, Cr: 12%, Al: 1.8%, Ti: 0.6%, C: 0.10%, B: 0.01%, and N: 0.08% by weight were weighed and subjected to vacuum induction melting, then cast into Φ150mm round ingots. Homogenization was carried out at 1180℃ for 3 hours. Tube blank preparation: The alloy ingot is heated to 1150℃ and pierced by skew rolling to form a rough tube of Φ60×8mm; Solution treatment: Hold the rough tube at 1150℃ for 1 hour, then quench it in water to room temperature; Multi-field coupled asynchronous cold rolling: Equipment: Roll diameter 300mm, asynchronous speed ratio set to 1.15:1.

[0037] Parameters: Only one pass of rolling is performed. The inlet ultra-high frequency induction heating module instantly heats the surface of the billet to about 950°C (Th). The operating frequency of the ultra-high frequency induction heater used is about 200 kHz. During the rolling process, the strong pulse magnetic field module applies a magnetic field with an intensity of 8 T and a pulse width of 50 ms. The outlet ultra-high speed aerosol deep cooling module uses liquid nitrogen aerosol to cool the surface of the pipe to about -80°C within 50 ms.

[0038] Rolling results: The tube was rolled to Φ48×6.5mm, with a diameter reduction rate of 20.0% and a wall reduction rate of 18.8%.

[0039] Finished product: After rolling, the pipe is straightened and cut to obtain the finished pipe, without any subsequent heat treatment.

[0040] Tissue and properties: Observation was performed using a field emission transmission electron microscope (TEM, model JEM-F200) at an accelerating voltage of 200 kV. Figure 2 As shown, the microstructure analysis indicates that it is composed of equiaxed ultrafine crystals with an average grain size of approximately (180±50) nm. The high-angle annular dark-field image shows that there are parallel nano-contrast fringes in the crystals. Fourier filter analysis confirms that they are composition-modulated lamellae generated by Spinodal decomposition, with an average interlamellar spacing of approximately (4±1) nm. At the same time, high-density bright contrast particles with a size of less than 10 nm are diffusely distributed in the matrix. Selected area electron diffraction analysis indicates that they are mainly B2 ordered phase and TiC carbides.

[0041] The tested mechanical properties at room temperature are as follows: tensile strength (Rm) 1850 MPa, yield strength (Rp0.2) 1680 MPa, elongation after fracture (A) 10.5%, and pitting potential measured in 3.5% NaCl solution is +0.32 V (vs. SCE).

[0042] Example 2 This invention provides a method for manufacturing high-strength cold-rolled tubes, such as... Figure 1 As shown, it includes the following steps: Alloy preparation: The composition was adjusted to Fe: 44%, Co: 19%, Ni: 18%, Cr: 11%, Al: 2.2%, Ti: 0.8%, C: 0.12%, B: 0.015%, N: 0.06%, and the preparation process was the same as in Example 1.

[0043] Tube blank preparation: Same as in Example 1, to obtain a rough tube of Φ60×8mm.

[0044] Solution treatment: Hold at 1170℃ for 50 minutes, then oil quench.

[0045] Multi-field coupled asynchronous cold rolling: Two rolling passes are performed; first pass: asynchronous speed ratio 1.10:1, heated to 1000℃, magnetic field strength 5T, rolled to Φ53×7.2mm.

[0046] Second pass: asynchronous speed ratio 1.20:1, heated to 900℃, using a heating module with a frequency of 150 kHz, magnetic field strength of 10T, rolled to Φ45×6.0mm.

[0047] Both exits undergo cryogenic treatment.

[0048] Finished product: Same as in Example 1.

[0049] Performance: Rm=1980 MPa, Rp0.2=1780 MPa, A=9.0%. Pitting potential +0.30 V.

[0050] Example 3 This invention provides a method for manufacturing high-strength cold-rolled tubes, such as... Figure 1 As shown, it includes the following steps: Alloy preparation: The composition was adjusted to Fe: 48%, Co: 16%, Ni: 16%, Cr: 14%, Al: 1.2%, Ti: 0.4%, C: 0.09%, B: 0.008%, N: 0.10%, and the preparation process was the same as in Example 1.

[0051] Process adjustments: The solution treatment temperature is 1120℃; single-pass rolling is adopted, but the pulse magnetic field strength is increased to 12T and the thermal shock temperature is reduced to 880℃.

[0052] Finished product performance: Rm=1720 MPa, Rp0.2=1550 MPa, A=12.8%, pitting potential +0.35 V. This example demonstrates that by adjusting the field parameters, strength and plasticity can be balanced within a certain range.

[0053] Example 4 This embodiment uses a rough tube with a wall thickness of 8mm to meet the space requirements of the gradient design.

[0054] Alloy design and preparation: The basic composition is the same as in Example 1 (Fe: 46.5%, Co: 18%, Ni: 17%, Cr: 12%, Al: 1.8%, Ti: 0.6%, C: 0.10%, B: 0.01%, N: 0.08%); vacuum induction melting gradient control technology is used: first at ≤5.0×10 -2The matrix alloy (Fe, Co, Ni, Cr and all Al, Ti, C) is melted under a vacuum of Pa. After melting and heating to 1580℃, it is held at that temperature. Then, the melt temperature is controlled at 1520-1550℃. During the casting process, a master alloy liquid rich in Cr, N, and B elements is continuously injected into the center of the melt flow through a multi-channel gating system. By utilizing the temperature and flow rate difference between the inner and outer layers of the melt, a target composition gradient is formed from the core to the surface during solidification. Finally, 0.05% Y is added to the ladle. The ingot is then subjected to homogenization and diffusion treatment at 1150℃ for 20 hours to ensure a smooth gradient transition.

[0055] Subsequent processes, such as solution treatment and multi-field coupled asynchronous cold rolling (with parameters the same as in Example 1), are exactly the same.

[0056] Properties and structure: Finished tube properties: Rm=1920 MPa, Rp0.2=1740 MPa, A=10.8%.

[0057] Gradient performance and structural characterization: Electrochemical performance gradient: Using a micro-area electrochemical workstation (equipped with a 10 μm diameter capillary), the pitting potential of the outer surface was +0.38 V (vs. SCE) and the pitting potential of the core was +0.31 V, indicating that the surface layer has significantly better pitting resistance than the core.

[0058] Mechanical property gradient: Array tests were conducted along the radial direction of the tube using a nanoindenter (Berkovich indenter, maximum load 50mN); the results showed that the average nanohardness of the core region was 12.5 GPa, and that of the surface region was 11.6 GPa, indicating an improvement in core strength; Microstructure gradient analysis: Observations were made using a field emission transmission electron microscope (TEM, JEOL JEM-F200, 200kV) equipped with an energy dispersive spectroscopy (EDS) instrument. Surface region (<100 μm from the outer surface): TEM bright-field image shows grain size of approximately 150-300 nm. High-angle annular dark-field (HAADF) image combined with surface scanning EDS confirms the presence of Cr- and N-rich nanosheets (bright contrast), with an average interlamellar spacing of approximately 3-5 nm and a high volume fraction; the B2 ordered phase and TiC particle density are relatively low. Core region: Grain size is slightly coarser, about 200-400 nm. HAADF images show that the contrast of Cr and N-rich nanosheets is shallower and the spacing is slightly increased (about 5-8 nm). However, significantly higher density of bright particles (B2 phase) with a size of 5-15 nm and TiC particles <10 nm are observed. Transition region: The above features are in a continuous transition state. Selected area electron diffraction (SAED) patterns show that all regions are BCC+FCC dual-phase structures, and the diffraction rings are continuous, indicating that the grain orientation is random and the grain boundaries are clean. As can be seen from the above, through the synergy of gradient composition design and multi-field coupling process, a pipe with radial functional gradient was successfully prepared: the surface layer is mainly composed of fine Cr / N rich nanosheets, which gives it excellent corrosion resistance; the core is mainly reinforced by high-density nanoprecipitates, which provides ultra-high strength; the middle is a continuous transition; compared with Comparative Example 4 (uniform composition), this embodiment improves the surface corrosion resistance by more than 15% while maintaining the same strength.

[0059] Example 5 Alloy and tube blank: Same as in Example 1 (homogeneous composition).

[0060] Multi-field coupling process upgrade: Based on the process in Example 1, two modifications were made to the equipment: The static pulsed magnetic field generator was replaced with a rotatable magnetic pole system, and the magnetic pole disk rotated at a constant speed of 100 rpm during rolling.

[0061] An ultrasonic transducer is installed near the bearing housing of the upper and lower rolls. Its probe is coupled to the billet in a non-contact manner through a coupling agent to apply ultrasonic vibration with a frequency of 28 kHz and a power of 10 kW.

[0062] Performance and structure: Finished tube performance: Rm=1880 MPa, Rp0.2=1700 MPa, A=11.8% (elongation is significantly improved compared to Example 1).

[0063] Uniformity verification: Vickers hardness was tested at 12 points along the circumference of the pipe, and the standard deviation was only HV 15 (HV 40 in Example 1).

[0064] Microstructure uniformity and refinement: Electron backscatter diffraction (EBSD) analysis: scan step size 0.1 μm. The results showed that the average grain size was (180±40) nm, the uniformity of the grain size distribution was significantly better than that of Example 1, and no obvious texture concentration was found.

[0065] Transmission electron microscopy (TEM) analysis: Nanosheets: High-resolution TEM showed that the component-modulated nanosheets produced by Spinodal decomposition had a more concentrated thickness distribution, mainly between 2-4 nm (2-10 nm in Example 1). A key finding was that the orientation of these sheets within different grains was more random, without the predominantly parallel orientation observed in Example 1, which is consistent with the mechanism of the dynamic rotating magnetic field.

[0066] Nanoparticles and Defects: The "micro-forging" effect of the ultrasonic vibration field promoted dislocation reorganization. Dark-field TEM images showed less dislocation entanglement and straighter dislocation lines, indicating more complete dynamic recovery. The B2 ordered phase and TiC particles were extremely uniformly distributed, with no aggregation.

[0067] Preliminary small-angle X-ray scattering (SAXS) analysis: Curve fitting shows that the size distribution peaks of the nanoprecipitates are narrower, and the volume fraction is estimated to be (3.2±0.3)%, indicating good homogeneity.

[0068] Fracture surface analysis: Scanning electron microscopy revealed that the tensile fracture surface was dimple-shaped with deep and uniform dimples, which is typical of ductile fracture and consistent with the increase in elongation.

[0069] As can be seen from the above, the dynamic rotating magnetic field breaks the directional arrangement of nanostructures caused by the static magnetic field, and ultrasonic vibration promotes dislocation movement and healing of micro-defects. The two work together to significantly improve the uniformity and integrity of the three-dimensional nano-interlocked structure in the circumferential and micro-scale, so that the material can achieve increased elongation and reduced performance fluctuation while maintaining ultra-high strength. Compared with Comparative Example 5 (static magnetic field only), this embodiment has an overwhelming advantage in uniformity index.

[0070] Example 6 The alloy is formulated by weight percentage as follows: Fe: 40%, Co: 15%, Ni: 15%, Cr: 10%, Al: 1.0%, Ti: 0.3%, C: 0.08%, B: 0.005%, N: 0.05%, with the balance being Fe and unavoidable impurities (Ti / C atomic ratio is approximately 1.04). The rough tubes are made into Φ60×8mm tubes through smelting, casting, homogenization and hot piercing; After solution treatment at 1120℃ for 1 hour, the material was water quenched and then fed into a multi-field coupling unit for single-pass rolling. The process parameters were taken at or near the lower limit of the range: ultra-high frequency heating time of 0.8 seconds to raise the surface temperature to about Ac3+110℃; asynchronous speed ratio of 1.06:1; application of a 4T static pulse magnetic field; and deep cooling with -55℃ gas mist for about 80 milliseconds after rolling. The final rolling result was Φ48×6.8mm with a diameter reduction rate of 20.0% and a wall reduction rate of 15%.

[0071] Test results: The tensile strength (Rm) of the finished pipe is 1480 MPa, the yield strength (Rp0.2) is 1350 MPa, the elongation after fracture (A) is 7.0%, and the pitting potential is +0.28 V.

[0072] TEM observation showed that the tissue was composed of equiaxed crystals with an average size of about 300 nm, and parallel stripes (the prototype of nanosheets) could be identified within the crystals, but the contrast was shallower than that of Example 1; at the same time, a small number of nanoparticles were distributed, and their strength and toughness were still significantly higher than those of Comparative Example 1.

[0073] Example 7 The alloy is formulated by weight percentage as follows: Fe: 50%, Co: 20%, Ni: 20%, Cr: 15%, Al: 2.5%, Ti: 1.0%, C: 0.15%, B: 0.02%, N: 0.10%, with the balance being Fe and unavoidable impurities (Ti / C atomic ratio is approximately 1.17). After being formed into rough tubes, they are solution treated at 1180℃ for 0.5 hours and then oil quenched. Single-pass rolling is adopted, and the process parameters are taken at or near the upper limit of the range: ultra-high frequency heating time of 2.8 seconds to raise the surface temperature to about Ac3+240℃; asynchronous speed ratio of 1.28:1; a strong pulsed magnetic field of 14T is applied (static); after rolling, it is rapidly deep cooled with liquid nitrogen mist at -180℃ in about 15 milliseconds, and finally rolled to Φ48×6.0mm.

[0074] Test results: The finished pipe has a tensile strength (Rm) of up to 2150 MPa, a yield strength (Rp0.2) of 1950 MPa, and an elongation after fracture (A) of 6.5%. The pitting potential is +0.34 V.

[0075] TEM showed that the microstructure was extremely fine, with an average grain size of less than 100 nm. The composition-modulated nanosheets were clear and dense, with a thickness of about 2-3 nm, and the density of nanoprecipitated phases was extremely high.

[0076] Comparative Example 1 (Traditional asynchronous rolling + post-heat treatment) The same alloy composition as in Example 1 was used; after the same solution treatment, the rough tube was cold rolled in two passes on an ordinary asynchronous rolling mill without any additional energy field (no thermal shock, no magnetic field, no special deep cryogenic) to the same specifications (Φ50×6.5mm); after rolling, it was aged at 480℃ for 2 hours in accordance with the conventional high-strength alloy treatment method.

[0077] Properties and structure: Rm = 1520 MPa, Rp0.2 = 1410 MPa, A = 7.5%; TEM observation showed that the microstructure was a restored subcrystalline structure with uneven grain size (200 nm-1 μm), no obvious nanosheet structure, only a small amount of coarse precipitates, and a pitting potential of +0.28 V.

[0078] Comparative Example 2 (lacking magnetic field) Alloy and process: Same as in Example 1.

[0079] Process adjustment: During multi-field coupled rolling, the strong pulse magnetic field module is turned off, and only thermal shock and deep cooling are performed.

[0080] Performance and microstructure: Rm=1650 MPa, Rp0.2=1500 MPa, A=8.2%. Microstructure analysis showed that the grains were refined, but there were no compositionally modulated nanosheets. Amplitude modulation decomposition was suppressed. The performance was lower than that of Example 1, and the improvement in toughness was limited.

[0081] Comparative Example 3 (lacking thermal shock field) Alloy and process: Same as in Example 1.

[0082] Process adjustment: During multi-field coupled rolling, the ultra-high frequency induction heating module is turned off, and only magnetic field and cryogenic assisted rolling are performed.

[0083] Result: The rolling force increased sharply, and the billet cracked severely in one pass, making it impossible to complete the rolling. This shows that thermal shock is crucial for reducing the deformation resistance of this alloy under high strength conditions and achieving large deformation rolling.

[0084] Comparative Example 4 Alloy and process: The alloy with the same final composition as in Example 4 but completely homogeneous (i.e., the average value of the gradient composition) was used, and the process parameters were exactly the same as in Example 1.

[0085] Results: Finished product performance: Rm=1800 MPa, Rp0.2=1630 MPa, A=10.0%. The difference between the surface pitting potential (+0.33V) and the core potential (+0.30V) is much smaller than that in Example 4, indicating that the gradient design does indeed bring about targeted performance improvement and functional differentiation.

[0086] Comparative Example 5 Process: The same alloy as in Example 5 was used, but in its multi-field coupling process, the ultrasound was turned off and a static magnetic field was used (same as in Example 1).

[0087] Results: Finished product performance: Rm=1830 MPa, Rp0.2=1660 MPa, A=10.2%. The standard deviation of circumferential hardness fluctuation was HV 38, which is similar to that of Example 1 and much larger than that of Example 5, indicating that the dynamic magnetic field and ultrasound have a significant effect on improving the uniformity of performance.

[0088] It should be noted that, for the sake of simplicity, the foregoing embodiments are all described as a series of actions. However, those skilled in the art should understand that the present invention is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to the present invention. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions and modules involved are not necessarily essential to the present invention.

[0089] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art can still combine, add, delete, or otherwise adjust the features of the various embodiments of the present invention according to the circumstances without conflict or creative effort, thereby obtaining different technical solutions that do not fundamentally depart from the concept of the present invention. These technical solutions also fall within the scope of protection of the present invention.

Claims

1. A method for manufacturing high-strength cold-rolled tubes, characterized in that, Includes the following steps: S1. Alloy smelting and tube blank preparation: Alloys containing Fe, Co, Ni, Cr, Al, Ti, C, B and N are prepared by weight percentage, and then smelted, cast, homogenized and hot pierced to produce rough tubes; S2. Solution pretreatment: The raw tube is solution treated and then rapidly cooled to obtain a supersaturated solid solution; S3. Multi-field coupled asynchronous cold rolling: The processed tube billet is fed into a multi-field coupled asynchronous cold rolling mill for rolling; the mill includes asynchronous rolls, and an ultra-high frequency pulse induction heating module, a strong pulse magnetic field generating module, and an ultra-high speed gas mist deep cooling module integrated in the rolling deformation zone; during the rolling process, the above three modules act synchronously with the rolling deformation, wherein the direction of the strong pulse magnetic field is perpendicular to the rolling direction; S4. Finished product processing: The rolled tubes are finished cold-rolled tubes after finishing, without subsequent aging or tempering heat treatment.

2. The method for manufacturing high-strength cold-rolled tubes as described in claim 1, characterized in that, The alloy described in step S1 has the following weight percentage composition: Fe: 40-50%, Co: 15-20%, Ni: 15-20%, Cr: 10-15%, Al: 1.0-2.5%, Ti: 0.3-1.0%, C: 0.08-0.15%, B: 0.005-0.02%, N: 0.05-0.10%, with the balance being unavoidable impurities; and the atomic ratio of Ti to C is 0.8-1.

2.

3. The method for manufacturing high-strength cold-rolled tubes as described in claim 2, characterized in that, The rough tube prepared in step S1 has a continuous gradient distribution of chemical composition in the radial direction: within a 1 mm depth range from the outer surface inward, the contents of Cr, N, and B elements are 10-20 wt% higher than those in the core area of ​​the tube; within a 1 mm radius range from the core outward, the contents of Ti and Al elements are 8-15 wt% higher than those in the outer surface area; the contents of the remaining major elements Fe, Co, and Ni remain uniform in the radial direction; and 0.01-0.3 wt% of Ce or Y is also added to the alloy.

4. The method for manufacturing high-strength cold-rolled tubes as described in claim 1, characterized in that, In step S3, the ultra-high frequency pulse induction heating module is used to instantaneously heat the surface of the billet to a temperature 100-250°C above the Ac3 phase transformation point within 0.5-3 seconds before the billet enters the rolling mill.

5. The method for manufacturing high-strength cold-rolled tubes as described in claim 1, characterized in that, The strong pulse magnetic field generating module applies a magnetic field strength of 3-15 T and a single pulse width of 10-100 milliseconds.

6. The method for manufacturing high-strength cold-rolled tubes as described in claim 5, characterized in that, The magnetic field generated by the strong pulse magnetic field generating module is a dynamic rotating magnetic field. During the rolling process, its magnetic poles rotate around the tube axis at a speed of 50-200 rpm, thereby causing the direction of the applied magnetic field to change continuously relative to the tube.

7. The method for manufacturing high-strength cold-rolled tubes as described in claim 6, characterized in that, In step S3, the ultra-high-speed aerosol deep cooling module is used to rapidly cool the surface of the billet to below -50°C within 10-100 milliseconds after the billet leaves the rolls. The ratio of the upper and lower linear speeds of the asynchronous roll is from 1.05:1 to 1.30:1; The rolling process consists of 1-3 passes, with a total diameter reduction rate of 20%-50% and a total wall reduction rate of 15%-40%.

8. The method for manufacturing high-strength cold-rolled tubes as described in claim 1, characterized in that, In step S3, an ultrasonic vibration field is also applied synchronously in the roll deformation zone. The ultrasonic vibration is generated by a non-contact transducer close to the surface of the tube and the vibration energy is transmitted through the coupling medium. The frequency is 20-40 kHz and the power is 5-15 kW.

9. The high-strength and high-toughness nanostructured cold-rolled tube prepared by the method according to any one of claims 1-8, characterized in that, Its microstructure comprises a three-dimensional nano-interlocking structure, which consists of an ultrafine crystalline biphase matrix, compositionally modulated nanosheets distributed parallel to the magnetic field direction, and diffusely distributed nanoparticles.

10. The high-strength cold-rolled tube as described in claim 9, characterized in that, The thickness of the component-modulated nanosheets is 2-10 nm, and the nanoparticles include an ordered B2 phase with a size of 5-20 nm and TiC carbides with a size of less than 10 nm.

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