Gradient structure metal matrix seamless pipe and preparation method

Abstract

The invention relates to the technical field of material processing, and discloses a gradient structure metal matrix seamless pipe and a preparation method thereof, the preparation method comprises the following steps: (1) three-stage temperature control rolling forming; (2) interface reconstruction: applying a pulse electromagnetic field forming an asymmetric included angle with the rolling direction to the pipe rolled and formed in the step (1); the specific conditions of the pulse electromagnetic field are as follows: the magnetic field intensity is 0.5-5T; the pulse frequency f satisfies f = (v / d) * k; in the formula, v is the moving speed (m / s) of the pipe, d is the wall thickness (mm) of the pipe, and k is an adjustment coefficient 103-105; tissue regulation and control: performing selective laser impact and electromagnetic oscillation coupling treatment on the pipe obtained in the step (2); the impact energy density is 5-15 J / cm < 2 >, and the oscillation frequency is 20-100 kHz. The toughness of the pipe can be synergistically improved, the fatigue life is remarkably prolonged, and the corrosion resistance is improved in a breakthrough manner.

Description

Technical Field

[0001] The invention relates to the technical field of material processing, and in particular to a gradient structure metal-based seamless pipe and a preparation method thereof. Background Art

[0002] Metal pipes are important parts of industrial equipment that transport gases and liquids. However, in some applications, the strength and toughness of metal pipes often fail to meet the requirements, and the surface of the pipes is impacted by solid and liquid media, causing various defects such as wear, corrosion and fatigue on the surface of the pipes, which makes the pipes fail and reduces the service life of the metal pipes. Improving the strength, toughness, and service performance of metal pipes has always been a hot topic for researchers.

[0003] Gradient structure metal refers to a metal material whose internal structure, composition or performance presents a continuous or step-like change along a certain direction. The design of gradient structure can make the hardness, strength, toughness and other properties of metal materials achieve a smooth transition inside the material, avoiding stress concentration and use risks caused by sudden changes in performance.

[0004] Traditional metal seamless pipes are mainly prepared by hot rolling (such as oblique rolling and piercing), cold drawing, extrusion and spinning. Among them, the hot rolling method forms a tube billet through high-temperature plastic deformation at 1100~1250℃. Although it is highly efficient, it leads to grain coarsening (20~50μm) and severe surface oxidation; the cold drawing method can obtain high-precision pipes (tolerance ±0.05mm) with the help of multiple cold deformations, but the residual stress reaches 200~400MPa, which increases the risk of stress corrosion; although the extrusion method can process difficult-to-deform metals, it is limited in application due to high mold costs (50,000~200,000 US dollars per set) and microstructure anisotropy (performance difference ≥15%). These traditional processes generally have inversion of strength and toughness (such as elongation ≤10% when the yield strength of cold-drawn tubes is ≥600MPa), low fatigue life (<1.5×10 6 The pipe has many defects, such as high energy consumption (hot rolling ≥ 300kWh / ton), and cannot coordinately regulate the radial performance gradient of the pipe. For example, the external compressive strength of homogeneous hot-rolled pipe is only 500~700MPa, and single cold drawing strengthening will double the sensitivity of intergranular corrosion due to residual tensile stress (pitting potential drops by 0.1~0.15V), which seriously restricts its application reliability in extreme environments such as aerospace and deep-sea engineering. Summary of the invention

[0005] Purpose of the invention: In view of the problems existing in the prior art, the present invention provides a gradient structure metal-based seamless pipe and a preparation method thereof, through three-stage gradient temperature controlled rolling (T1→T2→T3 temperature gradient and ε 1 →ε 2 →ε 3Deformation coordination), constructing a fine outer (≤5μm) and coarse inner (15-25μm) grain structure in the radial direction of the tube, breaking through the inversion limit of strength and toughness (anti-external compressive strength 880MPa / elongation 15%); combining asymmetric pulsed electromagnetic field (30°-60° angle, 0.5-5T) to break the grain boundary oxide, forming a 10-30nm amorphous interface layer, which increases the interface strength by 50% to 300MPa; using laser-electromagnetic coupling treatment to reconstruct the three-dimensional dislocation network, eliminate anisotropy (difference ≤5%), and the residual compressive stress layer (300-500MPa) increases the fatigue life to 3.5×10 6 times (1.2×10 6 times); integrated intelligent lubrication and digital twin models, the rolling temperature is reduced to 800℃ (energy saving 40%), the surface roughness Ra≤0.4μm, and the pitting potential reaches 0.38V (increased by 52%), which can meet the extreme working conditions such as deep sea (pressure resistance 120MPa) and aerospace, and realize the design and manufacture of high-performance pipes.

[0006] Technical solution: In the first aspect, the present invention provides a method for preparing a gradient structure metal-based seamless pipe, comprising the following steps: (1) Rolling forming: (a) heating the metal blank to a first temperature T1 and keeping the temperature for 20 to 60 min; (b) rolling the metal blank obtained in step (a) for the first time, and then cooling it with water to a second temperature T2; the specific conditions of the first rolling are: the deformation amount ε 1 =40%~60%, rolling speed v 1 =0.5~1.2m / s; (c) rolling the metal blank obtained in step (b) for a second time, and then cooling it with water to a third temperature T3; the specific conditions of the second rolling are: the deformation amount ε 2 =30%~50%, rolling speed v 2 =0.8~1.5m / s; (d) rolling the metal blank obtained in step (c) for a third time; the specific conditions of the third rolling are: the deformation amount ε 3 =20%~40%, rolling speed v 3 =1.0~2.0m / s; Wherein, the first temperature T1=0.8Tm~0.9Tm, Tm is the melting point of the metal; the second temperature T2=T1-150℃~200℃; the third temperature T3=T2-100℃~150℃; The gradient temperature controlled rolling process can significantly improve the comprehensive performance of metal seamless pipes: by controlling the temperature gradient (T1→T2→T3) and the deformation gradient (ε 1 →ε2 →ε 3 ) form a dynamic recrystallization gradient during the rolling process. Due to the strong thermal-mechanical coupling effect of low temperature (400-600℃) and large deformation (55%), the grain boundary migration is inhibited in the outer layer, and dynamic recrystallization forms ultrafine grains (≤5μm); while the inner layer gradually coarsens (15-25μm) through dislocation recombination and local recrystallization at relatively high temperature (600-800℃) and small deformation (35%). This gradient structure of fine outside and coarse inside increases the material's compressive strength to ≥880MPa (fine-grain Hall-Petch strengthening). At the same time, the inner coarse grains absorb the crack propagation energy, which increases the fatigue life to 3.5×10 6 cycles (3 times higher than the traditional homogeneous structure). Combined with the surface 300-500MPa gradient compressive stress (due to the thermal expansion difference caused by the temperature gradient) and the fine-grained dense oxide film (pitting potential 0.38V), the comprehensive performance breaks through the strength and toughness contradiction of the traditional process. If homogenized rolling (single temperature ≥1000℃) is adopted, the uniform coarse-grained structure (about 15μm) will lead to stress concentration sensitivity (fatigue life is only 1.2×10 6 The excessive growth of grains (>20μm) caused by high temperature will further weaken the strength (≤620MPa), increase energy consumption by more than 30%, and the thickening of oxide scale will deteriorate the corrosion resistance (pitting potential 0.25V). The gradient temperature control process fundamentally solves the industry problem that the organization and performance cannot be coordinated and optimized under a single process parameter through thermodynamic regulation of spatial partitioning.

[0007] (2) Interface reconstruction: A pulse electromagnetic field with an asymmetric angle to the rolling direction is applied to the tube formed by rolling in step (1); the specific conditions of the pulse electromagnetic field are: the magnetic field intensity is 0.5~5T; the pulse frequency f satisfies: f = (v / d)×k In the formula, v is the moving speed of the pipe (m / s), d is the wall thickness of the pipe (mm), and k is the adjustment coefficient 10 3 ~10 5 ; Dynamic interface reconstruction treatment achieves cross-scale optimization of the interface structure of the pipe through the directional interaction between the asymmetric pulsed electromagnetic field and the microscopic defects of the material: when a pulsed magnetic field (0.5~5T) with an angle of 30°~60° to the rolling direction is applied, the dislocation movement driven by the Lorentz force and the atomic diffusion induced by the electron wind effect produce a synergistic effect - the fast rising edge pulse (≤50μs) breaks the original grain boundary oxide through high-energy electron impact, the flat top duration (occupying 1 / 3~1 / 2 of the period) promotes the dislocation recombination to form a low-energy interface, and the slow falling edge (≥100μs) guides the solute atoms (such as Cr, Mo) to segregate at the interface (concentration gradient reaches 5~8at.%). This asymmetric energy input in time and space increases the interface bonding strength by more than 50% (up to 300MPa), and forms a dense amorphous transition layer with a thickness of 10~30nm, which increases the energy required for crack initiation to 2.3 times that of the traditional interface. Compared with the non-gradient process, this treatment can reduce the intergranular corrosion rate to 1 / 4 (0.02mm / year), and form a stress-structure dual gradient match with the fine-grained surface layer of gradient temperature-controlled rolling (outer layer compressive stress 300MPa + nanocrystalline and amorphous interface synergistically inhibit crack propagation). Without this treatment, the coarse precipitate phase (size>500nm) and oxygen segregation (>3at.%) of the traditional homogeneous interface (bonding strength ≤200MPa) will lead to early fatigue failure (lifetime <1×10 6 The dynamic interface reconstruction breaks through the technical bottleneck of strengthening and toughening the interface of metal pipes and resisting environmental damage through electromagnetic-mechanical-chemical multi-field coupling.

[0008] (3) Tissue control: The surface of the tube obtained in step (2) is subjected to laser shock and electromagnetic oscillation coupling treatment; the shock energy density is 5~15J / cm 2 , oscillation frequency 20~100kHz.

[0009] Furthermore, in step (1), the temperature between the first temperature T1, the second temperature T2 and the third temperature T3 is achieved by a high-frequency coil and a medium-frequency coil; wherein the high-frequency coil controls the surface temperature of the pipe, and the medium-frequency coil controls the core temperature of the pipe.

[0010] Furthermore, the operating frequency of the high frequency coil is 100-300 kHz; the operating frequency of the medium frequency coil is 10-50 kHz.

[0011] Furthermore, in step (2), the pulse electromagnetic field adopts an asymmetric waveform modulation technology, and in a single cycle includes: rising edge time tr≤50μs; flat top duration tp = (1 / 3~1 / 2)T, T is the pulse period; falling edge time tf≥100μs.

[0012] Furthermore, the magnetic poles of the pulse electromagnetic field are arranged at an angle of θ=30°~60° with the rolling center line.

[0013] Furthermore, in step (3), the spatiotemporal coupling relationship between the laser selective impact and the electromagnetic oscillation satisfies: the phase difference Δφ between the laser pulse and the electromagnetic oscillation = 90°±10°, and the spatial overlap between the laser action area and the peak area of ​​the electromagnetic field intensity is ≥85%.

[0014] Furthermore, during the rolling forming process of step (1), an axial vibration load is also applied synchronously; the specific conditions of the axial vibration load are: vibration frequency fv = 50~200Hz; amplitude A = (0.005~0.015)D, where D is the outer diameter of the pipe.

[0015] During the rolling of seamless steel pipes, an axial vibration load (frequency 50-500Hz, amplitude 0.01-0.5mm) is applied to induce the dynamic softening effect of the material through high-frequency micro-amplitude vibration, reducing the rolling force by 10-20%, while promoting dislocation movement and dynamic recrystallization, refining the grains by 1-2 levels, eliminating the inner wall folding defects and improving the dimensional accuracy. This technology combines the coordinated regulation of vibration energy and plastic deformation, breaking through the limitations of traditional static rolling on the forming of high-strength materials, and has the dual advantages of energy saving and consumption reduction (energy consumption reduced by 12-18%) and organizational performance optimization, and is suitable for the efficient processing of difficult-to-deform metals.

[0016] In the second aspect, the present invention provides a gradient structure metal-based seamless pipe prepared by the method as described in any of the above items, wherein the pipe has a three-layer gradient structure: outer layer: nanocrystalline layer, grain size ≤500nm, thickness accounts for 10%~15% of the wall thickness of the pipe; transition layer: dislocation cell structure, cell wall spacing 50~200nm, thickness accounts for 20%~30% of the wall thickness of the pipe; inner layer: submicron grains, grain size 1~3μm, thickness accounts for 55%~70% of the wall thickness of the pipe.

[0017] Furthermore, the tube satisfies the following parameters simultaneously in the tube wall thickness direction: microhardness gradient HV outer layer / HV inner layer ≥ 1.5, residual stress σ of gradient compressive stress layer ≥ 300MPa, gradient change rate ≥ 50MPa / mm; texture strength ratio, {110} outer layer / {111} inner layer = 2.5~4.0.

[0018] The present invention breaks through the contradiction between strength and toughness by gradient temperature controlled rolling (400-600℃ fine grain strengthening for outer layer / 600-800℃ coarse grain toughening for inner layer) and asymmetric electromagnetic pulse treatment (0.5-5T, 30°-60° angle), so that the external compressive strength reaches 800-950MPa (increased by 40%) and the elongation is ≥15%, and the stress corrosion rate is suppressed to ≤10 through the 300-500MPa compressive stress layer on the surface.-8 mm / s. Dynamic interface reconstruction technology removes grain boundary oxides and constructs a 10-30nm amorphous transition layer, increasing the pitting potential to 0.38V and extending the fatigue life to 3.5×10 6 The cross-scale organization regulation (laser shock + electromagnetic oscillation) induces a three-dimensional dislocation network, eliminates anisotropy (difference ≤ 5%), and cooperates with the gradient structure design to increase the buckling strength to 120MPa, and withstands -196~300℃ thermal shock cycles. The process energy consumption is reduced by 40% (≤180kWh / ton), solving the problem of high-performance pipes in aerospace hydraulic systems, deep-sea oil and gas transportation, and other fields, achieving a leap from homogeneous manufacturing to performance design.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following specific beneficial effects: 1. Synergistic improvement of strength and resilience By coupling gradient temperature-controlled rolling with a large deformation of 55% in the outer layer, a gradient structure of fine outer grains (≤5μm) and coarse inner grains (15-25μm) is formed, breaking through the contradiction between strength and toughness of traditional homogeneous materials. The external compressive strength reaches 880MPa (40% higher than that of traditional processes) while the elongation remains ≥15%, solving the industry problem of "high strength and brittleness" of aerospace hydraulic pipes.

[0020] 2. Significantly extended fatigue life Asymmetric electromagnetic pulse treatment (0.5-5T, 30°-60° angle) generates a 300-500MPa gradient compressive stress layer on the surface, combined with the external fine grain barrier effect, which increases the fatigue life to 3.5×10 6 Cycle (conventional process 1.2×10 6 times), the crack growth rate is reduced to ≤10 -8 mm / cycle, meeting the 20-year maintenance-free requirement for deep-sea oil and gas pipelines.

[0021] 3. Breakthrough improvement in corrosion resistance Dynamic interface reconstruction technology removes grain boundary oxides (oxygen content ≤ 0.05wt%), forming a 10-30nm dense amorphous transition layer, increasing the pitting potential to 0.38V (52% higher than the traditional process 0.25V), and reducing the intergranular corrosion rate to 0.02mm / year (traditional process 0.08mm / year), which is suitable for high Cl - Marine environment.

[0022] 4. Reduce energy consumption and costs The gradient temperature control process reduces the maximum rolling temperature to 800°C (300°C lower than traditional hot rolling). Combined with the intelligent lubrication system (nano-graphene lubricant usage is reduced by 50%) and digital twin optimization, the comprehensive energy consumption is ≤180kWh / ton (a 40% decrease), the product qualification rate is increased from 85% to 98%, and the production cost is reduced by 35%.

[0023] 5. Enhanced universality in extreme environments Cross-scale organizational regulation (laser shock + electromagnetic oscillation) constructs a three-dimensional dislocation network, making the anisotropy index ≤5% (conventional ≥15%), the buckling strength reaches 120MPa (conventional 80MPa), and it can withstand -196~300℃ thermal shock cycles ≥50 times (conventional ≤5 times), adapting to the alternating working conditions of ultra-low temperature in deep space exploration and high temperature in geothermal pipelines. DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with the embodiments.

[0025] In the present invention, the preparation of gradient structure metal-based seamless pipes is achieved through a multi-band composite induction rolling mill, an asymmetric electromagnetic pulse generator, a laser-electromagnetic coupling processing device, and the like.

[0026] Embodiment 1: This embodiment provides a method for preparing a gradient structure metal-based seamless pipe, and the specific steps are as follows: (1) Rolling forming: (a) Heat 304 stainless steel to 1100℃ (austenitizing temperature) and keep it at this temperature for t1=30min; (b) Perform the first stage deformation in the rolling equipment, with the deformation amount ε 1 =50% (rolling force control ≤800kN), rolling speed v 1 =0.8m / s, water cooled to 950℃ immediately after rolling; (c) second stage deformation at 950℃, deformation ε 2 =40% (roller inclination 10°), rolling speed v 2 =1.0m / s, air cooling to 800℃ after rolling; (d) third stage deformation at 800℃, deformation ε 3 =30% (roller liquid nitrogen cooling), rolling speed v 3 =1.5m / s; (2) Interface reconstruction: A pulsed electromagnetic field is applied to the rolled tube. The magnetic poles of the pulsed electromagnetic field are arranged at an angle of θ=45° to the rolling center line. The magnetic field intensity is 2T, and the pulse frequency f satisfies: f= (v / d) × k=(1.0 / 5)×10 4 =2000Hz(k=10 4 , unit matching correction), where v is the pipe moving speed (m / s), d is the pipe wall thickness (mm), and k is the adjustment coefficient 103 ~10 5 ; The pulse electromagnetic field adopts asymmetric waveform modulation technology, which includes the following in a single cycle: rising edge time tr≤40μs; flat top duration tp = (1 / 3~1 / 2)T =0.3ms, T is the pulse period, when T=1ms; falling edge time tf≥120μs; Tissue control: In the final heat treatment stage, laser shock and electromagnetic oscillation coupling treatment is used, and the impact energy density of laser shock is 10J / cm 2 (Pulse width 20ns), the oscillation frequency of the electromagnetic oscillation is 50kHz; the phase difference between the laser pulse and the electromagnetic oscillation is Δφ = 90°, and the spatial overlap between the laser action area and the peak area of ​​the electromagnetic field intensity is 90%.

[0027] Optionally, during the rolling forming process, an axial vibration load is also applied synchronously, with a vibration frequency of fv = 100 Hz; an amplitude of A = (0.005~0.015)D = 0.5 mm (when D = 89 mm, A = 0.005×89≈0.45 mm), where D is the outer diameter of the pipe.

[0028] The gradient structure metal-based seamless pipe prepared in this embodiment has a three-layer gradient structure: outer layer: nanocrystalline layer (grain size 400nm, thickness 0.6mm, accounting for 12%); transition layer: dislocation cell structure (cell wall spacing 120nm, thickness 1.5mm, accounting for 30%); inner layer: submicron crystal (grain size 2μm, thickness 2.9mm, accounting for 58%). Mechanical properties: tensile strength ≥850MPa (conventional process 680MPa), elongation 35%, grain size gradient difference up to 3 levels (ASTM 9 to 6).

[0029] Embodiment 2: This embodiment provides a method for preparing a gradient structure metal-based seamless pipe, and the specific steps are as follows: (1) Rolling forming: (a) Heat 42CrMo alloy to 1150℃ (austenitization + carbide dissolution), holding time t1 = 45min; (b) First stage deformation: deformation ε 1 =55% (rolling force ≤ 1200kN), rolling speed v 1 =0.6m / s, water cooled to 1000℃ after rolling; (c) Second stage deformation: carried out at 1000℃, deformation ε 2 =45% (roller inclination 8°), rolling speed v 2 =0.9m / s, air cooling to 850℃; (d) The third stage deformation: carried out at 850℃, the deformation amount ε 3 =35% (roller liquid nitrogen cooling), rolling speed v 3 =1.2m / s.

[0030] (2) Interface reconstruction: A pulsed electromagnetic field is applied to the rolled tube. The magnetic poles of the pulsed electromagnetic field are arranged at an angle of θ = 50° with the rolling center line. The magnetic field intensity is 3T. The pulse frequency f satisfies: f = v / d × k = 0.90 / 008 × 8 × 10 3 =900 Hz, (v=0.9m / s, d=8mm=0.008m, k=8×10 3 ) In the formula, v is the moving speed of the pipe (m / s), d is the wall thickness of the pipe (mm), and k is the adjustment coefficient 10 3 ~10 5 ; The pulse electromagnetic field adopts asymmetric waveform modulation technology, which includes the following in a single cycle: rising edge time tr≤30μs; flat top duration tp = (1 / 3~1 / 2)T=0.25ms (T=0.8ms), T is the pulse period; falling edge time tf≥150μs; Tissue control: In the final heat treatment stage, laser shock and electromagnetic oscillation coupling treatment is used, and the impact energy density of laser shock is 12J / cm 2 , inducing surface phase change, the oscillation frequency of electromagnetic oscillation is 80kHz; the phase difference between laser pulse and electromagnetic oscillation is Δφ = 85°, and the spatial overlap between the laser action area and the peak area of ​​electromagnetic field intensity is 88%.

[0031] Optionally, during the rolling forming process, an axial vibration load is also applied synchronously, with a vibration frequency of fv = 150 Hz; an amplitude of A = (0.005~0.015)D = 0.8 mm (when D = 159 mm, A = 0.005D), where D is the outer diameter of the pipe.

[0032] The gradient structure metal-based seamless pipe prepared in this embodiment has a three-layer gradient structure: outer layer: nano-scale bainite layer (grain size 300nm, thickness 1.2mm, accounting for 15%); transition layer: lath martensite + residual austenite with dislocation cell structure (lath width 200nm, thickness 2.4mm, accounting for 30%); inner layer: submicron tempered troostite (grain size 1.5μm, thickness 4.4mm, accounting for 55%).

[0033] Mechanical properties: tensile strength 1100MPa (30% higher than traditional process), elongation 18%, impact energy AKU=65J (40% higher), hardness gradient HRC 50-42-35.

[0034] Embodiment 3: This embodiment provides a method for preparing a gradient structure metal-based seamless pipe, and the specific steps are as follows: (1) Rolling forming: (a) Pure titanium TA2 is heated to 920°C and kept at this temperature for t1 = 50 min; (b) The first stage of deformation is carried out in the rolling equipment, and the deformation amount ε 1 =60%, rolling speed v 1 =0.5m / s, water cooled to 750℃ immediately after rolling; (c) second stage deformation at 750℃, deformation ε 2 =40%, rolling speed v 2 =0.8m / s, air-cooled to 600℃ after rolling; (d) third stage deformation at 600℃, deformation ε 3 =25%, rolling speed v 3 =1.0m / s; (2) Interface reconstruction: A pulsed electromagnetic field is applied to the rolled tube. The magnetic poles of the pulsed electromagnetic field are arranged at an angle of θ=60° to the rolling center line. The magnetic field intensity is 1.5T, and the pulse frequency f satisfies: f = (v / d) × k=0.7 / 0.006×5×10 3 ≈583 kHz; In the formula, v is the moving speed of the pipe (m / s), d is the wall thickness of the pipe (mm), and k is the adjustment coefficient 10 3 ~10 5 ; The pulse electromagnetic field adopts asymmetric waveform modulation technology, which includes the following in a single cycle: rising edge time tr=20μs; flat top duration tp = (1 / 3~1 / 2)T=0.2ms (T=0.6ms), T is the pulse period; falling edge time tf=200μs; Tissue control: In the final heat treatment stage, laser shock and electromagnetic oscillation coupling treatment is used, and the impact energy density of laser shock is 8J / cm 2 , the oscillation frequency of electromagnetic oscillation is 30kHz; the phase difference between laser pulse and electromagnetic oscillation is Δφ = 95°, and the spatial overlap between the laser action area and the peak area of ​​electromagnetic field intensity is ≥92%.

[0035] Optionally, during the rolling forming process, an axial vibration load is also applied synchronously, with a vibration frequency of fv = 80 Hz; an amplitude of A = (0.005~0.015)D==0.57 mm (when D = 114 mm, A = 0.005D), where D is the outer diameter of the pipe.

[0036] The gradient structure metal-based seamless pipe prepared in this embodiment has a three-layer gradient structure: outer layer: ultrafine equiaxed α-crystal nanocrystalline layer, with a grain size of 200nm and a thickness of 15% of the pipe wall thickness, about 0.9mm; transition layer: dislocation entanglement + nano-twin structure, with a twin thickness of 50nm, a cell wall spacing of 50~200nm, and a thickness of 25% of the pipe wall thickness, about 1.5mm; inner layer: submicron grains, coarse lamellar α (chip width 1.2μm) grain size 1~3μm, thickness accounting for 60% of the pipe wall thickness, about 3.6mm.

[0037] The properties of the pipes prepared in Examples 1-3 and the pipes prepared by the traditional manufacturing method were tested, and the specific data are as follows:

[0038] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a gradient structure metal-based seamless pipe, characterized in that: The following steps are involved: (1) Rolling forming: (a) heating the metal blank to a first temperature T1 and keeping the temperature for 20 to 60 min; (b) performing a first rolling on the metal billet obtained in step (a), and then water cooling to a second temperature T2; the specific conditions of the first rolling are: deformation ε1=40%~60%, and rolling speed v1=0.5~1.2m / s; (c) rolling the metal billet obtained in step (b) for a second time, and then water cooling it to a third temperature T3; the specific conditions of the second rolling are: deformation ε2=30%~50%, rolling speed v2=0.8~1.5m / s; (d) performing a third rolling on the metal billet obtained in step (c); the specific conditions of the third rolling are: deformation ε3 = 20% to 40%, and rolling speed v3 = 1.0 to 2.0 m / s; Wherein, the first temperature T1=0.8Tm~0.9Tm, Tm is the melting point of the metal; the second temperature T2=T1-150℃~200℃; the third temperature T3=T2-100℃~150℃; Interface reconstruction: A pulse electromagnetic field with an asymmetric angle to the rolling direction is applied to the tube formed by rolling in step (1); the specific conditions of the pulse electromagnetic field are: the magnetic field intensity is 0.5~5T; the pulse frequency f satisfies: f = (v / d)×k In the formula, v is the moving speed of the pipe (m / s), d is the wall thickness of the pipe (mm), and k is the adjustment coefficient 10 3 ~10 5 ; (3) Tissue control: The surface of the tube obtained in step (2) is subjected to laser shock and electromagnetic oscillation coupling treatment; the laser shock energy density is 5~15J / cm 2 , electromagnetic oscillation frequency 20~100kHz.

2. The method for preparing a gradient structure metal-based seamless pipe according to claim 1, characterized in that: In step (1), the temperature between the first temperature T1, the second temperature T2 and the third temperature T3 is achieved by a high-frequency coil and an intermediate-frequency coil; wherein the high-frequency coil controls the surface temperature of the pipe, and the intermediate-frequency coil controls the core temperature of the pipe.

3. The method for preparing a gradient structure metal-based seamless pipe according to claim 2, characterized in that: The working frequency of the high frequency coil is 100-300kHz; the working frequency of the medium frequency coil is 10-50kHz.

4. The method for preparing a gradient structure metal-based seamless pipe according to claim 1, characterized in that: In step (2), the pulse electromagnetic field adopts an asymmetric waveform modulation technology, which includes in a single cycle: rising edge time tr≤50μs; flat top duration tp = (1 / 3~1 / 2)T, T is the pulse period; falling edge time tf≥100μs.

5. The method for preparing a gradient structure metal-based seamless pipe according to claim 4, characterized in that: The magnetic poles of the pulse electromagnetic field are arranged at an angle of θ=30°~60° with the rolling center line.

6. The method for preparing a gradient structure metal-based seamless pipe according to claim 1, characterized in that: In step (3), the spatiotemporal coupling relationship between the laser selective impact and the electromagnetic oscillation satisfies: the phase difference Δφ between the laser pulse and the electromagnetic oscillation is 90°±10°, and the spatial overlap between the laser action area and the peak area of ​​the electromagnetic field intensity is ≥85%.

7. The method for preparing a gradient structure metal-based seamless pipe according to claim 1, characterized in that: During the rolling process of step (1), an axial vibration load is also applied synchronously; the specific conditions of the axial vibration load are: vibration frequency fv = 50~200Hz; amplitude A = (0.005~0.015)D, where D is the outer diameter of the pipe.

8. A gradient structure metal-based seamless pipe prepared by the method according to any one of claims 1 to 7, characterized in that: The tube has a three-layer gradient structure: outer layer: nanocrystalline layer, grain size ≤500nm, thickness accounts for 10%~15% of the tube wall thickness; transition layer: dislocation cell structure, cell wall spacing 50~200nm, thickness accounts for 20%~30% of the tube wall thickness; inner layer: submicron grains, grain size 1~3μm, thickness accounts for 55%~70% of the tube wall thickness.

9. The gradient structure metal-based seamless pipe according to claim 8, characterized in that: The pipe satisfies the following parameters simultaneously in the wall thickness direction: microhardness gradient HV outer layer / HV inner layer ≥ 1.5, residual stress σ of gradient compressive stress layer ≥ 300MPa, gradient change rate ≥ 50MPa / mm; texture strength ratio, {110} outer layer / {111} inner layer = 2.5~4.0.

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