A method for preparing high-strength and high-plasticity gradient structure wire

Abstract

The present invention discloses a method for preparing a high-strength and high-plasticity gradient structure wire rod, which comprises the following preparation steps: S1 Select an industrial pure iron rod; S2 Mechanically straighten it; S3 Unidirectional pre-torsion deformation and cold drawing deformation; S4 Take up the wire. In S3, Ne is the number of torsion turns corresponding to the yield torque; Nmax is the number of torsion turns corresponding to the maximum torque; N is the number of torsion turns of the pre-torsion deformation; ε is the cold drawing deformation amount; the number of torsion turns N of the pre-torsion deformation satisfies the following conditions: Ne < N < Nmax; the cold drawing deformation amount ε satisfies the following conditions: when 0.8 < ε < 2.5, a grain size gradient structure with fibrous grains in the core and ultrafine equiaxed grains on the surface layer is formed; when ε ≥ 2.5, a gradient lamellar structure with gradually decreasing lamellar thickness from the core to the surface layer is formed. The beneficial effects of the present invention are as follows: The tensile strength is increased by more than 30%, and higher plasticity can be maintained; the hardness value of the prepared high-strength and high-plasticity gradient structure pure iron wire shows a linear increasing trend from the core to the surface layer.

Description

Technical Field

[0001] The present invention relates to the technical field of metal wire processing and preparation, and in particular to a method for preparing high-strength and high-plasticity gradient structure wire. Background Art

[0002] Typically, metal wires, such as steel wire, are produced primarily through cold drawing. However, during the cold drawing process, significant work hardening occurs, resulting in increased strength and decreased ductility. In particular, when producing ultrafine steel wire, severe cold drawing can induce coarsening of the ferrite lamellae, making it difficult to increase wire strength.

[0003] In recent years, gradient structures have been introduced into metal materials to overcome their inverted strength-plasticity relationship. Gradient structured metals have gradients in grain size, twin thickness and / or layer thickness in their internal microstructure, which gradually change from the surface to the inside, and their characteristic length range can range from a few nanometers to hundreds of microns, or even up to the millimeter level. These metal materials with gradient structures exhibit higher strength and plasticity and excellent work hardening ability compared to their corresponding homogeneous structured materials. For example, a grain size gradient structure can be prepared on the surface of IF steel by surface mechanical grinding treatment (SMAT). This gradient structure can produce unique additional strain hardening, providing a new mechanism for solving the strength-plasticity contradiction problem of traditional homogeneous materials. However, SMAT requires the use of thin plate samples to prepare the gradient structure and cannot be used for the preparation of metal wires. For example, although surface mechanical grinding treatment (SMGT) and surface mechanical rolling treatment (SMRT) technologies are suitable for cylindrical rod samples, they cannot be applied to metal wires with thinner diameters, especially metal wires such as ultra-fine steel wires, which are difficult to obtain gradient structures through surface mechanical treatment methods. More importantly, the gradient structure layer produced by surface mechanical treatment methods such as SMAT, SMGT, and SMAT is relatively shallow, typically only tens to hundreds of microns, resulting in a minimal strengthening effect, with strength gains typically rarely exceeding 20%. Accumulative rolling bond (ARB) involves using two rollers to compress multiple layers of metal sheets to create a strong interfacial bond between the layers. With each rolling cycle, the sample thickness decreases, while additional shear deformation is applied to induce grain refinement, forming a gradient structure similar to SMRT. However, ARB is primarily applied to sheet materials and therefore cannot be applied to metal wire production. In addition, physical or chemical deposition methods, including electrodeposition, magnetron sputtering, and laser or electron beam deposition, are also effective methods for producing gradient structures. Specifically, by adjusting the deposition kinetics and other parameters (such as temperature, current density, and additive content), precise control of the gradient structure, including grain, twin, phase size, or composition, can be achieved, allowing the excellent properties of the gradient structure to be fully utilized in their specific application contexts. However, due to the specific process conditions of physical or chemical deposition methods, they are also difficult to apply to the production of ultrafine steel wires that pursue high production efficiency.

[0004] Torsion, as a common deformation technique, can also form strain gradient structures with unique advantages. For example, patent (CN 117385149A) discloses an austenitic stainless steel wire with a gradient nano-dislocation structure and its preparation method: the steel is austenitized to obtain a steel with a coarse-grained single-phase austenite structure; the steel with the coarse-grained single-phase austenite structure is then subjected to small-angle, multi-pass elastic-plastic torsion deformation to obtain an austenitic stainless steel wire with a gradient nano-dislocation structure. However, this method has certain application limitations and is generally only applicable to metal materials such as austenitic stainless steel with low stacking fault energy (SFE). Just as with TWIP steel with low SFE, it has been reported that pre-torsion deformation can introduce gradient grains and nano-twin structures. Subsequent tensile deformation activates different twin systems, ultimately forming a gradient nano-twin structure, achieving a significant increase in strength without sacrificing plasticity (Nat. Commun. 2014, 5:1-8).

[0005] In the prior art, a patent (CN 114749506 B) discloses a gradient structured rod and its preparation apparatus and method: The invention is used to process a rod with an elliptical cross-section into a circular cross-section. Cyclic torsion is used to apply a radial strain differential to the rod, resulting in surface grain refinement through large plastic deformation. The strain in the core of the rod is small and remains coarse-grained, ultimately producing a gradient structured metal rod with a radially gradient distribution of grains. However, this invention is limited to rods and is difficult to apply to the preparation of wires, especially ultrafine wires. Furthermore, the inventors state that their method is widely applicable to industrially pure titanium, copper, aluminum, and alloys with good plasticity, and qualitatively describe the invention as being able to achieve a synergistic improvement in material strength and plasticity. However, for aluminum alloys with high SFE (6061 aluminum alloy), it has been demonstrated that while pre-torsion deformation can produce a radial gradient strain field, due to the difficulty in forming deformation twins at room temperature, this results in increased strength and a significant deterioration in plasticity (Nat. Commun. 2014, 5:1-8).

[0006] In summary, although pre-twisting in the existing technology can introduce a gradient strain field distributed along the radial direction in the metal wire, how to achieve strength improvement while maintaining high plasticity and break the limitations of its application scope still needs further exploration.

[0007] Therefore, for metal wires, especially metal wires with high SFE, it is urgent to develop a new method for preparing high-strength and high-plasticity gradient structure wires. Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing high-strength and high-plasticity gradient structure wire. This method addresses the problem that it is difficult to achieve strength improvement of metal wire through traditional severe cold drawing deformation, and provides a new method for preparing high-strength and high-plasticity gradient structure wire, which has the advantages of simple operation and universal applicability.

[0009] More specific:

[0010] Compared with the pure iron wire with the same cold-drawn deformation prepared by the traditional cold-drawing method, the gradient structure pure iron wire prepared by the process steps and parameters of the present invention has a tensile strength increased by more than 30%, and can maintain higher plasticity; the hardness value of the prepared high-strength and high-plasticity gradient structure pure iron wire shows a linear increasing trend from the core to the surface.

[0011] To achieve the above object, the present invention is implemented through the following technical solutions:

[0012] A method for preparing high-strength and high-plasticity gradient structure wire,

[0013] The method comprises the following preparation steps:

[0014] S1 chooses industrial pure iron rod;

[0015] S2 mechanical straightening;

[0016] S3 unidirectional pre-torsion deformation;

[0017] S4 cold drawing deformation;

[0018] S5 reel in.

[0019] As a further preferred embodiment, in S3,

[0020] Ne is the number of torsional turns corresponding to the yield torque;

[0021] Nmax is the number of torsional turns corresponding to the maximum torque;

[0022] N is the number of torsion turns of pre-torsion deformation;

[0023] ε is the cold drawing deformation;

[0024] The number of torsion circles N of the pre-torsion deformation satisfies the following conditions: Ne <N<Nmax;

[0025] The cold drawing deformation ε satisfies the following conditions:

[0026] When 0.8<ε<2.5, a grain size gradient structure is formed with fibrous grains in the core and ultrafine equiaxed grains on the surface;

[0027] When ε≥2.5, a gradient lamellar structure is formed in which the lamellar thickness gradually decreases from the core to the surface.

[0028] In this embodiment, the higher the number of pre-twisting turns and the larger the cold drawing deformation, the more significant the obtained grain size gradient and lamellar structure gradient.

[0029] The present invention requires that the number of twisting turns during pre-torsion deformation be controlled to be no less than the number of twisting turns Ne corresponding to the yield torque because only when the number of twisting turns exceeds Ne can the industrial pure iron rod (wire) undergo uniform plastic deformation during the pre-torsion stage. Furthermore, the number of twisting turns must not exceed the number of twisting turns Nmax corresponding to the maximum torque because, if the number of twisting turns exceeds Nmax, the industrial pure iron rod (wire) will suffer severe deformation damage and may even develop torsional microcracks, which will affect the strengthening effect after the combined deformation.

[0030] To achieve a grain size gradient structure with ultrafine equiaxed crystals on the surface, the present invention requires that the cold drawing deformation (ε) be controlled within a range of 0.8 < ε < 2.5. If the cold drawing deformation is too low, the numerous low-angle grain boundaries generated during the torsional gradient deformation process cannot be transformed into high-angle grain boundaries, and thus the subgrain structure cannot be transformed into equiaxed crystals. Excessive cold drawing deformation can cause the equiaxed crystals formed on the surface to undergo a fiberization transformation. Therefore, to achieve a gradient lamellar structure with gradually decreasing lamellar thickness from the core to the surface, the present invention requires that the cold drawing deformation ε be controlled to be ≥ 2.5.

[0031] The present invention requires that within the control range of the pre-twisting and cold-drawing deformation degrees, a higher number of pre-twisting cycles and a larger cold-drawing deformation ε be used to achieve a more significant grain size gradient and lamellar structure gradient. This is because a higher number of pre-twisting cycles can cause the sample to undergo a larger gradient deformation. The structural gradient causes the incoordination of plastic deformation, which usually generates geometrically required dislocations (GNDs) to adapt, which further leads to plastic strain gradients and stress gradients. The higher density of GNDs stacking and interaction plays a very important role in the strengthening and excellent work hardening properties of gradient structure materials. In addition, the use of a higher cold-drawing deformation will promote the transformation of shear texture into recrystallization texture and the transformation of low-angle grain boundaries (LAGBs) into high-angle grain boundaries (HAGBs), which effectively promotes dynamic recrystallization and induces the formation of ultrafine equiaxed grains. Further cold-drawing with a larger deformation will promote the fiberization transformation of ultrafine equiaxed grains, forming a significant gradient lamellar structure and achieving continuous deformation strengthening.

[0032] As a further improvement of this solution, in S1, the diameter of the industrial pure iron rod is d0, which satisfies the quantitative relationship: 0.1mm≤d0≤14mm;

[0033] The iron content is not less than 99.50wt.%, the carbon content does not exceed 0.04wt.%, the structure is approximately equiaxed single-phase ferrite, the surface has no defects, and the tensile strength ranges from 150MPa to 450MPa.

[0034] As a further improvement of this solution, in S2, the mechanical straightening is cold straightening, and after straightening, the curvature of the industrial pure iron rod (wire) is less than 1.5 mm / m and the ovality is less than 5%.

[0035] In this embodiment, the surface of the industrial pure iron rod (wire) after straightening has no defects or damage.

[0036] As a further improvement of this solution, in S3,

[0037] Pre-torsion is a unidirectional torsional deformation and is carried out at room temperature of 25±5℃;

[0038] When 0.1mm≤d0<1mm, the torsion speed (ω) is controlled at ≤1r / s;

[0039] When 1mm≤d0<5mm, ω≤0.5r / s;

[0040] When 5mm≤d0≤10mm, ω≤0.25r / s;

[0041] When d0>10mm, ω≤0.1r / s;

[0042] In addition, when d0≤10mm, a tensioning force ≤2% of the tensile strength stress value of the specimen needs to be applied to the specimen during torsion; when d0>10mm, no tensioning force needs to be applied.

[0043] The present invention requires controlling the ambient temperature and deformation speed during pre-twisting and cold drawing because these speeds not only affect the plastic deformation process of the steel wire but also the drawing temperature rise during deformation. Excessively high pre-twisting and drawing speeds can easily lead to excessively high drawing temperatures and even adiabatic shear, deteriorating the steel wire's microstructure and properties. Furthermore, excessively high ambient temperatures can exacerbate the effects of the drawing temperature rise on steel wire properties. Furthermore, the present invention requires appropriately low deformation speeds for thicker diameter steel wires because thicker wires typically experience more uneven stress and temperature distribution during deformation. Excessively fast pre-twisting or cold drawing speeds can lead to localized excessive temperatures or internal stress concentrations, potentially causing fracture and other problems. Furthermore, thicker wires take longer to deform, so excessively fast pre-twisting or cold drawing speeds can result in uneven deformation and even lead to quality issues such as excessive surface roughness and dimensional deviations.

[0044] As a further improvement of this scheme, in S3, the cold drawing is carried out at room temperature 25±5°C, and the single-pass compression rate is controlled at 10% to 25%;

[0045] When the diameter of the cold-drawn pure iron wire (dn) satisfies dn<1mm, the cold drawing speed (ν) is controlled to not exceed 8m / s;

[0046] When 1mm≤dn<5mm, ν≤6m / s;

[0047] When 5mm≤dn≤10mm, ν≤3m / s;

[0048] When dn>10mm, ν≤1m / s.

[0049] As a further improvement of the present solution, in S4, the size of the surface ultrafine equiaxed crystals in the grain size gradient structure is about 0.5 μm to 1 μm; the thickness of the surface lamellae in the gradient lamellae structure is less than 0.2 μm.

[0050] The method of preparing a high-strength and high-plasticity gradient structure wire of the present invention has the following beneficial effects:

[0051] The gradient structure fabricated by the present invention through a combined pre-torsion and cold-drawing deformation method achieves a thicker gradient layer compared to gradient structures fabricated by surface mechanical treatment, cumulative rolling, and physical or chemical deposition. In particular, the strain gradient can be controlled by controlling the pre-torsion deformation, while controlling the cold-drawing deformation can yield a surface-layered structure with ultrafine equiaxed grains and a gradient lamellar structure.

[0052] Conventional pre-twisting and cold-drawing methods typically result in increased strength and decreased plasticity in the produced pure iron wire. Compared to single pre-twisting and cold-drawing, the composite deformation method of pre-twisting + cold-drawing disclosed in the present invention can significantly increase the strength of pure iron wire while maintaining good plasticity. For example, compared to pure iron wire produced by the traditional cold-drawing method with the same cold-drawn deformation, the composite-deformed pure iron wire can achieve higher strength and plasticity, with the tensile strength increased by more than 30%. In particular, when meeting specific strength and wire diameter requirements, the gradient structure pure iron wire produced by the present invention requires fewer cold-drawing passes, which can effectively reduce expensive mold costs.

[0053] The method disclosed herein involves pre-twisting and cold drawing, both traditional deformation methods, which are simple and easy to implement without increasing processing difficulty. The method disclosed herein is universally applicable to introducing grain size gradient structures and gradient lamellar structures into other metal wires with good deformability. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 Schematic diagram of the formation of the grain size gradient structure of the present invention;

[0055] Figure 2 TEM micromorphology of the surface of the pre-twisted pure iron rod (N=40) of the present invention;

[0056] Figure 3 TEM micromorphology of the surface layer of the composite deformed pure iron wire (N=40, ε=1.5) of the present invention;

[0057] Figure 4 TEM micromorphology of the composite deformed pure iron wire (N=28, ε=4.0) of the present invention;

[0058] Figure 5 Engineering stress-strain curves of the composite deformed pure iron wire and the cold-drawn pure iron wire of the present invention. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the present invention clearer, the following examples, comparative examples and accompanying drawings are given. Figures 1 to 5 The present invention will be further described:

[0060] A method for preparing high-strength and high-plasticity gradient structure wire, the specific process flow is: industrial pure iron rod (wire) → straightening → pre-twisting → cold drawing → wire winding.

[0061] A method for preparing high-strength and high-plasticity gradient structure wire, the specific technical solution is as follows:

[0062] 1) Select industrial pure iron rods (wires) with composition, organization and mechanical properties that meet the requirements, with a diameter (d0) of 0.1mm≤d0≤14mm, an iron content of not less than 99.50wt.%, a carbon content of not more than 0.04wt.%, an approximately equiaxed single-phase ferrite organization, no surface defects, and a tensile strength of 150MPa~450MPa.

[0063] 2) The industrial pure iron rod (wire) is subjected to cold mechanical straightening. After straightening, the curvature of the pure iron rod (wire) is less than 1.5 mm / m, the ovality is less than 5%, and the surface of the pure iron rod (wire) is free of defects and damage.

[0064] 3) Carry out unidirectional pre-torsion deformation on the straightened industrial pure iron rod (wire) at room temperature of 25 ± 5 °C. The number of torsion turns of the pre-torsion deformation is controlled such that Ne (the number of torsion turns corresponding to the yield torque) < N < Nmax (the number of torsion turns corresponding to the maximum torque). When 0.1 mm ≤ d0 < 1 mm, the torsion speed (ω) is controlled not to exceed 1 r / s; when 1 mm ≤ d0 < 5 mm, ω ≤ 0.5 r / s; when 5 mm ≤ d0 ≤ 10 mm, ω ≤ 0.25 r / s; when d0 > 10 mm, ω ≤ 0.1 r / s. In addition, when d0 ≤ 10 mm, a tension force not greater than 2% of the tensile strength stress value of the specimen needs to be applied during torsion, and when d0 > 10 mm, no tension force needs to be applied.

[0065] 4) Carry out cold drawing deformation on the pre-torsioned industrial pure iron rod (wire) at room temperature of 25 ± 5 °C. When the cold drawing deformation amount (ε) is controlled such that 0.8 < ε < 2.5, a grain size gradient structure with fibrous grains in the core and ultrafine equiaxed grains on the surface is formed. When the cold drawing deformation amount (ε) is controlled such that ε ≥ 2.5, a gradient lamellar structure with gradually decreasing lamellar thickness from the core to the surface is formed; the single-pass compression ratio is controlled at 10% - 25%; when dn < 1 mm, the cold drawing speed (ν) is controlled not to exceed 8 m / s; when 1 mm ≤ dn < 5 mm, ν ≤ 6 m / s; when 5 mm ≤ dn ≤ 10 mm, ν ≤ 3 m / s; when dn > 10 mm, ν ≤ 1 m / s.

[0066] 5) Wire drawing

[0067] Example 1

[0068] Select an industrial pure iron rod with a diameter of 8 mm to prepare a pure iron wire with a grain size gradient structure and a diameter of 3.8 mm.

[0069] 1) Select an industrial pure iron rod with a diameter of 8 mm, an iron content of 99.8 wt.%, a carbon content of 0.03 wt.%, an approximately equiaxed single-phase ferrite structure, no surface defects, and a tensile strength of 406 MPa.

[0070] 2) Carry out cold mechanical straightening on the industrial pure iron rod with a diameter of 8 mm. After straightening, the bending degree of the industrial pure iron rod is 1.1 mm / m, the ovality is 3%, and there are no surface defects and damages on the straightened industrial pure iron rod.

[0071] 3) Carry out unidirectional pre-torsion deformation on the straightened industrial pure iron rod at room temperature of 26 °C. The number of torsion turns is N = 40 turns; the torsion speed (ω) is controlled at ω = 0.03 r / s. A tension force of 200 N is applied during torsion. After the pre-torsion deformation, the grains in the core will undergo slight deformation, while the grains on the surface will be significantly refined, as Figure 1In addition, the gradient shear deformation caused by pre-torsion forms many approximately equiaxed subgrains inside the surface grains. A large number of GNDs generated by the gradient strain slip and aggregate inside the coarse grains to form dislocation walls and dislocation cell structures, as shown in Figure 2 As shown by the white arrows in the middle, the high-density GNDs mainly participate in the formation of small-angle grain boundaries, thereby forming a large number of approximately equiaxed subgrain structures.

[0072] 4) The pre-twisted industrial pure iron rod is subjected to cold drawing deformation at room temperature of 26°C, with a cold drawing deformation of ε=1.5, a single-pass compression ratio of 15%, and a cold drawing speed (ν) of 5m / s. After pre-twisting and cold drawing, the core grains undergo significant fiberization, while a large number of ultrafine equiaxed grains are formed on the surface, such as Figure 1 After the surface grains of the pre-twisted sample are cold-drawn, the slip and aggregation of GNDs inside the grains further increase the misorientation, causing the low-angle grain boundaries to transform into high-angle grain boundaries, forming ultrafine equiaxed grains, as shown in Figure 2. Figure 3 After the composite deformation of pre-torsion (N=40) and subsequent cold drawing (ε=1.5), a grain size gradient structure with fibrous grains in the core and ultrafine equiaxed grains on the surface is formed in the pure iron wire, as shown in Figure 2. Figure 1 shown.

[0073] 5) Reel in the line.

[0074] Example 2

[0075] Industrial pure iron rods with a diameter of 12 mm were used to prepare pure iron wires with a grain size gradient structure and a diameter of 5.1 mm.

[0076] 1) Select an industrial pure iron rod with a diameter of 12 mm, an iron content of 99.7 wt.%, a carbon content of 0.03 wt.%, a structure of approximately equiaxed single-phase ferrite, no surface defects, and a tensile strength of 392 MPa.

[0077] 2) An industrial pure iron rod with a diameter of 12 mm was subjected to cold mechanical straightening. After straightening, the curvature of the industrial pure iron rod was 1.0 mm / m, the ovality was 4%, and the surface of the industrial pure iron rod was free of defects and damage.

[0078] 3) The straightened industrial pure iron rod is subjected to unidirectional pre-torsion deformation at room temperature (24° C.), with the number of torsion turns being N=28 turns; and the torsion speed (ω) being controlled at ω=0.05 r / s.

[0079] 4) The pre-twisted industrial pure iron rod is subjected to cold drawing deformation at room temperature (24° C.), with a cold drawing deformation of ε=1.7, a single-pass compression ratio controlled at 16%, and a cold drawing speed (ν) controlled at 2 m / s.

[0080] 5) Reel in the line.

[0081] Example 3

[0082] Industrial pure iron rod with a diameter of 12 mm was selected to prepare gradient lamellar structure pure iron wire with a diameter of 2.65 mm.

[0083] 1) Select an industrial pure iron rod with a diameter of 12 mm, an iron content of 99.7 wt.%, a carbon content of 0.03 wt.%, a structure of approximately equiaxed single-phase ferrite, no surface defects, and a tensile strength of 392 MPa.

[0084] 2) An industrial pure iron rod with a diameter of 12 mm was subjected to cold mechanical straightening. After straightening, the curvature of the industrial pure iron rod was 1.0 mm / m, the ovality was 4%, and the surface of the industrial pure iron rod was free of defects and damage.

[0085] 3) The straightened industrial pure iron rod is subjected to unidirectional pre-torsion deformation at room temperature (24° C.), with the number of torsion turns being N=28 turns; and the torsion speed (ω) being controlled at ω=0.05 r / s.

[0086] 4) The pre-twisted industrial pure iron rod is subjected to cold drawing deformation at room temperature (24° C.), with a cold drawing deformation of ε=3.0, a single-pass compression ratio controlled at 16%, and a cold drawing speed (ν) controlled at 5 m / s.

[0087] 5) Reel in the line.

[0088] Example 4

[0089] Industrial pure iron rod with a diameter of 12 mm was selected to prepare gradient lamellar structure pure iron wire with a diameter of 1.62 mm.

[0090] 1) Select an industrial pure iron rod with a diameter of 12 mm, an iron content of 99.7 wt.%, a carbon content of 0.03 wt.%, a structure of approximately equiaxed single-phase ferrite, no surface defects, and a tensile strength of 392 MPa.

[0091] 2) An industrial pure iron rod with a diameter of 12 mm was subjected to cold mechanical straightening. After straightening, the curvature of the industrial pure iron rod was 1.0 mm / m, the ovality was 4%, and the surface of the industrial pure iron rod was free of defects and damage.

[0092] 3) The straightened industrial pure iron rod is subjected to unidirectional pre-torsion deformation at room temperature (24° C.), with the number of torsion turns being N=28 turns; and the torsion speed (ω) being controlled at ω=0.05 r / s.

[0093] 4) The pre-twisted industrial pure iron rod is subjected to cold drawing deformation at room temperature (24°C), with a cold drawing deformation of ε = 4.0, a single-pass compression ratio controlled at 16%, and a cold drawing speed (ν) controlled at 4 m / s. After the ultra-large cold drawing with a deformation of ε = 4.0, the fiberized grains in the core formed under the original lower deformation (ε < 2.5) are further refined, while the ultrafine equiaxed grains on the surface gradually transform into fiberized grains, ultimately forming a gradient lamellar structure with a gradually decreasing lamellar thickness from the core to the surface, as shown in Figure 4. Figure 4 shown.

[0094] 5) Reel in the line.

[0095] Comparative Example 1

[0096] The same as Example 2, except that the pure iron rod with a diameter of 12 mm is not subjected to pre-torsion deformation, but only to cold drawing with ε=1.7.

[0097] Comparative Example 2

[0098] The same as Example 3, except that the pure iron rod with a diameter of 12 mm is not subjected to pre-torsion deformation, but only cold drawing with ε=3.0.

[0099] Comparative Example 3

[0100] The same as Example 4, except that the pure iron rod with a diameter of 12 mm is not subjected to pre-torsion deformation, but only cold drawing with ε=4.0.

[0101] Table 1 Comparison of mechanical properties of pure iron wire in the embodiment and comparative example

[0102]

[0103] like Figures 1 to 5 , and the comparative results analysis of the embodiments and comparative examples in Table 1:

[0104] The pure iron wires of Examples 2 to 4 and Comparative Examples 1 to 3 were sampled and tested for mechanical properties. Figure 5 It can be found that under different deformation amounts, the tensile strength and elongation at break of the composite deformed pure iron wire are higher than those of the single cold-drawn pure iron wire. That is, according to the method and parameter requirements specified in the claims, a high-strength and high-plasticity gradient structure pure iron wire can be obtained.

[0105] From the mechanical property test results in Table 1, it can be seen that the tensile strength of the composite deformed pure iron wire (N=28, ε=1.7) is about 180MPa higher than that of the single cold-drawn pure iron wire (N=0, ε=1.7). As the cold-drawing deformation increases, the difference in tensile strength between the two also increases. When the cold-drawing deformation reaches ε=3.0, the tensile strength of the composite deformed pure iron wire is about 325MPa higher than that of the single cold-drawn pure iron wire. In fact, the gradient structure pure iron wire prepared according to the method and parameter requirements specified in the present claims has a tensile strength increase of more than 30% compared with the pure iron wire with the same cold-drawing deformation prepared by the traditional cold drawing method, and can maintain higher plasticity.

[0106] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent transformations made using the present invention are within the scope of patent protection of the present invention.

Claims

1. A method for preparing a high-strength and high-plasticity gradient structure wire, characterized in that: The method comprises the following preparation steps: S1 chooses industrial pure iron rod; S2 mechanical straightening; S3 unidirectional pre-torsion deformation; S4 cold drawing deformation; S5 reel in; In S3, Unidirectional pre-torsion deformation, carried out at room temperature 25±5℃; When 0.1mm≤d0<1mm, the torsion speed (ω) is controlled at ≤1r / s; When 1mm≤d0<5mm, ω≤0.5r / s; When 5mm≤d0≤10mm, ω≤0.25r / s; When d0>10mm, ω≤0.1r / s; In addition, when d0≤10mm, a tension of ≤2% of its tensile strength stress value needs to be applied to the specimen during torsion; when d0>10mm, no tension is required. In S3, cold drawing is carried out at room temperature 25±5°C, and the compression ratio of a single pass is controlled at 10% to 25%; When the diameter of the cold-drawn pure iron wire (dn) satisfies dn<1mm, the cold drawing speed (ν) is controlled to not exceed 8m / s; When 1mm≤dn<5mm, ν≤6m / s; When 5mm≤dn≤10mm, ν≤3m / s; When dn>10mm, ν≤1m / s.

2. The method for preparing a high-strength and high-plasticity gradient structure wire according to claim 1, characterized in that: In S3~S4, Ne is the number of torsional turns corresponding to the yield torque; Nmax is the number of torsional turns corresponding to the maximum torque; N is the number of torsion turns of pre-torsion deformation; ε is the cold drawing deformation; The number of torsion circles N of the pre-torsion deformation satisfies the following conditions: Ne <N<Nmax; The cold drawing deformation ε satisfies the following conditions: When 0.8<ε<2.5, a grain size gradient structure is formed with fibrous grains in the core and ultrafine equiaxed grains on the surface; When ε≥2.5, a gradient lamellar structure is formed in which the lamellar thickness gradually decreases from the core to the surface.

3. The method for preparing a high-strength and high-plasticity gradient structure wire according to claim 1, characterized in that: In S1, the diameter of the industrial pure iron rod is d0, which satisfies the quantitative relationship: 0.1 mm ≤ d0 ≤ 14 mm; The iron content is not less than 99.50wt.%, the carbon content does not exceed 0.04wt.%, the structure is approximately equiaxed single-phase ferrite, the surface has no defects, and the tensile strength ranges from 150MPa to 450MPa.

4. The method for preparing a high-strength and high-plasticity gradient structure wire according to claim 1, characterized in that: In S2, the mechanical straightening is cold straightening, and after straightening, the curvature of the industrial pure iron rod (wire) is less than 1.5 mm / m and the ovality is less than 5%.

5. The method for preparing a high-strength and high-plasticity gradient structure wire according to claim 2, characterized in that: In S4, the size of the surface ultrafine equiaxed crystals in the grain size gradient structure is 0.5 μm to 1 μm; the thickness of the surface lamellae in the gradient lamellae structure is less than 0.2 μm.

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