A method for drawing and strengthening a profiled steel wire by means of a roller die

Abstract

The application discloses a special-shaped steel wire roller die drawing strengthening method, which comprises the following steps: special-shaped steel wire blank is drawn through at least three passes of roller dies in sequence, the roller die drawing is divided into an early stage and a later stage according to the pass sequence, the reduction of each pass in the early stage is 20-30%, the reduction of each pass in the later stage is 10-15%, and after the last pass in the later stage, precision sizing is carried out by using a roller die, and the reduction of the precision sizing is less than 5%. Through the front large and rear small gradient reduction distribution, the early large reduction is used to quickly accumulate deformation to realize sufficient strengthening, the later small reduction is used to finely control deformation uniformity, and the roller die precision sizing is combined to maintain surface quality, so that the special-shaped steel wire simultaneously obtains high strength and excellent bending and torsional performance, and the problems of poor product quality and low production efficiency in the prior art are effectively solved.

Description

Technical Field

[0001] This application belongs to the field of metal wire processing technology, and specifically relates to a method for strengthening irregular steel wire by roller drawing. Background Technology

[0002] A typical structure of a sealed wire rope is as follows: Figure 1 As shown in a and b, it is composed of multiple irregularly shaped steel wires twisted together, and is widely used as the outer sealing wire in fully sealed steel wire ropes, bridge cables, and overhead conductors. The cross-sectional shape of the Z-shaped steel wire is as follows: Figure 2 As shown, it has a Z-shaped profile consisting of two planar regions of different widths and an inclined edge region connecting the two planar regions. Adjacent steel wires achieve surface contact sealing through the interlocking of the cross-section hook parts.

[0003] Z-shaped cross-section steel wire can be formed using methods such as fixed die drawing or roll die drawing. During fixed die drawing, there is relative sliding between the steel wire and the die. The edges and hook-lock areas of the Z-shaped cross-section are prone to localized contact and stress concentration, which may lead to die wear, scratches on the steel wire surface, and increased drawing resistance. Roll die drawing uses rolls with forming holes to continuously roll and form the steel wire. The relative sliding between the steel wire and the rolls is small, and it is often used for multi-pass forming of Z-shaped cross-section steel wire.

[0004] However, in multi-pass drawing processes, existing technologies typically distribute the reduction in surface area evenly or nearly evenly across passes. For high-carbon steel wire, as the number of drawing passes increases, the degree of work hardening gradually increases. If the overall reduction rate for each pass is small, the early deformation accumulation is slow, requiring more passes. If the overall reduction rate for each pass is large, the wire is already highly work-hardened in the later stages of drawing, yet still experiences the same reduction rate as in the early stages, leading to deformation concentrating in localized areas within the cross-section. This problem is even more pronounced for Z-shaped cross-section wire. The deformation paths of the edge regions and planar regions of a Z-shaped cross-section differ, resulting in inherently uneven deformation within the cross-section. As the number of drawing passes increases and the degree of work hardening improves, the differences in deformation resistance across different parts further intensify. This uneven deformation accumulates between passes, causing the wire's bending, torsional, and other toughness indicators to deteriorate. It becomes difficult to simultaneously achieve high strength, good toughness, and surface quality.

[0005] Furthermore, drawing speed determines production efficiency, and higher drawing speeds are preferred in actual production. However, as the drawing speed increases, the deformation heat generated per unit time increases, and the temperature of the steel wire rises accordingly. When the temperature is too high, the steel wire recovers during the drawing process, and the work hardening effect already obtained is partially offset, resulting in a decrease in tensile strength. At the same time, the load-bearing capacity of the lubricating film decreases with increasing temperature, and scratches are more likely to appear on the surface of the steel wire.

[0006] Therefore, how to balance high strength with good plasticity, bending and torsional properties in multi-pass roll drawing of Z-shaped steel wire is a problem that existing technologies need to solve. Summary of the Invention

[0007] To address the aforementioned technical problems, this application is aimed at... Figure 2 The Z-shaped cross-section of the irregular steel wire shown provides a method for strengthening irregular steel wire by roller drawing. Through a specific roller drawing process, the cross-section of each pass is gradually formed from the blank to the target Z shape, while taking into account high strength, excellent bending and torsional performance and surface quality.

[0008] This application provides a method for strengthening irregularly shaped steel wire by roller drawing, including the following steps: The shaped steel wire blank is drawn sequentially through at least three roller dies. The roller drawing is divided into an early stage and a late stage according to the number of passes. The surface reduction rate of each pass in the early stage is 20-30%, and the surface reduction rate of each pass in the late stage is 10-15%. After the last pass in the late stage, the roller dies are used for fine sizing, and the surface reduction rate of the fine sizing is less than 5%.

[0009] Furthermore, the number of passes in the early stage accounts for 60-75% of the total number of passes in the roller drawing process, and the later stage consists of 2-3 passes.

[0010] Furthermore, the cumulative equivalent strain of the steel wire at the end of the aforementioned preliminary stage The cumulative equivalent strain is 1.0 to 1.8. Calculate according to formula (1): (1) in The initial cross-sectional area of ​​the billet. This refers to the cross-sectional area of ​​the steel wire at the end of the initial stage.

[0011] Furthermore, in the aforementioned early and late stages, the reduction rate of each pass decreases sequentially along the drawing direction, and satisfies the following: The difference in area reduction rate between adjacent passes within the same phase shall not exceed 3 percentage points; The difference in surface reduction rate between the last pass of the early stage and the first pass of the later stage shall not be less than 5 percentage points.

[0012] Furthermore, in the early and late stages, the reduction rate of each pass along the drawing direction decreases linearly or stepwise.

[0013] Furthermore, the demolding temperature of each drawing pass in the early stage is controlled within 120°C, and the demolding temperature of each drawing pass in the later stage is controlled within 70°C.

[0014] Furthermore, the drawing speed for each pass in the early and late stages is 15–25 m / min.

[0015] Furthermore, during the drawing process, circulating water cooling is used to cool the steel wire in each pass, with the cooling water temperature being 20-30℃ and the cooling water pressure being 0.3-0.5MPa.

[0016] Furthermore, the reduction rate of the fine sizing is 2-5%, and the exit temperature of the steel wire after fine sizing is not higher than 60°C.

[0017] Furthermore, before drawing the shaped steel wire blank, a blank preparation step is also included: After the wire rod undergoes pickling and phosphating surface pretreatment, it is rough drawn in a preset number of passes using a circular die, then heat-treated and reheated, and finally pickled, phosphating, and saponified to become the shaped steel wire blank. Among them, the phosphating process forms a layer on the surface of the wire rod with a mass of 3-8 g / m² per unit area. 2 Phosphating layer.

[0018] The beneficial effects of this application are as follows: 1. This application achieves a dual-gradient synergy by distributing the reduction rate of Z-shaped steel wire in the drawing process of rollers in a gradient manner, with a larger reduction rate in the early stage driving the grains to be rapidly sheared and crushed along the drawing direction and quickly accumulating work hardening to build strength. In the later stage, a smaller reduction rate is used to finely control the deformation uniformity. The two work together to overcome the defects of insufficient strengthening in the early stage and uneven deformation in the later stage of the existing uniform reduction rate process, so that the Z-shaped steel wire can obtain high strength while maintaining good bending and torsional properties.

[0019] 2. This application replaces the fixed die cold drawing sizing with roller die precision sizing after the last pass, and controls the surface reduction rate of precision sizing within a small range. It replaces sliding friction with full circumferential rolling contact of the roller, thus avoiding surface scratches introduced by cold drawing sizing. It maintains surface brightness while ensuring the geometric accuracy of the cross section, and solves the problem of surface quality damage caused by cold drawing sizing. Attached Figure Description

[0020] Figure 1 Diagram showing the shape of a sealing steel wire rope; Figure 2 This is a schematic diagram of the finished cross-section of the Z-shaped steel wire; Figure 3 This is a schematic diagram illustrating the changes in the drawing die shape at each stage of the Z-shaped steel wire in one embodiment of this application; wherein, Figure 3 a is the cross-section of the billet. Figure 3 b represents the exit section of the first pass in the initial stage. Figure 3 c represents the exit section of the last pass in the initial stage. Figure 3 d represents the exit section of the last pass in the later stage. Figure 3 e is the fine-diameter outlet section. Detailed Implementation

[0021] The embodiments of the technical solution of this application will be described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0022] This application provides a method for strengthening irregularly shaped steel wire by roller drawing, including the following steps: The shaped steel wire blank is drawn sequentially through at least three roller dies. The roller drawing is divided into an early stage and a late stage according to the number of passes. The surface reduction rate of each pass in the early stage is 20-30%, and the surface reduction rate of each pass in the late stage is 10-15%. After the final pass in the later stage, a roller die is used for fine sizing, and the reduction rate of the fine sizing is less than 5%.

[0023] Specifically, the die profile for each pass is a transitional profile that gradually approaches the target irregular cross-section along the drawing direction, and the roll gap tolerance for each pass is controlled within ±0.05mm. Each pass is formed in one step according to the design dimensions for that pass. The successive approximation of the transitional die profile and the accuracy of the roll gap ensure the cross-sectional shape and dimensional accuracy of each pass. The following is a combination of... Figure 3 The drawing process of this embodiment will be described in detail: Figure 3 The diagram illustrates the change in the cross-sectional area of ​​the roller die transition section during each drawing stage of the Z-shaped steel wire. Specifically: Figure 3 a is the cross section of the billet. After pretreatment, the billet enters the roller drawing process. Figure 3 b represents the first exit section in the early stage, after which the section begins to take initial shape following the large reduction in surface area during the early stage of drawing. Figure 3 c represents the exit section of the last pass in the early stage. After the cumulative deformation of each pass in the early stage, the section has basically approached the target shape. Figure 3 d represents the final exit section in the later stage, where the deformation uniformity is further improved after the small reduction in surface area during the later stage of drawing. Figure 3 e represents the precision-calibrated exit section, i.e., the Z-formed product, which achieves precise final cross-sectional dimensions and surface quality after precision calibration. Figure 3 It can be seen that as the drawing passes progress, the cross section gradually transitions from the billet to a Z-shape, and the reduction rate of each stage shows a decreasing trend from large to small. The early stage rapidly accumulates deformation to achieve sufficient strengthening, while the later stage finely controls the uniformity of deformation. Combined with precise sizing, the geometric accuracy and surface quality of the cross section are guaranteed.

[0024] Preferably, during the drawing process, circulating water cooling is used to cool the steel wire in each pass. The cooling water temperature is 20-30℃ and the cooling water pressure is 0.3-0.5MPa, in order to meet the control requirements of the demolding temperature at each stage.

[0025] Preferably, before drawing the shaped steel wire billet, a billet preparation step is included. This step involves pre-treating the wire rod by pickling and phosphating, first performing a predetermined number of rough draws using a circular die, then heat-treating and reheating, and finally obtaining the billet after pickling, phosphating, and saponification. Optionally, the pickling process uses hydrochloric acid solution (concentration 15-20%, temperature 40-60℃) to remove surface iron oxide scale, with a pickling time of 5-10 minutes; the phosphating process forms a uniform phosphating lubricating carrier layer on the steel wire surface, with a phosphating layer mass of 3-8 g / m² per unit area. 2 This reduces the coefficient of friction during drawing. The saponification treatment uses industrial soap solution, with an immersion time of 2-3 minutes, to form a saponified lubricating film on the surface of the phosphated layer.

[0026] Furthermore, the number of passes in the early stage accounts for 60-75% of the total number of passes in the roller drawing process, and the later stage consists of 2-3 passes. By controlling the proportion of passes in the early stage, sufficient deformation is accumulated in the early stage to establish the basic work hardening, while reserving 2-3 passes for uniform deformation control in the later stage. If only one pass remains in the later stage, the uneven deformation accumulated on the irregular cross-section due to the large deformation in the early stage cannot be effectively eliminated. If there are too many passes in the later stage, the proportion of the total deformation used for strength establishment is insufficient, and the increased number of passes reduces production efficiency. Furthermore, the cumulative equivalent effect of the steel wire at the end of the early stage becomes 1.0-1.8.

[0027] Specifically, the cumulative equivalent strain is calculated using the following formula: (1) Where A0 is the initial cross-sectional area of ​​the billet, and A is the cross-sectional area of ​​the steel wire at the end of the early stage. According to the work hardening law of high carbon steel wire drawing, the work hardening rate is relatively high when ε < 1.0, and the rate of increase slows down and tends to saturate when 1.0 < ε < 2.0. The accumulated equivalent strain in the early stage is controlled at 1.0 to 1.8 to ensure that the basic strength is established in the rapid work hardening stage, while avoiding excessive accumulation of strain that leads to excessive consumption of plastic reserves, thus reserving plastic space for the later uniform deformation control.

[0028] Furthermore, in the early and late stages, the reduction rate of each pass decreases sequentially along the drawing direction, satisfying the following conditions: the difference in reduction rate between adjacent passes within the same stage is no greater than 3 percentage points; the difference in reduction rate between the last pass of the early stage and the first pass of the late stage is no less than 5 percentage points. Controlling the difference in reduction rate between adjacent passes within a stage to within 3 percentage points ensures a smooth transition between work hardening and uniform deformation control, preventing abrupt changes in deformation between passes that could increase the hardness difference between the edge and planar regions of the irregular cross-section. A reduction rate step of no less than 5 percentage points is set between the early and late stages to create a clear deformation boundary at the stage transition, ensuring that each later pass truly enters a small reduction rate uniform control mode, and avoiding an ambiguous distribution of deformation between the two stages in the stage transition zone.

[0029] Optionally, the reduction rate of the surface area reduction in each pass can be linear or stepped. Stepped reduction is easier to implement in terms of process and can reduce the frequency of roll gap adjustment between passes. In one implementation, the surface area reduction rate of the precision sizing is 2-5%. When the surface area reduction rate of the precision sizing is higher than 5%, even with roll die precision sizing, the steel wire may still have a significant cross-sectional shape deviation when passing through the precision sizing roll die due to the excessive adjustment range of the roll gap, affecting dimensional accuracy; at the same time, when the surface area reduction rate is too large, the deformation heat effect increases, the steel wire exit temperature rises, which may lead to surface oxidation and discoloration, affecting surface quality. By controlling the surface area reduction rate of the precision sizing to 2-5%, the cross-sectional dimensional accuracy is ensured while the exit temperature is controlled below 60℃, avoiding surface quality deterioration.

[0030] Furthermore, the die exit temperature for each drawing pass in the early stage is controlled below 120℃, and the die exit temperature for each drawing pass in the later stage is controlled below 70℃. In the early stage, the reduction in surface area is large and the deformation heat is concentrated; controlling the die exit temperature below 120℃ avoids the enhanced dynamic recovery caused by high temperature, which partially offsets the work hardening effect. In the later stage, the work hardening degree of the steel wire is already high, and the cross-section gradually approaches the finished product shape; further controlling the die exit temperature below 70℃ helps avoid the exacerbation of the hardness difference between the edge area and the flat area caused by deformation heat, and ensures the surface quality of each pass before the finished product. Furthermore, the drawing speed for each pass in both the early and later stages is 15–25 m / min. Drawing speed affects the deformation heat effect and work hardening rate. When the drawing speed is below 15 m / min, although the deformation temperature rise is lower and beneficial for microstructure control, the production efficiency is too low. When the drawing speed is above 25 m / min, the deformation heat effect increases significantly, and the wire exit temperature may exceed 120°C. The high temperature leads to enhanced dynamic recovery, partially offsetting the work hardening effect and resulting in a decrease in strength. Therefore, controlling the drawing speed within the range of 15–25 m / min can achieve a balance between production efficiency and performance.

[0031] Those skilled in the art will understand that roller drawing changes the sliding friction between the steel wire and the die wall to rolling friction, and its lubrication requirements are lower than those of fixed die drawing. However, in the multi-pass forming process of high-carbon steel irregular cross-sections with a total reduction in surface area exceeding 80% as described in this application, the contact stress at the contact point between the roller surface and the edge of the irregular cross-section is high, and the accumulated deformation heat is large. During the drawing process, dry wire drawing powder can be selectively introduced to prevent steel chips from adhering to the roller surface and scratching the steel wire surface, and to coordinate with circulating water cooling to control the die exit temperature and protect the surface quality of the edge. The specific type of wire drawing powder can be selected according to the process conditions at each stage.

[0032] The present invention will be further illustrated below through examples and comparative examples.

[0033] The raw materials used in the following examples and comparative examples were: 82B high-carbon steel wire rod, with a carbon content of 0.81% ± 0.02% and a diameter of Φ12.5mm. The chemical composition (mass fraction) of the 82B wire rod was: C 0.79–0.86%, Si 0.15–0.35%, Mn 0.60–0.90%, P ≤ 0.025%, and S ≤ 0.025%. The wire rod had a smooth surface, free from harmful defects such as cracks, folds, scabs, and burrs, and contained more than 85% sorbite.

[0034] The target finished product is: outer sealing wire for Z4.2 specification sealed steel wire rope, with cross-sectional dimensions of height (h) 4.2±0.05mm, large face (a) 3.4±0.05mm, small face (b) 3.0±0.05mm, diagonal (c) 6.2±0.05mm, and a finished product cross-sectional area of ​​13.0mm². 2 .

[0035] The process parameters and wire performance test results of each embodiment and comparative example are summarized in Table 1 and Table 2.

[0036] Example 1 The preparation method of this embodiment includes the following steps: S1. The 82B wire rod is pretreated by pickling and phosphating, and a surface coating with a unit area mass of approximately 5 g / m² is formed on the wire rod surface. 2 After phosphate coating, the material is rough-drawn in two passes using a circular die to a diameter of Φ10.6±0.2mm. It then undergoes lead bath quenching, tempering, pickling, phosphate coating, and saponification to become the billet. The billet has a cross-sectional area of ​​approximately 88.2mm². 2 Each pretreatment step uses conventional process parameters in this field.

[0037] S2. The billet is sequentially drawn through the pre-roll die unit in 5 passes at a drawing speed of 20 m / min. The target reduction rate for each pass is 30%, 28%, 27%, 26%, and 25%, respectively. The main roller of the roller die has a diameter of 200mm, and the die shape is a transitional shape that gradually approaches the target Z-shaped cross-section. The roller gap tolerance is controlled within ±0.05mm. Under circulating water cooling (cooling water temperature 25℃, cooling water pressure 0.4MPa), the measured exit temperatures of each pass are approximately 102℃, 107℃, 110℃, 113℃, and 116℃, respectively, all controlled within 120℃. At the end of the initial stage, the cross-sectional area of ​​the steel wire is approximately 18.0mm². 2 The cumulative equivalent becomes 1.59.

[0038] S3. The steel wire, after initial drawing, is sequentially passed through the subsequent roller die unit for two passes of drawing. The target reduction rates for each pass are 15% and 12%, respectively. The measured exit temperatures for each pass in the subsequent stage are approximately 63℃ and 66℃, respectively, both below 70℃. At the end of the subsequent stage, the cross-sectional area of ​​the steel wire is approximately 13.5 mm². 2 .

[0039] S4. After the final pass in the later stage, a roller die precision sizing unit is used for precision sizing, with a target reduction in surface area of ​​3%. The measured exit temperature is approximately 55℃. After precision sizing, the finished product cross-sectional area is approximately 13.0 mm². 2 .

[0040] Example 2 The difference between this embodiment and Embodiment 1 is that: the initial five passes use a stepped decreasing reduction rate, with reduction rates of 30%, 30%, 27%, 27%, and 24% respectively; the demolding temperatures for each of the initial passes are approximately 106℃, 109℃, 112℃, 114℃, and 117℃ respectively, all controlled below 120℃; and the wire cross-sectional area at the end of the initial stage is approximately 17.5mm². 2 The cumulative equivalent becomes 1.62; The target reduction rates for the two later passes are 14% and 12%, respectively; the demolding temperatures for each later pass are approximately 66℃ and 68℃, respectively, both below 70℃. The target reduction in surface area for precision sizing is 2%, and the measured demolding temperature is approximately 56℃; the cross-sectional area of ​​the finished product after precision sizing is approximately 13.0 mm². 2 .

[0041] The drawing speed for each pass was adjusted to 25 m / min, and the rest of the configuration and steps were the same as in Example 1.

[0042] Example 3 The difference between this embodiment and Embodiment 1 is that an 8-pass roller drawing process is used, with 5 passes in the early stage and 3 passes in the later stage. The initial 5 passes employ a linearly decreasing reduction rate, at 28%, 27%, 26%, 25%, and 24% respectively. The ex-die temperatures for each of the early passes are approximately 95℃, 99℃, 103℃, 106℃, and 109℃, respectively, all controlled below 120℃. At the end of the early stage, the wire cross-sectional area is approximately 19.6 mm². 2 The cumulative equivalent becomes 1.50.

[0043] The target reduction rates for the three later passes were 13%, 12%, and 11%, respectively. The demolding temperatures for each of the later passes were approximately 61℃, 64℃, and 67℃, all below 70℃. At the end of the later stage, the cross-sectional area of ​​the steel wire was approximately 13.4 mm². 2 .

[0044] The target reduction in surface area for precision sizing is 3%, the measured demolding temperature is approximately 55℃, and the cross-sectional area of ​​the finished product after precision sizing is approximately 13.0 mm². 2 The finished product's cross-sectional dimensions conform to the design tolerance requirements of specification Z4.2.

[0045] The remaining configurations and steps are the same as in Example 1.

[0046] Comparative Example 1 The difference between this comparative example and Example 1 is that: 11 passes of roller drawing are used, with uniform reduction rate distribution in each pass, and a target reduction rate of 16% for all passes, with no distinction between early and late stages; the reduction rate for fine sizing is 3%, and the cross-sectional area of ​​the finished product after fine sizing is approximately 12.6 mm². 2 The cumulative equivalent effect over the entire process (including the fine-tuning) becomes 1.95.

[0047] The remaining configurations and steps are the same as in Example 1.

[0048] Comparative Example 2 The difference between this comparative example and Example 1 is that a fixed die cold drawing sizing is used instead of a roller die for precision sizing after the final pass. The die working cone angle is 12°, the sizing band length is 3mm, the target reduction rate of the cold drawing sizing is 3%, and the finished product cross-sectional area is approximately 13.0mm². 2 .

[0049] The remaining configurations and steps are the same as in Example 1.

[0050] Comparative Example 3 The difference between this comparative example and Example 1 is that the target reduction rate of the roll die after the final pass for precision sizing is adjusted to 8%. The cross-sectional area of ​​the finished product after precision sizing is approximately 12.4 mm². 2 The final sizing temperature is approximately 78℃.

[0051] The remaining configurations and steps are the same as in Example 1.

[0052] Comparative Example 4 The difference between this comparative example and Example 1 is that an 8-pass roller drawing process was used, with 7 passes in the early stage and 1 pass in the later stage; the target reduction rate for each pass in the early stage was 22%, the target reduction rate for the later stage was 15%, and the reduction rate for precision sizing was 3%. At the end of the early stage, the cross-sectional area of ​​the steel wire was approximately 15.5 mm². 2 The cumulative equivalent effect becomes 1.74; the finished product cross-sectional area after precision sizing is approximately 12.8 mm². 2 .

[0053] The remaining configurations and steps are the same as in Example 1.

[0054] Comparative Example 5 The difference between this comparative example and Example 1 is that the target surface reduction rate for the first 5 passes is adjusted to 30%, 30%, 28%, 28%, and 20%, with the surface reduction rate difference between the 4th and 5th passes being 8 percentage points; the configuration of the later 2 passes and the fine sizing is the same as in Example 1.

[0055] The remaining configurations and steps are the same as in Example 1.

[0056] Comparative Example 6 The difference between this comparative example and Example 1 is that the drawing speed of each pass in the early and late stages was adjusted to 30 m / min (including fine sizing). The measured demolding temperatures of each pass in the early stage were approximately 121°C, 125°C, 128°C, 131°C, and 134°C, all exceeding 120°C. The measured demolding temperatures of each pass in the late stage were approximately 79°C and 76°C, and the measured demolding temperature for fine sizing was approximately 68°C.

[0057] The remaining configurations and steps are the same as in Example 1.

[0058] The key parameters of each embodiment and comparative example are summarized in Table 1: Table 1 Summary of process parameters for each embodiment and comparative example

[0059] The following performance tests were performed on the steel wires obtained in Examples 1-3 and Comparative Examples 1-6: (1) Tensile strength and elongation after fracture: Tested according to GB / T 36915-2019 "General Test Methods for Steel Wire and Steel Wire Products"; (2) Number of repeated bending: The test shall be conducted in accordance with GB / T 238-2013 "Metallic Materials Wire Test Method", and the number of bending before the specimen breaks shall be recorded; (3) Number of unidirectional torsion cycles: Performed according to GB / T 239.1-2023 "Metallic Materials Wire - Part 1: Unidirectional Torsion Test Method", and record the number of torsion cycles before the specimen breaks; (4) Surface quality: Under natural light or equivalent artificial lighting, visually inspect each surface of the wire, including the flat areas, edges, and rounded transition areas, with a 10x magnifying glass if necessary. Evaluate according to the following four levels: a) Smooth and free of visible defects: All planes and edges are smooth and shiny, free of visible cracks, folds, scars, burrs, scratches, pits, rust and oxide scale, etc. b) Minor scratches: There are minor longitudinal scratches that are visible to the naked eye in the flat area. The depth of these scratches does not exceed half of the tolerance value of the characteristic dimension of the wire cross section, and the number of scratches does not exceed 3 per meter length. Slight rounding of the edges is allowed, but there are no burrs. c) Obvious scratches: There are easily visible scratches or local pitting on the flat area, the scratch depth exceeds half of the tolerance value of the cross-sectional characteristic dimension, or the number of scratches per meter length exceeds 3; or visible burrs appear on the edge. d) Rough surface: The surface is continuously pitted, rough and dull, or has defects such as rust, oxide scale, folds, and edge cracks, which have an adverse effect on the performance of the steel wire. (5) Overall Rockwell hardness: The test shall be conducted in accordance with GB / T 230.1-2018 "Metallic materials Rockwell hardness test - Part 1: Test method". The test shall be conducted in the plane area of ​​the cross-section of the steel wire and the arithmetic mean of 5 points shall be taken.

[0060] Representative test results for each embodiment and comparative example are shown in Table 2.

[0061] Table 2 Performance test results of each embodiment and comparative example

[0062] Results analysis: As can be seen from Tables 1 and 2, the cross-sectional area of ​​the billet in each embodiment and comparative example is 88.2 mm². 2 The finished product has a cross-sectional area of ​​12.4–13.0 mm². 2 The total compression rate is 85.3% to 85.9%, and the total deformation is at the same level.

[0063] The tensile strengths of Examples 1-3 were 1918 MPa, 1905 MPa, and 1911 MPa, respectively; the elongation after fracture were 4.5%, 4.4%, and 4.6%, respectively; the number of repeated bending cycles were 14, 12, and 13; and the number of unidirectional torsion cycles were 25, 23, and 24, respectively. The finished product surfaces were all smooth and free of visible defects. Examples 1 and 3 were drawn at 20 m / min. The demolding temperatures for the early passes were 102–116°C and 95–109°C, respectively; the demolding temperatures for the later passes were 63–66°C and 61–67°C, respectively; and the final sizing demolding temperature was 55°C, all below the corresponding upper limits. The above data shows that when the proportion of early passes is between 62.5% and 71.4%, the number of later passes is 2 to 3, the reduction rate in later passes is between 10% and 15%, the drawing speed is between 20 and 25 m / min, and the reduction rate in fine sizing is between 2% and 3%, both linear and step-reduction methods can achieve tensile strength of over 1870 MPa and the above-mentioned toughness indicators.

[0064] The total compression ratio of Comparative Example 1 and Example 1 was 85.3%. Example 1 involved 5 decreasing draw passes in the early stage and 2 small reduction draw passes in the later stage. Comparative Example 1 used 11 evenly distributed draw passes, with a reduction rate of 16% for each pass. The reduction rate per pass was lower than that of the early passes in Example 1, and remained at 16% until the final pass. Comparative Example 1 had 8 repeated bending cycles, 13 unidirectional torsion cycles, and an elongation after fracture of 2.9%, lower than the 14, 25, and 4.5% of Example 1, respectively. Comparative Example 4 involved 7 passes in the early stage, with a reduction rate of 22% for each pass, representing 87.5% of the total draw length. The later stage had only 1 pass with a reduction rate of 15%. It had 10 repeated bending cycles, 16 unidirectional torsion cycles, and an elongation after fracture of 3.2%, all lower than Example 1. Comparative Example 5 had the same total number of passes, stage division, cumulative equivalent strain of 1.59 at the end of the early stage, and finished product cross-sectional area of ​​13.0 mm². 2 All were identical, the only difference being that the difference in surface reduction rate between the 4th and 5th passes was 8 percentage points, exceeding the range where the difference in surface reduction rate between adjacent passes within the same stage should not exceed 3 percentage points; the finished product of Comparative Example 5 had a smooth surface, with 12 repeated bending cycles and 22 unidirectional torsion cycles, lower than the 14 and 25 cycles of Example 1, and its tensile strength was 1913 MPa, close to the 1918 MPa of Example 1. The above data indicate that the distribution of surface reduction rate at the end of the drawing process is related to the toughness index: when the surface reduction rate is maintained at a high level at the end, the toughness index decreases; when 2-3 passes are set in the later stage, the surface reduction rate does not exceed 15% and decreases step by step, the toughness index remains at the level of Examples 1-3; when the surface reduction rate changes abruptly by 8 percentage points within the same stage, the toughness index also decreases.

[0065] Comparative Example 2 used a fixed die cold drawing sizing method instead of a roller die for precision sizing. Its tensile strength was 1917 MPa, elongation after fracture was 4.4%, the number of repeated bending cycles was 13, and the number of unidirectional torsion cycles was 24, similar to Example 1. However, the finished product showed obvious scratches distributed along the drawing direction, accompanied by a decrease in straightness. Comparative Example 3 increased the surface area reduction rate of the precision sizing to 8%, with other conditions the same as Example 1. Its precision sizing exit temperature was 78°C, exceeding 60°C, while Example 1's was 55°C at a 3% surface area reduction rate. The finished product of Comparative Example 3 showed slight scratches, the number of repeated bending cycles was 12, the number of unidirectional torsion cycles was 21, and the elongation after fracture was 4.1%, all lower than Example 1. The above data indicate that the sizing method is related to the surface quality and straightness of the finished product, and the surface area reduction rate of the precision sizing is related to the exit temperature and the surface quality of the finished product.

[0066] Comparative Example 6 increased the drawing speed of each pass to 30 m / min, and the circulating water cooling conditions were the same as in Example 1, with a cooling water temperature of 25°C and a cooling water pressure of 0.4 MPa. The demolding temperatures of Comparative Example 6 in the early passes were 121–134°C, all exceeding 120°C; the demolding temperatures of the later passes were 76–79°C, all exceeding 70°C; and the demolding temperature for precision sizing was 68°C, exceeding 60°C. In Example 1, at 20 m / min, the above temperatures were 102–116°C, 63–66°C, and 55°C, respectively, all below the corresponding upper limits. The tensile strength of Comparative Example 6 was 1863 MPa, lower than the strength grade requirement of 1870 MPa, making it the only example below this requirement. Its repeated bending cycles were 10, its unidirectional torsion cycles were 20, and its elongation after fracture was 3.8%, all lower than in Example 1. Slight scratches appeared on the surface of the finished product. Under the same cooling conditions, when the drawing speed is increased from 20m / min to 30m / min, the exit temperature of each pass increases and exceeds the corresponding upper limit, and the tensile strength, toughness and surface quality decrease simultaneously.

[0067] In summary, Examples 1-3, under a total compression ratio of 85.3%-85.9%, achieved a tensile strength of 1905-1918 MPa, elongation after fracture of 4.4%-4.6%, 12-14 cycles of repeated bending, 23-25 ​​cycles of unidirectional torsion, and a smooth surface without visible defects. The data from the comparative examples show that the two-stage deformation regime, the smooth transition of the reduction rate within the same stage, the precise sizing of the roller die, the range of the reduction rate during precise sizing, and the correspondence between drawing speed and demolding temperature are all related to obtaining the aforementioned performance combination. Furthermore, the beneficial effects of this application are significant.

[0068] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for strengthening irregularly shaped steel wire by roller drawing, characterized in that, Includes the following steps: The shaped steel wire blank is drawn sequentially through at least three roller dies. The roller drawing is divided into an early stage and a late stage according to the number of passes. The surface reduction rate of each pass in the early stage is 20-30%, and the surface reduction rate of each pass in the late stage is 10-15%. After the final pass in the later stage, a roller die is used for fine sizing, and the reduction rate of the fine sizing is less than 5%.

2. The method for strengthening irregularly shaped steel wire by roller drawing according to claim 1, characterized in that, The number of passes in the early stage accounts for 60-75% of the total number of passes in the roller drawing process, and the later stage consists of 2-3 passes.

3. The method for strengthening irregularly shaped steel wire by roller drawing according to claim 1, characterized in that, The cumulative equivalent strain of the steel wire at the end of the initial stage The cumulative equivalent strain is 1.0 to 1.

8. Calculated according to formula (1) （1） in The initial cross-sectional area of ​​the billet. This refers to the cross-sectional area of ​​the steel wire at the end of the initial stage.

4. The method for strengthening irregularly shaped steel wire by roller drawing according to claim 1, characterized in that, In the aforementioned early and late stages, the reduction rate of each pass decreases sequentially along the drawing direction, and satisfies the following: The difference in area reduction rate between adjacent passes within the same phase shall not exceed 3 percentage points; The difference in surface reduction rate between the last pass of the early stage and the first pass of the later stage shall not be less than 5 percentage points.

5. The method for strengthening irregularly shaped steel wire by roller drawing according to claim 4, characterized in that, In the early and late stages, the reduction rate of each pass along the drawing direction decreases linearly or stepwise.

6. The method for strengthening irregularly shaped steel wire by roller drawing according to claim 1, characterized in that, The expulsion temperature of each drawing pass in the early stage is controlled below 120℃, and the expulsion temperature of each drawing pass in the later stage is controlled below 70℃.

7. The method for strengthening irregularly shaped steel wire by roller drawing according to claim 6, characterized in that, The pulling speed for each pass in the early and late stages is 15–25 m / min.

8. The method for strengthening irregularly shaped steel wire by roller drawing according to claim 7, characterized in that, During the drawing process, the steel wire is cooled by circulating water in each pass. The cooling water temperature is 20-30℃ and the cooling water pressure is 0.3-0.5MPa.

9. The method for strengthening irregularly shaped steel wire by roller drawing according to claim 1, characterized in that, The reduction rate of the fine sizing is 2-5%, and the exit temperature of the steel wire after fine sizing is not higher than 60°C.

10. The method for strengthening irregularly shaped steel wire by roller drawing according to claim 1, characterized in that, Before drawing the shaped steel wire blank, a blank preparation step is also included: After the wire rod undergoes pickling and phosphating surface pretreatment, it is rough drawn in a preset number of passes using a circular die, then heat-treated and reheated, and finally pickled, phosphating, and saponified to become the shaped steel wire blank. Among them, the phosphating process forms a layer on the surface of the wire rod with a mass of 3-8 g / m² per unit area. 2 Phosphating layer.

Images