Spheroidizing-annealing-free SWRCH35K cold heading steel wire rod based on heat engine rolling and production method thereof

Abstract

The invention discloses a spheroidizing-annealing-free SWRCH35K cold heading steel wire rod based on hot machine rolling and a production method of the spheroidizing-annealing-free SWRCH35K cold heading steel wire rod. The cold heading steel wire rod comprises the chemical components of C, Si, Mn, P, S, Als, Cr, Ni, Cu, Mo, V and the balance Fe and inevitable impurities. The production method comprises the steps of 130-ton combined blown converter smelting, LF furnace refining, continuous casting, casting blank heating, heat engine rolling, reducing first and second unit rolling, spinning, air cooling line rolling, finishing and packaging and warehousing. The plastic extension strength Rp0.2 of the produced cold heading steel wire rod is 356-408 MPa, the tensile strength is 546-583 MPa, the percentage elongation after fracture is 26-31%, the percentage reduction of area is 62-73%, no complete decarburization layer exists, the total decarburization layer depth is 0.02-0.04 mm, the cold heading steel wire rod has good drawing machining performance and good surface quality, the obtained wire rod structure is spheroidized ferrite and pearlite structures, and the cold heading steel wire rod is suitable for being used as a cold heading steel wire rod. And the heat treatment procedure of subsequent spheroidizing annealing of a traditional cold heading steel wire rod is omitted, the production cost of subsequent machining is greatly saved, and the market competitiveness of products is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of ferrous metal smelting and rolling, and particularly relates to a spheroidizing-free annealing SWRCH35K cold heading steel wire rod based on thermomechanical rolling and a production method thereof. Background Art

[0002] SWRCH35K cold heading steel wire rod is mainly used to produce 8.8 to 10.9 grade high strength fasteners. SWRCH35K belongs to the carbon steel for cold heading in the JISG3507 standard, which is equivalent to the ML35Mn material in the national standard GB / T 6478. It is a typical medium carbon cold heading steel. As a medium carbon cold heading steel, SWRCH35K is widely used in the production of 8.8 grade high strength standard parts in the fields of automobiles, machinery, home appliances, etc., such as bolts, nuts, screws and other fasteners. The cold heading steel wire rod diameter is required to be Φ5.5 to 16 mm, and the plastic elongation strength R p0.2 With tensile strength above 315MPa, tensile strength above 530MPa, elongation after fracture greater than 20%, reduction of area greater than 60%, and a complete decarburization depth less than 0.02mm, SWRCH35K cold heading steel has excellent drawing performance and good surface quality. As industrial development continues to increase the performance requirements of fasteners, the production process and technology of SWRCH35K cold heading steel are also facing new challenges.

[0003] The common process for processing cold-headed steel wire rod into fasteners such as bolts, nuts, and screws is as follows: raw material (wire rod) → pickling / phosphating → pretreatment (spheroidizing annealing) → cold heading → threading → heat treatment → surface treatment → testing → packaging. Due to the need for cold heading and surface treatment, the raw wire rod must possess good cold heading properties and surface quality.

[0004] Medium-carbon cold-heading steel wire rods, such as SWRCH35K, typically require a spheroidizing annealing pretreatment before cold heading to improve cold heading performance, spheroidize cementite, reduce hardness, and improve plasticity. The dependency on spheroidizing annealing is a major bottleneck in the application of SWRCH35K. Traditional hot-rolled SWRCH35K has a high hardness (typically a surface hardness ≥82 HRB), lamellar pearlite, and insufficient cold heading performance. Users must perform spheroidizing annealing before it can be used in the production of 8.8-grade fasteners. The spheroidizing annealing process has a long cycle (typically over 20 hours) and high energy consumption, which not only increases production costs (200 to 300 yuan / ton) but also causes decarburization on the wire rod surface (the decarburization layer can reach 0.2 to 0.5%d, where d is the wire diameter), affecting the performance of the final product. Furthermore, the existing spheroidizing annealing process itself is inefficient.

[0005] Conventional spheroidizing annealing uses a cyclic annealing furnace, which needs to be heated to above AC1 (730-740°C) with the furnace, kept warm for more than 8 hours, and then slowly cooled (cooling rate 10-12°C / h). The total processing time exceeds 20 hours. In addition, it is difficult to completely avoid decarburization with the existing annealing process. Even if a protective atmosphere is used, the decarburization layer may still reach more than 12μm, affecting the fatigue performance of high-end fasteners. In order to solve the problem of spheroidizing annealing of cold heading steel during use and reduce user costs, it is necessary to optimize the production process of cold heading steel wire rod to obtain a wire rod with good cold heading forming performance and eliminating the annealing process before forming.

[0006] SWRCH35K is a carbon steel for cold heading, as specified in the JIS G3507 standard. Its typical chemical composition range is: C: 0.32-0.38%, Si: 0.10-0.35%, Mn: 0.60-0.90%, P ≤ 0.030%, S ≤ 0.035%. Carbon content determines the steel's strength and hardness, but excessive levels can reduce cold heading performance. Silicon content affects the steel's deoxidation and strength, but increases its tendency to work hardening. Manganese improves hardenability, but excessive levels promote bainite formation, hindering cold heading.

[0007] In addition, the traditional high-speed wire rolling process adopts high-temperature rolling (heating temperature 1030~1100℃), finishing rolling temperature 850~880℃, spinning temperature 800~850℃, and then controlled cooling through the Stelmor line.

[0008] The structure obtained by this process is usually ferrite + pearlite, with ferrite in blocky form, accounting for 30-50%, and a grain size of 9-10. Although a higher grain size improves strength, it also deteriorates cold heading performance.

[0009] Therefore, how to ensure that the cold heading steel wire rod has appropriate strength while meeting the cold heading performance and eliminating the spheroidizing annealing process in the subsequent processing process requires the optimization of the rolling process and chemical composition. The purpose of the present invention is to provide a spheroidizing annealing-free SWRCH35K cold heading steel wire rod based on thermal mechanical rolling and a production method thereof. Summary of the Invention

[0010] The purpose of the present invention is to provide a spheroidizing annealing-free SWRCH35K cold heading steel wire rod based on hot mechanical rolling and a production method thereof, in order to improve the cold heading processing performance, spheroidize the cementite, reduce the hardness and improve the plasticity of the existing SWRCH35K medium carbon cold heading steel wire rod before cold heading forming, which usually requires spheroidizing annealing pretreatment, resulting in high processing costs and decarburization of the wire rod surface, affecting the performance of the final product.

[0011] The present invention discloses a spheroidizing-free annealing SWRCH35K cold heading steel wire rod based on hot mechanical rolling. The cold heading steel wire rod comprises the following components in weight percentage: C: 0.33-0.37%; Si: 0.17-0.26%; Mn: 0.65-0.80%; P≤0.025%; S≤0.015%; Als: 0.015-0.035%; Cr≤0.08%; Ni≤0.05%; Cu≤0.10%; Mo≤0.010%; V≤0.010%; the balance being Fe and unavoidable impurities.

[0012] The cold heading steel wire rod produced by the method of the present invention has a diameter of Φ5.5-16 mm.

[0013] The plastic elongation strength R of the cold heading steel wire rod produced by the method of the present invention is p0.2 The tensile strength is 356-408MPa, the tensile strength is 546-583MPa, the elongation after fracture is 26-31%, the cross-sectional shrinkage is 62-73%, there is no complete decarburization layer, the total decarburization layer depth is 0.02-0.04mm, and it has good drawing processing performance and good surface quality.

[0014] The metallographic structure of the cold heading steel wire rod produced by the method of the present invention is mainly ferrite and pearlite, without abnormal structure, the grain size reaches 9.0 to 10, the non-metallic inclusions are 0 to 0.5 for category A, 0 to 0.5 for category B, 0 for category C, 0 for category D, and 0 for category DS. Other indicators meet the requirements of national standards and user technical agreements.

[0015] The present invention provides a method for producing a spheroidizing-free annealing SWRCH35K cold heading steel wire rod based on hot mechanical rolling, comprising the following steps: (1) Incoming molten iron: S content ≤ 0.035%, temperature ≥ 1300℃, slag layer thickness ≤ 50mm; (2) Converter smelting: Molten iron is smelted in a 130-ton converter using the double slag method. 4-5 kg / t of active lime is placed at the bottom of the molten steel tank. The endpoint temperature range is 1590-1630°C. The endpoint C is controlled to be 0.06-0.20%, and P ≤ 0.020%. Silicon-manganese alloy or metallic manganese and ferrosilicon alloy are added for alloying. At the same time, aluminum ingots or Taiwan aluminum are added for deoxidation. The alloy and deoxidation materials are added when 1 / 3 of the steel is tapped and are completed before 4 / 5 of the steel is tapped. (3) Argon station treatment: After the molten steel arrives at the argon station, the total treatment time of the argon station is 2 to 6 minutes; (4) LF furnace refining: The temperature of the molten steel entering the refining station is measured, and the inlet temperature is ≥1530℃. Active lime and fluorite balls are added to make slag, and calcium carbide is added to deoxidize the slag surface. Ensure that the white slag is maintained for ≥15min during the refining period; after the slag surface is deoxidized, soft argon is blown for ≥15min. The argon blowing intensity requires that the slag surface has obvious fluctuations but the steel liquid surface is not exposed; the ladle temperature is 1555~1565℃; the first furnace is controlled at 1575~1585℃, and the refining cycle is ≥45min; (5) Continuous casting: Use a stopper rod tundish, the tundish baking time is 3 to 4 hours, the tundish wall temperature after baking is ≥1000℃, the water nozzle and the tundish are baked synchronously, the immersed nozzle is baked for 1.0 to 1.5 hours, and the tundish is purged with argon before pouring. Calcium iron wire must not be added to the tundish. Wollastonite + alkaline covering agent is added to prevent carbon rise; pouring begins after the weight of the tundish is ≥20t, medium carbon steel protective slag is used, electromagnetic stirring is used, the superheat target of the molten steel in the tundish of the continuous casting furnace is 15 to 35℃, the typical casting speed is controlled at 2.3±0.1m / min, and the billet is stacked and slowly cooled for ≥24 hours after it comes off the line before being sent down; (6) Billet heating: The billets that have passed the acceptance test are heated in a walking beam heating furnace with the soaking section temperature at 1110-1160°C and the heating time ≥60 min; (7) Rolling: starting rolling temperature 950-1050℃, finishing rolling temperature 830-870℃, reducing mill temperature 1 and 2 730-770℃, spinning temperature 760-800℃; (8) Controlled cooling: All fans of the Stelmor air cooling line are turned off, the 1# insulation cover is turned on, and the other insulation covers are all closed; the speed of the first section of the air cooling roller is 0.30m / s, and the speed of each subsequent section increases by 0.01m / s to ensure that the cooling rate is less than 1℃ / s.

[0016] In the above step (5), the quality of the copper tube should be carefully checked before the immersion nozzle is put into operation. Scratches, deformation and coating shedding are not allowed.

[0017] The method of the present invention is developed based on the process characteristics of the thermo-mechanical rolling technology. Based on the characteristics of the thermo-mechanical rolling process, the opening of each section of the water tank is key to the control of the finishing temperature and the spinning temperature, otherwise abnormal structures are likely to be generated. The present invention combines the thermo-mechanical rolling process, appropriately optimizes the mass fraction of Mn and Si to reduce the strength, and optimizes the heating temperature, spinning temperature, air cooling process and other process parameters to improve the internal structure of the wire rod and obtain a spheroidized pearlite structure, thereby eliminating the need for the traditional cold heading steel wire rod to undergo a spheroidizing annealing heat treatment process during subsequent processing, greatly saving the production cost of subsequent processing and improving the market competitiveness of the product.

[0018] The reasons for limiting the amounts of the main chemical components in the present invention are described in detail below: 1. Reasons for limiting the amount of chemical components (C, Si, Mn, P, S, Als, etc.) Considering that the steel of the present invention is a medium-carbon steel, its performance mainly depends on ensuring tensile strength, elongation after fracture, and cross-sectional reduction rate. Therefore, the purity of the molten steel must be strictly controlled during steelmaking. The C content determines the strength and hardness of the steel, but too high a content will lead to a decrease in cold heading performance. Therefore, the C content is controlled to 0.33-0.37% in the present invention. The Si content affects the degree of deoxidation and strength of the steel, but increases the tendency to work hardening. In the present invention, the Si content is optimized to 0.17-0.26%. The Mn element can improve hardenability, but too high a content will promote bainite formation, which is not conducive to cold heading. In the present invention, the Mn content is optimized to 0.65-0.80%. In this way, the C, Si, and Mn contents of the present invention are designed to ensure the strength and toughness of the steel. P and S, as harmful elements, have an adverse effect on the toughness of the steel and need to be reduced as much as possible. An appropriate amount of Als can refine grains and improve the strength and toughness of steel, but too high a content may lead to excessive aggregation of precipitated phases, which in turn reduces toughness and plasticity and may cause brittleness. Therefore, the present invention controls Als to 0.015-0.035%. Considering that the elements Cr, Ni, Cu, Mo, and V have a significant impact on the brittleness of steel, the present invention strictly limits Cr to ≤ 0.08%; Ni to ≤ 0.05%; Cu to ≤ 0.10%; Mo to ≤ 0.010%; and V to ≤ 0.010% to reduce the tendency of steel structure segregation.

[0019] 2. Reasons for setting the production process (1) Steelmaking process By controlling the sulfur content of incoming molten iron, the company achieves a low sulfur content, reducing slag removal steps, lowering costs, and accelerating production. The carbon content of the tapped steel is controlled in a 130t top-and-bottom combined-blowing converter. Alloying is added when the tapping volume reaches 1 / 3 to ensure effective dissolution of the alloy. Silicon, aluminum, and barium are also added for deoxidation. Slag baffles are used to prevent excessive slag buildup, and spot blowing is strictly prohibited to prevent nitrogen and oxygen addition. The refining time outside the furnace is controlled at ≥30 minutes to maximize desulfurization and deoxidation, preventing the deterioration of impact toughness due to high sulfur and oxygen contents. Argon blowing is used to ensure uniform composition and temperature of the molten steel. Superheat is controlled between 6 and 15°C, casting speed is maintained between 2.30 and 2.50 m / min, and the ingot is slowly cooled to reduce center porosity and segregation, thereby improving internal quality.

[0020] (2) Steel rolling process The present invention controls the ingot's furnace temperature within a certain range to ensure sufficient dissolution of the ingot's microalloys, while also ensuring a relatively long heating time for full austenitization and homogenization, mitigating internal defects such as center segregation, and controlling the austenite grain size within an appropriate range. After exiting the furnace, high-pressure water descaling is used to effectively remove surface oxide scale from the ingot, preventing it from being pressed into the steel during subsequent rolling. The finishing rolling temperature, as well as the temperatures of the first and second reducing mills, are controlled to ensure that the finishing stage is rolled in the two-phase region, implementing a thermomechanical rolling process. This results in a finer and more uniform grain size and a spheroidizing transformation of the resulting pearlite structure.

[0021] Controlling the spinning temperature means controlling the cooling temperature, controlling the roller speed of the air cooling line and the opening of the insulation cover and fan, that is, controlling the cooling rate, so as to obtain uniform ferrite and pearlite structure, without producing other abnormal structures, so as to obtain better cold heading performance.

[0022] The method of the present invention is based on the wire rod production process flow of smelting in a 130-ton combined-blowing converter → refining in an LF furnace → continuous casting in a 7-mill 7-strand billet caster → heating in a walking beam heating furnace → rolling in a roughing and intermediate rolling mill → rolling in a pre-finishing rolling mill → rolling in a finishing rolling mill → rolling in the first and second diameter reducing mills → laying out → air cooling line → finishing → packaging and warehousing. The rolling process is a thermomechanical rolling process, and the method is used to produce cold heading steel SWRCH35K wire rod, achieving the following effects: (1) When producing SWRCH35K, the converter adopts low iron consumption mode, strengthens the end carbon retention control measures to prevent overoxidation of molten steel, controls the refining deoxidation and slag making processes, and uses ferrosilicon powder for diffusion deoxidation to ensure that the slag basicity is reduced and Als burnout is prevented, ensuring that the Als of the finished product is controlled within the range of 0.015-0.035; optimizes the water distribution in continuous casting to ensure the accuracy of each strand casting machine and ensure the low-multiple quality of the ingot. Reduce oxide inclusions and cracks in the steel.

[0023] (2) Ensure that 100% of the steel is poured out under the condition of low carbon at the end, reduce the erosion of low carbon steel on the furnace lining, and the Mn and Si of the finished product are controlled at the lower and middle limits; stably control the carbon at the end, appropriately increase the amount of metallic manganese, and ensure that the C finished product composition is controlled at C: 0.33~0.37%, Si: 0.10~0.25%, Mn: 0.70~0.90%. Through precise composition control, the problem of high strength caused by composition fluctuations is solved.

[0024] (3) Taking advantage of the high-speed wire hot-rolling process, the rolling temperature of finishing rolling and reducing group 1 and reducing group 2 was adjusted to 750±20℃, and the spinning temperature was adjusted to 780±20℃. The pearlite structure was spheroidized by low-temperature controlled rolling in the two-phase zone, so that the subsequent processing could be free of spheroidizing annealing.

[0025] (4) Adjust the roller speed of the air cooling line to reduce the cooling rate by less than 1°C, improve the plasticity of the finished wire rod, and increase the cross-sectional shrinkage rate to more than 60%.

[0026] Compared with the prior art, the technical solution provided by the present invention has the following advantages: (1) Plastic elongation strength R of SWRCH35K cold heading steel wire rod with a diameter of 5.5-16 mm produced by the method of the present invention p0.2 The steel has a tensile strength of 356-408 MPa, a tensile strength of 546-583 MPa, a cross-sectional shrinkage of 62-73%, an elongation of 26-31%, no complete decarburization layer, a total decarburization layer depth of 0.02-0.04 mm, and non-metallic inclusions of type A are 0-0.5, type B are 0-0.5, type C is 0, type D is 0, and type DS is 0; the metallographic structure is mainly ferrite and pearlite, with no abnormal structure, the grain size reaches 9.0-10, and other relevant indicators meet the requirements of national standards and user technical agreements.

[0027] (2) The present invention does not add pig iron to the converter, ensuring that 100% of the steel is poured out under the final low-carbon condition, reducing the erosion of the furnace lining by the low-carbon steel, and the Mn and Si contents of the finished product are controlled at the lower limit, and the C content is controlled in the range of 0.07-0.09%. From the aspect of composition, the strength of the wire rod is reduced and the plasticity is improved.

[0028] (3) The present invention adopts a hot rolling process in terms of rolling technology, and controls the finishing rolling temperature, so that the finishing rolling and the first and second diameter reducing units are rolled in the two-phase region to obtain a more uniform and refined grain structure, while achieving pearlite spheroidization, improving the cold heading performance of the wire rod, and allowing users to avoid the spheroidizing annealing process before forming.

[0029] (4) The present invention adopts a delayed cooling process in terms of cooling process. By controlling the spinning temperature at 760-800°C, the 1# insulation cover is turned on to ensure that the temperature entering the insulation cover, i.e., the cooling start temperature, is about 800°C. The speed of the air-cooling roller is adjusted, the speed of the first section is set to 0.30m / s, and the speed of each subsequent section is increased by 0.01m / s. The 2# and subsequent insulation covers are all closed to ensure that the cooling rate on the Stelmore air-cooling line is less than 1°C / s. When producing SWRCH35K cold heading steel wire rod, all doors and windows in the coiling area, PF transport line area, and the area to the baling machine are closed, and the fan is not allowed to blow towards the steel coil to avoid accelerated cooling. Through the above cooling process, the plasticity of the wire rod is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a metallographic structure diagram of the cold heading steel wire rod prepared in Example 4 of the present invention (magnified 50 times); Figure 2 1 is a metallographic structure diagram of the cold heading steel wire rod prepared in Example 4 of the present invention (magnified 100 times). DETAILED DESCRIPTION

[0031] In order to better explain the technical solution of the present invention, the technical solution of the present invention is further described below in conjunction with specific embodiments. The following embodiments are merely illustrative of the technical solution of the present invention and do not limit the present invention in any form.

[0032] Table 1 below is a list of chemical composition values ​​(wt%) of cold heading steel wire rods according to various embodiments of the present invention; Table 2 below is a list of the main process parameter values ​​for cold heading steel wire rods according to various embodiments of the present invention; Table 3 below lists the metallographic examination and main mechanical property test results of the cold heading steel wire rods according to various embodiments of the present invention.

[0033] A method for producing a spheroidizing-free annealing SWRCH35K cold heading steel wire rod based on thermomechanical rolling according to various embodiments of the present invention comprises the following steps: (1) Incoming molten iron: S content ≤ 0.035%, temperature ≥ 1300℃, slag layer thickness ≤ 50mm; (2) Converter smelting: molten iron is smelted in a 130-ton converter using the double slag method. 4-5 kg / t of active lime is placed at the bottom of the molten steel tank. The endpoint temperature range is 1600-1640°C. The endpoint C is controlled at 0.06-0.20%, and P ≤ 0.020%. When the tapping volume reaches 1 / 3, silicon-manganese alloy or metallic manganese and ferrosilicon alloy are added for alloying. At the same time, aluminum ingots or Taiwan aluminum are added for deoxidation. The alloy and deoxidation materials are added when the tapping volume reaches 1 / 3 and are completed before the tapping volume reaches 4 / 5. (3) Argon station treatment: After the molten steel arrives at the argon station, the total treatment time of the argon station is 2 to 6 minutes; (4) LF furnace refining: The temperature of the molten steel entering the refining station is measured, and the inlet temperature is ≥1530℃. Active lime and fluorite balls are added to make slag, and calcium carbide is added to deoxidize the slag surface. Ensure that the white slag is maintained for ≥15min during the refining period; after the slag surface is deoxidized, soft argon is blown for ≥15min. The argon blowing intensity requires that the slag surface has obvious fluctuations but the molten steel surface is not exposed; the ladle temperature: 1575~1585℃ for the first furnace and 1555~1565℃ for the continuous furnace; the refining cycle is ≥45min; (5) Continuous casting: Use a stopper rod tundish, the tundish baking time is 2.5 to 4 hours, the tundish wall temperature after baking is ≥1000℃, the water nozzle and the tundish are baked synchronously, the immersed nozzle is baked for 1.0 to 1.5 hours, and the tundish is purged with argon before pouring. Calcium iron wire shall not be added to the tundish. Wollastonite + environmentally friendly covering agent shall be added to prevent carbon rise; pouring shall be started after the weight of the tundish is ≥20t, low carbon steel protective slag shall be used, electromagnetic stirring shall be used, the superheat target of the molten steel in the tundish of the continuous casting furnace is 15 to 35℃, the typical casting speed shall be controlled at 2.3±0.1m / min, and the billet shall be stacked and slowly cooled for ≥24 hours after it comes off the line before being sent down; (6) Billet heating: The billets that have passed the acceptance test are heated in a walking beam heating furnace with the soaking section temperature at 1110-1160°C and the heating time ≥60 min; (7) Rolling: starting rolling temperature 950-1050℃, finishing rolling temperature 830-870℃, reducing mill temperature 1 and 2 730-770℃, spinning temperature 760-800℃; (8) Controlled cooling: All fans of the Stelmor air cooling line are turned off, the 1# insulation cover is turned on, and the other insulation covers are all closed; the speed of the first section of the air cooling roller is 0.30m / s, and the speed of each subsequent section increases by 0.01m / s to ensure that the cooling rate is less than 1℃ / s.

[0034] Table 1 Chemical composition values ​​of cold heading steel wire rods according to various embodiments of the present invention (wt%)

[0035] Table 2 List of main process parameter values ​​for cold heading steel wire rod in various embodiments of the present invention Table 3 Metallographic examination and main mechanical properties test results of cold heading steel wire rods according to various embodiments of the present invention

[0036] As can be seen from Table 3 above, the non-metallic inclusions of the Φ5.5-16mm SWRCH35K cold heading steel wire rod produced by the present invention are 0-0.5 for Class A, 0-0.5 for Class B, 0 for Class C, 0 for Class D, and 0 for Class DS, and the interior is relatively pure; the metallographic structure is mainly ferrite and pearlite, without abnormal structure, and the spheroidizing annealing process can be avoided; the grain size reaches 9.0-10, and the structure is stable and uniform; the plastic elongation strength R p0.2 The steel has a hardness of 356-408 MPa, a tensile strength of 546-583 MPa, a cross-sectional shrinkage of 62-73%, an elongation of 26-31%, and good plasticity index, which can meet the requirements of cold heading. There is basically no complete decarburization layer on the surface, and the total decarburization layer depth is 0.02-0.04 mm. The surface iron oxide scale is mainly in block or flake form and is easy to remove. The relevant indicators meet and exceed the requirements of national standards and user technical agreements. Figure 1 and Figure 2 This is a metallographic structure diagram of the cold heading steel wire rod produced in Example 4 of the present invention. As can be seen from the figure, the metallographic structure is mainly ferrite and pearlite, and no abnormal structure is found.

[0037] The above embodiments are merely specific examples given by the present invention to explain the present invention and do not limit the present invention in any form. Any non-substantial changes made by anyone based on the above content and form that do not deviate from the scope of protection of the claims of the present invention should be deemed to fall within the scope of protection of the claims of the present invention.

Claims

1. A spheroidizing-free annealing SWRCH35K cold heading steel wire rod based on thermomechanical rolling, characterized in that The cold heading steel wire rod comprises the following components in weight percentage: C: 0.33-0.37%; Si: 0.17-0.26%; Mn: 0.65-0.80%; P≤0.025%; S≤0.015%; Als: 0.015~0.035%; Cr≤0.08%; Ni≤0.05%; Cu≤0.10%; Mo≤0.010%; V≤0.010%; the balance is Fe and unavoidable impurities.

2. The spheroidizing-free annealing SWRCH35K cold heading steel wire rod based on thermomechanical rolling according to claim 1, characterized in that: The diameter of the cold heading steel wire rod is Φ5.5-16 mm.

3. The spheroidizing-free annealing cold heading steel wire rod based on thermomechanical rolling according to claim 1 or 2, characterized in that: The plastic extension strength R of the cold heading steel wire rod p0.2 The tensile strength is 356-408MPa, the tensile strength is 546-583MPa, the elongation after fracture is 26-31%, the cross-sectional shrinkage is 62-73%, there is no complete decarburization layer, the total decarburization layer depth is 0.02-0.04mm, and it has good drawing processing performance and good surface quality.

4. The spheroidizing-free annealing cold heading steel wire rod based on thermomechanical rolling according to claim 1 or 2, characterized in that: The metallographic structure of the cold heading steel wire rod is mainly ferrite and pearlite, without abnormal structure, the grain size reaches 9.0 to 10 levels, the non-metallic inclusions of type A are 0 to 0.5 levels, type B are 0 to 0.5 levels, type C is 0, type D is 0, and type DS is 0. Other indicators meet the requirements of national standards and user technical agreements.

5. A method for producing spheroidizing-free annealing SWRCH35K cold heading steel wire rod based on thermomechanical rolling according to any one of claims 1 to 4, characterized in that The steps include: (1) Incoming molten iron: S content ≤ 0.035%, temperature ≥ 1300℃, slag layer thickness ≤ 50mm; (2) Converter smelting: Molten iron is smelted in a 130-ton converter using the double slag method. 4-5 kg / t of active lime is placed at the bottom of the molten steel tank. The endpoint temperature range is 1590-1630°C. The endpoint C is controlled to be 0.06-0.20%, and P ≤ 0.020%. Silicon-manganese alloy or metallic manganese and ferrosilicon alloy are added for alloying. At the same time, aluminum ingots or Taiwan aluminum are added for deoxidation. The alloy and deoxidation materials are added when 1 / 3 of the steel is tapped and are completed before 4 / 5 of the steel is tapped. (3) Argon station treatment: After the molten steel arrives at the argon station, the total treatment time of the argon station is 2 to 6 minutes; (4) LF furnace refining: The temperature of the molten steel entering the refining station is measured, and the inlet temperature is ≥1530℃. Active lime and fluorite balls are added to make slag, and calcium carbide is added to deoxidize the slag surface. Ensure that the white slag is maintained for ≥15min during the refining period; after the slag surface is deoxidized, soft argon is blown for ≥15min. The argon blowing intensity requires that the slag surface has obvious fluctuations but the steel liquid surface is not exposed; the ladle temperature is 1555~1565℃; the first furnace is controlled at 1575~1585℃, and the refining cycle is ≥45min; (5) Continuous casting: Use a stopper rod tundish, the tundish baking time is 3 to 4 hours, the tundish wall temperature after baking is ≥1000℃, the water nozzle and the tundish are baked synchronously, the immersed nozzle is baked for 1.0 to 1.5 hours, and the tundish is purged with argon before pouring. Calcium iron wire must not be added to the tundish. Wollastonite + alkaline covering agent is added to prevent carbon rise; pouring begins after the weight of the tundish is ≥20t, medium carbon steel protective slag is used, electromagnetic stirring is used, the superheat target of the molten steel in the tundish of the continuous casting furnace is 15 to 35℃, the typical casting speed is controlled at 2.3±0.1m / min, and the billet is stacked and slowly cooled for ≥24 hours after it comes off the line before being sent down; (6) Billet heating: The billets that have passed the acceptance test are heated in a walking beam heating furnace with the soaking section temperature at 1110-1160°C and the heating time ≥60 min; (7) Rolling: starting rolling temperature 950-1050℃, finishing rolling temperature 830-870℃, reducing mill temperature 1 and 2 730-770℃, spinning temperature 760-800℃; (8) Controlled cooling: All fans of the Stelmor air cooling line are turned off, the 1# insulation cover is turned on, and the other insulation covers are all closed; the speed of the first section of the air cooling roller is 0.30m / s, and the speed of each subsequent section increases by 0.01m / s to ensure that the cooling rate is less than 1℃ / s.

6. The method for producing spheroidizing-free annealing SWRCH35K cold heading steel wire rod based on thermomechanical rolling according to claim 4, characterized in that: Carefully check the quality of the copper tube before the immersion nozzle is put into production. Scratches, deformation and coating shedding are not allowed.

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