Non-quenched steel wire rod, its production method and use

Abstract

This invention belongs to the field of iron and steel metallurgical technology, specifically relating to a non-quenched and tempered steel wire rod, its production method, and its application. The production method includes the following steps: a large continuously cast billet undergoes initial rolling to obtain a small billet, which is then used to prepare a non-quenched and tempered steel wire rod; the initial rolling includes heating and rolling. The non-quenched and tempered steel wire rod provided by this invention has a grain size ≥10, no complete decarburization, and a total decarburization depth within 0.05mm; dimensional tolerance is -0.15mm to 0.15mm; yield strength is above 520MPa, tensile strength is 800MPa to 950MPa, elongation after fracture is above 17%, and reduction of area is above 50%.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically relating to a non-quenched and tempered steel wire rod, its production method, and its application. Background Technology

[0002] Non-quenched and tempered steel refers to medium carbon steel in which elements with strong carbide-forming properties, such as V, Nb, and Ti, are added. During controlled cooling after hot rolling, these elements precipitate as carbides / nitrides in the ferrite and pearlite, providing strengthening and achieving the same level of strength as tempered medium carbon steel. This eliminates the need for tempering and simplifies the process. Non-quenched and tempered steel not only saves energy and significantly shortens the production cycle but also avoids deformation and cracking caused by quenching, effectively improving product quality and reducing manufacturing costs. Therefore, non-quenched and tempered steel is widely used as bar stock in manufacturing industries such as automobiles.

[0003] However, the lack of strength and toughness matching, poor cold working performance, and high composition sensitivity of non-quenched and tempered steel limits its application range as wire rod. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a non-quenched and tempered steel wire rod, its production method, and its application, thereby resolving at least one aspect of the aforementioned technical issues.

[0005] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for producing non-quenched and tempered steel wire rod, comprising the following steps: The large continuously cast billet is subjected to initial rolling to obtain a small billet, which is then used to prepare non-quenched and tempered steel wire rod. The initial rolling process includes heating and rolling; During the heating process, the preheating temperature is controlled at 690℃~710℃; the first heating temperature is controlled at 950℃~1050℃; the second heating temperature is controlled at 1180℃~1230℃; the soaking temperature is controlled at 1190℃~1220℃; and the total heating time is 420min~450min. During the rolling process, the initial rolling temperature is 1180℃~1210℃, the final rolling temperature is 1000℃~1080℃, and the sawing temperature is controlled to be no less than 550℃.

[0006] In some possible implementations, the preparation of the continuously cast large billet includes the following steps: The molten steel is continuously cast to obtain a large square billet, which is then cooled for more than 24 hours.

[0007] In some possible implementations, the preparation of the continuously cast large billet includes the following steps: Molten iron is smelted in a converter, refined by LF and VD to obtain molten steel; The molten steel is continuously cast to obtain the continuously cast large square billet.

[0008] In some possible implementations, during the converter smelting process, 1.25 kg / t to 1.43 kg / t of synthetic slag is added for slag formation, and the tapping temperature is ≥1580℃; slag-blocking tapping is adopted.

[0009] In some possible implementations, the synthetic slag is MJ-55 produced by Henan Rongjin High Temperature Materials Co., Ltd.

[0010] In some possible implementations, during the converter smelting, the P content of the tapped steel is less than 0.009% and the S content is less than 0.015%.

[0011] In some possible implementations, during the converter smelting process, at least one of aluminum blocks, silicon-manganese alloy, medium-carbon ferrochrome, and vanadium-nitrogen alloy is added.

[0012] In some possible implementations, during the LF refining process, the refining time is more than 40 minutes, the white slag retention time is more than 30 minutes, the total slag amount is controlled at 10 kg / t to 12 kg / t, nitrogen is added to the nitrogen-feeding alloy wire after the molten steel temperature reaches 1590℃ to 1600℃, the composition is slightly adjusted according to the target composition of the non-quenched and tempered steel wire rod, and the basicity is controlled at 4.0 to 5.0.

[0013] In some possible implementations, the VD refining process involves a refining time of at least 30 minutes and a vacuum holding time of at least 15 minutes. During the vacuum treatment, nitrogen is circulated, and after the vacuum is broken, the soft argon blowing time is controlled to be 20-30 minutes. In this case, since a certain amount of nitrogen will be removed during the vacuum treatment, using circulating nitrogen to increase nitrogen content during the vacuum treatment can ensure the relative stability of the nitrogen content in the steel. Controlling the soft argon blowing time after the vacuum is broken allows inclusions sufficient time to float and be removed, improving the cleanliness of the molten steel.

[0014] In some possible implementations, during continuous casting, the casting speed is below 0.70 m / min, preferably 0.65 m / min to 0.70 m / min; the superheat is below 20°C, preferably 12°C to 18°C; the secondary cooling in continuous casting uses a specific water volume of 0.33 L / kg to 0.37 L / kg; the liquid level in the crystallizer and the stroke of the stopper rod are controlled stably during the casting process, with liquid level fluctuations controlled within ±5 mm. It should be noted that operations and related material quantities not mentioned in continuous casting are conventional in the art and are not particularly limited in this invention; however, as examples, in some examples, the straightening machine uses a light reduction technique to reduce center segregation and center porosity of the billet; the electromagnetic stirring parameters in the crystallizer are 250 A and 2.5 Hz to promote inclusion flotation and increase the equiaxed crystals in the large square billet; the electromagnetic stirring parameters at the end of solidification are 250 A and 8.0 Hz.

[0015] In some possible implementations, the stack cooling time is 24h to 30h.

[0016] In some possible implementations, the cross-sectional dimensions of the continuously cast large billet are (345mm~355mm) × (425mm~435mm).

[0017] In some possible implementations, the initial rolling process specifically includes the following steps: After descaling, heating, rolling and heat preservation of the large billet, a small billet is obtained.

[0018] The descaling and heat preservation mentioned herein are conventional techniques and conditions in the field and are not specifically limited in this invention.

[0019] In some possible implementations, the step of preparing non-quenched and tempered steel wire rod from the small billet includes: After the small square billet is ground, it undergoes heat treatment, descaling, alternating horizontal and vertical rolling, sizing, wire cutting, cooling, coiling, and pickling to obtain the non-quenched and tempered steel wire rod.

[0020] In some possible implementations, the small blank is a cube with a side length of 150mm ± 0.5mm and a corner radius of less than 25mm.

[0021] In some possible implementations, the grinding process involves using a grinding wheel-type peeling machine to grind the steel billet (i.e., small square billet), wherein the grinding depth of the steel billet face is 1.0mm ± 0.2mm, and the grinding width of the steel billet corners is 10.0mm ± 0.2mm; after the steel billet is ground, it is subjected to flaw detection, and a magnetic particle flaw detector is used to check the surface quality of the ground steel billet to ensure that the surface quality of the steel billet is normal.

[0022] In some possible implementations, the preheating zone temperature is below 850°C, the homogenization zone temperature is 1180°C to 1220°C, and the total heating time is 140 min to 160 min.

[0023] In some possible implementations, the finishing temperature in the alternating flat and vertical rolling process is below 960°C, preferably 950°C to 960°C.

[0024] In some possible implementations, in the alternating flat and vertical rolling mill, the roughing, intermediate, and pre-finishing mills are rolled at 952°C with temperature control, and the finishing mill is rolled at 825°C in the two-phase zone with temperature control. After rolling, the wire rod is cooled by the Stellmore controlled cooling line, and the fans and insulation cover are turned off. After the controlled cooling is completed, the wire rod leaves the controlled cooling line and enters the PF line for normal circulation. When it is cooled to 55°C, it is covered with protective outer packaging.

[0025] In some possible implementations, the sizing temperature is below 845°C during the sizing process.

[0026] In some possible implementations, the spinning temperature is below 845°C, preferably 835°C to 840°C.

[0027] In some possible implementations, the cooling is controlled by a Stellmore air-cooled line.

[0028] In some possible implementations, the roller speed in the roll assembly is 20 rpm to 30 rpm.

[0029] In some possible implementations, the non-quenched and tempered steel wire rod consists of the following mass fractions: C: 0.32%~0.40%, Mn: 1.30%~1.55%, Si: 0.20%~0.30%, Cr: 0.10%~0.30%, Al: 0.010%~0.030%, V: 0.05%~0.12%, Ti: 0.010%~0.030%, N: 0.012%~0.022%, P≤0.020%, S≤0.004%, with the balance being iron and unavoidable impurities.

[0030] In some possible implementations, the non-quenched and tempered steel wire rod consists of the following components by mass fraction: C: 0.37%~0.38%, Mn: 1.42%~1.43%, Si: 0.26%~0.28%, Cr: 0.19%~0.20%, Al: 0.017%~0.018%, V: 0.09%~0.10%, Ti: 0.020%~0.021%, N: 0.019%~0.020%, P: 0.011%~0.012%, S: 0.003%~0.004%, with the balance being iron and unavoidable impurities.

[0031] In some possible implementations, the non-quenched and tempered steel wire rod consists of the following components by mass fraction: C: 0.37%, Mn: 1.42%, Si: 0.28%, Cr: 0.19%, Al: 0.018%, V: 0.09%, Ti: 0.021%, N: 0.019%, P: 0.012%, S: 0.004%, with the balance being iron and unavoidable impurities.

[0032] In some possible implementations, the non-quenched and tempered steel wire rod consists of the following components by mass fraction: C: 0.38%, Mn: 1.43%, Si: 0.26%, Cr: 0.20%, Al: 0.017%, V: 0.09%, Ti: 0.020%, N: 0.019%, P: 0.012%, S: 0.003%, with the balance being iron and unavoidable impurities.

[0033] Secondly, the present invention provides a method for producing non-quenched and tempered steel wire rods, the diameter of which is 16mm to 22mm.

[0034] Thirdly, the present invention provides an application of the non-quenched and tempered steel wire rod provided by the present invention in the field of automobile manufacturing technology.

[0035] The present invention provides a non-quenched and tempered steel wire rod and its production method, which, compared with the prior art, have at least the following beneficial technical effects: (1) The production method of non-quenched and tempered steel wire rod provided by the present invention involves primary rolling (secondary rolling) of the continuously cast large square billet, followed by grinding and subsequent processing, which can significantly reduce surface defects of the product. Grinding can remove defects such as scabs, cracks, pinholes, pits, sand holes, non-metallic inclusions, dents with a depth greater than 1.5 mm, and cracks with a depth greater than 0.2 mm from the surface of the small square billet, making the surface of the small square billet smooth and providing billet with good surface quality for subsequent processing. The non-quenched and tempered steel wire rod produced by the production method has a yield strength of 520 MPa or more, a tensile strength of 800 MPa to 950 MPa, and an elongation after fracture of 17% or more.

[0036] (2) The non-quenched and tempered steel wire rod provided by the present invention has a grain size ≥ 10, no full decarburization, and the total decarburization depth is within 0.05 mm; the dimensional tolerance is -0.15 mm to 0.15 mm; the yield strength is above 520 MPa, the tensile strength is 800 MPa to 950 MPa, the elongation after fracture is above 17%, and the reduction of area is above 50%. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of this drawing or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this drawing. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0038] Figure 1 The metallographic structure (1000X) of the non-quenched and tempered steel wire rod produced by the production method of non-quenched and tempered steel wire rod in Embodiment 1 of the present invention. Figure 2 This is a diagram (100X) showing the decarburization microstructure control effect of the non-quenched and tempered steel wire rod produced by the production method of non-quenched and tempered steel wire rod in Embodiment 1 of the present invention.

[0039] The purpose, features, and advantages of this accompanying drawing will be further explained in conjunction with the embodiments and with reference to the accompanying drawing. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described and illustrated below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. All other embodiments obtained by those skilled in the art based on the embodiments provided by this invention without inventive effort are within the scope of protection of this invention.

[0041] Obviously, the following description is merely some examples or embodiments of the present invention. Those skilled in the art can apply the present invention to other similar scenarios without any inventive effort. Furthermore, it is understood that although the effort involved in such development may be complex and lengthy, for those skilled in the art related to the content disclosed in this invention, modifications to design, manufacturing, or production based on the technical content disclosed in this invention are merely conventional technical means and should not be construed as insufficient disclosure of the present invention.

[0042] However, there may be instances where unnecessary detailed descriptions are omitted. For example, detailed descriptions of well-known matters or repetitive descriptions of essentially the same structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the following description is provided to enable those skilled in the art to fully understand the invention and is not intended to limit the subject matter of the claims.

[0043] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions, and all technical features and optional technical features of the present invention can be combined with each other to form new technical solutions.

[0044] The following description, in conjunction with specific embodiments, provides further details. Operations not mentioned in the production methods for non-quenched and tempered steel wire rods involved in the embodiments can be performed using conventional production operations in the art, and will not be specifically described or illustrated in this application's embodiments.

[0045] Example 1 Example 1 provides a method for producing non-quenched and tempered steel wire rod, wherein the target composition of the non-quenched and tempered steel wire rod is: C: 0.37%, Mn: 1.42%, Si: 0.28%, Cr: 0.19%, Al: 0.018%, V: 0.09%, Ti: 0.021%, N: 0.019%, P: 0.012%, S: 0.004%, with the balance being iron and unavoidable impurities.

[0046] The steps are as follows: S1. The molten steel is continuously cast to obtain a large square billet, and then cooled for 30 hours. S1.1. The steps for preparing molten steel are as follows: S1.1.1. Obtain 122t of molten iron and 29t of scrap steel to produce molten iron for smelting. After the molten iron is smelted in a converter, refined by LF and VD, molten steel is obtained.

[0047] In the converter smelting process, nitrogen blowing and stirring are carried out throughout the process. 500 kg of lime and 200 kg of synthetic slag are added to form slag. The tapping temperature is 1618℃. Slag-blocking tapping is adopted. The carbon content of the tapped steel is 0.05%, the P content is 0.009%, and the S content is 0.015%. Aluminum blocks, silicon-manganese alloy, medium carbon ferrochrome and vanadium-nitrogen alloy are added during the tapping process to adjust the composition.

[0048] In LF refining, silicon carbide and a small amount of aluminum particles are used for diffusion deoxidation; the refining white slag is maintained for about 25 minutes, the total slag amount is controlled at 10 kg / ton of steel, and nitrogen is added to the nitrogen alloy line after the molten steel temperature reaches 1590℃. The composition is finely adjusted according to the target composition, and the alkalinity is controlled to a target of 4.0.

[0049] In VD refining, the refining time is 32 minutes, the vacuum holding time is 15 minutes, nitrogen is circulated during the vacuum process, and the soft blowing argon time is controlled to be 22 minutes after the vacuum is broken.

[0050] S1.2. Continuous casting of molten steel: A 350×430 rectangular billet continuous casting machine is used, with a casting speed of 0.70m / min and a superheat of 15±3℃; the straightening machine adopts a light reduction technology; the secondary cooling of continuous casting uses a specific water volume of 0.35L / kg; the liquid level and stopper stroke of the crystallizer are controlled stably during the casting process, and the liquid level fluctuation is controlled within ±5mm; the electromagnetic stirring parameters of the crystallizer are 250A and 2.5Hz, and the electromagnetic stirring parameters at the end of solidification are 250A and 8.0Hz.

[0051] S2. The continuously cast large square billet after stacking and cooling is subjected to initial rolling to obtain a small square billet; S2.1. The initial rolling blanking process is as follows: S2.1.1. The large square billet is descaled, heated, rolled, and held at a constant temperature to obtain a small square billet; During heating, the preheating temperature is controlled at 700℃; the first heating stage furnace temperature is 1000℃; the second heating stage furnace temperature is 1200℃; the soaking stage temperature is 1200℃, and the total heating time is 420 min. During rolling, the initial rolling temperature is 1180℃, the final rolling temperature is 1000℃, and the sawing temperature is controlled at 550℃. S3. After grinding the small square billet, it undergoes heat treatment, descaling, alternating flat and vertical rolling, sizing, wire cutting, cooling, coiling, and pickling to obtain non-quenched and tempered steel wire rod. The grinding process involves using a grinding wheel-type peeling machine to grind the steel billet. The grinding depth of the steel billet face is 1.0 mm, and the grinding width of the steel billet corners is 10.0 mm. After the steel billet is ground, it is subjected to flaw detection using a magnetic particle flaw detector to check the surface quality of the ground steel billet. During the heat treatment, the preheating zone temperature was 850℃, the soaking zone temperature was 1200℃, and the total heating time was 150 minutes. The roughing, intermediate, and pre-finishing mills used controlled rolling at 952℃, while the finishing mill used controlled rolling in the two-phase zone at 825℃. After rolling, the material was wired at a low temperature of 838℃. After rolling, the material was cooled using the Steyrmore controlled cooling line, with the fans and insulation hood turned off.

[0052] Example 2 Example 2 provides a method for producing non-quenched and tempered steel wire rod, wherein the target composition of the non-quenched and tempered steel wire rod is: C: 0.38%, Mn: 1.43%, Si: 0.26%, Cr: 0.20%, Al: 0.017%, V: 0.09%, Ti: 0.020%, N: 0.019%, P: 0.012%, S: 0.003%, with the balance being iron and unavoidable impurities.

[0053] The steps are as follows: S1. The molten steel is continuously cast to obtain a large square billet, and then cooled for 30 hours. S1.1. The steps for preparing molten steel are as follows: S1.1.1. Obtain 121t of molten iron and 29t of scrap steel to produce molten iron for smelting. After the molten iron is smelted in a converter, refined by LF and VD, molten steel is obtained.

[0054] In the converter smelting process, nitrogen blowing and stirring are carried out throughout the process. 500 kg of lime and 200 kg of synthetic slag are added to form slag. The tapping temperature is 1605℃. Slag-blocking tapping is adopted. The carbon content of the tapped steel is 0.04%, the P content is 0.008%, and the S content is 0.012%. Aluminum blocks, silicon-manganese alloy, medium carbon ferrochrome and vanadium-nitrogen alloy are added during the tapping process to adjust the composition.

[0055] In LF refining, silicon carbide and a small amount of aluminum particles are used for diffusion deoxidation; the white slag holding time is 26 minutes, the total slag amount is controlled at 10 kg / ton of steel, and nitrogen is added to the nitrogen alloy feed line after the molten steel temperature reaches 1595℃. The composition is finely adjusted according to the target composition, and the alkalinity control target is 4.0.

[0056] In VD refining, the refining time is 34 min, the vacuum holding time is 15 min, nitrogen is circulated during the vacuum process, and the soft blowing argon time is controlled at 23 min after the vacuum is broken.

[0057] S1.2. Continuous casting of molten steel: A 350×430 rectangular billet continuous casting machine is used, with a casting speed of 0.70m / min and a superheat of 16±3℃; the straightening machine adopts a light reduction technology; the secondary cooling of continuous casting uses a specific water volume of 0.35L / kg; the liquid level and stopper stroke of the crystallizer are controlled stably during the casting process, and the liquid level fluctuation is controlled within ±5mm; the electromagnetic stirring parameters of the crystallizer are 250A and 2.5Hz, and the electromagnetic stirring parameters at the end of solidification are 250A and 8.0Hz.

[0058] S2. The continuously cast large square billet after stacking and cooling is subjected to initial rolling to obtain a small square billet; S2.1. The initial rolling blanking process is as follows: S2.1.1. The large square billet is descaled, rolled, and then kept at a constant temperature to obtain a small square billet; In step S2.1.1, rolling consists of heating and rolling. During heating, the preheating temperature is controlled at 700℃; the first heating temperature is 1050℃; the second heating temperature is 1230℃; the soaking temperature is 1210℃, and the total heating time is 420 min. During rolling, the initial rolling temperature is 1200℃, the final rolling temperature is 1080℃, and the sawing temperature is controlled at 580℃. S3. After grinding the small square billet, it undergoes heat treatment, descaling, alternating flat and vertical rolling, sizing, wire cutting, cooling, coiling, and pickling to obtain non-quenched and tempered steel wire rod. The grinding process involves using a grinding wheel-type peeling machine to grind the steel billet. The grinding depth of the steel billet face is 1.0 mm, and the grinding width of the steel billet corners is 10.0 mm. After the steel billet is ground, it is subjected to flaw detection using a magnetic particle flaw detector to check the surface quality of the ground steel billet. During the heat treatment, the preheating zone temperature was 830℃, the soaking zone temperature was 1220℃, and the total heating time was 150 minutes. The roughing, intermediate, and pre-finishing mills used 950℃ temperature-controlled rolling, while the finishing mill used 827℃ two-phase zone controlled rolling, followed by low-temperature wire drawing at 837℃. After rolling, the material was cooled via the Steyrmore controlled cooling line, with the fans and insulation hood turned off.

[0059] Comparative Example 1 Comparative Example 1: A method for producing non-quenched and tempered steel wire rod, comprising the following steps: SD1. Continuously cast molten steel to obtain a large square billet, and then stack it for cooling for 30 hours; SD2. After the continuously cast large square billet is cooled, it undergoes heat treatment, descaling, alternating flat and vertical rolling, sizing, wire cutting, cooling, coiling, and pickling to obtain non-quenched and tempered steel wire rod. The conditions for the preparation, continuous casting, homogenization, descaling, alternating horizontal and vertical rolling, sizing, wire cutting, cooling, coiling, and pickling of the finished steel are the same as in Example 1.

[0060] To verify the advancement of the production method for non-quenched and tempered steel wire rod in this invention, the non-quenched and tempered steel wire rods produced by the methods of the embodiments and comparative examples were tested for mechanical properties such as yield strength, tensile strength, elongation after fracture, and reduction of area. The non-metallic inclusions, microstructure type, grain size, total decarburization, and total decarburization were also tested, as shown in Tables 1-3 below. Taking Example 1 as an example, the non-quenched and tempered steel wire rod was subjected to metallographic testing and decarburization microstructure control effect testing, and the results are shown in the appendix to the specification. Figures 1-2 As shown.

[0061] Table 1

[0062] Table 2

[0063] Table 3

[0064] From Tables 1-3 above and the appendix to the instruction manual Figures 1-2 At least the following conclusions can be drawn: (1) The production method of non-quenched and tempered steel wire rod provided in this embodiment of the invention involves primary rolling (secondary rolling) of the continuously cast large square billet, followed by grinding and subsequent processing, which can significantly reduce surface defects of the product. Grinding can remove defects such as scabs, cracks, pinholes, pits, sand holes, and non-metallic inclusions, as well as dents with a depth greater than 1.5 mm and cracks with a depth greater than 0.2 mm from the surface of the small square billet, making the surface of the small square billet smooth and providing billets with good surface quality for subsequent processing. The non-quenched and tempered steel wire rod produced by the production method has a yield strength of 520 MPa or more, a tensile strength of 800 MPa to 950 MPa, and an elongation after fracture of 17% or more.

[0065] (2) The non-quenched and tempered steel wire rod provided in the embodiments of the present invention has a grain size ≥10, no complete decarburization, and the total decarburization depth is within 0.05mm; the dimensional tolerance is -0.15mm~0.15mm; the yield strength is above 520MPa, the tensile strength is 800MPa~950MPa, the elongation after fracture is above 17%, and the reduction of area is above 50%.

[0066] It should be noted that the present invention is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments that have the same structure and perform the same effects as the technical concept within the scope of the present invention are included within the scope of the present invention. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of the present invention, are also included within the scope of the present invention.

Claims

1. A method for producing non-quenched and tempered steel wire rod, characterized in that, Includes the following steps: The large continuously cast billet is subjected to initial rolling to obtain a small billet, which is then used to prepare non-quenched and tempered steel wire rod. The initial rolling process includes heating and rolling; During the heating process, the preheating temperature is controlled at 690℃~710℃; the first heating temperature is controlled at 950℃~1050℃; the second heating temperature is controlled at 1180℃~1230℃; the soaking temperature is controlled at 1190℃~1220℃; and the total heating time is 420min~450min. During the rolling process, the initial rolling temperature is 1180℃~1210℃, the final rolling temperature is 1000℃~1080℃, and the sawing temperature is controlled to be no less than 550℃. The non-quenched and tempered steel wire rod produced by the aforementioned production method has a yield strength of 520 MPa or more, a tensile strength of 800 MPa to 950 MPa, and an elongation after fracture of 17% or more. The non-quenched and tempered steel wire rod consists of the following mass fractions composition: C: 0.32%~0.40%, Mn: 1.30%~1.55%, Si: 0.20%~0.30%, Cr: 0.10%~0.30%, Al: 0.010%~0.030%, V: 0.05%~0.12%, Ti: 0.010%~0.030%, N: 0.012%~0.022%, P≤0.020%, S≤0.004%, with the balance being iron and unavoidable impurities.

2. The method for producing non-quenched and tempered steel wire rod according to claim 1, characterized in that, The preparation of the continuously cast large square billet includes the following steps: Molten iron is smelted in a converter, refined by LF and VD to obtain molten steel; The molten steel is continuously cast to obtain the continuously cast large square billet.

3. The method for producing non-quenched and tempered steel wire rod according to claim 2, characterized in that, In the converter smelting process, 1.25 kg / t to 1.43 kg / t of synthetic slag is added for slag formation, and the tapping temperature is ≥1580℃.

4. The method for producing non-quenched and tempered steel wire rod according to claim 2 or 3, characterized in that, In the LF refining process, the refining time is more than 40 minutes, the white slag retention time is more than 30 minutes, and the total slag volume is controlled at 10 kg / t to 12 kg / t.

5. The method for producing non-quenched and tempered steel wire rod according to claim 2, characterized in that, In the VD refining process, the refining time is more than 30 minutes, the vacuum holding time is more than 15 minutes, nitrogen is circulated during the vacuum treatment process, and the soft blowing argon time is controlled to be 20 minutes to 30 minutes after the vacuum is broken.

6. The method for producing non-quenched and tempered steel wire rod according to claim 2, characterized in that, In the continuous casting process, the casting speed is below 0.70 m / min; the superheat is below 20°C.

7. The method for producing non-quenched and tempered steel wire rod according to claim 2, characterized in that, The initial rolling and billet preparation specifically includes the following steps: After descaling, heating, rolling and heat preservation of the large billet, a small billet is obtained.

8. A non-quenched and tempered steel wire rod produced by the production method of any one of claims 1 to 7, characterized in that, The diameter is 16mm~22mm.

9. The application of the non-quenched and tempered steel wire rod produced by the production method of non-quenched and tempered steel wire rod as described in claim 8 in the field of automobile manufacturing technology.

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