Cold heading steel wire rod for high-strength fasteners and production method thereof

Abstract

The present invention discloses a production method of cold heading steel wire rod for high-strength fasteners, including continuous casting of large square billets, blanking and high-speed rolling. During high-speed rolling, the heating temperature is 1040-1080°C, the starting rolling temperature is 940-960°C, and the finishing rolling entrance temperature is 860-890°C. The present invention also provides cold heading steel wire rod for high-strength fasteners obtained by the above production method. The present invention adopts a reasonable high-speed rolling production process and a post-rolling cooling process, that is, a cooling process of first rapid cooling and then slow cooling is adopted to avoid the generation of a large amount of pearlite structure with a slow spheroidization speed in the wire rod. The wire rod structure is mainly bainite + martensite, so that a high density of dislocations and twin substructures are present in the steel, so that carbides are rapidly nucleated at the dislocations and substructures, thereby achieving the purpose of rapid spheroidization of the wire rod and shortening the spheroidizing annealing time.

Description

Technical Field

[0001] The present invention relates to the field of steel smelting, and in particular to a cold heading steel wire rod for high-strength fasteners and a production method thereof. Background Art

[0002] To meet the demands of the times and the increasing pressure on production costs, spheroidizing annealing, due to its high heating temperature, long heating time, and high energy consumption, has become a hot process in the fastener industry for reducing carbon emissions and increasing efficiency. The primary measures for reducing carbon emissions or lowering costs and increasing efficiency in the spheroidizing annealing process are to lower the heating temperature or shorten the spheroidizing time. However, these measures can lead to varying degrees of decline in the wire rod's spheroidizing rating, ultimately leading to problems such as deformation and cracking during cold heading, or increased die loss. This problem is particularly prominent in cold heading steel wire rod for high-strength fasteners.

[0003] Fasteners, which fasten parts or components together into a single, integral whole, are a crucial building block used in a wide range of applications, including machinery, automobiles, ships, railways, and bridges. As fasteners face increasingly harsh operating environments and their service life continues to increase, the demand for high-strength fasteners (strength grade 10.9 or higher) is growing. Spheroidizing annealing is a necessary and crucial step in the processing of high-strength fasteners. Spheroidizing annealing improves the wire rod's deformability, enhances cold heading performance, and reduces cold heading cracking. Cold-heading steel wire rod for high-strength fasteners requires very high spheroidization requirements, with a spheroidization microstructure rating of 5-6 required. However, the addition of strong carbide-forming elements such as Cr and Mo increases the activation energy for carbon atoms to diffuse in austenite, reducing the diffusion coefficient and hindering carbon diffusion. Furthermore, the diffusion rate of alloying elements themselves is much lower than that of carbon atoms. Therefore, the addition of these elements slows down the spheroidization process. Consequently, the heating temperature and spheroidization time of cold-heading steel wire rod for high-strength fasteners are higher. Due to the high heating temperature, long heating time, and high energy consumption of the spheroidizing annealing process, it has long been a key process in the fastener industry for reducing carbon emissions, lowering costs, and increasing efficiency. The primary measures for reducing carbon emissions or lowering costs and increasing efficiency in the spheroidizing annealing process are to lower the heating temperature or shorten the heating time. However, these measures can lead to varying degrees of decline in the wire rod's spheroidizing rating, ultimately leading to problems such as deformation and cracking during cold heading or increased die loss. This problem is particularly prominent in cold heading steel wire rods for high-strength fasteners, as spheroidizing annealing is difficult due to the addition of strong carbide elements such as Cr and Mo to the steel.

[0004] Chinese patents CN103060675A, CN102321851A, and CN103060676A disclose annealing-free cold-heading steel wire rod. Their inventive concepts include: 1. Low-temperature rolling increases the ferrite content and improves the wire rod's deformability; 2. Reducing the content of strengthening elements such as carbon, manganese, and chromium increases the ferrite content, improving the wire rod's deformability, while simultaneously adding boron to ensure the steel's hardenability. The advantage of this annealing-free solution lies in eliminating the spheroidizing annealing step, significantly reducing carbon emissions and increasing efficiency while also lowering energy consumption. However, annealing-free cold heading steel wire rod has the following disadvantages: 1. The production of annealing-free wire rod adopts low-temperature rolling, which has high requirements on the capacity of rolling equipment, and not all steel mills' rolling equipment can meet the requirements; 2. Annealing-free wire rod can only be used to produce parts with small cold heading deformation (such as nuts, screw rods, etc.). For parts with large cold heading deformation and complex deformation (such as flange bolts), the use of annealing-free cold heading steel wire rod will result in high cold heading cracking rate and high die loss; 3. Annealing-free technology is not suitable for the production of cold heading steel wire rod for high-strength fasteners. This is because high-strength fasteners use wire rods. In order to ensure that the tensile strength of the fasteners is above 1000MPa, a large amount of alloying elements such as Mn, Cr and Mo are added to the steel. The wire rod has high hardenability. Through annealing-free technology (low-temperature rolling, composition adjustment and slow cooling control), the wire rod metallographic structure still contains a large amount of pearlite, bainite and even martensite structure. The hot-rolled wire rod has poor cold heading deformation ability and must undergo spheroidizing annealing. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to solve the defects of long spheroidizing annealing time, low production efficiency and high energy consumption of cold heading steel wire rod for high strength fasteners, thereby providing a cold heading steel wire rod for high strength fasteners and a production method thereof.

[0006] To this end, the present invention adopts the following technical solutions:

[0007] The present invention provides a production method of cold heading steel wire rod for high-strength fasteners, comprising bloom continuous casting, blooming and high-speed wire rolling. During high-speed wire rolling, the heating temperature is 1040-1080°C, the start rolling temperature is 940-960°C, and the finishing rolling inlet temperature is 860-890°C.

[0008] The spinning temperature is 820-840℃, and the cooling speed of the wire rod is controlled at 3.0-5.0k / s in the temperature range from the spinning temperature to 600℃. Then the wire rod enters the heat preservation cover and the cooling speed is controlled at 0.1-1k / s.

[0009] The roller speed of the Stelmor entrance section is 0.2-0.4m / s, the air volume of 1-4# fans is 80-100%, and the other fans are closed; the insulation cover corresponding to the 5# fan and subsequent insulation covers are all closed.

[0010] Furthermore, the superheat degree of the molten steel in the continuous casting of large square blooms is 20-30°C, the casting speed is 0.60-0.65m / min, the secondary cooling water volume is 1.25-1.30L per kilogram of molten steel, and the specification of the continuous casting bloom is 300mm×390mm.

[0011] The heating temperature for blanking is 1140-1170°C, the heating time is 210-250min, the rolling temperature is 1000-1030°C, and the specification of the intermediate blank obtained by blanking is (140-150)mm×(140-150)mm.

[0012] The rolling specification of the cold heading steel wire rod is 5.5-24 mm.

[0013] The present invention also provides a wire rod obtained by the above production method, wherein the chemical composition of the wire rod, measured by mass percentage, comprises: C 0.35-0.38%, Si 0.25-0.35%, Mn 0.80-0.90%, Cr 0.85-0.95%, P≤0.018%, S≤0.015%, Al 0.020-0.045%, Mo 0.15-0.20%, and the remainder is Fe and unavoidable impurities.

[0014] The content of bainite+martensite in the metallographic structure of the wire rod is ≥75%, and the content of bainite is ≥60%.

[0015] The technical solution of the present invention has the following advantages:

[0016] (1) It is well known in the art that controlling the austenite grain size helps to refine the metallographic structure of the wire rod (for example, refining the pearlite and martensite grain size), thereby increasing the number of grain boundaries. There are a large number of microscopic defects or dislocations near the grain boundaries, and these microscopic defects or dislocations are nucleation points for spheroidization and carbonization precipitation. The more grain boundaries there are, the more nucleation points there are, making it easier for the wire rod to spheroidize. In the high-speed wire rolling process, the heating temperature, the starting rolling temperature and the finishing rolling entrance temperature are the main factors affecting the grain size. If the temperature is controlled too high, the wire rod grain size will be large, thereby reducing the number of grain boundaries in the steel. Controlling a lower rolling temperature will be beneficial to refining the grain size, thereby increasing the number of grain boundaries, and then increasing the spheroidization nucleation points and reducing the difficulty of spheroidization. However, if the rolling temperature is too low, higher requirements will be placed on the rolling mill equipment capacity and motor load, and there is a risk of equipment damage. Based on the actual equipment capacity and the control of grain size, during high-speed wire rolling, the heating temperature of the present invention is 1040-1080°C, the start rolling temperature is 940-960°C, and the finishing rolling entrance temperature is 860-890°C.

[0017] Different metallographic microstructures significantly influence the effects of spheroidizing annealing. Compared to pearlite, martensite and bainite contain a high density of dislocations and twin substructures, which rapidly nucleate carbides at these dislocations and substructures, leading to rapid spheroidization of the wire rod. Therefore, post-rolling cooling requires rapid cooling to avoid the pearlite transformation zone and enter the bainite and martensite transformation zones, allowing the wire rod to acquire martensite and bainite structures. This control of the wire rod structure can increase the speed of wire rod spheroidization. A low spinning temperature allows for rapid cooling, allowing for rapid entry into the bainite and martensite transformation zones. However, excessively low spinning temperatures require a high flow of cooling water from the water tank before spinning. This high flow of cooling water, applied to the wire rod by impact cooling, can cause the wire rod to wobble, collide with the guide grooves, and scratch, resulting in surface defects and impacting the wire rod's cold heading performance. Furthermore, excessively low spinning temperatures can make spinning difficult and disrupt production. Therefore, the present invention controls a suitable low spinning temperature, and the spinning temperature is 820-840°C; in order to avoid the pearlite transformation zone, the present invention controls the cooling rate in the temperature range from the spinning temperature to 600°C to be 3.0-5.0k / s. A slow cooling rate will lead to the production of a large amount of pearlite and ferrite. Too fast a cooling rate will cause the wire rod structure to be a single martensite structure. The single martensite structure makes the wire rod strong and poor in plasticity, which ultimately leads to difficulty in packaging and brittle fracture of the wire rod, affecting subsequent use; in order to ensure sufficient transformation of bainite and martensite, the present invention cools the wire rod to 600°C before entering the insulation cover, controls the cooling rate to ≤1k / s, and controls the temperature of the wire rod entering the insulation cover at 600°C, which can ensure that the wire rod enters the bainite transformation zone. The temperature of the wire rod entering the insulation cover is higher than 600°C, and the structure transformation zone is still in the pearlite transformation zone, which will cause the wire rod to produce a large amount of pearlite.

[0018] In order to achieve rapid cooling after rolling and avoid pearlite transformation, the roller speed of the entrance section of the present invention is 0.2-0.4m / s, the air volume of 1-4# fans is 80-100%, and the other fans are closed; the insulation cover corresponding to the 5# fan and the subsequent insulation covers are all closed to allow the wire rod to fully transform into bainite and martensite structures.

[0019] (2) The present invention increases the content of strengthening elements carbon and silicon and weak carbide element manganese, while reducing the strong carbide elements chromium and molybdenum, thereby increasing the diffusion coefficient of carbon atoms in steel and thus increasing the spheroidization speed;

[0020] Among them, C is the most basic strengthening element in steel. However, as the carbon content increases, the hardenability of the wire rod will increase, but the plasticity of the wire rod will deteriorate. Therefore, the carbon content of the present invention is limited to 0.35-0.38%.

[0021] Si is a strengthening and deoxidizing element in steel, but too much silicon will reduce the drawing performance of the wire rod. In the present invention, the silicon content range is 0.25-0.35%.

[0022] Mn is a weak carbide element that can improve the hardenability and strength of steel. In the present invention, the manganese content is controlled at 0.80-0.90%.

[0023] Cr is a commonly used alloying element to improve the hardenability of steel and can increase the strength of steel. However, chromium is a strong carbide-forming element and excessive Cr will lead to difficulty in spheroidization. In order to balance strength and spheroidization effect, the chromium content in the present invention is controlled at 0.90-1.00%.

[0024] Mo can improve the hardenability, strength and wear resistance of steel, but Mo is a strong carbide element. Excessive Mo will lead to difficulty in spheroidization and increase the alloy cost. In the present invention, the Mo content is controlled at 0.15-0.20%.

[0025] Al is a deoxidizing element in steel, effectively removing oxygen from it and improving its cleanliness. It also forms AlN with nitrogen, which refines the grain size. The aluminum content in the present invention is controlled within a range of 0.020 to 0.045%.

[0026] P and S are impurity elements in steel. P and S segregate at grain boundaries, embrittle the grain boundaries, and thus reduce the strength and plasticity of the steel. The present invention controls the P content to below 0.018% and the S content to below 0.015%.

[0027] (3) The present invention adopts a reasonable post-rolling cooling process, that is, a cooling process of first rapid cooling and then slow cooling, to avoid the generation of a large amount of pearlite structure with a slow spheroidization speed in the wire rod. The wire rod structure is mainly bainite + martensite, so that a high density of dislocations and twin substructures exist in the steel, and carbides are rapidly nucleated at the dislocations and substructures, achieving the purpose of rapid spheroidization of the wire rod and shortening the spheroidizing annealing time. In order to ensure a better rapid spheroidization effect, the content of bainite + martensite is controlled to be ≥75%, and the content of bainite is controlled to be ≥60%. At the same time, the heating and rolling temperatures are controlled to be lower, the grains are refined, the number of grain boundaries is increased, the number of carbide precipitation points is increased, and the spheroidization speed is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 This is a metallographic image of Example 1 of the present invention;

[0030] Figure 2 It is the metallographic structure picture of comparative example 4 in the present invention. DETAILED DESCRIPTION

[0031] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.

[0032] If no specific experimental steps or conditions are specified, the experiments were performed according to the conventional experimental steps or conditions described in the literature in this field. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.

[0033] Example 1

[0034] This embodiment provides a method for producing cold heading steel wire rod for high-strength fasteners, which adopts a production process of bloom continuous casting + blooming + high-strength wire rolling. The specific steps are as follows:

[0035] The superheat degree of the molten steel in continuous casting of large square blooms is 25℃, the casting speed is 0.61m / min, the secondary cooling water volume is 1.27L per kilogram of molten steel, and the specifications of the continuous casting blooms are 300mm×390mm.

[0036] The heating temperature for blanking is 1160°C, the heating time is 240 min, the rolling temperature is 1015°C, and the specification of the intermediate blank obtained by blanking is 140mm×140mm.

[0037] During high-speed wire rolling, the heating temperature is 1060℃, the starting rolling temperature is 950℃, the finishing rolling entrance temperature is 870℃, the wire drawing temperature is 810℃, and the cooling rate in the temperature range of 810℃ to 600℃ is controlled at 4k / s. Then the wire rod enters the insulation cover with a cooling rate of 0.75k / s.

[0038] The specification of the rolled wire rod is 14mm, the Stelmor inlet roller speed is 0.30m / s, the air volume of 1-4# fans is 90%, and the other fans are closed; the insulation cover corresponding to the 5# fan and subsequent insulation covers are all closed.

[0039] The chemical composition of the obtained wire rod is shown in Table 1, and the remainder is Fe and inevitable impurities.

[0040] The metallographic structure of the product is shown in the figure below: Figure 1 As shown, it can be seen that the metallographic structure of the wire rod before spheroidization is mainly bainite + martensite, the content of bainite + martensite is 92% (the content of bainite is 77%), and the content of ferrite + pearlite is 8%.

[0041] Example 2

[0042] This embodiment provides a method for producing cold heading steel wire rod for high-strength fasteners, which adopts a production process of bloom continuous casting + blooming + high-strength wire rolling. The specific steps are as follows:

[0043] The superheat degree of the molten steel in continuous casting of large square blooms is 23°C, the casting speed is 0.62m / min, the secondary cooling water volume is 1.25L per kilogram of molten steel, and the specifications of the continuous casting blooms are 300mm×390mm.

[0044] The heating temperature for blanking is 1150°C, the heating time is 250 min, the rolling temperature is 1020°C, and the specification of the intermediate blank obtained by blanking is 140mm×140mm.

[0045] During high-speed wire rolling, the heating temperature is 1070℃, the starting rolling temperature is 955℃, the finishing rolling entrance temperature is 860℃, the spinning temperature is 820℃, and the cooling rate in the temperature range of 820℃ to 600℃ is controlled at 3.5k / s. Then the wire rod enters the insulation cover with a cooling rate of 0.55k / s.

[0046] The rolling specification is 16mm, the roller speed of the Stelmor entrance section is 0.2m / s, the air volume of 1-4# fans is 90%, and the other fans are closed; the insulation cover corresponding to the 5# fan and subsequent insulation covers are all closed.

[0047] The chemical composition of the obtained wire rod is shown in Table 1, and the remainder is Fe and inevitable impurities.

[0048] Example 3

[0049] This embodiment provides a method for producing cold heading steel wire rod for high-strength fasteners, which adopts a production process of bloom continuous casting + blooming + high-strength wire rolling. The specific steps are as follows:

[0050] The superheat degree of the molten steel in continuous casting of large square blooms is 21°C, the casting speed is 0.64m / min, the secondary cooling water volume is 1.29L per kilogram of molten steel, and the specifications of the continuous casting blooms are 300mm×390mm.

[0051] The heating temperature for blanking is 1170°C, the heating time is 240 min, the rolling temperature is 1010°C, and the specification of the intermediate blank obtained by blanking is 140mm×140mm.

[0052] During high-speed wire rolling, the heating temperature is 1045℃, the starting rolling temperature is 945℃, the finishing rolling entrance temperature is 880℃, the spinning temperature is 830℃, and the cooling rate in the temperature range of 830℃ to 600℃ is controlled at 4.5k / s. Then the wire rod enters the insulation cover with a cooling rate of 0.95k / s.

[0053] The rolling specification is 12mm, the roller speed of the Stelmor entrance section is 0.40m / s, the air volume of 1-4# fans is 100%, and the other fans are closed; the insulation cover corresponding to the 5# fan and subsequent insulation covers are all closed.

[0054] The chemical composition of the obtained wire rod is shown in Table 1, and the remainder is Fe and inevitable impurities.

[0055] Comparative Example 1

[0056] This comparative example provides a method for producing cold heading steel wire rod for high-strength fasteners, which adopts a large square bloom continuous casting + blanking + high-speed wire rolling production process and uses the intermediate billet obtained in Example 1.

[0057] The difference from Example 1 is that during high-speed wire rolling, the heating temperature is 1060°C, the start rolling temperature is 950°C, the finishing rolling entrance temperature is 870°C, the spinning temperature is 860°C, and the cooling rate in the temperature range of 860°C to 600°C is controlled at 0.55k / s.

[0058] The specification of the rolled wire rod is 14 mm, the Stelmor inlet roller speed is 0.18 m / s, the fan is turned off, and the insulation cover is closed.

[0059] The chemical composition of the obtained wire rod is shown in Table 1, and the remainder is Fe and inevitable impurities.

[0060] Comparative Example 2

[0061] This comparative example provides a method for producing cold heading steel wire rod for high-strength fasteners, which adopts a large square bloom continuous casting + blanking + high-speed wire rolling production process, and uses the intermediate billet obtained in Example 2.

[0062] The difference from Example 2 is that during high-speed wire rolling, the heating temperature is 1110°C, the start rolling temperature is 990°C, the finishing rolling entrance temperature is 905°C, the spinning temperature is 820°C, and the cooling rate in the temperature range of 820°C to 600°C is controlled at 3.5k / s, and then the wire rod enters the insulation cover with a cooling rate of 0.55k / s.

[0063] The rolling specification is 16mm, the roller speed of the Stelmor entrance section is 0.2m / s, the air volume of 1-4# fans is 90%, and the other fans are closed; the insulation cover corresponding to the 5# fan and subsequent insulation covers are all closed.

[0064] The chemical composition of the obtained wire rod is shown in Table 1, and the remainder is Fe and inevitable impurities.

[0065] Comparative Example 3

[0066] This comparative example provides a method for producing cold heading steel wire rod for high-strength fasteners, which adopts a production process of bloom continuous casting + blooming + high-speed wire rolling. The specific steps are as follows:

[0067] The superheat degree of the molten steel in continuous casting of large square blooms is 25℃, the casting speed is 0.61m / min, the secondary cooling water volume is 1.27L per kilogram of molten steel, and the specifications of the continuous casting blooms are 300mm×390mm.

[0068] The heating temperature for blanking is 1160°C, the heating time is 240 min, the rolling temperature is 1015°C, and the specification of the intermediate blank obtained by blanking is 140mm×140mm.

[0069] During high-speed wire rolling, the heating temperature is 1045℃, the starting rolling temperature is 945℃, the finishing rolling entrance temperature is 880℃, the spinning temperature is 830℃, and the cooling rate in the temperature range of 830℃ to 600℃ is controlled at 4.5k / s. Then the wire rod enters the insulation cover with a cooling rate of 0.95k / s.

[0070] The rolling specification is 12mm, the roller speed of the Stelmor entrance section is 0.40m / s, the air volume of 1-4# fans is 100%, and the other fans are closed; the insulation cover corresponding to the 5# fan and subsequent insulation covers are all closed.

[0071] The chemical composition of the obtained wire rod is shown in Table 1, and the remainder is Fe and inevitable impurities.

[0072] Comparative Example 4

[0073] This comparative example provides a production method for cold heading steel wire rod for high-strength fasteners, which adopts a large square bloom continuous casting + blanking + high-speed wire rolling production process, and uses the intermediate billet obtained in comparative example 3.

[0074] The difference from Comparative Example 3 is that during high-speed wire rolling, the heating temperature is 1110°C, the start rolling temperature is 990°C, the finishing rolling entrance temperature is 905°C, the spinning temperature is 870°C, and the cooling rate in the temperature range of 870°C to 600°C is controlled to be 0.50k / s.

[0075] The rolling specification is 12mm, the roller speed in the entrance section is 0.2m / s, and the fan and insulation cover are all closed.

[0076] The chemical composition of the obtained wire rod is shown in Table 1, and the remainder is Fe and inevitable impurities.

[0077] The metallographic structure of the product is shown in the figure below: Figure 2 As shown, it can be seen that the metallographic structure of the wire rod before spheroidizing is mainly ferrite + pearlite, with a ferrite + pearlite content of 82%, and the rest is bainite + martensite, with a bainite + martensite content of 18% (bainite content is 13%).

[0078] Table 1 Chemical composition of Examples 1-3 and Comparative Examples 1-4 (%)

[0079]

[0080]

[0081] The chemical compositions of the wire rods obtained in Examples 1-3 and Comparative Examples 1-4 are shown in Table 1. After annealing, the spheroidization level of both the wire rods of Examples and Comparative Examples is Level 5, but the spheroidization time of the wire rods of Examples is 25-28 hours, and the gas consumption is 37-40m3. 3 / ton, the composition and production method of comparative example 4 are completely inconsistent with those of the present invention, the spheroidization time is 43h, and the gas consumption is 58m 3 / ton; Comparative Examples 1-2 have the same chemical composition and partial production methods as the present invention, while Comparative Example 3 has different components but the same production method. The spheroidization time and gas consumption of Comparative Examples 1-3 are better than those of Comparative Example 4, but significantly worse than those of Examples 1-3, as shown in Table 2.

[0082] Table 2 Spheroidization data of Examples 1-3 and Comparative Examples 1-4

[0083]

[0084] As can be seen from the above table, under the conditions of the same spheroidizing effect, the spheroidizing time and gas consumption of the wire rod of the embodiment of the present invention are significantly lower than those of the comparative example. While ensuring the spheroidizing effect, the solution provided by the present invention significantly reduces the heating time and energy consumption of the spheroidizing annealing process, thereby reducing production costs and carbon emissions.

[0085] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for producing cold heading steel wire rod for high-strength fasteners, comprising bloom continuous casting, blooming and high-speed wire rolling, characterized in that: During high-speed wire rolling, the heating temperature is 1040-1080℃, the starting rolling temperature is 940-960℃, and the finishing rolling entrance temperature is 860-890℃; The spinning temperature is 820-840℃, and the cooling speed of the wire rod is controlled at 3.0-4.5k / s in the temperature range from spinning temperature to 600℃. Then the wire rod enters the heat preservation cover and the cooling speed is controlled at 0.1-1k / s. The chemical composition of the wire rod, in percentage by mass, comprises: C 0.35-0.38%, Si 0.25-0.35%, Mn 0.80-0.90%, Cr 0.85-0.95%, P≤0.018%, S≤0.015%, Al 0.020-0.045%, Mo 0.15-0.20%, and the remainder is Fe and unavoidable impurities; The metallographic structure of the wire rod has a bainite + martensite content of ≥75%, and a bainite content of ≥60%; The roller speed of the Stelmor entrance section is 0.2-0.4m / s, the air volume of 1-4# fans is 80-100%, and the other fans are turned off; the insulation cover corresponding to the 5# fan and subsequent insulation covers are all closed.

2. The production method according to claim 1, characterized in that The superheat degree of molten steel in continuous casting of large square blooms is 20-30℃, the casting speed is 0.60-0.65m / min, the secondary cooling water volume is 1.25~1.30L per kilogram of molten steel, and the specification of continuous casting blooms is 300mm×390mm.

3. The production method according to claim 1, characterized in that The heating temperature for blanking is 1140-1170°C, the heating time is 210-250min, the rolling temperature is 1000-1030°C, and the specification of the intermediate blank obtained by blanking is (140-150) mm×(140-150) mm.

4. The production method according to claim 1, characterized in that The rolling specification of the cold heading steel wire rod is 5.5-24 mm.

5. The wire rod produced by the production method according to any one of claims 1 to 4, characterized in that: The chemical composition of the wire rod, measured in percentage by mass, includes: C 0.35-0.38%, Si 0.25-0.35%, Mn 0.80-0.90%, Cr 0.85-0.95%, P≤0.018%, S≤0.015%, Al 0.020-0.045%, Mo 0.15-0.20%, and the remainder is Fe and unavoidable impurities.

6. The wire rod according to claim 5, characterized in that The content of bainite+martensite in the metallographic structure of the wire rod is ≥75%, and the content of bainite is ≥60%.

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