A cold-heading steel with high cold-heading performance and high plasticity that does not require annealing, its manufacturing method, and fasteners

Abstract

The present invention discloses a cold-heading steel with high cold-heading performance and high plasticity without annealing, and its manufacturing method and fasteners. The cold-heading steel contains C, Si, Mn, Al, B, Mg, Pr, and its metallographic structure is ferrite + degenerated pearlite. The hot-rolled wire rod of the cold-heading steel has low strength, high plasticity, and high cold-heading performance, and does not require spheroidizing annealing treatment. It can be directly drawn and cold-headed into fasteners with large deformation amounts, and has excellent drawing and cold-heading performance. It can be used to manufacture fasteners with large deformation amounts of 8.8 to 9.8 grades. In addition, the cold-heading steel has high purity, and both the steel and the fasteners have high fatigue performance and long service life.

Description

Technical Field

[0001] The present invention belongs to the technical field of cold heading steel, and particularly relates to a non-annealed cold heading steel with high cold heading performance and high plasticity, a manufacturing method thereof, and fasteners. Background Art

[0002] Fasteners are mainly formed by cold heading. During the manufacturing process of workpieces, they often have to withstand a total deformation of 70-80%. Therefore, in addition to having good internal metallurgical quality and excellent surface quality, the raw materials are particularly required to have low hardness and good plasticity before cold working, so as to obtain low deformation resistance and high deformation ability. Therefore, cold heading steel wire rods usually need to go through several processes such as pickling, drawing, spheroidizing (softening) annealing, and secondary drawing before cold heading. Some steels also need to undergo multiple spheroidizing annealings, and then quenching and tempering treatment after cold heading.

[0003] For example, Chinese Patent CN 114231703 A discloses a production method of high-strength simplified annealing cold heading steel, which includes successively performing electric furnace smelting, LF refining, RH vacuum degassing, bloom continuous casting, bloom rolling, and high-speed wire rod rolling on raw materials according to element ratios to obtain hot-rolled wire rods, and annealing the hot-rolled wire rods to obtain cold heading steel; the element ratios of the raw materials include at least 96.2 wt% of Fe, 0.01 wt% - 0.1 wt% of V, 0.01 wt - 0.1 wt% of Nb, and 0.002 wt% - 0.01 wt% of N; (V + Nb) / N = 7 - 15; the high-speed wire rod rolling includes rolling the wire rod on rough and medium rolling mills at a temperature above 950 °C, then controlling the temperature of the wire rod entering the reducing sizing mill to be 790 °C - 860 °C, and rapidly cooling it to the laying temperature of 770 °C - 800 °C through a water tank. In this patent, the cold heading steel needs to be spheroidized annealed, and the process is complex.

[0004] Spheroidizing annealing and quenching and tempering treatment are the most energy-consuming and time-consuming processes in the fastener industry. They not only increase production costs, but also increase emissions and pollute the environment. If the process control is improper, it will also lead to unstable fastener quality. Non-annealed cold heading steel is an important development direction in cold heading. Summary of the Invention

[0005] The purpose of the present invention is to provide a non-annealed cold heading steel with high cold heading performance and high plasticity and a manufacturing method thereof. The hot-rolled wire rods of the cold heading steel have low strength, high plasticity, and high cold heading performance, do not require spheroidizing annealing treatment, can be directly drawn and cold headed into fasteners with large deformation, have excellent drawing and cold heading performance, can produce fasteners with large deformation of grades 8.8 - 9.8. In addition, the cold heading steel has high purity, and both the steel and the fasteners have high fatigue performance and long service life.

[0006] To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0007] A cold-heading steel with high cold-heading performance and high plasticity that does not require annealing. The cold-heading steel with high cold-heading performance and high plasticity contains the following by weight percentage: C 0.10% - 0.30%, Si ≤ 0.15%, Mn 0.60% - 0.90%, Al 0.060% - 0.080%, B 0.0035% - 0.0055%, Mg 0.0010% - 0.0030%, Pr 0.0040% - 0.0070%, P ≤ 0.015%, S ≤ 0.015%, O ≤ 0.0015%, N ≤ 0.007%, and the rest is Fe and other inevitable impurities;

[0008] Among them, Al / N = 10.0 - 13.0, which can give full play to the effective role of B in the steel;

[0009] The W value ≥ 1.60, W = 29.3*(%B) + 11.7*(%Al) + 0.86*(%Mn) + 1.22*(%C), which can ensure the hardenability of the steel;

[0010] The D value ≤ 0.07, D = 10.0*(%S) + 19.9*(%O), which can ensure that the recovery rate of Pr and Mg alloys reaches more than 80%.

[0011] The metallographic structure of the cold-heading steel with high cold-heading performance and high plasticity that does not require annealing is ferrite + degenerated pearlite, where the volume percentage of the ferrite structure is 80% - 85%, and the volume percentage of the degenerated pearlite structure is 15% - 20%, and the average ferrite grain size is 10μm - 13μm; the cold-heading steel with such a structure has low strength and hardness, good plasticity, excellent cold-heading performance, and sufficient hardenability and high purity, and can be used for large-deformation fasteners that can be directly drawn and cold-headed without spheroidizing annealing treatment.

[0012] The R of the hot-rolled wire rod of the cold-heading steel with high cold-heading performance and high plasticity that does not require annealing m ≤ 480 MPa, A ≥ 30%, Z ≥ 65%, hardness ≤ 75 HRB; the inclusions in the cold-heading steel are all plastic inclusions, and the inclusion size is below 6.5μm.

[0013] The cold-heading steel with high cold-heading performance and high plasticity that does not require annealing reaches a strength level of 8.8 - 9.8 grades, hardness HRC 26 - 33, and the axial fatigue life under a 100 KN load > 3 million times after quenching and tempering heat treatment.

[0014] The present invention also provides a manufacturing method for the cold-heading steel with high cold-heading performance and high plasticity that does not require annealing. The manufacturing method includes the following steps: hot metal pretreatment → converter / electric furnace smelting → LF furnace refining → bloom / round billet continuous casting → bloom / round billet heating → high-speed wire rod rolling → cooling on the Stelmor cooling line → slow cooling in the insulation channel → finished hot-rolled wire rod.

[0015] The specifications of the finished hot-rolled wire rod are Φ6mm to Φ30mm.

[0016] In the converter smelting step: the C content at the end of the converter is ≤0.10%, and the P content is ≤0.008%; slagging is carried out during tapping, and the amount of slag flowing into the ladle is strictly controlled. The thickness of the slag layer in the ladle is ≤100mm, and the tapping time is ≥5min.

[0017] In the LF furnace refining step, the LF refining time is ≥30min, and the white slag holding time is ≥20min to ensure sufficient deoxidation, desulfurization, and dephosphorization. After alloying, Mg wire is fed, and the wire feeding speed is controlled at 30m / min to 40m / min. If the speed is higher than this value, the plasticization of inclusions cannot be fully achieved, and if the speed is lower than this value, the efficiency of the LF process will be affected.

[0018] In the billet / round billet continuous casting step, Pr wire is added to the center of the mold, and the wire feeding speed is controlled at 15m / min to 30m / min. In addition, the ratio of the wire feeding speed to the casting speed is maintained at 8 to 15. If the ratio is lower than this value, the Pr recovery rate is relatively low, and the wire feeding amount is insufficient, resulting in a low Pr content. If the ratio is higher than this value, the effect of Pr on modifying inclusions in the steel is insufficient, and the full plasticization effect cannot be achieved.

[0019] In the billet / round billet heating step: the soaking temperature of the billet / round billet is controlled at 1000 - 1100°C. If the temperature is lower than this value, alloying elements cannot be fully dissolved in austenite, and if the temperature is higher than this value, severe decarburization will occur.

[0020] In the high-speed wire rod rolling step: the finishing rolling temperature is controlled at 800°C - 850°C, and the sizing temperature is controlled at 790°C - 840°C. Rolling is carried out in the non-recrystallization zone of austenite, and it will not cause excessive refinement of ferrite grain size.

[0021] In the cooling step of the Stelmor cooling line: the laying temperature is controlled at 800°C - 850°C, the reference speed of the roller table is controlled at 0.10m / s - 0.15m / s, and the insulation hood is fully closed to obtain a degenerated pearlite structure.

[0022] In the slow cooling step of the insulation channel: after exiting the Stelmor cooling line, it enters the insulation channel for slow cooling and further on-line softening. The reference speed of the insulation channel is 0.15m / s - 0.25m / s. If the speed is higher than this value, the hardness in the hot-rolled state is relatively high, and if the speed is lower than this value, the softening effect will no longer improve.

[0023] The functions and controls of the components in the cold heading steel with high cold heading performance and high plasticity provided by the present invention are as follows:

[0024] C: C is the most basic and effective strengthening element in steel. However, as its content increases, the ductility decreases. To balance the high cold heading performance, high plasticity of the steel of the present invention and ensure the final strength level of the fasteners, the C content is controlled at 0.10% - 0.30%.

[0025] Si: Most of Si dissolves in ferrite, strengthening the ferrite, thereby increasing the strength and hardness of the cold heading steel. However, Si forms brittle inclusions SiO2 in steel, reducing the plasticity and cold heading performance. To ensure the low strength, high plasticity, and high purity of the steel of the present invention in the hot-rolled state, the Si content is controlled ≤ 0.15%.

[0026] Mn: Mn forms a solid solution with Fe, increasing the hardness and strength of ferrite and austenite in steel and improving the hardenability of the steel. However, excessive Mn reduces the plasticity of the steel. The Mn content is controlled at 0.60% - 0.90%.

[0027] Al: Part of Al in steel acts as a nitrogen-fixing element to promote the solid solution of B, and the other part co-dissolves with B in steel, inhibiting the transformation of pearlite and ferrite, increasing the ability of the experimental steel to obtain martensite at a lower cooling rate, and improving the hardenability of the steel. However, excessive Al forms too many AlN precipitation phases with N, resulting in excessive grain refinement by pinning at the grain boundaries, leading to too high strength in the hot-rolled state. In addition, excessive Al forms coarse inclusions, reducing the purity of the steel. The Mn content is controlled at 0.60% - 0.90%. To ensure the solid solution of effective boron and the hardenability of the steel, it is necessary to control w(Al) / w(N) = 10.0 - 13.0. Below this value, sufficient hardenability cannot be guaranteed, and above this value, the requirements for grain size and purity do not meet the requirements of the invention.

[0028] B: The B content is one of the main elements to ensure hardenability. By adding B, the manganese and carbon contents can be reduced, thereby significantly reducing the strength and hardness of the steel. In addition, during the rolling process of hot-rolled wire rods, due to the strong grain boundary segregation phenomenon of boron, the concentration of dissolved boron is high at the α / γ interface. Using the slow cooling phase transformation process after thermo-mechanical rolling, an appropriate amount of boron phase [M3(C,B)+M 23(C,B)6] becomes the deposition core of excess carbon, accelerating carbon deposition, thereby promoting the moderate growth of the α-phase, enabling the hot-rolled wire rod to obtain degenerated pearlite and the ferrite not being overly refined, forming the best microstructure beneficial for cold heading. However, B and nitrogen have a strong affinity and often form inclusions such as boron nitride during the steelmaking process, reducing the recovery rate of effective boron and resulting in insufficient hardenability of the steel. Therefore, Al element is added for nitrogen fixation. When the B content is added too much, the above effects are no longer obvious, and the B content is controlled at 0.0035% - 0.0055%. In addition, to ensure that the steel has sufficient hardenability, it is also necessary to ensure that the W value ≥ 1.60, W = 29.3*(%B) + 11.7*(%Al) + 0.86*(%Mn) + 1.22*(%C), and the coefficients in the formula are determined according to the contribution of each alloy element to hardenability.

[0029] Mg, Pr: Mg and Pr form a composite modifier in the steel, which is more effective than single addition. First of all, Mg not only has an excellent affinity with oxygen and sulfur, but also has a very strong ability to control the morphology and size of inclusions. Mg can change the Al2O3 inclusions in the steel into high-melting-point MgO·Al2O3. Since it exists in a solid state in the molten steel and there is no process of aggregation and growth, the size of its oxide inclusions is very small and is dispersed in the steel, having basically no negative impact on the mechanical properties of the steel. When an appropriate amount of Pr element is added to the steel, inclusions such as SiO2 and A12O3 can be metamorphosed into spherical rare earth composite oxysulfides, thereby improving the mechanical properties and fatigue life of the steel. Control Mg at 0.0010% - 0.0030% and Pr at 0.0040% - 0.0070%.

[0030] P: P is an element with a strong segregation tendency, which will cause cold brittleness and lead to cold heading cracking. Control P ≤ 0.015%.

[0031] S, O: S is easy to form MnS inclusions in the steel, which is harmful to the processing performance of the steel; O forms oxide inclusions in the steel, damaging the processing performance and service life of the steel. Control S ≤ 0.015% and O ≤ 0.0015%. In addition, since Mg and Pr are easy to react with S and O to produce slag inclusions, in order to ensure that the recovery rate of Pr and Mg alloys reaches more than 80%, it is also necessary to control the D value ≤ 0.07, D = 10.0*(%S) + 19.9*(%O).

[0032] The cross-sectional microstructure of the hot-rolled wire rod of the cold heading steel manufactured according to the composition of the present invention is a ferrite + degenerated pearlite microstructure, where the volume percentage of the ferrite microstructure is 80% - 85%, the volume percentage of the degenerated pearlite microstructure is 15% - 20%, the average ferrite grain size is 10μm - 13μm, and the inclusions in the steel are all plastic inclusions with an inclusion size below 6.5μm. The mechanical properties of the hot-rolled wire rod: R m≤480 MPa, A ≥ 30%, Z ≥ 65%, hardness ≤ 75 HRB, with low strength, high plasticity, and excellent cold heading performance. Its one-seventh cold heading is qualified, and it has excellent drawing and cold heading performance.

[0033] Due to the low strength, high plasticity, and excellent cold heading performance of the hot-rolled wire rods of the cold heading steel provided by the present invention, spheroidizing annealing treatment is not required, and it can be directly drawn and cold headed into fasteners with large deformation amounts, such as flange bolts, sleeves, etc. After the fasteners are made and subjected to conventional quenching and tempering heat treatment, among them, the quenching temperature is 870 - 900 °C, and the tempering temperature is 450 - 550 °C. The strength level reaches 8.8 - 9.8 levels (8.8 level: R m ≥ 800 MPa, R p0.2 ≥ 640 MPa, A ≥ 12%, Z ≥ 50%, yield ratio ≥ 0.8; 9.8 level: R m ≥ 900 MPa, R p0.2 ≥ 720 MPa, A ≥ 10%, Z ≥ 48%, yield ratio ≥ 0.8), hardness HRC 26 - 33, and the axial fatigue cycle times under 100 KN load > 3 million times.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. By controlling Al / N = 10.0 - 13.0, the present invention ensures the solution of effective boron and the hardenability of the steel.

[0036] 2. By restricting the elements B, Al, Mn, and C, which have a significant impact on hardenability, in the W value formula, and stipulating that W = 29.3*(%B) + 11.7*(%Al) + 0.86*(%Mn) + 1.22*(%C) ≥ 1.60, the present invention further ensures that the steel has sufficient hardenability.

[0037] 3. By adding Mg and Pr to form a composite modifier for inclusions in the steel, the present invention improves the mechanical properties and fatigue life of the steel; and in order to ensure that the recovery rates of Pr and Mg alloys reach more than 80%, D value ≤ 0.07 is controlled, where D = 10.0*(%S) + 19.9*(%O).

[0038] 4. The manufacturing method of the cold heading steel provided by the present invention has low manufacturing cost, does not require spheroidizing annealing treatment, can be directly drawn and cold headed into fasteners with large deformation amounts, and after quenching and tempering heat treatment, the strength level of the fasteners reaches 8.8 - 9.8 levels, hardness HRC 26 - 33, and the axial fatigue life under 100 KN load > 3 million times. Description of the Drawings

[0039] Figure 1It is the metallographic structure diagram of the cold heading steel in Example 1, which is 80% ferrite + 20% degenerated pearlite structure;

[0040] Figure 2 It is the metallographic structure diagram of the cold heading steel in Comparative Example 1, which is 60% ferrite + 40% pearlite structure. Specific implementation manners

[0041] An anneal-free cold heading steel with high cold heading performance and high plasticity provided by the present invention, the cold heading steel with high cold heading performance and high plasticity contains by weight percentage: C 0.10% - 0.30%, Si ≤ 0.15%, Mn 0.60% - 0.90%, Al 0.060% - 0.080%, B 0.0035% - 0.0055%, Mg 0.0010% - 0.0030%, Pr 0.0040% - 0.0070%, P ≤ 0.015%, S ≤ 0.015%, O ≤ 0.0015%, N ≤ 0.007%, and the rest are Fe and other inevitable impurities;

[0042] Among them, Al / N = 10.0 - 13.0, which can give full play to the effective role of B in the steel;

[0043] The value of W ≥ 1.60, W = 29.3*(%B) + 11.7*(%Al) + 0.86*(%Mn) + 1.22*(%C), which can ensure the hardenability of the steel;

[0044] The value of D ≤ 0.07, Z = 10.0*(%S) + 19.9*(%O), which can ensure that the recovery rate of Pr and Mg alloys reaches more than 80%.

[0045] The manufacturing method of the anneal-free cold heading steel with high cold heading performance and high plasticity includes the following steps: hot metal pretreatment → converter / electric furnace smelting → LF furnace refining → bloom / billet continuous casting → bloom / billet heating → high-speed wire rod rolling → cooling by Stelmor cooling line → slow cooling in the insulation channel → hot rolled wire rod finished product.

[0046] The specifications of the hot rolled wire rod finished product are Φ6mm - Φ30mm.

[0047] In the converter smelting step: the converter end point C ≤ 0.10%, P ≤ 0.008%; slag blocking and tapping, strictly controlling the slag volume, the slag layer thickness of the ladle ≤ 100mm, and the tapping time ≥ 5min.

[0048] In the LF furnace refining step, the LF refining time ≥ 30min, and the white slag holding time ≥ 20min to ensure sufficient deoxidation, desulfurization and dephosphorization. After alloying, feed Mg wire, and the wire feeding speed is controlled at 30m / min - 40m / min.

[0049] In the continuous casting step of the billet / round billet, Pr wire is added to the center of the mold, and the wire feeding speed is controlled at 15 m / min to 30 m / min. In addition, the ratio of the wire feeding speed to the casting speed is maintained at 8 to 15.

[0050] In the heating step of the billet / round billet: the soaking temperature of the billet / round billet is controlled at 1000 to 1100 °C.

[0051] In the high-speed wire rod rolling step: the finishing rolling temperature is controlled at 800 °C to 850 °C, and the sizing temperature is controlled at 790 °C to 840 °C.

[0052] In the cooling step of the Stelmor cooling line: the laying temperature is controlled at 800 °C to 850 °C, the reference speed of the roller table is controlled at 0.10 m / s to 0.15 m / s, and the heat preservation cover is fully closed.

[0053] In the slow cooling step of the heat preservation channel: after exiting the Stelmor cooling line, it enters the heat preservation channel for slow cooling and further on-line softening, and the reference speed of the heat preservation channel is 0.15 m / s to 0.25 m / s.

[0054] The present invention will be described in detail below with reference to the embodiments.

[0055] The compositions and weight percentages of the steel grades used for the cold heading steel in each of the examples and comparative examples are shown in Table 1, and the balance is iron and unavoidable impurities.

[0056] Table 1

[0057]

[0058]

[0059] The production process parameters of the cold heading steel in each of the examples and comparative examples are shown in Table 2.

[0060] Table 2 Production process parameters

[0061]

[0062]

[0063]

[0064] The performance detection method of the hot-rolled wire rod is as follows:

[0065] Microstructure and ferrite grain size: Take a 15-mm-long specimen from the wire rod, polish the cross-section, etch it with 4% nitric acid alcohol, evaluate the microstructure according to GB / T 13298 "Test Methods for Metallographic Microstructure of Metals", and measure the average grain size according to GB / T 6394 "Determination Method for Average Grain Size of Metals".

[0066] Inclusion size measurement: The size of inclusions on the longitudinal surface of the steel was measured and statistically calculated using an ASPEX scanning electron microscope, and the detection area was 160 mm 2 .

[0067] Tensile properties in the hot-rolled state: A specimen with a length of 400 mm was taken from the wire rod for a tensile test to measure the R m , A, and Z values.

[0068] Hardness: Three-point hardness tests were carried out on the cross-section in accordance with GB / T 230.1 "Metallic materials - Rockwell hardness test - Part 1: Test method", and the average value was calculated.

[0069] Cold upsetting: The wire rod was cold upset according to the following requirements: X = h1 / h = 1 / 7; (where: h is the height of the specimen before cold upsetting (twice the wire rod diameter); h1 is the height of the specimen after cold upsetting.) After the cold upset test, no visible cracks, fissures, cracks, or hairline defects should appear on the surface of the specimen. For a group of 10 specimens, all being qualified is considered qualified; otherwise, the qualification rate is calculated.

[0070] The performance detection methods for fasteners are as follows:

[0071] Tensile properties and hardness of fasteners in the heat-treated state: Tensile properties and HRC hardness tests of fasteners were carried out in accordance with GB / T 3098.1 "Mechanical properties of fasteners - Bolts, screws and studs".

[0072] Fatigue test of fasteners: An axial fatigue test was carried out on an MTS fatigue testing machine, with axial stress control, a strain cycle characteristic of R = -1, a controlled load of 100 KN, a frequency of 10 Hz. A group consisted of 20 bolts, and if the number of cycles of 80% of the specimens exceeded 3 million times, the test was considered successful.

[0073] The properties of the cold heading steel hot-rolled wire rods prepared in each example and comparative example are shown in Table 3, and the quenching and tempering heat treatment processes and properties of the fasteners are shown in Table 4.

[0074] Table 3 List of performance detection of hot-rolled wire rods

[0075]

[0076]

[0077] Table 4 List of performance detection of examples and comparative examples of the present invention

[0078]

[0079]

[0080] The chemical compositions of the steel in Examples 1 to 8 and the manufacturing methods are properly controlled, and are applicable to the production of Φ6mm - Φ30mm hot-rolled wire rods in the as-rolled state without annealing. Their microstructure is ferrite + degenerated pearlite, with low strength and hardness, good plasticity, excellent cold heading performance, sufficient hardenability and high purity. They can be used to produce large-deformation fasteners that can be directly drawn and cold headed without spheroidizing annealing. After conventional quenching and tempering treatment, the strength grade of the fasteners is 8.8 - 9.8, and they have high fatigue performance.

[0081] Although the chemical compositions of Comparative Example 1 and Comparative Example 2 are within the required range, the production process control is improper. In Comparative Example 1, both the reducing and sizing temperature and the wire laying temperature are relatively high, and the roller table speed is too fast during subsequent cooling, resulting in more pearlite microstructure and no obvious degeneration. The obtained hot-rolled wire rods have too high hardness and strength, and cracking occurs during direct drawing and cold heading without annealing, and qualified bolts cannot be obtained. In Comparative Example 2, the feeding speeds of Mg wire and Pr wire, and the ratio of the feeding speed to the casting speed are all improperly controlled, resulting in low purity of the steel and low fatigue life of the fasteners. In Comparative Example 3, both the w(Al) / w(N) value and the hardenability index W value are improperly controlled, resulting in insufficient hardenability of the steel. The fasteners made cannot meet the requirements of 8.8 - 9.8 grade, and due to insufficient strength of the fastener products, the axial fatigue life is low under a load of 100KN. In Comparative Example 4, the D value is improperly controlled, resulting in low recovery rates of Pr and Mg alloys, and the purity of the steel does not meet the requirements, and the fatigue life of the fasteners made is low. Comparative Example 5 is the market-common 8.8-grade B-containing cold heading steel 10B21, which cannot be used to produce large-deformation fasteners without annealing, and cracking occurs during cold heading of the fasteners, and qualified bolts cannot be obtained.

[0082] The above detailed description of a non-annealing cold heading steel with high cold heading performance and high plasticity, its manufacturing method and fasteners with reference to the examples is illustrative rather than restrictive. Several examples can be listed according to the defined scope. Therefore, changes and modifications within the general concept of the present invention should fall within the protection scope of the present invention.

Claims

1. A cold heading steel with high cold heading performance and high plasticity that does not require annealing, characterized in that, The cold heading steel with high cold heading performance and high plasticity contains the following components by weight percentage: C 0.10% - 0.30%, Si ≤ 0.15%, Mn 0.60% - 0.90%, Al 0.060% - 0.080%, B 0.0035% - 0.0055%, Mg 0.0010% - 0.0030%, Pr 0.0040% - 0.0070%, P ≤ 0.015%, S ≤ 0.015%, O ≤ 0.0015%, N ≤ 0.007%, and the balance is Fe and other inevitable impurities; wherein, Al / N = 10.0 - 13.0; The value of W ≥ 1.60, and W = 29.3*(%B) + 11.7*(%Al) + 0.86*(%Mn) + 1.22*(%C); The value of D ≤ 0.07, and s = 10.0*(%S) + 19.9*(%O).

2. The cold-heading steel with high cold-heading performance and high plasticity without annealing according to claim 1, characterized in that, The metallographic structure of the cold heading steel with high cold heading performance and high plasticity and without annealing is ferrite + degenerated pearlite, wherein the volume percentage of the ferrite structure is 80% - 85%, the volume percentage of the degenerated pearlite structure is 15% - 20%, and the average ferrite grain size is 10μm - 13μm.

3. The cold heading steel with high cold heading performance and high plasticity without annealing according to claim 1, characterized in that The R of the cold-heading steel hot-rolled wire rod with high cold-heading performance and high plasticity without annealing m ≤ 480 MPa, Z ≥ 65%, A ≥ 30%, hardness ≤ 75 HRB; all the inclusions in the cold-heading steel are plastic inclusions, and the inclusion size is below 6.5 μm.

4. The cold-heading steel with high cold-heading performance and high plasticity without annealing according to claim 1, characterized in that The cold heading steel with high cold heading performance and high plasticity and without annealing reaches a strength level of 8.8 - 9.8 grades, a hardness of HRC 26 - 33, and an axial fatigue life of > 3 million times under a load of 100KN after quenching and tempering heat treatment.

5. The manufacturing method of the cold heading steel with high cold heading performance and high plasticity that does not require annealing according to any one of claims 1-4, characterized in that, The manufacturing method includes the following steps: hot metal pretreatment → converter / electric furnace smelting → LF furnace refining → bloom / round billet continuous casting → bloom / round billet heating → high-speed wire rod rolling → cooling by Stelmor cooling line → slow cooling in the insulation channel → finished hot-rolled wire rod.

6. The manufacturing method according to claim 5, characterized in that, In the converter smelting step: the C content at the end of the converter ≤ 0.10%, P ≤ 0.008%; slag is blocked during tapping, the thickness of the slag layer in the ladle ≤ 100mm, and the tapping time ≥ 5min.

7. The manufacturing method according to claim 5, characterized in that In the LF furnace refining step, the LF refining time ≥ 30min, and the white slag holding time ≥ 20min; Mg wire is fed after alloying, and the wire feeding speed is controlled at 30m / min - 40m / min.

8. The manufacturing method according to claim 5, characterized in that, In the bloom / round billet continuous casting step, Pr wire is added to the center of the mold, the wire feeding speed is controlled at 15m / min - 30m / min, and the ratio of the wire feeding speed to the casting speed is maintained at 8 - 15.

9. The manufacturing method according to claim 5, characterized in that, In the bloom / round billet heating step: the soaking temperature of the bloom / round billet is controlled at 1000 - 1100°C.

10. The manufacturing method according to claim 5, characterized in that, In the high-speed wire rod rolling step: the finish rolling temperature is controlled at 800°C - 850°C, and the sizing and reducing temperature is controlled at 790°C - 840°C.

11. The manufacturing method according to claim 5, characterized in that, In the cooling step by the Stelmor cooling line: the laying temperature is controlled at 800°C - 850°C, the reference speed of the roller table is controlled at 0.10m / s - 0.15m / s, and the insulation hood is fully closed.

12. The manufacturing method according to claim 5, characterized in that, In the slow cooling step in the insulation channel: the reference speed of the insulation channel is 0.15m / s - 0.25m / s.

13. A fastener, characterized in that, It is obtained by quenching and tempering heat treatment after drawing or cold heading using the cold heading steel with high cold heading performance and high plasticity described in any one of claims 1 - 4.

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