High-toughness threaded steel and hot-rolling method thereof

Abstract

The application provides a high-toughness screw thread steel and a hot rolling method thereof, and the application relates to the technical field of steel rolling, and specifically relates to a high-toughness screw thread steel and a hot rolling method thereof. The high-toughness screw thread steel is prepared by casting molten steel into a billet and hot rolling the billet, and the chemical components of the high-toughness screw thread steel, in percentage by mass, comprise the following components: C 0.22-0.27%, Si 0.27-0.32%, Mn 1.15-1.25%, V 0.01-0.02%, Ti 0.01-0.015%, Zr 0.01-0.015%, S 0.02-0.03%, N 0.015-0.020%, and the rest is Fe and other inevitable impurities. The high-toughness screw thread steel prepared by the hot rolling method has high strength and good toughness, and can meet the use requirements of the steel bar market.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hot rolling of threaded steel, in particular to a high-strength and high-toughness threaded steel and a hot rolling method thereof. BACKGROUND

[0002] As the most basic and important building material, the quality of steel bars determines the safety and service life of buildings. In addition, the demand for steel bars in the large-scale construction industry far exceeds that of other steel grades. Therefore, the high quality and economy of steel bar production are important issues in actual production of steel enterprises. At the same time, due to the increasing height of modern buildings, the increasing requirements for fire resistance and seismic performance, and other elements, higher requirements are put forward for the strength and toughness of steel bars. Especially after the new national standard is issued, threaded steel cannot be subjected to strong water penetration (i.e., the temperature of the steel bar is rapidly reduced to the tempering temperature by strong water penetration during the production of the steel bar), and the steel bar cannot be strengthened by self-tempering during the cooling process of the steel bar, because both methods will produce martensite structure on the outer layer of the steel bar, although the strength of the steel bar can be temporarily increased, but since the martensite is a "metastable structure", it will decompose during use, resulting in a decrease in the performance of the steel bar.

[0003] At present, steel bars are mainly micro-alloyed by adding a large amount of Nb and V alloys. The specific alloys used are vanadium-nitrogen, vanadium nitride iron, and niobium iron, but the price of Nb and V alloys is relatively high, which increases the production cost of threaded steel, which is not conducive to the cost reduction and profit increase of enterprises. Nb is easy to exist in the form of niobium block in steel, and the process of steel containing Nb is relatively complex. Reducing costs and designing new components have become the focus of related steel enterprises. In addition, in order to solve the problem that threaded steel cannot be water-penetrated and self-tempered to improve performance, a new rolling method needs to be developed. In summary, there is an urgent need for a high-strength and high-toughness threaded steel and a hot rolling method thereof to solve the problems in the related art. SUMMARY

[0004] The main purpose of the present application is to provide a high-strength and high-toughness threaded steel and a hot rolling method thereof, to solve at least one of the technical problems of high-priced alloy components and innovative rolling methods in the related art.

[0005] To achieve the above-mentioned purpose, the present application provides a hot rolling method of a high-strength and high-toughness threaded steel, comprising: casting molten steel into a billet, and hot rolling the billet into a high-strength and high-toughness threaded steel; the hot rolling comprises a heating section, a soaking section, and a rolling section; the temperature of the heating section is 1100-1400℃, and the time is 1-1.5h; the temperature of the soaking section is 1040-1050℃, and the time is 1-1.5h; the rolling section comprises a first rolling, a second rolling, and air cooling, which are sequentially performed on the billet;

[0006] The first rolling temperature is 950-970 DEG C, the deformation is 70-80%, the second rolling temperature is 850-900 DEG C, and the deformation is 60-70%;

[0007] The chemical composition of the high strength and toughness screw steel includes, in mass percentage, C 0.22-0.27%, Si 0.27-0.32%, Mn 1.15-1.25%, V 0.01-0.02%, Ti 0.01-0.02%, Zr 0.01-0.02%, S 0.02-0.03%, N 0.015-0.020%, and the rest is Fe and other inevitable impurities.

[0008] Further, the preparation step of the molten steel includes the step of adding sponge titanium and sponge zirconium to the initial molten steel when the molten steel temperature is 1590-1610 DEG C, the oxygen content is 120-150 ppm, and the nitrogen content is ≦80 ppm, and the reaction time is 8-10 min, and the initial molten steel composition is adjusted to the target composition.

[0009] Further, the adjustment of the initial molten steel composition to the target composition includes nitrogen composition adjustment, and the nitrogen composition adjustment is performed in the form of bottom blowing nitrogen: the bottom blowing argon is switched to nitrogen before tapping, the bottom blowing nitrogen flow is 5-10 NL / min / ton of steel, and the argon blowing time is controlled according to the following formula:

[0010] H 钢水深度 is the depth of the molten steel in the ladle, T 铁水温度 is the temperature of the molten iron in the ladle.

[0011] Further, the molten steel superheat during the tapping process is 30-50 DEG C, and the withdrawal speed is 3.0-3.2 m / min.

[0012] The application provides a high strength and toughness screw steel, which is rolled by the hot rolling method according to any one of the preceding claims, and the chemical composition of the high strength and toughness screw steel includes, in mass percentage, C 0.22-0.27%, Si 0.27-0.32%, Mn 1.15-1.25%, V 0.01-0.02%, Ti 0.01-0.02%, Zr 0.01-0.02%, S 0.02-0.03%, N 0.015-0.020%, and the rest is Fe and other inevitable impurities.

[0013] Further, the sum of the mass fractions of Ti and Zr in the high strength and toughness screw steel is less than or equal to 0.03%.

[0014] Further, the high strength and toughness screw steel contains coated composite particles, and the coated composite particles are formed by MnS wrapping Ti oxide and Zr oxide.

[0015] Further, the microstructure of the high-toughness threaded steel includes ferrite, pearlite and carbonitride, the ferrite containing 50-60% acicular ferrite.

[0016] Further, the carbonitride contains V, the carbonitride size is 20-50nm, and the number is 10 15 ~10 18 / m 3 .

[0017] Further, the yield strength of the high-toughness threaded steel is 620-650MPa, the tensile strength is 750-780MPa, and the elongation is 14%-16%.

[0018] The beneficial effects of the application include:

[0019] The application provides a high-toughness threaded steel composition and a hot rolling method thereof.

[0020] The high-toughness threaded steel provided by the application does not contain Nb in the chemical composition, and the content of V is low, which reduces the production cost of the high-toughness threaded steel, avoids the problem that the steel bar is prone to bainite in the use of Nb micro-alloying in the conventional technology, causes the yield platform of the steel bar to disappear, and affects the service performance of the steel bar, and effectively avoids the possibility that the performance of the steel is reduced due to the improper operation of the niobium in the form of blocks in the steel; at the same time, bainite belongs to a metastable state, which will decompose during use and affect the long-term service performance of the steel bar, and reducing the content of bainite can also improve the long-term service performance of the steel bar.

[0021] In the high-toughness threaded steel, appropriate amounts of Ti and Zr are added, and the N content in the steel is adaptively increased. Ti and Zr have a synergistic effect, and by controlling the appropriate amount of addition, the strength and toughness of the high-toughness threaded steel can be improved to meet the service requirements of the steel bar. In addition, vanadium in the steel is more likely to exist in the form of solid solution in the steel, and the conventional technology usually increases the precipitation amount of vanadium by increasing the vanadium content, which is contrary to the demand of reducing the production cost of the high-strength threaded steel, therefore, the nitrogen content in the steel is controlled to 0.015%-0.020% in the application, and increasing the nitrogen content can effectively promote the precipitation of the vanadium-containing second phase to make up for the strength weakening caused by the reduction of the vanadium content. Ti, Zr and N also have certain binding capacity, and the application creatively designs as follows: first, Ti and Zr are deoxidized and alloyed to make Ti and Zr fully combine with elements such as O, and then N is alloyed, which can effectively avoid the precipitation of large-size TiN and deteriorate the performance of the steel, so that more N combines with V to form VN precipitates.

[0022] The hot rolling method provided by the application controls the temperature of each stage of hot rolling and the deformation amount in the rolling process, so that the high-strength deformed steel still has high strength and toughness under the condition of low alloy elements (Nb, V), and since neither the strong water penetration process nor the steel bar self-tempering process is used in the whole hot rolling process, martensite is not generated on the outer layer of the high-strength deformed steel; and the low V content can also reduce the possibility of the appearance of bainite, so that the microstructure of the obtained high-strength deformed steel is ferrite, pearlite and carbonitride, which are stable in nature and difficult to decompose during use, and do not reduce the long-term use performance of the steel bar. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0024] It should be noted that all directional indications (such as up, down, etc.) in the embodiments of the application are only used to explain the relative position relationship, movement condition, etc. between components in a certain posture, and if the certain posture changes, the directional indications also change accordingly.

[0025] In addition, the description such as "first", "second" and the like in the application is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first", "second" can be explicitly or implicitly included at least one of the features.

[0026] In addition, the technical solutions of the various embodiments of the application can be combined with each other, but it must be based on the fact that a person skilled in the art can realize it, and when the combination of technical solutions appears to be contradictory or unachievable, it should be considered that the combination of technical solutions does not exist and is not within the protection scope of the application.

[0027] The application provides a high-strength and high-toughness deformed steel, and the chemical components of the high-strength and high-toughness deformed steel include, in percentage by mass: C 0.22-0.27%, Si 0.27-0.32%, Mn 1.15-1.25%, V 0.01-0.02%, Ti 0.01-0.015%, Zr 0.01-0.015%, S 0.02-0.03%, N 0.015-0.020%, and the rest is Fe and other inevitable impurities.

[0028] In the formula, the content of the alloying element V is 0.01-0.02%, the content of the alloying element Ti is 0.01-0.015%, the content of the alloying element Zr is 0.01-0.015%, the content of the alloying element S is 0.02-0.03%, and the content of the alloying element N is 0.015-0.020%.

[0029] Carbon (C): Carbon is the main reinforcing element in deformed steel, carbon atoms can be dissolved in the iron matrix to form a solid solution, thereby enhancing the matrix strength, with the increase of carbon content, the strength and hardness of steel can be improved, but at the same time, the plasticity and toughness of the steel will be reduced, too high will lead to deformed steel prone to fracture or crack. In addition, too high carbon content will also reduce the welding performance of deformed steel. Therefore, considering the use scene of deformed steel, high strength, high toughness, high hardness and good welding performance are required, and the carbon content in the application is controlled at 0.22-0.27wt%.

[0030] Silicon (Si): Silicon is an important alloying element, which can form a stable oxide film layer in steel, effectively reducing the oxidation reaction of the matrix with air or moisture, improving the corrosion resistance of deformed steel, and too high silicon content will reduce the welding performance of deformed steel, therefore, the silicon content in the application is controlled at 0.27-0.32%.

[0031] Vanadium (V): Vanadium is an important micro-alloying element, which can significantly improve the welding performance of ordinary low-carbon low-alloy steel, and the carbide formed by vanadium and carbon in deformed steel can improve the hydrogen corrosion resistance of steel at high temperature and high pressure, and also can improve the elasticity, strength and wear resistance and burst resistance of steel, but with the increase of the amount of steel bar, the price of vanadium rises greatly, leading to the continuous rise of the production cost of steel bar, and the use amount of vanadium needs to be reduced, therefore, the vanadium content in the application is controlled at 0.01-0.02%.

[0032] Titanium (Ti): Titanium has strong affinity with nitrogen, oxygen, carbon and sulfur, and its affinity with sulfur is stronger than that with iron, which is a good deoxidizing and degassing agent and an effective element for fixing nitrogen and carbon. Titanium-containing oxysulfide is easily formed in steel, which can be used as nucleation sites for intracrystalline ferrite, and can refine the intracrystalline substructure. Although titanium is a strong carbide-forming element, it does not form complex compounds with other elements. Titanium carbide has strong binding force and is stable and not easy to decompose. It can only slowly dissolve into the solid solution in steel when heated to above 1000℃. In addition, as a ferrite stabilizing element, the addition of trace titanium in steel can greatly improve the stability of ferrite in steel.

[0033] Zirconium (Zr): Similar to titanium, zirconium has strong affinity with nitrogen, oxygen, carbon and sulfur, and its affinity with sulfur is stronger than that with iron. Titanium-containing oxysulfide is easily formed in steel, which can be used as nucleation sites for intracrystalline ferrite, and can refine the intracrystalline substructure. Titanium and zirconium-containing oxysulfide has a small lattice mismatch with ferrite, which is more conducive to the formation of intracrystalline ferrite. Zirconium is also a strong carbide-forming element, and the addition of a small amount of zirconium in steel has the effects of degassing, purification and grain refinement, which is beneficial to the low-temperature performance of steel and improves the stamping performance.

[0034] The high-strength and high-toughness rebar provided by this invention does not contain Nb in its chemical composition, has a low V content, and adds appropriate amounts of Ti and Zr. This reduces the production cost of high-strength and high-toughness rebar while avoiding the problem of bainite formation in the rebar during Nb microalloying in conventional technologies, which leads to the disappearance of the yield plateau and affects the rebar's performance. Furthermore, bainite is a metastable structure that decomposes during use, affecting the long-term performance of the rebar; reducing the bainite content also improves the long-term performance. Additionally, Ti and Zr have a synergistic effect; by controlling the appropriate addition amount, the strength and toughness of the high-strength and high-toughness rebar can be improved, meeting the market demands for rebar.

[0035] In some embodiments, the sum of the mass fractions of Ti and Zr in the high-strength and high-toughness rebar is less than or equal to 0.03%.

[0036] In some embodiments, the high-strength and high-toughness rebar contains coated composite particles, which are formed by MnS encapsulating Ti oxides and Zr oxides, which can effectively promote the nucleation of intragranular ferrite and refine the intragranular substructure.

[0037] In some embodiments, the microstructure of the high-strength and high-toughness rebar includes ferrite, pearlite, and carbonitrides.

[0038] In some embodiments, the ferrite contains 50-60% acicular ferrite.

[0039] Acicular ferrite contains finer ferrite particles with a larger phase interface area. Compared to ordinary ferrite, it more effectively improves the yield strength and tensile strength of rebar. Acicular ferrite can also effectively absorb and disperse impact energy, thus giving rebar better toughness and reducing the risk of brittle fracture. When using microalloying to reduce the addition of Nb and V alloys to lower costs, increasing the content of acicular ferrite in the ferrite can effectively maintain the performance of rebar.

[0040] In some embodiments, the carbonitride contains V, the carbonitride size is 20–50 nm, and the number is 10. 15 ~10 18 pcs / m 3 .

[0041] In some embodiments, the high-strength and high-toughness rebar has a yield strength of 620–650 MPa, a tensile strength of 750–780 MPa, and an elongation of 14%–16%.

[0042] The application further provides a hot rolling method for preparing the high-toughness threaded steel, which comprises the following steps: casting the molten steel into a billet, and hot rolling the billet into the high-toughness threaded steel; the hot rolling comprises a heating section, a soaking section and a rolling section; the temperature of the heating section is 1100-1400 ℃, and the time is 1-1.5 h; the temperature of the soaking section is 1040-1050 ℃, and the time is 1-1.5 h; the rolling section comprises first rolling, second rolling and air cooling which are sequentially performed on the billet, wherein the first rolling temperature is 950-970 ℃, and the deformation is 70-80 %; the second rolling temperature is 850-900 ℃, and the deformation is 60-70 %; and the high-toughness threaded steel has the same chemical composition as the high-toughness threaded steel.

[0043] The hot rolling method provided by the application controls the temperature of each stage of the hot rolling and the deformation in the rolling process, so that the threaded steel has high strength and toughness even if the content of alloy elements (Nb and V) is low, and the threaded steel does not have martensite (which belongs to a metastable structure and is decomposed in use, thereby reducing the long-term performance of the threaded steel) on the outer layer of the threaded steel because neither the strong water penetration process nor the steel bar self-tempering process is used in the whole hot rolling process; and the low content of V can reduce the possibility of the appearance of bainite, so that the microstructure of the obtained threaded steel is ferrite, pearlite and carbonitride, which are stable in nature and difficult to be decomposed in use, thereby not reducing the long-term performance of the threaded steel.

[0044] In some embodiments, the preparation step of the molten steel comprises adding sponge titanium and sponge zirconium into the initial molten steel when the temperature of the molten steel is 1590-1610 ℃, the oxygen content is 120-150 ppm, and the nitrogen content is ≤80 ppm, the reaction time is 8-10 min, and the initial molten steel composition is adjusted to the target composition to obtain the molten steel.

[0045] The temperature of the molten steel is 1590-1610 ℃, and the oxygen content is 120-150 ppm to generate zirconium titanium oxide.

[0046] Because titanium is easy to combine with nitrogen in the solidification process, the nitrogen content is limited to not higher than 80 ppm to avoid the precipitation of large-size TiN and the deterioration of the performance of the steel.

[0047] It should be noted that the nitrogen content is adjusted by using the bottom blowing nitrogen gas method.

[0048] Further, the sponge titanium is a porous titanium metal material. The sponge titanium is generally light gray and in the form of granules, and the surface is clean without visible inclusions. The purity (mass) of the sponge titanium is generally 99.1-99.7 %, the total amount of impurity elements (mass) is 0.3-0.9 %, the oxygen content (mass) of the impurity elements is 0.06-0.20 %, and the hardness (HB) is 100-157.

[0049] Further, sponge zirconium is a silver gray metal, appearance similar to steel, luster, melting point of 1852 ℃, density of 6.49 g / cm 3 It has strong affinity for oxygen, and can absorb a large amount of oxygen, hydrogen, nitrogen and other gases when heated.

[0050] In some embodiments, the molten steel overheating degree in the tapping process is 30-50 ℃, and the withdrawal speed is 3.0-3.2 m / min.

[0051] Embodiments

[0052] The following examples more specifically describe the present disclosure, which are only used for illustrative purposes, because various modifications and changes within the scope of the present disclosure are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used directly without further treatment, and the instruments used in the examples are commercially available.

[0053] Embodiment 1: A hot rolling method for preparing the above-mentioned high-toughness threaded steel, comprising: in the LF furnace smelting process, when the molten steel temperature is 1590 ℃, the oxygen content is 150 ppm, and the nitrogen content is 70 ppm, adding sponge titanium and sponge zirconium to the initial molten steel, the reaction time is 8 min, and the initial molten steel composition is adjusted to the target composition to obtain the molten steel, which comprises, in mass percentage: C 0.22%, Si 0.32%, Mn 1.25%, V 0.01%, Ti 0.01%, Zr 0.02%, S 0.02%, N 0.015%, and the balance of Fe and other unavoidable impurities. The adjustment of the nitrogen composition in the molten steel is carried out in the form of bottom blowing nitrogen, the bottom blowing argon is switched to nitrogen before tapping, the bottom blowing nitrogen flow is 6 NL / min / ton of steel, and the argon blowing time is 9 min (H 钢水深度 is 3.3 m, T 铁水温度 is 1593 ℃).

[0054] The molten steel is cast into a billet, and the billet is hot rolled into a high-toughness threaded steel; the hot rolling comprises a heating section, a soaking section, and a rolling section; the heating section temperature is 1400 ℃, and the time is 1 h; the soaking section temperature is 1050 ℃, and the time is 1 h; the rolling section comprises first rolling, second rolling, and air cooling which are sequentially performed on the billet, wherein the first rolling temperature is 970 ℃, the deformation is 80%, the second rolling temperature is 850 ℃, and the deformation is 60%; the chemical composition of the high-toughness threaded steel is the same as that of the above-mentioned high-toughness threaded steel.

[0055] Embodiment 2: a hot rolling method for preparing the high-toughness threaded steel, comprising: in the LF furnace smelting process, when the temperature of the molten steel is 1610℃, the oxygen content is 120ppm, and the nitrogen content is 68ppm, adding sponge titanium and sponge zirconium into the initial molten steel, the reaction time is 10min, the initial molten steel composition is adjusted to the target composition, and the molten steel obtained comprises, in mass percentage: C 0.27%, Si 0.27%, Mn 1.15%, V 0.02%, Ti 0.02%, Zr 0.01%, S 0.03%, N 0.020%, and the balance of Fe and other inevitable impurities. The adjustment of the nitrogen composition in the molten steel is performed in the form of bottom blowing nitrogen, the bottom blowing argon is switched to nitrogen before tapping, the bottom blowing nitrogen flow is 5NL / min / ton of steel, and the argon blowing time is 8.6min (H 钢水深度 is 3.4m, and T 铁水温度 is 1611℃.

[0056] The molten steel is cast into a billet, and the billet is hot rolled into the high-toughness threaded steel; the hot rolling comprises a heating section, a soaking section, and a rolling section; the temperature of the heating section is 1100℃, and the time is 1.5h; the temperature of the soaking section is 1040℃, and the time is 1.5h; the rolling section comprises first rolling, second rolling, and air cooling performed on the billet in sequence, wherein the first rolling temperature is 950℃, the deformation is 70%, the second rolling temperature is 900℃, and the deformation is 70%; the chemical composition of the high-toughness threaded steel is the same as that of the high-toughness threaded steel.

[0057] Embodiment 3: a hot rolling method for preparing the high-toughness threaded steel, comprising: in the LF furnace smelting process, when the temperature of the initial molten steel is 1600℃, the oxygen content is 140ppm, and the nitrogen content is 80ppm, adding sponge titanium and sponge zirconium into the initial molten steel, the reaction time is 9min, the initial molten steel composition is adjusted to the target composition, and the molten steel obtained comprises, in mass percentage: C 0.25%, Si 0.30%, Mn 1.18%, V 0.015%, Ti 0.016%, Zr 0.012%, S 0.025%, N 0.018%, and the balance of Fe and other inevitable impurities. The adjustment of the nitrogen composition in the molten steel is performed in the form of bottom blowing nitrogen, the bottom blowing argon is switched to nitrogen before tapping, the bottom blowing nitrogen flow is 10NL / min / ton of steel, and the argon blowing time is 5.2min. H 钢水深度 is 3.35m, and T 铁水温度 is 1598℃.

[0058] The molten steel is cast into billets, and the billets are hot-rolled into high-toughness threaded steel; the hot-rolling comprises a heating section, a soaking section and a rolling section; the temperature of the heating section is 1320 DEG C, and the time is 1.1 h; the temperature of the soaking section is 1045 DEG C, and the time is 1.1 h; the rolling section comprises first rolling, second rolling and air cooling which are sequentially performed on the billets, wherein the first rolling temperature is 960 DEG C, the deformation is 75%, the second rolling temperature is 880 DEG C, and the deformation is 64%; the chemical composition of the high-toughness threaded steel is the same as that of the above high-toughness threaded steel.

[0059] The threaded steel prepared in examples 1-3 is subjected to performance test, and the performance experiment comprises tensile test according to GB / T228.1-2010 and impact test according to GB / T 229-2007, and the test results are shown in table 1: 620-650 MPa, tensile strength is 750-780 MPa, and elongation is 14%-16%.

[0060] Table 1: performance test results of threaded steel prepared in examples 1-3

[0061]

[0062]

[0063] The above technical scheme of the present application, the above is only the preferred embodiment of the present application, not therefore limit the patent range of the present application, all in the technical concept of the present application, utilize the present application specification and the equivalent structure transformation of drawing contents, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A hot rolling method of high-toughness threaded steel, characterized by, The application relates to a high-toughness screw steel, and a preparation method thereof. The molten steel is cast into a steel billet, and the steel billet is hot-rolled into the high-toughness screw steel; the hot-rolling comprises a heating section, a soaking section and a rolling section; the temperature of the heating section is 1100-1400 DEG C, and the time is 1-1.5 h; the temperature of the soaking section is 1040-1050 DEG C, and the time is 1-1.5 h; the rolling section comprises a first rolling, a second rolling and air cooling which are sequentially performed on the steel billet; The temperature of the first rolling is 950-970 DEG C, and the deformation is 70-80%; the temperature of the second rolling is 850-900 DEG C, and the deformation is 60-70%. The chemical composition of the high-toughness screw steel comprises, in mass percentage, C 0.22-0.27%, Si 0.27-0.32%, Mn 1.15-1.25%, V 0.01-0.02%, Ti 0.01-0.02%, Zr 0.01-0.02%, S 0.02-0.03%, N 0.015-0.020%, and the rest is Fe and other inevitable impurities.

2. The hot rolling method according to claim 1, characterized by, The preparation step of the molten steel comprises the following steps: when the temperature of the molten steel is 1590-1610 DEG C, the oxygen content is 120-150 ppm, and the nitrogen content is <=80 ppm, sponge titanium and sponge zirconium are added into initial molten steel, the reaction time is 8-10 min, and the initial molten steel composition is adjusted to the target composition.

3. The hot rolling method according to claim 2, characterized by, The adjusting of the initial molten steel composition to the target composition includes nitrogen composition adjustment, which is performed by bottom blowing nitrogen gas: switching from bottom blowing argon to nitrogen before tapping, the bottom blowing nitrogen flow rate is 5-10 NL / min / ton of steel, and the blowing argon time is controlled according to the following formula: where H 钢水深度 is the depth of the liquid steel in the ladle, T 铁水温度 is the temperature of the liquid iron in the ladle.

4. The hot rolling method according to claim 3, characterized by The superheat of the molten steel in the tapping process is 30-50 DEG C, and the pulling speed is 3.0-3.2 m / min.

5. A high-toughness threaded steel bar, characterized by, The high-toughness screw steel prepared by the hot-rolling method in any one of claims 1-4 comprises, in mass percentage, C 0.22-0.27%, Si 0.27-0.32%, Mn 1.15-1.25%, V 0.01-0.02%, Ti 0.01-0.02%, Zr 0.01-0.02%, S 0.02-0.03%, N 0.015-0.020%, and the rest is Fe and other inevitable impurities.

6. The high-ductility threaded rod of claim 5, wherein, The sum of the mass fractions of Ti and Zr in the high-toughness screw steel is less than or equal to 0.03%.

7. The high-ductility threaded rod of claim 5, wherein, The high-toughness screw steel contains coated composite particles formed by MnS wrapping Ti oxide and Zr oxide.

8. The high-ductility threaded rod of claim 5, wherein, The microstructure of the high-toughness screw steel comprises ferrite, pearlite and carbonitride, and the ferrite contains 50-60% acicular ferrite.

9. The high-ductility threaded rod of claim 8, wherein, The carbonitride contains V, the carbonitride size is 20-50 nm, and the number is 10 15 ~10 18 / m 3 .

10. The high-ductility threaded steel rod of any one of claims 5-9, wherein, The yield strength of the high-toughness screw steel is 620-650 MPa, the tensile strength is 750-780 MPa, and the elongation is 14-16%.

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