Method for preparing threaded steel and threaded steel prepared therefrom

Abstract

The present invention provides a method for preparing threaded steel and the threaded steel prepared therefrom, relating to the field of metallurgy. The preparation method comprises: 1) converter smelting, wherein the element content of the steel tapped from the converter is controlled; 2) continuous casting, wherein the molten steel smelted in the converter is cast into a billet; 3) rolling, wherein the billet is heated and then held at a temperature of 0.6-0.88 MPa and rolled into a steel bar; 4) after the rolling process, a water cooling treatment is performed, wherein the water pressure of the water cooling is 0.6-0.88 MPa and the cooling time is 15-30 seconds; and 5) a high-frequency induction heating treatment is performed on the threaded steel after the water cooling, wherein the high-frequency induction frequency is controlled to 150-250 kHz and the holding time is 0.02-0.05 seconds. The present invention effectively improves the performance of the threaded steel and reduces production costs; can effectively eliminate closed-loop martensite, and at the same time improves the oxidation resistance of the threaded steel.

Description

Technical Field

[0001] The present invention relates to the technical field of metallurgy, and in particular to a method for preparing threaded steel and the threaded steel prepared therefrom. Background Art

[0002] Rebar is a widely used steel material in construction projects, and its performance directly determines the safety and service life of building structures. Traditional rebar production processes typically enhance strength and toughness by adding large amounts of alloying elements (such as manganese, vanadium, and niobium). However, this approach results in low resource utilization and high production costs, which is inconsistent with the green and low-carbon development requirements of the steel industry.

[0003] In its production process, the ingot is generally heated to 1100~1250℃, and after multiple rolling passes, the cross-section of the ingot is gradually reduced. The rebar after finish rolling passes through a water cooling device, and the surface is quickly cooled by high-pressure water, so that the temperature difference between the surface and the interior forms a different organizational structure. The surface is quickly cooled, and tempered martensite is formed on the surface to improve the strength. The core part is slowly cooled to form a ferrite plus pearlite structure to ensure plasticity and toughness.

[0004] The new national standard GB / T1499.2-2024 requires that the metallographic structure of rebar be primarily ferrite plus pearlite, with no tempered martensite present in the base circle. After water penetration, rebar tends to develop closed martensite within 1 mm of the surface. This structure, commonly known as the "black circle," is noticeably darker than the base structure during metallographic examination. To improve the pass rate of rebar metallographic inspection, current production processes generally utilize weak or no water penetration, while also increasing the alloying element content to enhance rebar strength. This results in increased alloy usage and higher production costs.

[0005] Therefore, it is necessary to add a small amount of alloying elements or no alloying elements and control the preparation process to obtain products whose performance and metallographic structure meet the requirements of national standards, thereby reducing alloy costs and improving product market competitiveness. Summary of the Invention

[0006] In order to solve the technical problems existing in the prior art, the embodiment of the present invention provides a method for preparing threaded steel and the threaded steel prepared therefrom. The technical solution is as follows:

[0007] A method for preparing threaded steel comprises the following steps:

[0008] 1) Converter smelting, in which the element content of converter steel is controlled;

[0009] 2) Continuous casting, in which molten steel from a converter is cast into billets;

[0010] 3) rolling, wherein the billet is heated and then kept warm, and then rolled into steel bars;

[0011] 4) After the rolling process, a water cooling treatment is performed, wherein the water pressure of the water cooling is 0.6-0.88 MPa and the cooling time is 15-30 seconds;

[0012] 5) The threaded steel bar that has been water-cooled is subjected to high-frequency induction heating treatment, wherein the high-frequency induction frequency is controlled to be 150-250 kHz, the holding time is 0.02-0.05 seconds, and the current density of the high-frequency induction heating treatment is 1×10 7 -1.3×10 7 A / m 2 .

[0013] Optionally, the method further comprises the following steps:

[0014] 6) After the high-frequency induction heating treatment, the rebar is air-cooled to room temperature.

[0015] Optionally, the composition of the threaded steel includes, in mass %, C 0.2-0.24%, Si 0.35-0.62%, Mn 0.65-0.95%, P≤0.03%, S≤0.03%, and the balance is Fe and unavoidable impurities.

[0016] Optionally, in step 2), the casting speed is controlled to be 1.3-1.7 m / min during the process of casting the molten steel smelted in the converter into billets.

[0017] Optionally, in step 3), the rolling process includes: heating the billet to 1100-1200° C., keeping the temperature for 50-70 minutes, and then rolling the billet into a steel bar with a diameter of 16-22 mm;

[0018] And / or, the square billet is rolled into a steel bar with a diameter of 16-22 mm through rough rolling, intermediate rolling and finish rolling.

[0019] Optionally, the threaded steel produced according to the production method does not contain the alloying elements manganese, vanadium and / or niobium.

[0020] The threaded steel prepared according to the preparation method has a lower yield strength of 410 MPa or more and a tensile strength of 550 MPa or more.

[0021] Optionally, the elongation after fracture of the threaded steel bar is greater than 19.5%.

[0022] Optionally, the red rust area of the threaded steel bar is ≤1% after being placed in the open air for 15 days.

[0023] Optionally, the rebar does not contain the alloying elements manganese, vanadium and / or niobium.

[0024] The beneficial effects brought about by the technical solution provided by the embodiment of the present invention include at least:

[0025] The technical solution of the present invention creatively proposes that, through the combination of water cooling + high-frequency induction heating, on the one hand, the technical advantage of water cooling to improve strength and ensure plasticity and toughness can be effectively utilized, and on the other hand, the closed-loop martensite formed by water cooling can be effectively eliminated. On this basis, it is particularly important to control the parameters of water cooling and high-frequency induction heating. In the present invention, the water pressure of water cooling is 0.6-0.88 MPa, and the cooling time is 15-30 seconds. The closed-loop martensite formed is formed within 1 mm from the surface of the substrate. Based on this, in order to eliminate the closed-loop martensite while preventing changes in the internal organizational structure and surface grain growth, the adapted high-frequency induction heating parameters should be a high-frequency induction frequency of 150-250 kHz and a holding time of 0.02-0.05 seconds. A frequency that is too low will cause the internal organization to change due to heat, affecting the internal quality and performance of the rebar. A frequency that is too high will cause the magnetic field penetration ability to decrease, and the heating energy will be overly concentrated on the surface, making it impossible to completely eliminate the "black circle"; a holding time that is too short cannot guarantee the elimination of the closed-loop martensite. A holding time that is too long will affect the progress of the subsequent rolling process on the one hand, and on the other hand, it will cause grain growth that affects the toughness and plasticity of the substrate.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This invention uses a combined process of water cooling and high-frequency induction heating to effectively improve the performance (strength, toughness, and plasticity) of rebar, thereby effectively reducing the amount of alloy elements added and lowering production costs.

[0028] 2. The present invention can effectively eliminate closed-loop martensite by selecting appropriate high-frequency induction heating parameters, while forming a dense oxide layer on the surface of the rebar, thereby improving the oxidation resistance of the rebar. DETAILED DESCRIPTION

[0029] The following will be a clear and complete description of the technical solutions in the embodiments. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] In order to solve the problems existing in the prior art, the present invention provides a threaded steel and a preparation method thereof, aiming to improve the performance of the threaded steel and reduce the production cost by reducing the amount of alloy used and combining special heat treatment.

[0031] In the present invention, water cooling refers to the rapid cooling of rebar by immersion in water after finish rolling. The water cooling process is a commonly used and effective controlled cooling method in the prior art to improve the structure and performance of bar materials.

[0032] In the present invention, high-frequency induction heating treatment refers to a process of using heat energy generated by high-frequency electromagnetic waves to heat the surface of threaded steel to transform its structure.

[0033] One aspect of the present invention provides a method for preparing threaded steel, comprising the following steps:

[0034] 1) After the rebar undergoes the rolling process, a water cooling process is performed, wherein the water pressure of the water cooling is 0.6-0.88 MPa and the cooling time is 15-30 seconds;

[0035] 2) The threaded steel bar that has been water-cooled is subjected to high-frequency induction heating treatment, wherein the high-frequency induction frequency is controlled to be 150-250 kHz and the holding time is 0.02-0.05 seconds.

[0036] As a preferred embodiment of the method for preparing threaded steel of the present invention, the current density of the high frequency induction heating is 1×10 7 -1.3×10 7 A / m 2 .

[0037] As a preferred embodiment of the method for preparing threaded steel of the present invention, the method further comprises the step of air cooling to room temperature after the high-frequency induction heating treatment.

[0038] As a preferred embodiment of a method for preparing threaded steel of the present invention, the composition of the threaded steel includes, by mass, C 0.2-0.24%, Si 0.35-0.62%, Mn 0.65-0.95%, P≤0.03%, S≤0.03%, and the balance is Fe and unavoidable impurities.

[0039] As a preferred embodiment of the method for preparing threaded steel of the present invention, the method further comprises:

[0040] The step of casting the molten steel smelted in the converter into a square billet, wherein the drawing speed is controlled to be 1.3-1.7m / min; the rolling process specifically includes: heating the square billet to 1100-1200℃, keeping it warm for 50-70min, and then using a rolling mill to roll the rebar into a steel bar with a diameter of 16-22mm.

[0041] Another aspect of the present invention provides a threaded steel bar prepared by the aforementioned method, wherein the threaded steel bar has a lower yield strength of 410 MPa or more, a tensile strength of 550 MPa or more, an elongation after fracture of 19.5% or more, and a red rust area of ≤1% after being placed in the open air for 15 days.

[0042] In the following embodiments, water cooling can be achieved by, for example, the SHM series water cooling device manufactured by Shenyang Heavy Machinery Co., Ltd. High-frequency induction heating can be achieved by, for example, the IEE-S2000 series high-frequency induction heating system manufactured by the Institute of Electrical Engineering, Chinese Academy of Sciences.

[0043] In the following examples, the determination of lower yield strength, tensile strength, elongation after fracture, etc. is carried out with reference to GB / T1499.2-2024.

[0044] Example 1

[0045] A method for preparing 16mm HRB400E rebar, wherein the rebar composition, by mass, is 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, and 0.02% S, with the balance being Fe and unavoidable impurities. The method comprises the following steps:

[0046] 1) Converter smelting, control the element content of converter steel to meet the above requirements;

[0047] 2) Continuous casting: pouring molten steel into 150mm×150mm billets at a casting speed of 1.6m / min;

[0048] 3) Rolling: The billet is heated to 1150°C and kept at this temperature for 60 minutes, and then subjected to two passes of rough rolling, two passes of intermediate rolling, and three passes of finish rolling to form a steel bar with a diameter of 16 mm.

[0049] 4) Water cooling: The steel bars are cooled by water with a water pressure of 0.6 MPa and a cooling time of 15 seconds;

[0050] 5) High-frequency induction heating: The cooled steel bars are subjected to high-frequency induction heating. The frequency of high-frequency induction is 200kHz and the current density is 1.0×10 7 A / m 2 , the holding time is 0.02 seconds;

[0051] 6) Air cool the steel bars after high-frequency induction heating to room temperature.

[0052] Experimental results:

[0053] After testing, the surface structure of the threaded steel obtained in this embodiment showed no closed-loop martensite, a lower yield strength of 410 MPa, a tensile strength of 553 MPa, an elongation after fracture of 22.39%, and a red rust area of 1% after being placed in the open air for 15 days.

[0054] Example 2

[0055] A method for preparing 20mm HRB500E threaded steel, wherein the threaded steel comprises, by mass, 0.24% C, 0.62% Si, 0.95% Mn, 0.025% P, and 0.021% S, with the remainder being Fe and unavoidable impurities. The method comprises the following steps:

[0056] 1) Converter smelting, control the element content of converter steel to meet the above requirements;

[0057] 2) Continuous casting: pouring molten steel into 150mm×150mm billets at a casting speed of 1.6m / min;

[0058] 3) Rolling: The billet is heated to 1180°C and kept at this temperature for 60 minutes, and then subjected to 2 passes of rough rolling, 2 passes of intermediate rolling, and 3 passes of finish rolling to form a steel bar with a diameter of 20 mm;

[0059] 4) Water cooling: The steel bars are cooled by water with a water pressure of 0.6 MPa and a cooling time of 20 seconds;

[0060] 5) High-frequency induction heating: The cooled steel bars are subjected to high-frequency induction heating. The frequency of high-frequency induction is 200kHz and the current density is 1.2×10 7 A / m 2 , the holding time is 0.02 seconds;

[0061] 6) Air-cool the steel bars after high-frequency induction heating to room temperature.

[0062] Experimental results:

[0063] After testing, the surface structure of the threaded steel obtained in this embodiment showed no closed-loop martensite, a lower yield strength of 512 MPa, a tensile strength of 653 MPa, an elongation after fracture of 20.73%, and a red rust area of 0.95% after being placed in the open air for 15 days.

[0064] Example 3

[0065] A method for preparing threaded steel, wherein the threaded steel comprises, by mass, 0.24% C, 0.62% Si, 0.95% Mn, 0.025% P, and 0.021% S, with the remainder being Fe and unavoidable impurities. The method comprises the following steps:

[0066] 1) Converter smelting, control the element content of converter steel to meet the above requirements;

[0067] 2) Continuous casting: pouring molten steel into 150mm×150mm billets at a casting speed of 1.6m / min;

[0068] 3) Rolling: The billet is heated to 1180°C and kept at this temperature for 60 minutes, and then subjected to 2 passes of rough rolling, 2 passes of intermediate rolling, and 3 passes of finish rolling to form a steel bar with a diameter of 20 mm;

[0069] 4) Water cooling: The steel bars are cooled by water with a water pressure of 0.8 MPa and a cooling time of 15 seconds;

[0070] 5) High-frequency induction heating: The cooled steel bars are subjected to high-frequency induction heating. The frequency of high-frequency induction is 250kHz and the current density is 1.3×10 7 A / m 2 , the holding time is 0.02 seconds;

[0071] 6) Air-cool the steel bars after high-frequency induction heating to room temperature.

[0072] Experimental results:

[0073] After testing, the threaded steel obtained in this embodiment has a lower yield strength of 515 MPa, a tensile strength of 648 MPa, an elongation after fracture of 19.85%, and a red rust area of 0.9% after being placed in the open air for 15 days.

[0074] Comparative Example 1

[0075] A method for preparing 16mm HRB400E rebar, wherein the rebar composition, by mass, is 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, and 0.02% S, with the balance being Fe and unavoidable impurities. The method comprises the following steps:

[0076] 1) Converter smelting, control the element content of converter steel to meet the above requirements;

[0077] 2) Continuous casting: pouring molten steel into 150mm×150mm billets at a casting speed of 1.6m / min;

[0078] 3) Rolling: The billet is heated to 1150°C and kept at this temperature for 60 minutes, and then subjected to two passes of rough rolling, two passes of intermediate rolling, and three passes of finish rolling to form a steel bar with a diameter of 16 mm.

[0079] 4) Water cooling: The steel bars are cooled through water with a water pressure of 0.6 MPa and a cooling time of 15 seconds.

[0080] Experimental results:

[0081] After testing, the surface structure of the rebar obtained in this comparative example showed closed-loop martensite, with a lower yield strength of 385 MPa, a tensile strength of 501 MPa, an elongation after fracture of 16.25%, and a red rust area of 1.5% after being placed in the open air for 15 days.

[0082] Comparative Example 2

[0083] A method for preparing 20mm HRB500E threaded steel, wherein the threaded steel comprises, by mass, 0.24% C, 0.62% Si, 0.95% Mn, 0.025% P, and 0.021% S, with the remainder being Fe and unavoidable impurities. The method comprises the following steps:

[0084] 1) Converter smelting, control the element content of converter steel to meet the above requirements;

[0085] 2) Continuous casting: pouring molten steel into 150mm×150mm billets at a casting speed of 1.6m / min;

[0086] 3) Rolling: The billet is heated to 1180°C and kept at this temperature for 60 minutes, and then subjected to 2 passes of rough rolling, 2 passes of intermediate rolling, and 3 passes of finish rolling to form a steel bar with a diameter of 20 mm;

[0087] 4) Water cooling: The steel bars are subjected to water cooling treatment with a cooling water pressure of 0.6 MPa and a cooling time of 20 seconds.

[0088] Experimental results:

[0089] After testing, the surface structure of the threaded steel obtained in this embodiment has closed-loop martensite, a lower yield strength of 485 MPa, a tensile strength of 556 MPa, an elongation after fracture of 13.64%, and a red rust area of 1.9% after being placed in the open air for 15 days.

[0090] Comparative Example 3

[0091] A method for preparing 16mm HRB400E rebar, wherein the rebar composition, by mass, is 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, and 0.02% S, with the balance being Fe and unavoidable impurities. The method comprises the following steps:

[0092] 1) Converter smelting, control the element content of converter steel to meet the above requirements;

[0093] 2) Continuous casting: pouring molten steel into 150mm×150mm billets at a casting speed of 1.6m / min;

[0094] 3) Rolling: The billet is heated to 1150°C and kept at this temperature for 60 minutes, and then subjected to two passes of rough rolling, two passes of intermediate rolling, and three passes of finish rolling to form a steel bar with a diameter of 16 mm.

[0095] 4) Water cooling: The steel bars are cooled by water with a water pressure of 0.6 MPa and a cooling time of 15 seconds;

[0096] 5) High-frequency induction heating: The cooled steel bars are subjected to high-frequency induction heating. The frequency of high-frequency induction is 100kHz and the current density is 1.0×10 7 A / m 2 , the holding time is 0.02 seconds;

[0097] 6) Air-cool the steel bars after high-frequency induction heating to room temperature.

[0098] Experimental results:

[0099] After testing, it was found that the martensite on the surface of the threaded steel obtained in this embodiment was not completely eliminated, and the lower yield strength was 396 MPa, the tensile strength was 521 MPa, the elongation after fracture was 15.56%, and the red rust area after being placed in the open air for 15 days was 1.0%.

[0100] Comparative Example 4

[0101] A method for preparing 16mm HRB400E rebar, wherein the rebar composition, by mass, is 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, and 0.02% S, with the balance being Fe and unavoidable impurities. The method comprises the following steps:

[0102] 1) Converter smelting, control the element content of converter steel to meet the above requirements;

[0103] 2) Continuous casting: pouring molten steel into 150mm×150mm billets at a casting speed of 1.6m / min;

[0104] 3) Rolling: The billet is heated to 1150°C and kept at this temperature for 60 minutes, and then subjected to two passes of rough rolling, two passes of intermediate rolling, and three passes of finish rolling to form a steel bar with a diameter of 16 mm.

[0105] 4) Water cooling: The steel bars are cooled by water with a water pressure of 0.6 MPa and a cooling time of 15 seconds;

[0106] 5) High-frequency induction heating: The cooled steel bars are subjected to high-frequency induction heating. The frequency of high-frequency induction is 300kHz and the current density is 1.5×10 7 A / m 2 , the holding time is 0.02 seconds;

[0107] 6) Air-cool the steel bars after high-frequency induction heating to room temperature.

[0108] Experimental results:

[0109] After testing, the threaded steel obtained in this comparative example had a lower yield strength of 395 MPa, a tensile strength of 496 MPa, an elongation after fracture of 21.65%, and a red rust area of 0.9% after being placed in the open air for 15 days.

[0110] Comparative Example 5

[0111] A method for preparing 16mm HRB400E rebar, wherein the rebar composition, by mass, is 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, and 0.02% S, with the balance being Fe and unavoidable impurities. The method comprises the following steps:

[0112] 1) Converter smelting, control the element content of converter steel to meet the above requirements;

[0113] 2) Continuous casting: pouring molten steel into 150mm×150mm billets at a casting speed of 1.6m / min;

[0114] 3) Rolling: The billet is heated to 1150°C and kept at this temperature for 60 minutes, and then subjected to two passes of rough rolling, two passes of intermediate rolling, and three passes of finish rolling to form a steel bar with a diameter of 16 mm.

[0115] 4) Water cooling: The steel bars are cooled by water with a water pressure of 0.6 MPa and a cooling time of 15 seconds;

[0116] 5) High-frequency induction heating: The cooled steel bars are subjected to high-frequency induction heating. The frequency of high-frequency induction is 200kHz and the current density is 1.8×10 7 A / m 2 , the holding time is 0.02 seconds;

[0117] 6) Air-cool the steel bars after high-frequency induction heating to room temperature.

[0118] Experimental results:

[0119] After testing, the rebar obtained in this comparative example has a lower yield strength of 489 MPa, a tensile strength of 521 MPa, an elongation after fracture of 20.36%, and a red rust area of 0.95% after being placed in the open air for 15 days.

[0120] Comparative Example 6

[0121] A method for preparing 16mm HRB400E rebar, wherein the rebar composition, by mass, is 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, and 0.02% S, with the balance being Fe and unavoidable impurities. The method comprises the following steps:

[0122] 1) Converter smelting, control the element content of converter steel to meet the above requirements;

[0123] 2) Continuous casting: pouring molten steel into 150mm×150mm billets at a casting speed of 1.6m / min;

[0124] 3) Rolling: The billet is heated to 1150°C and kept at this temperature for 60 minutes, and then subjected to two passes of rough rolling, two passes of intermediate rolling, and three passes of finish rolling to form a steel bar with a diameter of 16 mm.

[0125] 4) Water cooling: The steel bars are cooled by water with a water pressure of 0.8 MPa and a cooling time of 15 seconds;

[0126] 5) High-frequency induction heating: The cooled steel bars are subjected to high-frequency induction heating. The frequency of high-frequency induction is 200kHz and the current density is 1.5×10 7 A / m 2 , the holding time is 0.08 seconds;

[0127] 6) Air-cool the steel bars after high-frequency induction heating to room temperature.

[0128] Experimental results:

[0129] After testing, the rebar obtained in this comparative example has a lower yield strength of 385 MPa, a tensile strength of 498 MPa, an elongation after fracture of 23.24%, and a red rust area of 0.5% after being placed in the open air for 15 days.

[0130] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing threaded steel, characterized in that: The steps include: 1) Converter smelting, in which the element content of converter steel is controlled; 2) Continuous casting, in which molten steel from a converter is cast into billets; 3) rolling, wherein the billet is heated and then kept warm, and then rolled into steel bars; 4) After the rolling process, a water cooling treatment is performed, wherein the water pressure of the water cooling is 0.6-0.88 MPa and the cooling time is 15-30 seconds; 5) The threaded steel bar that has been water-cooled is subjected to high-frequency induction heating treatment, wherein the high-frequency induction frequency is controlled to be 150-250 kHz, the holding time is 0.02-0.05 seconds, and the current density of the high-frequency induction heating treatment is 1×10 7 -1.3×10 7 A / m 2 , The composition of the threaded steel includes, by mass%, C 0.2-0.24%, Si 0.35-0.62%, Mn 0.65-0.95%, P≤0.03%, S≤0.03%, and the balance is Fe and unavoidable impurities.

2. The preparation method according to claim 1, characterized in that The method further comprises the following steps: 6) After the high-frequency induction heating treatment, the rebar is air-cooled to room temperature.

3. The preparation method according to claim 1, characterized in that In step 2), the casting speed is controlled to be 1.3-1.7 m / min during the process of casting the molten steel smelted in the converter into billets.

4. The preparation method according to claim 1, characterized in that In step 3), the rolling process includes: heating the billet to 1100-1200° C., keeping the temperature for 50-70 minutes, and then rolling the billet into a steel bar with a diameter of 16-22 mm; And / or, the square billet is rolled into a steel bar with a diameter of 16-22 mm through rough rolling, intermediate rolling and finish rolling.

5. The preparation method according to claim 1, characterized in that The threaded steel produced according to the production method does not contain the alloying elements manganese, vanadium and / or niobium.

6. The threaded steel bar prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The threaded steel has a lower yield strength of 410 MPa or more and a tensile strength of 550 MPa or more. The threaded steel comprises, by mass%, C 0.2-0.24%, Si 0.35-0.62%, Mn 0.65-0.95%, P≤0.03%, S≤0.03%, with the remainder being Fe and unavoidable impurities, and no closed-loop martensite is present on the surface of the threaded steel.

7. The threaded steel bar according to claim 6, characterized in that The elongation after fracture of the threaded steel bar is greater than 19.5%.

8. The threaded steel bar according to claim 6 or 7, characterized in that: The red rust area of the threaded steel bar is ≤1% after being placed in the open air for 15 days.

9. The threaded steel bar according to claim 6 or 7, characterized in that: The rebar does not contain the alloying elements manganese, vanadium and / or niobium.