Preparation method of deformed steel bar and deformed steel bar prepared by same

Abstract

The invention provides a preparation method of deformed steel bar and the deformed steel bar prepared by the preparation method, and relates to the technical field of metallurgy. The preparation method comprises the following steps: 1) converter smelting: controlling the content of converter tapping elements; (2) continuous casting is conducted, specifically, molten steel smelted through a converter is poured into square billets; (3) rolling: heating the square billet, preserving heat, and rolling the square billet into a reinforcing steel bar; (4) after the rolling technology is conducted, through-water cooling treatment is conducted, the water pressure of through-water cooling ranges from 0.6 MPa to 0.88 MPa, and the cooling time ranges from 15 seconds to 30 seconds; and 5) performing high-frequency induction heating treatment on the deformed steel bar subjected to water cooling, and controlling the high-frequency induction frequency to be 150-250kHz and the heat preservation time to be 0.02-0.05 second. According to the method, the performance of the deformed steel bar is effectively improved, the production cost is reduced, closed-loop martensite can be effectively eliminated, and meanwhile, the oxidation resistance of the deformed steel bar is improved.

Description

Technical Field

[0001] The 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 usually improve strength and toughness by adding a large amount of alloying elements (such as manganese, vanadium, niobium, etc.), but this method has low resource utilization and high production costs, which does not meet the requirements of green and low-carbon development 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 inside 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 is mainly ferrite plus pearlite, and tempered martensite structure shall not appear in the base circle. After water penetration, rebar tends to form closed martensite structure within 1mm of the surface. The color of this structure is obviously darker than the base structure during metallographic detection, commonly known as "black circle". In order to improve the pass rate of metallographic structure inspection of rebar, the current production process generally adopts weak water penetration or no water penetration process, and at the same time increases the content of alloy elements to improve the strength of rebar, resulting in increased alloy usage and increased production costs.

[0005] Therefore, it is necessary to add a small amount of alloy elements or no alloy elements and control the preparation process to obtain products whose performance and metallographic structure meet the requirements of national standards, so as to reduce alloy costs and improve 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 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 cooled by water 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, 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.

[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 the billet.

[0017] Optionally, in step 3), the rolling process comprises: heating the square billet to 1100-1200° C., keeping the temperature for 50-70 minutes, and then rolling the square 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 is greater than 19.5%.

[0022] Optionally, the red rust area of ​​the rebar 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 based on 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 0.6-0.88MPa, and the cooling time is 15-30 seconds. The closed-loop martensite formed is formed within 1mm from the surface of the substrate. Based on this, in order to eliminate the closed-loop martensite and prevent 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 150-250kHz 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 to affect the toughness and plasticity of the substrate.

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

[0027] 1. The present invention adopts a combined process of water cooling + high-frequency induction heating to effectively improve the performance (strength, toughness and plasticity) of threaded steel, thereby effectively reducing the amount of alloy elements added and reducing production costs.

[0028] 2. The present invention can effectively eliminate closed-loop martensite by selecting appropriate high-frequency induction heating parameters, and at the same time form 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 described clearly and completely in conjunction with the technical solutions in the embodiments. Obviously, the described embodiments 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 creative work 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 treatment refers to rapid cooling of the threaded steel bar 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 the bar.

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

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

[0034] 1) After the rebar has been subjected to 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;

[0035] 2) The threaded steel bar that has been cooled by water 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 remainder is Fe and unavoidable impurities.

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

[0040] The step of pouring 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 comprises: heating the square billet to 1100-1200°C, keeping it warm for 50-70min, and then rolling the rebar into a steel bar with a diameter of 16-22mm by a rolling mill.

[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 of Shenyang Heavy Machinery Co., Ltd. High-frequency induction heating can be achieved by, for example, the IEE-S2000 series high-frequency induction heating system of the Institute of Electrical Engineering of the Chinese Academy of Sciences.

[0043] In the following embodiments, 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 threaded steel, wherein the threaded steel comprises, by mass, 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, 0.02% S, and the remainder is 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 small square billets of 150 mm × 150 mm at a pulling speed of 1.6 m / min;

[0048] 3) Rolling: the billet is heated to 1150°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 finishing rolling to be rolled into 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 the 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 has no closed-loop martensite, the lower yield strength is 410 MPa, the tensile strength is 553 MPa, the elongation after fracture is 22.39%, and the red rust area after being placed in the open air for 15 days is 1%.

[0054] Example 2

[0055] A method for preparing 20 mm HRB500E threaded steel, wherein the threaded steel comprises, by mass, 0.24% C, 0.62% Si, 0.95% Mn, 0.025% P, 0.021% S, and the remainder is 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 small square billets of 150 mm × 150 mm at a pulling speed of 1.6 m / 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 be rolled into 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 the high-frequency induction is 200 kHz 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 has no closed-loop martensite, the lower yield strength is 512 MPa, the tensile strength is 653 MPa, the elongation after fracture is 20.73%, and the red rust area after being placed in the open air for 15 days is 0.95%.

[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, 0.021% S, and the remainder is 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 small square billets of 150 mm × 150 mm at a pulling speed of 1.6 m / 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 be rolled into 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 the 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 threaded steel, wherein the threaded steel comprises, by mass, 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, 0.02% S, and the remainder is 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 small square billets of 150 mm × 150 mm at a pulling speed of 1.6 m / min;

[0078] 3) Rolling: the billet is heated to 1150°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 finishing rolling to be rolled into 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 20 mm HRB500E threaded steel, wherein the threaded steel comprises, by mass, 0.24% C, 0.62% Si, 0.95% Mn, 0.025% P, 0.021% S, and the remainder is 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 small square billets of 150 mm × 150 mm at a pulling speed of 1.6 m / 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 be rolled into a steel bar with a diameter of 20 mm;

[0087] 4) Water cooling: The steel bars are cooled through water with a 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, the lower yield strength is 485 MPa, the tensile strength is 556 MPa, the elongation after fracture is 13.64%, and the red rust area after being placed in the open air for 15 days is 1.9%.

[0090] Comparative Example 3

[0091] A method for preparing 16mm HRB400E threaded steel, wherein the threaded steel comprises, by mass, 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, 0.02% S, and the remainder is 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 small square billets of 150 mm × 150 mm at a pulling speed of 1.6 m / min;

[0094] 3) Rolling: the billet is heated to 1150°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 finishing rolling to be rolled into 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 the high-frequency induction is 100 kHz 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 threaded steel, wherein the threaded steel comprises, by mass, 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, 0.02% S, and the remainder is 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 small square billets of 150 mm × 150 mm at a pulling speed of 1.6 m / min;

[0104] 3) Rolling: the billet is heated to 1150°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 finishing rolling to be rolled into 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 the 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 rebar obtained in this comparative example has 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 threaded steel, wherein the threaded steel comprises, by mass, 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, 0.02% S, and the remainder is 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 small square billets of 150 mm × 150 mm at a pulling speed of 1.6 m / min;

[0114] 3) Rolling: the billet is heated to 1150°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 finishing rolling to be rolled into 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 the 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 threaded steel, wherein the threaded steel comprises, by mass, 0.2% C, 0.35% Si, 0.65% Mn, 0.02% P, 0.02% S, and the remainder is 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 small square billets of 150 mm × 150 mm at a pulling speed of 1.6 m / min;

[0124] 3) Rolling: the billet is heated to 1150°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 finishing rolling to be rolled into 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 the high-frequency induction is 200 kHz 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 is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope 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 cooled by water 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 .

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 terms of mass %, the composition of the threaded steel includes: 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.

4. 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 square billets.

5. The preparation method according to claim 1, characterized in that: In step 3), the rolling process includes: heating the square billet to 1100-1200° C., keeping the temperature for 50-70 minutes, and then rolling the square 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.

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

7. The threaded steel bar prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The lower yield strength of the threaded steel is greater than 410 MPa and the tensile strength is greater than 550 MPa.

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

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

10. The threaded steel bar according to claim 7 or 8, characterized in that: The rebar does not contain the alloying elements manganese, vanadium and / or niobium.