High-strength steel bar with excellent low-temperature performance and welding performance and preparation method of high-strength steel bar

Abstract

The invention relates to a high-strength steel bar with excellent low-temperature performance and welding performance, which is characterized in that the steel bar comprises the following chemical components in percentage by mass: 0.25-0.30% of C, 0.60-1.00% of Si, 1.30-1.80% of Mn, 0.20-0.25% of V, 0.02-0.03% of N, less than 0.35 ppm of H and the balance of Fe and inevitable impurity elements, and the relationship between the mass percentage content [N] of N in the steel and the mass percentage content [V] of a V element with fixed N atoms meets the following condition: [N] / (0.16 [C] + 0.275 [V]) is more than or equal to 0.2 and less than or equal to 0.3, and the balance of Fe and inevitable impurity elements. The microstructure of the steel is ferrite, pearlite and bainite, the average grain size of the microstructure is smaller than or equal to 10 micrometers, the content of the ferrite is 60% by volume or above, and the content of the bainite is 10-30% by volume. The steel bar provided by the invention simultaneously meets the requirements of high strength, excellent weldability, good strength and plasticity matching and good low-temperature performance.

Description

Technical Field

[0001] This invention relates to the field of high-strength steel bars, and more particularly to a high-strength steel bar with excellent low-temperature performance and weldability, and a method for preparing the same. Background Technology

[0002] As my country's construction industry continues to develop towards large-scale operations, large public buildings and high-rise buildings have increasingly complex structures, which places stringent requirements on the strength and comprehensive performance of steel reinforcement.

[0003] Currently, 400 / 500MPa grade threaded steel bars are commonly used in my country's construction steel, with only the HRB600 national standard available. In contrast, foreign construction steel bars have already reached the 700MPa level. Furthermore, increasing the strength grade of steel bars primarily involves increasing the carbon content, but this increased carbon content can impair weldability.

[0004] Patent application CN110938777A discloses a hot-rolled ribbed steel bar for high-strength anchor bolts with a strength of 700MPa. The chemical composition and its mass percentage are as follows: C: 0.24-0.30%, Si: 0.6-0.8%, Mn: 1.40-1.60%, V: 0.15-0.20%, P≤0.030%, S≤0.015%, N: 0.020-0.030%, with the remainder being Fe and unavoidable impurities. The yield strength is 710-810MPa, the tensile strength is 870-990MPa, and the elongation after fracture A≥20%. Although it has high strength, it does not address low-temperature performance and cannot meet the requirements for use under low-temperature conditions (e.g., -40℃), nor does it address weldability.

[0005] Patent application CN103741022A discloses a high-strength steel bar for construction, characterized by a chemical composition by weight percentage of: C 0.22~0.25%, Si 0.60~0.75%, Mn 1.50~1.60%, P≤0.03%, S≤0.03%, V 0.13~0.20%, [N] 140~220ppm, RE≤0.0015, with the remainder being iron and unavoidable impurities. The yield strength is ≥600MPa, tensile strength is ≥750MPa, and elongation is ≥14%. However, this steel bar does not address low-temperature performance and weldability, and cannot meet the requirements for use at temperatures below -40℃.

[0006] Therefore, there is an urgent need to develop steel bars with high strength, excellent low-temperature performance, and good weldability. Summary of the Invention

[0007] The purpose of this invention is to provide a high-strength steel bar with excellent low-temperature performance and weldability, and a method for preparing the same. This steel bar has the characteristics of high strength, good strength-plasticity matching, low-temperature resistance and excellent weldability, so as to solve the problems of insufficient strength margin, contradiction between strength and weldability and poor low-temperature resistance of existing steel bars.

[0008] In a first aspect, the present invention proposes a high-strength steel bar with excellent low-temperature performance and weldability. The chemical composition of the steel bar, by mass percentage, is as follows: C: 0.10-0.30%, Si: 0.60-1.00%, Mn: 1.30-2.00%, V: 0.20-0.25%, N: 0.02-0.03%, Ni: 0.1-0.3%, Cu: 0.05-0.2%, H: less than 0.35ppm, with the remainder being Fe and unavoidable impurity elements. The relationship between the mass percentage of N in the steel [N] and the mass percentage of V with fixed N atoms [V] conforms to the following: 0.2≤[N] / (0.16[C]+0.275[V])≤0.3. The microstructure of the steel is ferrite, pearlite, and bainite, with an average grain size ≤10μm, wherein the content of ferrite is more than 60% by volume, and the content of bainite is 10-30% by volume.

[0009] Furthermore, the relationship between the mass percentage of nitrogen (N) in the steel and the mass percentage of nitrogen (V) with fixed nitrogen atoms conforms to the following: 0.22 ≤ [N] / (0.16[C]+0.275[V]) ≤ 0.28 ([N] / 14+[V] / 51).

[0010] Furthermore, the ferrite content is 60–75% by volume, the pearlite content is 15–30% by volume, and the bainite content is 10–25% by volume.

[0011] Furthermore, the yield strength of the steel bar is 600-700 MPa, the tensile strength is 760-920 MPa, the elongation after fracture is ≥19%, the total elongation at maximum force is ≥9%, and the longitudinal impact energy at -40℃ is ≥60 J.

[0012] Furthermore, the H content of the steel reinforcement is below 0.3 ppm.

[0013] Secondly, the present invention provides a method for preparing high-strength steel bars with excellent low-temperature performance and weldability, for preparing the aforementioned high-strength steel bars with excellent low-temperature performance and weldability. The preparation method includes the following process steps: hot metal pretreatment, converter smelting, ladle refining, continuous casting, continuous rolling, and heat treatment. The specific process is as follows:

[0014] (1) Hot metal pretreatment: Hot metal pretreatment reduces impurity elements in steel, ensuring that the S content is less than 0.002% after KR desulfurization or powder injection desulfurization.

[0015] (2) Converter smelting + ladle refining: High-quality scrap steel is added for converter smelting. The steel composition and temperature are controlled through the refining process, degassing, desulfurization and argon blowing in the later stage of refining to control the content of inclusions in the steel.

[0016] (3) Continuously cast into square or rectangular billets;

[0017] (4) Continuously rolled into steel bars;

[0018] (5) Heat treatment: The rolled steel bars are kept at a temperature of 100-300℃ for 0.5h-100h.

[0019] Furthermore, the continuous casting adopts full-process protective casting, the target superheat of the molten steel in the tundish is ≤25℃, and it enters the slow cooling pit after continuous casting.

[0020] Furthermore, in the continuous rolling process, the heating temperature is between 1100 and 1150°C, and the heating time is between 180 and 240 minutes.

[0021] Furthermore, in the continuous rolling process, the initial rolling temperature is 1050℃~1100℃, and the final rolling temperature is 900~1000℃.

[0022] Furthermore, in the post-rolling cooling process, air cooling is performed after rolling, with a cooling rate of 11-16 m / s.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0024] 1. This invention controls the elemental ratio of V and C in steel to ensure the precipitation of carbides while keeping the carbon content within the limit, thus ensuring that the microstructure of the steel plate is ferrite, pearlite and bainite, with an average grain size ≤10μm.

[0025] 2. This invention controls the rolling, cooling, and heat treatment processes of the steel plate. The billet is heated to 1100–1150℃ for 180–240 min, with an initial rolling temperature of 1050–1100℃ and a final rolling temperature of 900–1000℃. After rolling, the steel is air-cooled at a rate of 11–16 m / s, and then held at 100–300℃ for 0.5–100 h. This rolling process facilitates the precipitation of V in ferrite, inhibits ferrite grain growth, refines the grains, and strengthens the steel through precipitation. It also ensures the microstructure of the steel and guarantees that the H content meets requirements.

[0026] 3. This invention achieves excellent mechanical properties of steel bars by controlling the types and contents of elements, especially the ratio of V and C, combined with rolling, cooling and heat treatment processes. The yield strength is 600-700MPa, the tensile strength is 760-920MPa, the elongation after fracture is ≥19%, the maximum force total elongation Att is ≥9%, and the longitudinal impact energy at -40℃ is ≥60J.

[0027] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0028] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0029] Figure 1 This is a typical microstructure diagram of high-strength steel bars with excellent low-temperature performance and weldability. Detailed Implementation

[0030] This invention provides a high-strength steel bar with excellent low-temperature performance and weldability, and a method for preparing the same. The steel bar has the characteristics of high strength, good strength-plasticity matching, excellent weldability, and low-temperature resistance, which solves the problems of insufficient strength grade, contradiction between strength and weldability, and insufficient low-temperature resistance of existing steel bars.

[0031] In one preferred embodiment, the high-strength steel bar provided by the present invention has a yield strength of 600-700 MPa, a tensile strength of 760-920 MPa, an elongation after fracture ≥19%, a maximum force total elongation At ≥9%, and a longitudinal impact energy at -40℃ ≥60 J.

[0032] In one preferred embodiment, the yield strength of the steel bar is 620-700 MPa, preferably 630-700 MPa, more preferably 650-700 MPa; the tensile strength is 800-920 MPa, preferably 820-910 MPa; the elongation after fracture is 19-25%, the total elongation at maximum force (Agt) is 9-12%, and the longitudinal impact energy at -40℃ is 80-200 J.

[0033] In one preferred embodiment, the average grain size of ferrite, pearlite and bainite in the microstructure of the reinforcing steel is ≤8μm.

[0034] Regarding the content of each phase in the microstructure, the ferrite content is above 60% by volume, preferably above 65% by volume. Ferrite has slightly lower strength but better plasticity and toughness. Pearlite has higher strength than ferrite, but lower plasticity and toughness. The bainite content is 10-30% by volume, preferably 12-25% by volume, and more preferably 15-20% by volume. By controlling the cooling method and heat treatment process after steel bar rolling, fine and uniform bainite can be introduced into the steel, thereby further improving the strength and low-temperature performance of the steel bar, ensuring that the steel bar still has excellent performance below -40℃, and meeting the requirements for use at low temperatures. Under these composition and process conditions, the steel bar obtains a specific microstructure ratio and morphology, which can simultaneously guarantee strength and plasticity, resulting in a good strength-toughness balance and low-temperature performance.

[0035] In one preferred embodiment, the longitudinal impact energy of the steel bar at -40℃ is ≥60J, preferably ≥80J, and more preferably ≥100J, and the steel bar has excellent low-temperature performance.

[0036] The chemical composition of the high-strength steel bar with excellent low-temperature performance and weldability provided by this invention, by mass percentage, is as follows: C: 0.15-0.30%, Si: 0.60-1.00%, Mn: 1.30-2.00%, V: 0.20-0.25%, N: 0.02-0.03%, Ni: 0.1-0.3%, Cu: 0.05-0.2%, H: less than 0.35ppm, with the remainder being Fe and unavoidable impurity elements.

[0037] The reasons for limiting the composition of the billet of the high-strength steel bar with excellent low-temperature performance and weldability and its preparation method in this invention will be explained. Hereinafter, only the mass percentage of the composition is expressed as %.

[0038] C: Carbon is an essential element for increasing strength, but it also reduces the weldability of materials. When the carbon content is below 0.10%, the strength of the steel plate will decrease, but excessive carbon content will adversely affect the weldability and low-temperature toughness of the steel plate. Considering both aspects, the C content should be controlled between 0.10% and 0.30%, which can be 0.12%, 0.15%, 0.18%, 0.2%, 0.23%, 0.25%, 0.27%, or 0.28%.

[0039] Meanwhile, to ensure sufficient precipitation strengthening, systematic experimental research and theoretical analysis revealed that the relationship between the mass percentage of nitrogen (N) and the mass percentage of nitrogen atoms (V) is: 0.2 ≤ [N] / (0.16 [C] + 0.275 [V]) ≤ 0.3. If the value is less than 0.2, the yield strength and tensile strength of the steel reinforcement will be low. If the value is higher than 0.3, although the strength requirements are met, the elongation after fracture and the total elongation at maximum force will be low, failing to meet the requirements. Under this ratio, carbide precipitation can be guaranteed while ensuring that the carbon content does not exceed the standard. "Not exceeding the standard" here means that excessive carbon content will lead to reduced plasticity. However, if the carbon content is reduced, the strength of the steel cannot be guaranteed. In this case, to improve the strength, precipitation strengthening and grain refinement are necessary. Controlling the C and V content within the range shown in the formula will generate a certain amount of precipitates, thereby improving the strength. Furthermore, the vanadium precipitates can inhibit ferrite grain growth during rolling, thereby refining the grain size. This also results in a better strength-ductility ratio in the obtained steel reinforcement, preferably 0.22 ≤ [N] / (0.16 [C] + 0.275 [V]) ≤ 0.28.

[0040] Silicon (Si): As a deoxidizing element and a solid solution strengthening element, silicon can improve the strength of steel. However, excessive silicon content can reduce the low-temperature toughness and weldability of steel. Therefore, the Si content should be controlled between 0.60% and 1.00%.

[0041] Manganese (Mn) is an essential element for ensuring the strength and toughness of steel. It not only delays the ferrite phase transformation and refines ferrite grains, but also combines with sulfur (S) to form MnS, preventing the formation of FeS at grain boundaries and thus avoiding hot cracking. To obtain high-strength steel plates, the Mn content needs to be controlled above 1.30%. However, excessively high Mn content will cause center segregation, reducing toughness and weldability. Therefore, the Mn content should be controlled between 1.30% and 2.00%, specifically 1.40%, 1.50%, 1.60%, 1.70%, 1.80%, 1.90%, or 1.95%.

[0042] Vanadium (V) is a commonly used microalloying element with significant precipitation strengthening effects. It can form V(C,N) precipitates with nitrogen, thus achieving precipitation strengthening. The V content should be controlled between 0.20% and 0.25%.

[0043] Nitrogen (N): A certain amount of nitrogen can form V(C,N) with v, increasing strength. However, excessive nitrogen content will affect the low-temperature toughness of the material. Therefore, the nitrogen content is controlled between 0.02% and 0.03%.

[0044] Ni: Introducing Ni into steel reinforcement can improve its low-temperature performance. To achieve the desired low-temperature performance, a Ni content of 0.1% or higher is effective. However, excessively high Ni content can affect the weldability of the steel reinforcement. To ensure weldability, the Ni content should be below 0.3%. The Ni content should be controlled between 0.1% and 0.3%, preferably 0.15% to 0.25%.

[0045] Cu: Adding Cu to steel bars can also improve their low-temperature performance. To achieve the desired low-temperature performance, the Cu content should be above 0.05%. However, excessive Cu content will make the steel bars brittle and affect their weldability. To ensure weldability, the Cu content should be below 0.2%. The Cu content should be controlled between 0.05% and 0.2%, preferably between 0.1% and 0.15%.

[0046] H: The H content in steel bars needs to be controlled below 0.35ppm, preferably below 0.3ppm, and even better below 0.28ppm. If the H content exceeds 0.35ppm, it will affect the elongation and low-temperature performance of the steel bars. The elongation after fracture of the steel bars will be less than 19%, and the maximum total elongation At will also fail to meet the requirement of ≥9%. At the same time, the low-temperature toughness will decrease significantly.

[0047] The preparation method of the high-strength steel bar with excellent low-temperature performance and weldability described in this invention is as follows:

[0048] (1) Hot metal pretreatment: Hot metal pretreatment reduces impurity elements in steel, ensuring that the S content is less than 0.002% after KR desulfurization or powder injection desulfurization.

[0049] (2) Converter smelting + ladle refining: High-quality scrap steel is added for converter smelting. The steel composition and temperature are controlled through refining process, degassing, desulfurization and argon blowing in the later stage of refining to control the content of inclusions in the steel.

[0050] (3) Continuously cast into square or rectangular billets, wherein the continuous casting process adopts full-process protective casting, the target superheat of the molten steel in the tundish is ≤25℃, and after continuous casting, it enters the slow cooling pit for treatment.

[0051] (4) Continuous rolling into steel bars: The heating temperature of the billet is between 1100 and 1150℃, the heating time is 180 to 240 min, the initial rolling temperature is between 1050℃ and 1100℃, the final rolling temperature is 900 to 1000℃, and the billet is air-cooled after rolling at a rate of 11-16 m / s.

[0052] (5) Heat treatment: The rolled steel bars are kept at a temperature of 100-300℃ for 0.5h-100h.

[0053] It should be noted that rolling under this process facilitates the precipitation of V in ferrite, inhibits ferrite grain growth, and plays a role in precipitation strengthening. Through the above rolling method, fine ferrite, pearlite, and bainite grains with a size ≤10μm can be obtained, while simultaneously controlling the proportions of each microstructure to ferrite content of ≥60% by volume, pearlite content of 15-30% by volume, and bainite content of 10-25% by volume.

[0054] If the cooling rate is too fast, the required ferrite content cannot be obtained, and the elongation after fracture, total elongation at maximum force, and weldability of the steel bar will not meet the requirements. If the cooling rate is too low, the bainite content will be too low, and the yield strength and tensile strength of the steel bar will not meet the requirements.

[0055] Heat treatment can reduce the H content to below 0.35 ppm, ensuring that the H content in the steel meets the requirements, thereby ensuring the required low-temperature performance. In addition, it can also improve the elongation after fracture and the total elongation at maximum force of the steel bars.

[0056] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0057] Example

[0058] This embodiment discloses 11 types of steel bars (1#-11#).

[0059] All 1#-9# use the same process: (1) KR desulfurization; (2) converter smelting + ladle refining; (3) continuous casting into square billets: the target superheat of the molten steel in the ladle is ≤25℃, and after continuous casting, it enters the slow cooling pit for treatment; (4) continuous rolling into reinforcing bars: the heating temperature of the billet is between 1100 and 1150℃, the heating time is 180 to 240 min, the initial rolling temperature is between 1050℃ and 1100℃, the final rolling temperature is 900 to 1000℃, and after rolling, it is air cooled at a cooling rate of 11 m / s to 16 m / s, and kept at a temperature of 100℃ to 300℃ for 0.5h to 100h.

[0060] The elemental composition mass percentages of steels #1 to #4, #10, and #11 all meet the requirements of this invention. The elemental composition mass percentages of steels #5 and #6 meet the requirements of this invention, but do not conform to the formula 0.2≤[N] / (0.16[C]+0.275[V])≤0.3. The elemental composition mass percentages of steels #7 to #9 do not meet the requirements of this invention. The differences in their elemental composition are shown in Table 1. The microstructure of steel #1 is shown below. Figure 1 As shown.

[0061] The process parameters for steels #1 to #9 all meet the requirements of this invention, while the process parameters for steels #10 and #11 do not meet the requirements of this invention. The differences in their process parameters are shown in Table 2.

[0062] Table 1 Chemical composition (wt, %) of steel bars #1-#11

[0063]

[0064] Table 2. Process parameters for steel bars #1-#11

[0065]

[0066]

[0067] The properties, grain size, and microstructure of steel bars #1-#11 are shown in Table 3.

[0068] Table 3 Properties, grain size and microstructure of steel bars #1-#11

[0069]

[0070] The mechanical properties of the welded joints of reinforcing bars are shown in Table 4.

[0071] Table 4 Mechanical properties of welded joints of reinforcing bars

[0072]

[0073] Comparison reveals that the smelting methods and process parameters for steel bars #1 to #9 are the same or similar. However, the elemental composition mass percentages of steel bars #1 to #4 all meet the requirements of this invention. The elemental composition mass percentages of steel bars #5 and #6 meet the requirements of this invention, but do not meet the requirement of formula 0.2≤[N] / (0.16[C]+0.275[V])≤0.3. The [N] / (0.16[C]+0.275[V]) of steel bar #5 is less than 0.2, and the [N] / (0.16[C]+0.275[V]) of steel bar #6 is less than 0.2. The elemental composition mass percentages of steel bars #7 to #9 (275V) exceed 0.3 and do not meet the requirements of this invention. Among them, the yield strength and tensile strength of steel bars #5 and #7 are significantly lower than those of steel bars #1 to #4. The yield strength and tensile strength of steel bar #6 meet the requirements, but the elongation does not. Steel bar #8 does not meet the requirements for low-temperature performance because it does not contain Ni and Cu. Steel bar #9 does not meet the requirements because the content of Ni and Cu exceeds the requirements of this invention, and its elongation and weldability are poor. The elemental composition of steel bars #1 to #4, #10, and #11 has the same or similar mass percentage. However, the smelting methods and process parameters of steel bars #1 to #4 all meet the requirements of this invention, while the process parameters of steel bar #10 do not. The elongation after fracture, total elongation at maximum force, and mechanical properties of welded joints of steel bar #10 are significantly lower than those of steel bars #1 to #4, making it difficult to meet the requirements for plasticity and weldability. It is speculated that this is mainly due to the excessively rapid cooling rate, which results in the steel bar's microstructure not meeting the requirements. For steel bar #11, the lack of subsequent heat treatment resulted in the H content in the steel bar not meeting the requirements, and the ferrite content in the microstructure was also low, leading to the steel bar's low-temperature performance and elongation not meeting the requirements.

[0074] Comparison shows that this invention achieves excellent mechanical properties of steel bars based on special steel element composition and rolling and cooling process. The yield strength of the steel bars is 600-700MPa, the tensile strength is 760-920MPa, the elongation after fracture is ≥19%, the maximum force total elongation Att is ≥9%, and the longitudinal impact energy at -40℃ is ≥60J.

[0075] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A high-strength steel bar with excellent low-temperature performance and weldability, characterized in that, The chemical composition of the steel reinforcement, by mass percentage, is as follows: C: 0.10–0.30%, Si: 0.60–1.00%, Mn: 1.30–2.00%, V: 0.20–0.25%, N: 0.02–0.03%, Ni: 0.1–0.3%, Cu: 0.05–0.2%, H: less than 0.35 ppm, with the remainder being Fe and unavoidable impurity elements. The relationship between the mass percentage of N in the steel reinforcement [N] and the mass percentage of V with fixed N atoms [V] conforms to the following: 0.2 ≤ [N] / (0.16 [C] + 0.275 [V]) ≤ 0.

3. The microstructure of the steel reinforcement consists of ferrite, pearlite, and bainite, with an average grain size ≤ 10 μm, wherein the ferrite content is above 60% by volume and the bainite content is 10–30% by volume.

2. The high-strength steel bar with excellent low-temperature performance and weldability according to claim 1, characterized in that: The relationship between the mass percentage of nitrogen (N) in the steel reinforcement and the mass percentage of nitrogen (V) with fixed nitrogen atoms is: 0.22 ≤ [N] / (0.16 [C] + 0.275 [V]) ≤ 0.

28.

3. The high-strength steel bar with excellent low-temperature performance and weldability according to claim 1, characterized in that: The content of ferrite is 60-75% by volume, the content of pearlite is 15-30% by volume, and the content of bainite is 10-25% by volume.

4. The high-strength steel bar with excellent low-temperature performance and weldability according to any one of claims 1 to 3, characterized in that: The steel bars have a yield strength of 600-700 MPa, a tensile strength of 760-920 MPa, an elongation after fracture of ≥19%, a maximum total elongation at maximum force (Agt) of ≥9%, and a longitudinal impact energy at -40℃ of ≥60 J.

5. The high-strength steel bar with excellent low-temperature performance and weldability according to claim 4, characterized in that: H: below 0.3 ppm, and / or, Ni: 0.15-0.25%, and / or, Cu: 0.1-0.15%, and / or, yield strength of 650-700 MPa, and / or, tensile strength of 800-920 MPa, and / or, elongation after fracture of 19-25%, and / or, total elongation at maximum force Ag of 9-12%, and / or, longitudinal impact energy at -40℃ of 80-200 J.

6. A method for preparing high-strength steel bars with excellent low-temperature performance and weldability, characterized in that, The method for preparing the high-strength steel bars with excellent low-temperature performance and weldability as described in claims 1 to 5 includes the following steps: hot metal pretreatment, converter smelting, ladle refining, continuous casting, continuous rolling, and heat treatment. The specific process is as follows: (1) Hot metal pretreatment: Hot metal pretreatment reduces impurity elements in steel, ensuring that the S content is less than 0.002% after desulfurization; (2) Converter smelting + ladle refining: High-quality scrap steel is added for converter smelting. The steel composition and temperature are controlled through the refining process, degassing, desulfurization and argon blowing in the later stage of refining to control the content of inclusions in the steel. (3) Continuously cast square or rectangular billets; (4) Continuous rolling into steel bars; (5) Heat treatment: The rolled steel bars are kept at a temperature of 100-300℃ for 0.5h-100h.

7. The method for preparing high-strength steel bars with excellent low-temperature performance and weldability according to claim 6, characterized in that, The continuous casting process adopts full-process protective casting, with the target superheat of the molten steel in the tundish being ≤25℃, and the steel is then treated in a slow cooling pit after continuous casting.

8. The method for preparing high-strength steel bars with excellent low-temperature performance and weldability according to claim 6, characterized in that, The heating temperature is between 1100 and 1150℃, and the heating time is between 180 and 240 minutes.

9. The method for preparing high-strength steel bars with excellent low-temperature performance and weldability according to claim 6, characterized in that, The initial rolling temperature is 1050℃~1100℃, and the final rolling temperature is 900~1000℃.

10. The method for preparing high-strength steel bars with excellent low-temperature performance and weldability according to claim 9, characterized in that, After rolling, air cooling is performed at a rate of 11-16 m / s.

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