Production method of high-strength and high-toughness spring steel bar

Abstract

The invention belongs to the technical field of metallurgy, and relates to a production method of a high-strength and high-toughness spring steel bar. Comprising the procedures of combined blown converter smelting, ladle furnace refining, RH vacuum degassing treatment, rectangular blank continuous casting production, cogging rolling, steel blank coping, round steel rolling and slow cooling after rolling. In the ladle furnace refining procedure, an alkaline slag former is added in the early stage of refining according to the weight of molten steel, an acid slag former is added in the middle stage of refining, and the alkalinity in the steel is maintained to be 0.8-1.0; in the rectangular blank continuous casting production procedure, the solidification tail end of a casting blank is subjected to a light and heavy pressing process, and 2-9 frames are totally pressed by 26 mm; in the round steel rolling procedure, the heating temperature of a soaking section is 1040-1070 DEG C, and the reduction rate of the first pass and the reduction rate of the second pass are larger than 60%; the final rolling temperature ranges from 650 DEG C to 700 DEG C, and the accumulated reduction rate is larger than 80%. The produced product is low in non-metallic inclusion content, the grain size can reach 9.5 level, and carbon component segregation is within 1.05.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology and relates to a method for producing high-strength and high-toughness spring steel bars. Background Technology

[0002] Spring bars are crucial power transmission mechanical components in rail transit vehicles. Many factors, including the material, processing technology, lubrication, friction, and the geometric parameters and load patterns of the drive shaft, all influence the failure mode of spring bars. With increasing energy consumption and stringent environmental protection requirements, spring bar technology is evolving towards higher fatigue life, improved transmission accuracy, and reduced costs.

[0003] Currently, the main raw materials for spring bars in domestic rail transit vehicles are medium-carbon Cr-Mo-V series steels. This type of steel has excellent processing performance and can meet the strength and toughness requirements of drive shafts. However, it has a high Mo and V content, resulting in high cost. Therefore, it is particularly important to find a material with the same strength and high cost performance.

[0004] Therefore, based on the quality requirements of a benchmark high-strength and high-toughness spring bar in a certain domestic industry, we have developed a production method for high-end high-strength and high-toughness spring bar Si-Cr-V steel, which is of great significance. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides a method for producing high-strength and high-toughness spring steel bars, which solves the problems existing in the prior art.

[0006] The technical solution adopted in this invention is a production method for high-strength and high-toughness spring bars, including smelting in a combined blowing converter, refining in a ladle furnace, RH vacuum degassing treatment, continuous casting of rectangular billets, billet rolling, billet grinding, round bar rolling, and slow cooling after rolling.

[0007] In the ladle furnace refining process, an alkaline slagging agent is added in the early stage of refining according to the weight of the molten steel, and an acidic slagging agent is added in the middle stage to maintain the basicity of the steel between 0.8 and 1.0.

[0008] In the rectangular billet continuous casting production process, the billet solidification end adopts a light and heavy pressing process, pressing down a total of 26mm in 2 to 9 stands;

[0009] In the round steel rolling process, the heating temperature of the soaking zone is 1040-1070℃, and the reduction rate of the first and second passes is greater than 60%; water-controlled rolling is carried out, with a final rolling temperature of 650-700℃ and a cumulative reduction rate of greater than 80%.

[0010] The chemical composition of the steel used for spring bars, by weight percentage, is as follows: C: 0.40%–0.60%, Si: 1.00%–2.00%, Mn: 0.5%–1.00%, P≤0.012%, S≤0.012%, Cr: 0.50%–1.00%, Mo: 0.01%–0.05%, Al≤0.0040%, V: 0.10%–0.40%, N≤0.0040%, O≤0.0010%, Ca≤0.0020%, with the remainder being Fe and unavoidable impurities.

[0011] Furthermore, in the combined blowing converter smelting process, the ratio of molten iron to scrap steel is controlled at 7:3, the P content at the smelting endpoint does not exceed 0.010%, a composite deoxidizer is added in the early stage of tapping for slag formation and deoxidation, a low-N alloy is added in the middle stage of tapping for alloying, and a steel retention operation is adopted in the later stage of tapping to avoid oxidizing slag from entering the ladle.

[0012] Furthermore, in the ladle furnace refining process, according to the weight of the molten steel, in the early stage of refining, low-N refining synthetic slag and alkaline slagging agent of 5 kg / t molten steel are added to create refining white slag for deoxidation, desulfurization and removal of inclusions; in the middle stage of refining, acidic slagging agent of 8 kg / t molten steel is added, aluminum is controlled below 0.0040%, and after a soft blowing time of 8 minutes, the molten steel is transferred to the RH furnace for degassing treatment. No calcium treatment is performed during the entire refining process. Then, a covering agent is added to protect the molten steel; the refining time is between 55 and 75 minutes.

[0013] Furthermore, in the vacuum degassing process, after the RH is evacuated to below 67 Pa and the vacuum is maintained for 15 minutes, the hydrogen content of the molten steel is determined by breaking the vacuum and controlling the hydrogen content to ≤1.5ppm; after a soft blowing time of 15 minutes before leaving the station, the argon gas is turned off and the molten steel is allowed to stand for 10 minutes.

[0014] Furthermore, in the rectangular billet continuous casting production process, a 350×430mm cross-section continuous casting production is adopted, the billet pulling speed is controlled at a constant speed of 0.55m / min, the electromagnetic stirring of the crystallizer and the electromagnetic stirring at the solidification end are controlled at 200A, 2.0Hz and 400A, 16.0Hz respectively, the primary cooling water flow rate is 3000L / min, and the secondary cooling water flow rate is 0.36L / kg.

[0015] Furthermore, in the billet rolling process, a primary rolling mill with a cross-section of 1100mm is used for billet rolling, and finally a 7-stand rolling mill is used to roll out the finished product; the preheating section of the cast billet is ≤650℃, the high temperature section is 1200~1260℃, the high temperature section is held for 3h~4h, and the total heating time is 6-8h; the initial rolling temperature is ≥1150℃, the primary rolling billet is rolled in 7 passes, the first two passes are used to continuously roll the narrow face of the billet and then the edge is rolled, the single pass reduction is more than 25%, after billet rolling, it is rolled in a continuous rolling mill and stacked for slow cooling for 24h.

[0016] Furthermore, in the billet grinding process, the grinding depth on one side is controlled between 1.0mm and 1.5mm. After grinding, magnetic particle testing is used to manually repair the local areas.

[0017] Furthermore, in the post-rolling slow cooling process, the post-rolling water cooling is performed, the upper cooling bed temperature is 760±30℃, the cooling bed is densely packed for slow cooling, and the exit temperature is below 500℃.

[0018] Furthermore, the spring bar has a total oxygen content of ≤0.0010%, a grain size of 9.5, a banded structure of ≤1.5, and a low-magnification segregation index of less than 1.05.

[0019] The principle of the technical solution of this invention:

[0020] (1) High strength and high toughness: The strength of the material has a great influence on the heat treatment of the spring bar. Under the same heat treatment conditions, the stability of the quenching + tempering temperature determines the deformation index of the finished product. The same quenching + tempering temperature is beneficial to the processing of the spring bar and improves its meshing accuracy. This invention achieves precise and uniform control of the composition by adopting a narrow composition design and specially designed production process parameters. The carbon segregation index is within 1.05, reaching the international advanced level.

[0021] (2) Requirements for Oxygen Content and Inclusions in Steel: Numerous experimental studies have investigated the impact of oxygen content on the fatigue life of spring bars. When the oxygen content decreases from 20 ppm to below 10 ppm, the fatigue life can increase several times over. The fatigue life of B and D type inclusions in non-metallic inclusions is also significantly affected. These two types of inclusions are related to oxygen content, as well as the size and distribution of the non-metallic inclusions. Currently, spring steel customers require that B type inclusions not exceed level 2 and D type inclusions not exceed level 1. To meet these customer requirements, special refining and continuous casting processes must be employed for control; otherwise, it will be difficult to satisfy the spring bar steel customer requirements. C type inclusions are silicate inclusions, which can be reduced to below level 1 under existing equipment conditions.

[0022] (3) Grain size: Grain size is another important indicator of spring steel bars. Fine and uniform austenite grain size is of great significance for reducing the deformation of finished products after heat treatment and improving the brittle fracture resistance of spring steel. If mixed grains occur, the heat treatment deformation between parts may become irregular and they cannot be matched. The steel grade of this invention mainly uses V and Mo to refine the grains. By designing and controlling the Al and N content of V-Mo series spring steel within a reasonable range, a finer grain structure can be obtained, and the austenite grain size can reach grade 9.5 or above.

[0023] (5) Banded structure: During the solidification process of steel, due to selective crystallization, component segregation occurs in both the transverse and longitudinal directions of the billet. During the cooling process after rolling, component segregation forms a layered distribution of microstructure (ferrite and pearlite), i.e., banded structure. Severe banded structure not only increases the degree of deformation after the spring bar is processed into parts, but also causes differences in microhardness in different parts, affecting the fatigue life of the spring. Therefore, it is difficult for continuously cast materials to meet the requirement of below grade 1.5. The fundamental solution to banded structure lies in reducing component segregation, combined with an appropriate cooling rate after rolling. This invention, through the reasonable combination of continuous casting and rolling processes, can stably control the banded structure of rolled round steel within grade 1.5.

[0024] Other aspects: Since Si has already undergone decarburization during the heating process, the present invention avoids complete decarburization by controlling the rolling temperature and time and online cooling, and also reduces the depth of the incomplete decarburized layer.

[0025] The beneficial effects of this invention are as follows: This invention closely combines the requirements and characteristics of rail transit drive shafts, producing high-strength, high-toughness spring bar products that surpass the quality levels of products produced by previous processes in terms of steel purity, banded structure, component segregation, and product fatigue life. The finished products are rolled round bars with specifications ranging from φ20mm to φ80mm. Key quality indicators include low non-metallic inclusion content, total oxygen content ≤10ppm, grain size up to grade 9.5, banded structure ≤1.5, and carbon segregation within 1.05. Products made with this steel grade exhibit high processing precision, minimal heat treatment deformation, long fatigue life, and excellent comprehensive mechanical properties, meeting customers' requirements for advanced quality performance, high purity, ultra-fine structure, and high precision, thus fulfilling the application requirements of high-strength, high-toughness spring bars. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a metallographic diagram of the round steel in Embodiment 1 of the present invention. Detailed Implementation

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0029] A method for producing high-strength and high-toughness spring bars, producing rolled round bars with a diameter of φ20mm to φ80mm, the key quality indicator of which is low non-metallic inclusion content.

[0030] High-strength and high-toughness spring bar steel and its production method. The chemical composition of the steel by weight percentage is C: 0.40%~0.60%, Si: 1.00%~2.00%, Mn: 0.5%~1.00%, P≤0.012%, S≤0.012%, Cr: 0.50%~1.00%, Mo: 0.01%~0.05%, Al≤0.0040%, V: 0.10%~0.40%, N≤0.0040%, O≤0.0010%, Ca≤0.0020%, with the remainder being Fe and unavoidable impurities.

[0031] The process steps include:

[0032] (1) Combined blowing converter smelting: control the ratio of molten iron to scrap steel in the converter at 7:3, control the P content at the end of smelting to not exceed 0.010%, add composite deoxidizer in the early stage of tapping for slag formation and deoxidation, add low N alloy in the middle stage of tapping for alloying, and adopt the steel retention operation in the later stage of tapping to avoid oxidizing slag from entering the ladle.

[0033] (2) Ladle furnace refining: In the early stage of refining, 5 kg / t of low-N refining synthetic slag and 12 kg / t of alkaline slag-forming agent are added to the molten steel to make refining white slag for deoxidation, desulfurization and removal of inclusions. Alloys are added in the early stage and fine-tuned in the middle stage to control the composition to enter the target range. In the middle stage of refining, 8 kg / t of acidic slag-forming agent is added to maintain the final slag basicity between 0.8 and 1.0 to plastically deform inclusions and control the aluminum in the molten steel to below 0.0040%. After soft blowing for 8 minutes, the molten steel is transferred to the RH furnace for degassing. No calcium treatment is performed in the entire refining process. Then, a covering agent is added to protect the molten steel. The refining time is between 55 and 75 minutes.

[0034] (3) Vacuum degassing treatment: After the RH is evacuated to below 67Pa and the vacuum is maintained for 15 minutes, the hydrogen content of the molten steel is determined and controlled to be ≤1.5ppm. Before leaving the station, the argon gas is turned off after a soft blowing time of 15 minutes, and the molten steel is allowed to stand for 10 minutes to promote the adsorption of large inclusions.

[0035] (4) Rectangular billet continuous casting production: 350×430mm cross section continuous casting production is adopted. The billet pulling speed is controlled at a constant speed of 0.55m / min. The electromagnetic stirring of the crystallizer and the electromagnetic stirring at the solidification end are controlled at 200A, 2.0Hz and 400A, 16.0Hz respectively. The primary cooling water flow rate is 3000L / min and the secondary cooling water flow rate is 0.36L / kg. The billet solidification end adopts a light and heavy pressing process, that is, multiple sets of upper pressing zone rollers and lower pressing zone rollers are used. The pressing amount of the upper pressing zone rollers gradually increases in the pulling direction. The total pressing amount of 26mm is reduced from 2 to 9 stands. The low magnification segregation index of continuous casting is controlled within 1.05.

[0036] (5) Billet rolling: The billet is rolled using a primary rolling mill with a cross section of 1100mm, and the finished product is rolled using a 7-stand horizontal and vertical rolling mill. The billet heating adopts a diffusion process of low temperature (≤650℃) in the preheating section and high temperature (1200~1260℃) in the high temperature section. The high temperature section is held for 3h~4h, and the total heating time is 6-8h. The initial rolling temperature is ≥1150℃. The primary rolling billet is rolled in 7 passes. The billet is rolled in the first two passes to make the narrow face of the billet, and then rolled in the flanging section to ensure that the reduction per pass is more than 25% to refine the grains. After the billet is rolled, it is rolled in a continuous rolling mill. Finally, the billet size is controlled within 180 square ±2mm, and it is stacked and slowly cooled for 24h.

[0037] (6) Steel billet grinding: After the steel billet is slowly cooled, it is ground. The grinding depth on one side is controlled between 1.0mm and 1.5mm. After grinding, magnetic particle testing is used to manually repair the local areas.

[0038] (7) Round steel rolling: control the heating temperature of the soaking zone to 1040-1070℃, and the reduction rate of the first and second passes to be greater than 60%; carry out water-controlled rolling, with an ultra-low temperature final rolling temperature of 650-700℃ and a cumulative reduction rate of greater than 80%.

[0039] (8) Slow cooling after rolling: After rolling, water cooling is applied to control the temperature of the upper cooling bed at 760±30℃, and slow cooling is applied to the densely packed cooling bed to control the temperature of the exiting the cover at below 500℃.

[0040] The rolled round steel produced by the above process has an original microstructure of S+P+F and no brittle microstructure B.

[0041] The following examples provide further details.

[0042] The chemical composition of the steel in each embodiment is shown in Table 1, with the remainder being Fe and unavoidable impurities; the banded structure, grain size, and performance results of the round steel produced in each embodiment are shown in Table 2.

[0043] Example 1:

[0044] The chemical composition (by weight percentage) of the steel used for spring bars is: C: 0.56%, Si: 1.68%, Mn: 0.70%, P: 0.009%, S: 0.005%, Cr: 0.80%, Mo: 0.02%, Al T 0.0030%, V: 0.16%, N: 0.0030%, O: 0.0008%, Ca: 0.0010%, with the remainder being Fe and unavoidable impurities.

[0045] Key process steps and parameters:

[0046] (1) Smelting: The weight of molten iron fed into the converter was 109 tons, and the weight of scrap steel was 46 tons; the final molten steel had a carbon content of 0.08% and a phosphorus content of 0.009%.

[0047] (2) Refining: Al at the LF furnace outlet is 0.0030%; RH soft blowing for 15 minutes, standing for 11 minutes, outlet temperature is 1555℃.

[0048] (3) Continuous casting: The secondary cooling water ratio is 0.36L / KG, the superheat of the tundish is 25℃, and the reduction parameters are finely adjusted to ensure that the reduction is 26mm.

[0049] (4) Rolling: The billet is heated for 420 minutes, and the temperature in the high-temperature section is controlled at 1220℃ for 205 minutes.

[0050] (5) The temperature of the upper cooling bed is 760℃, and the rolling cooling bed is densely packed and slowly cooled. The temperature of the exit of the slow cooling zone is 480℃.

[0051] The metallographic structure of the round steel produced according to the above method is as follows: Figure 1 As shown.

[0052] Example 2:

[0053] The chemical composition (by weight percentage) of the steel used for spring bars is: C: 0.56%, Si: 1.60%, Mn: 0.74%, P: 0.008%, S: 0.009%, Cr: 0.85%, Mo: 0.02%, Al... T 0.0015%, V: 0.15%, N: 0.0035%, O: 0.0007%, Ca: 0.0012%, with the remainder being Fe and unavoidable impurities.

[0054] Key process steps and parameters:

[0055] (1) Smelting: The weight of molten iron entering the converter is 110 tons, and the weight of scrap steel is 45 tons; the final molten steel has C of 0.10% and P of 0.007%;

[0056] (2) Refining: Al at the LF furnace outlet is 0.0020%; RH soft blowing for 15 minutes, standing for 12 minutes, outlet temperature is 1556℃.

[0057] (3) Continuous casting: The secondary cooling water ratio is 0.36L / KG, the superheat of the tundish is 26℃, and the reduction parameters are finely adjusted to ensure that the reduction is 26mm.

[0058] (4) Rolling: The billet is heated for 400 minutes, and the temperature in the high-temperature section is controlled at 1220℃ for 220 minutes.

[0059] (5) The temperature of the upper cooling bed is 750℃, and the rolling cooling bed is densely packed and slowly cooled. The temperature of the exit of the slow cooling zone is 470℃.

[0060] Example 3:

[0061] The chemical composition (by weight percentage) of the steel used for spring bars is: C: 0.58%, Si: 1.65%, Mn: 0.78%, P: 0.010%, S: 0.007%, Cr: 0.84%, Mo: 0.02%, Al... T 0.0035%, V: 0.15%, N: 0.0035%, O: 0.0004%, Ca: 0.0012%, with the remainder being Fe and unavoidable impurities.

[0062] Key process steps and parameters:

[0063] (1) Smelting: The weight of molten iron fed into the converter is 107 tons, and the weight of scrap steel is 47 tons; the final molten steel has a carbon content of 0.11% and a phosphorus content of 0.009%;

[0064] (2) Refining: Al at the LF furnace outlet is 0.0040%; RH soft blowing for 15 minutes, standing for 12 minutes, outlet temperature is 1560℃.

[0065] (3) Continuous casting: The secondary cooling water ratio is 0.36L / KG, the superheat of the tundish is 24℃, and the reduction parameters are finely adjusted to ensure that the reduction is 26mm.

[0066] (4) Rolling: The billet is heated for 460 minutes, and the temperature in the high-temperature section is controlled at 1210℃ for 240 minutes.

[0067] (5) The temperature of the upper cooling bed is 740℃, and the rolling cooling bed is densely packed and slowly cooled. The temperature of the exit of the slow cooling zone is 420℃.

[0068] Example 4:

[0069] The chemical composition (by weight percentage) of the steel used for spring bars is: C: 0.57%, Si: 1.70%, Mn: 0.75%, P: 0.009%, S: 0.007%, Cr: 0.82%, Mo: 0.02%, Al...T 0.0030%, V: 0.16%, N: 0.0032%, O: 0.0005%, Ca: 0.0010%, with the remainder being Fe and unavoidable impurities.

[0070] Key process steps and parameters:

[0071] (1) Smelting: The weight of molten iron entering the converter is 111 tons, and the weight of scrap steel is 45 tons; the final molten steel has a carbon content of 0.06% and a phosphorus content of 0.008%;

[0072] (2) Refining: Al at the LF furnace outlet is 0.0035%; RH soft blowing for 15 minutes, standing for 14 minutes, outlet temperature is 1559℃.

[0073] (3) Continuous casting: The secondary cooling water volume is 0.36L / KG, the superheat of the tundish is 22℃, and the reduction parameters are finely adjusted to ensure that the reduction is 26mm.

[0074] (4) Rolling: The billet is heated for 415 minutes, and the temperature in the high-temperature section is controlled at 1225℃ for 230 minutes.

[0075] (5) The temperature of the upper cooling bed is 800℃, and the rolling cooling bed is densely packed and slowly cooled. The temperature of the exit of the slow cooling zone is 490℃.

[0076] Table 1. Chemical composition (%) of the steel in each embodiment.

[0077]

[0078] Table 2 Product Performance Testing Indicators of Examples

[0079]

[0080] In summary, the technical solution of this invention can produce rolled round steel with a finished product size of φ20mm to φ80mm. The key quality indicators of the product are low non-metallic inclusion content, total oxygen content ≤10ppm, grain size up to grade 9.5, banded structure ≤1.5, and carbon segregation within 1.05.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for producing high-strength, high-toughness spring bars, characterized in that, The process includes reflow converter smelting, ladle furnace refining, RH vacuum degassing, rectangular billet continuous casting production, billet rolling, billet grinding, round steel rolling, and post-rolling slow cooling. In the ladle furnace refining process, an alkaline slagging agent is added in the early stage of refining according to the weight of the molten steel, and an acidic slagging agent is added in the middle stage to maintain the basicity of the steel between 0.8 and 1.

0. In the rectangular billet continuous casting process, the billet solidification end adopts a light and heavy reduction process, with a total reduction of 26mm in 2 to 9 stands; in the round steel rolling process, the heating temperature of the soaking zone is 1040-1070℃, and the reduction rate of the first and second passes is greater than 60%; water-controlled rolling is carried out, with a final rolling temperature of 650-700℃ and a cumulative reduction rate of greater than 80%; The chemical composition of the steel used for spring bars, by weight percentage, is as follows: C: 0.40%–0.60%, Si: 1.00%–2.00%, Mn: 0.5%–1.00%, P≤0.012%, S≤0.012%, Cr: 0.50%–1.00%, Mo: 0.01%–0.05%, Al≤0.0040%, V: 0.10%–0.40%, N≤0.0040%, O≤0.0010%, Ca≤0.0020%, with the remainder being Fe and unavoidable impurities.

2. The method for producing a high-strength, high-toughness spring bar as described in claim 1, characterized in that, In the aforementioned combined blowing converter smelting process, the ratio of molten iron to scrap steel is controlled at 7:3, and the P content at the smelting endpoint does not exceed 0.010%. A composite deoxidizer is added in the early stage of tapping for slag formation and deoxidation, a low-N alloy is added in the middle stage of tapping for alloying, and a steel retention operation is adopted in the later stage of tapping to prevent oxidized slag from entering the ladle.

3. The method for producing a high-strength, high-toughness spring bar as described in claim 2, characterized in that, In the ladle furnace refining process, based on the weight of the molten steel, in the early stage of refining, low-N refining synthetic slag and alkaline slag-forming agent are added at a rate of 5 kg / t of molten steel to create refining white slag for deoxidation, desulfurization, and removal of inclusions. In the middle stage of refining, acidic slag-forming agent is added at a rate of 8 kg / t of molten steel, with aluminum content controlled below 0.0040%. After a soft blowing time of 8 minutes, the molten steel is transferred to an RH furnace for degassing. No calcium treatment is performed during the entire refining process. Then, a covering agent is added to protect the molten steel. The refining time is between 55 and 75 minutes.

4. The method for producing a high-strength, high-toughness spring bar as described in claim 3, characterized in that, In the vacuum degassing process, after the RH is evacuated to below 67Pa and the vacuum is maintained for 15 minutes, the hydrogen content of the molten steel is determined by breaking the vacuum and controlling the hydrogen content to ≤1.5ppm. After a soft blowing time of 15 minutes before leaving the station, the argon gas is turned off and the molten steel is allowed to stand for 10 minutes.

5. The method for producing a high-strength, high-toughness spring bar as described in claim 4, characterized in that, In the rectangular billet continuous casting production process, a 350×430mm cross-section continuous casting production is adopted, the billet pulling speed is controlled at a constant speed of 0.55m / min, the electromagnetic stirring of the crystallizer and the electromagnetic stirring at the solidification end are controlled at 200A, 2.0Hz and 400A, 16.0Hz respectively, the primary cooling water flow rate is 3000L / min, and the secondary cooling water flow rate is 0.36L / kg.

6. The method for producing a high-strength, high-toughness spring bar as described in claim 5, characterized in that, In the billet rolling process, a primary rolling mill with a cross-section of 1100mm is used for billet rolling, and finally a 7-stand rolling mill is used to roll out the finished product; the preheating section of the cast billet is ≤650℃, the high temperature section is 1200~1260℃, the high temperature section is held for 3h~4h, and the total heating time is 6-8h; the initial rolling temperature is ≥1150℃, the primary rolling billet is rolled in 7 passes, the first two passes are used to continuously roll the narrow face of the billet and then the edge is rolled, the single pass reduction is more than 25%, after billet rolling, it is rolled in a continuous rolling mill and stacked for slow cooling for 24h.

7. The method for producing a high-strength, high-toughness spring bar as described in claim 6, characterized in that, In the billet grinding process, the grinding depth on one side is controlled between 1.0 mm and 1.5 mm. After grinding, magnetic particle testing is used to manually repair the local areas.

8. The method for producing a high-strength, high-toughness spring bar as described in claim 7, characterized in that, In the post-rolling slow cooling process, the roll is subjected to water-cooled rapid cooling, the upper cooling bed temperature is 760±30℃, the cooling bed is densely packed for slow cooling, and the exit temperature is below 500℃.

9. The method for producing a high-strength, high-toughness spring bar as described in claim 8, characterized in that, The spring bar has a total oxygen content of ≤0.0010%, a grain size of 9.5 grade, a banded structure of ≤1.5 grade, and a low-magnification segregation index of less than 1.05.

Images