Method for improving center segregation and wire performance of spring steel small square billet

Abstract

The invention discloses a method for improving center segregation and wire performance of a spring steel small square billet, which comprises the following steps: converter smelting, LF refining, RH vacuum degassing and continuous casting: the spring steel comprises the following chemical components in percentage by mass: 0.53-0.58% of C, 1.42-1.52% of Si, 0.60-0.70% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, 0.60-0.70% of Cr and the balance of Fe and inevitable trace impurities, and the total mass fraction is 100%. According to the method for improving the center segregation and the wire performance of the small square billet of the spring steel, the superheat degree of molten steel and the electromagnetic stirring current are strictly controlled in the smelting process, the center segregation of the casting billet is remarkably reduced, the mechanical performance of the spring steel is improved, and therefore the spring steel with the excellent performance is produced; and the overall service life and the safety of the spring are remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting, and in particular relates to a method for improving the central segregation of a spring steel billet and the performance of a wire. Background Art

[0002] Spring steel is widely used in the automotive industry and other fields. 55SiCr spring steel is mainly used to make automobile suspension springs and valve springs and other parts. Due to its harsh service environment, it needs to have high strength, fatigue life and sufficient plastic toughness. A steel plant uses 150mm×150mm small square billets to produce 55SiCr spring steel wire rod products. The cross-sectional shrinkage of the tempered steel wire after user processing is less than 40%, which affects the subsequent coiling process and the service life of the spring. Studies have shown that the width of the two-phase zone of 55SiCr spring steel is large, and segregation is easy to occur during the solidification process. Center segregation has become the main factor affecting the performance of spring steel at present, especially the cross-sectional shrinkage of spring steel wire treated by the quenching and tempering process. By studying the influencing factors of the center segregation of small square billets, it is found that the superheat of molten steel and the electromagnetic stirring current of the crystallizer in the continuous casting process have a great influence on the center segregation of small square billets. The present invention successfully reduces the average carbon segregation index at the center of the ingot by strictly controlling the superheat of molten steel and the electromagnetic stirring current, improves the cross-sectional shrinkage rate of the product in the quenched and tempered state, and meets the use requirements of users in the subsequent processing process.

[0003] Publication No. CN 117428158 A introduces a continuous casting method for improving carbon segregation of spring steel rectangular billets. By precisely controlling multiple parameters such as molten steel superheat and drawing speed in the continuous casting process and process equipment, an ideal carbon segregation index and cross-sectional carbon extreme difference are obtained. This patent introduces a method for improving the center segregation of spring steel billets and wire performance. Through converter smelting, LF refining and other processes, the molten steel superheat and the electromagnetic stirring current of the crystallizer are controlled to reduce the center carbon segregation index of the billet and improve the wire performance. This patent focuses on the improvement of the center segregation of billets and wire performance. Through specific chemical composition and more sophisticated process control (such as parameters of each link), it can better reflect its advantages in segregation improvement and performance improvement, and can better meet the production needs of spring steel.

[0004] Publication No. CN 118549423 A introduces a method for determining the degree of center segregation of 55SiCrA spring steel. The degree of segregation is determined based on the number and width of white bands in the center of the wire rod sample by heat treatment, processing, inlaying, grinding, polishing, etching, etc. This patent introduces a method for improving the center segregation of spring steel billets and wire performance. Through a series of processes such as specific chemical composition and converter smelting, LF refining, etc., parameters such as molten steel superheat and electromagnetic stirring current are controlled to reduce the carbon segregation index of the ingot center and improve the wire performance. This patent focuses on improving the center segregation of spring steel billets and wire performance. A systematic study has been conducted from chemical composition design to various process links. The performance changes under different conditions are fully demonstrated through example comparison, which can more accurately optimize the production process and ensure product quality.

[0005] Publication No. CN 118166256 A introduces a process for improving the cross-sectional shrinkage of 55SiCr spring steel quenched and tempered steel wire. By controlling the key parameters of continuous casting, billet opening, rolling and heat treatment processes, the center segregation of the steel billet is improved and the cross-sectional shrinkage of the steel wire is improved. This patent introduces a method for improving the center segregation of spring steel billets and wire performance. By setting a specific chemical composition range and strictly controlling the key parameters (such as molten steel superheat, electromagnetic stirring current, etc.) in a series of process processes such as converter smelting and LF refining, the center carbon segregation index of the billet is effectively reduced, and the wire performance is significantly improved. This patent focuses on the improvement of the center segregation of spring steel billets and wire performance, and has conducted detailed and in-depth research from chemical composition to various process links. Through a wealth of examples and comparative examples, the performance changes under different conditions are fully presented, which can more accurately optimize the production process and ensure product quality. Summary of the invention

[0006] The purpose of the present invention is to provide a method for improving the center segregation of spring steel billets and wire properties. By strictly controlling the superheat of molten steel and the electromagnetic stirring current during the smelting process, the center segregation of the billet is significantly reduced, the mechanical properties of the spring steel are improved, and spring steel with excellent performance is produced, thereby significantly improving the overall life and safety of the spring.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for improving the central segregation of spring steel billets and wire properties, comprising: converter smelting, LF refining, RH vacuum degassing, and continuous casting, wherein:

[0009] After pretreatment, the molten iron enters the furnace. At this time, the phosphorus content P% of the molten iron entering the furnace is required to be ≤0.140%, and the sulfur content S% is ≤0.015%. Low residual element scrap steel is used. At the end of smelting, the carbon content C% is guaranteed to be ≥0.06%. The end temperature is controlled at around 1640℃, and a fluctuation of ±10℃ is allowed. During the steelmaking process, low nitrogen carburizer, silicon-manganese alloy, and ferrosilicon are added to adjust the composition.

[0010] During the refining stage, the chemical composition is fine-tuned and low-basicity slag is produced. The slag basicity is controlled within the range of 1.5-2.0, and the white slag is kept for ≥20 minutes to promote the denaturation of inclusions and make them float up for removal.

[0011] Use RH vacuum treatment method to reduce the content of hydrogen, oxygen and nitrogen in molten steel; in this process, the vacuum degree is controlled below 100Pa, and the vacuum treatment time is ≥20min, and the soft argon blowing time is ≥15min;

[0012] Dynamic soft pressure reduction at the end of solidification, electromagnetic stirring, weak cooling in the second cooling stage and correction technology are adopted; the billet drawing speed during continuous casting is strictly controlled within the range of 1.5-1.6m / min, and the superheat of molten steel is strictly controlled to be between 30 and 35°C; the electromagnetic stirring current of the crystallizer is controlled at 150-200A; medium carbon protective slag is used, and the liquid level fluctuation is strictly controlled to reduce the center segregation and center loose defects of the continuous casting billet; the slow cooling time of the billet should be more than 36 hours;

[0013] The chemical components of the spring steel include by weight percentage: C 0.53% to 0.58%, Si 1.42% to 1.52%, Mn 0.60% to 0.70%, P≤0.020%, S≤0.010%, Cr 0.60% to 0.70%, and the rest are Fe and unavoidable trace impurities, with a total weight fraction of 100%.

[0014] Furthermore, the chemical composition of the spring steel includes by weight percentage: C 0.55%, Si 1.47%, Mn 0.65%, P 0.008%, S 0.005%, Cr 0.65%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0015] Furthermore, the chemical composition of the spring steel includes by weight percentage: C 0.56%, Si 1.45%, Mn 0.66%, P 0.007%, S 0.004%, Cr 0.64%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0016] Furthermore, the chemical composition of the spring steel includes by weight percentage: C 0.54%, Si 1.48%, Mn 0.67%, P 0.009%, S 0.006%, Cr 0.66%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0017] Further, it specifically includes:

[0018] After pretreatment, the molten iron enters the furnace. At this time, the phosphorus content P% of the molten iron entering the furnace is required to be ≤0.140%, and the sulfur content S% is ≤0.015%; low residual element scrap steel is used, and at the end of smelting, the carbon content C% is guaranteed to be 0.10%, and the end temperature is controlled at 1642℃; during the steelmaking process, low nitrogen recarburizer, silicon-manganese alloy, and ferrosilicon are added to adjust the composition;

[0019] During the refining stage, the chemical composition is fine-tuned and low-basicity slag is produced. The slag basicity is controlled at 1.6 and the white slag is kept for 25 minutes to promote the denaturation of inclusions and make them float up for removal.

[0020] The RH vacuum treatment method is used to reduce the content of hydrogen, oxygen and nitrogen in the molten steel. During this process, the vacuum degree is controlled at 80Pa, the vacuum treatment time is 22 minutes, and the soft argon blowing time is 17 minutes.

[0021] Dynamic soft pressure at the end of solidification, electromagnetic stirring, weak cooling in the second cooling stage and correction technology are used. The billet drawing speed during continuous casting is 1.5m / min, the superheat is 32℃; the crystallizer electromagnetic stirring current is 180A; medium carbon protective slag is used, and the liquid level fluctuation is strictly controlled to reduce the center segregation and center loose defects of the continuous casting billet; the slow cooling time of the billet should be more than 36 hours.

[0022] Furthermore, the carbon segregation index at the center of the ingot was successfully reduced to 1.02-1.03.

[0023] Compared with the prior art, the beneficial technical effects of the present invention are:

[0024] (1) By strictly controlling the superheat of molten steel and the electromagnetic stirring current of the crystallizer during the continuous casting process, the present invention successfully reduced the central carbon segregation index of the ingot from 1.12 to 1.03, significantly improving the central segregation of the small square billet. (2) By optimizing process control, the present invention increased the cross-sectional shrinkage rate of the tempered spring steel wire from the original 35% to 46%, greatly improving the plasticity and toughness of the material and improving its performance in subsequent processing. (3) By reducing segregation and optimizing the smelting and continuous casting processes, the mechanical properties of the spring steel are significantly improved, thereby increasing the overall service life and safety of the spring, and meeting the high performance requirements of automobile suspension springs. DETAILED DESCRIPTION

[0025] Embodiment 1: A method for producing a spring flat steel according to the present invention is carried out in the following steps:

[0026] After pretreatment, the molten iron enters the furnace. At this time, the phosphorus content P% of the molten iron entering the furnace is required to be ≤0.140%, and the sulfur content S% is ≤0.015%. The self-produced low-residual element scrap steel is used. At the end of smelting, the carbon content C% is guaranteed to be 0.10%, and the end temperature is controlled at 1642℃. In the process of steel tapping, low-nitrogen carburizer, silicon-manganese alloy, and ferrosilicon are added to adjust the composition;

[0027] During the refining stage, the chemical composition is fine-tuned and low-basicity slag is produced. The slag basicity is controlled at 1.6 and the white slag is kept for 25 minutes to promote the denaturation of inclusions and make them float up for removal.

[0028] The RH vacuum treatment method is used to reduce the content of hydrogen, oxygen, nitrogen and other gases in the molten steel. In this process, the vacuum degree is controlled at 80Pa, the vacuum treatment time is 22 minutes, and the soft argon blowing time is 17 minutes;

[0029] Dynamic soft pressure at the end of solidification, electromagnetic stirring, weak cooling in the second cooling stage and correction technology are used. The billet drawing speed during continuous casting is 1.5m / min, and the superheat is 32℃. The electromagnetic stirring current of the crystallizer is 180A. Medium carbon protective slag is used, and the liquid level fluctuation is strictly controlled to reduce defects such as center segregation and center looseness of the continuous casting billet. The slow cooling time of the billet should be more than 36 hours.

[0030] Embodiment 2-3:

[0031] In Example 2-3, except for some specific process parameters which are different from those in Example 1 (see Table 1), the rest are exactly the same as those in Example 1.

[0032] Comparative Example 1:

[0033] In Comparative Example 1, except for the molten steel superheat and the electromagnetic stirring current which are different from those in Example 1 (see Table 1), the rest is exactly the same as in Example 1. In this comparative example, the molten steel superheat is 18°C ​​and the electromagnetic stirring current is 280A.

[0034] Comparative Example 2:

[0035] In Comparative Example 2, except for the molten steel superheat and the electromagnetic stirring current which are different from those in Example 1 (see Table 1), the rest is exactly the same as Example 1. In this comparative example, the molten steel superheat is 22°C and the electromagnetic stirring current is 300A.

[0036] Comparative Example 3:

[0037] In Comparative Example 3, except that the molten steel superheat and the electromagnetic stirring current are different from those in Example 1 (see Table 1), the rest is exactly the same as in Example 1. In this comparative example, the molten steel superheat is 20° C. and the electromagnetic stirring current is 270 A. The differences in specific process parameters between the embodiments and comparative examples are shown in Table 1.

[0038] Table 1 Differences in process parameters of various embodiments

[0039]

[0040]

[0041] Table 2 shows the chemical compositions of three embodiments and three comparative examples of the present invention. Table 2 and Table 3 further illustrate the present invention.

[0042] Table 2 Chemical composition of various examples of spring steel (mass percentage / %)

[0043] Example C Si Mn P S Cr Example 1 0.55 1.47 0.65 0.008 0.005 0.65 Example 2 0.56 1.45 0.66 0.007 0.004 0.64 Example 3 0.54 1.48 0.67 0.009 0.006 0.66 Comparative Example 1 0.57 1.46 0.64 0.008 0.005 0.63 Comparative Example 2 0.55 1.49 0.68 0.007 0.005 0.65 Comparative Example 3 0.53 1.44 0.66 0.009 0.004 0.64

[0044] Table 2 Mechanical properties of each example

[0045]

[0046] By comparing the above comparative examples, the embodiments of the present invention have significant advantages over the comparative examples. The embodiments successfully reduce the carbon segregation index of the ingot center to 1.02-1.03 by controlling the superheat of the molten steel between 30-35°C and adjusting the electromagnetic stirring current of the crystallizer between 150-200A. Compared with 1.08-1.12 of the comparative example, the segregation is greatly reduced. In the embodiments, the cross-sectional shrinkage rate of the quenched and tempered state reaches 46%-47%, which is significantly higher than 37%-41% of the comparative example, which indicates that the plasticity of the material in processing and use is significantly improved.

[0047] It can be seen from the above examples and comparative examples that by optimizing the continuous casting process (such as the control of the superheat of molten steel and the electromagnetic stirring current), the examples significantly reduce the central segregation index of the ingot, which shows that the optimization of process parameters plays an important role in reducing segregation. The cross-sectional shrinkage in the examples is significantly higher than that in the comparative examples, indicating that by improving the process conditions, the plasticity and toughness of the material can be effectively improved, and the performance in subsequent processing and use can be enhanced. Compared with the comparative examples, the examples verify the positive effect of strictly controlling the smelting and continuous casting process parameters on the performance of the final product.

[0048] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for improving the center segregation of spring steel billets and wire properties, characterized in that: include: Converter smelting, LF refining, RH vacuum degassing, continuous casting: Among them: After pretreatment, the molten iron enters the furnace. At this time, the phosphorus content P% of the molten iron entering the furnace is required to be ≤0.140%, and the sulfur content S% is ≤0.015%. Low residual element scrap steel is used. At the end of smelting, the carbon content C% is guaranteed to be ≥0.06%. The end temperature is controlled at around 1640℃, and a fluctuation of ±10℃ is allowed. During the steelmaking process, low nitrogen carburizer, silicon-manganese alloy, and ferrosilicon are added to adjust the composition. During the refining stage, the chemical composition is fine-tuned and low-basicity slag is produced. The slag basicity is controlled within the range of 1.5-2.0, and the white slag is kept for ≥20 minutes to promote the denaturation of inclusions and make them float up for removal. Use RH vacuum treatment method to reduce the content of hydrogen, oxygen and nitrogen in molten steel; in this process, the vacuum degree is controlled below 100Pa, and the vacuum treatment time is ≥20min, and the soft argon blowing time is ≥15min; Dynamic soft pressure reduction at the end of solidification, electromagnetic stirring, weak cooling in the second cooling stage and correction technology are adopted; the billet drawing speed during continuous casting is strictly controlled within the range of 1.5-1.6m / min, and the superheat of molten steel is strictly controlled to be between 30 and 35°C; the electromagnetic stirring current of the crystallizer is controlled at 150-200A; medium carbon protective slag is used, and the liquid level fluctuation is strictly controlled to reduce the center segregation and center loose defects of the continuous casting billet; the slow cooling time of the billet should be more than 36 hours; The chemical components of the spring steel include by weight percentage: C 0.53% to 0.58%, Si 1.42% to 1.52%, Mn 0.60% to 0.70%, P≤0.020%, S≤0.010%, Cr 0.60% to 0.70%, and the rest are Fe and unavoidable trace impurities, with a total weight fraction of 100%.

2. The method for improving the center segregation of spring steel billets and wire properties according to claim 1, characterized in that: The chemical components of the spring steel include by weight percentage: C 0.55%, Si 1.47%, Mn 0.65%, P 0.008%, S0.005%, Cr 0.65%, and the rest are Fe and inevitable trace impurities, with a total weight fraction of 100%.

3. The method for improving the center segregation of spring steel billets and wire properties according to claim 1, characterized in that: The chemical components of the spring steel include by weight percentage: C 0.56%, Si 1.45%, Mn 0.66%, P 0.007%, S 0.004%, Cr 0.64%, and the rest are Fe and inevitable trace impurities, with a total weight fraction of 100%.

4. The method for improving the center segregation of spring steel billets and wire properties according to claim 1, characterized in that: The chemical components of the spring steel include by weight percentage: C 0.54%, Si 1.48%, Mn 0.67%, P 0.009%, S 0.006%, Cr 0.66%, and the rest are Fe and inevitable trace impurities, with a total weight fraction of 100%.

5. The method for improving the center segregation of spring steel billets and wire properties according to claim 1, characterized in that: Specifically include: After pretreatment, the molten iron enters the furnace. At this time, the phosphorus content P% of the molten iron entering the furnace is required to be ≤0.140%, and the sulfur content S% is ≤0.015%; low residual element scrap steel is used, and at the end of smelting, the carbon content C% is guaranteed to be 0.10%, and the end temperature is controlled at 1642℃; during the steelmaking process, low nitrogen recarburizer, silicon-manganese alloy, and ferrosilicon are added to adjust the composition; During the refining stage, the chemical composition is fine-tuned and low-basicity slag is produced. The slag basicity is controlled at 1.6 and the white slag is kept for 25 minutes to promote the denaturation of inclusions and make them float up for removal. The RH vacuum treatment method is used to reduce the content of hydrogen, oxygen and nitrogen in the molten steel. During this process, the vacuum degree is controlled at 80Pa, the vacuum treatment time is 22 minutes, and the soft argon blowing time is 17 minutes. Dynamic soft pressure at the end of solidification, electromagnetic stirring, weak cooling in the second cooling stage and correction technology are used. The billet drawing speed during continuous casting is 1.5m / min, the superheat is 32℃; the crystallizer electromagnetic stirring current is 180A; medium carbon protective slag is used, and the liquid level fluctuation is strictly controlled to reduce the center segregation and center loose defects of the continuous casting billet; the slow cooling time of the billet should be more than 36 hours.

6. The method for improving the center segregation of spring steel billets and wire properties according to claim 5, characterized in that: The carbon segregation index at the center of the ingot was successfully reduced to 1.02-1.03.

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