Production method of 2000MPa-grade spring steel

Abstract

The invention discloses a production method of 2000MPa-grade spring steel, which is characterized by comprising the steps of converter smelting, LF (ladle furnace) refining, VD (vacuum degassing), continuous casting, heating of a casting blank heating furnace and round steel rolling, the steel comprises the following chemical components in percentage by mass: 0.50%-0.70% of C, 1.40%-1.70% of Si, 0.50%-0.80% of Mn, less than or equal to 0.015% of P, less than or equal to 0.015% of S, 0.60%-0.90% of Cr, 0.10%-0.20% of V and the balance of Fe and inevitable trace impurities, and the total mass fraction is 100%. The Cr and V microalloying principle is utilized, on the premise that the production cost is reduced, the mechanical property of the hot-rolled round steel is remarkably improved, so that the 2000MPa-grade spring steel is produced, the overall service life of the spring is remarkably prolonged, and the safety of the spring is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting and rolling, and in particular relates to a production method of 2000MPa grade spring steel. Background Art

[0002] With the continuous improvement of modern industry's requirements for material performance, especially in the fields of automobile, aerospace, energy and machinery manufacturing, the strength and toughness of spring steel are crucial. 2000MPa grade spring steel has extremely high strength and can withstand greater loads under smaller cross-sections, thereby reducing the weight of parts and improving the overall energy efficiency of equipment. This performance has a direct driving effect on the automotive industry to reduce vehicle weight, improve fuel efficiency and reduce carbon emissions, and is also in line with the current global trend of energy conservation and emission reduction. The application of 2000MPa grade spring steel in mechanical equipment, rail transportation and precision instruments is also expected to expand. For example, the demand for high-strength springs in shock absorbers and suspension systems has increased, and high-performance spring steel can significantly improve their service life and reliability. The research and development of 2000MPa grade spring steel can promote technological breakthroughs and industrial upgrading in my country's high-end material manufacturing field, and enhance the competitiveness of the domestic steel industry in the world. The research and development and application of 2000MPa grade spring steel can not only meet the urgent needs of the high-end manufacturing industry, but also have broad market potential and economic benefits.

[0003] Announcement No. CN 117888034 B introduces a 2000MPa grade vanadium-containing 55SiCr spring steel hot-rolled wire rod and its production process, including its chemical composition, production process steps and parameters. This patent discloses a 2000MPa grade spring steel and its production method, including chemical composition, production process and process parameter control, as well as the advantages reflected by comparison. The total content of alloy elements in the 2000MPa grade spring steel in this patent is low, which can significantly reduce production costs without affecting high performance.

[0004] Document 2 introduces that Maanshan Iron and Steel Co., Ltd. has successfully developed 2100MPa grade hot-rolled 54SiCrV6 spring steel round bars of different diameters through chemical composition optimization and controlled rolling and controlled cooling processes. This patent introduces the chemical composition and production method of a 2000MPa grade spring steel, including converter smelting, LF refining and other processes. Through reasonable design and process control, the spring steel has high tensile strength and other properties. The use of Cr and V microalloying reduces costs and improves production stability and controllability. The spring steel involved in this patent has higher tensile strength, and the production cost is reduced through the principle of microalloying. At the same time, the control of various process parameters in the production process is more detailed and accurate, which improves the stability and controllability of production.

[0005] Announcement No. CN 114959448 B introduces an efficient production method for 1900MPa grade suspension spring steel. Through the steps of converter primary smelting, LF furnace refining, continuous casting by continuous casting machine, and the use of electromagnetic stirring and light pressure reduction technology at the end of continuous casting solidification, the requirements for automobile suspension spring processing and use are met. This patent uses the Cr and V microalloying principle to control the chemical composition and production process through converter smelting, LF refining and other processes to produce spring steel with excellent comprehensive mechanical properties. The spring steel involved in this patent has higher strength, and the Cr and V microalloying principle is used to control the chemical composition and production process to obtain excellent comprehensive mechanical properties. Summary of the invention

[0006] The purpose of the present invention is to provide a production method of 2000MPa grade spring steel, which utilizes the Cr and V microalloying principle to significantly improve the mechanical properties of hot-rolled round steel while reducing production costs, thereby producing 2000MPa grade spring steel, 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 production method of 2000MPa grade spring steel, comprising: converter smelting, LF refining, VD vacuum degassing, continuous casting, heating in a casting furnace, and round steel rolling; wherein:

[0009] Combined blowing converter smelting: add molten iron, scrap steel and pig iron into LD oxygen converter, carry out conventional top and bottom composite blowing, add lime to make slag, control the final carbon content ≥ 0.10%, and the steel tapping temperature < 1670℃; after steel tapping, carry out argon blowing operation, and the argon blowing time is > 10min;

[0010] Refining white slag operation, ensure that the white slag refining time is greater than 15min, feed the calcium line for inclusion deformation treatment, the calcium line is 100m long; desulfurization, composition fine-tuning and temperature increase operations are carried out according to the composition and temperature of the converter molten steel, and the soft blowing time is greater than 10min;

[0011] The vacuum degree of molten steel in VD vacuum degassing is less than 67Pa to prevent the molten steel from churning and contacting with air to absorb nitrogen, and to prevent re-oxidation. The weak stirring time before leaving the station is guaranteed to be ≥28min, so as to facilitate the floating of alumina inclusions.

[0012] Constant pulling speed control is adopted, the pulling speed is 1.8~2.1m / min, protective casting is adopted throughout the process, the tundish temperature is 1510~1530℃, the superheat ΔT is 20~25℃, the secondary cooling adopts the cold cooling process, and the specific water volume is 1.2~1.4L / kg; the billet specification is a small square billet of 150mm×150mm, which is slowly cooled in the slow cooling pit for 48h;

[0013] The billet heating temperature is 1080~1120℃, the allowable temperature difference is ≤30℃, and the total heating time is controlled to be 2h. During the billet heating process, it must quickly pass through the decarburization sensitive zone of 850~900℃ to avoid decarburization on the round steel surface;

[0014] The starting rolling temperature is 1030-1050℃, followed by rolling at a lower temperature, and the cooling rate after rolling is controlled, and the final rolling temperature is 780-820℃; the heat treatment system is quenching oil cooling at 880℃, tempering water cooling at 400℃;

[0015] The mass percentage of its chemical composition includes: C 0.50%~0.70%, Si 1.40%~1.70%, Mn0.50%~0.80%, P≤0.015%, S≤0.015%, Cr 0.60%~0.90%, V 0.10%~0.20%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0016] Furthermore, the spring steel produced by the chemical composition and process flow of the present invention has longitudinal mechanical properties that meet the following requirements: Rm≥2000MPa, ReL≥1800MPa, A≥10.0%, Z≥40%, the austenite grain size of the steel is ≥8 grades, and there are no cracks, scars, folds or inclusions on the surface of the steel.

[0017] Furthermore, the mass percentage of its chemical composition includes: C 0.55%, Si 1.50%, Mn 0.72%, P0.008%, S 0.005%, Cr 0.73%, V 0.17%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0018] Furthermore, the mass percentage of its chemical composition includes: C 0.58%, Si 1.45%, Mn 0.68%, P0.006%, S 0.003%, Cr 0.77%, V 0.19%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0019] Furthermore, the mass percentage of its chemical composition includes: C 0.57%, Si 1.48%, Mn 0.71%, P0.008%, S 0.005%, Cr 0.74%, V 0.16%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are:

[0021] (1) Through reasonable chemical composition design and production process control, the developed 2000MPa grade spring steel has high tensile strength (≥2000MPa), high yield strength (≥1800MPa) and good plasticity (elongation A≥10%), which meets the application requirements of high-demand fields such as automobiles and aerospace, and significantly improves the material's bearing capacity and service life. (2) The present invention adopts Cr and V microalloying technology to effectively reduce the total content of alloy elements. Without affecting the high performance of steel, it achieves a significant reduction in production costs, is suitable for large-scale industrial production, and improves economic benefits. (3) By optimizing the smelting, refining and rolling process flow, such as controlling key process parameters such as steel tapping temperature, refining time, vacuum degassing, etc., the present invention improves the stability and controllability of the production process. DETAILED DESCRIPTION

[0022] The spring steel and the production method thereof of the present invention are further described in detail below.

[0023] Embodiment 1: A method for producing a 2000MPa grade spring steel according to the present invention is carried out in the following steps:

[0024] Combined blowing converter smelting: add molten iron, scrap steel and pig iron into LD oxygen converter, carry out conventional top and bottom composite blowing, add lime to make slag, control the final carbon content ≥ 0.10%, and the tapping temperature is 1650℃. After tapping, carry out argon blowing operation, and the blowing time is 15min;

[0025] Refining white slag operation, ensure that the white slag refining time is 16 minutes, feed the calcium line for inclusion deformation treatment, the calcium line is 100 meters long; desulfurization, composition fine-tuning and temperature increase operations are carried out according to the composition and temperature of the converter molten steel, and the soft blowing time is 13 minutes;

[0026] The molten steel is degassed in VD at a vacuum degree of 65Pa to prevent the molten steel from churning and contacting with air to absorb nitrogen, and to prevent re-oxidation. The weak stirring time before leaving the station is guaranteed to be 30 minutes to facilitate the floating of alumina inclusions.

[0027] Constant pulling speed control is adopted, the pulling speed is 1.9m / min, protective casting is adopted throughout the process, the tundish temperature is 1510~1530℃, the superheat ΔT is 22℃, the secondary cooling adopts the cold cooling process, and the specific water volume is 1.2~1.4L / kg. The billet specification is a small square billet of 150mm×150mm, which is slowly cooled in the slow cooling pit for 48h;

[0028] The heating temperature of the steel billet is 1090℃, the allowable temperature difference is ≤30℃, and the total heating time is controlled to be 2h. During the heating process of the steel billet, it must quickly pass through the decarburization sensitive zone of 850-900℃ to avoid decarburization on the surface of the round steel.

[0029] The starting rolling temperature is 1030℃, followed by rolling at a lower temperature, and the cooling rate after rolling is controlled. The final rolling temperature is 800℃. Pay attention to the condition of the rolls, steel turning machine, guide plate, roller table and cover plate, and ensure that they are smooth and have no sharp edges and corners to avoid scratches and dents on the surface of the rolled piece. The finished product specification is φ21mm. The heat treatment system is quenching oil cooling at 880℃ and tempering water cooling at 400℃.

[0030] Embodiment 2-3:

[0031] In Example 2-3, except for some specific process parameters which are different from those in Example 1, the rest are exactly the same as those in Example 1. The differences in specific process parameters are shown in Table 4.

[0032] Table 4 Differences in process parameters of the embodiments

[0033]

[0034]

[0035] Comparative Example 1:

[0036] In Comparative Example 1, except for the C content which is different from that in Example 1, the rest is exactly the same as that in Example 1. In this comparative example, the C content is 0.40%.

[0037] Comparative Example 2:

[0038] In Comparative Example 2, except that the contents of C, P and S are different from those in Example 1, the rest are exactly the same as in Example 1. In this comparative example, the C content is 0.60%, the P content is 0.020%, and the S content is 0.010%.

[0039] Comparative Example 3:

[0040] In Comparative Example 3, except for the V content being different from that in Example 1, the rest is exactly the same as that in Example 1. In this comparative example, the V content is 0.27%.

[0041] Table 1 shows the chemical compositions of three embodiments and three comparative examples of the present invention, and Table 2 and Table 3 further illustrate the present invention.

[0042] Table 1 Chemical composition of spring steel examples (mass percentage / %)

[0043] Example C Si Mn P S Cr V Example 1 0.55 1.50 0.72 0.008 0.005 0.73 0.17 Example 2 0.58 1.45 0.68 0.006 0.003 0.77 0.19 Example 3 0.57 1.48 0.71 0.008 0.005 0.74 0.16 Comparative Example 1 0.40 1.50 0.70 0.010 0.005 0.80 0.15 Comparative Example 2 0.60 1.50 0.70 0.020 0.010 0.75 0.18 Comparative Example 3 0.55 1.50 0.72 0.008 0.005 0.73 0.27

[0044] Table 2 Mechanical properties of spring steel examples

[0045]

[0046] Table 3 Non-metallic inclusions and austenite grain size of various examples of spring steel

[0047]

[0048] It can be seen from Tables 1-4 that: (1) The C content in Example 1 is controlled within the range of 0.50%-0.70%, and the higher C content than that in Comparative Example 1 improves the strength. At the same time, the appropriate Cr and V content optimizes the alloying effect, reduces non-metallic inclusions, and increases the grain size, thereby significantly improving the mechanical properties. (2) Compared with Comparative Example 2, the low carbon content (0.50%-0.70%) in Example 2 effectively controls the brittleness and overcomes the problem of increased brittleness caused by high P and S contents in Comparative Example 2. (3) Compared with Comparative Example 3, the V content in Example 3 is controlled within the range of 0.10%-0.20%, which not only ensures the refinement effect of the steel, but also avoids the problems of increased inclusions and increased process difficulty caused by excessively high V content.

[0049] The present invention achieves high strength and good plasticity of 2000MPa spring steel by accurately controlling the content of alloying elements such as C, Si, Mn, Cr, V, and optimizing production process parameters. The synergistic effect of microalloying (Cr, V) and specific process parameters (such as vacuum degree, weak stirring time, superheat, etc.) adopted by the present invention can significantly improve the comprehensive mechanical properties of steel. By comparison with comparative examples 1, 2, and 3, the spring steel in the embodiment shows obvious advantages in mechanical properties such as tensile strength and elongation, and also shows better quality in non-metallic inclusion control and grain refinement.

[0050] 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 producing 2000MPa grade spring steel, characterized in that: include: Converter smelting, LF refining, VD vacuum degassing, continuous casting, billet heating furnace heating, round steel rolling; among them: Combined blowing converter smelting: add molten iron, scrap steel and pig iron into LD oxygen converter, carry out conventional top and bottom composite blowing, add lime to make slag, control the final carbon content ≥ 0.10%, and the steel tapping temperature < 1670℃; after steel tapping, carry out argon blowing operation, and the argon blowing time is > 10min; Refining white slag operation, ensure that the white slag refining time is greater than 15min, feed the calcium line for inclusion deformation treatment, the calcium line is 100m long; desulfurization, composition fine-tuning and temperature increase operations are carried out according to the composition and temperature of the converter molten steel, and the soft blowing time is greater than 10min; The vacuum degree of molten steel in VD vacuum degassing is less than 67Pa to prevent the molten steel from churning and contacting with air to absorb nitrogen, and to prevent re-oxidation. The weak stirring time before leaving the station is guaranteed to be ≥28min, so as to facilitate the floating of alumina inclusions. Constant pulling speed control is adopted, the pulling speed is 1.8~2.1m / min, protective casting is adopted throughout the process, the tundish temperature is 1510~1530℃, the superheat ΔT is 20~25℃, the secondary cooling adopts the cold cooling process, and the specific water volume is 1.2~1.4L / kg; the billet specification is a small square billet of 150mm×150mm, which is slowly cooled in the slow cooling pit for 48h; The billet heating temperature is 1080~1120℃, the allowable temperature difference is ≤30℃, and the total heating time is controlled to be 2h. During the billet heating process, it must quickly pass through the decarburization sensitive zone of 850~900℃ to avoid decarburization on the round steel surface; The starting rolling temperature is 1030-1050℃, followed by rolling at a lower temperature, and the cooling rate after rolling is controlled, and the final rolling temperature is 780-820℃; the heat treatment system is quenching oil cooling at 880℃, tempering water cooling at 400℃; The mass percentage of its chemical composition includes: C 0.50%~0.70%, Si 1.40%~1.70%, Mn0.50%~0.80%, P≤0.015%, S≤0.015%, Cr 0.60%~0.90%, V 0.10%~0.20%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

2. The method for producing 2000MPa grade spring steel according to claim 1, characterized in that: The spring steel produced by the chemical composition and process flow of the present invention has longitudinal mechanical properties that meet the following requirements: Rm≥2000MPa, ReL≥1800MPa, A≥10.0%, Z≥40%, austenite grain size of the steel≥8 levels, and no cracks, scars, folds or inclusions on the surface of the steel.

3. The method for producing 2000MPa grade spring steel according to claim 1, characterized in that: The mass percentages of its chemical components include: C 0.55%, Si 1.50%, Mn 0.72%, P 0.008%, S 0.005%, Cr 0.73%, V 0.17%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

4. The method for producing 2000MPa grade spring steel according to claim 1, characterized in that: The mass percentages of its chemical components include: C 0.58%, Si 1.45%, Mn 0.68%, P 0.006%, S 0.003%, Cr 0.77%, V 0.19%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

5. The method for producing 2000MPa grade spring steel according to claim 1, characterized in that: The mass percentages of its chemical components include: C 0.57%, Si 1.48%, Mn 0.71%, P 0.008%, S 0.005%, Cr 0.74%, V 0.16%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

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