Production method of spring steel

Abstract

The invention discloses a spring steel production method which comprises the steps of converter smelting, LF refining, continuous casting, casting blank heating furnace heating and round steel rolling, and related processes and parameters are limited. The steel plate has the mark of 70 # and comprises the following chemical components in percentage by mass: 0.67%-0.75% of C, 0.17%-0.27% of Si, 0.50%-0.70% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, less than or equal to 0.25% of Cr, less than or equal to 0.35% of Ni, less than or equal to 0.25% of Cu and the balance of Fe and inevitable impurities, and the total mass fraction is 100%. According to the production method of the spring steel, the mechanical property of hot-rolled round steel is remarkably improved on the premise that the production cost is reduced by utilizing the microalloying principle of Cr, Ni and Cu, so that 70 # 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 present invention belongs to the technical field of steel smelting and rolling, and particularly relates to a production method of spring steel. Background Art

[0002] Spring steel needs to have excellent elasticity and resilience, and be able to quickly return to its original state after being compressed or stretched. The spring steel developed by the steel mill can ensure that the spring maintains stable elastic properties during long-term use, improving its service life and performance stability. Springs are subjected to frequent loading and unloading during use, so spring steel needs to have good fatigue strength and be able to withstand loading for a long time without permanent deformation or fracture. The spring steel developed by the steel mill can meet the strict requirements for fatigue strength in the spring manufacturing process. With the development of industries such as automobiles, machinery manufacturing, and electronics, the demand for springs is also increasing continuously. As an indispensable part of various mechanical equipment and products, the quality and performance of springs directly affect the performance and reliability of products. Therefore, the high-quality spring steel developed by the steel mill will be widely applied and recognized in the market. The popularization and application of the spring steel developed by the steel mill have clear feasibility and broad prospects. By meeting the market requirements for performance, quality, and cost, the steel mill can gain an important position in various industries, obtaining considerable market share and economic benefits.

[0003] Publication No. CN 118109740 A introduces a suspension spring, a spring steel wire rod and its preparation method, including processes such as molten steel smelting, bloom continuous casting, blooming, grinding and flaw detection, spraying anti-decarburization coating, hot rolling, and controlled cooling, and introduces the process parameters and product performance of each process. This patent introduces a production method of 70# spring steel, introduces its chemical composition, and through processes such as converter smelting and LF refining, develops 70# spring steel with excellent comprehensive mechanical properties. This patent can better reflect its advantages in comprehensive mechanical properties and quality stability through more refined process control (such as chemical composition, parameters of each link) and the setting of comparison ratios, and the developed 70# spring steel has a unique design in alloying treatment and can better meet the spring production requirements.

[0004] Publication number CN 110592313 A introduces a refining process for producing spring steel in an electric furnace, including steps of electric furnace smelting, LF furnace smelting and RH smelting, introduces the processes and control key points of each step, and can achieve the purpose of precise control of the composition of the refining slag. This patent introduces a production method of 70# spring steel, introduces its chemical composition, and through processes such as converter smelting and LF refining, develops 70# spring steel with excellent comprehensive mechanical properties. Through more refined process control (such as chemical composition and parameters of each link) and the setting of comparison ratios, its advantages in comprehensive mechanical properties and quality stability can be more reflected, and the developed 70# spring steel has a unique design in alloying treatment and process route, which better meets the production requirements of spring steel.

[0005] Publication number CN 118668136 A introduces a spring steel for construction machinery and its preparation method and application, introduces its chemical composition, including processes such as converter smelting and deoxidation alloying treatment, and improves the performance of spring steel and reduces the content of gas and inclusions through composition adjustment and process optimization. Through more refined process control (such as chemical composition and parameters of each link) and the setting of comparison ratios, its advantages in comprehensive mechanical properties and quality stability can be more reflected, and the developed 70# spring steel has a unique design in alloying treatment and can better meet the production requirements of springs. Summary of the Invention

[0006] The purpose of the present invention is to provide a production method of spring steel, which uses the principle of microalloying of Cr, Ni, and Cu to significantly improve the mechanical properties of hot-rolled round steel on the premise of reducing production costs, thereby producing 70# spring steel, and further significantly improving the overall life and safety of springs.

[0007] To solve the above technical problems, the present invention adopts the following technical solutions:

[0008] A production method of spring steel of the present invention includes converter smelting, LF refining, continuous casting, heating in a slab heating furnace, and round steel rolling, and is characterized in that:

[0009] Converter smelting: In combined blowing converter smelting, molten iron, scrap steel and pig iron are added into an LD oxygen converter for conventional top-bottom combined blowing, lime is added to make slag, and the end point carbon content is controlled ≥ 0.10%, and the tapping temperature <

[0010] 1670 °C; After tapping, argon blowing operation is carried out, and the argon blowing time > 10 min;

[0011] LF refining: Refining with white slag operation, ensuring that the white slag refining time > 15 min, feeding a calcium wire for inclusion deformation treatment, and the calcium wire is 100 m long; Desulfurization, composition fine-tuning and temperature raising operations are carried out according to the composition and temperature of the converter molten steel, and the soft blowing time ≥ 10 min;

[0012] Continuous casting: Constant casting speed control is adopted, with the casting speed of 1.8 - 2.1 m / min. Protective casting is used throughout the process. The tundish temperature is 1510 - 1530 °C, and the superheat ΔT is 20 - 25 °C. Soft cooling process is adopted for secondary cooling, and the specific water consumption is 1.2 - 1.4 L / kg. The billet specification is a small square billet of 150 mm × 150 mm, which is slowly cooled in a slow cooling pit for 48 h.

[0013] Billet heating furnace heating: The billet heating temperature is 1080 - 1120 °C, the allowable temperature difference ≤ 30 °C, the total heating time is controlled at 2 h, and the rolling start temperature is 1030 - 1050 °C.

[0014] Round steel rolling: The finished rolling specification is φ80 mm. The heat treatment system is quenching at 830 °C and tempering at 480 °C.

[0015] The mass percentage content of the chemical composition of the spring steel includes: C 0.67% - 0.75%, Si 0.17% - 0.27%, Mn 0.50% - 0.70%, P ≤ 0.015%, S ≤ 0.005%, Cr ≤ 0.25%, Ni ≤ 0.35%, Cu ≤ 0.25%, and the rest are Fe and inevitable impurities, with the total mass fraction being 100%.

[0016] Further, the mass percentage content of the chemical composition of the spring steel includes: C 0.70%, Si 0.25%, Mn 0.62%, P 0.014%, S 0.0053%, Cr 0.14%, Ni 0.24%, Cu 0.13%, and the rest are Fe and inevitable impurities, with the total mass fraction being 100%.

[0017] Further, the mass percentage content of the chemical composition of the spring steel includes: C 0.69%, Si 0.24%, Mn 0.60%, P 0.015%, S 0.0058%, Cr 0.16%, Ni 0.23%, Cu 0.15%, and the rest are Fe and inevitable impurities, with the total mass fraction being 100%.

[0018] Further, the mass percentage content of the chemical composition of the spring steel includes: C 0.72%, Si 0.26%, Mn 0.63%, P 0.012%, S 0.0045%, Cr 0.15%, Ni 0.22%, Cu 0.14%, and the rest are Fe and inevitable impurities, with the total mass fraction being 100%.

[0019] Further, the tensile strength Rm of the produced spring steel all exceeds 1120 MPa, and the yield strength Rp0.2 all exceeds 899 MPa.

[0020] Furthermore, the elongation A of the produced spring steel is ≥ 11.0%, and the reduction of area Z is ≥ 44%.

[0021] Furthermore, pay attention to the conditions of the rolling mill, steel turning machine, guide guard plate, roller table and cover plate, and ensure they are smooth without sharp edges and corners to avoid scratches and bruises on the surface of the rolled piece.

[0022] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0023] (1) By precisely controlling the types and contents of alloying elements, especially the microalloying treatment of trace amounts of Cr, Ni, and Cu, the strength of the steel is improved, making the product perform more excellently in high-strength working environments; (2) The combined blowing converter and LF refining processes are adopted to effectively remove non-metallic inclusions in the steel, significantly improve the cleanliness of the steel, reduce the generation of defects, and thus extend the service life of the steel; (3) By optimizing the smelting and rolling processes and reasonably controlling the heating temperature and rolling temperature, high-quality material properties are ensured. Specific Embodiments

[0024] The following further details the spring steel of the present invention and its production method.

[0025] Example: This example is a preferred example among various embodiments of the present invention.

[0026] For the spring steel of this example and its production method, the mass percentage contents of its chemical components include: C 0.67% - 0.75%, Si 0.17% - 0.27%, Mn 0.50% - 0.70%, P ≤ 0.015%, S ≤ 0.005%, Cr ≤ 0.25%, Ni ≤ 0.35%, Cu ≤ 0.25%, and the rest are Fe and inevitable trace impurities, with the total mass fraction being 100%.

[0027] The production method of the spring steel in this example is: converter smelting, LF refining, continuous casting, heating in a slab reheating furnace, and round steel rolling.

[0028] Furthermore: In combined blowing converter smelting, hot metal, scrap steel and pig iron are added into the LD oxygen converter for conventional top-bottom combined blowing, lime is added to make slag, and the end point carbon content is controlled to be ≥ 0.10%, and the tapping temperature is < 1670°C. After tapping, argon blowing operation is carried out, and the argon blowing time is > 10 min;

[0029] Furthermore: In refining white slag operation, ensure that the white slag refining time is > 15 min, feed in the calcium wire for inclusion deformation treatment, and the length of the calcium wire is 100 m; carry out desulfurization, composition fine-tuning and temperature raising operations according to the composition and temperature of the converter molten steel, and the soft blowing time is ≥ 10 min;

[0030] Furthermore: Adopt constant casting speed control, with the casting speed of 1.8 - 2.1 m / min. Protective casting is adopted throughout the process. The tundish temperature is 1510 - 1530 °C, and the superheat ΔT is 20 - 25 °C. The secondary cooling adopts weak cooling process, and the specific water volume is 1.2 - 1.4 L / kg. The billet specification is a small square billet of 150 mm × 150 mm, which is put into the slow cooling pit for slow cooling for 48 h;

[0031] Furthermore: The heating temperature of the steel billet is 1080 - 1120 °C, the allowable temperature difference ≤ 30 °C, the total heating time is controlled at 2 h, and the rolling start temperature is 1030 - 1050 °C. Prevent overheating, overburning and decarburization, heat up slowly, ensure the uniform heating temperature of the steel billet and reduce the temperature difference;

[0032] Furthermore: Pay attention to the conditions of the rolling rolls, steel turning machine, guide guards, roller table and covers, and ensure they are smooth without sharp edges and corners to avoid defects such as scratches and dents on the surface of the rolled piece. The rolled product specification is φ80 mm. The heat treatment system is quenching at 830 °C and tempering at 480 °C.

[0033] For the spring steel produced by using the chemical composition and process flow of the present invention, the longitudinal mechanical properties of the steel can reach Rm ≥ 1030 MPa, ReL ≥ 835 MPa, A ≥ 8.0%, Z ≥ 30%, the austenite grain size of the steel ≥ grade 8, and there are no cracks, scabs, folds or inclusions on the surface of the steel.

[0034] Example 1: A production method of a spring steel of the present invention, with the grade of 70#, and is carried out according to the following steps:

[0035] Smelting in a combined blowing converter, adding hot metal, scrap steel and pig iron into the LD oxygen converter, carrying out conventional top and bottom combined blowing, adding lime to make slag, controlling the end carbon content ≥ 0.10%, and the tapping temperature < 1670 °C. After tapping, argon blowing operation is carried out, and the argon blowing time is 13 min;

[0036] Refining with white slag operation, ensuring the white slag refining time of 16 min, feeding in calcium wire for inclusion deformation treatment, and the length of the calcium wire is 100 m; Carry out desulfurization, composition fine-tuning and temperature raising operations according to the composition and temperature of the converter molten steel, and the soft blowing time is 10 min;

[0037] Adopt constant casting speed control, with the casting speed of 1.9 m / min. Protective casting is adopted throughout the process. The tundish temperature is 1518 °C, and the superheat ΔT is 23 °C. The secondary cooling adopts weak cooling process, and the specific water volume is 1.2 L / kg. The billet specification is a small square billet of 150 mm × 150 mm, which is put into the slow cooling pit for slow cooling for 48 h;

[0038] The heating temperature of the steel billet is 1090 °C, controlling the total heating time at 2 h, and the rolling start temperature is 1030 °C;

[0039] The rolled product specification is φ80 mm. The heat treatment system is quenching at 830 °C and tempering at 480 °C.

[0040] Example 2-3:

[0041] In Example 2-3, except for some specific process parameters being different from those in Example 1, the rest are exactly the same as in Example 1.

[0042] Comparative Example 1:

[0043] In Comparative Example 1, except for the contents of Cu 0.09%, Ni 0.09%, and Cr 0.05%, the rest are exactly the same as in Example 1.

[0044] Comparative Example 2:

[0045] In Comparative Example 2, except that the tempering temperature is 550 °C, the rest are exactly the same as in Example 1.

[0046] Comparative Example 3:

[0047] In Comparative Example 3, except that the secondary cooling water ratio is 2 L / kg, the rest are exactly the same as in Example 1.

[0048] Comparative Example 4:

[0049] In Comparative Example 4, except that the heating temperature of the steel billet is set to 1200 °C and the rolling temperature is 1150 °C, the rest are exactly the same as in Example 1.

[0050] Table 1 shows the chemical compositions of the three examples and four comparative examples of the present invention, in combination with Tables 2, 3, and 4 for further illustration of the present invention.

[0051] Table 1 Chemical Compositions of Each Example of Spring Steel (Mass Percentage / %)

[0052] Example C Si Mn P S Cr Ni Cu Example 1 0.70 0.25 0.62 0.014 0.0053 0.14 0.24 0.13 Example 2 0.69 0.24 0.60 0.015 0.0058 0.16 0.23 0.15 Example 3 0.72 0.26 0.63 0.012 0.0045 0.15 0.22 0.14 Comparative Example 1 0.71 0.23 0.61 0.013 0.0051 0.04 0.09 0.05 Comparative Example 2 0.68 0.27 0.59 0.014 0.0056 0.13 0.21 0.12 Comparative Example 3 0.73 0.24 0.64 0.011 0.0048 0.17 0.25 0.14 Comparative Example 4 0.69 0.22 0.65 0.013 0.0050 0.15 0.20 0.13

[0053] Table 2 Specific Process Parameters of Each Example and Comparative Example

[0054]

[0055] Table 3 Mechanical Property Indexes of Each Example of Spring Steel

[0056]

[0057] Table 4 Non-Metallic Inclusions and Austenite Grain Sizes of Each Example of Spring Steel

[0058]

[0059] As can be seen from Tables 2 to 4, (1) the tensile strength (Rm) of the embodiments of the present invention all exceed 1120 MPa, the yield strength (Rp0.2) all exceed 899 MPa, and the elongation and reduction of area are also relatively high (A≥11.0%, Z≥44%), which are superior to the indexes of multiple comparative examples, demonstrating excellent strength; (2) the grain sizes of the present invention all reach level 8 and above, significantly superior to the grain sizes of level 7 or even lower in the comparative examples, indicating that the microstructure of the material is more uniform and delicate, which helps to improve the fatigue performance and fracture resistance; (3) the grades of non-metallic inclusions in the embodiments are much lower than those in the comparative examples, especially the contents of inclusions of types A, B, and C are less (mostly ≤0.5), which greatly improves the purity and fatigue life of the material.

[0060] As can be seen from the above embodiments and comparative examples: (1) Compared with Comparative Example 1, after the contents of Cr, Ni, and Cu are increased in the embodiment, the strength of the material is improved, especially the grain size becomes finer, which can extend the service life of the spring steel. Through the microalloying treatment of Cr, Ni, and Cu in the embodiment, as well as the adoption of refining and controlled rolling processes, the mechanical properties of the steel and the uniformity of the microstructure are significantly improved. (2) Compared with Comparative Example 2, the tempering temperature is reduced in the embodiment, resulting in an increase in the strength and plasticity of the steel. The embodiment adopts a heat treatment system of tempering at 480°C, and by tempering at a relatively low temperature, the strength and plasticity of the material are balanced. (3) Compared with Comparative Example 3, the weak cooling process is adopted in the embodiment. By precisely controlling the secondary cooling process, the cleanliness of the microstructure of the material is significantly improved, the inclusion content is reduced, and the service life of the material is better. (4) In Comparative Example 4, due to the too high heating and rolling temperatures, the grain size of the steel becomes coarser, resulting in a decrease in the strength of the steel. In the embodiment, the heating temperature is controlled between 1080 - 1120°C, ensuring the uniformity of the grains and effectively preventing overheating and decarburization phenomena, thereby improving the mechanical properties of the material.

[0061] By comparing different comparative examples, the embodiments demonstrate their superiority in many aspects, including the selection of alloying elements, the optimization of smelting and rolling processes, and the precise control of heat treatment processes. These differences have brought about a significant improvement in mechanical properties.

[0062] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A production method of spring steel, including converter smelting, LF refining, continuous casting, heating in a slab reheating furnace, and round steel rolling, characterized in that: Converter smelting: Double combined blowing converter smelting. Molten iron, scrap steel and pig iron are added into an LD oxygen converter for conventional top and bottom combined blowing. Lime is added to make slag. The end point carbon content is controlled to be ≥0.10%, and the tapping temperature is <1670°C. After tapping, argon blowing operation is carried out, and the argon blowing time > 10 min; LF refining: Refining with white slag operation, ensuring that the white slag refining time > 15 min. Feed calcium wire for inclusion deformation treatment, and the length of the calcium wire is 100 m. Desulfurization, composition fine-tuning and temperature raising operations are carried out according to the composition and temperature of the converter molten steel, and the soft blowing time ≥ 10 min; Continuous casting: Adopt constant casting speed control, the casting speed is 1.8 - 2.1 m / min. Protective casting is adopted throughout the process. The tundish temperature is 1510 - 1530°C, and the superheat ΔT is 20 - 25°C. The secondary cooling adopts weak cooling process, and the specific water volume is 1.2 - 1.4 L / kg. The slab specification is a small square slab of 150 mm × 150 mm, and it is slowly cooled in a slow cooling pit for 48 h; Heating in a slab reheating furnace: The heating temperature of the steel slab is 1080 - 1120°C, the allowable temperature difference ≤ 30°C, the total heating time is controlled to be 2 h, and the rolling start temperature is 1030 - 1050°C; Round steel rolling: The finished rolling specification is φ80 mm. The heat treatment system is quenching at 830°C and tempering at 480°C; The mass percentage content of the chemical composition of the spring steel includes: C 0.67% - 0.75%, Si 0.17% - 0.27%, Mn 0.50% - 0.70%, P ≤ 0.015%, S ≤ 0.005%, Cr ≤ 0.25%, Ni ≤ 0.35%, Cu ≤ 0.25%, and the rest are Fe and inevitable impurities, and the total mass fraction is 100%.

2. The production method of the spring steel according to claim 1, characterized in that, The mass percentage content of the chemical composition of the spring steel includes: C 0.70%, Si 0.25%, Mn 0.62%, P 0.014%, S 0.0053%, Cr 0.14%, Ni 0.24%, Cu 0.13%, and the rest are Fe and inevitable impurities, and the total mass fraction is 100%.

3. The production method of the spring steel according to claim 1, characterized in that, The mass percentage content of the chemical composition of the spring steel includes: C 0.69%, Si 0.24%, Mn 0.60%, P 0.015%, S 0.0058%, Cr 0.16%, Ni 0.23%, Cu 0.15%, and the rest are Fe and inevitable impurities, and the total mass fraction is 100%.

4. The production method of the spring steel according to claim 1, characterized in that, The mass percentage content of the chemical composition of the spring steel includes: C 0.72%, Si 0.26%, Mn 0.63%, P 0.012%, S 0.0045%, Cr 0.15%, Ni 0.22%, Cu 0.14%, and the rest are Fe and inevitable impurities, and the total mass fraction is 100%.

5. The production method of the spring steel according to claim 1, characterized in that, The tensile strength Rm of the produced spring steel all exceeds 1120 MPa, and the yield strength Rp0.2 all exceeds 899 MPa.

6. The production method of the spring steel according to claim 1, characterized in that, The elongation A of the produced spring steel ≥ 11.0%, and the reduction of area Z ≥ 44%.

7. The production method of the spring steel according to claim 1, characterized in that, Pay attention to the conditions of the rolling rolls, tilters, guides, roller tables, and covers, and ensure they are smooth without sharp edges and corners to avoid scratches and dents on the surface of the rolled pieces.

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