Production method of 80 # spring steel

Abstract

The invention discloses a production method of 80 # spring steel. The 80 # spring steel comprises the following chemical components in percentage by mass: 0.77%-0.85% 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, 0.05%-0.25% of Cr, 0.01%-0.35% of Ni, 0.05%-0.25% of Cu and the balance of Fe and inevitable impurities, and the total mass fraction is 100%. The production process comprises the following steps: 1) converter smelting; (2) LF refining; (3) continuous casting; 4) heating the casting blank in a heating furnace; and (5) round steel rolling and heat treatment. Through the Cr-Ni-Cu ternary microalloying synergistic effect, the extreme impurity control design and fine matching of process parameters, the strength of the 80 # spring steel is improved, meanwhile, excellent toughness and fatigue life are ensured, the production cost is reduced, and the application requirements of high-load springs in the high-end field are met.

Description

Technical Field

[0001] This invention relates to the fields of smelting and rolling technology, and in particular to a method for producing 80# spring steel. Background Technology

[0002] As a core component in mechanical equipment and industrial products, springs must withstand frequent loading and unloading cycles over long periods, thus placing stringent requirements on the elasticity, resilience, fatigue strength, and structural stability of spring steel. With the automotive, machinery manufacturing, and high-speed rail industries moving towards high-end and heavy-duty applications, the market demand for high-strength spring steel is increasingly urgent, necessitating the development of spring steel products with strength ≥1080MPa, excellent toughness, and controllable cost.

[0003] In existing technologies, such as the 65# spring steel disclosed in the prior art, a Cr-Ni binary microalloying design is used, with the carbon content controlled at 0.62% to 0.70%. Although this can meet the requirements of low- and medium-load scenarios, the upper limit of tensile strength is only 1070 MPa, which cannot be adapted to high-load applications. Traditional 80# spring steel (0.8% carbon content) suffers from the technical bottleneck of "high carbon inevitably leads to brittleness." While the strength is improved, the toughness is significantly reduced, the reduction of area is usually ≤25%, the fatigue life is short, and brittle fracture is prone to occur. In addition, existing technologies do not have sufficient precision in controlling harmful impurities (S, P) and do not pay attention to the synergistic effect of Cu in spring steel. At the same time, the matching of process parameters is poor, resulting in unstable overall product performance and high production costs.

[0004] Therefore, developing a production method for 80# spring steel that can overcome the contradiction between strength and toughness and combine high cleanliness, long service life and low cost has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a production method for 80# spring steel. Through the synergistic effect of Cr-Ni-Cu ternary microalloying, extreme impurity control design, and refined matching of process parameters, the method can improve the strength of 80# spring steel while ensuring excellent toughness and fatigue life, reducing production costs, and meeting the application requirements of high-load springs in high-end fields.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] This invention discloses a method for producing 80# spring steel, the chemical composition of which comprises, by mass percentage: C 0.77%–0.85%, Si 0.17%–0.27%, Mn 0.50%–0.70%, P ≤ 0.015%, S ≤ 0.005%, Cr 0.05–0.25%, Ni 0.01–0.35%, Cu 0.05–0.25%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass. The production process includes:

[0008] 1) Converter smelting: The combined blowing converter is used for smelting. Molten iron, scrap steel and pig iron are added to the LD oxygen converter for top and bottom combined blowing. Lime is added to form slag. The carbon content at the end point is controlled to be ≥0.10% and the tapping temperature is <1670℃. After tapping, argon blowing is performed for more than 10 minutes to reduce the oxidizability of the molten steel and reduce decarburization.

[0009] 2) LF Refining: Refining white slag is adopted to ensure that the white slag refining time is >15min; 100m calcium wire is fed in to deform inclusions and avoid nozzle nodules; desulfurization, composition fine-tuning and temperature increase are carried out according to the composition and temperature of the converter steel, and the soft blowing time is 10min to ensure that inclusions float up fully and improve the cleanliness of the steel.

[0010] 3) Continuous casting: Constant casting speed control is adopted, with a casting speed of 1.8 to 2.1 m / min; protective casting is used throughout the process, with a tundish temperature of 1510 to 1530℃ and a superheat ΔT of 20 to 25℃; a weak cooling process is adopted for the secondary cooling, with a water content of 1.2 to 1.4 L / kg; slow cooling in the slow cooling pit for 48 hours is used to release internal stress and avoid cracks and segregation defects;

[0011] 4) Billet heating furnace heating: The billet heating temperature is 1080~1120℃, the allowable temperature difference is ≤30℃, and the total heating time is controlled at 2h; the initial rolling temperature is 1030~1050℃, and the temperature is slowly increased to ensure uniform heating of the billet and prevent overheating, burning and decarburization.

[0012] 5) Round steel rolling and heat treatment: Ensure that the surfaces of the rolls, turning machine, and guide plate equipment are smooth and free of sharp edges to avoid scratches and dents on the surface of the rolled parts. The rolled product specification is φ90mm. The heat treatment process is 820℃ quenching and oil cooling + 480℃ tempering and air cooling to optimize the microstructure and balance strength and toughness.

[0013] Furthermore, the billet specifications are small square billets of 150mm×150mm.

[0014] Furthermore, its chemical composition by mass percentage includes: C 0.80%, Si 0.27%, Mn 0.66%, P 0.014%, S 0.0053%, Cr 0.18%, Ni 0.25%, Cu 0.18%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0015] Furthermore, its chemical composition by mass percentage includes: C 0.79%, Si 0.28%, Mn 0.65%, P 0.015%, S 0.0058%, Cr 0.17%, Ni 0.26%, Cu 0.19%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0016] Furthermore, its chemical composition by mass percentage includes: C 0.82%, Si 0.27%, Mn 0.66%, P 0.012%, S 0.0045%, Cr 0.18%, Ni 0.25%, Cu 0.18%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0017] Furthermore, the 80# spring steel has a yield strength ReL≥930MPa, tensile strength Rm≥1080MPa, elongation after fracture A≥6.0%, reduction of area Z≥30%, and austenite grain size≥6.

[0018] Furthermore, this method achieves a synergistic effect of "high strength + high toughness" under high carbon content, breaking through the bottleneck of traditional technology.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0020] 1. Excellent comprehensive mechanical properties: The yield strength ReL of the 80# spring steel of this invention is ≥930MPa, tensile strength Rm ≥1080MPa, elongation after fracture A ≥6.0%, reduction of area Z ≥30%, and austenite grain size ≥6. It achieves the synergy of "high strength + high toughness" under high carbon content, breaking through the bottleneck of traditional technology.

[0021] 2. Long fatigue life: Through extreme impurity control (S≤0.005%, P≤0.015%), LF refining and impurity removal, and calcium wire treatment, the content of non-metallic inclusions is significantly reduced, and the fatigue life of the steel reaches 1.2×10⁻⁶. 7 More than once, it is 50% higher than the 65# spring steel in the comparison document.

[0022] 3. Controllable production costs: By using converter smelting instead of electric furnace, optimizing process parameters, the total content of alloying elements is low, the unit energy consumption is reduced by 12%, the production efficiency is increased by 15%, and the surface defect rate is only 0.3%, which is far lower than the existing technology level.

[0023] 4. Wide range of applications: The product can be adapted to high-end and high-load scenarios such as heavy truck shock absorber springs, engineering machinery hydraulic springs, and high-speed rail contact wire springs, filling the gap in existing technology in this field. Detailed Implementation

[0024] The spring steel and its production method of the present invention will be described in further detail below.

[0025] Implementation Design

[0026] This embodiment provides three preferred embodiments (Examples 1-3) and four comparative examples to verify the superiority of the technical solution of the present invention through comparison. All embodiments and comparative examples use the same production equipment and basic processes, differing only in chemical composition or key process parameters.

[0027] Examples 1-3 (Technical Solutions of the Invention)

[0028] The mass percentage of its chemical components is shown in Table 1 below, and the production process strictly follows the parameter requirements of the above-mentioned technical solution of this invention.

[0029] Table 1. Chemical composition (mass percentage) of Examples 1-3

[0030] Example C Si Mn P S Cr Ni Cu Example 1 0.80 0.27 0.66 0.014 0.005 0.18 0.25 0.18 Example 2 0.79 0.28 0.65 0.015 0.005 0.17 0.26 0.19 Example 3 0.82 0.27 0.66 0.012 0.004 0.18 0.25 0.18

[0031] Proportional Design

[0032] Comparative Example 1: Referring to the comparative patent (2025100816709-A Production Method of 65# Spring Steel) 65# Spring Steel composition (C 0.65%, no Cu element), the process parameters of this invention (continuous casting speed 1.9m / min, 820℃ quenching oil cooling + 480℃ tempering air cooling) were adopted.

[0033] Comparative Example 2: The chemical composition of the present invention (the composition of Example 1) was used, and the process parameters of the comparative patent (2025100816709-A method for producing 65# spring steel) were used (no slow cooling process, quenching at 840℃ + tempering at 500℃).

[0034] Comparative Example 3: The chemical composition of this invention was used, but the Cu content exceeded the upper limit (Cu 0.30%), and other processes were the same as those of this invention.

[0035] Comparative Example 4: The chemical composition of the present invention was used, but the sulfur content was relaxed to 0.010% (compared to the upper limit of patent 2025100816709 - a method for producing 65# spring steel), and other processes were the same as those of the present invention.

[0036] The differences in key parameters of the manufacturing process between this invention and the comparative patent are specifically explained below:

[0037] Continuous casting process: The continuous casting speed of this application is 1.8 to 2.1 m / min, the tundish temperature is 1510 to 1530℃, the superheat is 20 to 25℃, the billet size is 150mm×150mm, and the slow cooling time is 48h; the prior art does not specify the control of casting speed and superheat, the billet size is φ120mm, and there is no requirement for slow cooling process.

[0038] Heating and rolling: The allowable temperature difference for billet heating in this application is ≤30℃, while the prior art document specifies ≤50℃, indicating higher temperature control precision; the finished product specification rolled in this application is φ90mm, while the prior art document specifies φ120mm.

[0039] 3. Heat treatment process: The heat treatment process of this application is quenching at 820℃ with oil cooling + tempering at 480℃ with air cooling; the prior art is quenching at 830~850℃ + tempering at 500℃, with a lower quenching temperature and a more precise cooling method.

[0040] 4. Refining process: This application specifies that the LF refining time for white slag is >15 min, and 100 m of calcium wire is fed in for inclusion deformation treatment; the prior art only requires a soft blowing time ≥10 min, and does not specify the amount of calcium wire fed in.

[0041] Performance test results:

[0042] Mechanical properties, fatigue life, and surface defect rate of the steels in Examples 1-3 and Comparative Examples 1-4 were tested, and the results are shown in Table 2 below.

[0043] Table 2 Performance test results of the examples and comparative examples

[0044]

[0045] Non-metallic inclusions and grain size testing

[0046] Non-metallic inclusion rating and austenite grain size test were performed on the steels of Examples 1-3 and Comparative Examples 1-4. The results are shown in Table 3 below (the inclusion rating adopts the GB / T 10561-2005 standard).

[0047] Table 3 Results of non-metallic inclusions and austenite grain size tests

[0048]

[0049] Results Analysis

[0050] 1. Performance advantages of Examples 1-3: Examples 1-3 using the technical solution of this invention all exhibit tensile strength ≥1173MPa, reduction of area ≥45%, and fatigue life ≥118×10⁻⁶. 6Secondly, the surface defect rate is ≤0.4%, and the non-metallic inclusions are uniformly controlled and of low grade, achieving a synergistic improvement in high strength and high toughness, fully meeting the needs of high-end and high-load scenarios.

[0051] 2. Limitations of Comparative Example 1: Using the composition of the comparative document (low carbon, Cu-free), even with the application of the process of this invention, the tensile strength is only 1050 MPa and the fatigue life is only 80 × 10⁻⁶. 6 The fact that it cannot meet the strength requirements of high-load scenarios proves that low-carbon components are difficult to exceed the strength limit.

[0052] 3. Defects of Comparative Example 2: While using the components of this invention, the process was not matched (no slow cooling, excessively high heat treatment temperature), resulting in a sharp decrease in toughness (Z% = 28%) and a fatigue life of only 65 × 10⁻⁶. 6 The surface defect rate reached 1.8%, proving that precise matching of process parameters and composition is the key to achieving performance advantages.

[0053] 4. Problem with Comparative Example 3: The Cu content exceeded the upper limit (0.30%), leading to increased hot brittleness and a significant decrease in plasticity and fatigue life (Z% = 22%, fatigue life = 50 × 10⁻⁶). 6 (This demonstrates the rationality and necessity of controlling the Cu content to ≤0.25% in this invention).

[0054] 5. Shortcomings of Comparative Example 4: The sulfur content was relaxed to the level of the comparative patent (0.010%), resulting in an increase in inclusion content and a decrease in toughness and fatigue life (Z% = 32%, fatigue life = 75 × 10⁻⁶). 6 (This demonstrates the significant importance of the invention's extreme complexity control design).

[0055] This application has a higher carbon content (0.8%), and while significantly improving strength, its plasticity remains close to that of the prior art, breaking the industry perception that "high carbon content inevitably leads to brittleness." With a carbon content 0.15 percentage points higher, this application achieves the same reduction of area as the prior art, demonstrating a significant advantage in toughness. This application does not pursue excessively high grain size, but achieves a balance between strength and toughness through component synergy, which is more in line with practical application needs. This application has more balanced control of inclusions and no obvious defect types.

[0056] This invention resolves the "strength-toughness" contradiction in high-carbon spring steel: Compared to patented 65# spring steel, which has a lower carbon content (0.62%-0.70%), although it has better plasticity, its upper limit of strength is only 1070MPa, failing to meet the high-strength spring requirements of high-end machinery and automotive fields; while traditional 80# spring steel (carbon content 0.8%) generally suffers from insufficient toughness and easy fracture (typically Z% ≤ 25%). This application, through the innovative introduction of Cu and the synergistic effect of Cr and Ni, achieves a reduction of area of ​​45% even with a 0.15 percentage point increase in carbon content, breaking through the industry's technical bottleneck of "high carbon inevitably leads to brittleness".

[0057] This invention reduces the impact of harmful impurities on performance: In the prior art, S ≤ 0.010% and P ≤ 0.020%, while this application controls S to ≤ 0.005% and P ≤ 0.015%. Combined with extended LF refining white slag time (>15 min) and precise calcium wire feeding (100 m), the content of non-metallic inclusions is significantly reduced (e.g., in Example 1, the fine inclusion B is only grade 0.5), solving the problem of insufficient fatigue life caused by inclusions in the prior art. Actual measurements show that the fatigue life of the spring steel in this application reaches 1.2 × 10⁻⁶. 7 The comparison file was only 8×10. 6 This represents a 50% increase.

[0058] This invention achieves a balance between optimizing production costs and production efficiency: This application adopts a 150mm×150mm small square billet + 480℃ tempering process, which, compared with the φ120mm cast billet + 500℃ tempering process in the prior art, reduces unit energy consumption by 12%, increases production efficiency by 15%, and the surface defect rate of the finished product is only 0.3%, which is far lower than the 1.1% in the prior art.

[0059] In summary, this invention has successfully broken through the technical bottleneck of traditional high-carbon spring steel through innovative design of chemical composition (Cr-Ni-Cu ternary synergy and extreme impurity control) and precise matching of process parameters. The comprehensive performance of the product is significantly better than that of the existing technology, and the production method is cost-controllable and suitable for large-scale production, which has important industrial application value.

[0060] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing 80# spring steel, characterized in that: Its chemical composition by mass percentage includes: C 0.77%–0.85%, Si 0.17%–0.27%, Mn 0.50%–0.70%, P ≤0.015%, S ≤0.005%, Cr 0.15–0.25%, Ni 0.20–0.35%, Cu 0.15–0.25%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass. Its production process includes: 1) Converter smelting: The combined blowing converter is used for smelting. Molten iron, scrap steel and pig iron are added to the LD oxygen converter for top and bottom combined blowing. Lime is added to form slag. The carbon content at the end point is controlled to be ≥0.10% and the tapping temperature is <1670℃. After tapping, argon blowing is performed for more than 10 minutes to reduce the oxidizability of the molten steel and reduce decarburization. 2) LF Refining: Refining white slag is adopted to ensure that the white slag refining time is >15min; 100m calcium wire is fed in to deform inclusions and avoid nozzle nodules; desulfurization, composition fine-tuning and temperature increase are carried out according to the composition and temperature of the converter steel, and the soft blowing time is 10min to ensure that inclusions float up fully and improve the cleanliness of the steel. 3) Continuous casting: Constant casting speed control is adopted, with a casting speed of 1.8 to 2.1 m / min; protective casting is used throughout the process, with a tundish temperature of 1510 to 1530℃ and a superheat ΔT of 20 to 25℃; a weak cooling process is adopted for the secondary cooling, with a water content of 1.2 to 1.4 L / kg; slow cooling in the slow cooling pit for 48 hours is used to release internal stress and avoid cracks and segregation defects; 4) Billet heating furnace heating: The billet heating temperature is 1080~1120℃, the allowable temperature difference is ≤30℃, and the total heating time is controlled at 2h; the initial rolling temperature is 1030~1050℃, and the temperature is slowly increased to ensure uniform heating of the billet and prevent overheating, burning and decarburization. 5) Round steel rolling and heat treatment: Ensure that the surfaces of the rolls, turning machine, and guide plate equipment are smooth and free of sharp edges to avoid scratches and dents on the surface of the rolled parts. The rolled product specification is φ90mm. The heat treatment process is 820℃ quenching and oil cooling + 480℃ tempering and air cooling to optimize the microstructure and balance strength and toughness.

2. The method for producing 80# spring steel according to claim 1, characterized in that: The billet is a small square billet with a size of 150mm × 150mm.

3. The method for producing 80# spring steel according to claim 1, characterized in that: Its chemical composition by mass percentage includes: C 0.80%, Si 0.27%, Mn 0.66%, P 0.014%, S 0.0053%, Cr 0.18%, Ni 0.25%, Cu 0.18%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

4. The method for producing 80# spring steel according to claim 1, characterized in that: Its chemical composition by mass percentage includes: C 0.79%, Si 0.28%, Mn 0.65%, P 0.015%, S 0.0058%, Cr 0.17%, Ni 0.26%, Cu 0.19%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

5. The method for producing 80# spring steel according to claim 1, characterized in that: Its chemical composition by mass percentage includes: C 0.82%, Si 0.27%, Mn 0.66%, P 0.012%, S 0.0045%, Cr 0.18%, Ni 0.25%, Cu 0.18%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

6. The method for producing 80# spring steel according to claim 1, characterized in that: The 80# spring steel has a yield strength ReL≥930MPa, tensile strength Rm≥1080MPa, elongation after fracture A≥6.0%, reduction of area Z≥30%, and austenite grain size≥6.

7. The method for producing 80# spring steel according to claim 1, characterized in that: This method achieves a synergistic effect of "high strength + high toughness" under high carbon content, breaking through the bottleneck of traditional technology.

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