High-stress spring steel wire for automotive suspension and production method of high-stress spring steel wire

Abstract

The high-stress spring steel wire comprises the following chemical components in percentage by mass: 0.50 to 0.65 percent of C, 1.30 to 1.80 percent of Si, 0.50 to 0.80 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.015 percent of S, 0.80 to 1.00 percent of Cr, less than or equal to 0.10 percent of Cu, less than or equal to 0.06 percent of Mo, 0.20 to 0.50 percent of Ni, 0.02 to 0.05 percent of Nb, 0.05 to 0.15 percent of V, 0.03 to 0.06 percent of Ti, less than or equal to 0.008 percent of N, less than or equal to 0.02 percent of As, less than or equal to 0.015 percent of Sn, less than or equal to 0.0020 percent of O, less than or equal to 0.00010 percent of H and the balance of Fe. The method has the advantages that the strength and the fatigue performance of the device are effectively improved, the cost is saved, the influence of inclusions on the fatigue limit is greatly reduced, and the fatigue life of the material is remarkably prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a spring steel wire for high-stress automobile suspension and a production method thereof. Background Art

[0002] A sedan uses approximately 850-900kg of steel, of which suspension springs account for approximately 10-15kg, or about 1.5% of the total steel consumption. While this small proportion of suspension spring steel represents a significant portion of the overall technical level of the spring manufacturing and processing industry chain, encompassing smelting, rolling, heat treatment, and machining. Automotive suspension springs typically undergo high-frequency reciprocating compression motion, primarily providing cushioning and shock absorption. Their quality plays a crucial role in vehicle stability and safety.

[0003] In the era of gasoline-powered vehicles, vehicle weights typically hovered around 1.6 tons, and there was no urgent need for high-strength and lightweight suspension spring steel. Consequently, the strength of suspension spring steel typically ranged from 1700 to 1900 MPa. However, in the era of new energy vehicles, with batteries typically weighing over 300 kg, vehicle weights have reached 2.2 to 2.4 tons. Reusing the chassis and materials of gasoline-powered vehicles would inevitably require increasing the spring diameter, resulting in increased spring weight. This would not only hinder vehicle performance but also undermine competitive range.

[0004] In existing technology, as described in the document "Industrial Trial Production of Ultra-High-Strength Suspension Spring Steel 55SiCrNb," a small amount of Nb alloy is added to 55SiCr to increase the strength of spring steel after heat treatment, achieving a tensile strength exceeding 2160 MPa and enabling application under high stress conditions of 1400 MPa. However, actual production and testing have shown that the maximum tensile strength of 55SiCr after heat treatment can reach 2050 MPa. However, with only 0.01-0.05% Nb added, 2160 MPa cannot be achieved under current conventional domestic drawing and medium-frequency + high-frequency rapid water quenching conditions, requiring the addition of other alloying elements. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem that existing spring steel wires for automobile suspension cannot strike a balance between weight and performance and have limited tensile strength. The present invention provides a high-stress spring steel wire for automobile suspension, which can effectively improve the strength and fatigue performance of the spring steel wire without adding expensive rare earth or micro-alloying elements, saving costs, controlling the generation of inclusions, greatly reducing the impact of inclusions on the fatigue limit, and significantly improving the fatigue life of the material.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A high-stress spring steel wire for automobile suspension, the chemical composition and mass percentage of which include: C: 0.50-0.65%, Si: 1.30-1.80%, Mn: 0.50-0.80%, P≤0.015%, S≤0.015%, Cr: 0.80-1.00%, Cu≤0.10%, Mo≤0.06%, Ni: 0.20-0.50%, Nb: 0.02-0.05%, V: 0.05-0.15%, Ti: 0.03-0.06%, N≤0.008%, As≤0.02%, Sn≤0.015%, O≤0.0020%, H≤0.00010%, and the remainder is Fe.

[0007] Furthermore, the chemical composition and mass percentage of the high-stress spring steel wire for automobile suspension include: C: 0.58%, Si: 1.55%, Mn: 0.68%, P: 0.009%, S: 0.003%, Cr: 0.93%, Cu: 0.04%, Mo: 0.03%, Ni: 0.34%, Nb: 0.028%, V: 0.13%, N: 0.004%, As: 0.01%, Sn: 0.010%, O: 0.0012%, H: 0.00008%, and the rest is Fe.

[0008] Furthermore, the chemical composition and mass percentage of the high-stress spring steel wire for automobile suspension include: C: 0.57%, Si: 1.58%, Mn: 0.73%, P: 0.010%, S: 0.002%, Cr: 0.95%, Cu: 0.04%, Mo: 0.03%, Ni: 0.38%, Nb: 0.025%, V: 0.18%, N: 0.003%, As: 0.01%, Sn: 0.010%, O: 0.0010%, H: 0.00009%, and the rest is Fe.

[0009] To further achieve the object of the present invention, a method for producing high-stress spring steel wire for automobile suspension is provided, comprising converter smelting, LF refining, RH vacuum degassing, bloom continuous casting, blooming, grinding and rolling, as follows: (1) Ultra-pure quality smelting technology is used in converter smelting, and 90% by mass of molten iron and 10% of high-quality scrap steel are added during the converter smelting process; (2) Deoxidation: Select micro-aluminum alloys with Al ≤ 0.03% to control the high melting point inclusions Al2O3, CaO･Al2O3, and MgO･Al2O3 produced by the inevitable mixing of Al; (3) Refining uses low-basicity refined slag with a slag basicity of 0.9~1.50, and the Al2O3 content in the refined slag is ≤10%, thereby obtaining smaller plastic inclusions and improving the fatigue life of electric vehicle suspension springs; (4) The vacuum degree of the RH vacuum degassing process is ≤2mbar, the static stirring time is ≥50min, and the hydrogen content after degassing is ≤1ppm. Reducing the hydrogen content in the spring steel helps to avoid hydrogen-induced delayed fracture caused by high stress conditions above 1000MPa. (5) The continuous casting billet shape is 320×420mm, the pulling speed is 0.45~0.55m / min, the superheat of continuous casting is controlled at 10~30℃, the water volume of the continuous casting mold is 2000~4500L / min, the electromagnetic stirring of continuous casting is 200~500×2A*Hz, and light pressure is used at the end of continuous casting solidification. Finally, by adopting a large cross-section and matching appropriate continuous casting process parameters, an ultra-pure and highly homogenized billet of electric vehicle suspension spring steel wire rod with a tensile strength ≥2200Mpa, an elongation after fracture ≥10%, and an area reduction rate ≥42% is obtained.

[0010] Furthermore, in the blooming process, a high-temperature, long-time diffusion heating system is adopted, the blooming temperature is 1200-1250°C, and the temperature is kept for 4-6 hours for high-temperature diffusion, thereby reducing the central segregation of the large square bloom and improving the uniformity of the finished spring steel wire rod.

[0011] Furthermore, in the grinding process, the grinding depth of the blank surface is ≥1.0 mm, which can improve the surface quality of the spring steel wire rod and reduce surface decarburization of the spring steel wire rod.

[0012] Furthermore, in the rolling process, the soaking zone temperature is 980-1080°C, the start rolling temperature is 950-1050°C, the final rolling temperature is 840-900°C, the wire laying temperature is 840-900°C, and the hood entry temperature is 740-800°C.

[0013] Furthermore, the hot-rolled spring steel wire rod undergoes straightening, shot blasting, flaw detection, and grinding before undergoing a single-pass cold drawing with an area reduction of 10-15%. It then undergoes online medium- and high-frequency heating to 900-960°C for water quenching at a temperature of 35-45°C, and finally tempering at 350-450°C. The resulting spring steel wire achieves a tensile strength exceeding 2150 MPa and a post-break reduction exceeding 35%.

[0014] Furthermore, in steps (2) and (3), Si-Mn deoxidation is used for deoxidation, micro-aluminum alloy is selected for deoxidation, and the Al2O3 content in the refined slag is 8%.

[0015] Compared with the prior art, the advantages of the technical solution of the present invention are: (1) The high-stress spring steel wire for automobile suspension of the present invention has excellent strength and fatigue performance, with a tensile strength of ≥2150MPa, an elongation after fracture of ≥10%, a cross-sectional shrinkage of ≥42%, and a fatigue life of ≥500,000 times under a stress of 1400MPa. It is suitable for the design and material selection of suspension springs for new energy vehicles with high requirements for fatigue performance, segregation and hydrogen-induced delayed fracture; (2) The method of the present invention does not require the addition of expensive rare earth elements such as Zr, Re, and other precious microalloying elements, and the alloy system is simple to control. The preparation method is simple and easy to operate, which reduces production costs and facilitates mass production. (3) The present invention improves the center segregation of spring steel, so that the shrinkage of the finished steel wire after heat treatment is ≥35%, thereby avoiding the spring breakage caused by the center segregation. By controlling the hydrogen content in the spring steel wire rod to ≤1ppm, hydrogen-induced delayed fracture caused by high stress conditions of more than 1400MPa can be avoided. (4) The present invention controls the size and composition of inclusions to make them easily deformable plastic inclusions with a size of less than 20 μm. When the tensile strength is ≥ 2150 MPa, the influence of inclusions on the fatigue limit is greatly reduced, and the fatigue life of the material can be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a table of converter smelting process parameters in Example 1 of the present invention; Figure 2 This is a table of process parameters for blanking and rolling in Example 1 of the present invention; Figure 3 This is a table of drawing and heat treatment process parameters in Example 1 of the present invention; Figure 4 This is a table of test results of finished products in Example 1 of the present invention; Figure 5 This is a table of converter smelting process parameters in Example 2 of the present invention; Figure 6 This is a table of process parameters for blanking and rolling in Example 2 of the present invention; Figure 7 This is a table of drawing and heat treatment process parameters in Example 2 of the present invention; Figure 8 This is a table of test results of finished products in Example 2 of the present invention. DETAILED DESCRIPTION Example 1

[0017] To make the present invention more clearly understood, a high-stress spring steel wire for automobile suspension and a production method thereof are further described below with reference to the accompanying drawings. The specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] In this embodiment, high-purity pure metal spring steel wire is prepared into high-stress spring steel wire for automobile suspension with a tensile strength ≥ 2150 MPa by high-purity pure metal converter smelting - LF refining - RH vacuum degassing - large square billet continuous casting - high-temperature diffusion blanking - billet surface grinding - high-speed wire rolling - drawing - heat treatment. The mass percentage of the chemical composition is as follows: C: 0.58%, Si: 1.55%, Mn: 0.68%, P: 0.009%, S: 0.003%, Cr: 0.93%, Cu: 0.04%, Mo: 0.03%, Ni: 0.34%, Nb: 0.028%, V: 0.13%, N: 0.004%, As: 0.01%, Sn: 0.010%, O: 0.0012%, H: 0.00008%, and the rest is Fe.

[0019] In this embodiment, Si-Mn deoxidation is used, micro-aluminum alloy is selected for deoxidation, Al2O3 in the refined slag is 8%, the water volume of the continuous casting mold is 3500L / min, the electromagnetic stirring of the continuous casting is 300×2A*Hz, and the water distribution of the continuous casting is weak cooling; the surface grinding depth of the billet is 1.10mm, the rolling cover temperature is 780℃, and the specific process parameters are as follows Figures 1-3 Processing of the table shown.

[0020] The test results of the high stress automobile suspension spring steel wire produced by the method of this embodiment are as follows: Figure 4 shown. Example 2

[0021] In this embodiment, high-purity pure metallurgical converter smelting - LF refining - RH vacuum degassing - large square bloom continuous casting - high-temperature diffusion blanking - billet surface grinding - high-speed wire rolling - drawing - heat treatment are used to prepare the metal raw material into high-stress spring steel wire for automobile suspension with a tensile strength of ≥2150 MPa. The mass percentage of the chemical composition is: C: 0.57%, Si: 1.58%, Mn: 0.73%, P: 0.010%, S: 0.002%, Cr: 0.95%, Cu: 0.04%, Mo: 0.03%, Ni: 0.38%, Nb: 0.025%, V: 0.18%, N: 0.003%, As: 0.01%, Sn: 0.010%, O: 0.0010%, H: 0.00009%, and the rest is Fe.

[0022] In this embodiment, Si-Mn deoxidation is used, micro-aluminum alloy is selected for deoxidation, Al2O3 in the refined slag is 8%, the water volume of the continuous casting mold is 3500L / min, the electromagnetic stirring of the continuous casting is 300×2A*Hz; the surface grinding depth of the billet is 1.10mm, the rolling cover temperature is 770℃, and the specific process parameters are as follows Figures 5-7 Processing of the table shown.

[0023] The test results of the high stress automobile suspension spring steel wire produced by the method of this embodiment are as follows: Figure 8 shown.

[0024] It can be seen that the present invention can increase the shrinkage of the finished steel wire after heat treatment by increasing the center segregation of the spring steel, thereby avoiding the fracture of the coil spring caused by the severe center segregation. By controlling the hydrogen content in the spring steel wire rod to ≤1ppm, hydrogen-induced delayed fracture caused by high stress conditions of 1400MPa or above can be avoided. By controlling the size and composition of inclusions, the inclusions are controlled to be easily deformable plastic inclusions with a size of less than 20μm. When the tensile strength is ≥2150MPa, the influence of the inclusions on the fatigue limit is greatly reduced, and the fatigue life of the material can be significantly improved, ensuring that the fatigue life is ≥500,000 times under a fatigue stress of 1400MPa.

[0025] In addition to the above embodiments, the present invention may also have other implementations. Any technical solution formed by equivalent replacement or equivalent transformation falls within the scope of protection required by the present invention.

Claims

1. A high-stress spring steel wire for automobile suspension, characterized by: The chemical composition and mass percentage of spring steel wire include: C: 0.50~0.65%, Si: 1.30~1.80%, Mn: 0.50~0.80%, P≤0.015%, S≤0.015%, Cr: 0.80~1.00%, Cu≤0.10%, Mo≤0.06%, Ni: 0.20~0.50%, Nb: 0.02~0.05%, V: 0.05~0.15%, Ti: 0.03~0.06%, N≤0.008%, As≤0.02%, Sn≤0.015%, O≤0.0020%, H≤0.00010%, and the rest is Fe.

2. The high stress spring steel wire for automobile suspension according to claim 1, characterized in that: The chemical composition and mass percentage of the spring steel wire for high-stress automobile suspension include: C: 0.58%, Si: 1.55%, Mn: 0.68%, P: 0.009%, S: 0.003%, Cr: 0.93%, Cu: 0.04%, Mo: 0.03%, Ni: 0.34%, Nb: 0.028%, V: 0.13%, N: 0.004%, As: 0.01%, Sn: 0.010%, O: 0.0012%, H: 0.00008%, and the rest is Fe.

3. The high stress spring steel wire for automobile suspension according to claim 1, characterized in that: The chemical composition and mass percentage of the spring steel wire for high-stress automobile suspension include: C: 0.57%, Si: 1.58%, Mn: 0.73%, P: 0.010%, S: 0.002%, Cr: 0.95%, Cu: 0.04%, Mo: 0.03%, Ni: 0.38%, Nb: 0.025%, V: 0.18%, N: 0.003%, As: 0.01%, Sn: 0.010%, O: 0.0010%, H: 0.00009%, and the rest is Fe.

4. A method for producing high-stress spring steel wire for automobile suspension according to claim 1, comprising converter smelting, LF refining, RH vacuum degassing, bloom continuous casting, blooming, grinding and rolling, characterized in that: (1) Ultra-pure quality smelting technology is used in converter smelting, and 90% by mass of molten iron and 10% of high-quality scrap steel are added during the converter smelting process; (2) For deoxidation, select micro-aluminum alloy with Al≤0.03%; (3) Low basicity refining slag with a slag basicity of 0.9~1.50 is used for refining, and Al2O3 in the refined slag is ≤10%; (4) The vacuum degree of the RH vacuum degassing process is ≤2mbar, the static stirring time is ≥50min, and the H content after breaking the air is ≤1ppm; (5) The continuous casting billet shape is 320×420mm, the pulling speed is 0.45~0.55m / min, the superheat of continuous casting is controlled at 10~30℃, the water volume of the continuous casting mold is 2000~4500L / min, the electromagnetic stirring of continuous casting is 200~500×2A*Hz, and light pressure is used at the end of continuous casting solidification. Finally, by adopting a large cross-section and matching appropriate continuous casting process parameters, an ultra-pure and highly homogenized billet of electric vehicle suspension spring steel wire rod with a tensile strength ≥2200Mpa, an elongation after fracture ≥10%, and an area reduction rate ≥42% is obtained.

5. The method for producing high-stress spring steel wire for automobile suspension according to claim 4, characterized in that: In the blanking process, a high-temperature, long-time diffusion heating system is adopted, the blanking temperature is 1200-1250° C., and the temperature is kept for 4-6 hours for high-temperature diffusion.

6. The method for producing high-stress spring steel wire for automobile suspension according to claim 4, characterized in that: In the grinding process, the grinding depth of the blank surface is ≥1.0mm.

7. The method for producing high-stress spring steel wire for automobile suspension according to claim 4, characterized in that: In the rolling process, the soaking zone temperature is 980-1080°C, the start rolling temperature is 950-1050°C, the final rolling temperature is 840-900°C, the wire laying temperature is 840-900°C, and the cover entry temperature is 740-800°C.

8. The method for producing high-stress spring steel wire for automobile suspension according to claim 4, characterized in that: The hot-rolled spring steel wire rod undergoes straightening, shot blasting, flaw detection, and grinding, followed by a single-pass cold drawing with a 10-15% area reduction. It then undergoes online medium- and high-frequency heating to 900-960°C for water quenching at 35-45°C, and finally tempering at 350-450°C. The resulting spring steel wire achieves a tensile strength exceeding 2150 MPa and a post-break reduction exceeding 35%.

9. The method for producing high-stress spring steel wire for automobile suspension according to claim 4, characterized in that: In the steps (2) and (3), Si-Mn deoxidation is adopted for deoxidation, micro-aluminum alloy is selected for deoxidation, and the Al2O3 content in the refined slag is 8%.

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