Production method of 65 # spring steel

Abstract

The invention discloses a production method of 65 # spring steel. The production method comprises the steps of converter smelting, LF refining, continuous casting, heating of a casting blank heating furnace, round steel rolling and heat treatment. The heat treatment system is as follows: quenching at 830-850 DEG C and tempering at 500 DEG C The 65 # spring steel comprises the following chemical components in percentage by mass: 0.62%-0.70% of C, 0.17%-0.37% of Si, 0.50%-0.80% of Mn, less than or equal to 0.020% of P, less than or equal to 0.010% of S, less than or equal to 0.25% of Cr, less than or equal to 0.35% of Ni and the balance of Fe and inevitable trace impurities, and the total mass fraction is 100%. According to the production method of the 65 # spring steel, the Cr and Ni microalloying principle is utilized, on the premise that the production cost is reduced, the mechanical property of hot-rolled round steel is remarkably improved, and therefore the 65 # 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 relates to the technical field of smelting and rolling, and in particular to a production method of 65# spring steel. Background Art

[0002] Springs are frequently loaded and unloaded 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 breakage. The spring steel developed by the steel mill can meet the strict requirements for fatigue strength in the spring manufacturing process. Springs are often placed in harsh working environments and may be affected by corrosion and oxidation. Therefore, spring steel needs to have good corrosion resistance and stability to resist damage to the springs by environmental factors and ensure its long-term stable operation. The use of high-performance spring steel can reduce the manufacturing and maintenance costs of springs and improve the overall performance and economy of springs. Extending the service life of springs can also reduce the frequency of replacement and maintenance, saving costs for manufacturers and users. With the development of industries such as automobiles, machinery manufacturing, and electronics, the demand for springs is also increasing. As an indispensable component 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 steel mills will be widely used and recognized in the market. Summary of the invention

[0003] The purpose of the present invention is to provide a production method of 65# spring steel, which utilizes the principle of Cr and Ni microalloying to significantly improve the mechanical properties of hot-rolled round steel while reducing production costs, thereby producing 65# spring steel, thereby significantly improving the overall life and safety of the spring.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0005] The present invention provides a production method of 65# spring steel, including converter smelting, LF refining, continuous casting, heating in a casting furnace, round steel rolling, and heat treatment; wherein:

[0006] Combined blowing converter smelting ensures that the smelting materials are dry to avoid water vapor entering the steel to produce white spots; requirements [P] < 0.012%, [S] < 0.030%; nitrogen and argon blowing at the bottom of the converter ensures that carbon is pulled once and avoids post-blowing, and the end point carbon is controlled to be > 0.10%, reducing the oxidation of molten steel and reducing decarburization; the end point [P] ≤ 0.020%; slag blocking during steel tapping, and argon blowing throughout the steel tapping process;

[0007] During the refining of white slag, the molten steel must not be exposed throughout the whole process; the calcium feeding line is used to deform the inclusions to avoid nozzle nodules; no slag is added after the calcium feeding line to purify the molten steel, and the soft blowing time is ≥10min to ensure that the inclusions fully float;

[0008] Strictly implement the tundish baking system to ensure the tundish baking time and baking temperature; the molten steel outside the long nozzle cannot be exposed to prevent secondary oxidation of the molten steel; ensure that the crystallizer is centered, the secondary cooling adopts weak cooling and constant casting speed; use electromagnetic stirring to improve the surface quality of the ingot;

[0009] The billet heating temperature is 1080~1120℃, the allowable temperature difference is ≤50℃, the total heating time is controlled to be 2h, the rolling temperature is 1030~1050℃, prevent overheating, overburning and decarburization, and heat up slowly to ensure uniform billet heating temperature and reduce temperature difference;

[0010] Pay attention to the condition of the rollers, steel turning machine, guide plate, roller table and cover plate, and ensure that they are smooth without sharp edges and corners to avoid scratches and knocks on the surface of the rolled product. The specification of the rolled product is φ120mm;

[0011] The heat treatment system is quenching at 830-850℃ and tempering at 500℃;

[0012] The mass percentage of the chemical composition of the 65# spring steel includes: C 0.62% to 0.70%, Si 0.17% to 0.37%, Mn 0.50% to 0.80%, P≤0.020%, S≤0.010%, Cr≤0.25%, Ni≤0.35%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

[0013] Furthermore, the chemical composition of the 65# spring steel includes by weight percentage: C 0.65%, Si 0.23%, Mn 0.57%, P 0.014%, S 0.0048%, Cr 0.06%, Ni 0.04%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0014] Furthermore, the chemical composition of the 65# spring steel includes by weight percentage: C 0.68%, Si 0.25%, Mn 0.65%, P 0.017%, S 0.0055%, Cr 0.08%, Ni 0.05%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0015] Furthermore, the chemical composition of the 65# spring steel includes by weight percentage: C 0.66%, Si 0.20%, Mn 0.60%, P 0.014%, S 0.0056%, Cr 0.10%, Ni 0.06%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

[0016] Furthermore, the soft blowing time produced is 15 minutes.

[0017] Furthermore, the heat treatment system includes quenching at 840°C.

[0018] Furthermore, the grain size of the 65# spring steel satisfies: ≥8.0.

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

[0020] 1) By finely controlling the content of alloying elements (such as sulfur, phosphorus, chromium, etc.) in 65# spring steel and optimizing the smelting process, the present invention significantly improves the strength, toughness and ductility of the steel, ensures the stability of the material under cyclic load, and is particularly suitable for the manufacture of high-strength springs; (2) By adopting converter smelting (BOF) instead of electric arc furnace (EAF) and combining LF refining process, the present invention not only reduces energy consumption, but also reduces the impurity content in the production process, greatly reduces the overall production cost, and is suitable for large-scale industrial production; (3) By strictly controlling the content of harmful elements such as phosphorus and sulfur, the present invention effectively reduces non-metallic inclusions in steel, improves the fatigue life and brittle fracture resistance of the material, thereby extending the service life of the steel, especially in applications under high load conditions. DETAILED DESCRIPTION

[0021] Embodiment 1:

[0022] The present invention provides a method for producing spring steel, wherein the production process is carried out according to the following steps:

[0023] Combined blowing converter smelting ensures that the smelting materials are dry to avoid water vapor entering the steel to produce white spots; requirements [P] < 0.012%, [S] < 0.030%; nitrogen and argon blowing at the bottom of the converter ensures that carbon is pulled once and avoids post-blowing, and the end point carbon is controlled at 0.13% to reduce the oxidation of molten steel and reduce decarburization; the end point [P] is 0.013%; slag is blocked when tapping, and argon is blown throughout the tapping process;

[0024] Further: During the refining of white slag, the molten steel must not be exposed throughout the process; the calcium feeding line is used to deform the inclusions to avoid nodules; no slag is added after the calcium feeding line to purify the molten steel, and the soft blowing time is 15 minutes to ensure that the inclusions fully float up;

[0025] Strictly implement the tundish baking system to ensure the tundish baking time and baking temperature; the molten steel outside the long nozzle cannot be exposed to prevent secondary oxidation of the molten steel; ensure that the crystallizer is centered, the secondary cooling adopts weak cooling and constant casting speed; use electromagnetic stirring to improve the surface quality of the ingot;

[0026] The billet heating temperature is 1095℃, the total heating time is controlled to 2h, the rolling temperature is 1032℃, and overheating, overburning and decarburization are prevented. The temperature is raised slowly to ensure uniform billet heating temperature and reduce temperature difference.

[0027] Pay attention to the condition of the rolls, steel turning machine, guide plate, roller table and cover plate, and ensure that they are smooth without sharp edges and corners to avoid scratches and knocks on the surface of the rolled piece. The specification of the rolled product is φ120mm. The heat treatment system is quenching at 840℃ and tempering at 500℃.

[0028] Embodiment 2-3:

[0029] Except for some specific process parameters that are different from those in Example 1, the rest of Example 2-3 is exactly the same as that in Example 1. The specific process parameters are shown in Table 1.

[0030] Table 1 Process parameters of each embodiment

[0031]

[0032] Comparative Example 1:

[0033] Comparative Example 1 is completely the same as Example 1 except that the S content is different from that of Example 1 and LF refining is not performed.

[0034] Comparative Example 2:

[0035] Comparative Example 2 is completely the same as Example 1 except that the Cr content is different from that of Example 1. The Cr content of this comparative example is 0.55%.

[0036] Comparative Example 3:

[0037] Comparative Example 3 is exactly the same as Example 1 except that the converter smelting is changed to electric furnace smelting.

[0038] Comparative Example 4:

[0039] Comparative Example 4 is completely the same as Example 1 except that the P content is different from that of Example 1. The P content of this comparative example is 0.025%.

[0040] Table 2 shows the chemical compositions of three embodiments and four comparative examples of the present invention, and Tables 3 and 4 further illustrate the present invention.

[0041] Table 1 Chemical composition of spring steel examples (mass percentage / %)

[0042]

[0043]

[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]

[0049] It can be seen from the above examples and comparative examples that: (1) In comparative example 1, LF refining was not performed and desulfurization was insufficient. The steel was directly cast after converter treatment, resulting in more non-metallic inclusions, poor strength and low elongation. The embodiment adopted LF refining, which significantly reduced the sulfur content to ≤0.005%, improved fatigue performance and toughness. The mechanical properties of the clean steel were improved, and the problems caused by non-metallic inclusions were eliminated, thereby increasing the service life of the steel. (2) In comparative example 2, the chromium content was increased to 0.55% to improve corrosion resistance. Although the mechanical properties were slightly improved, the increase in chromium content led to an increase in production costs. (3) In comparative example 3, the production cost was high and more electricity was required. The present invention uses converter smelting instead, which significantly reduces energy consumption while maintaining similar mechanical properties. The converter process is more suitable for large-scale industrial production, further reducing production costs. (4) In comparative example 4, the higher phosphorus content leads to increased brittleness and decreased ductility, which can lead to unstable performance under cyclic loads. This patent avoids the brittleness problem and improves ductility by strictly controlling the phosphorus content to ≤0.015%. This makes the steel more suitable for applications that frequently withstand cyclic loads.

[0050] It can be seen from Tables 1 to 4 that the embodiments show significant superiority in mechanical properties and organizational structure compared to the comparative examples. The tensile strength (Rm) and yield strength (Rp0.2) of the embodiments are significantly higher than those of the comparative examples, while the plasticity (A%) and cross-sectional shrinkage (Z%) are better. In addition, the non-metallic inclusion content of the embodiments is low, and the austenite grain size reaches a higher level (≥8 levels), which significantly improves the fatigue life and brittle fracture resistance of the material. These advantages are derived from strictly controlled alloying elements, optimized smelting and rolling processes, and precise operation of refining and heating links, which ensure the stability and long life of the material under high load environments.

[0051] 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 65# spring steel, characterized in that: Including converter smelting, LF refining, continuous casting, billet heating furnace heating, round steel rolling, heat treatment; among which: Combined blowing converter smelting ensures that the smelting materials are dry to avoid water vapor entering the steel to produce white spots; requirements [P] < 0.012%, [S] < 0.030%; nitrogen and argon blowing at the bottom of the converter ensures that carbon is pulled once and avoids post-blowing, and the end point carbon is controlled to be > 0.10%, reducing the oxidation of molten steel and reducing decarburization; the end point [P] ≤ 0.020%; slag blocking during steel tapping, and argon blowing throughout the steel tapping process; During the refining of white slag, the molten steel must not be exposed throughout the whole process; the calcium feeding line is used to deform the inclusions to avoid nozzle nodules; no slag is added after the calcium feeding line to purify the molten steel, and the soft blowing time is ≥10min to ensure that the inclusions fully float; Strictly implement the tundish baking system to ensure the tundish baking time and baking temperature; the molten steel outside the long nozzle cannot be exposed to prevent secondary oxidation of the molten steel; ensure that the crystallizer is centered, the secondary cooling adopts weak cooling and constant casting speed; use electromagnetic stirring to improve the surface quality of the ingot; The billet heating temperature is 1080~1120℃, the allowable temperature difference is ≤50℃, the total heating time is controlled to be 2h, the rolling temperature is 1030~1050℃, prevent overheating, overburning and decarburization, and heat up slowly to ensure uniform billet heating temperature and reduce temperature difference; Pay attention to the condition of the rollers, steel turning machines, guide plates, roller tables and covers, and ensure that they are smooth without sharp edges and corners to avoid scratches and knocks on the surface of the rolled product. The specification of the rolled product is φ120mm; The heat treatment system is quenching at 830-850℃ and tempering at 500℃; The mass percentage of the chemical composition of the 65# spring steel includes: C 0.62% to 0.70%, Si 0.17% to 0.37%, Mn 0.50% to 0.80%, P≤0.020%, S≤0.010%, Cr≤0.25%, Ni≤0.35%, and the rest is Fe and inevitable trace impurities, with a total mass fraction of 100%.

2. The production method of 65# spring steel according to claim 1, characterized in that: The chemical composition of the 65# spring steel includes by weight percentage: C 0.65%, Si 0.23%, Mn 0.57%, P 0.014%, S 0.0048%, Cr 0.06%, Ni 0.04%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

3. The production method of 65# spring steel according to claim 1, characterized in that: The chemical composition of the 65# spring steel includes by weight percentage: C 0.68%, Si 0.25%, Mn 0.65%, P 0.017%, S 0.0055%, Cr 0.08%, Ni 0.05%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

4. The production method of 65# spring steel according to claim 1, characterized in that: The chemical composition of the 65# spring steel includes by weight percentage: C 0.66%, Si 0.20%, Mn 0.60%, P 0.014%, S 0.0056%, Cr 0.10%, Ni 0.06%, and the rest is Fe and inevitable trace impurities, with a total weight fraction of 100%.

5. The production method of 65# spring steel according to claim 1, characterized in that: The soft blowing time produced is 15 minutes.

6. The production method of 65# spring steel according to claim 1, characterized in that: The heat treatment system includes quenching at 840°C.

7. The production method of 65# spring steel according to claim 1, characterized in that: The grain size of the 65# spring steel meets the requirement of: ≥8.0.

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