High-strength, high-ductility, high-carbon, low-alloy spring steel wire and its ultra-fast induction heating production method

Abstract

This invention discloses a high-strength, high-carbon, low-alloy spring steel wire and its production method using ultra-fast induction heating. The production method employs an ultra-fast induction heating process. This includes ultra-fast induction heating of the cold-drawn steel wire to the austenitic single-phase temperature range, followed by a short-term holding within this temperature range, and then water quenching; immediately afterward, ultra-fast induction heating to the tempering temperature range, followed by a short-term holding within this temperature range, and then water quenching. The ultra-high-strength, high-carbon, low-alloy steel of this invention exhibits excellent strength and ductility, with a tensile strength of 1796-2092 MPa, a yield strength of 1681-1887 MPa, an elongation after fracture of 11.23%-17.27%, and a strength-ductility product of 20.17-36.13 GPa·%. Compared to traditional heat treatment, this invention improves production efficiency by 50%-200% and significantly reduces production costs.

Description

Technical Field

[0001] This invention relates to the field of heat treatment technology for materials, specifically to high-strength, high-carbon, low-alloy spring steel wire and its ultra-fast induction heating production method. Background Technology

[0002] Steel has been the most widely used metallic material for the past few centuries. Ultra-high strength steel with excellent ductility has always been a goal pursued by scientists and a societal expectation, aiming to reduce oil and resource consumption by reducing the weight of cars and trucks, thereby alleviating severe environmental pollution and energy shortages. However, in most metallic materials, increased strength comes at the cost of reduced ductility, demonstrating a trade-off between strength and ductility. This limits the widespread use of high-strength alloys. Martensitic aging steel is a typical ultra-high strength alloy, achieving a strength of up to 2.4 GPa and exhibiting good ductility. However, the addition of expensive metals such as Ni, Co, and Mo significantly limits its large-scale application in industrial production. In recent decades, low-alloy high-strength steel has attracted considerable interest from researchers due to its low cost. Since the early 20th century, many researchers have increased the strength of steel by increasing the carbon content; however, ductility and other mechanical properties deteriorate with increasing carbon content. Simultaneously improving the strength and ductility of materials using inexpensive carbon is a research goal and aspiration.

[0003] To improve productivity and enhance microstructure and material properties through grain refinement, rapid heat treatment has recently been widely recognized as an alternative to traditional heat treatment, which requires several hours of processing time. Rapid heat treatment technologies, employing sustainable and energy-efficient manufacturing processes such as induction heating or laser heating, will facilitate numerous applications of hardened and tempered steels, particularly in the energy, defense, and transportation sectors. Overall, rapid heat treatment technologies offer significant advantages in improving production efficiency, reducing energy consumption, enhancing product quality, and enabling precise material control. This makes it an important process in many manufacturing and engineering fields. Due to its small diameter, rapid heat treatment technology can quickly transfer heat to the core of spring steel wire. Therefore, combining rapid heat treatment technology with high-carbon, low-alloy spring steel wire holds great promise for future applications.

[0004] In the prior art, Chinese patent CN116732426A discloses a high-carbon steel 65Mn hot-rolled steel plate and its manufacturing method. The steel plate composition is: C: 0.64%-0.70%, Si: 0.20%-0.30%, Mn: 0.9%-1.1%, P≤0.018%, S≤0.005%, Cr: 0.02%-0.08%, N≤0.006%, Al: 0.010%-0.050%, Ca: 0.0005%-0.0040%, with the remainder being Fe and unavoidable impurities. This invention involves heat treatment under conventional heating conditions, with the continuous casting slab heating time being 180-250 minutes, significantly reducing production efficiency. Furthermore, while the material has a high C content, its tensile strength is only 800-1020 MPa, failing to achieve the goals of energy conservation and emission reduction.

[0005] Chinese patent 201711385126.5 discloses "a 780MPa grade low-carbon low-alloy TRIP steel." This invention achieves this through rapid heat treatment: the strip is rapidly heated to the two-phase region of 790-830℃ at a heating rate of 40-300℃ / s, then held at this temperature for 60-100s; the strip is then rapidly cooled from this temperature to 410-430℃, held within this temperature range for 200-300s, and then rapidly cooled to room temperature. This achieves grain refinement and improves mechanical properties. However, the soaking time of this invention is 60-100s, requiring an additional 200-300s of bainitic isothermal treatment. This is not significantly different from the heating time of traditional heat treatment. It is not energy-efficient and clearly does not represent rapid heating in the strict sense. Furthermore, it weakens the grain refinement effect produced by rapid heating, thus hindering the improvement of the material's strength and plasticity. Summary of the Invention

[0006] Therefore, it is necessary to provide a high-strength, high-ductility, high-carbon, low-alloy spring steel wire that combines high strength and high ductility, as well as an ultra-fast induction heating production method for the high-strength, high-ductility, high-carbon, low-alloy spring steel wire.

[0007] The technical solution of the present invention is as follows:

[0008] High-strength, high-ductility, high-carbon, low-alloy spring steel wire has the following chemical composition by mass percentage: C: 0.63%-0.68%, Si: 1.45%-1.49%, Mn: 0.66%-0.70%, Cr: 0.67%-0.71%, V: 0.11%-0.131%, Cu: 0.019%-0.021%, with the balance being Fe and unavoidable impurities;

[0009] The high-strength, high-carbon, low-alloy spring steel wire is produced by ultra-fast induction heating, including the following steps:

[0010] (1) Heat the steel billet to solidify it;

[0011] (2) Forge the steel billet after solution treatment in step (1) to obtain a forged billet;

[0012] (3) The forging billet obtained in step (2) is hot rolled to obtain hot-rolled wire;

[0013] (4) The hot-rolled wire obtained in step (3) is cold-drawn to obtain cold-drawn steel wire;

[0014] (5) The cold-drawn steel wire obtained in step (4) is first ultra-fast induction heated to 800-900℃ at a heating rate of 50-100℃ / s, held for 1-4s, and then water-quenched to 40-60℃ for the first time; the steel wire after the first water quenching is then ultra-fast induction heated to 400-600℃ at a heating rate of 40-70℃ / s for the second time, held for 1-4s, and then water-quenched to 40-60℃ for the second time to obtain high-strength, high-carbon, low-alloy spring steel wire.

[0015] Preferably, the chemical composition of the high-strength, high-carbon, low-alloy spring steel wire is as follows (by mass percentage): C: 0.65%, Si: 1.48%, Mn: 0.67%, Cr: 0.71%, V: 0.131%, Cu: 0.02%, with the balance being Fe and unavoidable impurities.

[0016] Preferably, the high-strength, high-ductility, high-carbon, low-alloy spring steel wire comprises a martensitic matrix, a thin-film retained austenite, and dispersed fine carbides. The thin-film retained austenite and dispersed carbides effectively improve the strength and ductility of the high-carbon, low-alloy steel.

[0017] Preferably, the mass percentage of impurity chemical components is controlled as follows: P≤0.008%, S≤0.008%, O2≤10ppm, H2≤10ppm.

[0018] Preferably, the high-strength-ductility-product high-carbon low-alloy spring steel wire has a tensile strength of 1796-2092 MPa, a yield strength of 1681-1887 MPa, an elongation after fracture of 11.23%-17.27%, and a strength-ductility-product of 20.17-36.13 GPa·s.

[0019] Preferably, the heating and solution treatment in step (1) is carried out at 1260-1300℃ for 2.5-3 hours;

[0020] Preferably, the final forging temperature in step (2) is 1000℃-1100℃;

[0021] Preferably, the hot rolling in step (3) specifically involves heating the forging billet to 1220-1250℃ and holding it for 2-3 hours, wherein the initial rolling temperature is 900-1000℃ and the final rolling temperature is 800-980℃.

[0022] Preferably, the hot-rolled wire described in step (3) is pickled before being cold-drawn in step (4);

[0023] More preferably, the temperature of the pickling solution is 70-85℃, and the pickling speed is 90-100m / min.

[0024] Preferably, the total reduction rate of the cold drawing in step (4) is 70-90%; the diameter of the cold-drawn steel wire is 3-10mm.

[0025] Preferably, the temperature of the first ultra-fast induction heating in step (5) is 850-890℃; the temperature of the second ultra-fast induction heating is 460-524℃;

[0026] Preferably, the cooling rate of the first water quench in step (5) is 200-500℃ / s; and the cooling rate of the second water quench is 150-400℃ / s.

[0027] The above-mentioned ultra-fast induction heating production method for high-strength, high-carbon, low-alloy spring steel wire includes the following steps:

[0028] (1) Heat the steel billet to solidify it;

[0029] (2) Forge the steel billet after solution treatment in step (1) to obtain a forged billet;

[0030] (3) The forging billet obtained in step (2) is hot rolled to obtain hot-rolled wire;

[0031] (4) The hot-rolled wire obtained in step (3) is cold-drawn to obtain cold-drawn steel wire;

[0032] (5) The cold-drawn steel wire obtained in step (4) is first ultra-fast induction heated to 800-900℃ at a heating rate of 50-100℃ / s, held for 1-4s, and then water-quenched to 40-60℃ for the first time; the steel wire after the first water quenching is then ultra-fast induction heated to 400-600℃ at a heating rate of 40-70℃ / s for the second time, held for 1-4s, and then water-quenched to 40-60℃ for the second time to obtain high-strength, high-carbon, low-alloy spring steel wire.

[0033] Preferably, the method for preparing the steel billet in step (1) is as follows: the raw materials are melted and smelted in an oxidizing atmosphere to obtain molten steel; then, the molten steel is refined in a reducing atmosphere to obtain high-purity refined steel; finally, the refined steel is continuously cast to obtain a steel billet.

[0034] In the composition design of the high-carbon low-alloy steel of this invention:

[0035] C: Carbon is the most common strengthening element in steel. 1. It forms a solid solution structure, increasing the strength of the steel. 2. It forms a carbide structure, which can increase the hardness and wear resistance of the steel.

[0036] Mn: Manganese provides solid solution strengthening and enables steel to obtain finer and stronger pearlite during the cooling process after hot rolling. The pearlite content increases with increasing manganese content. Manganese is also a carbide-forming element; manganese carbides can dissolve into cementite, thereby indirectly enhancing the strength of pearlite. Manganese can also improve the hardenability of steel, further increasing its strength.

[0037] Silicon (Si): Silicon forms a solid solution in ferrite or austenite, thereby enhancing the yield strength and tensile strength of steel. Furthermore, silicon increases the cold work hardening rate of steel, making it a beneficial element in alloy steels. Silicon can improve the strength, hardness, and wear resistance of steel, and within a certain range, it does not significantly reduce the plasticity of steel.

[0038] Cr: Chromium primarily improves the hardenability of steel, giving it excellent overall mechanical properties. Chromium forms various carbides with carbon, exhibiting a greater affinity for carbon than iron and manganese. Chromium can also form intermetallic compounds with iron.

[0039] Microalloying elements V and Cu: Adding microalloying elements V and Cu to steel can refine the grain size and greatly improve the strength and toughness of the steel. While microalloying elements are beneficial in this invention, excessive addition should be avoided considering cost and other factors.

[0040] The high-strength, high-ductility, high-carbon, low-alloy spring steel wire obtained by this invention has a microstructure comprising a martensitic matrix, thin-film retained austenite, and dispersed fine carbides. The thin-film retained austenite provides a sustained TRIP effect, enabling the high-carbon, low-alloy spring steel wire to possess both high strength and ductility.

[0041] In one embodiment, the structure is primarily a martensitic matrix and diffusely distributed fine carbides.

[0042] In one embodiment, the structure is primarily a martensitic matrix and slightly coarse spherical carbides.

[0043] In one embodiment, the structure is primarily a martensitic matrix and interconnected chain-like carbides.

[0044] The high-strength, high-ductility, high-carbon, low-alloy spring steel wire obtained by the above method has a microstructure comprising a martensitic matrix, thin-film retained austenite, and dispersed fine carbides. The thin-film retained austenite provides a sustained TRIP effect, enabling the high-carbon, low-alloy spring steel wire to possess both high strength and ductility.

[0045] The advantages of this invention compared to traditional heat treatment technologies are:

[0046] (1) The above-mentioned ultra-fast induction heating preparation method, due to the use of a heating rate of 50-100℃ / s and a holding time of 1-4s, can improve the production efficiency by 50%-200% compared with traditional heat treatment. The above-mentioned method for producing high-strength, high-ductility, high-carbon, low-alloy spring steel wire by ultra-fast induction heating prepares the initial product of steel bars from raw materials with appropriate proportions, and then performs rapid quenching and tempering treatment. In the rapid hot austenitization process, ferrite undergoes austenitization transformation without recrystallization, and many defects still exist. This provides a large number of austenite nucleation sites, greatly refines the austenite grains, and thus obtains the final microstructure. Carbide precipitation, decomposition of residual austenite, recovery, and recrystallization are the main changes that occur during the tempering process. In the rapid tempering process, the shorter treatment time reduces the annihilation of dislocations, resulting in more nucleation sites for cementite precipitation and a more uniform distribution of temper precipitates. Ultimately, high-carbon, low-alloy spring steel wire can have both high strength and high ductility. Compared to other high-alloy steels such as martensitic steel, it reduces alloy costs while maintaining high mechanical properties.

[0047] (2) Compared with traditional heat treatment processes, the high carbon low alloy spring steel wire obtained by ultra-fast induction heating heat treatment technology has a significantly improved surface quality due to the reduced heating and homogenization time and shorter furnace length. Furthermore, the high carbon low alloy spring steel wire obtained by the present invention has improved forming performance and performance due to the refinement of product grains and the reduction of material alloy content.

[0048] (3) Compared to high-carbon low-alloy spring steel wire obtained by traditional heat treatment methods, the high-strength-ductility-product high-carbon low-alloy spring steel wire obtained by this invention has a tensile strength of 1796-2092 MPa, a yield strength of 1681-1887 MPa, an elongation after fracture of 11.23%-17.27%, and a strength-ductility-product of 20.17-36.13 GPa·%. This material achieves ultra-high strength using only the cheapest carbon while maintaining good ductility, significantly reducing costs compared to maraging steel. It can be used in automotive structural components, such as spring steel in suspension systems, greatly improving vehicle safety performance. Attached Figure Description

[0049] Figure 1 The following are engineering stress-strain curves of the high-strength, high-carbon, low-alloy spring steel wires produced in Examples 1-4 of this invention.

[0050] Figure 2 These are scanning electron microscope (SEM) images of the high-strength, high-density, high-carbon, low-alloy spring steel wires produced in Examples 1-4 of this invention. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of this invention clearer, a detailed description will be provided below in conjunction with various embodiments and accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the invention; however, the embodiments of the invention are not limited thereto. Those skilled in the art can make similar modifications without departing from the spirit of the invention; therefore, the invention is not limited to the specific embodiments described below.

[0052] Unless otherwise defined, the technical terms used below have the same meaning as commonly understood by those skilled in the art, and all raw materials, reagents, instruments and equipment used in this invention can be purchased on the market or prepared by existing methods.

[0053] The present invention provides a method for producing high-strength, high-carbon, low-alloy spring steel wire using ultra-fast induction heating, comprising the following steps: Step 1, composition design; Step 2, solution treatment; Step 3, forging; Step 4, hot rolling; Step 5, pickling; Step 6, cold drawing; and Step 7, ultra-fast induction heating heat treatment.

[0054] In step one, according to the chemical composition ratio of high carbon low alloy spring steel wire, iron ore, quicklime, vanadium stone, iron-silicon alloy, iron-manganese alloy and iron-chromium alloy are placed in an oxidizing atmosphere furnace for melting and smelting to obtain molten steel, which is then transferred to a reducing atmosphere furnace for refining to obtain refined molten steel. The refined molten steel is then continuously cast to obtain steel billets.

[0055] In step two, the steel billet obtained in step one is placed in a walking beam furnace and heated at 1260-1300℃ for 2.5-3 hours. This allows all elements C, Si, Mn, V, Cr, and Cu to be dissolved in solid solution.

[0056] In step three, the solution-treated steel billet from step two is forged at a final forging temperature of 1000℃-1100℃ to obtain a forged billet.

[0057] In step four, the forging billet obtained in step three is heated to 1220-1250℃ and held for 2-3 hours, with the initial rolling temperature being 900-1000℃ and the final rolling temperature being 800-980℃, to obtain hot-rolled steel bars.

[0058] In step five, the hot-rolled steel bar obtained in step four is pickled at an acid temperature of 70-85℃ and a pickling speed of 90-100m / min.

[0059] In step six, the steel strip pickled in step five is cold-drawn. The total reduction in surface area after cold drawing is 70-90%, and the diameter of the cold-drawn steel wire after 70-90% cold drawing is 3-10mm.

[0060] In step seven, the cold-drawn steel wire obtained in step six is ​​subjected to ultra-fast induction heating treatment, which is quenching and tempering. The quenching method is heating followed by water quenching. The cold-drawn steel wire is heated to 850-890℃ at a rate of 50-100℃ / s, held for 1-4s, and then water quenched to 40-60℃. Then, it is heated to a tempering temperature of 460-524℃ at a rate of 40-70℃ / s, held for 1-4s, and then water quenched to 40-60℃ to obtain the high-carbon low-alloy spring steel wire.

[0061] Example 1

[0062] A method for producing high-strength, high-carbon, low-alloy spring steel wire using ultra-fast induction heating includes the following steps:

[0063] Step 1: According to the chemical composition ratio of high carbon low alloy spring steel in Table 1 below, iron ore, quicklime, vanadium stone, iron-silicon alloy, iron-manganese alloy, and iron-chromium alloy are placed in an oxidizing atmosphere furnace for melting and smelting to obtain molten steel. Then, the molten steel is transferred to a reducing atmosphere furnace for refining to obtain refined molten steel. The refined molten steel is then continuously cast to obtain steel billets.

[0064] Step two: Place the steel billet obtained in step one into a walking beam furnace and heat it at 1260-1300℃ for 2.5-3 hours. This allows all C, Si, Mn, V, Cr, and Cu elements to be dissolved in solid solution.

[0065] Step 3: Forge the solution-treated steel billet from Step 2 at a final forging temperature of 1000℃-1100℃ to obtain a forged billet.

[0066] Step 4: Heat the forging billet obtained in Step 3 to 1220-1250℃ and hold for 2-3 hours, with the initial rolling temperature at 900-1000℃ and the final rolling temperature at 800-980℃, to obtain hot-rolled steel bars.

[0067] Step 5: Pickle the hot-rolled steel bar obtained in Step 4. The acid temperature is 70-85℃ and the pickling speed is 90-100m / min.

[0068] Step six: The steel strip pickled in step five is cold-drawn. The total reduction in surface area after cold drawing is 80%, and the diameter of the cold-drawn steel wire after 80% cold drawing is 6.5mm.

[0069] Step 7: The cold-drawn steel wire obtained in Step 6 is subjected to ultra-fast induction heating treatment. The heat treatment method is quenching + tempering. The quenching method is water quenching after heating. The cold-drawn steel wire is heated to 890℃ at a rate of 50℃ / s, held for 2s, and then water quenched to 40-60℃. Then, the temperature is raised to 524℃ at a rate of 40℃ / s and held for 2s, and then water quenched to 40-60℃. The high-carbon low-alloy spring steel wire is obtained.

[0070] Example 2

[0071] A method for producing high-strength, high-carbon, low-alloy spring steel wire using ultra-fast induction heating includes the following steps:

[0072] Step 1: According to the chemical composition ratio of high carbon low alloy spring steel in Table 1 below, iron ore, quicklime, vanadium stone, iron-silicon alloy, iron-manganese alloy, and iron-chromium alloy are placed in an oxidizing atmosphere furnace for melting and smelting to obtain molten steel. Then, the molten steel is transferred to a reducing atmosphere furnace for refining to obtain refined molten steel. The refined molten steel is then continuously cast to obtain steel billets.

[0073] Step two: Place the steel billet obtained in step one into a walking beam furnace and heat it at 1260-1300℃ for 2.5-3 hours. This allows all C, Si, Mn, V, Cr, and Cu elements to be dissolved in solid solution.

[0074] Step 3: Forge the solution-treated steel billet from Step 2 at a final forging temperature of 1000℃-1100℃ to obtain a forged billet.

[0075] Step 4: Heat the forging billet obtained in Step 3 to 1220-1250℃ and hold for 2-3 hours, with the initial rolling temperature at 900-1000℃ and the final rolling temperature at 800-980℃, to obtain hot-rolled steel bars.

[0076] Step 5: Pickle the hot-rolled steel bar obtained in Step 4. The acid temperature is 70-85℃ and the pickling speed is 90-100m / min.

[0077] Step six: The steel strip pickled in step five is cold-drawn. The total reduction in surface area after cold drawing is 70%, and the diameter of the cold-drawn steel wire after 70% cold drawing is 6.5mm.

[0078] Step 7: The cold-drawn steel wire obtained in Step 6 is subjected to ultra-fast induction heating treatment. The heat treatment method is quenching + tempering. The quenching method is heating followed by water quenching. The cold-drawn steel wire is heated to 860℃ at a rate of 70℃ / s, held for 1.5s, and then water quenched to 40-60℃. Then, it is heated to a tempering temperature of 492℃ at a rate of 65℃ / s, held for 1s, and then water quenched to 40-60℃. The high-carbon low-alloy spring steel wire is obtained.

[0079] Example 3

[0080] A method for producing high-strength, high-carbon, low-alloy spring steel wire using ultra-fast induction heating includes the following steps:

[0081] Step 1: According to the chemical composition ratio of high carbon low alloy spring steel in Table 1 below, iron ore, quicklime, vanadium stone, iron-silicon alloy, iron-manganese alloy, iron-chromium alloy, etc. are placed in an oxidizing atmosphere furnace for melting and smelting to obtain molten steel. Then, the molten steel is transferred to a reducing atmosphere furnace for refining to obtain refined molten steel. The refined molten steel is then continuously cast to obtain steel billets.

[0082] Step two: Place the steel billet obtained in step one into a walking beam furnace and heat it at 1260-1300℃ for 2.5-3 hours. This allows all C, Si, Mn, V, Cr, and Cu elements to be dissolved in solid solution.

[0083] Step 3: Forge the solution-treated steel billet from Step 2 at a final forging temperature of 1000℃-1100℃ to obtain a forged billet.

[0084] Step 4: Heat the forging billet obtained in Step 3 to 1220-1250℃ and hold for 2-3 hours, with the initial rolling temperature at 900-1000℃ and the final rolling temperature at 800-980℃, to obtain hot-rolled steel bars.

[0085] Step 5: Pickle the hot-rolled steel bar obtained in Step 4. The acid temperature is 70-85℃ and the pickling speed is 90-100m / min.

[0086] Step six: The steel strip pickled in step five is cold-drawn. The total reduction in surface area after cold drawing is 85%, and the diameter of the cold-drawn steel wire after 85% cold drawing is 6.5mm.

[0087] Step 7: The cold-drawn steel wire obtained in Step 6 is subjected to ultra-fast induction heating treatment. The heat treatment method is quenching + tempering. The quenching method is heating followed by water quenching. The cold-drawn steel wire is heated to 850℃ at a rate of 60℃ / s, held for 2s, and then water quenched to 40-60℃. Then, it is heated to a tempering temperature of 473℃ at a rate of 50℃ / s, held for 1.5s, and then water quenched to 40-60℃ to obtain the high-carbon low-alloy steel.

[0088] Example 4

[0089] A method for producing high-strength, high-carbon, low-alloy spring steel wire using ultra-fast induction heating includes the following steps:

[0090] Step 1: According to the chemical composition ratio of high carbon low alloy spring steel in Table 1 below, iron ore, quicklime, vanadium stone, iron-silicon alloy, iron-manganese alloy, and iron-chromium alloy are placed in an oxidizing atmosphere furnace for melting and smelting to obtain molten steel. Then, the molten steel is transferred to a reducing atmosphere furnace for refining to obtain refined molten steel. The refined molten steel is then continuously cast to obtain steel billets.

[0091] Step two: Place the steel billet obtained in step one into a walking beam furnace and heat it at 1260-1300℃ for 2.5-3 hours. This allows all C, Si, Mn, V, Cr, and Cu elements to be dissolved in solid solution.

[0092] Step 3: Forge the solution-treated steel billet from Step 2 at a final forging temperature of 1000℃-1100℃ to obtain a forged billet.

[0093] Step 4: Heat the forging billet obtained in Step 3 to 1220-1250℃ and hold for 2-3 hours, with the initial rolling temperature at 900-1000℃ and the final rolling temperature at 800-980℃, to obtain hot-rolled steel bars.

[0094] Step 5: Pickle the hot-rolled steel bar obtained in Step 4. The acid temperature is 70-85℃ and the pickling speed is 90-100m / min.

[0095] Step six: The steel strip pickled in step five is cold-drawn. The total reduction in surface area after cold drawing is 90%, and the diameter of the cold-drawn steel wire after 90% cold drawing is 6.5mm.

[0096] Step 7: The cold-drawn steel wire obtained in Step 6 is subjected to ultra-fast induction heating treatment. The heat treatment method is quenching + tempering. The quenching method is heating followed by water quenching. The cold-drawn steel wire is heated to 880℃ at a rate of 55℃ / s, held for 1s, and then water quenched to 40-60℃. Then, it is heated to a tempering temperature of 460℃ at a rate of 55℃ / s and held for 2.5s, and then water quenched to 40-60℃ to obtain the high-carbon low-alloy steel.

[0097] Table 1 is a list of the chemical components of the above embodiments of the present invention;

[0098] Table 1. Chemical composition (mass percentage) of each embodiment.

[0099]

[0100]

[0101] Table 2 shows the cold drawing and rapid heat treatment process parameters of the above embodiments of the present invention;

[0102] Table 2. Process parameters for cold drawing and rapid heat treatment in each embodiment.

[0103]

[0104] The high-carbon low-alloy spring steel wires prepared in the above embodiments were subjected to mechanical property tests, and the test results are shown in Table 3.

[0105] Table 3. Mechanical properties of the high-carbon low-alloy spring steel wires prepared in each example.

[0106]

[0107] As shown in Tables 1-3, the method of this invention can produce high-strength-ductility-product high-carbon low-alloy spring steel wire with excellent mechanical properties. Its tensile strength is above 1796 MPa, yield strength is above 1681 MPa, elongation after fracture is above 11.23%, and strength-ductility-product is above 20.17 GPa·%. Simultaneously, the significantly refined microstructure and dispersed carbides ensure the high strength-ductility-product of the high-carbon low-alloy steel. In particular, the lower tempering temperature in Example 4 retained some thin-film retained austenite, providing a TRIP effect and further improving mechanical properties. The tensile strength reached 2092 MPa, the ductility reached 17.27%, and the strength-ductility-product reached 36.13%, which is higher than that of high-carbon low-alloy spring steel produced by traditional processes.

[0108] Figure 1 The figures show the engineering stress-strain curves of the high-strength, high-ductility, high-carbon, low-alloy steels prepared in Examples 1-4 of this invention. It can be seen that as the tempering temperature decreases, the tensile strength of the examples increases, and the ductility also increases. When the tempering temperature decreases from 524℃ to 460℃, the tensile strength increases by 296 MPa, and the elongation after fracture increases by 6.04%.

[0109] Figure 2 SEM images of the high-strength, high-ductility, high-carbon, low-alloy steels prepared in Examples 1-4 are shown. (a) represents Example 1, (b) represents Example 2, (c) represents Example 3, and (d) represents Example 4. It can be seen that... Figure 2 The four martensitic structures in the wire are relatively fine. This is because the ultra-rapid heating causes austenitization before the ferrite can recover, resulting in numerous austenite nucleation sites and refining the grain size. Furthermore, the rapid heating rate pushes the austenitization temperature to a higher level, further accelerating the nucleation rate and refining the microstructure, ultimately improving the material's mechanical properties. In Examples 1 to 4, as the tempering temperature decreases, the carbide distribution becomes more dispersed, which not only improves the strength of the high-carbon low-alloy spring steel wire but also further enhances its plasticity. In particular, Example 4, due to its lower tempering temperature, still contains a small amount of thin-film retained austenite, providing a significant TRIP effect. In summary, the high-carbon low-alloy spring steel produced using an ultra-rapid induction heating wire maintains high strength while possessing excellent plasticity. With reasonable parameter adjustments, a high-performance high-carbon low-alloy steel with a tensile strength of 2092 MPa, an elongation after fracture of 17.27%, and a strength-ductility product of 36.13% can be obtained.

[0110] In summary, this invention utilizes ultra-fast induction heating to produce high-strength, high-carbon, low-alloy spring steel wire, achieving a refined microstructure while retaining a large number of dislocations, thus resulting in excellent mechanical properties. By using only inexpensive carbon, without the addition of many expensive rare metals, the performance of steel can be significantly improved. Furthermore, rapid heat treatment has immense development and application value. The combination of these two factors will undoubtedly provide greater scope for the development and production of high-carbon, low-alloy steel!

[0111] The embodiments described above merely illustrate concentrated implementations of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still make various modifications and improvements to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, without departing from the concept of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention. Therefore, the protection scope of this patent should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A high-strength, high-carbon, low-alloy spring steel wire, characterized in that, Its chemical composition by mass percentage is as follows: C: 0.63%-0.68%, Si: 1.45%-1.49%, Mn: 0.66%-0.70%, Cr: 0.67%-0.71%, V: 0.11%-0.131%, Cu: 0.019%-0.021%; the balance is Fe and unavoidable impurities. The high-strength, high-carbon, low-alloy spring steel wire is produced by ultra-fast induction heating, including the following steps: (1) Heat the steel billet to solidify it; (2) Forge the steel billet after solution treatment in step (1) to obtain a forged billet; (3) The forging billet obtained in step (2) is hot rolled to obtain hot-rolled wire; (4) The hot-rolled wire obtained in step (3) is cold-drawn to obtain cold-drawn steel wire; (5) The cold-drawn steel wire obtained in step (4) is first ultra-fast induction heated to 800-900℃ at a heating rate of 50-100℃ / s, held for 1-4s, and then water-quenched to 40-60℃ for the first time; the steel wire after the first water quenching is then ultra-fast induction heated to 400-600℃ at a heating rate of 40-70℃ / s for the second time, held for 1-4s, and then water-quenched to 40-60℃ for the second time to obtain high-strength, high-carbon, low-alloy spring steel wire.

2. The high-strength, high-carbon, low-alloy spring steel wire according to claim 1, characterized in that, The chemical composition of the high-strength, high-carbon, low-alloy spring steel wire by mass percentage is as follows: C: 0.65%, Si: 1.48%, Mn: 0.67%, Cr: 0.71%, V: 0.131%, Cu: 0.02%, with the balance being Fe and unavoidable impurities.

3. The high-strength, high-carbon, low-alloy spring steel wire according to claim 1, characterized in that, The high-strength, high-carbon, low-alloy spring steel wire comprises a martensitic matrix, a thin film of retained austenite, and dispersed fine carbides. Control the mass percentage of impurity chemical components: P≤0.008%, S≤0.008%, O2≤10ppm, H2≤10ppm.

4. The high-strength, high-carbon, low-alloy spring steel wire according to claim 1, characterized in that, The high-strength, high-ductility, high-carbon, low-alloy spring steel wire has a tensile strength of 1796-2092 MPa, a yield strength of 1681-1887 MPa, an elongation after fracture of 11.23%-17.27%, and a strength-ductility product of 20.17-36.13 GPa·s.

5. The high-strength, high-carbon, low-alloy spring steel wire according to claim 1, characterized in that, The heating and solution treatment in step (1) is carried out at 1260-1300℃ for 2.5-3 hours; The final forging temperature in step (2) is 1000℃-1100℃; The hot rolling in step (3) specifically involves heating the forging billet to 1220-1250℃ and holding it for 2-3 hours, wherein the initial rolling temperature is 900-1000℃ and the final rolling temperature is 800-980℃.

6. The high-strength, high-carbon, low-alloy spring steel wire according to claim 1, characterized in that, The hot-rolled wire described in step (3) is pickled and then cold-drawn in step (4); The temperature of the pickling solution is 70-85℃, and the pickling speed is 90-100m / min.

7. The high-strength, high-carbon, low-alloy spring steel wire according to claim 1, characterized in that, The total reduction rate of the cold drawing in step (4) is 70-90%; the diameter of the cold-drawn steel wire is 3-10mm.

8. The high-strength, high-carbon, low-alloy spring steel wire according to claim 1, characterized in that, The temperature of the first ultra-fast induction heating in step (5) is 850-890℃; the temperature of the second ultra-fast induction heating is 460-524℃; The cooling rate of the first water quench in step (5) is 200-500℃ / s; the cooling rate of the second water quench is 150-400℃ / s.

9. The ultra-fast induction heating production method of high-strength, high-carbon, low-alloy spring steel wire according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Heat the steel billet to solidify it; (2) Forge the steel billet after solution treatment in step (1) to obtain a forged billet; (3) The forging billet obtained in step (2) is hot rolled to obtain hot-rolled wire; (4) The hot-rolled wire obtained in step (3) is cold-drawn to obtain cold-drawn steel wire; (5) The cold-drawn steel wire obtained in step (4) is first ultra-fast induction heated to 800-900℃ at a heating rate of 50-100℃ / s, held for 1-4s, and then water-quenched to 40-60℃ for the first time; the steel wire after the first water quenching is then ultra-fast induction heated to 400-600℃ at a heating rate of 40-70℃ / s for the second time, held for 1-4s, and then water-quenched to 40-60℃ for the second time to obtain high-strength, high-carbon, low-alloy spring steel wire.

10. The ultra-fast induction heating production method for high-strength, high-carbon, low-alloy spring steel wire according to claim 9, characterized in that, The method for preparing the steel billet in step (1) is as follows: the raw materials are melted and smelted in an oxidizing atmosphere to obtain molten steel; then, the molten steel is refined in a reducing atmosphere to obtain high-purity refined steel; finally, the refined steel is continuously cast to obtain the steel billet.

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