2200mpa grade high strength and toughness spring steel wire and a preparation method thereof

Abstract

The application discloses a 2200MPa-grade high-strength and high-toughness spring steel wire and a preparation method thereof, and belongs to the technical field of spring steel, and solves the problem that spring steel wires cannot simultaneously have high strength and high plasticity and toughness in the prior art.The chemical components of the 2200MPa-grade high-strength and high-toughness spring steel wire include the following in percentage by mass: C 0.45%-0.70%, Si 1.00%-2.50%, Mn 0.40%-3.00%, Cr 0.10%-3.00%, Mo 0.02%-0.30%, Nb 0.02%-0.30%, V 0.02%-0.30%, N 0.008%-0.012%, P≤0.015%, S≤0.002%, and the rest is Fe and inevitable impurities.The 2200MPa-grade high-strength and high-toughness spring steel wire has high strength and good plasticity and toughness.

Description

Technical Field

[0001] This invention relates to the field of spring steel technology, and in particular to a 2200MPa grade high-strength and high-toughness spring steel wire and its preparation method. Background Technology

[0002] Springs are important components for vibration damping and anti-slack functions, capable of withstanding and transmitting vertical loads and mitigating the impact of uneven road surfaces. Therefore, they are widely used in the transportation sector, such as in automotive suspension systems. As transportation vehicles develop towards lighter weight, higher speed, heavier loads, and higher safety, the performance of traditional springs can no longer meet the demands, necessitating the development of spring steels with higher strength and toughness.

[0003] Currently, domestic and international companies generally use a process of primary refining → refining → vacuum degassing → continuous casting → billet preparation → intermediate billet grinding → high-speed wire rod rolling → diameter reduction rolling → drawing → oil quenching and tempering → coiling to produce springs. Traditional methods for improving the strength of spring steel wire mainly include adjusting the heat treatment process and optimizing the alloy composition. For example, lowering the tempering temperature in the oil quenching and tempering stage can improve the strength of the spring, but it will cause a decrease in the spring's plasticity, harming the winding and coiling performance of the spring steel wire. Some studies have improved the strength of spring steel by adding silicon, but silicon increases the spring's decarburization sensitivity, which is detrimental to the spring's fatigue performance.

[0004] CN109457187A discloses a high-strength spring steel with a tensile strength exceeding 2100 MPa and its production method. This method improves strength by adding the microalloying element V, forming nanoscale vanadium carbide particles at grain boundaries and utilizing precipitation strengthening. However, excessively high V content in high-carbon alloy systems can easily lead to the precipitation of large vanadium carbide and vanadium carbonitride particles during solidification and high-temperature rolling, thus compromising the material's toughness. Furthermore, while the relatively low tempering temperature in this invention increases the material's strength, it reduces the reduction of area and elongation at fracture, resulting in a decrease in ductility and toughness.

[0005] Therefore, how to provide a high-strength and high-toughness spring steel wire has become an urgent problem to be solved. Summary of the Invention

[0006] In view of the above, the present invention aims to provide a 2200MPa grade high-strength and high-toughness spring steel wire and its preparation method, in order to solve the problem that existing spring steel wires cannot simultaneously achieve high strength and high plasticity and toughness.

[0007] The objective of this invention is mainly achieved through the following technical solutions:

[0008] On one hand, the present invention provides a 2200MPa grade high-strength and high-toughness spring steel wire. The chemical composition of the 2200MPa grade high-strength and high-toughness spring steel wire, by mass percentage, includes: C 0.45%~0.70%, Si 1.00%~2.50%, Mn 0.40%~3.00%, Cr 0.10%~3.00%, Mo 0.02%~0.30%, Nb 0.02%~0.30%, V 0.02%~0.30%, N 0.008%~0.012%, P≤0.015%, S≤0.002%, with the remainder being Fe and unavoidable impurities.

[0009] Furthermore, the chemical composition of 2200MPa grade high-strength and high-toughness spring steel wire contains 1.3% <Mn+Cr<3.5%,0.05%<Nb+V<0.2%。

[0010] Furthermore, the chemical composition of the 2200MPa grade high-strength and high-toughness spring steel wire, by mass percentage, includes: C 0.5%–0.70%, Si 1.40%–2.50%, Mn 0.80%–3.00%, Cr 0.30%–3.00%, Mo 0.02%–0.25%, Nb 0.02%–0.25%, V 0.02%–0.25%, N 0.008%–0.012%, P≤0.015%, S≤0.002%, with the remainder being Fe and unavoidable impurities.

[0011] Furthermore, the chemical composition of 2200MPa grade high-strength and high-toughness spring steel wire contains 1.3% <Mn+Cr<3.0%,0.08%<Nb+V<0.2%。

[0012] Furthermore, the microstructure of the 2200MPa grade high-strength and high-toughness spring steel wire includes tempered martensite, retained austenite, and dispersed carbonitrides.

[0013] Furthermore, in the microstructure of 2200MPa grade high strength and toughness spring steel wire, the content of Mn+Cr in tempered martensite is lower than the content of Mn+Cr in retained austenite.

[0014] Furthermore, in the microstructure of 2200MPa grade high-strength and high-toughness spring steel wire, the volume fraction of retained austenite is 6% to 20%.

[0015] Furthermore, the microstructure of the 2200MPa high-strength and high-toughness spring steel wire consists of nanoscale tempered martensite laths and lamellar retained austenite stacked together.

[0016] This invention also provides a method for preparing the above-mentioned 2200MPa grade high-strength and high-toughness spring steel wire, comprising:

[0017] Step 1: Prepare the materials according to the chemical composition of 2200MPa grade high-strength and tough spring steel wire;

[0018] Step 2: Smelting and casting are carried out sequentially to obtain a continuously cast billet;

[0019] Step 3: The continuously cast billet is sequentially heated and held at the temperature, then rough rolled, finish rolled, and wire rod produced to obtain wire rod;

[0020] Step 4: Pickle the wire rod and draw it with a reduction rate of 5% to 10% per pass;

[0021] Step 5: Perform rapid austenitization and prepare 2200MPa grade high-strength and tough spring steel wire using quenching-partitioning treatment.

[0022] Furthermore, in step 3, the temperature is controlled to 1200–1250°C and held for 1–3 hours.

[0023] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0024] a) The 2200MPa grade high-strength and high-toughness spring steel wire provided by this invention, while ensuring the control of S and P content, adds appropriate amounts of Mn, Cr, Mo, Nb, and V elements; by increasing the Mn and Cr content in the pearlitic wire rod, the degree of alloy element distribution is increased, and heterogeneous high-temperature austenite is constructed; Mo element can increase the heterogeneity of Mn and Cr elements in high-temperature austenite through solute dragging effect, and synergistically precipitate and refine carbonitride particles with Nb, V, etc., reducing the interfacial energy between carbonitrides and the matrix, making the precipitated phase less prone to coarsening (concentrated in the two ranges of 0-60nm and 200-300nm), thereby improving the strength of the wire rod and ensuring a good match between strength and toughness.

[0025] (b) The preparation method of the 2200MPa high-strength and high-toughness spring steel wire provided by this invention adopts a quenching-partitioning process. Based on the natural distribution of Mn and Cr elements between cementite and ferrite lamellae in pearlitic wire rods (cementite is rich in Mn and Cr, while ferrite is poor in Mn and Cr), induction heating is combined to construct high-temperature austenite with uneven distribution of Mn and Cr elements. Since Mn and Cr are both austenite-stabilizing elements, the difference in Mn and Cr content in the uneven high-temperature austenite can regulate the martensitic transformation during the quenching stage, preparing a microstructure of martensitic laths and austenitic lamellae stacked together. Combined with the enrichment of C from martensite to austenite during the partitioning stage, a sufficient amount of stable lamellar morphology retained austenite is obtained. High strength is ensured by tempering the martensitic matrix, and the C, Mn, and Cr-rich retained austenite with lamellar morphology is used to improve the plasticity and toughness of the steel wire.

[0026] c) The 2200MPa grade high-strength and high-toughness spring steel wire provided by this invention can be obtained by relying on existing production equipment and adjusting the heat treatment process. The mechanical properties of the 2200MPa grade high-strength and high-toughness spring steel wire are as follows: tensile strength ≥2200MPa (e.g., 2200MPa~2270MPa), yield strength ≥1790MPa (e.g., 1790MPa~2018MPa), elongation ≥10.5% (e.g., 10.9%~16.2%), and reduction of area ≥40% (e.g., 40%~55%), achieving a good match between strength and toughness. The production process is simple and suitable for large-scale industrial production.

[0027] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of what is particularly pointed out in the written description, claims, and drawings. Attached Figure Description

[0028] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0029] Figure 1 Here is a SEM image of the wire rod from Example 1;

[0030] Figure 2 TEM image of the wire rod in Example 1;

[0031] Figure 3 SEM image of the 2200MPa grade high-strength and tough spring steel wire of Example 1. Detailed Implementation

[0032] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and, together with the embodiments of the present invention, serve to illustrate the principles of the present invention.

[0033] This invention provides a 2200MPa grade high-strength and high-toughness spring steel wire. The chemical composition of this wire, by mass percentage, includes: C 0.45%–0.70%, Si 1.00%–2.50%, Mn 0.40%–3.00%, Cr 0.10%–3.00%, Mo 0.02%–0.30%, Nb 0.02%–0.30%, V 0.02%–0.30%, N 0.008%–0.012%, P ≤ 0.015%, S ≤ 0.002%, with the remainder being Fe and unavoidable impurities. To balance the good performance and low cost of the spring steel wire, the synergistic relationship of the alloying elements is as follows: 1.3% <Mn+Cr<3.5%,0.05%<Nb+V<0.2%。

[0034] The following details the function and dosage selection of the ingredients contained in this invention:

[0035] Carbon (C) is a major strengthening element in spring steel, significantly affecting the strength and toughness of the steel. Increasing the carbon content is also necessary for the formation of microalloyed carbonitrides. However, excessive carbon content can compromise the ductility and toughness of the steel. Therefore, considering all factors, the carbon content in this invention ranges from 0.45% to 0.70%.

[0036] Silicon (Si) is a deoxidizer used in steelmaking, possessing a certain solid solution strengthening effect. It can influence resistance to elastic reduction and is an important element for ensuring a good elastic limit. Silicon also improves the tempering stability of steel and promotes the fine and dispersed distribution of carbides. However, silicon accelerates carbon diffusion in steel, and excessive silicon content can exacerbate decarburization on the surface of spring steel. Therefore, considering all factors, the silicon content in this invention ranges from 1.00% to 2.50%.

[0037] Manganese (Mn): An element that improves hardenability and is inexpensive. It can simultaneously improve strength and toughness within a certain range, strengthen the matrix, and improve the steel's resistance to elastic degradation. However, excessive content can easily lead to macroscopic segregation and a decrease in toughness. This invention, however, avoids the macroscopic segregation and toughness reduction caused by manganese by constructing a non-uniform high-temperature austenite and enriching manganese in the retained austenite. Therefore, considering all factors, the manganese content in this invention ranges from 0.40% to 3.00%.

[0038] Chromium (Cr): It improves hardenability, slows down the decarburization tendency of spring steel, and increases the strength of the steel. However, excessive chromium content will reduce the resistance to elastic reduction and increase the cost of the alloy. Therefore, considering all factors, the chromium content in this invention ranges from 0.10% to 3.00%.

[0039] Molybdenum (Mo): An element that improves hardenability, Molybdenum enhances the strength of spring steel by strengthening the matrix through solid solution, reducing pinning defects through precipitation, and improving the thermal stability of the microstructure. Molybdenum can hinder the diffusion of substitutional alloying elements through the solute dragging effect, contributing to the formation of inhomogeneous high-temperature austenite. However, Molybdenum is a valuable alloying element, significantly increasing alloy costs. Furthermore, excessively high Mo content severely hinders the pearlite transformation. Therefore, considering all factors, the Molybdenum content in this invention ranges from 0.02% to 0.30%.

[0040] Niobium (Nb) is a microalloying carbonitride forming element. During rolling, both niobium dissolved in austenite and deformation-induced niobium carbonitride precipitation have a grain-refining effect. During post-rolling cooling, it refines the pearlite lamellar spacing of spring wire rods. Niobium dissolved in austenite increases carbon diffusion resistance and reduces the decarburization sensitivity of spring steel; niobium dissolved in ferrite tends to segregate at interfaces, dislocations, and other defects, which is beneficial for improving the strength of spring steel. Therefore, considering all factors, the niobium content in this invention ranges from 0.02% to 0.30%.

[0041] Vanadium (V): A microalloying carbonitride forming element, vanadium has a low solid solution temperature, which effectively improves hardenability and recrystallization temperature during rolling, and refines the pearlite lamellar spacing of spring wire rods during post-rolling cooling. Vanadium has high solubility in austenite but relatively low solubility in ferrite, thus it mainly precipitates in ferrite, exhibiting a significant precipitation strengthening effect. Therefore, considering all factors, the vanadium content in this invention ranges from 0.02% to 0.30%.

[0042] Nitrogen (N): It is an effective interstitial solid solution strengthening element in spring steel. At high temperatures, the solid solubility of niobium and vanadium carbonitrides is high, and nitrogen mainly exists in a solid solution state. During post-rolling cooling, it precipitates carbonitrides in synergy with molybdenum, niobium, and vanadium, exhibiting a significant precipitation strengthening effect. Therefore, considering all factors, the nitrogen content in this invention ranges from 0.008% to 0.012%.

[0043] Phosphorus (P): A harmful element in spring steel. While phosphorus can increase the strength of spring steel, it significantly reduces its ductility, toughness, and cold working ability. To ensure good drawing performance of wire rod, the phosphorus content of spring steel should be strictly controlled. Therefore, considering all factors, the phosphorus content in this invention is within the range of 0.015%.

[0044] Sulfur (S) is a harmful element in spring steel. It combines with manganese to form manganese sulfide inclusions, reducing the ductility and cold working properties of spring steel. Therefore, considering all factors, the sulfur content in this invention is within the range of 0.002%.

[0045] To further improve the overall performance of the aforementioned 2200MPa grade high-strength and high-toughness spring steel wire, the chemical composition of the aforementioned 2200MPa grade high-strength and high-toughness spring steel wire, by mass percentage, includes: C 0.5%–0.70%, Si 1.40%–2.50%, Mn 0.80%–3.00%, Cr 0.30%–3.00%, Mo 0.02%–0.25%, Nb 0.02%–0.25%, V 0.02%–0.25%, N 0.008%–0.012%, P ≤ 0.015%, S ≤ 0.002%, with the remainder being Fe and unavoidable impurities.

[0046] Specifically, to balance the good properties and low cost of the spring steel wire, the synergistic relationship of alloying elements is as follows: 1.3% < Mn + Cr < 3.0%, 0.08% < Nb + V < 0.2%.

[0047] Specifically, the microstructure of the above-mentioned 2200 MPa grade high-strength and tough spring steel wire includes tempered martensite, retained austenite and dispersed carbonitrides.

[0048] Specifically, in the microstructure of the above-mentioned 2200 MPa grade high-strength and tough spring steel wire, the volume fraction of retained austenite is about 6% - 20%.

[0049] Specifically, the microstructure of the above-mentioned 2200 MPa grade high-strength and tough spring steel wire is composed of nano-scale tempered martensite laths and lamellar retained austenite stacked on each other.

[0050] Specifically, in the microstructure of the above-mentioned 2200 MPa grade high-strength and tough spring steel wire, the lath width of the tempered martensite laths is about 80 - 230 nm, and the lamellar thickness of the lamellar retained austenite is about 12 - 50 nm.

[0051] Specifically, in the microstructure of the above-mentioned 2200 MPa grade high-strength and tough spring steel wire, Mn and Cr elements show uneven distribution between the tempered martensite laths and the retained austenite lamellae. Among them, the Mn and Cr elements are poor in the tempered martensite laths, and the content of Mn and Cr elements in the tempered martensite laths is about: 0.5% < Mn + Cr < 2.1%; the Mn and Cr elements are enriched in the retained austenite, and the content of Mn and Cr elements in the retained austenite is about: 3.5% < Mn + Cr < 25%.

[0052] Specifically, in the microstructure of the above-mentioned 2200 MPa grade high-strength and tough spring steel wire, fine carbonitrides are dispersed in the tempered martensite laths and the retained austenite lamellae. Among them, the density and size of the carbonitrides in the tempered martensite are higher than those in the retained austenite. At the same time, the size of the carbonitrides is concentrated in two ranges of 0 - 60 nm and 200 - 300 nm.

[0053] The present invention also provides a preparation method for a 2200 MPa grade high-strength and tough spring steel wire, including:

[0054] Step 1:配料 according to the chemical composition of the 2200 MPa grade high-strength and tough spring steel wire;

[0055] Step 2:依次进行冶炼和铸造,得到连铸坯;

[0056] Step 3:对连铸坯依次进行加热保温、粗轧、精轧、吐丝得到盘条;

[0057] It should be noted that there is an unclear expression "配料" in the original text. It might be better to use a more accurate term like "proportioning materials" or something similar for a more precise translation. Also, the Chinese expression "依次进行冶炼和铸造,得到连铸坯" and "对连铸坯依次进行加热保温、粗轧、精轧、吐丝得到盘条" could be more clearly translated to better convey the process details, but following the instruction to maintain the original line breaks and such, this is the closest translation.Step 4: Pickle the wire rod and draw it with a reduction rate of 5% to 10% per pass;

[0058] Step 5: Perform rapid austenitization and prepare 2200MPa grade high-strength and tough spring steel wire using quenching-partitioning treatment.

[0059] Specifically, in step 2 above, a converter or electric furnace is used for smelting, and continuous casting is used for casting.

[0060] Specifically, in step 3 above, considering that excessively high temperatures and prolonged holding times in the heating and holding process will exacerbate the decarburization layer depth of the billet, while excessively low temperatures and prolonged holding times will cause uneven microstructure and composition of the billet, the heating is controlled to 1200–1250℃ and held for 1–3 hours to obtain a homogenized billet.

[0061] Specifically, in step 3 above, excessively high roughing temperatures will increase the austenite grain size and the depth of the decarburized layer, while excessively low temperatures will increase the mill load. Therefore, the roughing temperature should be controlled between 1000 and 1175°C.

[0062] Specifically, in step 3 above, the roughing billet needs to be surface-processed before finishing rolling. The surface processing mainly includes surface treatment of the roughing billet to ensure that the surface of the roughing billet is free of decarburization and defects.

[0063] Specifically, in step 3 above, the rough rolled billet after surface processing is continuously rolled through the intermediate rolling mill, finishing mill and sizing mill to form wire rod.

[0064] Specifically, in step 3 above, excessively high initial rolling temperature will increase the austenite grain size and decarburized layer depth, while excessively low temperature will increase the mill load. Therefore, the initial rolling temperature of the finishing mill should be controlled at 850–1000℃, and the final rolling temperature should be controlled at 830–900℃.

[0065] Specifically, in step 3 above, the wire drawing temperature is controlled within the austenite and ferrite two-phase region; the wire rod after wire drawing is cooled in two stages, wherein the cooling rate of the first stage is greater than that of the second stage.

[0066] Specifically, in step 3 above, excessively high winding temperature will exacerbate the oxidation of the wire rod and impair its ellipticity, while excessively low winding temperature will reduce the plasticity of the wire rod and impair its surface quality. Therefore, the winding temperature should be controlled between 830 and 850°C.

[0067] Specifically, in step 3 above, the two-stage cooling of the wire rod after drawing includes: the first stage cooling to 650-700℃ at a cooling rate of 10℃ / s or higher. This cooling process is used to reduce the precipitation of proeutectoid ferrite and quickly enter the pearlite transformation temperature range; the second stage cooling rate is selected as 0.2-2℃ / s to allow the supercooled austenite to fully undergo pearlite transformation, ensuring that the wire rod has a pearlite structure of more than 90%, and controlling the pearlite lamellar spacing to ensure the deformation capacity and strength during the drawing stage.

[0068] Specifically, in step 3 above, the microstructure of the wire rod after two-stage cooling consists of pearlite, a small amount of ferrite, and a small amount of carbonitrides, wherein the volume fraction of pearlite is not less than 90% (e.g., more than 94%), the interlamellar spacing of pearlite is 80-250 nm, and the average size of carbonitrides is about 140-240 nm.

[0069] Specifically, in step 3 above, the pearlite microstructure consists of alternating layers of ferrite and cementite, with a strong heterogeneous distribution of Mn and Cr elements between the ferrite and cementite. The ferrite layers are Mn and Cr-poor, while the cementite layers are Mn and Cr-rich. Specifically, the Mn+Cr content in the ferrite layers is approximately 0.5%–1.5%, and the Mn+Cr content in the cementite layers is approximately 14%–34%.

[0070] Specifically, in step 4 above, considering that an excessive reduction rate would harm the surface quality of the wire rod, while an insufficient reduction rate would not provide adequate strengthening, a reduction rate of 5-10% per pass is used to draw the wire into a specific diameter.

[0071] Specifically, in step 5 above, the steel wire is rapidly austenitized by induction heating to the austenitic single-phase region (e.g., 800-870℃) (holding for 10-600 seconds).

[0072] Specifically, in step 5 above, the quenching-partitioning process includes:

[0073] Step a: The rapidly austenitized steel wire is quenched online to 25-150℃ using an oil bath at 25-150℃;

[0074] Step b: Heat the steel wire treated in step a to a distribution temperature of 300-500℃ online using a lead bath, salt bath, or induction heating, hold for 10-1800s, and finally cool to room temperature.

[0075] Specifically, in the above step a, after online quenching, a mixed structure of martensite (volume fraction of 75% - 90%) and austenite (volume fraction of 10% - 25%) is obtained; then it is rapidly heated to the partitioning temperature and held using molten lead, molten salt or an induction device to promote the entry of carbon atoms in the martensite into the austenite; finally, it is cooled to room temperature to obtain a 2200 MPa grade high-strength and tough spring steel wire.

[0076] Specifically, in the above step b, the wire drawing speed of the spring steel wire is controlled to be 0.01 - 0.5 m / s.

[0077] Compared with the prior art, for the 2200 MPa grade high-strength and tough spring steel wire provided by the present invention, on the basis of ensuring the control of the S and P contents, appropriate amounts of Mn, Cr, Mo, Nb, and V elements are added; by increasing the Mn and Cr contents in the pearlitic wire rod (for example, 1.5% < Mn + Cr < 3.5%), the degree of alloy element partitioning is increased to construct non-uniform high-temperature austenite; the Mo element can increase the non-uniformity degree of Mn and Cr elements in the high-temperature austenite through the solute drag effect, and cooperate with Nb, V, etc. to precipitate and refine carbonitride particles, reducing the interfacial energy between the carbonitride and the matrix, making the precipitated phase not easily coarsen (concentrated in two intervals of 0 - 60 nm and 200 - 300 nm), thereby improving the strength of the wire rod.

[0078] The preparation method of the 2200 MPa grade high-strength and tough spring steel wire provided by the present invention adopts a quenching-partitioning process. Based on the partitioning of Mn and Cr elements in the cementite and ferrite lamellae of the pearlitic wire rod, combined with induction heating to construct non-uniform high-temperature austenite, the martensite transformation in the quenching stage is regulated to prepare a structure in which martensite laths and austenite lamellae are stacked on top of each other. Combining the enrichment of C from martensite to austenite in the partitioning stage, a sufficient amount of stable lamellar morphology retained austenite is obtained. The high strength is ensured by the tempered martensite matrix, and the plasticity and toughness of the steel wire are improved simultaneously by the C, Mn, Cr-rich retained austenite with lamellar morphology.

[0079] The 2200 MPa grade high-strength and tough spring steel wire provided by the present invention can rely on existing production equipment. By regulating the heat treatment process, the mechanical properties of the obtained 2200 MPa grade high-strength and tough spring steel wire are as follows: tensile strength ≥ 2200 MPa (for example, 2200 MPa - 2270 MPa), yield strength ≥ 1790 MPa (for example, 1790 MPa - 2018 MPa), elongation ≥ 10.5% (for example, 10.9 - 16.2%), reduction of area ≥ 40% (for example, 40 - 55%), hardness above 54 HRC (for example, 54.2 - 59.5 HRC), achieving a good match between strength and toughness. The production process is simple and suitable for large-scale industrial production.

[0080] The following specific embodiments and comparative examples demonstrate the advantages of precise control of composition and process parameters in the 2200MPa grade high-strength and tough spring steel wire and its preparation method of the present invention.

[0081] Examples 1-5 of the present invention provide a 2200MPa grade high-strength and high-toughness spring steel wire and its preparation method. The chemical composition of the spring steel wire in Examples 1-5 is shown in Table 1.

[0082] The method for preparing the spring steel wire in Example 1 includes:

[0083] Step 1: Prepare the ingredients according to their chemical composition;

[0084] Step 2: Smelting and continuous casting are carried out sequentially to obtain a continuously cast billet;

[0085] Step 3: Heat the continuously cast billet to 1230℃ and hold for 2 hours. The roughing rolling start temperature is 1150℃, the roughing rolling finish temperature is 1005℃, the finishing rolling start temperature is 983℃, and the finishing rolling finish temperature is 873℃. Cool the billet to 651℃ in the Steyrmo air-cooling line at a cooling rate of 25℃ / s, and then reduce the fan power to cool it to room temperature at a rate of 1.0℃ / s.

[0086] Step 4: Pickle the wire rod and draw it with a reduction rate of 5% to 10% per pass;

[0087] Step 5: Perform rapid austenitization and prepare 2200MPa grade high-strength and tough spring steel wire using quenching-partitioning treatment.

[0088] The specific heat treatment process and parameters for step 5 are as follows: the steel wire is induction heated to 830℃, then quenched in an oil bath at 50℃, and then heated to 351℃ by induction heating for distribution treatment. The take-up speed of the steel wire in online processing is set to 0.2m / s.

[0089] The preparation method of the spring steel wire in Example 2 includes:

[0090] Step 1: Prepare the ingredients according to their chemical composition;

[0091] Step 2: Smelting and continuous casting are carried out sequentially to obtain a continuously cast billet;

[0092] Step 3: Heat the continuously cast billet to 1200℃ and hold it for 3 hours. The roughing rolling start temperature is 1175℃, the roughing rolling finish temperature is 1025℃, the finishing rolling start temperature is 998℃, and the finishing rolling finish temperature is 871℃. Cool the billet to 663℃ in the Steyrmo air-cooling line at a cooling rate of 20℃ / s, and then reduce the fan power to cool it to room temperature at a rate of 1.5℃ / s.

[0093] Step 4: Pickle the wire rod and draw it with a reduction rate of 5% to 10% per pass;

[0094] Step 5: Perform rapid austenitization and prepare 2200MPa grade high-strength and tough spring steel wire using quenching-partitioning treatment.

[0095] The specific heat treatment process and parameters for step 5 are as follows: the steel wire is induction heated to 870℃, then quenched in an oil bath at 80℃, and then heated to 400℃ by induction heating for distribution treatment. The take-up speed of the steel wire in online processing is set to 0.25m / s.

[0096] The preparation method of the spring steel wire in Example 3 includes:

[0097] Step 1: Prepare the ingredients according to their chemical composition;

[0098] Step 2: Smelting and continuous casting are carried out sequentially to obtain a continuously cast billet;

[0099] Step 3: Heat the continuously cast billet to 1250℃ and hold it for 1 hour. The roughing rolling start temperature is 1151℃, the roughing rolling finish temperature is 1044℃, the finishing rolling start temperature is 958℃, and the finishing rolling finish temperature is 854℃. Cool the spring steel to 693℃ in the Steyrmo air-cooling line at a cooling rate of 12℃ / s, and then reduce the fan power to cool it to room temperature at a rate of 0.5℃ / s.

[0100] Step 4: Pickle the wire rod and draw it with a reduction rate of 5% to 10% per pass;

[0101] Step 5: Perform rapid austenitization and prepare 2200MPa grade high-strength and tough spring steel wire using quenching-partitioning treatment.

[0102] The specific heat treatment process and parameters for step 5 are as follows: the steel wire is induction heated to 820℃, then quenched in an oil bath at 40℃, and then heated to 363℃ in a lead bath for fractionation treatment. The take-up speed of the steel wire in the online treatment is set to 0.47m / s.

[0103] The preparation methods of Examples 4 and 5 are the same as those of Example 1. The specific process parameters are shown in Tables 2 and 3 below, and will not be repeated here.

[0104] Five samples were prepared for each embodiment.

[0105] Some process parameters for Examples 1-5 are shown in Tables 2 and 3 below.

[0106] The microstructure of the wire rods in Examples 1-5 is shown in Table 4 below.

[0107] The microstructure of the 2200MPa grade high-strength and high-toughness spring steel wires in Examples 1-5 is shown in Table 5 below.

[0108] The properties of the 2200MPa grade high-strength and high-toughness spring steel wires in Examples 1-5 are shown in Table 6 below.

[0109] Figure 1 The image shown is an SEM image of the wire rod from Example 1. Figure 2 The image shown is a TEM image of the wire rod from Example 1. It can be seen that nanoscale (Nb,V)(C,N) particles are present. Figure 3 The image shown is an SEM image of the 2200MPa grade high-strength and tough spring steel wire of Example 1.

[0110] Table 1 Chemical composition (wt.%)

[0111] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 C 0.65 0.57 0.62 0.56 0.63 0.65 0.65 Si 1.51 1.74 1.53 2.11 1.62 1.52 1.51 Mn 0.82 1.80 1.15 1.35 1.08 0.51 0.82 Cr 0.55 0.70 0.85 1.10 1.25 0.21 0.55 Mo 0.05 0.05 0.15 0.10 0.12 0.01 0.05 Nb 0.05 0.08 0.07 0.05 0.12 0.01 0.05 V 0.09 0.10 0.08 0.12 0.05 0.005 0.09 P 0.013 0.009 0.013 0.005 0.008 0.010 0.013 S 0.001 0.0007 0.001 0.0009 0.001 0.001 0.001 N 0.008 0.008 0.011 0.006 0.007 0.008 0.008 Mn+Cr 1.37 2.50 2.00 2.45 2.33 0.72 1.37 Nb+V 0.14 0.18 0.15 0.17 0.17 0.015 0.14

[0112] Table 2 Process Parameters

[0113]

[0114]

[0115] Table 3 Process Parameters

[0116]

[0117] Table 4 Microstructure of wire rod

[0118]

[0119] Table 5 Microstructure of spring steel wire

[0120]

[0121] Table 6 Mechanical Properties of Spring Steel Wire

[0122] Yield strength tensile strength elongation Reduction of area hardness Example 1 1987±22MPa 2245±17MPa 11.3±0.2％ 45.5±2.3％ 56.3±0.2HRC Example 2 1881±13MPa 2213±10MPa 12.5±0.7％ 51.3±3.1％ 55.7±0.1HRC Example 3 1972±35MPa 2226±21MPa 11.6±0.2％ 47.9±0.8％ 56.8±0.7HRC Example 4 1803±10MPa 2284±17MPa 15.5±0.7％ 41.1±0.2％ 54.7±0.5HRC Example 5 2007±11MPa 2206±6MPa 11.2±0.3％ 43.2±3.2％ 58.3±0.2HRC Comparative Example 1 1756±21MPa 2105±25MPa 10.5±0.2％ 48.6±2.3％ 55.1±0.4HRC Comparative Example 2 2012±26MPa 2119±42MPa 6.3±1.2％ 35.5±1.3％ 54.8±0.2HRC

[0123] The inventors conducted extensive experimental research during the research process, and some poorly performing solutions are now presented as comparative examples.

[0124] Comparative Example 1

[0125] This comparative example provides a spring steel wire and its preparation method. The components are shown in Table 1. The preparation method is the same as that in Example 1, and will not be repeated here.

[0126] The spring steel wire prepared by the method in this comparative example has a high elongation, but its yield strength and tensile strength are significantly insufficient. This is mainly due to the reduction of Mo, V and Nb elements, which weakens the precipitation strengthening effect. At the same time, the insufficient Mn+Cr content in the retained austenite leads to insufficient stability of the retained austenite, which then transforms into a large amount of fresh martensite during the stretching process. Although this provides a significant work hardening effect, the plasticity is reduced.

[0127] Comparative Example 2

[0128] This comparative example provides a spring steel wire and its preparation method. Its composition is the same as that of Example 1, and will not be repeated here. The method includes:

[0129] Step 1: Prepare the ingredients according to their chemical composition;

[0130] Step 2: Smelting and continuous casting are carried out sequentially to obtain a continuously cast billet;

[0131] Step 3: Heat the continuously cast billet to 1230℃ and hold for 2 hours. The roughing rolling start temperature is 1150℃, the roughing rolling finish temperature is 1005℃, the finishing rolling start temperature is 983℃, and the finishing rolling finish temperature is 873℃. Cool the billet to 651℃ in the Steyrmo air-cooling line at a cooling rate of 25℃ / s, and then reduce the fan power to cool it to room temperature at a rate of 1.0℃ / s. The specific heat treatment process and parameters are as follows: Induction heat the steel wire to 830℃, then quench it in an oil bath at 250℃, and then induction heat it to 351℃ for distribution treatment. The take-up speed of the steel wire in the online treatment is set to 0.2m / s.

[0132] This comparative example used a higher oil quenching temperature, resulting in a significant decrease in the elongation, reduction of area, and tensile strength of the spring steel wire. This is mainly due to the increased austenite content after oil quenching caused by the higher quenching temperature. The carbon elements distributing from martensite to austenite are insufficient to stabilize all the austenite at room temperature. Therefore, the final microstructure consists of tempered martensite, retained austenite, and fresh martensite. Fresh martensite is a hard and brittle phase, which easily induces stress concentration during tensile testing. The sample cannot undergo effective work hardening and fractures, leading to a decrease in both the strength and toughness of the steel.

[0133] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A 2200MPa grade high-strength and high-toughness spring steel wire, characterized in that, The chemical composition of the 2200MPa grade high-strength and tough spring steel wire, by mass percentage, includes: C 0.45%~0.70%, Si 1.00%~2.50%, Mn 0.40%~3.00%, Cr 0.10%~3.00%, Mo 0.02%~0.30%, Nb 0.02%~0.30%, V 0.02%~0.30%, N 0.008%~0.012%, P≤0.015%, S≤0.002%, with the remainder being Fe and unavoidable impurities; The chemical composition of the 2200MPa grade high-strength and high-toughness spring steel wire contains 1.3% <Mn+Cr<3.5%,0.05%<Nb+V<0.2%; The preparation method of the 2200MPa grade high-strength and high-toughness spring steel wire includes: Step 1: Prepare the materials according to the chemical composition of 2200MPa grade high-strength and tough spring steel wire; Step 2: Smelting and casting are carried out sequentially to obtain a continuously cast billet; Step 3: The continuously cast billet is sequentially heated and held at the temperature, then rough rolled, finish rolled, and wire rod produced to obtain wire rod; Step 4: Pickle the wire rod and draw it with a 5%~10% reduction in surface area per pass; Step 5: Perform rapid austenitization and prepare 2200MPa grade high-strength and tough spring steel wire using quenching-partitioning treatment; The specific quenching-partitioning process and parameters for step 5 are as follows: the steel wire is induction heated to 820~870℃, then quenched in an oil bath at 40~80℃, and then induction heated to 351~400℃ for partitioning. The wire take-up speed for online processing is set to 0.2~0.47m / s.

2. The 2200MPa grade high-strength and high-toughness spring steel wire according to claim 1, characterized in that, The chemical composition of the 2200MPa grade high-strength and tough spring steel wire, by mass percentage, includes: C 0.5%~0.70%, Si 1.40%~2.50%, Mn 0.80%~3.00%, Cr 0.30%~3.00%, Mo 0.02%~0.25%, Nb 0.02%~0.25%, V 0.02%~0.25%, N 0.008%~0.012%, P≤0.015%, S≤0.002%, with the remainder being Fe and unavoidable impurities.

3. The 2200MPa grade high-strength and high-toughness spring steel wire according to claim 1, characterized in that, The chemical composition of the 2200MPa grade high-strength and high-toughness spring steel wire contains 1.3% <Mn+Cr<3.0%,0.08%<Nb+V<0.2%。 4. The 2200MPa grade high-strength and high-toughness spring steel wire according to claim 1, characterized in that, The microstructure of the 2200MPa grade high-strength and tough spring steel wire includes tempered martensite, retained austenite, and dispersed carbonitrides.

5. The 2200MPa grade high-strength and high-toughness spring steel wire according to claim 1, characterized in that, In the microstructure of the 2200MPa grade high-strength and tough spring steel wire, the Mn+Cr content in the tempered martensite is lower than the Mn+Cr content in the retained austenite.

6. The 2200MPa grade high-strength and high-toughness spring steel wire according to claim 1, characterized in that, The microstructure of the 2200MPa grade high-strength and tough spring steel wire has a retained austenite volume fraction of 6% to 20%.

7. The 2200MPa grade high-strength and high-toughness spring steel wire according to any one of claims 1 to 6, characterized in that, The microstructure of the 2200MPa high-strength and high-toughness spring steel wire consists of nanoscale tempered martensite laths and lamellar retained austenite stacked together.

8. A method for preparing 2200MPa grade high-strength and high-toughness spring steel wire according to any one of claims 1 to 7, characterized in that, include: Step 1: Prepare the materials according to the chemical composition of 2200MPa grade high-strength and tough spring steel wire; Step 2: Smelting and casting are carried out sequentially to obtain a continuously cast billet; Step 3: The continuously cast billet is sequentially heated and held at the temperature, then rough rolled, finish rolled, and wire rod produced to obtain wire rod; Step 4: Pickle the wire rod and draw it with a 5%~10% reduction in surface area per pass; Step 5: Perform rapid austenitization and prepare 2200MPa grade high-strength and tough spring steel wire using quenching-partitioning treatment.

9. The preparation method according to claim 8, characterized in that, In step 3, the temperature is controlled to 1200~1250℃ and kept warm for 1~3 hours.

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