Steel wire for spring, and manufacturing method thereof

Abstract

According to the present invention, it is possible to provide a steel wire for a spring, the steel wire containing, in wt%, 0.57-0.69% of C, 1.5-2.0% of Si, 0.2-1.0% of Mn, 0.7-1.3% of Cr, 0.05-0.26% of Mo, 0.015% or less of P, and 0.020% or less of S, with the remainder comprising Fe and inevitable impurities, wherein the microstructure of the steel wire includes 9-30% of retained austenite in terms of area fraction and the grain size of the retained austenite is 2.9 µm or less.

Description

Steel wire for springs and method for manufacturing the same

[0001] The present invention relates to a steel wire for a spring and a method for manufacturing the same.

[0002] Suspension springs are designed to undergo repeated fatigue loads within the elastic range below their yield strength. However, localized plastic deformation can occur, leading to fatigue failure. Furthermore, suspension springs are constantly subjected to compressive stress due to the vehicle's unloaded weight, resulting in localized permanent deformation.

[0003] The cause of this local plastic deformation is the movement of dislocations due to repeated fatigue loads and static loads that occur at stresses below the yield strength.

[0004] The microstructure of currently commercially available springs utilizes tempered martensite, which boasts superior fatigue strength and permanent deformation resistance. Tempered martensite exhibits superior fatigue strength and permanent deformation resistance due to the carbides formed during tempering that restrict dislocation movement.

[0005] Recently, Remalli reported in Materials Science and Engineering A Vol.887 (2023) p.145751 that a martempering heat treatment was performed on commercial standard steel SAE9254, which was heated and then held at 250℃ for 60 seconds, which is between the martensitic transformation start temperature (Ms) and the martensitic transformation finish temperature (Mf), to form retained austenite, thereby limiting dislocation movement and improving permanent deformation resistance. On the other hand, this heat treatment was reported to have a tensile strength of 1112 MPa at room temperature, which is effective in improving permanent deformation resistance, but has a problem in that the fatigue strength of the spring is reduced due to the low tensile strength.

[0006] On the other hand, high-strength spring steel wires are highly susceptible to hydrogen embrittlement. To suppress this hydrogen embrittlement sensitivity, expensive elements such as vanadium (V), niobium (Nb), and molybdenum (Mo) are utilized to precipitate nano-sized carbides, trapping hydrogen and enhancing hydrogen embrittlement resistance. However, industrially, there is a need to omit expensive elements to reduce costs, and some research has reported utilizing austenite for this purpose. Austenite has an FCC (Fibre Crust) lattice structure, which slows the diffusion of hydrogen, and is known to have superior hydrogen embrittlement resistance compared to tempered martensite, pearlite, and ferrite, which have a BCC (Basic Crust) lattice structure. Therefore, it is necessary to develop alloying components and manufacturing processes that appropriately utilize the austenite phase in high-strength spring steel wires.

[0007] The purpose of the disclosed invention to solve the above-described problem is to provide a spring steel wire and a method for manufacturing the same, which have improved permanent deformation resistance, fatigue strength, and hydrogen embrittlement resistance by controlling the alloy composition and manufacturing process.

[0008] A steel wire for a spring according to one embodiment of the present invention comprises, in weight %, C: 0.58 to 0.68%, Si: 1.6 to 1.9%, Mn: 0.3 to 0.9%, Cr: 0.8 to 1.2%, Mo: 0.08 to 0.23%, P: 0.015% or less, and S: 0.020% or less, the remainder being Fe and unavoidable impurities, and a microstructure comprising 9 to 30% of retained austenite in area fraction, the grain size of the retained austenite being 2.9 μm or less.

[0009] In addition, the steel wire for a spring according to one embodiment of the present invention may have a permanent deformation of the steel wire such that the height difference before / after compression for 48 hours under a stress of 1300 MPa is 3.5% or less.

[0010] In addition, the steel wire for a spring according to one embodiment of the present invention may have a room temperature tensile strength of 1980 MPa or more.

[0011] In addition, the steel wire for a spring according to one embodiment of the present invention may have a critical hydrogen concentration of 0.02 ppm or more.

[0012] According to another embodiment of the present invention, a method for manufacturing a spring steel wire comprises the steps of: manufacturing a billet including, in wt%, C: 0.58 to 0.68%, Si: 1.6 to 1.9%, Mn: 0.3 to 0.9%, Cr: 0.8 to 1.2%, Mo: 0.08 to 0.23%, P: 0.015% or less, and S: 0.020% or less, with the remainder being Fe and unavoidable impurities; finish-rolling the billet at 920°C to 960°C to manufacture a wire rod; cooling the wire rod to 730°C at a cooling rate of 10°C / s or more; reheating the cooled wire rod at 900°C to 980°C and then quenching it; and tempering the quenched steel wire at 415°C to 485°C.

[0013] In addition, in the method for manufacturing a spring steel wire according to one embodiment of the present invention, the reheating step can be performed at 930°C to 970°C.

[0014] According to the present invention, a spring steel wire having improved permanent deformation resistance, fatigue strength, and hydrogen embrittlement resistance can be provided by controlling the alloy components and manufacturing method, and a manufacturing method thereof.

[0015] Preferred embodiments of the present invention are described below. However, the embodiments of the present invention may be modified in various ways, and the technical concept of the present invention is not limited to the embodiments described below. Furthermore, the embodiments of the present invention are provided to more fully explain the present invention to those of ordinary skill in the art.

[0016] The terminology used in this application is solely for the purpose of describing specific examples. Therefore, for example, singular expressions include plural expressions unless the context clearly dictates otherwise. Additionally, it should be noted that terms such as "comprise" or "have" used in this application are used to clearly indicate the presence of features, steps, functions, components, or combinations thereof described in the specification, and are not used to preliminarily exclude the presence of other features, steps, functions, components, or combinations thereof.

[0017] Meanwhile, unless otherwise defined, all terms used herein should be considered to have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Therefore, unless explicitly defined herein, specific terms should not be interpreted in an overly idealistic or formal sense.

[0018] In addition, the terms "about", "substantially", etc. in this specification are used in the sense of or close to the numerical value when manufacturing and material tolerances inherent to the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly using the disclosure in which exact or absolute numerical values ​​are mentioned to aid understanding of the present invention.

[0019] First, let's explain the steel wire for the spring.

[0020] A steel wire for a spring according to one embodiment of the present invention comprises, in weight %, C: 0.58 to 0.68%, Si: 1.6 to 1.9%, Mn: 0.3 to 0.9%, Cr: 0.8 to 1.2%, Mo: 0.08 to 0.23%, P: 0.015% or less, and S: 0.020% or less, the remainder being Fe and unavoidable impurities, and a microstructure comprising 9 to 30% of retained austenite in area fraction, the grain size of the retained austenite being 2.9 μm or less.

[0021] Hereinafter, the reasons for numerical limitations on the alloy component content in the embodiments of the present invention will be described. Hereinafter, unless otherwise specified, the unit is weight percent.

[0022] The C (carbon) content can be 0.58 to 0.68%.

[0023] C is an effective element for increasing strength through solid solution strengthening, precipitation strengthening, and martensitic strengthening. Considering this, C can be added in amounts of 0.58% or more. However, excessive C content can lead to reduced toughness and sudden brittle fracture. Considering this, the upper limit of the C content may be limited to 0.68%. Preferably, it may be 0.59 to 0.67%.

[0024] The content of Si (silicon) can be 1.6 to 1.9%.

[0025] Si can be utilized for deoxidation of steel, and it is an element that suppresses the growth of carbides during tempering, enabling an increase in the tempering temperature. As the tempering temperature increases, the precipitation strengthening effect increases by forming ultrafine carbides at the target strength, and the dislocation strengthening effect can be reduced by dislocation quenching. Therefore, the addition of Si can improve permanent deformation resistance by minimizing mobile dislocation quenching during repeated fatigue, and improve hydrogen embrittlement resistance through hydrogen trapping of ultrafine carbides. Considering this, Si can be added in an amount of 1.6% or more. However, if the content of Si is excessive, it can cause surface decarburization during the wire rod manufacturing process, which can lower the fatigue strength. Considering this, the content of Si can be limited to 1.9%. Preferably, it can be 1.65 to 1.85%.

[0026] The content of Mn (manganese) can be 0.3 to 0.9%.

[0027] Manganese is an element that improves hardenability. In addition, adding manganese can prevent surface absorption by low-melting-point sulfides by precipitating sulfur, an impurity in steel, as manganese sulfide (MnS). Considering this, manganese can be added in an amount of 0.3% or more. However, if the manganese content is excessive, the dislocation density may increase during quenching heat treatment, which may deteriorate permanent deformation resistance and hydrogen embrittlement resistance. Considering this, the manganese content may be limited to 0.9%. Preferably, it may be 0.35 to 0.85%.

[0028] The content of Cr (chromium) can be 0.8 to 1.2%.

[0029] Cr is an austenite stabilizing element, and is an effective element for forming retained austenite during heat treatment. In addition, Cr is an element that suppresses carbide growth during tempering, similar to Si. Considering this, the Cr content may be added in an amount of 0.8% or more. However, if the Cr content is excessive, the retained austenite grain size becomes coarse, thereby reducing the effects of improving permanent deformation resistance and hydrogen embrittlement resistance. Considering this, the upper limit of the Cr content may be limited to 1.2%. Preferably, it may be 0.85 to 1.15%.

[0030] The content of Mo (molybdenum) can be 0.08 to 0.23%.

[0031] Mo, like Cr, is an austenite stabilizing element and is an effective element for forming retained austenite during heat treatment. In addition, Mo is an element that forms fine retained austenite through local segregation during the casting process. Considering this, the Mo content may be added in an amount of 0.08% or more. However, if the Mo content is excessive, the retained austenite fraction increases, making it difficult to secure the target tensile strength, and the retained austenite grain size becomes coarse, reducing the effects of improving permanent deformation resistance and hydrogen embrittlement resistance. Considering this, the upper limit of the Mo content may be limited to 0.23%. Preferably, it may be 0.09 to 0.22%.

[0032] The content of P(phosphorus) may be less than 0.015%.

[0033] Phosphorus (P) is an element that can segregate at grain boundaries and reduce impact toughness. Considering this, the P content may be limited to 0.015% or less.

[0034] The content of S (sulfur) may be less than 0.02%.

[0035] S, like P, is an element that not only reduces toughness by segregating at grain boundaries, but also forms low-melting-point sulfides, hindering hot rolling. Considering this, the S content may be 0.02% or less.

[0036] The remaining component of the disclosed invention is iron (Fe). However, since unintended impurities from raw materials or the surrounding environment can inevitably be mixed in during the typical manufacturing process, this cannot be ruled out. Since these impurities are readily apparent to anyone skilled in the art of conventional manufacturing, their full details are not specifically discussed in this specification.

[0037] The spring steel wire according to the present invention contains 9% to 30% of a retained austenite structure. If the fraction of retained austenite is low, the movement of dislocations during use of the spring becomes easy, resulting in local plastic working due to the disappearance of dislocations, which may result in permanent deformation and reduced fatigue life. In addition, the hydrogen diffusion rate is delayed, making it difficult to secure hydrogen embrittlement resistance. If the fraction of retained austenite is high, a strength of 1,980 MPa or more cannot be achieved.

[0038] The spring steel wire according to the present invention has a retained austenite grain size of 2.9 ㎛ or less. Since retained austenite has lower local strength than tempered martensite structure, it is deformed first during spring use, which makes the movement of dislocations in the tempered martensite structure unnecessary and prevents the dislocations from annihilating, thereby improving permanent deformation resistance and fatigue strength. In addition, since retained austenite has an FCC lattice structure, the diffusion rate of hydrogen is slow, so it acts as a barrier to hydrogen diffusion, thereby improving hydrogen embrittlement resistance. On the other hand, when the retained austenite grain size exceeds 2.9 ㎛, plastic-induced transformation is easy, so the plastic-induced phase transformation is completed early, making it impossible to secure the targeted permanent deformation resistance and fatigue strength. In addition, there is a problem in that the austenite phase is dispersed, which prevents the purpose of delaying the diffusion of hydrogen.

[0039] In addition, the steel wire for a spring according to one embodiment of the present invention may have a permanent deformation of the steel wire such that the height difference before / after compression for 48 hours under a stress of 1300 MPa is 3.5% or less.

[0040] In addition, the steel wire for a spring according to one embodiment of the present invention may have a room temperature tensile strength of 1980 MPa or more.

[0041] In addition, the steel wire for a spring according to one embodiment of the present invention may have a critical hydrogen concentration of 0.02 ppm or more.

[0042]

[0043] Next, the method for manufacturing steel wire for springs is described.

[0044] According to another embodiment of the present invention, a method for manufacturing a spring steel wire comprises the steps of: manufacturing a billet including, in wt%, C: 0.58 to 0.68%, Si: 1.6 to 1.9%, Mn: 0.3 to 0.9%, Cr: 0.8 to 1.2%, Mo: 0.08 to 0.23%, P: 0.015% or less, and S: 0.020% or less, with the remainder being Fe and unavoidable impurities; finish-rolling the billet at 920°C to 960°C to manufacture a wire rod; cooling the wire rod to 730°C at a cooling rate of 10°C / s or more; reheating the cooled wire rod at 900°C to 980°C and then quenching it; and tempering the quenched steel wire at 415°C to 485°C.

[0045] The reason for limiting the numerical value of the component range of each alloy composition is as described above, and each manufacturing step is explained in more detail below.

[0046] After manufacturing a billet that satisfies the above alloy composition, it can undergo a series of finishing rolling, cooling, reheating, quenching, and tempering processes.

[0047] First, the billet can be finished rolled at 920 to 960°C to produce wire rods. At low finish rolling temperatures, surface ferrite decarburization may occur. However, at high finish rolling temperatures, the grain size becomes coarse, making it difficult to achieve the desired permanent deformation resistance.

[0048] The above cooling step may include a step of cooling to 730°C at a rate of 10°C / s or more. In the step of cooling at the above cooling rate, rapid cooling is performed to the pearlite transformation region, thereby avoiding the temperature region where the surface layer decarburizes due to the ferrite phase transformation.

[0049] The cooled wire rod can be reheated at 900 to 980°C and then quenched. If the reheating temperature is high, the grain size may become coarser. However, if the reheating temperature is low, the pearlite may not be sufficiently reversed, resulting in a poor tensile cross-sectional area reduction due to the residual pearlite. Preferably, the reheating can be performed at 930 to 970°C.

[0050] Quenched steel wire can be tempered at 415°C to 485°C, unlike the general quenching temperature. If the tempering temperature is high, the target tensile strength may not be satisfied. However, if the tempering temperature is low, the dislocation density is high, and when fatigue stress is applied, the fatigue strength is reduced due to the disappearance of mobile dislocations, and permanent deformation may occur.

[0051] Hereinafter, the present invention will be described in more detail through examples. However, the description of these examples is merely intended to illustrate the implementation of the present invention and is not intended to limit the present invention. This is because the scope of the present invention is determined by the matters set forth in the claims and matters reasonably inferred therefrom.

[0052] {Example}

[0053] For the various alloy composition ranges shown in Table 1 below, billets were manufactured in a vacuum induction melting furnace and finish-rolled at 935°C into wire rods with a diameter of 15.5 mm. Next, the billets were rapidly cooled to 730°C at an average cooling rate of 12°C / s and then slowly cooled to room temperature. Afterwards, they were drawn to a diameter of 14.3 mm and reheated at 950°C using an induction heating heat treatment method, followed by quenching. The quenched wire rods were tempered at 445°C to manufacture steel wires.

[0054] The residual austenite fraction of the material was measured using an X-ray diffractometer (model number Rigaku D / Max2500) to measure the fractions of BCC and FCC, and FCC was defined as the residual austenite fraction. The specimens were cut along the C-section and then polished with 5% perchloric acid in 95% acetic acid using a Lectropol-5 electropolishing machine from Struers for analysis. This was to prevent the residual austenite from undergoing phase transformation during mechanical polishing.

[0055] The grain size of the austenite structure was measured by photographing five random areas at a magnification of x1,500 using an EBSD device attached to a Fe-SEM of the specimen prepared by the above method, and then using TSL-OIM software to measure the grain size of the austenite. Typically, tempered martensite structures have a high dislocation density, resulting in a low CI (Confidence Index) after EBSD observation. Therefore, error data was removed from the program and measured. At this time, CIs below 0.1 were removed.

[0056] Tensile strength was measured by processing heat-treated steel wire into ASTM E8M subsize specimens and then performing a tensile test using a Zwick Z 250 model.

[0057] Hydrogen embrittlement test was conducted using the experimental method of ISO 16573. At this time, a smooth specimen within the standard was used for the constant loading test, and the hydrogen concentration that did not fracture for more than 100 hours at 0.9 times the tensile strength was defined as the critical hydrogen concentration.

[0058] The permanent deformation test was performed on the spring of the Hyundai Avante N model, which is being produced in 2023, and the change in length after 48 hours of compression under a stress of 1300 MPa after molding was measured, and the permanent deformation was defined as the ratio (%) of the height after compression to the initial spring height.

[0059] CSiMnCrMoPS Residual γ (%)GS (㎛)TS (MPa)Hc (ppm)Permanent strain (%)Example 10.581.690.570.970.140.0070.005101.119800.133.4Example 20.681.760.540.940.120.0080.004272.819970.142.7Example 30.621.610.550.970.110.010.004160.820410.093.1Example 40.611.890.570.930.130.0090.004130.920990.072.9Example 50 .631.670.31.010.130.0110.004100.720050.123.3Example60.671.680.881.120.140.0110.004272.219820.132.9Example70.621.770.710.810.130.0090 .004111.220220.093.2Example 80.631.780.681.20.120.010.004191.420550.043Example 90.641.810.811.110.080.0070.00490.920010.083.5Example 100.631 .70.431.10.230.0070.004302.920070.193.4Example 110.651.670.441.010.140.0150.004131.320440.023Example 120.641.760.571.020.150.0090.0215 1.520570.032.9Comparative Example 10.571.670.640.820.090.0080.00461.119800.133.6Comparative Example 20.691.750.540.940.180.0080.004332.819790.033.7Comparative Example 30.621.58 0.570.960.130.0070.00491.219770.153.6Comparative Example 40.641.930.620.980.140.0080.00431320010.143.6Comparative Example 50.591.630.290.870.130.0090.00472.12 0220.013.7Comparative Example 60.671.750.911.140.130.0080.004313.119760.133.6Comparative Example 70.61.620.610.780.120.010.00471.820010.113.6Comparative Example 80.621.770.621.230.210.0110.004323.119730.193.7Comparative Example90.661.750.71.010.070.0090.00461.720050.073.7Comparative Example100.641.70.751.050.240.010.00431319970.143.6Comparative Example110.671.690.720.890.140.0160.019142.120100.01-Comparative Example120.641.810.70.910.130.0150.02113220430.01-.

[0060] Examples 1 to 12 had a retained austenite fraction (retained γ) of 9 to 30%, a retained austenite grain size (GS) controlled to 2.9 ㎛, a tensile strength (TS) of 1980 MPa or more, a critical hydrogen concentration of 0.02 ppm or more, and a permanent strain of 3.5% or less.

[0061] On the other hand, Comparative Example 1 had a low carbon concentration and a low retained austenite fraction, resulting in poor permanent deformation resistance. Comparative Example 2 had a high carbon concentration and a high retained austenite fraction, resulting in low tensile strength and poor permanent deformation resistance. Comparative Example 3 had a low silicon concentration and a low tensile strength and poor permanent deformation resistance. Comparative Example 4 had a high silicon concentration and a high retained austenite fraction, resulting in poor permanent deformation resistance. Comparative Example 5 had a low manganese concentration and a low retained austenite fraction, resulting in poor hydrogen embrittlement resistance and permanent deformation resistance. Comparative Example 6 had a high manganese concentration and a high retained austenite fraction and a coarse grain size, resulting in low tensile strength and poor permanent deformation resistance. Comparative Example 7 had a low chromium concentration, which resulted in a low residual austenite fraction and poor permanent deformation resistance. Comparative Example 8 had a high chromium concentration, which resulted in a high residual austenite fraction and coarse grain size, resulting in low tensile strength and poor permanent deformation resistance. Comparative Example 9 had a low molybdenum concentration, which resulted in a low residual austenite fraction and poor permanent deformation resistance. Comparative Example 10 had a high molybdenum concentration, which resulted in a high residual austenite fraction and coarse grain size, resulting in low tensile strength and poor permanent deformation resistance. Comparative Example 11 had a high phosphorus concentration, which resulted in poor hydrogen embrittlement resistance. Comparative Example 12 had a high sulfur concentration, which resulted in poor hydrogen embrittlement resistance.

[0062] For the alloy compositions of Examples 1 and 2 shown in Table 2 below, billets were manufactured in a vacuum induction melting furnace, and finish rolling was performed over various ranges into wire rods with a diameter of 15.5 mm. Next, the billets were rapidly cooled to 730°C at various cooling rates and then slowly cooled to room temperature. Afterwards, they were drawn to a diameter of 14.3 mm, reheated at various austenitizing temperatures using an induction heating heat treatment method, and then quenched. The quenched wire rods were tempered at various temperatures to manufacture steel wires.

[0063] Rolling temperature (℃) Cooling rate (℃ / s) up to 730℃ Reheating austenizing temperature (℃) Tempering temperature (℃) Residual γ (%) TS (MPa) Permanent strain (%) Remarks Example 1935129504451019803.4 Comparative example 13917129504451019783.7 Surface decarburization Comparative example 14962129504451019763.6 Surface decarburization Comparative example 1593589504451019773.8 Surface decarburization Comparative example 1693512899445819743.6 Comparative example 1793512981445820013.7 Example 2935129504452719972.7 Comparative Example 18935129504143119793.7 Comparative Example 19935129504862418893.8

[0064] Example 1 secured the target appropriate residual austenite fraction, and thus had high tensile strength and excellent permanent deformation resistance. Experiments of Comparative Examples 13 to 17 were performed using materials having the alloy composition of Example 1. In Comparative Example 13, the rolling temperature was low, so decarburization occurred on the surface of the wire rod, resulting in low tensile strength and poor permanent deformation resistance. In Comparative Example 14, the rolling temperature was high, so decarburization occurred on the surface of the wire rod, resulting in low tensile strength and poor permanent deformation resistance. In Comparative Example 15, the cooling rate up to 730°C was slow, so surface decarburization occurred, resulting in low tensile strength and poor permanent deformation resistance.

[0065] Comparative Example 16 had a low reheating austenitizing temperature, so the retained austenite fraction was low and the tensile strength was low, resulting in inferior permanent deformation. Comparative Example 17 had an excessively high reheating austenitizing temperature, so the retained austenite fraction was low and the tensile strength was low, resulting in inferior permanent deformation. Experiments of Comparative Examples 18 and 19 were performed using materials having the alloy composition of Example 1. Comparative Example 8 had an excessively high retained austenite fraction and low tensile strength due to a low tempering temperature, resulting in inferior permanent deformation. This is because the retained austenite formed during quenching was not properly decomposed during tempering. Comparative Example 9 had a low tensile strength due to a high tempering temperature, resulting in inferior permanent deformation.

[0066] Although exemplary embodiments of the present invention have been described above, the present invention is not limited thereto, and those skilled in the art will understand that various changes and modifications are possible within the scope and spirit of the claims set forth below.

Claims

1. Contains, in wt%, C: 0.58 to 0.68%, Si: 1.6 to 1.9%, Mn: 0.3 to 0.9%, Cr: 0.8 to 1.2%, Mo: 0.08 to 0.23%, P: 0.015% or less, and S: 0.020% or less, the remainder being Fe and unavoidable impurities. In terms of area fraction, the microstructure contains 9 to 30% retained austenite. A spring steel wire having a crystal grain size of the above-mentioned retained austenite of 2.9㎛ or less.

2. In claim 1, The permanent deformation of the above steel wire is a steel wire for springs, the height difference before and after compression for 48 hours under a stress of 1300 MPa is 3.5% or less.

3. In claim 1, A steel wire for springs, the room temperature tensile strength of which is 1980 MPa or more.

4. In claim 1, A spring steel wire having a critical hydrogen concentration of 0.02 ppm or more.

5. A step for manufacturing a billet including, in wt%, C: 0.58 to 0.68%, Si: 1.6 to 1.9%, Mn: 0.3 to 0.9%, Cr: 0.8 to 1.2%, Mo: 0.08 to 0.23%, P: 0.015% or less, and S: 0.020% or less, the remainder being Fe and unavoidable impurities; A step of manufacturing a wire rod by finish rolling the above billet at 920°C to 960°C; A step of cooling the above-mentioned preform to 730℃ at a cooling rate of 10℃ / s or more; A step of reheating the cooled wire at 900°C to 980°C and then quenching it; and A step of tempering the above-mentioned quenched steel wire at 415°C to 485°C. A method for manufacturing a steel wire for a spring, comprising:

6. In claim 5, A method for manufacturing a spring steel wire, wherein the above reheating step is performed at 930°C to 970°C.