Wire rod that can omit softening heat treatment and its manufacturing method

Abstract

A wire rod that can omit a softening heat treatment and a method for manufacturing the same are provided. [Solution] The wire rod of the present invention, which can be freed from softening heat treatment, is characterized by comprising, by weight, C: 0.2-0.45%, Si: 0.02-0.4%, Mn: 0.3-1.5%, Cr: 0.01-1.5%, Al: 0.02-0.05%, Mo: 0.01-0.5%, N: 0.01% or less, with the remainder being Fe and other unavoidable impurities, the microstructure being a composite structure in which the main phase is pro-eutectoid ferrite and pearlite, containing 10% by area or less (including 0%) of one or more of bainite or martensite, and the average size of the pearlite colonies being 5 μm or less.

Description

[Technical Field]

[0001] The present invention relates to a wire rod that can be used without a softening heat treatment and a manufacturing method thereof, and more particularly to a wire rod for machine structures that can be used for automobiles, construction parts, etc., and a manufacturing method thereof. [Background technology]

[0002] Conventionally, softening materials for cold working required long-term heat treatment at high temperatures of 600 to 800°C for 10 to 20 hours or more, and many technologies have been developed to shorten or eliminate this treatment.

[0003] A representative technique is disclosed in Patent Document 1. This technique refines the ferrite grain size by controlling the grain size to 11 or more, and controls the hard plate-like cementite phase in the pearlite structure to have a segmented form, thereby making it possible to omit the subsequent softening heat treatment step. However, the production of such a material can only be achieved by a very slow cooling rate of 0.02 to 0.3°C / s during cooling after hot rolling. Such a slow cooling rate reduces productivity and, depending on the environmental atmosphere, may require additional slow cooling equipment and a slow cooling yard. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-336456 Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide a method for omitting the softening heat treatment required during cold working of automobile and construction parts. For mechanical structures such as automobiles and construction parts The present invention provides a wire rod and a method for manufacturing the same. [Means for solving the problem]

[0006] The wire rod of the present invention, which can be freed from the softening heat treatment, is characterized by comprising, by weight, 0.2 to 0.45% C, 0.02 to 0.4% Si, 0.3 to 1.5% Mn, 0.01 to 1.5% Cr, 0.02 to 0.05% Al, 0.01 to 0.5% Mo, 0.01% or less N, with the remainder being Fe and other unavoidable impurities, the microstructure being a composite structure of columnar pro-eutectoid ferrite and pearlite, containing 10% by area or less (including 0%) of one or more of bainite or martensite, and the average size of the pearlite colonies being 5 μm or less.

[0007] The method for producing a wire rod according to the present invention, which can omit the softening heat treatment, comprises the steps of heating a billet consisting of, by weight, 0.2 to 0.45% C, 0.02 to 0.4% Si, 0.3 to 1.5% Mn, 0.01 to 1.5% Cr, 0.02 to 0.05% Al, 0.01 to 0.5% Mo, 0.01% or less N, and the balance being Fe and other inevitable impurities, at 950 to 1050°C, deforming the heated billet at 730°C to 2030°C. amount and cooling the wire rod to a temperature of Ae1 or lower at a rate of 2°C / sec or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to omit the softening heat treatment required during cold working of automobile and construction parts. For mechanical structures such as automobiles and construction parts A wire rod and a method for manufacturing the same can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a photograph of the microstructure of Comparative Example 1 before finish hot rolling, observed with an optical microscope. [Figure 2] 1 is a photograph of the microstructure of Example 1 before finish hot rolling, observed with an optical microscope. [Figure 3] 1 is a photograph of the microstructure of Comparative Example 1 after rolling and cooling, observed with an SEM. [Figure 4]1 is a photograph of the microstructure of Example 1 after rolling and cooling, observed with an SEM. [Figure 5] 1 is a photograph of the microstructure of Comparative Example 1 after spheroidizing heat treatment, observed with an SEM. [Figure 6] 1 is a photograph of the microstructure of Invention Example 1 after spheroidizing heat treatment, observed with an SEM. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a wire rod having excellent spheroidizing heat treatability according to one embodiment of the present invention will be described. First, the alloy composition of the present invention will be described. The contents of the alloy composition described below are in weight percent unless otherwise specified.

[0011] C: 0.2 to 0.45% C is an element added to ensure a certain level of strength. If the C content exceeds 0.45%, the entire structure will be pearlite, making it difficult to achieve the ferrite structure desired by the present invention. Hardenability may be excessively increased, potentially resulting in the formation of a light low-temperature transformation structure. On the other hand, if the C content is less than 0.2%, the strength of the base metal will decrease, making it difficult to ensure sufficient strength after the quenching and tempering heat treatments performed after the softening heat treatment and forging processes. Therefore, the C content is preferably in the range of 0.2 to 0.45%. The lower limit of the C content is more preferably 0.22%, even more preferably 0.24%, and most preferably 0.26%. The upper limit of the C content is more preferably 0.43%, even more preferably 0.41%, and most preferably 0.39%.

[0012] Si: 0.02 to 0.4% Si is a typical substitutional element that is added to ensure a certain level of strength. If the Si content is less than 0.02%, it is difficult to ensure the strength and sufficient hardenability of the steel, and if it exceeds 0.4%, there is a drawback in that the cold forgeability during forging after softening heat treatment is deteriorated. Therefore, the Si content is preferably in the range of 0.02 to 0.4%. The lower limit of the Si content is more preferably 0.022%, even more preferably 0.024%, and most preferably 0.026%. The upper limit of the Si content is more preferably 0.038%, even more preferably 0.036%, and most preferably 0.034%.

[0013] Mn: 0.3 to 1.5% Mn forms a substitutional solid solution in the matrix, lowers the Al temperature, refines the spacing between pearlite layers, and increases the number of subgrains in the ferrite structure. If the Mn content exceeds 1.5%, manganese segregation can cause structural heterogeneity, resulting in detrimental effects. While macrosegregation and microsegregation are likely to occur due to the segregation mechanism during steel solidification, Mn promotes the formation of segregation zones due to its relatively low diffusion coefficient compared to other elements. This improved hardenability is the main cause of the formation of low-temperature structures such as martensite in the center. On the other hand, if the Mn content is less than 0.3%, it is difficult to ensure sufficient hardenability to ensure a martensite structure after the quenching and tempering heat treatments performed after the softening heat treatment and forging process. Therefore, the Mn content is preferably in the range of 0.3 to 1.5%. The lower limit of the Mn content is more preferably 0.4%, even more preferably 0.5%, and most preferably 0.6%. The upper limit of the Mn content is more preferably 1.4%, further preferably 1.3%, and most preferably 1.2%.

[0014] Cr: 0.01 to 1.5% Like Mn, Cr is primarily used as an element to improve the hardenability of steel. If the Cr content is less than 0.01%, it is difficult to ensure sufficient hardenability to obtain martensite during the quenching and tempering heat treatments performed after the softening heat treatment and forging process. If the Cr content exceeds 1.5%, the promotion of center segregation increases the likelihood of low-temperature structures occurring within the wire rod. Therefore, the Cr content is preferably in the range of 0.01 to 1.5%. The lower limit of the Cr content is more preferably 0.1%, even more preferably 0.3%, and most preferably 0.5%. The upper limit of the Cr content is more preferably 1.4%, even more preferably 1.3%, and most preferably 1.2%.

[0015] Al: 0.02 to 0.05% Al not only has a deoxidizing effect, but also precipitates Al-based carbonitrides, which helps inhibit the growth of austenite grains and maintain the pro-eutectoid ferrite fraction close to the equilibrium phase. If the Al content is less than 0.02%, the deoxidizing effect is insufficient. If the Al content exceeds 0.05%, the amount of hard inclusions such as Al2O3 may increase, which may cause nozzle clogging, particularly during continuous casting. Therefore, the Al content is preferably in the range of 0.02 to 0.05%. The lower limit of the Al content is more preferably 0.022%, even more preferably 0.024%, and most preferably 0.026%. The upper limit of the Al content is more preferably 0.048%, even more preferably 0.046%, and most preferably 0.044%.

[0016] Mo: 0.01 to 0.5% Mo not only precipitates Mo-based carbonitrides, inhibits austenite grain growth, and helps maintain the proeutectoid ferrite fraction close to the equilibrium phase, but also effectively suppresses strength loss (temper softening) due to the formation of MoC precipitates during tempering, which is one of the heat treatments performed after softening heat treatment and forging. If the Mo content is less than 0.01%, it is difficult to sufficiently suppress strength loss. If it exceeds 0.5%, low-temperature structures may occur in the wire rod, which may require additional heat treatment costs to remove the low-temperature structures. Therefore, the Mo content is preferably in the range of 0.01 to 0.5%. The lower limit of the Mo content is more preferably 0.012%, even more preferably 0.013%, and most preferably 0.014%. The upper limit of the Mo content is more preferably 0.49%, even more preferably 0.48%, and most preferably 0.47%.

[0017] N: 0.01% or less N is an impurity element, and if it exceeds 0.01%, the toughness and ductility of the material may be reduced due to the dissolved nitrogen that is not bound to the precipitates. Therefore, the N content is preferably in the range of 0.01% or less. stomach.

[0018] The remaining component of the present invention is iron (Fe). However, in a normal manufacturing process, unintended impurities may be inevitably mixed in from raw materials or the surrounding environment, and this cannot be excluded. Since these impurities are known to anyone skilled in normal manufacturing processes, the contents of all of them will not be specifically described in this specification.

[0019] The microstructure of the wire rod of the present invention is preferably a composite structure of pro-eutectoid ferrite and pearlite. From the perspective of spheroidization of steel, bainitic steels with fine cementite are advantageous. However, cementite spheroidized by bainite has been reported to be excessively fine and grow very slowly. A composite structure of ferrite, pearlite, and bainite is disadvantageous in terms of microstructural homogenization. Therefore, in the present invention, by controlling the microstructure of the wire rod to a composite structure of pro-eutectoid ferrite and pearlite, not only spheroidizing heat treatability can be improved but also the structure can be more homogenized. Here, the fraction of pro-eutectoid ferrite is preferably 80% or more of the equilibrium phase. If the fraction is less than 80%, a relatively light low-temperature structure is formed in large amounts, making it difficult to effectively ensure spheroidizing heat treatability. However, in the present invention, low-temperature structures that may be unavoidably formed during manufacturing, such as one or more of bainite and martensite, may be present in an amount of 10% by area or less. That is, the microstructure of the present invention has a composite structure in which the main phase is ferrite and pearlite, and may contain 10% by area or less (including 0%) of one or more of bainite or martensite. The fraction of one or more of bainite or martensite is more preferably 5% by area or less. Meanwhile, the equilibrium phase of pro-eutectoid ferrite refers to the maximum fraction of pro-eutectoid ferrite that can be present in a stable state on the Fe3C phase diagram. Those skilled in the art can easily derive the equilibrium phase of pro-eutectoid ferrite from the Fe3C phase diagram, taking into account the C content and the contents of other alloying elements.

[0020] In this case, the average size of the pearlite colonies is preferably 5 μm or less. By finely controlling the average size of the pearlite colonies as described above, the segmentation effect of cementite can be improved and the spheroidization rate of cementite during spheroidizing heat treatment can be increased.

[0021] The average grain size of the pro-eutectoid ferrite is preferably 7 μm or less. By finely controlling the average grain size of the ferrite, the size of the pearlite colonies can also be refined, thereby increasing the spheroidization rate of cementite during spheroidizing heat treatment.

[0022] In addition, the average size of the major axis of cementite in the pearlite colonies is preferably 5 μm or less. By controlling the average size of the major axis of cementite in the pearlite colonies to be small in this way, that is, by controlling the aspect ratio of cementite to be small, the spheroidization rate of cementite can be increased during spheroidizing heat treatment.

[0023] Meanwhile, in the present invention, the average size of the pearlite colonies, the average size of the pro-eutectoid ferrite grains, and the average size of the major axes of the cementite in the pearlite colonies may be in the reference center of the diameter of the wire rod, for example, in the region from 2 / 5 to 3 / 5 of the way down from the surface based on the diameter. Generally, the surface layer portion of the wire rod is subjected to a strong rolling force during rolling, so the average size of the pearlite colonies, the average size of the pro-eutectoid ferrite grains, and the average size of the major axes of the cementite in the pearlite colonies in the surface layer portion may be fine. Meanwhile, in the present invention, the average size of the pearlite colonies and the average size of the ferrite grains are refined not only in the surface layer portion of the wire rod but also in the center portion, thereby effectively increasing the spheroidization rate of cementite during spheroidizing heat treatment.

[0024] The wire rod provided by the present invention may have a tensile strength of 800 MPa or less. Generally, to manufacture a wire rod from a steel wire, the process involves a primary softening heat treatment, a primary wiredrawing process, a secondary softening heat treatment, and a secondary wiredrawing process. However, in the case of the wire rod of the present invention, the processes corresponding to the primary softening heat treatment and the primary wiredrawing process can be omitted due to the sufficient softening of the material. Meanwhile, examples of the softening heat treatment referred to in the present invention include low-temperature annealing heat treatment performed below the Ae1 phase transformation point, intermediate-temperature annealing heat treatment performed near Ae1, and spheroidizing annealing heat treatment performed above Ae1.

[0025] Furthermore, the wire rod of the present invention may have an average aspect ratio of cementite of 2.5 or less after a single spheroidizing annealing heat treatment. It is generally known that the more times the spheroidizing annealing heat treatment is performed, the more effective the spheroidizing of cementite becomes. However, in the present invention, cementite can be sufficiently spheroidized with only a single spheroidizing annealing heat treatment. As described above, the surface layer of the wire rod is subjected to a strong rolling force during rolling, which facilitates the spheroidization of cementite. However, in the present invention, cementite can also be sufficiently spheroidized in the center of the diameter of the wire rod, specifically, in the region from the 1 / 4 point to the 1 / 2 point from the surface based on the diameter, and the average aspect ratio of cementite at the center of the wire rod may be 2.5 or less. Furthermore, the wire rod of the present invention may have a tensile strength of 540 MPa or less after a single spheroidizing heat treatment, thereby facilitating cold heading or cold forging for manufacturing final products.

[0026] A method for producing a wire rod having excellent spheroidizing heat treatability according to one embodiment of the present invention will now be described.

[0027] First, a billet having the above-mentioned alloy composition is heated to 950 to 1050° C. If the billet heating temperature is less than 950° C., rollability decreases, whereas if the billet heating temperature exceeds 1050° C., rapid cooling is required for rolling, making cooling control difficult and potentially causing cracks and other problems, making it difficult to ensure good product quality.

[0028] The heating time is preferably 90 minutes or less. If the heating time exceeds 90 minutes, the depth of the surface decarburized layer may become so large that the decarburized layer may remain after the rolling is completed.

[0029] After this, the heated billet was deformed by 0.3 to 2.0 at 730°C to Ae3. amount (ε) to obtain wire rod. The wire rod rolling speed is very fast and falls within the dynamic recrystallization range. Research results to date have revealed that under dynamic recrystallization conditions, the size of austenite grains depends only on the deformation speed and deformation temperature. Due to the characteristics of wire rod rolling, once the wire diameter is determined, the deformation amount The deformation rate is determined, and the size of the austenite grains can be changed by adjusting the deformation temperature. In the present invention, the dynamic deformation-induced transformation phenomenon of dynamic recrystallization is utilized to refine the grains. In order to utilize this phenomenon to ensure the fine grain structure that the present invention aims to achieve, it is preferable to control the finish rolling temperature to 730°C to Ae3. If the finish rolling temperature exceeds Ae3, it is difficult to obtain the fine grain structure that the present invention aims to achieve, and it is difficult to obtain sufficient spheroidizing heat treatability. If the finish rolling temperature is less than 730°C, the load on the equipment increases, and there is a risk that the life of the equipment will be rapidly reduced. In addition, the above deformation amount If (ε) is less than 0.3, the rolling reduction is insufficient, making it difficult to sufficiently refine the microstructure at the center of the wire rod, which may result in a deterioration in the spheroidizing heat treatability of the resulting wire rod. If (ε) is more than 2.0, the rolling load may cause a decrease in productivity and a rapid shortening of the life of the equipment due to damage to the equipment bearings, etc.

[0030] On the other hand, the average size of the austenite grains in the billet before the above-mentioned finish hot rolling is preferably 5 to 20 μm. It is known that ferrite grows by nucleating from the austenite grain boundaries. If the austenite grains in the parent phase are fine, the ferrite nucleated from the grain boundaries can also start to form finely, so by controlling the average size of the austenite grains in the billet before the finish hot rolling as described above, it is possible to obtain the effect of refining the ferrite grains. If the average size of the austenite grains exceeds 20 μm, it is difficult to obtain the effect of refining the ferrite grains, and in order to obtain an average austenite grain size of less than 5 μm, high deformation such as under heavy compression is required. amount However, there is a drawback in that a separate facility for adding the

[0031] The wire is then cooled to a temperature of Ae1 or lower at a rate of 2°C / sec or less. If the cooling rate of the wire exceeds 2°C / sec, a low-temperature structure such as bainite may form in the fine segregation region of the wire. In the fine segregation region, segregation may be formed that is twice or more the average of the wire, which may result in the formation of a low-temperature structure even at a low cooling rate, which may adversely affect the homogenization of the steel structure. Therefore, the cooling rate of the wire is more preferably 0.5 to 2°C / sec from the viewpoint of refining the crystal grains of the fine structure.

[0032] In the present invention, after the cooling, the wire rod may be further subjected to a spheroidizing heat treatment, in which the wire rod is heated to Ae1 to Ae1 + 40°C, maintained for 10 to 15 hours, and then cooled to 660°C at a rate of 20°C / hr or less. If the heating temperature is less than Ae1, the spheroidizing heat treatment time may be prolonged. If the heating temperature exceeds Ae1 + 40°C, the number of spheroidized carbide seeds may decrease, resulting in an insufficient effect of the spheroidizing heat treatment. If the maintenance time is less than 10 hours, the spheroidizing heat treatment may not be sufficient, resulting in an increase in the aspect ratio of cementite. If the maintenance time exceeds 15 hours, the cost may increase. If the cooling rate exceeds 20°C / hr, the rapid cooling rate may result in the re-formation of pearlite. However, as described above, in the present invention, sufficient spheroidizing heat treatability can be ensured even if only the spheroidizing heat treatment is performed without the primary softening heat treatment and primary wiredrawing. [Example]

[0033] The present invention will be described in more detail below with reference to examples. However, it should be noted that the following examples are merely for the purpose of illustrating and explaining the present invention in more detail, and are not intended to limit the scope of the present invention, as the scope of the present invention is determined by the matters described in the claims and matters that can be reasonably inferred therefrom.

[0034] A billet having the alloy composition shown in Table 1 below was prepared, and then a wire having a diameter of 9 mm was manufactured using the conditions shown in Table 2 below. The microstructure, average size of pro-eutectoid ferrite grains, average size of pearlite colonies, average size of cementite major axes within pearlite colonies, and tensile strength of the manufactured wire were measured, and the results are shown in Table 3 below. In addition, the wire was subjected to a single spheroidizing heat treatment under the conditions shown in Table 4 below, and then the average aspect ratio of cementite and tensile strength were measured, and the results are shown in Table 4 below. In this case, the spheroidizing heat treatment was performed on a test piece of the manufactured wire without performing a primary softening treatment and a primary wiredrawing process.

[0035] The average austenite grain size (AGS) was measured via a crop performed before finish hot rolling.

[0036] Ae1 and Ae3 are values calculated using the commonly used program JmatPro.

[0037] The mean grain size (FGS) of proeutectoid ferrite was measured at three arbitrary points between 2 / 5 and 3 / 5 of the diameter of the sampled specimen after removing the uncooled portion after wire rolling, using the ASTM E112 method, and the result was expressed as the average value.

[0038] The average size of the pearlite colonies was determined by using the ASTM E112 method, randomly selecting 10 pearlite colonies at the same location as the FGS measurement, calculating the value of (long axis + shortening) / 2 for each colony, and then averaging the measured colony sizes.

[0039] The average aspect ratio of cementite after spheroidizing heat treatment was calculated by photographing three fields of view at 1 / 4 to 1 / 2 points in the diameter direction of the wire rod using an SEM at 2000x (magnification), automatically measuring the long axis / short axis of cementite within the fields of view using an image measurement program, and then calculating it through statistical processing.

[0040] [Table 1]

[0041] [Table 2] TIFF0007721438000002.tif113149

[0042] [Table 3]

[0043] [Table 4]

[0044] As shown in Tables 1 to 4 above, in the case of Examples 1 to 5, which satisfy the alloy compositions and manufacturing conditions proposed by the present invention, it can be seen that by ensuring not only the type and fraction of the microstructure of the present invention but also fine crystal grains, an average aspect ratio of cementite of 2.5 or less can be obtained by just one spheroidizing heat treatment.

[0045] However, in the case of Comparative Examples 1 to 4, which do not satisfy the alloy composition or manufacturing conditions proposed by the present invention, the type and fraction of the microstructure of the present invention are not satisfied, or fine crystal grains cannot be secured, and therefore the average aspect ratio of cementite after one spheroidizing heat treatment is at a high level. As a result, it can be confirmed that further spheroidizing heat treatment is required for application to final products.

[0046] Fig. 1 is a photograph of the microstructure of Comparative Example 1 before finish hot rolling, observed with an optical microscope, and Fig. 2 is a photograph of the microstructure of Invention Example 1 before finish hot rolling, observed with an optical microscope. As shown in Figs. 1 and 2, Invention Example 1 has a relatively finer AGS before finish hot rolling than Comparative Example 1.

[0047] Fig. 3 is a photograph of the microstructure of Comparative Example 1 after rolling and cooling, observed with an SEM, and Fig. 4 is a photograph of the microstructure of Invention Example 1 after rolling and cooling, observed with an SEM. As shown in Figs. 3 and 4, it can be seen that the microstructure of Invention Example 1 after rolling and cooling is refined compared to Comparative Example 1, and the cementite is segmented.

[0048] Fig. 5 is a SEM photograph of the microstructure after spheroidizing heat treatment in Comparative Example 1, and Fig. 6 is a SEM photograph of the microstructure after spheroidizing heat treatment in Invention Example 1. As shown in Figs. 5 and 6, it can be seen that the microstructure after spheroidizing heat treatment in Invention Example 1 is more spheroidized than in Comparative Example 1.

Claims

1. In weight percent, C: 0.2 to 0.45%, Si: 0.02 to 0.4%, Mn: 0.3 to 1.5%, Cr: 0.01 to 1.5%, Al: 0.02 to 0.05%, Mo: 0.01 to 0.5%, N: 0.01% or less, and the balance being Fe and other unavoidable impurities, The microstructure contains one or more of bainite or martensite in an area percentage of 10% or less (including 0%), and the remainder is a composite structure of pro-eutectoid ferrite and pearlite, The average size of the pearlite colonies is 5 μm or less, A wire rod capable of omitting a softening heat treatment, characterized in that the fraction of the pro-eutectoid ferrite is 80% or more of the equilibrium phase of the pro-eutectoid ferrite.

2. 2. The wire rod according to claim 1, wherein the wire rod has an average size of pro-eutectoid ferrite crystal grains of 7 μm or less.

3. 2. The wire rod according to claim 1, wherein the average size of the major axis of cementite in the pearlite colonies is 5 μm or less.

4. 2. The wire according to claim 1, wherein the wire has a tensile strength of 800 MPa or less.

5. The wire rod according to claim 1, which can omit the softening heat treatment, is characterized in that the wire rod has an average aspect ratio of cementite of 2.5 or less after a single spheroidizing heat treatment in which the wire rod is heated to Ae1 to Ae1+40°C, maintained at that temperature for 10 to 15 hours, and then cooled to 660°C at a rate of 20°C / hr or less.

6. The wire rod according to claim 1, which can omit the softening heat treatment, has a tensile strength of 540 MPa or less after a single spheroidizing heat treatment in which the wire rod is heated to Ae1 to Ae1+40°C, maintained at that temperature for 10 to 15 hours, and then cooled to 660°C at a rate of 20°C / hr or less.

7. 2. A method for manufacturing a wire rod that can omit the softening heat treatment according to claim 1, comprising: heating a billet consisting of, by weight percent, 0.2 to 0.45% C, 0.02 to 0.4% Si, 0.3 to 1.5% Mn, 0.01 to 1.5% Cr, 0.02 to 0.05% Al, 0.01 to 0.5% Mo, 0.01% or less N, and the balance being Fe and other inevitable impurities, at 950 to 1050°C; Finish hot rolling the heated billet at a temperature range of 730°C to Ae3 throughout the entire range from the start to the end of finish hot rolling with a wire drawing deformation (ε) of 0.3 to 2.0 to obtain a wire rod; The method for manufacturing a wire, which can omit a softening heat treatment, comprises a step of cooling the wire to a temperature of Ae1 or less at a rate of 2° C. / sec or less. Here, the wire drawing deformation amount (ε) of the wire is an amount calculated by ε = 2 In (d0 / d1), In is the natural logarithm, d0 is the diameter (mm) of the steel wire before processing, and d1 is the diameter (mm) of the steel wire after processing.

8. 8. The method for manufacturing a wire rod according to claim 7, wherein the heating time is 90 minutes or less.

9. 8. The method for producing a wire rod according to claim 7, wherein the average size of the austenite grains in the billet before the finish hot rolling is 5 to 20 μm.

10. 8. The method for manufacturing a wire that can omit the softening heat treatment according to claim 7, further comprising a spheroidizing annealing heat treatment in which the cooled wire is heated to Ae1 to Ae1+40°C, maintained for 10 to 15 hours, and then cooled to 660°C at a rate of 20°C / hr or less.

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