WO2007074986A1

WO2007074986A1 - Steel wire having excellent cold heading quality and quenching property, and method for producing the same

Info

Publication number: WO2007074986A1
Application number: PCT/KR2006/005520
Authority: WO
Inventors: Sang-Woo Choi; Duk-Lak Lee; Sang-Yoon Lee; Hyo-An Jung; Mo-Chang Kang
Original assignee: Posco Co Ltd
Current assignee: Posco Holdings Inc
Priority date: 2005-12-27
Filing date: 2006-12-18
Publication date: 2007-07-05
Anticipated expiration: 2008-06-27
Also published as: CN101365819A; CN101365819B; JP2009527638A; KR20070068511A; KR100742820B1; JP4966316B2

Abstract

A steel wire having excellent cold heading quality and quenching properties, and a method fo producing the same are provided. The steel wire has a noticeably low strength even without spheroidizing annealing to allow easy cold working of the steel wire, and assures a noticeable increase in strength through quenching in the future. The steel wire comprises, by weight%, C: 0.1~0.4%, Si: 0.3~1.5%, Mn: 0.3~1.7%, P: 0.015% or less, S: 0.015% or less, Cr: 0.05~1.7%, Al: 0.05% or less, B: 0.001~0.005%, Ti: 0.01~0.05%, N: 0.015% or less, and the balance of Fe and other unavoidable impurities.

Description

STEEL WIRE HAVING EXCELLENT COLD HEADING QUALITY AND QUENCHING PROPERTY, AND METHOD FOR

PRODUCING THE SAME

Technical Field

[1] The present invention relates to a method for producing a steel wire useful for materials for cold working. More particularly, the present invention relates to a steel wire having excellent cold workability and quenching properties, which has a noticeably low strength even without spheroidizing annealing in a state of the steel wire to allow easy cold working of the steel wire, and assures a noticeable increase in strength through quenching in the future, and a method for producing the same.

[2]

Background Art

[3] In general, cold working has been widely applied as an effective method for producing vehicle components and machinery components such as bolts, nuts, screws, etc. due to its higher productivity compared with hot working or cutting.

[4] Since cold working involves forging operations directly performed on steel without a specific heating or cutting process, it is necessary for the steel subjected to cold working to have suitable mechanical properties. In other words, it is necessary for the steel to have sufficiently low tensile strength so as to ensure sufficient formability with a low external force, and to have excellent ductility so as not to be fractured upon cold deep drawing.

[5] However, since the components produced by cold working include the vehicle components or machinery components such as bolts, nuts, screws, etc. as described above, it is necessary for the components to have high strength.

[6] In summary, superior steel for cold working should have low strength and high ductility before cold working, but have high strength during a manufacturing process into final products. Since such properties are incompatible, it is necessary to perform a suitable treatment at every working stage to impart both required properties to the steel at the same time. Typically, final components produced through cold working undergo quenching to have increased strength. In order to allow the components to satisfy a desired strength requirement through quenching, the steel contains suitable levels of elements capable of increasing quenching properties.

[7] Conventionally, the steel contains a high amount of carbon in order to improve the quenching properties. Carbon is one of representative elements which can improve the quenching properties, and serves to noticeably improve the strength of the components through quenching.

[8] However, when the steel contains such a high amount of carbon, the steel has too high a degree in hardness and strength even without quenching to be directly applied to cold forging, and thus requires specific treatments therefor. In other words, when carbon is dissolvedin the steel, it causes solid solution strengthening so that the steel is increased in strength. As a result, when the steel undergoes cold working to form a tool, not only does the tool have a shortened service life, but also suffers cracks due to insufficient ductility.

[9] Accordingly, when the steel containing the high amounts of carbon is applied to cold work, it is necessary to perform first a process of suppressing the solid solution strengthening caused by dissolved carbon in the matrix of the steel through precipitation of carbon in the form of spheroidal cementite in order to prevent reduction in workability upon machining of the steel due to carbon. The process of precipitating the spheroidal cementite is referred to as "spheroidizing annealing".

[10] Thus, to produce high strength components by machining a steel wire having a high content of carbon, the steel wire is sequentially subjected to spheroidizing annealing, cold working and quenching, and is often subjected to annealing treatment as a final process to improve toughness of the components.

[11] However, since spheroidizing annealing requires heat treatment ranging from several hours to several dozens of hours, it causes not only a reduction in productivity but also an increase in manufacturing costs. Thus, it is desirable to omit spheroidizing annealing, if possible.

[12] In order to solve the above problem, Japanese Patent Laid-open No. 2001 -0303189 discloses a steel wire, which comprises by weight%: at least one of B: 0.0055% or less and Zr: 0.035% or less; and N: 0.0005 ~ 0.0070%, wherein B, Zr and N satisfy relationship: -0.001 < [N] - 1.3[B] - 0.15[Zr] < 0.0020 to suppress refinement of ferrite crystal grains, thereby suppressing an increase in strain resistance at room temperature or in a work heating range.

[13] This patent of the disclosure is characterized in that dissolved carbon and nitrogen are pinned and the refinement of the ferrite crystal grains is suppressed through addition of B or Zr, thereby avoiding the increase in strain resistance during cold working. However, this invention does not consider the tensile strength of the steel prior to cold working, which is the most important factor in cold working of the steel wire produced without spheroidizing annealing. Although it is well known in the art that the lower the tensile strength of the steel prior to the cold working, the more advantageous in terms of machining due to low strain energy, there is a limitation in reduction of the strength of the steel only through suppression on the refinement of the ferrite crystal grains. As a result, when the steel wire is subjected to cold working without spheroidizing annealing, there are problems of lifetime reduction of a tool made from the steel wire or of creation of cracks in the steel wire. [14]

Disclosure of Invention Technical Problem

[15] The present invention has been made to solve the foregoing problems of the prior art, and it is an object of the present invention to provide a steel wire having excellent cold workability and quenching properties, which has a sufficiently low strength even without spheroidizing annealing to provide an advantage in view of cold workability, and assures a noticeable increase in strength through quenching in the future, and a method for producing the same.

[16]

Technical Solution

[17] In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of a steel wire, comprising, by weight%: C: 0.1-0.4%; Si: 0.3-1.5%; Mn: 0.3-1.7%; P: 0.015% or less; S: 0.015% or less; Cr: 0.05-1.7%; Al: 0.05% or less; B: 0.001-0.005%; Ti: 0.01-0.05%; N: 0.015% or less; and the balance of Fe and other unavoidable impurities.

[18] Preferably, a ratio (Ti/N) of Ti to N is 1.39 or more in terms of atomic weight, and a ratio (B/Cr) of B to Cr is 0.04 or less in terms of weight.

[19] Preferably, the steel wire comprises ferrite and pearlite structures.

[20] Preferably, the steel wire comprises the ferrite structure in a fraction of 50% or more.

[21] Preferably, the steel wire comprises bainite and martensite structures in a total fraction of 0.5% or less.

[22] Preferably, the steel wire comprises a tensile strength of 590 MPa or less to assure cold workability, the tensile strength being expressed by Equation:

[23] TS(MPa) = 258 + 959*[C] + 112*[Si] + lll*[Mn] + 5*[Cr] + 439*[Ti] -

0.7* [ferrite fraction]

[24] In accordance with another aspect of the present invention, a method for producing a steel wire is provided, comprising: heating a steel billet to 1,000 - 1,100 °C, the billet comprising, by weight%, C: 0.1-0.4%, Si: 0.3-1.5%, Mn: 0.3-1.7%, P: 0.015% or less, S: 0.015% or less, Cr: 0.05-1.7%, Al: 0.05% or less, B: 0.001-0.005%, Ti: 0.01-0.05%, N: 0.015% or less, and the balance of Fe and other unavoidable impurities and rolling the steel billet to produce a steel wire, followed by cooling the steel wire to 500 °C or less at a rate of 0.1 - 5 °C/sec.

[25] Preferably, the rolling of the steel billet comprises finish rolling performed at a finish rolling temperature of 850 °C or less. [26] Preferably, a ratio (Ti/N) of Ti to N is 1.39 or more in terms of atomic weight, and a ratio (B/Cr) of B to Cr is 0.04 or less in terms of weight. [27] Preferably, the steel wire has a tensile strength of 590 MPa or less to assure cold workability, the tensile strength being expressed by Equation: [28] TS(MPa) = 258 + 959*[C] + 112*[Si] + lll*[Mn] + 5*[Cr] + 439*[Ti] -

0.7*[ferrite fraction] [29]

Advantageous Effects [30] As apparent from the above description, the present invention provides metal components having excellent cold workability even without heat treatment for cold working, and a method for producing the same. [31] The components produced by the method of the present invention can be applied to various fields such as machinery components, vehicle components, materials for building construction, etc. which require high strength. [32]

Brief Description of the Drawings [33] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[34] Fig. 1 is a graph depicting cold dice lifetimes related to inventive steels and conventional steels for comparison; and [35] Fig. 2 is a graph depicting quenching properties of the inventive steels and the comparative steels for comparison. [36]

Best Mode for Carrying Out the Invention [37] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. [38] The present inventors conducted extensive investigation to find desirable mechanical properties of a steel wire, and concluded that the desirable mechanical properties could be obtained by a tensile strength of 590 MPa or less and an increasing degree of 100 MPa or more in strength through quenching. From these results, the inventors tried to develop the steel wire under these requirements, and a method for producing the same. [39]

[40] Composition of steel wire

[41] It is necessary for the steel wire according to the present invention to have a composition described below for the purpose of improving both cold workability and quenching properties. In the following description, it should be noted that the content of each component is denoted by weight% unless there is other reference. The inventors found that it was important for the steel wire to have the composition which can remarkably improve the quenching property so as to allow the steel wire to have a low strength in a state of the steel wire for the purpose of improving the cold forging properties without spheroidizing annealing, and to have a high tensile strength after quenching and tempering.

[42] For this purpose, the inventors conducted preliminary experiments in such a way of heating steel wire samples at a temperature of 880 °C, followed by oil cooling, to confirm improvement in quenching properties depending on composition systems which comprise several major elements as shown in a graph of Fig. 1. From results of the preliminary experiments, they found that the steel wire of a composition system containing C-Si-Mn-Cr-B as major elements provided the most excellent quenching properties. In the graph, the quenching properties are shown by an increasing rate of hardness of a quenched and tempered part to hardness of a steel wire used for the part before quenching.

[43]

[44] C: 0.1 ~ 0.4 wt%

[45] Since an excessive addition of carbon causes deterioration in cold workability, carbon must be added to steel in a suitable range. If carbon content exceeds 0.4 wt%, a fraction of pearlite in the steel becomes 50% or more, causing deterioration in cold heading quality. On the other hand, if the carbon content is significantly low, less than 0.1 wt%, the quenching properties are degraded, causing deterioration in tensile strength or fatigue strength of a final product. Thus, the carbon content is preferably in the range of 0.1 ~ 0.4 wt%.

[46]

[47] Si: 0.3 ~ 1.5 wt%

[48] Typically, silicon is an element necessary for deoxidization of steel during a steel manufacturing process, and for ensuring the strength of a final product. However, if silicon content exceeds 1.5 wt%, it is undesirable in that the strain resistance is significantly increased during cold work, causing rapid reduction of the cold heading quality. On the other hand, if the silicon content is less than 0.3 wt%, it is difficult not only to obtain desired strength after quenching and tempering, but also to have ferrite in a fraction of 50% or more after rolling. Thus, the silicon content is preferably in the range of 0.3 - 1.5 wt%.

[49]

[50] Mn: 0.3 ~ 1.7 wt% [51] Manganese is an element serving to improve the quenching properties while increasing the strength without deteriorating impact toughness. If Mn content is less than 0.3 wt%, it is difficult to obtain these effects. On the other hand, if the Mn content exceeds 1.7 wt%, the steel wire is excessively increased in tensile strength after hot rolling, thereby deteriorating the cold heading quality. Thus, the Mn content is preferably in the range of 0.3 - 1.7 wt%.

[52]

[53] P: 0.015 wt% or less

[54] Phosphorus is likely to be segregated in grain boundaries, and deteriorates the toughness and the hydrogen embrittlement resistance of the steel. Thus, phosphorus content is preferably 0.015 wt% or less.

[55]

[56] S: 0.015 wt% or less

[57] Sulfur is also segregated in grain boundaries, and deteriorates the toughness and the hydrogen induced crack(HIC) resistance of the steel. Thus, sulfur content is preferably 0.015 wt% or less.

[58]

[59] Cr: 0.05 ~ 1.7 wt%

[60] Chromium is an element serving to generate stable martensite structure after quenching by improving the quenching properties of the steel while increasing the strength of the steel by suppressing rapid softening of martensite. If Cr content is too low, it is difficult to obtain these effects. On the other hand, if the Cr content is excessively high, the effects can be saturated. Thus, the Cr content is preferably in the range of 0.05 - 1.7 wt%.

[61]

[62] Al: 0.05 wt% or less

[63] Since aluminum is an element useful for deoxidization, it is preferably added in an amount of 0.05 wt% or less.

[64]

[65] B: 0.001 ~ 0.005 wt%

[66] Boron serves to significantly increase the quenching properties with a small added amount, and thus allows the steel to have the quenching properties even with reduction in the added amount of carbon. If boron is added in an amount of 0.005 wt% or more or in an amount of 0.001 wt% or less, the quenching properties are rapidly deteriorated. Thus, boron content is preferably in the range of 0.001 ~ 0.005 wt%.

[67]

[68] Ti: 0.01 ~ 0.05 wt%

[69] Titanium is an essential element to assure the quenching properties through addition of boron by pinning nitrogen in the steel. Ti is capable of suppressing fatigue fracture of the steel by suppressing growth of austenite grains while the steel is heated before quenching. In order to assure these effects, it is desirable to add Ti in an amount of 0.01 wt% or more. If titanium content exceeds 0.05 wt%, the steel wire suffers from problems such as increase in strength and deterioration in cold heading quality due to Ti-based precipitation and solid solution. Thus, the titanium content is preferably in the range of 0.01 ~ 0.05 wt%.

[70]

[71] N: 0.015 wt% or less

[72] Nitrogen is likely to combine with boron and form BN. Thus, it is desirable that nitrogen content is as low as possible. If the nitrogen content exceeds 0.015 wt%, it is difficult to obtain sufficient quenching effect.

[73]

[74] Ti/N: 1.39 or more (in terms of the number of atoms)

[75] As described above, since nitrogen is an element which combines with boron and deteriorates the quenching properties of the steel wire by reducing an effective amount of boron (B ), it is desirable that nitrogen content is as low as possible in the steel wire. However, since it is difficult to remove nitrogen during the steel manufacturing process, approach of reducing the activity of nitrogen is effectively applied by other methods. Specifically, one of elements having an affinity to nitrogen is titanium, and thus, if the steel wire contains titanium along with nitrogen, it is possible to reduce the activity of nitrogen through formation of TiN or the like. Since reduction in activity of nitrogen weakens a driving force of BN formation, the reduction in activity of nitrogen leads to an increase in amount of effective boron, improving the quenching properties of the steel wire. For the purpose of increasing the amount of effective boron through reduction of the activity of nitrogen as described above, it is necessary to have Ti/N of 1.39 or more. If Ti/N is less than 1.39, it fails to achieve a sufficient effect of pinning nitrogen through addition of Ti so that the quenching properties cannot be sufficiently improved.

[76]

[77] B/Cr: 0.04 or less (in terms of weight)

[78] The inventors conducted various investigations on factors for improving the quenching properties of the steel wire and found that, when the steel contains boron along with chromium rather than containing boron alone, it is very effective in improvement of the quenching properties. The relationship between chromium and boron is preferably 0.04 or less in a ratio of B/Cr.

[79]

[80] Microstructure [81] According to the present invention, the steel wire preferably has ferrite in a fraction of 50% or more in terms of area. If the steel wire has other microstructures in a fraction of 50% or more, the steel wire is increased in strength, causing deterioration of formability. In particular, it is preferable that a total fraction of martensite and bainite is 0.5% or less. If hard microstructures such as martensite and bainite are formed in the steel wire, these microstructures cause significant deterioration in formability of the steel wire. Accordingly, the present invention provides the steel wire which is preferably composed of ferrite and pearlite as major microstructures wherein ferrite has a fraction of 50% or more, martensite and bainite has a total fraction of 0.5% or less, and pearlite has the remaining balance fraction in terms of area.

[82]

[83] Method for producing a steel wire

[84] As described above, to obtain the microstructures of the invention wherein ferrite has the fraction of 50% or more, martensite and bainite have the total fraction of 0.5% or less, and pearlite has the remaining balance fraction, the steel wire should be produced under conditions as follows. A steel billet is typically heated at temperatures in the range of 1,000 ~ 1,100 °C as a typical heating condition for a steel wire, and is then hot-rolled to produce a steel wire at a finish rolling-delivery side temperature of 850 °C or less for refinement of austenite crystal grains in the steel under hot rolling. The hot-rolled steel wire is cooled to 500 °C at a cooling rate of 0.1 ~ 5 °C/sec in order to promote nucleation of ferrite from refined crystal grains and to increase a ferrite fraction while cooling the steel wire.

[85]

[86] Reheating temperature of steel billet: 1 ,000 ~ 1 , 100 °C

[87] The billet is preferably reheated at the temperatures of 1 ,000 ~ 1 , 100 °C. This condition is the same as that of the typical heating condition of the steel wire.

[88]

[89] Cooling rate of steel wire: 0.1 - 5 °C/sec

[90] After the billet is hot rolled to the steel wire, the steel wire is preferably cooled at a cooling rate of 0.1 ~ 5 °C/sec. As described above, since the present invention is directed to a method for producing metal components by use of cold working of the steel wire, excessively high strength of the steel wire causes high strain resistance, which can reduce lifetime of a dice. Thus, it is preferable that the steel wire is cooled as slowly as possible in a slow cooling pattern. If the cooling rate exceeds 5 °C/sec, the strength of the steel wire is increased as described above, making it difficult to perform efficient cold working. On the other hand, according to the invention, the lower limit of cooling rate is set to 0.1 °C/sec, because it is difficult in practice to cool the steel wire at a cooling rate below 0.1 °C/sec. [92] Cooling stop temperature: 500 °C or less

[93] The steel wire is cooled at the cooling rate described above in a controlled cooling method(TMCP) until the temperature of the steel wire reaches 500 °C or less. When the temperature of the steel wire reaches 500 °C or less, there is no cause of changing the structure or the strength of the steel wire, and there is a likelihood of deterioration in productivity if the slow cooling condition is kept. Thus, the controlled cooling is stopped at the temperatures of 500 °C or less.

[94] [95] Under the above conditions, the billet is preferably rolled at the finish rolling delivery side temperature of 850 °C or less. Such limitation in finish rolling delivery side temperature is for the purpose of obtaining fine crystal grains. If the billet undergoes finish rolling at a temperature exceeding 850 °C, the crystal grains are coarsened. Coarsening of the crystal grains disadvantageously results in reduction of the number of nucleation sites for ferrite, thereby possibly increasing the ferrite fraction along with the total fraction of martensite and bainite.

[96] By producing the steel wire under all the conditions described above, the steel wire may have a tensile strength of 590 MPa or less. [97]

Mode for the Invention

[98] Examples [99] The present invention will be described in detail with reference to examples. It should be noted that the examples are provided for illustrative purposes and do not limit the scope of the present invention.

[100] Table 1 shows compositions of inventive examples and comparative examples. For every case, P and S were controlled to be 0.02 wt% or less during a steel manufacturing process.

[101] [102] Table 1

IE Inventive Example, CE Comparative Example

[103]

[104] In Table 1, Inventive Examples 1 to 7 satisfied the composition according to the present invention.

[105] However, comparative Example 1 did not satisfy the composition of the invention in view of C and Si contents, and did not contain Cr, B, and Ti, which should be added for advantageous effect of the present invention. Comparative Example 2 had the Ti content exceeding the upper limit of this invention. Comparative Examples 3 and 5 had the Si content less than the lower limit of the invention. Comparative Example 4 had the Ti content deviating from the composition of this invention. Comparative Example 6 did not contain Cr, and Comparative Example 7 did not contain B and Ti.

[106] Steel wire samples were produced from steels having the compositions of Table 1 under the conditions of Table 2.

[107] [108] Table 2

IE Inventive Example, CE Comparative Example

[109] [HO] [111] Among the above examples, Comparative Examples 1 to 6, which did not satisfy the composition of the invention, were produced under the conditions of the present invention for comparison of effects according to the compositions. Exceptionally, when producing Comparative Example 1, the cooling stop temperature was set above 500 °C of the present invention for comparison of effects of the cooling stop temperature.

[112] Furthermore, for comparison of effects according to the conditions, Inventive Examples 4 and 5 were rolled with finish rolling at excessive finish rolling delivery- side temperatures, respectively.

[113] Inventive Examples 1 to 3, 6 and 7 were produced under the conditions of the present invention. [114] Table 3 shows results of physical analysis with respect to the steel wire samples produced under the conditions of Table 2, and results of microstructure analysis with respect to quenched and tempered bolts obtained by machining the above steel wire samples through cold forging without particular spheroidizing annealing.

[115] [116] Table 3

IE Inventive Example, CE Comparative Example, F Ferrite fraction, B+M Total fraction of baimte and martensite, TS Tensile Strength, Q

[117] Quenching, T Tempenng

[118] [119] As can be seen from Table 3, for Inventive Examples 1 to 3, 6 and 7 satisfying both the composition and the conditions of the present invention, the ferrite fraction exceeded 50%, and the total fraction of martensite and bainite was less than 0.5%. In addition, all these inventive examples had tensile strengths of 550 MPa or less, and had properties to enable a single dice to produce 99,000 or more bolts through direct cold forging without particular spheroidizing annealing.

[120] For Inventive Examples 4 and 5 which were rolled at the higher finish rolling delivery-side temperatures than the present invention while satisfying the composition of the invention, the ferrite fraction decreases, and the total fraction of martensite and bainite increases due to coarsened crystal grains so that cold forging properties were deteriorated.

[121] For Comparative Examples 1 to 7 which did not satisfy the composition of the invention and were produced under the conditions of the invention, not only were martensite and bainite created in large amounts, but the strength was also high above 600 MPa, making it difficult to perform the cold forging operation. In addition, when performing the cold working operation on these comparative examples, the lifetime of the dice was also noticeably decreased, and an increasing degree in strength after quenching and tempering was not so high.

[122] In summary, it can be appreciated that as the ferrite fraction increases and the total fraction of martensite and bainite decreases, the cold heading quality of the steel wire increases. From the above results, it can be found that the ferrite fraction is 50% or more and the total fraction of martensite and bainite is 0.5% or less in order to ensure the cold heading quality.

[123] Fig. 2 is a graph depicting results of comparison in terms of dice lifetimes between

Inventive Example 1 produced under the condition of this invention and a steel sample labeled SWRCH45 generally used for cold forging after spheroidizing annealing. As can be seen from the graph, Inventive Example 1 shows substantially the same dice lifetime as that of SWRCH45 subjected to spheroidizing annealing, and thus it can be confirmed that the steel wire of the present invention and the method of producing the same are superior to the conventional steel wire and the method for producing the same.

[124] Fig. 1 is a graph depicting results of comparing the quenching properties depending on composition systems for observing influence of the respective composition systems. In Fig. 1, C-Mn, C-Mn-B, C-Mn-Cr, and C-Mn-Cr-B indicate Comparative Examples 1, 6 and 7, and Inventive Example 2, respectively. As can be seen from Fig. 1, Inventive Example 2 exhibits the superior quenching properties.

[125] From the above results obtained through observation of influence of the compositions on the tensile strength, the inventors obtained the following Regression Equation:

[126] TS(MPa) =258 + 959*[C] + 112*[Si] + lll*[Mn] + 5*[Cr] + 439*[Ti] -

0.7* [ferrite fraction]

[127] Since it is possible to predict the tensile strength of a steel wire somewhat precisely by use of this equation, the steel wire having required tensile strength can be produced through selection of composition and manufacturing conditions based on this regression equation. Thus, this equation is useful for production of the steel wire which has a tensile strength of 590 MPa or less as the target strength of the present invention. From the equation described above, it is necessary to limit the contents of C, Si, Mn, Cr, Ti and the like in order to lower the tensile strength of the steel wire. However, reduction in contents of such elements makes it difficult to assure the quenching properties, which results in failure of assuring the strength after machining machine components such as bolts using the steel wire. In order to overcome this problem, the steel wire of the present invention comprises boron, which is an element useful for assuring the strength of the machine components without increasing the tensile strength of the steel wire.

Claims

[1] A steel wire having excellent cold heading quality and quenching properties, comprising, by weight%: C: 0.1-0.4%; Si: 0.3-1.5%; Mn: 0.3-1.7%; P: 0.015% or less; S: 0.015% or less; Cr: 0.05-1.7%; Al: 0.05% or less; B: 0.001-0.005%;

Ti: 0.01-0.05%; N: 0.015% or less; and the balance of Fe and other unavoidable impurities. [2] The steel wire according to claim 1, wherein a ratio (Ti/N) of Ti to N is 1.39 or more in terms of atomic weight, and a ratio (B/Cr) of B to Cr is 0.04 or less in terms of weight. [3] The steel wire according to claim 1 or 2, wherein the steel wire comprise ferrite and pearlite structures. [4] The steel wire according to claim 3, wherein the steel wire comprises the ferrite structure in a fraction of 50% or more. [5] The steel wire according to claim 4, wherein the steel wire comprises bainite and martensite structures in a total fraction of 0.5% or less. [6] The steel wire according to claim 5, wherein the steel wire has a tensile strength of 590 MPa or less, the tensile strength being expressed by Equation:

TS(MPa) = 258+ 959*[C]+ 112*[Si]+ lll*[Mn] + 5*[Cr] + 439* [Ti]-

0.7* [ferrite fraction] [7] A method for producing a steel wire having excellent cold heading quality and q uenching properties, comprising: heating a steel billet to 1,000 - 1,100 °C, the billet comprising, by weight%, C:

0.1-0.4%, Si: 0.3-1.5%, Mn: 0.3-1.7%, P: 0.015% or less, S: 0.015% or less,

Cr: 0.05-1.7%, Al: 0.05% or less, B: 0.001-0.005%, Ti: 0.01-0.05%, N: 0.015% or less, and the balance of Fe and other unavoidable impurities; and rolling the steel billet to produce a steel wire, followed by cooling the steel wire to 500 °C or less at a rate of 0.1 - 5 °C/sec. [8] The method according to claim 7, wherein the rolling of the steel billet comprises finish rolling performed at a finish rolling temperature of 850 °C or less. [9] The method according to claim 7 or 8, wherein a ratio (Ti/N) of Ti to N is 1.39 or more in terms of atomic weight, and a ratio (B/Cr) of B to Cr is 0.04 or less in terms of weight. [10] The method according to claim 7 or 8, wherein the steel wire has a tensile strength of 590 MPa or less, the tensile strength being expressed by Equation:

TS(MPa) = 258+ 959*[C]+ 112*[Si]+ lll*[Mn] + 5*[Cr] + 439* [Ti]-

0.7* [ferrite fraction]