WO2018117157A1

WO2018117157A1 - Wire rod

Info

Publication number: WO2018117157A1
Application number: PCT/JP2017/045740
Authority: WO
Inventors: 大藤　善弘
Original assignee: 新日鐵住金株式会社
Priority date: 2016-12-20
Filing date: 2017-12-20
Publication date: 2018-06-28
Also published as: JP6725007B2; EP3561100A4; JPWO2018117157A1; CN110088318A; US20200071791A1; EP3561100A1

Abstract

The purpose of the present invention is to provide a wire rod that has excellent wire drawability and makes it possible to produce steel wire that has a high tensile strength. A wire rod according to one embodiment of the present invention is configured such that: chemical components are within predetermined ranges; the mean value of %Mn+2×%Cr over the entirety of the wire rod is 0.50 to 1.00%; the metallographic structure is 90% or more perlite by area fraction; the area fraction of cementite is less than 3%; the maximum grain size of TiN is less than 15 μm; the maximum value of %Mn+2×%Cr in a region where the S content and O content are less than 1% in a center section is at most 2.0 times the mean value of the %Mn+2×%Cr over the entirety of the wire road; and the ratio of the maximum value and minimum value of %Mn+2×%Cr in a region where the S content and O content are less than 1% in an outer peripheral section is 2.0 or less.

Description

wire

The present invention relates to a wire.
This application claims priority based on Japanese Patent Application No. 2016-246866 filed in Japan on December 20, 2016, the contents of which are incorporated herein by reference.

A steel wire for a steel cord used as a reinforcing material for a radial tire of an automobile, various belts and hoses, or a steel wire for a sawing wire is generally obtained by the procedure described below. First, a steel wire with a diameter of 4 to 6 mm that has been adjusted and cooled after hot rolling (hereinafter, “steel wire” is simply referred to as “wire”) is subjected to primary wire drawing to a diameter of 3 to 4 mm. Next, an intermediate patenting process is performed, and further secondary wire drawing is performed to obtain a diameter of 1 to 2 mm. In many cases, the diameter is 1 to 2 mm by omitting the intermediate patenting process for cost reduction. The steel wire drawn to a diameter of 1 to 2 mm is then subjected to a final patenting treatment, followed by brass plating and further a final wet drawing to a diameter of 0.06 to 0.40 mm. . The thin high-strength steel wire (extra fine steel wire) manufactured in this way is twisted into a “twisted steel wire” by, for example, twisting to form a steel cord or the like.

Generally, when a wire breakage occurs when a wire rod is processed into a steel wire or a steel wire is twisted, productivity and yield are greatly reduced. Therefore, a wire belonging to the above technical field and a steel wire processed from the wire are strongly required not to be disconnected during wire drawing or twisting. Among the wire drawing processes, particularly in the above-described final wet wire drawing process, the wire diameter of the workpiece is smaller than that in the primary wire drawing process and the secondary wire drawing process. On the other hand, it becomes sensitive, and the wire drawing length per unit mass becomes long. For this reason, the occurrence frequency of disconnection is high in the final wet wire drawing.

In recent years, there has been an increasing trend to reduce the weight of steel cords for various purposes. For this reason, high strength is required for the steel wire, and desired strength is obtained by techniques such as addition of alloy elements and increase in the final wet wire drawing amount. However, when the above-described high-strength technique is used, the frequency of occurrence of disconnection in the final wet wire drawing tends to increase. Therefore, mass production of steel cord with higher strength has not progressed much. For this reason, there is a great demand for a wire having excellent wire drawing workability and high strength that can prevent disconnection in the final wet wire drawing.

In response to the above-mentioned demands from the industry in recent years, wire and steel wire drawing workability is reduced by techniques such as reducing impurity elements, controlling inclusions, suppressing the formation of proeutectoid cementite and managing hot rolling conditions. A technique for improving the above has been proposed.

For example, in Patent Document 1, in mass%, C: 0.6 to 1.1%, Si: 0.1 to 1.5%, Mn: 0.2 to 1%, P: 0.025% or less , S: not more than 0.025%, Al: not more than 0.003%, and if necessary, further containing Ni, Co, Cu, Cr, V, total oxygen amount, average composition of nonmetallic inclusions In addition, “high carbon steel wire rods excellent in wire drawability and stranded wire properties” defined for Ti content is disclosed. The technique proposed in Patent Document 1 limits the amount of Ti for the control of oxide-based nonmetallic inclusions, and does not consider TiN. In addition, the technique proposed in Patent Document 1 does not consider element segregation. Therefore, according to the technique proposed in Patent Document 1, when the processing amount in the final wet wire drawing process, that is, the true strain amount is increased in order to increase the strength, the frequency of occurrence of disconnection tends to increase. It is difficult to produce a steel wire industrially stably.

In Patent Document 2, in mass%, C: 0.70 to 0.90%, Si: 0.05 to 1.20%, Mn: 0.10 to 1.0%, Al: 0.05% or less “High carbon steel wire rods with excellent resistance to breakage of coupling” are disclosed which each contain (not including 0%), consist of the remainder Fe and inevitable impurities, and define the Si concentration in the cross section of the wire rod. In the technique proposed in Patent Document 2, segregation of Mn and Cr is not considered, and TiN is not considered. Therefore, according to the technique proposed in Patent Document 2, if the amount of processing in the final wet wire drawing, that is, the amount of true strain is increased in order to increase the strength, the frequency of occurrence of disconnection tends to increase. It was difficult to produce a steel wire industrially stably.

Japanese Unexamined Patent Publication No. 6-330239 Japanese Laid-Open Patent Publication No. 2007-297474

The present invention has been made in view of the above situation, and its purpose is to produce a steel wire that is suitable for processing to steel cords, sawing wires, etc., has excellent wire drawing workability, and has high tensile strength. It is to provide a wire that is possible.

In order to solve the above-mentioned problems, the present inventors have repeatedly investigated and studied the influence of the chemical composition, microstructure, and inclusions of the wire on the disconnection during wire drawing, and analyzed the results in detail. Upon examination, the following findings were obtained.

(A) In order to improve the strength of the steel wire after the final wire drawing, it is effective to increase the amount of C and add Cr.

(B) In order to suppress breakage of the wire during the primary wire drawing, it is preferable that the wire has a pearlite structure and the remainder is any of ferrite, cementite, and bainite, and does not include a martensite structure. .

(C) Mn and Cr are elements that are easily segregated in the wire. In particular, Mn and Cr are likely to segregate positively (concentrate) at the center of the wire. Therefore, the strength of the central portion of the wire is likely to increase, and the deformability decreases accordingly. Further, a high tensile stress is applied to the central portion of the wire during the wire drawing process. For this reason, if the positive segregation of Mn and Cr at the center of the wire is large, disconnection is likely to occur during wire drawing. Further, when Mn and Cr are positively segregated at the center of the wire, martensitic transformation is likely to occur at the center. This also contributes to the occurrence of disconnection. Therefore, it is necessary to appropriately control the amount of Mn and the amount of Cr. In addition, the degree of the influence of Cr on the tensile strength of the wire and the formation of martensite is about twice that of Mn.

(D) Mn and Cr are liable to segregate even in areas other than the center of the wire. In the wire rod, Mn and Cr are easily segregated in a band shape. This band-shaped segregation can be observed in a cross section parallel to the rolling direction. Since the segregated portion becomes hard and cracks easily develop along the segregated portion by wire drawing, the band-shaped segregation easily causes disconnection. Even in this case, the degree of influence of Cr on the disconnection is about twice that of Mn.

(E) Since the segregation in the wire described in (c) and (d) above remains even after performing the patenting after the primary wire drawing, the above-described influence is exerted on the wire drawing workability until the final wire drawing. .

The present inventors conducted further detailed experiments and research based on these findings (a) to (e). As a result, it was found that the component composition of the wire, the condition of the metal structure mainly composed of pearlite, the size of TiN, and the segregation of Mn and Cr may be appropriately adjusted. And according to the wire rod in which these items are within an appropriate range, the present inventors can solve the above-mentioned problems, and stably produce a high-strength steel wire suitable as a steel cord material with a low frequency of disconnection. The present invention has been conceived after confirming that it is possible.

The gist of the present invention is as follows.
(1) In the wire according to one embodiment of the present invention, the chemical component is mass%, C: 0.90 to 1.20%, Si: 0.10 to 1.00%, Mn: 0.20 to 0 80%, Cr: 0.10 to 0.40%, Al: 0 to 0.002%, Ti: 0 to 0.002%, N: 0 to 0.0050%, P: 0 to 0.020% , S: 0 to 0.010%, O: 0 to 0.0040%, Mo: 0 to 0.20%, B: 0 to 0.0030%, with the balance being Fe and impurities, The average value of% Mn + 2 ×% Cr over the entire area is 0.50 to 1.00%, and the metal structure is pearlite with an area fraction of 90% or more, and the balance is either ferrite, cementite, or bainite. 1 type or 2 types or more are included, the area fraction of the said cementite is less than 3%, and the largest particle size of TiN is 15 micrometers. S content and O content in the central part, which is less than m and measured in a section perpendicular to the length direction of the wire, from the central axis of the wire to 1/10 of the diameter of the wire The maximum value of% Mn + 2 ×% Cr in the region where the amount is less than 1% is 2.0 times or less of the average value of% Mn + 2 ×% Cr over the entire wire, and in the length direction of the wire % Mn + 2 of the region where the S content and the O content are less than 1% in the outer peripheral portion, which is the region from the outer edge of the central portion to the depth of 0.1 mm of the surface of the wire, measured at the perpendicular cutting plane The ratio of the maximum value and the minimum value of x% Cr is 2.0 or less. Here,% Mn and% Cr represent the content in mass% of Mn and Cr.
(2) In the wire according to (1), the chemical component is any one of Mo: 0.02 to 0.20% and B: 0.0003 to 0.0030% in mass%. You may contain 2 types.

According to the wire rod of the present invention, it is possible to stably produce a steel wire for steel cord, a steel wire for sawing wire or the like having a high strength of, for example, 4100 MPa or more with a low disconnection frequency.

It is explanatory drawing for demonstrating the measuring method of Mn and Cr density | concentration of center part. It is explanatory drawing for demonstrating the measuring method of Mn and Cr density | concentration of an outer peripheral part.

The chemical component composition of the wire according to one embodiment of the present invention (hereinafter sometimes simply referred to as “wire”), the condition of the metal structure, and the like will be described in more detail. The wire 1 according to the present embodiment includes a central portion 11 that is a region from the central axis of the wire to 1/10 of the diameter of the wire, and a region from the outer edge of the central portion 11 to a depth of 0.1 mm on the surface of the wire 1. A certain outer peripheral portion 12.

<Ingredient composition>
Below, the chemical component of the wire which concerns on this embodiment is demonstrated. In addition, the chemical component of the wire according to the present embodiment described below is the amount of the alloy element contained in the material of the wire, and thus is the average value of the chemical components over the entire wire. The chemical composition of the wire is measured not by a local analysis that is affected by element segregation but by an analysis that measures the average value of a region of a certain size.

C: 0.90 to 1.20%
C is an effective component for increasing the tensile strength of steel. However, when the C content is less than 0.90%, it is difficult to stably impart a high strength to the final product, for example, a tensile strength of 4100 MPa. Furthermore, it is effective to increase the C content in order to stably obtain a high-strength final product, and in order to obtain a final product having a tensile strength of 4300 MPa or more, the lower limit of the C content is 1.00. % Or more is desirable. On the other hand, if the C content is too large, the steel material becomes hard and breaks during wire drawing. In particular, if the C content exceeds 1.20%, the influence becomes significant, and stable mass production of steel wires becomes industrially difficult. Therefore, the C content is determined to be in the range of 0.90 to 1.20%. The lower limit value of the C content may be 0.92%, 0.95%, or 1.00%. Moreover, it is good also considering the upper limit of C content as 1.15%, 1.12%, or 1.10%.

Si: 0.10 to 1.00%
Si is also an effective component for increasing the strength of the steel material, and is also a necessary component as a deoxidizer. However, if the Si content is less than 0.10%, the effect of Si cannot be sufficiently obtained. On the other hand, if Si is contained exceeding 1.00%, the ductility of the wire rod or steel wire after wire drawing will fall. Therefore, the Si content is determined to be in the range of 0.10 to 1.00%. Since Si is an element that affects the hardenability of steel materials and the formation of proeutectoid cementite, the Si content is 0.30 to 0.80% from the viewpoint of ensuring a desired microstructure stably in the wire. It is more desirable to adjust within the range. The lower limit value of the Si content may be 0.15%, 0.20%, 0.30%, or 0.40%. Further, the upper limit value of the Si content may be 0.95%, 0.90%, 0.85%, 0.80%, 0.70%, or 0.50%.

Mn: 0.20 to 0.80%
Mn affects the time required for the phase transformation from austenite to various low-temperature structures, and is an effective component for generating a stable pearlite structure in the wire, and at the same time, has the effect of increasing the strength of the final product. However, if the Mn content is less than 0.20%, the above effect cannot be obtained sufficiently. On the other hand, Mn is an element that easily segregates, and if it is contained in excess of 0.80%, Mn is segregated particularly in the central portion 11 of the wire, and martensite is generated in the segregated portion. Disconnection is likely to occur. Therefore, the Mn content is determined to be in the range of 0.20 to 0.80%. The lower limit value of the Mn content may be 0.25%, 0.30%, or 0.40%. Moreover, it is good also considering the upper limit of Mn content as 0.75%, 0.70%, or 0.60%.

Cr: 0.10 to 0.40%
Cr greatly affects the time required for the phase transformation from austenite to various low-temperature structures, and is effective for generating a stable pearlite structure in the wire, and at the same time increases the strength of the final product by reducing the pearlite lamella spacing. There is an effect. And, in order to stably obtain a tensile strength of 4100 MPa or more in the final product, a Cr content of 0.10% or more is required. However, if Cr is contained exceeding 0.40%, Cr is segregated particularly in the central portion 11 of the wire, martensite is generated in the segregated portion, and breakage is likely to occur during wire drawing. . Therefore, the Cr content is determined to be in the range of 0.10 to 0.40%. The lower limit value of the Cr content may be 0.12%, 0.15%, or 0.20%. Moreover, it is good also considering the upper limit of Cr content as 0.35%, 0.30%, or 0.25%.

Average value of% Mn + 2 ×% Cr throughout the wire: 0.50 to 1.00%
As described above, Mn and Cr greatly affect the phase transformation time from austenite to various low-temperature structures, and in order to obtain a stable pearlite structure with a wire, each content of Mn and Cr must be within a predetermined range. Don't be. However, in addition to the above-mentioned limitations, the present inventors also set the average value of the Mn content throughout the wire and the total value of the average value of the Cr content throughout the wire multiplied by 2 within the predetermined range. I found it necessary to do. Hereinafter, the Mn content is indicated by the symbol “% Mn”, and the Cr content is indicated by the symbol “% Cr”.

The effect of Cr on tensile strength is about twice that of Mn. If the average value of% Mn + 2 ×% Cr (hereinafter sometimes referred to as Mn + 2Cr) throughout the wire is less than 0.50%, the final product cannot stably obtain a tensile strength of 4100 MPa or more. Therefore, the lower limit of the average value of Mn + 2Cr over the entire wire is 0.50% or more. In order to further improve the tensile strength, the average value of Mn + 2Cr over the entire wire is preferably 0.60% or more, 0.70% or more, or 0.80% or more. On the other hand, as described above, both Mn and Cr are easily segregated at the central portion 11 of the wire, and when the average value of Mn + 2Cr over the wire exceeds 1.00%, the segregated portion of Mn and Cr is martensified. A site is generated, and disconnection is likely to occur during wire drawing. Therefore, the average value of Mn + 2Cr over the entire wire was determined to be in the range of 0.50 to 1.00%. The upper limit of the average value of Mn + 2Cr over the entire wire may be 0.95%, 0.90%, or 0.80%.

The wire according to the present embodiment includes the above-described essential elements, and may further include an arbitrary element described below. However, since the wire according to the present embodiment can solve the problem without including an arbitrary element, the lower limit value of each arbitrary element is 0%.

Al: 0 to 0.002%
Al is an element that forms oxide inclusions containing Al ₂ O ₃ as a main component and reduces the wire drawing workability of the wire. In particular, when the Al content exceeds 0.002%, the oxide inclusions become coarse, frequent breaks occur during wire drawing, and wire drawing workability deteriorates remarkably. Therefore, the Al content is regulated to 0.002% or less. Preferably, the Al content is 0.001% or less. As described above, the wire according to the present embodiment does not require any Al in order to solve the problem, and can obtain good characteristics even if the Al content is 0%. Therefore, the lower limit of the Al content is 0%. On the other hand, since the manufacturing cost may increase due to the reduction of the Al content, the Al content may be defined as 0.0005% or more, or 0.001% or more.

Ti: 0 to 0.002%
Ti tends to form TiN when the wire contains N. Since TiN is very hard and does not deform by hot rolling or wire drawing, it is likely to become a disconnection starting point during wire drawing. Even if the manufacturing method is taken into consideration, if the Ti content exceeds 0.002%, it is difficult to make the maximum particle size of TiN of the wire measured by the method described below less than 15 μm, and disconnection may occur during wire drawing. It tends to occur. Therefore, the Ti content is regulated to 0.002% or less. Preferably, the Ti content is 0.001% or less. As described above, the wire according to the present embodiment does not require any Ti in order to solve the problem, and can obtain good characteristics even when the Ti content is 0%. Therefore, the lower limit of the Ti content is 0%. On the other hand, since the manufacturing cost may increase due to the reduction of the Ti content, the Ti content may be defined as 0.0005% or more, or 0.001% or more.

N: 0 to 0.0050%
N easily forms TiN when the wire contains Ti, and TiN is very hard and is not deformed by hot rolling or wire drawing. Therefore, N tends to be a starting point of wire breakage during wire drawing. Even if the manufacturing method is taken into consideration, if the N content exceeds 0.0050%, it is difficult to make the maximum particle size of TiN of the wire measured by the method described below less than 15 μm, and disconnection occurs during wire drawing. It tends to occur. Therefore, the N content is restricted to 0.0050% or less. Preferably, the N content is 0.0040% or less.

P: 0 to 0.020%
P is an element that segregates at the grain boundary and lowers the wire drawing workability. In particular, when the P content exceeds 0.020%, the wire drawing workability is significantly lowered. Therefore, the P content is restricted to 0.020% or less. Preferably, the P content is 0.010% or less.

S: 0 to 0.010%
S is also an element that reduces wire drawing workability. And when S content exceeds 0.010% especially, since the fall of wire drawing work will become remarkable, S content will be controlled to 0.010% or less. Preferably, the S content is 0.008% or less.

O: 0 to 0.0040%
O is an element that easily forms an oxide, and when it is present in the wire together with Al, it is an element that forms oxide inclusions mainly composed of hard Al ₂ O ₃ and lowers the wire drawing workability. In particular, when the O content exceeds 0.0040%, even if the Al content is regulated within the above range, the oxide inclusions become coarse, resulting in frequent breakage during wire drawing, and wire drawing. The fall of the property becomes remarkable. Therefore, the O content is regulated to 0.0040% or less. Preferably, the O content is 0.0030% or less, or 0.0025% or less.

Mo: 0 to 0.20%
Mo has the effect of increasing the tensile strength of the steel wire after wire drawing. In order to obtain this effect, the Mo content is preferably 0.02% or more. However, if the Mo content exceeds 0.20%, a martensite structure is likely to be generated, and the wire drawing workability may be reduced. Therefore, the upper limit of the Mo content is 0.20%. More preferably, the upper limit of the Mo content is 0.10% or 0.07%. On the other hand, from the viewpoint of optimizing the balance between tensile strength and ductility of the wire or steel wire, the lower limit of the Mo content is more preferably 0.04%.

B: 0 to 0.0030%
B has the effect of increasing the balance between tensile strength and ductility of the steel wire after wire drawing. In order to acquire this effect, it is preferable to make B content 0.0003% or more. However, if the B content exceeds 0.0030%, coarse BN is likely to be generated, and the wire drawing workability may be lowered. Therefore, the upper limit of the B content is set to 0.0030%. More preferably, the upper limit of the B content is 0.0020% or 0.0015%. On the other hand, from the viewpoint of optimizing the balance between the tensile strength and ductility of the wire or steel wire, the lower limit of the B content is more preferably 0.0005%.

The balance of the chemical component of the wire contains Fe and impurities. Impurities are components that are mixed due to various factors in the production process, such as ore or scrap, when industrially producing steel materials, and do not adversely affect the wire according to the present embodiment. Means what is allowed.

<Area fraction of pearlite structure and remaining structure>
In order to stably prevent disconnection or the like during primary wire drawing, the area fraction of the pearlite structure of the wire must be 90% or more. The area fraction of pearlite may be 92% or more, 95% or more, 97% or more, or 100%. Furthermore, the remainder (non-pearlite region) of the structure of the wire contains one or more of ferrite, cementite, bainite, and the like, and the area fraction of cementite needs to be less than 3%. The remainder of the wire structure preferably does not contain martensite, but the martensite content is allowed up to a maximum area fraction of about 0.2%.

From a wire having such a metal structure, a high-strength steel wire can be obtained with a low disconnection frequency during wire drawing. In addition, the ferrite structure in the wire according to the present embodiment does not include the ferrite structure in the pearlite structure and the ferrite structure in the bainite structure. Moreover, the cementite structure in the wire according to the present embodiment is a pro-eutectoid cementite that transforms into a prior austenite grain boundary, and does not include cementite in the pearlite structure and cementite structure in the bainite structure. In order to make the metal structure of the wire within the above range, it is necessary to preferably control the heating temperature before hot rolling, the finishing temperature of hot rolling, the cooling rate after hot rolling, and the like.

<Maximum particle size of TiN>
When Al was 0.002% or less and O was 0.0040% or less in the chemical composition of the wire, inclusions other than TiN, that is, sulfides and oxides, were not observed at the starting point of the disconnection. When the maximum particle size of TiN measured by the method described later is 15 μm or more, disconnection occurred during wire drawing even if other requirements were satisfied. Therefore, in the wire according to the present embodiment, the maximum particle size of TiN is restricted to less than 15 μm. The maximum particle size of TiN is preferably 12 μm or less, more preferably 10 μm or less. Although it is not necessary to define the lower limit of the maximum particle size of TiN, it may be 5 μm or 6 μm. In order to reduce the maximum particle size of TiN of the wire material, it is necessary to at least increase the solidification rate as much as possible when producing a slab to be a material of the wire material.

<Measuring method of metal structure>
Next, a method for measuring the metal structure of the wire and the maximum particle size of TiN according to the present embodiment will be described.

The area fraction of the pearlite structure is measured by the following method. First, the cross section of the wire (that is, the cut surface perpendicular to the length direction of the wire) is mirror-polished, and then corroded with picral to reveal the structure to obtain an observation sample. Next, using a field emission type scanning electron microscope (FE-SEM), 10 points on the observation surface of the sample are photographed at a magnification of 3000 times. The observation locations are 5 locations where the depth from the surface of the wire includes a position that is 1/4 of the radius of the wire, and 4 locations where the depth from the surface of the wire includes a location that is 1/2 of the radius of the wire. It is one location which is a location and a region in the center of the wire. It is preferable to separate the measurement points as much as possible. The observation may be performed on a plurality of cross sections. The area per field of view is 5.0 × 10 ⁻⁴ mm ² (vertical 20 μm, horizontal 25 μm). Subsequently, using the photograph, the area fraction of the tissue other than the pearlite structure is obtained by an image analysis apparatus capable of analyzing the shape and area of the crystal grains. The value obtained by removing the area fraction (%) other than the pearlite structure from 100% is defined as the area fraction of the pearlite structure. At this time, the area fractions of the ferrite structure, cementite structure, bainite structure, etc. are also determined by the same method.

The maximum particle size of TiN is measured by the following method. First, a cross section perpendicular to the rolling direction (the length direction of the wire) is cut out from the wire, and the cross section is mirror-polished to obtain an observation sample, and TiN in the sample is observed with an optical microscope. Observation is performed for each 2.5 mm × 2.5 mm range, a photograph is taken of the maximum TiN within this observation range, the area of the maximum TiN is obtained by image analysis of the photograph, and the maximum TiN area is calculated. The 1/2 power is regarded as the maximum grain size of TiN. That is, the length of one side when the maximum TiN shape within the observation range is regarded as a square is regarded as the maximum TiN particle size within the observation range. The above-mentioned cross section is prepared for 20 samples per sample, and this measurement is carried out for each sample by 20 fields of view, thereby obtaining the maximum particle size of TiN in the observation range of 125 mm ² in total.
The maximum particle size of TiN confirmed in the observation range of 125 mm ² in total has a strong correlation with the maximum particle size of TiN contained in the entire wire. It is impossible to make the entire TiN particle size measurement object, and in the case of a wire with the maximum particle size of TiN confirmed in the observation range of 125 mm ² in total within the above range, the wire is TiN at the time of wire drawing. The possibility of causing disconnection is extremely low. Therefore, in the wire in this embodiment, the maximum particle diameter of TiN confirmed in the observation range of 125 mm ² in total is referred to as the maximum particle diameter of TiN of the wire.
Moreover, since TiN exhibits a gold color when observed with an optical microscope, it can be easily distinguished from other inclusions. In addition, when there is an inclusion that is difficult to identify based on color, whether or not it is TiN may be specified by an energy dispersive electron beam microanalyzer (EPMA) described later.

The observation range of 2.5 mm × 2.5 mm described above is arranged at the center of the cross section of the wire. That is, the center of the observation range substantially coincides with the center of the cross section of the wire. This is because coarse TiN tends to segregate in the vicinity of the central axis of the wire. In addition, when the diameter of a wire is small and the observation range of 2.5 mm x 2.5 mm mentioned above does not fit in the cross section of a wire, you may reduce the observation range of TiN suitably. In this case, the total area of the observation range may be set to 125 mm ² or more by increasing the number of measurement cross sections. Further, it is desirable that the length of the diagonal line in the observation range of TiN be 90% or less of the diameter of the wire.

<Maximum value of% Mn + 2 ×% Cr in the central portion 11 of the wire>
The chemical component of the wire according to the present embodiment (the average value of the chemical components over the entire wire) is as described above. However, the chemical component obtained by local analysis of the cross section of the wire using EPMA or the like may be slightly different from the average value of the chemical component of the wire due to the segregation of the alloy component and the effect of precipitation of inclusions. is there. In the wire according to the present embodiment, segregation of the alloy elements is suppressed within a predetermined range, thereby having the characteristics described below.

The region from the central axis to 1/10 of the diameter of the wire rod of the wire rod 1 according to the present embodiment is defined as the central portion 11. Maximum of% Mn + 2 ×% Cr (hereinafter sometimes referred to as Mn + 2Cr) in a region where the S content and O content in the central portion 11 are less than 1%, as measured at a cut surface perpendicular to the length direction The value is not more than 2.0 times the average value of% Mn + 2 ×% Cr throughout the wire. Here, in evaluating the segregation of Mn and Cr, the influence of sulfides and oxides needs to be excluded. In the region of sulfides and oxides, the S content or the O content greatly exceeds 1%. Therefore, the region where the S content and the O content are less than 1% can be regarded as a region in which no sulfide and oxide are present in the wire according to the present embodiment having the above-described chemical components. Hereinafter,% Mn + 2 ×% Cr of the region where the S content and O content of the central portion 11 are less than 1%, measured by a cutting plane perpendicular to the length direction of the wire, is simply referred to as “Mn + 2Cr of the central portion 11”. May be written.

When the maximum value of Mn + 2Cr in the central portion 11 exceeds 2.0 times the Mn + 2Cr of the entire wire 1, the deformability of the central portion 11 is significantly reduced. As a result, disconnection is likely to occur during wire drawing. Therefore, the maximum value of Mn + 2Cr in the central portion 11 is set to 2.0 times or less of the entire Mn + 2Cr. The maximum value of Mn + 2Cr in the central portion 11 is preferably 1.7 times or less, more preferably 1.5 times or less of the entire Mn + 2Cr. As described above, in this specification,% Mn and% Cr represent the contents in terms of mass% of Mn and Cr, respectively. Although it is not necessary to define the lower limit of the ratio between the maximum value of Mn + 2Cr in the central portion 11 and the overall Mn + 2Cr, it may be 1.2, 1.4, or 1.5. Hereinafter, the ratio of the maximum value of Mn + 2Cr in the central part 11 and the average value of Mn + 2C of the whole wire 1 (maximum value of Mn + 2Cr in the central part / Mn + 2C average value in the whole wire) is referred to as “central Mn + 2Cr segregation amount”. There is a case.

<Ratio between the maximum value and the minimum value of% Mn + 2 ×% Cr in the outer peripheral portion 12 of the wire (maximum value / minimum value)>
The area | region from the outer edge of the center part to the 0.1-mm depth of the surface of the wire which concerns on this embodiment is defined as the outer peripheral part 12. FIG. The ratio between the maximum value and the minimum value of% Mn + 2 ×% Cr in the region where the S content and the O content in the outer peripheral portion 12 are less than 1%, as measured at the cutting plane perpendicular to the length direction (ie, Maximum value / minimum value) is 2.0 or less. Also in the outer peripheral part 12, like the central part 11, in evaluating the segregation of Mn and Cr, the influence of sulfide and oxide needs to be excluded. Therefore, the region where the S content or O content exceeds 1% is excluded, and the value of% Mn + 2 ×% Cr in the region where the S content and O content is less than 1% is measured. Hereinafter,% Mn + 2 ×% Cr of the region where the S content and O content of the outer peripheral portion 12 are less than 1%, measured by a cut surface perpendicular to the length direction of the wire, is simply referred to as “Mn + 2Cr of the outer peripheral portion 12”. May be written.

If the ratio between the maximum value and the minimum value of Mn + 2Cr in the outer peripheral portion 12 exceeds 2.0, Mn and Cr are segregated in a band shape and become hard in the wire, so that cracking occurs along that region by wire drawing. Progresses and breaks easily. Therefore, the ratio between the maximum value and the minimum value of Mn + 2Cr in the outer peripheral portion 12 is set to 2.0 or less. The ratio between the maximum value and the minimum value of Mn + 2Cr in the outer peripheral portion 12 is preferably 1.6 or less, and more preferably 1.4 or less. In order to eliminate the segregation of Mn and Cr in the central part 11 and the outer peripheral part 12 of the wire, at least electromagnetic stirring is performed when producing a slab as a material of the wire, and the solidification rate is increased as much as possible. It is necessary to hold the pieces and the steel pieces at a sufficiently high temperature for a long time. Although it is not necessary to define the lower limit value of the ratio between the maximum value and the minimum value of Mn + 2Cr in the outer peripheral portion 12, it may be 1.3, 1.4, or 1.5. Hereinafter, the ratio (maximum value of Mn + 2Cr / minimum value of Mn + 2Cr) between the maximum value and the minimum value of Mn + 2Cr in the outer peripheral part 12 may be referred to as “peripheral part Mn + 2Cr segregation amount”.

<Measuring method of Mn and Cr concentration of the central portion 11 and the outer peripheral portion 12>
The Mn concentration and the Cr concentration in the region where the S content and the O content are less than 1% in the central portion 11 of the wire, as measured at the cutting plane perpendicular to the length direction of the wire, are as follows. taking measurement. First, five cross sections (cut surfaces perpendicular to the length direction) are cut out from the wire at intervals of 200 mm in length. Next, as shown in FIG. 1, in the line analysis region 13 extending from the center of each cut surface to 1/10 of the diameter D, energy dispersive electrons are obtained for each element of Mn, Cr, S, and O. Line analysis is performed using a line microanalyzer (EPMA), and the concentration distribution of each element in the line analysis region 13 of each cut surface is measured. The line analysis by EPMA is preferably performed at an acceleration voltage of 15 kV, a beam diameter of 1 μm, a scanning speed of 200 μm / min, and a measurement point interval of 2 μm.

Next, the measurement results of the region where 1% or more S exists and / or the region where 1% or more of O exists are excluded from the measurement results of the Mn and Cr concentration line analysis obtained. By this operation, the influence of oxides and sulfides that are inclusions can be removed from the segregation evaluation result. Then, the maximum value of% Mn + 2 ×% Cr is obtained for the line analysis region 13 of each cut surface excluding the region where 1% or more S exists and / or the region where 1% or more O exists. The maximum value of% Mn + 2 ×% Cr in the line analysis region 13 of the five cut surfaces is measured at a cut surface perpendicular to the length direction of the wire, and the S content and O content in the central portion 11 are 1 The maximum value of% Mn + 2 ×% Cr in the region of less than%.

The average value of% Mn + 2 ×% Cr over the entire wire may be calculated based on the chemical composition of the wire (the average value of the chemical composition over the entire wire). That is, when the material of the wire is known, the average value of% Mn + 2 ×% Cr over the entire wire may be calculated based on the amount of Mn and the amount of Cr contained in the wire material. When the material of the wire is unknown, the average value of the Mn content and the average value of the Cr content are obtained by the usual chemical composition analysis method, and based on these, the% Mn + 2 ×% Cr throughout the wire What is necessary is just to calculate the average value.

The% Mn + 2 ×% Cr of the region where the S content and the O content are less than 1% of the outer peripheral portion 12 of the wire, which is measured at a cutting plane perpendicular to the length direction of the wire, is measured by the following method. . First, similarly to the measurement of the concentration of Mn and Cr in the central portion 11, five cross sections (cut surfaces perpendicular to the length direction) are cut out from the wire at intervals of 200 mm in length. Next, as shown in FIG. 2, along the straight line passing through the center of the cross section of the wire rod, the wire rod is separated from the center of the cross section of the wire rod by 1/10 of the diameter D (that is, the outer edge of the center portion 11). In the line analysis region 14 extending from the outer edge of the cross section to a position 0.1 mm deep, the concentration of Mn, Cr, S, and O in the central portion 11 for each element of Mn, Cr, S, and O Similar to the measurement, line analysis is performed using EPMA, and the concentration distribution of each element in the line analysis region 14 of each cut surface is measured.

Next, the measurement results of the region where 1% or more of S exists and / or the region where 1% or more of O exists are excluded from the obtained Mn and Cr concentration line analysis results. By this operation, the influence of sulfides and oxides that are inclusions can be excluded from the segregation evaluation results. Then, the maximum value of% Mn + 2 ×% Cr is obtained for the line analysis region 14 of each cut surface excluding the region where 1% or more S exists and / or the region where 1% or more O exists. The maximum value of% Mn + 2 ×% Cr in the line analysis region 14 at the five cut surfaces is measured at a cut surface perpendicular to the length direction of the wire, and the S content and O content in the outer peripheral portion 12 are 1 The maximum value of% Mn + 2 ×% Cr in the region of less than%. In addition, the minimum value of% Mn + 2 ×% Cr concentration is determined for the line analysis region 14 of each cut surface excluding the region where 1% or more S exists and / or the region where 1% or more O exists. The minimum content of% Mn + 2 ×% Cr concentration in the line analysis region 14 of the five cut surfaces is determined and measured at the cut surface perpendicular to the length direction of the wire, S content and O content in the outer peripheral portion 12 Is the minimum value of% Mn + 2 ×% Cr in the region where the ratio is less than 1%. Using the results of the maximum value and the minimum value of% Mn + 2 ×% Cr thus obtained, the ratio between the maximum value and the minimum value (maximum value / minimum value) was calculated, The ratio between the maximum value and the minimum value of% Mn + 2 ×% Cr in the region where the S content and the O content are less than 1% in the outer peripheral portion 12 measured at the cut surface perpendicular to the length direction (maximum Value / minimum value).

The diameter of the wire according to this embodiment is not particularly limited. Currently, the diameter of the wire distributed in the market is often in the range of 3.6 to 8.0 mm, so the diameter of the wire according to the present embodiment may be 3.6 to 8.0 mm.

<Manufacturing method>
Next, a method for manufacturing the wire according to this embodiment will be described.

When manufacturing the wire according to the present embodiment, the composition of steel, the target performance, the wire, so that the area fraction of pearlite, the structure other than pearlite, and the maximum particle size of TiN can reliably satisfy the above-mentioned conditions. What is necessary is just to set a process and each process condition according to a diameter.

When casting a small amount of steel for the experiment, if the weight of the steel is 150 kg or less, the raw material is first melted and then evacuated for 20 minutes or more, and then cast using a mold having an internal average cross-sectional area of 120 cm ² or less. And get an ingot. Examples of the material of the mold used when obtaining the ingot include cast iron. An example of an undesirable material is silica. In addition, from the both ends in the longitudinal direction of the ingot after casting, a portion with a volume fraction of 15% is not used, and the portion of the ingot is cut before hot forging.

Next, the ingot from which both ends have been removed is heated at 1260 to 1300 ° C. for 8 to 12 hours and cooled to 500 ° C. or less in the furnace. Next, the ingot is heated to 1200 to 1250 ° C. and then hot forged to obtain a steel slab.

When manufacturing the wire according to the present embodiment by a manufacturing method including continuous casting, after melting the molten steel by a converter, the molten steel is sufficiently stirred, and the average cooling rate from the start of solidification to the end of solidification is 5 ° C. / Min. And slab is obtained by further rolling down during solidification.

Next, the cast slab is heated at 1260 to 1300 ° C. for 8 to 12 hours and cooled to 500 ° C. or less in the furnace. Next, the slab is heated at 1200 to 1250 ° C. for 4 to 6 hours, and then rolled into pieces to obtain a steel slab.

The steel slab produced by any of the above methods is heated to 1050 to 1150 ° C., held in this temperature range for 40 to 60 minutes, and then hot rolled at a rolling finish temperature of 900 to 1000 ° C. The diameter of the wire after hot rolling is not particularly limited, but is often set to 3.6 to 8.0 mm as described above. The wire rod after finish rolling is cooled immediately after finishing finish rolling by cooling (primary cooling) combined with water cooling and air cooling until it reaches the temperature range of 680 to 730 ° C. at an average cooling rate of 30 ° C./s or more. Then, the air is cooled by air cooling (secondary cooling) in the atmosphere at an average cooling rate of 10 to 20 ° C./second until it reaches a temperature range of 610 to 650 ° C., and then left to cool to 500 ° C. or less (third cooling). ) The wire according to the present embodiment is manufactured by the above method. The wire thus obtained is a so-called hot-rolled wire, but the wire obtained by further performing cold working such as cold rolling and wire drawing also satisfies the above requirements. It is a wire concerning this embodiment.

In this specification, the heating temperature of the steel slab refers to the surface temperature of the steel slab, the rolling finish temperature refers to the surface temperature of the wire immediately after finish rolling, and the cooling rate after finish rolling is the surface of the wire. Refers to the cooling rate in In addition, the average cooling rate in the primary cooling combined with water cooling and air cooling is the surface temperature of the wire at the time when the injection of water or air into the wire starts and the injection of water or air into the wire ends This is a value obtained by dividing the difference from the surface temperature of the wire at the point of time by the injection time. The average cooling rate in air cooling (secondary cooling) by the air is the surface temperature of the wire at the time when injection into the air wire is started, and the surface temperature of the wire at the time when injection into the air is finished Is a value obtained by dividing the difference by the injection time. In addition, as long as the cooling rate condition mentioned above is satisfy | filled, the refrigerant | coolant injected to a wire in primary cooling and secondary cooling is not limited to water or air | atmosphere.

As described above, the wire according to the present embodiment has a predetermined component composition, has a metal structure in which the area fraction of the pearlite structure is 90% or more, and the balance is any of ferrite, cementite, bainite, and the like. Or an area fraction of cementite of less than 3% or less, a maximum particle size of TiN of less than 15 μm, and measured at a cutting plane perpendicular to the length direction of the wire. The maximum value of% Mn + 2 ×% Cr in the region where the S content and the O content are less than 1% in the central portion 11 which is a region from the central axis of the wire to 1/10 of the diameter of the wire extends over the entire wire. The area from the outer edge of the central part to the depth of 0.1 mm of the surface (outer peripheral surface), which is not more than 2.0 times the average value of% Mn + 2 ×% Cr and is measured by a cut surface perpendicular to the length direction of the wire S content in the outer periphery 12 And the ratio of the O content is between the maximum value and the minimum value of% Mn + 2 ×% Cr area is less than 1% (maximum value / minimum value) of 2.0 or less. For this reason, the wire rod of this embodiment is excellent in a wire drawing workability, and when a wire drawing process is performed to make a steel wire, a high-strength steel wire can be produced with a low disconnection frequency.

Next, examples of the present invention will be described. The conditions of the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. It is not something. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Steels A1 to Z1, A2, and G2 having the component compositions (chemical compositions) shown in Table 1 were cast into ingots having an average cross-sectional area shown in Table 1 and a weight of 50 kg or 150 kg. When obtaining the ingot, a mold made of the mold material shown in Table 1 was used. Moreover, both ends in the longitudinal direction of the ingot were cut and removed at the volume fraction shown in Table 1.

Next, the ingot from which both ends were removed was heat-treated under the heat treatment conditions (ingot heat treatment conditions) shown in Table 1, and cooled to 400 ° C. in a furnace. Next, the ingot was heated to 1230 ° C., formed into a steel piece having a diameter of 80 mm by hot forging, and allowed to cool to room temperature.

Further, steels B2 to F2 having the component compositions (chemical compositions) shown in Table 2 were melted by a converter and then continuously cast. During casting, the molten steel was sufficiently agitated, the average cooling rate from the start of solidification to the end of solidification was 6 ° C./min, and further reduced during the solidification. Next, the cast slab was heat-treated under the heat treatment conditions (slab slab heat treatment conditions) shown in Table 2 and allowed to cool to 500 ° C. or lower in the furnace. Next, after heating under the conditions shown in Table 2, a 122 mm square steel piece was obtained by split rolling.

The steel slab manufactured by the above method is heated to the steel slab heating temperature shown in Table 3, and the temperature is maintained at the same heating temperature only during the steel slab heating and holding time shown in Table 3, and the rolling shown in Table 3 is performed. The hot rolling process was performed so that the finish rolling diameter (diameter) was 5.5 mm at the finishing temperature. After finish rolling, the wire was cooled to 700 ° C. at an average cooling rate shown in Table 3 by cooling (primary cooling) combining water cooling and air cooling by the atmosphere. Thereafter, the wire was cooled from 700 ° C. to 610 ° C. at an average cooling rate shown in Table 3 by air cooling (secondary cooling) with the air. The average cooling rate to 700 ° C. (primary cooling rate) and the average cooling rate from 700 ° C. to 610 ° C. (secondary cooling rate) for each sample were as shown in the table. Thereafter, the wire rod having a temperature of less than 610 ° C. was allowed to cool (tertiary cooling) to obtain a wire rod.

About the obtained wire, using the measurement method described above, the area fraction of the pearlite structure, ferrite structure, cementite structure, bainite structure, center Mn + 2Cr segregation amount (that is, measured at the cut surface perpendicular to the length direction of the wire) The ratio of the maximum value of% Mn + 2 ×% Cr in the region where the S content and the O content are less than 1% in the center and the average value of% Mn + 2 ×% Cr over the entire wire)), outer periphery Mn + 2Cr segregation amount (that is, the maximum value and the minimum value of% Mn + 2 ×% Cr in the region where the S content and the O content are less than 1% in the outer peripheral portion, as measured by a cut surface perpendicular to the length direction of the wire) Value) and the maximum particle size of TiN. The results are shown in Tables 4 and 5.

About said wire, after performing descaling and a lubrication process by a normal method, the dry drawing process was performed by the pass schedule from which the area reduction rate in each die | dye becomes 18% on average. An 18 kg wire was drawn from a diameter of 5.5 mm to a diameter of 1.50 mm, and a 10 kg wire was drawn from a diameter of 5.5 mm to a diameter of 1.10 mm. Among these, Table 4 and Table 5 show the number of disconnections when wire drawing is performed from a diameter of 5.5 mm to a diameter of 1.10 mm. For the wire drawn from a diameter of 5.5 mm to a diameter of 1.50 mm, the primary wire drawing workability was not evaluated, and the secondary wire drawing workability described later was evaluated. When dry drawing was performed from a diameter of 5.5 mm to a diameter of 1.10 mm and the wire was not broken once, it was evaluated that the primary drawing workability was good. Note that the true strain when the wire is drawn from a diameter of 5.5 mm to a diameter of 1.10 mm is 3.22.
Here, the true strain (ε) is expressed by the following equation (i) using the diameter (d ₀ ) before wire drawing and the diameter (d) of the steel wire after wire drawing.

ε = 2ln (d ₀ / d) (i)

Subsequently, the above-described wire drawing material (steel wire) having a diameter of 1.50 mm was subjected to a patenting treatment using a heating furnace and a lead bath furnace. The heating furnace was set so that the temperature of the steel wire was maintained at 975 to 990 ° C. for 5 to 15 seconds. The temperature of the lead bath was 585 to 595 ° C., and the immersion time in the lead bath was 7 to 10 seconds. The steel wire after patenting was subsequently subjected to brass plating by a usual method.

The steel wire subjected to brass plating was subjected to wet wire drawing (final wire drawing) to a diameter of 0.19 mm with a pass schedule in which the area reduction rate of each die was 15% on average. The true strain when the wire is drawn from a diameter of 1.50 mm to a diameter of 0.19 mm is 4.13. In this wet wire drawing (final wire drawing), wire drawing workability was evaluated, and the results are shown in Table 4 and Table 5. In addition, the case where the wire drawing of 18 kg from a diameter of 1.50 mm to a diameter of 0.19 mm was wet drawn was evaluated as having good secondary drawing workability when the number of breaks was zero. On the other hand, when the number of disconnections was 1 or more, it was evaluated that the wire drawing workability was poor. Note that when the number of wire breaks was two, wire drawing up to a diameter of 0.19 mm and evaluation thereafter were stopped.

The strength of the steel wire after wet drawing was examined as follows. About the steel wire which could be drawn to a diameter of 0.19 mm, the tension test was done for 3 each, the tensile strength was measured, and the average value of 3 tensile strength was shown in Table 4 and Table 5.

The target performance of the wire rod of the present invention is that the number of wire breaks when a 10 kg wire rod is dry-drawn to a true strain of 3.22 is 0, and 18 kg with a patenting and brass plating. The number of wire breaks when the steel wire is wet-drawn to a true strain of 4.13 is 0, and the tensile strength of a steel wire having a diameter of 0.19 mm is 4100 MPa or more.

From Tables 4 and 5, it is clear that the test numbers satisfying all the conditions defined in the present invention satisfy all the above-mentioned performances. Moreover, about some test numbers, the preferable result from which the tensile strength of a steel wire with a diameter of 0.19 mm became 4300 Mpa or more was shown.
A test number outside the conditions defined in the present invention did not satisfy at least one of the above-described performances. Hereinafter, test numbers that deviate from the conditions defined in the present invention will be described.

Test No. 1 has a C content outside the scope of the present invention, Test No. 3 has Mn + 2Cr outside the scope of the present invention, and Test No. 5 has a Cr content outside the scope of the present invention. Therefore, the tensile strength of the steel wire was insufficient for any of the test numbers.

In test number 6, Mn + 2Cr was outside the scope of the present invention. In addition, since martensite was generated in the wire rod, the steel wire was disconnected during dry wire drawing and wet wire drawing.
In Test No. 8, the Cr content and Mn + 2Cr were out of the scope of the present invention. Moreover, since the area fraction of pearlite did not satisfy the scope of the present invention and martensite was generated in the steel structure, the steel wire was disconnected during the dry wire drawing and wet wire drawing.

Test No. 10 had a C content outside the scope of the present invention. Moreover, since the area fraction of cementite did not satisfy the scope of the present invention, the steel wire was disconnected during dry wire drawing and wet wire drawing.
Test No. 11 had an Al content outside the scope of the present invention. Therefore, the steel wire was disconnected during wet wire drawing.

Test No. 12 has a Ti content outside the scope of the present invention, and Test No. 13 has an N content outside the scope of the present invention. Moreover, since the maximum particle diameter of TiN did not satisfy the scope of the present invention in any of the test numbers, the steel wire was disconnected during wet wire drawing.
In Test No. 14, the O content was outside the range of the present invention, and the evacuation time was 10 minutes. Therefore, the steel wire was disconnected at the time of dry drawing and wet drawing.

In Test No. 15, since the average cross-sectional area of the ingot was not preferable, the ratio between the maximum particle size of TiN and the maximum value and the minimum value of Mn + 2Cr in the outer peripheral portion 12 was out of the scope of the present invention. Therefore, the steel wire was disconnected at the time of dry drawing and wet drawing.
In Test No. 16, since a mold made of silica was used during casting, the ratio between the maximum particle size of TiN and the maximum value and average value of Mn + 2Cr in the central portion 11 was out of the scope of the present invention. Therefore, the steel wire was disconnected at the time of dry drawing and wet drawing.

Since test number 17 is not preferable for the average cross-sectional area of the ingot, test number 18 has a cut volume fraction of 5% at both ends of the ingot, and therefore, the maximum particle size of TiN is within the scope of the present invention. It was outside. Therefore, the steel wire was disconnected during wet wire drawing.
In Test No. 22, Mn + 2Cr was out of the scope of the present invention, and martensite was generated in the steel structure. Therefore, the steel wire was disconnected during dry wire drawing and wet wire drawing.

Test No. 24, Test No. 25, Test No. 27, and Test No. 43 are not preferable for the heat treatment conditions of the ingot. Therefore, the ratio between the maximum value and the average value of Mn + 2Cr in the central portion 11 and the maximum value of Mn + 2Cr in the outer peripheral portion 12 The ratio with the minimum value was out of the scope of the present invention. Therefore, in all the test numbers, the steel wire was disconnected at the time of dry drawing and wet drawing.

In Test No. 26, since the heat treatment conditions of the ingot were not preferable, the ratio between the maximum value and the average value of Mn + 2Cr in the central portion 11 was out of the scope of the present invention. Therefore, the steel wire was disconnected at the time of dry drawing and wet drawing.

In Test No. 28, since the rolling finishing temperature was not preferable, the area fraction of cementite was out of the scope of the present invention. Therefore, the steel wire was disconnected during dry wire drawing and wet wire drawing.
In Test No. 29, the average cooling rate up to 700 ° C. is not preferable, and in Test No. 30, Test No. 39 and Test No. 40, the average cooling rate from 700 ° C. to 610 ° C. is not preferable. It was out of the scope of the present invention. Therefore, the steel wire was disconnected during the dry drawing process.

Test number 33 is not preferable for the average cooling rate from 700 ° C. to 610 ° C., and test number 34 is not preferable for the heating temperature of the steel slab, and the rolling finishing temperature is not preferable. The area fraction was out of the scope of the present invention. Therefore, the steel wire was disconnected during the dry drawing process.

In test number 45, since the heat treatment condition of the steel slab before hot rolling is not preferable, the ratio between the maximum value and the minimum value of Mn + 2Cr in the outer peripheral portion 12 is out of the scope of the present invention. Therefore, the steel wire was disconnected during wet wire drawing.

The preferred embodiments and examples of the present invention have been described above, but these embodiments and examples are merely examples within the scope of the present invention, and do not depart from the scope of the present invention. Thus, addition, omission, replacement, and other changes of the configuration are possible. That is, the present invention is not limited by the above description, is limited only by the description of the scope of claims, and can be changed as appropriate within the scope.

DESCRIPTION OF SYMBOLS 1 Wire material 11 Center part 12 Outer

peripheral part

13, 14 Wire analysis area

Claims

Chemical composition is mass%,
C: 0.90 to 1.20%,
Si: 0.10 to 1.00%,
Mn: 0.20 to 0.80%,
Cr: 0.10 to 0.40%,
Al: 0 to 0.002%,
Ti: 0 to 0.002%,
N: 0 to 0.0050%,
P: 0 to 0.020%,
S: 0 to 0.010%,
O: 0 to 0.0040%,
Mo: 0 to 0.20%,
B: 0 to 0.0030%,
And the balance consists of Fe and impurities,
The average value of% Mn + 2 ×% Cr throughout the wire is 0.50 to 1.00%,
In the metal structure, 90% or more of the area fraction is pearlite, and the balance includes one or more of ferrite, cementite, and bainite,
The cementite has an area fraction of less than 3%,
The maximum particle size of TiN is less than 15 μm,
The S content and the O content are less than 1% in the central portion, which is a region from the central axis of the wire to 1/10 of the diameter of the wire, as measured by a cutting plane perpendicular to the length direction of the wire. The maximum value of% Mn + 2 ×% Cr in the region is 2.0% or less of the average value of% Mn + 2 ×% Cr over the entire wire,
The S content and the O content are 1 in the outer peripheral portion, which is a region from the outer edge of the central portion to the depth of 0.1 mm of the surface of the wire, measured at the cut surface perpendicular to the length direction of the wire. A wire rod having a ratio between the maximum value and the minimum value of% Mn + 2 ×% Cr in a region of less than% is 2.0 or less.
Here,% Mn and% Cr represent the content in mass% of Mn and Cr.
The chemical component is mass%,
Mo: 0.02 to 0.20%, and B: 0.0003 to 0.0030%
Any 1 type or 2 types of these are contained, The wire of Claim 1 characterized by the above-mentioned.