WO2012144630A1

WO2012144630A1 - High carbon steel wire rod and method for producing high carbon steel wire rod

Info

Publication number: WO2012144630A1
Application number: PCT/JP2012/060783
Authority: WO
Inventors: ▲琢▼哉高知; 土田　武広; 智一増田; 染川　雅実; 悠士中河原; 千葉　政道
Original assignee: 株式会社神戸製鋼所
Priority date: 2011-04-20
Filing date: 2012-04-20
Publication date: 2012-10-26
Also published as: JP5204328B2; TW201305352A; JP2012233254A

Abstract

Provided are: a high carbon steel wire rod which is sufficiently reduced in hardness and is capable of reducing the spheroidization time during the production thereof; and a method for producing a high carbon steel wire rod. The present invention relates to a high carbon steel wire rod which contains, in mass%, 0.95-1.10% of C, 0.15-0.70% of Si, 1.15% or less of Mn (excluding 0%), 0.90-1.60% of Cr, 0.050% or less of P, 0.050% or less of S, 0.100% or less of Al, 0.015% or less of Ti, 0.025% or less of N and 0.0025% or less of O, with the balance made up of iron and unavoidable impurities. This high carbon steel wire rod has a ferrite crystal grain size of 20.0 μm or less and a Cr concentration in the carbides of 6.0% by mass or more.

Description

High carbon steel wire and method for producing high carbon steel wire

The present invention relates to a high carbon steel wire used as a bearing material in automobiles and various industrial machines and a method for producing the high carbon steel wire.

Conventionally, carbon steel and alloy steel have been widely used as materials for machine parts used in automobiles and various industrial machines. Among them, high carbon chromium bearing steel (SUJ material) defined in “JIS G 4805 (2008)” is often used as a bearing material. These bearings are generally obtained by hot rolling these materials into steel wire, then spheroidizing annealing, cutting, cold forging into a predetermined shape, quenching and tempering, and finally finishing. Is manufactured.

In this manufacturing process, a particularly long time is required for spheroidizing annealing, and shortening of the spheroidizing time is required from the viewpoint of cost and environmental load. Further, from the viewpoint of improving the die life during cold forging and saving power, it is also required to reduce the material hardness after the spheroidizing treatment. Under such circumstances, some proposals have been made from the viewpoint of shortening the spheroidizing time.

According to Patent Document 1, a magnetic field is applied in the temperature range of 800 to 500 ° C. during cooling after hot rolling, and the cooling rate in the temperature range is set to 10 ° C./s or less to suppress the precipitation of proeutectoid cementite. A method has been proposed in which the time required for the spheroidizing annealing in the next step can be shortened by shortening the lamella spacing in the pearlite. However, in order to implement this proposal, special equipment for applying a magnetic field is required, resulting in an increase in production cost and offsetting the cost reduction effect by shortening the spheroidizing time. End up.

Further, according to Patent Document 2, a high carbon chromium bearing steel having a predetermined component composition is rolled while being controlled so that the temperature in the entire cross section is between the A1 point and the Acm point from extraction to finish rolling. Thus, by obtaining a spheroidized structure, a method that can omit or shorten the next spheroidizing annealing has been proposed. However, in order to implement this proposal, special equipment called a rapid rolling mill is required. This proposal, like the previous proposal, causes an increase in production costs and shortens the spheroidizing time. The cost reduction effect is offset.

Further, according to Patent Document 3, a material to be rolled having a predetermined component composition is heated to a temperature range of Ae 1 point to Aem point, and then rolled at a relatively low temperature of 680 ° C. to (Aem point −30 °) 2 Rolling is performed by the above-described rolling process and an all-continuous hot rolling method including one or more intermediate cooling processes between the rolling processes. Further, after rolling, the temperature range up to 400 ° C is 5 ° C / s. A method of final cooling under the following conditions has been proposed. Although the spheroidizing annealing can be simplified by implementing this proposal, it is considered that the hardness of the material after the spheroidizing treatment is not sufficiently reduced.

Japanese Unexamined Patent Publication No. 10-298641 Japanese Laid-Open Patent Publication No. 11-286724 Japanese Unexamined Patent Publication No. 2009-275263

The present invention has been made as a solution to the above-described conventional problems. In addition to shortening the spheroidizing time during production, the high carbon steel wire material capable of sufficiently reducing hardness and the high carbon An object of the present invention is to provide a method for producing a steel wire rod.

The present invention provides the following high carbon steel wire and method for producing the high carbon steel wire.
(1) By mass%, C: 0.95 to 1.10%, Si: 0.15 to 0.70%, Mn: 1.15% or less (excluding 0%), Cr: 0.90 to 1.60%, P: 0.050% or less (not including 0%), S: 0.050% or less (not including 0%), Al: 0.100% or less (not including 0%), Ti: 0.015% or less (not including 0%), N: 0.025% or less (not including 0%), O: 0.0025% or less (not including 0%), the balance being Consisting of iron and inevitable impurities,
The ferrite crystal grain size is 20.0 μm or less,
And the Cr density | concentration in carbide | carbonized_material is 6.0% or more by mass%, The high carbon steel wire characterized by the above-mentioned.

(2) Further, by mass%, Cu: 0.25% or less (excluding 0%), Ni: 0.25% or less (excluding 0%), Mo: 0.25% or less (0% The high carbon steel wire according to (1), which contains one or more of (not included).

(3) Further, by mass%, Nb: 0.5% or less (excluding 0%), V: 0.5% or less (excluding 0%), B: 0.005% or less (0% The high carbon steel wire according to (1) or (2), which contains one or more of (not included).

(4) Further, in terms of mass%, Ca: 0.05% or less (excluding 0%), REM: 0.05% or less (not including 0%), Mg: 0.02% or less (0% (1) to (3) containing one or more of Li: 0.02% or less (not including 0%), Zr: 0.2% or less (not including 0%) The high carbon steel wire according to one.

(5) Further, by mass%, Pb: 0.5% or less (excluding 0%), Bi: 0.5% or less (excluding 0%), Te: 0.1% or less (0% The high carbon steel wire according to any one of (1) to (4), which contains one or more of (not included).

(6) The high carbon steel wire according to any one of (1) to (5), further containing, by mass%, As: 0.02% or less (not including 0%).

(7) maintain the steel at 750-870 ° C. from heating to finish rolling;
Performing finish rolling at 850 ° C. or lower,
After finish rolling, cooling to 740 ° C. at an average cooling rate of 10 ° C./s or more, and
Cooling from 740 ° C to 500 ° C at an average cooling rate of 5 ° C / s or less,
The high carbon wire manufacturing method according to any one of (1) to (6), including:

According to the production method of the high carbon steel wire and the high carbon steel wire of the present invention, from the viewpoint of cost and environmental load, it is possible to shorten the spheroidizing treatment time during production, and at the same time, the die during cold forging The life can be improved, and the hardness can be sufficiently reduced from the viewpoint of power saving during production.

As described above, carbon steel and alloy steel have been widely used as materials for machine parts used in automobiles and various industrial machines. Among them, a high carbon chromium bearing steel (SUJ material) defined by “JIS G 4805” is often used as a bearing material. When manufacturing a bearing using bearing steel such as SUJ material, usually, the bearing steel is hot-rolled into a rolled wire rod, then spheroidized, cut, and cold forged into a predetermined shape. It is manufactured by quenching and tempering, and finally finishing.

In general hot rolling of bearing steel, the material is heated to the austenite single-phase region and rolled in the austenite state. After rolling, the material is cooled relatively slowly (slow cooling). The metal structure becomes pearlite. Spheroidizing annealing is a treatment for softening a carbide (cementite) in steel by making it spherical and coarsening. When the structure before the spheroidizing annealing is pearlite, it takes a long time for the fine lamellar cementite in the pearlite to be divided and coarsely spheroidized.

There is such a situation, and as described above, by rolling after heating to the austenite + cementite two-phase region, spherical carbide (cementite) is present as it is rolled, promoting the spheroidization and coarsening of the carbide The technology development to be performed has been performed conventionally. Furthermore, by appropriately adjusting the heating, rolling, and cooling temperatures, a technique has been developed that suppresses the formation of a pearlite structure while rolling and obtains a pseudo-spherical structure, thereby eliminating or shortening the spheroidizing treatment. It was.

However, with these conventionally developed technologies, a structure in which cementite is spheroidized can be obtained, but on the other hand, there is a tendency for hardness to increase, and the spheroidizing treatment time can be sufficiently shortened. I couldn't.

(Ferrite crystal grain size)
The inventors of the present invention have made extensive studies in order to find a method capable of shortening the spheroidizing time during production and obtaining a high carbon steel wire material having sufficiently reduced hardness. As a result, during the spheroidization heating, when the matrix structure is reverse transformed from ferrite to austenite, the spheroidization of the carbides easily proceeds. I found out that I can do it.

In order to promote reverse transformation of the matrix structure from ferrite to austenite, the ferrite crystal grain size (average crystal grain size of ferrite) before reverse transformation may be 20.0 μm or less. As the crystal grain refinement increases the interfacial area of the crystal grain, which is a nucleation site during reverse transformation, reverse transformation is promoted. The ferrite crystal grain size before reverse transformation is preferably 15.0 μm or less, more preferably 10.0 μm or less, and even more preferably 7.5 μm or less. On the other hand, the ferrite crystal grain size before reverse transformation is preferably as small as possible. In the present invention, the lower limit value is not particularly specified, but the actual lower limit value is considered to be about 1.0 μm.
The ferrite crystal grain size can be obtained by the following method. For the cross section perpendicular to the longitudinal direction of the rolled wire rod, mirror polishing, etching with nital, and observation of the structure with an optical microscope, the structure size of the D / 4 position (D: diameter) of a total of 10 cross sections A total of 400 to 1000 times of photographs are taken, and the results for a total of 30 fields are averaged. The particle size number N is obtained by a comparative method, and the ferrite crystal particle size can be obtained by converting the particle size Dα (unit: μm) from the following formula.
Dα = [0.254 / 2 ^{(N-1) / 2} ] × 1000

(Cr concentration in carbide)
On the other hand, when the heating temperature of the spheroidizing treatment is increased, the diffusion rate is increased and the reverse transformation proceeds, so that the spheroidization and coarsening of the carbide (cementite) are promoted. However, if the heating temperature is too high, the amount of carbide dissolved increases, pearlite is easily generated during cooling, and the hardness increases. The slow cooling can suppress the formation of pearlite, but the time cannot be shortened.

The present inventors have intensively studied to deal with these contradictory problems. As a result, the inventors have found a method capable of shortening the spheroidizing time while maintaining the spheroidized structure by making the carbides difficult to dissolve.

It has been found that the dissolution of carbide is greatly affected by the composition of the carbide, and particularly in the case of bearing steel, it is greatly affected by the Cr concentration in the carbide. The more concentrated Cr is in the carbide, the more difficult it is to melt during heating, and the spheroidizing time can be shortened while maintaining low hardness by suppressing the formation of pearlite. Moreover, the Cr solid solution strengthening of ferrite falls with the increase in the Cr concentration of cementite, and a low hardness can be obtained in a stable state. In order to exert such an action, the Cr concentration in the carbide needs to be 6.0% by mass or more. It is preferably 6.5% by mass or more, more preferably 7.0% by mass or more. In the present invention, the upper limit value is not particularly defined, but the actual upper limit value is considered to be about 10.0% by mass.

(Component composition)
The high carbon steel wire rod of the present invention has a component range including all high carbon chromium bearing steel materials (SUJ materials 2 to 5) defined in “JIS G 4805 (2008)”. Specifically, in terms of mass%, C: 0.95 to 1.10%, Si: 0.15 to 0.70%, Mn: 1.15% or less (not including 0%), Cr: 0.00. It shall contain 90 to 1.60%. In addition, although all units are described as%, all the mass% is included unless otherwise specified, including descriptions in other specifications.

Of the above-mentioned SUJ materials, the SUJ2 materials are C: 0.95 to 1.10%, Si: 0.15 to 0.35%, Mn: 0.50% or less, Cr: 1.30 to 1. Containing 60%, SUJ3 material is C: 0.95 to 1.10%, Si: 0.40 to 0.70%, Mn: 0.90 to 1.15%, Cr: 0.90 to 1 20%, SUJ4 material is C: 0.95 to 1.10%, Si: 0.15 to 0.35%, Mn: 0.50% or less, Cr: 1.30 to 1.60 The SUJ5 material contains C: 0.95 to 1.10%, Si: 0.40 to 0.70%, Mn: 0.90 to 1.15%, Cr: 0.90 to 1.%. Contains 20%.

・ C: 0.95 to 1.10%
C is an essential element for increasing the quenching hardness and maintaining the strength at room temperature and high temperature to impart wear resistance. Therefore, it is necessary to contain 0.95% or more. However, if the C content is excessively large, giant carbides are likely to be generated and adversely affect the rolling fatigue characteristics. Therefore, the C content must be suppressed to 1.10% or less. The minimum with preferable content of C is 0.98%, and a preferable upper limit is 1.05%.

・ Cr: 0.90 to 1.60%
Cr is an element that combines with C to form fine carbides, imparts wear resistance, and contributes to improved hardenability. Further, when Cr is concentrated in the carbide, it becomes difficult to dissolve during heating, which contributes to the promotion of spheroidization. In order to exert such an effect, it is necessary to contain 0.90% or more of Cr. However, when the Cr content is excessive, coarse carbides are generated and the rolling fatigue life is reduced. Therefore, the Cr content is 1.60% or less. The preferable lower limit of the Cr content is 1.00%, and the preferable upper limit is 1.55%.

Si: 0.15 to 0.70%, Mn: 1.15% or less (excluding 0%)
Si is an element useful for improving the solid solution strengthening and hardenability of the matrix. In order to exert such effects, it is necessary to contain Si by 0.15% or more, preferably 0.20% or more (more preferably 0.25% or more). However, since the workability and machinability are remarkably lowered when the Si content is excessively increased, the Si content is 0.70% or less, preferably 0.65% or less (more preferably 0.60% or less). Should be suppressed.
Mn is an element useful for improving the solid solution strengthening and hardenability of the matrix. However, if the Mn content is excessively increased, the workability and machinability are remarkably lowered, so the Mn content is 1.15. % Or less, preferably 1.10% or less (more preferably 1.05% or less). Although the lower limit is not particularly defined, it is necessary to contain 0.1% or more, preferably 0.15% or more (more preferably 0.2% or more) in order to obtain the effects of solid solution strengthening and hardenability improvement. It is desirable to contain.

In addition, in addition to the improvement of the spheroidizing property that is the subject of the present invention, the content of various elements is usually limited in bearing steel from the viewpoint of rolling fatigue properties and machinability. In the present invention, various elements shown below are defined as follows from their respective roles. If content of various elements is in the following range, the effect of the present invention will not be hindered.

・ P: 0.050% or less (not including 0%), S: 0.050% or less (not including 0%)
P deteriorates the toughness and workability at the segregation part, and S forms inclusions and deteriorates the rolling fatigue characteristics. Further, “JIS G 4805 (2008)” defines the upper limits of P and S, and it is preferable that both be 0.025% or less. A more preferred upper limit is 0.020%, and a still more preferred upper limit is 0.015%.

・ Al: 0.100% or less (excluding 0%)
Al has the action of forming nitrides, refining the structure, and improving rolling fatigue characteristics. On the other hand, if it is contained excessively, decarburization is promoted, resulting in problems in rolling fatigue characteristics and the like. Therefore, in the present invention, the upper limit of the Al content is 0.100%. A preferable upper limit is 0.050%, a more preferable upper limit is 0.030%, and a further preferable upper limit is 0.010%.

Ti: 0.015% or less (excluding 0%)
Ti forms nitrides like Al. However, since the nitrides are relatively coarse, the contribution to the refinement of the structure is small and rolling fatigue characteristics may be deteriorated. Therefore, in the present invention, the upper limit of the Ti content is 0.015%. A preferable upper limit is 0.010%, a more preferable upper limit is 0.005%, and a further preferable upper limit is 0.002%.

・ N: 0.025% or less (excluding 0%)
N is an element effective for solid solution strengthening, and contributes to the improvement of rolling fatigue characteristics as described above. However, if the content is excessive, problems such as deterioration of workability due to strain aging are caused. Therefore, even when it is actively contained, the content is made 0.025% or less. A preferable upper limit is 0.020%, a more preferable upper limit is 0.010%, and a further preferable upper limit is 0.0050%.

O: 0.0025% or less (excluding 0%)
It is known that rolling fatigue breaks starting from inclusions mainly composed of oxide, and O is preferably reduced as much as possible. In the present invention, the upper limit of the O content is 0.0025%. A preferable upper limit is 0.0020%, a more preferable upper limit is 0.0015%, and a further preferable upper limit is 0.0010%.

As the steel material of the present invention, there is an embodiment in which the above components are included and the balance is iron and inevitable impurities. Although the essential components contained in the steel are as described above, the following elements may be contained within a predetermined range as necessary. In addition to the above-described components, the steel material of the present invention includes the following elements, with the balance being iron and inevitable impurities.

Cu: 0.25% or less (not including 0%), Ni: 0.25% or less (not including 0%), Mo: 0.25% or less (not including 0%)
Cu, Ni, and Mo all have the effect of improving the hardenability and contribute to the improvement of rolling fatigue characteristics as described above. However, if the content is excessive, problems such as deterioration of workability are caused, so Cu: 0.25% or less, Ni: 0.25% or less, and Mo: 0.25% or less. In any case, the preferable upper limit is 0.20%, the more preferable upper limit is 0.15%, and the more preferable upper limit is 0.10%. Mo is an essential element of the SUJ4 material and the SUJ5 material, and both are contained in an amount of 0.10 to 0.25%.

Nb: 0.5% or less (not including 0%), V: 0.5% or less (not including 0%), B: 0.005% or less (not including 0%)
Nb, V, and B all have the effect of improving the hardenability and contribute to the improvement of the rolling fatigue characteristics as described above, so are contained as necessary. However, if the content is excessive, characteristic deterioration is caused. Therefore, Nb: 0.5% or less, V: 0.5% or less, and B: 0.005% or less. The upper limit with preferable content of Nb and V is 0.25%, a more preferable upper limit is 0.10%, and a still more preferable upper limit is 0.05%. Moreover, the upper limit with preferable content of B is 0.004%, a more preferable upper limit is 0.003%, and a still more preferable upper limit is 0.002%.

Ca: 0.05% or less (not including 0%), REM: 0.05% or less (not including 0%), Mg: 0.02% or less (not including 0%), Li: 0.00 02% or less (not including 0%), Zr: 0.2% or less (not including 0%)
Ca, REM (Ce, Y, La, Nd), Mg, Li, and Zr all have the effect of refining oxide and sulfide inclusions, and contribute to the improvement of rolling fatigue characteristics. It is contained as necessary. However, if the content is excessive, deterioration of characteristics is caused. Therefore, Ca: 0.05% or less, REM: 0.05% or less, Mg: 0.02% or less, Li: 0.02% or less, Zr : 0.2% or less. The upper limit with preferable content of Ca and REM is 0.02%, A more preferable upper limit is 0.01%, Furthermore, a preferable upper limit is 0.005%. Moreover, the upper limit with preferable content of Mg and Li is 0.01%, A more preferable upper limit is 0.005%, Furthermore, a preferable upper limit is 0.001%. The preferable upper limit of the Zr content is 0.1%, the more preferable upper limit is 0.05%, and the more preferable upper limit is 0.01%. Note that, as described above, REM represents one or more of Ce, Y, La and Nd, and when contained alone, the single amount only needs to satisfy the above range, and when two or more are used in combination, The total amount only needs to satisfy the above range.

Pb: 0.5% or less (not including 0%), Bi: 0.5% or less (not including 0%), Te: 0.1% or less (not including 0%)
Pb, Bi, and Te all have an effect of improving machinability and are contained as necessary. However, if the content is excessive, problems such as deterioration of hot working characteristics and generation of wrinkles are caused. Therefore, Pb: 0.5% or less, Bi: 0.5% or less, Te: 0.1% The following. A preferable upper limit of the content of Pb and Bi is 0.2%, a more preferable upper limit is 0.1%, and a further preferable upper limit is 0.05%. Moreover, the upper limit with preferable content of Te is 0.05%, a more preferable upper limit is 0.02%, and a still more preferable upper limit is 0.01%.

As: 0.02% or less (excluding 0%)
As is a harmful element that causes embrittlement of the steel material, and is preferably reduced as much as possible. However, an unnecessarily reduced increase causes an increase in cost, which is not industrially preferable. Therefore, As: 0.02% or less. The upper limit of the preferable content is 0.01%, the more preferable upper limit is 0.005%, and the more preferable upper limit is 0.002%.

(Production conditions)
As described above, the bearing is rolled into a rolled wire rod by hot rolling the bearing steel, then spheroidizing annealing, cutting, cold forging into a predetermined shape, quenching and tempering, and finally finishing. Can be manufactured.

In order to make the ferrite crystal grain size 20 μm or less as defined in the present invention, it is necessary to control the finish rolling temperature in the hot rolling process and the cooling rate after finish rolling. Conventionally, from the viewpoint of softening the material, cooling after finish rolling has been generally performed by slow cooling. However, if annealing is performed after finish rolling, the austenite coarsens during the slow cooling, and as a result, the ferrite after transformation also tends to coarsen.

As a result of intensive studies by the present inventors, it has been found that the coarsening of ferrite reduces the hardness as it is rolled, but it does not necessarily lead to a decrease in hardness after spheroidizing treatment. As a result of further investigation, the inventors have suppressed the austenite coarsening by setting the final rolling temperature to 850 ° C. or lower and the average cooling rate to 740 ° C. after finishing rolling to 10 ° C./s or higher. It was found that the ferrite crystal grain size could be 20.0 μm or less.

On the other hand, it can be said that the Cr concentration in the carbide (cementite) is greatly affected by the heating temperature and the rolling temperature. In order to increase the Cr concentration in the carbide, it is necessary that the cementite remains at a high temperature. The higher the temperature, the more the diffusion is promoted and the Cr concentration proceeds. On the other hand, when the temperature is too high, the cementite dissolves and the volume fraction of the Cr-concentrated cementite decreases. Since cementite precipitated during cooling does not have a high Cr concentration, when the cementite fraction during cooling increases, the proportion of carbides with a high Cr concentration decreases. In particular, the Cr concentration in cementite that precipitates during cooling decreases as it precipitates at low temperatures. Based on these findings, the present inventors have studied, and as a result, the temperature from heating to finish rolling is set to a temperature range of 750 to 870 ° C., and the average cooling rate from 740 ° C. to 500 ° C. is 5 ° C. / It was confirmed that the Cr concentration in the carbide could be 6.0% by mass or more by setting it to s or less.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples, but may be implemented with appropriate modifications within a scope that can meet the gist of the present invention. These are all included in the technical scope of the present invention.

In the examples of the present invention, first, slabs were manufactured by continuous casting using steels having respective component compositions shown in Table 1, and the slabs were disassembled and rolled into 155 mm square steel slabs. Using this steel slab, rolled wire rods were obtained under the production conditions shown in Tables 2 and 3. Various measurements and tests shown below were carried out using this rolled wire. In each component composition shown in Table 1, the balance is iron and inevitable impurities.

(Ferrite crystal grain size)
The ferrite crystal grain size was determined by performing mirror polishing on the cross section perpendicular to the longitudinal direction of the rolled wire rod, etching with nital, and observing the structure with an optical microscope. ), 400-1000 times photographs were taken according to the tissue size, and the results for a total of 30 fields were averaged. The grain size number N of the ferrite crystal grain size was determined by a comparison method, and converted to the grain size Dα (unit: μm) from the following formula.
Dα = [0.254 / 2 ^{(N-1) / 2} ] × 1000

The high carbon steel wire of the present invention may have a mixed structure of ferrite and pearlite or a structure mainly composed of pearlite. For pearlite, the pearlite nodule (block) size corresponding to the crystal grain size of ferrite is measured. did. Regarding the particle size measurement of ferrite and pearlite, “JIS G 0551” describes a particle size measurement method for only the ferrite portion excluding the pearlite portion. On the other hand, for the measurement of pearlite nodules (blocks), as described in “Takahashi, Nagumo, Asano, Journal of the Japan Institute of Metals, 42, 1978, p. 708”, the crystal unit is determined by the contrast after etching. did. In the case of a mixed structure, the ferrite particle size and pearlite nodule size were collectively measured.

(Cr concentration in carbide)
The Cr concentration in the carbide was determined by measuring the Cr concentration in the electrolytically extracted residue. First, the rolled wire was cut to a length of 20 mm, and then the portion from the outer surface to D / 4 (D: diameter) was removed by grinding to obtain a sample for electrolysis. Next, in order to remove the processed layer, preliminary electrolysis was performed by a constant current electrolysis method using a 10% AA-based electrolytic solution (% is a mass ratio). Thereafter, electrolysis by a constant current electrolysis method using a 10% AA-based electrolyte as main electrolysis was performed, and the residue was collected by filtering the electrolyte solution by a suction filtration method. For filtration, a polycarbonate mesh having a pore size of 0.1 μm was used. The obtained residue was treated for analysis, and then the Cr concentration was measured by ICP issuance analysis.

(Spheroidizing annealing conditions)
(H1) Normal conditions: Soaking 785 ° C. × 6 hours → Slow cooling (cooling rate: 10 ° C./h)
(H2) Shortening conditions: soaking 785 ° C. × 6 hours → slow cooling (cooling rate: 30 ° C./h)

(Vickers hardness)
Vickers hardness was measured using each rolled wire after spheroidizing annealing. About the cross section perpendicular | vertical with respect to the longitudinal direction of a rolled wire rod, the Vickers hardness (Hv) of a total of 4 points | pieces was measured for D / 4 position (D: diameter) of a rolled wire rod, after a mirror surface grinding | polishing, and making a load 1 kg. Let the average value of 4 points | pieces be the Vickers hardness of each rolling wire after spheroidizing annealing.

The test results are shown in Tables 2-3. In this test, even when spheroidizing annealing is carried out under shortening conditions, a test with a Vickers hardness of 190 Hv or less is accepted.

No. 8, 9, 11 to 14, 17 to 19, 21, 22, 24 to 37 are examples of the invention that satisfy the requirements of the present invention. Even when the spheroidizing annealing is performed under a shortened condition, it is the same as the normal condition. The Vickers hardness was 190 Hv or less. From this result, no. Nos. 8, 9, 11 to 14, 17 to 19, 21, 22, 24 to 37 are high carbon steels capable of shortening the spheroidizing time during production and sufficiently reducing the hardness after spheronizing. It can be said that it is a wire.

In contrast, No. which does not satisfy the requirements of the present invention. In 1 to 7, 10, 15, 16, 20, and 23, when the spheroidizing annealing is performed under a shortened condition (No. 2 to 4 are normal conditions), the Vickers hardness exceeds 190 Hv.

Although this application has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on April 20, 2011 (Japanese Patent Application No. 2011-094098), the contents of which are incorporated herein by reference.

Claims

% By mass: C: 0.95 to 1.10%, Si: 0.15 to 0.70%, Mn: 1.15% or less (excluding 0%), Cr: 0.90 to 1.60 %, P: 0.050% or less (not including 0%), S: 0.050% or less (not including 0%), Al: 0.100% or less (not including 0%), Ti: 0 0.15% or less (excluding 0%), N: 0.025% or less (not including 0%), O: 0.0025% or less (not including 0%), the balance being iron and inevitable Consisting of mechanical impurities
The ferrite crystal grain size is 20.0 μm or less,
And the Cr density | concentration in carbide | carbonized_material is 6.0% or more by mass%, The high carbon steel wire characterized by the above-mentioned.
Further, by mass%, Cu: 0.25% or less (excluding 0%), Ni: 0.25% or less (not including 0%), Mo: 0.25% or less (not including 0%) The high carbon steel wire according to claim 1, which contains at least one of the following.
Furthermore, by mass%, Nb: 0.5% or less (excluding 0%), V: 0.5% or less (not including 0%), B: 0.005% or less (not including 0%) The high carbon steel wire according to claim 1 or 2, comprising at least one of the following.
Furthermore, in mass%, Ca: 0.05% or less (excluding 0%), REM: 0.05% or less (not including 0%), Mg: 0.02% or less (not including 0%) , Li: 0.02% or less (excluding 0%), Zr: 0.2% or less (not including 0%) High carbon steel wire.
Furthermore, by mass%, Pb: 0.5% or less (excluding 0%), Bi: 0.5% or less (not including 0%), Te: 0.1% or less (not including 0%) The high carbon steel wire according to any one of claims 1 to 4, comprising one or more of the following.
Furthermore, the high carbon steel wire according to any one of claims 1 to 5, further comprising, by mass%, As: 0.02% or less (not including 0%).
Maintaining the steel at 750-870 ° C from heating to finish rolling;
Performing finish rolling at 850 ° C. or lower,
After finish rolling, cooling to 740 ° C. at an average cooling rate of 10 ° C./s or more, and
Cooling from 740 ° C to 500 ° C at an average cooling rate of 5 ° C / s or less,
The manufacturing method of the high carbon wire as described in any one of Claims 1 thru | or 6 containing these in this order.