JP2022153697A - Wire for bearing - Google Patents

Abstract

To provide a wire for bearings that can be subjected to a drawing process without applying intermediate annealing, by improving drawing processability of the wire for bearings.MEANS FOR SOLVING THE PROBLEM: A wire for bearings comprises as a chemical composition, in mass%, C: 0.95 to 1.10%, Si: 0.10 to 0.70%, Mn: 0.20 to 1.20%, Cr: 0.90 to 1.60%, Al: 0.050% or less, P: 0.020% or less, S: 0.015% or less, O: 0.0020% or less, N: 0.030% or less, and the balance being Fe and impurities, containing proeutectoid cementite, and when a radius of the wire is set to R, an area ratio of proeutectoid cementite is 3.0% or less at a center within (1/2) R from a center of a cross section of the wire, the area ratio of pearlite is 94.0% or more, an average thickness of proeutectoid cementite is 0.8 μm or less, and an average aspect ratio of proeutectoid cementite is 5.0 or more.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a wire rod for bearings having excellent wire drawability.

High-carbon chromium bearing steel materials specified in JIS G 4805:2019 are used as materials for steel balls of ball bearings, rollers of roller bearings, and the like. These bearing steel materials are hypereutectoid steels having a C content equal to or higher than the eutectoid point, and since Cr is added, proeutectoid cementite and martensite structures appear in the as-hot-rolled state. Machinability is remarkably lowered. Therefore, JIS G 4805:2019 describes that hot-rolled steel is sometimes subjected to spheroidizing annealing in order to improve cold workability.
In particular, when manufacturing small-diameter bearing products such as needle bearings, hot-rolled wire rods are generally spheroidized and then drawn.

However, even if a hot-rolled wire rod is spheroidized and annealed for wire drawing in manufacturing a small-diameter bearing component, sufficient wire drawability cannot necessarily be obtained.
Therefore, after the hot-rolled wire that has been spheroidized and annealed is drawn, it is again annealed at a low temperature and then drawn. Such an increase in the number of times of annealing causes a decrease in production efficiency and an increase in cost.
In recent years, in order to reduce costs, there has been a demand for a wire rod for bearings that is excellent in wire drawability and that can omit low-temperature annealing when manufacturing bearing parts.

A wire rod having a perlite structure has been proposed as a wire rod for bearings having excellent wire drawability.
For example, the wire rod for bearings described in Patent Document 1 has a microstructure consisting of pearlite, pro-eutectoid cementite, and the remainder, and has a reduced area ratio of pro-eutectoid cementite and a specific hardness distribution, thereby improving wire drawability. It discloses a technology that allows
Patent Document 2 discloses a wire or bar steel with improved wire drawability due to a reduction in the aspect ratio of the proeutectoid cementite and a reduction in the average diameter of the regions surrounded by the proeutectoid cementite.

WO2016/063867 JP-A-2003-129176

Patent Literature 1 and Patent Literature 2 propose steel materials for bearings in which annealing before the first wire drawing process can be omitted. Furthermore, if the intermediate annealing can be omitted, it would be of great industrial advantage.
SUMMARY OF THE INVENTION An object of the present invention is to provide a wire rod for bearings excellent in wire drawability, which can omit part of the annealing before the first wire drawing and the intermediate annealing in the manufacturing process of the bearing component.

The gist of the present invention is as follows.
(1) The bearing wire rod according to one aspect of the present invention has a chemical composition of C: 0.95 to 1.10%, Si: 0.10 to 0.70%, and Mn: 0.20% by mass. ~1.20%, Cr: 0.90 to 1.60%, Al: 0.050% or less, P: 0.020% or less, S: 0.015% or less, O: 0.0020% or less, N : containing 0.030% or less, the balance being Fe and impurities, containing pro-eutectoid cementite, and, where R is the radius of the wire, within (1/2) R from the center of the cross section of the wire In the central portion, the area ratio of proeutectoid cementite is 3.0% or less, the area ratio of pearlite is 94.0% or more, the average thickness of proeutectoid cementite is 0.8 μm or less, and the The proeutectoid cementite has an average aspect ratio of 5.0 or more.
(2) In the bearing wire rod described in (1) above, Mo: 0.25% or less, B: 0.0050% or less, Ti: 0.050% or less, V: 0.20% or less, Nb: 0.20% or less, Cu: 0.25% or less, Ni: 0.20% or less may be contained.
(3) In the bearing wire rod described in (1) or (2) above, proeutectoid cementite having a thickness of 0.5 μm or more has an area ratio of 0.5% or less, and the standard deviation of hardness in the cross section is The Vickers hardness may be HV25 or less.
(4) In the bearing wire rod according to any one of items (1) to (3), the area ratio of spherical pearlite in which the aspect ratio of lamellar cementite in the pearlite is 2.0 or less is 10.0% or less. may be

According to the aspect, excellent wire drawability can be achieved by appropriately controlling the structure, proeutectoid cementite, and pearlite of the bearing wire. Therefore, the wire rod for bearings of the present invention can be drawn without being spheroidized and annealed, thereby improving the productivity of bearings and reducing manufacturing costs.

It is an SEM observation example of pro-eutectoid cementite. FIG. 3 is a schematic diagram showing the precipitation state of proeutectoid cementite at prior austenite grain boundaries. It is a figure explaining the measuring method of the thickness and length of pro-eutectoid cementite. It is a figure explaining the measuring method of the thickness and length of pro-eutectoid cementite. It is a figure explaining the measuring method of the thickness and length of pro-eutectoid cementite.

Metal structures other than pearlite, ie, proeutectoid cementite, ferrite, and bainite, in the wire rod for bearings impede the wire drawability of the wire rod. On the other hand, it is difficult to manufacture a bearing wire completely free of proeutectoid cementite, ferrite and bainite.
The present inventors have studied in detail the relationship between the structure of the bearing wire and the wire drawability. As a result, the present inventors found that although excessive precipitation of proeutectoid cementite reduces wire drawability,
- to suppress the area fraction of proeutectoid cementite,
- reducing the thickness of the pro-eutectoid cementite, and
- It was found that by increasing the aspect ratio of pro-eutectoid cementite, wire drawability is improved even if bainite and ferrite are generated to some extent.

An embodiment of a wire rod for bearings excellent in wire drawability according to the present invention based on the above findings will be described below. The embodiments described below are for better understanding of the gist of the present invention, and the bearing wire according to the present invention is not limited to the description of the following embodiments.
The wire rod for bearings according to the present embodiment (hereinafter sometimes simply referred to as wire rod) has a chemical composition of C: 0.95 to 1.10% and Si: 0.10 to 0.70% by mass. %, Mn: 0.20 to 1.20%, Cr: 0.90 to 1.60%, Al: 0.050% or less, P: 0.020% or less, S: 0.015% or less, O: 0.0020% or less N: 0.030% or less Mo: 0.25% or less B: 0.0050% or less Ti: 0.050% or less V: 0.20% or less Nb: 0.05% or less It contains 20% or less, Cu: 0.25% or less, Ni: 0.20% or less, and the balance consists of Fe and impurities.

In the numerical ranges described in this specification, the numerical range represented by using "~" is a range that includes the numerical values described before and after "~" as lower and upper limits, unless otherwise specified. means. Therefore, for example, 0.95% to 1.10% means a range of 0.95% or more and 1.10% or less.

The steel composition of the wire rod for bearings according to this embodiment will be described below. Unless otherwise specified, the unit of content is % by mass.
<C (carbon): 0.95 to 1.10%>
C is an element that increases the wear resistance and rolling fatigue strength of bearing products. Therefore, the wire contains 0.95% or more of C. The C content is preferably 0.96% or more, more preferably 0.97% or more.
On the other hand, if the C content exceeds 1.10%, the amount of precipitated proeutectoid cementite increases and the wire drawability is impaired, so the C content is made 1.10% or less. The C content is preferably 1.05% or less, more preferably 1.03% or less.

<Si (silicon): 0.10 to 0.70%>
Si is an element useful as a deoxidizing agent during steelmaking. In addition, Si suppresses the precipitation of proeutectoid cementite during cooling immediately after the hot rolling of the bearing wire. Furthermore, Si has the effect of increasing the ferrite strength in pearlite. In order to exhibit such action, the wire contains 0.10% or more of Si. The Si content is preferably 0.15% or more, more preferably 0.20% or more.
On the other hand, if the wire rod contains excessive Si, the completion of transformation during cooling after hot rolling is delayed, so supercooled structures such as bainite and martensite are likely to occur. Therefore, wire drawability is lowered. Therefore, the Si content is set to 0.70% or less. The Si content is preferably 0.50% or less, more preferably 0.40% or less.

<Mn (manganese): 0.20 to 1.20%>
Mn suppresses the formation of proeutectoid cementite during cooling after wire rod rolling. Mn also improves the hardenability of steel and the wear resistance of bearing products. In order to exhibit such effects, the wire contains 0.20% or more of Mn. The Mn content is preferably 0.25% or more, more preferably 0.28% or more.
However, if the wire rod contains an excessive amount of Mn, martensite, which is harmful to wire drawability, is likely to occur during the cooling process after hot rolling. Also, Mn takes a long time to complete the transformation, resulting in a decrease in productivity. Therefore, the upper limit of the Mn content is made 1.20% or less. The Mn content is preferably 1.00% or less, more preferably 0.50% or less.

<Cr (chromium): 0.90 to 1.60%>
Cr raises the solid solution temperature of cementite, uniformly disperses spherical cementite after quenching of the bearing product, and improves wear resistance. Also, Cr suppresses the formation of proeutectoid cementite during cooling after wire rod rolling. However, if the Cr content is less than 0.90%, sufficient effects cannot be obtained. Therefore, the Cr content is 0.90% or more, preferably 1.00% or more, and more preferably 1.30% or more.
On the other hand, if the Cr content exceeds 1.60%, the hardenability becomes excessive, so supercooled structures such as bainite and martensite are likely to occur in the cooling process after wire rod rolling. Therefore, the Cr content is 1.60% or less, preferably 1.50% or less, and more preferably 1.45% or less.

<Al (aluminum): 0.050% or less>
Al may not be contained. Al added during steelmaking is effective as a deoxidizing element. On the other hand, when the Al content exceeds 0.050%, the Al oxide inclusions in the steel become coarse, so that the wire drawability of the wire rod and the wear resistance of the bearing parts deteriorate. Therefore, the Al content is set to 0.050% or less. The Al content is preferably 0.030% or less in order to more reliably prevent deterioration of wire drawability and abrasion resistance.
The lower limit of the Al content may be 0% or more than 0%, but when actively used as a deoxidizing element, the Al content is preferably 0.005% or more, more preferably 0.010%. % or more.

<P (phosphorus): 0.020% or less>
P is an impurity. P degrades the wire drawability of the wire by segregating at grain boundaries. It is preferable to reduce the P content as much as possible. Therefore, the P content is 0.020% or less, preferably 0.015% or less, and more preferably 0.010% or less.
The lower limit of the P content does not have to be particularly limited, but excessive reduction increases the production cost, so the lower limit may be 0.005%.

<S (sulfur): 0.015% or less>
S is an impurity. S generates MnS and lowers the wire drawability of the wire. Therefore, it is preferable to reduce the S content as much as possible. Therefore, the S content is 0.015% or less, preferably 0.010% or less, and more preferably 0.008% or less.
The lower limit of S does not need to be particularly limited, but excessive reduction increases manufacturing costs, so the lower limit may be 0.003%.

<O (oxygen): 0.0020% or less>
O is an impurity. If the O content exceeds 0.0020%, the wire drawability of the wire rod and the wear resistance of the bearing parts are lowered due to the formation of oxide inclusions. Therefore, the O content is 0.0020% or less, preferably 0.0015% or less, and more preferably 0.0010% or less.
The lower limit of the O content is not particularly limited, but from the viewpoint of steelmaking costs, the lower limit of the O content may be 0.0001%. Considering normal operating conditions, the O content is preferably 0.0005% to 0.0020%, more preferably 0.0005% to 0.0010%.

<N (nitrogen): 0.030% or less>
N is an impurity. If the N content exceeds 0.030%, coarse inclusions are formed, and the wire drawability of the wire rod and the wear resistance of the bearing parts deteriorate. Therefore, the N content is 0.030% or less, preferably 0.020% or less, and more preferably 0.015% or less.
N combines with Al, Ti, V, Nb and B to form nitrides. The nitrides function as pinning particles at the austenite grain boundaries to refine the crystal grains. Therefore, the steel may contain N if the N content is small. For example, the lower limit of N content may be 0.003%. In order to further enhance the effect of refining crystal grains, the lower limit of the N content may be 0.005%.

The steel composition of the wire according to the present embodiment may positively contain one or more of the following arbitrary elements in the wire. Since these elements do not have to be contained in the wire, the lower limit is 0%.

<Mo (molybdenum): 0.25% or less>
Mo may be contained in the wire in order to improve hardenability. In order to obtain this effect, the Mo content is preferably 0.05% or more, more preferably 0.10% or more.
However, if the Mo content exceeds 0.25%, the hardenability becomes excessive, and supercooled structures such as bainite and martensite tend to occur in the cooling process after hot rolling. Therefore, the Mo content is 0.25% or less, preferably 0.23% or less, and more preferably 0.20% or less.

<B (boron): 0.0050% or less>
B may be contained in the wire in order to improve hardenability. In order to obtain this effect, the B content is preferably 0.0005% or more, more preferably 0.0010% or more.
However, if the wire rod contains an excessive amount of B, carbides such as Fe ₂₃ (CB) ₆ are formed in the austenite, deteriorating wire drawability. Therefore, the B content is 0.0050% or less, preferably 0.0040% or less, more preferably 0.0030% or less.

<Ti (titanium): 0.050% or less>
When Ti forms coarse oxides, it may reduce wire drawability. On the other hand, when it precipitates as a nitride, it may be contained in the wire in order to prevent coarsening of the austenite crystal grains. The Ti content for preventing the oxide from coarsening is 0.050% or less, preferably 0.030% or less, and more preferably 0.020% or less. When Ti is contained in the wire for the purpose of preventing grain coarsening, the Ti content is preferably 0.005% or more, more preferably 0.010% or more.

<V (vanadium): 0.20% or less>
<Nb (niobium): 0.20% or less>
Since V and Nb are precipitated as fine carbonitrides and have the effect of increasing the strength of the base material, they may be contained in the wire. The V content and Nb content for suppressing the formation of coarse precipitates are each 0.20% or less, preferably 0.15% or less, and more preferably 0.10% or less. When V and Nb are contained in the wire, the V content and the Nb content are each preferably 0.03% or more, more preferably 0.05% or more, from the viewpoint of obtaining the above effects.

<Cu (copper): 0.25% or less>
Cu may be contained in the wire in order to improve hardenability. In order to exhibit the effect of hardenability, the Cu content is preferably 0.05% or more, more preferably 0.08% or more.
When the content of Cu exceeds 0.25% in the wire rod, CuS precipitates at the austenite grain boundary and causes flaws in the steel ingot and the wire rod in the manufacturing process of the wire rod. In order to prevent such adverse effects, the Cu content is 0.25% or less. The Cu content is preferably 0.20% or less, more preferably 0.18% or less.

<Ni (nickel): 0.20% or less>
Ni has the effect of increasing the hardenability and further increasing the toughness of the bearing product, so it may be contained in the wire rod. The content of 0.05% or more is preferable in order to exhibit such effects. More preferably, the Ni content is 0.08% or more.
On the other hand, if the Ni content exceeds 0.20% in the wire rod, it is not preferable because it takes a long time to complete the pearlite transformation in the cooling after the wire rod rolling. Therefore, the Ni content is set to 0.20% or less. The Ni content is preferably 0.18% or less, more preferably 0.15% or less.

<Remainder>
The remainder of the chemical composition of the bearing wire in this embodiment consists of Fe and impurities. The term "impurity" as used herein means an element that is mixed in from the ore, scrap, or the environment during the manufacturing process that is used as a raw material for steel.

<Perlite area ratio: 94.0% or more>
The main metal structure of the wire according to this embodiment is pearlite. Thereby, wire drawability can be improved. Specifically, the area ratio of pearlite is 94.0% or more, preferably 96.0% or more, and more preferably 97.0% or more.

The rest of the structure other than pearlite contains proeutectoid cementite. The non-perlite residual structure may also include ferrite, bainite, spheroidal cementite and martensite.
Proeutectoid cementite usually has the following properties.
・Because it is difficult to deform, it splits during wire drawing ・Proeutectoid cementite has the property of forming voids at the interface with ferrite. Especially thick pro-eutectoid cementite has a remarkable effect.
However, the inventors
- regulating the formation of proeutectoid cementite to a small amount,
- thinning the thickness of the proeutectoid cementite, and
- increasing the aspect ratio of the proeutectoid cementite,
Therefore, it was found that wire drawability can be improved even if pro-eutectoid cementite exists in the structure.

Pro-eutectoid cementite is cementite precipitated at prior austenite grain boundaries. One prior austenite grain forms a polygonal outline, therefore, as shown in FIG. do. If the amount of pro-eutectoid cementite is small, polygonal traces may not be possible. In such cases, the cementite existing at the boundary between pearlite colonies is also determined to be pro-eutectoid cementite. Another feature is that the pro-eutectoid cementite is often thicker than the lamellar cementite precipitated in the prior austenite grains. Among the pro-eutectoid cementite judged to be pro-eutectoid cementite from such characteristics, those having a thickness of 0.1 μm or more are defined as pro-eutectoid cementite in the present application.

<Area ratio of proeutectoid cementite: 3.0% or less>
In the cross section of the wire, the area ratio of proeutectoid cementite in the center within (1/2)R (R represents the radius of the wire) from the center is 3.0% or less of the entire structure. Thereby, wire drawability can be improved. The area ratio of proeutectoid cementite is preferably 2.0% or less, more preferably 1.0% or less.
In addition, the lower the amount of pro-eutectoid cementite, the better, and the lower limit of the area ratio of pro-eutectoid cementite may be more than 0%. On the other hand, it is difficult in industrial production to completely suppress proeutectoid cementite within the composition range of the present application. From the viewpoint of production equipment costs, the area ratio of proeutectoid cementite is preferably 0.1% or more.

<Area ratio of proeutectoid cementite having a thickness of 0.5 μm or more>
In order to obtain suitable wire drawability, the area ratio of proeutectoid cementite having a thickness of 0.5 μm or more in the center within (1/2) R from the center of the cross section of the wire is 0.5 in the entire structure. % or less, more preferably 0.4% or less of the whole tissue, and more preferably 0.3% or less of the whole tissue.

<Average thickness of proeutectoid cementite: 0.8 μm or less>
In order to obtain suitable wire drawability, the average thickness of the proeutectoid cementite in the central portion within (1/2) R from the center of the cross section of the wire is 0.8 µm or less, preferably 0.5 µm or less. and more preferably 0.3 μm or less.

<Average aspect ratio of proeutectoid cementite: 5.0 or more>
In order to obtain suitable wire drawability, the proeutectoid cementite has an average aspect ratio of 5.0 or more, preferably 7.0 or more, in the center within (1/2) R from the center of the cross section of the wire. and more preferably 10.0 or more.

<Ferrite, Bainite, Martensite Structure>
Ferrite, bainite, and martensite differ from pearlite in the amount of deformation during wire drawing, and therefore serve as locations where cracks occur or propagate. Therefore, ferrite, bainite, and martensite are the cause of deterioration in wire drawability. However, by controlling the area ratio and morphology of the proeutectoid cementite and improving the wire drawability as described above, the desired wire drawability can be secured even if a small amount of ferrite, bainite, and martensite precipitate. The inventors have found that it is possible. Therefore, these area ratios may exceed 0% of the entire tissue.
Although the total area ratio of ferrite, bainite, and martensite is not particularly defined in the present embodiment, it is preferably 6.0% or less, more preferably 4.0% or less, of the entire structure.

<Area ratio of spherical perlite>
A part of the plate-shaped lamellar cementite deforms into a spherical shape due to the cooling rate during pearlitic transformation and the holding at a high temperature after pearlitic transformation. In the present application, pearlite that is part of a lamellar cementite structure and has an aspect ratio of 2.0 or less is defined as spherical pearlite. Spherical pearlite differs from lamellar pearlite in the amount of deformation during working, so it becomes a site where cracks propagate during working, which is a factor in the deterioration of wire drawability.
In order to improve the wire drawability of the wire, the area ratio of spherical pearlite is preferably 10.0% or less of the entire structure. More preferably, the area ratio of spherical pearlite is 8.0% or less, more preferably 6.0% or less, of the entire structure.

<Method for measuring the area ratio of proeutectoid cementite and the area ratio of pearlite>
The area ratio of proeutectoid cementite and the area ratio of pearlite are measured by observation using a scanning electron microscope (SEM). A sample for measurement can be prepared by the following procedure.
1. Cut the wire and fill it with resin so that the cross section perpendicular to the longitudinal direction can be observed.
2. The resin-filled wire is polished with polishing paper or alumina abrasive grains to mirror finish.
3. The mirror-finished portion is corroded by immersing it in a picral solution having a picric acid concentration of 3% and a temperature of 40° C. for 60 seconds. The picral solution is a mixed solution of picric acid and ethyl alcohol.
4. After the corroded portion is immediately and thoroughly washed with water, it is quickly dried with cool or warm air to obtain an observation surface.

From the observed surface thus obtained, the area ratio of each metal structure is measured by the following method.
1. At the center of the cross-sectional sample of the wire corroded with the picral solution, in the circular area within (1/2) R from the center, draw crosshairs perpendicular to each other with the center of the circle as the intersection, and on the vertical and horizontal lines ( 1/4) Take 5 points in the R interval. Since the observation positions of the center points of the circles overlap, a total of 9 points (5 points + 5 points - 1 point) are used as the observation positions.
2. Subsequently, a range of at least 17 μm×17 μm is photographed with an SEM at a magnification of 5000 for nine observation positions.
3. In the 17 μm×17 μm area of the photographed SEM image, 15 straight lines are drawn vertically and horizontally at intervals of 1 μm in a grid pattern, and the area is partitioned so that there are 225 intersection points.
4. After that, the tissue on the intersection point is determined, and the area ratio of the tissue is calculated from the ratio of the intersection point determined to the specific tissue to the total number of intersection points (225 points/field of view)×9 fields of view=2025 points.
In particular,
· The area ratio (%) of the pro-eutectoid cementite is calculated by (total number of intersection points determined to be pro-eutectoid cementite / 2025) × 100,
The perlite area ratio (%) is calculated by (total number of intersection points determined to be perlite/2025)×100.
Similarly, the area ratio (%) of the pro-eutectoid cementite having a thickness of 0.5 μm or more is calculated by (total number of intersections judged to be pro-eutectoid cementite having a thickness of 0.5 μm or more/2025)×100.

<Method for measuring area ratio of spherical pearlite>
Subsequently, the area ratio of spherical pearlite is also measured using the same sample and the same method as for measuring the area ratio of proeutectoid cementite and the area ratio of pearlite. If, among 2025 intersections, the intersection is in pearlite and the aspect ratio of the lamellar cementite on or closest to the intersection is 2.0 or less, the texture at the intersection is determined to be spherical pearlite.
The area ratio (%) of spherical pearlite is calculated by (total number of intersection points determined to be spherical pearlite/2025)×100.
If the intersection points are in proeutectoid cementite, bainite, ferrite, or martensite, they are not judged to be spherical pearlite.

<Method for measuring pro-eutectoid cementite thickness and pro-eutectoid cementite aspect ratio>
The thickness of the pro-eutectoid cementite and the aspect ratio of the pro-eutectoid cementite are measured at the same time when the area ratio of the pro-eutectoid cementite is measured by the above method.

<Definition of thickness and length of proeutectoid cementite>
The definition of the thickness and length of the proeutectoid cementite will be described in detail below.
FIG. 2 is a schematic diagram showing the precipitation state of proeutectoid cementite at prior austenite grain boundaries. FIG. 3 is a diagram illustrating a method for measuring the thickness and length of the proeutectoid cementite 10a of FIG. FIGS. 4 and 5 are diagrams for explaining methods of measuring the thickness and length of the proeutectoid cementites 10b and 10c of FIG. 2, respectively.
In the wire of the present invention, the prior austenite grain boundaries may not be clearly observed by SEM observation. Nevertheless, as shown in FIG. 2, it is clear that the imaginary line connecting adjacent proeutectoid cementites is the prior austenite grain boundary, and determination of the prior austenite grain boundary is easy.

The pro-eutectoid cementite precipitates along the prior austenite grain boundaries. Specifically, as shown in FIG. 2, the proeutectoid cementites 10a to 10d are precipitated along the prior austenite grain boundaries 20. As shown in FIG. For each proeutectoid cementite, the length is defined in the direction along the prior austenite grain boundaries and the thickness is defined in the direction perpendicular to the prior austenite grain boundaries.
The thickness of the pro-eutectoid cementite is measured at three locations in the direction along the prior austenite grain boundary at intervals that divide the length into quarters, and the average of these measured values is defined as the thickness of the pro-eutectoid cementite. . In addition, in the measurement of the proeutectoid cementite thickness, if the measurement point is a branch point or an edge, the point is not included in the average.

That is, in FIG. 3, the length of the pro-eutectoid cementite 10a is L1, and the thickness of the pro-eutectoid cementite 10a is the average of T1, T2, and T3. As for the proeutectoid cementite having branches, such as the proeutectoid cementite 10b in FIG. 2, the total length of each branch is defined as the length of the proeutectoid cementite.
That is, in FIG. 4, the length of the proeutectoid cementite 10b is the sum of OA, OB and OC. In addition, the thickness of the pro-eutectoid cementite is measured at three locations in each branch at intervals that divide the length into four equal parts in the direction along the prior austenite grain boundary as described above, and the average of these measured values is the thickness of the pro-eutectoid cementite. Define thickness. That is, in FIG. 4, the thickness of the proeutectoid cementite 10b is the average of TA1, TA2, TA3, TB1, TB2, TB3, TC1, TC2, and TC3.

For the pro-eutectoid cementite having a curved shape along the prior austenite grain boundary, such as the pro-eutectoid cementite 10c in FIG. 2, the length is measured along the prior austenite grain boundary. That is, in FIG. 5, the length of the proeutectoid cementite 10c is the sum of O'D and O'E. In addition, the thickness is divided at the bent point, and each part is measured at three points in the direction along the former austenite grain boundary as described above, and the length is divided into four equal parts, and the average of the measured values is the proeutectoid Defined as cementite thickness.
That is, in FIG. 5, the thickness of the proeutectoid cementite 10c is the average of TD1, TD2, TD3, TE1, TE2, and TE3. The total length of the proeutectoid cementite in FIG. 2 is the sum of the lengths of the proeutectoid cementites 10a, 10b, 10c and 10d.

The same work is performed on the same wire in 10 fields of view, the average value is obtained, and the average value is defined as the average thickness of the proeutectoid cementite of the wire. The average aspect ratio of the proeutectoid cementite is obtained by dividing the length by the thickness of each proeutectoid cementite measured above, and the average is defined as the average aspect ratio of the proeutectoid cementite of the wire rod.

<Hardness distribution of wire>
In order to obtain suitable wire drawability, it is preferable to control the hardness distribution of the wire. If the degree of non-uniformity in hardness is large within the wire, the deformation becomes non-uniform within the cross section even during wire drawing. Therefore, it becomes a cause of delamination in the wire drawn material, and the wire drawability deteriorates. Therefore, the standard deviation of hardness in the cross section of the wire is preferably 25 HV or less in Vickers hardness, and more preferably 20 HV or less in Vickers hardness.
The hardness distribution of the wire is measured on a straight line passing through the center point in the cross section of the wire. On a straight line, positions 70 μm from the surface are set as the start and end points, respectively, and 9 points are measured at equal intervals between the two points (that is, 11 points are measured on a straight line having a diameter of one). A similar operation is performed on the orthogonal straight lines, and the standard deviation of a total of 21 points (measurement of the center point is made once) is taken as the hardness distribution of the wire.

<Tensile strength of wire>
In this embodiment, the tensile strength of the wire is not specified, but it is preferably 1300 MPa or more, more preferably 1350 MPa or more, and still more preferably 1400 MPa or more. The increase in tensile strength is brought about by the refinement of the lamellar spacing, and the refinement of the lamellar spacing promotes spheroidization in annealing after wire drawing. In addition, an increase in tensile strength results in a reduction in the thickness of proeutectoid cementite and a reduction in variation in hardness, thereby improving wire drawability. However, if the tensile strength is excessively high, the handling during wire drawing and the load on the wire drawing machine increase. In addition, during pickling or mechanical descaling before wire drawing, wire breakage occurs due to penetration of hydrogen and deterioration of bending workability. Therefore, the tensile strength of the wire is preferably 1700 MPa or less, more preferably 1600 MPa or less.
The tensile strength of the wire is measured by performing a tensile test according to JIS Z 2241:2011. The tensile strength of the wire is obtained by calculating the average value of the tensile strengths obtained from the three samples.

<Method for evaluating wire drawability>
The drawability of a wire rod for bearings is industrially evaluated, for example, by the number of wire breakages per lot when wire rod coils are drawn. Further, in the field of high-carbon steel mainly composed of pearlite, such as the steel material for bearings of the present invention, the torsional properties of the drawn wire are used as an index of the drawability. In the present invention, in order to predict the possibility of wire breakage during wire drawing, the true strain value at which delamination occurs when a wire rod is subjected to a twisting test is employed.

<Manufacturing method of wire>
Next, a method for manufacturing a wire according to this embodiment will be described.
The manufacturing method described below is an example of a method of manufacturing a wire, and is not limited to the following procedures and methods. is also possible.

As an example of the wire manufacturing method according to the present embodiment, first, steel having the chemical composition described above is cast. After casting, the slab may be subjected to a soaking treatment (a heat treatment for reducing segregation). After that, by blooming, a billet having a size suitable for wire rod rolling is produced and subjected to wire rod rolling.
Wire rod rolling is performed in a hot state by heating a steel billet.
Hot rolling is performed under the condition that austenite single phase having an average grain size of 15 μm to 50 μm is obtained at the end of rolling (first step).
After the end of the first step, cooling is performed at an average cooling rate of 10° C./second or more to cool to an arbitrary temperature in the range of 600 to 670° C. in a cooling time of 25 seconds or less from the start of cooling (second step). .
After completion of the second step, the temperature is maintained at the temperature at the end of the second step for 50 to 200 seconds, or cooling is performed from the temperature at the end of the second step to a lower limit of 600° C. (third step).
After completion of the third step, cooling is performed to 400° C. at an average cooling rate of 5° C./sec or more (fourth step).

Although the wire diameter of the wire according to the present embodiment is not particularly limited, the diameter of the wire is preferably 3.0 mm to 7.0 mm in consideration of the productivity of small-diameter bearings.

In addition, the 1st process can also employ methods other than hot rolling. For example, after obtaining a wire by hot rolling and cooling to room temperature, the wire can be reheated to obtain an austenite single phase with an average grain size of 15 μm to 50 μm. In order to create an austenite single phase with an average grain size of 15 μm to 50 μm by reheating, the wire may be heated to a temperature of 950 to 1020° C. and held for 1 to 5 minutes. In the subsequent cooling step, following the holding, the second step and the third step are performed by immersing in a lead bath at 600 to 620 ° C. for 90 to 150 seconds within 2 seconds, taking out, and air cooling. realizable. The above method is a heat treatment method called patenting.
After cooling to less than 600° C., controlled cooling is performed to 400° C. at an average cooling rate of 5° C./second or more (fourth step).
The following description of each step includes both the case where the first step is hot rolling and the case where it is reheating on the premise of patenting.
The temperature shown in each step below is the surface temperature of the wire when heating and cooling are performed in the atmosphere, and the temperature of the coolant when cooling in a coolant such as a lead bath.

<First step>
In the first step of the wire rod manufacturing method according to the present embodiment, the steel billet is heated to 950 ° C. to 1300 ° C., and then hot rolled by hot rolling or patenting heating, so that the average grain size is 15 μm to 15 μm. A single austenite phase of 50 μm is used.
The reason why the average grain size of austenite is set to 15 μm to 50 μm by reheating after hot rolling or patenting is that below 15 μm, the precipitation of proeutectoid cementite is promoted during cooling, and the area ratio of proeutectoid cementite increases. In addition, the pro-eutectoid cementite is easily split, and the aspect ratio becomes small. On the other hand, if the average grain size of austenite exceeds 50 μm, the grain size after transformation of pearlite increases, ductility decreases, and wire drawability decreases.
The average grain size of austenite is preferably 25-40 μm.

It is difficult to measure the average grain size of the structure (austenite phase) before pearlite transformation by observing the wire itself having a structure mainly composed of pearlite. In this embodiment, the average grain size of the austenite single phase is measured by the following procedure. That is, a portion of the wire rod immediately after hot rolling or immediately after heating and holding at a constant temperature is cut and quenched to make the main structure a supercooled structure (martensite or lower bainite). A portion of the quenched wire rod is further cut in a cross section perpendicular to the longitudinal direction, and the prior austenite grain size is measured by observing the cross section. Specifically, according to JIS G 0551:2020, the prior austenite grain size is calculated by the cutting method.

<Second step>
After the first step, cooling is performed to an arbitrary temperature in the range of 600 to 670°C within 25 seconds from the start of cooling at an average cooling rate of 10°C/second or more.
If the average cooling rate to an arbitrary temperature in the range of 600° C. to 670° C. is less than 10° C./second, the area ratio of proeutectoid cementite increases, so the average cooling rate is made 10° C./second or more. The average cooling rate is preferably 20° C./second or more, more preferably 30° C./second or more. Although the upper limit of the average cooling rate is not particularly specified, it is preferably 200° C./sec or less considering the capacity of cooling equipment.
In the above temperature range, if the temperature is lower than 600°C, bainite is likely to form, while if the temperature is higher than 670°C, the proeutectoid cementite area ratio increases and the proeutectoid cementite becomes thicker. A more preferred temperature range is 610°C to 650°C. The temperature range of 600 to 670° C. is the temperature range in which pearlite transformation occurs, and by cooling down to within this range at the average cooling rate, the target structure can be obtained. If the temperature reaches 600 to 670° C. when the pearlite transformation starts after cooling, the temperature may be temporarily lowered to 600° C. or less.
Also, the cooling rate to the above temperature range may not always be constant. The average cooling rate should be 10° C./second or more so that the proeutectoid cementite can be controlled within the range of the present embodiment.

<Third step>
In the third step, the structure of the wire is transformed into pearlite. In the third step, the temperature is maintained at the temperature at the end of the second step for 50 to 200 seconds, or the temperature at the end of the second step is cooled down to 600° C. as a lower limit.
If the holding time at the temperature at the end of the second step or the cooling time from the temperature at the end of the second step to 600° C. is less than 50 seconds, pearlite transformation will not be completed. As a result, the area ratio of bainite increases, which is not preferable. On the other hand, when it exceeds 200 seconds, the thickness of the proeutectoid cementite increases, the area ratio of ferrite increases, and further, the division of lamellar cementite of pearlite progresses, and the area ratio of spherical pearlite increases. I don't like it because

<Fourth step>
In the fourth step, cooling is performed from the temperature at the end of the heat retention or cooling in the third step to 400° C. at an average cooling rate of 5° C./second or more. The reason why the average cooling rate in the fourth step is set to 5°C/second or more is that if the average cooling rate is less than 5°C/second, the temperature is maintained at a high temperature even after the transformation, and the lamellar cementite is fragmented. be. Although the upper limit of the average cooling rate is not specified in the present embodiment, it is preferable to set the average cooling rate to less than 20° C./sec because increasing the average cooling rate requires equipment cost.

When the wire temperature is 400° C. or less, the thermal effect on the properties of the wire is slight. Therefore, after reaching 400° C. or lower, the cooling method to 400° C. may be continued, or cooling may be performed by air.

The wire produced by the above-described manufacturing method contains specified amounts of C, Si, Mn, and Cr, has a proeutectoid cementite area ratio of 3.0% or less, a pearlite area ratio of 94.0% or more, and has an initial The thickness of the eutectoid cementite is 0.8 μm or less, the aspect ratio of the proeutectoid cementite is 5.0 or more, and the wire drawability is excellent.
By using the wire of the present invention, good wire drawability can be obtained even if the spheroidizing annealing before wire drawing, which is required in the conventional manufacturing process, is omitted.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples of the wire rod according to the present invention, but the wire rod for bearings of the present invention is not limited to the following examples.
In this example, steel slabs adjusted to the steel compositions shown in Tables 1 and 2 below were prepared, heated to 1100°C in a heating furnace, and then hot rolled to 4.0 0.5 mm wires were produced. Austenite grain size was controlled by adjusting rolling conditions.

Regarding cooling after hot rolling, the average cooling rate from the temperature after rolling to the temperature range of 600 to 670 ° C. (cooling rate 1 in the second step in Table 3), the time until 600 ° C., from 600 ° C. Hot rolling was performed by controlling the average cooling rate up to 400° C. (cooling rate 2 in the fourth step in Table 3) to each value shown in Table 3.
In addition, A6 was subjected to patenting treatment after hot rolling. In the patenting treatment, after being held at 950° C. for 2 minutes, it was immersed in a lead bath at 620° C. within 2 seconds, immersed for 100 seconds, removed from the lead bath, and air-cooled.
In B18, spheroidizing annealing (SA annealing) was performed after hot rolling. In the spheroidizing annealing, the steel was held at 850° C. for 3 hours, cooled to 600° C. at 10° C./hour, and air-cooled.
Table 3 shows the manufacturing conditions used in each example and comparative example.

Table 4 shows the measurement results of the following structures of each sample.
・Proeutectoid cementite area ratio (%)
・ Area ratio (%) of proeutectoid cementite with a thickness of 0.5 μm or more
・ Perlite area ratio (%)
・Spherical perlite area ratio (%)
The meanings of the indications in the organization column of Table 4 are as follows.
P: perlite,
B/F: bainite/ferrite,
θ: proeutectoid cementite,
M: martensite,
Spherical θ: Spherical cementite

The measurement of the structure was performed by observation of the structure using a scanning electron microscope (SEM).
First, a sample for measurement was prepared by the following procedure.
1. Cut the wire and fill it with resin so that the cross section perpendicular to the longitudinal direction can be observed.
2. The resin-filled wire is polished with polishing paper or alumina abrasive grains to mirror finish.
3. The mirror-finished portion is corroded by immersing it in a picral solution having a picric acid concentration of 3% and a temperature of 40° C. for 60 seconds. The picral solution is a mixed solution of picric acid and ethyl alcohol.
4. After the corroded portion is immediately and thoroughly washed with water, it is quickly dried with cool or warm air to obtain an observation surface.

From the observation surface thus obtained, the area ratio of pro-eutectoid cementite, pro-eutectoid cementite having a thickness of 0.5 μm or more, pearlite, and spherical pearlite were measured by the following method.
1. At the center of the cross-sectional sample of the wire corroded with the picral solution, in the circular area within (1/2) R from the center, draw crosshairs perpendicular to each other with the center of the circle as the intersection, and on the vertical and horizontal lines ( 1/4) Take 5 points in the R interval. Since the observation positions of the center points of the circles overlap, a total of 9 points (5 points + 5 points - 1 point) are used as the observation positions.
2. Subsequently, a range of at least 17 μm×17 μm is photographed with an SEM at a magnification of 5000 for nine observation positions.
3. In the 17 μm×17 μm area of the photographed SEM image, 15 straight lines are drawn vertically and horizontally at intervals of 1 μm in a grid pattern, and the area is partitioned so that there are 225 intersection points.
4. After that, the tissue on the intersection point is determined, and the area ratio of the tissue is calculated from the ratio of the intersection point determined to the specific tissue to the total number of intersection points (225 points/field of view)×9 fields of view=2025 points.
In particular,
・ The area ratio (%) of the pro-eutectoid cementite is calculated by (total number of intersection points determined to be pro-eutectoid cementite / 2025) × 100,
The area ratio (%) of pro-eutectoid cementite with a thickness of 0.5 μm or more is calculated by (total number of intersections determined to be pro-eutectoid cementite with a thickness of 0.5 μm or more/2025)×100,
・ Perlite area ratio (%) is calculated by (total number of intersections determined to be pearlite / 2025) × 100,
- The area ratio (%) of spherical pearlite was calculated by (total number of intersections determined to be spherical pearlite/2025) x 100.

When it was difficult to determine the structure, the structure was observed at a magnification of 5000 times, and the structure was determined and measured.

Table 4 also shows the following measurement results.
・Thickness of pro-eutectoid cementite (μm)
- Aspect ratio of pro-eutectoid cementite The thickness of the pro-eutectoid cementite and the aspect ratio of the pro-eutectoid cementite were measured at the same time when the area ratio of the pro-eutectoid cementite was measured by the above method.

Table 4 also shows the following evaluation results of each sample.
・Tensile strength (TS: MPa)
・PBS (perlite block size: μm)
・Hardness distribution of wire (standard deviation of hardness distribution in cross section: HV)
・Wire drawing limit (true strain)

<Tensile strength>
Tensile strength was tested according to JIS Z 2241:2011. The tensile strength of the wire was obtained by calculating the average value of the tensile strength obtained from the three samples. The tensile test was performed with a sample length of 400 mm, a crosshead speed of 10 mm/min, and a jig distance of 200 mm.

<PBS (perlite block size)>
PBS was measured using a backscatter diffractometer (EBSD). The C section of the obtained wire was embedded in a resin, polished with alumina, and further polished with colloidal silica to remove strain, and then subjected to measurement. Polishing may be electrolytic polishing or the like.
Measurement is taken at a magnification of 300 times or more within (1/2) R from the center of the wire, and a ferrite crystal orientation data map is collected at 0.4 μm/step in an area of 150 μm × 150 μm per field of view, and the crystal orientation difference The PBS measurement was performed by setting blocks within 9° and connected by 10 pixels or more as the same perlite block. A similar operation was carried out for multiple fields of view, and measurements were taken in a field of view of 50000 μm ² or more, and the average of the obtained particle diameters was taken as PBS.

<Hardness distribution of wire>
The hardness distribution of the wire rod was measured using the resin-filled sample used in the above measurement.
Measurements were taken on a straight line passing through the center point in the cross section of the wire.
On a straight line, positions 70 μm from the surface were defined as the start and end points, respectively, and 9 points were measured at equal intervals between the two points (that is, 11 points were measured on a straight line having a diameter of one).
A similar operation was performed on orthogonal diameters, and the standard deviation of a total of 21 points (one measurement at the center) was taken as the hardness distribution of the wire.
Hardness was measured using a Vickers hardness tester under a load of 200 gf.

Next, the wire drawability evaluation test will be described.
<Limit of wire drawing (true strain)>
The wire rod produced as described above is subjected to descaling treatment by pickling, lubricating coating treatment by applying bonder and lime coating as a pre-wire drawing process without being subjected to spheroidizing annealing, and then wire drawing. A processability test was performed.
In the wire drawing workability evaluation test, 25 m of each wire was sampled and drawn with a dry single-head wire drawing machine at a rate of area reduction of about 20% per pass and a wire drawing speed of 50 m/min. rice field. After the wire drawing, the collected sample was subjected to a twisting test, and the true strain when delamination occurred during the twisting test (2 × Ln (d ₀ / d), d: wire diameter of the drawn wire, d ₀ : drawn Wire drawability was evaluated by the value of the wire diameter of the wire before wire (Ln is the natural logarithm).
In Table 4, the value of true strain at which delamination occurs is described as "drawing limit". In the twisting test, the applied load was 1% of the tensile breaking strength, the length of the sample subjected to twisting evaluation was 100 times the wire diameter of the drawn wire, and each pass was evaluated three times.
The above results are summarized in Table 4 below.

All test examples A1 to A20 are wire rods that adopt appropriate conditions, and all hot-rolled wire rods do not undergo delamination even if wire drawing with a true strain of more than 1.5 is performed without performing spheroidizing annealing. Excellent wire drawability was exhibited without occurrence of

In the above examples, C: 0.96 to 1.05%, Si: 0.12 to 0.61%, Mn: 0.23 to 1.11%, Cr: 0.91 to 1.55% A wire rod was manufactured from the steel material containing. These steel materials have O content of 0.0015% or less, N content of 0.011% or less, and Al content of 0.025% or less.
Also, for some of the samples, wire rods could be obtained from steel materials containing 0.03 to 0.23% Mo and 0.0001 to 0.0030% B in addition to the above compositions.
These wires had structures containing proeutectoid cementite, pearlite and spherical pearlite. In addition, in these wires, the proeutectoid cementite has an area ratio of 0.3 to 2.6%, a proeutectoid cementite thickness of 0.2 to 0.8 μm, and a proeutectoid cementite aspect ratio of 5. .2 to 25.6 and had a structure with a pearlite area ratio of 94.7 to 99.5%.
These example samples show values in the range of 1.6 to 2.3 for the true strain at which delamination occurs, and all samples are better in wire drawing than the test examples B1 to B18 described below. showed sex.

On the other hand, Test Examples B1 to B18 did not satisfy any of the requirements defined in the present invention, and were therefore inferior to the Examples of the present invention in wire drawability.
Since B1 had a high C content, the area ratio of proeutectoid cementite in the wire increased, and the wire drawability was not suitable.
Since B2 had a low Si content, the area ratio of proeutectoid cementite in the wire increased, and the wire drawability was not suitable.
Because B3 had a high Si content, B4 had a high Mn content, B7 had a high Cr content, and B8 had a high Mo content, wire drawability was not suitable.
Since B5 had a low Mn content, the area ratio of proeutectoid cementite increased, the aspect ratio of proeutectoid cementite decreased, and the area ratio of pearlite decreased, resulting in poor wire drawability.
Since B6 had a low Cr content, the aspect ratio of the proeutectoid cementite was lowered and the area ratio of pearlite was decreased, so the wire drawability was not suitable. In addition, since the Cr content is low, there is concern about insufficient wear resistance as a bearing steel.

Since B9 had a high B content, inclusions were precipitated at grain boundaries, and wire drawability was not suitable.
In B10 and B15, the area ratio of proeutectoid cementite increased because the cooling rate 1 in the second step was small. Also, in B10, the thickness of the pro-eutectoid cementite increased, and in B15, the aspect ratio of the pro-eutectoid cementite was small. As a result, B10 and B15 were not suitable for wire drawability.
In B11, the austenite grain size was small and the cooling rate 1 in the second step was small, so the area ratio of proeutectoid cementite increased, the thickness of proeutectoid cementite increased, and the aspect ratio of proeutectoid cementite increased. was small. As a result, B11 was not suitable for wire drawability.

In B12, the time of the 3rd process was long. As a result, in B12, although the area ratio of proeutectoid cementite was as low as 1.0% or less, the aspect ratio of proeutectoid cementite decreased, the area ratio of pearlite decreased, and spheroidization of lamellar cementite progressed. Therefore, wire drawability was not suitable.
In B13, the pro-eutectoid cementite area ratio and the pro-eutectoid cementite thickness satisfied the requirements of the present invention, but the austenite grain size was small. Therefore, in B13, the aspect ratio of the proeutectoid cementite was small, and wire drawability was not suitable.
In B14, after cooling at cooling rate 1 in the second step, it took a short time to reach below 600° C., so martensite and bainite were precipitated, and the area ratio of pearlite was reduced. As a result, the wire drawability of B14 was not suitable.

In B16, although the proeutectoid cementite area ratio was as low as 3.0% or less, cementite spheroidization progressed because the cooling rate 2 in the fourth step was low. As a result, the area ratio of pearlite was small and the area ratio of spherical pearlite was large, resulting in poor wire drawability.
In B17, since the time required to reach below 600° C. was very short, quenching occurred before pearlite transformation was completed, martensite was generated, and the area ratio of pearlite was small. As a result, wire breakage occurred in B17 during wire drawing ("-" in the item of "wire drawing limit" in Table 4 indicates that wire breakage occurred during wire drawing).
In B18, which is an example in which wire drawing was performed after spheroidizing annealing, the wire drawability was inferior to that of the invention examples.
Test examples A1 to A20 exhibited excellent tensile strength of 1315 to 1504 MPa. These wires are characterized by having a tensile strength of 1300 MPa or more.

In test examples A1 to A20 shown in Table 4, the values of pearlite block size (PBS) were 7.7 to 15.2 μm. The perlite block size is preferably in the range of 5.0 to 18.0 μm.

According to the present invention, it is possible to omit the spheroidizing annealing that is required before wire drawing in the conventional wire rod manufacturing process, and it is also possible to omit the intermediate annealing that is required during conventional wire drawing. Therefore, it contributes to the improvement of productivity and the reduction of manufacturing cost.

Claims (4)

As a chemical composition, in mass %,
C: 0.95 to 1.10%,
Si: 0.10 to 0.70%,
Mn: 0.20-1.20%,
Cr: 0.90 to 1.60%,
Al: 0.050% or less,
P: 0.020% or less,
S: 0.015% or less,
O: 0.0020% or less,
N: contains 0.030% or less,
The balance consists of Fe and impurities,
Contains proeutectoid cementite,
When the radius of the wire is R, at the center within (1/2) R from the center of the cross section of the wire,
The area ratio of the proeutectoid cementite is 3.0% or less,
The perlite area ratio is 94.0% or more,
The average thickness of the proeutectoid cementite is 0.8 μm or less,
A wire rod for a bearing, wherein the proeutectoid cementite has an average aspect ratio of 5.0 or more. Instead of part of the Fe, in mass %,
Mo: 0.25% or less,
B: 0.0050% or less,
Ti: 0.050% or less,
V: 0.20% or less,
Nb: 0.20% or less,
Cu: 0.25% or less,
2. The wire rod for bearings according to claim 1, comprising one or more selected from the group consisting of Ni: 0.20% or less. Proeutectoid cementite having a thickness of 0.5 μm or more is 0.5% or less in area ratio,
3. The wire for bearings according to claim 1, wherein the standard deviation of hardness in a cross section is 25 HV or less in terms of Vickers hardness. The wire rod for bearings according to any one of claims 1 to 3, wherein the spherical pearlite having an aspect ratio of lamellar cementite of 2.0 or less in the pearlite has an area ratio of 10.0% or less. .

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