JP2000008140A - Linear or bar-shaped steel and machine parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a linear or bar-shaped steel excellent in cold workability in hot-rolled state as it is even if spheroidizing annealing is eliminate. SOLUTION: This linear or bar-shaped steel is the one in which, in the ferritic structure lying in the range from the center to diameter/8 of a rolling stock, carbides are present by >=25 pieces/25 μm2 on the average, where the one in which carbides are composed of ferrous carbides such as cementite is a preferable one, and by precipitating such carbides, its deformation resistance in the temp. rising region (about 100 to 350 deg.C) generated by working heat generation can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear or rod-shaped steel excellent in cold workability (hereinafter sometimes abbreviated as steel) and a mechanical part obtained by using the steel. When manufacturing bolts and nuts, electrical parts and machine parts with complex shapes by cold working such as cold forging, cold forging, cold rolling, etc., it is excellent even as it is hot rolled without heat treatment The present invention relates to a linear or rod-shaped steel having cold workability.

[0002]

2. Description of the Related Art Cold working is more efficient than hot working and mechanical cutting, and has a good yield of steel. Therefore, cold working is required to efficiently manufacture bolts, nuts, and other mechanical parts. It is widely used as a method.

[0003] Therefore, the steel used for such cold working is required to be essentially excellent in cold workability. Specifically, it is necessary that the deformation resistance during cold working is low and the ductility (elongation, drawing) is high. If the deformation resistance of steel is high, the life of a tool used for cold working is reduced, while if the ductility is low, cracks are liable to occur during cold working, which causes defective products.

Therefore, in order to reduce the deformation resistance of the steel and increase the ductility, a spheroidizing annealing treatment is usually performed before cold working, so that the steel material is softened and the cold work is performed while the ductility is increased. A method of processing has conventionally been employed.

However, spheroidizing annealing requires a long time treatment (1.
0-20 hours), to improve productivity, save energy, and reduce costs.
There is a strong need for the development of linear or rod-shaped steels which can omit the spheroidizing annealing treatment and have excellent cold workability.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an excellent cold workability as hot rolling even if the spheroidizing annealing treatment is omitted. It is an object of the present invention to provide a linear or rod-shaped steel and mechanical parts such as bolts and nuts obtained by using the linear or rod-shaped steel.

[0007]

The wire or rod-shaped steel excellent in cold workability of the present invention which has solved the above-mentioned problems is characterized in that the ferrite structure in the range from the center to the diameter / 8 of the rolled material is
The gist lies in that carbides having an average of 25 or more / 25 μm ² are present. Here, it is a preferred embodiment of the present invention that the carbide is an iron-based carbide such as cementite. By precipitating such a carbide, a temperature rise region (generally 100 ° C) generated by processing heat during cold working. (−350 ° C.), which is extremely useful in that the deformation resistance can be reduced.

[0008] The above-mentioned wire rod or bar-shaped steel is C: 0.00.
It is preferable to contain 1 to 0.5% (mass%, the same applies hereinafter). Further, Cr: 1.2% or less (excluding 0%), Ti: 0.2% or less (excluding 0%), B
: 0.01% or less (excluding 0%), Nb: 0.1
5% or less (excluding 0%), V: 0.2% or less
(Excluding 0%), at least one of Zr: 0.1% or less (excluding 0%), and / or Al: 0.1%
Or less (not including 0%), N: 0.015% or less (not including 0%), Mn: 0.035 to 2%, Si:
0.5% or less (excluding 0%), S: 0.02
% (Not including 0%) is recommended. In addition, a case where a trace component or an unavoidable impurity is included is also included in the technical scope of the present invention.

[0009] Machine parts obtained by using the above-mentioned linear or bar steel are also included in the scope of the present invention.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In order to provide a steel excellent in cold workability as it is hot-rolled, the present inventors have developed a solid solution C which controls deformation resistance among cold workability. We have been paying attention and have examined it in detail. As a result, even if the initial strength is the same, a predetermined number or more of carbides such as cementite (Fe ₃ C) are contained in the ferrite grains in the ferrite-pearlite structure constituting the internal structure of the linear or rod-shaped steel. By precipitating, the solid solution C can be fixed, and the dynamic strain aging can be suppressed, so that the deformation resistance can be reduced; The inventors have found that the deformation resistance can be suppressed not only in the initial stage but also when the processing proceeds and the temperature reaches around 300 ° C., and the present invention has been completed.

As in the present invention, a method of producing steel excellent in cold workability even if the spheroidizing annealing treatment is omitted by focusing on solid solution C has been proposed.

For example, Japanese Patent Publication No. 61-35249 discloses a method of reducing the solid solution C and the solid solution N by controlling rolling conditions and cooling conditions, suppressing work hardening caused by strain aging, and reducing deformation resistance. Is disclosed.

Other techniques that focus on solid solution N instead of solid solution C are disclosed in JP-A-56-158841 and JP-A-56-15884.
7-39002. These are based on the finding that, when solid solution N is fixed, a reduction in hardness and a reduction in work hardening rate can be obtained. In the former, the use of Ti or B as a nitride-forming element is ,
The latter discloses a method of manufacturing a hot-rolled wire having excellent die life by controlling Al / N.

Japanese Patent Application Laid-Open No. 57-63635 discloses A
_c1 transformation point, dissipate sufficiently aggregated cementite by 5 hours or more to a temperature not less than 50 ° C. from the transformation point A _c1, by fixing dissolved N by controlling the Al content, the machining tool life A method of making an enhanced cold forged bar is disclosed.

However, in each of the above-mentioned methods, in order to fix solid solution C and solid solution N which adversely affect the reduction of deformation resistance, the chemical components in the steel are controlled, and the rolling conditions and cooling conditions are controlled. Even if the above publication is carefully examined, precipitation of a predetermined number or more of carbides in ferrite grains is extremely effective in reducing solid solution C;
As a result, not only the initial stage of the cold working but also the later stage
There is no disclosure or suggestion that the deformation resistance can be kept low even when the temperature reaches about 350 ° C.
By the way, in above-mentioned, no attention is paid to the reduction of the deformation resistance in the later stage of processing. As described above, there has been no conventional study that pays attention to the relationship between the number of carbides in the ferrite structure and the deformation resistance, and is a finding first found by the present inventors. There is a meaningful significance.

Hereinafter, each requirement for specifying the present invention will be described.

As described above, the linear or rod-shaped steel of the present invention has a ferrite structure in the range from the center of the rolled material to the diameter of / 8, and has an average of at least 25 carbides / 25 μm ^{2 in} the ferrite structure. However, it has features. By precipitating a predetermined number or more of carbides in the ferrite structure in this way, it is possible to fix solid solution C that has an adverse effect on deformation resistance. An excellent effect that the deformation resistance can be reduced can be obtained. Examples of the carbide include iron, such as cementite (Fe ₃ C), and Cr, Ti, N
Carbide in which one or more kinds of carbide-forming elements such as b, V, and Zr are combined with C in steel; these iron carbides and Mn, P, S, etc. are precipitated in solid form in the iron carbide and carbide. And the like.

Next, regarding the reason for setting the number of carbides,
This will be described with reference to FIG.

FIG. 1 is a schematic diagram showing the operation of No. 1 described in the embodiment described later.
Using the test pieces 1 and 3, 25 ° C (normal temperature), 78 ° C, 1
5 is a graph showing deformation resistance when the temperature is raised to 50 ° C., 220 ° C., 330 ° C., 350 ° C., and 424 ° C. In the figure, ● (No. 1) is an example of the present invention (78 pieces) having a predetermined number of carbides (cementite) specified in the present invention,
◆ (No. 3) is a comparative example (21 pieces) having no predetermined number of cementite.

FIG. 2 shows that No. does not satisfy the requirements of the present invention.
3 indicates that the deformation resistance increases as the temperature increases,
It can be seen that the deformation resistance becomes maximum around 00 ° C. This is because dynamic strain aging due to solid solution C and solid solution N occurred remarkably. On the other hand, No. satisfying the requirements of the present invention.
In No. 1, since a predetermined number of cementite is formed in the ferrite, the above-mentioned dynamic strain aging is suppressed. As a result, even if the temperature due to processing reaches around 300 ° C., an increase in deformation resistance can be effectively suppressed. .

The reason why the deformation resistance at around 300 ° C. can be suppressed extremely low by forming a predetermined number of carbides in the ferrite structure as described above is considered as follows. In general, when the amount of solute C in ferrite increases, work hardening due to strain aging increases, and deformation resistance increases. In the present invention, however, the solute C that adversely affects the deformation resistance is bonded to Fe, It is considered that deformation resistance could be suppressed to a low level by forming a carbide such as Fe ₃ C, that is, cementite.

In order to effectively exert the effect of reducing the deformation resistance due to the formation of such carbides, the center of the rolled material to the diameter /
In the ferrite structure in the range of 8, it is necessary that carbides of 25 or more / 25 μm ^{2 on} average exist. This number is closely related to the average diameter of the carbide and the like. For example, as the cooling rate decreases and the average particle diameter of the carbide increases, the number decreases. Therefore, the number of the carbides should be strictly determined in relation to the average diameter of the carbides, but generally, the average diameter of the carbides is 10 to 50.
In the case of nm, it is recommended that the number be 35 or more / 25 μm ^{2 on} average (more preferably 40 or more / 25 μm ² , even more preferably 45 or more / 25 μm ² ).
When the average diameter of the carbide is 50 to 500 nm,
25 or more / 25 μm ^{2 on} average (more preferably 30 or more / 25 μm ² , still more preferably 35 or more / 2
5 μm ² ) is recommended.

The metal structure of the steel according to the present invention after hot rolling is mainly composed of the above-mentioned structure having carbides. Specifically, the ferrite area ratio in the metal structure is 20% or more. Preferably, there is. In the present invention, it is intended to keep the deformation resistance low even if the ferrite fraction is the same. In order to effectively exert the effect of the precipitates described above, the ferrite area ratio in the metal structure must be 2%.
It is recommended to be 0% or more (more preferably 25% or more).

Next, the chemical components in the steel of the present invention will be described.

As described above, the most important point of the present invention is
The reason is that a predetermined number of carbides are present in the ferrite structure. Accordingly, it is recommended to specify C and further add various carbide-forming elements so that a predetermined carbide is formed with respect to the chemical components in the steel.

C: 0.001 to 0.5% C is an essential element for imparting the necessary strength of the steel material. If the content is less than 0.001%, the desired strength cannot be obtained, and if the concentration is controlled to such a low level, the cost is industrially high and the method is not economical. Preferably it is 0.003% or more, more preferably 0.005% or more. on the other hand,
If it exceeds 0.5%, the ferrite fraction becomes low, and the desired effect cannot be obtained. Preferably it is 0.48% or less.

In the present invention, the C component in the above range is basically contained, and the balance is iron and unavoidable impurities. In addition, the following elements can be positively added.

Cr: 1.2% or less, Ti: 0.2% or less
Lower, B: 0.01% or less, Nb: 0.15% or less, V:
From the group consisting of 0.2% or less and Zr: 0.1% or less
At least one selected (all elements contain 0%
None) Elements excluding B (Cr, Ti, Nb, V, Zr)
Is a carbide and / or nitride-forming element, and B is a nitride-forming element like Al, and by adding these elements, it is possible to reduce solid solution C and solid solution N which adversely affect deformation resistance. become. In order to effectively exert such an effect, Cr: 0.02% or more, Ti: 0.01% or more, B: 0.0003% or more, Nb: 0.005% or more, V: 0.01 %, Zr: 0.005% or more is recommended. However, the effect is saturated even if it is added beyond the above range, and it is economically useless. Preferably, Cr: 1% or less, Ti: 0.15% or less, B:
0.008% or less, Nb: 0.1% or less, V: 0.15
% Or less, Zr: 0.08% or less. One or more of these elements can be used.

In addition, at least one of the following elements can be positively added.

Al: 0.1% or less (excluding 0%) Al is useful for deoxidation, and is added to fix solid solution N and generate nitride (AlN). For that, 0.
It is preferable to add 005% or more. However, 0.1%
Even if added in excess of the above, the above action is saturated,
It is economically useless. It is more preferably at most 0.08%.

N: 0.015% or less (excluding 0%) N is an unnecessary element in consideration of the fact that solid solution N has a bad influence on a decrease in deformation resistance. On the other hand, when the content exceeds 0.015%, the amount of alloying elements added for precipitating a predetermined nitride increases, so that the cost increases. More preferably, it is 0.005% or less.

Mn: 0.035 to 2% When the amount of Mn is less than 0.035%, S cannot be completely MnS, and the workability is deteriorated. More preferably, it is 0.05% or more. On the other hand, if it exceeds 2%, the rolling load is too high and the tool life is shortened. It is more preferably at most 1.8%.

Si: 0.5% or less (excluding 0%) Si is one of the deoxidizing agents, and it is preferable to add 0.005% or more to effectively exert such an effect. . More preferably, it is 0.008% or more. on the other hand,
Even if it exceeds 0.5%, the effect is saturated,
The deformation resistance also increases. More preferably 0.45%
It is as follows.

S: 0.02% or less (excluding 0%) If the S content exceeds 0.02%, cracks are likely to occur during cold working. More preferably, it is 0.018% or less.

Next, a method of manufacturing a wire or a rod according to the present invention will be described.

In order to obtain a predetermined number of carbides intended in the present invention, a steel slab is heated to a range of 900 to 1050 ° C., rolled to a predetermined wire diameter in a range of 725 to 1000 ° C., and then cooled by a water flow. Cool at a cooling rate of 600-6000 ° C./min to 725-950 ° C.
It is necessary to cool to 400 ° C at a cooling rate of ° C / min. Hereinafter, each requirement will be described.

Heating temperature of steel slab: 850 to 1050 ° C. This heating temperature is set to partially dissolve nitrides such as AlN and to precipitate finely after rolling.
When heating is performed at a temperature exceeding 1050 ° C., the precipitated nitride completely dissolves to form solid solution N. Therefore, no matter how the subsequent manufacturing process is controlled, the nitride can be precipitated. It will be difficult. Preferably it is 1025 ° C or less, more preferably 1000 ° C or less. On the other hand, when the heating temperature is 8
When the temperature is lower than 50 ° C., nitrides such as AlN do not form a solid solution at all, and do not act as carbide precipitation nuclei. It is preferably at least 870 ° C, more preferably at least 890 ° C.

Rolling temperature: 725 to 1000 ° C. This temperature is the same as during the rolling of the slab during rolling.
This is set to prevent the solid solution of nitride, and at the same time, dislocation is given to the structure in the steel, so that the dissolved N is finely reprecipitated as nitride in ferrite. Thus, a synergistic effect of further depositing carbides such as cementite is set. However,
From the viewpoint of preventing an increase in the load of the rolling roll, a decrease in dimensional accuracy, and the occurrence of surface flaws, it is practically 750 to 750.
It is recommended that the rolling temperature be about 1000 ° C. Preferably it is 775 ° C or more and 975 ° C or less.

Winding temperature: 725 to 950 ° C. Specifically, after the final rolling, 600
Cool to 725-950 ° C. at a cooling rate of ６6000 ° C./min. If the temperature is higher than 950 ° C., the precipitation of nitrides will be delayed, and it will hinder the reduction of solid solution C and solid solution N. At an actual operation level, the temperature is preferably 900 ° C. or less. On the other hand, 725
If the temperature is lower than 0 ° C., a martensite structure is generated in the surface layer, and the steel becomes hard and brittle, so that it is not suitable for cold working. The preferable temperature is 750 ° C. or more at the actual operation level.

Cooling rate: 3 to 600 ° C./min (up to 400 ° C.)
In order to precipitate solid solution C as carbides such as cementite, it is preferable to lower the cooling rate. However, if it is too slow, the lamellar spacing in pearlite (a layered structure of ferrite and cementite) becomes wider and ductility is poor. May be an organization. Practically, the temperature is preferably from 6 ° C./min to 500 ° C./min.

According to the present invention, excellent cold workability can be obtained even with a hot-rolled wire or steel bar. However, an acid (hydrochloric acid, sulfuric acid, or the like) may be further added to the wire or the steel bar or mechanically. After removing scale by imparting strain to the steel wire, the same excellent properties can be obtained for steel wires that have been drawn or cold-rolled using zinc phosphate coating, calcium phosphate coating, lime, metal soap, etc. as lubricant. Cold workability is obtained.

Hereinafter, the present invention will be described in detail with reference to examples.
However, the following examples do not limit the present invention,
All modifications and alterations without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

[0043]

EXAMPLES Using test steels having the component compositions shown in Table 1 (units in the table are% by mass), they were rolled into φ12 mm wires under various production conditions shown in Table 2. The following items were measured using this wire.

[Measurement of Average Number of Carbide Precipitated in Wire] In order to avoid the effect of decarburization by hot rolling, as shown in FIG. The number of precipitates at five points was counted. Specifically, the precipitate was photographed (8000 times) with a scanning electron microscope (SEM), and then subjected to image analysis (FRM wool kit) to count, and the average value was calculated. FIGS. 3 and 4 show test pieces of No. 2 shown in Table 2 (Examples of the present invention).
For the test pieces No. 3 and No. 3 (Comparative Example), electron micrographs showing the precipitates precipitated in the ferrite structure are shown.

[Confirmation of the composition of the precipitate]
Whether it is cementite with nuclei as the nucleus was confirmed by a transmission electron microscope (FE-TEM) with a magnification of 1,000,000 times.
After the result of analysis by EELS (energy loss spectroscopy) was imaged by GIF (imaging filter manufactured by GATAN), the composition was analyzed. FIG. 5 shows that, for a test piece of No. 2 (Example of the present invention) same as FIG.
FIG. 6 is a micrograph magnified 10,000 times and FIG. 6 is a photograph (in the figures, (a) and (b)) showing the analysis result of the compound composition by EDX. FIG. 5 shows C and C in addition to Fe and C.
Although a peak of u can be seen, it can be ignored since it responds to the stage of the test piece.

[Measurement of Deformation Resistance] The deformation resistance is an index of cold workability, and was measured by performing an upsetting test using a press in the following manner. First, the above wire rod was φ1 in order to obtain a shape recommended by the Japan Society for Plastic Working (forging, plastic working technology series 4, p55, Corona).
After cutting to a size of 0 × 15 mm and making this a cylindrical test piece for upsetting, upsetting was performed by using a constrained thick plate with concentric grooves as upsetting rolling. The test conditions were a compressibility of 60%, the maximum load applied at this time was measured, and the deformation resistance was calculated by the following formula.

Deformation resistance (kgf / mm ² ) = Load (kgf) / A / f where A: cross-sectional area of test piece (mm ² ) f: Constraint coefficient In the above equation, for example, when φ = 10 mm, A = 78.
5 mm ² , and f = 2.77 at 60% compression.

In measuring the deformation resistance of the upsetting test piece, in actual operation, cold multi-stage processing (strain speed 2 to 5) was performed.
100 / sec), assuming that the material to be processed reaches a temperature of several hundred degrees Celsius due to the heat generated during the processing, the temperature of the workpiece is set to 78 at room temperature (25 ° C.)
° C, 150 ° C, 220 ° C, 320 ° C, 350 ° C, 424
The deformation resistance when the temperature was raised to ° C. was measured.
Further, in order to examine the effect of dynamic strain aging on deformation resistance, the amount of increase in deformation resistance (kgf / mm ² ) due to dynamic strain aging was calculated based on the following equation.

Increase in deformation resistance = [deformation resistance at 320 ° C. (σ 320)] − [deformation resistance at normal temperature (25 ° C.) (σ 25)] These results are also shown in Table 2.

[0050]

[Table 1]

[0051]

[Table 2]

The following can be considered from the table.

First, Nos. 1, 2, 5, 7 and 2 shown in Table 2
No. 2 is an example of the present invention in which a predetermined number or more of carbides were formed in the ferrite structure, and the increase in deformation resistance due to dynamic strain aging could be suppressed to a low level. In addition, from the result of FIG.
It was confirmed that the composition of the carbide precipitated in the ferrite structure was Fe ₃ C.

On the other hand, Nos. 3, 4, and 6 are comparative examples in which predetermined carbides are not formed because the production conditions do not satisfy the requirements of the present invention. I have.

[0055]

According to the present invention, as described above, even if the spheroidizing annealing treatment is omitted, it is possible to efficiently provide a linear or rod-shaped steel excellent in cold workability as it is in hot rolling. I was able to. In particular, the linear or bar steel of the present invention,
During cold working, it is extremely useful in that the deformation resistance in the temperature rise region (around 100 to 350 ° C.) caused by the heat generated by working can be reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between a test temperature and deformation resistance.

FIG. 2 is a schematic explanatory view showing a method for measuring the number of precipitates.

FIG. 3 is an electron micrograph showing the appearance of precipitates precipitated in a ferrite structure for the example of the present invention.

FIG. 4 is an electron micrograph showing a state of a precipitate precipitated in a ferrite structure in a comparative example.

FIG. 5 is a micrograph of a precipitate in an example of the present invention.

FIG. 6 is a diagram showing analysis results [(a) and (b)] of the compound composition by EDX analysis of the precipitate in the example of the present invention.

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 25, 1999 (1999.5.2
5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

[Title of the Invention] Wire or bar steel and machine parts

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

Wherein C: 0.001 to 0.5% (mass%, hereinafter the same), a linear or rod-shaped steel according to claim 1 or 2 containing.

4. Cr: 1.2% or less (excluding 0%), Ti: 0.2% or less (excluding 0%),
B: 0.01% or less (excluding 0%), Nb: 0.
15% or less (excluding 0%), V: 0.2% or less
(Excluding 0%), Zr: 0.1% or less (excluding 0%).
3. The linear or rod-shaped steel according to 3.

5. Al: 0.1% or less (excluding 0%), N: 0.015% or less (excluding 0%), Mn: 0.035 to 2%, Si: 0. 5% or less
(Not including 0%), S: 0.02% or less (0%
The linear or rod-shaped steel according to claim 3 or 4, which contains

6. A machine part obtained by using the linear or bar-shaped steel according to any one of claims 1 to 5 .

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[0001]

The present invention relates to a linear or rod-shaped steel (hereinafter, sometimes abbreviated as steel) in which deformation resistance in a temperature rise region caused by working heat is suppressed during cold working. The present invention relates to mechanical parts obtained using steel. According to the present invention, when manufacturing mechanical parts such as bolts and nuts by cold working such as cold forging, cold forging, cold rolling, etc. This is extremely useful because it can provide a linear or rod-shaped steel with reduced deformation resistance in the temperature rising region.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0005

[Correction method] Change

[Correction contents]

However, spheroidizing annealing requires a long time treatment (1.
0-20 hours), to improve productivity, save energy, and reduce costs.
There is a strong need for the development of a linear or rod-shaped steel capable of omitting the spheroidizing annealing treatment and suppressing deformation resistance in a temperature rise region caused by processing heat during cold working.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction contents]

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and its object is to leave hot rolling as it is even when the spheroidizing annealing treatment is omitted. It is an object of the present invention to provide a linear or rod-shaped steel in which deformation resistance in a temperature rise region caused by processing heat is suppressed, and mechanical parts such as bolts and nuts obtained by using the linear or rod-shaped steel.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

[0007]

The wire or rod-shaped steel of the present invention which has solved the above-mentioned problems is defined as the center of the rolled material to the diameter of / 8.
In the ferrite structure in the range of
The gist is that the precipitation resistance in the temperature range (approximately 100 to 350 ° C.) at the time of the temperature rise caused by the heat generated by the processing during the cold working is suppressed by precipitating the carbide of 25 μm ² . Here, those in which the carbide is an iron-based carbide such as cementite are a preferred embodiment of the present invention.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

As described above, the linear or rod-shaped steel of the present invention has a ferrite structure in the range from the center of the rolled material to the diameter of / 8, and has an average of at least 25 carbides / 25 μm ^{2 in} the ferrite structure. However, it has features. Here, as the observation position of “the ferrite structure in the range from the center of the rolled material to the diameter / 8”, for example, the structure observation position shown in FIG. 2 can be referred to. By precipitating a predetermined number or more of carbides in the ferrite structure in this way, it is possible to fix solid solution C that has an adverse effect on deformation resistance. An excellent effect that the deformation resistance can be reduced can be obtained.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0036

[Correction method] Change

[Correction contents]

In order to obtain a predetermined number of carbides intended in the present invention, a steel slab is heated to a range of 850 to 1050 ° C., rolled to a predetermined wire diameter in a range of 725 to 1000 ° C., and then cooled by a water flow. Cool at a cooling rate of 600-6000 ° C./min to 725-950 ° C.
It is necessary to cool to 400 ° C at a cooling rate of ° C / min. Hereinafter, each requirement will be described.

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0050

[Correction method] Change

[Correction contents]

[0050]

[Table 1]

[Procedure amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0051

[Correction method] Change

[Correction contents]

[0051]

[Table 2]

[Procedure amendment 11]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction contents]

First, Nos. 1, 2, 5, 7 to 1 shown in Table 2
No. 8 is an example of the present invention in which a predetermined number or more of carbides were formed in the ferrite structure, and the amount of increase in deformation resistance due to dynamic strain aging could be suppressed low. In addition, from the result of FIG.
It was confirmed that the composition of the carbide precipitated in the ferrite structure was Fe ₃ C.

[Procedure amendment 12]

[Document name to be amended] Statement

[Correction target item name] 0055

[Correction method] Change

[Correction contents]

[0055]

As described above, the present invention is constructed as described above. Therefore, even if the spheroidizing annealing is omitted, the hot-rolled state is maintained, and the temperature rise region (100 to 100) caused by the heat generated during the cold working is obtained. A linear or rod-shaped steel with suppressed deformation resistance at around 350 ° C.) could be efficiently provided.

Claims (7)

[Claims] 1. An excellent cold workability characterized in that the ferrite structure in the range from the center to the diameter / 8 of the rolled material contains an average of at least 25 carbides / 25 μm ² . Wire or bar steel. 2. The carbide according to claim 1, wherein the carbide is an iron-based carbide.
Or a steel rod or bar. 3. The linear or rod-shaped steel according to claim 1, wherein the deformation resistance in a temperature rising region caused by heat generated during the cold working is small. 4. The linear or rod-shaped steel according to claim 1, containing C: 0.001 to 0.5% (% by mass, the same applies hereinafter). 5. Further, Cr: 1.2% or less (excluding 0%), Ti: 0.2% or less (excluding 0%),
B: 0.01% or less (excluding 0%), Nb: 0.
15% or less (excluding 0%), V: 0.2% or less
The linear or rod-shaped steel according to claim 4, which contains at least one of (0% not included) and Zr: 0.1% or less (excluding 0%). 6. Al: 0.1% or less (excluding 0%), N: 0.015% or less (excluding 0%), Mn: 0.035 to 2%, Si: 0. 5% or less
(Not including 0%), S: 0.02% or less (0%
The linear or rod-shaped steel according to claim 4 or 5, which comprises 7. A machine part obtained by using the linear or bar-shaped steel according to claim 1.