JP2000008139A - Linear or bar-shaped steel or machine parts - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide linear or bar-shaped steel excellent in cold workability in hot rolled state as it is even if spheroidizing annealing is eliminated. SOLUTION: In the ferritic structure in the range from the center to diameter/8 of a rolling stock, nitrides and carbides are present by >=25 pieces/25 μm2 on the average in a mixed or compounded state. By precipitating such nitrides and carbides, its deformation resistance in the temp. rising range caused by working heat generation at the time of cold working 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
In a state where nitride and carbide are mixed or compounded,
The gist is that there are 25 or more particles / 25 μm ^{2 on} average. Specifically, in the ferrite structure, carbide having nitride as a nucleus is 25 or more / 25 on average.
μm ² exists. By precipitating such nitrides and carbides, during cold working, the temperature rise region (generally 100 to 350) generated by the heat generated during processing.
This is extremely useful in that the deformation resistance at (° C.) can be reduced.

[0008] The above-mentioned wire rod or bar-shaped steel is C: 0.00.
Al: 0.1% or less (not including 0%), N
: 0.015% or less (excluding 0%), and 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%) and / or M
n: 0.035 to 2%, Si: 0.5% or less (excluding 0%), S: 0.02% or less (excluding 0%)
Is preferable. 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 of N and Investigations have been made in detail focusing on solid solution C. As a result, even if the initial strength is the same, even in the ferrite-pearlite structure constituting the internal structure of the linear or rod-shaped steel, a predetermined number of nitrides are finely precipitated in the ferrite grains, and By precipitating a predetermined number or more of carbides such as cementite as nuclei, solid solution N and solid solution C can be fixed as nitrides and carbides, thereby suppressing dynamic strain aging and reducing deformation resistance. It has been found that, by adopting such a configuration, not only in the initial stage of cold working but also in the case where the working progresses and the temperature reaches around 300 ° C., the deformation resistance can be kept low, The present invention has been completed.

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

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.

In addition, JP-A-56-158841 and JP-A-57-39002 are based on the finding that fixing solid solution N can lower the hardness and decrease the work hardening rate. Discloses a method for producing a hot-rolled wire having excellent die life by controlling the Al / N ratio by using Ti or B.

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, it is very effective to precipitate a predetermined number of nitrides and carbides in ferrite grains in order to reduce solid solution N and solid solution C; There is no disclosure or suggestion that the deformation resistance can be kept low not only in the initial stage of the interworking but also in the case of reaching around 100 to 350 ° C. in the later stage of the working. 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 study that has focused on the relationship between the number of nitrides and carbides in the ferrite structure and the deformation resistance, and this is the finding first found by the present inventors. The technical significance of the present invention exists.

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 an average of 25 in a state in which nitrides and carbides are mixed or compounded in a ferrite structure ranging from the center to the diameter / 8 of the rolled material. It is characterized in that it exists at least 25 μm ² . By precipitating a predetermined number or more of nitrides and carbides in the ferrite structure, solid solution N and solid solution C which adversely affect deformation resistance are obtained.
Can be fixed, and an excellent effect that the deformation resistance can be reduced not only in the initial stage of processing but also in the latter stage of processing (around 100 to 350 ° C.) can be obtained.

Here, the above-mentioned nitride refers to Al, Cr, T
One or more nitride-forming elements such as i, B, Nb, V, and Zr are combined with solute N and precipitated as nitrides.

The above carbides include iron carbides such as cementite (Fe ₃ C), and Cr, Ti, Nb,
Carbide in which one or more carbide-forming elements such as V, Zr, etc. are bonded to C in steel; those in which Mn, P, S, etc. are precipitated in solid form in these iron carbides and carbides And the like.

In the present invention, these nitrides and carbides exist in a mixed or composite state.
An example of such an example is one in which carbides are precipitated with nitrides as nuclei. For one embodiment of such precipitates, for example, see FIG. 4 described later. In the following description, nitrides and carbides having such an existing form may be abbreviated as “nitrides and carbides” or “precipitates” for convenience.

Next, the reason for setting the number of nitrides and carbides precipitated will be described with reference to FIG.

FIG. 1 is a circuit diagram showing the operation of No. 1 described in an 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 nitrides and carbides specified in the present invention.
(No. 3) is a comparative example (21 pieces) having no predetermined number.

As shown in the figure, No. which 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 nitrides and carbides are formed in the ferrite, the dynamic strain aging is suppressed,
Even if the temperature due to processing reaches around 300 ° C., it is possible to effectively suppress an increase in deformation resistance.

The reason why the deformation resistance at around 300 ° C. can be suppressed to a remarkably low level by forming a predetermined number of nitrides and carbides in the ferrite structure as described above is considered as follows. Generally, solid solution N in ferrite
When the amount and the amount of solute C increase, the work hardening due to strain aging increases and the deformation resistance increases. However, in the present invention, the solute N which adversely affects the deformation resistance is converted into a nitride-forming element such as Al. It is considered that the deformation resistance was able to be suppressed to a low level by precipitating a predetermined number or more of nitrides by combining them with fine particles and using the nuclei as a nucleus to precipitate a predetermined number or more of carbides such as cementite.

In order to effectively exert the effect of reducing the deformation resistance due to the formation of nitrides and carbides, nitrides and carbides are mixed or mixed in the ferrite structure in the range from the center to the diameter / 8 of the rolled material. In the composite state, it is necessary that at least 25 particles / 25 μm ² exist on average. This number is closely related to the average diameter of nitrides and carbides and the like. For example, as the cooling rate decreases and the average particle size of these precipitates increases, the number of the precipitates decreases. Therefore, the number of the nitrides and carbides should be strictly determined in relation to the average diameter of the nitrides and carbides.
When the average diameter of the carbide is 10 to 50 nm at 0 nm,
In a state where nitride and carbide are mixed or compounded,
35 or more / 25 μm ^{2 on} average (more preferably 40 or more / 25 μm ² , still more preferably 45 or more / 2
5 μm ² ) is recommended. The average diameter of the nitride is 10 to 50 nm and the average diameter of the carbide is 50 to 50 nm.
In the case of 500 nm, the number of the precipitates is 25 or more / 25 μm ^{2 on} average (more preferably 30 or more / 25 μm).
m ² , even more preferably 35 or more / 25 μm ² ).

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

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 nitrides and carbides are present in the ferrite structure. Therefore, it is recommended that C, N, and Al be added as basic components and that various carbide-forming elements and nitride-forming elements be positively added so that predetermined nitrides and carbides can be obtained.

C: 0.001 to 0.5% C is an essential element for imparting the required 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.

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 can be said to be an unnecessary element in consideration of the fact that solid solution N has a bad effect on the reduction of deformation resistance.
In order to precipitate carbides such as cementite by using nitrides such as nuclei as nuclei, a certain amount of addition is necessary. Preferably it is 0.001% or more. 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. Preferably 0.
01% or less.

The steel of the present invention basically contains the above-mentioned components, and the balance is iron and inevitable 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.

Further, the following elements can be added.

Mn: 0.035 to 2% When the amount of Mn is less than 0.035%, S cannot be completely converted to MnS, and 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 in order 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 for producing a wire or a rod according to the present invention will be described.

In order to obtain a predetermined number of nitrides and carbides intended in the present invention, a steel slab is heated to a range of 900 to 1050 ° C. and rolled to a predetermined wire diameter in a range of 725 to 1000 ° C. Cooling at a cooling rate of 600-6000 ° C./min to 725-950 ° C. with a stream of water,
It is necessary to cool to 400 ° C. at a cooling rate of 3 to 600 ° C./min. Hereinafter, each requirement will be described.

Heating temperature of steel slab: 850 to 1050 ° C. This heating temperature is set so that a nitride such as AlN is partially dissolved and finely precipitated 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 in the case of heating 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 and solid solution N as carbides and nitrides, it is preferable to reduce the cooling rate. However, if the cooling rate is too low, the lamellar spacing in pearlite (laminate structure of ferrite and cementite) increases. May result in a poorly ductile tissue. Practically 6 ° C / min or more, 500 ° C
/ Min or less is preferred.

According to the present invention, excellent cold workability can be obtained even with a hot-rolled wire or a steel bar. The same applies to steel wire that has been subjected to wire drawing, cold rolling, etc. using zinc phosphate coating, calcium phosphate coating, lime, metal soap, etc. as a lubricant after removing scale by imparting strain, etc. Excellent 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.

[0046]

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 Nitride and Carbide Precipitated in Wire] In order to avoid the influence of decarburization by hot rolling, as shown in FIG. The number of precipitates at five points in the structure was counted. Specifically, the precipitate was subjected to a scanning electron microscope (SE
M), take a photograph (8000x), and analyze the image (FR
M wool kit), and the average value was calculated. FIGS. 3 and 4 show the test pieces No. 1 (Example of the present invention) and the test pieces No. 3 (Comparative Examples) shown in Table 2.
Each electron micrograph showing the state of the precipitates precipitated in the ferrite structure is 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. 5 to 7 are photomicrographs showing the results of analysis of precipitates in the test piece No. 2 (Example of the present invention) shown in Table 2. Of these, FIG.
A micrograph showing that the cementite is a nucleus,
FIG. 6 is a micrograph showing a nitrogen composition image, and FIG. 7 is a micrograph showing a carbon composition image.

[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 specimen, 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.

[0053]

[Table 1]

[0054]

[Table 2]

The following can be considered from the table.

First, Nos. 1, 2, 5, 7 to 2 shown in Table 2
No. 2 is an example of the present invention in which a predetermined number or more of nitrides and carbides were formed in the ferrite structure, and the increase in deformation resistance due to dynamic strain aging could be suppressed low. FIG.
From the results, it was confirmed that the composition of the nitride precipitated in the ferrite structure was AlN.

On the other hand, Nos. 3, 4, and 6 are comparative examples in which predetermined nitrides and carbides are not formed because the manufacturing conditions do not satisfy the requirements of the present invention. Is getting higher.

[0058]

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 a temperature range (approximately 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.

6 is a micrograph showing a nitrogen composition image in FIG.

FIG. 7 is a micrograph showing a carbon composition image in FIG.

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[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]

3. C: 0.001 to 0.5% (mass%, the same applies hereinafter), Al: 0.1% or less (not including 0%), N: 0.015% or less (including 0%) The linear or rod-shaped steel according to claim 1 or 2 , wherein

4. Further, Cr: 1.2% or less (not including 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 (0 % Not included),
The linear or bar-shaped steel according to claim 3 , which contains at least one kind of Zr: 0.1% or less (excluding 0%).

5. Mn: 0.035 to 2%, Si: 0.5% or less (0%
), S: 0.02% or less (excluding 0%) of the linear or bar-shaped steel according to claim 3 or 4 .

6. A machine part obtained by using the linear or rod-shaped steel according to claim 1.

[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 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
In a state where nitride and carbide are mixed or compounded,
By precipitating 25 or more / 25 μm ^{2 on} average,
The point is that the deformation resistance in the temperature range (approximately 100 to 350 ° C.) at the time of the temperature rise caused by the heat generated during the cold working is suppressed. Specifically, the ferrite structure contains carbides having nitrides as nuclei at an average of 25 or more / 25 μm ² .

[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 an average of 25 in a state in which nitrides and carbides are mixed or compounded in a ferrite structure ranging from the center to the diameter / 8 of the rolled material. It is characterized in that it exists at least 25 μm ² . Here, "the center of the rolled material ~
As the observation position of the "ferrite structure in the range of diameter / 8", for example, the structure observation position shown in FIG. 2 can be referred to. By precipitating a predetermined number or more of nitrides and carbides in the ferrite structure, solid solution N and solid solution C, which adversely affect deformation resistance, can be fixed. 100-350 ° C
(In the vicinity), it is possible to obtain an excellent effect that the deformation resistance can be reduced.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0039

[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] 0053

[Correction method] Change

[Correction contents]

[0053]

[Table 1]

[Procedure amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0054

[Correction method] Change

[Correction contents]

[0054]

[Table 2]

[Procedure amendment 11]

[Document name to be amended] Statement

[Correction target item name] 0056

[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 nitrides and carbides were formed in the ferrite structure, and the increase in deformation resistance due to dynamic strain aging could be suppressed low. FIG.
From the results, it was confirmed that the composition of the nitride precipitated in the ferrite structure was AlN.

[Procedure amendment 12]

[Document name to be amended] Statement

[Correction target item name] 0058

[Correction method] Change

[Correction contents]

[0058]

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. A ferrite structure in the range from the center to the diameter / 8 of a rolled material, wherein nitrides and carbides are present in a mixed or composite state in an average of 25 or more / 25 μm ^2. Wire or bar steel with excellent cold workability. 2. The ferrite structure in the range from the center to the diameter / 8 of the rolled material contains an average of 2% of carbides having nitrides as nuclei.
A linear or rod-shaped steel excellent in cold workability, characterized in that 5 or more / 25 μm ² are present. 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. C: 0.001 to 0.5% (mass%, the same applies hereinafter), Al: 0.1% or less (not including 0%), N: 0.015% or less (including 0%) The linear or bar-shaped steel according to any one of claims 1 to 3, wherein 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. Mn: 0.035 to 2%, Si: 0.5% or less (0%
The linear or rod-shaped steel according to claim 4 or 5, wherein S: 0.02% or less (excluding 0%). 7. A machine part obtained by using the linear or bar steel according to claim 1.