JP3527641B2 - Steel wire with excellent cold workability - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel wire rod for use in manufacturing mechanical structural parts by cold plastic working such as cold forging, cold forging, and cold rolling. The present invention relates to a steel wire rod that can exhibit good cold workability even if the spheroidizing annealing step before cold working is simplified or omitted, and that energy consumption can be saved.

[0002]

2. Description of the Related Art Wire rods made of low-medium carbon steel and low-medium carbon low-alloy steel are widely used for mechanical structural parts such as shafts, bolts and nuts, which require relatively high strength. This steel wire rod is manufactured by cold plastic working such as cold forging, cold forging, and cold rolling. However, such steel wire rod is required to have low deformation resistance. For the purpose of lowering the deformation resistance of the steel wire and imparting the deformability, it is common to make the carbide in the steel spherical.

The spheroidizing treatment is a treatment in which a hot rolled steel material is reheated and then gradually cooled. However, the spheroidizing treatment requires 10 hours for a short treatment time and 20 hours or more for a long treatment time, which is a manufacturing cost bottleneck.

That is, the spheroidizing treatment is usually performed by spheroidizing annealing.
(1) A method of gradually heating after heating above the A ₁ transformation point,
There are various known methods, such as (2) holding just below the A ₁ transformation point, (3) repeating heating and cooling above and below the A ₁ transformation point, and even if either method is adopted, the final temperature is room temperature. There is a problem that the processing cost such as time and energy is very high because it needs to be gradually cooled. For these reasons, various studies have been conducted on various means for reducing the time required for the spheroidizing treatment.

As one of such techniques, a method of performing cold working such as wire drawing before performing spheroidizing treatment to destroy carbides in steel and promoting fragmentation and aggregation of carbides in subsequent spheroidizing annealing. Conventionally, a method of shortening the processing time has been generally performed. However, this method has the effect of shortening the processing time, but since the cold working step is added, the effect of shortening the processing time throughout the manufacturing process is not so epoch-making.

Further, it is possible to shorten the spheroidizing treatment time by devising the hot rolling process of the wire.
For example, in Japanese Patent Laid-Open No. 59-166622, it is known that it is effective to pre-process the steel to deform and fracture the carbide, and then to perform spheroidizing annealing. Therefore, steel containing 2% by mass or less of C is used. On the other hand, pearlite is divided by giving a plastic deformation of 10% or more in a two-phase region of Ac ₁ or less and 500 ° C. or more (ferrite + pearlite), and the (ferrite + austenite) temperature range is finished by the processing heat. A method of gradually cooling a specific temperature range has been proposed.

According to this method, a spheroidization rate of more than 90% can be obtained depending on the cooling rate in a specific temperature range,
As a result, the spheroidizing time can be shortened to 1/5 or less.
However, in this method, since it is essential to process the steel material at a low temperature of Ac ₁ or less, there is a problem that the load of the rolling mill is large and the rolling is not easy.

Further, in JP-A-59-136421,
Similarly, in steel containing 2% by mass or less of C, during finish rolling, the steel material is once cooled to Ar ₁ point to form a (ferrite + pearlite) structure, and pearlite is divided by rolling from that temperature, and subsequently the processing is performed. A method has been proposed in which the (ferrite + austenite) temperature range is set as a finishing temperature and gradually cooled by heat. However, in this method, since it is indispensable to process the steel material at Ar ₁ or lower, which is lower than the above-mentioned technique, the load on the rolling mill is further increased, and the rolling is not easy.

As a method for solving the problem of the rolling temperature as described above, for example, in Japanese Patent Laid-Open No. 59-136422, rolling is carried out in a metastable austenite temperature range, and by utilizing the work-induced transformation, Ae ₁ or less Ar ₁ 10% in the above temperature range
The method of giving the above plastic deformation is proposed. However, even with this method, it is essential that the rolling temperature be lower than Ae ₁ , and the rolling load is still large.

As a fact common to the above-mentioned conventional examples proposed so far, in such rolling in the temperature range near the A ₁ transformation point, the strain accumulated in the ferrite formed at the same time as the carbide causes the subsequent processing heat generation. However, there is a problem in terms of the life of the cold working tool because the spheroidizing rate does not sufficiently recover and the deformation resistance does not sufficiently decrease with the slow cooling treatment.

On the other hand, in Japanese Patent Laid-Open No. 8-246040, the spheroidizing treatment time can be increased by performing each of the following elementary processes (1) and (2) once or in combination during the temperature rise of the steel material. A rapid continuous spheroidizing annealing method that shortens to 1 hour or less is disclosed, and it is considered that the development of this technique will achieve a significant reduction in the spheroidizing processing time.
However, even with this technique, the spheroidizing annealing cannot be completely omitted, and further improvement is desired.

(1) Ae ₁ point or more, Ae ₁ point + 150K
The following temperature range, 1K / sec or more was heated heated at a Atsushi Nobori rate, after holding time of less than 0 seconds 600 seconds in the temperature range, Ae ₁ point or more, Ae ₁ point + 50K~Ae ₁ point +1
Cooling within a temperature range of 50 K at a cooling rate of 5 K / sec or less, or maintaining the temperature in the temperature range, (2) A
e ₁ point + 80K or more, Ae ₁ point + 270K or less at a temperature rising rate of 1 K / sec or more, and after heating for 0 seconds or more and less than 120 seconds within the temperature range, Ae ₁ point or more , the temperature range of Ae ₁ point ~Ae ₁ point -150K 5K
Cool at a cooling rate of less than 1 second / sec or keep the temperature in the temperature range.

[0013]

As described above, various techniques relating to simplification of the spheroidizing annealing treatment have been proposed for low-medium carbon steels, particularly medium carbon steels with C: 0.3% or more. Although each has its technical significance, none of them is sufficient from the viewpoint of completely omitting the spheroidizing annealing treatment, and cannot be a definitive method.

The present invention has been made under such circumstances, and an object thereof is to reduce the deformation resistance in a low-medium carbon steel or a low-medium carbon low alloy steel that has been hot-rolled to obtain sufficient deformability. It is intended to provide a steel wire rod excellent in cold workability even if the spheroidizing annealing treatment is simplified or omitted.

[0015]

The present invention which has achieved the above object is a steel wire containing C: 0.03 to 0.8 mass% and having an average ferrite grain size of 2 to 5. A region where the cementite with a major axis of 5 μm and a major axis of 3 μm or less and an aspect ratio represented by (major axis / minor axis) of 3 or less is 70 area% or more based on all cementites is 10% or more of the wire diameter from the surface. It is a steel wire rod having the gist in the area.

The steel wire rod of the present invention defines the crystal structure in the wire rod as described above. The specific chemical composition of the wire rod is Si: 0.004 to 0.5.
Mass%, Mn: 0.05-2 mass% and Al: 0.0
1 to 0.08 mass% respectively, P: 0.03 mass% or less (including 0%), S: 0.03 mass% or less (0
%) And N: 0.07 mass% or less (including 0%).

In the steel wire rod of the present invention, if necessary, (1) Cr: 1.5% by mass or less (not including 0%), Mo: 1.0% by mass or less (not including 0%), N
i: 1.0% by mass or less (not including 0%) and B:
One or more kinds selected from the group consisting of 0.0025% by mass or less (not including 0%), (2) Ti: 0.5% by mass or less (not including 0%), V: 0.6% by mass or less (0% is not included), Nb: 0.4 mass% or less (0% is not included)
It is also effective to add Zr: at least one selected from the group consisting of 0.3% by mass or less (not including 0%), and the like, whereby the characteristics of the steel wire rod can be further improved.

The average grain size of ferrite is the average grain size of ferrite measured in a structure observed by an optical microscope or a scanning electron microscope (SEM) after polishing and etching the cross section of a wire. .

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have made detailed investigations on the locations of cracks generated during cold working, and have found that they are in the vicinity of the surface of a part, that is, a rolled wire, in most cases. More specifically, it has been found that cracks are generated in the region from the surface of the wire to a depth of about 10% of the diameter, leading to breakage. This region corresponds to the region having the largest strain during cold working as a part.

Furthermore, the origin of cracks is 5.5 μm.
It was found that this was a fine scratch on the interface between the ferrite and the second phase (here, pearlite) having the above size, the inside of pearlite, or the surface. The cracks generated outside this region are due to coarse inclusions and the like, which is a problem that can be solved by steelmaking technology such as removal of inclusions.

Therefore, it is considered that the frequency of cracks can be suppressed by reducing the grain size of ferrite to 5.5 μm or less and reducing the interface in contact with the second phase.

In addition to such an idea, the deformation resistance, which is another characteristic required for the cold workability, can be easily understood from the known fact that the spheroidizing treatment improves the deformation resistance and the deformability. As described above, the deformation resistance can be effectively reduced when the pearlite has a divided structure that is as close to spherical as possible.

However, although the spheroidization of cementite proceeds by the usual spheroidization treatment, it is difficult to control the ferrite grain size. For example, see References (Materials Sc).
As described in "Ience and Engineering 62 (1983) p163-171", the average grain size of ferrite can be controlled only to about 5.8 to 15 µm in the entire cross section of the wire.

Therefore, as a result of intensive studies by the present inventors, by using high-frequency heating for a short time together with cold working,
We succeeded in refining the ferrite in the fractured cementite structure. The principle of this method is as follows.

First, a steel wire rod is subjected to a skin pass with a surface reduction rate of about 5%. Next, this wire is heated to a point immediately below the Ac ₃ point in the ferrite (α) + austenite (γ) two-phase temperature region by rapid heating at a heating rate of 400 ° C./s or more. The Ac ₃ point here is the temperature at which α disappears completely during continuous heating and becomes a γ single phase. Then, after heating to a predetermined temperature, the heating is immediately stopped and cooling is performed at a cooling rate of 10 ° C./s or more and a critical cooling rate or less. The above process is repeated 3 to 4 times. By such a treatment, the pearlite structure is divided, and α is further refined.

It can be considered that this is a result of the following tissue change. First, the pearlite structure is rapidly decomposed by heating immediately under the Ac ₃ point, but by immediately starting the cooling immediately under the Ac ₃ , the pro-eutectoid α which has not been transformed into γ remains in the steel. It will be.

On the other hand, the cementite (θ) precipitated in a plate shape in pearlite is also decomposed, but it is not decomposed uniformly, but is preferentially decomposed in the vicinity of grain boundaries where carbon diffuses rapidly and in the vicinity of lattice defects. , Spherical cementite remains. This θ
The decomposition process of is the same as the θ decomposition process in the conventionally known spheroidizing process. However, the heating temperature in the usual spheroidizing treatment is in the vicinity of the _Al point, while this rapid heating treatment is characterized in that it is at a higher temperature. For this reason, it becomes a condition that it is possible to easily achieve the refinement of pro-eutectoid α.

Further, in the cooling under the above conditions, the undissolved θ remains as it is, and the pearlite transformation proceeds while depositing new pro-eutectoid α at the γ-α interface.

Therefore, a structure in which fine pro-eutectoid cementite, fragmented cementite and pearlite coexist is obtained by one rapid heating and cooling.

By repeating the above processing,
The volume ratio of pearlite exhibiting a lamellar structure is reduced, and a steel material having a microstructure close to a spheroidized material composed of divided θ and fine α can be obtained. However, the manufacturing method shown here is merely an example for obtaining the steel material structure of the present invention, and does not impose any limitation to the other manufacturing methods.

The characteristic of the steel wire rod of the present invention lies in the fact that its structure is regulated, but the reasons for limiting each requirement prescribed in the present invention will be explained.

Average particle size of ferrite: 2 to 5.5 μm In the steel wire rod of the present invention, the average particle size of ferrite is 2 to 5.5 μm in the region of 10% or more of the wire diameter from the surface.
Must be If the average grain size of ferrite is less than 2 μm, although it is effective in suppressing the occurrence of cracks, the increase in strength due to the refinement of the crystal grains becomes remarkable, and rather the deformation resistance increases. Further, as described above, if the average grain size of ferrite exceeds 5.5 μm, the deformation resistance and deformability equivalent to those of the conventional spheroidized material are reached, so the upper limit was made 5.5 μm or less. As a method for controlling the average grain size of ferrite to 5.5 μm or less, high-frequency heating / cooling for a short time can be mentioned as described above.
There is no problem even if other methods are used.

Shown by (major axis / minor axis) when major axis is 3 μm or less
In the wire of the present invention, the major axis of the segmented cementite is 3 μm or less, and the aspect ratio represented by (major axis / minor axis) is 3 or less. First, cementite having a major axis of more than 3 μm is likely to be a starting point for early generation of cracks and voids at the interface with ferrite. Further, the aspect ratio is defined as 3 or less because cementite longer than this becomes an obstacle to the plastic flow during cold working and is particularly likely to be a starting point of void generation near the surface of the steel material. The void occurrence frequency from cementite smaller than this is remarkably reduced.

70% by area or more with respect to all cementites The fraction of fractured cementites is 7 with respect to all cementites.
This is because it is necessary to be 0 area% or more, but if the fraction is less than 70 area%, the effect of improving the cold workability by the split cementite and the fine ferrite intended by the present invention does not clearly appear. The upper limit of this fraction is not particularly limited,
Although it depends on the manufacturing method, it is 10 from the effect of reducing deformation resistance.
It is desirable to be close to 0%.

Region from the surface to 10% or more of the wire diameter In the wire rod of the present invention, the split cementite having the above-mentioned fraction of 70% by area or more has the above-mentioned structure (the average grain size of ferrite is 2 to 5. 5 μm and the fraction of fragmented cementite is 70 area% or more based on the total cementite)
By exhibiting, the deformability is dramatically improved in addition to the deformation resistance similar to that of the ordinary spheroidizing material, and the processing into a complicated shape is facilitated. However, even if only the region of about 10% from the surface has the above-mentioned structure, it has an effect of shortening the time of the current spheroidizing treatment. Since the effect of shortening spheroidizing annealing is small only in the region of less than 10%, in the present invention, it was defined as 10% or more of the wire diameter from the surface. 10% of wire diameter from the surface
The region of means that the region of 20% with respect to the wire diameter is divided cementite with the above-mentioned fraction of 70 area% or more when viewed as a whole wire, and therefore this region is 50%. When it becomes, it means that the fraction is 70% by area or more and is divided cementite over the entire wire.

The steel wire rod of the present invention basically has a C content of 0.03.
.About.0.8%, but as a specific chemical component composition, Si: 0.004 to 0.5 mass%, Mn:
0.05 to 2 mass% and Al: 0.01 to 0.08 mass%, respectively, and P: 0.03 mass% or less (0%
, S: 0.03 mass% or less (including 0%) and N: 0.07 mass% or less (including 0%), respectively, but the reasons for limiting the range of these elements are included. Is as follows.

C: 0.03 to 0.8% by mass C is an essential element for giving desired strength to the wire,
Therefore, it is necessary to contain at least 0.03 mass% or more. However, if the C content becomes excessive, the deformation resistance increases more than necessary and the toughness decreases, so the upper limit is 0.8% by mass. The preferable lower limit of the C content is 0.2
It is 0% by mass, and the preferable upper limit is 0.60%.

Si: 0.004 to 0.5 mass% Si is added as a deoxidizing agent in the steel making process, but for that purpose, it is necessary to contain 0.004 mass% or more.
However, if the Si content is excessive, the deformation resistance is significantly increased, so the upper limit is 0.5% by mass. The preferable lower limit of the Si content is 0.01% by mass, and the preferable upper limit is 0.3% by mass.

Mn: 0.05 to 2 mass% Mn is an element necessary for fixing S, which is an impurity, to render it harmless, and for adjusting the strength of the steel after tempering. . It is also effective for improving toughness. In order to exert these effects, it is necessary to contain Mn in an amount of at least 0.05 mass% or more. However, if it is contained in excess, the hardenability is improved, and bainite or the like is generated during hot rolling to cause deformation resistance. 2 because it causes a rise
It needs to be less than or equal to mass%. The preferable lower limit of the Mn content is 0.4% by mass, and the preferable upper limit is 1.2% by mass.

Al: 0.01 to 0.08 mass% Al acts as a deoxidizing agent in the steelmaking process, and is necessary for fixing N as AlN to reduce solid solution N and reduce deformation resistance. Is. In order to exert such effects, it is necessary to contain 0.01% by mass or more. However, if Al is contained excessively, it becomes coarse AlN and deteriorates the cold workability, so 0.08 mass% is made the upper limit.

P: 0.03% or less by mass (including 0%),
S: 0.03% by mass or less (including 0%) These elements are segregated at the grain boundaries or exist as compound inclusions, and 0.03% by mass to prevent cold workability.
Must be: The content of each of these elements is preferably 0.016 mass% or less.

N: 0.07% by Mass or Less (Including 0%) N significantly increases the deformation resistance, so it is necessary to suppress it to 0.07% or less in order to obtain good cold workability. . From this viewpoint, the N content is preferably 0.010 mass% or less.

The basic chemical composition of the steel wire rod of the present invention is as described above, and the balance consists of Fe and inevitable impurities. In the steel wire rod of the present invention, (1) Cr: 1.5% by mass or less (not including 0%), Mo: 1.0% by mass or less (not including 0%), Ni: 1.0% by mass or less (not including 0%) and B: 0. One or more elements selected from the group consisting of 0025 mass% or less (not including 0%), (2) Ti: 0.
5 mass% or less (0% is not included), V: 0.6 mass% or less (0% is not included), Nb: 0.4 mass% or less (0%
It is also effective to add one or more elements selected from the group consisting of Zr: 0.3 mass% or less (not including 0%), and the like, thereby further improving the characteristics of the steel wire rod. Can be improved. The reasons for limiting the ranges of these elements are as follows. The steel wire rod of the present invention includes
In addition to these, trace amounts of components that do not impair the characteristics of the wire may be included, and such steel wire is also included in the scope of the present invention.

[0044]Cr: 1.5% by mass or less (0% is not included
I), Mo: 1.0 mass% or less (not including 0%), N
i: 1.0% by mass or less (not including 0%) and B:
Group consisting of 0.0025% by mass or less (not including 0%)
One or more elements selected from Cr, Mo, Ni and B are quenching adjusting elements, and
Added to adjust strength and toughness by quenching and tempering
Be done. However, if it is contained excessively, it will increase the deformation resistance.
It is not preferable because it causes rise. From this viewpoint, Cr is
The upper limit is set to 1.5% by mass, and Mo and Ni are
The limit is 1.0% by mass, and the upper limit of B is 0.0025
The amount was set to%. In addition, the above effects due to the addition of these elements are
It increases as the content increases within the above range,
In order to exert the above effect, Cr is 0.03 mass% or less.
Above, 0.01% by mass or more for Mo and Ni, 0.0 for B
It is preferable to contain 003 mass% or more.

[0045]Ti: 0.5% by mass or less (not including 0%
), V: 0.6 mass% or less (not including 0%), N
b: 0.4 mass% or less (not including 0%) and Zr:
Select from the group consisting of 0.3 mass% or less (not including 0%)
One or more elements exposed Ti, V, Nb and Zr are all fine carbonitrides
Formed and adjusted the strength and ductility balance of the heat-treated material by precipitation hardening
It is added for the purpose of adjusting. However, excessive content
If so, deformation resistance is increased, which is not preferable. This way
From the viewpoint, the upper limit of each is set to 0.2% by mass.
In addition, the above-mentioned effects due to the addition of these elements are included within the above range.
It increases as the abundance increases, but the above effects are produced.
In order to vaporize, 0.015 mass% or more of Ti, V, N
b and Zr may be contained in an amount of 0.010 mass% or more.
preferable.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are not intended to limit the present invention, and any modification of the design of the present invention can be made without departing from the spirit of the preceding and the following. Are included in the technical scope of. In the examples below, the microstructure was determined according to the following procedure.

[Ferrite grain size investigation] Polishing of wire cross section
The average grain section of ferrite was measured in the structure that was etched and observed by an optical microscope or SEM. The measurement was carried out by observing an area of 100 μm × 250 μm in five or more visual fields and measuring the average.

[Investigation of Split Cementite Phase] A structural photograph taken with an SEM at a magnification of 1000 times in an observation field of a cross-section of a wire was subjected to image analysis. The divided cementite area ratios of the following parts were measured. The measurement was performed by observing five or more fields of view and averaging the same as in the ferrite grain size survey.

[Determination of major axis and minor axis] The longest section of cementite was defined as the major axis, and the maximum section in the direction perpendicular to this major axis was defined as the minor axis.

[Determination of Microstructure Depth] At an arbitrary radius, observation is performed from the surface in steps of 5% toward the center, and the [Ferrite grain size inspection] and [Separation cementite phase inspection] described above are carried out to obtain 5 fields of view. The average value was calculated. The depth from the surface that satisfies both the conditions of the ferrite grain size and the fragmented cementite was defined as the texture depth. At this time, when there is a tissue depth in the middle of the observed dark field, the median value was obtained by the gradient averaging in all cases, and made the tissue depth (a region satisfying the tissue defined in the present invention).

[0051]

[Example] [Example 1] Using a steel composition equivalent to JIS S30C, a rapid heating test by high frequency was conducted to examine the influence on cold workability. That is, a steel wire rod having a chemical composition shown in Table 1 below and having a wire diameter of 16 mm was subjected to a wire drawing-high frequency heating test, and a trial production of a fine ferrite + divided cementite structure was carried out.

[0052]

[Table 1]

Table 2 below shows the experimental conditions and the obtained structures. In addition, "repetition number" in Table 2 means (high frequency heating →
The number of times the cooling process is repeated is shown. As described above, the "structural depth" indicates the depth (% of the wire diameter) from the surface of the region that satisfies both the conditions of the ferrite grain size and the divided cementite structure, and 0% means no None, 50% means the state obtained on the entire cross section of the wire. Test No. No. 1 is a conventional example, which has been subjected to ordinary spheroidizing treatment, and the spheroidizing treatment conditions at this time are a heating temperature of 740 ° C. and an overall spheroidizing treatment temperature of 20.
It's time.

[0054]

[Table 2]

FIG. 1 shows the test No. The evaluation results of the cold workability (cracking limit upsetting ratio, tensile strength TS) of Nos. 1 to 5 (conventional example, and those having a structure depth of 50% or more) are shown. As is clear from this result, when the requirements specified in the present invention are satisfied (test Nos. 2 to 4),
Although not subjected to spheroidization treatment, it has TS similar to that of ordinary spheroidization treatment material, and has an increase in crack generation limit upset rate of 5% or more, which indicates that cold workability is remarkably improved. I understand.

Further, the test No. in which the tissue depth was less than 50%. The spheroidizing treatments of 7 to 9 were carried out for 2 hours. The evaluation results of these cold workability were tested N
o. 2 is shown together with the conventional example of No. 1, but as is clear from FIG. 2, when the requirements specified by the present invention are satisfied (Test Nos. 7 and 8), it is 1/10 of the usual spheroidizing treatment. It can be seen that the cold workability is equivalent to that of the conventional example even in terms of time, and the processing time can be shortened.

Example 2 Next, in order to study the influence of the chemical composition, various steel materials shown in Table 3 were prepared, and Example 1 was used.
The tissue was prepared by wire drawing-high frequency heating in the same manner as in. At this time, the wire drawing ratio was 5% uniformly, the number of repetitions was all 4 times, and the maximum heating temperature was right below the Ac ₃ point in each sample. Samples whose chemical composition is within the preferred range (N
o. With respect to 1 to 15), those having a microstructure depth of 50% were left as they were, and those having a microstructure depth of less than 50% were subjected to a simple spheroidizing treatment for 2 hours, and then cold workability was investigated.
In addition, a sample whose chemical composition is out of the preferable range (N
o. 16-29), all the samples were subjected to a simple spheroidizing treatment to confirm the effect.

[0058]

[Table 3]

Table 4 below shows the obtained structures and the results of cold workability. As is clear from this table, composition steels (Sample Nos. 1 to 1) that correspond to the preferred chemical composition of the present invention.
In 5), the one with a tissue depth of 50% remains the same,
If less than 50%, a simple spheroidizing treatment is performed for 2 hours, and all of them are shown as conventional examples in S30C.
It can be seen that it has cold workability equal to or higher than that of the spheroidized material.

On the other hand, in the composition steels (Sample Nos. 16 to 29) which deviate from the preferable chemical composition of the present invention, even if the simple spheroidizing treatment is carried out, the crack generation limit is low and the deformation resistance is high. You can see that

[0061]

[Table 4]

[0062]

EFFECTS OF THE INVENTION The present invention is constituted as described above, and the steel wire rod according to the present invention can greatly reduce the spheroidizing annealing treatment and, if necessary, can completely omit the spheroidizing annealing. Become.

[Brief description of drawings]

1 is a test No. of Table 2. It is a graph which shows the evaluation result of cold workability about 1-5.

FIG. 2 Test No. of Table 2 It is a graph which shows the evaluation result of the cold workability about 7-9.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-268546 (JP, A) JP-A-2-213415 (JP, A) JP-A-63-69914 (JP, A) JP-A-5- 339677 (JP, A) JP-A 5-339676 (JP, A) JP-A 63-20419 (JP, A) JP-A 62-139817 (JP, A) JP-A 8-295933 (JP, A) JP-A-57-52540 (JP, A) JP-A-55-94447 (JP, A) JP-A-49-115928 (JP, A) JP-A-49-40221 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C22C 38/00

Claims (3)

(57) [Claims] 1. C: 0.03 to 0.8% by mass , Si:
0.004 to 0.5 mass%, Mn: 0.05 to 2 mass%
And Al: 0.01 to 0.08% by mass, respectively.
, P: 0.03 mass% or less (including 0%), S: 0.
03 mass% or less (including 0%) and N: 0.07 mass
% Or less (including 0%), and balance iron
A steel wire rod made of evasive impurities , having a diameter of 10 mm from the surface.
%, The average grain size of ferrite is 2 to
The cold workability is characterized in that the cementite having an aspect ratio of 3 or less and having a major axis of 3 μm or less and a major axis of 3 μm or less is 70 area% or more with respect to the total cementite. Excellent steel wire rod. 2. A further, Cr: 1.5 wt% or less (not including 0%), Mo: 1.0 wt% or less (not including 0%), Ni: 1.0 wt% or less (0% the exclusive) and B: 0.0025 mass% or less (claim 1 is intended to include one or more selected from the group consisting of 0%)
Steel wire material according to. 3. A further, Ti: 0.5 wt% or less (not including 0%), V: 0.6 mass% or less (not including 0%), Nb: 0.4 wt% or less (0% 1) or more and Zr: 0.3 mass% or less (0% is not included) selected from the group consisting of 1.
Is a steel wire rod according to 2.