JPH062039A - Manufacturing method of medium carbon ultrafine steel wire - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] Diameter 0.4 mm or less, tensile strength 300 kg
Provide a method for manufacturing a high-strength, high-ductility ultrafine steel wire with f / mm ² or more. [Composition] C: 0.30 to 0.60% by weight, Si:
A chemical composition containing 0.10 to 0.50% and Mn: 0.60 to 1.5%, consisting of the balance iron and unavoidable impurities, and having an Al content of unavoidably 0.003% or less. And the tensile strength after final patenting is 103 × (% C) + 45 ≦ TS (kgf / mm ² ) ≦ 1
It is in the range of 03 × (% C) +55, and the pearlite structure has an area ratio of 99.5.
% Or more, the presence of pro-eutectoid ferrite in the area ratio of 0.5% or less is subjected to a drawing process of 4.5 or more in true strain to a drawn wire of medium carbon steel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-strength, high-ductility ultrafine wire, and particularly for an ultrafine wire having a wire diameter of 0.4 mm or less and a tensile strength of 300 kgf / mm ² or more, The present invention relates to a method for manufacturing a medium carbon ultrafine steel wire having excellent ductility such as twist value and kink.

[0002]

^2. Description of the Related Art Conventionally, in order to manufacture an ultrafine steel wire having a tensile strength of 300 kgf / mm ² or more including steel cords for tires, the carbon content is 0.7 to 0.8%.
JIS G 3502 (SWRS72A, SWR)
High carbon steel wire equivalent to S82A) is used. Normal,
A 5.5 mm wire rod was subjected to patenting treatment about twice on the way to obtain a steel cord filament (0.15 mm).
.About.0.38 mm). This utilizes the fact that a uniform and fine pearlite structure can be obtained by the patenting treatment. However, since the wire drawing limit of high carbon steel after patenting is usually as low as about 4 true strain, the smaller the final wire drawing diameter, the smaller the final heat treatment diameter, and the problem that the number of patenting must be increased. there were. Furthermore, in the medium to low carbon steel having a carbon content of 0.6% or less, it is difficult to obtain a uniform fine pearlite structure because proeutectoid ferrite is formed even if the patenting treatment is performed.

On the other hand, as an attempt to manufacture a high-strength steel wire using a low-carbon steel wire, after adjusting to a mixed structure of ferrite and acicular martensite or bainite structure in Japanese Patent Publication No. 1-15563, it is mainly used. Although a method for obtaining high strength by wire drawing is disclosed, heat treatment strength is 70 kgf /
Since it is as low as mm ² and its work hardening rate is lower than that of pearlite steel, when applied to ultra-fine wire of about 0.2 mm, the heat treatment wire diameter must be made quite large to take large wire drawing strain. Not getting the desired strength 5.5 mm
In the above large diameter heat treatment, the structure between the steel wire surface layer and the central portion is likely to be non-uniform, and with a slight formation of massive martensite,
There is a problem that it leads to early wire breakage and deterioration of mechanical properties. Therefore, it has been limited to the application to ultrafine wires of 0.15 mm or less. Japanese Unexamined Patent Publication (Kokai) No. 2-209425 discloses a method combining water quenching-processing-rapid heating-lead patenting in order to obtain a fine two-phase structure of ferrite and pearlite using low carbon steel. However, since the heat treatment process is complicated and the heat treatment strength and work hardening rate are lower than that of pearlite steel, it is necessary to make the heat treatment wire diameter considerably large in the same manner, and it is difficult to obtain a uniform fine heat treatment structure. there were. In addition, JP-A-2-30
In 5937, the average particle size of pearlite colonies is 5
Although a steel material adjusted to have a thickness of less than μm is disclosed, such miniaturization cannot be realized by ordinary patenting treatment.

[0004]

[Problems to be Solved by the Invention] In the conventional high carbon steel,
If the wire drawing strain after tenting becomes 4.5 or more, it will break.
Ductility values such as draw reduction, twist value, and kink sharply decreased.
Therefore, it is difficult to achieve both high strength and high ductility. This
This is almost proportional to the increase in carbon content,
Deterioration of ductility is observed at an early stage. Also, the tensile strength is 3
50 kgf / mm ²Drawing and twisting of high carbon ultra-fine steel wire exceeding
Ductility values such as rounding and kink are generally low, and improvements are desired.
There is.

On the other hand, low carbon steel has a wire drawing strain of 7 to 10
Although the ductility value related to the breaking area is relatively high,
Since the fiber structure of the fine pearlite structure is not the base, the twist value and kink are not as high as expected from the fracture drawing, and are generally low values. An object of the present invention is to provide a method of manufacturing an ultrafine steel wire which is basically a pearlite structure and which has been overlooked in the past and which has high strength and high ductility in medium carbon steel. Specifically, tensile strength 3
An object of the present invention is to provide a method for producing a high-strength, high-ductility ultrafine steel wire having a tensile strength of 00 kgf / mm ² or more, a breaking reduction of 40% or more, a twist value of 25 times or more, and a kink load ratio of 18% or more.

[0006]

[Means and Actions for Solving the Problems] The inventors of the present invention have been able to form proeutectoid ferrite that inhibits wire drawability and work hardening rate by adjusting alloy components and selecting appropriate patenting conditions even in medium carbon steel. It is possible to adjust to a fine all-pearlite structure with the area ratio suppressed to 0.5% or less. Furthermore, this pearlite structure is superior to the pearlite structure of high carbon steel in that it has excellent workability due to its large ferrite thickness. The present invention was constructed by discovering that even if the area-reducing ratio wire drawing process is performed, it is excellent in ductility such as break drawing, twist value, and kink.

That is, the gist of the present invention is
C: 0.30 to 0.60% by weight%, Si: 0.10 to
0.50%, Mn: 0.60 to 1.5%, a balance of iron and inevitable impurities, and an inevitable Al content of 0.003% or less.
The tensile strength after final patenting is the following formula 103 × (% C) + 45 ≦ TS (kgf / mm ² ) ≦ 1
It is in the range of 03 × (% C) +55, and the pearlite structure has an area ratio of 99.5.
% Or more, the presence of pro-eutectoid ferrite is 0.5% or less in area ratio, and a diameter of 0.4 mm or less, which is characterized by subjecting a drawn medium carbon steel wire to a true strain of 4.5 or more. And a high strength and high ductility medium carbon ultrafine steel wire having a tensile strength of 300 kgf / mm ² or more.

The reasons for limiting the starting steel composition of the present invention are as follows. When C is less than 0.30%, it is inevitable that proeutectoid ferrite precipitates with an area ratio of more than 0.5% regardless of the alloy composition and patenting conditions selected, and a fine all-perlite structure is obtained. Because it disappears
C was set to 0.30% or more. When the pro-eutectoid ferrite is formed in an area ratio of more than 0.5%, both the heat treatment strength and the wire work hardening rate are lowered, and even if the true strain of 4.5 or more is added, it is 300 kgf / mm ² or more. Tensile strength cannot be obtained. Also, disconnection during wire drawing is likely to occur. On the other hand, if C exceeds 0.60%, an all-pearlite structure can be easily obtained, but if processing with a true strain of 4.5 or more is caused, ductility deteriorates remarkably, and high strength and high ductility cannot be achieved at the same time. It was set to 0.60%.

Si is an element necessary for deoxidizing steel, and if its content is less than 0.10%, its effect is insufficient.
It was set to 0.10% or more. Further, Si dissolves in the ferrite phase in the pearlite obtained after patenting to increase the heat treatment strength, but on the other hand reduces the ductility of ferrite,
In order to reduce the ductility of the ultrafine wire after drawing, it was set to 0.50% or less.

Mn is specified from the need of ensuring the hardenability of steel and suppressing the proeutectoid ferrite after patenting. That is, when Mn is less than 0.60%, pro-eutectoid ferrite is generated in an area ratio of more than 0.5%, and an all-pearlite structure cannot be obtained. Therefore, the lower limit was made 0.60%. Further, if it exceeds 1.5%, the pearlite transformation time becomes remarkably long and it is not practical, and the effect is saturated, so 1.5% was made the upper limit.

The Al content is specified to be 0.003% or less so that hard non-deformable alumina-based non-metallic inclusions are not generated to cause deterioration of ductility and deterioration of wire drawability of the ultrafine steel wire. The impurity elements P and S are not particularly specified, but each is 0.0 from the viewpoint of ensuring ductility as in the case of conventional ultrafine steel wire.
It is preferably 20% or less. Next, in order to obtain a tensile strength of 300 mmf / mm ² or more with a diameter of 0.4 mm or less, the tensile strength after final patenting depends on the C amount and is expressed by the following formula 103 × (% C) + 45 ≦ TS (kgf / mm ² ) ≦ 1
It was specified to adjust to the range of 03 × (% C) +55. If the tensile strength after the final patenting is less than 103 × (% C) +45,
A mixed structure of pro-eutectoid ferrite and pearlite is likely to be formed, and even if wire drawing is performed thereafter, a high work strength cannot be obtained due to a low work hardening rate. Further, if 103 × (% C) +55 or more, bainite or martensite structure is mixed. And the wire drawability deteriorates,
Processing with a true strain of 4.5 or more is difficult. That is, an all-perlite structure can be obtained only in the above tensile strength range, and high wire drawability and high strength after wire drawing can be realized.

The final wire drawing is usually performed by a slip type continuous ultrafine wire drawing machine, and the wire drawing strain (true strain) at this time is 4.
Specified to be 5 or more. This has a tensile strength of 300k
It is necessary to obtain gf / mm ² or more.

[0013]

EXAMPLE According to the present invention, a steel having the composition shown in Table 1 was used to manufacture a 0.2 mm ultrafine steel wire. Symbols A to F are examples of the present invention, and symbols G to P are comparative examples. FIG. 1 shows an example of manufacturing steps and manufacturing conditions. 5.5 mm for the present invention steel
After the hot-rolled wire of (1) was drawn to 1.9 to 4.4 mmφ and drawn only once, an extra-fine steel wire of 0.2 mm could be manufactured. By performing brass plating, Ni plating, etc. after patenting, it was possible to impart functions such as a lubricating effect at the time of wire drawing, adhesion of the final wire drawn material to rubber, and corrosion resistance. Although the manufacturing process of conventional high carbon steel is also shown together, the patenting treatment is required at least twice, and the true strain in the final wet wire drawing that can secure the ductility value is about 4, and the true strain is When it was 4.5 or more, the ductility value deteriorated remarkably.

The mechanical properties after final patenting manufactured according to FIG. 1 and the area ratio of abnormal structures other than pearlite are shown in Table 2 as LP material properties, and the mechanical properties of 0.2 mm drawn wire are summarized in Table 3. Indicate. Final P of the invention material
b The tensile strength after patenting depends on the C content and is expressed by the following formula 103 × (% C) + 45 ≦ TS (kgf / mm ² ) ≦ 1
It is adjusted so as to satisfy the range of 03 × (% C) +55. FIG. 2 shows the relationship between the C content and the tensile strength of heat-treated materials (mainly patenting). In the range of the present invention, C is 0.3 to 0.6% and the tensile strength satisfies the above formula. The patenting structure was a fine pearlite structure, and the pro-eutectoid ferrite had an area ratio of 0.5% or less. Further, after brass plating, final wet wire drawing processing (final wire drawing speed of 600 m / min) was performed, but processing of true strain of 4.5 or more is possible without disconnection.
The wire drawability was extremely good. Regarding the mechanical properties of the 0.2 mm final drawn wire, the tensile strength is 300 kgf / mm ²
As described above, it was confirmed that the fracture drawing was 40% or more, the twisting value was 25 times or more, and the kink load ratio was 18% or more, and that the characteristics exhibiting both high strength and high ductility were exhibited. Although not shown in Table 3, the strand could be formed into a cord with a bunching type twisting tester.

Comparative Example G is an example in which since C was less than the specified range, proeutectoid ferrite was deposited after patenting, and high strength of 300 kgf / mm ² or more in tensile strength could not be obtained. In Comparative Example H, since Si was less than the specified range and 0.050% of Al was added for deoxidation,
0.2 mm due to the formation of hard non-metallic inclusions of alumina type
This is an example in which ultra-fine wire drawing could not be performed. On the contrary, Comparative Example I
Is an example in which since the amount of Si was more than the specified range, the cementite forming pearlite was hardened, and although a 0.2 mm drawn wire was obtained, the twisting value, ductility such as kink was deteriorated.

In Comparative Example J, since Mn was less than the specified range, a sufficient supercooling effect was not obtained after patenting, and proeutectoid ferrite was deposited, and desired strength and ductility were not obtained. Is. On the contrary, Comparative Example K is an example in which the pearlite transformation time was too long because Mn was more than the specified range, and martensite was generated due to incomplete transformation.

In both Comparative Examples L and M, the components satisfy the specified ranges, but the Pb patenting temperatures are too low and too high, respectively, and the area ratio of abnormal tissues other than the pearlite structure is 0. This is an example in which the ratio did not fall below 5%. The former cannot perform ultrafine wire drawing up to 0.2 mm due to the bainite structure, and the latter is 0.2% due to the influence of proeutectoid ferrite.
This is an example in which the ductility of the mm drawn wire is lowered.

Comparative Examples N and O are conventional high carbon steels, and the true strain of the final wet drawn wire was less than 4.5, and both of them were 0.
The 2 mm drawn wire had high tensile strength but low ductility. Also, as shown in FIG. 1, patenting was required twice, from the hot rolled wire of 5.5 mm to the final drawn wire of 0.2 mm, and the number of heat treatments was larger than that of the material of the present invention. Comparative Example P is an example in which low-carbon steel was adjusted to a two-phase structure of ferrite-acicular martensite at 5.5 mm and then drawn to 0.2 mm, but the tensile strength was less than 300 kgf / mm ² . The values of twist, kink were extremely low.

FIG. 3 shows the influence of wire drawing strain (true strain) on the tensile strength and drawing of the wire drawn materials of the present invention steel and the comparative steel.
Shown in. As a result, the invention steel D can maintain the drawing generally higher than the comparative steel O (conventional high carbon steel) and has a true strain of 4.5.
By the above processing, equivalent or higher high strength is obtained. Since the comparative steel P has a smaller heat treatment strength and a smaller wire work hardening rate than the pearlite steel, the tensile strength is 30 even when the true strain is 6.6.
It does not reach 0 kgf / mm ² .

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

As described above, according to the present invention, the number of patenting is reduced as compared with the conventional high carbon steel, and 300 kgf / m.
It is possible to manufacture a high-strength ultrafine steel wire having a tensile strength of m ² or more, and at the same time, high ductility of 40% or more at breakage, 25 or more twist values, and 18% or more kink load ratio is satisfied. Further, if the strand of the material of the present invention is used for twisting, a cord having high strength and high ductility can be manufactured. Since the fine pearlite structure is the base, fatigue properties and relaxation properties are basically the same as those of conventional high carbon steel. On the other hand, since the wire drawing process is longer than that of the conventional high carbon steel, the work hardening amount per die is dispersed, which is also effective in reducing die wear.

[Brief description of drawings]

FIG. 1 is a diagram showing a manufacturing process and manufacturing conditions of an example.

FIG. 2 is a diagram showing the relationship between the patenting strength and the C content of the material of the present invention.

FIG. 3 is a diagram showing a comparison of wire drawing work hardening curves of the medium carbon steel of the present invention and the conventional high carbon steel.

Claims (1)

[Claims] 1. C: 0.30 to 0.60%, Si: 0.10 to 0.50%, Mn: 0.60 to 1.5% by weight, and the balance iron and unavoidable impurities. And having an Al content of unavoidably 0.003% or less, the tensile strength after final patenting is expressed by the following formula 103 × (% C) + 45 ≦ TS (kgf / mm ² ) ≤ 1
It is in the range of 03 × (% C) +55, and the pearlite structure has an area ratio of 99.5.
% Or more, the presence of pro-eutectoid ferrite is 0.5% or less in area ratio, and a diameter of 0.4 mm or less, which is characterized by subjecting a drawn medium carbon steel wire to a true strain of 4.5 or more. And method for producing high-strength and high-ductility medium carbon ultrafine steel wire with tensile strength of 300 kgf / mm ² or more.