JP2641081B2 - Steel cord manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, high-ductility steel cord used for reinforcing rubber tires for trucks, buses, passenger cars and the like, or belts for power transmission, etc. It relates to a manufacturing method.

[0002]

2. Description of the Related Art After a steel cord has a pearlite structure by controlled cooling after hot rolling, it is processed by 30 to 70% by wire drawing, and a pearlite structure which is not affected by the processing by a patenting process. 30 ~
70% processing to make a wire of a predetermined wire diameter, and to a wire of 0.15 to 0.35 mmφ by final wet drawing,
This is twisted and used as a steel cord.

As a method for obtaining a pearlite structure by controlled cooling after hot rolling, there are methods described in JP-B-60-56215 and JP-B-60-7004. Japanese Patent Publication No. 60-56215 discloses that C: 0.
2 to 1.0 wt%, Si: 0.30 wt% or less, Mn:
KNO after hot rolling of steel consisting of 0.3-0.9 wt%
_3. A heat treatment method for a wire rod, which is quenched in a NaNO ₃ salt bath to obtain a wire rod having a fine pearlite structure to directly produce a wire product of 1 to 5 mmφ. Also,
Japanese Patent Publication No. 60-7004 discloses C: 0.75 to 1.
0 wt%, Si: 0.5 to 1.5 wt%, Mn: 0.6
After hot rolling a steel containing 0.1 to 1.3 wt%, Al: 0.1 wt% or less, and Cr: 0.3 wt% or less as necessary,
A method for producing a steel wire rod having excellent drawability, in which the cooling rate after cooling to 50 ° C. is 7 ° C./s, is described.

[0004]

In recent years, it has become necessary to manufacture products with energy savings, especially in the industrial field due to energy problems. In a process of repeating heat treatment and cooling like steel products, a heat treatment process is required. Is required. Also in the production of steel cords, heat treatment is performed by repeating drawing and patenting after hot rolling.
Therefore, a method of manufacturing a steel cord that can omit steps as much as possible is expected.

The present invention relates to a method of producing a steel cord from a hot-rolled wire having a diameter of 4.5 to 6.5 mm by wire drawing, wherein a minimum of one patent required between the hot-rolled wire and the final wire is provided. The present invention provides a method of manufacturing a steel cord by a heating process.

[0006]

Means for Solving the Problems The gist of the present invention is that the weight%
0.80% to 0.90% of C, 0.1% to 1.5% of Si, 0.1% to 1.0% of Mn, Cr 0.10% to 1.0% as necessary Containing the following, consisting of iron and unavoidable impurities, and
In the hot-rolled wire of 4.5 to 6.5 mmφ with the unavoidable Al content of 0.003% or less, the existence ratio of cementite having an aspect ratio of 10 or less in the wire cross section is 75% or more. After adjusting and cooling, wire drawing is performed to obtain a wire having a diameter of 0.6 to 1.3 mm, then final patenting is performed, and further brass plating is performed. 0.
3mmφ wire with tensile strength of 2800MPa or more,
Thereafter, the cord is twisted to form a cord. However, as the adjusted cooling, the wire after the completion of the hot rolling is heated to 450 ° C. at a cooling rate of 50 ° C./s or more from a temperature range of 800 ° C. to 1100 ° C.
After cooling to a temperature of not less than 550 ° C. and
0 ℃ terminate the transformation in the temperature range below, held within 120s to 450 ° C. or higher, if necessary, it cooled <br/> to room temperature.

[0007]

The reasons for limiting the steel composition of the present invention are as follows.

Since the primary drawability is significantly reduced when the amount of C added is 0.8% or more, the lower limit is set to 0.8%. Further, the upper limit is set to 0.9 which is not affected by the center segregation.
% Or less.

[0009] Si is an element necessary for deoxidizing steel, and if the content is too small, the deoxidizing effect becomes insufficient, so the lower limit is made 0.1%. Also, Si forms a solid solution in the ferrite phase in pearlite formed after heat treatment and increases the strength after patenting, but on the other hand, it lowers the ductility of ferrite and lowers the ductility of the ultrafine wire after drawing, so an upper limit is set. 1.5%.

The lower limit of Mn is set to 0.1% in order to secure the hardenability of steel. However, the addition of a large amount of Mn causes segregation, generates a supercooled structure of bainite and martensite at the time of patenting, and impairs the subsequent drawability, so the upper limit is made 1.0%.

In the case of hypereutectoid steel, a cementite network is likely to be generated in the structure after patenting,
Thick cementite tends to precipitate. In order to realize high strength and high ductility in this steel, it is necessary to make pearlite fine and eliminate cementite network and thick cementite. Cr is added as necessary because it has the effect of suppressing the appearance of such an abnormal portion of cementite and making pearlite finer. The lower limit is set to 0.1% or more where the effect can be expected. But,
The addition of a large amount increases the dislocation density in the ferrite after the heat treatment, and thus significantly impairs the ductility of the ultrafine wire after the drawing. Therefore, the upper limit is set to 1.0% or less which does not impair ductility.

Similar to the conventional ultrafine steel wire, the content of S is set to 0.020% or less in order to ensure ductility, and P also impairs the ductility of the wire similarly to S, so the content is set to 0.020% or less. It is desirable that

[0013] As a cause of reducing the ductility of the ultrafine wire, A
There are non-ductile inclusions mainly composed of Al ₂ O ₃ such as l ₂ O ₃ and MgO-Al ₂ O ₃ . Therefore, in the present invention, in order to avoid a decrease in ductility due to non-ductile inclusions, Al
The content is set to 0.003% or less.

The reasons for limiting the manufacturing conditions are as follows.

[0015] The C content is adjusted to 0.82wt by controlled cooling.
% Or more of steel having a pearlite structure, a hot-rolled wire of 4.5 to 6.5 mmφ with a true strain of 3 to 4.5 mm in diameter under practical production conditions may be used to improve wire drawability. It was not possible to process to over 0.0. This is described by Oka et al. [Materials and Processes, 4 (1991) 2
042], when the pearlite structure is used, a fine pearlite structure increases the work hardening rate, thereby reducing workability. A coarse pearlite structure increases the thickness of the cementite phase and decreases workability. ing.

Therefore, the present inventors focused on the shape of cementite formed after hot rolling, and as the abundance of cementite having an aspect ratio of 10 or less observed in the cross section of the wire increased, the work hardening rate increased. Was found to be reduced and workability could be improved.

In order to reduce the aspect ratio of cementite to 10 or less, for example, 800 ° C. or more after hot rolling
The cooling rate from a temperature range of 0 ° C. or less is set to 50 ° C./s or more so as not to cause pearlite transformation. The upper limit of the isothermal transformation temperature is set to 550 ° C., because a higher transformation temperature leads to the development of a lamellar structure in which cementite is less likely to be spheroidized. Further, when the transformation temperature is lowered, the time until the completion of the transformation becomes longer and the productivity is lowered, so the lower limit is set to 450 ° C.

Further, in order to make the abundance of cementite having an aspect ratio of 10 or less 80% or more, the pearlite structure is spheroidized by maintaining the temperature at or above the transformation temperature within 120 s after completion of the transformation, if necessary. Can be promoted.

The finished wire diameter in the primary drawing after hot rolling is set to 1.3 mmφ or less, which is a difference from the pearlite steel. Further, if finished to less than 0.6 mmφ, the wire characteristics obtained by subsequent processing will be deteriorated.
φ or more.

[0020]

EXAMPLE A steel cord was manufactured using steel having the component elements shown in Table 1 according to the manufacturing conditions shown in Table 2.

[0021]

[Table 1]

[0022]

[Table 2]

Sample Nos. 1 to 10 are samples for the present invention.
Sample numbers 11 to 14 are samples for a comparative example.

The production process is as shown in FIG. 1, and a wire rod of 4.5 to 6.5 mmφ produced by conditioning and cooling after hot rolling was made to have a wire diameter to be subjected to a final patenting process by wire drawing. After the final patenting treatment was performed on this wire, brass plating was performed, and final wet drawing was performed to obtain a final wire.

The texture ratio in Table 2 indicates the presence ratio of cementite having an aspect ratio of 10 or less in the cementite existing in the cross section of the wire.

The results of the primary wire drawing final diameter in Table 2 show the limit wire sample diameter at which delamination does not occur in the twisting test after taking out the sample in the wire drawing process.

The number of breaks at the time of the stranded wire shown in Table 2 is
The figure shows the number of disconnections when m is twisted by two strands.

Sample Nos. 1 to 1 manufactured according to the method of the present invention
No. 10 can be drawn with a predetermined wire diameter without any problem, and does not break even in stranded wire processing.

Sample No. 11 has a low isothermal transformation temperature.
Despite having a predetermined texture ratio, the strength after rolling was high, so that delamination occurred before reaching the target wire diameter in the primary drawing, and the steel wire could not reach the target wire diameter.

Sample No. 12 had a high isothermal transformation temperature and a high transformation temperature, so that the layered structure became sound. Even when the temperature was maintained for 120 s, the spheroidization of the lamellar structure was not promoted, and the structure ratio was as low as 30%. ing. For this reason, delamination occurred at 1.20 mmφ of the primary wire drawing, and could not reach the target wire diameter.

Sample No. 13 has different cooling rates.
Due to the low cooling rate, a pearlite structure appeared, and the subsequent cementite fragmentation did not proceed. For this reason, delamination occurs at 1.20 mmφ of the primary wire drawing, and although wire drawing was performed to the target wire diameter, the strength and ductility are reduced due to the inclusion of defects inside the wire.

Sample No. 14 had a holding temperature of 4 after the transformation was completed.
Because the holding temperature after transformation is low at a level lower than 50 ° C,
Organization rate is low. For this reason, although the final wire can be manufactured, the number of disconnections in the stranded wire processing is increasing.

[0033]

According to the present invention, in the production of a steel cord by drawing from a hot-rolled wire of 4.5 to 6.5 mmφ, at least one patenting process is required between the hot-rolled wire and the final wire. 280 tensile strength
A steel cord of 0 MPa or more can be manufactured.

[Brief description of the drawings]

FIG. 1 is a view showing a manufacturing process of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location C22C 38/18 C22C 38/18 (72) Inventor Seio Ochiai 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation (56) References JP-A-2-263951 (JP, A) JP-A-58-27926 (JP, A)

Claims (3)

(57) [Claims] In claim 1 the weight%, C 0.80% to 0.90% or less, Si 0.1% or more and 1.5% or less, and containing 1.0% or less than 0.1% Mn, the balance Consisting of iron and unavoidable impurities, and
In the hot-rolled wire of 4.5 to 6.5 mmφ with the unavoidable Al content of 0.003% or less, the existence ratio of cementite having an aspect ratio of 10 or less in the wire cross section is 75% or more. The following adjustment cooling is performed, and then a wire of 0.6 to 1.3 mmφ is drawn by wire drawing.
After that, a final patenting process was performed, and a brass plating process was further performed.
A method for producing a steel cord, comprising: forming a wire having a tensile strength of 2800 MPa or more at a diameter of 0.3 mmφ and then twisting to form a cord. Adjusting cooling, hot pressure
After the completion of the drawing, the wire is kept in a temperature range
450 ° C or more and 550 at a cooling rate of 50 ° C / s or more from the surrounding area
After cooling to a temperature of 450 ° C or less,
Finish the transformation in the temperature range and cool to room temperature. 2. The hot-rolled wire further contains 0.10%
The stee according to claim 1, which contains Cr in an amount of not less than 1.0% and not more than 1.0%.
Manufacturing method (3) As the adjustment cooling, after the completion of hot rolling
The wire is moved from a temperature range of 800 ° C or higher and 1100 ° C or lower to 50
Temperature of 450 ° C or more and 550 ° C or less at a cooling rate of 100 ° C / s or more
After cooling to a temperature between 450 ° C and 550 ° C
Finish the transformation and keep it at 450 ° C or higher for 120s or less.
The steam according to claim 1, wherein the steam is held and cooled to room temperature.
Manufacturing method