JPH05156369A - Manufacture of steel cord - Google Patents

Abstract

PURPOSE:To manufacture a steel cord by one time patenting after the rolling of wire rod. CONSTITUTION:Hot rolled wire rod of 4.5 to 6.5mmphi contg., by weight, 0.80 to 0.90% C, 0.1 to 1.5% Si and 0.1 to 1.0% Mn, furthermore contg., at need, 0.10 to 1.0% Cr and the balance iron which inevitable impurities and in which the content of Al included inevitably is regulated to <=0.003% is used. It is cooled from the temp. range of 800 to 1100 deg.C to 450 to 550 deg.C at >=50 deg.C/s cooling rate. After that, its transformation is completed in the temp. range of 450 to 550 deg.C, and according to necessity, it is held to >=450 deg.C for <=120s and is cooled to a room temp. By wire drawing, it is formed into a wire of 0.6 to 1.3mmphi, which is subjected to final patenting treatment, is subjected to blast plating treatment and is thereafter formed into a wire of 0.10 to 0.3mmphi by final wet wire drawing. The objective steel cord having >=2800MPa tensile strength of wire rod can be manufactured.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Steel cords are made into a pearlite structure by adjusting and cooling after hot rolling, and then 30 to 70% are processed by wire drawing, and a pearlite structure which is not affected by the processing by patenting treatment. 30 ~
The wire having a predetermined wire diameter is processed by 70%, and finally wet drawn to a wire having a diameter of 0.15 to 0.35 mmφ,
These are twisted together 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 Examined Patent Publication No. 60-56215 discloses C: 0.
2 to 1.0 wt%, Si: 0.30 wt% or less, Mn:
KNO after hot rolling of steel consisting of 0.3 to 0.9 wt%
₃ , a heat treatment method of a wire rod for directly producing a wire product having a diameter of 1 to 5 mm by quenching in a NaNO ₃ salt bath to obtain a wire rod having a fine pearlite structure. Also,
In Japanese Examined Patent Publication No. 60-7004, C: 0.75-1.
0 wt%, Si: 0.5 to 1.5 wt%, Mn: 0.6
~ 1.3 wt%, Al: 0.1 wt% or less, and optionally Cr: 0.3 wt% or less after hot rolling 8
After cooling to 50 ° C., a method for producing a steel wire rod having excellent wire drawability is described in which the subsequent cooling rate is 7 ° C./s.

[0004]

Recently, due to energy problems, it has been required to manufacture products with energy saving especially in the industrial field. In the process of repeating heat treatment and cooling like steel products, the heat treatment process should be performed as much as possible. There is a need for a manufacturing process that omits. Also in the production of steel cords, heat treatment is performed by repeating wire drawing after hot rolling and patenting treatment.
Therefore, a method of manufacturing a steel cord that is capable of omitting steps as much as possible is expected.

The present invention is a method for producing a steel cord from a hot-rolled wire rod having a diameter of 4.5 to 6.5 mm by wire-drawing. A method of manufacturing a steel cord by a coating process is provided.

[0006]

SUMMARY OF THE INVENTION The gist of the present invention is the weight%
, C 0.80% or more and 0.90% or less, Si 0.
1% or more and 1.5% or less, Mn 0.1% or more and 1.0% or less, and if necessary, Cr 0.10% or more and 1.0% or less, and the balance is iron and inevitable impurities, and is unavoidable. 4.5 with Al content of 0.003% or less
A hot-rolled wire rod having a diameter of ~ 6.5 mmφ is subjected to controlled cooling such that the abundance of cementite having an aspect ratio of 10 or less present in the cross section of the wire rod becomes 75% or more, and then 0.6-1. 3mmφ wire, then final patenting treatment, brass plating treatment, then final wet drawing 0.10-0.3mm
A steel cord manufacturing method is characterized in that a wire having a tensile strength of 2800 MPa or more at φ is formed and then twisted to form a cord. As the adjustment cooling, the wire rod after the hot rolling is finished is heated from 450 ° C to 550 ° C at a cooling rate of 50 ° C / s or more from a temperature range of 800 ° C to 1100 ° C.
After cooling to the temperature below, the transformation is completed within the temperature range of 450 ° C to 550 ° C, and if necessary, 450 ° C.
It is preferable to hold it for 120 s or more and cool it to room temperature.

[0007]

The reason for limiting the steel composition of the present invention is as follows.

The primary drawability is remarkably lowered when the amount of C added is 0.8% or more, so the lower limit is made 0.8%. The upper limit is 0.9, which is not affected by center segregation.
% Or less.

Si is an element necessary for deoxidizing steel, and if the content is too small, the deoxidizing effect will be insufficient, so the lower limit is made 0.1%. Further, Si dissolves in the ferrite phase in pearlite formed after heat treatment to increase the strength after patenting, but on the other hand, it lowers the ductility of ferrite and lowers the ductility of ultrafine wires after drawing, so the upper limit is set. 1.5%.

The lower limit of Mn is 0.1% in order to secure the hardenability of steel. However, the addition of a large amount of Mn causes segregation, and a supercooled structure such as bainite and martensite is generated during patenting, which impairs the subsequent wire drawability, so the upper limit is made 1.0%.

In the case of hyper-eutectoid steel, a cementite network is likely to occur in the structure after patenting,
Cementite with a large thickness easily precipitates. In order to achieve high strength and high ductility in this steel, it is necessary to make pearlite fine and to eliminate the cementite network and thick cementite. Cr suppresses the appearance of such an abnormal portion of cementite and further has the effect of refining pearlite, so Cr is added if necessary. The lower limit is set to 0.1% or more where the effect can be expected. But,
Addition of a large amount increases the dislocation density in the ferrite after heat treatment, and therefore significantly impairs the ductility of the ultrafine wire after drawing. Therefore, the upper limit is set to 1.0% or less, which does not impair the ductility.

Similar to the conventional ultra-fine steel wire, the S content is 0.020% or less in order to secure the ductility, and P also impairs the ductility of the wire like S, so the content is 0.020% or less. Is desirable.

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

The reasons for limiting the manufacturing conditions are as described below.

C content was 0.82 wt% by controlled cooling
% Steel having a pearlite structure, any structure for improving the wire drawability, under practical manufacturing conditions, a hot-rolled wire of 4.5 to 6.5 mmφ with a true strain of 3 It was impossible to process to more than 0.0. This is Oka et al. [Materials and Process, 4 (1991) 2
According to [042], when the pearlite structure is used, if the fine pearlite structure is used, the work hardening rate is increased and the workability is lowered, and if the coarse pearlite structure is used, the thickness of the cementite phase is increased and the workability is decreased. ing.

Therefore, the present inventors have paid attention to the shape of cementite formed after hot rolling, and the work hardening rate increases as the abundance of cementite having an aspect ratio of 10 or less observed in the cross section of the wire increases. It was found that the workability was improved and the workability was improved.

In order to set the aspect ratio of cementite to 10 or less, for example, 800 ° C. or more after hot rolling and 110
The cooling rate from the temperature range of 0 ° C. or lower is set to 50 ° C./s or higher so as not to cause pearlite transformation. The isothermal transformation temperature has an upper limit of 550 ° C. because a lamellar structure in which cementite is hard to be spheroidized develops when the transformation temperature rises. Further, when the transformation temperature is low, the time until the transformation is completed is long and the productivity is lowered. Therefore, 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, if necessary, the pearlite structure is spheroidized by maintaining the temperature above the transformation temperature within 120 s after the transformation is completed. Can be promoted.

The finished wire diameter in the primary wire drawing after hot rolling is set to 1.3 mmφ or less, which is different from that of pearlite steel. Also, if the finish is less than 0.6 mmφ, the wire characteristics obtained by subsequent processing deteriorate, so 0.6 mm
φ or more.

[0020]

EXAMPLES Steel cords were manufactured by using the steels having the constituent 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 examples of the present invention.
Sample numbers 11 to 14 are samples for comparative examples.

The manufacturing process is as shown in FIG. 1, and a wire diameter of 4.5 to 6.5 mmφ manufactured by controlled cooling after hot rolling was set to a wire diameter for final patenting treatment by wire drawing. After performing the final patenting treatment on this wire, brass plating was performed, and further final wet drawing was performed to obtain a final wire.

The microstructures shown in Table 2 indicate the abundance of cementite existing in the cross section of the wire rod and having an aspect ratio of 10 or less.

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

The number of breaks in the stranded wire in Table 2 is 4000
The number of wire breakages when the twisted wire is processed by twisting m into two strands is shown.

Sample Nos. 1 to 1 produced according to the method of the present invention
No. 10 is capable of wire drawing with a predetermined wire diameter without any problem, and has not been broken even in twisted wire processing.

Since the sample No. 11 has a low isothermal transformation temperature,
Although it has a predetermined microstructure rate, since the strength after rolling is high, delamination occurred before reaching the target wire diameter in the primary wire drawing, and the target wire diameter could not be reached.

Sample No. 12 has a high isothermal transformation temperature and a high transformation temperature, so that the layered structure is sound, the spheroidization of the lamellar structure is not promoted even after 120 s is retained, and the structure ratio is as low as 30%. ing. Therefore, delamination occurred at the primary wire drawing of 1.20 mmφ and the target wire diameter could not be reached.

Sample No. 13 has different cooling rates,
Since the cooling rate is low, a pearlite structure appears, and subsequent fragmentation of cementite has not progressed. For this reason, delamination occurred at the primary wire drawing of 1.20 mmφ, and although wire drawing could be performed up to the target wire diameter, since the wire contains defects, the strength and ductility are reduced.

Sample No. 14 has a holding temperature of 4 after the transformation.
At a level lower than 50 ° C, the holding temperature after transformation is low, so
The organization rate is low. For this reason, although the final wire can be manufactured, the number of breaks in the twisted wire processing is large.

[0033]

INDUSTRIAL APPLICABILITY In the production of a steel cord by wire drawing from a hot-rolled wire having a diameter of 4.5 to 6.5 mm, a minimum required one patenting treatment is performed between the hot-rolled wire and the final wire. The tensile strength of the wire is 280
A steel cord of 0 MPa or more can be manufactured.

[Brief description of drawings]

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

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location C22C 38/18 (72) Inventor Masao Ochiai 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Kimitsu Co., Ltd. Inside the ironworks

Claims (2)

[Claims] 1. By weight%, C 0.80% or more and 0.90% or less, Si 0.1% or more and 1.5% or less, Mn 0.1% or more and 1.0% or less, and if necessary Cr 0. 10% or more and 1.0% or less, balance iron and inevitable impurities, and
The abundance of cementite having an aspect ratio of 10 or less in the cross section of the wire in a hot-rolled wire of 4.5 to 6.5 mmφ with an Al content of unavoidably 0.003% or less is 75% or more. After adjusting and cooling, a wire having a diameter of 0.6 to 1.3 mmφ is drawn by wire drawing, then a final patenting process is performed, and a brass plating process is further performed. 0.
Wire with 3 mmφ and tensile strength of 2800 MPa or more,
A method for manufacturing a steel cord, which is characterized by twisting the cords into cords thereafter. 2. As the conditioning cooling, the wire rod after the hot rolling is finished is heated in a temperature range from 800 ° C. to 1100 ° C.
After cooling to a temperature of 450 ° C. or higher and 550 ° C. or lower at a cooling rate of C ° C./s or higher, the transformation is completed within a temperature range of 450 ° C. or higher and 550 ° C.
The method for manufacturing a steel cord according to claim 1, wherein the steel cord is held for 20 seconds and cooled to room temperature.