JP3300932B2 - Manufacturing method of high strength steel wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to twisting a high-strength thin wire such as a steel cord used for reinforcing rubber tires of trucks, buses and passenger cars or a belt cord used for reinforcing belts. The present invention relates to a method for manufacturing a high-tensile steel wire obtained by joining.

[0002]

2. Description of the Related Art Steel wire manufacturing methods utilizing pearlite transformation have been used for a long time. Generally A ₃ point or more temperature region heated to (750 to 1100 ° C.), was treated γ of, to obtain a pearlite structure performs isothermal transformation treatment at a temperature range of the quenching to five hundred fifty to six hundred eighty ° C., further the tissue Is used as a wire by wire drawing.

[0003] As a method of controlling the pearlite transformation, there is a method described in JP-A-1-316420.
This cools to 900-800 ° C in the austenitic range,
This is a method for producing a high-strength, high-fatigue-strength cord wire that is plastically worked at a working degree of 20 to 40% in this temperature range and then immersed in lead.

[0004]

The most important factor in producing a high-strength steel wire is a structure formed in final patenting. Generally, the heat treatment process is adjusted so as to form a uniform pearlite structure by a patenting process. However, in the conventional patenting treatment, even in the hypereutectoid steel, a thin ferrite or pseudo-pearlite structure precipitates along the old γ grain boundary. This phase becomes a starting point of a crack in the wire drawing process, and therefore needs to be suppressed as much as possible. Therefore, the emergence of a production method that renders this phase harmless is expected.

[0005]

The gist of the present invention is as follows. (1) In the method for manufacturing a steel wire which comprises performing the wire drawing the steel wire after final patenting treatment, after the austenitizing, the A ₁ transformation temperature below the temperature, final
The transformation of steel caused by the patenting process
That is, a thin ferrite formed early in the pearlite transformation
Before or after the formation of
-A method for producing a high-strength steel wire, wherein the final patenting treatment is performed while processing the steel wire during the light transformation .

(2) In a method for producing a steel wire, which comprises drawing the steel wire after the final patenting treatment, C: 0.90% to 1.10% by weight, Si: 0. 4% or less, Mn: 0.5% or less, Cr: 0.10% to 0.30%, Ni: 0.10% to 1.00%, Cu: 0.10% to 0.80% comprise one or more of the following, will than the remainder iron and unavoidable impurities, and the Al content falling unavoidable with the steel wire 0.003% or less, after the austenitizing, a ₁ transformation temperature below the temperature In the final patenting process
The transformation of steel caused by
Initially formed thin ferrite or pseudo-pearlite
A method for producing a high-strength steel wire, wherein the final patenting treatment is performed while the steel wire is being processed before the formation of the microstructure or during the pearlite transformation .

(3) In a method for producing a steel wire, which comprises drawing a steel wire after the final patenting treatment, the steel wire is austenitized and then caused by the final patenting treatment at a temperature not higher than the A ₁ transformation temperature. Re
Formed in the early stage of the transformation of
Thin ferrite or pseudo-pearlite structure
D / d ≦ 2 before or during pearlite transformation
A method for producing a high-tensile steel wire, wherein the final patenting treatment is performed while performing bending with a roll satisfying 0 (D: roll diameter, d: wire diameter).

[0008]

The reasons for limiting the steel composition of the present invention are as follows. C is an economical and effective strengthening element, but it is necessary that the addition amount be 0.90% or more in order to sufficiently exert the effect of C. However, if it is too high, the ductility decreases and the drawability deteriorates, so the upper limit is set to 1.10%.

[0009] Si is an element necessary for deoxidizing steel, and if its content is too small, the deoxidizing effect becomes insufficient. Also, Si forms a solid solution in the ferrite phase in pearlite formed after heat treatment and increases the strength after patenting, but decreases the ductility of ferrite,
0.4% or less to reduce the ductility of the ultrafine wire after drawing.

Mn is desirably added in a small amount to ensure the hardenability of steel. However, the addition of a large amount of Mn causes segregation, and during patenting, bainite,
A supercooled structure such as martensite is generated, which impairs the drawability thereafter, so that the content is 0.5% or less. Cr, Ni, Cu
Is added for at least one of the following reasons.

In the case of the hypereutectoid steel as in the present invention, a cementite network is easily generated in the structure after patenting, and a thick cementite is easily precipitated. In order to realize high strength and high ductility in this steel, it is necessary to make pearlite fine and eliminate the cementite network and thick cementite as described above. Cr has the effect of suppressing the appearance of such abnormal portions of cementite and further reducing pearlite. However, the addition of a large amount increases the dislocation density in the ferrite after the heat treatment, and significantly impairs the ductility of the ultrafine wire after the drawing. Therefore, the amount of Cr added is set to 0.10% or more where the effect can be expected, and the dislocation density in ferrite is increased to 0.30% without impairing ductility.
% Or less.

Since Ni also has the same effect as Cr, if necessary, 0.10% or more is added to exhibit the effect. Ni
If the addition amount is too large, the ductility of the ferrite phase is reduced, so the upper limit is made 1.00%. Since Cu is an element for improving the corrosion fatigue properties of the wire, it is desirable to add 0.10% or more that exhibits its effect. If the addition amount of Cu is too large, the ductility of the ferrite phase is reduced, so the upper limit is made 0.80%.

[0013] The content of S is set to 0.020% or less in order to secure the ductility similarly to the conventional ultrafine steel wire, and the content of P is set to 0.020% or less because P also impairs the ductility of the wire similarly to S. It is desirable to do. As a cause of reducing the ductility of the ultrafine wire, there is a non-ductile inclusion mainly composed of Al ₂ O ₃ such as Al ₂ O ₃ and MgO—Al ₂ O ₃ . Therefore, in the present invention, the Al content is set to 0.003% or less in order to avoid a decrease in ductility due to non-ductile inclusions.

The reasons for limiting the production method of the present invention are as follows. By the final heat treatment, a ferrite phase or a pseudo-pearlite phase precipitates along with the former austenite grain boundary. Since this phase becomes a starting point of cracking during wire drawing, it is necessary to suppress precipitation as much as possible or to change the precipitation form to a form in which cracks are unlikely to occur. This precipitation cannot be suppressed in the ordinary patenting treatment. Therefore, it is necessary to make the deposit harmless by changing the form of the deposition. In order to render the precipitation form harmless, it is necessary to change the site of precipitation from a plane to a point by imparting strain to the prior austenite grain boundaries. To this end, enters easily the most work strain, with the A ₁ transformation temperature or lower temperatures after austenitizing, the steel caused by the final patenting treatment
Transformation, a thin formed early in the pearlite transformation
Before ferrite or pseudo-pearlite structure is formed
Alternatively, it is necessary to perform a final patenting process while processing the steel wire during the pearlite transformation .

The processing may be any processing as long as processing distortion can be given. For example,
Any of rolling, bending, swaging, etc. is effective. Further, since the bending process hardly changes the shape of the wire due to the bending process, the wire can be easily introduced. However, since bending deformation introduced into the wire in bending is small, it is necessary to perform bending that satisfies at least D / d ≦ 20 (D: roll diameter, d: wire diameter).

[0016]

EXAMPLES As shown in Table 1 (chemical components) and Table 2 (processing conditions and characteristics), saw wires were manufactured using manufacturing methods 11 to 14 for comparison with manufacturing methods 1 to 10 according to the present invention. did. The manufacturing process is as shown in FIG. 1. A 5.5 mmφ wire rod manufactured by hot rolling is made into a wire having a wire diameter for performing the final patenting treatment shown in Table 2 by wire drawing and LP treatment. Using this wire, heat treatment was performed according to the method of the present invention and the comparative method shown in Table 2. After that, a wire having a final wire diameter was formed by wire drawing using a die having a die approach angle of 14 °. At this time, the number of microcracks present in the wire was measured at a 1/2 part of the L cross section when the area reduction rate in the wire drawing became about 1.0 in true strain. In addition, a tensile test and a torsion test were performed on the final wire, and the mechanical properties of the final wire were investigated.

In Nos. 1 to 10, no microcracks were observed during drawing, and even in a wire produced by subsequent drawing, a wire free of delamination was obtained by a twist test. No. 11 is a level that has not performed the processing in the following _point A. Microcracks occur during the wire drawing process, and delamination also occurs in the final wire.

Reference numeral 12 denotes a level at which processing was not performed at the point A ₁ or less. Micro cracks occur during the wire drawing process,
Delamination has also occurred in the final wire. No. 13 is a case of performing processing at _one point than A. In this case, since the processing temperature is high, the effect of processing does not remain,
Improvement of bad organization cannot be expected. For this reason, microcracks occur during the wire drawing process, and delamination also occurs in the final wire.

No. 14 indicates that the D / d value is 2 in bending.
This is the case when the value exceeds 0. In this case, since the processing is light, the influence of the processing does not remain, and improvement of the defective structure cannot be expected.
For this reason, microcracks occur during the wire drawing process, and delamination also occurs in the final wire.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

According to the present invention, a wire having excellent wire drawing properties can be obtained by the final patenting treatment according to the present invention, and a high tensile strength steel wire having more excellent ductility can be obtained by subsequent wire drawing. .

[Brief description of the drawings]

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

Claims (3)

(57) [Claims] 1. A method for producing a steel wire, comprising drawing a steel wire after a final patenting process, wherein the steel wire is austenitized and then caused by the final patenting process at a temperature not higher than the A ₁ transformation temperature. Steel
Transformation, a thin formed early in the pearlite transformation
Before ferrite or pseudo-pearlite structure is formed
Or a method of manufacturing a high-strength steel wire, wherein the final patenting treatment is performed while processing the steel wire during pearlite transformation . 2. A method for manufacturing a steel wire, comprising drawing a steel wire after the final patenting treatment, wherein C: 0.90% to 1.10% by weight, Si: 0.4% by weight. %: Mn: 0.5% or less, Cr: 0.10% to 0.30%, Ni: 0.10% to 1.00%, Cu: 0.10% to 0.80% of including one or more, than the remainder iron and unavoidable impurities, and with a steel wire having an Al content is set to 0.003% or less to enter the inevitable, after austenitizing, the a ₁ transformation temperature below the temperature , Due to the final patenting process
The transformation of steel caused by
Initially formed thin ferrite or pseudo-pearlite
A method for producing a high-strength steel wire, wherein the final patenting treatment is performed while the steel wire is being processed before the formation of the microstructure or during the pearlite transformation . 3. A method for manufacturing a steel wire, comprising drawing a steel wire after a final patenting process, wherein the steel wire is austenitized and then caused by the final patenting process at a temperature not higher than the A ₁ transformation temperature. Steel
Transformation, a thin formed early in the pearlite transformation
Before ferrite or pseudo-pearlite structure is formed
Or D / d ≦ 20 on steel wire during pearlite transformation
(D: roll diameter, d: diameter of wire) A method for producing a high-tensile steel wire, wherein the final patenting treatment is performed while performing bending with a roll satisfying (d: diameter of wire).