JP2922316B2 - Manufacturing method of high strength steel wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a steel cord, Z
The present invention relates to a method for manufacturing a high-strength steel wire used for an n-plated steel stranded wire, a PC steel wire, a suspension bridge cable, and the like.

[0002]

2. Description of the Related Art As a measure for increasing the strength of a high carbon steel wire,
Increasing the C content is the most industrially desirable method because it is inexpensive and has a high effect. However, in the hypereutectoid region, that is, the region where C is usually more than 0.9%,
During patenting, brittle pro-eutectoid cementite is formed in a network along the prior austenite grain boundaries. For this reason, at the time of wire drawing, grain boundaries along pro-eutectoid cementite tend to occur, and wire drawing with a high area reduction becomes impossible.

Conventionally, as a method of improving the drawability of hypereutectoid steel, a method of suppressing the formation of proeutectoid cementite by heat treatment or addition of an alloy element, or a method of evoking proeutectoid cementite by devising a drawing method. Methods have been developed to prevent ductile degradation. For example,
No. 6-8893 discloses a method of changing the structure to a pearlite structure in which granular cementite is dispersed by heat treatment. This is austenitized hypereutectoid steel wire, after oil quenching to martensite structure,
The mixture was rapidly heated to a temperature range of 770 to 930 ° C. to precipitate particulate cementite.
This is a method of performing a patenting process at a temperature of ６660 ° C. This method is excellent as a method of raising the drawing limit, but the cementite that has been granulated has a small contribution to strengthening unlike cementite developed in a layered form (the strength after patenting is low, (The work hardening is also small.) Therefore, the effect of increasing the C content cannot be utilized.

The inventors of the present invention have studied a method of suppressing the generation of proeutectoid cementite by utilizing the effect of adding an alloy element.
Patent application No. -76825. All of them are characterized by adding 0.1 to 0.3% of Cr, but they cannot prevent the formation of a small amount of proeutectoid cementite.

Japanese Patent Application Laid-Open No. Sho 63-186852 discloses that 5-50 ppm of REM and Ca, Mg, Ba, S
A method is disclosed in which at least one of r is added in a total of 5 to 50 ppm. All of these elements are elements that simultaneously generate sulfide and oxide. In this method, pearlite transformation is promoted using fine sulfide oxides containing REM, Ca, Mg, Ba, and Sr generated by these additions as nuclei to suppress the formation of martensite and proeutectoid cementite. However, in this method, not only the addition of the above-mentioned trace elements, but also the content of S, O, and Al must be controlled in order to make fine sulfide oxides appear, so that production control is extremely complicated. It will be.

[0006] On the other hand, as an example of improvement from the plastic working surface so that the drawability is not deteriorated even if proeutectoid cementite is present, roller dies or cold rolling is performed before drawing. The method is described in JP-A-63-4016, and the method of drawing while reducing the approach angle of the die to about 10 degrees is described in Japanese Patent Application No. 1-281825. These are all intended to suppress the occurrence of internal cracks due to proeutectoid cementite by reducing the tensile stress applied to the center of the steel wire during wire drawing. However, this method is effective only when the amount of generated pro-eutectoid cementite is small and thinly present at the grain boundary, that is, when C is 1% or less or when a small amount of Cr is added. Only when the formation of proeutectoid cementite is suppressed. On the other hand, these methods have many manufacturing problems such as the necessity of newly installing a roller die and a rolling mill separately from the wire drawing machine, and the necessity of strictly managing and strictly controlling the dies.

[0007]

As described above, the prior art cannot completely prevent the generation of grain boundary proeutectoid cementite in hypereutectoid steel. The present invention has been made to solve the above-mentioned problems of the prior art, and completely prevents the generation of grain boundary proeutectoid cementite in hypereutectoid steel, thereby enabling wire drawing with high area reduction. It is an object of the present invention to provide a method for manufacturing a high-strength steel wire that makes full use of the effect of increasing the C content as much as possible.

[0008]

That is, according to the present invention, as a weight ratio, C: more than 0.90 to 1.25%, Si: 0.15 to 1.5%, Mn: 0.3 to 1.0%. %, Ni: 0.1 to 0.5%, if necessary, one or two kinds of Cr: 0.1 to 1.0%, and V: 0.02 to 0.30%, and further, Al, One or more of Ti, Nb, Zr, and B are each contained in an amount of 0.1% or less, and the remainder is austenitized by heating a steel wire composed of Fe and unavoidable impurities, and then defined by equation (1). 400 to 6 at a cooling rate in the range
A method for producing a high-strength steel wire, characterized by quenching in a refrigerant maintained at 50 ° C. and subsequently completing isothermal transformation in the refrigerant to obtain a fine pearlite structure free of proeutectoid cementite. Y ≦ 0.16 logX + 0.82 (1) where Y is the C content (%) of the steel, and X is the cooling rate (° C. /
sec).

[0009]

Hereinafter, the present invention will be described in detail.

The present inventors have conducted many experiments to improve the drawability of hypereutectoid steel, and selected cooling conditions from the austenitizing temperature to reduce the proeutectoid cementite as described below. We have obtained new knowledge that generation can be prevented.

That is, the present inventors produced a columnar sample having a diameter of 3 mm and a height of 10 mm from a wire rod obtained by hot rolling a vacuum-melted steel having the composition shown in Table 1, and immersing it in an Ar gas at 95%.
After induction heating to 0 to 1000 ° C. to austenitize, continuous cooling was performed at various cooling rates. After cooling, the sample was polished, etched by the method specified in JIS G0551, and then the state of formation of proeutectoid cementite was examined by an optical microscope. The formation state of the film-like cementite having a thin grain boundary was observed using a scanning electron microscope after the polished sample was etched with picral. FIG.
The relationship between the generation limit of proeutectoid cementite, the C content, and the cooling rate is shown in FIG. As described above, the formation of proeutectoid cementite depends on the cooling rate in addition to the C content, and the formation can be prevented by increasing the cooling rate even at the same C content. From FIG. 1, the condition in which proeutectoid cementite does not occur is represented by the following equation (1) when the C content of steel and the cooling rate from the austenite region are expressed. Y ≦ 0.16 logX + 0.82 (1) where Y is the C content (%) of the steel, and X is the cooling rate (° C. /
sec).

In the actual patenting of a high-strength steel wire, the pearlite transformation time is insufficient in continuous cooling, so it is necessary to perform lead patenting or fluidized bed patenting treatment to transform the pearlite into fine pearlite at a constant temperature. At that time, by controlling the temperature of the molten lead or the fluidized bed as the refrigerant and selecting the cooling rate of the steel wire within the range satisfying the expression (1), it is possible to completely prevent the generation of proeutectoid cementite. It is. However, when the refrigerant temperature is lower than 400 ° C., bainite is generated on the surface of the steel wire, and the wire drawing limit is reduced. On the other hand, when the temperature exceeds 650 ° C., the layer structure of pearlite is broken, and therefore, both the strength and the limit of wire drawing are reduced. Therefore, the refrigerant temperature is set to 400 to 650 ° C.
The temperature in the cooling bath does not need to be uniform. That is, in order to obtain the cooling rate of the formula (1), the temperature of the refrigerant on the side where the glowing steel wire enters is set low, and the temperature of the other portions is set to the temperature at which fine layered pearlite can be obtained according to the steel composition. Should be kept. For this purpose,
It is desirable that the cooling tank has a structure that can perform inclined heating, and more preferably, a cooling tank divided into a plurality of cooling zones is used.

Next, the reasons for limiting the components of the present invention will be described. C is an effective and economical element for increasing the strength, and is one of the most important elements of the present invention. As the C content is increased, the strength after patenting and the amount of work hardening during drawing are increased. Therefore, in order to obtain a high strength steel wire by wire drawing, C content is advantageously higher, in the present invention, to 0.90 percent. On the other hand, C
If the content exceeds 1.25%, the cooling rate required to prevent the generation of pro-eutectoid cementite exceeds 480 ° C./sec, as indicated by the equation (1), so that it is difficult to realize industrially. Becomes Therefore, the upper limit of the C content is 1.25%.
And

[0014] Si is added as a deoxidizing agent in an amount of 0.15% or more. On the other hand, Si, as an alloy element, forms a solid solution in ferrite and exhibits a remarkable solid solution strengthening action. In addition, S in ferrite
i is an indispensable element in the production of high-strength steel wires because it has the effect of reducing the strength reduction during hot-dip galvanizing after drawing and bluing. However, if it exceeds 1.5%,
Since the ductility of the drawn steel wire is reduced, the upper limit is 1.5%.

Mn is also added as a deoxidizing agent in an amount of 0.3% or more. In addition, since Mn has a large quenching property improving effect, when the wire diameter is large, it is possible to increase the Mn content to improve the uniformity in the cross section, and to improve the ductility of the steel wire after drawing. It is valid. However, if it exceeds 1.0%,
Since martensite is generated in the center segregation part and wire drawing workability is deteriorated, the upper limit is 1.0%.

Ni, like Mn, is added in an amount of 0.1% or more to increase the strength and toughness of pearlite. If it is less than 0.1%, the effect is not sufficient. On the other hand, if it exceeds 0.5%, the time required for transformation becomes longer and martensite is easily generated, so the upper limit is 0.5%.

Cr is added in an amount of 0.1% or more as necessary to reduce the lamellar spacing of pearlite and to improve the strength and drawability of the steel wire. If it is less than 0.1%, the effect is not sufficient. On the other hand, if it exceeds 1.0%, the time required for transformation becomes longer, and the productivity is significantly reduced.
0% is the upper limit. V improves hardenability, like Mn, but forms carbides and strengthens pearlite by precipitation hardening. For this purpose, 0.0
Add 2% or more. However, the addition of V delays the pearlite transformation and facilitates the formation of martensite and bainite. Further, the precipitation hardening effect of V carbide is saturated, so the upper limit is 0.3%.

In addition to the above strengthening elements, A
1, one, two or more of Ti, Nb, Zr, and B.
Add 1% or less. All of these elements tend to form nitrides and carbides, and therefore have a strong tendency to reduce austenite grains. In order to increase the drawing value of the steel wire after patenting and improve drawability, it is effective to make austenite grains fine. Therefore, in the case of manufacturing a suspension bridge cable wire or the like, a favorable result can be obtained by adding these nitride and carbide forming elements. However, the addition of more than 0.1% not only saturates the effect but also increases nonmetallic inclusions.
The upper limit is 1%.

[0019]

Embodiment 1 In this embodiment, a thin wire having a tensile strength of 400 kgf / mm ² or more is used as a target material of the method of the present invention. Will be described. A 2.7 mm diameter steel wire having the chemical composition shown in Table 2 was drawn after lead patenting to produce a 0.45 mm fine wire. Table 3 shows the patenting conditions, the characteristics after patenting, and the characteristics of the fine wire after drawing. When the C content is 0.86% (A-1 steel), the target strength cannot be obtained. On the other hand, when the C content is 1.35% (A-4 steel), proeutectoid cementite is generated due to insufficient cooling rate, and I could not draw. Similarly, when the C content is 1.20% (A-
3a steel), as shown in Table 3, the cooling rate was 20 ° C. /
When sec and the formula (1) were not satisfied, proeutectoid cementite was formed and the torsion value after drawing was lowered, so that the target thin wire could not be produced. The B-added steel (A-3 steel) has a higher drawing value after patenting and a higher torsion value after wire drawing than the non-added steel (A-2 steel). The conventional method is
This is a method described in Japanese Patent Application No. 1-281825. Each of the thin wires manufactured by the method of the present invention has a weight of 400 kgf / mm ^2.
It has the above strength, and has higher strength and ductility, especially excellent torsion value, as compared with those manufactured by the conventional method.

[0020]

[Embodiment 2] The production results of a high-strength galvanized steel wire for supporting a suspension bridge or a cable-stayed bridge will be described below. Table 4 shows the chemical composition of the steel wire. Each steel of B-1 to B-4 has a diameter of 7
The purpose is to produce steel wires with a tensile strength of 210 kgf / mm ² or more in mm and each of steels C-1 to C-4 with a diameter of 5 mm and a tensile strength of 230 kgf / mm ² or more. The purpose is. The conventional methods are all disclosed in Japanese Patent Application No. Hei.
This is the method described in the issue. As shown in Table 5, the diameter 1
After lead patenting of 3 mm and 11 mm steel wires, the wire was drawn to a target wire diameter and then hot-dip galvanized. Si
The strength increases with an increase in the content, but 1.61% (B
-3 steel), the ductility was insufficient, and the twist value of the plated steel wire was reduced. On the other hand, when Mn was 1.08% (C-3 steel), the torsion value of the plated steel wire was significantly reduced due to the martensite generated in the central segregation portion. In addition, the transformation time of the B-1a steel patented at a low lead bath temperature of 375 ° C. was insufficient, and martensite was generated, so that the torsion value of the plated steel wire was significantly reduced. As described above, if a hot-dip galvanized steel wire is manufactured by the method of the present invention, a high-strength steel wire that cannot be obtained by the conventional method, that is, a strength of about 30 kgf / mm
⁽²⁾ It is possible to obtain a steel wire which is higher and more excellent in twisting characteristics.

[0021]

Embodiment 3 A high-strength galvanized steel strand (ACSR)
The production results of the steel wire for use in the present invention will be described. Table 6 shows the chemical composition of the steel wire. Each steel from D-1 to D-5 has a diameter of 2.
8mm and each steel from E-1 to E-5 has a diameter of 2.0
It is intended to produce high-strength steel wires each having a tensile strength of 250 kgf / mm ² or more in mm. After 10 mm and 7 mm steel wires were patented in a fluidized bed, they were drawn to a target wire diameter, and then hot-dip galvanized. Table 7 shows the results. C
When the r content is 0.06% (D-1 steel), the effect is small and the target strength cannot be obtained. On the other hand, 1.11% (D-
In the case of No. 4 steel), martensite was generated in the patenting structure due to insufficient transformation time, so that disconnection frequently occurred and wire drawing was impossible. When the patenting condition is out of the range of the present invention (D-2a steel), the target strength and torsion value are not reached. On the other hand, no carbonitride forming element is added (E
(E-1 steel) also failed to obtain the tensile strength targeted in this example (therefore, E-1 steel was a comparative method in this example), and a large amount of V was added (E-4). Steel) has a low torsion value. The conventional method (D-5 steel) is disclosed in
No. 016, in which a normal drawing is performed after drawing a roller die. The conventional method (E-5 steel) is a method disclosed in JP-A-63-186852. As shown in Table 7, the strength achievable by the conventional method is of the order of 220 kgf / mm ² and the twist value is low. On the other hand, according to the method of the present invention, 250 kgf / mm ²
Since the production of grades is possible and the production of pro-eutectoid cementite is completely suppressed, the torsion properties are improved despite the high strength.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

[Table 5]

[0027]

[Table 6]

[0028]

[Table 7]

[0029]

As described above, according to the method of the present invention, a steel cord, a steel wire for an ACSR, a cable for a suspension bridge,
It is possible to manufacture high-strength steel wires such as steel wires.

[Brief description of the drawings]

FIG. 1 shows the relationship between the generation limit of proeutectoid cementite, the C content, and the cooling rate.

Continuation of the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C21D 9/52 103 C21D 6/00 C21D 8/06 C22C 38/00 301 C22C 38/08

Claims (2)

(57) [Claims] 1. A weight ratio of C: more than 0.90 to 1.25%, Si: 0.15 to 1.5%, Mn: 0.3 to 1.0%, Ni: 0.1 to 0.1%. 5%, a steel wire consisting of Fe and unavoidable impurities is heated to austenite, and then quenched in a refrigerant maintained at 400 to 650 ° C. at a cooling rate in a range defined by the formula (1). A method for producing a high-strength steel wire, characterized by obtaining a fine pearlite structure not containing pro-eutectoid cementite by continuously completing isothermal transformation in the refrigerant. Y ≦ 0.16 logX + 0.82 (1) where Y is the C content (%) of the steel, and X is the cooling rate (° C. /
sec). 2. A weight ratio of C: more than 0.90 to 1.25%, Si: 0.15 to 1.5%, Mn: 0.3 to 1.0%, Ni: 0.1 to 0.1%. 5%, 1 to 2 types of Cr: 0.1 to 1.0%, V: 0.02 to 0.30%, and 1 to 2 or more types of Al, Ti, Nb, Zr, B A steel wire containing 0.1% or less of each and the remainder consisting of Fe and unavoidable impurities is heated to austenite, and then cooled at a cooling rate in the range defined by the formula (1).
A method for producing a high-strength steel wire, characterized by quenching in a refrigerant maintained at 0 to 650 ° C. and subsequently completing the isothermal transformation in the refrigerant to obtain a fine pearlite structure free of proeutectoid cementite. Y ≦ 0.16 logX + 0.82 (1) where Y is the C content (%) of the steel, and X is the cooling rate (° C. /
sec).