JP3036393B2 - High strength and high toughness hot-dip galvanized steel wire and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized steel wire used as a PC steel wire, a galvanized steel stranded wire, a spring steel wire, a suspension bridge cable, and the like. The present invention relates to a hot-dip galvanized steel wire having excellent strength and toughness by maximizing the properties of a Si-containing wire rod and a method for producing the same.

[0002]

2. Description of the Related Art In manufacturing PC steel wires and cables for suspension bridges that require corrosion resistance, high-carbon steel wires are subjected to a patenting process, then to a drawing process, and then to a hot-dip galvanizing process. It is common to use Through such a manufacturing process, the strength of the wire is increased. However, there is a problem that the strength is reduced during a hot-dip plating process in which the wire is heated to a temperature of 400 ° C. or more in the final stage. Also, the higher the strength by drawing, the more
There is a tendency that the strength decrease during the plating process tends to increase, and as a result, it is difficult to increase the strength of the plated steel wire.

As a means for increasing the strength of a high carbon steel wire, it is known that increasing the C content in a steel material component is the most economical and effective means. However, when the steel material has a hypereutectoid composition (C content of 0.9% or more) due to an increase in the C content, brittle proeutectoid cementite tends to form in a network along the austenite grain boundaries during the patenting treatment. is there. For this reason, breakage occurs from the cracks of proeutectoid cementite at the time of wire drawing, and wire drawing workability deteriorates. In particular, when the C content is 1.
With hypereutectoid steel of 2% or more, it is impossible to prevent the precipitation of proeutectoid cementite, no matter how the production process and components are devised. Therefore, there is a limit to achieving high strength by adding only C. was there.

[0004] Further, C does not have the effect of suppressing a decrease in strength during hot-dip plating, and it is not possible to increase the strength of a plated steel wire in accordance with the added amount.

On the other hand, S, which is an element usually contained in steel wire,
In the case of i, it has the effect of increasing the strength of the steel wire after the patenting treatment and also increasing the strength of the steel material after drawing, and also has the effect of improving the hardenability of the steel wire and suppressing the precipitation of proeutectoid cementite. is there. Moreover, Si has an effect of suppressing a decrease in strength during hot-dip plating, and is a very effective element for increasing the strength of hot-dip coated steel wires.

[0006] From such a viewpoint, there have been proposed many techniques for adding Si to a steel wire to be hot-dipped. For example, Japanese Patent Application Laid-Open No. 4-246125 (conventional example) discloses that a steel wire containing up to 1.3% of Si is subjected to hot-dip plating, followed by straightening and bluing. Japanese Patent Application Laid-Open No. 4-325627 (conventional example) discloses that the amount of Si added is limited according to the amount of wire drawing.

On the other hand, in the hot-dip galvanized steel wire as described above, it is known that the maximum strength of vertical crack generation during a twist test, which is one of the important characteristics, depends on the wire diameter of the wire. The larger the wire diameter, the lower the critical strength at which vertical cracks occur.

From these viewpoints, for example, Japanese Patent Application Laid-Open No.
No. 9129 (conventional example) proposes a technique of mechanically correcting the occurrence of vertical cracks.

[0009]

However, in the above-mentioned prior art, there is no mention of the relationship between the strength of the steel wire or the wire diameter and the amount of Si, so that the effect of adding Si is maximized. The requirements to be fulfilled have not been elucidated, and there has been a limit to technical improvement.

Further, the conventional technique has a disadvantage that it cannot be applied to products which cannot be straightened after plating, such as steel wires for a long suspension bridge.

The present invention has been made in view of the above-mentioned circumstances, and has as its object to provide a hot-dip galvanized steel having excellent strength and toughness by maximizing the effect of adding Si in a wire. An object of the present invention is to provide a wire and a method of manufacturing the wire.

[0012]

The high-strength, high-toughness hot-dip galvanized steel wire according to the present invention, which has achieved the above-mentioned object, comprises:
C: 0.7 to 1.2%, Si: 0.5 to 2%, Mn:
0.2-1%, Al: more than 0.05-0.5%, N: 0.
002-0.008%, O: 0.002% or less (including 0%), and the balance consists of Fe and unavoidable impurities, and satisfies the relationship of the following formula (1). This is referred to as a first invention). TS <33.4 × ln ｛[Si] + 3 × ([Al] −0.05)｝ -57.8 × ln
(D) +310.6… (1) [Si]: Si content (%) [Al]: Al content (%) TS: Tensile strength (kgf / mm ² ) D: Wire diameter (mm) In the first invention, an upper limit is set for the TS, but if necessary, the TS may be configured to satisfy a lower limit condition represented by the following equation (2). TS> A−50.3 × ln (D)… (2) A: Constant

The constant A can be arbitrarily determined in consideration of practical strength, but is generally set to 280.9. More preferably, the constant A is 290.9, and still more preferably, the constant A is 300.9.
, And even more preferably, the constant A is 310.9.

The high-strength, high-toughness hot-dip galvanized steel wire of the first invention preferably contains 0.005 to 0.02% by weight of Ge.

In addition, the high-strength high-toughness hot-dip galvanized steel wire of the first invention has a Cu content of 0.05 to 0.5% and a Cr content of 0.0%.
More preferably, it contains at least one member selected from the group consisting of 5 to 1% and W: 0.05 to 1%. Further Ni:
It is preferable to appropriately contain 0.05 to 1% or Co: 0.05 to 1%. Further, it is desirable to contain at least one selected from the group consisting of Ca: 0.001 to 0.01% by weight and REM: 0.001 to 0.01% by weight. In addition, as other elements, V: 0.05 to 0.5%, Nb:
More preferably, it contains at least one member selected from the group consisting of 0.01 to 0.2% and Ti: 0.01 to 0.2%.

The method for producing a high-strength, high-toughness hot-dip galvanized steel wire according to the present invention is characterized in that a high-carbon steel wire containing each of the above components is hot-rolled and then subjected to a patenting treatment or after re-austenitization. Perform a patenting process,
The gist of the invention is that the obtained wire is cold-drawn and then hot-dip galvanized or hot-dip zinc alloy-plated (hereinafter, referred to as a second invention). At this time, not only is it possible to manufacture a steel wire that satisfies the formula (1) by controlling the manufacturing conditions by using a material in which each of the components satisfies the first invention, but also to perform a predetermined manufacturing process. According to the conditions, it is also possible to design and carry out at least the contents of Si and Al so as to satisfy the above formula (1).

It is more preferable that the wire before cold drawing has a structure mainly composed of fine pearlite. In addition, the wire diameter after cold drawing is more preferably 4 to 8 mm.

[0018]

According to the present invention, there is provided S having an effect of suppressing strength reduction.
Focusing on i, the effect is further extracted to obtain a hot-dip steel wire with high strength and toughness.

The hot-dip steel wire is manufactured with a balance between the required strength and toughness in mind, since the toughness is reduced if the strength is too high. Therefore, a description will be first given of the Si content that maximizes the above-described effects of Si while maintaining the required toughness.

FIG. 1 is a graph showing the relationship between the critical tensile strength (TS: kgf / mm ² ) and the wire diameter (D: mm) at which longitudinal cracks occur during the torsion test. It has been examined. The torsion test is a test that serves as an index of toughness,
As described above, a steel wire having a high tensile strength has a low toughness, and accordingly, the torsion test is poor. On the contrary, a steel wire having a good torsion test has a low tensile strength.

As is apparent from FIG. 1, the strength decreases as the wire diameter increases. On the other hand, it can also be seen that the strength increases as the Si content increases.

The present inventors have found that the wire diameter, strength and S
Further investigation of the relationship between the i content shows that in the state where the effect of adding Si is maximized, there is a specific relationship as shown by the following formula (E) between the Si content and the strength and wire diameter. Revealed that there is. TS <33.4 × ln ([Si]) − 57.8 × ln (D) +310.6 (E) [Si]: Si content (%) TS: Tensile strength (kgf / mm ² ) D: Wire diameter ( mm)

In other words, the equation in which the inequality sign in the equation (E) is replaced by an equal sign indicates a case where the highest tensile strength corresponding to the Si content is obtained, and a steel wire having a higher strength than the strength obtained at that time is obtained by: Even if the steel wire is manufactured using the manufacturing conditions, the resulting steel wire has reduced toughness and is not useful. In other words, it is possible to control the strength itself by making full use of the manufacturing method, but as long as securing toughness is a parallel issue, it is by no means simply aiming for high strength. Is naturally limited, and as described above, there is an appropriate upper limit strength corresponding to the Si content. Therefore, in order to exhibit an effect corresponding to the amount of Si contained (in other words, to obtain a useful steel wire by exhibiting the maximum allowable tensile strength in accordance with the Si content), the above formula ( It is necessary to satisfy E).

Next, a case where a steel wire is actually manufactured will be described.

Since it is not necessary to increase the strength beyond the required strength TS as a product, the necessary target strength TS is first set, and the maximum strength that satisfies the above formula (E) is exhibited. In some cases, the inequality sign in the above formula (E) is replaced with an equal sign to calculate the amount of Si. In this case, the wire diameter required for the product is also predetermined. If the wire diameter is variable, the wire diameter can be processed as a variable.

A hot-dip coated steel wire is manufactured by using a material whose component is designed so as to satisfy the Si amount obtained from the formula (E) and the following component ranges. That is, C: 0.7 to
1.2%, Si: 0.5-2%, Mn: 0.2-1%,
Al: 0.02 to 0.05%, N: 0.002 to 0.0
It is a hot-dip galvanized steel wire that contains 15% each and the balance is Fe and unavoidable impurities and satisfies the relationship of the above formula (E) (hereinafter, this plated steel wire may be referred to as “Reference Example a”. Further, the above component composition may be referred to as “component (B)”).

If a steel wire that does not satisfy the above formula (E), that is, a steel wire with an unnecessarily high strength is manufactured, the toughness is poor and the product is unsuitable as a product. Examples of the manufacturing conditions for controlling the strength include a method of changing the area reduction rate in wire drawing, and variously changing the patenting conditions.

Next, the first invention of the present invention will be described.

The present inventors have conducted intensive studies on additional elements that can bring out the effect of Si more significantly, and found that Al is effective. That is, it has been found that by simultaneously adding Si and Al, it is possible to obtain a high-strength, high-toughness hot-dip galvanized steel wire that further enhances the effect of Si (first invention).

It is already known that the addition of Al at a high concentration lowers the drawing limit due to Al-based inclusions and the like. However, in the first aspect of the present invention, by reducing the amount of inclusions such as aluminum oxide by reducing oxygen, high A
Even with l-added steel, sufficient wire drawing was enabled, and finally high strength and high toughness were achieved. Further, if the inclusion form control by Ca, REM or the like is used together, the drawability of the high Al-added steel is further improved.

Next, the equation (1) will be described.

FIG. 2 shows the tensile strength (strength: TS: kgf / mm ² ) on the vertical axis and the horizontal axis on the assumption that the wire diameter (D: mm) is constant.
It is the graph which took [Si] + 3x ([Al] -0.05) and plotted the limit strength which a longitudinal crack generate | occur | produces at the time of a torsion test about the steel wire manufactured under various conditions, respectively. △ is good torsion,
■ and ■ indicate poor twisting, △ and ● are steel wires manufactured using a material having a composition within the range of the component elements of the first invention, and the manufacturing conditions are variously changed. Steel wire (1) has an Al content less than the range of the elemental components of the first invention.

As shown in FIG. 2, it has been found that the quality of the torsion is divided by a line represented by the following equation (3). In FIG. 2, ■ indicates a case where the Al content is 0.05% or less,
It can be seen that the line of equation (3) exists when the Al content is 0.05% or more. TS = 33.4 × [LN ｛[Si] + 3 × ([Al] −0.05)｝ -1.73 × LN (D)
+9.3] (3) That is, from the graph of FIG. 2, it can be seen that the steel wire below the line of the formula (3) has a good twist and therefore has a high toughness.

The torsion test was performed on ten steel wires according to the method of the torsion test of JIS G-3521,3522. The determination of the quality of the torsion was made as a poor torsion when one of the ten steel wires had a vertical crack in the torsion test, and as a good torsion when no vertical crack had occurred.

FIG. 3 is a graph showing the critical strength at which longitudinal cracking of a steel wire occurs for various types of [Si] + 3 × ([Al] −0.05), with the horizontal axis representing the wire diameter and the vertical axis representing the tensile strength. It is. That is, [Si] +3
× ([Al] −0.05) corresponds to the line drawn by the equation (3). In FIG. 3, as in FIG.
As the wire diameter increases, the strength decreases, and [Si] + 3 × ([Al] −
As the value of (0.05) increases, the strength increases.

Also in the graph shown in FIG. 3, the steel wire below the line obtained from the equation (3) has a good twist test,
The steel wire above the wire had a poor twisting test.

The above equation (3) is transformed into the above equation (1), and [Si] (Si content) in the above equation (E) is expressed as [Si] + 3 × ([Al] −
0.05). TS <33.4 × ln ｛[Si] + 3 × ([Al] −0.05)｝ -57.8 × ln
(D) +310.6… (1)

According to the first aspect of the present invention, while satisfying the above-mentioned elemental component range, the amount of Si and the amount of Al are calculated from the target strength TS by regarding the equation (1) as an equation, and the material of the component is used. If a hot-dip galvanized steel wire is manufactured to satisfy equation (1), A
1 provides a high-strength, high-toughness hot-dipped steel wire in which the effect of Si is further enhanced.

Next, Ge will be described. Ge is also an effective element capable of achieving high strength and high toughness of a hot-dip galvanized steel wire by being simultaneously added with Si, similarly to Al, and by further adding Ge to the first invention,
An even higher strength and higher toughness hot-dipped steel wire can be obtained.

By setting the conditions so as to satisfy the expression (1), a high-strength, high-toughness hot-dip steel wire capable of maximizing the effect of Si can be obtained.

As the strength TS approaches the value on the right-hand side of the equation (E), the effect of Si is exerted more, and the effect of Si is less exhibited as the strength TS is increased. Satisfies equation (2). TS> A −50.3 × ln (D)… (2) A: Constant

Next, the reason for determining the component composition of the high carbon steel used in the present invention will be described.

C: 0.7-1.2% C is an effective and economical element for increasing the strength of the steel material. As the C content is increased, the strength after the patenting process and the strength at the time of wire drawing are increased. The amount of work hardening and the strength after drawing increase. Therefore, a higher C content is more effective,
In the present invention, it is necessary to contain 0.7% or more of C in order to secure the minimum target strength. However, when the amount of C is too large, precipitation of proeutectoid cementite cannot be prevented and not only is it easy to cause breakage during wire drawing, but also the toughness and ductility of the obtained steel wire deteriorates, so that the content is 1.2% or less. Must be suppressed.

Si: 0.5 to 2% Si is useful as a deoxidizing element, and has a remarkable solid solution strengthening effect by forming a solid solution with ferrite. It also has the effect of reducing the strength reduction during ing or hot-dip galvanizing, and is an effective element for increasing the strength of steel wires. In order to sufficiently exhibit these effects, the content must be 0.5% or more. However, if added excessively, the ductility of the drawn steel wire becomes poor, so the upper limit was set to 2%.

Mn: 0.2 to 1% Mn is also an element useful as a deoxidizing agent, like Si, and also has the effect of increasing the hardenability of steel to increase the uniformity of the structure in the cross section of the steel wire. These effects are effectively exhibited by containing 0.2% or more. However, if the amount of Mn is too large, Mn segregation occurs, and a supercooled structure such as martensite or bainite is formed in the segregated portion to deteriorate the drawability. Therefore, the content must be suppressed to 1% or less.

Al: more than 0.05 to 0.5% Al acts as a deoxidizing agent and is an element necessary for exhibiting an effect of preventing the austenite grain size from being coarsened by adding N in combination.

Further, by adding Al simultaneously with Si,
Suppresses the decrease in strength after hot-dip galvanizing and effectively works to increase the strength of hot-dip galvanized steel wire. Therefore, in the first aspect of the present invention, by limiting the amount of N and the amount of O as described below, it is possible to add Al in a large amount such as the above 0.05%, thereby exhibiting the above effects. . However, even if Al is added excessively, the effect is saturated, which may cause clogging of the nozzle for continuous casting, which may cause troubles in production. Therefore, the upper limit is set to 0.5%. To maintain good productivity without causing the above manufacturing trouble, 0.2%
Is more preferably the upper limit.

N: 0.002 to 0.008% N forms an Al and a nitride in the steel and has an action of preventing the austenite grain size from being coarsened during heating. , 0.002% or more N. On the other hand, the upper limit of N is set to 0.008% so that Al does not become a nitride and effectively exerts the action of Al coexisting with Si.

O: 0.002% or less (including 0%) O reacts with Al to form Al ₂ O ₃ and becomes an inclusion, deteriorating drawability and lowering the draw limit. O is preferably as small as possible, and its limit is set to 0.002% or less.

The high-carbon steel wire used as the material of the hot-dip steel wire according to the present invention contains the above-mentioned elements as basic components, and the balance consists of Fe and unavoidable pure substances. Cr, Ni, Co, W, V, Nb,
It is also effective to include an element such as Ti. The reasons for limiting the component ranges of these elements are as follows.

Ge: 0.005 to 0.02% As in the case of Al, Ge is simultaneously added with Si to suppress a decrease in strength after hot-dip galvanizing and to increase the strength of hot-dip galvanized steel wire. Work effectively. In order to effectively exhibit this effect, the content should be 0.005% or more. On the other hand, even if it is excessively added, the effect is saturated, and the amount of Ge nitride becomes too large, which adversely affects the drawability. From
The upper limit is set to 0.02%.

Cu: 0.05 to 0.5%, Cr: 0.05 to 1%, W: 0.05 to 1% Cu, Cr and W are effective elements for increasing the strength of the wire. .

Of these, Cu must be contained in an amount of 0.05% or more in order to achieve high strength of the steel material by the precipitation hardening effect and to exert such an effect. However, an excessive addition not only saturates the effect but also causes grain boundary embrittlement and may cause cracks on the surface of the steel ingot during hot rolling. Therefore, the upper limit is set to 0.5%.

Cr has the effect of reducing the lamella spacing of pearlite, not only increasing the strength of the wire, but also enhancing the wire drawing workability, and these effects are effectively exhibited at 0.05% or more. However, if it exceeds 1.0%, the transformation end time becomes too long, which leads to an increase in the size of the equipment and a decrease in productivity. Therefore, the upper limit is set to 1%.

As described above, W also has the effect of increasing the strength of the wire rod, and the effect is effectively exhibited when the content is 0.05% or more. However, if the content is too large, not only the strength improving effect is saturated, but also the ductility may decrease, so the content must be suppressed to 1% or less.

Ni: 0.05-1% Ni does not contribute much to the increase in the strength of the wire, but has the effect of increasing the toughness of the drawn wire.
% Or more is effectively exhibited. However, if the amount of Ni is excessive, the transformation end time becomes too long, resulting in an increase in the size of the equipment and a decrease in productivity. Therefore, the upper limit is 1%.

Co: 0.05 to 1% Co is effective for suppressing the precipitation of proeutectoid cementite, and the effect is effectively exhibited by containing 0.05% or more. However, the effect saturates at 1%, so further additions are economically useless.

Ca: 0.001 to 0.01%, REM: 0.001 to 0.01% Ca and REM control the form of inclusions harmful to wire drawing, such as alumina inclusions, to render them harmless. effective. To make this effect work effectively,
It is better to add at least 01%, while adding more than 0.01% increases the cost, so the upper limits were each set at 0.01%.

V: 0.05-0.5%, Nb: 0.01-0.2%, Ti: 0.01-0.2% These elements form fine carbonitrides in steel. However, precipitation strengthening has the effect of improving the strength and has the effect of preventing the austenite grains from becoming coarse during heating. These effects are effectively exerted by containing each of the above-mentioned lower limits or more. However, if the content exceeds the respective upper limit values, not only does the amount of carbonitride increase too much, but also the particle size of the carbonitride increases, deteriorating the toughness.

As a manufacturing method, a method of manufacturing by the following steps is recommended. That is, a high carbon steel wire satisfying the requirements of the above component composition is directly patented after hot rolling,
Alternatively, a wire rod having a structure mainly composed of fine pearlite is cold drawn by performing patenting treatment after re-austenitization, and then hot-dip galvanizing or hot-dip zinc alloy plating is applied (second invention).

The patenting process is described as “after hot rolling,
Or "after re-austenite" for the following reason. That is, in order to obtain a fine pearlite by performing a patenting process, the steel wire is heated to an austenite region, and then the pearlite transformation is terminated at a constant temperature near a predetermined temperature by a certain refrigerant. The following two methods (a) and (b) can be used for heating, and it has been shown that either method can be adopted in the present invention. (a) After hot rolling, the steel wire has reached the temperature in the austenitic region, and this temperature is used. → Direct patenting after hot rolling (b) Normal steel wire is stored and transported at room temperature. Therefore, heating to the austenite region is performed again to perform patenting. → Patenting treatment after re-austenitization The wire diameter of the hot-dip coated steel wire of the present invention is not particularly limited, but the effect is most exhibited when the wire diameter is 4 to 8 mm. The reason is as follows.

[0062] In the case of a thin wire such as a tire cord, the degree of wire drawing at the time of manufacturing is high. Therefore, the presence of pro-eutectoid cementite and supercooled structure accompanying the above-mentioned center segregation greatly affects the degree of wire drawing. Does not affect. On the other hand, in the case of a steel wire having a relatively large diameter (about 4 to 8 mm in diameter) such as a PC steel wire,
Although the degree of wire drawing at the time of manufacturing is smaller than that at the time of manufacturing a thin wire, the deformation form at the time of wire drawing is significantly different between the central part and the surface side of the wire, and the center of the wire after patenting is different from the surface side. Since the structure of the portion is likely to be non-uniform, there is a high possibility that an internal crack will occur at the center of the wire. For this reason, the effect of pro-eutectoid cementite due to the center segregation at the center of the wire tends to be more remarkable than that of small-diameter wire, and as a result, the frequency of wire breakage during wire drawing increases, resulting in increased productivity and yield. In addition, the toughness of the wire after the wire drawing is deteriorated.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following examples are not intended to limit the present invention, and the present invention will be described with appropriate modifications within a range that can be adapted to the purpose described above. It is of course possible to do so, and they are all included in the technical scope of the present invention.

[0064]

EXAMPLES <Reference Example a> A high-carbon steel having the chemical composition shown in Table 1 was used and hot-rolled into a steel wire having a diameter of 11 to 14 mm, and then subjected to lead patenting. The lead patenting treatment condition at this time is reheating 950 ° C. × 5 minutes → constant temperature transformation 540 ° C. × 4 minutes.

Next, the steel wire was moved to the target wire diameter of 5.0 to 5.0.
Continuous wire drawing was performed to 7.0 mm (area reduction: 71.0 to 87.2%). At this time, the wire was cooled at the die outlet, and the wire temperature was kept at 170 ° C. or lower. After that, straight line processing,
Further, a hot-dip galvanizing treatment was performed at 440 to 455 ° C.
Table 2 shows the properties of the obtained galvanized steel wire. The reason why the strength is different for the same steel type is that the wire diameter during the patenting process is different.

[0066]

[Table 1]

[0067]

[Table 2]

From Tables 1 and 2, the following can be considered.

First, the test steels No. 1 and No. 6 were C and C, respectively.
Since the amount of Mn is less than the lower limit of the component (B), the strength after drawing is a target value (a target value when the wire diameter is 5 mm: 200 kg).
f / mm ² ).

In No. 4, since C exceeded the upper limit of the component (B), a large amount of proeutectoid cementite was precipitated.
Drawability is poor and breakage occurs during drawing.

In No. 5, the wire can be drawn to the target wire diameter and the strength has reached the target value.
Since the value exceeds the upper limit of (B), the fracture drawing, which is a measure of toughness, is low.

In No. 7, the Mn content exceeded the upper limit of the component (B), and the wire was broken during drawing due to the presence of a supercooled structure.

In No. 8, since Al was insufficient, the crystal grain size became coarse, the ductility of the LP material was poor, and the wire was broken during drawing.

In No. 9, although the Al content and the N content were within the range of the first invention, the result that the wire drawing was impossible was strictly controlled so that the oxygen content became 0.002% or less. This was because the amount of oxygen became excessive. Also many Al
, Coarse inclusions (oxides, nitrides, etc.) are formed inside the wire, internal cracks originating from the inclusions are generated, and the fracture reduction value is low.

In No. 12, since the amount of Cr exceeded the upper limit of the component (B), it took a long time to complete the transformation, the transformation was not completed during lead patenting, and the supercooled structure The wire was broken during drawing due to the presence.

In No. 19, since N exceeded the upper limit of the component (B), age hardening during drawing was remarkable, and the wire was broken during drawing.

In Nos. 2b, 3b and 11b, the component composition satisfies the requirement of the above-mentioned component (B), but the strength of the plated steel wire does not satisfy the above formula (E), and A vertical crack occurred.

On the other hand, Nos. 2a, 3a, 10, 11
a, 13 to 18 satisfy all of the above-mentioned component (B) (provided that the wire diameter is 5.0 mm), and all have very excellent values in both strength and toughness after drawing.

Next, for Nos. 2c and 3c, the wire diameter was 7.0 m.
This is a reference example a in the case of m. All of the above component (B)
And has good mechanical properties. On the other hand, No. 2d and 3d have the chemical composition
(B) is satisfied, but since the strength does not satisfy the expression (E), a vertical crack is generated at the time of twisting.

<Example of the First Invention> A high-carbon steel having the chemical composition shown in Table 3 was used and hot-rolled into a steel wire having a diameter of 11 to 14 mm, and then subjected to a lead patenting treatment. The lead patenting treatment condition at this time is reheating 950 ° C. × 5 minutes → constant temperature transformation 540 ° C. × 4 minutes.

Next, the steel wire was continuously drawn to a target wire diameter of 5 mm (area reduction: 71.0 to 87.2%). At this time, the wire is cooled at the die outlet, and the wire temperature is set to 170
C. or less. After that, linear processing is performed, and
Hot dip galvanizing was performed at 55 ° C. Table 4 shows the properties of the obtained galvanized steel wire. The reason why the strength is different between the same steel types is that the wire diameters during the patenting process are different, that is, the wire diameters before the start of drawing are different, so that there is a difference in the area reduction rate in drawing. In addition, the strength is affected not only by Si and Al, but also by chemical components such as C and Cr, and also by heat treatment conditions before drawing.

[0082]

[Table 3]

[0083]

[Table 4]

Tables 3 and 4 can be considered as follows.

[0086] The test steel No. 20 was poorly twisted because the amount of Al added was small and the crystal grain size was coarse. On the other hand, No. 43 could not be drawn to the target wire diameter and was broken. This is because the amount of Al added is too large.

In Nos. 22, 25 and 26, the strength after drawing did not reach the target, because the added amounts of C, Si and Mn were respectively below the lower limits.

In No. 23, a large amount of proeutectoid cementite was precipitated, the wire drawing property was deteriorated, and as a result, the wire was broken during the wire drawing. This is because C is added in excess of the upper limit.

In No. 24, the wire could be drawn to the target wire diameter and the strength achieved the target value, but the fracture draw, which is a measure of toughness, was reduced. This is because Si is added to the upper limit or more.

In No. 27, a supercooled structure was present, and the wire was broken during drawing. This is because Mn is added to the upper limit or more.

In No. 30, the transformation took a long time to complete, and the transformation was not completed during lead patenting, and a supercooled structure was present, which caused disconnection during wire drawing. This is C
This is because r is added to the upper limit or more.

In No. 37, age hardening remarkably appeared during wire drawing and the wire was broken during wire drawing, because N was excessively added in excess of the upper limit.

In No. 38, the number of disconnections frequently occurred because the N amount was insufficient.

In No. 41, a disconnection occurred, but this
Is excessive, so that a large amount of alumina was produced.

In Nos. 21b, 29b and 39b, vertical cracks occurred when twisted. This is because the chemical composition range of these steel wires satisfies the composition range of the second invention, but does not satisfy the formula (1).

No. 21a, 28, 29a, 31-36
Reference numerals 39a, 40, and 42 are wires that correspond to the first invention, and have good strength and toughness after wire drawing, indicating that the first invention is excellent.

Nos. 21a to 21f are cases where the component compositions are the same and the finished wire diameters are variously changed. From these results, it is found that if the strength is higher than the theoretical strength obtained from the equation (1), poor twisting occurs. Therefore, it can be understood that the relationship between the wire diameter, the strength, and the torsion characteristics can be arranged by the equation (1).

[0097]

According to the present invention, the composition of the steel material to be used is specified, and Si and Al
Content, tensile strength and wire diameter are in a predetermined relationship (formula
By satisfying (1)), the effect of Si can be further enhanced, and a desired high-strength, high-toughness plated steel wire can be obtained. These steel wires are most suitable as materials for PC steel wires, galvanized steel wires, steel wires for springs, cables for suspension bridges, and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a critical strength at which a vertical crack occurs during a twist test and a wire diameter in Reference Example a.

FIG. 2 is a graph showing the relationship between [Si] + 3 × ([Al] −0.05) and the limit strength at which a vertical crack occurs during a twist test in the first invention.

FIG. 3 is a graph showing a relationship between a limit strength and a wire diameter at which a vertical crack occurs during a torsion test in the first invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI C23C 2/38 C23C 2/38 (72) Inventor Koichi Makii 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Kobe Co., Ltd. Steel Works Kobe Research Institute (72) Inventor Yasuhiro Oki 2 Nadahama Higashi-cho, Nada-ku, Kobe City, Hyogo Prefecture Kobe Steel Works, Ltd.Kobe Works (56) References JP-A-4-246125 (JP, A) JP-A-63-186852 (JP, A) JP-A-60-50147 (JP, A) JP-A-1-177336 (JP, A) JP-A-3-281049 (JP, A) JP-A-4-289128 ( JP, A) JP-A-62-238354 (JP, A) JP-A-63-103052 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60 C21D 8/06 C23C 2/06 C23C 2/38

Claims (13)

(57) [Claims] 1. C: 0.7 to 1.2% (meaning by weight%,
The same shall apply hereinafter) , Si: 0.5 to 2%, Mn: 0.2 to 1%, Al: more than 0.05 to 0.5%, N: 0.002 to 0.008%, O: 0.002 % Or less (including 0%), with the balance being Fe and unavoidable impurities, satisfying the following formula (1) . TS <33.4 × ln ｛[Si] + 3 × ([Al] −0.05)｝ -57.8 × ln
(D) +310.6… (1) [Si]: Si content (%) [Al]: Al content (%) TS: Tensile strength (kgf / mm ² ) D: Wire diameter (mm) 2. The high-strength, high-toughness hot-dip galvanized steel wire according to claim 1, which satisfies the following expression (2) . TS> A−50.3 × ln (D)… (2) TS: Tensile strength (kgf / mm ² ) D: Wire diameter (mm) A: Constant 3. The hot-dip galvanized steel wire according to claim 1 , further comprising 0.005 to 0.02% by weight of Ge as another element. line. 4. The high-strength, high-toughness hot-dip galvanized steel wire according to any one of claims 1 to 3 , further comprising Cu: 0.05 to 0.5%, and Cr: 0.05. High strength and high toughness hot-dip steel wire containing at least one member selected from the group consisting of 〜1% and W: 0.05-1%. 5. The high-strength, high-toughness hot-dip galvanized steel wire according to any one of claims 1 to 4 , further comprising Ni: 0.05 to 1% as another element. Plated steel wire. 6. The high-strength, high-toughness hot-dip steel wire according to any one of claims 1 to 5 , further comprising Co: 0.05 to 1% as another element. Plated steel wire. 7. The high-strength, high-toughness hot-dip galvanized steel wire according to any one of claims 1 to 6 , further comprising: Ca: 0.001 to 0.01%, REM: 0.001 A high-strength, high-toughness hot-dip galvanized steel wire containing at least one selected from the group consisting of -0.01%. 8. The high-strength, high-toughness hot-dip galvanized steel wire according to any one of claims 1 to 7 , wherein V: 0.05 to 0.5%, and Nb: 0.01 as other elements. 1 selected from the group consisting of -0.2%, Ti: 0.01-0.2%
High strength and toughness hot-dip galvanized steel wire containing more than one kind. 9. A method for producing a high-strength, high-toughness hot-dip galvanized steel wire according to any one of claims 1 to 8 , wherein the high-carbon steel wire containing each of the above components is hot-rolled. High strength characterized by performing a drawing process or performing a patenting process after re-austenitization, cold drawing the obtained wire, and then performing hot dip galvanizing or hot dip zinc alloy plating Manufacturing method of high toughness hot-dip coated steel wire. 10. A high-strength and high-toughness hot-dip galvanized steel according to claim 9 , wherein a material having a predetermined content of an alloying element is used, and a production condition is controlled to produce a steel wire satisfying the expression (1). Wire manufacturing method. 11. The high-strength and high-toughness hot-dip galvanizing method according to claim 9 , wherein the manufacturing conditions are determined according to a prescribed method, and at least the contents of Si and Al are designed so as to satisfy the formula (1). Steel wire manufacturing method. 12. The method of claim 9 wherein the cold drawing before the wire is one having mainly a fine pearlite structure
12. The method for producing a high-strength, high-toughness hot-dip galvanized steel wire according to any one of items 11 to 11 . 13. The method for producing a high-strength high-toughness hot-dip galvanized steel wire according to claim 9 , wherein the wire diameter after cold drawing is 4 to 8 mm.