JP2609387B2 - High-strength high-toughness ultrafine steel wire wire, high-strength high-toughness ultrafine steel wire, twisted product using the ultrafine steel wire, and method for producing the ultrafine steel wire - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a low-strength, high-strength and high-toughness material used as a reinforcing material for rubber such as a belt cord or a tire cord or a material such as a miniature rope or a missile wire. The present invention relates to an alloy ultrafine steel wire, a wire for producing such an ultrafine steel wire, a method for producing the ultrafine steel wire, a twisted product obtained by twisting the ultrafine steel wire, and the like.

[0002]

2. Description of the Related Art An ultrafine steel wire used as a rubber reinforcing material is usually produced by the following procedure. That is, a steel having a predetermined chemical composition is hot-rolled, then adjusted and cooled as needed, and the obtained wire having a wire diameter of 4.0 to 6.4 mm is subjected to primary drawing.
After sequentially applying a patenting process, a secondary wire drawing process, a re-patenting process, a plating process, and the like, finally, a wet wire drawing process is applied to obtain an ultrafine steel wire. The ultrafine steel wire obtained in this way is used as a missile wire as it is, and when used as a steel cord, for example, it is used for various product processing such as forming a steel cord by twisting a plurality of strands by stranded wire processing. Have been.

[0003] In recent years, in particular, a steel cord for reinforcing a tire has tended to use an ultra-fine steel wire having higher strength from the viewpoints of reducing the weight of the tire, improving ride comfort and improving steering stability. . As a method for achieving high strength of the ultrafine steel wire, for example, (1) a method of using a high carbon steel having an increased carbon content to increase the patenting strength before final drawing, 2) Methods to maximize the amount of processing strain up to the finished wire diameter have been implemented.

Conventionally, carbon steels equivalent to JIS SWRS72A and SWRS82A have been used as wires for steel tire cords. To meet the above requirements, tensile strength is increased by increasing the amount of wire drawing strain up to the finished wire diameter. When the tensile strength is increased, remarkable deterioration in toughness and ductility accompanying high strength is caused, such as a decrease in the drawing value and the occurrence of vertical cracks at the beginning of the torsion test. In addition, if the amount of carbon is simply increased to increase the patenting strength with respect to the above-mentioned steel, eutectoid cementite is precipitated in a network at austenite grain boundaries,
Again, toughness and ductility deteriorate. When toughness and ductility are deteriorated, breakage occurs frequently during wet wire drawing and stranded wire processing, particularly in a steel tire cord strand, and productivity is significantly reduced.

[0005] Steel tire cords are manufactured by the above-described process. However, when the carbon content is increased only for the purpose of increasing the strength, pro-eutectoid cementite precipitates at the former austenite crystal grain boundaries in the rolled wire or the like. In addition, breakage occurs frequently in the primary drawing or the like, which is an intermediate manufacturing process, which leads to extremely lower productivity.

[0006]

SUMMARY OF THE INVENTION The present invention has been made under such circumstances, and its object is to provide a rubber reinforcing material such as a belt cord or a tire cord or a stranded wire processed product such as a miniature rope. Ultrafine steel wire having high strength and high toughness suitable as a material for producing steel, or as a missile wire, a wire material for obtaining the ultrafine steel wire, a product using such an ultrafine steel wire, and the ultrafine wire It is to provide a method for obtaining a steel wire.

[0007]

Means for Solving the Problems The present invention which has achieved the above object is characterized by: C: 0.85 to 1.2% by weight (preferably more than 0.9%).
1.2 wt%), Si: less than 0.45 wt%, Mn: 0.3 to
1% by weight, Ni: 0.1-4% and C
o: contains at least one selected from the group consisting of 0.05 to 4% by weight, and optionally contains Cu, Cr, W, Nb, Zr,
The alloy contains the element Mo and the balance consists of Fe and unavoidable impurities, and among the impurities, Al, N, P, S
, Al: 0.005% by weight or less, N: 0.005% by weight or less, P: 0.02% by weight or less, S: 0.015% by weight or less. It is a high-strength and high-toughness wire rod for ultrafine steel wire which has a gist in that the average area ratio of cementite is 10% or less. Further, from the viewpoint of suppressing disconnection, the composition of the non-metallic inclusions in the unavoidable impurities is not more than 20% by weight of Al ₂ O _{3 and} 40% by weight of MnO, based on the total amount of the inclusions. % Or less, SiO ₂ : 20 to 70% by weight, or Al ₂ O ₃ : 20% by weight or less, C
aO-: 50 wt% or less, SiO _2: 20 to 70 wt% or less, preferably satisfies the requirement.

Further, the method for producing a high-strength, high-toughness ultrafine steel wire according to the present invention is to use a wire for an ultrafine steel wire having the above various compositional requirements, and draw the wire into an ultrafine wire having a wire diameter of 0.4 mm or less. In doing so, the gist is that the processing strain is applied so that the total cross-sectional reduction rate in the wire drawing after the final patenting is 95% or more. According to the above method, 270− (130 × log ₁₀
D) Tensile strength (kgf / mm ² ) of (D is wire diameter: unit mm) or more
And a high-strength and high-toughness ultrafine steel wire having a wire diameter of 0.4 mm or less and having a characteristic of a fracture drawing value of 35% or more.
Further, if the ultrafine steel wire thus obtained is stranded, various products such as a steel cord, a tire cord, and a miniature rope can be obtained.

[0009]

[Function] For conventional hard steel wires (for example, JIS G 3506) and piano wires (for example, JIS G 3502), for example, for ultrafine steel wires with a wire diameter of 0.4 mm, the total cross-section reduction rate during drawing exceeds 95%. When the tensile strength of the drawn wire becomes 320 kgf / mm ² or more, there is a problem that a sharp reduction in the break drawing value is caused. When the breaking reduction value falls to less than 35%, breakage frequently occurs at the time of final wet wire drawing or stranded wire processing. Therefore, the breaking reduction value of the ultrafine steel wire needs to be 35% or more. Also, in the case of conventional materials, if the strength is increased, the occurrence of longitudinal cracks in the torsion test becomes unavoidable, which also causes frequent breakage in the twisting process to the steel cord and uneven pitch of the steel cord, resulting in increased strength. Had limitations. For example, a rolled material having a wire diameter of 5.5 mm is subjected to primary drawing to a wire diameter of about 3 mm. In the case of hypereutectoid steel, a large amount of proeutectoid cementite precipitates at the old austenite crystal grain boundaries, resulting in disconnection. There were problems such as frequent occurrence, lowering of productivity, and the occurrence of fine cracks in the steel even if it did not lead to disconnection, leading to disconnection at the time of secondary drawing and deterioration of properties of ultrafine steel wire.

According to the study of the present inventors, a steel material having the composition and structure specified in the present invention can secure good toughness and ductility in a manufacturing process such as wire drawing, and has a wire diameter of 0.4 m.
For ultra-fine steel wires with a tensile strength of 270- (130 ×
log ₁₀ D) (D is a wire diameter: unit mm) or more, it was found that good toughness and ductility could be secured. According to the results of an experiment in which the effect of increasing the cross-sectional reduction rate during wire drawing was ascertained, it was found that after the final patenting, the tensile strength was more than the above formula and the breaking reduction value was 35% or more. It has been found that the reduction rate of the total cross section in the wire drawing (final wire drawing process) should be 95% or more, and the present invention has been completed. The reasons for limiting the chemical components in the present invention are as follows.

C: 0.85 to 1.2% by weight The higher the amount of C, the higher the strength of the ultrafine steel wire. However, if the amount of C is simply increased, the primary precipitation occurs during rolling or patenting. Cementite precipitates, and the wire breaks frequently during final wire drawing or stranded wire processing. This point is suppressed by the effect of adding Co, which will be described later. However, if C is contained in excess of 1.2% by weight, segregation will significantly increase, and the need for Co for performing rolling or patenting without proeutectoid cementite will increase. The amount of addition increases, the production cost increases, and in the resulting pearlite structure, the amount of cementite relative to the amount of ferrite increases, thereby deteriorating the toughness and ductility of the ultrafine steel wire, and the above-described disconnection frequently occurs. Therefore, the C content needs to be 1.2% by weight or less, but if it is less than 0.85% by weight, a predetermined tensile strength in the ultrafine steel wire cannot be obtained. From the viewpoint of achieving higher strength, the content of C is preferably set to an amount exceeding 0.9% by weight.

Si: less than 0.45% by weight Si is an element effective for solid solution strengthening of ferrite, increasing the tensile strength of a patenting material and deoxidizing. However, when added in an amount of 0.45% by weight or more, the generation of subscale increases, and the grain boundary oxidation increases, thereby deteriorating the mechanical descalability of the secondary scale.

Mn: 0.3-1% by weight Mn is effective as a deoxidizing element in the smelting process. In particular, since the steel of the present invention is a low Si steel, it is necessary to add Mn. Mn has an effect of fixing S in steel as MnS, and has an effect of preventing the toughness and ductility of a steel wire rod from being deteriorated by S dissolved in steel. To exert these effects, it is necessary to add 0.3% by weight or more. Furthermore, Mn is an important element in adjusting the composition of nonmetallic inclusions that cause disconnection in the wet drawing process or the stranded wire process to a composite composition having good ductility. Also, addition of an appropriate amount of Mn is indispensable. On the other hand, Mn is an element that increases the hardenability of steel and is easily segregated. Therefore, when added in excess of 1% by weight, a low-temperature transformation generation phase such as martensite is generated in the segregated portion, and a cuppy-like phase is formed. It may cause disconnection.

Ni: 0.1 to 4% by weight Ni is a solid solution in ferrite and is an effective element for improving the toughness of ferrite. However, if it is less than 0.1% by weight, it has no effect, and 4% by weight. The effect is saturated even if it is added in excess of. Co: 0.05 to 4% by weight Co is effective for preventing precipitation of proeutectoid cementite and for reducing the pearlite lamellar interval. To exert such an effect, it is necessary to add 0.05% by weight or more.
Even if it is added in excess of weight%, the effect is saturated and the cost increases.

The high-strength, high-toughness wire rod for ultra-fine steel wire or ultra-fine steel wire of the present invention comprises the above elements as basic components and the balance of iron and unavoidable impurities. , S need to be regulated as follows.

Al: 0.005% by weight or less Al is an element effective as a deoxidizing element at the time of melting and for preventing the austenite grain size from becoming coarse.
More than 05% by weight as Al ₂ O ₃ or MgO-Al ₂ O ₃ based nonmetallic inclusions, such as are produced in large quantities, the disconnection cause of a wet drawing process or twisted wire process. These non-metallic inclusions not only shorten the die life in the final wet drawing, but also
It also degrades the fatigue properties of steel cords and strands for steel cords. Therefore, in the steel of the present invention, the Al content should be as small as possible, and should be at least 0.005% by weight or less (including 0).
The content is preferably 0.003% by weight or less.

N: 0.005% by weight or less If N exceeds 0.005% by weight, the strain aging adversely affects toughness and ductility. Therefore, it is necessary to regulate the content to 0.005% by weight or less. P: 0.02% by weight or less P is an element that lowers the toughness and ductility of steel, like S, and is an element that is easily segregated. Therefore, in the present invention, the P content needs to be 0.02% by weight or less, preferably 0.015% by weight.
% By weight or less.

S: 0.015% by weight or less As described above, S is an element that lowers the toughness and ductility of steel and is an element that is easily segregated. Therefore, in the present invention, the S content needs to be 0.015% by weight or less, preferably 0.001% by weight or less.

The wire rod for ultra-high strength and high toughness ultra-fine steel wire or ultra-fine steel wire of the present invention may be made of Cu, Cr, W, Nb,
It may contain elements of Zr and Mo.
The contents and the reasons for limitation when these elements are added are as follows.

Cu: 0.05 to 0.5% by weight Cu is an element effective for improving corrosion resistance like Cr, which will be described later. For that purpose, it is necessary to add 0.05% by weight or more. However, if it is added in a large amount exceeding 0.5% by weight, it segregates at the crystal grain boundaries, and promotes the generation of cracks or flaws during the ingot sizing process or hot rolling of the wire.

Cr: 0.05 to 0.5% by weight Cr has the effect of improving the corrosion resistance of steel. In addition, since it has the effect of increasing the work hardening rate in wire drawing, Cr
High strength can be obtained even at a relatively low processing rate by adding. To exert these effects, it is necessary to add 0.05% by weight or more, but if added excessively, the hardenability against the pearlite transformation increases, the patenting treatment becomes difficult, and the secondary scale becomes too dense, Because mechanical descaling property and pickling property deteriorate,
It must be less than 0.5% by weight.

W: 0.02 to 0.5% by weight W is effective for improving the corrosion resistance. However, its effect is not exhibited if it is less than 0.02% by weight, and its effect is saturated even if it exceeds 0.5% by weight. Nb: 0.01 to 0.1% by weight, Zr: 0.05 to 0.1% by weight Nb, Zr, and the like are elements effective for refining the austenite crystal grain size during patenting and improving the toughness and ductility of the ultrafine steel wire. In order to exert this effect, Nb
It is necessary to add 0.01% by weight or more and for Zr 0.05% by weight or more. However, the effect is almost saturated when Nb and Zr are 0.1% by weight.

Mo: 0.02 to 0.5% by weight Mo is an element effective for suppressing the segregation of P at the grain boundaries and improving the toughness of the ultrafine steel wire. To exert this effect, it must be added in an amount of 0.02% by weight or more, but if it is added in excess of 0.5% by weight, the pearlite transformation in patenting requires a long time and the cost increases.

In addition to the above components, if necessary, Ca, La,
REM such as Ce can also be added. From the viewpoint of suppressing disconnection during wire drawing and twisting, it is preferable that the composition of the nonmetallic inclusions is as follows (all ratios to the total amount of the nonmetallic inclusions). _{(1) Al 2 O 3:} 20 wt% or less, MnO: 40 wt% or less, SiO _2: 20 to 70 wt% (more if necessary Mg
O: 15 wt% or _{less) (2) Al 2 O 3} : 20 wt% or less, CaO: 50 wt% or less, SiO _2: 20 to 70 wt% (more if necessary Mg
O: 15% by weight or less).

When the ultrafine wire of the present invention is applied to, for example, a steel cord, Japanese Patent Application Laid-Open No. 57-19325
3, 55-90692, 62-222910, U.S. Pat. Nos. 4,627,229, 4,258,543 and 58-92395. However, it is useful for weight reduction.

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 any changes in the design based on the above and following gist are all within the technical scope of the present invention. It is included in.

[0027]

EXAMPLES Example 1 Table 1 shows the chemical components of test steels (Nos. 1 to 17) melted in a vacuum melting furnace.

[0028]

[Table 1]

[0029] A 150kg steel ingot melted under vacuum is 115x115 (m
m) hot forged into a billet with a wire diameter of 5.5 mm
Was hot rolled while adjusting the rolling temperature and cooling rate. The cross-sectional structures of these wires were observed, and the area ratio of proeutectoid cementite precipitated at the prior austenite grain boundaries was measured by an image analyzer. The results are also shown in Table 1.

These wires were drawn to a wire diameter of 2.65 mm, and the number of disconnections during the drawing was measured. FIG. 1 shows the relationship between the area ratio of proeutectoid cementite in the rolled material and the number of disconnections of the wire. As is clear from FIG. 1, it can be seen that by setting the area ratio of proeutectoid cementite to 10% or less, disconnection during wire drawing is extremely suppressed.

The obtained steel wire was subjected to a lead patenting treatment, and then a wire drawing was performed to a wire diameter of 1.3 mm.
The steel wire was further subjected to lead patenting and plating, and was wet-drawn to an ultra-fine steel wire having a wire diameter of 0.2 mm (total cross-sectional reduction rate: 97.6%). Table 2 shows the properties (tensile strength, rupture reduction value, presence / absence of longitudinal cracks during the torsion test) of the obtained ultrafine steel wire. As is clear from Table 2, it is understood that the wire rod according to the present invention is excellent in toughness and ductility, and that an ultrafine steel wire having high strength and high toughness is obtained.

[0032]

[Table 2]

Next, regarding the test steel Nos. 1, 10, and 17,
When the relationship between the number of breaks during wire drawing and the nonmetallic inclusion composition when wire drawing was performed to a wire diameter of 0.2 mm was investigated,
The results shown in Table 3 were obtained. As is evident from Table 3, by appropriately adjusting the composition of the nonmetallic inclusions, it can be seen that breakage during wire drawing can be minimized.

[0034]

[Table 3]

Next, for the test steel Nos. 1 and 15, the final patenting diameter was set to 1.0 mm and 0.85 mm (for the test steel 15 only 0.85 mm), and the wet drawing was performed on an ultrafine steel wire having a wire diameter of 0.2 mm. The relationship between the total cross-sectional reduction ratio in the drawn wire after the final patenting and the properties (tensile strength, breaking reduction value) of the ultrafine steel wire was investigated. The result is the final patenting diameter.
Table 4 compared with the case of 1.3 mm (the result shown in Table 2)
Shown in As is evident from Table 4, by setting the total cross-sectional reduction rate in the final wire drawing step to 95% or more, a high-strength and high-toughness ultrafine steel wire can be obtained.

[0036]

[Table 4]

The inventors of the present invention investigated the relationship between the wire diameter and the tensile strength of the ultrafine steel wire of the present invention.
The result shown in FIG. As is clear from FIG. 2, it is understood that the extremely fine steel wire of the present invention has an extremely high strength.

Example 2 Table 5 shows the chemical components of test steels Nos. 18 to 37 melted in a vacuum melting furnace.

[0039]

[Table 5]

A 150 kg steel ingot melted in a vacuum at 115 × 115 (m
m) hot forged into a billet with a wire diameter of 5.5 mm
Was hot-rolled. Table 5 also shows the area ratio of proeutectoid cementite measured for these wires in the same manner as in Example 1. These wires were repeatedly heat-treated and drawn to obtain a wire diameter of 1.75 mm, then subjected to a patenting treatment, and further wet-drawn to an ultra-fine wire having a wire diameter of 0.25 mm or 0.3 mm. Table 6 shows the characteristics (tensile strength, squeeze value at break, presence / absence of longitudinal cracking during torsion test) of the obtained ultrafine wire together with the wire diameter and the cross-sectional reduction rate. As is evident from Table 6, the ultrafine wire according to the present invention achieves high strength and high toughness.

[0041]

[Table 6]

On the other hand, the present inventors evaluated the releasability of the secondary scale by the residual scale amount after performing a mechanical descale test on the hot-rolled wire. S
FIG. 3 shows the relationship between the i amount and the residual scale amount, and FIG. 4 shows the relationship between the Cr amount and the residual scale amount. From this result, it can be seen that the ultrafine wire according to the present invention also has good secondary scale releasability.

Example 3 Table 7 shows the chemical components of test steels Nos. 38 to 56 melted in a vacuum melting furnace.

[0044]

[Table 7]

A 150 kg steel ingot melted under vacuum is 115 × 115 (m
m) hot forged into a billet with a wire diameter of 5.5 mm
Was hot rolled while adjusting the rolling temperature and cooling rate. The structures of these wires were observed, and the area ratio of proeutectoid cementite precipitated at the former austenite grain boundaries was measured by an image analyzer. The results are shown in Table 7.

These wires were drawn to a wire diameter of 2.65 mm, and the number of breaks during the drawing was measured. Table 8 shows the results.
This wire is subjected to lead patenting and then the wire diameter
Wire drawing was performed to 1.3 mm. The drawn material was further subjected to lead patenting treatment and plating treatment, and was wet drawn into a fine steel wire having a wire diameter of 0.2 mm (total cross-sectional reduction rate of 97.6%). Table 8 also shows the properties (tensile strength, reduction value, presence or absence of longitudinal cracks in the torsion test) of the obtained ultrafine steel wire. As is clear from Table 8, it is understood that the wire rod according to the present invention is excellent in toughness and ductility, and that an ultrafine steel wire having high strength and toughness is obtained.

[0047]

[Table 8]

Next, for the test steels Nos. 39, 54 and 56, the relationship between the number of breaks during wet drawing to a wire diameter of 0.2 mm and the composition of nonmetallic inclusions was examined. The results shown in Table 9 were obtained. Was done. As is clear from Table 9, disconnection during wire drawing can be minimized by appropriately adjusting the composition of the nonmetallic inclusions.

[0049]

[Table 9]

[0050]

The present invention is configured as described above, and by appropriately adjusting the component composition and the structure, a high-strength and high-toughness wire rod for a fine steel wire can be obtained. Further, by using the wire material and reducing the total cross-sectional reduction rate in the wire drawing step after final patenting to 95% or more, an ultrafine wire material having high strength and high toughness was obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the area ratio of proeutectoid cementite in a rolled material and the number of disconnections of a wire.

FIG. 2 is a graph showing a relationship between a wire diameter of an ultrafine steel wire and a tensile strength.

FIG. 3 is a graph showing a relationship between a Si content and a residual scale amount.

FIG. 4 is a graph showing a relationship between a Cr content and a residual scale amount.

Continuation of front page (56) References JP-A-63-4039 (JP, A) JP-A-60-152659 (JP, A) JP-A-3-226337 (JP, A) JP-A-3-82709 (JP) , A) JP-A-52-82621 (JP, A)

Claims (7)

(57) [Claims] 1. C: 0.85 to 1.2% by weight, Si: less than 0.45% by weight, Mn: 0.3 to 1% by weight, and N
i: 0.1 to 4 wt% and Co: at least one selected from the group consisting of 0.05 to 4 wt%, the balance being iron and unavoidable impurities, of which Al, N, P, S
Is restricted to not more than 0.005% by weight of Al, not more than 0.005% by weight of N, not more than 0.02% by weight of P and not more than 0.015% by weight of S. The high-strength and high-toughness wire rod for ultrafine steel wires, characterized in that the average content area ratio is 10% or less. 2. The wire rod for an ultrafine steel wire according to claim 1, further selected from the group consisting of 0.05 to 0.5% by weight of Cu, 0.05 to 0.5% by weight of Cr and 0.02 to 0.5% by weight of W. A high-strength, high-toughness wire rod for ultrafine steel wire containing at least one species. 3. The ultrafine steel wire according to claim 1, wherein Nb: 0.01 to 0.1% by weight, Zr: 0.05.
A high-strength high-toughness ultrafine steel wire wire comprising at least one selected from the group consisting of 0.1 to 0.1% by weight and Mo: 0.02 to 0.5% by weight. 4. The wire rod for an ultrafine steel wire according to claim 1, wherein the composition of the non-metallic inclusions in the inevitable impurities is Al ₂ O ₃ : 20% by weight based on the total amount of the inclusions.
Hereinafter, MnO: 40 wt% or less, SiO _2: 20 to 70
% By weight or Al ₂ O ₃ : not more than 20% by weight,
CaO: 50 wt% or less, SiO _2: 20 to 70 wt%
Is a high-strength, high-toughness wire rod for ultrafine steel wire. 5. When the wire for ultrafine steel wire according to any one of claims 1 to 4 is processed into an ultrafine steel wire having a wire diameter of 0.4 mm or less, a wire after final patenting is drawn. A method for producing a high-strength, high-toughness ultrafine steel wire, characterized by imparting a working strain so that the total cross-sectional reduction rate becomes 95% or more. 6. A wire diameter produced by the method of claim 5.
A following fine steel wire _{0.4mm, 270- (130 × log 10} D)
(D is a wire diameter: unit mm) or higher tensile strength (kgf / mm ² ), and a high strength and high toughness ultrafine steel wire, characterized in that the drawing value at break is 35% or more. 7. A twisted product obtained by subjecting the ultrafine steel wire according to claim 6 to stranded wire processing.