JPH04371549A - Wire rod extra fine steel wire with high strength and high toughness, extra fine steel wire with high strength and high toughness, stranded product using the extra fine steel wire, and production of the extra fine steel wire - Google Patents

Abstract

PURPOSE:To provide an extra fine steel wire suitable for reinforcement for rubber, such as belt cord and tire cord, or missile wire and having high strength and high toughness, a wire rod for extra fine steel wire used for producing the above-mentioned extra fine steel wire, a method therefor, a stranded product prepared by using the above-mentioned extra fine steel wire, etc. CONSTITUTION:The wire rod for extra fine steel wire has a composition consisting of, by weight, 0.85-1.2% C, <0.45% Si, 0.3-1% Mn, 0.1-4% Ni and/or 0.05-4% Co, and the balance Fe with inevitable impurities and containing, if necessary, prescribed amounts of Cu, Cr, W, V, Nb, Zr, Mo, etc. In the above composition, the contents of Al, N, P, and S among the inevitable impurities are limited to <=0.005%, <=0.005%, <=0.02%, and <=0.015%, respectively, and further, at the time of rolling or reheating treatment after rolling, the average space factor of pro-eutectoid cementite is regulated to <=10%.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a low-carbon material with high strength and high toughness that is used as a material for rubber reinforcing materials such as belt cords and tire cords, miniature ropes, etc., or as missile wire, etc. The present invention relates to alloy ultrafine steel wires, wire rods for producing such ultrafine steel wires, methods for producing the ultrafine steel wires, and twisted products obtained by twisting the ultrafine steel wires.

0002

BACKGROUND OF THE INVENTION Ultrafine steel wire used as a reinforcing material for rubber is usually manufactured by the following procedure. That is, after hot rolling steel having a predetermined chemical composition, adjusting and cooling as necessary, the obtained wire rod with a wire diameter of 4.0 to 6.4 mm is subjected to a primary wire drawing process, a patenting treatment, and a secondary process. After sequentially applying wire drawing processing, re-patenting processing, plating processing, etc.
Finally, a wet wire drawing process is added to create ultra-fine steel wire. The ultra-fine steel wire obtained in this way can be used as is as missile wire, or when used as steel cord, it can be used for various product processing, such as twisting multiple wires together to form a steel cord. has been done.

[0003] In recent years, particularly in steel cords for reinforcing tires, there has been a tendency to use ultra-fine steel wires with even higher strength from the viewpoint of reducing tire weight, improving riding comfort, and improving handling stability. . Examples of methods for achieving high strength of ultra-fine steel wire include (1) a method of using high carbon steel with increased carbon content to increase the patenting strength before the final wire drawing process; 2) Methods are being implemented to increase the amount of processing strain to the finished wire diameter as much as possible.

[0004] Carbon steel equivalent to JIS SWRS72A and SWRS82A has conventionally been used as wire rod for steel tire cords, but in order to meet the above requirements, the tensile strength has been increased by increasing the amount of wire drawing strain up to the finished wire diameter. Increasing this leads to a significant deterioration in toughness and ductility as the strength increases, such as a decrease in the area of area and the occurrence of vertical cracks in the early stages of the torsion test. Furthermore, if the patenting strength of the above-mentioned steel is simply increased by increasing the amount of carbon, pro-eutectoid cementite will precipitate in a network shape at the austenite grain boundaries, resulting in deterioration of toughness and ductility. When the toughness and ductility deteriorate, wire breakage occurs frequently during wet wire drawing or stranding, particularly in steel tire cord strands, resulting in a significant decrease in productivity.

[0005] Steel tire cords are manufactured using the process described above, but when increasing the carbon content with the sole aim of increasing strength, pro-eutectoid cementite precipitates at the prior austenite grain boundaries in rolled wire rods, etc. , wire breakage occurs frequently during primary wire drawing, which is an intermediate manufacturing process, resulting in an extreme drop in productivity.

[0006]

[Problems to be Solved by the Invention] The present invention has been made under these circumstances, and its purpose is to provide reinforcing materials for rubber such as belt cords and tire cords, or stranded wire products such as miniature ropes. An ultra-fine steel wire with high strength and toughness suitable as a material for making or missile wire, a wire rod for obtaining the ultra-fine steel wire, products using such an ultra-fine steel wire, and the ultra-fine steel wire. The object of the present invention is to provide a method for obtaining steel wire.

[0007]

[Means for Solving the Problems] The present invention that achieves the above object is based on C: 0.85 to 1.2% by weight (preferably 0.
．． 9 to 1.2% by weight), Si: less than 0.45% by weight, and Mn: 0.3 to 1% by weight, respectively.
Ni: 0.1 to 4% and Co: 0.05 to 4% by weight
Contains one or more selected from the group consisting of, if necessary, contains elements such as Cu, Cr, W, V, Nb, Zr, Mo, and the remainder consists of Fe and unavoidable impurities. , for Al, N, P, and S among the impurities,
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, and as rolled or after rolling. This is a high-strength, high-toughness wire rod for ultra-fine steel wire that has an average area ratio of pro-eutectoid cementite of 10% or less in reheat treatment. In addition, from the viewpoint of suppressing wire breakage, the above-mentioned wire rod for ultra-fine steel wire has a composition of nonmetallic inclusions among the inevitable impurities that is Al2O3:2 with respect to the total amount of the inclusions.
0% by weight or less, MnO: 40% by weight or less, SiO2:
20-70% by weight or Al2O3:2
0% by weight or less, CaO: 50% by weight or less, SiO2:
It is preferable to satisfy the requirement of 20 to 70% by weight or less.

Furthermore, the method for producing a high-strength, high-toughness ultra-fine steel wire of the present invention uses a wire rod for ultra-fine steel wire having the various compositional requirements described above, and draws the wire rod into an ultra-fine wire with a wire diameter of 0.4 mm or less. The gist is that during processing, processing strain is applied so that the total cross-sectional reduction rate in wire drawing after final patenting is 95% or more.

According to the above method, 270-(130
×log10D) (D is wire diameter in mm) or more, and has a tensile strength (kgf/mm2) or more, and has an aperture value of 3
A high-strength, high-toughness ultra-fine steel wire with a wire diameter of 0.4 mm or less and a characteristic of 5% or more can be obtained. If the ultra-fine steel wires thus obtained are twisted, they can be made into various products such as steel cords, tire cords, and miniature ropes.

0010

[Operation] Conventional hard steel wire (e.g. JIS G 3506
) and piano wire (e.g. JIS G 3502),
For example, in an ultra-fine steel wire with a wire diameter of 0.4 mm, the total cross-sectional reduction rate during wire drawing exceeds 95%, and the tensile strength of the wire drawn material is 32.
When it exceeds 0 kgf/mm2, there is a problem in that the breaking aperture value rapidly decreases. If the breaking aperture value falls below 35%, wire breakage will occur frequently during the final wet wire drawing process or stranding process, so the breaking aperture value of the ultra-fine steel wire needs to be 35% or more. In addition, in the case of conventional materials, increasing the strength inevitably causes vertical cracks to occur in torsion tests, which also causes frequent wire breaks during the process of twisting steel cords and uneven pitch of the steel cords. had its limits. Additionally, for example, a rolled material with a wire diameter of 5.5 mm is subjected to primary wire drawing until the wire diameter is around 3 mm, but in the case of hypereutectoid steel, a large amount of pro-eutectoid cementite precipitates at the prior austenite grain boundaries. There were problems such as frequent wire breakage, which caused a drop in productivity, and even if wire breakage did not occur, microscopic cracks remained in the steel, leading to wire breakage during secondary wire drawing and deterioration of the characteristics of the ultra-fine steel wire. .

According to the research conducted by the present inventors, the steel material having the composition and structure specified in the present invention can ensure good toughness and ductility in manufacturing processes such as wire drawing, and also has a wire diameter of 0.
Ultra-fine steel wire of 4 mm or less has a tensile strength of 270
-(130×log10 D) (D is wire diameter: unit mm
) or above, it was found that good toughness and ductility could be ensured. Furthermore, according to the results of experiments to understand the effect of increasing the area reduction rate during wire drawing, in order to have a tensile strength that exceeds the above formula and a breaking area of 35% or more, it is necessary to The present invention was completed based on the discovery that the total cross-sectional reduction rate in the wire drawing process (final wire drawing process) should be 95% or more. 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 ultra-fine steel wire. However, simply increasing the amount of C will cause problems during rolling or patenting. Pro-eutectoid cementite precipitates during processing, and wire breakage occurs frequently, especially during final wire drawing or stranding. Although this point can be suppressed by the effect of Co addition, which will be described later, if C is contained in excess of 1.2% by weight, segregation will increase significantly, and Co The required amount of addition increases, manufacturing cost increases, and in the obtained pearlite structure, the amount of cementite relative to the amount of ferrite increases, the toughness and ductility of the ultra-fine steel wire deteriorates, and the above-mentioned wire breakage occurs frequently. Therefore, the C content needs to be 1.2% by weight or less, but if it is less than 0.85% by weight, the predetermined tensile strength of the ultra-fine steel wire cannot be obtained. From the viewpoint of achieving higher strength, it is preferable that the C content exceeds 0.9% by weight.

Si: less than 0.45% by weight Si is an element that strengthens ferrite as a solid solution, increases the tensile strength of patented materials, and is effective in deoxidizing. However, 0.
Adding more than 45% by weight increases the formation of subscales, increases grain boundary oxidation, and deteriorates the mechanical descaling properties of secondary scales.

Mn: 0.3 to 1% by weight Mn is effective as a deoxidizing element in the melting process, and especially the steel of the present invention has a low Si content.
Since it is steel, it is necessary to add Mn. Furthermore, Mn has the effect of fixing S in steel as MnS, and has the effect of preventing deterioration of the toughness and ductility of the steel wire due to S dissolved in the steel. In order to exhibit 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 wire breakage in the wet wire drawing process and wire stranding process to a composite composition with good ductility. It is also essential to add an appropriate amount of Mn. On the other hand, Mn increases the hardenability of steel and is an element that tends to segregate, so if it is added in excess of 1% by weight, low-temperature transformation phases such as martensite will occur in the segregated areas, resulting in cuppy-shaped This may cause wire breakage.

Ni: 0.1 to 4% by weight Ni is an element that dissolves in solid solution in ferrite and is effective in improving the toughness of ferrite, but if it is less than 0.1% by weight, it has no effect; Further, even if it is added in an amount exceeding 4% by weight, the effect is saturated.

Co: 0.05 to 4% by weight Co is effective in preventing the precipitation of pro-eutectoid cementite and refining the pearlite lamellar spacing. To achieve this effect, 0
．． It is necessary to add 0.5% by weight or more, but even if it is added in excess of 4% by weight, the effect will be saturated and the cost will increase.

The high-strength, high-toughness ultra-fine steel wire rod or ultra-fine steel wire of the present invention has the above-mentioned elements as its basic components, with the balance consisting of iron and inevitable impurities, among which Al, N, and P , S, it is necessary to regulate their contents as shown below.

Al: 0.005% by weight or less Al is an effective element as a deoxidizing element during melting and for preventing coarsening of austenite crystal grain size, but if it exceeds 0.005% by weight, Al2 O3 or MgO-Al2 O3
A large amount of non-metallic inclusions such as metal alloys are generated, which causes wire breakage during the wet wire drawing process and wire stranding process. Moreover, these nonmetallic inclusions not only shorten the life of the die in the final wet wire drawing, but also deteriorate the fatigue characteristics of the steel cord and the strands for steel cord. Therefore, in the steel of the present invention, the amount of Al is preferably as small as possible, and is at least 0.00
It needs to be 5% by weight or less (including the case of 0), preferably 0.003% by weight or less.

[0019] N: 0.005 Weight% or less N is 0.00
If it exceeds 5% by weight, strain aging will adversely affect toughness and ductility, so it is necessary to limit the content to 0.005% by weight or less.

P: 0.02% by weight or less P, like S, is an element that reduces the toughness and ductility of steel, and is also an element that tends to segregate. Therefore, in the present invention, the amount of P needs to be 0.02% by weight or less, preferably
The content shall be 0.015% by weight or less.

S: 0.015% by weight or less As mentioned above, S is an element that reduces the toughness and ductility of steel, and is also an element that tends to segregate. Therefore, in the present invention, the amount of S is set to 0.
0.015% by weight or less, preferably 0.015% by weight or less.
001% by weight or less.

The wire rod for high-strength, high-toughness ultra-fine steel wire or ultra-fine steel wire of the present invention may contain Cu, Cr, W, V, N, if necessary.
It may contain elements such as b, Z, and Mo. The contents and reasons for limitations when adding these elements are as follows.

Cu: 0.05 to 0.5% by weight Cu is an element effective in improving corrosion resistance like Cr described later, and for this 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 will segregate at grain boundaries, promoting the occurrence of cracks or flaws during the blooming process of steel ingots or during hot rolling of wire rods.

Cr: 0.05-0.5% by weight Cr has the effect of improving the corrosion resistance of steel. Furthermore, since it has the effect of increasing the work hardening rate in wire drawing, high strength can be obtained even at a relatively low working rate by adding Cr. In order to exhibit these effects, it is necessary to add 0.05% by weight or more, but if too much is added, the hardenability against pearlite transformation will increase, making patenting processing difficult, and furthermore, secondary scale will become denser. If too much is used, mechanical descaling properties and pickling properties will deteriorate.
．． It is necessary to keep it below 5% by weight.

W: 0.02 to 0.5 wt% W is effective for improving corrosion resistance, but if it is less than 0.02 wt%, the effect is not exhibited, and if it is added in excess of 0.5 wt%, W is effective for improving corrosion resistance. However, the effect is saturated.

[0026] V: 0.05-0.5 wt%, Nb: 0
．． 01-0.1 wt%, Zr: 0.05-0.1 wt% V, Nb, Zr, etc. are elements that are effective in refining the austenite grain size during patenting and improving the toughness and ductility of ultra-fine steel wire. be. In order to exhibit this effect, V and Zr must be added in an amount of 0.05% by weight or more, and Nb must be added in an amount of 0.01% by weight or more. However, the effect is almost saturated at 0.5% by weight for V and 0.1% by weight for Nb and Zr.

Mo: 0.02-0.5% by weight Mo is an effective element for suppressing the segregation of P at grain boundaries and improving the toughness of ultra-fine steel wire. In order to exhibit this effect, it is necessary to add 0.02% by weight or more, but if it is added in excess of 0.5% by weight, it will take a long time for pearlite transformation in patenting, increasing costs.

In addition to the above components, Ca, La,
REM such as Ce can also be added.

From the viewpoint of suppressing wire breakage during wire drawing and wire twisting, it is preferable that the composition of the nonmetallic inclusions be as follows (all ratios to the total amount of nonmetallic inclusions). (1) Al2O3: 20% by weight or less, MnO: 4
0% by weight or less, SiO2: 20 to 70% by weight (further MgO: 15% by weight or less if necessary) (2) Al2O3: 20% by weight or less, CaO: 5
0% by weight or less, SiO2: 20 to 70% by weight (if necessary, further MgO: 15% by weight or less)

[0030] Furthermore, when the ultrafine wire of the present invention is applied to, for example, a steel cord,
, No. 55-90692, No. 62-222910, U.S. Pat. No. 4,627,229, No. 4,258,543, U.S. Pat. It also helps to reduce the weight.

[0031] The present invention will be explained in more detail with reference to examples below. However, the following examples do not limit the present invention, and any design changes in accordance with the spirit of the above and below are within the technical scope of the present invention. It is included in

[0032]

【Example】

Example 1 Table 1 shows test steels (No. 1 to 18) melted in a vacuum melting furnace.
) shows the chemical composition of

[0033]

[Table 1]

[0034] 150 kg of vacuum melted steel ingot was 115
This billet was hot-rolled into a wire rod with a wire diameter of 5.5 mm while adjusting the rolling temperature and cooling rate. The cross-sectional structures of these wires were observed, and the area ratio of pro-eutectoid cementite precipitated at prior austenite grain boundaries was measured using an image analysis device. The results are also listed in Table 1.

These wire rods were drawn to a wire diameter of 2.65 mm, and the number of wire breaks during wire drawing was measured. FIG. 1 shows the relationship between the area ratio of pro-eutectoid cementite in the rolled material and the number of wire breaks. As is clear from FIG. 1, wire breakage during wire drawing is extremely suppressed by setting the pro-eutectoid cementite area ratio to 10% or less.

The obtained steel wire was subjected to lead patenting treatment and then wire drawn to a wire diameter of 1.3 mm. The steel wire was further subjected to lead patenting and plating treatment, and then wet drawn into an ultra-fine steel wire with a wire diameter of 0.2 mm (total cross-sectional reduction rate: 97.6%). Table 2 shows the properties of the obtained ultra-fine steel wire (tensile strength, reduction of area at break, presence or absence of longitudinal cracks during torsion test). As is clear from Table 2, the wire rod according to the present invention has excellent toughness and ductility, and it can be seen that an ultra-fine steel wire having high strength and high toughness is obtained.

[0037]

[Table 2]

Next, test steel No. When No. 1, No. 10 and No. 18 were wire drawn to a wire diameter of 0.2 mm, the relationship between the number of wire breaks during wire drawing and the composition of nonmetallic inclusions was investigated, and the results shown in Table 3 were obtained. As is clear from Table 3, by appropriately adjusting the nonmetallic inclusion composition,
It can be seen that wire breakage during wire drawing can be minimized.

[0039]

[Table 3]

Next, test steel No. 1,16, the final patenting diameter is 1.0 mm, 0.85 mm (only 0.85 mm for sample steel 16), and the wire diameter is 0.
．． A 2 mm ultra-fine steel wire was subjected to wet wire drawing, and the relationship between the total area reduction rate during wire drawing after final patenting and the properties of the ultra-fine steel wire (tensile strength, reduction of area at break) was investigated. The results are calculated when the final patenting diameter is 1.3 mm (
Table 4 shows a comparison with the results shown in Table 2. As is clear from Table 4, the total cross-sectional reduction rate in the final wire drawing process was 95
% or more, it can be seen that an ultra-fine steel wire with high strength and high toughness is obtained.

[0041]

[Table 4]

When the present inventors investigated the relationship between the wire diameter and tensile strength of the ultrafine steel wire of the present invention, the results shown in FIG. 2 were obtained. As is clear from FIG. 2, it can be seen that the ultra-fine steel wire of the present invention has extremely high strength.

Example 2 Table 5 shows test steel No. 1 melted in a vacuum melting furnace. 19-39
The chemical composition of

[0044]

[Table 5]

[0045] 150 kg of vacuum melted steel ingot was 115
x 115 (mm), and this billet was hot rolled into a wire rod with a wire diameter of 5.5 mm. In these wire rods, the pro-eutectoid cementite area ratios measured in the same manner as in Example 1 are also listed in Table 5.

[0046] These wires were repeatedly subjected to heat treatment and wire drawing to obtain a wire diameter of 1.75 mm, and then subjected to a patenting treatment, and further wet-drawn into ultrafine wires with a wire diameter of 0.25 mm or 0.3 mm. The properties of the obtained ultrafine wire (tensile strength, reduction of area at break, presence or absence of vertical cracks during torsion test) are shown in Table 6 along with the wire diameter and area reduction rate. As is clear from Table 6, it can be seen that the ultrafine wire according to the present invention has achieved high strength and high toughness.

[0047]

[Table 6]

On the other hand, the present inventors evaluated the removability of secondary scale by the amount of residual scale after performing a mechanical descaling test on a hot rolled wire rod. S
The relationship between the amount of i and the amount of residual scale is shown in FIG. 3, and the relationship between the amount of Cr and the amount of residual scale is shown in FIG. 4, respectively. From this result, it can be seen that the ultrafine wire material according to the present invention also has good removability of secondary scale.

Example 3 Table 7 shows test steel No. 3 melted in a vacuum melting furnace. 40-59
The chemical composition of

[0050]

[Table 7]

[0051] 150 kg of vacuum melted steel ingot was 115
This billet was hot-rolled into a wire rod with a wire diameter of 5.5 mm while adjusting the rolling temperature and cooling rate. The structures of these wire rods were observed, and the area ratio of pro-eutectoid cementite precipitated at prior austenite grain boundaries was measured using an image analysis device. The results are also listed in Table 7.

These wire rods were drawn to a wire diameter of 2.65 mm, and the number of wire breaks during wire drawing was measured. The results are shown in Table 8. This drawn wire material was subjected to lead patenting treatment, and then wire drawn to a wire diameter of 1.3 mm. The drawn wire material is further subjected to lead patenting treatment and plating treatment, resulting in a wire diameter of 0.
Wet-drawn 2 mm ultra-fine steel wire (total cross-sectional reduction rate 97
．． 6%). The properties of the obtained ultra-fine steel wire (tensile strength, reduction of area, presence or absence of vertical cracks during torsion test) are also listed in Table 8. As is clear from Table 8, the wire rod according to the present invention has excellent toughness and ductility, and it can be seen that an ultra-fine steel wire having high strength and high toughness is obtained.

[0053]

[Table 8]

Next, test steel No. For No. 41, No. 57, No. 59, the relationship between the number of wire breaks during wet wire drawing up to a wire diameter of 0.2 mm and the composition of nonmetallic inclusions was investigated, and the results shown in Table 9 were obtained. As is clear from Table 9, wire breakage during wire drawing can be minimized by appropriately adjusting the composition of nonmetallic inclusions.

[0055]

[Table 9]

[0056]

[Effects of the Invention] The present invention is constructed as described above, and by appropriately adjusting the component composition and structure, a wire rod for ultra-fine steel wire with high strength and high toughness was obtained. Further, by using the wire rod and making the total cross-sectional reduction rate in the wire drawing process after final patenting 95% or more, an ultrafine wire rod with high strength and high toughness was obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the pro-eutectoid cementite area ratio of a rolled material and the number of wire breaks.

FIG. 2 is a graph showing the relationship between wire diameter and tensile strength of ultra-fine steel wire.

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

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

Claims (7)

[Claims] [Claim 1] C: 0.85-1.2% by weight, Si
: less than 0.45% by weight, Mn: 0.3-1% by weight
In addition to containing 0.1 to 4% by weight of Ni and C
o: Contains one or more selected from the group consisting of 0.05 to 4% by weight, with the balance consisting of iron and unavoidable impurities, and among the impurities, Al, N, P, and S are Al: 0.05 to 4% by weight.
005 weight% or less, N: 0.005 weight% or less, P
: 0.02% by weight or less and S: 0.015% by weight or less, respectively, and the average content area ratio of pro-eutectoid cementite is 10% or less in as-rolled or after-rolling reheat treatment. Wire rod for high-strength, high-toughness ultra-fine steel wire. 2. The wire rod for ultrafine steel wire according to claim 1, further comprising Cu: 0.05 to 0.5% by weight, and Cr: 0.
．． 05-0.5 Weight% and W: 0.02-0.5
A wire rod for a high-strength, high-toughness extra-fine steel wire, which contains one or more types selected from the group consisting of % by weight. 3. The wire rod for ultrafine steel wire according to claim 1 or 2, further comprising V: 0.05 to 0.5% by weight, N
b: 0.01-0.1% by weight, Zr: 0.05-0.
1% by weight and one or more selected from the group consisting of Mo: 0.02 to 0.5% by weight. 4. The wire rod for ultrafine steel wire according to claim 1, wherein the composition of the nonmetallic inclusions among the inevitable impurities is Al2O3:20 with respect to the total amount of the inclusions.
Weight % or less, MnO: 40 weight % or less, SiO2: 2
0-70% by weight or Al2O3:20
Weight % or less, CaO: 50 weight % or less, SiO2: 2
A wire rod for high-strength, high-toughness ultrafine steel wire having a content of 0 to 70% by weight. 5. When processing the wire rod for ultra-fine steel wire according to any one of claims 1 to 4 into an ultra-fine steel wire with a wire diameter of 0.4 mm or less, the stretching after final patenting is performed. A method for producing a high-strength, high-toughness ultra-fine steel wire, which comprises applying processing strain so that the total cross-sectional reduction rate in the wire is 95% or more. 6. An ultra-fine steel wire with a wire diameter of 0.4 mm or less produced by the method of claim 5, 270-(1
A high-strength, high-toughness ultra-fine steel wire having a tensile strength (kgf/mm2) of 30×log10 D) (D is wire diameter in mm) or more, and an area of area at break of 35% or more. . 7. A twisted product characterized by being made by processing the ultra-fine steel wire according to claim 6 into a twisted wire.