JPH07115062B2 - Method for manufacturing brass-plated ultrafine steel wire - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a brass fine wire.

(Prior Art) In the present invention, a wire diameter of brass ultrafine steel wire is generally
A steel wire having a thickness of 1 mm or less to several tens of μm and having a brass layer on the surface thereof, which is used as a tire cord wire, a high pressure hose wire, and the like. Conventionally, these brass fine ultra-fine steel wires, since the toughness of the drawn wire decreases with each wire drawing process, while normally performing a few degrees of patenting treatment from the high carbon steel 5.5 mm diameter rolled wire,
After manufacturing extra-fine steel wire with a predetermined diameter by cold drawing over several orders, it is manufactured by brass plating, which requires a large number of manufacturing steps and high manufacturing costs. I have no choice.

On the other hand, there is pure iron and mild steel wire rods that can do this, but only in the case of strong cold-drawing from wire rod to ultra-fine steel wire, the increase in strength due to wire-drawing is small, so it is extremely fine as the final product. Low strength in steel wire. That is, 95-99%
Even in the case of hard working wire drawing, the strength is 70 to 130 kgf / mm ² , and it is impossible to achieve a strength of 170 kgf / mm ² or more.
In addition, the strength is 19 even by wire drawing with a processing rate of 99% or more.
It is 0 kgf / mm ² or less.

The present inventors, in place of the high carbon steel wire rod and mild steel wire rod,
As a result of earnest research to obtain a low carbon steel wire rod excellent in strong workability, as already described in JP-A-60-152655, the structure of the low carbon steel wire rod for cold drawing is retained austenite in advance. It may contain bainite, martensite or a fine mixed structure thereof (pre-structure), and then by transforming austenite reverse transformed from this under predetermined cooling conditions, as a final structure, Needle-like bainite, which may partially contain retained austenite, a fine low-temperature transformation-forming phase consisting of martensite or a mixed structure of these is formed into a composite structure in which the fine structure is uniformly dispersed in the ferrite phase. The structure wire has excellent workability, and high strength ultrafine steel wire with a diameter of 1 mm to several tens of μm can be obtained by continuous cold drawing with a total area reduction rate of 90% or more. I have found a door.

However, in continuous cold drawing of the wire rod, according to the conventional lubrication treatment with a phosphate coating, lubrication for cold working becomes difficult as the working degree increases,
In the case of continuous cold wire drawing with a work reduction rate of 90% or more, preferably 98% or more, an ultrafine steel wire having a uniform surface property cannot be obtained due to insufficient lubrication. That is, it was found that a non-uniform deformation layer is formed on the outermost surface of the wire drawing where the wire drawing and the die contact each other during continuous wire drawing. Since such a non-uniform deformation layer grows and expands for each die, it becomes more remarkable as the strength is increased, and the non-uniform deformation layer expands to such an extent that the ductility of wire drawing is impaired. In conventional high carbon steel wire rod,
Since the wire itself lacks strong workability, since the patenting treatment is performed in the middle, the above-mentioned non-uniform deformation layer accumulation and expansion does not occur.

More specifically, when the lubricity deteriorates during wire drawing, the wire drawing material and the die make metal contact with each other, so that the surface of the wire drawing material is smooth, and it is difficult for powdered lubricant to adhere to the wire drawing material. Therefore, the amount introduced into the die is reduced. The amount of lubricant adhered to the wire drawing material is an index showing the above-mentioned lubricity, and this amount becomes smaller as the die angle becomes larger and the wire drawing speed becomes faster. Further, as the number of dies, that is, the number of repeated passes increases, the amount of lubricant adhered significantly decreases.

FIG. 4 shows a change in the amount of lubricant adhered with an increase in the number of wire drawing passes for a conventional high carbon steel lead patenting (LP) treated wire and a wire having a composite structure having strong workability described above. As shown in II and III, when the composite textured wire is subjected to continuous cold wire drawing at a total area reduction rate of 90% or more, the number of passes is large, and the lubricant adhesion amount is significantly reduced with this pass number. Therefore, cold wire drawing with poor lubricity cannot be avoided, and as a result, the ductility of the wire drawn material deteriorates.

(Purpose of the invention) Therefore, the present inventors further researched a method for producing a surface brass fine ultrafine steel wire by using the composite texture wire having strong workability described above, and as a result, By applying the brushing treatment before or during the continuous cold wire drawing and utilizing the lubricating action of the plating layer, it is possible to obtain high strength immediately without heat treatment such as patenting during wire drawing. It has been found that a high ductility brass fine wire can be obtained.

From another side, conventionally, in order to manufacture a surface brass ultrafine steel wire, brass plating is applied to patenting during wire drawing of the wire rod or wire drawing after wire drawing, but according to the present invention, By applying brass plating before wire drawing, or by applying brass in the middle of wire drawing, the surface reduction rate is 98% or more due to the lubricating action of this metal plating.
According to a preferred embodiment, it is possible to easily carry out continuous wire drawing with 99% or more, and to obtain a brushed extra fine steel wire without requiring patenting treatment or the like. Moreover, the brass fine extra fine steel wire obtained by such a method has improved ductility and, as a result of promoting the homogenization of the fine layer due to the strong working after plating, the adhesion with rubber is remarkably improved. It

Therefore, the present invention generally aims to provide a method for producing a brass fine extra fine steel wire, and in particular, a continuous cold wire drawing is performed after the low carbon steel wire rod having a predetermined composite structure is brushed. Accordingly, it is an object of the present invention to provide a method for producing a brass fine extra fine steel wire which has improved ductility and has excellent adhesion to rubber because the plating layer is homogenized and homogenized.

(Structure of the Invention) The method for producing a brushed extra fine steel wire according to the present invention comprises, by weight%, C 0.01 to 0.30%, Si 2.0% or less, Mn 0.3 to 2.5%, balance iron and unavoidable impurities, and acicular martensite. , A bainite or a mixture of these low-temperature transformation-generated phases with a volume fraction of 15 to 40% is uniformly dispersed in the ferrite phase. Before wire drawing, or during the wire drawing, a brushing layer made of Cu 40 to 65% and Zn 35 to 60%, and the balance unavoidable impurities, is provided.

First, the chemical components of the composite textured wire used in the method of the present invention and the production thereof will be described. In the following, the tissue having a needle-like shape (elongated or acicular) means that the tissue particles have a directionality, and the lumpy (globular) means that the particles do not have a directionality. Further, the converted particle diameter of the acicular particles means the diameter when the area of the acicular particles is converted into a circle.

C is 0. in order to make the hot rolled wire rod from a steel slab into a wire rod having a predetermined composite structure by a predetermined heat treatment described later.
It is necessary to add 01% or more, but when it is added in excess of 0.30%, a low-temperature transformation-producing phase consisting of acicular martensite, bainite, or a mixed structure of these (hereinafter simply referred to as the second phase However, the ductility of the steel will deteriorate. Therefore, in the present invention, the amount of C added is in the range of 0.01 to 0.30%.

Si is effective as a strengthening element for the ferrite phase, but 2.
If it is added in excess of 0%, the transformation temperature will be shifted to the extremely high temperature side, and decarburization of the surface of the wire will be likely to occur, so the upper limit of addition is 2.0%.

It is necessary to add 0.3% or more of Mn in order to strengthen the wire rod, enhance the hardenability of the second phase, and make the morphology acicular, but added in excess of 2.5%. However, the effect is saturated, so the amount of Mn added is 0.3 to 2.5.
%.

In the present invention, at least one element selected from Nb, V and Ti can be further added in order to refine the metal structure of the wire. For the refinement of this structure, addition of 0.005% or more is necessary for all elements, but even if added in excess, the effect saturates and it is economically disadvantageous. , Its upper limit is Nb
Is 0.2% and V and Ti are 0.3%.

Further, the elements inevitably contained in the wire rod in the present invention or the elements which may be contained therein will be described.

S is preferably 0.005% or less in order to reduce the amount of MsS in the wire, which improves the ductility of the wire. Further, it is preferably 0.003% or less in order to prevent deterioration of ductility due to hydrogen during pickling or plating treatment.

Since P is an element with significant grain boundary segregation, its content should be 0.
It is preferably 01 or less.

N is an element most easily aged when it exists in a solid solution state. Therefore, the workability is hindered by aging during working, or the workability is also aged after working to deteriorate the ductility of the ultrafine wire obtained by wire drawing, so 0.003% or less is preferable.

Al forms oxide-based inclusions, and since these oxide-based inclusions are difficult to deform, they may hinder the workability of the wire.
During the wire drawing of the wire rod, the inclusion is likely to cause a breakage. Therefore, the Al content is usually preferably 0.01% or less. Particularly, it is preferably 0.005% or less.

Also, when the Si / Al ratio in the wire increases, the silicate inclusions increase, especially when the amount of Al is small,
The amount of silicate-based inclusions suddenly increases, which not only deteriorates the wire drawability of the wire rod, but also deteriorates the fatigue properties of the wire rod obtained by wire drawing. Therefore, in the present invention, the Si / Al ratio is preferably 500 or less. Furthermore, according to the present invention, Si
The / Mn ratio is preferably 0.7 or less. This is because when the Si / Mn ratio exceeds 0.7, the composition and morphology of the inclusions change, and the dispersion or distribution of the inclusions may cause the wire drawability of the wire to deteriorate.

On the other hand, by adding rare earth elements such as Ca and Ce,
It is also preferable to adjust the shape of the MnS inclusions.

Further, solid solution C or N can be fixed by adding Al or the like including Nb, V and Ti described above. Further, depending on the use of the ultra-fine steel wire according to the present invention, the wire rods to be used contain Cr, Cu and / or Mo at 1.0% or less and Ni at 6% or less.
% Or less, Al and / or P is 0.1% or less, and B is 0.0
2% or less can be appropriately added.

The composite structure wire rod in the present invention, after austenitizing the hot-rolled wire rod having the predetermined chemical component under predetermined conditions, then rapidly cooled to have a predetermined front structure, and then,
This wire can be obtained by further heat-treating it to give it a predetermined composite structure.

That is, by subjecting a steel slab having the above-mentioned chemical composition to the required hot working and heat treatment, the structure thereof is changed to austenite grain size of bainite of 35 μ or less, martensite or a mixed structure thereof, and then Ac ₁ ~ Heat to the Ac ₃ temperature range,
By promoting the austenitization so that the austenitization fraction is about 20% or more, and then cooling the wire rod thus obtained from room temperature to 500 ° C at an average cooling rate of 40 to 150 ° C / sec. As a result, it is possible to obtain the composite textured wire having the above-mentioned strong workability. The method for producing a surface brass ultrafine steel wire according to the present invention is such that, when cold drawing of such a composite structure wire rod at a total area reduction ratio of 98% or more, Cu 40 to 65% and Zn 35 to 65% before or during wire drawing. It is made by brushing with -60% of the balance unavoidable impurities and then wire drawing.

First, in order to obtain a composite structure wire rod in which the second phase is a fine needle-shaped structure, before heating the hot-rolled wire rod having the above-mentioned predetermined chemical component composition to the Ac ₁ to Ac ₃ temperature range, By subjecting it to a heat treatment at, the structure of the former austenite grain size which may partially contain retained austenite is
A bainite, martensite, or a finely mixed structure thereof having a size of 35 μ or less, preferably 20 μ or less (hereinafter, these may be simply referred to as a pre-structure). By refining the front structure in this way, it is possible to refine the final structure and improve the ductility and toughness of the composite structure wire, thus imparting the required strength.

To adjust the former austenite grain size to 35 μ or less, when hot working a steel piece obtained by ingot casting or continuous casting, a temperature range in which recrystallization of austenite and the progress of grain growth are extremely slow, that is, 980 ° C. It is necessary to perform hot working at a surface reduction rate of 30% or more in the temperature range of Ar ₃ or more, which is the following. When the hot working temperature is higher than 980 ° C, austenite easily recrystallizes or grows grains,
Also, when the work area reduction rate is less than 30%, the austenite grain size cannot be reduced. Furthermore, in order to obtain austenite fine particles of about 10 to 20μ, in addition to the above processing conditions, the final processing pass must be 900 ° C or less. To obtain ultrafine particles of about 5 to 10μ, It is necessary to process at a strain rate of 300 / sec or more.

It is also possible to add cold working after the hot working for adjusting the prior austenite grain size to obtain a desired shape, but in this case, the working rate of cold working is up to 40%. When cold working of more than 40% is applied to the previous structure,
Reheating of martensite occurs during heating to the Ac ₁ to Ac ₃ temperature range described below, and the desired final structure cannot be obtained.

Next, the following method can be used to make the preceding structure a bainite, martensite, or a mixed structure thereof.

The first is a method of obtaining a required pre-structure during a rolling process, in which a steel slab is controlled-rolled or hot-rolled and then accelerated and rapidly cooled. The cooling rate is required to be 5 ° C./second or more. This is because at a cooling rate lower than this, a normal ferrite / pearlite structure is formed.

The second method for obtaining the pre-structure is a method in which the rolled steel material is heat-treated again, and the steel is heated to the austenite region of Ac ₃ point or more and then adjusted and cooled. Also in the case of this method, the heating temperature is preferably in the range of Ac ₃ to Ac ₃ + 100 ° C. as in the case of the first method.

As described above, the structure before heating to the Ac ₁ to Ac ₃ region is replaced with a conventional ferrite-pearlite structure, and low-temperature transformation formation of martensite that may contain retained austenite, bainite, or a mixed structure thereof is formed. By heating the rolled steel material as a phase to the Ac ₁ to Ac ₃ region, the retained austenite or cementite existing at the lath boundary of the low-temperature transformation forming phase is used as a priority nucleus, and a large number of initial austenite grains are generated, and the lath boundary is generated. Grow along with.

Then, the martensite or bainite transformed from this austenite by cooling under a predetermined condition is made needle-like to have a good consistency with the surrounding ferrite phase, and thus the conventional pre-ferrite-perlite structure is obtained. Compared with, the second phase particles are remarkably miniaturized. Therefore,
The conditions of heating and cooling in the Ac _{1 to} Ac ₃ region are important. That is, depending on the conditions, the second phase is agglomerated, or agglomerated particles are mixed in the second phase, which impairs the strong workability.

More specifically, fine transformation of bainite, a martensite or a pre-structure composed of a mixed structure thereof into the austenite region is a reverse transformation, and the austenite fraction is up to about 20% from the austenite grain boundary to the massive austenite. Is generated and acicular austenite is generated from the inside of the grain. Therefore, from this state, by rapidly cooling at a cooling rate of, for example, 150 to 200 ° C./second or more, the acicular and agglomerated low temperature A structure in which the transformation-generated phase is dispersed in ferrite is obtained. Therefore, the finer the grain size of prior austenite, the higher the frequency of formation of massive austenite. When the austenite formation progresses by about 40% or more, the acicular austenite particles coalesce with each other and change into massive austenite. Therefore, when rapidly cooled from this state, a mixed structure of ferrite and coarse massive low-temperature transformation forming phase is formed. . Further, if the austenitization progresses by about 90% or more, the massive austenites grow together and the austenitization is completed. Therefore, if the material is rapidly cooled from this state, the structure mainly composed of the low temperature transformation forming phase is formed.

Therefore, in the present invention, the steel adjusted to the previous structure is
When heating in the Ac _{1 to} Ac ₃ region, the austenitizing fraction should be about 20% or more, and from this state, cool to room temperature to 500 ° C at an average cooling rate of 40 to 150 ° C / sec. By, by separating the ferrite and acicular austenite from the bulk austenite in the transformation process during cooling, by transforming the acicular austenite to the low temperature transformation-generated phase, acicular bainite that may contain some residual austenite Thus, a fine metallurgical transformation phase composed of martensite or a mixed structure thereof is uniformly dispersed in the ferrite phase to obtain a final metal structure.

The average cooling rate after heating the wire to the Ac ₁ to Ac ₃ region is limited as described above. When the cooling rate is slower than 40 ° C / sec, polygonal ferrite is generated from the massive austenite, and the residual massive austenite particles are transformed into the massive second phase, while the cooling rate is faster than 150 ° C / sec. This is because, in this case as well, the massive second phase is generated as described above.
In the present invention, the second phase in the ferrite phase is used.
The volume fraction of the phase should be in the range of 15-40%. When the volume fraction of the second phase is within this range, the second phase particles are acicular, and their average reduced particle size is 3 μm or less, thus,
The wire obtained has excellent strong workability because it has a unique composite structure that has never existed before. When the volume fraction of the second phase is out of the above range, the massive second phase is likely to be mixed in the final structure even by cooling under the above conditions.

The cooling stop temperature is room temperature to 500 ° C. This is to obtain bainite, martensite, or a mixed structure thereof as a low-temperature transformation-producing phase, and by slowing or stopping the cooling rate within this temperature range, tempering of the produced second phase is performed. This is because it can also be combined with.

According to the method of the present invention, such a wire material is subjected to brass-meshing treatment of a predetermined composition before or during wire drawing, and by continuous cold wire drawing with a working rate of 98% or more, good lubricity of the metal layer is obtained. As a result, a high-strength and high-ductility brass wire can be obtained.

In the method of the present invention, the brass plating treatment means that a brass plating layer having a high extensibility is attached to the wire material by a method such as electrical plating, chemical plating or molten plating. In the present invention, this brass composition is Cu40-65%,
Zn is in the range of 60 to 35%. As in the prior art, by wire-drawing a wire rod to produce a surface-coated ultrafine steel wire, the brass composition is usually Cu60-70%, Zn40
It is said that the content is up to 30%, and making Zn in a larger amount than this deteriorates the quality of the brass ultrafine steel wire because the brass layer has poor malleability. However, according to the method of the present invention, even if the amount of Zn is increased as described above, by strongly working this brass layer as a lubricant, the reason is not necessarily clear, but the brass layer is a wire rod. Not only can it exert a good lubricating effect during wire drawing, prevent the formation of a non-uniform layer on the surface of wire drawing during wire drawing, and ensure excellent continuous cold wire drawability, but also unexpectedly. In addition, the ductility of the obtained wire drawing is improved, and further,
It is possible to obtain a surface brushed ultrafine steel wire having a uniform and uniform brushed layer. In particular, such a surface-polished ultrafine steel wire has a markedly improved adhesion to rubber as compared with a normal surface-etched ultrafine steel wire produced by a conventional method.

In the present invention, the amount of brush attachment is required to obtain a uniform brush thickness even after strong working, and it depends on the diameter of the ultrafine steel wire, but it is approximately 1 to 15 g per 1 kg of wire rod.
Is preferred. In particular, by holding the brass layer in the range of 0.2 to 1.0% by weight with respect to the ultrafine steel wire to be finally obtained, the properties of the brass layer itself, for example,
Uniformity and homogeneity can be extremely enhanced.

In the present invention, in the wire drawing of the wire material after brushing, it is preferable that the approach angle of the wire drawing die is 4 to 15 °, and the total workability after plating is about 80%. In the first half of wire drawing with a strength of 120 kgf / mm ² or less, it is preferable that the approach angle is 4 to 8 °. This method facilitates uniform processing of the plated layer and prevents nonuniformity of the plated layer.

As described above, the wire rod used in the present invention has a structure of low carbon steel as bainite, martensite or a fine mixed structure thereof in advance, and the bulk austenite reversely transformed from this is transformed under predetermined cooling conditions to obtain a fine grain. It has a unique fine composite structure in which the acicular low-temperature transformation-generated phase is uniformly dispersed in the ferrite phase at a volume fraction of 15 to 40%, and good lubricity of the brass layer is obtained. Thus, by continuous cold drawing with a working rate of 98% or more, a high-strength and high-ductility brass fine extra-fine steel wire can be obtained.

Further, according to the method of the present invention, the above-described composite texture wire is cold-drawn at a total area reduction rate of 98% or more, to produce an ultra-fine steel wire, at the recrystallization temperature of the following during drawing. By applying a heat treatment of cooling after heating to a temperature, the strength increase with respect to the surface reduction rate is large compared to a wire rod not subjected to such heat treatment, so it is possible to finally obtain an ultrafine steel wire with higher strength. You can

In the method of the present invention, when melt plating is used in the plating treatment, the composition of the plating may be adjusted so that its melting point is a desired temperature, and the above heat treatment can be carried out simultaneously. That is, as a heating bath and a cooling bath in the heat treatment step, a metal plating bath can be used.

In the method of the present invention, the heat treatment means heating at a temperature and for a time that does not destroy the tissue flow formed by the two phases of ferrite and martensite stretched in the processing direction. Although it depends on the time, it is usually in the range of 200 to 700 ° C, preferably in the range of 300 to 600 ° C.

In general, the wire rod is drawn by drawing, and each phase in the structure is elongated in the working direction to form a so-called structure flow, and microscopically, a substructure is generated due to dislocations in each phase, With these changes, the strength of the wire drawing material increases. According to the method of the present invention, the lower structure is partially recovered by heating to such an extent that the structure flow is not destroyed in the course of wire drawing, and fine precipitation of elements such as C and N occurs in each phase. Happens within. Therefore, when the drawn wire material that has been subjected to such heat treatment is further subjected to cold wire drawing, a new substructure is formed and developed with the precipitates existing in the substructure as nuclei, while the structure flow is Since the wire drawing process is followed by the development of each wire drawing process, it is considered that as a result, the working limit of the wire rod is improved and the strength of the wire rod is increased.

Therefore, in order to form and develop the structure flow and the substructure by the wire drawing before the heat treatment, the minimum wire drawing degree is defined, and in the wire drawing after the heat treatment,
In order to form and develop a new substructure, the minimum wire drawing workability will be defined, but according to the study by the present inventors, the above-mentioned minimum workability is approximately 50 to 50%.
It is about 80%. Further, the strength after heat treatment and the work hardening rate due to the subsequent processing change depending on the degree of recovery of the lower structure during heat treatment and the precipitation state of elements such as C and N. The time is preferably set optimally according to the purpose.

Conventionally, there is known a method in which a wire drawing processed to near the processing limit is heated to a temperature higher than the recrystallization temperature to discontinue the processed structure, restore the state before processing, and process again. However, the heat treatment in this case is a so-called annealing treatment, and on the other hand, the heat treatment in the method of the present invention is heating to the recrystallization temperature or lower, which is different from the conventional annealing treatment. In the method of the present invention, when the heat treatment temperature is equal to or higher than the recrystallization temperature, the strength after the heat treatment decreases, and thereafter, again,
Even if cold working is performed, strength is not improved, and only working is possible.

(Effect of the Invention) According to the method of the present invention, when a wire rod having a predetermined composite structure is cold-worked to manufacture an ultrafine steel wire, a predetermined brass-meshing treatment is performed before or during wire drawing, and this plating is performed. By the lubrication action of the layer, while ensuring good cold drawability,
The wire can be cold drawn and, in this way, an ultra-fine steel wire with uniform and uniform brushing and improved ductility can be obtained.

In particular, the surface brushed ultrafine steel wire according to the present invention is remarkably excellent in adhesiveness with rubber because the brasset containing a large amount of Zn which has not been hitherto is homogenized and homogenized by the strong working of the wire. .

Further, the strength of the ultrafine steel wire finally obtained can be improved by performing a heat treatment of heating and cooling to a temperature equal to or lower than the recrystallization temperature during the wire drawing.

(Examples) The present invention will be described below with reference to Examples and Reference Examples.
The invention is in no way limited by these examples.

Reference Example 1 (Production and Properties of Composite Microstructure Wire) As shown in Table 1, steels A and B having the chemical composition specified in the present invention were water-cooled after rolling to make the pre-structure a fine martensite structure. The wire rods were A1 and B1, respectively. As comparative steels, steel rods A and B were air-cooled after rolling, and wire rods having a ferrite / pearlite structure as the front structure were respectively A2 and
B2. The former austenite grain sizes are all 20 μ or less.

Next, the wires A1 and B1 were heated and held in the Ac ₁ to Ac ₃ regions for 3 minutes so as to have different austenite fractions, and cooled to room temperature at various average cooling rates. The morphology of the second phase particles and the volume fraction thereof with respect to the heating temperature and cooling rate are shown in FIG. The solid line indicates the uniform mixed structure of the ferrite and the acicular second phase, and the broken line indicates the mixed structure of the ferrite and the massive second phase, or the ferrite and the acicular or massive second phase.

Next, after heating and holding A1 and B1 in the Ac ₁ to Ac ₃ range and then cooling at an average cooling rate of 125 ° C./sec or 80 ° C./sec, the second phase form of the obtained rolled wire rod is needle-shaped. The organization is this second
Phase is uniformly dispersed in the ferrite phase,
The volume fraction of the second phase is almost constant regardless of the heating temperature. On the other hand, even if the previous organization is the same,
When the average cooling rate is 170 ° C./sec or more, the second phase morphology becomes a lump, or a mixture of a lump and a needle, and the second phase fraction increases as the heating temperature increases.

FIG. 2 shows steels A and B (Table 1) having the chemical composition defined in the present invention, which were water-cooled after rolling to make wire rods having a fine martensite structure as a pre-structure, respectively, A1 and B1, respectively. For this purpose, the above steels A and B were air-cooled after rolling, and the wire rods with the pre-structures of ferrite and pearlite were respectively A2.
And B2, in the case of obtaining a composite structure wire rod, after heating and holding these in the Ac ₁ to Ac ₃ region for a predetermined time, followed by rapid cooling,
It is a graph which shows the 2nd phase volume fraction contained in the final organization, the form of a 2nd phase particle, and the relation of average conversion particle diameter. Here, the average reduced particle diameter means the average diameter when the area is converted to a circle as described above in any of the forms.

The particle size of the second-phase particles is
Although it increases as the phase volume fraction increases, when the second phase fraction is the same, the particle size of the particles obtained from the pre-martensite structure is the particle size of the particles obtained from the pre-ferrite / pearlite structure. Remarkably smaller than. That is, even for steels having the same composition, the second phase particles can be remarkably refined by adjusting the pre-structure from the ferrite-pearlite structure to the martensite structure. By the miniaturization of the second phase particles, the ductility of the wire is greatly improved,
However, it is not always rich in strong workability. That is,
By setting the volume fraction of the second phase in the range of 15 to 40%, the morphology of the second phase is mainly needle-like, and the second phase is fine needle-like with an average reduced particle size of 3 μm or less. It is composed of particles, and since such fine needle-shaped second phase is uniformly dispersed and distributed in the ferrite, it has excellent strong workability.
Of course, the above also applies when the second phase is acicular bainite or a mixed structure of this and martensite.

Reference Example 2 Next, the rolled wire A1 having fine martensite as a pre-structure and the rolled wire A2 having a ferrite / pearlite structure as a pre-structure were heat-treated under various conditions as shown in Table 2. Table 2 shows the heating and cooling conditions in this heat treatment, and the final structure and mechanical properties of the composite texture wire obtained thereby.

Steel Nos. 3 and 4 obtained by heating A1 having a fine structure of fine martensite in the Ac ₁ to Ac ₃ region so that the austenitizing fraction is 20% or more and then cooling at 125 ° C./sec. The wire rods of 5 and 6 have a composite structure in which fine acicular martensite (second phase) is uniformly mixed and dispersed in the ferrite phase within a volume fraction of 15 to 40%, and the tensile strength is It is clear that the strength and ductility balance, which is defined by the product of

On the other hand, the rolled wire A2 having a pre-structure of ferrite / pearlite has the second structure regardless of the heating and cooling conditions.
Steel Nos. 10, 11 or 12 in which the phase morphology is lumpy, all of which have poor balance of strength and ductility.

On the other hand, although the former structure is martensite (A
1), for the cooling rate after heating the steel No. 1 Ac ₁ to Ac ₃ range is too slow, also steel No. 2, Ac ₁ to Ac ₃ austenitizing fraction when heated to zone 16% Therefore, the structure is a fine mixed structure of ferrite and massive and acicular martensite, which is superior to steel Nos. 10 to 12 in strength / ductility balance, but steel Nos. 3 and 4 5,
And 6 are inferior. Further, it is clear that the wire rods of steel numbers 7 to 9 all have a mixed structure of ferrite and massive martensite, and generally have poor strength / ductility balance.

Reference Example 3 Next, strong working by cold drawing was applied to the 6.4 mm diameter wire rod having the different second phase morphology obtained as described above. The properties after this processing are shown in Table 3.

As described above, the wire having the steel symbol A1 of Steel No. 1 is obtained from the wire having a fine martensite structure as the front structure, and has fine needles in the ferrite as defined in the present invention. It has a composite structure in which the martensite particles are uniformly dispersed. Therefore, as shown in Table 3, according to such a wire rod, the drawing strength is 90% and the tensile strength is 90 kgf / m.
It is possible to obtain a wire rod with a diameter of 2 mm, which has a m ² of 58% and a breaking reduction of 58%.
A wire drawing rate of 99% makes it possible to obtain 0.7 mm diameter wire rod with even higher strength.

On the other hand, the wire having the steel symbol A2 of Steel No. 2 is obtained from a wire having a ferrite / pearlite structure as the front structure, and the second phase in the composite structure is massive, which is defined by the present invention. As described above, according to such a wire rod, as shown in Table 3, ductility deteriorates sharply as the workability increases, since it does not have a composite structure composed of ferrite and acicular martensite. A wire break occurred at a workability of about 90%.

The wire having the steel symbol A1 of Steel No. 3 has a complex structure defined by the present invention, although the final structure after heat treatment is a mixed structure of ferrite and lumpy and acicular martensite, although the preceding structure is composed of fine martensite. It has no organization.
Therefore, according to such a wire rod, since it has a finer structure than the wire rod of the steel symbol A2 of the steel number 2, the strong workability is superior to that of the steel rod of the steel symbol A2 of the steel number 2, However, when compared with the wire having the steel symbol A1 of the steel number 1 defined by the present invention, the property after processing is inferior.

Reference Example 4 Steels B and C having the chemical composition defined in the present invention (first
According to the present invention, a wire having a diameter of 5.5 mm and having a uniform fine composite structure of ferrite and acicular martensite was prepared according to the present invention. Let these be B1 and C1, respectively.

Both B1 and C1 have high ductility, and 99.9% strong working is possible, and the ultrafine steel wire thus obtained also has high strength and ductility. Table 4 shows the mechanical properties of the wire rods B1 and C1 and the mechanical properties of the ultrafine steel wire obtained by drawing these wire rods to a wire diameter of 1.0 mm or less.

In addition, a wire with steel symbol C1 was drawn at a working rate of 97.0% (wire diameter 0.
95mm), this is a low temperature heat treatment at a temperature of 300-400 ℃ (hereinafter,
It may be called low temperature annealing. )did. As shown in Table 4 for the mechanical properties of the low temperature annealed wire, it is clear that the ductility of the wire is improved by the low temperature annealing.
No decrease in strength is observed.

Generally, by low-temperature annealing the wire drawing, the removal of residual stress caused by wire drawing and the increase of the yield point are recognized, but according to the present invention, in the wire drawing produced from the composite structure wire rod, Ductility is also improved. Therefore, by low temperature annealing,
The ductility of the wire can be improved, and the ductility of the wire obtained can be further increased by combining low temperature annealing in the drawing process of the wire.

Example 1 As shown in Table 5, steels with steel symbols A and B having the chemical composition defined in the present invention were hot-rolled into a wire having a diameter of 5.5 mm and then water-cooled, and each structure was mainly composed of martensite. Then, after heating to 820 ℃, cool at a rate of 80 ℃ / sec,
The mixed structure of ferrite and acicular martensite is designated as A1 and B1 for steel symbols A and B, respectively. On the other hand, steel symbol A in which the cooling rate after heating in the above heat treatment is 15 ° C./sec is A2.

As described above, regarding the wire rods A1 and B1 having the composite structure in the range specified by the present invention and the wire rod A2 having the composite structure not in the range specified by the present invention, the second phase volume fraction, the particle diameter and the morphology, and the tensile The characteristics are shown in Table 6.

Wire A2 has a mixed structure of ferrite and second phase,
The second phase is mainly composed of the acicular second phase, but since it is a composite textured wire partly containing the massive second phase, the ferrite and the acicular second phase are included.
The ductility is slightly inferior to the wire rods A1 and B1 having a composite structure composed of phases. B1 has a lower Al content than A1 and has a high ductility.

Next, after pickling the above 5.5 mm diameter wire A1 with a pickling treatment of Cu65% -Zn35%, the mechanical properties of the drawn wire obtained by continuous cold drawing at a total area reduction rate of 98% were measured. It is shown in Table 7. 7th
For comparison, the table also shows the mechanical properties of the drawn wire obtained by continuous cold drawing of the same wire A1 after pickling, normal phosphate coating lubrication.

A wire rod that has been subjected to a normal phosphate coating lubrication treatment as a wire-drawing pretreatment has a small amount of lubricant adhering thereto, resulting in poor lubrication. On the other hand, when the brushing treatment is performed before wire drawing, even if the amount of the powdered lubricant introduced during wire drawing is insufficient, due to the presence of the metallized lubrication on the wire drawing surface,
The adverse effect on wire drawing is avoided. That is, the brassiness before wire drawing improves the lubricity during wire drawing. It is also clear that the ductility is improved.

In addition, it was obtained by pickling 5.5 mm diameter composite textured wire A1 with excellent workability, then subjecting it to ordinary phosphate treatment, and drawing it to a diameter of 0.29 mm (workability 99.7%) without plating treatment. Along with wire drawing (comparative example), a diameter of 1.5 mm in the middle of wire drawing and a tensile strength of 179 kgf / mm ²
Wire drawn to 0.29 mm diameter after brushing on the wire (invention), and wire drawn on 0.29 mm diameter after brushing to 5.5 mm diameter wire after pickling Regarding (the wire drawing of the present invention), the wire drawing characteristics and the adhesion to rubber were evaluated. The results are shown in Table 8. Incidentally, the composition of the brass is Cu64% -Zn36% for the wire A1, and the wire B1
Is Cu64% -Zn36% or Cu55% -Zn45%.
It is clear that the wire drawing according to the present invention is not only excellent in ductility but also remarkably excellent in adhesion to rubber.

Next, the composite texture wire B1 with excellent strong workability is also
It was drawn by brushing on a 5.5 mm diameter wire before drawing. Regarding this wire drawing (invention), Table 8 shows the wire drawing characteristics and the adhesion to rubber. Regardless of the Zn concentration in brass, it is possible to obtain excellent wire drawability and excellent wire drawability. Further, it is clear that the brushed wire material having a high Zn concentration has further excellent adhesion to rubber. As described above, it is one of the important features of the present invention that good wire drawability can be ensured even for a wire rod with high-concentration Zn brushing.

Example 3 (Production of Extra Fine Steel Wire) Steel symbol D having the chemical composition shown in Table 9 was hot rolled into a wire having a diameter of 5.5 mm, and after rolling, water cooling was performed. 810 this rolled wire rod
After heating to 0 ° C., it was oil-cooled to form martensite, and as shown in Table 9, a wire D1 having a mixed structure composed of a second phase composed of acicular martensite and ferrite was manufactured.

This wire material D1 was pickled, brushed with a composition of Cu45% -Zn55%, drawn to a diameter of 0.96 mm, heat-treated at a predetermined temperature, and further drawn to a diameter of 0.30 mm. For comparison, the wire D1 was pickled, brushed, and then drawn to a diameter of 0.30 mm without heat treatment during drawing.

FIG. 3 shows the drawing strain after heat treatment and the tensile strength of the obtained ultrafine steel wire. It is clear that the strength is remarkably increased by drawing the wire after the heat treatment.

[Brief description of drawings]

FIG. 1 shows that steels A and B having the composition specified in the present invention are hot-rolled and then water-cooled to have martensite structure as a pre-structure to be wire rods A1 and B1, which are various austenite fractions. In the case where a composite textured wire is obtained by heating and holding in the Ac ₁ to Ac ₃ region for a predetermined time so as to have a composite textured wire at various average cooling rates, It is a graph which shows the form of a phase particle, and its volume fraction. FIG. 2 shows the steels A and B having the chemical composition defined in the present invention, which were water-cooled after rolling to obtain wire rods having a fine martensite structure as the front structure, respectively, A1 and B1, respectively. After A and B are air-cooled after rolling, wire rods having a ferrite / pearlite structure as the previous structure are A2 and B2, respectively, and these are heated and held in the Ac ₁ to Ac ₃ regions for a predetermined time,
It is a graph which shows the relationship of a 2nd phase volume fraction, a form of a 2nd phase particle, and an average conversion particle size, when it is rapidly cooled and a composite textured wire is obtained. FIG. 3 is a graph showing the relationship between the wire drawing strain, the heat treatment temperature, and the tensile strength of the resulting wire drawing material when the composite texture wire material or the wire drawing material from this is heat treated according to the method of the present invention. FIG. 4 is a graph showing the relationship between the area reduction rate and the amount of lubricant adhered when the conventional high carbon steel wire rod and the composite texture wire rod used in the present invention are dry continuously drawn.

Claims (2)

[Claims] 1. Low-temperature transformation formation comprising 0.01% to 0.30% by weight of C, 2.0% to less than Si, 0.3% to 2.5% of Mn, balance iron and inevitable impurities, and acicular martensite, bainite, or a mixed structure thereof. When continuous cold drawing is performed at a surface reduction rate of 98% or more for a wire rod having a composite structure in which the phase is uniformly dispersed in the ferrite phase at a volume ratio of 15 to 40%, or before this wire drawing. A method for producing an ultrafine steel wire for brushing, characterized in that a brushing layer consisting of Cu 40 to 65% and Zn 35 to 60% inevitable impurities is provided on the way. 2. The method for producing a brass fine extra fine steel wire according to claim 1, wherein the wire contains 0.005% or less of Al.