JPH0526845B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing ultra-fine steel wire, and more specifically, the present invention relates to a method for manufacturing ultra-fine steel wire, and more specifically, by plating a wire rod with a predetermined composite structure and then subjecting it to continuous cold drawing, a wire rod with high strength and high ductility is produced. The present invention relates to a method for manufacturing surface-plated extra-fine steel wire. (Prior art) In the present invention, a surface-plated ultra-fine steel wire refers to an ultra-fine steel wire with a wire diameter of approximately 2 mm or less to several tens of μm and having a plating layer on the surface depending on the purpose and use. It is used as rope wire, bead wire, tire cord wire, high pressure hose wire, etc. Conventionally, these surface-plated ultra-fine steel wires are made from high carbon steel 5.5 mm diameter rolled wire rods with several patenting treatments, as the toughness of the drawn wire material decreases with each wire drawing process.
The wire is manufactured by manufacturing ultra-fine steel wire of a predetermined diameter through several stages of cold wire drawing, and then plating it, which requires a large number of manufacturing steps and is expensive to manufacture. I have no choice but to do so. On the other hand, if we look only at strong cold drawing of wire rods into ultra-fine steel wires, there are pure iron and mild steel wire rods that can be used for this purpose, but since the increase in strength due to wire drawing is small, it is difficult to draw ultra-fine steel wires as final products. Low strength in steel wire. That is, even in the case of 95-99% strong wire drawing, the strength is 70-130Kgf/ ^mm2 , and 170Kg
It is not possible to achieve a strength of f/mm ² or higher. Further, even when wire drawing is performed at a processing rate of 99% or more, the strength is 190 Kgf/mm ² or less. The present inventors have conducted intensive research to obtain a low carbon steel wire rod with excellent strong workability in place of the above-mentioned high carbon steel wire rod and mild steel wire rod. First, the structure of a low carbon steel wire rod for cold wire drawing is made into bainite, martensite, or a fine mixed structure thereof (pre-structure) which may contain residual austenite, and then austenite which is reverse-transformed from this structure is prepared. By transforming under predetermined cooling conditions, the final structure is a fine low-temperature transformation product phase consisting of bainite, martensite, or a mixed structure thereof, which may contain some residual austenite, in the ferrite phase. When formed into a composite structure in which the composite structure is uniformly dispersed in It has been discovered that a high-strength ultra-fine steel wire of 10 μm can be obtained. However, in continuous cold wire drawing of the above wire rods, according to the conventional lubrication treatment using phosphate coating, lubrication for cold working becomes difficult as the degree of working increases, and the working area reduction rate exceeds 90%. When continuous cold wire drawing is carried out, preferably at 98% or more, it is not possible to obtain an ultra-fine steel wire with uniform surface properties due to insufficient lubrication. That is, it has been found that a non-uniform deformed layer is generated on the outermost surface of the drawn wire where the drawn wire and the die come into contact during continuous wire drawing. Such a non-uniform deformation layer grows and expands with each dime, so the stronger the working is, the more the non-uniform deformation layer expands to the extent that it impairs the ductility of wire drawing. In conventional high-carbon steel wire rods, the wire rod itself lacks strong workability, so the patenting treatment is performed midway through the wire rod, which prevents the accumulation and expansion of the above-mentioned non-uniform deformed layer. More specifically, if the lubricity deteriorates during wire drawing, the wire drawing material and die come into metal contact, and the surface of the wire drawing material becomes smooth, making it difficult for powdered lubricant to adhere to the wire drawing material. , the amount introduced into the die decreases. The amount of lubricant adhered to the wire drawing material is an index representing the above-mentioned lubricity, and this amount decreases as the die angle increases and the wire drawing speed increases. Also,
As the number of dice increases, that is, the number of repeated passes increases, the amount of lubricant deposited decreases significantly. FIG. 4 shows changes in the amount of lubricant deposited as the number of wire drawing passes increases for a conventional high carbon steel lead patented (LP) treated wire rod and a wire rod having a composite structure with strong workability as described above. As shown in and, the composite structure wire has a total area reduction of 90
% or more, the number of passes is large, and the amount of lubricant deposited decreases significantly with the number of passes. Therefore, cold wire drawing with poor lubricity cannot be avoided. As a result, the ductility of the drawn wire material deteriorates. (Purpose of the Invention) Therefore, as a result of further research into a method for producing ultra-fine steel wire from the above-mentioned composite-structured wire having strong workability, the present inventors found that continuous cold drawing of the above-mentioned composite-structured wire By performing plating treatment before or during processing and utilizing the lubrication effect, surface-plated ultrafine steel wire with high strength and high ductility can be produced immediately without the need for heat treatment such as patenting treatment during wire drawing. I found that it is possible to obtain From another aspect, conventionally, in order to manufacture a surface-plated ultra-fine steel wire, plating is applied during the wire drawing process or after the wire is drawn, but according to the present invention, By plating before the wire drawing process or by plating during the wire drawing process, the area reduction rate is 90% or more, and in a preferred embodiment 98% due to the lubricating effect of the plating. With the above, continuous wire drawing can be easily performed, and
Surface-plated ultra-fine steel wire can be obtained without the need for patenting treatment or the like. Moreover,
The surface-plated extra-fine steel wire obtained by this method not only has excellent ductility and strength, but also has a very highly homogeneous plating layer. Therefore, an object of the present invention is to provide a method for producing an ultra-fine steel wire that is highly ductile and has high strength and has a homogenized plating layer. (Structure of the Invention) The first method for producing an ultra-fine steel wire according to the present invention consists of 0.01 to 0.30% C, 2.0% or less Si, 0.3 to 2.5% Mn, the balance being iron and inevitable impurities, and having an acicular shape. A wire rod with a composite structure in which a low-temperature transformation phase mainly consisting of martensite, bainite, or a mixed structure of these is uniformly dispersed in a ferrite phase at a volume ratio of 10 to 55%, with an area reduction ratio of 90% or more. The method of producing ultra-fine steel wire by continuous cold drawing is characterized in that plating is performed before or during the wire drawing. Moreover, the second method of manufacturing ultra-fine steel wire according to the present invention
is characterized by plating the above-mentioned composite textured wire material before or during the drawing process, and during the drawing process, performing a low-temperature treatment of heating to a temperature below the recrystallization temperature of the wire drawing and cooling it. do. First, the chemical components of the composite wire used in the method of the present invention and its production will be explained.
In addition, in the following, the tissue is acicular (elongated or
Acicular means that the tissue particles have directionality, and globular means that the particles do not have directionality. Further, the equivalent particle diameter of the acicular particles means the diameter when the area of the acicular particles is converted into a circle. It is necessary to add C in an amount of 0.01% or more in order to make a hot-rolled wire rod from a steel billet into a wire rod having a predetermined composite structure through the predetermined heat treatment described below, but it is necessary to add C in an amount exceeding 0.30%. When adding too much,
The ductility of the low-temperature transformation-generated phase (hereinafter sometimes simply referred to as the second phase) consisting of acicular martensite, bainite, or a mixed structure thereof begins to deteriorate. Therefore, in the present invention, the amount of C added is
It should be in the range of 0.01-0.30%. Si is effective as a reinforcing element for the ferrite phase, but when added in excess of 2.0%, it significantly shifts the transformation temperature to a higher temperature side and also makes it easier to decarburize the surface of the wire. The amount is 2.0
The upper limit is % or more. Mn strengthens the wire, increases the hardenability of the second phase, and makes the shape acicular.
It is necessary to add 0.3% or more, but 2.5%
Even if Mn is added in a large amount exceeding this amount, the effect will be saturated, so the amount of Mn added is set at 0.3 to 2.5%. In the present invention, in order to refine the metal structure of the wire, at least one element selected from Nb, V, and Ti may be further added. In order to refine this structure, it is necessary to add 0.005% or more of each element.
If added in excess, the effect will be saturated and it will also be economically disadvantageous, so the upper limit is set at 0.2% for Nb and 0.3% for each of V and Ti. Furthermore, elements that are inevitably included in the wire rod in the present invention or elements that may be included will be explained. S is used to reduce the amount of MnS in the wire.
The content is preferably 0.005% or less, which improves the ductility of the wire. In addition, in order to prevent ductility deterioration due to hydrogen during pickling and plating, 0.003%
The following is preferable. Since P is an element that is significantly segregated at grain boundaries, it is preferable that its content be 0.01% or less. When N exists in a solid solution state, it is the element that is most easily aged. Therefore, the 0.003
% or less. Al forms oxide-based inclusions, and since these oxide-based inclusions are difficult to deform, they may impede the workability of the wire, and breakage may occur starting from these inclusions during wire drawing. Easy to occur. Therefore, the Al content is usually preferably 0.01% or less. In particular, it is preferably 0.005% or less. In addition, when the Si/Al ratio in the wire increases, the number of silicate inclusions increases, and especially when the amount of Al is small, the number of silicate inclusions increases rapidly, which not only deteriorates the drawability of the wire but also , the fatigue properties of the drawn wire material obtained by wire drawing deteriorate. Therefore, in the present invention, preferably Si/
The Al ratio should be 500 or less. Furthermore, according to the present invention,
It is preferable that the Si/Mn ratio is 0.7 or less. Si/
This is because when the Mn ratio exceeds 0.7, the composition, morphology, etc. of inclusions change, and the dispersion and distribution of inclusions may cause deterioration in the drawability of the wire. On the other hand, it is also preferable to adjust the shape of the MnS inclusions by adding rare earth elements such as Ca and Ce. Further, solid solution C and N can also be fixed by adding Al, etc., including the above-mentioned Nb, V, and Ti. Furthermore, depending on the use of the ultra-fine wire according to the present invention, the wire used may contain 1.0% or less of each of Cr, Cu and/or Mo, 6% or less of Ni, 0.1% or less of each of Al and/or P, and 0.02% or less of B. % or less can also be added as appropriate. The method of the present invention produces a composite wire rod having the above-mentioned chemical components and in which a low-temperature transformation phase mainly composed of acicular martensite, bainite, or a mixed structure thereof is uniformly dispersed in a ferrite phase. When cold drawing with a total area reduction of 90% or more,
A plated extra-fine steel wire with improved ductility is produced by performing a plating treatment before or during wire drawing and then drawing the wire. Here, in the present invention, the low-temperature transformation-generated phase mainly consisting of acicular martensite, bainite, or a mixed structure thereof refers to a structure in which the acicular structure accounts for about 80% or more in the second phase; The second phase structure may be included. However, a wire having a composite structure consisting only of ferrite and a massive second phase structure is not a composite structure wire according to the present invention. The composite tissue wire used in the method of the present invention is
The hot-rolled wire rod having the above-mentioned predetermined chemical components is austenitized under predetermined conditions to have a predetermined pre-structure, and then this wire is further heat-treated to have a predetermined composite structure. You can get it by twisting it. That is, after subjecting a steel billet having the above-mentioned chemical composition to the required hot working and heat treatment to change its structure to bainite, martensite, or a mixed structure thereof with a prior austenite grain size of 35μ or less, this is
The wire rod thus obtained is heated to a temperature range of Ac ₁ to _{Ac 3} to advance austenitization such that the austenitization fraction becomes about 10% or more, and then the wire rod thus obtained is preferably cooled at an average cooling rate of 10 to 200°C. By cooling from room temperature to 500° C. at a rate of 100° C./sec, a composite wire rod with excellent strong workability for use in the present invention is produced. The method of the present invention relates to a method of cold drawing such a composite textured wire at a total area reduction of 90% or more to obtain an ultra-fine steel wire. First, in order to make the second phase in the wire mainly consist of a fine acicular structure, the hot-rolled wire having the predetermined chemical composition is heated under predetermined conditions before being heated to a temperature range of Ac ₁ to _{Ac 3} . By applying heat treatment,
The structure may be a bainite, martensite, or a fine mixed structure thereof (hereinafter, these may be simply referred to as a previous structure) with a prior austenite grain size of 35μ or less, preferably 20μ or less, which may contain some residual austenite. ). By refining the previous structure in this way, the final structure is refined and the ductility and toughness of the composite structure wire are improved.
In this way, the required strength can be imparted. In order to adjust the prior austenite grain size to 35μ or less, when hot working the steel slab obtained by ingot formation or continuous casting, the temperature range where austenite recrystallization and grain growth progress is extremely slow, i.e. 980°C. It is necessary to perform hot working with an area reduction rate of 30% or more in a temperature range of ₃ or more Ar points. When the hot working temperature exceeds 980℃, austenite tends to recrystallize and grow grains, and when the working area reduction rate is less than 30%, it is difficult to refine the austenite grain size. Because you can't. Furthermore, in order to obtain fine austenite grains of about 10 to 20μ, in addition to the above processing conditions,
The final processing pass must be below 900℃, and
In order to obtain ultrafine grains of about 10 μm, it is necessary to perform the final processing at a strain rate of 300/sec or higher. Note that a desired shape can be obtained by adding cold working after the above hot working to adjust the prior austenite grain size, but in this case, the processing rate of cold working is up to 40%. When cold working greater than 40% is applied to the above-mentioned previous structure, Ac ₁ to _{Ac 3} described later
Recrystallization of martensite occurs during heating to a temperature range, making it impossible to obtain the desired final structure. Next, in order to make the previous structure a bainite, martensite, or a mixed structure thereof, the following method can be used. The first method is to obtain the required pre-structure during the rolling process, by subjecting the billet to controlled rolling or hot rolling followed by accelerated cooling. Its cooling rate is 5
It is necessary to set the temperature to ℃/second or higher. This is because if the cooling rate is lower than this, a normal ferrite/pearlite structure will be formed. The second method for obtaining a pre-structure is to heat-treat the rolled steel material again, in which the steel is heated to an austenite region of Ac ₃ or higher and then adjusted and cooled. Also in the case of this method, the heating temperature is Ac ₃ - Ac ₃ +100, as described for the first method.
It is desirable that the temperature is in the range of ℃. In this way, the tissue before being heated to the Ac ₁ to _{Ac 3} range,
By heating a rolled steel material with a low-temperature transformation phase consisting of martensite, bainite, or a mixed structure thereof, which may contain residual austenite, instead of the conventional ferrite/pearlite structure, to the Ac ₁ to Ac ₃ range. , a large number of initial austenite grains are generated with retained austenite or cementite present at the lath boundaries of the low-temperature transformation phase forming preferential nuclei, and grow along the lath boundaries. This martensite or bainite transformed from austenite is then made into needles by cooling under certain conditions, making it more consistent with the surrounding ferrite phase, thus forming a conventional ferrite-pearlite structure. The second phase particles are made much finer compared to the previous method. Therefore, heating and cooling conditions in the Ac ₁ to Ac ₃ range are required. That is, depending on the conditions, the second phase becomes agglomerated or contains agglomerated particles in the second phase. Ac ₁ ~ _{Ac 3}
The cooling rate after heating to the area is usually 10 to 200℃/
A range of seconds is appropriate. To explain in more detail, the reverse transformation when heating a prestructure consisting of fine bainite, martensite, or a mixture thereof to an austenite region is as follows.
Until the austenite fraction reaches approximately 20%, massive austenite is generated from the prior austenite grain boundaries, and acicular austenite is generated from within the grains. From this state, for example,
By rapidly cooling at a cooling rate of 150 to 200° C./second or more, a structure in which needle-like and lump-like low-temperature transformation product phases are dispersed in ferrite is obtained. Therefore, the finer the prior austenite, the higher the frequency of formation of massive austenite. When austenitization progresses by about 40% or more, the acicular austenite particles coalesce with each other and change to massive austenite. When this state is rapidly cooled, a mixed structure of ferrite and a coarse, massive, low-temperature transformation product phase is formed. . Furthermore, if the austenitization progresses to about 90% or more, the massive austenite will coalesce and grow and the austenitization will be completed, so if the austenitization is rapidly cooled from this state, the structure will be mainly composed of the phase formed by low-temperature transformation. However, in the present invention, when the steel adjusted to the pre-structure is heated to the Ac ₁ to Ac ₃ range, the austenitization is performed until the austenitization fraction is approximately 10.
% or more, preferably 20% or more, and by cooling from this state preferably at an average cooling rate of 10 to 150°C/sec to a temperature of room temperature to 500°C,
In the transformation process during cooling, ferrite and acicular austenite are separated from massive austenite, and this acicular austenite is transformed into a low-temperature transformation phase, thereby producing acicular bainite and marten, which may contain some residual austenite. A final metal structure is obtained in which a fine phase formed by low-temperature transformation consisting of sites or a mixed structure thereof is uniformly dispersed in the ferrite phase. In the present invention, the volume fraction of the second phase in the ferrite phase is in the range of 10 to 55%. When the volume fraction of the second phase is within this range, the second phase particles are mainly acicular and excellent cold drawability can be ensured.
When the content is in the range of 15 to 40%, substantially all of the second phase particles become acicular and have an average equivalent particle diameter of 3μ or less, and thus the obtained wire rod is
Because it has a unique composite structure that has never been seen before, it has exceptionally strong workability. When the volume fraction of the second phase is out of the range of 10 to 55%, the final structure will mainly consist of the massive second phase even by cooling under the above conditions. The cooling stop temperature is between room temperature and 500°C. this is,
The purpose is to obtain bainite, martensite, or a mixed structure thereof as a low-temperature transformation generation phase, and also to temper the generated second phase by slowing down or stopping the cooling rate within this temperature range. This is because it is possible. As mentioned above, the wire used in the present invention is
The structure of low carbon steel is made into bainite, martensite, or a fine mixed structure of these in advance, and the massive austenite that is reversely transformed from this is transformed under predetermined cooling conditions to produce mainly acicular low-temperature transformation phases.
It is uniformly dispersed in a ferrite phase at a volume fraction of 10 to 55%, and has a unique fine composite structure never seen before. According to the method of the present invention, after plating the wire before or during wire drawing, the plating layer is removed by continuous cold drawing at a processing rate of 90% or more, and in a preferred embodiment, 98% or more. It is possible to obtain a matted extra-fine steel wire with good lubricity and high strength and high ductility. In particular, the volume fraction of low-temperature transformation products is 15-40
As a percentage, when the average equivalent particle diameter is 3 μ or less,
By cold drawing with a processing rate of 98% or more, it is possible to obtain ultra-fine steel wire with unprecedented high strength and high ductility. In the method of the present invention, the plating treatment refers to attaching a highly extensible plating layer to the wire by electrical plating, chemical plating, melt plating, or the like. The plating composition is not particularly limited, and examples include Cu, Cu alloy, Al, and Al alloy. It is also possible to form the plating deposit into a single layer or multiple layers and then homogenize it. In the present invention, in the case of brass plating, the composition is in the range of 40 to 70% Cu and 60 to 30% Zn. In the conventional method of producing surface-plated ultrafine steel wire by plating the wire rod after drawing, the brass plating composition is usually 60 to 70% Cu,
The Zn content is 40 to 30%, and it is said that increasing the amount of Zn higher than this causes the quality of the plated extra-fine steel wire to deteriorate because the plated layer has poor extensibility. However, according to the method of the present invention, even if the amount of Zn is increased to a range of 40 to 65% Cu and 60 to 35% Zn,
By using this plating layer as a lubricant during intense processing, the plating layer exerts a good lubricating effect during drawing of the wire rod, although the reason is not necessarily clear. Not only is it possible to prevent the formation of a single layer and ensure excellent continuous cold drawability, but unexpectedly, the ductility of the resulting wire is improved, and the surface has a uniform plating layer. This makes it possible to obtain extra-fine steel wire. In particular, Cu and Cu alloy-plated ultra-fine steel wires, especially the surface-brass-plated ultra-fine steel wire of the present invention with an increased amount of Zn, have remarkable adhesion to rubber compared to conventional surface-plated ultra-fine steel wires. Improved. In the present invention, the amount of plating deposited is necessary to obtain a uniform plating thickness even after heavy working, and is preferably about 1 to 15 g per 1 kg of wire, although it depends on the diameter of the ultra-fine steel wire. In particular, in heavy processing of 98% or more, the properties of the plating layer itself can be improved, such as by keeping the plating layer within a range of 0.2 to 1.0% by weight relative to the ultimately obtained ultra-fine steel wire. Uniformity and homogeneity can be extremely improved. In the present invention, when drawing the wire rod after plating, it is preferable that the approach angle of the die for wire drawing is 4 to 15 degrees, and the total processing degree after plating is about 80%. 120Kg as strength
In the first half of wire drawing below f/mm ² , the approach angle is preferably 4 to 8 degrees. This method facilitates uniform processing of the plating layer and prevents non-uniformity of the plating layer. Further, according to the method of the present invention, when producing an ultra-fine steel wire by continuously cold drawing the above-mentioned composite textured wire at a total area reduction rate of 90% or more, the temperature is lower than the recrystallization temperature during the drawing. By performing a heat treatment of heating to a temperature of I can do it. In the method of the present invention, when melt plating is used in the plating process, the plating composition may be adjusted to have a desired melting point, and the heat treatment may be performed at the same time. That is, as a heating bath and/or cooling bath in the heat treatment step,
You can use the bath. In the method of the present invention, the heat treatment refers to two types of ferrite and martensite that are elongated in the processing direction.
It means heating at a temperature and time that does not destroy the structure flow formed by the phase, and the heating temperature is usually in the range of 200 to 700 °C, preferably 300 to 600 °C, although it depends on the heating time. ℃ range. Generally, when a wire is drawn, each phase in the structure is elongated in the processing direction, forming a so-called structure flow, and microscopically, a substructure is generated within each phase due to dislocations, etc. Along with these changes, the strength of the drawn wire material increases. According to the method of the present invention, by heating to an extent that does not destroy this structure flow during wire drawing, the underlying structure is partially recovered, and fine precipitation of elements such as C and N is caused in each phase. It happens within. Therefore, when the wire drawing material subjected to such heat treatment is further subjected to cold wire drawing, a new substructure is formed and developed with the above-mentioned precipitates existing in the substructure as a nucleus, while the structure flow is Following the wire drawing process, it develops in each wire drawing process, and as a result, it is thought that the processing limit of the wire rod is improved and the strength of the wire rod is also increased. Therefore, in order to form and develop the tissue flow and underlying structure by wire drawing before heat treatment,
The minimum degree of wire drawing is specified, and in the wire drawing after heat treatment, the minimum degree of wire drawing is specified in order to form and develop a new underlying structure. According to the inventors' research, the above-mentioned minimum processing degrees are approximately 50 to 80.
It is about %. In addition, the strength after heat treatment and the work hardening rate due to subsequent processing change depending on the degree of recovery of the underlying structure during heat treatment and the precipitation state of elements such as C and N. The time is preferably set optimally depending on the purpose. Conventionally, drawn wire that has been processed to near the processing limit is heated above the recrystallization temperature to eliminate the processed structure.
A method is known in which the material is returned to its pre-processing state and processed 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 a temperature below the recrystallization temperature, so it is different from the conventional annealing treatment. In the method of the present invention, when the heat treatment temperature is higher than the recrystallization temperature, the strength after the heat treatment decreases, and even if cold working is performed again after that, the strength does not improve and the strength is simply worked. It just becomes possible. (Effects of the Invention) According to the method of the present invention, when a wire rod having a predetermined composite structure is cold-strengthened to produce an extra-fine steel wire, plating treatment is performed before or during wire drawing, and the plating layer is Due to the lubrication effect, the wire can be cold drawn while ensuring good cold drawability.
Moreover, in this way, an ultra-fine steel wire having a uniform plating layer and improved ductility can be obtained. Furthermore, by performing heat treatment to heat and cool the wire to a temperature equal to or lower than the recrystallization temperature during the wire drawing process, the strength of the ultimately obtained ultra-fine steel wire can be improved. (Examples) The present invention will be described below with reference to Examples and Reference Examples, but the present invention is not limited to these Examples in any way. Reference Example 1 (Manufacture and Properties of Composite Structure Wire Rod) As shown in Tables 1 and 2, steels A and B having the chemical composition specified in the present invention were water-cooled after rolling to transform the previous structure into fine marten. The site structures are designated as A1 and B1 respectively, and as comparison steels,
Steels A and B are air-cooled after rolling to change the previous structure to a ferrite/pearlite structure, and these are referred to as A2 and B2, respectively. Both prior austenite grain sizes are
It is less than 20μ.

【table】

[Table] 20μ or less. Next, the above-mentioned A1 and B1 were heated and held in the Ac ₁ to Ac ₃ region for 3 minutes so as to have different austenite fractions, and cooled to room temperature at various average cooling rates. FIG. 1 shows the morphology of second phase particles and their volume fractions with respect to heating temperature and cooling rate. The solid line indicates a uniform mixed structure of ferrite and acicular second phase,
The broken line indicates a mixed structure of ferrite and a massive second phase, or a mixed structure of ferrite and an acicular or massive second phase. After heating and holding A1 and B1 to the Ac ₁ to Ac ₃ region, when 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 acicular,
The structure is formed by uniformly dispersing this second phase in the ferrite phase, and the volume fraction of the second phase is almost constant regardless of the heating temperature. On the other hand, even if the previous structure is the same, when the average cooling rate is 170°C/sec or more, the second phase morphology is lumpy,
Alternatively, it becomes a mixture of lumps and needles, and the second phase fraction increases as the heating temperature increases. Figure 2 shows the relationship between the volume fraction of the second phase contained in the final structure, the morphology of the second phase particles, and the average converted particle diameter for A1 and B1 of the pre-martensitic structure, and A2 and B2 of the pre-ferrite/pearlite structure. Each is shown below. Here, the average converted particle diameter means the average diameter when the area is converted into a circle as described above for any form. For any wire rod, the particle diameter of the second phase particles increases as the second phase volume fraction increases, but when the second phase fraction is the same, particles obtained from a pre-martensitic structure The particle size is significantly smaller than that of particles obtained from the ferrite-pearlite pre-structure. That is, even if steels have the same composition, the second phase particles can be made much finer by adjusting the previous structure from ferrite/pearlite to martensitic structure. This second
Although the ductility of the wire rod is greatly improved by making the phase particles finer, it does not necessarily improve the strong workability. That is, the volume fraction of the second phase is 10 to 55%.
By setting the volume fraction of the second phase to a range of 15 to 45, the shape of the second phase becomes mainly acicular.
% range, the second phase has an average equivalent particle diameter
It is composed of fine acicular particles of 3 μm or less in size, and furthermore, since such a fine acicular second phase is uniformly dispersed 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 acicular bainite and martensite. Next, the rolled wire rods A1 and A2 having fine martensite as a pre-structure were heat treated under the conditions shown in Table 3. Table 2 shows the heating and cooling conditions in this heat treatment, the final structure and mechanical properties of the composite wire rod obtained thereby. Ac ₁ to Ac ₃ so that the austenitization fraction of A1, which has a fine martensite structure, is 20% or more.
Steel No. 3, 4, 5, and 6 wire rods obtained by heating to a temperature of It is clear that it has a composite structure that is uniformly mixed and dispersed within the range of ~40%, and has an extremely excellent balance of strength and ductility. On the other hand, rolled wire rod A2 whose prestructure is ferrite/pearlite is a steel number whose second phase is blocky regardless of heating and cooling conditions.
10, 11 or 12, all of which are inferior in strength and ductility balance. On the other hand, although the previous structure is martensite (A1), Steel No. 1 has a slow cooling rate after heating in the Ac ₁ to Ac ₃ region, and Steel No. 2 has a martensitic structure in the Ac ₁ to Ac 3 region.
Because the austenitization fraction when heated to the Ac ₃ region is small, the structure is a mixed structure of ferrite and massive and acicular martensite,
Therefore, it has a better balance of strength and ductility than the above-mentioned steel numbers 10 to 12, but steel numbers 3, 4, 5, and 6
inferior to. In addition, the wire rods of steel numbers 7 and 8 are
Both have a mixed structure of ferrite and massive martensite, and are clearly inferior in strength and ductility balance. Next, the 6.4 mm diameter wire rods having different second phase configurations obtained as described above were subjected to severe working by cold wire drawing. Properties after this processing are shown in Table 3.

[Table] (b) Wire broke during wire drawing.
Steel No. 1 wire rod has a composite structure in which fine acicular martensite is uniformly dispersed in ferrite (A1), and according to this wire rod, the wire drawing rate is 90.
%, a 2 mm diameter wire with a tensile strength of 90 Kgf/mm ² and a breaking area of 58% can be obtained, and a 0.7 mm diameter wire with even higher strength can be obtained with a wire drawing rate of 99%. On the other hand, according to the comparison steel wire of Steel No. 2 having a lumpy second phase, the ductility deteriorated rapidly as the working degree increased, and wire breakage occurred at about 90% working degree. The wire rod of the present invention, Steel No. 3, has a second phase of a mixture of acicular and lumpy martensite, and has a finer structure than the comparative steel wire rod of Steel No. 2, so it maintains strong workability of 90% or more. are doing. Further, as shown in Table 1, steels B and C having the chemical composition specified by the present invention were made into wire rods with a wire diameter of 5.5 mm having a uniform fine composite structure of ferrite and acicular martensite according to the present invention. did. Let these be B1 and C1, respectively. Both B1 and C1 have high ductility and can be subjected to strong processing of 99.9%, and the ultra-fine steel wire thus obtained also has high strength and high ductility. Table 4 shows the mechanical properties of the wires B1 and C1 and the mechanical properties of the ultra-fine steel wire obtained by drawing these wires to a wire diameter of 1.0 mm or less. In addition, a wire rod with steel code C1 was drawn at a processing rate of 97.0% (wire diameter 0.95 mm), and this was subjected to low-temperature heat treatment (hereinafter sometimes referred to as low-temperature annealing) at a temperature of 300 to 400°C.
As the mechanical properties of these low-temperature annealed wire drawings are shown in Table 4, it is clear that the ductility of the wire drawing is improved by low-temperature annealing. No decrease in strength was observed. Generally, by annealing the drawn wire at a low temperature, it is recognized that the residual stress caused by the wire drawing process is removed and the yield point is increased, but the drawn wire manufactured from the composite textured wire according to the present invention also improves ductility. be done. Therefore, the ductility of the wire can be improved by low-temperature annealing, and the ductility of the resulting wire can be further increased by combining low-temperature annealing during the wire drawing process. Example 1

[Table] Steel codes A and B shown in Table 5 were hot-rolled into 5.5 mm diameter wire rods, water-cooled to make each structure mainly martensite, then heated to 820°C, heated to 80°C.
It is cooled at a rate of ℃/second to form a mixed structure of ferrite and acicular martensite, which is designated by steel code A.
and B are respectively A2 and B2. On the other hand, the steel symbol A in which the cooling rate after the heat treatment was 15° C./sec is designated as A1. Table 6 shows the second phase volume fraction, particle size and morphology, and tensile properties of the composite structure wires A1, A2, and B2 after such heat treatment. Wire A1 is a composite wire rod mainly composed of acicular second phase and partially containing lumpy second phase, so the wire rod
Slightly inferior ductility compared to A2 and B2. B2 is
It has a lower Al content and higher ductility than A2. Next, pickle the 5.5 mm diameter wire rods A1 and A2,
Table 7 shows the mechanical properties of wire drawn by continuous cold drawing at a total area reduction of 97% after brush plating with Cu or 65% Cu-35% Zn. Table 7 shows the same wire rods A1 and A for comparison.

【table】

[Table] (Note) (a) Same as Table 2.

【table】

【table】

[Table] The mechanical properties of the drawn wire obtained by pickling No. 2, subjecting it to the usual phosphate coating and lubrication treatment, and then subjecting it to continuous cold drawing are also shown. Wire rods that have been lubricated with a normal phosphate coating before wire drawing are A1 and A2.
Both had a small amount of adhesion, causing poor lubrication. On the other hand, if the brush plating treatment is applied before wire drawing, as seen in the drawing of wire rod A1, even if the amount of powdered lubricant introduced during wire drawing is insufficient, Due to the presence of plating lubrication on the wire surface,
Adverse effects on wire drawing are avoided. That is, according to the present invention, the brush plating before wire drawing improves the lubricity during wire drawing. Furthermore, it is clear that the ductility is improved by drawing the wire rod A2. In addition, after pickling the 5.5 mm diameter composite wire A2, which has excellent strong workability, we applied the usual phosphate treatment.
Along with the wire drawing (comparative example) obtained by drawing wire to a diameter of 0.29 mm (processing rate 99.7%) without plating treatment,
A drawn wire of 1.5 mm diameter and a tensile strength of 179 Kgf/mm ² was brush plated and then drawn to a diameter of 0.29 mm (the present invention), and a 5.5 mm diameter wire was pickled and then brush plated to 0.29 mm diameter. The wire drawn to a diameter of mm (wire drawing of the present invention) was evaluated for wire drawing characteristics and adhesion to rubber. The results are shown in Table 8. The composition of the above brass plating is Cu64% for wire A2.
Zn36%, and Cu64%−Zn36 for wire B2
% or Cu55%-Zn45%. It is clear that the wire drawn according to the present invention not only has excellent ductility but also extremely good adhesion to rubber. Next, we also have composite structure wire B2, which has excellent strong workability.
Similarly, the 5.5 mm diameter wire material before wire drawing was brushed and drawn. Table 8 also shows the wire drawing properties and adhesion to rubber for this wire drawing (invention). Regardless of the Zn concentration in the brass plating, excellent wire drawability can be obtained in all cases, and the wire drawing properties are excellent. Furthermore, it is clear that wire rods that have been subjected to brass plating with a high Zn concentration have even better adhesion to rubber. As described above, one of the important features of the present invention is that good wire drawability can be ensured even when the wire is brushed with high concentration Zn.

[Table] Example 3 (Manufacture of ultra-fine steel wire) Steel code A having the chemical composition shown in Table 9 was 5.5
It was hot rolled into a wire rod with a diameter of mm, and after rolling, it was water-cooled. This rolled wire rod is heated to 810°C and then cooled with oil to turn it into martensite, producing wire rod A having a mixed structure consisting of a second phase of acicular martensite and ferrite, as shown in Table 9. did. The above wire A was pickled, brushed with a composition of 45% Cu-55% Zn, drawn to a diameter of 0.96 mm, heat-treated at a predetermined temperature, and then further drawn to a diameter of 0.30 mm.
The wire was drawn to the diameter. For comparison, the wire A was pickled and brushed, and then drawn to a diameter of 0.30 mm without any heat treatment during drawing. Figure 3 shows the drawing strain after heat treatment and the tensile strength of the obtained ultra-fine steel wire. It is clear that the strength is significantly increased by wire drawing after heat treatment.

[Brief explanation of the drawing]

Figure 1 shows steel having the composition specified in the present invention.
Figure 2 is a graph showing the relationship between the morphology of the low-temperature transformation product phase and its volume fraction in the ferrite phase with respect to the heating temperature and average cooling rate when heating to the Ac ₁ to Ac ₃ region and cooling. The relationship between the volume fraction of the second phase, the morphology of the second phase, and the average equivalent particle diameter of the particles is shown for the comparison steel wire rod having a ferrite-pearlite structure and the steel wire rod of the present invention having a ferrite-martensitic structure. The graph shown in FIG. 3 is a graph showing the relationship between wire drawing strain, heat treatment temperature, and tensile strength of the obtained wire drawn material when a composite wire rod or a wire drawn material to be obtained 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 deposited when a conventional high-carbon steel wire rod and a composite texture wire rod used in the present invention are subjected to continuous dry drawing.

Claims (1)

[Claims] 1% by weight: C 0.01~0.30%, Si 2.0% or less, Mn 0.3~2.5%, balance iron and unavoidable impurities, mainly composed of acicular martensite, bainite, or a mixed structure thereof. An ultra-fine steel wire is produced by continuous cold drawing of a wire having a composite structure in which a low-temperature transformation phase is uniformly dispersed in a ferrite phase at a volume fraction of 10 to 55% at an area reduction rate of 90% or more. A method for producing an ultra-fine steel wire, characterized in that plating is applied before or during the wire drawing. 2. The method for producing an ultra-fine steel wire according to claim 1, wherein the wire contains 0.005% or less of Al. 3. Contains low-temperature transformation products at a volume fraction of 15 to 40%,
2. The method for producing an ultra-fine steel wire according to claim 1, wherein the wire rod in which the low-temperature transformation product is in the form of needles is subjected to continuous cold drawing at an area reduction rate of 98% or more. 4% by weight: C 0.01~0.30%, Si 2.0% or less, Mn 0.3~2.5%, the balance iron and unavoidable impurities, and the low-temperature transformation phase mainly consists of acicular martensite, bainite, or a mixed structure of these. In a method for producing an ultra-fine steel wire by cold continuous drawing of a wire having a composite structure uniformly dispersed in a ferrite phase at a volume fraction of 10 to 55% at an area reduction ratio of 90% or more, A method for producing an ultra-fine steel wire, which comprises plating before or during wire drawing, and performing low-temperature heat treatment during wire drawing in which the wire is heated to a temperature below the recrystallization temperature of wire drawing and then cooled. 5. The method for producing an ultra-fine steel wire according to claim 4, wherein the wire contains 0.005% or less of Al. 6. Contains low-temperature transformation products at a volume fraction of 15 to 40%,
5. The method for producing an ultra-fine steel wire according to claim 4, wherein the wire rod in which the low-temperature transformation product is acicular is subjected to continuous cold drawing at an area reduction rate of 98% or more.