HIGH CARBON STEEL WIRE MATERIAL HAVING EXCELLENT WIRE DRAWABILITY AND MANUFACTURING PROCESS THEREOF

Information

  • Patent Application
  • 20090223610
  • Publication Number
    20090223610
  • Date Filed
    May 15, 2009
    15 years ago
  • Date Published
    September 10, 2009
    15 years ago
Abstract
A high carbon steel wire material which is made of high carbon steel as a raw material for wire products such as steel cords, bead wires, PC steel wires and spring steel, allows for these wire products to be manufactured efficiently at a high wire drawing rate and has excellent wire drawability and a manufacturing process thereof.
Description
BACKGROUND OF THE INVENTION

1. Field of the Invention


The present invention relates to a carbon steel wire material which is made of high carbon steel as a raw material for wire products such as steel cords, bead wires, PC steel wires and spring steel, allows for these wire products to be manufactured efficiently at a high wire drawing rate and has excellent wire drawability.


2. Description of Related Art


To manufacture the above wire products, wire drawing is carried out on a steel wire material as a raw material for the control of size and material (mechanical properties) in most cases. Therefore, the improvement of the wire drawability of a steel wire material is extremely useful for the enhancement of productivity and the like. When wire drawability is improved, many advantages such as the improvement of productivity by an increase in wire drawing rate and a reduction in the number of passes for wire drawing and also the extension of the service life of a die can be enjoyed.


As for wire drawing, researches have been mainly focused on wire breakage resistance at the time of wire drawing. For example, patent document 1 discloses technology for improving wire breakage resistance by optimizing the size of a pearlite block, the amount of proeutectoid cementite, the thickness of cementite and the Cr content of cementite, paying attention to these.


Patent document 2 reveals that the wire drawing limit is improved by controlling the area ratio of upper bainite and the size of bainite contained. Further, patent document 3 discloses technology for improving where breakage resistance and the service life of a die by controlling the total amount of oxygen contained in steel and the composition of a non-viscous inclusion. As for the service life of a die, the descalability of the surface of a steel wire material is also important. If scale remains on the surface of a steel wire material due to poor descalability, it causes the chipping of the die at the time of wire drawing. Therefore, patent document 4 discloses technology for improving mechanical descalability by controlling pores existent in scale.


However, the above prior arts place main emphasis on the improvement of wire breakage resistance under specific wire drawing conditions and rarely pay attention to the improvement of wire drawing rate, the reduction of the number of passes for wire drawing and the extension of the service life of a die from the viewpoint of wire drawability. As previously disclosed, increases in wire drawing rate and the area reduction rate per pass lead to the deterioration of the ductility of wire products and the shortage of the service life of the die. However, the effect of improving wire drawability to such an extent that increases in wire drawing rate and area reduction rate can be achieved at practical levels is not obtained yet from the above prior arts.


Patent document 1 JP-A2004-91912 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)


Patent document 2 JP-A 8-295930


Patent document 3 JP-A 62-130258


Patent document 4 Japanese Patent No. 3544804


SUMMARY OF THE INVENTION

It is an object of the present invention which has been made in the view of the above situation to provide a steel wire material having excellent wire drawability which makes it possible to increase the wire drawing rate and the area reduction rate and extend the service life of a die, attaching great importance to productivity, and a process capable of manufacturing the steel wire material efficiently.


As for the constitution of the high carbon steel wire material having excellent wire drawability of the present invention which can attain the above object, the high carbon steel wire material contains 0.6 to 1.1% by mass of C, 0.1 to 2.0% by mass of Si, 0.1 to 1.0% by mass of Mn, 0.020% or less by mass of P, 0.020% or less by mass of S, 0.006% or less by mass of N, 0.03% or less by mass of Al and 0.0030% or less by mass of 0, the balance consisting of Fe and unavoidable impurities, the Bcc-Fe crystal grains of its metal structure having an average crystal grain diameter (Dave) of 20 μm or less and a maximum crystal grain diameter (Dmax) of 120 μm or less.


As a preferred mode of the above steel material according to the present invention, the bcc-Fe crystal grains of the above metal structure have an area ratio of crystal grains having a diameter of 80 μm or more of 40% or less, an average sub grain diameter (dave) of 10 μm or less, a maximum sub grain diameter (dmax) of 50 μm or less, and a (Dave/dave) ratio of the average crystal grain diameter (Dave) to the average sub grain diameter (dave) of 4.5 or less, and further when the tensile strength of the steel wire material is represented by TS and the content of C in the steel wire material is represented by Wc, they satisfy the relationship of the following expression (1):






TS≦1240×Wc0.52  (1)


The steel wire material of the present invention may contain at least one element selected from 1.5% or less (not including 0%) by mass of Cr, 1.0% or less (not including 0%) by mass of Cu and 1.0% or less (not including 0%) by mass of Ni or at least one element selected from 5 ppm or less (not including 0 ppm) of Mg, 5 ppm or less (not including 0 ppm) of Ca and 1.5 ppm or less (not including 0 ppm) of REM.


Preferably, in the steel wire material of the present invention, the total decarbonization of the surface layer (Dm=T) is 100 μm or less and the adhesion of scale is 0.15 to 0.85% by mass.


Further, the process of the present invention is useful for the manufacture of a high carbon steel wire material having excellent wire drawability and the above characteristic properties.


A first manufacturing process comprises the steps of cooling a steel wire material made of steel which satisfies the above requirements for composition and heated at 730 to 1,050° C. to 470 to 640° C. (T1) at an average cooling rate of 15° C./sec or more and heating it to 550 to 720° C. (T2) which is higher than the above temperature (T1) at an average temperature elevation rate of 3° C./sec or more.


A second manufacturing process comprises the steps of heating a steel material which satisfies the above requirements for composition at 900 to 1260° C., hot rolling it at a temperature of 740° C. or higher, finish rolling at a temperature of 1,100° C. or lower, cooling it with water to 750 to 950° C., winding it on a conveyor device, cooling it at an average cooling rate of 15° C./sec or more to 500 to 630° C. (T3) within 20 seconds after winding, and heating it to 580 to 720° C. (T4) within 45 seconds after winding. Herein, (T4) is higher than the above value (T3).


According to the present invention, a high carbon steel wire material which has excellent wire drawability and can enhance productivity due to increases in wire drawing rate and area reduction rate and can extend the service life of a die and a process capable of manufacturing the high carbon steel wire material having excellent wire drawability surely and efficiently can be provided by specifying the contents of C, Si, Mn, P, S, N, Al and O in the steel, specifying the average crystal grain diameter and the maximum crystal grain diameter of the bcc-Fe crystal grains of its metal structure, preferably suppressing the area ratio of coarse crystal grains and further specifying the average sub grain diameter and maximum sub grain diameter of the above bcc-Fe crystal grains and the ratio of these.





BRIEF DESCRIPTION OF DRAWINGS


FIG. 1 is a schematic diagram of a production pattern employed in Experimental Example 1;



FIG. 2 is a diagram showing an example of the boundary map of the steel wire material obtained in the present invention;



FIGS. 3(A), 3(B) and 3(C) are graphs showing the evaluation examples of the crystal units of the steel wire material obtained in Experimental Example 1;



FIG. 4 is a graph showing the influence upon performance of average crystal grain diameter and maximum crystal grain diameter obtained in Experimental Example 1;



FIG. 5 is a schematic diagram of a production pattern employed in Experimental Example 2; and



FIG. 6 is a graph showing the influence upon performance of average crystal grain diameter and maximum crystal grain diameter obtained in Experimental Example 2.





DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The reason why the chemical components of the steel material are specified in the present invention will be clarified and then the reason why the crystal grain diameter of the structure of the steel material will be explained in detail hereinunder.


The reason why the chemical components of the steel material are specified will be first explained.


C: 0.6% to 1.1% by mass


This is an element which has an influence upon the strength of an iron steel material. 0.6% or more by mass of C must be added to ensure strength required for steel cords, bead wires and PC steel wires to which the present invention is directed to. When the content of C is increased, strength becomes high but when it is too high, ductility deteriorates. Therefore, the upper limit of the content is set to 1.1% by mass.


Si: 0.1 to 2.0% by mass


This element is added specially for the deoxidation of a steel material which is drawn into a wire at a high ratio. 0.1% or more by mass of Si must be added. Since Si contributes to the strengthening of a steel material, its amount is increased as required. However, when it is added too much, upgrade solution solubility is increased and decarbonization is promoted, to which attention should be paid. In the present invention, the upper limit of this content is set to 2.0° by mass from the viewpoint of reducing strength and preventing decarbonization. The content of Si is more preferably 0.15 to 1.8% by mass.


Mn: 0.1 to 1.0% by mass


0.1% or more by mass of Mn must be added for deoxidation and to stabilize and make the harmful element S harmless as MnS. Mn also has the function of stabilizing a carbide contained in steel. However, when the content of Mn is too high, wire drawability is deteriorated by segregation and the formation of a supercooling structure. Therefore, the content of Mn must be reduced to 1.0% or less by mass. The content of Mn is more preferably 0.15 to 0.9% by mass.


P: 0.020% or more by mass


P is an element specially harmful for wire drawability. When it is too much, the ductility of a steel material deteriorates. Therefore, the upper limit of the content of P is set to 0.020% by mass in the present invention. The content of P is more preferably 0.015% or less by mass, much more preferably 0.010% or less by mass.


S: 0.020% or less


Although it is a harmful element, it can be stabilized as MnS by adding Mn as described above. However, when the content of S is to high, the amount and size of MnS become large and ductility deteriorates. Therefore, the upper limit of the content of S is set to 0.020% by mass in the present invention. The content of S is more preferably 0.015% or less by mass, much more preferably 0.010% or less by mass.


N: 0.006% or less by mass


It contributes to a rise in strength by age hardening but deteriorates ductility. Therefore, the upper limit of its content is set to 0.006% by mass in the present invention. The content of N is more preferably 0.004% or less by mass, much more preferably 0.003% or less by mass.


Al: 0.03% or less by mass


Al is effective as a deoxidizer and contributes to the formation of a fine metal structure when it is bonded to N to form AlN. However, when the content of Al is too high, a coarse oxide is formed to deteriorate wire drawability. Therefore, the upper limit of its content is set to 0.03% in the present invention. The content of Al is more preferably 0.01% or less by mass, much more preferably 0.005% or less by mass.


O: 0.003% or less by mass


When the amount of O contained in steel is large, a coarse oxide is readily formed and wire drawability deteriorates. Therefore, the upper limit of its content is set to 0.003% by mass in the present invention. The content of O is more preferably 0.002% or less by mass, much more preferably 0.0015% or less by mass.


The steel wire material of the present invention comprises the above chemical components as basic components, and the balance consists of iron and unavoidable impurities. It may contain the following elements as required.


Cr: 1.5% or less by mass


This is an element effective in increasing the strength of a steel material. When it is added too much, a supercooling structure is readily formed to deteriorate wire drawability. Therefore, the amount of Cr must be reduced to 1.5% or less by mass.


Cu: 1.0% or less by mass


Since it has the function of suppressing the decarbonization of the surface layer and also the function of increasing corrosion resistance, it can be added as required. However, when it is added too much, it readily causes cracking during hot working and also exerts a bad influence upon wire drawability due to the formation of a supercooling structure. Therefore, the upper limit of its content is set to 1.0% by mass in the present invention.


Ni: 1.0% or less by mass


Since it is effective in suppressing the decarbonization of the surface layer and improving corrosion resistance like Cu, it is added as required. However, when it is added too much, wire drawability is deteriorated by the formation of a supercooling structure. Therefore, its content must be reduced to 1.0% or less by mass.


Mg: 5 ppm or less


Since Mg has the function of softening an oxide, it can be added as required. However, when it is added too much, the properties of an oxide change to deteriorate wire drawability. Therefore, its content is 5 ppm at maximum, preferably 2 ppm or less.


Ca: 5 ppm or less


Ca has the function of softening an oxide as well and may be added as required. However, when it is added too much, the properties of an oxide change to deteriorate wire drawability. Therefore, its content must be reduced to 5 ppm or less, preferably 2 ppm or less.


REM: 1.5 ppm or less


REM has the function of softening an oxide as well and may be added as required. However, when it is added too much, the properties of an oxide change to deteriorate wire drawability like Mg and Ca. Therefore, the upper limit of its content is set to 1.5 ppm. The content of REM is more preferably 0.5 ppm or less.


A description is subsequently given of the metal structure.


In the present invention, on condition that the above composition is satisfied, the essential feature of its metal structure is that “bcc-Fe crystal grains have an average crystal grain diameter (Dave) of 20 μm or less and a maximum crystal grain diameter (Dmax) of 120 μm or less”.


More preferably, the above bcc-Fe crystal grains have “an area ratio of crystal grains having a diameter of 80 μm or more of 40% or less of the total area”, “an average sub grain diameter (dave) of 10 μm or less and a maximum sub grain diameter (dmax) of 50 μm or less” or further “a (Dave/dave) ratio of the average crystal grain diameter (Dave) to the average sub grain diameter (dave) of 4.5 or less”.


Typical wire breaking during wire drawing is, for example, cupping breakage or longitudinal/shear cracking as shown in “Wire Drawing Limitation of Hard Steel Wires and Its Control Factors, Plasticity and Processing” (Takahashi et al.), vol. 19 (1978), pp. 726. According to this, the cupping breakage occurs when the pearlite block of a wire material is coarse and has poor ductility. For example, JP-A2004-91912 is also aimed to improve breakage resistance by controlling the grain no. of the pearlite block to Nos. 6 to 8. However, even in this invention, a rise in wire drawing rate at the time of drawing a wire is not realized yet.


Then the inventors of the present invention tried to control the sizes and distribution of crystal grain diameters based on the concept that “cupping breakage occurs because voids are formed and grow in a portion where crystal rotation does not take place smoothly during wire drawing and when coarse crystal grains are existent, voids are formed in that portion and cause breakage even though the average crystal grain diameter represented by crystal grain number is reduced.”


Since a relatively high carbon steel wire material to which the present invention is directed to is often controlled by the structure of pearlite mainly, the ductility of the wire material is often represented by a pearlite block (“factors of controlling the ductility of eutectoid pearlite steel”, Takahashi et al., bulletin of the Nippon Metal Society of Japan, vol. 42 (1978), pp. 708). However, as an ordinary steel material contains other structures such as ferrite and bainite, the inventors of the present invention have conducted studies based on the idea that the sizes and distribution of all crystal grain diameters including structures other than pearlite should be taken into consideration.


As a result, it has been found that when the average crystal grain diameter (Dave) is reduced to 20 μm or less and the maximum crystal grain diameter (Dmax) is controlled to 120 μm or less as specified by the present invention, wire drawability is greatly improved. When the average crystal grain diameter (Dave) is larger than 20 μm, the ductility of a wire becomes unsatisfactory. Even when the average crystal grain diameter (Dave) is 20 μm or less, if the maximum crystal grain diameter (Dmax) is larger than 120 μm, the wire is easily broken during wire drawing. Further, to obtain higher wire drawability, the average crystal grain diameter (Dave) is preferably set to 17 μm or less and the maximum crystal grain diameter (Dmax) is preferably set to 100 μm or less.


Although the object of the present invention is attained by specifying the above average crystal grain diameter (Dave) and the above maximum crystal grain diameter (Dmax) of the metal structure, in order to further improve wire drawability, the following requirements are desirably satisfied in addition to these requirements.


That is, when the area ratio of crystal grains having a diameter of 80 μm or more is controlled to 40% or less in the bcc-Fe crystal grains of the metal structure to make all the crystal grains uniform and fine, wire drawability can be further improved. The area ratio of crystal grains having a grain diameter of 80 μm or more is preferably 25% or less, particularly preferably 0%.


When studies have been conducted to further improve wire drawability, it has been found that so-called “sub grains” which are crystal units having a low angle boundary with adjacent crystals also have an influence upon crystal rotation and that wire drawability can be further improved by suppressing the average sub grain diameter (dave) to 10 μm or less and the maximum sub grain diameter (dmax) to 50 μm or less. That is, it is considered that when the number of coarse sub grains is made small and sub grains are made uniformly and fine, stress concentration is reduced and the formation of voids is suppressed. The average sub grain diameter (dave) and the maximum sub grain diameter (dmax) are preferably 7 μm or less and 40 μm or less, respectively, to obtain the above effect.


Further, as for the average crystal grain diameter (Dave) and the average sub grain diameter (dave), it has been confirmed that when the (Dave/dave) ratio of these is made small within the above ranges, wire drawability is further improved. This is considered to be because crystal rotation during wire drawing becomes smooth over the entire steel material, thereby making it difficult to cause the concentration of stress. The (Dave/dave) ratio is preferably 4.5 or less, more preferably 4.0 or less to obtain this function effectively.


In order to further improve wire (drawability in the present invention, the control of the tensile strength of a steel wire material and the content of C in the steel wire material to satisfy the relationship “TS [Mpa]≦1240×Wc0.52” (TS is the tensile strength of the steel wire material and Wc is the content of C in the steel wire material) is also effective.


When the wire drawing rate and the area reduction rate are increased, voids are readily formed and the temperatures of the steel wire material and the die rise, thereby causing wire breakage (longitudinal/shear cracking) and reducing the service life of the die. When the wire drawing rate and the area reduction rate remain unchanged, a temperature rise has a great influence upon the strength of the wire material. As the tensile strength is lower, the temperature rise becomes lower. It has been confirmed that the tensile strength is almost determined by the content of C in the steel wire material, and that when the relationship between the tensile strength (TS) and the content of C in the steel wire material (Wc) is controlled to satisfy the above expression, breakage caused by a temperature rise at the time of wire drawing is significantly suppressed and the service life of the die is improved.


In addition, in the present invention, when the influences of the decarbonization of the surface layer of the steel wire material and the adhesion of scale upon wire drawability has been studied to further improve wire drawability, it has been confirmed that a steel wire material having a total decarbonization of the surface layer (Dm-T) of 100 μm or less and an adhesion of scale to the surface layer of 0.15 to 0.85% by mass shows excellent wire drawability as well.


Even when wire drawability is improved by the component design and structure control of a steel wire material, wire drawability is influenced by the properties of scale on the surface of the steel wire material. Although a steel wire material is descaled chemically and mechanically before it is drawn, when wire drawing is carried out while scale is not removed completely and remains in the step, the die is chipped. The adhesion of scale has a great influence upon descalability. As the adhesion of scale is larger, descalability becomes better. When the adhesion is too large, scale is removed before descaling process and the wire material may be rusted. When decarbonization occurs on the surface of the steel wire material, even if the adhesion of scale is satisfactory, scale bites into the decarbonated portion, making descaling difficult. Therefore, in the present invention, when the requirements for reducing wire drawability impeding factors derived from scale as much as possible have been investigated, it has been confirmed that a reduction in wire drawability caused by scale can be suppressed immediately by controlling the total decarbonization of the surface layer (Dm-T) to 100 μm and the adhesion of scale to the surface layer to 0.15 to 0.85% by mass.


A description is subsequently given of the process for manufacturing a high carbon steel wire material having the above characteristic properties.


The first process comprises the steps of cooling a steel wire material heated at 730 to 1,050° C. and made of steel which satisfies the above requirements for Composition to 470 to 640° C. (T1) at an average cooling rate of 15° C./sec or more and heating it to 550 to 720° C. (T2) which is higher than the above temperature (T1) at an average temperature elevation rate of 3° C./sec or more.


The second process comprises the steps of heating a steel material which satisfies the above requirements for composition at 900 to 1,260° C., hot rolling it at a temperature of 740° C. or higher, finish rolling it at a temperature of 1,100° C. or lower, water cooling it to a temperature range of 750 to 950° C., winding it on a conveyor device, cooling it at an average cooling rate of 15° C./sec or more to 500 to 630° C. (T3) within 20 seconds after winding, and then heating it to 580 to 720° C. (T4) within 45 seconds after winding. Herein, (T4) is higher than the above value (T3) .


That is, to obtain a steel wire material having the above characteristic properties, a carbide in a steel material must be heated at 730° C. or higher to be dissolved so as to make its structure before transformation uniform. Although descalability improves as the heating temperature becomes higher, when the heating temperature exceeds 1,050° C., austenite grains before transformation become coarse, making it difficult to control the structure by transformation in the subsequent cooling step. Therefore, the heating temperature must be reduced to 1,050° C. or lower. The preferred heating temperature is 750 to 1,000° C.


In the cooling step after heating, the bcc crystal grain diameter after transformation which is controlled in the present invention is determined. To reduce the crystal grain diameter as uniform and small as possible, it is recommended to increase the cooling rate after heating as much as possible. The average cooling rate is set to 15° C./sec or more in the present invention.


As (T1) at the time of cooling is lower, the crystal grains become finer. However, when the steel material is cooled to a temperature below 470° C., a supercooling structure which impairs wire drawability is readily formed. Therefore, the lower limit is set to 470° C. Since the average grain diameter becomes large when (T1) is higher than 640° C., the steel material must be cooled to at least 640° C. The preferred (T1) at the time of cooling is 480 to 630° C.


In the present invention, the wire material must be heated to 550 to 720° C. which is higher than (T1) after the above cooling step for making the crystal grains fine. This temperature (T2) at the time of temperature elevation has a marked influence upon the strength of the steel material. As the temperature (T2) becomes higher, the strength lowers, which is advantageous for wire drawing. When the temperature is lower than 550° C., the reduction of strength becomes unsatisfactory and when the temperature is higher than 720° C. and becomes excessively high, transformation becomes uncompleted and may cause a rise in strength. (T2) at the time of temperature elevation is preferably 580 to 715° C.


That is, after the steel material is cooled to 470 to 640° C. (T1) (preferably 480 to 630° C.), it is re-heated at 550 to 720° C. (T2) (preferably 580 to 715° C., more preferably 580 to 710° C.) which is higher than T1 to obtain a steel material containing uniform and fine crystal grains and having low strength.


When the average temperature elevation rate from the temperature (T1) to the temperature (T2) is too low, the reduction of strength to the target level of the present invention is not effected. Therefore, the average temperature elevation rate between them must be 3° C./sec or more. That is, in order to obtain a steel wire material having excellent wire drawability with the above first process, it is important that a wire material heated at 730 to 1,050° C. (preferably 750 to 1,000° C.) should be cooled to 470 to 640° C. (T1) (preferably 480 to 630° C.) at an average cooling rate of 15° C./sec or more and then heated to 550 to 720° C. (T2) (preferably 580 to 715° C., more preferably 580 to 710° C.) at a rate of 3° C./sec or more. Herein, T2 is higher than T1.


Meanwhile, when a steel wire material to which the present invention is applied is a hot rolled wire material, the above second process is applied to control as follows.


First, the steel wire material is heated at 900 to 1,260° C. in a heating furnace, hot rolled at a temperature of 740° C. or higher and finish rolled at 1,100° C. or lower. When the heating temperature is lower than 900° C., heating is insufficient and when the temperature is higher than 1,260° C., the decarbonized area of the surface layer becomes wide. The heating temperature is preferably 900 to 1,250° C. When the rolling temperature is reduced, the decarbonization of the surface layer is promoted and descalability deteriorates. Therefore, the lower limit temperature of hot rolling is set to 740° C. The lower limit temperature is preferably 780° C. When the finish rolling temperature is higher than 1,100° C., the control of the transformation structure by cooling and re-heating in the subsequent step becomes difficult. Therefore, the upper limit of the finish rolling temperature is set to 1,100° C.


After finish rolling, the wire material is cooled to 750 to 950° C. with water and wound on a conveyor device such as a conveyor to be set. The control of temperature after water cooling is for the control of transformation and the control of scale in the subsequent step. When the temperature at the time of cooling becomes lower than 750° C., a supercooling structure is formed on the surface layer and when the temperature becomes higher than 950° C., the transformability of scale is lost and scale is peeled off at the time of transportation, causing the generation of rust by descaling during transportation.


After winding, it is important for obtaining a metal structure having excellent wire drawability that the steel material should be cooled at an average cooling rate of 15° C./sec or more, that the lowest value of the steel material temperature should be controlled to 500 to 630° C. (T3) within 20 seconds from winding and setting on the conveyor device, and that the steel material should be heated again to 580 to 720° C. (T4) higher than the above temperature (T3) from the temperature (T3) within 45 seconds after setting.


That is, by cooling the steel material at a rate of 15° C./sec or more so that the lowest temperature (T3) becomes 500 to 630° C. within 20 seconds after winding and setting, the crystal grains can be made uniform and fine. When the cooling rate is lower than 15° C./sec, the cooling rate is insufficient and the metal structure cannot be made uniform and fine fully and some coarse grains are formed. Although the higher cooling rate is effective in making the metal structure fine, in the case of cooling with an air blast after hot rolling, variations in the cooling rate in the steel wire material tend to become large. Therefore, the average cooling rate after winding and setting is preferably set to 120° C./sec or less, more preferably to 100° C./sec or less. Even when the temperature becomes lower than 480° C. in this cooling step, a supercooling structure is formed on the surface layer and when the temperature becomes higher than 630° C., a coarse grain tends to be formed. Even when the wire material is not cooled to a preferred temperature range within 20 seconds from winding and setting, the metal structure becomes coarse.


After cooling, the strength of the hot rolled material can be significantly reduced by controlling the highest value of the steel material temperature to 580 to 720° C. (T4) which is higher than the above temperature (T3) from the temperature (T3) within 45 seconds after winding and setting. To effectively promote the reduction of strength at this point, the time from winding and setting to the time when the above temperature range is reached is set to preferably 42 seconds or less, more preferably 40 seconds or less. When the temperature T4 is lower than the temperature T3 or when the temperature T4 is lower than 580° C., the reduction of strength becomes unsatisfactory and when the temperature T4 is higher than 720° C., both strength and ductility lower.


To obtain a hot rolled wire material having excellent wire drawability, the above second process is employed to heat a wire material at 900 to 1,260° C. (preferably 900 to 1,250° C.) in a heating furnace, hot roll it al a rolling temperature of 740° C. or higher (preferably 780° C. or higher), finish roll it at 1,100° C. or lower, cool it with water to 750 to 950° C. to be wound and set on the conveyor device, and cool it at a rate of 15° C./sec or more so as to control the lowest value of the steel material temperature to 500 to 630° C. (T3) within 20 seconds from winding and setting and then the highest value of the steel material temperature to 580 to 720° C. (T4), preferably to 580 to 715° C., more preferably to 580 to 710° C., which is higher than T3 from the temperature T3 within 45 seconds from winding and setting, thereby making it possible to obtain a high carbon steel wire material having excellent wire drawability efficiently.


EXAMPLES

The following experimental examples are provided to illustrate the constitution and function/effect of the present invention in more detail. It should be understood that the present invention is not limited by the following experimental examples and may be suitably modified in various ways without departing from the scope of the present invention and that all of them are included in the technical scope of the present invention.


Experimental Example 1

A hot rolled steel wire material having a diameter of 5.5 mm having chemical composition shown in Table 1 was manufactured. The amount of REM in Table 1 shows the total amount of La, Ce, Pr and Nd. The obtained hot rolled steel wire material was heated in an atmospheric furnace under conditions shown in FIG. 1 and Tables 2 and 3 and charged continuously into a lead furnace to be heated so as to obtain various steel wire materials. In this experimental example, the atmospheric furnace and the lead furnace were used to carry out the above heat treatment. The present invention is not limited to the use of these devices and other heating furnaces and holding furnaces may be used as a matter of course.


The structural features, scale characteristics and tensile characteristics of the obtained steel wire materials were evaluated. As for the crystal units of bcc crystal grains and sub grains out of the structural features, as the evaluation of variations in each crystal unit is important in the present invention, SEM/EBSP (Electron Back Scatter diffraction Pattern) was employed for the evaluation. The JSM-5410 of JEOL Ltd. was used as SEM and the OIM (Orientation Imaging Microscopy) System of TSL Co., Ltd. was used as EBSP.


After a sample was cut out from each steel wire material by wet cutting, wet polishing, buffing and chemical polishing were employed to prepare a sample for EBSP measurement, and a sample whose strain and surface unevenness caused by polishing were reduced as much as possible was thus prepared. The surface to be observed was polished as the longitudinal section of the steel wire material.


The obtained sample was measured with the center in the line diameter of the steel wire material as an EBSP measurement position. The measurement step was set to 0.5 μm or less, and the measurement area of each steel wire material was set to 60,000 μm2 or more. Although the analysis of crystal orientation was carried out after measurement, the measurement result of the average CI (Confidence Index) value which was 0.3 or more was used for analysis to enhance analytical reliability.


The analytical results (boundary map: one example is shown in FIG. 2) of the “bcc crystal grain” which is an area surrounded by a boundary with an azimuth difference of 10° or more and “sub grain” which is an area surrounded by a boundary with an azimuth difference of 2° or more as crystal units intended by the present invention are obtained by the analysis of the bcc-Fe crystal orientation. The obtained boundary map was processed by the Image-Pro image analyzing software to calculate and evaluate each crystal unit.


First, the area of each area (crystal unit) surrounded by a boundary is obtained based on the boundary map by the above Image-Pro. A circle diameter calculated by approximating each crystal unit to a circle equivalent diameter based on the area was used as the diameter of each crystal grain. The calculation results were statically processed as shown in examples of FIGS. 3(A) to 3(C) to obtain the average crystal grain diameter (Dave) i average sub grain diameter (dave), maximum crystal grain diameter (Dmax), maximum sub grain diameter (dmax), area ratio of crystal grains having a grain diameter of 80 μm or more and (Dave/dave) ratio of the average crystal grain diameter to the average sub grain diameter.


Out of the structure features, the total decarbonization is measured by the method described in Japanese Industrial Standards (JIS) G 0558. A sample was cut out from a steel wire material, buried in a resin so that the transverse section of the wire material became the surface to be observed, wet polished, baffed, and etched to expose the metal structure with 5% nital and observed through an optical microscope to measure the decarbonization of the surface layer of the steel wire material. The evaluation of decarbonization was made on two or more samples of each steel wire material to obtain a mean value.


The scale characteristics were evaluated based on the adhesion of scale to the surface layer of the steel wire material Stated more specifically, a 200 mm long sample was cut out from each steel wire material and the adhesion of scale was calculated from a weight difference of the sample before and after pickling with hydrochloric acid. The mean value of measurement data on 10 or more steel wire materials was used for the evaluation of scale.


As for the evaluation of tensile characteristics, a 400 mm long sample was cut out from each steel wire material and a tensile test was made on the sample by a universal testing machine at a cross head speed of 10 mm/min and a gauge length of 150 mm. 40 or more steel wire materials were measured to obtain a mean value of the measurement data as tensile strength (TS: MPa) and reduction of area (RA: %).


A description is subsequently given of the evaluation of wire drawability. Descaling and lubricant coating were made on each steel wire material as pre-treatments before wire drawing. For descaling, hydrochloric acid was used to remove scale by pickling. After descaling, the surface of each steel wire material was coated with phosphate as lubricant coating before wire drawing. Thereafter, dry wire drawing was carried out by a continuous wire drawing machine to a final wire diameter of 0.9 mm.


In this experimental example, to improve productivity at the time of wire drawing, wire drawing was carried out under three different conditions: (1) the final wire drawing rate was 600 mm/min and the number of dies was 14, (2) the final wire drawing rate was 800 mm/min and the number of dies was 14, and (3) the final wire drawing rate was 800 m/min and the number of dies was 12.


Although wire drawing productivity becomes higher from the conditions (1) to the conditions (3), wire drawing conditions become more harsh and a steel wire material to be drawn needs higher wire drawability. 50 tons of each steel wire material was drawn under the above three different conditions to evaluate the existence of wire breakage during wire drawing and the service life of each die. As for the evaluation of the service life of the die, when the die is broken during wire drawing, it is evaluated as (X), when the die is not broken during the drawing of 50 tons of the wire material but the die is worn away and must be exchanged for a new one after wire drawing, it is evaluated as (Δ), and when the die does not need to be exchanged due to the breakage and wear of the die after 50 tons of the wire material is drawn, it is evaluated as (◯). (-) means that the service life of the die cannot be evaluated due to breakage of the wire.


The results are shown in Table 4 and FIG. 4.












TABLE 1









Composition (mass %)
(ppm)





















Symbol
C
Si
Mn
P
S
Cu
Ni
Cr
Al
N
O
Mg
Ca
REM





A1
0.62
0.21
0.52
0.008
0.016
0.01
0.01
0.01
0.0011
0.0030
0.0011
0.1
0.4



A2
0.71
0.19
0.51
0.005
0.003
0.01
0.02
0.01
0.0012
0.0037
0.0013
0.1
1.0



A3
0.72
0.22
0.50
0.010
0.011
0.02
0.01
0.02
0.0005
0.0024
0.0014
0.1
0.7
0.1


A4
0.71
0.18
0.81
0.013
0.004
0.01
0.01
0.02
0.0020
0.0026
0.0013
0.2
1.7
0.1


A5
0.77
0.19
0.50
0.007
0.003
0.01
0.01
0.10
0.0022
0.0031
0.0014
0.1
1.3



A6
0.81
0.22
0.51
0.006
0.005
0.01
0.01
0.01
0.0003
0.0032
0.0012
0.1
0.9
0.2


A7
0.80
0.20
0.51
0.006
0.007
0.01
0.01
0.02
0.0010
0.0028
0.0013
0.1
0.7



A8
0.81
0.19
0.50
0.012
0.010
0.01
0.01
0.01
0.0020
0.0029
0.0014
0.1
0.8



A9
0.82
0.20
0.52
0.018
0.016
0.01
0.01
0.01
0.0011
0.0034
0.0014
0.2
1.2
0.1


A10
0.82
0.23
0.50
0.008
0.006
0.01
0.02
0.02
0.0110
0.0042
0.0021





A11
0.81
0.22
0.51
0.007
0.005



0.0018
0.0019
0.0015
0.9
2.1
0.4


A12
0.82
1.61
0.50
0.016
0.008
0.62
0.53
0.80
0.0275
0.0051
0.0016
2.1
2.7
1.0


A13
0.88
0.22
0.72
0.010
0.012
0.05
0.20
0.21
0.0016
0.0034
0.0017
0.1
1.2
0.1


A14
0.91
0.21
0.49
0.004
0.005
0.01
0.01
0.01
0.0010
0.0026
0.0012
0.1
0.8
0.1


A15
1.02
0.21
0.49
0.004
0.005
0.19
0.05
0.22
0.0004
0.0028
0.0010
0.1
1.5
0.1


A16
0.81
0.22
0.51
0.012
0.021
0.01
0.01
0.02
0.0011
0.0033
0.0014
0.1
1.6



A17
0.81
0.22
0.51
0.022
0.012
0.01
0.01
0.01
0.0008
0.0035
0.0017
0.2
2.1
0.1


A18
0.81
2.21
0.50
0.007
0.008
0.01
0.01
0.01
0.0008
0.0034
0.0014
0.1
1.3
0.1


A19
0.80
0.19
1.49
0.009
0.010
0.01
0.01
0.01
0.0006
0.0030
0.0013
0.1
1.3



A20
0.80
0.19
0.49
0.005
0.006
0.01
0.01
0.01
0.0022
0.0081
0.0017
0.1
0.9



A21
1.21
0.21
0.49
0.007
0.005
0.02
0.21
0.20
0.0108
0.0044
0.0015
0.1
0.9


























TABLE 2
















Area ratio of





Average

Average



crystal grains



Type
heating
cooling
Control
temperature
Control
Average crystal
Maximum crystal
having a diameter



of
temperature
rate
temperature 1
elevation rate
temperature 2
grain diameter
grain diameter
of 80 μm or more


No.
steel
T0(° C.)
° C./SEC
T1(° C.)
° C./SEC
T2(° C.)
Dave (μm)
Dmax (μm)
AF80 (%)





1
A1
924
31
573
12
641
7.8
53.4
0


2
A1
924
30
611
11
640
18.2
79.9
0


3
A2
744
16
581
12
640
6.2
29.8
0


4
A2
771
49
578
14
641
6.9
38.8
0


5
A2
923
32
574
14
638
7.8
63.2
0


6
A3
922
22
612
12
663
14.5
89.3
21.6















7
A3
924
31
642
Maintaining the same
22.3
100.7
55.2







temperature


8
A3
925
30
670
Maintaining the same
34.9
126.8
68.3







temperature
















9
A4
924
32
571
15
640
9.5
61.0
0















10
A4
951
31
671
Left to be gradually cooled
31.7
120.8
60.2
















11
A5
922
16
572
11
641
11.5
77.7
0


12
A6
814
28
614
6
677
9.3
53.9
0


13
A6
852
34
579
10
634
8.4
40.1
0


14
A6
851
32
628
5
678
9.9
101.0
39.8


15
A6
922
31
572
20
641
10.1
79.3
0


16
A7
924
29
588
48
681
13.8
88.1
23.2


17
A7
951
11
612
11
678
21.2
91.8
46.7


18
A7
950
31
609
10
681
17.6
86.2
40.6


19
A8
974
32
538
12
605
10.7
66.3
0


20
A8
977
87
561
22
701
9.5
44.2
0


21
A8
970
92
562
25
713
10.1
47.1
0


22
A8
970
112
558
25
707
9.3
50.4
0


23
A8
975
31
642
11
668
26.6
125.8
67.9


24
A9
974
33
637
11
679
18.1
102.4
41.2






















Crystal grain











diameter/Sub
Total



Average sub
Maximum sub
grain diameter
decarbon-
Adhesion
Tensile

Reduction



grain diameter
grain diameter
ratio
ization
of scale
strength
TS ≦ 1240 ×
of area


No.
dave (μm)
dmax (μm)
Dave/dave
Dm · T (μm)
mass %
TS (Mpa)
Wc0.52
RA (%)
Remarks





1
4.3
24.3
1.8
38
0.599
961

55


2
10.3
51.7
1.8
41
0.567
950

51


3
3.0
13.5
2.1
48
0.132
974

49
Descalability:











Δ


4
3.2
17.7
2.2
53
0.189
991

52


5
2.8
23.2
2.8
63
0.597
1007

45


6
5.1
34.2
2.8
62
0.580
998

41


7
5.3
46.7
4.2
57
0.554
1002

30


8
7.6
51.1
4.6
55
0.543
987

28


9
4.2
24.5
2.3
47
0.611
1011

47


10
6.2
47.2
5.1
52
0.557
992

28


11
4.6
26.2
2.5
46
0.583
1036

46


12
4.5
27.6
2.1
40
0.293
1023

41


13
3.1
18.1
2.7
52
0.338
1031

43


14
4.6
23.8
2.2
41
0.280
1010

39


15
4.2
28.8
2.4
38
0.588
1032

39


16
4.7
33.3
2.9
48
0.522
1018

36


17
5.6
36.1
3.8
56
0.610
1005

32


18
5.5
38.2
3.2
54
0.634
1008

35


19
3.7
19.7
2.9
61
0.821
1051

40


20
4.2
21.0
2.3
58
0.757
1002

38


21
4.8
23.5
2.1
52
0.702
997

35


22
4.7
22.3
2.0
55
0.690
1010

39


23
7.0
50.8
3.8
62
0.678
1002

31


24
6.2
40.1
2.9
66
0.699
1010

35

























TABLE 3
















Area ratio of





Average

Average



crystal grains



Type
heating
cooling
Control
temperature
Control
Average crystal
Maximum crystal
having a diameter



of
temperature
rate
temperature 1
elevation rate
temperature 2
grain diameter
grain diameter
of 80 μm or more


No.
steel
T0(° C.)
° C./SEC
T1(° C.)
° C./SEC
T2(° C.)
Dave (μm)
Dmax (μm)
AF80 (%)


















25
A9
976
29
641
Left to be gradually cooled
18.7
121.4
62.2


26
A9
976
31
641
Maintaining the same
24.5
122.1
66.3







temperature


27
A9
975
29
670
Maintaining the same
36.8
128.9
70.8







temperature
















28
A10
822
48
577
7
642
9.5
43.2
0


29
A10
821
46
522
15
576
7.5
40.6
0


30
A10
951
47
531
10
551
8.7
50.8
0


31
A11
848
47
521
43
638
7.6
41.0
0


32
A12
947
19
559
21
637
11.2
72.4
0


33
A13
848
39
578
8
641
8.1
42.1
0


34
A13
924
38
580
9
642
9.9
63.4
0


35
A14
850
67
578
10
644
7.7
39.0
0


36
A14
882
54
581
19
640
9.1
42.1
0


37
A14
923
71
577
10
643
10.3
61.7
0


38
A14
921
99
558
20
698
9.7
50.1
0


39
A14
920
98
552
22
680
9.3
48.2
0


40
A14
950
47
488
22
601
8.2
35.5
0


41
A14
1021
70
581
12
644
18.9
91.3
42.5


42
A15
924
68
558
19
640
8.6
64.6
0


43
A16
925
29
581
24
639
10.3
74.4
0


44
A17
923
30
576
24
638
11.1
85.7
12.7


45
A18
930
30
573
25
641
9.6
71.5
0


46
A19
924
28
579
22
637
8.8
88.8
18.6


47
A20
924
29
577
24
639
13.2
74.3
0


48
A21
924
30
575
24
639
11.9
65.2
























Crystal grain












diameter/Sub
Total




Average sub
Maximum sub
grain diameter
decarbon-
Adhesion
Tensile

Reduction




grain diameter
grain diameter
ratio
ization
of scale
strength
TS < 1240 ×
of area



No.
dave (μm)
dmax (μm)
Dave/dave
Dm · T (μm)
mass %
TS (Mpa)
Wc0.52
RA (%)
Remarks







25
5.1
42.4
3.7
66
0.761
1025

34



26
5.8
46.0
4.2
65
0.720
1011

32



27
8.2
52.0
4.5
67
0.751
979

27



28
3.3
20.2
2.9
53
0.314
1031

45



29
2.0
13.7
3.8
48
0.298
1121
X
39



30
1.8
14.4
4.8
55
0.570
1131
X
37



31
3.2
17.6
2.4
47
0.326
1027

41



32
4.4
31.1
2.5
83
0.559
1082

44



33
3.6
22.5
2.3
45
0.322
1109

39



34
3.7
24.1
2.7
46
0.533
1121

38



35
2.9
17.1
2.7
42
0.313
1119

37



36
3.1
20.2
2.9
49
0.431
1130

38



37
2.8
18.2
3.7
51
0.498
1142

39



38
3.8
27.2
2.6
55
0.452
1079

36



39
3.5
23.2
2.7
54
0.459
1096

36



40
2.1
17.5
3.9
56
0.523
1191
X
40



41
4.7
34.9
4.0
75
0.910
1155

40
Rust on surface












layer: existent



42
2.7
17.4
3.2
61
0.501
1240

38



43
4.3
27.3
2.4
40
0.565
1041

32



44
3.8
25.6
2.9
47
0.519
1038

31



45
4.1
25.9
2.3
124
0.522
1120
X
40
Descalability: x



46
2.8
19.7
3.1
32
0.551
1223
X
38
Supercooling












structure:












existence



47
4.2
26.5
3.1
42
0.509
1081

31



48
2.4
19.2
5.0
62
0.574
1331

32





















TABLE 4









Wire drawing condition (1)
Wire drawing condition (2)
Wire drawing condition (3)














Existence of wire
Service life
Existence of wire
Service life
Existence of wire
Service life


No.
breakage
of die
breakage
of die
breakage
of die
















1
Non-existence

Non-existence

Non-existence



2
Non-existence

Non-existence

Existence



3
Non-existence
Δ
Non-existence
Δ
Non-existence
Δ


4
Non-existence

Non-existence

Non-existence



5
Non-existence

Non-existence

Non-existence



6
Non-existence

Non-existence

Non-existence



7
Existence

Existence

Existence



8
Existence

Existence

Existence



9
Non-existence

Non-existence

Non-existence



10
Existence

Existence

Existence



11
Non-existence

Non-existence

Non-existence



12
Non-existence

Non-existence

Non-existence



13
Non-existence

Non-existence

Non-existence



14
Non-existence

Non-existence

Non-existence



15
Non-existence

Non-existence

Non-existence



16
Non-existence

Non-existence

Non-existence



17
Existence

Existence

Existence



18
Non-existence

Non-existence

Existence



19
Non-existence

Non-existence

Non-existence



20
Non-existence

Non-existence

Non-existence



21
Non-existence

Non-existence

Non-existence



22
Non-existence

Non-existence

Non-existence



23
Existence

Existence

Existence



24
Non-existence

Non-existence

Existence



25
Existence

Existence

Existence



26
Existence

Existence

Existence



27
Existence

Existence

Existence



28
Non-existence

Non-existence

Non-existence



29
Non-existence
Δ
Non-existence
Δ
Existence



30
Non-existence
Δ
Non-existence
Δ
Existence



31
Non-existence

Non-existence

Non-existence



32
Non-existence

Non-existence

Non-existence



33
Non-existence

Non-existence

Non-existence



34
Non-existence

Non-existence

Non-existence



35
Non-existence

Non-existence

Non-existence



36
Non-existence

Non-existence

Non-existence



37
Non-existence

Non-existence

Non-existence



38
Non-existence

Non-existence

Non-existence



39
Non-existence

Non-existence

Non-existence



40
Non-existence
Δ
Non-existence
Δ
Existence



41
Non-existence

Non-existence

Existence



42
Non-existence

Non-existence

Non-existence



43
Existence

Existence

Existence



44
Existence

Existence

Existence



45
Non-existence
X
Existence

Existence



46
Existence

Existence

Existence



47
Existence

Existence

Existence



48
Existence

Existence

Existence










The following can be analyzed as follows from Tables 1 to 4.


Wire drawability is improved by controlling the average crystal grain diameter (Dave) to 20 μm or less and the maximum crystal grain diameter (Dmax) to 120 μm or less as shown in FIG. 4. Therefore, even when the wire drawing rate is increased, high-speed wire drawing is made possible without breaking the wire material. Further, when the structure is made uniform and fine by controlling (Dave) to 17 μm or less and (Dmax) to 100 μm or less; TS is reduced to 1,240×Wc0.52 or less; the average sub grain diameter (dave) is controlled to 10 μm or less; the maximum sub grain diameter (dmax) is controlled to 50 μm or less; and the (Dave/dave) ratio is controlled to 4.5 or less as additional requirements, wire drawing is made possible without wire breakage even if the number of dies is reduced and the wire drawing rate is increased. Consequently, wire drawability can be further improved.


Steel wire materials Nos. 2, 14, 18, 24, 29, 30, 40 and 41 which satisfy the requirements for the average crystal grail diameter (Dave) and the maximum crystal grain diameter (Dmax) but not the above additional requirements are broken when the number of dies is small though high-speed wire drawing is possible. In case of steel wire material No. 3 in Tables 2 to 4 which is inferior in descalability from the viewpoint of the service life of the die, wire breakage does not occur during wire drawing even when wire drawing conditions acre made harsh but a bad influence upon the service life of the die is seen to such an extent that the die must be exchanged after wire drawing. Also in case of steel wire materials Nos. 29, 30 and 40 in Tables 2 to 4 which are unsatisfactory in the softening of steel and do not satisfy “TS≦1240×Wc0.52”, the service life of the die is short.


The influence upon wire drawability of the composition appears in steel wire materials Nos. 43 to 48 in Tables 3 and 4. That is, as A16 and A17 which are used in steel wire materials Nos. 43 and 44 of Tables 3 and 4 have high contents of P and S, wire breakage occurs though their metal structures are suitably controlled. Since A18 which is used in steel wire material No. 45 of Tables 3 and 4 contains Si too much, marked decarbonization occurs, descalability is poor and strength is too high, thereby causing the breakage of the die and wire breakage during wire drawing.


As A19 used in the steel wire material No. 46 of Tables 3 and 4 contains Mn too much, a supercooling structure is formed and strength is high. Since A20 of steel wire material No. 47 contains N too much, ductility becomes unsatisfactory and strain aging embrittlement readily occurs during wire drawing. Since A21 of steel wire material No. 48 contains C more than the specified value, its ductility is poor and strain aging embrittlement readily occurs during wire drawing.


A steel wire material whose steel components are outside the specified range of the present invention does not achieve satisfactory wire drawability though it has the structural features of the present invention.


Experimental Example 2

To improve wire drawability as hot rolled, types of steel shown in Table 5 below were used and studied. The amount of REM in Table 5 shows the total amount of La, Ce, Pr and Nd. All the types of steel shown in Table 5 satisfy the requirements for composition specified by the present invention.


The types of steel shown in Table 5 were hot rolled under conditions shown in Table 6 and FIG. 5. In the case of a hot rolled material, all the steps from a heating furnace to rolling and cooling must be controlled. As shown in FIG. 5, the control items are more complicated than in the above Experimental Example 1 (FIG. 1). The structural features, scale characteristics, tensile characteristics and wire drawability of the obtained hot rolled materials were evaluated in the same manner as in the above Experimental Example 1.


The results are shown in Tables 6 to 8 and FIG. 6. By suitably controlling a series of steps from heating to winding and cooling for hot rolling, the structural features, scale characteristics and tensile characteristics can be controlled to the ranges specified by the present invention as well, and it can be confirmed from the results of the evaluation of wire drawability that excellent wire drawability can be obtained as the wire material is hot rolled.












TABLE 5









Composition (Mass %)
(ppm)





















Symbol
C
Si
Mn
P
S
Cu
Ni
Cr
Al
N
O
Mg
Ca
REM





B1
0.61
0.20
0.51
0.009
0.012
0.01
0.01
0.02
0.0008
0.0032
0.0013
0.1
0.7



B2
0.71
0.21
0.48
0.004
0.005
0.01
0.01
0.01
0.0010
0.0030
0.0013
0.1
1.2



B3
0.72
0.20
0.88
0.008
0.010
0.01
0.01
0.01
0.0009
0.0028
0.0014
0.2
1.4
0.2


B4
0.72
0.19
0.83
0.006
0.005
0.01
0.02

0.0278
0.0032
0.0013





B5
0.77
0.20
0.50
0.006
0.005
0.19
0.01
0.20
0.0022
0.0031
0.0014
0.1
1.3



B6
0.80
0.21
0.52
0.005
0.004
0.01
0.01
0.01
0.0004
0.0032
0.0013
0.1
0.8



B7
0.81
0.20
0.51
0.006
0.006
0.01
0.01
0.01
0.0005
0.0030
0.0014
0.1
1.0



B8
0.82
0.21
0.51
0.006
0.007
0.01
0.01
0.02
0.0003
0.0029
0.0014
0.1
1.2



B9
0.88
0.25
0.79
0.010
0.007
0.20
0.02
0.22
0.0311
0.0047
0.0015
0.1
0.6
0.1


B10
0.89
0.92
0.72
0.011
0.008
0.01
0.01
0.25
0.0306
0.0041
0.0014
0.1
1.0



B11
0.91
0.19
0.50
0.005
0.004
0.19
0.02
0.20
0.0007
0.0027
0.0013
0.1
0.8



B12
0.92
0.19
0.49
0.004
0.005
0.18

0.20
0.0006
0.0027
0.0011

1.0
0.1


B13
1.07
0.21
0.51
0.006
0.006
0.21
0.01
0.21
0.0005
0.0028
0.0012
0.2
1.3
0.1


























TABLE 6









Temper-
Lowest
Finish


Control
Control
Average
Maximum



ature of
rolling
rolling
Temperature
Average
temperature 1
temperature 2
crystal
crystal




















Type
heating
temper-
temper-
after water
cooling
Time from
Temper-
Time for
Temper-
grain
grain



of
furnace
ature
ature
cooling
rate
setting
ature
setting
ature
diameter
diameter


No.
steel
° C.
° C.
° C.
° C.
° C./SEC
SEC
T3(° C.)
SEC
T4(° C.)
Dave(μm)
Dmax(μm)






















1
B1
1152
902
984
852
17
16
580
28
640
8.2
45.4


2
B1
1151
948
1027
847
21
13
574
27
644
8.7
47.2


3
B1
1147
955
1031
922
17
16
650
39
696
23.4
122.1


4
B2
1151
835
932
902
35
9
587
31
653
8.5
43.2


5
B2
1150
911
979
910
31
11
569
30
645
10.3
54.3


6
B2
1148
942
1031
901
37
9
568
33
676
14.1
65.8


7
B2
1147
937
1025
899
13
19
652
34
667
22.7
120.2


8
B3
1102
822
912
823
29
10
533
28
623
8.5
52.5


9
B3
1110
824
920
900
53
7
529
27
629
8.1
49.2


10
B4
1152
932
1022
905
55
6
575
20
645
8.2
47.3


11
B4
1154
938
1031
912
97
4
573
12
599
8.1
42.1


12
B4
1150
935
1027
907
109
3
580
13
630
7.5
43.5


13
B5
1012
802
908
823
24
11
559
22
625
8.6
46.1


14
B5
1022
743
851
822
25
11
547
24
625
7.8
41.4


15
B6
973
808
901
844
37
8
548
23
638
8.3
42.5


16
B6
1102
854
944
863
42
8
527
22
597
9.1
43.1


17
B6
1102
883
1012
882
41
8
554
23
644
10.7
50.5


18
B7
1149
822
943
914
17
17
625
28
664
14.7
82.8


19
B7
1150
905
987
913
16
18
625
27
659
17.9
90.1


20
B7
1155
933
1045
903
12
22
639
27
669
22.3
113.4


21
B7
1152
940
1044
900
71
5
545
27
699
7.6
44.0


22
B7
1150
935
955
911
115
3
566
24
711
8.0
39.5


23
B8
1222
989
1077
925
22
17
551
36
608
12.4
63.2


24
B8
1231
987
1063
932
22
19
514
42
583
10.1
54.2


25
B8
1256
992
1080
931
24
16
547
36
607
13.2
67.7


26
B8
1226
995
1112
973
23
16
605
35
662
21.2
101.2


27
B9
1148
931
989
808
21
9
619
27
682
16.2
91.4


28
B9
1152
923
974
912
17
16
640
42
679
19.5
121.3


29
B10
1155
927
978
802
22
11
560
28
645
10.5
49.7


30
B11
1152
932
982
801
21
11
570
31
670
11.2
52.9


31
B11
1151
921
979
898
16
16
642
38
664
20.8
117.9


32
B12
1151
977
1046
922
47
7
593
17
701
18.7
105.5


33
B12
1150
973
1040
853
99
3
556
23
706
8.1
40.8


34
B13
1148
929
984
872
28
11
564
32
669
12.2
53.1


























TABLE 7







Area ratio of












crystal grains


Crystal grain




having a diam-
Average
Maximum
diameter/



Type
eter of 80
sub grain
sub grain
Sub grain
Total
Adhesion
Tensile
Reduction



of
μm or more
diameter
diameter
diameter ratio
decarbonization
of scale
strength
of area


No.
Steel
AF80 (%)
dave/μm
dmax(μm)
Dave/dave
Dm · T(μm)
mass %
TS (MPa)
RA(%)
Remarks

























1
B1
0
5.2
24.3
1.6
62
0.389
948
54



2
B1
0
5.4
27.6
1.6
71
0.375
951
52


3
B1
61.1
11.4
50.2
2.1
65
0.721
930
46


4
B2
0
4.3
25.2
2.0
73
0.577
998
48


5
B2
0
4.5
25.9
2.3
65
0.592
1008
50


6
B2
0
5.1
27.7
2.8
66
0.565
982
48


7
B2
58.7
10.6
48.7
2.1
67
0.534
967
42


8
B3
0
4.5
26.1
1.9
54
0.298
1012
46


9
B3
0
2.9
22.4
2.8
57
0.552
1046
45


10
B4
0
3.4
32.1
2.4
65
0.501
1002
35


11
B4
0
5.1
29.8
1.6
69
0.450
1030
38


12
B4
0
6.2
30.7
1.2
64
0.469
1007
37


13
B5
0
3.3
21.6
2.6
71
0.287
1052
43


14
B5
0
3.4
20.5
2.3
103
0.256
1048
42
DESCAL-












ABILITY: Δ


15
B6
0
3.5
23.3
2.4
43
0.334
1027
40


16
B6
0
2.6
20.1
3.5
61
0.422
1078
42


17
B6
0
2.8
21.0
3.8
63
0.498
1031
40


18
B7
24.7
6.3
34.2
2.3
65
0.621
1017
37


19
B7
40.9
7.2
35.3
2.5
67
0.613
1006
36


20
B7
52.2
7.6
37.8
2.9
62
0.603
1005
33


21
B7
0
2.9
22.7
2.6
55
0.522
1002
34


22
B7
0
3.2
29.1
2.5
58
0.551
998
34


23
B8
0
5.3
23.8
2.3
89
0.778
1059
41


24
B8
0
3.2
24.1
3.2
91
0.812
1110
43


25
B8
0
5.1
25.2
2.6
113
0.781
1050
39
DESCAL-












ABILITY: Δ


26
B8
50.9
7.9
40.1
2.7
92
0.911
1011
33


27
B9
37.5
9.3
43.2
1.7
60
0.235
1110
35


28
B9
58.6
10.2
47.8
1.9
58
0.619
1102
29


29
B10
0
3.2
23.5
3.3
72
0.211
1121
36


30
B11
0
3.5
31.6
3.2
65
0.254
1107
36


31
B11
55.1
6.5
47.6
3.2
59
0.604
1107
28


32
B12
48.3
9.2
43.6
2.0
64
0.645
1090
31


33
B12
0
2.9
20.0
2.8
60
0.352
1068
34


34
B13
0
3.3
33.2
3.7
68
0.510
1213
35




















TABLE 8











Wire drawing condition3



Wire drawing condition1
Wire drawing condition2
(number of dies is reduced)



600 m/min
800 m/min
800 m/min














Existence of
Service life
Existence of
Service life
Existence of
Service life


No.
disconnection
of die
disconnection
of die
disconnection
of die
















1
Non-existence

Non-existence

Non-existence



2
Non-existence

Non-existence

Non-existence



3
Existence

Existence

Existence



4
Non-existence

Non-existence

Non-existence



5
Non-existence

Non-existence

Non-existence



6
Non-existence

Non-existence

Non-existence



7
Existence

Existence

Existence



8
Non-existence

Non-existence

Non-existence



9
Non-existence
Δ
Non-existence
Δ
Existence



10
Non-existence

Non-existence

Non-existence



11
Non-existence

Non-existence

Non-existence



12
Non-existence

Non-existence

Non-existence



13
Non-existence

Non-existence

Non-existence



14
Non-existence
Δ
Non-existence
Δ
Non-existence
Δ


15
Non-existence

Non-existence

Non-existence



16
Non-existence

Non-existence

Non-existence



17
Non-existence

Non-existence

Non-existence



18
Non-existence

Non-existence

Non-existence



19
Non-existence

Non-existence

Existence



20
Existence

Existence

Existence



21
Non-existence

Non-existence

Non-existence



22
Non-existence

Non-existence

Non-existence



23
Non-existence

Non-existence

Non-existence



24
Non-existence
Δ
Non-existence
Δ
Existence



25
Non-existence
Δ
Non-existence
Δ
Non-existence
Δ


26
Existence

Existence

Existence



27
Non-existence

Non-existence

Non-existence



28
Existence

Existence

Existence



29
Non-existence

Non-existence

Non-existence



30
Non-existence

Non-existence

Non-existence



31
Existence

Existence

Existence



32
Non-existence

Non-existence

Existence



33
Non-existence

Non-existence

Non-existence



34
Non-existence

Non-existence

Non-existence










A high carbon steel wire material having excellent wire drawability can be obtained by controlling especially the average crystal grain diameter (Dave) of a carbon steel wire which satisfies the predetermined requirements for composition to 20 μm or less and the maximum crystal grain diameter (Dmax) to 120 μm or less and reducing variations in the sizes of the metal structure units and making the metal structure uniform and fine.

Claims
  • 1-8. (canceled)
  • 9. A process for manufacturing a high carbon steel wire material having excellent wire drawability, the process comprising heating at 730 to 1,050° C. a steel comprising 0.6 to 1.1% by mass of C,0.1 to 2.0% by mass of Si,0.1 to 1.0% by mass of Mn,0.020% or less by mass of P,0.020% or less by mass of S,0.006% or less by mass of N,0.03% or less by mass of Al and0.0030% or less by mass of O,the balance being Fe and unavoidable impurities;then cooling the steel to a temperature T1 in a range of from 470 to 640° C. at an average cooling rate of 15° C./sec or more; and then heating the steel to a temperature T2 in a range of from 550 to 720° C. at an average temperature elevation rate of 3° C./sec or more, where T2 is higher than T1.
  • 10. The process according to claim 9, wherein the steel further comprises at least one selected from the group consisting of 1.5% or less (not including 0%) by mass of Cr,1.0% or less (not including 0%) by mass of Cu, and1.0% or less (not including 0%) by mass of Ni.
  • 11. The process according to claim 9, wherein the steel further comprises at least one selected from the group consisting of 5 ppm or less (not including 0 ppm) of Mg,5 ppm or less (not including 0 ppm) of Ca, and1.5 ppm or less (not including 0 ppm) of REM.
  • 12. A process for manufacturing a high carbon steel wire material having excellent wire drawability, the process comprising heating at 900 to 1,260° C. a steel comprising 0.6 to 1.1% by mass of C,0.1 to 2.0% by mass of Si,0.1 to 1.0% by mass of Mn,0.020% or less by mass of P,0.020% or less by mass of S,0.006% or less by mass of N,0.03% or less by mass of Al and0.0030% or less by mass of O,the balance being Fe and unavoidable impurities:then hot rolling the steel at a temperature of 740° C. or higher to subject the steel to finish rolling at a temperature of 1,100° C. or lower;then cooling the steel with water to 750 to 950° C. and winding the steel on a conveyor device;then cooling the steel at an average cooling rate of 15° C./sec or more to a temperature T3 in a range of from 500 to 630° C. within 20 seconds after the winding; andthen reheating the steel to a temperature T4 in a range of from 580 to 720° C. 4) within 45 seconds after the winding, where T4 higher than T3.
  • 13. The process according to claim 12 wherein the steel further comprises at least one selected from the group consisting of 1.5% or less (not including 0%) by mass of Cr.1.0% or less (not including 0%) by mass of Cu, and1.0% or less (not including 0%) by mass of Ni.
  • 14. The process according to claim 12, wherein the steel further comprises at least one selected from the group consisting of 5 ppm or less (not including 0 ppm) of Mg,5 ppm or less (not including 0 ppm) of Ca, and1.5 ppm or less (not including 0 ppm) of REM.
  • 15. The process according to claim 9, wherein the steel wire material mainly comprises pearlite.
  • 16. The process according to claim 9, wherein the steel wire material comprises bcc-Fe crystal grains having an average crystal grain diameter (Dave) of 20 μm or less and a maximum crystal grain diameter (Dmax) of 120 μm or less.
  • 17. The process according to claim 9, wherein the steel wire material comprises bcc-Fe crystal grains having a diameter of 80 μm or more in an area ratio of 40% or less.
  • 18. The process according to claim 9, further comprising, after the heating to 550 to 720° C., drawing the steel into a wire.
  • 19. The process according to claim 12, wherein the steel wire material mainly comprises pearlite.
  • 20. The process according to claim 12, wherein the steel wire material comprises bcc-Fe crystal grains having an average crystal grain diameter (Dave) of 20 μm or less and a maximum crystal grain diameter (Dmax) of 120 μm or less.
  • 21. The process according to claim 12, wherein the steel wire material comprises bcc-Fe crystal grains having a diameter of 80 μm or more in an area ratio of 40% or less.
  • 22. The process according to claim 12, further comprising, after the reheating, drawing the steel into a wire.
Priority Claims (1)
Number Date Country Kind
2004-371901 Dec 2004 JP national
Divisions (1)
Number Date Country
Parent 11296299 Dec 2005 US
Child 12466865 US