TWI516611B - Wire rod, hyper-eutectoid bainite steel wire, and method for manufacturing thereof - Google Patents

Description

Wire, hypereutectoid toughened iron steel wire, and manufacturing method thereof Technical field

The present invention relates to a wire for a hypereutectoid toughened iron steel wire excellent in wire drawing characteristics and delayed fracture resistance, a hypereutectoid toughened iron steel wire produced from the wire, and a method for producing the same.

The present application claims priority on Japanese Patent Application No. 2013-211365, filed on Jan.

Background technique

Wire material is the material of various mechanical parts such as steel wire. When manufacturing various mechanical parts (hereinafter referred to as final products) from a wire, it is usually performed by mechanical processing and annealing such as wire drawing. The tensile strength of the final product is mainly affected by the composition of the wire, especially the C content of the wire. On the other hand, the metal structure of the wire will be changed by the metamorphosis during annealing. Therefore, when the final article is manufactured by the step of annealing, the metal structure of the wire will not affect the tensile strength of the final article. For the above reasons, when the final product is produced in the step of annealing, the composition of the wire needs to correspond to the tensile strength required for the final product.

On the other hand, irrespective of the tensile strength of the final product, the tensile strength of the wire is preferably low. The wire having high tensile strength has low machinability and low wire drawing characteristics. In addition, the wire having a high tensile strength is easily affected by delayed breaking (broken by hydrogen embrittlement), and is easily damaged during its manufacture, storage, and transportation. In particular, when the C content of the wire is 0.8% by mass or more (that is, when the C content of the wire is larger than the eutectoid point, the wire is hypereutectoid steel), the wire material is susceptible to delayed fracture (hydrogen embrittlement). The problem. As a result, when the manufactured wire is bundled into a coil shape for storage and transportation, the wire is broken due to the stress at the time of binding. The loss of the wire will result in a decrease in the processing efficiency of the wire. In addition, when the length of the broken wire is shorter than the length required for the final product, the wire cannot be used as the material of the final product.

In order to prevent the breakage caused by delayed breaking (hydrogen embrittlement), some people have come up with a slowing of the binding conditions, for example, reducing the force of binding the wire. However, by slowing down the bundling conditions, the storage stability of the coil, the transportability of the coil, and the safety when handling the coil are impaired.

By adjusting the composition of the wire, for example, reducing the C content to reduce the tensile strength of the wire, the problems associated with delayed breaking and machinability will be solved. However, as described above, the composition of the wire material needs to be the tensile strength required for the final product. Therefore, it is not possible to use the composition of the adjusting wire as a method of preventing delayed breaking.

The tensile strength of the wire can be reduced by changing the heat treatment conditions at the time of manufacturing the wire. In the past, the metal structure of the over-eutectoid wire (the wire having a C content greater than the eutectoid point) was mainly composed of Borite. The conventional method for producing a hypereutectoid wire comprises the steps of obtaining a wire after rolling the steel material, and cooling the wire The steps. The metal structure of the wire will become the Borne iron during the cooling step. In the manufacturing method, the tensile strength of the wire can be reduced by first heating the rolled wire to a temperature range of the Wolsfield iron and then cooling at a slower cooling rate. However, in the production method using a wire having a C content higher than the eutectoid point, when a production condition with a slow cooling rate is used, not only the formation of a wave of iron but also a large amount of pre-eutectoid stellite is generated during cooling. Pre-eutectification of the former Xueming carbon iron will deteriorate the processability of the wire. Therefore, it is not possible to use a method of slowing down the cooling rate of the wire as a method of preventing delayed breakage.

In view of the above, the present inventors reviewed the use of a metal structure for adjusting a wire as a method of reducing the tensile strength. As described above, when the final article is manufactured by the step of annealing, the metal structure of the wire will not affect the tensile strength of the final article. The general wire of the prior art is mainly composed of a Borne iron structure, and such a wire is called a Bored iron wire. On the other hand, a wire rod (toughened iron wire material) mainly composed of a toughened iron as a main structure is known to have excellent wire drawing characteristics than a ferrite wire (see, for example, Patent Documents 1 to 7). Further, the tensile strength of the hypereutectoid toughened iron wire having a C content greater than the eutectoid point is the same as that of the toughened iron wire, and the tensile strength of the ferroelectric wire having a C content is lower. For example, the inventors of the present invention observed that the average tensile strength of the toughened iron wire having a C content of 1.1% is 200 to 300 MPa lower than the average tensile strength of the wave iron wire having a C content of 1.1%. By making the metal structure of the wire material into toughened iron, the tensile strength of the wire can be reduced irrespective of the tensile strength sought by the final product after annealing (ie, irrespective of the C content sought by the steel wire), thereby achieving The improvement of the pull line characteristics and the suppression of the delay break.

However, the toughened iron wire has a problem that the tensile strength is easily uneven. The state in which the tensile strength of the wire is uneven is a state in which the measured values are uneven when the tensile strength is measured at a plurality of points in one wire. When the tensile strength of the wire is uneven, the tensile strength is high and it is susceptible to delayed fracture (hydrogen embrittlement), which causes breakage. Further, when the tensile strength of the wire is uneven, the workability of the wire is uneven, so that mechanical processing of the wire becomes difficult. Patent Documents 1 to 7 disclose a method of producing a toughened iron wire. However, the present inventors have observed that when the toughened iron wire is produced according to the manufacturing method specifically disclosed in the documents, the tensile strength of the wire is largely uneven. First, the inventors cut the wire obtained by the above-described manufacturing method into a length of 3,200 mm. Then, the inventors of the present invention made eight test pieces having a length of 400 mm by dividing the wire into eight equal portions, and subjected the tensile test to the test pieces. The difference between the maximum value and the minimum value of the tensile strength of the test pieces (hereinafter referred to as the difference amount of the tensile strength) is more than 100 N/mm ² . On the other hand, as a result of the review by the inventors of the present invention, it has been found that a wire having a difference in tensile strength of the wire of more than 50 N/mm ² is not easily industrially used.

Prior technical literature Patent literature

Patent Document 1: Japanese Patent Laid-Open No. Hei 05-117762

Patent Document 2: Japanese Patent Laid-Open No. 06-017190

Patent Document 3: Japanese Patent Laid-Open No. 06-017191

Patent Document 4: Japanese Patent Laid-Open No. Hei 06-017192

Patent Document 5: Japanese Patent Laid-Open No. Hei 06-073502

Patent Document 6: Japanese Patent Laid-Open No. Hei 06-330240

Patent Document 7: Japanese Patent Laid-Open Publication No. Hei 08-003639

Summary of invention

As described above, in the prior art, the Wrought iron wire has a high tensile strength, so that there is a problem that the breakage is likely to occur. In view of the required specifications of the final product obtained from the Whale wire, it is difficult to reduce the tensile strength by reducing the C content of the iron wire. On the other hand, in the method for producing a Wolla wire, the method of reducing the tensile strength by reducing the cooling rate causes an increase in the amount of Xueming carbon iron before the eutectoid, which is not preferable. The increase in the amount of snow and carbon in the pre-eutectoid will reduce the machinability of the wire. Further, the toughened iron wire of the prior art, in particular, the hypereutectoid toughened iron wire having a C content greater than the eutectoid point has a problem that the tensile strength is likely to be uneven. The unevenness in tensile strength causes an increase in the frequency of occurrence of delayed breakage and a decrease in machinability.

The object of the present invention is to reduce the tensile strength and the high ductility of a wire having a C content greater than an eutectoid point by using a toughened iron as a metal structure of a wire material, so as to improve wire drawing characteristics and resistance to breakage of the wire. characteristic. Further, the subject of the present invention is to suppress the unevenness of the tensile strength of the wire. Further, an object of the present invention is to provide a wire material capable of solving such problems, a hypereutectoid toughened iron steel wire produced using the wire material, and a production method for stably producing the wire.

The inventors of the present invention have found that the above-described problems can be solved by producing a wire rod based on a production condition capable of producing a toughened iron structure capable of suppressing both the pre-eutectoid smear carbon and the low-strength wire.

The present invention has been made in accordance with the above-observed knowledge, and the gist thereof is as follows.

(1) A wire according to an aspect of the present invention has the following composition: in terms of unit mass%, C: more than 0.80 to 1.20%, Si: 0.10 to 1.50%, Mn: 0 to 1.00%, P: 0 ~0.02%, S: 0~0.02%, Cr: 0~1.00%, Ni: 0~1.00%, Cu: 0~1.00%, Mo: 0~0.50%, Ti: 0~0.20%, Nb: 0~ 0.20%, V: 0~0.20%, B: 0~0.0050%, Al: 0~0.10%, and Ca: 0~0.05%, and the remaining part is composed of Fe and impurities; the metal structure contains 90~100 area % toughened iron; the average value of the tensile strength of each of the above test pieces TS is in units of N by cutting a wire having a length of 3,200 mm into eight pieces of the same length to produce eight test pieces having a length of 400 mm. / mm ² gauge satisfy the following formula 1, each of the tensile strength of each test piece of the difference between the maximum value and the minimum value based 50N / mm ² or less, each section of the test piece was cut in the unit of the average values RA The % meter satisfies the following formula 2.

[TS]≦810×[C]+475‧‧‧(Form 1)

[RA]≧-0.083×[TS]+154‧‧‧(Form 2)

Here, [C] is the C content of the wire indicated by unit mass%, and [TS] is the aforementioned average value TS of the tensile strength expressed in units of N/mm ² , and [RA] is expressed in units of %. The aforementioned average value RA of the aforementioned section reduction value.

(2) The hypereutectoid toughened iron steel wire of the other aspect of the present invention is obtained by processing the wire material as described in the above (1) by wire drawing.

(3) A method of producing a wire according to the above aspect (1), which comprises the steps of: rolling a steel sheet to obtain a wire, the steel sheet having the following composition; Composition: in terms of unit mass%, containing: C: greater than 0.80 to 1.20%, Si: 0.10 to 1.50%, Mn: 0 to 1.00%, P: 0 to 0.02%, S: 0 to 0.02%, Cr: 0~ 1.00%, Ni: 0~1.00%, Cu: 0~1.00%, Mo: 0~0.50%, Ti: 0~0.20%, Nb: 0~0.20%, V: 0~0.20%, B: 0~0.0050 %, Al: 0 to 0.10%, and Ca: 0 to 0.05%, and the remainder is composed of Fe and impurities; the wire of 850 to 1050 ° C is immersed in the first molten salt bath or melted at 350 to 450 ° C In the lead bath, the step of taking out the wire from the first molten salt bath or the molten lead bath; the time point within 5 seconds after the extraction and the wire beginning toughen the iron metamorphosis t _s seconds before ~ t _s seconds a step of immersing the wire in a second molten salt bath or a molten lead bath at 530 to 600 ° C at a later point; and, after the said toughened iron metamorphosis is completely completed, the wire is melted or melted from the second molten salt bath The step of taking out the lead bath.

t _s =0.05×t _complete ‧‧‧(式3)

The t _complete is expressed in units of seconds after the wire is continuously immersed in the first molten salt bath or the molten lead bath, and the time from the deformation of the wire to the end of the deformation of the wire is completed.

(4) The method for producing a wire according to the above aspect, wherein the wire is immersed in the first molten salt bath or the molten lead bath, and the wire is immersed in the second molten salt bath or the molten lead bath. The elapsed time between the points can also be 10 to 40 seconds.

(5) The method for producing a wire according to the above (3), wherein, in the first molten salt bath or the molten lead bath, the wire is in a state in which the toughened iron is deformed, and the reheating of the wire is detected. determination.

(6) A method for producing a hypereutectoid toughened iron steel wire according to another aspect of the present invention, which is the method for producing a hypereutectoid toughened iron steel wire according to the above (2), which has the following steps: a step of obtaining a wire after rolling, the steel sheet having the following composition: in terms of unit mass%, containing: C: more than 0.80 to 1.20%, Si: 0.10 to 1.50%, Mn: 0 to 1.00%, P: 0.02 % or less, S: 0.02% or less, Cr: 0 to 1.00%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, Mo: 0 to 0.50%, Ti: 0 to 0.20%, Nb: 0 to 0.20% , V: 0~0.20%, B: 0~0.0050%, Al: 0~0.10%, and Ca: 0~0.05%, and the remaining part is composed of Fe and impurities; 850~1050°C wire is immersed in a step of taking out the wire from the first molten salt bath or the molten lead bath in the first molten salt bath or the molten lead bath at 350 to 450 ° C; at the time of 5 seconds after the removal, the wire starts toughen a step of immersing the wire in a second molten salt bath or a molten lead bath at 530 to 600 ° C at a time point after t _s seconds to t _s seconds before the iron metamorphosis; after the said toughened iron metamorphosis is completely finished, the wire is From the second molten salt bath or melting Bath step taken; and, have been since the second molten salt or molten lead bath, the wire taken out of the wire drawing step of purposes.

t _s =0.05×t _complete

The t _complete is expressed in units of seconds after the wire is continuously immersed in the first molten salt bath or the molten lead bath, and the time from the deformation of the wire to the end of the deformation of the wire is completed.

(7) The method for producing a hypereutectoid toughened iron steel wire according to the above (6), wherein the wire is immersed in the first molten salt bath or the molten lead bath for 10 to 40 seconds.

(8) The manufacturer of the hypereutectoid toughened iron steel wire as described in the above (6) In the above method, in the first molten salt bath or the molten lead bath, the aforementioned time when the wire rod starts to deform into the tough iron can be determined by examining the reheating of the wire.

(9) A method for producing a hypereutectoid toughened iron steel wire according to another aspect of the present invention, which is the method for producing a hypereutectoid toughened iron steel wire according to the above (2), which has the following steps: a step of preparing a steel wire by drawing a wire obtained by rolling, the steel sheet having the following composition: in terms of unit mass%, containing: C: greater than 0.80 to 1.20%, Si: 0.10 to 1.50%, Mn: 0 to 1.00%, P: 0 to 0.02%, S: 0 to 0.02%, Cr: 0 to 1.00%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, Mo: 0 to 0.50%, Ti :0~0.20%, Nb:0~0.20%, V:0~0.20%, B:0~0.0050%, Al:0~0.10%, and Ca:0~0.05%, and the rest is made of Fe and impurities The step of immersing the steel wire at 850 to 1050 ° C in a first molten salt bath or a molten lead bath at 350 to 450 ° C, and then taking out the steel wire from the first molten salt bath or the molten lead bath The second steel salt bath is immersed in a second molten salt bath at 530-600 ° C at a time point within 5 seconds after the extraction and at a time point after t _s seconds to t _s seconds before the steel wire begins to toughen the iron metamorphosis. a step in the molten lead bath; and, in the foregoing, the toughened iron metamorphosis is completely ended The aforementioned steel wire from the second bath of molten lead or molten salt bath of the extraction step.

t _s =0.05×t _complete

The t _complete is expressed in units of seconds after the wire is continuously immersed in the first molten salt bath or the molten lead bath, and the time from the deformation of the wire to the end of the deformation of the wire is completed.

(10) Manufacture of a hypereutectoid toughened iron steel wire as described in the above (9) In the method, when the steel wire is immersed in the first molten salt bath or the molten lead bath, the elapsed time between the time when the steel wire is immersed in the second molten salt bath or the molten lead bath may be 10 ~40 seconds.

(11) The method for producing a hypereutectoid toughened iron steel wire according to the above (9), wherein the first molten salt bath or the molten lead bath may be borrowed from the time when the steel wire starts to deform into a tough iron It is determined by detecting the reheating of the aforementioned steel wire.

(12) The method for producing a hypereutectoid toughened iron steel wire according to any one of the above (9) to (11), wherein a pair of the molten iron steel wire may be taken out from the second molten salt bath or the molten lead bath. The aforementioned steel wire is subjected to the step of drawing the wire.

According to the present invention, it is possible to obtain a lower tensile strength and a higher ductility than the conventional wave iron wire, and the difference in tensile strength is smaller than that of the conventional tough iron wire. The occurrence of breakage can be suppressed when the wire of the present invention is bundled or in a state in which the wire of the present invention is bundled. Further, the workability of the wire rod of the present invention and the workability of the steel wire of the present invention obtained by wire drawing the wire material are good. Therefore, according to the present invention, it is possible to provide a wire for a hypereutectoid toughened iron steel wire having excellent wire drawing characteristics and delayed fracture resistance, a hypereutectoid toughened iron steel wire produced using the wire, and stably producing the wire. And other manufacturing methods.

1‧‧‧Wire section

2‧‧‧Photographing area

11‧‧‧ Central Department

12‧‧‧ Surface Department

13‧‧‧Intermediate

Fig. 1 is a view for explaining heat treatment conditions in a method for producing a wire according to an embodiment of the present invention.

Fig. 2 is a view showing an example of the relationship between the tensile strength TS (N/mm ² ) and the C content (% by mass) of the wire rod according to the embodiment of the present invention.

Fig. 3 is a view showing the relationship between the heat treatment conditions and the tensile strength unevenness of the wire in the method for producing a wire according to an embodiment of the present invention.

Fig. 4 is a flow chart showing a method of manufacturing a wire or a steel wire according to an embodiment of the present invention.

Fig. 5 is a flow chart showing a method of manufacturing a steel wire according to another embodiment of the present invention.

Fig. 6 is a view showing a method of obtaining an area ratio of toughened iron.

Fig. 7 is a schematic view showing the shape of a wire to be immersed in a molten salt bath or a molten lead bath.

Form for implementing the invention

Hereinafter, embodiments of the present invention will be described.

A wire for a hypereutectoid toughened iron steel wire which is excellent in the wire drawing characteristics and the delayed breaking resistance of the present embodiment (hereinafter referred to as "the wire material of the present embodiment").

The wire rod of the present embodiment has a composition of C: more than 0.80 to 1.20%, Si: 0.10 to 1.50%, Mn: 0 to 1.00%, P: 0 to 0.02%, and S: 0 in terms of unit mass%. ~0.02%, Cr: 0~1.00%, Ni: 0~1.00%, Cu: 0~1.00%, Mo: 0~0.50%, Ti: 0~0.20%, Nb: 0~0.20%, V: 0~ 0.20%, B: 0~0.0050%, Al: 0~0.10%, and Ca: 0~0.05%, and the remaining part is composed of Fe and impurities, by cutting the wire of 3200mm in length into 8 pieces of the same When the test piece of the length of 400 mm is produced, the average tensile strength TS of each of the test pieces satisfies the following formula 1 in units of N/mm ² , and each of the aforementioned tensile strengths of each of the test pieces The difference between the maximum value and the minimum value is 50 N/mm ² or less, and the average cross-sectional reduction value RA of each of the test pieces satisfies the following Expression 2 in units of %.

[TS]≦810×[C]+475‧‧‧(Form 1)

[RA]≧-0.083×[TS]+154‧‧‧(Form 2)

Here, [C] is the C content of the wire indicated by unit mass%, and [TS] is the average tensile strength TS expressed by the unit N/mm ² .

First, the component composition of the wire rod of the present embodiment will be described. Hereinafter, the unit "%" means "% by mass".

C: greater than 0.80 to 1.20%

C is an element that increases the hardenability and tensile strength of the wire. By increasing the hardenability of the wire, the main structure of the wire will become toughened iron. When the C content is more than 0.80%, the desired hardenability and tensile strength can be obtained. On the other hand, when the C content is more than 1.20%, the pre-eutectoid snow carbon is generated, and the wire is easily broken when the wire is drawn. Therefore, in order to suppress the formation of Xueming carbon iron before the eutectoid, the upper limit of the C content is set to 1.20%. In order to more easily form the toughened iron, the lower limit of the C content may be set to 0.85%, 0.90%, or 0.95%. Further, when the tensile strength is too high, since the wire is more likely to be affected by the delayed fracture, the lower limit of the C content may be set to 1.15%, 1.10%, or 1.05%.

Si: 0.10~1.50%

The Si system is an element that increases the tensile strength of the wire. Further, Si is an element having a function as a deoxidizer. When the Si content is less than 0.10%, the above effect is not obtained, so the lower limit of the Si content is made 0.10%. However, Si in hypereutectoid steel will promote the precipitation of ferrite iron before eutectoid precipitation. Before the eutectoid, the ferrite iron has doubts about the disconnection when the wire is drawn. In addition, Si also has a pull wire added to the hypereutectoid steel. Doubts about the decline in processing limits. Therefore, the upper limit of the Si content is set to 1.50%. In order to further improve the above effect of Si, the lower limit of the Si content may be set to 0.15%, 0.20%, or 0.25%. Further, in order to facilitate the drawing process, the upper limit of the Si content may be set to 1.45%, 1.40%, or 1.35%.

Mn: 0~1.00%

The wire of the present embodiment does not need to contain Mn. Therefore, the lower limit of the Mn content of the wire rod of the present embodiment is 0%. However, Mn has an effect of improving the strength of the wire by improving the hardenability of the wire. Further, Mn is the same as Si and has an element acting as a deoxidizing agent. Therefore, it is also possible to contain Mn in the wire as needed. When the Mn content is more than 1.00%, the hardenability in the segregation portion of Mn is increased, and the time until the end of the metamorphosis becomes long. In other words, at this time, the hardenability of the wire becomes inconsistent, and the granulated iron is formed at a place where the hardenability is high, and the slab iron is a cause of disconnection during wire drawing. Therefore, the upper limit of the Mn content needs to be set to 1.00%. Further, in order to further improve the wire drawing characteristics, the upper limit of the Mn content may be set to 0.90% or 0.80%. The lower limit of the Mn content is 0%, but in order to obtain the above effect, the lower limit of the Mn content is preferably 0.20%, preferably 0.40%.

P: 0~0.02%

S: 0~0.02%

P and S are not pure elements. When there is a large amount of P and S in the wire, the ductility of the wire will decrease. Therefore, the upper limits of P and S are both 0.02%. The upper limit of the P content and the S content is preferably 0.01%, preferably 0.005%. The P content and the S content are preferably as small as possible, so the lower limit of the P content and the S content is 0%. However, reducing the content of these elements to less than 0.001% will result in wire rods. The manufacturing cost has increased. Therefore, in practical steel, the lower limit of the P content and the S content is usually set to 0.001%.

In addition to the above-described elements, the wire material of the present embodiment may appropriately contain Cr, Ni, Cu, Mo, Ti, Nb, V, B, Al, and Ca within a range that does not inhibit the wire properties of the present embodiment. However, it is not necessary to contain these elements, so the lower limit of the content of these elements is 0%.

Cr: 0~1.00%

The Cr system enhances the hardenability of the wire, thereby promoting the transformation of the iron metamorphic element. When the Cr content is more than 1.00%, the time required from the start of the metamorphosis to the end of the metamorphosis becomes long, and the heat treatment time until the completion of the transformation of the toughened iron becomes long, which is not preferable. Further, similarly to Mn, Cr greater than 1.00% also has doubts about the formation of granulated iron in the wire. Therefore, the upper limit of the Cr content is set to 1.00%. The Cr content is preferably 0.50% or less, more preferably 0.30% or less. The lower limit of the Cr content is 0%, but in order to obtain the above effects, it may contain 0.01% or more, preferably 0.05% or more of Cr.

Ni: 0~1.00%

Like Cr, Ni enhances the hardenability of the wire, thereby promoting the transformation of the iron metamorphic element. When the Ni content is more than 1.00%, the ductility of the ferrite iron phase will decrease. Therefore, the upper limit of the Ni content is set to 1.00%. The Ni content is preferably 0.70% or less, more preferably 0.50% or less. The lower limit of the Ni content is 0%. In order to obtain the above effects, Ni may preferably be contained in an amount of 0.05% or more, preferably 0.10% or more.

Cu: 0~1.00%

Cu is an element that enhances the corrosion fatigue properties of the wire. Cu content is greater than At 1.00%, the ductility of the ferrite iron in the toughened iron decreases. Therefore, the upper limit of the Cu content is set to 1.00%. The Cu content is preferably 0.70% or less, more preferably 0.50% or less. The lower limit of the Cu content is 0%, but in order to obtain the above effects, Cu may be contained in an amount of preferably 0.05% or more, preferably 0.10% or more.

Mo: 0~0.50%

Mo is an element that enhances the hardenability of the wire. When the Mo content is more than 0.50%, the hardenability of the wire is excessively increased, and there is a fear that the micro-separation iron is precipitated in the Mo segregation portion. The micro-mass loose iron has a situation in which the ductility of the wire is lowered. Therefore, the upper limit of the Mo content is set to 0.50%. The Mo content is preferably 0.30% or less, more preferably 0.10% or less. The lower limit of the Mo content is 0%, but in order to obtain the above effects, it may preferably be 0.01% or more, preferably 0.03% or more.

Ti: 0~0.20%

Nb: 0~0.20%

V: 0~0.20%

Ti, Nb, and V can refine the γ particle diameter of the heated wire. At this time, since the structure formed when the wire is cooled is refined, the toughness of the wire is improved. On the other hand, when the content of Ti, Nb, and V is more than 0.20%, the characteristics of the wire of the present embodiment are adversely affected. Therefore, the upper limit of the contents of Ti, Nb, and V is set to 0.20%. The content of Ti, Nb, and V is preferably 0.15% or less, more preferably 0.10% or less. The lower limits of the Ti, Nb, and V contents are all 0%, but for the above effects, the lower limits of the Ti, Nb, and V contents are preferably 0.01%, preferably 0.02%.

B: 0~0.0050%

B can improve the hardenability of the wire. When the B content is more than 0.0050%, the hardenability of the wire material becomes too high, and there is a concern that the ductility of the wire rod is lowered due to the iron in the wire formed in the wire. Therefore, the upper limit of the B content is set to 0.0050%. The B content is preferably 0.0040% or less, more preferably 0.0030% or less. The lower limit of the B content is 0%, but in order to obtain the above effects, it may preferably be 0.0005% or more, more preferably 0.0010% or more.

Al: 0~0.10%

Al acts as an element of the action of the deoxidizer. When the Al content is more than 0.10%, a hard alumina-based inclusion is formed, which will reduce the ductility and linearity of the wire. Therefore, the upper limit of the Al content is set to 0.10%. The Al content is preferably 0.07% or less, more preferably 0.05% or less. The lower limit of the Al content is 0%, but in order to obtain the above effects, it may preferably contain 0.01% or more, preferably 0.02% or more of Al.

Ca: 0~0.05%

Ca improves the resistance to delayed breaking of the wire by adjusting the MnS form of the inclusions in the wire. However, when the Ca content is more than 0.05%, Ca will generate coarse inclusions, whereby the resistance to delayed fracture of the wire is lowered. Therefore, the upper limit of the Ca content is set to 0.05%. The Ca content is preferably 0.04% or less, more preferably 0.03% or less. The lower limit of the Ca content is 0%, but in order to obtain the above effects, it may preferably contain 0.001% or more, preferably 0.005% or more of Ca.

The remainder of the component composition of the wire rod of the present embodiment is composed of Fe and impurities. An impurity is a component that is mixed with raw materials such as ore or scrap, or various factors of a manufacturing step when industrially producing steel. It is allowed to be within a range that does not adversely affect the wire of the present embodiment.

Next, the metal structure of the wire rod of the present embodiment will be described.

Toughened iron: 90~100 area%

The metal structure of the wire rod of the present embodiment contains 90 to 100 area% of toughened iron. A wire having a toughness of 90 to 100% of the metal structure (toughened iron wire) has a wire drawing property superior to that of a metal wire mainly composed of a wave of iron (Bulaite wire). Moreover, the swarf carbon iron contained in the toughened iron is finer than the swarf carbon iron contained in the stellite iron, so when the composition of the same toughened iron wire and the ferritic wire is compared, the toughened iron wire is The tensile strength is lower than the tensile strength of the Whale wire. When the tensile strength of the wire is low, the wire, and the steel wire obtained by the wire drawing process have high ductility, wire drawing characteristics, and workability. In order to further enhance these characteristics, the lower limit of the toughening iron content may be set to 95 area% or 98 area%. In addition to the toughening iron, the metal structure of the wire may contain, for example, microscopic granulated iron (MA), pre-eutectoid stellite, and the like. This may be allowed to be contained as long as the content of the toughening iron is 90 area% or more.

The content of the toughened iron can be obtained by observing the cross section of the wire perpendicular to the direction of the wire. An example of a method for determining the toughening iron content is as follows. First, a metal structure image is obtained at a plurality of cross sections of the wire perpendicular to the wire drawing direction. Next, the average value of the area ratio of the toughened iron of each metal structure image was obtained. The photographing area where the metal tissue image is obtained is not particularly limited. For example, as shown in FIG. 6, the center portion 11 of the wire cross section 1 perpendicular to the wire drawing direction, the surface layer portion 12, and the intermediate portion 13 of the 1/4 depth region of the wire diameter are included. It is preferable to separate the four shooting areas 2 as much as possible. The method for obtaining a metal structure image is not particularly limited. For example, it is preferable to photograph a metal tissue image at a magnification of 1000 times using an SEM (Scanning Electron Microscope). The method of discriminating the toughened iron in the metal structure image is not particularly limited. In view of the composition of the composition, since the wire rod which can be regarded as the embodiment does not include the structure of Bora iron, 麻田散铁 (including microscopic 麻田散铁), pre-eutectoid stellite, and toughened iron, In the metal structure image of the wire rod of the embodiment, a structure other than the pulverized iron, the granulated iron, and the pre-eutectoid stellite may be used as the toughened iron.

Next, the mechanical properties of the wire rod of the present embodiment will be described.

Average tensile strength of wire: TS: 810 × [C] + 475N / mm ² or less

The mechanical properties of the wire of the present embodiment can be evaluated by measuring the characteristics of eight test pieces of 400 mm length which are obtained by cutting a wire having a length of 3,200 mm into eight pieces having the same length. The average value of the tensile strengths of the above eight test pieces was defined as the average tensile strength TS of the wire. The average tensile strength TS of the wire rod of the present embodiment satisfies the following formula 1.

[TS]≦810×[C]+475‧‧‧(1)

Here, [C] is the C content of the wire expressed in units of mass%, and [TS] is the average tensile strength TS expressed in units of N/mm ² .

The main factor for increasing the tensile strength of the wire is the C content of the wire and the heat treatment conditions for the wire. The increase in tensile strength due to the C content of the wire does not cause uneven tensile strength of the wire. This is because the increase in tensile strength as the C content increases is uniformly generated by the entire wire. On the other hand, the heat treatment caused by the manufacture of the wire An increase in the tensile strength of the condition has a concern that the tensile strength of the wire is not uniform. In particular, when the diameter of the wire is small, the heat capacity per unit length of the wire is small, and the temperature distribution in the longitudinal direction of the wire becomes large. Therefore, it is not easy to uniformly heat the entire wire, and unevenness in tensile strength is likely to occur. The greater the effect of the heat treatment on the tensile strength, the greater the unevenness of the tensile strength. When the tensile strength of the wire is uneven, the machining of the wire and the steel wire is uneven, and the machining of the wire and the steel wire becomes difficult. Further, at this time, the tensile strength of the wire is likely to be affected by delayed fracture (hydrogen embrittlement), and breakage occurs.

In view of the above, the average tensile strength of the wire of the present embodiment needs to be lower than the upper limit defined by the C content alone. The inventors of the present invention defined the upper limit of the average tensile strength TS by the above formula 1.

The coefficients "810" and "475" of the above formula 1 are coefficients obtained by the inventors of the present invention by using a wire having an experimental C content of more than 0.80%, that is, a wire having a C content larger than the point of the eutectoid. The inventors have observed that the average tensile strength TS of the wire is greater than the upper limit specified by the formula 1 (that is, when the average tensile strength relative to the C content is too high), the tensile strength due to the heat treatment The effect is raised to an inappropriate level, so that the unevenness of the tensile strength of the wire becomes large, thereby impairing the stability of the machining process and easily causing breakage. At this time, the heat treatment conditions at the time of manufacturing the wire rod were not appropriate, and therefore, it was found that the tensile strength of the wire rod was unevenly increased.

Fig. 2 shows an example of the relationship between the average tensile strength TS (N/mm ² ) and the C content (% by mass). As can be seen from the figure, the average tensile strength TS of the wire of the present embodiment is in the region of "[TS] ≦ 810 × [C] + 475".

The lower limit of the tensile strength of the wire is not particularly limited. However, a certain degree of tensile strength is usually required for the wire system used in the industry. When the average tensile strength of the wire is too low relative to the C content, it will not be easy to use the wire industrially. Therefore, the average tensile strength of the wire rod of the present embodiment can be defined by the following formula 1', formula 1", or formula 1"'.

810×[C]+425≦[TS]≦810×[C]+475‧‧‧(式1’)

810×[C]+435≦[TS]≦810×[C]+475‧‧‧(式1”)

810×[C]+445≦[TS]≦810×[C]+475‧‧‧(式1''')

Average cross-sectional reduction of wire: RA: -0.083 × TS + 154 or more

The evaluation of the mechanical properties of the wire rod of the present embodiment was carried out by measuring the characteristics of eight test pieces of 400 mm in length which were obtained by cutting a wire having a length of 3,200 mm into eight pieces having the same length. The average of the cross-sectional reduction of the above eight test pieces is defined as the average cross-sectional reduction value RA of the wire. The average cross-sectional reduction value RA of the wire rod of the present embodiment satisfies the following formula 2.

[RA]≧-0.083×[TS]+154‧‧‧(Form 2)

Here, [TS] is an average tensile strength TS expressed in units of N/mm ² .

Further, in the wire rod of the present embodiment, the lower limit value of the average section reduction value RA is limited to the lower limit value calculated from the average tensile strength TS.

The coefficient "-0.083" and "154" of the above formula 2 are coefficients obtained by the inventors of the present invention by experimentally investigating the average tensile strength and the average reduction value of various wires in the region of the hypereutectoid region. . The cross-sectional reduction value of the wire obtained by the production method of the present embodiment, which will be described later, has at least an average reduction value of "-0.083 × [TS] + 154" or more. Average section The reduction value is greater than the average reduction in the average cross-section of the incoming wire. On the other hand, the average cross-sectional reduction value of the wire having no toughness of 90 to 100% of the metal structure is lower than the above lower limit. Further, the metal structure is mainly composed of toughened iron, but the average reduction in the value of the toughness of the wire obtained by the Worthite iron in the supercooled state before the start of the toughening iron metamorphosis is also lower than the above. lower limit.

The difference in tensile strength of the wire: the difference between the maximum and minimum of each tensile strength of the eight test pieces is 50 N/mm ² or less

The evaluation of the mechanical properties of the wire rod of the present embodiment was carried out by measuring the characteristics of eight test pieces of 400 mm in length which were obtained by cutting a wire having a length of 3,200 mm into eight pieces having the same length. In the wire rod of the present embodiment, the difference between the maximum value and the minimum value of each of the tensile strengths of the respective test pieces is defined as the difference amount of the tensile strength of the wire rod. The difference in tensile strength of the wire rod of the present embodiment is 50 N/mm ² or less.

When the tensile strength of the wire is large, the workability of the wire and the steel wire obtained by wire drawing the wire will be small. When the difference in tensile strength of the wire is more than 50 N/mm ² , it is not easy to process the wire under fixed conditions, and the steel wire obtained by drawing the wire. Further, at this time, the tensile strength of the wire is likely to be affected by delayed fracture (hydrogen embrittlement), and breakage occurs. In order to facilitate the processing of the wire and the steel wire, and to prevent the occurrence of the breakage of the wire, the difference in the tensile strength of the wire may be 45 N/mm ² or less, 40 N/mm ² or less, 35 N/mm ² or less, or 30 N. /mm ² or less.

The diameter of the wire rod of the present embodiment is not particularly specified. However, in order to further suppress the unevenness of the tensile strength of the wire, the wire diameter can also be set to 3.5~16.0mm. As described above, when the wire diameter is less than 3.5 mm, the heat capacity per unit of the wire is small, and the temperature distribution in the longitudinal direction of the wire becomes large. Therefore, it is not easy to perform uniform heat treatment of the entire wire, and unevenness in tensile strength is likely to occur. On the other hand, when the wire diameter is larger than 16.0 mm, it is difficult to uniformly cool the center portion and the surface portion of the wire rod, and it is difficult to make the metal structure of the center portion of the wire material into a predetermined one.

Next, a method of manufacturing the wire rod and the steel wire according to the present embodiment (hereinafter referred to as "the manufacturing method of the present embodiment") will be described.

As shown in Fig. 4, the method for producing a wire rod according to the present embodiment includes (a) a step of rolling a steel sheet having the composition of the wire material of the above-described embodiment to obtain a wire, and (b) a wire of 850 to 1050 ° C. Immersed in a first molten salt bath or a molten lead bath at 350 to 450 ° C, followed by a step of taking out the wire from the first molten salt bath or the molten lead bath, and (c) at a time point within 5 seconds from the time of taking out and the wire The step of immersing the wire in the second molten salt bath or the molten lead bath at 530-600 ° C, and (d) completely deforming the toughened iron, at the time after t _s seconds to t _s seconds before the toughness of the iron metamorphosis After the completion, the wire is taken out from the second molten salt bath or the molten lead bath. t _s can be obtained by the following formula 3.

t _s =0.05×t _complete ‧‧‧(式3)

The t _complete is expressed in units of seconds after the wire is continuously immersed in the first molten salt bath or the molten lead bath, and the time from the transformation of the wire to the end of the transformation of the iron to the end is completed. As shown in Fig. 4, in addition to the above (a) to (d), the method for producing a hypereutectic toughened iron steel wire according to the present embodiment has a wire rod immersed in a first molten salt bath or a molten lead bath. The step of obtaining a steel wire after the wire drawing process. Further, as shown in Fig. 5, in the method for producing a hypereutectoid toughened iron steel wire according to another embodiment of the present invention, in addition to the above (a) to (d), the (e) pair has been subjected to the second molten salt bath. Or the wire drawn from the molten lead bath is subjected to a wire drawing process. In addition, in FIG. 4 and FIG. 5, only "molten salt bath or molten lead bath" is described as "bath". Thereafter, the wire starts to become tough iron metamorphosis seconds ago ~ t _s s t _s after the time point of the second wire is immersed in a molten salt bath or in a molten lead bath, described as "the ductile iron wire begins to substantially simultaneously the metamorphosis The wire is immersed in the second molten salt bath or the molten lead bath.

The heat treatment of the production method of this embodiment is shown in Fig. 1 . In the figure, the arrow marked with the symbol (b) indicates that the wire rod of 850 to 1050 ° C is immersed in the first molten salt bath or the molten lead bath at a temperature T ₁ in the range of 350 to 450 ° C, and then taken out, that is, the above (b) ). (b) The center wire is maintained at the temperature T ₁ , taken out, and then transferred to the second molten salt bath or the molten lead bath. In the figure, t ₁ shows the time during which the wire material is immersed in the first molten salt bath or the molten lead bath, and the time during which the wire material is transferred from the first molten salt bath or the molten lead bath to the second molten salt bath or the molten lead bath. In total, (i.e., the time from when the wire is immersed in the first molten salt bath or the molten lead bath to when the wire is immersed in the second molten salt bath or the molten lead bath). In the figure, the arrow marked with the symbol (c) is shown in the second molten salt bath or melted by immersing the wire in a temperature range of 530 to 600 ° C (T ₁ + ΔT) substantially simultaneously with the start of the toughening iron metamorphosis. Lead bath, ie (c) above. In the figure, the arrow marked with the symbol (d) indicates that the wire is maintained in the second molten salt bath or the molten lead bath until the toughened iron metamorphosis is completely completed, that is, the above (d).

Temperature of wire immersed in the first molten salt bath or molten lead bath: 850~1050 °C

In the method for producing a wire rod according to the present embodiment, first, the rolling has the present A steel sheet having a wire component composition of the embodiment is obtained as a wire. Next, the wire is immersed in a first molten salt bath or a molten lead bath. Between the rolling and the impregnation, the wire can be temporarily cooled, followed by reheating, or it can be cooled and reheated between rolling and dipping. Moreover, the wire can be drawn between the rolling and the dipping. In either case, the temperature of the wire immersed in the first molten salt bath or the molten lead bath is 850 to 1050 °C. Usually, since the temperature of the wire after rolling is 1050 ° C or lower, the wire after rolling or the wire after the wire is directly immersed in the first molten salt bath or the molten lead bath (that is, without cooling and reheating) In the case of impregnation, the upper limit of the temperature of the impregnated wire or steel wire is substantially 1050 °C. Further, the wire after the rolling or the wire after the wire is temporarily cooled, and then immersed in the first molten salt bath or the molten lead bath after heating, or may be immersed in the first molten salt bath or the molten lead bath. The upper limit of the temperature of the wire or steel wire is set to 1050 °C. Because there is no benefit of heating the wire or steel wire above 1050 °C. When the temperature of the wire or steel wire immersed in the first molten salt bath or the molten lead bath is less than 850 ° C, the steel wire or the steel wire is not sufficiently quenched, so that it is immersed in the first molten salt bath or the molten lead bath. The lower limit of the temperature of the wire or steel wire is set to 850 °C. In addition, when the wire is drawn between the rolling and the immersion, the "wire" is appropriately referred to as "steel wire" in the description of the subsequent steps.

Temperature of the first molten salt bath or molten lead bath: 350~450°C

In the method for producing a wire rod of the present embodiment, the wire rod of 850 to 1050 ° C is immersed in the first molten salt bath or the molten lead bath to be rapidly cooled (Fig. 1 (b)). The temperature T ₁ of the first molten salt bath or the molten lead bath is 350 to 450 °C. With this rapid cooling, the metal structure of the wire becomes a supercooled Worthite iron. When the wire is held isothermally in this state, the Worthite iron in the supercooled state begins to become tough and iron metamorphosis.

When the temperature T _{1 of the} first molten salt bath or the molten lead bath is more than 450 ° C, the cooling rate of the wire is lowered, and the metal structure of the wire is subjected to a toughening iron transformation before the Worth iron which is in a supercooled state. At this time, the tensile strength of the wire will decrease, but the pre-eutectoid snowy carbon will precipitate in the wire. Pre-eutectification of the former Xueming carbon iron will deteriorate the wire drawing characteristics of the wire. Therefore, in order to rapidly cool the wire, the temperature T _{1 of the} first molten salt bath or the molten lead bath needs to be 450 ° C or lower. On the other hand, when the temperature T _{1 of the} first molten salt bath or the molten lead bath is less than 350 ° C, there is a concern that the first molten salt bath or the molten lead bath is solidified. The time during which the wire is immersed in the first molten salt bath or the molten lead bath is appropriately adjusted so that the wire can be immersed in the second molten salt bath or the molten lead bath as required.

When the wire is immersed in the second molten salt bath or the molten lead bath: the time point within 5 seconds after the wire is taken out from the first molten salt bath or the molten lead bath, and the wire starts toughen the iron metamorphosis t _s seconds before ~t _s Time after seconds

A method of manufacturing a wire form of the present embodiment, since the temperature T in the molten salt bath ₁₁ of molten lead bath or removed within 5 seconds after the point of wire, and the wire begins to ductile iron metamorphosis seconds ago t _s ~ t _s s At the later time, the wire was immersed in a second molten salt bath or a molten lead bath at a temperature T ₂ .

The inventors of the present invention manufactured a wire by changing various manufacturing conditions of temperature T ₁ of t ₁ and a first molten salt bath or a molten lead bath, and measured the amount of difference in tensile strength of the wire, the t ₁ is When the wire is immersed in the first molten salt bath or the molten lead bath, the time until the wire is immersed in the second molten salt bath or the molten lead bath (that is, the wire is immersed in the first molten salt bath or the molten lead bath) The time is the total time of the time when the wire is transferred from the first molten salt bath or the molten lead bath to the second molten salt bath or the molten lead bath. Using the data thus obtained, the relationship between the temperature T ₁ , the time t ₁ , and the difference in tensile strength was investigated. As a result, the result as shown in Fig. 3 was obtained.

The curve marked with the symbol "S" in Fig. 3 is a graph showing the temperature and time at which the toughness iron metamorphosis starts (hereinafter referred to as an S curve). This curve varies with the composition of the wire. The data points shown in Fig. 3 indicate the temperature T ₁ and time t ₁ when the wire of the data point is manufactured. The wire located at the data point on the left side of the curve is a wire immersed in the second molten salt bath or the molten lead bath before the transformation of the toughened iron, and the wire located at the data point on the right side of the curve is immersed in the transformation of the toughened iron. A wire of a second molten salt bath or a molten lead bath. In Fig. 3, the dotted line described in relation to each data point shows the heat history of the wire of each data point. The difference in the tensile strength of the wire with the data point type "BAD" is greater than 50 N/mm ² , and the difference in the tensile strength of the wire with the data point type "GOOD" is greater than 40 N/mm ² and 50 N/mm ² or less. The difference in the tensile strength of the wire having the data point type "VERY GOOD" is 40 N/mm ² or less.

As shown in FIG. 3, the amount of difference in tensile strength of the wire near the data point of the curve (that is, the wire immersed in the second molten salt bath or the molten lead bath substantially simultaneously with the start of the toughened iron metamorphosis) is small.

Appropriately set the time t _1, so that the wire start to toughen iron metamorphosis T _s seconds ago ~ t _s after the second time point, the second wire is immersed in a molten salt bath or the molten lead bath. t _s is a value obtained by the formula 3 shown below.

t _s =0.05×t _complete ‧‧‧(式3)

The t _complete is expressed in units of seconds after the wire is continuously immersed in the first molten salt bath or the molten lead bath, and the time from the transformation of the wire to the end of the transformation of the iron to the end is completed.

The time and t _s after the wire is immersed in the first molten salt bath or the molten lead bath until the wire starts toughen the iron metamorphosis, with the S curve corresponding to the composition of the wire, and the first molten salt bath or the molten lead bath The temperature is determined. Therefore, the time t _{1 is} obtained by simulation and/or preliminary experiment based on the composition of the wire material and the temperature of the first molten salt bath or the molten lead bath. Further, as will be described later, by detecting the reheating of the wire rod, the time from the immersion of the wire rod in the first molten salt bath or the molten lead bath to the time when the wire starts to become tough and iron is determined. Thus, before the wire manufacturing, by the method described above can also be used to determine in advance the time t ₁ investigation.

The reason why the wire material is immersed in the second molten salt bath or the molten lead bath substantially simultaneously with the transformation of the wire into the second molten salt bath or the molten lead bath can suppress the unevenness of the tensile strength of the wire. However, the reason is the following explanation. When it is immersed in the first molten salt bath or the molten lead bath, or transferred to the second molten salt bath or the molten lead bath, the strands are transformed into a tough iron, which is immersed in the first heat due to reheating (allergic heat). The temperature of the wire increases between the molten salt bath or the molten lead bath or in the second molten salt bath or the molten lead bath. At this time, the rise in the temperature of the wire material causes a non-uniform concern. This is because, when the wire is heat-treated in a molten salt bath or a molten lead bath, the wire is taken out in a molten salt bath or a molten lead bath, for example, in a coil shape as shown in FIG. When the wire rod in the heat treatment has a coil shape, the temperature at which the portions where the wires overlap each other due to reheating is increased more than the other portions. This is because the cooling effect by the first molten salt bath or the molten lead bath is less likely to reach the portion where the wires overlap each other. Thus, due to the above-mentioned times t ₁ becomes long, the wire delay the start of heating, due to the rise in temperature of the wires of the unevenly, resulting in unevenness of the tensile strength of the wire. In addition, the wire shape is formed into a coil shape during heat treatment, which is indispensable for improving the manufacturing efficiency of the wire. If there is no particular reason, it is not necessary to immerse the wire in a molten salt bath or a molten lead bath in a state in which the wires do not overlap each other. On the other hand, to the times t ₁ becomes shorter, the start toughening abnormal iron is greater than t _s seconds ago the wire was immersed in a second bath of molten lead or molten salt bath, the early start due to abnormal, so that abnormal start temperature becomes higher. At this time, the strength of the wire is increased and the ductility of the wire is lowered.

For the above reasons, it is preferable to immerse the wire in the second molten salt bath or the molten lead bath at the same time as the wire starts to be toughened and deformed. However, the inventors of the present invention have observed from the experimental observation that in the wire rod in which the transformation of the toughened iron is fast and the temperature rise due to reheating is large, if the time between the impregnation of the wire and the start of the deformation of the wire is 5 seconds or less, The unevenness of the tensile strength of the wire can be sufficiently suppressed, and in the wire in which the temperature of the toughened iron is slow and the temperature rises due to reheating is low, the time between the impregnation of the wire and the beginning of the deformation of the wire is greater than 5 Seconds can still suppress unevenness. Based on the knowledge obtained in the observation, in the method for producing a wire according to the present embodiment, the time between the immersion of the wire and the start of the deformation of the wire is defined by the value t _s determined by the speed of the transformation of the toughened iron. Further, in the wire rod of the present embodiment, since t _{complete is} not less than 100 seconds, the upper limit of t _s may be set to 5 seconds.

In general, the elapsed time t ₁ between the point when the wire is immersed in the first molten salt bath or the molten lead bath and the time when the wire is immersed in the second molten salt bath or the molten lead bath is preferably 10 to 40 seconds. In view of the composition of the wire rod of the present embodiment, when the time t _{1 is} less than 10 seconds or more than 40 seconds, it is difficult to appropriately immerse the wire in the second molten salt bath or the molten lead bath.

In addition to the above, the wire is immersed in the second molten salt bath or the molten lead bath within 5 seconds after the wire is taken out from the first molten salt bath or the molten lead bath. When the wire is taken out from the time of immersion, that is, when the wire transfer time is more than 5 seconds, the wire is immersed in the wire at the same time as the wire starts to become tough and iron due to the temperature fluctuation of the wire between the wires. The second molten salt bath or the molten lead bath system is extremely difficult.

It is also possible to determine the time at which the wire in the first molten salt bath or the molten lead bath starts to transform into a metamorphic iron by examining the reheating (alteration heat) of the wire. The reheating system of the present embodiment is a phenomenon in which the temperature of the wire rod rises due to the transformation of the toughened iron in the wire material. The reheating can be performed by, for example, comparing the temperature of the wire taken out after being immersed in the first molten salt bath or the molten lead bath with the temperature of the first molten salt bath or the molten lead bath. When the temperature of the wire is higher than the temperature of the first molten salt bath or the molten lead bath, it is judged that the wire has reheated. Investigated separately by various changes by re-heat time Degree of wire within the lead bath is immersed in a first molten salt bath or melt, can be obtained by immersing the wire results in the shortest time to re-heat the t _min. The wire can be immersed in the first molten salt bath or the molten lead bath and only after t _min is passed, as the point at which the wire starts to transform the iron into a metamorphic state. In this way, the time at which the toughened iron metamorphosis is started in the wire is previously determined by the reheating, and the wire manufacturing is preferably performed.

Further, when the time of immersing in the first molten salt bath or the molten lead bath is less than 5 seconds, even if the temperature of the wire is higher than that of the first molten salt bath or the molten lead bath, Still can't judge whether the wire has reheated. This is because the temperature of the wire material is not raised by reheating but by insufficient immersion time.

Temperature of the second molten salt bath or molten lead bath: 530~600°C

When the wire is taken out from the second molten salt bath or the molten lead bath: the time after the tough iron is completely terminated

The wire is immersed in the second molten salt bath or the molten lead bath at a temperature T ₂ substantially simultaneously with the beginning of the toughening of the wire. The temperature T ₂ is 530 to 600 ° C. Thereby, the wire is rapidly heated to a temperature of 530 to 600 ° C (Fig. 1 (c)), and the temperature can be maintained until the toughened iron metamorphosis is completely completed. When the wire is rapidly heated to a temperature of 530 to 600 ° C substantially simultaneously with the beginning of the toughening of the wire, the interval of the stellite in the toughened iron becomes large. As a result, the strength of the wire is lowered as compared with the case where the heating is not rapid. When the temperature of the second molten salt bath or the molten lead bath is less than 530 ° C or more than 600 ° C, it takes a long time until the metamorphic iron metamorphosis is completed. Therefore, in order to surely terminate the toughening iron metamorphism in a short period of time, the temperature of the second molten salt bath or the molten lead bath is set to 530 to 600 °C. The heating rate at which the wire is heated to the aforementioned temperature range is not particularly limited. However, in order to shorten the time until the end of the toughened iron metamorphosis, it is preferable to accelerate the heating rate, specifically, 10 to 50 ° C / sec. Such a heating rate can be obtained by dipping the wire into a molten salt bath or a molten lead bath having a residual temperature of 530 to 600 °C. When the wire is taken out from the second molten salt bath or the molten lead bath before the end of the toughened iron metamorphosis, MA is formed in the wire, and this MA has a concern that the workability of the wire is lowered.

After the wire is immersed in the first molten salt bath or the molten lead bath to start the transformation of the tough iron, the wire is maintained in this state, and the growth is fine and tough. Iron organization. The strength of the wire that has a fine toughened iron structure will be higher than that of the wire that is rapidly heated at about the same time as the toughened iron metamorphosis begins. Therefore, in the wire rod of the present embodiment, by rapidly heating the wire rod, the interval between the precipitated swarf carbon iron can be increased, and the strength can be lowered.

In the hypereutectic toughened iron steel wire (hereinafter referred to as "the steel wire of the present embodiment") which is excellent in the delayed fracture resistance of the present embodiment, the wire of the present embodiment having excellent wire drawing characteristics is pulled. Line processor. The wire drawing process is usually a wire drawing process, and the reduction rate is not particularly limited. Since the steel wire according to the present embodiment is excellent in resistance to delayed fracture, the steel wire is greatly expanded in use.

Example

Next, the examples of the present invention will be described, but the conditions of the examples are a conditional example used to confirm the practicability and effects of the present invention, and the present invention is not limited by the conditional examples. The present invention can be obtained using various conditions as long as it can achieve the object of the invention without departing from the gist of the invention.

(Example 1)

The hypereutectoid steel sheets having the composition shown in Table 1 were rolled into the wire diameters shown in Table 2, and the toughened iron metamorphosis was completed under the temperature conditions shown in Table 2. Average tensile strength (N / mm ^2), an average value of reduction of area (%), and the difference in the amount of tensile strength (N / mm ²⁾ was measured after the end of the toughening abnormal iron wire. The average tensile strength of the wire is the average of the tensile strengths of the test pieces of 8 lengths of 400 mm obtained by cutting a wire having a length of 3200 mm into 8 pieces having the same length. The average cross-sectional reduction value of the wire is an average value of the section reduction values of the test pieces of eight lengths of 400 mm which are obtained by cutting a wire having a length of 3,200 mm into eight pieces having the same length. The difference in tensile strength of the wire is the difference between the maximum and minimum tensile strengths of the test pieces of 8 lengths of 400 mm obtained by cutting a wire having a length of 3200 mm into eight pieces having the same length. The measurement results are shown together in Table 2. Further, the heating rate when the wire is immersed in the second molten salt bath or the molten lead bath is 10 to 50 ° C / sec.

In Table 2, T ₀ is a temperature of a wire immersed in a first molten salt bath or a molten lead bath, a temperature of a T ₁ -based first molten salt bath or a molten lead bath, and a t ₁ -type wire is immersed in a first molten salt bath or The time from the inside of the molten lead bath to the time when the wire is immersed in the second molten salt bath or the molten lead bath, and the ΔT is the temperature at which the wire is immersed in the second molten salt bath or the molten lead bath, and the T ₂ second melting The temperature of the salt bath or the molten lead bath, the upper limit of the TS from the C content, and the upper limit of the average tensile strength calculated by the formula 1, the average tensile strength of the TS average (N/mm ² ), and the tensile strength of the TS maximum. The maximum value (N/mm ² ), the minimum value of the TS minimum tensile strength (N/mm ² ), the TS difference is the difference between the TS maximum and the TS minimum (N/mm ² ), and the RA lower limit is the average tensile resistance. The upper limit of the strength and the upper limit of the average reduction of the angle calculated from the equation 2, the average reduction of the RA average (%), the maximum value of the RA reduction (%), and the minimum RA The minimum value (%) of the reduction value of the section and the difference of RA are the difference (%) between the maximum RA and the minimum of RA. In the case of the invention of No. 1 to 7, the immersion time t of the first molten salt bath or the molten lead bath wire can be appropriately selected so that the wire is immersed in the second molten salt bath or the molten lead bath and the tough iron is metamorphosed. Start roughly at the same time. In the comparative example of No. 8, the wire was immersed in the second molten salt bath or the molten lead bath. In the comparative examples of Nos. 9 and 10, the wire was immersed in the second molten salt bath or the molten lead bath after a long period of time after the start of the toughening iron metamorphosis. Further, in Inventive Examples No. 1 to 7, Comparative Example No. 9, and Comparative Example No. 10, the wire was immersed in the second molten salt bath or molten lead within 5 seconds after being taken out from the first molten salt bath or the molten lead bath. Inside the bath.

As is clear from Table 2, in the invention examples of Nos. 1 to 7, the TS average and the RA average satisfy the formulas 1 and 2, and the TS difference amount is 50 N/mm ₂ or less. As a result, in the invention examples of Nos. 1 to 7, the retardation breaking resistance was improved, and no breakage occurred during the binding of the wire and the state of the bundle.

Industrial availability

As described above, according to the present invention, it is possible to provide a wire having a lower strength and a higher ductility than that of the ferritic steel, and it is possible to suppress the breakage of the wire during the binding work or the bundled state, and the wire pull property and the late break resistance are excellent. A wire, a hypereutectoid toughened iron steel wire produced using the wire, and a manufacturing method for stably producing the wire. Thereby, the present invention has high availability in the steel industry.

Claims (12)

A wire material characterized by having the following composition: in terms of unit mass%, containing: C: more than 0.80 to 1.20%, Si: 0.10 to 1.50%, Mn: 0 to 1.00%, P: 0 to 0.02%, S : 0~0.02%, Cr: 0~1.00%, Ni: 0~1.00%, Cu: 0~1.00%, Mo: 0~0.50%, Ti: 0~0.20%, Nb: 0~0.20%, V: 0~0.20%, B: 0~0.0050%, Al: 0~0.10%, and Ca: 0~0.05%, and the remaining part is composed of Fe and impurities; the metal structure contains 90~100 area% of toughened iron When the test piece having a length of 400 mm is produced by cutting a wire having a length of 3200 mm into eight pieces of the same length, the average value TS of the tensile strength of each of the test pieces is satisfied in units of N/mm ² . In the following formula 1, the difference between the maximum value and the minimum value of each of the tensile strengths of the respective test pieces is 50 N/mm ² or less, and the average value RA of the reduction values of the cross-sectional areas of the respective test pieces satisfies the following in % Equation 2, [TS] ≦ 810 × [C] + 475‧ ‧ (Formula 1), [RA] ≧ -0.083 × [TS] + 154‧ ‧ (Formula 2), where [C] The unit content % indicates the C content of the wire, and [TS] is the aforementioned average value of the tensile strength expressed in units of N/mm ² . TS, [RA] is the aforementioned average value RA of the aforementioned reduction in area in units of %. A hypereutectoid toughened iron steel wire characterized by being processed by wire drawing, such as the wire of claim 1. A method for producing a wire, which is a method for producing a wire according to claim 1, characterized by the step of: rolling a steel sheet to obtain a wire, the steel sheet having the following composition: in mass%, Contains: C: greater than 0.80 to 1.20%, Si: 0.10 to 1.50%, Mn: 0 to 1.00%, P: 0 to 0.02%, S: 0 to 0.02%, Cr: 0 to 1.00%, Ni: 0 to 1.00 %, Cu: 0~1.00%, Mo: 0~0.50%, Ti: 0~0.20%, Nb: 0~0.20%, V: 0~0.20%, B: 0~0.0050%, Al: 0~0.10% And Ca: 0 to 0.05%, and the remainder is composed of Fe and impurities; the wire of 850 to 1050 ° C is immersed in a first molten salt bath or a molten lead bath at 350 to 450 ° C, and then the wire is since the first step of the molten salt bath or a bath of molten lead removed; at time of 5 seconds or less removed from the wire and the ductile iron begins to abnormal t _s of seconds ago ~ t _s after the second point, the wire will be immersed a step of the second molten salt bath or the molten lead bath at 530 to 600 ° C; and a step of removing the wire from the second molten salt bath or the molten lead bath after the said toughened iron metamorphosis is completely finished; t _s = 0.05×t _{complet e} ‧ ‧ (3), t _complete is expressed in units of seconds after the wire is continuously immersed in the first molten salt bath or the molten lead bath, and the time from the deformation of the wire to the end of the deformation of the wire is completed. The method for producing a wire according to claim 3, wherein the wire is immersed in the first molten salt bath or the molten lead bath, and the time when the wire is immersed in the second molten salt bath or the molten lead bath After passing The system is 10 to 40 seconds. The method for producing a wire according to claim 3, wherein the point at which the wire rod starts to deform in the first molten salt bath or the molten lead bath is determined by detecting reheating of the wire. A method for producing a hypereutectoid toughened iron steel wire, which is a method for producing a hypereutectoid toughened iron steel wire according to claim 2, characterized in that it has the following steps: a step of rolling a steel sheet to obtain a wire, which The steel sheet has the following composition: in terms of unit mass%, C: more than 0.80 to 1.20%, Si: 0.10 to 1.50%, Mn: 0 to 1.00%, P: 0 to 0.02%, S: 0 to 0.02 %, Cr: 0~1.00%, Ni: 0~1.00%, Cu: 0~1.00%, Mo: 0~0.50%, Ti: 0~0.20%, Nb: 0~0.20%, V: 0~0.20% , B: 0~0.0050%, Al: 0~0.10%, and Ca: 0~0.05%, and the remaining part is composed of Fe and impurities; 850~1050°C wire is immersed in the first of 350~450°C a step of taking out the wire from the molten salt bath or the molten lead bath, and then taking out the wire from the first molten salt bath or the molten lead bath; at a time point within 5 seconds after the above extraction and before the wire starts toughen the iron metamorphosis t _s seconds ago At a time after ~t _s seconds, the wire is immersed in a second molten salt bath or a molten lead bath at 530 to 600 ° C; after the toughened iron metamorphosis is completely completed, the wire is taken from the second molten salt bath or The step of taking out the molten lead bath; Since the wire is of the second molten bath remove the molten lead bath or administration step of wire _{drawing; t s = 0.05 × t complete} , t complete unit in seconds based on the continuous wire was immersed in the melt 1 After the salt bath or the molten lead bath, the time from the metamorphic iron metamorphosis to the end of the wire is started. The method for producing a hypereutectoid toughened iron steel wire according to claim 6, wherein the wire is immersed in the first molten salt bath or the molten lead bath for 10 to 40 seconds. The method for producing a hypereutectoid toughened iron steel wire according to claim 6, wherein the aforementioned first molten salt bath or the molten lead bath is in the aforementioned point of the said toughened iron metamorphosis, and the reheating of the wire is checked To judge. A method for producing a hypereutectoid toughened iron steel wire, which is a method for producing a hypereutectoid toughened iron steel wire according to claim 2, characterized in that the method has the following steps: Pulling a wire obtained by rolling a steel sheet The step of processing to obtain a steel wire having the following composition: in terms of unit mass%, containing: C: greater than 0.80 to 1.20%, Si: 0.10 to 1.50%, Mn: 0 to 1.00%, P: 0~0.02%, S: 0~0.02%, Cr: 0~1.00%, Ni: 0~1.00%, Cu: 0~1.00%, Mo: 0~0.50%, Ti: 0~0.20%, Nb: 0 ~0.20%, V:0~0.20%, B:0~0.0050%, Al:0~0.10%, and Ca:0~0.05%, and the rest is composed of Fe and impurities; 850~1050°C The steel wire is immersed in a first molten salt bath or a molten lead bath at 350 to 450 ° C, and then the step of taking out the steel wire from the first molten salt bath or the molten lead bath; at a time within 5 seconds after the removal of the steel wire and the wire begins to t _s of ductile iron metamorphosis seconds ago ~ t _s after the second point, the steel wire is immersed in the second molten salt bath of 530 ~ 600 ℃ or molten lead bath in the step; and the variations in After the tough iron metamorphosis is completely over, the aforementioned steel wire is from the foregoing a step of taking out the second molten salt bath or the molten lead bath; t _s = 0.05 × t _complete , t _complete is expressed in units of seconds after continuously immersing the steel wire in the first molten salt bath or the molten lead bath, from the steel The line starts the time until the end of the toughened iron metamorphosis. The method for producing a hypereutectoid toughened iron steel wire according to claim 9, wherein the steel wire is immersed in the first molten salt bath or the molten lead bath, and the steel wire is immersed in the second molten salt bath or The elapsed time between the points in the molten lead bath is 10 to 40 seconds. The method for producing a hypereutectoid toughened iron steel wire according to claim 9, wherein the aforementioned steel wire in the first molten salt bath or the molten lead bath starts the aforementioned toughening iron metamorphosis, by detecting the steel wire Reheating to determine. The method for producing a hypereutectoid toughened iron steel wire according to any one of claims 9 to 11, further comprising a pair of the steel wires which have been taken out from the second molten salt bath or the molten lead bath. step.