JP2015067841A - Method of producing wire rod for cold forging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a wire rod for cold forging in which the generation of oblique flaws can be suppressed.SOLUTION: Provided is a method of producing a wire rod for cold forging comprising: a step in which a steel billet comprising 0.01 to 0.30% C and satisfying inequality (1) is prepared; a step in which the steel billet is hot-rolled to produce a wire rod; a step in which the wire rod is spirally formed and is dropt to the surface of a conveyer 5, and the surface temperature of the wire rod when it is dropt to the surface of the conveyer 5 is controlled to 850°C or less; a step in which the wire rod is cooled at the average cooling velocity of 2.5°C/s or more in a meantime in which the surface temperature of the wire rod reaches 600°C, a step in which the wire rod is cooled at the average cooling velocity of 0.5°C/s or less in a meanwhile in which the surface temperature of the wire rod being 600 to 100°C, and a step in which the coil of the wire rod whose surface temperature is 100°C or less is bound at a compressibility ratio of 40% or less: (Al+Ti)/N≥7 (1).

Description

  The present invention relates to a method for manufacturing a wire, and more particularly to a method for manufacturing a wire for cold forging.

  A cold forging wire that is a hot-rolled material may be subjected to pickling and lubrication before cold forging. In this case, the lubricated wire is drawn to produce a steel wire. The steel wire is used for cold forging and formed into a predetermined shape.

  When carbon steel wire with a C content of 0.30% or less is subjected to pickling and lubrication, shallow wrinkles extending obliquely or perpendicularly to the axial direction (rolling direction) of the wire are observed There is. The depth of the wrinkles is about 1/100 to 3/100 mm and does not affect the mechanical characteristics. However, when a plating process is performed on a product after cold forging, only the heel portion is different in color from other portions, and the heel portion may be conspicuous. Such wrinkles are referred to herein as “inclined wrinkles”. In the carbon steel wire described above, it is preferable to suppress the occurrence of inclined wrinkles.

  Japanese Patent Application Laid-Open No. 62-56531 (Patent Document 1) proposes a technique for suppressing inclined wrinkles (referred to as “chicken foot” in Patent Document 1). In this document, the C content is 0.20% or less. After hot rolling a low carbon steel having Al / N of 15 or more, it is gradually cooled at a cooling rate of 3 ° C./second or less. In the examples, the cooling rate after hot rolling is 2 ° C./second.

JP-A 62-56531

  However, even if the wire is manufactured by the manufacturing method of Patent Document 1, the inclined wrinkles may occur.

  The objective of this invention is providing the manufacturing method of the wire for cold forging which can suppress generation | occurrence | production of an inclination flaw.

The manufacturing method of the wire for cold forging by this invention is the mass%, C: 0.01-0.30%, Si: 0.50% or less, Mn: 0.10-1.50%, P: 0 0.050% or less, S: 0.050% or less, Al: 0.020 to 0.100%, N: 0.0100% or less, and Ti: 0 to 0.100%, the formula (1) A step of preparing a steel billet that satisfies the requirements, a step of manufacturing a wire rod by hot rolling the steel billet, and forming the wire rod in a spiral shape and dropping it on the conveyor, and the surface temperature of the wire rod when dropped on the conveyor The step of cooling to 850 ° C. or lower, the step of cooling at an average cooling rate of 2.5 ° C./second or more until the surface temperature of the wire dropped on the conveyor reaches 600 ° C., and the surface temperature of the wire from 600 ° C. A step of cooling at an average cooling rate of 0.5 ° C./second or less between 100 ° C. and surface Degrees comprises a step of coils 100 ° C. or less of the wire, bundling the following compression of 40%.
(Al + Ti) / N ≧ 7 (1)
Here, the content (atomic%) of the corresponding element is substituted for the element symbol in the formula (1). When Ti is not contained, 0 is substituted for Ti in formula (1).

  In the wire manufactured by the method of manufacturing a steel wire for cold forging according to the present invention, the occurrence of inclined wrinkles is suppressed.

  Preferably, in the step of hot rolling the steel billet of the above manufacturing method, the steel billet heated to 1150 ° C. or less is hot rolled.

  In this case, the occurrence of inclined wrinkles is further suppressed.

FIG. 1 is a photographic image showing an example of an inclined flaw generated in a wire for cold forging having a C content of 0.30% or less. FIG. 2 is a functional block diagram of a production line used in the method for producing a cold forging wire according to the present embodiment. FIG. 3 is a flowchart showing the manufacturing process of the method for manufacturing the wire for cold forging according to the present embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  As described above, a plurality of inclined ridges 20 shown in FIG. 1 may be generated on the surface of the carbon steel wire having a C content of 0.30% or less. The inclined rod 20 extends obliquely or perpendicularly to the axial direction (rolling direction) CL of the wire. The depth of the inclined ridge 20 is 1/100 to 3/100 mm. The inclined rod 20 does not affect the mechanical characteristics. However, when pickling and lubrication are performed, the inclined rod 20 is visually confirmed, and if the cold forging and the plating treatment are performed, the inclined rod 20 is further conspicuous.

  The present inventors investigated and examined the inclined ridge 20. As a result, the present inventors obtained the following knowledge.

  There are two factors that cause the inclined ridge 20. One is an inclined wrinkle caused by strain age hardening. The other is an inclined wrinkle resulting from cracking of the scale formed on the surface of the wire.

  Strain age hardening occurs when solute N forms a Cottrell atmosphere around dislocations. Therefore, it is preferable to suppress the solid solution N in order to suppress the inclined wrinkles due to strain age hardening.

  In order to suppress solute N, Al is contained, and Ti is further contained as an optional element. Al and Ti combine with N to form a nitride. If nitride is formed, solid solution N is suppressed. Therefore, strain age hardening is suppressed and inclined wrinkles are suppressed.

  On the other hand, scale cracks occur when strain is applied to the scale formed on the surface of the wire. When the scale is cracked, the degree of corrosion differs between the surface of the wire material where the scale is cracked and peeled during the pickling treatment and the surface of the wire material covered with the scale. Due to this difference in the degree of corrosion, inclined ridges are formed.

  In order to suppress the occurrence of scale cracks, it is only necessary to suppress the strain from being applied to the scale. If the scale thickness is further reduced, scale cracks are less likely to occur.

  In order to reduce the scale thickness, the cooling rate for the wire rod after finish rolling may be increased. However, if the cooling rate is increased, the wire is cooled in a short time, so that the time for forming the nitride of AlN or TiN at a high temperature is insufficient. Therefore, it is preferable to adjust the cooling rate so that the time for forming AlN and TiN at high temperatures can be secured while reducing the scale thickness.

  In this embodiment, when the surface temperature of the wire is between the coiling temperature and 600 ° C., the average cooling rate is 2.5 ° C./second or more, and when the surface temperature is between 600 ° C. and 100 ° C., the average cooling rate is 0.00. Set to 5 ° C / second or less. The scale is promoted to be formed at 600 ° C. or more, but is not so much formed at less than 600 ° C. Accordingly, between the coiling temperature and 600 ° C., the average cooling rate is increased and the generation of scale is suppressed. On the other hand, between 600 ° C. and 100 ° C., the average cooling rate is 0.5 ° C./second or less so that AlN and TiN are sufficiently formed. In this way, by changing the average cooling rate according to the temperature range of the wire, both the scale wrinkles due to scale and the solid wrinkles due to solid solution N are suppressed.

Furthermore, Al and Ti are contained in a large amount relative to N so that Al and Ti can be sufficiently combined with N even at the above average cooling rate. Specifically, the Al content, Ti content, and N content in the steel billet satisfy the formula (1).
(Al + Ti) / N ≧ 7 (1)
Here, the content (atomic%) of the corresponding element is substituted for the element symbol in the formula (1).
When Ti is not contained, “0” is substituted for Ti in formula (1).

  If solid solution N still remains after the above-described steps, if the diffusion rate of solid solution N is suppressed, the generation of inclined soot is suppressed. Therefore, in order to suppress the diffusion rate of solute N, the temperature of the wire coil before binding is lowered.

  Furthermore, even if the scale is thin, it will crack if strain is applied. Therefore, in order to suppress the strain from entering the scale, the compression rate (%) is lowered when the wire coils are bound using the binding device.

  With the above production conditions, it is possible to suppress the occurrence of inclined defects in the cold forging wire having a C content of 0.30% or less. Hereinafter, the manufacturing method of the wire for cold forging by this embodiment is explained in full detail.

[Production line of steel wire for cold forging]
In FIG. 2, an example of the manufacturing line of the wire for cold forging of this Embodiment is shown. Referring to FIG. 2, a production line 10 includes a heating furnace 1, a roughing and intermediate rolling mill 2, a finishing rolling mill 3, a winding device (laying head) 4, a conveyor 5, and a focusing device 6. The conveyor 7 and the bundling device 8 are provided.

  The heating furnace 1 heats a steel billet that is a material for a wire for cold forging. The rough and intermediate rolling mill 2 includes a rough rolling mill and an intermediate rolling mill. The intermediate rolling mill is disposed behind the rough rolling mill. The rough rolling mill includes a plurality of rolling stands arranged in a line. Each rolling stand includes a plurality of rolls. Similarly, the intermediate rolling mill includes a plurality of rolling stands arranged in a row.

  The finishing mill 3 is arranged behind the rough and intermediate rolling mill 2. The finish rolling mill 3 includes a plurality of rolls arranged in a row. The finishing mill 3 increases the roundness of the wire.

  The winding device 4 is also called a laying head and is arranged behind the finishing mill 3. The winding device 4 forms and discharges the wire rod after finish rolling in a spiral shape and drops it onto the conveyor 5.

  The conveyor 5 is a steermore type conveyor, and includes a conveyor and a cooling device. The cooling device is disposed below the conveyor. The conveyor 5 develops the wire formed in a spiral shape by the winding device 4 into a non-concentric circle and cools it on the conveyor while being conveyed.

  The focusing device 6 is arranged at the rear end of the conveyor 5. The focusing device 6 includes a cylinder and a nose cone disposed at the center of the cylinder. The focusing device 6 focuses the wire cooled by the conveyor 5 in a coil shape around the nose cone, thereby forming a wire coil.

  The conveyor 7 is a hook conveyor including a plurality of hooks. The wire coil formed by the converging device 6 is hooked and conveyed. During conveyance on the conveyor 7, the wire coil is cooled while being hung on the hook.

  The bundling device 8 is disposed in the vicinity of the conveyor 7. The bundling device 8 compresses the wire coil in the axial direction and binds the compressed wire coil using a band material.

[Method of manufacturing wire for cold forging]
FIG. 3 is a flowchart showing an example of a method for manufacturing a wire for cold forging according to the embodiment of the present invention. Referring to FIG. 3, the manufacturing method of the present embodiment includes a material preparation step (S1), a hot rolling step (S2), a winding step (S3), a first cooling step (S4), Two cooling processes (S5) and a bundling process (S6) are provided. Hereinafter, each process is explained in full detail.

[Material preparation step (S1)]
In the material preparation step, a steel billet that is a material of the wire is prepared. The chemical composition of the steel billet contains at least the following elements. Hereinafter,% related to elements means mass%.

C: 0.01 to 0.30%
Carbon (C) increases the strength of the steel. If the C content is too low, this effect cannot be obtained. On the other hand, if the C content is too high, the deformation resistance of the steel during cold forging becomes excessively high and cold forgeability is reduced. Therefore, the C content is 0.01 to 0.30%. The upper limit with preferable C content is 0.25%.

Si: 0.50% or less Silicon (Si) is inevitably contained. Si deoxidizes steel. On the other hand, if the Si content is too high, the ferrite is solid-solution strengthened by Si and the cold forgeability is lowered. Therefore, the Si content is 0.50% or less. When Si is used as a deoxidizer, the preferable lower limit of the Si content is 0.01%. The upper limit with preferable Si content is 0.35%.

Mn: 0.10 to 1.50%
Manganese (Mn) increases the hardenability of the steel and increases the strength of the steel. Further, Mn combines with S in the steel to form MnS and enhances the machinability of the steel. If the Mn content is too low, the above effect cannot be obtained. On the other hand, if the Mn content is too high, the hardness of the steel becomes excessively high and the cold forgeability decreases. Therefore, the Mn content is 0.10 to 1.50%. The upper limit with preferable Mn content is 1.00%.

P: 0.050% or less Phosphorus (P) is an impurity. P segregates at the grain boundaries and lowers the toughness of the steel. Therefore, the one where P content is low is preferable. Therefore, the P content is 0.050% or less. A preferable P content is 0.030% or less.

S: 0.050% or less Sulfur (S) is inevitably contained. S segregates at the grain boundaries and lowers the toughness of the steel. Therefore, the one where S content is low is preferable. Accordingly, the S content is 0.050% or less. A preferable S content is 0.035% or less. As described above, when MnS is formed to improve the machinability of steel, the preferable lower limit of the S content is 0.015%.

Al: 0.020 to 0.100%
Aluminum (Al) deoxidizes steel. Further, Al combines with N in the steel to form AlN, thereby reducing solute N. If the solute N is reduced, strain age hardening is suppressed. Therefore, the occurrence of inclined wrinkles is suppressed. If the Al content is too low, the above effect cannot be obtained. On the other hand, if the Al content is too high, coarse Al oxide is generated, and cold forgeability is lowered. Therefore, the Al content is 0.020 to 0.100%. A preferable lower limit of the Al content is 0.060%. Al content in this specification is sol. Al (acid-soluble Al) is meant.

N: 0.0100% or less Nitrogen (N) is an impurity and is inevitably contained. N forms a Cottrell atmosphere. If dislocations are fixed in a Cottrell atmosphere, strain age hardening occurs. Strain age hardening causes inclined wrinkles. Therefore, the N content is preferably as low as possible. Therefore, the N content is 0.0100% or less. The upper limit with preferable N content is 0.0060%, More preferably, it is 0.0050%. As described above, the lower the N content, the better. However, the lower limit of N content in industrial production is 0.0030%.

Ti: 0 to 0.100%
Ti may not be contained. Ti is an optional element. When Ti is contained, Ti combines with N to form TiN, and reduces solid solution N. If the solute N is reduced, strain age hardening is suppressed. Therefore, the occurrence of inclined wrinkles is suppressed. On the other hand, if the Ti content is too high, carbides are formed and the strength of the wire becomes too high. Therefore, the Ti content is 0 to 0.100%. The minimum with preferable Ti content is 0.0005%, More preferably, it is 0.001%. The upper limit with preferable Ti content is 0.060%, More preferably, it is 0.040%.

  The balance of the chemical composition of the steel billet of this embodiment may be composed of Fe and impurities, and the chemical composition of the steel billet may contain other elements other than those described above. Other elements are Cu, Ni, Cr, Mo, Nb, B etc., for example. The chemical composition of the steel billet of this embodiment includes a chemical composition corresponding to a carbon steel wire for cold heading (SWRCH) defined in JIS G3507. In addition, in this specification, an impurity means the thing mixed from the ore as a raw material, a scrap, or a manufacturing environment, when manufacturing steel materials industrially.

The chemical composition of the steel billet further satisfies the following formula (1).
(Al + Ti) / N ≧ 7 (1)
Here, the content (atomic%) of the corresponding element is substituted for the element symbol in the formula (1).
When Ti is not contained, “0” is substituted for Ti in formula (1).

  As described above, Al suppresses strain age hardening due to solute N. In this embodiment, in order to suppress the film thickness of the scale formed on the surface of the wire, the wire is rapidly cooled until the surface temperature of the wire reaches 600 ° C. When the surface temperature of the wire is rapidly cooled, if the Al content and the Ti content with respect to N are too low, it is difficult to form AlN and TiN.

  If Al content and Ti content satisfy | fill Formula (1), even if it quenches rapidly, since AlN or AlN and TiN are fully formed, the amount of solid solution N can be suppressed. Therefore, strain age hardening is suppressed and the generation of inclined wrinkles is suppressed.

  The above-described steel billet is manufactured, for example, by the following method. A molten steel that satisfies the above-described chemical composition and formula (1) is manufactured. The produced molten steel is used to make a slab by a casting method. You may make molten steel into an ingot (steel ingot) by the ingot-making method. A steel billet is manufactured by hot working a slab or an ingot.

[Hot rolling process (S2)]
The prepared steel billet is hot-rolled to produce a wire (cold forging wire) (S2). Specifically, a steel billet is inserted into the heating furnace 1 and heated. The upper limit with preferable heating temperature of the heating furnace 1 is 1150 degreeC. If the heating temperature is too high, AlN in the steel billet will dissolve and N will easily dissolve in the steel. In this case, inclined wrinkles may occur. If heating temperature is 1150 degrees C or less, melt | dissolution of AlN in a steel billet can be suppressed and increase of the solid solution N can be suppressed.

  If the heating temperature is too low, the deformation resistance of the steel billet is increased, so that the rolling load on the roughing mill, intermediate rolling mill and finish rolling mill increases excessively. Therefore, the minimum with preferable heating temperature is 850 degreeC, More preferably, it is 950 degreeC.

  The steel billet heated to the heating temperature is extracted from the heating furnace 1 and hot rolled. Hot rolling is performed by a roughing and intermediate rolling mill 2 and a finish rolling mill 3.

[Winding process (S3)]
The wire rod after rolling by the finish rolling mill 3 is conveyed to the winding device 4. Using a winding device (laying head) 4, the wire is formed in a spiral shape. Then, the wire formed in a spiral shape is dropped onto the conveyor 5. The surface temperature of the ring-shaped wire immediately after dropping on the conveyor 5 is defined as “winding temperature” (° C.). In this embodiment, the winding temperature is set to 850 ° C. or lower.

  The coiling temperature can be measured, for example, with a radiation thermometer directed to the wire drop position. Although not shown in FIG. 2, a water cooling device is disposed between the finishing mill 3 and the winding device 4 and between the rough and intermediate rolling mill 2 and the finishing mill 3. The coiling temperature is set to 850 ° C. or lower by controlling the cooling by the water cooling device.

  If the winding temperature is too high, the scale thickness will be too thick. If the scale thickness is thick, the scale is easily broken. If the scale is cracked and part of the scale is peeled off, the corrosion rate of the surface during pickling differs between the surface covered with the scale and the surface from which the scale is peeled off. Therefore, it becomes easy to generate inclined wrinkles.

  In this embodiment, since the coiling temperature is 850 ° C. or less, the scale thickness can be suppressed. Therefore, cracking of the scale can be suppressed, and the generation of inclined wrinkles due to the scale can be suppressed. The upper limit with preferable coiling temperature is 830 degreeC, More preferably, it is 800 degreeC.

  If the winding temperature is too low, other wrinkles other than inclined wrinkles are likely to occur on the surface of the wire. Furthermore, it may be difficult to convey the wire coil on the stealmore conveyor. Therefore, the preferable lower limit of the coiling temperature is 750 ° C.

[First cooling step (S4)]
The ring-shaped wire discharged from the winding device 4 is unconcentrically developed and conveyed on the conveyor 5. Further, the developed wire is cooled by the conveyor 5. At this time, the average cooling rate (henceforth a 1st cooling rate) between the coiling | winding temperature (850 degrees C or less)-600 degreeC is 2.5 degrees C / second or more.

  In the first cooling step, the wire is rapidly cooled at the first cooling rate in order to suppress the generation of scale as much as possible. In this case, scale generation is suppressed and the scale thickness is reduced. A preferable lower limit of the first cooling rate is 3.0 ° C./second, more preferably 3.5 ° C./second. On the other hand, if the first cooling rate is too high, the structure of the wire may become bainite depending on the steel component. These structures reduce the cold forgeability. Therefore, a preferable upper limit of the first cooling rate is 7 ° C./second, more preferably 5 ° C./second.

  The first cooling step is performed until the surface temperature of the wire reaches 600 ° C. Scales are less likely to be generated below 600 ° C. Furthermore, when cooling the wire at an average cooling rate of 2.5 ° C./second or more to a temperature range of less than 600 ° C., the time required for forming AlN and TiN even if the formula (1) is satisfied. Run short. Therefore, solid solution N is not suppressed. Therefore, in the first cooling step, cooling is performed at the first cooling rate until the surface temperature of the wire reaches 600 ° C.

[Second cooling step (S5)]
A 2nd cooling process is implemented after a 1st cooling process (S5). As described above, in the embodiment of the present invention, the inclined wrinkles due to the scale and the inclined wrinkles due to the solid solution N are suppressed. In the winding process (S3) and the first cooling process (S4), a condition for suppressing the inclination wrinkles due to the scale is set. In the second cooling step, conditions are set for suppressing inclined soot caused by the solid solution N. Specifically, in the second cooling step, the average cooling rate (hereinafter referred to as the second cooling rate) between the surface temperature of the wire rods of 600 ° C. to 100 ° C. is set to 0.5 ° C./second or less.

  A spiral wire rod is dropped from the conveyor 5 onto the focusing device 6 to form a wire coil. The wire coil is hung on the hook and cooled while being conveyed by the conveyor 7. The surface temperature of the wire in the focusing device 6 is around 600 ° C. Therefore, the second cooling step corresponds to a cooling step with the wire coil being conveyed by the conveyor 7 after the wire coil is formed by the converging device 6.

  If the second cooling rate is too fast, the time required for the generation of AlN and TiN is insufficient even if the formula (1) is satisfied. Therefore, after cooling, the amount of solute N is excessively large, and inclined soot is easily generated. Therefore, the second cooling rate is 0.5 ° C./second or less. A preferable upper limit of the second cooling rate is 0.4 ° C./second, more preferably 0.3 ° C./second. The average cooling rate when the surface temperature of the wire is 100 ° C. or lower is not particularly limited.

  For example, a part of the path of the conveyor 7 is covered with a heat insulating material, and a wire coil hung on a hook is conveyed in an area surrounded by the heat insulating material. Thereby, an average cooling rate can be 0.5 degrees C / sec or less.

[Bundling step (S6)]
The wire coil conveyed by the hook conveyor is compressed in the axial direction of the wire coil by using the bundling device 8 and bound by the band material. The surface temperature of the wire coil during compression is set to 100 ° C. or lower. Furthermore, the compression rate (%) of the wire coil defined by the formula (2) is set to 40% or less.
Compression rate = (L0−L1) / L0 × 100 (2)
Here, L0 is the axial length (mm) of the wire coil before compression, and L1 is the axial length (mm) of the wire coil after compression.

  The bundling device 8 compresses the wire coil by pressing in the axial direction of the wire coil hung on the hook. At this time, if the surface temperature of the wire coil at the time of bundling is 100 ° C. or less, the diffusion rate of the solid solution N is suppressed even if the solid solution N still remains after the above-described steps, and strain age hardening is performed. The occurrence of inclined wrinkles due to the is suppressed. A preferable surface temperature is 50 ° C. or less. The temperature before binding can be measured with a radiation thermometer, for example.

  Furthermore, if the bundling device 8 compresses the wire coil excessively, the wire coil is distorted and strain age hardening is likely to occur. Furthermore, the scale may be peeled off. If the compressibility by the bundling device 8 is 40% or less, the wire coil is less likely to be distorted, and scale peeling is also suppressed. Therefore, the occurrence of inclined defects in the cold forged product is suppressed.

[About the process after binding]
A pickling process and a lubrication process are implemented with respect to the wire for cold forging manufactured as mentioned above. Furthermore, cold forging (drawing) with a surface reduction rate of 10% or less is performed on the lubricated wire to produce a steel wire for cold forging. The steel wire for cold forging is formed into a predetermined shape by cold forging.

  In the wire manufactured by the above manufacturing method, the occurrence of inclined wrinkles is suppressed. For this reason, inclined wrinkles are less noticeable even after lubrication. Therefore, even if the plating process is performed on the steel wire, the inclined wrinkles are not noticeable on the steel wire after the plating process.

  Steel billets with test numbers 1 to 27 shown in Table 1 were prepared.

  In the “F1” column in Table 1, the value of F1 = (Al + Ti) / N, which is the left side of the formula (1), is described. In the table, “-” in the “Ti” column indicates that it is not substantially contained. In this case, “0” was substituted for “Ti” in equation (1).

  Each element range of the chemical composition of the steel billets of test numbers 1 to 27 was within the scope of the present invention. However, the chemical compositions of test numbers 1 to 3 and 24 to 27 did not satisfy the formula (1).

  For the steel billet of test numbers 1 to 27, the production flow shown in FIG. 3 is carried out using the production line shown in FIG. 2, and for cold forging having the diameter described in the “diameter” column in Table 1 A wire was manufactured. Conditions in each manufacturing process (heating temperature, winding temperature, first cooling rate, second cooling rate, pre-bundling temperature, and compressibility) were as shown in Table 1.

[Inclined wrinkle observation test]
With respect to the manufactured cold forging wire of each test number, pickling treatment and lubrication treatment were performed under the same conditions for each test number.

  Specifically, the wire coils of each test number were immersed for a total of 300 seconds in a pickling line including a plurality of hydrochloric acid baths containing 3 to 35% by volume hydrochloric acid solution. After immersion, the wire coil was pulled up. The wire coil was immersed in a washing tank containing normal temperature water, and hydrochloric acid was removed from the surface of the wire coil.

  A lubrication treatment was performed on the wire coil subjected to the pickling treatment. The lubrication apparatus used for the lubrication treatment was provided with a chemical conversion treatment tank, a hot water washing tank, a lubricant tank, and a drying furnace.

  The treatment liquid (trade name: Palbond PB181X) in the chemical conversion treatment tank contained zinc phosphate. The free acidity of the treatment liquid in the chemical conversion treatment tank was adjusted to 4 to 7 points and the total acidity was adjusted to 30 to 36 points, and the coil of each test number was treated with the treatment liquid. The temperature of the treatment liquid in the chemical conversion treatment tank was controlled at 70 to 80 ° C. In the lubricant tank, an aqueous solution containing sodium stearate with a concentration adjusted to 1.5 to 2.5 points for each test number (trade name: Paloub 235) was stored. The lubricant liquid was adjusted to 70 to 90 ° C.

  The wire coil of each test number was immersed in a chemical conversion treatment tank for 300 seconds. Next, the wire coil was immersed in a hot water bath. Next, the wire coil was immersed in a lubricant tank for 300 seconds. Finally, the wire coil was dried at 100 ° C. for 600 seconds in a drying furnace to produce a wire coil on which a lubricating film was formed.

  Samples of 3 turns (6 turns in total) were taken from both ends of the wire coil of each test number after the lubrication treatment. The surface of the sample was visually observed to determine the presence or absence of inclined wrinkles shown in FIG. When inclined wrinkles occurred, the number was counted. For each test number, the ratio (pieces / m) of the total number of inclined ridges confirmed in the 6-roll sample to the total length (21 m) of the sample (6 rolls in total) was determined.

[Test results]
The test results are shown in the “Evaluation” column of Table 1. The “◎” mark in the “疵 evaluation” column means that the number of inclined wrinkles was 0 / m. “◯” means that the inclined wrinkles were 0.1 pieces / m or less. “X” means that the number of inclined wrinkles is more than 0.1 / m. When the inclination wrinkles was 0.1 piece / m or less, it was evaluated that the inclination wrinkles were suppressed.

  With reference to Table 1, in the wire coils of test numbers 4 to 7, 14, 16 to 18, and 21 to 23, the chemical composition was within the scope of the present invention, and the formula (1) was satisfied. Furthermore, the coiling temperature, the first and second cooling rates, the pre-bundling temperature, and the compressibility were within the scope of the present invention. Therefore, in these test numbers, inclined wrinkles were 0.1 pieces / m or less.

  Furthermore, in the wire coils of test numbers 4, 5, 14, 16-18, and 21-23, the heating temperature was 1150 ° C. or lower. Therefore, no inclined wrinkles were observed in these test numbers.

  On the other hand, in the test number 1, the F1 value was less than 7. Furthermore, the coiling temperature was too high and the first cooling rate was too low. Therefore, more inclined wrinkles were observed than 0.1 / m. Since the F1 value was less than 7, inclined wrinkles due to strain age hardening occurred, and the winding temperature was too high, and the first cooling rate was too low, so it was considered that inclined wrinkles due to scale also occurred. .

  In test numbers 2, 3, and 24 to 27, the F1 value was less than 7. Therefore, in these test numbers, inclined wrinkles were observed more than 0.1 pieces / m. Since the F1 value was less than 7, it is considered that inclined wrinkles due to strain age hardening occurred.

  In test numbers 8 and 9, the chemical composition was within the range of the present invention, and the F1 value was 7 or more. However, the coiling temperature exceeded 850 ° C. Therefore, more inclined wrinkles were observed than 0.1 / m. It is considered that inclined wrinkles due to scale cracking occurred because the winding temperature was too high and the scale thickness was increased.

  In test numbers 10 and 11, the chemical composition was within the range of the present invention, and the F1 value was 7 or more. However, the first cooling rate was less than 2.5 ° C./second. Therefore, more inclined wrinkles were observed than 0.1 / m. Since the first cooling rate is too low and the scale thickness is increased, it is considered that the inclined wrinkles due to the scale cracking occurred.

  In test numbers 12 and 13, the chemical composition was within the range of the present invention, and the F1 value was 7 or more. However, the second cooling rate exceeded 0.5 ° C./second. Therefore, more inclined wrinkles were observed than 0.1 / m. Since the second cooling rate was too high, AlN and TiN were not sufficiently formed, and it is considered that inclined wrinkles based on strain age hardening occurred.

  In test number 15, the chemical composition was within the range of the present invention, and the F1 value was 7 or more. However, the pre-bundling temperature exceeded 100 ° C. Therefore, more inclined wrinkles were observed than 0.1 / m. It is considered that since the temperature before binding was too high, the solid solution N remaining in the steel diffused, and inclined creases based on strain age hardening occurred.

  In test numbers 19 and 20, the chemical composition was within the range of the present invention, and the F1 value was 7 or more. However, the compression rate at the time of binding exceeded 40%. Therefore, inclined wrinkles were observed. It is thought that because the compressibility at the time of binding was too high, strain was introduced at the time of binding and inclined wrinkles based on strain age hardening occurred.

  The embodiment of the present invention has been described above. However, the above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately changing the above-described embodiment without departing from the spirit thereof.

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Coarse and intermediate rolling mill 3 Finishing rolling mill 4 Winding device 5 Stealmore conveyor 6 Converging device 7 Hook conveyor 8 Bundling device 10 Production line 20

Claims (2)

In mass%, C: 0.01 to 0.30%, Si: 0.50% or less, Mn: 0.10 to 1.50%, P: 0.050% or less, S: 0.050% or less, A step of preparing a steel billet containing Al: 0.020 to 0.100%, N: 0.0100% or less, and Ti: 0 to 0.100% and satisfying the formula (1);
A step of producing a wire rod by hot rolling the steel billet;
Forming the wire rod in a spiral shape and dropping it on a conveyor, setting the surface temperature of the wire rod to 850 ° C. or less when dropped on the conveyor;
A step of cooling the wire at an average cooling rate of 2.5 ° C./second or more until the surface temperature of the wire dropped on the conveyor reaches 600 ° C .;
The step of cooling the wire at an average cooling rate of 0.5 ° C./second or less, while the surface temperature of the wire is between 600 ° C. and 100 ° C .;
A method of manufacturing a wire for cold forging, comprising a step of binding a coil of the wire having a surface temperature of 100 ° C. or less at a compression rate of 40% or less.
(Al + Ti) / N ≧ 7 (1)
Here, the content (atomic%) of the corresponding element is substituted for the element symbol in the formula (1). When Ti is not contained, 0 is substituted for Ti in formula (1). It is a manufacturing method of the wire for cold forging according to claim 1,
In the step of hot rolling the steel billet, a method for producing a wire for cold forging, wherein the steel billet heated to 1150 ° C. or less is hot-rolled.