JP5707177B2 - Manufacturing method of steel wire for cold forging - Google Patents

Description

  The present invention relates to a method for manufacturing a steel wire for cold forging, and more particularly to a method for manufacturing a steel wire for cold forging in which a lubricating film is formed on the surface.

  The steel wire for cold forging is a “wire” that is a hot-rolled material or a “steel wire” obtained by primary wire drawing (hereinafter, “wire” and “steel wire” are collectively referred to as “element wire”). On the other hand, it is manufactured by carrying out a lubrication treatment for the purpose of improving lubricity. In the lubrication treatment, a lubricating film including a phosphate film and a metal soap layer is usually formed on the surface of the strand. The steel wire for cold forging is subsequently subjected to secondary wire drawing and finished to the required dimensional tolerance and hardness. Further, the secondary wire drawing increases the adhesion of the lubricating film. The steel wire for cold forging subjected to secondary wire drawing is used for cold forging and is formed into a predetermined part. When a cold forging steel wire is cut to a predetermined length and cold forged, the lubricating film formed on the surface of the cold forging steel wire is used for the cold forging die and cold forging. Prevent seizure with steel wire.

There are various methods for producing a steel wire for cold forging from a wire rod which is a hot rolled material. FIG. 9 shows the manufacturing process (pattern 1 to pattern 3). With reference to FIG. 9, the manufacturing process of pattern 1 is a steel wire for cold forging by performing one heat treatment (S108) and one wire drawing (S111) on the wire rod after rolling (S101). Manufacturing. In the manufacturing process of pattern 2, the steel wire for cold forging is manufactured by performing one heat treatment (S108) and two wire drawing (S106 and S111) on the wire rod after rolling (S101). . The manufacturing process of pattern 3 is to produce a steel wire for cold forging by performing two heat treatments (S103 and S108) and two wire drawing (S106 and S111) on the wire rod after rolling (S101). To do. As described above, the wire drawing is performed twice in the manufacturing process of the pattern 2 and the pattern 3. Therefore, the former drawing (S106) is called primary drawing, and the latter drawing (S111) is called secondary drawing.
When the wire manufactured by hot rolling (S101) is not sufficiently softened, the pattern 1 manufacturing process is performed. In this case, the wire is subjected to heat treatment (S108) such as spheroidizing annealing before the lubrication treatment (S110). Moreover, in the case of the manufacturing process of the pattern 2 and the pattern 3, the steel wire manufactured by primary wire drawing (S106) is heat processing (S108), such as annealing for the purpose of softening, in order to remove the process distortion of primary wire drawing. ) Is implemented.

  A scale generated by hot rolling (S101) is attached to the surface of the wire. In the manufacturing process of pattern 1, when the heat treatment (S108) is performed on the wire in a state where the scale is generated on the surface, the surface layer of the wire may be decarburized due to the scale on the surface of the wire. Therefore, in the pattern 1 manufacturing process, the scale is removed from the surface of the wire before the heat treatment (S108) by the pickling process (S107).

  Moreover, in the case of the manufacturing process of the pattern 2 and the pattern 3, the lubricant has adhered to the surface of the steel wire after primary wire drawing (S106) by the lubrication process (S105) before primary wire drawing. When the steel wire is heat-treated (S108) with the surface lubricated, the gas composition in the furnace atmosphere of the heat treatment furnace is changed by the lubricant on the surface of the steel wire, and the surface layer of the steel wire is decarburized or decarburized. May be carburized. Moreover, the heat treatment furnace may be contaminated by the lubricant on the surface of the steel wire. Therefore, in the manufacturing process of pattern 2 and pattern 3, the lubricant is removed from the surface of the steel wire before the heat treatment by pickling treatment (S107).

Furthermore, in the manufacturing process of pattern 1 to pattern 3, a scale is generated on the surface of the strand by heat treatment (S108). If the lubrication treatment (S110) is performed on the strands generated by the scale, the lubricating film is formed on the scale, so that the lubricating film is easily peeled off. Therefore, the scale is removed from the surface of the strand before the lubrication process (S110) by the pickling process (S109).
As described above, two pickling processes (S107 and S109) are performed in the steps (S107 to S111) performed in any of the manufacturing methods of patterns 1 to 3.

  In the past, various pickling treatment methods have been proposed. Japanese Patent Laid-Open No. 50-104113 (Patent Document 1) discloses a method for removing the scale of a steel wire by performing pickling while maintaining an aqueous solution containing sulfuric acid or an aqueous solution containing hydrochloric acid at 70 ° C. or higher. Disclose.

  Japanese Patent Laid-Open No. 2000-192300 (Patent Document 2) discloses a method of performing pickling using a sulfuric acid-nitric acid pickling solution. Patent Document 2 describes that by using a sulfuric acid-nitric acid pickling solution, smoothening of the surface of the wire can be suppressed and the amount of the lubricating film retained on the surface of the wire can be secured. Furthermore, it is described that the influence on the environment caused by the waste liquid containing nitric acid can be suppressed as compared with the case of using the nitric acid pickling liquid.

  Japanese Patent Application Laid-Open No. 2004-256896 (Patent Document 3) discloses a method of performing a pickling treatment using a hydrochloric acid-based pickling solution after performing the pickling treatment using a fluorinated hydrofluoric acid-based pickling solution. . In Patent Document 3, by carrying out such a two-step pickling treatment, the surface removal depth can be made 30 μm or more, the time during which the surface abnormal layer and wrinkles can be removed can be shortened, and the surface can also be removed. It is stated that it will not be rough.

  Japanese Unexamined Patent Publication No. 2006-169616 (Patent Document 4) discloses a base metal part of a steel wire by pickling with a sulfuric acid solution for the purpose of reducing surface defects of the steel wire after wire drawing. A method for removing 10 to 150 μm from the surface is disclosed.

  Japanese Patent Application Laid-Open No. 8-120472 (Patent Document 5) discloses a method of stirring and flowing an acid solution having trivalent iron ions for the purpose of efficiently peeling the scale of the overlapping portion of the wire during pickling. To do.

JP 50-104113 A JP 2000-192300 A JP 2004-256896 A JP 2006-169616 A JP-A-8-120472

  However, although the manufacturing method of the steel wire disclosed by patent documents 1, 3-5 mentions the external appearance property of the surface of a steel wire, it does not mention improvement of lubricity. Therefore, when the steel wire for cold forging is manufactured by the manufacturing method disclosed in these documents, there are cases where excellent lubricity cannot be obtained.

  Patent document 2 mentions the lubricity of a steel wire. However, it is difficult to obtain a steel wire having excellent appearance and excellent lubricity only by the pickling treatment with a pickling solution containing sulfuric acid. Further, the pickling solution of Patent Document 2 contains nitric acid although it is lower than the conventional one, so that it may affect the environment due to the nitric acid waste solution.

  The objective of this invention is providing the manufacturing method of the steel wire for cold forging excellent in lubricity and external appearance property.

Means for Solving the Problems and Effects of the Invention

  The manufacturing method of the steel wire for cold forging by this Embodiment is the 1st pickling process process which implements a pickling process with a sulfuric acid solution with respect to a strand, and the strand which implemented the pickling process with a sulfuric acid solution A heat-treating step, a second pickling treatment step of performing a pickling treatment with a hydrochloric acid solution on the heat-treated strand, and a strand subjected to a pickling treatment with a hydrochloric acid solution And a step of performing a lubrication treatment and forming a lubricant film on the surface of the element wire.

  The manufacturing method of the steel wire for cold forging by this Embodiment can manufacture the steel wire for cold forging excellent in lubricity and external appearance property.

  Preferably, in the first pickling treatment step, the strands are transported to a first pickling apparatus including a sulfuric acid tank in which a sulfuric acid solution is stored to perform the pickling treatment, and in the second pickling treatment step, The wire is transported to a second pickling apparatus including a hydrochloric acid tank in which a hydrochloric acid solution is stored, and pickling treatment is performed.

  In this case, a steel wire for cold forging excellent in lubricity and appearance can be produced, and high productivity can be obtained.

  In the present invention, “sulfuric acid solution” means an aqueous sulfuric acid solution, and “hydrochloric acid solution” means an aqueous hydrochloric acid solution.

It is a block diagram which shows the manufacturing line of the steel wire for cold forging by embodiment of this invention. It is a block diagram which shows the manufacturing line of the conventional steel wire for cold forging. It is a block diagram which shows the structure of the 1st pickling apparatus in FIG. It is a block diagram which shows the structure of the 2nd pickling apparatus in FIG. It is sectional drawing of the lubricating film formed on the surface of the steel wire for cold forging. It is a block diagram which shows the structure of the lubricating device in FIG. It is a flowchart which shows the manufacturing process of the steel wire for cold forging by embodiment of this invention. It is a figure which shows the relationship between the surface roughness of the steel wire in the pickling process with a hydrochloric acid solution, and acid immersion time. It is a flowchart which shows the process of manufacturing the steel wire for cold forging from a wire.

  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.

[Outline of manufacturing method of steel wire for cold forging according to this embodiment]
The present inventors conducted various studies in order to produce a steel wire for cold forging excellent in lubricity and appearance. As a result, the present inventors obtained the following knowledge.

  (1) The pickling treatment with a sulfuric acid solution roughens the surface of the strand to some extent. Therefore, the adhesion of the lubricating film can be enhanced. On the other hand, pickling with a sulfuric acid solution generates a large number of smuts on the surface of the strand. The smut is mainly composed of metal carbides typified by cementite and chrome carbides, oxides typified by iron-based oxides and iron-chromium-based composite oxides, and the like. Iron (Fe) is dissolved by the sulfuric acid solution. However, the smut remains undissolved in the sulfuric acid solution and remains on the surface of the strand.

  The smut is black and powdery. When a lubricating film is formed with a large number of smuts remaining on the surface of the strands, the smut is seen through the lubricating film. Therefore, an excellent appearance cannot be obtained. Furthermore, the smut is physically easy to peel off. Therefore, if a lubricating film is formed on the smut, the lubricating film may be peeled off together with the smut at the time of wire drawing or cold forging. Therefore, when carrying out the pickling treatment with the sulfuric acid solution, a method for removing the smut must be considered separately.

  (2) On the other hand, since the hydrochloric acid solution dissolves the strands relatively uniformly, the pickling treatment with the hydrochloric acid solution tends to smooth the surface of the strands and hardly generate smut. Therefore, if a pickling treatment with a hydrochloric acid solution is employed, a steel wire with excellent appearance can be obtained even after the formation of the lubricating film. However, in pickling treatment with a hydrochloric acid solution, the surface of the strand becomes smooth, and therefore the adhesion of the lubricating film is low. Therefore, the lubricity of the steel wire is low.

  (3) Then, the present inventors considered performing the pickling process with a sulfuric acid solution first, and then performing the pickling process with a hydrochloric acid solution. If pickling treatment is performed in this order, the surface of the strands can be roughened to some extent by pickling treatment with a sulfuric acid solution. And since a hydrochloric acid solution melt | dissolves a strand comparatively uniformly, the roughness of the surface of a strand can be maintained by the pickling process by the hydrochloric acid solution of a post process.

  (4) The present inventors further performed pickling treatment with a sulfuric acid solution in the step before the final heat treatment (S108 in FIG. 9) and the post-lubrication treatment (S110), that is, the final pickling treatment step (S109). The pickling treatment with the hydrochloric acid solution is not carried out continuously, but the sulfuric acid solution is used in the pickling treatment (S107) before the final heat treatment (S108), and the pickling after the final heat treatment (S108). It was considered to use a hydrochloric acid solution in the treatment (S109). The pickling treatment (S107) before the final heat treatment (S108) has conventionally been sufficient if the scale and lubricant can be removed. By performing the pickling treatment with the sulfuric acid solution before the final heat treatment (S108), not only the scale and the lubricant can be removed, but also the surface of the strand can be roughened to some extent. Therefore, not only can the gas composition in the furnace atmosphere of the heat treatment furnace be stabilized and contamination of the heat treatment furnace can be prevented, but also the adhesion of the lubricating film can be improved in the subsequent process. Further, the smut on the surface of the wire generated by the pickling treatment with the sulfuric acid solution can be removed by the final heat treatment (S108) and the pickling treatment with the hydrochloric acid solution (S109), thereby forming a lubricating film. Even afterwards, the appearance of the steel wire is excellent. Therefore, a steel wire excellent in lubricity and appearance can be obtained.

  Based on the above knowledge, the present inventors completed the manufacturing method of the steel wire for cold forging by the following this embodiment. Hereafter, the detail of the manufacturing method of the steel wire for cold forging by this Embodiment is demonstrated.

[production equipment]
FIG. 1 is a block diagram showing an example of a cold forging steel wire production line according to an embodiment of the present invention. FIG. 2 is a block diagram showing an example of a conventional cold forging steel wire production line.

  With reference to FIG. 1, the production line of the steel wire for cold forging by this Embodiment is the 1st pickling apparatus 1, the heat processing apparatus 2, the 2nd pickling apparatus 3, the lubrication apparatus 4, And a wire machine 5. In the conventional manufacturing line of FIG. 2, there is one pickling device (pickling device 10), whereas in the manufacturing line according to the present embodiment, two pickling devices are arranged. Each facility will be described below.

[First pickling apparatus 1]
With reference to FIG. 3, the 1st pickling apparatus 1 pickles the strand W using a sulfuric acid solution. The first pickling device 1 includes a transport device 20, a sulfuric acid tank 30, a water washing tank 40, a neutralization tank 50, and a drying device 60. The sulfuric acid tank 30, the water washing tank 40, the neutralization tank 50, and the drying device 60 are arranged in a line.

  The transfer device 20 is disposed above the plurality of tanks 30, 40, 50 and the drying device 60 arranged in a row, and transfers the coiled wire W to the respective tanks 30, 40, 50 and the drying device 60. The transport device 20 includes a transport rail 23, a drive device 21, and a hanging tool 22. The transport rail 23 is disposed above the tanks 30, 40, 50 and the drying device 60 and extends in the arrangement direction of the tanks 30, 40, 50 and the drying device 60. The driving device 21 moves on the transport rail 23 and raises and lowers the hanging tool 22. The hanging tool 22 is a hook. The coiled wire W is hooked on the hanging tool 22. The drive device 21 conveys the strand W into the respective tanks 30, 40, 50 and the drying device 60 by moving and lifting the hanging tool 22.

  The sulfuric acid tank 30 pickles the wire W. The sulfuric acid tank 30 stores a sulfuric acid solution. The sulfuric acid solution is an aqueous solution containing sulfuric acid having a concentration of 5 to 25% by mass / volume. A preferable sulfuric acid concentration is 10 to 25 mass / volume%. The sulfuric acid solution dissolves and removes the scale and lubricant generated on the surface of the wire W. The sulfuric acid tank 30 includes a temperature adjusting device (not shown). The temperature adjusting device adjusts the temperature of the sulfuric acid solution.

  The rinsing tank 40 stores room temperature water. The strand W pulled up from the sulfuric acid bath 30 is transported and immersed in the washing bath 40. The strand W is removed from the sulfuric acid solution adhering to the surface in the washing tank 40. The neutralization tank 50 stores a neutralization solution. The neutralization solution is a solution containing a neutralizing agent, for example, a slaked lime solution. The wire W pulled up from the washing tank 40 is conveyed to the neutralization tank 50 and immersed therein. Thereby, the sulfuric acid solution remaining on the surface of the strand W is neutralized. The drying device 60 dries the wire W pulled up from the neutralization tank 50 at normal temperature or high temperature. Since the lime film is adhered to the surface of the dried wire W, welding between the wires W is suppressed during the subsequent heat treatment.

  In FIG. 3, each tank 30, 40, 50 is arranged one by one, but a plurality of each tank 30, 40, 50 may be arranged. For example, a plurality of sulfuric acid tanks 30 may be arranged, and a plurality of water washing tanks 40 may be arranged.

[Heat treatment equipment 2]
The heat treatment apparatus 2 performs heat treatment on the wire W. In this example, the heat treatment apparatus 2 performs an annealing process on the wire W to soften the wire W. Thereby, the workability of the strand W at the time of subsequent wire drawing is improved, and it adjusts below the hardness of a requirement specification.
The heat treatment apparatus 2 has a well-known structure and performs an annealing process under well-known heat treatment conditions. The heat treatment apparatus 2 uses a continuous annealing furnace divided into a plurality of zones. Each zone is arranged in a line from the beginning to the end of the heat treatment apparatus 2, and the furnace temperature can be adjusted for each zone. The heat treatment apparatus 2 may be a batch furnace.

The atmosphere in the furnace of the heat treatment apparatus 2 during the annealing treatment makes nitrogen gas, CO gas, and CO ₂ gas constant at a predetermined ratio. Thereby, the PF value of the furnace atmosphere becomes constant. If the PF value becomes excessively high, the surface layer of the strand W is carburized, and if the PF value is excessively low, the surface layer of the strand W is decarburized. The PF value is an index calculated by (CO gas%) ² / (CO ₂ gas%).

[Second pickling device 3]
The 2nd pickling apparatus 3 pickles a strand using a hydrochloric acid solution. Referring to FIG. 4, the second pickling apparatus 3 includes a transfer device 20, a plurality of hydrochloric acid tanks 70, and a water washing tank 40. The plurality of hydrochloric acid tanks 70 and the rinsing tank 40 are arranged in a line.

  The hydrochloric acid tank 70 stores a hydrochloric acid solution. The hydrochloric acid solution is an aqueous solution containing hydrochloric acid having a concentration of 5 to 25% by mass / volume. A preferable hydrochloric acid concentration is 15 to 25% by mass / volume. Similar to the sulfuric acid solution, the hydrochloric acid solution dissolves and removes the scale on the surface of the wire W. In this example, a plurality of hydrochloric acid tanks 70 are arranged, but one hydrochloric acid tank 70 may be provided.

[Lubrication device 4]
The lubricating device 4 forms a lubricating film on the surface of the pickled strand W. As shown in FIG. 5, the lubricating film includes a phosphate film 11, a reaction layer 12, and an unreacted layer 13. The phosphate film 11 is made of phosphate and is formed on the surface of the strand W. The reaction layer 12 is made of a metal soap and is formed on the phosphate film 11. The unreacted layer 13 is made of sodium soap.

  With reference to FIG. 6, the lubricating device 4 includes a transport device 20, one or a plurality of chemical conversion treatment tanks 80, a hot water washing tank 90, a lubricant tank 100, and a drying device 60.

  In the chemical conversion treatment tank 80, a treatment liquid containing a phosphate is stored. The phosphate is, for example, zinc phosphate. The phosphate content of the treatment liquid used in this example is within a well-known range. By immersing the strand W in the chemical conversion treatment tank 80, the phosphate film 11 is formed on the surface of the strand W.

  Hot water is stored in the hot water bath 90. The wire W pulled up from the one or more chemical conversion treatment tanks 80 is immersed in the hot water washing tank 90, and the excess treatment liquid on the surface of the wire W is removed.

  Lubricant is stored in the lubricant tank 100. The lubricating liquid contains sodium soap. Sodium soap is, for example, sodium stearate. When the strand W on which the phosphate coating 11 is formed is immersed in the lubricant tank 100, the lubricating liquid reacts with the phosphate coating 11 to form a reaction layer 12 on the phosphate coating 11. Therefore, the phosphate film 11 and the reaction layer 12 are formed on the surface of the wire W pulled up from the lubricant tank 100. Furthermore, when the strand W is dried by the drying device 60, the lubricating liquid adhering to the reaction layer 12 becomes the unreacted layer 13 in which sodium stearate is dried. In this way, a steel wire for cold forging is manufactured.

[Wire drawing machine 5]
The wire drawing machine 5 has a known configuration. The wire drawing machine 5 includes a die and draws a steel wire for cold forging. The wire drawing machine 5 may not be arranged on the same production line as the first pickling device 1 to the lubricating device 4.

[Method of manufacturing steel wire for cold forging]
The manufacturing method of the steel wire for cold forging using the manufacturing line shown in FIG. 1 is demonstrated. FIG. 7 is a flowchart showing the manufacturing process of the steel wire for cold forging according to the present embodiment. With reference to FIG. 7, in the manufacturing process of the steel wire for cold forging by this Embodiment, the process of preparing a strand (S1: strand preparation process), and the process of performing the pickling process with a sulfuric acid solution (S2: first pickling treatment step), a step of performing heat treatment (S3: heat treatment step), a step of performing pickling treatment with a hydrochloric acid solution (S4: second pickling treatment step), and a lubrication treatment The step of performing (S5: lubrication treatment step) and the step of drawing (S6: wire drawing step) are performed in order. Hereinafter, each process is explained in full detail.

[Wire preparation step (S1)]
First, a wire W to be processed is prepared (S1). In this example, a coiled wire W is prepared. The strand W may be a wire that is a hot-rolled material, or may be a steel wire obtained by primary drawing of the hot-rolled material. The scale is attached to the surface of the wire. The steel wire has a lubricant on its surface.

[First Pickling Process (S2)]
The prepared strand W is pickled with a sulfuric acid solution (S2). Specifically, the prepared strand W is transported while being held by the hanging tool 22 and immersed in the sulfuric acid tank 30 in the first pickling apparatus 1. At this time, the scale and lubricant on the surface of the wire W are dissolved and removed. Preferably, the temperature of the sulfuric acid solution in the sulfuric acid tank 30 is controlled to 60 ° C to 80 ° C. In this case, the pickling speed is increased.

  By pickling with a sulfuric acid solution, not only the scale and lubricant, but also the surface of the wire W is dissolved. The surface roughness of the strand W at this time can be made rougher than the pickling process with a hydrochloric acid solution. However, in this step, since pickling treatment is performed with a sulfuric acid solution, a large number of smuts are generated on the surface of the wire W.

  After pickling in the sulfuric acid tank 30, the wire W is pulled up from the sulfuric acid tank 30 and conveyed to the water washing tank 40. And the strand W is immersed in the washing tank 40, and the sulfuric acid solution adhering to the surface of the strand W is removed. Furthermore, the strand W pulled up from the washing tank 40 is conveyed to the neutralization tank 50 and immersed in the neutralization tank 50. Thereby, the sulfuric acid solution remaining on the surface of the strand W is neutralized. The wire W pulled up from the neutralization tank 50 is dried by the drying device 60. A lime film is adhered to the surface of the dried wire W. Thereby, welding between the strands W in the subsequent heat treatment process is suppressed.

  Through the above process, the scale and lubricant of the wire W prepared in step S1 are removed. When heat treatment is performed in the heat treatment apparatus 2 with the scale attached to the surface of the strand W, the surface layer of the strand W is decarburized by the scale. Further, if the heat treatment is performed in the heat treatment apparatus 2 while the lubricant remains on the surface of the wire W, the gas composition in the furnace atmosphere of the heat treatment apparatus 2 may vary. If the gas composition in the furnace atmosphere varies, the surface layer of the wire W may be carburized or decarburized. Further, if the heat treatment is performed in the heat treatment apparatus 2 while the lubricant remains on the surface of the wire W, the heat treatment furnace may be contaminated by the lubricant. Since the scale and lubricant of the wire W are removed in step S2, when the heat treatment is performed on the wire W, the gas composition in the furnace atmosphere of the heat treatment apparatus 2 is stabilized.

  Further, in step S2, the strand W is pickled using a sulfuric acid solution. Therefore, the surface of the strand W can be roughened compared with the pickling treatment with a hydrochloric acid solution. The rough surface is effective in the subsequent lubrication process (S5).

[Heat treatment step (S3)]
After the first pickling treatment step (S2), heat treatment is performed on the strand W (S3). In this example, the heat treatment apparatus 2 is used to perform an annealing process on the wire W and soften the wire W. The annealing process is performed under known conditions. At this time, the atmosphere in the furnace of the heat treatment apparatus 2 makes nitrogen gas, CO gas, and CO ₂ gas constant at a predetermined ratio. As described above, since the scale and the lubricant are removed from the surface of the wire W by the first pickling process (S2), the gas composition in the furnace atmosphere of the heat treatment apparatus 2 is stabilized.

[Second Pickling Process (S4)]
The strand W after the heat treatment step (S3) is pickled with hydrochloric acid (S4). Specifically, the wire W after the heat treatment is transferred to the second pickling apparatus 3. Then, the wire W is conveyed to the hydrochloric acid tank 70 while being held by the hanging tool 22 and immersed therein. In the case where another hydrochloric acid tank 70 is disposed in the subsequent stage, the strand W is pulled up from the hydrochloric acid tank 70 and then immersed in the other hydrochloric acid tank 70 in the subsequent stage. In short, when a plurality of hydrochloric acid tanks 70 are arranged, the wire W is immersed in the plurality of hydrochloric acid tanks 70 sequentially. If there is only one hydrochloric acid tank 70 instead of a plurality of hydrochloric acid tanks 70, the pickling process for the subsequent strand W cannot be started unless the pickling process for the preceding strand W is completed. If a plurality of hydrochloric acid tanks 70 are arranged and the strands W are sequentially dipped in the plurality of hydrochloric acid chambers 70 to perform the pickling process, the subsequent strands W complete the pickling process of the preceding strand W. Pickling treatment can be started without waiting. That is, by arranging a plurality of hydrochloric acid tanks 70, the waiting time for the pickling treatment of the wire W can be reduced, and the production efficiency can be increased.

  By the pickling treatment with the hydrochloric acid solution, the scale generated on the surface of the strand W in the heat treatment step (S3) is removed.

  The surface of the strand W is slightly dissolved by the pickling treatment with the hydrochloric acid solution, but the surface roughness of the strand W is already roughened by the pickling treatment with sulfuric acid in step S2. Since the hydrochloric acid solution dissolves the wire W relatively uniformly, even if the surface of the wire W is slightly dissolved, the surface roughness of the wire W after the first pickling process is substantially maintained. Therefore, the surface roughness of the strand W after the second pickling treatment step (that is, the surface roughness of the strand W after the first pickling treatment step and the second pickling treatment step) is the first. Both the pickling treatment step and the second pickling treatment step are rougher than when pickling treatment with a hydrochloric acid solution is performed.

Specifically, in the case of the manufacturing method according to the present embodiment, the surface roughness of the strand W after the second pickling treatment step (S4) can be adjusted to 2.0 μm or more. The surface roughness mentioned here is the center line average roughness when the 2RC filter of JIS-B0601 (2001) Annex 2 (reference) is applied, and is represented by Ra ₇₅ .

  Further, a large number of smuts generated on the surface of the wire W in the first pickling treatment step (S2) are also removed after the heat treatment step (S3) and the second pickling treatment step (S4). . Therefore, the appearance of the strand W is excellent.

  If the surface roughness of the strand W is too rough, it may cause noise of eddy current flaw detection performed at the time of wire drawing and defective product skin (such as poor gloss) after cold forging. Therefore, the upper limit with preferable surface roughness of the strand W after a 2nd pickling process process (S4) is 10 micrometers. The surface roughness of the strand W can be adjusted by the sulfuric acid concentration in the sulfuric acid solution in Step S2, the immersion time of the strand W in the sulfuric acid tank 30, the temperature of the sulfuric acid solution, and the like.

On the other hand, the surface roughness of the strand W when only pickling with a hydrochloric acid solution is performed is smaller than the surface roughness of the strand W in the present embodiment. FIG. 8 is a diagram showing the relationship between the surface roughness of the wire W and the acid dipping time when only pickling with a hydrochloric acid solution is performed. FIG. 8 was obtained by the following method. Using a hydrochloric acid solution containing 20 mass / volume% hydrochloric acid, the strand W having a chemical composition corresponding to JIS standard SCM420 was pickled in various acid immersion times. After pickling, based on JIS-B0601 (2001) Annex 2 (reference), the center line average roughness (Ra ₇₅ ) of the surface of the strand W was determined, and FIG. 8 was obtained. Referring to FIG. 8, in the case of only pickling treatment with a hydrochloric acid solution, the surface roughness of the strand W is less than 2.0 μm even if the immersion time is increased.

  From the above, in this embodiment, after pickling with a sulfuric acid solution, the surface roughness of the wire W is only pickled with a hydrochloric acid solution by performing a pickling with a hydrochloric acid solution. Can be made rougher. This surface roughness can improve the adhesion of the lubricating film.

  The pickled strand W is pulled up from the hydrochloric acid bath 70 and immersed in the water bath 40. Through the above steps, the hydrochloric acid solution adhering to the surface of the wire W is removed.

[Lubrication treatment step (S5)]
Lubricating treatment is performed on the wire W after the second pickling treatment step (S4) (S5). Specifically, the strand W is immersed in the chemical conversion treatment tank 80 in the lubricating device 4 to form the phosphate film 11 on the surface of the strand W. Next, the strand W on which the phosphate film 11 is formed is immersed in the hot water bath 90, and unnecessary treatment liquid adhering to the surface of the strand W is removed.

  Next, the strand W on which the phosphate film 11 is formed is immersed in the lubricant tank 100 to form the reaction layer 12. Then, the wire W is pulled up from the lubricant tank 100 and dried by the drying device 60. As a result, the lubricating liquid adhering to the reaction layer 12 is dried to become the unreacted layer 13, and a lubricant film composed of the phosphate film 11, the reaction layer 12, and the unreacted layer 13 is completed on the surface of the steel wire W. The steel wire for cold forging is manufactured by the above process.

  In the above process, the smut generated on the surface of the strand W in the first pickling process (S2) is removed after the second pickling process (S4). Therefore, the steel wire for cold forging after the lubricating treatment step (S5) is excellent in appearance. Furthermore, the surface of the strand W can be roughened by the first pickling treatment step (S2), and the surface roughness of the strand W is substantially maintained even after the second pickling treatment step (S4). Thus, a large amount of the phosphate film 11 can be formed, and as a result, the adhesion between the strand W and the lubricating film can be improved. As a result, the steel wire for cold forging is excellent in lubricity.

[Wire drawing process (S6)]
The steel wire for cold forging manufactured by the above process is drawn by the wire drawing machine 5. At this time, the lubricating film formed on the surface of the wire W exhibits a lubricating action, and reduces the coefficient of friction between the die of the wire drawing machine 5 and the steel wire for cold forging. Therefore, the die life is extended.

  The steel wire for cold forging manufactured by the above process is used for cold forging, and is formed into a predetermined part. When a cold forging steel wire is cut to a predetermined length and cold forged, the lubricating film formed on the surface of the cold forging steel wire is used for the cold forging die and cold forging. Prevent seizure of steel wire. As described above, the phosphate coating 11 is thick and has excellent adhesion between the strand W and the lubricating coating. Therefore, the steel wire for cold forging according to the present embodiment is excellent in lubricity in the cold forging process.

[Effects of using two pickling devices]
In the manufacturing process of the conventional steel wire for cold forging, the manufacturing line shown in FIG. 2 is generally used. In this case, there is one pickling apparatus 10. Therefore, the pickling solution is usually one type. For example, when the pickling solution is a hydrochloric acid solution, the pickling treatment is performed before the heat treatment step and before the lubricating treatment step, but only the pickling treatment with the hydrochloric acid solution is performed. Therefore, the adhesion of the lubricating film is low, and the lubricity of the steel wire for cold forging is low.

  On the other hand, when the pickling solution of the pickling apparatus 10 is a sulfuric acid solution, a large number of smuts remain on the surface of the strand before the lubricating treatment step. For this reason, the appearance of the cold forging steel wire after the formation of the lubricant film is reduced, and the adhesion of the lubricant film is also reduced by the smut.

  On the other hand, in the manufacturing method of the steel wire for cold forging by this Embodiment, two pickling apparatuses (the 1st pickling apparatus 1 and the 2nd pickling apparatus 3) are used, and before a heat treatment process (S3) The first pickling process step (S2) is performed using the first pickling apparatus 1, and the second pickling process step (S4) is performed using the second pickling apparatus 3 before the lubrication process step (S5). carry out. Since the smut generated in the first pickling treatment step (S2) is removed after the second pickling treatment step (S4), a cold forging steel wire excellent in appearance is obtained. Furthermore, since the surface of the wire W can be roughened in the first pickling treatment step (S2), and the surface roughness is substantially maintained in the second pickling treatment step (S4), the lubricity is improved. Excellent steel wire for cold forging can be obtained.

  As described above, in the method of manufacturing a steel wire for cold forging according to the present embodiment, it is preferable to use two pickling apparatuses. It is also conceivable to prepare a sulfuric acid tank and a hydrochloric acid tank as a pickling tank in the pickling apparatus 10 in the conventional manufacturing line shown in FIG. 2, and to carry out the manufacturing flow shown in FIG. In this case, when the first pickling process (S2) is performed, the pickling tank of the pickling apparatus 10 is used as a sulfuric acid tank, and when the second pickling process (S4) is performed, the acid of the pickling apparatus 10 is used. It is conceivable to switch the washing tank to a hydrochloric acid tank.

  However, in this case, since it takes time to switch the sulfuric acid tank to the hydrochloric acid tank, productivity decreases.

  In the pickling apparatus 10, a sulfuric acid tank, a hydrochloric acid tank, a water washing tank, and a neutralization tank may be arranged in a row and the production flow of FIG. However, in this case, since the hydrochloric acid bath is not used in the first pickling treatment step (S2), the strand W pulled up from the sulfuric acid bath passes above the hydrochloric acid bath and is immersed in the washing bath. When the strand W passes over the hydrochloric acid tank, the sulfuric acid solution attached to the strand W can be dropped into the hydrochloric acid bath.

  In short, when a sulfuric acid tank and a hydrochloric acid tank are mixed in one pickling apparatus 10, the sulfuric acid solution may be mixed into the hydrochloric acid tank and contaminated. Moreover, since two pickling processes (S2 and S4) are implemented with one pickling apparatus 10, productivity also falls.

  In this Embodiment, it is high by preparing the 1st pickling apparatus 1 for the 1st pickling process (S2) and the 2nd pickling apparatus 3 for the 2nd pickling process (S4). Productivity can be obtained, and contamination of the pickling solution can be suppressed.

  The sulfuric acid solution used in the first pickling treatment step (S2) is an aqueous solution containing sulfuric acid and does not contain nitric acid. Similarly, the hydrochloric acid solution used in the second pickling treatment step (S4) is an aqueous solution containing hydrochloric acid and does not contain nitric acid. Therefore, the environmental impact caused by the nitric acid waste liquid does not occur.

  In the above-described embodiment, the tanks 30, 40, 50 and the drying device 60 in the first pickling apparatus 1 are arranged in a row, but these devices do not have to be arranged in a row. Similarly, the tanks 70 and 40 in the second pickling apparatus 2 may not be arranged in a row.

  In the manufacturing flow shown in FIG. 7, the wire drawing step (S6) is performed after the lubrication treatment step (S5), but the steel wire after the lubrication treatment step (S5) is shipped as a steel wire for cold forging. The wire drawing step (S6) may be performed.

  A steel wire for cold forging manufactured by the manufacturing method according to the above-described embodiment and a steel wire for cold forging manufactured only by pickling with a hydrochloric acid solution are prepared. The surface roughness of the strands of the wire, the lubricity of the steel wire for cold forging, the adhesion amount of the lubricating film and the adhesion of the lubricating film were evaluated.

[Test method]
A wire manufactured by coil-shaped hot rolling with a diameter of 24.0 mm was prepared. The chemical composition of the wire is as shown in Table 1, and corresponds to JIS standard SCM420.

  The wire was pickled with a hydrochloric acid solution to remove the scale on the surface of the wire. Subsequently, a lubricating treatment was performed to form a lubricating film on the surface. The lubricating treatment was performed by immersing in a treatment liquid containing zinc phosphate and then immersing in a treatment liquid containing limestone soap. A primary wire drawing process was performed on the test material on which the lubricating film was formed to produce a steel wire having a diameter of 21.0 mm (hereinafter referred to as a test material).

  The following production examples of the present invention and comparative examples were carried out on the test materials, and cold forging steel wires of the present invention examples and comparative examples were produced.

[Example of the present invention]
In the present invention example, the same manufacturing process as that of FIG. First, pickling treatment (first pickling treatment: S2) was performed on the test material. Specifically, the test material was immersed for 900 seconds in a sulfuric acid tank in which a sulfuric acid solution containing 11.2 mass / volume% sulfuric acid was stored. The temperature of the sulfuric acid solution at this time was controlled at 60 ° C. The test material was pulled up from the sulfuric acid tank, and the test material was immersed in a washing tank in which room temperature water was stored, and the sulfuric acid solution was removed from the surface of the test material. Furthermore, the test material was immersed in the neutralization tank which accommodated the slaked lime solution, and the sulfuric acid solution remaining on the surface of the test material was neutralized. And the test material was dried with the drying apparatus (blower).

Then, heat processing (S3) was implemented with respect to the test material. Specifically, the spheroidizing annealing treatment was performed on the test material in an atmosphere composed of nitrogen gas, CO gas, and CO ₂ gas.

  After the heat treatment, a pickling treatment (second pickling treatment: S4) was performed on the test material. In the present invention example, the second pickling apparatus includes five hydrochloric acid tanks (first to fifth hydrochloric acid tanks) and a water washing tank. The hydrochloric acid solution in the first hydrochloric acid tank contained 7.3 mass / volume% hydrochloric acid. The hydrochloric acid solution in the second pickling tank contained 10.6% mass / volume hydrochloric acid. The hydrochloric acid solution in the third hydrochloric acid tank contained 14.7 mass / volume% hydrochloric acid. The hydrochloric acid solution in the fourth hydrochloric acid tank contained 15.9 mass / volume% hydrochloric acid. The hydrochloric acid solution in the fifth hydrochloric acid tank contained 24.8 mass / volume% hydrochloric acid. The temperature control of the hydrochloric acid solution in each hydrochloric acid tank was not performed.

  The test materials were immersed in the first to fifth hydrochloric acid tanks in the order of the first to fifth hydrochloric acid tanks. The immersion time in each tank was 340 seconds.

  After pulling up the test material from the fifth hydrochloric acid tank, the test material was immersed in a washing tank to remove the hydrochloric acid solution adhering to the surface of the test material.

  After the pickling treatment with hydrochloric acid, the test material was lubricated (S5). The lubrication apparatus was provided with two chemical conversion treatment tanks (a first chemical conversion treatment tank and a second chemical conversion treatment tank), a hot water washing tank, a lubricant tank, and a drying device (drying furnace).

  The processing liquid of the 1st chemical conversion treatment tank and the 2nd chemical conversion treatment tank contained zinc phosphate. The free acidity of the treatment liquid in the first chemical conversion treatment tank and the second chemical conversion treatment tank was adjusted to 3 to 8 points, and the total acidity was adjusted to 30 to 45 points. Here, the free acidity was defined as follows. Bromophenol blue was added as an indicator to 10 ml of the treatment solution, and titrated with a 0.1 N sodium hydroxide solution. The amount (ml) of 0.1 N sodium hydroxide solution required for neutralization was defined as the free acidity (point). Total acidity was defined as follows: To 10 ml of the treatment solution, phenolphthalein was added as an indicator and titrated with a 0.1 N sodium hydroxide solution. And the quantity (ml) of 0.1N sodium hydroxide solution required for neutralization was defined as the total acidity (points).

  The process liquid temperature of the 1st chemical conversion treatment tank and the 2nd chemical conversion treatment tank was controlled at 70-80 ° C.

  A lubricant solution was stored in the lubricant tank. The lubricant solution was an aqueous solution containing 0.5 to 2.0 points of sodium stearate. The lubricant liquid was controlled at 70-80 ° C. The concentration of the lubricant liquid was measured as follows. 10 ml of the lubricant liquid was collected in a milk fat meter, and 10 ml of isopropyl alcohol was added and stirred. Thereafter, 10 ml of 50 mass / volume% sulfuric acid was added and heated in a hot water bath for 5 to 10 minutes. Hot water was poured into the milk fat meter so that the fat layer was at the height of the scale portion of the milk fat meter, and the difference between the upper and lower scales of the fat layer was measured.

  In the lubrication treatment (S5), the test material was immersed in the first chemical conversion treatment tank for 400 seconds, and then immersed in the second chemical conversion treatment tank for 400 seconds. Next, the test material was immersed in a hot water bath. Next, the test material was immersed in a lubricant tank for 300 seconds. Finally, the test material was dried at 100 ° C. for 650 seconds in a drying apparatus (drying furnace) to produce a steel wire for cold forging according to an example of the present invention in which a lubricating film was formed.

  The appearance of the steel wire for cold forging of the example of the present invention was visually observed. As a result, the smut was not seen through the lubricating film, and the steel wire for cold forging according to the example of the present invention showed excellent appearance.

[Comparative example]
In the comparative example, a pickling treatment with a hydrochloric acid solution was performed in place of the pickling treatment with sulfuric acid (first pickling treatment step: S2) before the heat treatment of the above-described example of the present invention. Other manufacturing processes and conditions of each manufacturing process were the same as those of the present invention example.

  The pickling treatment with hydrochloric acid before the heat treatment was performed under the following conditions. The pickling apparatus for performing the pickling treatment with hydrochloric acid before the heat treatment includes first to fifth hydrochloric acid tanks, a water washing tank, a neutralization tank, and a drying furnace. The hydrochloric acid solution in the first hydrochloric acid tank contained 4.0% by mass / volume hydrochloric acid. The hydrochloric acid solution in the second pickling tank contained 6.6% mass / volume hydrochloric acid. The hydrochloric acid solution in the third hydrochloric acid tank contained 13.1 mass / volume% hydrochloric acid. The hydrochloric acid solution in the fourth hydrochloric acid tank contained 16.0 mass / volume% hydrochloric acid. The hydrochloric acid solution in the fifth hydrochloric acid tank contained 20.9 mass / volume% hydrochloric acid. The temperature control of the hydrochloric acid solution in each hydrochloric acid tank was not performed.

  The neutralization tank accommodated a slaked lime solution containing 0.8% by mass of slaked lime with a solid content concentration. The temperature of the slaked lime solution was controlled at 60 ° C.

  The test materials were immersed in the first to fifth hydrochloric acid tanks in the order of the first to fifth hydrochloric acid tanks. The immersion time in each tank was 220 seconds.

  After pulling up the test material from the fifth hydrochloric acid tank, the test material was immersed in a washing tank to remove the hydrochloric acid solution adhering to the surface of the test material. Next, the test material was immersed in a neutralization tank for 90 seconds. Next, the test material was dried at 100 ° C. for 300 seconds in a drying apparatus (drying furnace).

  Using the test material obtained by the above pickling treatment, a heat treatment step, a second pickling treatment step, and a lubrication step are performed under the same conditions as in the present invention example to produce a steel wire for cold forging of a comparative example. did.

  The following investigation tests were carried out using the cold forging steel wires of the present invention and the comparative example manufactured by the above-described manufacturing method.

[Surface roughness investigation test]
One coil-shaped cold forging steel wire (diameter: 21.0 mm) manufactured by the above-described manufacturing method of the present invention example and the comparative example was prepared for each of the present invention example and the comparative example. One sample having a diameter of 21.0 mm and a length of 50.0 mm was taken from the coils of the present invention and the comparative example. First, each sample was immersed in boiling hot water for 30 minutes and subjected to hot water washing treatment. Since the unreacted layer was made of sodium stearate, it was dissolved by hot water washing treatment. Next, the surface of each sample was washed with alcohol. Since the reaction layer was made of metal soap, the reaction layer was dissolved in alcohol, which is an organic solvent. Further, the surface of each sample was washed with an aqueous chromic acid solution. This removed the phosphate coating from the sample, exposing the strands. Then, as measured in accordance center line average roughness of the surface of the sample to expose the wires a _{(Ra 75)} in JIS-B0601 (2001) Annex 2 (reference). The center line average roughness was measured at any two locations in the circumferential direction of each sample, and the average value was defined as the surface roughness (unit: μm) of the present invention example and the comparative example.

[Lubricity investigation test]
A plurality of coil-shaped cold forging steel wires (diameter: 21.0 mm) manufactured by the manufacturing methods of the above-described inventive examples and comparative examples were prepared. Then, two dies of the same material and shape were prepared, one for the example of the present invention and the other for the comparative example. The steel wires of the inventive examples and comparative examples were subjected to wire drawing, that is, secondary wire drawing, to produce steel wires with a diameter of 20.0 mm. The diameter of the steel wire after wire drawing was controlled at 19.95 to 20.00 mm, and the diameter of the steel wire was measured every time one coil was drawn. When the measured diameter of the steel wire exceeded 20.00 mm, it was judged that the die had reached the end of its life. Then, the mass (unit: ton) of the cold forging steel wire that was drawn until the die reached the end of its life was investigated.

[Investigation test of lubricant film amount]
The amount of lubricating film formed on the steel wire for cold forging of the present invention example and the comparative example that were subjected to secondary wire drawing to 20.0 mm in the above-described lubricity investigation test was investigated by the following method. As described above, the lubricating coating includes an unreacted layer, a reactive layer, and a phosphate coating. Three samples each having a diameter of 21.0 mm and a length of 50.0 mm were taken from the steel wire for cold forging of the inventive example and the comparative example. And using each sample, the unreacted layer amount of this invention example and the comparative example, the reaction layer amount, and the phosphate film amount were measured as follows.

[Investigation test of unreacted layer amount]
The mass (referred to as initial mass) of each sample of the inventive example and the comparative example was measured. Next, each sample was immersed in boiling hot water for 30 minutes and subjected to a hot water washing treatment. Since the unreacted layer was made of sodium stearate, it was dissolved by hot water washing treatment. On the other hand, the reaction layer and the phosphate film did not dissolve. Next, a water washing treatment was performed on the sample after the hot water washing treatment. Next, the sample after the water washing treatment was dried, and the mass of the dried sample (referred to as mass after washing with hot water) was measured. The average value (average value of three samples) of the value (unit: g / mm ² ) obtained by dividing the value obtained by subtracting the mass after washing with hot water from the initial mass by the surface area of the peripheral surface of the sample is the “unreacted layer amount”. Defined.

[Investigation test of reaction layer amount]
The surface of the sample for which the unreacted layer amount investigation test was completed was cleaned with alcohol. Since the reaction layer was made of metal soap, the reaction layer was dissolved in alcohol, which is an organic solvent. On the other hand, the phosphate film did not dissolve with alcohol. Next, the sample was washed with water and dried, and the mass of the sample after drying (referred to as mass after alcohol washing) was measured. The average value (average value of three samples) of the value (unit: g / mm ² ) obtained by dividing the value obtained by subtracting the mass after alcohol washing from the mass after hot water washing by the surface area of the peripheral surface of the sample is “reaction layer amount”. Defined.

[Investigation test of phosphate coating amount]
The surface of the sample for which the reaction layer amount investigation test was completed was washed with an aqueous chromic acid solution. This removed the phosphate coating from the sample. Next, the sample was washed with water and dried, and the mass of the sample after drying (referred to as mass after chromic acid washing) was measured. The average value (average value of three samples) of the value (unit: g / mm ² ) obtained by dividing the value obtained by subtracting the mass after chromic acid washing from the mass after alcohol washing by the surface area of the peripheral surface of the sample is expressed as “phosphate film Defined as “amount”.

[Investigation test for adhesion of lubricating film]
The adhesiveness of the lubricant films of the present invention and the comparative examples was investigated by a Bowden test. Specifically, a sample having a diameter of 20.0 mm and a length of 50.0 mm was obtained from the cold forging steel wires of the present invention and the comparative example, which were second drawn to 20.0 mm in the above-described lubricity investigation test. One by one was collected. At any three locations on the surface of each sample collected, a steel ball having a chemical composition corresponding to JIS standard SUJ was pressed against the surface of the sample with a load of 3 kgf, and in the range of 20 mm in the axial direction of the sample. Slid. The friction coefficient μ of the steel ball during sliding is measured, and the number of sliding times (the number of reciprocations, that is, the range of 20 mm) until the friction coefficient μ becomes 0.20 (corresponding to the friction coefficient between iron and steel balls) or more. ) Was measured by counting once). A reciprocating sliding friction tester manufactured by Shinko Machine Co., Ltd. was used for the test.

[Investigation result]
The survey results are shown in Table 2.

  Referring to Table 2, the surface roughness of the inventive example exceeded 2.0 μm, whereas the surface roughness of the comparative example was less than 2.0 μm.

  Furthermore, in the mass of the steel wire for cold forging drawn until reaching the die life, the example of the present invention is more than five times that of the comparative example, and the lubricity in the secondary wire drawing process of the example of the present invention is comparative. It was significantly better than the example.

Further, the amount of unreacted layer and the amount of reacted layer in the inventive examples were almost the same as those in the comparative example. However, the amount of the phosphate film (g / mm ² ) of the inventive example was larger than that of the comparative example. In the example of the present invention, since the surface roughness was large, it was estimated that the phosphate film was formed thick, and as a result, the amount of the phosphate film was large.

  Furthermore, the sliding frequency of the inventive example according to the Bowden test was about twice as large as that of the comparative example. Therefore, the adhesion of the lubricating film after the secondary wire drawing process of the inventive example was superior to the comparative example. That is, it is considered that the inventive examples exhibit excellent lubricity during cold forging.

  While the embodiments of the present invention have been described above, the above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

DESCRIPTION OF SYMBOLS 1 1st pickling apparatus 2 Heat processing apparatus 3 2nd pickling apparatus 4 Lubricating apparatus 5 Wire drawing machine 10 Pickling apparatus 11 Phosphate film 12 Reaction layer 13 Unreacted layer 20 Conveyance apparatus 30 Sulfuric acid tank 40 Flushing tank 50 Neutralization tank 60 Drying device 70 Hydrochloric acid tank 80 Chemical conversion treatment tank 90 Hot water washing tank 100 Lubricant tank W Wire

Claims (2)

A first pickling process for performing pickling with a sulfuric acid solution on the strands;
Performing a heat treatment on the strands that have been pickled with the sulfuric acid solution; and
A second pickling treatment step of performing a pickling treatment with a hydrochloric acid solution on the strands after the heat treatment;
The manufacturing method of the steel wire for cold forging provided with the process of performing a lubrication process with respect to the said strand by which the pickling process was implemented with the said hydrochloric acid solution, and forming a lubricating film on the surface of the said strand. It is a manufacturing method of the steel wire for cold forging of Claim 1,
In the first pickling treatment step, the strand is transported to a first pickling apparatus including a sulfuric acid tank in which the sulfuric acid solution is stored, and the pickling treatment is performed.
In the second pickling treatment step, the wire is transported to a second pickling apparatus including a hydrochloric acid tank in which the hydrochloric acid solution is stored, and the pickling treatment is performed. Method.

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