JP2013072130A - Method for manufacturing hot-dip galvanized steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing, stably and in a short period of time, a hot-dip galvanized steel sheet having excellent press formability.SOLUTION: The method includes the steps of: hot-dip galvanizing a steel sheet; temper-rolling the steel sheet; subsequently making the steel sheet brought into contact with an acidic solution having a pH buffer action and containing an iron masking agent; holding the steel sheet for 1 to 60 seconds after the contact treatment; and washing the steel sheet with water. Thereby, a zinc based oxide layer is formed on a surface of the plated steel sheet. In the iron masking agent, it is preferable that a logarithm of the formation constant of a complexation reaction with Fe(II) is 3.0 or more, and that the logarithm of the formation constant of the complexation reaction with Fe(II) is higher than a logarithm of a formation constant of the complexation reaction with Zn(II).

Description

  The present invention relates to a method for producing a hot-dip galvanized steel sheet having excellent press formability with low sliding resistance during press forming.

  Hot-dip galvanized steel sheets are widely used in a wide range of fields, mainly for automobile body applications, and in such applications, they are subjected to press forming and used. However, the hot dip galvanized steel sheet has the disadvantage that the press formability is inferior to that of the cold rolled steel sheet. This is because the sliding resistance of the hot dip galvanized steel sheet in the press mold is larger than that of the cold rolled steel sheet. The hot dip galvanized steel sheet is pressed in the part where the sliding resistance between the mold and the bead is large. It becomes difficult to flow into the mold, and the steel sheet tends to break.

  Here, the hot dip galvanized steel sheet may or may not be alloyed after plating. Especially when not alloyed, there is a phenomenon that the sliding resistance further increases due to the adhesion of the plating to the mold (mold galling), and cracking occurs in the middle of continuous press molding. Has a serious adverse effect.

  In response to the above, as a method for improving the press formability when using a hot dip galvanized steel sheet, a method of applying a high viscosity lubricant is widely used. However, in this method, since the lubricating oil is highly viscous, a coating defect due to poor degreasing occurs in the coating process. In addition, there is a problem that the press performance becomes unstable due to oil shortage during pressing.

  As a method for solving the above-mentioned problem, Patent Document 1 and Patent Document 2 disclose that after hot-dip galvanized steel sheet that has been alloyed after plating is brought into contact with an acidic solution having a pH buffering action, It discloses a technique for improving the press formability by forming a zinc-based oxide on the surface layer of a hot-dip galvanized steel sheet by allowing it to stand for 30 seconds and then drying with water.

  In addition, a small amount of Al is added to the hot dip galvanizing bath for the purpose of adjusting the alloying reaction between the base iron and zinc, and there is Al oxide derived from Al in the bath on the surface of the hot dip galvanized steel sheet. Therefore, a hot-dip galvanized steel sheet that is not alloyed after plating has a higher surface Al oxide concentration and lower surface activity than a hot-dip galvanized steel sheet that has been alloyed after plating.

  In order to solve such a problem, Patent Document 3 discloses a method of forming the zinc-based oxide on a hot-dip galvanized steel sheet that is not subjected to alloying after plating, particularly when the surface activity is low. A method is disclosed in which the Al oxide on the surface is removed by contact with the surface to activate the surface and promote the formation of a zinc-based oxide.

  Patent Document 4 corresponds to the manufacturing conditions at high speed of a hot-dip galvanized steel sheet that is not alloyed after plating. Therefore, at least one of Ti, Zr, and Sn is added to the technique disclosed in Patent Document 3. A technique is disclosed in which a sufficient zinc-based oxide layer is formed in a short period of time by containing more than one kind in an acidic solution to obtain good press formability.

JP 2002-256448 A JP 2003-306781 A JP 2004-3004 A JP 2010-77456 A

  However, in Patent Documents 1 and 2, the film thickness is insufficient in press molding of automotive parts having a long sliding distance, and mold galling may occur in the production process of automotive parts.

Also in Patent Document 3, mold galling may occur in an automotive part having a long sliding distance as described above.
Furthermore, when the technique disclosed in Patent Document 4 is applied, the cost of Ti, Zr, and Sn (added amount: 0.1 to 50 g / L) contained in the acidic solution is added in addition to the conventional manufacturing cost. Therefore, the problem that a manufacturing cost increases arises.

  An object of the present invention is to provide a method for improving the above-mentioned problems and stably producing a hot-dip galvanized steel sheet having excellent press formability in a short time.

  As a result of intensive research to solve the above-mentioned problems, the present inventors applied hot-dip galvanizing to the steel sheet, tempered rolling, and then brought into contact with an acidic solution having a pH buffering action, thereby completing the contact. After forming the zinc-based oxide layer on the surface of the plated steel plate by holding it for 1 to 60 seconds and then washing with water, it contains zinc masking agent in the acidic solution, and has excellent press formability and zinc. It has been found that the formation time of the system oxide layer can be shortened.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

[1] After hot-dip galvanizing treatment and temper rolling on the steel sheet, the steel sheet is brought into contact with an acidic solution having a pH buffering action, held for 1 to 60 seconds after completion of contact, and then washed with water to thereby galvanize the surface of the plated steel sheet. In the manufacturing method of the hot dip galvanized steel plate which forms a system oxide layer, the said acidic solution contains an iron masking agent, The manufacturing method of the hot dip galvanized steel plate characterized by the above-mentioned.
[2] The iron masking agent has a logarithm of a complex formation reaction with Fe (II) of 3.0 or more and a logarithm of a complex formation reaction with Fe (II) of Zn ( The method for producing a hot-dip galvanized steel sheet according to [1] above, which is higher than the logarithm of the formation constant of the complex formation reaction with II).
[3] The method for producing a hot-dip galvanized steel sheet according to [1] or [2], wherein the concentration of the iron masking agent is 0.01 to 5 g / L.
[4] The acidic solution having a pH buffering action is at least one of acetate, phthalate, citrate, succinate, lactate, tartrate, borate, phosphate, and sulfate. The method for producing a hot dip galvanized steel sheet according to any one of the above [1] to [3], wherein the solution is an acidic solution having a pH in the range of 1.0 to 5.0. .
[5] The liquid film amount on the surface of the plated steel sheet at the end of contact with the acidic solution having a pH buffering action is 15 g / m ² or less, according to any one of [1] to [4], Manufacturing method of hot-dip galvanized steel sheet.

  In the present invention, the hot-dip galvanized steel sheet includes both a steel sheet (hereinafter referred to as GA) that is subjected to an alloying treatment after plating and a steel sheet that is not subjected to an alloying process (hereinafter referred to as GI).

According to the present invention, a hot dip galvanized steel sheet having a small sliding resistance during press forming and excellent press formability can be obtained. Furthermore, even when the time for forming the zinc-based oxide layer can be ensured only for a short time under high-speed production conditions, the hot-dip galvanized steel sheet having excellent press formability with small sliding resistance during press forming can be stabilized. Can be manufactured.

It is a schematic front view which shows a friction coefficient measuring apparatus. It is a schematic perspective view which shows the bead shape and dimension in FIG. It is a schematic perspective view which shows the bead shape and dimension in FIG.

  In the present invention, the hot dip galvanized steel sheet is brought into contact with an acidic solution, held for 1 to 60 seconds after completion of contact, and washed with water to form a zinc-based oxide layer on the hot dip galvanized steel sheet surface. Contains an iron masking agent. Thus, the use of an acidic solution containing an iron masking agent is an important requirement and a feature in the present invention.

The mechanism by which the zinc-based oxide layer is formed in a short time by containing an iron masking agent in the acidic solution is not clear, but can be considered as follows.
Usually, when a hot-dip galvanized steel sheet is brought into contact with an acidic solution, dissolution of zinc occurs from the steel sheet side. Since the dissolution of zinc causes a hydrogen generation reaction at the same time, as the dissolution of zinc proceeds, the hydrogen ion concentration in the solution decreases, and as a result, the pH of the solution increases, and the surface of the galvanized steel sheet is mainly composed of zinc. It is considered that an oxide layer is formed. When the pH rises, the dissolution of zinc, which has occurred with the hydrogen generation reaction, will occur with the reduction reaction of dissolved oxygen. In addition to the zinc dissolution reaction, an iron dissolution reaction from the steel sheet may also occur in the acidic solution. When iron ions, especially Fe (II), are present in an acidic solution, dissolved oxygen is consumed to oxidize Fe (II), and the amount of dissolved oxygen consumed to dissolve zinc decreases, resulting in a dissolution rate of zinc. Is expected to decrease.
On the other hand, when an acidic solution containing an iron masking agent is contained, dissolved Fe (II) and the iron masking agent form a stable complex to deactivate Fe (II), thereby dissolving oxygen. Consumption can be suppressed. Therefore, it is considered that an oxide layer can be formed on the surface of the hot dip galvanized steel sheet in a short time without hindering dissolution of zinc at the time of pH increase, and good press formability can be obtained.

  As such an iron masking agent, the logarithm of the formation constant of the complex formation reaction with Fe (II) is 3.0 or more, and the logarithm of the formation constant of the complex formation reaction with Fe (II) is Zn. It is preferable to use an iron masking agent higher than the logarithm of the formation constant of the complex formation reaction with (II). The effect of the present invention can be sufficiently obtained.

  If the logarithm of the formation constant of the complex formation reaction with Fe (II) is less than 3.0, the stabilizing effect of Fe (II) may be insufficient, and the consumption of dissolved oxygen may not be suppressed. In addition, when an iron masking agent having a lower logarithm of a complex formation reaction with Fe (II) than a logarithm of a complex formation reaction with Zn (II) is used, Zn (II) is inactivated. Therefore, the formation of the zinc-based oxide layer may be hindered.

  The concentration of the iron masking agent is preferably 0.01 to 5 g / L. If the concentration is less than 0.01 g / L, the stabilizing effect of Fe (II) becomes insufficient, and thus consumption of dissolved oxygen may not be suppressed. On the other hand, when it exceeds 5 g / L, the amount taken into the oxide layer increases, which may affect the slidability.

As such an iron masking agent, at least one of histamine, inosine, β-phenylalanine, polyphosphate, proline, sarcosine, serine, threonine, valine, acetylacetone and the like can be used.
For reference, Table 1 shows logarithms of formation constants of complex formation reactions between a part of iron masking agents applicable to the present invention and Fe (II) and Zn (II).

  The acidic solution used in the present invention has a pH buffering action. If an acidic solution that does not have a pH buffering action is used, the pH of the solution rises instantaneously, and zinc cannot be dissolved sufficiently to form an oxide layer. An oxide layer does not form. On the other hand, when an acidic solution having a pH buffering action is used, even if zinc is dissolved and a hydrogen generation reaction occurs, the pH of the solution gradually increases, so that further dissolution of zinc proceeds. Thus, a zinc-based oxide sufficient for improving the slidability is generated.

  If the pH of the acidic solution is too low, dissolution of zinc is promoted, but it is difficult to form an oxide. Therefore, the pH is preferably 1.0 or more. On the other hand, if the pH is too high, the reaction rate of zinc dissolution becomes low, so the pH of the solution is desirably 5.0 or less.

  The acidic solution having a pH buffering action is preferably one having a pH buffering action in a pH range of 2.0 to 5.0. This is because when an acidic solution having a pH buffering action in a pH range of 2.0 to 5.0 is used, the oxide layer targeted by the present invention is stabilized by holding the acidic solution for a predetermined time after contact. This is because it can be obtained.

Examples of such an acidic solution having a pH buffering action include acetates such as sodium acetate (CH ₃ COONa), phthalates such as potassium hydrogen phthalate ((KOOC) ₂ C ₆ H ₄ ), sodium citrate (Na Citrates such as ₃ C ₆ H ₅ O ₇ ) and potassium dihydrogen citrate (KH ₂ C ₆ H ₅ O ₇ ), succinates such as sodium succinate (Na ₂ C ₄ H ₄ O ₄ ), and lactic acid At least one of lactate such as sodium (NaCH ₃ CHOHCO ₂ ), tartrate such as sodium tartrate (Na ₂ C ₄ H ₄ O ₆ ), borate, phosphate, sulfate, An aqueous solution containing the component in a range of 5 to 50 g / L can be used. If the concentration is less than 5 g / L, the pH of the solution rises relatively quickly with the dissolution of zinc, so that an oxide layer sufficient for improving the slidability cannot be formed, and 50 g / L is reduced. If it exceeds, dissolution of zinc is promoted, and not only does the formation of the oxide layer take a long time, but also the plating layer is severely damaged, and the original role as a rust-proof steel sheet may be lost.

There is no particular limitation on the method of bringing the hot dip galvanized steel plate into contact with the acidic solution. The method of immersing the plated steel plate in the acidic solution, the method of spraying the acidic solution onto the plated steel plate, and applying the acidic solution to the plated steel plate via the coating roll. There are ways to do this. Finally, it is desirable that the acidic solution is in the form of a thin liquid film and is present on the steel sheet surface. If the amount of liquid film present on the surface of the steel sheet is small, an oxide layer having a desired thickness cannot be formed on the plating surface. However, if the amount of the acidic solution present on the surface of the steel sheet is too large, the pH of the solution does not increase even if zinc dissolution occurs, and only zinc dissolution occurs one after another. It has a long time, the plating layer is severely damaged, and it is considered that the original role as a rust-proof steel sheet is lost. From such a viewpoint, it is effective to adjust the liquid film amount on the surface of the steel sheet at the end of contact with the acidic solution to 15 g / m ² or less. On the other hand, the lower limit is preferably 1 g / m ² or more. The liquid film amount can be adjusted by a squeeze roll, air wiping or the like. In the case of the method of immersing in the acidic solution, “at the end of the contact” is “end of immersing”, in the case of the method of spraying the acidic solution onto the plated steel plate, “end of spraying”, the method of applying the acidic solution via the coating roll In this case, it means “coating end”.

  Moreover, after completion | finish of contact with a pickling solution, it hold | maintains for 1 to 60 seconds, and sets time to water washing (holding time to water washing) to 1 to 60 seconds. This is because, if the time until washing with water is less than 1 second, the acidic solution is washed out before the pH of the solution rises and the oxide layer mainly composed of zinc is formed, so that the effect of improving the slidability is obtained. I can't get it. On the other hand, even if it exceeds 60 seconds, there is no change in the amount of the oxide layer.

  If the above conditions are satisfied, a zinc-based oxide layer can be efficiently and stably formed on the surface of the hot dip galvanized steel sheet.

  After the temper rolling, the steel plate may be brought into contact with the alkaline solution before being brought into contact with the acidic solution and forming the zinc-based oxide layer. During the temper rolling, the Al oxide on the surface layer is destroyed by contact with the rolling roll, but a part of the Al oxide may remain. On the other hand, by making it contact with an alkaline solution, it becomes possible to remove the Al oxide layer remaining on the surface layer and to activate the surface more. There is no restriction | limiting in particular in the method of making it contact with alkaline solution, It can process by immersion or a spray. If the pH is low, the reaction is slow and it takes a long time for the treatment. Therefore, the pH is preferably 10 or more. If it is pH within the said range, there will be no restriction | limiting in the kind of solution, For example, sodium hydroxide etc. can be used.

If the acidic solution remains on the surface of the steel plate after washing with water, rust is likely to occur when the steel plate coil is stored for a long time. From the viewpoint of preventing the occurrence of rust, after contacting and holding the acidic solution, before washing with water, the alkaline solution and the steel plate are contacted by a method such as immersion in an alkaline solution or sprayed with an alkaline solution, and remain on the steel plate surface. You may give the process which neutralizes the acidic solution which exists. The alkaline solution preferably has a pH of 12 or less in order to prevent dissolution of the zinc-based oxide formed on the surface. If it is in the said pH range, there will be no restriction | limiting in the solution to be used, For example, sodium hydroxide, sodium phosphate, etc. can be used. The zinc-type oxide in this invention mainly has zinc as a metal component. Oxides and hydroxides, when the total amount of metal components such as iron and Al is less than zinc, or the total amount of anions such as sulfuric acid, nitric acid, and chlorine is less than the number of moles of oxygen and hydroxyl groups When it contains, it is contained in the zinc-type oxide of this invention.

  In addition, anionic components such as sulfate ions used for adjusting the pH of the acidic solution in the zinc-based oxide layer may be contained in the zinc-based oxide layer, but anionic components such as sulfate ions and components of the iron masking agent Impurities such as S, N, P, B, Cl, Na, Mn, Ca, Mg, Ba, Sr, Si, S, N, P, B, Cl, Na Even if a compound comprising Mn, Ca, Mg, Ba, Sr, Si, O, and C is incorporated into the zinc-based oxide layer, the effect of the present invention is not impaired.

  Among ions contained in an acidic solution as a pH buffering agent, in particular, acetate ion (logarithm of production constant 1.9), tartrate ion (logarithm of production constant 2.7), phosphate ion (logarithm of production constant 2) .7) is easy to complex with Fe (II), but by using an iron masking agent having a logarithm of the formation constant of the complexation reaction with Fe (II) of 3.0 or more, The effect of the invention is not impaired. Preferably, it is desirable to use an iron masking agent having a logarithm of the formation constant of a complex formation reaction with Fe (II) of 5.0 or more.

  Further, by using an iron masking agent whose logarithm of the complex formation reaction with Fe (II) is higher than the logarithm of the complex formation reaction with Zn (II), a zinc-based oxide layer is formed. By suppressing the reaction, the effect of the present invention is not impaired.

  The thickness of the zinc-based oxide layer formed on the surface of the plated steel plate is preferably 10 nm or more. By setting it to 10 nm or more, a hot-dip galvanized steel sheet exhibiting good slidability can be obtained. In order to acquire a further effect, More preferably, it is 20 nm or more, More preferably, it is 30 nm or more. If the thickness is 10 nm or more, the zinc-based oxide layer remains even in the case where the surface oxide layer is worn in the press molding process in which the contact area between the mold and the workpiece becomes large, and the sliding property is lowered. There is no. On the other hand, the upper limit of the thickness of the oxide layer is not particularly provided, but if it exceeds 200 nm, the surface reactivity is lowered and the amount of zinc-based oxide film produced is reduced.

  When manufacturing the hot dip galvanized steel sheet of the present invention, it is necessary that Al is added to the plating bath, but the additive element components other than Al are not particularly limited. That is, even if Pb, Sb, Si, Sn, Mg, Mn, Ni, Ti, Li, Cu or the like is contained or added in addition to Al, the effect of the present invention is not impaired.

Next, the present invention will be described in more detail with reference to examples.
On a steel sheet having a thickness of 0.7 mm annealed after cold rolling, hot dip galvanizing was performed by a conventional method, and then temper rolling was performed. After temper rolling, the surface activation treatment was performed by immersing in an alkaline solution (sodium hydroxide aqueous solution) having a pH of 10 and a temperature of 50 ° C. for 3 seconds and then washing with water. After surface activation treatment, in an acidic solution tank, containing 30 g / L of sodium acetate, immersed in an acidic solution at 35 ° C. and pH 1.5, pulled up, and then applied to the steel sheet surface with a squeeze roll on the acid solution tank outlet side. The amount of liquid film to be adhered was adjusted. The amount of liquid film was adjusted by changing the pressure of the squeeze roll. After leaving (holding) for a predetermined time after adjusting the liquid film amount, an alkaline solution (sodium hydroxide aqueous solution) having a pH of 10 and a temperature of 50 ° C. is sprayed to neutralize the acidic solution remaining on the steel sheet surface, and then 50 The steel sheet was sprayed and washed with hot water at 0 ° C., dried and dried to form a zinc-based oxide layer on the plating surface. Some performed only temper rolling, and after temper rolling, the oxide formation process by contact with an acidic solution was not performed.

  With respect to the hot dip galvanized steel sheet obtained as described above, the oxide layer thickness of the plating surface layer and the sliding characteristics during press forming were investigated. The sliding characteristics during press molding were evaluated by the friction coefficient.

The following is a method for investigating the sliding characteristics during the measurement of the oxide layer thickness and press molding.
Measurement of oxide layer thickness An X-ray fluorescence analyzer was used to measure the oxide layer thickness. The tube voltage and current during the measurement were 30 kV and 100 mA, the spectroscopic crystal was set to TAP, and the O-Kα ray was detected. When measuring the O-Kα line, in addition to the peak position, the intensity at the background position was also measured so that the net intensity of the O-Kα line could be calculated. The integration time at the peak position and the background position was 20 seconds, respectively. Further, a silicon wafer on which silicon oxide films having a thickness of 96 nm, 54 nm, and 24 nm cleaved to an appropriate size were simultaneously measured, and the Zn-based oxide layer was determined from the measured O-Kα ray intensity and silicon oxide film thickness. The thickness of was calculated.

Method for Measuring Friction Coefficient In order to evaluate press formability, the friction coefficient of each test material was measured as follows.
FIG. 1 is a schematic front view showing a friction coefficient measuring apparatus. As shown in the figure, a friction coefficient measurement sample 1 collected from a test material is fixed to a sample table 2, and the sample table 2 is fixed to the upper surface of a slide table 3 that can move horizontally. A slide table support 5 having a roller 4 in contact with the slide table 3 is provided on the lower surface of the slide table 3, and when this is pushed up, a pressing load N applied to the friction coefficient measurement sample 1 by the bead 6. A first load cell 7 is attached to the slide table support 5. A second load cell 8 for measuring a sliding resistance force F for moving the slide table 3 in the horizontal direction in a state where the pressing force is applied is attached to one end of the slide table 3. In addition, as a lubricating oil, a rust preventive cleaning oil (Preton R352L, Preton is a registered trademark) manufactured by Sugimura Chemical Industry Co., Ltd. was applied to the surface of Sample 1 and tested.

  2 and 3 are schematic perspective views showing the shape and dimensions of the beads used. The bead 6 slides with its lower surface pressed against the surface of the sample 1. The bead 6 shown in FIG. 2 has a width of 10 mm, a length of 12 mm in the sliding direction of the sample, and a lower portion at both ends of the sliding direction is formed by a curved surface having a radius of curvature of 4.5 mm. It has a plane with a moving direction length of 3 mm. The bead 6 shown in FIG. 3 has a width of 10 mm, a length of 59 mm in the sliding direction of the sample, and a lower portion at both ends in the sliding direction is formed by a curved surface having a curvature of 4.5 mmR. It has a plane with a direction length of 50 mm.

The coefficient of friction was measured under the following two conditions.
[Condition 1]
The bead shown in FIG. 2 was used, the pressing load N was 400 kgf, and the sample drawing speed (horizontal moving speed of the slide table 3) was 100 cm / min.
[Condition 2]
The bead shown in FIG. 3 was used, the pressing load N was 400 kgf, and the sample drawing speed (horizontal moving speed of the slide table 3) was 20 cm / min.
The friction coefficient μ between the test material and the bead was calculated by the formula: μ = F / N.

  The results obtained above are shown in Table 2 together with the conditions.

From Table 2, the following matters became clear.
No. 1 is a comparative example in which treatment with an acidic solution is not performed. In conditions 1 and 2, the friction coefficient is high.
No. Nos. 7 to 21 use an acidic solution containing polyphosphate (logarithm of production constant: 3.0), acetylacetone (logarithm of production constant: 5.07), and histamine (logarithm of production constant: 9.6) which are iron masking agents. This is an example of the present invention. No. 1 using an acidic solution containing acetate ions (logarithm of the production constant of 1.9), which is a pH buffer, and no iron masking agent. Compared with 2-6, in the case of the same time until water washing, the thickness of the oxide layer is thicker in the examples of the present invention in any treatment, and the formation of the oxide layer is promoted. Recognize. Further, in the example of the present invention, in conditions 1 and 2, No. Compared with 2-6, the friction coefficient of substantially equal or less can be ensured.
From the above results, it can be seen that in the example of the present invention, a hot-dip galvanized steel sheet having excellent press formability can be stably produced in a short time.

  Since the hot-dip galvanized steel sheet of the present invention is excellent in press formability, it can be applied in a wide range of fields mainly for automobile body applications.

DESCRIPTION OF SYMBOLS 1 Friction coefficient measurement sample 2 Sample stand 3 Slide table 4 Roller 5 Slide table support stand 6 Bead 7 1st load cell 8 2nd load cell 9 Rail N Pushing load F Sliding resistance force

Claims (5)

The steel sheet is subjected to hot dip galvanizing treatment, tempered and rolled, and then brought into contact with an acidic solution having a pH buffering action. In the method for producing a hot-dip galvanized steel sheet forming a layer,
The said acidic solution contains an iron masking agent, The manufacturing method of the hot dip galvanized steel plate characterized by the above-mentioned.   The iron masking agent has a logarithm of complex formation reaction with Fe (II) of 3.0 or more and a logarithm of complex formation reaction with Fe (II) of Zn (II). The method for producing a hot-dip galvanized steel sheet according to claim 1, wherein the production constant is higher than the logarithm of the formation constant of the complex formation reaction.   The method for producing a hot-dip galvanized steel sheet according to claim 1 or 2, wherein the concentration of the iron masking agent is 0.01 to 5 g / L.   The acidic solution having a pH buffering action contains at least one of acetate, phthalate, citrate, succinate, lactate, tartrate, borate, phosphate and sulfate. And the manufacturing method of the hot dip galvanized steel sheet as described in any one of Claims 1-3 characterized by being an acidic solution whose pH exists in the range of 1.0-5.0. 5. The hot dip galvanized steel sheet according to claim 1, wherein the amount of the liquid film on the surface of the plated steel sheet at the end of contact with the acidic solution having a pH buffering action is 15 g / m ² or less. Production method.

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