JP4826486B2 - Method for producing galvannealed steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a process for producing hot dip galvannealed steel sheet having excellent press formability even for a material having high forming load and easy to generate die galling. <P>SOLUTION: The process for producing the hot dip galvannealed steel sheet comprises depositing a Zn-based oxide layer having a thickness of &ge;10 nm on the surface of a galvanized steel sheet by subjecting a steel sheet to hot dip galvanizing and to galvannealing by heating, after temper rolling, bringing the resulting steel sheet into contact with an acid solution, after completing the contact, allowing the steel sheet to stand for 1 to 120 s, and rinsing the steel sheet allowed to stand with water, wherein Sn ions are incorporated in the acid solution. Thus, the oxide layer having a mean thickness of &ge;10 nm and containing, as essential components, Zn and metal particles mainly comprising Sn is deposited on the surface of the galvanized steel sheet. The acid solution preferably contains at least one kind of sulfate, nitrate, chloride and phosphate of Sn so that the Sn ion concentration is within a range of 0.1 to 50 g/l. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet having excellent press formability even in a material having a high forming load, such as a high-strength alloyed hot-dip galvanized steel sheet, which tends to cause mold galling.

An alloyed hot-dip galvanized steel sheet is widely used in a wide range of fields, mainly for automobile body applications, because it is superior in weldability and paintability compared to a galvanized steel sheet that is not subjected to alloying treatment. The alloyed hot-dip galvanized steel sheet for such applications is subjected to press forming and used. However, the alloyed hot-dip galvanized steel sheet has a disadvantage that its press formability is inferior to that of a cold-rolled steel sheet. This is because the sliding resistance of the alloyed hot-dip steel sheet in the press die is larger than that of the cold-rolled steel sheet. That is, the alloyed hot-dip galvanized steel sheet is less likely to flow into the press mold at the portion where the sliding resistance between the mold and the bead is large, and the steel sheet tends to break.

An alloyed hot-dip galvanized steel sheet is formed by galvanizing the steel sheet and then heat-treating to form an Fe-Zn alloy phase by diffusion of Fe in the steel sheet and Zn in the plating layer to cause an alloying reaction. It has been made. This Fe-Zn alloy phase is usually a film composed of a Γ phase, a δ ₁ phase, and a ζ phase. As the Fe concentration decreases, that is, in the order of Γ phase → δ ₁ phase → ζ phase, hardness and melting point Tends to decrease. For this reason, from the viewpoint of slidability, a coating with high hardness, high melting point and high Fe concentration is effective, and alloyed hot-dip galvanized steel sheet, which emphasizes press formability, Manufactured with high average Fe concentration.

  However, a coating film having a high Fe concentration has a problem that a hard and brittle Γ phase is easily formed at the plating-steel plate interface, and a phenomenon of peeling from the interface during processing, that is, so-called powdering is likely to occur. Therefore, as shown in Patent Document 1, in order to achieve both slidability and powdering resistance, there is a method of applying a hard Fe-based alloy as a second layer to the upper layer by a method such as electroplating. It has been taken.

  In addition to this, as a method for improving the press formability when using a galvanized steel sheet, a method of applying a high-viscosity lubricating oil is widely used. However, this method has problems such as a coating defect due to poor degreasing in the painting process due to the high viscosity of the lubricating oil, and press performance becoming unstable due to oil shortage during pressing. Therefore, there is a strong demand for improving the press formability of the galvannealed steel sheet itself.

  As a method for solving the above problems, Patent Document 2 and Patent Document 3 describe that the surface of a zinc-based plated steel sheet is subjected to electrolytic treatment, dipping treatment, coating oxidation treatment, or heat treatment to oxidize mainly ZnO. A technique for improving weldability and workability by forming a film is disclosed.

  Patent Document 4 discloses that by immersing a plated steel sheet in an aqueous solution containing 5 to 60 g / l of sodium phosphate and having a pH of 2 to 6 on the surface of the zinc-based plated steel sheet, performing electrolytic treatment, or applying the above aqueous solution, P A technique for improving press moldability and chemical conversion treatment by forming an oxide film mainly composed of oxides is disclosed.

  In Patent Document 5, the surface of a zinc-based plated steel sheet is improved in press formability and chemical conversion treatment by generating Ni oxide by electrolytic treatment, dipping treatment, coating treatment, coating oxidation treatment, or heat treatment. Technology is disclosed.

In Patent Document 6, an alloyed hot-dip galvanized steel sheet is brought into contact with an acidic solution to form an oxide mainly composed of Zn on the surface of the steel sheet, suppressing adhesion between the plating layer and the press mold, and slidability. A technique for improving the above is disclosed.
Japanese Patent No. 1-319661 JP-A-53-60332 Japanese Patent Laid-Open No. 2-190483 JP-A-4-88196 Japanese Patent Laid-Open No. 3-191093 Japanese Patent Application No. 2002-116026

  However, Patent Documents 1 to 6 are effective for a relatively low-strength alloyed hot-dip galvanized steel sheet that is often used for automobile outer plates, but because of the high load during press molding, In a high-strength galvannealed steel sheet with increased contact surface pressure, the effect of improving press formability cannot always be obtained stably.

  In view of such circumstances, the present invention provides a method for producing an alloyed hot-dip galvanized steel sheet having excellent press formability even in a material having a high forming load, such as a high-strength alloyed hot-dip galvanized steel sheet, which is likely to cause mold galling. For the purpose.

The inventors of the present invention made further studies to solve the above problems. As a result, the following knowledge was obtained.
On the surface of the galvannealed steel sheet produced by the method of Patent Document 6, an oxide layer mainly composed of Zn is formed, and most of it is formed in the pressure adjusting portion. In actual press molding, the surface that preferentially contacts the mold is this pressure control part, and when the contact surface pressure is low, the Zn-based oxide on the surface of the pressure control part is The effect of improving press formability can be obtained by suppressing direct contact. However, when high strength steel is used as the plating base steel sheet, the forming load is higher than that of soft steel, and galling or cracking is likely to occur. In such a case, in the Zn-based oxide described in Patent Document 6, It was found that the effect was insufficient. Further, as a result of further research, the present inventors have a limit in expressing high lubricity even when the molding load is high only with the Zn-based oxide layer, and in addition to the Zn-based oxide layer, the present inventors mainly It was found that high slidability can be obtained by mixing the metal particles. The reason for this is that the presence of a soft metal (Sn) on the surface compared to the Zn-Fe alloy and Zn-based oxide, which are plating components, gives the effect of reducing the shear resistance with the mold. Think. Further, in the present invention, it is essential to mix with the Zn-based oxide, so it is estimated that there is a concerted effect with the adhesion suppression effect by the Zn-based oxide.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] Hot dip galvanizing is applied to the steel sheet, alloyed by heat treatment, temper rolled, contacted with an acidic solution, left for 1 to 120 seconds after contact is completed, and then washed with water to form zinc. A method for producing an alloyed hot-dip galvanized steel sheet, wherein the acidic solution contains Sn ions in the method for producing an alloyed hot-dip galvanized steel sheet having a Zn-based oxide layer of 10 nm or more formed on the surface of the plated steel sheet .
[2] In the above [1], the acidic solution contains at least one of Sn sulfate, nitrate, chloride, and phosphate in the range of 0.1 to 50 g / l as the Sn ion concentration. A method for producing an alloyed hot-dip galvanized steel sheet.
[3] In the above [1] or [2], the acidic solution has a pH buffering action, and 1.0 mol / l water necessary for increasing the pH of 1 liter of acidic solution from 2.0 to 5.0. A method for producing an alloyed hot-dip galvanized steel sheet, wherein the pH increase defined by the amount (l) of sodium oxide solution is in the range of 0.05 to 0.5.
[4] In any one of the above [1] to [3], the acidic solution includes acetate, phthalate, citrate, succinate, lactate, tartrate, borate, phosphate. An alloyed hot-dip galvanized steel sheet containing at least one of them in a component content of 5 to 50 g / l, a pH of 0.5 to 2.0, and a liquid temperature of 20 to 70 ° C. Manufacturing method.
[5] The alloyed molten zinc according to any one of the above [1] to [4], wherein the acidic solution film formed on the surface of the steel sheet after contact with the acidic solution is 50 g / m ² or less Manufacturing method of plated steel sheet.

  According to the present invention, when manufacturing a high-strength galvannealed steel sheet that has a high forming load and is likely to cause mold galling, the sliding resistance during press forming is small and excellent press formability can be achieved. And in this invention, the above-mentioned galvannealed steel plate excellent in press formability can be manufactured stably.

In the production of galvannealed steel sheet, after galvanizing the steel sheet, it is further heated and alloyed, and due to the difference in the reactivity of the steel sheet-plating interface during this alloying process. There are irregularities on the surface of the galvannealed steel sheet. However, after the alloying treatment, temper rolling is usually performed for securing the material, and the plating surface is smoothed and unevenness is alleviated by contact with the roll during the temper rolling. Therefore, at the time of press molding, the force required for the mold to crush the plating surface convex portion is reduced, and the sliding characteristics can be improved.

  When the load at the time of press forming is low, the part where the mold is in direct contact is the pressure adjusting part on the surface of the galvannealed steel sheet, but when the load at the time of press forming is high, the surface of the steel sheet is not adjusted. It is expected that the pressure part also comes into direct contact with the mold together with the pressure adjusting part. Therefore, it is important to improve the slidability that hard and high melting point materials that prevent adhesion to the mold exist in the pressure-regulated and unregulated parts of the galvannealed steel sheet surface. It is. In this respect, the presence of the oxide layer on the surface of the steel sheet is effective in improving the sliding characteristics because the oxide layer prevents adhesion with the mold.

At the time of actual press molding, the oxide on the surface layer is worn away and scraped off. Therefore, when the contact area between the mold and the workpiece is large, it is necessary to have a sufficiently thick oxide layer. In addition, although oxide is formed on the surface of the plating layer by heating during the alloying treatment, most of the oxide layer is destroyed by contact with the roll during temper rolling, and the new surface is exposed. In order to obtain mobility, a thick oxide layer must be formed before temper rolling. However, taking these into consideration, even if a thick oxide layer is formed before temper rolling, it is not possible to avoid the destruction of the oxide layer that occurs during temper rolling. It exists unevenly and good slidability cannot be obtained stably.

  For this reason, good slidability can be stably obtained by applying a treatment to uniformly form an oxide layer on the surface of the galvannealed steel sheet that has been subjected to temper rolling, particularly the surface of the plated steel sheet. become.

  The alloyed hot-dip galvanized steel sheet after temper rolling is brought into contact with an acidic solution, and after that, the oxide liquid layer is formed on the plating surface layer by washing with water and drying after holding the acidic liquid film on the surface of the steel sheet for a predetermined time. Can be formed. At this time, the oxide layer to be formed is mainly composed of Zn and is mainly formed in the pressure regulating portion on the surface of the plated steel sheet. In the alloyed hot-dip galvanized steel sheet, which is often used for automobile outer plates, the forming load is low, so it is mainly the pressure-regulating part on the surface of the plating layer that directly contacts the mold during press molding. Therefore, good press formability can be obtained by forming the oxide layer on the pressure adjusting portion on the surface of the plating layer. However, under more severe conditions such as when the load during press molding is high, the plating surface and the mold come into contact with each other at high surface pressure and receive sliding, so even if a Zn-based oxide layer exists on the surface The plating alloy surface and the mold come into direct contact and cause adhesion. In that case, the shearing stress between the plating alloy and the mold becomes a large sliding resistance. Here, when Sn metal particles are mixed, the sliding resistance is reduced. The reason for this is thought to be due to the presence of soft Sn, which is extended during sliding and spreads between the plating surface and the mold to prevent direct contact between them. Since metal Sn has a very small shear stress, the contact resistance between the mold and the plating surface is small. However, Sn must be present at the same time as the Zn-based oxide layer. For example, even if metal Sn alone is applied to the alloyed hot dip galvanized surface, it has the effect of reducing contact resistance, but the Sn layer is easily deformed, so it is easily cut off at the apex of the plating unevenness and the unevenness of the mold The effect disappears in a short time. Therefore, the effect is insufficient. In the present invention, suppression of adhesion of a hard Zn-based oxide having a relatively high melting point is also utilized by mixing metal Sn with the Zn-based oxide layer. Moreover, the effect can be exhibited in the place crushed by making metal Sn into a particle form instead of a layer form. It is also estimated that the Zn-based oxide has an effect of holding the metal Sn particles on the plating surface.

  As described above, in the present invention, hot dip galvanizing is applied to the steel sheet, further alloyed by heat treatment, subjected to temper rolling, brought into contact with an acidic solution, and left for 1 to 120 seconds after completion of the contact, and then washed with water. By performing, when forming a Zn-type oxide layer of 10 nm or more on the surface of a galvanized steel sheet, the acidic solution contains Sn ions. This is the most important requirement in the present invention.

  In order to contain Sn ions in the acidic solution, it is preferable to contain at least one of Sn sulfate, nitrate, chloride, and phosphate in the range of 0.1 to 50 g / l as the Sn ion concentration. . When the Sn ion concentration is less than 0.1 g / l, the amount of formed metal particles mainly composed of Sn is small, and the oxide layer is mainly composed of Zn. It may not be obtained. On the other hand, if it exceeds 50 g / l, the ratio of formed metal particles mainly composed of Sn is large and effective in improving the sliding characteristics. However, these metal particles mainly composed of Sn are alloyed hot dip galvanized. There is a tendency to degrade the compatibility with adhesives designed for steel plates.

  The acidic solution used preferably has a pH buffering action in the pH range of 2.0 to 5.0. This is because when an acidic solution having a pH buffering action in the pH range of 2.0 to 5.0 is used, it is maintained for a predetermined time after contact with the acidic solution, so that the dissolution of Zn and the Zn-based oxidation are caused by the reaction between the acidic solution and the plating layer. This is because a product formation reaction occurs sufficiently, and an oxide layer can be stably obtained on the steel sheet surface. In addition, as an indicator of such pH buffering action, the degree of pH increase defined by the amount (l) of 1.0 mol / l aqueous sodium hydroxide solution required to increase the pH of a 1 liter acidic solution from 2.0 to 5.0. It can be evaluated and this value is preferably in the range of 0.05 to 0.5. If the pH increase is less than 0.05, the pH rises rapidly and Zn cannot be dissolved sufficiently to form an oxide, so that the oxide layer may not be sufficiently formed. On the other hand, if it exceeds 0.5, dissolution of Zn is promoted, and not only does it take a long time to form an oxide layer, but the plating layer is also severely damaged, and it may be possible to lose its original role as a rust-proof steel plate. Because. The degree of pH increase is evaluated by adding an inorganic acid that has almost no buffering property in the pH range of 2.0 to 5.0 to an acidic solution having a pH value exceeding 2.0, and lowering the pH value to 2.0 once. To do.

Acidic solutions with such pH buffering properties 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 Examples thereof include lactate salts such as sodium (NaCH ₃ CHOHCO ₂ ), tartrate salts such as sodium tartrate (Na ₂ C ₄ H ₄ O ₆ ), borate salts, and phosphate salts. It is preferable to use an aqueous solution containing each component in a range of 5 to 50 g / l. When 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. On the other hand, if it exceeds 50 g / l, dissolution of zinc is promoted, and not only does it take a long time to form an oxide layer, but the plating layer is also severely damaged, and it may lose its original role as a rust-proof steel sheet. Because it is.

  The pH of the acidic solution is desirably in the range of 0.5 to 2.0. When the pH exceeds 2.0, precipitation of Sn ions (formation of hydroxide) occurs in the solution, and it may be impossible to stably impart Sn metal particles to the surface of the plated steel sheet. On the other hand, if the pH is too low, dissolution of zinc is promoted and not only the amount of plating is reduced, but also the plating film is cracked and easily peeled during processing. Therefore, the pH is preferably 0.5 or more. When the pH of the acidic solution is higher than the range of 0.5 to 2.0, the pH can be adjusted with an inorganic acid having no pH buffering property such as sulfuric acid.

  The temperature of the acidic solution is preferably in the range of 20 to 70 ° C. If it is less than 20 ° C., the production reaction of the oxide layer takes a long time, and the productivity may be lowered. On the other hand, when the temperature is high, the reaction proceeds relatively quickly, but conversely, processing unevenness tends to occur on the surface of the steel sheet, so it is desirable to control the temperature to 70 ° C. or lower.

  In the present invention, if the acidic solution to be used contains Sn ions, it is possible to stably form Sn metal particles and Zn-based oxide layers with excellent slidability. Even if the metal ions or inorganic compounds are intentionally contained as impurities, the effect of the present invention is not impaired. In particular, since Zn ions are ions that elute when the steel sheet comes into contact with the acidic solution, an increase in the Zn concentration in the acidic solution is observed during operation. It has no particular effect.

  As described above, an oxide layer having an average thickness of 10 nm or more is obtained on the surface of the plated steel sheet of the present invention, containing metal particles containing Sn as main components and Zn as essential components.

There is no particular limitation on the method of bringing the alloyed hot-dip galvanized steel sheet into contact with the acidic solution. The method of immersing the plated steel sheet in the acidic solution, the method of spraying the acidic solution onto the plated steel sheet, and the steel sheet plated with the acidic solution through the coating roll It is desirable that the film is finally formed in a thin liquid film form on the surface of the steel sheet. This is because when the amount of acidic solution present on the steel sheet surface is large, the pH of the solution does not increase even if zinc dissolution occurs, and only zinc dissolution occurs one after another. This is because it not only has a long time but also severely damages the plating layer, and it is considered that the original role as a rust-proof steel sheet is lost. From this viewpoint, it is preferable and effective to prepare the acidic solution film formed on the surface of the steel sheet to 50 g / m ² or less. The amount of the solution film can be adjusted by a squeeze roll, air wiping or the like.

  In addition, the time from the contact with the acidic solution to the water washing (retention time until the water washing) needs to be 1 to 120 seconds. If the time until washing with water is less than 1 second, the acidic solution is washed away before the pH of the solution rises and the Sn metal particles and Zn-based oxide layer are formed. This is because no effect is obtained, and even if the time exceeds 120 seconds, no change is observed in the amount of Sn metal particles and the amount of oxide layer.

  The oxide layer in the present invention is a layer made of an oxide and / or hydroxide containing Zn as an essential component. The average thickness of such an oxide layer containing Zn as an essential component needs to be 10 nm or more in the pressure-regulating portion surface layer and the non-pressure-regulating portion surface layer. If the average thickness of the oxide layer is reduced to less than 10 nm in the pressure adjusting portion and the non-pressure adjusting portion, the effect of reducing the sliding resistance becomes insufficient. On the other hand, if the average thickness of the oxide layer containing Zn as an essential component exceeds 100 nm in the pressure-regulating part and the non-pressure-regulating part, the film breaks during press working, the sliding resistance increases, and the weldability decreases. It is not preferable because it tends to be.

  In addition, for producing the galvannealed steel sheet according to the present invention, it is necessary that Al be 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.

  Furthermore, even if impurities are included in the treatment liquid used for oxidation treatment, etc., S, N, Pb, Cl, Na, Mn, Ca, Mg, Ba, Sr, Si, etc. may be taken into the oxide layer. The effect of the present invention is not impaired.

Next, the present invention will be described in more detail with reference to examples.
A conventional alloyed hot-dip galvanized film was formed on a cold-rolled steel sheet having a thickness of 0.8 mm, and further temper rolled. Subsequently, as an oxide formation treatment, the solution was immersed for 3 seconds in an acidic solution of Sn acetate (added as tin (II) sulfate) in an acidic aqueous solution of 40 g / l of sodium acetate and the temperature of the solution appropriately changed. The pH values of the acidic solutions were all 1.5. Then, after carrying out roll squeezing and adjusting the liquid amount, it was allowed to stand at room temperature in the atmosphere for 1 to 120 seconds, sufficiently washed with water and then dried.

  Next, for the steel sheet produced as described above, the film thickness of the oxide layer of the pressure-regulating part and the non-pressure-regulating part of the plating surface layer is measured, and the friction coefficient is measured as a method for simply evaluating the press formability. Went. The measuring method is as follows.

(1) Slidability evaluation test (Friction coefficient measurement test)
In order to evaluate the 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 measuring 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. On the lower surface of the slide table 3, there is provided a slide table support base 5 having a roller 4 in contact with the slide table 3 and capable of moving up and down, and by pushing it up, a pressing load N applied to the friction coefficient measurement sample 1 by the bead 6 is applied. A first load cell 7 for measurement 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, the cleaning oil Preton R352L for press made by Sugimura Chemical Co., Ltd. was applied to the surface of the friction coefficient measurement sample 1 as a lubricant, and the test was performed.

  FIG. 2 is a schematic perspective view showing the shape and dimensions of the beads used. The bead 6 slides with its lower surface pressed against the surface of the friction coefficient measurement sample 1. The shape of the bead 6 shown in FIG. 2 is 10 mm wide, 12 mm long in the sliding direction of the sample, the lower part of both ends of the sliding direction is a curved surface with a curvature of 4.5 mmR, and the bottom surface of the bead to which the sample is pressed is 10 mm wide and in the sliding direction It has a 3mm long plane.

  For the measurement of the friction coefficient, the pressing load N is set to 400 kgf at room temperature (25 ° C), assuming a severe press environment with a high strength alloyed hot-dip galvanized steel sheet that has high forming load and is prone to die galling. Changed to 1500 kgf. The sample drawing speed (the horizontal moving speed of the slide table 3) is 100 cm / min. Under these conditions, the pressing load N and the pulling load F were measured, and the coefficient of friction μ between the test material and the bead was calculated by the formula: μ = F / N.

(2) Measurement of oxide thickness Measure the content (at.%) Of each element in the pressure-regulating and non-pressure-regulating parts of the plating surface layer by Auger electron spectroscopy (AES). After sputtering, the content of each element in the plating film was measured by AES, and the composition distribution of each element in the depth direction was measured by repeating this. The depth at which the O content due to oxides and hydroxides is half the sum of the maximum value and the constant value at a position deeper than the maximum value is defined as the oxide thickness. The thicknesses of the oxides were measured at two locations for each of the pressure regulating portions, and the average values of these were the oxide thicknesses of the pressure regulating portion and the non-pressure regulating portion, respectively. As a pretreatment, Ar contamination was performed for 30 seconds to remove the contamination layer on the surface of the test material.

(3) Determination of metallic Sn
Metal Sn provided on the Zn-based oxide layer was evaluated as a mass per unit area by an ICP (inductive plasma emission analysis) method.

  The test results obtained from the above are shown in Table 1. In Table 1, condition 1 indicates a pressing load of 400 kgf and a sample temperature of 25 ° C. (room temperature), and condition 2 indicates a pressing load of 1500 kgf and a sample temperature of 25 ° C. (room temperature).

From the test results shown in Table 1, the following matters were clarified.
In the comparative example of No.1, since the treatment with the acidic solution was not performed, an oxide film sufficient to improve the slidability was not formed in the pressure adjusting part and the non-pressure adjusting part. Also has a high coefficient of friction. Further, in condition 2 where the surface pressure was high, the coefficient of friction was further increased, and mold galling occurred.
The comparative examples of Nos. 2 to 4 are comparative examples using a bath that does not contain Sn ions although it is treated with an acidic solution. In this case, since the oxide layer mainly composed of Zn is formed mainly on the pressure-regulating part on the surface of the plated steel sheet, the friction under the condition 1 where the contact pressure with the mold mainly forms the pressure-adjusting part at the time of molding is low. Although an improvement effect of the coefficient is seen, a high friction coefficient is shown under condition 2 where the surface pressure is high such that the contact with the mold extends over the pressure-regulating part and the non-pressure-adjusting part.
On the other hand, Nos. 5-28 are examples using a bath containing Sn ions. In the present invention example except No. 14 which was washed with water without holding, since the oxide layer containing Sn metal particles and Zn is present on the surface of the plated steel sheet, in addition to the condition 1 with low surface pressure, Even under condition 2 where the surface pressure is high, the friction coefficient is low and stable.
Nos. 5 to 7 are examples of the present invention in which the treatment with an acidic solution containing Sn ions was performed, and in addition to the low surface pressure condition 1, the friction coefficient of the high surface pressure condition 2 was also reduced. . In addition, Nos. 8 to 10, 16 to 18, and 26 to 28 are examples of the present invention in which the Sn ion concentration in the liquid was increased under the same processing conditions as No. 5 to 7, but under any conditions The coefficient of friction is stable at a low level.
Nos. 14 to 19 are examples in which an acidic solution film was formed on the steel sheet surface and the time until washing with water was changed. In the comparative example of No. 14, which was washed with water without being retained, an oxide film sufficient to improve the slidability was not formed in the pressure-regulating part and the non-pressure-regulating part. Thus, the friction coefficient also increases under the condition 2 where the surface pressure is high. Nos. 15 to 19 having a holding time of 1 second or more have a low coefficient of friction and are stable under any conditions.
Nos. 11 to 13, 16 to 18, and 20 to 25 are examples of the present invention in which the temperature of the treatment liquid was changed, and the effect of improving the friction coefficient in both the low surface pressure condition 1 and the high surface pressure condition 2 is It is enough. However, in No. 20 to 25, it is necessary to make equipment specifications with higher heat resistance at the time of manufacturing, and the amount of liquid evaporation at the time of manufacturing increases, so it becomes somewhat difficult to control the amount of liquid film.

  Since it is excellent in press formability, it can be applied in a wide range of fields, mainly for automobile body applications.

Schematic front view showing friction coefficient measuring device Schematic perspective view showing bead shape and dimensions in FIG.

Explanation of symbols

1 Friction coefficient measurement sample
2 Sample stage
3 slide table
4 rollers
5 Slide table support
6 beads
7 First load cell
8 Second load cell
N Push load
F Sliding resistance force

Claims (5)

  The surface of the galvanized steel sheet is subjected to hot dip galvanizing on the steel sheet, alloyed by heat treatment, temper rolled, contacted with an acidic solution, left for 1 to 120 seconds after contact is completed, and then washed with water. A method for producing an alloyed hot-dip galvanized steel sheet, which comprises forming a Zn-based oxide layer having a thickness of 10 nm or more on the surface, wherein the acidic solution contains Sn ions.   2. The acidic solution according to claim 1, wherein at least one of Sn sulfate, nitrate, chloride, and phosphate is contained in the range of 0.1 to 50 g / l as Sn ion concentration. The manufacturing method of the galvannealed steel plate of description.   The acidic solution has a pH buffering action and a pH increase defined by the amount (l) of 1.0 mol / l sodium hydroxide solution required to increase the pH of 1 liter acidic solution from 2.0 to 5.0 The method for producing a galvannealed steel sheet according to claim 1 or 2, wherein the degree is in a range of 0.05 to 0.5.   The acidic solution contains at least one of acetate, phthalate, citrate, succinate, lactate, tartrate, borate and phosphate, and a component content of 5 to 50 g / l. The method for producing an alloyed hot-dip galvanized steel sheet according to any one of claims 1 to 3, wherein the pH is 0.5 to 2.0 and the liquid temperature is 20 to 70 ° C. The method for producing an galvannealed steel sheet according to any one of claims 1 to 4, wherein the acidic solution film formed on the surface of the steel sheet after being brought into contact with the acidic solution is 50 g / m ² or less. .

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