JP5044924B2 - Method for producing alloyed hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot dip galvannealed steel sheet manufacturing method of a hot dip galvannealed steel sheet having excellent press-forming property even for a material such as a high-strength hot dip galvannealed steel sheet having high forming load and easy to generate die galling, and the hot dip galvannealed steel sheet. <P>SOLUTION: A steel sheet is subjected to the hot dip galvanizing, and further galvannealing by the heating, and brought into contact with an acid solution after temper rolling. After completing the contact, the steel sheet is naturally left for 1-30 seconds, and rinsed with water. When depositing a Zn-based oxide layer of the thickness of &ge;10 nm on the surface of the galvanized steel sheet, Zr ions are contained in the acid solution. Thus, the oxide layer having the mean thickness of &ge;10 nm and containing Zn and Zr as essential components 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 Zr with the Zr ion concentration in a range of 0.1-50 g/l. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

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

  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, and 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 high Fe concentration film tends to form a hard and brittle Γ phase at the plating-steel sheet interface, and has a problem that 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 technique 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.

  Patent Document 5 discloses a technique for improving press formability and chemical conversion treatment by generating Ni oxide by electrolytic treatment, dipping treatment, coating treatment, coating oxidation treatment, or heat treatment on the surface of a galvanized steel sheet. 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 an automobile outer plate, but because of the high load during press forming, 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, and alloying. An object is to provide a hot-dip galvanized steel sheet.

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, as the contact surface pressure increases, it is necessary to consider direct contact between the mold and the unregulated portion in addition to the pressure regulating portion. In particular, when a high-strength steel sheet such as a high-strength galvannealed steel sheet is used, it is necessary to form a higher hardness oxide in both the pressure-regulating part and the unregulated part. The inventors have found that it is effective to use a treatment liquid containing Zr ions as an acidic solution in order to form a Zn-based oxide in both the pressure regulation part and the non-pressure regulation part.

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, further alloyed by heat treatment, temper rolling, contact with an acidic solution, left for 1 to 30 seconds after contact is completed, and then washed with water, In the manufacturing method of the galvannealed steel sheet in which a Zn-based oxide layer having a thickness of 10 nm or more is formed on the surface of the galvanized steel sheet, the method for manufacturing the galvannealed steel sheet characterized by containing Zr ions in the acidic solution .

[2] In the above [1], the acidic solution contains at least one of Zr sulfate, nitrate, chloride, and phosphate in a range of 0.1 to 50 g / l as a Zr 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, characterized in that the degree of increase in pH 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] In any one of the above [1] to [4], the acidic solution film formed on the steel sheet surface after contact with the acidic solution is 3 g / m ² or less, and the acidic solution film is a steel sheet A method for producing an alloyed hot-dip galvanized steel sheet, wherein the holding time in the state formed on the surface is in the range of 1 to 30 seconds.
[6] A plated steel sheet produced by the method for producing an galvannealed steel sheet according to any one of [1] to [5], wherein the average thickness of the oxide layer on the surface of the plated steel sheet is 10 nm or more An alloyed hot-dip galvanized steel sheet, wherein the oxide layer contains Zn and Zr as essential components.

  According to the present invention, in a high-strength galvannealed steel sheet that has a high forming load and is likely to cause 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. In this case, an oxide layer mainly composed of Zn is formed mainly on 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 the direct contact with the mold during press forming is mainly at the pressure-regulating part on the surface of the plating layer. Therefore, good press formability can be obtained by forming the oxide layer on the pressure-regulating portion on the surface of the plating layer. However, in high-strength galvannealed steel sheets such as those used for structural members, the molding load is high, so that the mold may be in direct contact with not only the pressure-regulating part but also the non-pressure-regulating part during press molding. Conceivable. Therefore, good press formability cannot be ensured only by forming the oxide layer only on the pressure adjusting portion. In contrast, when an acidic solution containing Zr is used, an oxide layer containing Zn and Zr can be formed in the pressure-regulating part and the non-pressure-regulating part, and Zr is harder than Zn. Therefore, a harder oxide layer can be formed as compared with the oxide layer of Zn alone. The oxide layer thus formed is not easily broken even when the contact surface pressure with the mold is high, and suppresses direct contact between the mold and the plating layer surface. As a result, even in a high-strength galvannealed steel sheet that has a high forming load and is likely to cause mold galling, good press formability is exhibited.

  Although the oxide layer formation mechanism is not clear, it can be considered as follows. When the galvannealed steel sheet is brought into contact with an acidic solution, zinc is dissolved from the steel sheet side. This dissolution of zinc causes hydrogen generation at the same time. As the dissolution of zinc proceeds, the hydrogen ion concentration in the acidic solution decreases, resulting in an increase in the pH of the acidic solution and the stabilization of the oxide (hydroxide). It is considered that an oxide layer is formed on the surface of the alloyed hot-dip galvanized steel sheet when reaching the pH range. At this time, when an acidic solution containing Zr is used, a Zr-based oxide formation reaction occurs in a pH range lower than that of the Zn-based oxide formation reaction, and when the pH further increases, the Zn-based oxide formation reaction occurs. Therefore, it is conceivable that the oxide formation reaction easily occurs as compared with the case of Zn alone. In addition, since this Zr-based oxide formation reaction occurs in the low pH region, it is considered that the steel sheet is strongly etched, and the oxide formation reaction also occurs in the unregulated portion that is inferior in reactivity to the pressure-regulated portion. It seems to happen easily. In addition, since such an oxide formation method proceeds while slightly dissolving the surface of the plating layer, it is more closely adhered to a layer obtained by a coating process using a solvent in which the oxide is dispersed. Since the property is good and the precipitation reaction of hydroxide is used, a thick film can be formed as compared with a film obtained by completely covering the surface by heat treatment or the like. In addition, when making it contact with an acidic solution and leaving it for 1 to 30 seconds after completion | finish of contact, you may heat a steel plate by induction heating, radiation heating, etc.

  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, contacted with an acidic solution, left for 1 to 30 seconds after completion of contact, and then washed with water. By carrying out, when forming a Zn-type oxide layer 10 nm or more in the surface of a galvanized steel plate, it shall contain Zr ion in the said acidic solution. This is the most important requirement in the present invention.

  In order to contain Zr ions in the acidic solution, it is preferable to contain at least one of Zr sulfate, nitrate, chloride, and phosphate in the range of 0.1 to 50 g / l as the Zr ion concentration. . If the Zr ion concentration is less than 0.1 g / l, the amount of Zr-based oxide formed is small and the oxide layer is centered on Zn, so the effect of improving press formability when the surface pressure increases cannot be obtained sufficiently. There is a case. On the other hand, if it exceeds 50 g / l, the ratio of Zr-based oxides formed is large and effective in improving the sliding characteristics. However, these Zr-based oxides are designed for galvannealed steel sheets. There is a tendency to deteriorate the compatibility with the adhesive.

  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 2.0 to 5.0 region is used, it is kept for a predetermined time after contact with the acidic solution, so that the dissolution of Zn and the Zr-based oxidation by the reaction between the acidic solution and the plating layer occur. This is because the formation reaction of the oxide and the Zn-based oxide 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 will increase rapidly and sufficient zinc dissolution for oxide formation may not be obtained, so that a sufficient oxide layer may not be formed. On the other hand, if it exceeds 0.5, 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 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. This is because when the pH exceeds 2.0, precipitation of Zr ions (formation of hydroxide) occurs in the solution, and the Zr-based oxide is not taken into the oxide layer. 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 is likely to occur on the surface of the steel sheet.

  In the present invention, if Zr ions are contained in the acidic solution to be used, an oxide layer excellent in slidability can be stably formed, so other metal ions, inorganic compounds, etc. in the acidic solution. Even if it is contained as an impurity or intentionally, 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 of 10 nm or more containing Zn and Zr as essential components is obtained on the surface of the plated steel sheet of the present invention.

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 that the amount of the solution film formed on the steel sheet surface is adjusted to 3 g / m ² or less. The amount of the solution film can be adjusted by a squeeze roll, air wiping or the like.

  Moreover, after contacting an acidic solution, the time to water washing (holding time to water washing) needs 1 to 30 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 Zr-based oxide layer and Zn-based oxide layer are formed. This is because the improvement effect cannot be obtained, and even if it exceeds 30 seconds, the amount of the oxide layer is not changed.

  The oxide layer in the present invention is a layer made of an oxide and / or hydroxide containing Zn and Zr as essential elements. The average thickness of such an oxide layer containing Zn and Zr as essential components needs to be 10 nm or more in the pressure-regulating portion surface layer and the unregulated portion surface layer. When 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 and Zr as an essential component exceeds 100 nm in the pressure-regulated part and the non-pressure-regulated part, the film breaks during press working and the sliding resistance increases, and the weldability Is not preferable because of a tendency to decrease.

  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 forming treatment, the substrate was immersed for 3 seconds in an acidic solution in which the Zr ion concentration and the temperature of the solution were appropriately changed in an acidic aqueous solution of sodium acetate 40 g / l. Then, after carrying out roll squeezing and adjusting the amount of liquid, it was allowed to stand at room temperature in the atmosphere for 1 to 30 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.
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 therewith and capable of moving up and down, and by pushing it up, a pressing load N on the friction coefficient measurement sample 1 by the bead 6 is applied. A first load cell 7 for measuring 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 with the pressing force 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 sample 11 as a lubricating oil, 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.

When measuring the friction coefficient, assuming a severe press environment with high strength alloyed hot dip galvanized steel sheet with high forming load and high galling, press load N is 400 kgf at room temperature (25 ° C). Changed to 1500 kgf. The sample drawing speed (the horizontal movement 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.
Measurement of oxide thickness After measuring the content of each element (at.%) In the pressure-regulating part and non-regulating part of the plating surface layer by Auger electron spectroscopy (AES), and subsequently performing Ar sputtering to a predetermined depth The content ratio 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.

  The test results obtained 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 Zr 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 to 31 are examples using a bath containing Zr ions. In this case, in the present invention example except No. 14 which was washed without holding, a hard material containing Zn and Zr Since a simple oxide layer is formed on the pressure-regulated part and non-regulated part on the surface of the plated steel plate, the friction coefficient is stable at a low level not only under condition 1 with low surface pressure but also under condition 2 with high surface pressure. Yes.
Nos. 5 to 7 are examples of the present invention that were treated with an acidic solution containing Zr ions, and in addition to the low surface pressure condition 1, the friction coefficient of the high surface pressure condition 2 was also reduced. . Nos. 8-10, 16-18, 29-31 are examples of the present invention in which the Zr ion concentration in the liquid was increased under the same processing conditions as Nos. 5-7. The friction coefficient is low and stable.
Nos. 14 to 19 are examples of the present invention 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 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. 11-13 and 23-28 are examples of the present invention in which the treatment liquid temperature was changed, and the effect of improving the friction coefficient is sufficient in both conditions 1 where the surface pressure is low and conditions 2 where the surface pressure is high. When manufacturing, it becomes necessary to make the specification of equipment with higher heat resistance, and since the amount of evaporation of the liquid at the time of manufacturing increases, it becomes somewhat difficult to control the amount of liquid film.
No. 20 to 22 are examples of the present invention in which the amount of liquid film formation was changed as compared with No. 16 to 18, but compared with the same retention time until water washing, Since the pH of the solution is less likely to be increased and the oxide layer is not easily formed as compared with the case where the amount of film is large, the friction coefficient is slightly high under conditions 1 where the surface pressure is low and conditions 2 where the surface pressure is high.

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

It is a schematic front view which shows a friction coefficient measuring apparatus. FIG. 2 is a schematic perspective view showing bead shapes and dimensions in FIG. 1.

Explanation of symbols

1 Sample for friction coefficient measurement
2 Sample stage
3 Slide table
4 Roller
5 Slide table support
6 Bead 7 First load cell
8 Second load cell
N Push load
F Sliding resistance force

Claims (6)

  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 30 seconds after contact is completed, and then washed with water. A method for producing an alloyed hot-dip galvanized steel sheet, wherein a Zr ion is contained in the acidic solution in a method for producing an alloyed hot-dip galvanized steel sheet in which a Zn-based oxide layer having a thickness of 10 nm or more is formed.   2. The acidic solution according to claim 1, wherein at least one of Zr sulfate, nitrate, chloride, and phosphate is contained in a range of 0.1 to 50 g / l as a Zr 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 an 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. In the range of
And the pH is 0.5-2.0, and liquid temperature is 20-70 degreeC, The manufacturing method of the galvannealed steel plate in any one of Claims 1-3 characterized by the above-mentioned. The acidic solution film formed on the steel sheet surface after contacting with the acidic solution is 3 g / m ² or less,
And the retention time in the state in which the said acidic solution film was formed in the steel plate surface is the range of 1-30 seconds, The alloyed hot-dip galvanized steel plate in any one of Claims 1-4 characterized by the above-mentioned. Production method.   A plated steel sheet produced by the method for producing an galvannealed steel sheet according to any one of claims 1 to 5, wherein the average thickness of the oxide layer on the surface of the plated steel sheet is 10 nm or more, and oxidation An alloyed hot-dip galvanized steel sheet characterized in that the material layer contains Zn and Zr as essential components.

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