JP2009127077A - Method for production of hot-dip galvannealed steel sheet, and hot-dip galvannealed steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing a hot-dip galvannealed steel sheet excellent in press moldability by forming an oxide layer with sufficient thickness on a plated surface in a short period of time even under a high-speed production condition, and to provide the hot-dip galvannealed steel sheet produced thereby. <P>SOLUTION: The method of producing the hot-dip galvannealed steel sheet having the oxide layer on the plated surface includes: performing the alloying and temper rolling treatments on the plated steel sheet after hot dip galvanization; mixing, on the plated steel sheet, a first solution comprising the alkaline colloidal solution containing zinc hydroxide of ≥10 g/l in terms of Zn with a second solution comprising the acidic solution containing a sulfate ion of ≥5 g/l; and rinsing and drying the steel sheet after the lapse of a prescribed time to form a Zn- and S-containing oxide layer on the surface of the plated steel sheet. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing an galvannealed steel sheet excellent in press formability and an galvannealed steel sheet.

  Alloyed hot-dip galvanized steel sheets that have been alloyed after hot dip galvanization have superior weldability and paintability compared to galvanized steel sheets that have not been hot-dip galvanized and alloyed. Widely used in a wide range of fields. The alloyed hot-dip galvanized steel sheet for such use 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 causing Fe in the steel sheet and Zn in the plating layer to diffuse and 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 a high hardness, a high melting point and a high Fe concentration that is difficult to cause adhesion is effective, and an alloyed hot-dip galvanized steel sheet that places importance on press formability Manufactured with high average Fe concentration.

  However, a coating with 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. For this reason, 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. This method is expensive to manufacture.

  In addition to this, a method of applying a high-viscosity lubricating oil is widely used as a method for improving the press formability when using a galvanized steel sheet. 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 to improve the press formability of the galvannealed steel sheet itself.

  As a method for solving the above problems, Patent Document 2 and Patent Document 3 disclose that an oxide film mainly composed of ZnO is obtained by subjecting the surface of a zinc-based plated steel sheet to electrolytic treatment, immersion treatment, coating oxidation treatment, or heat treatment. Discloses a technique for improving weldability or workability by forming a film.

  Patent Document 4 discloses that the surface of a zinc-based plated steel sheet is obtained by immersing a plated steel sheet in an aqueous solution containing 5 to 60 g / l of sodium phosphate, performing an electrolytic treatment, or applying the aqueous solution. Discloses a technique for improving the press formability and chemical conversion processability by forming an oxide film mainly composed of P oxide.

  Patent document 5 is disclosing the technique which improves press-formability and chemical conversion treatment property by producing | generating Ni oxide on the surface of a zinc-plated steel plate by electrolytic treatment.

  However, when the above prior art is applied to an alloyed hot-dip galvanized steel sheet, the effect of improving press formability cannot be stably obtained. As a result of detailed investigations about the causes of the present invention, the alloyed hot-dip steel sheet is caused by the presence of Al oxide, resulting in poor surface reactivity and large surface irregularities. I found out. That is, when the prior art is applied to an alloyed hot-dip steel sheet, the surface reactivity is low, so that a predetermined film is formed on the surface even when electrolytic treatment, immersion treatment, coating oxidation treatment, heat treatment, etc. are performed. Is difficult, and the film thickness becomes thin in a portion with low reactivity, that is, a portion with a large amount of Al oxide. In addition, since the surface irregularities are large, it is the convex portions on the surface that directly contact the press mold during press molding, but the sliding resistance at the contact portion between the thin portion of the convex portions and the mold As a result, the effect of improving press formability cannot be sufficiently obtained. That is, it has been found that it is difficult to efficiently form a film having a lubricating effect on the convex portions when electrolytic treatment, immersion treatment, coating oxidation treatment, heat treatment, and the like are performed.

  In general, alloyed hot-dip galvanized steel sheets are subjected to temper rolling after being subjected to alloying treatment after hot dip galvanization. In comparison with the surroundings, it exists as a convex part. Since the flat part is the main component that actually contacts the press mold during press molding, the press formability can be stably improved by reducing the sliding resistance at the flat part. In order to reduce the sliding resistance in this flat part, it is effective to prevent adhesion between the plating layer and the mold. To that end, a hard and high melting point film should be formed on the surface of the plating layer. It is known that a method of forming an oxide layer on the plating surface layer by contacting with an acidic solution is effective for forming such an oxide layer.

For example, in Patent Document 6, after hot-dip galvanizing on a steel sheet, alloying is performed by heat treatment, temper rolling is further performed, a flat portion is formed on the surface of the iron-zinc alloy plating, and then contacted with an acidic solution. There has been proposed a method for producing an alloyed hot-dip galvanized steel sheet in which a film having a lubricating effect is efficiently formed on the convex portions by holding for 2 seconds and then washing with water.
Japanese Unexamined Patent Publication 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 JP 2002-256448 A

  When the technique disclosed in Patent Document 6 is applied, good press formability can be obtained under the conventional production conditions. However, in recent high-speed production conditions, contact is made with an acidic solution. In the process of holding for 1 to 30 seconds later, the acid solution present on the surface of the steel sheet is dried instantaneously due to the increase in relative wind speed with respect to the steel sheet in the atmosphere in which the steel sheet travels. It became clear that good press formability could not be obtained. In order to solve such a problem, it is effective to increase the amount of the liquid film of the acidic solution on the surface of the steel sheet. However, in the solution composition described in Patent Document 6, even if the amount of the liquid film is increased. An oxide layer with a required thickness cannot be formed in a short time.

  In view of such circumstances, the present invention is a method for producing an alloyed hot-dip galvanized steel sheet that is excellent in press formability by forming an oxide layer having a sufficient thickness on a plating surface in a short period even under high-speed production conditions. And it aims at providing a galvannealed steel plate.

  The inventors of the present invention made further studies to solve the above problems. As a result, the acidic solution used in the technique of Patent Document 6 has a pH buffering action for the purpose of accelerating the dissolution of Zn. I found out that the formation was delayed. Furthermore, it discovered that an oxide layer could be formed in the plating surface in a short time by mixing the alkaline colloid solution containing Zn hydroxide, and the acidic solution containing a sulfate ion on a plated steel plate.

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

  (1) A method for producing an alloyed hot-dip galvanized steel sheet having an oxide layer on the plated surface, wherein the zinc alloy is plated on the plated steel sheet after alloying and temper rolling after hot-dip galvanization. After mixing a first solution consisting of an alkaline colloidal solution containing 10 g / l or more of hydroxide in terms of Zn and a second solution consisting of an acidic solution containing 5 g / l or more of sulfate ions, after a lapse of a predetermined time A method for producing an galvannealed steel sheet, characterized by forming an oxide layer containing Zn and S on a plating surface by washing with water and drying.

  (2) The first solution has a liquid temperature of 20 to 70 ° C, and the second solution has a pH of 2.5 to 6.0 and a liquid temperature of 20 to 70 ° C (1) The manufacturing method of the galvannealed steel plate as described in 2.

(3) The liquid film amount of the mixed solution of the first solution and the second solution on the plated steel sheet is 30 g / m ² or less, and the predetermined time is 1 to 60 seconds (1) or (2) ). The manufacturing method of the galvannealed steel plate described in 1).

  (4) After temper rolling, before the step of mixing the first solution and the second solution on the plated steel sheet, a step of activating the plating surface by contacting with an alkaline aqueous solution is performed. (1) The manufacturing method of the galvannealed steel plate in any one of (3).

  (5) A step of neutralizing the mixed solution of the first solution and the second solution remaining on the plating surface by contacting with an alkaline aqueous solution before the step of washing with water after a predetermined time has elapsed (1) )-(4) The manufacturing method of the galvannealed steel plate in any one of.

  (6) An alloyed hot-dip galvanized steel sheet manufactured by the manufacturing method according to any one of (1) to (5), wherein an oxide layer containing Zn and S formed on a flat portion of a plating surface An alloyed hot-dip galvanized steel sheet having a thickness of 20 nm or more.

  According to the present invention, an oxide layer having a required thickness can be formed on a steel sheet surface in a short time. According to the present invention, even when the steel sheet passing speed is increased, an alloyed hot-dip galvanized steel sheet with low sliding resistance during press forming and excellent press formability can be stably produced.

  When producing an alloyed hot dip galvanized steel sheet, the steel sheet is hot dip galvanized and then further heated and subjected to an alloying treatment. Due to the difference in reactivity at the steel sheet-plating interface during the alloying treatment, Irregularities are present on the plated 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 temper rolling. Therefore, at the time of press molding, the force required for the mold to crush the convex portion on the plating surface is reduced, and the sliding characteristics can be improved.

  Since the plated surface of such an alloyed hot-dip galvanized steel sheet is crushed and flattened by temper rolling or the like (hereinafter referred to as a flat part), the mold is in direct contact with it during press molding. It is important for improving the slidability that a hard and high melting point substance that prevents adhesion to the mold exists in the flat portion. In this respect, the presence of the oxide layer on the surface layer is effective in improving the sliding characteristics because the oxide layer prevents adhesion with the mold.

  During 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, a sufficiently thick oxide layer must be present. Although an oxide layer is formed on the plating surface by heating during alloying treatment, most of it is destroyed by contact with the roll during temper rolling, and the new surface is exposed. In order to obtain this, a thick oxide layer must be formed before temper rolling. However, taking this into account, even if a thick oxide layer is formed before temper rolling, it is impossible to avoid the destruction of the oxide layer that occurs during temper rolling. It exists unevenly and good slidability cannot be obtained stably. However, when the alloyed hot-dip galvanized steel sheet that has been temper-rolled is treated to form an oxide layer, it is possible to form an oxide layer uniformly on the plated surface, particularly on the flat surface of the plated surface. Slidability can be obtained stably.

  In the present invention, a first solution composed of an alkaline colloidal solution containing Zn hydroxide and a second solution composed of an acidic solution containing sulfate ions are used, and alloying is performed after temper rolling after alloying treatment. These two types of solutions are mixed on a hot-dip galvanized steel sheet, and after a predetermined time has passed in a state where a liquid film of the mixed liquid is formed on the surface of the plated steel sheet, the plate is washed with water and dried. In the present invention, since the Zn hydroxide contained in the mixed solution is a Zn source for forming the oxide layer, an oxide layer having a sufficient thickness can be formed on the plating surface in a short time. . This oxide layer is an oxide layer containing Zn and S.

  In order to form an oxide layer with excellent press formability on the plating surface with a sufficient thickness in a short time, an alkaline colloidal solution containing Zn hydroxide and an acidic solution containing sulfate ions are applied on the plated steel sheet. It is important to mix. When Zn contained in the alkaline solution of the first solution is not a colloidal Zn hydroxide, or when the acidic solution of the second solution does not contain sulfate ions, an oxide layer containing Zn and S is formed on the plating surface. It cannot be formed to a sufficient thickness in a short time.

  The formation mechanism of the oxide layer on the plating surface is not clear, but can be considered as follows.

  Sulfate ions have the effect of aggregating Zn hydroxide. When the first solution and the second solution are mixed on the plated steel sheet, a neutralization reaction occurs. At that time, colloidal Zn hydroxide aggregates and an oxide layer containing Zn and S is deposited on the plated surface. By this action, an oxide layer having a sufficient thickness can be formed on the plating surface in a short time.

  When the first solution and the second solution are mixed in advance and this mixed solution is brought into contact with the steel plate surface, the Zn hydroxide aggregates in the mixed solution when the first solution and the second solution are mixed. Even if a liquid film of a solution in which Zn hydroxide is aggregated is formed on the plated steel sheet, Zn hydroxide cannot be deposited on the plating surface.

  The amount of Zn hydroxide in the first solution affects the amount of oxide formed on the plating surface. It is necessary to contain in the range of 10 g / l or more as Zn density | concentration in a solution. When the amount is less than 10 g / l, sufficient press formability cannot be obtained because the amount of oxide formed on the plating surface is small. Although more than 300 g / l may be contained, the effect of improving the press formability due to oxide formation is saturated, which is not economically preferable. The solution temperature is preferably in the range of 20 to 70 ° C. When the temperature is 20 ° C. or higher, the reactivity is improved and the film forming speed is improved, so that the productivity is increased. Further, when the temperature is 70 ° C. or lower, it is not necessary to consider moisture evaporation, and not only the solution concentration management becomes easy, but also the drying on the steel plate is in an appropriate range, so that Zn hydroxide aggregates in the liquid. Without being deposited on the plated surface, an oxide layer having a sufficient thickness can be formed.

  In order to obtain a colloidal solution containing colloidal Zn hydroxide, the first solution needs to be alkaline. In order to prepare an alkaline colloidal solution containing Zn hydroxide, it is preferable to use zinc nitrate as a zinc salt. Specifically, it can be produced by mixing an aqueous zinc nitrate solution and a sodium hydroxide solution at room temperature. Each concentration can be prepared by mixing 100 g / l as zinc nitrate hexahydrate and 30-50 g / l as sodium hydroxide. With zinc salts other than zinc nitrate, for example, zinc chloride precipitates as basic zinc chloride, so colloidal Zn hydroxide cannot be obtained.

  The sulfate ion concentration in the second solution needs to be 5 g / l or more. When the amount is less than 5 g / l, the above-described aggregation effect due to sulfate ions is small, and an oxide cannot be efficiently formed on the steel sheet. If the content exceeds 50 g / l, the effect of improving press formability due to oxide formation is saturated, which is economically undesirable, and sulfate ions tend to remain on the plating surface, causing spot rust when left for a long period of time. Therefore, it is preferably 50 g / l or less.

  There is no restriction | limiting of the cation with respect to a sulfate ion, A well-known sulfate can be used. Examples thereof include zinc sulfate, aluminum sulfate, titanium sulfate, nickel sulfate, iron sulfate, indium sulfate, and tin sulfate.

  The pH of the second solution is preferably in the range of 2.5 to 6.0. When the pH is 2.5 or more, it does not take excessive time to reach the oxide precipitation pH, and thus productivity is not hindered. Further, when the pH of the solution is 6.0 or less, a precipitation reaction occurs in the mixed solution, so that an oxide layer having poor adhesion is not formed on the plating surface, and a sufficient amount of the oxide layer is short. Can be formed in time. The solution temperature is preferably 20 to 70 ° C. When it is 20 ° C. or higher, the reactivity is improved and productivity is not hindered. Further, when the temperature is 70 ° C. or lower, it is not necessary to consider the evaporation of water, and not only the solution concentration management becomes easy, but also the drying on the steel plate is in an appropriate range, so that an oxide layer having a sufficient thickness is formed. Is done.

  In addition, when a part that is easily dried or a part that is difficult to dry is generated during running of the steel sheet during production, appearance unevenness that is visually recognized may occur. Appearance unevenness tends to be affected by the temperature of the first solution and the second solution. In particular, when the liquid temperature of the solution applied later to the steel plate is higher than 70 ° C., appearance unevenness is likely to occur. Even if there is no significant problem in performance, uneven appearance is not preferable because it may be regarded as a defect when used by a user.

  The first solution and the second solution are mixed on the plated steel sheet, and after a predetermined time has passed in a state where a liquid film of the mixed solution is formed on the plating surface, the plate is washed with water and dried. This is because if the water is washed immediately without elapse of a predetermined time, oxides are not formed and press formability is not improved. A preferable elapsed time is 1 second to 60 seconds. When it is 1 second or more and 60 seconds or less, sufficient press formability can be obtained.

The liquid film amount of the mixed solution of the first solution and the second solution present on the plated steel sheet is preferably 30 g / m ² or less. When the liquid film amount of the mixed liquid is 30 g / m ² or less, the proportion of Zn hydroxide precipitated on the steel sheet increases, which is efficient. The lower limit of the amount of the liquid film is not particularly limited, but is preferably 3 g / m ² or more in order to ensure the amount of oxide necessary for improving the press formability. Further, when the mixing ratio of the first solution and the second solution is set to the first solution: second solution = 2-4: 1 as the liquid volume ratio, the oxide layer can be efficiently formed. However, even if one of the solutions exceeds this ratio, it is washed in the subsequent water washing step, which is economically disadvantageous, but does not affect the oxide layer deposition.

  The method for mixing the first solution and the second solution on the plated steel sheet is not particularly limited. After the liquid film of the first solution is formed on the plated steel plate, the second solution may be applied on the plated steel plate and the first solution and the second solution may be mixed. After forming the liquid film on the plated steel plate, the first solution may be applied onto the plated steel plate and the first solution and the second solution may be mixed. Moreover, you may mix on a steel plate by discharging a 1st solution and a 2nd solution simultaneously on a steel plate.

  In addition, after temper rolling, before the step of mixing the first solution and the second solution on the plated steel sheet, a treatment (pretreatment) for bringing the plating surface into contact with an alkaline aqueous solution is performed. Effective for oxide formation. By dissolving zinc oxide and Al oxide formed on the plated surface after temper rolling, the surface can be activated, and as a result, subsequent oxide formation is facilitated.

  The alloyed hot-dip galvanized steel sheet produced by the above-described method may be stored for a long period of time before being used at a customer site. From the viewpoint of preventing spot rusting during storage, after a predetermined time has elapsed, before the step of washing with water, the mixed solution of the first solution and the second solution remaining on the surface is brought into contact with an alkaline aqueous solution and neutralized. It is preferable to carry out the treatment. The method of this treatment is not particularly limited, and can be performed by a known method such as dipping or spraying.

  The alkaline aqueous solution used for the treatment can be an aqueous solution of sodium hydroxide, calcium hydroxide, potassium hydroxide, sodium carbonate, sodium pyrophosphate, or a commercially available degreasing agent using these. The contact method is not particularly limited, and a known method such as dipping or spraying can be employed.

  By the above method, an oxide layer containing Zn and S is formed on the plating surface.

  By forming the oxide layer containing Zn and S so as to have a thickness of 20 nm or more on the flat portion of the surface of the galvanized steel sheet, the press formability is remarkably improved. This is because if it is lower than 20 nm, it is impossible to satisfy the recent severe press forming ability.

  Here, the amount of the oxide layer can be determined as follows. First, the average thickness of the oxide layer is determined by Auger electron spectroscopy (AES) combined with Ar ion sputtering. In this method, after sputtering to a predetermined thickness, the composition at that depth can be obtained by correcting the relative sensitivity factor from the spectral intensity of each element to be measured. Among these, the content of 0 attributed to the oxide decreases and becomes constant after reaching a maximum value at a certain depth (this may be the outermost layer). At a position where the content of 0 is deeper than the maximum value, the depth that is ½ of the sum of the maximum value and the constant value is defined as the oxide thickness. The oxide layer in the present invention is a layer made of an oxide and / or hydroxide containing Zn and S as essential components.

  Moreover, when manufacturing the alloyed hot-dip galvanized 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.

Next, the present invention will be described in more detail with reference to examples.
A conventional alloyed hot-dip galvanized layer was formed on a cold-rolled steel plate having a thickness of 0.8 mm, and a temper-rolled steel plate was used as a test material. All the test materials were subjected to ultrasonic degreasing using a solvent, and then subjected to oxide forming treatment containing Mn and S by the following method.

  As the first solution, an aqueous zinc nitrate solution and an aqueous sodium hydroxide solution were mixed at room temperature to prepare an alkaline colloidal solution containing Zn hydroxide. The Zn concentration was adjusted with the zinc nitrate concentration. The second solution was an aqueous zinc sulfate solution. The pH was adjusted with sulfuric acid.

  The steel plate is immersed in a beaker filled with the first solution, left for 3 seconds, then taken out and immediately passed between the squeeze rolls 2a and 2b of the apparatus of FIG. Controlled. The amount of liquid film on the steel plate 1 was adjusted by adjusting the rolling force between the squeeze rolls 2a and 2b. 1B, the second solution in the coater pan 5 is transferred to the squeeze roll 3a through the pickup roll 4, and the second solution in the coater pan 6 is pumped up by the squeeze roll 3b. 1 was passed between the squeezing rolls 3a and 3b to give a second solution having a controlled amount of solution on the steel plate 1, and the first solution and the second solution were mixed on the steel plate. The liquid film amount of the second solution on the steel plate 1 was adjusted by adjusting the rolling force between the squeeze rolls 3a and 3b. The liquid film amounts of the first solution and the second solution were set so that the first solution: the second solution = 3: 1.

  After the first solution and the second solution are mixed on the steel plate, after a predetermined time has passed, the mixture is washed with tap water to remove the mixed solution of the first solution and the second solution remaining on the steel plate, and a hot air dryer The test piece was produced by performing drying by. Washing with tap water was performed by immersing in a water tank containing tap water, and partly with tap water spray. Some samples are pre-treated to activate the surface by contact with an alkaline aqueous solution, and then the oxide formation treatment is performed, and some samples are neutralized by immersion in an alkaline solution before washing with water. Went.

  The solution compositions of the first solution and the second solution are shown in Table 1. The amount of the liquid film was calculated by measuring the weight of the steel sheet before and after passing through the squeeze roll to determine the weight difference, and dividing this weight difference by the solution adhesion area. Elapsed time is 0 seconds when the steel plate leaves the squeeze roll applied with the second solution (in the order of the second solution → first solution, or the first solution when only the first solution is applied). The time until the start of water washing (when neutralization is performed, the time until the start of neutralization).

The pretreatment method and neutralization treatment method are described below.
Pretreatment: A 10 g / l aqueous sodium hydroxide solution was used, and an immersion treatment was carried out for 10 seconds in an aqueous sodium hydroxide solution maintained at 50 ° C.
Neutralization treatment: A 1 g / l sodium pyrophosphate aqueous solution was used, and an immersion treatment was carried out for 3 seconds in a sodium pyrophosphate aqueous solution maintained at 50 ° C.

Next, the friction coefficient was measured as a method for simply evaluating the press formability of the steel sheet produced as described above. The friction coefficient was measured and evaluated as follows.
(1) Press formability 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. 2 is a schematic front view showing the friction coefficient measuring apparatus. As shown in the figure, a friction coefficient measurement sample 11 collected from a test material is fixed to a sample table 12, and the sample table 12 is fixed to the upper surface of a slide table 13 that can move horizontally. On the lower surface of the slide table 13 is provided a slide table support base 15 having a roller 14 in contact with the slide table 13 and capable of moving up and down, and by pushing it up, a pressing load N applied to the friction coefficient measurement sample 11 by the bead 16. A first load cell 17 is attached to the slide table support 15. A second load cell 18 for measuring a sliding resistance force F for moving the slide table 13 in the horizontal direction in a state where the pressing force is applied is attached to one end of the slide table 13. In addition, the cleaning oil Preton (registered trademark) R352L for press manufactured by Sugimura Chemical Co., Ltd. was applied to the surface of the sample 11 as a lubricant, and the test was performed.

  3 and 4 are schematic perspective views showing the shape and dimensions of the beads used. The bead 16 slides with its lower surface pressed against the surface of the sample 11. The bead 16 shown in FIG. 3 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 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 3 mm. The bead 16 shown in FIG. 4 is 10 mm wide, 69 mm long in the sliding direction of the sample, the lower part at both ends of the sliding direction is a curved surface having a curvature of 4.5 mmR, and the bottom surface of the bead against which the sample is pressed is 10 mm wide and sliding. It has a plane with a direction length of 60 mm.

The friction coefficient measurement test was performed under the following two conditions.
[Condition 1]
The bead shown in FIG. 3 was used, the pressing load N was 3923N (400 kgf), and the sample drawing speed (horizontal movement speed of the slide table 13) was 100 cm / min.
[Condition 2]
The bead shown in FIG. 4 was used, the pressing load N was 3923N (400 kgf), and the sample drawing speed (horizontal moving speed of the slide table 13) was 20 cm / min.
The friction coefficient μ between the test material and the bead was calculated by the formula: μ = F / N.

  The test results obtained above are shown in Table 1.

From the test results shown in Table 1, the following matters became clear.
(1) No. No. 1 is not subjected to the treatment according to the present invention, so that an oxide film sufficient to improve the slidability is not formed on the flat portion, and the friction coefficient is high and the press formability is low.
(2) No. Nos. 2 to 6 are examples in which the Zn ion concentration of the first solution was changed. Nos. 3 to 6 have an oxide film of 20 nm or more and a friction coefficient of No. 3-6. 1 and no. Since it is significantly lower than 2, it can be seen that high press formability is obtained. Further, when comparing the oxide film thickness, it can be seen that the oxide film thickness increases as the Zn ion concentration increases, but is almost saturated between 200 and 350 g / l.

(3) No. 4 and no. Nos. 7 to 12 are examples in which the elapsed time was changed. 7 shows that no oxide film is formed and the friction coefficient is increased. On the other hand, it can be seen that by providing the elapsed time, the oxide film is formed thick in any case and exhibits a low coefficient of friction. Focusing on the elapsed time and the oxide film thickness, it can be seen that the effect of increasing the oxide film thickness is saturated and hardly changed even after 60 seconds or more.
(4) No. No. 13 is an example of treatment with only the first solution, No. 13 No. 14 is an example in which the treatment was performed only with the second solution. In any case, it can be seen that the oxide film is thin and the press moldability is low.
(5) No. 4 and no. Nos. 15 to 18 are examples in which the sulfate ion concentration of the second solution was changed. It can be seen that 16 to 18 have an oxide film of 20 nm or more and a low coefficient of friction. Focusing on the concentration and the friction coefficient, particularly the friction coefficient in Condition 2, it can be seen that a lower friction coefficient can be obtained by setting the sulfate ion concentration of the second solution to 5 g / l or more.

(6) No. 4 and no. 19 to 21 are examples in which the pH of the second solution was changed. In any case, it can be seen that an oxide film having a thickness of 20 nm or more was formed, and a low friction coefficient was obtained. Focusing on the pH and the oxide film thickness, it can be seen that when the pH is 2.0, it is significantly thinner than the pH 3.0.
(7) No. 4 and no. Although 22-24 are the examples which changed the temperature of the process liquid, it turns out that it is a low friction coefficient in any case. However, when the temperature was high at 80 ° C., the oxide film thickness was thin, and processing unevenness that could be visually confirmed on the steel sheet was confirmed.
(8) No. No. 25 is an example in which pre-processing is performed. It can be seen that the oxide film is formed to be significantly thicker by performing the pretreatment than 4.
(9) No. 4 and no. Nos. 26 to 28 are examples in which the liquid film amount is changed, but it is understood that a low friction coefficient is obtained at any liquid film amount. No. with a large amount of liquid film In the case of 28, it turns out that the oxide film thickness is thin.

(10) No. 29 is an example in which neutralization treatment was performed after oxide formation treatment. After the sample was prepared, 1.5 g / m ^{2 of} commercially available rust preventive oil was applied and left in the factory for 6 months, but no spot rust occurred even after 6 months.
(11) No. 4, no. 30 and no. No. 31 is an example in which the cation species of the second solution is changed, but it can be seen that an oxide film is formed in any cation species, and a low friction coefficient is obtained.
(12) No. 4 and no. No. 32 is an example in which the influence of the processing order is investigated, but it can be seen that even if the processing order is changed, an equivalent oxide film is formed, and a low friction coefficient can be obtained in any case.

  The manufacturing method of the galvannealed steel sheet of this invention can be utilized as a manufacturing method of the galvannealed steel sheet which is excellent in press formability. Since the alloyed 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.

The apparatus used for control of the coating amount of the 1st solution of an oxide formation process of an Example and a 2nd solution is shown, (a) is the aperture device used for control of the coating amount of a 1st solution, (b) is the 1st. It is a conceptual diagram of the roll coater used for control of the coating amount of two solutions. 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.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate 2a, 2b, 3a, 3b Drawing roll 4 Pickup roll 5, 6 Coater pan 11 Friction coefficient measurement sample 12 Sample stand 13 Slide table 14 Roller 15 Slide table support stand 16 Bead 17 First load cell 18 Second load cell 19 Rail N Pressing load F Sliding resistance force

Claims (6)

  A method for producing an alloyed hot dip galvanized steel sheet having an oxide layer on a plated surface, wherein the zinc hydroxide is applied to the plated steel sheet subjected to alloying treatment and temper rolling after hot dip galvanization. After mixing a first solution composed of an alkaline colloidal solution containing 10 g / l or more in terms of Zn and a second solution consisting of an acidic solution containing 5 g / l or more of sulfate ions, the mixture is washed with water and dried after a predetermined time. And forming an oxide layer containing Zn and S on the plating surface. The liquid temperature of the first solution is 20 to 70 ° C, the pH of the second solution is 2.5 to 6.0, and the liquid temperature is 20 to 70 ° C. A method for producing a galvannealed steel sheet. 3. The alloy according to claim 1, wherein a liquid film amount of a mixed solution of the first solution and the second solution on the plated steel sheet is 30 g / m ² or less, and the predetermined time is 1 to 60 seconds. Method for producing a galvannealed steel sheet. 2. A step of activating the plating surface by contacting with an alkaline aqueous solution after the temper rolling and before the step of mixing the first solution and the second solution on the plated steel sheet. The manufacturing method of the galvannealed steel plate as described in any one of -3. The step of neutralizing the mixed solution of the first solution and the second solution remaining on the plating surface by contacting with an alkaline aqueous solution before the step of washing with water after a predetermined time has passed is performed. 5. The method for producing an alloyed hot-dip galvanized steel sheet according to any one of 4 above. The alloyed hot-dip galvanized steel sheet produced by the production method according to any one of claims 1 to 5, wherein the thickness of the oxide layer containing Zn and S formed on the flat part of the plating surface is An alloyed hot-dip galvanized steel sheet characterized by being 20 nm or more.

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