JP2003306756A - Hot dip galvanized steel sheet and method of producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot dip galvanized steel sheet which exhibits a low sliding resistance when it is press formed and stably shows excellent press formability. <P>SOLUTION: A method for producing the hot dip galvanized steel sheet includes a process for hot dip galvanizing a steel sheet by dipping it in a hot dip galvanizing bath and passing it through the bath, a process for controlling the plated coating weight after pulling the steel sheet from the hot dip galvanizing bath and cooling the pulled steel sheet to a temperature not higher than the solidifying point of the plated metal, a roughness control process for controlling the surface roughness of the hot dip galvanized steel sheet by projecting solid particles onto the surface of the hot dip galvanized steel sheet being cooled to a temperature not higher than the solidifying point of the plated metal, and an oxidation treatment process for forming an oxide on the surface of the steel sheet subjected to the surface roughness control. In the surface roughness control process, fine dimple-shaped unevennesses are imparted to the plated surface. The average diameter of the solid particles used for the projection is 10 to 300 μm. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized steel sheet having excellent slidability during press forming and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, from the viewpoint of improving anticorrosion properties, the use ratio of galvanized steel sheets, particularly hot dip galvanized steel sheets, has been increasing for automobile panel parts. There are two types of hot dip galvanized steel sheet which are alloyed after galvanizing and those which are not galvanized. The former is generally called galvannealed steel sheet and the latter is hot dip galvanized steel sheet. Usually, hot-dip galvanized steel sheets used for automobile panels are alloyed and melted by applying an alloying treatment by heating to around 500 ° C after hot-dip galvanizing, taking advantage of their excellent weldability and paintability. Galvanized steel sheet is used.

Further, in order to further improve the rust preventive property, automobile manufacturers are increasingly demanding a zinc-based plated steel sheet having a thick weight. If the above-mentioned alloyed hot-dip galvanized steel sheet is made to have a thick weight, It takes a long time for alloying and poor alloying, so-called uneven burning, is likely to occur.On the contrary, when attempting to complete alloying for the entire plating layer, overalloying occurs and brittle Γ phase is generated at the plating-steel plate interface. However, it is very difficult to produce a thick-grained alloyed hot-dip galvanized steel sheet because plating peeling easily occurs during processing.

Therefore, hot-dip galvanized steel sheets are effective for thickening the weight, and there is a movement to adopt hot-dip galvanized steel sheets for automobile panels. However,
When press-molding a hot-dip galvanized steel sheet into an automobile panel, when compared with the alloyed hot-dip galvanized steel sheet,
Since the sliding resistance with the mold is large and the melting point of the surface is low, there is a problem that adhesion is likely to occur and press cracking is likely to occur.

[0005]

As a method for solving such a problem, Japanese Patent Laid-Open No. 2002-4019 and Japanese Patent Laid-Open No. 2002-
Japanese Patent No. 4020 proposes a method of controlling the surface roughness of a hot-dip galvanized steel sheet to suppress die galling during press forming, and a method of improving deep drawability. However,
When a detailed study was conducted on such a hot-dip galvanized steel sheet, when the sliding distance with the mold was short, it had the effect of suppressing the adhesion with the mold, but the longer the sliding distance, the more The effect becomes small and the improvement effect cannot be obtained depending on the sliding condition. Further, in the above proposal, as a method of imparting such roughness, there is a method of controlling the roll condition / rolling condition of skin pass rolling, but in reality, since zinc causes clogging of the roll, It is difficult to stably impart a predetermined roughness to the surface of the hot-dip galvanized steel sheet.

Further, Japanese Patent Laid-Open No. 2-190483 proposes a galvanized steel sheet in which an oxide film mainly containing ZnO is formed on the plated surface. However, it is difficult to apply this technique to hot-dip galvanized steel sheets. Usually, when manufacturing a hot-dip galvanized steel sheet, when immersed in a zinc bath, a small amount of Al is contained in the zinc bath in order to suppress an excessive Fe-Zn alloying reaction and secure plating adhesion. Has been added. Due to this small amount of Al, Al-based oxides are densely formed on the surface of the hot-dip galvanized steel sheet, so that the surface is inactive and an oxide film mainly composed of ZnO cannot be formed. Suppose that such an oxide film is densely formed.
Even if it is applied to the upper layer of the Al-based oxide layer, the adhesion between the applied oxide film and the underlying layer is poor and not only a sufficient effect cannot be obtained, but it also adheres to the press die during processing and creates a scratch on the surface. There is a problem that adversely affects the pressed product.

In addition to this, Japanese Patent Laid-Open No. 3-101091 discloses Mo.
An oxide film, a Co-based oxide film in JP-A-3-91092, a Ni-oxide film in JP-A-3-91093, and a Ca-based oxide film in JP-A-3-91094. Although a galvanized steel sheet formed on the surface has been proposed, a sufficient effect cannot be obtained for the same reason as the above-mentioned ZnO-based oxide film.

In view of the above problems, it is an object of the present invention to provide a hot-dip galvanized steel sheet having a small sliding resistance during press forming and stably exhibiting excellent press formability, and a method for producing the same. To do.

[0009]

Means for Solving the Problems As a result of various studies to solve the above-mentioned problems, the present inventors have found that Zn-based oxides are surface-coated with Al-based oxides that are unique to the surface of hot-dip galvanized steel sheets. It was found that by forming the film in a good condition, good pressability can be obtained under a wide range of sliding conditions. This is for the following reasons.

As described above, since the Al-based oxide layer is formed on the surface of the hot-dip galvanized steel sheet, it is possible to suppress the adhesion with the die during press forming to some extent.
Therefore, in order to further improve the sliding characteristics during pressing, it is considered effective to form a thicker Al-based oxide layer, but in order to grow the Al-based oxide layer thick, It is necessary to oxidize at a high temperature for a long time, which is difficult in practical use, and at this time, there is a drawback that the Fe-Zn alloying reaction gradually progresses and the plating adhesion is deteriorated.
On the contrary, in order to form the Zn-based oxide layer, it is necessary to completely remove the Al-based oxide layer on the surface, so that this treatment has a drawback that it takes a long time.

On the other hand, when the surface of the Al-based oxide layer is partially destroyed to expose the new surface and then the surface is oxidized, Zn-based oxide is formed on the new surface, and the Zn oxide on the new surface is formed. The Zn-based oxide layer can be easily applied. The oxide layer on the plating surface thus formed coexists with Zn-based oxides and Al-based oxides, which strengthens the suppression of adhesion with the press die, so that it can be used under a wide range of sliding conditions. Good press formability can be obtained.

When the above-mentioned oxide layer is formed on a hot-dip galvanized steel sheet having a predetermined roughness, the surface roughness reduces the effect of retaining the lubricating oil and the oxide layer suppresses the adhesion between the die and the die. Shows excellent sliding properties. As a method of imparting this roughness, it is effective to project solid fine particles onto the plating surface, and by forming dimple-like fine irregularities on the plating surface, it is possible to improve sliding characteristics, Since the physical layer is easily broken and the oxide layer can be effectively formed, the sliding property is more excellent.

The present invention has been made based on the above findings, and its gist is as follows. (1) a step of dipping the steel sheet in a hot dip galvanizing bath to perform hot dip galvanizing, after pulling the steel sheet from the hot dip galvanizing bath, adjusting the amount of plating adhered, further to the freezing point of the plating metal On the surface of the hot-dip galvanized steel sheet whose cooling step and temperature are below the solidification temperature of the plating metal,
Molten zinc characterized by having a roughness adjustment step of projecting solid fine particles to adjust the surface roughness of a plated steel sheet and an oxidation treatment step of forming an oxide on the surface of the steel sheet having the adjusted surface roughness. Manufacturing method of plated steel sheet.

(2) In the roughness adjusting step, dimple-like fine irregularities are provided on the plating surface.
The method for producing a hot-dip galvanized steel sheet according to (1).

(3) The average particle size of the projected solid fine particles is 1
The method for producing a hot-dip galvanized steel sheet according to (1) or (2) above, which is 0 to 300 μm.

(4) The projection speed of the solid particles projected is 30 m
/ sec or more, the method for producing a hot-dip galvanized steel sheet according to any one of the above (1) to (3).

(5) The projection density of the projected solid fine particles is 0.2
Method for manufacturing a galvanized steel sheet according to any one of (1) to (4), which is a 60 kg / m ^2.

(6) The melting according to any one of (1) to (5), wherein the surface roughness adjusting step adjusts the center line average roughness Ra to 0.5 μm or more and 2.0 μm or less. Manufacturing method of galvanized steel sheet.

(7) In the oxidation treatment step, the steel sheet is brought into contact with an acidic solution having a pH buffering action, held for 1 to 30 seconds, and then rinsed with water. The manufacturing method of the hot dip galvanized steel sheet in any one of 1).

(8) In the oxidation treatment step, the steel sheet is brought into contact with an alkaline solution having a pH of 10 or more, and then brought into contact with an acidic solution. Manufacturing method of galvanized steel sheet.

(9) The hot dip galvanizing method according to any one of (1) to (8), wherein the oxidation treatment step forms an oxide containing a Zn-based oxide and an Al-based oxide. Steel plate manufacturing method.

(10) The method for producing a hot-dip galvanized steel sheet according to any one of (1) to (9) above, wherein the oxidation treatment step forms the thickness of the oxide nonuniformly.

(11) The method for producing a hot-dip galvanized steel sheet according to any one of (1) to (10), wherein the oxidation treatment step forms an oxide having an average thickness of 10 nm or more. .

(12) A hot-dip galvanized steel sheet mainly composed of η phase, in which solid fine particles are projected on the plated surface to form dimple-like fine irregularities, and an oxide having an average thickness of 10 nm or more is formed on the plated surface. A galvanized steel sheet characterized by the presence of layers.

(13) Center line average roughness Ra of the plated surface is 0.5
The hot-dip galvanized steel sheet according to (12) above, wherein the hot-dip galvanized steel sheet has a thickness of not less than μm and not more than 2.0 μm.

(14) The hot dip galvanized steel sheet according to (12) or (13), wherein the oxide layer is an oxide layer having a non-uniform thickness.

(15) The oxide layer is made of Zn-based oxide and Al.
The oxide characterized in that it contains an oxide (12)
~ The hot dip galvanized steel sheet according to any one of (14).

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Since a hot-dip galvanized steel sheet is usually produced by immersing in a zinc bath containing a trace amount of Al, the plating film mainly consists of η phase, and the surface layer has a zinc bath surface. It is a film in which an Al-based oxide layer formed of contained Al is formed. The η phase is softer than the ζ phase and the δ phase, which are alloy phases of the galvannealed film,
In addition, since the melting point is low, adhesion is likely to occur and slidability during press molding is poor. However, in the case of hot-dip galvanized steel sheet, since the Al-based oxide layer is formed on the surface, the effect of suppressing the adhesion of the mold is slightly observed, so the sliding distance with the mold is particularly short. In some cases, the sliding characteristics may not be deteriorated. However, since the Al-based oxide layer formed on this surface is thin, adhesion tends to occur when the sliding distance becomes long, and satisfactory press formability cannot be obtained under a wide range of sliding conditions.

In order to suppress the adhesion between the hot-dip galvanized steel sheet and the mold, it is effective to form a thick oxide layer on the surface. Therefore, a part of the Al-based oxide layer existing on the surface of the plated steel sheet is destroyed, and a Zn-based oxide layer is formed by performing an oxidation treatment, and finally the Zn-based oxide and Al
Forming an oxide layer in which a system oxide coexists is effective in improving the sliding characteristics of the galvanized steel sheet.

Although the reason for this is not clear, it can be estimated that the sliding characteristics are improved by the following mechanism. A part of the Al-based oxide layer existing on the surface of the plated steel sheet is destroyed, and the reaction becomes active in the part where the new surface is exposed,
While Zn-based oxide can be easily generated,
Since the portion where the Al-based oxide layer remains is inactive, the oxidation reaction does not proceed. For this reason, the difference in the oxide film thickness between the thick portion and the thin portion occurs and a non-uniform oxide film is formed. Since the oxide film thickness can be easily controlled in the portion where the Zn-based oxide is formed, it is possible to provide the oxide film thickness necessary for improving the sliding characteristics. At the time of actual press molding, the mold comes into contact with the oxide layer in which both the Zn-based oxide and the Al-based oxide coexist, but the Al-based oxide layer is scraped off due to sliding conditions, and adhesion is likely to occur. Even if occurs, the coexisting Zn-based oxide layer can exert the effect of suppressing the adhesion, so that the press formability can be improved.

Further, in controlling the oxide film thickness, if an attempt is made to produce a thick oxide film, the Zn-based oxide is thickened in the portion where it is present and the Al-based oxide is not thickened in the remaining portion. When viewed as a whole, an oxide layer having a non-uniform thickness is formed in which a thick oxide portion and a thin oxide portion coexist, but an improvement in slidability can be obtained for the same reason as described above. . In addition, even if a part of the thin part where the oxide layer is not formed exists for some reason, the slidability can be improved by the same mechanism.

Regarding the oxide layer in the plating surface layer, good slidability can be obtained by setting the average thickness of the oxide layer to 10 nm or more, but it is more effective if the average thickness of the oxide layer is 20 nm or more. is there. This is because, in the press forming process in which the contact area between the die and the work piece becomes large, even if the oxide layer as the surface layer is worn, the oxide layer remains and the slidability is not deteriorated. On the other hand, there is no upper limit to the average thickness of the oxide layer from the viewpoint of slidability, but when a thick oxide layer is formed, the reactivity of the surface is extremely reduced, making it difficult to form a chemical conversion coating. Therefore, it is desirable to set the thickness to 200 nm or less.

The average thickness of the oxide layer is determined by Auger electron spectroscopy (AES) combined with Ar ion sputtering.
Can be obtained by 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. Of these, O due to oxides
After reaching the maximum value at a certain depth (this may be the outermost layer), the content rate of decreases with a constant value. At a position where the content ratio of O is deeper than the maximum value, the depth at which the sum of the maximum value and the constant value is 1/2 is defined as the oxide thickness.

Further, the presence or absence of an oxide layer having a non-uniform thickness can be determined from the result of measurement by Auger electron spectroscopy (AES). This is because the thick part is mainly made of Zn-based oxide and the thin part is made of Al-based oxide, which can be evaluated by the Zn / Al ratio in the surface layer. That is, a portion where the Zn / Al ratio exceeds 1.0 is a thick portion, and a portion where the Zn / Al ratio is 1.0 or less is a thin portion. Further, this determination is made by conducting analysis at arbitrary points, and if there is a portion with a Zn / Al ratio of 1.0 or less even at one location, it can be determined that an oxide layer having a non-uniform thickness is formed. The proportion of the thick and thin portions is not specified, but if there are many thin portions, the average thickness of the oxide will be less than 10 nm, and the effect of improving slidability cannot be obtained. If the value is within the range of the present invention, the characteristics can be satisfied.

As a method for forming such an oxide layer, it is effective to bring the hot-dip galvanized steel sheet into contact with an acidic solution, then leave it for 1 to 30 seconds, and then wash and dry it.

Although the mechanism of forming the oxide layer is not clear, it can be considered as follows. When the hot-dip galvanized steel sheet is brought into contact with the acidic solution, zinc is dissolved from the steel sheet side. This dissolution of zinc causes a hydrogen evolution reaction at the same time, so as the dissolution of zinc proceeds, the concentration of hydrogen ions in the solution decreases, resulting in an increase in the pH of the solution.
It is considered that a Zn-based oxide layer is formed on the surface of the hot-dip galvanized steel sheet.

As described above, in order to form the Zn-based oxide, the pH of the solution in contact with the steel plate is dissolved together with the dissolution of zinc.
Therefore, it is effective to adjust the holding time until the steel sheet is washed with water after the steel sheet is contacted with the acidic solution. At this time, if the holding time is less than 1 second, since the solution is washed out before the pH of the solution in contact with the steel sheet rises, a thick oxide layer cannot be formed, while it is left for 30 seconds or more. However, this is because the oxide production amount is saturated.

The acidic solution used for such oxidation treatment is not particularly limited, but the pH of the solution is preferably in the range of 1.0 to 5.0. This is because if the pH exceeds 5.0, the dissolution rate of zinc will be slow, while if it is less than 1.0, the promotion of dissolution of zinc will be excessive and the rate of oxide formation will be slow. Further, it is desirable to use a chemical solution having a pH buffering action as the acidic solution. This is because not only the pH stability of the processing solution is provided during actual manufacturing, but also the pH rise necessary for oxide formation is activated, and a thick oxide film with a thickness of 10 nm or more can be efficiently produced. Is.

As the acidic solution having the pH buffering action,
At least acetate, phthalate, citrate, succinate, lactate, tartrate, borate, phosphate
An acidic solution containing at least one kind and having a content in the range of 5 to 50 g / l can be used.

The method of contacting with the acidic solution is not particularly limited, and the method of immersing the coated steel sheet in the acidic solution, the method of spraying the coated steel sheet with the acidic solution, and the method of coating the coated steel sheet with the acidic solution via a coating roll. However, it is desirable that the thin film finally exists on the surface of the steel sheet.
This is because when the amount of acidic solution present on the surface of the steel sheet is large, the pH of the solution does not rise even if dissolution of zinc occurs, and only dissolution of zinc occurs one after another, until the oxide layer is formed. This is because not only it takes a long time, but also the plating layer is severely damaged, and the original role of the rust preventive steel sheet may be lost. From this viewpoint, the amount of the liquid film is preferably adjusted to 3 g / m ² or less, and the amount of the liquid film can be adjusted with a squeeze roll, air wiping, or the like.

In the present invention, before contact with the pickling solution,
It may be immersed in an alkaline aqueous solution. This has the effect of further removing the Al-based oxide and exposing the new surface on the surface. If it is an alkaline solution, the surface can be activated, but if the pH is low, the reaction is slow and the treatment takes a long time. Therefore, the pH is preferably 10 or more. PH within the above range
So long as the type of solution is not limited, sodium hydroxide or the like can be used.

As described above, Zn-based oxide and Al are formed on the plating surface.
By forming an oxide layer in which the system oxide coexists, the effect of improving the sliding property of the galvanized steel sheet can be obtained, but by imparting roughness to the plating surface before forming the oxide layer, The slidability can be improved. This is considered to be because, by imparting roughness, the ability to retain the lubricating oil used during press molding is improved, and sufficient oil can always be supplied between the die and the workpiece.

This roughness can be evaluated by the centerline average roughness Ra. To obtain the above-mentioned effect, the centerline average roughness Ra is
It may be 0.5 μm or more and 2.0 μm or less. This is because if the centerline average roughness Ra is less than 0.5 μm, the lubricating oil may not be retained sufficiently and oil may run out in some cases, so that the centerline average roughness Ra is 2.0 μm. This is because the effect of supplying the lubricating oil between the die and the work material is saturated even if it exceeds the limit.

Further, as a method for imparting a predetermined roughness to the plating surface, a method of projecting solid fine particles onto the plating surface is effective.

By injecting solid fine particles onto the surface of the galvanized steel sheet, an indentation is formed on the surface of the coating film. When a large number of solid particles collide with the galvanized steel sheet, a large number of irregularities are formed on the surface of the galvanized steel sheet, and a certain microscopic irregularity morphology is imparted. The depth and size of the unevenness, the pitch of the adjacent unevenness, the collision speed of the liquid to be ejected, the mass and particle diameter of the solid particles, the injection amount of solid particles per unit area,
It is determined according to the hardness of the galvanized film. Therefore, these factors can be controlled to adjust the surface morphology, such as surface roughness.

The projection of solid fine particles on the plating surface to adjust the surface roughness has the following advantages.

First, the morphological characteristics of microscopic unevenness formed by projecting solid fine particles onto a galvanized steel sheet are as follows:
This is the point that concave-shaped indentations are mainly formed on the surface of the galvanized steel sheet, and such a surface morphology has the effect of improving the oil retention with the die during press molding. On the other hand, in the temper rolling method, which is a conventional technique, in order to impart a concave shape to the surface of the galvanized steel sheet, a surface morphology mainly including microscopic convex portions is applied to the surface of the rolling roll. There is a need to. However, it is generally difficult to precisely process microscopic projections on the surface of the rolling roll, and shot blasting, electric discharge machining, laser machining, and electron beam machining on the surface of the rolling roll are also theoretically possible. There is no choice but to give the surface of the roll a concave shape.

Therefore, in the case of a galvanized steel sheet obtained by projecting solid fine particles, when using an index such as average roughness Ra which is a parameter representative of the morphology of the surface microscopic unevenness, those values are conventionally Even if it is the same as the galvanized steel sheet by the technology, it will exhibit more excellent press formability. In that respect, it can be said that the method is essentially different from the surface conditioning method of the galvanized steel sheet by temper rolling which is a conventional technique.

As solid fine particles, shot blast having a substantially spherical particle shape or grit blast having an angular shape is known.

In adjusting the surface morphology of the galvanized steel sheet targeted by the present invention, it is desirable to use substantially spherical shot particles from the viewpoint of press formability of the steel sheet. When substantially spherical particles are used, fine dimples are formed on the surface of the steel sheet as indentations and improve the oil retention with the press die, thus reducing the sliding resistance during press forming. , The effect of preventing galling with the mold becomes higher.

Here, the term "dimple" refers to a form in which the shape of the dents on the surface is mainly composed of a curved surface, and a large number of crater-like dents formed by a spherical object colliding with the surface are formed. Further, “providing dimple-like fine unevenness on the plating surface” means forming fine unevenness according to the above-mentioned form on the plating surface.

Further, when the grit-shaped solid particles are used, there is a case where the action of polishing the coating layer of the galvanized steel sheet may occur depending on the spraying conditions, and by using the substantially spherical solid particles, Such a problem does not occur. It should be noted that "almost spherical" means that even if it is not a perfect sphere, it is considered to be a sphere, and that the difference between the longest diameter and the shortest diameter is within 20% of the average diameter. It is meant to include things.

Secondly, there is an advantage that the Al-based oxide can be easily destroyed as compared with the roughness imparting in the temper rolling described above. As a result, the oxide existing on the plating surface is thick and thin. It becomes possible to form a film having a nonuniform thickness in which parts coexist.

Thirdly, when the solid fine particles collide, the formed roughness is limited to the vicinity of the galvanized coating layer, so that there is an advantage that the hardness of the base material steel is not affected, and When transferring the surface roughness of the rolling roll by rolling, it is difficult to impart a predetermined roughness to the galvanized steel sheet having different steel types as the base material within the range of elongation rate limited by the material. However, there is no such limitation.

When projecting such solid fine particles,
It is necessary that the average particle size of the solid fine particles is 10 to 300 μm. This is because if the average particle size is less than 10 μm, the speed of the projected solid particles decreases in the air, so unless the projection speed is made extremely high, the roughness cannot be effectively imparted. is there. On the other hand, if the average particle size exceeds 300 μm, the recesses formed on the surface of the galvanized steel sheet become large, and it is difficult to control the roughness described above.

Further, the projection speed of the solid fine particles needs to be 30 m / sec or more. This is because if the projection speed is less than 30 m / s, sufficient kinetic energy for forming roughness will not be applied. When the initial velocity of the projection speed is 30 m / sec or more, the distance to the plate surface is preferably 700 mm or less. This is because when the distance from the plate surface is larger than 700 mm, the effect of deceleration by air becomes excessive and it becomes difficult to impart a predetermined roughness.

Further, the projection density of the solid fine particles is 0.2 to 6
It should be 0kg / m ² . Here, the projection density is the weight of solid fine particles projected per unit area of the steel plate surface. Strictly speaking, the projection density has a constant distribution in the projected range, but here, it means the total weight of projection with respect to the area where the surface is provided with roughness. When the projection density is less than 0.2 kg / m ² , solid fine particles are projected sparsely on the surface of the galvanized steel sheet, and therefore it is difficult to sufficiently form recesses having oil retaining property on the surface, and If it exceeds 60 kg / m ² , more solid particles than necessary will be projected onto the surface, and the roughness once formed will be crushed by the solid particles that are projected later, giving a predetermined roughness. This is because it is difficult to do.

In the present invention, the steel sheet can be temper-rolled before the solid fine particles are projected onto the surface of the plated steel sheet. In the present invention, since the surface roughness of the steel sheet is adjusted by projecting the solid fine particles, a required elongation rate may be given in temper rolling for the purpose of adjusting the mechanical properties of the steel sheet. The temper rolling also has an effect of destroying a part of the Al-based oxide present on the surface of the steel sheet at the same time. The surface of the temper rolling roll may be processed by any of shot blast processing, electric discharge processing, laser processing, and electron beam processing, as long as the Al-based oxide on the plated surface can be destroyed.

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

Further, due to the inclusion of impurities during the oxidation treatment, P, S, N, B, Cl, Na, Mn, Ca, Mg, Ba, Sr, Si
The effect of the present invention is not impaired even if a small amount of the above is incorporated into the oxide layer.

[0061]

EXAMPLES Next, the present invention will be described in more detail by way of examples. On a cold-rolled steel sheet with a thickness of 0.8 mm, a conventional hot-dip galvanized film is formed to 70 g / m ² per side, further temper-rolled, and then solid particles with a substantially spherical particle shape. Was projected. A centrifugal rotor type device was used as the projection device, and the distance from the rotor to the test piece was 300 mm. SUS304 was used as the solid particles, and as shown in Table 1, the average particle diameter, the projection density, and the projection speed of the solid particles were changed. Subsequently, a treatment for forming an oxide layer on the surface layer was carried out by immersing in an aqueous solution of sodium acetate 40 g / l, 60 ° C., pH 2 for 30 seconds, leaving it for 1 to 30 seconds, and then washing with water. Before the above treatment, sodium hydroxide 20g / l, 30 ℃
The solution (1) was used to immerse it in an alkaline aqueous solution (degreasing treatment).

Further, when the solid fine particles were projected, plating peeling was observed under some conditions. Therefore, the plating amount after the projection was measured by a gravimetric method using dilute hydrochloric acid, and compared with the plating amount before the projection. Those that decreased to less than or equal to% were defined as x.

For comparison, a test material was prepared by temper rolling using a dull roll that was textured by electric discharge dull machining.

Next, a press formability test and measurement of the thickness of the oxide layer were performed on the test material produced by the above method. The press formability test and the measurement of the oxide layer thickness were performed 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. 1 is a schematic front view showing a friction coefficient measuring device. As shown in the figure, a friction coefficient measurement sample 1 collected from a sample material is fixed to a sample table 2, and the sample table 2 is fixed to an upper surface of a horizontally movable slide table 3. On the lower surface of the slide table 3, a vertically movable slide table support 5 having a roller 4 in contact with the slide table 3 is provided. By pushing up the slide table support 5, a pressing load N on the friction coefficient measurement sample 1 by the bead 6 is applied. First for measuring
The load cell 7 is attached to the slide table support 5. A second load cell 8 for measuring a sliding resistance force F for moving the slide table 3 in the horizontal direction while applying the pressing force is attached to one end of the slide table 3. As a lubricating oil, Knox Thrust 550HN manufactured by Nippon Parkerizing Co., Ltd. was applied to the surface of Sample 1 and tested.

FIG. 2 is a schematic perspective view showing the shape and dimensions of the beads used. The lower surface of the bead 6 slides while being pressed against the surface of the sample 1. The shape of the bead 6 shown in Fig. 2 is 10 mm in width, the sliding direction length of the sample is 69 mm, the lower part of both ends in the sliding direction is composed of a curved surface with a curvature of 4.5 mm R, and the bead lower surface on which the sample is pressed is 10 mm in width and the sliding direction. It has a flat surface with a length of 60 mm.

The friction coefficient measurement test was conducted under the following conditions. Using the beads shown in Fig. 2, pressing load N: 400kgf,
Sample withdrawal speed (horizontal movement speed of slide table 3): 20 cm / min. The friction coefficient μ between the test material and the bead was calculated by the formula: μ = F / N.

(2) Measurement of Thickness of Oxide Layer The content (at%) of each element in the flat portion was measured by Auger electron spectroscopy (AES), followed by Ar sputtering to a predetermined depth, and then by AES. The content of each element in the plating film was measured, and by repeating this, the composition distribution of each element in the depth direction was measured. The O content due to oxides and hydroxides reaches a maximum at a certain depth, then decreases and becomes constant. The depth at which the O content was deeper than the maximum value and was half the sum of the maximum value and the constant value was defined as the oxide thickness. As a preliminary treatment, Ar sputtering was performed for 30 seconds to remove the contamination layer on the surface of the test material.

The depth distribution of each element was measured at arbitrary points in this way.
There were some with an l ratio exceeding 1 and those with a Zn / Al ratio of less than 1. Further, when the relationship between these and the oxide film thickness was investigated, the oxide film thickness was larger in the portion where the Zn / Al ratio exceeded 1 than in the portion where it was less than 1. Therefore, these average values were used as the average oxide film thickness. (3) Measurement of area ratio of oxide layer Zn, Al, O by X-ray microanalyzer (EPMA)
Quantitative analysis of the surface direction (mapping), Zn and
The area ratio of each region was measured with the region where O was analyzed as a Zn oxide region and the region where Al and O were analyzed as an Al oxide region.

The test results are shown in Table 1.

[0072]

【table 1】

The following can be seen from Table 1. (1) There is solid fine particle projection and oxidation treatment, and the average particle diameter, projection speed, and projection density of the projected solid fine particles are No. 1 to 18, 28, 29 (invention projected under the conditions within the scope of the present invention. Example)
Has a surface roughness Ra within the range of the present invention and has a thicker oxide layer, and thus has a low friction coefficient and excellent slidability.

(2) No. 19 solid particle projection and no oxidation treatment, No. 20, 21 not oxidation treatment,
No. 27, 30, 31, which solid particle projection is not performed, because the thickness of the oxide layer is thin compared to the example of the present invention, No. 1 ~
Compared with 18, 28, 29, it has a higher friction coefficient and inferior slidability.

(3) Even if the solid fine particles are projected and oxidized, the average particle diameter of the projected solid fine particles, the projection speed,
Projection density is No. 22 to 2 projected under conditions outside the scope of the present invention.
No. 1 to 1 because the surface roughness Ra is out of the range of the present invention.
Compared with 8, 28 and 29, the coefficient of friction is high and the slidability is poor.

In Nos. 1 to 18, 28 and 29, since the oxide layer has a thickness of 200 nm or less, it is possible to form a uniform chemical conversion coating.

[0077]

EFFECTS OF THE INVENTION The hot-dip galvanized steel sheet of the present invention has a small sliding resistance during press forming, and stable and excellent press formability can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic front view showing a friction coefficient measuring device.

FIG. 2 is a schematic perspective view showing the bead shape and dimensions in FIG. 1.

[Explanation of symbols]

1 Friction coefficient measurement sample 2 sample table 3 slide table 4 rollers 5 Slide table support 6 beads 7 1st load cell 8 Second load cell 9 rails N pressing load F sliding resistance P tensile load

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshiharu Sugimoto             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Junichi Inagaki             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Masaaki Yamashita             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Masayasu Ueno             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Yukio Kimura             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. (72) Inventor Yasuhiro Soya             1-2-1, Marunouchi, Chiyoda-ku, Tokyo             Main Steel Pipe Co., Ltd. F term (reference) 4K026 AA02 AA07 AA13 AA22 BA08                       BB09 CA12 CA37 CA38 DA03                       EA01 EA08                 4K027 AA05 AA22 AB02 AB35 AB42                       AC82 AC86 AD28

Claims (15)

[Claims] [Claim 1] A step of dipping a steel sheet in a hot dip galvanizing bath to perform hot dip galvanizing, and after pulling the steel sheet out of the hot dip galvanizing bath, adjusting the amount of plating applied,
Further, a step of cooling below the freezing point of the plating metal, and a roughness adjusting step of projecting solid fine particles onto the surface of the galvanized steel sheet whose temperature is below the freezing temperature of the plating metal to adjust the surface roughness of the plated steel sheet. And an oxidation treatment step of forming an oxide on the surface of the steel sheet having the adjusted surface roughness, the method for producing a hot-dip galvanized steel sheet. 2. The roughness adjusting step is characterized by providing dimple-like fine irregularities on the plating surface.
1. The method for producing a hot-dip galvanized steel sheet according to 1. 3. The average particle size of the projected solid fine particles is 10
3. The method for producing a hot-dip galvanized steel sheet according to claim 1 or 2, wherein the thickness is 300 μm. 4. The projection speed of the solid particles projected is 30 m / s.
The method for producing a hot-dip galvanized steel sheet according to any one of claims 1 to 3, wherein ec or more. 5. The projection density of the projected solid fine particles is 0.2 to
Method for manufacturing a galvanized steel sheet according to any one of claims 1 to 4, characterized in that a 60 kg / m ^2. 6. The hot dip galvanizing according to any one of claims 1 to 5, wherein the surface roughness adjusting step adjusts the center line average roughness Ra to 0.5 μm or more and 2.0 μm or less. Steel plate manufacturing method. 7. The oxidation treatment step according to claim 1, wherein the steel sheet is brought into contact with an acidic solution having a pH buffering action, held for 1 to 30 seconds, and then washed with water. The method for producing a hot-dip galvanized steel sheet according to the item. 8. The molten zinc according to claim 1, wherein in the oxidation treatment step, the steel sheet is brought into contact with an alkaline solution having a pH of 10 or more and then brought into contact with the acidic solution. Manufacturing method of plated steel sheet. 9. The oxidation treatment step comprises a Zn-based oxide and A
The method for producing a hot-dip galvanized steel sheet according to claim 1, wherein an oxide containing an l-based oxide is formed. 10. The method for manufacturing a hot-dip galvanized steel sheet according to claim 1, wherein the oxidation treatment step forms the thickness of the oxide unevenly. 11. The method for producing a hot-dip galvanized steel sheet according to claim 1, wherein the oxidation treatment step forms an oxide having an average thickness of 10 nm or more. 12. A hot dip galvanized steel sheet mainly consisting of η phase, in which solid fine particles are projected on the plated surface to form dimple-like fine irregularities, and an oxide layer having an average thickness of 10 nm or more is formed on the plated surface. The present invention is a hot-dip galvanized steel sheet. 13. The center line average roughness Ra of the plating surface is 0.5 μm.
13. The hot dip galvanized steel sheet according to claim 12, wherein the thickness is 2.0 μm or less. 14. The hot-dip galvanized steel sheet according to claim 12, wherein the oxide layer is an oxide layer having a non-uniform thickness. 15. The oxide layer is an oxide containing a Zn-based oxide and an Al-based oxide.
15. The hot dip galvanized steel sheet according to any one of 14 items.