JP2002012958A - Alloyed hot-dip galvanized steel sheet and method for producing the same - Google Patents

Abstract

(57) [Problem] To provide an alloyed hot-dip coated steel sheet excellent in slidability at the time of press forming and a method for producing the same. SOLUTION: An alloyed hot-dip galvanized steel sheet having a flat portion on the surface of an iron-zinc alloy plating and having an oxide layer having a thickness of 10 nm or more on the surface layer of the flat portion. The area ratio of the flat portion on the surface of the iron-zinc alloy plating is 20 to 80%.
The iron - zinc alloy plating layer composed mainly [delta] ₁ phase,
Also contains ζ phase. In manufacturing the alloyed hot-dip galvanized steel sheet, the steel sheet is subjected to hot-dip galvanizing, further alloyed by heat treatment, and subjected to temper rolling, and then an oxide layer is formed on the plating surface layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Alloyed hot-dip galvanized steel sheets have better weldability and paintability than galvanized steel sheets.
It is widely used in a wide range of fields, mainly for automotive body applications. Alloyed hot-dip galvanized steel sheet for such applications is
It is press-formed and used. However, the galvannealed steel sheet has a drawback that press formability is inferior to that of a cold-rolled steel sheet. This is because the sliding resistance of the alloyed hot-dip coated steel sheet in the press die is larger than that of the cold-rolled steel sheet. That is, the galvannealed steel sheet is less likely to flow into the press die in a portion where the sliding resistance between the die and the bead is large, and the steel sheet is easily broken.

[0003] An alloyed hot-dip galvanized steel sheet is subjected to a heat treatment after galvanizing the steel sheet, thereby causing an alloying reaction in which Fe in the steel sheet and Zn in the plating layer diffuse.
This is the one in which an Fe-Zn alloy phase is formed. This Fe-Zn alloy phase is usually a film composed of a Γ phase, a δ ₁ phase, and a ζ phase,
As the concentration decreases, that is, in the order of す な わ ち phase → δ ₁ phase → Γ phase, the hardness and melting point tend to decrease. For this reason, from the viewpoint of slidability, a film having a high hardness, a high melting point and a high Fe concentration, in which adhesion is unlikely to occur, is effective. It is manufactured with a high average Fe concentration.

[0004] However, a film having a high Fe concentration has a problem that a hard and brittle や す く phase is easily formed at the interface between the plating and the steel sheet, and the phenomenon of peeling from the interface during processing, that is, so-called powdering is apt to occur. For this reason, JP-A-1-319661
As shown in the publication, in order to achieve both slidability and powdering resistance, a method of applying a hard Fe-based alloy as a second layer to the upper layer by a method such as electroplating has been taken. .

[0005] 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, in this method, there are problems such as the occurrence of coating defects due to poor degreasing in the coating process due to the high viscosity of the lubricating oil, and the unstable press performance due to running out of oil during pressing. Therefore, there is a strong demand that the press formability of the galvannealed alloy itself be improved.

As a method for solving the above problem, Japanese Patent Application Laid-Open
No. 53-60332 and JP-A-2-190483 describe that an oxide film mainly composed of ZnO is formed by subjecting the surface of a zinc-based plated steel sheet to electrolytic treatment, immersion treatment, coating oxidation treatment, or heat treatment. It discloses a technique for improving weldability or workability.

Japanese Patent Application Laid-Open No. 4-88196 discloses that a galvanized steel sheet is immersed in an aqueous solution containing 5 to 60 g / l of sodium phosphate and having a pH of 2 to 6 or subjected to electrolytic treatment.
Alternatively, there is disclosed a technique of forming an oxide film mainly composed of a P oxide by applying the aqueous solution to improve press formability and chemical conversion treatment.

[0008] Japanese Patent Application Laid-Open No. 3-91093 discloses that the surface of a galvanized steel sheet is subjected to electrolytic treatment, immersion treatment, coating treatment, coating oxidation treatment, or heat treatment to produce Ni oxide, thereby improving the press formability. A technique for improving chemical conversion treatment is disclosed.

[0009]

However, when the above prior art is applied to a galvannealed steel sheet,
The effect of improving press formability cannot be obtained stably. The present inventors have conducted a detailed study on the cause, and as a result, the alloyed hot-dip coated steel sheet is inferior in surface reactivity due to the presence of Al oxide, and due to large surface irregularities. I found that. That is, when the prior art is applied to an alloyed hot-dip coated steel sheet, the reactivity of the surface is low, so that a predetermined film is formed on the surface even when performing electrolytic treatment, dipping treatment, coating oxidation treatment, heat treatment, and the like. Is difficult, and the film thickness becomes thin in a portion having low reactivity, that is, a portion having a large amount of Al oxide. Also, due to the large irregularities on the surface, the direct contact with the press mold during press molding is the convex part of the surface, but the sliding resistance at the contact part between the thin part of the convex part and the mold is high. And the effect of improving press formability cannot be sufficiently obtained.

An object of the present invention is to solve the above problems and to provide an alloyed hot-dip coated steel sheet having excellent slidability during press forming and a method for producing the same.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have controlled the thickness of the oxide layer of the flat surface layer existing on the surface of the alloyed hot-dip coated steel sheet. By doing so, it was found that excellent press formability can be obtained stably.

The flat part on the surface of the galvannealed steel sheet exists as a convex part as compared with the surrounding area. The flat portion mainly contacts the press mold during the press forming, so that if the sliding resistance in the flat portion is reduced, the press formability can be stably improved. In order to reduce the sliding resistance in this flat part, it is effective to prevent adhesion between the plating layer and the mold. For this purpose, it is necessary to form a hard and high-melting coating on the surface of the plating layer. Is valid. As a result of study from this point of view, it is effective to control the thickness of the oxide layer on the surface layer of the flat part. And no mold adhesion, and good sliding properties. As described above, in a film in which the ζ phase exists in the surface layer, the existence ratio of the 少 な い phase is small, so that there is no possibility of powdering during press molding, which is very advantageous.

In order to control the thickness of the oxide film, the steel sheet is immersed in an iron-zinc alloy plating bath such as that used for applying an upper plating to a galvannealed steel sheet without electricity, and It has been found that by performing washing, an oxide layer can be uniformly applied to the surface of a plated steel sheet, and by contacting the iron-zinc alloy plating bath with a diluted solution, an oxide layer can be uniformly applied to the surface of the plated steel sheet. Was. Furthermore, as a result of further study, they have found that the same effect can be obtained when they are brought into contact with an acidic solution such as sulfuric acid, nitric acid and hydrochloric acid.

The galvannealed steel sheet obtained by subjecting the steel sheet to galvanization and further alloying by heat treatment is usually subjected to temper rolling in order to secure the quality of the steel sheet. Because a flat portion is formed on the plating surface layer by contact with the roll during the temper rolling, it has been found that it is effective to control the oxide layer thickness after the temper rolling.

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

According to a first aspect of the present invention, there is provided an alloyed hot-dip galvanized steel sheet having a flat portion on an iron-zinc alloy-plated surface, and having an oxide layer having a thickness of 10 nm or more on a surface layer of the flat portion. provide.

A second invention provides the galvannealed steel sheet according to the first invention, wherein an area ratio of the flat portion on the surface of the iron-zinc alloy plating is 20 to 80%.

The third invention is the first and second inventions, wherein
Iron - made of zinc alloy plating layer mainly [delta] _1-phase, also possible to provide a galvannealed steel sheet characterized by containing the ζ phase.

[0019] In a fourth aspect based on the first to third aspects, at least a surface of the iron-zinc alloy plating layer on one surface of the steel sheet is formed by adding
Phase is present, the balance to provide a galvannealed steel sheet, wherein the alloy phase is formed is a [delta] ₁ phase.

A fifth invention is the invention according to the first to fourth inventions, wherein the iron-
Provided is an alloyed hot-dip galvanized steel sheet, wherein the ratio of the X-ray diffraction peak (ピ ー ク / δ) of the ζ phase and the δ ₁ phase in the zinc alloy plating layer is 0.2 or more.

According to a sixth aspect, in the first to fifth aspects, the iron-
Provided is an alloyed hot-dip galvanized steel sheet characterized in that a surface area ratio of a zinc alloy plating layer surface is 10% or more.

A seventh invention provides a method for producing the galvannealed steel sheet according to any one of the first to sixth inventions, wherein the steel sheet is hot-dip galvanized, further alloyed by a heat treatment, and subjected to temper rolling. A method for producing an alloyed hot-dip galvanized steel sheet comprising forming an oxide layer on a plating surface layer.

[0023] An eighth invention is the alloyed hot-dip galvanized steel sheet according to the seventh invention, characterized in that after the temper rolling is performed, an oxide layer is formed on the surface layer of the plating by contacting with high-temperature steam. And a method for producing the same.

A ninth invention is the alloy according to the seventh invention, wherein the oxide layer is formed on the plating surface layer by heating in an atmosphere having an oxygen concentration of 20% or more after temper rolling. Provided is a method for producing a galvannealed steel sheet.

According to a tenth aspect, in the seventh aspect, an alloy layer is formed by forming an oxide layer on a plating surface layer by contacting with an aqueous solution containing an oxidizing agent after temper rolling. Provided is a method for manufacturing a galvanized steel sheet.

According to an eleventh aspect, in the seventh aspect, after temper rolling is performed, a process of drying immediately after contacting water with the galvannealed steel sheet is repeatedly performed,
Provided is a method for producing an alloyed hot-dip galvanized steel sheet, comprising forming an oxide layer on a plating surface layer.

A twelfth invention is directed to the galvannealed steel sheet according to the eleventh invention, wherein the temperature of water for contacting the galvannealed steel sheet after temper rolling is 50 ° C. or more. And a method for producing the same.

According to a thirteenth aspect, in the eleventh and twelfth aspects,
Provided is a method for producing an alloyed hot-dip galvanized steel sheet, wherein the above treatment is repeated three or more times after temper rolling.

A fourteenth invention is directed to the galvannealed steel sheet according to the seventh invention, characterized in that an oxide layer is formed on the surface of the plating by contacting with an acidic solution after temper rolling. A manufacturing method is provided.

A fifteenth invention provides the method for producing a galvannealed steel sheet according to the fourteenth invention, wherein the acidic solution has a pH of 1 or more and a temperature of 50 ° C. or more.

According to a sixteenth aspect, in the fourteenth and fifteenth aspects,
A method for producing an alloyed hot-dip galvanized steel sheet, comprising washing with high-temperature water of 50 ° C. or more after contact with the acidic solution.

A seventeenth invention provides a method for producing a galvannealed steel sheet according to the fourteenth invention, wherein the acidic solution is an acidic solution containing Fe and Zn ions.

An eighteenth invention is the invention according to the fourteenth to seventeenth inventions, wherein the acidic solution containing Fe and Zn ions comprises a sulfate of Fe and Zn,
Provided is a method for producing an alloyed hot-dip galvanized steel sheet, which is a bath containing one or more of nitrates and chlorides.

A nineteenth invention is the invention according to the seventh to eighteenth inventions, wherein the surface is activated by removing the oxide layer formed during the alloying treatment after the temper rolling, and thereafter the oxide surface is formed on the plating surface layer. A method for producing an alloyed hot-dip galvanized steel sheet, comprising forming a layer.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION In the production of an alloyed hot-dip galvanized steel sheet, the steel sheet is subjected to hot-dip galvanizing and then further heated and alloyed. Irregularities exist on the surface of the galvannealed steel sheet due to the difference in reactivity at the plating interface. However, after the alloying treatment, temper rolling is usually performed to secure the material, and the contact with the roll at the time of the temper rolling causes the plating surface to be smoothed and unevenness is reduced. Therefore, at the time of press molding, the force required for the mold to crush the projections on the plating surface is reduced, and the sliding characteristics can be improved.

Since the flat portion of the surface of the alloyed hot-dip galvanized steel sheet is in direct contact with the mold during press forming, the presence of a hard and high-melting substance that prevents adhesion to the mold is present. It is important for improving the slidability. In this regard, a δ ₁ single-phase film containing no ζ phase in the surface layer is effective for improving the slidability, but in order for the surface layer to be completely δ ₁ phase, the Fe An alloying treatment must be performed to increase the concentration. As a result, a thick, hard and brittle Γ phase is formed at the interface between the plating and the steel sheet, and there is a problem that powdering is likely to occur during press forming. On the other hand, if an alloying treatment is performed to reduce the thickness of the Γ phase in order to prevent powdering, the ζ phase remains on the surface layer, and there is a problem that the slidability is poor.

From this viewpoint, although the Fe concentration and the Al concentration of the plating film of the galvannealed steel sheet used in the present invention are not particularly specified, the plating layer is mainly δ
_An ideal structure is composed of _one phase and further contains a ζ phase.

On the other hand, the presence of the oxide layer on the surface layer is effective for improving the sliding characteristics even in a film in which the ζ phase remains, since the oxide layer prevents adhesion to the mold. Furthermore,
If ζ phase plating film surface is present, since the reactivity of the surface is increased, the surface as compared with the case of [delta] ₁ single phase, it is possible to generate effectively the oxide layer on the flat portion. At the time of actual press forming, the oxide on the surface layer is worn out and scraped off. Therefore, when the contact area between the mold and the workpiece is large, a sufficiently thick oxide film is required. Although an oxide layer is formed on the plating surface by heating during the alloying treatment, most of it is destroyed by contact with the roll during temper rolling, and the new surface is exposed, so good sliding properties In order to obtain a high quality, a thick oxide layer must be formed before temper rolling. Also, taking this into consideration, even if a thick oxide layer is formed before the temper rolling, the oxide layer at the flat portion cannot be prevented from being destroyed at the time of the temper rolling. It is not uniform, and good slidability cannot be obtained stably.

[0039] Therefore, when a treatment for uniformly forming an oxide layer on a tempered rolled alloyed hot-dip galvanized steel sheet, particularly on a flat portion of the plated surface, it is possible to stably obtain good slidability. Can be.

As a method of providing an oxide film on the flat portion of the plating surface, a method of bringing a steel sheet into contact with high-temperature steam is effective. Zinc easily forms a zinc-based oxide upon contact with a neutral solution, and the reaction proceeds rapidly in a high temperature state, so that an oxide layer necessary for improving slidability can be formed in a short time. It is. Further, even when heat treatment is performed in an atmosphere having an oxygen concentration of 20% or more, an oxide layer can be formed as a surface layer. As described above, even when the spraying of steam or the heat treatment is impossible due to the facility, the oxide layer can be formed at a relatively low temperature of about room temperature by contact with an aqueous solution containing an oxidizing agent.

In addition to the above-mentioned method, an oxide film can be provided on the flat portion of the plating surface by the following method. That is, when the process of drying immediately after contacting the galvannealed steel sheet with water is repeated, the oxide layer can be effectively formed on the flat portion of the plating surface. Although the mechanism of this oxide layer formation is not clear, zinc is likely to generate a zinc-based oxide upon contact with a neutral solution, and further promotes the formation reaction of the oxide upon contact with air. Conceivable. If the temperature of the water contacting the alloyed hot-dip galvanized steel sheet is less than 50 ° C, the formation reaction of the oxide layer is slow, and the contact must be performed for a long time.
The temperature must be 50 ° C or higher. If the number of repetitions of the contact with water and the drying treatment is less than 3, the formation of the oxide layer on the flat surface of the plating is insufficient and uneven, so that the slidability can be improved stably. It is necessary to repeat the above processing three times or more because it is difficult to obtain the above.

Further, by contacting the alloyed hot-dip galvanized steel sheet with an acidic solution, followed by washing with hot water and drying, an oxide layer can be formed on the flat portion of the plating surface. Although the mechanism of this oxide layer formation is not clear,
It can be considered as follows. When an alloyed hot-dip galvanized steel sheet is brought into contact with an acidic solution, zinc dissolution occurs on the surface layer of the coating. During the dissolution of zinc, hydrogen is generated at the same time, so the pH of the solution on the plating surface layer increases,
Zinc hydroxide is easily generated. Further, it is considered that when the coated steel sheet is washed with high-temperature water, the reaction for generating the hydroxide is promoted, and the oxide can be easily formed on the plating surface layer.

If the pH of the acidic solution used in the above treatment is too low, the dissolution of zinc is promoted, but the formation of oxides becomes difficult, so that the pH must be 1 or more. On the other hand, p
If the H is too high, the reaction rate for dissolving zinc will be low, so the pH of the solution is desirably 5 or less. The liquid temperature is 50 ℃
If it is less than 1, the dissolution rate of zinc and the generation reaction rate of oxides become slow. Therefore, the liquid temperature needs to be 50 ° C. or more. At the same time, the temperature of the high-temperature water used for washing with hot water must be 50 ° C. or higher.

As the acidic solution used in the above treatment, Fe
And an acidic solution containing Zn ions. Fe and
The use of a solution containing Zn ions has the effect of reducing the variation in the coefficient of friction after oxidation treatment, and since these are components contained in the plating film, these components have an adverse effect even if they remain on the plating surface. There is no. An iron-zinc alloy plating bath can also be used as an acidic solution containing Fe and Zn ions. In particular, when an electroplating facility is provided in the process after the alloying process to perform electroplating of iron-zinc on the upper layer, the same effect can be obtained by passing the steel sheet without electricity. Obtainable. As the acidic solution containing Fe and Zn ions, a solution containing sulfate, nitrate, and chloride of iron and zinc can be used.
It suffices that the pH is within the above-mentioned range, and the concentration is not particularly limited.

When an iron-zinc alloy plating bath is used as an acidic solution containing Fe and Zn ions, it may be brought into contact with the diluted solution, or may be used to form an oxide layer on a flat portion of the plating surface. It is valid. Although the mechanism of forming the oxide layer is not clear, it can be considered as follows. Since the iron-zinc alloy plating bath is acidic, when the alloyed hot-dip galvanized steel sheet is immersed, dissolution of zinc occurs on the plating surface layer. When dissolving this zinc,
At the same time, hydrogen is generated, so the pH of the solution on the plating surface layer
And zinc hydroxide is easily generated. When contacted with a normal iron-zinc alloy plating bath, the pH of the solution
It is necessary to remove the remaining solution to prevent the galvanized surface layer from being over-etched, as well as further raise the pH of the surface layer and promote the formation of zinc hydroxide. When contacted with plating solution,
Since the pH of the solution is high, there is no danger that the zinc plating surface layer will be over-etched, and even if a small amount of zinc is dissolved, the pH of the solution on the plating surface layer easily rises, so that the oxide layer can be formed relatively easily. There are advantages. The dilution ratio of the solution needs to be 100 times or more from the viewpoint of preventing over-etching. However, if the solution is diluted too much, the dissolution reaction of zinc hardly occurs.

As described above, before forming the oxide layer,
It is more effective to remove the oxide layer remaining on the surface layer. This is because the surface oxide is destroyed by the contact with the roll at the time of temper rolling, but a part of the surface oxide remains but the reactivity of the surface is uneven. As a method of removing the oxide layer remaining on the surface layer, a method of mechanical removal such as polishing, or a method of chemically removing by treatment by dipping or spraying in an alkali solution can be considered. It is only necessary that the surface oxide layer be removed before the oxidation treatment, and the method is not limited.

The oxide layer in the present invention includes Zn, Fe, Al
And one or more oxides and / or hydroxides of other metal elements.

Here, the film in which the ζ phase remains on the surface layer is as follows:
In a photograph in which the plating surface is observed with an SEM or the like, this indicates a film in which the presence of a ζ phase can be confirmed. It can be defined by the following two methods. One method is based on X-ray diffraction. From among the X-ray diffraction peaks on the plating surface, d = 1.900 (ζ
Phase), and d = 1.990 (δ ₁ phase) on a ratio but minus the respective background value from the corresponding peak intensities (zeta
If the value is 0.2 or more with respect to the value of (/ δ), it can be considered as a film in which the ζ phase remains. In addition, the ratio of the phase (area ratio) to the entire photo is 10% for the photo taken of the SEM image of the plating surface, with the columnar crystal as the phase.
The above can also be considered as a film in which the ζ phase remains. However, if a portion crushed by pressure adjustment or the like is present on the plating surface, it is difficult to judge from the shape, and such a portion is excluded in advance and the area ratio is calculated. The film in which the ζ phase remains can be determined by any of the methods described above.
Film less than or ζ phase area ratio of the coating of less than 10%, although sometimes the presence of partially ζ phase is confirmed, since it is film substantially entirely [delta] ₁ phase, the ζ phase remains As compared with, adhesion to the mold is prevented and the slidability is improved, but on the contrary, the powdering resistance may be inferior.

By setting the thickness of the oxide layer in the flat portion of the plating surface layer to 10 nm or more, an alloyed hot-dip galvanized steel sheet exhibiting good slidability can be obtained, but the thickness of the oxide layer is set to 20 nm or more. Is more effective. This is because in a press forming process in which the contact area between the mold and the workpiece increases, even if the surface oxide layer is worn, the oxide layer remains and does not cause a decrease in slidability. On the other hand, the upper limit of the thickness of the oxide layer is not particularly provided, but if it exceeds 200 nm, the reactivity of the surface is extremely reduced, and it becomes difficult to form a chemical conversion treatment film. .

The thickness of the oxide layer on the surface of the flat portion is Ar
It can be determined by Auger electron spectroscopy (AES) in combination with ion sputtering. In this method, after sputtering to a predetermined thickness, the composition at the depth can be obtained by correcting the relative sensitivity factor from the spectral intensity of each element to be measured. The O content due to oxides or hydroxides reaches a maximum at a certain depth (which may be the outermost layer), and then decreases and becomes constant.
At a position where the O content 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.

Here, the area ratio of the flat portion on the plating surface is desirably 20 to 80%. If it is less than 20%, the contact area with the mold in the portion (concave portion) excluding the flat portion becomes large, and the area ratio of the flat portion in which the oxide thickness can be reliably controlled in the area actually in contact with the mold. , The effect of improving press formability is reduced. In addition, the portion excluding the flat portion has a role of holding press oil at the time of press molding. Therefore, when the area ratio of the portion excluding the flat portion is less than 20% (when the area ratio of the flat portion exceeds 80%), oil shortage tends to occur during press molding, and the effect of improving press moldability is reduced.

The flat portion of the plating surface can be easily identified by observing the surface with an optical microscope or a scanning electron microscope. The area ratio of the flat portion on the plating surface can be determined by image analysis of the micrograph.

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

Further, since impurities are contained in the processing solution used for the oxidation treatment or the like, S, N, P, B, Cl, Na, M
Even if n, Ca, Mg, Ba, Sr, Si and the like are taken into the oxide layer, the effect of the present invention is not impaired.

[0055]

Next, the present invention will be described in more detail with reference to examples. Example 1 On a cold-rolled steel sheet having a thickness of 0.8 mm, a coating weight of 60 g / m ² and a predetermined Fe
A plated film having a high concentration was formed, and further temper rolling was performed. At this time, the area ratio of the flat portion on the surface was changed by changing the rolling load of the temper rolling. Subsequently, the following two kinds of treatments were performed to form an oxide layer on the surface layer of the flat portion.

(Forming Method A) The above alloyed hot-dip galvanized steel sheet is immersed in a sulfuric acid acidic hydrogen peroxide aqueous solution having a pH of 3. Temperature 5
0 ° C. The thickness of the oxide layer in the flat part was adjusted by changing the concentration of hydrogen peroxide in various ways.

(Forming Method B) The galvannealed steel sheet is immersed in a sulfuric acid acidic sodium nitrate aqueous solution of pH 2 and subjected to cathodic electrolysis. Temperature 50 ° C. The thickness of the oxide layer in the flat part was adjusted by changing the current density and the conduction time in various ways.

Next, the specimens prepared as described above were subjected to measurement of the Fe concentration in the plating film, the area ratio of the flat portion, the thickness of the oxide layer, and a press formability test. The measurement of the thickness of the oxide layer on the flat portion and the press formability test were performed as follows.

(1) Thickness Measurement 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, followed 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. After the content of O due to oxides and hydroxides reaches a maximum at a certain depth,
Decreases and becomes constant. The depth at which the O content was half of the sum of the maximum value and the constant value at a position deeper than the maximum value was defined as the oxide thickness. The thickness of the oxide on the flat portion at a plurality of arbitrarily selected portions (n = 3) was measured, and the average value was determined. Note that, as a preliminary treatment, Ar sputtering was performed for 30 seconds to remove the contamination layer on the surface of the test material.

(2) Evaluation Test of Press Formability (Test for Measuring Friction Coefficient) 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 test 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, there is provided a vertically movable slide table support 5 having a roller 4 in contact with the slide table 3. By pushing up the slide table support 5, a load N on the sample 1 for friction coefficient measurement by the beads 6 is measured. The first for measuring
A load cell 7 is mounted on 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. As a lubricating oil, Noxlast 550HN manufactured by Nippon Parkerizing Co., Ltd. was applied to the surface of Sample 1 for a test.

FIGS. 2 and 3 are schematic perspective views showing the shapes 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 wide, the length in the sliding direction of the sample is 12 mm, the lower part of both ends in the sliding direction is a curved surface with a curvature of 4.5 mmR, the lower surface of the bead on which the sample is pressed is 10 mm in width, the sliding direction It has a plane with a length of 3 mm. The shape of the bead 6 shown in Fig. 3 is 10 mm wide, the length of the sample in the sliding direction is 69 mm, the lower part of both ends in the sliding direction is a curved surface with a curvature of 4.5 mmR, the lower surface of the bead against which the sample is pressed is 10 mm in width, the sliding direction It has a plane with a length of 60 mm.

The friction coefficient measurement test was performed under the following two conditions. (Condition 1) Using the bead shown in Fig. 2, pressing force N: 400
kgf, sample withdrawal speed (horizontal movement speed of slide table 3): 100 cm / min. (Condition 2) Using the bead shown in Fig. 3, pressing force N: 400
kgf, sample withdrawal speed (horizontal movement speed of slide table 3): 20 cm / min.

The coefficient of friction μ between the test material and the bead is
Formula: Calculated as μ = F / N. Table 1 shows the test results.

[0065]

【table 1】

From the test results in Table 1, the following matters are clear. (1) Comparative Example 1 is an example of an alloyed hot-dip galvanized steel sheet that has not been subjected to temper rolling, and has a high coefficient of friction. (2) In Comparative Example 2, since the oxide forming treatment was not performed after the temper rolling, the oxide thickness was as thin as 7 nm and the friction coefficient was high. (3) In Comparative Example 3, although the oxide forming treatment was performed after the temper rolling, since the thickness of the oxide in the flat portion was smaller than the range of the present invention, almost the effect of improving the friction coefficient was obtained. Not. (4) Invention Examples 1 to 17 are subjected to oxide forming treatment after temper rolling, the thickness of the oxide in the flat portion is within the range of the present invention, and the friction coefficient is 0.160 or less under condition 1, the condition In 2 it is improved to 0.190 or less. Further, in Invention Examples 4 to 7, and 10 to 15, the area ratio of the flat portion is in the range of 20 to 80%, and therefore, the effect of improving the friction coefficient under Condition 2 is large, being 0.170 or less.

(Example 2) An alloyed hot-dip galvanized film was formed on a cold-rolled steel sheet having a thickness of 0.8 mm by a conventional method, and further temper rolling was performed. At this time, the ζ phase ratio of the surface layer was changed by changing the alloying conditions, and the flat area ratio on the surface was changed by changing the rolling load of the temper rolling. Subsequently, two types of oxidation treatments (formation methods A and B) described in Example 1 were performed to form an oxide layer on the surface layer of the flat portion. Before the above treatment, the substrate was immersed in an aqueous solution of sodium hydroxide having a pH of 12 to remove an oxide layer generated by heating during the alloying treatment.

Next, for the test material produced by the above method, the Fe content in the plating film, the ζ / δ value, the ζ phase area ratio,
The flat area ratio, the thickness of the oxide layer, and the press formability were evaluated. The measurement of the thickness of the oxide layer and the evaluation of press formability were performed by the method described in Example 1. Table 2 shows the test results.

[0069]

[Table 2]

As shown in Table 2, when the oxide film thickness of the surface layer and the flat area ratio of the surface layer were within the range of the present invention (Example 5 of the present invention)
2424) show that the ζ / δ value and ζ phase area ratio are high, and even in a film with 皮膜 phase clearly present on the surface layer, the friction coefficient under condition 1 is all very low and the oxide film thickness When the thickness was as thick as 20 nm or more (Examples 11 to 24 of the present invention), the coefficient of friction under Condition 2 was also a low value, and further excellent sliding characteristics were exhibited. On the other hand, the comparative examples (Comparative Examples 1 to 4) in which the oxide film thickness of the surface layer is out of the range of the present invention show high values of any of the friction coefficients,
The sliding characteristics were reduced. On the other hand, even when the oxide film thickness of the surface layer is included in the range of the present invention, when the flat area ratio is out of the range of the present invention (Examples 1 to 4), the friction coefficient of the condition 1 is slightly reduced. However, the friction coefficient under condition 2 did not decrease at all, and there was no effect of improving the sliding characteristics.

Example 3 An alloyed hot-dip galvanized film was formed on a cold-rolled steel sheet having a thickness of 0.8 mm by a conventional method, followed by temper rolling. At this time, the flat portion area ratio on the surface was changed by changing the rolling load of the temper rolling. Then, to form an oxide layer on the surface layer of the flat part,
Three oxidation treatments were performed.

(Formation Method 1) Steam at 100 ° C. was sprayed on the galvannealed steel sheet. At this time, the thickness of the oxide layer in the flat portion was adjusted by variously changing the spraying time.

(Formation Method 2) The alloyed hot-dip galvanized steel sheet was subjected to a heat treatment in an atmosphere at 250 ° C. and an oxygen concentration of 40%. At this time, the thickness of the oxide layer in the flat portion was adjusted by variously changing the heating time.

(Forming Method 3) The alloyed hot-dip galvanized steel sheet was immersed in a sulfuric acid acidic hydrogen peroxide aqueous solution at 50 ° C. and pH3. At this time, the thickness of the oxide layer in the flat portion was adjusted by variously changing the concentration of hydrogen peroxide.

Before the oxidation treatment, the substrate was immersed in an aqueous solution of sodium hydroxide having a pH of 12 to remove an oxide layer generated by heating during the alloying treatment.

Next, the Fe content in the plating film, the flat area ratio, the thickness of the oxide layer, and the press formability of the test material produced by the above method were evaluated. The measurement of the thickness of the oxide layer and the evaluation of press formability were performed by the method described in Example 1. The test results are shown in Tables 3 and 4.

[0077]

[Table 3]

[0078]

[Table 4]

As shown in Tables 3 and 4, the oxide remaining in the surface layer was removed by alkali treatment as a pretreatment, and an oxide layer was formed by the method described in the present invention. When the thickness is within the range of the present invention (Examples 7 to 3 of the present invention)
In (3), the friction coefficients under condition 1 are all very low, and when the oxide film thickness is as thick as 20 nm or more (Example of the present invention)
In 10-33), the friction coefficient under condition 2 was also a low value, showing even better sliding characteristics. On the other hand, when the alkali treatment and the oxidation treatment were not performed (Comparative Examples 1 and 2),
The coefficient of friction showed a very high value, and the sliding characteristics were reduced.
In addition, even when the oxidation treatment was performed, when the oxide film thickness of the surface layer was out of the range of the present invention (Comparative Examples 3 to 5), the effect of improving the sliding characteristics was small although the friction coefficient was slightly reduced. Furthermore, even when the oxidation treatment is performed and the oxide film thickness of the surface layer is included in the range of the present invention, when the flat area ratio is out of the range of the present invention (Examples 1 to 6 of the present invention), the friction of Condition 1 is satisfied. Although the coefficient decreased slightly, the friction coefficient under Condition 2 did not decrease at all, and the effect of improving the sliding characteristics was smaller than that of Examples 7 to 33 of the present invention.

Example 4 An alloyed hot-dip galvanized film was formed on a cold-rolled steel sheet having a thickness of 0.8 mm by a conventional method, followed by temper rolling. At this time, the flat portion area ratio on the surface was changed by changing the rolling load of the temper rolling. Subsequently, a process of drying immediately after spraying the steel sheet on filtered water at a predetermined temperature for 5 seconds was repeated a predetermined number of times, thereby forming an oxide layer on the surface layer of the flat portion.

Before the above treatment, the substrate was immersed in an aqueous solution of sodium hydroxide having a pH of 12 to remove an oxide layer formed by heating during the alloying treatment.

Next, the Fe content in the plating film, the flat area ratio, the oxide layer thickness, and the press formability of the test material prepared by the above method were evaluated. The measurement of the thickness of the oxide layer, the evaluation of the press formability, and the test conditions for measuring the coefficient of friction were performed by the methods described in Example 1. The test results are shown in Tables 5 and 6.

[0083]

[Table 5]

[0084]

[Table 6]

As shown in Tables 5 and 6, the oxide remaining on the surface layer was removed by alkali treatment as a pretreatment, and an oxide layer was formed by the method shown in the present invention. When the thickness is within the range of the present invention (Examples 7 to 3 of the present invention)
In (0), the friction coefficients in Condition 1 are all very low, and when the oxide film thickness is as thick as 20 nm or more,
The coefficient of friction of No. 2 also became a low value, and showed better sliding characteristics. On the other hand, when the contact and drying with water were not repeated after the alkali treatment and the temper rolling (Comparative Examples 1 and 2), the friction coefficient showed a very high value, and the sliding characteristics decreased. . In addition, even when the above processing was performed, when the processing conditions were out of the range of the present invention (Comparative Examples 3 to 10),
Although the coefficient of friction was slightly reduced, the effect of improving the sliding characteristics was small. Further, even when the processing conditions are included in the range of the present invention, when the flat portion area ratio is out of the range of the present invention (Examples 1 to 6 of the present invention), the friction coefficient of the condition 1 is slightly reduced. The coefficient of friction under Condition 2 did not decrease at all, and the effect of improving the sliding characteristics was smaller than Examples 7 to 30 of the present invention.

Example 5 An alloyed hot-dip galvanized film was formed on a cold-rolled steel sheet having a thickness of 0.8 mm by a conventional method, followed by temper rolling. At this time, the flat area ratio on the surface was changed by changing the rolling load of the temper rolling, and thereafter, immersion treatment was performed in a sulfuric acid solution at a predetermined temperature and a predetermined pH. In addition, ferrous sulfate 1.0 mol / l, zinc sulfate
An immersion treatment in an iron-zinc alloy plating bath containing 0.1 mol / l was also performed. Note that diluted sulfuric acid was used for pH adjustment of the plating bath.

Before the above treatment, the substrate was immersed in an aqueous solution of sodium hydroxide having a pH of 12 to remove an oxide layer formed by heating during the alloying treatment.

Next, with respect to the test material produced by the above method, the Fe content in the plating film, the flat area ratio, the oxide layer thickness and the press formability were evaluated. The measurement of the thickness of the oxide layer, the evaluation of the press formability, and the test conditions for measuring the coefficient of friction were performed by the methods described in Example 1. The test results are shown in Tables 7 and 8.

[0089]

[Table 7]

[0090]

[Table 8]

As shown in Tables 7 and 8, when immersed in an acidic solution by the method described in the present invention and the area ratio of the flat portion of the surface layer and the oxide film thickness were within the range of the present invention (Example 7 of the present invention) ~Four
In 2), all of the friction coefficients in condition 1 are very low, and when the oxide film thickness is as thick as 20 nm or more,
The coefficient of friction of No. 2 also became a low value, and showed better sliding characteristics. In contrast, after temper rolling, alkali treatment,
When the immersion treatment in an acidic solution and the washing with high-temperature water were not performed (Comparative Examples 1 and 2), the friction coefficient showed a very high value.
The sliding characteristics were reduced. In addition, when the processing conditions are out of the range of the present invention even when the above processing is performed (Comparative Examples 3 to 9)
However, although the coefficient of friction was slightly reduced, the effect of improving the sliding characteristics was small. Furthermore, even if the processing conditions are included in the range of the present invention, when the flat portion area ratio deviates from the range of the present invention (Examples 1 to 6 of the present invention), the friction coefficient of the condition 1 is slightly reduced. The coefficient of friction under Condition 2 did not decrease at all, and the effect of improving the sliding characteristics was smaller than those of Examples 7 to 42 of the present invention.

Example 6 An alloyed hot-dip galvanized film was formed on a cold-rolled steel sheet having a thickness of 0.8 mm by a conventional method, followed by temper rolling. At this time, the flat portion area ratio on the surface was changed by changing the rolling load of the temper rolling. Subsequently, an iron-zinc alloy plating bath containing 1.0 mol / l of ferrous sulfate and 0.1 mol / l of zinc sulfate and adjusted to pH 2 using dilute sulfuric acid was prepared. And dried at a predetermined temperature for a predetermined time.

Before the above treatment, the substrate was immersed in an aqueous solution of sodium hydroxide having a pH of 12 to remove an oxide layer formed by heating during the alloying treatment.

Next, with respect to the test materials produced by the above method, the Fe content in the plating film, the flat area ratio, the oxide layer thickness and the press formability were evaluated. The measurement of the thickness of the oxide layer, the evaluation of the press formability, and the test conditions for measuring the coefficient of friction were performed by the method described in Example 1. The test results are shown in Tables 9 and 10.

[0095]

[Table 9]

[0096]

[Table 10]

As shown in Tables 9 and 10, the sample was brought into contact with an iron-zinc alloy plating bath diluted by the method shown in the present invention, and the area ratio of the flat portion of the surface layer and the oxide film thickness were within the range of the present invention. In (Examples 5 to 28 of the present invention), the coefficient of friction under Condition 1 is all very low, and when the oxide film thickness is as thick as 20 nm or more, the coefficient of friction under Condition 2 is also low, and The sliding characteristics were shown. On the other hand, when the alkali-treated and diluted iron-zinc alloy plating bath was not contacted after the temper rolling (Comparative Examples 1 and 2), the friction coefficient showed a very high value, Properties deteriorated. In addition, when the processing conditions were out of the range of the present invention (Comparative Examples 3 to 11) even when the above processing was performed, the friction coefficient was slightly reduced, but the effect of improving the sliding characteristics was small. Further, even when the processing conditions are included in the range of the present invention, when the flat portion area ratio is out of the range of the present invention (Examples 1 to 4 of the present invention), the friction coefficient of the condition 1 is slightly reduced. The coefficient of friction under Condition 2 did not decrease at all, and the effect of improving the sliding characteristics was
Was smaller than ~ 28.

[0098]

The alloyed hot-dip galvanized steel sheet of the present invention comprises:
Even if the ζ phase remains in the plating layer, the sliding resistance during press forming is small, and excellent press formability can be obtained stably.

[Brief description of the drawings]

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

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

FIG. 3 is a schematic perspective view showing another bead shape and dimensions in FIG. 1.

[Explanation of symbols]

 1 Sample for coefficient of friction measurement 2 Sample table 3 Slide table 4 Roller 5 Slide table support 6 Bead 7 First load cell 8 Second load cell 9 Rail N Pressing load F Sliding resistance P Pulling load

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Junichi Inagaki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Toru 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Sun Inside the Kokan Co., Ltd. (72) Inventor Shuji Nomura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Inside the Kokan Co., Ltd. (72) Inventor Yoshitaka Sakurai 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Inside Steel Pipe Co., Ltd. (72) Inventor Masaaki Yamashita 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Inside Pipe Co., Ltd. (72) Inventor Shinya Okude 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Incorporated (72) Inventor Kaoru Sato 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. F-term (reference) 4K027 AA05 AA22 AB02 AB28 AB 36 AB37 AB42 AB44 AC73 AC82 AC87

Claims (19)

[Claims] 1. An alloyed hot-dip galvanized steel sheet having a flat portion on the surface of an iron-zinc alloy plating, and having an oxide layer having a thickness of 10 nm or more on a surface layer of the flat portion. 2. The galvannealed steel sheet according to claim 1, wherein an area ratio of the flat portion on the surface of the iron-zinc alloy plating is 20 to 80%. 3. Iron - Claim zinc alloy plating layer composed mainly [delta] ₁ phase, also characterized in that it comprises a ζ phase 1
And 2. The galvannealed steel sheet according to 2. 4. An alloy phase in which a ζ phase is present on at least a surface layer of an iron-zinc alloy plating layer on one side of a steel sheet, and an alloy phase having a balance of δ ₁ phase is formed. 2. A galvannealed steel sheet according to claim 1. 5. The ζ phase and δ ₁ in the iron-zinc alloy plating layer
5. The galvannealed steel sheet according to claim 1, wherein the X-ray diffraction peak ratio (ζ / δ) of the phase is 0.2 or more. 6. The galvannealed steel sheet according to claim 1, wherein the surface area ratio of the iron-zinc alloy plating layer is 10% or more. In producing the galvannealed steel sheet according to any one of claims 1 to 6, the steel sheet is subjected to hot-dip galvanizing, further alloyed by heat treatment, and subjected to temper rolling, and then to a plating surface layer. A method for producing an alloyed hot-dip galvanized steel sheet, comprising forming an oxide layer. 8. The production of an alloyed hot-dip galvanized steel sheet according to claim 7, wherein after performing temper rolling, an oxide layer is formed on a surface layer of the plating by being brought into contact with high-temperature steam. Method. 9. The alloying and melting according to claim 7, wherein after performing the temper rolling, heating is performed in an atmosphere having an oxygen concentration of 20% or more to form an oxide layer on the plating surface layer. Manufacturing method of galvanized steel sheet. 10. The alloyed hot-dip galvanizing according to claim 7, wherein an oxide layer is formed on a plating surface layer by contacting with an aqueous solution containing an oxidizing agent after temper rolling. Steel plate manufacturing method. 11. After the temper rolling, an oxide layer is formed on the plating surface layer by repeatedly performing a drying process immediately after contacting water with the alloyed hot-dip galvanized steel sheet. 8. A method for producing the galvannealed steel sheet according to claim 7. 12. The production of an alloyed hot-dip galvanized steel sheet according to claim 11, wherein the temperature of water brought into contact with the alloyed hot-dip galvanized steel sheet after temper rolling is 50 ° C. or higher. Method. 13. The method for producing an alloyed hot-dip galvanized steel sheet according to claim 11, wherein the treatment is repeated three times or more after temper rolling. 14. The method for producing an alloyed hot-dip galvanized steel sheet according to claim 7, wherein an oxide layer is formed on a surface layer of the plating by contacting with an acidic solution after temper rolling. . 15. The method for producing a galvannealed steel sheet according to claim 14, wherein the acidic solution has a pH of 1 or more and a temperature of 50 ° C. or more. 16. The method according to claim 14, wherein after contact with the acidic solution, washing with high-temperature water of 50 ° C. or more is performed.
16. The method for producing a galvannealed steel sheet according to item 15. 17. The method for producing a galvannealed steel sheet according to claim 14, wherein the acidic solution is an acidic solution containing Fe and Zn ions. 18. The method according to claim 17, wherein the acidic solution containing Fe and Zn ions is Fe solution.
18. The method for producing an alloyed hot-dip galvanized steel sheet according to claim 17, wherein the bath contains one or more of sulfates, nitrates, and chlorides of Zn. 19. The method according to claim 19, wherein after performing the temper rolling, the oxide layer formed at the time of the alloying treatment is removed to activate the surface, and then the oxide layer is formed on the plating surface layer. Item 19. The method for producing a galvannealed steel sheet according to any one of Items 7 to 18.