JPH10259468A - Galvanized steel sheet excellent in press formability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a galvanized steel sheet excellent in press formability by reducing its sliding resistance on a press die. SOLUTION: This galvanized steel sheet 21 is one in which Ni-Zn-O series coating 23 contg. metallic Ni and the oxides of Ni and Zn or the oxides and hydroxides of them is formed on the surface of a plating layer at least in one side. The surface layer part of the Ni-Zn-O series coating 23 is composed of an oxide layer 24 consisting of the oxides of Ni and Zn or the oxides and hydroxides of them, the thickness of the oxide layer 24 is regulated to be 0.5 to 50 nm, and the ratio of the Zn content (wt.%) to the total of the Ni content (wt.%) and the Zn content (wt.%) in the Ni-Zn-O series coating 23 is regulated to be <=0.6. The hard Fe-Ni-Zn-O series coating 23 having the high m.p. prevents the coagulating phenomenon of zinc at the time of press forming. The adsorbing action of lubricating oil by the metallic Ni improves the effect. The oxide layer 24 on the surface layer part improves its press formability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of a galvanized steel sheet, and more particularly to a galvanized steel sheet excellent in press formability.

[0002]

2. Description of the Related Art Galvanized steel sheets are widely used as various kinds of rust-preventive steel sheets because they have various excellent characteristics. In order to use this galvanized steel sheet as a rustproof steel sheet for automobiles, it is required not only to have performance such as corrosion resistance, but also to be excellent in press formability in a vehicle body manufacturing process.

[0003] However, zinc-based plated steel sheets generally have a drawback that press formability is inferior to cold-rolled steel sheets. This is because the sliding resistance between the galvanized steel sheet and the press die is larger than that of the cold-rolled steel sheet. That is, when the sliding resistance is large, the galvanized steel sheet hardly flows into the mold at the portion where the steel sheet slides vigorously between the bead and the steel sheet, and the steel sheet is easily broken.

[0004] As a method for improving the press formability of a galvanized steel sheet, generally, a method of applying a high-viscosity lubricating oil is widely used. However, this method has problems such as a coating defect due to poor degreasing in the coating process due to the high viscosity of the lubricating oil and an unstable press performance due to lack of oil during pressing. Therefore, there is a strong demand for improving the press formability of zinc-coated steel sheets.

As methods for solving the above-mentioned problems, Japanese Patent Application Laid-Open Nos. 53-60332 and 2-190483 disclose electrolytic treatment, immersion treatment, coating oxidation treatment, or heat treatment on the surface of a zinc-based plated steel sheet. Discloses a technique for forming an oxide film mainly composed of ZnO (hereinafter referred to as prior art 1).

[0006] Japanese Patent Application Laid-Open No. Hei 3-91093 discloses that a nickel oxide film is formed on a surface of a galvanized steel sheet by electrolytic treatment, immersion treatment, coating treatment, coating oxidation treatment or heat treatment, thereby obtaining press formability. A technique (hereinafter referred to as prior art 2) for improving the chemical conversion property is disclosed.

JP-A-58-67885 does not particularly limit the method on the surface of a galvanized steel sheet,
For example, by electroplating or chemical plating, Ni and
A technique for forming a metal film such as Fe to improve corrosion resistance (hereinafter referred to as prior art 3) is disclosed.

[0008]

The above prior art has the following problems.

In the prior art 1, since an oxide film mainly composed of ZnO is formed on the surface of the plating layer, ordinary weldability and workability are improved, but the sliding resistance between the press die and the plated steel sheet is sufficiently small. Therefore, the effect of improving press formability is small.

In the prior art 2, since the formed Ni oxide film is brittle and easily undergoes cohesive failure, the press formability varies greatly, and excellent press formability cannot be obtained stably. In the case of performing salt treatment, there is also a problem that chemical conversion treatment is insufficient due to a small amount of Zn for forming a phosphate.

In prior art 3, the corrosion resistance is improved because it consists of a film of only metal such as Ni, but the metal film adheres to the metal mold due to the metal contact between the metal film and the press mold.
There is a problem that press formability is inferior.

Accordingly, it is an object of the present invention to provide a galvanized steel sheet excellent in press formability by solving the above-mentioned problems and reducing the sliding resistance with a press die.

[0013]

Means for Solving the Problems In order to solve the above-mentioned problems, as a result of intensive studies by the present inventors, metal Ni and oxides or oxides and hydroxides of Ni and Zn on the surface of the plating layer. A mixed film (hereinafter referred to as “Ni-Zn-O-based film”) is formed, and the Ni-Zn-O
The surface layer portion of the system coating is an oxide or oxide of Ni and Zn and a hydroxide (referred to as an “oxide system layer” in this specification).
It has been found that some of the zinc-based plated steel sheets whose thickness of the oxide-based layer is appropriately controlled have excellent press formability.

As described above, since the galvanized steel sheet has a higher sliding resistance with the press die than the cold-rolled steel sheet, the press formability of the galvanized steel sheet is lower than that of the cold-rolled steel sheet. Inferior. The reason why the sliding resistance is large is that zinc having a low melting point causes a cohesion phenomenon with a mold under a high surface pressure in the case of a galvanized steel sheet. Then, it was considered effective to form a film harder and higher in melting point than the zinc or zinc alloy plating layer.

The present inventors have conducted further research based on the above considerations. As a result, by forming an appropriate Ni-Zn-O-based film on the surface of a galvanized steel sheet, the plating layer during press forming was formed. It has been found that the sliding resistance between the surface and the press die can be reduced, so that the galvanized steel sheet can easily slide into the press die and the press formability can be improved.

The present invention has been made based on the above-mentioned findings, and the zinc-based galvanized steel sheet of the present invention has metal Ni and Ni and Ni
Ni-Z containing Zn oxide or oxide and hydroxide
A zinc-based plated steel sheet having an nO-based coating formed thereon, wherein the surface layer portion of the Ni-Zn-O-based coating is an oxide-based layer composed of an oxide or oxide of Ni and Zn or an oxide. Wherein the thickness of the oxide-based layer is in the range of 0.5 to 50 nm, and the sum of the Ni content (wt%) and the Zn content (wt%) of the Ni-Zn-O-based film. The ratio of Zn content (wt%) to
It is characterized by being within the following range.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the composition of the Ni-Zn-O-based film formed on the surface of the plating layer of the zinc-based plated steel sheet of the present invention, and the surface layer formed on the Ni-Zn-O-based film are formed. The reason why the thickness of the oxide-based layer is limited as described above will be described.

FIG. 1 shows a cross section of a galvanized steel sheet of the present invention. 21 is a steel sheet, 22 is a zinc-based plating layer, 23 is a Ni-Zn-O-based coating containing metallic Ni and oxides or oxides and hydroxides of Ni and Zn, and 24 is an oxide or oxide of Ni and Zn. An oxide-based layer composed of a substance and a hydroxide.

In the present invention, a Ni-Zn-O-based coating containing metal Ni and oxides or oxides and hydroxides of Ni and Zn is formed on the surface of the zinc-based plating layer. here,
Ni-Zn-O-based coatings include oxides of Ni and Zn and metallic Ni
The reason for including not only Ni and Zn hydroxides is that the surface of galvanized steel sheet such as galvanized steel sheet has N
This is because, when a film containing an oxide of i and Zn and metal Ni is formed, depending on the forming method, these hydroxides may be inevitably formed along with the film.

The Ni-Zn- formed on the surface of the zinc-based plating layer
Since the O-based coating has a higher melting point and a harder coating than zinc, it prevents the zinc adhesion phenomenon during press molding and reduces sliding resistance. Furthermore, since metallic Ni has a property of easily adsorbing lubricating oil when the surface oxide-based layer falls off and a new surface is exposed during sliding at a high surface pressure, the lubricating oil adsorbing film causes the above-described condensation. The effect of suppressing the adhesion phenomenon is further improved to prevent an increase in sliding resistance. By such an action, press formability is improved.

Further, Ni in the Ni—Zn—O-based film contributes to improvement of weldability. It is not clear why the presence of Ni improves weldability, but very high melting Ni oxides
To suppress the diffusion of zinc to the copper electrode and reduce the wear of the copper electrode, or to react Ni with Zn to form a high melting point Ni-Zn alloy and suppress the reaction between zinc and the copper electrode. Presumed.

The Ni-Zn-O-based film may further contain Zn in the form of metal Zn in addition to Zn existing in the form of oxide or hydroxide.

The Ni content (wt%) of the Ni—Zn—O based film
If the ratio of the Zn content (wt%) to the sum of the Zn content (wt%) (hereinafter referred to as “Zn / (Ni + Zn)”) exceeds 0.6, press formability deteriorates. Therefore, Ni-Zn-O-based coatings
Zn / (Ni + Zn) should be in the range of 0.6 or less.

Even if the Ni-Zn-O-based film is the above-mentioned film, the effect of improving the press formability is reduced when a single metal such as metal Ni or metal Zn is partially present on the surface. . Therefore, the surface layer of the film is limited to an oxide-based layer composed of an oxide of Ni or Zn or an oxide and a hydroxide.

When the thickness of the oxide-based layer in the surface layer of the Ni-Zn-O-based coating is less than 0.5 nm, the surface of the oxide-based layer is partially covered with a single metal such as metal Ni or metal Zn. Are present, and the effect of improving press formability is reduced. On the other hand, when the thickness of the oxide-based layer exceeds 50 nm, cohesive failure of the oxide-based layer occurs, and conversely, the press-formability is reduced.

Therefore, the thickness of the oxide-based film in the surface layer of the Ni-Zn-O-based film formed on the plating layer surface of the zinc-based plated steel sheet should be limited to the range of 0.5 to 50 nm.

As described above, a Ni-Zn-O-based film is formed, and an oxide-based layer having a thickness in the range of 0.5 to 50 nm is formed on the surface of the Ni-Zn-O-based film. Press formability is improved.

Further, by making the amount of the Ni-Zn-O-based film adhere to 10 mg / m ² or more in terms of the total amount of metal in the film,
Press formability is further improved, and excellent chemical conversion property and spot weldability can be secured. However, the adhesion amount is 20
If it exceeds 00 mg / m ² , the effect of improving press formability will be saturated, and the formation of phosphate crystals will be suppressed, deteriorating the chemical conversion property.

Therefore, in order to ensure excellent spot weldability in addition to excellent press formability, the amount of the Ni-Zn-O-based film to be applied is 10 mg / m ² or more, and excellent chemical conversion treatment and to obtain the spot weldability, it is desirable that the amount of adhered Ni-Zn-O-based film in the range of 10~2000mg / m ^2.

The thickness of the Ni-Zn-O-based film of the present invention is
As a method for measuring the composition and thickness of the surface oxide-based layer in the Ni-Zn-O-based coating, depth analysis from the surface by Auger electron spectroscopy (AES) combined with Ar ion sputtering was performed. There is a way to do it.

That is, after sputtering to a predetermined depth,
The composition of each element at that depth can be obtained by correcting the relative sensitivity factor from the spectral intensity of each element to be measured. By repeating this analysis from the surface, the composition distribution of each element in the depth direction of the plating film can be measured. In this method, the amount of oxide or hydroxide peaks at a certain depth and then decreases and becomes constant. At a position where the oxygen concentration due to the oxide or hydroxide is deeper than the maximum concentration, 1 / of the sum of the maximum concentration and the constant concentration is obtained.
The depth of 2 is defined as the thickness of the surface oxide-based layer in the Ni-Zn-O-based coating.

The galvanized steel sheet according to the present invention is a steel sheet in which a zinc-based plating layer is formed on a base steel sheet by a method such as hot-dip plating, electroplating, or vapor phase plating. Layers are pure zinc, Cr, Co, Ni, F
e, Mn, Mo, Al, Ti, Si, W, Sn, Pb, Nb, Ta or other metal or oxides of these metals, or a single layer containing a predetermined amount of one or more of these organic materials Alternatively, a multi-layer plating layer may be used. In addition, the plating layer is made of Si.
Fine particles such as O ₂ and Al ₂ O ₃ may be contained. In addition, as a zinc-based plated steel sheet, a multi-layer plated steel sheet composed of multiple layers having different compositions and the same component elements of the plated layer, and the same constituent elements of the plated layer, in the depth direction of the plated layer It is also possible to use a functionally graded plated steel sheet having a different composition.

The Ni-Zn-O-based film in the present invention may be made of metal
In addition to oxides and hydroxides of Ni, Ni and Zn, Zn which is present in the form of a simple metal may be further contained, or may be contained inevitably as a component element of the underlying zinc-based plating layer. Component elements such as Cr, Fe, Co, Mn, Mo, Al, T
Elements such as i, Si, W, Sn, Pb, Nb and Ta may be incorporated in the form of oxides, hydroxides and / or simple metals. Even in such a case, the above-mentioned Ni-Zn-
This is because the effect of the O-based film is exhibited.

In the oxide-based layer according to the present invention, Ni-Zn-O
The system coating may contain an oxide or hydroxide of the above-mentioned component element which is inevitably contained in the system coating.

Since the above-mentioned Ni-Zn-O-based film is formed on the plating layer surface of at least one surface of the zinc-based plated steel sheet, in any process of the vehicle body manufacturing process, on any body portion Depending on the steel plate used,
One formed on one side or both sides can be appropriately selected.

The method for forming the Ni-Zn-O-based film of the present invention is not particularly limited, but may be carried out by displacement plating using an aqueous solution having a predetermined chemical component, electroplating, or immersion in an aqueous solution containing an oxidizing agent. Method, cathodic or anodic electrolytic treatment in an aqueous solution containing an oxidizing agent, spraying of an aqueous solution having a predetermined chemical component, roll coating, etc., and gaseous phase such as laser CVD, optical CVD, vacuum evaporation method and sputter evaporation method A plating method can be adopted.

When the Ni-Zn-O-based film of the present invention is formed by dipping or cathodic electrolysis, the following method can be used. That is, the total ion concentration of Ni ²⁺ and Zn ²⁺ is set to 0.
Immersion treatment in a hydrochloric acid aqueous solution containing at least 1 mol / l at a temperature of 40 to 70 ° C and a pH of 2.0 to 4.0 for 5 to 50 seconds, or
In a plating bath containing nickel sulfate and zinc sulfate,
Total ion concentration of Ni2 ⁺ and Zn2 ⁺ : 0.1 to 2.0 mol / l, pH:
Under a condition of 1.0 to 3.0, a Ni-Zn-O-based film is formed by electrolysis using a zinc-based plated steel sheet as a cathode. Also,
After forming the Ni-Zn-O-based film, immerse it in an aqueous solution containing an oxidizing agent such as hydrogen peroxide, potassium permanganate, nitric acid, or nitrous acid. Then, a predetermined oxide-based film of the present invention is formed.

[0038]

Next, the present invention will be described with reference to examples. (1) Preparation of Sample First, a zinc-plated steel sheet (hereinafter, referred to as an original sheet) before forming a Ni-Zn-O-based film was prepared. The adjusted original plate was composed of three types of plating having a thickness of 0.8 mm, and was indicated by the following symbols according to the plating method, the plating composition, and the coating weight. GA: Alloyed hot-dip galvanized steel sheet (10% Fe, balance Zn)
The adhesion amount is 60 g / m ² on both sides. GI: Hot-dip galvanized steel sheet, the adhesion amount is 90 g / m ² on both sides. EG: Electrogalvanized steel sheet, the adhesion amount is 40 g / m ² on both sides.

A Ni-Zn-O-based film was formed on the surface of the thus-prepared zinc-coated steel sheet by dipping in a hydrochloric acid aqueous solution and cathodic electrolysis.

For the immersion treatment, the galvanized steel sheet prepared as described above contains Ni ²⁺ and Zn ²⁺ , and has a total ion concentration of 0.5 to 2.0 mol / l, a pH of 2.5, and a liquid temperature of 50 to 50. It was immersed in a hydrochloric acid solution at 60 ° C for 5 to 20 seconds to form a Ni-Zn-O-based film. The composition of Ni and Zn in the Ni-Zn-O-based coating is
The ratio was changed by changing the respective ion concentration ratios of i ²⁺ and Zn ²⁺ , and the amount of adhesion was changed by changing the immersion time.

For the cathodic electrolysis, nickel sulfate and
And zinc sulfate, Ni²⁺And Zn²⁺Total ion concentration of:
0.1 to 2.0 mol / l, pH: 1.0 to 3.0
Current density: 1 ~ 150mA / cm, using plated steel sheet as cathode^Two,liquid
Temperature: 30 to 70 ° C to form an Ni-Zn-O-based
Was. The composition of Ni and Zn in the Ni-Zn-O-based coating
²⁺, Zn²⁺By changing each ion concentration ratio and pH
And change the amount of adhesion by changing the electrolysis time.
Was.

Further, the galvanized steel sheet on which the Ni-Zn-O-based film was formed was immersed in an aqueous solution to which hydrogen peroxide was added as an oxidizing agent, and the surface portion of the Ni-Zn-O-based film was To
An oxide-based layer was formed. The thickness of the oxide-based layer was adjusted by changing the immersion time.

For each of the galvanized steel sheets obtained above,
The thickness of the oxide layer on the surface of the Ni-Zn-O-based film, Ni-Zn-
The composition and adhesion amount of the O-based film were measured, and evaluation tests for press formability, spot weldability and chemical conversion treatment were performed.

The press formability was evaluated by the coefficient of friction between the specimen and the bead of the press, the spot weldability was evaluated by the number of continuous spot welding points, and the chemical conversion treatment was evaluated by the state of formation of zinc phosphate film crystals.

For comparison, a similar evaluation test was performed on a steel sheet on which the above-mentioned film was not formed.

Specific measurement methods and evaluation test methods will be described below. Table 1 shows the obtained results.

[0047]

[Table 1]

In Table 1, the specimens Nos. 1 to 21 are zinc-plated steel sheets within the scope of the present invention (hereinafter referred to as “the present invention specimens”).
That. ), And the specimens Nos. 22 to 30 are galvanized steel sheets (hereinafter referred to as "comparative specimens") outside the scope of the present invention.

(2) Measurement of the thickness of the surface oxide layer, the composition of the Ni-Zn-O-based film, and the amount of the Ni-Zn-O-based film in the Ni-Zn-O-based film The thickness of the surface oxide-based layer of the coating, the composition of the Ni-Zn-O-based coating, and the amount of the coating were measured by a combination of the ICP method, Ar ion sputtering, and AES as follows.

In the ICP method, it is difficult to completely separate the constituent elements of both layers of the same Ni—Zn—O based film component and the lower plating layer component that are the same. Therefore,
By the ICP method, Ni, which is an element not contained in the lower plating layer in the Ni-Zn-O-based film, is quantitatively analyzed,
The amount of adhesion was determined.

Further, from the surface of the specimen to a predetermined depth,
After Ar ion sputtering, each element in the film was repeatedly measured by AES to measure the composition distribution of each element in the depth direction of the Ni-Zn-O-based film. In this method, the amount of oxygen due to oxides or hydroxides decreases to a constant after reaching a maximum concentration at a certain depth. At a position where the concentration of oxygen due to oxides or hydroxides is deeper than the maximum concentration, the depth at which the sum of the maximum concentration and the constant concentration is 1/2
The thickness of the surface oxide-based layer in the Ni-Zn-O-based film was set.
Note that SiO ₂ was used as a standard sample for the sputtering rate, and the sputtering rate was 4.5 nm / min.

(3) Measurement of Coefficient of Friction In order to evaluate press formability, the coefficient of friction of each specimen was measured by the following apparatus.

FIG. 2 is a front view showing the friction coefficient measuring device. As shown in FIG. 2, sample 1 collected from each co-specimen
Is fixed to the sample table 2, and the sample table 2 is fixed to the 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, the bead 6 is pressed against the sample 1 for friction coefficient measurement. A first load cell 7 for measuring the load N is attached to the slide table support 5. A second load cell 8 for measuring a sliding resistance force F 1 when the slide table 3 is moved in the horizontal direction while the pressing load N 2 is applied,
The slide table 3 is attached to one end in the horizontal direction.

As a lubricating oil, Noxlast 550HN manufactured by Nippon Parker Rising Co., Ltd. was applied to the surface of Sample 1 for a test.

The coefficient of friction μ between the specimen and the bead is given by the following equation: μ =
Calculated from F / N. However, pressing load N: 400kgf, pull-out speed (movement speed of slide table 3): 100cm / mi
n.

FIG. 3 is a schematic perspective view showing the shapes and dimensions of the beads used. The bead 6 slides while being pressed against the surface of the sample 1. As shown in FIG. 3, the bead 6 has a length in the sliding direction of 12 mm and a width of 10 mm, and has a bottom surface having a flat surface of 3 mm in the center in the sliding direction and 4.5 mmR in front and rear thereof. It is composed of curved surfaces.

(4) Continuous Dotability Test In order to evaluate the spot weldability, each specimen was
A continuous weldability test was performed.

Two specimens having the same No. are stacked, sandwiched between a pair of electrode tips from both sides, and resistance welding (spot welding) in which current is concentrated by applying pressure is continuously performed under the following welding conditions. Carried out. Electrode tip: Dome type with tip diameter 6mm Pressure: 250kgf Welding time: 12 cycles Welding current: 11.0kA Welding speed: 1 point / sec

The evaluation of the continuous hitting property is as follows. During the spot welding, a molten and solidified metal portion (shape: goishi shape, hereinafter referred to as a nugget) formed at a joint portion of two superposed welding base materials (specimens) is obtained. The number of continuous dots welded until the diameter became less than 4t ^1/2 (t: thickness of one sheet) was used. The number of hits is defined as the electrode life.When the electrode life is 5,000 points or more, ◎, when the electrode life is 3,000 points or more, ○;
When it was less than 00 points, it was evaluated as x.

(5) Chemical conversion property In order to evaluate the chemical conversion property, the following test was carried out.

Each specimen was treated with a immersion type zinc phosphate treatment solution (PBL3080 manufactured by Nippon Parker Rising Co., Ltd.)
) Under normal conditions to form a zinc phosphate film on the surface. The thus formed zinc phosphate film was observed by a scanning electron microscope (SEM). As a result, ○ indicates that the zinc phosphate film was formed normally, and X indicates that the zinc phosphate film was not formed or the crystal was invisible.

The following can be seen from the results shown in Table 1. The comparative specimens outside the scope of the present invention are as follows.

In the case where the Ni-Zn-O-based film was not formed, the press formability was poor even if the plating type was any of the symbols: GA, EG and GI (Comparative Sample No. 22 ~ 24).

Even if an oxide-based layer on the surface of the Ni-Zn-O-based coating is formed, if the thickness is smaller than the range of the present invention, the press-formability is poor (comparative specimen). No.25,
28).

Even if an oxide-based layer in the surface layer of the Ni-Zn-O-based coating is formed, if the thickness is larger than the range of the present invention, the effect of improving press formability cannot be obtained. (Refer to comparative specimens Nos. 27 and 30).

If the thickness of the oxide-based layer in the surface layer of the Ni-Zn-O-based coating is within the range of the present invention, but Zn / (Ni + Zn) is larger than the range of the present invention, press molding is performed. Poor properties (see comparative specimens Nos. 26 and 29).

On the other hand, the test specimens of the present invention which are within the scope of the present invention have excellent press moldability regardless of the type of plating: GA, EG or GI (the present invention). Specimens Nos. 1 to 21). Of what these Ni-Zn-O-based coating weight of 10~2000mg / m ² of the film, further spot weldability, excellent chemical conversion treatability, also, the amount of deposition of Ni-Zn-O-based film is 15
If it exceeds 00 mg / m ² , it is inferior in chemical conversion property, but also excellent in spot weldability.

[0068]

According to the present invention, the sliding resistance between the plating layer surface and the press mold during press forming of the zinc-based plated steel sheet is reduced, and the zinc-based plated steel sheet is transferred to the press mold. It becomes easy to slide. Thus, it is possible to provide a galvanized steel sheet having excellent press formability.
An industrially useful effect is provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a galvanized steel sheet according to the present invention.

FIG. 2 is a schematic front view showing a friction coefficient measuring device.

FIG. 3 is a schematic perspective view showing a bead shape and dimensions of the friction coefficient measuring device of FIG. 2;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 sample 2 sample table 3 slide table 4 roller 5 slide table support 6 bead 7 first load cell 8 second load cell 9 rail 21 steel plate 22 zinc-based plating layer 23 Ni-Zn-O-based coating 24 oxide-based layer P Load N Sliding resistance

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takayuki Urakawa 1-1-2 Marunouchi, Chiyoda-ku, Tokyo, Japan Inside Nihon Kokan Co., Ltd. (72) Inventor Junichi Inagaki 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan (72) Inventor Masaru Sagiyama 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd.

Claims (1)

[Claims] 1. The method according to claim 1, wherein at least one surface of the plating layer has
A zinc-plated steel sheet on which a Ni-Zn-O-based film containing a metal Ni and an oxide or oxide of Ni and Zn and a hydroxide is formed, wherein the Ni-Zn-O-based film is Is composed of an oxide-based layer composed of an oxide or oxide of Ni and Zn or a hydroxide, and the thickness of the oxide-based layer is 0.5
5050 nm, and the Ni-Zn-O-based coating
Zn content with respect to the sum of content (wt%) and Zn content (wt%)
(% by weight) is in the range of 0.6 or less. A galvanized steel sheet having excellent press formability.