JPH07136701A - Galvanized steel sheet excellent in slidability and paint image clarity - Google Patents

Abstract

PURPOSE:To produce a steel sheet excellent in slidability and paint image clarity by providing fine projection and recess in a specific area range on its surface and regulating the Vickers hardness of a galvanized layer and the sum of recessed part volumes per a unit area to satisfy specific inequalities. CONSTITUTION:The sheet is a galvanized sheet having fine recessed parts of 0.0001mm<2> to 0.01mm<2> area on its surface, and whose Vickers hardness(Hv) of a galvanized layer and the sum (w) of recessed part volumes per unit area satisfy inequalities. It is known that the surface hardness of the galvanized layer and the recessed part volumes on a plated surface, that is, an oil retaining quantity per unit area of the surface at the time of pressing can be operated as a parameter in the inequlities, and the paint image clarity and the slidability of a galvanized sheet can be mad compatible with each other. Such a sheet is developed. The galvanized sheet obtained by these processes is excellent in the image clarity after painting and press formability, and it is most suitable for the body of an automobile, especially for the outside plates of door, fender, hood, etc., and the outside plates, etc., of an electric refrigerator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc-based plated steel sheet having excellent slidability and coating clarity, and more specifically, after being processed by press working of automobiles, household appliances, etc.,
The present invention relates to a zinc-based plated steel sheet that is excellent in slidability and paint clarity when it is painted into a final product.

[0002]

2. Description of the Related Art Generally, a thin steel sheet used for press working of a car body or a housing of a household electric appliance is used for holding lubricating oil during press working to prevent seizure with a mold. The so-called dull finish, which is a fine satin-textured fine unevenness, is applied to the surface of the thin steel sheet.

However, on such a dull-finished surface, even if it is pressed and then usually painted to prevent rust and beautify the surface, it is not completely smoothed, resulting in a satin-finished surface. Since the waviness remains, the image clarity of the surrounding scenery reflected on the painted surface is poor.

Therefore, until now, in order to improve the image clarity, the thickness of the coating film is increased, or the coating is multilayered with 2 coats, 3 coats and 4 coats, or undercoating is performed. Previously, measures such as smoothing the surface of the undercoat coating film have been taken by water research.

However, such a measure is a factor that increases the work complexity and cost due to painting beyond the rust prevention and beautification of the surface where painting is originally required. It has been desired to simplify the coating process by controlling the temperature.

[0006]

DISCLOSURE OF THE INVENTION In order to solve the various problems of the prior art in the zinc-based plated steel sheet described above, the present invention has been earnestly studied by the present inventors, and as a result of repeated studies, Then, so-called laser dull finishing, which was temper rolling of steel sheet using rolling rolls with regular unevenness by laser processing, was put into practical use, and both press formability and paint clarity were realized. I can now prepare.

However, zinc-plated galvannealing, Zn-Ni alloy electroplating, and Zn-Fe, which are zinc-based plated on the laser-rolled cold-rolled steel sheet, are used.
In the system alloy electroplating, the press formability changes depending on the surface hardness, and the range that combines both the image clarity and the slidability is the surface hardness of the zinc-based plating layer and the concave volume of the plating surface, that is, It was discovered that the amount of oil retained per unit surface area can be arranged as a parameter, and a zinc-based plated steel sheet that can achieve both coating clarity and slidability of the zinc-based plated steel sheet was developed.

[0008]

A feature of the zinc-based plated steel sheet according to the present invention, which is excellent in slidability and coating clarity, is that the zinc-based plated steel sheet has an area of 0.000 on the surface.
Of 1mm ² ~0.01mm ² has a fine concave and in that the zinc-based plating layer the Vickers hardness (Hv), the sum of the recess volume per unit area (w) satisfies the following expression. 100 ≦ Hv ≦ 500 (1) w ≦ −0.50 × 10 ⁻⁵ × Hv + 4.5 × 10 ⁻³ (mm)・ ・ ・ ・ (2) w ≧ −0.25 × 10 ^-5 × Hv + 1.75 × 10 ^-3 (mm) ・ ・ ・ ・ (3)

The zinc-based plated steel sheet according to the present invention, which is excellent in slidability and coating clarity, will be described in detail below.

First, fine recesses present on the surface of a galvanized steel sheet, which are fine recesses for holding oil components such as press oil, lubricating oil and rust preventive oil, will be described. That is, the zinc-based plated steel sheet has an average surface pressure of 1 kgf / mm ² and a maximum of 10 between the molds during press forming.
It is processed by sliding between dies while being pressed by a surface pressure of kgf / mm ² or more.

The oil accumulated in the fine recesses on the surface during this sliding oozes out between the die and the surface of the zinc-based plated steel sheet, thereby preventing direct metal contact between the steel sheet and the die, The galvanized steel sheet and the mold are kept lubricated normally.

Therefore, when the plated surface of the zinc-based plated steel sheet becomes softer, even if the same surface pressure is applied, the fine recesses on the surface are more likely to be crushed and the oil content is reduced, so that when processing is performed, gold Metal contact between the mold and the plated surface is likely to occur, resulting in seizure of the plated metal on the mold surface and occurrence of scratches on the mold surface.
The sliding resistance of the galvanized steel sheet increases and the steel sheet breaks, making press forming impossible.

Next, the influence of fine recesses existing on the surface of the zinc-plated steel sheet will be described. That is, when manufacturing a zinc-based plated steel sheet, the fine recesses on the surface are filled and smoothed by the coating performed after press forming.

In this case, if the number of the fine concave portions on the surface is small, the amount of the paint sucked into the concave portions is small, and the smoothness is promptly smoothed so that the image clarity after coating is not affected. The surface is not completely smoothed even if the above procedure is carried out, so that the paint clarity is deteriorated.

Further, the fine recesses on the surface of the zinc-based plated steel sheet are partially filled by sliding during pressing, but the higher the hardness of plating is, the higher the plating hardness is, the larger the recessed volume due to sliding becomes. Is small, the amount of paint sucked in at the time of painting is large, and thus the image clarity of the coating is greatly deteriorated.

FIG. 1 shows the relationship between the coating image clarity of a zinc-based plated steel sheet and the press slidability. That is, a cold-rolled steel sheet was produced in which the pitch of the surface fine recesses of the laser dull finish and the rolling reduction during rolling were changed to change the sum (w) of the volume of the fine recesses per unit area.

By varying the Ni content on the surface of the cold-rolled steel sheet thus produced, various kinds of Zn-Ni alloy electroplating in which the hardness (Hv) of the plating layer is changed are produced to produce a plated steel sheet. In this case, the relationship between the coating clarity of the plated steel sheet and the press slidability is shown. In FIG. 1, ◯ is good in both press and sharpness, Δ is poor in pressability,
▲ indicates poor image clarity, and × indicates poor press and image clarity.

From this FIG. 1, the plating layer hardness (Hv) is 1
When it is less than 00, it can be seen that the press formability is poor no matter how large the sum (w) of the concave volume per unit area is. Further, if the plating layer hardness (Hv) exceeds 500, it is substantially difficult to perform Zn-based alloy plating, so the upper limit of the plating layer hardness (Hv) is set to 500. Therefore, the Vickers hardness of the zinc-based plating layer is 100 ≦ Hv ≦
Set to 500.

Further, in FIG. 1, w ≦ −0.50 × 10 ⁻⁵ × Hv + 4.5 × 10 ⁻³ (mm) .. It can be seen that the sum of the volumes (w) becomes too large, resulting in poor image clarity.

Further, in FIG. 1, if w ≧ −0.25 × 10 ⁻⁵ × Hv + 1.75 × 10 ⁻³ (mm). It can be seen that the sum (w) of the recess volume becomes too small, and the press formability is poor.

Regarding the relationship between the plating layer hardness (Hv), the sum of the concave volume per unit area (w) and the image clarity and the press formability, zinc-based plating other than Zn-Ni-based alloy plating is used. The same applies to steel sheets.

Furthermore, the area of the fine recesses on the surface of the galvanized steel sheet is required to be 0.0001～0.04Mm ^2, the area of the fine recesses oil retention force is less than 0.0001 mm ² is not Since it is sufficient, the press formability is deteriorated, and if it exceeds 0.04 mm ² , the fine concave portions remain after the coating regardless of how the coating is performed, and the image clarity is deteriorated.

As the zinc-based plated steel sheet excellent in slidability and coating clarity according to the present invention, Zn-Ni-based and Zn-based
-Fe system, Zn-Co-based, Zn-Mn system, electroplated steel sheet of Zn-Cr system, etc., dispersion plating steel sheet containing dispersed SiO _2, Al ₂ O ₃ or the like in the plating layer, galvannealed steel sheets , Zn-Al-based hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet having an Fe-rich layer flash-plated on the surface, and the like. The plating layer hardness (Hv) is not limited to the type of plating as long as it is within the specified range.

As a method for forming recesses on the surface of a zinc-based plated steel sheet, a method of forming a cold-rolled steel sheet by temper rolling and then performing plating or a method of performing plating and then temper rolling is performed. There is.

Further, in the case of forming fine recesses on the surface of the zinc-based plated steel sheet by the projections provided on the rolling roll, as a method of forming the projections on the rolling roll, a method by laser processing, a method by photoetching, There is a method such as meal engraving, and any method may be used.

[0026]

[Examples] Examples of zinc-plated steel sheets according to the present invention having excellent slidability and coating clarity will be described.

[0027]

[Example 1] A low carbon aluminum killed steel sheet having a plate thickness of 0.8 mm was used by using a rolling roll having a laser dull finish with a varying recess pitch, and the rolling reduction at the time of rolling was changed to form the recess volume per unit area. Cold-rolled steel sheets having different sums (w) were produced.

Next, 20 g / m ² of Zn—Ni alloy plating having a different Ni content was plated on the surface of this cold rolled steel sheet by electroplating to obtain a Zn—Ni alloy having a hardness (Hv) of the plating layer changed. An alloy electroplated steel sheet was produced. After performing 3 coat coating for automobiles on this plated steel sheet,
The image clarity was measured.

(Visibility evaluation method) -Coating 3 coats Phosphate treatment Immersion zinc phosphate treatment Electrodeposition coating Cationic type 20 μm Intermediate coat 40 μm Top coat 40 μm-Dismicity measuring instrument DOI meter (ATI
The DOI meter, which is made by SYSTEMS INC., Displays the image clarity as a value of 0 to 100, and the image clarity of 95 or more is good.

(Evaluated by press formability and cylindrical deep-drawing test.)-Cylinder deep-drawing tester Blank diameter 110 mm Punch diameter 50 mm Drawing ratio 2.2 Wrinkle suppressing force 600 kgf Lubricating rust preventive oil (Knoxlast 530
F)

(Plating layer hardness, Hv) Micro Vickers hardness meter It was measured from the surface of the plating layer under the condition of a load of 1 kgf.

(Sum of concave volume per unit area, w) Three-dimensional surface roughness measuring device The concave volume was calculated from the surface profile obtained by this device.

FIG. 1 shows the thus obtained data with the hardness (Hv) of the plating layer as the horizontal axis and the sum (w) of the concave volume per unit area as the vertical axis.

[0034]

[Example 2] Plate thickness 0.8 mm, coating weight 60 g /
m ² alloyed hot-dip galvanized steel sheet with a base length of 125 μm,
Prepared an alloyed hot-dip galvanized steel sheet in which the sum (w) of the recess volume per unit area was changed by performing temper rolling while changing the reduction ratio with an engraving roll having a 40-μm-high pyramidal protrusion. did.

The average Fe content of the plating layer was 11%, and the hardness of the plating layer was 280. With respect to these steel sheets, the coating clarity and press formability were evaluated by the same method as in Example 1. The results are shown in Table 1.

[0036]

[Table 1]

Thus, from the first and second embodiments,
It is clear that the zinc-based plated steel sheet according to the present invention, which is excellent in sliding property and coating sharpness, is excellent in sharpness after coating and press formability. Therefore, the car body, particularly the door, It has an effect that it is particularly suitable for so-called outer plates such as fenders and hoods, and also for electric refrigerator outer plates and the like.

[0037]

As described above, the zinc-based plated steel sheet according to the present invention which is excellent in slidability and coating sharpness has the above-mentioned constitution. Also, it is excellent in press formability, and is suitable for use in so-called outer panels of automobile bodies, particularly doors, fenders, hoods, etc., and in electric refrigerator outer panels and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a plating layer hardness (Hv) and a recess volume per unit area (w).

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display location C23C 30/00 B C25D 5/26 F 15/02 Z (72) Inventor Hiroaki Nakano Hyogo prefecture 1 Kanazawa-machi, Kakogawa City Kadogawa Steel Works Co., Ltd.

Claims (1)

[Claims] 1. A zinc-plated steel sheet, has a fine concave area 0.0001mm ² ~0.01mm ² on the surface, and, zinc-based plating layer the Vickers hardness (Hv), per unit area A zinc-based plated steel sheet excellent in slidability and coating clarity, characterized in that the sum (w) of the volume of recesses satisfies the following formula. 100 ≦ Hv ≦ 500 (1) w ≦ −0.50 × 10 ⁻⁵ × Hv + 4.5 × 10 ⁻³ (mm)・ ・ ・ ・ (2) w ≧ −0.25 × 10 ^-5 × Hv + 1.75 × 10 ^-3 (mm) ・ ・ ・ ・ (3)