JPH0718401A - Alloy designed galvanized steel sheet - Google Patents

Abstract

PURPOSE:To secure corrosion resistance, press formability, and image clarity after coating by specifying the recessed and the projecting part of surface rough ness at the outermost surface, respectively, in an alloy designed galvanized steel sheet having an Fe-Zn alloy layer. CONSTITUTION:This alloy designed galvanized steel sheet can be obtained by subjecting a steel sheet to hot-dip galvanizing and then to alloying treatment and has, e.g. a concentration gradient of 6 to 10% Fe from the surface toward the interface of the steel sheet. Further, in the form where the projecting part is crushed and the recessed part alone is allowed to remain, the recessed part of surface roughness at the outermost surface is regulated to 3-10mum, by which plating adhesion, corrosion resistance, and press formability is secured. Further, the projecting part is regulated to <=3mum to secure image clarity after coating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloyed hot-dip galvanized steel sheet, and more particularly to an alloyed hot-dip galvanized steel sheet having improved image clarity after painting.

[0002]

2. Description of the Related Art FIG. 2 (a) is a cross-sectional view of the outermost surface of an alloyed hot-dip galvanized steel sheet according to the prior art, showing the state of surface roughness, in which the concave portions are 5-10 .mu.m and the convex portions are 5 10μ
It is about m.

[0003]

As a problem of the prior art, if the concave portion is 3 to 10 μm in order to maintain the press formability, the convex portion is larger than 3 μm and the sharpness cannot be secured.
On the contrary, if the convex portion is 3 μm or less to secure the sharpness, the concave portion becomes less than 3 μm and the oil pool disappears, and the press moldability cannot be secured. Therefore, the sharpness cannot be secured and the press moldability cannot be provided. It was

[0004]

The present invention advantageously solves the problems of the prior art, and its gist is to provide an alloyed hot-dip galvanized steel sheet having an Fe-Zn alloy layer on the outermost surface. In the alloyed hot-dip galvanized steel sheet, the concave portion having a surface roughness of 3 to 10 μm and the convex portion is 3 μm or less.

The present invention will be described below with reference to the drawings.

[0006]

1 is a diagram schematically showing a cross section of a galvannealed steel sheet according to the present invention. The steel plate is an Nb-Ti based ultra low carbon steel, C: 10 to 20 ppm, Ti: 10 to 6
It is a steel sheet containing 0 ppm and Nb: 10 to 60 ppm and having good yield strength of 10 to 20 kgf / cm ² , tensile strength of 30 to 35 kgf / cm ² , and elongation of 35 to 40% and good press formability. .

The Fe-Zn alloy layer is obtained by hot dip galvanizing a steel sheet and then alloying the Fe: 8 to 14%,
Al: 0.2 to 0.4%, the composition of the remaining Zn, and there is a concentration gradient of Fe of 6 to 100% from the surface toward the steel sheet interface. The characteristics are excellent in corrosion resistance after coating, paint adhesion, and weldability. FIG. 2 (b) is a sectional view of the outermost surface of the galvannealed steel sheet according to the present invention, showing the state of surface roughness.

The feature is that only the concave portion remains while the convex portion is crushed. If the recesses are less than 3 μm, there is no oil pool and the press formability is impaired. If it exceeds 10 μm, the corrosion resistance and the plating adhesion are significantly impaired. Therefore, in the present invention, the concave portion is preferably 3 to 10 μm in order to secure the plating adhesion, corrosion resistance and press formability. When the protrusions are more than 3 μm, the gloss of the original plating plate is deteriorated and the image clarity after coating is deteriorated. Therefore, in the present invention, it is desirable that the protrusions have a thickness of 3 μm or less in order to secure the image clarity.

[0009]

EXAMPLE A galvannealed steel sheet according to the present invention is prepared by annealing a steel sheet having a roughness Ra of 0.4 to 0.6 μm before plating in a plating step, subjecting it to a plating alloying treatment, and temper rolling. It can be manufactured by rolling with a roll having a roll roughness Ra = 0.05 to 0.15 μm and a load of 300 to 350 ton per 1 m of rolling force width.

FIG. 3 shows the glossiness of a plated original plate and the PGD after coating, which is an index of the image clarity, by comparing the present invention with the conventional method.
(Portable Cross and Dist
FIG. 8 is a diagram showing a relationship with an nct. As shown in FIG. 4, the glossiness of the original plating plate is the glossiness value of the sample when the optical glass (refractive index 1.567) serving as the black reference surface is used.

The PGD value is a PG for evaluating the image clarity after coating.
It is the value of the image clarity of the sample when using the D meter. The paint used in FIG. 4 is EuW10μ (primer) + FLC1500H.
Q16 μm (paint). As shown in FIG. 3, there is a positive correlation between the glossiness of the original plate and the PGD value, and it is generally said that the PGD value is ≧ 0.5 as good image clarity after coating. %, The gloss level is 20 to 40% in the conventional level, whereas it is 70 to 100% in the present invention.

In the alloyed hot-dip galvanized steel sheet of the present invention, the convex portions are crushed while maintaining the concave portions of the surface roughness of the outermost surface, so that an oil pool at the time of pressing is secured and the press formability is impaired. The effect of improving the sharpness of the image after painting is exhibited without any trouble.

[0013]

EFFECTS OF THE INVENTION According to the present invention, press-formability is ensured while ensuring sharpness by setting the recesses of the alloyed hot-dip galvanized steel sheet having the Fe--Zn alloy layer to 3 to 10 μm and the protrusions to 3 μm or less. Can be provided.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross section of a galvannealed steel sheet of the present invention.

FIG. 2 is a view showing a cross section of the outermost surface of an alloyed hot-dip galvanized steel sheet, (a) showing a conventional example and (b) showing the present invention example.

FIG. 3 is a diagram showing a relationship between the glossiness of a plated steel sheet and a PGD value after coating, which is an index of image clarity.

FIG. 4 is a diagram showing the principle of glossiness measurement of FIG.

Claims (1)

[Claims] 1. An alloyed hot-dip galvanized steel sheet having a Fe—Zn alloy layer has a recessed portion having a surface roughness of 3 to 3 at the outermost surface.
An alloyed hot-dip galvanized steel sheet having a thickness of 10 μm and a protrusion of 3 μm or less.