JPH0355543B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a molten alloyed galvanized steel sheet. Specifically, the present invention relates to a melt-alloyed galvanized steel sheet that is excellent in various workability such as bending workability and beaded tensile workability. (Prior art, problems) In galvanized steel sheets that have been subjected to iron-zinc alloying treatment in which hot-dip galvanized steel sheets are heated to diffuse the iron of the plating original sheet into the plating layer, the plating layer may peel off during processing. There are some drawbacks such as: In order to eliminate these drawbacks, for example, the generation of the Γ phase in the lower layer of the Metsuki layer (at the boundary with the base railway) is suppressed as much as possible, and the upper layer is made of the Metsuki layer consisting of the η phase, δ ₁ phase, and ι phase. Furthermore, it has been disclosed that iron plating is applied on a molten alloy layer (mainly Γ phase) (Japanese Patent Application Laid-Open No. 1989-1999-
228662), but the current situation is that satisfactory results have not yet been obtained. The present invention has been made to advantageously solve these difficulties. (Means for Solving the Problems) The present invention is a molten alloyed galvanized steel sheet in which crystal grains mainly consisting of ζ phase are formed on the surface of an alloy layer consisting of 7 to 13% iron and residual zinc. (Function) Such a ζ phase has extensibility and exhibits a lubricating effect during processing, and at the same time prevents the propagation of cracks generated in the lower layer, thereby improving formability. For example, in the case of a plated steel plate that undergoes relatively light processing such as bending, ζ on the surface of the alloy layer is the average layer thickness.
It only needs to be 1.0 μm or more, and the upper limit may be about 10 μm. In addition, in the case of plated steel sheets subjected to processing that adds drawing, such as bead processing, the ζ phase on the plated surface should be formed to an average layer thickness of 4.0 μm or less, with the lower limit being just enough to exist. Good, 4.0μm
If it becomes too thick, the zeta phase (plated metal) will accumulate on the die part corresponding to the bead forming part due to its extensibility, and in some cases it may transfer to the die and punch, impairing the quality of the molded product. Undesirable. Furthermore, the deformation load may increase due to an increase in sliding resistance. Such a configuration condition of the ζ phase can reliably improve the formability under the condition that the iron content in the plating layer is 7 to 13% as described above, that is, the hardness of the plating layer at this iron content. In addition, the lower layer of this ζ phase may have normal crystal grains such as δ ₁ phase, and it is better to have as little Γ phase as possible.
The thickness is preferably 1.5 μm or less. For example, in order to improve corrosion resistance etc. to such an iron-zinc alloy plating phase, Mn, Mg, P, Ni,
Similar excellent moldability effects can be obtained even with materials containing Sb or the like. The amount of alloy plating applied is 20 to 100 g/m.
(3 to 15 μm) and can be applied to various uses. The plated steel sheet of the present invention is plated in a hot-dip galvanizing bath containing Al: 0.003 to 0.13%, and then heat-treated, and the amount of Al in the bath is reduced by heating within 15 seconds at a plate temperature of 520 to 470°C. By performing the heat treatment at a relatively low temperature, it is possible to reliably produce the ζ phase on the surface of the plating layer. Defects such as spots caused by cationic electrodeposition coating can be eliminated by electroplating the upper layer of the plated steel sheet with 1 to 7 g/m ² of 60% or more iron and residual zinc. (Examples) Examples of the present invention are shown in Table 1 along with comparative examples.

【table】

[Table] (Effects of the Invention) The present invention has excellent effects such as improving the adhesion of the plating layer of a molten alloyed galvanized steel sheet, improving workability, and improving quality.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a workability test apparatus used in Examples. 1...Punch, 2...Dice, 3...Test piece.

Claims (1)

[Scope of Claims] 1. A molten alloyed galvanized steel sheet in which crystal grains mainly consisting of ζ phase are formed on the surface of an alloy layer consisting of 7 to 13% iron and residual zinc. 2 Crystal grains mainly composed of ζ phase with an average layer thickness of 10μ
The melt-alloyed galvanized steel sheet according to claim 1, which is formed to have a thickness of less than m. 3. The melt-alloyed galvanized steel sheet according to claim 1 or 2, wherein the upper layer is electroplated with 60% or more of iron and the remaining zinc.