KR910000915B1 - Alloyed-zinc- plated steel sheet and process for preparing the same - Google Patents

Abstract

No content.

Description

Alloyed zinc-plated steel sheet and method for manufacturing same

1 is a schematic of a continuous vacuum deposition plating apparatus that can be used to practice the method of the present invention.

2 and 3 are electron micrographs showing the structures of the alloyed zinc-plated steel sheet alloy layers of Example 3 and Comparative Example 2, respectively.

The present invention relates to an alloyed zinc-plated steel sheet and a method of manufacturing the same.

Alloyed zinc-plated steel sheet is superior to conventional zinc-plated steel sheet in the continuous workability of spot welding, the adhesion and corrosion resistance of the electrodeposited coating. Thus, they are widely used in the automotive industry and a wide range of other industries.

Although alloyed zinc-coated steel sheets are excellent in adhesion of the coating and weldability in spot welding as described above, they are generally poor in workability due to brittleness of the intermetallic compounds formed in the alloy layer. In particular, alloyed zinc-plated steel sheets prepared by conventional hot plating and electroplating methods have been found to be significantly powdered as the coating weight and Fe content in the alloy layer increase.

On the other hand, in addition to conventional hot dip and electroplating, continuous vacuum evaporation galvanization has become practically available today and the manufacture of alloyed metal-plated steel sheets by vacuum evaporation is also attempted. The continuous vacuum deposition plating method is far superior to the conventional hot dip plating and electroplating in that it is easy to manufacture a single-sided and double-sided sheet or a double-sided coated sheet having a different thickness from a thin thickness to a high speed easily.

The inventors have found that when the vacuum evaporation galvanizing is performed under an oxygen-containing atmosphere controlled to a prescribed level, the alloy layer is finely bubbled, thereby sufficiently preventing powdering of the resulting alloy layer.

The present invention provides an alloyed zinc-plated steel sheet in which the alloy layer is finely bubbled.

The present invention also provides a method for producing an alloyed zinc-plated steel sheet, which is characterized by performing vacuum evaporation galvanizing of the steel sheet under an inert atmosphere having an oxygen concentration of 1.0 to 30 ppm, thereby heat-treating the plated steel sheet.

In the present invention, the term "alloy layer" means a zinc-iron alloy layer that is substantially an intermetallic compound.

"Cellulation" means that the alloy layer consists of finely distributed and well-grown particles of iron-zinc intermetallic compound, the size of which is 10 ⁴ to 10 ⁶ grains per mm ² .

In the method of the present invention, the vacuum deposition method of plating zinc on a steel sheet can be performed using a known vacuum deposition plating apparatus.

When the vacuum evaporation galvanizing is carried out in an atmosphere containing oxygen maintained at the above defined level and the heat treatment to alloy the zinc-plated steel sheet is performed, the alloy layer is finely bubbled. The cause for such bubbling is not entirely clear, but it is presumed that a small amount of oxygen present in the atmosphere performing the deposition forms an extremely thin oxide that is finely distributed on the surface of the steel sheet before zinc deposition. Zinc vapor is deposited on the oxides thus distributed. Therefore, this finely distributed oxide acts as a barrier, extremely prevents mutual diffusion between iron and zinc, and bubbles the formed iron-zinc intermetallic compound.

If the oxygen concentration in the atmosphere is less than 1.0 ppm, the alloy layer is not bubbled to such a satisfactory level that the powdering prevention effect is not sufficient. When the oxygen concentration exceeds 30 ppm, oxides are produced in excess, and adhesion of the plating layer is impaired. More preferred oxygen concentration is 1.5 to 15 ppm.

Deposition and alloying per se are already established techniques. The alloying process can be carried out using a conventional furnace or batch furnace such as installed in a conventional hot dip plating line.

The preferred temperature of the steel strip just prior to deposition is 190 ° C to 280 ° C.

Preferred alloying temperatures are 220 ° C to 360 ° C.

The preferred size of the particles of iron-zinc intermetallic compounds (called bubbles) is 10 ⁴ to 10 ⁶ grains per mm ² .

The alloyed zinc-plated steel sheet of the present invention in which the alloy layer is finely bubbled is excellent in workability. Since the alloy layer is finely bubbled, the stress generated in the alloy layer when it is processed is reduced through the edges or spaces between the fine particles, so that the alloy layer powdering is significantly prevented.

The vacuum deposition method is used in the method of the present invention. Thus, the method can obtain the advantages of vacuum deposition. That is, by this method, it is possible to produce an alloyed zinc-plated steel sheet or an alloyed zinc-plated steel sheet having a different plating thickness from a thin plating thickness to either one of single-side plating or double-side plating. Therefore, an alloyed zinc-plated steel sheet excellent in workability and resistant to powdering can be easily manufactured.

Several types of continuous vacuum deposition plating apparatus have been proposed. One example is shown in FIG. Such devices are mentioned, for example, in Nisshin Giho No. 51. The apparatus mentioned here has two deposition chambers for carrying out double-sided plating. Only one deposition chamber is sufficient for single-sided plating.

The deposition line is a pretreatment furnace (2), gas jet cooler (3), compression chamber (4), first and second sealing roller chamber (5a, 5b), first deposition chamber (6a), second deposition chamber ( 6b), a cooling chamber 7 in which the plated steel sheet is cooled, and an alloyed furnace (not shown). In the vacuum deposition chambers 6a and 6b, guide rollers 8a and 8b and zinc-vapor baths (not shown) are mounted. The steel strip 1 passes through this deposition line.

The pretreatment furnace 1 has an atmosphere that is slightly oxidized and / or reduced below ambient pressure. The surface of the steel strip is cleaned as the steel strip passes through the preheating furnace.

The gas jet cooler 3 cools the pretreated steel strip to the temperature desired for deposition.

The compression chamber 4 includes an ambient pressure system including a pretreatment furnace 2, a gas jet cooler 3, and the like, and an exhaust system including a sealing roller chamber 5a, 5b, a deposition chamber 6a, 6b, and the like. Connected.

The sealing roller chamber is equipped with a pair of sealing rollers each and includes a plurality of vacuum chambers leading to the discharge system and is discharged in stages until the pressure in the deposition chamber is 0.01 to 0.1 Torr.

The compression chamber 4 is inert gas (e.g. nitrogen) such that the pressure may be slightly higher than the ambient pressure system to prevent the introduction of air or hydrogen into the vacuum deposition chamber (s), which may cause an explosion. Pressurize.

The oxygen concentration in the atmosphere where the vacuum deposition is carried out is controlled by mixing the specified amount of oxygen with an inert gas (eg nitrogen) introduced into the compression chamber.

The invention is illustrated by the following examples and comparative examples.

Continuous vacuum deposition galvanizing is carried out using the apparatus substantially described in FIG. 1 under the conditions described in Table 1. The total length of the plating line is 70m. The heat treatment of the alloy is carried out using a separate batch furnace.

TABLE 1

TABLE 2

Powdered resistance is when the plated specimen is bent at an angle of 180 ° at an interval of six times the thickness of the test piece and then restored to its original state, and the tape is removed after the cellophane adhesive tape is applied to the site, and it is bent and returned to its original state. Judging from the powdering occurring in the The degree to which the plating layer peels off is observed.

The plating layer is alloyed to the surface by the alloy treatment. 2 is an electron micrograph of the product surface of Example 3, and FIG. 3 is an electron micrograph of the product of Comparative Example 2. FIG.

As can be seen in FIG. 2, the separation crystals, ie bubbles, are well developed while the alloy layer in FIG. 3 is blurred.

Claims (4)

Alloyed zinc-plated steel sheet with finely bubbled alloy layer. The alloyed zinc-coated steel sheet according to claim 1, wherein the alloy layer is bubbled into particles having a size of 10 ⁴ to 10 ⁶ grains per 1 mm ² . A method of producing an alloyed zinc-plated steel sheet, characterized in that the alloy is performed by vacuum-deposited galvanizing the steel sheet under an inert atmosphere having an oxygen concentration of 1.0 to 30 ppm and then heat-treating the plated steel sheet. The method of claim 3 wherein the oxygen concentration in the vacuum deposition atmosphere is between 1.5 and 15 ppm.

Images