JP3071350B2 - Manufacturing method of galvannealed steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet. The present invention relates to a method of manufacturing with productivity.

[0002]

2. Description of the Related Art After a steel sheet is immersed in a molten zinc bath, the amount of zinc applied is controlled to a target amount by using a gas wiping device, and the steel sheet is heated in an alloying furnace to perform galvannealing. The production method is currently widely and industrially used. Further, a spray plating method and apparatus for atomizing a molten metal by spraying and attaching it to the surface of a continuously fed strip-shaped steel plate for plating are disclosed in JP-A-53-99047 and JP-A-53-99047. 1-22014
As disclosed in Japanese Patent Publication No. 6 (1994), there is a technique in which, as a pretreatment, a steel sheet is continuously heated and cleaned in a reducing atmosphere, and then spray plating is performed with the temperature of the steel sheet kept at a temperature equal to or higher than the melting point of the plated metal.

[0003]

However, in the conventional hot-dip plating method for controlling the amount of plating by gas wiping, it is necessary to increase the pressure of the wiping gas as the sheet passing speed increases. When the wiping gas pressure increases, a phenomenon called splash, in which zinc is scattered, occurs. When a splash occurs,
The scattered zinc adheres to the steel plate or the gas wiping device, and the plating quality is deteriorated or, in the worst case, plating is impossible. Therefore, a galvanized line by the conventional gas wiping method can be produced only at a line speed of 180 mpm or less at which no splash occurs.

On the other hand, in the spray plating method, there is no restriction on the line speed due to the occurrence of splash. However, JP-A-53-99047 and JP-A-1-20
In the spray plating method disclosed in Japanese Patent No. 1456, since the temperature of the steel sheet at the time of plating is high, an alloying reaction between zinc and the steel sheet occurs during plating.

Therefore, the wettability between the steel sheet and zinc becomes non-uniform in the surface of the steel sheet, and irregular flow of zinc occurs, so that it is extremely difficult to obtain a uniform plating appearance. Even if the galvanized steel sheet with such uneven appearance is alloyed,
The uneven appearance remains as it is, and a high quality alloyed hot-dip coated steel sheet cannot be obtained. Also, the reheating conditions for obtaining an alloyed hot-dip galvanized steel sheet are different from those of the conventional hot-dip galvanizing method. Galvanized steel sheets cannot be obtained.

The present invention provides a method for producing a uniform and high-quality galvannealed steel sheet with high productivity by a method different from the conventional method for producing a galvannealed steel sheet by a gas wiping method or a spray plating method. The purpose is to provide.

[0007]

SUMMARY OF THE INVENTION The present invention is a method for producing an alloyed hot-dip galvanized steel sheet which can advantageously eliminate the above-mentioned drawbacks of the conventional method. In the spray plating method of plating by spraying fine particles, a strip-shaped steel plate to be plated is subjected to gas reduction or pickling as a pretreatment, and zinc fine particles containing more than 0.08 wt% and less than 0.50 wt% of Al in a non-oxidizing atmosphere. A method for producing an alloyed hot-dip galvanized steel sheet, comprising spraying and plating on a strip steel sheet having a melting point lower than the melting point of the plated metal, and reheating the strip steel sheet to a temperature equal to or higher than the melting point of the plated metal after plating.

(2) The method according to claim 1, wherein the coating weight is 100 g / m ² · one side or less, and the reheating condition is within the range of the steel sheet temperature and the heating time shown in the following equation. A method for producing an alloyed hot-dip galvanized steel sheet. − (T + Δt) + 450 ≦ T ≦ − (t + Δt) +600 Δt = 0.111 exp (15 + W _Al ) where T: steel sheet temperature (° C.), t: reheating time (s),
W _Al : Al concentration in zinc (wt%)

[0009]

The present invention will be described below in detail. In the present invention, the strip-shaped steel sheet to be plated is a strip-shaped steel sheet subjected to gas reduction or pickling, and an oxide having poor wettability with zinc is formed on the surface of the steel sheet after hot rolling or cold rolling. This is because the sprayed zinc does not adhere to the surface of the steel sheet because it is generated. By performing gas reduction or pickling, the surface of the steel sheet is cleaned, and the wettability between zinc and the steel sheet can be improved.

[0010] When galvanizing a strip-shaped steel sheet by the spray plating method, if the temperature of the steel sheet is higher than the melting point of zinc, an alloying reaction between zinc and the steel sheet occurs during the plating. Therefore, the wettability between the steel sheet and zinc becomes uneven in the surface of the steel sheet, and irregular flow of zinc occurs, so that it is extremely difficult to obtain a uniform plating appearance. Even if the galvanized steel sheet having such a non-uniform appearance is alloyed, the non-uniform appearance remains as it is, and a uniform alloyed hot-dip galvanized steel sheet cannot be obtained. The conditions for producing a uniform alloyed hot-dip galvanized steel sheet by spray plating are as follows: first, the temperature of the strip-shaped steel sheet during plating must be lower than the melting point of zinc, and second, reheating after spray plating is performed. is necessary.

In the first condition, that is, when the temperature of the strip-shaped steel sheet at the time of plating is equal to or lower than the melting point of zinc, the sprayed zinc immediately solidifies on the steel sheet and does not cause fluidization or alloying reaction on the steel sheet. . Therefore, it is possible to obtain a plated steel sheet having a uniform and uniform appearance. In the present invention, Al
It is necessary to spray molten zinc containing more than 0.08 wt% and not more than 0.50 wt% in a non-oxidizing atmosphere. This is because when the Al concentration is 0.08% by weight or less, even when the temperature of the steel sheet is equal to or lower than the zinc melting point, an alloying reaction occurs between the steel sheet and the steel sheet due to the heat content of the molten zinc. If the Al concentration is more than 0.5% by weight, the surface tension of the molten zinc increases, and zinc is condensed on the surface of the steel sheet, resulting in uneven plating appearance.

Regarding the second condition, when spray plating is performed under the first steel sheet temperature condition, there are many voids in the plating layer, the surface has minute irregularities, and almost no alloying reaction occurs. Instead, it is necessary to cause the plating layer to be smooth and alloyed, and for that purpose, it has been found that the steel sheet is reheated to a temperature equal to or higher than the melting point of the plated metal. In the present invention, the reheating condition needs to be performed within the relational range between the steel sheet temperature and the heating time represented by the following equation. − (T + Δt) + 450 ≦ T ≦ − (t + Δt) +600 Δt = 0.111 exp (15 + W _Al ) where T: steel sheet temperature (° C.), t: reheating time (s),
W _Al : Al concentration in zinc (wt%)

This is because, as shown in FIG. 1, above the temperature on the right side of the above equation, the Fe concentration in the plating layer exceeds 16 wt%, and the range of the galvannealed steel sheet specified in JIS G 3302 is Because it will exceed. Below the temperature on the left side of the above formula, re-dissolution of solidified zinc becomes insufficient,
Undissolved zinc remains, and a uniform alloyed hot-dip galvanized steel sheet cannot be obtained. Therefore, the most desirable reheating condition is within the relational range of the steel sheet temperature and the heating time shown by the above equation.

It is desirable that the basis weight of zinc be suppressed to 100 g / m ² per side. This is because powdered peeling occurs in the alloyed hot-dip galvanized steel sheet when the plated steel sheet is processed. If the amount of adhesion is more than 100 g / m ^{2 on} one side, the amount of powdering peeling becomes remarkable, so that press working flaws occur frequently and are not practical.

[0015]

【Example】

(Example 1) An Al-K steel sheet was plated under the conditions shown in Table 1, and the quality of the steel sheet after plating was examined. As a result, a large number of splashes were generated in the galvannealed steel sheet manufactured using the conventional gas wiping. On the other hand, according to the method of the present invention, a galvannealed steel sheet having a uniform appearance was obtained.

[0016]

[Table 1]

Example 2 An IF steel sheet was plated under the conditions shown in Table 2, and the quality of the plated steel sheet was examined. As a result, the alloyed hot-dip galvanized steel sheet manufactured using conventional gas wiping became overalloyed. On the other hand, according to the method of the present invention, a uniform and good alloyed hot-dip galvanized steel sheet was obtained.

[0018]

[Table 2]

[0019]

According to the present invention, a uniform and high-quality alloyed hot-dip galvanized steel sheet can be manufactured with high productivity by the spray plating method.

[Brief description of the drawings]

FIG. 1 shows that a strip-shaped steel sheet which has been subjected to a reduction treatment in an N ₂ + 10% H ₂ atmosphere for 20 seconds contains Al in a non-oxidizing atmosphere.
Relationship between reheating condition and quality of alloy hot-dip steel sheet when re-heating after re-heating after spraying 100 g / m ² single-sided sprayed steel sheet with Zn fine particles containing more than 08 wt% and not more than 0.50 wt% at a plating temperature of less than the zinc melting point FIG.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C23C 4/02-4/16

Claims (2)

(57) [Claims] In a spray plating method in which plating is performed by spraying zinc fine particles, a strip-shaped steel plate to be plated is subjected to gas reduction or pickling as a pretreatment, and Al is added in a non-oxidizing atmosphere to more than 0.08 wt% to 0.50 wt%. %. A method for producing an alloyed hot-dip galvanized steel sheet, comprising spraying and plating zinc fine particles containing not more than 0.1% on a strip steel sheet having a melting point lower than the melting point of a plated metal, and reheating the strip steel sheet to a temperature higher than the melting point of the plated metal after plating. 2. The alloy according to claim 1, wherein the coating weight is 100 g / m ² or less on one side, and the reheating condition is within the range of the steel sheet temperature and the heating time shown in the following formula. Manufacturing method of galvannealed steel sheet. − (T + Δt) + 450 ≦ T ≦ − (t + Δt) +600 Δt = 0.111 exp (15 + W _Al ) where T: steel sheet temperature (° C.), t: reheating time (s),
W _Al : Al concentration in zinc (wt%)