JP2648844B2 - Manufacturing method of hot-dip plating with excellent adhesion - 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 hot-dip galvanizing a hard-to-plate steel sheet containing a large amount of Si (0.3% or more) in steel without causing non-plating or poor adhesion. Things.

[0002]

2. Description of the Related Art In a hot-dip galvanizing line currently being used, a steel sheet is annealed using a heating furnace such as a Zenzimer system or an indirect heating system using a radiant tube, and a mixed gas of hydrogen and nitrogen is introduced into the furnace for reduction. By reducing the Fe oxide film generated on the steel sheet
Thereafter, it is continuously passed through a molten zinc bath. According to this method, the Fe oxide film generated in the furnace is extremely thin (Senzimer method) or not formed at all (indirect heating method), and a smooth iron-plating interface is obtained and hot-dip galvanizing with excellent adhesion A steel sheet is obtained.

[0003]

However, in recent years, the requirements for materials have been diversified and various elements have been added to steel in many cases. In particular, elements such as Si, Mn, Al and P are more easily oxidized than Fe. Is contained, since the atmosphere of the annealing furnace is oxidizing to these elements, they are selectively oxidized and concentrated on the steel sheet surface during the annealing process. In particular, Si oxides are considered to significantly impair the wettability with the plating bath, and at present, the amount of added Si is greatly restricted in designing materials.

On the other hand, it has been proposed by Flintham et al. To improve the plating property by operating a high air ratio in the initial stage of annealing in an annealing furnace of the Sendzimer system. This is intended to suppress the diffusion of Si or the like into the surface layer by intentionally forming an Fe oxide film. However, it is difficult to control an appropriate Fe oxide film. If the thickness is too large, the Fe oxide film remains. If the amount is too small, the concentration proceeds, and in any case, the plating property is impaired. Therefore, in order to ensure the plating property by this method, it is essential to devise a process such as controlling the oxide film thickness while measuring it online. In addition, in the indirect heating method, it is impossible to suppress this enrichment phenomenon thermodynamically, and other measures are indispensable.

[0005]

Means for Solving the Problems The present inventors have pursued a mechanism by which these surface oxides impair the plating property. Even if the oxide is present on the surface of the steel sheet, the plating property is not impaired and the plated steel sheet is excellent. And found a method of manufacturing. The present invention advantageously solves the problems of the prior art.
i in a hard-to-plate steel sheet containing 0.3 to 1.1% of Al.
0.05-0.3%, Mg 0.02-0.3%, and the balance Z
This is a method for producing hot-dip galvanizing characterized by having excellent plating adhesion using a hot-dip galvanizing bath having a composition comprising n and unavoidable impurities.

Hereinafter, the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an embodiment of the present invention. The steel sheet 1 is a hard-to-plate, high-tensile steel sheet having a thickness of 0.2 to 4.5 mm and a width of 600 to 1800 mm and containing 0.3% or more of Si in steel. The steel sheet 1 is passed at a line speed of 40 to 180 mpm, and is turned into a hot-dip plating pot 3 after being turned by a turndown roll 2. The steel sheet 1 introduced into the hot-dip plating pot 3 is turned in the vertical direction by the pot roll 4, the warp is corrected and flapping is suppressed by the support rolls 5 and 6, and the amount of plating applied is controlled by the wiping nozzle 7. 8 is Al 0.05-0.3%, Mg 0.0
This is a zinc plating bath having a composition of 2 to 0.3%, Zn, and unavoidable impurities. If Al is contained in the zinc bath but Mg is not added, the Si oxide concentrated on the steel sheet surface during the annealing process is reduced by the Al in the bath, but the resulting Si dissolves in Zn and Al. The plating properties are impaired due to poor properties.

Therefore, as a countermeasure against this, in order to prevent precipitation of Si alone, it is effective to add an element which forms a stable solid solution or an intermetallic compound with Si generated by the reduction reaction to the bath. (1) Si and Mg ₂ Si
(2) Mg has a strong reducing power and can effectively reduce Si oxide, (3) Mg
Is an element that is very effective in improving the plating property because it dissolves in a liquid state in a molten zinc bath containing Al in a normal operation range. If the content of Mg in the plating bath is less than 0.02%, Mg
Hardly shows any effect of adding. On the other hand, if Mg exceeds 0.3%, dross mainly composed of MgO is generated, and workability is deteriorated, and appearance is hindered by adhesion to the plating surface. If the Al content is less than 0.05%, an iron-zinc alloy is formed at the steel plate-plating interface, which adversely affects the workability. When Al exceeds 0.03%, the effect of Mg is lost if added.

[0008]

[Example] Thickness: 0.2 to 4.5 mm, board width: 600 to 18
Using a steel plate with a different Si content at 00 mm
The plating was performed by changing the amount in various ways, and the plating appearance and plating adhesion were evaluated. Table 1 shows the results. Here, Table 1
The plating appearance shown in Table 1 indicates A: non-plating, foreign matter (precipitation of Si, etc.), and B: adhesion of dross on the bath, and was evaluated using a standard sample. The plating adhesion was evaluated by a ball impact test, and the evaluation was made using a standard sample.

[0009]

[Table 1]

From Table 1, the following results were obtained. (1) Good plating appearance and appearance depending on Si content in steel
Al and Mg additions required to obtain plating adhesion
Required. For example, when the Si content in steel is 0.30%,
For each case of 0.50%, 0.80% and 1.1%
Is Al 0.05-0.3%, Mg 0.02-0.3%
To improve plating appearance and plating density
Adhesion can be obtained (Examples Nos. 1 to 16). (2) On the other hand, high steel containing 0.3% or more of Si content in steel
In the case of a tensile steel sheet, the Mg addition ratio exceeds 0.3%
And, although the plating adhesion is good or slightly peeled,
A large amount of dross such as MgO was generated at the top of the plating bath.
Reappears on the plating surface, impairing the plating appearance
(Nos. 18, 22, 26, 30). In the bath A
When l is high , the reaction between SiO ₂ and Mg on the steel sheet surface
Is no longer performed effectively, and the plating property is improved by Mg.
Disappears (No. 20, 24, 28, 32). (3) When the Mg addition ratio is outside the range of the present invention,
Poor adhesion (Nos. 17, 21, 25, 29). Ma
In addition, when the addition ratio of Al is out of the range of the present invention,
Bad appearance (Nos. 19, 23, 27, 31). These results, occurrence of non-plating in the plating bath Al, and by that to contain restriction Mg as the present invention in the case of high-tensile steel sheet containing 0.3 to 1.1% of Si in the steel And hot-dip galvanizing without causing poor adhesion.

[0011]

Effect of the Invention] The present invention, in the Si-based high-tensile steel sheet is difficult to apply the conventional plating, appearance defects, it becomes possible to perform the hot-dip galvanized without causing poor adhesion.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Steel plate 2 Turndown roll 3 Hot-dip plating pot 4 Pot roll 5 and 6 Support roll 7 Wiping nozzle 8 Plating bath

Claims (1)

(57) [Claims] 1. A hard-to-plate steel sheet containing 0.3 to 1.1% of Si in a steel, containing 0.05 to 0.3% of Al and 0.02% of Mg.
A method for producing hot-dip galvanizing characterized by having excellent plating adhesion using a hot-dip galvanizing bath having a composition of about 0.3%, the balance being Zn and unavoidable impurities.