JPH04168258A - Production of galvanized steel sheet excellent in workability - Google Patents

Abstract

PURPOSE:To prevent the cracking of the bent part of a plating layer by brushing the galvanized surface of a steel sheet with a metallic wire brush. CONSTITUTION:The surface of the plating layer of a galvanized steel sheet is brushed with a metallic wire brush. The treatment can be conducted before or after the steel sheet is subjected to skin pass rolling or leveling. The steel sheet is chromated, as required, and then coated. The diameter of the wire to be used for the metallic brush is preferably controlled to >= about 0.05mm, and a brush roll is favorably used. The turning rate of the brush roll is controlled to >= about 300 r.p.m. or especially to about 800-3000 r.p.m., and the brush is lightly pused against the steel sheet. When the galvanized steel sheet thus treated is bent, the bent part is never cracked.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is directed to hot-dip galvanized steel sheets with good workability (that is, hot-dip galvanized steel sheets including both hot-dip zinc and hot-dip zinc alloy coated steel sheets). This paper proposes a plating layer strengthening technology that is effective in preventing cracking of the plating layer, especially in the processed areas. Similarly, we propose a hot-dip galvanized steel sheet having a coating or film coating (hereinafter collectively referred to as "coating layer") on the surface of such a coating layer.

[Conventional technology]

It is generally known that when a zinc-based plated steel sheet or a zinc-based coated steel sheet is bent, cracks occur in the plating layer at the processed portion, resulting in a significant deterioration in corrosion resistance. Further, this phenomenon is also observed in steel sheets in which a film is further laminated on the plating layer. The so-called cracks that occur in the plating layer propagate to the coating layer and cause cracks, which significantly deteriorates the corrosion resistance of the processed portion. For this reason, in the past, processed parts were generally excluded when guaranteeing corrosion resistance, but this is an important issue in practice, and warranties are now required for the entire plated steel sheet, including processed parts. This is a situation that is increasingly desired.

Now, in response to such demands, for example, a method of performing recrystallization heat treatment on a plated steel sheet after cold rolling the plated layer (Japanese Unexamined Patent Publication No. 58-84963), and furthermore, , method of blasting the surface of the plating layer (JP-A-59-6363, JP-A-62-60)
No. 853) etc. were proposed.

[Problem to be solved by the invention]

However, the former method is not a method that can sufficiently prevent the occurrence of cracks in the plating layer of the processed area, and the latter method involves many technically difficult problems when applied to on-site processes. The reality is that it has not been put into practical use.

In addition, other methods to improve the workability of the plating layer include:
A method of thinning the plating layer is also known, but this method has the fundamental drawback that sufficient corrosion resistance cannot be obtained.

Therefore, an object of the present invention is to develop and propose a new method that does not have the above-mentioned problems of the light pressure recrystallization method and the blasting method and is effective in preventing cracking of the plating layer.

[Means to solve the problem]

In order to achieve the above purpose, that is, to prevent deterioration of the corrosion resistance of the processed parts of hot-dip galvanized steel sheets, it is necessary to prevent cracks from occurring in the coating layer of the processed parts when processing galvanized steel sheets. The most important thing is to prevent this, and it is thought that this makes it possible to make the corrosion resistance of the bent part comparable to that of the unprocessed part.

Based on this idea, the inventors of the present invention
As a result of intensive research into a method for manufacturing galvanized steel sheets that does not cause cracks in the coating layer, we found that when the surface of the coating layer of hot-dip galvanized steel sheets is brushed with a metal wire brush, the processability is significantly improved. They have found that it is possible to prevent cracking of the plating phase during normal bending.

In addition, the present invention also applies to the coating of a resin with excellent corrosion resistance on the plating layer, and also to the steel plate coated with a resin film, which is a so-called coating layer, to prevent cracks in the base plating layer. It was found that since there is no corrosion, there is no propagation, and therefore, the plated steel sheet has excellent corrosion resistance in the processed parts.

[Function] As mentioned above, the reason why cracks do not occur in the bending part of the plating layer when the surface of the plating layer is brushed is not very clear, but if desired deformation is applied in an appropriate state, the movability will be improved. This is thought to be because the introduction of dislocations easily causes plastic deformation. However, with this process,
It is clear that no cracks occur in the plating layer even during bending.

This invention improves workability by brushing the surface of the plating layer of a plated steel sheet manufactured by passing the steel sheet immersed in a hot-dip galvanizing bath or a hot-dip zinc alloy plating bath with a metal wire brush. This is a way to improve. The brushing treatment mentioned here may be performed before or after the skin pass or leveler treatment performed in the conventional treatment process. Further, the plated steel plate subjected to such treatment may be subjected to chromate treatment and may be used as a product as it is, or may be used as a colored steel plate after being painted or coated.

Brushing treatment has traditionally been used in cleaning or surface treatment lines to remove surface dirt or to activate the surface. This nylon brush is used to remove oxides, etc. from the surface. These brushes used for so-called pre-treatment of surface treatment are not effective in improving workability.

In the case of the present invention, it must be a metal brush. For example, stainless steel wire, piano wire, brass wire, etc. may be used. In addition, the diameter of the wire used is not effective if it is too thin, so it is better to have a diameter of 0.05wφ or more, and 0.2~
0.5 Mnφ is preferred. It is effective to make this metal brush into a roll for brushing within the line, and the rotation speed of this brush roll is not effective if it is too slow, so it is 800 to 300 rpm over 300 rpm.
It is preferable to press lightly with 0r, po+ and rotate.

These metal brush conditions are important in imparting appropriate ductility to the surface of the plating layer, and brushing treatment outside these conditions will not produce the desired effect of improving workability.

〔Example〕

After plating in continuous hot-dip plating equipment, before the skin pass (at the rear of the cooling zone), the diameter of the wire is 0.3 am + φ, and the outer diameter of the roll is 30 mm.
A wire brush roll made of 0Wφ, 5US304 wire was installed, rotated at 1500 rpm, and pressed against the surface of the plated steel plate with appropriate pressure to perform brushing treatment. At the same time, this equipment also made it possible to disable brushing treatment, making it possible to produce both types separately.

Experiments were conducted to examine changes in workability due to the presence or absence of brushing for products manufactured under different conditions such as the composition of the plating layer, plate thickness, area weight, and spangle size. A study was conducted on colored iron plates painted through. The workability was determined by observing the bent portion after Ot bending with a magnifying glass, and Table 1 shows the determination criteria.

Table 2 shows the workability evaluation results of the plated plate and the coated steel plate.

Table 1 Note: The amount of plating deposited on both sides is g/m" As is clear from the results of this example, the effect of the plated steel sheet of the present invention is obvious. In other words, the workability is significantly improved by brushing treatment. What will be done is
Even if the plating is normal zinc plating (Gl), Zn-
5% AI alloy plating (Galfan; GF), Zn-5
It is clear that this is always observed, even when using 5% AI alloy plating (Galvalume; GL), even when the plate thickness, area weight, or spangle shape changes, and even when painting or resin coating is applied. became.

〔Effect of the invention〕

As explained above, according to the present invention, the workability of hot-dip galvanized steel sheets, especially when bending is performed, there is no cracking in the processed parts, so that the corrosion resistance as a whole is significantly superior. Steel plates can be manufactured.

Claims (2)

[Claims] 1. A method for producing a hot-dip galvanized steel sheet with good workability, which comprises brushing the plated surface of the hot-dip galvanized steel sheet with a metal wire brush. 2. Hot-dip zinc with good workability, characterized in that the plated surface of a hot-dip galvanized steel plate is brushed with a metal wire brush, and then a coating layer is further formed on the brushed plating layer. Method for manufacturing galvanized steel sheets.