JPH05271892A - Method for controlling galvanizing bath - Google Patents

Abstract

PURPOSE:To reduce the [Al]ef concn. in the bath in a short time, in the manufacture of a galvanized steel sheet by adding Ni to the bath at the time of changing from the manufacture of a nonalloyed plated steel sheet to the manufacture of an alloyed plated steel sheet. CONSTITUTION:In the manufacture of a galvanized steel sheet, at the time of changing from the manufacture of a nonalloyed plated steel sheet to the manufacture of an alloyed plated steel sheet by using a plating bath contg. 0.05 to 0.20% Al, Ni satisfying [Ni(%)]>=4{[Al(%)]-0.11} is added to the plating bath, and then, it is changed to the manufacture of the alloyed placed steel sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plating bath control method for producing non-alloyed galvanized steel sheets and alloyed galvanized steel sheets using the same equipment and the same bath.

[0002]

2. Description of the Related Art Conventionally, alloyed hot-dip galvanized steel sheets (hereinafter referred to as GA) have the same zinc bath in the same manufacturing equipment as hot-dip galvanized steel sheets (hereinafter referred to as GI) in view of equipment, cost and the like. It is usually produced by using the following method, and is obtained by performing a heat diffusion treatment at 450 to 650 ° C. in a heating furnace subsequent to plating.

By the way, in the case of manufacturing the above-mentioned GI, 0.08 to 0.20% of Al is added to the hot-dip galvanizing bath (hereinafter,% representing the component ratio is mass%). However, some of the added Al is bonded to Fe existing in the molten zinc bath, and Fe-Zn-A including Zn is contained.
The concentration of Al dissolved in the Zn liquid phase is lower than the concentration of all Al in the zinc bath because it forms the l compound and disperses it in the molten state in the solid state (this is generally called dross). Become. Therefore, although it is a simple method, the concentration of dissolved Al is usually defined as the effective Al concentration [Al] _ef .

[Al] _ef = [Al] T- [Fe] T [Al] T: analytical value of Al in zinc bath [Fe] T: analytical value of Fe in zinc bath It is used as a management index.

The purpose of adding Al to the zinc bath is to suppress the Fe--Zn based intermetallic compound layer formed on the surface of the steel sheet during hot dipping. That is, if the Fe—Zn based intermetallic compound layer grows thick, the workability of the product is adversely affected. In order to secure sufficient film workability of the hot dip galvanized steel sheet, [Al] _ef of the hot dip galvanized bath is 0.1
It must be adjusted to be 4% or more.

On the other hand, in the production of GA, zinc bath [Al] _ef is high, the process on a delay in the progress of alloying, for causing a great deal of trouble, the [Al] _ef is as much as possible Need to lower. Therefore, the [Al] _ef in the zinc bath when GA is manufactured is generally adjusted to 0.11% or less.

Therefore, in manufacturing GI and GA in which the same molten zinc bath is commonly used, conventionally, in the case of GI, the zinc bath was carried out under the condition that [Al] _ef ≧ 0.14%. , GA, the zinc bath has been carried out under the condition that [Al] _ef ≦ 0.11% while switching and adjusting each.

However, in actual work, it is easy to raise the [Al] _ef in the molten zinc bath, but conversely there is no suitable measure to reduce the [Al] _ef , and therefore GI to GA When switching production to
The current situation is to wait for the [Al] _ef to gradually decrease.

[0009]

In the prior art, GI is used.
During the transition period of decrease of [Al] _ef when switching from manufacturing to GA manufacturing, that is, 0.11% <[Al] _ef <0.14%, bath conditions unsuitable for any manufacturing of GI <GA When the GI production is continued, the Fe—Zn based intermetallic compound layer grows thick, so that only the workability of the plating film was poor. Therefore, in the present invention, in the hot-dip galvanized steel sheet manufacturing facility, the transition time when switching from GI manufacturing to GA manufacturing is the same as the conventional [A
l] By performing in as short a time as possible as compared with the _ef control method,
The objective is to provide plated products of good quality with high efficiency and high yield.

[0010]

[Means for Solving the Problems] As a result of repeated experiments and studies in order to achieve the above objects, the following findings were obtained. That is, when a certain amount or more of Ni is added to the plating bath, it reacts with Al in the plating bath to form dross mainly composed of Ni ₂ Al ₃ . This reduces the Al concentration in the plating bath. Since this dross has a lower specific gravity than Zn, it can be easily recovered as top dross.
Therefore, in combination with the conventional Al addition means at the time of GI production, when the GA production is switched, the Ni content exceeding the specific amount is exceeded.
It has been found that the addition of the compound significantly shortens the operation transition time from GI production to GA production.

The present invention has been made on the basis of the above findings, and in the production of hot-dip galvanized steel sheet,
A hot dip galvanizing bath containing 05 to 0.20% Al dissolved and contained was used, and when switching from GI production to GA production, [Ni (%)] ≧ 4 {[Al (%)] − in the plating bath. The present invention provides a method for controlling a hot-dip galvanizing bath, which comprises adding Ni satisfying 0.11} and then shifting to the production of GA.

[0012]

The features of the present invention will be described in detail below with reference to the action, with reference to the drawings. When Ni is added to a hot dip galvanizing bath containing Al, an intermetallic compound (dross) of Ni ₂ Al ₃ is generated as the amount of Ni added increases, as shown in FIG. 1, and [Al] in the bath is increased. _{The ef} concentration decreases. Therefore, when switching from GI manufacturing to GA manufacturing, Ni is added to the plating bath and the [Al] _ef concentration in the bath is adjusted to immediately prepare the GA manufacturing system, which may cause quality deterioration during the transitional period. It is possible to continue the smooth operation without doing so.

Further, in the present invention, when the dissolved Al concentration (= [Al] _ef ) in the hot dip galvanizing bath is lower than 0.05%, the deterioration of plating adhesion during GI production becomes remarkable,
On the other hand, if the dissolved Al concentration exceeds 0.20%, GA
Since the required amount of Ni required for the conversion increases, it was determined that the concentration of molten Al in the hot dip galvanizing bath should be adjusted to 0.05 to 0.20%.

FIG. 2 shows a conventional method for controlling the composition of a plating bath (FIG. 2 (a)) in the production of a hot-dip galvanized steel sheet.
It is a conceptual diagram which compared with the control method (FIG.2 (b)) of the plating bath composition by this invention. As is clear from FIG.
In the present invention, by adding Ni at a critical concentration or higher when switching from GI production to GA production, operation switching can be performed extremely smoothly, and deterioration of product performance that tends to occur during the transitional transition period can be prevented. The retention is greatly improved.

[0015]

EXAMPLES The present invention will be specifically described based on examples. 50% of low carbon aluminum killed steel with a plate thickness of 0.7 mm was obtained using a hot dipping simulator (Resc Co., Ltd.).
H ₂ -N ₂ performs plating in an atmosphere, the coating weight 6
It was set to 0 ± 10 g / m ² . At this time, the plating bath temperature is 460
Predetermined Al and Ni were added to the bath at ± 5 ° C. Subsequently, alloying treatment was performed at 500 ° C. for 15 seconds in an infrared heating furnace to prepare a galvannealed steel sheet, and the appearance of the plating layer at this time was investigated. The result is shown in FIG.

FIG. 3 shows the [Al] _ef and Ni concentrations in the bath on the coordinate axes, and shows the results of investigations on whether or not alloying is possible in each composition. The appearance at this time was evaluated as shown below. ◯: Complete alloying Δ: Burning unevenness partially, η-Zn remained in part X: η-Zn remained in most part From this FIG. 3 as well, the Ni concentration in the plating bath is expressed by the formula [Ni (%)] ≧ 4. It can be confirmed that alloying is possible in the range satisfying {[Al (%)]-0.11}. In addition, Table 1 shows a part of the results shown in FIG. 3 for the present invention and a comparative example. As described above, according to the present invention, it is possible to completely alloy the surface and manufacture GA.

[0017]

[Table 1]

[0018]

As described above, by carrying out the present invention, it is possible to switch from GI production to GA in the production of hot-dip galvanized steel sheets in a short time, and to stabilize products of good quality. Since it can be supplied by supplying it, it brings about an extremely useful effect in industry.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the amount of Ni added and the Al concentration in a bath.

FIG. 2 is a conceptual diagram showing an example of controlling a plating bath composition in the production of hot-dip galvanized steel sheet, FIG. 2 (a) shows a conventional method, and FIG. 2 (b) shows the present invention.

FIG. 3 is a plating bath [Ni], [Al] _{ef in the example.}
3 is a graph showing the results of an inspection of the appearance of plating with respect to.

Claims (1)

[Claims] 1. In the production of hot-dip galvanized steel sheet,
When using a hot dip galvanizing bath containing 0.05 to 0.20 mass% of Al and switching from the production of the non-alloyed galvanized steel sheet to the production of the alloyed galvanized steel sheet, [Ni (%) ≧ 4 A method for managing a hot dip galvanizing bath, characterized in that Ni which satisfies 4 {[Al (%)]-0.11} is added, and then the production of alloyed steel sheet is started.