JPH07145468A - Manufacture of galvannealed steel sheet by spray plating - Google Patents

Abstract

PURPOSE:To provide galvannealed steel sheet excellent for the appearance, the workability and the deep drawability by specifying the temperature and the coating weight and re-heating the plated steel sheet under the prescribed conditions in executing the spray plaining of the molten Zn on the surface of the strip-shaped steel sheet. CONSTITUTION:After the surface of the low carbon Al-killed cold rolled steel sheet 1 is preliminarily cleaned, the steel sheet is heated at the temperature below the melting point of Zn by an induction heating equipment 5, and carried to a plating chamber 3 through a deflector roll 2. The temperature of the steel sheet 1 is measured by a thermometer 7, and the output of the heating equipment 5 is adjusted by an output control device 8 to correctly keep the temperature of the steel sheet 1 below the melting point of Zn. The molten Zn is blown from a nozzle 4 in the plating chamber 3 to execute the spray plating so that the coating weight per one side of the steel sheet 1 may be <=130g/m<2>. After the plated Zn is solidified, the plated steel sheet is placed in a re-heating furnace 6 where the temperature T of the steel sheet 1 is below the melting point of Zn, and the plated Zn is alloyed with Fe of the steel sheet by executing the re-heating under the conditions to satisfy the inequality with the heating time >=5sec.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip zinc spray plating method for strip steel plates, and more particularly to a plating method capable of obtaining high quality strip steel plates.

[0002]

2. Description of the Related Art A spray plating method in which a molten metal such as molten zinc is atomized by spraying and is deposited on the surface of a strip-shaped steel sheet which is continuously fed and plated is conventionally known from JP-A-53-53. Japanese Patent Publication No. 99047, JP-A 1-2
It is known from Japanese Patent No. 01456. In each case, it is stated that the temperature of the strip-shaped steel sheet during plating is 450 ° C. or higher.

[0003]

However, in the above-mentioned hot-dip zinc spraying method, since the temperature of the strip-shaped steel sheet during plating is high, the hot-dip zinc and strip-shaped steel sheet are reactively alloyed, and in some places the hot-dip zinc and strip-shaped steel sheet. Changes the wettability of. Therefore, irregular flow of molten zinc occurs on the strip steel sheet, and it becomes difficult to obtain a uniform plating appearance. For example, in the part where the wettability of molten zinc and strip steel deteriorates,
Molten zinc does not spread sufficiently, and remains in the form of spots that remain aggregated in the form of drops. Therefore, according to the conventional hot-dip galvanizing method, even if the alloying heat treatment is continuously performed after the spray-plating, the spotted pattern remains as it is, and the whole galvanized galvanized steel sheet has a uniform appearance. Is extremely difficult.

As described above, the conventional hot-dip zinc spray plating method has a good appearance and good workability,
It is not possible to produce a galvannealed steel sheet having deep drawability. An object of the present invention is to provide a method for producing an alloyed hot-dip galvanized steel sheet having a good appearance, good workability and deep drawability by the hot-dip galvanizing method.

[0005]

To achieve this object, the gist of the present invention is to provide fine particles of molten zinc in a non-oxidizing atmosphere on the surface of a strip-shaped steel sheet that has been pretreated and continuously fed. When spray-plating by spraying, lower the temperature of the strip-shaped steel sheet before it is sent to the plating step below the melting point of zinc,
After spray-galvanizing at 30 g / m ² or less, and then the molten zinc is solidified, the temperature T of the strip steel plate is set to at least the melting point of zinc and the heating time t ≧ 5 seconds, and the strip steel plate represented by the following formula In the method for producing an alloyed hot-dip galvanized steel sheet, the galvanized steel sheet is reheated within a condition range of temperature T and heating time t. 600-0.5 x t ≥ T (° C) ≥ 8430 / ln (t / 0.00025
8) −273

[0006]

The present inventors set the temperature of the strip-shaped steel sheet at the time of plating to be equal to or lower than the melting point of zinc, so that the spray-plated molten zinc is solidified on the strip-shaped steel sheet and fluidized or strip-shaped on the strip-shaped steel sheet. It was confirmed that it is possible to obtain a plated steel sheet which has no unevenness in the plating appearance and has a uniform appearance over the entire surface of the strip-shaped steel sheet because it does not cause an alloying reaction with the steel sheet. However, as it is, voids are present in the plating layer, the surface becomes uneven, and almost no alloying reaction occurs, so that it is insufficient as a galvannealed steel sheet.

Therefore, the present inventors further subject this plated steel sheet to an appropriate reheating treatment, whereby the solidified zinc is uniformly remelted and alloyed, and an alloyed zinc having a smooth surface without pores is formed. It was confirmed that a plated steel sheet could be obtained. That is, when the temperature and reheating time of a predetermined strip steel sheet are set and the reheating treatment is performed, it is possible to produce an alloyed hot-dip galvanized steel sheet having both properties of good alloying plating appearance and plating adhesion. You can do it. We have
As a result of diligent studies on the reheating conditions, it was found that it is desirable to keep the range of the manufacturing conditions described below as the conditions for obtaining a better alloyed hot-dip galvanized steel sheet.

The weight per unit area of zinc is 130 g / m ² per side.
It is desirable to keep below. Above this, the adhesiveness of the plating is extremely deteriorated, and the powdering phenomenon in which the plating is separated in powder form becomes prominent. Further, it is desirable that the temperature of the strip-shaped steel sheet at the time of reheating is equal to or higher than the melting point of the lowest temperature zinc. Zinc manages to melt below this temperature, but in order to obtain a proper galvannealed steel sheet, re-heating time is required for a long time, and if it remains as it is, the in-furnace time will be extremely long. It is not practical to think about. Further, the reheating time needs to be at least 5 seconds or more. Even if the temperature of the strip-shaped steel sheet is raised for a shorter time than this, uneven melting occurs in places, and the appearance of the plating is significantly impaired.

In addition to the above conditions, the inventors of the present invention set the reheating conditions as follows: the strip-shaped steel plate temperature T and the heating time t represented by the following equation.
It was found that it is most desirable to stay within the relation range of. 600-0.5 x t ≥ T (° C) ≥ 8430 / ln (t / 0.00025
8) -273 (however, temperature T of strip steel sheet ≥ melting point of zinc, heating time t ≥
5 seconds)

Above the temperature on the left side of the above formula, overalloying occurs,
Plating adhesion is significantly impaired. On the other hand, below the temperature on the right side of the above formula, remelting of solidified zinc becomes insufficient, unmelted zinc remains, and a proper alloyed hot-dip galvanized steel sheet cannot be obtained. Therefore, the most preferable reheating condition is the range of the relation between the temperature and the heating time of the strip steel sheet shown by the above formula.

[0011]

FIG. 1 shows an example of a manufacturing process for carrying out the present invention. In this example, an alloyed hot-dip galvanized steel sheet was manufactured according to the manufacturing conditions shown in the left column of Table 1. Table 1
The specific manufacturing method according to the manufacturing conditions is shown below.

As a strip steel material, a cold-rolled steel sheet having a thickness of 0.75 mm and a width of 500 mm and low carbon Al-killed steel was used as a plating original plate. The strip-shaped steel sheet 1 is sufficiently degreased in advance by a pickling treatment or a hydrogen reduction heating treatment to clean the surface. Next, using an induction heating device 6 under a non-oxidizing atmosphere,
It is heated to an appropriate temperature of the strip steel plate below the melting point of zinc and sent to the plating chamber 3 as it is. The feature of the present invention resides in that the temperature of the strip-shaped steel sheet during spray plating is suppressed to be equal to or lower than the melting point of zinc. Therefore, the radiation thermometer 7 is installed at an appropriate position before being sent to the plating chamber 3, the temperature of the strip-shaped steel sheet is measured, and the output of the induction heating device 6 is adjusted by the output control device 8 to obtain the strip-shaped steel sheet. Control the temperature of. The strip steel plate 1 is sent to the plating chamber 3 via the deflector roll 2.
In the plating chamber 3, with the nozzle 4 for spraying molten zinc,
Hot-dip zinc is sprayed on both sides of the strip steel plate and spray-plated.

The coating weight of the plating is adjusted by the supply pressure of molten zinc to the nozzle and the line speed of the strip steel plate. The molten zinc temperature is 460 ° C. Reheating furnace 5 adjusted to a non-oxidizing atmosphere, followed by spray-plated strip steel
To introduce. In this reheating furnace 5, the temperature of the strip steel plate is adjusted to about 15
The temperature is raised to a predetermined temperature of the strip-shaped steel sheet in seconds, and heat treatment is performed while maintaining this temperature for an appropriate reheating time. The reheating method is radiant heating with a radiant tube burner. The reheating condition is adjusted by measuring the temperature with a radiation thermometer installed in the reheating furnace 5 and adjusting the output of the burner and the line speed of the strip steel sheet. Then, cool to room temperature with a jet cooler.

According to the manufacturing process of FIG. 1, the results of investigation of the plating quality of the product manufactured by the method for manufacturing the galvannealed steel sheet of the present invention and the comparative material manufactured by the conventional spray galvanizing method are shown in Table 1. Shown in the right column.

In FIG. 2, the optimum reheating condition range according to the present invention is shown by hatching. The ◯ plot in FIG. 2 is a sample value of a galvannealed steel sheet having a good appearance manufactured by this method and having excellent workability and deep drawability. The x-plot of comparative condition 1 in FIG. 2 shows a sample with poor plating adhesion due to overalloying, and the x-plot of comparative condition 2 shows a sample with remelting or insufficient alloying. It is unacceptable as a galvanized steel sheet.

As described above, according to the present invention, an alloyed hot-dip galvanized steel sheet having a good appearance, good workability and deep drawability can be obtained by the hot-dip galvanizing method.

[0017]

[Table 1]

[0018]

According to the present invention, an alloyed hot-dip galvanized steel sheet having a good appearance, good workability and deep drawability can be obtained by the hot-dip galvanizing method.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a manufacturing process for carrying out the present invention.

FIG. 2 is an explanatory view showing an optimum reheating condition range according to the present invention.

[Explanation of symbols]

 1 strip steel plate 2 deflector roll 3 plating chamber 4 spray nozzle 5 reheating furnace 6 induction heating device 7 radiation thermometer 8 output control device

Claims (1)

[Claims] 1. When performing spray plating by spraying fine particles of molten zinc in a non-oxidizing atmosphere onto the surface of a strip-shaped steel sheet that has been pretreated and continuously fed, before being sent to the plating step. After lowering the temperature of the strip steel plate below the melting point of zinc, the basis weight per side is 130 g / m
After performing hot dip galvanizing at ² or less and then solidifying the molten zinc, the temperature T of the strip steel plate is set to at least the melting point of zinc and the heating time t ≧ 5 seconds, and the temperature T of the strip steel plate represented by the following formula And a method of manufacturing an alloyed hot-dip galvanized steel sheet, wherein the galvanized steel sheet is reheated within a condition range of heating time t. 600-0.5 x t ≥ T (° C) ≥ 8430 / ln (t / 0.00025
8) −273