JPH1025558A - Production of zinc-iron alloyed hot dip plated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain uniform allaying in a steel sheet by heating both edge parts in the width direction of a steel strip to raise the temps. thereof before its introduction into a plating bath. SOLUTION: In the poststage of heat treatment for a steel strip, both edge parts in the width direction of the steel strip are heated to raise the temps. thereof, is introduced into a galvanizing bath and is applied with plating. Since the temps. of both the edge parts are higher than that of the center part, zinc- iron alloying is promoted in the plating bath, and in both edge parts, the formation of an initial alloy layer is promoted compared to the case of the center part. Thus, after the plating, in the case alloying treatment is executed subsequently to the regulation of the coating weight, even if Si series and P series oxides are formed by high temp. coiling in hot rolling for the steel strip, by the development of the initial alloy layer, the plating layer in both edge parts can be subjected to the allaying treatment to the content of iron approximately equal to that in the center part. In the case both the edge parts are heated to raise the temps. thereof, by increasing them by 10 to 50 deg.C above that of the center part, more secure uniformizing treatment is made possible.

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 a zinc-iron alloyed hot-dip coated steel sheet.

[0002]

2. Description of the Related Art After heat treatment of a steel strip, it is led to a hot-dip galvanizing bath, and after plating, is controlled to a predetermined amount. Then, it is led to an alloying furnace by gas heating, induction electric heating, etc., and iron (steel strip) is added to the plating layer. Is known to produce a zinc-iron alloyed hot-dip galvanized steel strip. In the production of such a zinc-iron alloyed hot-dip galvanized steel strip, the temperature at both ends is lower than that at the center in the width direction of the coated steel strip during the transfer of the coated steel strip to the alloying furnace after plating. When the galvanized steel strip is heated and alloyed in a furnace, both ends in the width direction of the coated steel strip may become unalloyed.To prevent this, both ends of the steel strip are heated at the inlet side of the alloying furnace. To an alloying furnace for alloying.

[0003]

As described above, both ends of the plated steel strip are heated on the inlet side of the alloying furnace and guided to the alloying furnace.
Even if the alloying treatment is performed, it is difficult to perform the alloying treatment uniformly in the width direction of the steel strip. As a result of various studies conducted by the present inventors, there is a steel strip that improves workability by increasing the winding temperature after rolling in a continuous hot rolling step to about 700 ° C. depending on the type of steel. After winding, both ends of the steel strip come into contact with the atmosphere after winding, generating a large amount of oxides.
In the next step of pickling, both ends of the steel strip have large surface roughness, and the activity is increased, so that Si and P in the steel (in the steel sheet) are concentrated. During the cooling process, Si-based and P-based oxides are generated on the surface layer of the steel sheet (band), and the Si-based and P-based oxides act as barriers in the alloying process after plating, preventing the thermal diffusion of iron to the plated layer. It was found that the alloy was unalloyed. Further, when the plating amount after plating is controlled to a predetermined amount by gas wipe, the amount of adhesion at both ends of the plated steel strip is larger than that at the center. It has been found that the occurrence of a so-called edge overcoat promotes unalloying at both ends of the plated steel strip in combination with the above-described action.

[0004] Further, while the coated steel strip is conveyed by a hearth roll (conveying roll) through a pretreatment furnace comprising a heating zone, a soaking zone and a cooling zone, the steel strip is subjected to a continuous heat treatment, and then to a hot dip galvanizing bath. This is a process in which a lead plating is performed and the resultant is guided to an alloying furnace, where an alloying process is performed. The temperature in such a pretreatment furnace is about 850 ° C. in the heating zone, about 800 ° C. in the soaking zone, and about 3 ° in the cooling zone.
The surface portion of the hearth roll at which the steel strip to be heat-treated is in contact with the heat-treated steel strip is almost at the temperature of the heat-treated steel strip.
Because the ambient temperature around the hearth roll is low due to cooling,
It is very cold. For this reason, if the steel strip to be plated is changed from narrow to wide, the ends of the changed wide steel strip will be in contact with the low-temperature part of the hearth roll, and the lower temperature will be lower than at the center. When the low-temperature steel strip at both ends is introduced into the alloying furnace after plating and heat-alloyed, both ends cannot be heated sufficiently compared to the center in the width direction of the steel strip, and the plating at both ends of the plated steel strip Problems were clarified, such as the layer becoming unalloyed due to insufficient alloying. The method of the present invention has been made to solve such problems advantageously, by heating and raising the temperature of both ends of the steel strip before introduction into a hot-dip galvanizing bath, and performing a heat alloying treatment after plating. It is an object of the present invention to provide a method for uniformly alloying.

[0005]

The feature of the method of the present invention is that after the heat treatment of the steel strip, both ends in the width direction of the steel strip are heated from the center to the hot-dip galvanizing bath, and the plating is performed. A method for producing a zinc-iron alloyed hot-dip coated steel sheet, which comprises applying a heat-alloying treatment after controlling the applied amount to a predetermined amount.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, in the method of the present invention, both ends of the steel strip in the width direction are heated and heated to a hot-dip galvanizing bath after the heat treatment of the steel strip, and the steel strip is heated in the width direction. Since both ends have a higher temperature than the center, the formation of a zinc-iron alloy is promoted in the hot-dip galvanizing bath, and the formation of an initial alloy layer is promoted at both ends as compared with the center. Therefore, when the alloying process is performed after the coating weight control after plating,
As mentioned above, hot rolling of steel strip
Even if a system-based or P-based oxide is generated, the plating layers at both ends in the width direction of the steel strip can be alloyed to an iron content substantially equal to that of the central portion due to the development of the initial alloy layer. In addition, when controlling the plating amount, both ends in the width direction of the steel strip are overcoated compared to the center, but as described above, the alloying reaction at the both ends in the width direction is promoted as compared with the center, so that uniform alloying is similarly performed. It can be processed. Further, as described above, the both ends of the steel strip in the width direction due to the change of the width of the steel strip are lowered, and the unalloying due to insufficient heating of the both ends in the width direction of the steel strip during the alloying treatment is reliably prevented, and the uniformity is obtained. It can be subjected to alloying treatment.

[0007] Generally, between the hot-dip galvanizing bath and the alloying furnace, both ends in the width direction of the coated steel strip are easier to cool than the central part. Therefore, usually, both ends are locally heated with a combustion burner or the like to promote alloying. It is often used. Therefore, the method of the present invention can be applied not only to the above-described embodiment but also to the production of all zinc-iron alloyed hot-dip galvanized steel strips (plates).

[0008] Next, the temperature at which both ends in the width direction of the steel strip are heated is raised by 10 to 50 ° C from the center in the width direction of the steel strip to ensure uniform alloying during the alloying process. If the temperature is less than 10 ° C., depending on the plating bath temperature, the initial alloying in the plating bath may not be sufficient, and uniform alloying may be difficult. On the other hand, when the temperature exceeds 50 ° C., the alloy layer becomes excessive in the plating bath, and a brittle alloy layer is formed, which may cause peeling, which is not preferable. In addition, by heating about 80 mm from both ends of the steel strip to the center (inside) from both ends of the steel strip in the width direction, uniform alloying processing can be surely performed.

In order to heat both ends in the width direction of the steel strip in this manner, an induction electric heating device or the like is attached to the hearth roll at the cooling strip exit side of the pretreatment furnace of the steel strip or at the snout part (inclined part), ie, after the heat treatment. After heating both ends of the steel strip in the width direction and bringing the hearth roll into contact with the steel strip, both ends of the steel strip in the width direction are heated to a predetermined temperature and then introduced into the plating bath. As a result, alloying at both ends in the width direction of the steel strip is promoted, and the temperature can be controlled to a temperature at which uniform alloying can be performed reliably during alloying.

Next, an example of the method of the present invention will be described with reference to the drawings. In FIG. 1, the steel strip 2 on the exit side of the pretreatment filter cooling zone 1 of the continuous hot-dip galvanizing equipment 2
As shown in (1), an induction electric heating device 4 is provided as a heating body, and both ends in the width direction of the steel strip 2 are heated and heated, and the steel strip 2 is guided to a hot-dip galvanizing bath 5 for plating. After the coating amount of the plated steel strip 2a is controlled to a predetermined amount, it is guided to the alloying furnace 7 and heated to uniformly diffuse zinc-iron by heat diffusion of iron into the plating layer.

[0011]

Next, examples of the method of the present invention will be described together with comparative examples.

[Table 1]

[0012]

[Table 2] Continued from Table 1

Note 1: Examples 1 and Comparative Example 2 were wound at a normal winding temperature (550 ° C.) in a continuous hot rolling process.
A cold-rolled steel strip made of low-carbon Al-killed steel with a thickness of 0.8 mm and a width of 1200 mm. Example 2 and Comparative Example 1 are steel strips in which the both ends in the steel strip width direction have been cooled by changing the steel strip width in the pretreatment furnace. In Example 3 and Comparative Example 3, ultra-low carbon steel (C: 0.003%, Mn: 0.15%, Si: 0.0
02%, P: 0.01%, S: 0.01%, Ti: 0.
015%, Nb: 0.015%, remaining Fe and other impurities) in a continuous hot hot rolling step at a winding temperature of 700 ° C., using a hot-rolled steel strip as a material, having a sheet thickness of 0.8 mm and a sheet width of 120.
Each of the 0 mm cold-rolled steel strips was subjected to an alloying treatment after plating as shown in the above table. Note 2: The steel strip temperature is the temperature at which the steel strip is introduced into the plating bath (Al: 0.11% residual zinc and other impurities). The heating temperature was raised by an induction electric heater provided inside a hearth roll on the cooling outlet side (after the heat treatment furnace). In the comparative example,
At the inlet of the alloying furnace, both ends in the width direction of the plated steel strip were heated by a gas flame. Note 3: The alloying furnace was alloyed by heating the gas (coke oven gas). Note 4: The end of the iron content and the plating amount is the end of the steel strip width direction 50 mm.

[0014]

According to the method of the present invention, a uniform zinc-iron alloyed hot-dip galvanized steel strip (plate) can be reliably produced. Further, the quality of the product can be improved and the yield can be improved. Furthermore, the both ends of the steel strip in the width direction are heated and heated,
It can be easily done by alloying after plating,
An excellent effect is obtained such that it can be reliably performed on an industrial scale and can be advantageous in terms of cost.

[Brief description of the drawings]

FIG. 1 is a side view showing an example of the method of the present invention.

FIG. 2 is a lateral side view of a hearth roll.

Continued on the front page (72) Inventor Toshikazu Mashimo 5-3 Tokai-cho, Tokai-shi, Aichi Prefecture Nippon Steel Corporation Nagoya Works (72) Inventor Atsushi Sokutoku 5-3 Tokai-cho, Tokai-shi, Aichi Prefecture New Japan Inside Nagoya Works, Steel Works

Claims (2)

[Claims] 1. After the heat treatment of a steel strip, both ends in the width direction of the steel strip are heated from the center to a hot-dip galvanizing bath, plated, controlled to a predetermined adhesion amount, and then heat-alloyed. A method for producing a zinc-iron alloyed hot-dip galvanized steel sheet. 2. The method for producing a zinc-iron alloyed hot-dip coated steel sheet according to claim 1, wherein the both ends in the width direction of the steel strip are heated from 10 to 50.degree.