JP3302265B2 - Manufacturing method of zinc-iron alloyed hot-dip coated steel sheet - 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 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]

However, as described above,
Even if both ends of the plated steel strip are heated on the inlet side of the alloying furnace and guided to the alloying furnace, it is difficult to reliably perform the alloying process uniformly in the width direction of the steel strip even if the alloying process is performed. As a result of various studies by the present inventors on the reason, there is a steel strip whose workability is improved 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 at high temperature, both ends of the steel strip come into contact with the atmosphere after the winding and a large amount of oxides are generated, and the next step of pickling increases the surface roughness of both ends of the steel strip, and the activity increases. S in steel (in steel plate)
i and P are concentrated, and Si-based and P-based oxides are generated in the surface layer of the steel sheet (band) during the heating and cooling processes in the heat treatment before hot-dip galvanizing, and the Si-based and P-based oxides are formed in the alloying process after plating. It has been clarified that the system oxide acts as a barrier, hinders the thermal diffusion of iron into the plating layer, and becomes 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, when the steel strip to be plated is changed from narrow to wide, both ends of the changed wide steel strip come into contact with the low-temperature part of the hearth roll, and the lower temperature is lower than that in 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 in order to advantageously solve such problems, and has been carried out at a high temperature after continuous hot rolling.
Heating by heat treatment before hot-dip galvanizing,
During the cooling process, Si-based and P-based oxides are formed on the surface of the steel strip.
For even a steel strip, and Atsushi Nobori to strip both ends prior to introduction into the molten zinc plating bath, by treating plating after heat alloying, to provide a method which can uniformly alloying treatment It is intended for.

[0005]

The feature of the method of the present invention resides in that high-temperature winding is performed after continuous hot rolling.
Heating and cooling in the heat treatment before hot-dip galvanizing
A steel strip in which Si-based and P-based oxides are formed in the surface layer of the steel strip is heat-treated at both ends in the width direction of the steel strip from the center at 10 to 5
0 ℃ Atsushi Nobori to molten zinc Me and have electrically to the molten zinc plating bath
To promote the formation of the initial alloy layers in Kki Yokunai, by treating heat alloying after the, message of the steel strip width direction end portions
The iron content of the coating layer is almost the same as the iron content of the central plating layer.
Zinc and wherein the constant and the child - is a manufacturing method of iron alloyed hot dip plated steel sheet.

[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. those that can be subjected to alloying treatment.

[0007]

[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), that is, 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 Figure 1, such is shown in Figure 2 the cooling zone 1 outlet side hearth rolls 3,3a pretreatment furnace of the continuous galvanizing line, the width direction of the strip 2 an induction electric heating device 4 internally provided as the heating member Both ends are heated and heated, and hot-dip galvanizing bath 5
After applying a plating to the steel strip 2a, a gas is injected from the nozzle 6 to control the coating weight of the plated steel strip 2a to a predetermined amount, and then guided to the alloying furnace 7 and heated to thermally diffuse iron into the plating layer. And uniformly apply a zinc-iron alloying treatment .

[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: In both Examples and Comparative Examples, ultra low carbon steel (C: 0.003%, Mn: 0.15%, Si:
0.002%, P: 0.01%, S: 0.01%, T
i: 0.015%, Nb: 0.015%, remaining Fe and other impurities) in a continuous hot hot rolling step at a winding temperature of 700 ° C.
Each of the cold-rolled steel strips having a thickness of 0.8 mm and a width of 1200 mm using the hot-rolled steel strip taken as a raw material as described above 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, after continuous hot rolling,
High-temperature winding allows heat treatment before hot-dip galvanizing.
Oxidation of Si-based and P-based on steel strip surface layer during heating and cooling process
A uniform zinc-iron alloyed hot-dip galvanized steel strip (plate) can be reliably produced even for a steel strip in which a product is generated .
Further, the quality of the product can be improved and the yield can be improved. Furthermore, it is easy to heat up the both ends in the width direction of the steel strip, and it is easy to perform the alloying treatment after plating, and it is reliable on an industrial scale, and it is advantageous in terms of cost. The effect is obtained.

[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.

──────────────────────────────────────────────────続 き Continuing 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 Nippon Steel Corporation Nagoya Works (56) References JP-A-5-117833 (JP, A) JP-A-3-177554 (JP, A) (58) Fields studied (Int. Cl. ⁷ , (DB name) C23C 2/00-2/40

Claims (1)

(57) [Claims] 1. High temperature winding after continuous hot rolling
Heating and cooling process in heat treatment before hot-dip galvanizing
The steel strip in which Si-based and P-based oxides were formed on the surface layer of the steel strip by heat treatment, and both ends of the steel strip in the width direction at the later stage of the heat treatment from the central part by one.
0 to 50 ° C. Atsushi Nobori to melting have electrically to the molten zinc plating bath
Promotes the formation of an initial alloy layer in the galvanizing bath,
By treating heat alloying after, the strip width direction end portions
The iron content of the plating layer at the center is
A method for producing a zinc-iron alloyed hot-dip coated steel sheet, which is substantially equivalent .