JPH0645852B2 - Method for producing alloyed hot-dip galvanized steel strip - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing an alloyed hot-dip galvanized steel strip. Specifically, the temperature of the steel strip immersed in the zinc bath is adjusted in the width direction to obtain an alloyed hot-dip galvanized steel strip having a uniform degree of alloying over the entire surface. A method for manufacturing a belt.

<Prior art> Alloyed hot-dip galvanized steel in which the galvanized layer is Fe—Zn alloyed again by heat treatment in order to improve the coating properties, coating film adhesion, weldability, etc. of the hot-dip galvanized steel strip. Belts are known.

An example of a method of manufacturing such an alloyed hot-dip galvanized steel strip will be described with reference to FIG. 1. First, a steel strip A is annealed in a furnace 1.
It is heated to a predetermined temperature by passing through 2. The annealing furnace 12 includes a heating zone 18 and a cooling zone 20 arranged behind the heating zone 18 (hereinafter, the rear side is the downstream side in the moving direction of the steel strip).
The steel strip A is first heated in the heating zone 18 to about 800 ° C. mainly by the radiant tube, and then cooled in the cooling zone 20 to about 470 ° C. by a gas jet method or the like.

The steel strip A heated and cooled to a predetermined temperature in the annealing furnace 12 is then immersed in the zinc bath 14 at about 460 ° C., and molten zinc is attached to its surface.

The steel strip A to which the molten zinc has been adhered is pulled up from the zinc bath 14 in a substantially vertical direction, and the amount of zinc adhered is controlled by the gas injection nozzle 22 by gas injection, and is provided behind (above) it. About 500 ℃ in alloying furnace 16
It is reheated to be alloyed and sent to the next step.

This alloying treatment forms an Fe—Zn alloy layer by diffusing the iron of the steel strip A into the galvanized layer in order to improve the coatability of the galvanized steel strip A as described above. It is a thing. Such alloying is started from the moment the steel strip A is immersed in the zinc bath 14 and is completed by reheating in the alloying furnace 16.

Here, the degree of progress of the alloy in this alloying, that is, the degree of alloying can be quantitatively evaluated by the concentration of iron contained in the galvanized layer. Therefore, in a normal galvannealing apparatus, for example, a measuring apparatus for the degree of alloying (alloying degree meter 24) is arranged at the exit of the alloying furnace 16 to alloy the steel strip that has been alloyed. Measure the degree,
The measured value is used to determine whether the product is acceptable or not, or the reheating temperature in the alloying furnace 16 is adjusted.

<Problems to be Solved by the Invention> By the way, when manufacturing an alloyed hot-dip galvanized steel strip by such a method, uneven alloying degree in the width direction of the steel strip A, especially alloying near both ends in the width direction There are many cases where there is a shortage.

The unevenness of the alloying degree such as the occurrence of the insufficient portion of the alloying degree becomes the metallic color unevenness, and when the color coating is performed later, it becomes the uneven glossiness, and the appearance of the product is remarkably deteriorated.

Such unevenness in alloying degree in the width direction of the steel strip A is caused by uneven heating temperature in the width direction during reheating for alloying treatment. When adjusting the amount of molten zinc deposited by the gas throttle nozzle, both end portions in the width direction are particularly supercooled by the jet gas, and as it is reheated uniformly in the width direction in the alloying furnace, Both ends in the width direction are insufficiently heated.

Cold air is entrained as the steel strip is carried into the alloying furnace that performs the alloying process.

Is considered to be the main cause.

In order to prevent such unevenness of the alloying degree in the width direction,
For example, Japanese Patent Application Laid-Open No. 50-44931 discloses an alloying furnace 16
"Auxiliary burner for heating that is vertically arranged along the length direction of the steel strip and that can be heated and adjusted in the width direction of the steel strip" heats the place where alloying degree may be uneven. A method for preventing the occurrence of metallic color unevenness is disclosed.

However, this method has low thermal efficiency because it uses burner combustion in the atmosphere.

It is necessary to secure a space for arranging the burner between the nozzle for adjusting the amount of molten zinc adhered (the nozzle 22 for gas restriction) and the alloying furnace 16. Moreover, since the temperature of the steel strip A decreases during that time (the auxiliary burner does not heat the whole), it is necessary to use a large amount of fuel in the alloying furnace 16 to cover it, or to reduce the line speed, Thermal efficiency and productivity decrease.

Since the flame of the auxiliary burner locally hits the surface of the steel strip A, a flame pattern is generated and appearance defects are likely to occur.

There are problems such as.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing an alloyed hot-dip galvanized steel strip capable of efficiently eliminating unevenness of the alloying degree in the width direction of the steel strip. is there.

<Means for Solving the Problems> In order to achieve the above object, the inventors of the present invention have conducted extensive studies and changed the temperature of the steel strip when immersed in a zinc bath to achieve galvanization in an alloying furnace. To find that the alloying degree of the galvanized layer can be controlled by controlling the temperature distribution of the steel strip immersed in the zinc bath in the width direction. Thus, the present invention has been completed.

That is, according to the present invention, after heating a steel strip to a predetermined temperature in an annealing furnace and then cooling the steel strip to a predetermined temperature, the steel strip is immersed in a zinc bath, and then a zinc injection amount is controlled by gas injection from a gas drawing nozzle. After that, in the method for producing an alloyed hot-dip galvanized steel strip that undergoes a synthesizing treatment, cooling after heating the steel strip is adjusted in the width direction of the steel strip, and the temperature of the steel strip immersed in the zinc bath is set in the width direction. A method for producing an alloyed hot-dip galvanized steel strip is provided.

Further, the alloying degree distribution in the width direction of the steel strip is measured after the alloying treatment, and cooling after heating of the steel strip makes the alloying degree distribution in the width direction of the steel strip uniform according to the measurement result. Thus, it is preferable to adjust the width of the steel strip and the temperature of the steel strip immersed in the zinc bath in the width direction.

<Operation> FIG. 1 shows a conceptual diagram of an example of an alloying hot-dip galvanizing apparatus for carrying out the method for producing an alloyed hot-dip galvanized steel strip according to the present invention.

The alloying hot-dip galvanizing apparatus 10 (hereinafter referred to as the plating apparatus 10) shown in FIG.
And a zinc bath 14 and an alloying furnace 16.

The annealing furnace 12 includes a heating zone 18 and a cooling zone 20. The steel strip A is first heated by the heating zone 18 to about 800 ° C. also as annealing, and then cooled in the cooling zone 20 to about 470 ° C. by the gas jet cooling method.

Here, in the present invention, the cooling after the heating is performed by the steel strip A.
So as to adjust the temperature distribution in the width direction (hereinafter, simply referred to as the width direction), preferably in accordance with the distribution in the width direction of the alloying degree of the plating layer measured by the alloying degree meter 24 described later. The temperature distribution is adjusted in the width direction. The cooling zone 20 and the method of adjusting the temperature distribution will be described in detail later.

Next, the steel strip A is immersed in the zinc bath 14 at about 460 ° C. as it is, and molten zinc is attached thereto.

The steel strip A to which the molten zinc has adhered in the zinc bath 14 is pulled up in a substantially vertical direction, gas is jetted from the gas restricting nozzle 22 to control the amount of molten zinc adhered, and is arranged above (downstream) thereof. Sent to the alloying furnace 16.

The steel strip A is reheated to about 500 ° C. in the alloying furnace 16, the galvanized layer is alloyed, and transported to the next step.

Furthermore, in the plating apparatus 10 of the illustrated example, an alloying degree meter 24 is arranged above the alloying furnace 16 as a preferable mode, and the alloying degree of the galvanized layer after the alloying treatment is measured in the width direction, The alloying degree distribution is measured.

In the method for producing an alloyed hot-dip galvanized steel strip of the present invention, as described above, the cooling in the cooling zone 20 after the heating by the heating zone 18 in the annealing furnace 12 causes the temperature distribution in the width direction of the steel strip A. The temperature distribution is adjusted and preferably adjusted in the width direction according to the distribution of the alloying degree in the width direction measured by the alloying degree meter 24.

FIG. 2 shows the zinc bath 14 which is the basis of the technical idea in the method for producing an alloyed hot-dip galvanized steel strip according to the present invention.
The relationship between the temperature of the steel strip A in the alloying furnace 16 on the inlet side and the degree of alloying of the galvanized layer is conceptually shown with the temperature of the steel strip A immersed in the steel sheet as a parameter.

In FIG. 2, the horizontal axis represents the temperature of the steel strip on the inlet side in the alloying furnace 16, and the vertical axis represents the degree of alloying of the galvanized layer. Curves A, B and C show the case where the temperature of the steel strip A immersed in the zinc bath 14 is different as a parameter, the curve A has the highest immersion temperature in the zinc bath 14, and the curve C has the highest immersion. The temperature is low.

As is clear from FIG. 2, when the in-reacting time of the steel strip A in the alloying furnace 16 is the same, the alloying degree increases as the inlet steel strip temperature rises.

Further, as indicated by the curves A, B and C in the figure as parameters, when the temperature of the steel strip A immersed in the zinc bath 14 becomes higher, the alloying degree also increases. That is, zinc bath 1
By adjusting the temperature of the steel strip A immersed in No. 4, it is possible to adjust the alloying degree of the galvanized layer.

From this FIG. 2, it is possible to easily understand the cause of the uneven alloying degree in the width direction of the galvanized layer which has occurred in the conventional manufacturing method.

That is, the steel strip A, which is immersed in the zinc bath 14 and to which the molten zinc is adhered, is pulled up from the zinc bath 14 in a substantially vertical direction as described above, and zinc is drawn by the throttle gas injected from the gas throttle nozzle 22. The amount of adhesion is adjusted.

Here, since the temperature of the widthwise end portions of the steel strip A tends to be lower than that of the central portion due to the drawing gas, the temperature of the widthwise end portions of the steel strip A carried into the alloying furnace 16 becomes low. If gone, for example the inlet side steel strip temperature in the alloying furnace 16 the central portion is T _C, when the both ends has become a T _E, the temperature of the steel strip a in the alloying furnace 16 in curve B when the temperature was the indicated alloy degree central portion F _C, the both end portions becomes a F _E, a low alloyed at both ends,
That is, the alloying degree becomes uneven in the width direction.

In the method disclosed in Japanese Unexamined Patent Publication No. 50-44931, the above-mentioned predetermined auxiliary heating burner is arranged in front of the alloying furnace to heat the low temperature part of the steel strip to bring it into the alloying furnace. The purpose of this is to make the temperature of the steel strip to be uniform over the entire width direction and to make the degree of alloying uniform. However, as described above, this method has problems such as a decrease in thermal efficiency and an appearance defect such as a flame pattern.

On the other hand, the alloying hot-dip galvanizing method of the present invention can adjust the degree of alloying by the temperature of the steel strip A immersed in the zinc bath 1, as shown by the curves A, B and C as parameters. The finding is that the temperature distribution of the steel strip A before being immersed in the zinc bath 14 is adjusted in the width direction by cooling the steel strip A in the cooling zone 20, thereby adjusting the alloying degree of the zinc plating layer.

That is, when the target degree of alloying is F _C , the temperature of the inlet side steel strip of the steel strip A in the alloying furnace 16 is T _{C at the} center.
If both end portions become T _E , the alloying degree becomes F _{C at} the central portion and F _{E at} both end portions as described above. Here, by adjusting the temperature distribution of the steel strip A immersed in the zinc bath 14 to the normal temperature shown by the curve B at the center and the temperature shown by the curve A at both ends, which is higher than that, the alloy the degree central portion and both end portions and F _C together, thereby obtaining a hot-dip galvanized steel strip having a predetermined alloyed over the entire surface.

According to this method, since it is only necessary to adjust the temperature distribution in the width direction of the steel strip A immersed in the zinc bath 14 by the cooling zone 20, a separate heating (cooling) device is not required. Further, since the gas jet cooling method or the like is usually applied as the cooling method in the cooling zone 20, the temperature control response is fast and the loss is very small. Furthermore, according to this method,
There is no need to adjust the reheating temperature of the alloying furnace 16 or change the line speed of the steel strip A, and the production efficiency of the galvannealed steel strip does not decrease.

In the present invention, the adjustment of the temperature distribution in the width direction of the steel strip A in the cooling zone 20 is preferably performed by adjusting the width of the alloying degree of the steel strip A measured by the alloying degree meter 24 as described above. It is preferable to carry out according to the distribution of directions.

With such a structure, the present invention can be more easily carried out and the production control can be suitably performed. Therefore, the galvannealed alloy having a uniform degree of alloying over the entire surface can be obtained. It is possible to manufacture the steel strip better and surely.

The present invention is not limited to this. For example, when there is little change in the temperature distribution in the width direction of the steel strip A after the adjustment of the zinc deposition amount by the gas throttle nozzle 22, the steel produced by the cooling zone 20 is used. The zone A may be cooled by a temperature distribution preset so that the alloying degree of the plating layer becomes uniform in the width direction, and the alloying furnace 1 may be formed by various known methods.
The temperature distribution in the width direction of the steel strip A on the 6th entry side may be measured, and the temperature distribution in the width direction of the steel strip A immersed in the zinc bath 14 may be adjusted according to the result.

FIG. 3a shows a schematic longitudinal sectional view of a steel strip A of an example of the cooling strip 20 of the apparatus shown in FIG. 1, FIG. 3b a schematic plan view thereof, and further FIG. 3c a steel strip A. A cross-sectional schematic view in the width direction is shown.

In the cooling zone 20, a gas chamber 26 is arranged so as to sandwich the traveling path of the steel strip A. The gas chamber 26 has a beak-shaped slit having a longitudinal direction in a direction perpendicular to the width direction of the steel strip A. A plurality of shaped gas nozzles 28 are arranged in parallel. That is, the heated gas for cooling the steel strip A is injected from the gas chamber 26 through the gas nozzle 28 and sprayed onto the steel strip A.

In addition, at a cooling gas introduction portion of the gas nozzle 28, that is, at a connection portion between the gas chamber 26 and the gas nozzle 28, a seal plate 30 that is movable in the width direction (arrow W) of the steel strip A.
Are placed.

In the cooling zone 20 of the illustrated example, the opening portion of the gas nozzle 28 is adjusted by moving the sealing plate 30, and as described above, the temperature distribution in the width direction of the steel strip A immersed in the zinc bath 14 and further Adjusts the blowing amount and the blowing position of the cooling gas according to the width of the steel strip A.

In addition, in the cooling zone 20 applied to the method for producing the galvannealed steel strip of the present invention, the method of adjusting the spraying amount and the spraying position of the cooling gas is limited to the method using the seal plate 30 described above. However, various methods such as a method of providing the gas nozzle 28 with blades for adjusting the injection direction of the cooling gas are applicable. Further, it is not limited to the one that adjusts only the widthwise both ends of the steel strip A as in the illustrated example, and a plurality of sealing plates 30 are configured to be detachable, and the blowing amount of the cooling gas at the center in the widthwise direction. May be adjusted to adjust the temperature distribution of the steel strip A.

Further, the seal plate 30 may not be provided, and the temperature distribution of the cooling gas injected from the gas nozzle 28 may be adjusted according to the desired temperature distribution of the steel strip A.

<Example> Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

An alloyed hot-dip galvanized steel strip was produced using the plating apparatus 10 shown in FIG.

Steel strip A having a thickness of 0.8 mm and a width of 1500 mm was used, and was run at a line speed of 90 mpm.

The steel strip A was heated to 800 ° C. in the heating zone 18 of the annealing furnace 12, then cooled to 470 ° C. to 500 ° C. in the cooling zone 20, and then immersed in the zinc bath 14 having a bath temperature of 460 ° C.

The steel strip A immersed in the zinc bath 14 is discharged from the zinc bath 14 by pulling it up in the vertical direction, and then the amount of zinc deposited is adjusted to 45 g / m ² by the gas restricting nozzle 22 and then 500 in the alloying furnace 16. It was reheated to ℃ and alloyed. The heating time in the alloying furnace 16 was 12 seconds.

Using the above as standard conditions, the following points were changed to manufacture an alloyed hot-dip galvanized steel strip.

[Inventive Example] In the cooling zone 20, the temperature at the widthwise end portions 50 mm of the steel strip A immersed in the zinc bath 14 is about 30 as compared with the central portion.
The seal plate 30 was set so that the temperature became higher by 0 ° C., and the steel strip A was cooled.

[Comparative Example 1] As shown in Japanese Patent Laid-Open No. 50-44931, an alloying furnace 1
Auxiliary burners are installed at both ends in the front of 6 in the width direction.
After heating both ends of the steel strip A at 0 × 10 ³ kcal / h, 100 × 10 ³ kcal / h in total, the steel strip A was loaded into the alloying furnace 16.

Comparative Example 2 An alloyed hot-dip galvanized steel strip was produced by the conventional method without changing any of the standard conditions described above.

Regarding the galvannealing produced under the above respective conditions, the alloying degree in the width direction of the steel strip A is measured by the alloying degree meter 24 arranged above the alloying furnace 16 to measure the unevenness of the alloying degree. In addition, the amount of fuel used by the alloying furnace 16 and the auxiliary burner was measured. The alloying degree meter 24 used was one that measures the alloying degree by an X-ray diffraction method.

The results are shown in Table 1.

As shown in Table 1, in the example of the present invention, the cooling zone 20
The cooling conditions are adjusted so that the temperature at both ends 50 mm of the steel strip A immersed in the zinc bath 14 is about 3 compared to the center.
Since the temperature was increased by 0 ° C., the temperature distribution in the width direction of the steel strip A when being carried into the alloying furnace 16 was 440 ° C. at the central part and 420 ° C. at both ends, which were lower at both ends, but the auxiliary burner, alloy Even if the reheating temperature in the chemical conversion furnace 16 was not adjusted, the alloying zinc-plated layer of the obtained steel strip had no uneven alloying degree.

In Comparative Example 1, since the auxiliary burner was arranged, the steel strip A carried into the alloying furnace 16 had no uneven temperature distribution, and thus the alloyed zinc-plated layer of the obtained steel strip A was alloyed. The unevenness does not occur. However, this requires 100 x 10 ³ kca because it requires an auxiliary burner.
Since the fuel of 1 / h is applied and the distance from the zinc bath 14 to the alloying furnace 16 is lengthened by the amount of the auxiliary burner installed, the temperature of the steel strip carried into the alloying furnace 16 is 430 ° C. As compared with the other examples, more fuel was required in the alloying furnace 16 than in the other examples in order to obtain a predetermined degree of alloying.

Further, in Comparative Example 2 which is a normal method, the temperature distribution in the width direction of the steel strip A when it is carried into the alloying furnace 16 is 440 ° C. at the central portion and 420 ° C. at both ends, and the both end portions are Became lower, and the alloying galvanized layer of the obtained steel strip had uneven alloying degree.

From the above results, the effect of the present invention is clear.

<Effects of the Invention> As described in detail above, according to the method for producing an alloyed hot-dip galvanized steel strip of the present invention, a good alloyed hot-dip galvanized steel strip having a uniform degree of alloying over the entire surface is obtained. It is possible to manufacture easily and stably.

Moreover, since there is no need to adjust the reheating temperature in the alloying furnace and no auxiliary burner or the like is used, no extra fuel is used and there is no appearance defect such as a flame pattern.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of an example of an alloying hot-dip galvanizing apparatus for carrying out the method for producing an alloyed hot-dip galvanized steel strip according to the present invention. FIG. 2 is a conceptual diagram showing the relationship between the temperature of the steel strip on the alloying furnace entrance side and the degree of alloying of the galvanized layer with the temperature of the steel strip immersed in the zinc bath as a parameter. FIG. 3a is a schematic sectional view in the longitudinal direction of a steel strip of an example of a cooling zone applied to the alloy hot-dip galvanizing apparatus shown in FIG. 1, FIG. 3b is the same schematic plan view, and FIG. 3c is the same. It is a schematic sectional drawing of the width direction of a steel strip. Explanation of symbols 10 ... Alloying hot dip galvanizing equipment, 12 ... Annealing furnace, 14 ... Zinc bath, 16 ... Alloying furnace, 18 ... Heating zone, 20 ... Cooling zone, 22 ... For gas restriction Nozzle, 24 ... Alloying degree meter, 26 ... Gas chamber, 28 ... Gas nozzle, 30 ... Seal plate, A ... Steel strip

Claims (2)

[Claims] 1. A steel strip is heated to a predetermined temperature in an annealing furnace, cooled to a predetermined temperature, and then immersed in a zinc bath,
Then, after controlling the amount of zinc deposited by gas injection from a gas restricting nozzle, in a method for producing an alloyed hot-dip galvanized steel strip which performs an alloying treatment, cooling after heating the steel strip in the width direction of the steel strip. A method for producing an alloyed hot dip galvanized steel strip, which comprises adjusting the temperature of the steel strip immersed in the zinc bath in the width direction. 2. The alloying degree distribution in the width direction of the steel strip is measured after the alloying treatment, and cooling of the steel strip after heating is performed according to the measurement result to determine the alloying degree distribution in the width direction of the steel strip. The method for producing an alloyed hot dip galvanized steel strip according to claim 1, wherein the width of the steel strip is adjusted to be uniform, and the temperature of the steel strip immersed in the zinc bath is adjusted in the width direction.