JPH072983B2 - 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, in the production of galvannealing by continuous plating, by adjusting the immersion length of the steel strip in the zinc bath according to changes in the alloying temperature, alloying melting with a constant degree of alloying The present invention relates to a method for manufacturing an alloyed hot-dip galvanized steel strip that can obtain a galvanized steel strip.

<Prior Art> An alloyed hot-dip galvanized steel strip in which a galvanized layer is Fe—Zn alloyed is known in order to improve paintability, coating film adhesion, weldability, etc. of the hot-dip galvanized steel strip.

An example of the method for producing such an alloyed hot-dip galvanized steel strip will be described with reference to FIG.
Is heated to a predetermined temperature. The annealing furnace 12 includes a heating zone 18 and its rear side (hereinafter, the rear side means a steel strip A).
The steel strip A is first heated to about 800 ° C. in the heating zone 18 and then cooled to about 470 ° C. in the cooling zone 20.

Steel strip A heated / cooled to a predetermined temperature in the annealing furnace 12
Is then immersed in a zinc bath 14 at about 460 ° C. and molten zinc is deposited on its surface.

The steel strip A to which the molten zinc is attached is pulled up from the zinc bath 14 in a substantially vertical direction, the amount of zinc attached is controlled by the throttle nozzle 22, and in the alloying furnace 16 provided at the rear (upper) thereof. It is reheated to about 500 ° C, alloyed and sent to the next step.

As described above, this alloying treatment forms the Fe-Zn alloy layer by diffusing the iron of the steel strip A into the galvanized layer in order to improve the paintability of the galvanized steel strip. is there. Note that 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 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 device for measuring the degree of alloying (alloying degree meter 24) is arranged at the outlet of the alloying furnace 16 to alloy the steel strip that has been alloyed. The temperature is measured, and the product pass / fail judgment is made using the measured value, or the reheating temperature in the alloying furnace 16 is adjusted.

For example, in JP-A-62-123935, the alloying degree of a galvanized layer is measured using an alloying degree meter to which X-ray diffraction is applied, and the result is measured as a reheating temperature in an alloying furnace 16 and / or
Alternatively, a method of feeding back the time of the steel strip A in the furnace is disclosed. That is, this method, by measuring the alloying degree of the galvanized layer, even when the thickness and width of the steel strip to be processed changes and the temperature of the alloying furnace 16 changes, in the alloying furnace 16 By adjusting the combustion amount in the alloying furnace 16 so that the reheating temperature becomes constant, or by adjusting the alloying treatment temperature even when the amount of molten zinc deposited changes, a constant degree of alloying is maintained. It is possible to obtain the alloyed hot-dip galvanized steel sheet.

<Problems to be Solved by the Invention> However, as in the method disclosed in JP-A-62-123935, the galvanizing layer is alloyed by adjusting the heating temperature in the alloying furnace 16. There are various problems in the method of setting the degree to a predetermined target value.

That is, the alloying furnace 16 is generally composed of a wall of refractory insulation bricks having a large heat capacity, and the heating of the steel strip A is mainly radiative heat transfer from this wall. Therefore, the alloying furnace 16
In order to adjust the reheating temperature in, it is necessary to change the temperature of the wall having a large heat capacity, so that it takes a very long time to adjust the temperature.

Therefore, the steel strip A that has passed through the alloying furnace 16 during that time (during temperature adjustment) suffers from poor product quality such as insufficient alloying or excessive alloying, and a good alloyed hot-dip galvanized steel strip can be obtained. Can not.

Further, when the reheating conditions in the alloying furnace 16 are greatly changed, it is necessary to pass a dummy steel strip called a strip material in order to avoid the above-mentioned inconvenience, so that the productivity is greatly impaired.

There is also a method of adjusting the alloying degree to a predetermined target value by adjusting the in-furnace time of the steel strip A, but this method inevitably changes the line speed of the steel strip movement, which also impedes productivity. In addition, it becomes a factor that hinders the control of the amount of molten zinc adhered to the steel strip A, which is a great disadvantage.

An object of the present invention is to solve the above-mentioned problems of the prior art. Even when the plate thickness or width of the steel strip changes, or when the amount of molten zinc in the steel strip changes, insufficient alloying occurs. Providing a method for producing alloyed hot-dip galvanized steel strip that can obtain good alloyed hot-dip galvanized steel strip without causing quality defects such as over-alloying and over-alloying, and does not impede productivity To do.

<Means for Solving the Problems> In order to achieve the above-mentioned object, the inventors of the present invention have made extensive studies, and by changing the dipping time of the steel strip in a zinc bath, the alloy of the zinc plating layer in the alloying furnace is changed. It was found that the degree of galvanization changes, and therefore the degree of alloying of the galvanized layer is controlled by adjusting the dipping time of the steel strip in the zinc bath, that is, the dipping length when the transport speed of the steel strip is constant. The present invention has been completed by finding out what can be done.

That is, according to the first aspect of the present invention, a steel strip heated to a predetermined temperature in an annealing furnace and then cooled to a predetermined temperature is immersed in a zinc bath connected to the annealing furnace, and then the zinc adhesion amount is controlled. After that, in a method for producing an alloyed hot-dip galvanized steel strip that is continuously alloyed, the relationship between the treatment temperature in the alloying treatment and the immersion time in the zinc bath is defined by the alloying degree of zinc plating being predetermined. Of the alloyed hot dip galvanized steel strip characterized in that the immersion length of the steel sheet in the zinc bath is determined from the threading speed of the steel sheet according to the relationship. A manufacturing method is provided.

In a second aspect of the present invention, a steel strip that has been heated to a predetermined temperature in an annealing furnace and then cooled to a predetermined temperature is immersed in a zinc bath connected to the annealing furnace, and then the zinc adhesion amount is controlled. After that, in a method for producing an alloyed hot-dip galvanized steel strip which is continuously alloyed, the degree of alloying of the galvanizing after the alloying is measured, and the galvanization is alloyed according to the measurement result. Provided is a method for producing an alloyed hot-dip galvanized steel strip, wherein the immersion length of the steel strip immersed in the zinc bath is determined from the threading speed of the steel sheet so that the degree becomes a predetermined target value.

<Operation> Hereinafter, the method for producing the galvannealed steel strip according to the present invention will be described in detail.

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 shown in FIG. 1 (hereinafter,
The plating apparatus 10 is basically an annealing furnace 12 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 to about 80 by the heating zone 18 and also serves as an annealing.
It is heated to 0 ° C. and then cooled by cooling zone 20 to about 470 ° C. in a gas jet cooling manner.

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

Here, the zinc bath 14 is configured so that the immersion length of the steel strip A in the zinc bath 14 in molten zinc (hereinafter referred to as the immersion length) can be changed by adjusting (elevating) the position of the sink roll 26. It

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

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

Further, in the plating apparatus 10 of the illustrated example, an alloying degree meter 24 is arranged above the alloying furnace 16 to measure the alloying degree of the galvanized layer after the alloying treatment.

Here, in the first aspect of the present invention, depending on the relationship between the preset reheating temperature in the alloying furnace 16 and the immersion time in the zinc bath 14, and in the second aspect, alloying is performed. The immersion length in the zinc bath 14 is set and adjusted according to the sheet passing speed of the steel sheet A so that the desired degree of alloying is obtained according to the measurement result by the pedometer 24.

FIG. 2 shows an alloying furnace in the method for producing a galvannealed steel strip according to the present invention, which is the basis of the technical concept of the steel strip A, in which the immersion time of the zinc bath 14 in the molten zinc is a parameter. The relation between the treatment temperature (reheating temperature) in 16 and the alloying degree of the galvanized layer is conceptually shown.

In FIG. 2, the horizontal axis represents the reheating temperature in the alloying furnace 16 and the vertical axis represents the degree of alloying of the zinc plating layer. Further, the curve A as a parameter indicates the steel for the zinc bath 14. If the immersion time of zone A is long, and curve B is zinc bath
It shows the relationship between the reheating temperature and the degree of alloying when the immersion time of the steel strip A in 14 is short.

As is clear from FIG. 2, the steel strip A in the alloying furnace 16
When the in-furnace time is the same, the alloying degree increases as the reheating temperature in the alloying furnace 16 increases.

Further, as shown by the curves A and B in the figure as parameters, when the immersion time of the steel strip A in the zinc bath 14 becomes longer,
After all, the alloying degree increases. That is, by adjusting the immersion time of the steel strip A in the zinc bath 14, the degree of alloying of the zinc plating layer can be adjusted.

When the strip running speed of the steel strip A is constant, for example, the steel strip A
The thickness of the changes from thin to thick, etc.
When the reheating temperature in the alloying furnace 16 is lowered from T ₁ to T ₂ , when the steel strip A is immersed in the alloying furnace 16 for the time shown by the curve B, the alloying degree is also increased. It drops from F ₁ to F ₂ .

Here, in the conventional method, when the temperature change of the steel strip in such an alloying furnace occurs, by adjusting the temperature of the alloying furnace 16, for example, when the temperature is lowered as described above. Was increasing the reheating temperature to T ₁ again by a method such as increasing the amount of fuel input to the alloying furnace 16. However, in this method, it takes time to raise (lower) the reheating temperature to a predetermined temperature, and during that period, alloying becomes insufficient (alloying excessively), as described above.

On the other hand, in the alloying hot-dip galvanizing method of the present invention, the immersion time of the steel strip A in the zinc bath 14, specifically, the strip running speed of the steel strip A is constant, so the immersion length is adjusted. By doing so, the degree of alloying of the steel strip A is adjusted.

That is, when the reheating temperature of the steel strip A in the alloying furnace 16 decreases from T ₁ to T ₂ , the immersion time of the steel strip A in the zinc bath 14 is represented by the curve B from the time represented by the curve B. The alloying degree is increased from F ₂ to F ₁ by adjusting the time to be longer, and a hot-dip galvanized steel strip having a predetermined alloying degree is obtained.

Therefore, in the case of excessive alloying, the zinc bath of steel strip A
Immersion time in 14, i.e., by shortening the immersion length, and by similarly increasing the immersion length in the zinc bath 14 in the case of insufficient alloying, always having a predetermined alloying degree. Alloyed hot-dip galvanized steel strips can be produced.

In the method for producing a galvannealed steel strip according to the first aspect of the present invention, the relationship between the reheating temperature in the alloying furnace 16 and the dipping time of the steel strip A in the zinc bath 14 is alloyed by galvanizing. Is set in advance so that the degree becomes a predetermined target value, depending on the change in the reheating temperature in the alloying furnace 16, and in the second embodiment, according to the measurement result of the alloying degree meter 24,
By adjusting the dipping time of the steel strip A in the zinc bath 14, that is, the dipping length, the alloyed hot-dip galvanized steel having a predetermined degree of alloying with good response and without excess or deficiency of the degree of alloying. Bands can be manufactured.

FIG. 3 shows a conceptual diagram of the zinc bath 14 of the galvannealing apparatus 10.

As described above, the method for producing an alloyed hot-dip galvanized steel strip according to the present invention adjusts the target alloying degree by adjusting the immersion length of the steel strip A in the zinc bath 14 according to the strip running speed of the steel strip A. It is for obtaining an alloyed hot-dip galvanized steel strip.

In the zinc bath 14 shown in FIG.
Is supported from above by a lifting cylinder 28. The sink roll 26 is moved up and down by the lifting cylinder 28 to adjust the immersion length of the steel strip A, that is, the sink roll is lowered to increase the immersion length, and the sink roll 26 is increased to decrease the immersion length. The immersion time of the steel strip A in the zinc bath 14 is adjusted.

FIG. 4 shows another example of the zinc bath in which the immersion length of the steel strip A applicable to the present invention can be changed.

The zinc bath 30 shown in FIG. 4 has a sub-zinc bath 32, both of which have a reversible pump 34 and a transfer pipe.
Connected at 36.

In the apparatus of the illustrated example, when the immersion length of the steel strip A is lengthened, the molten zinc is transferred from the sub-zinc bath 32 to the zinc bath 30 to raise the liquid level by the pump 34, and conversely the immersion length is increased. When shortening the temperature of the steel strip A, the pump 34 is reversed to transfer molten zinc from the zinc bath 30 to the sub-zinc bath 32 to lower the liquid level, so that the steel strip A is immersed in the zinc bath 30. It adjusts the time.

In the above description, the temperature of the alloying furnace 16 was measured in the first embodiment of the present invention, and the immersion length of the steel strip A in the zinc bath 14 was adjusted according to this result. The first aspect of the invention is not limited to this, and the reheating temperature of the alloying furnace 16 is read from the measurement result of the alloying degree by the alloying degree meter 24 to dip the steel strip A in the zinc bath 14. The length may be adjusted.

Further, in the apparatus for carrying out the first aspect of the present invention,
The alloying degree meter 24 does not necessarily have to be arranged. However, it is a matter of course that the alloying degree meter 24 is preferably arranged in terms of the control of the entire plating apparatus and the quality control of the obtained galvannealed steel strip.

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

Using the plating apparatus 10 shown in FIG. 1, an alloyed hot-dip galvanized steel strip was produced by the method for producing an alloyed hot-dip galvanized steel strip of the present invention.

The steel strip A used had a plate thickness of 0.8 mm and a plate width of 1500 mm, and was run at a line speed of 90 mpm.

This steel strip A is heated to 800 ° C. in the heating zone 18 of the annealing furnace 12, then cooled to 470 ° C. in the cooling zone 20, and then the bath temperature is 460 ° C.
It was immersed in a zinc bath 14 of. Here, the immersion length of the steel strip A in the zinc bath 14 in the molten zinc was 4.5 m, and the immersion time was 3 seconds.

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 nozzle for gas restriction.
After adjusting the zinc adhesion amount to 45 g / m ² by 22, alloying was performed by reheating to 500 ° C. in the alloying furnace 16. The heating time in the alloying furnace 16 was 12 seconds.

When the alloying degree of the steel strip A was measured by the alloying degree meter 24 which is arranged above the alloying furnace 16 and measures the alloying degree by the X-ray diffraction method, a predetermined concentration of Fe of 10% in the plating layer was determined. An alloyed hot-dip galvanized steel strip having a degree of alloying of 1 was obtained.

Here, since the plate thickness of the steel strip A changed from 0.8 mm to 1.2 mm and the reheating temperature in the alloying furnace 16 dropped to 485 ° C.,
Steel strip A in zinc bath 14 with sink roll 26 lowered by about 0.5 m
The immersion length was adjusted from 4.5 m to 5.7 m and the immersion time was increased from 3 seconds to 3.8 seconds, but the alloying degree did not decrease, and hot dip galvanizing with the same prescribed alloying degree. I was able to get a steel strip. Further, since the operation is only to lower the sink roll 26 by the lifting cylinder 28,
The response was good and there was almost no loss.

For adjusting the immersion length of the steel strip A in the zinc bath 14, the measurement result of the alloying degree by the alloying degree meter 24 is transferred to the lifting cylinder 28 via the alloying degree-steel strip temperature converting means. It was done by giving feedback.

On the other hand, as in the conventional method, when the fuel input amount supplied to the alloying furnace 16 is increased (about 1.6 times) as the reheating temperature in the alloying furnace 16 is lowered, It takes about 10 minutes for the heating temperature to return from 485 ° C. to 500 ° C., and the steel strip (900 m) that has passed through the alloying furnace 16 during this time does not have the above-described predetermined alloying degree, It became an alloyed hot-dip galvanized steel strip with insufficient alloying.

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, the plate thickness and width of the steel strip are changed, Even if the reheating temperature of the alloying process changes due to the change in the amount, the immersion time of the steel strip in the zinc bath, that is, the strip running speed of the steel strip under constant conditions Since the degree of alloying is adjusted by adjusting the immersion length, it is possible to obtain a good galvannealed steel strip without causing quality defects such as insufficient alloying and excessive alloying.

Moreover, adjustment of the alloying degree by adjusting the immersion length of the steel strip in this zinc bath is different from the case of raising the reheating temperature for alloying as in the conventional method, for example, a sink roll arranged in the zinc bath. Since it is possible to easily and quickly adjust the position of, and adjust the height of the liquid surface of the zinc bath, the loss can be extremely reduced, and the effect is very high.

Further, it is not necessary to use a dummy steel strip called a strip material, and the productivity is improved.

[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 processing temperature in the alloying furnace and the degree of alloying of the galvanized layer, with the immersion time of the steel strip in the zinc bath (molten zinc) as a parameter. FIG. 3 is a conceptual diagram of a zinc bath of the hot dip galvanizing apparatus shown in FIG. FIG. 4 is a conceptual diagram of another example of a zinc bath applicable to the present invention. Explanation of symbols 10 …… Alloying hot dip galvanizing equipment, 12 …… annealing furnace, 14,30 …… zinc bath, 16 …… alloying furnace, 18 …… heating zone, 20 …… cooling zone, 22 …… gas Nozzle for drawing, 24 …… Alloying degree meter, 26 …… Sink roll, 28 …… Cylinder for raising / lowering, 32 …… Sub zinc bath, 34 …… Pump, 36 …… Transfer piping, A …… Steel strip

Continuation of front page (56) References JP-A-61-147809 (JP, A) JP-B-55-15543 (JP, B2)

Claims (2)

[Claims] 1. A steel strip, which has been heated to a predetermined temperature in an annealing furnace and then cooled to a predetermined temperature, is immersed in a zinc bath connected to the annealing furnace, and then the amount of zinc deposited is controlled, followed by continuous alloying. In the method for producing an alloyed hot-dip galvanized steel strip for performing a galvanizing treatment, the relationship between the treating temperature in the alloying treatment and the immersion time in the zinc bath is set so that the degree of galvannealing becomes a predetermined target value. And the immersion length of the steel sheet in the zinc bath is determined from the threading speed of the steel sheet according to the above relationship. 2. A steel strip, which has been heated to a predetermined temperature in an annealing furnace and then cooled to a predetermined temperature, is immersed in a zinc bath connected to the annealing furnace, and then the zinc deposition amount is controlled, and then the alloy is continuously alloyed. In the method for producing an alloyed hot-dip galvanized steel strip that undergoes a galvanizing treatment, the galvannealing degree after the galvanizing treatment is measured, and depending on the measurement result, the galvannealing degree is a predetermined target value. The method for producing an alloyed hot-dip galvanized steel strip according to which the immersion length of the steel strip immersed in the zinc bath is determined from the passing speed of the steel sheet.