JPH0645851B2 - 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, by adjusting the temperature of the steel strip immersed in the zinc bath according to changes in the alloying treatment temperature, etc., it is possible to always obtain an alloyed hot-dip galvanized steel strip with a constant degree of alloying. The present invention relates to a method for manufacturing a steel strip.

<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 2 arranged behind the heating zone 18 (hereinafter, the rear side is the downstream side in the moving direction of the steel strip A).
0, the steel strip A is first heated to about 800 ° C. in the heating zone 18 and then to about 470 in the cooling zone 20.
It is cooled to ℃.

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 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.

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 as described above. Is. It should be noted that such alloying is performed by steel strip A
Is started at the moment of immersion 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.

For example, in Japanese Unexamined Patent Publication No. 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 Alternatively, a method of feeding back the time of the steel strip A in the furnace is disclosed. That is, this method measures the alloying degree of the galvanized layer so that the reheating temperature in the alloying furnace 16 becomes constant even if the plate thickness or the plate width of the steel strip to be treated changes. It is possible to obtain an alloyed hot dip galvanized steel sheet having a constant degree of alloying by adjusting the reheating temperature when the combustion amount in the gasification furnace 16 is adjusted or when the amount of hot dip zinc deposited changes. It was possible.

<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 heat-insulating brick having a large heat capacity, and the heating of the steel strip A is mainly radiative heat transfer from this wall. Therefore, in order to adjust the reheating temperature in the alloying furnace 16, 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 galvannealed 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 sheet passing 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 the plate width of the steel strip is changed, or when the amount of molten zinc adhered to the steel strip is changed, alloying is performed. A method for producing an alloyed hot-dip galvanized steel strip that can obtain a good alloyed hot-dip galvanized steel strip without causing quality defects such as shortage or excessive alloying, and that does not hinder productivity. To provide.

<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. The present invention has been completed by finding that the degree of alloying of the layer changes, and thus by finding that the degree of alloying of the galvanized layer can be controlled by controlling the temperature of the steel strip immersed in the zinc bath.

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, and then the zinc deposition amount is controlled, and then an alloying treatment is performed. In the method for producing an alloyed hot-dip galvanized steel strip, the alloying degree of the galvanizing after the alloying treatment is measured, and the alloying degree of the galvanizing becomes a predetermined target value according to the measurement result. A method for producing an alloyed hot dip galvanized steel strip is provided, which comprises adjusting the temperature of the steel strip immersed in the zinc bath.

In a second aspect of the present invention, a steel strip that has been heated to a predetermined temperature and then cooled to a predetermined temperature in an annealing furnace is immersed in a zinc bath, and the zinc deposition amount is controlled, and then an alloying treatment is performed. In the method for producing an alloyed hot-dip galvanized steel strip, the relationship between the processing temperature in the alloying treatment and the temperature of the steel strip immersed in the zinc bath is adjusted so that the degree of alloying of galvanization becomes a predetermined target value. It has been set in advance, the temperature of the steel strip immersed in the zinc bath according to the change in the treatment temperature in the alloying treatment, the alloyed hot dip galvanized steel strip characterized by adjusting based on the relationship A manufacturing method is provided.

<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 (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 to about 800 ° C. in the heating zone 18 also as annealing, and then cooled to about 470 ° C. in the cooling zone 20 by the gas jet cooling method.

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

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.

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

Here, in the first aspect of the present invention, according to the measurement result of the alloying degree of the alloying degree meter 24 as shown by the alternate long and short dash line in FIG. 1, and in the second aspect, Steel to be immersed in the zinc bath 14 by adjusting the cooling temperature of the steel strip A in the cooling zone 20 according to the change of the treatment (reheating) temperature in the alloying furnace 16 as shown by the chain double-dashed line in FIG. The temperature of the zone A is adjusted.

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.
Alloy furnace 1 with the temperature of steel strip A immersed in
The relationship between the treatment temperature (reheating temperature) and the degree of alloying of the galvanized layer in No. 6 is conceptually shown.

In FIG. 2, the horizontal axis represents the reheating temperature in the alloying furnace 16, and the vertical axis represents the alloying degree of the zinc plating layer. Further, the curve A shows the zinc bath 1 as a parameter.
When the temperature of the steel strip immersed in 4 is high, curve B shows zinc bath 1
4 shows the relationship between the reheating temperature and the degree of alloying when the temperature of the steel strip immersed in No. 4 is low.

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

In addition, as shown as parameters in the figure, the zinc bath 1
When the temperature of the steel strip A immersed in No. 4 becomes higher, the alloying degree also increases. That is, by adjusting the temperature of the steel strip A immersed in the zinc bath 14, it is possible to adjust the alloying degree of the zinc plating layer.

When the strip running speed of the steel strip A is constant, for example, the steel strip A
The thickness of the sheet changes from thin to thick,
When the reheating temperature in the alloying furnace 16 is lowered from T ₁ to T ₂ , when the temperature of the steel strip A in the alloying furnace 16 is the temperature shown by the curve B, alloying is performed. The degree also decreases 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, for example, when the temperature is lowered as described above, The reheating temperature was again raised to T ₁ by a method such as increasing the amount of fuel input to the alloying furnace. 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 reheating temperature of the steel strip A in the alloying furnace 16 is adjusted by adjusting the temperature of the steel strip A before being immersed in the zinc bath 14. When the temperature decreases from T ₁ to T ₂ , the temperature of the steel strip A immersed in the zinc bath 14 is increased from the temperature shown by the curve B to the temperature shown by the curve A, so that the alloying degree is F ₂ To F ₁ to obtain a hot-dip galvanized steel strip having a predetermined degree of alloying.

Therefore, when the alloying is excessive, by lowering the cooling temperature of the steel strip A in the cooling zone 20 to lower the temperature of the steel sheet A immersed in the zinc bath 14, or when the alloying is insufficient. Similarly, by increasing the temperature of the steel strip A immersed in the zinc bath 14 in the same manner, an alloyed hot-dip galvanized steel strip having a predetermined alloying degree is always produced without causing excess or deficiency of the alloying degree. It can be manufactured.

In the method for producing an alloyed hot-dip galvanized steel strip according to the first aspect of the present invention, according to the measurement result of the alloying degree meter 24,
Further, in the second aspect, the relationship between the reheating temperature in the alloying furnace 16 and the temperature of the steel strip A immersed in the zinc bath 14 is preset so that the alloying degree of galvanization becomes a predetermined target value. Every time, by adjusting the cooling temperature in the cooling zone 20 in accordance with the change in the reheating temperature in the alloying furnace 16 to adjust the temperature of the steel strip A immersed in the zinc bath 14, the alloy with good responsiveness can be obtained. An alloyed hot-dip galvanized steel strip having a predetermined degree of alloying can be manufactured without causing excess or deficiency of the degree of alloying.

By the way, in alloying hot-dip galvanizing, the temperature adjustment of the steel strip before the steel strip is immersed in a zinc bath is usually to heat to a high temperature without annealing and then to cool to a predetermined temperature, In the apparatus of the illustrated example, the steel strip A is first heated in the heating zone 18 to about 8 in the annealing furnace 12 as described above.
It is heated to 00 ° C. and then cooled to about 470 ° C. in cooling zone 20.

Since such cooling is usually performed by a method such as a gas jet cooling method, the response is very fast. Therefore, it is possible to instantly change the temperature of the steel strip A immersed in the zinc bath 14, and the method for producing the alloyed hot-dip galvanized steel strip according to the present invention is the same as the conventional method in the alloying furnace. It is possible to produce an alloyed hot-dip galvanized steel strip very efficiently without causing insufficient alloying (excessive alloying) while increasing (decreasing) the heating temperature.

In the manufacturing method of the present invention, as the method for adjusting the cooling temperature of the steel strip A in the cooling zone 20, for example, in the case of the gas jet method of the illustrated example, a method of adjusting the blowing amount of the cooling gas, the gas temperature of the cooling gas Any known method such as a method of adjusting the can be applied.

In the above description, in the second aspect of the present invention, the reheating temperature of the alloying furnace 16 is directly measured, and the cooling temperature of the steel strip A in the cooling zone 20 is adjusted according to this result. However, the second aspect of the present invention is not limited to this, the temperature of the alloying furnace 16 is read from the measurement result of the alloying degree by the alloying degree meter 24, and the temperature of the steel strip A in the cooling zone 20 is measured. The temperature of the steel strip A immersed in the zinc bath 14 may be adjusted by adjusting the cooling temperature.

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

<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.

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.

This steel strip A was 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 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 a substantially vertical direction, and then the amount of zinc adhered is adjusted to 45 g / m ² by the gas throttle nozzle 22 and then in the alloying furnace 16. Reheating to 500 ° C. was performed for alloying. The heating time in the alloying furnace 16 was 12 seconds.

When the alloying degree of the steel strip A was measured by an alloying degree meter 24 using X-ray diffraction arranged above the alloying furnace 16, it was confirmed that the Fe concentration in the plating layer was 10%. A galvannealed steel strip having was obtained.

Here, since the plate thickness of the steel strip A changed to 1.2 mm and the reheating temperature in the alloying furnace 16 dropped to 485 ° C., the cooling temperature in the cooling zone 20 was adjusted and immersed in the zinc bath 14. When the temperature of the steel strip A to be heated was raised to 495 ° C., the alloying degree did not decrease, and a galvannealed steel strip having a similar predetermined alloying degree could be obtained.

The temperature of the steel strip A immersed in the zinc bath 14 is adjusted by measuring the alloying degree measured by the alloying degree meter 24 and adjusting the temperature of the cooling zone 20 via the alloying degree-steel strip temperature converting means. This was done by feeding back to a meter (not shown).

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, the alloying furnace 16 It takes about 10 minutes for the reheating temperature in the furnace to return from 485 ° C. to 500 ° C. During this time, the alloying furnace 1
The steel strip (900 m) that passed through No. 6 became an alloyed hot dip galvanized steel strip that did not have the above-mentioned predetermined degree of alloying and was insufficiently alloyed.

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 when the amount of deposit changes and the reheating temperature of alloying process changes, the degree of alloying is adjusted by adjusting the temperature of the steel strip immersed in the zinc bath. A good alloyed hot-dip galvanized steel strip can be obtained without causing quality defects such as excessive alloying.

Moreover, unlike the conventional method in which the reheating temperature for alloying is changed, the adjustment of the steel strip temperature can be performed instantaneously, so that the loss can be extremely reduced. , Very efficient.

Further, since it is not necessary to change the traveling speed of the steel strip, the productivity is not hindered, and since it is not necessary to use a dummy steel strip called a sheet passing material, 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 temperature of the steel strip immersed in the zinc bath as a parameter. 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, A ... Steel strip

Claims (2)

[Claims] 1. An alloyed hot dip galvanized steel in which a steel strip which has been heated to a predetermined temperature in an annealing furnace and then cooled to a predetermined temperature is dipped in a zinc bath and then the amount of zinc deposited is controlled, and then an alloying treatment is carried out. In the method for manufacturing a strip, the alloying degree of the zinc plating after the alloying treatment is measured, and the alloying degree of the zinc plating is adjusted to a predetermined target value according to the measurement result, soaking in the zinc bath. A method for producing an alloyed hot-dip galvanized steel strip, characterized in that the temperature of the steel strip is adjusted. 2. An alloyed hot dip galvanized steel in which 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, and then the amount of zinc deposited is controlled, and then an alloying treatment is performed. In the method for manufacturing a strip, the relationship between the treatment temperature in the alloying treatment and the temperature of the steel strip immersed in the zinc bath is preset such that the alloying degree of galvanization is a predetermined target value, A method for producing an alloyed hot-dip galvanized steel strip, characterized in that the temperature of the steel strip immersed in the zinc bath is adjusted based on the above relationship in accordance with the change in the treatment temperature in the alloying treatment.