JP3482739B2 - Manufacturing method of hot-dip galvanized steel sheet - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to depositing a molten zinc to the steel strip surface, solidifying the molten zinc adhering to relate the steel strip surface in preparation how galvanized steel sheet coated with a metal.

[0002]

2. Description of the Related Art A metal-plated steel sheet whose surface is coated with a metal is widely used in order to improve the corrosion resistance and wear resistance of the steel sheet. As one of the methods for producing the metal-plated steel sheet, a method for producing a metal-plated steel sheet using a molten metal plating bath is known. Zinc, aluminum, lead, tin and the like are used as the metal with which the surface of the steel sheet is coated. Here, as an example of the hot-dip galvanized steel sheet, a general method for manufacturing a hot-dip galvanized steel sheet having a galvanized layer formed on the surface will be described.

The surface of the cold-rolled steel sheet is washed, and the washed cold-rolled steel sheet is annealed by heating in a non-oxidizing atmosphere or a reducing atmosphere, and is cooled to a temperature suitable for plating without being oxidized. A sink roll for carrying the strip is continuously immersed in a molten zinc bath installed obliquely from above so that the molten zinc adheres to the surface of the steel sheet. After that, the direction of travel of the steel sheet is converted vertically upward with a sink roll, the steel sheet with molten zinc attached is pulled up from the molten zinc bath, and the excessive amount of molten zinc that has attached to the steel sheet surface is attached to the prescribed amount using an attachment amount adjustment device. The amount is adjusted, and the steel sheet is naturally cooled to solidify the molten zinc, thereby producing a hot dip galvanized steel sheet. In addition, in order to improve the workability and paintability of the steel sheet, after solidifying the molten zinc that has adhered to the steel sheet surface, the steel sheet is subsequently subjected to heat treatment using an alloying heating furnace, and the zinc that has adhered to the steel sheet surface There is also known a method of alloying the above to produce an alloyed hot-dip galvanized steel sheet.

The molten zinc bath used in the above-mentioned manufacturing method is usually a large-capacity bath containing about 200 tons of molten zinc. Therefore, there are problems that maintenance of the sink roll installed in the bath is complicated, and that dross in the bath is caught between the sink roll and the steel plate and the steel plate is damaged. Therefore, an apparatus that includes a container holding a molten metal bath, penetrates an opening formed in the bottom wall of the container, and runs a steel strip from below to above to plate the steel strip (so-called aerial pot system: Japanese Patent Application Laid-Open No. 4-356), an apparatus for holding a hot-dip plating bath in a container by electromagnetic force to perform plating on a steel strip (so-called electromagnetic seal air pot system: see Japanese Patent Application Laid-Open No. 7-48660), a pair. There is proposed a device for forming a pool of hot-dip galvanizing bath between the rolls and performing plating by passing a steel strip between the rolls (seal roll system: see JP-A-1-139744). When these devices are used, it is possible to perform plating with a plating bath having a small capacity of less than 10 tons, but since the plating bath has a small capacity, the productivity of plated steel strip can be improved by the conventional method described above. If it is attempted to maintain the same level, the time required for the steel strip to be immersed in the plating bath, the so-called immersion time in the plating bath, will be an extremely short time of approximately 1 second or less.

By the way, a hard and brittle Fe-Zn alloy layer exists in the galvanized layer. When this Fe-Zn alloy layer is formed at the interface between the base steel sheet and the galvanized layer, the galvanized layer adheres to the steel sheet. Sex decreases. Therefore, a small amount of Al is usually added to the molten zinc bath, and
Is preferentially reacted with the steel sheet to form an Al-rich layer (Fe-Al intermetallic compound) at the interface between the base steel sheet and the galvanized layer, and the hard and brittle Fe-Zn alloy layer is the base steel sheet and the galvanized layer. Suppresses generation at the interface with. As described above, when a small amount of Al is added to the hot-dip galvanized bath, a hot-dip galvanized steel sheet having good adhesion and an alloyed hot-dip galvanized steel sheet having good workability can be produced.

It is said that the above reaction for forming the Fe-Zn alloy layer is diffusion-controlled, and this reaction continues in the plating bath and until the molten zinc on the surface of the steel sheet solidifies after the steel sheet is pulled out of the plating bath. On the other hand, the above-mentioned Al-rich layer formation reaction also continues in the plating bath and after the steel plate is pulled out from the plating bath until the molten zinc on the surface of the steel plate solidifies. That is, the Al-enriched layer is formed in the plating bath by Al added to the plating bath, and the Al-enriched layer is formed on the surface of the steel sheet until the molten zinc on the steel sheet surface is solidified after the steel sheet is pulled up from the plating bath. Continue to be generated. However, in the above-mentioned air pot method, electromagnetic seal air pot method, and seal roll method, as described above, since the immersion time in the plating bath is an extremely short time of about 1 second or less, Fe--Zn Not enough Al-rich layer is formed in the plating bath to suppress the formation of the alloy layer. As a result, the Fe-Zn alloy layer is often formed in the plating layer in the plating bath and after being pulled out of the plating bath, the adhesion of the plating layer is reduced, and the workability of the galvannealed steel sheet is reduced. There is a problem of doing.

[0007]

In order to solve such a problem, a method of increasing the amount of Al added to the hot-dip galvanizing bath can be considered. However, in order to suppress the formation of the Fe-Zn alloy layer, a sufficient amount of A
When 1 is added, a thick Al-rich layer is formed at the interface between the base steel sheet and the galvanized layer during the cooling process. Thus, when the Al-rich layer is thickly formed at the interface between the base steel sheet and the galvanized layer, the molten zinc adhering to the surface of the steel sheet is solidified and then the heat treatment is applied to the steel sheet, and the zinc adhering to the surface of the steel sheet When alloyed with Al to produce a galvannealed steel sheet, the thick Al-rich layer formed at the interface interferes with the alloying of Fe and Zn. For this reason, it is necessary to raise the heating temperature for alloying or lengthen the heating time, which causes new problems such as an increase in the amount of electricity used, an increase in heating equipment, and a decrease in line speed. Further, if the alloying of Fe and Zn is excessively hindered by the Al-rich layer, uneven burning occurs, which causes a problem in surface appearance.

[0008]

[0009] The present invention includes aims in view of the above circumstances, a good adhesion of the plated layer to the basis steel sheet, or to provide a manufacturing how the galvanized steel sheet can be manufactured good workability galvannealed steel sheet To do.

[0010]

A method of manufacturing a hot- dip galvanized steel sheet according to the present invention for achieving the above-mentioned object is to fill a hot- dip galvanized bath, pass through the hot- dip galvanized bath, and extend vertically upward to a steel strip. 40~90g but in the manufacturing method of the galvanized steel sheet using a hot-dip zinc holding vessel traveling, the steel strip is traveling
Melted the steel strip so as to deposit molten zinc of 1 / m2.
Immerse in the lead plating bath for less than 1.0 second and pull it up.
The molten zinc adhering to the steel strip solidified at an average cooling rate of more than 10 ° C. / sec, and is characterized in forming a zinc plating layer on the steel strip.

[0011] The molten metal adhering to the upper Symbol steel strip surface after solidified by the above average cooling rate, the metal plating layer may be alloyed by heating the steel strip to a temperature within a predetermined range.

[0012]

[0013]

[0014]

[0015]

According to the manufacturing method of the galvanized steel sheet the present invention, since the molten zinc adhering to the steel strip is solidified at an average cooling rate of more than 10 ° C. / sec, less molten zinc with the addition amount of the prescribed metal element Even when a hot- dip galvanized steel sheet is manufactured using a plating bath for a short time, an alloy of the above-mentioned predetermined metal element is formed at the interface between the base steel sheet and the plating layer, and the adhesion of the plating layer to the base steel sheet. Good meltability or workability
Capable of producing a zinc-plated steel plate.

Here, when the molten zinc is adhered to the running steel strip, when the steel strip is immersed in a hot dip galvanizing bath for 1.0 second or less and pulled up,
It can maintain high productivity of galvanized steel. Further, the molten zinc adhering to the steel strip surfaces was allowed to solidify at the average cooling rate, when obtained by alloying the galvanizing layer by heating the steel strip to a temperature within a predetermined range, it is melted Taa
An alloy of lead and iron can be formed, and workability and paintability can be improved.

Further, the molten alloy used in the practice of the present invention
In an apparatus for manufacturing a lead- plated steel sheet, an adhesion amount adjusting device is used to adjust the adhesion amount of molten zinc adhering to the steel strip, and then a cooling device is used to cool at least one surface of the running steel strip. By doing so, the molten zinc adhering to the steel strip can be solidified at an average cooling rate of 10 ° C./second or more, so that the molten zinc containing a small amount of a predetermined metal element can be solidified. Even when producing a hot- dip galvanized steel sheet with a short immersion time using a tin plate, an alloy of the predetermined metal element is formed at the interface between the base steel sheet and the plating layer, and the adhesion of the plating layer to the base steel sheet is good, or A hot- dip galvanized steel sheet with good workability can be manufactured.

Here, when the cooling device is provided with a nozzle that blows a cooling gas onto both sides of the running steel strip, the average cooling rate can be controlled relatively easily. In addition, if the above nozzle sprays non-oxidizing cooling gas onto both sides of the running steel strip,
It can prevent the oxidation of zinc . Furthermore, among the nozzles provided in the cooling device, a nozzle installed in the traveling direction most upstream, so also functions to adjust the adhesion amount of molten zinc adhering to the steel strip, separately attached to the steel strip It is not necessary to provide an adhesion amount adjusting device for adjusting the adhesion amount of the molten zinc.
Therefore, using the nozzle installed in the most upstream in the traveling direction,
The amount of molten zinc adhering to the running steel strip is adjusted and the running steel strip is cooled. By doing so, the molten zinc adhering to the steel strip can be solidified at an average cooling rate of 10 ° C./sec or more, so that the molten zinc can be melted in a short dipping time by using the molten galvanization with a small addition amount of a predetermined metal element. Even if a galvanized steel sheet is manufactured, an alloy of the predetermined metal element is formed at the interface between the base steel sheet and the plated layer,
It is possible to manufacture a hot- dip galvanized steel sheet having good adhesion of the plating layer to the base steel sheet or good workability.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a first embodiment of a hot- dip galvanized steel sheet manufacturing apparatus used for carrying out the present invention. Melting nitrous
The lead- plated steel sheet manufacturing apparatus 10 includes a plating tank 14 that stores molten zinc 12, and an opening 14b through which a steel strip 16 running in the direction of arrow A penetrates is formed in a bottom wall 14a of the plating tank 14. ing. In order to prevent the molten zinc 12 from leaking through the opening 14b and falling around the plating tank 14,
A magnetic field applying device 18 is installed. Running direction (arrow A
The steel strip 16 traveling from the upstream side is turned upward by the deflector roll 20, passes through the two support rolls 22 and the pair of guide rolls 24, passes through the opening 14b, and is stored in the plating tank 14. The molten zinc 12 is soaked in the molten zinc 12 and the molten zinc 12 is attached. Steel strip 16
Is immersed in the molten zinc 12 for less than 1 second. The steel strip 16 pulled up from the plating tank 14 passes through an adhesion amount adjusting device 26 for adjusting the adhesion amount of the molten zinc 12 adhering to the steel strip 16, whereby the adhesion amount of the adhered molten zinc 12 is adjusted. It The steel strip 16 that has passed through the adhesion amount adjusting device 26 passes through a cooling device 28 that solidifies the molten zinc 12 that has adhered to the steel strip 16. In this cooling device 28, a plurality of nozzles 30 (six nozzles are shown in FIG. 1) are installed along the traveling direction of the steel strip 16, and each nozzle 30 is non-oxidized toward the steel strip 16. Spray a cooling gas of nature. When the steel strip 16 that has passed through the attachment amount adjusting device 26 passes through the cooling device 28, the molten zinc that has attached to the steel strip 16 solidifies at an average cooling rate of 10 ° C./sec or more. The steel strip 16 that has passed through the cooling device 28 enters the alloying furnace 34 via the guide roll 32, and this alloying furnace 34
Then, the solidified hot- dip zinc 12 is alloyed, thereby producing a hot- dip galvanized steel sheet. In addition, in the hot- dip galvanized steel sheet manufacturing apparatus 10 described above, the plating tank 14
The width of the opening 14b is 10 mm, and the length of the opening is 2000 m
m. In addition, the output of the magnetic field applying device 18 is 500 kW
And

[0020]

[0021]

Next, using a hot-dip galvanized steel sheet production apparatus 10 shown in FIG. 1, to produce a galvanized steel sheet will be described the results of the adhesion experiments. An ultra-low carbon steel strip was heated in an N ₂ -5% H ₂ atmosphere, annealed, and then immersed in a hot dip galvanizing bath for various times of less than 1.0 second. The composition of the hot dip galvanizing bath is 0.2 wt% Al-Z
n. After pulling the steel strip from the hot dip galvanizing bath,
The adhesion amount adjusting device 26 is used to adjust the adhesion amount of the molten metal to 40 to
It was adjusted to 90 g / m ² . Then, using the cooling device 28, the molten zinc was cooled and solidified at various cooling rates to manufacture a galvanized steel sheet. In addition, here
The alloying furnace 34 was not used.

The hot dip galvanized steel sheet produced as described above was sampled at an arbitrary position and the adhesion of the coating was evaluated by an adhesion peeling test. There were three evaluation levels.
The adhesion peeling test will be described with reference to FIG. In this adhesion peeling test, a sample was prepared by applying an adhesive 42 to a hot-dip galvanized steel sheet 40 and adhering an aluminum-killed cold-rolled steel sheet 44. This sample was placed in an oven at 170 ° C for 1 hour.
Heat for 5 minutes and air cool. The air-cooled sample was peeled off using a tensile tester (made by Shimadzu).

The sample size of the adhesive part is 20 mm × 15
mm, and SR bond E-56 (manufactured by Sunrise Meisei) was used as the adhesive. Table 1 shows the production conditions of the hot-dip galvanized steel sheet and the results of the adhesion peeling test. The conditions not shown in Table 1 are the plate width and the penetration temperature (the temperature immediately before the steel strip is immersed in the hot dip galvanizing bath). Here, the plate width is 1000 to 1200 mm and the penetration temperature is the bath. The temperature was ± 10 ° C.

[0025]

[Table 1]

The evaluation of plating adhesion in Table 1 is as follows. ◯: No peeling of plating layer, no crack Δ: Crack in plating layer ×: There is peeling of the plating layer Is.

For example, in Table 1, Example No. 5 and Comparative Example N
o. As can be seen from 1, when the manufacturing conditions are almost the same except for the average cooling rate after pulling the steel strip from the hot dip galvanizing bath, when the average cooling rate is 10 ° C / sec or more, the adhesion A hot-dip galvanized steel sheet having excellent properties can be manufactured. Then, in the same manner as described above, by using the molten zinc Me <br/> Kki steel sheet production apparatus 10 shown in FIG. 1, to produce a galvanized steel sheet, illustrating the results of processing of the experimental.

An ultra-low carbon steel strip was heated in an N ₂ -5% H ₂ atmosphere and annealed, and then in a hot dip galvanizing bath.
Immersion was performed for various times of 0 seconds or less. The composition of the hot dip galvanizing bath is 0.18 wt% Al-Zn. After pulling up from the hot dip galvanizing bath, the amount of molten metal deposited was adjusted to 30 to 50 g / m ² by using the deposition amount adjusting device 26. Thereafter, the cooling device 28 is used to cool and solidify the molten zinc at various cooling rates, and then the alloying furnace 34 is used.
Was used for alloying heat treatment at various temperatures. Here, the alloying conditions were adjusted so that the Fe content in the plating layer was 9 to 12 wt%. An arbitrary position of the alloyed hot-dip galvanized steel sheet produced in this manner was sampled and the workability was evaluated by a 180 ° bending test. There were three evaluation levels.

Table 2 shows the production conditions of the hot-dip galvanized steel sheet and the results of the workability test. The plate width is 1000 to 120
0mm, bath temperature 470 ± 10 ℃, penetration temperature 470 ± 1
It was set to 0 ° C. Here, the 180 ° bending test means applying a cellophane tape on the compression bending side of the galvannealed steel sheet, and
After the 80 ° bending back test, the cellophane tape was peeled off, and the peeling amount of the zinc alloy adhering to the tape was evaluated on a three-stage scale. ◯ is good, x is bad, and Δ is between ◯ and x.

[0030]

[Table 2]

For example, in Table 2, Example No. 1 and Comparative Example N
o. As can be seen from 1, when the manufacturing conditions were almost the same except the average cooling rate after pulling the steel strip from the hot dip galvanizing bath, the average cooling rate was changed to 10
When it is set to be at least ° C / sec, a galvannealed steel sheet with good workability can be produced.

[0032]

As described above, according to the method for manufacturing a hot- dip galvanized steel sheet of the present invention, the plating bath for an extremely short time is used.
Since solidifying at an average cooling rate of more than 10 ° C. / sec molten zinc adhering to the steel strip in the immersion in, good adhesion of the plating layer to the base steel sheet, or workability Tsu good Me molten zinc <br/> It is possible to manufacture a steel plate.

[0033]

[Brief description of drawings]

FIG. 1 is the first of the apparatus for producing a hot-dip galvanized steel sheet according to the present invention.
It is a schematic diagram which shows an Example.

FIG. 2 is a cross-sectional view showing a sample of an adhesion peeling test.

[Explanation of symbols]

10 Hot- dip galvanized steel sheet manufacturing apparatus 12 Hot- dip zinc 14 Plating tank 16 Steel strip 26 Adhesion amount adjusting device 28 Cooling device 30 Nozzle 100 Hot- dip galvanized steel sheet manufacturing apparatus

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Mochizuki, 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Technical Research Institute, Kawasaki Steel Co., Ltd. (72) Masuto Shimizu 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Manufacturing Co., Ltd. Chiba Steel Works (56) Reference JP 63-111163 (JP, A) JP 63-14847 (JP, A) JP 55-79863 (JP, A) JP 5-125515 (JP, A) JP 5-106002 (JP, A) JP 4-103748 (JP, A) JP 4-356 (JP, A) JP 2-182870 (JP, A) (JP 58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (2)

(57) [Claims] 1. A satisfies the molten zinc, in the manufacturing method of hot-dip galvanized steel sheet using a hot-dip zinc holding container strip towards the vertically upward through the therein travels, 40 the steel strip traveling The steel strip was placed in a hot dip galvanizing bath for 1.0 second so that 90 g / m2 of hot dip zinc was deposited.
It pulled to time soaking of less than between, adhered to the steel strip melted
A method for producing a hot- dip galvanized steel sheet, characterized in that zinc is solidified at an average cooling rate of 10 ° C / sec or more to form a galvanized layer on the steel strip. Wherein the molten zinc adhering to the steel strip surface after solidified with the average cooling rate, and wherein the alloying said galvanized layer by heating the steel strip to a temperature within a predetermined range method for manufacturing a galvanized steel sheet according to claim 1 Symbol mounting to.