KR101505271B1 - Gas wiping apparatus and method of manufacturing galvannealed steel sheet using the same - Google Patents

Abstract

A gas wiping apparatus capable of producing a steel sheet excellent in slidability and plating adhesion by performing gas wiping using a high-temperature and high-pressure heating gas, and a method of manufacturing a hot-dip galvanized steel sheet using the same.
The gas wiping apparatus according to the present invention comprises a gas wiping body which is passed through the inside of a plating bath and then is mounted so as to be parallel to the strip before the alloying heat treatment is carried out or after the alloying heat treatment is performed; A plurality of nozzles mounted on the ends of the gas wiping body so as to be mutually separated so as to jet hot gases of high and high pressure separately to the surface of the strip; And a drive control unit for individually controlling on and off of the plurality of nozzles.

Description

TECHNICAL FIELD [0001] The present invention relates to a gas wiping apparatus and a method of manufacturing a hot dip galvanized steel sheet using the same,

The present invention relates to a gas wiping apparatus and a method of manufacturing a hot dip galvanized steel sheet using the same, and more particularly, to a hot dip galvanized steel sheet having excellent slidability and plating adhesion And a method of manufacturing a hot dip galvanized steel sheet using the same.

The galvannealed hot-dip galvanized steel sheet is immersed in the galvanizing bath to anneal the hot-rolled steel sheet to adhere molten zinc to the surface of the steel sheet. After that, compressed air is sprayed on both sides of the steel sheet by using a gas wiping device to adjust the amount of plating, and then an alloying heat treatment for reacting iron with zinc is performed.

At this time, in order to raise the temperature to the alloying reaction temperature, the alloying reaction is performed through the temperature rising section. However, this temperature raising section is very short and the raising speed is not high because the raising speed is high.

A related prior art is Korean Patent Laid-Open No. 10-2011-0040473 (Apr. 20, 2011), which discloses a gas wiping apparatus for hot-dip coating.

An object of the present invention is to provide a gas wiping device capable of producing a steel sheet having a high-quality form having excellent slidability and plating adhesion by allowing the Zn - > σ ₁ phase to be directly generated by causing the alloying process to be performed while maintaining a high temperature .

Another object of the present invention is to provide a method for producing a Zn - > ₁ phase by causing a galvannealing process to occur at a high temperature by spraying high temperature and high pressure heating gas using the gas wiping apparatus, And to provide a method for producing a hot-dip galvanized steel sheet having excellent solidification.

In order to accomplish the above object, a gas wiping apparatus according to an embodiment of the present invention may be configured to pass through the inside of a galvanizing bath, and then be separated from the strip before the alloying heat treatment, or parallel to the strip after the alloying heat treatment A gas wiping body mounted; A plurality of nozzles mounted on the ends of the gas wiping body so as to be mutually separated so as to jet hot gases of high and high pressure separately to the surface of the strip; And a drive control unit for individually controlling on and off of the plurality of nozzles.

According to another aspect of the present invention, there is provided a method of manufacturing a hot dip galvanized steel sheet, comprising: (a) pickling a hot rolled steel sheet and cold rolling the same; (b) annealing the cold-rolled steel sheet; (c) cooling the annealed heat treated steel sheet; (d) performing hot dip galvanizing on the cooled steel sheet; (e) spraying high-temperature and high-pressure heating gas onto the surface of the steel sheet by using a gas wiping device having a nozzle mounted on the hot-dip galvanized steel sheet so as to be separated from each other; And (f) subjecting the steel sheet subjected to the heating gas injection to an alloying heat treatment.

A gas wiping apparatus and a method for manufacturing a hot dip galvanized steel sheet using the same according to the present invention are designed to prevent the temperature of a strip from being lowered in consideration of a heating rate limit of a temperature rising section, Instead, the Zn -> σ ₁ phase is directly generated by causing the galvannealing process to be carried out while spraying high temperature and high pressure heating gas onto the strip by using a plurality of nozzles which are mutually separated from each other and maintaining a high temperature. Thus, slip property and plating adhesion A hot-dip galvanized steel sheet having excellent solidification can be produced.

1 is a schematic cross-sectional view of a gas wiping apparatus according to an embodiment of the present invention.
Fig. 2 is a perspective view showing the gas wiping device of Fig. 1 in detail.
3 is a process flow chart showing a method of manufacturing a hot-dip galvanized steel sheet according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a gas wiping apparatus according to a preferred embodiment of the present invention and a method of manufacturing a hot dip galvanized steel sheet using the same will be described in detail with reference to the accompanying drawings.

Gas wiping device

FIG. 1 is a schematic cross-sectional view of a gas wiping apparatus according to an embodiment of the present invention, and FIG. 2 is a perspective view showing a gas wiping apparatus of FIG. 1 in detail.

Referring to FIGS. 1 and 2, a gas wiping apparatus 100 according to an embodiment of the present invention includes a gas wiping body 120, a plurality of nozzles 140, and a drive control unit 160.

The gas wiping body 120 may be mounted so as to be parallel to the strip 20 before passing through the inside of the plating bath 10 and before the alloying heat treatment. Alternatively, the gas wiping body 120 may be mounted so as to be parallel to the strip 20 after passing through the interior of the plating bath 10 and then subjected to the alloying heat treatment.

The plurality of nozzles 140 are mounted on the end of the gas wiping body 120 so as to be separated from each other, and serve to individually spray the high-temperature and high-pressure heating gas against the surface of the strip 20.

At this time, the plurality of nozzles 140 are designed to be spaced along the width W of the strip 20. In particular, it is preferable that the plurality of nozzles 140 are arranged in two or more rows along the width W of the strip 20. This is because when the plurality of nozzles 140 are installed in two or more rows, It is possible to minimize the temperature deviation in the width (W) and length (L) directions.

The plurality of nozzles 140 may have the same or different diameters. Particularly, it is desirable that the diameter of the plurality of nozzles 140 is designed to have a diameter smaller than that of the portion corresponding to the center of the strip 20, Because the temperature drop in

In this case, the high temperature and high pressure are defined as the temperature of 490 to 650 ° C and the injection pressure of 30 to 60 bar. If the temperature of the heating gas is less than 490 ° C or the injection pressure of the heating gas is less than 30 bar, it may be difficult to directly transform the Zn -> σ ₁ phase during the alloying process due to low temperature and injection pressure. Conversely, when the temperature of the heating gas exceeds 650 DEG C or when the injection pressure of the heating gas exceeds 60 bar, it acts only as a factor for raising the manufacturing cost without increasing any further effect, which is not economical.

As the heating gas, at least one selected from Ar, O ₂ , H ₂ , H ₂ O and the like can be used.

The driving control unit 160 controls ON and OFF of the plurality of nozzles 140 individually.

Since the gas wiping apparatus 100 according to the present invention can individually turn on and off the plurality of nozzles 140 through the driving control unit 160, The heating gas can be selectively injected onto the surface of the strip 20, so that the deposition amount of the plating layer 30 coated on the surface of the strip 20 can be uniformly controlled.

The gas wiping apparatus according to the above-described embodiment of the present invention can uniformly maintain the temperature of the entire surface of the steel sheet by spraying the heated gas onto the surface of the steel sheet using a plurality of nozzles whose ON and OFF are controlled individually have.

Therefore, in order to prevent the temperature of the strip from being lowered in advance in consideration of the temperature rise speed limit of the temperature rising section, the gas wiping apparatus according to the embodiment of the present invention may use a plurality of The Zn -> σ ₁ phase is generated immediately by causing the high temperature and high pressure heating gas to be injected into the strip by using separate nozzles to maintain the high temperature and to achieve the formation of solidification with excellent slidability and plating adhesion Can be produced.

Hereinafter, a method of manufacturing a hot dip galvanized steel sheet using the gas wiping apparatus according to an embodiment of the present invention will be described in more detail.

Manufacturing method of hot-dip galvanized steel sheet

3 is a process flow chart showing a method of manufacturing a hot-dip galvanized steel sheet according to an embodiment of the present invention.

Referring to FIG. 3, the method for manufacturing a hot dip galvanized steel sheet according to an embodiment of the present invention includes a pickling and cold rolling step S210, a annealing heat treatment step S220, a cooling step S230, a hot dip galvanizing step S240 ), A heated gas injection step (S250), and an alloying heat treatment step (S260).

Pickling and cold rolling

In the pickling and cold rolling step (S210), the hot-rolled steel sheet is pickled and then cold-rolled.

Such a hot-rolled steel sheet can be produced through a hot-rolling process such as slab reheating, hot rolling and cooling / winding. At this time, the pickling is performed for the purpose of removing the scale of the hot-rolled steel sheet produced through the hot rolling process.

In this step, cold rolling is preferably carried out at a cold reduction of 60 to 80%. When the cold rolling reduction is less than 60%, the deformation effect of the hot-rolled steel is small. On the other hand, when the cold rolling reduction ratio exceeds 80%, not only the cost required for cold rolling increases, but also drawability is hindered and cracks are generated at the edges of the steel sheet, which may cause the steel sheet to break.

Annealing heat treatment

In the annealing heat treatment step S220, the cold-rolled steel sheet is annealed.

In this step, the annealing heat treatment temperature is preferably carried out at 780 to 850 DEG C for 100 to 150 seconds to make a two-phase structure of ferrite and austenite. If the continuous annealing temperature is less than 780 占 폚 or the continuous annealing time is less than 100 seconds, there is a problem that the ductility is lowered. On the other hand, if the continuous annealing temperature exceeds 850 占 폚 or the continuous annealing time exceeds 150 seconds, the physical properties of the steel sheet may deteriorate due to an increase in the austenite grain size.

Cooling

In the cooling step (S230), the annealed steel sheet is cooled to 480 to 540 占 폚. At this time, cooling may be performed by a method such as gas jet cooling (GJC).

In this step, when the cooling end temperature is less than 480 DEG C, the steel sheet temperature becomes too low when the steel sheet is immersed in the plating bath, which may cause plating defects. On the other hand, if the cooling end temperature exceeds 540 占 폚, the austenite is transformed into ferrite and bainite during the cooling process, resulting in material unevenness. At this time, the cooling is preferably performed at a rate of 5 DEG C / sec or more, but it is not necessarily limited to this.

Hot-dip galvanizing

In the hot dip galvanizing step (S240), hot dip galvanizing is performed on the cooled steel sheet.

At this time, hot dip galvanizing is carried out by immersing the steel sheet in a plating bath. At this time, the plating solution may contain 0.05 to 0.25% of Al, 0.05% or less of Fe, 0.003% or less of Pb, and the remainder of Zn in weight percent, but it is not necessarily limited thereto. In such hot dip galvanizing, the plating bath is preferably maintained at 440 to 480 캜.

Heating gas injection

In the heating gas injection step (S250), hot gas and high-pressure heating gas is sprayed onto the surface of the steel sheet using a gas wiping device having a nozzle mounted so that a plurality of the hot-dip galvanized steel sheets are mutually separated.

In this case, the high temperature and high pressure are defined as the temperature of 490 to 650 ° C and the injection pressure of 30 to 60 bar. If the temperature of the heating gas is less than 490 ° C or the injection pressure of the heating gas is less than 30 bar, it may be difficult to directly transform the Zn -> σ ₁ phase during the alloying process due to low temperature and injection pressure. Conversely, when the temperature of the heating gas exceeds 650 DEG C or when the injection pressure of the heating gas exceeds 60 bar, it acts only as a factor for raising the manufacturing cost without increasing any further effect, which is not economical. As the heating gas, at least one selected from Ar, O ₂ , H ₂ , H ₂ O and the like can be used.

Generally, the plating layer on the surface of the steel sheet mainly consists of ζ phase, σ ₁ phase, and γ phase, and the mechanical characteristics of the surface vary depending on the fraction of each phase. Particularly, the degree of alloying reaction varies depending on the alloying reaction temperature and time to be described later, and the fraction of the plating layer phase (ζ phase, σ ₁ phase, γ phase) changes by controlling the degree of alloying reaction. That is, it is generally known that the σ ₁ phase (Zn → σ ₁ phase) directly formed from Zn is excellent in slip property and adhesion property of the product, and the temperature at which the Zn → σ ₁ phase is generated is generated at about 490 to 650 ° C. In contrast, the ζ phase is impaired, slip property, is produced from low 470 ~ 490 ℃ than ₁ σ phase.

Thus, while transformation with Zn → σ → ζ phase ₁ the ζ phase, σ phase ₁ there is a fraction of the crystal, so the ζ phase immediately after the generation, the generated phase Zn σ ₁ σ ₁ than the slip property is poor.

Therefore, as described above, in the present invention, high temperature and high pressure heating gas is injected from the nozzle of the gas wiping apparatus in order to prevent the temperature of the steel plate from falling down in consideration of the heating rate limit of the heating section. As described above, the alloying process is performed in a state where the high temperature is maintained, so that the Zn → σ ₁ phase is generated, whereby the slip property and the plating adhesion of the steel sheet can be improved.

Alloying heat treatment

In the alloying heat treatment step (S260), alloying heat treatment is performed on the steel sheet subjected to the hot gas injection.

In this step, the alloying heat treatment temperature is preferably 480 to 650 ° C. If the alloying heat treatment temperature is too low (less than 480 ° C), manganese enrichment in the alloying plating layer is not sufficient and it is difficult to secure the desired manganese content. Conversely, if the alloying heat treatment temperature exceeds 650 DEG C, material deterioration may occur.

At this time, the alloying temperature is a very important factor, and the phase fraction of the plating layer is changed according to the alloying temperature, and the difference in the fraction of phases having different characteristics is an important factor that can ultimately determine the surface quality of the product . Therefore, the alloying temperature control is an essential condition in order to produce a product that meets the product surface characteristics required according to each product and the type of steel. In the present invention, a method of spraying high temperature and high pressure heating gas is proposed.

At this time, the alloying temperature of the hot-dip galvanized steel sheet differs depending on the steel grade and the product use. Particularly, as described in the present invention, when the alloying process is performed immediately after the heating gas injection using the high-temperature and high-pressure heating gas is performed so as to cause the alloying reaction at the high temperature, the alloying process , A Zn - > ₁ phase is immediately produced, and a hot-dip galvanized steel sheet having a high-quality formation excellent in slidability and plating adhesion can be produced.

The hot-dip galvanized steel sheet produced in the above-described processes (S210 to S260) may be used in place of the compressed air sprayed from the nozzle of the gas wiping apparatus, in order to prevent the temperature of the strip from being lowered in advance, The Zn -> σ ₁ phase can be directly generated by causing the hot gas and the high pressure gas to be injected onto the strip by using a plurality of nozzles which are mutually separated from each other to maintain the high temperature and to carry out the alloying process, A hot-dip galvanized steel sheet having a desired thickness can be produced.

Meanwhile, although not shown in the drawings, the method of manufacturing a hot dip galvanized steel sheet according to an embodiment of the present invention may further include a cooling gas injection step (not shown) performed after the alloying heat treatment step S260.

In the cooling gas spraying step, the cooling gas is sprayed onto the surface of the steel sheet by using an additional gas wiping device having a nozzle mounted so as to be mutually separated from each other by the alloying heat treated steel sheet.

At this time, the additional gas wiping device has substantially the same configuration as the gas wiping device. That is, the additional gas wiping device has a plurality of nozzles, and the cooling gas is sprayed onto the surface of the steel sheet subjected to alloying heat treatment through a plurality of nozzles. In this manner, by spraying the cooling gas using a plurality of nozzles, it becomes possible to perform a minute temperature control.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

100: gas wiping device 120: gas wiping body
140: gas wiping nozzle 160: drive control unit
10: Plating bath 20: Strip
30: Plating layer
S210: pickling and cold rolling step
S220: Annealing heat treatment step
S230: Cooling step
S240: Hot-dip galvanizing step
S250: heating gas injection step
S260: Alloying heat treatment step

Claims (8)

A gas wiping body that is installed to be spaced parallel to the strip before being subjected to the alloying heat treatment, the plating solution being coated through the inside of the plating bath;
A plurality of nozzles mounted on the ends of the gas wiping body so as to be mutually separated to separately inject a heating gas at a temperature of 490 to 650 DEG C and a pressure of 30 to 60 bar onto the surface of the strip; And
And a drive control unit for individually controlling on and off of the plurality of nozzles,
Wherein the plurality of nozzles have a diameter smaller than a diameter of a portion corresponding to a center of the strip and a diameter of a portion corresponding to an edge of the strip.
The method according to claim 1,
The plurality of nozzles
And is designed to be spaced apart along the width direction of the strip.
delete The method according to claim 1,
The heating gas
And at least one of Ar, O ₂ , H ₂ , and H ₂ O.
(a) pickling a hot-rolled steel sheet and cold-rolling it;
(b) annealing the cold-rolled steel sheet;
(c) cooling the annealed heat treated steel sheet;
(d) performing hot dip galvanizing on the cooled steel sheet;
(e) Using a gas wiping apparatus having a nozzle mounted thereon so as to be mutually separated from each other, the hot-dip galvanized steel sheet is heated to a temperature of 490 to 650 DEG C and a spray pressure of 30 to 60 bar Injecting a heating gas of a predetermined temperature; And
(f) alloying heat treatment on the steel sheet subjected to the heating gas injection,
Wherein the plurality of nozzles have a diameter smaller than a diameter of a portion corresponding to a center of the strip and a diameter of a portion corresponding to an edge of the strip.
delete 6. The method of claim 5,
The heating gas
Wherein at least one of Ar, O ₂ , H ₂ , and H ₂ O is contained in the molten zinc plated steel sheet.
6. The method of claim 5,
After the step (f)
(g) spraying a cooling gas onto the surface of the steel sheet using an additional gas wiping device having a nozzle mounted so as to be mutually separated from the alloyed heat treated steel sheet A method for manufacturing a hot dip galvanized steel sheet.

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