KR102413245B1 - Galvanized steel sheet with excellent corrosion resistance in chloride containing environment and method for manufacturing thereof - Google Patents

Abstract

Provided are a hot-dip galvanized steel sheet having excellent corrosion resistance in a chloride environment and a method for manufacturing the same.
The hot-dip galvanized steel sheet of the present invention is formed on at least one surface of the base steel sheet and the base steel sheet, and by weight% by itself, at least one selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La. Total: 0.01 to 0.3%, Al: 0.01 to 0.15%, the remainder of the hot-dip galvanized layer including Zn and other unavoidable impurities; in the hot-dip galvanized layer, the Ti, A first region in which the sum of the content of one or more elements selected from the group consisting of V, Nb, Ni, Cu, Zr, Y and La is 20% or more and a second region in which the sum of the content is less than 20% is formed, , and in the first region, the size is 0.01 to 10 μm and is composed of a (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound having a polygonal shape.

Description

Hot-dip galvanized steel sheet with excellent corrosion resistance in a chloride environment and manufacturing method thereof

The present invention relates to a galvanized steel sheet, and more particularly, to a galvanized steel sheet having excellent corrosion resistance in a chloride-containing environment and a method for manufacturing the same.

Galvanized steel sheet (GALVANIZED STEEL) is made by adding a small amount of elements to improve some plating properties with zinc as the main component. This hot-dip galvanized steel sheet actively utilizes the sacrificial corrosion resistance of zinc, which has superior oxidation properties than the base material, to prevent corrosion, oxidation, or the appearance of red rust caused by red oxide caused by Fe-based oxide as much as possible. do.

As a way to improve the corrosion resistance of these products, there are basically methods of increasing the plating adhesion amount and controlling the above-mentioned hot-dip galvanizing components. There is a limit because various problems such as plating peeling problem after press forming due to the thick plating layer and LIQUID METAL EMBRITTLEMENT in the case of welding increase. In the latter case, zinc is the main component, but magnesium (Mg), which has a dramatic effect on improving corrosion resistance by changing the structure of corrosion products, is added, and aluminum (Al) is added to stabilize it. (Zn-Al-Mg) development has been actively carried out so far, and commercialization has been achieved and is sold as a product. Examples include ZAM of NSSMC of Japan, Dyma, Super-Dyma of Nippon Steel, Magnelis of Arcelormittal, PosMAC1.5 and PosMAC3.0 of POSCO.

However, since these ternary hot-dip galvanizing basically contain the composition content ratio of [Al+Mg] from a minimum of 3.0 wt.% to a maximum of 15.0 wt.%, there are various constituent phases including a single Zn phase in the plating layer. There are many difficulties in maintaining a homogeneous surface phase due to the composition of the plating molten metal and the oxidation of the molten metal surface by Mg.

Accordingly, there is a need to develop a technique for improving workability in the production line through the addition of a small amount of alloying elements in the existing hot-dip galvanizing and, at the same time, to bring about a drastic improvement in corrosion resistance compared to the existing hot-dip galvanizing. to be.

Korean Patent Publication No. 2013-0133358

The present invention relates to a hot-dip galvanized steel sheet capable of dramatically improving corrosion resistance in an environment containing chloride in an existing hot-dip galvanized steel sheet and its corrosion resistance by inducing structural modification of surface oxides by adding a small amount of alloying elements An object of the present invention is to provide a manufacturing method.

The subject of the present invention is not limited to the above. Those of ordinary skill in the art to which the present invention pertains will have no difficulty in understanding the additional problems of the present invention from the contents throughout the present specification.

One aspect of the present invention is

Soji steel plate and

Formed on at least one surface of the base steel sheet, by weight% of one or more selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La: 0.01 to 0.3%, Al: 0.01 to 0.15 %, a hot-dip galvanized layer containing the remainder Zn and other unavoidable impurities;

In the hot-dip galvanized layer, the sum of the contents of one or more elements selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La, in weight % with respect to the whole of the hot-dip galvanized layer, is 20% or more A first region and a second region in which the sum of the content is less than 20% is formed,

Chloride, characterized in that it is composed of (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound having a size of 0.01 to 10 μm and a polygonal shape in the first region It relates to a hot-dip galvanized steel sheet having excellent corrosion resistance in the environment.

Another aspect of the present invention is

Preparing a base steel plate;

At least one selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La: 0.01 to 0.3% in total, Al: 0.01 to 0.15%, remainder galvanizing containing Zn and other unavoidable impurities preparing a bath;

hot-dip galvanizing by immersing the steel sheet in an inert atmosphere in a hot-dip galvanizing bath having a temperature greater than 450°C and less than 550°C;

first cooling the hot-dip galvanized steel sheet to a temperature range of 230 to 270 °C at a cooling rate of 0.01 to 20 °C/s; and

It relates to a method of manufacturing a hot-dip galvanized steel sheet excellent in corrosion resistance in a chloride environment, including; secondary cooling of the primary cooled hot-dip galvanized steel sheet to room temperature at a cooling rate in the range of 0.01 to 10°C/.

According to one aspect of the present invention, a hot-dip galvanized steel sheet with excellent corrosion resistance, with reduced sensitivity to corrosion due to shape modification of the surface layer oxide in contact with the external environment in a corrosive environment condition containing chloride compared to the existing hot-dip galvanized material, and A manufacturing method thereof can be provided.

1 is a photograph showing cross-sections of an invention material and a comparative material according to an embodiment of the present invention observed at a magnification of 1000 using a back-sacattered image (BSI) in an electron scanning microscope.
2 shows the chemical composition results obtained by 2D scanning with Electron-Probe Micro-Analysis (EPMA) for the inventive material and the comparative material according to an embodiment of the present invention.
3 shows the results of a co-potential polarization test in which the corrosion potential and corrosion current are measured by exposing the invention material and the comparative material according to an embodiment of the present invention to a corrosive atmosphere containing chloride.
Figure 4 is a photograph of the cross-sectional structure of the corrosion product by performing cross-section processing using a Focused-Ion Beam (FIB) after corrosion test of the invention material and the comparative material according to an embodiment of the present invention.

The present inventors provide a method to increase corrosion resistance in a corrosive environment including chloride, and add a specific element to the corrosion product by adding a specific element, rather than a galvanized layer, where penetration of the external corrosive environment is easy due to corrosion products having an existing porous structure. Research was conducted to improve the corrosion resistance by changing the structure to make a dense state. As a result, by optimizing the alloy composition and plating conditions in the hot-dip galvanizing bath, a plating layer capable of forming an intermetallic compound of a certain size in the hot-dip galvanizing process atmosphere is controlled so that the compound can be uniformly dispersed in the plating layer. A new method was devised, and through this, it was confirmed that a galvanized steel sheet having intended physical properties could be provided, and the present invention was completed.

Hereinafter, the hot-dip galvanized steel sheet of the present invention excellent in corrosion resistance containing chloride will be described in detail. In the present invention, when the content of each element is expressed, it means weight % unless otherwise specified.

The hot-dip galvanized steel sheet having excellent corrosion resistance in the corrosive mirror containing chloride according to an aspect of the present invention is formed on at least one surface of the base steel sheet and the base steel sheet, and by weight% of Ti, V, Nb, Ni, Cu, Zr, Y and La at least one sum selected from the group consisting of: 0.01 to 0.3%, Al: 0.01 to 0.15%, the remainder of the hot-dip galvanized layer containing Zn and other unavoidable impurities; may include.

In the present invention, there is no particular limitation on the type of the holding steel sheet. For example, it may be a Fe-based base steel sheet used as a base of a conventional galvanized steel sheet, that is, a hot-rolled steel sheet or a cold-rolled steel sheet, but is not limited thereto. In addition, the base steel sheet may include, for example, carbon steel, ultra-low carbon steel, and high manganese steel used as a material for automobiles, but is not limited thereto.

However, in the case of a hot-rolled steel sheet, there may be a problem of having a large amount of oxide scale on the surface, and such oxide scale deteriorates plating adhesion and deteriorates plating quality. Therefore, when using a hot-rolled steel sheet as a base steel sheet, it can be made into a hot-rolled steel sheet from which oxide scale has been previously removed by an acid solution.

In addition, in the present invention, the hot-dip galvanizing layer may be formed on one side or both sides of the base steel sheet. In addition, the hot-dip galvanized layer is, by weight%, of one or more selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La: 0.01 to 0.3%, Al: 0.01 to 0.15%, balance Zn and other unavoidable impurities.

[Plating layer composition]

The sum of at least one selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La: 0.01 to 0.3%

The hot-dip galvanized layer of the present invention is a group consisting of titanium (Ti), vanadium (V), neobium (Nb), nickel (Ni), copper (Cu), zirconium (Zr), yttrium (Y) and lanthanum (La). It may include one or more selected from, and the content may be 0.01 to 0.3% in total.

The elements of Ti, V, Nb, Ni, Cu, Zr, Y, and La are elements that play a very important role in controlling the shape of corrosion products when the corrosion of the galvanized layer proceeds. It is an element that can form an intermetallic compound with Al in the vicinity of 400~500℃, and at the same time induces nucleation of corrosion products.

Specifically, the elements of Ti, V, Nb, Ni, Cu, Zr, Y, and La are (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al based on the surface layer and inside of the plating layer during the plating process. By creating a secondary phase, which is an intermetallic compound, the hot-dip galvanized layer is exposed to a corrosive environment and at the same time acts as a nucleation site for corrosion products that are deposited on the surface. Corrosion resistance can be improved compared to conventional hot-dip galvanizing. These corrosion products have the effect of suppressing microcracks that may occur at the boundary with the base material compared to the existing ones, so the effect of corrosion resistance is further doubled.

One selected from the group consisting of titanium (Ti), vanadium (V), neobium (Nb), nickel (Ni), copper (Cu), zirconium (Zr), yttrium (Y) and lanthanum (La) in the present invention If the total content of the above is less than 0.01%, the effect of improving corrosion resistance by reforming corrosion products can be sufficiently obtained by generating (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compounds. none. On the other hand, at least one selected from the group consisting of titanium (Ti), vanadium (V), neobium (Nb), nickel (Ni), copper (Cu), zirconium (Zr), yttrium (Y), and lanthanum (La) If the total content exceeds 0.3%, it is rather difficult to form an inhibition layer that inhibits excessive growth of the compound and the diffusion of Fe-burst into the plating layer during hot-dip galvanizing. An incidental problem different from the object of the invention arises.

Therefore, in the present invention, the total content of at least one selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La in the hot-dip galvanizing layer may be 0.01 to 0.3%, preferably 0.01 to 0.25% may be, and more preferably 0.05 to 0.25%.

Meanwhile, in the present invention, the meaning of the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound is Ti, V, Nb, Ni, Cu, Zr, Y and La It refers to a case in which one or more elements selected from the group consisting of Al and Al form an intermetallic compound.

Al: 0.01~0.15%

The aluminum (Al) in the hot-dip galvanizing layer forms an inhibition layer that prevents Fe diffusion into the plating layer by generating an Fe-Al-based intermetallic compound at the interface between the plating layer and the base steel sheet in the hot-dip zinc alloy plating bath. However, in the present invention, there is also a purpose for the formation of an (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound, which is an essential requirement for exhibiting the desired effect. do.

Therefore, if the Al content in the zinc plating layer is less than 0.01%, the continuous formation of the aforementioned suppression layer becomes difficult, and the effect of the suppression layer for preventing Fe diffusion into the plating layer cannot be sufficiently obtained. On the other hand, when the Al content in the zinc plating layer exceeds 0.15%, an excessive Zn/Al binary eutectic phase is formed in the plating layer, thereby reducing the sacrificial anticorrosive effect of zinc plating on the cross section and the painted portion. Accordingly, in the present invention, it is preferable to include Al in an amount of 0.01 to 0.15%, and more preferably 0.1 to 0.15% of Al in the galvanized layer.

In the present invention, in addition to the composition of the hot-dip galvanizing layer, the remainder may be Zn and other unavoidable impurities. Here, other unavoidable impurities may be unintentionally mixed in the manufacturing process of a conventional hot-dip galvanized steel sheet and cannot be completely excluded, and those skilled in the art can easily understand the meaning, so it is not defined does not

On the other hand, the other unavoidable impurities may include Fe, which is likely to be introduced by diffusion from the base steel sheet to the plating layer. Specifically, since the diffusion of Fe from the base steel sheet to the plating layer is limited by an inhibition layer to be described later formed at the interface between the base steel sheet and the zinc plated layer, the amount in the plating layer is insignificant, so level, and in some cases, the Fe content can be ignored.

[Plating layer microstructure]

Furthermore, according to one aspect of the present invention, in the hot-dip galvanizing layer, regions having different contents of one or more elements selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La may be separated and present. have. Specifically, in the hot-dip galvanizing layer of the present invention, the total content of at least one element selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La by weight % is 20% or more of the first A second region is formed in which the total content of the region and at least one element selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La is less than 20%. As such, the reason for the division of the region is due to the non-uniform/non-equilibrium element diffusion of elements immediately after passing through the molten metal, that is, supercooling during plating, and is directly related to the port temperature/pot charging time/cooling rate, which will be described later. By intentionally applying accelerated cooling during primary cooling among the two-stage cooling of the plated steel sheet manufacturing process, regions of the plated layer can be formed separately.

In the present invention, when the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound corresponds to the first region in which the composition ratio is 20% or more, nuclei of the compound are generated and grown is possible, and when it corresponds to the second region, which is less than 20%, nucleation in the corresponding hot-dip galvanizing layer is impossible, so that it is impossible to precipitate as a secondary phase (a hexagonal polygonal shape in the present invention). However, at the boundary between the first region and the Zn single phase, there may be some regions with less than 20% due to a partial concentration gradient.

And, according to one aspect of the present invention, in the first region, the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound has a size of 0.01 to 10 μm and a polygonal shape. can be accomplished with

In the present invention, the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound is homogeneously generated inside and outside the hot-dip galvanized layer. In particular, when the compound present in the plating surface layer is exposed to a corrosive atmosphere containing chloride, it allows corrosion products having a dense structure through uniform generation and growth of corrosion products. Additionally, by blocking additional corrosion factors through suppression of corrosion cracking, the effect of improved corrosion resistance is obtained.

Meanwhile, according to an aspect of the present invention, the size of the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound may be in the range of 0.01 to 10 μm. In the present invention, the size of the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound is measured to penetrate the center of the intermetallic compound when the intermetallic compound is observed. It can be defined as the arithmetic mean value of the major and minor axis, that is, '(major axis + minor axis)/2'.

In the present invention, the upper limit size of the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound is not particularly limited in relation to corrosion resistance, but when it exceeds 10 μm It is expected that there is a high possibility of causing adverse functions with respect to other physical properties other than the improvement of corrosion resistance, which is the purpose of the present invention, such as hydrogen embrittlement and liquefied metal embrittlement. However, in the case of the lower limit, the finer the size of the (Ti, V, Ni, Nb, Cu, Zr, Y, La)-Al-based intermetallic compound is, the more effective it is to achieve the object of the present invention. Although not limited, the lower limit of the size of the compound may be limited to 0.01 μm in consideration of the temperature conditions and cooling process of hot-dip galvanizing.

In the present invention, the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound having the above-mentioned size of 0.01 to 10 μm and a polygonal shape in the hot-dip galvanizing layer is applied to the entire area of the plating layer. is formed over the , and, according to the plating conditions proposed in the present invention, each region may be formed separately as in the above-described first region and second region.

That is, according to one aspect of the present invention, in the zinc plating layer of the present invention, the first region and the second region may be formed in a dispersed form over the entire region of the plating layer.

Meanwhile, according to an aspect of the present invention, the hot-dip galvanized layer may have a thickness of 1 to 30 μm, and more preferably, a thickness of 5 to 20 μm.

In addition, the hot-dip galvanized steel sheet of the present invention may include a suppression layer mainly composed of an Fe-Al-based intermetallic compound between the base steel sheet and the above-described hot-dip galvanized layer. The suppression layer may be formed by diffusion of Fe of the steel sheet in the initial stage of plating and Al in the plating bath, and serves to improve the adhesion between the steel sheet and the zinc plating layer, and at the same time, the amount of Fe from the steel sheet to the zinc plating layer. It acts as a barrier to spread.

The hot-dip galvanized steel sheet of the present invention including the hot-dip galvanized layer having the configuration as described above does not contain (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compounds in the galvanized layer. Compared with the conventional galvanized steel sheet that does not contain zinc, it suppresses the inflow of external corrosive substances by increasing the adhesion between the corrosion product and the steel sheet at the same time as the zinc sacrificial method. can induce

Next, a method for manufacturing a hot-dip galvanized steel sheet having excellent corrosion resistance in a chloride environment according to another aspect of the present invention will be described in detail.

A method for manufacturing a hot-dip galvanized steel sheet according to an embodiment of the present invention, comprising the steps of preparing a base steel sheet; At least one selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La: 0.01 to 0.3% in total, Al: 0.01 to 0.15%, remainder galvanizing containing Zn and other unavoidable impurities preparing a bath; hot-dip galvanizing by immersing the steel sheet in an inert atmosphere in a hot-dip galvanizing bath having a temperature greater than 450°C and less than 550°C; first cooling the hot-dip galvanized steel sheet to a temperature range of 230 to 270 °C at a cooling rate of 0.01 to 20 °C/s; and secondary cooling of the firstly cooled hot-dip galvanized steel sheet to room temperature at a cooling rate in the range of 0.01 to 10° C./.

First, in the present invention, a steel sheet is prepared, and the description thereof is as described above.

Next, in the present invention, a hot-dip galvanizing bath is prepared.

In the present invention, the hot-dip galvanizing bath is 0.01 to 0.3%, Al: 0.01 to 0.15 in terms of its own weight %, in the total of one or more selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La %, balance Zn and other unavoidable impurities.

And in some cases, the Al content in the hot-dip galvanizing bath may be managed to 0.10 to 0.15%. In addition, the total content of at least one selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La in the hot-dip galvanizing bath may be managed in the range of 0.05 to 0.25%.

In addition, in the present invention, in order to obtain the above-mentioned hot-dip galvanizing layer, it is very important that at least one component selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La is sufficiently melted in the plating bath. . However, the commonly known melting point of Ti is about 1668°C, the melting point of V is about 1910°C, the melting point of Nb is about 2477°C, the melting point of Ni is about 1455°C, the melting point of Cu is about 1085°C, and the melting point of Zr is about 1855° C., the melting point of Y is 1526° C., and the melting point of La is about 920° C. In general, considering that the temperature of the plating bath during hot-dip galvanizing does not exceed the zinc melting point (about 419.5° C.) and up to 500° C., it may be difficult to thermodynamically melt even if the above components are added to the plating bath.

However, in the present invention, the method of melting one or more components selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La in the plating bath is not specifically limited, and plating as an embodiment The components can be sufficiently melted in the plating bath by adding the above components to the bath and erosion-melting the components by maintaining them at a normal plating bath temperature for a long time (eg, about 24 hours or more). More specifically, if the reaction is performed at the galvanizing bath temperature for a long time, erosion may occur due to the flow of liquid zinc in the molten metal, and due to such erosion, Ti, V, Nb, Ni, Cu, Zr, Y and La One or more components selected from may be melted.

And in the present invention, hot-dip galvanizing is performed by immersing the base steel sheet in a hot-dip galvanizing bath having a temperature of more than 450°C and less than 550°C in an inert atmosphere. In this case, the hot-dip galvanizing layer formed by the hot-dip galvanizing may be formed on one or both surfaces of the base steel sheet.

In the present invention, the temperature of the hot-dip galvanizing bath may be greater than 450°C and less than 550°C. Conventionally, in the case of manufacturing a galvanized steel sheet, the temperature of the plating bath is controlled to a temperature that does not exceed 500°C above the melting point, whereas in the present invention, the temperature of the zinc plating bath is controlled relatively high to be more than 450°C and less than 550°C. The structure of the intended plating layer can be obtained.

In this way, when the temperature of the galvanizing bath is controlled to be high, one or more components selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y, and La in the plating bath are easily eroded during preparation of the plating bath. When plating is performed by immersing the steel sheet in a zinc plating bath at the same time, (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound can be formed Sufficient thermal energy may be provided.

That is, in the present invention, when plating is performed by immersing the base steel sheet in a zinc plating bath, one or more components selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La in the zinc plating bath are preferentially added. It is necessary to sufficiently provide thermal energy so that it is melted through solid solution with zinc and at the same time, (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound can be formed. This is made possible by controlling the above-mentioned temperature of the galvanizing bath to be more than 450°C and less than 550°C, and cannot be achieved when the temperature of the galvanizing bath is set to 450°C or lower or 550°C or higher.

Specifically, in the present invention, when the temperature of the galvanizing bath is 450° C. or less, (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compounds are not sufficiently generated, resulting in intended chloride-containing corrosion It is not possible to obtain a galvanized layer that can improve corrosion resistance in the environment. On the other hand, if the temperature of the galvanizing bath is 550° C. or higher, the possibility of erosion of the base steel sheet and the equipment inside the plating bath increases the possibility of shortening the life of the equipment.

In addition, according to one aspect of the present invention, during hot-dip galvanizing, the pull-in temperature when the base steel sheet is immersed in the galvanizing bath may be higher than the temperature of the galvanizing bath by 5°C or more, and in some cases by 20°C or more. . In the present invention, the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound is formed in the zinc plating layer by controlling the pull-in temperature of the steel sheet to be 5° C. or higher higher than the temperature of the plating bath. It is possible to provide sufficient thermal energy to enable That is, when the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound is sufficiently generated, a galvanized layer having the intended characteristics can be obtained.

More preferably, the pull-in temperature of the base steel sheet when immersed in the galvanizing bath may be more than 565 ℃ and less than 600 ℃. By controlling the lead-in temperature of the base steel sheet to less than 600° C., it is possible to secure the corrosion resistance of the zinc plating and also the gloss of the plating material by preventing the Fe-burst region from being excessively generated. On the other hand, by controlling the lead-in temperature of the base steel sheet to more than 565° C., there is an effect that plating can proceed in a range that does not affect the temperature condition of the plating port set above as much as possible.

In addition, according to one aspect of the present invention, one or more components selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La, which are elements having high oxygen affinity in the temperature atmosphere of the plating bath, are aluminum ( In order to form a stable intermetallic compound with Al), it is preferable to perform plating in an inert atmosphere for the purpose of suppressing the formation of oxides or nitrides of the elements, and it is more preferable to use argon gas in an inert gas.

That is, according to one aspect of the present invention, in order to block or remove an active gas containing oxygen during plating, plating may be performed in a corresponding atmosphere using argon gas, which is an inert gas. More specifically, it can be performed by spraying argon gas at the time of plating.

In addition, according to an aspect of the present invention, it may further include the step of gas wiping treatment for the base steel sheet selectively formed with a plating layer before the subsequent cooling process. The gas wiping is a process for adjusting the plating adhesion amount, and the method is not particularly limited.

In this case, air or an inert gas may be used as the gas used in the present invention, but preferably, an inert gas such as nitrogen or argon may be sprayed to prevent formation of additional oxides or nitrides in the zinc plating layer. Specifically, air may be used as the gas used in the process, but an inert gas such as nitrogen or argon is preferably used, and more preferably argon gas should be used. This is because, when an active gas containing oxygen is used, a coarse oxide or film of (Ti, V, Ni, Nb, Cu, Zr, Y, La) is formed on the surface of the plating layer, thereby causing surface defects of the plating layer, thereby lowering the corrosion resistance because it can cause

According to one aspect of the present invention, in performing plating, the plating amount per side may be in the range of 30 to 150 g/m ² , and through this, a galvanized layer having a thickness of 5 to 20 μm can be obtained.

Finally, in the present invention, the hot-dip galvanized base steel sheet is cooled, and in this case, cooling can be performed in stages.

Specifically, in the present invention, the step of primary cooling the hot-dip galvanized steel sheet to a temperature range within 230 ~ 270 ℃ / s at a cooling rate of 0.01 ~ 20 ℃ / s; and secondary cooling of the firstly cooled hot-dip galvanized steel sheet to room temperature at a cooling rate in the range of 0.01 to 10° C./.

In the present invention, in order to obtain a hot-dip galvanized layer having a prismatic (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound having the above-mentioned predetermined size, stepwise cooling is performed. desirable. .

Specifically, in the present invention, the solid-liquid phase of zinc is properly formed while sufficiently solidifying the zinc single phase through the first cooling process, and (Ti, V, Nb, Ni, Cu, It is possible to shorten the time for coarsening and growth of the Zr, Y, La)-Al-based intermetallic compound, and then, in the second cooling process, by lowering the cooling rate relative to the first cooling rate, It can be solidified by minimizing thermal shock.

Specifically, in the present invention, the size of the intermetallic oxide formed in the first region can be controlled by controlling the cooling step. In other words. During cooling, the growth of the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound in the first region proceeds. By controlling as , a (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound having a size of 0.1 to 10 μm can be formed in the first region. On the other hand, in the second cooling step, since the cooling is already completed, the size and distribution of the (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compounds are not significantly affected, but the plating In consideration of the thermal shock that may occur on the surface layer, weak cooling may be performed.

At this time, in the present invention, in the cooling step, gas is sprayed to both the front and back surfaces of the plating material, and preferably, an inert gas such as argon is sprayed to prevent further oxidation.

According to the present invention, in order to obtain a zinc plating layer having the size and shape of the above-described (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound, a method of cooling including moisture during cooling It is preferable to exclude In consideration of this, in the present invention, gas may be sprayed to both the front and back surfaces of the plating material to be cooled, and preferably, an inert gas such as nitrogen or argon may be sprayed for cooling, but the present invention is not limited thereto.

Through the manufacturing process as described above, in the present invention, a (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound having a size of 0.01 to 10 μm and a polygonal shape inside the hot-dip galvanizing layer A hot-dip galvanized steel sheet having this dispersed microstructure can be obtained.

In the hot-dip galvanized steel sheet according to the present invention, since zinc-based oxide is formed in an actual use environment, the intermetallic compound acts as a nucleation site according to the potential difference. Corrosion resistance can be improved according to structural densification and the effect of suppressing cracks at the plating layer/steel plate interface.

Hereinafter, the present invention will be described in detail through examples.

(Example)

As a test piece for hot-dip galvanizing, a cold-rolled steel sheet of TRansformation Induced Plasticity (TRIP) steel having a thickness of 1.0 mm, a width of 110 mm, and a length of 200 mm and having the composition shown in Table 1 below was prepared as a base steel sheet. Thus, the base steel sheet was subjected to hot-dip galvanizing under the conditions of Tables 2 and 3 to prepare hot-dip galvanized steel sheets, respectively. Meanwhile, in the plating process, all active gases such as oxygen were blocked or removed, and argon gas, an inert gas, was used to suppress the formation of (Ti, V, Nb, Ni, Cu, Zr, Y, La) related oxides. The experiment was conducted through atmosphere control using In the cooling process after plating, nitrogen was sprayed on the front and back surfaces of the steel sheet to cool to room temperature.

division Substance steel sheet composition (wt%) C Mn Si P S Sol. Al leftover content 0.18 2.45 1.40 0.01 0.003 0.03 Fe and impurities

division Hot-dip galvanizing bath composition (wt%) Ti, V, Nb, Ni, Cu, Zr, Y and La at least one total content selected from the group consisting of Al Mg invention 0.17 0.14 Tr. comparative goods - 0.13 Tr.

*The remainder of the composition of the hot-dip galvanizing bath in Table 2 is Zn and unavoidable impurities.

division Plating conditions Plating layer thickness (㎛) Plating bath temperature (℃) Steel plate inlet temperature
(℃) first cooling rate
(℃/s) 2nd cooling rate
(℃/s) invention 500 567 15.0 8.0 12.98 comparative goods 485 565 15.0 8.0 9.10

First, a scanning electron microscope (SEM) was used to observe the structure of the hot-dip galvanized steel sheet manufactured as described above. 1 shows a photograph of the cross-sections of the inventive material and the comparative material according to an embodiment of the present invention observed at 1000 magnification using a back-sacattered image (BSI) in an electron scanning microscope. is shown, and Figure 1 (b) shows a comparative material.

As shown in Fig. 1(a), it can be seen that the invention material is divided into three phases according to the degree of contrast, unlike the comparative material of Fig. 1(b). 1 is taken with a back-scattered image (BSI) in a scanning electron microscope, and the contrast is different depending on the density of each constituent element. That is, it is confirmed that the hot-dip galvanized steel sheet of the invention material is divided into a galvanized layer area, a polygonal (Ti,V,Ni,Nb,Cu,Zr,Y,La)-Al-based intermetallic area, and a base steel sheet area. can In addition, the size of the intermetallic compound can be confirmed in the corresponding FIG. 1, and the size was 0.01 to 10 μm.

In addition, to confirm the distribution of each element, the chemical composition was 2D scanned by electron-backscattered diffraction (EBSD), and the results are shown in FIG. 2 . Figure 2 (a) shows the invention material, Figure 2 (b) shows the comparative material, in the case of the invention material of Figure 2 (a), in the plating layer (Ti, V, Ni, Nb, Cu, Zr, It can be confirmed that the Y,La)-Al-based intermetallic compound exists in the form of a polygon in the hot-dip galvanizing layer.

In the present invention, the method of measuring the component ratios of Ti, V, Nb, Ni, Cu, Zr, Y and La uses energy dispersive spectroscopy using a scanning electron microscope [ENERGY DISPERSIVE SPECTROMETER] for each metal at a specific location in the plating layer. It can be identified through the intrinsic energy value emitted from the electron orbital shell of the element, and the ratio of the constituents of each metal element can be measured through the energy ratio generated. In the case of the present invention, a region in which the weight% of at least one element among Ti, V, Nb, Ni, Cu, Zr, Y and La in the plating layer is 20% or more, and (Ti, V having a polygonal shape in the region) , Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compounds were confirmed to be formed. On the other hand, in the case of the comparative material, since the plating layer consists of a region in which the weight % of one or more of Ti, V, Nb, Ni, Cu, Zr, Y and La is less than 20%, therefore, the component elements in the galvanized layer are dissolved It was confirmed that it exists in the state [SOLID SOLUTION].

On the other hand, the galvanized steel sheets of the invention material and the comparative material prepared according to the above were exposed to an environment containing chloride, and corrosion resistance over time was evaluated. In other words, in order to confirm the corrosion resistance of the present invention material and the comparative material when exposed to chloride in a corrosive atmosphere, a potentiostatic polarization test was performed to measure the corrosion potential and corrosion current according to time in a solution containing 3.5 wt.% NaCl, The results are shown in FIG. 3 .

In FIG. 3, the point where the oxidation curve of the metal corresponding to the upper part and the reduction curve corresponding to the lower part meet means the corrosion state occurring in the exposed atmosphere, and the Y-axis value at that point represents the corrosion potential and the X-axis value represents the corrosion current. corresponds to Here, the corrosion potential is a measure of stability with respect to thermodynamic oxidation, and in general, the higher the Y-axis value is, the less metal oxidation occurs (NOBLE), and the lower the value, the more oxidation occurs (ACTIVE). In the case of corrosion current, it means the actual rate of corrosion. In general, the higher the value of the current, the faster the metal oxidation proceeds. In the same sense, the value of the corrosion current when exposed to the same environment. The higher the value, the faster the progress of corrosion.

Therefore, as a result of measuring the corrosion potential and corrosion current of the inventive material and the comparative material, the corrosion potential of the inventive material showed thermodynamically ACTIVE behavior under the influence of intermetallic compounds, but the corrosion current indicating the rate of metal corrosion was 39.7 compared to the comparative material. It can be seen that the % is lowered. It can be seen that this behavior is a corrosion behavior similar to that of stainless steel in which the corrosion potential is ACTIVE, but the corrosion resistance is significantly improved by forming a dense passive film, and the corrosion current is significantly reduced.

Meanwhile, FIG. 4 is a photograph of a cross-sectional structure of a corrosion product by performing a corrosion test on an invention material and a comparative material according to an embodiment of the present invention, and then cross-sectioning using a Focused-Ion Beam (FIB). That is, after the corrosion test of the invention material and the comparative material in the chloride environment was completed, the corrosion products of the test piece were observed under the same conditions to confirm the corresponding behavior. The results observed under a microscope are shown in FIG. 4 , and FIG. 4 ( a ) shows the inventive material, and FIG. 4 ( b ) shows the comparative material.

As shown in Figure 4 (a-b), it can be confirmed that structurally completely different from each other in the surface and cross-sectional microstructure of the corrosion product. That is, the intermetallic compound intentionally created in the plating layer serves as a nucleation site for corrosion products to have a more dense and dense structure in the same chloride-containing environment, which is not observed in corrosion products observed in comparative materials. It is a phenomenon. Also, in the case of comparative materials, which are corrosion products of coarse structures, the corrosion resistance of zinc as a sacrificial anode can be expected to some extent. Corrosion progresses faster than invention materials, which can be seen as a factor that shortens the life of the steel sheet.

As described above, in the detailed description of the present invention, a preferred embodiment of the present invention has been described, but those of ordinary skill in the art to which the present invention pertains may make various modifications within the limits that do not depart from the scope of the present invention. Of course it is possible. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the following claims as well as equivalents thereof.

Claims (9)

Soji steel plate and
Formed on at least one surface of the base steel sheet, by its own weight %, the total of one or more selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La: 0.01 to 0.3%, Al: 0.01 to 0.15 %, a hot-dip galvanized layer containing the remainder Zn and other unavoidable impurities;
In the hot-dip galvanized layer, the sum of the contents of one or more elements selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La in weight % with respect to the whole of the hot-dip galvanized layer is 20% or more The first region and the second region in which the sum of the content is less than 20% (excluding 0%) are formed,
Chloride, characterized in that it is composed of (Ti, V, Nb, Ni, Cu, Zr, Y, La)-Al-based intermetallic compound having a size of 0.01 to 10 μm and a polygonal shape in the first region Hot-dip galvanized steel sheet with excellent corrosion resistance in the environment.
The hot-dip galvanized steel sheet having excellent corrosion resistance in a chloride environment according to claim 1, wherein a suppression layer made of an intermetallic compound of Fe and Al is formed between the base steel sheet and the hot-dip galvanized layer.
The method according to claim 1, wherein the hot-dip galvanized layer contains at least one selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La in a total content in the range of 0.05 to 0.25%. Hot-dip galvanized steel sheet with excellent corrosion resistance in a chloride environment.
The hot-dip galvanized steel sheet having excellent corrosion resistance in a chloride environment according to claim 1, wherein the content of A of the hot-dip galvanized layer is 0.1 to 0.15%.
Preparing a base steel plate;
At least one selected from the group consisting of Ti, V, Nb, Ni, Cu, Zr, Y and La: 0.01 to 0.3% in total, Al: 0.01 to 0.15%, remainder galvanizing containing Zn and other unavoidable impurities preparing a bath;
hot-dip galvanizing by immersing the steel sheet in an inert atmosphere in a hot-dip galvanizing bath having a temperature greater than 450°C and less than 550°C;
first cooling the hot-dip galvanized steel sheet to a temperature range of 230 to 270° C. at a cooling rate of 0.01 to 20° C./s; and
Secondary cooling of the firstly cooled hot-dip galvanized steel sheet to room temperature at a cooling rate in the range of 0.01 to 10° C./Method for manufacturing a hot-dip galvanized steel sheet having excellent corrosion resistance in a chloride environment, including
[Claim 6] The chloride environment according to claim 5, wherein when the hot-dip galvanizing bath of the base steel sheet is drawn in, the inlet temperature is controlled to be 5°C or more higher than the temperature of the hot-dip galvanizing bath within the range of more than 565°C and less than 600°C. A method for manufacturing a hot-dip galvanized steel sheet with excellent corrosion resistance in
delete [6] The method of claim 5, wherein the inert atmosphere uses argon gas.
[6] The method of claim 5, wherein in the first and second cooling steps, an inert gas is sprayed on the front and back surfaces of the hot-dip galvanized steel sheet for cooling. .

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