KR101800550B1 - Coated steel material and method for producing the same - Google Patents

Abstract

It is an object of the present invention to provide a coated steel material in which excellent salt resistance is maintained for a relatively long period of time.
The coated steel of the present invention is a coated steel comprising a base steel and a coating layer formed on the surface of the base steel, wherein the coating layer has an average thickness of 8 탆 or more and 105 탆 or less and further contains an Al compound, a Cr compound, Wherein the compound is an oxide, an oxyhydroxide, or a combination thereof. Wherein the coating layer contains 0.08 to 10.5% by mass of Al oxide, Al oxyhydroxide or a combination thereof, 0.08 to 10.5% by mass of Cr oxide, 0.08 to 10.5% by mass of Cu oxide, Fe ₃ O ₄ and? -FeOOH as Fe oxyhydroxide may be contained in a total amount of 29.5 mass% or more. The average particle diameter of Fe ₃ O ₄ and α-FeOOH is preferably 4.5 nm or more and 22 nm or less, respectively.

Description

TECHNICAL FIELD [0001] The present invention relates to a coated steel material,

The present invention relates to a coated steel and a method of manufacturing the same.

Steel is widely used as a member of various structures. However, when it is used in seashells or seawater constructions such as ships, marine structures, and bridges used under corrosive environments where seawater and / or flying sea salt particles are the main cause, And the formation of corrosion holes, etc., may be caused to decrease the strength. In particular, it is known that ballast tanks of ships are exposed to severe corrosive environments. In recent years, as a clean energy generation technology that does not emit carbon dioxide, which is a greenhouse effect gas, from the viewpoint of global environmental conservation, it can be applied to the generation of wind power, blue power, tidal power, ocean current, Technology is attracting attention. Such marine structures are also expected to be exposed to more corrosive environments than conventional beaches or structures in seawater. For these reasons, it is required to improve the flame resistance of these steels by a corrosion technique.

Examples of the system technology include an electric system, a surface treatment, and the like. Examples of the surface treatment include a spray coating in which a coating is formed by coating, and a type spraying in which a coating is formed by spraying. Further, it is known that the rust formed on the surface of the steel acts as a protective coating for improving the resistance to water. Therefore, a method of using rust for surface treatment of the steel is also conceivable. Further, a method of combining the improvement of the steel itself and the improvement of the steel itself and the surface treatment is also proposed.

The electric system, which is one type of technique, is a method for suppressing corrosion by manipulating the electrode potential and is effective for improving the salt water resistance of a steel material that is always immersed in seawater. However, improvement of the salt water resistance of a steel material, which is not always immersed in seawater, It is not very effective. Specific examples of the steel material for which the improvement of the saline resistance by the electric system is not effective include a steel material in a maritime part of an offshore structure exposed to a corrosive environment such as seawater splashes, A steel material on the inner surface of a ballast tank for repeating the injection and drainage of seawater according to the loading load, and the like. In addition, as another concrete example, a steel material of a structure such as an iron bridge which is exposed to flysch of sea salt which is a fine particle made of salt originating from seawater and which is close to a coast where a drying environment and a wet environment are repeated is also cited. Thus, the electrical system is not very effective for steel used for ballast tanks or marine structures of ships.

In addition, the conventional coating method, which is a technique of other systems, is a method of coating a coating material containing various resins such as epoxy resin, chlorinated rubber, acrylic resin, uretene resin, and fluorine resin as a main component according to the environment, Thereby improving the flame resistance. However, the coating film is easily scratched or peeled off due to deterioration due to ultraviolet rays, damage due to some external mechanical action, or the like, and as a result, there is a possibility that the steel material is exposed and the corrosion progresses. For example, there is a case where the amount of corrosion wear in a year is 1 mm in a portion where a coating film of a ballast tank of a ship is peeled off. For this reason, the anticorrosion coating requires maintenance such as regular inspection and repainting after coating, but requires considerable expense and air (construction period) for repainting. In addition, the structures such as ships, offshore structures, bridges, etc. are difficult to access in the sea, high places that can not be reached without footing, structurally entangled places, and the like. Therefore, from the viewpoint that the period of time in which the salt water resistance is maintained is short, the anti-corrosive coating may not be practical for the steel used for the ballast tank of the ship or the structure of the marine structure.

Another type of technology spraying is a method in which a thermal sprayed coating is formed on the surface of a steel material by using a metal or alloy that is nobler than steel such as zinc, aluminum or magnesium as a thermal spraying material, Action. However, this type of spraying requires the maintenance of an average thickness of the thermal sprayed coating by periodic reuse because it exerts a corrosive action by the consumption of the thermal sprayed coating. However, as described above, There are many places. Therefore, the method spraying may not be practical for the steel used for the ballast tank of the ship or the marine structure in view of the short period of time in which the salt water resistance is maintained, as in the case of the anti-corrosion coating.

On the other hand, it acts as a molten, protection film for suppressing the intrusion of corrosive substances of Fe compounds, such as α-FeOOH, β-FeOOH, γ-FeOOH, Fe ₃ O ₄ formed on the surface of the steel in seawater corrosive environments, steel It is well known that the corrosion of austenitic stainless steels is slightly inhibited. However, since the grain size of the Fe compound is relatively large due to lack of denseness, the effect of suppressing the penetration of the corrosive substance is small, and thus the resistance to flame resistance is not remarkably improved. In addition, since the adhesion of the molten metal to the steel is relatively low, it easily peels off and falls off. Therefore, the method of using the rust for the surface treatment of the steel can not be said to be very practical.

Further, in addition to the above-described surface treatment with the steel material, a technique for combining the improvement of the steel itself and the improvement of the steel itself and the surface treatment has been proposed. Specifically, for example, there is known a method using a steel material for coating having a specific composition (see Japanese Patent Application Laid-Open No. 12-211117), a method using a steel material having a specific chemical composition covered with a protective growth layer containing a specific metal 2014-5499) and the like have been proposed. However, even with the above-described conventional methods, the period in which excellent salt water resistance is maintained is insufficient.

Japanese Patent Application Laid-Open No. 1222117 Japanese Patent Application Laid-Open No. 2014-5499

The present invention has been accomplished on the basis of the above-described circumstances, and it is an object of the present invention to provide a coated steel material in which excellent salt resistance is maintained for a relatively long period of time and a method for producing the same.

The inventors of the present invention have studied corrosion mechanism of steel in a seawater corrosion environment and studied a new technique that does not depend on the surface treatment such as conventional coating. As a result, as described above, since the rust formed from the Fe compound formed on the surface of the steel in the seawater-corrosion environment does not significantly improve the resistance to salt water, and is easily peeled off and removed from the steel, I can not say that it is practical. However, it has been found that a coated steel containing a Fe compound and having a coating layer having an appropriate average thickness formed on the surface of the base steel can maintain the flame resistance for a relatively long period of time. In addition, since the coating layer contains a Cu compound, the coating layer is improved in denseness, and the corrosion-resistant material can be rendered harmless by further containing the Al compound and the Cr compound. As a result, penetration of the corrosive substance into the non- It is possible to remarkably suppress and improve the saline resistance.

That is, the invention made to solve the above problem is a coated steel comprising a base steel and a coating layer formed on the surface of the base steel, wherein the coating layer has an average thickness of 8 μm or more and 105 μm or less, A Cr compound, a Cu compound, and an Fe compound, wherein the compound is an oxide, an oxyhydroxide, or a combination thereof.

Such coated steel can improve the adhesion between the coating layer and the base steel because the coating layer contains an Fe compound excellent in adhesion with the base steel. In addition, since the coating layer has an average thickness in the above range, the penetration of the corrosive substance into the base steel can be suppressed. As a result, excellent salt resistance can be maintained for a long time. In addition, the coated steel material of the present invention is characterized in that the Al compound contained in the coating layer is fixed by fixing a corrosive chloride, the Cr compound is fixed by fixing the caustic sulphate, and further the Cu compound improves the denseness of the coating layer, The penetration of the corrosive substance into the base steel is remarkably suppressed, so that the salt resistance can be improved.

The coating layer may contain Al oxide, Al oxyhydroxide, or a combination thereof, Cr oxide, Cu oxide, and Fe ₃ O ₄ and? -FeOOH as the Fe oxide and Fe oxyhydroxide. In this case, the content of Al oxide, Al oxyhydroxide or a combination thereof is preferably 0.08 mass% or more and 10.5 mass% or less. The content of Cr oxide is preferably 0.08 mass% or more and 10.5 mass% or less. The content of the Cu oxide is preferably 0.08 mass% or more and 10.5 mass% or less. The total content of Fe ₃ O ₄ and α-FeOOH is preferably 29.5 mass% or more. Further, the mean particle diameters of the Fe ₃ O ₄ and the α-FeOOH are preferably 4.5 nm or more and 22 nm or less, respectively.

Since the coating layer contains Al oxide and / or Al oxyhydroxide as the Al compound, the fixation of the corrosive chloride can be further promoted. Further, since the coating layer contains Cr oxide as a Cr compound, the fixing of the caustic sulphate can be further promoted. Further, the coating layer contains Cu oxide as the Cu compound, so that the coating layer can be made more dense. As a result, the salt resistance can be further improved. In addition, the content of the compound in the coating layer is a specific amount, whereby cracking can be suppressed in the coating layer due to the temperature change at the time of use while improving the resistance to salt. Furthermore, among the Fe compounds as the Fe oxide and Fe oxyhydroxide, the coating layer contains Fe ₃ O ₄ and? -FeOOH which are particularly excellent in adhesion to the base steel, and their average particle diameter is in the above range, It is possible to further improve the adhesion between the base steel and the base steel. As a result, the salt water resistance and the sustainability of this salt water resistance can be further improved.

The steel according to any one of claims 1 to 3, wherein the base steel has a composition of C: not less than 0.008 mass% and not more than 0.32 mass%, Si: not less than 0.05 mass% and not more than 2.0 mass%, Mn: not less than 0.08 mass% nor more than 3.0 mass%, P not less than 0.001 mass% nor more than 0.05 mass% : 0.05 mass% or less, Al: 0.001 mass% or more and 1.6 mass% or less, N: 0.001 mass% or more and 0.015 mass% or less, and the remainder: Fe and inevitable impurities. Thus, by having the above-mentioned composition of the base steel material, the salt water resistance can be further improved.

Wherein the base steel has a composition of P: 0.004 mass% to 0.05 mass% and Al: 0.008 mass% to 1.6 mass%, Cu: 0.08 mass% to 2.2 mass%, Cr: 0.08 mass% By mass or less, Mo: 0.008% by mass or more and 2.2% by mass or less, and W: 0.008% by mass or more and 2.2% by mass or less. By thus setting the content of P in the base steel to a specific amount, the protective property of the coating layer is improved. Further, by setting the content of P and Al in the base steel to a specific amount, the salt resistance can be further improved. Further, by containing the specific amount of Cu and Cr in the base steel, the denseness of the coating layer is further improved. Further, when the base steel contains a specific amount of at least one of Mo and W, Mo and / or W is dissolved in the ferrite and the activity of the dissolution reaction is lowered. As a result, the salt resistance can be further improved.

The base steel may further contain at least one of 0.008 mass% to 5.2 mass% of Ni and 0.008 mass% to 5.0 mass% of Co. As described above, since the base steel contains at least one of Ni and Co in a specific amount, the salt resistance and strength can be further improved.

The base steel may contain at least one of 0.0004 mass% or more and 0.01 mass% or less of Mg, 0.0004 mass% or more and 0.01 mass% or less of Ca, and 0.0004 mass% or more and 0.01 mass% or less of rare earth metal. As described above, since the base steel further contains at least one of Mg, Ca and rare earth metals in a specified amount, the pH of the base steel in the vicinity of the surface can be prevented from lowering, and as a result, the salt resistance can be further improved.

The base steel may further contain at least one of Sn: at least 0.0008 mass% to 0.2 mass%, Sb: at least 0.0008 mass% to 0.2 mass%, and Se: at least 0.0008 mass% to 0.2 mass%. As described above, by containing at least one of Sn, Sb and Se in a specific amount, the salt resistance can be further improved.

The steel sheet according to any one of claims 1 to 3, wherein the base steel comprises at least one of Ti: 0 to 0.2 mass%, Nb: 0 to 0.2 mass%, Zr: 0 to 0.2 mass%, V: And B: at least one of 0 mass% and 0.01 mass% or less. As described above, the strength of the base steel can be further improved by containing at least one of Ti, Nb, Zr, V and B in a specified amount.

According to another aspect of the present invention, there is provided a method for manufacturing a coating layer, comprising the steps of: preparing a base steel; preparing a composition for forming a coating layer in which an Al compound, a Cr compound, a Cu compound, and an Fe compound are dispersed in a solvent; Wherein the compound is an oxide, an oxyhydroxide, or a combination thereof, and a coating layer having an average thickness of 8 占 퐉 or more and 105 占 퐉 or less in the coating process; to be.

Here, the "average thickness" refers to an average value of the thicknesses measured at arbitrary 10 points. The term " average particle diameter " means that particles of Fe ₃ O ₄ and α-FeOOH in cross section of the coating layer are observed at an appropriate magnification using an electric field transmission type transmission electron microscope (FE-TEM) Means the average value of the diameter of a circle.

The coated steel material and the method for producing the same can provide a coated steel material in which excellent salt water resistance is maintained for a relatively long period of time.

1 is a schematic plan view showing a test surface of a test piece used in an embodiment of the present invention.

≪ Coated steel material &

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a coated steel material and a manufacturing method thereof according to the present invention will be described. The coated steel material includes a base steel and a coating layer formed on the surface of the base steel.

(Base steel)

As the base steel, there is no particular limitation, and conventionally known steel materials can be used. As the base steel, 0.008 mass% or more and 0.32 mass% or less of C (carbon), 0.05 mass% or more and 2.0 mass% or less of Si (silicon), 0.08 mass% or more and 3.0 mass% or less of P (Al): not less than 0.001 mass% and not more than 1.6 mass%, N (nitrogen): not less than 0.001 mass% and not more than 0.015 mass%, and the balance: Fe (iron ) And inevitable impurities. In the coated steel, since the base steel contains a specific amount of P, Al and N, excellent salt-resistance can be maintained easily and surely for a long time by synergism with the coating layer. In addition, the coated steel material can easily and surely satisfy the mechanical properties required for the structure and the weldability of the structure, because the coated steel contains a specific amount of C, Si, Mn, S and N. Hereinafter, each component will be described.

[C (Carbon)]

C in the base steel is an effective element for securing the strength of the coated steel. The lower limit of the content of C in the base steel is preferably 0.008 mass%, more preferably 0.02 mass%, and still more preferably 0.03 mass%. On the other hand, the upper limit of the content of C is preferably 0.32% by mass, more preferably 0.29% by mass, and most preferably 0.28% by mass. When the content of C is smaller than the above lower limit, there is a fear that the strength of the coated steel is lowered. On the contrary, when the content of C exceeds the upper limit, the amount of cementite which acts as the cathode site in the corrosive environment increases, so that the corrosion reaction is promoted. As a result, the corrosion resistance of the coated steel is lowered, There is a risk of degradation.

[Si (silicon)]

Si in the base steel is an effective element for deoxidizing the base steel and securing the strength of the coated steel. The lower limit of the Si content in the base steel is preferably 0.05% by mass, more preferably 0.08% by mass, and most preferably 0.10% by mass. On the other hand, the upper limit of the content of Si is preferably 2.0% by mass, more preferably 1.95% by mass, and further preferably 1.90% by mass. When the content of Si is smaller than the above lower limit, there is a possibility that deoxidation of the above-mentioned base steel and securing of strength of the coated steel are insufficient. On the other hand, when the content of Si exceeds the upper limit, there is a possibility that welding of the coated steel becomes difficult.

[Mn (manganese)]

Mn in the base steel is an element effective for deoxidation of the base steel and securing strength of the base steel as well as Si. The lower limit of the content of Mn in the base steel is preferably 0.08% by mass, more preferably 0.15% by mass, and most preferably 0.2% by mass. On the other hand, the upper limit of the Mn content is preferably 3.0% by mass, more preferably 2.9% by mass, and further preferably 2.8% by mass. When the content of Mn is smaller than the above lower limit, there is a possibility that the strength of the coated steel material required for the structure can not be secured. On the contrary, when the content of Mn exceeds the upper limit, there is a possibility that the toughness of the coated steel is lowered.

[P (in)]

P in the base steel is an effective element for increasing the protection of the coating layer and further improving the water resistance of the coated steel. The lower limit of the content of P in the base steel is preferably 0.001% by mass, more preferably 0.004% by mass, still more preferably 0.008% by mass, and particularly preferably 0.017% by mass. On the other hand, the upper limit of the content of P is preferably 0.05% by mass, more preferably 0.045% by mass, and still more preferably 0.04% by mass. When the content of P is smaller than the above lower limit, there is a possibility that the water resistance of the coated steel is lowered. On the other hand, when the content of P exceeds the upper limit, there is a fear that the toughness of the coated steel is lowered and the welding becomes difficult.

[S (sulfur)]

S in the base steel is an element which lowers the toughness of the coated steel and also makes welding difficult. Therefore, the smaller the content of S in the base steel, the better, but it is difficult to industrially make the content of S 0 mass%. Therefore, the upper limit of the content of S in the base steel is preferably 0.05% by mass, more preferably 0.045% by mass, and still more preferably 0.04% by mass. On the other hand, the lower limit of the content of S is not particularly limited, but is, for example, 0.0001 mass%.

[Al (aluminum)]

Al in the base steel is an effective element for forming a stable oxide in the sea water corrosion environment and further improving the water resistance of the coated steel. Al is also an element effective for deoxidation of the base steel and securing the strength of the coated steel as well as Si and Mn described above. The lower limit of the content of Al in the base steel is preferably 0.001 mass%, more preferably 0.008 mass%, and even more preferably 0.010 mass%. On the other hand, the upper limit of the content of Al is preferably 1.6% by mass, more preferably 1.45% by mass, and further preferably 1.4% by mass. When the content of Al is smaller than the above lower limit, there is a possibility that the effect of dechlorination of the base steel material and the improvement of the water resistance of the coating steel mentioned above and securing strength are not obtained sufficiently. On the other hand, when the content of Al exceeds the upper limit, there is a fear that welding of the coated steel becomes difficult.

[N (Nitrogen)]

N in the non-coated steel is an element effective for improving the resistance to salt water and strength of the coated steel by forming finely dispersed particles of nitride in the non-coated steel. The lower limit of the content of N in the base steel is preferably 0.001% by mass, more preferably 0.15% by mass, and still more preferably 0.002% by mass. On the other hand, the upper limit of the content of N is preferably 0.015% by mass, more preferably 0.014% by mass, and still more preferably 0.013% by mass. When the content of N is smaller than the above lower limit, there is a fear that the water resistance and strength of the coated steel are lowered. On the other hand, when the content of N exceeds the upper limit, there is a possibility that the toughness of the coated steel is lowered and the welding becomes difficult.

[Remaining]

Of the composition of the base steel, the balance other than the above-mentioned components may be Fe (iron) and inevitable impurities. Examples of such inevitable impurities include O (oxygen) and H (hydrogen). The total content of inevitable impurities in the base steel is not particularly limited so long as it does not impair various properties of the coated steel. The upper limit of the total content of the inevitable impurities in the concrete base steel is preferably 0.1% by mass, more preferably 0.09% by mass, still more preferably 0.05% by mass, and particularly preferably 0.01% by mass. By setting the total content of inevitable impurities to the above range, the water resistance of the coated steel can be further improved.

It is more preferable that the base steel material further contains the following elements. Hereinafter, each element will be described.

[Cu (copper)]

Cu in the base steel is an effective element for improving the durability of the coating steel by improving the denseness of the coating layer. The lower limit of the content of Cu in the base steel is preferably 0.08% by mass, more preferably 0.12% by mass, and most preferably 0.15% by mass. On the other hand, the upper limit of the content of Cu is preferably 2.2% by mass, more preferably 1.95% by mass, and further preferably 1.90% by mass. When the content of Cu is smaller than the above lower limit, there is a fear that the water resistance of the coated steel is lowered. On the other hand, when the content of Cu exceeds the upper limit, there is a fear that welding or hot working of the coated steel becomes difficult.

[Cr (chromium)]

Cr in the base steel is an element effective for improving the water resistance of the coated steel by making the coating layer more dense like Cu. The lower limit of the Cr content in the base steel is preferably 0.08% by mass, more preferably 0.12% by mass, and still more preferably 0.15% by mass. On the other hand, the upper limit of the Cr content is preferably 3.0% by mass, more preferably 2.9% by mass, and further preferably 2.8% by mass. When the content of Cr is smaller than the above lower limit, there is a fear that the water resistance of the coated steel is lowered. On the contrary, when the content of Cr exceeds the upper limit, there is a possibility that welding or hot working of the coated steel becomes difficult.

[Mo (molybdenum) and W (tungsten)]

Mo and W in the base steel are elements which act to lower the activity of the dissolution reaction by being dissolved in ferrite, respectively. Therefore, when the base steel contains Mo and / or W, the water resistance of the coated steel is further improved. Further, by containing the Mo and / or W in a proper amount, the strength of the coated steel is also improved.

The lower limit of the content of Mo in the base steel is preferably 0.008 mass%, more preferably 0.02 mass%, and still more preferably 0.03 mass%. On the other hand, the upper limit of the Mo content is preferably 2.2% by mass, more preferably 1.9% by mass, and further preferably 1.8% by mass. When the content of Mo is smaller than the above lower limit, there is a possibility that the water resistance and strength of the coated steel are lowered. On the other hand, when the content of Mo exceeds the upper limit, there is a fear that welding or hot working of the coated steel becomes difficult.

 The lower limit of the content of W in the base steel is preferably 0.008 mass%, more preferably 0.02 mass%, and still more preferably 0.03 mass%. On the other hand, the upper limit of the content of W is preferably 2.2% by mass, more preferably 1.9% by mass, and further preferably 1.8% by mass. When the content of W is smaller than the above lower limit, there is a fear that the water resistance and strength of the coated steel are lowered. On the other hand, when the content of W exceeds the upper limit, there is a fear that welding or hot working of the coated steel becomes difficult.

[Ni (nickel) and Co (cobalt)]

The base steel preferably further contains at least one of Ni and Co. Ni and Co in the base steels are elements that further improve the salt water resistance and strength of the coated steel.

The lower limit of the content of Ni in the base steel is preferably 0.008% by mass, more preferably 0.02% by mass, still more preferably 0.03% by mass, and particularly preferably 0.08% by mass. On the other hand, the upper limit of the content of Ni is preferably 5.2% by mass, more preferably 4.9% by mass, still more preferably 4.8% by mass, particularly preferably 1% by mass. When the content of Ni is smaller than the above lower limit, there is a fear that the water resistance and strength of the coated steel are lowered. On the other hand, when the content of Ni exceeds the upper limit, there is a possibility that welding or hot working of the coated steel becomes difficult.

The lower limit of the content of Co in the base steel is preferably 0.008% by mass, more preferably 0.02% by mass, still more preferably 0.03% by mass, and particularly preferably 0.04% by mass. On the other hand, the upper limit of the content of Co is preferably 5.0% by mass, more preferably 4.9% by mass, still more preferably 4.8% by mass, and particularly preferably 1% by mass. When the content of Co is smaller than the above lower limit, there is a fear that the water resistance and strength of the coated steel are lowered. On the other hand, when the content of Co exceeds the upper limit, there is a fear that welding or hot working of the coated steel becomes difficult.

[Mg (magnesium), Ca (calcium) and rare earth metals (REM)]

The base steel preferably further contains at least one of Mg, Ca and rare earth metals. Mg, Ca and the rare earth metal in the non-coated steel material are each dissolved by corrosion and react with the hydrogen ions to suppress the pH drop in the vicinity of the surface of the non-coated steel, and as a result, to be.

The lower limit of the content of Mg in the base steel is preferably 0.0004 mass%, more preferably 0.006 mass%, still more preferably 0.0007 mass%, and particularly preferably 0.0009 mass%. On the other hand, the upper limit of the Mg content is preferably 0.01% by mass, more preferably 0.0095% by mass, still more preferably 0.009% by mass, and particularly preferably 0.003% by mass. When the content of Mg is smaller than the above lower limit, there is a possibility that the water resistance of the coated steel is lowered. On the other hand, when the content of Mg exceeds the upper limit, there is a fear that welding or hot working of the coated steel becomes difficult.

The lower limit of the content of Ca in the base steel is preferably 0.0004 mass%, more preferably 0.0006 mass%, still more preferably 0.0007 mass%, particularly preferably 0.0013 mass%. On the other hand, the upper limit of the Ca content is preferably 0.01% by mass, more preferably 0.0095% by mass, still more preferably 0.009% by mass, particularly preferably 0.004% by mass. When the content of Ca is smaller than the above lower limit, there is a fear that the water resistance of the coated steel is lowered. On the other hand, when the content of Ca exceeds the upper limit, there is a fear that welding or hot working of the coated steel becomes difficult.

The lower limit of the content of the rare earth metal in the base steel is preferably 0.0004 mass%, more preferably 0.0006 mass%, still more preferably 0.0007 mass%, particularly preferably 0.001 mass%. On the other hand, the upper limit of the content of the rare earth metal is preferably 0.01% by mass, more preferably 0.0095% by mass, still more preferably 0.009% by mass, particularly preferably 0.003% by mass. When the content of the rare earth metal is smaller than the above lower limit, there is a possibility that the water resistance of the coated steel is lowered. On the other hand, when the content of the rare earth metal exceeds the upper limit, there is a possibility that welding or hot working of the coated steel becomes difficult.

[Sn (tin), Sb (antimony) and Se (selenium)]

The base steel preferably further contains at least one of Sn, Sb and Se. Sn, Sb, and Se in the non-coated steel material are elements that further improve the water resistance of the coated steel.

The lower limit of the content of Sn in the base steel is preferably 0.0008% by mass, more preferably 0.002% by mass, still more preferably 0.003% by mass, and particularly preferably 0.008% by mass. On the other hand, the upper limit of the content of Sn is preferably 0.2% by mass, more preferably 0.19% by mass, still more preferably 0.18% by mass, particularly preferably 0.1% by mass. When the content of Sn is smaller than the above lower limit, there is a fear that the water resistance of the coated steel is lowered. On the other hand, when the content of Sn exceeds the upper limit, there is a possibility that welding or hot working of the coated steel becomes difficult.

The lower limit of the content of Sb in the base steel is preferably 0.0008% by mass, more preferably 0.002% by mass, still more preferably 0.003% by mass, and particularly preferably 0.008% by mass. On the other hand, the upper limit of the content of Sb is preferably 0.2% by mass, more preferably 0.19% by mass, still more preferably 0.18% by mass, and particularly preferably 0.10% by mass. When the content of Sb is smaller than the above lower limit, there is a fear that the water resistance of the coated steel is lowered. On the other hand, when the content of Sb exceeds the upper limit, there is a fear that welding or hot working of the coated steel becomes difficult.

The lower limit of the content of Se in the base steel is preferably 0.0008% by mass, more preferably 0.002% by mass, still more preferably 0.003% by mass, particularly preferably 0.008% by mass. On the other hand, the upper limit of the content of Se is preferably 0.2% by mass, more preferably 0.19% by mass, still more preferably 0.18% by mass, and particularly preferably 0.10% by mass. When the content of Se is smaller than the above lower limit, there is a possibility that the water resistance of the coated steel is lowered. On the other hand, when the content of Se exceeds the upper limit, there is a fear that welding or hot working of the coated steel becomes difficult.

[Ti (titanium), Nb (niobium), Zr (zirconium), V (vanadium) and B (boron)]

The base steel preferably further contains at least one of Ti, Nb, Zr, V and B, Ti, Nb, Zr, V, and B in the base steel are elements that further improve the strength of the coated steel.

The content of Ti in the base steel is preferably more than 0% by mass. The lower limit of the content of Ti is more preferably 0.001 mass%, and still more preferably 0.008 mass%. On the other hand, the upper limit of the Ti content is preferably 0.2% by mass, more preferably 0.19% by mass, still more preferably 0.18% by mass, and particularly preferably 0.10% by mass. When the content of Ti is smaller than the above lower limit, there is a fear that the strength of the coated steel is lowered. On the other hand, when the content of Ti exceeds the upper limit, there is a fear that the toughness of the base steel is lowered or the welding of the coated steel is difficult.

The content of Nb in the base steel is preferably more than 0% by mass. The lower limit of the content of Nb is preferably 0.001 mass%, more preferably 0.008 mass%. On the other hand, the upper limit of the content of Nb is preferably 0.2% by mass, more preferably 0.19% by mass, still more preferably 0.18% by mass, and particularly preferably 0.10% by mass. When the content of Nb is smaller than the above lower limit, there is a fear that the strength of the coated steel is lowered. On the other hand, when the content of Nb exceeds the upper limit, there is a possibility that the toughness of the base steel is lowered or the welding of the coated steel is difficult.

The content of Zr in the base steel is preferably more than 0% by mass. The lower limit of the content of Zr is preferably 0.001 mass%, more preferably 0.06 mass%. On the other hand, the upper limit of the content of Zr is preferably 0.2% by mass, more preferably 0.19% by mass, still more preferably 0.18% by mass, and particularly preferably 0.10% by mass. When the content of Zr is smaller than the above lower limit, there is a fear that the strength of the coated steel is lowered. On the other hand, when the content of Zr exceeds the upper limit, there is a possibility that the toughness of the base steel is lowered or the welding of the coated steel is difficult.

The content of V in the base steel is preferably more than 0% by mass. The lower limit of the content of V is more preferably 0.001% by mass, and still more preferably 0.02% by mass. On the other hand, the upper limit of the content of V is preferably 0.2% by mass, more preferably 0.19% by mass, still more preferably 0.18% by mass, and particularly preferably 0.10% by mass. When the content of V is smaller than the above lower limit, there is a fear that the strength of the coated steel is lowered. On the other hand, when the content of V exceeds the upper limit, there is a fear that the toughness of the base steel is lowered or the welding of the coated steel is difficult.

The content of B in the base steel is preferably more than 0% by mass. The lower limit of the content of B is preferably 0.0001 mass%, more preferably 0.00015 mass%. On the other hand, the upper limit of the content of B is preferably 0.01% by mass, more preferably 0.0095% by mass, still more preferably 0.009% by mass, and particularly preferably 0.001% by mass. When the content of B is smaller than the above lower limit, the strength of the coated steel may be lowered. On the other hand, when the content of B exceeds the upper limit, there is a possibility that the toughness of the base steel is lowered or the welding of the coated steel is difficult.

In particular, the base steel has a composition of C: 0.008 to 0.32 mass%, Si: 0.05 to 2.0 mass%, Mn: 0.08 to 3.0 mass%, P: 0.004 to 0.05 mass% S: not more than 0.05 mass%, Al: not less than 0.008 mass% nor more than 1.6 mass%, Cu: not less than 0.08 mass% nor more than 2.2 mass%, Cr: not less than 0.08 mass% nor more than 3.0 mass% , The remainder being Fe and inevitable impurities, at least one of 0.008 mass% to 2.2 mass% of Mo and 0.008 mass% or more and 2.2 mass% or less of W is preferably contained. More preferably, the base steel further contains Ni, Co, Mg, Ca, a rare earth metal, Sn, Sb, Ti, Nb, Zr, V, B, Se or a combination thereof in addition to the above- Do. It is particularly preferable that the base steel contains at least one of Ni and Co and at least one of Sn, Sb and Se as the above-mentioned Ni and the like. It is particularly preferable that the base steel contains at least one of Mg, Ca and rare-earth metals as Ni as described above, and further contains at least one of Sn, Sb and Se.

(Coating layer)

The coating layer contains an Al compound, a Cr compound, a Cu compound and an Fe compound, and the compound is an oxide, an oxyhydroxide or a combination thereof. That is, the coating layer contains Al oxide and / or Al oxyhydroxide, Cr oxide and / or Cr oxyhydroxide, Cu oxide and / or Cu oxyhydroxide, Fe oxide and / or Fe oxyhydroxide.

The lower limit of the average thickness of the coating layer is preferably 8 占 퐉, more preferably 14 占 퐉, and still more preferably 21.5 占 퐉. On the other hand, the upper limit of the average thickness of the coating layer is preferably 105 占 퐉, more preferably 80 占 퐉, and even more preferably 60 占 퐉. If the average thickness of the coating layer is smaller than the above lower limit, the penetration of the corrosive substance into the base steel can not be suppressed sufficiently, and there is a fear that the water resistance of the coated steel is lowered. On the contrary, when the average thickness of the coating layer exceeds the upper limit, cracks tend to be formed in the coating layer due to the temperature change at the time of use, and local corrosion of the non-coated steel material exposed to the surface in the crack may proceed.

[Al compound]

The Al compound contained in the coating layer fixes corrosive chloride to detoxify, thereby suppressing invasion into the base steel, and as a result, enhancing the salt-resistance of the base steel. Of the Al compound to the coating layer contains, there may be mentioned AlOOH such as Al oxy hydroxide, as the Al oxide and the like can be mentioned Al ₂ O _3.

The lower limit of the content of the Al compound in the coating layer is preferably 0.08 mass%, more preferably 0.4 mass%, and even more preferably 0.8 mass%. On the other hand, the upper limit of the content of the Al compound is preferably 10.5 mass%, more preferably 6.0 mass%, still more preferably 2.5 mass%, and particularly preferably 1.2 mass%. When the content of the Al compound is smaller than the above lower limit, there is a fear that the water resistance of the coated steel is lowered. On the contrary, when the content of the Al compound exceeds the upper limit, cracks are likely to be formed in the coating layer due to the temperature change at the time of use, and as a result, local corrosion of the base steel may occur.

[Cr compound]

The Cr compound contained in the coating layer is immiscible by fixing a caustic sulphate, thereby suppressing intrusion into the base steel, and as a result, improving the flame resistance of the base steel. Of the Cr-containing compound to the coating layer, there may be mentioned such as the CrOOH Cr oxy-hydroxide, there may be mentioned _{CrO 2, CrO 3, Cr 2} O 3 such as Cr oxide. As the Cr compound, Cr oxide is preferable, and Cr ₂ O ₃ is more preferable.

When the coating layer contains Cr oxide, the lower limit of the content of Cr oxide in the coating layer is preferably 0.08 mass%, more preferably 0.4 mass%, still more preferably 0.8 mass%. On the other hand, the upper limit of the content of Cr oxide is preferably 10.5 mass%, more preferably 3.5 mass%, and further preferably 1.2 mass%. When the content of Cr oxide is smaller than the above lower limit, there is a fear that the water resistance of the coated steel is lowered. Conversely, when the content of the Cr oxide exceeds the upper limit, a crack is formed in the coating layer due to the temperature change during use, and local corrosion may proceed.

[Cu compound]

The Cu compound contained in the coating layer suppresses penetration of the corrosive substance into the base steel by making the coating layer dense, and as a result, improves the water resistance of the coated steel. Of the Cu compounds contained in the coating layer, examples of the Cu oxide include CuO and Cu ₂ O.

When the coating layer contains Cu oxide, the lower limit of the content of Cu oxide in the coating layer is preferably 0.08% by mass, more preferably 0.4% by mass, and most preferably 0.8% by mass. On the other hand, the upper limit of the content of the Cu oxide is preferably 10.5% by mass, more preferably 3.5% by mass, and further preferably 1.2% by mass. When the content of Cu oxide is smaller than the above lower limit, there is a fear that the water resistance of the coated steel is lowered. On the contrary, when the content of Cu oxide exceeds the upper limit, cracks are likely to be formed in the coating layer due to the temperature change during use, and as a result, local corrosion of the base steel may occur.

[Fe compound]

The Fe compound contained in the coating layer improves the adhesion between the coating layer and the base steel. Of the Fe compounds contained in the coating layer, examples of the Fe oxyhydroxide include? -FeOOH,? -FeOOH,? -FeOOH, and the Fe oxides include Fe ₂ O ₃ and Fe ₃ O ₄ . Among the Fe compounds, Fe ₃ O ₄ and α-FeOOH are preferable, and a combination of Fe ₃ O ₄ and α-FeOOH is more preferable.

When the covering layer containing the α-FeOOH and / or Fe ₃ O _4, as the lower limit of the total content of the Fe ₃ O ₄ and α-FeOOH in the coating layer, and a 29.5% by weight preferred, and 35% by weight preferably, And more preferably 40 mass%. On the other hand, the upper limit of the total content is not particularly limited, but is, for example, 99.5% by mass, preferably 97.5% by mass, and more preferably 95.5% by mass. When the total content is smaller than the above lower limit, the adhesion of the coating layer and the base steel is lowered, and there is a fear that the flame retardancy of the coated steel is not maintained for a long period of time. On the contrary, when the total content exceeds the upper limit, the contents of the Al compound, Cr compound and Cu compound in the coating layer become insufficient, and as a result, there is a fear that the water resistance of the coated steel is lowered.

When the coating layer contains? -FeOOH, the lower limit of the content of? -FeOOH in the covering layer is preferably 8% by mass, more preferably 28% by mass. On the other hand, the upper limit of the content of? -FeOOH is preferably 90% by mass, more preferably 65% by mass, and still more preferably 55% by mass. When the coating layer contains Fe ₃ O ₄ , the lower limit of the content of Fe ₃ O _{4 in} the coating layer is preferably 10% by mass, more preferably 28% by mass, still more preferably 38% by mass. On the other hand, the upper limit of the content of Fe ₃ O ₄ is preferably 95% by mass, more preferably 75% by mass, and still more preferably 52% by mass. If the contents of Fe ₃ O ₄ and? -FeOOH are both lower than the lower limit described above, the adhesion of the coating layer and the base steel is lowered, and there is a fear that the flame retardancy of the coated steel is not maintained for a long period of time. On the contrary, when the content of at least one of Fe ₃ O ₄ and α-FeOOH exceeds the upper limit, the content of the Al compound, Cr compound and Cu compound in the coating layer becomes insufficient, and as a result, May be deteriorated.

When the coating layer contains? -FeOOH, the lower limit of the average particle diameter of? -FeOOH is preferably 4.5 nm, more preferably 12 nm, and further preferably 15.5 nm. On the other hand, the upper limit of the average particle diameter of? -FeOOH is preferably 22 nm, more preferably 19 nm. When the coating layer contains Fe ₃ O ₄ , the lower limit of the average particle diameter of Fe ₃ O ₄ is preferably 4.5 nm, more preferably 8 nm, and further preferably 13 nm. On the other hand, the upper limit of the average particle size of Fe ₃ O ₄ is preferably 22 nm, more preferably 18 nm. When the average particle diameter of at least one of Fe ₃ O ₄ and? -FeOOH is smaller than the lower limit described above, the volume of the coating layer is largely shrunk by evaporation of the solvent between the particles during the formation of the coating layer, thereby causing defects such as cracks. As a result, the inhibition of the penetration of the corrosive substance into the base steel by the coating layer becomes insufficient, the local corrosion of the base steel exposed to the surface in the crack is likely to proceed, and corrosion of the base steel near the interface with the coating layer may occur . Further, due to the above-mentioned corrosion of the base steel material, the coating layer may peel off and fall off, and corrosion may further proceed. On the contrary, when the average particle diameter of at least one of Fe ₃ O ₄ and? -FeOOH exceeds the upper limit, the gap between the particles easily occurs, and the denseness of the coating layer is lowered. As a result, There is a possibility that the corrosion resistance of the coated steel material is lowered due to the easy penetration into the non-coated steel material.

Particularly, the coating layer may contain Al oxide and / or Al oxyhydroxide, Cr oxide, Cu oxide, Fe oxide, Fe ₃ O ₄ and? -FeOOH as Fe oxyhydroxide. In this case, the content of the Al oxide and / or Al oxyhydroxide is preferably 0.08 mass% or more and 10.5 mass% or less. The content of Cr oxide is preferably 0.08 mass% or more and 10.5 mass% or less. The content of the Cu oxide is preferably 0.08 mass% or more and 10.5 mass% or less. The total content of Fe ₃ O ₄ and α-FeOOH is preferably 29.5 mass% or more. Further, the mean particle diameters of the Fe ₃ O ₄ and the α-FeOOH are preferably 4.5 nm or more and 22 nm or less, respectively. When the coating layer satisfies these conditions, it is possible to further improve the salt water resistance of the coated steel and the sustainability of the salt water resistance.

From the viewpoints of improving the adhesion with the base steel and improving the flame resistance of the coated steel, the coating layer contains a metal oxide hydroxide and / or another metal oxide other than the above-mentioned Al compound, Cr compound, Cu compound and Fe compound desirable. Examples of the other metal oxides include SiO ₂ , TiO ₂ , ZrO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , V ₂ O ₅ , La ₂ O ₃ and Ce ₂ O ₃ . However, the coating layer contains only the Al compound, the Cr compound, the Cu compound and the Fe compound, and the content of the other metal oxide and the other metal oxyhydroxide may be substantially 0 mass%. The coating layer may contain components other than the above-mentioned Al compound, Cr compound, Cu compound, Fe compound, metal oxide and metal oxyhydroxide.

(Type and use of coated steel)

Examples of the shape of the coated steel include a steel plate, a steel pipe, a bar steel, a wire rod, a section steel and the like. Further, even in a corrosive environment in which the steels are constantly immersed in seawater, the coated steels suppress corrosion due to seawater and the like even under corrosive environments, which are not always immersed in seawater, . Therefore, examples of applications of the coated steel include ships, offshore structures, bridges and the like. Examples of the ship include a cargo ship such as a tanker, a container ship, and a bulker, a vessel ship, a ship, and a ship. When the coated steel material is used for ships, it can be suitably used for various types of upper steel structures such as ballast tanks, upper decks, ship bridges, hatch covers, cranes, various piping, stairs and railings. Examples of the offshore structure include excavation facilities for excavating oil or natural gas in the ocean, in-body facilities for producing, storing and extracting oil and natural gas from the ocean, wind power generation in the ocean, Power generation facilities that perform algae generation, ocean current generation, temperature difference generation, and solar power generation. Further, when the coated steel is used for a bridge, it can be suitably used as a steel for bridges in an environment having a large salinity, where the amount of fly ash exceeds 0.1 mdd.

≪ Method of producing coated steel material >

A method for producing the coated steel material comprises the steps of preparing a base steel (base steel preparation step), preparing a composition for forming a coating layer in which an Al compound, a Cr compound, a Cu compound and an Fe compound are dispersed in a solvent (a preparation step) And a step of coating the composition for forming a coating layer on the surface of the base steel (coating step). Each step will be described below.

(Base steel preparation process)

In this step, a base steel having a desired composition is prepared. The method for producing the base steel is not particularly limited, and a normal steelmaking method typified by a conversion steelmaking method, an electric furnace steelmaking method, or the like can be employed. Hereinafter, a specific manufacturing method of the base steel will be described. First, molten steel introduced from a converter or an electric furnace into a ladle is adjusted to have a desired composition using a RH (Ruhrstahl-Heraeus) vacuum degassing apparatus, and secondary refining is carried out by adjusting the temperature I do. Thereafter, a cast steel is obtained as a steel ingot by a conventional casting method such as a continuous casting method and a roughing method. From the viewpoint of securing the basic characteristics required for the steel used for the structures such as the mechanical properties and the weldability of the welded steel, dead steel is preferably killed steel, and Al killed steel More preferable.

(Preparation process)

In this step, a coating layer forming composition is prepared by dispersing an Al compound, a Cr compound, a Cu compound, and an Fe compound in a solvent. In the present step, the above-mentioned other metal oxyhydroxides and / or other metal oxides may be further dispersed in a solvent. The solvent is not particularly limited, and examples thereof include an organic solvent such as an alkyl silicate, water, etc. Among them, an organic solvent is preferable, and an alkyl silicate is more preferable. The solid content concentration of the coating layer forming composition is not particularly limited, but is, for example, 10 mass% or more and 60 mass% or less. In the composition for forming a coating layer, since each component dispersed in a solvent is stable and hardly causes a chemical reaction, the composition other than the solvent usually becomes the composition of the coating layer as it is. Therefore, it is possible to easily and surely form a coating layer having a desired composition by adjusting the composition and particle diameter of each component of the coating layer-forming composition.

(Coating process)

In this step, the coating layer forming composition is coated on the surface of the base steel to form a coating layer on the surface of the base steel. The method for coating the composition for forming a coating layer on the surface of the base steel is not particularly limited, and for example, a method of drying at 70 DEG C or more and 150 DEG C or less after application by spray coating or the like can be mentioned. On the other hand, the coating layer having a desired average thickness can be easily and reliably formed by adjusting the solid content concentration and the coating amount of the coating layer forming composition used in the present step.

Before the present step, it is preferable to pretreat the surface of the base steel. Examples of the pretreatment include removal of surface deposits such as scales and salts by grinding, shot blasting, and the like. In this step, it is particularly preferable to reduce the amount of salt adhered on the surface of the base steel as much as possible. Specifically, it is preferable to be less than 0.1 g / m ^{2 in} terms of NaCl, for example.

In addition, as the pretreatment, a treatment for imparting appropriate surface roughness to the base steel is also preferable from the viewpoint of securing adhesion between the coating layer and the base steel. As a method for imparting a suitable surface roughness to the base steel, conventionally known methods can be employed, and for example, shot blast treatment and grid blast treatment can be given. The lower limit of the surface roughness of the specific base steel is preferably 10 占 퐉. On the other hand, the upper limit of the surface roughness of the base steel is preferably 80 mu m. When the surface roughness of the base steel is smaller than the above lower limit, the adhesion between the coating layer and the base steel may be deteriorated. On the contrary, when the surface roughness of the base steel exceeds the upper limit, bubbles enter the recessed portion of the base steel after the application of the coating layer forming composition, and as a result, the coating layer and the base steel do not adhere to each other, There is a concern. The term "surface roughness" as used herein refers to a 10-point average roughness (Rz) measured in accordance with JIS-B0601: 2001 "Geometric Property Specification (GPS) - Surface Property: Outline Curve Method - Term, Definition and Surface Property Parameter" , The evaluation length is 12.5 mm, and the cut-off value lambda c is 2.5 mm.

Example

Hereinafter, the coated steel material of the present invention and the method of producing the same will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples, and the present invention is not limited thereto. It is of course possible to carry out the invention by making changes, all of which are included in the technical scope of the present invention.

[Production of coated steel]

Steels having the compositions shown in Tables 1 and 2 were each dissolved in a vacuum melting furnace to obtain 50 kg of ingot. The obtained ingot was heated to 1,150 캜 and hot-rolled to obtain a steel material having an average thickness of 10 mm. Test pieces of 150 x 70 x 5 [mm] were cut from each steel material, and these were used as base steels B1 to B54. One side of the test piece was used as a test surface, and the test surface was subjected to shot blasting so as to have a finish with Rz of 30 占 퐉, followed by washing with water and acetone. After the cleaning, the mass of the test piece and the thickness thereof were measured, and this was regarded as the mass and thickness of the pre-test steel. As shown in Fig. 1, the thickness of the test piece is set such that an area of 140 x 60 [mm] on the inner side of 5 mm or more from each side of the test surface is set as the test area A, and 5 × 13 = 65 points. The thickness was measured using an ultrasonic wave thickness meter from the back surface of the test surface. Thereafter, a coating layer was formed on the test piece by the following method.

Powders of Fe ₃ O ₄ and α-FeOOH adjusted to a desired average particle diameter and other metal oxyhydroxides and powders of other metal oxides were mixed and dispersed in an alkyl silicate as a solvent to prepare a coating layer forming composition. The solid content concentration of the coating layer forming composition was set to 40% by mass. A composition for forming a coating layer was applied on the surface of the test piece by spray coating and then dried in a drier at 100 캜 to obtain a test piece having a coating layer. This test piece was coated on the coated steel No. 1. 2 to No. 65. On the other hand, the composition of the coating layer can be controlled by adjusting the mixing ratio of the respective components of the coating layer forming composition, and the composition of the solid content other than the solvent in the coating layer forming composition can be regarded as the composition of the coating layer. The average thickness of the coating layer was adjusted by the applied amount of the coating layer forming composition and measured by an electromagnetic (electromagnetic) film thickness meter. After formation of the coating layer, a region B other than the test region on the test surface of the test piece and a surface other than the test surface were coated with Teflon (registered trademark) tape. On the other hand, a region B other than the test region is a region having a distance from each side of less than 5 mm. Thereafter, the following corrosion test was carried out. In Table 3 and Table 4, 1 to No. 65, respectively. On the other hand, 1, a coating layer is not formed. The "other components" in Tables 3 and 4 refer to the other metal oxides and other metal oxyhydroxides.

[Corrosion test]

Cyclic Corrosion Testing (CCT) using artificial seawater was conducted as a corrosion test simulating the corrosion environment caused by seawater. Specifically, (I) the artificial seawater spraying at 35 DEG C was conducted for 1.5 hours, (II) the test was conducted at a temperature of 60 DEG C and a humidity of 20% RH for 2.5 hours, (III) RH for (I) - (III) for 2.5 hours. On the other hand, when changing the temperature and humidity in (I) to (III), the transition time necessary for stabilizing the conditions was 0.5 hours. The test period was 84 days. In addition, three test pieces were used and N = 3 was set.

After CCT termination, the mass change and corrosion depth of the test piece were measured. First, after the completion of the CCT, the coating layer and the corrosion product of the test piece were removed by a negative electrolytic solution in a 10% aqueous solution of ammonium hydrogencarbonate, followed by washing with water and acetone. After cleaning, the mass of the test piece was measured, and this was regarded as the mass of the ground steel after the test. The difference between the mass of the non-treated steel after the test and the mass of the non-treated steel before the test was taken as the corrosion amount due to corrosion, and the average value of the three test pieces was taken as the average corrosion amount. Further, at the grid point X of 65 shown in Fig. 1, the thickness was measured from the back surface of the test surface of the test piece by an ultrasonic wave thickness meter. The difference between the thickness of the base steel before testing and the thickness of the base steel after the test at each lattice point X was determined to be the corrosion depth of the lattice point X. [ The corrosion depth of each of the grid points X of 65 of the three test pieces was measured to determine the maximum value of the corrosion depth of the grid point X of 195 points as the maximum corrosion depth.

Coated steel No. 1 to No. 65, the coated steel No. < RTI ID = 0.0 > 1 and the maximum corrosion depth were respectively 100, and the relative values were divided into A to E by the following criteria. The relative values of the average corrosion amount and the maximum corrosion depth indicate that the lower the numerical value, the better the salt resistance.

A: No. If the relative value for 1 is less than 55

B: No. Relative value of 1 to 55 or more and less than 70

C: No. Relative value for 1 is not less than 70 but less than 85

D: No. Relative value of 1 to 85 or more and less than 95

E: No. 1, relative value is 95 or more

In addition, 1 to No. 65 were classified into A to F in the order of excellent salt-resistance by the following criteria, and this was evaluated as an overall evaluation. The comprehensive evaluation can evaluate "A", "B", "C", "D", "E" and "F" as "pass" and "G" as " The evaluation results are shown in Table 5.

A: The evaluation of the average corrosion amount and the maximum corrosion depth are all A

B: One of the evaluation of the average corrosion amount and the maximum corrosion depth is A and the other is B

C: The evaluation of the average corrosion amount and the maximum corrosion depth are both B

D: One of the evaluation of the average corrosion amount and the maximum corrosion depth is C, and the other is B

E: The evaluation of average corrosion and maximum corrosion depth is C

F: Any one of the evaluation of the average corrosion amount and the maximum corrosion depth is D or less. Except where the average corrosion rate and the maximum corrosion depth are all E

G: The evaluation of the average corrosion rate and the maximum corrosion depth is E

Coated steel No. 1, No. 10 and No. 11 corresponded to the comparative example of the present invention, and the overall evaluation was G, and the salt water resistance was unsatisfactory. Hereinafter, each comparative example will be examined.

Coated steel No. 1 is a general steel material not having a coating layer. Coated steel No. 1, a rust coating was formed on the surface in the corrosion test, but sufficient salt water resistance was not obtained.

Coated steel No. 10 and No. 11 is a comparative example in which the average thickness of the coating layer is excessively small and a comparatively large comparative example, and sufficient salt water resistance is not obtained in all cases.

On the other hand, in the case of the coated steel material corresponding to the embodiment satisfying the constitution of the present invention. 2 to 9 and No. 12 to No. 65 showed excellent salt resistance due to the relative value of the average corrosion amount and the maximum corrosion depth being less than 95%. Each embodiment will be examined below.

Coated steel No. 12 to No. 17 is an embodiment using base steels B1 to C6 containing C, Si, Mn, P, S, Al, N, Fe and inevitable impurities. Hereinafter, the above-mentioned composition of the base steel is also referred to as basic composition 1. Coated steel No. 12 to No. 17 was superior to the coated steel of the comparative example, but was lowest in the examples.

Coated steel No. 2 to No. 9 is an example using a base steel B7 containing a specific amount of P and Al in the basic composition 1 and containing Cu and Cr and Mo and / or W. Hereinafter, the above-mentioned composition of the base steel is also referred to as basic composition 2. Coated steel No. 2 to No. 9 was superior to the coated steel of the comparative example but the lowest in the examples using the base steel having the basic composition 2.

Coated steel No. 18 ~ No. 65 is an example in which the base steels B7 to B64 having the basic composition 2 are used and the kind, content and average particle size of the Al compound, Cr compound, Cu compound and Fe compound in the coating layer are adjusted to an appropriate range. Concretely, the Al compound contains a specific amount of Al oxide and / or Al oxyhydroxide, the Cr compound contains a specific amount of Cr oxide, and the Cu compound contains a specific amount of Cu oxide. The Fe compound contains a total amount of Fe ₃ O ₄ and α-FeOOH in a specific amount, and the average particle sizes of Fe ₃ O ₄ and α-FeOOH are 4.5 nm or more and 22 nm or less, respectively. Coated steel No. 18 ~ No. 65 is a cross-sectional view of the above-mentioned coated steel No. 5; 2 to No. Compared with 9, at least the average corrosion amount and the maximum corrosion depth were superior. Hereinafter, 18 ~ No. 65 are reviewed.

Coated steel No. 18 ~ No. 20 is an embodiment using base steels B7 to B9 having a basic composition of 2 only. Coated steel No. 18 ~ No. 20 is a cross-sectional view of the above-mentioned coated steel No. 3; 2 to No. 9, it was possible to further reduce the average amount of corrosion.

Coated steel No. 21 to No. 23 is an example using base steels B10 to B12 containing a specific amount of Ni and / or Co in addition to the basic composition 2. Coated steel No. 21 to No. 23 is a cross-sectional view of the above-mentioned coated steel No. 3; 18 ~ No. 20, the maximum corrosion depth could be further reduced.

Coated steel No. 24 ~ No. 29 is an embodiment using base steels B13 to B18 containing a specific amount of Mg, Ca and / or REM in addition to the basic composition 2. Coated steel No. 24 ~ No. 29 is a cross-sectional view of the above-mentioned coated steel material No. 2; 18 ~ No. 20, the maximum corrosion depth could be further reduced.

Coated steel No. 30 ~ No. 34 is an example using base steels B19 to B23 containing Ni and / or Co and a specific amount of Mg, Ca and / or REM in addition to the basic composition 2. Coated steel No. 30 ~ No. 34 is a cross-sectional view of the above-mentioned coated steel material No. 1; 18 ~ No. Compared with 20, the average amount of corrosion and the maximum corrosion depth could be further reduced.

Coated steel No. 35 ~ No. 40 is an example using base steels B24 to B29 containing a certain amount of Sn, Sb and / or Se in addition to the basic composition 2. Coated steel No. 35 ~ No. 40 is a cross-sectional view of the above-mentioned coated steel material No. 3; 18 ~ No. 20, the maximum corrosion depth could be further reduced.

Coated steel No. 41 to No. 44 is an example using base steels B30 to B33 containing a specific amount of Ni and / or Co and Sn, Sb and / or Se in addition to the basic composition 2. Coated steel No. 41 to No. 44 is a cross-sectional view of the above-mentioned coated steel material No. 3; 18 ~ No. Compared with 20, the average amount of corrosion and the maximum corrosion depth could be further reduced.

Coated steel No. 45 to No. 48 is an embodiment using base steels B34 to B37 containing Mg, Ca and / or REM and Sn, Sb and / or Se in a specific amount in addition to the basic composition 2. Coated steel No. 45 to No. 48 is a cross section of the above-mentioned coated steel material No. 2. 18 ~ No. 20, the maximum corrosion depth could be remarkably reduced.

Coated steel No. 49 to No. 53 is an embodiment using base steels B38 to B42 containing Ni and / or Co, Mg, Ca and / or REM, and Sn, Sb and / or Se in a specific amount in addition to the basic composition 2. Coated steel No. 49 to No. 53 is a cross-sectional view of the above-mentioned coated steel No. 3; 18 ~ No. 20, the average corrosion amount and the maximum corrosion depth can be further reduced, and in particular, the maximum corrosion depth can be remarkably reduced. Coated steel No. 49 to No. Reference numeral 53 denotes a coated steel material No. 5 to be described later. 63 and No. After 65, it showed excellent salt water resistance.

Coated steel No. 54 to No. 55 is an example using base steels B43 to B44 containing a specific amount of Ti, Nb, Zr, V and / or B in addition to the basic composition 2. Coated steel No. 54 to No. 55 is a cross-sectional view of the above-mentioned coated steel No. 5; 18 ~ No. 20, it was possible to slightly reduce the average corrosion amount and the maximum corrosion depth.

Coated steel No. 56 ~ No. 57 is an embodiment using base steels B45 to B46 containing Ni and / or Co and a specific amount of Ti, Nb, Zr, V and / or B in addition to the basic composition 2. Coated steel No. 56 ~ No. 57 is a cross-sectional view of the above-mentioned coated steel No. 5; 18 ~ No. 20, the maximum corrosion depth could be further reduced.

Coated steel No. 58 and No. 64 is an example using base steels B47 and B53 containing Mg, Ca and / or REM and Ti, Nb, Zr, V and / or B in a specific amount in addition to the basic composition 2. Coated steel No. 58 and No. 64 is a cross-sectional view of the above-mentioned coated steel No. 3; 18 ~ No. 20, the maximum corrosion depth could be further reduced. Further, the coated steel material containing the specific amount of V as the base steel. 64 is a cross-sectional view of the above-mentioned coated steel No. 3; 18 ~ No. Compared with 20, the average amount of corrosion was also reduced.

Coated steel No. 59 to No. 60 is carried out using base steels B48 to B49 containing Ni and / or Co, Mg, Ca and / or REM and Ti, Nb, Zr, V and / or B in a specific amount in addition to the basic composition 2 Yes. Coated steel No. 59 to No. 60 is a cross-sectional view of the above- 18 ~ No. Compared with 20, the average amount of corrosion and the maximum corrosion depth could be further reduced.

Coated steel No. 61 is an embodiment using a base steel material B50 containing a specific amount of Sn, Sb and / or Se and Ti, Nb, Zr, V and / or B in addition to the basic composition 2. Coated steel No. 61 is a cross-sectional view of the above-mentioned coated steel material No. 1; 18 ~ No. 20, the maximum corrosion depth could be further reduced.

Coated steel No. 62 is an example using a base steel material B51 containing a specific amount of Ni and / or Co and Sn, Sb and / or Se and Ti, Nb, Zr, V and / or B in addition to the basic composition 2 . Coated steel No. 62 is a cross-sectional view of the above-mentioned coated steel material No. 1; 18 ~ No. Compared with 20, the average amount of corrosion and the maximum corrosion depth could be further reduced.

Coated steel No. 63 and No. 65 is a mixture of Ni and / or Co, Mg, Ca and / or REM, Sn, Sb and / or Se and Ti, Nb, Zr, V and / In which the base steel materials B52 and B54 are used. Coated steel No. 63 and No. 65 is a cross-sectional view of the above-mentioned coated steel No. 5; 18 ~ No. 20, the average corrosion amount and the maximum corrosion depth can be further reduced, and in particular, the maximum corrosion depth can be remarkably reduced. Coated steel No. 63 and No. 65 exhibited the best salt resistance in the Examples.

As described above, it can be judged that the water resistance can be improved by providing the coating layer satisfying the constitution of the present invention. Further, it is judged that the base steel 1 can further improve the flame resistance by containing the basic composition 1 and can further improve the flame resistance by containing the base composition 2. Further, it is preferred that the base steel comprises at least one of Ni and / or Co, Mg, Ca and / or REM, Sn, Sb and / or Se and Ti, Nb, Zr, V and / It is judged that the flame retardancy can be further improved by containing at least one of them in a specific amount, and particularly the flame resistance can be remarkably improved by containing all of them in a specific amount.

From the above results, it is judged that the coated steel of the present invention exhibits excellent flame resistance in seawater environment and can be suitably used for structures exposed to sea water or seaweed salt particles. Further, the method for producing a coated steel material of the present invention can provide the coated steel material.

The coated steel material and the method for producing the same can provide a coated steel material in which excellent salt water resistance is maintained for a relatively long period of time.

A: Test area
B: an area other than the test area
X: grid point

Claims (9)

A coated steel material comprising a base steel material and a coating layer formed on the surface of the base steel material,
Wherein the coating layer has an average thickness of 8 占 퐉 or more and 105 占 퐉 or less and further contains an Al compound, a Cr compound, a Cu compound, and an Fe compound,
Wherein said compound is an oxide, an oxyhydroxide or a combination thereof. The method according to claim 1,
Wherein,
Al oxide, Al oxyhydroxide, or a combination thereof in an amount of 0.08 mass% or more and 10.5 mass% or less,
0.08 to 10.5 mass% of Cr oxide,
0.08 to 10.5% by mass of Cu oxide, and
Fe ₃ O ₄ and? -FeOOH as Fe oxides and Fe oxyhydroxides in a total amount of 29.5 mass% or more,
Wherein said Fe ₃ O ₄ and α-FeOOH have an average particle diameter of 4.5 nm or more and 22 nm or less, respectively. The method according to claim 1,
The above-
C: not less than 0.008 mass% and not more than 0.32 mass%
Si: 0.05% by mass or more and 2.0% by mass or less,
Mn: 0.08% by mass or more and 3.0% by mass or less,
P: 0.001 mass% or more and 0.05 mass% or less,
S: not less than 0.0001 mass% and not more than 0.05 mass%
Al: 0.001 mass% or more and 1.6 mass% or less,
N: 0.001% by mass or more and 0.015% by mass or less, and
Balance: Fe and inevitable impurities
Lt; / RTI > The method of claim 3,
The above-
P: not less than 0.004 mass% and not more than 0.05 mass%, and
Al: 0.008 mass% or more and 1.6 mass% or less
Lt; / RTI >
0.08% by mass or more and 2.2% by mass or less of Cu, and
Cr: 0.08 mass% or more and 3.0 mass% or less
, And further contains
Mo: 0.008 mass% or more and 2.2 mass% or less, and
W: 0.008 mass% or more and 2.2 mass% or less
≪ / RTI > The method according to claim 3 or 4,
The above-
Ni: 0.008 mass% or more and 5.2 mass% or less, and
Co: 0.008 mass% or more and 5.0 mass% or less
≪ / RTI > The method according to claim 3 or 4,
The above-
Mg: 0.0004 mass% or more and 0.01 mass% or less,
Ca: 0.0004 mass% or more and 0.01 mass% or less, and
Rare earth metals: 0.0004 mass% or more and 0.01 mass% or less
≪ / RTI > The method according to claim 3 or 4,
The above-
Sn: not less than 0.0008 mass% and not more than 0.2 mass%
Sb: 0.0008% by mass or more and 0.2% by mass or less, and
Se: 0.0008 mass% or more and 0.2 mass% or less
≪ / RTI > The method according to claim 3 or 4,
The above-
Ti: more than 0 mass% and not more than 0.2 mass%
Nb: more than 0 mass% and not more than 0.2 mass%
Zr: more than 0 mass% and not more than 0.2 mass%
V: more than 0 mass% and 0.2 mass% or less, and
B: more than 0% by mass and not more than 0.01% by mass
≪ / RTI > Comprising the steps of preparing a base steel material,
A step of preparing a composition for forming a coating layer in which an Al compound, a Cr compound, a Cu compound and an Fe compound are dispersed in a solvent;
A step of coating the surface of the non-coated steel material with the coating layer forming composition
And,
Wherein the compound is an oxide, an oxyhydroxide or a combination thereof,
Wherein a coating layer having an average thickness of 8 占 퐉 or more and 105 占 퐉 or less is formed in the coating process.

Images