JP2017039974A - Coated steel material, and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated steel material kept in excellent salt water resistance for a relatively long term.SOLUTION: A coated steel material comprises a basis steel material, and a coating layer formed on the surface of the basis steel material. The coating layer is characterized in that: it has an average thickness of 8 μm to 105 μm; it contains an Al compound, a Cr compound, a Cu compound and an Fe compound; and said chemical compound is an oxide or an oxyhydroxide or their combination. The coating layer may contain an Al oxide, an Al oxyhydrooxide or their combination by 0.08 mass% or more and 10.5 mass% or less, a Cr oxide by 0.08 mass% or more and 10.5 mass% or less, a Cu oxide by 0.08 mass% or more and 10.5 mass% or less, and the total of FeOand α-FeOOH by 29.5 mass% or more in total. Moreover, it is preferred that the average particle diameters of the FeOand α-FeOOH are individually 4.5 nm to 22 nm.SELECTED DRAWING: None

Description

  The present invention relates to a coated steel material and a manufacturing method thereof.

  Steel is widely used as a member of various structures, but ships, marine structures, bridges and other beaches and structures in seawater used in corrosive environments mainly caused by seawater and / or flying sea salt particles When used in the above, the strength may decrease due to reduction in plate thickness, formation of corrosion holes, or the like. In particular, ship ballast tanks are known to be exposed to severe corrosive environments. In recent years, as a clean energy generation technology that does not emit carbon dioxide, a greenhouse gas, from the viewpoint of global environmental conservation, wind power generation, ocean wave power generation, tidal current power generation, ocean current power generation, temperature difference power generation, solar power generation Power generation technology such as Such marine structures are also likely to be exposed to more severe corrosive environments than conventional beaches and structures in seawater. Therefore, these steel materials are required to improve salt water resistance by anticorrosion technology.

  Examples of the anticorrosion technique include cathodic protection and surface treatment. Examples of the surface treatment include anticorrosion coating for forming a coating by coating, anticorrosion spraying for forming a coating by thermal spraying, and the like. Moreover, since it is known that the rust formed on the surface of the steel material acts as a protective film for improving salt water resistance, a method of using rust for the surface treatment of the steel material is also conceivable. Furthermore, methods for improving the steel material itself and combining the steel material itself with surface treatment have also been proposed.

  Electrocorrosion, which is one of the anticorrosion techniques, is a method of suppressing corrosion by manipulating electrode potential, and is effective in improving the saltwater resistance of steel materials that are constantly immersed in seawater. It is not very effective in improving the salt water resistance of steel materials that are not. Specific examples of steel materials that are not effective in improving salt water resistance due to cathodic protection include steel materials in the upper part of marine structures exposed to corrosive environments such as seawater splashes, especially steel materials in the vicinity of the sea surface, and ship loading The steel material etc. of the inner surface of the ballast tank which repeats injection | pouring and drainage of seawater according to are mentioned. As another specific example, steel materials of structures such as iron bridges close to the coast that are exposed to the arrival of sea salt particles, which are fine particles composed of salt derived from seawater, and repeat a dry environment and a humid environment, etc. . Thus, cathodic protection is not very effective for steel materials used in ship ballast tanks and marine structures.

  Another anti-corrosion technology is anti-corrosion coating, which uses anti-corrosion paints mainly composed of various resins such as epoxy resin, chlorinated rubber, acrylic resin, urethane resin, and fluorine resin according to the environment. Or it is the method of improving salt water resistance by forming the coating film of a multilayer. However, the coating film is easily wrinkled and peeled due to deterioration with time due to ultraviolet rays, damage due to some external mechanical action, and the like, and as a result, the steel material may be exposed and corrosion may progress. For example, in a place where the coating film of a ship's ballast tank is peeled off, the amount of corrosive wear per year may reach 1 mm. For this reason, anticorrosion coating requires maintenance such as periodic inspection and repainting after painting, but recoating requires a considerable cost and construction period. In addition, there are many places where structures such as ships, offshore structures and bridges cannot be approached without underwater or scaffolding, and where the above-mentioned inspection and maintenance are not easy due to the difficulty of approaching structurally complicated places. . Therefore, anticorrosion coating may not be practical for steel materials used in ship ballast tanks and offshore structures from the viewpoint of the short period during which saltwater resistance is maintained.

  Another anti-corrosion technology, anti-corrosion spraying, uses a base metal or alloy, such as zinc, aluminum, or magnesium, as the thermal spray material to form a thermal spray coating on the surface of the steel, and the sacrificial anodic action of this thermal spray coating prevents corrosion. Get action. However, since this anti-corrosion spray exhibits anti-corrosion action due to the consumption of the spray coating, it is necessary to maintain the average thickness of the spray coating by periodic re-spraying, but it is difficult to access the structure as described above. There are many places where re-spraying is not easy. Therefore, anticorrosion spraying, like anticorrosion coating, may not be practical for steel materials used in ship ballast tanks and marine structures from the viewpoint of the short period during which saltwater resistance is maintained. .

On the other hand, rust made of Fe compounds such as α-FeOOH, β-FeOOH, γ-FeOOH, and Fe ₃ O ₄ formed on the surface of steel in a seawater corrosive environment acts as a protective coating that suppresses the invasion of corrosive substances. However, it is known that corrosion of steel materials is somewhat suppressed. However, rust formed on normal steel materials has a relatively large Fe compound particle size and lacks precision, and therefore has little effect of suppressing the entry of corrosive substances, and does not significantly improve salt water resistance. Moreover, since the said rust has comparatively low adhesiveness with steel materials, it peels off and drops easily. Therefore, the method of using rust for the surface treatment of steel is not very practical.

  Furthermore, in addition to the above-described surface treatment for steel materials, there has been proposed an anticorrosion technique in which the steel material itself is improved, or the improvement of the steel material itself and the surface treatment are combined. Specifically, for example, a method using a coating steel material having a specific composition (see JP 2012-122117 A), a steel material having a specific chemical composition covered with a protective rust layer containing a specific metal. A method to be used (see Japanese Patent Application Laid-Open No. 2014-5499) has been proposed. However, even with the above-described conventional method, the period during which excellent salt water resistance is maintained is insufficient.

JP 2012-122117 A JP 2014-5499 A

  This invention is made | formed based on the above situations, and makes it a subject to provide the coated steel material by which the outstanding salt-water resistance is maintained for a comparatively long period, and its manufacturing method.

  The present inventors have investigated the corrosion progress mechanism of steel materials in a seawater corrosive environment, and have studied a new anticorrosion technique that does not depend on surface treatment such as conventional anticorrosion coating. As a result, as described above, rust composed of Fe compounds formed on the surface of steel in a seawater corrosive environment does not significantly improve saltwater resistance, and easily peels off and falls off from steel. It is not practical as a surface treatment. However, it has been found that a coated steel material containing a Fe compound and having a coating layer having an appropriate average thickness formed on the surface of the base steel material can maintain salt water resistance for a relatively long period of time. Moreover, the said coating layer contains Cu compound, the density of the said coating layer improves, Furthermore, a corrosive substance can be detoxified by containing Al compound and Cr compound, and, as a result, to a base steel material It has been found that salt water resistance can be improved by significantly suppressing the intrusion of corrosive substances.

  That is, the invention made to solve the above problems is 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 μm or more and 105 μm or less. And containing an Al compound, a Cr compound, a Cu compound, and an Fe compound, wherein the compound is an oxide, an oxyhydroxide, or a combination thereof.

  The said coating steel material can improve the adhesiveness of a coating layer and a base steel material because a coating layer contains the Fe compound which is excellent in adhesiveness with a base steel material. Moreover, the penetration | invasion to the base steel material of a corrosive substance can be suppressed because a coating layer has the average thickness of the said range. As a result, excellent salt water resistance can be maintained for a long time. Further, in the coated steel material, the Al compound contained in the coating layer fixes the corrosive chloride and renders it harmless, the Cr compound fixes the corrosive sulfate and renders it harmless, and the Cu compound contains the dense coating layer. By improving the thickness, the penetration of corrosive substances into the base steel is remarkably suppressed, so that the salt water resistance can be improved.

The coating layer contains Al oxide, Al oxyhydroxide or a combination thereof, Cr oxide, Cu oxide, and Fe ₃ O ₄ and α-FeOOH as the Fe oxide and Fe oxyhydroxide. Good. In this case, the content of Al oxide, Al oxyhydroxide, or a combination thereof is preferably 0.08% by mass or more and 10.5% by mass or less. Moreover, as content of Cr oxide, 0.08 mass% or more and 10.5 mass% or less are preferable. Furthermore, as content of Cu oxide, 0.08 mass% or more and 10.5 mass% or less are preferable. Furthermore, the total content of Fe ₃ O ₄ and α-FeOOH is preferably 29.5% by mass or more. Furthermore, the average particle diameter of the Fe ₃ O ₄ and α-FeOOH is preferably 4.5 nm or more and 22 nm or less, respectively.

When the coating layer contains Al oxide and / or Al oxyhydroxide as the Al compound, fixing of the corrosive chloride can be further promoted. Moreover, fixation of corrosive sulfate can be further accelerated | stimulated because a coating layer contains Cr oxide as a Cr compound. Furthermore, a coating layer can be made denser because a coating layer contains Cu oxide as a Cu compound. As a result, the salt water resistance can be further improved. Furthermore, when the content of the compound in the coating layer is a specific amount, the formation of cracks in the coating layer due to a temperature change during use can be suppressed while improving the salt water resistance. Further, the coating layer contains Fe ₃ O ₄ and α-FeOOH, which are particularly excellent in adhesion to a base steel material among Fe compounds as Fe oxide and Fe oxyhydroxide, and the average particle size of the coating layer is in the above range. By doing, the denseness of a coating layer and adhesiveness with a base steel material can be improved more. As a result, the salt water resistance and the durability of the salt water resistance can be further improved.

  The base steel material is C: 0.008 mass% or more and 0.32 mass% or less, Si: 0.05 mass% or more and 2.0 mass% or less, Mn: 0.08 mass% or more and 3.0 mass% or less, P: 0.001% by mass to 0.05% by mass, S: 0.05% by mass or less, Al: 0.001% by mass to 1.6% by mass, N: 0.001% by mass to 0.015% It is good to have a composition that is not more than mass%, and the balance is Fe and inevitable impurities. Thus, salt water resistance can be improved more because the said base steel material has the said composition.

  The base steel material has a composition of P: 0.004% by mass or more and 0.05% by mass or less, and Al: 0.008% by mass or more and 1.6% by mass or less, and Cu: 0.08% by mass or more. 2.2% by mass or less, and Cr: 0.08% by mass or more and 3.0% 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 may be further contained. Thus, the protective property of the said coating layer improves by making content of P of the said base steel material into a specific amount. Moreover, salt water resistance can be improved more by making content of P and Al of the said base steel material into a specific amount. Furthermore, the denseness of a coating layer improves more because the said base steel materials contain Cu and Cr specific amount. Furthermore, when the said base steel material contains a specific amount of at least one of Mo and W, Mo and / or W is dissolved in ferrite and the activity of the dissolution reaction is lowered. As a result, the salt water resistance can be further improved.

  The base steel material may further contain at least one of Ni: 0.008% by mass to 5.2% by mass and Co: 0.008% by mass to 5.0% by mass. Thus, salt water resistance and intensity | strength can be improved more because a base steel material contains further a specific amount of at least 1 sort (s) among Ni and Co.

  The base steel material is 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 metal: 0.0004 mass% or more and 0.01 mass% or less. At least one of the following may be further contained. Thus, when the base steel material further contains a specific amount of at least one of Mg, Ca, and rare earth metal, it is possible to suppress a decrease in pH in the vicinity of the surface of the base steel material, and as a result, the salt water resistance can be further improved.

  The base steel material is Sn: 0.0008% by mass to 0.2% by mass, Sb: 0.0008% by mass to 0.2% by mass, and Se: 0.0008% by mass to 0.2% by mass. It is good to further contain at least one of them. Thus, salt water resistance can be improved more because a base steel material contains at least 1 sort (s) of Sn, Sb, and Se further.

  The base steel material is Ti: more than 0% by weight, 0.2% by weight or less, Nb: more than 0% by weight, 0.2% by weight or less, Zr: more than 0% by weight, 0.2% by weight or less, V: more than 0% by weight It is preferable to further contain at least one of 0.2% by mass or less and B: more than 0% by mass and 0.01% by mass or less. Thus, the strength can be further improved when the base steel material further contains a specific amount of at least one of Ti, Nb, Zr, V, and B.

  Another invention made in order to solve the above problems includes a step 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, Coating the composition for forming a coating layer on the surface of the base steel material, and the compound is an oxide, an oxyhydroxide, or a combination thereof. In the coating step, the average thickness is This is a method for producing a coated steel material for forming a coating layer of 8 μm or more and 105 μm or less.

Here, “average thickness” means an average value of thicknesses measured at arbitrary ten points. The “average particle size” means that the particles of Fe ₃ O ₄ and α-FeOOH in the cross section of the coating layer are observed at an appropriate magnification using a field emission transmission electron microscope (FE-TEM), and an arbitrary 10 It means the average value of the diameter of a perfect circle having the same area as the cross-sectional area of the particle.

  The said coated steel material and its manufacturing method can provide the coated steel material by which outstanding salt water resistance is maintained for a comparatively long period of time.

It is a typical top view which shows the test surface of the test piece used in the Example of this invention.

<Coated steel>
Hereinafter, embodiments of the coated steel material and the manufacturing method thereof according to the present invention will be described. The said covering steel material is equipped with a base steel material and the coating layer formed in the surface of this base steel material.

(Base steel)
It does not specifically limit as a base steel material, A conventionally well-known steel material can be used. As the base steel material, C (carbon): 0.008 mass% to 0.32 mass%, Si (silicon): 0.05 mass% to 2.0 mass%, Mn: 0.08 mass% to 3 0.0 mass% or less, P (phosphorus): 0.001 mass% to 0.05 mass%, S (sulfur): 0.05 mass% or less, Al (aluminum): 0.001 mass% to 1.6 Those having a composition of mass% or less, N (nitrogen): 0.001 mass% or more and 0.015 mass% or less, balance: Fe (iron) and inevitable impurities are preferable. Since the base steel material contains specific amounts of P, Al, and N, the coated steel material can easily and reliably maintain excellent salt water resistance due to a synergistic action with the coating layer for a long time. In addition, since the base steel material contains a specific amount of C, Si, Mn, S, and N, the coated steel material can easily and reliably satisfy the mechanical characteristics required for the material of the structure and the ease of welding. . Hereinafter, each component will be described.

[C (carbon)]
C in the base steel material is an effective element for ensuring the strength of the coated steel material. As a minimum of content of C in a base steel material, 0.008 mass% is preferred, 0.02 mass% is more preferred, and 0.03% mass is still more preferred. On the other hand, the upper limit of the C content is preferably 0.32% by mass, more preferably 0.29% by mass, and still more preferably 0.28% by mass. When content of C is smaller than the said minimum, there exists a possibility that the intensity | strength of the said covering steel material may fall. Conversely, when the C content exceeds the upper limit, the amount of cementite that acts as a cathode site in the corrosive environment is increased, which accelerates the corrosion reaction, and as a result, the salt water resistance of the coated steel material may be reduced. In addition, the toughness may also decrease.

[Si (silicon)]
Si in the base steel material is an effective element for deoxidizing the base steel material and ensuring the strength of the coated steel material. As a minimum of content of Si in a base steel material, 0.05 mass% is preferred, 0.08 mass% is more preferred, and 0.10 mass% is still more preferred. On the other hand, the upper limit of the Si content is preferably 2.0% by mass, more preferably 1.95% by mass, and even more preferably 1.90% by mass. When the content of Si is smaller than the lower limit, there is a risk that deoxidation of the base steel material and securing of the strength of the coated steel material are insufficient. Conversely, when the Si content exceeds the upper limit, welding of the coated steel material may be difficult.

[Mn (manganese)]
Mn in the base steel material is an effective element for deoxidizing the base steel material and ensuring the strength of the coated steel material, similarly to Si. As a minimum of content of Mn in a base steel material, 0.08 mass% is preferred, 0.15 mass% is more preferred, and 0.2 mass% is still more preferred. On the other hand, the upper limit of the Mn content is preferably 3.0% by mass, more preferably 2.9% by mass, and even more preferably 2.8% by mass. When the Mn content is smaller than the lower limit, the coated steel material may not be able to secure the strength required for the structure. Conversely, if the Mn content exceeds the above upper limit, the toughness of the coated steel material may be reduced.

[P (phosphorus)]
P in the base steel material is an element effective for enhancing the protection of the coating layer and further improving the salt water resistance of the coating steel material. As a minimum of content of P in a base steel material, 0.001 mass% is preferred, 0.004 mass% is more preferred, 0.008 mass% is still more preferred, and 0.017 mass% is especially preferred. On the other hand, the upper limit of the P content is preferably 0.05% by mass, more preferably 0.045% by mass, and still more preferably 0.04% by mass. When content of P is smaller than the said minimum, there exists a possibility that the salt-water resistance of the said coated steel materials may fall. Conversely, if the P content exceeds the above upper limit, the toughness of the coated steel material may be reduced or welding may be difficult.

[S (sulfur)]
S in the base steel material is an element that lowers the toughness of the coated steel material and makes welding difficult. Therefore, although the content of S in the base steel material is preferably as small as possible, it is difficult to make the S content 0 mass% industrially. Therefore, the upper limit of the S content in the base steel material 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 S content is not particularly limited, but is, for example, 0.0001% by mass.

[Al (aluminum)]
Al in the base steel material is an element effective for forming a stable oxide in a seawater corrosive environment and further improving the salt water resistance of the coated steel material. Moreover, Al is also an effective element for deoxidizing the base steel material and ensuring the strength of the coated steel material, similarly to the above-described Si and Mn. As a minimum of content of Al in a base steel material, 0.001 mass% is preferred, 0.008 mass% is more preferred, and 0.010 mass% is still more preferred. On the other hand, the upper limit of the Al content is preferably 1.6% by mass, more preferably 1.45% by mass, and still more preferably 1.4% by mass. If the Al content is smaller than the lower limit, the effects of improving the salt water resistance and securing the strength of the coated steel material and deoxidizing the base steel material may not be sufficiently obtained. Conversely, if the Al content exceeds the upper limit, welding of the coated steel material may be difficult.

[N (nitrogen)]
N in the base steel material is an element effective for improving the salt water resistance and strength of the coated steel material by forming finely dispersed particles of nitride in the base steel material. As a minimum of content of N in a base steel material, 0.001 mass% is preferred, 0.0015 mass% is more preferred, and 0.002 mass% is still more preferred. On the other hand, the upper limit of the N content is preferably 0.015% by mass, more preferably 0.014% by mass, and still more preferably 0.013% by mass. When content of N is smaller than the said minimum, there exists a possibility that the salt-water resistance and intensity | strength of the said coating steel material may fall. Conversely, if the N content exceeds the above upper limit, the toughness of the coated steel material may be reduced, or welding may be difficult.

[Remainder]
Of the composition of the base steel material, the balance other than the components described above 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 material is not particularly limited as long as the various characteristics of the coated steel material are not impaired. As an upper limit of the total content of inevitable impurities in a specific base steel material, 0.1% by mass is preferable, 0.09% by mass is more preferable, 0.05% by mass is further preferable, and 0.01% by mass is preferable. Particularly preferred. By making the total content of inevitable impurities in the above range, the salt water resistance of the coated steel material 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 material is an element effective for improving the salt water resistance of the coating steel material by improving the denseness of the coating layer. As a minimum of content of Cu in a base steel material, 0.08 mass% is preferred, 0.12 mass% is more preferred, and 0.15 mass% is still more preferred. On the other hand, the upper limit of the Cu content is preferably 2.2% by mass, more preferably 1.95% by mass, and even more preferably 1.90% by mass. When content of Cu is smaller than the said minimum, there exists a possibility that the salt water resistance of the said coated steel material may fall. On the other hand, when the Cu content exceeds the above upper limit, welding and hot working of the coated steel material may be difficult.

[Cr (chrome)]
Similar to Cu, Cr in the base steel material is an element effective for improving the salt water resistance of the coated steel material by making the coating layer denser. As a minimum of content of Cr in a base steel material, 0.08 mass% is preferred, 0.12 mass% is more preferred, and 0.15 mass% is still more preferred. On the other hand, the upper limit of the Cr content is preferably 3.0% by mass, more preferably 2.9% by mass, and even more preferably 2.8% by mass. When content of Cr is smaller than the said minimum, there exists a possibility that the salt water resistance of the said coated steel materials may fall. On the other hand, when the Cr content exceeds the above upper limit, welding and hot working of the coated steel material may be difficult.

[Mo (molybdenum) and W (tungsten)]
Mo and W in the base steel material are elements having an action of lowering the activity of the dissolution reaction by dissolving in ferrite. Therefore, when the base steel material contains Mo and / or W, the salt water resistance of the coated steel material is further improved. Moreover, when the base steel material contains an appropriate amount of Mo and / or W, the strength of the coated steel material is also improved.

  As a minimum of content of Mo in a base steel material, 0.008 mass% is preferred, 0.02 mass% is more preferred, and 0.03 mass% is still more preferred. On the other hand, the upper limit of the Mo content is preferably 2.2% by mass, more preferably 1.9% by mass, and still more preferably 1.8% by mass. When the Mo content is smaller than the lower limit, the salt water resistance and strength of the coated steel material may be reduced. Conversely, if the Mo content exceeds the upper limit, welding and hot working of the coated steel material may be difficult.

  As a minimum of content of W in a base steel material, 0.008 mass% is preferred, 0.02 mass% is more preferred, and 0.03% mass is still more preferred. On the other hand, the upper limit of the W content is preferably 2.2% by mass, more preferably 1.9% by mass, and even more preferably 1.8% by mass. When content of W is smaller than the said minimum, there exists a possibility that the salt-water resistance and intensity | strength of the said coating steel material may fall. Conversely, when the W content exceeds the above upper limit, welding and hot working of the coated steel material may be difficult.

[Ni (nickel) and Co (cobalt)]
The base steel material preferably further contains at least one of Ni and Co. Ni and Co in the base steel material are elements that further improve the salt water resistance and strength of the coated steel material, respectively.

  As a minimum of content of Ni in a base steel material, 0.008 mass% is preferred, 0.02 mass% is more preferred, 0.03 mass% is still more preferred, and 0.08 mass% is especially preferred. On the other hand, the upper limit of the Ni content is preferably 5.2% by mass, more preferably 4.9% by mass, still more preferably 4.8% by mass, and particularly preferably 1% by mass. If the Ni content is less than the lower limit, the salt water resistance and strength of the coated steel material may be reduced. Conversely, when the Ni content exceeds the upper limit, welding and hot working of the coated steel material may be difficult.

  As a minimum of content of Co in a base steel material, 0.008 mass% is preferred, 0.02 mass% is more preferred, 0.03 mass% is still more preferred, and 0.04 mass% is especially preferred. On the other hand, the upper limit of the Co content 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. If the Co content is less than the lower limit, the salt water resistance and strength of the coated steel material may be reduced. Conversely, when the Co content exceeds the upper limit, welding and hot working of the coated steel material may be difficult.

[Mg (magnesium), Ca (calcium) and rare earth metals (REM)]
The base steel material preferably further contains at least one of Mg, Ca and rare earth metals. Mg, Ca, and rare earth metal in the base steel material each suppresses a decrease in pH near the surface of the base steel material by reacting and dissolving with hydrogen ions, thereby further improving the salt water resistance of the coated steel material. It is an element.

  As a minimum of content of Mg in a base steel material, 0.0004 mass% is preferred, 0.006 mass% is more preferred, 0.0007 mass% is still more preferred, and 0.0009 mass% is especially preferred. 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. If the Mg content is smaller than the lower limit, the salt water resistance of the coated steel material may be reduced. Conversely, when the Mg content exceeds the above upper limit, welding and hot working of the coated steel material may be difficult.

  As a minimum of content of Ca in a base steel material, 0.0004 mass% is preferred, 0.0006 mass% is more preferred, 0.0007 mass% is still more preferred, and 0.0013 mass% is especially preferred. 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, and particularly preferably 0.004% by mass. If the Ca content is smaller than the lower limit, the salt water resistance of the coated steel material may be reduced. Conversely, when the Ca content exceeds the above upper limit, welding and hot working of the coated steel material may be difficult.

  The lower limit of the rare earth metal content in the base steel material is preferably 0.0004% by mass, more preferably 0.0006% by mass, further preferably 0.0007% by mass, and particularly preferably 0.001% by mass. On the other hand, the upper limit of the rare earth metal 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 rare earth metal content is smaller than the lower limit, the salt water resistance of the coated steel material may be lowered. Conversely, when the rare earth metal content exceeds the above upper limit, welding and hot working of the coated steel material may be difficult.

[Sn (tin), Sb (antimony) and Se (selenium)]
The base steel material preferably further contains at least one of Sn, Sb and Se. Sn, Sb, and Se in the base steel material are elements that further improve the salt water resistance of the coated steel material.

  As a minimum of content of Sn in a base steel material, 0.0008 mass% is preferred, 0.002 mass% is more preferred, 0.003 mass% is still more preferred, and 0.008 mass% is especially preferred. On the other hand, the upper limit of the Sn content is preferably 0.2% by mass, more preferably 0.19% by mass, further preferably 0.18% by mass, and particularly preferably 0.1% by mass. When content of Sn is smaller than the said minimum, there exists a possibility that the salt water resistance of the said coated steel materials may fall. Conversely, when the Sn content exceeds the above upper limit, welding and hot working of the coated steel material may be difficult.

  As a minimum of content of Sb in a base steel material, 0.0008 mass% is preferred, 0.002 mass% is more preferred, 0.003 mass% is still more preferred, and 0.008 mass% is especially preferred. On the other hand, the upper limit of the Sb content is preferably 0.2% by mass, more preferably 0.19% by mass, further preferably 0.18% by mass, and particularly preferably 0.10% by mass. When content of Sb is smaller than the said minimum, there exists a possibility that the salt water resistance of the said coated steel materials may fall. Conversely, when the Sb content exceeds the above upper limit, welding and hot working of the coated steel material may be difficult.

  As a minimum of content of Se in a base steel material, 0.0008 mass% is preferred, 0.002 mass% is more preferred, 0.003 mass% is still more preferred, and 0.008 mass% is especially preferred. On the other hand, the upper limit of the Se content is preferably 0.2% by mass, more preferably 0.19% by mass, further preferably 0.18% by mass, and particularly preferably 0.10% by mass. If the Se content is less than the lower limit, the salt water resistance of the coated steel material may be reduced. Conversely, when the Se content exceeds the above upper limit, welding and hot working of the coated steel material may be difficult.

[Ti (titanium), Nb (niobium), Zr (zirconium), V (vanadium) and B (boron)]
The base steel material preferably further contains at least one of Ti, Nb, Zr, V and B. Ti, Nb, Zr, V, and B in the base steel material are elements that further improve the strength of the coated steel material.

  As content of Ti in a base steel material, more than 0 mass% is preferable. As a minimum of content of Ti, 0.001 mass% is more preferable, and 0.008 mass% is further more preferable. On the other hand, the upper limit of the Ti content is preferably 0.2% by mass, more preferably 0.19% by mass, further preferably 0.18% by mass, and particularly preferably 0.10% by mass. When the Ti content is smaller than the lower limit, the strength of the coated steel material may be reduced. On the other hand, when the Ti content exceeds the above upper limit, the toughness of the base steel material may be reduced, and welding of the coated steel material may be difficult.

  The Nb content in the base steel material is preferably more than 0% by mass. As a minimum of content of Nb, 0.001 mass% is more preferred, and 0.008 mass% is still more preferred. On the other hand, the upper limit of the Nb content is preferably 0.2% by mass, more preferably 0.19% by mass, further preferably 0.18% by mass, and particularly preferably 0.10% by mass. When content of Nb is smaller than the said minimum, there exists a possibility that the intensity | strength of the said covering steel material may fall. On the other hand, when the Nb content exceeds the above upper limit, the toughness of the base steel material may be reduced, and welding of the coated steel material may be difficult.

  The Zr content in the base steel material is preferably more than 0% by mass. As a minimum of the content of Zr, 0.001 mass% is more preferred, and 0.06 mass% is still more preferred. On the other hand, the upper limit of the Zr content is preferably 0.2% by mass, more preferably 0.19% by mass, further preferably 0.18% by mass, and particularly preferably 0.10% by mass. When content of Zr is smaller than the said minimum, there exists a possibility that the intensity | strength of the said covering steel material may fall. On the other hand, when the Zr content exceeds the above upper limit, the toughness of the base steel material may be reduced, and it may be difficult to weld the coated steel material.

  As content of V in a base steel material, more than 0 mass% is preferable. As a minimum of content of V, 0.001 mass% is more preferable, and 0.02 mass% is further more preferable. On the other hand, the upper limit of the V content is preferably 0.2% by mass, more preferably 0.19% by mass, further preferably 0.18% by mass, and particularly preferably 0.10% by mass. When content of V is smaller than the said minimum, there exists a possibility that the intensity | strength of the said covering steel material may fall. On the other hand, when the V content exceeds the above upper limit, the toughness of the base steel material may be lowered, and welding of the coated steel material may be difficult.

  As content of B in a base steel material, more than 0 mass% is preferable. As a minimum of content of B, 0.0001 mass% is more preferable, and 0.00015 mass% is further more preferable. On the other hand, the upper limit of the B content 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 content of B is smaller than the said minimum, there exists a possibility that the intensity | strength of the said covering steel materials may fall. On the other hand, when the B content exceeds the above upper limit, the toughness of the base steel material may be reduced, and it may be difficult to weld the coated steel material.

  In particular, the base steel material is C: 0.008% by mass to 0.32% by mass, Si: 0.05% by mass to 2.0% by mass, Mn: 0.08% by mass to 3.0% by mass. P: 0.004 mass% or more and 0.05 mass% or less, S: 0.05 mass% or less, Al: 0.008 mass% or more and 1.6 mass% or less, Cu: 0.08 mass% or more. 2% by mass or less, Cr: 0.08% by mass or more and 3.0% by mass or less, N: 0.001% by mass or more and 0.015% by mass or less, balance: Fe and inevitable impurities, Mo : It is preferable to contain at least one of 0.008% by mass to 2.2% by mass and W: 0.008% by mass to 2.2% by mass. Further, the base steel material may further contain Ni, Co, Mg, Ca, rare earth metal, Sn, Sb, Ti, Nb, Zr, V, B, Se, or a combination thereof in addition to the above-described elements. preferable. It is particularly preferable that the base steel material contains at least one of Ni and Co as Ni described above and at least one of Sn, Sb and Se. Moreover, it is also especially preferable that a base steel material contains at least 1 sort (s) among Mg, Ca, and a rare earth metal as said Ni etc., and contains at least 1 sort (s) among 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 is made of Al oxide and / or Al oxyhydroxide, Cr oxide and / or Cr oxyhydroxide, Cu oxide and / or Cu oxyhydroxide, Fe oxide and / or Or it contains Fe oxyhydroxide.

  The lower limit of the average thickness of the coating layer is 8 μm, preferably 14 μm, and more preferably 21.5 μm. On the other hand, the upper limit of the average thickness of the coating layer is 105 μm, preferably 80 μm, and more preferably 60 μm. When the average thickness of the coating layer is smaller than the above lower limit, the penetration of the corrosive substance into the base steel material cannot be sufficiently suppressed, and the salt water resistance of the coating steel material may be lowered. Conversely, when the average thickness of the coating layer exceeds the above upper limit, cracks are likely to be formed in the coating layer due to temperature changes during use, and local corrosion of the base steel material exposed on the surface due to the cracks proceeds. There is a risk.

[Al compound]
The Al compound contained in the coating layer suppresses intrusion into the base steel material by fixing the corrosive chloride and rendering it harmless, and as a result, improves the salt water resistance of the coated steel material. Among the Al compounds contained in the coating layer, examples of the Al oxyhydroxide include AlOOH, and examples of the Al oxide include Al ₂ O ₃ .

  As a minimum of content of Al compound in a coating layer, 0.08 mass% is preferred, 0.4 mass% is more preferred, and 0.8 mass% is still more preferred. On the other hand, the upper limit of the content of the Al compound is preferably 10.5% by mass, more preferably 6.0% by mass, further preferably 2.5% by mass, and particularly preferably 1.2% by mass. When content of Al compound is smaller than the said minimum, there exists a possibility that the salt water resistance of the said coated steel materials may fall. Conversely, when the content of the Al compound exceeds the above upper limit, cracks are likely to be formed in the coating layer due to temperature changes during use, and as a result, local corrosion of the base steel material may occur.

[Cr compound]
The Cr compound contained in the coating layer suppresses intrusion into the base steel material by fixing the corrosive sulfate and rendering it harmless, and as a result, improves the salt water resistance of the coated steel material. Among the Cr compounds contained in the coating layer, examples of the Cr oxyhydroxide include CrOOH, and examples of the Cr oxide include CrO ₂ , CrO ₃ , and Cr ₂ O ₃ . As the Cr compound, Cr oxide is preferable, and Cr ₂ O ₃ is more preferable.

  When the coating layer contains a Cr oxide, the lower limit of the Cr oxide content in the coating layer is preferably 0.08% by mass, more preferably 0.4% by mass, and even more preferably 0.8% by mass. . On the other hand, the upper limit of the Cr oxide content is preferably 10.5% by mass, more preferably 3.5% by mass, and even more preferably 1.2% by mass. When content of Cr oxide is smaller than the said minimum, there exists a possibility that the salt water resistance of the said coated steel materials may fall. Conversely, when the Cr oxide content exceeds the above upper limit, cracks are formed in the coating layer due to temperature changes during use, and local corrosion may proceed.

[Cu compound]
The Cu compound contained in the coating layer suppresses the intrusion of the corrosive substance into the base steel material by densifying the coating layer, and as a result, improves the salt water resistance of the coated steel material. Among Cu compounds contained in the coating layer, examples of the Cu oxide include CuO and Cu ₂ O.

  When a coating layer contains Cu oxide, as a minimum of content of Cu oxide in a coating layer, 0.08 mass% is preferred, 0.4 mass% is more preferred, and 0.8 mass% is still more preferred. . On the other hand, the upper limit of the Cu oxide content is preferably 10.5% by mass, more preferably 3.5% by mass, and even more preferably 1.2% by mass. When content of Cu oxide is smaller than the said minimum, there exists a possibility that the salt water resistance of the said covering steel material may fall. Conversely, when the content of Cu oxide exceeds the above upper limit, cracks are likely to be formed in the coating layer due to temperature changes during use, and as a result, local corrosion of the base steel material may occur.

[Fe compound]
The Fe compound contained in the coating layer improves the adhesion between the coating layer and the base steel material. Among the Fe compounds contained in the coating layer, examples of the Fe oxyhydroxide include α-FeOOH, β-FeOOH, and γ-FeOOH, and examples of the Fe oxide include Fe ₂ O ₃ and Fe ₃ O _4. It is done. Among these, Fe ₃ O ₄ and α-FeOOH are preferable as the Fe compound, and a combination of Fe ₃ O ₄ and α-FeOOH is more preferable.

When the coating layer contains α-FeOOH and / or Fe ₃ O ₄ , the lower limit of the total content of Fe ₃ O ₄ and α-FeOOH in the coating layer is preferably 29.5% by mass, and 35% by mass Preferably, 40 mass% is more preferable. 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 said total content is smaller than the said minimum, the adhesiveness of a coating layer and a base steel material falls, and there exists a possibility that the salt water resistance of the said coating steel material may not be maintained for a long period of time. Conversely, when the total content 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, the salt water resistance of the coated steel material may be reduced.

When the coating layer contains α-FeOOH, the lower limit of the α-FeOOH content in the coating layer is preferably 8% by mass, and more preferably 28% by mass. On the other hand, the upper limit of the content of α-FeOOH is preferably 90% by mass, more preferably 65% by mass, and still more preferably 55% by mass. Also, if the coating layer contains a _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, more preferably 38% by mass. On the other hand, the upper limit of the content of _Fe 3 _{O 4,} preferably 95% by mass, more preferably 75% by mass, more preferably 52% by mass. When the contents of Fe ₃ O ₄ and α-FeOOH are both smaller than the lower limit, the adhesion between the coating layer and the base steel material is lowered, and the salt water resistance of the coating steel material may not be maintained for a long time. Conversely, when the content of at least one of Fe ₃ O ₄ and α-FeOOH exceeds the above upper limit, the content of the Al compound, Cr compound and Cu compound in the coating layer becomes insufficient, and as a result, There is a possibility that the salt water resistance is lowered.

When the coating layer contains α-FeOOH, the lower limit of the average particle size of α-FeOOH is preferably 4.5 nm, more preferably 12 nm, and even more preferably 15.5 nm. On the other hand, the upper limit of the average particle diameter of α-FeOOH is preferably 22 nm, and more preferably 19 nm. Also, if the coating layer contains a _Fe 3 _{O 4,} the lower limit of the average particle diameter of _Fe 3 _{O 4,} preferably 4.5 nm, more preferably 8 nm, 13 nm is more preferred. On the other hand, the upper limit of the average particle size of Fe ₃ O ₄ is preferably 22 nm, and more preferably 18 nm. When the average particle diameter of at least one of Fe ₃ O ₄ and α-FeOOH is smaller than the lower limit, defects such as cracks are caused when the volume of the coating layer is greatly contracted by evaporation of the solvent between the particles when the coating layer is formed. May occur. As a result, the invasion of the corrosive substance into the base steel material by the coating layer becomes insufficient, and the local corrosion of the base steel material exposed to the surface due to the cracks may progress, or the base steel material near the interface with the coating layer Corrosion may occur. Further, the coating layer may be peeled off and dropped due to the corrosion of the base steel material described above, and further corrosion may progress. Conversely, when the average particle size of at least one of Fe ₃ O ₄ and α-FeOOH exceeds the above upper limit, the gap between the particles tends to be formed, so that the denseness of the coating layer is reduced. Therefore, the corrosive substance easily enters the base steel material, so that the salt water resistance of the coated steel material may be reduced.

In particular, the coating layer comprises Al oxide and / or Al oxyhydroxide, Cr oxide, Cu oxide, Fe ₃ O ₄ and α-FeOOH as the Fe oxide and Fe oxyhydroxide. It is good to contain. In this case, the content of Al oxide and / or Al oxyhydroxide is preferably 0.08% by mass or more and 10.5% by mass or less. Moreover, as content of Cr oxide, 0.08 mass% or more and 10.5 mass% or less are preferable. Furthermore, as content of Cu oxide, 0.08 mass% or more and 10.5 mass% or less are preferable. Furthermore, the total content of Fe ₃ O ₄ and α-FeOOH is preferably 29.5% by mass or more. Furthermore, the average particle diameter of the Fe ₃ O ₄ and α-FeOOH is preferably 4.5 nm or more and 22 nm or less, respectively. When the coating layer satisfies these conditions, the salt water resistance of the coated steel material and the durability of the salt water resistance can be further improved.

From the viewpoint of improving adhesion to the base steel material and improving the salt water resistance of the coated steel material, the coating layer is composed of other metal oxyhydroxides and / or other than the above-mentioned Al compound, Cr compound, Cu compound and Fe compound. It is preferable to contain a metal oxide. As the other metal oxides, for example _{SiO 2, TiO 2, ZrO 2} , Nb 2 O 5, Ta 2 O 5, V 2 O 5, La 2 O 3, Ce 2 O 3 and the like. However, the coating layer contains only the Al compound, Cr compound, Cu compound and Fe compound, and the content of the other metal oxide and other metal oxyhydroxide is substantially 0% by mass. Good. Moreover, a coating layer may contain components other than the above-mentioned Al compound, Cr compound, Cu compound, Fe compound, the said metal oxide, and a metal oxyhydroxide.

(Form and application of coated steel)
Examples of the form of the coated steel material include a steel plate, a steel pipe, a steel bar, a wire, and a shaped steel. In addition, the coated steel material can be used in a corrosive environment that is constantly immersed in seawater, in a corrosive environment that is not always immersed in seawater, particularly in a corrosive environment mainly caused by flying sea salt particles and droplets. Corrosion due to etc. can be suppressed. Therefore, examples of the application of the coated steel material include ships, offshore structures, bridges, and the like. Examples of the ship include cargo ships such as tankers, container ships, and bulkers, freight passenger ships, passenger ships, warships, and the like. When the coated steel material is used for a ship, it can be suitably used for various upper steel structures such as a ballast tank, an upper deck, a bridge, a hatch cover, a crane, various pipes, stairs, handrails, and the like. The offshore structure includes, for example, a drilling facility for drilling oil and natural gas on the ocean, a floating facility for producing, storing and shipping oil and natural gas on the ocean, wind power generation in the ocean, and waves. Examples include power generation facilities that perform power generation, tidal current power generation, ocean current power generation, temperature difference power generation, solar power generation, and the like. Furthermore, when the said covering steel material is used for a bridge, it can be conveniently used as a steel material for bridges in an environment where the amount of incoming salt is more than 0.1 mdd and the amount of incoming salt is large.

<Method for producing coated steel>
The method for producing the coated steel material includes a step of preparing a base steel material (base steel material preparing step) and 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 (preparation) Step) and a step (coating step) of applying the coating layer forming composition onto the surface of the base steel material. Hereinafter, each step will be described.

(Base steel preparation process)
In this step, a base steel material having a desired composition is prepared. The method for producing the base steel material is not particularly limited, and a normal steelmaking method represented by a converter steelmaking method, an electric furnace steelmaking method, or the like can be adopted. Below, the specific manufacturing method of a base steel material is demonstrated. First, the molten steel discharged from the converter or electric furnace to the ladle is adjusted to a desired composition using an RH (Ruhrstahl-Heraeus) vacuum degassing device, and secondary refining is performed by adjusting the temperature. Do. Then, a base steel material is obtained by making it a steel ingot by normal casting methods, such as a continuous casting method and an ingot-making method. In addition, as a classification according to the deoxidation type of the base steel material, killed steel is preferable from the viewpoint of securing basic characteristics required for steel materials used for structures such as mechanical characteristics and ease of welding, and Al killed steel. Is more preferable.

(Preparation process)
In this step, a composition for forming a coating layer is prepared by dispersing an Al compound, a Cr compound, a Cu compound, and an Fe compound in a solvent. In this step, the other metal oxyhydroxide and / or other metal oxide described above may be further dispersed in a solvent. Although it does not specifically limit as said solvent, For example, organic solvents, such as an alkyl silicate, water, etc. are mentioned, Among these, an organic solvent is preferable and an alkyl silicate is more preferable. Although it does not specifically limit as solid content concentration of the composition for coating layer formation, For example, they are 10 mass% or more and 60 mass% or less. In the composition for forming a coating layer, since each component dispersed in the solvent is stable and hardly causes a chemical reaction, the composition other than the solvent is usually the composition of the coating layer as it is. Therefore, a coating layer having a desired composition can be easily and reliably formed by adjusting the composition and particle size of each component of the composition for forming a coating layer.

(Coating process)
In this step, the coating layer forming composition is applied to the surface of the base steel material to form a coating layer on the surface of the base steel material. The method for coating the composition for forming a coating layer on the surface of the base steel material is not particularly limited, and examples thereof include a method of applying the composition at a temperature of 70 ° C. or higher and 150 ° C. or lower after application by spray coating or the like. In addition, the coating layer of desired average thickness can be formed easily and reliably by adjusting the solid content concentration and application quantity of the composition for coating layer formation used at this process.

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

  Moreover, as said pretreatment, the process which provides moderate surface roughness to a base steel material from a viewpoint of ensuring the adhesiveness of a coating layer and a base steel material is also preferable. As a method of imparting an appropriate surface roughness to the base steel material, a conventionally known method can be adopted, and examples thereof include shot blasting and grid blasting. A specific lower limit of the surface roughness of the base steel material is preferably 10 μm. On the other hand, the upper limit of the surface roughness of the base steel material is preferably 80 μm. When the surface roughness of the base steel material is smaller than the above lower limit, the adhesion between the coating layer and the base steel material may be reduced. Conversely, when the surface roughness of the base steel material exceeds the above upper limit, air bubbles enter the concave portions of the base steel material after application of the coating layer forming composition, and as a result, a portion where the coating layer and the base steel material do not adhere is formed. There is a possibility that the adhesion may be reduced. Here, “surface roughness” means ten-point average roughness measured in accordance with JIS-B0601: 2001 “Product Geometrical Specification (GPS) —Surface Properties: Contour Curve Method—Terms, Definitions, and Surface Properties Parameters”. (Rz) is an evaluation length of 12.5 mm and a cutoff value λc of 2.5 mm.

  Hereinafter, the coated steel material of the present invention and the method for producing the same will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, and can be adapted to the above and below-mentioned purposes. It is of course possible to carry out the invention with appropriate modifications, and these are all included in the technical scope of the present invention.

[Production of coated steel]
Steel materials having the compositions shown in Table 1 and Table 2 were melted in a vacuum melting furnace to obtain 50 kg steel ingots. Each steel ingot obtained was heated to 1,150 ° C. and then hot-rolled to obtain steel materials having an average thickness of 10 mm. A test piece of 150 × 70 × 5 [mm] was cut out from each steel material, and these were used as base steel materials B1 to B54. One surface of the test piece was used as a test surface, and this test surface was shot blasted so as to have a finish of Rz of 30 μm, and then washed with water and acetone. After washing, the mass measurement and thickness of the test piece were measured, and this was taken as the mass and thickness of the base steel before testing. As shown in FIG. 1, the thickness of the test piece is measured by setting a 140 × 60 [mm] area 5 mm or more inside each piece of the test surface as a test area A, and the test area A has an interval of 10 mm vertically and horizontally. The measurement was performed at 5 × 13 = 65 lattice points X. The thickness was measured using an ultrasonic plate thickness meter from the back side 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 are mixed with powders of other metal oxyhydroxides and other metal oxides, dispersed in an alkyl silicate as a solvent, and coated A layer forming composition was prepared. The solid content concentration of the composition for forming a coating layer was 40% by mass. The composition for forming a coating layer was applied to the surface of the test piece by spray coating, and then dried with a dryer at 100 ° C. to obtain a test piece having a coating layer. The test piece was coated with steel plate No. 2-No. 65. The composition of the coating layer can be adjusted by the mixing ratio of each component of the composition for forming the coating layer, and the composition of solids other than the solvent in the composition for forming the coating layer can be regarded as the composition of the coating layer. . Moreover, the average thickness of the coating layer was adjusted by the coating amount of the composition for forming a coating layer, and measured with an electromagnetic film thickness meter. After the formation of the coating layer, the region B other than the test region on the test surface of the test piece and the surface other than the test surface were coated with Teflon (registered trademark) tape. The region B other than the test region is a region whose distance from each side is less than 5 mm. Thereafter, the following corrosion test was performed. In Tables 3 and 4, the coated steel material No. 1-No. 65 shows the base steel material and the composition of the coating layer. The coated steel material No. In 1, no coating layer is formed. Further, “other components” in Tables 3 and 4 represent the other metal oxides and other metal oxyhydroxides.

[Corrosion test]
As a corrosion test for simulating the corrosive environment by seawater, a combined cycle corrosion test (CCT) using artificial seawater was performed. Specifically, (I) artificial seawater spraying at 35 ° C. for 1.5 hours, (II) temperature 60 ° C., humidity 20% RH for 2.5 hours, and (III) temperature 50 against the test surface of the test piece. (I) to (III) were repeated for 2.5 hours at ° C. and humidity of 95% RH. In addition, when changing temperature and humidity in (I)-(III), the transition time required for the stability of conditions was 0.5 hour. The test period was 84 days. Further, three test pieces were used, and N = 3.

  After the CCT, the test piece was measured for mass change and corrosion depth. First, after completion of CCT, the coating layer and the corrosion product of the test piece were removed by a cathodic electrolysis method in a 10% diammonium hydrogen citrate aqueous solution, and then washed with water and acetone. After washing, the mass of the test piece was measured and used as the mass of the base steel material after the test. The difference between the mass of the base steel material after the test and the mass of the base steel material before the test was the corrosion amount due to corrosion, and the average value of the three test pieces was the average corrosion amount. Moreover, the thickness was measured with the ultrasonic plate | board thickness meter from the back surface of the test surface of a test piece in 65 lattice points X shown in FIG. The difference between the thickness of the base steel material before the test at each lattice point X and the thickness of the base steel material after the test was determined, and this was defined as the corrosion depth of the lattice point X. The corrosion depth of each of the 65 lattice points X of the three test pieces was measured, and the maximum corrosion depth of the 195 lattice points X was defined as the maximum corrosion depth.

Coated steel No. 1-No. 65, the coated steel material No. Relative values when the average corrosion amount and the maximum corrosion depth of 1 were each set to 100 were determined and classified into A to E according to the following criteria. The relative values of the average corrosion amount and the maximum corrosion depth indicate that the smaller the value, the better the salt water resistance.
A: No. The relative value with respect to 1 is less than 55. B: No. 1 or more and less than 70 C: No. 1 or more and less than 85 D: No. 1 or more and less than 95 E: No. The relative value to 1 is 95 or more

Further, the coated steel material No. 1-No. About 65, it divided into AF by the order which is excellent in salt-water resistance by the following reference | standard, and made this comprehensive evaluation. Comprehensive evaluation can evaluate A, B, C, D, E, and F as “pass” and G as “fail”. The evaluation results are shown in Table 5.
A: Both average corrosion amount and maximum corrosion depth are evaluated as A
B: One of the evaluation of average corrosion amount and maximum corrosion depth is A, and the other is B
C: Average corrosion amount and 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 or more E: Both the evaluation of the average corrosion amount and the maximum corrosion depth is C
F: Either the average corrosion amount or the maximum corrosion depth is evaluated as D or less. However, the average corrosion amount and the maximum corrosion depth are both evaluated as E. G: The average corrosion amount and the maximum corrosion depth are both evaluated as E.

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

  Coated steel No. Reference numeral 1 assumes a normal steel material that does not include a coating layer. Coated steel No. In No. 1, a rust film 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 too small and a comparative example that is too large, and sufficient salt water resistance was not obtained.

  On the other hand, the coated steel material No. corresponding to the example satisfying the configuration of the present invention. 2-9 and no. 12-No. In 65, the relative values of the average corrosion amount and the maximum corrosion depth were both less than 95 and exhibited excellent salt water resistance. Hereinafter, each example will be examined.

  Coated steel No. 12-No. 17 is an example using the base steel materials B1 to B containing C, Si, Mn, P, S, Al, N, Fe and inevitable impurities. Hereinafter, the above-described composition of the base steel material is also referred to as a basic composition 1. Coated steel No. 12-No. The salt water resistance of 17 was superior to the coated steel material of the comparative example, but was the lowest among the examples.

  Coated steel No. 2-No. 9 is an example using the base steel material B7 containing the P and Al contents of the basic composition 1 as specific amounts and containing Cu and Cr and Mo and / or W. Hereinafter, the above-described composition of the base steel material is also referred to as a basic composition 2. Coated steel No. 2-No. The salt water resistance of No. 9 was superior to the coated steel material of the comparative example, but was the lowest among the examples using the base steel material having the basic composition 2.

Coated steel No. 18-No. 65 is an example in which the base steel materials B7 to B64 having the basic composition 2 are used, and the types, contents and average particle diameters of the Al compound, Cr compound, Cu compound and Fe compound in the coating layer are adjusted to an appropriate range. is there. Specifically, 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. Further, the _Fe 3 _{O 4} and alpha-FeOOH containing a specific amount in total as Fe compound, the average particle diameter of the _Fe 3 _{O 4} and alpha-FeOOH is less than 4.5nm or more, respectively 22 nm. Coated steel No. 18-No. 65 is the above-mentioned coated steel material No. 2-No. Compared to 9, the average corrosion amount and the average corrosion amount of the maximum corrosion depth were excellent. Hereinafter, coated steel material No. 18-No. Consider 65.

  Coated steel No. 18-No. 20 is an example using the base steel materials B7 to B9 having only the basic composition 2. Coated steel No. 18-No. 20 is the above-mentioned coated steel material No. 2-No. Compared with 9, the average amount of corrosion could be further reduced.

  Coated steel No. 21-No. 23 is an example using base steel materials B10 to B12 that further contain a specific amount of Ni and / or Co in addition to the basic composition 2. Coated steel No. 21-No. 23 is the above-mentioned coated steel material No. 18-No. Compared with 20, the maximum corrosion depth could be further reduced.

  Coated steel No. 24-No. 29 is an example using the base steel materials B13 to B18 that further contain a specific amount of Mg, Ca and / or REM in addition to the basic composition 2. Coated steel No. 24-No. 29 is the above-mentioned coated steel material No. 18-No. Compared with 20, the maximum corrosion depth could be further reduced.

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

  Coated steel No. 35-No. 40 is an example using the base steel materials B24 to B29 further containing a specific amount of Sn, Sb and / or Se in addition to the basic composition 2. Coated steel No. 35-No. 40 is the above-mentioned coated steel material No. 18-No. Compared with 20, the maximum corrosion depth could be further reduced.

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

  Coated steel No. 45-No. 48 is an example using the base steel materials B34 to B37 which contain 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-No. 48 is the above-mentioned coated steel material No. 18-No. Compared to 20, the maximum corrosion depth could be remarkably reduced.

  Coated steel No. 49-No. 53 is an example using the base steel materials B38 to B42 further containing a specific amount of Ni and / or Co, Mg, Ca and / or REM, and Sn, Sb and / or Se in addition to the basic composition 2. is there. Coated steel No. 49-No. 53 is the above-mentioned coated steel material No. 18-No. Compared to 20, the average corrosion amount and the maximum corrosion depth could be further reduced, and in particular, the maximum corrosion depth could be significantly reduced. Coated steel No. 49-No. 53 is a coated steel material No. described later. 63 and no. Excellent salt water resistance after 65.

  Coated steel No. 54-No. 55 is an example using the base steel materials B43 to B44 further containing a specific amount of Ti, Nb, Zr, V and / or B in addition to the basic composition 2. Coated steel No. 54-No. 55 is the above-mentioned coated steel material No. 18-No. Compared to 20, the average corrosion amount and the maximum corrosion depth could be slightly reduced.

  Coated steel No. 56-No. 57 is an example in which, in addition to the basic composition 2, Ni and / or Co and base steel materials B45 to B46 further containing specific amounts of Ti, Nb, Zr, V and / or B are used. Coated steel No. 56-No. 57 is the above-mentioned coated steel material No. 18-No. Compared with 20, the maximum corrosion depth could be further reduced.

  Coated steel No. 58 and no. 64 is an example using the base steel materials B47 and B53 which further contain 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 the above-mentioned coated steel material No. 18-No. Compared with 20, the maximum corrosion depth could be further reduced. Further, the coated steel material No. in which the base steel material contains a specific amount of V. 64 is the above-mentioned coated steel material No. 18-No. Compared with 20, the average amount of corrosion could be further reduced.

  Coated steel No. 59-No. 60 uses the base steel materials B48 to B49 which contain Ni and / or Co, Mg, Ca and / or REM, and Ti, Nb, Zr, V and / or B further in a specific amount in addition to the basic composition 2 Example. Coated steel No. 59-No. 60 is the above-mentioned coated steel material No. 18-No. Compared with 20, the average corrosion amount and the maximum corrosion depth could be further reduced.

  Coated steel No. 61 is an example using the base steel material B50 which contains Sn, Sb and / or Se and Ti, Nb, Zr, V and / or B further in a specific amount in addition to the basic composition 2. Coated steel No. 61 is the above-mentioned coated steel material No. 18-No. Compared with 20, the maximum corrosion depth could be further reduced.

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

  Coated steel No. 63 and no. 65 is a specific amount of Ni and / or Co, Mg, Ca and / or REM, Sn, Sb and / or Se, and Ti, Nb, Zr, V and / or B in addition to the basic composition 2 This is an example using the base steel materials B52 and B54 contained. Coated steel No. 63 and no. 65 is the above-mentioned coated steel material No. 18-No. Compared to 20, the average corrosion amount and the maximum corrosion depth could be further reduced, and in particular, the maximum corrosion depth could be significantly reduced. Coated steel No. 63 and no. No. 65 exhibited the most excellent salt water resistance among the examples.

  Thus, it can be judged that salt water resistance can be improved by providing the coating layer which satisfy | fills the structure of this invention. Further, it is judged that the base steel material can further improve the salt water resistance by containing the basic composition 1, and can further improve the salt water resistance by containing the basic composition 2. Furthermore, in addition to the basic composition 2, the base steel material is made of Ni and / or Co, Mg, Ca and / or REM, Sn, Sb and / or Se, Ti, Nb, Zr, V and / or B. It is judged that the salt water resistance can be further improved by containing a specific amount of at least one of them, and that the salt water 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 material of the present invention exhibits excellent salt water resistance in a seawater environment, and can be suitably used for structures exposed to seawater and flying sea salt particles. Moreover, the manufacturing method of the coated steel material of this invention can provide this coated steel material.

  The said coated steel material and its manufacturing method can provide the coated steel material by which outstanding salt water resistance is maintained for a comparatively long period of time.

A Test area B Area other than 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,
The coating layer has an average thickness of 8 μm or more and 105 μm or less, and contains an Al compound, a Cr compound, a Cu compound, and an Fe compound,
A coated steel material wherein the compound is an oxide, an oxyhydroxide, or a combination thereof. The coating layer is
Al oxide, Al oxyhydroxide or a combination thereof is 0.08% by mass or more and 10.5% by mass or less,
0.08 mass% or more and 10.5 mass% or less of Cr oxide,
Cu oxide is 0.08 mass% or more and 10.5 mass% or less, and Fe ₃ O ₄ and α-FeOOH as the Fe oxide and Fe oxyhydroxide are contained in total of 29.5 mass% or more,
2. The coated steel material according to claim 1, wherein the average particle diameters of the Fe ₃ O ₄ and α-FeOOH are 4.5 nm or more and 22 nm or less, respectively. The base steel material is
C: 0.008 mass% or more and 0.32 mass% or less,
Si: 0.05 mass% or more and 2.0 mass% or less,
Mn: 0.08 mass% or more and 3.0 mass% or less,
P: 0.001% by mass or more and 0.05% by mass or less,
S: 0.05 mass% or less,
Al: 0.001% by mass or more and 1.6% by mass or less,
N: 0.001 mass% or more and 0.015 mass% or less, and the remainder: Coated steel materials of Claim 1 or Claim 2 which have a composition which is Fe and an unavoidable impurity. The base steel material is
P: 0.004 mass% or more and 0.05 mass% or less, and Al: 0.008 mass% or more and 1.6 mass% or less,
Cu: 0.08% by mass to 2.2% by mass; and Cr: 0.08% by mass to 3.0% by mass; and Mo: 0.008% by mass to 2.2% by mass And W: The covering steel materials of Claim 3 which further contain at least 1 sort (s) among 0.008 mass% or more and 2.2 mass% or less. The base steel material is
The coating according to claim 3 or 4, further comprising at least one of Ni: 0.008 mass% to 5.2 mass% and Co: 0.008 mass% to 5.0 mass%. Steel material. The base steel material is
Mg: 0.0004 mass% or more and 0.01 mass% or less,
The at least 1 type is further contained among 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. 5. The coated steel material according to 5. The base steel material is
Sn: 0.0008% by mass or more and 0.2% by mass or less,
Any one of Claims 3-6 which further contains at least 1 sort (s) among Sb: 0.0008 mass% or more and 0.2 mass% or less, and Se: 0.0008 mass% or more and 0.2 mass% or less. Coated steel material according to item. The base steel material is
Ti: more than 0% by mass and 0.2% by mass or less,
Nb: more than 0% by mass and 0.2% by mass or less,
Zr: more than 0% by mass and 0.2% by mass or less,
8. The composition according to any one of claims 3 to 7, further comprising at least one of V: more than 0% by mass and 0.2% by mass or less, and B: more than 0% by mass and 0.01% by mass or less. Coated steel. 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;
Coating the composition for forming a coating layer on the surface of the base steel material,
The compound is an oxide, an oxyhydroxide or a combination thereof,
In the coating step, a method for producing a coated steel material that forms a coating layer having an average thickness of 8 μm to 105 μm.

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