KR101929104B1 - Corrosion-proof steel material, production method therefor, method for corrosion proofing steel material, and ballast tank - Google Patents

Abstract

It is an object of the present invention to provide a corrosion resistant steel capable of maintaining excellent corrosion resistance over a long period of time.
In order to attain the above object, the present invention provides a method of manufacturing a structural steel which comprises a steel material and a coating film having a thickness of 10 탆 or more formed on the surface of the steel material, wherein the steel material contains 0.001 to 0.20% Wherein the coating film is formed by curing the alkali silicate inorganic zinc coating composition, wherein the coating film contains a silicon atom and an alkali metal atom, And a nitrogen atom, wherein the molar ratio represented by {the number of moles of silicon atom Si in the coating film} / {the total number of moles of alkali metal atoms and nitrogen sources in the coating film} is 2.0 to 125, Wherein the coating composition contains alkali silicate and zinc particles, and a mass ratio represented by "mass of solid component of binder component / mass of zinc particle" is 0.01 to 0.35.

Description

{Corrosion-proof steel material, production method therefor, method for corrosion proofing steel material, and ballast tank}

The present invention relates to a structural steel and a method of manufacturing the same, a method of machining steel, and a ballast tank.

When steel is used over a long period of time in a corrosive environment containing chloride ions, it is necessary to take measures such as improving corrosion resistance or coating by optimizing steel components. Especially, the inside of ballast tanks of ships has to be stamped by international treaties because it is a severe corrosive environment, which is the repetition of wet atmosphere including seawater dipping and salinity.

However, the life expectancy of the coating standards mandated by international treaties is 15 years, which is shorter than the life span of 25 years. Therefore, after 15 years, it is considered that the replacement of the corroded steel or the repair of the coating will be necessary. Therefore, in order to suppress economic loss such as maintenance cost or extension of dock period (time loss), it is required to develop a new corrosion prevention technology that realizes corrosion resistance over a long period of time.

There has been proposed a method for appropriately controlling the composition and surface properties of a steel material or appropriately controlling properties of an inorganic zinc coating film in order to meet the demand for improvement in performance of a corrosion resistant steel material having an inorganic zinc coating film (for example, Patent Document 1 ~ 12).

Japanese Patent Publication No. 51-028650 Japanese Patent Laid-Open Publication No. 51-106134 Japanese Patent Application Laid-Open No. 51-123229 Japanese Patent Application Laid-Open No. 59-051951 Japanese Patent Application Laid-Open No. 2002-285102 Japanese Patent Publication No. 2003-531924 Japanese Patent Publication No. 2005-510584 Japanese Patent Application Laid-Open No. 2007-191730 Japanese Patent Application Laid-Open No. 2008-144204 Japanese Patent Application Laid-Open No. 2010-018846 Japanese Patent Application Laid-Open No. 2011-021247 Japanese Patent Application Laid-Open No. 2011-021248

Although the composition of the steel material affects the corrosion resistance, the performance of the corrosion-resistant steel material provided with the inorganic zinc coating film is mainly due to the sacrificial corrosion protection effect of zinc particles, It is not assumed that the other components included in the corrosion-resistant steel material affects the performance of the corrosion resistant steel provided with the inorganic zinc coating film. Therefore, an attempt has not been made to substantially improve the performance of the corrosion-resistant steel material in which the inorganic zinc coating film and the steel material are recognized as a single unit.

In addition, in order to obtain long-term corrosion resistance of the ballast tank of a ship, an overcoating film such as an organic resin layer is further provided on the inorganic zinc coat. However, in the case of the method described in the patent documents, the organ corrosion resistance in the case of not providing the top coat is still insufficient.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a corrosion resistant steel material capable of maintaining excellent corrosion resistance over a long period of time, a method of manufacturing the steel material, a steel material corrosion method, and a ballast tank.

The present invention focuses attention on the synergistic effect of the components contained in the inorganic zinc coating and the components contained in the steel, thereby remarkably improving the performance of the corrosion resistant steel provided with the inorganic zinc coating.

[1] A steel material comprising a steel material and a coating film having a thickness of 10 탆 or more formed on the surface of the steel material, wherein the steel material contains 0.001 to 0.20% of C, 0.01 to 3.0% of Si, Wherein the coating film is formed by curing the alkali silicate inorganic zinc coating composition, wherein the coating film contains at least one atom selected from a silicon atom, an alkali metal atom and a nitrogen atom, Wherein the molar ratio expressed by {the number of moles of silicon atom Si in the coating film} / {the total number of moles of alkali metal atoms and nitrogen atoms in the coating film} is 2.0 to 125, and the inorganic zinc coating composition is composed of alkali silicate and zinc particles , And a mass ratio represented by "mass of solid component of binder component / mass of zinc particle" is 0.01 to 0.35.

[2] The method according to [1], wherein the Cr content in the steel material and the molar ratio of the coating film satisfy the following conditional expression (1). (Molar ratio (Si / M)) + 0.5} x 20 (占 퐉) / (film thickness (占 퐉) of the coating film formed on the surface of the steel material) x a / (Si / M) is {the number of moles of Si atoms in the coating film} / {alkali metal atoms and nitrogen atoms in the coating film (1) , A is 7, and b is 6.]

[3] The method steel material according to [1], wherein the Cr content in the steel material and the molar ratio in the coating film satisfy the following conditional expression (1). (Molar ratio (Si / M)) + 0.5} x 20 (占 퐉) / (film thickness (占 퐉) of the coating film formed on the surface of the steel material) x a / (Si / M) is {the number of moles of Si atoms in the coating film} / {alkali metal atoms and nitrogen atoms in the coating film (1) , A is 17, and b is 6.]

[4] The steel material according to any one of [1] to [3], wherein the coating film contains a silicon atom and an alkali metal atom.

[5] The steel material according to any one of [1] to [4], wherein the coating film contains a silicon atom and a nitrogen atom.

[6] The method according to any one of [1] to [4], wherein the alkali silicate is M1 ₂ O.nSiO ₂ [In the formula, M1 is an alkali metal or amine component or an ammonium component, and n is a positive number].

[7] The steel material according to any one of [1] to [6], wherein the alkali silicate includes at least one selected from lithium silicate, sodium silicate and potassium silicate.

[8] The alkaline silicate of claim 1, wherein the alkali silicate comprises at least one member selected from the group consisting of primary silane, The method according to any one of the above [1] to [7], further comprising:

[9] The steel material according to any one of [1] to [8], wherein the alkali silicate comprises a quaternary ammonium silicate composed of quaternary ammonium and silicate.

[10] The steel material according to any one of [1] to [9], wherein the inorganic zinc coating composition is substantially free of an alkyl silicate binder and an organic solvent.

[11] The method of any one of the above-mentioned [1] to [10], wherein the thickness of the coating film is 200 μm or less.

[12] A steel material according to any one of [1] to [11], wherein the steel material and the coating film are provided and the coating film is not provided on the coating film and is used for a ballast tank.

[13] A steel material according to any one of [1] to [12], wherein the steel contains 0.3% to 3.0% Cr by mass%.

In addition to C, Si, Mn and Cr in addition to C, Si, Mn and Cr in the steel, it is preferable that the alloy contains 2.0% or less of Al, 1.0% or less of Cu, 2.0% or less of Ni, 0.5% or less of Mo, : Not more than 0.5%, Sb not more than 0.5%, V not more than 0.2%, Nb not more than 0.08%, Ti not more than 0.1%, Mg not more than 0.01%, Zr not more than 0.05%, B not more than 0.0050% Of the above-mentioned [1] to [13], characterized in that it is an iron and inevitable impurities of not more than 0.02%, REM: not more than 0.02%, P: not more than 0.03%, S: not more than 0.01% ≪ / RTI >

[15] A ballast tank constructed using the corrosion-resistant steel material according to any one of [1] to [14].

[16] A steel sheet comprising 0.001 to 0.20% of C, 0.01 to 3.0% of Si, 0.1 to 3.0% of Mn, and 0.1 to 9.99% of Cr, Based inorganic zinc coating composition containing zinc particles and having a mass ratio of 0.01 to 0.35 represented by "mass of solid component of binder component / mass of zinc particle" is coated so as to have a thickness of not less than 10 μm after curing, And a molar ratio expressed by {the number of moles of Si atoms in the coating film} / {the total number of moles of alkali metal atoms and nitrogen atoms in the coating film} is 2.0 to 125 And forming a coating film on the surface of the steel sheet.

[17] The method according to the above-mentioned [16], wherein the Cr content in the steel material and the molar ratio in the coating film satisfy the following conditional expression (1). (Molar ratio (Si / M)) + 0.5} x 20 (占 퐉) / (film thickness (占 퐉) of the coating film formed on the surface of the steel material) x a / (Si / M) is {the number of moles of Si atoms in the coating film} / {alkali metal atoms and nitrogen atoms in the coating film (1) , A is 7, and b is 6.]

[18] A method of producing a corrosion resistant steel material according to the above [16] or [17], wherein a coating film is formed on the surface of the steel material by self-hardening the inorganic zinc paint composition.

[19] The steel sheet according to any one of [1] to [4], wherein the surface of the steel containing 0.001 to 0.20% of C, 0.01 to 3.0% of Si, 0.1 to 3.0% of Mn, and 0.1 to 9.99% of Cr, Based inorganic zinc coating composition containing zinc particles and having a mass ratio of 0.01 to 0.35 represented by "mass of solid component of binder component / mass of zinc particle" is coated so as to have a thickness of not less than 10 μm after curing, And a molar ratio expressed by {the number of moles of Si atoms in the coating film} / {the total number of moles of alkali metal atoms and nitrogen atoms in the coating film} is 2.0 to 125 And a step of forming a coating film on the surface of the steel material.

[20] The method according to the above-mentioned [19], wherein the Cr content in the steel material and the molar ratio in the coating film satisfy the following conditional expression (1). (Molar ratio (Si / M)) + 0.5} x 20 (占 퐉) / (film thickness (占 퐉) of the coating film formed on the surface of the steel material) x a / (Si / M) is {the number of moles of Si atoms in the coating film} / {alkali metal atoms and nitrogen atoms in the coating film (1) , A is 7, and b is 6.]

[21] A method of treating a steel material as described in [19] or [20], wherein a coating film is formed on the surface of the steel material by self-hardening the inorganic zinc paint composition.

As described above, according to the present invention, it is possible to maintain excellent corrosion resistance over a long period of time by providing a coating film formed by curing an alkali silicate inorganic zinc coating composition having a predetermined component on the surface of a steel material containing a specific component It becomes.

FIG. 1 is a graph plotting the Cr content in the steel with respect to the atomic mole ratio (Si / M) in the coating film.
2 is a graph plotting the Cr content in the steel with respect to the film thickness of the coating film.

Hereinafter, preferred embodiments of the present invention will be described in detail.

[STABILIZED STEEL AND PROCESS FOR PRODUCING THE SAME

The corrosion-resistant steel of the present invention is a corrosion-resistant steel having excellent corrosion resistance over a long period of time, and comprises a steel material containing a predetermined component used as a base material and a coating film formed on the surface of the steel material. A coating film is formed on a part or all of the steel material surface.

That is, the corrosion-resistant steel material of the present invention is a corrosion-resistant steel material comprising a steel material and a coating film having a thickness of 10 탆 or more formed on the surface of the steel material, wherein the steel material contains Cr in an amount of 0.1 to 9.99% Wherein the coating film contains at least one atom selected from a silicon atom, an alkali metal atom and a nitrogen atom, wherein {the number of moles of the silicon atom Si in the coating film} / {the alkali metal atom in the coating film and Wherein the inorganic zinc coating composition contains alkali silicate and zinc particles, and the mass ratio represented by " mass of solids of binder component / mass of zinc particles " is from 0.01 to 2, 0.35.

These steel materials and coated films are described in detail below.

<Component of Steel>

The components of the steel material used as the base material will be described. In the following description of the contained elements, the notation &quot;% &quot; means mass% (i.e.,% by weight).

[C: 0.001 to 0.20%]

C is an effective element for improving the strength of steel. In the present invention, the amount of C is 0.001% or more in order to maintain the required strength. The C content is preferably 0.005% or more, more preferably 0.01% or more, 0.03% or more, or 0.05% or more. On the other hand, if the C content exceeds 0.20%, the weldability and toughness may be lowered, so the upper limit is set to 0.20%. The C content is more preferably 0.16% or less considering the weldability, and more preferably 0.14% or less or 0.12% or less from the viewpoint of workability.

[ Si : 0.01 to 3.0%]

Si acts as a deoxidizing agent and is an effective element for improving the strength. If the amount of Si is less than 0.01%, deoxidation may be insufficient, so that the lower limit is set to 0.01% in the present invention. In order to perform deoxidation more stably, the Si content is more preferably 0.05% or more or 0.10% or more. On the other hand, when the amount of Si exceeds 3.0%, the ductility is lowered, so the upper limit is set to 3.0%. Also, considering the weldability and toughness of the steel, the Si content is more preferably 0.5% or less or 0.4% or less.

[ Mn : 0.1 to 3.0%]

Mn is an element effective for controlling the texture of steel. In the present invention, the Mn content is 0.1% or more. The Mn content is more preferably 0.5% or more for stably controlling the structure. On the other hand, if the Mn content exceeds 3.0%, the ductility or toughness may be lowered, so the upper limit is set to 3.0%. Further, the Mn content is more preferably 2.5% or less in order to improve the manufacturability such as rolling and the weldability. The upper limit of the amount of Mn may be set to 2.0%, 1.6%, or 1.4% for improving the weldability. The lower limit of the amount of Mn may be set to 0.6%, 0.8% or 1.0% in order to improve ductility or toughness.

[ Cr : 0.1 to 9.99%]

Cr is an important element for improving the corrosion resistance of steel. In the present invention, the amount of Cr is 0.1% or more in order to obtain a remarkable effect of improving the corrosion resistance by the interaction of the alkali silicate inorganic zinc coating film formed as a coating film and the steel material. In order to improve the corrosion resistance, the amount of Cr is preferably 0.2% or more, 0.3% or more, 0.5% or more, or 0.7% or more, more preferably 1% or more. On the other hand, if the Cr content exceeds 9.99%, the transformation does not occur during the cooling process of the cast steel, and the ferrite single-phase structure is formed to cause cracking of the cast steel, so the upper limit is set to 9.99%. The amount of Cr is preferably 8.0% or less, and more preferably 6.5% or less, in order to reduce the cost of the alloy. The amount of Cr may be limited to 5.0% or less, 4.0% or less, 3.0% or less, 2.0% or less, 1.5% or less, 1.2% or 1.0% or less considering the weldability and the like.

The steel material used in the present invention may contain one or more of Al, Cu, Ni, Mo, W, Sn, and Sb to further improve the corrosion resistance of the steel material. The reasons for limiting the contents of Al, Cu, Ni, Mo, W, Sn, and Sb are described below.

[ Al : 2.0% or less]

Al is generally used as a deoxidizer, but in the present invention, the steel may contain Al as necessary in order to further improve the corrosion resistance of the steel. On the other hand, if the amount of Al exceeds 2.0%, the transformation does not occur during the cooling process of the cast steel, and the casting cracks may occur due to the ferrite single phase structure, so that the upper limit is preferably 2.0%. The amount of Al is more preferably 1.5% or less. The upper limit of the amount of Al may be set to 1.0%, 0.5%, 0.2%, 0.1%, or 0.08% in order to reduce Al-based inclusions. The lower limit of the amount of Al does not need to be specified but may be 0%, but it is preferably 0.002% and more preferably 0.01% in order to further improve the corrosion resistance of the steel material. The Al content is more preferably 0.02% or more.

[ Cu : 1.0% or less]

Since Cu is an element improving the corrosion resistance of the steel, the steel may contain Cu as occasion demands. On the other hand, when the amount of Cu exceeds 1.0%, the steel material may become brittle, so it is preferable to set the upper limit to 1.0%. The amount of Cu is more preferably 0.5% or less, and still more preferably 0.3% or less. The lower limit of the amount of Cu is not particularly limited and may be 0%, but 0.05% is preferable in order to stably improve the corrosion resistance of the steel. Further, Cu is an element for improving the strength and preventing cracking of the billet, and therefore, the Cu content is more preferably 0.10% or more.

[ Ni : 2.0% or less]

Ni is an element for improving the corrosion resistance of a steel material, and when the steel material contains Cu, it is possible to prevent the deterioration of the manufacturability by containing Ni at the same time. On the other hand, Ni is an expensive element, and the above effect is preferably saturated when the steel contains more than 2.0% of Ni, so that the upper limit is preferably set to 2.0%. The amount of Ni is more preferably 0.5% or less, and still more preferably 0.3% or less. The lower limit of the amount of Ni is not particularly limited and may be 0%, but 0.05% is preferable and 0.10% is more preferable in order to stably obtain the above effect.

[ Mo : Not more than 0.5%] [W: not more than 0.5%]

Mo and W are elements which improve the corrosion resistance of the steel, and the steel may contain these elements as needed. On the other hand, since Mo and W are saturated even when the steel contains more than 0.5%, the upper limit is preferably 0.5%. The amount of Mo and the amount of W are more preferably 0.1% or less. The lower limit of the Mo content and the W content is not particularly specified but may be 0%, but 0.01% is preferable and 0.03% is more preferable in order to stably improve the corrosion resistance of the steel material.

[ Sn : 0.5% or less]

Sn is an element for improving the corrosion resistance of a steel material, and the steel material may contain Sn if necessary. On the other hand, if the steel contains excess Sn, the composition and the mechanical properties may be impaired. Therefore, the upper limit of the amount of Sn is preferably 0.5%. The amount of Sn is more preferably 0.2% or less. The lower limit of the amount of Sn is not particularly limited and may be 0%, but it is preferably 0.01% and more preferably 0.05% in order to stably improve the corrosion resistance of the steel material.

[ Sb : 0.5% or less]

Sb is an element that improves the corrosion resistance of the steel, and the steel may contain Sb as needed. On the other hand, if the steel contains excess Sb, it may impair the composition and mechanical properties of the steel, so the upper limit of the amount of Sb is preferably 0.5%. The amount of Sb is more preferably 0.2% or less. The lower limit of the amount of Sb does not need to be specified and may be 0%, but is preferably 0.01% and more preferably 0.05% in order to stably improve the corrosion resistance of the steel material.

The steel material used in the present invention may further contain at least one of V, Nb, Ti, Mg, Zr, B, Ca and REM from the viewpoint of improvement of mechanical characteristics, use performance and production stability.

[V: 0.2% or less]

V is an element that improves mechanical characteristics, use performance, and manufacturing stability. The steel may contain V as necessary. On the other hand, if the steel contains V in excess, there is a possibility of deteriorating the kicking resistance, so it is preferable to set the upper limit of the V amount to 0.2%. The V content is more preferably 0.05% or less. The lower limit of the amount of V need not necessarily be specified but may be 0%, but it is preferably 0.005% and more preferably 0.01% in order to stably improve various properties of the steel.

[ Nb : 0.08% or less]

Nb is an element which improves the mechanical characteristics, the use performance and the manufacturing stability. The steel may contain Nb if necessary. On the other hand, if the steel contains an excess amount of Nb, there is a possibility of deteriorating repellency. Therefore, the upper limit of the amount of Nb is preferably 0.08%. The amount of Nb is more preferably 0.03% or less. The lower limit of the amount of Nb is not particularly limited and may be 0%, but is preferably 0.002% and more preferably 0.005% in order to stably improve various properties of the steel.

[ Ti : 0.1% or less]

Ti is an element which improves the mechanical characteristics, the use performance and the manufacturing stability, and the steel may contain Ti as occasion demands. On the other hand, if the steel contains an excessive amount of Ti, there is a possibility of deteriorating the kicking resistance. Therefore, the upper limit of the amount of Ti is preferably 0.1%. The amount of Ti is more preferably 0.03% or less. The lower limit of the amount of Ti is not particularly limited but may be 0%, but it is preferably 0.005% and more preferably 0.01% in order to stably improve various properties of the steel.

[ Mg : 0.01% or less]

Mg is an element that improves mechanical characteristics, use performance, and manufacturing stability. The steel may contain Mg as occasion demands. On the other hand, if the steel contains an excessive amount of Mg, there is a possibility of deteriorating the kicking resistance. Therefore, the upper limit of the amount of Mg is preferably 0.01%. The Mg content is more preferably 0.002% or less. The lower limit of the amount of Mg is not particularly limited and may be 0%, but it is preferably 0.0001% and more preferably 0.0005% in order to stably improve various properties of the steel.

[ Zr : 0.05% or less]

Zr is an element which improves the mechanical properties, the use performance and the manufacturing stability. The steel may contain Zr as occasion demands. On the other hand, if the steel contains Zr excessively, there is a possibility of deteriorating the sparkling resistance. Therefore, the upper limit of the amount of Zr is preferably 0.05%. The amount of Zr is more preferably 0.02% or less. The lower limit of the amount of Zr is not particularly limited and may be 0%, but it is preferably 0.003% and more preferably 0.005% in order to stably improve various properties of the steel.

[B: 0.0050% or less]

B is an element which improves the mechanical properties, the use performance and the manufacturing stability. The steel may contain B as occasion demands. On the other hand, if the steel contains excess B, there is a possibility of deteriorating the sparkling resistance. Therefore, the upper limit of the B content is preferably 0.0050%. The amount of B is more preferably 0.002% or less. The lower limit of the amount of B need not necessarily be specified but may be 0%, but it is preferably 0.0002% and more preferably 0.0005% in order to stably improve various properties of the steel.

[ Ca : 0.02% or less]

Ca is an element which improves the mechanical characteristics, the use performance and the manufacturing stability. The steel may contain Ca as occasion demands. On the other hand, if the steel contains Ca in excess, there is a possibility of deteriorating the kicking resistance, so it is preferable to set the upper limit of the Ca amount to 0.02%. The amount of Ca is more preferably 0.003% or less. The lower limit of the amount of Ca is not particularly specified but may be 0%, but it is preferably 0.0002% and more preferably 0.0005% in order to stably improve various properties of the steel.

[ REM : 0.02% or less]

REM is an element that improves mechanical properties, use performance and manufacturing stability. Steel may contain REM as needed. REM represents Rare Earth Metals and corresponds to so-called lanthanoid elements of La from atomic number 57 to atomic number 71. In the present embodiment, the steel material may contain a single element or compound of one element belonging to the REM, or may contain a mixture containing plural kinds of REMs. Examples of such a mixture include Misch metal mainly containing Ce, La, Nd and the like.

On the other hand, if the steel material contains REM excessively, there is a possibility of deteriorating the kicking resistance. Therefore, the upper limit of the amount of REM is preferably 0.02%. The amount of REM is more preferably 0.01% or less. The lower limit of the amount of REM is not particularly specified but may be 0%, but it is preferably 0.0002% and more preferably 0.0005% in order to stably improve various properties of the steel.

The content of the above-described selective elements (Al, Cu, Ni, Mo, W, Sn, Sb, V, Nb, Ti, Mg, Zr, B, Ca and REM) , More preferably not more than 1.0%, not more than 0.8%, not more than 0.6%, or not more than 0.4%.

In the case of steels used in the present invention, the remainder other than the above elements are Fe and inevitable impurities. Examples of such inevitable impurities include P, S, N and the like, and they are permissible within a range that does not hinder the improvement in the detonation resistance of the steel material.

[P: 0.03% or less]

If the amount of P exceeds 0.03%, the toughness or ductility may be lowered. Therefore, the upper limit is preferably set to 0.03%. More preferably, the upper limit of the amount of P is 0.02% or 0.01%. On the other hand, there is no need to specify the lower limit of the amount of P and the lower limit of the amount of P may be set to 0%. However, if the amount of P is reduced to less than 0.001%, the production cost rises.

[S: 0.01% or less]

When the amount of S exceeds 0.01%, the toughness and ductility may deteriorate or the hot workability may be impaired. Therefore, the upper limit is preferably 0.01%. More preferably, the upper limit of the amount of S is 0.006% or 0.003%. On the other hand, there is no need to specify the lower limit of the amount of S and the lower limit of the amount of S may be set to 0%. However, if the amount of S is reduced to less than 0.0001%, the production cost increases.

[N: 0.02% or less]

If the amount of N exceeds 0.02%, the toughness or ductility may be lowered. Therefore, the upper limit is preferably set to 0.02%. More preferably, the upper limit of the amount of N is 0.01%, more preferably 0.006%. On the other hand, there is no need to specify the lower limit of the amount of N and the lower limit of the amount of N may be set to 0%. However, if the amount of N is reduced to less than 0.001%, the production cost is increased.

Further, the total content of elements other than C, Si, Mn, Cr and Fe may be limited to 2.0% or less. If necessary, the total amount may be 1.6% or less, 1.2% or less, 0.9% or less, 0.6% or 0.4% or less. The lower limit of the sum does not need to be specially specified, but the lower limit may be set to 0%.

The steel material used in the present invention is manufactured through a general manufacturing process (for example, casting, heating / rolling, cold rolling and heat treatment as required). That is, in the present invention, molten steel is cast into a piece of steel, followed by hot rolling, cold rolling and the like, followed by heat treatment, if necessary, in the form of a steel plate, a steel strip, a steel section, a steel pipe, A steel material produced through a common general steelmaking process can be used. Also, the present invention can be applied to a welded structure or a steel structure constructed using such a steel material. The thickness of the steel material is not particularly limited, but is usually 3 to 50 mm. The lower limit is preferably 6 mm, more preferably 10 mm, and the upper limit is preferably 40 mm, more preferably 30 mm.

The steel plate used for the ballast tank generally has a strength (tensile strength) of 400 MPa or more and 650 MPa or less, and a steel plate having the above strength may be used. The method of producing the steel sheet having the above strength is generally performed by TMCP (thermo-mechanical control process) or normalizing heat treatment (normalizing) as it is determined by the rules of each classification society such as NK, ABS and LR. Quenched, quenched and tempered steel sheets are rarely used. For this reason, the steel used in the present invention may be defined as a steel sheet produced by TMCP or normalizing as it is.

[Coating]

The coating film constituting the corrosion-resistant steel of the present invention is formed by curing an alkali silicate-based inorganic zinc coating composition containing an alkali silicate and zinc particles. The components contained in the alkaline silicate-based inorganic zinc coating composition will be described in detail below.

&Lt; Containing Components of Coating Composition &gt;

&Quot; Alkali silicate &quot;

The alkali silicate used in the present invention is M ₂ O.nSiO ₂ Wherein M1 is an alkali metal or amine component or an ammonium component, and n is a positive number, usually 1 to 100, preferably 1 to 70. [

In the case of alkali silicates containing an alkali metal as M1, alkali metal silicates composed of an alkali metal and silicic acid can be cited. Examples of such compounds include lithium silicate (Li ₂ O.SiO ₂ , Etc.), there may be mentioned a silicate compound such as sodium silicate _{(Na 2 O · SiO 2,} Na 2 O · 2SiO 2, Na 2 O · 4SiO 2 , and so on), potassium silicate (K ₂ O · SiO _2, etc.).

In the case of an alkali silicate containing an amine component or an ammonium component as M1, ammonium silicate consisting of primary amine, secondary amine or tertiary amine and silicic acid, quaternary ammonium silicate composed of quaternary ammonium and silicic acid, . The amine component and the ammonium component derived from ammonium silicate may remain in the coating film without being partially volatilized at the time of forming the coating film, and may contribute to the system effect as an alkali component.

Examples of the primary amine, secondary amine, and tertiary amine components include NR &lt; ₃ &gt; And an amine component represented by the formula (1). In the formula (1), R is independently a hydrogen atom, a hydrocarbon group having 1 to 4 carbon atoms, or a group obtained by substituting one or two or more hydrogen atoms of the hydrocarbon group with a substituent such as a hydroxyl group. Provided that not all Rs are simultaneously hydrogen atoms, and two Rs may combine with each other to form a cyclic group. R is preferably each independently a hydrogen atom, an alkyl group or a hydroxyalkyl group.

As the quaternary ammonium component, for example, NR ₄ ⁺ ... And ammonium cations represented by the formula (2). In the formula (2), R is independently a hydrocarbon group having 1 to 4 carbon atoms, or a group obtained by substituting one or two or more hydrogen atoms of the hydrocarbon group with a substituent such as a hydroxyl group. However, two Rs may be bonded to each other to form a cyclic group. R is preferably each independently an alkyl group or a hydroxyalkyl group.

In the above formulas (1) and (2), the number of carbon atoms of the alkyl group is usually 1 to 4, preferably 1 to 2. The number of carbon atoms of the hydroxyalkyl group is usually 1 to 4, preferably 1 to 2.

Specific examples of the amine component and the ammonium component include, for example, tetramethylammonium, tetraethylammonium, tetrapropylammonium, methyltriethanolammonium, ethyltriethanolammonium, methyltripropanolammonium, isopropyltriethanolammonium, dimethyldiethanolammonium, tetraethanolammonium , And quaternary ammonium components such as methylamine, ethylamine, ethanolamine, diethanolamine, triethanolamine, and other primary, secondary, and tertiary amine components. Among these, a tertiary amine component and a quaternary ammonium component are preferable, and a quaternary ammonium component is more preferable.

Of the alkaline silicates containing an amine component or an ammonium component, ammonium silicate and quaternary ammonium silicate using a tertiary amine component are preferred from the viewpoints of remaining in the coating film at the time of forming a coating film and the unpleasant smell of the coating material And quaternary ammonium silicate is more preferable.

Alkali silicates containing an amine component or an ammonium component are commercially available, for example, from QS-25 (SiO ₂ Solid content: 25 mass%) and QAS-40 (SiO ₂ Solid content: 40% by mass) or ammonium silicate 17804 (manufactured by Nippon Chemical Industry Co., Ltd., SiO ₂ Solid content: 40% by weight) and ammonium silicate 88J3 (SiO ₂ Solid content: 20% by mass).

The alkali silicate is a compound which functions as a binder component and is also a source of alkali metals and amine components or ammonium components, which are alkaline components for the expression of the system effect by the interaction with Cr contained in the steel.

The alkali silicate may be used alone or in combination of two or more.

"Anhydrous silicic acid"

Anhydrous silicic acid can be used to obtain good magnetic hardenability in an inorganic zinc coating composition. The anhydrous silicic acid can be used to adjust the atomic mole ratio (Si / M) as described later.

When anhydrous silicic acid is used, it can be incorporated in the coating composition as an aqueous sol. Aqueous sol of anhydrous silicic acid (hereinafter, also referred to as &quot; aqueous silica sol &quot;) is a colloidal solution in which ultrafine particles of silicic anhydride are dispersed in water using water as a dispersion medium, and aqueous colloidal silica is generally used. When the inorganic zinc coating composition contains an aqueous silica sol, the coating film self-hardens by the dehydration condensation reaction of the aqueous silica sol.

"Zinc Particles"

The zinc particles are incorporated into the alkali silicate-based inorganic zinc coating composition in order to obtain a sacrificial effect of the steel material. As such zinc particles, it is possible to use, for example, zinc powder, zinc alloy powder or a mixture thereof. Examples of the zinc alloy include aluminum and an alloy of tin and zinc.

The average particle diameter of the zinc particles is preferably 2 to 20 占 퐉, for example. The average particle size of these zinc particles can be measured by determining the specific surface area of the particles using a blaze air-permeable device.

" Acid component  And bicarbonate &quot;

The alkali silicate-based inorganic zinc coating composition is a self-curing composition. Concretely, the coating composition absorbs carbon dioxide gas and moisture in the air to precipitate an alkali-generating salt composed of a carbonate such as sodium carbonate, potassium carbonate, lithium carbonate or ammonium carbonate to cure the composition, and thus the curing rate is also fast. Therefore, in the drying and curing step of the coating composition, the acid treatment necessary for the conventional post-curing type alkali silicate inorganic zinc coating composition, specifically, the acid treatment on the surface of the dry coating film is carried out to promote the neutralization reaction to cure the coating film . In addition, there is a system effect by the interaction between the alkali component contained in the paint composition and Cr contained in the steel material.

The alkali silicate-based inorganic zinc coating composition may further contain an acidic component and a bicarbonate salt, if necessary. This makes it possible to further improve the magnetic curability of the coating composition.

The acidic component is not particularly limited as long as it is an acidic component containing no halogen ion, and for example, boric acid is preferably used. The type of the hydrogencarbonate is not particularly limited, but it is preferable to use at least one selected from sodium hydrogencarbonate, potassium hydrogencarbonate, calcium hydrogencarbonate and ammonium hydrogencarbonate. These alkaline metals derived from sodium hydrogencarbonate and potassium carbonate and ammonium components derived from ammonium hydrogen carbonate which remain in the film without being volatilized can also contribute to the system effect as an alkali component.

By further compounding the acid component and the hydrogencarbonate in the composition, in the drying and curing process of the coating composition, a neutralization reaction of the acid component and the hydrogencarbonate occurs and carbon dioxide gas is generated. This reaction of the carbonic acid gas with the alkali metal and the amine component or the ammonium component in the alkali silicate is accelerated to improve the curability. Even if the acid component alone is used, the neutralization reaction with the alkali silicate occurs, so that good curability can be obtained. However, the effect is further improved by using the acid component in combination with the hydrogencarbonate.

The total content of the acidic component and the hydrogencarbonate is preferably 0.1 to 5.0 parts by mass, more preferably 0.5 to 3.0 parts by mass based on 100 parts by mass of the total amount of the aqueous solution of the alkali silicate or the aqueous sol and the aqueous solution of silicic anhydride. When the content is above the lower limit value, better curability can be obtained. If the content is not more than the upper limit, the storage stability of the silicate compound of alkali silicate is good.

" As dispersion medium  water"

The alkali silicate-based inorganic zinc coating composition usually contains water as a dispersion medium. When the coating composition is prepared, for example, an aqueous solution of an alkali silicate or an aqueous sol, and an aqueous sol of anhydrous silicic acid may be mixed. The water as the dispersion medium may be an aqueous solution of these components, water derived from the sol, or water added separately.

The content of water in the alkaline silicate-based inorganic zinc coating composition is preferably 3 to 50 mass%, more preferably 10 to 30 mass%, based on the total amount of the composition. When the content is within the above range, it is preferable from the viewpoint of dispersibility of each component contained in the coating composition.

&Quot; Recycle system  Binders and organic solvents &quot;

The alkali silicate-based inorganic zinc coating composition is preferably substantially free of an alkyl silicate-based binder and an organic solvent. That is, the coating composition is preferably a water-based coating composition.

Means that the content of the alkyl silicate based binder is 1% by mass or less, preferably 0.5% by mass or less, more preferably 0% by mass or less, relative to the total amount of the composition, Mass%, and the content of the organic solvent is 0.5 mass% or less, preferably 0.3 mass% or less, and more preferably 0 mass% or less, relative to the total amount of the composition.

&Quot; Alkylsilicate-based binder &quot; is an alkylsilicate compound such as tetraalkoxysilicate, alkyltrialkoxysilicate, dialkyldialkoxysilicate, and partial condensates thereof.

Conventional inorganic zinc coating films are mainly made by drying and curing an organic solvent type coating material containing an alkyl silicate coupling agent. In the case of this organic solvent type paint, a large amount of organic solvent is required for preparing the paint, and since a large amount of zinc particles are required to obtain a sacrificial effect of the steel, it is necessary to increase the film thickness of the coating film .

Setting the content of the alkyl silicate-based binder and the organic solvent within the above-mentioned range means that the inorganic zinc coating composition is made into an aqueous paint, not an organic solvent-based paint. In the case of the water-based paint, since an organic solvent is not required, it is preferable from the viewpoint of VOC, and since there is a system effect by the interaction of the alkali component contained in the coating film and Cr contained in the steel material, the conventional inorganic zinc coating film It is possible to make the film thickness thinner by comparison.

"Organic resin"

The alkali silicate-based inorganic zinc coating composition is preferably substantially free of an organic resin. Since the coating composition does not contain an organic resin, the effect of sacrificing the zinc particles is improved.

Means that the content of the organic resin is 1% by mass or less, preferably 0.5% by mass or less, more preferably 0% by mass with respect to the total amount of the composition.

<Atomic mole ratio ( Si / M)>

In the present invention, the coating film formed from the alkali silicate-based inorganic zinc coating composition contains at least one atom selected from a silicon atom, an alkali metal atom and a nitrogen atom. Here, alkali metal atoms and nitrogen atoms are collectively referred to as &quot; M &quot;.

In the present invention, the ratio of the number of moles of Si atoms in the coating film to the total number of moles of alkali metal atoms and nitrogen atoms in the coating film, that is, the atomic mole ratio (Si / M) is 2.0 to 125. The upper limit of the atomic mole ratio (Si / M) is preferably 60, more preferably 35, and the lower limit of the atomic mole ratio (Si / M) is preferably 2.2, more preferably 2.3. A more preferable numerical value range of the atomic mole ratio (Si / M) is 2.2 to 60, and a more preferable numerical value range is 2.3 to 35. The nitrogen atom is preferably a nitrogen atom derived from the above-mentioned ammonium silicate or quaternary ammonium silicate.

When the atomic molar ratio is in the above range, both the corrosion resistance of the coating film and the alkali component in the coating film and the interaction of Cr in the steel can be realized. If the proportion of Si in the composition is too high, the ratio of alkali metal atoms and nitrogen atoms in the composition becomes low, and the interaction with Cr in the steel can not be sufficiently obtained. If the proportion of Si in the composition is too low, the corrosion resistance of the coating film can not be improved.

When a plurality of kinds of alkali silicates are used, the number of moles of M is the total number of moles of alkali metal and nitrogen atoms that can be contained in the coating film. That is, when one or more selected from among alkali silicates such as lithium silicate, sodium silicate, potassium silicate, ammonium silicate and quaternary ammonium silicate is used, the atomic mole ratio in the coating film is preferably (Si (Mol number of moles) / (number of moles of Li + Na + K + N), and for the unused components of the alkali silicate, the corresponding mol number may be treated as zero. Further, the mixing ratio (ratio of Li / Na / K / N) of alkali metal atoms and nitrogen atoms is not particularly limited.

The atomic mole ratio of the coating film can be realized by adjusting the kind and amount of the alkali silicate to be added when preparing the alkali silicate-based inorganic zinc coating composition, the amount of the anhydrous silicic acid to be added and the amount of the hydrogen carbonate to be added, if necessary. When ammonium silicate and / or quaternary ammonium silicate is used, the amount of the nitrogen atom-containing component (for example, amine component and ammonium component) derived from the silicate is partially volatilized during film formation, .

Further, the number of moles of Si or M contained in the coating film after the self-curing can be further measured by using a known measuring method such as an ICP emission spectrometer, a fluorescent X-ray spectrometry, or a micro total nitrogen analyzer.

&Lt; Mass ratio of binder component to zinc particles &gt;

In the case of the alkali silicate-based inorganic zinc coating composition, the mass ratio represented by "mass of solids of binder component / mass of zinc particles" is 0.01 to 0.35, preferably 0.02 to 0.25. The solid content of the binder component means, for example, an alkali silicate and optionally anhydrous silicic acid.

When the mass ratio is within the above range, the balance between the corrosion resistance of the coating film and the effect of the sacrificial mode can be well maintained. Concretely, when the mass ratio is 0.01 or more, the corrosion resistance of the coating film formed of alkali silicate or the like as a binder component can be sufficiently obtained. If the mass ratio is 0.35 or less, the effect of the sacrificial system by zinc particles can be sufficiently obtained.

<Atomic mole ratio ( Si / M) and Cr  Relationship of contents>

1 and 2 showing the results of the CCT test (articulation test 3 to be described later) using artificial seawater as described in [Examples] to be described later, CCT tests with an acceleration rate of 6 times for one year (365 days) (1): [Cr] ≥ {0.25 × ln (molar ratio (Si / M)) + 0.5} × 20 (탆) / (the thickness of the steel formed on the surface of the steel material (Film thickness of the coating film (mu m)).

According to CSR-T rule of the steel wire, the local corrosion preliminary thickness at the uppermost part of the ballast tank which is most corrosive is 4.0 mm. The corrosion rate in the ballast tanks is up to 0.5 (mm / year), so the corrosion preliminary thickness is reached in 8 years. In order to realize better corrosion resistance over 15 years, for example, in consideration of this steel corrosion period of 8 years, it is preferable to set the break prevention period to 7 years.

In the one-year CCT test (corrosion test 3 described later) in Figs. 1 and 2, the cycle in which the environment of day and night in the ballast tank is assumed is carried out six times a day, and the acceleration rate is six times. It is well known that the anti-blooming period is proportional to the film thickness of the coating film.

In view of this fact, in order to realize excellent corrosion resistance (that is, corrosion resistance over a longer period of time than in the prior art) over 15 years in the present invention, the coating film formed from the steel material and the alkali silicate-based inorganic zinc coating composition satisfies the following condition (1) Is satisfied.

(Molar ratio (Si / M)) + 0.5} x 20 (占 퐉) / (film thickness (占 퐉) of the coating film formed on the surface of the steel material) x a / b

In the condition (1), [Cr] is the Cr content (mass%) in the steel. The molar ratio (Si / M) is the ratio of the number of moles of Si atoms in the coating film to the total number of moles of alkali metal atoms and nitrogen atoms in the coating film. Here, a and b are determined based on the anti-burglary period and the acceleration rate in the CCT test, respectively, and a = 7 and b = 6 in the case of realizing the corrosion resistance for 15 years.

It is preferable that the steel sheet and the coating film satisfy the conditional expression (1) of a = 12 and b = 6, since it is preferable to set the anti-burglarproof period to 12 years in order to realize better corrosion resistance over 20 years. It is desirable that the anti-bug day is 17 years in order to realize better corrosion resistance over 25 years. Therefore, it is preferable that the steel material and the coated film satisfy the conditional expression (1) of a = 17 and b = 6. It is preferable that the steel material and the coating film satisfy the conditional expression (1) of a = 25 and b = 6 for prevention of the leakage for 25 years.

In addition to satisfying each of the conditions of the coating film molar ratio (Si / M) and the mass ratio, if the steel material and the coating film satisfy the conditional expression (1), a particularly preferred method steel material is obtained in realizing the corrosion resistance over a long period of time.

When the steel and the coating satisfy the condition (1), the film thickness necessary for realizing the corrosion resistance in the above period (for example, 15 years, 20 years, 25 years) depends on the Cr amount of the steel material. It is possible to make the film thickness much thinner than the film thickness of mandatory coating standard of 320 탆 or more. The multilayer coating is also unnecessary, and the coating film can be made into a single film. Further, when corrosion resistance of the above-mentioned period is required, it is also possible to further coat an epoxy resin coating material on a structural steel material having a steel material and a coating film satisfying the conditional expression (1).

<Alkali silicate Inorganic zinc paint  Preparation of composition &gt;

The alkali silicate-based inorganic zinc coating composition can be produced by stirring and mixing the respective components. In the stirring and mixing, known mixing and stirring apparatuses such as an electric stirrer and a sand mill and a dispersing apparatus can be suitably used.

[Long-term corrosion resistance of corrosion-resistant steel]

The coating film composed of the alkali silicate-based inorganic zinc coating composition becomes alkaline (for example, it can be measured by water in contact with the coating film before formation of the corrosion product). By adding various alloying elements including Cr to the steel material serving as the base material, a passive film is formed on the steel material interface under the alkaline condition, and it is possible to improve the corrosion resistance of the steel material over a long period of time.

In addition, since the coating contains zinc particles, corrosion products of zinc are formed on the coating film, thereby protecting the steel itself by the effect of the sacrificial effect of zinc. Also, the formed corrosion products of zinc prevent the alkali components (for example, alkali metal ions, amines, ammonium ions) or steel components present in the coating film from leaking to the outside, and the liquidity of the coating film is maintained. As described above, a passive film is formed under the maintained alkali condition. Therefore, it is possible to maintain the corrosion resistance of the steel material over a long period of time.

It is impossible to directly observe the structure and composition of the highly protective film formed under the coating surface in the corrosive environment, but it is considered that a film with high protection is formed from the results of various corrosion tests in the present invention.

The anti-corrosive steel of the present invention has excellent long-term corrosion resistance as described above, specifically, long-term repellency and does not require an overcoat film such as an organic resin coating on an alkali silicate inorganic zinc coating film for the purpose of improving corrosion resistance . Therefore, it is superior in terms of the painting work process as compared with the conventional alkyl silicate paint or epoxy paint.

&Lt; Method of forming coating film;

In the present invention, a coating film can be formed by coating an alkaline silicate-based inorganic zinc coating composition on a surface of a steel material by a known method such as air spraying or airless spraying to form a dry conductive film, and drying the coating film. The curing conditions are, for example, a temperature of usually 5 to 30 ° C, preferably room temperature, a relative humidity of usually 5 to 85%, preferably 10 to 60%, a curing time of usually 1 to 30 days, Is 2 to 15 days. By drying, the dried conductive film is self-cured. In this manner, a corrosion-resistant steel material having a coating film having a thickness of 10 mu m or more and formed on the surface of the steel material and the steel material can be obtained.

At this time, the coating composition is applied so that the thickness of the coating film is at least 10 mu m in order to obtain an interaction between the alkali component in the coating film and Cr in the steel. The thickness of the coating film is preferably 200 mu m or less, more preferably 120 mu m or less, and further preferably 80 mu m or less.

If the thickness of the coating film is less than 10 탆, the corrosion of the zinc particles after the corrosion test is promoted, and the effect of the sacrificial method is lost early, so that the protective effect by the corrosion products can not be sufficiently obtained. If the thickness of the coating film is 10 탆 or more, the surface of the coating film is protected by the corrosion product of the weakly alkaline zinc particle, and the alkali component in the coating film is also maintained. As a result, a film having high protection is formed on the surface of the steel by the synergistic effect of the corrosion product, the alkali component and Cr, and excellent corrosion resistance is obtained over a long period of time. The thickness of the coating film is preferably 20 占 퐉 or more, more preferably 30 占 퐉 or more, and further preferably 50 占 퐉 or more.

In addition, coating standards mandated by international treaties for marine ballast tanks of ships are multilayer coating of epoxy resin coating, and the dry film thickness (film thickness) of the coating film becomes 320 ㎛ from the previous 250 ㎛, The number of processes was remarkably increased. For this reason, there is a demand for a technique (for example, making a coat of a coat thin or thin) that can reduce the number of work processes related to coating. In the present invention, even when the thickness of the coating film is 80 m or less, excellent corrosion resistance over a long period of time can be obtained when the alkali silicate inorganic zinc coating film is provided on the steel material.

[ ballast  Tank〕

The ballast tank of the present invention is constructed using the steels of the present invention. This ballast tank does not require an additional top coat on the alkali silicate inorganic zinc coating and has excellent organ corrosion resistance.

Example

EXAMPLES Hereinafter, the present invention will be described concretely with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Unless otherwise stated in the description of the examples below, &quot; part &quot; is used to mean &quot; part by mass &quot;.

< Base material person  Production of steel sheet>

The steel having the composition shown in Table 1 was melted and subjected to a normal manufacturing process such as hot rolling and normalizing heat treatment to obtain a steel sheet having a thickness of 14 mm. With respect to the components shown in Table 1, the remainder is Fe and inevitable impurities. In Table 1, steel types No. A-1 to A-22 correspond to steel used in the present invention, steel types No. B-1 to B-2 correspond to conventional steels .

<Alkali silicate system  Preparation of Inorganic Zinc Coating Composition &gt;

[Preparation Example 2]

75 parts of a lithium silicate aqueous solution "Lithium silicate 1: 4" (trade name: molar ratio (SiO _{2 /} Li ₂ O) = 4.0 (catalog value), solid content concentration = 22.6 mass%, manufactured by Honjo Chemical Co., 22.5 parts of silica "SNOWTEX 20" (trade name: solid content concentration = 20% by mass; manufactured by Nissan Chemical Industries, Ltd.) were placed in a vessel with stirring. The resulting mixture was taken as a subject. To this subject, 325 parts of zinc powder "F-2000" (trade name; average particle diameter: 4 μm; manufactured by Honjo Chemical Co., Ltd.) was added. The resulting composition was designated as Paint C-1.

[Preparation Examples 1, 3 to 36]

Each coating material was obtained in the same manner as in Preparation Example 2 except that the blending amounts of the respective components in Preparation Example 2 were changed as shown in Tables 2-1 and 2-2. In Tables 2-1 and 2-2, Pigment No. C-1 to C-25 correspond to the alkali silicate inorganic zinc coating composition used in the present invention, Pigment No. D-1 to D- Corresponding to the target coating composition.

In addition, the atomic mole ratio (Si / M) in Tables 2-1 and 2-2 was measured by using a CIROS CCD (manufactured by Rigaku Corporation) as an ICP emission spectrometer, The nitrogen analyzer is a value measured using a model TN-110 (manufactured by Mitsubishi Chemical Co., Ltd.).

[Table 2-1]

[Table 2-2]

Details of each component in Table 2-1 and 2-2 are as follows.

(Lithium silicate 1: 4) (trade name: molar ratio SiO _{2 /} Li ₂ O = 4.0; solid concentration = 22.6 mass%; manufactured by Honjo Chemical Co., Ltd.)

(SiO _{2 /} Na ₂ O) = 3.2; solid concentration = 40% by mass; manufactured by Nippon Chemical Industry Co., Ltd.)

(SiO _{2 /} Na ₂ O) = 3.4; solid content concentration = 35 mass%; manufactured by Nippon Chemical Industrial Co., Ltd.)

, Potassium silicate aqueous solution: "2K potassium silicate" (trade name; the molar ratio _{(SiO 2 / K 2 O)} = 3.6; solid concentration = 30% by mass; manufactured by Nippon Chemical Industrial Co., Ltd.)

Quaternary ammonium silicate: "QAS-25" (trade name: quaternary ammonium component; solid concentration = 25 mass%; manufactured by Nissan Chemical Industries, Ltd.)

The molar ratio (SiO _{2 /} M ₂ O) is a catalog value.

Aqueous colloidal silica: &quot; Snowtex 20 &quot; (trade name; solid concentration = 20 mass%; manufactured by Nissan Chemical Industries, Ltd.)

Zinc powder: "F-2000" (trade name; average particle size: 4 μm; manufactured by Honjo Chemical Co., Ltd.)

Zinc flake ZnAl7 (trade name: average particle diameter: 18 占 퐉; alloy powder of 93 mass% of zinc and 7 mass% of aluminum; manufactured by ECKART GmbH)

<Formation of Coating Film>

Test pieces having a width of 70 mm, a length of 150 mm and a thickness of 3 mm were taken from the steel sheet shown in Table 1 and degreased to obtain a degree of clarity (cleanliness) in accordance with ISO 8501-1. Blast treatment was carried out. The surface of the test piece was coated with the alkaline silicate inorganic zinc coating composition shown in Tables 2-1 and 2-2, and then allowed to stand for one week in a constant temperature chamber at a temperature of 23 DEG C and a relative humidity of 50% to form a coating film . CIROS CCD (manufactured by Rigaku Corporation) was used as an ICP emission spectrometer and TN-110 type (manufactured by Mitsubishi Chemical Corporation) was used as a trace total nitrogen analyzer. Manufactured by Agaratech Co., Ltd.) was used to measure Si amount and M amount. The combination of the steel sheet and the alkali silicate based inorganic zinc coating composition and the thickness of the coating film are as shown in Table 3 (Table 3-1, Table 3-2) and Table 4 to Table 8 below.

&Lt; Evaluation of steel material &

A test piece having a coating film formed of an alkali silicate-based inorganic zinc coating composition was subjected to pretreatment such as coating other than the test surface, and the following test was carried out.

<Corrosion test 1>

Corrosion test 1 is a composite corrosion test. Using artificial seawater, the test was carried out at 35 ° C for 1 hour → drying to 60 ° C, RH (relative humidity) 15 to 25%, 2h → wet 50 ° C, RH 98% A corrosion test (combined cycle test; CCT test) was performed in which the process, the drying process and the wetting process were sequentially repeated.

After the completion of the test, the nakedness was evaluated visually. In the corrosion test 1, a rating number method of JIS Z2371 (salt spray test method) was used. In the evaluation standard α, 9.8-1 was rated AA, 9.8-1 was exceeded, 9.3-2 was rated BB, 9.3-3 And the evaluation criterion β was A to 9.8-1, 9.8-1, B to 5-2, and C to 5-3, respectively.

The obtained results are shown together in Tables 3 to 8 below. Table 4 shows the influence of the Cr content in the steel on the corrosion test results, and Table 5 shows the influence of the coating thickness on the corrosion test results.

<Corrosion test 2>

In the corrosion test 2, a coating film was formed on the test piece at a coating film thickness of 15 탆 in the same manner as the above &quot; Coating film formation &quot;, and a composite cycle test of 840 cycles was carried out. The results were evaluated. The corrosion test 2 was evaluated on the same basis as the corrosion test 1. The results obtained are shown in Table 6 below.

<Corrosion Test 3>

In the corrosion test 3, the same combined cycle test as in the corrosion test 1 was carried out up to 2190 cycles, and the breakability was visually evaluated. From the viewpoint of judging whether or not the rinse is inhibited in the corrosion test 3, A is selected to be 9.8-1 by the rating number method of JIS Z2371 (salt spray test method), B is exceeded to 9.8-1, B is taken to be 5-3 C &lt; / RTI &gt; The obtained results are shown in Tables 3 to 8 below.

[Table 3-1]

[Table 3-2]

Table 4 shows the results of the above corrosion tests 1 and 3 by installing an alkali silicate inorganic zinc coating film on the surface of steel of the present invention and conventional steel. According to Table 4, when the inorganic zinc coating film is provided on the steel of the present invention, the detonation resistance is improved more than expected from the result of the conventional steel. Further, the analysis of the rust formed in the steel provided with the inorganic zinc coating film by wide angle X-ray diffraction revealed that corrosion products containing Fe or Zn were found. Therefore, it is considered that one of the reasons for improvement of the unbreakability of the steel of the present invention in which an inorganic zinc coating film is provided is believed to be due to the synergistic effect of Cr contained in a specific amount of the steel and the corrosion product.

Table 5 shows the results of the above corrosion tests 1 and 3 by installing inorganic zinc coating films having various thicknesses on the surfaces of the inventive steel and conventional steel. According to Table 5, it was found that, in the case of the steel of the present invention, in the condition of the film thickness of 8 탆, On the other hand, in the case of the steel having a thickness of 10 탆 or more, the result of the inventive steel still deteriorating in anti-kicking properties was obtained, whereas the steel of the present invention was found to be excellent in anti-kicking properties.

Table 6 shows the results of corrosion tests 2 and 3 for the alkali steel silicate based inorganic zinc coating film or the comparative inorganic zinc coating film for the steel of the present invention or conventional steel. When the steel according to the present invention was used and the atomic mole ratio (Si / M) of the coating film was in the range of 2.0 to 125, it was found that the resistance to kicking was excellent. On the other hand, if the molar ratio is out of the above range, even when the steel of the present invention is used, the result is that the knockability is deteriorated. Further, even when the molar ratio was within the above-mentioned range, it was found that when conventional steel was used, the knockability was poor. Therefore, it is considered that excellent corrosion resistance is obtained over the long term due to the synergistic effect of the corrosion product, the alkali component, and Cr.

Table 7 shows the results of corrosion tests 1 and 3 in which the alkali silicate inorganic zinc coating film of the present invention was applied to steel of the present invention. In Examples D1 to D9, since the atomic mole ratio (Si / M) in the coating film was in the range of 2.0 to 125, the corrosion resistance test 1 for 180 days showed excellent resistance to knockout. Also, in Examples E1 to E9, the evaluation B (9.8-1 and up to 5-2) according to the rating number method was particularly excellent in the corrosion test 3 for 365 days.

1 is a graph plotting the Cr content in the steel with respect to atomic molar ratio (Si / M) (logarithmic scale) in Examples 1 to D9 and Examples E1 to E9.

From the results of the numerical analysis for each point in Fig. 1, the straight line that divides Examples D1 to D9 of evaluation C by the rating number method in Examples 3 and E1 to E9 of Evaluation B by the rating number method into { 0.25 x ln (molar ratio (Si / M)) + 0.5. From these results, in Examples E1 to E9 satisfying the formula: [Cr] &gt; = 0.25 x ln (molar ratio (Si / M)) + 0.5 in a coating film having a film thickness of 20 m, longer- In Test 3, it was also found that the resistance to knockout was excellent. That is, in the case of the combination of the steel material and the coating film satisfying the above formula, it can be seen that the anticorrosive coating film excellent in anti-kicking property is obtained over one year in the corrosion test 3.

Table 8 shows the results of corrosion tests 1 and 3 in which the alkali silicate-based inorganic zinc coating film of the present invention was applied to steel of the present invention. In Examples D10 to D16, since the atomic mole ratio (Si / M) of the coating film was in the range of 2.0 to 125, the corrosion resistance test 1 for 180 days showed excellent resistance to ignition. (Example 1) satisfying the formula: [Cr]? 0.25 占 퐉 (molar ratio Si / M) + 0.5 占 20 占 퐉 / (film thickness (占 퐉) of the coating film formed on the surface of the steel material) In E10 to E16, even in the longer-term corrosion test 3 for 365 days, it was found that the resistance to knocking was excellent. The results are shown in Fig. 2 (log display).

From the numerical analysis results for each point in Fig. 2, it can be seen that the Cr content required in the steel is inversely proportional to the film thickness of the coating film. Therefore, it is necessary to multiply 20 (占 퐉) / (film thickness (占 퐉) of the coating film) by the formula: {0.25 占 In (molar ratio Si / M) + 0.5} .

(1): [Cr] &gt; = 0.25 x ln (mole ratio Si / M) + 0.5 x 20 (占 퐉) / (film thickness of the coating film formed on the surface of the steel material (占 퐉)), it is possible to obtain a corrosion-resistant steel excellent in resistance to rubbing even in the corrosion test 3 for 365 days which is longer.

As shown in Tables 3 to 6, even if the empirical formula (1) is satisfied, the thickness of the coating film is less than 10 占 퐉, the atomic mole ratio Si / M is out of the range of 2.0 to 125, When the zinc particles (mass ratio) is out of the range of 0.01 to 0.35, a corrosion-resistant steel excellent in anti-kicking properties can not be obtained in the corrosion tests 1 and 3. Therefore, when the coating film thickness, the atomic molar ratio (Si / M) and the binder solid content / zinc particle (mass ratio) are in the above ranges and the empirical formula (1) is satisfied, Can be obtained.

Claims (21)

Steel and
A coating film having a thickness of 10 mu m or more formed on the surface of the steel material
;
When the steel is in mass%
C: 0.001% to 0.20%
Si: 0.01% to 3.0%
Mn: 0.1% to 3.0%
Cr: 0.1% to 9.99%
Respectively;
Wherein the coating film is formed by curing an alkali silicate inorganic zinc coating composition, wherein the coating film contains at least one atom selected from a silicon atom, an alkali metal atom and a nitrogen atom, {the number of moles of silicon atom Si in the coating film} / { The total molar number of alkali metal atoms and nitrogen atoms in the coating film} is 2.0 to 125;
Wherein the inorganic zinc coating composition contains alkali silicate and zinc particles, and a mass ratio represented by "mass of solid component of binder component / mass of zinc particle" is 0.01 to 0.35
Characterized in that it is made of a steel material. The method according to claim 1,
Wherein the Cr content in the steel material and the molar ratio of the coating film satisfy the following condition (1).
(Molar ratio (Si / M)) + 0.5} x 20 (占 퐉) / (film thickness (占 퐉) of the coating film formed on the surface of the steel material) x a / b
The molar ratio (Si / M) is {the number of moles of silicon atoms Si in the coating film} / {the number of alkali metal atoms and nitrogen atoms in the coating film Total number of moles}, a is 7, and b is 6.] The method according to claim 1,
Wherein the Cr content in the steel material and the molar ratio of the coating film satisfy the following condition (1).
(Molar ratio (Si / M)) + 0.5} x 20 (占 퐉) / (film thickness (占 퐉) of the coating film formed on the surface of the steel material) x a / b
The molar ratio (Si / M) is {the number of moles of silicon atoms Si in the coating film} / {the number of alkali metal atoms and nitrogen atoms in the coating film Total number of moles}, a is 17, and b is 6.] 4. The method according to any one of claims 1 to 3,
Wherein the coating film contains a silicon atom and an alkali metal atom. 4. The method according to any one of claims 1 to 3,
Wherein said coating film contains a silicon atom and a nitrogen atom. 4. The method according to any one of claims 1 to 3,
Wherein said alkaline silicate is a compound represented by M ₂ O.nSiO ₂ wherein M ₁ is an alkali metal or an amine component or an ammonium component and n is a positive number. 4. The method according to any one of claims 1 to 3,
Wherein said alkali silicate comprises at least one selected from lithium silicate, sodium silicate and potassium silicate. 4. The method according to any one of claims 1 to 3,
Wherein said alkali silicate is at least one selected from quaternary ammonium, silicate of quaternary ammonium, quaternary ammonium or quaternary ammonium silicate consisting of quaternary ammonium and silicate, . 4. The method according to any one of claims 1 to 3,
Wherein said alkali silicate comprises a quaternary ammonium silicate composed of quaternary ammonium and silicic acid. 4. The method according to any one of claims 1 to 3,
Wherein the inorganic zinc coating composition is substantially free of an alkyl silicate based binder and an organic solvent
Characterized in that it is made of a steel material. 4. The method according to any one of claims 1 to 3,
When the thickness of the coating film is 200 mu m or less
Characterized in that it is made of a steel material. 4. The method according to any one of claims 1 to 3,
And a coating film formed of the steel material and the coating film and having no coating film on the coating film,
Ballast tank
Characterized in that it is made of a steel material. 4. The method according to any one of claims 1 to 3,
When the steel is in mass%
Cr: 0.3% to 3.0%
By weight. 4. The method according to any one of claims 1 to 3,
In addition to C, Si, Mn and Cr in the steel material,
Al: 2.0% or less
Cu: not more than 1.0%
Ni: not more than 2.0%
Mo: 0.5% or less
W: not more than 0.5%
Sn: not more than 0.5%
Sb: not more than 0.5%
V: not more than 0.2%
Nb: not more than 0.08%
Ti: 0.1% or less
Mg: not more than 0.01%
Zr: not more than 0.05%
B: not more than 0.0050%
Ca: not more than 0.02%
REM: 0.02% or less
P: not more than 0.03%
S: not more than 0.01%
N: 0.02% or less
The remainder: iron and inevitable impurities
. &Lt; / RTI &gt; A ballast tank constructed using the corrosion-resistant steel according to any one of claims 1 to 3. In mass%
C: 0.001% to 0.20%
Si: 0.01% to 3.0%
Mn: 0.1% to 3.0%
Cr: 0.1% to 9.99%
To the surface of the steel material,
An alkaline silicate based inorganic zinc coating composition containing an alkaline silicate and zinc particles and having a mass ratio of 0.01 to 0.35 represented by "mass of solid component of binder component / mass of zinc particle" is applied so that the thickness of the coating film after curing is 10 μm or more ,
At least one atom selected from a silicon atom, an alkali metal atom and a nitrogen atom, and the molar ratio expressed by {the number of moles of silicon atom Si in the film} / {the total number of moles of alkali metal atoms and nitrogen atoms in the film} &Lt; 125 &gt;
Wherein the method comprises the steps of: 17. The method of claim 16,
Wherein the Cr content in the steel material and the molar ratio of the coating film satisfy the following conditional expression (1).
(Molar ratio (Si / M)) + 0.5} x 20 (占 퐉) / (film thickness (占 퐉) of the coating film formed on the surface of the steel material) x a / b
The molar ratio (Si / M) is {the number of moles of silicon atoms Si in the coating film} / {the number of alkali metal atoms and nitrogen atoms in the coating film Total number of moles}, a is 7, and b is 6.] 18. The method according to claim 16 or 17,
And a coating film is formed on the surface of the steel by self-hardening the inorganic zinc coating composition. In mass%
C: 0.001% to 0.20%
Si: 0.01% to 3.0%
Mn: 0.1% to 3.0%
Cr: 0.1% to 9.99%
To the surface of the steel material,
An alkaline silicate based inorganic zinc coating composition containing an alkaline silicate and zinc particles and having a mass ratio of 0.01 to 0.35 represented by "mass of solid component of binder component / mass of zinc particle" is applied so that the thickness of the coating film after curing is 10 μm or more ,
At least one atom selected from a silicon atom, an alkali metal atom and a nitrogen atom, and the molar ratio expressed by {the number of moles of silicon atom Si in the film} / {the total number of moles of alkali metal atoms and nitrogen atoms in the film} &Lt; 125 &gt;
Wherein the steel material is a steel material. 20. The method of claim 19,
Wherein the Cr content in the steel material and the molar ratio of the coating film satisfy the following conditional expression (1).
(Molar ratio (Si / M)) + 0.5} x 20 (占 퐉) / (film thickness (占 퐉) of the coating film formed on the surface of the steel material) x a / b
The molar ratio (Si / M) is {the number of moles of silicon atoms Si in the coating film} / {the number of alkali metal atoms and nitrogen atoms in the coating film Total number of moles}, a is 7, and b is 6.] 21. The method according to claim 19 or 20,
Characterized in that a coating film is formed on the surface of the steel by self-hardening the inorganic zinc coating composition.

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