KR20160120236A - Steel material for painting excellent in corrosion resistance - Google Patents

Abstract

Provided is a steel material for painting with excellent corrosion resistance capable of preventing corrosion influenced by a corrosive activity of seawater, salt particles, or the like. The steel material comprises: 0.04-0.30% of C, 0.05-1.0% of Si, 0.1-2.5% of Mn, 0.04% or less of P, 0.04% or less of S, 0.005-0.20% of Al, 0.05-1.0% of Cu, 0.05-1.0% of Cr, and 0.001-0.015% of N, and one or two among 0.005-0.1% of Ti and 0.005-0.1% of Nb, and a coating layer including 20-200 g/m^2 of Zn and 0.3-20.0 g/m^2 of Cu and one or two among 0.3-20.0 g/m^2 of Cr and 0.3-20.0 g/m^2 of Ni.

Description

[0001] STEEL MATERIAL FOR PAINTING EXCELLENT IN CORROSION RESISTANCE [0002]

TECHNICAL FIELD The present invention relates to a steel material for use in steel structures such as ships, offshore structures, bridges, and the like. More particularly, the present invention relates to a steel material for coating, which is used in corrosion environments, And a steel for painting.

Steel is widely used as a structural member of various structures, but when it is used as a structural member of a structure affected by seawater such as a ship, an offshore structure, or a bridge, the steel is subjected to a corrosive action such as seawater, There is a problem that the strength of the structure is lowered due to the presence of a crack or the like.

Such corrosion of the steel material by seawater can be prevented by electrolysis (corrosion prevention) when the steel material is used only in a region where the steel material is completely immersed in seawater. However, it is possible to prevent the steel material from being always immersed in seawater near the sea surface, The electric system does not work and it is exposed to a severe corrosive environment caused by splashes of seawater, so that it is difficult to prevent it by the electric method.

Further, when the steel material is used as the structural member of the ballast tank of a ship, it is necessary to inject and discharge the seawater into the ballast tank in accordance with the loading load, so that the inner surface of the ballast tank is not always immersed in seawater, Can not be obtained sufficiently.

Furthermore, since structures such as iron bridges near the coast are also exposed to the atmospheric corrosion environment caused by the seawater particles, application of the electric system is often not always effective even when a steel material is used as a structural member of such a structure .

As described above, the application of the electric system is not always effective in structures such as ships, marine structures, and bridges that are affected by seawater. Therefore, conventionally, when the anticorrosive coating is formed on the surface of steel . Examples of the paints used for the anticorrosion coating include various anticorrosive paints such as epoxy resin, chlorinated rubber, acrylic resin, urethane resin and fluororesin, and coating systems optimal for the environment are used. there was.

However, the anticorrosive coating film may be deteriorated by aging due to ultraviolet rays or by some external mechanical action. Since corrosion of the steel material advances at the scratch portion of such a coating film, regular maintenance is required. However, in the case of structures such as ships, offshore structures, bridges, etc., there are places where it is necessary to install a scaffold for the inspection and maintenance of the condition of the anticorrosion coating, There are many places where it is not easy to inspect and maintain. In this way, from the viewpoint of ensuring safety and reducing the maintenance load, it is a technical problem that suppression of corrosion from the scratch area of the anticorrosive coating film is very important.

As a countermeasure against such a problem, a technique for improving the corrosion resistance of the steel itself by the adjustment of the chemical composition of the steel material and the improvement of the manufacturing method, and thereby contributing to the suppression of the corrosion of the scratch- Many have been proposed. By employing these techniques, the corrosion resistance of the steel for painting is surely improved, but it is in the present state that further improvement of the corrosion resistance is demanded.

Particularly, in a ballast tank of a ship, there is a case where the amount of corrosion wear is 1 mm for one year at a portion where the coating film is peeled off, and an extremely corrosive environment is set, and corrosion prevention of the scratch portion of the corrosion coating film is strongly desired. In recent years, there has been a growing demand for extending the useful life of ships. Therefore, the life expectancy of the ballast tanks with the worst coating deterioration in ships is expected to increase to more than 15 years .

In particular, in recent years, clean energy that does not emit carbon dioxide, a greenhouse gas, has attracted attention from the viewpoint of conservation of the global environment, and it is expected to be used in a variety of fields such as wind power generation, blue power generation, Development of power generation technology is underway.

These environment conditions are expected to have more corrosiveness than the seawater and seawater environments of conventional structures. Therefore, there is a need for a corrosion and corrosion technology that can be applied to harsh environmental conditions. In the realization of these, it is difficult to inspect the coating state of the steel material and to perform maintenance work such as repainting. Therefore, from the viewpoint of the life cycle cost, the demand for further extending the service life of the steel material is enhanced, It is desired to develop a corrosion resistance improving technique of a steel material.

Japanese Patent Application Laid-Open No. 2010-229526 Japanese Patent Application Laid-Open No. H9-92404

SUMMARY OF THE INVENTION The present invention has been made in view of the above conventional circumstances, and an object of the present invention is to provide a coating steel material excellent in corrosion resistance that can be prevented from being corroded under the influence of corrosion action of seawater or seashell particles.

Particularly, in a steel plate, a thick steel plate and a steel plate having a plate thickness of 3 mm or more, even if they are used as a structural member of a structure under a seawater corrosive environment or in a corrosive environment in which seaweed salt particles are a major cause, The present invention also provides a steel material for painting which is excellent in corrosion resistance and does not cause corrosion.

A coated steel material excellent in corrosion resistance of the present invention is a coated steel material comprising a base steel and a surface layer formed on the surface of the base steel, wherein the base steel comprises, by mass%, 0.04 to 0.30% 0.05% to 1.0% of Si, 0.1 to 2.5% of Mn, more than 0% to 0.04% of P, By mass of Ti and 0.005 to 0.1% of Nb and 0.001 to 0.015% of N and 0.005 to 0.1% of Nb and 0.005 to 0.1% of Nb and the balance of Fe and inevitable impurities , and also the surface ^{layer, Zn: 20~200g / m 2,} Cu: In addition to containing from ^{0.3~20.0g / m 2, Cr: 0.3~20.0g} / m 2, Ni: 0.3~20.0g / m 2 , Or a mixture thereof.

Further, it is preferable that the base steel further contains one or two or more of Ni: 0.01 to 6.0%, Co: 0.01 to 5.0%, Mo: 0.01 to 2.0% and W: 0.01 to 2.0% .

Further, it is preferable that the above-mentioned ground steel further contains at least one or more of 0.0005 to 0.01% of Mg, 0.0005 to 0.01% of Ca and 0.0005 to 0.01% of REM in terms of mass%.

It is also preferable that the base steel further contains at least one of Sn, 0.001 to 0.2%, Sb: 0.001 to 0.2% and Se: 0.001 to 0.2% in mass%.

The base steel according to any one of the above items, wherein the base steel contains, in terms of mass%, B: more than 0% and not more than 0.01%, V: more than 0% and not more than 0.1%, Zr: more than 0% Or two or more of them.

According to the steel material for coating having excellent corrosion resistance of the present invention, even if it is used in a steel structure in a highly corrosive environment such as a ship, an offshore structure, or a bridge, which is highly susceptible to corrosion due to the corrosive action of seawater or seashell particles, Corrosion resistance can be demonstrated.

It is known that, in a steel material coated on the surface thereof, the effect of suppressing the corrosion of the steel material is great when the coating film formed on the surface thereof is sound, and furthermore, a high corrosion prevention effect can be obtained by selecting an appropriate paint system. However, when a defect occurs in a coating film or when a scratch occurs in which the coated steel sheet is exposed to the coating film, corrosion of the coated steel sheet occurs starting from the scratch on the coated film, and further, the coating is advanced.

The inventors of the present invention have conducted studies on the occurrence of corrosion of a base steel material starting from such a coating film scratch, and furthermore, a method of suppressing the progress of the corrosion. As a result, in addition to the occurrence of a corrosion reaction in the exposed portion of the coated steel sheet, corrosion factors such as water and chloride ions enter the interface between the coated film and the non-coated steel sheet from the scratched portion, And it was found that these were largely concerned with corrosion progress and expansion of the base steel material in the coating film scratch area.

Further, in the case of a steel material coated with a surface, by forming a layer containing Zn at the interface between the coating film and the base steel material, corrosion progress and coating film deterioration of the film scratch portion are suppressed by the effect of the sacrificial effect of Zn, Is improved. From such a viewpoint, there is a case where a surface layer containing Zn is formed on the base steel by application of an inorganic zinc primer or the like in the coating steel for improving the corrosion resistance.

The inventors of the present invention studied the effect of the layer formed on the interface between the base steel and the coating film to further suppress the corrosion protection property of the corrosion product although there is suppression of corrosion progress and coating film deterioration due to the effect of the sacrificial system. As a result, it has been found that, in addition to Cu and Cr, an appropriate amount of one or both of Ti and Nb is added in an appropriate amount, and the surface of the steel further contains an appropriate amount of Cu in addition to Zn, Or two kinds of the surface layer is further formed, synergistic improvement effect of the corrosion product is obtained in addition to the effect of the sacrificial system of Zn in the scratch portion of the coating film, so that the corrosion progress from the scratch portion of the coating film is significantly And the corrosion resistance of the steel for painting can be greatly improved. The present invention has been accomplished based on these findings.

On the other hand, it is already known that the corrosion resistance is improved by adding Cu or Cr or the like to the base steel to improve the corrosion resistance of the iron rust. However, in the present invention, in addition to the above- And the surface layer formed on the surface of the base steel material is additionally provided, the corrosion resistance of the corrosion product of the coating film scratch can be remarkably improved and the corrosion resistance effect can be obtained.

Hereinafter, the present invention will be described in detail based on embodiments. On the other hand, the coating of the base steel, the surface layer, and further the surface thereof constituting the steel for painting according to the present invention will also be described in turn.

<Composition of Substrates>

In addition to excellent corrosion resistance, base steel needs to satisfy mechanical properties and weldability as structural members. From these viewpoints, it is necessary to appropriately adjust the contents of Si, Mn, Al, P and S in addition to the above-mentioned Cu, Cr, Ti and Nb. Hereinafter, the reason for limiting the range of components of these various added elements will be described. On the other hand, the units are expressed as%, and they represent% by mass.

C: 0.04 to 0.30%

C is a basic additive element necessary for securing the strength of the base steel. In order to obtain the strength characteristic generally required as the base steel, it is necessary to contain at least 0.04% or more. However, if C is excessively contained, the amount of cementite that acts as a cathode site in the acid solution increases, accelerating the corrosion reaction and deteriorating the corrosion resistance. In addition, the toughness also deteriorates. In order not to cause such an adverse effect by excessive addition of C, it is necessary to suppress the content of C to 0.30% at most. Therefore, the content of C was 0.04 to 0.30%. On the other hand, the lower limit of the content of C is preferably 0.045%, more preferably 0.05% or more. The preferable upper limit of the content of C is 0.29%, more preferably 0.28% or less.

Si: 0.05 to 1.0%

Si is an element necessary for deoxidation and strength assurance. If Si is not contained in an amount of at least 0.05%, these effects can not be obtained. However, if it exceeds 1.0%, the weldability deteriorates. Therefore, the content of Si is set in the range of 0.05 to 1.0%. On the other hand, the lower limit of the Si content is preferably 0.08%, more preferably 0.10% or more. The upper limit of the Si content is preferably 0.95%, more preferably 0.90% or less.

Mn: 0.1 to 2.5%

Like Mn, Mn is an element necessary for deoxidation and strength assurance. If the content of Mn is less than 0.1%, the lowest strength as a steel member used as a structural member can not be secured. However, if it is contained in excess of 2.5%, the toughness deteriorates. Therefore, the content of Mn was set to 0.1 to 2.5%. On the other hand, the lower limit of the Mn content is preferably 0.15%, more preferably 0.2% or more. The upper limit of the Mn content is preferably 2.4%, more preferably 2.3% or less.

P: not less than 0% and not more than 0.04%

P is an element that deteriorates toughness and weldability when contained in excess, and the upper limit of the allowable content of P is 0.04%. The content of P is preferably as small as possible, and a more preferable upper limit of the content of P is 0.038%, more preferably 0.035% or less. However, it is difficult to industrially make P in the base steel to 0%.

· S: more than 0% and less than 0.04%

When the S content is increased, the element tends to deteriorate toughness and weldability. The upper limit of the allowable content is 0.04%. A more preferable upper limit of the content of S is 0.038%, more preferably 0.035% or less. However, it is difficult to industrially make S in the base steel to 0%.

Al: 0.005 to 0.20%

Al is an element necessary for deoxidation and strength assurance like Si and Mn described above. In order to effectively exhibit such action, it is necessary to contain 0.005% or more. However, if it is contained in an amount exceeding 0.20%, the weldability is deteriorated. Therefore, the content of Al is 0.005 to 0.20%. On the other hand, the lower limit of the content of Al is preferably 0.008%, more preferably 0.010% or more. The upper limit of the content of Al is preferably 0.19%, more preferably 0.18% or less.

Cu: 0.05 to 1.0%

Cu is dissolved in ferrite to reduce the activity of the anode in the exposed part of the coated steel in the coated film scratch and also has the function of forming a dense rust coating on the surface of the coated steel and is an element necessary for improving the corrosion resistance of the scratch on the coated film . In order to exhibit such an effect, it is necessary to contain at least 0.05% or more. However, if it is contained in an excess amount, the weldability and hot workability deteriorate, so the content of Cu should be 1.0% or less. Therefore, the content of Cu is set to 0.05 to 1.0%. On the other hand, the lower limit of the Cu content is preferably 0.06%, and more preferably, the lower limit is 0.07%. The preferable upper limit of the Cu content is 0.95%, and the more preferable upper limit is 0.90%.

Cr: 0.05 to 1.0%

Cr is dissolved in ferrite in the same manner as Cu and has an action of forming a dense rust coating on the surface of the base steel in addition to lowering the activity of the anode in the exposed portion of the base steel in the scratch of the coating film and improving the corrosion resistance of the scratch of the coating It is a necessary element. In order to exhibit such an effect, it is necessary to contain at least 0.05% or more. However, if it is contained in an excess amount, the weldability and hot workability deteriorate. Therefore, the content of Cr should be 1.0% or less. Therefore, the content of Cr was set in the range of 0.05 to 1.0%. On the other hand, the lower limit of the Cr content is preferably 0.06%, and the lower limit is more preferably 0.07%. The preferable upper limit of the Cr content is 0.95%, and the more preferable upper limit is 0.90%.

N: 0.001 to 0.015%

N is an element effective for improving the corrosion resistance and securing strength of the base steel by forming finely dispersed particles of nitride in the steel. In order to obtain such an effect, the N content needs to be 0.001% or more. However, if the content is excessive, the toughness of the base steel is adversely affected, and the weldability is deteriorated. Therefore, the upper limit of the content of N is set to 0.015%. Therefore, the range of the content of N was set to 0.001 to 0.015%. On the other hand, the lower limit of the content of N is preferably 0.0015%, more preferably 0.002% or more. The preferable upper limit of the content of N is 0.014%, more preferably 0.013% or less.

Ti: 0.005 to 0.1%, Nb: 0.005 to 0.1%

Ti and Nb have the function of forming a dense rust coating on the surface of the base steel under the coexistence of Cu and Cr, and are elements necessary for improving the corrosion resistance. In order to exhibit such an effect, it is necessary to contain at least 0.005% each. However, if it is contained in an excessive amount, the weldability and hot workability deteriorate. Therefore, the contents of Ti and Nb should be 0.1% or less, respectively. The preferable lower limit of the contents of Ti and Nb is 0.006%, and the lower limit is more preferably 0.007%. The preferable upper limit of the content of Ti and Nb is 0.095%, and the upper limit is 0.09%.

The above is the reason for limiting the range of the essential additive elements of the base steel constituting the steel for painting according to the present invention, and the balance is Fe and inevitable impurities. The inevitable impurities include O and H, and these elements may be contained to such an extent as not to impair various properties of the base steel. However, by suppressing the total content of these inevitable impurities to 0.1% or less, preferably 0.09% or less, the effect of manifesting the corrosion resistance according to the present invention can be maximized.

Further, it is more effective to contain the following elements in the base steel constituting the coating steel of the present invention. The reason for limiting the range of components when these elements are contained will be described below.

0.01 to 2.0% of Ni, 0.01 to 6.0% of Ni, 0.01 to 5.0% of Co, 0.01 to 2.0% of Mo and 0.01 to 2.0% of W

Ni, Co, Mo, and W are dissolved in ferrite to lower the activity of the dissolution reaction, and are effective elements for improving corrosion resistance. The appropriate amounts of Ni, Co, Mo and W are also effective for improving the strength characteristics of the base steel and are added as required. In order to exhibit such an effect, it is preferable to contain 0.01% or more of each. However, when the content of these elements is excessive, the weldability and hot workability deteriorate. Therefore, when it is contained, the content of Ni is set to 6.0% or less, the content of Co to 5.0% or less, and the content of Mo and W to 2.0% or less. When Ni, Co, Mo, and W are contained, the lower limit is more preferably 0.02% and more preferably 0.03% or more. A more preferable upper limit when Ni is contained is 5.9%, more preferably 5.8% or less. A more preferable upper limit when Co is contained is 4.9%, more preferably 4.8% or less. A more preferable upper limit when Mo and W are contained is 1.9%, and more preferably 1.8% or less.

Mg: 0.0005 to 0.01%, Ca: 0.0005 to 0.01%, and REM: 0.0005 to 0.01%

Mg, Ca, and REM have an effect of suppressing the pH lowering in the vicinity of the surface of the steel in the use environment, and are effective elements for further improving the corrosion resistance. This action is exerted when these elements are dissolved by corrosion and react with hydrogen ions. In order to exhibit such an effect effectively, it is preferable that each is contained in an amount of 0.0005% or more. However, when the content of these elements is excessive, the weldability and the hot workability deteriorate. When these elements are contained, the content is made 0.0005 to 0.01%. When Mg, Ca and REM are contained, the lower limit is more preferably 0.0006%, and still more preferably 0.0007%. On the other hand, when Mg, Ca and REM are contained, the more preferable upper limit is 0.0095%, and the more preferable upper limit is 0.009%, respectively.

0.001 to 0.2% of Sn, 0.001 to 0.2% of Sb, and 0.001 to 0.2% of Se.

Sn, Sb and Se are effective addition elements for improving the corrosion resistance. The corrosion resistance improving effect is effectively exhibited by containing 0.001% or more of each of these elements. However, when the content of these elements is excessive, the weldability and hot workability deteriorate. When these elements are contained, the content is made 0.001 to 0.2%. A more preferable lower limit when Sn, Sb and Se are contained is 0.002%, and a more preferable lower limit is 0.003%, respectively. On the other hand, when containing Sn, Sb and Se, the more preferable upper limit is 0.19%, and the more preferable upper limit is 0.18%, respectively.

B: not less than 0% but not more than 0.01%, V: not less than 0% but not more than 0.1%, Zr: not less than 0% and not more than 0.1%, Zn: not less than 0%

B, V, Zr, Zn and the like can be contained as needed. When these added elements are contained in an extremely small amount, the strength improving effect is exhibited. For example, when B is contained at 0.0001% or more and V, Zr and Zn are contained at 0.001% or more, the strength improving effect is more reliably expressed. However, if these elements are contained excessively, the toughness and weldability of the base material deteriorate. Therefore, the content of these elements is limited. When B is contained, it is not more than 0.01%. When V, Zr and Zn are contained, each is not more than 0.1%. The more preferable upper limit when B is contained is 0.0095%, and the more preferable upper limit is 0.009%. Further, when V, Zr and Zn are contained, the more preferable upper limit is 0.095%, and the more preferable upper limit is 0.09%.

<Structure of Undrawn Steel>

The structure of the base steel constituting the steel for painting according to the present invention is not particularly limited. However, in order to obtain sufficient mechanical properties, it is recommended to use a structure made of ferrite and pearlite or a structure made of ferrite and bainite.

&Lt; Production method of base steel material >

In order to reliably produce the base steel constituting the steel for painting according to the present invention, it is preferable to produce the base steel by the method described below, for example. First, the molten steel introduced from a converter or an electric furnace into a ladle is adjusted to the composition specified in the present invention by using an RH vacuum degassing apparatus, and the temperature is adjusted to 2 Car refining is performed. Thereafter, the ingot is cast by a conventional casting method such as a continuous casting method or a roughing method. On the other hand, as a structural member, in order to secure basic characteristics such as mechanical properties and weldability necessary for a steel material, it is preferable to use killed steel as a deoxidation type, and more preferably to use an Al killed steel.

&Lt; Surface layer &

Coating the steel material of the present invention, the surface of the substrate ^{steel, Zn: 20~200g / m 2,} Cu: In addition to containing from ^{0.3~20.0g / m 2, Cr: 0.3~20.0g} / m 2, Ni: And 0.3 to 20.0 g / m &lt; ^{2 &} gt ;.

Zn in the surface layer acts to suppress the corrosion progress of the base steel by the effect of the sacrificial system, and such an effect is exhibited when the Zn adhesion amount of the surface layer is 20 g / m ² or more. A more preferable lower limit of the Zn deposition amount is 25 g / m ² , and more preferably 30 g / m ² or more. Further, if the Zn deposition amount is increased to some extent, not only the effect of the sacrificial method is saturated but also it becomes easy to peel off from the base steel, so that the effective period of the sacrificial operation may be shortened. From this point of view, it is recommended that the amount of Zn deposited be 200 g / m ² or less. A more preferable upper limit of the Zn deposition amount is 190 g / m ² , and more preferably 180 g / m ² or less.

Further, when Cu and Cr, Cu and Ni, Cu and Ni and Cr are coexisted in the surface layer containing the chemical components in the above-mentioned content range, the rust which is the corrosion product of the steel in the scratch portion of the coating film is further densified And the effect of inhibiting the penetration of corrosion factors such as water and chloride ions into the green layer is exerted. Therefore, the corrosion reaction of the base steel is suppressed, contributing to the improvement of the corrosion resistance.

Such an effect is exhibited by setting the adhesion amount of Cu in the surface layer to 0.3 g / m ² or more and further containing 0.3 g / m ² or more of any one or two of Cr and Ni. More preferable deposition amounts of Cu, Cr and Ni in the surface layer are 0.4 g / m ² or more, and more preferably 0.5 g / m ² or more. However, if the adhesion amount of Cu, Cr and Ni is excessively large, the adhesion between the surface layer and the base steel is lowered, and the surface layer is likely to be peeled off from the base steel. In order to avoid such adverse influences, it is recommended that the adhesion amounts of Cu, Cr and Ni are each 20.0 g / m ² or less. A more preferable upper limit of the amount of deposition of the Cu, Cr and Ni is more preferable that each 19.5g / m ² or less, and less than 19.0g / m ^2.

Examples of the method of forming the surface layer include mixing the Zn powder, the Cu powder, the Cr powder, and the Ni powder with a suitable solvent such as an alkyl silicate, followed by spraying or brushing. It is also possible to prepare powders of Zn-Cu-Cr alloy, Zn-Cu-Ni alloy or Zn-Cu-Cr-Ni alloy having an appropriate composition and use this alloy powder in a usual primer coating process. At this time, a suitable pigment may be added if necessary. It is also possible to form the surface layer with a desired deposition amount of Zn, Cu, Cr, and Ni by using a thermal spraying method such as spraying or arc spraying. On the other hand, as a pretreatment for forming the surface layer, it is preferable to remove scale or the like on the surface of the base steel by shot blasting or the like.

In order to assure the adhesion strength between the surface layer and the base steel, it is preferable that the roughness of the surface of the base steel be at least some degree of roughness. However, if the surface roughness is too rough, bubbles will enter the recesses, There is a possibility that the bonding strength is lowered. From this point of view, it is recommended that the surface of the base steel be treated with an appropriate surface roughness.

As the specific surface roughness of the base steel, it is recommended that the ten point average roughness Rzjis specified in JIS B 0601: 2001 be 10 μm to 80 μm, for example. On the other hand, the surface roughness of the base steel can be adjusted by, for example, ordinary shot blasting or grid blasting.

<Painting>

The steel material for painting of the present invention is practiced by further coating on the surface layer. As paints used for painting, paints such as epoxy resin, chlorinated rubber, acrylic resin, fluororesin, and urethane resin can be applied, and it is also possible to use a plurality of paints to make the coating film multi-layered.

For example, as the paint for forming the epoxy resin coating film, any paint may be used as long as it is a paint used as an anticorrosive coating and includes an epoxy resin as a transportation means, and is not particularly limited. Specific examples of paints include epoxy resin paints, modified epoxy resin paints, tar epoxy resin paints and the like.

As the coating material for forming the chlorinated rubber coating film, any coating material containing chlorinated resin as the main material may be used, and there is no particular limitation. Specific examples of the coating material include a coating material composed mainly of a chlorinated resin such as chlorinated rubber and chlorinated polyolefin.

As the coating material for forming the acrylic resin coating film, there can be enumerated coating materials such as usual acrylic resin coating material, acrylic emulsion resin coating material, acrylic urethane-based emulsion coating material, acrylic silicone emulsion coating material and acrylic lacquer.

As the paint for forming the fluororesin coating film, a paint such as a tetrafluoroethylene resin paint, a perfluoroalkoxy resin paint, a fluorinated ethylene propylene resin paint and the like can be mentioned.

Examples of paints for forming the urethane resin coating film include paints such as polyurethane resin coating, polyester urethane resin coating, moisture-curing polyurethane resin coating, epoxy urethane paint, and modified epoxy urethane resin coating can do.

If the coating thickness of these coatings is too thin, the coating effect becomes insufficient. On the contrary, if it is excessively large, the coating film tends to be peeled off. From this point of view, it is recommended that the film thickness of the coating be a dry film thickness, for example, a thickness of 100 to 1000 m.

In addition, the coating process for forming the coating film is not particularly limited, and ordinary coating methods such as spray coating and brushing can be applied. However, it is necessary to appropriately clean the surface of the base steel material to be a coating material before coating. For example, the surface of the steel material is cleaned so that the attached salt concentration is 50 mg / m ² or less, preferably 10 mg / m ² or less Is recommended.

Examples of the form of the coating steel of the present invention include steel sheet, steel pipe, bar steel, wire rod, section steel and the like. Examples of applications include those used as structural members of ballast tanks in cargo ships such as tankers, container ships, and bulker vessels, vessels such as vans, passenger ships, and naval vessels. In addition, It can also be used for steel structures for various ships such as ship bridge, hatch cover, crane, various piping, stairs, railing, and the like.

In addition, the offshore structures include structures for excavating oil and natural gas in the ocean, floating structures for producing, storing and extracting oil and gas from the ocean, wind power generation in the ocean, , Aviation and ocean current generation, temperature difference generation, and photovoltaic power generation. Also, in the field of bridges, it is possible to exemplify a steel material for bridges in a high salinity saline environment where the salinity of the salinity exceeds approximately 0.1 mdd: mg / dm ² / day.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to the following Examples, of course, All of which are included in the technical scope of the present invention.

[Production of the disclosure material]

A steel material having various compositional compositions shown in Table 1 was dissolved by a vacuum melting furnace to obtain a steel ingot of 50 kg. The obtained ingot was heated to 1150 占 폚 and then subjected to hot rolling to obtain a steel material having a thickness of 10 mm. Test pieces of size 150mm × 70mm × 5mm were cut out from the steel material. Shot blast treatment was carried out on one side having a width of 150 mm x 70 mm to be a test surface of all of the cut test pieces so that the ten point average roughness Rzjis defined by JIS B 0601: 2001 was 30 10 m, washed with water and acetone Painting was carried out.

A surface layer appropriately containing Zn, Cu, Cr, and Ni was formed on one side of a test piece having a size of 150 mm x 70 mm by the above shot blasting treatment. The surface layer was formed by spraying and coating the test liquid with an alkyl silicate as a solvent and appropriately mixing powders of metal Zn, metal Cu, metal Cr and metal Ni as a coating liquid. On the other hand, the amount of Zn, Cu, Cr and Ni deposited on the surface layer was changed by suitably adjusting the amounts of Zn, Cu, Cr and Ni to be added and the amount of coating.

The surface of 150 mm x 70 mm in which the surface layer containing Zn, Cu and the like was formed was coated with a modified epoxy resin-based paint by spraying. The film thickness of the coating is 200 ± 20 μm as a dry film thickness. The coating surface of the modified epoxy resin-based coating material was dried, and a coating film scratch was formed on the coating surface to reach a steel substrate having a length of 80 mm and a width of 3 mm.

All the test pieces were covered with the silicone rubber sealant and the other corrosion test was made on the coated surface having the scratches formed thereon as the test surface and the surfaces other than the test surface covered with the silicone sealant.

[Corrosion test method]

As a corrosion test simulating the corrosive environment caused by seawater, a combined cycle test using artificial seawater: CCT was conducted. The cycling conditions were 1) spraying artificial seawater at 35 ° C for 1.5 hours, 2) temperature 60 ° C, relative humidity 20% RH, 2.5 hours, 3) temperature 50 ° C, relative humidity 95% RH, 2.5 hours.

On the other hand, the transit time until stabilization by changing the temperature and humidity between each process is 0.5 hours. The test period was 3 months. The samples were subjected to the same treatment as in Example 1, 1 to No. 49 were announced for each three.

The corrosion area and the corrosion depth from the scratch portion of the coating film of the test piece were determined after completion of the CCT as the evaluation of the deterioration of the coating film from the coating film scratch portion and the progress of the corrosion. The corrosion area was determined as the average of the test pieces of each of the three test pieces as the total area of the area of the portion where the coated film was swollen due to corrosion of the coating film from the scratch on the coated film and the area of the scratch on the coated film.

As for the depth of corrosion, the coating film scratches and the depth of corrosion around them were measured to obtain the maximum value of each of the three test pieces. On the other hand, the corrosion depth was measured by peeling off the coating film of the test piece after completion of the CCT and performing de-caking treatment by cathodic electrolysis in a 10% aqueous solution of ammonium hydrogencarbonate, followed by measurement with a depth gauge.

[Combined cycle test result]

Combined cycle test: Corrosion area and corrosion depth obtained after CCT are as shown in Table 2. On the other hand, the corrosion area and the corrosion depth of each sample are as follows. 1 is a relative value when the corrosion area and the corrosion depth of the sample are 100, respectively.

The evaluation criteria of corrosion area and corrosion depth are as follows. The relative values of the corrosion area and the corrosion depth were both A and AAA. Relative values were between 80 and less than 90, and those with a relative value of 70 or more and less than 80 were rated AA. Relative values of less than 70 were rated AAA. It was evaluated that it was a steel for painting with excellent corrosion resistance.

No. 1 to No. 12, the relative value of the corrosion area and the corrosion depth is 90 to 100, and the corrosion resistance of the scratch area of the coating film is not sufficient. No. 2, No. 6 and No. 7 contains Zn, Cu and Cr according to the present invention in the surface layer. However, since the Cu content of the steel is too small, the corrosion resistance of the scratch portion of the coating film is not sufficiently improved.

No. 3 and No. 8 contains Zn, Cu and Cr according to the present invention in the surface layer, but since the Cr content of the base steel is too small, the corrosion resistance of the scratch portion of the coating film can not be sufficiently improved.

No. 4 and No. 2. 5 contains Zn, Cu and Cr according to the present invention in the surface layer. However, since the Ti content or the Nb content of the base steel is too small, the corrosion resistance of the coating film scratch can not be sufficiently improved.

In addition, 9 and No. 10 all satisfy the requirements of the present invention, but since Zn or Cu in the surface layer is too small, the corrosion resistance of the scratch portion of the coating film can not be sufficiently improved.

No. 11 and No. 12 all satisfy the requirements of the present invention, while the composition of the non-coated steel and Zn and Cu of the surface layer satisfy the requirements of the present invention. However, since the Cr or Ni of the surface layer is excessively small, the corrosion resistance of the scratch portion of the coating film is not sufficiently improved.

Compared with these comparative examples, it is possible to obtain a comparative example in which all the requirements of the present invention are satisfied. 13 to No. 49 are all suppressed to be less than 90 in both of the relative values of the corrosion area and the corrosion depth, and the excellent corrosion resistance of the coating film scratches is exhibited.

Particularly, in S12 to S18 base steels containing any one or more of Ni, Co, Mo and W in an appropriate amount, a steel having no surface layer according to the present invention is obtained. 18 ~ No. 27 shows a remarkable effect of inhibiting the corrosion area.

To the non-coated steels of S28 and S29 containing a proper amount of any one or more of Sn, Sb and Se in addition thereto, were added 0.1 g of the No. 40 to No. 42 samples are more effective in inhibiting the corrosion area.

Further, the base steels of S19 to S21 containing any one or more of Mg, Ca and REM in an appropriate amount were added to the base steel of S19 to S21. 28 to No. The sample of 31 is remarkably effective in suppressing the corrosion depth.

To these non-coated steels of S30 to S32 containing any one or more of Sn, Sb and Se in an appropriate amount, were added the surface layer of the present invention. 43 to No. The sample of 46 is more effective in suppressing corrosion depth.

As described above, all of the coating steels of the present invention exhibit excellent corrosion resistance of the coating film scratches under the seawater environment, and are suitable as structural members exposed to sea water or seaweed salt particles.

Claims (2)

A steel material for painting comprising a base steel material and a surface layer formed on the surface of the base steel material,
The steel according to claim 1, wherein the base steel comprises, by mass%, 0.04 to 0.30% of C, 0.05 to 1.0% of Si, 0.1 to 2.5% of Mn, 0.005 to 0.20% of Cu, 0.05 to 1.0% of Cu, 0.05 to 1.0% of Cr, 0.001 to 0.015% of N and 0.005 to 0.1% of Ti and 0.005 to 0.1% of Nb, And the remainder being Fe and inevitable impurities,
The surface layer preferably contains 0.3 to 20.0 g / m ² of Cr, 0.3 to 20.0 g / m ² of Ni, and 0.3 to 20.0 g / m ² of Cr, in addition to ²⁰ to 200 g / m ^{2 of} Zn and 0.3 to 20.0 g / A steel material for painting which is excellent in corrosion resistance, which comprises one or two of them. The method according to claim 1,
The steel according to claim 1, wherein the base steel comprises, by mass%, 0.01 to 6.0% of Ni, 0.01 to 5.0% of Co, 0.01 to 2.0% of Mo, 0.01 to 2.0% of W, 0.0005 to 0.01% of Mg, 0.0005 to 0.01% 0.001 to 0.2%, S: 0.001 to 0.2%, B: more than 0% to 0.01%, V: more than 0% and not more than 0.1%, Zr: 0 to 0.001%, REM: 0.0005 to 0.01%, Sn: 0.001 to 0.2% 0.1% or more, and Zn: 0% or more and 0.1% or less.