KR20150080014A - Surface-treated hot-dipped steel material - Google Patents

Abstract

This surface-treated hot-dip coated steel material has a steel material and a coating on the surface of the steel material, and the coating has a coating layer and a coating film containing an organic resin on the surface of the coating layer, Wherein the plating layer contains Al, Zn, Si, and Mg as constituent elements, the Al content is 25 to 75 mass%, the Mg content is 0.1 to 10 mass%, and the plating layer contains 0.2 to 15 volume% of the Si- Wherein the mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plating layer is 3% or more and 100% or less, and the organic resin is a silane coupling agent, a crosslinkable zirconium compound, a crosslinkable titanium compound, A compound, and an amino resin.

Description

[0001] SURFACE-TREATED HOT-DIPPED STEEL MATERIAL [0002]

The present invention relates to a surface-treated hot-rolled steel material.

The present application claims priority based on Japanese Patent Application No. 2011-182916 filed on August 24, 2011, the contents of which are incorporated herein by reference.

BACKGROUND ART Conventionally, molten Zn-Al-based plated steel has been widely used for applications such as building materials, automobile materials, and materials for home appliances. Among them, high aluminum (25 to 75 mass%) · zinc alloy plated steel sheet typified by 55% aluminum-zinc alloy plated steel plate [Galvarum Steel Plate (registered trademark)] has excellent corrosion resistance as compared with ordinary hot dip galvanized steel plate , Demand continues to expand. In recent years, in particular, in response to a request for improvement of corrosion resistance and workability of a single layer against construction materials, improvement in corrosion resistance and the like of a molten Zn-Al based plated steel material by adding Mg or the like to the plated layer has been attempted (see Patent Documents 1 to 3) 4).

However, in the case of a high-aluminum-zinc alloy plated steel sheet containing Mg, wrinkles are likely to occur on the surface of the plating layer, resulting in deterioration of the surface appearance. In addition, when the plating layer is chemically treated to form the chemical conversion treatment layer, or the coating layer is formed by such a wrinkle, a steep ridge is generated on the surface of the plating layer. In the case where the chemical conversion treatment layer or the coating layer The thickness tends to become uneven. As a result, there is a problem that the improvement of the corrosion resistance of the coated steel sheet due to painting or the like is not sufficiently achieved.

For example, Patent Document 1 discloses a method for producing a copper alloy having a surface of a molten plated layer containing 3 to 13% by mass of Si, 2 to 8% of Mg and 2 to 10% of Zn and a remaining amount of Al and inevitable impurities Al-Si-Mg-Zn based molten Al-base coated steel sheet. In Patent Document 1, the molten plated layer also contains 0.002 to 0.08% of Be and 0 to 0.1% of Sr, or 3 to 13% of Si, 2 to 8% of Mg, 2 to 10% of Zn, and 0.003 , 0 to 0.1% of Sr, 3 to 13% of Si, 2 to 8% of Mg, 2 to 10% of Zn, 0 to 0.003% of Be and 0.07 to 1.7% of Sr Or 3 to 13% of Si, 2 to 8% of Mg, 2 to 10% of Zn, 0 to 0.003% of Be and 0.1 to 1.0% of Sr, or 3 to 13% Or more of Zn, 2 to 10% of Zn, 0.003 to 0.08% of Be, 0.1 to 1.7% of Sr, 3 to 13% of Si, 2 to 8% of Mg, 2 to 10% of Zn, Of 0.003 to 0.05% and Sr of 0.1 to 1.0%.

In the technique disclosed in Patent Document 1, the corrosion resistance of the hot-dip coated steel material is improved by adding Mg to the plated layer, but wrinkles are likely to occur in the plated layer due to the addition of Mg. Patent Document 1 also discloses that oxidation of Mg is suppressed by adding Sr or Be to the plating layer, and as a result, wrinkles are suppressed. However, suppression of wrinkles is not sufficient.

It is difficult to sufficiently remove the wrinkles formed on the plated layer by the temper rolling treatment and the like, and the appearance of the hot-dip coated steel material has been deteriorated.

In addition, the conventional high aluminum (25 to 75 mass%) -zinc alloy plated steel sheet is excellent in durability (corrosion rate of the plated layer) and resistance to rusting (resistance against red rust generated from the steel plate) The rust resistance and the coating film expansion property of the cut end face portion are improved. However, the rust resistance of the plating layer (the ability to suppress the deterioration of the appearance due to the corrosion of the plating layer due to the generation of white rust) There is no consideration for the point of scratching, scratch resistance, and contamination resistance.

Japanese Patent Laid-Open No. 11-279735 Japanese Patent No. 3718479 International Publication No. 2008/025066 pamphlet Japanese Patent Application Laid-Open No. 2007-284718

The present invention has been made in view of the above-mentioned reasons. It is an object of the present invention to provide a surface-treated hot-rolled steel material having a favorable outer appearance with good whiteness resistance, scratch resistance and stain resistance of a machined portion, and no bad appearance due to a plating layer.

The inventors of the present invention investigated the problem of deterioration of the appearance of the plating layer as follows. Since Mg is an element that is easily oxidized as compared with other elements constituting the plating layer during the hot dip treatment using a hot dip galvanizing bath containing Mg, Mg reacts with oxygen in the atmosphere in the surface layer of the hot- Whereby Mg-based oxides are produced. Along with this, Mg is concentrated in the surface layer of the molten plated metal, and the formation of the Mg-based oxide film (the film composed of the oxide of the metal including Mg) is accelerated in the surface layer of the molten plated metal. In the process of cooling and solidifying the molten plated metal, before the solidification of the molten plated metal is completed, the Mg-based oxide film is formed, resulting in a difference in fluidity between the surface layer and the interior of the molten plated metal. As a result, even if the inside of the molten plated metal flows, the Mg-based oxide film on the surface layer does not follow, and as a result, wrinkles and sagging are thought to occur.

Therefore, the inventors of the present invention have found a means for suppressing the deterioration of appearance such as wrinkles and sagging by intensive research to suppress the difference in flowability in the molten plated metal during the above-mentioned hot-dip plating treatment.

On the other hand, the surface treatment of a hot-dip coating material capable of suppressing the deterioration of the process portion corrosion resistance caused by the deterioration of the processability caused thereby and the surface treatment of the hot dip galvanizing material caused by the Zn or Mg sacrificial corrosion- As a result of intensive research on the surface treatment of a hot-dip coating material which is capable of suppressing the occurrence of white rust which is likely to occur in the part subjected to processing and which can maintain a beautiful appearance over a long period of time and also has excellent scratch resistance and stain resistance, .

That is, the gist of the present invention will be described together with the preferred embodiments as follows.

(1) The surface-treated hot-rolled steel material according to the first aspect of the present invention comprises a steel material and a coating on the surface of the steel material, wherein the coating is formed on the surface of the plating layer, Wherein the plating layer contains Al, Zn, Si and Mg as constituent elements, the Al content is 25 to 75 mass%, the Mg content is 0.1 to 10 mass%, and the plating layer is 0.2 Wherein the mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plating layer is 3% or more and 100% or less, and the organic resin is a silane coupling agent, a crosslinking agent A crosslinked titanium compound, an epoxy compound, and an amino resin.

(2) The surface-treated hot-rolled steel sheet according to (1) above, in an outermost layer at a depth of 50 nm from the surface of the plating layer, in any region having a size of 4 mm in diameter and a depth of 50 nm, May be 0 mass% or more and less than 60 mass%.

(3) In the surface-treated hot-rolled steel material according to (1) or (2), the plating layer may further contain 0.02 to 1.0% by mass of Cr as a constituent element.

(4) In the surface-treated hot-rolled steel material according to any one of (1) to (3), the thickness of the coating film may be 0.1 to 10 m.

(5) The surface-treated hot-rolled steel material according to any one of (1) to (4) above may further contain the above-mentioned coated silica particles.

(6) The surface-treated hot-rolled steel material according to (5) above may have a solid mass ratio A / B of 2 to 20 with the organic resin as A and the silica particles as B.

(7) The surface-treated hot-rolled steel material according to (5) or (6), wherein the silica particles contain spherical silica particles having an average particle diameter of 5 to 20 nm and spherical silica particles having an average particle diameter of 0.08 to 2 do.

(8) The surface-treated hot-rolled steel material according to any one of the above items (1) to (7) may further contain the coating film lubricant.

(9) The surface-treated hot-rolled steel material according to any one of the above items (1) to (8) may further contain the above coating film phosphoric acid compound.

(10) The surface-treated hot-rolled steel material according to any one of (1) to (9) above may further contain the above-mentioned coating color pigment.

(11) The surface-treated hot-rolled steel material described in any one of (1) to (10) above may have a base treatment layer containing a component originating from an organic resin and a silane coupling agent in the lower layer of the coating film.

(12) The surface-treated hot-rolled steel material according to any one of (1) to (11), wherein the organic resin and the plating layer are made of a silane coupling agent, a crosslinkable zirconium compound, a crosslinkable titanium compound, And may be crosslinked by at least one kind selected from resins.

According to the embodiments described in the above items (1) to (12), it is possible to provide a surface-treated hot-dip galvanized steel sheet, which is excellent in resistance to scratching, scratch resistance and stain resistance of a machined portion, Steel is provided.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic view showing an example of a hot-dip plating apparatus in an embodiment of the present invention. FIG.
Fig. 2 is a schematic view of a part showing another example of the above-mentioned hot-dip coating processing apparatus.
Fig. 3A is a schematic diagram showing an example of a heating apparatus used in overexposure treatment in the embodiment of the present invention. Fig.
Fig. 3B is a schematic view showing an example of a warming container used in the overflow treatment in the embodiment of the present invention. Fig.
Fig. 4A is an image obtained by photographing the cut surface of the hot-dip coated steel sheet obtained at the level M5 of the embodiment by an electron microscope. Fig.
4B is a graph showing an elemental analysis result of the Si-Mg phase at the level M5 of the embodiment.
FIG. 5A is a graph showing the results of the depth direction analysis of the plating layer by the glow discharge emission spectrometer with respect to the level M5 of the embodiment. FIG.
FIG. 5B is a graph showing the results of the depth direction analysis of the plating layer by the glow discharge emission spectrometer with respect to the level M50 of the embodiment. FIG.
Fig. 6 is an image obtained by photographing the surface of the plated layer in the molten plated steel sheet obtained at the level M5 of the embodiment by an electron microscope. Fig.
7A shows a photograph of the appearance of the plating layer with respect to the level M5 of the embodiment.
Fig. 7B shows a photograph of the appearance of the plating layer with respect to the level M10 of the embodiment.
8A shows an optical microscope photograph of the appearance of the plating layer with respect to the level M62 of the embodiment.
8B shows an optical microscope photograph of the appearance of the plating layer with respect to the level M5 of the embodiment.
Fig. 9 shows a photograph of the appearance of the plating layer with respect to the level M50 of the embodiment. Fig.
Fig. 10 is a graph showing the result of evaluation of the overfitting treatment on the level M5 of the embodiment of the molten plated steel sheet. Fig.
11A is an example of a schematic diagram showing a layer structure of a surface-treated hot-rolled steel material in an embodiment of the present invention.
Fig. 11B is a schematic diagram showing a layer structure of the surface-treated hot-rolled steel material in the embodiment of the present invention. Fig.
11C is an example of a schematic diagram showing the layer structure of the surface-treated hot-rolled steel material in the embodiment of the present invention.
11D is an example of a schematic diagram showing the layer structure of the surface-treated hot-rolled steel material in the embodiment of the present invention.
11E is an example of a schematic diagram showing the layer structure of the surface-treated hot-rolled steel material in the embodiment of the present invention.
11F is an example of a schematic diagram showing a layer structure of a surface-treated hot-rolled steel material in an embodiment of the present invention.
11G is an example of a schematic diagram showing the layer structure of the surface-treated hot-rolled steel material in the embodiment of the present invention.
11H is an example of a schematic diagram showing the layer structure of the surface-treated hot-rolled steel material in the embodiment of the present invention.

Hereinafter, the present invention will be described in detail.

[Surface-treated hot-dip galvanized steel]

The surface-treated hot-rolled steel material according to the present embodiment has a steel material 1 and a coating 28 on the surface of the steel material 1, as shown in Figs. 11A to 11H. This coating 28 is composed of an aluminum-zinc alloy plating layer 23 (hereinafter referred to as "plating layer 23") and a coating film 23 containing an organic resin on the surface of the plating layer 23 (24). That is, the plating layer 23 is plated on the surface of the steel material 1, and the upper layer is coated with a coating film 24 composed of organic resin as a film component. As the steel material 1, various members such as a thin steel plate, a post-steel plate, a section steel, a steel pipe, and a steel wire can be cited. That is, the shape of the steel material 1 is not particularly limited. The plating layer 23 is formed by a hot-dip plating process.

[Plating layer (23)]

The plating layer 23 includes Al, Zn, Si, and Mg as constituent elements. The Al content in the plating layer 23 is 25 to 75 mass%. The Mg content is 0.1 to 10 mass%. As a result, the corrosion resistance of the surface of the plated layer 23 is improved particularly by Al, and the edge creep on the cut end face of the molten plated steel, in particular, is suppressed by the action of the sacrifice by Zn, Corrosion resistance is imparted. Further, excessive alloying of Al in the plated layer 23 and the steel material 1 is suppressed by Si, and the alloy layer 25 (described later) interposed between the plated layer 23 and the steel material 1 prevents the molten- Is prevented from being impaired. Further, the plating layer 23 contains Mg, which is a metal that is more active than Zn, so that the sacrificial action of the plating layer 23 is strengthened, and the corrosion resistance of the molten plated steel is further improved.

The plating layer 23 contains 0.2 to 15% by volume of the Si-Mg phase. The Si-Mg phase is an image composed of an intermetallic compound of Si and Mg, and is dispersed and present in the plating layer 23.

The volume ratio of the Si-Mg phase in the plating layer 23 is equal to the area ratio of the Si-Mg phase in the cut surface when the plating layer 23 is cut in the thickness direction. The Si-Mg phase on the cut surface of the plating layer 23 can be clearly identified by an electron microscope observation. Therefore, by measuring the area ratio of the Si-Mg phase on the cut surface, the volume ratio of the Si-Mg phase in the plating layer 23 can be indirectly measured.

The higher the volume ratio of the Si-Mg phase in the plating layer 23, the more the generation of wrinkles in the plating layer 23 is suppressed. This is because in the process of solidifying the plated layer 23 by cooling the molten plated metal during the production of the plated steel material, the Si-Mg phase is precipitated in the molten plated metal before the plated metal is completely solidified, -Mg phase suppresses the flow of the molten plated metal. The volume ratio of the Si-Mg phase is more preferably 0.2 to 10%, and more preferably 0.4 to 5%.

The plating layer 23 is composed of a Si-Mg phase and a phase containing other Zn and Al. The phase containing Zn and Al is mainly composed of an α-Al phase (dendrite structure) and a Zn-Al-Mg phase (interdendrite structure). The phase containing Zn and Al may be an image formed of Mg-Zn ₂ (Mg-Zn ₂ phase), an image made of Si (Si phase), or an Fe-Al intermetallic compound depending on the composition of the plating layer 23 (Fe-Al phase), and the like. The phase containing Zn and Al occupies a portion of the plating layer 23 excluding the Si-Mg phase. Therefore, the volume ratio of the phase containing Zn and Al in the plating layer 23 is preferably in the range of 99.8 to 85%, more preferably in the range of 99.8 to 90%, further preferably in the range of 99.6 to 95%.

The mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plating layer 23 is 3 mass% or more and 100 mass% or less. Mg not contained in the Si-Mg phase is contained in the phase containing Zn and Al. In the phase containing Zn and Al, Mg or the like it is contained in the Mg-containing oxide film formed on the plating surface of the of the α-phase of the Al, Zn-Al-Mg-phase process, the Mg-Zn _2. When Mg is contained in the? -Al phase, Mg solidifies in the? -Al phase.

The mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plating layer 23 can be calculated after considering that the Si-Mg phase has a stoichiometric composition of Mg ₂ Si. Actually, the Si-Mg phase may contain a small amount of elements other than Si and Mg such as Al, Zn, Cr, and Fe, and the composition ratio of Si and Mg in the Si-Mg phase may vary slightly from the stoichiometric composition However, considering these factors, it is very difficult to strictly determine the amount of Mg in the Si-Mg phase. Therefore, in the present invention, when the mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plating layer 23 is determined, it is considered that the Si-Mg phase has a stoichiometric composition of Mg ₂ Si .

The mass ratio R of Mg in the Si-Mg phase to the total amount of Mg in the plating layer 23 is calculated by the following equation (1).

R is the mass ratio (mass%) of Mg in the Si-Mg phase to the total amount of Mg in the plating layer 23 and AMg is the amount of Mg in the Si-Mg phase in the plating layer 23 per unit area in plan view of the plating layer 23 M is the mass (g / m 2) of the plating layer 23 per unit area in plan view of the plating layer 23 and CMG is the content (mass%) of the total Mg in the plating layer 23 Respectively. Here, the mass M of the plating layer 23 per unit area of the plating layer 23 in plan view means the mass of the plating layer 23 attached per unit area on the surface of the steel sheet with reference to the surface of the steel sheet.

AMg is calculated from the following equation (2).

V ₂ represents the volume (m 3 / m 2) of the Si-Mg phase in the plating layer 23 per unit area in plan view of the plating layer 23. ρ ₂ represents the density of the Si-Mg phase, and its value is 1.94 × 10 ⁶ (g / m 3). ? represents the mass ratio of Mg contained in the Si-Mg phase, and the value is 0.63.

V ₂ is calculated from the following equation (3).

V ₁ represents the total volume (m 3 / m 2) of the plating layer 23 per unit area in plan view of the plating layer 23 and R ₂ represents the volume ratio (volume%) of Si-Mg in the plating layer 23.

V ₁ is calculated from the following equation (4).

ρ ₁ represents the density (g / m 3) of the entire plating layer 23. The value of rho ₁ is calculated by weighted averaging the density of the constituent elements of the plating layer 23 at room temperature based on the composition of the plating layer 23.

In the present embodiment, Mg in the plating layer 23 is included in the Si-Mg phase at a high ratio as described above. As a result, the amount of Mg present in the surface layer of the plating layer 23 is reduced, and thereby the formation of the Mg-based oxide film in the surface layer of the plating layer 23 is suppressed. Therefore, wrinkles of the plating layer 23 caused by the Mg-based oxide film are suppressed. As the ratio of Mg in the Si-Mg phase to the total amount of Mg is larger, the occurrence of wrinkles is suppressed. This ratio is more preferably 5 mass% or more, more preferably 20 mass% or more, and particularly preferably 50 mass% or more. The upper limit of the ratio of Mg in the Si-Mg phase to the total amount of Mg is not particularly limited, and this ratio may be 100% by mass.

In any region where the size is 4 mm in diameter (measured portion diameter) and the depth is 50 nm, the Mg content is 0 mass% to less than 60 mass% in the outermost layer at a depth of 50 nm from the surface of the plating layer 23 . The Mg content in the outermost layer of the plating layer 23 is measured by Glow Discharge-Optical Emission Spectroscopy (GD-OES). More specifically, as a more specific measuring method, the respective glow discharge intensities derived from the respective elements detected are converted into the mass ratio of the elements by converting them into coefficients obtained from measurement values of known or known standard samples, On the other hand, the grit luminescence time corresponding to the depth of 50 nm is determined by a standard sample, and the mass ratio in terms of the glow discharge intensity ratio of Mg is 0 mass% or more at any point up to the emission time obtained by the standard sample And less than 60% by mass.

The smaller the Mg content in the outermost layer of the plating layer 23, the wrinkles caused by the Mg-based oxide film are suppressed. This Mg content is more preferably less than 40% by mass, more preferably less than 20% by mass, more preferably less than 10% by mass in any region where the diameter of the outermost layer of the plating layer 23 is 4 mm and the depth is 50 nm. %.

It is preferable that the area ratio of the Si-Mg phase on the surface of the plating layer 23 is 30% or less. When the Si-Mg phase is present in the plating layer 23, the Si-Mg phase is easily formed thinly on the surface of the plating layer 23 and the appearance of the plating layer 23 is changed when the area ratio of the Si-Mg phase is large . When the state of distribution of the surface of the plating surface on the Si-Mg is uneven, unevenness of gloss is observed on the outer surface of the plating layer 23 by naked eyes. This glossy stain is a poor appearance called sagging. When the area ratio of the Si-Mg phase on the surface of the plating layer 23 is 30% or less, sagging is suppressed and the appearance of the plating layer 23 is improved. The presence of the Si-Mg phase on the surface of the plating layer 23 is also effective for maintaining the corrosion resistance of the plating layer 23 for a long period of time. When the precipitation of the Si-Mg phase on the surface of the plating layer 23 is suppressed, the deposition amount of the Si-Mg phase in the plating layer 23 relatively increases. As a result, the amount of Mg in the plating layer 23 is increased, whereby the action of sacrificing Mg in the plating layer 23 is exerted for a long period of time, whereby the high corrosion resistance of the plating layer 23 is maintained for a long period of time do. In order to improve the appearance of the plating layer 23 and maintain the corrosion resistance of the plating layer 23, the area ratio of the Si-Mg phase on the surface of the plating layer 23 is more preferably 20% or less, more preferably 10% , And particularly preferably 5% or less.

The content of Mg in the plating layer 23 is in the range of 0.1 to 10 mass% as described above. If the Mg content is less than 0.1 mass%, the corrosion resistance of the plating layer 23 is not sufficiently secured. When the content is more than 10% by mass, not only the function of improving the corrosion resistance is saturated but also dross is easily generated in the hot-dip galvanizing bath 2 at the time of producing the hot-dip galvanized steel. The content of Mg is further preferably 0.5% by mass or more, more preferably 1.0% by mass or more. The Mg content is particularly preferably 5.0 mass% or less, and more preferably 3.0 mass% or less. It is particularly preferable that the content of Mg is in the range of 1.0 to 3.0 mass%.

The content of Al in the plating layer 23 is in the range of 25 to 75 mass%. When the content is 25 mass% or more, the Zn content in the plating layer 23 is not excessive, and the corrosion resistance on the surface of the plating layer 23 is sufficiently secured. When the content is 75 mass% or less, the effect of the sacrificial system by Zn is sufficiently exhibited, and the hardening of the plating layer 23 is suppressed, so that the workability of the hot-dip galvanized steel is improved. The content of Al is not more than 75 mass% from the viewpoint of further suppressing the wrinkling of the plating layer 23 by preventing the flowability of the molten plated metal from being excessively lowered during the production of the hot-dip galvanized steel. The content of Al is particularly preferably 45 mass% or more. The content of Al is particularly preferably 65 mass% or less. The content of Al is particularly preferably in the range of 45 to 65% by mass.

The content of Si in the plating layer 23 is preferably in the range of 0.5 to 10 mass% with respect to the content of Al. If the content of Si relative to Al is 0.5 mass% or more, excessive alloying of Al and the steel material 1 in the plating layer 23 is sufficiently suppressed. When the content is more than 10 mass%, not only the action of Si is saturated but also dross is easily generated in the hot-dip galvanizing bath 2 during the production of the hot-dip galvanized steel. The Si content is particularly preferably at least 1.0% by mass. The Si content is particularly preferably 5.0 mass% or less. It is particularly preferable that the content of Si is in the range of 1.0 to 5.0 mass%.

It is also preferable that the mass ratio of Si: Mg in the plating layer 23 is in the range of 100: 50 to 100: 300. In this case, the formation of the Si-Mg layer in the plating layer 23 is particularly promoted, and generation of wrinkles in the plating layer 23 is further suppressed. The mass ratio of Si: Mg is also preferably 100: 70 to 100: 250, more preferably 100: 100 to 100: 200.

The plating layer 23 preferably further contains Cr as a constituent element. In this case, the growth of the Si-Mg phase in the plating layer 23 is promoted by Cr to increase the volume ratio of the Si-Mg phase in the plating layer 23, and the Si-Mg phase to the total amount of Mg in the plating layer 23 The ratio of Mg is increased. As a result, the wrinkles of the plating layer 23 are further suppressed. The content of Cr in the plating layer 23 is preferably in the range of 0.02 to 1.0 mass%. If the content of Cr in the plating layer 23 is more than 1.0% by mass, not only the above-mentioned action is saturated but also dross is easily generated in the hot-dip galvanizing bath 2 during production of the hot-dip galvanized steel. The content of Cr is particularly preferably 0.05 mass% or more. The content of Cr is particularly preferably 0.5 mass% or less. The content of Cr is more preferably in the range of 0.07 to 0.2 mass%.

When the plating layer 23 contains Cr, it is preferable that the content of Cr in the outermost layer at a depth of 50 nm from the surface of the plating layer 23 is 100 to 500 mass ppm. In this case, the corrosion resistance of the plating layer 23 is further improved. This is presumably because, if Cr is present in the outermost layer, a passive film is formed on the plating layer 23, thereby suppressing the anode dissolution of the plating layer 23. The content of Cr is further preferably 150 to 450 mass ppm, more preferably 200 to 400 mass ppm.

It is preferable that an alloy layer 25 containing Al and Cr is interposed between the plating layer 23 and the steel material 1. [ In the embodiment of the present invention, the alloy layer 25 is regarded as a layer different from the plating layer 23. The alloy layer 25 may contain various metal elements such as Mn, Fe, Co, Ni, Cu, Zn, and Sn in addition to Al and Cr as constituent elements. When the alloy layer 25 is present, the growth of the Si-Mg phase in the plating layer 23 is promoted by Cr in the alloy layer 25 to increase the volume ratio of the Si-Mg phase in the plating layer 23, The ratio of Mg in the Si-Mg phase to the total amount of Mg in the Mg-free layer 23 becomes high. As a result, wrinkling or sagging of the plating layer 23 is further suppressed. Particularly, the ratio of the content of Cr in the alloy layer 25 to the content of Cr in the plating layer 23 is preferably 2 to 50. In this case, since the growth of the Si-Mg phase is promoted in the vicinity of the alloy layer 25 in the plating layer 23, the area ratio of the Si-Mg phase on the surface of the plating layer 23 is lowered, The corrosion resistance of the plating layer 23 is maintained for a longer period of time. The ratio of the content of Cr in the alloy layer 25 to the content of Cr in the plating layer 23 is preferably 3 to 40, more preferably 4 to 25. The amount of Cr in the alloy layer 25 can be derived by measuring the cross section of the plating layer 23 using an energy dispersive X-ray analyzer (EDS).

The thickness of the alloy layer 25 is preferably in the range of 0.05 to 5 mu m. When the thickness is 0.05 탆 or more, the above-described action by the alloy layer 25 is effectively exhibited. If the thickness is 5 占 퐉 or less, the alloy layer 25 makes it difficult to impair the workability of the hot-dip galvanized steel.

When the plating layer 23 contains Cr, the corrosion resistance after the processing of the plating layer 23 is also improved. The reason is thought to be as follows. When the plating layer 23 is subjected to severe processing, cracks may be generated in the plating layer 23 in some cases. At this time, water or oxygen enters the plating layer 23 through the crack, and the alloy in the plating layer 23 is directly exposed to the corrosive factor. However, the Cr present in the surface layer of the plating layer 23 and the Cr present in the alloy layer 25 suppress the corrosion reaction of the plating layer 23, thereby suppressing the expansion of corrosion starting from the crack. In order that the corrosion resistance after the processing of the plating layer 23 is particularly improved, the content of Cr in the outermost layer at a depth of 50 nm from the surface of the plating layer 23 is preferably 300 mass ppm or more, more preferably 200 to 400 mass ppm . The ratio of the content of Cr in the alloy layer 25 to the content of Cr in the plating layer 23 is preferably 20 or more and particularly preferably 20 to 30 in order to particularly improve the corrosion resistance after processing of the plating layer 23 .

The plating layer 23 preferably further contains Sr as a constituent element. In this case, the formation of the Si-Mg layer in the plating layer 23 is particularly promoted by Sr. The formation of the Mg-based oxide film in the surface layer of the plating layer 23 is suppressed by Sr. This is presumably because the oxide film of Sr is preferentially formed more preferentially than the Mg-based oxide film, and formation of the Mg-based oxide film is inhibited. As a result, the generation of wrinkles in the plating layer 23 is further suppressed. The content of Sr in the plating layer 23 is preferably in the range of 1 to 1000 mass ppm. If the content of Sr is less than 1 mass ppm, the above-mentioned action will not be exerted. If the content is more than 1000 mass ppm, the action of Sr will be saturated. In addition, Dross is liable to occur. The content of Sr is particularly preferably 5 mass ppm or more. The content of Sr is particularly preferably 500 mass ppm or less, and more preferably 300 mass ppm or less. The content of Sr is more preferably in the range of 20 to 50 mass ppm.

The plating layer 23 preferably further contains Fe as a constituent element. In this case, the formation of the Si-Mg layer in the plating layer 23 is particularly promoted by Fe. Further, Fe contributes to miniaturization of the microstructure and the sequin structure of the plating layer 23, whereby the appearance and workability of the plating layer 23 are improved. The content of Fe in the plating layer 23 is preferably in the range of 0.1 to 0.6 mass%. If the content of Fe is less than 0.1% by mass, the microstructure and the sequin structure of the plating layer 23 are coarsened, and the appearance of the plating layer 23 is deteriorated and the processability is deteriorated. If the content is more than 0.6% by mass, the sequins of the plating layer 23 become very fine or disappear, so that the outer appearance can not be improved due to the sequins. In addition, during the production of the hot-dip galvanized steel, Dross is easily generated and the appearance of the plating layer 23 is further deteriorated. The content of Fe is particularly preferably 0.2 mass% or more. The Fe content is particularly preferably 0.5 mass% or less. It is particularly preferable that the content of Fe is in the range of 0.2 to 0.5 mass%. After plating, the flower pattern appearing on the surface of the steel plate 1 is called a sequin.

The plating layer 23 may further contain an element selected from alkaline earth elements, Sc, Y, lanthanoid elements, Ti and B as constituent elements.

The alkaline earth elements (Be, Ca, Ba, Ra), Sc, Y and lanthanoid elements (La, Ce, Pr, Nd, Pm, Sm, Eu and the like) exert the same effect as Sr. The total content of these components in the plating layer 23 is preferably 1.0 mass% or less by mass.

If the plating layer 23 contains at least one of Ti and B, the α-Al phase (dendritic structure) of the plating layer 23 becomes finer and the sequins become finer. As a result, the appearance of the plating layer 23 . Further, generation of wrinkles in the plating layer 23 is further suppressed by at least one of Ti and B. This is because the Si-Mg phase is finely smoothed by the action of Ti and B, and the finely divided Si-Mg phase effectively suppresses the flow of the molten plated metal in the process of solidifying the molten plated metal to form the plated layer 23 . Further, due to the miniaturization of the plating structure, concentration of stress in the plating layer 23 at the time of bending is relaxed, generation of large cracks is suppressed, and the bending workability of the plating layer 23 is further improved. In order for this action to be exhibited, it is preferable that the total content of Ti and B in the hot-dip galvanizing bath 2 is in the range of 0.0005 to 0.1 mass% by mass. The total content of Ti and B is particularly preferably 0.001% by mass or more. The total content of Ti and B is particularly preferably 0.05% by mass or less. It is particularly preferable that the total content of Ti and B is in the range of 0.001 to 0.05 mass%.

Zn occupies the remainder portion excluding the constituent elements other than Zn out of the constituent elements of the plating layer 23.

It is preferable that the plating layer 23 does not contain any other element as the constituent element. In particular, the plating layer 23 contains only Al, Zn, Si, Mg, Cr, Sr and Fe as constituent elements, or Al, Zn, Si, Mg, Cr, Sr and Fe and alkaline earth elements Sc, Y , Lanthanoid element, Ti and B as constituent elements.

However, of course, the plating layer 23 may contain inevitable impurities such as Pb, Cd, Cu, and Mn. It is preferable that the content of the inevitable impurities is as small as possible, and in particular, the total content of the inevitable impurities is preferably not more than 1% by mass with respect to the plating layer 23.

[Coating film (24)]

The coating film 24 coated on the upper layer of the plating layer 23 is formed by using an organic resin as an essential film forming component and forming an organic resin or an organic resin and the aluminum-zinc alloy plating layer 23 in the form of a silane coupling agent, a crosslinkable zirconium compound, Is crosslinked by at least one member selected from the group consisting of a titanium compound, an epoxy compound and an amino resin. The aluminum-zinc alloy plating layer 23 contains Al at a relatively high concentration and also contains Mg. Thereby, the surface of the plating layer 23 is covered with the Mg-based oxide film or the Al-based oxide film. In order to improve the corrosion resistance and scratch resistance, it is important to improve adhesion between the oxide film and the coating film. As a result of intensive investigations, the inventors of the present invention have found that an organic resin is used as an essential film-forming component, and the organic resin or the organic resin and the aluminum-zinc alloy plating layer 23 are coated with a silane coupling agent, a crosslinkable zirconium compound, An epoxy compound and an amino resin to form a coating film which is crosslinked by at least one kind selected from the group consisting of an epoxy compound and an amino resin is effective for maximizing adhesion between the oxide film and a coating film. Further, by forming such a coating film, it is possible to increase the barrier property to the corrosion factor (water, oxygen, etc.) of the coating film, to slow the progress of corrosion, and to obtain knowledge that the corrosion resistance is remarkably improved. Further, the coating film 24 having an organic resin as a film-forming component also has a characteristic of being excellent in contamination resistance. Here, the stain resistance refers to a performance that is less noticeable even when oil-based stains such as fingerprints adhere and relatively easily removes stains.

The plating layer 23 of the present invention contains 25 to 75 mass% of Al and 0.2 to 15 volume% of a Si-Mg phase. As the volume ratio of the Si-Mg phase in the plating layer 23 is higher as described above, the generation of wrinkles in the plating layer 23 is suppressed, while the Si-Mg phase is hard and fragile. 23), cracks tend to occur at the time of processing. Even if cracks are generated, the sacrificial mode action of Zn and Mg in the plating layer 23 is exerted, so that the anti-rust property is not impaired. However, back rust, which is a corrosion product of Zn and Mg, is likely to be generated in the processed region. Wherein the organic resin or the organic resin and the aluminum-zinc alloy plating layer (23) are made of at least one material selected from a silane coupling agent, a crosslinkable zirconium compound, a crosslinkable titanium compound, an epoxy compound and an amino resin The crosslinked coating film 24 also has a characteristic of being excellent in flexibility and sliding property with respect to a relatively hard material such as a press mold. In other words, in addition to excellent followability to the deformation (elongation and compression) of the steel material 1 generated when the hot-dip coated steel material is machined, it has an effect of reducing the frictional resistance to be applied upon contact with the press mold. The surface-treated hot-rolled steel sheet coated with the coating film 24 is uniformly coated with the coating film 24 without being damaged by cracks or scratches, And the stain resistance can be maintained. In addition, the excellent scratch resistance of the coating film 24 as described above is also excellent in scratch resistance. Here, the fact that the coating film 24 is crosslinked can be verified by measurement of a Fourier transform infrared spectrophotometer (FT-IR), for example.

Hereinafter, the structure of the coating film 24 will be described.

≪ About the thickness of the coating film 24 >

The thickness of the coating film 24 is not particularly limited, but is preferably 0.1 탆 or more and 10 탆 or less, more preferably 0.3 탆 or more and 7 탆 or less, further preferably 0.5 탆 or more and 5 탆 or less. If the thickness of the coating film 24 is less than 0.1 탆, sufficient corrosion resistance, scratch resistance and stain resistance may not be obtained. On the other hand, if the thickness of the coating film 24 is more than 10 mu m, it is economically disadvantageous. In addition, when the coating film 24 is formed of a water-based coating material, defects such as pin holes may occur, The appearance and performance as a product may not be obtained stably.

The thickness of the coating film 24 can be measured by observing a cross section of the coating film 24 or using an electronic film thickness measuring instrument or the like. Alternatively, the mass of the coating film 24 attached per unit area of the plated steel material may be calculated by dividing the specific gravity of the coating film 24 or the specific gravity after drying of the coating solution. The adhesion mass of the coating film 24 can be determined by calculating the mass difference between the coated steel before and after coating and by calculating the mass difference of the plated steel before and after peeling the coated film 24 after coating, And X-ray analysis to measure the abundance of an element which is known in advance in the coating film. The specific gravity of the coating film 24 or the specific gravity after drying of the coating solution can be measured by measuring the volume and mass of the separated coating film 24 and measuring the volume and mass after drying a suitable amount of the coating solution in the container , Or a method selected from a conventional method such as a method of calculating from the blending amount of the component of the coating film and the known specific gravity of each component.

Among the various measuring methods described above, even the coating film 24 having a different specific gravity can be easily measured with high accuracy. Therefore, as a method of measuring the thickness of the coating film 24, it is preferable to use the observation of the cross section of the coating film 24.

Although there is no particular limitation on the method of observing the coating film 24, there is a method in which a coated plated steel material is embedded in a room temperature drying type epoxy resin so that the vertical cross section of the coating film 24 can be seen, Observation using a FIB (focused ion beam) apparatus, a sample for observation having a thickness of 50 nm to 100 nm is cut out from the coated plated steel so that the vertical cross section of the coating film 24 can be seen, And observation with a TEM (transmission electron microscope).

≪ About organic resin &

The organic resin is not limited to a specific kind, and examples thereof include a polyester resin, a polyurethane resin, an epoxy resin, an acrylic resin, a polyolefin resin, or a modified product of these resins. Here, the denaturant refers to a resin obtained by reacting a reactive group (such as a monomer or a crosslinking agent) containing a functional group capable of reacting with the functional group in the structure with a reactive functional group contained in the structure of these resins. The organic resin may be a mixture of one or more kinds of organic resins (unmodified ones), or may be an organic resin obtained by modifying at least one other organic resin in the presence of at least one organic resin. One or more resins may be used in combination.

The polyester resin is not particularly limited, and for example, a polyester resin obtained by condensation polymerization of a polyester raw material comprising a polycarboxylic acid component and a polyol component can be used. The polyester resin thus obtained may be water-soluble by dissolving or dispersing it in water.

Examples of the polycarboxylic acid component include phthalic acid, phthalic anhydride, tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyltetrahalphthalic acid, methyltetrahydrophthalic anhydride, anhydrous hyaluronic acid, trimellitic acid , Maleic anhydride, maleic anhydride, fumaric acid, itaconic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, succinic anhydride, dicarboxylic acid, dodecenyl Succinic acid, dodecenylsuccinic anhydride, cyclohexane-1,4-dicarboxylic acid, and anhydrous anodic acid. As the polycarboxylic acid component, one of the above components may be used, or a plurality of these components may be used.

Examples of the polyol component include ethylene glycol, diethylene glycol, 1,3-propanediol, 1,2-propanediol, triethylene glycol, 2-methyl-1,3-propanediol, 2,2- Propane diol, 1,4-butanediol, 2-methyl-1,4-butanediol, 2-methyl- Butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, Hexane dimethanol, hydrogenated bisphenol A, dimer diol, trimethylol ethane, trimethylol propane, glycerin, pentaerythritol and the like. As the polyol component, one of the components may be used, or a plurality of the components may be used.

The polyurethane resin is not particularly limited, and examples thereof include those obtained by reacting a polyol compound with a polyisocyanate compound, and then subjecting the resultant mixture to a re-stretch forming agent. The polyol compound is not particularly limited as long as it is a compound containing two or more hydroxyl groups per molecule, and examples thereof include ethylene glycol, propylene glycol, diethylene glycol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, Polyether polyols such as glycerin, trimethylol ethane, trimethylol propane, polycarbonate polyol, polyester polyol and bisphenol hydroxypropyl ether; polyester amide polyols; acrylic polyols; polyurethane polyols; and mixtures thereof. The polyisocyanate compound is not particularly limited as long as it is a compound containing two or more isocyanate groups per molecule, and examples thereof include aliphatic isocyanates such as hexamethylene diisocyanate (HDI) and alicyclic diisocyanates such as isophorone diisocyanate (IPDI) Aromatic diisocyanates such as isocyanate and tolylene diisocyanate (TDI), aromatic aliphatic diisocyanates such as diphenylmethane diisocyanate (MDI), and mixtures thereof. The above-described chain extender is not particularly limited as long as it is a compound containing at least one active hydrogen in the molecule, and examples thereof include ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine, dipropylenetriamine, Aliphatic polyamines such as tetramethylenepentamine and tetraethylenepentamine, aromatic polyamines such as tolylene diamine, xylylenediamine and diaminodiphenylmethane, diaminocyclohexylmethane, piperazine, 2,5-dimethylpiperazine, isophoronediamine , Hydrazines such as hydrazine, succinic dihydrazide, adipic acid dihydrazide and phthalic acid dihydrazide, and hydrazines such as hydroxyethyldiethylenetriamine, 2- [(2-aminoethyl) amino] ethanol, And alkanolamines such as 3-aminopropane diol. These compounds may be used alone or in combination of two or more.

Examples of the epoxy resin include, but are not limited to, bisphenol A type epoxy resins, bisphenol F type epoxy resins, hydrogenated bisphenol A type epoxy resins, hydrogenated bisphenol F type epoxy resins, resole type epoxy resins, novolak type epoxy resins An epoxy resin such as a resin can be used. Examples of the epoxy resin include epoxy resins obtained by emulsifying these epoxy resins with a surfactant and then hydrolyzing these epoxy resins with amine compounds such as diethanolamine and N-methylethanolamine, and then neutralizing them with an organic acid or inorganic acid Or a resin obtained by radical polymerization of a high-acid value acrylic resin in the presence of these epoxy resins, followed by neutralization with ammonia or an amine compound, and so on.

The acrylic resin is not particularly limited and includes, for example, alkyl (meth) acrylates such as ethyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, Hydroxyalkyl (meth) acrylate such as hydroxyethyl (meth) acrylate, or a (meth) acrylic acid ester such as alkoxysilane (meth) acrylate is reacted with (meth) acrylic acid in the presence of a radical initiator And those obtained by polymerization. The polymerization initiator is not particularly limited and azo compounds such as persulfates such as potassium persulfate and ammonium persulfate, azobiscyano valeric acid and azobisisobutyronitrile can be used. Here, "(meth) acrylate" means acrylate and methacrylate, and "(meth) acrylic acid" means acrylic acid and methacrylic acid.

The polyolefin resin is not particularly limited and examples thereof include radical polymerization of unsaturated carboxylic acids such as ethylene and methacrylic acid, acrylic acid, maleic acid, fumaric acid, itaconic acid and crotonic acid at high temperature and high pressure, , Basic metal compounds such as KOH, NaOH, and LiOH, or ammonia or amine compounds containing the metal compounds, and the like.

The organic resin preferably contains a resin containing at least one functional group selected from an ester group, a urethane group and a urea group in the structure in order to improve the corrosion resistance and scratch resistance as a surface-treated hot-rolled steel Do. In order to improve the corrosion resistance of the surface-treated hot-rolled steel, it is preferable that the coated film 24 uniformly covers the plated steel material as a base material without damages such as cracks (excellent workability) But it is important to suppress the permeability of the corrosion factor. On the other hand, in order to improve the scratch resistance as a surface-treated hot-rolled steel material, it is preferable that the hardness of the coating film 24 and the adhesion strength with the plated steel material (base treatment layer 27 in the case of the base treatment layer 27 described later) High is important. In order to realize such a coating film 24, it is preferable to use an organic resin containing a specific resin structure as a film forming component. More specifically, a functional group having a specific cohesive energy as described above is introduced into the resin structure of the organic resin Both the elongation and the strength of the coating film 24 can be increased to a higher dimension and the adhesion and the corrosion resistance can be increased.

The resin containing the ester group, the urethane group and the urea group in the resin structure includes, but not limited to, a polyester resin containing an ester group, a polyurethane resin containing a urethane group, a urethane And polyurethane resins containing both of them. These may be used alone or in combination of two or more. For example, those containing an ester group, a urethane group and a urea group obtained by mixing a polyester resin containing an ester group and a polyurethane resin containing both urethane groups and urea groups may be used as an organic resin .

The content of the organic resin containing at least one functional group selected from an ester group, a urethane group and a urea group in the resin structure is preferably 60% by mass or more and 100% by mass or less in the organic resin, more preferably 80% Or more and 100 mass% or less. If it is less than 60% by mass, corrosion resistance and scratch resistance as a surface-treated hot-rolled steel material may not be compatible with each other.

≪ About silica particles >

It is preferable that the coating film 24 further contains silica particles. By containing the silica particles, the corrosion resistance and scratch resistance can be further improved. Particularly, in order to improve the scratch resistance, it is conceivable to make the coating film 24 hard. However, when the organic resin as the film forming component is hardened, the coating film 24 of the surface treated hot- There is a possibility that the corrosion resistance of the processed portion is lowered. On the other hand, the coating film 24 obtained by compounding silica particles relatively hard in an organic resin is less likely to lower workability as compared with a hardened organic resin and has an effect of improving the corrosion resistance even in the silica particles themselves, Can be made compatible at a high level.

Here, it is preferable that the organic resin is A and the silica particles are B, and the solid mass ratio A / B is 2 or more and 20 or less. If A / B is less than 2, corrosion resistance and stain resistance may be lowered. If A / B is more than 20, the effect of improving corrosion resistance and scratch resistance may not be obtained.

The kind of the silica particles is not particularly limited, and examples thereof include silica particles such as colloidal silica and fumed silica. Examples of commercially available products include commercially available products such as Snowtex O, Snowtex N, Snowtex C, Snowtex IPA-ST (manufactured by Nissan Chemical Industries), Adelite AT-20N, Adelite AT-20A (manufactured by Asahi Denka Kogyo Co., Ltd.) (Manufactured by Nippon Aerosil Co., Ltd.), a functional spherical silica HPS series (manufactured by Toagosei Co., Ltd.), and a Nipsil series (manufactured by Tosoh Silica Co., Ltd.).

Also, it is preferable that the silica particles contain spherical silica particles having an average particle diameter of 5 nm or more and 20 nm or less as the silica particles to improve the corrosion resistance. If the average particle diameter of the spherical silica particles is less than 5 nm, there may be a problem such as gelation of the coating composition for forming the coating film 24. When the average particle diameter exceeds 20 nm, the effect of improving the corrosion resistance is sufficient May not be obtained.

Further, it is preferable that the silica particles include both spherical silica particles having an average particle diameter of 5 nm or more and 20 nm or less and spherical silica particles having an average particle diameter of 0.08 to 2 m, both of which are high in both corrosion resistance and scratch resistance . If the average particle diameter of the spherical silica particles is less than 0.08 탆, the effect of improving the scratch resistance may not be sufficiently obtained, and if the average particle diameter exceeds 2 탆, the corrosion resistance may be lowered. The content ratio of the spherical silica particles having an average particle diameter of 5 nm or more and 20 nm or less and the spherical silica particles having an average particle diameter of 0.08 μm or more and 2 μm or less in the coating film 24 is in the range of 30/70 to 80/20 And more preferably in the range of 40/60 to 50/50. The ratio of the spherical silica particles having an average particle diameter of 5 nm or more and 20 nm or less and the average particle diameter of the spherical silica particles having an average particle diameter of 0.08 μm or more and 2 μm or less and contained in the coating film 24 is preferably 1/350 to 1 / 16, and more preferably in the range of 1/150 to 1/30.

The crosslinking agent for crosslinking the organic resin is limited to at least one member selected from a silane coupling agent, a crosslinkable zirconium compound, a crosslinkable titanium compound, an epoxy compound and an amino resin from the viewpoints of corrosion resistance and scratch resistance. These crosslinking agents may be used alone or in combination of two or more. The crosslinking agent may be used either as a raw material for a coating composition for forming a coating film or as a raw material for a coating composition in which a crosslinking agent has been previously crosslinked in the step of producing an organic resin, A crosslinking reaction may be carried out at the time of coating film formation.

Examples of the silane coupling agent include, but are not limited to, vinyltrimethoxysilane sold by Shinetsu Chemical Co., Ltd., Toray, Dow Corning, Chisso Corporation, Momentive Performance Materials, Japan, Aminopropyltrimethoxysilane, gamma -aminopropylethoxysilane, N- [2- (vinylbenzylamino) ethyl] -3-aminopropyltrimethoxysilane, gamma -aminopropyltrimethoxysilane, Methacryloxypropylmethyldimethoxysilane,? -Methacryloxypropyltrimethoxysilane,? -Methacryloxypropylmethyldiethoxysilane,? -Methacryloxypropyltriethoxysilane,? -Glycidoxypropyltriethoxysilane,? -Methacryloxypropyltrimethoxysilane, Glycidoxypropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, N -? - (aminoethyl) silane, -aminopropyltrimethoxysilane, N -? - (aminoethyl) -? - aminopropyltrimethoxysilane, N- aminopropyltriethoxysilane, N-β- (aminoethyl) - γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, etc. . These silane coupling agents may be used alone or in combination of two or more.

The crosslinkable zirconium compound is not particularly limited, and examples thereof include zirconyl nitrate, zirconyl acetate, zirconyl sulfate, ammonium zirconium carbonate, potassium zirconium carbonate, sodium zirconium carbonate and zirconium acetate. Of these compounds, zirconium compounds containing zirconium complex ions are preferable. As the zirconium compound containing zirconium carbonate complex ions is not particularly limited, zirconium carbonate complex ions _{[Zr (CO 3) 2 (OH} ) 2 ] ^2- or _{[Zr (CO 3) 3 (OH} ) ] ^3-a Ammonium salts, potassium salts, and sodium salts. These crosslinkable zirconium compounds may be used alone or in combination of two or more.

Examples of the crosslinkable titanium compound include, but are not limited to, dipropoxy bis (triethanolamine) titanium, dipropoxy bis (diethanolaminate) titanium, propoxytris (diethanolamine) titanium, (Triethanolamine) titanium, dibutoxybis (diethanolaminate) titanium, dipropoxy bis (acetylacetonate) titanium, dibutoxybis (acetylacetonate) titanium, dihydroxybis (lactate) titanium (Monoammonium oxalate), isopropyltri (N-amidoethylaminoethyl) titanate, and the like may be used as the monoammonium salt, dihydroxybis (lactate) titanium diammonium salt, propanedioxy titanium bis . These crosslinkable titanium compounds may be used alone or in combination of two or more.

The epoxy compound is not particularly limited as long as it is a compound having a plurality of epoxy groups (oxirane rings) which are cyclic ether groups of a 3-membered ring, and examples thereof include adipic acid diglycidyl ester, phthalic acid diglycidyl ester, terephthalic acid diglycidyl Ester, sorbitan polyglycidyl ether, pentaerythritol polyglycidyl ether, glycerin polyglycidyl ether, trimethylpropane polyglycidyl ether, neopentyl glycol polyglycidyl ether, ethylene glycol diglycidyl ether , Polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, 2,2-bis- (4-glycidyloxyphenyl) propane, tris (2,3- Propyl) isocyanurate, bisphenol A diglycidyl ether, hydrogenated bisphenol A diglycidyl ether, and the like. These epoxy compounds may be used alone or in combination of two or more. Most of these epoxy compounds contain a glycidyl group in the compound name since they have a glycidyl group in which one group of -CH ₂ - is added to the epoxy group.

The amino resin is not particularly limited, and examples thereof include melamine resin, benzoguanamine resin, urea resin, and glycoluril resin. These amino resins may be used alone or in combination of two or more kinds.

The content of the crosslinking agent is preferably 0.1% by mass or more and 20% by mass or less, more preferably 1% by mass or more and 15% by mass or less in the coating film (24). When the content of the crosslinking agent is less than 0.1% by mass, the amount of the crosslinking agent to be used is insufficient and the effect of addition may not be obtained. When the amount exceeds 20% by mass, the coating film 24 is weakened by excessive crosslinking, .

<About Lubricants>

The coating film 24 preferably contains a lubricant in order to improve corrosion resistance and scratch resistance. The inclusion of the lubricant enhances the lubricity of the surface-treated hot-rolled steel material, in other words, the effect of reducing the frictional resistance to be applied upon contact with the press mold or the like is enhanced, It is possible to prevent the occurrence of scratches.

The lubricant is not particularly limited and a known lubricant can be used, but it is preferable to use at least one selected from a fluororesin-based lubricant and a polyolefin resin-based lubricant.

The fluororesin-based lubricant is not particularly limited and includes, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PTFE), polychlorotrifluoroethylene (PCTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE) and the like. These fluororesin-based lubricants may be used alone or in combination of two or more.

The polyolefin resin-based lubricant is not particularly limited, and examples thereof include hydrocarbon waxes such as paraffin, microcrystalline, polyethylene, and polypropylene, and derivatives thereof. The derivative of the hydrocarbon wax is not particularly limited, and examples thereof include a carboxylated polyolefin and a chlorinated polyolefin. These polyolefin-based lubricants may be used singly or in combination of two or more.

Among the above lubricants, it is particularly preferable to use polyolefin resin particles as the lubricant in order to improve the corrosion resistance and scratch resistance. In the case of using the polyolefin resin particles, it is preferable that the polyolefin resin has a softening point of not less than 125 占 폚 and an average particle diameter of not less than 0.5 占 퐉 and not more than 3 占 퐉 in view of corrosion resistance and scratch resistance. As used herein, the softening point of the polyolefin resin particles refers to the temperature at which the heated polyolefin resin particles begin to soften and deform, and refers to the temperature measured by the method described in JIS K 2207.

Examples of the polyolefin resin particles having a softening point of not less than 125 占 폚 include Kemi Pearl W900, W700, W300, W308, W800 and W310 (above, softening point 132 占 폚) manufactured by Mitsui Chemicals, E-4A, E-4B, and E-1000 manufactured by Tohoku Kagaku Kogyo Co., Ltd., A-113 (softening point 126 ° C), A-375, A- E-6314 (above, softening point of 138 占 폚), Kemi Pearl WP100 (softening point 148 占 폚) manufactured by Mitsui Chemicals, Inc., AC-35 (softening point 143 占 폚) manufactured by Gita Selatsugu Seisho Co., Ltd., And polypropylene resin particles such as high-tech P-5043 (softening point: 157 占 폚) and P-5300 (softening point: 145 占 폚) manufactured by High School Corporation.

The content of the lubricant in the coating film 24 is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 5% by mass or less. If the content of the lubricant is less than 0.5% by mass, the effect of improving the corrosion resistance and scratch resistance may not be obtained. If the content is more than 10% by mass, the corrosion resistance may be deteriorated.

&Lt; About phosphoric acid compound >

The coating film 24 preferably contains a phosphoric acid compound in order to improve the corrosion resistance. It is more preferable that the phosphate compound is a phosphate ion releasing compound. When the phosphoric acid compound is contained, when the coating composition for forming it is in contact with the plating layer 23 at the time of forming the coating film, or when phosphate ions derived from the phosphoric acid compound are eluted from the coating film 24 after the formation of the coating film, 23) surface to form an insoluble phosphoric acid Mg-based coating film on the surface of the plating layer 23. Thereby, it is possible to significantly improve the anti-rusting property. When the phosphate compound does not release phosphate ions, that is, it is inexpensive in the environment, the insoluble phosphate compound inhibits migration of corrosion factors such as water and oxygen, thereby improving the corrosion resistance.

Examples of the phosphoric acid compound include, but are not limited to, phosphoric acids such as orthophosphoric acid, metaphosphoric acid, pyrophosphoric acid, triphosphoric acid and tetraphosphoric acid and their salts, aminotri (methylenephosphonic acid), 1-hydroxyethyl Diphosphonic acids such as ethylene diamine tetra (methylene phosphonic acid) and diethylenetriamine penta (methylene phosphonic acid) and salts thereof, organic phosphoric acids such as phytic acid, Salts and the like. The cation species of the salt is not particularly limited and examples thereof include Cu, Co, Fe, Mn, Sn, V, Mg, Ba, Al, Ca, Sr, Nb, Y, Ni and Zn. These phosphoric acid compounds may be used alone or in combination of two or more.

The content of the phosphoric acid compound in the coating film 24 is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less. If the content of the phosphoric acid compound is less than 0.1 mass%, the effect of improving the corrosion resistance may not be obtained. If the content is more than 5 mass%, the corrosion resistance may be lowered or the paint stability for forming the coating film 24 may be lowered , Problems such as gelation and precipitation of agglomerates may occur).

&Lt; About colored pigment >

It is preferable that the coating film 24 further contains a coloring pigment in order to enhance the design of the surface-treated hot-rolled steel material. Examples of the coloring pigment include, but are not limited to, colored inorganic pigments such as titanium dioxide, carbon black, graphite, iron oxide, lead oxide, talc, talc, cadmium yellow, cadmium red, chromium yellow, Anthraquinone dyes, anthraquinone dyes, anthraquinone dyes, anthraquinone dyes, quinacridones, perylene, anthrapyrimidine, carbazole violet, anthrapyridine, azo orange, There can be mentioned a colored organic pigment such as red, azo red, and anthraquinone red, and a coloring organic pigment such as an aluminum powder, an alumina powder, a bronze powder, a copper powder, a tin powder, a zinc powder, Glass powders, titanium dioxide-coated alumina powders, and the like.

When the coating film 24 is colored with a thickening agent or when a film having a thickness of 10 탆 or less is applied to the coating film 24, the coating film 24 may contain carbon black as a coloring pigment . The kind of the carbon black is not particularly limited, and known carbon black such as furnace black, ketjen black, acetylene black, and channel black can be used. In addition, carbon black that has been subjected to known ozone treatment, plasma treatment, or liquid phase oxidation treatment may also be used. The particle diameter of the carbon black to be used in the colored pigment is not particularly limited as long as it does not cause problems in dispersibility, coating film quality and paintability in the paint composition for forming a coating film. Specifically, the particle diameter is preferably 10 nm to 120 Nm can be used. Considering the design and corrosion resistance of the thin film, it is preferable to use fine particle carbon black having a primary particle diameter of 10 nm to 50 nm as the coloring pigment. When these carbon blacks are dispersed in an aqueous solvent, aggregation occurs in the dispersing process, so that it is generally difficult to disperse the carbon black particles as they are in the primary particle diameter. That is, in practice, the particulate carbon black is present in the form of secondary particles having a particle diameter larger than the primary particle diameter in the coating composition (coating solution) for forming a coating film, and the particulate carbon black The coating film 24 exists in a similar manner. It is preferable to control the particle diameter of the carbon black dispersed in the coating film 24 to be important and the average particle diameter to be 20 nm to 300 nm in order to secure the design and corrosion resistance in the thin film.

It is preferable that the content of the carbon black in the coating film 24 is d% by mass and the thickness of the coating film 24 is b 占 퐉. In order to ensure design (concealability), it is also essential to secure an absolute amount of the carbon black contained in the coating film 24 to a certain amount or more. The absolute amount of carbon black can be represented by the product of the content (d mass%) of the carbon black contained in the coating film 24 and the coating film thickness (b m). That is, when dxb is less than 20, the designability (concealability) may decrease. If d is more than 15, the film formability of the coating film 24 is lowered, and corrosion resistance and scratch resistance may be lowered.

When coloring the coating film 24 on the coating film 24, it is preferable to contain titanium dioxide as a coloring pigment. The content of the titanium dioxide in the coating film 24 in this case is preferably 10 mass% or more and 70 mass% or less. If the content of titanium dioxide is less than 10 mass%, the decorative properties (hiding property) may be lowered. When the content is more than 70 mass%, the corrosion resistance, scratch resistance and stain resistance may be lowered. In general, when the coating film 24 contains carbon black and is colored with a thickening agent, it is more likely to be noticeable when scratches occur, than when the coating film 24 does not exhibit coloring or is colored I have. Titanium dioxide has an effect of raising the scratch resistance, and has an effect of making the appearance of the surface close to a pale color and making the scratches less noticeable. Therefore, in order to improve the scratch resistance while securing the decorative properties (hiding ability) and corrosion resistance during coloring in a thin film having a film thickness of 10 탆 or less, it is preferable that carbon black and titanium dioxide It is preferable to contain both of them. In this case, it is preferable that carbon black and titanium dioxide are contained in a ratio of 0.5 / 9.5 to 3/7 by mass ratio.

&Lt; About the particulate component in the coating film 24 >

In the coating film 24, at least one of silica particles, polyolefin resin particles and colored pigment may be present as particulate components, if necessary.

In general, it may be difficult to specify the shape and size of the particles contained in the thin coating film 24. [ Nevertheless, the particulate component contained in the coating composition used for forming the coating film 24 is not limited to any physical or chemical change (for example, bonding or aggregation of the particles, It can be regarded that the shape and size of the resin when present in the coating are maintained even after the formation of the coating film, unless the resin is dissolved, dissolved in the solvent, reacted with other components, and the like). The particulate silica particles, the polyolefin resin particles and the colored pigment used in the present invention are not significantly dissolved in the solvent of the coating composition used for forming the coating film 24 and are not reacted with solvents or other components of the coating film Is selected. For the purpose of enhancing the retentivity of the presence of these particulate components in the coating material, those dispersed in a solvent by a previously known dispersant such as a surfactant or a dispersing resin may be used as a raw material for the coating composition, if necessary. Therefore, the particle diameters of these particulate components contained in the coating film 24 defined in the present invention can be represented by their particle diameters in the coating composition used for the formation of the coating film 24.

Specifically, the particle diameters of the silica particles, the polyolefin resin particles and the colored pigment used in the present invention can be measured by a dynamic light scattering method (nanotrack method). According to the dynamic scattering method, the diameter of the fine particles in the dispersion medium in which the temperature, the viscosity and the refractive index are known can be simply obtained. Since the particulate component used in the present invention is selected so as not to be significantly dissolved in the solvent of the coating material and to not react with the solvent or other components of the coating film, the particle diameter is measured in a predetermined dispersion medium, As the particle diameter of the particles. In the dynamic light scattering method, scattered light from particles is observed by irradiating laser light to fine particles dispersed in a dispersion medium in a dispersion medium, and an autocorrelation function is obtained by a photon correlation method, and the particle diameter is measured by the Curitel method . As a particle size measuring apparatus by the dynamic light scattering method, for example, FPAR-1000 manufactured by Otsuka Chemical Co., Ltd. can be used. In the present invention, the dispersoid sample containing the particles to be measured is measured at 25 占 폚 to determine the average particle diameter of the quarts run, and the average of five measurements is taken as the average particle diameter of the particles. Measurement of the average particle diameter by the dynamic light scattering method is described in detail in Journal of Chemical Physics, Vol. 57, No. 11 (December 1972), page 4814, for example.

When at least one of the silica particles, the polyolefin resin particles and the colored pigment is present as a particulate component in the coating film 24, it is also possible to directly observe the coating film 24 from its end face and to measure its shape and particle diameter . Although there is no particular limitation on the method of observing the cross section of the coating film 24, the surface-treated hot-dip coated steel is buried in a room temperature drying type epoxy resin so that the vertical cross section of the coating film 24 can be seen, (A scanning electron microscope) or a FIB (focused ion beam) apparatus is used to cut an observation sample having a thickness of 50 nm to 100 nm so that the vertical cross section of the coating film 24 can be seen from the surface- And a method of observing the cross section of the coated film with a TEM (transmission electron microscope) can be appropriately used.

[Base Treatment Layer (27)]

It is preferable to further provide the base treatment layer 27 between the lower layer of the coating film 24, that is, between the coating film 24 and the plated steel. The composition of the base treatment layer 27 is not particularly limited. However, by providing the base treatment layer 27 containing at least one kind selected from a silane coupling agent and an organic resin, the coating layer 24, The corrosion resistance and scratch resistance of the surface-treated hot-rolled steel material can be further enhanced. Further, by providing the base treatment layer 27 including both the silane coupling agent and the organic resin, it is possible to prevent the coating film 24 (i.e., the base coat layer 27) ) And the plated steel material as a base material can be further enhanced, and the corrosion resistance and scratch resistance of the surface-treated hot-rolled steel material can be further enhanced.

The silane coupling agent contained in the base treatment layer 27 is not particularly limited, and examples thereof include Shinetsugaku Kogaku Co., Ltd., Toray Dow Corning Co., Ltd., Chisso Co., Momentive Performance Materals Japan Co., Ltd. Vinyltrimethoxysilane,? -Aminopropyltrimethoxysilane,? -Aminopropylethoxysilane, N- [2- (vinylbenzylamino) ethyl] -3-aminopropyl Methacryloxypropylmethyldimethoxysilane,? -Methacryloxypropyltrimethoxysilane,? -Methacryloxypropylmethyldiethoxysilane,? -Methacryloxypropyltriethoxysilane,? -Methacryloxypropyltrimethoxysilane,? -Methacryloxypropyltrimethoxysilane,? -Methacryloxypropyltrimethoxysilane, -Glycidoxypropyltriethoxysilane,? -Glycidoxypropylmethyldiethoxysilane,? -Glycidoxypropyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, N - (aminoethyl) -? - aminopropyltrimethoxysilane, N -? - (Aminoethyl) -? - aminopropyltriethoxysilane, N -? - (aminoethyl) -? - aminopropylmethyldimethoxysilane, N-phenyl-? -Aminopropyltrimethoxysilane,? -Mercaptopropyl Trimethoxysilane, and the like. These silane coupling agents may be used alone or in combination of two or more.

The organic resin contained in the base treatment layer 27 is not particularly limited and a known organic resin such as a polyester resin, a polyurethane resin, an epoxy resin, a phenol resin, an acrylic resin, and a polyolefin resin may be used . In order to further improve the adhesion between the coating film 24 and the base plated steel, it is preferable to use at least one of a polyester resin, a polyurethane resin, an epoxy resin and a phenol resin. In the case where the organic resin contained in the coating film 24 is a polyester resin, in order to enhance the compatibility with the organic resin in the coating film 24 and improve the adhesion of the coating film 24 to the base plated steel material, It is particularly preferable that the polyester resin (27) also contains a polyester resin.

The content of the at least one material selected from the silane coupling agent and the organic resin contained in the base treatment layer 27 is not particularly limited, but is preferably 50 mass% or more in the base treatment layer 27. When the content is less than 50 mass%, the content is small and the effect of improving the adhesion with the coating film (24), corrosion resistance and scratch resistance may not be obtained.

The base treatment layer 27 preferably further contains a polyphenol compound. The polyphenol compound refers to a compound having two or more phenolic hydroxyl groups bonded to a benzene ring, or a condensate thereof. Examples of the compound having two or more phenolic hydroxyl groups bonded to the benzene ring include gallic acid, pyrogallol, catechol, and the like. The condensate of the compound having two or more phenolic hydroxyl groups bonded to the benzene ring is not particularly limited and includes, for example, a polyphenol compound widely distributed in plants called tannic acid.

Tannic acid is a generic term for aromatic compounds having a complex structure having a large number of phenolic hydroxyl groups distributed widely in plants. The tannic acid used in the base treatment layer 27 may be a hydrolyzable tannic acid or a condensed tannic acid. Examples of the tannic acid include, but are not limited to, hammamititanin, persimmon tannin, chatin tannin, hiba tannin, myrrhic tannin, mirovalan tannin, have. Examples of tannic acid include those commercially available such as "Tannic acid extract A", "B tannic acid", "N tannic acid", "industrial tannic acid", "purified tannic acid", "Hi tannic acid", "F tannic acid" ) Tannic acid "(all manufactured by Dainippon Ink and Chemicals, Inc.) and" tannic acid: AL "(manufactured by Fuji Kagaku Kogyo Co., Ltd.) may be used. These tannic acids may be used singly or in combination of two or more.

The base treatment layer 27 preferably further contains silica particles. The kind of the silica particles is not particularly limited, and examples thereof include silica particles such as colloidal silica and fumed silica. Examples of commercially available products include commercially available products such as SNOWTEX O, SNOWTEX N, SNOWTEX C, SNOWTEX IPA-ST (manufactured by Nissan Chemical Industries, Ltd.), Adelite AT-20N and AT-20A (manufactured by Asahi Denka Kogyo) (Manufactured by Nippon Aerosil Co., Ltd.). The silica particles preferably contain spherical silica particles having an average particle diameter of 5 nm or more and 20 nm or less in order to improve corrosion resistance.

It is preferable that the base treatment layer 27 further contain at least one kind selected from a phosphate compound, a fluoro complex and a vanadium (IV) compound in order to improve the corrosion resistance.

The phosphoric acid compound is not particularly limited, and examples thereof include phosphoric acid, ammonium salts of phosphoric acid, alkali metal salts of phosphoric acid, and alkaline earth metal salts of phosphoric acid. The fluoro complex is not particularly limited, and examples thereof include titanium hydrofluoric acid and zirconium hydrofluoric acid, and ammonium salts and alkali metal salts thereof. Examples of the vanadium (IV) compound include, but are not limited to, vanadium pentoxide (V ₂ O ₅ ), metavanadic acid (HVO ₃ ), ammonium metavanadate (NH ₄ VO ₃ ), sodium metavanadate ₃ ) and vanadium trichloride (VOCl ₃ ) are reduced with vanadium (IV) using a reducing agent such as an alcohol or an organic acid, or vanadium (V ₂ ), vanadium oxy acetylacetonate _{(VO (C 5 H 7 O} 2) 2), oxy-sulfate, vanadium (VOSO _4), such as vanadium (IV) containing compounds, vanadium acetylacetonate _{(V (C 5 H 7 O} 2) 3), 3 And vanadium (III) of a compound such as vanadium oxide (V ₂ O ₃ ) and vanadium trichloride (VCl ₃ ) is oxidized to vanadium (IV) by an optional oxidizing agent.

The adhesion amount of the base treatment layer 27 is not particularly limited, but is preferably in the range of 10 mg / m 2 to 1000 mg / m 2. When the deposition amount of the base treatment layer 27 is less than 10 mg / m 2, the effect of providing the base treatment layer 27 is not sufficiently obtained. When the deposition amount exceeds 1000 mg / m 2, And the adhesion to the base metal sheet may be lowered. From the viewpoint of the stable effect and economical efficiency, the more preferable range of the adhesion amount is from 50 mg / m 2 to 700 mg / m 2.

[Method of producing surface-treated hot-rolled steel material]

The surface-treated hot-rolled steel material according to the present embodiment is produced by coating an aluminum-zinc alloy on the surface of a steel material 1 and coating a coat film 24 having an organic resin as a film component on the upper layer.

[Process for producing hot-dip galvanized steel]

In the preferred embodiment, a hot-dip coating bath 2 having a composition that matches the composition of the constituent elements of the plating layer 23 is prepared at the time of manufacturing the hot-dip galvanized steel. The alloy layer 25 is formed between the steel material 1 and the plating layer 23 by the hot-dip plating treatment, but the fluctuation of the composition due to the alloy layer 25 is negligibly small.

In this embodiment mode, for example, Al, 0.5 to 10 mass% of Mg, 0.02 to 1.0 mass% of Cr, 0.5 to 10 mass% of Si, 1 to 1000 mass ppm of Sr , And 0.1 to 1.0 mass% of Fe and Zn are prepared. Zn occupies the remaining portion excluding the components other than Zn in the entire components in the hot dip coating bath (2). The mass ratio of Si: Mg in the hot dip coating bath 2 is preferably in the range of 100: 50 to 100: 300.

The hot-dip coating bath 2 may contain a component selected from an alkaline earth element, Sc, Y, a lanthanoid element, Ti and B, These components are contained in the hot-dip coating bath 2 as required. The total amount of the alkaline earth elements (Be, Ca, Ba, Ra), Sc, Y and lanthanoid elements (La, Ce, Pr, Nd, Pm, Sm, Eu and the like) in the hot- , And preferably not more than 1.0% by mass. When the hot-dip coating bath 2 contains a component composed of at least one of Ti and B, the total content of Ti and B in the hot-dip coating bath 2 is preferably in the range of 0.0005 to 0.1% .

It is preferable that the hot-dip coating bath 2 does not contain any components other than those described above. In particular, it is preferable that the hot-dip coating bath 2 contains only Al, Zn, Si, Mg, Cr, Sr and Fe. It is also preferable that the hot dip coating bath 2 contains only elements selected from Al, Zn, Si, Mg, Cr, Sr and Fe and alkaline earth elements, Sc, Y, lanthanoid elements,

For example, in preparation of the hot dip coating bath 2, the hot dip coating bath 2 is preferably provided with 25 to 75% of Al, 0.02 to 1.0% of Cr, 0.5 to 0.5 To 10% of Mg, 0.1 to 0.5% of Mg, 0.1 to 0.6% of Fe, and 1 to 500 ppm of Sr, or further contains a component selected from alkaline earth elements, lanthanoid elements, Ti and B , And the remaining part is Zn.

However, of course, the hot dip coating bath 2 may contain inevitable impurities such as Pb, Cd, Cu, and Mn. The content of the inevitable impurities is preferably as small as possible, and it is particularly preferable that the total content of the inevitable impurities is 1% by mass or less with respect to the molten bath 2 in mass ratio.

When the hot-dip coating process is applied to the steel material 1 using the hot-dip galvanizing bath 2 having such a composition, the corrosion resistance of the surface of the hot-rolled material layer 23 is improved particularly by Al, In particular, edge creep at the cut end face of the hot-dip galvanized steel is suppressed, and high corrosion resistance is imparted to the hot-dip galvanized steel.

Further, since the plating layer 23 contains Mg, which is a metal more active than Zn, the sacrificial action of the plating layer 23 is strengthened further, and the corrosion resistance of the hot-dip coated steel material is further improved.

Further, wrinkles are less likely to be generated in the plating layer 23 formed by the hot-dip plating treatment. Conventionally, when a molten metal (molten plated metal) containing Mg is attached to the steel material 1 by the hot dip treatment, Mg is easily concentrated in the surface layer of the molten plated metal, thereby forming the Mg based oxide film , And the plating layer 23 was liable to wrinkle due to the Mg-based oxide film. However, when the plating layer 23 is formed by using the hot-dip galvanizing bath 2 having the above composition, Mg concentration in the surface layer of the hot-dip metal attached to the steel 1 is suppressed, The surface of the plating layer 23 is hardly wrinkled. Further, the fluidity in the molten-plated metal is reduced, and the flow of the molten plated metal itself is suppressed, so that the wrinkles are less likely to occur.

It is considered that the Mg concentration and the flow of the molten plated metal as described above are suppressed by the following mechanism.

In the process of cooling and solidifying the molten plated metal adhered on the surface of the steel material 1, the? -Al phase first precipitates as a precipitate and grows into a dendritic phase. When the solidification of the Al-rich Al-Al phase proceeds as described above, the Mg and Si concentrations in the molten plated metal in the remaining portion (that is, in the components that have not yet solidified in the molten plated metal) gradually increase. Next, when the steel material 1 is cooled and its temperature is further lowered, a Si-containing phase (Si-Mg phase) containing Si is coagulated and precipitated from the molten plated metal in the remaining portion. This Si-Mg phase is an alloy composed of Mg and Si as described above. This precipitation / growth of the Si-Mg phase is promoted by Cr, Fe and Sr. By introducing Mg in the molten plated metal onto the Si-Mg, migration of Mg to the surface layer of the molten plated metal is inhibited, and concentration of Mg in the surface layer of the molten plated metal is suppressed.

Also, Sr in the molten plated metal contributes to suppression of Mg concentration. This is considered to be because Sr is an element easily oxidized in the molten plated metal like Mg, and Sr forms an oxide film on the plating surface in a competitive manner with Mg, resulting in suppression of Mg-based oxide film formation.

Further, as described above, the Si-Mg phase is solidified and grown in the molten plated metal in the remaining portion other than the superlattice? -Al phase, whereby the molten plated metal is brought into a solid state (solid solution) state, And as a result, generation of wrinkles on the surface of the plating layer is suppressed.

Fe is important in controlling the microstructure and sequins of the plating layer 23. The reason why Fe affects the structure of the plating layer 23 is not necessarily clear at this point, but Fe is alloyed with Si in the hot-dip plating metal, and this alloy becomes a solidifying nucleus upon solidification of the molten metal I think.

Further, since Sr is an active element like Mg, the sacrificial action of the plating layer 23 is strengthened by Sr, and the corrosion resistance of the hot-dip galvanized steel is further improved. Sr also acts to inhibit the precipitation of the precipitated form of the Si phase and the Si-Mg phase, and consequently the Si phase and the Si-Mg phase are spheroidized, and cracking in the plating layer 23 is suppressed.

An alloy layer 25 containing a part of Al in the molten plated metal is also formed between the plated layer 23 and the steel material 1 during the hot dip treatment. For example, in the case where the steel material 1 is not subjected to the pre-plating described below, an Fe-Al alloy layer 25 mainly composed of Al in the hot-dip galvanizing bath 2 and Fe in the steel material 1, . In the case where the steel material 1 is pre-plated as described later, the steel material 1 may contain some or all of the constituent elements of Al and pre-plating in the hot-dip galvanizing bath 2, or an alloy containing Fe in the steel material 1 A layer 25 is formed.

When the hot dip coating bath 2 contains Cr, the alloy layer 25 further contains Cr together with Al as a constituent element. The alloy layer 25 may contain Si, Mn, Fe, Co, Ni, Cu, or the like as a constituent element in addition to Al and Cr, depending on the composition of the molten bath 2, Zn, Sn, and the like.

In the alloy layer 25, a part of Cr in the molten plated metal is contained at a higher concentration than in the plating layer 23. When the alloy layer 25 is formed, the growth of the Si-Mg phase in the plating layer 23 is promoted by the Cr in the alloy layer 25 to increase the volume ratio of the Si-Mg phase in the plating layer 23, The ratio of Mg in the Si-Mg phase to the total amount of Mg in the Mg-free layer 23 becomes high. As a result, the wrinkles of the plating layer are further suppressed. Further, since the alloy layer 25 is formed, the corrosion resistance of the hot-dip galvanized steel is further improved. That is, the growth of the Si-Mg phase is promoted in the vicinity of the alloy layer 25 in the plating layer 23, so that the area ratio of the Si-Mg phase on the surface of the plating layer 23 is lowered, Sagging of the plating layer 23 is suppressed and the corrosion resistance of the plating layer 23 is maintained for a longer period of time. Particularly, the ratio of the content of Cr in the alloy layer 25 to the content of Cr in the plating layer 23 is preferably 2 to 50. The ratio of the content of Cr in the alloy layer 25 to the content of Cr in the plating layer 23 is more preferably from 3 to 40, and still more preferably from 4 to 25. [ The amount of Cr in the alloy layer 25 can be derived by measuring the cross section of the plating layer 23 using an energy dispersive X-ray analyzer (EDS).

If the thickness of the alloy layer 25 is excessive, the workability of the hot-dip coated steel material is lowered, but the excessive growth of the alloy layer 25 is suppressed by the action of Si in the hot-dip coating bath 2, Good workability of the plated steel is ensured. The thickness of the alloy layer 25 is preferably in the range of 0.05 to 5 mu m. When the thickness of the alloy layer 25 is within the above range, the corrosion resistance of the hot-dip galvanized steel is sufficiently improved and the workability is sufficiently improved.

Further, in the plating layer 23, the concentration of Cr is maintained in a certain range in the vicinity of the surface thereof, and the corrosion resistance of the plating layer 23 is further improved. The reason for this is not clear, but it is presumed that the complex oxide film is formed near the surface of the plating layer 23 by the combination of Cr with oxygen. In order to improve the corrosion resistance of the plating layer 23, it is preferable that the content of Cr in the outermost layer at a depth of 50 nm in the plating layer 23 is 100 to 500 mass ppm.

When the hot dip coating bath 2 contains Cr, the corrosion resistance of the plating layer 23 after bending and deformation is also improved. The reason is thought to be as follows. Cracks may be generated in the coating film on the plating layer 23 and the coating layer 23 in some cases. At this time, water or oxygen enters the plating layer 23 through the crack, and the alloy in the plating layer 23 is directly exposed to the corrosive factor. However, the Cr present in the surface layer of the plating layer 23 and the Cr present in the alloy layer 25 suppress the corrosion reaction of the plating layer 23, thereby suppressing the expansion of corrosion starting from the crack.

The molten metal to be treated in the above preferred embodiment is a multi-component molten metal containing seven or more elements, and the coagulation process is extremely complicated and it is difficult to predict theoretically. However, , And to gain the above-mentioned important knowledge.

By adjusting the composition of the hot-dip coating bath 2 as described above, it is possible to suppress wrinkling and sagging in the coating layer 23 and to secure the corrosion resistance and workability of the hot-dip coated steel material as described above.

When the content of Al in this hot-dip coating bath 2 is less than 25%, the Zn content in the plating layer 23 becomes excessive, the corrosion resistance on the surface of the plating layer 23 becomes insufficient, %, The effect of the sacrificial effect by Zn is reduced, and the plating layer 23 is hardened and the bending workability of the hot-dip coated steel material is lowered. If the content is more than 75%, the flowability of the molten plated metal becomes large, and there is a fear that the plated layer 23 may be wrinkled. The content of Al is particularly preferably 45% or more. The content of Al is particularly preferably 65% or less. Particularly, the content of Al is preferably in the range of 45 to 65%.

If the content of Cr in the hot-dip coating bath 2 is less than 0.02%, the corrosion resistance of the plating layer 23 is not sufficiently ensured and the wrinkling or sagging of the plating layer 23 is hardly suppressed sufficiently, If it exceeds 1.0%, the action of improving the corrosion resistance is not only saturated but also dross is easily generated in the hot dip coating bath 2. The content of Cr is particularly preferably 0.05% or more. The content of Cr is particularly preferably 0.5% or less. The content of Cr is more preferably in the range of 0.07 to 0.2%.

If the content of Si in the hot-dip galvanizing bath 2 is less than 0.5%, the above-mentioned effect will not be exhibited. If the content is more than 10%, the action due to Si will be saturated and the hot- 2), it becomes easy to generate dross. The content of Si is particularly preferably 1.0% or more. The content of Si is particularly preferably 5.0% or less. It is more preferable that the Si content is in the range of 1.0 to 5.0%.

If the content of Mg in the hot dip coating bath 2 is less than 0.1%, the corrosion resistance of the plating layer 23 is not ensured sufficiently. If the content of Mg exceeds 10%, the action of improving the corrosion resistance is saturated, Dross is easily generated in the bath 2. The Mg content is preferably 0.5% or more, and more preferably 1.0% or more. The Mg content is preferably 5.0% or less, more preferably 3.0% or less. In particular, the content of Mg is preferably in the range of 1.0 to 3.0%.

If the content of Fe in the hot-dip coating bath 2 is less than 0.1%, the microstructure and the sequin structure of the plating layer 23 are coarsened, thereby deteriorating the appearance of the plating layer 23 and deteriorating workability. If the content is more than 0.6%, the sequins of the plating layer 23 become very fine or disappear, so that appearance improvement due to sequins can not be achieved, and dross is easily generated in the hot dip coating bath 2 Throw away. The content of Fe is particularly preferably 0.2% or more. The content of Fe is particularly preferably 0.5% or less. Particularly, the content of Fe is preferably in the range of 0.2 to 0.5%.

If the content of Sr in the hot dip coating bath 2 is less than 1 ppm, the above-mentioned effect will not be exhibited. If the content is more than 500 ppm, the action of Sr will be saturated, It becomes easy to generate. The content of Sr is particularly preferably 5 ppm or more. The content of Sr is particularly preferably 300 ppm or less. The content of Sr is more preferably in the range of 20 to 50 ppm.

The alkaline earth elements (Be, Ca, Ba, and Ra), Sc and Y, and the lanthanoid elements (La, Ce, Pr, Nd, Pm, Sm, Eu, etc.) exert the same effect as Sr. The total amount of these components in the hot-dip coating bath 2 is preferably not more than 1.0% by mass as described above.

When the hot dip coating bath 2 contains Ca in particular, the generation of dross in the hot dip coating bath 2 is remarkably suppressed. In the case where the molten bath 2 contains Mg, it is difficult to avoid the generation of a certain degree of dross even if the Mg content is 10% by mass or less. In order to secure a good appearance of the molten plated steel, It is necessary to remove the dross from the plating bath 2. However, if the hot dip coating bath 2 further contains Ca, the generation of dross due to Mg is remarkably suppressed. This further suppresses deterioration of the appearance of the hot-dip galvanized steel by the dross and reduces the labor required for removing the dross from the hot dip galvanizing bath 2. The content of Ca in the hot-dip coating bath 2 is preferably in the range of 100 to 5000 mass ppm. With this content being 100 mass ppm or more, the occurrence of dross in the hot dip coating bath 2 is effectively suppressed. If the content of Ca is excessive, dross due to Ca may occur. However, if the content of Ca is 5000 mass ppm or less, dross due to Ca is suppressed. The content is more preferably in the range of 200 to 1000 mass ppm.

When the at least one of Ti and B is contained in the hot dip coating bath 2, the α-Al phase (dendritic structure) of the plating layer 23 is made finer to make the sequins of the plating layer 23 finer, The appearance of the plating layer 23 is improved. Further, generation of wrinkles in the plating layer 23 is further suppressed. This is because the Si-Mg phase is finely smoothened by the action of Ti and B and the finely divided Si-Mg phase effectively suppresses the flow of the molten plated metal in the process of solidifying the molten plated metal to form the plated layer 23 . Further, by miniaturization of the plating structure, concentration of stress in the plating layer 23 at the time of bending is relaxed, generation of a large crack is suppressed, and bending workability is further improved. In order to exhibit the above-described action, it is preferable that the total content of Ti and B in the hot-dip galvanizing bath 2 is in the range of 0.0005 to 0.1% by mass ratio. The total content of Ti and B is particularly preferably 0.001% or more. The total content of Ti and B is particularly preferably 0.05% or less. In particular, it is preferable that the total content of Ti and B is in the range of 0.001 to 0.05%.

The plating layer 23 is formed by a hot-dip coating process using such a hot-dip coating bath 2. In the plating layer 23, Mg concentration in the surface layer is suppressed as described above. Thus, as described above, in any region where the size is 4 mm in diameter and the depth is 50 nm in the outermost layer at a depth of 50 nm from the surface of the plating layer 23, the Mg content is less than 60 mass% . In this case, the amount of the Mg-based oxide film in the outermost layer of the plating layer 23 becomes particularly small, and wrinkles caused by the Mg-based oxide film are further suppressed. The smaller the Mg content in the outermost layer, the wrinkles caused by the Mg-based oxide film are suppressed. This Mg content is more preferably less than 40 mass%, more preferably less than 20 mass%, and particularly preferably less than 10 mass%. Particularly, it is preferable that the portion where the Mg content is 60 mass% or more is not present in the outermost layer of the thickness of 50 nm of the plating layer 23, and it is more preferable that there is no portion where the Mg content is 40 mass% or more , And it is more preferable that the portion where the Mg content is 20 mass% or more is not present.

The physical meaning of the Mg content will be described. The Mg content of the stoichiometric MgO oxide is about 60 mass%. That is, when the Mg content is less than 60 mass%, MgO (MgO-only oxide film) of the stoichiometric composition is not present in the outermost layer of the plating layer 23, or MgO of this stoichiometric composition is remarkably formed It is inhibited. In the present embodiment, excessive oxidation of Mg in the outermost layer of the plating layer 23 is suppressed, so that the formation of an oxide film of MgO alone is suppressed. A composite oxide containing a small amount or a large amount of oxides of elements other than Mg such as Al, Zn, and Sr is formed in the outermost layer of the plating layer 23, so that the Mg content in the surface layer of the plating layer 23 Is lowered.

The Mg content in the outermost layer of the plating layer 23 can be analyzed using a glow discharge spectrometer. When it is difficult to obtain a high-precision quantitative concentration analysis value, it is confirmed that the oxide film of MgO alone is not visible in the outermost layer of the plating layer 23 by comparing the concentration curves of the respective elements contained in the plating layer 23 .

The volume ratio of the Si-Mg phase in the plating layer 23 is preferably in the range of 0.2 to 15% by volume. The volume ratio of the Si-Mg phase is more preferably 0.2 to 10%, more preferably 0.3 to 8%, and particularly preferably 0.4 to 5%. When the Si-Mg phase is present in the plating layer 23 as described above, Mg at the time of forming the plating layer is sufficiently introduced onto the Si-Mg and the flow of the molten plated metal is sufficiently inhibited by the Si-Mg phase. As a result, 23 is further suppressed.

In the hot-dip galvanized steel, as described above, the wrinkles on the surface of the plating layer 23 are suppressed, and in particular, the surface of the plating layer 23 has a height of more than 200 mu m, . The steepness is a value defined by [the height of elevation (占 퐉)] / (width of elevation of elevation (占 퐉)]. The bottom of the ridge refers to the point where the ridge intersects the virtual plane including the flat surface around the ridge. The height of the ridge is the height from the bottom of the ridge to the tip of the ridge. When the sharpness is low, the appearance of the plating layer 23 is further improved. When the coating film 24 is formed on the plating layer 23 as described later, it is possible to prevent the ridges from breaking over the coating film 24 and to easily make the thickness of the coating film 24 uniform . As a result, the appearance of the surface-treated hot-rolled steel sheet on which the coating layer is formed is improved, and the surface-treated hot-rolled steel sheet can exhibit better corrosion resistance and the like by the coating layer.

The adjustment of the degree of Mg concentration, the state of the Si-Mg phase, the thickness of the alloy layer 25 and the steepness of the ridges of the surface of the plating layer 23 can be controlled by adjusting the steepness of the molten bath 2, And then performing a hot-dip coating process.

In the hot-dip plating treatment, a steel sheet 1 on which a pre-plating layer 26 containing at least one component selected from Cr, Mn, Fe, Co, Ni, Cu, A hot-dip coating process may be performed. The pre-plating process is performed on the steel material 1 before the above-mentioned hot-dip plating process, so that the pre-plated layer 26 is formed on the surface of the steel material 1. This pre-plated layer 26 improves the wettability of the steel material 1 and the molten plated metal during the hot-dip plating treatment and improves the adhesion between the steel material 1 and the plated layer 23.

The pre-plated layer 26 depends on the kind of metal constituting the pre-plated layer 26, but also contributes to an improvement in the surface appearance and corrosion resistance of the plated layer 23. For example, when the pre-plating layer 26 containing Cr is formed, the formation of the alloy layer 25 containing Cr is promoted between the steel 1 and the plating layer 23, and the corrosion resistance of the molten- . For example, when the pre-plating layer 26 containing Fe or Ni is formed, the wettability of the steel material 1 and the molten plated metal is improved, and the adhesion of the plating layer 23 is greatly improved. Further, And the surface appearance of the plating layer 23 is further improved. It is considered that the promotion of precipitation of the Si-Mg phase is caused by the reaction of the pre-plating layer 26 and the molten plated metal.

The amount of deposition of the pre-plated layer 26 is not particularly limited, but it is preferable that the amount of deposition on one side of the steel material 1 is in the range of 0.1 to 3 g / m &lt; 2 &gt;. If the deposition amount is less than 0.1 g / m 2, it is difficult to cover the surface of the steel material by the pre-plating layer 26, and the improvement effect by pre-plating is not sufficiently exhibited. In addition, when the adhesion amount exceeds 3 g / m 2, not only the improvement effect is saturated but also the manufacturing cost is increased.

Hereinafter, the outline of the hot-dip plating apparatus for performing the hot-dip plating treatment on the steel material 1 and the suitable processing conditions for the hot-dip plating treatment will be described.

The steel material 1 to be treated is a member formed of steel such as carbon steel, alloy steel, stainless steel, nickel chrome steel, nickel chrome molybdenum steel, chromium steel, chromium molybdenum steel, and manganese steel. As the steel material 1, various members such as a thin steel plate, a post-steel plate, a section steel, a steel pipe, and a steel wire can be cited. That is, the shape of the steel material 1 is not particularly limited.

The steel material 1 may be subjected to flux treatment before the hot-dip coating process. By this flux treatment, the wettability and adhesion of the steel material 1 to the hot-dip coating bath 2 are improved. The steel material 1 may be subjected to a heating annealing and reduction treatment before being dipped in the hot dip coating bath 2, and this treatment may be omitted. As described above, the steel material 1 may be pre-plated before the hot-dip coating process.

Hereinafter, the manufacturing process of the molten plated steel material (molten plated steel sheet) when the plate material (steel plate 1a) is employed as the steel material 1, that is, when the molten plated steel sheet is produced, will be described.

The hot dip treatment apparatus shown in Fig. 1 is provided with a conveying device for continuously conveying the steel sheet 1a. This conveying device is constituted by a feeder 3, a winder 12 and a plurality of conveying rolls 15. In this conveying apparatus, the coils 13 (first coils 13) of the long steel plate 1a are held by the feeder 3. The first coil 13 is released by the feeder 3 and the steel plate 1a is conveyed to the winding machine 12 while being supported by the conveying roll 15. [ The steel plate 1a is wound by the winder 12 and the winder 12 holds the coil 14 (second coil 14) of the steel plate 1a.

In this hot-dip coating apparatus, the heating furnace 4, the annealing and cooling section 5, the sloshing 6, the ports 7, and the heating section 5 are disposed in this order from the upstream side of the conveyance path of the steel sheet 1a by the above- An injection nozzle 9, a cooling device 10, and a rough rolling / shape correcting device 11 are sequentially installed. The heating furnace 4 heats the steel sheet 1a. This heating furnace 4 is constituted by a non-oxidizing furnace or the like. The annealing and cooling section 5 heats and anneals the steel sheet 1a, followed by cooling. The annealing and cooling unit 5 is connected to the heating furnace 4, and has an annealing furnace on the upstream side and a cooling stand (cooler) on the downstream side. The inside of the annealing / cooling section 5 is maintained in a reducing atmosphere. The snout 6 is a tubular member in which the steel sheet 1a is conveyed and one end thereof is connected to the annealing and cooling unit 5 and the other end is connected to the hot- . The inside of the Snart 6 is maintained in a reducing atmosphere as in the annealing / cooling part 5. The port 7 is a container for storing the hot-dip coating bath 2, and a sink roll 8 is disposed therein. The injection nozzle 9 injects gas toward the steel plate 1a. The injection nozzle 9 is disposed above the port 7. The injection nozzle 9 is disposed at a position where the gas can be injected toward both surfaces of the steel sheet 1a pulled up from the port 7. The cooling device (10) cools the molten plated metal attached to the steel plate. As the cooling device 10, a cooling device, a mist cooling device and the like are provided, and the cooling device 10 cools the steel plate 1a. The rough rolling and shape correcting apparatus 11 performs temper rolling and shape correction of the steel sheet 1a on which the plating layer 23 is formed. The rough rolling and shape correcting apparatus 11 is provided with a skin pass mill or the like for performing rough rolling on the steel sheet 1a or a tension leveler for performing shape correction on the steel sheet 1a after rough rolling do.

In the hot-dip plating treatment using the hot-dip plating apparatus, the steel sheet 1a is first loosened from the feeder 3 and continuously fed. After the steel sheet 1a is heated in the heating furnace 4, the steel sheet 1a is conveyed to the annealing and cooling section 5 in the reducing atmosphere and annealed in the annealing furnace, After the surface is cleaned, such as removing or reducing oxide film, cooling is performed in the cooling zone. Next, the steel sheet 1a passes through the Snart 6, enters the port 7 again, and is immersed in the hot-dip plating bath 2 in the port 7. The steel sheet 1a is supported in the sink roll 8 in the port 7 so that its conveying direction is switched upward and drawn out from the hot- As a result, the molten metal is attached to the steel sheet 1a.

Next, gas is sprayed onto the both surfaces of the steel sheet 1a from the injection nozzle 9, thereby adjusting the adhesion amount of the molten plated metal adhered to the steel sheet 1a. The method of adjusting the deposition amount by the gas injection is referred to as the gas wiping method. It is preferable that the adhesion amount of the molten plated metal is adjusted to be in the range of 40 to 200 g / m &lt; 2 &gt; together on both sides of the steel sheet 1a.

Examples of the gas (wiping gas) to be sprayed on the steel sheet 1a in the gas wiping method include air, nitrogen, argon, helium, steam and the like. These wiping gases may be sprayed on the steel plate 1a after being preheated. In the present embodiment, the surface oxidation of Mg in the molten plated metal (oxidation of Mg in the surface layer of the molten plated metal and increase of the Mg concentration) is essentially suppressed by using the molten bath 2 of a specific composition. Therefore, even when oxygen is contained in the wiping gas or oxygen is contained in the air stream accompanying the spraying of the wiping gas, the amount of plating adhered The amount of the molten plated metal can be adjusted.

The method of adjusting the plating amount is not limited to the gas wiping method described above, and various deposition amount control methods can be applied. Examples of the deposition amount control method other than the gas wiping method include a roll compression method in which the steel sheet 1a is passed between a pair of rolls disposed immediately above the bath surface of the hot dip coating bath 2, A method in which a shielding plate is arranged close to the steel plate 1a and the molten plated metal is smoldered by the shield plate; a method in which an electromagnetic force is applied to the molten plated metal attached to the steel plate 1a, A wiping method, and a method of adjusting a plating adhesion amount by using a natural gravity drop without externally applying force. Two or more types of plating adhesion amount adjusting methods may be combined.

Next, the steel sheet 1a is conveyed further upward than the position of the injection nozzle 9, and then conveyed so as to be bent downward by being supported by the two conveyance rolls 15. That is, the steel sheet 1a is transported in the reverse U-shaped path. In this inverted U-shaped path, the steel sheet 1a is cooled in the cooling device 10 by air cooling, mist cooling, or the like. As a result, the molten plated metal adhered on the surface of the steel sheet 1a is solidified, and the plated layer 23 is formed.

The surface temperature of the molten plated metal (or the plated layer 23) is controlled to be 300 占 폚 or lower by the cooling device 10 on the steel plate 1a in order to complete the solidification of the plated metal by cooling by the cooling device 10 Lt; / RTI &gt; The surface temperature of the molten plated metal is measured, for example, by a radiation thermometer or the like. In order to form the plating layer 23 in this manner, the cooling rate during the period from the time when the steel sheet 1a is taken out of the hot-dip coating bath 2 to the time when the surface of the hot- It is preferably in the range of 5 to 100 占 폚 / sec. In order to control the cooling rate of the steel sheet 1a, it is preferable that the cooling device 10 has a temperature control function for adjusting the temperature of the steel sheet 1a along the conveying direction and the plate width direction. The cooling device 10 may be divided into a plurality of parts along the conveying direction of the steel sheet 1a. 1 shows a primary cooling device 101 for cooling the steel plate 1a in a path further upward than the position of the injection nozzle 9 and a primary cooling device 101 for cooling the steel plate 1a A secondary cooling device 102 for cooling the secondary cooling device 1a is provided. The primary cooling apparatus 101 and the secondary cooling apparatus 102 may be further divided into a plurality of units. In this case, for example, in the primary cooling apparatus 101, the steel sheet 1a is cooled until the surface of the molten plated metal becomes 300 ° C or lower, (1 a) is introduced into the rough rolling and shape correcting apparatus (11) so that the temperature is 100 캜 or lower.

In the process of cooling the steel sheet 1a, it is preferable that the cooling rate of the surface of the molten plated metal is 50 DEG C / sec or less while the surface temperature of the molten plated metal on the steel sheet 1a is 500 DEG C or more. In this case, the precipitation of the Si-Mg phase on the surface of the plating layer 23 is particularly suppressed, thereby suppressing the occurrence of sagging. The reason why the cooling rate in this temperature range affects the precipitation behavior of the Si-Mg phase is not necessarily clear at this point, but if the cooling rate in this temperature range is fast, the temperature gradient in the thickness direction of the molten plated metal becomes large , So that precipitation of the Mg-Si layer is preferentially promoted on the surface of the molten plated metal having a lower temperature. As a result, it is considered that the deposition amount of the Si-Mg phase on the plating surface increases. The cooling rate in this temperature range is more preferably 40 DEG C / sec or less, and particularly preferably 35 DEG C / sec or less.

After cooling, the steel sheet 1a is subjected to temper rolling by the temper rolling and shape correcting device 11, and shape correction is carried out. The rolling reduction by temper rolling is preferably in the range of 0.3 to 3%. It is preferable that the elongation percentage of the steel sheet 1a by shape correction is 3% or less.

Subsequently, the steel plate 1a is wound by a winder 12, and the coil 14 of the steel plate 1a is held by the winder 12. As shown in Fig.

The temperature of the hot dip coating bath 2 in the port 7 is higher than the solidification starting temperature of the hot dip coating bath 2 and lower than or equal to the temperature . It is more preferable that the temperature of the hot dip coating bath 2 in the port 7 is higher than the solidification starting temperature of the hot dip coating bath 2 and lower than or equal to the temperature 25 占 폚 higher than the solidification starting temperature. When the upper limit of the temperature of the hot-dip coating bath 2 is limited in this manner, the steel sheet 1a is taken out of the hot-dip coating bath 2, and the hot- Time is shortened. As a result, the time during which the molten plated metal adhered to the steel sheet 1a is in a flowable state is shortened, thereby making it more difficult for wrinkles to be generated in the plated layer 23. When the temperature of the hot-dip coating bath 2 is 20 캜 or higher than the solidification-starting temperature of the hot-dip coating bath 2, the generation of the wrinkles in the coating layer 23 is remarkably suppressed.

When the steel sheet 1a is taken out from the hot dip galvanizing bath 2, it may be drawn out into a non-oxidizing atmosphere or a low oxidizing atmosphere, and the steel sheet 1a may be melted by the gas wiping method The adjustment amount of the plating metal may be adjusted. For this purpose, for example, as shown in Fig. 2, the transfer path (the upper side from the hot-dip coating bath 2) of the steel material 1 pulled out of the hot-dip coating bath 2 on the upstream side of the hot- The hollow member 22 is preferably filled with a non-oxidizing gas such as nitrogen gas or a low oxidizing gas. Non-oxidizing gas or low oxidizing gas means a gas having a lower oxygen concentration than the atmosphere. It is preferable that the oxygen concentration of the non-oxidizing gas or the low oxidizing gas is 1000 ppm or less. The atmosphere filled with the non-oxidizing gas or the low oxidizing gas is a non-oxidizing atmosphere or a low oxidizing atmosphere. The oxidation reaction is suppressed in this atmosphere. The injection nozzle 9 is disposed inside the hollow member 22. The hollow member 22 is provided so as to surround the conveying path of the steel material 1 from the upper side of the hot-dip galvanizing bath 2 in the hot-dip galvanizing bath 2 to above the hot-dip galvanizing bath 2 have. It is also preferable that the gas injected from the injection nozzle 9 is a non-oxidizing gas such as nitrogen gas or a low oxidizing gas. In this case, since the steel sheet 1a drawn out from the hot dip galvanizing bath 2 is exposed to the non-oxidizing atmosphere or the low oxidizing atmosphere, the oxidation of the hot-dip metal attached to the steel sheet 1a is suppressed, It is difficult to further form the Mg-based oxide film on the surface layer. As a result, the generation of wrinkles in the plating layer 23 is further suppressed. Instead of using the hollow member 22, a part of the hot-dip plating apparatus including the conveying path of the steel sheet 1a or the entire hot-dip galvanizing apparatus may be disposed in a non-oxidizing atmosphere or a low-oxidizing atmosphere.

It is also preferable that the steel plate 1a after the hot-dip coating treatment is further subjected to an overexposure treatment. In this case, the workability of the hot-dip coated steel material is further improved. The overheating treatment is carried out by maintaining the steel sheet 1a within a predetermined temperature range for a predetermined period of time.

Fig. 3A and Fig. 3B show an apparatus used for overexposure treatment, wherein Fig. 3A shows a heating apparatus. 3 (b) shows the warming container 20. The heating device has a conveying device in which the steel sheet 1a after hot-dip treatment is continuously conveyed. This conveying device is constituted by a feeder 16, a winder 17, and a plurality of conveying rolls 21 in the same manner as the conveying device in the hot-dip galvanizing apparatus. A heating furnace 18 such as an induction heating furnace is provided on the conveying path of the steel plate 1a by this conveying device. The heat insulating container 20 is not particularly limited as long as it can hold the coil 19 of the steel sheet 1a inside and is also a heat insulating container. The thermal insulation container 20 may be a large-sized container (thermal insulation room).

When the overheating treatment is applied to the steel sheet 1a, first, the coil 14 of the steel sheet 1a after the hot-dip coating treatment is carried by a crane, a truck or the like from the winder 12 of the hot- And is held by the feeder 16 of the feeder. In the heating apparatus, the steel plate 1a is loosened from the feeder 16 and fed out continuously. The steel sheet 1a is heated to a temperature suitable for overexposure treatment in the heating furnace 18 and then wound by a winder 17. The coil 19 of the steel sheet 1a is wound by the winder 17, Respectively.

Subsequently, the coil 19 of the steel plate 1a is carried by a crane, a truck or the like from the winder 17, and is held in the warming container 20. The coil 19 of the steel sheet 1a is held in the warming container 20 for a certain period of time, so that the steel sheet 1a is subjected to overtaking treatment.

The plating layer 23 formed on the surface of the steel sheet 1a according to the present embodiment contains Mg and the Mg-based oxide coating is present on the surface of the plating layer 23 in a small amount, Even if the plating layers 23 are overlapped with each other in the coils of the plating layers 23, As a result, even if the keeping time at the time of the overflow treatment is prolonged or the holding temperature is high, it is difficult to cause seizure, so that the steel sheet 1a can be subjected to sufficient overaging treatment. As a result, the workability of the hot-dip coated steel sheet is greatly improved and the efficiency of the overflow treatment is improved.

In the overflow treatment, particularly, the temperature of the steel sheet 1a after heating by the heating apparatus is in the range of 180 to 220 deg. C, that is, when the temperature of the steel sheet 1a is within the above range, It is preferable to be transferred into the container. It is preferable that the holding time y (hr) of the steel sheet 1a in the warming container satisfies the following formula (5).

(150? T? 250)

T (占 폚) in the formula (5) is the temperature (holding temperature) of the steel sheet 1a during the holding time y (hr) and is the lowest temperature when the temperature fluctuation occurs in the steel sheet 1a.

Further, in the present embodiment, the hot dip galvanizing apparatus and the heating apparatus are separate apparatuses, but the hot dip galvanizing apparatus may also serve as the heating apparatus by providing the heating furnace 18. In these devices, various elements may be added, removed or replaced as necessary, so that the design may be appropriately changed. The hot-dip coating apparatus and the heating apparatus according to the present embodiment are suitable for the case where the steel material 1 is the steel sheet 1a, but the configurations of the hot-dip coating apparatus and the heating apparatus are variously varied depending on the shape of the steel material 1 Design changes are possible. In the case where the preliminary plating treatment is applied to the steel material 1, this preliminary plating treatment can also be variously changed depending on the kind, shape, and the like of the steel material 1.

[Surface Treatment Method on Plating Layer (23)] [

The surface-treated hot-rolled steel material according to each embodiment of the present invention is produced by forming the above-described coating film 24 on the upper layer of the steel material 1 subjected to the above-mentioned hot-dip coating treatment. When the base treatment layer 27 described above is provided, the base treatment layer 27 is formed on the upper layer of the steel material 1 subjected to the above-mentioned hot-dip treatment, and the surface of the base treatment layer 27 A coating film 24 is laminated on the substrate. Here, when the coating film 24 and the base treatment layer 27 are formed, the base treatment layer 27 is coated on the steel material 1 and dried and baked. Thereafter, the coating film 24 is coated on the base treatment layer 27 And dried and baked. The coating composition for forming a film and the coating composition for forming a base treatment layer may be applied to the base steel 1 by wet-on-wet or multilayer simultaneous coating, and then both the coating compositions may be simultaneously baked and dried.

The plating layer 23 may be subjected to a nickel plating treatment or a cobalt plating treatment before the base coat layer 27 and the coating film 24 are formed. Alternatively, the plating layer 23 may be cleaned with pure water or various organic solvent solutions, An aqueous solution optionally containing an alkali or various etching agents, or a cleaning with various organic solvent solutions may be performed. When the surface of the plating layer 23 is cleaned in this manner, even if a small amount of the Mg-based oxide film is present on the surface layer of the plating layer 23 or an inorganic or organic contaminant adheres to the surface of the plating layer 23, Or contaminants are removed from the plating layer 23 and the adhesion between the plating layer 23 and the base treatment layer 27 or the coating film 24 is improved. Hereinafter, details of the method of forming the coating film 24 and the base treatment layer 27 will be described.

&Lt; Method of forming coating film 24 >

The method for forming the coating film 24 is not particularly limited, and it can be formed, for example, by coating a coating composition containing an organic resin in an aqueous solvent or an organic solvent-based solvent on a plated steel and heating and drying it. When a coating composition using an aqueous solvent (hereinafter referred to as a water-based coating) is used, a coating line dedicated for use of a coating composition using an organic solvent-based solvent (hereinafter referred to as an organic solvent-based coating) (VOC) can be largely suppressed in addition to the fact that it is possible to greatly reduce the manufacturing cost since the necessity of the water-borne coating . Here, the water-based solvent used in the water-based paint means that water is a solvent which is the main component of the solvent. The amount of water in the solvent is preferably 50% by mass or more. The solvent other than water may be an organic solvent, but it may be an organic solvent-based solvent. However, the amount of the organic solvent contained in the organic solvent content defined in the Ordinance for Prevention of Organic Solvent Poisoning under the Industrial Safety and Health Law (5% Is contained in an amount exceeding the above range). Further, the organic solvent-based solvent means that the organic solvent is a solvent which is the main component of the solvent.

The coating composition for forming the coating film 24 is not limited to a specific method and can be obtained by an arbitrary method. As an example, a preferable coating composition is taken as an example, and the components of the coating film 24 are added to an aqueous solvent or an organic solvent, which is a dispersion medium, and the mixture is stirred by a disperser to dissolve or disperse the dispersion. In the case where the dispersion medium is an aqueous solvent, in order to improve the solubility or dispersibility of each constituent component, a known hydrophilic solvent such as alcohols such as ethanol, isopropyl alcohol, t-butyl alcohol and propylene glycol , Ethylene glycol monobutyl ether and ethylene glycol monoethyl ether, esters such as ethyl acetate and butyl acetate, and ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone.

As a coating method of the coating composition on the plated steel material, any known method may be used without particular limitation. For example, roll coating, curtain coating, spray coating, bar coating, dipping, electrostatic coating and the like can be used as a coating method.

The heating and drying method for forming the coating film 24 from the coating composition is not particularly limited and can be carried out by any method. For example, it is possible to heat the plated steel material before coating the coating composition, or to heat the plated steel material after the coating, or to perform drying by combining them. There is no particular limitation on the heating method, and the coating composition can be dried and baked using hot air, induction heating, near-infrared rays, direct burning, or the like, alone or in combination. The drying baking temperature is preferably in the range of 100 ° C to 250 ° C, more preferably 120 ° C to 230 ° C, and most preferably 130 ° C to 220 ° C. If the reaching plate temperature is less than 100 캜, the coating film 24 may be insufficiently formed and corrosion resistance, scratch resistance and stain resistance may be lowered. On the other hand, if it exceeds 250 캜, baking hardening becomes excessive and corrosion resistance is lowered . The drying baking time (heating time) is preferably 1 second to 60 seconds, more preferably 3 seconds to 20 seconds. If the drying baking time is less than 1 second, the coating film 24 may be insufficiently formed and the corrosion resistance, scratch resistance and stain resistance may be lowered.

&Lt; Method of Forming Base Treatment Layer 27 >

The base treatment layer 27 is formed by applying a coating agent for forming the base treatment layer 27 to at least one side of the plated steel and heating and drying the same. The coating method of the coating agent is not particularly limited, but known roll coating, spray coating, bar coating, dipping, electrostatic coating and the like can be suitably used. The baking drying method is not particularly limited, and the plated steel material may be heated in advance, or the plated steel material may be heated after the application, or the combination may be combined and dried. The heating method is not particularly limited, and hot air, induction heating, near infrared rays, direct heating, etc. may be used alone or in combination. The baking drying temperature is preferably 60 占 폚 to 150 占 폚 at the reached temperature. If the temperature is reached to less than 60 캜, drying may be insufficient and the adhesion between the coating film 24 and the base plated steel and the corrosion resistance of the surface-treated hot plated steel may be lowered. If the temperature is higher than 150 캜, The adhesion of the adhesive layer may be deteriorated. A more preferable arrival temperature is 70 占 폚 to 130 占 폚.

The surface-treated hot-rolled steel material produced by the present embodiment suppresses irregularities on the surface of the plating due to wrinkling or sagging of the plating layer 23, . In addition, the effect of the coating film 24 is excellent especially in the white rust resistance of the processed portion, and also the scratch resistance and the stain resistance are excellent. The scratch resistance, scratch resistance and stain resistance of the machined portion are characteristics that were not considered in conventional high-Al-containing and Mg-containing plated steel materials.

This surface-treated hot-dip coated steel material can be employed in construction materials, automobile materials, materials for household appliances, and various other applications, and can be suitably used particularly for applications requiring corrosion resistance at the processing portion.

11A to 11H show the layer structure of the surface-treated hot-rolled steel in the embodiment of the present invention. 11A shows a layer structure formed of a steel material 1, a plated layer 23 and a coated film 24. Fig. Fig. 11B shows a layer structure formed of the steel material 1, the alloy layer 25, the plated layer 23, and the coating film 24. Fig. 11C shows a layer structure formed of the steel material 1, the pre-plated layer 26, the plated layer 23, and the coated film 24. Fig. Fig. 11D shows a layer structure formed of the steel material 1, the plating layer 23, the base treatment layer 27, and the coating film 24. Fig. 11E shows a layer structure formed of the steel material 1, the alloy layer 25, the plated layer 23, the base treatment layer 27, and the coating film 24. Fig. 11F shows a layer structure formed of the steel material 1, the pre-plated layer 26, the plated layer 23, the base treatment layer 27, and the coating film 24. 11G shows a layer structure formed of the steel material 1, the pre-plated layer 26, the alloy layer 25, the plated layer 23, and the coating film 24. 11H shows a layer structure formed of the steel material 1, the pre-plated layer 26, the alloy layer 25, the plated layer 23, the base treatment layer 27, and the coating film 24.

Example

The present invention will be further described with reference to examples in which a hot-dip coated steel sheet is used as the hot-dip galvanized steel. However, the present invention is not limited to the following examples.

(1) Hot-dip coated steel sheet (Hot-dip galvanized steel sheet)

First, a method of manufacturing a hot-dip coated steel sheet, an evaluation test method and a test result of the hot-dip coated steel sheet obtained by the method will be described.

[1.1. Production method of hot-dip coated steel sheet]

A long steel sheet 1a (low carbon aluminum killed steel) having a thickness of 0.80 mm and a width of 1000 mm was used as the steel material 1. This steel sheet 1a was subjected to hot-dip coating treatment using the hot-dip coating apparatus shown in Fig. The treatment conditions are shown in Tables 1 to 3. The solidification starting temperatures shown in Tables 1 to 3 are values derived from the liquid phase curve of the state diagram of the bath of the Zn-Al binary system, and the contents of Al in each of the molten bath bath compositions shown in Tables 1 to 3 Is the corresponding value. In the level M68 and M69, Ni plating was carried out before the steel sheet 1a was subjected to the hot-dip plating treatment. In the level M68, the adhesion amount (single side) was 0.5 g / M &lt; 2 &gt; of pre-plated layer 26 was formed. At the level M70, a pre-plating layer 26 of 1.0 g / m 2 in adhesion amount (single side) was formed by Zn-10% Cr pre-plating treatment. In other Examples and Comparative Examples, pre-plating treatment was not performed.

The temperature at the time of penetration of the steel sheet 1a into the hot-dip galvanizing bath 2 was 580 캜. When the steel sheet 1a was taken out of the hot-dip coating bath 2, it was drawn out into the air atmosphere and the gas wiping was also performed in the air atmosphere. However, for the level M71, the conveyance path of the steel sheet 1a on the upstream side of the hot-dip coating bath 2 is surrounded by the seal box (hollow member 22), and the injection nozzle 9) were disposed. The interior of the seal box was made to be a nitrogen atmosphere and the inside of the hollow member 22 was subjected to gas wiping with nitrogen gas.

In the cooling device 10, the steel sheet 1a was cooled until the surface temperature of the molten plated metal (the plated layer 23) became 300 캜. The cooling rate at the time of cooling was 45 占 폚 / sec. However, for the levels M76 and M77, the cooling rate in the temperature range where the surface temperature of the plated metal is 500 DEG C or higher is changed, and the cooling rate at the level M76 is 38 DEG C / sec in this process. The cooling rate was set at 28 DEG C / sec.

The reduction rate at the time of temper rolling was 1%, and the elongation rate of the steel sheet 1a at the time of shape correction was 1%.

[1.2. Evaluation test of hot-dip coated steel sheet]

The following evaluation tests were performed on the hot-dip coated steel sheet obtained by manufacturing the above-mentioned hot-dip coated steel sheet.

(1.2.1 Evaluation of volume ratio of Si-Mg phase)

The hot-dip coated steel sheet was cut in the thickness direction to obtain a sample. This sample was embedded in a resin so that the cut surface was exposed, and then the cut surface was polished into a mirror-like shape. The cut surface was observed by an electron microscope. The cut surface clearly showed a Si-Mg phase distributed in the plating layer 23.

An image obtained by photographing the cut surface of the hot-dip coated steel sheet obtained at the level M5 by an electron microscope is shown in Fig. Further, for the portion where the precipitation of the Si-Mg phase was confirmed, elemental analysis was performed using an energy dispersive X-ray analyzer (EDS). The results are shown in FIG. 4B. According to these results, it can be seen that only the two elements of Mg and Si are strongly detected. O (oxygen) was also detected, because oxygen adsorbed to the sample was detected in the sample production step.

The area ratio (%) of the Si-Mg phase on the cut surface is obtained by performing image analysis based on the sensed image with respect to the range of 20 mm in the direction orthogonal to the thickness direction on the cut surface of the plated layer 23, ) Were measured. Since the Si-Mg phase exhibits a dark gray shade and is clearly distinguished from the other phases, it was possible to easily discriminate by image analysis.

The area ratio (%) thus obtained was considered to be in agreement with the volume ratio of the Si-Mg phase, and the volume ratio of the Si-Mg phase was evaluated. The results are shown in Tables 4 to 6.

(1.2.2 Evaluation of mass ratio of Mg amount in Si-Mg phase to total Mg amount)

The mass ratio of the amount of Mg in the Si-Mg phase to the total amount of Mg in the plating layer 23 (mass ratio of Mg amount in Tables 4 to 6) was calculated by the aforementioned equations (1) to (4) . The results are shown in Tables 4 to 6.

(1.2.3. Evaluation of surface Mg content)

Elemental analysis of the component contained in the plating layer 23 in the hot-dip galvanized steel sheet in the depth direction (the thickness direction of the plating layer 23) was carried out by Glow Discharge-Optical Emission Spectroscopy (GD-OES) . In the measurement, the diameter of the measurement region was 4 mm, the output was 35 W, the measurement atmosphere was Ar gas, the measurement pressure was 600 Pa, the discharge mode was normal sputtering, the duty cycle was 0.1, the analysis time was 80 seconds, The light emission intensity of the element contained in the plating layer 23 was measured. In order to convert the obtained light emission intensity value into a quantitative concentration value (mass% concentration), elemental analysis of a standard sample such as a 7000-series Al alloy or a steel material with a known component concentration was also performed separately. Since the GD-OES data is in the form of a change with respect to the sputter time of the light emission intensity, the sputter depth is measured by cross-section observation of the sample after completion of the measurement, and the sputter depth is divided by the total sputter time, To specify the depth position of the plating layer 23 in the GD-OES depth direction profile.

As for the level M5 and the level M50, the analysis results are shown in Figs. 5A and 5B, respectively. According to this, it can be seen that at the level M50, the Mg concentration in the surface layer of the plating layer 23 rises sharply.

Based on this result, the content of Mg in the region where the size was 4 mm in diameter and the depth was 50 nm in the outermost layer at a depth of 50 nm in the plating layer 23 was derived. The results are shown in Tables 4 to 6.

(1.2.4. Evaluation of surface Cr content)

As in the case of the evaluation of the surface layer Mg amount, the integrated value of the Cr light emission intensity in the region having a diameter of 4 mm and a depth of 50 nm from the outermost surface of the plating layer was measured by GD-OES. Similarly, the integral value of the Cr light emission intensity of the entire plating layer 23 was also measured, and the ratio of the integral value of the Cr light emission intensity in this region to this value was obtained. Based on the ratio of the integral value of the Cr emission intensity and the chemical analysis value of the total amount of Cr in the plated layer 23 by ICP, the ratio of the Cr value in the region where the diameter is 4 mm and the depth from the top surface of the plating layer is 50 nm And the content of Cr was calculated. The results are shown in Tables 4 to 6.

(1.2.5 Evaluation of area ratio of Si-Mg phase on the surface of plating layer)

The surface of the plating layer 23 was observed by an electron microscope. A photograph of the surface M5 of the surface of the plating layer 23 taken by an electron microscope is shown in Fig. According to this observation result, it can be confirmed that the Si-Mg phase is distributed on the surface of the plating layer 23. Based on this result, the area of the Si-Mg phase on the surface of the plating layer 23 was measured, and based on this, the area ratio of the Si-Mg phase on the surface of the plating layer was calculated. The results are shown in Tables 4 to 6.

(1.2.6 Evaluation of alloy layer 25)

The hot-dip coated steel sheet was cut in the thickness direction to obtain a sample. This sample was embedded in a resin so that the cut surface was exposed, and then the cut surface was polished into a mirror-like shape. An alloy layer 25 interposed between the plating layer 23 and the steel sheet 1a appears on this cut surface. The thickness of the alloy layer 25 was measured. Further, a 10 占 퐉 20 占 퐉 portion of the polished surface was sampled from the polished surface by a focused ion beam apparatus to prepare a micro sample processed to a thickness of 50 nm or less. For this micro sample, the Cr concentration in the alloy layer 25 was quantitatively analyzed under the conditions of an acceleration voltage of 200 kV and a probe diameter of 1 nm using an energy dispersive X-ray analyzer (EDS).

Based on this result, the ratio of the mass ratio of Cr in the alloy layer 25 to the mass ratio of Cr in the plating layer 23 was calculated (Cr content ratio in Tables 4 to 6). The results are shown in Tables 4 to 6.

(1.2.7. Appearance evaluation)

The appearance of the surface of the plated layer 23 in the hot-dip coated steel sheet was visually observed by an optical microscope. 7A shows a photograph of the surface of the plating layer 23 at the level M5. 7B shows a photograph of the surface of the plating layer 23 at the level M10. 8A shows an optical microscope photograph of the surface of the plating layer 23 at the level M62. 8B shows an optical microscope photograph of the surface of the plating layer 23 at the level M5. Fig. 9 shows a photograph of the appearance of the plating layer 23 at the level M50.

Based on the observation result, the degree of wrinkling on the surface of the plating layer 23 was evaluated by the following criteria. The results are shown in Tables 4 to 6.

5: The wrinkles are not confirmed.

4: Wrinkles are slight (wrinkles of the degree shown in FIG. 7A).

3: Small degree of wrinkle (in the case of evaluation with a degree of wrinkle of between 4 and 2).

2: Wrinkle is moderate (better than that shown in Fig. 7B).

1: wrinkles are noticeable (wrinkles of the degree shown in Fig. 7B).

Based on the observation result, the degree of sagging of the surface of the plating layer 23 was evaluated by the following criteria. The results are shown in Tables 4 to 6.

2: Sagging is not confirmed.

1: Sagging is confirmed (sagging to the extent shown in FIG. 9).

In addition, based on the observation result, the degree of the dross adhering to the plating layer 23 was evaluated by the following criteria. The results are shown in Tables 4 to 6.

2: The surface of the plated layer 23 is free of adhesion of dross accompanied by unevenness, or adhesion of dross accompanying unevenness is confirmed at less than 5 sites per 1 m &lt; 2 &gt;.

1: At least 5 drosses per 1 m &lt; 2 &gt; of the surface of the plated layer 23 are observed.

Further, by observing the appearance characteristics of the plating layer 23 except for the wrinkles, sagging and dross, a leveling of the sequins was confirmed at the level M78 (see "Others " in Table 6).

(1.2.8 Evaluation of over-treatment)

The heat insulation temperature t (° C) and the insulation time y (hr) were varied with respect to the coil of the molten steel sheet of the level M5, and the overhanging treatment was carried out. The results were evaluated as follows.

3: No adhesion occurred between the plating layers on the coil, and the workability was improved.

2: No adhesion occurs between the plating layers on the coil, but the workability is not improved.

1: Cohesion occurred between the plating layers on the coil.

The results are shown in the graph of Fig. The abscissa in the graph represents the test temperature t (占 폚), and the ordinate represents the test condition for the keeping time y (hr). The evaluation results in the insulated temperature and the insulated time are shown at positions corresponding to the insulated temperature t (占 폚) and the insulated time y (hr) during the test in this graph. The area sandwiched between the broken lines in the graph is the area where the keeping temperature t (占 폚) and the keeping time y (hr) satisfy the following formula (5).

(150? T? 250)

(2) Surface-treated hot-dip coated steel sheet (surface-treated hot-rolled steel sheet)

Next, a method for manufacturing a surface-treated hot-dip coated steel sheet, an evaluation test method and a test result of the surface-treated hot-rolled steel sheet obtained by the method will be described.

[2.1. Method of producing surface-treated hot-dip coated steel sheet]

(2.1.1. Base treatment layer 27)

The coating agent for forming the base treatment layer 27 is composed of the organic resin shown in Table 7, the silane coupling agent shown in Table 8, the polyphenol compound shown in Table 9, the silica particles shown in Table 10, , The fluoro complexes shown in Table 12 and the vanadium (IV) compounds shown in Table 13 were compounded in the amounts shown in Table 14 (% by mass of solid content) and stirred using a paint disperser . Subsequently, the above-mentioned coating agent was coated on the surface of the hot-dip coated steel sheet produced by the above-mentioned method for producing a hot-dip coated steel sheet by a roll coater so as to have an adhesion amount of 100 mg / m 2 and dried at a temperature of a final plate temperature of 70 ° C, Thereby forming the base treatment layer 27.

(2.1.2. Coating film (24) and surface-treated hot-dip coated steel sheet)

The coating composition for forming the coating film 24 was prepared by mixing the organic resin shown in Table 15, the silica particles shown in Table 16, the lubricant shown in Table 17, the phosphoric acid compound shown in Table 18, the coloring pigment shown in Table 19 , And the crosslinking agents shown in Table 20 were compounded in amounts shown in Tables 21 to 29 (mass% of solid content) and stirred using a paint disperser. The coating composition is applied to the upper layer of the base treatment layer 27 formed in (2.1.1) (the molten plated steel sheet prepared in [1.1] in the case where there is no base treatment layer 27) Coated with a roll coater so as to be heated and dried to a predetermined arrival plate temperature to form a coating film 24, thereby obtaining a surface-treated hot-dip coated steel sheet. The coating film composition of the surface-treated hot-dip coated steel sheet and the film thickness and the reaching plate temperature of the coating film 24 are also shown in Tables 21 to 29. [

(2.1.3 Evaluation test)

A test piece of 70 mm x 150 mm in size was cut from the surface-treated hot-dip coated steel sheet obtained in the above (2.1.2), and the corrosion resistance, scratch resistance and stain resistance of the processed portion were evaluated by the following evaluation methods and evaluation standards. The evaluation results are shown in Tables 30 to 38.

[Process corrosion resistance]

A 6 mm extrusion process was performed on the center portion of the test piece by an Erichsen tester (in accordance with the A dimension of JIS Z 2247), then the end surface was tape-sealed, and a salt spray test according to JIS Z 2371 Hour, 72 hours, and 120 hours, and the occurrence of rust in each test time of the portion subjected to Erichen processing was observed, and evaluated by the following evaluation criteria.

5: Less than 1% area of occurrence of white rust.

4: Occurrence area of white rust is 1% or more and less than 5%.

3: area of occurrence of white rust is 5% or more and less than 10%.

2: Occurrence area of white rust is 10% or more and less than 30%.

1: White rust occurrence area is 30% or more.

[Scratch resistance]

After placing the test piece on a rubbing tester (manufactured by Daicel Chemical Industries, Ltd.), a 30 mm x 30 mm corrugated cardboard was placed on the tip of the sliding jig of the rubbing tester so as to be parallel to the test piece, , And the state of the film after rubbing 5 reciprocations and 10 reciprocations was evaluated by the following evaluation criteria.

5: There is no trace on the friction surface.

4: Scratches very slightly on the friction surface (the level at which the scratch can barely be judged by stare).

3: A slight sliding on the friction surface results in a scratch (a level at which scratches can be distinguished easily when striking).

2: Clear sliding scratches on the friction surface (level at which scratches can be distinguished quickly).

1: The coating on the friction surface is dropped, and the metal plate of the base is exposed.

[Pollution resistance]

The fingerprint was attached to the test piece by pressing the finger, and the fingerprint was wiped with the cotton cloth after standing at room temperature for 1 hour, and the remaining marks of the fingerprint were evaluated by the following evaluation criteria.

5: There is no fingerprints.

4: The fingerprints remain very small (the level at which you can barely detect the fingerprints).

3: Fingerprints are slightly left (level at which fingerprints can be easily distinguished when you take a finger).

2: The fingerprints remain (the fingerprints can be identified in an instant, but the fingerprints and hue are not clearly changed).

1: The fingerprint remains clearly (the fingerprint can be identified in an instant, and the fingerprint area and the hue are clearly changed).

As shown in Tables 30 to 38, the examples of the present invention exhibited excellent machining corrosion resistance, scratch resistance and stain resistance at all three points or more in any evaluation test. On the other hand, in Comparative Examples 1 to 10, 12 and 13 in which the content of the molten plated layer was out of the range of the present invention, the corrosion resistance of the processed portion was deteriorated. In Comparative Example 11 in which the coating film 24 was not coated, corrosion resistance, scratch resistance and stain resistance of the processed portion were poor.

While the preferred embodiments of the present invention have been described above, it goes without saying that the present invention is not limited to these examples. Those skilled in the art will appreciate that within the scope of the claims, it is obvious that various changes or modifications may be made and obviously also fall within the technical scope of the invention.

According to the present invention, there is provided a surface-treated hot-plated steel material having excellent anti-whiteness, scratch resistance and stain resistance of a machined portion and suppressing occurrence of wrinkles and sagging on the surface of the plating layer.

1: Steel
1a: steel plate
2: Hot-dip coating bath
3: Feeder
4: heating furnace
5: Annealing and cooling section
6: Snout
7: Port
8: sink roll
9: Spray nozzle
10: Cooling unit
11: rough rolling and shape correcting device
12: Winder
13: coil (first coil)
14: coil (second coil)
15: conveying roll
16: Feeder
17: Winder
18: Heating furnace
19: Coil
20: Insulation container
21: conveying roll
22: hollow member
23: Aluminum-zinc alloy plating layer (plating layer)
24:
25: alloy layer
26: Pre-plated layer
27: base treatment layer
28: Cover
101: Primary cooling system
102: Secondary cooling system

Claims (11)

Steel,
And a coating on the surface of the steel,
Wherein the coating comprises a plating layer and a coating film containing an organic resin on the surface of the plating layer in the order of the steel material,
Wherein the plating layer contains Al, Zn, Si, Mg and Cr as constituent elements and further contains Al in an amount of 25 to 75 mass%, Mg in an amount of 0.1 to 10 mass%, Cr in an amount of 0.02 to 1.0 mass% 0.5 to 10% by mass with respect to the Al content, the balance being Zn and inevitable impurities,
Wherein the plating layer contains 0.2 to 15% by volume of a Si-Mg phase,
The mass ratio of Mg in the Si-Mg phase to the total amount of Mg in the plating layer is not less than 3% and not more than 100%
A ridge having a height greater than 200 占 퐉 and a steepness greater than 1.0 is not present on the surface of the plating layer,
Wherein the organic resin is crosslinked by at least one member selected from a silane coupling agent, a crosslinkable zirconium compound, a crosslinkable titanium compound, an epoxy compound and an amino resin. The steel sheet according to claim 1, wherein the Mg content is 0 mass% or more and less than 60 mass% in any region where the diameter is 4 mm and the depth is 50 nm in the outermost layer at a depth of 50 nm from the surface of the plating layer Wherein the surface-treated hot-dip galvanized steel material is characterized by: The surface-treated hot-rolled steel material according to claim 1, wherein the coating film has a thickness of 0.1 to 10 占 퐉. The surface-treated hot-rolled steel material according to claim 1, wherein the coating further contains silica particles. The surface-treated hot-rolled steel material according to claim 4, wherein the organic resin is A and the silica particles are B, and the solid content mass ratio A / B is 2 to 20. The surface-treated hot-rolled steel sheet according to claim 4 or 5, wherein the silica particles contain spherical silica particles having an average particle diameter of 5 to 20 nm and spherical silica particles having an average particle diameter of 0.08 to 2 m . The surface-treated hot-rolled steel material according to any one of claims 1 to 4, wherein the coating further contains at least one of a lubricant, a phosphoric acid compound and a colored pigment. The surface-treated hot-rolled steel material according to any one of claims 1 to 4, further comprising a base treatment layer containing a component derived from an organic resin and a silane coupling agent in a lower layer of the coating film. The surface-treated hot-rolled steel material according to claim 7, further comprising a base treatment layer containing a component originating from an organic resin and a silane coupling agent in a lower layer of the coating film. The organic electroluminescent device according to claim 8, wherein the organic resin and the plating layer are crosslinked by at least one member selected from a silane coupling agent, a crosslinkable zirconium compound, a crosslinkable titanium compound, an epoxy compound and an amino resin. Treated hot-rolled steel. The organic electroluminescent device according to claim 9, wherein the organic resin and the plating layer are crosslinked by at least one member selected from a silane coupling agent, a crosslinkable zirconium compound, a crosslinkable titanium compound, an epoxy compound and an amino resin. Treated hot-rolled steel.

Images