JP2003231826A - Coating material for preventing oxidation and decarbonization of steel material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coating material for preventing the oxidation and the decarbonization of a steel material, having excellent adhesion to the surface of the steel material and excellent functions for preventing the oxidation and the decarbonization. <P>SOLUTION: The coating material for preventing the oxidation and the decarbonization of the steel material contains a refractory powder and a binder. The refractory powder contains a silicon carbide powder, and an aqueous solution containing a colloidal silica and ammonium silicate is used as the binder. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel material oxidation and decarburization coating composition for preventing oxidation and decarburization on and near the surface of a steel material heated to a high temperature.

[0002]

2. Description of the Related Art Generally, a steel material is melted, continuously cast or ingot-cast and then slab-rolled to be formed into a billet slab (hereinafter abbreviated as a slab). After being heated to a desired temperature in a heating furnace, hot rolling is performed to form a hot rolled steel strip. A hot-rolled steel strip or a so-called cold-rolled steel strip rolled in a room temperature environment and a cut plate obtained by cutting these steel strips are used for various applications as a steel product.

The operating conditions of the heating furnace or soaking furnace for heating the slab before hot rolling differ depending on the material and size of the slab and the restrictions of peripheral equipment such as the rolling capacity of the hot rolling apparatus. The temperature is about 1100 to 1300
Reach high temperature of ℃. Therefore, the slab that is heated to a high temperature in the atmosphere generates scale due to surface oxidation while being heated to a high temperature, and this oxidized scale is lost due to pickling treatment after hot rolling, etc. It will be a loss. For example, with ordinary steel having a slab thickness of about 250 mm, the above-mentioned yield loss may be 1% by weight or more.

Carbon, which is a relatively easy-to-diffuse element, reacts with oxygen in the heating atmosphere to generate carbon dioxide when it diffuses and moves to the surface of the slab and is released from the slab. May occur.
When decarburization is performed from the surface layer of the slab, the decarburization layer near the surface and the inner layer of the slab having the original carbon composition cause a difference in the metal structure based on the difference in the carbon composition. When the metal structure differs between the surface layer and the inner layer of the slab, for example, the characteristics such as high-temperature deformability are different.Therefore, defects due to local differences in high-temperature deformability during hot rolling, that is, surface cracking of the steel strip and Defects such as edge cracks, which are cracks in the widthwise ends, occur and the quality deteriorates. Therefore, an effective technique for preventing oxidation and decarburization during heating of the slab is required.

[0005]

There is a case where a non-oxidizing furnace is used as one means for preventing oxidation and decarburization at the time of heating or soaking the slab as described above. The non-oxidizing furnace, for example, injects fuel from a burner into the radiant tube to burn it to avoid direct flame heating, and heats the slab in an atmosphere of an inert gas such as nitrogen to oxidize and decarburize the slab. To prevent. However, compared with an atmospheric furnace that heats a slab in the atmosphere, a non-oxidizing furnace has a complicated structure and thus requires a high equipment cost, and the cost of an inert gas used is also high. There is a problem that it can only be used for high-grade steel materials such as alloy steel.

[0006] Therefore, a conventional technique for preventing oxidation and decarburization of steel materials is to shield the slab surface from the atmosphere by mechanically covering the slab or applying a coating material to the slab. . As a means for mechanically covering the slab, it is known to provide a surface protective cover for the slab with a thin steel plate. However, the method of providing the surface protection cover requires a great deal of labor and time for attaching the surface protection cover to the slab, and
Since it will be the indirect heating of the slab through the surface protection cover,
There are problems such as worsening the fuel consumption rate of the furnace.

As a method of applying a coating material to a slab, there is a method of applying a high temperature antioxidant coating material containing a silica-based, magnesia-based, low melting point metal or an inorganic salt, and JP-A-2-205622 discloses A method for applying a high-temperature decarburization preventing coating material composed of silicon carbide powder, silica sol, emulsion resin and the like is disclosed, and is disclosed in JP-A-5-171261.
The official gazette discloses a method of applying an anti-oxidizing paint made of silicon carbide powder, low melting point glass, colloidal silica or the like.

However, silica type, magnesia type,
High-temperature antioxidant coatings containing low melting point metals or inorganic salts can be oxidized by different slab steel types with different contents of elements such as Cu, Ni, Cr and different heating furnace systems such as continuous or batch systems. There is a problem in that there is a difference in prevention effect, and there is also a problem in that no effect can be obtained for preventing decarburization. In addition, although the antioxidant coating composed of silicon carbide powder, low melting point glass, colloidal silica, etc. is excellent in the paint peeling property when the coated steel material is taken out of the furnace, it has variations in the antioxidant and decarburization prevention performance. There's a problem.

[0009] In a paint for preventing the oxidation and decarburization of the steel material by blocking the surface of the steel material during heating from the atmosphere, the binder plays a large role. That is, the binder not only binds the refractory powder, but does not cause the paint to adhere to the slab surface during heating of the steel material to cause peeling and cracks, and to heat the slab before hot rolling. When taken out of the furnace, it is required to be easily peeled off so as not to hinder hot rolling.

The above-mentioned prior art, Japanese Patent Laid-Open No. 2-205
In 622, an alkaline aqueous silica sol stabilized with an alkali metal as a binder for colloidal silica,
An acidic silica sol to which a stabilizing amount of a nitrogen-containing organic group such as a monoethanolamine or a quaternary ammonium salt is added is disclosed, and JP-A-5-171261 discloses a binder such as sodium aluminate, a low melting point glass, and colloidal. Silica, alumina sol and the like are disclosed.

However, the coating materials using any of the binders disclosed in the prior art are compatible with any of various types of steel materials having different compositions and do not cause peeling while being heated in a heating furnace for a long time. In addition, it is not always satisfactory from the viewpoint of adhering to the slab surface without causing cracks and realizing a sufficient oxidation and decarburization preventing function.

An object of the present invention is to provide a coating material for preventing oxidation and decarburization of steel material, which has excellent adhesion to the surface of steel material and excellent function of preventing oxidation and decarburization.

[0013]

The present invention is a steel material oxidation and decarburization preventing paint comprising a refractory powder and a binder, wherein the refractory powder comprises silicon carbide powder and the binder is colloidal silica. A paint for preventing oxidation and decarburization of steel, which is an aqueous solution containing ammonium silicate.

According to the present invention, the coating for preventing oxidation and decarburization of steel material uses an aqueous solution containing silicon carbide powder as the refractory powder and colloidal silica and ammonium silicate as the binder. As a result, while the steel material to which the steel material oxidation and decarburization preventing paint has been applied is heated to a high temperature, the paint does not adhere to the steel material surface and cause peeling and cracking, which effectively protects the atmosphere. It can be blocked to prevent oxidation and decarburization of the steel surface. Further, since silicon carbide (carbon (C) and silicon (Si)) contained in the paint is preferentially oxidized over, for example, iron (Fe) and carbon (C) existing on the surface of the steel material, oxidation and decarburization of the steel material. Prevention is realized.

In the present invention, the ammonium silicate contained in the binder is a quaternary ammonium having a chemical structure represented by the following general formula (I) in 100 parts by weight of colloidal silica dispersion in terms of SiO _2. 5 to 3
It is characterized by being produced from a part of colloidal silica by adding 5 parts by weight.

[0016]

[Chemical 2]

(In the above general formula (I), R1 to R4
Are each independently an alkyl group having 1 to 4 carbon atoms, and 1 to 4 carbon atoms.
4 represents an alkoxyl group or a benzyl group. )

According to the present invention, the ammonium silicate contained in the binder is produced from a part of the colloidal silica by adding quaternary ammonium to the colloidal silica dispersion. In this way, the coexistence of colloidal silica and ammonium silicate, which is necessary for the composition of the binder, is achieved by the addition of quaternary ammonium to the colloidal silica dispersion liquid. Both improvement of storage stability can be realized.

The present invention is also characterized in that the binder is an aqueous solution containing 25% by weight or more of Si content in terms of SiO ₂ .

According to the present invention, since the binder contains colloidal silica in a suitable range, the miscibility between the silicon carbide powder, which is a refractory powder, and the binder is kept good.

In the present invention, the ratio (Wc) of the weight Wc of the silicon carbide powder contained in the refractory powder to the SiO ₂ equivalent weight Ws of silicon (Si) contained in the binder.
/ Ws) is 2 to 50.

According to the present invention, the ratio (Wc / W) of the weight Wc of the silicon carbide powder contained in the refractory powder to the SiO ₂ equivalent weight Ws of silicon (Si) contained in the binder.
Since s) is selected within a suitable range, it is possible to obtain a coating material for preventing oxidation and decarburization of steel material, which has excellent binder binding force and excellent film forming property.

The present invention is also characterized in that the silicon carbide powder contained in the refractory powder has an average particle diameter of 0.1 to 20 μm.

According to the present invention, since the average particle diameter of the silicon carbide powder contained in the refractory powder is selected within a suitable range, it has excellent miscibility with the binder and may become porous at the time of forming the coating film. It also prevents cracking during heating of the coating film formed on the steel surface.

The present invention is also characterized in that the refractory powder contains 80% by weight or more of silicon carbide powder.

According to the present invention, since the refractory powder contains silicon carbide powder in a preferable range, a coating material for preventing oxidation and decarburization of steel having a sufficient function of preventing oxidation and decarburization can be realized. .

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION A coating material for preventing oxidation and decarburization of steel (hereinafter simply referred to as coating material for preventing oxidation and decarburization) is
Includes refractory powder and binder. The refractory powder of the present embodiment contains 80% by weight or more of silicon carbide powder, and the silicon carbide powder contained in the refractory powder has an average particle size of 0.
It is 1 to 20 μm. When the steel material coated with the oxidation and decarburization preventing coating material containing silicon carbide powder is heated to a high temperature in the air atmosphere, the silicon carbide contained in the coating material contains iron (Fe) and carbon ( Prevents oxidation and decarburization of steel by reacting with oxygen in the atmosphere and oxidizing preferentially over C).

Here, the reason for limiting the content of the silicon carbide powder in the refractory powder and the range of the average particle diameter will be described. If the content of the silicon carbide powder is less than 80% by weight, Fe and C contained in the steel material preferentially react with oxygen in the atmosphere to cause a shortage of an oxidizable source to be oxidized. The prevention function, especially the decarburization prevention function, will not be fully exerted. Therefore, it is set to 80 wt% or more. The content of the silicon carbide powder that exhibits even more sufficient oxidation prevention and decarburization prevention functions is more preferably 90%.
It is at least wt%, more preferably at least 95 wt%. Other refractory powders such as silicon oxide powder may be used together with the silicon carbide powder under the condition that the content of the silicon carbide powder satisfies the above-mentioned preferable range.

The silicon carbide powder has an average particle diameter of 0.1 μm.
When it is less than m, the miscibility with the binder is poor, and cracks are likely to occur in the coating film, and when it exceeds 20 μm, the coating film tends to be porous. Therefore, the thickness is set to 0.1 to 20 μm.
An even more preferable average particle diameter of the silicon carbide powder is 0.
It is 2 to 10 μm.

The binder is an aqueous solution containing colloidal silica and ammonium silicate, and the Si content in the aqueous solution is 25% by weight or more in terms of SiO ₂ . Further, ammonium silicate contained in the binder of the present embodiment is
Formed from a part of colloidal silica by adding 5 to 35 parts by weight of quaternary ammonium having a chemical structure represented by the following general formula (I) to 100 parts by weight of colloidal silica dispersion calculated as SiO _2. To be done.

[0031]

[Chemical 3]

(In the above general formula (I), R1 to R4
Are each independently an alkyl group having 1 to 4 carbon atoms, and 1 to 4 carbon atoms.
4 represents an alkoxyl group or a benzyl group. )

By using the binder in which the colloidal silica and ammonium silicate coexist in the aqueous solution for the coating material, the adhesion of the coating material to the surface of the steel material is improved, and the steel material coated with the coating material is heated to a high temperature in the atmosphere. When heated, the coating film does not crack, and peeling from the steel surface is prevented. Although it is not clear what the effect of such a binder is based on, the ammonium silicate contained in the binder is dissolved in water as an ion, so that even inside the surface oxide film of the steel material It is considered that this is due to synergistic effects such as easy penetration, increasing the binding force of the coating film formed by coating, and suppressing the change with time of colloidal silica.

Such a binder is produced as a coexisting aqueous solution of ammonium silicate and colloidal silica by adding quaternary ammonium to a usual silica sol and reacting it as described above. The reason for limiting the addition range of quaternary ammonium with respect to colloidal silica will be described below. If the addition amount is less than 5 parts by weight, the amount of ammonium silicate produced by the reaction with the colloidal silica is small, and a binder exhibiting the desired effect cannot be obtained. If the addition amount exceeds 35 parts by weight, the stability of the colloidal silica is improved. Make it worse. Therefore, the addition amount is set to 5 to 35 parts by weight. The quaternary ammonium may be one given by the general formula (I), but choline is preferably used.

The reason for limiting the content of Si in the aqueous solution will be described. The Si content is 25 in terms of SiO _2.
If it is less than wt%, the miscibility with the silicon carbide powder will deteriorate, so it was set to 25 wt% or more. Still more preferably, the Si content is 30% by weight or more in terms of SiO ₂ .

The binder as described above can be obtained by mixing a commercially available silica sol (for example, Adelite AT-40 manufactured by Asahi Denka Co., Ltd.) with a quaternary ammonium salt and reacting them.

The mixing ratio of the refractory powder and the binder is
It is defined as follows. When the weight of the silicon carbide powder contained in the refractory powder is Wc and the SiO ₂ conversion weight of silicon (Si) contained in the binder is Ws, the weight ratio (Wc / Ws) is 2 to 50. Mixed in. If the weight ratio (Wc / Ws) is less than 2, the amount of silicon carbide powder is too small and the film-forming property is deteriorated.
When it exceeds the above range, the silicon carbide powder is too much and the bond strength of the coating is deteriorated. Therefore, the weight ratio (Wc / Ws) should be 2 to 50.
And

(Examples) Examples of the present invention will be described below, but the present invention is not limited to these examples. The coating materials of the respective Examples and Comparative Examples described below were applied to the test steel material while adjusting the coating film thickness and heated at a predetermined temperature for a predetermined time, and then the residual amount WR of the base metal of the steel material and the decarburized layer depth Dt were measured. The measurement was performed to evaluate the oxidation and decarburization prevention performance of each paint.
Next, a method for measuring the coating film thickness, the residual amount WR of the base metal and the decarburized layer depth Dt for the test steel material will be described.

(1) Coating film thickness: A predetermined amount of coating material was applied to the test steel material, and then the coating film was air dried. The coating film after drying was measured using an electromagnetic film thickness meter SL-200E (manufactured by Sankou Denshi Kenkyusho).

(2) Residual amount of base metal WR: The weight of the test steel material before applying the coating material is W1, the coating material is applied and heated in a heating furnace at a predetermined temperature for a predetermined time. The weight of the test steel material after removing the generated oxide scale is W2. Since the oxide scale has a weak adhesive strength with the substrate due to heat shock when taken out from the furnace, it can be easily peeled and removed by applying a light impact with a mallet or the like. In this example, the sample steel was taken out of the furnace, allowed to cool and cooled, and then the surface of the sample steel was hit with a mallet or spatula corner made of SUS to give an impact to remove the scale.

The residual amount WR of the base material is given by the following equation. WR (%) = 100 × W2 / W1 That is, the residual amount WR of the base material represents the yield after oxidation reduction by heating. The larger the value, the better the yield, and the better the antioxidant effect of the paint. Represents

(3) Decarburized layer depth Dt: The coating material was applied to the test steel material and heated at a predetermined temperature for a predetermined time in a heating furnace, and then the coating material and the oxide scale formed on the test steel material were removed. Further, the test steel material was cut, the cut surface was polished by sandpaper and buffing, the polished surface was etched and observed under a microscope, and the decarburized layer depth Dt was measured. The smaller the decarburized layer depth Dt, the better the decarburization prevention effect.

(Binder Production Example 1) About 40 grams of silica sol (AT-50 manufactured by Asahi Denka Co., Ltd .: 50% by weight as SiO ₂ ) was placed in a beaker having a volume of 200 mL (milliliter), and an aqueous choline solution was added to 80 parts by weight of the silica sol. 20 parts by weight (concentration of 50% by weight) was added dropwise to the mixture with stirring with a magnetic stirrer at room temperature for about 30 minutes. The binder obtained at this time is referred to as binder A.

(Binder Production Example 2) Silica sol (Adelite AT-40 manufactured by Asahi Denka: 40% by weight as SiO ₂ )
About 40 grams was placed in a 200 mL beaker, and 20 parts by weight of an aqueous choline solution (concentration: 50% by weight) was added dropwise and mixed with 80 parts by weight of the silica sol at room temperature for about 30 minutes while stirring with a magnetic stirrer. The binder obtained at this time is referred to as Binder B.

(Binder Production Example 3) Silica sol (Adelite AT-40 manufactured by Asahi Denka: 40% by weight as SiO ₂ )
About 40 grams was placed in a 200 mL beaker, and 15 parts by weight of an aqueous choline solution (concentration: 50% by weight) was added dropwise to the silica sol (85 parts by weight) at room temperature for about 30 minutes while stirring with a magnetic stirrer. The binder obtained at this time is called binder C.

(Binder Production Example 4) Silica sol (Adelite AT-40 manufactured by Asahi Denka Co., Ltd .: 40 wt% as SiO ₂ )
About 40 grams was placed in a 200 mL beaker, and 10 parts by weight of a choline aqueous solution (concentration: 50% by weight) was added dropwise to about 90 parts by weight of the silica sol at room temperature for about 30 minutes while stirring with a magnetic stirrer. The binder obtained at this time is referred to as a binder D.

Example 1 Commercially available powder having a purity of 95% and an average particle diameter of 1 μm was used as the silicon carbide powder. 100 parts by weight of the binder A of Production Example 1 was added as a binder to 100 parts by weight of the above-mentioned silicon carbide powder, and mixed with a stirrer to prepare a coating material 1 of the embodiment.

The binder A is an aqueous solution in which colloidal silica having an Si content of 40% by weight in terms of SiO ₂ concentration and choline of 10% by weight and ammonium silicate coexist.

Example paint 1 produced as described above
The dimensions are: width: 50 mm, length: 30 mm, thickness: 1
A 0 mm high carbon steel SK4 (a carbon tool steel material specified in Japanese Industrial Standard G4401) was applied twice with a brush and naturally dried at room temperature. The coating film thickness was 120 μm. The steel material coated with the paint of Example 1 was charged into an electric furnace, held at 1160 ° C. for 90 minutes in the air atmosphere, and then taken out from the electric furnace to remove the coating film and the oxide scale layer, and the base material remained. The amount WR and the decarburized layer depth Dt were measured. The measurement results were as follows. Base material residual amount WR is 99.8% by weight
(Oxidation weight loss 0.2% by weight), and the decarburized layer depth Dt is
It was zero (hereinafter referred to as 0) μm.

Example 2 67 parts of the binder B of Production Example 2 was added to 100 parts by weight of the same silicon carbide powder as in Example 1.
Part by weight was added and mixed with a stirrer to prepare Example Paint 2. The binder B is an aqueous solution in which colloidal silica whose Si content is adjusted to 32 wt% in terms of SiO ₂ concentration and choline is adjusted to 10 wt% and ammonium silicate coexist.

The coating material of Example 2 was brush coated on high carbon steel SK4 having the same dimensions as in Example 1 and naturally dried. The coating thickness is
It was 100 μm. The test was conducted in the same manner as in Example 1, and the residual amount WR of the base material and the decarburized layer depth Dt were measured. The measurement results were as follows. Base material residual amount WR is 99.9
% By weight (oxidation weight loss 0.1% by weight), depth of decarburized layer D
t was 0 μm.

Example 3 To 100 parts by weight of a commercially available silicon carbide powder having a purity of 98.7% and an average particle diameter of 7 μm, 100 parts by weight of the binder A similar to that in Example 1 was added and mixed with a stirrer. Example paint 3 was prepared.

The coating material of Example 3 was brush coated on high carbon steel SK4 having the same dimensions as in Example 1 and naturally dried. The coating thickness is
It was 150 μm. The test was conducted in the same manner as in Example 1, and the residual amount WR of the base material and the decarburized layer depth Dt were measured. The measurement results were as follows. Base material residual amount WR is 98.7
% By weight (oxidation weight loss: 1.3% by weight), depth of decarburized layer D
t was 50 μm.

Example 4 100 parts by weight of commercially available silicon carbide powder having a purity of 95% and an average particle diameter of 1 μm was added with 100 parts by weight of the binder C of Production Example 3 as a binder and mixed by a stirrer. Then, Example Paint 4 was prepared. The binder C has a Si content of 34% by weight in terms of SiO ₂ conversion concentration,
It is an aqueous solution in which colloidal silica having a choline content adjusted to 7.5% by weight and ammonium silicate coexist.

The coating material of Example 4 was brush coated on high carbon steel SK4 having the same dimensions as in Example 1 and naturally dried. The coating thickness is
It was 120 μm. The test was conducted in the same manner as in Example 1, and the residual amount WR of the base material and the decarburized layer depth Dt were measured. The measurement results were as follows. Base material residual amount WR is 99.1
% By weight (oxidation weight loss: 0.9% by weight), depth of decarburized layer D
t was 10 μm.

Example 5 To 100 parts by weight of commercially available silicon carbide powder having a purity of 95% and an average particle size of 1 μm, 100 parts by weight of the binder D of Production Example 4 was added as a binder and mixed by a stirrer. Then, Example Paint 5 was prepared. The binder D has a Si content of 36% by weight in terms of SiO ₂ conversion concentration,
It is an aqueous solution in which colloidal silica in which choline is adjusted to 5% by weight and ammonium silicate coexist.

The coating material of Example 5 was brush coated on high carbon steel SK4 having the same dimensions as in Example 1 and naturally dried. The coating thickness is
It was 100 μm. The test was conducted in the same manner as in Example 1, and the residual amount WR of the base material and the decarburized layer depth Dt were measured. The measurement results were as follows. Base material residual amount WR is 99.7
% By weight (oxidation weight loss: 0.3% by weight), depth of decarburized layer D
t was 10 μm.

Example 6 A refractory powder, 90 parts by weight of the same silicon carbide powder as in Example 1, and a commercially available average particle size of 5 were used.
Example Paint 6 was prepared in the same manner as Example 1 except that 10 parts by weight of silicon oxide powder having a particle size of 10 μm was used.

The coating material of Example 6 was brush coated on high carbon steel SK4 having the same dimensions as in Example 1 and naturally dried. The coating thickness is
It was 120 μm. The test was conducted in the same manner as in Example 1, and the residual amount WR of the base material and the decarburized layer depth Dt were measured. The measurement results were as follows. Base material residual amount WR is 98.8
% By weight (oxidation weight loss: 1.2% by weight), depth of decarburized layer D
t was 30 μm.

As described above, in the coating materials 1 to 6 of the present invention, excellent oxidation and decarburization preventing effects were recognized. Although the residual amount WR of the base metal exceeds 1% by weight, this is because the dimension of the test steel material is smaller than that of the slab, and this is because the specific surface area relative to the weight of the test steel material is large. When the size is increased and the specific surface area with respect to the weight is small as described above, the improved result is less than 1% by weight.

(Comparative Example 1) Silica Doll 30B manufactured by Nippon Kagaku Kogyo Co., Ltd. containing 30% by weight of colloidal silica as a binder in terms of SiO ₂ with respect to 100 parts by weight of the same silicon carbide powder as in Example 1 (trade name) ) 67 parts by weight was added, and Comparative Paint 1 was prepared in the same manner as in Example 1.

Comparative paint 1 was brush coated on high carbon steel SK4 having the same dimensions as in Example 1 and naturally dried. The coating thickness is
It was 100 μm. The test was conducted in the same manner as in Example 1, and the residual amount WR of the base material and the decarburized layer depth Dt were measured. The measurement results were as follows. Base material residual amount WR is 98.6.
% (Oxidation loss 1.4%), the decarburization layer depth Dt was as large as 500 μm, and the decarburization prevention effect was insufficient.

Comparative Example 2 A soda-stabilized silica sol manufactured by Nippon Kagaku Kogyo Co., Ltd. containing 40 parts by weight of colloidal silica as a binder in terms of SiO ₂ with respect to 100 parts by weight of the same silicon carbide powder as in Example 1. 67 parts by weight of Silica Doll 40 (trade name) was added, and Comparative Example Paint 2 was prepared in the same manner as in Example 1. The comparative paint 2 was highly viscous and could not be used as a paint 1 hour after the preparation.

[0064]

According to the present invention, the coating for preventing oxidation and decarburization of steel material uses an aqueous solution containing silicon carbide powder as the refractory powder and colloidal silica and ammonium silicate as the binder. As a result, while the steel material to which the steel material oxidation and decarburization preventing paint has been applied is heated to a high temperature, the paint does not adhere to the steel material surface and cause peeling and cracking, which effectively protects the atmosphere. It can be blocked to prevent oxidation and decarburization of the steel surface. Further, since silicon carbide (carbon (C) and silicon (Si)) contained in the paint is preferentially oxidized over, for example, iron (Fe) and carbon (C) existing on the surface of the steel material, oxidation and decarburization of the steel material. Prevention is realized.

Further, according to the present invention, the ammonium silicate contained in the binder is produced from a part of the colloidal silica by adding the quaternary ammonium to the colloidal silica dispersion. In this way, the coexistence of colloidal silica and ammonium silicate, which is necessary for the composition of the binder, is achieved by the addition of quaternary ammonium to the colloidal silica dispersion liquid. Both improvement of storage stability can be realized.

Further, according to the present invention, since the binder contains colloidal silica in a preferable range, the miscibility between the silicon carbide powder, which is a refractory powder, and the binder is kept good.

Further, according to the present invention, the ratio of the weight Wc of the silicon carbide powder contained in the refractory powder to the SiO ₂ equivalent weight Ws of the colloidal silica contained in the binder (Wc /
Since Ws) is selected within a suitable range, it is possible to obtain a coating material for preventing oxidation and decarburization of steel which is excellent in binder binding force and coating film forming property.

Further, according to the present invention, since the average particle diameter of the silicon carbide powder contained in the refractory powder is selected within a suitable range, it has excellent miscibility with the binder and prevents the generation of bubbles during the formation of the coating film. In addition, the occurrence of cracks during heating of the coating film formed on the surface of the steel material is prevented.

Further, according to the present invention, since the refractory powder contains silicon carbide powder in a preferable range, a coating material for preventing oxidation and decarburization of steel having a sufficient function of preventing oxidation and decarburization can be realized. It

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4J038 AA011 HA436 HA441 HA451                       JB01 MA08 MA10 NA01 PA19                       PC02

Claims (6)

[Claims] 1. A paint for preventing oxidation and decarburization of steel material, which comprises refractory powder and a binder, wherein the refractory powder contains silicon carbide powder, and the binder is an aqueous solution containing colloidal silica and ammonium silicate. A paint for preventing oxidation and decarburization of steel, which is characterized by being present. 2. The ammonium silicate contained in the binder is 5 parts by weight of quaternary ammonium having a chemical structure represented by the following general formula (I) in 100 parts by weight of colloidal silica dispersion in terms of SiO _2. The paint for preventing oxidation and decarburization of steel according to claim 1, which is produced from a part of colloidal silica by adding 35 parts by weight. [Chemical 1] (In the general formula (I), R1 to R4 each independently represent an alkyl group having 1 to 4 carbon atoms, an alkoxyl group having 1 to 4 carbon atoms, or a benzyl group.) 3. The paint for preventing oxidation and decarburization of steel according to claim 1 or 2, wherein the binder is an aqueous solution containing 25% by weight or more of Si in terms of SiO ₂ . 4. The ratio (Wc / Ws) of the weight Wc of the silicon carbide powder contained in the refractory powder to the SiO ₂ equivalent weight Ws of silicon (Si) contained in the binder is 2 to 50. A paint for preventing oxidation and decarburization of steel according to any one of claims 1 to 3, which is characterized in that. 5. The oxidation and decarburization of the steel material according to claim 1, wherein the silicon carbide powder contained in the refractory powder has an average particle diameter of 0.1 to 20 μm. Preventive paint. 6. The paint for preventing oxidation and decarburization of steel according to claim 1, wherein the refractory powder contains 80% by weight or more of silicon carbide powder.