JPH0762428A - Anti-oxidizing agent for steel belt - Google Patents

Abstract

PURPOSE:To provide an anti-oxidizing gent for a steel belt which prevents the formation of an oxidized scale in the case of annealing treatment under a high temp. oxidizing atmosphere and can easily be removed after annealing treatment. CONSTITUTION:The anti-oxidizing agent is incorporated with at least one kind inorg. colloidal matter selected from the group consisting of zirconia, titania, tungusten oxide, vanadium oxide, yttrium oxide and iron oxide and having <=1300 deg.C crystallization temp. and the inorg. metallic having <=1300 deg.C melting temp. as an active component. The agent forms dense amorphous coating film on the surface of the steel belt and the formation of the oxidized scale is prevented, and the coating film is easily peeled from the surface of the steel belt by being converted to a crystalline coating film when temp. is allowed to rise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antioxidant applied to the surface of a steel strip prior to continuous annealing and pickling of the steel strip. More specifically, it prevents generation of oxide scale in a high temperature oxidizing atmosphere. , An antioxidant for steel strips that can be stripped completely and easily.

[0002]

2. Description of the Related Art Generally, a steel strip after cold rolling is annealed to obtain mechanical properties. The conventional annealing treatment is, for example, H ₂ (3% to 15%) in the case of carbon steel.
%) + N ₂ (85% to 97%) in the weak reducing atmosphere of the CA method or H ₂ (75% in the case of stainless steel).
%) + N ₂ (25%) in a strongly reducing atmosphere, BA method, or O ₂ (2% to 3%) in an oxidizing atmosphere, AP method.

Of these, in order to avoid the formation of oxide scale on the surface of the steel strip during the annealing step, the CA method or BA method is used.
Although the methods are suitable, both have the disadvantages of low thermal efficiency and high cost. On the other hand, the AP method is relatively low in cost as compared with the above-mentioned two methods using a reducing atmosphere, but has a drawback that dense oxide scale is generated due to the oxidizing atmosphere.

Hereinafter, the annealing process of the AP method will be described in detail with reference to FIG. The steel strip after cold rolling, for example, a stainless steel strip, is annealed and pickled in a continuous annealing pickling line. FIG. 1 is a schematic diagram of a continuous annealing pickling line (hereinafter referred to as APL) that is generally performed. In the figure, 1 is a payoff reel, 2 is an entrance side shear, 3 is a welder, and 4 is degreasing. The devices 5 are entrance loopers. An annealing furnace 6 is composed of a heating part 7 and a cooling part 8, and the heating part 7 is composed of a pre-tropical zone, a heating zone, a soaking zone and the like.
Reference numerals 9, 10, and 11 denote a plurality of pickling tanks in which a salt bath, a neutral salt electrolytic bath, a nitric acid bath, a nitric hydrofluoric acid bath, and the like are appropriately combined. Reference numeral 12 is a cleaning device, 13 is a dryer, 14 is an exit looper, 15 is a split shear, and 16 is a tension reel.

In this APL, first, the cold rolled stainless steel strip S rewound by the pay-off reel 1 is used.
Is cut at the leading end or the rear end at the entrance side shear 2 and is connected to the preceding coil by the welder 3. Next, in the stainless steel strip S, the cold rolling oil adhered to the surface is removed by the degreasing device 4
And then sent to the annealing furnace 6 through the entrance looper 5 and subjected to a predetermined heat treatment. At this time, the heating unit 7
In, the stainless steel strip S is supported in a catenary form by the asbestos roll 71 and heat-treated by an open flame burner. After that, cooling by an air jet is performed in the cooling unit 8. Since the annealing is performed in the combustion gas atmosphere by the direct flame burner in this manner, a dense oxide scale layer having a thickness of about 20 to 400 mμ is formed on the surface of the stainless steel strip S. Therefore, in order to remove the dense oxide scale layer, the plurality of pickling tanks 9 to 11 are used to descale the stainless steel strip S and passivate it.

Next, the surface is cleaned by a cleaning device 12 that performs brushing, spraying, etc., and dried by a dryer 13. After that, the split shear 1 is passed through the exit looper 14.
After being cut into a predetermined length by 5, the tension reel 1
Take up to 6.

[0007]

However, the conventional annealing process of the AP method has the following problems. (1) The surface of the steel strip after cold rolling has a low heat absorption rate because it is close to a mirror surface, and a long furnace is required to raise the annealing temperature in the heating part 7 of the annealing furnace 6 of APL. Or, the strip running speed in the furnace must be reduced.

(2) A plurality of pickling facilities are required to remove the dense oxide scale layer formed on the surface of the steel strip by the AP method. In particular, since the oxide scale of the stainless steel strip is denser than that of carbon steel, a long pickling facility is required to remove the oxide scale layer. Furthermore, since the types and amounts of chemicals used are large, the labor and cost of treating the waste liquid also become great.

For this AP method, CA for carbon steel
Method, the BA method for stainless steel does not generate oxide scale due to heat treatment in a reducing atmosphere, but since indirect heating is required, the thermal efficiency is poor and the treatment cost is high as described above. There was a problem that it would be expensive. As a solution to such a problem, for example, Japanese Patent Publication Sho 56
-8092 discloses a method in which carbon, a black dye, or a mixture thereof is applied to the surface of a steel strip and continuously annealed.

However, although this conventional method can improve the heat absorption rate on the surface of the steel strip, it has various problems as described below. The adhesion of the coating film of carbon, black dye or the like to the surface of the steel strip is insufficient, and a uniform coating film cannot be formed. Since the coating film decomposes in the furnace, the formation of oxide scale cannot be prevented.

When the entire coating film is not completely decomposed in the furnace, the remaining fired coating film can prevent the formation of oxide scale on the surface of the steel strip in that portion, but after the annealing step is completed, The residual fired coating cannot be completely and easily removed from the band surface. Oxide scale produced on the surface of the steel strip adheres to the hearth roll in the furnace, and growth of this causes pick-up flaws on the surface of the steel strip. For this reason, frequent replacement of hearth rolls is required, resulting in reduced productivity and increased maintenance.

Therefore, the present invention has been made by paying attention to the above-mentioned conventional problems, and it is possible to improve the heat absorption rate in the annealing step and prevent the generation of oxide scale in a high temperature oxidizing atmosphere. And further reduce the labor and cost of waste pickling in the pickling step after annealing,
Moreover, it is an object of the present invention to solve the above-mentioned conventional problems by providing an antioxidant for a steel strip that can be easily removed after annealing.

[0013]

The antioxidant of the steel strip of the present invention which achieves the above object comprises zirconia, titania, tungsten oxide, vanadium oxide, yttrium oxide and iron oxide which crystallize at 1300 ° C. or less. 1300 at least one kind of inorganic colloidal material selected from the group
An inorganic metal salt having a melting point of 0 ° C. or lower is contained as an active ingredient.

The inorganic metal salt may be composed of at least one selected from the group consisting of alkali metal salts or alkaline earth metal salts of silicic acid, boric acid and phosphoric acid. Further, the antioxidant of the steel strip of the present invention may further contain a refractory material in addition to the inorganic colloidal substance and the inorganic metal salt.

The refractory material may be composed of at least one selected from the group consisting of metal oxides, composite oxides, and carbides. The present invention will be described in detail below. Generally, the steel strip after cold rolling is subjected to an annealing treatment in order to improve mechanical properties. In continuous annealing, which is one of the annealing treatments, the annealing temperature of the steel strip differs depending on the steel type, and for example, SUS304 is 1120-1200 ° C, and SUS430 is 800-90.
The processing temperature is 0 ° C. and 700 to 800 ° C. for electromagnetic steel and carbon steel, which is approximately 1300 ° C. or less.

The inorganic colloidal substance used for the antioxidant of the present invention is zirconia which has a crystallization temperature of 1300 ° C. or less and is thermally stable in view of the treatment temperature of the steel strip.
It is selected from the group of oxides consisting of titania, tungsten oxide, vanadium oxide, yttrium oxide and iron oxide.
These inorganic colloidal substances have a particle size of 5 mμ-100
Since it is as small as mμ, when it is applied to the surface of the steel strip, the surface of the steel strip can be densely covered and fine irregularities can be formed. Due to the unevenness, the specularity of the surface of the steel strip is lost, the apparent heat receiving area increases, and the heat absorption rate of the surface of the steel strip increases. As a result, it becomes easy to raise the temperature in the annealing step, and it is not necessary to use a long annealing furnace as in the past. Moreover, productivity can be improved without lowering the steel sheet passing speed.

The inorganic colloidal substance sprayed on the surface of the steel strip forms an apparent dry film by the temperature rise in the annealing furnace, and then dehydration of fine inorganic substance particles occurs at about 300 to 600 ° C. When the temperature exceeds ℃, condensation occurs between particles and a strong amorphous amorphous film is formed. Due to the formation of this amorphous coating, oxidizing components (O ₂ , C in the annealing atmosphere)
O ₂ and H ₂ O) are cut off from the surface of the steel strip to prevent the formation of oxide scale in the furnace.

When the temperature further rises, the amorphous amorphous film has a thermal characteristic that it changes into a crystalline film. Since this crystalline coating has a smaller coefficient of linear expansion than steel strip, cracks occur in the coating due to the difference in shrinkage ratio with the steel strip in the next cooling step, and a simple mechanical method such as water washing or nylon brushing is used. Can be easily removed from the surface of the steel strip.

Therefore, the inorganic colloidal substance used in the present invention forms a crystalline film by crystallizing at 1300 ° C. or lower, which is the upper limit of the annealing temperature of the steel strip in continuous annealing, preferably 700 to 1300 ° C. is there. If an inorganic colloidal substance having a crystallization temperature of more than 1300 ° C is used, the amorphous amorphous film formed on the surface of the steel strip during annealing remains fused on the surface of the steel strip. In addition, it becomes difficult to easily peel and remove it.

The antioxidant of the steel strip according to the present invention further comprises 13
An inorganic metal salt having a melting point of 00 ° C. or lower is blended with the above inorganic colloidal substance. As a result, the "non-crystalline amorphous film formation temperature" of the inorganic substance forming the inorganic colloidal substance
And "the temperature at which the crystalline film is formed" can be changed,
By adjusting the blending amount, the most suitable antioxidant can be provided according to the type of the target steel strip product.

Further, by blending the inorganic metal salt, the amorphous amorphous film and the crystalline film become more dense, the adhesion to the steel strip surface is improved, and the function of preventing the formation of oxide scale can be further enhanced. The above-mentioned inorganic metal salts having a melting point of 1300 ° C. or lower are alkali metal salts and alkaline earth metal salts of silicic acid, boric acid and phosphoric acid, and specific examples thereof include lithium silicate, potassium silicate and sodium silicate. , Magnesium silicate, aluminum silicate, lithium borate, potassium borate, sodium borate, calcium borate, potassium phosphate, sodium phosphate, magnesium phosphate, calcium phosphate, and the like, including at least one of these. It is a waste. Melting point 13
If the temperature exceeds 00 ° C, the "amorphous amorphous film formation temperature" and "crystalline film formation temperature" of the inorganic substance forming the colloid cannot be adjusted, and the film adhered to the steel strip surface remains. Is not preferable.

FIG. 2 shows changes in the "formation temperature of the amorphous amorphous film" and the "formation temperature of the crystalline film" when the inorganic colloidal substance is mixed with the inorganic metal salt sodium silicate. From the figure, it can be seen that the “formation temperature of the amorphous amorphous film” and the “formation temperature of the crystalline film” gradually decrease as the compounding amount of sodium silicate increases.

Taking advantage of this, in the antioxidant of the present invention, the compounding ratio of the inorganic colloidal substance and the inorganic metal salt is, for example, stainless steel, electromagnetic steel or carbon steel. To produce an antioxidant coating with thermal properties that are best matched to the respective annealing temperature. The antioxidant of the steel strip of the present invention may further contain an appropriate amount of a dispersant in order to obtain a uniform and smooth dry coating film on the surface of the steel strip.

The dispersant used is an organic polymer such as corn starch, tapioca starch, sodium alginate,
Guar gum, xanthan gum, pullulan, casein, gelatin, α-starch, dextrin, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose,
It contains at least one selected from the group consisting of carboxymethyl cellulose, hydroxymethylpropyl cellulose, polyvinyl alcohol, polypropylene glycol, polyethylene oxide, polyvinyl butyral, and the like.

When the steel strip antioxidant of the present invention is annealed at a high temperature for a long time, a refractory material as an active ingredient, an inorganic colloidal substance or an inorganic colloidal substance and 1300 are used. Incorporation in a mixture with an inorganic metal salt having a melting point of not higher than 0 ° C. can further improve the prevention of oxide scale formation. The refractory material, chemically stable aluminum resistant to high temperatures, silicon, magnesium, zirconium, metal oxides of titanium, such as alumina, silica, magnesia, zirconia, titania and the like, further mullite, Andalusite, chamotte, magnesite, spinel, dolomite, montmorillonite, kaolinite, a group consisting of composite oxides such as sepiolite, and silicon carbide,
It contains at least one selected from the group consisting of carbides such as titanium carbide, tungsten carbide, boron carbide and molybdenum carbide.

The average particle size of these refractory materials is 10 μm.
It is preferably m or less. If the particle size exceeds 10 μm, the refractory material particles adhere to the hearth roll in the annealing furnace to cause a flaw on the surface of the steel strip, which is not preferable. In the antioxidant of the steel strip of the present invention, as a solvent for dispersing the inorganic colloidal substance, the inorganic metal salt, the dispersant, and the refractory material, water or a mixture of water and an organic solvent having a boiling point of 150 ° C. or less Can be used.

A solvent having a boiling point of more than 150 ° C. slows the drying speed of the coating film, leading to a reduction in the plate passing speed, and swelling or peeling of the coating film due to volatilization of the organic solvent in the annealing furnace to prevent oxidation. It is not preferable because the effect cannot be obtained. Suitable organic solvents include alcohols such as methanol, ethanol, propanol, butanol, 2-butanol, isopropanol, pentanol, ethylene glycol, 2-ethoxyethanol and propylene glycol methyl ether.

The application of the antioxidant to the steel strip of the present invention is usually carried out by means of applying the antioxidant uniformly and evenly to the surface of the steel strip at the entrance side of the annealing furnace, for example, mist spray, roll coater. An electrostatic coating device or the like can be used, but the invention is not limited thereto.

[0029]

When the steel strip antioxidant of the present invention is applied to the surface of the steel strip and annealed, a fine inorganic colloidal substance film is formed on the surface of the steel strip and the specularity of the steel strip surface disappears. The heat absorption rate of the belt is improved. Further, the apparent heat receiving area is also increased and the temperature rise in the furnace is promoted.

The fine particles of the inorganic colloidal substance are
When the temperature is about 300 ° C to 600 ° C, a dehydration reaction occurs, and when the temperature exceeds 600 ° C, the particles are condensed with each other to form a strong and dense amorphous amorphous coating and adhere to the surface of the steel strip.
This coating blocks the oxidizing components in the oxidizing atmosphere of the annealing furnace and prevents the formation of oxide scale on the surface of the steel sheet. When the temperature further rises, this amorphous amorphous coating changes to a crystalline coating due to its thermal characteristics, so the coefficient of linear expansion becomes smaller than that of the steel strip, and many cracks due to the difference in the shrinkage rate of the two in the coating. Occurs. As a result, the fired coating film of the antioxidant can be easily separated from the surface of the steel strip by washing with water and brushing in the cooling process after annealing.

[0031]

EXAMPLES The present invention will be described below with reference to examples.
In this example, an inorganic colloidal substance, an inorganic metal salt, a refractory material, an antioxidant of the steel strip of the present invention blended with a dispersant, and an antioxidant of a blend different from this as a comparative example, Continuous annealing of the stainless steel strip in the continuous annealing pickling line (APL) of FIG. 1 was carried out, and the performance of the antioxidant (antioxidant property, peeling property) was measured after the temperature rising time in the annealing furnace and after passing through the annealing furnace. Tested and evaluated.

[Chemicals Used in Test] Inorganic Colloidal Substance Zirconia; Nippon Shokubai Co., Ltd., Titania; Nissan Chemical Co., Ltd., "TA-10 (trade name)" Vanadium Oxide; Nissan Chemical Co., Ltd. Inorganic metal salts lithium borate, calcium borate, sodium silicate, potassium silicate, lithium silicate, potassium phosphate, magnesium phosphate, sodium phosphate, as comparative examples, zirconium phosphate, zinc phosphate, vanadium phosphate , Sodium molybdate, potassium vanadate; all reagents used were manufactured by Kanto Chemical Co., Inc.

Refractory material Alumina; Showa Denko KK "Alumina A-42-
1 (trade name) "Magnesia; Sobuecure Co., Ltd.," Magnesia powder "Mullite; Kinsei Matec Co., Ltd.," Mullite Flower "Silicon Carbide; Taiheiyo Random Co., Ltd.," GMF-6 "
"S (trade name)" As a comparative example, silicon nitride; manufactured by Kinsei Matech Co., Ltd., titanium nitride; manufactured by Kinsei Matech Co., Ltd., iron oxide; manufactured by Nissou Sangyo Co., Ltd., "iron oxide NAT (trade name)" Oxidation Yttrium; manufactured by Shin-Etsu Chemical Co., Ltd., dispersant Zansan gum; manufactured by Kelco Company, hydroxypropylmethyl cellulose; manufactured by Shin-Etsu Chemical Co., Ltd., polyethylene oxide; manufactured by Sumitomo Seika Chemicals, "PE
O-3 (trade name) "[steel strip used for test] Stainless steel strip; SUS304, width 1.0 m x length 10.0 m
× Plate thickness 1.0 mm [Test method] In a continuous annealing pickling line for stainless steel strip, the antioxidant of the present invention and the antioxidant of Comparative Example were roll coater-processed on the entire surface of the steel strip on the entrance side of the annealing furnace. After coating, the temperature rise time in the annealing furnace and the performance (antioxidation property, peeling property) after passing through the annealing furnace were evaluated.

The film thickness after coating is 20 μm to 3 by wet.
The thickness was 0 μm and the dry thickness was 1 μm to 2 μm. The baked coating after annealing was removed by air jetting on the outlet side of the annealing furnace, followed by washing with water and a nylon brush. The compositions (wt%) and viscosities of the examples of the antioxidant of the present invention used in this evaluation test are shown in Tables 1 and 2.

[0035]

[Table 1]

[0036]

[Table 2]

Table 3 shows the composition (% by weight) and viscosity of the antioxidant of the comparative example used in this evaluation test.

[0038]

[Table 3]

Table 4 shows the evaluation results of the antioxidants shown in Table 1, Table 2 and Table 3, respectively.

[0040]

[Table 4]

The "adhesion of dry coating film", "antioxidation performance in annealing furnace" and "peeling performance after annealing" in Table 4 were all evaluated by visual area ratio. The "oxidation prevention performance in the annealing furnace" was evaluated by the area ratio of the residual scale on the surface after the evaluation of the "peeling performance after annealing". In addition, “whether or not adhered to hearth roll” was evaluated by observing the surface of the hearth roll after application on the entire surface and evaluating the adhesion between the antioxidant of the present invention and the antioxidant of the comparative example.

From the results shown in Table 4, it can be said that the antioxidant of the present invention is superior to all the evaluation items in comparison with the comparative example. Above all, the antioxidant effect in the annealing furnace and the steel strip after annealing are excellent. It is recognized that the peeling property from the surface is particularly excellent. Further, the thickness of the oxide scale generated in the steel strip surface after annealing, GDS (G low D ischar
ge atomic emission S pectr
The results of measurement by oscopy) are shown in FIGS. 3 (a) and 3 (b). The figure (a) shows the case where the antioxidant is not applied, and the figure (b) shows the case where the antioxidant of the present invention (No. 5 in Table 1) is applied.

From FIG. 3, the thickness of the oxide scale layer is about 450 mμ for the uncoated material, while it is about 1.8 mμ for the coated material. By using the antioxidant of the present invention, the oxide scale layer is It is clear that the generation thickness of was reduced to about 1/250. FIG. 4 shows the temperature 113 in the annealing furnace.
The results of measuring the temperature rising time required for the steel strip surface temperature to reach 1120 ° C. at 0 ° C. by a thermocouple are shown.

From the figure, in the case of the antioxidant-coated material of the present invention (No. 5 in Table 1), the heating time up to the heating temperature of 1120 ° C. was shortened by about 45% as compared with the uncoated material. I understand. In other words, by using the antioxidant of the present invention, the furnace length could be shortened by 49% and the strip running speed in the furnace could be increased by about 1.9 times. Although the stainless steel strip (SUS304) has been described above, the present invention can be applied to other stainless steel strips (SUS430 series, SUS420 series, etc.) and ordinary steel, high carbon steel, silicon steel, and the like.

[0045]

As described above, the antioxidant of the steel strip of the present invention is zirconia which crystallizes at 1300 ° C. or lower,
Since the composition contains at least one kind of inorganic colloidal substance selected from the group consisting of titania, tungsten oxide, vanadium oxide, yttrium oxide, and iron oxide, and an inorganic metal salt having a melting point of 1300 ° C. or less as an active ingredient , When this is applied to the surface of a steel strip and annealed, a dense amorphous amorphous film with fine irregularities is formed, which covers the surface of the steel strip and shields it from the oxidizing atmosphere in the furnace to form oxide scale. Prevent the occurrence of heat, improve the heat absorption rate of the steel strip and increase the apparent heat receiving area, and
When the temperature further rises, the amorphous amorphous coating changes to a crystalline coating with a linear expansion coefficient smaller than that of the steel strip, and many cracks occur in the coating during the cooling process, making it possible to easily peel from the steel strip surface. Along with this, the following various effects are obtained.

(1) By improving the heat absorption efficiency of the surface of the steel strip, it is possible to shorten the annealing time or shorten the furnace length, and as a result, it is possible to save energy costs. (2) Further, the productivity can be improved by increasing the strip running speed of the steel strip. (3) By preventing the generation of oxide scale on the surface of the steel strip, not only the pickling equipment can be simplified, but also the running cost such as the cost of chemicals used for pickling or the waste acid treatment cost can be reduced.

(4) It is possible to prevent pick-up defects due to the hearth roll due to the oxide scale and improve the quality of the steel strip. (5) Since it is possible to prevent the formation of oxide scale even in a direct-fired annealing furnace, an uneconomical annealing method such as CA method or BA method is unnecessary. (6) Since the peelability after annealing is good, it can be easily removed from the surface of the steel strip on the outlet side of the annealing furnace by simple mechanical means.
Does not reduce product quality.

[Brief description of drawings]

FIG. 1 is a schematic view of a continuous annealing pickling line for steel strips.

FIG. 2 is a graph showing the relationship between the compounding ratio of the antioxidant of the present invention and the thermal characteristics of the antioxidant coating.

FIG. 3 is a graph showing the oxide scale formation preventing effect of the antioxidant of the present invention. FIG. 3 (a) shows the case where the antioxidant is not applied, and FIG. It is the figure which showed thickness.

FIG. 4 is a graph showing the annealing time shortening effect of the antioxidant of the present invention.

[Explanation of symbols]

 6 Annealing furnace 7 Heating part 8 Cooling part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Zenji Yamaguchi Yokkaichi-shi, Mie 6-6-9 In Yokkaichi Research Center, Hakuto Co., Ltd. (72) Inventor Masaharu Ikeda 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Inside the Chiba Steel Works (72) Genichi Ishibashi No. 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside Kawasaki Works Chiba Works Co., Ltd. (72) Kuniaki Sato No. 1 Kawasaki-cho, Chuo-ku, Chiba City Made in Kawasaki Chiba Steel Works, Ltd.

Claims (4)

[Claims] 1. At least one inorganic colloidal substance selected from the group consisting of zirconia, titania, tungsten oxide, vanadium oxide, yttrium oxide, and iron oxide, which crystallizes at 1300 ° C. or lower, and a melting point at 1300 ° C. or lower. An antioxidant for a steel strip, which comprises an inorganic metal salt having an active ingredient. 2. The inorganic metal salt is composed of at least one selected from the group consisting of alkali metal salts of silicic acid, boric acid and phosphoric acid or alkaline earth metal salts. The antioxidant for steel strips according to 1. 3. The antioxidant for a steel strip according to claim 1, which contains a refractory material. 4. The refractory material is a metal oxide, a composite oxide,
The steel strip antioxidant according to claim 3, wherein the antioxidant is composed of at least one selected from the group consisting of carbides.