JPH0323611B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a cold rolled steel strip with good surface properties, particularly phosphating properties and surface cleanliness, in a method of producing a cold rolled steel strip by a continuous annealing method. It is something. [Conventional technology] In recent years, instead of annealing using batch furnaces,
The continuous annealing method, in which a coiled material is charged from one end of the annealing furnace and subjected to a prescribed heat treatment inside the furnace, has been adopted to improve productivity and reduce quality variations. I'm getting old. In continuous annealing, a cold-rolled steel strip is charged into a continuous annealing furnace and is gradually heated while being mechanically fed. After the recrystallization process, it undergoes primary cooling, and then undergoes overaging treatment and secondary cooling. is common. So far,
In continuous annealing, various studies have been made regarding heat treatment conditions, particularly cooling rate, cooling atmosphere, cooling water, etc. For example, one example of this is the conventional method of preventing the formation of an oxide film on the steel sheet surface during water quenching during continuous annealing of cold rolled steel sheets, in which the cooling water contains a compound commonly called an organic acid. Can be seen. The conventionally used organic acids are as follows. Specifically, Japanese Patent Publication No. 57-47738 describes linear aliphatic acids such as formic acid, acetic acid, propionic acid, oxalic acid, and succinic acid; oxyacids such as citric acid, lactic acid, gluconic acid, and tartaric acid; triacetic acid,
Examples include ethylenediaminetetraacetic acid disodium. The nitrilotriacetic acid and ethylenediaminetetraacetic acid are aminopolycarboxylic acids, do not belong to the amino acid category, and are completely different. Further, JP-A-57-85923 discloses a metal coolant consisting of a water-soluble organic acid and a water-soluble organic amine, and the organic acid specifically includes water-soluble dicarboxylic acids having 3 or more carbon atoms. As, saturated dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, unsaturated dicarboxylic acids such as maleic acid and itaconic acid, malic acid,
Oxycarboxylic acids such as tartaric acid are mentioned as preferred examples. Further, JP-A-58-55533 describes a hardening method using an aqueous solution containing an organic acid such as malonic acid, formic acid, citric acid, acetic acid, lactic acid, succinic acid, tartaric acid, or the like. As mentioned above, various organic acids have been described, but depending on the temperature conditions of the solution and the temperature conditions of the cold-rolled steel strip after cooling, they may not be able to sufficiently suppress the oxide film generated. , removal of the oxide film may be difficult. Furthermore, when a cold rolled steel sheet obtained from these cold rolled steel strips is subjected to phosphate treatment, a non-uniform treatment film may be formed in some cases. On the other hand, in order to improve the phosphoric acid treatment properties and the corrosion resistance and paintability of cold-rolled steel sheets, there is a method that uses a steel sheet annealing process to generate trace amounts of metals or metal oxides on the steel sheet surface. It has been known.
For example, regarding phosphate treatment, JP-A-55-
14854, JP-A-49-34437 for corrosion resistance and paint adhesion, and JP-A-48-34738 and JP-B-49-48823 for materials suitable for can manufacturing. be. In these known techniques, the metal compound is made into an aqueous solution as a means to uniformly disperse and adhere metal ions to the surface of the steel sheet, and the making of the metal compound into an aqueous solution itself does not serve any other purpose. . Furthermore, in order to generate a metal or metal oxide on the surface of a steel sheet, it is necessary to apply an aqueous solution containing a metal compound to the cold-rolled steel sheet and dry it before the annealing step. This is because if the steel plate is subjected to the annealing process with water still attached to it, the surface of the steel plate will be oxidized as the dew point increases due to the water, and the metal will not be sufficiently reduced, making precipitation difficult. Furthermore, in JP-A No. 57-149429, when continuously annealing a cold rolled steel sheet, water quenching is performed with an aqueous solution containing a metal compound, and by adhering the metal, a cold rolled steel sheet with excellent corrosion resistance and chemical conversion treatment property is developed. BACKGROUND ART Methods for manufacturing rolled steel plates are known. In this known technology,
Difficult to maintain constant surface cleanliness. That is, depending on the cooling conditions of the cold-rolled steel strip, it may be difficult to suppress the formation of an oxide film on the surface of the steel strip. [Problems to be Solved by the Invention] The present invention aims to thin the oxide film of a cold rolled steel sheet during continuous annealing, improve the appearance, and at the same time maintain a surface condition excellent in phosphating properties. A manufacturing method is provided. [Means for Solving the Problems] The present invention improves the surface cleanliness of a cold rolled steel strip by using an aqueous solution containing a metal compound and an α-amino acid as the primary cooling water in continuous annealing. At the same time, it is possible to effectively perform an effective pretreatment for phosphate treatment. The metal compound used in the present invention may be either an inorganic compound or an organic compound as long as it is water-soluble and produces metal or metal oxide on the surface of the steel strip when used in the primary cooling water. I can do it. Metal elements include Ni, Co, Mn, Zn, Cu,
Cr, Mo, Ti, W, etc. (excluding Na); in the case of organic compounds, formic acid, acetic acid, citric acid, tartaric acid,
These are salts of succinic acid, lactic acid, oxalic acid, etc. For example, in the case of Ni, they are nickel formate, nickel acetate, and nickel citrate. In the case of inorganic compounds, Mo may be ammonium molybdate, W may be ammonium tungstate, etc., and the solution may be an aqueous solution containing one or more of these organic compounds and inorganic compounds. The lower limit of the concentration of the metal compound applied to the present invention is the concentration that can play an effective role in phosphating properties, but the upper limit is the concentration that prevents the metal precipitated on the surface of the cold rolled steel strip from being retained in the form of nuclei. Limited to what you can get. In other words, the amount of metal deposited on the cold-rolled steel sheet manufactured using the cooling water is sufficient to be suitable for phosphate treatment, and the metal precipitated on the surface of the steel strip will cause the surface of the steel sheet to become glossy. There is no need to generate a large amount of metal that would affect the process or cause the nuclei of the precipitated metal to connect with each other to form a metal film like plating. That is, the amount may be within a range suitable for pretreatment of phosphate treatment. After recrystallization heating (including soaking), the aqueous solution containing the metal compound of the present invention is subjected to a continuous annealing process.
When used as cooling water during the primary cooling of a cold-rolled steel strip heated to ℃, the metal compounds in the cooling water are thermally decomposed, producing metals or metal oxides on the surface of the steel strip, and then undergoing an overaging treatment process. In the non-oxidizing reducing atmosphere at , metal precipitates and diffuses onto the surface of the steel strip. The amount is in the range of 1 to 100 mg/m ² , preferably 5 to 50 mg/m ² in terms of metal. i.e. 1mg/
If it is less than m ² , it will not contribute to improving phosphate treatment properties. Moreover, if it exceeds 100 mg/m ² , it affects the cleanliness of the cold rolled steel sheet and the refinement of crystal grains on the steel sheet surface due to phosphate treatment, and the effect decreases. In the present invention, an aqueous solution containing a water-soluble metal oxide and an α-amino acid is used during the above-mentioned primary cooling, but if necessary, an aqueous solution containing an α-amino acid is used during the secondary cooling after overaging treatment. is used as cooling water. The amino acid referred to in the present invention is a general term for compounds having an amino group (-NH ₂ ) and a carboxyl group (-COOH) in the molecule, and an α-amino acid is a carbon atom (α -carbon) with an amino group attached. Amino acids are constituents of proteins, and are different from commonly-called organic acids. The α-amino acids used in the present invention are . Examples of aliphatic amino acids include (A) neutral amino acids, (B) basic amino acids, (C) acidic amino acids and their amides, (D) sulfur-containing amino acids, . Aromatic amino acids. It is a heterocyclic cyclic amino acid that includes hydrochloride, acetate, sodium salt, amine salt, and ammonium salt.Most of them exhibit a pH close to neutrality when made into an aqueous solution, but they have a pH value close to that of a weakly acidic one. For what is shown,
It can also be used in a neutral range by adjusting the pH as described above. For example, aliphatic amino acids include alanine, arginine, arginine hydrochloride, asparagine, aspartic acid, aspartate sodium salt, aspartate amine salt, aspartate ammonium salt, titrulline, cysteine hydrochloride, cystine,
Glutamine, glutamic acid, glutamic acid sodium salt, glutamic acid amine salt, glutamic acid ammonium salt, glycine, leucine, isoleucine, lysine, lysine hydrochloride, lysine acetate, etc.; aromatic amino acids include phenylalanine,
Examples of heterocyclic amino acids include tyrosine, proline, histidine, oxyproline, and tryptophan. During water quenching after heat treatment (including soaking) during continuous annealing of cold-rolled steel sheets, even if air-water cooling is performed and an inert gas such as nitrogen gas is used, the water vapor generated during air-water spray cooling will Therefore, the surface of the steel sheet is oxidized by steam, and it is difficult to avoid the formation of an oxide film. In this case, in addition to just water, α−
By using an aqueous solution containing 0.1 to 20% amino acids, a steel strip with excellent surface cleanliness and subsequent chemical conversion treatment properties can be obtained. The lower limit of the concentration of α-amino acid is the concentration at which the effect is recognized, and there is no need to limit the upper limit from a technical point of view, but from an economic standpoint, about 20% is desirable. From a practical point of view, the concentration of α-amino acids is used in the range of 0.1 to 5%, taking into consideration economic efficiency as well as the amount of excess adhesion that is carried out when the steel plate is cooled and the ease with which it can be washed off afterwards. It is desirable to do so. Furthermore, it is also effective to add a surfactant to the cooling water as necessary during the primary cooling or secondary cooling of the cold-rolled steel strip in order to improve water wettability. [Example] Example 1 High strength cold rolled steel plate (C0.05%, Mn1.3%, Si0.01
%, S0.005%, P0.01%, N0.003%, Al0.03%,
35 x 130 x 1.2 mm), heat treatment and water cooling tests were conducted using the following procedures (1) and (2). (1) Recrystallization heat treatment was performed at 800°C in a nitrogen gas (98%) + hydrogen gas (2%) atmosphere. (2) A heat-treated 800℃ steel plate is mixed with a metal compound and α
- After cooling by immersing in water containing amino acids, the steel plate was taken out, washed with water, and dried with a dryer. Table 1 shows the results of immersion cooling in an aqueous solution containing α-amino acids. Example 2 A heat treatment and air/water spray cooling test using a cold rolled steel plate (SPC, 5 x 130 x 1.2 mm) was conducted according to the following procedures (1) to (4). (1) Recrystallization heating was performed at 750°C in a nitrogen gas (98%) + hydrogen gas (2%) atmosphere. (2) A heat-treated steel plate at 750°C was primarily cooled to 400°C by air-water spraying using nitrogen gas using water containing a water-soluble metal compound and an α-amino acid. The cooling rate of the steel plate at this time is 100
Conditions were set so that the temperature was ℃/second. (3) After the primary cooling, the steel plate was subsequently overaged in a nitrogen gas (98%) + hydrogen gas (2%) atmosphere at 400°C. (4) A steel plate that has been over-aged at 400°C is heated to 300°C in the same gas atmosphere, and then an aqueous solution containing α-amino acids is sprayed with nitrogen gas.
After cooling to 50°C, the steel plate was taken out, washed with water, and dried with a hair dryer. The water flow density of the cooling water in the above primary and secondary cooling was 100 m ³ /m ³ ·min. The test results are shown in Table 2. Example 3 A heat treatment and water cooling test using a cold rolled steel plate (SPC, 35 x 130 x 1.2 mm) was conducted according to the following procedures (1) to (4). (1) Recrystallization heating was performed at 750°C in a nitrogen gas (98%) + hydrogen gas (2%) atmosphere. (2) A heat-treated 750°C steel plate is immersed in water containing a water-soluble metal compound and α-amino acid.
Then it was cooled. (3) After the first cooling, the steel plate is heated to 400°C with nitrogen gas (98%).
+Overaging treatment was performed in a hydrogen gas (2%) atmosphere. (4) A steel plate that had been overaged at 400°C was immersed in water containing α-amino acids, cooled to 50°C, and then taken out, washed with water, and dried with a dryer. The test results are shown in Table 3.

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[Table] [Effects of the invention] As described above, the metal compound or α
- By using cooling water containing amino acids, it is possible to thin the oxide film of a cold rolled steel sheet during continuous annealing, improve the appearance, and at the same time maintain a surface condition that is excellent in phosphating properties.

Claims (1)

[Claims] 1 After heat treatment, primary cooling or overaging treatment,
In continuous heat treatment of cold-rolled steel strip for secondary cooling, water-soluble metal compounds and metals that, when used as primary cooling water, produce metals or metal oxides (excluding Na or Na oxides) on the surface of the steel strip. A method for producing a cold-rolled steel strip with good surface properties, characterized by performing primary cooling with an aqueous solution containing α-amino acids.