JPH0371487B2 - - 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 straight-chain aliphatic acids such as formic acid, acetic acid, propionic acid, oxalic acid, and succinic acid, and oxidic acids such as citric acid, lactic acid, gluconic acid, and tartaric acid. and nitrilotriacetic acid, ethylenediaminetetraacetic acid disodium, etc. The nitrilotriacetic acid and ethylenediaminetetraacetic acid are aminopolycarboxylic acids, do not belong to the amino acid category, and are completely different. Furthermore, JP-A-57-85923 discloses a metal coolant consisting of a water-soluble organic acid and a water-soluble organic amine.
The above water-soluble dicarboxylic acids include saturated dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, and pimelic acid; unsaturated dicarboxylic acids such as maleic acid and itaconic acid; and oxycarboxylic acids such as malic acid and tartaric acid. is listed as a preferred example. Further, JP-A-58-55533 describes a quenching method using a water-soluble organic acid such as malonic acid, formic acid, citric acid, acetic acid, lactic acid, succinic acid, tartaric acid, and 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 it difficult to separate. 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. Although a method for manufacturing rolled steel sheets is known, it is difficult to maintain constant surface cleanliness with this known technique. 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 uses a water-soluble metal compound or water-soluble water containing a metal compound and α-amino acid as the primary cooling water in continuous annealing, and uses α-amino acid as the secondary cooling water.
- By using an aqueous solution containing amino acids, oxide films are generated during recrystallization heating of cold-rolled steel strips, or after over-aging treatment, generation occurs due to air-water spray cooling during secondary cooling. This effectively suppresses and removes the oxidized film produced by the cooling process, improves the surface cleanliness of the cooled steel strip, and provides an effective pretreatment for phosphate treatment. As the metal compound used in the present invention, any inorganic compound or organic compound can be used as long as it is water-soluble. Metal elements include Ni,
Co, Mn, Zn, Cu, Cr, Mo, Ti, W, etc., and in the case of organic compounds, salts such as formic acid, acetic acid, citric acid, tartaric acid, succinic acid, lactic acid, oxalic acid, etc. Then, nickel formate, nickel acetate,
It is like 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 at the upper limit, the metal precipitated on the surface of the cold rolled steel strip is retained in the form of nuclei. limited to what is possible. In other words, it is sufficient that the amount of metal deposited on the cold rolled steel sheet manufactured using the cooling water is suitable for applying phosphate treatment, and the metal precipitated on the surface of the steel strip will cause the surface of the steel sheet to There is no need to generate a large amount of metal that would affect the gloss or cause the cores 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 , the 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. 1
If it is less than mg/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, a water-soluble metal oxide or a water-soluble metal oxide containing an α-amino acid is used during the above-mentioned primary cooling, but an α-amino acid is used during the secondary cooling after overaging treatment. An aqueous solution containing 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 include I. Aliphatic amino acids, (A) neutral amino acids, (B) basic amino acids, (C) acidic amino acids and amides thereof, (D) sulfur-containing amino acids, . Aromatic amino acids. It is a heterocyclic amino acid that includes hydrochloride, acetate, sodium salt, amine salt, and ammonium salt, and most of them exhibit a pH close to neutrality when made water-soluble, but are weakly acidic. For those exhibiting this, the pH can be adjusted as described above and used in the neutral range. 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 the upper limit does not need to be limited 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. [Examples] Example 1 A test of heat treatment and air/water spray cooling 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 steel plate at 750°C was primarily cooled to 400°C by air-water spraying with nitrogen gas using water containing a water-soluble metal compound. The cooling rate of the steel plate at this time was set to 100°C/sec. (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 1. The oxide film thickness in the table is based on iron oxides such as FeO, Fe ₂ O ₃ , and
Assuming that the average specific gravity of Fe ₅ O ₄ is 5.9, 5.1, and 5.2 to give a specific gravity of 5.4, a steel plate sample was placed in a 5% hydrochloric acid aqueous solution with an inhibitor.
Pickling is carried out using a pickling solution containing 0.5%,
It was calculated from the difference in weight before and after pickling using the above average specific gravity. The method for analyzing the amount of attached metal ions is to use a standard solution, for example, for Ni, use nickel chloride/hydrochloric acid (1+1).
A standard sample was water in which different nickel concentrations were applied to the surface of a steel plate as an aqueous solution, a calibration curve was created using fluorescent X-ray analysis, and quantitative analysis of the actual sample was performed. The zero point of the calibration curve was the strength (mV) of the untreated steel plate. Regarding the analysis of the amount of metal adhesion of Ti and W, a steel plate sample was dissolved in hydrofluoric acid and quantitatively analyzed. Phosphate treatment is made by Nippon Parkerizing Co., Ltd.
Using FC# 363, temperature 60℃, spray pressure 1.5
After degreasing at Kg/ ^cm2 for 3 minutes, washing with hot water and water, apply Bt-137 at a temperature of 55℃ and a spray pressure of 1.0Kg/ ^cm2.
Then, phosphate treatment was carried out for 2 minutes, followed by washing with water and drying with hot air. Observation of the phosphate-treated film crystals was determined from micrographs using a conventional method. The crystal grain size was determined by classifying the grain size into 10 levels from 1: very coarse to 10: extremely dense, and observing it with a scanning electron microscope. The SST (salt spray test) results were tested using Elekron 7200 (manufactured by Kansai Paint Co., Ltd.) on a phosphate-treated steel plate.
Electrodeposited at a temperature of 30℃ and voltage of 110V so that the coating film was 20 to 21μ, baked at 170℃ for 25 minutes, and then made cross-cut scratches with a sharp knife until it reached the base material. After spraying with saline for 200 hours in accordance with JIS-Z-2371, the cross-cut portion was peeled off with cellophane tape, and the peeling width is shown. Example 2 A heat treatment and air/water spray 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 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 the steel plate was taken out and dried in a washing dryer. The test results are shown in Table 3. Example 4 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 steel plate at 750°C was first cooled by immersing it in water containing a water-soluble metal compound. (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 4.

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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. Primary cooling or over-aging treatment after heat treatment. 2.
In the continuous heat treatment of a cold rolled steel strip that is subjected to subsequent cooling, cooling with good surface properties is achieved by first cooling with an aqueous solution containing a water-soluble metal compound and secondly cooling with an aqueous solution containing an α-amino acid. Method for manufacturing rolled steel strip. 2 After heat treatment, primary cooling or overaging treatment 2
In continuous heat treatment of a cold-rolled steel strip that is subjected to subsequent cooling, surface characteristics are characterized by first cooling with an aqueous solution containing a water-soluble metal compound and an α-amino acid, and second cooling with an aqueous solution containing an α-amino acid. A method for producing a good cold rolled steel strip.