JPH031365B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) The present invention relates to a method for producing cold rolled steel strips with good surface properties, particularly phosphating properties and surface cleanliness, in a method of producing cold rolled steel strips by continuous annealing. 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 is a method in which a compound commonly referred to as an organic acid is added to the cooling water to prevent the formation of an oxide film on the surface of the steel sheet during water quenching during continuous annealing of cold rolled steel strip. 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 and ditonalium. 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 malonic acid,
Preferred examples include saturated dicarboxylic acids such as 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. In addition, JP-A-58-55533 discloses malonic acid,
A method of quenching using an aqueous solution containing an organic acid such as formic acid, citric acid, acetic acid, lactic acid, succinic acid, tartaric acid, etc. is described. 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, the annealing process of steel sheets has been used to remove trace amounts of metal on the surface of the steel sheets.
Alternatively, methods for producing metal oxides are 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, JP-B-49-48823, etc. for materials suitable for can manufacturing. There is. 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. do not have. 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 strip in advance 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 water will raise the dew point, which will oxidize the steel plate surface, preventing the metal from being sufficiently reduced and 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 to adhere the metal, thereby achieving excellent corrosion resistance and chemical conversion treatment properties. Although a method for manufacturing cold-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 sheet. (Problems to be Solved by the Invention) The present invention thins the oxide film of a cold rolled steel sheet during continuous annealing, improves the appearance of the cold rolled steel sheet, and at the same time maintains a surface condition excellent in phosphating properties. The present invention provides a method for manufacturing. (Means for Solving the Problems) The present invention provides continuous heat treatment of cold-rolled steel strips including the steps of recrystallization heat treatment, primary cooling, overaging treatment, and secondary cooling. Production of a cold-rolled steel strip with good surface properties characterized by primary cooling and secondary cooling with an aqueous solution containing one or more of Ni, Co, Mn, Zn, Ti, and W salts. It's a method. 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, Ti, W, etc., and in the case of organic compounds, salts of formic acid and acetic acid; for example, in the case of Ni, such as nickel formate, nickel acetate, and nickel citrate. 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. When the aqueous solution containing the metal compound of the present invention is used as cooling water during the primary cooling and secondary cooling of the cold rolled steel strip in the continuous annealing process, the metal compound in the cooling water is thermally decomposed and the steel strip surface Metals or metal oxides are produced during the overaging treatment process, and the metals precipitate and diffuse on the surface of the steel strip in a non-oxidizing reducing atmosphere during the overaging process. 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. If it exceeds 100 mg/m ² , it affects the cleanliness of the cold-rolled steel sheet, the refinement of crystal grains on the surface of the steel sheet due to phosphate treatment, or the surface of the steel sheet, and the effect thereof decreases. 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 constituent components of proteins, and are different from commonly-called organic acids. The α-amino acids used in the present invention include, as aliphatic amino acids, (A) neutral amino acids, (B) basic amino acids, (C) acidic amino acids and their amides, and (D) sulfur-containing amino acids, aromatic amino acids, and heterologous amino acids. These are nodular cyclic amino acids, including their hydrochlorides, acetates, sodium salts, amine salts, and ammonium salts.Most of them exhibit a pH close to neutrality when made into an aqueous solution, 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, glutamate sodium salt, glutamate amine salt, glutamate 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 should be set 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 use it. Furthermore, it is also effective to add a surfactant to the cooling water, if necessary, in order to improve water wettability during the primary cooling or secondary cooling of the cold rolled steel strip. (Example) Example 1 Using a cold rolled steel plate (SPC, 35 x 130 x 1.2 mm),
Heat treatment and air/water spray cooling tests were conducted using 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 using water containing a water-soluble metal compound and α-amino acid by air-water spraying with nitrogen gas. The cooling rate of the steel plate at this time is 100℃/
The conditions were set so that it was seconds. (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 a water-soluble metal compound and an α-amino acid is sprayed with nitrogen gas for about 50°C. After cooling to ℃, the steel plate was taken out, washed with water, and dried with a 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.

【table】

[Table] (Effects of the invention) As described above, by using the cooling water containing the metal compound and α-amino acid of the present invention, the oxide film on the cold rolled steel strip during continuous annealing can be thinned and the appearance improved. At the same time, it is possible to maintain a surface condition that is excellent in phosphate treatment properties.

Claims (1)

[Claims] 1. In the continuous heat treatment of cold rolled steel strip, which includes the steps of recrystallization heat treatment, primary cooling, overaging treatment, and secondary cooling, α-amino acids and Ni in formic acid or acetic acid,
A method for producing a cold-rolled steel strip with good surface properties, which comprises performing primary cooling and secondary cooling using an aqueous solution containing one or more of Co, Mn, Zn, Ti, and W salts.