JPS62207830A - Production of cold rolled steel strip having good surface characteristic - Google Patents

Abstract

PURPOSE:To decrease the thickness of the oxide film on a cold rolled steel strip and to improve the appearance and phosphate treatability of the strip by incorporating a water soluble metallic compd. into primary and secondary cooling water in the continuous heat treatment of the cold rolled steel strip at the time of producing the cold rolled steel strip by a continuous annealing method. CONSTITUTION:An aq. soln. contg. the water soluble metallic compd. or contg. an alpha-amino acid therein is used for the primary and secondary cooling water in the continuous heat treatment of the cold rolled steel strip having respective stages for a recrystallization heating treatment, primary cooling, overaging treatment and secondary cooling. Any of inorg. or org. compd. which is water soluble is usable as the metallic compd. to be used in this case. The surface cleanliness of the cold rolled steel strip is improved and the effective pretreatment for the phosphate treatment is executed by the above-mentioned method.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a method for producing cold rolled steel strip by continuous annealing. The present invention relates to a method of manufacturing steel strip.

(Prior art) In recent years, instead of annealing using a batch furnace, continuous annealing is used to charge a coiled material from one end of the annealing furnace.
Continuous annealing, in which a predetermined heat treatment is performed in a furnace, has been adopted to improve productivity and reduce variations in quality.

In continuous annealing, the cold rolled steel strip charged into the continuous annealing furnace is
Generally, the material is gradually heated while being mechanically fed, and after the recrystallization process, primary cooling is performed, followed by overaging treatment and secondary cooling. Until now, various studies have been made regarding heat treatment conditions, particularly cooling rate, cooling atmosphere, cooling water, etc., in continuous annealing.

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; These include triacetate, ethylenediaminetetraacetic acid and 2'f thorium. the nitrilotriacetic acid;
Ethylenediaminetetraacetic acid is an aminopolycarboxylic acid, does not belong to the amino acid category, and is completely different.

Furthermore, JP-A-57-85923 discloses a metal coolant consisting of a water-soluble organic acid and a water-soluble organic amine. As acids, saturated dicarboxylic acids such as malonic acid, succinic acid, geltaric acid, adipic acid, and pimelic acid, and unsaturated dicarboxylic acids such as maleic acid and itaconic acid,
Preferred examples include oxycarbon groups such as malic acid and tartaric acid.

Further, JP-A-58-55533 describes a quenching method using an aqueous solution containing an organic acid such as malonic acid, formic acid, citric acid, acetic acid, lactic acid, succinic acid, or tartaric acid.

As mentioned above, various methods have been described, but depending on the temperature conditions of the solution and the temperature conditions of the cold-rolled steel strip after cooling, the suppression of the generated oxide film may be insufficient. Oxide films can be difficult to remove. 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 is used to generate trace amounts of metals or metal oxides on the surface of the steel sheets. method is known.

For example, regarding phosphorous salt treatment, JP-A-55-14
No. 854, and regarding corrosion resistance and paint adhesion, see JP-A No. 4
No. 9-34437, and furthermore, as materials suitable for can manufacturing, Japanese Patent Application Laid-Open No. 48-34738 and Japanese Patent Publication No. 49
-48823, etc.

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 metals or metal oxides 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 firing process.

This is because if the steel sheet is subjected to the annealing process with water still attached to it, the water will raise the dew point, oxidizing the surface of the steel sheet, 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 to attach the metal to the cold rolled steel sheet. Although a method for manufacturing a steel plate is known, it is difficult to maintain constant surface cleanliness with this known temporary phase. 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 cold rolled steel sheets during continuous annealing.
The object of the present invention is to provide a method for producing a cold-rolled strip that has a good appearance and at the same time maintains a surface condition that is excellent in phosphate treatment properties.

(Means for solving the problems) The present invention uses a water bath metal compound or an aqueous solution containing an α-amino acid in the primary cooling water and secondary cooling water in continuous annealing. The surface cleanliness of the cold-rolled steel strip is improved, and an effective pretreatment for phosphate treatment can also be performed effectively.

Furthermore, the present invention uses a metal compound or an aqueous solution containing an α-amino acid as the primary cooling water and secondary cooling water in continuous annealing, thereby reducing the amount of water that occurs during recrystallization heating of a cold-rolled steel strip. Based on oxide film or over-aging treatment, 2
This effectively suppresses and removes the oxide film that occurs during the air-water spray cooling during the next cooling, and can effectively improve the surface cleanliness of the cold-rolled steel strip.

In the present invention, a water-soluble metal compound is used as the primary cooling water and secondary cooling water in the continuous heat treatment of a cold rolled steel strip that is subjected to recrystallization heat treatment and includes each step of primary cooling, overaging treatment, and secondary cooling. Alternatively, an aqueous solution containing an α-amino acid is used.

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, formic acid, vinegar, citric acid, tartar, amber, lactic acid,
For example, for Ni, there are salts such as nickel formate, nickel acetate, and nickel chloride.

In the case of inorganic compounds, molybdenum ammonium is used for Mo, ammonium tungstate is used for W, and the solution is 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 deposited on the surface of the steel strip will affect the surface gloss of the steel sheet. It is not necessary to generate a large amount of metal, which would cause a large amount of metal to be produced, or where the nuclei of the precipitated metal would connect with each other to form a metal film such as 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.
Metals or metal oxides are produced on the surface of the steel strip, and the metals are further precipitated and diffused on the surface of the steel strip in the oxidation reducing atmosphere in the overaging treatment step.

The amount is in the range of 1-100 #i/m', preferably 5-501 #i/- in terms of metal. That is, 1■/
rr? If it is less than this, it will not contribute to improving the phosphate processability. Moreover, if it exceeds 100Tn9/mF, it will affect 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 will be reduced.

The present invention applies to the above-mentioned primary cooling and secondary cooling.

Cooling water containing a bath metal compound is used, or an aqueous solution containing a water-soluble metal compound and an α-amino acid is used as the cooling water.

The amino acid referred to in the present invention refers to an amine group (-Na
Z) and a carboxyl group <-cooH), and an α-amino acid is one in which an amino group is attached to the carbon atom (α-carbon) to which a carboxyl group is bonded. Amino acids are constituents of proteins and proteins, and are different from organic acids.

The α-amino acids used in the present invention include (4) neutral aminos and (B) basic amino acids (0 acidic amino acids and their amides, ■ sulfur-containing amino acids, ■
Aromatic amino acids (■) are heterocyclic amino acids that contain their hydrochlorides, acetates, sodium salts, amine salts, and ammonium salts; If the pH is close to that of the one described above, but it is weakly acidic, the pH can be adjusted as described above and used in the neutral range.

For example, aliphatic amino acids include alanine, arginine, arginine hydrochloride, asnoξlagin, asnoξlaginic acid,
Asparaginpo sodium salt, aspartate amine salt, aspartate ammonium salt, titrulline, cysteine vanilate, cystine, glutamine, glutamic acid, glutamate sodium salt, glutamate amine salt, glutamine ammonium salt, glycine, leucine, inleucine, lysine, No lysine hydrochloride, lysine acetate, etc.
, aromatic amino acids include phenylalanine, tyrosine, etc., and heterocyclic amino acids include proline, histidine, oxyproline, tryptophan, etc.

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 crab gas is used, water vapor generated during air-water spray cooling. As a result, water vapor is converted to the surface of the steel sheet, making it difficult to avoid the formation of an oxide film. In this case, by using not only water but also an aqueous solution containing 0.1 to 20% of α-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 economically it is preferably about 20%. From a practical point of view, the amount of excess adhesion and removal when the steel plate is cooled,
We considered economic efficiency as well as ease of removal with water washing afterwards.
It is desirable to use the α-amino acid concentration in the range of 0.1 to 5%.

Furthermore, it is also effective to add a surfactant, if necessary, to improve the water wettability of the cooling water during the primary cooling or secondary cooling of the cold-rolled steel strip.

(Example) Example 1 A test of heat treatment and air/water spray cooling using a cold rolled steel strip < spc, 35X130X1,2++s
This was done according to step (4).

(1) Recrystallization heating was performed at 750° C. in an atmosphere of hydrogen gas (98%) and decahydrogen gas (2%).

(2) A heat-treated steel plate at 750°C was primarily cooled to 400°C by air-water spraying using crab gas using water containing a water-soluble metal compound. The cooling rate of the copper plate at this time was set to 100° C./sec.

(3) After the primary cooling, the copper plate was subsequently subjected to an overaging treatment in a nitrogen gas (98%) and dehydrogen 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 is sprayed with air and water using nitrogen gas, and heated to 50°C.
After cooling to a certain temperature, 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 rrl/m''·min.

The test results are shown in Table 1.

The oxide film thickness in the table is based on iron oxides such as FeO, Fetus, and Fe50+ since the oxide composition on the surface of the copper plate cannot be specified.
Average the specific gravity of 5.9, 5.1, 5.2, specific gravity of 5.4
Assuming that, the steel plate sample was pickled using a pickling solution containing 5% aqueous acid solution and 0.5% inhibitor added, and the average specific gravity was calculated from the weight difference before and after pickling using the average specific gravity described above. .

The method for analyzing the amount of metal ions deposited is to use a standard solution (for example, in the case of Ni, nickel chloride/salt Fil C1+1) aqueous solutions with different concentrations of nickel applied to the surface of a steel plate, water as a standard sample, and fluorescence X-ray analysis. A constant weight was prepared using an analytical method, and quantitative analysis of the actual sample was performed. The zero point of the calibration curve was the intensity (mV) of the untreated 4wA plate.

Regarding the analysis of the amount of metal adhesion of W, a steel plate sample was dissolved in hydrogen fluoride solution and quantitatively analyzed.

For phosphate treatment, FC manufactured by Nippon Parkerizing (closed)
+363, temperature 60 °C, spray pressure 1,5 K
After degreasing at 910 rb" for 3 minutes, washing with hot water and water, at-137 was sprayed at a temperature of 55°C and a spray pressure of 1, Q
Phosphate treatment was performed for 2 minutes using K110wn2, followed by washing with water and drying with hot air.

Observation of crystals in the v-noate salt-treated film was determined from microscopic photographs using a conventional method. To measure the grain size, the size of the grain is l:
It was classified into 10 grades: very coarse - 1O: extremely dense, and was determined by observation with a scanning electron microscope.

The SST (salt spray test wave) results were obtained by electrodepositing Nireclone 7200 (manufactured by Kansai Paint Co., Ltd.) on a phosphate-treated plate at a temperature of 30°C and a voltage of 110V so that the coating film was 20 to 21μ. After painting and baking at 170℃ for 25 minutes, cross-cut the surface with a sharp knife until it reaches the base, use 5% salt solution, and follow JIS-Z-2371.
After spraying for 200 hours, the cross-cut portion was peeled off with cellophane tape.

Example 2 A test sample of heat treatment and air/water spray cooling using a cold-rolled plate (5PC135X130X1.2 area) was carried out in the following (1) to (4).
).

(1) Chiang crystal was heated at 750° C. in a nitrogen gas (98%) and decahydrogen 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 was set to 100°C/sec.

(3) After the primary cooling, the steel plate is heated to 400℃ nitrogen gas (
98%) was subjected to overaging treatment in a decahydrate gas (2%) atmosphere.

(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 is sprayed with air and water using nitrogen gas, and heated to 50°C.
After cooling to a certain temperature, 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''/m2·min.

The test results are shown in Table 2.

Example 3 A cold-rolled steel plate (5PC135x130x1.2rtan) was subjected to heat treatment and water cooling tests using the following methods (1) to (4).
) was followed.

(1) Re-robust heating was performed at 750° C. in a nitrogen gas (98%) and dehydrogen gas (2%) atmosphere.

(2) A heat-treated steel plate at 750°C was primarily cooled by immersing it in water containing a water-soluble metal compound.

(3) The primary cooled copper plate was heated to 400°C using nitrogen gas (98%
) Over-aging treatment was carried out in a hydrogen (2%) atmosphere.

(4) A steel plate that has been overaged at 400°C is immersed in water containing a water-soluble metal compound and an α-amino acid.
After cooling to 0° C., the copper plate was taken out, washed with water, and dried with a dryer.

The test results are shown in Table 3.

Example 4 Cold rolled steel plate (5PC535X130X1.211111)
The heat treatment and air-water spray cooling tests were performed using the following (1)
) to (4).

(1) Recrystallization heating was performed at 750° C. in a nitrogen gas (98%) and decahydrogen gas (2%) atmosphere.

(2) The 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 and α-aminofluoride. Conditions were set so that the cooling rate of the steel plate at this time was 10,067 seconds.

(3) After the primary cooling, the steel plate was subsequently overaged in a nitrogen gas (98%) and dehydrogen gas (2%) atmosphere at 400°C.

(4) A steel plate that has been overaged at 400°C is heated to 300°C in the same gas atmosphere, and then mixed with a water-soluble metal compound and α
- After the aqueous solution containing the amino acid was sprayed with air and water using boron gas and cooled to about 50°C, 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 performed with a crop rotation of 100 i/m'min.

The test results are shown in Table 4.

(Effects of the Invention) As described above, by using the cooling water containing the metal compound or α-amino acid of the present invention, the oxide film of the cold rolled steel sheet during continuous annealing can be thinned, and at the same time, the appearance can be improved, and the It is possible to maintain the surface condition that has been damaged by salt treatment.

Claims (1)

[Claims] 1. A water-soluble metal compound is added to the primary and secondary cooling water in the continuous heat treatment of a cold rolled steel strip, which includes the steps of recrystallization heat treatment, primary cooling, overaging treatment, and secondary cooling. 1. A method for producing a cold-rolled steel strip with good surface properties, characterized by comprising: 2. 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-
A method for producing a cold-rolled steel strip with good surface properties, which comprises first cooling with an aqueous solution containing an amino acid and a water-soluble metal compound, and second cooling with an aqueous solution containing a water-soluble metal compound. 3. In continuous heat treatment of a cold rolled steel strip, which includes the steps of recrystallization heat treatment, primary cooling, overaging treatment, and secondary cooling, primary cooling is performed with an aqueous solution containing a water-soluble metal compound,
A method for producing a cold-rolled steel strip with good surface properties, which comprises performing secondary cooling with an aqueous solution containing an α-amino acid and a water-soluble metal compound. 4 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-
A method for producing a cold-rolled steel strip with good surface properties, characterized by performing primary cooling and secondary cooling with an aqueous solution containing an amino acid and a water-soluble metal compound.