JPS62205290A - Manufacture of cold rolled steel strip having satisfactory surface characteristic - Google Patents

Abstract

PURPOSE:To manufacture a cold rolled steel strip having satisfactory surface characteristics by continuously heat treating a cold rolled steel strip by heating, primary cooling or overaging and secondary cooling with an aqueous soln. contg. a water soluble metallic compound and an alpha-amino acid. CONSTITUTION:A cold rolled steel strip is continuously heat treated by heating, primary cooling or overaging and secondary cooling with an aqueous soln. contg. a water soluble metallic compound and an alpha-amino acid as cooling water. Primary cooling with an aqueous soln. contg. the alpha-amino acid and secondary cooling with an aqueous soln. contg. the water soluble metallic compound or an aqueous soln. contg. the water soluble metallic compound and the alpha-amino acid may be carried out as required. By the heat treatment, a cold rolled steel strip having superior surface characteristics, especially suitability to phosphating and surface cleaning is obtd. The oxide film of the steel strip is thin and has fine appearance.

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.
The continuous annealing method, in which a predetermined heat treatment is performed in a furnace, has been adopted in order 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, undergoes primary cooling after the recrystallization process, and is then subjected to 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 of the methods used to prevent the formation of an oxide film on the steel sheet surface during water quenching during continuous annealing of cold rolled steel sheets is to add a compound called an organic acid (C) to the cooling water. 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 oxyacids such as citric acid, hylactate heavy gluco/acid, and tartaric acid. and nitrilotriacetic acid, ethylenediaminetetraacetic acid disodium, etc. the nitrilotriacetic acid;
Ethylenediaminetetraacetic acid is an aminopolycarboxylic acid, does not belong to the amino acid category, and is completely different.

Furthermore, JP-A No. 57-85923 discloses a metal coolant consisting of a water-soluble organic acid and a water-soluble organic amine. Preferred examples include saturated dicarboxylic acids such as malonic acid, succinic acid, geltaric acid, adipic acid, and pimelic acid; unsaturated dicarboxylic acids such as maleic acid and itaconic acid; and oxycarbo/acids such as malic acid and tartaric acid. ing. 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 organic acids have been described.

Depending on the temperature conditions of the solution and the temperature conditions of the cold rolled steel strip after cooling, it may be insufficient to suppress the generated oxide film or it may be difficult to remove the oxide film. However, when cold-rolled steel sheets obtained from these cold-rolled steel strips are 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 properties, 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 technologies, the metal compound is made into an aqueous solution, and the metal ions are uniformly dispersed on the surface of the steel sheet.

It is a prescribed means of attachment, and the aqueous solution itself does not serve any other purpose.

Furthermore, in order to generate metal oxides on the surface of the 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 process. 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 and the surface of the steel plate will oxidize.
This is because the metal is not sufficiently reduced and precipitation becomes difficult.

Mano JP-A No. 57-149429 discloses that 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, which has excellent corrosion resistance and chemical conversion treatment properties. Although a method for manufacturing steel plates 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 copper 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 present invention provides a method for producing a cold-rolled steel strip that has a good appearance and at the same time maintains a surface condition that is excellent in phosphating properties.

(Determined Means for Solving the Problems) The present invention improves the surface cleanliness of cold-rolled steel strips by fully using secondary cooling water (aqueous solution containing C1 metal compound and α-amino acid) during continuous annealing. In addition to the improvement, it is also possible to effectively perform an effective pretreatment for phosphate treatment.

Furthermore, the present invention uses an aqueous solution containing all α-amino acids as the primary cooling water in continuous annealing, and uses an aqueous solution containing a water-soluble metal compound or a water-soluble metal compound and an α-amino acid as the secondary cooling water. By using this method, it is possible to suppress and remove oxide films that occur during re-heating of cold-rolled steel strips, as well as oxide films that occur during over-aging treatment, air-water spray cooling during secondary cooling, etc. This is effective and improves the surface cleanliness of the cold-rolled steel strip.

An effective pretreatment for phosphate treatment can also be performed effectively.

In the present invention, as secondary cooling water after recrystallization heat treatment and primary cooling or overaging treatment, an aqueous solution containing a water-soluble metal compound, or a metal compound and all α-amino acids,
Use an aqueous solution containing both.

As the metal compound used in the present invention, any non-acid compound or organic compound can be used as long as it is water-soluble. Ni is a metallic element.

Co, Mn, Zn, Cu, Cr, Mo
, Ti, W, etc., and in the case of organic compounds, they are salts such as formic acid, acetic acid, citric acid, tartaric acid, cono-phosphoric acid, lactic acid, oxalic acid, etc. For example, in the case of Ni, nickel formate, nickel acetate, citric acid, etc. It is like nickel.

In the case of inorganic compounds, Mo is ammonium molybdate, W is ammonium tungstate, etc., and it is a water@liquid 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, it is sufficient that the amount of metal deposited is suitable for applying phosphate treatment to a tomo-rolled steel sheet that has been manufactured into a product using the cooling water, and the metal deposited on the surface of the steel strip will improve the surface gloss of the steel sheet. 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 such as plating. That is, the amount may be within a range suitable for pretreatment and beating of phosphate treatment.

When the aqueous solution containing the metal compound of the present invention is used as cooling water for secondary cooling of a cold-rolled steel strip heated to about 400C after overaging in a continuous annealing process, the The metal compound decomposes thermally and forms metal or metal oxide on the surface of the steel strip.

The amount is 1 to 100 zn/m2, preferably 5 to 50 zn/m2 in terms of metal. / m2 range. That is, if it is less than 1η/m2, it will not contribute to improving the phosphate treatment properties. If it exceeds 100 η/m 2 , it will affect the cleanliness of the cold-rolled steel sheet and the refinement of the crystal grains on the surface of the steel sheet due to phosphate treatment, or the surface of the steel sheet, and the effect will decrease.

In the present invention, an aqueous solution containing a water-soluble metal oxide or an α-amino acid is used during the secondary cooling described above, but if necessary, during the primary cooling after the recrystallization heat treatment,
An aqueous solution containing α-amino acids is used as cooling water.

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

The α-amino acids used in the present invention are % II aliphatic amino acids, (A) neutral amino acids, (B) basic amino acids, (C) acidic amino acids and their amides, (D) sulfur-containing amino acids, ■, aromatic amino acids, ■Heterogeneous cyclic amino acids, including their hydrochlorides, acetates, sodium salts, amine salts, and ammonium salts.Many of them exhibit a pH close to neutrality when made into aqueous solutions, but have a weak pH. For those that exhibit acidity, they can be used in a neutral range by adjusting the temperature as described above.

For example, aliphatic amino acids include alanine, arginine, arginine hydrochloride, asparagine, aspartic acid, aspartate sodium salt, as-(laginate amine salt,
Aspartate ammonium salt, titrulline, cysteine hydrochloride, cystine, glutamine, glutamic acid, glutamate sodium salt, glutamate amine salt, glutamate ammonium salt, glycine, leucine, inleucine, lysine, lysine hydrochloride, lysine acetate group, etc.
Aromatic amino acids include phenylalanine and tyrosine, and cyclic amino acids include proline, histidine, ogiciproline, and tritophane.

Even if one-air water cooling is performed during water quenching after heat treatment (including soaking) during continuous annealing of cold-rolled steel sheets, and an inert gas such as nitrogen gas is used, water vapor generated during air-water spray cooling may The surface of the steel sheet is oxidized by steam, and it is difficult to prevent the formation of an oxide film. In this case, by using not only water but also an aqueous solution containing 061 to 20% of α-amino acids, a copper 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,
Considering the economic efficiency as well as the ease of washing with water afterwards and the accuracy, α
- It is desirable to use the amino acid in a range of 0.1 to 5%.

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 Cold-rolled steel plate (SPC, 35X1 : 30X1.2+U) Test of kumquat heat treatment and air/water spray cooling.
Steps 1) to (4) were followed to (1) Recrystallization was heated at 7500 ℃ in a nitrogen gas (98%) and dehydrogen gas (2%) atmosphere.

(2) A heat-treated 750C steel plate was heated using water containing α-amino acids by air-water spraying with nitrogen gas.
It was first cooled down to 000. The cooling rate of the steel plate at this time is
Conditions were set to 100 C/sec.

(3) After the primary cooling, the steel plate was subsequently over-aged in a 400C nitrogen gas (98%) decahydrogen gas (2C) atmosphere.

(4) 400t? After heating the over-aged steel sheet metal to 3000C in the same gas atmosphere, an aqueous solution containing a water-soluble metal compound was sprayed with air and water using nitrogen gas, and after cooling to 50C, the steel sheet was taken out and washed with water. Dry with a hair dryer.

The water flow density of the cooling water in the above primary and secondary cooling was 100 m37m3.

The test results are shown in Table 1.

The oxide film thickness in the table is calculated by averaging the specific gravity of iron oxides FcO, Fe2O3, and Fe3O4 of 5.9, 5.1, and 5.2, since the oxide composition on the surface of the steel sheet cannot be specified.
Assuming this, a steel plate sample was pickled using a pickling solution containing 5% aqueous hydrochloric acid and 0.5% I/inhibitor.

It was calculated from the difference in weight 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, a nickel chloride/hydrochloric acid (1+1) aqueous solution for Ni, with different concentrations of nickel applied to the surface of a steel plate, and use water as a standard sample, and perform fluorescent X-ray analysis. A calibration curve was created using the method, and quantitative analysis of actual samples was performed. The zero point of the calibration curve is
The strength (mV) of the untreated steel plate was taken as the strength (mV).

Regarding the analysis of the amount of metal adhesion of Ti and W, please refer to the steel sheet sample. It was dissolved in hydrofluoric acid and quantitatively analyzed.

Phosphate treatment is performed using F manufactured by Nippon Barcalizing Co., Ltd.
Using C8463, temperature 60C, spray pressure 1.5K
After degreasing for 3 minutes at f/cm2, washing with hot water and water,
Bt-137 was applied at a temperature of 55C and a spray pressure of 1. Oky/
Phosphate treatment for 2 minutes at cm2.

After washing with water and drying with hot air, the crystals of the o phosphate-treated film were observed using a microscopic photograph using a conventional method. To measure the grain size, set the grain size to 1:
Very coarse - 10: extremely dense, classified into 10 levels and determined by observation with a scanning electron microscope. The SST (salt spray test) results are based on Nirekron 7200 on a phosphate-treated steel plate. (manufactured by Kansai Paint Co., Ltd.) at a temperature of 30C and a voltage of 110V, the coating film was 20 to 21μ.
After applying the electrodeposition coating and baking it for 125 minutes at 170C, use a sharp knife to cross-cut the scratches until it reaches the base material. After spraying N'f for 200 hours in accordance with JIS-Z-2371 using 5% saline, the cross-cut portion was peeled off with cellophane tape.

Example 2 Test sound of heat treatment and air/water spray cooling using cold rolled steel plate (SPC, 35X130X1.2+111), following (1)
t0 (1) Heating for recrystallization at 7500 ℃ in a nitrogen gas (98%) decahydrogen gas (2%) atmosphere.

(2) A heat-treated 750C steel plate was primarily cooled to 400C using water containing α-amino acids by air-water spraying with nitrogen gas. The cooling rate of the steel plate at this time was set to 100 C7 seconds.

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

(4) After over-aging the steel plate for 400 tl' and raising the temperature to 300C in the same gas atmosphere, an aqueous solution containing a water-soluble metal compound and an α-amino acid was sprayed with air and water using nitrogen gas to 50C. After cooling down, 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 performed under the following conditions: 1 OOm3/m3.

The test results are shown in Table 2.

Example 3 Heat treatment and water cooling tests using a cold rolled steel plate (SPC, 35X130X1.2 report) were conducted according to the following procedures (1) to (4).

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

(2) A heat-treated steel sheet metal of 750 t:' was immersed in water containing α-amino acids for primary cooling.

(3) The primarily cooled steel plate was heated with 400C nitrogen gas (98
%) decahydrogen gas (2%) atmosphere.

(4) A 400t:" over-aged steel plate was immersed in water containing water-soluble metal compounds and cooled to 50C. The steel plate was taken out, washed with water, and dried with a dryer. Table 3 shows the test results. Shown below.

Example 4 Using cold-rolled steel plates (SPC, 35 x 130
Follow the steps in 4).

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

(2) A heat-treated i750 C steel plate was primarily cooled to 400 t:' by air-water spraying using nitrogen gas. The cooling rate of the steel plate at this time was set to 100 C/sec.

(3) After the first cooling, the steel plate is continued to be heated to 400 tl? An overaging treatment was performed in an atmosphere of nitrogen gas (98%) and decahydrogen gas (2%).

(4) 400C over-aging treatment The steel plate was heated to 300C in the same gas atmosphere, and then cooled to about 50C by spraying an aqueous solution containing a water-soluble metal compound and α-amino acid with nitrogen gas. The water flow density of the cooling water in the primary and secondary cooling of 0 or more after taking out the steel plate, washing it with water, and drying it in a dryer is shown in Table 4.

Example 5 A heat treatment and water cooling test using a cold rolled steel plate (SPC, 35X130X1.2IIIB) was conducted using the following (1) to (4).
).

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

(2) A heat-treated 750C steel plate was immersed in water containing α-amino acids for primary cooling.

(3) The primarily cooled steel plate was heated with 400C nitrogen gas (98
%) decahydrogen gas (2%) atmosphere.

(4) A 400C over-aged steel plate was immersed in water containing a water-soluble metal compound and an α-amino acid, and
After cooling to 0C, the steel plate was taken out, washed with water, and dried with a dryer.The test results are shown in Table 5.

(Effects of the Invention) As described above, by using the cooling water containing the gold/fertilized crop or α-amino acid of the present invention, the oxide film of the cold rolled steel sheet during continuous annealing can be thinned and the external FQ k can be improved. At the same time, a surface condition excellent in phosphate treatment properties can be maintained.

Claims (1)

[Scope of Claims] 1. In the continuous heat treatment of cold rolled steel strip, which involves primary cooling or overaging treatment after heat treatment and secondary cooling, secondary cooling is performed using an aqueous solution containing a water-soluble metal compound and an α-amino acid. A method for producing a cold-rolled steel strip with good surface properties, characterized by cooling. 2. In the continuous heat treatment of cold-rolled steel strips, which involves primary cooling after heat treatment or overaging treatment followed by secondary cooling, primary cooling is performed with an aqueous solution containing α-amino acids, and then 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. 3. In continuous heat treatment of cold-rolled steel strips, which involves primary cooling after heat treatment or overaging treatment followed by secondary cooling, primary cooling is performed with an aqueous solution containing α-amino acids to remove water-soluble metal compounds and α-amino acids. A method for producing a cold-rolled steel strip with good surface properties, characterized by performing secondary cooling with an aqueous solution containing the same.