JPH1136045A - Cold rolled steel sheet for can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet for cans, giving a reduced number of defective cans caused by oxide inclusions even under severe working conditions. SOLUTION: The cold rolled steel sheet for can is manufactured by successively subjecting a continuously cast slab to hot rolling, to cold rolling, to continuous annealing, and further to temper rolling or to secondary rolling (DR rolling) and then applying surface treatment to the resultant cold rolled steel sheet. In this case, the total number of oxide inclusions contained in the cold rolled steel sheet is regulated to <=10<7> pieces per gram of sample, and further, the difference between the number of oxide inclusions of >=10 μm grain size contained in a cast slab for the manufacture of the cold rolled steel sheet and the number of oxide inclusions of >=10 μm grain size contained in the cold rolled steel sheet is regulated to <=2×10<3> pieces per gram of sample.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold-rolled steel sheet for cans in which can-making defects caused by oxide-based inclusions are reduced.

[0002]

2. Description of the Related Art In recent years, as a material for cans, a continuously cast slab of a predetermined chemical composition is subjected to hot rolling, pickling, cold rolling, continuous annealing, and further temper rolling or secondary rolling (DR rolling). It is manufactured by subjecting a cold-rolled steel sheet obtained by the above to a surface treatment.

[0003] In particular, in a material for cans manufactured from Al-killed steel, oxide inclusions (deoxidation products) generated during deoxidation in the above process are present in the steel. At the time of can manufacturing, there is a problem that can manufacturing defects such as pinhole-like defects and breakage of side walls of the can body are caused.

[0004] Conventionally, in order to reduce can-making defects caused by oxide-based inclusions, the particle size of oxide-based inclusions in a slab,
There is disclosed a method of limiting the number density and characteristics and controlling the form or distribution of oxide inclusions after rolling.

[0005] For example, Japanese Patent Application Laid-Open No. 6-172925 discloses that, in a slab, oxide-based inclusions having a particle size of 200 µm or less are dispersed to 10 ³ or less per kg, and oxide-based inclusions contained in the slab are dispersed. Inclusion melting point 1350 ℃ or less or 1650
A method is disclosed in which when the temperature is set to not less than 0 ° C., the thickness of oxide-based inclusions crushed during rolling is suppressed to 5 μm or less, and can-making defects such as pinholes and flange cracks are reduced.

Japanese Patent Application Laid-Open No. 7-207403 discloses that in a slab, oxide-based inclusions having a particle size of 200 μm or less are dispersed to 10 ³ or less per kg, and oxide-based inclusions contained in the slab are By including at least 4% by weight of MgO in the inclusions, the thickness of the oxide-based inclusions crushed during rolling is suppressed to 5 μm or less,
By making the oxide-based inclusions difficult to disperse, it is possible to prevent the oxide-based inclusions crushed after rolling from elongating to a continuous distribution state, thereby preventing pinholes and fractured bodies. A method for reducing the failure in can-making is disclosed.

[0007]

However, in recent years,
Due to the need for weight reduction and cost reduction of beverage cans and food cans, along with the development of can making processing technology, materials for cans are required to have higher strength, thinner wall, and high speed can making. As a result, more severe processing has been performed than before.

Under such circumstances, Japanese Patent Laid-Open No.
In a cold-rolled steel sheet manufactured based on a slab disclosed in Japanese Patent No. 72925 or JP-A-7-207403, it has become impossible to sufficiently reduce can-making defects.

Also, as disclosed in JP-A-6-172925 and JP-A-7-207403, at the steelmaking stage, oxide inclusions having a particle size of 200 μm or less are dispersed to 10 ³ or less per kg. If we consider in detail to produce a cast slab obtained by, if a spherical inclusions having a particle size of 200μm were present 10 ³ per 1Kg, in this case
Estimating the TO value gives TO = about 0.01 ppm. The slabs produced on the actual mass production scale (converter, electric furnace-continuous casting) have a TO value of at least about 4-5 ppm (Reference: No.
126,127 Nishiyama Memorial Lecture “High Purity Steel” p.123 (s63)). Therefore, production of such steel is not desirable from the viewpoint of cost reduction due to remarkable reduction in operability and yield.

The present invention has been made in order to solve such a problem, and provides a cold-rolled steel sheet for cans with less can-making defects caused by oxide inclusions even under severe processing conditions. The purpose is to:

[0011]

The gist of the present invention is to reduce the total number of oxide-based inclusions contained in a cold-rolled steel sheet to a predetermined value or less and to reduce the number of oxide inclusions contained in a slab to a specific particle size or more. The difference between the number of material-based inclusions and the number of oxide-based inclusions having a specific grain size or more contained in the cold-rolled steel sheet, that is, a specific grain size or more that is crushed by rolling a billet The object is to reduce the number of oxide-based inclusions to a predetermined value or less.

That is, the object is to provide a continuous cast slab.
A cold-rolled steel sheet for cans manufactured by surface-treating a cold-rolled steel sheet obtained by hot rolling, cold rolling, continuous annealing, and further temper rolling or secondary rolling (DR rolling). The total number of oxide-based inclusions contained in the cold-rolled steel sheet is 10 ⁷ or less per 1 g of the sample, and the particle size contained in the slab for producing the cold-rolled steel sheet. The difference between the number of oxide-based inclusions of 10 μm or more and the number of oxide-based inclusions of 10 μm or more in grain size contained in the cold-rolled steel sheet is 2 × 10 ³ or less per 1 g of the sample. The problem is solved by a cold-rolled steel sheet for cans characterized by the following.

(Circumstances leading to the invention) The present inventors have intensively studied to solve the above-mentioned problems. First, the actual situation of can-making defects occurring during can-making processing was investigated. Examination of the components of the oxide-based inclusions present in the defective part of the can made revealed that about 60% of the inclusions were Al ₂ O ₃ alone, and about 40% were 80 parts by weight.
0% of Al component, the balance was _{Mg, Ca, Fe, Al 2} O 3 inclusions of multi-component comprising a component such as Si. It was also found that most of these oxide-based inclusions were present in the cold-rolled steel sheet with a particle size of 20 μm or less. This is because oxide inclusions were very finely crushed in the rolling process.

[0014] The particle diameter 20 existing in the defective part of the can
It was also found that fine oxide-based inclusions of μm or less exist as if forming perforations in the rolling direction in a straight line and without overlapping each other.

Based on the above findings, the present inventors have focused on the fact that there is a relationship between the particle size and the number of oxide-based inclusions crushed by rolling and the incidence of can-making defects. A survey was conducted.

First, a can-making test was carried out in a laboratory using can materials obtained by subjecting a cold-rolled steel sheet coil manufactured under various conditions to surface treatment. In the case of a can manufacturing test in a laboratory, if the rate of occurrence of defective cans is 1% or less, there is no problem in an actual continuous can manufacturing line.

Next, a sample was sampled from the cast slab and the cold-rolled steel sheet of the can material subjected to the can-making test, extracted with acid, and then subjected to light diffraction to determine the particle size of the oxide-based inclusions. And the number was measured.

Originally, steel contains nitride-based inclusions, carbide-based inclusions, sulfide-based inclusions, etc. in addition to oxide-based inclusions. , A halogen-organic solvent extraction method and an electrolytic extraction method.
However, the acid dissolution extraction method is most suitable for selectively extracting only oxide inclusions mainly composed of Al ₂ O ₃ .

In addition, the light diffraction method can accurately measure the particle size, weight, and number of inclusions as compared with the conventional slime method and microscopic method.

FIG. 1 shows the relationship between the number of oxide-based inclusions and the rate of occurrence of defective cans.

The total number of oxide inclusions contained in the cold-rolled steel sheet, exceeds 10 ⁷ per sample 1g canning defect rate undesirably exceed 1%.

Also, the difference between the number of oxide-based inclusions having a grain size of 10 μm or more contained in the slab and the number of the oxide-based inclusions having a grain size of 10 μm or more contained in the cold-rolled steel sheet is as follows: If the number exceeds 2 × 10 ³ per gram of the sample, even if the total number of oxide-based inclusions contained in the cold-rolled steel sheet is 10 ⁷ or less per gram of the sample, the rate of occurrence of defective cans is 1%. Is not desirable.

Therefore, the total number of the oxide-based inclusions contained in the cold-rolled steel sheet is 10 ⁷ or less per gram of the sample, and the oxide-based inclusions having a particle size of 10 μm or more contained in the slab are not included. The difference between the number and the number of oxide-based inclusions having a particle size of 10 μm or more contained in the cold-rolled steel sheet was 2 × / g of the sample.
In the case of 10 ³ or less is found that can manufacturing defect rate is suppressed below 1%, good can-making results,
The present invention has been completed.

(Desirable Manufacturing Conditions) The present invention relates to a steel composition,
Although there is no particular limitation on the manufacturing method, desirable conditions will be described below.

As the steel composition, for example, C:
0.01-0.12%, Si: 0.05% or less, Mn: 0.1-0.6%,
P: 0.03% or less, S: 0.03% or less, sol. Al: 0.02-0.
A cast slab containing 1%, N: 0.005% or less, and the balance being Fe can be used. In addition, the addition of an alloying element such as B as required does not impair the function and effect of the present invention.

The steel adjusted to a predetermined composition by a converter, secondary refining, etc. is cast into a slab by continuous casting. Next, the continuous cast slab is hot-rolled, pickled, cold-rolled and then continuously annealed.
Further, temper rolling or secondary rolling (DR rolling) and surface treatment are performed.

The hot rolling is performed according to a conventional method, and the heating temperature is from 1100 to
1250 ℃, Finishing temperature: 800-900 ℃, Winding temperature: 500-700 ℃
Degree. In cold rolling,
It is desirable that the cold pressure rate is about 80 to 95% and the annealing temperature is equal to or higher than the recrystallization temperature.
The elongation and rolling reduction of (rolling) may be appropriately selected according to the sheet thickness, strength, workability, and the like.

The type of surface treatment is not particularly limited, and various surface treatments such as electrolytic chromate treatment and tin plating may be selected according to the purpose. Furthermore, after the surface treatment, a pre-coat or a film lamination such as a PET film may be performed, and in such a case, the effect of the present invention is sufficiently exhibited.

[0029]

The present invention will be described below with reference to examples. C:
0.03 to 0.05%, Si: 0.01%, Mn: 0.15 to 0.25%,
P: 0.01 to 0.02%, S: 0.005 to 0.02%, sol. Al: 0.0
In order to refine 3 to 0.06% of molten steel, it is adjusted to a predetermined carbon concentration after blowing in a converter, CaO for solidifying slag is injected, and slag stoppers are used to prevent outflow of converter slag while using a slag stopper. did.

Next, a vacuum degassing treatment is performed in the RH, aluminum is charged to deoxidize, and further refluxed while bubbling Ar gas to aggregate Al ₂ O ₃ particles as deoxidized products. Coalescence and floating removal.

Thereafter, a vertical bending type continuous casting machine was used to produce 220
After casting into a ~ 250mm thick slab, reheat at 1200 ° C,
It was hot rolled to a thickness of 1.8 to 2.0 mm. Then, after pickling, cold rolling, continuous annealing, and DR rolling are performed.
m of cold-rolled steel coil was produced.

A sample of about 100 g was sampled from the thus obtained slab and the coil of the cold-rolled steel sheet.
And the measurement procedure of FIG. 3 (Materia Vol. 35, No. 4 (1
996)), the particle size and the number of oxide-based inclusions were measured.

FIG. 2 is a flowchart showing a procedure for extracting oxide-based inclusions from a sample. FIG. 3 detects the particle size and the number of the extracted oxide-based inclusions by an optical diffraction method. It is a flowchart which shows a procedure. Hereinafter, these procedures will be described in detail.

A 50-100 g sample of steel is placed in a 2 liter beaker. Then, H 3 in the ratio of water 3 to HNO ₃ 1
A solution obtained by adding 7 ml of H ₂ SO _{4 to} 1000 ml of an aqueous solution of NO ₃ ,
Dissolve all in a 87 ° C warm bath. Then, 0.2μ pore size
The residue is removed by filtration through a 47 mmφ Nuclepore filter. Since the residue contains nitride, carbide, and carbon, it is removed in the following steps to extract only oxide-based inclusions.

That is, put the residue in a 300 ml beaker,
87 ml of 50 ml of a 1: 1 H ₂ SO ₄ aqueous solution of H ₂ SO ₄ and water
Heat in a warm bath for 40 minutes. Next, 25 ml of a saturated KMnO ₄ solution is added, and the mixture is heated in a warm bath at 90 to 92 ° C. for 40 minutes. Thereafter, H ₂ O ₂ is added to dissolve the precipitate of MnO ₂ . Then, the mixture was heated in a hot bath at 87 ° C., and excess H ₂ was added.
After removing O ₂ , the residue is removed by filtration through a Nuclepore filter having a pore size of 0.2 μm and 47 mmφ. Since this residue is an oxide-based inclusion, it is dried and weighed.

In FIG. 3, the extracted oxide-based inclusions were put into a 50 ml beaker together with a lipopore filter having a pore diameter of 0.2 μm and 47 mmφ, and 20 ml of a 0.2 wt% sodium hexametaphosphate aqueous solution was added. Then, oxide inclusions adhering to the filter are peeled off. Then, 5 to 7 ml is put into the measurement cell, and the particle diameter and the number thereof are measured by an optical diffraction method.

After subjecting the coil surface of the cold-rolled steel sheet to electrolytic chromate treatment, a PET resin film was heat-sealed and subjected to a can making test in a laboratory.

The total number of oxide-based inclusions per gram of the sample of the cold-rolled steel sheet for cans manufactured as described above, and the grain size per gram of the slab sample used for manufacturing the steel sheet were 10%.
μm or more of oxide-based inclusions having a particle size of 10 μm or more per 1 g of the sample of the cold-rolled steel sheet for cans B, AB, and defective rate of can-making Table 1
Shown in

Table 1 shows comparative values of comparative examples manufactured by a method different from that of the present embodiment.

[0040]

[Table 1]

In Comparative Example 1, the total number of oxide-based inclusions contained in the cold-rolled steel sheet exceeded 10 ⁷ per gram of the sample, and the oxide inclusions contained in the slab had a particle size of 10 μm or more. Number of inclusions and grain size 1 in cold-rolled steel sheet
The difference from the number of oxide-based inclusions of 0 μm or more is 1 g of the sample.
This is an example in which the rate of occurrence of can-making defects is high because the number of pieces per unit is 2 × 10 ³ or more.

Comparative Example 2 has a particle size of 10 μm contained in the slab.
The difference between the number of oxide-based inclusions of m or more and the number of oxide-based inclusions of a particle size of 10 μm or more contained in the cold-rolled steel sheet is 2 × 10 ³ or less per 1 g of the sample. , the total number is per sample 1g of oxide inclusions contained in the cold-rolled steel sheet, since it exceeds 10 ⁷ a, canning defect rate is high example.

Comparative Example 3 shows that the total number of oxide-based inclusions contained in the cold-rolled steel sheet is 10 ⁷ or less per gram of the sample, but the oxide-based inclusions contained in the slabs have a particle size of 10 μm or more. The number of inclusions and the particle size of 10 μm contained in the cold-rolled steel sheet
The difference from the number of oxide-based inclusions described above is
Since the number exceeds 2 × 10 ³ , this is an example in which the rate of defective cans is high.

In contrast, Examples 1 to 6, which are within the scope of the present invention, have a can-making defect occurrence rate of 1% or less, and good can-making results are obtained.

[0045]

As described above, in the present invention, the continuous cast slab is obtained by hot rolling, cold rolling, continuous annealing, and further temper rolling or secondary rolling (DR rolling). A cold-rolled steel sheet for cans manufactured by surface-treating the obtained cold-rolled steel sheet, wherein the total number of oxide-based inclusions contained in the cold-rolled steel sheet is 10 ⁷ or less per 1 g of the sample. And the number of oxide-based inclusions having a grain size of 10 μm or more contained in a slab for producing the cold-rolled steel sheet, and a grain size 1 contained in the cold-rolled steel sheet.
The difference from the number of oxide-based inclusions of 0 μm or more is 1 g of the sample.
Since it is set to 2 × 10 ³ or less per unit, by providing a cold-rolled steel sheet excellent in cleanliness, can-making defects caused by oxide-based inclusions can be reduced,
Significant improvement in can making technology can be achieved.

Also, in the inspection stage of a product, it is determined whether or not the condition of the present invention is satisfied, and only the product which satisfies the condition is shipped, thereby preventing defective products from being shipped to customers. Can be.

Further, in the inspection stage, if a product that does not satisfy the conditions of the present invention is found, it is immediately fed back to the steel making process and the rolling process to change the operating conditions, so that a large number of defective products are obtained. This can be prevented from occurring.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the number of oxide-based inclusions obtained by an optical diffraction method after extraction by acid dissolution and the rate of occurrence of can-making defects.

FIG. 2 is a flowchart illustrating an operation procedure of acid dissolution extraction.

FIG. 3 is a flowchart illustrating an operation procedure of the light diffraction method.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hidetoshi Matsuno 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Hiroshi Shimizu 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor Katsumi Tanikawa 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Pipe Co., Ltd.

Claims (1)

[Claims] 1. A continuous cast slab is subjected to hot rolling, cold rolling,
A cold-rolled steel sheet for cans manufactured by surface-treating a cold-rolled steel sheet obtained by continuous annealing and further temper rolling or secondary rolling (DR rolling),
The total number of oxide-based inclusions contained in the cold-rolled steel sheet is 10 ⁷ or less per 1 g of the sample, and the grain size is 10 μm or more contained in the slab for producing the cold-rolled steel sheet. The difference between the number of oxide-based inclusions and the number of oxide-based inclusions having a particle size of 10 μm or more contained in the cold-rolled steel sheet is 2 × 10 ³ or less per 1 g of a sample, Cold rolled steel sheet for cans.