JP2000256787A - Cold roller steel sheet for can - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold rolled steel sheet for a can small in defect in can- making caused by oxide based inclusions even under severe working conditions and furthermore mass-producible at a low cost. SOLUTION: The fact that, by controlling the total weight of oxide based inclusions included in a cold rolled steel sheet and the weight of oxide based inclusions of grain size equal to or above the specified one to the levels equal to or below the prescribed ones, defects in can-making caused by oxide based inclusions can effectively be reduced even under severe working conditions has been found, and, the total weight of oxide based inclusions included in the steel sheet is controlled to <=50 ppm, the weight of oxide based inclusions of >=5 μm grain size included in the steel sheet is controlled to <=10 ppm, and, preferably, the weight of oxide based inclusions of >=10 μm grain size is <=1 ppm.

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 which can reduce can-making defects caused by oxide inclusions.

[0002]

2. Description of the Related Art In recent years, cold-rolled steel sheets for cans are prepared by hot rolling, pickling, and continuously casting cast slabs having predetermined chemical components.
It is manufactured by subjecting a cold-rolled steel sheet obtained by cold rolling, continuous annealing, temper rolling or secondary rolling (DR rolling) to a surface treatment. Among such cold-rolled steel sheets for cans, in particular, cold-rolled steel sheets for cans manufactured from Al-killed steel contain oxide-based inclusions (deoxidation products) generated during deoxidation in the above process. This causes a problem that can-making defects such as pinhole-shaped defects and breakage of the side wall of the can body are caused during can-making.

[0003] Conventionally, in order to reduce can-forming defects caused by such oxide-based inclusions, the grain size, number density and characteristics of oxide-based inclusions in a slab are limited to reduce the quality of the product after rolling. A method for controlling the existence form and distribution of the oxide-based inclusions is disclosed. For example, JP-A-6-172925
In the publication, oxide inclusions having a particle size of 200 μm or less are dispersed in 10 ³ or less per kg, and the melting point of the oxide inclusions contained in the slab is 1350 ° C. or less or 1650 ° C. or more. Thus, a method is disclosed in which the thickness of oxide-based inclusions crushed during rolling is suppressed to 5 μm or less, thereby reducing can-making defects such as pinholes and flange cracks.

In Japanese Patent Application Laid-Open No. Hei 7-207403, oxide inclusions having a particle size of 200 μm or less are dispersed to 10 ³ or less per kg in a slab, and oxide inclusions contained in the slab are reduced to 10 ³ or less. By containing at least 4% by weight of MgO, the thickness of oxide-based inclusions crushed during rolling is suppressed to 5 μm or less, and the oxide-based inclusions are made to be difficult to elongate, so that crushing after rolling is performed. There is disclosed a method of preventing a grown oxide-based inclusion from elongating to a continuous distribution state, thereby reducing can-making defects such as pinholes and broken cylinders.

[0005]

However, in recent years, due to the need for weight reduction and cost reduction of beverage cans, food cans, and the like, along with the development of can-making technology, cold-rolled steel sheets for cans have high strength. Demands have been made for thinning, thinning, and high-speed can-making, and for this reason, more severe processing has been performed than ever before. Under these circumstances, the above-mentioned Japanese Patent Application Laid-Open
In a cold-rolled steel sheet manufactured based on a slab disclosed in JP-A-172925 or JP-A-7-207403, it has become impossible to sufficiently reduce can-making defects.

Further, as disclosed in JP-A Hei 6-172925 and JP 7-207403, in 10 ³ or less per 1kg particle size 200μm following oxide inclusions in the steel making step When the production of dispersed slabs is examined in detail, there are the following problems. That is, the T.V. of slabs produced on an actual mass production scale (converter or electric furnace-continuous casting method). The O value is at least about 4 to 5 ppm (for example, the 126th and 127th Nishiyama Memorial Lecture “Highly Clean Steel” p.123 (s63)), but it is assumed that spherical inclusions having a particle diameter of 200 μm are 10 ³ per kg. T. when there are When the O value is estimated, O = 0.0
It is about 1 ppm, and in the production of such steel, the operability and the yield are remarkably reduced, so that it is difficult to mass-produce at low cost.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, to reduce can-making defects caused by oxide-based inclusions even under severe processing conditions, and to mass-produce cans at low cost. It is an object of the present invention to provide a cold-rolled steel sheet.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the total weight of oxide-based inclusions contained in a cold-rolled steel sheet manufactured from Al-killed steel. And that the weight of the oxide-based inclusions having a specific particle size or more is restricted to a predetermined level or less, thereby effectively reducing can-making defects caused by the oxide-based inclusions even under severe processing conditions. I found

The present invention has been made based on such findings, and the features thereof are as follows. [1] The total weight of oxide-based inclusions contained in the steel sheet is 50p
A cold-rolled steel sheet for cans, wherein the weight of oxide-based inclusions having a particle size of 5 μm or more contained in the steel sheet is 10 ppm or less. [2] In the cold-rolled steel sheet for cans according to the above [1], the weight of oxide-based inclusions having a particle size of 10 μm or more contained in the steel sheet is 1p.
pm or less.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention and the reasons for limiting the same will be described below. The present inventors first investigated the actual state of can-making defects that occur during can-making in cold-rolled steel sheets for cans manufactured from Al-killed steel. Examination of the components of the oxide-based inclusions existing in the defective can-making site revealed that about 60% of the inclusions were Al ₂ O ₃ alone, and the remaining about 40% were 80% by weight of the Al component. The balance is Mg, Ca, Fe, S
It was a multi-component Al ₂ O ₃ -based inclusion containing components such as i. It was also found that most of these oxide-based inclusions existed 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. In addition, fine oxide-based inclusions having a particle size of 20 μm or less, which are present in the defective part of the can,
It was also found that they existed in the form of perforations in a straight line along the rolling direction and without overlapping each other.

The present inventors have further studied on the basis of the above findings, and have found a relationship between the particle size and content of oxide-based inclusions present in the cold-rolled steel sheet and the incidence of defective cans. Focusing on the fact that there is, we conducted the following survey. First, a can-making test was carried out in a laboratory using cold-rolled steel sheets for cans obtained by subjecting a cold-rolled steel sheet coil manufactured from continuous cast slabs manufactured under various conditions to surface treatment. In the case of a can-making test in a laboratory, if the rate of defective can-making is 1% or less, there is no problem in an actual continuous can-making line.

Further, a sample was sampled from the cold-rolled steel sheet for a can which was subjected to the can-making test, and after the acid dissolution and extraction, the particle size and weight of the oxide-based inclusions were measured by an optical diffraction method. Steel contains nitride-based inclusions, carbide-based inclusions, sulfide-based inclusions, etc. in addition to oxide-based inclusions, and halogen-organic solvent-based methods are used to extract these inclusions. There are an extraction method and an electrolytic extraction method, and the above-mentioned acid-dissolution extraction method is most suitable for selectively extracting only oxide-based inclusions mainly composed of Al ₂ O ₃ . In addition, the light diffraction method can accurately measure the particle size distribution of inclusions as compared with the conventional slime method and microscopic method.

FIG. 1 shows the total weight and particle size of the oxide-based inclusions present in the cold-rolled steel sheet for cans (where the particle size is the particle size at the maximum diameter portion of each inclusion; the same applies hereinafter). The relationship between the weight of the oxide-based inclusions having a size of 5 μm or more and the incidence of defective cans was shown. According to the figure, the total weight of oxide-based inclusions is 50 ppm or less, and the weight of oxide-based inclusions having a particle size of 5 μm or more is 10 ppm.
It can be seen that in the region of ppm or less, the rate of defective can production is suppressed to 1% or less. Therefore, in the present invention, the total weight of the oxide-based inclusions contained in the cold-rolled steel sheet is 50 p.
pm or less and the weight of the oxide-based inclusion having a particle size of 5 μm or more is 10 ppm or less.

Further, when the total weight of the oxide-based inclusions is 50 p
pm or less, and in the region where the weight of the oxide-based inclusions having a particle size of 5 μm or more is 10 ppm or less, the result of examining the relationship between the weight of the oxide-based inclusions having a particle size of 10 μm or more and the incidence rate of can-making defects is shown. As shown in FIG. According to the figure, when the weight of the oxide-based inclusions having a particle size of 10 μm or more is 1 ppm or less, defective can-making is completely suppressed. For this reason, in order to obtain particularly excellent can-manufacturing properties in which almost no can-making defect occurs, the amount of oxide-based inclusions contained in the cold-rolled steel sheet is 50 ppm or less and the oxide-based inclusions having a particle size of 5 μm or more are used. Inclusion amount is 10p
pm or less, and the weight of the oxide-based inclusions having a particle size of 10 μm or more is preferably 1 ppm or less.

The cold-rolled steel sheet for cans of the present invention is a cold-rolled steel sheet manufactured from Al-killed steel, and its composition and manufacturing method are not particularly limited, but preferable conditions thereof will be described below. As the steel composition, for example,
C: 0.01 to 0.12% by weight, Si: 0.05% by weight
Mn: 0.1 to 0.6% by weight, P: 0.03% by weight or less, S: 0.03% by weight or less, sol. Al: 0.
It has a composition consisting of 02 to 0.1% by weight, N: 0.005% by weight or less, with the balance being Fe and inevitable impurities. Also,
Even if an alloying element such as B is added as required, the effects of the present invention are not impaired.

Regarding the production conditions, steel adjusted to a predetermined composition by converter blowing, secondary refining and the like is cast into slabs by continuous casting, and the continuous cast slabs are hot-rolled, pickled, and cold-rolled. After rolling, the steel sheet is subjected to continuous annealing, and further temper rolling or secondary rolling (DR rolling), and thereafter, the cold-rolled steel sheet is subjected to surface treatment. Hot rolling is performed according to a conventional method.
00 to 1250 ° C, finishing temperature: 800 to 900 ° C, and winding temperature: about 500 to 700 ° C. In the cold rolling, it is desirable that the cold pressure ratio is about 80 to 95% and the annealing temperature is higher than the recrystallization temperature. Further, the elongation rate and the reduction rate of the temper rolling or the secondary rolling (DR 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. Further, after the surface treatment, pre-coating or lamination of a film such as a PET film may be performed. In this case, the effect of the present invention is sufficiently exhibited.

[0018]

EXAMPLES C: 0.03 to 0.05% by weight, Si: 0.
01% by weight, Mn: 0.15 to 0.25% by weight, P:
0.01 to 0.02% by weight, S: 0.005 to 0.02
% By weight, sol. Al: In order to refine molten steel of 0.03 to 0.06% by weight, after being blown in a converter and adjusted to a predetermined carbon concentration, CaO for solidifying slag is charged, and the converter is converted using a slag stopper. While preventing slag outflow,
Steel tapping.

Next, a vacuum degassing process is performed in the RH, aluminum is charged to deoxidize, and reflux is performed while bubbling Ar gas, whereby Al ₂ O ₃ particles which are deoxidized products are aggregated. They were combined and floated off.
Then, with a vertical bending type continuous casting machine, 220 to 250 mm
After casting into thick slabs, the slabs were reheated at 1200 ° C. and hot rolled to 1.8-2.0 mm thickness. Then
After pickling this hot-rolled steel sheet, cold rolling, continuous annealing,
DR rolling was performed, and finally a cold-rolled steel sheet coil having a sheet thickness of 0.2 mm was produced.

From the cold-rolled steel sheet thus obtained, a sample of about 100 g was sampled, and the measurement procedure shown in FIGS. 3 and 4 (“Materia”, Vol. 35, No. 4, (199)
The particle size and weight of the oxide-based inclusions were measured according to 6)). FIG. 3 is a flowchart showing a procedure for extracting oxide-based inclusions from a sample, and FIG. 4 is a flowchart showing a procedure for measuring the particle size distribution of the extracted oxide-based inclusions by an optical diffraction method. Hereinafter, these procedures will be described in detail.

First, a procedure for extracting oxide-based inclusions (FIG. 3)
, 50 to 100 g of a steel sample was placed in a 2 liter beaker, and the steel sample was mixed with 7 ml of H ₂ SO _{4 in} 1000 ml of an aqueous HNO ₃ solution containing concentrated HNO ₃ and water at a ratio of 1: 3.
Is dissolved in a 87 ° C. warm bath consisting of a solution to which is added.
Thereafter, the residue is filtered through a Leuclipore filter having a pore size of 0.2 μm and a diameter of 47 mm to remove the residue. Since the residue contains nitride, carbide and carbon, these are removed in the following step to extract only oxide-based inclusions.

[0022] That is, placed the residue 300ml _beaker, H 2 SO ₄ and water 1: 1 aqueous _H 2 SO ₄ 5
Heat in a 0 ml 87 ° C. water bath for 40 minutes. Next, 25 ml of a saturated KMnO ₄ solution was added, and 90 to 9
Warm in a 2 ° C. water bath for 40 minutes. Then, H ₂ O ₂ was added to remove MnO ₂ , and further heated in a hot bath at 87 ° C. to remove excess H ₂ O ₂ , and the pore size was 0.2 μm.
The residue is taken out by filtering through a 47 mmφ Nuclepore filter. Since this residue is an oxide-based inclusion,
After being dried, it is weighed.

Next, in the detection procedure by the optical diffraction method (FIG. 4), the oxide inclusions extracted as described above were put into a 50 ml beaker together with a lipopore filter having a pore diameter of 0.2 μm and 47 mmφ. After adding 20 ml of a 2 wt% sodium hexametaphosphate aqueous solution, ultrasonic vibration is applied to separate the oxide inclusions attached to the filter. Then, 5 to 7 ml of the aqueous solution is put into the measurement cell in a state where the oxide-based inclusions are sufficiently dispersed in the aqueous solution, and the particle size distribution is measured by an optical diffraction method.

On the other hand, after the surface of the cold-rolled steel sheet was subjected to electrolytic chromate treatment, a PET resin film was heat-sealed, and a can-making test was performed on the surface-treated steel sheet in a laboratory. Table 1 shows the total weight of the oxide-based inclusions in the cold-rolled steel sheet for cans, the weight of the oxide-based inclusions having a particle size of 5 μm or more, the weight of the oxide-based inclusions having a particle size of 10 μm or more, and can making. The failure rate was shown.

[0025]

[Table 1]

In Table 1, in Comparative Examples 1 and 2, the total weight of the oxide inclusions exceeded 50 ppm, and the weight of the oxide inclusions having a particle size of 5 μm or more also exceeded 10 ppm. High rate of defective cans. Comparative Example 3
Means that the weight of oxide-based inclusions having a particle size of 5 μm or more is 10 pp
m or less, but the total weight of the oxide-based inclusions is 50 ppm
, The incidence of defective cans is high. In Comparative Examples 4 to 6, the total weight of the oxide-based inclusions was 50 pp.
m or less, but since the weight of the oxide-based inclusions having a particle size of 5 μm or more exceeds 10 ppm, the rate of occurrence of defective cans is high.

In contrast, Examples 1 to 9 of the present invention satisfying the conditions of the present invention all have a low can-making defect rate,
It turns out that the cold-rolled steel plate for cans with excellent cleanliness has been obtained. Above all, the total weight of oxide inclusions is 50 ppm or less, and the weight of oxide inclusions having a particle size of 5 μm or more is 10 pp.
Inventive Example 6 to Inventive Example 9 in which the weight of oxide-based inclusions having a particle size of 10 μm or more is 1 ppm or less.
The occurrence of defective can is almost completely suppressed.

[0028]

As described above, according to the present invention, the total weight of oxide-based inclusions is reduced to some extent,
μm or more oxide-based inclusions, more preferably a particle size of 10 μm
By simply reducing the weight of the oxide-based inclusions of m or more to a specific level or less, it is possible to effectively suppress the occurrence of can-making defects caused by the oxide-based inclusions and to reduce the occurrence of can-making defects. Cold-rolled steel sheets can be obtained at low cost. Therefore, by using the cold-rolled steel sheet for a can of the present invention, a great improvement in can-making technology can be achieved.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the total weight of oxide-based inclusions present in a cold-rolled steel sheet for cans and the weight of oxide-based inclusions having a particle size of 5 μm or more and the rate of occurrence of defective cans.

FIG. 2 shows that the total weight of oxide-based inclusions is 50 ppm or less,
And the weight of the oxide-based inclusions having a particle size of 5 μm or more is 10 pp.
is a graph showing the relationship between the weight of oxide-based inclusions having a particle size of 10 μm or more and the incidence rate of can-making defects in a region of not more than m.

FIG. 3 is a flowchart showing a procedure for extracting oxide-based inclusions from a steel sheet sample.

FIG. 4 is a flowchart showing a procedure for measuring a particle size distribution of extracted oxide-based inclusions by an optical diffraction method.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kentaro Mori 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Jun Kubota 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun (72) Inventor: Hidetoshi Matsuno 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Nihon Kokan Co., Ltd. (72) Inventor: Hiroshi Shimizu 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Inside (72) Inventor Go Murai 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Katsumi Tanikawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. Inside

Claims (2)

[Claims] 1. The total weight of oxide inclusions contained in a steel sheet is 50 ppm or less, and the weight of oxide inclusions having a particle size of 5 μm or more contained in a steel sheet is 10 ppm or less. Features Cold rolled steel sheet for cans. 2. The cold-rolled steel sheet for cans according to claim 1, wherein the weight of the oxide-based inclusions having a particle size of 10 μm or more contained in the steel sheet is 1 ppm or less.