JPH08311609A - Steel sheet for di can excellent in compressive strength and neck workability and its production - Google Patents

Abstract

PURPOSE: To produce a steel sheet for DI cans excellent in pressure withstanding strength and neck workability and to provide a method for producing the same. CONSTITUTION: This steel sheet for DI cans is the one having a compsn. contg. 0.01 to 0.08% C, <=0.5% Mn, <=0.20% SolAl and <=0.01% N, furthermore contg., at need, at least one kind among Si, Cr, Cu and Ni by <=0.1% and/or at least one kind of Ti and Nb by <=0.1%, and in which the content of solid solution C is regulated to 5 to 25ppm, YP in the L direction is regulated to 30 to 44Kgf/ mm<2> , and the difference in YP between the L direction and C direction is regulated to <=2Kgf/mm<2> . As for the method for producing the same, the hot rolled sheet having the same components is subjected to cold rolling, is recrystallized, is thereafter cooled at >=60 deg.C/sec and is held at 300 to 450 deg.C for 30 to 180sec. After that, it is subjected to wet skinpass rolling of 3 to 12%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet used for a body of a two-piece can (hereinafter referred to as DI can) by the DI method and a method for manufacturing the steel sheet.

[0002]

2. Description of the Related Art Tin cans, which are tin-plated thin steel plates or tin-free steels that are treated with chromic acid, are widely used for food cans, aerosol cans, and easy open cans. As a method of making a can, there are used a three-piece can made up of three parts of a lid, a body, and a bottom, and a two-piece can made up of a body and a bottom integrally and two parts together with the lid. DI (Drawing & Ironing) is a typical manufacturing method for the body of a 2-piece can.
Is the law. Hereinafter, with respect to describing the characteristics required for the DI can, the pressure resistance of the can body, which is the object of the present invention,
This section describes the body that requires severe properties such as neck-in processability after baking.

A process for making a can of the body by the DI method will be briefly described. First, a disk-shaped blank is punched out from a steel strip, and shallow drawing cup molding is performed using a punch and a die. Next, with a DI processing machine, a side wall is squeezed by using a punch and a die having a clearance thinner than the wall thickness of the cup to form a cup-shaped body of a cup having a predetermined depth, and a can bottom is formed into a dome shape. . Further, the end of the formed body is cut off to make the height of the upper end of the body uniform. After that, cleaning, drying, coating, and dry baking are performed, and necking processing for reducing the opening diameter of the can body is further performed, and then flange processing is performed at the opening end portion so as to extend outward in the diametrical direction.

The characteristics required for steel sheets for DI cans are as follows:
Conventionally, the DI workability and the flange workability have been mainly used, but for the purpose of resource saving, as the steel plate thickness becomes smaller, neck workability and pressure resistance after forming a can body become important.
DI processability refers to performance such as less wear of the die, processing with a small processing energy, and no material breakage during processing. Flanging processability refers to the flange when the flange part is stretch-formed. This refers to the performance called cracking, which is less likely to cause cracks. On the other hand, the neck workability is the ability to smoothly perform neck processing without causing defects such as wrinkles, and the pressure resistance is, for example, in the body part, a portion with low strength such as a can bottom has an internal pressure. It refers to the external force that causes buckling.

As a steel plate for such a DI can,
For example, a material made of boron-added aluminum killed steel and annealed by a batch annealing method (refer to Japanese Patent Laid-Open No. 53-48913), a material made of a copper-added low carbon steel and annealed by a batch annealing method (Japanese Patent Publication No. 52-16965). The batch annealed material has been mainly applied as described in Japanese Patent No. It is considered that the batch annealed material was superior to the continuous annealed material in DI processability and flange processability in terms of extensibility and deep drawability. However, recently, with the progress of the continuous annealing method, an aluminum killed steel is used as a material, and a steel sheet annealed by the continuous annealing method has been used. (Iron and steel
Vol.80 1994 No.11 “Applying bake hardenable steel sheet to lightweight 2-piece cans”).

This continuous annealed steel sheet has excellent features such as bake hardenability, that the uniformity of properties is better than that of a steel sheet that has been subjected to batch annealing, and that the manufacturing cost can be reduced. The combined use of over-aging treatment in annealing has DI workability and flange workability comparable to those of batch annealed materials.

[0007]

The plate thickness of steel sheets for DI cans has been greatly reduced in recent years, and was once 0.30 to 0.3.
It was generally 5 mm, but it is becoming 0.22 mm or less from 0.22 to 0.30 mm. Such thinning causes problems of reduction in pressure strength and neck workability.

The pressure resistance of the can is generally (plate thickness) ² ×
The decrease in plate thickness requires a large increase in yield strength as determined by (yield strength). To solve this problem,
A steel sheet that is soft and advantageous for DI processability is not sufficient. As a measure against this, the above-mentioned continuous annealed steel sheet utilizes the hardening characteristics by baking, but this is not sufficient for a sheet thickness of 0.22 mm or less.

Further, neck workability is greatly influenced by the plate thickness,
The thinner the plate, the more easily wrinkles occur. As an improvement from the material side of neck workability, generally, a steel plate that is soft and has little work hardening is advantageous, but such characteristics contradict pressure resistance, and with the progress of thinning, In that respect, new steel plates are needed.

As a measure to cope with the reduction of the plate thickness, it is conceivable to increase the strength of the steel sheet by adding a strength element. There are problems such as deterioration of neck workability and flange workability due to excess,
Not appropriate.

The present invention provides a steel plate suitable for thinning at a low cost regardless of such a method. That is, in the present invention, as the skeleton of the manufacturing method, first, a continuous annealing method that is more homogeneous than the batch annealing method, and is particularly easy to obtain a high hardness steel plate without using an additional element, and is advantageous in terms of manufacturing cost. The method of annealing is adopted. The present invention
Further, based on the findings of the experimental investigations by the present inventors, a steel sheet for DI cans suitable for thinning, that is, a steel sheet having high strength, good neck formability, and little anisotropy, and a method for producing the same are provided. Is intended.

[0012]

That is, the present invention is as follows.
(1) Carbon by weight%: 0.01 to 0.08%, manganese: 0.5% or less, acid-soluble aluminum: 0.20% or less, nitrogen: 0.01% or less, if necessary. 0.1
% Or less of at least one of sulfur, chromium, copper and nickel and / or 0.1% or less of at least one of titanium and niobium, and the balance being iron and unavoidable impurities,
In addition, the amount of solute C is 5 to 25 ppm, the YP (yield strength) in the L direction (rolling direction) is 30 to 44 Kgf / mm ² ,
A steel plate for a DI can excellent in pressure resistance and neck workability, which has a YP difference of ² Kgf / mm ² or less in the L direction and the C direction (steel plate width direction). And (2) carbon by weight: 0.
01-0.08%, manganese: 0.5% or less, acid-soluble aluminum: 0.20% or less, nitrogen: 0.01% or less, and if necessary 0.1% or less of sulfur, chromium, copper,
Continuous casting or ingot-making of steel containing at least one kind of nickel and / or at least 0.1% of titanium and at least one kind of niobium, and the balance of iron and unavoidable impurities.
Slab rolling into billets, hot rolling, descaling,
Then, after performing cold rolling in a conventional method, the material is soaked at a temperature of recrystallization temperature or more and less than Ac ₁ point in continuous annealing, cooled at a cooling rate of 60 ° C./second or more, and in a temperature range of 300 to 450 ° C. The steel plate is annealed for 30 to 180 seconds to reduce the amount of solute carbon in the steel sheet to 5 to 25 ppm, and is temper-rolled at a rolling reduction of 3 to 12% by wet temper rolling using a lubricant. A method for producing a steel plate for a DI can, which is excellent in pressure resistance and neck-in processability, is characterized by plating tin, nickel, chromium or the like for a steel plate for a can.

Hereinafter, the present invention will be described in detail. As a method of imparting the necessary strength with the reduction in thickness, the inventors have focused on imparting the strength by temper rolling. Although the strength imparting method itself by temper rolling is a conventionally known method, the inventors have found that not only the strength imparting but the pressure resistance strength of the DI can is strongly controlled by the average strength of the steel sheet. Of course, it is important to reduce the anisotropy in order to improve the compressive strength, and in neck processing, it is important to have uniform characteristics by the circumferential method in addition to being soft and easy to process. Focusing on the above, we investigated a method of imparting strength while maintaining directional uniformity.

FIG. 1 shows C: 0.02%, Mn: 0.025.
%, Acid-soluble Al: 0.05%, N: 0.004%, a coiling temperature was 670 ° C., and continuous annealing was performed so that the amount of solute carbon after annealing was 15 ppm. After that, the temper rolling method and the rolling reduction were changed to investigate the anisotropy of strength. It can be seen from FIG. 1 that there is an optimum point in the temper rolling reduction for reducing the anisotropy of strength, which is near the temper rolling reduction of 6% in this material.

FIG. 2 is a temper rolling in the case where the amount of solid solution carbon in the steel sheet was changed to 0.30 ppm by changing the amount of carbon contained in the steel sheet or adding titanium as a precipitation fixing element of carbon. This is a survey of changes in anisotropy due to. In these cases, the optimum point does not always exist, and it is understood that the temper rolling ratio should not be increased from the viewpoint of anisotropy.

According to the above investigations, the inventors have made it possible to achieve both strength and anisotropy by appropriately adjusting the amount of solute carbon and imparting strength by temper rolling in a range where anisotropy is small. It was discovered that Necessary rolling reduction, namely 3 to 1
It is necessary to perform wet temper rolling as a temper rolling method for giving a reduction rate of 2%. In this case, temper rolling may be performed in the same line as the annealing line or in a different line.

Next, as known from the above-mentioned literatures, it is extremely useful as a material for thinning, to utilize the bake hardening by the dry bake treatment after coating performed at a temperature of about 200 ° C. to improve the strength. Therefore, the change of the strength of the steel sheet with the temper rolling ratio of FIG. 1 changed by holding for 30 minutes at 210 ° C. was investigated. Figure 3 shows the results of the survey
Shown in From FIG. 3, it can be seen that the increase in the strength after the treatment at 210 ° C. due to the temper rolling reduction is smaller than the increase in the strength before the treatment at 210 ° C. due to the temper rolling reduction. Further consideration, it is advantageous to increase the temper rolling rate to increase the strength, but on the other hand, the increase in strength due to the temper rolling rate is gradually saturated, and it is premised on the treatment at 210 ° C. In consideration of the above, when the temper rolling ratio is 15% or more, the tendency of saturation becomes remarkable.

When the results of FIG. 1 and FIG. 2 are combined, it is disadvantageous in terms of processing that the direction uniformity is lost when the temper rolling rate is significantly increased, while the dry baking treatment is taken into consideration.
Even if the temper rolling rate is significantly increased, the strength increase will be saturated, so
It can be seen that the temper rolling ratio has an appropriate range.

The reason for using the strength of the steel sheet as an index for the pressure resistance of the can is that the body portion of the can after DI processing has a thin plate thickness, but the strength increases significantly due to work hardening. This is because the strength of the bottom of the can, which is a portion that is hardly processed during DI processing, poses a practical problem.

The annealed steel sheet has anisotropy from a structural point of view such as crystal grains. On the other hand, temper rolling is also unidirectional and causes anisotropy, but when solid solution C remains and the anisotropies of the two are opposite, perhaps due to different slip systems, an effect of canceling each other occurs. As a result, it is considered that the characteristics shown in FIG. 1 are generated.

On the other hand, when the temper rolling ratio is increased, the dislocation density rises to harden it. However, when the dislocation density rises, the solid solution C, which is the source of the bake hardenability, moves in the steel sheet to fix the dislocations. It is considered that the amount of bake-hardening at the high-quality rolling rate is reduced because the effect of this on strength is reduced.

Next, the reasons for limitation of the present invention will be described.
When the total carbon content as a steel sheet component is less than 0.01%, the cementite formation driving force in the cooling process in continuous annealing becomes small, and the solid solution carbon content increases rather than when it is 0.01% or more. Greater than 30 ppm.
When the amount of component carbon is in the range of 10 to 20 ppm, the amount of solid solution carbon decreases and the above conditions are satisfied, but the strength of the steel sheet decreases in such a region, so the amount of component carbon is 0.01
% Or more. On the other hand, if the amount of component carbon exceeds 0.08%, the amount of cementite formed is large, cracking is likely to occur during processing, and the workability deteriorates. Therefore, the amount of component carbon is set to 0.08% or less.

When the amount of solute carbon in the steel plate becomes zero, the result of FIG.
As can be seen, the anisotropy does not become smaller than a certain value (0.8 Kgf / mm ² ). On the other hand, when the amount of solute carbon increases to 30 ppm, the anisotropy also has a lower limit value.
It does not become smaller than 0 Kgf / mm ² . That is, the amount of solute carbon must be greater than zero and less than 30 ppm. The amount of solute carbon was set to 5 to 25 ppm in consideration of manufacturing variations. In order to adjust the amount of solute carbon by continuous annealing to 5 to 25 ppm, after soaking, it is rapidly cooled to 60 ° C / sec or more, and 300 to 450
A method of carrying out cementite precipitation treatment by holding the temperature at 30 ° C. for 30 to 180 seconds at this temperature is extremely desirable.

If the amount of component manganese exceeds 0.5%, the work hardening increases, which is not suitable for DI processing. Therefore, the amount of component manganese is set to 0.5% or less. The amount of acid-soluble aluminum, which is the amount of aluminum that is not in the form of oxide, is added to fix and fix the nitrogen.
If it is more than 100%, problems such as increase of alumina inclusions and hardening due to grain refinement due to precipitation of aluminum nitride occur. If the amount of the component nitrogen exceeds 0.01%, the amount of the additional element used for fixing the precipitation of nitrogen becomes large. For example, the precipitation of AIN when aluminum is used and the precipitation of TIN when titanium is used. Therefore, the workability is deteriorated, so the amount of nitrogen is made 0.01% or less.

When the temper rolling ratio is less than 3%, YP is less than 30 Kgf / mm ^2, as can be seen from the white circle line in FIG.
If YP is less than 30 Kgf / mm ² , desired thickness resistance cannot be secured after can forming and baking. When the temper rolling ratio exceeds 12%, the anisotropy increases and the strength is saturated after the baking treatment as shown in FIGS. 1 and 3, so the temper rolling ratio is set to 12% or less. When the temper rolling rate is 12%, the YP becomes 44 Kgf / mm ² (Fig. 1), but when YP exceeds this value, wrinkles occur during neck processing. In addition, the temper rolling ratio is set to 3% or more in consideration of the need for strength imparting by wet temper rolling and variation in manufacturing, including 6% which is the optimum point of anisotropy in FIG.

As the plating method, tin plating, nickel, chrome plating or the like which is usually used for steel plates for cans is used. For DI processing, tin plating is often used in terms of surface lubricity.

In the steel sheet for cans, it may be necessary to enhance the corrosion resistance depending on the type of contents.
Chromium, nickel, copper may be used. If the content of these elements exceeds 0.1%, it is harmful to DI processing due to an increase in work hardening, formation of precipitates, etc. Therefore, if a corrosion resistance enhancing element is used, the content should be 0.1% or less.

Although aluminum is used for precipitating nitrogen as described above, it is also possible to use a fixed element of an interstitial solid solution element such as titanium in place of a part of aluminum. However, if titanium is added excessively, T
Forming iN, TiC, etc., impairs workability,
It becomes difficult to secure a solid solution carbon amount of 2 to 25 ppm which is a constituent element of the present invention. Therefore, when the fixed element of the interstitial solid solution element such as titanium is added, the addition is limited to 0.1% or less.

The yield strength difference in the L and C directions is ² Kgf / mm ²
The reason for the following is because, as shown in the following examples, in practice, wrinkles occur in neck forming in a material having a yield strength difference of more than ² Kgf / mm ² . The yield strength difference of ² Kgf / mm ² corresponds to the anisotropy that occurs at the temper rolling rate of 12% according to FIG.

[0030]

EXAMPLE Steels having the components shown in Table 1 were melted in a converter,
After making hot steel billet by continuous casting, cool it to room temperature,
It was reheated to around 250 ° C, hot-rolled to a thickness of 2 to 3 mm in a temperature range of Ar ₃ points or more, and wound at 630 to 720 ° C. This hot-rolled steel strip was pickled, cold-rolled, re-crystallized and annealed at around 700 ° C., and then temper-rolled to the plate thickness shown in Table 1 and tin. Plated.

Table 2 shows the results obtained by subjecting the materials in Table 1 to can manufacturing. Performs neck molding with an experimental can making device,
The result was judged, and the flange formability was judged by the cone test shown in FIG. As shown in Table 2,
With respect to the steel sheet of the present invention, the neck processing after the DI processing, the flange forming, and the compressive strength passed, whereas no other material simultaneously satisfied the neck forming property, the flange formability, and the compressive strength.

In Table 1, the hardness was measured according to JIS by taking a sample from a steel plate for DI can after tin plating. The tensile strength was measured according to JIS by taking a sample from the tin-plated steel sheet for DI cans. The reason for the failure in the neck processing in Table 2 is the occurrence of wrinkles.
The cone test method for measuring the flange formability is as shown in FIG. 4, in which a cone-shaped cone is pressed against the opening of the DI can,
It measures the stroke length until cracking occurs, and if the stroke length is 7 mm or more, it is judged that the material is of good flange formability that does not easily cause flange cracking. The pass / fail of the compressive strength is judged by whether or not compressed air is introduced into the can body manufactured by DI processing to cause buckling of the can bottom.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

EFFECTS OF THE INVENTION The present invention provides a steel sheet for a thin DI can and a method of producing the same which satisfies both the strength of the can and the formability of the DI can, especially the neck formability, which cannot be achieved by the conventional techniques. The resource-saving effect by allowing the use of thin materials is extremely large.

[Brief description of drawings]

FIG. 1 is a temper rolling ratio and a yield strength anisotropy (= C direction YP−) of a steel sheet which has been annealed so as to have a solute carbon content of 15 ppm.
The figure which shows the relationship with L direction YP).

FIG. 2 is a diagram showing a relationship between a temper rolling ratio and a yield strength anisotropy when solid solution carbons are different.

FIG. 3 is a view showing a temper rolling rate and an increase in yield strength due to baking.

FIG. 4 is a diagram showing an outline of a cone test method for determining flange formability.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shikichi Tsujimura 1-1 Tobahata-cho, Tobata-ku, Kitakyushu City, Fukuoka Prefecture (72) Inside the Yawata Works (72) Inventor Mima Hiroto Tobata, Kitakyushu City, Fukuoka Prefecture 1-1 Hibata-cho, Shin-Nippon Steel Co., Ltd., Yawata Works

Claims (6)

[Claims] 1. By weight%, carbon: 0.01 to 0.08%, manganese: 0.5% or less, acid-soluble aluminum: 0.20% or less, nitrogen: 0.01% or less, and the balance. Is iron and unavoidable impurities, the amount of dissolved C is 5 to 25 ppm, and the YP (yield strength) in the L direction (rolling direction) is 30 to 4
4 Kgf / mm ² , Y in the L and C directions (steel width direction)
A steel plate for a DI can, which is excellent in pressure resistance and neck workability, and has a P difference of ² Kgf / mm ² or less. 2. The DI excellent in pressure resistance and neck formability according to claim 1, further comprising 0.1% or less of at least one of sulfur, chromium, copper and nickel as a steel component. Steel plate for cans. 3. A DI can excellent in pressure resistance and neck workability according to claim 1 or 2, further comprising 0.1% or less of at least one of titanium and niobium as a steel component. steel sheet. 4. By weight%, carbon: 0.01 to 0.08%, manganese: 0.5% or less, acid-soluble aluminum: 0.20% or less, nitrogen: 0.01% or less, and the balance. Steel consisting of iron and unavoidable impurities is made into a billet by continuous casting or ingot-slump rolling, hot rolling is performed, descaling is performed, and then cold rolling is performed by a conventional method, followed by continuous annealing. At a temperature above the recrystallization temperature and below the Ac ₁ point, and cooled at a cooling rate of 60 ° C./sec or higher, in the temperature range of 300 to 450 ° C. for 30 to
Annealing for 180 seconds is performed to make the amount of solute carbon in the steel sheet 5 to 25 ppm, and temper rolling is performed by wet temper rolling using a lubricant at a reduction rate of 3 to 12%. A method for producing a steel plate for a DI can, which is excellent in pressure resistance and neck-in processability, characterized by plating a steel plate for a can with chrome or the like. 5. A steel component further containing 0.1% or less of at least one of sulfur, chromium, copper, and nickel, which is excellent in pressure resistance and neck-in workability. Manufacturing method of steel sheet for DI can. 6. A DI can excellent in pressure resistance and neck-in workability according to claim 4 or 5, further comprising 0.1% or less of at least one of titanium and niobium as a steel component. Method for manufacturing steel sheet.