JPH05345927A - Production of extra thin steel sheet for high strength dwi can excellent in can manufacturing workability - Google Patents

Abstract

PURPOSE:To secure superior necking workability and corrosion resistance by hot-rolling a hot steel slab with specific composition, coiling the resulting plate while applying water cooling, performing pickling, primary cold rolling, and annealing, and then performing secondary cold rolling at specific draft. CONSTITUTION:The steel has a composition consisting of, by weight, <=0.0015% C, 0.05-0.40% Mn, <=0.06% P and S, <=0.10% acid-soluble Al, <=0.0010% N, and the balance iron with inevitable impurities. A hot slab of this steel is hot- rolled to >=2.2mm sheet thickness at >=850 deg.C finishing temp. Subsequently, within 1.5sec from coming out of the final finish stand, the resulting steel sheet is coiled while being water-cooled on a run-out table from >=[fishing temp. -30] deg.C. Then, pickling, primary cold rolling, and continuous annealing are done, followed by secondary cold rolling at <=50% draft. By this method, the extra thin steel sheet for high strength DWI can excellent in can manufacturing workability can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ultra-thin steel sheet for a high-strength DWI can which is excellent in can-making workability.

[0002]

2. Description of the Related Art Can steel plates such as tin-plated tin plates or chrome-treated tin-free steel plates are widely used for food cans, aerosol cans, and easy-open cans. Conventionally, many cans made of these steel plates were three-piece cans consisting of a lid, a body, and a bottom. However, in recent years, the body and the bottom have become one piece, and a two-piece can made up of two parts together with the lid. The technology for making cans from steel sheets was developed.
Since 2-piece cans have a low can-making cost, 2-piece cans tend to gradually grow in place of 3-piece cans. Two-piece cans are subjected to severe processing such as multi-step drawing processing or DWI processing (that is, ironing processing is performed after deep drawing processing), and not only corrosion resistance but also excellent workability is required.

An example of a general manufacturing process of a DWI can is as follows. First, a disk-shaped blank plate is punched from a steel strip with a cupping press machine, and at the same time, the blank plate is shallow-drawn using a punch and a die to form a cup. Next, with a DWI press machine, a punch and a die with a clearance smaller than the thickness of the side wall of the cup are used to draw the side wall while squeezing it to form a cup-shaped can body with a predetermined depth by reducing the thickness of the side wall. (This molding is referred to as DWI processing), and the bottom of the can body is made to collide with a bottom former to form the can bottom into a convex dome shape.

During the DWI processing, due to the anisotropy of the workability of the material, the height of the cylinder after processing is not constant along the circumferential direction, and the upper end of the cylinder after processing corrugates in the circumferential direction. A phenomenon called earring occurs. The protrusion on the upper end of the torso that produces the earrings is called an ear or ear. On the next trimmer machine, the ears are trimmed and the can body is flushed and dried with a washer machine after leveling the top of the barrel. Next, the outer surface of the can is printed and painted by a printer machine, and the can bottom is also painted, and then these paints are dried by a pin oven machine. Next, the inner coating is applied, the inner coating is dried with a belt oven machine, and then a necker / flanger machine is used to perform a multi-step necking process to reduce the opening diameter of the can, and to attach a lid to the opening end of the can. Then, flanging is performed to form a flange portion extending outward in the diametrical direction at the opening end. In this state, the can body is shipped from the can manufacturing company to the contents filling company, and after the contents are filled, the lid is wound to form a canned product.

Important properties required of the steel sheet for DWI cans are DWI workability, earring property, neck workability, flange workability, pressure resistance and paneling strength after forming into a can, and steels having these properties. Uniformity in the width and length directions.

[0006] DWI processability means in DWI process
It means the performance that the mold wear is small, the mold galling is small, and the processing energy is small. What is earring property?
It is the ability to make earrings as small as possible during WI processing. Since the ear part is cut off by a trimmer before the neck processing, there is a problem that the yield of the material is reduced when the earring is large. Neck processability refers to the performance in which wrinkles do not occur in multi-step necking. The flanging property refers to a property of hardly causing cracks that cause leakage of the contents of the can to the flange portion during flanging, that is, defects called flange cracks. The compressive strength means a critical internal pressure of a can that causes a buckling phenomenon in which a weak portion of the can body protrudes outward due to the internal pressure after the lid is wound. It is the can bottom and the lid that are weak against the internal pressure of the can, and the pressure resistance strength is often controlled by the mechanical strength of the can bottom and the lid.
The paneling strength means a critical external pressure at which the body of the can is inwardly dented by the external pressure after the lid is wound. The strength against external force during handling such as packing of canned goods, transportation, unpacking, and dropping in a vending machine is often represented by this paneling strength.

Such a steel sheet for a DWI can has conventionally been obtained by batch-annealing, for example, a B-added Al-killed steel (JP-A-53).
No. -48913), and Cu-added low carbon steel batch annealed (see Japanese Patent Publication No. 52-16965), almost all batch annealed materials have been applied. The batch annealed material has better elongation and deep drawability.
This is because it was considered to be suitable for I processing applications. In particular, it is very important to have good flange formability in the forming process of DWI cans, and it is necessary to suppress the defect rate to several tens ppm or less. For that reason, it stretches as a steel plate,
Conventionally, batch annealed materials having an excellent r value have been applied.

[0008]

On the other hand, the plate thickness of the conventional steel plate for a DWI can is generally about 0.30 to 0.35 mm, but in recent years, the plate thickness has been reduced from the viewpoint of resource saving. There is a trend. However, batch-annealed conventional D
In the steel plate for WI can, there has been a problem that the pressure resistance and the paneling strength are lowered as the thickness becomes thinner. The compressive strength of the can is determined by (plate thickness) ² × (yield strength), and thinning causes a decrease in compressive strength. Therefore, it is necessary to increase the yield strength of the material in order to reduce the thickness while ensuring a predetermined compressive strength. However, in order to increase the yield strength of the batch annealed steel sheet, it is necessary to add a strengthening element to make it a relatively high alloy component. In this case, there is a problem that the DWI workability deteriorates. That is, if the strength of the batch annealed steel sheet is increased, the DW
I has the drawback that galling is likely to occur during processing, the wear of the mold is large, and the processing energy also increases.

This problem can be solved by structurally increasing the strength of the can body. That is,
By forming a can body having a high strength in terms of structural mechanics, it is possible to secure a predetermined can strength even when the material is thin, without increasing the yield strength of the material. Examples of the improvement of the can strength by the shape of the can body include an improvement in the paneling strength by performing a corrugation process called corrugation on the can body portion, and an improvement in the pressure resistance strength by the improvement of the can bottom shape. A DWI can having a predetermined can strength structurally secured by such a can shape is referred to as a high strength DWI.
Called a can.

However, even if the problems of pressure resistance and paneling strength were solved by the high-strength DWI can, the conventional batch-annealed steel plate for DWI can had the following three problems. First, there is a problem that neck workability deteriorates as the thickness decreases. To solve this, it needs to be softer. However, in the batch annealed steel sheet, there is a problem that seizure of the steel strip occurs when the annealing temperature is raised for softening. Secondly, there is a problem that the adverse effect of the nonuniformity of the characteristics of the steel strip in the width / length direction becomes apparent. In batch annealing, the rolled steel strips are stacked in such a posture that the holes of the rolled steel strip are vertical and heated by the burner from the surroundings, so the temperature in the height and diameter direction is large, which is the width of the strip.
Material is likely to be uneven in the length direction. The non-uniformity of the material causes a decrease in material yield, destabilization of the DWI working state, and destabilization of the can size and can strength. This problem,
The smaller the plate thickness, the more obvious it becomes. In order to solve this problem, application of continuous annealed steel sheet is effective, but conventional continuous annealed steel sheet is generally harder than batch annealed steel sheet, and has a drawback that neck workability, DWI workability, flange workability, etc. are inferior. there were. Thirdly, there is a problem that the corrosion resistance is deteriorated. The smaller the plate thickness of the batch annealed steel sheet, the more easily puncture corrosion occurs. This tendency is especially remarkable with specific contents such as light-colored fruits. To solve this problem, application of a continuous annealed steel sheet is effective, but the continuous annealed steel sheet has the above-mentioned drawbacks.

The present invention solves the above-mentioned problems and manufactures an ultra-thin steel sheet for a high-strength DWI can, which has a thin plate thickness as required by a can manufacturer and has excellent neck workability, uniform properties, and excellent corrosion resistance. It is intended to provide the law.

[0012]

Means for Solving the Problems The present inventors have conducted various studies on various properties required for a high strength steel sheet for DWI cans in order to achieve the above objects, and as a result, the above various properties and their controlling factors. In summary, it was found that by adjusting the composition of the steel sheet, the hot rolling condition and the secondary cold rolling condition and combining them, it is possible to industrially cope with the thinning of the plate thickness of 0.25 mm or less.

The present invention is constructed on the basis of this finding, and the gist thereof is as follows: C: 0.0015% or less by weight%, Mn: 0.05 to 0.40%, P: 0.06% Hereinafter, S: 0.06% or less, acid-soluble Al: 0.10% or less, N: 0.0100% or less, and the balance is a hot steel slab (slab) consisting of iron and unavoidable impurities, After hot rolling to a plate thickness of 2.2 mm or more at a finishing temperature of 850 ° C. or more, within 1.5 seconds after the hot-rolled steel strip exits the finishing stand of the hot rolling mill, [finishing temperature −30 ] Winding this on a run-out table with water cooling from a temperature of ℃ or more, pickling, primary cold rolling, continuous annealing, and secondary cold rolling at a reduction rate of 50% This is a method for producing an ultra-thin steel sheet for a DWI can, which is excellent in can workability.

The present invention will be described in detail below. The C content is the most important constituent element of the present invention. If the C content exceeds 0.0015%, the ultra-thin steel sheet for high-strength DWI cans has neck workability, flange workability, DWI workability,
Since the earring property is deteriorated, it is limited to 0.0015% or less.

Although their mechanism is not clear, excellent neck formability is exhibited because the steel of the present invention has an extremely low C content and no carbides harder than ferrite are present.
It is conceivable that the amount of strain accumulated around the carbide in the subsequent cold rolling and DWI working steps is small and the deformation resistance during neck working is small. Further, excellent flange formability is exhibited because the steel of the present invention has extremely low C content and exhibits high local ductility due to the absence of carbides which are harmful to ductility, and thus has high potential deformability of the material in flanging. It is possible. It is conceivable that the more excellent earrings have a low C content of the steel of the present invention and the components are highly purified, so that the texture that controls the earring properties is improved. Furthermore, the reason why the steel of the present invention exhibits excellent DWI workability is that the steel of the present invention has an extremely low C content and does not contain carbides harder than ferrite, so that the C content in the secondary cold rolling and DWI processing is relatively high. Although a large amount of non-invention steel accumulates a high strain around the carbide, it is considered that the invented steel has a small amount of internally accumulated strain and a small deformation resistance during DWI processing. In order to manufacture an ultrathin steel sheet for a DWI can having a thinner plate thickness and excellent flange formability, it is desirable that the C content be 0.0010% or less.

If the amount of Mn is less than 0.05%, hot embrittlement occurs and a steel sheet for cans cannot be manufactured. Therefore, Mn must be contained in an amount of 0.05% or more. On the other hand, when the amount exceeds 0.40%, the steel plate becomes excessively hard and neck workability, flange workability and DWI workability deteriorate, and further, the effect of purifying the components obtained by reducing the C content is improved. Since it is reduced and the earring property is deteriorated and the cost becomes high, the content is limited to 0.05 to 0.40%.

Although it is not necessary to intentionally add P, it is an unavoidable impurity element that significantly hardens the steel.
If it exceeds 06%, the steel plate becomes excessively hard and neck workability, flange workability, and DWI workability deteriorate, and the effect of purifying the components obtained by reducing the C content is diminished and earring properties deteriorate. As the corrosion resistance deteriorates,
The upper limit is 0.06%. In order to obtain more excellent neck workability, flange workability, DWI workability, earring property and corrosion resistance, it is desirable that the content be 0.02% or less.

Although it is not necessary to intentionally add S, it is an unavoidable impurity element that promotes hot brittleness. If this amount exceeds 0.06%, a steel sheet for cans cannot be manufactured due to hot brittleness. The upper limit was limited to 0.06%. A more preferable range is 0.02% or less.

It is not necessary to intentionally add acid-soluble Al, but 0.100% from the viewpoint of integrating steel components with other types.
If the amount is below, the effect of the present invention is not lost even if added.
However, if this amount exceeds 0.100%, the amount of Al ₂ O ₃ -based inclusions increases, which causes flange cracks and DWI processability deterioration during can manufacturing, and also increases costs, so the upper limit is set to 0. Limited to 100%.

N is not required to be added intentionally, but it is an unavoidable impurity element that hardens the steel, and this amount is 0.01.
If it exceeds 00%, the steel plate is excessively hardened to deteriorate the neck workability, the flange workability and the DWI workability, and the effect of purifying the components obtained by reducing the C content is reduced to improve the earring property. As it deteriorates, its upper limit is 0.0100%
Limited to.

The steel having the composition as described above can achieve the object of the present invention in combination with the manufacturing process described below. The manufacturing process conditions will be described below. The steel having the above-described composition is made into a hot steel billet (slab) by a continuous casting method or an ingot agglomeration method using a normal melting furnace such as a converter or an electric furnace, and is subjected to hot rolling. The heat history of the hot steel slab before hot rolling does not matter. In other words, after continuous casting, it may be inserted into a heating furnace as it is without cooling and hot rolling may be started, or so-called direct feed rolling in which hot-rolling is immediately started by omitting soaking in the heating furnace is also possible. Is. Of course, once cooled, it may be reheated in a heating furnace.

When reheating the steel slab, the reheating temperature does not matter. However, in the present invention, since it is essential to secure the hot rolling finish temperature at 850 ° C. or higher, it is not possible to take an excessively low reheating temperature at which the hot rolling finish temperature cannot be secured. In the case of normal hot rolling equipment, if the reheating temperature falls below 1000 ° C, the finishing temperature will be 8
Since it is difficult to ensure the temperature of 50 ° C. or higher, it is desirable that the reheating temperature is 1000 ° C. or higher.

The hot rolling finishing temperature is also one of the most important constituents of the present invention along with the C content. If the hot rolling finishing temperature is lower than 850 ° C, the object of the present invention cannot be achieved for the reason described below. First, the austenite structure and the ferrite structure are mixed and rolled, and as a result, it becomes difficult to control the plate thickness of the hot rolled steel strip. As a result, it becomes difficult to control the plate thickness in the cold rolling, and the plate thickness accuracy of the product steel plate deteriorates. With
Plate breaks often occur during cold rolling operations. Thickness 0.2
This is a fatal drawback in manufacturing an ultra-thin steel sheet for a high-strength DWI can of 5 mm or less. Also, the finishing temperature is 85
If the temperature is lower than 0 ° C, a texture that is harmful to the earring properties is formed in the hot-rolled steel strip, and as a result, the earrings during the DWI processing of the product steel sheet become large, and the yield at the can manufacturer is deteriorated. Therefore, the hot rolling finishing temperature is 85
It is necessary to limit the temperature to 0 ° C or higher.

According to the research conducted by the present inventors, the time from when the hot-rolled steel strip leaves the final finishing stand to when the cooling on the run-out table is started and the temperature at which the cooling is started are , It was found that it has a great influence on the flange formability of the product steel sheet. First, if the time from when the hot-rolled steel strip leaves the final finishing stand to when it starts to be cooled on the run-out table exceeds 1.5 seconds, the flange formability of the product steel sheet deteriorates. So 1.5
Must be limited to seconds or less. Further, the temperature at which the cooling is started must be limited to [finishing temperature -30] ° C or higher, because if the temperature is lower than [finishing temperature -30] ° C, the flange workability of the product steel sheet is deteriorated. The reason for these phenomena is not always clear, but it is considered that these limitations are related to the reduction in grain size of the hot-rolled steel strip.

The winding temperature for hot rolling may be any value.
However, if it exceeds 720 ° C, the scale production amount of the hot-rolled steel strip becomes excessively large, and the production amount of the pickling step is hindered, so the winding temperature is preferably 720 ° C or less. Finished plate thickness of hot rolling, if this is less than 2.2 mm,
Since the earring property of the product steel plate deteriorates, it is necessary to limit it to 2.2 mm or more.

The steel strip after hot rolling is
After pickling and cold rolling, recrystallization annealing is performed in a continuous annealing furnace. The method of recrystallization annealing has to be limited to the continuous annealing method because the batch annealing has the disadvantages of poor uniformity of properties and poor corrosion resistance as described above.

After the recrystallization annealing, secondary cold rolling is performed if necessary. When the rolling reduction ratio of the secondary cold rolling exceeds 50%, the steel plate becomes excessively hardened and the neck formability, the flange formability and the DWI formability are deteriorated, so the upper limit was set to 50%. In particular, in order to produce an ultra-thin steel sheet for DWI cans with even better earring properties, the first cold rolling and 2
The total cold rolling reduction ratio (that is, the reduction ratio of the final product sheet thickness to the hot rolled steel strip sheet thickness) including the subsequent cold rolling is 88.
It is desirable to select the primary cold rolling reduction rate and the secondary cold rolling reduction rate so as to be at least%. Secondary cold rolling does not necessarily have to be performed, but since it is difficult to adjust the shape and surface roughness of the steel strip as it is annealed, the rolling reduction is 0.6.
It is desirable to perform temper rolling or secondary cold rolling at a rate of not less than%.

The surface coating applied to the steel sheet by the manufacturing method of the present invention does not matter. That is, tin plating,
The effect of the present invention can be applied to any surface coating used for a high strength DWI can steel sheet, such as nickel plating, a method of performing tin plating with a very thin weight after a special undercoating, or a method of attaching a polymer organic film. The effect is demonstrated. Further, the effect of the present invention can be exerted not only in the DWI processing method but also in the multistage drawing method as the can manufacturing method.

[0029]

EXAMPLES Steel having the components shown in Table 1 was melted in a converter,
After cooling the slab to room temperature, prior to hot rolling Table 2
After heating to the slab reheating temperature shown in Table 2, the finishing temperature shown in Table 2 and the hot-rolled steel strip are run after the finishing final stand.
Time to start cooling on the out table,
At the cooling start time and the winding temperature, hot rolling was performed to a sheet thickness of 3.0 mm, pickling, cold rolling, continuous annealing, and a sheet thickness of 0 at the secondary cold rolling reduction ratio shown in the table. Secondary cold rolling was conducted to 20 mm and tin plating was performed.

Table 2 shows the neck workability, flange workability and earring property of the tin-plated steel sheet thus obtained.
Shown in. The neck workability was evaluated by using a DWI processing tester in the laboratory of the present inventors to actually make cans of these steel plates for DWI cans, trimming the open ends, and then performing a coating and drying process in an atmosphere drying furnace. After the heat treatment of No. 3, the neck tester in the same laboratory was used to actually perform three-stage necking to observe the occurrence of wrinkles. Then, "pass" if no wrinkles were found on any of the tested can bodies.
When one wrinkle occurred, it was evaluated as "fail".

The flange workability was evaluated by forming a DWI can body with a DWI working tester in the same laboratory, trimming the opening end, and then inserting a conical punch into the opening end with the flange working tester. In the case where a test for expanding the diameter of the open end was performed, the processing rate was determined until the fracture occurred. In the case of the measurement method in the laboratory of the inventors of the present invention, it is known that 9.0% or more of this processing rate is evaluated as acceptable even by the customer, so 9.0% or more is “passed”, Less than 9.0% was judged as "fail". The earring property was evaluated by performing cup molding with a laboratory drawing machine and dividing the difference between the average height of the ridges of the earrings and the average height of the valleys by the average height of the valleys and expressing it as a percentage. In the case of the drawing machine of the inventors of the present invention, it is known that even a consumer who manufactures a two-piece can has no problem if the earring rate is 3.5% or less. 5% or less "pass",
More than 3.5% was judged as "fail".

In these tables, numerical values outside the claims of the present invention are underlined.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

As can be seen from Tables 1 to 3, the steels of the present invention can sufficiently compensate for the deterioration of the neck workability due to the thinning of the plate thickness, and are excellent in the earring property and the flange workability. On the other hand, the steels other than the present invention cannot guarantee the deterioration of the neck workability due to the reduction in thickness, and also have poor earring and flange formability, so that the steel cannot be made thinner.

[0037]

INDUSTRIAL APPLICABILITY The present invention uses a high strength DWI can for DW.
When thinning the steel sheet for I cans, we succeeded in ensuring neck formability, excellent uniformity of properties, and excellent corrosion resistance that could not be obtained with conventional technology, and high strength with excellent can forming processability. It provides a method for producing an ultra-thin steel sheet for a DWI can, and its industrial value is extremely large.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masayuki Matsuda 1-1 Tobahata-cho, Tobata-ku, Kitakyushu, Fukuoka Prefecture Inside Nippon Steel Co., Ltd. Yawata Works (72) Inventor Tsujimura Tokichi Tobata, Kitakyushu, Fukuoka Prefecture No. 1-1, Hibata-cho, Tokyo, Japan Yawata Works, Nippon Steel Corporation

Claims (1)

[Claims] 1. By weight%, C: 0.0015% or less, Mn: 0.05 to 0.40%, P: 0.06% or less, S: 0.06% or less, acid-soluble Al: 0. After hot rolling a hot steel slab containing 10% or less, N: 0.00100% or less, and the balance of iron and unavoidable impurities at a finishing temperature of 850 ° C. or more to a plate thickness of 2.2 mm or more. Within 1.5 seconds after the hot-rolled steel strip comes out of the finishing stand of the hot-rolling mill, [finishing temperature-3
It is coiled with water on a run-out table from a temperature of 0] ° C or higher, pickled, primary cold-rolled, continuously annealed, and secondary cold-rolled at a rolling reduction of 50% or less. A method for producing an ultra-thin steel sheet for a high-strength DWI can, which is excellent in can-making processability, characterized by being applied.