JPH0892692A - Steel plate for containers with excellent flange formability - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a container base plate that enables a further reduction in the thickness of a can, a weight reduction of the can, and a saving of resources. [Constitution] An original plate for a container, which has a processed structure in which the ratio of the major axis to the minor axis is 5 or more on average in the plate thickness cross section perpendicular to the rolling direction, and the average major axis of the crystal grains is 8 μm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet for containers which has excellent flanging workability even though it has a working structure.

[0002]

2. Description of the Related Art Original containers for containers are DI (Drawing & Ironing)
It is used for two-piece cans such as cans, three-piece cans such as welding cans, adhesive cans, and can lids. Recently, as the weight of cans has been reduced, the thickness of the original plate has been reduced. However, 1% to 8% without annealing after cold rolling as in the past
If you try to manufacture a container base plate with a skin pass of a certain degree, the plate thickness during annealing will be too thin, and if you try to perform continuous annealing, the plateability will be poor and it will break or change in shape on the way. There is. Special measures 1 as measures against this
No. 52451 discloses a DR (Doubl) in which the plate thickness during annealing is kept relatively thick and 20% to 50% rolling is performed after annealing.
A method for manufacturing a container original plate by the e Reduce) method is disclosed.

However, since this method is premised on annealing, a significant cost reduction cannot be achieved in terms of manufacturing cost. Therefore, as a method for producing a lower cost original plate for a container, Japanese Patent Publication No. 54-1244 has developed a technique in which annealing after cold rolling is omitted. Since the steel sheets for containers at that time were relatively thick and the workability was low, the frequency of flange cracks was low. However, as steel sheets have become thinner in recent years, when cold-rolled materials are used to form a container, cracks frequently occur at the flanged portion.

[0004]

In view of the state of the art as described above, the present invention provides a steel sheet in which cracks are not generated as much as possible during flanging when a container is formed using a cold-rolled material which has a low manufacturing cost. To the purpose.

[0005]

Means for Solving the Problems The gist of the present invention is that (1) the ratio of the major axis to the minor axis of the crystal grains in the structure of the plate thickness section perpendicular to the rolling direction is 5 or more on average, and A steel sheet for containers having excellent flange formability, which has a processed structure in which the average major axis length of crystal grains is 8 μm or less, and (2) wt% C: 0.01 to 0.
2%, Mn: 0.05-1.5%, Al: 0.005-
A steel containing 0.2% and the balance being Fe and inevitable impurities, and the ratio of the major axis to the minor axis of the crystal grains in the structure of the plate thickness cross section perpendicular to the rolling direction is 5 or more on average,
A steel sheet for containers having excellent flange formability, which has a processed structure in which the average major axis length of the crystal grains is 8 μm or less, and (3) C: 0.01% by weight.
0.2%, Mn: 0.05 to 1.5%, Al: 0.00
5 to 0.2%, including Nb: 0.002 to 0.05%,
The balance is steel consisting of Fe and unavoidable impurities, the ratio of the major axis to the minor axis of the crystal grains in the structure of the plate thickness section perpendicular to the rolling direction is 5 or more on average, and the average length of the major axis of the crystal grains is Is a steel sheet for a container having excellent flange formability, which has a worked structure having a size of 8 μm or less.

The present invention will be described in detail below. The present invention cold-rolled various steel sheets for containers by 50% or more, and examined the flange formability. As a result, the flange formability of the material that has been processed at a certain cold rolling rate or more largely depends on the average length of the major axis of the crystal grains in the plate thickness cross section perpendicular to the rolling direction (hereinafter, the average length of the crystal grain major axis). I found a thing.

[0007] Fig. 1 shows the flange formability (hole expansion ratio) of a container base plate of C: 0.04% low carbon steel and C: 0.1% medium carbon steel in Fig. 2. The average length is shown as a parameter for each cold rolling rate. As can be seen from these figures, when the major axis length of crystal grains, that is, the crystal grain size of the hot-rolled sheet is large,
If the cold rolling reduction ratio is increased to manufacture a thin material, the hole expansion ratio will be significantly reduced. Further, as shown in these figures, when the cold rolling rate of both steel sheets becomes 80% or more, the dependency of the flange formability on the major axis of crystal grains becomes apparent. And the average length of major axis of crystal grains for improving flange formability is 8 μm for both steel sheets.
It turns out that Here, the numerical value given as an index of the flange processability is a hole expansion ratio by pushing up a conical punch having an apex angle of 60 degrees. The sample was a disc with a diameter of 100 mm having a hole with an inner diameter of 20 mm at the center, the inner diameter of the wrinkle suppressing die was 40 mm, the wrinkle suppressing force was set to 30 tons, and the inflow of the material was suppressed to carry out the experiment. The hole expansion ratio was shown by the ratio of the inner diameter (mm) of the sample when cracking occurred / the initial inner diameter (20 mm).

The reasons for limiting the present invention will be described based on these findings. When the cold rolling rate is 80% or more, as shown in FIGS. 1 and 2, the effect of the average length of the crystal grain major axis on the hole expansion ratio becomes apparent particularly when the crystal grain major axis is 10 μm or less.
Further, at that time, the structure has a plate thickness cross section perpendicular to the rolling direction, and the processed structure has an average ratio of the major axis to the minor axis of 5 or more.

As described above, the effect of the average length of the major axis of crystal grains on the hole expansion ratio becomes apparent when the ratio of the major axis to the minor axis of the cross section perpendicular to the rolling direction is 5 or more, and the average of the major axis is large. This effect becomes remarkable when the value is 8 μm or less, so the range is limited to this range.

Next, the components are not particularly limited, but it is desirable that the components are within the ranges described below. The amount of C is preferably 0.01% or more because it is difficult to make the hot-rolled sheet into a fine structure if the amount of C is less than 0.0%, and it is 0.03 in order to avoid extreme large reduction rolling and low temperature rolling. % Or more is more preferable. Also, 0.
The reason why 2% or less is desirable is that it is not desirable because the addition of more than 2% reduces the ferrite structure ratio and makes it difficult to sufficiently exert the effect of refining the ferrite structure.

It is desirable that the Mn content be 0.05% or more.
This is because it is difficult to make the hot rolled sheet into a fine structure if the Mn content is less than this. Further, the reason why 0.2% or less is desirable is that the addition of more than 0.2% reduces the ferrite structure ratio and the effect of refining the ferrite structure is not sufficiently exhibited. The reason why the amount of Al is preferably 0.005% or more is
This is because if the amount of Al is less than this, sufficient deoxidation cannot be performed. Further, the reason why 0.2% or less is preferable is that workability may be deteriorated.

If necessary, Nb is added because it is effective for producing a fine hot-rolled sheet, and the lower limit addition amount at which the effect appears is set to 0.002%. Further, the upper limit is set to 0.05% because the addition of more than this decreases the ferrite structure ratio and the effect of refining the ferrite structure is not sufficiently exhibited.

[0013] To obtain a structure after cold rolling as in the present invention,
This can be achieved by making the ferrite structure of the hot-rolled sheet fine and subjecting it to strong reduction. This is because when the hot rolled sheet is cold rolled, its crystal grains are stretched in the rolling direction and the width of the grains does not change.

There are various methods for making the ferrite structure finer. For example, the hot rolling finishing temperature is set to an austenite region near the Ar ₃ transformation point, the total rolling reduction of the hot rolling is increased, or the cold speed is increased. There is a method of using controlled rolling / controlled cooling technology. In addition, as another method, it is possible to make it finer by powder metallurgy.

[0015]

[Example] Using three types of steels whose chemical compositions are shown in Table 1, D
When flange processing after I processing

[Table 1] As shown in FIG. 3, the frequency of cracks occurring in the sample was shown by taking the average length of the major axis of the crystal grains in the structure of the plate thickness cross section perpendicular to the rolling direction on the horizontal axis. The ratio of the major axis to the minor axis observed in the structure of the plate thickness section perpendicular to the rolling direction of the used material was 9.6 on average for each material. The number of experiments was performed by molding 100 pieces for each crystal grain size and determining the frequency. After heating this steel plate at 1200 ° C, finish temperature is 880 ° C
At 960 ° C, the final pressing ratio was changed from 10% to 50%, and hot rolling was performed to obtain a hot rolled sheet having a thickness of 2.3 mm. Cold speed is also 20 ℃ / s
Various particle sizes were secured by controlling in the range of ec to 120 ° C / sec. This hot-rolled sheet was cold-rolled at a compression rate of 89%.

As is clear from these results, the average length of the major axis of the crystal grains of the structure of the plate thickness section perpendicular to the rolling direction is 8
If it exceeds μm, the frequency of flange cracking becomes significant. Flanging of can lids under these experimental conditions did not completely suppress cracking even when the average length of major axis of crystal grains was 8 μm or less, but it is important that the frequency of flange cracking is the average of major axis of crystal grains. When the length is 5 μm or less, the inclination is different.

[0017]

As described above, according to the present invention, the annealing step can be omitted in the production of the original plate for a container, and the can material can be further thinned, which leads to energy saving and resource saving.
The industrial meaning is great.

[Brief description of drawings]

FIG. 1 is a diagram showing the flange formability of a raw plate for a container of C: 0.04% low carbon steel, with the horizontal axis representing the crystal grain size of the hot rolled sheet and the cold rolling rate as a parameter.

FIG. 2 is a view showing the flange formability of C: 0.1% medium carbon steel sheet stock for a container, with the horizontal axis representing the crystal grain size of the hot rolled sheet and the cold rolling rate as a parameter.

FIG. 3 is a diagram showing the frequency of cracks generated during flanging with the crystal grain size of the hot-rolled sheet as a parameter on the horizontal axis for each component steel.

Claims (3)

[Claims] 1. A processed structure in which the ratio of the major axis to the minor axis of the crystal grains in the microstructure of the plate thickness cross section perpendicular to the rolling direction is 5 or more on average, and the average length of the major axis of the crystal grains is 8 μm or less. A steel plate for a container having excellent flange formability, characterized by having. 2. C: 0.01 to 0.2%, Mn: 0.05 to 1.5%, Al: 0.005 to 0.2% by weight, with the balance being Fe and unavoidable impurities. Steel having a ratio of the major axis to the minor axis of the crystal grains in the structure of the plate thickness cross section perpendicular to the rolling direction is 5 or more on average, and the average length of the major axis of the crystal grains is 8 μm or less. A steel sheet for containers, which has a structure and is excellent in flange formability. 3. By weight%, C: 0.01 to 0.2%, Mn: 0.05 to 1.5%, Al: 0.005 to 0.2%, Nb: 0.002 to 0.05. %, With the balance being Fe and inevitable impurities, the ratio of the major axis to the minor axis of the crystal grains in the structure of the plate thickness section perpendicular to the rolling direction is 5 or more on average, and A steel sheet for a container having excellent flange formability, which has a worked structure having an average major axis length of 8 μm or less.