JP4438758B2 - Cold rolled steel sheet for 2-piece cans - Google Patents

Description

  The present invention relates to a cold-rolled steel sheet used for a two-piece can used as a beverage can and the like, and in particular, proposes a cold-rolled steel sheet for a two-piece can that provides a high product yield.

Cans for containers used for beverage cans and the like are classified into two-piece cans and three-piece cans based on the difference in form.
The two-piece can is a can composed of two parts of an integrated body / bottom and lid, and the main deformation mode during processing is by deep drawing. On the other hand, a three-piece can consists of three parts, which are a body part, a bottom part, and a cover part. The main deformation mode is roll molding, and the molded body is formed into a cylinder by bonding or welding.
Among these, the two-piece can is advantageous over the three-piece can in that the manufacturing process is shorter, and there is no “seam”, and uniform and high-precision winding is possible.
Now, the yield of these products (referring to the yield of cans / cold rolled steel sheets, hereinafter simply abbreviated as “yield”) differs between 2-piece cans and 3-piece cans as follows.
First, in the three-piece can, since the truncation unlike the two-piece can does not occur in principle, there is no major problem in terms of yield from the cutting of the steel plate to the product with little loss of material.

However, in the production of a two-piece can, a steel plate laminated with a resin film such as plating or PET is first formed into a circular shape as shown in FIG. After that, one or more deep-drawing, re-squeezing, and ironing are performed, and during this process, the diameter of the can is gradually reduced and the height is increased in each process. The product has a predetermined shape.
In such cylindrical molding in a two-piece can, when the in-plane anisotropy of the mechanical properties of the steel sheet is large, a problem of so-called earring (earing) occurs. This is a problem in the following points.
That is, trimming is performed in the final step of can making to form the can body and the bottom of the can, and the height of the can is kept constant. At this time, if the earring is large, the trimming amount, that is, the cut-off amount becomes large. Therefore, in consideration of this at the time of punching, measures such as increasing the initial blank diameter in advance have been taken. However, with this measure, the amount of truncation increases substantially, resulting in a decrease in yield, which is not preferable.

  Therefore, if the two-piece can can be manufactured with a high yield, resource saving can be achieved and the manufacturing cost can be reduced. Therefore, the advantages of the two-piece can can be expected to be further exhibited. In addition, as two-piece cans, so-called DI cans (Drain & Ironed can) that combine deep drawing and ironing, DRD cans (Drawn & Re-Drawn can) that can be made by drawing and redrawing, Examples include DTR cans (Drawn Thin Raw cann) that reduce the thickness of the steel sheet by subjecting the steel sheet to stretch processing in the redrawing process.

By the way, in the measures for improving the yield of the two-piece can which has been conventionally proposed, the emphasis is on improving the in-plane anisotropy of the mechanical properties of the steel sheet, particularly the in-plane anisotropy of the r value. I have been placed. That is, Δr representing the in-plane anisotropy of the r value.
Δr = ((r ₀ + r ₉₀ ) −2 × r ₄₅ ) / 2
However, steel sheets have been developed so that the absolute value becomes zero.
For example, Patent Document 1 discloses a technique for manufacturing a so-called non-earring steel sheet by optimizing the steel composition, hot rolling conditions, and cold rolling conditions. However, even if Δr≈0 is achieved by this technique, since the shape of the can molding material (blank) is circular, it can reach only about 85% at the maximum.

On the other hand, from the viewpoint of reducing can manufacturing costs, it is directed to reduce the thickness of steel plates for cans. As a technique for coping with a decrease in can strength accompanying such a reduction in plate thickness, there is a proposal described in Patent Document 2, for example.
In this proposal, the secondary cold rolling after annealing, so-called double reduction (hereinafter abbreviated as DR), ensures the hardness of the steel sheet and reduces the thickness, so that it does not become excessively hard after the DR. In this technique, the coiling temperature after hot rolling is controlled to fix the solid solution N in the steel as AlN.
However, the Δr value of the steel sheet manufactured by this method is generally a large negative value (about −0.4 or less), and in the case of a circular can molding material (blank), the village is 45 ° in the rolling direction of the steel sheet. There was a problem that a large ear was produced in the direction and the yield was greatly reduced.
Japanese Patent Application Laid-Open No. 06-041683 JP 51-131413 A

  Therefore, the present invention solves the above-mentioned problems in the raw material for producing a two-piece can and the can-making process, and even in a disadvantageous situation where the thinning of the steel plate has further progressed, the can-making can be performed with a good yield. It aims at providing the manufacturing method of the cold-rolled steel plate for 2-piece cans, and the punching method of the cold-rolled steel plate for 2-piece cans.

As a result of many experiments and researches to solve the above problems, the inventors have optimized the r value based on the texture control of the cold-rolled steel sheet and the steel sheet punching method in the can manufacturing process. As a result, it was found that the yield can be significantly improved.
Conventionally, for deep drawing applications such as two-piece cans, a high r value (mostly an average r value) is obtained from the viewpoint of ensuring deep drawability, and it is small from the viewpoint of suppressing the generation of ears (earrings) during canning. Δr (absolute value) has been required. However, in recent years, technology (high lubrication technology) that reduces friction during the forming of steel sheets has been improved, and since processing is extremely good forming, there is almost no need for an extremely high r value. there were.

  On the other hand, from the viewpoint of the yield of the material at the time of can making, the conventional method of punching in a circular shape naturally has a limit. In order to improve this, as shown in FIG. 1 (b), it is advantageous to form by punching as close to a square as possible, but in this case, the conventional cold-rolled steel sheet is wrinkled at the time of forming. In addition to the problem that cracks are likely to occur, considering the so-called trimming process that finally cuts the edge of the cup, such a non-circular blank material only increases the amount of cut off, which improves the yield. There was a problem of not contributing.

In order to achieve the final yield improvement by the non-circular blank material in the formation of the two-piece can, the inventors have reviewed the conventional punching method and the material characteristics of the steel plate in view of the above-described viewpoint. Therefore, the optimization control of the texture of the steel sheet was considered essential.
Then, the steel sheet having different mechanical properties and textures was manufactured by changing the composition of the steel sheet, hot rolling conditions, cold rolling, annealing conditions and the like, and a simulation test of can manufacturing was performed. As a result, steel with a reduced amount of C compared to conventional steel is used, hot rolling finish and coiling temperature are controlled in the proper range, and the primary cold rolling reduction ratio is reduced by reducing the thickness of the hot rolled steel sheet. It has been found that this goal can be achieved by manufacturing steel sheets combined with reductions compared to the above.

This invention is comprised based on the above knowledge, and the place made into the summary is as follows.
(1) C: 0.02 mass% or less, Si: 0.10 mass% or less, Mn: 0.1 to 1.5 mass%, P: 0.02 mass% or less, S: 0.020 mass% or less, Al: 0.0. 150Mass% or less, N: contains less 0.0050 mass%, a further, Nb: 0.003~0.030mass%, Ti: 0.003~0.020mass% and B: 0.0050 mass% or less of the first One or more selected from the group and / or the second group of Cu: 0.2 mass% or less, Ni: 0.2 mass% or less, Cr: 0.2 mass% or less and Mo: 0.2 mass% or less containing an inner shell one or more selected, the balance being Fe and unavoidable impurities, 2 Pi where r values of the plate surface each direction and satisfies the following relationship (1) Cold-rolled steel sheet for the scan can.
(R ₆₀ + r ₁₂₀ ) / 2 + (r ₃₀ + r ₃₃₀ ) / 2 ≧ (r ₃₀ + r ₆₀ ) (1)
However, r ₃₀ , r ₆₀ , r ₁₂₀ , r ₃₃₀ : r values in directions of 30 °, 60 °, 120 °, and 330 ° with respect to the rolling direction, respectively.

  As described above, according to the present invention, by controlling the steel composition and production conditions, the texture (in-plane anisotropy) of the steel sheet is controlled, and the yield when forming into a two-piece can is high. A rolled steel sheet can be provided.

First, the reason for limiting the chemical composition of steel will be described.
C: 0.02% or less Since the content of C exceeds 0.02 mass%, the steel plate after DR hardens, so that canability and neck workability deteriorate, so the upper limit is 0.02 mass%. To do. In addition, when the amount of C is extremely low, it is necessary to secure a reduction in can strength accompanying the coarsening of crystal grains by secondary cold rolling at a high pressure reduction rate, and therefore ductility in the direction perpendicular to rolling deteriorates. In addition, since uniform deep drawing is difficult, the C content is preferably 0.0005 mass% or more. Furthermore, from the viewpoint of improving workability, 0.015 mass% or less is more desirable.

Si: 0.10 mass% or less Si, if contained in a large amount, causes problems such as deterioration of surface treatment properties and corrosion resistance, so the upper limit is made 0.10 mass%. When particularly excellent corrosion resistance is required, it is preferable to limit to 0.02 mass% or less.

Mn: 0.1 to 1.5 mass%
Mn is an effective element for preventing hot cracking due to S and an element for refining crystal grains. In order to exert these effects, it is necessary to add at least 0.1 mass%. On the other hand, when Mn is added excessively, the corrosion resistance is easily deteriorated, and the steel plate is hardened to deteriorate the flange workability and the neck workability. Therefore, the upper limit is set to 1.5 mass%. In applications where better moldability is required, a range of 0.90 mass% or less is desirable.

P: 0.02 mass% or less When P is contained in a large amount, it hardens the steel, deteriorates flange workability and neck workability, and deteriorates corrosion resistance. Therefore, the upper limit is set to 0.02 mass%. When these characteristics are regarded as particularly important, it is desirable that the content be 0.01% by mass or less.

S: 0.020 mass% or less S is an element that exists as an inclusion in steel, reduces the ductility of the steel sheet, and further causes deterioration of corrosion resistance. Therefore, the upper limit is set to 0.020 mass%. In applications where particularly good workability is required, it is desirable to limit to 0.010 mass% or less.

Al: 0.150 mass% or less Al is an element advantageous for reducing the O concentration in steel and improving cleanliness. However, when the content is excessively large, surface properties are deteriorated and press forming is unstable due to an increase in anisotropy in the rolling direction. Therefore, the upper limit is set to 0.150 mass%. From the viewpoint of the stability of the material, the range of 0.008 to 0.100 mass% is desirable.

N: 0.0050 mass% or less When N is contained in excess of 0.0050 mass%, the aging property is remarkably increased by increasing the probability of remaining in a non-equilibrium state as a solid solution N at the final product stage. The upper limit is set to 0.0050 mass%. If it is this range, the problem of remarkable material deterioration by the solid solution N will not arise even under severe accelerated aging conditions. From the viewpoint of the stability of the material considering the entire manufacturing process, a range of 0.0005 to 0.0040 mass% is preferable.

Nb: 0.003-0.030 mass%
Nb contributes to refinement of the steel structure, and is an element effective in improving the stretch flangeability, which is important in flange forming, which is the final process in two-piece cans, and preventing rough skin. When added in excess of 0.030 mass%, the steel is markedly hardened, and the hot rollability and cold rollability deteriorate. Moreover, it becomes a cause of various cracks also at the time of slab manufacture. In addition, the said effect by Nb addition is exhibited substantially by addition of 0.003 mass% or more. Therefore, the Nb addition amount is set to 0.003 to 0.030 mass%. More preferable in terms of material is 0.02 mass% or less.

Ti: 0.003-0.020 mass%
Ti also has substantially the same effect as Nb, but when added in excess of 0.020 mass%, the occurrence of surface defects that can be considered fatal in steel sheets for cans increases. In addition, 0.003 mass% or more needs to be added to make the structure finer. Therefore, the Ti addition amount is set to 0.003 to 0.020 mass%. More preferable in terms of material is 0.015 mass% or less.

B: 0.0050 mass% or less B is an element effective for controlling the refinement of the structure and the aging, but if added over 0.0050 mass%, the in-plane anisotropy of the steel sheet is preferably increased. Absent. In addition, the said effect by B addition is acquired by addition of 0.0002 mass% or more in general. Therefore, the B addition amount is 0.0050 mass% or less, preferably 0.0002 to 0.0020 mass%. A more desirable range is 0.0005 to 0.0010 mass%.

Cu: 0.2 mass% or less, Ni: 0.2 mass% or less, Cr: 0.2 mass% or less and Mo: 0.2 mass% or less Cu, Ni, Cr and Mo are all added in an amount of approximately 0.01 mass% or more. Therefore, it is a useful element that further promotes uniform and refinement of the structure of the steel sheet. However, when it is added exceeding 0.2 mass%, the surface properties deteriorate in addition to the decrease in cold rollability. Therefore, all of these elements are added in an amount of 0.2 mass% or less, preferably in the range of 0.01 to 0.2 mass%.

  These selective additive elements described above may be added individually in each group, may be added in combination, or may be added in combination over each group. In any case, the desired effects of these elements are not offset.

Next, manufacturing conditions will be described. The slab heating temperature may be a minimum temperature for securing a sufficient hot rolling finish temperature in hot rolling.
Finishing rolling temperature: 950-700 ° C
The finish rolling temperature is an important requirement for forming the desired texture desired in the present invention. Although the detailed mechanism is not necessarily clear, it is necessary to finish the finish rolling at least in the high temperature region of the ferrite phase. Although there is no noticeable deterioration of the material due to finishing at a high temperature, the risk of causing problems such as a decrease in the line speed increases in pickling which is the next process due to an increase in scale thickness and the like. Accordingly, the finish rolling temperature is 950 to 700 ° C. In addition, from the viewpoint of improving the moldability of the final product, a temperature of 800 ° C. or higher is preferable.

Thickness of hot-rolled steel sheet: 1.80 mm or less The thickness of the hot-rolled steel sheet is an important requirement for ensuring the uniformity of the material. By making this thickness 1.80 mm or less, the material of the final product (particularly r Value) can be made uniform. Although the detailed mechanism is not necessarily clear, it is considered that one of the factors is that the surface layer portion and the internal structure of the hot-rolled steel sheet become uniform when the thickness is 1.8 mm or less. In addition, from the top of the material, it is preferably 1.2 mm or less, and if it is 1.0 mm or less, further uniform material can be achieved.

Winding temperature: 800-500 ° C
The coiling temperature is determined from the viewpoints of operational efficiency, steel plate shape, material uniformity, and in-plane anisotropy of r value, which is the main point of the present invention. By setting the coiling temperature to 500 ° C. or higher, it is possible to obtain desirable moldability that is the main point of the present invention. Although this effect tends to be further improved by increasing the effect, when it is wound at a high temperature exceeding 800 ° C., the risk of occurrence of defects due to scale increases.
Therefore, the coiling temperature is set to 800 to 500 ° C. in consideration of these points. From the viewpoint of the r value, the winding temperature is preferably 750 to 600 ° C.
Moreover, it is not necessary to specifically limit about the removal of the scale after hot rolling, What is necessary is just to remove by the pickling method currently performed normally.

Primary cold rolling: reduction rate of 75% or less If the primary cold rolling exceeds 75%, the expression (1) cannot be satisfied, and the effect aimed by the present invention cannot be obtained. Therefore, the rolling reduction of primary cold rolling is 75% or less, preferably 50 to 75%.

Continuous annealing: above recrystallization temperature to 850 ° C
Continuous annealing is a very important process that determines the mechanical properties of steel sheets. The annealing temperature needs to be higher than the recrystallization temperature of the steel sheet. This is because, although a certain degree of ductility can be obtained even at a temperature lower than the recrystallization temperature, the improvement of the in-plane anisotropy of the r value required in the present invention cannot be achieved. If it is the condition range of the manufacturing method according to this invention, there will be no problem by making an annealing temperature high, and various mechanical properties will change to a desired direction. However, annealing at a temperature exceeding 850 ° C. causes remarkable grain growth and causes problems such as surface roughness and skin roughness during molding. Accordingly, the annealing temperature is set to the recrystallization temperature or higher and 850 ° C. or lower.

Secondary cold rolling (cold rolling after annealing): Reduction rate of 6% or less The purpose of secondary cold rolling is to reduce the sheet thickness to the product thickness and to harden it to a predetermined hardness by work hardening It is in. However, when the secondary cold rolling exceeds 6%, the mechanical properties of the steel sheet, particularly the in-plane anisotropy of the r value, remarkably increase.
For this reason, the upper limit of the rolling reduction of the secondary cold rolling is set to 6%. The lower limit of the rolling reduction is desirably 1% or more from the viewpoint of stable prevention of stretch yarn strain.

surface treatment:
The cold-rolled steel sheet obtained by the present invention is generally subjected to surface treatment. As the surface treatment to be applied, any of tin plating, chromium plating, nickel plating, nickel / chromium plating, etc., which are used for ordinary steel plates for cans, is possible.
In addition, the present invention can be applied without any problem to applications such as coating or making an organic resin film after making these platings.

In-plane anisotropy:
In-plane anisotropy is a particularly important requirement in the present invention. Conventionally, the in-plane anisotropy of a steel sheet has been evaluated using only values measured in directions of 0 °, 45 °, and 90 ° with respect to the rolling direction. For example, about r value (for example, thin manual cold-rolled steel sheet) which is a typical characteristic,
Δr = ((r ₀ + r ₉₀ ) −2 × r ₄₅ ) / 2
In-plane anisotropy is evaluated according to the parameters defined by: r = ((r ₀ + r ₉₀ ) + 2 × r ₄₅ ) / 4
The deep drawability was evaluated by the average r value defined by However, r ₀ , r ₄₅ , and r ₉₀ represent r values in the directions of 0 °, 45 °, and 90 °, respectively.
Among these parameters, conventionally, the average r value corresponds to deep drawability, and Δr corresponds to the occurrence of ears when deep drawing is performed (for example, Kawatetsu Technical Report 25 (1993) 1, 27-35). ).

The inventors investigated the mechanical properties of a cold-rolled steel sheet produced with various conditions of steel having various component compositions, and investigated the relationship between this and the occurrence of ears when deep drawing was performed.
As a result, in the evaluation based on the conventional parameters described above, the tendency of the ear generation at the time of forming the ultra-thin steel sheet as the object of the present invention cannot be expressed sufficiently, and a trouble occurs in the downstream process of the can manufacturing process. Etc. (limited to those thought to be caused by ear development) was found to be insufficient.

The inventors have further studied and examined the in-plane anisotropy of the steel sheet in more detail. In cold-rolled steel sheets for cans, the so-called hexagonal anisotropy in 30 ° increments and the so-called square anisotropy in 45 ° increments Can have complex in-plane anisotropy, and if the r-values of 60 °, 120 ° and 0 ° ± 30 ° are evaluated, the characteristics of the ear generation during molding of the material can be expressed. It became clear. Based on this knowledge, we investigated the optimization of the blank shape during cylindrical molding.
As a result, when the r value in the direction of 30 °, 60 °, 120 °, 330 ° (= −30 °) with respect to the rolling direction is r ₃₀ , r ₆₀ , r ₁₂₀ , r ₃₃₀ ,
(R ₆₀ + r ₁₂₀ ) / 2 + (r ₃₀ + r ₃₃₀ ) / 2 ≧ (r ₃₀ + r ₆₀ )
Is used as a can molding material, and D ₄₅ / D ₀ > 1.0
Here, D ₀ and D ₄₅ are blank diameters in the direction of 0 ° and 45 ° with respect to the rolling direction (punching diameter of the can molding material).
It was found that the yield of the steel sheet can be improved by adopting a blank shape that satisfies the above.

Note that the yield defined here is not just a geometrical relationship between the blank area and the remaining material, but is required for the product after obtaining a cylindrical press product with a specified depth by repeating multiple drawing operations. This is calculated based on the weight of the final product that has been trimmed after taking into consideration all the shape and dimensions. This is considered to include not only the effect simply predicted from the definition of the r value, but also a phenomenon that has not been known in the past in relation to the inflow state of the material in the circumferential direction.
The blank diameter ratio, D ₄₅ / D ₀ , can be further increased by controlling the r value of the cold-rolled steel sheet, but by exceeding 1.0, the can-making cost can be reduced. If this D ₄₅ / D ₀ is desirably 1.05 or more, more desirably 1.10 or more, a very large cost reduction can be achieved.

A steel composition containing the composition shown in Table 1 and the balance being substantially made of Fe is melted in a converter, and this steel slab is hot-rolled under the conditions shown in Table 2, and then primary cold rolling, continuous annealing, Secondary cold rolling was performed to obtain a cold rolled steel sheet having a final finished sheet thickness of 0.20 mm. Then, tin plating corresponding to No. 25 was continuously applied on a halogen type electric tin plating line to finish it with a tinplate. Table 3 shows the results of investigating the mechanical properties of the tin-plated steel sheet thus obtained.
According to this invention, it turns out that the steel plate which satisfy | fills previous (1) Formula can be manufactured. Using this steel plate, cylindrical drawing was performed under the conditions shown in Table 4, and the shape after processing was investigated. The results are also shown in Table 3.
It can be seen that the steel sheets of the present invention all exhibit sufficient deep drawability and can be formed even under such non-circular blank conditions.

Next, using steel 3, a cold-rolled steel sheet having a thickness of 0.26 mm was manufactured under the conditions shown in Table 5, and after Cr plating was performed on the surface, a resin film was bonded to manufacture a test steel sheet. The value of (r ₆₀ + r ₁₂₀ ) / 2 + (r ₃₀ + r ₃₃₀ ) / 2 of the obtained cold-rolled steel sheet is 3.05, and the value of (r ₃₀ + r ₆₀ ) is 2.40, and the formula (1) Was met.
Table 6 shows the results of calculating the yield improvement effect by changing the blank shape to various conditions shown in Table 6 and performing drawing and redrawing once using this steel plate.
Yield was evaluated by the ratio of the total weight of all cans after trimming (ear-cutting) of an appropriate amount in consideration of subsequent product characteristics with respect to the initial steel plate weight.

From Table 6, it is clear that a large yield improvement effect can be obtained by setting the ratio of the blank diameter in the 45 ° direction and the 0 ° direction to more than 1.00. Since this effect is a high-speed process with a very large number of punches, even a few percent improvement has a great advantage.
It has also become clear that the shape in the width direction and the uniformity of the material are important in order to sufficiently exhibit such a yield improvement effect. Incidentally, in the steel plate manufactured according to Steel 9 in Table 1, it was impossible to produce a can at the target level due to wrinkles and uneven wall thickness.

It is a figure which shows the plate removal method from a steel plate.

Claims (1)

C: 0.02 mass% or less, Si: 0.10 mass% or less, Mn: 0.1 to 1.5 mass%, P: 0.02 mass% or less, S: 0.020 mass% or less, Al: 0.150 mass% or less , N: contains less 0.0050 mass%, a further, Nb: 0.003~0.030mass%, Ti: 0.003~0.020mass% and B: of 0.0050 mass% or less of the first group And / or selected from the second group of Cu: 0.2 mass% or less, Ni: 0.2 mass% or less, Cr: 0.2 mass% or less, and Mo: 0.2 mass% or less . 2-piece cans containing one or more elements, the balance being Fe and unavoidable impurities, r value of the plate surface each direction and satisfies the following relationship (1) Cold-rolled steel sheet.
(R ₆₀ + r ₁₂₀ ) / 2 + (r ₃₀ + r ₃₃₀ ) / 2 ≧ (r ₃₀ + r ₆₀ ) (1)
However, r ₃₀ , r ₆₀ , r ₁₂₀ , r ₃₃₀ : r values in directions of 30 °, 60 °, 120 °, and 330 ° with respect to the rolling direction, respectively ”

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