JPH11209845A - Steel sheet for can, excellent in workability and surface roughing resistance, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel sheet for can, having workability necessary for can forming and excellent surface roughing resistance after can manufacture, and its manufacture. SOLUTION: A steel slab, having a composition consisting of, by weight, 0.001-0.005% C, <=0.10% Si, 0.4-1.0% Mn, <=0.04% P, <=0.02% s, 0.01-0.10% Al, <=0.0050% N, 0.008-0.10% Nb, and the balance Fe with inevitable impurities, is heated to 1000-1350 deg.C, and roughing is finished at a temp. between (Ar3 transformation point + 250 deg.C) and (Ar3 transformation point + 150 deg.C). Subsequently, finish rolling is performed at a temp. between (Ar3 transformation point + 100 deg.C) and (Ar3 transformation point - 50%oC). Within 2 sec after the completion of finish rolling, cooling is started at a rate of >=50 deg.C/sec. Then, coiling is done at <580 to 400 deg.C, and cold rolling is carried out at 80 to 95% draft. The resultant steel sheet is continuously annealed at a temp. between the recrystallization finishing temp. and 800 deg.C and further temper-rolled at 0.5 to 40%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate for cans suitable for use as a material for cans such as food and beverage cans, and more particularly to a thin-walled and excellent deep-drawing workable for deep-drawn cans.
The present invention relates to a steel plate for a can that does not cause roughening on the surface of the steel plate after processing and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, two-piece cans have been conventionally manufactured by DRD (Draw and
As seen in Redraw) cans, DWI (Draw and Wall Ironing) cans, etc., it was common to protect the contents of the can by applying an organic paint after molding. On the other hand, recently, a film-laminated steel sheet in which a metal plate before molding is coated with a resin film in advance has been receiving attention from the viewpoint of global environmental protection. For example, JP-A-2-269647 discloses a steel sheet in which a tin-free steel sheet is coated with biaxially stretched polyethylene terephthalate. In the latter method, since the metal plate is coated with the film in advance, the lubricating oil that has been required for deep drawing and ironing is no longer necessary. There is an advantage that no longer appears. In addition, since the steps of coating and baking the inner surface of the can for protecting the contents are not required, there is an advantage that carbon dioxide gas discharged from the oven during baking is also eliminated. .

[0003] The film lamination method is based on these points.
It is a can-making method that can contribute to the protection of the global environment, and is expected to become the mainstream technology in the future. However, this method uses D
Compared with RD cans and DWI cans, the total can manufacturing cost is higher. Therefore, it is required to reduce the material cost by reducing the material thickness. The characteristic value required for this kind of thin can material is as follows. First, a severe drawing process or a drawing-ironing process is performed until the final product shape of the can is obtained. High formability that can withstand the heat is required. At the same time, the surface properties of the steel sheet after processing is also an important factor. If the surface becomes rough, not only the appearance becomes poor, but also the coated film peels off from the mother plate, and the corrosion resistance deteriorates.

[0004]

Incidentally, as a technique for preventing rough skin after can-making, Japanese Patent Application Laid-Open No. 4-314535 has been proposed.
There is a method described in Japanese Unexamined Patent Application Publication No. 2000-205,878. In this method, the average crystal grain size is set to 5 μm or less, and the surface roughness Ra of the original plate is set to 0.5 μm or less, thereby preventing skin roughness. However, in order to achieve the refinement of crystal grains, the C content is 0.1 to 0.2.
Due to the large amount of wt%, the matrix is hardened, and further, there is a problem that workability such as r value is insufficient. This is the same even when a low-carbon steel of about C = 0.01 to 0.1% is used. Therefore, such a hard steel plate cannot sufficiently cope with the tendency of the material to become thinner in the future. For this reason, it is considered that a steel sheet which is softer, has better formability, and is excellent in surface roughening resistance will be required as a material for cans in the future.

However, even if a very low carbon component system in which the amount of carbon is extremely reduced is adopted in order to obtain a soft and moldable material, it is very difficult to make the crystal grain size fine with the conventional technology. Was. For this reason, under the conventional technology, it has been difficult to achieve both moldability and rough surface resistance.

Accordingly, a main object of the present invention is to provide a steel sheet for a can and a method for producing the same, which has the workability required for forming a can and has excellent resistance to rough skin after can production.

[0007]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors first prescribe a component system based on ultra-low carbon steel to achieve a fine grain system. The method was discussed. As a result, to refine the crystal grains of ultra-low carbon steel, the addition of Nb, shortening of the time until the start of rapid cooling of the strip after hot rolling finish rolling, appropriate reduction of the hot rolling winding temperature, and reduction of the rough rolling temperature It became clear that optimization and addition of Mn were effective.

In addition, the inventors conducted an actual can-making test using materials having different crystal grain sizes in advance in order to clarify the crystal grain size required for preventing roughening after can-making. Then, the relationship between skin roughness and crystal grain size was clarified. In addition, since the ultra-low carbon steel was used, all the crystal structures were substantially a ferrite single phase.

[0009] The investigation method is as follows. That is, a steel plate having a thickness of 0.180 mm is subjected to a surface treatment for forming a metal chromium layer and a chromium oxide, and a polyester film having a thickness of 20 μm and a melting point of 30 ° C. is thermally bonded to both surfaces of the surface-treated steel plate to form a resin. A film-coated steel sheet was obtained. Palm oil is applied to this resin film-coated steel sheet in advance,
It was punched into a 9 mm disk and formed into a shallow drawn cup according to a conventional method. The drawing ratio in this drawing step is 1.56.
Then, in the first, second, and re-drawing steps, molding was performed under the conditions of the drawing ratio of 1.37 and 1.27, respectively, and the cup diameter was 63 m.
m, a deep drawing cup with a cup height of 127 mm was obtained. Then, after performing bottom molding according to a conventional method, palm oil was degreased with washing water. Regarding the rough surface after can-making, the surface of the neck-in processed portion where the rough surface is particularly likely to occur was visually observed, and compared with the same type of commercially available can as a comparative material, and evaluated for its superiority. In addition, the average crystal grain size is measured using a cutting method described in JIS G 0552 in observing the crystal structure of the sheet thickness cross section (the center part in the sheet width direction), and calculating the average value of the entire sheet thickness excluding the outermost surface of 5 μm. I took it.

From the above experiments, it has been found that the average grain size of ferrite in a steel sheet must be 6 μm or less in order to prevent skin roughness (FIG. 1). Further, in order to evaluate the workability of the material for canning, the degree of neck forming wrinkles was evaluated in the processing of the neck portion, which has the highest degree of workability and requires formability in can making. As a result, in order to prevent the occurrence of neck wrinkles, it is important that the yield stress (YS) of the steel sheet after annealing, not the final product sheet after temper rolling, is low, and the value must be 350 MPa or less. It was also found that it was essential that the r value of the final product plate was 1.4 or more (FIG. 2). For example, in the steel sheet obtained by the method described in Japanese Patent Application Laid-Open No. 4-314535, it is considered that YS after annealing is about 450 MPa and the r value is about 1.0 in view of its components and production means. The present invention has been constructed based on such knowledge,
The summary is as follows.

(1) C: 0.001 to 0.005 wt%, Si: 0.10 wt%
%, Mn: 0.4 to 1.0 wt%, P: 0.04 wt% or less, S:
0.02wt% or less, Al: 0.01 to 0.10wt%, N: 0.0050wt% or less, Nb: 0.008 to 0.10wt%, the balance being Fe and inevitable impurities, and the average crystal grain size Is 6 μm or less.
A steel plate for cans with a workability of 0.20mm or less and excellent skin resistance.

(2) C: 0.001 to 0.005 wt%, Si: 0.10 wt%
%, Mn: 0.4 to 1.0 wt%, P: 0.04 wt% or less, S:
A steel slab containing 0.02 wt% or less, Al: 0.01 to 0.10 wt%, N: 0.0050 wt% or less, Nb: 0.008 to 0.10 wt%, and the balance consisting of Fe and unavoidable impurities is heated to 1000 to 1350 ° C. (Ar ₃ transformation point + 250 ° C) ~ (Ar ₃ transformation point + 150 ° C)
The rough rolling is completed in the temperature range of, and then (Ar ₃ transformation point +
100 ° C.) and finishing rolling at a temperature range of ~ (Ar ₃ transformation point -50 ° C.), a temperature range of the finish after rolling completion within 2 seconds to start the cooling at 50 ° C. / sec or higher, 580 ° C. below to 400 ° C. Winding, cold rolling at a reduction of 80 to 95%, above the recrystallization end temperature, 800 ° C
A method for producing a steel sheet for cans having excellent workability and surface roughening resistance, wherein the steel sheet is continuously annealed in the following manner and further temper-rolled at 0.5 to 40%.

Next, a description will be given of the reason for limiting the configuration as described above. (1) Steel component C: 0.001 to 0.005 wt% C is one of the important component elements in the present invention from the viewpoints of formability (reduction of YS after annealing and increase of r value) and refinement of crystal grains. It is. If the content is less than 0.001 wt%, it is difficult to reduce the crystal grain size of the steel sheet to 6 μm or less even if short-time annealing is performed by continuous annealing. On the other hand, if the content exceeds 0.005 wt%, the steel sheet becomes hard and the formability deteriorates. In recent years, from the viewpoint of cost reduction,
As the diameter of the canopy is reduced, the degree of neck-in processing applied to the top of the can is increasing. Accordingly, it is expected that it will be difficult to suppress the rough surface generated in the neck-in processed portion. Therefore, in order to obtain fine granules stably, C should be contained in the range of 0.0025 to 0.0050 wt%. desirable.

Si: 0.10 wt% or less If a large amount of Si is added, it causes problems such as deterioration of surface treatment properties and corrosion resistance. Therefore, the content of Si is set to 0.10 wt% or less, preferably 0.02 wt% or less.

Mn: 0.4 to 1.0 wt% Mn is necessary to prevent red hot embrittlement during hot rolling caused by S contained as an impurity, and is an effective element for refining crystal grains. These effects need to be 0.4 wt% or more. However, if the content exceeds 1.0 wt%, the corrosion resistance is reduced and the workability of cans is reduced due to excessive hardening of the steel sheet. wt%.

P: not more than 0.04 wt% When P is contained in a large amount, it hardens steel and lowers workability and lowers corrosion resistance.
04 wt%. When these characteristics are particularly important, the content is desirably 0.01 wt% or less.

S: 0.02 wt% or less S is an element existing as an inclusion in the steel, which reduces the ductility of the steel sheet and further deteriorates the corrosion resistance. Therefore, the upper limit is set to 0.02 wt%.

Al: 0.01 to 0.10 wt% Al is an element which is effective for immobilizing solid solution N in steel as AlN and imparting low aging property. To obtain such an effect, it is necessary to add 0.01% by weight or more, preferably 0.03% by weight or more. On the other hand, as the content increases, the frequency of occurrence of surface defects caused by alumina clusters etc. increases rapidly,
The upper limit is 0.10 wt%.

N: 0.0050 wt% or less N exceeds 0.0050 wt%, the steel sheet becomes hardened, the elongation is remarkably reduced, and the press workability is impaired.
50 wt%.

Nb: 0.008 to 0.10 wt% Nb is an element forming a carbonitride, and is added for the purpose of improving the elongation and the r value by reducing the solid solution C. Also, Nb
Addition makes it possible to refine crystal grains. If the amount is less than 0.008 wt%, the above effects cannot be obtained.
If it exceeds wt%, the recrystallization end temperature will be increased.
The range is 8 to 0.10 wt%. In addition, even if so-called tramp elements, such as Sn, Cu, and Cr, are mixed, as long as their contents are each approximately 0.10 wt% or less, the adverse effect on use characteristics as a can can be ignored.

(2) Manufacturing conditions Slab heating temperature: 1000-1350 ° C. The slab for hot rolling may be heated to _three or more Ac points. Specifically, a heating temperature of 1000 to 1350 ° C. with an average temperature (not the surface temperature but the average of the temperature of the entire slab, usually calculated from the surface temperature and the heating history) is suitable.

Rough rolling end temperature: (Ar ₃ transformation point + 250
℃) ~ (Ar ₃ transformation point + 150 ℃) Rough rolling (Ar ₃ transformation point + 250 ℃) ~ (Ar ₃ transformation point + 150
C), and the austenite grain size before finish rolling is adjusted to an appropriate size. (Ar ₃ transformation point + 150
When rough rolling is completed at a temperature lower than (° C.), growth of austenite grains until finish rolling is accelerated, which is disadvantageous for miniaturization. On the other hand, when rough rolling is performed at a high temperature exceeding (Ar ₃ transformation point + 250 ° C.), the austenite grain size after rough rolling does not become sufficiently small, and the life of the rolling roll is shortened. Therefore, the rough rolling end temperature is (Ar ₃ transformation point + 25
0 ° C) to (Ar ₃ transformation point + 150 ° C).

Temperature range of finish rolling: (Ar ₃ transformation point +10
0 ° C.) to (Ar ₃ transformation point −50 ° C.), cooling after rolling is completed: 2
Start within seconds and cool at 50 ° C / sec or more If finish rolling is performed at a temperature lower than (Ar ₃ transformation point −50 ° C), a coarse work structure extending in the rolling direction is obtained, and this structure is cooled. The crystal grain size cannot be reduced to 6 μm or less because it is inherited even after rolling and annealing. On the other hand, even if the rolling exceeds (Ar ₃ transformation point + 100 ° C), the crystal grains become coarse,
In addition to the fact that the crystal grain size cannot be reduced to 6 μm or less, burning scale is generated, surface flaws are generated on the steel strip, the scale thickness is increased, the pickling property is deteriorated, and the pickling process is deteriorated. It leads to lower yield. Therefore, finish rolling is (Ar ₃ transformation point + 100 ° C) ~ (Ar ₃ transformation point-50 ° C)
It is necessary to carry out in the temperature range.

[0024] After the finish rolling is completed within 2 seconds, preferably
Cooling rate 50 within 0.5 seconds, more preferably within 0.2 seconds
If the cooling is not started at a temperature of at least ° C / sec, fine particles will not be formed.
If the time until the start of rapid cooling exceeds the above range and air cooling is performed for a long time, the growth of austenite grains or ferrite grains proceeds, and fine grains do not become fine grains. In addition, since the steel strip has a temperature distribution in the width direction of the sheet, the grain growth rate is high in the central portion having a high sheet temperature and coarse grains are formed, whereas, in the vicinity of the width end portion where the sheet temperature is low, Conversely, since the crystal grains are relatively fine, the structure becomes uneven in the plate. In addition, cooling rate 50 ℃
If cooling cannot be performed at a rate of more than / g, the crystal grains stay in the high-temperature region for a long time, so that recrystallization / grain growth or recovery / grain growth proceeds, resulting in a coarse hot-rolled structure,
Even after annealing, this is inherited to form coarse crystal grains, and the crystal grain size cannot be reduced to 6 μm or less.

Winding temperature: less than 580 ° C. to 400 ° C. Winding after hot rolling must be performed in a temperature range of less than 580 ° C. to 400 ° C. At temperatures below 400 ° C, AlN or NbC
Is not sufficiently precipitated, thereby hindering recrystallization and grain growth during annealing, deteriorating the r value and its in-plane anisotropy (△ r),
Poor workability. Further, NbC becomes excessively fine, and YS after annealing increases. On the other hand, at temperatures above 580 ° C,
The crystal grains of the hot-rolled sheet become large, and the crystal grains after cold rolling and annealing are coarsened by inheriting this. Further, NbC is coarsened, and the effect of suppressing grain growth during recrystallization annealing is also reduced. In addition, the scale growth after winding becomes remarkable, causing problems such as a decrease in pickling properties. For these reasons,
The winding temperature is in the range of less than 580 ° C to 400 ° C, preferably less than 580 ° C to more than 450 ° C. After hot rolling,
Prior to cold rolling, oxide scale on the steel sheet surface is removed by pickling or the like as necessary.

Cold rolling reduction: 80 to 95% The cold rolling reduction is preferably as high as possible to meet the demand for thinning. If the rolling reduction is less than 80%, this requirement cannot be met, and in addition to abnormally coarsening or mixing of grains during the annealing process, the material deteriorates and a texture effective for deep drawability is obtained. It is difficult to develop. On the other hand, when a high pressure is applied such that the reduction ratio exceeds 95%, the r value decreases, and Δr increases to increase the earring. For this reason, the rolling reduction is in the range of 80% to 95%.

Annealing temperature: 800 ° C. or higher than the recrystallization end temperature
As the annealing method, continuous annealing is preferable in terms of excellent material uniformity and high productivity. The annealing temperature in continuous annealing must be equal to or higher than the recrystallization end temperature, but if it is too high, the crystal grains become abnormally coarse and the surface roughness after processing becomes large. The risk of breakage or buckling increases. Therefore, the upper limit of the annealing temperature is set to 800 ° C.

Temper rolling reduction: 0.5 to 40% The temper rolling reduction is appropriately determined according to the degree of tempering of the steel sheet. However, in order to prevent the occurrence of stretcher strain, the reduction is 0.5% or more. It is necessary to roll at a rate. On the other hand, if the rolling is performed at a rolling reduction of more than 40%, the steel sheet becomes excessively hard, and the workability is reduced. In addition, the r-value is reduced and the anisotropy of the r-value is increased. .

Sheet thickness: 0.20 mm or less Material thickness is being reduced from the viewpoint of cost reduction in can making, and the thickness is set to 0.20 mm or less in order to meet such requirements of the can making industry.

The steel sheet obtained by the above-described method has such a characteristic that no neck wrinkles are generated even when neck-in processing is performed with a high degree of processing, and no troubles such as cracks are generated even in drawing and ironing. In addition, it has excellent properties in terms of resistance to surface roughness after molding. After the annealing in the process of the present invention, the yield stress (YS)
400 MPa or less is obtained, and after temper rolling, an r value of 1.4 or more is obtained.

[0031]

EXAMPLE A steel containing the components shown in Table 1 and consisting essentially of Fe was smelted in a converter, and this steel slab was hot-rolled, cold-rolled, continuously annealed and tempered under the conditions shown in Table 2. The final finished plate thickness was 0.13 to 0.17 mm. Thereafter, a surface treatment was performed to form a metal chromium layer and a chromium oxide layer on the steel sheet surface. The characteristics of the tin-free steel sheet thus obtained were investigated by the following methods.

[0032]

[Table 1]

[0033]

[Table 2]

(A) Formability The r value of the steel sheet after temper rolling was determined as an average value by the following equation. r value = (r _L + r _C + 2r _D ) / 4 where r _L , r _C , and r _D are each 0 in the rolling direction.
The r-value in the direction of 90 degrees, 90 degrees and 45 degrees (using a JIS No. 13 tensile test piece). Note that the r value was almost the same even when measured after the surface treatment. (B) Yield stress after annealing (YS) To reduce the upper yield point on the annealed sheet, a rolling reduction of 1.0%
, And subjected to a tensile test. (C) Manufacturability (wrinkled neck, rough skin at neck part) The evaluation of can manufacture was performed in the same manner as described above. After coating the resin film on both surfaces of the surface-treated steel sheet, shallow draw cup forming, primary, secondary, redraw forming, and then bottom forming were performed. The appearance of the wrinkles and the rough surface were investigated by visually observing the neck-in processed part after the can-making. If the surface roughness was difficult to determine, the surface roughness Ra after film peeling was 1.0 μm or more, and “skin roughness was found”.

Table 3 shows the results. From Table 3, r
The value was 1.4 or more, and it had excellent molding workability without wrinkles even in the neck-in processed portion, and exhibited good characteristics that the surface after the can-making process did not have rough skin. On the other hand, the comparative example that did not satisfy the conditions of the present invention had any of the above-mentioned characteristics poor. When C is less than 0.0025% or the quenching start time after finish rolling is later than 0.2 seconds, the average grain size of ferrite grains is less than 6.0 μm, but there is not much room for grain size, and the average grain size is stable. 6.0 μ diameter
In order to obtain m or less, it is desirable to set C to 0.0025% or more, or to start quenching after finish rolling within 0.2 seconds. In the above embodiment, the test steel sheet is a tin-free steel sheet, but may be a tinned steel sheet, a composite plated steel sheet, or the like, or may be an oil-coated steel sheet that is not subjected to plating. Also, there is no problem if it is used for DI cans or three-piece cans.

[0036]

[Table 3]

[0037]

As described above, according to the present invention,
Since it is excellent in can formability and does not cause roughening after forming, a steel sheet for can suitable for recent severe processing applications can be provided. According to the present invention, it is possible to provide a steel sheet for a can which is particularly adapted to thinning of a resin film-coated steel sheet.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the crystal grain size of a steel plate (product plate) on the rough surface of a neck-in processed portion.

FIG. 2 is a graph showing the relationship between the yield stress after annealing and the r value of a steel sheet (product sheet).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Osamu Furukun 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Technical Research Institute of Kawasaki Steel Co., Ltd. (72) Makoto Aratani 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Chiba Works (72) Inventor Hideo Kukuminato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Kawasaki Steel Corporation Chiba Works

Claims (2)

[Claims] C: 0.001 to 0.005 wt%, Si: 0.10 wt% or less, Mn: 0.4 to 1.0 wt%, P: 0.04 wt% or less, S: 0.02 wt% or less, Al: 0.01 to 0.10 wt%, N: 0.0050% by weight or less, Nb: 0.008 to 0.10% by weight, the balance being a component composition comprising Fe and unavoidable impurities, and an average crystal grain size of 6 μm or less. With a workability of 0.20mm or less and excellent skin roughness resistance. 2. C: 0.001 to 0.005 wt%, Si: 0.10 wt% or less, Mn: 0.4 to 1.0 wt%, P: 0.04 wt% or less, S: 0.02 wt% or less, Al: 0.01 to 0.10 wt%, A steel slab containing N: 0.0050 wt% or less, Nb: 0.008 to 0.10 wt%, and the balance consisting of Fe and unavoidable impurities is heated to 1000 to 1350 ° C, and (Ar ₃ transformation point + 250
℃) ~ (Ar ₃ transformation point + 150 ℃) to complete the rough rolling, then finish rolling in the temperature range of (Ar ₃ transformation point + 100 ℃) ~ (Ar ₃ transformation point -50 ℃), finish Start cooling at 50 ° C / sec or more within 2 seconds after the end of rolling.
Rolling in the temperature range of 80 ° C, cold rolling at a reduction of 80 to 95%, continuous annealing at a temperature higher than the recrystallization end temperature and 800 ° C or lower, and further temper rolling at 0.5 to 40%. A method for producing a steel sheet for cans having excellent workability and resistance to rough skin.