JP3977951B2 - Steel plate for soft hard container after processing and method for manufacturing the same - Google Patents

Description

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【表２】

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【表３】

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【発明の効果】
以上述べた如く本発明によれば、低温巻取りによる熱延での高生産性及び低温焼鈍による焼鈍時の高生産性、結果として低コスト化を達成しつつ、絞り・しごきなど数次に及ぶ加工後においても軟質高延性であるため、フランジ加工など更なる加工においても成形性の良好な鋼板を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a steel plate used for a metal container such as a beverage can and a manufacturing method thereof.
[0002]
[Prior art]
For steel plates for containers represented by beverage cans, food cans, etc., there is a demand for thinner materials to reduce can costs. At this time, it is necessary to increase the strength of the steel sheet itself in order to compensate for the decrease in can strength accompanying the reduction in thickness. In general, high-strength materials are manufactured by adding Si, Mn, P, Nb, Ti, etc. However, steel plates for containers are also used in beverage cans, food cans, etc. From the viewpoint, addition of these elements is difficult to be adopted.
[0003]
In addition, in the thin material, the production may be hindered due to the buckling of the steel plate called a heat buckle in the annealing process. As countermeasures, it is effective to keep the annealing temperature of the steel sheet low or increase the plate thickness, and in the situation where the annealing temperature must be set high from the viewpoint of recrystallization, the target thickness during annealing is required. A method as disclosed in JP-A-3-257123, in which a thicker steel plate is passed through and then subjected to re-cold rolling (2CR) to obtain a target plate thickness, has been put into practical use.
This method is a convenient manufacturing method because the strength reduction due to the application of the ultrathin material is compensated by work hardening in terms of securing the can strength.
[0004]
However, with the progress of thinning of the steel sheet, there is a problem of workability deterioration due to ductility deterioration of the material due to the 2CR material that has already undergone cold working further subjected to can processing. A typical example is cracking in the process of expanding the diameter of the end of the can body (flange forming) when a can lid is wound around a can body of a two-piece can formed with drawing or ironing.
[0005]
[Problems to be solved by the invention]
The present invention avoids a decrease in productivity due to buckling in the annealing process, so that it exhibits relatively good workability even at a low annealing temperature and is hard to the extent that 2CR is not required. The objective is to provide a steel sheet that is soft and has good ductility even at the end of the machining process by reducing the degree of work hardening in the machining process that is necessary and cannot be avoided for can molding, such as drawing and ironing. .
[0006]
[Means for Solving the Problems]
As a result of examining the relationship between the material, the hot rolling conditions and the annealing conditions, and the material of the steel sheet having a sheet thickness of 0.4 mm or less with a 2CR ratio of 8% or less, the present inventors have determined the components, particularly the hot rolling conditions and the annealing. By adjusting the holding conditions in the high temperature range of 550 ° C or higher at the time, by controlling the crystal grain size and carbide form, and making the steel sheet built in a specific range of strength-elongation balance, subsequent processing will be as much as conventional steel The present invention has been completed by finding out that the workability does not deteriorate and ductility does not deteriorate.
[0007]
The present invention is summarized as follows in order to achieve the above object. That is,
% By mass
C: 0.005-0.070%, Si: 0.001-0.1%,
Mn: 0.01 to 0.5%, P: 0.002 to 0.04%,
S: 0.002 to 0.04%, Al: 0.010 to 0.100%,
N: 0.0005 to 0.0060%
And the balance is made of Fe and unavoidable impurities, the crystal grain size is 10 μm or less, and the density of carbides of 2 μm or more in any cross section of the steel sheet is 10 or less per 0.01 square mm. As N) / (N in steel) <0.7, Ti <0.005%, B <0.0005%, and further restricting the strength-elongation balance and work hardening behavior to specific ranges. It is a steel plate for hard containers that is soft after processing.
Moreover, in the manufacturing process of the steel sheet, by limiting the coiling temperature during hot rolling, annealing conditions after cold rolling, etc. to specific ranges, it is hard before forming and soft and highly ductile during and after forming. It is characterized by manufacturing a steel plate.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail below.
First, components will be described. The component amounts are all mass %.
C is set to 0.005% to 0.070% from which a soft effect can be obtained by limiting the hot rolling conditions in the present invention. When the amount of C is not within this range, the effect of the present invention cannot be obtained. C is 0.
If it exceeds 040%, the influence of hot rolling conditions becomes small, and it may be difficult to obtain a preferable carbide dispersion state depending on the coiling temperature and the like, so 0.040% or less is a more preferable range.
[0009]
Si, Mn, P, S, Al, N, etc. inevitably contained in ordinary steel plates are contained to the extent that steel plates generally used for containers contain. The ranges are: Si: 0.001-0.1%, Mn: 0.01-0.5%, P: 0.002-0.04%, S: 0.002-0.04%, Al: It is 0.010-0.100%, N: 0.0005-0.0060%.
[0010]
The particle size of the steel sheet is limited to 10 μm or less. The particle diameter is the diameter when the average area per crystal grain obtained in cross-sectional area structure observation is converted into a circle. When this diameter exceeds 10 μm, it is difficult to make the dispersion state of the carbide described below preferable in connection with the manufacturing conditions at that time, and the effects of the present invention cannot be fully exhibited.
[0011]
The carbide morphology in the steel is an important requirement of the present invention. When observing the structure of the steel plate cross-sectional area, iron carbide (cementite) was revealed by etching with a picric acid methanol solution, and the size distribution of the carbide was determined by observation with an optical microscope of about 400 times or more. ^In order to obtain the effect of the present invention, the number of carbides having a diameter of 2 μm or more per 2 is 10 or less, more preferably 1.2 μm or more.
[0012]
The cause of this is not clear, but in steel sheet manufacturing conditions that control the form of carbides that can be observed with an optical microscope as described above, the state of fine precipitates and solid solution elements that cannot be confirmed with an optical microscope It is closely related, and this seems to favorably change the work hardening behavior of the steel sheet. By changing the form of precipitates, complex confounding of dislocations concentrated around the precipitates in the initial stage of machining is avoided, and rearrangement of dislocations occurs due to Bauzinger's effective behavior during subsequent forming, resulting in distortion until breakage. This is thought to increase.
[0013]
One reason that the fine precipitates are considered to be affected is that the abundance ratio of AlN in the steel may have an adverse effect, so (N present as AlN) / (N in steel) <0. 7 is preferable.
[0014]
Moreover, it is preferable that there are few Ti and B which change the form of the fine precipitate represented by the nitride. Considering food hygiene, Ti <0.005% and B <0.0005% are preferable.
[0015]
The 0.2% proof stress in the JIS No. 5 tensile test of the present invention steel sheet is 200 to 450 MPa, the total elongation is 15% or more, and the increase in 0.2% proof stress when cold rolling is 10% is 150 MPa or less. In the steel sheet, the above effect appears remarkably. The work hardening amount in cold rolling usually varies slightly depending on rolling conditions such as roll diameter, number of passes, lubrication, temperature, etc., but in the present invention, conditions that can be performed in a normal laboratory, that is, roll diameter: 100 to 400 mm. The number of passes is 1 to 5 passes, the lubrication is palm oil, and the temperature is room temperature.
[0016]
Next, the manufacturing method of this invention is demonstrated.
The crystal grain size, carbide form, 0.2% proof stress, total elongation, etc. of the steel sheet can be controlled by the components, hot rolling, annealing, and 2CR conditions, but the work hardening behavior that is a feature of the present invention is preferably controlled. The hot rolling coiling temperature is 500 ° C. or lower, the slab heating temperature is 1100 ° C. or higher, the residence time in the temperature range of 550 ° C. or higher in annealing after cold rolling is less than 90 seconds, and the maximum temperature reached is 630 ° C. or lower, It is effective to set the 2CR rate after recrystallization annealing to 8% or less. In particular, the effect of the winding temperature is great. When the winding is performed at a room temperature of 200 ° C. or lower, more preferably 30 ° C. or lower, a further remarkable effect is obtained.
[0017]
The effect of the present invention does not depend on the thermal history and manufacturing history before annealing. The manufacturing method such as ingot method and continuous casting method is not limited for slab when performing hot rolling, and it does not depend on the heat history until hot rolling, so slab reheating method, reheating the cast slab The effect of the present invention can also be obtained by the CC-DR method in which hot rolling is performed directly, and also by thin slab casting in which rough rolling or the like is omitted.
[0018]
The steel sheet of the present invention is usually used as an original sheet for a surface-treated steel sheet, but the effect of the present invention is not impaired by the surface treatment. As the surface treatment for cans, tin, chromium (tin-free), etc. are usually applied. Moreover, it can be used, without impairing the effect of this invention, also as the negative | original plate for laminated steel plates which stuck the organic film which has come to be used in recent years.
[0019]
As described above, the present invention has been described on the assumption that it is applied to a container, but in applications where workability degradation is problematic in the process of several orders such as drawing, overhanging, bending, and pulling, particularly in the final stage, Similarly, the present invention can be applied.
[0020]
【Example】
The steel of each component shown in Table 1 was subjected to hot rolling, annealing, and 2CR shown in Table 2 to produce a steel plate, and after Sn plating, a can body was produced by constant drawing and ironing. A tensile test piece was prepared from the can body at a fixed position of the can, and the tensile strength and the total elongation were measured.
Table 3 shows the materials and materials after drawing and ironing. It can be confirmed that a soft and highly ductile material is obtained by controlling the components, crystal grain size, and carbide form within the scope of the present invention. It can also be seen that the material after can processing becomes better by controlling the material and manufacturing conditions of the material.
[0021]
[Table 1]

[0022]
[Table 2]

[0023]
[Table 3]

[0024]
【The invention's effect】
As described above, according to the present invention, high productivity in hot rolling by low temperature winding and high productivity in annealing by low temperature annealing, resulting in low cost, and several orders such as drawing and ironing are achieved. Since it is soft and highly ductile even after processing, a steel sheet with good formability can be obtained in further processing such as flange processing.

Claims (8)

% By mass
C: 0.005-0.070%,
Si: 0.001 to 0.1%,
Mn: 0.01 to 0.5%,
P: 0.002 to 0.04%,
S: 0.002 to 0.04%,
Al: 0.010 to 0.100%,
N: 0.0005 to 0.0060%
And the balance is made of Fe and unavoidable impurities, the crystal grain size is 10 μm or less, and the density of carbides of 2 μm or more in any cross section of the steel sheet is 10 or less per 0.01 square mm Post-soft steel plate for hard containers. The steel sheet according to claim 1, further comprising (N present as AlN) / (N in steel) <0.7.
A steel plate for a hard container that is soft after processing, characterized by being. In the steel sheet according to claim 1 or 2, further in mass%,
Ti <0.005%,
B <0.0005%
A steel plate for a hard container that is soft after processing, characterized by being.   The steel sheet according to any one of claims 1 to 3, further cold-rolled by 0.2% proof stress in a tensile test using a JIS No. 5 test piece: 200 to 450 MPa, total elongation: 15% or more, and 10%. A soft steel plate for a hard container after processing, wherein a difference in 0.2% proof stress in a tensile test using a later JIS No. 5 test piece is 150 MPa or less. % By mass
C: 0.005-0.070%,
Si: 0.001 to 0.1%,
Mn: 0.01 to 0.5%,
P: 0.002 to 0.04%,
S: 0.002 to 0.04%,
Al: 0.010 to 0.100%,
N: 0.0005 to 0.0060%
The steel comprising the balance Fe and inevitable impurities is reheated at a slab heating temperature of 1100 ° C. or higher, hot-rolled at a coiling temperature of 500 ° C. or lower, cold-rolled, and a temperature range of 550 ° C. or higher. The annealing time is less than 90 seconds and the maximum temperature reached 630 ° C. or less, re-rolling is performed at 8% or less, the crystal grain size is 10 μm or less, and 2 μm or more in any cross section of the steel sheet. A method for producing a soft steel plate for a hard container after processing, characterized in that a steel plate having a carbide density of 10 or less per 0.01 square mm is obtained. further,
(N present as AlN) / (N in steel) <0.7
The method for producing a soft steel plate for a hard container after processing according to claim 5. Furthermore in mass%,
Ti <0.005%,
B <0.0005%
The method for producing a soft steel plate for a hard container according to claim 5 or 6, wherein the steel plate is soft after processing.   Furthermore, 0.2% proof stress in a tensile test using a JIS No. 5 test piece: 200 to 450 MPa, total elongation: 15% or more, and 0.2% proof stress in a tensile test using a JIS No. 5 test piece after 10% cold rolling The method for producing a soft steel plate for a hard container according to any one of claims 5 to 7, wherein the difference is 150 MPa or less.