JP2000204439A - Steel sheet for hard vessel soft after working and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a steel sheet good in formability in the final stage of working because of small work hardening in the initial stage of the working though it is relatively hard before the working. SOLUTION: This steel sheet is the one in which the content of C is 0.005 to 0.070% wt.%, the crystal grain size is <=10 μm, the density of carbides of >=2 μm in the optional cross-section of the steel sheet is <=10 pieces per 0.01 mm2, 0.2% proof stress is 200 to 450 MPa, the total elongation is >=15%, and the difference in 0.2% proof stress before and after cold rolling is <=150 MPa. As to the method for producing it, particularly, the hot rolling coiling temp. is controlled to <=500 deg.C, the residence time at >=550 deg.C in an annealing stage is controlled to <=90 sec, and the draft by cold rolling after the annealing is controlled to <=8%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate used for a metal container such as a beverage can and a method for producing the same.

[0002]

2. Description of the Related Art Steel sheets for containers represented by beverage cans, food cans, and the like are required to be made thinner in order to reduce the cost of cans. 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 due to thinning. Generally, high-strength materials are manufactured by adding Si, Mn, P, Nb, Ti, etc., but steel plates for containers are also used for beverage cans, food cans, etc., so that food hygiene and low cost can be achieved. From the viewpoint, the addition of these elements is difficult to adopt.

[0003] In the case of a thin material, production may be hindered due to bending of a steel plate called a heat buckle in an annealing step. As a countermeasure, it is effective to keep the annealing temperature of the steel sheet low and to increase the thickness of the passing steel sheet.In a situation where the annealing temperature has to be set high from the viewpoint of recrystallization, A method as disclosed in Japanese Patent Application Laid-Open No. 3-257123 has been put to practical use in which a thicker steel sheet is passed and then subjected to re-cold rolling (2CR) to obtain a target thickness. In order to ensure the strength of the can, this method compensates for the decrease in strength due to the use of ultra-thin material by work hardening.
This is a convenient manufacturing method.

[0004] However, as the steel sheets become thinner, there has been a problem that the workability has been reduced due to the deterioration of the ductility of the material caused by the further cold working of the 2CR material which has already been cold worked. A typical example is cracking in the process of expanding the diameter of the end of the can body (flange forming) when the can lid is wound around the can body of a two-piece can formed by drawing and ironing.

[0005]

SUMMARY OF THE INVENTION The present invention shows a relatively good workability even at a low annealing temperature in order to avoid a drop in productivity due to bending in the annealing step.
Despite being hard to the extent that no CR is required, by reducing the degree of work hardening in the processing steps necessary and unavoidable for can forming such as drawing and ironing, it is soft and good even at the end of the processing process It is intended to provide a steel sheet having excellent ductility.

[0006]

Means for Solving the Problems The present inventors have particularly proposed 2C
A component of a steel plate having a plate thickness of 0.4 mm or less having an R rate of 8% or less,
As a result of studying the relationship between hot rolling conditions and annealing conditions and materials,
By adjusting the components, especially the hot rolling conditions and the holding conditions in the high temperature range of 550 ° C. or higher during annealing, the crystal grain size and the carbide morphology are controlled, and the strength and elongation balance is made into a specific range of the steel sheet. The present inventors have found that the subsequent working does not cause work hardening and ductility does not deteriorate as much as conventional steel, and the present invention has been completed.

The present invention has the following features in order to achieve the above object. That is, in weight%, C: 0.005 to
0.070%, the crystal grain size is 10 μm or less, the density of carbides of 2 μm or more in an arbitrary cross section of the steel sheet is 10 or less per 0.01 square mm, and if necessary, (N present as AlN) / (N in steel) <0.7, and Ti
<0.005%, B <0.0005%, and a steel sheet for a hard container after processing, characterized in that the balance between strength and elongation and the work hardening behavior are restricted to specific ranges. Also, in the manufacturing process of the steel sheet, the winding temperature at the time of hot rolling, annealing conditions after cold rolling and the like are limited to specific ranges, so that the material is hard before forming, and soft and high ductile during forming and after forming. It is characterized by producing a steel plate.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. First, the components will be described. All component amounts are% by weight. C is from 0.005% to 0.070% at which the soft effect can be obtained by the restriction of the hot rolling conditions in the present invention.
If the C content is not in this range, the effects of the present invention cannot be obtained. When C is more than 0.040%, the influence of the hot rolling conditions is reduced, and it may be difficult to obtain a preferable carbide dispersion state depending on the winding temperature and the like.
The following are more preferred ranges.

[0009] Si, which is inevitably contained in a normal steel sheet,
Mn, P, S, Al, N, etc. are contained to the extent that steel plates generally used for containers contain. The range is S
i: 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%.

[0010] The grain size of the steel sheet is limited to 10 µm or less. The particle size is a diameter when the average area per crystal grain obtained in observation of the cross-sectional area structure is converted into a circle. When the diameter exceeds 10 μm, the dispersion state of the carbide described below is also difficult to be preferable, and the effects of the present invention cannot be sufficiently exhibited, in relation to the production conditions at that time.

[0011] The form of the carbides in the steel is an important requirement of the present invention. In the microstructure observation of the steel sheet cross-sectional area, iron carbide (cementite) was revealed by etching with a methanolic picric acid solution, and an optical microscope observation of about 400 times or more was performed to determine the carbide size distribution.
01Mm ² number of carbides having per 2μm or more in diameter is 10 or less, more preferably be more than 1.2μm is 10 or less, it is necessary in order to obtain the effect of the present invention.

Although the cause is not clear, under the steel sheet manufacturing conditions in which the form of carbides that can be observed with an optical microscope is controlled as described above, fine precipitates and solid solution elements that cannot be confirmed with an optical microscope. It is considered that this is closely related to the work hardening behavior of the steel sheet. By changing the precipitate morphology, complex confounding of dislocations concentrated around the precipitates in the early stage of processing is avoided, and rearrangement of dislocations occurs due to the effective behavior of Bausinger during subsequent molding, resulting in distortion until fracture. It is thought to increase.

One of the reasons why fine precipitates are considered to have an effect is that the abundance ratio of AlN in steel may have an adverse effect, so that (N existing as AlN) /
(N in steel) <0.7 is preferred.

It is preferable that the amount of Ti and B that change the form of fine precipitates typified by nitrides is small. Considering food hygiene, etc., Ti <0.005%,
It is preferable to set B <0.0005%.

The steel sheet of the present invention has a 0.2% proof stress of 200 to 450 MPa and a total elongation of 15 in a JIS No. 5 tensile test.
0.2% when cold rolling of 10% or more and 10% is performed
In a steel sheet in which the amount of increase in proof stress is set to 150 MPa or less, the above-described effect is remarkably exhibited. The amount of work hardening in cold rolling is usually
Although it slightly varies depending on rolling conditions such as a roll diameter, the number of passes, lubrication, and temperature, in the present invention, conditions that can be performed in a normal laboratory, that is, a roll diameter: 100 to 400 mm, the number of passes is 1 to 5 passes, The lubrication is evaluated using palm oil, and the temperature is evaluated at room temperature.

Next, the manufacturing method of the present invention will be described. The crystal grain size, carbide morphology, 0.2% proof stress, total elongation, etc. of the steel sheet can be controlled by the components, hot rolling, annealing, and 2CR conditions. However, in order to preferably control the work hardening behavior characteristic of the present invention. Means that the hot rolling coiling temperature is 500 ° C. or less, the slab heating temperature is 1100 ° C. or more, and 5 in annealing after cold rolling.
It is effective to set the staying time in the temperature range of 50 ° C. or more to less than 90 seconds, the maximum temperature to 630 ° C. or less, and the 2CR ratio after recrystallization annealing to 8% or less. In particular, the effect of the winding temperature is great. If the film is wound at a room temperature of 200 ° C. or lower, more preferably 30 ° C. or lower, an even more remarkable effect can be obtained.

The effect of the present invention does not depend on the heat history and the manufacturing history before annealing. The slab for hot rolling is not limited to the manufacturing method such as ingot method and continuous casting method, and it does not depend on the heat history up to hot rolling, so the slab reheating method, reheating the cast slab CC-
The effect of the present invention can also be obtained by the DR method or thin slab casting in which rough rolling or the like is omitted.

The steel sheet of the present invention is usually used as an original sheet for a surface-treated steel sheet, but the surface treatment does not impair the effects of the present invention at all. As the surface treatment for cans, tin, chromium (tin-free) or the like is usually applied. In addition, it can be used as a base plate for a laminated steel sheet to which an organic film, which has been used in recent years, is attached without impairing the effects of the present invention.

The present invention has been described assuming application to a container. However, in an application in which deterioration of workability in a several-stage processing process such as drawing, overhanging, bending, and tensioning, particularly in the final stage, becomes a problem, The present invention can be applied similarly to the container use.

[0020]

EXAMPLES Steel having the respective components shown in Table 1 was subjected to hot rolling, annealing and 2CR shown in Table 2 to produce steel sheets. After Sn plating, can bodies were produced by constant drawing and ironing. Create a tensile test piece from the can body at the fixed position of this can,
Tensile strength and total elongation were measured. Table 3 shows the materials and the 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 range of the present invention. It can also be seen that by controlling the material and manufacturing conditions of the material, the material after can processing becomes better.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

[Table 3]

[0024]

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 can be achieved. Since it is soft and highly ductile even after several steps of processing, a steel sheet having good formability can be obtained even in further processing such as flange processing.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazunari Fushiya 1-1 Hibata-cho, Tobata-ku, Kitakyushu Nippon Steel Corporation Yawata Works (72) Inventor Masayoshi Suehiro 1-1, Hibata-cho, Tobata-ku, Kitakyushu-shi Nippon Steel Corporation Yawata Works F-term (reference) 4K037 EA02 EA18 EA31 FA02 FA03 FE01 FG00 FJ04 FM01

Claims (8)

[Claims] 1. The composition according to claim 1, wherein the content of C is 0.005 to 0.070% by weight, and the crystal grain size is 1%.
A steel sheet for a hard container after processing, characterized in that the density of carbide having a particle size of 0 μm or less and 2 μm or more in an arbitrary cross section of the steel sheet is 10 or less per 0.01 square mm. 2. The steel sheet according to claim 1, further comprising: (N present as AlN) / (N in steel) <0.7. 3. The steel sheet according to claim 1 or 2, wherein Ti <0.005% and B <0.0005%. 4. The steel sheet according to claim 1, further comprising: a 0.2% proof stress in a tensile test using a JIS No. 5 test piece: 200 to 450 MPa; a total elongation: 15% or more; % In a tensile test using a JIS No. 5 test piece after cold rolling of 15% is 15%.
A soft steel plate for a hard container after processing, characterized by being at most 0 MPa. 5. A steel containing, by weight, C: 0.005 to 0.070%, is reheated at a slab heating temperature of 1100 ° C. or higher, and a winding temperature of 500 ° C.
After hot rolling at a temperature of 550 ° C. or less, cold rolling is performed, and annealing is performed so that the residence time in a temperature range of 550 ° C. or more is less than 90 seconds and the maximum temperature is 630 ° C. or less. After cold rolling, the density of carbide having a crystal grain size of 10 μm or less and 2 μm or more in an arbitrary cross section of the steel sheet is 10 μm per 0.01 square mm.
A method for producing a steel plate for a hard container which is soft after processing, characterized by obtaining not more than a single steel plate. 6. The method according to claim 5, wherein (N present as AlN) / (N in steel) <0.7. 7. The method according to claim 5, wherein Ti <0.005% and B <0.0005%. 8. A 0.2% proof stress in a tensile test using a JIS No. 5 test piece: 200 to 450 MPa, a total elongation: 15% or more, and a 0% in a tensile test using a JIS No. 5 test piece after cold rolling of 10% or more. .2% proof stress difference is 15
The method for producing a soft steel sheet for a hard container after processing according to any one of claims 5 to 7, wherein the pressure is 0 MPa or less.