JP2000054070A - Steel sheet for can, excellent in surface roughing resistance and aging resistance, and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a steel sheet free from the occurrence of surface roughing and stretcher strain pattern after press forming by controlling the composition of an extra low carbon steel sheet and its manufacturing conditions and specifying the average value of crystal grain size and the value of aging index AI, respectively. SOLUTION: A steel composition, consisting of, by mass, 0.0005-0.0050% C, >0.50-1.5% Mn, 0.015-0.15% Al, <=0.0050% N, and the balance Fe, is provided. A slab of the steel is heated to a temperature between the Ac3 point and 1150 deg.C, roughed, and cooled rapidly at >=50 deg.C/sec cooling rate, by which the surface temperature of the resultant sheet bar is regulated to a value between the Ac1 point and Ac1 -30 deg.C. Successively, finish rolling is started within 1 to 5 sec and rolling is finished at a temperature not lower than the Ar3 point, and, within 1 sec, the resultant steel plate is cooled rapidly at a rate of 50 deg.C/sec until a plate surface temperature of <=600 deg.C is reached, followed by coiling at 450 to 600 deg.C. Then, cold rolling is performed at 80 to 95% draft, and the resultant steel sheet is temper rolled at 0. 5 to 3% draft after recrystallization annealing. By this method, the average value of grain size is regulated to <=10 μm in the region between the surface layer and a position at a depth of 20% of overall thickness and to 10 to 15 μm in the region of overall thickness, and also the value of aging index AI is regulated to <=30 MPa.

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 used for applications such as food cans and beverage cans, and particularly to roughened skin and stretcher strain patterns generated during processing such as press working, bending work, and can expanding work. Prevention of occurrence. In addition, the steel plate referred to in the present invention includes a steel strip.

[0002]

2. Description of the Related Art Deep drawn cans, DRD (Drawn and Redrawn)
The following properties are required for cold-rolled steel sheets used for two-piece cans such as cans and DI (Drawn and Ironined) cans. In other words, it has excellent press workability and does not generate defects such as cracks during processing.

[0003] The surface roughness of the steel sheet after pressing is small and the finished appearance is good. Low anisotropy, excellent earrings, and low ear formation after deep drawing. Is mentioned. In response to such a request, for example,
JP-A-59-129733 discloses a method for reducing the solute C and solute N by adding a carbonitride forming element such as Nb or Ti to improve the r value and aging resistance of a steel sheet for cans. Proposed.

[0004]

However, when Ti is added to a steel sheet for a can, the corrosion resistance is deteriorated, the crystal grains are coarsened and the surface is roughened after press working, and the crystal grains are coarsened. T1 level (HR30T: 49 ± 3) which is the softest standard for tinplate
In order to satisfy the above, there is a problem that it is necessary to perform high-pressure temper rolling at a reduction ratio of 5% or more.

[0005] In temper rolling at a rolling reduction of 3% or less, rolling can be performed with a dry skin pass specification that does not require rolling oil.
In the temper rolling in which the rolling reduction exceeds 3%, it is necessary to perform rolling with a wet skin pass specification requiring rolling oil. Therefore, when temper rolling with a reduction ratio of more than 3% is performed, a cost increase due to the use of rolling oil and a significant decrease in productivity due to a change in skin pass specification from dry to wet are caused.
For this reason, it has been strongly desired that tinplate from the T1 level to the T3 level can be manufactured by the passivation rolling of the dry skin pass specification.

[0006] When Nb is added to a steel sheet for cans, the crystal grains become finer and roughening after press forming is prevented.
There is an advantage that tinning from the T1 level to the T3 level can be manufactured by temper rolling of a dry skin pass specification as the material becomes harder as the crystal grains become finer. However, the recrystallization temperature rises extremely by the addition of Nb, and it is necessary to set the annealing temperature to a high temperature close to 800 ° C. In the continuous annealing of the steel sheet for thin cans, troubles such as buckling and breakage have occurred. Further, at the front and rear ends in the longitudinal direction of the coil, the recrystallization temperature becomes extremely high due to the poor precipitation of NbC. For this reason, the structure after annealing tends to be an unrecrystallized structure, and the problem that cracks occur during pressing frequently occurred.

[0007] The present invention solves the above-mentioned problems, and tinplate from T1 level to T3 level can be manufactured by temper rolling of a dry skin pass specification, and furthermore, there is no occurrence of roughened skin and stretcher strain pattern after press forming. It is an object of the present invention to provide a steel sheet for cans having excellent skin roughness resistance and aging resistance.

[0008]

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors diligently studied the surface roughening resistance and the aging resistance of an ultra-low carbon steel without addition of Ti and Nb. As a result, while reducing the N content to 0.0050 mass% or less,
It was found that the aging resistance was remarkably improved by increasing the amount of Mn added to 0.50 mass% or more and further reducing the slab heating temperature to 1150 ° C or less. In addition, in order to achieve both surface roughness resistance and press formability, it is effective to make the structure of the steel sheet a composite type structure having different crystal grain sizes between the front and back layers and the inner layer in the thickness direction. New knowledge was obtained.

First, the results of basic experiments performed by the present inventors will be described. 0.0025mass% C-0.2mass% Mn-0.04ma
Contains ss% Al, N content 0.0050, 0.0070, 0.0100ma
Ultra low carbon steel slab changed to ss%, heating temperature: 1100 ~
After heating (maintaining 60 minutes) to each temperature of 1200 ° C., hot rolling was performed at a finish rolling temperature of 900 ° C. to form a hot-rolled sheet, which was wound at a winding temperature of 500 ° C. Next, these hot-rolled sheets were subjected to cold rolling at a rolling reduction of 90%, and then annealed at 650 ° C. The amount of solute N in the cold rolled annealed sheet was determined. FIG.
The slab heating temperature and the solid solution N ratio (solid solution N amount / total N amount ×
100%).

From FIG. 1, it can be seen that the solid solution N ratio is significantly reduced by setting the slab heating temperature to 1150 ° C. or lower. If the slab heating temperature is lowered, the solute N ratio is significantly reduced, and aging caused by solute N can be reduced. However, when the total amount of N in steel increases, the solute N ratio tends to increase. In order to reduce the solid solution N ratio and reduce the aging, from FIG. 1, the slab heating temperature was reduced to 1150 ° C. or less, and further, the total N content in the steel was reduced to 0.0050 mass.
% Or less is effective.

Next, 0.0025 mass% C-0.0040 mass% N
-Contains 0.04 mass% Al and reduces the Mn content by 0.1 to 1.3 mass%
The ultra-low carbon steel slab that has been transformed into a hot rolled sheet is heated at a heating temperature of 1100 ° C (holding for 60 minutes), and then subjected to hot rolling at a finishing rolling temperature of 900 ° C to form a hot-rolled sheet and wound at a winding temperature of 550 ° C. I took it. Next, these hot-rolled sheets were subjected to cold rolling at a draft of 90%, annealed at 650 ° C., and then temper-rolled. The aging index AI value was determined for these cold-rolled annealed tempered sheets. The AI value was determined as the increase in yield stress before and after the heat treatment at a temperature of 100 ° C. for 30 min after a tensile prestrain of 7.5% was applied to the cold-rolled and annealed tempered sheet. . FIG. 2 shows the effect of the Mn content on the AI value.

FIG. 2 shows that although the detailed mechanism is unknown at present, the AI value decreases as the Mn content increases. That is, the AI value is obtained by setting the Mn content to 0.50.
By making it more than mass%, preferably more than 0.55mass%,
30MP virtually eliminates stretcher strain
a. Next, 0.0010
~ 0.0100mass% C-0.6mass% Mn-0.0040mass% N-0.
Ultra low carbon steel slab containing 04 mass% Al, heating temperature:
After heating to 1100 ° C. (holding 60 minutes), hot rolling was performed at a finish rolling temperature of 900 ° C. to form a hot-rolled sheet, which was wound at a winding temperature of 550 ° C. Next, these hot-rolled sheets were subjected to cold rolling at a draft of 90%, annealed at 650 ° C., and then temper-rolled. 350g of these cold rolled tempered sheets
The product was made into a can size DI can (outer diameter 6.83 mm) and subjected to four-step neck processing (neck diameter 6.03 mm). After can-making, the appearance of rough skin was visually observed, particularly for the neck processed portion, and evaluated on a 6-point scale. Further, after the can was made, the rate of occurrence of press cracking was determined to evaluate press formability. FIG. 3 shows the relationship between the surface roughness of the neck processed portion, the press formability, and the average grain size of the entire steel sheet thickness (total thickness).

FIG. 3 shows that the degree of skin roughness is good (evaluation 3 or less) when the average crystal grain size is 10 μm or less. In addition, press formability is determined by the average crystal grain size.
It can be seen that the range of 10 to 15 μm is the best.
If the average crystal grain size is less than 10 μm, the press forming load becomes large and press cracking occurs. Average grain size is 15μm
If the ratio exceeds 1, the crystal grains extend long in the rolling direction, become grains having a large aspect ratio, and the occurrence of earring becomes remarkable.

Therefore, there is no range of the average crystal grain size that achieves both the press formability and the rough surface resistance. In order to achieve both the press formability and the surface roughening resistance, the inventors of the present invention set the structure of the steel sheet to a composite type consisting of three layers having different crystal grain sizes between the front and back layers and the inner layer in the thickness direction. I thought that it would be good to have this organization.

In order to make the structure of the steel sheet a composite structure,
The present inventors paid attention to cooling rate control after hot rolling, and conducted the following experiments. 0.0025mass% C-0.56mass%
An ultra-low carbon steel slab containing Mn-0.0040 mass% N-0.04 mass% Al and the balance being substantially Fe (Ar ₃ transformation point: 860
℃, Ac ₁ transformation point 820 ℃), heating temperature: 1100 ℃ (hold 60 minutes), after finishing the rough rolling at 1000 ℃, using ultra-high pressure descaling equipment, the cooling rate, cooling end point temperature After changing the sheet bar surface (water cooling), the sheet bar was heated for 0.5 to 0.57 seconds. Next, finish rolling was performed at a finish rolling end temperature (FDT) of 880 ° C.
After the finish rolling, cooling was performed while changing the cooling start time, the cooling rate, and the cooling end point temperature, and wound around a coil. The coil winding temperature (CT) was 550 ° C except for No.11. Table 1 shows the hot rolling conditions.

[0016]

[Table 1]

Next, these hot-rolled sheets were subjected to cold rolling at a rolling reduction of 90%, annealed at 650 ° C., and then temper-rolled. With respect to these cold-rolled annealed sheets, the average grain size of the entire thickness and the average grain size of the surface layer from the surface layer to a depth of 20% of the total thickness were determined. FIG. 4 shows the relationship between the average crystal grain size of the entire thickness and the average crystal grain size of the surface layer region. FIG.
3 also shows the relationship between the crystal grain size shown in FIG. 3, the press formability, and the degree of surface roughness.

FIG. 4 shows that after the rolling is completed, the surface layer is cooled at a cooling rate.
Rapid cooling to ₁ point or less of Ac at 50 ° C / s or more, then start finish rolling in 1 second to 5 seconds, finish finish rolling in ₃ points or more of Ar, and cool at 50 ° C / s or less within 1 second. so
By rapidly cooling to 600 ° C or lower and winding in a temperature range of 450 to 600 ° C, the average grain size of the surface layer from the surface layer to a depth of 20% of the total thickness is 10 μm or less, and the average grain size of the entire thickness is 10 μm or less.
It can be seen that a cold-rolled annealed sheet having a composite structure having a thickness of about 15 μm can be obtained. In the cold-rolled annealed sheet having such a composite type structure, roughening of the surface after forming the DI can and generation of cracks during press forming were not observed at all.

The quenching after the rough rolling, the quenching after the finish rolling, and the winding temperature are adjusted so as to satisfy the above conditions. Further, by adjusting the amount of Mn added, as shown in FIG.
All steel sheets T1 to T3 can be manufactured by using a dry skin pass with a rolling reduction of 0.5 to 1.5% in temper rolling. The present invention
It is configured based on the above findings.

That is, in the first aspect of the present invention,
C: 0.0005 to 0.0050%, Mn: more than 0.50 to 1.5%, Al: 0.01
5 to 0.15%, N: 0.0050% or less, the composition consisting of the balance of Fe and unavoidable impurities, and the average value of the crystal grain size are 10 μm in the surface layer region having a depth from the surface layer to 20% of the total thickness. A steel sheet for cans having a structure having a total thickness of 10 to 15 μm and an aging index AI value of 30 MPa or less, which is excellent in surface roughening resistance and aging resistance. Also,
In the present invention, in addition to the above-mentioned composition, B:
It preferably contains 0.0003 to 0.003%.

In the second invention, the mass% and C: 0.
0005 to 0.0050%, Mn: more than 0.50 to 1.5%, Al: 0.015 to 0.1
5%, N: 0.0050% or less, or B: 0.0003 ~
A steel slab containing 0.003% is heated to a temperature range from the Ac ₃ transformation point to 1150 ° C., subjected to rough rolling, and then, at a cooling rate of 50 ° C./s or more, the sheet bar surface temperature is raised to the Ac ₁ transformation point or more ( Ac ₁
-30 ℃) Rapid cooling to the temperature below, then finish rolling is started in 1-5 seconds, finish rolling is finished at Ar ₃ transformation point or more, and it becomes hot rolled sheet. Then, cooling is started within 1 second after finishing rolling is completed. And rapidly cooled at a cooling rate of 50 ° C./s or more until the surface temperature of the hot-rolled sheet becomes 600 ° C. or less, and a winding temperature: 450 ° C.
After winding at ~ 600 ° C, rolling reduction: 80 ~ 95
% Cold-rolled to give a cold-rolled sheet, and then annealed at a temperature equal to or higher than the recrystallization end temperature, and then the rolling reduction: 0.5
This is a method for producing a steel sheet for cans having excellent skin roughness resistance and aging resistance, characterized in that temper rolling of up to 3% is performed.

[0022]

First, the reasons for limiting the chemical composition of the steel sheet of the present invention will be described. C: 0.0005% to 0.0050% C is an element that increases the strength, reduces elongation, and further enhances aging of a steel sheet. From the viewpoint of press workability and aging resistance, it is desirable to reduce as much as possible, but too little. In addition, the steel sheet is excessively softened and the strength of the can body cannot be ensured, and the crystal grains are coarsened to cause roughening after press working. For this reason, the lower limit of the C content is 0.
0005%. On the other hand, when the C content exceeds 0.0050%,
In addition to a decrease in workability, the aging property is increased, and a stretcher strain pattern is generated during press working. For this reason, the upper limit of the C content is set to 0.0050%.

Mn: more than 0.50% to 1.5% Mn is an effective element that combines with S to prevent red embrittlement during hot rolling, further reduce aging, and harden a steel sheet.
It is one of the important elements in the present invention. By reducing the content of C and N and increasing the content of Mn to more than 0.50%, the aging index AI value becomes 30 MPa or less. On the other hand, more than 1.5%
Mn content causes cracking during rolling and excessive hardening of the steel sheet. For this reason, Mn is limited to the range of 0.5 to 1.5%. Preferably, it is more than 0.50% to 1.0%. By adjusting the Mn content to be in the range of 0.5 to 1.5%, as shown in FIG. 5, the production of tinplates having a tempering degree of T1 to T3 by temper rolling of a dry skin pass specification with a draft of 0.51 to 3%. Becomes possible. The vertical axis in FIG. 5 is the surface hardness of the steel sheet after reflow (HR30T).

Al: 0.015% to 0.15% Al is an effective element that acts as a deoxidizing agent and fixes solid solution N as AlN. The Al content is 0.015%.
If it is less than 30, the deoxidizing effect is not recognized, the amount of solid solution N increases, and the aging property increases. Therefore, the lower limit of the Al content is 0.015%. On the other hand, if the content exceeds 0.15%, the effect saturates and an effect commensurate with the added amount cannot be expected, which is economically disadvantageous. Therefore, the upper limit of Al content is 0.15%.

N: 0.0050% or less N is an element that enhances aging, and it is desirable to reduce it as much as possible, but N is allowable up to 0.0050%. But,
If the N content exceeds 0.0050%, the steel sheet becomes hardened, the elongation is significantly reduced, the press workability is deteriorated, and the aging property is further increased. B: 0.0003% to 0.003% B is an element that forms nitrides to reduce solid solution N, thereby reducing aging properties and improving elongation, and can be added as necessary. Such an effect is observed when the content is 0.0003% or more, but when the content exceeds 0.003%, the recrystallization end temperature is significantly increased. Therefore, B is 0.0003 to 0.00
Preferably it is limited to the range of 3%.

The balance is Fe and inevitable impurities.
As unavoidable impurities, Si: 0.10% or less, P: 0.02% or less, and S: 0.02% or less are acceptable. Si: 0.10% or less, Si extremely hardens the steel sheet and is an element harmful to the corrosion resistance. It is desirable to reduce as much as possible in steel sheets for cans, but it is acceptable up to 0.10%.

P: 0.02% or less Since P increases the strength of the steel sheet and remarkably lowers the corrosion resistance, it is preferable to set P to 0.02% or less. S: 0.02% or less S is a harmful element that causes red hot brittleness, and it is desirable to reduce it as much as possible, but up to 0.02% is acceptable.

The steel sheet of the present invention has, in addition to the above-described composition,
Has a hybrid type structure in which the average crystal grain size in the surface layer from the surface layer of the steel sheet to a depth of 20% of the total thickness is 10 μm or less and the average crystal grain size in the entire thickness is 10 to 15 μm . This makes it possible to achieve both the press formability and the rough surface resistance. If the average crystal grain size in the surface region exceeds 10 μm, as described above, surface roughness occurs during press molding. When the average crystal grain size in the entire thickness is reduced to less than 10 μm, cracks occur during press molding, while when it exceeds 15 μm, earrings increase.

Next, the manufacturing conditions of the steel sheet of the present invention will be described. In the present invention, the molten steel having the above composition is smelted by a known smelting method such as a converter, and slab is formed by a normal method such as a continuous casting method or an ingot-bulking rolling method, and then the slab is heated. A hot rolled sheet is formed by hot rolling including rough rolling and finish rolling. Next, the hot-rolled sheet is subjected to pickling and cold-rolled to obtain a cold-rolled sheet having a predetermined size. Next, the cold-rolled sheet is subjected to recrystallization annealing, then temper-rolled, and if necessary, tin-plated to obtain a product sheet.

Hot rolling heating temperature: Ac ₃ transformation point to 1150 ° C. In order to improve the aging resistance, it is necessary to suppress the re-dissolution of AlN and to reduce the solute N as much as possible.
It is desirable to limit the temperature to 1150 ° C or lower. On the other hand, if the heating temperature is lower than the Ac ₃ transformation point, hot rolling becomes ferrite region rolling and the structure after annealing becomes a mixed grain structure, so that desired press workability cannot be secured.

The temperature range of the rough rolling is not particularly necessary to limit, (Ar ₃ transformation point +150 ℃) ~ (Ar ₃ transformation point + 50
(° C.). (Ar ₃ transformation point +15
When the temperature exceeds 0 ° C.), the wear of the rolling rolls is severe and the life of the rolling rolls is shortened. On the other hand, if it is less than (Ar ₃ transformation point + 50 ° C.), the finish rolling becomes a ferrite region, the structure after annealing becomes a mixed grain structure, and the press workability and the surface roughening resistance deteriorate.

Cooling conditions after rough rolling: rapidly cooling sheet bar surface temperature to a temperature of Ac ₁ to (Ac ₁ -30 ° C.) at a cooling rate of 50 ° C./s or more, cooling rate of sheet bar surface layer to 50 ° C./s or more And rapidly transform the steel into a ferrite phase, and then reverse transform again into an autotenite phase by the internal sensible heat of the steel material and the heat generated during the finish rolling, thereby refining the crystal grains. For this reason, the quenching end point temperature is set to the Ac ₁ point or less. However, if the cooling is excessive, the finish rolling temperature does not become higher than the Ar ₃ transformation point, so it is desirable to set the lower limit of cooling to (Ac ₁ -30 ° C.). If the cooling temperature is lower than 50 ° C./s, it is difficult to lower only the surface layer to the Ac ₁ point or less in the time until the start of the finish rolling.

In order to perform the above-mentioned rapid cooling, it is preferable in terms of cost to provide equipment for performing descaling using high-pressure water before the finish rolling mill, and to perform cooling simultaneously with descaling. Preferred descaling conditions here are ultrahigh-pressure water having a collision pressure p on the sheet bar (steel plate) surface of 25 kgf / cm ² or more and a liquid density of 0.002 liter / cm ² or more. Here, the liquid amount density indicates the total amount of liquid supplied per unit area of a sheet bar (steel plate) in descaling. Also,
In general, the collision pressure p is determined from the following equation from the projection pressure P and discharge amount Q of the nozzle, and the distance H between the steel sheet surface and the nozzle.
(“Iron and Steel”, vol. 77 (1991), No. 9, p11450) p = 5.64 PQ / H ² where p: collision pressure on the steel sheet surface (MPa) P: discharge pressure (MPa) Q: discharge Amount (1 / sec) H: distance between steel plate surface and nozzle (cm ² ) When the collision pressure (p) is made to be an extremely high pressure of 25 kgf / cm ² or more,
The unevenness of the surface layer disappears and is smoothed, the steel strip is not locally cooled, a uniform structure is obtained, and the water density is 0.002.
It is considered that by setting the volume to 1 liter / cm ² or more, only the pole surface is effectively cooled. In this connection, the collision pressure of the conventional descaling is about 1.0 ~4.0kgf / cm ^2, the 10
It is considered that the above-mentioned advantageous cooling effect is exhibited by employing an ultra-high pressure that is twice as high.

Time from quenching of the sheet bar to the start of finish rolling: 1 to 5 seconds The time from the end of quenching of the sheet bar to the start of finish rolling is from 1 second to 5 seconds. If it is shorter than 1 second, the recuperation due to the internal sensible heat is not sufficient, and the ferrite is processed at a low temperature, and the recovery / recrystallization in the finish rolling process does not occur sufficiently, and a sufficient refining effect cannot be obtained. . On the other hand, when the time exceeds 5 seconds, the reverse transformation proceeds before the start of the finish rolling, and the austenite fraction increases, so that the effect of fineness by working in the temperature raising process cannot be obtained.

Finish rolling end temperature: Ar ₃ transformation point to (Ar ₃
(+ 50 ° C.) In an ultra-low carbon steel that does not contain carbonitride forming elements such as Nb and Ti as in the steel sheet of the present invention, the grain growth rate is high. For this reason, in order to refine the crystal grains in the surface layer region, the lower the finish rolling temperature, the more the growth of austenite grains can be suppressed. However, in the case of a thin steel plate for a can, the temperature of the steel plate tends to decrease, and there is a possibility that the steel plate is rolled below the Ar ₃ transformation point. If the finish temperature of the finish rolling is lower than the Ar ₃ transformation point, the anisotropy increases after rolling, and the structure after annealing becomes a mixed grain structure of coarse crystal grains and relatively fine grains. Properties and rough skin resistance deteriorate. On the other hand, (A
When the temperature exceeds (r ₃ + 50 ° C.), the crystal grains cannot be refined in the surface layer region, and a burning scale is generated to significantly deteriorate the pickling property. For this reason, the finish rolling end temperature is desirably in the range from the Ar ₃ transformation point to (Ar ₃ + 50 ° C.).

Conditions for rapid cooling after finish rolling: Start time of rapid cooling: Within 1 sec after finish rolling Finish rapid cooling within 1 sec after finish rolling is completed to suppress the growth of austenite grains and refine crystal grains in the surface layer region. If the time until the start of quenching exceeds 1 sec, the crystal grains in the surface layer become coarse and the surface becomes rough after pressing.

Cooling rate: 50 ° C./s or more To suppress the growth of austenite grains, the cooling rate is
It is desirable to make it as large as possible. Cooling rate 50 ° C / s
If it is less than 1, the crystal grains in the surface layer region become coarse, and roughening occurs after press working. In addition, by setting the cooling rate to 50 ° C./s or more, preferably 80 ° C./s or less, in addition to the refinement of the crystal grains in the surface layer region, the crystal grains having the entire thickness and good press workability are obtained. The diameter can be 10 to 15 μm.

Rapid cooling end temperature: 600 ° C. at the temperature of the hot rolled sheet surface
Cooling after finishing rolling suppresses grain growth of austenite grains, and further suppresses nucleation of ferrite grains from austenite grains and growth of ferrite grains. In order to obtain fine ferrite grains, the surface of the hot-rolled sheet is cooled until the surface temperature becomes 600 ° C. or less. When cooling is completed at a high temperature of the hot-rolled sheet surface exceeding 600 ° C., the crystal grains in the surface layer region and other inner layers become coarse. After quenching, 450 ° C
It is preferable to make the above. If the temperature is lower than 450 ° C., the winding temperature cannot be in the desired range, and depending on the cooling rate, the crystal grains may be excessively refined.

Winding temperature: 450 to 600 ° C. In the present invention, the winding temperature may be low, but if the winding temperature is lower than 450 ° C., the shape of the hot rolled sheet becomes poor, The picking operation itself may be difficult.
For this reason, it is desirable that the winding temperature be 450 ° C. or higher. On the other hand, when the winding temperature exceeds 600 ° C., scale formation is remarkable, and the pickling property deteriorates. For this reason, the winding temperature is desirably in the range of 450 to 600 ° C.

The obtained hot rolled sheet has a composite type structure composed of three types of structures in which the surface layer region is fined. This composite structure is inherited even after cold rolling and annealing. Regarding the mechanism that will have such a complex type organization,
Although it is not clear, it is estimated as follows. In other words, by quenching the sheet bar surface after completion of rolling, the sheet bar surface layer part is cooled to below once Ac ₁ point, transformed to ferrite phase. However, after cooling is completed, the surface layer is regained by the internal sensible heat of the steel strip, and the temperature is raised again. During the heating process, the ferrite phase is processed by finish rolling. In the processing in the temperature raising process, a higher ferrite fraction can be obtained than in the processing in the normal temperature lowering process, and the ferrite can be processed in a higher temperature range. Therefore, the ferrite that has accumulated high strain easily recovers and recrystallizes,
Further, it is considered that the reverse transformation to austenite is caused by the processing heat of the finish rolling, and an ultrafine grain structure is formed in the surface layer of the steel material. However, after the finish rolling, it is necessary to rapidly cool to a low temperature region where grain growth of ferrite grains does not easily occur.

Cold rolling reduction: 80 to 95% The rolling reduction in the cold rolling is performed in order to obtain a texture having a desired texture and crystal grain size in a subsequent annealing step, and in accordance with the reduction in thickness of the steel sheet. It is desirable to make it 80% or more. On the other hand, when the rolling reduction exceeds 95%, the r value decreases, the deep drawability deteriorates, Δr further increases, and the earring increases. For this reason, it is desirable that the cold reduction is in the range of 80 to 95%.

Annealing temperature: at or above the recrystallization end temperature Annealing of the cold-rolled sheet is preferably continuous annealing from the viewpoint of productivity, but it goes without saying that box annealing may be used. The annealing temperature is equal to or higher than the recrystallization end temperature to make the structure a recrystallized structure. However, if the annealing temperature is too high, the grains become coarse due to abnormal growth of the crystal grains, resulting in rough surface after press working. On the other hand, if the annealing temperature is too high, continuous annealing of a thin material increases the risk of plate breakage or buckling in the annealing furnace. Therefore, the upper limit of the annealing temperature is desirably 750 ° C.

Temper rolling reduction: 0.5 to 3% The cold-rolled annealed sheet is then subjected to temper rolling. The rolling reduction of the temper rolling is determined appropriately according to the temper degree of the product sheet, but 0.5% to prevent the occurrence of stretcher strain
It is desirable to make the above. On the other hand, in the temper rolling in which the rolling reduction exceeds 3%, it is necessary to use a wet skin pass specification in which rolling is performed using a rolling oil, so that productivity is reduced. Further, when temper rolling with a rolling reduction exceeding 3% is performed, the steel sheet becomes hard and the press workability deteriorates. From such a thing,
The rolling reduction of the temper rolling is desirably 0.5 to 3%.

By satisfying the above composition and the above manufacturing conditions, the average grain size of the surface layer from the surface layer of the steel sheet to a depth of 20% of the total thickness of the steel sheet is 10 μm or less and the total thickness of the steel sheet is reduced. Can have a composite type structure having an average crystal grain size of 10 to 15 µm, and can be a steel sheet for cans excellent in press formability and surface roughness resistance.

[0045]

EXAMPLE Molten steel having the chemical composition shown in Table 2 was melted in a converter and slab was formed by continuous casting. These slabs were subjected to hot rolling, cold rolling, annealing, and temper rolling under the conditions shown in Table 3, and further tin-plated at the 25th to give product sheets. The crystal grain size, hardness, r value, and AI value were determined for these product plates.

Using these product plates, a 350 g DI can (can lid diameter 60.3 mmφ, can body diameter 68.3 mmφ, height
123 mm) and subjected to four-step neck processing (lid diameter: 206). The roughness of the skin, stretcher strain pattern, and occurrence of press cracking after can making were investigated. The survey method is as follows. (1) Grain size test A cross section perpendicular to the rolling direction of the product plate was polished, corroded, and the grain size was measured by an optical microscope. The crystal grain size is JIS G
In accordance with the provisions of 0552, the total thickness of the
% Was measured for the surface layer region up to the depth, and the respective average values were determined. (2) Tensile test Rolling direction, rolling direction and 45 ° direction of each product sheet, rolling direction
A JIS No. 5 tensile test was taken from the 90 ° direction, a tensile test was performed, the r value in each direction was determined, and the average r value and the in-plane anisotropy Δr of the r value were calculated. The average r value and Δr were defined by the following equations.

Average r value = (r ₀ + r ₉₀ + 2r ₄₅ ) / 4 Δr = (r ₀ + r ₉₀ -2r ₄₅ ) / 2 where r ₀ , r ₉₀ , and r ₄₅ are the rolling direction, the rolling direction, and 90 °, respectively. , The r value in the rolling direction and the 45 ° direction. (3) Hardness test For the product plate after each plating, treatment equivalent to reflow (250
℃ 3sec) after heat treatment in an oil bath.
The surface hardness was measured with a Rockwell hardness of 30T scale in accordance with JIS Z 2245. Note that the reflow treatment refers to a treatment for heating the plated steel sheet to adjust the shape and appearance of the surface of the plating layer. (4) Aging test A JIS No. 5 tensile test was taken from each product plate, a 7.5% tensile prestrain was applied, an aging treatment was performed at 100 ° C for 30 minutes, and a tensile test was performed. The amount of increase in yield stress was determined, and the value was taken as the AI value. (5) Can making test After making each product plate (without reflow treatment) into a DI can of 350 g size, the surface roughness Ra of the neck part of each can was measured, and Ra of commercially available normal cans (commercially available) Can) and Ra
(Commercially available cans) + 10%> Ra was not rough when Ra (commercially available) + 10% ≦ Ra was rough, and the rough skin resistance was evaluated.

After the can was made, the bottom of the can was visually observed to check for the occurrence of a stretcher strain pattern. Also,
After making the cans (the number of cans for each product plate is 10,000), the presence or absence of press cracks in each can is measured, and the rate of press cracking for each product plate (= number of cans with cracks / total number of cans × 100) %)
Press formability was evaluated. In addition, the degree of ear generation (earring) after can making was measured, and the ear height was 3 mm or more (about 2 mm of the can height).
%).

Table 4 shows the results of these various tests.

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

[0053]

[Table 5]

From Table 4, it can be seen that the examples of the present invention are excellent in rough surface resistance, aging resistance and press formability, and have a tempering degree of T1 to T1.
Tinplate of T3 level can be manufactured by temper rolling of dry skin pass specification. On the other hand, in Comparative Examples out of the scope of the present invention, rough skin, occurrence of a stretcher strain pattern, and press cracking were observed after can making. Steel sheets No. 22 to No. 25 in which C, Mn, N, and Al are out of the range of the present invention,
It shows high aging with an AI value of 40 to 50 MPa, and a stretcher strain pattern occurs after can making. Further, in steel sheets No. 22 and No. 24 having a high C or N content, press cracking occurs due to a decrease in ductility and the like due to hardening. The steel sheet No. 26 containing Nb had too fine crystal grains and was inferior in formability, so press cracking was observed, and the steel sheet No. 27 containing Ti had a large crystal grain size and rough surface was observed. Further, as shown in FIG. 6, the recrystallization ending temperature of the steel sheet No. 26 containing Nb is high, and changes greatly at each position in the rolling direction, especially at the front and rear ends of the coil. On the other hand, the recrystallization end temperature of the steel sheet No. 13 of the example of the present invention is low, and there is almost no change in the coil longitudinal direction.

In the case of the conventional IF steel to which Nb was added, the recrystallization end temperature was high, and the problem of poor recrystallization occurred. Nb
In the steel of the present invention where no is added,
The recrystallization end temperature is low and excellent in operability of continuous annealing and cost reduction.

[0056]

According to the present invention, it is possible to provide a steel sheet for cans which is free from rough surface after press molding and has no stretcher strain pattern, and which is excellent in rough surface resistance and aging resistance. It can be applied to various metal cans, including not only two-piece cans but also three-piece cans, as a material for cans, and has a remarkable industrial effect. Furthermore, since the recrystallization end temperature of the steel sheet of the present invention is low, and there is no problem of poor recrystallization due to little variation at each position of the steel sheet, the operability in continuous annealing is excellent, and thus there is also an effect that the cost can be reduced. . In addition to food and beverage cans, it can be expected to be applied to a wide range of applications, from dry cell interior cans to home electric parts and automobile parts.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of slab heating temperature and N content on the amount of solute N.

FIG. 2 is a graph showing the effect of the Mn content on the aging index AI value.

FIG. 3 is a graph showing the relationship between rough surface, press formability and crystal grain size.

FIG. 4 is an explanatory diagram showing the effect of cooling after the end of hot rolling on the relationship between the average crystal grain size of the entire thickness and the average crystal grain size of the surface layer region showing good press formability and good surface roughness resistance. It is.

FIG. 5 is a graph showing the effect of the temper rolling reduction on the steel sheet hardness after reflow.

FIG. 6 is a graph showing an example of a recrystallization end temperature distribution in a coil rolling direction.

 ──────────────────────────────────────────────────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 Kugaminato 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki Steel Corporation Chiba Works F-term 4K032 AA01 AA02 AA04 AA16 AA21 AA22 AA27 AA29 AA35 CA01 CA02 CC03 CC04 CD03 CD06 CE01 CG02 CH04 CM01 4K037 EA01 EA02 EA04 EA15 EA18 EA19 EA23 EA25 EA27 EA31 EB01 EB02 EB05 FA01 FA02 FB04 FC04 FC07 FD04 FD06 FE01 FE02 FE06 FH01 FM06 GA05

Claims (3)

[Claims] 1. A composition containing, by mass%, C: 0.0005 to 0.0050%, Mn: more than 0.50 to 1.5%, Al: 0.015 to 0.15%, and N: 0.0050% or less, with the balance being Fe and unavoidable impurities. ,
It has a structure in which the average value of the crystal grain size is 10 μm or less in the surface layer region from the surface layer to a depth of 20% of the total thickness, 10 to 15 μm in the total thickness, and the aging index AI value is A steel sheet for cans having excellent surface roughness and aging resistance, characterized by being 30 MPa or less. 2. In addition to the above composition, in mass%,
The steel sheet for cans according to claim 1, wherein the steel sheet contains B: 0.0003 to 0.003%. 3. A steel slab containing, by mass%, C: 0.0005 to 0.0050%, Mn: more than 0.50 to 1.5%, Al: 0.015 to 0.15%, and N: 0.0050% or less, by transforming the Ac ₃ transformation point to 1150 After heating to the temperature range of ℃ and rough rolling, the surface temperature of the sheet bar is raised above the Ac ₁ transformation point (Ac ₁ -30 ℃) at a cooling rate of 50 ℃ / s or more.
Rapidly cooled to the following temperature, followed by finish rolling in 1 to 5 seconds, finishing the finish rolling at the Ar ₃ transformation point or more, turning it into a hot-rolled sheet, then cooling within 1 second after finishing rolling, and starting at 50 ° C. / s or more at a cooling rate of more than 60
Cool rapidly to 0 ° C or less, winding temperature: 450-600 ° C
The hot-rolled sheet is subjected to cold rolling at a reduction ratio of 80 to 95% to form a cold-rolled sheet, and then the cold-rolled sheet is annealed at a temperature equal to or higher than the recrystallization ending temperature, and then subjected to a reduction rate. : A method for producing a steel sheet for cans having excellent skin roughness resistance and aging resistance, which is characterized by subjecting to 0.5 to 3% temper rolling.