JP3290693B2 - Steel plate for can excellent in weldability, method for producing the same and method for making can - Google Patents

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 a three-piece can having excellent weldability, which enables efficient production of a three-piece can.

[0002]

2. Description of the Related Art Cans such as a beverage can shown in FIG. 1A, an 18L can (for example, a kerosene can) shown in FIG. 1B, and a pail can shown in FIG. Can be classified into cans and three-piece cans. 2-piece cans are tin plated, chrome plated,
Surface-treated steel sheets that have been subjected to chemical conversion, oiling, etc.
Press processing, DWI (drawing and wall ironing) processing,
This is a two-part can that has been subjected to processing such as DRD (drawing and redrawing) processing and has a lid attached thereto. 3
The piece can is a three-piece can formed by bending a surface-treated steel sheet into a cylindrical shape or a rectangular tube shape and joining the ends (11 is a joined portion) to form a can body 12, and then attaching a canopy 13 and a bottom lid 14. It is. There are also cans that can be opened and closed by removing the canopy 13.
It is included in the category of piece cans and three piece cans. In FIG. 3B, reference numeral 15 denotes a handle, and reference numeral 16 denotes an inlet.

[0003] Although three-piece cans require a larger number of manufacturing steps and higher manufacturing costs than two-piece cans, press working, D
Since strong processing such as WI processing is not performed, artistic printing on the can body 12 becomes possible, and it is frequently used in terms of fashionability.

FIG. 2 shows a manufacturing process of a three-piece can. That is, a slab having a thickness of about 200 to 300 mm is formed into a hot-rolled steel strip having a thickness of 2 to 4 mm by hot rolling, and then wound at a high temperature and self-annealed. Next, pickling is performed to remove oxide scale on the surface, and then cold-rolled to a thickness of 0.1 to 0.6 mm.
Cold rolled steel strip. Then, by performing box annealing or continuous annealing, the rolled structure (fibrous structure) formed by cold rolling is recovered, recrystallized, and crystal grains are grown to obtain predetermined mechanical properties. In the case of continuous annealing, nickel plating may be applied before annealing for the purpose of improving corrosion resistance, rust resistance, and the like. Thereafter, a predetermined degree of tempering (T1 to T6, DR
In order to obtain 8 to 10), temper rolling is performed to obtain an original sheet for surface treatment. Next, the strip that has been surface-treated to form a surface-treated steel strip is sheared to a predetermined length by a shear line. FIG. 3 shows this state. The strip S is cut so that the longitudinal direction, that is, the rolling direction is the bending direction of the can body, to obtain the cut plate 1.
In the figure, reference numeral 2 denotes a cutting line at this time, and L is a cutting length.

[0005] In the coating line, the cut plate 1 thus obtained is coated and baked on the surface corresponding to the inner surface of the can, and then coated and baked on the other surface. It is to be noted that a paint corresponding to the outer surface of the can is generally coated with a white paint in consideration of the following printing. In the following multicolor printing, printing and printing have been repeated for each type of color before, but recently printing and printing are performed in one pass by connecting a plurality of printing machines. In addition, these coating printings are performed by removing the joints 5 indicated by oblique lines in FIG. This is because the bonding strength described below is reduced by the paint.

[0006] Next, the cutting plate 1 is cut by slit cutting.
The blank sheets 6 are made into a size per can, and the blank sheet 6 is bent into a cylindrical shape or a rectangular tube shape. In the figure, reference numeral 3 denotes a slit line, and the bending line when bending into a rectangular cylindrical shape is indicated by 4. Then, after joining the joints 5, 5 at both ends in the longitudinal direction of the blank sheet 6 by welding or an adhesive, the flange and, if necessary, the necking and the beading are applied to attach the canopy and the bottom lid. Finish. Here, the above-mentioned flange processing is performed to attach the canopy 13 and the bottom lid 14 by winding them together, and this is shown in FIG. In FIG.
Reference numeral 8 denotes a winding portion. Necking and beading are performed to increase the strength of the can.

[0007] The material of the steel plate for cans used for beverage cans, food cans and the like is defined by the degree of tempering. Temper is represented with a value of Rockwell T hardness (H _R -30T), the T1~T6 a soft ones in a single rolled products, twice rolled products are divided into similarly DR8~DR10 I have.

[0008] T3
The following various soft tinplates are made of low carbon Al-killed steel materials with varied C and Mn contents, and the materials are adjusted by the annealing temperature and time by the box annealing method. Finished by temper rolling. In addition, various hard tinplates of T4 or more are made of a low carbon Al-killed steel material having varied C and N contents, and the material is adjusted by a continuous annealing method at an annealing temperature and time, and then reduced by 1 to 3%. Rate of dry temper rolling. The DR material is wet-processed (using temper rolling oil or cold-rolling oil), rolled twice (double cold-reducing), and temper rolled using a variety of annealed T1 to T6 sheets at a rolling reduction of 5 to 50%. I've finished.

The inventors of the present invention have invented a technology which can be softened by a continuous annealing method having a quenching / overaging treatment zone by using a low-carbon Al-killed steel whose C and N contents are adjusted. Has been doing commercial production. However, since the softest T1 material could not be manufactured by the continuous annealing method, development of a method of manufacturing the T1 material by the continuous annealing method has been demanded.

On the other hand, as described above, since the manufacturing process of the three-piece can is complicated and causes an increase in cost, continuation and simplification of the manufacturing process are called for.

As one of the countermeasures, there is a method in which the conventional coating in the state of a cutting plate is applied in the state of a strip, and then the plate is cut. That is, in the cutting board coating, it is necessary to pass each cutting board and the front and back two times through a coating line to perform coating and baking (two coats, two bake, two coats, two bake).
However, in the case of a strip, the coating corresponding to the inner surface of the can and the coating corresponding to the outer surface of the can are continuously applied, and the next baking can be performed simultaneously on both sides (one coat and one bake). Then, by cutting the plate after baking in this coating line, simplification and continuity of the process can be realized.

However, the above-mentioned strip coating has the following problems. That is, as shown in FIG.
, And the width of the paint cut is usually about 6 mm, and it is very difficult to control the paint range. In addition, even if painting is possible, at the center position of the paint cut portion (that is, the position of 3 mm which is the center of the 6 mm width),
It is difficult to cut a strip moving at high speed.

If the control accuracy of the coating range and the cutting position is poor, the following troubles may occur. For example, when paint is present at the joint, if the paint is welded as it is, the paint will burn and a blast phenomenon will occur, causing not only the nugget not to be formed properly but also a hole. In addition, even if bonding is performed using an adhesive, sufficient adhesive strength cannot be obtained. Conversely, if the paint is not applied to the place where it should be painted, there is no problem in joining, but there are problems in terms of rust resistance, corrosion resistance and the like.

Further, it is known that the box annealing method has the following disadvantages (1) to (3). (1) Since the annealing is performed in a tight coil state, if the annealing temperature is increased, a sticking defect (Sticking Break) occurs and the yield decreases. (2) Since soaking requires several hours or more, C, Mn, and the like are enriched and concentrated at the grain boundaries on the steel sheet surface during annealing, and as a result, surface defects due to graphite are generated. The corrosion resistance of the tinplate was sometimes deteriorated. (3) The temperature of the coil becomes high in the outer winding part and the inner winding part, and becomes lower in the middle winding part. Therefore, the variation in hardness in the coil becomes large, and it is difficult to obtain a uniform original plate. The degree was also inferior.

As can be seen from the above description, it has been difficult to produce a high-quality T1-T3 grade so-called soft tinplate according to the conventional box annealing method.

Also, if the T1 material can be manufactured by the continuous annealing method, the T2 material or more can be separately formed by the work hardening method, so that the effect of rationalizing the manufacturing process was expected.

The present invention provides a tempering degree T1 to T1 of a quality which can be sufficiently satisfied not only by the conventional continuous annealing method but also by the box annealing method.
In view of the fact that tin-plated or tin-free steel sheets having T3 could not be manufactured, a method for manufacturing soft tin-plated or tin-free steel sheets excellent in press workability of high quality tempering degrees T1 to T3 by a continuous annealing method. T
1 to T6, DR8 to DR10 materials are provided.

A chromium-plated steel sheet, commonly called TFS, is a surface-treated steel sheet that can be produced at a low cost in steel sheets for cans, and is therefore often used for large-sized cans such as 18L cans and pail cans. As a method of forming these can bodies, if a chromium plating layer, especially chromium oxide, which is an electrically insulating material, is attached to a large amount, joining by electric resistance seam welding even if it has excellent rust resistance and corrosion resistance is possible. Because it is difficult, before welding, the plating layer is polished in advance with a grindstone or the like, and welding is performed in a state where a base metal is exposed.
However, even in welding lines designed to absorb and remove abrasive powder, the powder is scattered, and if mixed into the can, it will harm the human body if the can is filled with food, and if filled with paint etc. The surface of the coating film has a protrusion (convex defect) mainly composed of iron and Cr, which looks bad and rusts in a short period of time. The productivity is poor because the abrasive powder is thoroughly absorbed and removed.

[0019]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a single steel type having a good temper T1 and even a better temper by a proper selection of a reduction ratio of a continuous annealing method and a subsequent temper rolling. Hard temper T2-T6, DR8-DR
An object of the present invention is to provide a steel plate for a can having excellent weldability, obtained by obtaining a steel plate having an arbitrary temper degree of 10 and chromate-treating both end portions to be bonded to the steel plate so that the chromium oxide adhesion amount is reduced. It is in. Another object of the present invention is to cut the above-mentioned chromate-treated steel sheet (TFS) in a direction perpendicular to the rolling direction to obtain a blanking sheet, and to bend it in a direction perpendicular to the rolling direction to join both ends. In particular, it is an object of the present invention to provide a can-making method capable of easily manufacturing a three-piece can.

[0020]

SUMMARY OF THE INVENTION The present invention comprises a steel plate having a central portion forming a can body and both ends in a width direction of a joining plate, and a chromate-treated coating thereon, and is formed in a direction perpendicular to the rolling direction. A chromate-treated steel sheet for bending and joining the sheet width direction ends to form a can, wherein the amount of chromium oxide in the sheet chromate treatment film at both ends in the sheet width direction is equal to the amount of chromium oxide in the film chromate treatment film at the central part. less than the oxidation amount of chromium, Ri amount der to allow welding, the steel plate is a composition by weight, C: 0.004% or less, Si: 0.03% or less, Mn: 0.05 to 0 60%, P: 0.02% or less, S: 0.02% or less, N: 0.01% or less, Al: 0.02 to 0.20%, Nb: 0.1 to 0.001%, Ti: 0.1 to 0.0001%, Cr: 0.1% or less, Cu: 0.1% or less, i: 0.1% or less, B: 0.005 to 0.0001%, Mo: 0.01% or less, O: 0.01% or less, V: 0.01% or less, Zr: 0.01% or less , Ca: 0.005% or less, Sn: 0.01% or less, Sb: 0.01% or less, Rare earth element (REM): 0.005% or less, Na: 0.001% or less, Mg: 0.001 % Or less, As: 0.01 to 0.001%, Te: 0.01 to 0.0001%, the balance being hot cast into a continuous cast slab made of ultra-low carbon steel consisting of Fe and unavoidable impurities. Rolling, pickling,
After cold rolling, continuous annealing is performed, and the tempered degree is adjusted to T1 to T6 or DR8 to DR10 by subjecting the annealed sheet to temper rolling with an appropriately selected rolling reduction. To provide excellent steel plates for cans.
You . The amount of chromium oxide in the chromate-treated film at the center is 10 mg / m ² or more, and the amount of chromium oxide in the chromate-treated film at both ends in the width direction of the plate is 10 mg / m ^2.
m ² or less.

Further, in the present invention, when producing the above-mentioned chromate-treated steel sheet, the composition is, by weight, C: 0.004% or less, Si: 0.
03% or less, Mn: 0.05 to 0.60%, P: 0.0
2% or less, S: 0.02% or less, N: 0.0
1% or less, Al: 0.02 to 0.20%, Nb: 0.
1 to 0.001%, Ti: 0.1 to 0.0001%, Cr: 0.
1% or less, Cu: 0.1% or less, Ni: 0.
1% or less, B: 0.005 to 0.0001%, Mo: 0.
01% or less, O: 0.01% or less, V: 0.0
1% or less, Zr: 0.01% or less, Ca: 0.
005% or less, Sn: 0.01% or less, Sb: 0.
01% or less, rare earth element (REM): 0.005% or less, Na: 0.
001% or less, Mg: 0.001% or less, As: 0.
Hot-rolled, pickled, continuously cast slabs made of ultra-low carbon steel containing 0.01 to 0.001%, Te: 0.01 to 0.0001%, and the balance being Fe and unavoidable impurities.
After performing cold rolling, continuous annealing is performed, and a tempered degree is adjusted to T1 to T6 or DR8 to DR10 by subjecting the annealed sheet to temper rolling that appropriately selects a reduction ratio, to obtain a steel strip. An object of the present invention is to provide a method for producing a steel sheet for cans having excellent weldability, characterized in that a shielding plate is provided for a predetermined width at both ends in the width direction of the steel strip and subjected to electrolytic chromate treatment.

Further, according to the present invention, the chromate-treated steel strip obtained as described above is coated on both sides or one side of the steel strip by removing predetermined widths at both ends in the sheet width direction, and then baked. After printing and printing if necessary, cut to a predetermined length in a direction perpendicular to the rolling direction, further blanking to form a blanking sheet, and bending the blanking sheet in a direction perpendicular to the rolling direction The present invention also provides a method for manufacturing a three-piece can, characterized in that the unpainted portions are overlapped and joined, and then the canopy and the bottom lid are attached and finished by flange processing.

Hereinafter, the present invention will be described in more detail.

According to the present invention, vacuum degassing is effectively used during steel making, and the use of an Al-killed steel slab with an extremely small amount of C makes it possible to obtain the softest tinplate by continuous annealing. An Al-killed steel slab in which a temper T1 can be manufactured, and in which the Al-killed steel slab contains Nb, Ti, and B, which are carbide-forming elements and nitride-forming elements, as necessary. HAZ by coarsening the crystal grain size
A material more suitable for canning by the three-piece can method that can solve cracking can be used to manufacture an original plate having an arbitrary temper degree including the temper degree T1 by using a continuous annealing method.

The ultra-low carbon steel deteriorates in brittleness, but contains B, which is an element for increasing the grain boundary strength, if necessary.

Further, although the disadvantages (1) to (3) of the box annealing method can be solved by the continuous annealing method, in order to cope with the thinning of plating which is progressing in the field of cans, the surface of the box is annealed during annealing. If necessary, Te, As, Sn, and Sb, which have the effect of preventing the trace amount of C in the steel from concentrating on the surface by enrichment and concentrating and improving the adhesion and corrosion resistance of the plating, are added.

The present inventors systematically examined the relationship between tinsel and TFS and the solute C and N and the crystal grain size on the hardness of TFS. Based on this finding, it was considered that C in the molten steel for producing a continuous cast steel slab, which is a starting material, should be reduced in order to reduce solid solution C after annealing based on this finding.

On the other hand, when box annealing is performed on a cold-rolled steel sheet formed by a normal process using an Al-killed steel continuous casting slab, C is melted in the melting temperature range of C because the cooling rate after annealing is low. Since the dissolved C can be sufficiently precipitated, the residual amount of the solute C becomes very small. N is A
Since both the annealing temperature and the time in the 1N precipitation temperature (400 ° C. or higher) region are sufficient, almost all are precipitated as AlN, and since the annealing time is long, sufficient grain growth can be achieved. It is known that the later original plate is soft and non-ageing, so that the hardness of tinplate or TFS also becomes sufficiently soft.

The present inventors have previously invented a method for producing a soft tinned original sheet by a continuous annealing method and have disclosed a method disclosed in Japanese Patent Application No. 56-125.
No. 996 (JP-A-58-27932). According to the method, an Al-killed steel material containing a small amount of N and containing a certain amount of C is used. During hot rolling, the finishing temperature is in an α + γ coexistence region or a γ region, and the winding temperature is in a range in which carbides do not agglomerate. Using a hot-rolled sheet obtained at a medium temperature in step 1, annealing was performed at a recrystallization temperature or higher in a continuous annealing furnace having a quenching zone and an overaging zone, thereby obtaining a soft original sheet. However, tinsel or TFS hardness was T2 to T3, and T1 could not be obtained. The reason for this is that the precipitation site (Sit
e) In order to distribute cementite densely,
This is because even if the amount is contained to some extent or more and the winding temperature is set to a medium temperature or lower and the overaging treatment is performed in a continuous annealing furnace, cementite does not sufficiently precipitate. To promote the precipitation of the cementite, it is conceivable to lengthen the overaging treatment time, but for that purpose, it is necessary to lengthen the overaging treatment equipment, which is difficult to implement on an industrial scale. In addition, not only the plating base plate with the solid solution C and N remaining undergoes work hardening by temper rolling in the next step, but also
Furthermore, since the plated steel sheet undergoes water quenching from about 400 ° C. and undergoes strain aging hardening by reflow treatment (plating treatment) after plating, the increase in hardness increases in proportion to the amount of solute elements. Therefore, the present inventors have conceived that it is important to adjust the residual amount of the solid solution element to the same level as the box annealing material in order to manufacture a soft tinplate.

Based on the above considerations, the present inventors have conducted intensive studies. As a result, continuous annealing of an ultra-low carbon steel material was performed to finish the hardness to T1, and to change the rolling reduction in the subsequent temper rolling. The present inventors have newly found that they can be separately formed on the original plates T1 to DR10, and found that if they are used for TFS, they are suitable as steel plates for cans, and completed the present invention.

Next, the behavior of the constituent elements of the continuous cast steel slab as the starting material and the reason for limiting the constituent composition will be described.

C is an important element that largely controls the recrystallization temperature and suppresses the growth of the recrystallized grain size. According to the box annealing method, when the amount of C is increased, the crystal grain size becomes smaller and becomes harder. In the case of the continuous annealing method, there is no simple tendency to harden as the C content increases. FIG. 5 shows the effect of the C content on tint hardness. As can be seen from the figure, it shows a very complicated tendency. To explain this from a metallurgical point of view, as the C content becomes extremely small as about 0.004% or less, it becomes softer, while when the C content increases, a peak where the hardness becomes highest at about 0.01% is observed. Conversely, as the amount increases, the hardness decreases, and the C amount ranges from 0.02 to 0.2.
A valley is formed within the range of 07%, and the hardness increases as the C content further increases. It is considered that the reason why the carbon content becomes soft when the carbon content is about 0.004% or less is that the strain age hardening due to carbon becomes small due to a small absolute value of the amount of carbon dissolved at the melting temperature during annealing. The reason why a peak appears at a C content of 0.01% is that when dissolved C is precipitated, the amount of C is small, so the amount of Fe ₃ C as a precipitation nucleus is small, so that the precipitation movement distance becomes long, and thereby, in the cooling process. This is because the amount of precipitation decreases and a large amount remains. Therefore, those containing a certain amount of C exceeding 0.01% are effective in softening. However, when the amount of C further increases, Fe
_{Although 3} C is sufficiently present, it hardens because the crystal grain size becomes small. In order to uniformly coarsen the crystal grains, the content needs to be 0.004% by weight or less.

Therefore, in order to produce a soft tinned sheet having a tempering degree of T1 or less by a continuous annealing furnace, the C content needs to be 0.004% or less.

Si deteriorates the corrosion resistance of the tinplate,
Further, since it is an element that hardens the material extremely, it is necessary to avoid containing excessive Si. Therefore, it is important that the amount is reduced as much as possible in the steel making stage. In order to prevent the SiO ₂ in the refractory from being reduced by the Al in the molten steel, it is necessary to replace the chamotte type refractory which has been conventionally used. Care must be taken, such as using zircon refractories. That, Si is Si because it is impossible to produce a tin original plate was hardened temper T ₁ through T ₃ exceeds 0.03% should be less than or equal to 0.03%.

Mn must be added in order to prevent the occurrence of ear cracks in the hot-rolled coil. However, the above-described ear cracks are directly governed by S.
Is suppressed by the addition of Therefore, there is no need to intentionally add Mn if the amount of S is small, but it is necessary to add Mn since S is inevitably contained in steel. When Mn is less than 0.05%, generation of edge cracks cannot be prevented, while when Mn is more than 0.6%, the crystal grain size becomes finer and hardened.
It must be within the range of 0.6%.

If S is excessively contained in relation to the amount of Mn, it causes ear cracks in the hot-rolled coil, and also becomes an S-based inclusion and causes a press defect. Therefore, S must be made 0.02% or less. In particular, if the Mn / S ratio is less than 8, the above-mentioned edge cracks or press defects occur, so Mn / S must be 8 or more. If the amount of S is large, Mn precipitates and the crystal grain size becomes small.

Since P is an element that hardens the material and deteriorates the corrosion resistance of the tinplate, its excessive content is not preferred, and P must be 0.02% or less.

Al is an element exhibiting the function of a deoxidizing agent in the steel manufacturing process. As the content in steel increases, the cleanliness of the steel increases, but excessive addition is not economically preferable. Further suppress the growth of recrystallized grain size,
Al needs to be 0.20% or less. On the other hand, as the lower limit of Al, the amount of Al essentially corresponding to the amount of dissolved oxygen in the molten steel is added, and it is sufficient if the deoxidation can be completed. This is not necessary, but this will result in poor tinplate cleanliness. Further, in order to obtain soft tinsel, it is necessary to fix solid solution N with Al and reduce the remaining amount.
If the Al content is less than 0.02%, the amount of solute N in the steel increases, so the Al content needs to be 0.02% or more. Therefore, Al is limited to the range of 0.02 to 0.20%.

N is contained as a result of the incorporation of N in the air during the steel production process. However, if N is dissolved in steel, a soft steel plate cannot be obtained and N is an unnecessary element. In the process, N is reduced to 0.01% by minimizing the mixing of N from the air.
It must be: When N is large, precipitation of AlN also increases, and the crystal grain size is reduced.

Since Nb is a carbide and nitride forming element, it has a function of reducing the residual amount of solid solution C and solid solution N. On the other hand, when Nb is added in a large amount, Nb-based precipitates cause a pinning effect of the crystal grain boundaries. Since the recrystallization temperature becomes high and the workability of the continuous annealing furnace becomes poor, Nb is set to 0.1% or less, and the lower limit must be set to 0.001% which is necessary for exhibiting the effect of Nb.

Since Ti is a carbide and nitride forming element, it has a function of reducing the residual amounts of solid solution C and solid solution N. On the other hand, when a large amount of Ti is added, the cross section of a thin steel sheet can be observed with a microscope.
A sharp, very hard precipitate is found. In steel plates for cans, such inclusions are the most brilliant, deteriorating corrosion resistance, and are considered to be the cause of scratches when pressed. Therefore, Ti must be 0.1% or less, and the lower limit must be 0.0001%, which is necessary for exhibiting the effect of Ti.

In a thin steel sheet, if the solid solution C is extremely reduced by adding a carbide-forming element based on an ultra-low carbon steel, the strength of the recrystallized grain boundaries is weakened, and the use of cans or the use of cans is reduced. When stored at extremely low temperatures, there is a concern that embrittlement cracking may occur. It is effective to add B in order to produce a product which is satisfactory in quality for such applications. In the case of B, if solid solution C exists in the grain boundary, segregation of P becomes small, and the grain boundary strength becomes large, and there is no fear of poor embrittlement. However, when the amount of solid solution C decreases, P segregates at the grain boundary and becomes brittle. At this time, if B is present, it plays the role of solid solution C, or B itself increases the grain boundary strength, so that embrittlement failure can be solved. B is also effective for softening because it forms carbides and nitrides, but during continuous annealing, B segregates at the recrystallized grain boundaries, delays recrystallization, and impairs workability. The lower limit must be 0.005% or less, and the lower limit must be 0.0001% or more required to exhibit the effect of B.

Since O is an element that lowers the recrystallization temperature,
It is an element that can improve the workability of the continuous annealing furnace. However, when O is large, Al and Mn in steel or S in refractory
i, oxides are formed with Ca, Na, F, etc. of the flux, which may cause cracking during press working or deteriorate the corrosion resistance. As the method, an excellent cleanness can be obtained by adjusting the deoxidation by vacuum degassing, adjusting the weir shape of the tundish, the shape of the nozzle, and the casting speed. In the process, Al
If there is a large amount of inclusions, the inclusions form a cluster, which makes it easy to float according to Stokes' law, thereby improving the cleanliness. For this reason, it is better to have a large amount of Al or the like. Therefore, O is 0.01
% Or less.

Ca forms CaO in molten steel, and A
When l ₂ O ₃ reacts, it lowers the melting point of the ultra-hard Al ₂ O ₃ inclusion having a high melting point, and also reduces the hardness. Therefore, even if Al ₂ O ₃ is erroneously left in the thin steel sheet, it is soft and severe. It is divided by cold rolling and becomes smaller, thereby preventing quality deterioration. Therefore, it is an element that may be added if necessary.

It is necessary to pay attention that the carbon content is as small as 0.004% or less in producing the steel as the starting material of the present invention. For this purpose, the decarburization reaction is carried out by a vacuum degassing method. There is a method of lowering C by causing it to occur. On the other hand, the ordinary degassing method requires a long time,
%, It is difficult to reduce the temperature of the molten steel during the degassing process, and not only the casting operation becomes difficult in the subsequent continuous casting process, but also the inclusion of inclusions due to the decrease in the temperature of the molten steel. Since the floatability is poor and the cleanliness of the steel deteriorates, tinplate of satisfactory quality cannot be obtained.
Therefore, in order to obtain the starting material used in the present invention, it is important to improve degassing efficiency by subjecting molten steel to vacuum degassing. For this purpose, in the case of a bottom-blowing converter, it is effective to lower the blow stop C to 0.03% or less and to increase the reflux speed of the degassed molten steel. It is important to increase the amount of reflux gas for gas. According to the experiments of the present inventors, in a normal vacuum degassing process for decarburizing molten steel of C 0.03%, even if the ladle molten steel is refluxed five times, it is 0.005%.
By increasing the reflux gas amount and increasing the reflux velocity as described above, not only C can be reduced to 0.004% or less by the same rotational reflux, but also in a short time. The same rotary recirculation process is achieved, and the temperature drop can be minimized.

The continuously cast steel slab used in the present invention can be obtained by subjecting molten steel in a converter to vacuum degassing at an increased reflux rate as described above, and then continuously casting.

After finishing the T1 material by continuous annealing according to the above-mentioned method, it was found that the temper rolling reduction ratio can be increased, the work hardening degree can be increased, and those having different temper degrees can be produced. .

First, the process leading to the present invention will be described.
It has been conceived that the above-mentioned problem concerning the joint can be solved by changing the bending direction from the same direction as the conventional rolling direction to a direction perpendicular to the rolling direction. This is shown in FIG. The same parts as those in FIG. 3 showing the conventional example are denoted by the same symbols. Thus, the coating can be applied continuously in the longitudinal direction of the strip 1 by removing the joints 5 and 5 located at both ends of the strip 1, so that the above-mentioned problems caused by the coating can be solved at a stroke.

However, when the blank sheet 6 thus obtained was bent and then joined by seam welding and flanged, it was found that the frequency of cracking at the heat-affected zone (HAZ) was extremely high. Was. So this HAZ
A study was conducted to eliminate cracks.

The welding of the can body is usually performed by lap welding as described above using a so-called wire seam welding machine of a type using a body wire as an intermediate electrode. As a result, the overlapped portion is heated and melted by the resistance of the steel plate, and is bonded by the pressure of the electrode wheel. The temperature of the steel sheet during this welding is about 900 to 1500
The current and voltage are controlled to be in the range of ° C. 900
If the temperature is lower than ℃, the welding strength is insufficient, and if the temperature is higher than 1500 ° C, splash occurs. As a result of examining the HAZ crack of the can body joined by such a welding method,
It was found that the greater the thickness of the overlapped portion, the higher the frequency of occurrence of HAZ cracks.

This can be qualitatively explained as shown in FIG. 7A shows a case where the overlapping portion is thick, and FIG. 7B shows a case where the overlapping portion is thin. Here, 7 is a can body, 8 is a nugget, 9 is a die for flange processing, and 9 is a cylindrical shape. The manufacture of cans was taken as an example. At the time of flange processing, tensile forces F and F 'are generated in the overlapped portion, but the greater the thickness of the overlapped portion, the greater the tensile force (F>F'). For this reason, it is considered that HAZ cracks are more likely to occur as the thickness of the overlapped portion is larger.

Therefore, a method of crushing and reducing the thickness by increasing the pressing force of the electrode wheel can be considered, but there is a limit to this. That is, if the pressing force is excessive, as the welding progresses and approaches the end, the plates of the overlapping portion escape from each other, and the required overlapping width cannot be obtained, or the shape of the copper wire is deteriorated, and the normal There has been a problem that nuggets cannot be obtained continuously. In addition, it is conceivable to raise the temperature of the steel sheet by increasing the current value, but in this case, as described above, splash occurs, which scatters and adheres to the inner and outer surfaces of the can, and destroys the coating film and the printed film. And
Corrosion resistance, rust resistance, aesthetics, etc. are impaired and cannot be put to practical use.

While there was no problem with the method of manufacturing cans by bending in the rolling direction, the method of bending cans in the direction perpendicular to the rolling direction caused a high frequency of HAZ cracking. We considered the solution by improvement, but it was very difficult and could not solve it.

Then, the present inventors verified the manufacturing process of the steel sheet for cans. As a result, it was found that the HAZ crack was due to the anisotropy of the crystal structure due to rolling. For example, using a low carbon steel, temper degree T4, plate thickness 0.3
The following table shows an example of the result of a tensile test of a tinplate original finished to 2 mm.

Laboratory studies on this anisotropy revealed the following. That is, the anisotropy appears due to the effect of temper rolling. When the crystal grain size after annealing is large, the influence of the temper rolling in the next step is not so much affected. When the crystal grain size after annealing is small, anisotropy appears due to the influence of temper rolling in the next step. If the ratio between the major axis (rolling direction) and the minor axis (direction perpendicular to the rolling direction) of the crystal grains after temper rolling is within 1.5, the anisotropy does not appear so much. Even if the rolling reduction in temper rolling is increased to achieve a DR10 class hardness, the isotropic direction is maintained as long as the shaft diameter ratio is 1.5 or less.

Although the reason for the above is not clear,
It is inferred as follows. That is, when the crystal grains are small, they become hard, and plastic deformation during temper rolling is almost limited to the rolling direction. However, when the crystal grains are large, they become soft and plastic deformation occurs in the direction perpendicular to the rolling direction. It is considered to be.

The inventors of the present invention have conceived of using an ultra-low carbon steel having an extremely small amount of C as a material in order to enlarge the crystal grains.

Meanwhile, in the case of industrially manufactured steel plates for cans, it is very difficult to adjust the crystal grain structure to the same level even under the same manufacturing conditions, and there is almost no necessity for the conventional method. Was. Even if the manufacturing conditions are the same, the structure varies even if the composition varies in the steel refining process, the size of precipitates such as carbides, oxides, nitrides, and sulfides generated in heating furnaces, annealing furnaces, etc. , Amount and distribution.

Of these, carbides serve as crystal nuclei, so that the presence of a large amount of carbides reduces the crystal grain size. It is generally known that, in a region where the amount of C is small, the crystal grain size is uniquely determined by the amount of C in steel. However, C
Even if the amount is the same, there may be a so-called mixed grain structure in which small crystal grains exist next to large crystal grains, and as described above, the presence of small diameter crystal grains causes anisotropy. The fact that a mixed grain structure is not obtained makes industrial production difficult. Therefore, the use of ultra-low carbon steel with an extremely reduced amount of C as described above is effective not only in increasing the crystal grain size but also in eliminating the mixed grain structure.

However, this alone is still insufficient. That is, precipitates other than carbides (AlN, MnO, Mn
S, etc.) have the effect of inhibiting the growth of crystal grains and regulating the direction of growth, and therefore are harmful to the object of the present invention. As a countermeasure for this, it is conceivable to finely disperse the precipitate by adjusting the heat treatment temperature, but it is difficult to stably produce the precipitate by this method. Becomes M
A method of reducing the amount of n, S, N, etc. was adopted.

The present invention has been made based on the findings described above.

According to the present invention, since the crystal grains can be made large and the mixing ratio of small crystal grains can be greatly reduced, anisotropy due to rolling does not occur. Therefore, in manufacturing a three-piece can body, the heat-affected zone (HAZ) is not cracked even if it is bent in a direction perpendicular to the rolling direction and lap-welded, and flanged, and the strip plate is thereby formed. Since painting becomes possible, shortening of the manufacturing process and cost reduction can be achieved.

It is considered that this is made possible by a synergistic effect of the following actions. At the time of welding, the crystal grains of the heat-affected zone are coarsened. At this time, precipitates are reprecipitated at the grain boundaries to reduce the strength of the grain boundaries and induce HAZ cracking.
Since S, N, etc. are reduced, HAZ cracks due to reprecipitation can be reduced. Reducing Mn, S, and the like also has a secondary effect of reducing manufacturing costs. Since the amount of carbon is extremely reduced and precipitates are reduced to make the crystal grains coarse and uniform, the yield point is lowered, and plastic deformation during flange processing is performed smoothly.
The frequency of Z cracks is reduced. In order to prevent HAZ cracking, it is conceivable to reduce the total thickness of the overlapped portion during welding by reducing the thickness itself. However, reducing the plate thickness reduces the strength of the can.

In recent years, the thickness of the steel sheet has been reduced in order to reduce the cost of empty cans, but the hardness of the steel sheet has been increased in accordance with the thickness of the steel sheet in order to prevent the strength of the can from being reduced. There are two methods of hardening, a method of increasing the C content to reduce the crystal grain size and a method of increasing the rolling reduction in temper rolling. However, both methods exhibit anisotropy and cannot be used in the present invention.

However, in the present invention, ultra-low carbon steel is used, and there is no problem even if temper rolling is performed with a high reduction ratio for hardening. This is presumably because even when work hardening is performed by temper rolling at a high reduction rate, a kind of self-annealing proceeds in the vicinity of the welded portion due to welding heat, and the softness inherent to the original ultra-low carbon steel is obtained. Therefore, even if the flange processing is performed, the HAZ crack does not occur.

The continuous cast steel slab used in the present invention is subjected to vacuum degassing at a high reflux rate to the molten steel of the converter as described above, followed by hot rolling, pickling and cold rolling in a conventional manner. It can be obtained by continuous casting. A method of manufacturing a steel sheet for cans having an arbitrary temper degree of temper degrees T1 to T6 and DR8 to DR10 by temper rolling with an appropriately selected rolling reduction for this ultra-low carbon steel sheet will be briefly described. .

[0067] FIG. 8 shows an example of the relationship between temper (H _R -30T) and temper rolling reduction ratio. Temper rolling is performed on the steel sheet obtained by continuously annealing the ultra-low carbon steel sheet having the above-described composition. In the present invention, in order to use a steel type having the above composition, the steel sheet having the softest temper T1 is continuously annealed.
It can be manufactured by temper rolling. This has not been possible before.

As is apparent from the example shown in FIG.
1 when it is desired to obtain a steel sheet (49 ± 3 in H _R -30T), to the continuous annealing plates, it may be performed selected to temper rolling at a reduction ratio of several percent. The reduction ratio at the time of temper rolling may be selected from FIG. 8 such that the reduction ratio is about 10% at the temper T2. As described above, in the present invention, it is possible to manufacture steel plates for cans of all temper degrees with one steel type.

In this way, the steel sheet subjected to the temper rolling, in which the reduction ratio is appropriately selected so that the temper degree becomes a desired value, is subjected to the chromate treatment. Chromate treatment is chromic acid,
It is sufficient to adopt a conventional method of performing an electrolytic treatment in a solution containing Cr ⁶⁺ such as dichromic acid. The chromate treatment forms a chromate film on the steel sheet, which is composed of chromium metal and chromium oxide (including hydrated chromium oxide).

In the present invention, as described above with reference to FIG. 6, a blanking sheet from a temper-rolled steel strip is bent in a direction perpendicular to the rolling direction to form a can. For this reason, it is necessary to reduce the amount of chromium oxide that inhibits weldability at the time of chromate treatment at the joint of the blanking sheet, that is, at both ends (5 in FIG. 6) in the direction perpendicular to the rolling direction. The other part (center part) is in contact with the contents of the can, so it is necessary to have excellent corrosion resistance and rust resistance. A method of forming chromate films having different characteristics at the center and both ends of the blanking sheet and its mechanism will be described below.

Using a chrome-plated steel plate (commonly known as TFS), it is folded into a square or rounded to form a body for 18L cans and pail cans, and the ends are joined to form a body. Is an electrical resistance seam welding method in most cases. However, even if welding is performed by using TFS, the electric resistance is large, abnormal heat generation occurs, and splash (splash) occurs.
If frequent occurrences or deteriorations occur, the lap welds may become pinholes. In order to prevent this defect, if the current value is lowered, immediately below the current value at which no scattering occurs,
This time, the bonding strength cannot be obtained because the nugget is not sufficiently formed. Therefore, the range between the lower limit current value at which the joining strength is large enough to withstand practical use and the upper limit current value at which no scattering occurs, which is referred to as a proper weldable current range,
Unless this current range is wide, stable welding work cannot be performed. However, TFS cannot be welded because the current range is narrow as described above. Therefore, before welding is performed, the welded portion is removed by grinding with a predetermined width and a grindstone, and welding is performed after exposing the base metal surface. I have. However, since the TFS surface-treated surface has been ground and removed in advance, the base metal is active and easily rusts. In order to prevent rusting, repair painting is also applied and finished. Although the grinding powder is absorbed and removed, it is still scattered, so that the inside of the factory becomes dirty and the inner surface of the can becomes dirty.

As described above, it is known that there are problems in quality, workability, and the like, but TFS cannot be welded as it is, so grinding is unavoidable.
Repair painting is being performed.

The inventors of the present invention have conducted intensive studies on a method of performing welding without performing pre-grinding and finishing the surface treatment, and have found the following. Since the chromium-plated steel sheet cannot stably perform electric welding, it has been found that the chromium-plated steel sheet is caused by the adhesion amount of chromium oxide on the plating layer. This is because metallic chromium is a conductor, but chromium oxide is an electrical insulator. Therefore, it was found that it is effective to reduce the amount of chromium oxide attached or to reduce the film thickness. The amount is
It depends on the type of welding machine and welding conditions.
It was found that the problem could be solved by controlling the amount to mg / m ² or less. However, even if welding could be performed with a small amount of chromium oxide, rust resistance and corrosion resistance deteriorated. Therefore, the present inventors performed sufficient plating on places where the amount of chromium oxide is necessary,
It was conceived that it was very reasonable to plate only the unnecessary or less-needed places in an appropriate amount. That is, an example of an 18L can is shown below.

In the case of a conventional steel sheet made of low carbon Al-killed steel, the stripping as shown in FIG. 6 was not possible, and the welded portion was in a direction perpendicular to the rolling direction as shown in FIG. However, the use of the ultra-low carbon steel sheet of the present invention makes it possible to reduce the amount of chromium oxide adhering only at the end of the width of the strip, taking advantage of the above-described feature of the stripping shown in FIG. We have continued to study to make it possible to use the same amount of plating in the central part as possible.

As a result, it was possible to operate according to the following method, and to obtain TFS having an intended chromium deposition amount distribution.

FIG. 9 shows an example of the method. Electrode plate 21 such as Pb-Sn and band plate S in a chromate treatment tank
In the meantime, the shielding plate 22 is inserted into the end portion of the strip, and both ends of the strip are undercoated. For example, it can be achieved by the following method. If a shielding plate is not used, a large current flows at the end of the plate width, so that it is inevitable that a large amount of chromium oxide adheres to the end. However, by setting an appropriate position using a shielding plate, it is possible to reduce the amount of chromium oxide only at the position where welding is actually performed. When high-speed welding was actually performed using such a TFS, welding was sufficiently performed without grinding.

FIG. 10 shows an example in which a chromate treatment is performed using a shielding plate as shown in FIG. 9 at both ends of the strip. As the chromate treatment liquid, a liquid containing 60 g / l of CrO _{3 and} 0.8 g / l of sulfuric acid was used.
The chromate treatment was carried out under the electrolysis conditions of m, an electric quantity of 10 C / dm ² and a current density of 15 A / dm ² . At this time, as shown in FIG. 9, the distance covered by the shielding plate at the end of the strip was x. The result is shown in FIG. As is clear from FIG. 10, at the position where the nugget is actually formed by welding,
If a shielding plate is used, the amount of chromium oxide can be reduced at the end of the strip, and if x = 10 mm, the amount of chromium oxide can be reduced to 10 mg / m ² or less at the end of the strip.

As described in detail above, according to the present invention, extremely low carbon steel and continuous cast slab can be economically manufactured, and the steel sheet for cans can be economically manufactured using the slab of the steel type. Can be manufactured reasonably. As a result, the T1 material can be manufactured even by the continuous annealing method. Therefore, by adding work hardening to the original sheet, T1 to DR10 can be made with one steel type, and the process flow can be simplified and streamlined. Was.

Since it became possible to increase the crystal grain size in ultra-low carbon steel, the can body was conventionally bent or rolled in the rolling direction and joined.
It is now possible to reverse the direction by 0 ° and bend in the direction perpendicular to the rolling direction. Taking advantage of this feature, the end portion of the width of the plate becomes a welded portion, so that it can be painted in a band shape, which is more rational than that of cut plate painting. In addition, TFS
When welding was performed, the plated surface was ground and removed in advance, but by reducing the amount of plating at the end of the width of the plate during plating, welding could be performed without grinding. Also, as described above, even when bent in a direction perpendicular to the rolling direction, H
The invention was made practical because of the invention of an ultra-low carbon steel that does not cause AZ cracking.

[0080]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments. (Examples) Steels having the component compositions shown in Table 1 were melted by a 270-ton bottom-blowing converter, and the steel was produced with a C of 0.03%.
Subsequently, after performing RH vacuum degassing to decarbonize to 0.004% or less, Al is added, followed by a carbide forming element,
It was prepared by adding a nitride forming element and a thickening element to the steel sheet surface. These were cast by using a continuous casting machine to promote floating separation of inclusions to obtain steel slabs having excellent cleanliness. These steel slabs were each rolled around a hot finishing temperature of 850 ° C. and a winding temperature of 600 ° C. to form a hot-rolled coil having a thickness of 2.6 mm, followed by pickling and descaling. Then 6
After rolling to an extremely thin plate thickness by a stand tandem cold rolling mill, continuous annealing was performed. The thermal cycle was at 750 ° C. for 60 seconds. Subsequently, the rolling ratio was selected and rolled as shown in Table 2 by a temper rolling mill, and the final thickness was 0.32 mm. After temper rolling at various reduction rates shown in Table 2,
Using a chromate treatment bath containing 60 g / l of CrO _{3 and} 0.8 g / l of sulfuric acid, a chromate treatment was carried out using the shielding plate described in FIGS. 9 and 10 to finish TFS. Collected test material from TFS hardness (H _R -30T),

(Equation 1) Δr (Δr = (r _L + r _C −2r _D ) / 2), earrings, and evaluation of roughness of the can body were measured, and a bending test was performed to perform a fluting resistance test. In the evaluation of the flute test, bending was performed to correspond to the molding of the body of the can, and those that caused the body to break were not enough to be seen as a product (marked with x) and those that were not (marked with ○) Display). The hardness was measured for the entire width and the entire length of the coil. Also, after temper rolling, when finishing to chrome-plated steel sheet (TFS), it is painted and baked in a belt shape so as to bend in the direction perpendicular to the rolling direction, then sheared into a cutting plate, and Was further printed and baked clear. Splashing (spattering) of welding after forming by welding with a wire seam welding machine using a copper wire for the intermediate electrode as it is, without grinding and removing the plating layer of the weld in advance , And further, flange processing was performed with a die flanger, and flange cracking (HAZ cracking) was evaluated.

The finishing method of the chrome-plated steel sheet is No. 1
About 11, between the electrode and the strip at the time of chrome plating,
A "shield plate" was installed at the position corresponding to the width end of the strip to reduce the amount of chromium oxide in the weld. In addition, No. 12-1
No. 6, as before, was plated without using a "shield plate". In addition, painting and printing were performed without attaching an organic film to a position corresponding to welding. If necessary, repair coating may be applied immediately after welding, but this time the repair coating was not applied because the welding part was welded without grinding in advance.

From these results, it is clear that the steel sheet according to the present invention has a HAZ even when bent in a direction perpendicular to the rolling direction.
It is clear that the steel sheet is an excellent steel sheet which does not generate cracks and splashes and can be coated with a strip and welded without grinding.

[0083]

[Table 1]

[0084]

[Table 2]

[0085]

[Table 3]

[0086]

[Table 4]

[0087]

[Table 5]

[0088]

[Table 6]

[0089]

[Table 7]

[0090]

[Table 8]

[0091]

According to the present invention, since the ultra-low carbon steel capable of increasing the crystal grain size is used, a T1 material which could not be conventionally produced by the continuous annealing method using a single steel type can be produced.

[0092] Also, since the T1 material can be made,
T1 to T6, DR8 to DR1 by adding work hardening method
It is now possible to produce a zero temper sheet with a single steel grade. Therefore, the process time can be greatly reduced and rationalized.

Since the crystal grain size could be increased,
Conventionally, the bending and bending direction of the can body was performed only in the rolling direction. However, this method is reversed by 90 °, and after bending in the width direction of the sheet, performing welding, and performing flange processing,
AZ cracking did not occur. Since this feature has been obtained, coil coating can be performed instead of coating with a cutting board in the past, and the coating process was streamlined and the time was shortened.

Conventionally, a large medium-sized can such as an 18L can, a pail can, and an oil can was finished by welding using TFS, after grinding the Cr layer of TFS. Since the amount of Cr oxide was reduced by performing plating in which the amount of Cr adhered only to the portion was reduced, the welding could be improved without prior grinding. As a result, it was possible to solve the problem of dusting the welding plant, the inside of the can, and the scattering of the grinding powder, which was bad for environmental hygiene.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a three-piece can,
(A) shows an example of a beverage can, (b) shows an example of an 18L can, and (c) shows an example of a pail can.

FIG. 2 is an explanatory view of a manufacturing process of a three-piece can.

FIG. 3 is an explanatory view of a painting and cutting position of a conventional steel plate for a three-piece can.

FIG. 4 is an explanatory diagram of the flange processing.

FIG. 5 is a graph showing the relationship between the C content in steel and tinplate hardness.

FIG. 6 is an explanatory view of a joint, a coating and a cutting position of the steel plate for a three-piece can according to the present invention.

7A and 7B are cross-sectional views of a can body welding portion, in which FIG. 7A shows a case where an overlapping portion is thick, and FIG. 7B shows a case where the overlapping portion is thin.

[8] the temper rolling reduction ratio and Tin hardness (H _R -30
FIG. 9 is a diagram showing a relationship with T).

FIG. 9 is a diagram illustrating a method of reducing the amount of chromium oxide at both ends of the strip during the chromate treatment.

FIG. 10 is a diagram showing a result obtained by the method of FIG. 9;

[Explanation of symbols]

 S strip 1 cutting board 2 cutting line 3 slitting line 4 bending line 5 joining section 6 blank sheet 11 joining section 12 can body 13 canopy 14 bottom cover 15 handle 16 inlet 17 flange section 18 winding section 21 electrode 22 shielding plate

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 38/00 301 C21D 9/46 C23C 22/00 B23K 11/08 510

Claims (4)

(57) [Claims] 1. A steel plate having a central portion forming a can body and both end portions in a width direction of a joining plate, and a chromate-treated coating thereon, and bent at a right angle to a rolling direction to form an end portion in the width direction of the plate. A chromate-treated steel sheet for joining together to form a can, wherein the amount of chromium oxide in the chromate-treated coating at both ends in the width direction of the plate is smaller than the amount of chromium oxide in the chromate-treated coating at the center. possible the amount der to is, the steel sheet, the composition is a weight ratio, C: 0.004% or less, Si: 0.03% or less, Mn: 0.05~0.60%, P: 0.02 %: S: 0.02% or less, N: 0.01% or less, Al: 0.02 to 0.20%, Nb: 0.1 to 0.001%, Ti: 0.1 to 0.0001 %, Cr: 0.1% or less, Cu: 0.1% or less, Ni: 0.1% or less, B: 0 0.005% to 0.0001%, Mo: 0.01% or less, O: 0.01% or less, V: 0.01% or less, Zr: 0.01% or less, Ca: 0.005% or less, Sn: 0.01% or less, Sb: 0.01% or less, rare earth element (REM): 0.005% or less, Na: 0.001% or less, Mg: 0.001% or less, As: 0.01-0. 001%, Te: 0.01 to 0.0001% , with the balance being Fe and unavoidable impurities
Hot rolling, pickling, continuous casting slab made of low carbon steel
After cold rolling, continuous annealing is applied to this annealed plate.
Temper rolling by applying temper rolling with appropriately selected rolling reduction
Steel adjusted to T1 to T6 or DR8 to DR10
Excellent steel sheet for cans to Itadea Ru weldability. 2. The amount of chromium oxide in the chromate treatment film at the center is 10 mg / m ² or more, and the amount of chromium oxide in the chromate treatment film at both ends in the width direction of the plate is 10 mg / m ^2.
The steel sheet for cans excellent in weldability according to claim 1 , which is not more than / m ² . 3. The steel sheet for cans according to claim 1 or 2 , wherein the composition is, by weight, C: 0.004% or less, Si: 0.03% or less, and Mn: 0.05 to 0. 60%, P: 0.02% or less, S: 0.02% or less, N: 0.01% or less, Al: 0.02 to 0.20%, Nb: 0.1 to 0.001%, Ti: 0.1 to 0.0001%, Cr: 0.1% or less, Cu: 0.1% or less, Ni: 0.1% or less, B: 0.005 to 0.0001%, Mo: 0. 01% or less, O: 0.01% or less, V: 0.01% or less, Zr: 0.01% or less, Ca: 0.005% or less, Sn: 0.01% or less, Sb: 0.01% Rare earth element (REM): 0.005% or less, Na: 0.001% or less, Mg: 0.001% or less, As: 0.01 to 0.0 1% Te: contains from 0.01 to 0.0001%, the continuously cast slab balance consisting of ultra low carbon steel consisting of Fe and unavoidable impurities, hot rolling, pickling,
After performing cold rolling, continuous annealing is performed, and a tempered degree is adjusted to T1 to T6 or DR8 to DR10 by subjecting the annealed sheet to temper rolling that appropriately selects a reduction ratio, to obtain a steel strip. A method for manufacturing a steel plate for cans having excellent weldability, comprising: installing a shielding plate for a predetermined width at both ends in the width direction of the steel strip and performing an electrolytic chromate treatment. 4. A composition by weight: C: 0.004% or less, Si: 0.03% or less, Mn: 0.05 to 0.60%, P: 0.02% or less, S: 0. 02% or less, N: 0.01% or less, Al: 0.02 to 0.20%, Nb: 0.1 to 0.001%, Ti: 0.1 to 0.0001%, Cr: 0.1 %: Cu: 0.1% or less, Ni: 0.1% or less, B: 0.005 to 0.0001%, Mo: 0.01% or less, O: 0.01% or less, V: 0. 01% or less, Zr: 0.01% or less, Ca: 0.005% or less, Sn: 0.01% or less, Sb: 0.01% or less, Rare earth element (REM): 0.005% or less, Na: 0.001% or less, Mg: 0.001% or less, As: 0.01 to 0.001%, Te: 0.01 to 0.0001% Hot rolling, pickling, continuous casting slabs made of ultra-low carbon steel with a part consisting of Fe and unavoidable impurities
After performing cold rolling, continuous annealing is performed, and a tempered degree is adjusted to T1 to T6 or DR8 to DR10 by subjecting the annealed sheet to temper rolling that appropriately selects a reduction ratio, to obtain a steel strip. For this steel strip, for a predetermined width at both ends in the plate width direction, a shielding plate is installed and subjected to electrolytic chromate treatment,
After removing the predetermined widths at both ends in the sheet width direction of the chromate-treated steel strip, coating and baking both sides or one side of the steel strip, and then printing and baking as required, and then forming a right angle in the rolling direction. Cut to a predetermined length in the direction to be made, further blanking to form a blanking sheet, bending the blanking sheet in a direction perpendicular to the rolling direction, overlapping and joining the unpainted portion, then flange processing A method for manufacturing a three-piece can, comprising attaching and finishing a canopy and a bottom lid.