JPH07126806A - Steel sheet for can excellent in corrosion resistance and its production - Google Patents

Abstract

PURPOSE:To produce a steel sheet for a can excellent in corrosion resistance by subjecting the slab of a low carbon steel contg. small amounts of CaO-Al2O3 series inclusions to hot rolling, pickling, cold rolling and continuous annealing and thereafter executing temper rolling. CONSTITUTION:This is a low carbon steel having a compsn. contg., by weight, <0.02% or 0.09 to 0.2% C, <0.03% Si, 0.1 to 0.60% Mn, <0.02% P, <0.02% S, <0.02% N and 0.03 to 0.20% Al or furthermore contg. 0.001 to 0.1% Nb and 0.0001 to 0.0050% Bi, and by using an Al-Ca wire as a deoxidizer for the molten steel, the contents of O2 in the molten steel are regulated to <=30ppm, and nonmetallic inclusions are formed of soft Al2O3-CaO series having <=5mum grain diameter. This molten steel is rapidly rotated in a tundish, and the inclusions are aggregated and floated up to the central part to remove away. The obtd. molten steel high in cleanliness is cast, and the obtd. slab is subjected to hot rolling, pickling, cold rolling and continuous annealing and is thereafter subjected to temper rolling. The thin steel sheet for cans for food and drink which is soft or hard according to the difference in the contents of C and excellent in corrosion resistance is produced.

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 can which is subjected to a surface treatment such as plating, painting or film laminating and is subjected to press working, and particularly, the plating, painting and film laminating are broken by the press working. TECHNICAL FIELD The present invention relates to a steel plate for a can having excellent corrosion resistance for preventing corrosion due to corrosion and a method for manufacturing the same.

[0002]

2. Description of the Related Art Tin cans, which are tin-plated cold-rolled thin steel sheets, or tin-free steel (chromium, etc.) instead of tin, are used as can-making materials for food and beverage cans.
Generally, a surface-treated steel sheet having corrosion resistance such as l, TFS) is used. The main of these steel sheets for cans is tinplate, and their mechanical properties are Rockwell hardness (test load 30
kg, HR30T), tensile strength, yield point, elongation, etc., but most commonly it is indicated by the tempering degree that defines hardness. The tempering degree of the tin plate is specified in JIS G 3303 as follows. () Indicates target HR3 for manufacturing
Represents 0T, T-in order from soft to hard
1 (49 ± 3), T-2 (53 ± 3), T-3 (57 ±
3), T-4 (61 ± 3), T-5 (65 ± 3), T-
6 (69 ± 3), DR-8 (73), DR-9 (7
6), DR-9M (77), and DR-10 (80). Of these, T-1 to T-3 are so-called soft tin plate and T-4 to T-6 are hard tin plates, all of which are single-rolled products (single reduce, SR material). This SR material is annealed and further rolled to obtain a DR (double reduce) material.

Among the SR materials, the soft tin plate is a low carbon A
It is manufactured by a box annealing method using l-killed steel as a raw material, and is often used as a can steel plate for two-piece cans because it has good formability such as drawing. On the other hand, the hard tin plate is
It is manufactured by the continuous annealing method (CAL method) using low carbon Al killed steel whose C, N and Mn contents are adjusted, and has high productivity.

[0004] The DR material is manufactured by annealing the above SR material tin plate and then cold rolling it again, and becomes harder by work hardening. By the way, recent food cans,
BACKGROUND OF THE INVENTION Many beverage cans are so-called two-piece cans that are composed of two parts, a can body having a body and a bottom integrated with a lid.
In this product, tin-plated cold-rolled steel strip is cut into sheets of specified dimensions to form tinplate sheets, the surface of which is coated with a thermosetting resin and baked in a baking oven, and then the outer surface of the can. The surface of the can is printed and baked, and then the press body and drawing process are used to form the can body with the can body and bottom. The contents are filled in this, and a lid manufactured separately is attached. As a steel plate for a can, which is used for integrally forming the can body and the bottom in this way, the soft tin plate of T-1 to T-3, which has good press workability even with the SR material, is T-4 to T. It is more suitable than -6 hard tin plate.

Steel plates for cans used for such food cans and beverage cans are inevitably the important quality factor of corrosion resistance, and in order to improve them, it is important to improve the cleanliness of the original plate. However, the concrete measures have not been proposed yet. Therefore, in the production of T-1 to T-3 soft tin plate having good workability using the CAL method of continuous annealing, which is easier to obtain corrosion resistance superior to the box annealing method, the production of a steel sheet for cans having excellent corrosion resistance Development of a method was desired.

Recently, reduction of the cost of empty cans has become an important issue, and as one of the countermeasures against this, LTS (Lightly tin coated s) which reduces the tin weight per unit area of tinplate.
teel) is being used. As another measure, the weight reduction of empty cans is rapidly progressing. However, if the weight per unit area of tin is reduced, the corrosion resistance due to tin is reduced accordingly, and if the weight reduction of empty cans is promoted, the reduction of can strength is inevitable.

Therefore, there has been a demand for a master plate that can compensate for the deterioration of corrosion resistance due to the weight loss of tin. Also,
Regarding the reduction in can strength due to weight reduction, measures have been taken to ensure can strength by devising a can design, and complex can shapes are emerging. FIG. 1 shows an example of a can design that improves can strength. In the same figure (a), neck-in processing is applied to the top and bottom corners of the can.
A single-neck-in can with a stepped neck-in 1 is shown, (b) is a double-necked-in can with two stepped-in necks 2 at the top and bottom corners of the can, and (c) is a three-sided can at the top and bottom corners of the can. It is a triple neck-in can in which a stepped neck-in 3 is formed. Further, the number of stages of neck-in of 4 steps and 5 steps is increased and the diameter is reduced to increase the strength of the can. Further, in each case, the bead 4 is formed to improve the strength of the can body. In this way, it is recognized that the shape of the can gradually becomes more complicated than that of the conventional straight can shown in FIG.

Apart from reinforcement by such a can design,
Furthermore, for the same purpose, ultra-thin and high-strength steel plates are required as steel plates for cans, and are not specified in JIS standards, such as DR.
Ultra hard materials corresponding to -11 and DR-12 are also required.

[0009]

As described above, the recent steel plates for cans are thin tinted steel plates (LTS), ultra-thin and high-strength steel plates for the purpose of reducing the cost of empty cans, as described above. There is an increasing trend towards the adoption of complex can designs that compensate for the reduction in strength due to thinning.Therefore, compared with the era of conventional straight cans, where relatively thick steel plates are used to form simple shapes, Processing conditions are becoming more complicated and severe. Along with this tendency, the problem of deterioration of corrosion resistance from the can processing part has arisen. This phenomenon is similarly observed not only in the main body of the can, but also in the can lid that is beginning to employ ultra-thin high-strength steel sheets, and deterioration of corrosion resistance in the paneling portion of the can lid is beginning to be considered a problem.

In addition, for the purpose of improving the environment, coil-coated steel sheets for two-piece cans and film-laminated steel sheets are being adopted, but ultra-thin and high-strength steel sheets are used for these steel sheet materials, and severe processing is performed. At the same time, problems such as tearing of the coating film in the pressing process and tearing of the film laminate film to impair the corrosion resistance are beginning to be seen.

In order to avoid such troubles of deterioration of corrosion resistance, one important solution is to obtain a steel sheet for cans having excellent corrosion resistance and improve the corrosion resistance of the original plate itself.
It has already been known that such a steel sheet having good corrosion resistance can be easily obtained by manufacturing by the CAL method of continuous annealing. However, conventionally, the CAL method has not been able to obtain the same softness as the steel sheet obtained by the box annealing method.

That is, in order to manufacture a soft original plate by the CAL method, metallurgically, (1) the crystal grain size is increased,
(2) It is considered possible if the content of the age hardening component (solid solution C, solid solution N, etc.) is reduced. But in reality,
To increase the crystal grain size, the amount of C should be reduced,
On the contrary, when the amount of C is reduced (about 0.01%), the amount of dissolved C remains large, which is offset by the amount, so that the C does not become soft.

Therefore, by solving the conventional contradictory problems that have occurred when trying to obtain a soft original plate by the CAL method, (A) the amount of solid solution C can be drastically reduced and the crystal grain size is large. There has been a demand for a steel plate for soft cans that has excellent corrosion resistance and a manufacturing method thereof. On the other hand, as the original plate for a two-piece can manufactured by the press working method, the soft tin plate manufactured by the box annealing method having excellent press workability was adopted, but due to the improvement of the press working technology in recent years, It has become possible to use hard tin plate, which has been difficult in the past. In addition to this, by adopting a coated steel sheet or a film laminated steel sheet, it is possible to significantly improve the deep drawing workability by utilizing the lubrication effect of the coating and film. Therefore, double rolled material (DR material) and even J
Although an ultra-hard material, which is not in IS, has been used as a steel material for cans, such an ultra-hard steel sheet material for a can is manufactured by the conventional CAL annealing and double rolling process of low carbon Al killed steel. Can't get it.

Accordingly, in response to such recent progress in press working technology, there has been a demand for (B) a hard steel sheet for cans having excellent corrosion resistance and a manufacturing method thereof.
The present invention has been made in view of such a demand, and an object thereof is to provide a soft can steel sheet having excellent corrosion resistance and a method for manufacturing the same. Further, another object of the present invention is to
It is intended to provide a hard can steel plate having excellent corrosion resistance and a manufacturing method thereof.

[0015]

[Means for Solving the Problems] A book that achieves the above object.
In the steel sheet for a can according to claim 1 of the invention, the component composition is a weight ratio,
C: 0.08% or less, Si: 0.03% or less, Mn: 0.1 to 0.60
%, P: 0.02% or less, S: 0.02% or less, N: 0.02% or less
Bottom, Al: 0.03 to 0.20%, the balance except inevitable impurities
A carbon steel made of Fe with a total oxygen content of 30 pp
m or less, Al in steel ₂O₃Maximum diameter of system inclusions is 5 μm or less
The one below.

The steel sheet for a can according to claim 2 of the present invention is an ultra-low carbon steel having a carbon content of 0.02% or less in the composition of claim 1. Further, according to the steel plate for cans of claim 3 of the present invention, the carbon content in the component composition of claim 1 is 0.09 to 0.2%.
It is made of carbon steel. A steel sheet for a can according to claim 4 of the present invention is one in which Nb: 0.1 to 0.001% and B: 0.005 to 0.0001% are contained in the composition of any of the above claims 1 to 3.

In the steel sheet for cans according to claim 5 of the present invention, the composition of inclusions in the steel represented by any of the component compositions according to any one of claims 1 to 4 is CaO-Al ₂ O ₃ system. It is a thing. Further, the method for producing a steel sheet for a can of the present invention is such that the molten steel is degassed, decarburized and deoxidized and then transferred to a tundish to cause non-metallic inclusions to flocculate and separate by a swirling flow. The hot rolled, pickled and cold rolled steel slab of No. 2 is continuously annealed and then temper rolled.

[0018]

[Function] Among the non-metallic inclusions in the steel, Al ₂ O ₃ -based inclusions exposed on the surface of the original plate have a great influence on the occurrence of corrosion of the steel plate for a can. If the size of the Al ₂ O ₃ -based inclusions exceeds 5 μm, the base metal around the inclusions will be dissolved or pinholes will be generated in the tin plating when they come into contact with the corrosive liquid. If it is 5 μm or less, it does not act as a corrosion factor.

When the amount of Al in the steel is 0.03% or more, the amount of oxygen in the steel sharply decreases to 30 ppm or less, and at the same time, the size of Al ₂ O ₃ type inclusions also becomes 5 μm or less. In order to improve the corrosion resistance of the steel sheet for cans, in addition to controlling the presence of Al ₂ O ₃ -based inclusions having a size of more than 5 μm, Al ₂ O
It is also effective to control the morphology of ₃ type inclusions. That is, instead of introducing metallic Al into molten steel to deoxidize it, A
When deoxidized using the 1-Ca wire, the hard Al ₂ O ₃ -based inclusions change into a soft Al ₂ O ₃ -CaO form, and corrosion is prevented.

When the amount of C in the molten steel for producing the continuously cast steel billet, which is the starting material for the steel sheet for cans, is extremely reduced, the amount of solid solution C after annealing is reduced, and a product excellent in aging is obtained. To be Further, since carbides are also drastically reduced, a product excellent in corrosion resistance can be obtained. According to the present invention, the refining degree T-1 obtained by the continuous annealing method (CAL method) is controlled by making the amount of C extremely small.
A considerable amount of soft original plate can be manufactured. Furthermore, N is a carbide and nitride forming element in the steel during continuous cast steel production.
When b and B are added, the amounts of solid solution C and solid solution N are stably reduced, and it becomes possible to manufacture a T-1 equivalent soft original plate having more excellent mechanical properties and deep drawing workability.

Further, according to the present invention, the reduction ratio of the temper rolling is adjusted so that the tempers T-1 to T-6 and further the corrosion resistance of arbitrary hardness equivalent to the DR material are excellent. It is also possible to make steel sheets. Further, according to the present invention, conversely, when the CAL method is performed using a steel slab added with a larger amount of C than usual, it becomes hard even if the rolling reduction of the double rolling is low, and the rolling time is shortened as compared with the conventional one. It was found that the double-rolled product (DR product) can be manufactured as a steel sheet for cans having excellent corrosion resistance. By increasing the rolling reduction to some extent, an ultra-hard original plate that is more than a double rolled product can be obtained.

The present invention will be described in more detail below. [1] First, the means for producing a soft tin plate by the CAL method will be described. The present inventors effectively utilize vacuum degassing treatment during steel making and use an Al-killed steel slab with a very small amount of C, so that a soft original plate having a temper T-1 can be obtained by the CAL method as well. By using a slab that can be manufactured and contains Nb and B which are carbide and nitride forming elements in the above Al killed steel, it is equal to or more than that obtained by the conventional box annealing method. It has been found that it is possible to manufacture an original plate having mechanical properties and deep drawing workability.

That is, the present inventors systematically investigated the influence of solid solution C and solid solution N on the hardness of tinplate and the relationship with the crystal grain size. It was found that the amount becomes small and the crystal grain size becomes large, the material becomes soft. Based on this finding, in order to reduce the amount of solid solution C and the amount of solid solution N after annealing, it was considered that the amount of C in the molten steel for producing a continuous cast steel slab, which is a starting material, should be extremely reduced. Also, N becomes soft as it is deposited as AlN as much as possible.

As a result of repeated studies based on these viewpoints, it is possible to obtain a base plate having a temper degree T-1 even by the CAL method, and by changing the reduction ratio of temper rolling, T-1 to T- 6 Furthermore, it was found that it is possible to manufacture a master plate of a double-rolled DR product. In addition, when manufacturing the said steel slab, since the amount of solid solution C and the amount of solid solution N can be reduced stably by adding Nb and B, it was also discovered that the more excellent T-1 original plate can be manufactured. [2] Next, a method for manufacturing a double-rolled product and an original plate required to have a hardness higher than that will be described.

By the method [1] described above, a double rolled product can be manufactured. The steel sheet of this system is based on an ultra-low carbon steel having a large crystal grain size, and therefore has a property of excellent deep drawability. The reduction rate is inevitably high and the rolling time is long. Therefore, as a result of the research and development of a steel sheet having excellent double-rollability and capable of being efficiently manufactured, the present inventors have added a larger amount of C than usual, which is completely opposite to the case of an ultra-low carbon steel. When the CAL method is performed using a steel piece that is a fine-grained steel plate, it becomes hard even if the reduction ratio of the double rolling is low, and if the reduction ratio is slightly increased, it is possible to manufacture a base plate having a hardness exceeding the double rolling. I found it.

On the other hand, an extremely thin plate. Trouble due to corrosion resistance also occurred in the finished food cans and beverage cans having a complicated can shape using the high-strength steel plate. Therefore, the present inventors have conducted a large-scale and detailed investigation on the cause of the deterioration of corrosion resistance that occurs particularly in the thin tinned steel sheet, in relation to the material, and obtained the following serious results.

First, regarding the can whose inner surface is corroded,
The steel plate surface of the corroded part was observed with an electron microscope. As a result, it was found that the coating film was destroyed and pinholes were formed in the tin layer directly under the coating film, and the following investigation was further focused on this. That is, when making steel in the steelmaking process, the deoxidation method of molten steel is (A) Mn alone deoxidation-vacuum degassing, decarburization, deoxidation method, (B) Al small amount addition weak deoxidation-vacuum degassing, degassing Carbide, deoxidation method, (C) Al strong deoxidation-vacuum degassing, decarburization, deoxidation method are used to make steel pieces with a continuous casting machine. 10) A tin plate was produced.

Using this tin plate, a DRD can (Drawn
& Redlawn Can) was prepared, a can was filled with a highly corrosive seasoning liquid of fish meat, and the mixture was stored at 75 ° C. in a temperature-controlled room to carry out a corrosion acceleration test. The results were as follows. 1) Some ones began to corrode after one year had passed.

2) A difference in the degree of corrosion was recognized due to the difference in the deoxidizing method during steelmaking. From this, it is estimated that the cause of corrosion is also caused by the DRD processing in which cans are manufactured by press working, but the origin thereof is derived from the raw material plate. Table 1 shows the relationship between the corrosive can and the steel type in this corrosion test. The corrosive can was most often found in steel B, followed by steel C and steel A in that order.

[0030]

[Table 1]

Since the generation of corrosive can differs depending on the steel type (deoxidizing method), in order to pursue the metallurgical cause,
With respect to the tin tint (No. 10 basis weight) tin plate, which was the same as that used in the above-mentioned investigation, the tin plate surface was observed in detail with an electron microscope. As a result, the pinhole 5 in the tin layer as shown in the sketch of FIG. 2 was recognized, and the existence of non-metallic inclusions in the original plate (metal) was confirmed.

Then, when the tin layer on the surface of the same tin plate was peeled by the electrolytic peeling method and the surface of the original plate was observed again with an electron microscope, nonmetallic inclusions were found on the surface of the original plate (bare metal). It was also found that the composition of the non-metallic inclusions differs depending on the deoxidation method. Table 2 shows the number of non-metallic inclusions detected for each steel manufacturing method and composition of non-metallic inclusions.

[0033]

[Table 2]

In the steel A which was deoxidized by Mn alone-vacuum degassing, decarburized and deoxidized, the number of inclusions was large, but no Al ₂ O ₃ type was detected. In Steel B, which was Al weakly deoxidized-vacuum degassed, decarburized, and deoxidized, many Al ₂ O ₃ -based inclusions were detected. Its grain size is 12 compared to Steel C described later.
It was as large as ˜35 μm.

In the case of steel C that had undergone strong Al deoxidation-vacuum degassing, decarburization, and deoxidation, the number of Al ₂ O ₃ -based inclusions was extremely small, and the grain size was small, _{3 to} 11 μm. FIG. 3 shows the relationship between the number of Al ₂ O ₃ -based inclusions among the nonmetallic inclusions and the corrosion can generation index. From this graph, it was found that there is a very good correlation between the two. However, no correlation was found between the total number of non-metallic inclusions and the corrosive can generation index.

From the above results, it can be presumed that it is the Al ₂ O ₃ type inclusions exposed on the surface of the original plate which are the non-metallic inclusions in the steel that have a bad influence as the cause of the corrosion can. . Next, Al ₂ O ₃ system inclusions and MnO, Mn
It was detected that inclusions having different components such as S were exposed on the surface of the original plate, and the original plate was directly corroded with a corrosive liquid, and then similarly observed with an electron microscope. FIG. 4 shows the state after corrosion of Al ₂ O ₃ -based inclusions having a grain size of 16 μm, and FIG. 5 shows MnO and MnS.
After the corrosion of the system inclusions, a sketch of the observation field is shown.

From this observation, Fe (metal) around the Al ₂ O ₃ -based inclusions was largely dissolved, whereas M
It was found that Fe around the nO and MnS inclusions was hardly dissolved. Further, it was also found that the surrounding Fe was not dissolved in the Al ₂ O ₃ —CaO inclusions.
From these facts, the inclusions related to the corrosion of canned goods are Al
_It could be concluded that it was a ₂ O ₃ type inclusion.

Next, in the case of Al-killed steel, it is difficult to eliminate Al ₂ O ₃ -based inclusions industrially, and extremely minute ones that have not been found by electron microscope magnification should be exposed. However, if all of the exposed Al ₂ O ₃ -based inclusions lead to corrosive cans, it could be predicted that more corrosive cans may be generated. The difference between the predicted number of corrosive cans and the actual number indicates that there are some Al ₂ O ₃ -based inclusions that can actually become corrosive cans, and some do not, that is, do not cause harm. Thought to be Therefore, Al ₂ O ₃ -based inclusions having a size of about 5 μm, 10 μm, and 15 μm were detected and selected by an electron microscope, and the above-described corrosion test was performed on these samples.

As a result, in order for the metal around the Al ₂ O ₃ -based inclusions to be largely dissolved, the inclusions must have a certain size or more, and the Al ₂ O _{3 having} a size of 5 μm or less is required.
It was also found that even if the system inclusions were exposed on the original plate, dissolution was not affected. Similarly, as a result of observing the relationship between the size of the Al ₂ O ₃ -based inclusions and the pinhole of the tin layer by tinting the basis weight of 1.12 g / m ² , the result was 5 μm as in the corrosion test.
It was also clarified that the pinholes in the tin layer were generated from the places where the Al ₂ O ₃ -based inclusions having a size larger than the above were present.

The reason why the metal around the large Al ₂ O ₃ -based inclusions is dissolved is that the Al ₂ O ₃ -based inclusions have a high melting point and are not divided during rolling because they are superhard. It was considered that cracks occurred in the base metal during temper rolling and corrosion proceeded from there. On the other hand, in the case of MnO and MnS inclusions, since they have a low melting point and are soft, they are elongated in the rolling direction by hot rolling and cold rolling, and are elongated into individual pieces. The number of cracks that can become the starting point of corrosion is drastically reduced.

From the above, if a large Al ₂ O ₃ -based inclusion is exposed on the surface of the original plate, it becomes a pinhole in the tin layer of tinplate, and when it comes into contact with the corrosive liquid, the surrounding metal is largely dissolved. It can be easily guessed that it will become a corrosion can. On the other hand, the number of non-metallic inclusions present in Steel A is very large, but the size thereof is present in a continuous form with a size of about several tens of μm, and if this is plated with tin, it is sufficiently covered with tin. Because it is hidden, it is unlikely to cause any problems.

The composition of non-metallic inclusions is MnO, Mn.
Steel C, which is mainly S, has a low degree of melting of the surrounding metal,
There is a small amount of small Al ₂ O ₃ inclusions, but 5μ
Some of them exceed m, and it is considered that the metal around them melts to form a corrosion can. From the above, it can be said that a can steel sheet having excellent corrosion resistance is required to have cleanliness that does not lead to a corrosive can.

However, deoxidation with Mn causes another problem that a large amount of Mn is required and thus the product cost becomes high, and the work becomes hard and the workability deteriorates. Based on the investigation results as described above, Al ₂
Since the number and size of O ₃ -based inclusions were estimated to be related to the amount of Al in steel, the present inventors next examined the amount of Al in steel, oxygen in steel (corresponding to the total amount of inclusions) and Al. The relationship with the size of ₂ O ₃ -based inclusions was investigated.

As a result, it was found that when the amount of Al in the steel was increased to 0.03% or more and vacuum degassing, decarburization, and deoxidation treatment were performed, the amount of oxygen in the steel also decreased. However, the size of the inclusions did not fall below 5 μm. Since this oxygen easily forms Al ₂ O ₃ clusters in the Al strong deoxidized steel, it becomes apparently large inclusions and floats and separates according to Stokes' law, and it is considered that the oxygen content in the steel has decreased. . Correspondingly, Al _{2 in} steel
The amount of O ₃ -based inclusions is also reduced.

The present inventors have studied to reduce the size of inclusions remaining in steel to 5 μm or less based on the findings obtained as described above. That is, in the continuous casting method, for example, by utilizing the “apparatus for removing non-metallic inclusions in molten metal (Japanese Patent Laid-Open No. 1-312024)” previously filed by the present applicant, the molten steel of the ladle is placed in the apparatus. Was introduced into the tundish, and an attempt was made to make molten steel in the tundish into a swirl flow. As a result, when the steel is cast after the swirling flow, the oxygen content in the steel is reduced to 30 ppm or less, and at the same time, the amount of exposed inclusions becomes 5
It was found to be less than μm. Using the steel thus obtained, a tinted tin plate is manufactured by a conventional method, and using the tin plate, a DRD can is formed in the same manner as described above, and the corrosive fish meat is corroded by a seasoning liquid. The place where the acceleration test was done,
It was newly found that no corrosion cans were generated.

Furthermore, the present inventors have made extensive studies based on the above findings in order to control the morphology of Al ₂ O ₃ type inclusions. A method for controlling the morphology of Al ₂ O ₃ -based inclusions includes
Conventionally, a method of deoxidizing a metal Al rod by inserting it into molten steel has been carried out. However, the present inventors used Al instead of the metal Al rod.
-The method of deoxidizing using Ca wire was adopted. This is because it is considered that the inclusions can be changed to the form of Al ₂ O ₃ —CaO. The steel thus obtained was tinted by a conventional method, and a pinhole inspection in the tin layer and a non-metallic inclusion inspection in the original plate were performed. As a result, 2000
There is no Al ₂ O ₃ type inclusion of about 1 μm or more that can be detected at a magnification of ₂ times, and even if an inclusion of 5 μm or more is detected, it is all controlled by Al ₂ O ₃ -CaO. Was confirmed.

A DRD can was manufactured using this tin plate, and corrosion was evaluated by the above-described corrosion acceleration test. As a result, no corrosive can was found. From the above, ultra-thin high-strength steel sheets are used to maintain a strong can with a complicated can design, and in addition, tin can reduce the weight of tin to reduce the cost of empty cans, but corrosive cans do not corrode. In order to produce a steel sheet for cans that does not generate corrosion and has excellent corrosion resistance, there is no super hard Al ₂ O ₃ inclusions of 5 μm or more.
It has been newly revealed that the pm or less is effective, and the following means are effective for that.

The Al content in the steel is increased to 0.03% or more to obtain a steel having a low total oxygen content. The inclusions are controlled to form Al ₂ O ₃ —CaO. Inclusions are separated and removed by using the molten steel flow in the tundish as a swirling flow to produce steel in which the total oxygen content in the steel is 30 ppm or less, and this is used as a base plate. The present inventors have completed the present invention based on the findings obtained in the above research.

The critical significance of the content of each component element of the steel sheet for cans excellent in corrosion resistance of the present invention will be described below. C: 0.08 (wt)% or less of low carbon steel Carbon (C) has a great influence on hardness. T-1 to T-
In order to obtain hardness products of 6, DR-8 to DR-10,
The carbon content may be 0.08% or less, and the required product can be manufactured by satisfying the limiting conditions and adjusting the content according to the target hardness. However, as shown in FIG.
When the amount is 0.004 or less, it becomes soft, while when the amount of C increases, the hardness becomes highest at about 0.01%. Therefore, in order to manufacture a soft tin plate having a temper of T-3 or less by the CAL method, the C content needs to be 0.004 or less. In order to obtain a temper of T-3 or more with an extremely small amount of carbon, the rolling reduction of the temper rolling is set to a value according to the required hardness. Or 2
It can be obtained by rolling twice. In the case of carbon steel of C: 0.09 to 0.2% In order to obtain a superhard material having a product rolled twice or more, contrary to the above, the C content should be 0.09% or more and temper rolling at a low pressure reduction ratio. . However, if the amount of C exceeds 0.20%, it becomes hard and the flange formability deteriorates, so it is made 0.20% or less. Si: 0.03% or less Since Si is an element that deteriorates the corrosion resistance of tinplate and further hardens the material extremely, it should be avoided that Si is excessively contained. Therefore, Si is 0.03%.
Must be: Mn: 0.1 to 0.60% Mn is generally added to prevent the occurrence of ear cracks in the hot rolled coil. The amount necessary for preventing the occurrence of ear cracks is 0.05% or more of Mn, but in the present invention, the lower limit is set to 0.1% because the deoxidizing power of Mn is also utilized. On the other hand, Mn is also a substitutional solid solution strengthening element, so it is an effective component for forming a superhard material and is added as necessary. However, even if it is added in large amounts, it is not economical, so its upper limit is 0.60.
%.

S: 0.02% or less If S is contained excessively in relation to the amount of Mn, it will cause edge cracking of the hot rolled coil. Therefore, its content is 0.02%
Below. P: 0.02% or less P is an element that hardens the material and deteriorates the corrosion resistance of tinplate, so excessive content is not preferable and its content is
It should be 0.02% or less.

Al: 0.03 to 0.20% Al is an effective component for drastically reducing Al ₂ O ₃ inclusions, and the lower limit must be 0.03% even if vacuum degassing treatment is combined. The upper limit is 0.20% for economic reasons. N: 0.02% or less N is an unnecessary element that makes it difficult to obtain a soft steel sheet when it is in solid solution in steel, so its content must be 0.02% or less.

Nb: 0.001 to 0.1% Nb is a carbide forming element and has the function of reducing the amount of solid solution C remaining and improving the workability. To obtain these effects, 0.001% or more is added. is necessary. On the other hand, if added in a large amount, the production cost rises, so it is preferable to make it the necessary minimum. Further, due to the pinning effect of the crystal grain boundaries by the Nb-based precipitates, the recrystallization temperature becomes high and the workability of the continuous annealing furnace during striping deteriorates.
1% or less.

B: 0.0001 to 0.005% B, together with Nb, has an effect of preventing excessive coarsening of crystal grains. It is also useful for preventing secondary processing brittleness. Since B is a nitride-forming element, it is effective for softening, but B segregates at the recrystallization grain boundaries during continuous annealing and delays recrystallization, so the content is made 0.005% or less, and the lower limit is necessary to exert the above effect. It should be 0.0001% or more.

O: 30 ppm or less O must be 30 ppm or less in order to reduce Al ₂ O ₃ type inclusions as described above. If it is contained in excess of this amount, it forms an oxide with Al, Mn in steel, Si in refractory, Ca, Na, F, etc. in flux, which causes deterioration of the corrosion resistance of the can.

[0055]

EXAMPLES The present invention will be described in detail below with reference to examples. Steel 250t having the composition shown in Tables 3 and 4 was melted by a bottom blowing converter. Tables 5 and 6 show steel making conditions and rolling conditions. Table 3 shows the composition of the steel of the present invention.

[0056]

[Table 3]

Table 4 shows the composition of the comparative steels.

[0058]

[Table 4]

Table 5 shows the steel making and rolling conditions of the steel of the present invention.

[0060]

[Table 5]

Table 6 shows the steel making and rolling conditions for the comparative steels.

[0062]

[Table 6]

Those finished so as to have a C content of 0.03% or less (inventive steel Nos. 1 to 7 and all of the comparative steels) were smelted to have a C content of 0.03%, and then tapped, followed by R- H After vacuum degassing treatment to decarburize and deoxidize C to less than 0.03%,
l wire is introduced to deoxidize Al, and then Nb, Ti and B which are carbide and nitride forming elements are added if necessary,
We proceeded to continuous casting. In the steel of the present invention, in order to control the morphology of inclusions, instead of the Al bar, Al-Ca wire (C
(mixed with a) is also used.

Those finished so that the C content exceeds 0.03% (steel Nos. 8 to 15 of the present invention) were smelted to have a C content of 0.03%, and then tapped, followed by RH vacuum degassing treatment. After deoxidizing with C, C is added if necessary, and then Al, carbide,
A nitride-forming element was added if necessary, and the process was similarly advanced to continuous casting. For comparison, Comparative Steel Nos. 17 and 18 were manufactured with the amount of Al added less than the lower limit of 0.03% of the steel of the present invention. In addition, the amount of each component underlined in Table 4 of the comparative steel is a content outside the range of the steel of the present invention.

In order to remove the Al ₂ O ₃ -based inclusions generated by Al deoxidation by flocculation and separation by aggregation, degassing was performed for an appropriate time. Therefore, the tapping temperature was set high. In order to prevent non-metallic inclusions from remaining in the steel, the steel was cut into pieces with a converter and a coagulant was added to the pieces brought into the ladle to make it inert. Next, in continuous casting, a refractory nozzle was installed to prevent air from entering the ladle when transferring it from the ladle to the tundish. Poured.

Tundish (T / D) is large (75
In the case of the present invention steel and comparative steel No. 1
Regarding No. 8, molten steel in T / D was swirled using an electromagnetic stirrer and then poured into a mold. For other comparative steels, instead of the swirl flow method using an electromagnetic stirrer, casting was performed by a method of constructing a conventional weir, which was devised so that inclusions could be flocculated and aggregated in the T / D for comparison.

On the other hand, as the immersion nozzle at the time of injecting from the T / D into the mold, a nozzle having a nearly horizontal angle was used so that inclusions were not carried deep into the mold. In addition, the continuous casting machine is a vertical bending type continuous casting machine, and even if it is a small amount, it is devised so that the mixed inclusions are not deeply carried and trapped in the viscous layer, and the cleanliness of the inclusions is small. Care was taken to produce high ultra-cleanliness billets.

Next, the slab slab obtained by the above continuous casting was hot-rolled, pickled, cold-rolled, continuously annealed, and temper-rolled (where the rolling ratio was changed to 1 to 50%, the steel sheet (See Table 5 and Table 6), and then processed through various processes such as halogen type electrotin plating and epoxy phenolic coating to make tin plate for canning, and further manufacture using this tin plate. I made a can.

The can was filled with a seasoning liquid for fish meat as a content, and a time course was measured in a constant temperature chamber at 75 ° C. for one year. In addition, this can used the thing which performed each neck-in process of the single, double, and triple shown in FIG. The tests and inspection items conducted in the above-mentioned time course examination were a rust resistance test, inclusion inspection, and a leak can test.

In the rust resistance test, the uncoated test piece was kept for 96 hours in a test tank in which the dry state and the wet state were repeated every 30 minutes under the following conditions for 96 hours, and the rusting condition was observed. Dry state [Temperature 25 ° C, relative humidity 50%] Wet state [Temperature 50 ° C, relative humidity 98%] The results are shown in the table with a mark X when rust was observed, and with a mark O when it was not. 5, shown in Table 6.

The inclusions are inspected by observing 200 fields of view with a JIS optical microscope at a magnification of 400 times and observing Al ₂ O _{3 of} 5 μm or more.
The system inclusions were observed. The results are shown in Tables 5 and 6 in which the inclusions were found in x and the inclusions were not found. In the leak can test, the filled seasoning liquid is visually inspected for leaks, and if leaks are found, x
The marks and those not found are indicated by ◯ and shown in Tables 5 and 6.

According to the test results, in the case of each neck-in processed can using the steel of the present invention, the deoxidizing method is the Al bar deoxidizing method or the A deoxidizing method.
No leak cans were generated regardless of the l-Ca line deoxidation method.
On the other hand, a leak can having an occurrence rate of 1 ppm was generated from the one using the conventional steel billet by the Al rod deoxidizing method. No leak cans were generated in the steel containing oxygen of 30 ppm or less and the Al ₂ O ₃ -based inclusions having a particle diameter of 5 μm or less. Therefore, it has been found that the improvement of the cleanliness of steel has the effect of preventing the formation of a corrosion can.

After the electroplating with tin, the sample material was sampled and the Rockwell hardness (HR-30T) was measured. As a result, if the steel sheet had a composition within the range regulated by the present invention, the CAL method was used. The quality T-1 is obtained, and the workability is further increased by increasing the rolling ratio of temper rolling (steel No. 2, 3, 4, 5, 6, 7 of the present invention). T-2 to T-6 or DR-8 to DR- depending on the rate
It was revealed that 10 products were obtained.

Rockwell hardness (HR-30T) of 5
After the temperature is set to 0 or less, the tempering rate of the temper rolling is T-1 to T.
Can be divided into -6.

[0075]

As described above, according to the present invention,
While adjusting the Al content in the steel to 0.03% or more, the total oxygen content in the steel is 30 ppm or less, and the maximum diameter of the Al ₂ O ₃ -based inclusions in the steel is 5 μm or less.
Hot rolling, pickling, cold rolling followed by continuous annealing in the usual manner,
After that, the soft rolling material T-1 is obtained by temper rolling, and T-1 to T- can be obtained by changing the rolling ratio of the temper rolling.
6, DR-8 to DR-10 soft, hard, and super hard materials are created, and even in cans that have been subjected to various neck-in processes, it is possible to prevent the occurrence of leaking cans, improve productivity, and improve the defect rate. It is possible to obtain the effect of improving the above.

The steel sheet for cans having excellent corrosion resistance according to the present invention can be applied to Sn, Ni, Cu and Zn plating, and can be applied to DRD cans, DTR cans and DWI cans after coil coating or film lamination on these plated steel plates. It goes without saying that even if it is applied, it becomes a complete can.

[Brief description of drawings]

FIG. 1 is a diagram illustrating various can designs, in which (a) is a single neck-in can, (b) is a double-neck-in can, and (c).
Is a triple neck-in can, and (d) is a straight can.

FIG. 2 is a sketch diagram in which non-metallic inclusions on the tin plate surface subjected to a corrosion test are observed with an electron microscope.

FIG. 3 is a graph showing the relationship between the number of non-metallic inclusions in a can steel sheet and the corrosive can generation index.

FIG. 4 is a sketch diagram in which an Al ₂ O ₃ type inclusion on the tin plate surface subjected to a corrosion test is observed by an electron microscope.

FIG. 5: MnO and MnS on tin plate surface subjected to corrosion test
It is the sketch figure which observed the system inclusion with the electron microscope.

FIG. 6 is a graph showing the relationship between the amount of Al in steel and the amount of oxygen in steel.

FIG. 7 is a graph showing the relationship between the amount of C in steel and the Rockwell hardness of steel.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Minoru Ryusho Inventor 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Yasuko Furusho 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Co., Ltd. Chiba Works (72) Inventor Akio Tosaka 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.

Claims (6)

[Claims] 1. The weight ratio of the components is C: 0.08% or less,
Si: 0.03% or less, Mn: 0.1 to 0.60%, P: 0.02% or less, S: 0.02% or less, N: 0.02% or less, Al: 0.03 to 0.
Carbon steel consisting of 20%, the balance being Fe excluding unavoidable impurities, the total oxygen content in the steel being 30 ppm or less, Al in the steel
_A steel sheet for cans having excellent corrosion resistance, which has a maximum diameter of ₂ O ₃ -based inclusions of 5 μm or less. 2. A steel sheet for cans having excellent corrosion resistance, which is made of an ultra-low carbon steel having a C content of 0.02% or less according to claim 1. 3. A steel plate for a can having excellent corrosion resistance, which is made of carbon steel having a C content of 0.09 to 0.2% in claim 1. 4. Nb: 0.001 to 0.1% in the composition, B: 0.
The steel sheet for cans having excellent corrosion resistance according to any one of claims 1 to 3, which contains 0001 to 0.005%. 5. The composition of inclusions in steel is CaO--Al ₂ O.
_The steel sheet for cans having excellent corrosion resistance according to any one of claims 1 to 4, wherein the steel sheet is made of ₃ series. 6. The molten steel is degassed, decarburized and deoxidized, and then transferred to a tundish to cause inclusions to flocculate and separate by a swirling flow. The thus obtained high cleanliness steel strip is hot rolled, pickled,
The method for producing a steel sheet for cans having excellent corrosion resistance according to any one of claims 1 to 5, wherein the cold rolled material is continuously annealed and then temper-rolled.