JPH05117807A - Manufacture of steel strip for can of food - Google Patents

Abstract

PURPOSE:To manufacture a steel strip for can of food having excellent deep drawability by specifying finishing temp. of hot-rolling, coiling temp., continuous annealing condition after cold-rolling and temper-rolling to a continuously cast slab specifying the component composition. CONSTITUTION:To the continuously cast steel slab composed of by wt.%, 0.04-0.10% C, <=0.02% Si, 0.05-0.3% Mn, <=0.02% S, <=0.02% P, <=0.1% Al, <=0.01% N and the balance substantially Fe, the hot-rolling is applied so that the finishing temp. becomes the alpha range temp. Successively, after coiling at 600-660 deg.C the coiling temp., pickling and the cold-rolling are applied by the ordinary method and the continuous annealing is executed at the recrystallization temp. -800 deg.C in the condition of <=10sec. soaking time and further, the temper-rolling is applied in the range of <=3% rolling reduction ratio. By this method, the film laminated can product of the food further improving deep drawability is manufactured in good condition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin steel sheet for a highly corrosion-resistant food can, which is produced by deep drawing after laminating a thermoplastic resin film, and particularly a food excellent in deep drawing workability. The present invention relates to a method for manufacturing a thin steel sheet for cans.

[0002]

2. Description of the Related Art As food cans, there are many two-piece cans which are composed of a body and a bottom-integrated part and a lid. This two-piece can is manufactured by the following steps. A tin-plated steel strip is cut into sheets of a predetermined size to obtain tinplate sheets.

Next, a thermosetting resin is applied to one side of the sheet and baked in a baking oven. At this time, the sheet is heat-treated with the unpainted surface leaning against the support. As the thermosetting resin, a resin containing a phenolic resin, a urea resin, an ester resin, etc. as a curing agent based on an epoxy resin is generally used. The temperature condition in a baking furnace is 180 to 220 ° C. × 10 to 20 minutes. When the painting / baking of one surface is completed in this manner, the painting / baking of the other surface is similarly performed.

Next, printing / baking is performed on a surface corresponding to the outer surface of the can. This printing / baking is performed in the same manner as the above-mentioned painting / baking. Next, press working, DP (Drawing an
d Pressing, DRD (Drawing)
and Redrawing) processing, DTR (Dra
Wing and Thin Drawing) or the like is performed to obtain a can body in which the can body and the can bottom are integrated.

After filling the contents with this, a lid manufactured separately is attached. As described above, the tinplate sheet is coated with a thermosetting resin and subjected to a heat treatment (baking) for a long time of 180 to 220 ° C. × 10 to 20 minutes. At this time, the coating film has a three-dimensional network structure and is resistant to permeation (barrier property) with respect to the filling material.
It has excellent corrosion resistance.

However, the corrosion-resistant thin steel sheet for a can having the thermosetting resin coating film has a problem in terms of formability. That is, when forming processing such as press processing is performed,
The coating film may be finely cracked or damaged, or the coating film may be peeled off, and as a result, the corrosion resistance may not be sufficiently exhibited. Specifically, when a highly corrosive content is filled, black discoloration (SnS) and black spots (FeS) may occur. In particular, when liquid or gel foods are stored, even if there is one coating film defect on the inner surface of the can, corrosion of the metal material in the can progresses from this portion, and the flavor of the content food decreases. In addition to the deterioration of shelf life, heat sterilization and hot water treatment make the product worse and lose its commercial value. Such poor moldability is due to the use of a thermosetting resin as the paint. That is, in order to obtain corrosion resistance, it is necessary to react the unreacted functional groups in the polymer of the thermosetting resin to form a three-dimensional network structure in the molecular structure by crosslinking between the polymers, and for that reason Requires heat treatment. It is considered that the thermosetting by this baking process deteriorates the workability and causes defects such as cracks to easily occur.

When coating, as described above, 180 to 220 ° C. × 10 for each tinting sheet and for each front and back surface.
Since the heat treatment is carried out for a long time of ~ 20 minutes, the productivity is also very poor. On the other hand, a method for producing a coated metal structure in which a thermoplastic polyester resin film is adhered to a metal surface instead of the above-mentioned thermosetting resin layer is disclosed in JP-A-52-6.
It is disclosed in JP-A-1-145137.
No. 1,192,545 discloses a method for producing a composite steel sheet in which a polyester film is thermocompression-bonded to a tin plate under a specific temperature condition, and further, a polybutylene terephthalate film is heat-bonded to JP-A No. 1-180336. Proposals have been made for respective methods of manufacturing a composite steel sheet that is rapidly cooled later.

[0008]

However, it is difficult to obtain a product having a large drawing ratio even if an attempt is made to press a thin steel sheet coated with these conventional thermoplastic resin films to produce a two-piece can. It was That is, when a thin steel sheet coated with a thermoplastic resin film exceeds a certain drawing limit, the material around the punch head easily breaks, and when the drawing ratio increases, the film peels, breaks,
There is a problem that defects such as cracks and whitening are likely to occur, which eventually leads to metal elution into the can contents and corrosion such as pitting corrosion of the can body.

As a countermeasure, it is possible to apply a lubricant on the film coating to improve the drawability.
There is a fatal drawback in that it is difficult to degrease the lubricant of the coating film, and the lubricant remaining on the film coating tends to impair the flavor of foods whose subtle flavor is a life.
Further, the means of applying a good quality lubricant to the die face to reduce the frictional resistance is advantageous for breakage because the material inflow increases, but on the other hand, the tension acting on the flange portion becomes small, which is so-called. "Wrinkles" tend to occur. Further, the tension acting on the punch surface is also reduced, springback is increased, and defective phenomena such as surface strain are likely to occur. As a result, a fixed can shape cannot be obtained, resulting in an uneven food can product, which is not suitable for industrial production.

Therefore, the present invention has been made in view of the above-mentioned problems of the prior art. By restricting the component composition and heat treatment conditions within a predetermined range, the deep drawing workability is remarkably improved and the thermoplastic resin is improved. An object of the present invention is to provide a method for producing a thin steel sheet for a food can, which can favorably produce a food can product coated with a film and having a large drawing ratio, and solve the above-mentioned conventional problems.

[0011]

The present invention provides C; 0.004-
0.010% (weight ratio, the same below), Si; 0.02% or less, M
n: 0.05 to 0.3%, S: 0.02% or less, P: 0.02% or less,
Al: 0.1% or less, N: 0.01% or less, and the balance substantially F
The continuous cast steel slab made of e is wound at a finishing temperature of α region temperature at the time of hot rolling, and wound at a winding temperature of 600 to 660 ° C., then pickled and cold rolled in order by a conventional method, and thereafter. The present invention is characterized in that continuous annealing is performed under conditions of a recrystallization temperature or higher and 800 ° C. or lower and a soaking time of 10 seconds or shorter, and further, temper rolling is performed within a range of a rolling reduction of 3% or less.

[0012]

[Operation] Vacuum degassing during steelmaking produces a C content of 0.004
By using ultra low carbon steel with 0.010%, a thin steel sheet with a large grain size can be obtained by the continuous annealing method, and the r value (Rankford value) that governs the deep drawability of the steel sheet is large,
The Δr value (in-plane anisotropy of Rankford value) becomes small. Further, solid solution C remains after the continuous annealing and hardens due to strain aging even though the crystal grain size is large. Therefore, a large elongation can be obtained even if the reduction ratio in temper rolling after continuous annealing is reduced. Furthermore, the coiling temperature during hot rolling is increased to increase the grain size by self-annealing. In addition, continuous annealing is performed at a high temperature of up to 800 ° C. so as to coarsen the crystal grains after cold rolling.

When the Al content is 0.1% or less and the N content is 0.01% or less, precipitation of AlN is suppressed, the amount of solid solution N remaining is increased, and the yield strength is increased. The strength of the can after processing is increased. However, for that purpose, it is preferable to lower the winding temperature during hot rolling as much as possible. Therefore, in between the above-mentioned grain coarsening, the coiling at the time of hot rolling is performed at an intermediate temperature of 600 to 660 ° C.

The details will be described below. The inventors of the present invention were able to perform deep drawing with a conventional steel sheet coated with a thermosetting resin, but in the case of a thin steel sheet coated with a thermoplastic resin film, deep drawing was possible. The cause of the difficulty was examined. As a result, we came to think that this problem was due to the effect of lubrication. That is, the breaking limit in deep drawing is determined by the magnitude relationship between the drawing resistance of the flange and the breaking resistance of the punch shoulder as follows.

Punch shoulder rupture resistance> Forming is possible if flange part draw resistance <Punch shoulder rupture resistance <Fracture if flange part draw resistance where rupture resistance of punch shoulder part = thin steel plate Breaking resistance + Punch shoulder friction resistance Flange drawing resistance = Shrinkage of thin steel plate Flange resistance + Friction resistance on die face surface including die shoulder R part Therefore, even with the same thin steel plate, lubricity is good only on the die face surface. Then, the frictional resistance on that surface is reduced and the drawing resistance of the flange portion is reduced, and the molding limit is improved. On the other hand, when the lubricity of only the punch surface is improved, the frictional resistance of the punch shoulder R portion decreases and the rupture resistance of the punch shoulder portion decreases, which is considered to lower the forming limit.

From the above, it is considered that the reason why the deep drawing workability of the thin steel sheet coated with the thermoplastic resin film is poor is that the slippery thermoplastic resin film is attached to the inner surface of the can. Therefore, in order to compare the friction resistance between a thin steel sheet coated with a thermosetting resin (thickness of about 5 μm) and a thin steel sheet coated with a thermoplastic resin film (thickness of 20 μm), a sliding test was conducted to obtain a table. A result of 1 was obtained.

[0017]

[Table 1]

From these results, it can be seen that the friction resistance of the thermoplastic resin film coated surface is smaller than that of the tinted surface or the coating film coated surface of the thermosetting resin. In this way, it was confirmed that the thin steel sheet coated with the thermoplastic resin film has a lower frictional resistance at the punch shoulder R portion and lowers the molding limit. Therefore, the present inventors further conducted research with the intention of improving the forming limit of the thin steel sheet coated with the thermoplastic resin film. Generally, the deep drawability of thin steel sheet is
Dominated by r-value (Rankford value),
It is said that the influence of strength and ductility (elongation) such as yield point and tensile strength is small. However, in the case of a thin steel sheet coated with a thermoplastic resin film, not only the r value but also a large elongation is required to increase the drawing ratio when forming a two-piece can by deep drawing. It has been found.

In addition to this, the impact strength of the can is important from the viewpoint of the commercial value as a molded food can, and for that purpose, it is necessary that the thin steel sheet, which is a can-making material, has a high yield strength. .. However, a thin steel sheet with a large r value and a large elongation generally has a low yield strength. The realization of a thin steel sheet with a large r value, a large elongation and a large yield strength is contradictory metallurgically. It can be called a request.

In order to solve such a contradiction, the inventors of the present invention manufactured a thin steel sheet with variously changed rolling conditions and annealing conditions on the basis of low carbon Al killed steels having different components, Its hardness, elongation, mechanical properties such as r-value and Δr-value, and LDR (Limiting Draw)
ing Ratio: critical drawing ratio), and the press workability of LDR etc. of the nylon 6 film (20 μm thickness) coated on the tin plate was investigated and examined.

Table 2 shows an example of the examination results.

[0022]

[Table 2]

In Table 2, sample Nos. 1 to 3 are thin steel plates coated with a nylon film on a tin plate by a conventional manufacturing method using low carbon Al killed steel, which has a large amount of carbon and a small crystal grain size. The sample number has the smallest amount of C (0.03 wt%) among them, and has better press workability than the sample number, but the can strength is insufficient. On the other hand, the sample No. in which the amount of C (0.10 wt%) is increased has improved can strength, but has poor press workability. The reason why the sample number ~ can strength is small is A
This is because the solid solution N and the solid solution C hardly remain due to the 1-killed steel and the box annealing, so that the strain age hardening is very small. It was expected that the grain size would be reduced and fine grain hardening would be expected, but the extent was small.

Sample Nos. 1 to 3 are thin steel plates obtained by rolling a very low carbon Al killed steel sheet, continuously annealing and temper rolling it, and then tin plating the finished thin steel sheet tin plate with a nylon film. Sample No. has a very low C content of 0.0020 wt%, and has a C content of 0.007 wt%, which is somewhat high for an ultra low carbon steel. The sample number is a rolling reduction of 1%, and the press workability was good, but the can strength was insufficient. Is a temper rolling reduction of 5%
The work strength was sufficient, but the can strength was sufficient, but the press workability was poor. The reason why the press workability deteriorated despite the large r value is considered as follows. That is, when performing deep drawing to obtain the can height, it is necessary to stretch and flow the material around the can bottom (around the punch head). On the other hand, it is necessary for the flange portion to shrink and inflow the material. A steel plate having a large r value is advantageous in order to obtain the shrinkage inflow of the flange portion. On the other hand, in order to obtain the elongation outflow amount of the punch head, a steel sheet having a large elongation is required, and particularly in a film-coated thin steel sheet having a small friction coefficient, it is necessary to further increase the elongation. However, since the sample number was work-hardened by increasing the rolling reduction in temper rolling, the yield strength could be increased efficiently, but the elongation was extremely small on the other hand, and as a result, the elongation and outflow of the punch head became insufficient. The press workability around the bottom of the can is deteriorated.

Therefore, especially for a thin steel plate for a two-piece food can, one having a small elongation even if the r value is large is unsuitable. For each of the above sample numbers, the reduction ratio of the temper rolling was set to 1%, but it was found that the press workability and the can strength were sufficient, and it was suitable for a two-piece can.

As a result of the repeated investigations by the present inventors,
Various findings can be obtained regarding the composition of the thin steel sheet, the coarsening of carbide crystals, the conditions of hot rolling, the annealing conditions and the forming limit, and the present invention has been achieved based on these findings. First, the critical significance of the element content of the thin steel sheet for a food can of the present invention will be described. C: 0.004 to 0.010 (weight)% In order to obtain a thin steel sheet having a large r value and a large elongation, it is a priori rule to increase the crystal grain size. C, the core of recrystallization
The smaller the amount, the larger the crystal grain size, and a soft original plate excellent in deep drawability can be obtained even by the continuous annealing method. However, even if a two-piece can is made of a too soft thin steel plate by a deep drawing method, the strength of the can is so weak that it is easily deformed and has no commercial value. Therefore, the C content of the thin steel sheet of the present invention is not refined to an extremely small amount, but the hardness is adjusted within the minute amount range as described above.

Conventionally, the reduction ratio of temper rolling was made high in order to make it hard, but in that case, the "elongation" becomes extremely small as described above, and it is suitable for deep drawing in film-coated thin steel sheets. There was a limit. In the present invention, the C content is
When the content is 0.004 to 0.010%, the crystal grain size becomes moderately large, and further the amount of solid solution C remains in an appropriate amount.
Age hardening progresses in painting, printing, can making press processing,
As a result, it becomes possible to obtain a two-piece can having a high can strength. However, the crystals are still fine grains and the r value is a little small. Therefore, as a countermeasure, set the winding temperature during hot rolling to medium temperature and the continuous annealing temperature after cold rolling to high temperature as described later. This is intended to promote the coarsening of crystal grains. Si: 0.02% or less Si is an element that deteriorates the corrosion resistance of tinplate, and even if it is a thin steel sheet coated with a thermoplastic resin film having excellent corrosion resistance, it must be 0.02% or less. Mn: 0.05 to 0.3% Mn is added to prevent the occurrence of ear cracks in the hot rolled coil. However, if the amount added is less than 0.05%, the occurrence of ear cracking cannot be prevented. On the other hand, it is uneconomical to add more than 0.3%. S: 0.02% or less If S is contained excessively in relation to Mn, it may cause edge cracking of the hot rolled coil, and the amount of S-based inclusions may increase, which is not preferable. Therefore, make it 0.02% or less. P: 0.02% or less P is an element that deteriorates the corrosion resistance of tinplate and an excessive content is not preferable, so it is limited to 0.02% or less. Al; 0.1% or less Al is an element necessary for precipitating solid solution N as AlN. However, by allowing a large amount of solute N to remain,
Similar to solid solution C, strain age hardening is promoted and can strength can be expected to be improved. Therefore, addition of too much Al reduces the amount of solid solution N unfavorably. Therefore, it is limited to 0.1% or less. N: 0.01% or less N is an element that can form a solid solution in steel to promote strain age hardening, and is an effective component. In the steel of the present invention, solid solution N
It is preferable that a large amount remain as the point that the yield strength and hence the can strength are increased by the aging effect after the can manufacturing process. Therefore, in the steelmaking process, a large amount of N is added and the amount of Al added is reduced as described above to suppress precipitation of AlN, thereby increasing the residual amount of solid solution N, and thus the above content is set.

Next, the critical significance of the processing temperature in the hot rolling step and the continuous annealing step after cold rolling in the production of the thin steel sheet for food can of the present invention will be explained. Finishing temperature during hot rolling; α region temperature In the case of a thin steel sheet for cans having a small sheet thickness, low temperature rolling is particularly preferable. This is to prevent cracks from being generated on the roll surface due to thermal shock during hot rolling and contamination of the roll defects. From this point of view, α region rolling is performed.

Winding temperature during hot rolling: 600 to 660 ° C. In the manufacturing method of the present invention, the winding temperature is limited to the above-mentioned medium temperature range. In the present invention, a slight amount of C is left in the steel, so that the crystal grain size becomes slightly finer. In order to compensate for this, it is desirable to wind at a high temperature and promote the coarsening of crystal grains by self-annealing to improve the r value. But 660
When the temperature is higher than 0 ° C, the variation in the self-annealing method becomes large, and the scale loss is large, which is uneconomical. On the other hand, when the temperature is lower than 600 ° C., the amount of the solid solution N remaining is increased and the can strength is increased, which is preferable, but the coarsening of the crystal grain size is not promoted. Therefore, it was found that it is optimal to set the winding temperature during hot rolling within the above-mentioned medium temperature range.

Continuous annealing temperature; recrystallization temperature or higher and 800 ° C. or lower Continuous annealing is an important step for improving the material quality by recrystallizing and grain growing the cold rolling structure. Annealing is advantageous in that high-temperature short-time annealing promotes grain growth of crystal grains to achieve coarsening, and is also economical. However, when the temperature exceeds 800 ° C, the elongation decreases, so the temperature is set to 800 ° C or less.

Rolling reduction of temper rolling: 3% or less If the rolling reduction of temper rolling is increased, it easily becomes hard,
On the other hand, the elongation is extremely poor. Therefore, in the present invention, the rolling reduction is limited to 3% or less. According to the production method of the present invention, the r value is large and the Δr value (rank four value) is obtained by preparing the components, performing medium temperature winding, performing high temperature annealing, and adjusting the reduction ratio of the temper rolling. It has become possible to obtain a thin steel sheet for a food can that satisfies the contradictory requirements of low in-plane anisotropy), high elongation, and high yield strength. As a result, the deep drawability of the film-laminated thin steel sheet is remarkably improved, causing the material to break around the punch head during forming as in the past, and peeling, breakage, and cracking of the film when the draw ratio increases. ，
Without causing defects such as whitening, and without causing "wrinkles" during molding or increasing springback, it is now possible to satisfactorily produce film-laminated food can products with a large drawing ratio. ..

[0032]

[Example] Steel was melted in a bottom blowing converter, and the C content was 0.03.
Steel was tapped at a weight percentage of less. Subsequently, after subjecting to RH vacuum degassing treatment to adjust the C content to 0.01 to 0.004% by weight,
Al was added to obtain a plurality of types of Al-killed steel having the composition shown in Table 3. Using this, a continuous casting machine is used to manufacture billets,
These billets were hot rolled. The finishing temperature was set to a low temperature in the α region, the winding temperature was set to an intermediate temperature, and hot rolled coils each having a thickness of 2.0 mm were formed, followed by pickling and descaling. Then, with a 6-stand tandem cold rolling mill, a reduction rate of 9
Cold rolling was performed at 0% to obtain a thin steel plate having a plate thickness of 0.2 mm. Subsequently, this steel sheet was continuously annealed, and then temper-rolled to finish a test sample original plate. Table 3 also shows the data of the heat treatment conditions and the reduction ratio of the temper rolling for each sample.

This original plate was continuously subjected to # 25 (2.8 g / m ² ) tin plating, reflow treatment (molten tin treatment), and chromate treatment in a halogen type electric tin plating line,
I finished it in a tin plate.

[0034]

[Table 3]

The underlined numbers in Table 3 indicate that the values are out of the range specified in the claims of the present invention, and are for comparative steels. A nylon 6 film (20 μm thick) was attached to the above thin steel plate by an adhesive method using a film laminator to obtain a film laminated thin steel plate. A material having a predetermined size was sampled from the thus obtained film-laminated thin steel sheet and a material test was conducted. At the same time, two-piece cans were press-molded and the strength of the resulting cans was evaluated.

Table 4 shows the measurement results and evaluation results. In Table 4, LDR was calculated by the following formula, with the blank diameter kept constant at 120 mm, while the punch and die diameters were gradually reduced, press working was repeated several times until fracture. LDR = diameter before processing (blank diameter) / diameter after processing In addition, the impact strength of the can becomes important when evaluating a two-piece can. That is, if the cans collide with each other or if the cans are largely deformed when dropped, the commercial value is lost. Since it is a deep-drawn can, it is hardened by pressing, but it is unavoidable that the structure of the can is smaller than that of a three-piece can. The three-piece can has a double-tightened top and bottom plate around the body, so the can strength is sufficiently large. On the other hand, the canopy of the two-piece can has a double winding structure, but the bottom is weak because it is a pressed product. This time, the obtained two-piece can was filled with water and dropped from a height of 30 cm, and the impact strength was evaluated by the degree of depression. In the column of can strength in Table 4, “x” indicates that the dents are large and cannot be seen, and “o” indicates that the dents are hardly dented.

[0037]

[Table 4]

With the steel of the present invention, good results were obtained despite severe test evaluation. On the other hand, in the case of the comparative steel, the mechanical properties or the can strength of the film-laminated steel sheet before can making were inferior, and the overall evaluation was poor. In addition, although it was applied to the tin plate in the above-mentioned embodiment, it can also be applied to a chrome-plated steel sheet.

The film-laminated steel sheet for food cans according to the production method of the present invention can be applied not only to two-piece cans but also to three-piece cans. The production method of the present invention can also be applied to the production of thin steel plates for food cans in which films are attached to both front and back surfaces.

[0040]

EFFECTS OF THE INVENTION According to the present invention, by adjusting the amount of C in the trace amount range and using medium temperature winding and high temperature annealing together, the deep drawing workability is remarkably improved, and age hardening causes the can strength. The effect that a film laminated canned food product with a large drawing ratio can be satisfactorily produced can be obtained.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Chikako Fujinaga 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Akio Tosaka 1 Kawasaki-cho, Chiba, Chiba Kawasaki Steel Co., Ltd. Corporate Technology Research Division

Claims (1)

[Claims] 1. C: 0.004 to 0.010% (weight ratio, the same applies hereinafter), Si: 0.02% or less, Mn; 0.05 to 0.3%, S;
02% or less, P; 0.02% or less, Al; 0.1% or less, N;
The finishing temperature at the time of performing hot rolling on the continuously cast steel slab that is 01% or less and the balance is substantially Fe is defined as the α region temperature,
The material is wound at a winding temperature of 600 to 660 ° C., then pickled and cold-rolled in order by a conventional method, and then at a recrystallization temperature of 80 or higher.
Continuous annealing is performed under conditions of 0 ° C or less and soaking time of 10 seconds or less,
A method for producing a thin steel sheet for a food can, which further comprises temper rolling in a rolling reduction range of 3% or less.