JPH08176674A - Production of steel sheet for can - Google Patents

Abstract

PURPOSE: To obviate the necessity of continuous annealing stage and to produce an extra thin steel sheet with excellent characteristics at a low cost by specifying the composition of a steel minimal in contents of respective impurity components, hot rolling conditions, coiling temp. of steel sheet, etc., and reducing the strength of a cold rolled steel sheet. CONSTITUTION: A continuously cast slab, having a composition consisting of, by weight, <=0.0015% C, <=0.020% Si, <=0.10% Mn, <=0.010% P, <=0.005% S, <=0.0030% N, <=0.150% Al, further one or more kinds among 0.020-0.500% Cr, 0.0020-0.0200% Nb, 0.0050-0.0200% Ti, and 0.0002-0.0020% B, and the balance Fe, is used. This cast slab is hot-rolled under the conditions of <=95 deg.C finish rolling mill inlet temp., >=40% total draft thereat, >=25% final draft, and <=1.2mm final thickness of hot rolled stock. Coiling is performed at 500-750 deg.C, and, after ordinary acid pickling, cold rolling is performed at 50-98% draft. Moreover, the rolling by means of finish rolling mill can be carried out by lubricating rolling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a steel sheet for cans mainly used for beverage cans and the like.

[0002]

2. Description of the Related Art Beverage cans, which have been consumed in large quantities these days,
18-liter cans, pail cans, etc. can be roughly classified into two-piece cans and three-piece cans according to the can manufacturing method. A two-piece can consists of two parts: a surface-treated steel plate that has been tin-plated, chrome-plated, chemical conversion treated, oiled, etc., processed by shallow drawing, DWI processing, DRD processing, etc., and a lid attached to it. It is a can. A three-piece can is a three-piece can in which a surface-treated steel plate is bent into a cylindrical shape or a rectangular tube shape to join the ends to form a can body, and then a canopy and a bottom lid are attached to the can body. But,
Since the ratio of material cost to can cost is high for all cans, there is a strong demand for cost reduction of steel plate for cans.

Therefore, box annealing was used in the past, but this is because the manufacturing process is inefficient, and the material yield is high.
Due to the poor surface quality, continuous annealing, which has high production efficiency and excellent yield and surface quality, is now widely adopted.
For example, as in Japanese Patent Publication No. 63-10213, a soft steel sheet for containers up to about T2 has been manufactured by continuous annealing. In addition, a development for producing a soft steel plate by a continuous annealing method has been carried out. For example, as disclosed in Japanese Patent Publication No. 1-52452, ultra-low carbon steel is used and various hardened materials are combined with work hardening after annealing. A technology for making steel plates for cans has been developed.

Further, there is a movement for strengthening the diameter reduction (neck-in) forming aimed at reducing the thickness of the steel sheet used as one method of cost reduction and reducing the diameter of the upper lid, and more severe material characteristics are required. There is. Further, along with the reduction in wall thickness, in order to obtain the strength required for a can, it is required to be hardened, which is a characteristic that is contrary to the neck-in processing characteristic.

[0005]

However, the improvement of the conventional process described above cannot meet the strict demand for cost reduction, and requires a more innovative method. Therefore, it is an object of the present invention to provide a method of manufacturing a steel sheet for cans that can change the way of thinking and meet more stringent cost reduction requirements.

[0006]

According to the present invention, C: 0.0015% or less Si: 0.020% or less Mn: 0.10% or less P: 0.010% or less S: 0.005% or less N: 0.0030% or less Al: 0.150 % Or less, Cr: 0.020% to 0.500% Nb: 0.0020% to 0.0200% Ti: 0.0050% to 0.0200% B: 0.0002% to 0.0020%, and the balance is Fe and unavoidable. Continuous slab consisting of mechanically impure elements is reheated to 1050 ° C or lower and then hot-rolled so that the finish rolling mill inlet temperature is 950 ° C or less, the total reduction rate is 40% or more, and the final reduction rate is 25%. %, The final hot-rolled base plate thickness is 1.2 mm or less, the coil is wound at a temperature of 500 to 750 ° C, and after normal pickling, cold rolling with a reduction rate of 50 to 98% is performed. It is a method of manufacturing a steel plate for a can, which is a feature.

Further, in the present invention, it is desirable that the rolling in the finish rolling mill is lubrication rolling.

[0008]

In the present invention, attention is paid to the fact that the cost can be reduced by omitting the continuous annealing step, which was indispensable for the stabilization of the material in the conventional steps, and a component system and a manufacturing method suitable for it can be provided. It has been discovered. Since there is no annealing process, the technical point of the present invention is how to suppress the strength of the steel sheet to be low in the state of cold rolling. The present invention is intended for so-called 3P can materials such as welded cans, welded cans, and solder cans, but its application to 2P cans is not limited. Generally, in a process in which annealing is omitted, the steel sheet is in a fully hard state and is too hard, which causes a problem in use. Therefore, it is technically important how to achieve softening.

In order to achieve the above object, the present inventors have studied the components and hot rolling conditions, and further examined the metallurgical factors that govern the usage characteristics of the steel sheet for containers, and I got the knowledge. First of all, the important characteristics of a 3-piece can are as follows. 1) Unlike deep drawing steel sheets used for automobiles and the like, a high r value is not an essential condition.

2) It is desirable that the in-plane anisotropy (Δr) of the r value is small. 3) It is not allowed to cause nonuniformity of deformation such as ridging. 4) A fine structure is desirable in terms of uniformity of deformation. 5) Aging does not necessarily have to be completely non-aged as in box annealed materials (low carbon aluminum killed steel), but with non-aging as high as normal continuous annealed materials (low carbon aluminum killed steel), it can be used in the can making process and afterwards. Problems may occur in the second and third steps of

6) Local ductility at processing speeds that are one to two orders of magnitude faster than those obtained by conventional tensile tests is important. 7) As the mechanical properties, YS (yield strength) uniformity is particularly required. This is advantageous in that the amount of springback during bending is stabilized. 8) There is a lower limit of steel plate strength for maintaining the strength of the can body as the gauge decreases.

9) If the strength is too high (particularly YS), a problem occurs in the can making process, so that the strength of the steel sheet has an upper limit. As a manufacturing process that can achieve further low cost while satisfying these characteristics, various studies have been conducted on a process in which the conventional annealing process is omitted, and the present invention has been completed.

The main features of the present invention are to significantly reduce the respective impurity components, to strictly regulate the hot rolling conditions, and to minimize the amount of work hardening by cold rolling. Is to be made as thin as possible. First, the reasons for limiting the components will be described below. C: When the C content exceeds 0.0015%, the strength of the final product after cold rolling remarkably increases, and the ductility also deteriorates remarkably. Even if it is hard, it is necessary to endure flange processing after can making, and the C content is 0.0015% or less, more preferably
It is desirable to set it to 0.0010% or less. Regarding C, the lower limit of the component is not set, but it can be industrially produced at several ppm.
Even if the amount of C is 0, it is applicable without any problems.

Si: If the Si content exceeds 0.020%, not only is the surface property of the steel sheet deteriorated, which is not desirable as a surface-treated steel sheet, but also the steel hardens and the hot rolling process becomes difficult.
Limited to 020% or less. However, although the detailed mechanism is unknown, it is preferable to add about 0.005% of Si in terms of the effect of reducing inclusions. Mn: So-called hot brittleness is feared unless Mn is added in a certain amount or more, but in the present invention, since it is not particularly necessary to soak to a high temperature in a slab state, this is combined with the reduction of the S content. , Mn is not always necessary from the viewpoint of hot brittleness. Although the detailed reason is not clear, it was found that the strength of the steel sheet after cold rolling is significantly reduced by reducing the amount of Mn added. Therefore, there is no particular lower limit.
The upper limit is determined by the balance with the hardening of steel, but 0.10%
By making it below, it is possible to suppress remarkable hardening (increase in YS). More preferably, it is 0.05% or less.

P: P is also a strengthening element of steel and it is desirable to reduce it. However, further reducing P also has an effect of improving corrosion resistance. In addition, although the detailed mechanism of the reduction of P is unknown, it brings about an effect more than simple reduction of solid solution strengthening even for softening of the steel sheet in the as-hot-rolled state, so it is desirable to reduce it as much as possible. If it is 0.010% or less, almost satisfactory results can be obtained, but more preferably 0.00
It is 5% or less.

S: S must be reduced from the viewpoint of improving workability. Particularly in the steel of the present invention in which the hot-rolled steel sheet is cold-rolled, the non-metallic inclusions present in the steel are extremely harmful in terms of ensuring ductility, and it is desired to reduce the content to the limit. The appropriate range is determined in consideration of the Mn amount, but 0.00
If it is 5% or less, the workability (particularly the stretch flange property) is sufficiently improved, but if it is 0.003% or less, the workability is significantly improved.

N: N is an element to be reduced to the limit in the present invention because it remarkably strengthens steel. However, since the steel of the present invention also contains Al at the same time, 0.0030
Sufficient characteristics can be obtained when the content is less than or equal to%. However, if it is 0.0015% or less, the characteristics are improved and it is more desirable for some applications. Al: Al is a deoxidizing agent, and its addition is essential for improving cleanliness. The minimum amount of addition is 0.005%, but this is not particularly restricted.
Even if it is less than this, if the O content in the steel is sufficiently reduced, the solute N will not cause a problem because the damage to the ductility is small. However, if added in excess of 0.150%, its cleanliness improvement effect saturates, and it causes extremely serious problems as a steel sheet for cans, such as hardening of steel, increase in manufacturing cost, and increase in tendency of surface defects to occur. It is limited to 0.150% or less.
A more preferable range is 0.040% or less.

Next, the selective addition element will be described. Cr: It has been found that the addition of Cr has the effect of reducing the strength of the steel sheet in the as-hot rolled state, and as a result, the steel sheet strength after cold rolling can be reduced. Such effects are exhibited when 0.020% or more is added, and when it exceeds 0.500%, this useful effect tends to be saturated. Therefore, the range is limited to 0.020% to 0.500%. Furthermore, the preferable range from the viewpoint of material is 0.050% to 0.200%.
Is.

Nb: Nb is known as a strengthening element for steel, but when applied to the composition steels such as the steel of the present invention, hot rolling conditions and cold rolling conditions, the detailed mechanism is unknown. However, it was found that it is effective for refining the structure without increasing the strength of steel. It is from the addition of 0.0020% or more that such useful effects become apparent.
However, if it is added in excess of 0.0200%, the grain refining effect of the structure is saturated and the steel material is hardened. Therefore, the range is 0.0020% to 0.0200%. The more preferable range from the viewpoint of material is 0.0050% to 0.0100%.

Ti: Ti also has a finer structure of steel, like Nb,
It is also effective for stabilizing and fixing N in steel. Addition of 0.0050% or more gives such desirable curing. Further, if added in excess of 0.0200%, the steel becomes hard as in the case of Nb, which is not preferable. Therefore, the amount of Ti added is 0.
It was set to 0050% to 0.0200%. A more preferable range is 0.0070% to 0.0150% in terms of material.

B: B is especially used in a welding can or the like,
It is effective in suppressing abnormal grain growth in the heat affected zone, and its addition is desirable. The effect becomes apparent with the addition of 0.0002%, but even if added over 0.0020%, the effect saturates,
Furthermore, it is not preferable because it causes variations in materials. Therefore, it is limited to 0.0002% to 0.0020%. The more preferable range from the viewpoint of material is 0.0005% to 0.0015%.

Next, the reasons for limiting the hot rolling conditions will be described. Slab heating temperature: The slab heating temperature is one of the important conditions of the present invention, and it is required to be 1050 ° C or lower. Although the detailed mechanism is unknown, when performing hot rolling in a low temperature range like the present invention, when the slab heating temperature exceeds 1050 ° C, the structure of the final product tends to be nonuniform, and the appearance There is a high risk of causing defects. Further, there is no problem even if so-called direct rolling after continuous casting and hot piece insertion rolling into a heating furnace are applied, but in that case as well, the heating temperature needs to be 1050 ° C or lower. Moreover, considering the problem of the fuel consumption per unit of heating and the finish rolling temperature, it is considered preferable that the temperature is lower than the conventional temperature. Therefore, 1050 ° C. or lower is within the scope of the present invention, but more desirable from the viewpoint of material improvement.
It is below 1000 ℃. On the other hand, if the slab heating temperature is lower than 900 ° C, the load of hot rolling increases and it is difficult to secure the temperature uniformity, so the lower limit of the slab heating temperature is preferably 900 ° C. However, this is device dependent and can be lowered further.

Finishing rolling mill inlet side temperature and reduction ratio: The finishing rolling mill inlet side temperature needs to be regulated in order to make the structure uniform and fine. That is, if the temperature is higher than 950 ° C, the detailed mechanism is not clear, but recrystallized austenite probably grows grains easily, so that the grain size becomes coarse and the grain size is increased during the finish rolling stage. However, it is not possible to obtain the targeted uniform fine structure. From a material standpoint, 900 ° C or less is more desirable. However, the lower limit of the temperature on the inlet side of the finishing mill is 7
00 ° C is desirable.

Also, the total rolling reduction in the finishing rolling mill is 40%.
If it is above, and the final reduction rate is not more than 25%,
The nonuniformity of the structure cannot be sufficiently removed, resulting in nonuniform distortion that is considered to be ridging during can making, which is not desirable. The upper limits of these rolling reductions are inevitably determined to some extent by the slab thickness, the product thickness, and the cold rolling reduction to be applied. Naturally, the rolling reduction above the Ar ₃ transformation point also affects the material such as grain size, but the rolling reduction below the Ar ₃ transformation point is dominant, and it is desirable that the total reduction below the Ar ₃ transformation point is The rolling reduction is 40% or more, and the final rolling reduction is 25%.
It is desirable to set the above. Further, from the viewpoint of the material, the preferable conditions are a total reduction of 45% or more below the Ar ₃ transformation point and a final reduction of 30% or more.

When rolling below the Ar ₃ transformation point, lubrication rolling is not always necessary, but it is desirable to carry out lubrication rolling because rolling load can be reduced, and the structure of the steel sheet in the plate thickness direction can be reduced. Uniformity can be achieved. This contributes to the final homogenization of the material of the cold-rolled steel sheet and, in turn, the stabilization of the work in the can making process. In addition, the lubrication method and the like at this time are not particularly limited, and any desired method can be used as long as the friction coefficient can be reduced as compared with the conventional method.

Final Hot-Rolling Base Plate Thickness: In the present invention, the hot-rolling finish plate thickness must be 1.2 mm or less. Originally, it seems that the material is determined only by the cold rolling reduction, but the actual mechanism is unknown, but if the thickness of the hot-rolled steel sheet exceeds 1.2 mm, a good product is obtained. However, the shape of the surface cannot be ensured, and even in actual use, problems such as deterioration of the surface quality occur. This naturally depends on the capacity of the hot rolling equipment used for production, but more preferably 1.0 mm or less gave more excellent final product characteristics.

Winding temperature: The winding temperature is limited to a range where the final strength after cold rolling can be reduced as much as possible, in addition to not hindering the pickling / cold rolling which is the next step. At least, if it is not wound at a temperature higher than 500 ° C, the steel plate becomes hard, which is not desirable. More desirable temperature is 6
It is more than 00 ℃. On the other hand, if the coiling temperature exceeds 750 ° C, the scale thickness of the steel sheet increases significantly and the descaling property during pickling deteriorates, as well as the deformation of the coil due to the decrease in the high temperature strength of the steel sheet itself. Cause problems. Further, when it is wound at a temperature exceeding 750 ° C., the variation in the material in the longitudinal and width directions of the steel sheet is extremely increased, and as a result, the deterioration of the steel sheet shape after cold rolling becomes remarkable, which is not preferable. A more desirable upper limit is 700 ° C.

Pickling: An ordinary step can be adopted for pickling, and there is no particular restriction. Cold rolling reduction: Cold rolling reduction after pickling is 50-98
Limited to%. If you do not apply a cold reduction of 50% or more,
This is because it is difficult to obtain a normal target final thickness, and the detailed mechanism is unknown, but a sufficiently uniform material cannot be obtained. Also, the required cold reduction ratio is
If the hot-rolled base plate is thinned to less than 50%, the overall operating cost increases, which is rather undesirable. Therefore,
The lower limit of the cold reduction rate was 50%. On the other hand, the cold reduction rate is 98
When the content exceeds 100%, the strength after cold rolling remarkably increases and the ductility deteriorates remarkably regardless of the material of the hot-rolled base plate, which makes it practically difficult to use. Therefore, the upper limit was set to 98%. It is more desirable for the material to be 90% or less.

[0029]

EXAMPLES Example 1 Various steels shown in Table 1 were melted and hot rolled under the following conditions.
Table 2 shows the results of investigating the characteristics of the cold rolled steel sheet when various cold rolling conditions were changed. Among these, the ridging property was determined by visually observing ridging wrinkles after compressing the steel sheet by 2% in the direction perpendicular to the rolling direction. The r value and the Δr value were evaluated by the method of evaluating the anisotropy of elastic modulus defined in JIS G3135, but in the case of the examples of the present invention, there was no particular problem as a steel sheet for cans. The product thickness was fixed at 0.170 to 0.150 mm. The effect of the difference in plate thickness was considered in the evaluation contents.

The slab heating temperature during hot rolling is from 1000 to 10
The range was 40 ° C. Further, the rolling in the finish rolling mill was used as a lubricant, and the lubricant rolling was performed using a normal mineral oil-based lubricant.

[0031]

[Table 1]

[0032]

[Table 2]

As is apparent from the above, according to the method of the present invention, cold rolling is performed as is without accretion of ridging and relatively Y
It can be seen that a steel sheet for can having low S and good ductility, that is, good formability can be produced. The overall evaluation is YS ≤ 70 (k
gf / mm ² ), elongation ≧ 5%, no ridging and no defective shape.

(Example 2) Using the steel having the components shown in Table 1, Table 3
Cold-rolled steel sheet is manufactured under the conditions shown in Fig. 1, tinned to the equivalent of # 25 under normal conditions, roll-formed and high-speed seam welded to form a can body of a 3-piece can, and stretch flange processing is performed. The presence of cracks was investigated. Normal
3 in the flange forming test conducted under the condition of assuming a 350 ml can
The presence or absence of HAZ (heat affected zone) cracking of not less than% was determined. The product thickness was fixed at 0.200 mm. In addition, those having problems such as local breakage or stretcher strain during roll forming were marked with “X” in the table.

The slab heating temperature during hot rolling is 1100 to 10
The range was 50 ° C. Further, the rolling in the finish rolling mill was used as a lubricant, and the lubricant rolling was performed using a normal mineral oil-based lubricant.

[0036]

[Table 3]

It is clear that the products manufactured under the conditions of the method of the present invention satisfy the required properties. The comprehensive evaluation was performed in the same manner as in Example 1. (Example 3) Using the steels having the components shown in Table 1, cold-rolled steel sheets were produced under the production conditions shown in Table 4, the surfaces were subjected to Cr plating, and the so-called DRD cans were formed. . The product thickness was fixed at 0.150 mm.

[0038]

[Table 4]

It is clear that the products manufactured under the conditions of the method of the present invention satisfy the required properties. Also, the corrosion resistance was investigated according to a usual method, but there was no problem at all. The slab heating temperature during hot rolling is 1050 to 1000 ° C.
Range. Further, the rolling in the finish rolling mill was used as the lubricant, and the lubricant with the extreme pressure additive was used as the lubrication rolling.

[0040]

EFFECT OF THE INVENTION The steel sheet produced by the method of the present invention is substantially the same as that produced by the conventional process when it is formed and processed into a can or container even if it is not subjected to any special surface treatment. Has equivalent characteristics. Therefore, the cost can be reduced by the simplification of the process.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Toshiyuki Kato 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Steel Research Laboratory, Kawasaki Steel Co., Ltd. (72) Hideo Kuminato 1 Kawasaki-cho, Chuo-ku, Chiba Chiba Steel Works, Ltd.

Claims (2)

[Claims] 1. By weight ratio, C: 0.0015% or less Si: 0.020% or less Mn: 0.10% or less P: 0.010% or less S: 0.005% or less N: 0.0030% or less Al: 0.150% or less, and further Cr: : 0.020% ~ 0.500% Nb: 0.0020% ~ 0.0200% Ti: 0.0050% ~ 0.0200% B: 0.0002% ~ 0.0020% One or more kinds of continuously cast slabs with the balance being Fe and unavoidable impurity elements Is reheated to 1050 ° C or lower and then hot-rolled, the temperature at the finishing rolling mill inlet side is set to 950 ° C or lower, the total reduction rate there is set to 40% or more, and the final reduction rate is set to 25% or more. Manufacture of steel sheet for cans, characterized in that the thickness of the base plate is 1.2 mm or less, it is wound at a temperature of 500 to 750 ° C, and after normal pickling, cold rolling is performed at a reduction rate of 50 to 98%. Method. 2. The method for producing a steel sheet for a can according to claim 1, wherein the rolling in the finish rolling mill is a lubrication rolling.