JPH08176673A - 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 chemical composition of an extra low carbon steel, hot rolling conditions, coiling temp. of steel sheet, etc., to soften a base material and reducing the strength of a cold rolled steel sheet. CONSTITUTION: A continuously cast slab, having a composition which consists of, by weight, <=0.0050% C, <=0.020% Si, <=0.20% Mn, <=0.020% P, <=0.010% S, <=0.0030% N, <=0.200% Al, and the balance Fe and to which 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 are further added as additive elements, is used. This cast slab is hot-rolled under the conditions of <=950 deg.C finish rolling mill inlet temp., >=40% total draft at temps. not higher than the Ar3 transformation point, and >=25% final draft. The resultant hot rolled plate is coiled at 500-750 deg.C. After ordinary acid pickling, cold rolling is performed at 50-98% draft. Moreover, lubricating rolling is performed at the time of rolling at the temp. not higher than the Ar3 transformation point.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rational and highly efficient manufacturing method of steel plates for cans mainly used for beverage cans and the like. More specifically, in order to meet the demands for gauge down and price reduction of these steel sheets, which are rapidly progressing at present, the continuous annealing process after cold rolling, which was indispensable in the past, is omitted and commercialized as it is in cold rolling. To do.

[0002]

2. Description of the Related Art Beverage cans, which are consumed in large quantities these days, 1
Depending on the manufacturing method, 8 liter cans, pail cans, etc.
It can be roughly divided into two-piece cans and three-piece cans. 2 pics
The base can be tin plated, chrome plated, chemical conversion treated, oiled, etc.
Shallow drawing, DWI
(Draw and Wall Ironed) processing,
Processing such as DRD (Draw Redraw) processing
It is a two-part can with a lid attached to it. 3 pcs
For the can, bend the surface-treated steel plate into a cylindrical or square tube shape
After joining the cans to form a can body, attach the canopy and bottom cover to it.
It is a can made up of three attached parts. For these,
In both cases, the material cost accounts for a high proportion of the can cost.
There is a strong demand for steel plate cost reduction. Therefore, the manufacturing process is
Conventional box annealing that is efficient and has poor material yield and surface properties
, The production efficiency is high, and the yield and surface quality are excellent.
The application of continuous annealing is essential, for example, Japanese Patent Publication No. 63-102.
There is a technique as disclosed in Japanese Patent No. The technology is C, M
n, acid-soluble Al, Al killed steel with specified N content continuously
Casting or ingot-slab rolling to slab, then Ar
₁ Cool below the point and reapply the slab to 950 to 1100 ° C.
Finishing temperature in hot rolling by heating to low temperature slab heating
Degree Ar₃ Or more, the winding temperature is 620 to 710 ° C.,
After that, cold rolling, continuous annealing under specific conditions, then
Pressing load 1.7 tons / mm or more with high-pressure downward force of 1.5 to
The temper rolling is performed at a rolling reduction of 5.0%. The technology
Is a technology that is an improvement of the above-mentioned conventional technology, up to about T2.
Of soft steel sheets for containers have been manufactured.

Development has also been carried out for producing a softer steel sheet by a continuous annealing method. For example, as disclosed in Japanese Examined Patent Publication No. 1-52452, ultra-low carbon steel is used, and it is combined with work hardening after annealing in various ways. Techniques have been developed for making hard steel plates for cans. That is, 1050 continuous casting slab
After heating at ˜1150 ° C., hot rolling is completed within a temperature range of 600 to 770 ° C., and cold rolling and 720 to 8
The hardness is H _R 30 by continuous annealing in a temperature range of 50 ° C.
After T is set to 42 or less, it is tempered to a predetermined hardness by wet temper rolling with a rolling reduction of 5 to 10%. However, there was a demand for further cost reduction, and in order to meet this demand, it was necessary to develop new manufacturing processes and materials.

Further, there is a movement to strengthen the diameter reduction (neck-in) forming aiming at the reduction of the thickness of the steel sheet and the reduction of the diameter of the upper lid, which are used as one method of cost reduction. It is tough. Further, in order to obtain the required strength as a can, it was required to be hardened as the wall thickness was reduced, which was a property incompatible with the neck-in processing property.

[0005]

With methods other than the above-mentioned conventional processes, the demand for cost reduction cannot be met at all, and a more innovative method is required. Therefore, we paid attention to the fact that the cost can be reduced by omitting the continuous annealing process, which was indispensable for stabilizing the material in the conventional process, and we have developed a component system and manufacturing method suitable for it. Is. Since there is no annealing, the technical point is how to suppress the strength of the steel sheet in the cold rolled state. The present invention is intended for so-called three-piece can materials such as welding cans, adhesive cans, and solder cans, but the application to two-piece cans is not limited.

[0006]

In order to achieve the above-mentioned object, the present inventors have studied the components and hot rolling conditions, and further, the metallurgical factors that govern the usage characteristics of the steel sheet for containers. The following findings were obtained. First of all, the following characteristics are particularly important for 3-piece cans. 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 impossible to cause nonuniformity of deformation such as ridging. 4) A fine structure is desirable from the viewpoint of uniform deformation. 5) Aging does not have to be completely non-aged such as box annealed material (low carbon aluminum killed steel), but if it is not controlled to a standard level, normal continuous annealed material (low carbon aluminum killed steel) can Problems may occur in the subsequent secondary and tertiary steps.

6) Local ductility at processing speeds one to two orders of magnitude faster than those obtained by normal tensile testing is important. 7) As the mechanical properties, YS uniformity is particularly required. This is advantageous as a result of stabilizing the amount of springback during bending. 8) There is a lower limit value of steel plate strength for maintaining the strength of the can body with the gauge town.

9) Too high strength (especially yield strength: Y
In S), there is an upper limit in the strength of the steel sheet because a problem occurs in the can making process. While satisfying these characteristics, various studies have been conducted on a process that omits the conventional annealing process as a rational manufacturing process at a lower cost, and the following invention has been completed.

In the present invention, C: 0.0050% or less by weight, Si: 0.020% or less, Mn: 0.20% or less, P: 0.020% or less, S: 0.010% or less, N: 0.0030% Below Al: 0.200% or less Further as a selective addition element Cr: 0.020% to 0.500% Nb: 0.0020% to 0.0200% Ti: 0.0050% to 0.0200% B: 0. One or more of 0002% to 0.0020% is added alone or in combination, and the balance is F
a continuous cast slab consisting of e and inevitable impurity elements,
The temperature on the inlet side of the finish rolling mill is set to 950 ° C or lower and Ar ₃ transformation
40% or more of the total rolling reduction below the point, and the final rolling reduction
At 25% or more and at a temperature of 500 ° C to 750 ° C
After winding and ordinary pickling, cold reduction with a reduction rate of 50-98%
It is a method of manufacturing a steel sheet for a can, which is characterized by performing rolling.
Ar for this rolling₃ In the rolling process below the transformation point
Therefore, it is preferable to perform rolling while performing lubrication.

[0011]

The present invention uses ultra-low carbon steel as a raw material, optimizes the hot rolling finishing conditions to soften the base plate, and suppresses the strength of the cold rolled steel plate to a low level to simplify the conventional annealing process. Is what you can do. In order to improve the r-value, cold rolling and then recrystallization annealing are almost indispensable conditions, but it can be imagined that this step can be omitted if a high r-value is not required. .

However, by reducing the number of steps in which the structure can be controlled by one, it becomes difficult to reduce the size of the reverse structure, and
The risk of ridging increases. Furthermore, it was expected that the steel could be significantly hardened by omitting the annealing process for releasing the strain, and that the normal can-making process would make it impossible to make a can at all. Therefore, it is necessary to soften it so as not to cause excessive hardening. What made these possible is the combination of using steel whose components are properly controlled and strictly optimizing the thermomechanical treatment conditions in the hot rolling process.

The reasons for limiting the components of the present invention will be described below. C: When the C content exceeds 0.0050%, not only the strength of the final product after cold rolling remarkably increases, but also the ductility deteriorates remarkably. Even if it is hard, it is necessary to withstand flange processing after can manufacturing, and the C content needs to be 0.0050% or less, more preferably 15 ppm or less. Regarding this, the lower limit of the component is not set in particular, but even if the amount of C is several ppm which can be industrially produced, there is no problem and it can be applied.

Si: When 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. % Or less. Mn: If Mn is not added in a certain amount or more, so-called hot brittleness was feared. However, in the present invention, since it is not necessary to soak to a high temperature particularly in a slab state, it is coupled with the reduction of the S content. , Mn are not necessarily essential in terms of brittleness. Further, although the detailed reason is not clear, it has been found that the strength of the steel sheet after cold rolling is remarkably reduced by reducing the Mn addition amount. Therefore, there is no particular lower limit, and there is no problem even if it is about 0.010% which is industrially achieved. The upper limit is determined by the balance with the hardening of the steel, but by setting it to approximately 0.20% or less, remarkable hardening (increase in YS) can be suppressed. More preferably, 0.
It is 10% or less.

P: P is also a strengthening element of steel, and it is desirable to reduce it. However, not only that, but reducing P also has the effect of improving corrosion resistance. In addition, although the detailed mechanism is unknown, it is desirable to reduce as much as possible because it brings more effects than merely reducing solid solution strengthening to softening the steel sheet in the as-hot rolled state. If it is about 0.020% or less, almost satisfactory results are obtained, but it is more preferably 0.010% or less.

S: S needs to 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.
By setting the content to about 0.010% or less, the workability (particularly the stretch flange characteristic) is sufficiently improved, but further reduction, and by setting it to about 0.005% or less, an extremely large improvement effect can be obtained.

N: N is an element that is desired 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, it is almost 0.
Sufficient characteristics can be obtained by setting the content to 0030% or less. However, the characteristics can be improved by further reducing it, so 0.0020% or less is more desirable for some applications.

Al: Al is a deoxidizing agent, and its addition is essential to improve cleanliness. It is desirable to add about 0.005% as the minimum limit, but this is not particularly specified, and even if it is less than this, if the O in the steel can be sufficiently reduced, the damage of solid solution N is especially against ductility. Is small, so it is unlikely to cause a problem. However, when it is added in an amount exceeding 0.200%, the effect of improving the cleanliness is saturated, and the hardness of the steel is increased, the manufacturing cost is increased, and the tendency for the occurrence of surface defects is increased. Therefore, it is set to 0.200% or less. A more preferable range is 0.150% or less.

Next, the selective addition element will be described. Cr: Cr is not an essential element, but 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. . This effect is exhibited by addition of about 0.020% or more, and about 0.50
%, This useful effect tends to be saturated. Therefore, the range is 0.020% to 0.500%. In addition,
Further, the preferable range from the viewpoint of material is 0.050 to 0.20%.
Is.

Nb: Nb has been conventionally known as a strengthening element for steel, but when it is applied to the composition steel such as the steel of the present invention, hot rolling conditions and cold rolling conditions, detailed machinery etc. Although it is unknown, 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 material of the steel is hardened. Therefore 0.0020%
It was set to a range of 0.0200%. A more preferable range from the viewpoint of material is 0.0050 to 0.150%.

Similar to Nb, Ti: Ti is also effective for refining the structure of steel and stabilizing and fixing N in steel. About 0.0050% of such desired curing is obtained
The above is the addition. If it is added in excess of 0.0200%, the steel becomes hard as in the case of Nb, which is not preferable. Therefore, the Ti addition amount is 0.0050 to 0.0200%.
And A more preferable range from the viewpoint of material is 0.00
It is 70 to 0.0150%.

B: B is effective in suppressing abnormal grain growth in the heat-affected zone, especially when used in a welding can or the like, and is preferably added. The effect becomes apparent when the content is added in an amount of approximately 0.0002%, but even when the content is added in excess of 0.0020%, the effect is saturated, and further variation in material is caused, which is not preferable. Therefore, 0.0002% to 0.00
Limited to 20%. A 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. There are no particular restrictions on the slab heating temperature, but there is no particular problem within the normal range. Further, there is no problem even if direct rolling after so-called continuous casting or hot piece insertion rolling into a heating furnace is applied. However, in consideration of 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.

Temperature on the inlet side of the finish rolling mill: The temperature on the inlet side of the finish rolling mill needs to be regulated in order to make the structure uniform and fine. That is, if this temperature exceeds 950 ° C. (although the detailed mechanism is unknown, it is presumed that the initial austenite grain size is coarsened), it is targeted at the final stage of finish rolling. Since it is not possible to obtain a hot-rolled steel sheet having a uniform fine structure, the temperature is set to 950 ° C or lower.

Total rolling reduction below the Ar ₃ transformation point, final rolling reduction: Unless the total rolling reduction below the Ar ₃ transformation point is 40% or more and the final rolling reduction is 25% or more, the structural failure The uniformity cannot be removed sufficiently, resulting in non-uniform 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 based on the slab thickness, product thickness, and the cold rolling reduction to be applied. Naturally, the rolling reduction above the Ar ₃ transformation point also affects the material, but the rolling reduction below the Ar ₃ transformation point is dominant, and these conditions are secondarily determined. From a material standpoint, a more desirable condition is a total reduction of 45% or more and a final reduction of 30%
That is all.

Lubrication rolling: By performing lubrication rolling during rolling below the Ar ₃ transformation point, the rolling load can be reduced, and in addition, the homogenization of the structure in the thickness direction of the steel sheet can be achieved. Therefore, it is possible to contribute to the final homogenization of the material of the cold-rolled steel sheet and eventually to the stabilization of the work in the can making process. In addition, the lubricating method at this time is not particularly limited, and any desired method can enjoy the above-described desired effects as long as it is a method of reducing the friction coefficient as compared with the conventional method.

Winding temperature: The winding temperature is pickling in the next step.
It is important that the final strength after cold rolling can be reduced as much as possible, in addition to causing no hindrance to cold rolling. If the steel sheet is not wound at a temperature of at least 500 ° C., the steel sheet becomes hard, which is not desirable. More desirable temperature is 600 ℃
That is all. On the other hand, when the coiling temperature exceeds 750 ° C, the scale thickness of the steel sheet remarkably increases and the descaling property at the time of pickling deteriorates. Cause problems. Again 750
When coiled at a temperature exceeding ℃, the variation in the material in the longitudinal and width directions of the steel sheet will be extremely increased.
It is not preferable because deterioration of the steel sheet shape after cold rolling becomes remarkable. The upper limit is more preferably 700 ° C. or lower.

The pickling is almost the same as the usual process, and there is no particular restriction. The cold rolling after pickling is 50 to 98%. Unless a cold reduction of 50% or more is applied, it is difficult to obtain a normal target final thickness. Although the detailed mechanism is unknown, a sufficiently uniform material cannot be obtained. Further, if the hot-rolled base plate is thinned until the cold reduction becomes less than 50%, the overall operating cost increases, which is rather undesirable. Therefore, the lower limit of the cold reduction is set to 50%. On the other hand, when the cold rolling reduction exceeds 98%, the strength after cold rolling remarkably increases and the ductility deteriorates irrespective of the material of the hot rolled base material, which makes it practically difficult to use. Will be.
Therefore, the upper limit is set to 98%. It is more desirable for the material to be 90% or less.

[0029]

【Example】

[Example 1] Various steels shown in Table 1 were melted, and hot rolling conditions /
Table 2 shows the examination results of the characteristics of the cold rolled steel sheet when various cold rolling conditions were changed. Among them, the ridging property was determined by visually observing ridging wrinkles by pulling the steel sheet 5% in the direction perpendicular to the rolling direction.

The slab heating temperature during hot rolling is 1000.
The range was up to 1200 ° C. As is clear from Tables 1 and 2, according to the method of the present invention, it is possible to produce a steel sheet that does not cause ridging, has a relatively low YS, and has good ductility, that is, good formability. [Example 2] The cold-rolled steel sheet shown in Table 3 was produced using the steel having the components shown in Table 1, and was equivalent to # 25 under normal conditions (tin weight is 2.
8 g / m ² ) of tin was plated, and this was formed by roll-foaming and high-speed seam welding into a can body part of a three-piece can, stretch flange processing was performed, and the presence or absence of cracking was examined. In a flange forming test conducted under the conditions assuming a normal 350 ml can, the presence or absence of HAZ (heat affected zone) cracking of 3% or more was judged. The product thickness was fixed at 0.150 mm. In addition, those that caused local folds during roll forming, or problems such as stretcher strain that occurred were marked with an X in the table. It is clear that the products manufactured under the conditions of the present invention satisfy the required characteristics.

Example 3 Using the steels having the components shown in Table 1,
A cold-rolled steel sheet was manufactured under the manufacturing conditions shown in Table 4, the surface was plated with Cr, and a so-called DRD can was formed, and the surface condition and other conditions were investigated. It can be seen that the steel of the present invention satisfies the required properties. Further, the corrosion resistance was investigated according to a usual method, but there was no problem at all.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4]

[0036]

Since the present invention is constructed as described above, the steel sheet for containers using the steel of the present invention as the original plate can be formed and processed as a container even if no special surface treatment is performed. When used as, it has substantially the same characteristics as those manufactured by the conventional process. Therefore, it is a rational manufacturing method that can be manufactured at a lower cost because the process is simplified.

 ─────────────────────────────────────────────────── ─── 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: 0.0050% or less Si: 0.020% or less Mn: 0.20% or less P: 0.020% or less S: 0.010% or less N: 0.0030% or less Al: 0.200% or less Further as a selective addition element Cr: 0.020% to 0.500% Nb: 0.0020% to 0.0200% Ti: 0.0050% to 0.0200% B: 0.0002 % To 0.0020% alone or in combination of two or more, with the balance being F
a continuous cast slab consisting of e and inevitable impurity elements,
The finish rolling mill inlet temperature is 950 ° C. or lower, the total reduction ratio at the Ar ₃ transformation point or lower is 40% or more, and the final reduction ratio is 25.
% Or more, winding at a temperature of 500 ° C. or more and 750 ° C. or less, ordinary pickling, and then cold rolling at a rolling reduction of 50 to 98%. 2. The method for producing a steel sheet for a can according to claim 1, wherein lubrication rolling is performed when rolling at the Ar ₃ transformation point or lower.