JP2764626B2 - Continuous casting method of tinplate material by twin roll method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for continuously casting a tin material for a DI can by a twin-roll method.

(Prior art) In recent years, from the viewpoint of saving processes and energy, the technology to manufacture thin plates close to the final product at the casting stage, that is, Near Net S
hape CC is being developed. Among them, the thin type Near
The twin roll method is a prominent Net Shape CC (Japanese Patent Application Laid-Open No. 60-137562).

FIG. 5 is a diagram for explaining the outline of the twin roll method. In the twin-roll method, as shown in FIG. 5, molten steel 3 is supplied from a molten steel container 5 such as a tundish to a pool of water 2 defined by a pair of cooling rolls 1 rotating in opposite directions via a nozzle 4. This is a method of casting the slab 6 by doing so.

When casting a metal sheet by this method, stress is generated due to shrinkage during solidification, which causes a vertical crack. For this reason, the thickness of the slab 6 cast by the twin roll method is fixed to 3 mm or less, and the superheat degree when pouring between the rolls is suppressed to 15 ° C. or less, so that the influence of the stress generated at the time of solidification shrinkage is reduced. It is made smaller (JP-A-1-91941). Here, the degree of superheat is
The difference between the temperature of the molten metal and its liquidus temperature.

However, the brush material having a carbon concentration of 0.02% or less cast under such casting conditions causes the height of the ears 9 to be high when the DI can 8 shown in FIG. 4 is formed, which causes various troubles. Is generated. Here, the height of the ear 9 refers to the difference Δh between the maximum height and the minimum height of the can height after the can material is formed into the DI can 8 as shown in the figure. For this reason, the tin material cast by the twin-roll method is not suitable for the molding of the DI can 8, which is a major problem when applying the twin-roll method to the tin material.

(Problems to be Solved by the Invention) The tin DI can 8 is obtained by forming a tin material punched into a circular shape into a cup shape by a relatively shallow drawing process, and then forming a side wall of the cup-shaped molded product by a tandem method in several order. It is manufactured by a molding method of thinning by ironing. For this reason, if the height of the ears 9 is high or the ears 9 are not uniform, the ears are apt to be cut off during eye inning, and the torn ear pieces are pinched between the tool and the material, causing pinholes.

Also, when the can 8 is removed from the punch after the ironing process, a force is applied to the ear 9, which may cause a crack in the can 8 or a trimming trouble. Further, from the viewpoint of the yield of the trimming material, it is preferable that the height of the ear 9 is not high. Therefore, the quality required for the bulk material for the DI can 8 is that the height of the ear 9 is low.

However, under the above-mentioned casting conditions, the brush material having a carbon concentration of 0.02% or less cast by the twin-roll method has a high height of the ears 9, which causes various troubles at the time of forming the DI can 8. Become.

Then, as a result of investigating the cause in detail, it was found that the height of the ear 9 was increased when the DI can 8 was formed by the following mechanism.

Generally, the equiaxed crystal ratio is increased by reducing the degree of superheat. However, it is known that the equiaxed crystal ratio strongly depends on the carbon concentration, and the equiaxed crystal ratio decreases as the carbon concentration decreases. On the other hand, according to the study of the present inventors,
In particular, when casting a burr material for a DI can by the twin-roll method, it is necessary to improve the workability, so it is necessary to suppress the carbon concentration to 0.03% or less. For this reason, the slab is in a state in which an equiaxed crystal structure is hardly generated. Here, the equiaxed crystal ratio means a value obtained by dividing an equiaxed crystal thickness by a plate thickness. In FIG. 5, since the molten steel 3 is cooled more rapidly as the plate thickness is smaller, the growth rate of the solidified shell 7 having a columnar crystal structure is increased, and the equiaxed crystal ratio is further reduced.

For the above reasons, when a tin material having a carbon concentration of 0.03% or less is cast by a twin-roll method at a plate thickness of 3 mm or less, only a slight equiaxed crystal structure can be obtained even when the superheat degree is 15 ° C or less. For this reason, the solidification structure of the slab 6 of the brush material cast by the twin roll method is almost composed of a columnar crystal structure.
The crystal orientation is aligned with the preferential growth direction of the columnar crystal. Therefore, the slab 6 cast by the twin roll method has directionality. This slab is sent to the cold rolling process, but the preferred orientation of the crystal in the cold rolling and the preferred orientation of the columnar crystals match, so the bulk material cast by the twin roll method will have a stronger directionality. .

For this reason, the directionality cannot be sufficiently eliminated only by heat treatment such as annealing. Therefore, the anisotropy of the crystals remaining in the burr material becomes a difference in elongation depending on the orientation when the DI can 8 is formed, and the height of the ear 9 is increased. Since the conventional continuous cast material passes through the hot rolling process, even if it shows anisotropy at the casting stage, it is subjected to rolling at a high temperature and the structure becomes almost isotropic. For this reason, these problems did not occur in the conventional manufacturing process of the brush material.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a continuous casting method for reducing the height of ears during molding of a DI can by improving casting conditions and casting a tin material that can be molded into a DI can by a twin roll method.

(Means for Solving the Problems) The present invention provides a method of casting a tin material having a carbon concentration of 0.03% or less by a twin-roll method, in a range in which nozzle clogging of molten steel superheat when pouring between rolls does not occur. Make it smaller
Further, the present invention is a method for continuously casting a tinplate material by a twin-roll method, wherein the thickness of a cast sheet is more than 3.0 mm.

(Operation) FIG. 1 shows the relationship between the height of the lug 9 and the equiaxed crystal ratio of the slab 6 cast by the twin sole method shown in FIG. This figure shows that as the equiaxed crystal ratio increases, the height of the ears 9 decreases when the DI can 8 is formed. This means that the columnar crystal structure having directionality was reduced, and conversely, the isotropic crystal structure having isotropic property was increased, whereby the anisotropy was reduced and the height of the ears 9 was reduced.

FIG. 2 shows the relationship between the height of the ear 9 at the time of molding the DI can 8 and the incidence of defective DI cans caused by the height of the ear 9.
If the height of the ear 9 during the molding of the DI can 8 exceeds 3 mm, the defect rate suddenly increases. For this reason, in order to reduce the defect rate, it is necessary to keep the height of the ear 9 at 3 mm or less.

From the above results, the tin material cast by the twin roll method
In order to ensure the quality required for forming the DI can 8, it is necessary to reduce the directional columnar crystal structure and reduce the isotropic isotropic crystal structure to 30%.
% Or more must be secured.

Fig. 3 shows the burr material cast by the twin roll method.
The relationship between the degree of superheat of molten steel and the equiaxed crystal ratio when pouring between rolls is shown. Here, the equiaxed crystal ratio is represented by a value obtained by dividing the equiaxed crystal thickness by the plate thickness in percent. This figure shows that the equiaxed crystal ratio increases as the degree of superheat decreases and as the plate thickness increases. Further, since the minimum degree of superheat of molten steel at which the nozzle is not clogged is about 5 ° C., in order to obtain an equiaxed crystal ratio of 30% or more, it is necessary to secure a cast plate thickness of 3 mm or more.

From the above results, the carbon concentration of 0.03% or less was determined by the twin roll method.
When casting tin cans for DI cans, reduce the superheat of molten steel when pouring between twin rolls to the extent that nozzle clogging does not occur, and make the cast plate thickness more than 3.0 mm to achieve an equiaxed crystallinity of 3
0% or more can be secured, and it is possible to achieve a DI can molding defect rate of 0%.

Here, the lower the lower limit of the carbon concentration, the better the workability. However, from the viewpoint of cost increase, it is preferable to set the lower limit to about 0.005%. Also, as the thickness of the cast plate increases, the equiaxed crystal ratio increases, but the surface of the cast slab 6 after casting is wrinkled.

(Example) Table 1 shows molten steel components, and Table 2 shows casting conditions of Examples and Comparative Examples of the present invention, and DI can defect rates at the time of DI can processing after cold rolling.

Comparative Example 1 was prepared by melting molten steel of component a with a thickness of 2.5 mm and a degree of superheat of 10 ° C.
It was cast at a casting speed of 32 m / min, and the defect rate at the time of DI can molding was 20%. In this case, the equiaxed crystal ratio was 15%, and the height of the ear was 4.0 mm.

In Comparative Example 2, molten steel of component a was 2.0 mm in thickness, and the casting speed was 50 m /
Cast in minutes. The degree of superheat in this case was 4 ° C., the nozzle was blocked, and casting was abandoned halfway. Despite having reduced the degree of superheat to the limit of closing the nozzle, the obtained cast slab had an equiaxed crystal ratio of 22% and a lug height of 3.6 mm. At this time, the defect rate at the time of DI can molding was 10%.

In Example 1, molten steel of the component a was prepared with a thickness of 3.2 mm, a superheat degree of 5 ° C.,
Casting was performed at a casting speed of 20 m / min. The obtained cast slab had an equiaxed crystal ratio of 32% and a lug height of about 2.8 mm. In this case, the defect rate at the time of DI can molding was 0.

In Example 2, molten steel of the component a was prepared with a thickness of 4.0 mm, a degree of superheat of 8 ° C.,
It was cast at a casting speed of 13 m / min. The slab has a 33% equiaxed crystal structure and the ear height is 2.7mm when molding DI cans
Met. As a result, no defective DI cans were generated, and the burr material could be stably formed into DI cans.

In Example 3, molten steel of the component b was obtained with a thickness of 4.3 mm, a degree of superheat of 8 ° C.,
It was cast at a casting speed of 11 m / min. As in Example 2, the cast slab had an equiaxed crystal structure of 33%, the ear height was 2.7 mm when the DI can was formed, and the DI can was formed with a defect rate of 0.

In consideration of the yield of the trimming material, it is more effective to reduce the superheat degree as much as possible and to reduce the height of the ears. However, considering the nozzle clogging during casting, it is not preferable to reduce the superheat degree too much. In addition, considering that the casting speed is slowed down as the sheet thickness increases and the degree of superheat is suppressed to 15 ° C. or less, vertical cracks generated due to hot water stab between the roll 1 and the side wall are: Fine except for the slab edge.
The slab edge is premised on trimming due to shape problems. Therefore, since cracking does not become a problem, a tin material having a carbon concentration of 0.03% or less can be cast by the twin-roll method by the present casting method.

As described above, by applying the method of the present invention to the twin roll method, it has become possible to cast a tin material that can be formed into a stable DI can.

(Effect of the Invention) As described above, according to the continuous casting method of the present invention, the thickness of the cast sheet is set to more than 3 mm, the superheat degree of molten steel when pouring between rolls is reduced, and the equiaxed crystal ratio is reduced. By securing 30% or more, a tin material capable of forming a DI can and having a carbon concentration of 0.03% or less can be cast by the twin roll method.

Therefore, according to the present invention, a high quality tin material for DI cans can be cast by the twin roll method without performing special heat treatment or the like in the cold rolling step, and a significant cost advantage can be expected. Furthermore, the types of steel applicable to the twin roll method have been expanded, and the operation has been greatly improved.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the relationship between the equiaxed crystal ratio and the ear height Δh at the time of forming the DI can. FIG. 2 is an explanatory diagram showing the relationship between the ear height Δh and the DI can defective rate. 3 is an explanatory view showing the relationship between the degree of superheat and the equiaxed crystal ratio, FIG. 4 is an explanatory view showing the shape of the DI can after the DI can is formed, and FIG. 5 is a cross-sectional view showing continuous casting by the twin roll method. It is. 1 ... Cooling roll, 2 ... Pud pool, 3 ... Molten steel, 4 ...
... Nozzle, 5 ... molten steel container, 6 ... cast slab, 7 ... solidified shell, 8 ... DI can, 9 ... ear

Claims (1)

(57) [Claims] (1) When casting a tin material having a carbon concentration of 0.03% or less by a twin-roll method, when the molten steel is poured between rolls, the degree of superheat of molten steel is reduced within a range that does not cause nozzle clogging,
A method for continuously casting a tinplate material by a twin-roll method, wherein the thickness of a cast plate is more than 3.0 mm.