JPH0191941A - Method for continuously casting metal strip - Google Patents

Abstract

PURPOSE:To produce a product without any defects of longitudinal crack and inequal thickness by limiting over-heat degree at the time of pouring molten metal and specifying the thickness of a metal strip at the time of producing the metal strip by continuous casting with twin drum method. CONSTITUTION:Pouring basin part 3 is arranged at space between one pair of cooling drums 1a, 1b and solidified shells from the molten metal 4 supplied from there are formed and pressure-welded and integrated at the drum gap 6 part. Then, the over-heat degree at the time of pouring the molten metal is made to <=15 deg.C and the thickness of the metal strip is made to <=3mm. By this method, the product without any defects of longitudinal crack and inequal thickness can be produced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for continuously manufacturing a metal ribbon while preventing the occurrence of vertical cracks by reducing the shrinkage force during solidification. .

[Conventional technology]

BACKGROUND ART Recently, a method of directly manufacturing a ribbon having a thickness several orders of magnitude close to the final shape from molten metal such as molten steel has been attracting attention. When this continuous casting method is used, there is no need for a multi-step hot rolling process as in the conventional method (and only a light rolling process is required to form the final shape, so the process and equipment can be simplified.

One such continuous casting method is the twin drum method (see Japanese Patent Laid-Open No. 137562/1983).

FIG. 3 is a diagram for explaining the outline of this twin drum method. In this system, as shown in the perspective view of FIG. 3(a), a pair of cooling drums la and lb that rotate in opposite directions are arranged horizontally.
A hot water reservoir 3 is formed in a recess section defined by lb and sides tl12a and 2b. Molten metal is poured from a container such as a tundish into this sump 3 through a pouring nozzle. The molten metal 4 accommodated in the sump 3 is cooled and solidified at the portions that come into contact with the cooling drums la and lb to form solidified shells.

As shown in the cross-sectional view of Fig. 3, etc., this solidified shell 5 is accompanied by the rotation of the cooling drums la, lb, and forms a so-called drum gap region where the pair of cooling drums la, lb face each other at the closest position. Move to 6. In this drum gap portion 6, each cooling drum la,
The solidified shells 5 formed on the surface of lb are pressed against each other.
The metal ribbon 7 is then integrated into a single piece.

[Problem that the invention seeks to solve]

The solidified shell 5 grows to a predetermined thickness, and the thin metal strip 7
During the manufacturing process, the temperature of the solidified shell 5 decreases. As the temperature decreases, the coagulation shell 5 contracts. At this time, the sides of the cooling drums la and lb and the side j[12
There is a slight gap between the inner surfaces of a and 2b, and the molten metal 4 flows into this gap, creating a so-called hot water pourer. The molten metal R4 that has flowed into the gap solidifies there and becomes cast flash. This casting burr is continuous with the solidification well 5 from its raw Fft'a level.

The solidified shell 5, which contracts under such conditions, is restrained at both ends by flash. Therefore, the contraction force acts in the axial direction of the cooling drums la, lb, that is, in the width direction of the metal ribbon 7. The solidified shell 5 in the growth process is
Since it is still at a high temperature and has low rigidity, it is likely to break even when a small amount of force is applied to it. Then, due to the contraction force with which both ends are restrained, the thin metal strip 7 is broken in the longitudinal direction. Alternatively, even if it does not break, the solidified shell 5 is partially thinned due to this contraction force, and the thin metal strip 7
This causes wall thickness variation along the width direction.

In order to eliminate the influence of such contraction force, it is sufficient to prevent the formation of hot water between the side surfaces of the cooling drums la, lb and the inner surfaces of the sides i[2a, 2b. One possible way to eliminate the second hot water jug is to attach the side weirs 2a, 2b closely to the sides of the cooling drums la, lb. However, it is practically impossible to achieve this close contact state.

Therefore, the present invention improves the casting conditions to
Alleviates the effect of contraction force when both ends are restrained,
The purpose is to prevent vertical cracking and to produce a metal ribbon with less variation in wall thickness.

[Means for solving problems]

In order to achieve the object, the continuous casting method for metal ribbon of the present invention rapidly solidifies molten metal supplied to a sump provided between a pair of cooling drums to form a solidified shell. When manufacturing a metal ribbon by press-welding and integrating solidified shells at the drum gap, the degree of superheating of the molten metal during pouring is suppressed to 15°C or less, and the thickness of the metal ribbon is set to 3. It is characterized by being less than or equal to 100%.

Note that the degree of superheat here refers to the difference between the temperature of molten metal and its melting point.

[Effect]

FIG. 1 shows the influence of the degree of superheating of the molten metal 4 poured into the sump 3 on the strain and stress of the solidification well 5.

That is, when pouring molten metal with a large degree of superheat into the molten metal sump 3, the temperature of the molten metal 4 in the sump 3 increases according to the degree of superheat, and this high heat flows into the drum gap 6.
is transmitted to the solidified shell 5 located at The solidified shell 5 is in a state immediately after being solidified from the molten metal @4-, and its rigidity is greatly influenced by its temperature.

From this point of view, in the present invention, the degree of superheating of the molten metal poured into the pool 3 is suppressed to 15° C. or less. This makes it possible to cool the solidified shell 5 without applying excessive strain or stress to it. therefore,
Even if both ends are restrained by casting burrs, the metal ribbon 7 can be carried out from the drum gap 116 without causing vertical cracks. On the other hand, the degree of superheating is 15℃
As shown in FIG. 1, the strain and stress increase rapidly, and the stress generated in the solidification well 5 becomes larger than the deformation stress.

FIG. 2 is a diagram showing the influence of the thickness of the metal ribbon 7 on the occurrence of cracks. In this example, molten steel with a superheating degree of 10° C. was poured into the trough 3 to produce the metal ribbon 7.

The same figure (a) and (b) each have a plate thickness of 2.0ml11
and 5. The stress generation situation when manufacturing the metal thin strip 7 of Qmm was determined by calculation, and this was graphed using the cooling drum surface and the solidified shell thickness as both axes.

The generated stress is represented as an arrow whose length corresponds to its magnitude. Note that 1, 0 kgf/s' and 4.0 kgf/s' are shown with arrows at the bottom of the same figure.
"man" is a scale indicating the magnitude of stress value.

When producing a thin metal ribbon 7, the thickness of the solidified shell 5 at the drum gap portion 6 is reduced. Therefore, since the solidification time is short, the temperature of the solidified shell is high, and the stress acting on the solidified shell is also small, as shown in FIG. Therefore, even in the surface layer showing the maximum stress, the stress value does not exceed the deformation stress value, and no vertical cracks or the like occur.

On the other hand, when manufacturing a metal ribbon 7 with a large thickness, it is necessary to grow the solidified shell 5 to a sufficient thickness in the process of reaching the drum gap portion 6, which increases the cooling time. As a result, the temperature of the surface layer of the solidified shell decreases, and a large shrinkage stress is generated in the solidified shell 5, as shown in FIG. 5(b). At this time, in the surface layer showing the maximum stress,
Vertical cracking occurs because the stress value exceeds the deformation stress value.

That is, the stress generated in the surface layer of the solidified shell and the deformation stress value are reversed at the plate thickness of 3 m.

When the plate thickness is 3 mm or less, the generated stress value is less than the deformation stress value, so no vertical cracks occur, and when the plate thickness exceeds 3 mm, the generated stress value > the deformation stress value, so vertical cracks occur. do.

Further, the degree of superheating of the molten metal 4 needs to be 15° C. or less in a range where the plate thickness is 3fflI11 or less. The reason is,
When the degree of superheating is below 15℃, the generated stress value becomes equal to the deformation stress value, so no vertical cracking occurs, and when the degree of superheating exceeds 15℃, the generated stress value becomes greater than the deformation stress value, so vertical cracking occurs. It is.

In this way, according to the invention, the cooling drum la,
The solidified shell 5 is grown without causing defects such as vertical cracks while suppressing the influence of cast burrs generated between the side surface of the metal strip 7 and the inner surface of the side weirs 2a and 2b.
can be taken out from the drum gap portion 6.

〔Example〕

Next, specific operating conditions and properties of the obtained metal ribbon will be shown.

Molten steel with a common steel composition (melting point 1530°C) and a temperature of 1540°C at a flow rate of 1500 kg/min? '! A copper strip having a plate thickness of 2.0III11 was produced by pouring the metal into the grooved area. The obtained product had no vertical cracks, and the wall thickness variation in the width direction was extremely small, 100 p or less. On the other hand, when a copper strip with a thickness of 4.0 mm was manufactured by pouring molten steel at a temperature of 1560°C under the same conditions, many vertical cracks were observed along the longitudinal direction of the copper strip, and cracks in the width direction were observed. The wall thickness variation was also as large as 200p.

〔Effect of the invention〕

As explained above, in the present invention, by specifying the degree of superheating of the molten metal poured into the pool and the thickness of the metal ribbon to be manufactured, a solidified shell whose both ends are restrained by cast flash is produced. We manufacture thin metal strips that are free from defects such as vertical cracks and uneven wall thickness by reducing the effects of stress that occurs during shrinkage.

Therefore, even if there is a slight gap between the side of the cooling drum and the inner surface of the side weir, continuous casting can be continued without any problem, so the side weir can be placed tightly on the side of the cooling drum. There is no need to place it in close contact with the As described above, according to the present invention, the twin-drum continuous casting operation is facilitated, and the properties of the obtained metal ribbon are stabilized.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the effect of the degree of superheating of molten metal on the strain and stress of a metal ribbon, and FIG. 2 is a graph showing the effect of the wall thickness of a solidified shell on the occurrence of cracks. Further, FIG. 3 is a diagram for explaining continuous casting using the conventional twin drum method. Patent applicant: Nippon Steel Corporation (and one other person)
Masato Kobori (and 2 others) Figure 1 Figure 2 (0) (b) 1.0 kgf/mrrF 4. Okg
f/rrvr? Figure 3 CG) b l-Jade J Wantian Emperor

Claims (1)

[Claims] 1. Molten metal supplied to a pool provided between a pair of cooling drums is rapidly solidified to form a solidified shell, and the solidified shell is pressed and integrated at the drum gap to form a metal ribbon. 1. A continuous casting method for a metal ribbon, characterized in that the degree of superheating of the molten metal during pouring is suppressed to 15° C. or less, and the thickness of the metal ribbon is 3 mm or less.