JPH0199751A - Method for continuously casting strip - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for continuously casting a thin plate using a technique of directly casting slabs from molten metal.

[Conventional technology]

Recently, a number ff11 close to the final shape has been obtained from molten metal such as molten steel.
Continuous casting methods that directly produce slabs with a thickness of approximately 300 to 300 mm are attracting attention. When using this method, the multi-step rolling process required in the conventional method can be omitted, so that the process and equipment can be simplified. Furthermore, since heat treatment to heat the material to processing temperature between each process is essentially unnecessary, energy saving effects can also be expected. One such continuous casting method is the twin drum method.

Single drum system, twin belt system, single belt system.

Various types have been developed, such as the drum-belt system (
For example, "Iron and Steel" Japan Iron and Steel Institute, 71st year (198
5) No. 10, page A, page 200, JP-A-60-155247, etc.).

[Problem that the invention seeks to solve]

However, in this type of continuous casting method, since the molten metal is rapidly cooled and solidified to form a slab, the surface quality of the obtained product tends to be unstable.

For example, in the twin-drum method, a solidified shell is formed on the circumferential surface of the cooling drum from the molten metal in the pool formed between a pair of cooling drums, and a solidified shell is formed on the circumferential surface of each cooling drum. The shell is integrated at the drum gap. However, unevenness and microscopic surface cracks occur on the surface of the slab due to constraints on heat shrinkage of the slab, gasified components in the molten metal, and other causes.

In addition, in the single belt system, intermittent contact and separation occurs between the fixed weir that partitions the lower side of the pool and the solidified shell generated on the surface of the metal belt, resulting in what is called a cold shaft. Surface wrinkles are likely to occur.

Even with other methods, there are various problems such as cracks, unevenness, and double skin. In order to prevent such defects, improvements regarding casting conditions such as pouring temperature, casting speed, and contact state of molten metal have been proposed for each method. However, measures to fundamentally solve these deficiencies have not yet been established.

Therefore, the present invention aims to eliminate various defects occurring on the surface of slabs discharged from this type of continuous casting machine using a simple method, and to manufacture thin plate slabs with a surface condition that meets demand. With the goal.

[Means for Solving the Problems] In order to achieve the object, the thin plate continuous casting method of the present invention casts a slab immediately after being carried out from a continuous casting machine that produces slabs by rapid solidification of molten metal. The method is characterized in that a modified layer and/or a laminated solidified layer is formed on the surface of the slab by passing it through a molten metal bath.

[Effect]

Immediately after being unloaded from the continuous casting machine, the slab is in a high temperature and highly surface active state. When this slab is cooled to room temperature or around it, oxide scale etc. are generated on its surface.
Surface activity decreases. Therefore, in the present invention, the slab before this reduction in surface activity occurs is guided to a bath containing molten metal.

As a result, a surface-modified layer is deposited from the molten metal bath on the surface of the slab where the various defects described above have occurred. Formation of a modified layer and/or a laminated solidified layer on a slab in a bath can be divided into the following three cases.

The first is when the temperature of the slab in the public is low or the degree of heating of the bath is low, in which case the slab does not melt and a solidified layer is formed on the slab.

The second case, on the contrary, is when the temperature of the slab at the inlet is high or the degree of heating of the bath is high, and the slab melts from the surface, reducing its thickness, and in extreme cases, it melts entirely.

The third case occurs under conditions intermediate between the above two cases, and is a case where a new solidified shell is formed on the surface of the slab inserted into the bath once it has been melted.

In the first of these cases, the productivity of the slab can be increased, but the bonding strength between the base and the modified layer is weak, so auxiliary means such as pressing under strong pressure after leaving the bath are required.

In comparison, in the second or third cases, productivity is lower, but there is no problem with joint strength, and defects such as double skin and cracks on protruding parts of the slab surface before bath insertion are dissolved. No residue remains in the product.

Furthermore, the molten layer thickness and solidified layer thickness are determined by the average slab temperature.

It is also possible to adjust the heating degree of the bath and the residence time in the bath.

〔Example〕

Hereinafter, the features of the present invention will be specifically explained using examples with reference to the drawings.

FIG. 1 is a diagram showing the overall configuration of the apparatus used in this example. However, the portion surrounded by the dashed dotted line in the figure is shown enlarged relative to the outside of the frame. In this embodiment, a twin-belt type continuous casting machine is used in which the slab is conveyed from the sump in a downwardly inclined manner. However, the continuous casting machine is not limited to this, and various other types can be used.

A pair of running metal bells) 3a are injected from a molten metal container 1, such as a tundish, through an injection nozzle 2.

The molten metal poured into the pool 4 formed between the metal bells 3b is cooled by heat removal through the metal bells 3a and 3b, and becomes a solidified shell 5. This solidified shell 5 grows in the process of running in synchronization with the metal bells 3a and 3b,
The solidified shells 5 formed on the respective metal bells 3a and 3b are carried out from the continuous casting machine as an integrated slab 6.

The slab 6 is then guided by entry guide rolls 7 and into a bath 9 containing molten metal 8. In the bathtub 9, the slab 6
A solidified substance is deposited from the molten gold@8 on the surface of the molten gold.

This solidified material grows as the slab 6 advances in the bathtub 9 and becomes the surface modified layer 10. Thickness of surface modified layer lO,
Or the thickness of the laminated solidified layer, in other words, the cladding ratio is
The surface temperature of the slab 6 entering the

The distance through which the slab 6 is flowed in the bathtub 9 and the speed through which the slab is flown.

It can be controlled by changing the temperature of the molten metal 8, etc. For example, in order to keep or heat the molten metal 8 to a set temperature, the bathtub 9 is provided with a controllable heating mechanism. The molten metal 8 may be of the same type as the slab 6 or of a different type. For example, stainless steel, copper, aluminum, and nickel are used for slab 6 of ordinary steel composition.

A surface modified layer/laminated solidified layer 10 of tin or the like can be formed.

The slab 6 that has passed through the bath of molten metal 8 is guided by an exit guide roll 11 and led between a pair of reduction rolls 12 . The surface-modified layer 10 is pressed against the slab 6, which is the base, by the reduction roll 12, and the bonding strength between the surface-modified layer 10 and the base is improved. At this time, the exit guide roll 11 is provided with a wiper function, and the excess molten metal 8 is removed from the reduction roll 1.
It is also possible to prevent it from being carried away in two directions.

Alternatively, a squeezing roll may be provided separately.

Note that it is preferable to join a dummy sheet to the tip of the slab 6 so that the slab 6 passes through the bathtub 9 along a predetermined travel path.

Next, stainless steel (S
An example of operation when forming a surface modified layer according to US 304) will be explained.

As the slab 6, molten metal having a common steel composition and a temperature of 1580°C was poured at a pouring rate of 400 kg/min, and a molten metal of 5 m
Thickness: 30 mm, width: 300 mm, cast at a casting speed of /min.
A slab of fffffi was used. The surface temperature of this slab 6 at the time it was taken out from the continuous casting machine was 1320°C. During the process of conveying this slab 6 to the bathtub 9, its surface temperature decreased to 1210°C.
No occurrence of oxidized scale or the like which adversely affected the formation of 0 was observed.

As the molten metal 8, stainless steel I (SUS 304
) was prepared by melting it at a temperature of 1550°C. The slab 6 was passed through the bath of molten metal 8 at a predetermined plate passing speed. At this time, the hot water passing distance was 1.6 m, and the thickness before passing through the reduction roll 12 was 42, and the thickness after passing through the reduction roll 12 was 3,611,111. The obtained slab was in good condition with no defects on the surface.

In addition, in the above example, the case where the slab 6 carried out from the continuous casting machine was conveyed to the bathtub 9 while being open to the atmosphere was explained. However, the present invention is not limited to this, and the conveyance path of the slab 6 from the continuous casting machine to the surface modified layer forming process is covered with an appropriate hood, and the slab 6 is transported under a protective atmosphere. It can also be transported to the bathtub 9. Alternatively, a refrigerant that does not adversely affect the surface properties of the slab 6 can be supplied into the hood that covers the slab 6 in this manner, thereby imparting a rapid cooling effect to the slab 6.

〔Effect of the invention〕

As explained above, in the present invention, the slab immediately after being carried out from the continuous casting machine is passed through a molten metal bath of the same type or a different type while maintaining its surface condition.

As a result, surface defects in the slab formed during continuous casting are covered with the surface modification layer, so that they do not have an adverse effect on the product. Also, when the slab passes through the molten metal bath, double skin! Since defects such as wrinkles are remelted, the properties of the base slab are also improved. Furthermore, by selecting the temperature conditions in which the surface is solidified again after the surface is remelted, a slab with sufficient joint strength between the old solidified part and the newly solidified part can be obtained. In this way, according to the present invention, it is possible to manufacture thin sheets of excellent quality while compensating for the drawbacks of continuous thin sheet casting machines.

[Brief explanation of the drawing]

FIG. 1 shows the overall configuration of an apparatus used in an embodiment of the present invention. Patent applicant Nippon Steel Corporation

Claims (1)

[Claims] 1. The slab immediately after being carried out from a continuous casting machine that produces slabs by rapid solidification of molten metal is passed through a molten metal bath to form a modified layer and/or a laminated solidified layer on the surface of the slab. A thin plate continuous casting method characterized by forming.