JPS597464A - Method and device for continuous casting of thin steel plate - Google Patents

Abstract

PURPOSE:To increase the casting amt. of molten steel and to decrease the number of inclusions in an ingot and the local recesses in the surface, by forming a cylindrical shelllike ingot from the molten steel cooled by casting walls then applying rolling down force on the ingot with rolling rolls having gradually decreasing gaps. CONSTITUTION:The molten steel charged into a casting space from a charging nozzle 8 is cooled along circulating bodies 1, 1' and stationary side plates 19, 19' for cooling side surfaces, whereby a solidified shell is formed. The solidified shell grows gradually and moves forward while forming a cylindrical shelllike solidified shell. The solidified shell contg. the unsolidified molten steel 6 remaining in the inside is drawn out from the opening part on the side opposite to the side of the casting space where the molten steel is charged. The ingot grown to such cylindrical shelllike solidified shell receives gradually increasing rolling down force to decrease gradually in the thickness thereof in the stage of passing through the gaps of rolling rolls 9, 9'-18, 18' and is drawn out as an ingot 5 contg. no unsolidified molten steel in the inside and having a desired thickness on the outlet side of the final rolling rolls 18, 18'.

Description

[Detailed Description of the Invention] The present invention relates to a continuous casting method for thin steel sheets and an apparatus therefor, and is characterized in that a solidified shell crimping mechanism is employed in such technology for continuously casting thin steel sheets directly from molten steel. This is a proposal for a certain method and apparatus.

Conventionally, in order to manufacture thin steel sheets, a steel ingot is created by mass ingot processing, and then the ingot is bloomed and rolled to a thickness of 10() to 80%.
(After being made into a slab of 1 mm, it was further rolled into a thin steel plate of about 8Q mm by rough rolling, and then hot-striped into a thin copper strip of 0 mm or less.)

On the other hand, there is a conventional technique as shown in FIG. 1 in which a thin slab is directly cast by a continuous casting method and then rolled into a thin steel plate. This technique involves injecting molten metal (molten steel) into a water-cooled mold 102 through an injection nozzle 101 to generate a solidified shell 103 along the four walls, and then passing the solidified shell 108 through a guide roll 104 or the like. This method involves continuously drawing thick slabs and then rough rolling them into thin steel plates, but this method has the following problems. That is, in this method, since the thickness of the slab is determined by the diameter of the injection nozzle, the smaller the nozzle diameter is, the better. However, the nozzle diameter needs to be 100 mm or more to prevent the molten metal from solidifying inside during injection, and generally a nozzle with a diameter of 150-" 170 mm is used. are doing.

Therefore, the thickness of slabs that can be cast is at least 180 mm, and usually 200 to 260 mm thick. In this sense, the mold used in the conventional continuous casting method described above has a substantially rectangular shape as shown in FIG. 1, and has a structure that makes it difficult to draw out thin slabs.

On the other hand, there is a conventional continuous casting apparatus as shown in FIG. 2 which further improves the above-mentioned continuous casting apparatus.

This device consists of a circulating body 2 consisting of endless metal belts arranged facing each other at intervals approximately equal to the desired slab (steel plate) thickness.
Molten steel is injected into the gap that becomes the chimney space formed by 01 and 201' through a slit-shaped injection nozzle 202 having a molten steel flow path smaller than the gap, and the injected molten steel is cooled along the circulation bodies 1 and 1'. By the cooling action of the devices 808 and 808', the parts that are in contact with the circulating bodies 201 and 201' are sequentially cooled and solidified, and gradually grown.
The cast slab 205 is continuously drawn by drawing rolls 204 and 204' to obtain a slab 205 of a desired thickness. In this conventional device, there is a requirement that the size in the thickness direction of the molten steel flow path of the injection nozzle 2 that supplies molten steel into the casting gap must be small, from several mm to several tens of mm. Since the thickness of the refractory material at the tip of the injection nozzle 202 must also be reduced, the injection nozzle 20
There were fatal flaws such as molten steel solidifying inside the 2nd chamber, causing clogging, and the refractory being eroded, making it impossible to withstand continuous use for long periods of time.

In addition, as a further advanced continuous casting technology for thin steel sheets, a reduction metal is added to the slab that has already solidified or is in the final stage of solidification at a position below the circulating bodies 201 and 201' for final thickness adjustment. A method has been proposed.

The purpose of rolling in this technique is to reduce the center segregation of the slab by squeezing the impurity-concentrated molten steel at the center of the slab into the bulk molten steel above. Moreover, the characteristic force of this technology is that the thickness has already been reduced by adjusting the side wall shape, and the position where the reduction is applied is near the final solid part of the lead piece, and the reduction rate is at most several times. For example, it is a percentage.

An object of the present invention is to provide a continuous casting technique that can advantageously overcome the drawbacks of the continuous direct casting technique of thin copper plates using conventional slit-type nozzles as described above. The continuous casting method of the present invention consists of a pair of circulating bodies arranged opposite each other, which circulate while maintaining a gap for holding the cast molten steel over a certain distance, and both sides of the circulating bodies. In a method of directly casting thin copper sheet metal from molten steel through a thin steel sheet continuous casting device that constitutes a casting space with a pair of fixed side plates located at the edges, the molten steel injected into the casting space contacts the four walls. After cooling to produce a cylindrical slab with an unsolidified center, the thickness of the cylindrical slab is gradually reduced by rolling rolls whose spacing is gradually narrowed as the cylindrical slab grows. 1. The details of the method of the present invention will be explained below.

In the present invention, as described above, the solidified shell that has grown into a cylindrical shell shape with the center part in an unsolidified state is rolled down, and the thickness of the piece (thickness of the steel plate) is gradually adjusted as it cools and solidifies. However, what must be technically considered in this regard is the internal crack caused by the bulging of the slab in the gap between the rolling rolls used for rolling, and the short side shape of the three pieces (copper plate). There are two points regarding the transformation of .

When rolling unsolidified slabs using a conventional fixed mold continuous casting machine, the slab thickness is approximately 200 mm or more, so the diameter of the rolling rolls must be increased, and the roll pitch must be increased. The amount of internal cracks due to bulging during this period becomes large and cannot be ignored. For these reasons, in conventional fixed mold continuous casting machines, it has not been put to practical use to roll down the unsolidified slab to actively reduce the thickness of the slab.

Regarding this point, in order to reduce the internal cracking due to slab bulging between rolling rolls as in the method of the present invention to a level that does not pose a practical problem, it is possible to solve this problem by reducing the rolling roll diameter and reducing the roll pitch. . Note that by adopting this rolling reduction technology, the amount of roll reduction is smaller than that of large-diameter rolls, so in order to finally roll a thin steel plate to the desired thickness, it is necessary to reduce the initial thickness of the slab in advance. It is necessary to keep it.

However, in order to reduce the initial slab thickness to less than half of the conventional thickness, and to maintain the same production rate of 8M, the casting relationship must be set to 2.
In order to achieve this, it is difficult to support and cool the slab in the mold with a conventional fixed mold type continuous casting machine that has an inverted triangular fixed side plate and has a configuration in which the hearth surface is pre-squeezed. As described in the examples, it is a necessary condition to adopt the reduction adjustment technique of the present invention, which brings the solidified shell slab into close contact with the solidified shell slab and gradually reduces its thickness in accordance with the gradual growth of the solidified shell slab as it cools. Become.

@ Figures 3 and 4 show an apparatus suitably used for carrying out the above-described method of the present invention.

Reference numerals 1 and 1' in the figure indicate a pair of endlessly rotating metal belt circulation bodies facing each other at a distance larger than the desired thin steel plate thickness, and which are cast over a fixed distance by supporting rolls 7°71. Forms a gap that holds molten steel. These circulating bodies 1, 1' have surfaces (inner wall surfaces) in contact with the molten steel.
Cooling devices 3 and 8' are installed on the opposite side (outer surface), and cooling is achieved thereby. Their circulatory bodies l, 1
Fixed side plates 111. for the J-plane cooling body are provided on both side edges of the
19' is disposed, and together with the circulating bodies 1 and 1', the entire casting space is formed in which the molten steel is held over a certain distance and solidified.

In the slab drawing direction of the circulating bodies I and 1', the interval gradually increases from a distance that is approximately equal to or even smaller than the interval between the short sides of the slab in the casting space to an interval corresponding to the desired in-plate thickness. A plurality of pairs of rolling roll groups 9, 9' to l 8 whose distance is narrowed,
] 8' is placed. In the apparatus of the present invention, ten pairs of rolling rolls 9,9' to 18,1.8' were arranged. The molten steel injected into the casting space from the injection nozzle 8 is transferred to the circulating body 1.1' and the fixed side plate for side cooling] 9, 19
', a solidified shell is generated, which gradually grows and moves forward in the casting direction (drawing direction) while forming a cylindrical solidified shell, leaving unsolidified molten steel 6 inside. The raw material is extracted from the opening on the opposite side of the casting space from the molten steel injection side.

The slab that has grown into a cylindrical solidified shell is transferred to the rolling rolls 9, 9' to 18, 18' disposed in front of it in the sending direction.
When passing through the gap, ill! The final rolling rolls 18, 18 gradually reduce their thickness in response to the increasing rolling blades.
'On the outlet side, a slab 5 containing no unsolidified molten steel and having a desired thickness is extracted. Incidentally, changes in the shape of the slab due to the protrusion of the furnace side surface of one piece 5 during rolling can be easily prevented by providing the reduction roll itself with a flange that prevents the short side from protruding.

Below, by using the continuous casting apparatus of the present invention, a width of 500 mm,
Low carbon aluminum killed steel plate with a thickness of 10 to 60 ttLrn (composition: O: 0.085%, Si: tr, Mn
: 0.44%, P: 0.012%, S: 0.0
18%, A15ot: 0.027%) at 1000 per minute
The results of casting at a speed of 1W will be explained. As a conventional example, the results of casting thin steel plates of the same size and steel type at the same speed using the apparatus shown in FIG. 1 are shown.

In casting according to the present invention, a circular cross-section nozzle with a molten steel flow path diameter of φ5Q mm is used, and the interval between the circulating bodies 1 and 1' is 1 (10 m
Casting was carried out by setting the rolling reduction ratio at rolling rolls 9.9' to 18, ]8' as shown in Table 1. In addition, in the comparative example of casting by the conventional method, the thickness] I) m
rn, 20mm, 80mm, 40mm, 50mm.

When casting slabs of each thickness of 6Q mm, the molten steel flow path is 5 mm x 300 mm and 10 m, respectively.
m x 800mm, 20mm x 800mm
, 25 am x 800 mm.

Casting was carried out using a slit-type nozzle with a rectangular cross section of 80 mm x 60 mm. In each case, approximately 5000 kg of molten lead was used per casting.

Figure 5 shows the molten f cast per molten steel injection nozzle.
The relationship between iIAat and slab thickness is shown. In the comparative example, the nozzle was clogged during casting and only 700 to 7 molten steel could be cast at most, whereas in the present invention, the total amount of molten steel of about 5000 kt received for any slab thickness. was able to be cast.

Figure 6 shows the relationship between the weight of non-metallic inclusions contained per 1 kg of cast iron and the thickness of the fishing piece. was able to be reduced to

Figure 7 shows the relationship between the depth of local dents such as hot water wrinkles on the surface of the slab and the thickness of the slab.With the present invention, the depth of local dents on the surface of the slab is significantly reduced compared to the comparative example. did it.

As described above, according to the present invention, compared to the conventional method, it is not only possible to significantly increase the number of molten steel castings until casting becomes impossible due to blockage or melt damage of the molten lead injection nozzle, but also to reduce the number of inclusions in the fishing piece, η It is also possible to significantly improve local depressions on the surface of the slab.

In addition, by arranging the continuous casting apparatus JM'fr of the present invention so that the production direction is in the direction of the lead mold, and by appropriately setting the number of rolling rolls and the rolling reduction ratio, it is possible to 9. The cross-sectional shape of the casting space formed by IO' can be made the same as that of a conventional continuous slab caster, and by doing this, the tundish for pouring and the pouring nozzle This has the advantage that conventional continuous slab casting machines can be used as is.

[Brief explanation of the drawing]

Fig. 1 is a perspective view of a continuous casting apparatus for thin steel plates using a conventional fixed mold, Fig. 2 is a schematic diagram of a continuous casting apparatus for thin steel plates using a conventional slit-type injection nozzle, and Fig. 8 is a A schematic diagram of the continuous casting apparatus for thin steel sheets of the present invention; FIG. 4 is a sectional view taken along the line A-A' in FIG. 8; FIG. 5 is a graph showing the relationship between slab thickness and molten steel casting surface. , Figure 6 is a graph showing the relationship between slab thickness and the weight of non-metallic inclusions contained per 1 kf of slab, and Figure 7 is a graph showing the relationship between slab thickness and dent depth on the slab surface. It is. 1, ]'... Circulating body, 2... Slit type injection nozzle, 8.3'... Cooling device, 4, 4'... Drawing roll, 5... Slab, 6... Molten steel, 7, 7'...Support roll, 8...Injection nozzle, 919'...A1 rolling roll, 10.10'...42 rolling roll, 11
, l 1'...A3 rolling roll, 12.12'...
・A4 rolling roll, 18.18'... flat 5 rolling roll, 14.14'... A6 rolling roll,] 5, ]
5'...A7 rolling roll, ] 6, ] 6'.
...Y8 rolling roll, 17.17'-A9 rolling roll,
I 8 , ] 8'... Ago rolling roll, 19
, 19'...For side cooling? side plate. Figure 1 Figure 2 Figure 3 Figure 5 New)! 74 w <mm) Figure 6 麟片/! fN (mm)

Claims (1)

[Scope of Claims] L A pair of circulating bodies disposed opposite each other that circulate while maintaining a gap for holding cast molten steel over a certain distance, and a pair of circulating bodies located on both side lines between the circulating bodies. In a method of directly casting thin steel plates from molten steel through a continuous thin steel plate casting device that forms a casting space with a fixed side plate, the molten steel injected into the casting space is cooled in contact with the four walls, leaving the center unsolidified. After producing a cylindrical slab, solidification is completed by applying a rolling blade that gradually reduces the thickness of the slab using rolling rolls that gradually narrow the interval during the process of growth of the cylindrical slab. A method for continuous casting of thin steel sheets, characterized in that the steel sheets are turned into the required steel sheets at the end point of casting. λ A casting space is created by a pair of opposing circulating bodies that circulate while maintaining a gap to hold the cast molten steel over a certain distance, and a pair of fixed side plates located on both side edges between the circulating bodies. In the thin steel sheet continuous casting apparatus constituting the apparatus, a large number of pairs of rolling rolls, such as a pair of opposing rolls, are arranged in a row at a position adjacent to the end of the circulating body in the feeding direction, oriented in the solidified shell drawing direction. , and the spacing between the opposing rolls of the rolling rolls is gradually narrowed in the feeding direction, and the distance between the opposing rolls is tapered at the end point of the rolling rolls, and the distance between the rolling rolls is approximately equal to the thickness of the steel plate, A continuous casting device for thin steel sheets, characterized in that the gap between each rolling roll is reduced by a combination of small diameter rolls.