JP2987009B2 - Large reduction method of slab strand in continuous casting. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for producing a continuous strand under a continuous high pressure in the vicinity of a solidification completion point during the drawing movement of a slab strand drawn from a continuous casting mold. It is intended to improve the yield by preventing cracks in the vicinity of the top portion (the portion which is finally pulled out of the mold after the supply of the molten metal).

[0002]

2. Description of the Related Art Central unavoidable segregation in a slab strand obtained by continuous casting is extremely effectively reduced by rolling down the area near the solidification completion point in the process of drawing the slab strand during continuous casting. And many proposals have already been made, such as JP-A-60-217924.

[0003]

The rolling process in the vicinity of the solidification completion point of the slab strand includes a method using a roll and a method using a forging die. Due to the movement of the molten steel, the molten steel discharged from the top of the strand may damage the casting equipment. Therefore, when such processing is performed during continuous casting, the top of the slab strand is required. Flat metal parts
(Blind plate) was used to prevent the leakage.

[0004] By the way, the mounting of metal at the topmost part of the slab strand involves the movement of the unsolidified molten steel (mainly concentrated molten steel) due to the large pressure of the slab strand, and the pressure of the unsolidified portion in the slab strand is reduced. In order to increase the strength, especially in the rolling process in the vicinity of the topmost part, excessive tensile strain is generated in the solidified shell at the width direction end of the unsolidified molten steel, causing cracks (hereinafter, this crack is called breakage). It is easy to raise, and the top crop margin of the slab strand is 2 times smaller than the strand obtained by normal continuous casting without rolling.
It had to be more than doubled, leaving problems in terms of yield.

[0005] The internal quality can be improved without the leakage of molten steel and the occurrence of breakage in the region near the topmost portion, which are inevitable in continuous casting in which a large reduction is applied to the region near the solidification completion point of the slab strand. It is an object of the present invention to propose a rolling method.

According to the present invention, a continuous high pressure is applied to a region near the solidification completion point during the drawing movement of a slab strand drawn from a continuous casting mold to sequentially press-bond a solidified shell. A metal frame for accommodating unsolidified molten steel discharged by the large pressure reduction is attached to the topmost portion, and the topmost portion is kept in an unsolidified state, and the metal frame of the topmost portion of the slab strand at the same time as the large pressure reduction. A method for forcing a slab strand in continuous casting, characterized by forcibly discharging molten steel in an amount corresponding to the amount of concentrated molten steel.

[0007] In order to keep the topmost portion of the slab strand in an unsolidified state, after the injection of molten steel into the continuous casting mold is completed, for example, the drawing of the slab strand is temporarily stopped to stop the topmost portion. It is particularly preferable to attach a metal frame capable of accommodating unsolidified molten steel discharged under large pressure and to add a heat-generating powder or a heat insulator.

[0008]

[Action] The cracks that occur when a flat metal piece is mounted on the top of a slab strand or when a large pressure is applied while the portion is solidified or closed (hereinafter, this crack is referred to as a notch) Unlike the internal cracks and the center cracks of the slab strand, it is characterized in that a crack C as shown in FIG. 1 is generated near the topmost portion of the strand (both ends in the width direction of the unsolidified molten steel before the rolling process). Occurs at the part corresponding to the solidified shell located at), and the top crop allowance is now about 7.9 m for a slab strand with a width of about 560 mm and a thickness of about 400 mm (size before rolling) .

[0009] The occurrence of such a breakage is caused by the fact that no new molten steel is supplied at the topmost portion of the slab strand, so that the impurity concentration of the entire unsolidified portion becomes lower as the rolling point approaches the topmost portion. It is guessed that this is caused by the rise of the solidification delay, which causes excessive tensile strain as shown in FIG. 2 by the rolling process in a state where the solidified shell is not sufficiently formed.

FIG. 3 shows the ratio between the white band (segregation width) at each cross section and the width of the white band at the start of rolling when a slab strand obtained by applying a large reduction is rolled into a billet. According to this figure, the width of the white band rapidly increased from about 9 m before the top of the slab strand, and at the end point of the rolling process, the white band width was increased. 1.4 to 1.
It is apparent that the concentration of impurities has increased by about 7 times.

[0011] In this invention, as shown in FIG. 4, the metal frame 1 is mounted on the outermost top portion S ₁ of the slab strand S, the addition of exothermic powder or the like surrounded portion by the gold frame 1 Therefore, when the unsolidified molten steel existing inside the strand S is pushed to the top by large pressure, the amount of the concentrated molten steel is reduced. Is discharged into the metal frame, so that the pressure inside the strand does not increase, so that no crack occurs in the solidified shell located at the width end of the unsolidified molten steel. Further, since the molten steel discharged from the topmost portion is accommodated in the metal frame, the casting equipment is not damaged by the leakage of the molten steel.

When mounting a metal frame, there is a disadvantage that the temperature of the molten steel at the topmost portion is lowered. Therefore, it is preferable to apply a refractory lining on the inner surface. By doing so, the solidification of the molten steel discharged under a large pressure can be advantageously delayed.

[0013]

[Example] A slab strand with a width of 560 mm and a thickness of 400 mm
(C: 0.8% steel) during continuous casting of unsolidified molten steel
5 mm, the width of the unsolidified molten steel is 60 mm (18 m from the exit side of the mold) at the position where the forging die rolling (rolling conditions:
(The distance from the top to the end of the rolling process is 3 m, and the amount of rolling is 1.5 times or more the unsolidified thickness.) Stop and attach a metal frame (made of steel), and
_An exothermic powder containing ₂ O ₃ was added, and then a rolling operation was performed in which rolling was performed again to investigate the occurrence of breakage in the topmost portion of the slab strand. As a result, it was inevitable that the conventional type, in which the flat type plate was mounted on the top of the slab strand under the same conditions except that the flat plate was mounted on the top of the slab strand, would cause breakage, In this case, no crack was found at the topmost portion, and it was confirmed that the yield was improved by about 80%.

[0014]

According to the present invention, there is no possibility that the molten steel leaks from the topmost part of the slab strand to damage the casting equipment even when a large reduction is performed during continuous casting. In addition, since cracks peculiar to a region near the topmost portion can be effectively reduced, the yield can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a state of occurrence of cracks at the topmost portion of a slab tosland.

FIG. 2 is an explanatory diagram of a state of occurrence of disconnection.

FIG. 3 is a graph showing the results of an investigation on the tendency of increasing the impurity concentration.

FIG. 4 is an explanatory diagram of the embodiment of the present invention.

[Explanation of symbols]

1 Metal frame S Slab strand S ₁ Topmost part C Notched

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kenji Oshima 1-chome, Mizushima-Kawasaki-dori, Kurashiki-shi, Okayama Pref. Kawasaki Steel Corporation Mizushima Works (56) References JP-A-47-5359 (JP, A) (58) Fields surveyed (Int.Cl. ⁶ , DB name) B22D 11/10 B22D 11/128 B22D 11/16

Claims (2)

(57) [Claims] 1. During the drawing movement of a slab strand drawn from a continuous casting mold, a continuous large pressure is applied to a region near the solidification completion point to sequentially press-bond a solidified shell. A metal frame for accommodating the unsolidified molten steel discharged by the large reduction is attached to the portion, and the topmost portion is kept in an unsolidified state, and simultaneously with the large reduction, the metal frame of the topmost portion of the slab strand is placed in the metal frame. Characterized by forcibly discharging an amount of molten steel corresponding to the amount of concentrated molten steel,
A large reduction method for slab strands in continuous casting. 2. The method according to claim 1, wherein an exothermic powder or a heat insulating agent is added to the inside of the metal frame to maintain the topmost portion of the slab strand in an unsolidified state.