JP2740507B2 - Continuous casting method for metal ribbon - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a metal ribbon for continuously producing a metal ribbon by rapidly solidifying a molten metal on the surface of a cooling roll, such as a twin drum method. It relates to a continuous casting method. [Related Art] In recent years, a method of directly manufacturing a ribbon having a thickness of several mm close to the final shape from molten metal such as molten steel has attracted attention. According to this continuous casting method, the hot rolling step is not required, and the rolling to the final shape may be light, so that the steps and equipment can be simplified. As one of such continuous casting methods, there is a twin drum method (see JP-A-60-137562). In this method, a pair of cooling drums rotating in opposite directions to each other are horizontally arranged, and a pool is formed in the pair of cooling drums and, in some cases, a recess defined by a side weir.
A portion of the molten metal contained in the well is cooled by a portion in contact with the cooling drum to form a solidified nucleus to form a solidified shell. As the cooling drum rotates, the solidified shell moves to a so-called roll gap portion where the pair of cooling drums face each other at a position closest to each other as the cooling drum rotates. In this roll gap portion, the solidified shells formed on the surfaces of the respective cooling drums are pressed and integrated with each other to form a target metal ribbon. In addition to the twin drum method, there is also known a single roll method in which a single cooling drum is used, a pool is formed on the peripheral surface of the cooling drum, and a metal ribbon is similarly manufactured by rapid solidification. ing. (See JP-A-61-9948). [Problems to be Solved by the Invention] As described above, when the molten metal is quenched and solidified on the surface of the cooling drum to form a solidified shell, a small amount of the molten metal is formed near the end of the pool in the cooling drum. It will touch the surface. Therefore, at the beginning of solidification shell formation (at the time of solidification nucleation), an extremely large quenching effect is given to the molten metal,
Cracks in the width of the cooling drum
Non-uniform stress is likely to occur. Further, the upper end portion of the basin, that is, the meniscus portion is in an extremely unstable state in accordance with fluctuations in the vertical direction of the molten metal surface and in the width direction of the cooling drum. When determining the starting point of solidification shell formation (the generation point of solidification nuclei) at such a location,
The surface properties are deteriorated due to hot wrinkles in the width direction of the cooling drum of the grown solidified shell, and appear on the product as defects such as waving in the casting direction and the ribbon width direction and uneven thickness. In order to avoid this defect, Japanese Patent Application Laid-Open No. Sho 58-148056 discloses a method of lowering a solidification nucleus generation position (hereinafter, referred to as a solidification shell generation start point) from a molten metal surface using a refractory flapper. Has been proposed. However, according to this method, hot water is easily formed between the refractory flapper and the cooling drum, and secondary problems such as poor shape and deterioration of surface properties are generated. Further, since the flapper is melted, maintenance and management of the apparatus become complicated. Therefore, the present invention sets the starting point of solidification nucleus formation by controlling only the operating conditions without using such a refractory flapper from the lowermost limit of the fluctuation position of the molten metal level in the vertical and width directions. It is an object of the present invention to produce a metal ribbon of excellent quality by lowering and making the starting point of the formation of a solidified shell in the width direction of the cooling drum uniform. [Means for Solving the Problems] The continuous casting method of a metal ribbon according to the present invention, in order to achieve the object, supplied to the surface of a cooling drum in which no refractory coating material is provided on the surface. In producing metal ribbons by quenching and solidifying the molten metal under the surface, increasing or decreasing the degree of superheat of the molten metal, relaxing or strengthening the cooling conditions of the cooling drum, or increasing or decreasing the casting speed of the metal ribbon By adjusting one or more of the means to perform, the generation start point of the solidification nucleus, the cooling drum width direction of the pool section formed on the surface of the cooling drum and the upper and lower molten metal surface of the fluctuation width of the It is characterized in that the solidification depth below the molten metal level is maintained below the lower limit, and the interval between the solidification nucleus generation start position and the roll gap portion is made uniform in the width direction of the cooling drum. That is, in the present invention, when the degree of superheat of the molten metal is increased, the cooling condition of the cooling drum is relaxed and is not strengthened, and conversely, when the degree of superheat of the molten metal is reduced, The cooling conditions of the drum are strengthened and never relaxed. The submerged solidification depth means an interval from a meniscus portion to a solidification nucleus generation position (solidification shell generation start point). In addition, the roll gap means the closest position between the surfaces of the two cooling drums facing each other. Further, the width direction of the cooling drum is the axial direction of the drum rotating shaft, and means a direction connecting two opposing side dams on both sides of the drum end surface. [Operation] FIG. 1 is a view conceptually showing a process of forming a metal ribbon when the present invention is applied to a twin drum method. Molten metal poured from a tundish or the like (not shown) accumulates between a pair of cooling drums 1a and 1b to form a molten metal pool 2. The molten metal in the molten metal pool 2 is cooled by the cooling drums 1a and 1b, and forms a solidified shell 3 through solidification nucleation along the surfaces of the cooling drums 1a and 1b. Then, the solidified shells 3 formed on the surfaces of the cooling drums 1a and 1b are pressed and integrated at the roll gap portion 4 and are carried out as a thin metal strip 5. At this time, in the conventional method, the solidified shell 3 is first generated in the meniscus portions 2a and 2b of the molten metal pool 2. The meniscus portions 2a and 2b are always vertically moved in the range of ± 2 to 5 mm and in the width direction of the cooling drum in a range of ± 2 to 5 mm depending on the flow rate of the molten metal sent from the container and the amount taken out of the molten metal pool 2 as the metal ribbon 5. It fluctuates. When the generation start point of the solidified shell 3 is determined at such a location, the thickness of the generated / grown state of the solidified shell 3 becomes uneven in the vertical and horizontal directions of the cooling drum depending on the presence or absence of the surface of the molten metal pool 2 there. , Greatly fluctuate. For example, when the formation start point (solidification nucleus generation position) of the solidified shell 3 is at the same position as the scene of the molten metal pool 2 which fluctuates vertically and in the width direction of the cooling drum, solidification of the molten metal is extremely high. It is performed rapidly and the surface tends to be irregular in the slab width direction. As a result, vertical wrinkles and horizontal wrinkles occur in the obtained metal ribbon 5. Therefore, in the present invention, increasing or decreasing the degree of superheat of the molten metal, relaxing or strengthening the cooling conditions of the cooling drum, and adjusting one or more of increasing or decreasing the casting speed of the metal ribbon. As a result, the formation start points 3a, 3b of the solidified shell 3
Is set to be lower and uniform than any of the meniscus portions 2a and 2b in the width direction of the cooling drum. As described above, since the meniscus portions 2a and 2b usually fluctuate up and down in a range of ± 2 to 5 mm, the generation start points 3a and 3b are, for example, 5 mm or more based on the average height of the meniscus portions 2a and 2b. It is preferable that the temperature is set low and uniform in the width direction of the cooling drum. By setting the formation start points 3a and 3b of the solidified shell 3 in this way, it is possible to generate the solidified shell 3 under constant conditions regardless of the fluctuation of the molten metal level in the molten pool 2. Therefore, the surface properties of the obtained metal ribbon 5 become stable. In addition, the generation start point 3 of the solidified shell 3 is always
Since a and 3b are below the meniscus portions 2a and 2b, the molten metal is not cooled and solidified very rapidly to form the solidified shell 3. This also makes the surface properties of the metal ribbon 5 excellent, and prevents the internal stress in the vertical and horizontal directions from becoming uneven. [Examples] Hereinafter, the effects of the present invention will be specifically described with reference to examples. In this embodiment, the degree of superheat of the molten metal was employed as a control factor in order to lower the positions of the formation start points 3a and 3b of the solidified shell 3 below the average height of the meniscus portions 2a and 2b in the width direction of the cooling drum. Table 1 shows cooling drums 1a and 1b with a diameter of 600 mm.
While rotating at a peripheral speed of 60 m / min, the distance from the meniscus portion 2a, 2b at a specific location when the metal ribbon 5 is manufactured from molten steel having a normal steel composition to the formation start point 3a, 3b of the solidified shell 3 That is, the solidification depth 1 under the molten metal is expressed in relation to the temperature of the molten steel. Table 1 also lists Ra (center line average roughness) as the surface properties of the obtained metal ribbon 5. At this time, the molten steel was supplied at a rate of about 500 kg / min to produce a metal ribbon 5. The submerged solidification depth 1 was measured by a transmission X-ray method. As is clear from this table, by increasing the temperature of the molten metal and increasing the solidification depth l below the surface of the molten metal, the conditions for forming the solidified shell 3 are stabilized, and the metal ribbon 5 of constant quality is obtained. You can see that. Instead of controlling the degree of superheat of the molten steel, as means for lowering the generation start points 3a, 3b of the solidified shell 3 below the lower limit of the fluctuation of the meniscus portions 2a, 2b in the vertical and cooling drum width directions,
The same effect was obtained by relaxing the cooling conditions by the cold drums 1a and 1b and increasing the drawing speed of the metal ribbon 5. As a method of relaxing the cooling conditions by the cooling drums 1a and 1b, in addition to adjusting the temperature of the refrigerant supplied to the cooling drums 1a and 1b, a coating material having low thermal conductivity is sprayed on the surfaces of the cooling drums 1a and 1b. The method of doing was also adopted. The sprayed coating agent formed a film on the surfaces of the cooling drums 1a and 1b, thereby suppressing heat conduction from the molten metal pool 2 to the cooling drums 1a and 1b. In addition, even when the starting points 3a, 3b of the solidified shell 3 were lowered by combining such a plurality of conditions, a metal strip 5 having a similarly stable quality was obtained. [Effects of the Invention] As described above, in the present invention, the location where the solidified shell is initially generated on the surface of the cooling drum is set lower than the lower limit of the level of the molten metal pool that fluctuates. The formation of a solidified shell at the meniscus portion is prevented. That is, the molten metal is cooled and solidified inside the molten metal pool, and a solidified shell is formed on the surface of the cooling drum. A ribbon is obtained. In addition, since lowering of the solidification starting point is performed by adjusting operating conditions without specially using parts such as flappers, the continuous casting apparatus itself does not become complicated. .

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view schematically showing a process of forming a metal ribbon when the present invention is applied to a twin drum method, and FIG. It is the figure which expanded and showed.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Shigenori Tanaka               Kitakyushu City               Nippon Steel Corporation 3rd Technical Research Institute (72) Inventor Kunimasa Sasaki               3-6-22 Kannonshinmachi, Nishi-ku, Hiroshima-shi               Hiroshi Heavy Industries, Ltd. (72) Inventor Keiichi Yamamoto               3-6-22 Kannonshinmachi, Nishi-ku, Hiroshima-shi               Hiroshi Heavy Industries, Ltd.                (56) References JP-A-60-92051 (JP, A)                 JP-A-62-40955 (JP, A)                 JP-A-60-49835 (JP, A)

Claims (1)

(57) [Claims] When the molten metal supplied to the surface of the cooling drum, on which no refractory coating material is disposed, is rapidly cooled and solidified under the surface of the molten metal to produce a metal ribbon, the degree of superheat of the molten metal is increased or decreased, and the cooling is performed. By relaxing or enhancing the cooling condition of the drum, or adjusting one or more of the means for increasing or decreasing the casting speed of the metal ribbon, the starting point of the formation of solidification nuclei is set on the surface of the cooling drum. The gap between the solidification nucleus generation start position and the roll gap portion by maintaining the solidification depth below the lower surface of the formed pool in the cooling drum width direction and the upper and lower surfaces of the molten metal below the lower limit value of the fluctuation width. A continuous casting method of a metal ribbon in the width direction of the cooling drum.