JP2015164742A - Casting method and casting machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a casting method and a casting machine capable of preventing cracking of the central portion of a cast piece that may be generated in a casting process.SOLUTION: A casting method comprises at least a cooling step of cooling a cast piece including an unsolidified part and a solidified shell on an outer peripheral portion of the unsolidified part, the cooling step including suppressing cooling of the cast piece by cooling suppression means.

Description

  The present invention relates to a casting method and a casting apparatus, and more particularly to a casting method and a casting apparatus that prevent cracking of a central portion of a slab that occurs in a casting process.

  One of the steel production processes is the integrated steelmaking process. Specifically, it is a process in which hot metal is produced from iron ore in a blast furnace, and subsequently, molten steel is produced from hot metal in a converter, and then the molten steel highly purified by secondary refining is solidified by continuous casting. The finished cast product is hot-rolled after heating, and then becomes a steel product through a plurality of steps (Non-Patent Document 1).

  The continuous casting method is a method in which casting for solidifying molten steel is continuously performed, and is a method in which molten steel is continuously cast in a mold and solidified cast pieces are continuously taken out for production. The equipment of the continuous casting equipment includes a tundish that distributes molten steel from the ladle, an immersion nozzle that guides the molten steel to the mold, a mold that solidifies the molten steel to form a solidified shell, and a secondary cooling zone that cools the solidified shell from the surrounding , Etc.

  According to the continuous casting method, since the molten metal can be solidified without interruption, productivity can be increased. Further, it is a method capable of dealing with various metal materials such as iron-based, aluminum-based, copper-based and alloys thereof.

  Problems of the continuous casting method include surface cracks and internal cracks in the slab during the casting process. Since the molten metal gradually solidifies as the temperature decreases, depending on the composition of the metal material, it may become brittle and weak in elongation and bending in a specific temperature range during the casting process. If tensile stress is applied for some reason, cracks may occur in the slab. In particular, slabs with cracks in the center are difficult to satisfy the required performance as the final product, and cannot be transferred to the next process such as hot working, resulting in reduced productivity. .

Akira Tanaka, “Basics and Mechanisms of Latest Metals Understandable”, First Edition, Hidekazu System Co., Ltd., March 15, 2013, p. 124-125

  In view of the above problems, an object of the present invention is to provide a casting method and a casting apparatus that prevent cracking of a central portion of a slab that occurs in a casting process.

  In order to solve the above-mentioned problem, the present inventor has intensively studied a method for preventing the crack of the center portion of the slab generated in the casting process. As a result, it has been found that cracking of the center portion of the slab can be prevented by suppressing the cooling of the slab having the solidified shell on the outer periphery during the casting process. Furthermore, by suppressing the cooling, an excessive temperature drop of the slab can be prevented, and as a result, the burden of reheating the slab in the next process such as hot working can be reduced. The present inventor has obtained these findings and has come up with the present invention.

  That is, the casting method according to the present invention is a casting method including at least a cooling step of cooling an unsolidified portion and a slab having a solidified shell on an outer peripheral portion of the unsolidified portion, wherein the cooling step includes cooling suppression. It is a casting method including the cooling suppression process which suppresses cooling of the said slab by a means.

  In another aspect, the present invention is a casting apparatus, which cools the injected molten alloy to form a slab having a solidified shell on an unsolidified portion and an outer peripheral portion of the unsolidified portion. A casting apparatus including at least a mold and cooling suppression means for suppressing cooling of the cast slab that descends in a vertical direction from a lower part of the mold of the mold.

  According to the casting method and the casting apparatus of the present invention, it is possible to prevent cracking of the central portion of the slab that occurs in the casting process.

Sectional drawing which shows the one aspect | mode of the casting apparatus of this invention. Sectional drawing which shows the casting apparatus of the aspect different from FIG. Sectional drawing which shows the casting apparatus of the aspect different from FIG. 1, FIG. Sectional drawing which shows the casting apparatus of the aspect different from FIGS. The figure which shows the one aspect | mode of a cooling suppression means. Sectional drawing which shows the conventional casting apparatus. Sectional drawing of the slab cast by Example 1,2. Sectional drawing of the slab cast by Comparative Examples 1 and 2. FIG. Sectional drawing of the slab cast by Example 3. FIG.

  Hereinafter, the general form of the casting method and casting apparatus of the present invention will be described in detail. However, this invention is not limited by the form demonstrated below.

  The casting method of the present invention includes at least a cooling step of cooling an unsolidified portion and a slab having a solidified shell on the outer peripheral portion of the unsolidified portion. By cooling such a slab, solidification of the unsolidified portion surrounded by the solidified shell proceeds, resulting in a cast product. Depending on the heat capacity of the slab to be obtained, cooling may be forcibly cooled using a cooling facility or may be naturally cooled in a room temperature atmosphere under a casting environment. In the cooling step, natural cooling ( A cooling suppression step of suppressing the cooling of the slab so that the cooling rate is slower than that in the air. By this step, it is possible to prevent cracking of the center portion of the slab that occurs during cooling. In the cooling process, when the cooling is not suppressed, the cooling can be prevented at the time when the center portion of the slab is cracked, thereby preventing the occurrence of the crack. In addition to the time at which the cracks occur, cooling can also be suppressed at predetermined sites before and after the time. It is also possible to suppress cooling from the start to the end of the cooling process.

  The cooling suppression means may be any means that can suppress cooling of the slab. Although the slab has a solidified shell on the outer peripheral portion of the unsolidified portion, the surface temperature is very high because it is not completely cooled. Therefore, the cooling suppression means can include at least a heat insulating material having heat resistance capable of withstanding the surface temperature of the slab. As the heat insulating material, for example, ceramic fiber blanket, refractory brick, rock wool, heat insulating board, heat insulating brick and the like can be used. Examples of the cooling suppression means include means capable of covering the periphery of the solidified shell of the slab with the heat insulating material. For example, depending on the shape of the slab, it is a box shape or a cylindrical shape having a space portion penetrating in the vertical direction or a space portion penetrating in a direction perpendicular to the vertical direction, and the influence of the heat of the slab What received the inner wall coat | covered with the heat insulating material can be made into a cooling suppression means. The heat insulating material may be in contact with the solidified shell of the slab, or may be non-contact. However, in order to sufficiently obtain the effect of suppressing the cooling, the distance between the solidified shell of the slab and the heat insulating material is preferably 0 mm to 100 mm.

  The casting method of the present invention can be applied to various metal materials such as iron-based, aluminum-based, copper-based, and alloys thereof. However, the material of the slab can be a steel material. Steel materials are materials mainly composed of iron and are important industrial materials. The casting method of the present invention is a method that can target such a steel material.

  When the material of the slab is a steel material, the unsolidified portion of the slab is solidified by cooling to an austenite structure, and further cooled to a ferrite structure. In the case of carbon steel containing carbon, the unsolidified part of the slab is solidified by cooling to become a two-phase mixture of austenite and cementite, and further cooled to a pearlite structure that is a two-phase mixture of ferrite and cementite. It becomes. On the other hand, the solidified shell is further cooled from austenite to become ferrite, and in the case of carbon steel, it becomes pearlite from a two-phase mixture of austenite and cementite. Austenite has a face-centered cubic lattice structure and an atomic filling factor of 74%. On the other hand, ferrite has a body-centered cubic lattice structure, and the atomic filling rate is 68%. By transforming from austenite to ferrite, the atomic filling rate decreases, so the volume of the slab expands. In the cooling process, transformation from austenite to ferrite is performed from the surface of the slab to the inside, and volume expansion also proceeds from the surface of the casting to the inside. The slab from the beginning to the end of the volume expansion has a brittle property that is weak against elongation and bending. When the expansion of the volume of the slab is abrupt, if a tensile stress is applied for some reason before the expansion ends, a crack is easily generated at the center of the slab.

  In the casting method of the present invention, the cooling suppression step can include a first cooling suppression step of suppressing cooling in the process of transformation from an austenite structure to a ferrite structure or a pearlite structure. Since the rapid volume expansion of the slab due to cooling can be suppressed during the period from the start to the end of the volume expansion of the slab due to transformation, it is possible to prevent cracks occurring at the center of the slab. In the first cooling suppression step, the cooling suppression means can be used.

  The casting method of the present invention can be a continuous casting method. The continuous casting method includes at least a pouring step, a cast piece forming step, a removing step, and a cooling step. The pouring step is a step of pouring a molten steel material into a mold, and is a pre-step for solidifying the molten metal into a slab. The slab forming step is a step of forming a slab having a solidified shell on an unsolidified portion and an outer peripheral portion of the unsolidified portion by cooling the mold and cooling the molten metal. By this step, the molten metal is cooled to become a slab. The removal step is a step of removing the slab from the mold. By this step, the slab that has been taken out is cooled in the next step, and the molten metal is sequentially poured into the mold from which the slab has been taken out. The cooling step is a step of cooling the slab after the taking out step. By this step, the slab of the unsolidified portion and the solidified shell is transformed into a ferrite structure or a pearlite structure. By the continuous casting method including these steps, the molten metal can be continuously cast to produce a slab.

  The continuous casting method may further include a slab cutting step of cutting the slab after the cooling step. If necessary, the cut slab can be used as an electrode, and after passing through a process such as vacuum arc remelting or electroslag remelting, it can be transferred to the next hot working. Hot working is to perform plastic working such as rolling, forging, and extruding a metal material at a temperature higher than the recrystallization temperature. Therefore, when the cooled slab needs to be heated to the recrystallization temperature or higher, the cooling is suppressed until the slab is cut from the state transformed into the ferrite structure or pearlite structure, thereby reducing the heating burden. can do. Therefore, in the casting method of the present invention, the cooling suppression step can include a second cooling suppression step of suppressing cooling performed until the cast piece transformed into a ferrite structure or a pearlite structure is cut. The second cooling suppression step can use the cooling suppression means. Further, the first cooling suppression step and the second cooling suppression step can be discontinuous steps, and can be continuous steps. For example, it can be set as the continuous cooling suppression process by continuing suppressing the cooling of a slab by a cooling suppression means until the slab taken out from the casting_mold | template is cut | disconnected.

  The continuous casting method may include a secondary cooling step of cooling the slab after the take-out step and before the cooling step. By cooling the slab until just before the cooling needs to be suppressed by this step, the period for cooling the slab can be shortened, so that the casting efficiency can be increased. As the secondary cooling step, for example, a step of cooling the solidified shell of the slab from the outside by water spray, air-water spray or the like can be mentioned.

  Next, the casting apparatus of the present invention will be described. The casting apparatus of the present invention includes at least a mold and cooling suppression means. The mold cools the injected molten metal to form an unsolidified portion and a cast piece having a solidified shell on the outer peripheral portion of the unsolidified portion. As the mold, a mold can be used, and a mold having a space portion penetrating in the vertical direction in which a molten metal can be poured is preferable. This is because it is possible to inject a molten metal into the mold from the upper part of the space, cool the injected molten metal, and take out the slab from the lower part of the space, thereby increasing the production efficiency. The cooling suppression means is means for suppressing cooling of the slab that descends in a vertical direction from a lower part of the mold of the mold. The slab lowered from the mold is cooled by natural cooling or the like in a room temperature atmosphere in a casting environment. By using the cooling suppression means, it is possible to prevent cracking of the central portion of the slab that occurs during cooling. The cooling suppression means can be prevented from being cracked by being used at the time when the center portion of the slab is cracked during cooling. In addition to the time when the cracks occur, cooling can be suppressed before and after the time. It is also possible to suppress cooling from the start to the end of the cooling process.

  The said cooling suppression means can be equipped with the heat insulating material which has heat resistance at least. As the heat insulating material, for example, ceramic fiber blanket, refractory brick, rock wool, heat insulating board, heat insulating brick and the like can be used. Examples of the cooling suppression means include means capable of covering the periphery of the solidified shell of the slab with the heat insulating material. For example, depending on the shape of the slab, it is a box shape or a cylindrical shape having a space portion penetrating in the vertical direction, and a cooling suppression means that covers the inner wall affected by the heat of the slab with a heat insulating material It can be. The heat insulating material may be in contact with the solidified shell of the slab, or may be non-contact. However, in order to sufficiently obtain the effect of suppressing the cooling, the distance between the solidified shell of the slab and the heat insulating material is preferably 0 mm to 100 mm.

  The casting apparatus of the present invention can target a steel material by casting the material of the slab as a steel material. In this case, the cooling suppression means can include first cooling suppression means for suppressing cooling until the austenite structure of the slab is completely transformed into a ferrite structure or a pearlite structure. Since the rapid volume expansion of the slab due to cooling can be suppressed during the period from the start to the end of the volume expansion of the slab due to transformation, it is possible to prevent cracks occurring at the center of the slab. The cooling suppression means can be used as the first cooling suppression means.

  The casting apparatus of the present invention can be a continuous casting apparatus. The continuous casting apparatus includes at least a container, a mold, a control unit, and a cooling suppression unit. The container is a container that holds a molten steel material and injects the molten metal into the mold. An example of the container is a tundish. The tundish can adjust the flow rate of the molten metal, and can float and separate slag and inclusions in the molten metal. As for the mold, as described above, more specifically, a mold that is a water-cooled copper or iron mold and that has a space portion penetrating in the vertical direction is generally used. The control means is means for controlling a descending speed of the slab that descends in a vertical direction from a lower part of the mold. If the descending speed becomes too fast due to the weight of the slab, a thin portion of the solidified shell may be broken and a breakout may occur in which the unsolidified molten metal is exposed. Further, if the descending speed is too slow, the production efficiency is lowered. Therefore, in order to produce a stable slab while maintaining production efficiency, a control means for controlling the descending speed of the slab is required. As the control means, an elevating device capable of controlling the drawing of the slab can be used. The cooling suppression means is as described above.

  The continuous casting apparatus may further include slab cutting means for cutting the slab transformed into a ferrite structure or a pearlite structure. In this case, the cooling suppression means can include second cooling suppression means for suppressing cooling until the slab transformed to a ferrite structure or a pearlite structure is cut. By providing the second cooling suppression means, it is possible to reduce the burden of heating the ingot to the recrystallization temperature or higher in hot processing or the like in the next step. The cooling suppression means can be used as the second cooling suppression means. Further, the first cooling suppression means and the second cooling suppression means can be discontinuous means or can be continuous means. For example, the cooling of the slab can be continuously suppressed by the continuous cooling suppression means until the slab descended from the mold is cut.

  The continuous casting apparatus may include secondary cooling means for cooling the slab between the mold and the cooling suppression means. By using this means, the casting efficiency can be increased. Examples of the secondary cooling means include a secondary cooling zone provided with a spray nozzle.

  The continuous casting apparatus may include additional equipment such as an immersion nozzle that guides the molten metal in the tundish to the mold and a shield that blocks the molten metal from outside air.

  Hereinafter, embodiments of the casting method and the casting apparatus of the present invention will be described with reference to the drawings. In this case, the present invention is not limited to the embodiments of the drawings.

  FIG. 6 is a cross-sectional view showing a conventional casting apparatus. The illustrated casting apparatus 101 is a vertical casting apparatus including a tundish 103 for holding a molten steel material 102, a water-cooled mold 104 made of iron, and an elevating device 106 for controlling a descending speed of a cast piece 105. The molten metal 102 held by the tundish 103 is injected as a molten metal flow 108 from a nozzle 107 provided at the bottom of the tundish 103 into a water-cooled mold (mold) 104 provided with a slag 109. The molten metal 102 injected into the water-cooled mold 104 is cooled by being injected into the water-cooled mold 104, and then becomes the solid phase C from the melt A through the mixture B of the melt and the solid phase. The slab 105 that has become the solid phase C is pulled out of the water-cooled mold 104 by the lifting device 106 and cooled. The casting apparatus 101 can further include a shield 110 that blocks the molten metal 102 from the outside air, and a slab cutting device (not shown) that cuts the slab 105. The slab 105 that has become the solid phase C is transformed from an austenite structure to a ferrite structure or a pearlite structure from the surface to the inside by cooling, and the volume expands. The slab from the beginning to the end of the volume expansion has a brittle property that is weak against elongation and bending. If the expansion of the volume of the slab is abrupt, if a tensile stress is applied for some reason before the expansion ends, a crack may easily occur at the center of the slab.

  FIG. 1 is a cross-sectional view showing one embodiment of the casting apparatus of the present invention. The illustrated casting apparatus 1-1 is a vertical casting apparatus including a tundish 3 that holds a molten metal 2 of steel material, an iron water-cooled mold 4, and a lifting device 6 that controls a descending speed of a cast piece 5. In addition to these, the shield 10 that blocks the molten metal 2 from the outside air and the cast piece cutting device (not shown) that cuts the cast piece 5 can be provided in the same manner as the conventional casting device 101 shown in FIG. . The casting apparatus 1-1 is different from the casting apparatus 101 in that it includes a box 11 that further suppresses cooling.

  FIG. 5 is a diagram illustrating an aspect of the cooling suppression unit. FIG. 5A is a perspective view of the box 11, and the box body 12 has a space 13 that penetrates in the vertical direction, and the inner wall is covered with a heat insulating material 14. As shown in FIGS. 5 (b) to 5 (d), the box 11 can have a cross-sectional shape such as a square, a circle, or a polygon, and can take various shapes depending on the cross-sectional shape of the slab 5. . The length of the box 11 in the vertical direction is not particularly limited as long as it is possible to prevent a crack generated in the center portion of the slab 5.

  In the casting apparatus 1-1, the molten metal 2 held by the tundish 3 is injected as a molten metal flow 8 from the nozzle 7 provided at the bottom of the tundish 3 into the water-cooled mold 4 in which the slag 9 is arranged. The molten metal 2 injected into the water-cooled mold 4 is cooled by being injected into the water-cooled mold 4, and further becomes a solid phase C from the melt A through the mixture B of the melt and the solid phase. The slab 5 that has become the solid phase C is transformed from an austenite structure to a ferrite structure or a pearlite structure from the surface toward the inside by cooling, and the volume expands. By covering the cooling of the slab 5 from the start to the end of volume expansion with the box 11 and suppressing it, rapid volume expansion of the slab 5 due to cooling can be suppressed. Thereby, the crack which generate | occur | produces in the center part of the slab 5 can be prevented. The heat insulating material 14 of the box 11 is not in contact with the slab 5 and there is a gap 15. The slab 5 is pulled out from the water-cooled mold 4 and the box 11 by the lifting device 6.

  FIG. 2 is a cross-sectional view showing a casting apparatus having a mode different from that in FIG. The illustrated casting apparatus 1-2 further includes a box 16 for suppressing cooling and a slab cutting device 17 for cutting the slab 5 in addition to the apparatus configuration of the casting apparatus 1-1. The box 16 suppresses cooling until the slab 5 covered with the box 11 and transformed is cut by the slab cutting device 17. Thereby, the burden which heats the cut slab 5 more than recrystallization temperature in the hot processing of the next process, etc. can be reduced. In addition, it is preferable to provide the box 16 in order to suppress cooling of the slab to be cut on the lifting device 6 side. Thereby, the burden of reheating the slab described above can be further reduced. Similar to the box 11 shown in FIG. 4, the box 16 has a space portion that penetrates in the vertical direction, and the inner wall is covered with a heat insulating material. The cross section of the box 16 can take various shapes depending on the cross sectional shape of the slab 5. The length of the box 16 in the vertical direction is not particularly limited as long as cooling until the slab 5 is cut by the slab cutting device 17 can be suppressed. The heat insulating material 18 of the box 16 is not in contact with the slab 5 and there is a gap 19. In FIG. 2, the space is provided between the box 11 and the box 16, but the cooling can be more efficiently suppressed due to the absence of the space. Further, the casting apparatus of the present invention may include a box 20 in which the box 11 and the box 16 are integrated in the vertical direction instead of the box 11 and the box 16 as in the casting apparatus 1-3 shown in FIG. it can. If the box 20 is used, the crack which generate | occur | produces in the center part of the slab 5 can be prevented, and cooling of the subsequent slab 5 can be suppressed.

  FIG. 4 is a cross-sectional view showing a casting apparatus having a mode different from those shown in FIGS. The illustrated casting apparatus 1-4 includes a secondary cooling zone 21 that cools the slab 5 between the water-cooled mold 4 and the box 11 in addition to the apparatus configuration of the casting apparatus 1-1. The slab 5 can be cooled by the secondary cooling zone 21 until just before the cooling needs to be suppressed. As a result, since the period for cooling the slab 5 can be shortened, the casting efficiency can be increased.

  As described above, according to the casting method and casting apparatus of the present invention, it is possible to prevent cracking of the central portion of the slab that occurs in the casting process.

  EXAMPLES Hereinafter, although an Example etc. are shown and this invention is demonstrated concretely, this invention is not limited to these.

[Example 1]
Casting was performed using the casting apparatus shown in FIG. The molten metal was held in the tundish, and the molten metal was poured into a water-cooled mold in which slag that had been previously dissolved was disposed. The molten metal was cooled to a slab by a water-cooled mold, and the slab was pulled out from the lower part of the water-cooled mold by a lifting device. The slab drawn from the water-cooled mold suppressed cooling by cooling by a box for suppressing cooling. In accordance with the amount of molten metal injected into the water-cooled mold, the slab was pulled out of the water-cooled mold, whereby the molten metal surface in the water-cooled mold was held at a fixed position 150 mm below the inlet of the water-cooled mold. The composition of slag is shown in Table 1. As the molten metal, JIS SKD11 equivalent was used. Table 2 shows the components of the molten metal. The internal shape of the water-cooled mold is a cubic shape having a square cross section (length 400 mm, width 400 mm) and length 400 mm. As shown in FIGS. 5 (a) and 5 (b), the box is obtained by covering the inner wall of an iron box body with a heat insulating board having a thickness of 50 mm, having a space portion penetrating in the vertical direction, and having a cross section. It is a square shape. One side of the square was 460 mm, and it was arranged so as to provide a 30 mm gap with the surface of the slab. The height of the box was 1000 mm, and the box was placed so that the inlet of the box was 1300 mm below the hot water surface and the outlet of the box was 2300 mm below the hot water surface. The slag thickness was 50 mm, the molten metal temperature was 1500 ° C., and the casting speed was 35 kg / min (31.2 mm / min).

[Example 2]
As the water-cooled mold, a cylindrical mold having an inner shape of 450 mm and a length of 400 mm was used. Further, as shown in FIG. 5 (c), the box is obtained by covering the inner wall of an iron box body with a heat insulating board having a thickness of 50 mm, having a space portion penetrating in the vertical direction, and having a circular cross section. A shaped box was used. The inner diameter of the box was 510 mm, and it was arranged so as to provide a 30 mm gap with the surface of the slab. The height of the box was 1000 mm, and the box was placed so that the inlet of the box was 1300 mm below the hot water surface and the outlet of the box was 2300 mm below the hot water surface. In this way, casting was performed under the same conditions as in Example 1 except that the shape of the water-cooled mold and the box was changed in order to produce a slab having a circular cross section.

[Comparative Example 1]
Casting was performed under the same conditions as in Example 1 except that no box was used.

[Comparative Example 2]
Casting was performed under the same conditions as in Example 2 except that the box was not used.

  FIG. 7 is a cross-sectional photograph obtained by photographing a cross section with respect to the casting direction and a vertical section passing through the central axis after cooling the cast piece cast according to the example to room temperature or lower. FIG. 7A shows the results of Example 1. FIG. 7A is a cross-sectional photograph of a cross section, and FIG. FIG. 7B shows the results of Example 2. Similarly, FIG. 7B is a cross-sectional photograph of a cross section, and FIG. From the cross-sectional photograph of FIG. 7, no cracks were observed in the central part of the cross section of the slab in any of the results of Example 1 and Example 2.

  FIG. 8 is a cross-sectional photograph of a cross section taken through a cross section and a longitudinal section passing through the central axis after cooling a slab cast according to a comparative example to room temperature or lower. FIG. 8A shows the result of Comparative Example 1. FIG. 8A is a cross-sectional photograph of a cross section, and FIG. FIG. 8B shows the result of Comparative Example 2. Similarly, FIG. 8B is a cross-sectional photograph of a transverse section and FIG. 8B is a longitudinal section. From the cross-sectional photograph of FIG. 8, cracks were observed in the central portion of the cross section of the slab in both the results of Comparative Example 1 and Comparative Example 2.

[Example 3]
In Example 3, a slab having a larger cross section than that of Example 1 was cast.
The slag having the composition shown in Table 3 was used, and the internal shape of the water-cooled mold was a rectangular parallelepiped shape having a rectangular cross section (length 400 mm, width 600 mm) and length 400 mm. The box has a shape similar to FIGS. 5 (a) and 5 (b), the inner wall of the iron box body is covered with a heat insulating board having a thickness of 50 mm, and has a space portion penetrating vertically. The cross section was a rectangular shape with a length of 460 mm and a width of 660 mm, and the height of the box was 1000 mm. The casting speed was 30 mm / min and casting was performed up to 400 minutes. Other conditions were the same as those in Example 1.

  FIG. 9 is a cross-sectional photograph of a cross section taken in the casting direction after cooling the cast slab cast according to the example to room temperature or lower. From the cross-sectional photograph of FIG. 9, even in the results of Example 3, no cracks were observed at the center of the cross section of the slab.

  From the above results, the cooling of the slab from the start to the end of the expansion of the volume is suppressed by covering the slab with a box provided with a heat insulating material, thereby abruptly cooling the slab. As a result of being able to suppress the volume expansion, it was confirmed that the cracks generated at the central portion of the cross section of the slab can be prevented.

  According to the present invention, cracking of the center portion of the slab that occurs in the casting process can be prevented, which is industrially useful.

1-1 Casting device 1-2 Casting device 1-3 Casting device 1-4 Casting device 2 Molten metal 3 Tundish 4 Water-cooled mold 5 Slab 6 Lifting device 7 Nozzle 8 Molten metal flow 9 Slag 10 Shield 11 Box 12 Box body 13 Space part 14 Heat insulating material 15 Air gap 16 Box 17 Cast piece cutting device 18 Heat insulating material 19 Air gap 20 Box 21 Secondary cooling zone 101 Casting device 102 Molten metal 103 Tundish 104 Water cooling mold 105 Cast piece 106 Lifting device 107 Nozzle 108 Molten metal flow 109 Slag 110 Shield A Melt B Mixture of melt and solid phase C Solid phase

Claims (12)

A casting method including at least a cooling step of cooling a slab having a solidified shell on an unsolidified portion and an outer peripheral portion of the unsolidified portion,
The said cooling process is a casting method including the cooling suppression process which suppresses cooling of the said slab by a cooling suppression means.   The casting method according to claim 1, wherein the cooling suppression means includes at least a heat insulating material having heat resistance.   The material of the said slab is a steel material, The said cooling suppression process includes the 1st cooling suppression process which suppresses cooling in the process in which the austenite structure of the said slab transforms into a ferrite structure or a pearlite structure. The casting method according to claim 2. The casting method is:
An injection process for injecting a molten steel material into a mold;
A slab forming step of forming a slab having a solidified shell on the outer periphery of the unsolidified part and the unsolidified part by cooling the mold and cooling the molten metal,
Taking out the slab from the mold; and
The cooling step;
A continuous casting method comprising at least
The casting method according to claim 3, wherein the cooling step is a step of cooling the slab after the removing step.   The continuous casting method further includes a slab cutting step of cutting the slab after the cooling step, and the cooling suppression step suppresses cooling performed until the slab transformed into a ferrite structure or a pearlite structure is cut. The casting method according to claim 4, further comprising a second cooling suppression step.   The said continuous casting method is a casting method of Claim 4 or 5 further including the secondary cooling process which cools the said slab after the said taking-out process and before the said cooling process. A mold that cools the injected molten metal and forms a slab having a solidified shell at the outer periphery of the unsolidified portion and the unsolidified portion;
Cooling suppression means for suppressing cooling of the slab that descends vertically from the lower part of the mold of the mold;
A casting apparatus comprising at least.   The casting apparatus according to claim 7, wherein the cooling suppression means includes at least a heat insulating material having heat resistance.   The material of the said slab is a steel material, The said cooling suppression means is equipped with the 1st cooling suppression means which suppresses cooling in the process in which the austenite structure of the said slab transforms into a ferrite structure or a pearlite structure, or The casting apparatus according to claim 8. The casting apparatus is
Holding a molten steel material, a container for pouring the molten metal into the mold,
The mold;
Control means for controlling the descent speed of the slab that descends vertically from the lower part of the mold of the mold;
The cooling suppression means;
The casting apparatus according to claim 9, which is a continuous casting apparatus including at least   The continuous casting apparatus further includes a slab cutting means for cutting the slab transformed into a ferrite structure or a pearlite structure, and the cooling suppression means until the slab transformed into a ferrite structure or a pearlite structure is cut. The casting apparatus of Claim 10 provided with the 2nd cooling suppression means which suppresses cooling between.   The said continuous casting apparatus is a casting apparatus of Claim 10 or Claim 11 further equipped with the secondary cooling means which cools the said slab between the said casting_mold | template and the said cooling suppression means.