JP2017177146A - Method and apparatus for producing steel ingot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for producing a steel ingot which enable the occurrence of settling crystal to be sufficiently suppressed.SOLUTION: The method for producing a steel ingot according to the present invention comprises a step of pouring molten metal into a casting mold, and a step of charging a thermal insulation agent to a molten metal surface in the casting mold, a charging amount V[g/S] of the thermal insulation agent in the charging step satisfying the following expression (1): 4<V<8. An apparatus for producing a steel ingot is further provided that comprises: a casting mold into which a molten metal is poured; and a charging shooter which is located above the casting mold and is configured in such a way that the thermal insulation agent can be charged to the molten metal surface, a charging amount V[g/S] of the thermal insulation agent by the charging shooter satisfying the above expression (1). Preferably, the charging shooter has a lattice-like baffle plate at an exhaust port for the thermal insulation agent.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a steel ingot manufacturing method and a steel ingot manufacturing apparatus.

  An ingot-making method in which molten metal is poured into a mold and solidified is widely used. In this ingot-making method, (1) suppressing the ingot from solidifying from the top due to the temperature drop from the molten metal surface due to the radiation heat of the molten metal, (2) enhancing the heat insulation on the molten metal surface side. In order to make the final solidification part in the steel ingot as high as possible, (3) to prevent oxidation of the molten metal, etc., after injecting the molten metal into the mold to a specified amount, Insulate the hot water from above.

  However, since this heat insulating agent is usually charged in a state close to room temperature, when this heat insulating agent is added to the hot water surface, the molten metal that has come into contact with the heat insulating agent temporarily loses its heat to the heat insulating agent. The temperature drops. As a result, when the temperature falls below the liquidus temperature, precipitated crystals may be generated. And this precipitated crystal | crystallization will sink in the casting_mold | template containing a nonmetallic inclusion, and there exists a possibility of causing the defect of a product.

  For this reason, in order to suppress the generation of precipitated crystals, it has been studied to adjust the amount of the heat insulating agent introduced. In addition, as a device capable of adjusting the amount of the heat-retaining agent, a device for supplying a hot water-adjusting agent (heat-retaining agent) has been proposed (see Japanese Patent Application Laid-Open No. 2-142463).

  The apparatus described in this publication has a container made of a material that can be melted or burned by the heat of molten metal, and this container is partitioned into three chambers in the vertical direction. In this apparatus, a predetermined amount of a heat-retaining agent is charged in the lowermost chamber and the uppermost chamber among the three chambers, and the walls defining the three chambers are sequentially melted or burned by the heat of the molten metal. First, the heat insulating agent charged in the lowermost chamber is charged, and the heat insulating agent charged in the uppermost chamber can be charged after a predetermined time. According to this apparatus, since it is possible to prevent the necessary amount of the heat insulating agent from being charged all at once, it is considered that a decrease in the temperature of the molten metal can be suppressed to a certain extent.

  However, although this apparatus can alleviate the decrease in the temperature of the molten metal by performing the heat insulating agent input in two stages, since a predetermined amount of the heat insulating agent is input collectively in each stage, The temperature of the molten metal is likely to drop rapidly when the heat-retaining agent is added. Therefore, it is difficult for this apparatus to sufficiently suppress the generation of precipitated crystals.

Japanese Patent Laid-Open No. 2-142463

  This invention is made | formed in view of such a situation, and aims at provision of the manufacturing method of a steel ingot which can fully suppress generation | occurrence | production of a precipitation crystal | crystallization, and the manufacturing apparatus of a steel ingot.

The method for producing a steel ingot according to the present invention made to solve the above problems includes a step of injecting molten metal into a mold, and a step of injecting a heat-retaining agent into the molten metal surface in the mold after the injection step. A method for producing a steel ingot comprising a heat insulating agent input amount V [kg / s] in the input step satisfies the following formula (1).
4 <V <8 (1)

  The method of manufacturing the steel ingot sufficiently adjusts the amount V of the heat retaining agent to be poured into the molten metal surface after pouring the molten metal into the mold within the above range, so that the heat retaining effect by the heat retaining agent can be sufficiently obtained. While exhibiting, it is possible to sufficiently suppress an abrupt decrease in the temperature of the molten metal due to the introduction of the heat retaining agent. Therefore, the method for producing the steel ingot can sufficiently suppress the generation of precipitated crystals.

In addition, a steel ingot manufacturing apparatus according to the present invention, which has been made to solve the above-described problems, is configured to be provided with a mold for injecting molten metal and an upper side of the mold so that a heat-retaining agent can be introduced into the molten metal surface. A steel ingot manufacturing apparatus provided with a charging shooter, wherein a heat insulating agent charging amount V [kg / s] by the charging shooter satisfies the following formula (1).
4 <V <8 (1)

  The steel ingot manufacturing apparatus adjusts the amount V of the heat retaining agent by the charging shooter within the above range, thereby sufficiently exhibiting the heat retaining effect by the heat retaining agent, and the molten metal caused by the heat retaining agent being introduced. A rapid decrease in temperature can be sufficiently suppressed. Therefore, the steel ingot manufacturing apparatus can sufficiently suppress the generation of precipitated crystals.

  It is preferable that the charging shooter has a lattice-shaped baffle plate at a heat insulating agent outlet. Thus, since the charging shooter has the lattice-shaped baffle plate at the heat insulating agent discharge port, the charging amount V of the heat insulating agent can be easily and reliably adjusted within the above range.

  As described above, the steel ingot manufacturing method and the steel ingot manufacturing apparatus according to the present invention can sufficiently suppress the generation of precipitated crystals.

It is a schematic diagram which shows the manufacturing apparatus of the steel ingot which concerns on one Embodiment of this invention. It is the typical front view seen from the discharge direction side of the baffle plate with which the input shooter of the manufacturing apparatus of the steel ingot of FIG. It is the sectional view on the AA line of the baffle plate of FIG.

  Hereinafter, embodiments of the present invention will be described in detail.

<Steel ingot manufacturing equipment>
The steel ingot manufacturing apparatus (hereinafter, also simply referred to as “the manufacturing apparatus”) in FIG. 1 is a vacuum top pouring apparatus used in a vacuum casting method. The manufacturing apparatus includes a ladle 1, an intermediate pan 2 disposed downstream of the ladle 1, a mold 3 disposed downstream of the intermediate pan 2, and a charging shooter disposed above the mold 3. 4 is mainly provided. In addition, the manufacturing apparatus includes a vacuum tank 5 whose inside is in a substantially vacuum state during casting. In the manufacturing apparatus, a mold 3 is disposed in a vacuum tank 5. The said manufacturing apparatus is comprised so that a steel ingot can be manufactured by inject | pouring the molten metal X stored by the ladle 1 into the casting_mold | template 3 via the intermediate | middle pot 2, and solidifying.

(Ladle)
The ladle 1 is constituted by a ladle in which molten metal X is produced in a refining furnace such as an electric furnace or a converter and refined by a molten steel process.

(Intermediate pot)
The intermediate pan 2 has a nozzle 7 and a stopper 8 that can close the opening of the nozzle 7. A gas blowing port (not shown) for blowing inert gas or the like is provided at the lower end of the stopper 8. Moreover, the intermediate | middle pan 2 has a slide valve (illustration omitted) which can adjust opening and closing of the opening of the nozzle 7 in the lower end part of the nozzle 7. FIG. The intermediate pan 2 is configured to be able to control the injection amount of the molten metal X into the mold 3 by controlling the opening / closing state of the opening of the nozzle 7 by the stopper 8 or the slide valve. As a capacity | capacitance of the intermediate | middle pan 2, it can be 10 to 100 tons, for example.

(template)
Molten metal X is injected into the mold 3. As for the casting_mold | template 3, the heat insulating material 9 is provided in a part of inner wall. The heat insulating material 9 is provided over the entire periphery from the upper part of the inner wall to a position below the arrival height of the molten metal X. The heat insulating material 9 improves the heat insulating property at the time of solidification of the molten metal X forming the feeder part Y. As a capacity | capacitance of the casting_mold | template 3, it can be set as 20 to 500 tons, for example.

(Input shooter)
The charging shooter 4 is disposed on the upper side of the mold 3 and is configured so that the heat insulating agent Z can be charged onto the molten metal surface. The input shooter 4 includes a hopper-shaped main body 11 and a lattice-shaped baffle plate 12 provided at the discharge port of the heat insulating agent Z. The main body 11 has a cylindrical (in this embodiment, cylindrical) discharge portion for discharging the heat insulating agent Z, and the baffle plate 12 is formed in a disc shape so as to be fitted inside the discharge portion. . The input shooter 4 has a cylinder (not shown) that is slidably inserted into the outer wall of the main body 11. The input shooter 4 is configured to be able to discharge the heat-retaining agent Z stored inside by sliding the cylinder by using gravity.

The input amount V [kg / s] of the heat insulating agent Z in the input shooter 4 satisfies the following formula (1). Moreover, it is more preferable that the input amount V [kg / s] of the heat retaining agent Z of the input shooter 4 satisfies the following formula (2). In the manufacturing apparatus, the amount V of the heat insulating agent Z supplied by the input shooter 4 is adjusted within the following range so that the heat insulating effect by the heat insulating agent Z is sufficiently exhibited, and the molten metal resulting from the introduction of the heat insulating agent Z A rapid decrease in the temperature of X can be sufficiently suppressed. Thereby, the said manufacturing apparatus can fully suppress generation | occurrence | production of a precipitation crystal | crystallization.
4 <V <8 (1)
4 <V <6 (2)

  Further, in the manufacturing apparatus, since the charging shooter 4 has the lattice-shaped baffle plate 12 at the outlet of the heat insulating agent Z, the input amount V of the heat insulating agent Z can be easily and reliably adjusted.

  The lower limit of the average diameter of the discharge port of the input shooter 4 is preferably 150 mm, and more preferably 200 mm. On the other hand, the upper limit of the average diameter of the discharge port of the input shooter 4 is preferably 500 mm, more preferably 400 mm. If the average diameter of the discharge port of the charging shooter 4 is less than the lower limit, the charging amount V of the heat retaining agent Z may be insufficient. Further, if the average diameter of the discharge port of the charging shooter 4 is less than the above lower limit, the projected area of the heat insulating agent Z becomes too small and the temperature of the molten metal X is likely to be partially lowered. There is a possibility that the discharge port may be blocked by. On the other hand, if the average diameter of the discharge port of the charging shooter 4 exceeds the above upper limit, it may be difficult to control the charging amount V of the heat retaining agent Z within a desired range.

  The central axis of the discharge portion of the charging shooter 4 is inclined with respect to the hot water surface (horizontal plane). The lower limit of the angle α formed by the central axis and the molten metal surface is preferably 30 °, and more preferably 45 °. On the other hand, the upper limit of the angle α is preferably 80 °, more preferably 60 °. If the angle α formed is less than the lower limit, the heat insulating agent Z does not sufficiently flow toward the discharge port in the discharge portion, and the amount V of the heat insulating agent Z may be insufficient. On the other hand, when the angle α formed exceeds the upper limit, the projected area of the heat insulating agent Z becomes too small, and the temperature of the molten metal X may be partially lowered. Further, if the angle α formed exceeds the upper limit, the speed of the heat insulating material Z to be charged increases, and the molten metal X is scattered, and inclusions may occur when the molten metal X falls. There is.

  The baffle plate 12 is disposed so that the central axis of the discharge portion is parallel to the thickness direction. The baffle plate 12 is composed mainly of a metal such as steel or stainless steel. The baffle plate 12 has a lattice shape as shown in FIG. That is, the baffle plate 12 includes a plurality of holes penetrating in the thickness direction and a plurality of bars defining these holes. Since the baffle plate 12 has a lattice shape as described above, the manufacturing apparatus can easily perform the operation such as maintenance because the other side can be visually recognized from one side in the thickness direction. Further, the baffle plate 12 has an opening area of each hole formed in the lower portion larger than an opening area of each hole formed in the portion other than the lower portion. In the manufacturing apparatus, the supply amount of the heat retaining agent Z stored in the main body 11 of the charging shooter 4 to the baffle plate 12 gradually decreases immediately after the heat insulating agent Z starts to be charged. In this regard, if the baffle plate 12 does not have a plurality of holes in the upper part, the heat-retaining agent Z in the initial stage may adhere to the upper part of the baffle plate 12 and harden. On the contrary, if the opening area of each hole in the upper part of the baffle plate 12 is large, the heat insulating agent Z is excessively supplied through these holes, and there is a possibility that the input amount V of the heat insulating agent Z cannot be controlled sufficiently. Further, if the opening area of the hole in the lower part of the baffle plate 12 is small, the large heat insulating agent Z or the like cannot be passed through, and the large heat insulating agent Z may adhere to the lower part and harden. On the other hand, in the manufacturing apparatus, since the opening area of each hole formed below the baffle plate 12 is larger than the opening area of each hole formed other than the lower part, the heat insulating agent Z blocks the opening. It is possible to appropriately control the charging amount V of the heat insulating agent Z while preventing the shortage of the amount of the heat insulating agent Z that is caused. The shape of the plurality of holes in plan view is not particularly limited, but may be a square, a rectangle, a parallelogram, or a shape similar to these, for example, in terms of manufacturability. . Moreover, the planar shape of each hole may be the same or different.

  The lower limit of the average thickness of the baffle plate 12 (the average thickness of the portion excluding the plurality of holes) is preferably 10 mm, and more preferably 20 mm. On the other hand, the upper limit of the average thickness is preferably 200 mm, and more preferably 100 mm. If the average thickness is less than the lower limit, the baffle plate 12 may be deformed or melted by the heat of the molten metal X, the heat generation of the heat retaining agent Z, or the like. On the other hand, if the average thickness exceeds the upper limit, the baffle plate 12 becomes unnecessarily thick, and it may be difficult to control the amount V of the heat insulating agent Z.

  The lower limit of the average width of the crosspieces of the baffle plate 12 (average width of the crosspieces in plan view) is preferably 2 mm, and more preferably 4 mm. On the other hand, the upper limit of the average width is preferably 10 mm, and more preferably 7 mm. If the average width is less than the lower limit, the crosspieces may be deformed or melted by the heat of the molten metal X or the heat generation of the heat retaining agent Z. On the other hand, if the average width exceeds the upper limit, the width of each cross becomes unnecessarily large, and the input amount V of the heat retaining agent Z may be difficult to control.

The lower limit of the average opening area of the plurality of holes of baffle plate 12 (total value of the opening area obtained by dividing the number of holes of all the pores) is preferably 200 mm ^2, 400 mm ² and more preferably. On the other hand, the upper limit of the average open area, preferably 3600 mm ^2, 2000 mm ² and more preferably. If the average opening area is less than the lower limit, the amount V of the heat retaining agent Z may be insufficient. Conversely, if the average opening area exceeds the upper limit, it may be difficult to control the amount V of the heat insulating agent Z to be controlled.

  As shown in FIG. 3, the crosspieces 13 that define the holes at the bottom of the baffle plate 12 are inclined in the thickness direction. In the manufacturing apparatus, in a steady state other than the initial stage of introduction of the heat insulating agent Z, the heat insulating agent Z is mainly supplied from a plurality of holes formed in the lower part of the baffle plate 12. In this regard, the manufacturing apparatus can be adjusted so that the amount V of the heat insulating agent Z in a steady state is not increased by the crosspiece 13 formed below the baffle plate 12 being inclined in the thickness direction. it can.

  In particular, it is preferable that the baffle plate 12 has a pair of bars 13 extending in the vertical direction in parallel with each other when viewed from the front, and the pair of bars 13 are inclined in the thickness direction. Further, as shown in FIG. 3, the pair of crosspieces 13 is preferably formed so that the interval gradually decreases in the direction in which the heat insulating agent Z is charged. The manufacturing apparatus can adjust the charging amount V of the heat insulating agent Z in a steady state more accurately by forming the pair of crosspieces 13 so that the interval gradually decreases in the charging direction. .

  The lower limit of the inclination angle of the crosspiece 13 with respect to the thickness direction of the baffle plate 12 is preferably 15 °, and more preferably 20 °. On the other hand, the upper limit of the tilt angle is preferably 75 °, more preferably 40 °. If the inclination angle is less than the lower limit, the effect of suppressing the input amount V of the heat insulating agent Z in the steady state may be insufficient. On the contrary, if the inclination angle exceeds the upper limit, the amount V of the heat insulating agent Z in a steady state may be insufficient, and the heat insulating agent Z is likely to adhere to the crosspiece 13 and the discharge portion is blocked. May cause this.

  The lower limit of the area ratio of the lower part with respect to the entire baffle plate 12 is preferably 5%, and more preferably 10%. On the other hand, the upper limit of the area ratio is preferably 50%, more preferably 40%. If the area ratio is less than the lower limit, the amount V of the heat insulating agent Z may be insufficient. On the contrary, when the area ratio exceeds the upper limit, it is difficult to control the amount V of the heat insulating agent Z.

  The lower limit of the average interval on the introduction side of the heat insulating agent Z of the pair of bars 13 (that is, the side where the distance between the pair of bars 13 is the smallest) is preferably 20 mm, and more preferably 40 mm. On the other hand, the upper limit of the average interval is preferably 70 mm, and more preferably 50 mm. If the average interval is less than the lower limit, it may not be possible to pass a large heat insulating agent Z or the like. On the other hand, when the average interval exceeds the upper limit, the input amount V of the heat insulating agent Z in a steady state may be excessive.

(Heat insulating agent)
As the heat insulating agent Z, an exothermic heat insulating agent is used. Examples of the main component of the exothermic heat retention agent include metallic aluminum and metallic calcium. Further, the shape of the heat insulating agent Z is not particularly limited, and examples thereof include a spherical shape, a cylindrical shape, and a powder shape. The upper limit of the average particle size of the heat retaining agent Z is preferably 10 mm, and more preferably 8 mm. When the average particle diameter of the heat retaining agent Z exceeds the upper limit, the input amount V may be too small due to the baffle plate 12. On the other hand, the lower limit of the average particle diameter of the heat retaining agent Z is not particularly limited, and can be, for example, 1 mm. The “average particle size” is a volume-based integrated distribution calculated in accordance with JIS-Z8819-2: 2001 based on the particle size distribution measured by the laser diffraction / scattering method in accordance with JIS-Z8815: 2013. The value is 50%.

  The lower limit of the basic unit of the heat insulating agent [heat insulating agent kg / molten metal ton] is preferably 1 kg / ton, more preferably 2 kg / ton. On the other hand, the upper limit of the basic unit of the heat retaining agent Z is preferably 5 kg / ton, and more preferably 4 kg / ton. If the basic unit of the heat insulating agent Z is less than the lower limit, the desired effect due to the introduction of the heat insulating agent Z may not be sufficiently obtained. On the contrary, if the basic unit of the heat insulating agent Z exceeds the above upper limit, the heat insulating agent Z is unnecessarily increased, and the cost of the mold 3 needs to be increased to accommodate the heat insulating agent Z. May increase.

(Vacuum tank)
The vacuum tank 5 keeps the inside in a substantially vacuum state during casting as described above. The vacuum tank 5 has an opening directly below the nozzle 7 of the intermediate pan 2. This opening is sealed with an iron plate or the like before casting, and is formed by melting the iron plate with molten metal discharged from the intermediate pan 2 at the start of casting. The degree of vacuum in the vacuum tank 5 at the time of casting can be, for example, 0.1 to 100 torr.

<Method for producing steel ingot>
Next, a method for manufacturing a steel ingot using the manufacturing apparatus (hereinafter also simply referred to as “the manufacturing method”) will be described. The manufacturing method includes a step of injecting molten metal X into the mold 3 (injection step), and a step of injecting the heat retaining agent Z into the molten metal surface in the mold 3 after the injection (injection step). In addition, the manufacturing method may further include a step of introducing a heat insulating agent into the mold 3 (heat insulating agent charging step) after the charging step.

(Injection process)
In the injection step, molten metal X is injected from the intermediate pot 2 into the mold 3. The weight of the molten metal X injected in this injection step can be, for example, 20 to 500 tons. Moreover, as temperature of the molten metal X inject | poured by the said injection | pouring process, it can be set as 1500 degreeC or more and 1650 degrees C or less, for example. In addition, in the said injection | pouring process, you may blow in inert gas, such as argon gas, from the gas blowing inlet provided in the lower end part of the stopper 8 of the intermediate | middle pan 3. FIG.

  The lower limit of the casting rate (cooling rate) of the molten metal X injected in the injection step is preferably 1 ton / min, and more preferably 1.5 ton / min. On the other hand, the upper limit of the casting speed is preferably 15 ton / min, and more preferably 10 ton / min. If the casting speed is less than the lower limit, the production efficiency of the steel ingot may be insufficient, and the generation of sedimentary inclusions may be promoted by the temperature decrease of the molten metal X. On the contrary, when the casting speed exceeds the upper limit, there is a possibility that slag, scum, etc. floating in the intermediate pan 2 may be caught.

(Input process)
In the charging step, the heat retaining agent Z is charged from the charging shooter 4 described above. In the above charging process, it is preferable to introduce the heat retaining agent Z as soon as possible after the completion of the injection of the molten metal X in order to suppress the radiation extraction heat of the molten metal X. More preferably. On the other hand, in the charging step, when the charging speed of the heat retaining agent Z is too high, the temperature of the molten metal X is rapidly decreased and precipitation crystals are likely to be generated. Therefore, in the manufacturing method, the input amount V [kg / s] of the heat retaining agent Z in the input step satisfies the following formula (1). Moreover, in the said manufacturing method, it is more preferable that the charging amount V [kg / s] of the heat retaining agent Z in the charging step satisfies the following formula (2).
4 <V <8 (1)
4 <V <6 (2)

  The manufacturing method is caused by the introduction of the heat insulating agent Z by adjusting the amount V of the heat insulating agent Z to be introduced into the molten metal surface in the mold after the molten metal X is injected into the mold 3 within the above range. A rapid decrease in the temperature of the molten metal X can be sufficiently suppressed. Therefore, the production method can sufficiently suppress the generation of precipitated crystals.

  The lower limit of the basic unit of the heat retaining agent Z [heat retaining agent kg / molten metal ton] in the charging step is preferably 1 kg / ton, and more preferably 2 kg / ton. On the other hand, the upper limit of the basic unit of the heat retaining agent Z is preferably 5 kg / ton, and more preferably 4 kg / ton. If the basic unit of the heat insulating agent Z is less than the lower limit, the desired effect due to the introduction of the heat insulating agent Z may not be sufficiently obtained. On the contrary, when the basic unit of the heat insulating agent Z exceeds the upper limit, the heat insulating agent Z is unnecessarily increased or the capacity of the mold 3 needs to be increased to accommodate the heat insulating agent Z. Cost may increase.

The lower limit of the projection area of the heat retaining agent Z in the adding step is preferably 0.02 m ^2, 0.04 m ² is more preferable. If the projected area of the heat insulating agent Z is less than the lower limit, the temperature of the molten metal X may be partially lowered. The upper limit of the projected area of the heat retaining agent Z in the charging step is not particularly limited, but can be set to, for example, 0.1 m ² from the viewpoint of easy control of the charging amount V of the heat retaining agent Z.

  The heat-retaining agent Z charged in the charging step is layered on the hot water surface to form a heat-retaining agent layer. As a minimum of the average thickness of this heat retention agent layer, 10 mm is preferred and 15 mm is more preferred. On the other hand, the upper limit of the average thickness is preferably 100 mm, and more preferably 50 mm. If the average thickness is less than the lower limit, oxidation of the molten metal X may not be sufficiently prevented. On the other hand, if the average thickness exceeds the upper limit, the cost increases based on the fact that the heat insulating agent Z is unnecessarily increased or the capacity of the mold 3 needs to be increased to accommodate the heat insulating agent Z. There is a risk.

(Insulation process)
In the heat insulating agent charging step, the heat insulating agent is charged onto the heat insulating layer after the vacuum tank 5 is opened after the charging step. The said manufacturing method can suppress the segregation at the time of solidification of the molten metal X by this heat insulating agent injection | throwing-in process.

  The heat insulating agent charged in the heat insulating agent charging step is laminated on the heat insulating agent layer to constitute the heat insulating agent layer. As a minimum of the average thickness of this heat insulating material layer, 50 mm is preferred and 90 mm is more preferred. On the other hand, the upper limit of the average thickness is preferably 300 mm, and more preferably 200 mm. If the average thickness is less than the lower limit, segregation during melting of the molten metal X may not be sufficiently suppressed. On the contrary, when the average thickness exceeds the upper limit, the thickness of the heat insulating layer may be unnecessarily increased.

[Other Embodiments]
In addition, the manufacturing method of the steel ingot which concerns on this invention, and the manufacturing apparatus of a steel ingot can be implemented in the aspect which gave the various change and modification other than the said aspect. For example, the manufacturing apparatus need not be a vacuum casting apparatus. Moreover, the said manufacturing apparatus does not need to be an upper pouring casting apparatus, and may be a lower pouring casting apparatus. The manufacturing method need not be performed using the vacuum casting apparatus shown in the above-described embodiment. Moreover, the said manufacturing method does not need to be performed using a top pouring casting apparatus, and can also be performed using a bottom pouring casting apparatus.

  In the manufacturing apparatus, as long as the amount V of the heat insulating agent Z can be adjusted within the above range, the input shooter does not necessarily have a lattice-shaped baffle plate at the outlet of the heat insulating agent Z. Further, the specific configuration of the baffle plate is not limited to the shape of the above-described embodiment.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

  Using the steel ingot manufacturing apparatus shown in FIG. 1, molten metal X was injected into the bottomed cylindrical mold 3 having an inner diameter of 2.6 m while maintaining the vacuum degree in the vacuum tank 5 at 1 torr or less. The temperature in the mold 3 immediately after the injection of the molten metal X was 1550 ° C. While casting the molten metal X at a casting speed of 5 ton / min, the heat insulating agent Z was charged onto the molten metal surface by the charging shooter 4 immediately after the completion of the injection of the molten metal X. As the heat insulating agent Z, a cylindrical pellet having metal calcium as a main component and an average particle diameter of 5 mm was used. The total amount of the heat retaining agent Z was 300 kg.

  Further, after completion of the introduction of the heat insulating agent Z by the input shooter 4, the vacuum state in the vacuum tank 5 was released, and the heat insulating agent was supplied to the upper surface of the heat insulating agent layer having an average thickness of 20 mm formed by the heat insulating agent Z. . As this heat insulating agent, what has aluminum oxide as a main component was used. Moreover, the average thickness of the heat insulating material layer laminated | stacked on the heat insulating material layer with this heat insulating material was 130 mm.

<UT defect>
“USK-8S” manufactured by Kraut Kramer Co., Ltd. is used for the black skin (not machined) after forging the ingot, as shown in Table 1. A UT inspection (ultrasonic deep wound inspection) was performed using a UT device such as the above, and the size of the defect was evaluated according to the following criteria. Note that the input amount V [kg / s] of the heat insulating agent Z was adjusted by changing the lattice shape of the baffle plate.
A: No defect was detected.
B: One defect or a few scattered defects were detected.
C: A large number of dense defects were detected.

<PT defect>
The amount V [kg / s] of the heat insulating agent Z introduced by the above-mentioned injection shooter 4 is as shown in Table 1, and after machining the black skin of the ingot, a PT inspection (penetration deep damage inspection) is performed to determine the size of the defect. Was evaluated according to the following criteria.
A: No defect.
B: A defect having an aspect ratio of 3 or more and a maximum length of 1.6 mm or less, or a defect having an aspect ratio of less than 3 and a maximum length of 5.0 mm or less was detected.
C: A defect having an aspect ratio of 3 or more and a maximum length exceeding 1.6 mm, or a defect having an aspect ratio of less than 3 and a maximum length exceeding 5.0 mm was detected.

[Evaluation results]
As shown in Table 1, the amount V [kg / s] of the heat retaining agent Z satisfying 4 <V <8. 1-No. No. 16 indicates that a large number of defects that are densely detected when the UT inspection is performed are not detected, and defects that have an aspect ratio of 3 or more and a maximum length exceeding 1.6 mm when the PT inspection is performed, and an aspect ratio of 3 No defects less than and greater than 5.0 mm in length are detected. This is because when the input amount V [kg / s] of the heat insulating agent Z satisfies 4 <V <8, the rapid temperature drop of the molten metal X can be sufficiently suppressed. This is thought to be because the generation was sufficiently suppressed. On the other hand, the amount V [kg / s] of the heat retaining agent Z is 4 or less or 8 or more. 17-No. No. 23, a defect having an aspect ratio of 3 or more and a maximum length of more than 1.6 mm or a defect having an aspect ratio of less than 3 and a maximum length of more than 5.0 mm was detected when PT inspection was performed. 17 and no. In addition to this defect, a large number of defects that are densely packed when a UT inspection is performed are detected. This is presumably because precipitated crystals are likely to be generated due to a rapid temperature drop of the molten metal X.

  As described above, the steel ingot production method and the steel ingot production apparatus of the present invention can sufficiently suppress the generation of precipitated crystals, and are therefore suitable for the production of high-quality steel ingots with few defects. .

DESCRIPTION OF SYMBOLS 1 Ladle 2 Intermediate pan 3 Mold 4 Input shooter 5 Vacuum tank 7 Nozzle 8 Stopper 9 Heat insulating material 11 Main body 12 Baffle plate 13 Crosspiece X Molten metal Y Hot water supply part Z Insulation agent

Claims (3)

Injecting molten metal into the mold;
A method for producing a steel ingot comprising a step of supplying a heat-retaining agent to a molten metal surface in a mold after the pouring step,
A method for producing a steel ingot, characterized in that the amount of heat insulating agent V [kg / s] in the charging step satisfies the following formula (1).
4 <V <8 (1) A mold for injecting molten metal;
A steel ingot manufacturing apparatus provided with an input shooter arranged on the upper side of the mold and configured to be able to input a heat-retaining agent to a molten metal surface,
A steel ingot manufacturing apparatus, wherein the heat insulating agent input amount V [kg / s] by the input shooter satisfies the following formula (1).
4 <V <8 (1)   The apparatus for producing a steel ingot according to claim 2, wherein the charging shooter has a lattice-shaped baffle plate at a heat insulating agent outlet.

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