JP2013141677A - Bottom pouring ingot casting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bottom pouring ingot casting method which suppresses occurrence of coarse inclusions, and can produce an ingot having excellent cleanliness.SOLUTION: When a bottom pouring ingot casting method of charging a molten steel 2 into a mold 5 via a pouring tube 4 is performed, a coating material 10 for coating the molten steel 2 in the mold 5 with a bath face is added, and thereafter, Ca 12 as metal Ca and/or a Ca alloy with the average grain size of ≥200 μm is added thereto. The heat insulating material is added in such a manner that the addition amount of the Ca component in the Ca 12 to the surface area of the bath face reaches a value within the range of 0.35 to <10 kg/m, and further, [%Ca]/([%Al]+3[%FeO]+[%FeO]+2[%SiO]+2[%MnO]+[%S]) showing the relation between the component content of the heat insulating material and the Ca component content in the added Ca 12 reaches a value within the range of 0.08 to <0.25; wherein, [%X] denotes the X content (mol%) in the heat insulating material.

Description

  The present invention relates to an ingot casting method for producing an ingot by inserting molten steel into a mold through an injection tube.

As a method for producing an ingot by inserting molten steel into a mold via an injection tube, there is a bottom pouring ingot method for producing an ingot by injecting molten steel into the mold from below the mold. Patent Document 1 discloses such a down-pour ingot-making method.
In Patent Document 1, in producing killed steel by the down-pour method or the top-pour method, the temperature of the molten steel before casting is set to TL (liquid phase start temperature) + 20 ° C. or more and the molten steel is being injected or Immediately after that, an early combustion type high-calorie heat-retaining agent whose amount of total heat generation per ton of molten steel is 1800 Kcal or more, but with a peak time within 3 minutes to generate heat and reach the maximum temperature, coat the hot water surface in the mold, Inclusion accumulation in the precipitation zone at the bottom of the steel ingot is reduced.

Moreover, although it is not the bottom pouring method as shown in patent document 1, there exists what was disclosed by patent document 2 as what prevents the clustering of inclusions.
In Patent Document 2, when casting molten steel containing aluminum, titanium, zirconium or the like alone or in combination at an injection rate of 0.5 to 30 ton / min, metallic calcium or alloy grains containing calcium are added in an amount of 0.5 to 2. It is added to the molten molten steel stream at a feed rate of 0 kg / min.

JP 47-026334 A JP 49-035322 A

Patent Documents 1 and 2 disclose a technique for reducing accumulation of inclusions in an ingot. However, even if the techniques disclosed in these documents are used for the production of ingots by the down-pour ingot casting method, it is difficult to sufficiently reduce the accumulation of inclusions, and as a result, the inclusions are large in size. In fact, it is difficult to sufficiently suppress the generation of coarse inclusions.
This invention is made | formed in view of the above-mentioned problem, and suppresses generation | occurrence | production of the coarse inclusion in an ingot, and provides the bottom pouring ingot method which can manufacture the ingot which was excellent in the cleanliness. With the goal.

In order to achieve the above object, the present invention has taken the following measures.
That is, the technical means for solving the problem in the present invention is that the molten steel in the mold is produced by performing the pouring and ingot making method for producing the ingot by inserting the molten steel into the mold from below through the injection pipe. After adding the coating material for coating the bath surface, the metal Ca and / or Ca alloy having an average particle size of 200 μm or more is added before or simultaneously with the heat insulating material, and the surface area of the bath surface is increased. with the addition of Ca component of the metallic Ca and / or Ca alloy is added to the metallic Ca and / or Ca alloy to a value in the range of less than 0.35 kg / ^{m 2} or more 10 kg / ^{m 2,} insulation [% Ca] / ([% Al] +3 [% Fe ₂ O ₃ ] + [% FeO] +2 showing the relationship between the component content of the material and the Ca component content of the added metal Ca and / or Ca alloy) [% SiO ₂ ] +2 [% MnO ₂ ] + [% S]) is in a range of 0.08 or more and less than 0.25.

The other technical means of the present invention is to cover the molten steel in the mold with a bath surface when performing the pouring and ingot forming method for producing the ingot by inserting the molten steel into the mold from below through the injection pipe. After adding the covering material for the purpose, a heat insulating material containing metal Ca and / or Ca alloy having an average particle size of 200 μm or more is added, and the metal Ca and / or Ca alloy with respect to the surface area of the bath surface is added. with the addition amount of the Ca constituent is added the thermal insulation material so as to satisfy the ^{0.35kg / m 2 ~10kg / m 2} , Ca component content of the metal Ca and / or Ca alloy containing the ingredient content of a heat insulating material It shows the relationship between the amount _{[% Ca] / ([%} Al] +3 [% Fe 2 O 3] + [% FeO] +2 [% SiO 2] +2 [% MnO 2] + [% S]) is 0. To be a value within the range of 08 or more and less than 0.25 It is in the point. [% X] is the X content (mol%) in the heat insulating material.

  According to the present invention, it is possible to suppress the generation of coarse inclusions in an ingot and to manufacture an ingot having excellent cleanliness.

It is the schematic of the bottom pouring lump apparatus which performs bottom pouring lump. It is a figure which shows the flow of a bottom pouring ingot, Comprising: (a) It is the initial stage of ingot, (b) It is the middle stage of ingot, (c) It is the time of adding Ca in the final stage, d) The time when the heat insulating material is added in the final stage is shown. Up _{[% Ca] / ([%} Al] +3 [% Fe 2 O 3] + [% FeO] +2 [% SiO 2] +2 [% MnO 2] + [% S]) values of inclusions in Examples It is a relationship figure with a diameter. It is a related figure of the value of the addition amount of Ca in an Example, and the maximum diameter of an inclusion. It is a distribution diagram showing the result of the Example and comparative example at the time of adjusting the average particle diameter of Ca to 200 micrometers or more.

Hereinafter, the bottom pouring and ingot-making method according to the embodiment of the present invention will be described with reference to the drawings.
First, with reference to FIG. 1, the bottom pouring and ingot-making apparatus 1 to which the bottom pouring and ingot making method of this embodiment is applied will be described. FIG. 1 shows a schematic configuration of a bottom pouring and ingot forming apparatus 1 that performs bottom pouring and ingot making.
The bottom pouring and ingot-making apparatus 1 casts molten steel 2 by the bottom pouring and ingot casting method. An injection pipe 4 for injecting molten steel 2 in a ladle 3 and a molten steel 2 injected into the injection pipe 4 are provided. A casting mold 5 to be charged, and a surface plate 6 for communicating the injection tube 4 and the casting mold 5 are provided.

  A runner 7 through which the molten steel 2 passes is formed in the injection tube 4 and the surface plate 6, and the injection tube 4 is provided so as to stand upward from the surface plate 6. The casting mold 5 has a lower inlet 9 formed below and is placed on the surface plate 6. The mold 5 has a structure in which the molten steel 2 is inserted from the runner 7 of the surface plate 6 through the lower inlet 9 from below. A feeder frame 8 is attached to the upper part of the mold 5.

  In performing the bottom pouring and ingot using such a bottom pouring and ingot apparatus 1, first, the ladle 3 is placed on the pouring tube 4, and the molten steel 2 in the ladle 3 is poured into the pouring tube 4. The molten steel 2 passes through the runner 7 formed in the injection pipe 4 and the surface plate 6, reaches the mold 5 from below through the lower injection port 9, is cooled in the mold 5, and becomes an ingot such as an ingot. In this bottom pouring and ingot forming method, for example, an ingot that becomes a raw material such as a large forged product used for a marine component or a generator component can be manufactured.

The bottom pouring method of the present embodiment will be described in detail.
In the bottom pouring and ingot forming method, when the bath surface of the molten steel 2 charged in the mold 5 comes into contact with the atmosphere, the molten steel 2 is oxidized from the contact surface with the atmosphere to reduce the cleanliness. Therefore, in this embodiment, in order to prevent the molten steel 2 from being oxidized, the coating material 10 (C—SiO ₂ − for covering the bath surface of the molten steel 2 at the stage where the injection of the molten steel 2 into the mold 5 has started. CaO—Al ₂ O ₃ -based coating material) is added from above the mold 5.

Specifically, as shown in FIG. 2A, before the molten steel 2 is injected into the mold 5, the bag in which the covering material 10 is charged is disposed in the vicinity of the lower inlet 9 in the mold 5. To do. In this way, the bag is melted by the heat of the molten steel 2 immediately after the injection of the molten steel 2 into the mold 5 starts, so that the bath surface of the molten steel 2 is covered from the early stage when the injection of the molten steel 2 into the mold 5 starts. Covered with material 10.
Next, as shown in FIG. 2 (b), when the molten steel 2 is continuously charged into the mold 5, the bath surface of the molten steel 2 gradually rises, and the covering material 10 on the bath surface It is consumed while flowing between the molten steel 2 whose surface rises and the inner surface of the mold 5. In this process, the coating material 10 is additionally added from above the mold 5 in accordance with the consumption amount, so that the bath surface of the molten steel 2 is not exposed to the atmosphere as much as possible, and the contact of the molten steel 2 with the atmosphere is prevented. . The covering material 10 is added until the bath surface of the molten steel 2 reaches the feeder frame 8 after the molten steel 2 is inserted into the mold 5, and during that time, the surface area of the molten steel 2 (the area of the bath surface). 70% or more) was kept covered with the covering material 10. In addition, the addition method of the coating | covering material 10 is not restricted to the method mentioned above. Even if the bag containing the covering material 10 is not placed in the mold 5 before the injection of the molten steel 2 is started, the covering material 10 is placed on the molten steel 2 from above the mold 5 immediately after the injection of the molten steel 2 into the mold 5 starts. It may be added directly to the bath surface or may be added by other methods.

Usually, in the bottom pouring and ingot-making method, when the bath surface of the molten steel 2 reaches near the upper part of the mold 5, a heat insulating material 11 for maintaining the temperature of the molten steel 2 is added. Here, the iron oxide as a heat insulating material _{11 (Fe t O), MnO} 2, SiO 2, and although the addition of such particulate material containing Al, a large particle diameter of the high by the addition of heat insulating material 11 in the molten steel 2 Alumina inclusions (coarse inclusions) may be generated, and the cleanliness of the molten steel 2 may be reduced. The heat insulating material 11 may be a powder-shaped powder or a molded shape such as a board.

Therefore, in the present invention, calcium (Ca) 12 is added to the molten steel 2 before the heat insulating material 11 is added or simultaneously with the addition of the heat insulating material 11. With this added Ca12, the high alumina inclusions generated when the heat insulating material 11 is added are modified into CaO—Al ₂ O ₃ inclusions according to the following formulas (1) to (3). The CaO—Al ₂ O ₃ inclusions are less likely to agglomerate and the size thereof is smaller than that of the high alumina inclusions, so that the cleanliness of the molten steel 2 can be improved.

_{2Al + 3Fe t O = Al 2} O 3 + 3tFe ··· (1)
2Al + 3 / 2MnO ₂ = Al ₂ O ₃ + 3 / 2Mn (2)
2Al + 3 / 2SiO ₂ = Al ₂ O ₃ + 3 / 2Si (3)
Hereinafter, the addition method and addition amount of Ca12 will be described in detail.
In the present embodiment, as shown in FIG. 2 (c), Ca12 is inserted between the start of the injection of the molten steel 2 into the mold 5 and the time when the molten steel 2 reaches the feeder frame 8 and the casting is finished. Added. After the addition of Ca12, the heat insulating material 11 is added as shown in FIG.

Specifically, at the stage when the end of casting is near, Ca12 is added from above the covering material 10 covering the bath surface of the molten steel 2, and the heat insulating material 11 is added after the addition of Ca12.
The added Ca12 may be pure metal Ca (metal Ca) or a Ca alloy. Examples of the Ca alloy include a Ca—Si alloy and a Ca—Ni alloy, which can be arbitrarily selected according to the standard of steel components. Moreover, it is preferable that the heat insulating material 11 is continuously added following the addition of Ca12, and added within 1 minute from the addition of Ca12. The time from the addition of Ca12 to the addition of the heat insulating material 11 may be longer than 1 minute depending on the casting work procedure and the restrictions on the casting equipment, but when this time becomes too long, Since it should be noted that the above-mentioned modifier does not work sufficiently, it should be within 10 minutes at the longest.

Although it has been described that Ca12 is added at the stage where the end of casting is near, the stage where the end of casting is near is about 10 minutes before the end of casting. Of course, this guideline is not limited to 10 minutes, and can be arbitrarily changed according to the operating conditions of the casting process and the reaction rates of the above formulas (1) to (3).
As described above, Ca12 is added to the molten steel 2 before the heat insulating material 11 is added or simultaneously with the addition of the heat insulating material 11 for the purpose of suppressing the formation of high alumina inclusions (coarse inclusions) having a large particle size. Added. At this time, in this embodiment, two conditions are imposed on the amount of Ca12 added. Hereinafter, each condition will be described.

First, as the first condition, when adding Ca12, the addition amount per 1 m ² that is the addition amount (kg) of the Ca component (pure Ca) in Ca12 to the surface area (m ² ) of the bath surface of the molten steel 2, 0.35 kg / ^{m 2} or more 10 kg / ^{m 2} or less is set to satisfy the range of ^{(0.35kg / m 2 ~10kg / m} 2) ( first condition). In other words, a value obtained by dividing the Ca component equivalent amount in the added metal Ca and Ca alloy by the surface area of the inner bath surface from the feeder frame 8 is defined as the Ca component addition amount. Then, the addition amount of Ca12 is determined and added so that the addition amount of Ca component is in the range of 0.35 kg / m ^{2 to} 10 kg / m ² .

When the added amount of the Ca component is less than 0.35 kg / m ² , the Ca component is insufficient to sufficiently reform the high alumina-based inclusions into CaO—Al ₂ O ₃ -based inclusions. On the other hand, when there is more addition amount of Ca component than 10 kg / m < ² >, there exists a possibility that the cleanliness of the molten steel 2 may fall by generating the CaO type inclusion of a big particle size.
Meanwhile, heat insulating material _{11, Al, Si, Fe t O} , MnO, SiO 2, MnO 2, C, contains the components of the S. For example, the composition of the heat insulating material 11 is FeO: 10 to 20% by mass, Fe ₂ O ₃ : 10 to 20% by mass, Al: 20 to 25% by mass, Al ₂ O ₃ : 25 to 40% by mass, SiO ₂ : 5 to 10% by mass.

  Therefore, as the second condition, in this embodiment, the ratio (content ratio) of the content of Ca component (Ca component content) in Ca12 to the content (component content) of each component in heat insulating material 11 is specified. doing. In order to define the content ratio of the Ca component, the relationship between the content of each component of the heat insulating material 11 and the content of the Ca component is expressed by the following formula (4), and the value obtained by the formula (4) is The second condition is to satisfy a range from 0.08 to 0.25 (0.08 to 0.25) (second condition).

_{[% Ca] / ([%} Al] +3 [% Fe 2 O 3] + [% FeO] +2 [% SiO 2] +2 [% MnO 2] + [% S]) ··· (4)
However, “%” represented by the formula (4) is “mol%”.
Here, although the heat insulating material 11 contains sulfur S, the content of S is about 200 ppm (amount of inevitable impurities) and may be considered to be substantially zero (≈0). In other words, since the S content is very small compared to the other components, even if the S content is substituted into the formula (4), the value of the formula (4) does not change greatly, and substantially Will not be affected.

If the value of the formula (4) is less than 0.08, the amount of Ca component relative to the amount of high alumina inclusions produced by the heat insulating material 11 is too small. Cannot be modified into CaO—Al ₂ O ₃ inclusions. On the other hand, if the value of the formula (4) is larger than 0.25, the amount of Ca component with respect to the heat insulating material 11 is too large, so that a CaO-based inclusion with a large particle size is generated, and the cleanliness of the molten steel 2 May decrease.

Therefore, in the present embodiment, the first condition, that is, the addition amount of the Ca component is in the range of 0.35 kg / m ^{2 to} 10 kg / m ² , and the second condition is shown in the formula (4). Ca12 is added so as to satisfy simultaneously that the relationship becomes a value in the range of 0.08 to 0.25.
In addition, when adding the heat insulating material 11 and Ca12 separately, the heat insulating material 11 may contain a trace amount metal Ca and Ca alloy. Even when the heat insulating material 11 contains a trace amount of metal Ca and Ca alloy, the relationship between the content of each component in the heat insulating material 11 and the addition amount of the Ca component shown in Formula (4) is 0. Any value within the range of 0.08 to 0.25 may be used.

  In the above description, Ca12 and the heat insulating material 11 are added separately from the start of casting until the molten steel 2 reaches the feeder frame 8 and the casting is finished, but instead of this, the heat insulating material is replaced. 11 and Ca12 may be mixed and the heat insulating material 11 and Ca12 may be added simultaneously. For example, before adding the heat insulating material 11, the heat insulating material 11 is mixed with Ca12 made of metal Ca to prepare the heat insulating material 11 containing the Ca component, and the heat insulating material 11 is added to the molten steel 2. May be.

Also when adding the heat insulating material 11 in which Ca12 is mixed, the expression (4) indicating the relationship of the content of each component in the heat insulating material 11 may be a value included in the range of 0.08 to 0.25. . As described above, the heat insulating material 11 Ca12 is mixed, the addition amount of Ca component needs to be added so as to satisfy the ^{0.35kg / m 2 ~10kg / m 2} .

Table 1 shows an example in which an ingot was produced by the under-pour ingot casting method of the present invention, and a comparative example in which the ingot was produced by a method different from the under-ingot ingot ingot method of the present invention.

  In the examples and comparative examples, the primary refining before the bottom pouring and ingot casting method is performed by melting the scraps in an electric furnace according to the ordinary method of those skilled in the art, and the molten steel 2 of 20 to 100 tons is taken into the ladle 3 Steel was produced. Moreover, the secondary refining by the LF apparatus and a cover degassing apparatus (VD) was performed with respect to the molten steel 2 after the primary refining, and the component adjustment and temperature adjustment of the molten steel 2 were performed. With respect to the molten steel 2 in which the primary refining and the secondary refining were finished, an ingot was manufactured by the down-pour ingot casting method.

In this embodiment, after casting with the mold 5, the solidified ingot was heated to about 1300 ° C. by a conventional method of those skilled in the art, and formed into a forged material having a cross-sectional diameter of 150 to 700 mm by hot forging.
The primary refining described above may not be performed by an electric furnace, but may be performed by another apparatus such as a converter. The secondary refining is not necessarily performed by the LF apparatus or the lid degassing apparatus, and may be performed by other apparatuses such as a reflux degassing apparatus (RH) or a CAS apparatus. Furthermore, the components of the molten steel 2 in the primary refining and the secondary refining, the processing temperature, the amount of molten steel, and the like are not limited to those described above and are not related to the essence of the present invention. In addition, although the size of the casting_mold | template 5 in the bottom pouring ingot-making method shall be able to manufacture an ingot of 20 tons-90 tons, the size and shape of an ingot are not limited to what was disclosed by this embodiment. .

In addition, in performing the bottom pouring ingot method, in some of the comparative examples to be described later, the covering material 10 is consumed and the bath surface of the molten steel 2 is 80% in area ratio in order to make the comparison with the examples easy to understand. Even if it exposed above, additional coating | covering material 10 was not added, but Ca12 grade | etc., Was added, with some bath surfaces exposed.
Further, in the examples and comparative examples, some small-scale experiments simulating an induction melting furnace as the mold 5 were also performed. In a small experiment, molten steel 2 having a molten steel amount of 3 to 30 kg was melted in an induction melting furnace, and after adjusting the components, the covering material 10 was quickly added in the same manner as the mold 5. Thereafter, the addition amount of Ca component to the surface area of the bath surface of the molten steel 2 so as to satisfy the ^{0.35kg / m 2 ~10kg / m 2} , addition of heat insulating material 11 that does not contain powdered Ca12 and Ca components simultaneously, or The heat insulating material 11 containing Ca12 was added. Incidentally, when adding the heat insulating material 11 or Ca12 containing Ca component, equation (4) shown as a [% Ca] / ([% Al] +3 [% Fe 2 O 3] + [% FeO] +2 [ _{% SiO 2] +2 [% MnO} 2] + [% S]) was added heat insulating material 11 and Ca12 to satisfy 0.08 to 0.25. And after adding the heat insulating material 11, the electric power of the induction melting furnace was stopped and the molten steel 2 was solidified in the furnace.

A small piece was taken out as a sample from a steel ingot after forging or a steel ingot solidified in an induction melting furnace (small experiment) and polished, and the inclusions were observed with an electron microscope (SEM). In the examples and comparative examples, the size of the maximum inclusion detected in a 15 × 15 mm square field of view was defined as the inclusion size in the table.
As shown in Table 1, as a result of preparing and observing the sample in this way, in Examples 1 to 11, the size of the maximum inclusion was able to be 200 μm or less. In Examples 1 to 11, after the coating material 10 for coating the bath surface on the molten steel 2 in the mold 5 is added according to the above-described ingot casting method according to the present embodiment, the heat insulating material 11 containing Ca12 is added. Either the thermal insulation material 11 or Ca12 was added separately. At this time, as described above, the addition amount of the Ca component with respect to the surface area of the bath surface satisfies the range of 0.35 kg / m ^{2 to} 10 kg / m ² , and the value of the formula (4) is 0.08 to The range of 0.25 was satisfied.

FIG. 3 summarizes the relationship between the value of the above-described formula (4) and the maximum inclusion inclusion diameter shown in Table 1 for Examples 1 to 11. As shown in FIG. 3, when the addition amount of the Ca component is adjusted so as to be in the range of 0.35 kg / m ^{2 to} 10 kg / m ² , the value X of the formula (4) is 0.08 to 0.25. In the range, the maximum inclusion diameter is less than 200 μm. However, if the value X of the formula (4) is less than 0.08, the maximum diameter of inclusions is more than 200 μm and becomes 500 μm or more. Even when the value X of the formula (4) is more than 0.25, the inclusions It can be seen that the maximum diameter greatly exceeds 200 μm and becomes 400 μm or more. That is, also from the graph of FIG. 3, when the value of Formula (4) becomes 0.08 or 0.25, it becomes a boundary for reducing the maximum diameter of inclusions.

FIG. 4 summarizes the relationship between the amount of Ca component added and the maximum inclusion diameter for Examples 1 to 11. As shown in FIG. 4, when the value of Equation (4) is adjusted to a value in the range of 0.08 to 0.25, the amount of Ca component added is 0.35 kg / m ^{2 to} 10 kg / m ² . When in the range, the maximum inclusion diameter is less than 200 μm. However, if the addition amount of the Ca component is less than 0.35 kg / m ² , the maximum diameter of inclusions is more than 200 μm and becomes 350 μm or more, and even when the addition amount of the Ca component is more than 10 kg / m ² It can be seen that the maximum diameter greatly exceeds 200 μm and becomes 400 μm or more. In other words, even when viewed from the graph in FIG. 4, when the added amount of the Ca constituent became 0.35 kg / ^{m 2} and 10 kg / ^{m 2} becomes the boundary for reducing inclusions maximum diameter.

  On the other hand, in Comparative Examples 12 to 27 to which the coating material 10 is added, either the first condition regarding the addition amount of the Ca component or the second condition regarding the formula (4) is not satisfied, and the maximum diameter of inclusions Became larger than 200 μm. That is, in the comparative examples 12 to 27 in which the first condition is satisfied but the second condition is not satisfied, or the second condition is satisfied but the first condition is not satisfied, the inclusion maximum diameter Became larger than 200 μm.

Further, in Comparative Examples 28 to 32, when the covering material 10 is not added, or when the covering material 10 is consumed in the middle, the additional covering material 10 is not added (in the table, the addition of the covering material “pear”). In these cases, the maximum inclusion diameter was larger than 200 μm.
As described above, according to the bottom pouring ingot method of the present embodiment, after adding the coating material 10 for coating the bath surface to the molten steel 2 in the mold 5, the first condition and the second condition described above are satisfied. The heat insulating material 11 containing Ca12 is added, or Ca12 is added before or simultaneously with the addition of the heat insulating material 11. Thereby, generation | occurrence | production of the coarse inclusion in the molten steel 2 can be suppressed, and the maximum diameter of the inclusion in an ingot can be made 200 micrometers or less, and the ingot excellent in the cleanliness can be manufactured.

A method for further reducing the maximum inclusion diameter in the bottom pouring method according to the present embodiment described so far will be described below. In the above-described ingot casting method, it has been described that the maximum inclusion diameter can be suppressed to 200 μm or less by satisfying the first condition and the second condition, but in addition to satisfying the first condition and the second condition, Ca12 When the average particle diameter of the metal Ca and Ca alloy is adjusted, the maximum inclusion diameter can be suppressed to less than 200 μm, and the average particle diameter of the inclusion can also be suppressed.

  Specifically, the average particle diameter of Ca12 added to the molten steel 2 together with the heat insulating material 11 is adjusted to be 200 μm or more. As in Examples 1 to 20 shown in Table 2 below, in addition to satisfying the first condition and the second condition, the maximum particle size of inclusions is suppressed to 150 μm or less by setting the average particle size of Ca12 to 200 μm or more. can do.

As already described, the purpose of adding metal Ca or Ca alloy as Ca12 is to modify the high alumina inclusions that are formed when the heat insulating material 11 is added into CaO—Al ₂ O ₃ inclusions that are less likely to aggregate. It is to be. However, the Ca component of Ca12 is oxidized by Fe ₂ O ₃ , SiO _2, or the like, which is a component of the heat insulating material 11, before it contributes to the modification and changes to CaO. Therefore, the inventors of the present invention seem to obtain inclusion modification effect by remaining the Ca component in the central portion of the Ca12 in the heat insulating material 11 even if the Ca component on the surface side of the Ca12 is changed to CaO. In addition, an attempt was made to increase the average particle size of Ca12. As a result, excellent results as shown in Examples 1 to 20 in Table 2 could be obtained.

The comparative example of Table 2 is also mentioned. In Comparative Examples 19 to 26, although the average particle diameter of Ca12 was adjusted to be 200 μm or more, either of the first condition regarding the addition amount of the Ca component and the second condition regarding Formula (4) was satisfied. Did not meet. Accordingly, the maximum inclusion diameter was a large value far exceeding 150 μm.
In Comparative Examples 27 and 28, when the covering material 10 indicated as the mold internal layer is not added, or when the covering material 10 is consumed in the middle, no additional covering material 10 is added (in the table, the mold) The internal agent layer “pear”). In Comparative Example 27, after adjusting the average particle diameter of Ca12 to be 200 μm or more, even if both the first condition and the second condition were satisfied, the inclusion maximum diameter was a large value far exceeding 150 μm. . In Comparative Example 28, which did not satisfy the first condition regarding the amount of Ca component added, the maximum inclusion diameter was larger than the value in Comparative Example 27.

  In Comparative Examples 29 to 40, the average particle size of Ca12 was all less than 200 μm. However, except for Comparative Examples 31 and 32, both the first condition and the second condition were satisfied as described above, so that the maximum inclusion inclusion diameter was larger than 150 μm but could be suppressed to 200 μm or less. In Comparative Examples 31 and 32 that did not satisfy either the first condition relating to the addition amount of the Ca component or the second condition relating to the expression (4), the maximum inclusion diameter not only exceeded 150 μm, but also 200 μm. It was a big value that far exceeded.

  The graph of FIG. 5 is a distribution diagram showing the results of Examples 1 to 18 and Comparative Examples 19 to 40. Black diamonds show the results of Examples 1-18, and white squares show the results of Comparative Examples 19-40. As shown in FIG. 5, it can be seen at a glance that the inclusion maximum diameter (or inclusion maximum long diameter) is 150 μm or less in Examples 1 to 18 in which the average particle diameter of Ca12 is 200 μm or more.

  Thus, according to the bottom pouring ingot method of this embodiment, after adding the coating material 10 for covering the bath surface to the molten steel 2 in the mold 5, Ca12 having an average particle size of 200 μm or more is prepared. In order to satisfy the first condition and the second condition described above, the heat insulating material 11 containing Ca12 is added, or Ca12 is added before or simultaneously with the addition of the heat insulating material 11. Thus, by adjusting the average particle diameter of Ca12 to 200 μm or more, generation of coarse inclusions in the molten steel 2 can be suppressed and the maximum diameter of inclusions in the ingot can be reduced to 150 μm or less. It is possible to produce an excellent ingot.

  Here, although the average particle size of Ca12 is set to 200 μm or more, there is no particular upper limit on the average particle size. Although generally good results are obtained as the average particle size increases, the actual conditions of operation and the chemical reaction rate of the heat-retaining material 11 and Ca12 are considered in order to carry out the above-described ingot casting method. Thus, the upper limit of the average particle size of Ca12 is determined. The inventors of the present application obtained knowledge that, in the bottom pouring method according to this embodiment, an average particle diameter range of about 200 μm to 5 mm is suitable, and about 200 μm to 3 mm is more preferable. ing.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. In the above embodiment, the heat insulating material 11 is added during casting, but it may be at the end of casting (timing when the rise of the bath surface is stopped).

DESCRIPTION OF SYMBOLS 1 Bottom pouring and ingot making apparatus 2 Molten steel 3 Ladle 4 Injection pipe 5 Mold 6 Surface plate 7 Runway 8 Feeding frame 9 Lower inlet 10 Covering material 11 Heat insulating material

In order to achieve the above object, the present invention has taken the following measures.
That is, the technical means for solving the problem in the present invention is that the molten steel in the mold is produced by performing the pouring and ingot making method for producing the ingot by inserting the molten steel into the mold from below through the injection pipe. After adding the coating material for coating the bath surface, the metal Ca and / or Ca alloy having an average particle size of 200 μm or more is added before or simultaneously with the heat insulating material, and the surface area of the bath surface is increased. with the addition of Ca component of the metallic Ca and / or Ca alloy is added to the metallic Ca and / or Ca alloy to a value within the range of 0.35 kg / ^{m 2} or more 10 kg / ^{m 2} or less, thermal insulation [% Ca] / ([% Al] +3 [% Fe ₂ O ₃ ] + [% FeO] +2 showing the relationship between the component content of the material and the Ca component content of the added metal Ca and / or Ca alloy) [% SiO ₂ ] +2 [% MnO ₂ ] + [% S]) is in a range of 0.08 or more and 0.25 or less .

The other technical means of the present invention is to cover the molten steel in the mold with a bath surface when performing the pouring and ingot forming method for producing the ingot by inserting the molten steel into the mold from below through the injection pipe. After adding the covering material for the purpose, a heat insulating material containing metal Ca and / or Ca alloy having an average particle size of 200 μm or more is added, and the metal Ca and / or Ca alloy with respect to the surface area of the bath surface is added. with the addition amount of the Ca constituent is added the thermal insulation material so as to satisfy the 0.35 kg / ^{m 2} or more 10 kg / ^{m 2} or less, adding Ca component of the metallic Ca and / or Ca alloy and ingredient content of heat insulating material It shows the relationship between the content of _{[% Ca] / ([%} Al] +3 [% Fe 2 O 3] + [% FeO] +2 [% SiO 2] +2 [% MnO 2] + [% S]) is 0 It becomes a value within the range of .08 to 0.25 It lies in the fact that Unishi. [% X] is the X content (mol%) in the heat insulating material.

Claims (2)

In carrying out the bottom pouring and ingot-making method for producing an ingot by inserting molten steel into the mold from below through an injection tube,
After adding the coating material for coating the bath surface to the molten steel in the mold, the metal Ca and / or Ca alloy having an average particle size of 200 μm or more is added before or simultaneously with the addition of the heat retaining material,
The metallic Ca and / or Ca alloy as the added amount of the Ca constituent of the metallic Ca and / or Ca alloy to the surface area of the bath surface is within a range of less than 0.35 kg / ^{m 2} or more 10 kg / ^{m 2} [% Ca] / ([% Al] +3 [% Fe ₂ O ₃ ] showing the relationship between the component content of the heat insulating material and the Ca component content of the added metal Ca and / or Ca alloy. + [% FeO] +2 [% SiO ₂ ] +2 [% MnO ₂ ] + [% S]) is a value within the range of 0.08 or more and less than 0.25 Ingot-making method.
However, [% X]: X content in the heat insulating material (mol%). In carrying out the bottom pouring and ingot-making method for producing an ingot by inserting molten steel into the mold from below through an injection tube,
After adding a coating material for coating the bath surface to the molten steel in the mold, a heat insulating material containing metal Ca and / or Ca alloy having an average particle size of 200 μm or more is added,
With the addition of Ca component of the metallic Ca and / or Ca alloy to the surface area of the bath surface is added to the thermal insulation material so as to satisfy the ^{0.35kg / m 2 ~10kg / m 2} , content of the component heat insulating material [% Ca] / ([% Al] +3 [% Fe ₂ O ₃ ] + [% FeO] +2 [% SiO ₂ ]] showing the relationship between the Ca content of the added metal Ca and / or Ca alloy +2 [% MnO ₂ ] + [% S]) is set to a value within a range of 0.08 or more and less than 0.25.
However, [% X]: X content in the heat insulating material (mol%).

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