JP7748072B2 - Mold powder for continuous casting and method for manufacturing steel - Google Patents

Description

The present invention relates to mold powder for continuous casting and a method for producing steel.

When continuously casting molten steel using a continuous casting machine, the molten steel is first poured from a ladle through a tundish into a mold, where an initial solidified shell is formed. The molten steel is then cooled in the subsequent secondary cooling zone, and solidification progresses to the interior. During casting, continuous casting mold powder (hereinafter sometimes referred to as powder) is constantly added to the mold, and the molten powder penetrates between the mold and the solidified shell. During continuous casting, the powder improves lubrication between the solidified shell and mold and keeps the molten steel warm.

Generally, powders are primarily composed of CaO and _SiO2 , with _{Al2O3 , Na2O} , fluorine compounds, C, and other ingredients blended in depending on the desired properties. _SiO2 is added to lower the melting point and promote vitrification. However, if the Al concentration in the molten steel is high, a thermite reaction occurs during continuous casting, and oxides in the powder, particularly _SiO2 , are reduced by the Al in the molten steel. The thermite reaction between _SiO2 and Al is expressed by the following formula (1):
4[Al]+3( _SiO2 )→2( _Al2O3 ) ₊₃ [Si]...(1)
Here, [Al] and [Si] refer to components in the molten steel, and (SiO ₂ ) and (Al ₂ O ₃ ) refer to components in the powder.

The thermite reaction increases the _Al2O3 concentration of the powder. It is known that an increase in _{the Al2O3} concentration in the powder _can cause various problems. For example, when continuous casting is performed using powder containing CaO and _SiO2 , an increase in the _Al2O3 content can result in the formation of 2CaO· _Al2O3 · _SiO2 (gehlenite ₎ , a high-melting-point compound. _Gehlenite significantly deteriorates the lubricity of the powder, increasing the risk of an operational problem called breakout, in which the initial solidification shell breaks during casting and molten steel leaks. Furthermore, as _{the Al2O3} content increases, the melting point increases, and sintered powder lumps called bare particles are formed on the mold. When the bare particles become coarse, they push into the initial solidification shell, sometimes resulting in depressions on the slab surface.

Against this background, various powders have been proposed for continuous casting of high-Al steel, with the aim of producing high-quality cast slabs and preventing operational problems.

For example, Patent Document 1 proposes a mold powder for continuous casting of steel, characterized by an F content of 16 to 25 mass%, a CaO to _SiO2 mass ratio (CaO/ _SiO2 ) of 1.0 to 1.8, _{an Al2O3} content of 5 mass% or less (including zero), and an MgO content of 1.5 mass% or less (including zero). It is said that this powder can prevent restrictive breakouts and slag bear enlargement that are caused by large compositional fluctuations. Here, "compositional fluctuation" refers to a decrease in _SiO2 and an increase _{in Al2O3} in the molten slag.

Patent Document 2 proposes a mold powder for continuous casting that contains 10-35 wt% CaO, _10-35 wt% _Al2O3 , 3-15 wt% _TiO2 , 3-20 wt% Li2O, 5-40 wt% _BaO , 15 wt% or less F, 20 wt% or less _Na2O , and one or more of 0.5-4.0 wt% BN and 0.5-4.0 wt% C as aggregates, with the remainder consisting of unavoidable impurities. It is claimed that this powder can prevent deterioration of the slab surface quality and breakouts due to poor powder lubrication (alteration) when continuously casting steel containing slag-reducing metal elements.

JP 2017-170494 A Japanese Patent Application Publication No. 5-185195

However, the powder described in the above document has the following problems:

For example, the powder described in Patent Document 1 contains _SiO2 , which causes a thermite reaction when used. The invention described in Patent Document 1 aims to prevent the adverse effects of the increase _{in Al2O3} concentration in the powder that accompanies this reaction. However, the thermite reaction not only causes the above adverse effects but also causes adverse effects due to heat generation. First, the solidification of molten steel is delayed at the meniscus, causing the solidified shell to break (bleed) along the oscillation marks. This impairs the surface quality of the cast slab. Furthermore, the generation of flames can cause equipment failure and shutdowns.

Furthermore, the powder described in Patent Document 2 does not contain _SiO2 , but does contain _Na2O , _TiO2 , and _Li2O , and a thermite reaction occurs between these components and Al in the molten steel. As a result, heat is generated and _{the Al2O3} concentration increases, which can cause operational problems and deterioration in the quality of the cast slab.

The gist of the present invention, which aims to solve the above problems, is as follows:

1. Aggregate carbon,
_{Al2O3 ,}
BaO,
CaO,
MgO,
Fluorine compounds,
and the remainder being unavoidable impurities,
Total C content: 0.5 to 5.0% by mass,
Al ₂ O ₃ content: 15-35% by mass,
BaO content: 15 to 35% by mass,
CaO content: 30 to 40% by mass,
MgO content: 1.0 to 5.0% by mass,
F content: 10 to 20% by mass,
The total content of the inevitable impurities: 2.0% by mass or less;
This is a mold powder for continuous casting.

2. The mold powder for continuous casting according to the above item 1, wherein the component composition further contains a carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg.

3. The mold powder for continuous casting described in 1 or 2 above, wherein the maximum particle size of the mold powder is 250 μm or less.

4. The mold powder for continuous casting described in any one of items 1 to 3 above, wherein 50 mass% or more of the mold powder consists of premelt raw material.

5. A method for producing steel, comprising continuously casting steel containing 0.5 mass% or more of Al using the mold powder for continuous casting described in any one of 1 to 4 above.

6. A method for producing steel as described in 5 above, in which the powder consumption per ton of molten steel is 0.4 kg or more.

The present invention provides a mold powder for continuous casting that enables the production of high-quality cast pieces and the prevention of operational problems when continuously casting high-Al steel. It also provides a method for producing steel using the powder.

The present invention will now be described in detail. Note that in this specification, "%" as a unit of content refers to "% by mass" unless otherwise specified.

As described above, an increase in _{the Al2O3} concentration in the powder causes the formation of high-melting-point gehlenite and the coarsening of bare grains, which impairs operational stability and reduces the surface quality of the cast slab. Therefore, in order to obtain stable productivity and quality in the continuous casting of high-Al steel, it is desirable to keep the increase in the _Al2O3 concentration in the _powder during casting as small as possible.

Experiments conducted by the present inventors have revealed that factors that increase _{the Al2O3} concentration in powder during casting include not only the oxidation of Al in molten steel by oxides in the powder but also the oxidation of Al in molten _steel by the atmosphere. However, oxidation by the atmosphere is difficult to prevent. In other words, to minimize the increase in the _Al2O3 concentration, it is necessary to prevent as much as possible the oxidation of Al in molten steel by oxides in the powder. Furthermore, in order to produce steel without causing problems related to operation and quality, it is necessary to set the powder production and steel production conditions taking into account the fact that _{the Al2O3} content in the powder will increase to some extent during casting.

From these perspectives, the inventors focused on the solidification start temperature after the powder undergoes a chemical change during casting. They concluded that it would be preferable to lower the solidification start temperature after the chemical change (hereinafter, the solidification start temperature after the chemical change may be simply referred to as the solidification start temperature). In order to lower the solidification start temperature, the chemical composition of the powder and the steel manufacturing conditions are important.

Furthermore, the inventors have concluded that in order to stabilize operations and improve the surface quality of cast slabs, the content of oxides with _a standard free energy of formation higher than _Al2O3 at 1300°C should be minimized. This is due to the following reasons: First, 1300°C is the average temperature of the molten powder during casting. Oxides such as _SiO2 , _Na2O , _TiO2 , and _Li2O , which have a standard free energy of formation higher than _Al2O3 at that _temperature , will cause a thermite reaction with Al in the molten steel, causing the various adverse effects described above. Therefore, it is necessary to produce powder that contains almost no oxides _with a standard free energy of formation higher than _Al2O3 at 1300°C.

The component composition of the powder according to one embodiment of the present invention is described below.

[Aggregate carbon]
The aggregate carbon plays a role in adjusting the melting rate of the powder. Examples of the aggregate carbon include, but are not limited to, carbon black and coke powder. The content of the aggregate carbon is preferably 0.5% to 3.5%.

[Total C content: 0.5 to 5.0% by mass]
If the total C content is less than 0.5%, the effect as an aggregate cannot be obtained. From this viewpoint, the total C content is set to 0.5% or more, preferably 1.0% or more. On the other hand, if the total C content exceeds 5.0%, when a thermite reaction occurs, the C burns and generates a flame, which can cause equipment failure and operation shutdown. Therefore, from the viewpoint of preventing operational troubles, the total C content is set to 5.0% or less, preferably 3.0% or less. Here, the total C content can be calculated as the sum of the aggregate carbon content and the C content derived from carbonates, which will be described later. Furthermore, the C derived from carbonates is considered to be the sum of the C derived from carbonates remaining in the premelt raw material, which will be described later, and the C derived from carbonates blended other than the premelt raw material.

[Al ₂ O ₃ : 15-35%]
_Al2O3 is added to increase the activity _{of Al2O3} in the molten powder and suppress the oxidation reaction _{of Al in molten steel. If the Al2O3 content} is less than 15%, this effect cannot be obtained. Therefore _, the _Al2O3 content is set to 15% _or more, preferably 20% or more. On the other hand, if the _Al2O3 content is higher than 35%, the solidification start temperature _of the powder becomes very high, taking into account that _{the Al2O3} content _will further increase during casting. Therefore, the _Al2O3 content is set to 35% or less, preferably 30% or less. _{The Al2O3} content is determined by converting the Al content determined by fluorescent X-ray analysis _{into Al2O3} .

[BaO]
BaO has a lower standard free energy of formation at 1,300°C than _Al2O3 and hardly reacts with _Al in molten steel, so an increase in the _Al2O3 concentration in the powder during casting _is suppressed. In addition, BaO forms a complex _oxide with _Al2O3 , lowering the solidification start temperature of the powder.

[Ba oxide content: 15 to 35 mass %]
If the Ba oxide content is less than 15%, the above-mentioned effects of suppressing the increase in _Al2O3 concentration and lowering the solidification start temperature of the powder _cannot be obtained. Therefore, the Ba oxide content is set to 15% or more, preferably 20% or more. On the other hand, if the Ba oxide content is higher than 35%, the solidification start temperature will increase. Therefore, the Ba oxide content is set to 35% or less, preferably 30% or less. The above content is calculated by determining the Ba element content by X-ray fluorescence analysis and converting it into BaO.

[CaO]
CaO has a lower standard free energy of formation at 1,300°C than _Al2O3 and hardly reacts with _Al in molten steel, so an increase in the _Al2O3 concentration in the powder during casting _is suppressed. In addition, CaO forms a complex _oxide with _Al2O3 , lowering the solidification start temperature of the powder.

[Ca oxide content: 30 to 40 mass%]
If the Ca content in terms of oxide is less than 30%, the above-mentioned effects of suppressing the increase in _Al2O3 concentration and lowering the solidification start temperature of the powder _cannot be obtained. Therefore, the Ca content in terms of oxide is set to 30% or more, preferably 32% or more. On the other hand, if the Ca content in terms of oxide is higher than 40%, the solidification start temperature will increase. Therefore, the Ca content in terms of oxide is set to 40% or less, preferably 38% or less. The above content is calculated by determining the Ca element content by fluorescent X-ray analysis and converting it to CaO.

[MgO]
_Since MgO has a lower standard free energy of formation at 1300°C than _Al2O3 and hardly reacts with Al in molten steel, an increase in the _Al2O3 concentration in the powder during casting _can be suppressed. In addition, the solidification start temperature of the powder can be lowered.

[Mg oxide content: 1.0 to 5.0 mass%]
If the Mg content in terms of oxide is less than 1.0%, the above-mentioned effects of suppressing the increase in _Al2O3 concentration and lowering the solidification start temperature of the powder _cannot be obtained. Therefore, the Mg content in terms of oxide is set to 1.0% or more, preferably 1.5% or more. On the other hand, if the Mg content in terms of oxide exceeds 5.0%, the solidification start temperature will increase. Therefore, the Mg content in terms of oxide is set to 5.0% or less, preferably 3.0% or less. The above content is calculated by determining the Mg element content by X-ray fluorescence analysis and converting it into MgO.

[Fluorine compounds]
The fluorine compound is blended to lower the powder solidification initiation temperature and viscosity (described later). The fluorine compound is not particularly limited, and examples thereof include _CaF2 and _BaF2 . From the viewpoint of cost, it is preferable to use _CaF2 .

[F content: 10-20% by mass]
If the F content of the powder is less than 10%, the above-mentioned effects of the fluorine compound cannot be obtained. Therefore, the F content of the powder is set to 10% or more. On the other hand, if the F content of the powder exceeds 20%, not only does the effect saturate, but the risk of oxidation and deterioration of the continuous casting machine increases dramatically. Therefore, the F content of the powder is set to 20% or less. The F content can be measured using the X-ray fluorescence glass bead method.

[Carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg]
The powder may contain a carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg. This is for the following reason: In the production of powder, the component composition of an intermediate raw material such as a premelt raw material may deviate from the target. In such cases, the content of the element can be adjusted by mixing the carbonate into the intermediate raw material. Here, even when elements such as Ca, Ba, and Mg are contained as carbonates, the same effect as when oxides of the elements are contained can be obtained.

When elements such as Ca, Ba, and Mg are contained as carbonates, the total content of the elements converted into oxides is calculated by adding the content of the oxides of the elements and the content obtained by converting the carbonates of the elements into oxides.

Here, the carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg may be a carbonate of Ba.

The total content of the carbonates is not limited, as long as the content of each of the elements Ca, Ba, and Mg, calculated as an oxide, is sufficient. However, lowering the total content of the carbonates allows for an increase in the content of other components and prevents changes in melting properties during casting due to carbon dioxide gas. It also further suppresses the formation of bare spots. Therefore, the total content of the carbonates in the powder is preferably 10% or less, and more preferably 5% or less. On the other hand, the lower limit of the total content of the carbonates is not particularly limited and may be 0%, and the carbonates may not be present. From a similar perspective, the content of Ba carbonate in the powder calculated as BaO is preferably 10% or less. The lower limit of this content is not limited and may be 0%. From a similar perspective, the content of Ca carbonate in the powder calculated as CaO is preferably 10% or less. The lower limit of this content is not limited and may be 0%. From a similar perspective, the content of Mg carbonate in the powder calculated as MgO is preferably 10% or less. The lower limit of the content is not limited and may be 0%.

From a similar perspective, the ratio of the content of Ba carbonate in terms of BaO to the content of Ba in terms of BaO is preferably 50% or less. The lower limit of this ratio is not particularly limited and may be 0%, and Ba carbonate may not be included. From a similar perspective, the ratio of the content of Ca carbonate in terms of CaO to the content of Ca in terms of CaO is preferably 50% or less. The lower limit of this ratio is not particularly limited and may be 0%, and Ca carbonate may not be included. From a similar perspective, the ratio of the content of Mg carbonate in terms of MgO to the content of Mg in terms of MgO is preferably 50% or less. The lower limit of this ratio is not particularly limited and may be 0%, and Mg carbonate may not be included.

The component composition of the powder according to one embodiment of the present invention has been described above. The powder according to one embodiment of the present invention contains the above components, with the remainder consisting of unavoidable impurities.

The inevitable impurities may also include oxides whose standard free energy of formation at 1300°C is higher than that _{of Al2O3} . Examples of such oxides include _SiO2 , _Na2O , _TiO2 , and _Li2O . Because these oxides may be unavoidably mixed into the powder raw materials, it is difficult to completely remove them. However, their content must be as low as possible to prevent a thermite reaction with Al in the molten steel. Furthermore, eliminating _Li2O also leads to significant reductions in manufacturing costs. From this perspective, the total content of the inevitable impurities is set to 2.0% or less. In other words, the total content of _Al2O3 , _BaO , CaO, MgO, aggregate carbon, and fluorine compounds is set to 98.0% or more.

As described above, the powder according to one embodiment of the present invention comprises:
aggregate carbon,
_{Al2O3 ,}
BaO,
CaO,
MgO,
Fluorine compounds,
and the balance being unavoidable impurities,
Total C content: 0.5 to 5.0% by mass,
Al ₂ O ₃ content: 15-35% by mass,
Ba oxide content: 15 to 35 mass%
Ca oxide content: 30 to 40 mass%
Mg oxide content: 1.0 to 5.0 mass%
F content: 10 to 20% by mass,
The total content of the inevitable impurities: 2.0% by mass or less;
It is important that

The composition may further contain a carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg.

The powder according to the present invention can be produced, for example, by mixing raw materials to obtain the aforementioned component composition. The raw materials may comprise _aggregate carbon, _Al2O3 , CaO, BaO, MgO, and a fluorine compound. The raw materials may further contain a carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg. Some or all of the raw materials may be premelt raw materials. The particle size of the powder may be adjusted by techniques such as pulverization or classification.

[Premelt raw materials]
Premelt raw material refers to a material obtained by melting and pulverizing raw materials in advance. As mentioned above, carbonates such as _BaCO3 may be blended as powder raw materials. However, blending carbonates can generate gas when the powder melts during casting, which can adversely affect the quality of the cast slab, such as pinhole defects and inclusion entrapment defects, or can adversely affect operational aspects, such as melting of the submerged entry nozzle. The premelt raw material is used to reduce these effects and form a stable molten layer. Therefore, in a powder according to one embodiment of the present invention, the powder preferably comprises 50% by mass or more of premelt raw material, and more preferably 80% by mass or more of premelt raw material. The upper limit of the premelt raw material content is not particularly limited and may be 100% by mass. However, considering the blending of aggregate carbon, it is preferable that the powder comprises 99.5% by mass or less of premelt raw material. It is also more preferable that the powder comprises 90% by mass or less of premelt raw material.

The powder according to one embodiment of the present invention can be produced by blending additional materials with the premelt raw material to adjust the powder's component composition, etc. For example, if _Al2O3 is insufficient, _Al2O3 can be blended. If _CaO is insufficient, _CaF2 or CaO can be blended. If the F content is insufficient, _CaF2 can be blended. If _BaO is insufficient, _BaCO3 can be blended.

Here, aggregate carbon cannot normally be used as premelt raw material. In other words, the ratio of premelt raw material to the total amount of aggregate carbon may be 0%.

If carbonate is added after premelt to adjust the composition, the total C content increases, reducing the content of other components, and the molten state changes due to the influence of carbon dioxide gas. This can also lead to the generation of dust and flames. In other words, reducing the amount of carbonate added can further improve operability and quality. Therefore, for carbonates of at least one element selected from the group consisting of Ca, Ba, and Mg, the proportion of said carbonate other than the premelt raw materials relative to the total powder mass is preferably 10% or less, more preferably 5% or less. The lower limit of this proportion is not particularly limited and may be 0%.

[Particle size]
The use of finely ground powder facilitates the melting of the powder during casting, resulting in the formation of a stable molten layer. Therefore, the powder according to one embodiment of the present invention preferably has a maximum particle size of 250 μm or less. Here, a maximum particle size of 250 μm or less refers to a particle size that passes entirely through a 60-mesh (250 μm opening) standard sieve (SIK THE IIDA TESTING SIEVE) specified in JIS Z 8801. In other words, the powder preferably has a particle size that passes entirely through a 60-mesh sieve.

[Steel manufacturing method]
A method for producing steel according to one embodiment of the present invention will now be described. The method for producing steel according to one embodiment of the present invention is a method for continuously casting steel containing 0.5 mass % or more of Al using the powder described above.

When using the above powder in the continuous casting of high-Al steel, the occurrence of the thermite reaction can be suppressed, enabling the production of high-Al steel of consistent quality with high productivity. Therefore, the steel subjected to continuous casting by a steel manufacturing method according to one embodiment of the present invention contains 0.5 mass% or more of Al, preferably 1.0 mass% or more. In other words, the steel manufacturing method according to one embodiment of the present invention is a method for continuously casting steel containing 0.5 mass% or more of Al, preferably a method for continuously casting steel containing 1.0 mass% or more of Al.

[Solidification start temperature]
In continuous casting, in order to produce high-quality cast pieces while preventing operational problems, it is effective to lower the solidification start temperature of the powder during casting. Lowering the solidification start temperature increases the activity _{of Al2O3} and prevents the thermite reaction that occurs between Al in the molten steel and the components of the powder. This results in higher quality cast pieces and further reduces the risk of operational problems.

The average temperature of the molten powder during casting is 1300°C. Therefore, it is preferable that the powder solidification start temperature be 1300°C or lower. In other words, it is preferable to control the powder so that it reaches a completely liquid state at 1300°C during casting.

[viscosity]
Furthermore, according to the present invention, in order to produce a high-quality cast piece, it is preferable to reduce the viscosity of the powder at 1300°C during casting (hereinafter, the viscosity of the powder at 1300°C during casting may be simply referred to as viscosity). This is because reducing the viscosity at 1300°C, which is the average temperature in the molten state, ensures uniform flow when the powder is added, thereby reducing unevenness on the cast piece surface. From this perspective, it is preferable to control the viscosity to 10 poise or less.

The solidification start temperature and viscosity are measured as follows: First, a sample of the molten powder is collected during casting. Since the powder composition is changing during the initial stages of casting, causing the measured values to fluctuate, the sample is collected just before the end of the casting period, when the powder composition has reached a steady state.

Next, the solidification start temperature and viscosity are measured. The solidification start temperature can be measured using differential thermal analysis. Specifically, the sample is cooled from a molten state at a constant cooling rate, and the differential heat peak is measured using differential thermal analysis. The starting point on the high-temperature side of the peak (peak start temperature) is taken as the solidification start temperature. Viscosity can also be measured using a rotational viscometer.

[Powder consumption]
In a steel manufacturing method according to one embodiment of the present invention, powder is added to the meniscus when molten steel, which has been melted to have the above-mentioned Al content, is poured from a ladle into a mold via a tundish. After being supplied to the meniscus, the powder becomes molten, penetrates the gap between the mold and the solidified shell, and is withdrawn to the rear of the mold together with the slab. During this continuous casting process, the molten steel and the powder come into contact at the meniscus, and the Al in the molten steel reacts with the powder only during this contact. Therefore, if the powder consumption rate is low, the reaction time with the molten steel per unit amount of powder increases, which increases the _Al2O3 concentration in the powder and therefore increases the solidification start temperature. Furthermore, if the _powder consumption rate is low, the _Al2O3 content _, which causes high viscosity, increases, resulting in a lower viscosity at 1300°C.

Here, the reaction between the powder and molten steel does not reach equilibrium instantly, but changes gradually, and the components in the powder saturate at a certain value lower than the equilibrium value. Here, the balance equation for component i in the powder is expressed as follows using the powder consumption amount:
W・(dX _i /dt)=Q _P・(X _i,0 −X _i )+k _i・A・(X _i,E −X _i )……(2)
W: Weight of the fused powder layer (kg)
X _i : Concentration of component i in powder X _i,0 : Initial concentration of component i in powder X _i,E : Equilibrium concentration of component i between molten steel and powder t : Time (s)
_QP : Powder consumption (kg/s)
A: reaction area between molten steel and powder (m ² )
k _i : Reaction rate constant of component i (kg/m ² /s)
When the concentration of component i no longer changes (dX _i /dt=0), the concentration _Xi of component i can be expressed as follows:
X _i =(Q _P X _i,0 +k _i・A・X _i,E )/(Q _P +k _i・A)……(3)
From the above equation, it can be seen that _Xi decreases as the powder consumption _QP increases. In other words, if component i _{is Al2O3} , increasing the powder consumption dilutes the amount _{of Al2O3 that} increases during casting, reducing _{the Al2O3} concentration at saturation, and ultimately achieving a low solidification initiation temperature and low viscosity.

Therefore, to further reduce the solidification initiation temperature and viscosity and achieve more stable operation, it is advisable to increase the powder consumption.

The inventors then discovered that when continuously casting steel containing 0.5% or more by mass of Al, if powder is added at a powder consumption rate of less than 0.4 kg per ton of molten steel, the solidification start temperature exceeds 1300°C. On the other hand, by adding powder according to one embodiment of the present invention at a powder consumption rate of 0.4 kg or more per ton of molten steel, the solidification start temperature can be kept below 1300°C and the viscosity can be kept below 10 poise. This allows for stable operation and the production of cast pieces with no surface quality problems.

From this perspective, in a steel manufacturing method according to one embodiment of the present invention, it is preferable to limit the powder consumption per ton of molten steel to 0.4 kg or more.

There are no particular limitations on the method for controlling the powder consumption. However, since the mold generally vibrates in the casting direction, it is best to control the amplitude or frequency of the mold's vibration. Alternatively, the powder consumption may be controlled by adjusting the physical properties of the powder. Specifically, the powder consumption can be controlled by adjusting the viscosity and crystallization temperature. Furthermore, the vibration conditions of the mold, such as amplitude or frequency, may be changed depending on the physical properties of the powder.

Next, the present invention will be explained in more detail based on examples. However, the present invention is not limited to the following examples, and appropriate modifications can be made within the scope of the present invention, and all such modifications are within the technical scope of the present invention.

First, nine types of mold powders for continuous casting were prepared, each having the composition shown in Table _1. In the preparation, _Al2O3 , _CaF2 , _BaCO3, etc. were blended and then melted to prepare a premelt raw material. Next, Ba carbonate was blended into the premelt raw material as needed, and aggregate carbon was further blended to obtain the composition shown in Table 1. Carbon black was used as the aggregate carbon. The contents of F, _Al2O3 , BaO, CaO, and MgO were measured by the method described above. The proportion of premelt raw material in each _of the powders shown in Table 1 was 50% or more, and the maximum particle size was 250 μm or less.

Next, molten steel with a C concentration of 0.0040% and an Al concentration of 5% was produced, and continuous casting of a slab with a mold cross-sectional size of 200 mm x 1000 mm was carried out at a casting withdrawal speed of 0.6 m/min. During this process, the powder shown in Table 2 was supplied while adjusting the mold vibration conditions to achieve the powder consumption per ton of molten steel shown in Table 2.

Next, the solidification start temperature and viscosity were measured using the methods described above. Furthermore, as an evaluation of the operational aspects, the occurrence of smoke and flames during continuous casting and the corrosion state of the equipment after casting were investigated. Additionally, the resulting cast pieces were observed to investigate the number of bleeds (pieces/m ² ). Furthermore, as an evaluation of the quality of the cast pieces, the shaping yield was investigated. The shaping yield is a value calculated using the following formula (4).
Trimming yield (%) = (weight of slab after trimming) / (weight of slab before trimming) × 100 (4)
When defects such as depressions occur on the slab surface, the slab surface must be scraped off with a scarf or grinder to remove them, resulting in a decrease in yield. In other words, the higher the slab surface yield, the higher the quality of the slab.

The results are shown in Table 2. Inventive Examples No. 1 to 3, casting was possible without any operational issues. On the other hand, in Comparative Example No. 7, corrosion progressed throughout the continuous casting equipment, making continued use difficult. Furthermore, Comparative Example No. 10 experienced operational issues during casting, with small amounts of white smoke and flames emerging from the mold.

In summary, all of the inventive examples were able to produce high-quality cast slabs and achieve stable operation, while all of the comparative examples either produced inferior quality or encountered operational problems.

Claims (9)

aggregate carbon,
_{Al2O3 ,}
BaO,
CaO,
MgO,
Fluorine compounds,
and the remainder being unavoidable impurities,
Total C content: 0.5 to 5.0% by mass,
Al ₂ O ₃ content: 15-30 % by mass,
Ba oxide content: 15 to 35 mass%
Ca oxide content: 30 to 40 mass%
Mg oxide content: 1.0 to 5.0 mass%
F content: 10 to 20% by mass,
The total content of the inevitable impurities: 2.0% by mass or less;
This is a mold powder for continuous casting. aggregate carbon,
Al2O3 , _​ ​ _​
BaO,
CaO,
MgO,
Fluorine compounds,
a carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg ;
and the remainder being unavoidable impurities,
Total C content: 0.5 to 5.0% by mass,
Al2O3 content : 15-30% by _{mass ,}
Ba oxide content: 15 to 35 mass%
Ca oxide content: 30 to 40 mass%
Mg oxide content: 1.0 to 5.0 mass%
F content: 10 to 20% by mass,
The total content of the inevitable impurities: 2.0% by mass or less;
This is a mold powder for continuous casting. The mold powder for continuous casting according to claim 1, wherein the maximum particle size of the mold powder is 250 μm or less. The mold powder for continuous casting according to claim 2, wherein the maximum particle size of the mold powder is 250 μm or less. The mold powder for continuous casting according to any one of claims 1 to 4, wherein 50 mass% or more of the mold powder consists of premelt raw material. A method for producing steel, comprising continuously casting steel containing 0.5 mass% or more of Al using the mold powder for continuous casting described in any one of claims 1 to 4. A method for producing steel, comprising continuously casting steel containing 0.5 mass% or more of Al using the mold powder for continuous casting described in claim 5. The steel manufacturing method according to claim 6, wherein the powder consumption per ton of molten steel is 0.4 kg or more. The method for producing steel according to claim 7, wherein the powder consumption per ton of molten steel is 0.4 kg or more.