Mold powder for continuous casting and method for manufacturing steel

Abstract

To provide a mold powder for continuous casting capable of producing a high-quality cast slab and preventing operation trouble when continuously casting a high-Al steel.SOLUTION: A mold powder for continuous casting has a component composition consisting of aggregate carbon, Al2O3, BaO, CaO, MgO, a fluorine compound, and the remaining inevitable impurities. The total C content is 0.5-5.0 mass%, the Al2O3 content is 15-35 mass%, the Ba content in terms of oxides is 15-35 mass%, the Ca content in terms of oxides is 30-40 mass%, the Mg content in terms of oxides is 1.0-5.0 mass%, the F content is 10-20 mass%, and the total content of the inevitable impurities is 2.0 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a mold powder for continuous casting and a method for producing steel. [Background technology]

[0002] 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, where solidification progresses to the interior. During casting, mold powder for continuous casting (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 serves to improve lubrication between the solidified shell and the mold and to keep the molten steel warm.

[0003] Generally, powders are primarily composed of CaO and SiO2, with Al2O3, Na2O, fluorine compounds, C, and other ingredients added 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 equation (1): 4[Al]+3(SiO2)→2(Al2O3)+3[Si]……(1) Here, [Al] and [Si] refer to the components in the molten steel, and (SiO2) and (Al2O3) refer to the components in the powder.

[0004] 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 leads to the formation of 2CaO·Al2O3·SiO2 (gehlenite), a high-melting point alloy. Gehlenite significantly reduces 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, resulting in the formation of sintered powder chunks called bare chunks on the mold. When the bare chunks become large, they push into the initial solidification shell, sometimes resulting in depressions on the slab surface.

[0005] Against this background, various powders have been proposed for continuous casting of high-Al steels, with the aim of producing high-quality cast slabs and preventing operational problems.

[0006] 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.

[0007] 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, and 20 wt% or less Na2O, and further contains one or more of the following aggregates: 0.5-4.0 wt% BN and 0.5-4.0 wt% C, with the remainder consisting of unavoidable impurities. This powder is said to be able to prevent deterioration of slab surface quality and breakouts due to poor lubrication (alteration) of the powder when continuously casting steel containing slag-reducing metal elements. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-170494 [Patent Document 2] Japanese Patent Application Publication No. 5-185195 Summary of the Invention [Problem to be solved by the invention]

[0009] However, the powder described in the above document has the following problems.

[0010] 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 this reaction, which increases the Al2O3 concentration in the powder. However, the thermite reaction not only causes the above adverse effects, but also causes adverse effects due to heat generation. First, solidification of the 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.

[0011] 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, operational problems and deterioration in the quality of cast slabs occur due to heat generation and an increase in the Al2O3 concentration. [Means for solving the problem]

[0012] The gist of the present invention for solving the above problems is as follows.

[0013] 1. Aggregate carbon, Al2O3, BaO, CaO, MgO, Fluorine compounds, and the remainder being unavoidable impurities, Total C content: 0.5~5.0% by mass, Al2O3 content: 15~35% by mass, BaO content: 15~35% by mass, CaO content: 30~40% by mass, MgO content: 1.0~5.0% by mass, F content: 10~20% by mass, The total content of the inevitable impurities: 2.0% by mass or less; This is a mold powder for continuous casting.

[0014] 2. The component composition further comprises 2. The mold powder for continuous casting according to 1 above, which contains a carbonate of at least one element selected from the group consisting of Ca, Ba and Mg.

[0015] 3. The mold powder for continuous casting according to 1 or 2 above, wherein the maximum particle size of the mold powder is 250 μm or less.

[0016] 4. The mold powder for continuous casting according to any one of the above 1 to 3, wherein 50 mass % or more of the mold powder is made of a premelt raw material.

[0017] 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 according to any one of 1 to 4 above.

[0018] 6. A method for producing steel as set forth in 5 above, wherein the powder consumption per ton of molten steel is 0.4 kg or more. [Effects of the Invention]

[0019] According to the present invention, it is possible to provide 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, and also to provide a method for producing steel using the powder. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will be specifically described below. In this specification, "%" as a unit of content refers to "% by mass" unless otherwise specified.

[0021] As mentioned above, an increase in the Al2O3 concentration in the powder leads to the formation of gehlenite, which has a high melting point, 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.

[0022] Furthermore, the inventors' experiments have revealed that the Al2O3 concentration in powder increases during casting due to 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.

[0023] From the above viewpoints, the inventors focused on the solidification start temperature after the composition change of the powder during casting. They concluded that it is preferable to lower the solidification start temperature after the composition change (hereinafter, the solidification start temperature after the composition change may be simply referred to as the solidification start temperature). In order to lower the solidification start temperature, the composition of the powder and the manufacturing conditions of the steel are important.

[0024] 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. This will cause 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.

[0025] The component composition of the powder according to one embodiment of the present invention will be described below.

[0026] [Aggregate carbon] The aggregate carbon plays a role in adjusting the melting speed of the powder. Examples of aggregate carbon include, but are not limited to, carbon black and coke powder. The content of aggregate carbon is preferably 0.5% to 3.5%.

[0027] [Total C content: 0.5~5.0% by mass] If the total C content is less than 0.5%, the aggregate will not be effective. From this perspective, 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%, the C will burn when a thermite reaction occurs, generating a flame, which can lead to equipment failure and operational shutdowns. Therefore, from the perspective of preventing operational problems, 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.

[0028] [Al2O3: 15-35%] Al2O3 is added to increase the activity of Al2O3 in the molten powder and suppress the oxidation reaction of Al in the 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 X-ray fluorescence analysis into Al2O3.

[0029] [BaO] BaO has a lower standard free energy of formation at 1300°C than Al2O3 and hardly reacts with Al in molten steel, which prevents the increase in Al2O3 concentration in the powder during casting. BaO also forms a complex oxide with Al2O3, lowering the solidification start temperature of the powder.

[0030] [Ba oxide content: 15 to 35 mass%] If the Ba oxide content is less than 15%, the aforementioned effects of suppressing the increase in Al2O3 concentration and lowering the powder solidification start temperature 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.

[0031] [CaO] The standard free energy of formation of CaO at 1300°C is lower than that of Al2O3, and it hardly reacts with Al in molten steel, so the increase in the Al2O3 concentration in the powder during casting is suppressed. CaO also forms a complex oxide with Al2O3, lowering the solidification start temperature of the powder.

[0032] [Ca oxide content: 30-40% by 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 powder solidification start temperature 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. Note that the above content is calculated by determining the Ca element content by X-ray fluorescence analysis and converting it into CaO.

[0033] [MgO] MgO has a lower standard free energy of formation at 1300°C than Al2O3 and hardly reacts with Al in molten steel, so it can suppress the increase in Al2O3 concentration in the powder during casting. It can also lower the powder's solidification start temperature.

[0034] [Mg oxide content: 1.0 to 5.0 mass%] If the Mg content in terms of oxide is less than 1.0%, the aforementioned 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.

[0035] [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.

[0036] [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.

[0037] [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 with 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.

[0038] 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 together the content of the oxides of the elements and the content obtained by converting the carbonates of the elements into oxides.

[0039] Here, the carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg may be a carbonate of Ba.

[0040] The total content of the carbonates is not limited as long as the content of each of the elements Ca, Ba, and Mg in terms of oxide is satisfied. However, by reducing the total content of the carbonates, the content of other components can be increased and the melting property during casting can be prevented from being affected by carbon dioxide gas. Furthermore, the formation of bare spots can be further suppressed. Therefore, the total content of the carbonates in the powder is preferably 10% or less, 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 in terms of BaO is preferably 10% or less. The lower limit of the content is not limited and may be 0%. From a similar perspective, the content of Ca carbonate in the powder in terms of CaO is preferably 10% or less. The lower limit of the content is not limited and may be 0%. From a similar perspective, the content of Ca carbonate in the powder in terms of CaO is preferably 10% or less. The lower limit of the content is not limited and may be 0%. From a similar perspective, the content of Mg carbonate in the powder in terms of MgO is preferably 10% or less. The lower limit of the content is not limited and may be 0%.

[0041] From the same viewpoint, 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 the same viewpoint, 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 the same viewpoint, 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.

[0042] 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.

[0043] The unavoidable 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 unavoidable 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.

[0044] 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: 0.5~5.0% by mass, Al2O3 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: 10~20% by mass, The total content of the inevitable impurities: 2.0% by mass or less; It is important that

[0045] The composition may further contain a carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg.

[0046] 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.

[0047] [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 raw materials for powder. 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. 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.

[0048] A powder according to one embodiment of the present invention can be prepared 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.

[0049] Here, the aggregate carbon cannot normally be used as a premelt raw material, that is, the ratio of the premelt raw material to the total amount of aggregate carbon may be 0%.

[0050] If carbonate is added after premelt to adjust the composition, the total carbon content increases, reducing the content of other components, and the molten state changes due to the influence of carbon dioxide. 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, with regard to carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg, the proportion of the carbonate other than the premelt raw material 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%.

[0051] [Particle size] The use of finely ground powder facilitates the powder melting 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.

[0052] [Steel manufacturing method] A method for producing steel according to one embodiment of the present invention will be described below. 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.

[0053] In the continuous casting of high-Al steel, the use of the above-described powder can suppress the occurrence of the thermite reaction, enabling high-Al steel of stable quality to be produced with high productivity. Therefore, the steel subjected to continuous casting by a steel production 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 production 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.

[0054] [Solidification start temperature] In continuous casting, to produce high-quality cast pieces while preventing operational problems, it is beneficial 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 powder components. This results in higher quality cast pieces and further reduces the risk of operational problems.

[0055] The average temperature of the molten powder during casting is 1300° C. Therefore, it is preferable that the powder solidification start temperature is 1300° C. or lower. In other words, it is preferable to control the powder so that it becomes a completely liquid phase at 1300° C. during casting.

[0056] [viscosity] Furthermore, according to the present invention, in order to produce high-quality cast slabs, 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, and reduces unevenness on the cast slab surface. From this perspective, it is preferable to control the viscosity to 10 Poise or less.

[0057] The solidification start temperature and viscosity are measured as follows: First, the molten powder is sampled during casting. Since the powder composition is changing in the early stages of casting and the measured values ​​fluctuate, the sample is sampled just before the end of the casting period when the powder composition has reached a steady state.

[0058] Next, the solidification initiation temperature and viscosity are measured. The solidification initiation temperature can be measured using differential thermal analysis. Specifically, a 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 initiation temperature) is defined as the solidification initiation temperature. The viscosity can also be measured using a rotational viscometer.

[0059] [Powder consumption] In a steel production 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 from the mold along 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 leads to high viscosity, increases, resulting in a lower viscosity at 1300°C.

[0060] 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 fused powder layer (kg) X i : Concentration of component i in the powder X i,0 : initial concentration of component i in the powder X i,E : Equilibrium concentration of component i between molten steel and powder t: time (s) Q P : Powder consumption (kg / s) A: Reaction area between molten steel and powder (m 2 ) k i : Reaction rate constant of component i (kg / m2 / s) Here, the concentration of component i no longer changes (dX i / dt=0), the concentration of component i, X 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 formula, powder consumption Q P As X increases, i In other words, if component i is Al2O3, increasing the powder consumption dilutes the amount of Al2O3 that increases during casting, lowering the Al2O3 concentration at saturation, and ultimately achieving a low solidification start temperature and low viscosity.

[0061] Therefore, in order to further reduce the solidification initiation temperature and viscosity and achieve more stable operation, it is advisable to increase the powder consumption.

[0062] The inventors have found that when continuously casting steel containing 0.5% by mass or more 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 at 1300°C or lower and the viscosity can be kept at 10 Poise or lower. This allows for stable operation and the production of cast slabs with no problems in surface quality.

[0063] From this perspective, in a method for producing steel according to one embodiment of the present invention, it is preferable to set the powder consumption amount per ton of molten steel to 0.4 kg or more.

[0064] The method for controlling the powder consumption is not particularly limited. However, since the mold generally vibrates in the casting direction, it is preferable to control the amplitude or frequency of the mold vibration. The powder consumption may also be controlled by adjusting the physical properties of the powder. Specifically, the powder consumption can be controlled by adjusting the viscosity and crystallization temperature. The vibration conditions of the mold, such as the amplitude or frequency, may also be changed depending on the physical properties of the powder. [Example]

[0065] The present invention will now be described in more detail with reference to 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.

[0066] First, nine types of mold powders for continuous casting were prepared, each having the composition shown in Table 1. To prepare the powders, 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 using the methods 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.

[0067] [Table 1]

[0068] 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 × 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 so as to obtain the powder consumption per ton of molten steel shown in Table 2.

[0069] Next, the solidification start temperature and viscosity were measured by the above-mentioned methods. Furthermore, as an operational evaluation, the occurrence of smoke and flames during continuous casting and the corrosion status of the equipment after casting were investigated. Additionally, the number of bleeds (pieces / m) was measured by observing the resulting cast pieces. 2 ) was investigated. Furthermore, the trimming yield was investigated as an evaluation of the quality of the slab. The trimming yield is a value calculated by 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.

[0070] The results are shown in Table 2. Inventive Examples Nos. 1 to 3, casting was possible without any operational problems. On the other hand, Comparative Example No. 7 experienced widespread corrosion throughout the continuous casting equipment, making continued use difficult. Comparative Example No. 10 also experienced operational problems, with white smoke and a small amount of flame emitting from the mold during casting.

[0071] [Table 2]

[0072] 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

1. aggregate carbon, <h2 style=";text-align:left;direction:ltr">Al<h2 style=";text-align:left;direction:ltr"> ２ <h2 style=";text-align:left;direction:ltr"> O<h2 style=";text-align:left;direction:ltr"> ３ <h2 style=";text-align:left;direction:ltr"> 、 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.

2. 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, 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.

3. 2. The mold powder for continuous casting according to claim 1, wherein the maximum particle size of said mold powder is 250 μm or less.

4. 3. The mold powder for continuous casting according to claim 2, wherein the maximum particle size of said mold powder is 250 μm or less.

5. 5. The mold powder for continuous casting according to claim 1, wherein 50 mass % or more of the mold powder is made of a premelt raw material.

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

7. A method for producing steel, comprising continuously casting steel containing 0.5 mass % or more of Al using the mold powder for continuous casting according to claim 5.

8. The method for producing steel according to claim 6, wherein the powder consumption per ton of molten steel is 0.4 kg or more.

9. The method for producing steel according to claim 7, wherein the powder consumption per ton of molten steel is 0.4 kg or more.

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