Mold powder for continuous casting and method for producing 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 molten steel is continuously cast using a continuous casting machine, first, the molten steel is poured from a ladle through a tundish into a mold, and an initial solidified shell is formed in the mold. The molten steel is then cooled in the subsequent secondary cooling zone, and solidification progresses to the inside. 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. In continuous casting, the powder plays a role in improving the lubrication between the solidified shell and the mold, as well as in keeping the molten steel warm.

[0003] Generally, powders consist of CaO and SiO 2 The main component is Al, depending on the required characteristics. 2 O 3 , Na 2 Components such as O, fluorine compounds, and C are mixed. Here, SiO 2 Al is added to lower the melting point and promote vitrification. However, when the Al concentration in molten steel is high, a thermite reaction occurs during continuous casting, and the oxides in the powder, especially SiO 2 etc. are reduced by Al in the molten steel. Here, SiO 2 The thermite reaction between and Al is expressed by the following equation (1). 4[Al]+3(SiO 2 ) →2(Al 2 O 3 )+3[Si]……(1) Here, [Al] and [Si] are components in molten steel, (SiO 2 ) and (Al 2 O 3 ) refers to the ingredients in the powder.

[0004] The thermite reaction causes the powder Al 2 O 3The concentration of Al in the powder increases. 2 O 3 It is known that increasing the concentration of CaO and SiO 2 When continuous casting is performed using powder containing Al 2 O 3 By increasing the amount of CaO·Al, the powder contains 2CaO·Al with a high melting point. 2 O 3 SiO 2 Gehlenite is formed. Gehlenite significantly deteriorates the lubricity of the powder, increasing the risk of an operational problem called breakout, in which the initial solidified shell breaks during casting and molten steel leaks out. Furthermore, Al 2 O 3 As the content increases, the melting point becomes higher, and a mass of sintered powder called a bare mass is formed on the mold. When the bare mass becomes large, it pushes the initial solidified shell, which may cause a depression on the surface of the slab.

[0005] In light of this background, various powders have been proposed for continuous casting of high-Al steels in order to produce high-quality cast pieces and prevent operational problems.

[0006] For example, in Patent Document 1, the amount of F is 16 to 25 mass%, CaO and SiO 2 Mass ratio (CaO / SiO 2 ) is 1.0 to 1.8, Al 2 O 3 A mold powder for continuous casting of steel has been proposed, which is characterized by having an amount of SiO2 of 5 mass% or less (including zero) and an amount of MgO of 1.5 mass% or less (including zero). It is said that this powder can prevent restrictive breakouts and the enlargement of slag bears caused by large compositional fluctuations. Here, the compositional fluctuations are the amount of SiO2 in the molten slag, 2 decreases, and Al 2 O 3 This indicates that the number of

[0007] In addition, in Patent Document 2, CaO: 10 to 35 wt%, Al 2O 3 : 10~35wt%, TiO 2 : 3~15wt%, Li 2 O: 3~20wt%, BaO: 5~40wt%, F: 15wt% or less, Na 2 A mold powder for continuous casting has been proposed, which contains 20wt% or less O, and further contains at least one of 0.5-4.0wt% BN and 0.5-4.0wt% C as a bone agent, with the remainder being unavoidable impurities. It is said that this powder can prevent deterioration of the surface quality of a cast slab and breakouts caused by poor lubrication (alteration) of the powder when continuously casting steel containing slag-reducing metal elements. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] JP 2017-170494 A [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 is SiO 2 The use of this material causes a thermite reaction. The invention described in Patent Document 1 uses the powder's Al 2 O 3 This is to prevent the adverse effects of an increase in the concentration of molten steel. However, the thermite reaction not only causes the above-mentioned adverse effects, but also causes adverse effects due to heat generation. First, the solidification of the molten steel is delayed at the meniscus, and the solidified shell breaks (bleeds) along the oscillation marks. This impairs the surface quality of the slab. In addition, the generation of flames can cause equipment failure and shutdowns.

[0011] In addition, the powder described in Patent Document 2 contains SiO 2 does not contain Na 2 O, TiO 2 and Li 2 O, and a thermite reaction occurs between these components and the Al in the molten steel. 2 O 3 As the concentration increases, operational problems and deterioration of the quality of the cast slab are observed. [Means for solving the problem]

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

[0013] 1. Aggregate carbon, Al 2 O 3 , BaO, CaO, MgO, Fluorine compounds, and the remainder being unavoidable impurities, Total C content: 0.5~5.0% by mass, Al 2 O 3 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 unavoidable impurities: 2.0% by mass or less; This is a mold powder for continuous casting.

[0014] 2. The 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 1 to 3 above, 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 as defined in any one of 1 to 4 above.

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

[0019] According to the present invention, it is possible to provide a mold powder for continuous casting that enables production of high quality cast pieces and prevention of operational problems when continuously casting high Al steel, and a method for producing steel using the powder. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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, the powder Al 2 O 3 If the concentration of Al increases, the formation of high melting point gehlenite and the coarsening of the bare grains occur, which impairs the stability of the operation 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 necessary to reduce the Al concentration of the powder during casting. 2 O 3 A smaller increase in concentration is more desirable.

[0022] And, through the experiments of the present inventors, it was found that the Al of the powder during casting 2 O 3It was revealed that the cause of the increase in Al concentration was not only the oxidation of Al in the molten steel by oxides in the powder, but also the oxidation of Al in the molten steel by the atmosphere. However, it is difficult to prevent oxidation by the atmosphere. 2 O 3 In order to minimize the increase in Al concentration, it is necessary to prevent the oxidation of Al in molten steel by oxides in the powder as much as possible. 2 O 3 It is necessary to set the powder preparation and steel manufacturing conditions taking into account that the amount of ferrite increases to some extent during casting.

[0023] From the above viewpoints, the inventors have focused on the solidification start temperature after the composition change of the powder during casting. The inventors have 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 found that in order to stabilize the operation and improve the surface quality of the cast slab, the standard free energy of formation at 1300°C must be less than Al. 2 O 3 The conclusion was that the content of oxides higher than Al should be minimized as much as possible. This is for the following reasons. First, 1300°C is the average temperature of the molten powder during casting. And the standard free energy of formation at that temperature is Al 2 O 3 Higher than SiO 2 , Na 2 O, TiO 2 and Li 2 Oxides such as O cause thermite reactions with Al in molten steel. This causes the various adverse effects mentioned above. Therefore, the standard free energy of formation at 1300°C is Al 2 O 3 It is necessary to produce powders that contain very little of the higher oxides.

[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 of adjusting the melting speed 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%.

[0027] [Total C content: 0.5~5.0% by mass] If the total C content is less than 0.5%, the effect as aggregate cannot be obtained. From such a 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 the thermite reaction occurs, C burns and a flame occurs, which causes equipment failure and operation stoppage. Therefore, from the viewpoint of preventing operation trouble, 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 described later. In addition, the C derived from carbonates is considered to be the sum of the C derived from carbonates remaining in the premelt raw material described later and the C derived from carbonates blended other than the premelt raw material.

[0028] [Al 2 O 3 :15~35%] Al 2 O 3 is the Al in the molten powder. 2 O 3 It is added to increase the activity of Al and suppress the oxidation reaction of Al in molten steel. 2 O 3 If the content is less than 15%, such effects cannot be obtained. 2 O 3 The content is set to 15% or more, preferably 20% or more. 2 O 3 If the content is higher than 35%, additional Al is added during casting. 2 O 3Considering the increase in Al content, the powder solidification temperature becomes very high. 2 O 3 The content is 35% or less, preferably 30% or less. 2 O 3 The Al content was determined by fluorescent X-ray analysis. 2 O 3 Convert to and calculate.

[0029] [BaO] BaO has a standard free energy of formation of Al at 1300°C. 2 O 3 Since the Al content in the powder is lower than that in the molten steel and hardly reacts with the Al in the molten steel, 2 O 3 The increase in the concentration of Al is suppressed. 2 O 3 It forms a complex oxide with Cr and lowers the solidification start temperature of the powder.

[0030] [Ba oxide content: 15-35% by mass] When the content of Ba in terms of oxide is less than 15%, Al 2 O 3 If the Ba content is more than 35%, the solidification start temperature rises. Therefore, the Ba content in terms of oxide is set to 35% or less, preferably 30% or less. The Ba content is calculated by determining the Ba element content by X-ray fluorescence analysis and converting it to BaO.

[0031] [CaO] The standard free energy of formation of CaO at 1300°C is Al 2 O 3 Since the Al content in the powder is lower than that in the molten steel and hardly reacts with the Al in the molten steel, 2 O 3 The increase in the concentration of Al is suppressed. 2 O 3It forms a complex oxide with Cr and lowers the solidification start temperature of the powder.

[0032] [Ca content in terms of oxide: 30-40% by mass] When the Ca oxide content is less than 30%, Al 2 O 3 If the amount of Ca in the powder is less than 40%, the powder will not be able to obtain the above-mentioned effects of suppressing the increase in the concentration and lowering the powder's solidification start temperature. 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 into CaO.

[0033] [MgO] The standard free energy of formation of MgO at 1300°C is Al 2 O 3 Since the Al content in the powder is lower than that in the molten steel and hardly reacts with the Al in the molten steel, 2 O 3 The increase in concentration is suppressed, and the powder solidification start temperature can be lowered.

[0034] [Mg content in terms of oxide: 1.0-5.0 mass%] When the content of Mg in terms of oxide is less than 1.0%, Al 2 O 3 If the amount of Mg in the powder is less than 5.0%, the powder will not be able to obtain the above-mentioned effects of suppressing the increase in the concentration and lowering the powder's solidification start temperature. 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 added to lower the powder solidification start temperature and viscosity, which will be described later. There are no particular limitations on the fluorine compound, and examples of the fluorine compound include CaF 2 and BaF 2 However, from the viewpoint of cost, CaF 2 It is preferable to use:

[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 a case, 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 can be obtained as when the oxide of the element is contained.

[0038] When elements such as Ca, Ba, and Mg are contained as carbonates, the total content of the elements calculated as oxides is calculated by adding up the content of the oxides of the elements and the content of the carbonates of the elements calculated as 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 of the element is satisfied. However, by lowering 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 changed by carbon dioxide gas. Also, the generation of bare 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 included. From the same viewpoint, the content of Ba carbonate in terms of BaO in the powder is preferably 10% or less. The lower limit of the content is not limited, and may be 0%. From the same viewpoint, the content of Ca carbonate in terms of CaO in the powder is preferably 10% or less. The lower limit of the content is not limited, and may be 0%. From the same viewpoint, the content of Mg carbonate in terms of MgO in the powder 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 the above 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 the above 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 the above 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 being unavoidable impurities.

[0043] The unavoidable impurities include Al, whose standard free energy of formation of oxide at 1300°C is 1. 2 O 3 In some cases, oxides having a higher molecular weight than SiO may also be included. 2 , Na 2 O, TiO 2 and Li 2 O. The oxides mentioned above are unavoidably mixed into the powder raw materials, and although it is difficult to completely remove them, it is necessary to keep the content as low as possible to prevent thermite reaction with Al in the molten steel. 2 Not containing O also leads to a significant reduction in manufacturing costs. From this perspective, the total content of the unavoidable impurities is set to 2.0% or less. In other words, Al 2 O 3 The total content of BaO, CaO, MgO, aggregate carbon, and fluorine compounds must be 98.0% or more.

[0044] As described above, the powder according to one embodiment of the present invention comprises: Aggregate carbon, Al 2 O 3 , BaO, CaO, MgO, Fluorine compounds, and the balance being unavoidable impurities. Total C content: 0.5~5.0% 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 content in terms of oxide: 1.0 to 5.0 mass% F content: 10~20% by mass, The total content of the unavoidable 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 the raw materials so as to have the above-mentioned component composition. Here, the raw materials include aggregate carbon and Al. 2 O 3 The raw material may be composed of CaO, BaO, MgO, and a fluorine compound. The raw material may further contain a carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg. A part or all of the raw material may be composed of a premelt raw material. The particle size of the powder may be adjusted by a method such as grinding or classification.

[0047] [Premelt raw materials] Premelt raw material refers to a material that has been melted and crushed in advance. As mentioned above, BaCO 3 In some cases, carbonates such as fluorine, fluorine, and fluorine-containing carbonates are blended. However, when carbonates are blended, gas is generated by melting the powder during casting, which may adversely affect the quality of the cast slab, such as pinhole defects and inclusion entrapment defects, or may adversely affect the operation, such as melting damage of the submerged entry nozzle. The premelt raw material is used to reduce such effects and form a stable molten layer. Therefore, in the powder according to one embodiment of the present invention, it is preferable that 50 mass% or more of the powder is made of premelt raw material, and more preferably 80 mass% or more of the powder is made of premelt raw material. On the other hand, the upper limit of the proportion of the premelt raw material is not particularly limited, and may be 100 mass%. However, considering the blending of aggregate carbon, it is preferable that 99.5 mass% or less of the powder is made of premelt raw material. It is also more preferable that 90 mass% or less of the powder is made of premelt raw material.

[0048] The powder according to one embodiment of the present invention can be prepared by adding additional materials to the premelt raw material in order to adjust the powder composition. For example, Al 2 O 3If there is a shortage, Al 2 O 3 If CaO is insufficient, add CaF 2 If the F content is insufficient, CaF 2 If BaO is insufficient, BaCO 3 can be mixed.

[0049] Here, the aggregate carbon cannot be a premelt raw material, i.e., the ratio of the premelt raw material to the total amount of aggregate carbon may be 0%.

[0050] If carbonate is added after premelt for component adjustment, the total C content increases, the content of other components decreases, and the molten state changes due to the influence of carbon dioxide gas. Furthermore, it may lead to the generation of dust and flames. In other words, by reducing the amount of carbonate added, the operability and quality can be further improved. Therefore, for the carbonate of at least one element selected from the group consisting of Ca, Ba, and Mg, the ratio of the carbonate other than the premelt raw material to the total amount of powder is preferably 10% or less, more preferably 5% or less. The lower limit of the ratio is not particularly limited and may be 0%.

[0051] [Particle size] By using finely ground powder, the powder is easily melted during casting, and a stable molten layer is formed. 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 means that all particles pass 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 all particles pass 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 above powder.

[0053] In the continuous casting of high Al steel, the use of the above powder makes it possible to suppress the occurrence of thermite reactions and to produce high Al steel of stable quality with high productivity. Therefore, the steel subjected to continuous casting by the 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 order to produce high-quality cast pieces while preventing operational problems in continuous casting, it is advisable to lower the solidification start temperature of the powder during casting. 2 O 3 This increases the activity of Al in the molten steel and prevents thermite reaction between the Al in the molten steel and the powder components, resulting in higher quality slabs and further reducing 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 start to solidify at or below 1300° C. In other words, it is preferable to control the powder so that it becomes completely liquid at 1300° C. during casting.

[0056] [viscosity] Furthermore, according to the present invention, in order to produce a high-quality cast piece, it is preferable to lower 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 lowering 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 piece 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 measured values ​​fluctuate in the early stages of casting due to the ongoing compositional change of the powder, the sample is sampled immediately before the end of the casting period when the compositional change of the powder has reached a steady state.

[0058] 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 the molten state at a constant cooling rate, the differential heat peak is measured using differential thermal analysis, and the starting point on the high temperature side of the peak (peak starting temperature) is taken as the solidification start temperature. The viscosity can also be measured using a rotational viscometer.

[0059] [Powder consumption] In a steel manufacturing method according to one embodiment of the present invention, the 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 through a tundish into a mold. After being supplied to the meniscus, the powder becomes molten, penetrates into the gap between the mold and the solidified shell, and is pulled out to the rear of the mold together with the slab. During this continuous casting process, the molten steel and the powder come into contact with each other at the meniscus, and the Al in the molten steel reacts with the powder only while this contact is occurring. Therefore, if the amount of powder consumed is small, the reaction time with the molten steel per unit amount of powder becomes long, and the Al in the powder decreases. 2 O 3 The concentration increases, which leads to a higher solidification temperature. Furthermore, the low powder consumption leads to a higher Al concentration, which leads to a higher viscosity. 2 O3 The increase in β-silicate glass reduces the 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: Powder melt layer weight (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 / m 2 / s) Here, the concentration of component i no longer changes (dX i / dt=0), the concentration of component i is 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 By increasing, X i In other words, when component i is Al, 2 O 3 Then, by increasing the powder consumption, the amount of Al during casting can be reduced.2 O 3 The increase in is diluted, and the Al at saturation 2 O 3 The concentration is reduced and thus a lower solidification onset temperature and lower viscosity are achieved.

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

[0062] The inventors have found that, in continuous casting of steel containing 0.5% by mass or more of Al, if powder is charged 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 charging the 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 made 1300°C or lower and the viscosity can be made 10 Poise or lower. This allows stable operation and the production of cast slabs with no problems in surface quality.

[0063] From this viewpoint, in a steel production method according to an 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 powder consumption by the amplitude or frequency of the vibration of the mold. 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 according to the physical properties of the powder. EXAMPLES

[0065] Next, the present invention will be described 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 of these modifications are included in the technical scope of the present invention.

[0066] First, mold powders for continuous casting were prepared having the nine types of component compositions shown in Table 1. 2 O 3 , CaF 2 , BaCO 3 The premelt raw material was prepared by blending and then melting the mixture. Next, the premelt raw material was blended with a carbonate of Ba as required, and further with aggregate carbon to obtain the composition shown in Table 1. Carbon black was used as the aggregate carbon. F, Al 2 O 3 The contents of BaO, CaO, and MgO were measured by the method described above. The ratio of premelt raw material in 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 performed under the condition of a slab withdrawal speed of 0.6 m / min. At this time, the powder shown in Table 2 was supplied while adjusting the vibration conditions of the mold so that the powder consumption per ton of molten steel shown in Table 2 was achieved.

[0069] Next, the solidification start temperature and viscosity were measured by the above-mentioned method. In addition, as an evaluation of the operational aspect, the occurrence of smoke and flames during continuous casting and the corrosion state of the equipment after casting were investigated. In addition, the number of bleeds (pieces / m) was measured by observing the obtained 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, a trimming operation is performed to remove the defects by scraping the slab surface with a scarf or grinder, which reduces the yield. In other words, the higher the trimming yield, the higher the quality of the slab.

[0070] The results are shown in Table 2. Inventive Examples No. 1 to 3, casting was possible without any operational problems. On the other hand, in Comparative Example No. 7, corrosion progressed throughout the continuous casting equipment, making it difficult to continue using it. In Comparative Example No. 10, operational problems were observed in which a small amount of white smoke and flames were generated from the mold during casting.

[0071] [Table 2]

[0072] In summary, all of the inventive examples were able to achieve high quality cast pieces and stable operation, whereas all of the comparative examples either had 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, A ２ O ３ Content: 15-35% by mass, Ba oxide content: 15 to 35 mass% Ca oxide content: 30 to 40 mass% Mg content in terms of oxide: 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. The composition further comprises 2. The mold powder for continuous casting according to claim 1, which contains a carbonate of at least one element selected from the group consisting of Ca, Ba and Mg.

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

5. The mold powder for continuous casting according to any one of claims 1 to 4, 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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