Mold flux for continuous casting of steel and continuous casting method

Abstract

To disclose a mold flux capable of reducing enlargement of a rim during continuous casting of steel.SOLUTION: In a base material of the present disclosure which constitutes the mold flux: a SiO2 concentration WSiO2 is 20.0 mass% or more and 45.0 mass% or less; a CaO concentration WCaO is 30.0 mass% or more and 55.0 mass% or less; a Li2O concentration WLi2O is less than 2.0 mass%; a Na2O concentration WNa2O is 4.0 mass% or more and 10.0 mass% or less; a K2O concentration WK2O is 1.0 mass% or less; a total of WLi2O, WNa2O, and WK2O is 4.0 mass% or more and 10.0 mass% or less; a MnO concentration WMnO is 2.0 mass% or less; an F concentration WF is 5.0 mass% or more and 15.0 mass% or less; and a total concentration of other components is 10.0 mass% or less, wherein the base material also satisfies 1.6≤WCaO / WSiO2<1.8. A ratio of a premelted base material to the base material is less than 30 mass% or 70 mass% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This application discloses a mold flux for continuous casting of steel and a continuous casting method. [Background technology]

[0002] In continuous casting of steel, mold flux is supplied into the mold. The mold flux melted in the mold flows from the meniscus into the gap between the mold and the solidified shell to form a film, thereby exerting various functions such as lubrication. Mold fluxes with various compositions for continuous casting of steel are known (Patent Documents 1 to 7, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-179408 [Patent Document 2] Special Publication No. 2016-507382 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-136360 [Patent Document 4] Japanese Patent Application Laid-Open No. 2002-346708 [Patent Document 5] Japanese Patent Application Publication No. 7-164120 [Patent Document 6] Japanese Patent Application Laid-Open No. 2000-051998 [Patent Document 7] Japanese Patent Application Publication No. 10-258343 Summary of the Invention [Problem to be solved by the invention]

[0004] When continuous casting is performed using mold flux with a high basicity (the mass concentration ratio of CaO to SiO2, CaO / SiO2) and a high solidification point, a sintered area (rim) enlarges along the mold wall, obstructing the flow of mold flux and reducing lubrication. Furthermore, the enlarged rim vibrates up and down with the mold, pressing down on the front of the solidified shell, causing localized deformation of the front of the solidified shell and resulting in vertical cracks on the surface of the slab. Therefore, a new technology is needed to reduce rim enlargement during continuous casting of steel. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> A mold flux for continuous casting of steel, comprising: The mold flux includes a base material, The substrate is SiO2 concentration W SiO2 is 20.0% by mass or more and 45.0% by mass or less, CaO concentration W CaO is 30.0% by mass or more and 55.0% by mass or less, Li2O concentration W Li2O is less than 2.0% by mass, Na2O concentration W Na2O is 4.0% by mass or more and 10.0% by mass or less, K2O concentration W K2O is 1.0 mass% or less, W Li2O , W Na2O and W K2O The sum of the above is 4.0 mass% or more and 10.0 mass% or less, MnO concentration W MnO is 2.0 mass% or less, F concentration W F is 5.0% by mass or more and 15.0% by mass or less, The total concentration of other components is 10.0% by mass or less, It is said that The following formula (1): 1.6≦W CaO / W SiO2 <1.8 (1) It satisfies the following: The proportion of the premelt base material in the base material is less than 30% by mass or 70% by mass or more. Mold flux for continuous casting of steel. <Aspect 2> The MnO concentration W of the substrate MnO is set to 0.5% by mass or more and 2.0% by mass or less, 2. A mold flux for continuous casting of steel according to claim 1. <Aspect 3> the mold flux includes the base material and aggregate carbon powder, The aggregate carbon powder includes expandable graphite, The ratio of the aggregate carbon powder is 0.5% by mass or more and 10.0% by mass or less with respect to 100% by mass of the base material, The proportion of the expandable graphite is 0.5% by mass or more and 5.0% by mass or less with respect to 100% by mass of the base material. 3. A mold flux for continuous casting of steel according to embodiment 1 or 2. <Aspect 4> Supplying the mold flux according to any one of aspects 1 to 3 into a mold; A method for continuous casting of steel, comprising: [Effects of the Invention]

[0006] When the mold flux of the present disclosure is used in continuous casting of steel, rim enlargement can be reduced. DETAILED DESCRIPTION OF THE INVENTION

[0007] 1. Mold flux for continuous casting of steel The mold flux for continuous casting of steel according to the embodiment includes a base material. SiO2 concentration W SiO2 is 20.0% by mass or more and 45.0% by mass or less, CaO concentration W CaO is 30.0% by mass or more and 55.0% by mass or less, Li2O concentration W Li2O is less than 2.0% by mass, Na2O concentration W Na2O is 4.0% by mass or more and 10.0% by mass or less, K2O concentration W K2O is 1.0 mass% or less, W Li2O , W Na2O and W K2O The sum of the above is 4.0 mass% or more and 10.0 mass% or less, MnO concentration W MnO is 2.0 mass% or less, F concentration W F is 5.0% by mass or more and 15.0% by mass or less, The total concentration of other components is 10.0% by mass or less, It is said that The following formula (1): 1.6≦W CaO / W SiO2 <1.8 (1) In the present embodiment, the ratio of the premelt base material to the base material is less than 30% by mass or 70% by mass or more.

[0008] 1.1 Base material In this embodiment, the base material constituting the mold flux contains SiO2, CaO, Na2O, and F, and optionally contains Li2O, KO, MnO, and other components. Here, SiO2, CaO, Na2O, Li2O, KO, and MnO are calculated as the oxides of Si, Ca, Na, Li, K, and Mn contained in the mold flux. The concentration of each component in the mold flux can be easily determined by elemental analysis or the like.

[0009] 1.1.1 SiO2 concentration SiO2 concentration of the substrate W SiO2 is 20.0 mass% or more and 45.0 mass% or less. SiO2 is the CaO concentration W so that the basicity described below is satisfied. CaO It can be adjusted appropriately depending on the W SiO2The content may be 22.0 mass% or more, 24.0 mass% or more, 26.0 mass% or more, or 28.0 mass% or more, or 42.0 mass% or less, 39.0 mass% or less, 36.0 mass% or less, or 32.0 mass% or less. In mold flux, materials that can become SiO2 in oxide conversion include SiO2 itself, as well as composite oxides of Si and other elements and premelt. More specific examples include silica sand, diatomaceous earth, wollastonite, and Portland cement.

[0010] 1.1.2 CaO concentration CaO concentration of the substrate W CaO is 30.0 mass% or more and 55.0 mass% or less. CaO is the SiO2 concentration W mentioned above so that the basicity described below is satisfied. SiO2 It can be adjusted appropriately depending on the W CaO The content of CaO in the mold flux may be 35% by mass or more, 40% by mass or more, or 45% by mass or more, or 54.0% by mass or less, 53.0% by mass or less, 52.0% by mass or less, or 51.0% by mass or less. In mold flux, materials that can become CaO in oxide conversion include CaO itself, CaCO3, CaF2, complex oxides of Ca and other elements, premelt, etc. Furthermore, the above-mentioned wollastonite and Portland cement also fall under the category of materials that can become CaO in oxide conversion.

[0011] 1.1.3 Li2O concentration According to the findings of the present inventors, the Li2O concentration W Li2O If W is too high, the melting point of the mold flux as a whole will be too low, and when it is supplied into the mold during continuous casting, the molten and unmolten parts will coexist for a long period of time, which will make the rim easily enlarge. Li2O If the amount of W is less than 2.0 mass%, such a problem is unlikely to occur. Li2O may be 1.5% by mass or less, or less than 1.0% by mass. Li2OThe lower limit of the content is not particularly limited and may be 0 mass %. In the mold flux, materials that can become LiO in terms of oxide include LiO itself, LiCO, LiF, other compounds of Li and other elements, and premelt.

[0012] 1.1.4 Na2O concentration According to the findings of the present inventors, the NaO concentration W of the substrate Na2O If is too high, the Li2O concentration W Li2O Similarly to when W is too high, the melting point of the mold flux becomes too low, and when it is supplied into the mold during continuous casting, the molten and unmolten parts coexist for a long period of time, which makes the rim easily enlarged. Na2O If W is too low, the melting point of the mold flux becomes high, making it difficult for the mold flux to function properly as a lubricant in the mold during continuous casting. Na2O If the amount of W is 4.0 mass % or more and 10.0 mass % or less, such a problem is unlikely to occur. Na2O may be 4.5 mass% or more, 5.0 mass% or more, or 5.5 mass% or more, and may be 9.5 mass% or less, 9.0 mass% or less, or 8.5 mass% or less. In mold flux, materials that can become Na2O in oxide conversion include Na2O itself, Na2CO3, NaF, other compounds of Na and other elements, premelt, etc.

[0013] 1.1.5 K2O concentration According to the findings of the present inventors, the K2O concentration W of the substrate K2O If W is too high, the melting point of the mold flux as a whole will be too low, and when it is supplied into the mold during continuous casting, the molten and unmolten parts will coexist for a long period of time, which will make the rim easily enlarge. K2O If the content of W is 1.0 mass % or less, such a problem is unlikely to occur. K2O may be 0.8% by mass or less, 0.6% by mass or less, 0.4% by mass or less, or 0.2% by mass or less. K2OThe lower limit of the content is not particularly limited and may be 0 mass %. In mold flux, materials that can become KO in terms of oxide include KO itself, KCO, potassium halides, other compounds of K and other elements, premelt, etc.

[0014] 1.1.6 Sum of alkali metal oxide concentrations According to the inventor's findings, the W of the substrate Li2O , W Na2O and W K2O When the total amount of W is 4.0 mass % or more and 10.0 mass % or less, the mold flux has an appropriate melting point, and when supplied into the mold during continuous casting, the period during which the molten and unmolten parts coexist is shortened, and rim thickening is easily suppressed. Li2O , W Na2O and W K2O The total may be 4.5 mass % or more, 5.0 mass % or more, or 5.5 mass % or more, and may be 9.5 mass % or less, 9.0 mass % or less, or 8.5 mass % or less.

[0015] 1.1.7 MnO concentration The substrate may optionally contain MnO. The MnO concentration W of the substrate MnO The content of MnO may be 0% by mass or more than 0% by mass. When MnO is contained in the base material, it is possible to suppress the elution of Mn from the molten steel into the mold flux during continuous casting. In this regard, W MnO may be 0.1% by mass or more, 0.3% by mass or more, or 0.5% by mass or more. MnO If W is too high, there is concern about contamination of the molten steel and a decrease in cleanliness. MnO When the content of Mn is 2.0 mass% or less, such a problem is unlikely to occur. In mold flux, materials that can become MnO in terms of oxide include MnO itself, MnO2, other compounds of Mn and other elements, and premelt.

[0016] 1.1.8 F concentration According to the inventor's findings, the F concentration W of the substrate FWhen the W content is 5.0% by mass or more and 15.0% by mass or less, the mold flux has an appropriate melting point, and when supplied into the mold during continuous casting, the period during which the molten and unmolten parts coexist is shortened, and rim thickening is easily suppressed. F may be 6.0 mass% or more, 7.0 mass% or more, 8.0 mass% or more, or 9.0 mass% or more, and may be 14.0 mass% or less, 13.0 mass% or less, or 12.0 mass% or less. In the mold flux, materials that can be F include various fluorine compounds such as alkali metal fluorides and alkaline earth metal fluorides, premelts, etc.

[0017] 1.1.9 Total concentration of other ingredients The total concentration of other components in the base material is 10.0% by mass or less. The lower limit of the total concentration of other components is not particularly limited and may be 0% by mass. Examples of other components include at least one selected from MgO, SrO, BaO, Al2O3, ZrO2, and B2O3. Note that, like SiO2 and the like, Mg, Sr, Ba, Al, Zr, and B contained in the mold flux are calculated as oxides of these components.

[0018] 1.1.10 Basicity Generally, the basicity of the base material (W CaO / W SiO2The higher the basicity, the more likely lubrication in the mold is to be poor. This is because, as the basicity increases, the freezing point of the mold flux increases, resulting in insufficient flux flowing into the gap between the mold and the solidified shell. According to the inventors' findings, when continuous casting is performed using mold flux with such high basicity, a rim thickens along the mold wall, hindering the flow of mold flux and impairing lubrication. This problem is particularly likely to become apparent when the basicity of the base material is 1.6 or higher. In contrast, in this embodiment, by setting the base material's components as described above and the ratio of the premelt base material (described later) to a predetermined value or greater, the problem of rim thickening can be solved even when the base material's basicity is 1.6 or higher. However, if the base material's basicity is too high, rim thickening is likely to occur even when the base material's components and the ratio of the premelt base material are controlled within a predetermined range. Rim thickening can be appropriately reduced when the base material's basicity is less than 1.8.

[0019] 1.1.11 Premelt base material blend ratio To ensure a high melting rate in the mold, a premelt base material may be blended with the mold flux. However, according to the findings of the present inventors, if the blending ratio of this premelt base material is in the range of 30% by mass or more but less than 70% by mass, when the mold flux is supplied into the mold during continuous casting, molten and unmelted portions coexist for a long period of time, sintering of these portions is promoted, and the rim tends to become enlarged. In this regard, in this embodiment, it is important that the ratio of the premelt base material to the base material is less than 30% by mass or 70% by mass or more. The ratio of the premelt base material to the base material can be easily determined by observing the mold flux with an electron microscope or the like and performing elemental analysis.

[0020] According to the findings of the present inventors, when the proportion of the premelt base material in the substrate is less than 30 mass%, the premelt base material is less likely to function as a binder, which prevents excessive sintering and tends to reduce rim enlargement. The proportion of the premelt base material in the substrate may be 25 mass% or less, 20 mass% or less, 15 mass% or less, 10 mass% or less, or 5 mass% or less. The lower limit of this proportion is not particularly limited and may be 0 mass%.

[0021] Furthermore, according to the findings of the present inventors, when the proportion of the premelt base material in the base material is 70 mass% or more, the period during which the molten and unmolten portions coexist is shortened when mold flux is supplied into the mold during continuous casting, which tends to reduce rim thickening. The proportion of the premelt base material in the base material may be 75 mass% or more, 80 mass% or more, 85 mass% or more, 90 mass% or more, or 95 mass% or more. The upper limit of this proportion is not particularly limited, and may be 100 mass%.

[0022] 1.2 Aggregate carbon powder In this embodiment, the mold flux may contain aggregate carbon powder in addition to the base material. When the mold flux contains aggregate carbon powder, voids are formed due to CO gas generated by oxidation of the aggregate carbon powder when the mold flux is supplied into the mold during continuous casting, thereby preventing excessive sintering and further reducing rim enlargement. Furthermore, the aggregate carbon powder can also be expected to coat the surfaces of the raw material particles, preventing contact between the particles and slowing sintering. Any common carbon powder that functions as an aggregate in mold flux can be used as the aggregate carbon powder. Specific examples of aggregate carbon powder include coke powder, fine carbonaceous material, and expandable graphite. The size of the aggregate carbon powder is not particularly limited as long as it can function appropriately as an aggregate.

[0023] According to the findings of the present inventors, the above-mentioned rim thickening can be further reduced depending on the type of aggregate carbon powder and the blending ratio of the aggregate carbon powder to the base material. For example, when at least one of the following conditions (1) to (3) is satisfied, and especially when all of the following conditions (1) to (3) are satisfied, rim thickening can be significantly reduced. (1) The aggregate carbon powder contains expandable graphite. (2) The proportion of aggregate carbon powder is 0.5% by mass or more and 10.0% by mass or less with respect to 100% by mass of the base material (outer percentage with respect to the base material). (3) The proportion of expandable graphite is 0.5% by mass or more and 5.0% by mass or less with respect to 100% by mass of the substrate (outer percentage with respect to the substrate).

[0024] In the above (1), the proportion of expandable graphite in the aggregate carbon powder is not particularly limited. The proportion of expandable graphite in the aggregate carbon powder may be 0% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, or 90% by mass or more, or may be 100% by mass or less, 90% by mass or less, 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, 40% by mass or less, 30% by mass or less, 20% by mass or less, or 10% by mass or less.

[0025] In the above (2), the proportion of the aggregate carbon powder may be 0.5 mass% or more, 1.0 mass% or more, 1.5 mass% or more, or 2.0 mass% or more relative to 100 mass% of the base material (outer percentage relative to the base material), and may be 10.0 mass% or less, 9.0 mass% or less, 8.0 mass% or less, 7.0 mass% or less, or 6.0 mass% or less.

[0026] In the above (3), the proportion of expandable graphite may be 0.5% by mass or more, 1.0% by mass or more, 1.5% by mass or more, or 2.0% by mass or more relative to 100% by mass of the substrate (outer percentage relative to the substrate), and may be 10.0% by mass or less, 9.0% by mass or less, 8.0% by mass or less, 7.0% by mass or less, 6.0% by mass or less, 5.0% by mass or less, or 4.0% by mass or less.

[0027] 1.3 Freezing point The freezing point of the mold flux of the present disclosure is not particularly limited. In one embodiment, the freezing point of the mold flux may be 1200°C or higher, 1220°C or higher, or 1240°C or higher, or 1350°C or lower, 1300°C or lower, 1280°C or lower, or 1260°C or lower. In this embodiment, even if the mold flux has such a high freezing point, rim thickening can be reduced. The freezing point of the mold flux is the temperature at which the viscosity, as measured by a vibration viscometer, rises sharply when the mold flux is heated to 1400°C, melted, and then cooled at a rate of 2°C / min.

[0028] 1.4 Viscosity The viscosity of the mold flux of the present disclosure at 1300°C is not particularly limited. In one embodiment, the viscosity of the mold flux at 1300°C may be 0.2 poise or more, 0.4 poise or more, or 0.5 poise or more, or 1.0 poise or less, 0.8 poise or less, or 0.7 poise or less. A mold flux having such a viscosity can more easily ensure lubrication within the mold. To achieve such a viscosity, the concentrations of the above-mentioned components may be adjusted. The viscosity at 1300°C can be measured, for example, using a vibration-type viscometer.

[0029] 2. Continuous steel casting method The technology of the present disclosure also has an aspect as a continuous casting method for steel. That is, the continuous casting method for steel according to the embodiment includes supplying the mold flux of the present disclosure into a mold. In this embodiment, the continuous casting conditions for steel may be the same as conventional conditions except for the use of the mold flux of the present disclosure. In this embodiment, there are no particular limitations on the type of steel. It can be said that the effect of using the mold flux of the present disclosure (the effect of reducing rim thickening) is achieved regardless of the continuous casting conditions or the type of steel. The conditions for supplying mold flux to the mold during continuous casting, etc., are obvious to those skilled in the art, so a description thereof will be omitted here.

[0030] 3.Effects As described above, the mold flux for continuous casting of steel according to the present disclosure can reduce rim enlargement during continuous casting of steel. Furthermore, the mold flux for continuous casting of steel according to the present disclosure promotes crystallization of cuspidine in the flux film in the mold during continuous casting, and the resulting slow cooling effect can prevent longitudinal cracks on the surface of the slab. [Example]

[0031] The following examples of the present invention are given, but the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the invention and the object is achieved.

[0032] The raw materials were blended so that the composition and physical properties when melted would fall within the ranges shown in Table 1 below, and the blending ratio of the premelt base material was gradually changed to produce nine types of mold fluxes (Examples 1 to 5 and Comparative Examples 1 to 4) shown in Table 2 below.

[0033] [Table 1]

[0034] [Table 2]

[0035] These mold fluxes were used for continuous casting of steel. A vertical bending type continuous casting machine was used for continuous casting, and a drawing speed of 1.0 m / min was used to cast slabs with a width of 2200 mm, a thickness of 300 mm, and a length of 7000 to 9000 mm. Eight ladles, each with a capacity of 320 tonnes of molten steel, were connected (eight continuous castings were performed), for a total casting amount of 2560 tonnes per casting. Eight slabs were obtained from each ladle, for a total of 64 slabs per casting. Molten low-alloy steel having the composition shown in Table 3 below was used for casting.

[0036] [Table 3]

[0037] After continuous casting, the presence or absence of vertical cracks on the slab surface and the thickness of the rim remaining in the mold were evaluated. The surface of each of the eight slabs obtained from one ladle was visually inspected for the presence or absence of vertical cracks. A slab that required no trimming due to the occurrence of vertical cracks was rated as good (○), a slab that required only one trimming was rated as fair (△), and a slab that required two or more trimming was rated as poor (×). Furthermore, for the rim remaining in the mold, the maximum thickness of the rim on the inner surface of the mold was measured with a vernier caliper, and its severity was evaluated. The evaluation results are shown in Table 4 below.

[0038] [Table 4]

[0039] As shown in Table 4, when continuous casting was performed using the mold fluxes of Examples 1 to 5, the growth of the rim remaining in the mold after casting was 25 mm or less, which did not interfere with the operation of continuous casting. As a result, the mold flux consumption was ensured to be 0.34 kg / ton or more, and good lubrication in the mold was maintained throughout the entire casting. In addition, no longitudinal cracks occurred on the surface of the cast slab, so the slab could be sent to the rolling process without any treatment.

[0040] On the other hand, when continuous casting was performed using the mold flux of Comparative Example 1, the effect of slow cooling in the mold was not sufficient because the basicity was lower than that of the mold fluxes of Examples 1 to 5, and vertical cracks were scattered on the surface of the slab. When continuous casting was performed using the mold flux of Comparative Example 2, the slag rim became significantly thicker from the middle to the end of casting due to the excessively high basicity, and vertical cracks increased on the surface of the slab.

[0041] When continuous casting was performed using the mold fluxes of Comparative Examples 3 and 4, casting was possible up to the fifth consecutive casting run, not significantly different from Examples 1 to 5. However, in the latter half of the continuous casting run (from the sixth consecutive casting run onwards), the growth of the rim gradually became more pronounced, and the maximum thickness of the rim increased to 30 to 45 mm. Although there was no problem with lubrication, the mold flux consumption was 0.28 to 0.31 kg / ton, which was reduced compared to Examples 1 to 5. Furthermore, due to the increased rim size, vertical cracks began to appear on the surface of the slab from the seventh consecutive casting run onwards, requiring treatment.

[0042] In Comparative Examples 3 and 4, the proportion of the premelt base material in the base material was in the range of 30% by mass or more but less than 70% by mass. This prolonged the period in which molten and unmolten parts coexisted when mold flux was supplied into the mold during continuous casting, promoting sintering and resulting in rim enlargement. On the other hand, in Examples 1 to 3, the proportion of the premelt base material in the base material was less than 30% by mass, making it difficult for the premelt base material to function as a binder. This prevented excessive sintering and reduced rim enlargement. In Examples 4 and 5, the proportion of the premelt base material in the base material was 70% by mass or more. This prolonged period in which molten and unmolten parts coexisted when mold flux was supplied into the mold during continuous casting, reducing rim enlargement.

[0043] In the above examples, mold flux is produced using a specific base material and aggregate carbon powder, but the types of base material and aggregate carbon powder are not limited to these. Furthermore, in the above examples, continuous casting of steel having a specific chemical composition under specific conditions is exemplified, but the type of steel used for continuous casting and the continuous casting conditions are not limited to these.

[0044] From the results of the above examples, it can be said that mold flux for continuous casting that satisfies the following requirements (A) to (D) can reduce rim enlargement during continuous casting of steel and suppress longitudinal cracks in the slab.

[0045] (A) The mold flux includes a base material.

[0046] (B) The substrate is SiO2 concentration W SiO2 is 20.0% by mass or more and 45.0% by mass or less, CaO concentration W CaO is 30.0% by mass or more and 55.0% by mass or less, Li2O concentration W Li2O is less than 2.0% by mass, Na2O concentration W Na2O is 4.0% by mass or more and 10.0% by mass or less, K2O concentration W K2O is 1.0 mass% or less, W Li2O , W Na2O and W K2O The sum of the above is 4.0 mass% or more and 10.0 mass% or less, MnO concentration W MnO is 2.0 mass% or less, F concentration W F is 5.0% by mass or more and 15.0% by mass or less, The total concentration of other components is 10.0% by mass or less, It is said that.

[0047] (C) The substrate is a compound represented by the following formula (1): 1.6≦W CaO / W SiO2 <1.8 (1) It satisfies the above.

[0048] (D) The proportion of the premelt base material in the base material is less than 30% by mass or 70% by mass or more.

Claims

1. A mold flux for continuous casting of steel, comprising: The mold flux includes a base material, The substrate is SiO ２ Concentration W ＳｉＯ２ is 20.0% by mass or more and 45.0% by mass or less, CaO concentration W ＣａＯ is 30.0% by mass or more and 55.0% by mass or less, Li ２ O concentration W Ｌｉ２Ｏ is less than 2.0% by mass, Na ２ O concentration W Ｎａ２Ｏ is 4.0% by mass or more and 10.0% by mass or less, K ２ O concentration W Ｋ２Ｏ is 1.0 mass% or less, W Ｌｉ２Ｏ , W Ｎａ２Ｏ and W Ｋ２Ｏ The sum of these is 4.0 mass% or more and 10.0 mass% or less, MnO concentration W ＭｎＯ is 2.0 mass% or less, F concentration W Ｆ is 5.0% by mass or more and 15.0% by mass or less, The total concentration of other components is 10.0% by mass or less, It is said that The following formula (1): 1.6≦W ＣａＯ / W ＳｉＯ２ <1.8 ・・・(1) It satisfies the following: The proportion of the premelt base material in the base material is less than 30% by mass or 70% by mass or more. Mold flux for continuous casting of steel.

2. The MnO concentration W of the substrate ＭｎＯ is set to 0.5% by mass or more and 2.0% by mass or less, 2. The mold flux for continuous casting of steel according to claim 1.

3. the mold flux includes the base material and aggregate carbon powder, The aggregate carbon powder includes expandable graphite, The ratio of the aggregate carbon powder is 0.5% by mass or more and 10.0% by mass or less with respect to 100% by mass of the base material, The proportion of the expandable graphite is 0.5% by mass or more and 5.0% by mass or less with respect to 100% by mass of the base material.

2. The mold flux for continuous casting of steel according to claim 1.

4. Supplying the mold flux according to any one of claims 1 to 3 into a mold; A method for continuous casting of steel, comprising:

Images