Molten steel coating powder

Abstract

To provide a molten steel coating powder capable of forming a molten layer with less change in composition and physical property change resulting therein even if contacted with molten steel containing an active metal for a long time.SOLUTION: Molten steel coating powder contains 13.0≤SiO2≤28.0 mass%, 4.0≤Al2O3≤17.0 mass%, 14.0≤CaO+SrO≤40.0 mass%, 5.0≤Na2O≤8.0 mass%, 5.1≤F (CaF2 conversion)≤9.0 mass%, 5.0≤B2O3≤10.0 mass%, 10.7≤TiO2≤20.9 mass%, and 2.0≤T.C≤7.0 mass%. The molten steel coating powder preferably satisfies 0.8≤SiO2 / TiO2≤2.7 and SiO2+B2O3≥23.0 mass%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to molten steel coating powder, and more particularly to molten steel coating powder used to form a molten layer that covers the surface of molten steel poured into a mold. [Background technology]

[0002] In bottom-pour casting and continuous casting methods, mold powder (hereinafter also simply referred to as "powder") is added to the surface of the molten steel in the mold. The powder added to the surface of the molten steel melts and turns into slag, and the surface of the molten steel is covered with a layer of molten powder (hereinafter also referred to as the "molten layer"). The molten layer plays roles such as preventing oxidation of the surface of the molten steel, maintaining the temperature of the surface of the molten steel, absorbing nonmetallic inclusions in the molten steel, and, in the case of continuous casting, lubricating the space between the mold and the cast slab.

[0003] Various proposals have been made regarding this type of mold powder. For example, Patent Document 1 discloses a method for using mold powder with an SiO2 content of 3% by mass or less when continuously casting molten steel containing Ti. The document states: (A) When continuously casting molten steel containing Ti, if SiO2 is present in the mold powder, the reaction 2TiN + 2SiO2 → 2Si + 2TiO2 + N2 proceeds, generating a large amount of gas within the mold, and (B) When the amount of SiO2 in the mold powder is 3% by mass or less, the generation of N2 gas inside the mold is suppressed. It is stated.

[0004] Patent Document 2 discloses a coating agent comprising an oxide compound, a fluoride compound, and free carbon, wherein the free carbon content is 1-6% and the viscosity at 1300°C is 0.4-2.0 Pa·s. The document states: (A) When casting molten steel by pouring, adding a coating agent with a viscosity within a predetermined range to the surface of the molten steel makes it easier for gas to escape the molten layer of the coating agent, thereby suppressing the accumulation of bubbles in the meniscus of the molten steel. (B) This makes it less likely for pinholes to occur in the ingot. It is stated.

[0005] In casting molten steel containing highly reactive elements such as Ti and Al, when SiO2-containing powder is added to the molten steel surface, the SiO2 in the powder may be reduced by the highly reactive elements. As a result, (a) Formation of defects on the ingot surface due to reduction products, (b) Decrease in viscosity of the molten layer due to changes in the composition of the molten layer, (c) Increase in solidification temperature of the molten layer and the resulting decrease in stable castability Problems such as these may arise.

[0006] To address this problem, a technique has been reported in the past for controlling the activity of SiO2 in continuous casting by adjusting the composition of the mold powder. This technique allows for suppressing reactivity with molten steel while ensuring the appropriate viscosity due to SiO2 addition. Furthermore, Patent Document 1 reports on a technology for low-viscosity powder in continuous casting, focusing on suppressing the reaction between SiO2 and molten steel by adding only a minute amount of SiO2 to the mold powder.

[0007] However, conventional mold powders have not adequately suppressed reactivity with molten steel containing active metals. In particular, bottom-pouring casting has a longer contact time between the molten layer and the molten steel compared to continuous casting. Therefore, when the molten layer and the molten steel react, the composition of the molten layer changes, which can make stable casting of the molten steel difficult. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2019-115925 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-103255 [Summary of the Invention] [Problems to be Solved by the Invention]

[0009] The problem to be solved by the present invention is to provide a molten steel coating powder capable of forming a molten layer with little component change and physical property change resulting therefrom even when in contact with molten steel containing an active metal for a long time. [Means for Solving the Problems]

[0010] In order to solve the above problems, the molten steel coating powder according to the present invention is 13.0 ≦ SiO2 ≦ 28.0 mass%, 4.0 ≦ Al2O3 ≦ 17.0 mass%, 14.0 ≦ CaO + SrO ≦ 40.0 mass%, 5.0 ≦ Na2O ≦ 8.0 mass%, 5.1 ≦ F (in terms of CaF₂) ≦ 9.0 mass%, 5.0 ≦ B2O3 ≦ 10.0 mass%, 10.7 ≦ TiO2 ≦ 20.9 mass%, 2.0 ≦ T.C ≦ 7.0 mass%, and the balance being inevitable impurities and containing [Effects of the Invention]

[0011] When a molten steel coating powder containing a predetermined amount of TiO2 and Al2O3 is added to the surface of molten steel containing Ti and Al, pickup of TiO2 and Al2O3 into the molten layer and SiO2 loss in the molten layer can be suppressed while maintaining the viscosity of the molten layer within an appropriate range. This is considered to be because reduction of SiO2 by Ti and Al is suppressed since an appropriate amount of TiO2 and Al2O3 is contained in the molten layer. [Brief Description of the Drawings]

[0012] [Figure 1] It is a schematic diagram of a segregation test apparatus for molten steel coating powder.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, an embodiment of the present invention will be described in detail. [1. Molten Steel Coating Powder] [1.1. Components] The molten steel coating powder according to the present invention contains the following components, and the balance consists of inevitable impurities. The types of components, the component ranges, and the reasons for their limitations are as follows. Note that "the content (mass%) of component X , , ,

[0015] ,

[0016] , , (i≧1)" refers to the ratio of the mass (=X i ) of component X i to the total mass (=ΣX i ) of the i-th component (main component and inevitable impurities) contained in the molten steel coating powder, which is (=X i ×100 / ΣX i ).

[0014] (1) 13.0≦SiO2≦28.0 mass%: SiO2 acts as a network former in the molten layer and has the effect of increasing the viscosity of the molten layer. If the amount of SiO2 is too small, the viscosity of the molten layer becomes excessively small, and the surface of the molten steel is covered with a thin molten layer. Therefore, the meniscus formed between the molten steel and the mold is not sufficiently filled with the molten layer, and there is a risk that the molten steel and the mold directly contact near the meniscus. Therefore, the amount of SiO2 needs to be 13.0 mass% or more. The amount of SiO2 is preferably 18.0 mass% or more, and more preferably 20.0 mass% or more.

[0015] On the other hand, if the amount of SiO2 becomes excessive, there is a concern about an increase in reactivity with the active metal in the molten steel. Therefore, the amount of SiO2 needs to be 28.0 mass% or less.

[0016] (2) 4.0 ≤ Al2O3 ≤ 17.0 mass%: Al2O3 is an element with high stability as an oxide. Adding an appropriate amount of Al2O3 to molten steel coating powder can suppress the oxidation of active metals (especially Al) in the molten steel. To obtain this effect, the amount of Al2O3 must be 4.0 mass% or more.

[0017] On the other hand, if there is an excess of Al2O3, the melting temperature of the molten steel coating powder may rise excessively. Therefore, the amount of Al2O3 needs to be 17.0 mass% or less. Preferably, the amount of Al2O3 is 15.0 mass% or less, and more preferably 10.0 mass% or less.

[0018] (3)14.0≦CaO+SrO≦40.0mass%: CaO and SrO act as network modifiers in the molten layer, reducing its viscosity. Furthermore, both CaO and SrO increase the basicity of the molten layer, improving the cleanliness of the molten steel. The molten steel coating powder may contain either CaO or SrO, or both.

[0019] If the total amount of CaO and SrO is excessively low, there is a concern that the basicity of the molten layer will decrease excessively, leading to a deterioration in the cleanliness of the molten steel. Therefore, the total amount of CaO and SrO needs to be 14.0 mass% or more. On the other hand, if the total amount of CaO and SrO becomes excessive, the viscosity of the molten layer may decrease excessively. Therefore, the total amount of CaO and SrO must be 40.0 mass% or less. Preferably, the total amount is 35.0 mass% or less, and more preferably, 30.0 mass% or less.

[0020] (4) 5.0 ≤ Na2O ≤ 8.0 mass%: Na2O, like CaO and SrO, acts as a network modifier in the molten layer, reducing its viscosity. Furthermore, Na2O increases the basicity of the molten layer, improving the cleanliness of the molten steel.

[0021] If the amount of Na2O is excessively low, there is a concern that the basicity of the molten layer will decrease excessively, leading to a deterioration in the cleanliness of the molten steel. Therefore, the amount of Na2O needs to be 5.0 mass% or higher. On the other hand, if the amount of Na2O is excessive, the viscosity of the molten layer may decrease excessively. Therefore, the amount of Na2O needs to be 8.0 mass% or less.

[0022] (5) 5.1 ≤ F (CaF2 equivalent) ≤ 9.0 mass%: In this invention, "amount of F" refers to the value obtained by converting the mass of F in the molten steel coating powder into the mass of CaF2. CaF2 has the effect of lowering the melting temperature of the molten steel coating powder. In order to obtain a molten steel coating powder with a low melting temperature, the amount of F must be 5.1 mass% or more in terms of CaF2 equivalent.

[0023] On the other hand, if the amount of fluorine (F) is excessive, low-boiling point compounds (SiF4) may form locally, which can reduce castability. Therefore, the amount of fluorine (F) needs to be 9.0 mass% or less.

[0024] (6) 5.0 ≤ B2O3 ≤ 10.0 mass%: B2O3 acts as a network former in the molten layer, increasing its viscosity. If the amount of B2O3 is excessively low, the viscosity of the molten layer may decrease excessively, and the meniscus formed between the mold and the molten steel may not be sufficiently filled with the molten layer. Therefore, the amount of B2O3 needs to be 5.0 mass% or more. Preferably, the amount of B2O3 is 8.0 mass% or more.

[0025] On the other hand, since B2O3 is a low-boiling-point oxide, an excess of B2O3 can lead to localized fume generation, raising concerns about deterioration of castability. Therefore, the amount of B2O3 needs to be 10.0 mass% or less.

[0026] (7) 10.7 ≤ TiO2 ≤ 20.9 mass%: TiO2 has the effect of suppressing TiO2 pickup from the molten steel to the molten layer. To obtain this effect, the amount of TiO2 needs to be 10.7 mass% or more. Preferably, the amount of TiO2 is 12.0 mass% or more, and more preferably 16.0 mass% or more.

[0027] On the other hand, TiO2 acts as a network modifier in the molten layer, reducing its viscosity. Furthermore, excessive amounts of TiO2 raise concerns about the formation of perovskite (CaTiO3), a high-melting-point composite compound. Therefore, the amount of TiO2 needs to be 20.9 mass% or less.

[0028] (8) 2.0 ≤ TC ≤ 7.0 mass%: The carbon contained in the molten steel coating powder coats the surface of oxide particles, suppressing their rapid melting. If the total carbon (TC) content in the molten steel coating powder is too low, the oxide particles will melt rapidly when the powder is added to the molten steel surface. As a result, the amount of powder flowing into the molten steel-mold meniscus may be excessive in the initial stages of casting. Therefore, the TC content needs to be 2.0 mass% or higher.

[0029] On the other hand, if the TC (carbon content) is excessive, the start of powder melting will be delayed, and the amount of powder flowing into the meniscus between the molten steel and the mold may be insufficient. Therefore, the TC must be 7.0 mass% or less.

[0030] (9) Inevitable impurities: The molten steel coating powder according to the present invention may contain unavoidable impurities in addition to the components described above. Examples of unavoidable impurities include Fe2O3 and MgO. The content of unavoidable impurities in the molten steel coating powder should be as low as possible. Specifically, the content of unavoidable impurities in the molten steel coating powder should preferably be 5.0 mass% or less, 4.0 mass% or less, or 3.0 mass% or less.

[0031] [1.2. Ingredient Balance] In addition to containing the components described above, the molten steel coating powder according to the present invention preferably satisfies the following formulas (1) and (2). 0.8 ≤ SiO2 / TiO2 ≤ 2.7 …(1) SiO2 + B2O3 ≥ 23.0 mass% …(2)

[0032] [1.2.1. Formula (1)] If the SiO2 / TiO2 ratio becomes too low, the viscosity of the molten layer will decrease excessively. Therefore, a SiO2 / TiO2 ratio of 0.8 or higher is preferable. Preferably, the SiO2 / TiO2 ratio is 1.0 or higher, and more preferably, 1.4 or higher. On the other hand, if the SiO2 / TiO2 ratio becomes too high, the reactivity between SiO2 in the molten layer and Ti in the molten steel increases, which can lead to increased TiO2 pickup into the molten layer. Therefore, a SiO2 / TiO2 ratio of 2.7 or less is preferable. Preferably, the SiO2 / TiO2 ratio is 2.4 or less, and more preferably, 2.0 or less.

[0033] [1.2.2. Formula (2)] Both SiO2 and B2O3 act as network formers in the molten layer, increasing its viscosity. Therefore, if the total amount of SiO2 and B2O3 becomes too low, the viscosity of the molten layer may decrease excessively. Accordingly, the total amount of SiO2 and B2O3 is preferably 23.0 mass% or more. Preferably, the total amount is 28.0 mass% or more, and more preferably 31.0 mass% or more.

[0034] [1.3. Characteristics] [1.3.1. Viscosity] The viscosity of the molten steel coating powder during melting affects the quality of the ingot. When molten steel coating powder is added to the surface of molten steel, if the viscosity of the molten layer becomes too low, the surface of the molten steel will be covered with a thin molten layer. As a result, the meniscus formed between the molten steel and the mold will not be sufficiently filled with the molten layer, and there is a risk that the molten steel and the mold will come into direct contact near the meniscus. On the other hand, if the viscosity of the molten steel coating powder becomes too high during melting, the molten layer may not penetrate the meniscus between the molten steel and the mold, making it difficult to coat the molten steel near the meniscus.

[0035] The viscosity of the molten steel coating powder during melting can be adjusted by its composition. Optimizing the composition results in a viscosity of 1.0 poise (0.1 Pa·s) to 10.0 poise (1.0 Pa·s) at 1300°C. Further optimization of the composition results in a viscosity of 1.5 poise (0.15 Pa·s) to 6.0 poise (0.6 Pa·s) or 2.5 poise (0.25 Pa·s) to 4.0 poise (0.4 Pa·s) at 1300°C.

[0036] [1.3.2. Melting Initiation Temperature] The melting start temperature of the molten steel coating powder affects the quality of the ingot. If the melting start temperature of the molten steel coating powder is too low, the viscosity of the molten layer may become excessively low when the molten steel coating powder is added to the molten steel surface. On the other hand, if the melting start temperature of the molten steel coating powder is too high, when the molten steel coating powder is added to the surface of the molten steel, the powder may not melt, or the viscosity of the molten layer may become excessively high.

[0037] The melting start temperature of molten steel coating powder can be adjusted by its composition. By optimizing the composition, the melting start temperature of molten steel coating powder can be between 900°C and 1100°C.

[0038] [1.3.3. TiO2 pickup, Al2O3 pickup, SiO2 loss] When the molten steel coating powder according to the present invention is added to the surface of molten steel, if Ti and Al are present in the molten steel, Ti and Al reduce SiO2 in the molten layer as shown in the following equations (3) and (4). When SiO2 is reduced, the composition of the molten layer changes, and the physical properties of the molten layer change accordingly. Ti + SiO2 → Si + TiO2…(3) (4 / 3)Al+SiO2→ Si+(2 / 3)Al2O3…(4)

[0039] In contrast, the molten steel coating powder according to the present invention contains appropriate amounts of TiO2 and Al2O3, so even when molten steel containing Ti and Al comes into contact with the molten layer, the reactions of formulas (3) and (4) are less likely to proceed to the right. As a result, the pickup of TiO2 and Al2O3 into the molten layer is suppressed. Furthermore, this suppresses the loss of SiO2 from the molten layer. In other words, when the molten steel coating powder according to the present invention is used as a mold powder (coating agent) to coat the surface of molten steel containing Ti and Al, it is possible to suppress changes in the composition of the molten layer caused by the reaction between the molten steel and the molten layer, and the resulting changes in the physical properties of the molten layer.

[0040] For example, when molten steel containing 1.5 mass% to 2.5 mass% of Ti and 0.1 mass% to 0.5 mass% of Al is brought into contact with a molten layer containing melted molten steel coating powder at 1500°C for 10 minutes, optimizing the composition of the molten steel coating powder results in TiO2 pickup into the molten layer being 2.0 mass% or less, 1.6 mass% or less, or 1.0 mass% or less.

[0041] Similarly, when molten steel containing 1.5 mass% to 2.5 mass% of Ti and 0.1 mass% to 0.5 mass% of Al is brought into contact with a molten layer containing melted molten steel coating powder at 1500°C for 10 minutes, optimizing the composition of the molten steel coating powder results in Al2O3 pickup into the molten layer being 1.0 mass% or less.

[0042] Similarly, when molten steel containing 1.5 mass% to 2.5 mass% of Ti and 0.1 mass% to 0.5 mass% of Al is brought into contact with a molten layer containing melted molten steel coating powder at 1500°C for 10 minutes, optimizing the composition of the molten steel coating powder results in SiO2 loss in the molten layer of 3.5 mass% or less, 3.0 mass% or less, or 2.0 mass% or less.

[0043] [1.4. Purpose] [1.4.1. Casting Method] The molten steel coating powder according to the present invention can be used in various casting methods that require mold powder during casting. Casting methods to which the molten steel coating powder according to the present invention can be applied include, for example, bottom pouring casting, continuous casting, and top pouring casting.

[0044] The molten steel coating powder according to the present invention is particularly preferred for use in forming a molten layer that covers the surface of the molten steel poured into a mold when casting molten steel by pouring. In bottom-pouring casting, the contact time between the molten steel and the molten layer is long, making it prone to reactions. In contrast, the molten steel coating powder according to the present invention has optimized components, so it can suppress reactions between the molten steel and the molten layer even when the contact time between the molten steel and the molten layer is relatively long.

[0045] [1.4.2. Applicable steel type] The molten steel coating powder according to the present invention can be applied to various types of steel that require mold powder during casting. The molten steel coating powder according to the present invention is preferably used to form a molten layer that covers the surface of molten steel poured into a mold when casting molten steel containing Ti and Al. The molten steel containing Ti and Al is preferably one that contains 1.5 mass% to 2.5 mass% of Ti and 0.1 mass% to 0.5 mass% of Al.

[0046] [1.5. Effect] Some heat-resistant steels for automobiles have certain amounts of Al and Ti added to them. This is done to precipitate Ni3(Al,Ti) and improve high-temperature strength. For example, SUH660, known as a heat-resistant bolt steel for automobiles, is specified in JIS standards to contain 1.90 to 2.35 mass% Ti. In order to stably produce such heat-resistant steels, technology for stably casting molten steel containing highly active components such as Ti is essential.

[0047] While there have been various reports on techniques to suppress the reaction between Ti in molten steel and the molten layer and to achieve stable casting, most of these reports concern continuous casting. Furthermore, in continuous casting, solidification proceeds almost perpendicular to the mold surface, which presents a problem in that when molten steel containing Ti is continuously cast, a region of Ti concentration tends to form in the center of the cast slab.

[0048] On the other hand, bottom pouring casting can be suitable for casting molten steel containing Ti, especially when dealing with small-lot production and from the perspective of central properties (i.e., the formation of a Ti-enriched region in the center is less likely). However, while the casting speed of continuous casting is around 1.0 mm / min, the casting speed of bottom pouring casting is slower than that of continuous casting. As a result, in bottom pouring casting, the contact time between the molten steel and the molten layer is longer than in continuous casting, and particular attention must be paid to the decrease in viscosity of the molten layer due to reaction with the molten steel.

[0049] Furthermore, most previous reports focused on steel grades with a Ti content of around 0.1 to 1.0 mass%, and there are no reports on coatings for bottom-casting steel grades containing large amounts of Ti, such as SUS660H, with a Ti content of around 2.0 mass%.

[0050] In contrast, when a molten steel coating powder containing a predetermined amount of TiO2 and Al2O3 is added to the surface of molten steel containing Ti and Al, the viscosity of the molten layer can be maintained within an appropriate range, while the pickup of TiO2 and Al2O3 into the molten layer and the loss of SiO2 from the molten layer can be suppressed. This is thought to be because the reduction of SiO2 by Ti and Al is suppressed because the molten layer contains an appropriate amount of TiO2 and Al2O3. [Examples]

[0051] (Examples 1-4, Comparative Examples 1-2) [1. Materials] The alloys used for melting had the compositions shown in Table 1. The alloys with the compositions shown in Table 1 are alloys with compositions equivalent to SUS660.

[0052] [Table 1]

[0053] Furthermore, the molten steel coating powder used had the composition shown in Table 2. In Table 2, TC, SrO, Al2O3, CaF2, CaO, Na2O, SiO2, TiO2, and B2O3 are the main components, while Fe2O3 and MgO are unavoidable impurities.

[0054] [Table 2]

[0055] [2. Test Method] [2.1. Fluctuation Amount] Figure 1 shows a schematic diagram of a molten steel coating powder curing test apparatus (hereinafter also simply referred to as the "test apparatus"). In Figure 1, the test apparatus 10 comprises a graphite crucible 12, an outer crucible (alumina crucible) 14, an inner crucible (magnesia crucible) 16, and first to third thermocouples 18a to 18c. The inner crucible 16 is inserted into the outer crucible 14, and back sand 20 is filled between the outer surface of the inner crucible 16 and the inner surface of the outer crucible 14. Furthermore, the outer crucible 14 is inserted into the graphite crucible 12. The outer crucible 14 is movable up and down within the graphite crucible 12. Furthermore, the outer crucible 14 can be lowered even further than the lower end of the graphite crucible 12.

[0056] The first to third thermocouples 18a to 18c are inserted into the back sand 20. The first thermocouple 18a is for measuring the temperature near the bottom of the inner crucible 16. The second thermocouple 18b is for measuring the temperature near the center of the inner crucible 16. The third thermocouple 18c is for measuring the temperature near the top of the inner crucible 16.

[0057] The inner crucible 16 was filled with 250 g of alloy 22, and the alloy 22 was heated up to about 1550 °C (the melting point of the alloy + 150 °C) to melt the alloy 22. Then, the temperature of the alloy 22 was adjusted to about 1530 °C. After the temperature adjustment, 30.0 g of molten steel coating powder 24 was added from the upper part of the inner crucible 16, and isothermal holding was carried out for 10 to 15 minutes. After the holding was completed, with the electric current supplied to the heater (not shown) remaining constant, the outer crucible 14 was pulled down from the heating zone at a speed of 3 to 10 mm / min to fabricate a unidirectionally solidified sample.

[0058] After the outer crucible 14 was cooled to near room temperature, the molten layer on the surface of the alloy 22 was collected and chemical composition analysis was performed. Based on the content (X' i ) of the i-th component contained in the molten layer after the slagging test of the powder and the content (X i ) of the i-th component contained in the powder before the melting test, the variation amount (ΔX i = X' i - X i ) was calculated. When ΔX i > 0, it is called "pickup", and when ΔX i < 0, it is called "loss".

[0059] [2.2. Viscosity reduction resistance of the molten layer] The viscosity of the molten steel coating powder at 1300 °C was measured. The evaluation of the viscosity reduction resistance of the molten layer is as follows: when the viscosity of the molten layer at 1300 °C is (a) less than 1.0 poise (0.1 Pa·s), it is marked as "△", (b) 1.0 poise (0.1 Pa·s) or more and less than 1.5 poise (0.15 Pa·s), it is marked as "○", (c) 1.5 poise (​​​​​​​​​(1) In the case of Comparative Example 1, the TiO2 pickup was large, and the SiO2 loss was also large. This is thought to be because the molten coating powder does not contain TiO2. (2) In Comparative Example 2, the TiO2 pickup was equivalent to that in Comparative Example 1, but the SiO2 loss was smaller than in Comparative Example 1. (3) In all of Examples 1 to 4, the TiO2 pickup was small and the SiO2 loss was also small.

[0061] (4) In Example 2, the TiO2 pickup was smaller and the SiO2 loss was larger compared to Example 1. This is thought to be because the initial SiO2 / TiO2 ratio of the powder was higher in Example 1 than in Example 2, and the reduction of SiO2 by Ti proceeded more easily. (5) Similarly, in Example 3, the TiO2 pickup was smaller and the SiO2 loss was larger compared to Example 2. This is thought to be because the initial SiO2 / TiO2 ratio of the powder was higher in Example 2 than in Example 3, and the reduction of SiO2 by Ti proceeded more easily.

[0062] (6) In all of Examples 1-4 and Comparative Examples 1-2, the Al2O3 pickup was reduced. This is thought to be because the amount of Al contained in the alloy was small, and because an appropriate amount of Al2O3 was contained in the molten steel coating powder. (7) Example 4 showed a slight decrease in the viscosity degradation resistance of the molten layer compared to Example 1. This is thought to be because the SiO2 / TiO2 ratio was less than 0.8. Comparative Examples 1 and 2 showed an even further decrease in the viscosity degradation resistance of the molten layer compared to Example 4. This is thought to be because the SiO2 / TiO2 ratio exceeded 2.7.

[0063] [Table 3]

[0064] Although embodiments of the present invention have been described in detail above, the present invention is not limited in any way to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. [Industrial applicability]

[0065] The molten steel coating powder according to the present invention can be used as a mold powder when casting steel materials containing activated metals.

Claims

1. 13.0≦SiO 2 ≦28.0mass%、 4.0≦Al 2 O 3 ≦17.0mass%、 14.0≦CaO+SrO≦40.0 mass%, 5.0≦Na 2 O≦8.0mass%、 5.1≦F(CaF) 2 (Conversion) ≤ 9.0 mass% 5.0≦B 2 O 3 ≦10.0mass%、 10.7≦TiO 2 ≦20.9mass%、 2.0 ≤ T. C ≤ 7.0 mass%, and, Residual unavoidable impurities Molten steel coating powder containing [this ingredient].

2. The molten steel coating powder according to claim 1, satisfying the following formulas (1) and (2). 0.8≦SiO 2 / TO 2 ≦2.7 …(1) SiO 2 +B 2 O 3 ≧23.0mass% …(2)

3. The molten steel coating powder according to claim 2, wherein the viscosity at 1300°C is 1.0 poise (0.1 Pa·s) or more and 10.0 poise (1.0 Pa·s) or less.

4. The molten steel coating powder according to claim 2, wherein the melting start temperature is 900°C or higher and 1100°C or lower.

5. When molten steel containing 1.5 mass% to 2.5 mass% of Ti and 0.1 mass% to 0.5 mass% of Al is brought into contact with a molten layer obtained by melting the molten steel coating powder at 1500°C for 10 min, TiO to the molten layer 2 The pickup rate is 2.0 mass% or less. Al to the molten layer 2 O 3 The pickup rate is 1.0 mass% or less. The SiO of the molten layer 2 Loss is 3.5 mass% or less. The molten steel coating powder according to claim 2.

6. The molten steel coating powder according to claim 2, used for forming a molten layer that covers the surface of molten steel poured into a mold when casting molten steel by bottom pouring.

7. The molten steel coating powder according to claim 2, used for forming a molten layer that covers the surface of molten steel poured into a mold when casting molten steel containing Ti and Al.

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