Molten metal processing method and continuous casting method

Abstract

To provide a technique for improving durability by suppressing infiltration of slag into a refractory.SOLUTION: In a processing method for a molten metal, a refractory used for holding or processing the molten metal is in contact with slag on the molten metal. The processing method for the molten metal includes adjusting at least any one of a component promoting infiltration of the slag into the refractory and a component suppressing the infiltration in a composition of the slag, thereby securing a predetermined amount of a thickness te in which the slag non-infiltrates into the used refractory. When performing continuous casting, it is preferable that the refractory is a weir provided in a molten steel flow passage inside of a tundish between a pouring part, by which molten steel flows from a ladle, and a draining part by which molten steel flows out to a casting mold.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a method for treating molten metal that suppresses the infiltration of refractories by slag, and in particular to a continuous casting method that suppresses the infiltration of slag into a weir provided in a tundish, thereby improving its durability. [Background technology]

[0002] Refractory-lined processing vessels and functional materials made of refractories are used to handle molten metals, such as molten pig iron and molten steel. Refractories are used in blast furnace ladle, charging ladle, and ladle, as well as in desulfurization impellers, tundishes, their lids, weirs, long nozzles, and sliding nozzle plates. For example, continuous casting of steel involves pouring molten steel from a ladle into a tundish and then into a mold through a submerged entry nozzle. In this process, a weir is installed between the molten steel inlet in the tundish, which receives the molten steel from the ladle, and the tundish nozzle, which discharges the molten steel into the mold. Such a weir is expected to have the effect of controlling the molten steel flow in the tundish, such as preventing short-circuiting from the molten steel inlet toward the tundish nozzle, thereby promoting the floating and separation of inclusions. This inclusion removal allows for the production of highly clean cast slabs.

[0003] Tundish weirs often come into contact with slag flowing from the ladle. For corrosion resistance, they are typically constructed of refractories primarily composed of Al2O3 and MgO. However, high concentrations of single components such as Al2O3 and MgO can easily cause cracking due to thermal shock. Therefore, tundish weirs are typically manufactured with a composite composition that includes a material with a low volume expansion coefficient, such as SiO2. For these reasons, the composition ratio of refractories used in tundish weirs has been determined. Because there is a limit to the amount of tundish weirs that can be recycled, they often must be disposed of as industrial waste. Patent Document 1, for example, discloses a technology for reusing weirs with the aim of reducing refractory consumption.

[0004] Furthermore, when pouring molten steel from the ladle into the tundish, ladle slag inevitably gets mixed into the tundish. Such ladle slag does not have the components suitable for absorbing and removing the inclusions that float up in the tundish. In addition, the SiO2 and lower oxides (Fe x O y , MnO) may contaminate the molten steel. Therefore, it is necessary to control the slag composition in the tundish or to cover the molten steel with flux to prevent contact between the molten steel and air. For example, Patent Document 2 discloses a technique for adding flux to the tundish. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-183586 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-110946 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned conventional techniques have the following problems. That is, according to Patent Document 1, the weir refractory of a tundish recovered after use is exposed to various stresses due to heating, cooling, oxide infiltration, etc. As a result, it tends to be damaged and deformed, particularly to deform convexly from the ladle molten steel inlet side toward the mold outlet side due to molten steel pressure. Patent Document 1 describes the limit deformation amount for reuse when the tundish weir deforms convexly. However, it does not describe a technology for suppressing oxide infiltration into the weir refractory to prevent deformation.

[0007] Furthermore, Patent Document 2 describes a technique for controlling the slag composition by adding flux to the tundish, taking into account fluctuations in composition due to ladle slag and packing sand that flows out from the ladle at the start of pouring. However, the techniques described in Patent Document 2 aim to prevent molten steel contamination by absorbing and removing inclusions or reducing the degree of slag oxidation. However, there is no mention of a technique for suppressing oxide infiltration into the tundish gate. In other words, there is currently no technique that takes into account the influence of slag components on slag infiltration into refractories.

[0008] An object of the present invention is to solve the above-mentioned conventional problems and to provide a technology for suppressing the infiltration of refractories by slag and improving durability. [Means for solving the problem]

[0009] The method for treating molten metal according to the present invention, which advantageously solves the above-mentioned problems, is a method for treating molten metal in which a refractory used for holding or treating the molten metal comes into contact with slag on the molten metal, and the method comprises adjusting at least one of a component that promotes infiltration of the slag into the refractory and a component that inhibits infiltration of the slag into the refractory after use, so that the refractory is in a state where the slag has not infiltrated a thickness t e The present invention is characterized by securing a predetermined amount of

[0010] The method for treating molten metal according to the present invention is as follows: (a) the refractory material comprises Al2O3 and SiO2; (b) the refractory material contains 45% by mass or more of Al2O3 and 10% by mass or more of SiO2; (c) the components that promote the infiltration of slag into the refractory are iron oxide and manganese oxide in the slag, and the component that inhibits the infiltration of slag into the refractory is chromium oxide in the slag; This may be a more preferable solution.

[0011] The continuous casting method of the present invention, which advantageously solves the above-mentioned problems, is characterized in that, when continuous casting is performed using any of the above-mentioned molten metal treatment methods, the refractory material is a weir provided in a molten steel flow path in a tundish between a supply section for introducing molten steel from a ladle and a discharge section for discharging molten steel into a mold.

[0012] The continuous casting method according to the present invention includes the steps of: (d) The initial thickness of the weir is set to t0, and the thickness of the slag that has not yet penetrated the weir at the end of operation is calculated from the sum of the iron oxide content and manganese oxide content in the slag, which are components that promote the penetration of slag into the refractory of the weir, and the chromium oxide content in the slag, which is a component that inhibits the penetration of slag into the refractory of the weir. e adjusting the slag components so that the amount is a predetermined amount; (e) The thickness t of the slag that has not yet penetrated e is calculated by the following equation (1) (where t0 is the initial thickness of the weir (mm), t e : Thickness of the weir without slag penetration (mm), (Fe x O y +MnO): the sum of the iron oxide content and manganese oxide content in the slag (mass%), (Cr2O3): the chromium oxide content in the slag (mass%), a, b, c: coefficients and constants. This may be a more preferable solution. t e =t0-{a×(Fe x O y +MnO)-b×(Cr2O3)}+c (1) [Effects of the Invention]

[0013] The molten metal processing method and continuous casting method of the present invention can ensure a thickness of refractory material that is not infiltrated with slag after use by adjusting the slag composition, thereby improving the durability of the refractory material. Furthermore, deformation of the weir can be prevented, improving the durability of the weir. This, in turn, improves the recyclability of the refractory material and maintains high purity of the molten metal, making it industrially useful. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional conceptual diagram showing a tundish according to one embodiment of the present invention. [Figure 2] FIG. 1 is a cross-sectional conceptual diagram illustrating the state in which slag has infiltrated into the weir of the tundish during use in the above embodiment. [Figure 3] 1 is a graph comparing the amount of slag infiltration into the weir of a used tundish with and without composition adjustment of the tundish slag. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following describes in detail embodiments of the present invention. Note that the drawings are schematic and may differ from the actual embodiments. Furthermore, the following embodiments exemplify devices and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

[0016] 1 is a cross-sectional conceptual diagram showing the configuration of a tundish used in a continuous casting method according to one embodiment of the present invention. The tundish 10 used in this embodiment has a steel shell 1 with a refractory lining 2 applied to the inside. Molten steel 3 is poured from a ladle (not shown) into a molten metal supply section 4 through a long nozzle 11, and the molten steel 3 is poured into a mold (not shown) from a nozzle (not shown) installed below a molten metal discharge section 5.

[0017] The tundish 10 shown in Figure 1 is provided with a weir 8 that separates the slag 6, 7 in the tundish between the slag 6 on the supply side and the slag 7 on the discharge side. When continuous steel casting is performed using such a tundish 10, slag infiltration into the weir 8 progresses from both the slag 6 on the supply side and the slag 7 on the discharge side.

[0018] Although FIG. 1 shows an example of a tundish for a single-strand continuous casting machine, it may have multiple discharge sections so as to supply molten steel to multiple strands. In this case, a weir 8 can be provided in any of the molten steel flow paths from the supply section to the discharge section. The shape of the weir 8 is not limited to the plate shape shown in FIG. 1, and may be any shape that comes into contact with the slag in the tundish. The weir 8 is fixed by wedges 9 and resists the molten steel flow and buoyancy.

[0019] The refractory material constituting the weir 8 of the tundish 10 preferably has a composition containing Al2O3 and SiO2, taking into consideration the usage environment. The refractory composition preferably contains 45% by mass or more of Al2O3 and 10% by mass or more of SiO2. More preferably, the refractory composition contains 45% by mass or more of Al2O3 and 30% by mass or more of SiO2. This composition provides excellent corrosion resistance and thermal shock resistance. Other refractory components may include SiC and FC.

[0020] As shown in FIG. 2, the weir 8 of the tundish 10 has an initial thickness t0 (mm), where the thickness of the weir is the dimension in the vertical direction from the surface in contact with the slag 6, 7 in the tundish. The slag 6 on the supply side and the slag 7 on the discharge side infiltrate the refractory of the weir 8, forming an infiltration layer 8a. Within the infiltration layer 8a, Al2O3 and SiO2, which are the materials of the weir 8 of the tundish 10, react with the infiltrated slag to form a eutectic phase, and a liquid phase is formed at the temperature of the molten steel. This infiltration layer 8a does not contribute to the material strength of the weir 8 of the tundish 10. The thickness of the infiltration layer 8a is divided into two areas, the supply side 4 side and the discharge side 5 side, and each is defined as t m , t h Then, the effective thickness of the barrier that contributes to the material strength, that is, the thickness of the unpermeated slag, t e is expressed by the following equation (2). t e =t0-(t m +t h ) ···(2)

[0021] Effective weir thickness t that contributes to material strength eWhen the effective thickness t of the weir 8 becomes 0, the slag has infiltrated the entire thickness of the weir 8. If the strength of the weir 8 of the tundish 10 in the full-thickness infiltrated state becomes lower than the dynamic pressure from the molten steel 3, the dynamic pressure of the molten steel 3 will cause it to deform convexly toward the discharge section 5, which may lead to problems such as the collapse of the weir 8. Furthermore, if a through hole occurs in the weir 8, the slag 6 on the side of the supply section 4 will flow out toward the discharge section 5, which may cause quality problems. Therefore, the effective weir thickness t of the weir 8 e It is required to carry out continuous casting in a state where the thickness of the slag that has not infiltrated the weir 8 is ≥ 10 mm. Preferably, when the initial thickness t0 of the weir 8 is 100 mm, the effective weir thickness t e The distance should be ≧40mm.

[0022] As mentioned above, slag infiltration into the refractory material that makes up the weir 8 progresses when the infiltrated slag forms a eutectic phase with the material of the weir 8 itself. The lower the melting point and viscosity of the slag in contact with the weir 8, the deeper the slag infiltration will progress. Therefore, by controlling the composition of the slag in contact with the weir 8 so that it has a high melting point and high viscosity, slag infiltration into the weir 8 can be suppressed.

[0023] In this embodiment, the composition of the slags 6 and 7 in the tundish 10 is such that iron oxide (Fe x O y ) and manganese oxide (MnO) have the effect of lowering the melting point and viscosity of the slag, and are therefore components that promote the penetration of the slag into the refractory material of the gate 8. Similarly, chromium oxide (Cr2O3) has the effect of raising the melting point and viscosity of the slag, and is therefore a component that inhibits the penetration of the slag into the refractory material of the gate 8.

[0024] The inventors have investigated the amount (thickness) of slag infiltration into the refractory of the gate 8 within the range of 9 to 11 hours of use of the tundish 10 in continuous casting. m +t h As a result, the relationship in equation (3) below was derived. t m +t h = a × (Fe x O y +MnO)-b×(Cr2O3)-c (3) where: t m +t h : Slag penetration thickness into the refractory of weir 8 (mm), (Fe x O y +MnO): content of iron oxide and manganese oxide in the slag (mass%) (Cr2O3): chromium oxide content in slag (mass%), a, b, c: coefficients and constants Represents.

[0025] From the above equations (2) and (3), the effective weir thickness t e To ensure this, the following equation (4) must be satisfied. t0≧a×(Fe x O y +MnO)-b×(Cr2O3)-c+t e (4)

[0026] In the continuous casting method according to this embodiment, the initial thickness t0 of the gate 8 of the tundish 10 and the slag composition in the tundish 10 are adjusted to satisfy the above formula (4). For example, a reducing agent such as metallic Al can be added to the slag in the tundish to reduce lower oxides such as FeO and MnO. Chromium oxide can also be added to inhibit slag infiltration. The timing for adjusting the slag composition can be selected from among adding a reducing agent such as Al to the slag above the molten steel in the ladle during tapping, spraying a reducing agent or chromium oxide onto the slag above the molten steel in the ladle during secondary refining, and spraying a reducing agent or chromium oxide onto the slag above the molten steel in the tundish. To adjust the slag composition, the composition of the ladle slag is estimated or measured based on past results, and the slag composition in the tundish is estimated or measured to calculate the slag infiltration amount (thickness) t m +t h In this embodiment, it is preferable to calculate the thickness of the uninfiltrated slag t e The initial thickness t0 of the weir is selected and the slag composition is adjusted so that the thickness is 10 mm or more, preferably 40 mm or more.

[0027] By adjusting the slag composition in the tundish according to this embodiment, the thickness of the slag that has not yet penetrated the weir 8 after use is t e This ensures that the weir 8 maintains its hot strength. Therefore, deformation of the weir 8 is suppressed and the wedges 9 can maintain the weir 8 in place.

[0028] In the above embodiment, the continuous steel casting method has been described using a tundish weir as an example, but the present invention can also be applied to refractories constituting the vessel of a tundish, long nozzles for pouring molten steel from a ladle, and sliding nozzle plates. It can also be applied to other molten metal treatments. For example, it can be applied to refractories that come into contact with slag, such as blast furnace ladles and charging ladles used in the preliminary treatment of molten iron, and impellers of mechanically stirred desulfurization devices. [Example]

[0029] Continuous casting of steel was carried out using the tundish shown in Figure 1. The processing time was 9 to 11 hours, and the amount of molten steel passing through was approximately 3,000 to 4,000 tons. The relationship between the various slag compositions in the tundish and the amount of slag infiltrating into the weir is summarized in Table 1. The initial thickness t0 of the weir was set to 100 mm. The slag composition in the tundish was iron oxide (Fe x O y The contents (mass%) of manganese oxide (MnO) and chromium oxide (Cr2O3) were analyzed. Using these values, the amount of slag infiltration (t m +t h ) was calculated. In the formula, a = 2.89, b = 10.38, and c = -61.19. The tundish gate recovered after casting was inspected and used as the actual value for the amount of slag infiltration. The results in Table 1 show that the calculated and actual values ​​for the amount of slag infiltration are in good agreement.

[0030] [Table 1]

[0031] In Process No. 1, the amount of slag infiltration reached 100 mm, the same as the initial thickness t0 of the weir, and the weakened weir was pushed by the dynamic pressure of the molten steel flow, causing it to deform convexly toward the drain side. A crack caused by the deformation caused part of the weir to fall off.

[0032] Of the slag compositions in the tundish, iron oxide and manganese oxide are thought to originate from the converter slag. On the other hand, chromium oxide is thought to originate from the packing sand that flows in when pouring from the ladle begins. In Process No. 2, slag modification was insufficient, resulting in a remaining effective weir thickness of less than 10 mm. In Processes Nos. 3 to 6, slag modification ensured a remaining effective weir thickness of 10 mm or more. In Processes Nos. 4 to 6, metallic Al was added to the slag above the molten steel tapped from the converter into the ladle to reduce lower oxides. In Processes Nos. 3, 5, and 6, chromium oxide was added. In Processes Nos. 5 and 6 (inventive examples), in which the slag composition was adjusted, (Fe x O y + MnO) was reduced to 9 mass% or less. As shown in Figure 3, in the inventive examples corresponding to treatments No. 5 and 6, the slag infiltration amount was less than 60 mm, meaning that the thickness of the remaining effective weir was 40 mm or more, and a sound weir shape was maintained.

[0033] In this example, composition control was performed by adding metallic Al to the slag above the molten steel tapped into the ladle. However, this method is not limited to this, as long as it reduces low-grade oxides. Controlling slag composition by adding flux to the tundish is also effective. For example, adding a flux containing Cr2O3 can also suppress slag infiltration. [Industrial Applicability]

[0034] According to the continuous casting method of the present invention, the durability of the tundish gate is improved, so that continuous casting can be carried out stably and without trouble, and the quality of steel can be maintained, which is industrially useful. [Explanation of symbols]

[0035] 1 Ironhide 2 Refractory lining 3. Molten Steel 4. Hot water supply section (from ladle) 5. Drainage section (to the mold) 6 (Hot water supply side) Slag 7 (Discharge side) Slag 8 (tundish) weir 8a (slag) infiltration layer 9 Wedge 10 Tundish 11 Long nozzle

Claims

1. 1. A method for treating molten metal in which a refractory material used to hold or treat the molten metal contacts slag above the molten metal, comprising: In the composition of the slag, at least one of a component that promotes the infiltration of the slag into the refractory and a component that inhibits the infiltration of the slag is adjusted so that the refractory after use has a thickness t of the slag that is not infiltrated. ｅ In securing a specified amount of The refractory material contains Al 2 O 3 : 45 mass% or more and SiO 2 : 10 mass% or more, the components that promote the infiltration of the slag into the refractory are iron oxide and manganese oxide in the slag, A method for treating molten metal, wherein the component that inhibits the infiltration of slag into the refractory is chromium oxide in the slag.

2. When performing continuous casting using the molten metal processing method according to claim 1, a weir provided in a molten steel flow path in a tundish between a supply section through which molten steel flows from a ladle and a discharge section through which molten steel flows into a mold;

3. The initial thickness of the weir is t ０ year, the sum of the iron oxide content and the manganese oxide content in the slag as components that promote the infiltration of the slag into the refractory of the weir; The thickness t of the slag that has not been infiltrated at the end of operation is calculated from the content of chromium oxide in the slag, which is a component that inhibits the infiltration of the slag into the refractory of the weir. ｅ 3. The continuous casting method according to claim 2, wherein the slag components are adjusted so that the amount of the slag is a predetermined amount.

4. The thickness of the slag that has not yet infiltrated is t ｅ The continuous casting method according to claim 3, wherein the value of the melting point is calculated by the following formula (1): t ｅ =t ０ -{a×(Fe ｘ O ｙ +MnO)-b×(Cr ２ O ３ )}+c (1) where: t ０ : initial thickness of the weir (mm), t ｅ : Thickness of the weir not infiltrated with slag (mm), (Fe ｘ O ｙ + MnO): the sum of the iron oxide content and manganese oxide content in the slag (mass%), (Cr ２ O ３ ): chromium oxide content in slag (mass%), a, b, c: coefficients and constants Represents.

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