Continuous casting method for mold powder and steel

Abstract

To provide a mold powder that reduces the occurrence of constrained breakouts and enables stable continuous casting in the continuous casting of high-Al steel or high-Ti steel. [Solution] The mold powder contains CaO and Al2O3 as its main components, with a mass ratio (CaO / Al2O3) of 1.3 to 1.9, a total content of CaO and Al2O3 of 81.1% by mass or more, and contains 0.0 to 2.0% by mass of SiO2, 5.0% by mass or more of Li2O, and 4.0 to 16.0% by mass of F.

Description

[Technical Field]

[0001] This disclosure relates to mold powder and a continuous casting method for steel, which are suitable for continuous casting of high-alkaline steel and high-tiester steel. [Background technology]

[0002] In continuous casting of steel, molten steel is poured into a mold, where it cools and solidifies to form a solidified shell, which is then continuously withdrawn downwards. Inside the mold, mold powder (sometimes called mold flux) is introduced onto the surface of the molten steel. The mold powder melts due to the heat of the molten steel, forming a molten layer of powder slag (hereinafter, the molten mold powder is referred to as powder slag). The powder slag flows between the mold and the solidified shell, cools in the mold, solidifies into a film (hereinafter referred to as slag film), and is discharged from the bottom of the mold and consumed. The main roles of mold powder are: (1) heat retention and oxidation prevention of the molten steel surface, (2) absorption of non-metallic inclusions rising from the molten steel and purification of the molten steel, (3) ensuring lubrication between the mold and the solidified shell, and (4) uniform heat removal and slow cooling of the solidified shell by controlling the heat flux from the solidified shell to the mold.

[0003] Mold powders generally contain CaO and SiO2 as their main components, but mold powders that contain as little SiO2 as possible are known for use in continuous casting of high-Al steel and high-Ti steel. For example, Patent Document 1 discloses a mold flux in which the SiO2 content is restricted to 2.0 wt% or less, for the purpose of preventing deterioration of the slab surface quality due to poor lubrication and constrained breakout when continuously casting steel containing slag-reducing metal elements such as high-Al steel. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-000646 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, when the mold powder described in Patent Document 1 is used for continuous casting of high-Al steel or high-Ti steel, constrained breakout can still occur.

[0006] This disclosure is made in view of the above circumstances and aims to provide a mold powder that reduces the occurrence of constrained breakouts and enables stable continuous casting in the continuous casting of high-Al steel or high-Ti steel. [Means for solving the problem]

[0007] One aspect of this disclosure is, It mainly contains CaO and Al2O3, The mass ratio (CaO / Al2O3) is 1.3 to 1.9. The total content of CaO and Al2O3 is 81.1% by mass or more. SiO20.0~2.0% by mass, Li2O 5.0% by mass or more, This invention relates to a mold powder characterized by containing F 4.0 to 16.0% by mass.

[0008] When mold powder according to one embodiment of this disclosure is used for continuous casting of high-Al steel or high-Ti steel, the reaction between the molten steel and the powder slag is suppressed, and the crystallization temperature is maintained below 1200°C, ensuring lubrication. As a result, the occurrence of constrained breakout is reduced, and stable continuous casting can be performed.

[0009] In one aspect of this disclosure, The crystals that crystallize in the slag film are mainly Ca 12 Al 14 F2O 32 Preferably, it is and / or LiAlO2.

[0010] As a result, a crystallization temperature of 1200°C or lower and slow cooling are compatible, the mold thermocouple temperature is stabilized, the occurrence of restrictive breakouts is reduced, and more stable continuous casting can be performed.

[0011] Another aspect of the present disclosure is A method for continuous casting of steel, characterized in that the mold powder of one aspect of the present disclosure is used for continuous casting of high-Al steel containing 0.3 mass% or more of Al or high-Ti steel containing 0.2 mass% or more of Ti.

[0012] The reaction between the molten steel and the powder slag is suppressed, and the crystallization temperature is maintained at 1200°C or lower to ensure lubrication, so the occurrence of restrictive breakouts is reduced and stable continuous casting can be performed.

Embodiments for Carrying out the Invention

[0013] Hereinafter, preferred embodiments of the present disclosure will be described in detail. Note that the embodiments described below do not unduly limit the content of the present disclosure described in the claims, and not all of the configurations described in the embodiments are essential as the solution means of the present disclosure.

[0014] The mold powder of the present embodiment contains CaO and Al2O3 as main components, the mass ratio (CaO / Al2O3) is 1.3 to 1.9, the total content of CaO and Al2O3 is 81.1 mass% or more, SiO2 0.0 to 2.0 mass%, Li2O 5.0 mass% or more, and F 4.0 to 16.0 mass%. When the mold powder of the present embodiment is used for continuous casting of high-Al steel or high-Ti steel, the reaction between the molten steel and the powder slag is suppressed, and the crystallization temperature is maintained at 1200°C or lower to ensure lubrication, so the occurrence of restrictive breakouts is reduced and stable continuous casting can be performed.

[0015] In this specification, the content (i.e., chemical composition) of each component of the mold powder is the amount converted to oxides in the molten state, and F is the sum of F separated from fluorides. For example, when the mold powder contains carbonate or carbon, the carbonate decomposes during melting, and the carbon oxidizes and is released into the atmosphere as carbon dioxide. Therefore, the carbon contained in the carbonate or carbon is not considered in the chemical composition of the mold powder. Also, when the mold powder contains CaF2, the Ca in CaF2 is converted to CaO, and is added to the CaO converted from the CaO and other Ca-containing compounds contained in the mold powder. The F is separated and added to the F of other fluorides.

[0016] <Mass ratio (CaO / Al2O3)> The mold powder of this embodiment contains CaO and Al2O3 as main components, and the mass ratio (CaO / Al2O3) is 1.3 to 1.9, preferably 1.3 to 1.8. When the mass ratio (CaO / Al2O3) is 1.0 or less, the crystallization temperature becomes high, and lubrication becomes insufficient due to the crystallization of crystals. Also, when the mass ratio (CaO / Al2O3) is 2.0 or more, the melting temperature and the crystallization temperature become high, which is not preferable.

[0017] <sio2> The mold powder in this embodiment contains 0.0 to 2.0% by mass of SiO2. This suppresses the reaction between the molten steel and the powder slag, reduces the occurrence of constrained breakouts, and enables stable continuous casting.

[0018] <li2o> The mold powder of this embodiment contains 5.0% by mass or more of Li2O, preferably 6.0% by mass or more. A Li2O content of 3.0% by mass or less is undesirable because it results in a high crystallization temperature. There is no particular upper limit to the Li2O content, but considering the cost, it is preferable to have 20.0% by mass or less, as the raw material is expensive.

[0019] <f> The mold powder of this embodiment contains 4.0 to 16.0% by mass of F, preferably 5.0 to 15.0% by mass. If the F content is 3.0% by mass or less, the melting temperature becomes high, which is undesirable. If the F content is 17.1% by mass or more, the crystallization temperature becomes high, which is also undesirable.

[0020] <Crystallized crystals> The crystals that crystallize in the slag film are mainly Ca 12 Al 14 F2O 32 Preferably, it is and / or LiAlO2. This allows for both a crystallization temperature of 1200°C or lower and slow cooling, stabilizing the mold thermocouple temperature, reducing the occurrence of constrained breakouts, and enabling more stable continuous casting. [Examples]

[0021] The embodiments of this disclosure will be described in detail below.

[0022] [Experimental Method] Table 1 shows the chemical composition of the mold powder used in the experiment. The content of each component in the chemical composition is calculated by converting the molten state of the mold powder to oxides, and F is the sum of fluoride after separating F. For example, if the mold powder contains carbonate, the carbonate decomposes during melting and is released into the atmosphere as carbon dioxide; therefore, the carbon contained in the carbonate is not considered in the chemical composition of the mold powder. [Table 1]

[0023] Experimental Examples 1-6 involve varying the mass ratio (CaO / Al2O3), with Experimental Examples 1-2 and 6 being comparative examples of the present disclosure, and Experimental Examples 3-5 being embodiments of the present disclosure. Experimental Examples 7-12 involve varying the Li2O content, with Experimental Example 7 being a comparative example of the present disclosure, and Experimental Examples 8-12 being embodiments of the present disclosure. Experimental Examples 13-19 involve varying the F content, with Experimental Examples 13 and 19 being comparative examples of the present disclosure, and Experimental Examples 14-18 being embodiments of the present disclosure.

[0024] For the mold powders of Experimental Examples 1 to 19, the mellowness, crystallization temperature, and crystallized crystals were measured and evaluated using the method described below.

[0025] <Melting> The meltability of the mold powder was evaluated by the change in its morphology before and after heating. Specifically, a test piece formed from 1.5g of mold powder into a cylindrical shape was placed on a carbon base and heated in an electric furnace at 1250°C for 5 minutes, after which its morphology was observed. If the test piece became liquid or droplet-like, it was evaluated as melted and usable (○), and if unmelted areas or surface irregularities were observed, it was evaluated as unusable (×).

[0026] <Crystallization temperature> The crystallization temperature of the mold powder was measured using differential thermal analysis. Specifically, approximately 120g of powder slag was melted in an electric furnace at 1300°C, a thermocouple was inserted into the powder slag, and the temperature of the powder slag was measured while the temperature was reduced at 4°C / min. The temperature at which exothermic reaction associated with crystallization began was defined as the crystallization temperature. If the crystallization temperature exceeded 1200°C, it was evaluated as unusable (×) due to concerns about insufficient lubrication caused by premature crystallization, while if the crystallization temperature was 1200°C or lower, it was evaluated as usable (〇).

[0027] <Crystallized crystals> Crystals crystallized in the slag film were identified by pouring 1350°C powder slag into a water-cooled copper trough, crushing the resulting slag film, and then using X-ray powder diffraction. Slag with high crystallization temperatures and difficulty in pouring was marked as unevaluable (-).

[0028] <Overall Rating> Evaluation of fusibility and crystallization temperature is available (○), and the precipitated crystal is mainly Ca 12 Al 14 F2O 32 and / or in the case of LiAlO2, the comprehensive evaluation was rated as passing (○). In other cases, that is, when the evaluation of fusibility is not available (×), the evaluation of crystallization temperature is not available (×), and the precipitated crystal is mainly Ca 12 Al 14 F2O 32 and it contains at least one of LiAlO2 due to non-evaluability or non-evaluability, the comprehensive evaluation was rated as failing (×).

[0029] [[ID=十六]][Measurement and evaluation results] The measurement and evaluation results of Experimental Examples 1 to 19 are shown in Table 1.

[0030] Among Experimental Examples 1 to 6 where the mass ratio (CaO / Al2O3) was changed, Experimental Examples 3 to 5 of the Examples were available for evaluation of fusibility and crystallization temperature (○), and the precipitated crystal was mainly Ca 12 Al 14 F2O 32 and the comprehensive evaluation was passing (○). On the other hand, Experimental Examples 1 and 6 of the Comparative Examples were not available for evaluation of fusibility (×), not available for evaluation of crystallization temperature (×), and not evaluable for precipitated crystal, and the comprehensive evaluation was failing (×). Also, Experimental Example 2 of the Comparative Examples was not available for evaluation of crystallization temperature (×), and the comprehensive evaluation was failing (×). When the mass ratio (CaO / Al2O3) is 1.0 or less, the crystallization temperature becomes high, and it is considered that lubrication is insufficient due to crystal precipitation. Also, when the mass ratio (CaO / Al2O3) is 2.0 or more, the melting temperature and crystallization temperature become high, which is considered unfavorable. Therefore, the mass ratio (CaO / Al2O3) is considered to be 1.2 to 1.9, preferably 1.3 to 1.8.

[0031] Among Experimental Examples 7 to 12 where the content of Li2O was changed, Experimental Examples 8 to 12 of the Examples were available for evaluation of fusibility and crystallization temperature (○), and the precipitated crystal was mainly Ca 12 Al 14 F2O 32 The product was and / or LiAlO2, and the overall evaluation was a pass (○). On the other hand, in comparative example 7, the evaluation of the crystallization temperature was unusable (×) and the evaluation of crystallized crystals was unusable, and the overall evaluation was a fail (×). When the Li2O content is 3.0 mass% or less, the crystallization temperature becomes high, which is considered undesirable. Therefore, the Li2O content is considered to be 5.0 mass% or more, and preferably 6.0 mass% or more.

[0032] Of the experimental examples 13-19 in which the F content was varied, in the examples 14-18, the evaluation of mellowability and crystallization temperature was usable (○), and the crystallized crystals were mainly Ca 12 Al 14 F2O 32 The substance was and / or LiAlO2, and the overall evaluation was a pass (○). On the other hand, in comparative example 13, the evaluation of mellowability was unusable (×) and the evaluation of crystallization was unusable, and in comparative example 19, the evaluation of crystallization temperature was unusable (×) and the evaluation of crystallization was unusable, and the overall evaluation for both was a fail (×). When the F content is 3.0 mass% or less, the melting temperature becomes high, which is considered undesirable. When the F content is 17.1 mass% or more, the crystallization temperature becomes high, which is considered undesirable. Therefore, the F content is considered to be 4.0 to 16.0 mass%, preferably 5.0 to 15.0 mass%.

[0033] Although this embodiment has been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novelty and effects of this disclosure. Therefore, all such modifications are included within the scope of this disclosure. For example, any term that appears in the specification at least once alongside a broader or synonymous term may be replaced with that different term anywhere in the specification.< / f>

Claims

1. CaO and Al ２ O ３ It contains as its main component, Mass ratio (CaO / Al ２ O ３ ) is between 1.3 and 1.9, CaO and Al ２ O ３ The total content is 81.1% by mass or more. SiO ２ 0.0–2.0% by mass Li ２ O 5.0% by mass or more, A mold powder characterized by containing F 4.0 to 16.0% by mass.

2. In the mold powder according to claim 1, The crystals that crystallize in the slag film are mainly Ca １２ Al １４ F ２ O ３２ and / or LiAlO ２ The mold powder is characterized by this.

3. A method for continuous casting steel, characterized in that the mold powder described in claim 1 or 2 is used for continuous casting of high-Al steel containing 0.3% by mass or more of Al, or high-Ti steel containing 0.2% by mass or more of Ti.

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