Mold Powder

Abstract

To provide a mold powder having a high basicity, capable of reducing a dissolution loss rate of an immersion nozzle while ensuring lubrication between a solidifying shell and a mold.SOLUTION: A mold powder mainly comprises SiO2 and CaO. A mass ratio (T.CaO / SiO2) of T.CaO (where T.CaO means that all Ca contained is converted to CaO) to SiO2 is between 1.7 or more and 2.0 or less; an Al2O3 content is 10.0 mass% or less (excluding zero); an MgO content is 5.0 mass% or more and 15.0 mass% or less; an Na2O content is 10.0 mass% or less (excluding zero); and an F content is 5.0 mass% or more and 15.0 mass% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a molding powder suitable for continuous casting of steel. [Background technology]

[0002] In continuous casting of steel, molten steel stored in a tundish is poured into a mold through an immersion nozzle to be cooled and solidified, while the solidified shell is continuously pulled downwards into the mold using rolls, thereby continuously producing cast pieces of various shapes such as slabs, blooms, and billets. Powdered or granular mold powder is poured onto the surface of the molten steel in the mold. The mold powder melts due to the heat of the molten steel (hereinafter, the molten mold powder is referred to as "powder slag") and covers the surface of the molten steel, and the powder slag flows between the solidified shell and the mold and is consumed. The main roles of the mold powder from the time it is poured until it is consumed are as follows: (1) To keep the surface of molten steel warm and prevent oxidation (2) Absorption of non-metallic inclusions that float to the surface of molten steel and purification of molten steel (3) Ensuring lubrication between the solidified shell and the mold (4) Control of heat flux from the solidified shell to the mold

[0003] In order to ensure lubrication between the solidified shell and the mold, it is preferable that the powder slag has a low viscosity. To achieve a low viscosity powder slag, the content of flux components can be increased or the basicity of the mold powder (SiO of CaO) can be increased. 2 Mass ratio (CaO / SiO 2 In either method, the powder line of the SEN melts quickly, and the SEN must be replaced more frequently. Continuous casting must be stopped during replacement, which reduces productivity.

[0004] Patent Document 1 discloses that the use of a submerged entry nozzle having a specific composition makes it possible to reduce the rate of erosion even when a mold powder with high basicity is used. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-159342 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, there is a demand for a mold powder that can reduce the rate of corrosion of the submerged entry nozzle without using the submerged entry nozzle with the specific composition disclosed in Patent Document 1 and that has a high basicity.

[0007] The present disclosure has been made in consideration of the above circumstances, and an object of the present disclosure is to provide a mold powder with high basicity that can reduce the rate of erosion of the submerged entry nozzle while ensuring lubrication between the solidified shell and the mold. [Means for solving the problem]

[0008] (1) One aspect of the present disclosure is SiO 2 and CaO as the main components, SiO of T.CaO (where T.CaO is the total Ca content converted to CaO) 2 Mass ratio (T.CaO / SiO 2 ) is 1.7 or more and 2.0 or less, Al 2 O 3 The content is 10.0 mass% or less (excluding zero), The content of MgO is 5.0% by mass or more and 15.0% by mass or less, Na 2 The content of O is 10.0 mass% or less (excluding zero), The present disclosure relates to a mold powder having an F content of 5.0% by mass or more and 15.0% by mass or less. By using the mold powder of the present disclosure, the high basicity ensures lubrication between the solidified shell and the mold, while reducing the rate of erosion of the submerged nozzle.

[0009] (2) In one aspect of the present disclosure, Li 2 The O content is preferably 4.0 mass% or less (excluding zero). 2 Adding O makes it easier to adjust the viscosity of the powder slag.

[0010] (3) In one aspect of the present disclosure, The content of SrO is preferably 10.0 mass % or less (excluding zero). Addition of SrO reduces the melting damage of the nozzle.

[0011] (4) In one aspect of the present disclosure, The viscosity at 1300°C is preferably 0.04 Pa·s or more and 0.20 Pa·s or less. The low viscosity of the powder slag can better ensure lubrication between the solidified shell and the mold. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] A preferred embodiment of the present invention will be described in detail below. Note that the embodiment described below does not unduly limit the content of the present invention described in the claims, and all of the configurations described in the embodiment are not necessarily essential as the solution of the present invention.

[0013] The mold powder of this embodiment is SiO 2 and CaO as the main components, and the total CaO (T.CaO is calculated by converting all the Ca contained in the SiO 2 Mass ratio (T.CaO / SiO 2 ) is 1.7 or more and 2.0 or less, and Al 2 O 3The content of is 10.0 mass% or less (excluding zero), the content of MgO is 5.0 mass% or more and 15.0 mass% or less, and Na 2 The content of O is 10.0 mass% or less (excluding zero), and the content of F is 5.0 mass% or more and 15.0 mass% or less. By using the mold powder of this embodiment, the high basicity ensures lubrication between the solidified shell and the mold, while reducing the rate of wear of the submerged nozzle.

[0014] [Raw materials] The mold powder of this embodiment can be obtained by adjusting the blending ratio of known raw materials.

[0015] SiO contained as a main component in the mold powder of this embodiment 2 The raw materials for CaO are not particularly limited as long as they are generally used for molding powders. 2 Substrate materials and silica materials can be used. CaO-SiO 2 Examples of the base material that can be used include portland cement, limestone, quicklime, synthetic calcium silicate, wollastonite, phosphorus slag, blast furnace slag, dicalcium silicate, calcium carbonate, etc. Examples of the silica raw material that can be used include silica sand, feldspar, silica stone, diatomaceous earth, perlite, fly ash, glass powder, silica fume, silica flower, etc.

[0016] The mold powder of this embodiment may contain, as the raw material of the subcomponent, those generally used in mold powders, for example, flux raw materials and / or other raw materials. The flux raw materials have the role of adjusting the softening point, viscosity and / or crystallization temperature, and for example, fluorides such as sodium fluoride, lithium fluoride, cryolite, fluorite (calcium fluoride), and magnesium fluoride, carbonates such as sodium carbonate, lithium carbonate, and magnesium carbonate, boric acid, borax, and colemanite can be used. Other raw materials include carbon raw materials, magnesia, alumina, and the like. Examples of carbon raw materials include coke, graphite, and carbon black, and adjust the melting speed of the mold powder. The mold powder of this embodiment contains a trace amount of Fe as an inevitable component. 2 O 3 , TiO 2 , MnO, Cr 2 O 3 , P 2 O 5 , S, etc.

[0017] [Mass ratio (T.CaO / SiO 2 )] The above raw materials are mixed appropriately and the mass ratio (T.CaO / SiO 2 ) is adjusted. Here, T.CaO refers to Ca contained in the molding powder of this embodiment, converted into CaO. For example, Ca originating from calcium carbonate, calcium fluoride, etc. is converted into CaO. The mass ratio (T.CaO / SiO 2 ) is 1.7 or more and 2.0 or less, preferably 1.8 or more and 1.9 or less. A powder slag with low viscosity suitable for ensuring lubrication can be obtained by high basicity. The content of T.CaO is not particularly limited, but is preferably 40.0 mass% or more and 50.0 mass% or less, more preferably 42.0 mass% or more and 47.0 mass% or less. SiO 2 The content is not particularly limited, but is preferably from 20.0 mass % to 30.0 mass %, and more preferably from 23.0 mass % to 27.0 mass %.

[0018] [Al2 O 3 ] The Al of the mold powder of this embodiment 2 O 3 The content of is 10.0 mass % or less (excluding zero), preferably 8.0 mass % or less, and more preferably 5.0 mass % or less. When it is in this range, the viscosity of the powder slug is easily adjusted.

[0019] [MgO] The MgO content of the molding powder of this embodiment is 5.0 mass% or more and 15.0 mass% or less, preferably 7.0 mass% or more and 13.0 mass% or less, and more preferably 8.0 mass% or more and 12.0 mass% or less. When it is in this range, the melting damage of the nozzle is reduced.

[0020] [Na 2 O] The Na of the mold powder of this embodiment 2 The content of O is 10.0 mass % or less (excluding zero), preferably 8.0 mass % or less, and more preferably 5.0 mass % or less. When it is in this range, the viscosity of the powder slag can be easily adjusted.

[0021] [F] The F content of the molding powder of this embodiment is 5.0 mass% or more and 15.0 mass% or less, preferably 6.0 mass% or more and 14.0 mass% or less, and more preferably 7.0 mass% or more and 13.0 mass% or less. When it is in this range, the viscosity of the powder slug is easily adjusted.

[0022] [Li 2 O] In the mold powder of this embodiment, Li 2 O can be used selectively. 2 Adding O makes it easier to adjust the viscosity of the powder slag. 2 There is no particular upper limit to the O content, but a content of 4.0 mass % or less is preferable because it makes it easier to adjust the viscosity.

[0023] [SrO] In the mold powder of this embodiment, SrO can be selectively used. Adding SrO reduces the melting damage of the nozzle. There is no particular upper limit to the content of SrO, but if it is 10.0 mass% or less, the melting damage of the nozzle is further reduced, which is preferable.

[0024] [viscosity] The viscosity of the molding powder of this embodiment is preferably 0.04 Pa·s or more and 0.20 Pa·s or less at 1300° C. In this range, the lubrication between the solidified shell and the mold is improved.

[0025] [Mold powder form] The form of the molding powder of this embodiment is not particularly limited as long as it is one generally used for molding powders. For example, powder, extrusion molding granules, hollow spray granules, stirring granules, etc. can be used. EXAMPLES

[0026] Hereinafter, examples of the present invention will be described in detail.

[0027] The compositions of the molding powders used in Examples 1 to 15 and Comparative Examples 1 to 8 are shown in Table 1. [Table 1]

[0028] The following measurements and evaluations were carried out using the molding powders of the examples and comparative examples.

[0029] [Erosion rate] The erosion rate of the submerged nozzle was evaluated for the mold powders of the examples and comparative examples. The erosion rate was measured using an erosion test by immersion method. That is, 20 kg of pig iron was melted in an air atmosphere using a high-frequency induction furnace and kept at 1560 ° C. 500 g of mold powder was added to the molten iron, and a test piece (25 × 25 × 200 mm) was immersed for 90 minutes while rotating at a rotation speed of 80 rpm, and the erosion thickness was measured compared to before the erosion test. A typical zirconia-carbon material (zirconia 90 mass%, carbon 10 mass%) was used for the test piece for the submerged nozzle. The mold powder was replaced every 30 minutes.

[0030] The corrosion rate was evaluated as excellent (◎) when the corrosion thickness was equivalent to that of Example 1, as good (◯) when it was slightly larger than that of Example 1 but did not cause operational problems, and as poor (×) when it was significantly larger than that of Example 1 and caused operational problems.

[0031] [Lubricity] The viscosity of the mold powder at 1300°C was measured using the platinum ball pulling method. That is, a platinum ball with a diameter of 10 mm was suspended in about 120 g of powder slug at 1300°C, and the resistance force when it was pulled up at a speed of 8.5 mm / s was measured, and the viscosity (η) (unit: Pa s) was calculated using the Stokes' equation.

[0032] Lubricity was evaluated as excellent (◎) when the viscosity at 1,300°C was between 0.05 Pa·s and 0.19 Pa·s, good (○) when it was 0.04 Pa·s or 0.20 Pa·s, and poor (×) when it was less than 0.04 Pa·s or more than 0.20 Pa·s.

[0033] [comprehensive evaluation] The overall evaluation was given as excellent (◎) when both the evaluation of the erosion rate and the evaluation of the lubricity were excellent (◎), as good (○) when neither the evaluation of the erosion rate nor the evaluation of the lubricity were poor (×) and at least one was good (○), and as poor (×) when at least one of the evaluation of the erosion rate and the evaluation of the lubricity was poor (×).

[0034] [Evaluation Results] The results of the measurements and evaluations are shown in Table 2. [Table 2]

[0035] In all of Examples 1 to 15, the rate of corrosion was small, and stable operation was possible.

[0036] In Comparative Examples 1 and 2, the immersion nozzle was significantly melted. This is believed to be because the MgO content was outside the range of 5.0 mass% or more and 15.0 mass% or less. In Comparative Examples 3 and 4, an appropriate viscosity was not obtained. The mass ratio (T.CaO / SiO 2 It is considered that the viscosity of the powder slag was too high or too low, which resulted in unstable operation. In Comparative Example 5, an appropriate viscosity was not obtained. 2 O 3 It is considered that the viscosity of the powder slag was too high, which caused the operation to become unstable. In Comparative Example 6, an appropriate viscosity was not obtained. 2 It is believed that the O content was out of the range of 10.0 mass% or less, the viscosity of the powder slag was too low, and the operation became unstable. In Comparative Examples 7 and 8, an appropriate viscosity was not obtained. It is believed that the F content was out of the range of 5.0 mass% or more and 15.0 mass% or less, the viscosity of the powder slag was too high or too low, and the operation became unstable.

[0037] Although the present embodiment has been described in detail as above, it will be easily understood by those skilled in the art that many modifications are possible without substantially departing from the novel matters and effects of the present invention. Therefore, all such modifications are included in the scope of the present invention. For example, a term described at least once in the specification together with a different term having a broader meaning or the same meaning may be replaced with that different term anywhere in the specification. Furthermore, the configuration and operation of the manufacturing apparatus, etc. of the present embodiment are not limited to those described in the present embodiment, and various modifications are possible.

Claims

1. SiO ２ and CaO as main components, T. CaO (where T.CaO is the total Ca content converted to CaO) SiO ２ Mass ratio (T.CaO / SiO ２ ) is 1.7 or more and 2.0 or less, A ２ O ３ The content is 10.0 mass% or less (excluding zero), The content of MgO is 5.0 mass% or more and 15.0 mass% or less, Na ２ The content of O is 10.0 mass% or less (excluding 1.5 mass% or less), A molding powder having an F content of 5.0 mass % or more and 15.0 mass % or less.

2. The molding powder according to claim 1, Li ２ A molding powder having an O content of 4.0 mass% or less (excluding zero).

3. The molding powder according to claim 1, A molding powder having a SrO content of 10.0 mass % or less (excluding zero).

4. The molding powder according to any one of claims 1 to 3, A molding powder having a viscosity at 1300°C of 0.04 Pa·s or more and 0.20 Pa·s or less.

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