Mold powder

Abstract

To provide a mold powder which contains glass powder as a silica raw material and can maintain good operability and steel quality without generating sintered masses or slag bears.SOLUTION: A mold powder contains, as main raw materials, a CaO-SiO2-based raw material and a silica raw material. The silica raw material contains glass powder, a content of the glass powder is 2.0 to 40.0 mass% and a particle size of the glass powder is less than 140 μm.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Continuous casting of steel is a process for continuously producing cast pieces of various shapes, such as slabs, blooms, and billets, by pouring molten steel stored in a tundish into a mold through an immersion nozzle, where it is cooled and solidified, while the solidified shell (solidified shell) is continuously drawn downward through the mold using rolls. Powdered or granular mold powder is added to the surface of the molten steel in the mold. The mold powder melts due to the heat received from the molten steel (molten mold powder is sometimes called "powder slag," but hereafter referred to as "molten slag"), forming a molten slag layer that covers the surface of the molten steel. The molten slag flows between the solidified shell and the mold, and is discharged and consumed alongside the solidified shell. The main roles of mold powder from the time it is added until it is consumed are as follows: (1) Heat retention of the molten steel surface (2) Prevention of oxidation on the surface of molten steel (3) Absorption of non-metallic inclusions that float up from the molten steel and purification of the molten steel (4) Ensuring lubrication between the solidified shell and the mold (5) Control of heat flux from the solidified shell to the mold

[0003] Mold powder is generally composed of CaO-SiO2 base material, silica material, flux material, and / or other materials, and the components and materials are designed and adjusted so that when poured onto the surface of molten steel in the mold, it will melt due to the heat it receives from the molten steel.If the selection, combination, or content of the raw materials is inappropriate, the melting properties will deteriorate, and sintered chunks or large, semi-molten chunks called slag bares may form at the contact point with the mold wall.

[0004] Sintered lumps and slag bears can significantly worsen operability by causing an insufficient molten slag layer, obstructing the flow of molten slag between the solidified shell and mold, insufficient heat retention due to exposed slag, abnormal flames due to gas escape, breakouts, etc. Furthermore, they can cause inclusion defects, cracks on the surface of the cast slab, etc., which can have a negative impact on steel quality. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2023-114110 Summary of the Invention [Problem to be solved by the invention]

[0006] The CaO-SiO2 base material for mold powder is generally composed of minerals with relatively high melting points, such as tricalcium silicate, dicalcium silicate, and wollastonite. Patent Document 1, on the other hand, discloses glass powder as an example of a silica material for mold powder. Because glass powder has a relatively low melting temperature of approximately 800°C, it acts as a melting accelerator for mold powder. However, when the melting temperatures of the raw materials differ significantly, the proportion of a semi-molten layer, in which liquid and unmelted raw materials coexist, increases, which can result in sintered chunks or slag bears. Patent Document 1, however, does not disclose an appropriate method for incorporating glass powder.

[0007] The present disclosure has been made in consideration of the above-described circumstances, and an object of the present disclosure is to provide a molding powder that contains glass powder as a silica raw material but does not generate sintered lumps or slag bears, and can maintain good operability and steel quality. [Means for solving the problem]

[0008] One aspect of the present disclosure is The main raw materials include CaO-SiO2 base material and silica raw material, The silica raw material contains glass powder, The content of the glass powder is 2.0 to 40.0 mass %, The mold powder is characterized in that the particle size of the glass powder is less than 140 μm.

[0009] By using the mold powder according to one embodiment of the present disclosure in the continuous casting of steel, sintered lumps and slag bears are not generated even though the mold powder contains glass powder as a silica raw material, and therefore operability and steel quality can be maintained at a good level. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present disclosure will be described in detail below. 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 necessarily essential as means for solving the problems of the present disclosure.

[0011] The molding powder of this embodiment contains a CaO-SiO2 substrate raw material and a silica raw material as main raw materials, and the silica raw material contains glass powder, the content of the glass powder is 2.0 to 40.0 mass %, and the particle size of the glass powder is less than 140 μm. By using the molding powder of this embodiment in continuous casting of steel, sintered chunks and slag bears are not generated despite the inclusion of glass powder as the silica raw material, and therefore operability and steel quality can be maintained at a good level.

[0012] <Main raw materials> The CaO-SiO2 base material is not particularly limited as long as it is one that is generally used in mold powders, and examples thereof include portland cement, limestone, quicklime, synthetic calcium silicate, wollastonite, phosphorus slag, blast furnace slag, and dicalcium silicate. The CaO-SiO2 base material supplies the main components CaO and SiO2. The silica raw materials other than glass powder are not particularly limited as long as they are one that is generally used in mold powders, and examples thereof include silica sand, feldspar, silica stone, diatomaceous earth, perlite, fly ash, silica fume, and silica flour. The silica raw material adjusts the mass ratio (CaO / SiO2) of the mold powder.

[0013] <Glass powder> The content of the glass powder is 2.0 to 40.0% by mass, and more preferably 2.5 to 39.0% by mass. If the content of the glass powder is less than 2.0% by mass, the melting-promoting effect is not obtained and melting delay may occur, which is not preferable. On the other hand, if the content of the glass powder exceeds 40.0% by mass, melting may be excessively promoted, which may cause sintered lumps or slag bares, which is not preferable.

[0014] The particle size of the glass powder is less than 140 μm, and more preferably less than 110 μm. If the particle size of the glass powder is 140 μm or more, the proportion of localized pre-melting increases, which may deteriorate the melting properties, and is therefore undesirable. In this specification, a particle size of less than x μm means that the powder passed through a sieve with openings of x μm, and a particle size of x μm or more means that the powder did not pass through a sieve with openings of x μm.

[0015] The form of the glass powder is not particularly limited as long as it is one generally used for molding powder, and examples thereof include powder, extrusion molding granules, hollow spray granules, and agitation granulation. Powdered molding powder is obtained by mixing raw materials such as a CaO-SiO2 substrate raw material and a silica raw material in a mixer. Granular molding powder is further molded by adding a binder or the like as appropriate, using a spray granulation method, an extrusion molding method, an agitation granulation method, or the like.

[0016] The type of glass powder is not particularly limited, but recycled glass powder is preferred from the viewpoint of environmental protection, and waste glass from photovoltaic panels (PV) (hereinafter referred to as solar panel glass) is particularly preferred. This reduces the consumption of fossil fuels, minerals, etc., and the emission of CO2, industrial waste, etc. Solar panel glass is separated from PV and used as a raw material after undergoing processes such as sorting, crushing, and classification. Solar panel glass is broadly classified into soda glass and borosilicate glass, and both can be used as silica raw materials for molding powder. Soda glass contains, for example, 68 to 75 mass% SiO2, 0 to 5 mass% Al2O3, 5 to 15 mass% CaO, 1 to 8 mass% MgO, and 11 to 18 mass% Na2O. Borosilicate glass contains, for example, 30 to 50 mass % of SiO2, 5 to 15 mass % of Al2O3, 5 to 15 mass % of CaO, 0 to 8 mass % of MgO, 5 to 15 mass % of B2O3, and 5 to 15 mass % of SrO.

[0017] <Auxiliary raw materials> The auxiliary materials other than the main materials are not particularly limited as long as they are generally used in mold powders, and examples thereof include flux materials, carbon materials, magnesia, and alumina. Examples of flux materials include fluoride salts such as sodium fluoride, lithium fluoride, cryolite, fluorite (calcium fluoride), and magnesium fluoride; carbonates such as sodium carbonate, lithium carbonate, potassium carbonate, manganese carbonate, aluminum carbonate, magnesium carbonate, and strontium carbonate; and boron materials such as boric acid, borax, and colemanite, which adjust the softening point, viscosity, and solidification temperature of the mold powder. Examples of carbon materials include coke, graphite, and carbon black, which adjust the melting rate of the mold powder. The mold powder of this embodiment may contain a heat-generating material (reducing agent) such as a metal or alloy, such as Si, Al, or Ca-Si, to improve heat retention. When these heat-generating materials are included, an oxidizing agent may also be included to promote the reaction. [Example]

[0018] Hereinafter, examples of the present disclosure will be described in detail.

[0019] <Sample production> The CaO-SiO2 substrate raw material, silica raw material (excluding glass powder), glass powder, and auxiliary raw materials were mixed in a mixer to obtain mold powder. Solar panel glass was used as the glass powder. 1.5 g of mold powder was weighed and formed into a cylindrical briquette with an outer diameter of 10 mm using a briquetting machine to prepare a sample. The composition of the mold powder raw materials is shown in Tables 1 and 2. [Table 1] [Table 2]

[0020] In Examples 1 to 3 and Comparative Examples 1 to 4 (Table 1), solar panel glass made of soda glass was used as the glass powder. Examples 1 to 3 are examples of the present invention. In Comparative Examples 1 and 2, the soda glass content is lower than the range of the present invention, and in Comparative Example 3, the soda glass content is higher than the range of the present invention. The particle size of the soda glass in Examples 1 to 3 and Comparative Examples 1 to 3 is less than 140 μm. In Comparative Example 4, the raw materials were blended in the same manner as in Example 2, except that the particle size of the soda glass was 140 μm or more. Note that glass powder with a particle size less than 140 μm passed through a sieve with a mesh size of 140 μm, and glass powder with a particle size of 140 μm or more did not pass through a sieve with a mesh size of 140 μm (the same applies hereinafter). In Examples 1 to 3 and Comparative Examples 1 to 4, the raw materials were adjusted so that the chemical compositions were the same.

[0021] In Examples 4 to 6 and Comparative Examples 5 to 8 (Table 2), solar panel glass made of borosilicate glass was used as the glass powder. Examples 4 to 6 are Examples of the present invention. In Comparative Examples 5 and 6, the content of borosilicate glass is lower than the range of the present invention, and in Comparative Example 7, the content of borosilicate glass is higher than the range of the present invention. The particle size of the borosilicate glass in Examples 4 to 6 and Comparative Examples 4 to 7 is less than 140 μm. In Comparative Example 8, the raw materials were blended in the same manner as in Example 5, except that the particle size of the borosilicate glass was 140 μm or more. The raw materials were adjusted so that Examples 4 to 6 and Comparative Examples 5 to 8 had the same chemical composition.

[0022] <Measurement and evaluation methods> The obtained samples were subjected to the following measurements and evaluations.

[0023] The sample was inserted into a furnace capable of observing its melting state, such as a ring furnace with a high-purity silicon carbide heating element, and the melting state of the sample was observed while the temperature was raised at a rate of 5°C / min. The temperature at which the cylindrical shape was clearly distorted and deformed due to melting was taken as the softening point, and the temperature at which the sample became completely liquid like a droplet was taken as the melting temperature. The melting temperature range was calculated from the difference between these two values.

[0024] The shorter the melting temperature range, i.e., the closer the softening point and melting temperature, the faster the mold powder softens and melts, making it less likely to produce sintered lumps or slag bears, which is preferable. Therefore, the melting property of the mold powder was evaluated as excellent (◎) when the melting temperature range was 20°C or less, fair (〇) when it was 21 to 30°C, and poor (×) when it was 31°C or more.

[0025] <Measurement and evaluation results> The measurement and evaluation results are shown in Tables 1 and 2.

[0026] As can be seen from Table 1, Examples 1 to 3 had a short melting temperature interval and exhibited good meltability. On the other hand, Comparative Examples 1 and 2, which contained a small amount of soda glass, had a high melting temperature and a long melting temperature interval, resulting in poor meltability (×). Comparative Example 3, which contained a large amount of soda glass, had an excessively low softening point and a long melting temperature interval, resulting in poor meltability (×). Comparative Example 4, which contained a large particle size of soda glass, also had a long melting temperature interval and exhibited poor meltability (×).

[0027] In Examples 4 to 6 and Comparative Examples 5 to 8 (Table 2), solar panel glass made of borosilicate glass was used as the glass powder, but showed the same tendency as when soda-lime glass was used (Table 1). That is, Examples 4 to 6 had a short melting temperature range and showed good meltability. On the other hand, Comparative Examples 5 and 6, which had a low content of borosilicate glass, had high softening points and melting temperatures, and a long melting temperature range, resulting in poor meltability (×). Comparative Example 7, which had a high content of borosilicate glass, had an excessively low softening point, a long melting temperature range, and poor meltability (×). Comparative Example 4, which had a large particle size of borosilicate glass, also had a long melting temperature range and poor meltability (×).

[0028] In Comparative Examples 1 to 2 and 5 to 6, where the glass powder content is less than 2.0 mass%, the melting-promoting effect of the glass powder is not obtained, and melting delay is thought to occur. In Comparative Examples 3 and 7, where the glass powder content is more than 40.0 mass%, melting is excessively promoted, and sintered lumps and slag bares are thought to occur. Therefore, the glass powder content is preferably 2.0 to 40.0 mass%, and more preferably 2.5 to 39.0 mass%. Furthermore, in Comparative Examples 4 and 8, where the glass powder particle size is 140 μm or more, the proportion of localized pre-melting increases, and melting properties are thought to deteriorate. Therefore, the particle size of the glass powder is preferably less than 140 μm, and more preferably less than 110 μm.

[0029] Although the present 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 novel features and advantages of the present disclosure. Therefore, all such modifications are included within the scope of the present disclosure. For example, a term described at least once in the specification together with a different term having a broader or equivalent meaning may be replaced with that different term anywhere in the specification. Furthermore, the configuration and operation of the manufacturing apparatus and the like of the present embodiment are not limited to those described in the present embodiment, and various modifications are possible.

Claims

[Claim 1] The main raw material is CaO-SiO ２ a substrate raw material and a silica raw material; The silica raw material contains glass powder, The content of the glass powder is 2.0 to 40.0 mass %, The mold powder is characterized in that the particle size of the glass powder is less than 140 μm.

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