Mold Powder

Abstract

To provide a mold powder allowing for suppressing the change of characteristics due to moisture absorption and enabling stable continuous casting of steel.SOLUTION: A mold powder comprises a main material and a sub-material, the sub-material containing a carbon material and oxidant, and the oxidant containing calcium peroxide.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to mold powders 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 drawn 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 mold powder in a molten state is referred to as "molten slag"), forming a molten slag layer that covers the surface of the molten steel, and the molten slag flows between the solidified shell and the mold and is discharged in parallel with the solidified shell. The main functions of the mold powder from the time it is poured in until it is discharged are as follows: (1) Keeping the surface of molten steel in the mold warm (2) Preventing reoxidation of molten steel (3) Absorption of non-metallic inclusions that float to the surface of molten steel and purification of molten steel (4) Maintaining lubrication between the solidified shell and the mold (5) Control of heat flux from the solidified shell to the mold

[0003] High-speed casting is being promoted to improve productivity of continuous casting. In high-speed casting, maintaining lubrication between the solidified shell and the mold is particularly important. For this reason, the added mold powder needs to melt quickly and flow into the gap between the solidified shell and the mold. On the other hand, if the mold powder melts, flows into the gap between the solidified shell and the mold, and is discharged too quickly, the molten slag layer becomes thin, and defects such as unmelted mold powder being entrained in the molten steel may occur.

[0004] Therefore, carbon raw materials are used to adjust the melting speed of the mold powder. Patent Document 1 discloses that in order to quickly realize the function of the mold powder, sodium nitrate is added to the mold powder as a combustion improver (oxidizer) for the carbon raw material, and the carbon raw material is used as a heat source. Patent Document 2 discloses that reducing the content of the carbon raw material in the mold powder increases the melting speed, and increasing the content of the carbon raw material decreases the melting speed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-078035 A [Patent Document 2] WO2020 / 246498A1 Summary of the Invention [Problem to be solved by the invention]

[0006] However, nitrates are deliquescent and hygroscopic, so they can solidify when exposed to moisture. Solidified nitrates have a reduced ability to function as an oxidizer. Furthermore, mold powders containing solidified nitrates have reduced dispersibility, which can cause localized uneven melting and promote the formation of slag rim.

[0007] In addition, if the content of carbon raw materials in the mold powder is reduced, the mold powder becomes more susceptible to sintering, and its melting property may worsen. As a result, slag rim (slag bear) may occur in the mold, which may hinder stable continuous casting of steel.

[0008] The present disclosure has been made in view of the above circumstances, and has an object to provide a molding powder that suppresses changes in properties due to moisture absorption and enables stable continuous casting of steel. Another object is to provide a molding powder that enables stable continuous casting of steel by promoting sinterability and suppressing deterioration of meltability even when the carbon raw material content is reduced. [Means for solving the problem]

[0009] One aspect of the present disclosure is Contains main ingredients and auxiliary ingredients, The auxiliary raw material includes a carbon raw material and an oxidizing agent, The molding powder is characterized in that the oxidizing agent contains calcium peroxide.

[0010] Because calcium peroxide is not hygroscopic, it is possible to suppress changes in the properties of the mold powder due to moisture absorption, and the mold powder quickly melts and exerts its function due to the oxidation and exothermic reaction between calcium peroxide and the carbon raw material, resulting in stable continuous casting of steel.

[0011] In one aspect of the present disclosure, The content of calcium peroxide is preferably 0.05% by mass or more and 10.0% by mass or less.

[0012] This allows for a good balance between the melting rate and sinterability of the mold powder. In addition, calcium peroxide is not hygroscopic, so changes in the mold powder properties due to moisture absorption can be suppressed. As a result, stable continuous casting of steel is possible, and the quality of the cast pieces can be improved.

[0013] In one aspect of the present disclosure, The content of the carbon raw material is more preferably 0.5% by mass or more and 12.0% by mass or less.

[0014] Even if the carbon raw material content is reduced, a favorable balance between the melting rate and sinterability of the mold powder can be achieved, resulting in stable continuous casting of steel. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A preferred embodiment of the present disclosure will be described in detail below. Note that the embodiment described below does not unduly limit the contents of the present disclosure described in the claims, and all of the configurations described in the embodiment are not necessarily essential as a means for solving the problems of the present disclosure.

[0016] The molding powder of this embodiment includes a main raw material and an auxiliary raw material, the auxiliary raw material includes a carbon raw material and an oxidizing agent, and the oxidizing agent includes calcium peroxide. Since calcium peroxide is not hygroscopic, it is possible to suppress changes in the properties of the molding powder due to moisture absorption, and the molding powder melts early due to the oxidation and exothermic reaction between calcium peroxide and the carbon raw material, thereby exhibiting its function, and as a result, it is possible to stably continuously cast steel.

[0017] <Main raw materials> The main raw material contained in the mold powder of this embodiment is CaO SiO 2 There are no particular limitations as long as the raw material is of high quality, and examples that can be used include Portland cement, limestone, quicklime, calcium silicate, synthetic calcium silicate, wollastonite, phosphorus slag, blast furnace slag, dicalcium silicate, calcium carbonate, silica sand, feldspar, silica stone, diatomaceous earth, perlite, fly ash, glass powder, silica fume, and silica flower. 2 Mass ratio (CaO / SiO 2 ) is not particularly limited as long as it is one generally used in molding powders.

[0018] <Carbon raw materials> The carbon raw material contained in the mold powder of this embodiment is not particularly limited as long as it is generally used in mold powders, and for example, coke, graphite, carbon black, etc. can be used. The carbon raw material has a function of adjusting the melting speed of the mold powder and a function of generating heat. The content of the carbon raw material is preferably 0.3 mass% or more and 15.0 mass% or less, more preferably 0.5 mass% or more and 12.0 mass% or less, even more preferably 0.8 mass% or more and 10.0 mass% or less, and particularly preferably 0.8 mass% or more and 7.3 mass% or less. Even if the content of the carbon raw material is reduced, the melting speed and sinterability can be favorably balanced, and as a result, stable continuous casting of steel is possible.

[0019] <Calcium peroxide> The calcium peroxide contained in the mold powder of this embodiment oxidizes the carbon raw material and generates heat to promote the melting of the mold powder. The calcium peroxide may be a pure substance, or may be a preparation to which an auxiliary component is added, which is safer and easier to handle, and commercially available reagents or industrial chemicals can be used. The content of calcium peroxide is preferably 0.05% by mass or more and 10.0% by mass or less, more preferably 0.1% by mass or more and 7.0% by mass or less, and even more preferably 0.5% by mass or more and 5.0% by mass or less. This allows for a good balance between the melting rate and the sinterability. In addition, since calcium peroxide does not have hygroscopicity, it is possible to suppress changes in the characteristics of the mold powder due to moisture absorption. As a result, stable continuous casting of steel is possible, and the quality of the cast slab can be improved. The content of calcium peroxide when added in the form of a preparation is calculated based on the pure content of calcium peroxide excluding the auxiliary components.

[0020] <Other auxiliary ingredients> The molding powder of this embodiment may use, as auxiliary raw materials, an oxidizing agent, a flux raw material, and / or other raw materials that are generally used in molding powders.

[0021] As an oxidizing agent other than calcium peroxide, iron oxide may be used, and lithium peroxide, potassium permanganate, barium permanganate, various manganese oxides, cobalt oxide, nickel oxide, etc., which have low hygroscopicity, may also be used. The total content of the oxidizing agents is preferably 0.05% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less. This can further enhance the heat generating effect and can also reduce the mass ratio (CaO / SiO 2 ) is not affected, so composition design can be easily carried out.

[0022] Flux raw materials have the function of adjusting the softening point, viscosity, and crystallization temperature. For example, fluorides such as sodium fluoride, lithium fluoride, potassium fluoride, cryolite, fluorspar (calcium fluoride), and magnesium fluoride, carbonates such as sodium carbonate, lithium carbonate, potassium carbonate, magnesium carbonate, strontium carbonate, and barium carbonate, boric acid, borax, and colemanite can be used. Other raw materials that can be used include magnesia, alumina, and TiO depending on the required performance. 2 , MnO, Cr 2 O 3 , ZrO 2 Also, a small amount of Fe may be used as an inevitable component. 2 O 3 , P 2 O 5 , S, etc. may be included.

[0023] <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

[0024] Hereinafter, embodiments of the present disclosure will be described in detail.

[0025] <Sample> The compositions of the mold powder samples are shown in Tables 1 to 6. [Table 1] [Table 2] [Table 3] [Table 4] [Table 5] [Table 6]

[0026] Samples No. 1-1 to 1-9 (Table 1), Samples No. 2-1 to 2-9 (Table 2), Samples No. 3-1 to 3-9 (Table 3), Samples No. 4-1 to 4-9 (Table 4), Samples No. 5-1 to 5-9 (Table 5), and Samples No. 6-1 to 6-9 (Table 6) were designated as Series 1 to 6, respectively. Samples No. 1-1, 2-1 to 6-1 of each series were used without an oxidizing agent and were the reference samples of each series. Samples No. 1-2, 2-2 to 6-2 of each series were used as an oxidizing agent with fresh sodium nitrate (referred to as nitrate in the table) immediately after opening the moisture-proof packaging, and Samples No. 1-3, 2-3 to 6-3 were used as an oxidizing agent with sodium nitrate (referred to as solidified nitrate in the table) left in the air for two months after opening. Samples No. 1-1 to 1-3, 2-1 to 2-3, 6-1 to 6-3 are comparative examples for each series. Samples No. 1-4 to 1-9, 2-4 to 2-9, 6-4 to 6-9 are working examples for each series, and calcium peroxide that had been left in the air for two months after opening was used as the oxidizing agent. The main raw materials other than the oxidizing agent were CaO SiO 2Carbon raw materials, fluoride, carbonate, magnesia and alumina were used as the raw materials and auxiliary raw materials. In series 1 to 6, the content of the carbon raw material was fixed at 0.5 mass%, 0.8 mass%, 2.5 mass%, 7.3 mass%, 10.0 mass% and 12.0 mass%, respectively, and the content of calcium peroxide was changed. All raw materials were used in powder form.

[0027] Each sample was evaluated for moisture absorption, sinterability, and melting time as shown below (except for the reference sample that did not contain an oxidizing agent).

[0028] <Hygroscopicity> The samples were left in the air at room temperature for three days, and then the moisture content was measured using a heat-drying moisture meter. The moisture absorption of the samples was evaluated as follows: if the moisture content was 0.2% or less by mass, it was excellent (◎); if it was more than 0.2% and less than 0.5% by mass, it was good (○); if it was more than 0.5% and less than 0.9% by mass, it was fair (△); and if it was more than 0.9%, it was poor (×).

[0029] <Sinterability> 20 kg of pig iron was melted in a high-frequency induction furnace and maintained at 1500℃, and 400 g of the sample was scattered on the molten iron and visually confirmed for the presence or absence of sintering. The sinterability of the sample was evaluated as excellent (◎) if no sintered lumps were formed, fair (△) if sintered lumps of 3 cm or less were formed, and poor (×) if sintered lumps of more than 3 cm were formed.

[0030] <Melting time> A crucible filled with 1.5 g of sample was inserted into an electric furnace at 1300°C, and the time until the sample was completely melted was measured by visual inspection. A longer or shorter melting time indicates a slower or faster formation of the molten slag layer.

[0031] The melting time of a sample was evaluated as excellent (◎) if it was 30 seconds or more shorter than the reference sample of the same series, as good (◯) if it was 5 seconds or more but less than 30 seconds shorter, as acceptable (△) if it was less than 5 seconds shorter or less than 5 seconds longer, and as unacceptable (×) if it was 5 seconds or more longer.

[0032] <Overall rating> The overall evaluation was as follows: excellent (◎) if the evaluation of melting rate, sinterability, and moisture absorption was all excellent (◎) or good (○); good (○) if there was one fair (△) and the others were excellent (◎) or good (○); and poor (×) if there was one or more poor (×) or two or more fair (△) ratings.

[0033] <Evaluation Results> The evaluation results are shown in Tables 1 to 6.

[0034] From Table 1, the sinterability of the examples in Series 1 was fair (△), and although there was some sintering, the overall evaluations were all good (◯), and there was no practical problem. From Tables 2 and 3, the overall evaluations of the examples in Series 2 and 3 were all excellent (◎), and the results were good. From Table 4, the melting times of the examples in Series 4, Sample No. 4-4 containing 0.1 mass% calcium peroxide and Sample No. 4-9 containing 7.0 mass% calcium peroxide, were fair (△), but the overall evaluations were all excellent (◎) or good (◯), and there was a good result. From Table 5, the overall evaluations of the examples in Series 5 were all excellent (◎), and there was a good result. From Table 6, the melting times of the examples in Series 6 were fair (△), but the overall evaluations were all good (◯), and there was no practical problem.

[0035] From Tables 1 to 6, the content of calcium peroxide is preferably 0.05% by mass or more and 10.0% by mass or less, more preferably 0.1% by mass or more and 7.0% by mass or less, and even more preferably 0.5% by mass or more and 5.0% by mass or less. It is considered that it was possible to achieve a good balance between melting speed and sinterability, and that since calcium peroxide is not hygroscopic, it was possible to suppress changes in the properties of the mold powder due to moisture absorption. As a result, it became possible to perform stable continuous casting of steel, and the quality of the cast slabs was improved.

[0036] From Tables 1 to 6, the content of the carbon raw material is preferably 0.3 mass% or more and 15.0 mass% or less, more preferably 0.5 mass% or more and 12.0 mass% or less, further preferably 0.8 mass% or more and 10.0 mass% or less, and particularly preferably 0.8 mass% or more and 7.3 mass% or less. It is considered that even if the content of the carbon raw material is reduced, it is possible to achieve a good balance between the melting rate and the sinterability. As a result, it is possible to stably continuously cast steel and improve the quality of the cast slab.

[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 disclosure. Therefore, all such modifications are included in 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 meaning or the same meaning may be replaced with that different term anywhere in the specification. In addition, 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

[Claim 1] Contains main ingredients and auxiliary ingredients, The auxiliary raw material includes a carbon raw material and an oxidizing agent, the oxidizing agent comprises calcium peroxide; The content of the calcium peroxide is 0.05% by mass or more and 10.0% by mass or less, The mold powder is characterized in that the content of the carbon raw material is 0.5 mass % or more and 12.0 mass % or less.

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