Heat-generating front powder

Abstract

To provide an exothermic front powder even when stored for a long time, that is not solidified due to moisture, does not deteriorate the function as an oxidizing agent, supplies rapidly heat to a molten steel surface and forms a molten slag layer at a start of continuous casting, and can improve slab quality.SOLUTION: The exothermic front powder contains a base material, a metal or metal alloy and an oxidizing agent, and the oxidizing agent includes calcium peroxide.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to an exothermic front 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 drawn downwards through 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 the 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 and consumed in parallel with the solidified shell. 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] At the start of continuous casting, the molten steel is poured into a cooled mold, so the temperature of the molten steel surface drops, and for example, solidified steel (deckles) may form on the molten steel surface. In addition, the mold powder does not melt smoothly, and the above roles (1) to (4) are not fully fulfilled, and for example, inclusions and bubbles floating up from the molten steel may be captured in the solidified shell, resulting in inclusion defects and pinhole defects.

[0004] To solve the above problems, mold powder containing metal and oxidizer (exothermic front powder) is used at the start of casting. The exothermic front powder supplies heat to the molten steel surface through the exothermic reaction between the metal and oxidizer, and also melts quickly to form a molten slag layer.

[0005] Patent Document 1 discloses an exothermic front powder for continuous casting that contains 3 to 20 mass % of a metal or alloy and 3 to 15 mass % of an alkali metal nitrate. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-136766 A Summary of the Invention [Problem to be solved by the invention]

[0007] The nitrates disclosed in Patent Document 1 are useful as oxidizing agents. However, since nitrates are deliquescent and hygroscopic, they may solidify due to moisture during storage. The exothermic front powder containing solidified nitrates has reduced dispersibility and its function as an oxidizing agent is reduced. This can lead to insufficient heat supply to the molten steel surface and insufficient molten slag layer, which can lead to deterioration of slab quality, such as increased restraint breakouts and inclusion defects.

[0008] The present disclosure has been made in consideration of the above-mentioned circumstances, and has an object to provide an exothermic front powder that does not solidify due to moisture even when stored for a long period of time, does not lose its function as an oxidizing agent, and quickly supplies heat to the surface of molten steel at the start of continuous casting and quickly forms a molten slag layer, thereby improving the quality of the cast strand. [Means for solving the problem]

[0009] One aspect of the present disclosure is A substrate, a metal or alloy, and an oxidizing agent, The present invention relates to an exothermic front powder, characterized in that the oxidizing agent contains calcium peroxide.

[0010] When the exothermic front powder disclosed herein is used, it does not solidify due to moisture even when stored for a long time, its function as an oxidizing agent does not decrease, and the supply of heat to the molten steel surface and the formation of a molten slag layer at the start of continuous casting are rapid, thereby improving the quality of the cast piece.

[0011] In one aspect of the present disclosure, The content of calcium peroxide is preferably 2.5% by mass or more and 15.0% by mass or less.

[0012] In one aspect of the present disclosure, It is preferable that the metal or alloy is one or more selected from the group consisting of Si, Al, Ca-Si, Al-Mg, Al-Ca-Mg, and Fe-Si, and the total content of the metal or alloy is 5.0 mass% or more and 20.0 mass% or less. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] 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.

[0014] The exothermic front powder of the present embodiment includes a base material, a metal or alloy, and an oxidizer, the oxidizer including calcium peroxide. When the exothermic front powder of the present embodiment is used, it does not solidify due to moisture even when stored for a long time, its function as an oxidizer does not decrease, and the supply of heat to the molten steel surface and the formation of a molten slag layer at the start of continuous casting are rapid, thereby improving the quality of the cast slab.

[0015] <Base material> The base material contained in the exothermic front powder of this embodiment is not particularly limited as long as it is a CaO·SiO2-based raw material generally used in mold powders, and examples thereof 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, silica flower, etc. The mass ratio of CaO to SiO2 (CaO / SiO2) is not particularly limited as long as it is generally used in mold powders.

[0016] <Metal or alloy> The metal or alloy contained in the exothermic front powder of this embodiment functions as a heat generating material (reducing agent), and is preferably at least one selected from the group consisting of Si, Al, Ca-Si, Al-Mg, Al-Ca-Mg, and Fe-Si. The total content of the metal or alloy is preferably 5.0% by mass or more and 20.0% by mass or less, more preferably 5.0% by mass or more and 18.0% by mass or less, and even more preferably 6.0% by mass or more and 15.0% by mass or less. When the content is within a suitable range, the heat generation amount can be maximized.

[0017] <Oxidizing agent> The calcium peroxide contained in the exothermic front powder of this embodiment functions as an oxidizing agent, and may be a pure substance or a preparation with added subcomponents that is safer and easier to handle. Various commercially available calcium peroxide preparations can be used. By using calcium peroxide as an oxidizing agent, it is possible to prevent the oxidizing agent from losing its function due to moisture absorption. The calcium peroxide content is preferably 2.5% by mass or more and 15.0% by mass or less, more preferably 2.5% by mass or more and 14.0% by mass or less, and even more preferably 3.0% by mass or more and 13.0% by mass or less. Within the preferred range of content, the function as an oxidizing agent and the amount of heat generated can be maximized.

[0018] The exothermic front powder of this embodiment may contain iron oxide as an oxidizing agent other than calcium peroxide, and may further contain lithium peroxide, potassium permanganate, barium permanganate, various manganese oxides, cobalt oxide, nickel oxide, etc., which have low hygroscopicity. The total content of the oxidizing agent is preferably 2.5% by mass or more and 23.0% by mass or less, more preferably 2.5% by mass or more and 22.0% by mass or less, and even more preferably 3.0% by mass or more and 21.0% by mass or less. This can further enhance the exothermic effect, and since the mass ratio (CaO / SiO2) is not affected, the composition can be easily designed.

[0019] <Secondary ingredients> The exothermic front powder of this embodiment may contain, as a secondary component, a flux raw material, a carbon raw material, and / or other raw materials generally used in mold powders. The flux raw material has a role of adjusting the softening point, viscosity, and / or crystallization temperature, and can be, for example, fluoride salts such as sodium fluoride, lithium fluoride, cryolite, fluorite (calcium fluoride), and magnesium fluoride, carbonates such as sodium carbonate, lithium carbonate, magnesium carbonate, manganese carbonate, aluminum carbonate, and magnesium carbonate, boric acid, borax, colemanite, etc. The carbon raw material has a role of adjusting the slagification rate of the exothermic front powder, and can be, for example, coke, graphite, carbon black, etc. Other raw materials can be used, such as magnesia and alumina.

[0020] <Form> The form of the exothermic front powder of this embodiment is not particularly limited as long as it is one that is generally used for molding powders, and for example, powder, extrusion molding granules, hollow spray granules, stirring granules, etc. can be used. EXAMPLES

[0021] Hereinafter, embodiments of the present disclosure will be described in detail.

[0022] <Sample> The compositions of each sample of the heat-generating front powder are shown in Tables 1 to 5. [Table 1] [Table 2] [Table 3] [Table 4] [Table 5]

[0023] Samples No. 1 to 6 (Table 1), Samples No. 7 to 13 (Table 2), Samples No. 14 to 20 (Table 3), Samples No. 21 to 27 (Table 4), and Samples No. 28 to 34 (Table 5) were designated as Series 1 to 5, respectively. Samples No. 1, 7, 14, 21, and 28 were reference samples of the respective series, and fresh nitrate (sodium nitrate A) immediately after opening the moisture-proof packaging was used as the oxidizing agent. Samples No. 2, 8, 15, 22, and 29 were comparative examples of the respective series, and nitrate (sodium nitrate B) that had been left in the air for two months after opening was used as the oxidizing agent. Samples No. 3 to 6, 9 to 13, 16 to 20, 23 to 27, and 30 to 34 were examples of the respective series, and calcium peroxide that had been left in the air for two months after opening was used as the oxidizing agent. As for raw materials other than nitrate and calcium peroxide, series 1 used calcium silicate as the base material, silicon as the metal, and fluoride salts and carbonates as flux raw materials, while series 2 used the same raw materials as series 1, plus iron oxide as an oxidizing agent, and series 3 had a lower SiO2 content than series 2. Series 4 and 5 used the same raw materials as series 2, with the former having a higher silicon content and the latter a higher SiO2 content than series 2. All raw materials were powders.

[0024] Samples Nos. 1 to 34 were evaluated as follows. <Fever duration> The duration of heat generation from the start to the end of heat generation for Samples No. 1 to 34 was measured by differential thermal analysis. That is, a crucible filled with 16 g of the sample was inserted into an electric furnace at 900°C, and the differential thermal change with the alumina fine powder reference sample was recorded to determine the duration of heat generation. A long or short heat generation duration indicates that the oxidation reaction of the metal is delayed or accelerated.

[0025] Samples No. 1, 8, 15, 22, and 29 using fresh nitrate were used as the reference samples for series 1 to 5, and if the heat generation duration of each sample was 50 seconds or more longer or shorter than the reference sample of the same series, the metal oxidation reaction was evaluated as "slower" or "faster" than the reference sample. If the heat generation duration of each sample was 25 to 49 seconds longer or shorter than the reference sample of the same series, the metal oxidation reaction was evaluated as "slightly slower" or "slightly faster." If the difference was within ±24 seconds, the sample was evaluated as "same as" the reference sample.

[0026] <Melting time> A crucible filled with 3g of sample was inserted into an electric furnace at 1300℃, and the melting time required for melting was measured. A long or short melting time indicates a delayed or rapid formation of the molten slag layer.

[0027] If the melting time of each sample was 30 seconds or more longer or shorter than the reference sample of the same series, it was evaluated as "slower" or "faster" than the reference sample; if it was 15 to 29 seconds longer or shorter, it was evaluated as "slightly slower" or "slightly faster;" if the difference was within ±14 seconds, it was evaluated as "same as" the reference sample.

[0028] <Overall rating> The overall evaluation was made as follows: excellent (○) if both the fever duration and fever duration were "equivalent," fair (△) if at least one was "slightly slow" or "slightly fast," and unacceptable (×) if both were "slow" or "fast."

[0029] <Evaluation Results> The evaluation results are shown in Tables 1 to 5.

[0030] From Tables 1 to 5, after being left in the air for two months, samples Nos. 2, 8, 15, 22, and 29 using nitrate (sodium nitrate B) all had longer heat generation durations and melting times, and their function as exothermic front powders declined. In contrast, samples Nos. 3 to 6, 9 to 13, 16 to 20, 23 to 27, and 30 to 34 using calcium peroxide after being left in the air for two months were comparable in heat generation duration and melting time to the conventional reference samples using fresh nitrate, and their function as exothermic front powders was maintained.

[0031] From Table 1, the content of calcium peroxide is preferably 2.5% by mass or more and 15.0% by mass or less, more preferably 2.5% by mass or more and 14.0% by mass or less, and even more preferably 3.0% by mass or more and 13.0% by mass or less. It is considered that the function as an oxidizing agent and the calorific value can be maximized within the preferable content range.

[0032] From Tables 1 to 5, the total content of metals or alloys is preferably 5.0 mass% or more and 20.0 mass% or less, more preferably 5.0 mass% or more and 18.0 mass% or less, and even more preferably 6.0 mass% or more and 15.0 mass% or less. It is considered that the calorific value can be maximized within the preferable range of the content.

[0033] As can be seen from Tables 2 to 5, iron oxide may be further included as an oxidizing agent other than calcium peroxide, and the total content of the oxidizing agents is preferably 2.5% by mass to 23.0% by mass, more preferably 2.5% by mass to 22.0% by mass, and even more preferably 3.0% by mass to 21.0% by mass. It is believed that the iron oxide can further enhance the heat generating effect, and since it does not affect the mass ratio (CaO / SiO2), it is easy to design the components.

[0034] 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

1. A substrate, a metal or alloy, and an oxidizing agent, the oxidizing agent comprises calcium peroxide; An exothermic front powder characterized in that the calcium peroxide content is 2.5 mass % or more and 15.0 mass % or less.

2. In the heat-generating front powder according to claim 1, The metal or the alloy is one or more selected from the group consisting of Si, Al, Ca-Si, Al-Mg, Al-Ca-Mg, and Fe-Si, and the total content of the metal or the alloy is 5.0 mass% or more and 20.0 mass% or less.

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