Powder for casting and casting method

Abstract

To provide a casting powder and a casting method capable of suppressing hot embrittlement.SOLUTION: A casting powder comprises silicon oxide, aluminum oxide, calcium oxide, and nickel oxide, wherein the content of sodium oxide is less than 3 mass% and the content of fluorine is less than 5 mass%.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a powder for casting and a casting method.

Background Art

[0002] When a cast slab cast from molten steel in a casting process contains copper, hot embrittlement may occur in the cast slab. Therefore, a technique for suppressing hot embrittlement by spraying a powder for casting containing NiO onto molten steel has been disclosed (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, if the viscosity of the powder for casting for spraying onto molten steel is low, there is a risk that the reduction reaction of nickel oxide will not be sufficiently promoted.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a powder for casting and a casting method capable of suppressing hot embrittlement.

Means for Solving the Problems

[0006] The powder for casting according to the present invention contains silicon oxide, aluminum oxide, calcium oxide, and nickel oxide, and is characterized in that the content of sodium oxide is less than 3 mass% and the content of fluorine is less than 5 mass%.

[0007] The content of the nickel oxide may be 20.0 mass% or less. The content of the silicon oxide may be 27.1 mass% or more and 42.0 mass% or less. The content of the aluminum oxide may be 2.9 mass% or more and 7.5 mass% or less. The content of the calcium oxide may be 20.1 mass% or more and 39.0 mass% or less. The content of the magnesium oxide may be 0.0 mass% or more and 1.9 mass% or less. The content of the lithium oxide may be 2.2 mass% or less. The content of the sodium oxide may be 1.1 mass% or less. The content of the fluorine may be 2.6 mass% or less. The content of the boron oxide may be 2.9 mass% or less. The content ratio of the calcium oxide to the silicon oxide may be 1.2 or less. The carbon content may be 13.8 mass% or less.

[0008] The casting method according to the present invention includes a step of pouring molten steel having a Ni / Cu ratio of less than 0.9 into a mold and spraying the above-described casting powder onto the surface of the molten steel, and a step of semi-solidifying the molten steel in the mold to obtain a slab.

Effects of the Invention

[0009] According to the present invention, it is possible to provide a casting powder and a casting method capable of suppressing hot embrittlement.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

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Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Mode for Carrying Out the Invention

[0011] Figure 1 is a diagram illustrating the process of manufacturing steel of a predetermined shape from scrap iron. As illustrated in Figure 1, the scrap iron is melted in an electric furnace and then subjected to a secondary refining process before being supplied as molten steel to a continuous casting process. For example, in the continuous casting process, the molten steel is poured into a mold and the semi-solidified slab is continuously drawn out from the lower side of the mold, producing semi-finished products (slabs) in various shapes such as slabs, blooms, billets, and beam blanks. The obtained slab is heated to approximately 900°C to 1400°C in a heating furnace and rolled into the desired shape by a rolled steel mill. However, if the molten steel contains copper, there is a risk of hot embrittlement occurring in the slab in the heating furnace.

[0012] Figure 2 is a diagram for explaining hot embrittlement. As illustrated in Figure 2, by heating the slab 10 in a heating furnace, iron (Fe) is selectively oxidized near the surface of the slab 10, and iron oxide (Fe tA scale 11 containing components O and t (t > 0) is formed. If a scale has already been formed before charging into the heating furnace, the scale 11 will be further formed in addition to the said scale. In this case, the copper component 12 (Cu) contained near the surface of the slab 10 moves and concentrates near the interface between the scale 11 of the slab 10. Since the copper component 12 has a low melting point, it liquefies in the high-temperature heating furnace and penetrates into the γ grain boundaries in the slab 10. If hot rolling is to be performed on the slab 10 in this state, the copper component 12 that has penetrated into the γ grain boundaries may induce cracks 13. Thus, the occurrence of cracks 13 in the slab 10 due to the liquefied copper component 12 is called hot embrittlement.

[0013] To suppress this hot embrittlement, it is known to add nickel (Ni) to the molten steel. By adding nickel to the molten steel, the solid solubility limit of copper in the slab 10 obtained from the molten steel increases, the diffusion amount of copper into iron increases, and a copper-nickel alloy is formed. As illustrated in FIG. 3, since the copper-nickel alloy has a higher melting point than pure metallic copper, it is less likely to liquefy. Thereby, the liquid phase amount of the copper alloy decreases, and hot embrittlement is suppressed.

[0014] However, since nickel is a rare metal and expensive, it is desired to reduce the amount of nickel used as much as possible.

[0015] Therefore, it has been considered to lower the nickel concentration inside the molten steel to reduce the nickel usage cost and increase the solid solubility limit of copper on the surface of the slab by increasing the nickel concentration on the surface of the steel.

[0016] For example, it is conceivable to scatter fine powder of metallic nickel on the surface of steel. However, fine metallic powder is difficult to handle. This is because fine metallic powder is a combustible material and is difficult to handle in the open air. Therefore, it is difficult to scatter the fine powder of metallic nickel. Thus, it is conceivable to scatter nickel oxide powder (NiO) on the surface of steel and increase the nickel concentration on the surface of steel by the reduction reaction of nickel oxide. However, it is also difficult to scatter nickel oxide. This is because it is difficult to make it adhere uniformly.

[0017] Therefore, it is conceivable to scatter powder for casting containing nickel oxide on the surface of steel and increase the nickel concentration on the surface of steel by utilizing the substitution reaction of nickel oxide.

[0018] As illustrated in FIG. 4, molten steel 15 is supplied to a mold 50. Powder for casting 20 is scattered on the upper surface of the molten steel 15. However, if the viscosity of the powder for casting 20 is low, there is a possibility that the reduction reaction of nickel oxide cannot be sufficiently promoted. For example, since sufficient contact with steel cannot be obtained, there is a possibility that the reduction reaction of nickel oxide does not proceed sufficiently.

[0019] Therefore, in the present embodiment, a powder for casting 20 having a high viscosity is used to sufficiently promote the reduction reaction of nickel oxide. The powder for casting 20 according to the present embodiment contains silicon oxide, aluminum oxide, calcium oxide, and nickel oxide, and has a composition ratio in which the content of sodium oxide is less than 3 mass% and the content of fluorine is less than 5 mass%. By setting the content of sodium oxide to less than 3 mass% and the content of fluorine to less than 5 mass%, the viscosity of the powder for casting 20 can be increased. Thereby, when the powder for casting 20 is scattered on the surface of the molten steel, the reduction reaction of nickel oxide can be sufficiently promoted.

[0020] Next, the mechanism for suppressing hot embrittlement when using the powder for casting according to this embodiment will be described. As illustrated in FIG. 5, in the continuous casting process, molten steel 15 with scale 16 formed on its surface is obtained. In the molten steel 15, a small amount of copper component 12 is dissolved in iron. Also, due to the selective oxidation of the surface of the molten steel 15, it is considered that the copper component 12 is concentrated near the interface with the scale 16 of the molten steel 15.

[0021] Next, the powder for casting 20 according to this embodiment is sprayed onto the molten steel 15. As a result, the powder for casting 20 comes into contact with the surface of the scale 16. Under the conditions of the continuous casting process, iron is more likely to oxidize than nickel. As a result, reactions such as Fe + NiO → FeO + Ni proceed, the solid solubility limit of copper increases, and the diffusion amount of copper into iron increases.

[0022] As a result, within the scale 16, the copper component 12 and nickel alloyize. As a result, a copper-nickel alloy 14 is formed within the scale 16. Since the copper-nickel alloy 14 has a higher melting point than metallic copper, it is less likely to liquefy even when heated in a heating furnace after becoming the slab 10. As a result, the liquefaction of the copper component is suppressed, and hot embrittlement is suppressed.

[0023] For example, the powder for casting 20 preferably has a viscosity of 0.1 Pa·s or more, more preferably has a viscosity of 0.2 Pa·s or more, and even more preferably has a viscosity of 0.5 Pa·s or more.

[0024] On the other hand, if the viscosity of the powder for casting 20 is too high, the amount flowing into the gap between the mold and the slab may be insufficient, causing sticking between the mold and the slab and possibly resulting in breakout. Therefore, it is preferable to set an upper limit for the viscosity of the powder for casting 20. For example, the powder for casting 20 preferably has a viscosity of 5.0 Pa·s or less, more preferably has a viscosity of 3.5 Pa·s or less, and even more preferably has a viscosity of 1.5 Pa·s or less.

[0025] If the content of nickel oxide (e.g., NiO) in the casting powder 20 is low, there is a risk that the reduction reaction of nickel oxide cannot be sufficiently promoted. Therefore, it is preferable to set a lower limit for the content of nickel oxide in the casting powder 20. For example, the content of nickel oxide in the casting powder 20 is preferably 5.0 mass% or more, more preferably 10.0 mass% or more, and even more preferably 20.0 mass% or more.

[0026] On the other hand, if the content of nickel oxide in the casting powder 20 is high, there is a risk that the melting point will increase. Therefore, it is preferable to set an upper limit for the content of nickel oxide in the casting powder 20. For example, the content of nickel oxide in the casting powder 20 is preferably 50.0 mass% or less, more preferably 40.0 mass% or less, and even more preferably 20.0 mass% or less.

[0027] Since the reduction reaction of nickel oxide is sufficiently promoted due to the high viscosity of the casting powder 20, the content of nickel oxide in the casting powder 20 can be reduced. For example, even if the content of nickel oxide in the casting powder 20 is 5.0 mass% or less, the substitution reaction between iron and nickel can be sufficiently promoted.

[0028] If the content of silicon oxide (e.g., SiO2) in the casting powder 20 is low, there is a risk that the viscosity will decrease. Therefore, it is preferable to set a lower limit for the content of silicon oxide in the casting powder 20. For example, the content of silicon oxide in the casting powder 20 is preferably 20.0 mass% or more, more preferably 25.0 mass% or more, and even more preferably 27.1 mass% or more.

[0029] If the content of silicon oxide in the powder for casting 20 is too high, there is a risk that the viscosity will become too high. Therefore, it is preferable to set an upper limit for the content of silicon oxide in the powder for casting 20. For example, the content of silicon oxide in the powder for casting 20 is preferably 60.0 mass% or less, more preferably 50.0 mass% or less, and even more preferably 42.0 mass% or less.

[0030] If the content of aluminum oxide (e.g., Al2O3) in the powder for casting 20 is too low, there is a risk that the melting point will rise and the lubrication between the mold and the slab will be insufficient. Therefore, it is preferable to set a lower limit for the content of aluminum oxide in the powder for casting 20. For example, the content of aluminum oxide in the powder for casting 20 is preferably 2.9 mass% or more, more preferably 3.0 mass% or more, and even more preferably 5.0 mass% or more.

[0031] If the content of aluminum oxide in the powder for casting 20 is too high, there is a risk that the viscosity will become too high. Therefore, it is preferable to set an upper limit for the content of aluminum oxide in the powder for casting 20. For example, the content of aluminum oxide in the powder for casting 20 is preferably 15.0 mass% or less, more preferably 10.0 mass% or less, and even more preferably 7.5 mass% or less.

[0032] If the content of calcium oxide (e.g., CaO) in the powder for casting 20 is too low, there is a risk that the viscosity will become too high. Therefore, it is preferable to set a lower limit for the content of calcium oxide in the powder for casting 20. For example, the content of calcium oxide in the powder for casting 20 is preferably 10.0 mass% or more, more preferably 15.0 mass% or more, and even more preferably 20.1 mass% or more.

[0033] If the calcium oxide content in the casting powder 20 is high, the viscosity may decrease. Therefore, it is preferable to set an upper limit on the calcium oxide content in the casting powder 20. For example, the calcium oxide content in the casting powder 20 is preferably 50.0 mass% or less, more preferably 40.0 mass% or less, and even more preferably 39.0 mass% or less.

[0034] If the magnesium oxide (e.g., MgO) content in the casting powder 20 is high, the viscosity may decrease. Therefore, it is preferable to set an upper limit on the magnesium oxide content in the casting powder 20. For example, the magnesium oxide content in the casting powder 20 is preferably 10.0 mass% or less, more preferably 5.0 mass% or less, and even more preferably 1.9 mass% or less. Note that in the casting powder 20, magnesium oxide may not be contained (e.g., 0.0 mass%).

[0035] If the sodium oxide (e.g., Na2O) content in the casting powder 20 is high, the viscosity of the casting powder 20 may increase. Therefore, the sodium oxide content in the casting powder 20 is preferably 5.0 mass% or less, more preferably 3.0 mass% or less, and even more preferably 1.1 mass% or less.

[0036] If the fluorine (F) content in the casting powder 20 is high, the viscosity of the casting powder 20 may decrease. Therefore, the fluorine content in the casting powder 20 is preferably 10.0 mass% or less, more preferably 5.0 mass% or less, and even more preferably 2.6 mass% or less.

[0037] If the content of lithium oxide (e.g., Li2O) in the casting powder 20 is high, the viscosity may decrease. Therefore, the content of lithium oxide in the casting powder 20 is preferably 10.0 mass% or less, more preferably 5.0 mass% or less, and even more preferably 2.2 mass% or less.

[0038] If the content of boron oxide (e.g., B2O3) in the casting powder 20 is high, the viscosity may decrease too much. Therefore, it is preferable to set an upper limit for the content of boron oxide in the casting powder 20. For example, the content of boron oxide in the casting powder 20 is preferably 5.0 mass% or less, more preferably 4.0 mass% or less, and even more preferably 2.9 mass% or less.

[0039] In the casting powder 20, if the content ratio (mass% ratio) of calcium oxide / silicon oxide is high, the melting point may rise and lubrication may not be ensured. Therefore, it is preferable to set an upper limit for the content ratio of calcium oxide / silicon oxide in the casting powder 20. For example, in the casting powder 20, the content ratio of calcium oxide / silicon oxide is preferably 1.5 or less, more preferably 1.4 or less, and even more preferably 1.2 or less.

[0040] In the casting powder 20, if the content of carbon is high, the melting rate may be slow. Therefore, it is preferable to set an upper limit for the content of carbon in the casting powder 20. For example, in the casting powder 20, the content of carbon is preferably 20.0 mass% or less, more preferably 15.0 mass% or less, and even more preferably 13.8 mass% or less.

[0041] If the particle size of the powder for casting 20 is small, there is a risk of scattering. Therefore, it is preferably to set a lower limit for the particle size of the powder for casting 20. For example, the particle size of the powder for casting 20 is preferably 50 μm or more, more preferably 200 μm or more, and even more preferably 1000 μm or more.

[0042] On the other hand, if the particle size of the powder for casting 20 is large, there is a risk of poor melting. Therefore, it is preferably to set an upper limit for the particle size of the powder for casting 20. For example, the particle size of the powder for casting 20 is preferably 5000 μm or less, more preferably 3000 μm or less, and even more preferably 2000 μm or less.

[0043] In addition, if the molten steel 15 contains sufficient nickel, there is a possibility that hot embrittlement can be suppressed without including nickel oxide in the powder for casting 20. FIG. 6 is a diagram showing the relationship between the content ratio Ni / Cu (mass% ratio) of nickel and copper in the molten steel 15 and the Cu alloy liquid phase. As shown in FIG. 6, it can be seen that if the Ni / Cu ratio is 0.9 or more, almost no Cu alloy liquid phase is generated. Therefore, the powder for casting 20 according to the present embodiment is preferably applied to the molten steel 15 having a Ni / Cu ratio of less than 0.9, more preferably applied to the molten steel 15 having a Ni / Cu ratio of 0.75 or less, and even more preferably applied to the molten steel 15 having a Ni / Cu ratio of 0.5 or less.

[0044] (Casting method) Using the above-mentioned powder 20 for casting, casting can be performed as follows. For example, the casting method according to this embodiment includes a step of pouring molten steel 15 with an Ni / Cu ratio of less than 0.9 into a mold 50 illustrated in FIG. 4, a step of spraying the above-mentioned powder 20 for casting onto the surface of the molten steel 15, a step of continuously pulling out the cast slab solidified in the mold 50 to the lower side of the mold to produce cast slabs 10 of various shapes, a step of heating the obtained cast slab 10 in a heating furnace to 900°C to 1400°C, and a step of rolling it into a desired shape by a rolled steel mill. According to this casting method, since the powder 20 for casting has sufficient viscosity, the reduction reaction of nickel oxide is sufficiently promoted, and hot embrittlement can be suppressed.

Example

[0045] Hereinafter, an experiment was conducted to confirm the effect of the powder 20 for casting according to the above embodiment.

[0046] (Reference Example 1) First, Reference Example 1 will be described. In Reference Example 1, experiments were conducted in a laboratory. A cast slab 10 with a Cu content of 0.30 mass% and an Ni content of 0.10 mass% was prepared. The cast slab 10 was heated in a heating furnace and air-cooled to room temperature. When the surface of the cast slab 10 was checked, it was confirmed that defects such as cracks had occurred. This is presumably because hot embrittlement occurred due to the low Ni content contained in the cast slab 10.

[0047] Thereafter, the vicinity of the surface of the cast slab 10 was observed using a scanning electron microscope (SEM). The upper figure in FIG. 7 is an SEM image of the sample. Next, composition analysis was performed on the location indicated by the arrow in the SEM photograph (the location within scale 11) using an energy dispersive X-ray spectrometer (EDS). The middle and lower figures in FIG. 7 are diagrams showing the results of the composition analysis. Cu was confirmed at the interface between scale 11 and the cast slab 10. The distribution of Ni was small. When the elemental mapping in the vicinity of scale 11 was checked, it was confirmed that the positions of Cu and Ni did not match, indicating that Cu was not alloyed with Ni.

[0048] From the above results, in Reference Example 1, when the scale 11 was formed, it is considered that Cu contained near the surface of the slab 10 moved to the vicinity of the interface with the scale 11 of the slab 10, concentrated, liquefied, and penetrated into the γ grain boundaries in the slab.

[0049] (Reference Example 2) Next, Reference Example 2 will be described. Also in Reference Example 2, experiments were conducted in the laboratory. A slab 10 with a Cu content of 0.30 mass% and a Ni content of 0.30 mass% was prepared. The slab 10 was heated in a heating furnace and air-cooled to room temperature. When the surface of the slab 10 was checked, it was confirmed that no defects such as cracks occurred. This is considered to be because no hot embrittlement occurred due to the high Ni content contained in the slab 10.

[0050] After that, the vicinity of the surface of the slab 10 was observed using SEM. The upper figure in Fig. 8 is the SEM image of the sample. Next, composition analysis by EDS was performed on the location indicated by the arrow (the location within the scale 11). The middle figure and the lower figure in Fig. 8 are the figures showing the results of the composition analysis. Cu was confirmed at the interface between the scale 11 and the slab 10. Ni was distributed in the same way as Cu. When the elemental mapping near the scale 11 was checked, a plurality of locations where the positions of Cu and Ni coincided were confirmed. From these results, it is considered that Cu alloyed with Ni to form a Cu-Ni alloy.

[0051] From the results of Reference Example 1 and Reference Example 2, it was confirmed that hot embrittlement was suppressed by forming a copper-nickel alloy near the surface of the slab 10. Based on the above results, the following experiments were conducted.

[0052] (Examples 1 to 10 and Comparative Examples 1 to 4) In Examples 1 to 10 and Comparative Examples 1 to 4, in order to simulate the spraying of the casting powder onto the molten steel, as shown in Fig. 9(a), a metal Fe ingot 10 was placed in an alumina crucible 30. The casting powder 20 was sprayed onto the ingot 10 to obtain a sample. As shown in Fig. 9(b), the ingot 10 had a cubic shape of 10 mm × 10 mm × 10 mm.

[0053] The Cu content in the ingot 10 was set to 0.30 mass% in all of Examples 1 to 10 and Comparative Examples 1 to 4. The Ni content in the ingot 10 was set to 0.10 mass% in Examples 1 to 6, 8 to 10 and Comparative Examples 1 and 2, and was set to 0.30 mass% in Example 7 and Comparative Examples 3 and 4.

[0054] In Comparative Examples 2 and 4, the No. 1 casting powder was used. In Examples 1, 5, and 7, the No. 2 casting powder was used. In Examples 2 and 6, the No. 2 casting powder was used. In Examples 3 and 9, the No. 4 casting powder was used. In Example 4, the No. 5 casting powder was used. In Examples 8 and 10, the No. 10 casting powder was used. Note that in Comparative Examples 1 and 3, no casting powder was sprayed.

[0055] Next, as shown in Fig. 10, the inside of the heating furnace 40 was heated. The atmosphere inside the heating furnace 40 was air. In Examples 1 to 4, 7, 8 and Comparative Examples 1 to 4, the temperature inside the heating furnace 40 was set to 1150 °C. In Examples 5, 6, 9, 10, the temperature inside the heating furnace 40 was set to 1400 °C.

[0056] Next, the sample was placed in this heating furnace 40 and held for a predetermined time. In Examples 1, 2, 5, 7, 9 and Comparative Examples 2, 4, the holding time was set to 30 minutes. In Examples 3, 4, 6, 8, 10 and Comparative Examples 1, 3, the holding time was set to 10 minutes. Then, the sample was taken out from the heating furnace 40 and air-cooled to room temperature.

[0057] The conditions of Examples 1 to 10 and Comparative Examples 1 to 4 are shown in Table 1.

Table 1

[0058] Table 2 shows the compositions of the powders for casting Nos. 1 to 6. In the powder for casting No. 1, the content of NiO is 0.0 mass%, the content of SiO2 is 42.0 mass%, the content of Al2O3 is 7.5 mass%, the content of CaO is 25.1 mass%, the content of MgO is 1.9 mass%, the content of Na2O is 0.1 mass%, the content of F is 0.0 mass%, the content of Li2O is 2.2 mass%, the content of B2O3 is 2.9 mass%, the carbon content is 13.8 mass%, and the mass% ratio of CaO / SiO2 is 0.6.

[0059] In the powder for casting No. 2, the content of NiO is 5.0 mass%, the content of SiO2 is 39.9 mass%, the content of Al2O3 is 7.1 mass%, the content of CaO is 23.8 mass%, the content of MgO is 1.8 mass%, the content of Na2O is 0.1 mass%, the content of F is 0.0 mass%, the content of Li2O is 2.1 mass%, the content of B2O3 is 2.8 mass%, the carbon content is 13.1 mass%, and the mass% ratio of CaO / SiO2 is 0.6.

[0060] In the powder for casting No. 3, the content of NiO is 20.0 mass%, the content of SiO2 is 33.6 mass%, the content of Al2O3 is 6.0 mass%, the content of CaO is 20.1 mass%, the content of MgO is 1.5 mass%, the content of Na2O is 0.1 mass%, the content of F is 0.0 mass%, the content of Li2O is 1.8 mass%, the content of B2O3 is 2.3 mass%, the carbon content is 11.0 mass%, and the mass% ratio of CaO / SiO2 is 0.6.

[0061] In the No.4 powder for casting, the NiO content is 20.0 mass%, the SiO2 content is 27.1 mass%, the Al2O3 content is 5.6 mass%, the CaO content is 32.9 mass%, no MgO is added, no Na2O is added, the F content is 2.2 mass%, no Li2O is added, no B2O3 is added, the carbon content is 7.8 mass%, and the mass% ratio of CaO / SiO2 is 1.2.

[0062] In the No.5 powder for casting, the NiO content is 20.0 mass%, the SiO2 content is 33.1 mass%, the Al2O3 content is 2.9 mass%, the CaO content is 22.0 mass%, no MgO is added, the Na2O content is 1.1 mass%, the F content is 1.4 mass%, the Li2O content is 1.1 mass%, the B2O3 content is 2.7 mass%, the carbon content is 6.9 mass%, and the mass% ratio of CaO / SiO2 is 0.7.

[0063] In the No.6 powder for casting, the NiO content is 5.0 mass%, the SiO2 content is 32.2 mass%, the Al2O3 content is 6.7 mass%, the CaO content is 39.0 mass%, no MgO is added, no Na2O is added, the F content is 2.6 mass%, no Li2O is added, no B2O3 is added, the carbon content is 9.2 mass%, and the mass% ratio of CaO / SiO2 is 1.2.

Table 2

[0064] Thereafter, for the samples of Examples 1 to 10 and Comparative Examples 2 and 4, the vicinity of the interface between the casting powder 20 and the casting slab 10 was observed using SEM. In any of Examples 1 to 10 and Comparative Examples 2 and 4, it was confirmed that the casting powder 20 was adhered to the casting slab 10. This is presumably because a high viscosity was obtained since the sodium oxide content in the casting powder was less than 3 mass% and the fluorine content was less than 5 mass%.

[0065] The upper diagram of Fig. 11 is a SEM image of the sample of Example 1. Something like a Cu alloy was confirmed within the scale 11. Next, compositional analysis by EDS (energy dispersive X-ray spectrometer) was performed on the location indicated by the arrow (the location within the scale 11). The middle diagram and the lower diagram of Fig. 11 are diagrams showing the results of the compositional analysis. Cu and Ni were confirmed within the scale 11. 2.72 mass% of Ni was confirmed and 1.40 mass% of Cu was confirmed. Also, when element mapping was confirmed, a plurality of locations where the positions of Cu and Ni coincided were confirmed. From these results, it is considered that Cu was alloyed with Ni to form a Cu-Ni alloy.

[0066] Infiltration of Cu into the casting slab 10 was not confirmed. This is presumably because the Cu contained in the casting slab 10 was alloyed with Ni, resulting in a higher melting point and suppression of liquefaction.

[0067] When the SEM photographs of Examples 2 to 10 were confirmed, as in Example 1, a plurality of locations where the positions of Cu and Ni coincided were confirmed. From these results, as in Reference Example 2, it is considered that Cu was alloyed with Ni to form a Cu-Ni alloy. From the above, in Examples 1 to 10, it is considered that hot embrittlement is suppressed as in Reference Example 2.

[0068] The upper diagram in Fig. 12 is the SEM image of the sample of Comparative Example 2. Composition analysis by EDS was performed on the location indicated by the arrow (the location within the slab 10). The middle and lower diagrams in Fig. 12 are diagrams showing the results of the composition analysis. Cu was confirmed within the slab 10. 6.16 mass% of Cu was confirmed, but Ni was not confirmed. From these results, it is considered that the said location is the location where Cu infiltrated into the slab 10. Therefore, in Comparative Example 2, it is considered that hot embrittlement occurred as in Reference Example 1. In Comparative Example 1 as well, a location where Cu is considered to have infiltrated into the slab was confirmed, similar to Comparative Example 2.

[0069] (Example 11 and Comparative Example 5) In Example 11 and Comparative Example 5, experiments were conducted on the same day using a continuous casting actual machine. In Example 11, in the continuous casting actual machine, casting powder 20 was sprayed onto the molten steel 15 poured into the mold 50 to semi-solidify it, and a slab 10 was obtained. The obtained slab 10 was heated in a heating furnace and air-cooled to room temperature. In Example 11, the casting powder No. 6 was used. In Comparative Example 5, a casting powder not containing nickel oxide was used. In Example 11, 41 slabs were manufactured, and in Comparative Example 5, 27,174 slabs were manufactured. Whether there were any defects on the surface of each slab was visually confirmed. The results are shown in Fig. 13(a). As shown in Fig. 13(a), while the ratio of slabs with defects confirmed in Comparative Example 5 was 0.4%, the ratio of slabs with defects confirmed in Example 11 was 0%.

[0070] The upper diagram in Figure 14 is the SEM image of the sample of Example 11. Something like a Cu alloy was confirmed within Scale 11. Next, for the location indicated by the arrow (the location within Scale 11), composition analysis was performed by EDS (Energy Dispersive X-ray Spectrometer). The middle diagram and the lower diagram in Figure 14 are diagrams showing the results of the composition analysis. Cu and Ni were confirmed within Scale 11. 5.15 mass% of Ni was confirmed, and 4.22 mass% of Cu was confirmed. Also, when element mapping was confirmed, a plurality of locations where the positions of Cu and Ni coincided were confirmed. From these results, it is considered that Cu was alloyed with Ni to form a Cu-Ni alloy.

[0071] (Example 12 and Comparative Example 6) In Example 12 and Comparative Example 6, on the same day, experiments were conducted using a continuous casting actual machine. In Example 12, in the continuous casting actual machine, casting powder 20 was sprayed onto the molten steel 15 poured into the mold 50 to semi-solidify it, and a slab 10 was obtained. The obtained slab 10 was heated in a heating furnace and air-cooled to room temperature. In Example 12, No. 2 casting powder was used. In Comparative Example 6, a casting powder containing no nickel oxide was used. In Example 12, 55 slabs were manufactured, and in Comparative Example 5, 6,571 slabs were manufactured. Whether there were any defects on the surface of each slab was visually confirmed. The results are shown in Figure 13(b). As shown in Figure 13(b), in Comparative Example 6, the ratio of slabs with confirmed defects was 4.5%, while in Example 12, the ratio of slabs with confirmed defects was 1.8%.

[0072] The upper figure in Fig. 15 is an SEM image of the sample of Example 12. Something like a Cu alloy was confirmed within Scale 11. Next, composition analysis by EDS (energy dispersive X-ray spectrometer) was performed on the location indicated by the arrow (the location within Scale 11). The middle figure and the lower figure in Fig. 15 are diagrams showing the results of the composition analysis. Cu and Ni were confirmed within Scale 11. 4.21 mass% of Ni was confirmed, and 4.17 mass% of Cu was confirmed. Also, when element mapping was confirmed, a plurality of locations where the positions of Cu and Ni coincided were confirmed. From these results, it is considered that Cu was alloyed with Ni to form a Cu-Ni alloy.

[0073] As described above in detail with respect to the embodiments of the present invention, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Reference Numerals

[0074] 10 Cast slab 11 Scale 12 Copper component 13 Crack 14 Copper-nickel alloy 15 Molten steel 16 Scale 20 Powder for casting 30 Alumina crucible 40 Heating furnace 50 Mold

Claims

1. It contains silicon oxide, aluminum oxide, calcium oxide, and nickel oxide. Among magnesium oxide, sodium oxide, and fluorine, it contains magnesium oxide and sodium oxide and does not contain fluorine, or does not contain magnesium oxide and sodium oxide and contains fluorine, or contains sodium oxide and fluorine and does not contain magnesium oxide. The content of sodium oxide is 1.1 mass% or less, the content of fluorine is 2.6 mass% or less, the content of magnesium oxide is 1.8 mass% or less, the content of the aluminum oxide is 7.1 mass% or less, and the content of the nickel oxide is 20.0 mass% or less. A powder for casting, characterized in that.

2. The powder for casting according to claim 1, characterized in that the content of the silicon oxide is 27.1 mass% or more and 42.0 mass% or less.

3. The powder for casting according to claim 1, characterized in that the content of the aluminum oxide is 2.9 mass% or more.

4. The powder for casting according to claim 1, characterized in that the content of the calcium oxide is 20.1 mass% or more and 39.0 mass% or less.

5. The powder for casting according to claim 1, characterized in that the content of lithium oxide is 2.2 mass% or less.

6. The powder for casting according to claim 1, characterized in that the content of boron oxide is 2.9 mass% or less.

7. The powder for casting according to claim 1, characterized in that the content ratio of the calcium oxide to the silicon oxide is 1.2 or less.

8. The powder for casting according to claim 1, characterized in that the carbon content is 13.8 mass% or less.

9. A step of pouring molten steel with an Ni / Cu ratio of less than 0.9 into a mold and spraying the powder for casting according to claim 1 on the surface of the molten steel; A step of semi-solidifying the molten steel in the mold to obtain a slab, a casting method characterized by including.

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