A composite flux for rack steel layer casting and a method for preparing and using the same

Abstract

The present application relates to a kind of rack steel layered casting composite flux and its preparation, method for using, the component and content of composite flux are as follows: high-purity iron powder: 40%~50%, high-purity rare earth powder: 20%~30%, analytical pure sodium pyrovanadate: 20%~40%.Using layered casting process of composite flux with rack steel, the macrosegregation and shrinkage cavity defects of large rack steel ingot can be significantly improved, which provides a simple, feasible and effective way to improve the composition homogenization degree of ingot, helps to improve the overall quality of rack steel ingot, also shortens the production cycle and improves the production efficiency, thereby improves the production capacity of large rack steel ingot, reduces the production energy consumption and production cost;The present application has important significance for breaking through the bottleneck of high homogenization large rack steel ingot manufacturing, laying the new technical theoretical foundation and industrialization application of large rack steel ingot casting, and improving the manufacturing technology level of key components of large equipment in China.

Description

Technical Field

[0001] This invention relates to the field of metallurgical casting technology, and in particular to a composite flux for layered casting of rack steel and its preparation and application methods. Background Technology

[0002] Large rack steel is an essential basic material for high-end equipment in fields such as nuclear power. However, the heterogeneity of large rack steel ingots is a bottleneck restricting the manufacturing, service performance, and lifespan of key components of major equipment, and severe macroscopic segregation significantly affects the final performance of the ingots.

[0003] For large rack steel, the current manufacturing method in my country is to first cast the entire piece and then forge it. Because large rack steel ingots are large and have long solidification times, and because the molten metal flows violently, problems such as macroscopic segregation, uneven microstructure, and inclusion aggregation are unavoidable during the manufacturing process. These defects cannot be eliminated through subsequent processing, leading to low material utilization, substandard forging properties, and even the scrapping of the entire ingot. In fact, 60% of defects in large rack steel forgings are caused by ingot quality problems. The inherent solidification characteristics of large rack steel ingots and the size effect caused by their size determine that traditional integral casting methods cannot avoid solidification defects. Therefore, it is urgent to explore a new technology for preparing large rack steel ingots to resolve the contradiction between large size and homogeneity, ultimately improving the quality level of large rack steel forgings.

[0004] Currently, researchers have explored various casting techniques to improve the macrosegregation problem in large rack steel ingots. Among these, directional solidification and electroslag remelting can produce ingots with uniform composition and excellent microstructure by controlling the solidification direction. However, for the production of large rack steel ingots, directional solidification cannot effectively control liquid flow and solidification direction, resulting in a weak improvement in macrosegregation. Electroslag remelting, on the other hand, suffers from significant energy consumption and high pollutant emissions.

[0005] 3D printing technology is an emerging rapid prototyping technology with advantages such as simple process, material saving and wide application range. It can obtain castings with uniform microstructure and composition. However, this technology can produce defects such as porosity and looseness when printing metal materials, and the process cannot be applied to the preparation of large rack steel ingots for the time being.

[0006] Chinese patent application CN107335782A discloses "A Highly Efficient and Clean Riser Covering Agent for Ingot Casting and Its Preparation Method," which mixes 60% titanium dioxide and 40% aluminum powder to obtain the riser covering agent. This method solves the problems of poor working environment and contamination of molten steel caused by existing riser covering agents for ingot casting, and extends the feeding time. However, this method can only be applied to riser improvement in the casting process of small ingots and has little effect on the internal quality (segregation and shrinkage cavities) of large rack steel ingots.

[0007] Chinese invention patent CN108889915B discloses "A method for preparing ingots by layer-by-layer casting based on slag protection." The method involves dividing steel into several portions, melting each portion into molten steel, and adding protective slag sequentially, repeating this process until all the molten steel is poured. While the protective slag layer formed by this method floats on the surface of the molten steel, effectively preventing the formation of an oxide layer, this method has significant limitations. Impurities in the protective slag tend to remain trapped in the molten steel and are difficult to float, forming inclusions that degrade the steel's properties. Furthermore, it suffers from complex production processes, long workflows, and poor continuous production capacity, making large-scale mass production impossible.

[0008] Chinese invention patent CN101831579B discloses a "method for preparing large-size aluminum alloy ingots." The method involves spreading flux at the bottom of a melting furnace, adding the alloy to the furnace, spreading a covering agent, and then melting and casting to obtain large-size aluminum alloy ingots. While this method can improve defects in aluminum alloy ingots to some extent, it is difficult to improve the internal quality of large rack steel ingots because the heat transfer rate of iron is significantly lower than that of aluminum. Furthermore, the flux introduces many impurities, making it difficult to use in conjunction with layered casting processes for large rack steel. Summary of the Invention

[0009] This invention provides a composite flux for layered casting of rack steel, along with its preparation and application methods. Combined with the layered casting process for rack steel, it can significantly improve macroscopic segregation and shrinkage defects in large rack steel ingots, providing a simple, feasible, and effective way to improve the homogeneity of ingot composition. This helps improve the overall quality of rack steel ingots, while also shortening the production cycle and increasing production efficiency, thereby increasing the production capacity of large rack steel ingots and reducing production energy consumption and costs. This invention is of great significance for breaking through the bottleneck in manufacturing highly homogeneous large rack steel ingots, laying the theoretical foundation and industrial application of new technologies for casting large rack steel ingots, and improving the manufacturing technology level of key components for large equipment in my country.

[0010] To achieve the above objectives, the present invention employs the following technical solution:

[0011] A composite flux for layered casting of rack steel is a mixture of high-purity iron powder, high-purity rare earth powder, and analytical grade sodium vanadate. The content of each component by weight percentage is as follows: high-purity iron powder: 40% to 50%, high-purity rare earth powder: 20% to 30%, and analytical grade sodium vanadate: 20% to 40%.

[0012] Furthermore, the high-purity iron powder has an Fe content ≥ 99.8%; the high-purity rare earth powder has a Ce content ≥ 99.7%; and the analytical grade sodium vanadate has a Na4V2O7 content ≥ 99.95%.

[0013] A method for preparing a composite flux for layered casting of rack steel includes the following steps:

[0014] 1) Raw material mixing: Mix high-purity iron powder, high-purity rare earth powder and analytical grade sodium vanadate according to the specified ratio and stir evenly;

[0015] 2) Drying; the baking temperature is 150℃~200℃, and the baking time is 1~2 hours;

[0016] 3) Cooling; After the dried mixture is cooled, the composite flux is obtained.

[0017] Furthermore, in step 1), the raw materials are mixed and stirred evenly using ultrasonic vibration.

[0018] Furthermore, in step 3), the cooling method is air cooling.

[0019] A method for using a composite flux in the layered casting of rack steel: the casting process of the layered casting of rack steel is divided into several stages. After the casting process of each stage is completed, high-purity iron powder or composite flux is sprayed onto the surface of the molten steel. The spraying of high-purity iron powder and composite flux is carried out at intervals, so that the high-purity iron powder or composite flux is evenly covered on the surface of the molten steel.

[0020] Furthermore, the casting process of the layered casting process for the rack steel is divided into 5 to 10 stages. After each stage is cast, the process of spraying high-purity iron powder or composite flux is as follows:

[0021] Assuming the first casting stage has a spray thickness of A1, the second stage has a spray thickness of A2, and so on, with each stage having a spray thickness of A1, A2...A10; the odd-numbered stages have a spray composition of high-purity iron powder, and the even-numbered stages have a spray composition of composite flux. Therefore, the thickness of the high-purity iron powder or composite flux sprayed on each stage after casting is:

[0022] When casting in 5 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 1-2mm;

[0023] When casting in 6 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 2-3mm; A6 = 1-2mm;

[0024] When casting in 7 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 2-3mm; A6 = 2-3mm; A7 = 1-2mm;

[0025] When casting in 8 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 3-4mm; A6 = 2-3mm; A7 = 2-3mm; A8 = 1-2mm;

[0026] When casting in 9 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 3-4mm; A6 = 3-4mm; A7 = 2-3mm; A8 = 2-3mm; A9 = 1-2mm;

[0027] When casting in 10 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 3-4mm; A6 = 3-4mm; A7 = 2-3mm; A8 = 2-3mm; A9 = 2-3mm; A10 = 1-2mm.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1) The composite flux combined with the layered casting process of rack steel described in this invention (a patent application filed on the same day) can significantly improve the macroscopic segregation and shrinkage defects of large rack steel ingots, and provides a simple, feasible and effective way to improve the homogeneity of composition of large rack steel ingots.

[0030] 2) The composite flux described in this invention is used in the layered casting of rack steel, which helps to improve the overall quality of rack steel ingots, while also shortening the production cycle and improving production efficiency, thereby increasing the production capacity of large rack steel ingots and reducing production energy consumption and production costs.

[0031] 3) This invention is of great significance for breaking through the bottleneck in the manufacturing of highly homogeneous large rack steel ingots, laying the theoretical foundation and industrial application of new technologies for casting large rack steel ingots, and improving the manufacturing technology level of key components of large equipment in my country. Detailed Implementation

[0032] The composite flux for layered casting of rack steel described in this invention is a mixture of high-purity iron powder, high-purity rare earth powder, and analytical grade sodium vanadate; the content of each component by weight percentage is as follows: high-purity iron powder: 40% to 50%, high-purity rare earth powder: 20% to 30%, and analytical grade sodium vanadate: 20% to 40%.

[0033] Furthermore, the high-purity iron powder has an Fe content ≥ 99.8%; the high-purity rare earth powder has a Ce content ≥ 99.7%; and the analytical grade sodium vanadate has a Na4V2O7 content ≥ 99.95%.

[0034] The method for preparing a composite flux for layered casting of rack steel according to the present invention includes the following steps:

[0035] 1) Raw material mixing: Mix high-purity iron powder, high-purity rare earth powder and analytical grade sodium vanadate according to the specified ratio and stir evenly;

[0036] 2) Drying; the baking temperature is 150℃~200℃, and the baking time is 1~2 hours;

[0037] 3) Cooling; After the dried mixture is cooled, the composite flux is obtained.

[0038] Furthermore, in step 1), the raw materials are mixed and stirred evenly using ultrasonic vibration.

[0039] Furthermore, in step 3), the cooling method is air cooling.

[0040] The present invention describes a method for using a composite flux in the layered casting of rack steel. The casting process of the layered casting of rack steel is divided into several stages. After the casting process of each stage is completed, high-purity iron powder or composite flux is sprayed onto the surface of the molten steel. The spraying of high-purity iron powder and composite flux is carried out at intervals, so that the high-purity iron powder or composite flux is evenly covered on the surface of the molten steel.

[0041] Furthermore, the casting process of the layered casting process for the rack steel is divided into 5 to 10 stages. After each stage is cast, the process of spraying high-purity iron powder or composite flux is as follows:

[0042] Assuming the first casting stage has a spray thickness of A1, the second stage has a spray thickness of A2, and so on, with each stage having a spray thickness of A1, A2...A10; the odd-numbered stages have a spray composition of high-purity iron powder, and the even-numbered stages have a spray composition of composite flux. Therefore, the thickness of the high-purity iron powder or composite flux sprayed on each stage after casting is:

[0043] When casting in 5 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 1-2mm;

[0044] When casting in 6 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 2-3mm; A6 = 1-2mm;

[0045] When casting in 7 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 2-3mm; A6 = 2-3mm; A7 = 1-2mm;

[0046] When casting in 8 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 3-4mm; A6 = 2-3mm; A7 = 2-3mm; A8 = 1-2mm;

[0047] When casting in 9 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 3-4mm; A6 = 3-4mm; A7 = 2-3mm; A8 = 2-3mm; A9 = 1-2mm;

[0048] When casting in 10 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 3-4mm; A6 = 3-4mm; A7 = 2-3mm; A8 = 2-3mm; A9 = 2-3mm; A10 = 1-2mm.

[0049] In the composite flux for layered casting of rack steel described in this invention, the addition of high-purity iron powder can significantly improve porosity and shrinkage cavities during the solidification process of molten steel. High-purity rare earth element Ce can significantly improve the solidification structure of the ingot, increase the proportion of equiaxed crystals, refine the grains, and enhance performance. The addition of analytically pure sodium vanadate (Na4V2O7) can reduce the segregation of carbon.

[0050] The composite flux described in this invention is used in conjunction with the layered casting process of rack steel. With the layer-by-layer casting and the layer-by-layer spraying of the composite flux, the casting process of large rack steel ingots is divided into several small-batch casting processes. The composite flux will first melt and dissolve in the steel liquid that is about to solidify, replenishing the central porosity and shrinkage cavities, and improving element segregation.

[0051] The composite flux described in this invention, when used in conjunction with the layered casting process for rack steel, has been shown to effectively improve the internal quality of the steel. Compared to conventional processes, the low-magnification rating has improved from grade 1 to grade 0.5, a reduction of 0.5 grades. Segregation of various elements has been significantly reduced, with an average reduction in segregation rate of over 20%.

[0052] Conventional casting processes, which involve a single pour, easily lead to porosity and shrinkage cavities within the steel, as well as severe element segregation. This hinders subsequent forging and other processes, resulting in cracking due to insufficient internal quality during application. The composite flux described in this invention, used in conjunction with a layered casting process for rack steel, significantly improves macroscopic segregation and shrinkage defects in large rack steel ingots. It provides a simple, feasible, and effective way to improve the homogeneity of composition in large rack steel ingots, contributing to improved overall quality. It also shortens the production cycle, increases production efficiency, thereby increasing the production capacity of large rack steel ingots and reducing energy consumption and costs. This invention is of great significance for overcoming the bottleneck in manufacturing highly homogeneous large rack steel ingots, laying the theoretical foundation and industrial application of new casting technologies for large rack steel ingots, and improving the manufacturing technology level of key components for large equipment in my country.

[0053] The following embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0054]

Example

[0055] The present invention will be specifically described below with reference to comparative examples and embodiments 1-3, thereby making the advantages and various effects of the present invention more clearly apparent. Those skilled in the art should understand that these specific embodiments and examples are for illustrative purposes only and are not intended to limit the present invention.

[0056] Throughout this specification, unless otherwise specified, the terminology used herein should be understood as having the meaning commonly used in the art. Therefore, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In the event of any conflict, this specification shall prevail.

[0057] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0058] Four heats of rack steel were smelted in a 500kg vacuum induction furnace as experimental steel. The target composition of the experimental steel is shown in Table 1.

[0059] Table 1 Target Composition of Gear Steel (wt%)

[0060]

[0061] [Comparative Example]

[0062] The first batch of rack steel was cast using a conventional smelting and casting process. After the ingot had completely cooled, the longitudinal polished surface of the wide side of the ingot was ground to observe the distribution of shrinkage cavities, and then elemental segregation was tested.

[0063]

Example 1

[0064] The second batch of rack steel was cast using a "conventional smelting + layered casting" process, along with the composite flux described in this invention.

[0065] The specific process is as follows:

[0066] 1. The composite flux comprises, by weight percentage: 40% high-purity iron powder, 20% high-purity rare earth Ce powder, and 40% analytical grade sodium vanadate (Na4V2O7).

[0067] 2. The preparation process of the composite flux is as follows:

[0068] Step ① Raw material mixing: Mix high-purity iron powder, high-purity rare earth Ce powder and analytical grade sodium vanadate Na4V2O7 in a certain proportion and stir evenly using ultrasonic vibration.

[0069] Step ② Drying; the baking temperature is 200℃ and the baking time is 2 hours;

[0070] Step 3: Cooling. Air cooling is used to obtain the composite flux.

[0071] 3. The casting process of the layered casting process for rack steel is divided into six stages, as follows:

[0072] 1) First stage casting time: 0.5 min, interval: 35 s; 2) Second stage casting time: 0.5 min, interval: 75 s; 3) Third stage casting time: 0.5 min, interval: 95 s; 4) Fourth stage casting time: 0.5 min, interval: 135 s; 5) Fifth stage casting time: 0.5 min, interval: 55 s; 6) Casting continues until the mold is full.

[0073] The amount of molten steel poured in each section is as follows:

[0074] 1) 10% of the total amount of molten steel in the first stage; 2) 20% of the total amount of molten steel in the second stage; 3) 25% of the total amount of molten steel in the third stage; 4) 20% of the total amount of molten steel in the fourth stage; 5) 15% of the total amount of molten steel in the fifth stage; 6) the sixth stage is poured until the mold is full.

[0075] The spraying process of the composite flux is as follows:

[0076] 1) After the first stage of casting, spray a 1mm thick layer of high-purity iron powder; 2) After the second stage of casting, spray a 2mm thick layer of composite flux; 3) After the third stage of casting, spray a 3mm thick layer of high-purity iron powder; 4) After the fourth stage of casting, spray a 3mm thick layer of composite flux; 5) After the fifth stage of casting, spray a 2mm thick layer of high-purity iron powder; 6) After the sixth stage of casting, spray a 3mm thick layer of composite flux.

[0077] 4. After the ingot has completely cooled, polish the longitudinal surface of the wide side of the ingot and observe the distribution of shrinkage cavities, and then perform elemental segregation test.

[0078]

Example 2

[0079] The third batch of rack steel was cast using a "conventional smelting + layered casting" process, along with the composite flux described in this invention.

[0080] The specific process is as follows:

[0081] 1. The composite flux comprises, by weight percentage: 50% high-purity iron powder, 30% high-purity rare earth Ce powder, and 20% analytical grade sodium vanadate (Na4V2O7).

[0082] 2. The preparation process of the composite flux is as follows:

[0083] Step ① Raw material mixing: Mix high-purity iron powder, high-purity rare earth Ce powder and analytical grade sodium vanadate Na4V2O7 in a certain proportion and stir evenly using ultrasonic vibration.

[0084] Step ② Drying; the baking temperature is 180℃ and the baking time is 1.5h;

[0085] Step 3: Cooling. Air cooling is used to obtain the composite flux.

[0086] 3. The casting process of the layered casting process for rack steel is divided into six stages, as follows:

[0087] 1) First stage casting time: 0.5 min, interval: 45 s; 2) Second stage casting time: 0.5 min, interval: 85 s; 3) Third stage casting time: 0.5 min, interval: 105 s; 4) Fourth stage casting time: 0.5 min, interval: 145 s; 5) Fifth stage casting time: 0.5 min, interval: 65 s; 6) Sixth stage casting until the mold is full.

[0088] The amount of molten steel poured in each section is as follows:

[0089] 1) 15% of the total amount of molten steel in the first stage; 2) 15% of the total amount of molten steel in the second stage; 3) 20% of the total amount of molten steel in the third stage; 4) 20% of the total amount of molten steel in the fourth stage; 5) 20% of the total amount of molten steel in the fifth stage; 6) the sixth stage is poured until the mold is full.

[0090] The spraying process of the composite flux is as follows:

[0091] 1) After the first stage of casting, spray a 2mm thick layer of high-purity iron powder; 2) After the second stage of casting, spray a 2mm thick layer of composite flux; 3) After the third stage of casting, spray a 3mm thick layer of high-purity iron powder; 4) After the fourth stage of casting, spray a 4mm thick layer of composite flux; 5) After the fifth stage of casting, spray a 1mm thick layer of high-purity iron powder; 6) After the sixth stage of casting, spray a 2mm thick layer of composite flux.

[0092] 6. After the ingot has completely cooled, polish the longitudinal surface of the wide side of the ingot and observe the distribution of shrinkage cavities, and then perform elemental segregation test.

[0093]

Example 3

[0094] The fourth batch of rack steel was cast using a "conventional smelting + layered casting" process, along with the composite flux described in this invention.

[0095] The specific control methods are as follows:

[0096] 1. The composite flux comprises, by weight percentage: 45% high-purity iron powder, 25% high-purity rare earth Ce powder, and 30% analytical grade sodium vanadate (Na4V2O7).

[0097] 2. The preparation process of the composite flux is as follows:

[0098] Step ①: Raw material mixing; Mix high-purity iron powder, high-purity rare earth Ce powder and analytical grade sodium vanadate Na4V2O7 in a certain proportion and stir evenly using ultrasonic vibration.

[0099] Step 2: Drying; the baking temperature is 150℃ and the baking time is 1 hour;

[0100] Step 3: Cooling, using air cooling, to obtain the composite flux.

[0101] 3. The casting process of the layered casting process for rack steel is divided into six stages, as follows:

[0102] 1) First stage casting time: 0.5 min, interval: 40 s; 2) Second stage casting time: 0.5 min, interval: 80 s; 3) Third stage casting time: 0.5 min, interval: 100 s; 4) Fourth stage casting time: 0.5 min, interval: 140 s; 5) Fifth stage casting time: 0.5 min, interval: 60 s; 6) Sixth stage casting until the mold is full.

[0103] The amount of molten steel poured in each section is as follows:

[0104] 1) 12% of the total amount of molten steel in the first stage; 2) 17% of the total amount of molten steel in the second stage; 3) 25% of the total amount of molten steel in the third stage; 4) 18% of the total amount of molten steel in the fourth stage; 5) 10% of the total amount of molten steel in the fifth stage; 6) the sixth stage is poured until the mold is full.

[0105] The spraying process of the composite flux is as follows:

[0106] 1) After the first stage of casting, spray a 1mm thick layer of high-purity iron powder; 2) After the second stage of casting, spray a 3mm thick layer of composite flux; 3) After the third stage of casting, spray a 2mm thick layer of high-purity iron powder; 4) After the fourth stage of casting, spray a 3mm thick layer of composite flux; 5) After the fifth stage of casting, spray a 1mm thick layer of high-purity iron powder; 6) After the sixth stage of casting, spray a 2mm thick layer of composite flux.

[0107] 6. After the ingot has completely cooled, the longitudinal polished surface of the wide side of the ingot is ground and the distribution of shrinkage cavities is observed. Then, the elemental segregation is tested. The elemental segregation of the comparative examples and Examples 1-3 is shown in Table 2.

[0108] Table 2 Elemental Segregation

[0109]

[0110] The comparison shows that the internal quality of the large rack steel ingots cast in Examples 1-3 using the composite flux of the layered casting process for rack steel described in this invention is significantly higher than that of the comparative example. This significantly improves the macroscopic segregation and shrinkage defects of the large rack steel ingots, providing a simple, feasible, and effective way to improve the homogeneity of the composition of large rack steel ingots. This helps to improve the overall quality of rack steel ingots, while also shortening the production cycle, increasing production efficiency, thereby increasing the production capacity of large rack steel ingots and reducing production energy consumption and production costs.

[0111] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. For example, baking temperature, baking time, spraying thickness, etc. are also limited to the essential scope of the present invention. Variations and modifications of the above embodiments will fall within the protection scope of the claims of the present invention.

[0112] It should be understood that the endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0113] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A composite flux for layered casting of rack steel, characterized in that, The composite flux is a mixture of high-purity iron powder, high-purity rare earth powder, and analytical grade sodium vanadate; the content of each component by weight percentage is: high-purity iron powder: 40% to 50%, high-purity rare earth powder: 20% to 30%, and analytical grade sodium vanadate: 20% to 40%.

2. The composite flux for layered casting of rack steel according to claim 1, characterized in that, The high-purity iron powder has an Fe content ≥ 99.8%; the high-purity rare earth powder has a Ce content ≥ 99.7%; and the analytical grade sodium vanadate has a Na4V2O7 content ≥ 99.95%.

3. The method for preparing a composite flux for layered casting of rack steel as described in claim 1 or 2, characterized in that, Includes the following steps: 1) Raw material mixing: Mix high-purity iron powder, high-purity rare earth powder and analytical grade sodium vanadate according to the specified ratio and stir evenly; 2) Drying; the baking temperature is 150℃~200℃, and the baking time is 1~2 hours; 3) Cooling; After the dried mixture is cooled, the composite flux is obtained.

4. The method for preparing a composite flux for layered casting of rack steel according to claim 3, characterized in that, In step 1), the raw materials are mixed and stirred evenly using ultrasonic vibration.

5. The method for preparing a composite flux for layered casting of rack steel according to claim 3, characterized in that, In step 3), the cooling method is air cooling.

6. The method of using the composite flux for layered casting of rack steel as described in claim 1 or 2, characterized in that, The casting process of the layered casting process of rack steel is divided into several stages. After the casting process of each stage is completed, high-purity iron powder or composite flux is sprayed onto the surface of the molten steel. The spraying of high-purity iron powder and composite flux is carried out at intervals, so that the high-purity iron powder or composite flux is evenly covered on the surface of the molten steel.

7. The method of using the composite flux for layered casting of rack steel according to claim 6, characterized in that, The casting process of the layered casting process for the rack steel is divided into 5 to 10 stages. After each stage is cast, the process of spraying high-purity iron powder or composite flux is as follows: Assuming the first casting stage has a spray thickness of A1, the second stage has a spray thickness of A2, and so on, with each stage having a spray thickness of A1, A2...A10; the odd-numbered stages have a spray composition of high-purity iron powder, and the even-numbered stages have a spray composition of composite flux. Therefore, the thickness of the high-purity iron powder or composite flux sprayed on each stage after casting is: When casting in 5 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 1-2mm; When casting in 6 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 2-3mm; A6 = 1-2mm; When casting in 7 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 2-3mm; A6 = 2-3mm; A7 = 1-2mm; When casting in 8 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 3-4mm; A6 = 2-3mm; A7 = 2-3mm; A8 = 1-2mm; When casting in 9 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 3-4mm; A6 = 3-4mm; A7 = 2-3mm; A8 = 2-3mm; A9 = 1-2mm; When casting in 10 sections, A1 = 1-2mm; A2 = 2-3mm; A3 = 2-3mm; A4 = 3-4mm; A5 = 3-4mm; A6 = 3-4mm; A7 = 2-3mm; A8 = 2-3mm; A9 = 2-3mm; A10 = 1-2mm.

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