A method for smelting high-alloy heat-resistant steel castings for ultra-supercritical steam turbines

Abstract

The invention discloses a method for smelting ultra-supercritical steam turbine high-alloy heat-resistant steel castings, belonging to the field of high-alloy heat-resistant steel castings, and comprising the following steps: making low-phosphorus and low-carbon steel ingots from residual molten steel in an electric arc furnace; calculating the minimum addition ratio X of the low-phosphorus and low-carbon steel ingots; adding recycled materials accounting for Y amount of total molten steel and low-phosphorus and low-carbon steel ingots accounting for Z amount of total molten steel and melting them into a first molten steel; adding materials to the first molten steel and melting them into a second molten steel of the total molten steel, wherein the materials are recycled materials, low-phosphorus and low-carbon steel ingots or a mixture of the two; when the carbon content and phosphorus content of the second molten steel meet the requirements, pouring the second molten steel; the invention melts the low-phosphorus and low-carbon steel ingots and the recycled materials into the first molten steel; the materials are added to the first molten steel to form a second molten steel meeting the carbon and phosphorus contents of the target casting, and the high-alloy heat-resistant steel casting can be obtained by pouring the second molten steel, the recycled materials can be used in large quantities and ready-to-use, and the negative impact of residual molten steel in the electric arc furnace on subsequent production is solved.

Description

Technical Field

[0001] The invention relates to the field of high alloy heat-resistant steel castings, and in particular to a method for smelting high alloy heat-resistant steel castings for ultra-supercritical steam turbines. Background Art

[0002] The operating temperature of the main steam chamber of supercritical and ultra-supercritical thermal power units is generally above 560℃, and the steam pressure is not less than 20MPa. It has the advantages of high energy efficiency and low pollution, and is one of the most cutting-edge equipment in the development of thermal power. The steel castings used in supercritical and ultra-supercritical thermal power units are in harsh operating conditions and need to work for a long time in a high-temperature and highly corrosive environment. Therefore, such steel castings are required to have excellent high-temperature resistance, corrosion resistance and high-temperature creep resistance. Most of them are made of ferritic high-alloy heat-resistant steel. Since elements such as carbon and phosphorus will increase the hot brittleness of steel and reduce its corrosion resistance, the high-alloy heat-resistant steel castings used in supercritical and ultra-supercritical thermal power units have very strict restrictions on the content of elements such as carbon and phosphorus. Usually, the mass fraction of carbon does not exceed 0.15%, and the mass fraction of phosphorus does not exceed 0.015%.

[0003] When producing such high-alloy heat-resistant steel castings, steel foundries use a large number of auxiliary materials, such as metallurgical auxiliary materials (such as metallurgical lime, ladle refractory materials, etc.), casting auxiliary materials (such as ceramic pipe runners, high-temperature resistant coatings, riser insulation materials, casting sand and resins, etc.). The carbon, phosphorus and other element contents of these auxiliary materials are relatively high; during the melting, pouring and solidification of molten steel, complex chemical reactions will occur when different auxiliary materials come into contact with molten steel, resulting in carbon, phosphorus and other elements in some auxiliary materials contaminating the molten steel, increasing the carbon and phosphorus content of the produced castings; through inspection and a large amount of data testing, the increase in carbon content during smelting is usually about 0.02%, and the increase in phosphorus content is usually about 0.002%. During the pouring and solidification process, the increase in carbon content is usually about 0.01%, and the increase in phosphorus content is usually about 0.001%.

[0004] In addition, a large amount of scraps (such as runners, risers, processing steel chips, etc.) will be generated during the casting and processing of steel castings. In order to reduce production costs and reduce the amount of alloy used, steel foundries need to recycle the scraps as much as possible when producing high-alloy heat-resistant steel castings and use them as recycled materials for secondary melting. Since the carbon and phosphorus content in these recycled materials increases, and high-alloy heat-resistant steel castings have very strict requirements on carbon and phosphorus content, if too much recycled material is used, it will easily lead to excessive carbon and phosphorus content in high-alloy heat-resistant steel castings, which will cause the high-alloy heat-resistant steel castings to exceed the composition standard and be scrapped.

[0005] At present, when smelting high-alloy heat-resistant steel castings, in order to ensure that the carbon and phosphorus content of the castings does not exceed the standard, there are mainly two smelting methods: the first method is the oxidation method, that is, direct casting without recycled materials, and priority is given to smelting low-phosphorus and low-carbon molten steel during production, and then various alloys are added. Through spectral inspection or chemical analysis and other means, the content of each chemical element in the molten steel is confirmed to be qualified before pouring the casting. The advantage of this method is that it can ensure that the carbon and phosphorus content of the molten steel is qualified. The disadvantage is that a large amount of alloys (the weight of the alloy used exceeds 20% of the total weight of the molten steel) is required, the cost is high, and because recycled materials are not used, the generated recycled materials accumulate more and more, becoming a negative asset of the steel foundry. The recycled materials cannot be reused, resulting in a large backlog of recycled materials and a certain degree of resource waste; the second method The first is the return method, that is, after the recycled materials are accumulated to a certain weight, they are melted into molten steel in an electric furnace, and then a small amount of alloy is added to fine-tune the chemical composition. After the chemical composition is tested to be qualified, castings are cast. The advantage of this method is that the recycled materials can be used, saving part of the alloy, and the cost is lower than the oxidation method. However, due to the increase in the carbon and phosphorus content in the recycled materials, the carbon and phosphorus content of the molten steel during the secondary smelting will be higher than the normal value, or even exceed the standard, causing the molten steel to be scrapped. In addition, the recycled materials need to be accumulated to a certain amount before they can be used. The accumulation process of recycled materials is long, occupying a large amount of space and management costs. During this period, the recycled materials are negative assets of the steel foundry. The above two methods have not completely solved the problems of backlog of recycled materials and waste of resources, and it is impossible to use the recycled materials as soon as they are produced.

[0006] In addition, when the molten steel in the electric arc furnace is poured into the ladle, in order to prevent the slag on the surface of the molten steel from flowing into the ladle with the molten steel and contaminating the molten steel in the ladle, the process of retaining slag and tapping the steel will be adopted, that is, when pouring the molten steel, a part of the molten steel will remain in the electric arc furnace, so that the slag will remain in the electric arc furnace and will not enter the ladle; this part of the remaining molten steel in the electric arc furnace is usually used as the charge of the electric arc furnace and continues to participate in the subsequent steelmaking operations; however, the chemical composition of the remaining molten steel in the electric arc furnace may not meet the composition requirements of the subsequent steelmaking operations, which may cause the composition of the molten steel in the next furnace to change, affecting the quality of the molten steel of the next furnace product; for steel foundries, the less molten steel remains after each smelting in the electric arc furnace, the smaller the negative impact on subsequent production and the greater the production flexibility.

[0007] Therefore, it is an urgent problem to be solved at this stage to develop and design a method for smelting high-alloy heat-resistant steel castings that can use recycled materials in large quantities and immediately, while solving the negative impact of residual molten steel in the electric arc furnace on subsequent production, ensuring the qualified carbon and phosphorus content of the castings and saving costs. Summary of the invention

[0008] In view of the problems existing in the prior art, the present invention provides a method for smelting ultra-supercritical steam turbine high-alloy heat-resistant steel castings, wherein low-phosphorus and low-carbon steel ingots made from residual molten steel in an electric arc furnace are mixed with recycled materials in a certain proportion and melted into a first molten steel; according to the carbon content and phosphorus content of the first molten steel, a proper amount of material is added to the first molten steel to form a second molten steel that meets the target carbon content and phosphorus content of the casting, and the high-alloy heat-resistant steel casting can be obtained by pouring the second molten steel. The recycled materials can be used in large quantities and immediately, while the negative impact of the residual molten steel in the electric arc furnace on subsequent production is solved, effectively saving costs.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] The present invention provides a method for smelting ultra-supercritical steam turbine high-alloy heat-resistant steel castings, comprising the following steps:

[0011] S1: Make the remaining molten steel in the electric arc furnace into low-phosphorus and low-carbon steel ingots;

[0012] S2: Calculate the minimum addition ratio X of the low-phosphorus and low-carbon steel ingot according to the carbon content and phosphorus content of the recycled materials, the carbon addition amount and phosphorus addition amount during the smelting and casting process, and the carbon content and phosphorus content of the target casting;

[0013] S3: according to the total amount of molten steel to be melted, adding recycled materials accounting for Y amount of the total molten steel and the low-phosphorus and low-carbon steel ingots accounting for Z amount of the total molten steel, and melting Y amount of the recycled materials and Z amount of the low-phosphorus and low-carbon steel ingots into the first molten steel; wherein Y+Z<1, and Z≥X;

[0014] S4: measuring the carbon content and phosphorus content of the first molten steel, and according to the carbon content and phosphorus content of the target casting, adding material to the first molten steel and melting it into the second molten steel of the total molten steel amount, wherein the material is set to be the recycled material, the low-phosphorus and low-carbon steel ingot, or a mixture of the two;

[0015] S5: measuring the carbon content and the phosphorus content of the second molten steel; when the carbon content and the phosphorus content of the second molten steel are both lower than the carbon content and the phosphorus content of the target casting, pouring the second molten steel.

[0016] As a preferred technical solution, step S1 includes the following sub-steps:

[0017] S11: making a steel ingot mold for containing the remaining molten steel in the electric arc furnace;

[0018] S12: measuring the height of the lowest point of steel tapping of the electric arc furnace;

[0019] S13: manufacturing a support platform according to the height of the steel ingot mold and the height of the lowest point of steel tapping of the electric arc furnace.

[0020] As a preferred technical solution, in step S11, the steel ingot mold is set to a hollow rectangular parallelepiped structure with an open upper end;

[0021] And / or, in step S12, the electric arc furnace is controlled to tilt to a maximum angle, and the minimum distance between the lowest point of the steel outlet of the electric arc furnace and the transfer vehicle table is measured, that is, the height of the lowest point of steel outlet of the electric arc furnace;

[0022] And / or, in step S13, the height of the support platform is set to the height of the lowest point of steel tapping from the electric arc furnace minus the height of the ingot mold;

[0023] And / or, in step S13, the supporting platform is configured as a platform frame made of square tubes, a top surface of the platform frame is provided with a load-bearing steel plate, and the steel ingot mold is placed on the load-bearing steel plate.

[0024] As a preferred technical solution, step S1 also includes the following sub-steps:

[0025] S14: Producing protective tooling on the support platform.

[0026] As a preferred technical solution, the protective tooling is configured as a guardrail provided on the support platform, the guardrail is arranged around the ingot mold, the guardrail includes a fixed part and a detachable part, the fixed part is fixedly connected to the support platform, and the detachable part is detachably connected to the fixed part and / or the support platform.

[0027] As a preferred technical solution, before step S1, the remaining molten steel in the electric arc furnace needs to be oxidized by oxygen blowing, and the chemical composition of the remaining molten steel in the electric arc furnace is detected by spectral analysis until the remaining molten steel in the electric arc furnace meets the carbon content A1 (wt%) ≤ 0.05% and the phosphorus content A2 (wt%) ≤ 0.005%, and then the oxygen blowing oxidation is stopped.

[0028] As a preferred technical solution, in step S2, the carbon content B1 (wt%) of the recycled materials used in smelting is ≤0.13%, and the phosphorus content B2 (wt%) is ≤0.013%; the carbon addition amount C1 (wt%) in the smelting and casting process is ≤0.02%, and the phosphorus addition amount C2 (wt%) is ≤0.002%; the carbon content D1 (wt%) of the target casting is ≤0.14%, and the phosphorus content D2 (wt%) is ≤0.014%.

[0029] As a preferred technical solution, under the premise of meeting the carbon content of the target casting, the minimum addition ratio of the low-phosphorus and low-carbon steel ingot is ; Under the premise of meeting the phosphorus content of the target casting, the minimum addition ratio of the low-phosphorus low-carbon steel ingot is , the minimum addition ratio X of the low-phosphorus and low-carbon steel ingot is the larger value between X1 and X2.

[0030] As a preferred technical solution, in step S4, the carbon content of the first molten steel is E1, the phosphorus content is E2, and the carbon content of the material added to the first molten steel is , phosphorus content is .

[0031] As a preferred technical solution, in step S1, after the low-phosphorus and low-carbon steel ingot is solidified and demoulded, the surface of the low-phosphorus and low-carbon steel ingot needs to be cleaned by grinding and / or shot blasting;

[0032] And / or, in step S4, while replenishing the material into the first molten steel, alloys need to be added into the first molten steel to fine-tune the composition.

[0033] The beneficial effects of the present invention are as follows:

[0034] 1. Compared with the traditional process, the high alloy heat-resistant steel castings produced by the present invention can increase the utilization ratio of the recycled materials, and each batch of recycled materials produced can be fully utilized, reducing the backlog of recycled materials and simplifying production management; and the amount of alloy required to be used is also greatly reduced, and the smelting cost is significantly reduced.

[0035] 2. In the traditional process, a certain amount of returned furnace materials must be accumulated before the return method can be used for smelting, so the returned furnace materials will be stored for a long time, which puts forward relatively strict requirements on the management of the production workshop and the storage space. In the present invention, the returned furnace materials do not need to be accumulated in a certain amount. The generated returned furnace materials can be used at any time during each smelting of high-alloy heat-resistant steel castings. It is flexible and convenient, greatly saves storage space and management costs, and can maximize the use of the returned furnace materials generated by high-alloy heat-resistant steel castings.

[0036] 3. In the traditional steel casting process, the remaining molten steel after the electric arc furnace is discharged cannot be reused and will remain in the electric arc furnace, which is easy to pollute the composition of the subsequent molten steel, causing a relatively large negative impact on the smelting of the next batch of molten steel, and may even cause the composition of the next batch of molten steel to exceed the standard and be scrapped. In order to avoid such situations, steel foundries usually need to adjust production plans so that the material of continuously produced castings cannot change too much, which greatly limits the flexibility of production. The present invention utilizes the remaining molten steel in the electric arc furnace to cast low-phosphorus and low-carbon steel ingots, thereby avoiding the waste of the remaining molten steel in the electric arc furnace and solving the problem of the negative impact of the remaining molten steel in the electric arc furnace on subsequent production.

[0037] 4. The present invention makes the ingot mold and the support platform so that all the remaining molten steel in the electric arc furnace can be smoothly poured into the ingot mold, and there is no or only a trace amount of molten steel remaining in the electric arc furnace, thereby minimizing the impact on subsequent production.

[0038] 5. When using the traditional return process to produce high-alloy heat-resistant steel castings, since the carbon content in the returned materials is relatively high, the carbon content of the melted molten steel is also relatively high. The steel foundry usually needs to be equipped with VOD furnaces, AOD furnaces and other equipment to reduce the carbon content of the molten steel. VOD furnaces, AOD furnaces and other equipment have large one-time investments and complex processes, and have relatively high requirements for steel foundries. The present invention can effectively reduce the requirements for equipment.

[0039] 6. The present invention is not only applicable to high alloy heat-resistant steel castings, but also to other steel types with strict requirements on carbon or phosphorus content. It has a wide range of applications and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A process flow chart of an embodiment of a method for smelting ultra-supercritical steam turbine high-alloy heat-resistant steel castings according to the present invention;

[0041] Figure 2 It is a structural schematic diagram of pouring the remaining molten steel in the electric arc furnace into the ingot mold in one embodiment of a method for smelting ultra-supercritical steam turbine high-alloy heat-resistant steel castings of the present invention;

[0042] Figure 3 for Figure 2 Schematic diagram of the structure of the ingot mold, support platform and protective tooling.

[0043] In the figure: 1- electric arc furnace, 11- steel outlet, 2- ingot mold, 21- hanging handle, 3- supporting platform, 31- platform frame, 32- load-bearing steel plate, 33- diagonal brace, 4- protective tooling, 41- fixed part, 42- removable part, 5- transfer vehicle. DETAILED DESCRIPTION

[0044] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0045] Please refer to Figure 1-Figure 3 Table 1 is an embodiment of a method for smelting ultra-supercritical steam turbine high-alloy heat-resistant steel castings provided by the present invention, comprising the following steps:

[0046] S1: making the remaining molten steel in the electric arc furnace 1 into a low-phosphorus and low-carbon steel ingot, specifically, tilting the electric arc furnace 1 to a maximum angle, so that all the remaining molten steel in the electric arc furnace 1 is poured into the steel ingot mold 2, and solidified to form a low-phosphorus and low-carbon steel ingot;

[0047] It should be noted that in step S1, after the low-phosphorus and low-carbon steel ingot is solidified and demolded in the steel ingot mold 2, the slag inclusions on the surface of the low-phosphorus and low-carbon steel ingot need to be cleaned by grinding and / or shot blasting procedures;

[0048] Furthermore, step S1 includes the following sub-steps:

[0049] S11: making a steel ingot mold 2 for holding the remaining molten steel in the electric arc furnace 1; specifically, the steel ingot mold 2 is set as a hollow rectangular parallelepiped structure with an upper end opening, and the hollow part of the steel ingot mold 2 is used to hold the remaining molten steel in the electric arc furnace 1 and cast it into a low-phosphorus and low-carbon steel ingot. The material of the steel ingot mold 2 is preferably gray iron; two opposite sides of the steel ingot mold 2 should be provided with hanging handles 21 for easy hanging;

[0050] S12: measuring the height of the lowest point of steel tapping of the arc furnace 1; specifically, controlling the arc furnace 1 to tilt to a maximum angle, and measuring the minimum distance between the lowest point of the steel tapping port 11 of the arc furnace 1 and the table top of the transfer vehicle 5, which is the height of the lowest point of steel tapping of the arc furnace 1;

[0051] S13: According to the height of the ingot mold 2 and the height of the lowest point of the steel tapping of the arc furnace 1, a support platform 3 is made; specifically, the height of the support platform 3 is set to the height of the lowest point of the steel tapping of the arc furnace 1 minus the height of the ingot mold 2 and the reserved running gap between the top surface of the ingot mold 2 and the lowest point of the steel tapping port 11 of the arc furnace 1; further, the support platform 3 is preferably set to a platform frame 31 made of square tubes, and diagonal braces 33 are arranged around the supporting legs of the platform frame 31, and are firmly welded to the table top of the transfer flat car to prevent the transfer car 5 from shaking during operation, causing the ingot mold 2 to tip over; a load-bearing steel plate 32 is provided on the top surface of the platform frame 31, and the ingot mold 2 is placed on the load-bearing steel plate 32;

[0052] S14: Make a protective tooling 4 on the supporting platform 3; since the height of the ingot mold 2 is relatively high and the center of gravity is relatively high, the center of gravity of the transfer vehicle 5 is prone to be unstable when moving. The protective tooling 4 is arranged around the ingot mold 2 to effectively position the ingot mold 2 and prevent the ingot mold 2 from tipping over; specifically, the protective tooling 4 is arranged as a guardrail arranged on the supporting platform 3, and the guardrail includes columns arranged at the four corners of the load-bearing steel plate 32, and square tubes are arranged between adjacent columns to form a guardrail; further, the guardrail should include a fixed part 41 and a detachable part 42, the fixed part 41 is located on the side of the ingot mold 2 without the hanger 21 and is fixedly connected to the supporting platform 3 by welding, the detachable part 42 is located on the side of the ingot mold 2 with the hanger 21 and is detachably connected to the fixed part 41 and / or the supporting platform 3 by bolts or pins, and the detachable part 42 is removed when lifting the ingot mold 2 and installed when the transfer vehicle 5 moves.

[0053] It should be noted that before step S1, the remaining molten steel in the electric arc furnace 1 needs to be oxidized by oxygen blowing, which can oxidize the excess carbon and phosphorus in the remaining molten steel; during the oxygen blowing oxidation process, the chemical composition of the remaining molten steel in the electric arc furnace 1 is detected by spectral analysis, and the oxygen blowing oxidation is stopped until the remaining molten steel in the electric arc furnace 1 meets the carbon content A1 (wt%) ≤ 0.05% and the phosphorus content A2 (wt%) ≤ 0.005%. After the molten steel in the electric arc furnace 1 is poured into the ladle, the transfer vehicle 5 is driven to the bottom of the steel outlet 11, and the remaining molten steel in the electric arc furnace 1 is poured into the ingot mold 2, which can ensure that the carbon content A1 (wt%) of the produced low-phosphorus and low-carbon steel ingot is ≤ 0.05% and the phosphorus content A2 (wt%) ≤ 0.005%.

[0054] S2: Calculate the minimum addition ratio X of low-phosphorus and low-carbon steel ingots according to the carbon content and phosphorus content of the recycled materials, the carbon and phosphorus addition during the smelting and casting process, and the carbon and phosphorus content of the target castings;

[0055] Specifically, in step S2, the carbon content B1 (wt%) of the recycled materials used in smelting is ≤0.13%, and the phosphorus content B2 (wt%) is ≤0.013%; the carbon addition amount C1 (wt%) during the smelting and casting process is ≤0.02%, and the phosphorus addition amount C2 (wt%) is ≤0.002%; the carbon content D1 (wt%) of the target casting is ≤0.14%, and the phosphorus content D2 (wt%) is ≤0.014%;

[0056] Furthermore, under the premise of meeting the carbon content of the target casting, the minimum addition ratio of low-phosphorus and low-carbon steel ingots is ; Under the premise of meeting the phosphorus content of the target casting, the minimum addition ratio of low-phosphorus and low-carbon steel ingots The minimum addition ratio X of the low-phosphorus and low-carbon steel ingot is the larger value of X1 and X2; in the specific embodiment shown in Table 1, X is 12.5%.

[0057] S3: according to the total amount of molten steel to be melted, adding recycled materials accounting for Y amount of the total molten steel and low-phosphorus and low-carbon steel ingots accounting for Z amount of the total molten steel, and melting Y amount of recycled materials and Z amount of low-phosphorus and low-carbon steel ingots into the first molten steel; wherein Y+Z<1, and Z≥X; in a specific embodiment, Y may be 70%, and Z may be 20%;

[0058] S4: Measure the carbon content and phosphorus content of the first molten steel, and according to the carbon content and phosphorus content of the target casting, add 1-YZ parts of materials to the first molten steel and melt them into the second molten steel with the total molten steel volume. The materials can be set as recycled materials, low-phosphorus and low-carbon steel ingots or a mixture of the two according to the specific situation.

[0059] Further, in step S4, the carbon content of the first molten steel measured is E1, and the phosphorus content is E2. Accordingly, the carbon content of the material added to the first molten steel should be , the phosphorus content should be ; specifically, when F1 ≥ B1 and F2 ≥ B2, the material supplemented into the first molten steel can be directly set as the return material; when A1 ≤ F1 < B1 and A2 ≤ F2 < B2, the material supplemented into the first molten steel can be directly set as the low-phosphorus and low-carbon steel ingot, or can be set as a mixture of the low-phosphorus and low-carbon steel ingot and the return material, as long as the carbon content of the mixture is less than F1 and the phosphorus content is less than F2; when F1 < A1 and / or F2 < A2, then it is necessary to add low-phosphorus and low-carbon steel ingots that make the second molten steel exceed the total amount of molten steel, so as to make the carbon content and phosphorus content of the second molten steel meet the requirements.

[0060] It should be noted that in step S4, while supplementing the material into the first molten steel, an alloy also needs to be added to the first molten steel to fine-tune the composition.

[0061] S5: Measure the carbon content and phosphorus content of the second molten steel; when both the carbon content and phosphorus content of the second molten steel are lower than the carbon content and phosphorus content of the target casting, pour the second molten steel, and a high-alloy heat-resistant steel casting that meets the requirements can be obtained.

[0062] Table 1 Smelting and Casting Indexes for Smelting High-Alloy Heat-Resistant Steel Castings

[0063]

[0064] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for smelting high-alloy heat-resistant steel castings for ultra-supercritical steam turbines, characterized in that: The following steps are involved: S1: making the remaining molten steel in the electric arc furnace (1) into low-phosphorus and low-carbon steel ingots; S2: Calculate the minimum addition ratio X of the low-phosphorus and low-carbon steel ingot according to the carbon content and phosphorus content of the recycled materials, the carbon addition amount and phosphorus addition amount during the smelting and casting process, and the carbon content and phosphorus content of the target casting; S3: according to the total amount of molten steel to be melted, adding recycled materials accounting for Y amount of the total molten steel and the low-phosphorus and low-carbon steel ingots accounting for Z amount of the total molten steel, and melting Y amount of the recycled materials and Z amount of the low-phosphorus and low-carbon steel ingots into the first molten steel; wherein Y+Z<1, and Z≥X; S4: measuring the carbon content and phosphorus content of the first molten steel, and according to the carbon content and phosphorus content of the target casting, adding material to the first molten steel and melting it into the second molten steel of the total molten steel amount, wherein the material is set to be the recycled material, the low-phosphorus and low-carbon steel ingot, or a mixture of the two; S5: measuring the carbon content and the phosphorus content of the second molten steel; when the carbon content and the phosphorus content of the second molten steel are both lower than the carbon content and the phosphorus content of the target casting, pouring the second molten steel.

2. The method for smelting ultra-supercritical steam turbine high alloy heat-resistant steel castings according to claim 1, characterized in that: Step S1 includes the following sub-steps: S11: manufacturing a steel ingot mold (2) for containing the remaining molten steel in the electric arc furnace (1); S12: measuring the height of the lowest point of steel tapping of the electric arc furnace (1); S13: manufacturing a support platform (3) according to the height of the steel ingot mold (2) and the height of the lowest point of steel tapping of the electric arc furnace (1).

3. The method for smelting ultra-supercritical steam turbine high alloy heat-resistant steel castings according to claim 2, characterized in that: In step S11, the steel ingot mold (2) is set to a hollow rectangular parallelepiped structure with an open upper end; And / or, in step S12, the electric arc furnace (1) is controlled to tilt to a maximum angle, and the minimum distance between the lowest point of the steel tapping port (11) of the electric arc furnace (1) and the table top of the transfer vehicle (5) is measured, which is the height of the lowest point of steel tapping of the electric arc furnace (1); And / or, in step S13, the height of the support platform (3) is set to be the height of the lowest point of steel tapping of the electric arc furnace (1) minus the height of the steel ingot mold (2); And / or, in step S13, the supporting platform (3) is configured as a platform frame (31) made of a square tube, the top surface of the platform frame (31) is provided with a load-bearing steel plate (32), and the steel ingot mold (2) is placed on the load-bearing steel plate (32).

4. The method for smelting ultra-supercritical steam turbine high alloy heat-resistant steel castings according to claim 2, characterized in that: Step S1 also includes the following sub-steps: S14: Producing protective tooling (4) on the support platform (3).

5. The method for smelting ultra-supercritical steam turbine high alloy heat-resistant steel castings according to claim 4, characterized in that: The protective tooling (4) is configured as a guardrail provided on the support platform (3), the guardrail being arranged around the steel ingot mould (2), the guardrail comprising a fixed portion (41) and a detachable portion (42), the fixed portion (41) being fixedly connected to the support platform (3), and the detachable portion (42) being detachably connected to the fixed portion (41) and / or the support platform (3).

6. The method for smelting ultra-supercritical steam turbine high alloy heat-resistant steel castings according to claim 1, characterized in that: Prior to step S1, the remaining molten steel in the electric arc furnace (1) needs to be oxidized by blowing oxygen, and the chemical composition of the remaining molten steel in the electric arc furnace (1) needs to be detected by spectral analysis until the remaining molten steel in the electric arc furnace (1) meets the requirements of carbon content A1≤0.05% and phosphorus content A2≤0.005%, and then the oxygen blowing oxidation is stopped.

7. The method for smelting ultra-supercritical steam turbine high alloy heat-resistant steel castings according to claim 6, characterized in that: In step S2, the carbon content B1≤0.13% and the phosphorus content B2≤0.013% of the recycled materials used in smelting; the carbon addition amount C1≤0.02% and the phosphorus addition amount C2≤0.002% during the smelting and casting process; the carbon content D1≤0.14% and the phosphorus content D2≤0.014% of the target casting.

8. The method for smelting ultra-supercritical steam turbine high alloy heat-resistant steel castings according to claim 7, characterized in that: Under the premise of meeting the carbon content of the target casting, the minimum addition ratio of the low-phosphorus and low-carbon steel ingot is ; Under the premise of meeting the phosphorus content of the target casting, the minimum addition ratio of the low-phosphorus low-carbon steel ingot is , the minimum addition ratio X of the low-phosphorus and low-carbon steel ingot is the larger value between X1 and X2.

9. The method for smelting ultra-supercritical steam turbine high alloy heat-resistant steel castings according to claim 8, characterized in that: In step S4, the carbon content of the first molten steel is E1, the phosphorus content is E2, and the carbon content of the material added to the first molten steel is , phosphorus content is .

10. The method for smelting high alloy heat-resistant steel castings for ultra-supercritical steam turbines according to claim 1, characterized in that: In step S1, after the low-phosphorus and low-carbon steel ingot is solidified and demoulded, the surface of the low-phosphorus and low-carbon steel ingot needs to be cleaned by grinding and / or shot blasting; And / or, in step S4, while replenishing the material into the first molten steel, alloys need to be added into the first molten steel to fine-tune the composition.

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