High-chromium ultrapure base material for smelting high-end high-temperature alloy and preparation method of high-chromium ultrapure base material

Abstract

The invention belongs to the technical field of metallurgy, and relates to a high-chromium ultrapure base material, a preparation method thereof and application of the high-chromium ultrapure base material in preparation of a high-chromium high-temperature alloy. The preparation method of the high-chromium ultra-pure base material sequentially comprises a molten iron pretreatment procedure, a first slagging-off procedure, a K-OBM-S smelting procedure, a second slagging-off procedure, a VOD refining procedure, an LF refining procedure, a continuous casting procedure and a cutting procedure. The content of chromium in the ultra-pure base material prepared according to the method is 9.0-11.0%, the content of harmful impurity elements including sulfur (S is smaller than or equal to 0.00010%), phosphorus (P is smaller than or equal to 0.0080%), aluminum (Al is smaller than or equal to 0.015%), oxygen (O is smaller than or equal to 0.0025%) and nitrogen (P is smaller than or equal to 0.0080%) is extremely low, the content of P, S, Al, O and N in the ultra-pure base material is remarkably reduced compared with the content of P, S, Al, O and N in conventional raw materials including pure iron and ferrochrome alloy, and preparation of high-end high-chromium high-temperature alloy is met.

Description

Technical Field

[0001] The present invention relates to the field of metallurgical technology, and particularly relates to a high-chromium ultra-pure base material for smelting high-end superalloys and a preparation method thereof. Background Art

[0002] High-chromium superalloys have good high-temperature strength and excellent oxidation resistance, and are suitable for manufacturing hot-end components of aeroengines and gas turbines. The chromium content ranges from about 5% to 20%. One of the most important factors affecting the performance of high-chromium superalloys is the content of impurity elements. As the content of impurity elements in high-chromium superalloys increases, their high-temperature mechanical properties and oxidation resistance will decline sharply, thus showing a huge difference in performance. The most effective way to improve the quality of high-chromium superalloys and reduce the content of harmful impurity elements is to select high-quality ultra-pure raw materials.

[0003] The raw materials for smelting high-chromium superalloys are mainly pure iron + ferrochrome alloy or pure iron + metallic chromium. To reduce production costs and save energy, ferrochrome is mostly used for smelting. However, the content of impurity elements in ferrochrome and ordinary pure iron is relatively high, which cannot meet the requirements of the purity of high-end high-chromium superalloys. It is extremely difficult to smelt a high-purity base material with extremely low contents of harmful impurity elements, especially elements such as P, S, Al, O, and N. Mastering its preparation technology is of great significance to the performance of high-chromium superalloys.

[0004] Therefore, the present invention has developed a high-chromium ultra-pure base material for smelting superalloys. This ultra-pure base material has the advantages of both pure iron and ferrochrome, and has the characteristics of high chromium, extremely low sulfur, aluminum, phosphorus, oxygen, and nitrogen contents. Summary of the Invention

[0005] The object of the present invention is to provide a high-chromium ultra-pure base material for smelting high-end superalloys and a preparation method thereof in view of the above problems.

[0006] The object of the present invention is achieved as follows: A high-chromium ultra-pure base material for smelting high-end superalloys, the weight percentage of its components includes: Cr: 9.0 - 11.0%; C ≤ 0.005%; Si ≤ 0.30%; Mn ≤ 0.07%; P ≤ 0.0080%; S ≤ 0.0010%; Al ≤ 0.015%; O ≤ 0.0025%; N ≤ 0.0080%; Mo ≤ 0.0010%; Cu ≤ 0.015%; W ≤ 0.0010%; V ≤ 0.020%; the balance is Fe and impurities.

[0007] A preparation method of a high-chromium ultra-pure base material for smelting high-end superalloys, comprising the following steps: Step 1: Molten iron pretreatment: The temperature range of molten iron pretreatment is 1300 - 1350 °C. In the molten iron pretreatment stage, a deep dephosphorization slag system is used, and its components are: CaO: 38 - 42%; FeO: 10 - 15%; SiO2 : 17 - 22%; MgO: 4 - 7%; MnO: 5 - 7%; Al 2 O 3 : 2 - 3%; Basicity R: 1.7 - 2.5; Step 2: First slag skimming: The slag skimming process is controlled within 15 min - 25 min, and the remaining slag amount after slag skimming is 10% - 30% of the total slag amount; Step 3: K - OBM - S smelting: During the smelting process, 35 - 40 kg / t of steel of lime, 20 - 30 kg / t of steel of lightly burned dolomite, 2.0 - 3.5 kg / t of steel of fluorite, 12 - 16 kg / t of steel of ferrosilicon, and 150 - 180 kg / t of steel of ferrochrome are added. In the added ferrochrome, P ≤ 0.030%, V ≤ 0.10%, Cr: 66 - 70%, and the tapping temperature is 1660 - 1670 °C; Step 4: Second slag skimming: The slag skimming process is controlled within 15 min - 25 min, and the remaining slag amount ≤ 30 mm; Step 5: VOD refining: The starting treatment temperature is 1620 - 1640 °C, the ending temperature is 1590 - 1610 °C, the boiling vacuum degree is 1.1 - 1.4 mbar, the boiling time is 12 - 15 min, 13 - 18 kg / t of steel of lime, 1.4 - 2.2 kg / t of steel of fluorite, and 3.5 - 4.5 kg / t of steel of aluminum pellets are added. The reduction vacuum degree is 1.2 - 1.5 mbar, and the reduction time is 18 - 20 min; Step 6: LF refining: The LF treatment temperature is 1610 - 1630 °C, and deep desulfurization refining slag is used. The component of the refining slag is CaO: 45% - 60%, SiO 2 : 6 - 10%, Al 2 O 3 : 10 - 15%, MgO: 5 - 7%, CaF 2 : 5 - 7%; MnO + FeO: 0.3 - 0.6%; R: 6 - 10; MI, i.e., the Mannesmann index: CaO / (Al 2 O 3 ·SiO 2 ): 0.6 - 1.0, and the white slag time is 18 - 60 min; Step 7: Continuous casting: During the continuous casting process, tundish covering flux and mold powder are used to avoid secondary oxidation. The long nozzle is sealed with argon, and the submerged nozzle is an integrated nozzle. The insertion depth of the submerged nozzle is 150 - 200 mm. Square billet continuous casting with a specification of 200 mm × 200 mm - 240 mm × 240 mm is adopted. The process uses protective casting, and the superheat is controlled within 20 - 30 °C, and the casting speed is controlled at 0.85 - 1.05 m / min.

[0008] The beneficial effects of the present invention are as follows: The chromium content in the high-chromium ultra-pure base material prepared by the method of the present invention is 9.0% - 11.0%. At the same time, the contents of carbon (C≤0.005%), sulfur (S≤0.0010%), phosphorus (P≤0.0080%), aluminum (Al≤0.015%), oxygen (O≤0.0025%), and nitrogen (N≤0.0080%) are extremely low, which are significantly lower than the contents of P, S, Al, O, and N in conventional raw materials such as pure iron and ferrochromium alloys, meeting the preparation of high-end high-chromium superalloys. Specific Embodiments

[0009] A preparation method of a high-chromium ultra-pure base material successively includes: hot metal pretreatment process, first slag skimming process, K-OBM-S smelting process, second slag skimming process, VOD refining process, LF refining process, continuous casting process, and cutting process.

[0010] In the hot metal pretreatment temperature range of 1300 - 1350°C, a deep dephosphorization slag system was invented in the hot metal pretreatment stage, and its components are: CaO: 38 - 42%; FeO: 10 - 15%; SiO2: 17 - 22%; MgO: 4 - 7%; MnO: 5 - 7; Al2O3: 2 - 3; basicity R: 1.7 - 2.5.

[0011] During the LF refining process, the treatment temperature is 1610 - 1630°C, and a deep desulfurization refining slag was invented, and its components are CaO: 45% - 60%, SiO2: 6 - 10%, Al2O3: 10 - 15%, MgO: 5 - 7%, CaF2: 5 - 7%; MnO + FeO: 0.3 - 0.6%; R: 6 - 10; MI (Mannesmann Index: CaO / (Al2O3·SiO2): 0.6 - 1.0.

[0012] The high-chromium ultra-pure base material provided by the present invention, the weight percentages of its components include: Cr 9.0 - 11.0%; C≤0.005%; Si≤0.30%; Mn≤0.07%; P≤0.0080%; S≤0.0010%; Al≤0.015%; O≤0.0025%; N≤0.0080%; Mo≤0.0010%; Cu≤0.015%; W≤0.0010%; V≤0.020%; the balance is Fe and impurities.

[0013] To obtain a high-chromium (Cr: 9.0%-11.0%) ultra-pure base material with low contents of harmful impurity elements such as phosphorus, sulfur, aluminum, oxygen, and nitrogen for preparing high-end high-chromium superalloys, it is necessary to overcome the interactive effects of dephosphorization, desulfurization under high-chromium conditions, and deoxidation under low-aluminum conditions. According to the characteristics of the high-chromium ultra-pure base material, the present invention provides a preparation method, which successively includes: hot metal pretreatment process, the first slag skimming process, K-OBM-S smelting process, the second slag skimming process, VOD refining process, LF refining process, continuous casting process, and cutting process. A high-chromium ultra-pure base material with the compositional advantages of pure iron and ferrochrome and ensuring extremely low contents of sulfur, phosphorus, aluminum, oxygen, and nitrogen has been successfully developed.

[0014] Specific implementation process: To solve the problem of simultaneously achieving extremely low contents of P, S, Al, O, and N in the ultra-pure base material, the present invention proposes a process flow of hot metal pretreatment → slag skimming → K-OBM-S → slag skimming → VOD → LF → continuous casting, realizing the stable control of the ppm-level contents of key elements such as sulfur, phosphorus, aluminum, and nitrogen. The high-chromium ultra-pure base material provided by the present invention has the following component mass percentages: Cr 9.0-11.0%; C ≤ 0.005%; Si ≤ 0.30%; Mn ≤ 0.07%; P ≤ 0.0080%; S ≤ 0.0010%; Al ≤ 0.015%; O ≤ 0.0025%; N ≤ 0.0080%; Mo ≤ 0.0010%; Cu ≤ 0.015%; W ≤ 0.0010%; V ≤ 0.020%; the balance is Fe and impurities.

[0015] Based on the ultra-pure base material production method provided by the present invention, the weight percentage control resume of alloy element Cr and key impurity elements S, P, Al, O, and N is as follows: ① At the end of hot metal pretreatment, P ≤ 0.0020% and S ≤ 0.025%; ② After K-OBM-S smelting, Cr: 9.5-10.5% and P ≤ 0.0075%; ③ After VOD refining, S ≤ 0.0015% and P ≤ 0.0075%; ④ After LF refining, S ≤ 0.0010%, O ≤ 0.0020%, Al ≤ 0.015%, P ≤ 0.0080%, and N ≤ 0.080%. Thereby, the prepared high-chromium ultra-pure base material product meets the requirements for preparing high-purity and high-performance high-end high-chromium superalloys.

[0016] A key point of the present invention is that in the hot metal pretreatment temperature range of 1300-1350°C, a deep dephosphorization slag system is invented in the hot metal pretreatment stage, and its components are: CaO: 38-42%; FeO: 10-15%; SiO2: 17-22%; MgO: 4-7%; MnO: 5-7; Al2O3: 2-3; basicity R: 1.7-2.5. Under this slag system, the P content is controlled at ≤ 0.0020%.

[0017] Another key point of the present invention is that during the LF refining process, a deep desulfurization refining slag was invented, and its components are as follows: CaO: 45% - 60%, SiO2: 6 - 10%, Al2O3: 10 - 15%, MgO: 5 - 7%, CaF2: 5 - 7%; MnO + FeO: 0.3 - 0.6%; R: 6 - 10; MI (Mannesmann index: CaO / (Al2O3·SiO2)): 0.6 - 1.0. The weight percentage of S ≤ 0.0010%, the weight percentage of P ≤ 0.0080%, the weight percentage of O ≤ 0.0020%, and the weight percentage of Al ≤ 0.015%.

[0018] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions indicated in the following examples, they are carried out according to conventional methods and conditions. Example 1

[0019] The trial production was carried out using the process of "hot metal pretreatment → slag skimming → K-OBM-S → slag skimming → VOD → LF → continuous casting". The composition change process of the high-chromium ultra-pure base material is shown in Table 1. The specific steps of each process are as follows: The temperature range during the hot metal pretreatment process is 1300 °C, and the composition of the dephosphorization slag is: CaO: 38%; FeO: 12%; SiO 2 : 20%; MgO: 5%; MnO: 6%; Al 2 O 3 : 3%; basicity R: 1.9.

[0020] Slag skimming: To avoid excessive temperature drop of the molten steel, the entire slag skimming process is controlled within 25 minutes, and the remaining slag amount after slag skimming is 30% of the total slag amount.

[0021] K-OBM-S smelting: The main objectives during the K-OBM-S process are to increase the temperature, adjust the Cr content, and remove C and S. During the smelting process, 38.5 kg / t of lime, 26.2 kg / t of lightly burned dolomite, 2.6 kg / t of fluorite, 13.2 kg / t of ferrosilicon, and 166.5 kg / t of ferrochrome are added. According to the requirements of the steel grade composition characteristics, the P content in the added ferrochrome is ≤ 0.030%, the V content is ≤ 0.10%, and the Cr content is 66 - 70%. The tapping temperature is 1660 °C.

[0022] Slag skimming: The entire slag skimming process is controlled within 25 minutes, and the remaining slag amount is ≤ 30 mm.

[0023] VOD refining: The starting treatment temperature is 1620 °C, the ending temperature is 1590 °C, the boiling vacuum degree is 1.15 mbar, the boiling time is 13 minutes, 15 kg / t of lime, 1.4 kg / t of fluorite, and 3.5 kg / t of aluminum pellets are added. The reduction vacuum degree is 1.3 mbar, and the reduction time is 20 minutes.

[0024] LF refining: The LF treatment temperature is 1610 - 1630 °C, and the refining slag composition is CaO: 50%, SiO 2 : 6%, Al 2 O 3 : 10%, MgO: 5%, CaF 2 : 5%; MnO + FeO: 0.3%; R: 8.3; MI (Mannesmann Index: CaO / (Al 2 O 3 ·SiO 2 ): 0.83, and the white slag time is 18 min.

[0025] Billet continuous casting: In the billet continuous casting process, protective casting is adopted to prevent secondary oxidation. The superheat is controlled at 20 - 30 °C, and the drawing speed depends on the billet specifications. Example 2

[0026] Trial production is carried out using "hot metal pretreatment → slag skimming → K - OBM - S → slag skimming → VOD → LF → continuous casting". The composition change process of the high - chromium ultra - pure base material for superalloys is shown in Table 1. The specific steps of each process are as follows: The temperature range in the hot metal pretreatment process is 1320 °C, and the dephosphorization slag composition is: CaO: 40%; FeO: 10%; SiO 2 : 17%; MgO: 4%; MnO: 5%; Al 2 O 3 : 2%; basicity R: 2.35.

[0027] Slag skimming: The entire slag - skimming process is controlled within 22 min, and the remaining slag amount after slag skimming is 28% of the total slag amount.

[0028] K - OBM - S smelting: The main objectives of the K - OBM - S process are heating up, Cr alloying, C removal, and S removal. During the smelting process, 37.9 kg / t of lime, 25.8 kg / t of lightly burned dolomite, 2.4 kg / t of fluorite, 15.2 kg / t of ferrosilicon, and 170.7 kg / t of ferrochrome are added. The P ≤ 0.030%, V ≤ 0.10%, and Cr: 66 - 70% in the ferrochrome added according to the composition characteristics of the steel grade. The tapping temperature is 1670 °C.

[0029] Slag skimming: The entire slag - skimming process is controlled within 25 min, and the remaining slag amount ≤ 30 mm.

[0030] VOD refining: The starting treatment temperature is 1630 °C, the ending temperature is 1600 °C, the boiling vacuum degree is 1.2 mbar, the boiling time is 12 min, 14.5 kg / t of lime, 1.8 kg / t of fluorite, and 3.8 kg / t of aluminum pellets are added. The reduction vacuum degree is 1.25 mbar, and the reduction time is 18 min.

[0031] LF Refining: The LF treatment temperature is 1610 - 1630 °C, and the refining slag composition is CaO: 56%, SiO 2 : 7%, Al 2 O 3 : 12%, MgO: 6%, CaF 2 : 6%; MnO + FeO: 0.4%; R: 8.3; MI (Mannesmann Index: CaO / (Al 2 O 3 ·SiO 2 ): 0.67, and the white slag time is 20 min.

[0032] Billet Continuous Casting: In the billet continuous casting process, protective casting is adopted to prevent secondary oxidation. The superheat is controlled at 20 - 30 °C, and the casting speed depends on the billet specifications. Example 3

[0033] The trial production is carried out using the process of "hot metal pretreatment → slag skimming → K - OBM - S → slag skimming → VOD → LF → continuous casting". The composition change process of the high - chromium ultra - pure base material for superalloys is shown in Table 1. The specific steps of each process are as follows: The temperature range in the hot metal pretreatment process is 1350 °C, and the dephosphorization slag composition is: CaO: 42%; FeO: 15%; SiO 2 : 22%; MgO: 7%; MnO: 7%; Al 2 O 3 : 3%; basicity R: 1.9.

[0034] Slag Skimming: The entire slag - skimming process is controlled within 20 min, and the remaining slag amount after slag skimming is 26% of the total slag amount.

[0035] K - OBM - S Smelting: The main objectives of the K - OBM - S process are heating up, Cr addition, C and S removal. During the smelting process, 35.7 kg / t of lime, 20.2 kg / t of light - burned dolomite, 3.2 kg / t of fluorite, 12.4 kg / t of ferrosilicon, and 163.2 kg / t of ferrochrome are added. The P ≤ 0.030%, V ≤ 0.10%, and Cr: 66 - 70% in the ferrochrome added according to the composition characteristics of the steel grade. The tapping temperature is 1670 °C.

[0036] Slag Skimming: The entire slag - skimming process is controlled within 220 min, and the remaining slag amount ≤ 30 mm.

[0037] VOD Refining: The starting treatment temperature is 1640 °C, the ending temperature is 1610 °C, the boiling vacuum degree is 1.4 mbar, the boiling time is 15 min, 17.2 kg / t of lime, 2.2 kg / t of fluorite, and 4.2 kg / t of aluminum pellets are added. The reduction vacuum degree is 1.4 mbar, and the reduction time is 20 min.

[0038] LF refining: The LF treatment temperature is 1610 - 1630 °C, and the refining slag composition is CaO: 60%, SiO 2 : 10%, Al 2 O 3 : 10%, MgO: 7%, CaF 2 : 7%; MnO + FeO: 0.6%; R: 6; MI (Mannesmann Index: CaO / (Al 2 O 3 ·SiO 2 ): 0.6, and the white slag time is 20 min.

[0039] Billet continuous casting: Protective casting is adopted during the billet continuous casting process to prevent secondary oxidation. The superheat is controlled at 20 - 30 °C, and the drawing speed depends on the billet specifications.

[0040]

[0041] The above are only specific embodiments of the present invention, but the structural features within the protection scope of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the field of the present invention are covered by the patent scope of the present invention.

Claims

1. A high-chromium ultra-pure base material for smelting high-end high-temperature alloys, characterized in that: The weight percentages of its components include: Cr: 9.0-11.0%; C≤0.005%; Si≤0.30%; Mn≤0.07%; P≤0.0080%; S≤0.0010%; Al≤0.015%; O≤0.0025%; N≤0.0080%; Mo≤0.0010%; Cu≤0.015%; W≤0.0010%; V≤0.020%; the balance is Fe and impurities.

2. A method for preparing a high-chromium ultrapure base material for smelting high-end high-temperature alloys, characterized in that: The following steps are involved: Step 1: Hot metal pretreatment: The hot metal pretreatment temperature range is 1300-1350℃. In the hot metal pretreatment stage, a deep dephosphorization slag system is used, and its composition is: CaO: 38-42%; FeO: 10-15%; SiO2: 17-22%; MgO: 4-7%; MnO: 5-7%; Al2O3: 2-3%; Alkalinity R: 1.7-2.5; Step 2: First slag removal: The slag removal process is controlled within 15min-25min, and the amount of remaining slag after slag removal is 10%-30% of the total slag; Step 3: K-OBM-S smelting: During the smelting process, 35-40kg / t of lime, 20-30kg / t of light-burned dolomite, 2.0-3.5kg / t of fluorite, 12-16kg / t of ferrosilicon, and 150-180kg / t of ferrochrome are added. P≤0.030%, V≤0.10%, Cr: 66-70%, and the tapping temperature is 1660-1670℃. Step 4: Second slag removal: The slag removal process is controlled within 15min-25min, and the amount of slag left is ≤30mm; Step 5: VOD refining: starting treatment temperature 1620-1640℃, ending temperature 1590-1610℃, boiling vacuum degree 1.1-1.4mbar, boiling time 12-15min, adding lime 13-18kg / t steel, fluorite 1.4-2.2kg / t steel, aluminum shot 3.5-4.5kg / t steel, reduction vacuum degree 1.2-1.5mbar, reduction time 18-20min; Step 6: LF refining: LF treatment temperature is 1610-1630℃, deep desulfurization refining slag is used, and the refining slag components are CaO: 45%-60%, SiO2: 6-10%, Al2O3: 10-15%, MgO: 5-7%, CaF2: 5-7%; MnO+FeO: 0.3-0.6%; R: 6-10; MI is Mannesmann index: CaO / (Al2O3·SiO2): 0.6-1.0, white slag time 18-60min; Step seven: continuous casting: The continuous casting process uses a tundish covering agent and a mold protective slag to avoid secondary oxidation. The long nozzle is sealed with argon, and the submerged nozzle adopts an integrated nozzle. The insertion depth of the submerged nozzle is 150-200mm. Square billets with specifications of 200mm×200mm-240mm×240mm are used for continuous casting. The process adopts protective casting, the superheat is controlled at 20-30℃, and the pulling speed is controlled at 0.85-1.05m / min.

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