High-chromium ultra-pure base material for smelting high-end high-temperature alloy and preparation method thereof

Abstract

The application belongs to the technical field of metallurgy, and is a high-chromium ultra-pure base material, a preparation method thereof and application of the high-chromium ultra-pure base material in preparation of high-chromium high-temperature alloy. The preparation method of the high-chromium ultra-pure base material comprises, in sequence, a molten iron pretreatment process, a first slagging process, a K-OBM-S smelting process, a second slagging process, a VOD refining process, an LF refining process, a continuous casting process and a cutting process. The chromium content of the ultra-pure base material prepared according to the method of the application is 9.0-11.0%, and the contents of harmful impurity elements, such as sulfur (S≤0.00010%), phosphorus (P≤0.0080%), aluminum (Al≤0.015%), oxygen (O≤0.0025%) and nitrogen (P≤0.0080%), are extremely low, which is significantly lower than the contents of P, S, Al, O and N in conventional raw materials, such as pure iron and chromium-iron alloy, and meets the preparation of high-end high-chromium high-temperature alloy.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a high-chromium ultrapure base material for smelting high-end high-temperature alloys and its preparation method. Background Technology

[0002] High-chromium superalloys possess good high-temperature strength and excellent oxidation resistance, making them suitable for manufacturing hot-end components of aero engines and gas turbines. Their chromium content ranges from approximately 5% to 20% (Cr). 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 increases, their high-temperature mechanical properties and oxidation resistance decline sharply, resulting in significant performance differences. 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, ferrochrome and ordinary pure iron have high impurity element content, which cannot meet the purity requirements of high-end high-chromium superalloys. Smelting high-purity base materials with extremely low levels of harmful impurity elements, especially P, S, Al, O, and N, is extremely difficult. Mastering the preparation technology is of great significance to the performance of high-chromium superalloys.

[0004] To this end, the present invention develops a high-chromium ultrapure base material for smelting high-temperature alloys. This ultrapure base material has the advantages of both pure iron and ferrochrome, and features high chromium, extremely low sulfur, aluminum, phosphorus, oxygen and nitrogen content. Summary of the Invention

[0005] The purpose of this invention is to address the above-mentioned problems by providing a high-chromium ultrapure base material for smelting high-end high-temperature alloys and its preparation method.

[0006] The objective of this invention is achieved as follows: a high-chromium ultrapure base material for smelting high-end high-temperature alloys, the weight percentages of its components being: 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 being Fe and impurities.

[0007] A method for preparing high-chromium ultrapure base material for smelting high-end high-temperature alloys includes the following steps: Step 1: Hot metal pretreatment: The hot metal pretreatment temperature range is 1300-1350℃. A deep dephosphorization slag system is used in the hot metal pretreatment stage, with the following composition: CaO: 38-42%; FeO: 10-15%; SiO2: 17-22%; MgO: 4-7%; MnO: 5-7%; Al2O3: 2-3%; Basicity R: 1.7-2.5; Step 2: First slag removal: The slag removal process is controlled within 15-25 minutes, and the amount of slag remaining after slag removal is 10%-30% of the total slag amount; Step 3: K-O BM-S smelting: During the smelting process, add 35-40 kg / t of lime, 20-30 kg / t of lightly calcined dolomite, 2.0-3.5 kg / t of fluorite, 12-16 kg / t of ferrosilicon, and 150-180 kg / t of ferrochrome. The added ferrochrome should contain P ≤ 0.030%, V ≤ 0.10%, and Cr 66-70%. The tapping temperature is 1660-1670℃. Step four: Second slag removal: The slag removal process is controlled within 15-25 minutes, with a slag residue ≤ 30 mm. Step five: VOD refining: The initial processing temperature is 1620-1640℃, and the final temperature is 1590-1610℃. The boiling vacuum degree is 1.1-1.4 mbar, the boiling time is 12-15 min, and 13-18 kg / t steel of lime, 1.4-2.2 kg / t steel of fluorite, and 3.5-4.5 kg / t steel of aluminum shot 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℃, and deep desulfurization refining slag is used. The refining slag composition is 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, i.e., Mannesmann index: CaO / (Al2O3·SiO2): 0.6-1.0, white slag time 18-60min; Step 7: Continuous casting: In the continuous casting process, tundish covering agent and crystallizer protective slag are used to avoid secondary oxidation. The long nozzle is sealed with argon. The submerged nozzle is 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 casting speed is controlled at 0.85-1.05m / min.

[0008] The beneficial effects of this invention are as follows: the high-chromium ultrapure base material prepared according to the method of this invention has a chromium content of 9.0%~11.0%, while 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. Compared with the contents of P, S, Al, O, and N in conventional raw materials pure iron and ferrochrome alloys, this significantly reduces the content of P, S, Al, O, and N, thus meeting the requirements for the preparation of high-end high-chromium high-temperature alloys. Detailed Implementation

[0009] A method for preparing a high-chromium ultrapure base material includes, in sequence: molten iron pretreatment process, first slag removal process, K-OBM-S smelting process, second slag removal process, VOD refining process, LF refining process, continuous casting process, and cutting process.

[0010] The pretreatment temperature range for molten iron is 1300-1350℃, and a deep dephosphorization slag system was invented during the molten iron pretreatment stage. Its composition is as follows: 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] A deep desulfurization refining slag was invented with a processing temperature of 1610-1630℃ in the LF refining process. Its composition is 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 ultrapure base material provided by this invention comprises the following components by weight percentage: 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%; with the balance being Fe and impurities.

[0013] To obtain a high-chromium ultrapure base material with high chromium (Cr: 9.0%-11.0%) and low levels of harmful impurities such as phosphorus, sulfur, aluminum, oxygen, and nitrogen for the preparation of high-end high-chromium superalloys, it is necessary to overcome the interaction between dephosphorization and desulfurization under high chromium conditions and deoxidation under low aluminum conditions. Based on the characteristics of the high-chromium ultrapure base material, this invention provides a preparation method, which sequentially includes: a molten iron pretreatment process, a first slag removal process, a K-OBM-S smelting process, a second slag removal process, a VOD refining process, an LF refining process, a continuous casting process, and a cutting process. A high-chromium ultrapure base material with the compositional advantages of pure iron and ferrochrome, while ensuring extremely low sulfur, phosphorus, aluminum, oxygen, and nitrogen content, has been successfully developed.

[0014] Specific implementation process: To address the issue of simultaneously achieving extremely low contents of P, S, Al, O, and N in ultrapure base materials, this invention proposes a process flow of molten iron pretreatment → slag removal → K-OBM-S → slag removal → VOD → LF → continuous casting, achieving stable control of the ppm-level contents of key elements such as sulfur, phosphorus, aluminum, and nitrogen. The high-chromium ultrapure base material provided by this invention comprises the following components by mass percentage: 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%; with the balance being Fe and impurities.

[0015] Based on the ultrapure base material production method provided by this invention, the weight percentage control of alloying element Cr and key impurity elements S, P, Al, O, and N is as follows: ① At the end of molten iron 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%. Therefore, the prepared high-chromium ultrapure base material meets the requirements for the preparation of high-purity, high-performance, high-end high-chromium high-temperature alloys.

[0016] A key aspect of this invention is that a deep dephosphorization slag system was invented during the hot metal pretreatment stage, with a temperature range of 1300-1350℃ and the following composition: 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 this invention is the development of a deep desulfurization refining slag in the LF refining process, with the following composition: 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 percentages of S, P, O, and Al are ≤0.0010%, ≤0.0080%, ≤0.0020%, and ≤0.015%.

[0018] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, are performed according to conventional methods and conditions. Example 1

[0019] The process of "hot metal pretreatment → slag removal → K-OBM-S → slag removal → VOD → LF → continuous casting" was adopted for trial production. The composition change process of high chromium ultrapure base material is shown in Table 1. The specific steps of each process are as follows: The temperature range of the hot metal pretreatment process is 1300℃. The composition of the dephosphorized slag is: CaO: 38%; FeO: 12%; SiO2: 20%; MgO: 5%; MnO: 6%; Al2O3: 3%; basicity R: 1.9.

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

[0021] K-OBM-S smelting: The main objectives of the K-OBM-S process are to increase the temperature, add Cr, and remove C and S. During the smelting process, 38.5 kg / t of lime, 26.2 kg / t of lightly calcined 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 characteristics of the steel grade, the added ferrochrome has P≤0.030%, V≤0.10%, and Cr: 66-70%. The tapping temperature is 1660℃.

[0022] Slag removal: The entire slag removal process should be controlled within 25 minutes, with the amount of slag left ≤30mm.

[0023] VOD refining: starting temperature 1620℃, ending temperature 1590℃, boiling vacuum 1.15mbar, boiling time 13min, adding lime 15kg / t steel, fluorite 1.4kg / t, aluminum shot 3.5kg / t steel, reduction vacuum 1.3mbar, reduction time 20min.

[0024] LF refining: The LF treatment temperature is 1610-1630℃, and the refining slag composition is CaO: 50%, SiO2: 6%, Al2O3: 10%, MgO: 5%, CaF2: 5%; MnO+FeO: 0.3%; R: 8.3; MI (Mannesmann index: CaO / (Al2O3·SiO2): 0.83), and the white slag time is 18 min.

[0025] Continuous casting of billets: The continuous casting process of billets adopts protective casting to prevent secondary oxidation. The superheat is controlled at 20-30℃, and the casting speed is determined according to the billet specifications. Example 2

[0026] The process of "hot metal pretreatment → slag removal → K-OBM-S → slag removal → VOD → LF → continuous casting" was adopted for trial production. The composition changes of the high-chromium ultrapure base material for high-temperature alloys are shown in Table 1. The specific steps of each process are as follows: The temperature range of the hot metal pretreatment process is 1320℃. The composition of the dephosphorized slag is: CaO: 40%; FeO: 10%; SiO2: 17%; MgO: 4%; MnO: 5%; Al2O3: 2%; basicity R: 2.35.

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

[0028] K-OBM-S smelting: The main objectives of the K-OBM-S process are to increase the temperature, add Cr, and remove C and S. During the smelting process, 37.9 kg / t of lime, 25.8 kg / t of lightly calcined dolomite, 2.4 kg / t of fluorite, 15.2 kg / t of ferrosilicon, and 170.7 kg / t of ferrochrome are added. According to the characteristics of the steel grade, the added ferrochrome has P≤0.030%, V≤0.10%, and Cr:66-70%. The tapping temperature is 1670℃.

[0029] Slag removal: The entire slag removal process should be controlled within 25 minutes, with the amount of slag left ≤30mm.

[0030] VOD refining: starting temperature 1630℃, ending temperature 1600℃, boiling vacuum 1.2mbar, boiling time 12min, adding lime 14.5kg / t steel, fluorite 1.8kg / t, aluminum shot 3.8kg / t steel, reduction vacuum 1.25mbar, reduction time 18min.

[0031] LF refining: The LF treatment temperature is 1610-1630℃, and the refining slag composition is CaO: 56%, SiO2: 7%, Al2O3: 12%, MgO: 6%, CaF2: 6%; MnO+FeO: 0.4%; R: 8.3; MI (Mannesmann index: CaO / (Al2O3·SiO2): 0.67), and the white slag time is 20 min.

[0032] Continuous casting of billets: The continuous casting process of billets adopts protective casting to prevent secondary oxidation. The superheat is controlled at 20-30℃, and the casting speed is determined according to the billet specifications. Example 3

[0033] The process of "hot metal pretreatment → slag removal → K-OBM-S → slag removal → VOD → LF → continuous casting" was adopted for trial production. The composition change process of high-chromium ultrapure base material for high-temperature alloy is shown in Table 1. The specific steps of each process are as follows: The temperature range of the hot metal pretreatment process is 1350℃. The composition of the dephosphorized slag is: CaO: 42%; FeO: 15%; SiO2: 22%; MgO: 7%; MnO: 7%; Al2O3: 3%; basicity R: 1.9.

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

[0035] K-OBM-S smelting: The main objectives of the K-OBM-S process are to increase the temperature, add Cr, and remove C and S. During the smelting process, 35.7 kg / t of lime, 20.2 kg / t of lightly calcined dolomite, 3.2 kg / t of fluorite, 12.4 kg / t of ferrosilicon, and 163.2 kg / t of ferrochrome are added. According to the characteristics of the steel grade, the added ferrochrome has P≤0.030%, V≤0.10%, and Cr:66-70%. The tapping temperature is 1670℃.

[0036] Slag removal: The entire slag removal process is controlled within 220 minutes, and the amount of slag left is ≤30mm.

[0037] VOD refining: Starting temperature 1640℃, ending temperature 1610℃, boiling vacuum 1.4mbar, boiling time 15min, adding 17.2kg / t steel of lime, 2.2kg / t fluorite, and 4.2kg / t steel of aluminum shot. Reduction vacuum 1.4mbar, reduction time 20min.

[0038] LF refining: The LF treatment temperature is 1610-1630℃, and the refining slag composition is CaO: 60%, SiO2: 10%, Al2O3: 10%, MgO: 7%, CaF2: 7%; MnO+FeO: 0.6%; R: 6; MI (Mannesmann index: CaO / (Al2O3·SiO2): 0.6), and the white slag time is 20 min.

[0039] Continuous casting of billets: The continuous casting process of billets adopts protective casting to prevent secondary oxidation. The superheat is controlled at 20-30℃, and the casting speed is determined according to the billet specifications.

[0040]

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

Claims

1. A high-chromium ultrapure 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 being Fe and impurities. A method for preparing high-chromium ultrapure base material for smelting high-end high-temperature alloys includes the following steps: Step 1: Hot metal pretreatment: The hot metal pretreatment temperature range is 1300-1350℃. A deep dephosphorization slag system is used in the hot metal pretreatment stage, with the following composition: CaO: 38-42%; FeO: 10-15%; SiO2: 17-22%; MgO: 4-7%; MnO: 5-7%; Al2O3: 2-3%; Basicity R: 1.7-2.

5. Step Two: First Slag Removal: The slag removal process should be controlled within 15-25 minutes, and the amount of slag remaining after slag removal should be 10%-30% of the total slag. Step 3: K-OBM-S smelting: During the smelting process, add 35-40 kg / t of lime, 20-30 kg / t of lightly calcined dolomite, 2.0-3.5 kg / t of fluorite, 12-16 kg / t of ferrosilicon, and 150-180 kg / t of ferrochrome. The added ferrochrome contains P≤0.030%, V≤0.10%, and Cr: 66-70%. The tapping temperature is 1660-1670℃. Step 4: Second slag removal: The slag removal process should be controlled within 15-25 minutes, with the amount of slag left ≤30mm; Step 5: VOD Refining: Start processing temperature 1620-1640℃, end processing temperature 1590-1610℃, boiling vacuum degree 1.1-1.4mbar, boiling time 12-15min, add 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 Six: LF Refining: The LF treatment temperature is 1610-1630℃, using deep desulfurization refining slag. The refining slag composition is: 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, or Mannesmann index: CaO / (Al2O3·SiO2): 0.6-1.0, white residue time 18-60 min; Step 7: Continuous casting: During the continuous casting process, a tundish covering agent and a crystallizer protective slag are used to avoid secondary oxidation. The long nozzle is sealed with argon, and the submerged nozzle is an integrated nozzle with an insertion depth of 150-200mm. Square billets with specifications of 200mm×200mm-240mm×240mm are used for continuous casting. The process adopts protective casting, and the superheat is controlled at 20-30℃. The casting speed is controlled at 0.85-1.05m / min.

Images