Method for Precisely Controlling Ce in Electroslag Remelting of Ce-Containing High-Temperature Alloys

Abstract

The present invention discloses a method for accurately controlling cerium in electroslag remelting of a cerium-containing high-temperature alloy, which adopts the following method and process: (1) using the following consumable electrode for smelting: a hole is bored in the center of the consumable electrode along the length direction, and a filler is filled in the hole; the filler composition and its weight ratio to the electrode are: Ce-Fe alloy 0.01%-0.05%, MgO 0.1%-0.5%, Na2SiO3 0.02%-0.04%; the Ce content in the Ce-Fe alloy is 20%-30wt%; (2) the composition and mass fraction of the slag system used for electroslag remelting are: CaF2 44%-48%, BaF2 15%-17.5%, TiO2 1%-2%, CaO 20%-25%, Al2O3 10%-15%, Ce2O3 2%-5%; (3) the entire smelting process is protected by protective gas, and the oxygen content in the protective cover is controlled to be ≤0.01vol%. The present invention adds Ce-Fe through holes in the electrode, which can completely offset the oxidation of Ce in the electroslag process; adding BaF2 with a low melting point into the slag system is beneficial to controlling the slag temperature and improving the surface quality of the ingot; adding a certain amount of Ce2O3 into the slag system can effectively inhibit the oxidation of Ce; and the yield of cerium is stabilized at more than 95%.

Description

Technical Field

[0001] The invention relates to an electroslag remelting method, in particular to a method for accurately controlling cerium during electroslag remelting of a cerium-containing high-temperature alloy. Background Art

[0002] High-temperature alloys have excellent performance and are widely used in aerospace, petrochemical, electric power and other fields. The use temperature of high-temperature alloys is very high, reaching 650-1000℃. Long-term service at this temperature requires the material to have certain endurance strength, creep strength, thermal fatigue strength and corresponding toughness. These high-temperature strength indicators are closely related to the material's organizational morphology, grain boundary strength, and precipitates, especially the grain boundary strength. According to statistics, half of the failures of high-temperature alloys are grain boundary fractures. Therefore, improving the grain boundary strength of high-temperature alloys has always been one of the most important topics for metallurgical researchers. In foreign high-temperature alloys, elements such as C, Zr, and B are often added to strengthen the grain boundaries, such as Alloy 10, Haynes S, Nimonic 115, Udimet 720LI and other alloys. In domestic high-temperature alloys, the advantages of rare earth resources are fully utilized, and many grades add Ce for grain boundary strengthening, such as GH1015, GH2035A, GH3652, GH4133 and other materials.

[0003] Ce has two advantages as a grain boundary strengthening element in high-temperature alloys. First, it acts as a purifier, deoxidizing and desulfurizing, reducing the harmful effects of oxygen and sulfur at the grain boundaries. Second, it acts as a microalloying element, segregating at the grain boundaries, increasing the grain boundary bonding force and strengthening the grain boundaries.

[0004] Since Ce is highly oxidizing, cerium-containing high-temperature alloys are generally produced using a vacuum induction + vacuum consumable dual process. However, the production cost of vacuum consumables is high, the surface quality of the ingots is poor, and the production scale and efficiency are low, which limits the application of such materials. In recent years, Chinese metallurgical workers have sought to use electroslag furnaces to stably produce cerium-containing high-temperature alloys, but have achieved little. At present, the yield of electroslag remelting Ce is between 10% and 30%, which is not ideal.

[0005] Patent CN202010133680.X discloses a slag system for smelting GH3625 nickel-based alloy containing rare earth Ce and its electroslag remelting smelting method. The composition of the slag system of this method is CaO 20-25%, Al2O3 17-21%, NaF 5-7%, MgO 3-5%, TiO2 1-2%, CeO2 4-6%, SiO2 1-2%, and the balance is CaF2. CeO2 is added to the slag system of this method to suppress the reaction of 3Ce+2Al2O3=4Al+3CeO2. However, the inventors of this application have found through a large number of experiments that the addition of CeO2 will cause C+2CeO2=Ce2O3+CO↑, which will inevitably cause bubbles in the ingot, so this method is not advisable. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for accurately controlling cerium in electroslag remelting of cerium-containing high-temperature alloys, which can effectively stabilize the cerium yield.

[0007] In order to solve the above technical problems, the present invention adopts the following method and process: (1) The following consumable electrode is used for smelting: a hole is punched in the center of the consumable electrode along the length direction, and a filler is filled in the hole; the filler composition and its weight ratio to the electrode are: Ce-Fe alloy 0.01% to 0.05%, MgO 0.1% to 0.5%, Na2SiO3 0.02% to 0.04%; the Ce content in the Ce-Fe alloy is 20% to 30wt%;

[0008] (2) The composition and mass fraction of the slag system for electroslag remelting are: CaF2 44%-48%, BaF2 15%-17.5%, TiO2 1%-2%, CaO 20%-25%, Al2O3 10%-15%, Ce2O3 2%-5%;

[0009] (3) The entire smelting process is protected by protective gas, and the oxygen content in the protective cover is controlled to be ≤0.01vol%.

[0010] The hole diameter of the hole in the present invention is Φ1-3mm.

[0011] The consumable electrode of the present invention is sintered at 450-550° C. for 3-4 hours.

[0012] The slag for electroslag remelting of the present invention is pre-melted at 1500-1600°C, cooled, crushed, and then baked at 650-750°C.

[0013] The target composition and mass fraction of the cerium-containing high-temperature alloy of the present invention are: C≤0.10%, Si≤0.35%, Mn≤0.35%, P≤0.010%, S≤0.010%, Cr 32%-35%, W 4.3%-5.3%, Mo 2.3%-3.3%, Al 0.5%-1.1%, Ti 0.5%-1.1%, Nb 0.5%-1.1%, Ce 0.005%-0.030%, and Ni balance.

[0014] The beneficial effects of the above technical scheme are as follows: the present invention adds Ce-Fe by perforating the electrode, which can completely offset the oxidation of Ce in the electroslag process, adds binders Na2SiO3 and MgO to the filler, solidifies the powdered material through high-temperature sintering, does not cause block or powder falling during smelting, and can accurately control the amount of Ce added; the present invention adds low-melting-point BaF2 to the slag system, which is beneficial to controlling the slag temperature and improving the surface quality of the ingot; the present invention adds a certain amount of Ce2O3 to the slag system (adding Ce2O3 instead of CeO2), which can effectively inhibit the oxidation of Ce and avoid the occurrence of the C+2CeO2=Ce2O3+CO↑ reaction, thereby effectively avoiding the appearance of bubbles in the ingot.

[0015] The electroslag cerium-containing high-temperature alloy produced by the present invention has a stable cerium recovery rate of more than 95%, and the recovery rates of easily oxidizable elements such as Al and Ti are also more than 95%, and other elements are basically not burned, which fully meets the process requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0017] Figure 1 It is a schematic diagram of the structure of the consumable electrode of the present invention.

[0018] In the figure: 1 - auxiliary electrode; 2 - filler; 3 - consumable electrode; 4 - alloy sealing plate. DETAILED DESCRIPTION

[0019] The technical concept and process of the method for precisely controlling cerium in electroslag remelting of cerium-containing high-temperature alloys are as follows: In order to ensure and stabilize the yield of cerium, the chemical properties of Ce and the characteristics of the electroslag process should be analyzed first. Since Ce is an easily oxidizable element and is easily oxidized when exposed to air at high temperatures, it should be considered to use argon protection during electroslag remelting to minimize the oxygen content in the atmosphere. On the other hand, consideration should be given to compensating for the amount of Ce that is inevitably oxidized during the electroslag process, that is, adding an appropriate amount of Ce to offset the burning loss of Ce, and this compensation should be accurate and uniform. After analysis, it can be concluded that electroslag-containing Ce high-temperature alloys should first minimize the oxidation of Ce, and secondly, accurately and uniformly compensate for the oxidation amount of Ce to achieve a dynamic balance of burning loss compensation.

[0020] Based on the above technical concept, the method for accurately controlling cerium in electroslag remelting of cerium-containing high-temperature alloys adopts the following method and process: (1) using the following consumable electrode for smelting: the consumable electrode is polished and bright, Figure 1 As shown, the consumable electrode 3 is pierced with a Φ1-3 mm hole passing through the center along the length direction, that is, the position of the central axis of the consumable electrode 3 is pierced with a hole along the axial direction; the hole is filled with a filler 2, and the components of the filler 2 are Ce-Fe alloy, MgO and Na2SiO3, the weight of the Ce-Fe alloy is 0.01%-0.05% of the weight of the consumable electrode (excluding the filler), the weight of MgO is 0.1%-0.5% of the weight of the consumable electrode (excluding the filler), and the weight of Na2SiO3 is 0.02%-0.04% of the weight of the consumable electrode (excluding the filler), and the mass fraction of Ce in the Ce-Fe alloy is 20%-30%; the above powdered components are mixed and compacted to obtain the filler.

[0021] (2) Figure 1 As shown, the top of the consumable electrode is welded with an auxiliary electrode 1, and the bottom is welded with a 3-5 mm thick alloy sealing plate 4 with the same composition as the consumable electrode 3 base material for sealing; the consumable electrode is sintered at 450-550° C. for 3-4 hours and then used for smelting.

[0022] (3) The composition of the slag system for electroslag remelting is (wt): CaF2 44%~48%, BaF2 15%~17.5%, TiO2 1%~2%, CaO 20%~25%, Al2O3 10%~15%, Ce2O3 2%~5%.

[0023] The prepared slag is pre-melted at 1500-1600°C for 30-40 minutes, and then crushed into pre-melted slag after cooling to room temperature; the pre-melted slag is then baked at 650-750°C for 5-6 hours before use.

[0024] (4) Place 100-300g of blocky TiO2 arc starter on the bottom water tank and 200-1000g of CaF2 powder around it;

[0025] (5) Install the crystallizer and consumable electrode, and introduce protective gas into the protective cover to replace the air until the oxygen content is ≤0.01 vol%, and the protective gas is preferably argon; the descending electrode ignites the arc, and the pre-melted slag is added to start slagging. When the slag temperature rises to 1650-1750°C, it enters the stable smelting stage;

[0026] (6) Control the melting rate v=0.55~0.65D in the stable melting stage 结 ; said D 结 is the diameter of the crystallizer, mm; v is the melting rate, kg / h;

[0027] (7) After smelting, continue to introduce protective gas for 30 to 120 minutes before demolding.

[0028] (8) The target composition of the cerium-containing high-temperature alloy smelted by this method is (wt%): C≤0.10%, Si≤0.35%, Mn≤0.35%, P≤0.010%, S≤0.010%, Cr 32%~35%, W 4.3%~5.3%, Mo 2.3%~3.3%, Al 0.5%~1.1%, Ti 0.5%~1.1%, Nb 0.5%~1.1%, Ce 0.005%~0.030%, Ni balance.

[0029] Example 1: The method for accurately controlling cerium in electroslag remelting of a cerium-containing high-temperature alloy is specifically described as follows.

[0030] Consumable electrode specifications: Φ120×1650mm, weight 150kg, alloy composition see Table 1; crystallizer specifications: Φ160×1500mm; slag composition (wt): CaF2 44.5%, BaF2 17.5%, TiO2 1%, CaO 20%, Al2O3 15%, Ce2O3 2%; slag volume: 6kg. The smelting process is as follows:

[0031] (1) A circular hole with a diameter of 1 mm is pierced in the central axis of the consumable electrode, and the filling materials are: 15 g Ce-Fe, 150 g MgO, and 30 g Na2SiO3, and the Ce content in the Ce-Fe alloy is 30 wt%; an auxiliary electrode is welded on the top of the consumable electrode, and a 3 mm thick alloy sealing plate with the same composition as the base material is welded on the bottom; the consumable electrode is sintered at 450°C for 3 hours;

[0032] (2) Pre-melt the prepared slag at 1500℃ for 30 minutes, cool it to room temperature, crush it, and bake it in a 650℃ heating furnace for 5 hours;

[0033] (3) Lay 100g of TiO2 block arc starter in the bottom water tank and place 200g of CaF2 powder around it; install electrodes and crystallizer, introduce Ar to replace air into the crystallizer, and lower the electrode when the oxygen content in the protective cover reaches 0.008vol%;

[0034] (4) Ignite the arc, add slag, start the slagging stage, and when the slag temperature rises to 1750°C, enter the stable smelting stage; control the melting rate to 88 kg / h until the smelting is completed; continue to pass argon for 30 minutes and then demold; the electroslag ingot can be obtained, and the composition is tested. The results are shown in Table 1.

[0035] (5) Comparative example: Electrodes with the same composition were smelted using conventional technology. The electrode and mold specifications and slag amount were the same. The slag composition (wt%) was: CaF2 45%, BaF2 15%, CaO 20%, Al2O3 15%, TiO2 5%. Comparative electroslag ingots were obtained and their composition was tested. The results are shown in Table 1.

[0036] Table 1: Composition (wt) of electroslag ingots obtained in Example 1 and Comparative Example

[0037]

[0038] It can be seen from Table 1 that the Ce recovery rate of the electroslag casting ingot is 96%; the Ce recovery rate of the comparative electroslag casting ingot is only 36%.

[0039] Example 2: The method for accurately controlling cerium in electroslag remelting of a cerium-containing high-temperature alloy is specifically described as follows.

[0040] The consumable electrode specifications are: Φ220×2600mm, the mass is 800kg, and the alloy composition is shown in Table 1; the crystallizer specifications are: Φ300×1800mm; the slag composition (wt): CaF2 44%, BaF2 15%, TiO2 1.5%, CaO 25%, Al2O3 11%, Ce2O3 3.5%; the slag volume is 30kg. The smelting process is as follows:

[0041] (1) A circular hole with a diameter of 2 mm is pierced in the central axis of the consumable electrode, and the filling materials are: Ce-Fe 160g, MgO 1600g, Na2SiO3 240g, and the Ce content in the Ce-Fe alloy is 30wt%; an auxiliary electrode is welded on the top of the consumable electrode, and a 4mm thick alloy sealing plate with the same composition as the base material is welded on the bottom; the consumable electrode is sintered at 500°C for 3.5h;

[0042] (2) Pre-melt the prepared slag at 1550℃ for 35 minutes, cool it to room temperature, crush it, and bake it in a 700℃ heating furnace for 5 hours;

[0043] (3) Lay 250g of TiO2 arc starter block in the bottom water tank and place 500g of CaF2 powder around it; install electrodes and crystallizer, introduce Ar to replace air into the crystallizer, and lower the electrode when the oxygen content in the protective cover reaches 0.006vol%;

[0044] (4) Ignite the arc, add slag, start the slagging stage, and turn to stable smelting when the slag temperature rises to 1700℃; control the melting rate to 180kg / h until the smelting is completed; continue to pass argon gas for 60min and then demould; the electroslag ingot can be obtained, and the composition is tested. The results are shown in Table 2.

[0045] (5) Comparative example: Electrodes with the same composition were smelted using conventional technology. The electrode and mold specifications and slag amount were the same. The slag composition (wt%) was: CaF2 43%, BaF2 15%, CaO 20%, Al2O3 15%, TiO2 5%, Ce2O3 2%. Comparative electroslag ingots were obtained and their composition was tested. The results are shown in Table 2.

[0046] Table 2: Composition (wt) of electroslag ingots obtained in Example 2 and Comparative Example

[0047]

[0048] It can be seen from Table 2 that the Ce recovery rate of the electroslag casting ingot is 95%; compared with the electroslag casting ingot, 2% Ce2O3 was added to the slag, and the Ce recovery rate was improved, but it was only 42%.

[0049] Example 3: The method for accurately controlling cerium in electroslag remelting of cerium-containing high-temperature alloy is specifically described as follows.

[0050] The consumable electrode specifications are: Φ300×3000mm, mass 1700kg, alloy composition see Table 1; crystallizer specifications: Φ400×2000mm; slag composition (wt): CaF2 48%, BaF2 16%, TiO2 2%, CaO 20%, Al2O3 10%, Ce2O3 4%; slag volume: 55kg. The smelting process is as follows:

[0051] (1) A circular hole with a diameter of 2.5 mm is pierced in the central axis of the consumable electrode, and the filling materials are: 600 g of Ce-Fe, 6000 g of MgO, and 450 g of Na2SiO3, and the Ce content in the Ce-Fe alloy is 20 wt%; an auxiliary electrode is welded on the top of the consumable electrode, and a 5 mm thick alloy sealing plate with the same composition as the base material is welded on the bottom; the consumable electrode is sintered at 550°C for 4 hours;

[0052] (2) Pre-melt the prepared slag at 1600°C for 40 minutes, cool it to room temperature, crush it, and bake it in a heating furnace at 750°C for 6 hours;

[0053] (3) Lay 300g of TiO2 block arc starter in the bottom water tank and place 800g of CaF2 powder around it; install electrodes and crystallizer, introduce Ar to replace air into the crystallizer, and lower the electrode when the oxygen content in the protective cover is 0.01vol%;

[0054] (4) Ignite the arc, add slag, start the slagging stage, and turn to stable smelting when the slag temperature rises to 1650°C; control the melting rate to 260kg / h until the end of smelting; continue to pass argon gas for 80 minutes and then demold; the electroslag ingot can be obtained, and the composition is tested. The results are shown in Table 3.

[0055] (5) Comparative example: Electrodes with the same composition were smelted using conventional technology. The electrode and mold specifications and slag amount were the same. The slag composition (wt%) was: CaF2 40%, BaF2 15%, CaO 20%, Al2O3 15%, TiO2 5%, Ce2O3 5%. Comparative electroslag ingots were obtained and the composition was tested. The results are shown in Table 3.

[0056] Table 3: Composition (wt) of electroslag ingots obtained in Example 3 and Comparative Example

[0057]

[0058] It can be seen from Table 3 that the Ce recovery rate of the electroslag casting ingot is 95%; compared with the electroslag casting ingot, 5% Ce2O3 is added to the slag, and the Ce recovery rate is further improved, but it is only 55%.

[0059] Example 4: The method for accurately controlling cerium in electroslag remelting of cerium-containing high-temperature alloy is specifically described as follows.

[0060] Consumable electrode specifications: Φ420×4500mm, mass 5000kg, alloy composition see Table 1; crystallizer specifications: Φ630×2400mm; slag composition (wt): CaF2 45%, BaF2 16%, TiO2 2%, CaO 22%, Al2O3 10%, Ce2O3 5%; slag volume: 140kg. The smelting process is as follows:

[0061] (1) A circular hole with a diameter of 3 mm is pierced in the central axis of the consumable electrode, and the filling materials are: 2.5 kg of Ce-Fe, 25 kg of MgO, and 2 kg of Na2SiO3, and the Ce content in the Ce-Fe alloy is 25 wt%; an auxiliary electrode is welded on the top of the consumable electrode, and a 5 mm thick alloy sealing plate with the same composition as the base material is welded on the bottom; the consumable electrode is sintered at 550°C for 3.5 hours;

[0062] (2) Pre-melt the prepared slag at 1550°C for 40 minutes, cool it to room temperature, crush it, and bake it in a heating furnace at 750°C for 5.5 hours;

[0063] (3) Lay 300g of TiO2 arc starter block in the bottom water tank and place 1000g of CaF2 powder around it; install electrodes and crystallizer, introduce Ar to replace air into the crystallizer, and lower the electrode when the oxygen content in the protective cover reaches 0.007vol%;

[0064] (4) Ignite the arc, add slag, start the slagging stage, and turn to stable smelting when the slag temperature rises to 1720°C; control the melting rate to 400kg / h until the smelting is completed; continue to pass argon for 120min and then demould; the electroslag ingot can be obtained, and the composition is tested. The results are shown in Table 4.

[0065] (5) Comparative example: Electrodes with the same composition were smelted using conventional technology. The electrode and crystallizer specifications and slag amount were the same. The slag composition (wt%) was: CaF2 35%, BaF2 15%, CaO 20%, Al2O3 15%, TiO2 5%, Ce2O3 10%. Comparative electroslag ingots were obtained and the composition was tested. The results are shown in Table 4.

[0066] Table 4: Composition (wt) of electroslag ingots obtained in Example 4 and Comparative Example

[0067]

[0068] It can be seen from Table 4 that the Ce recovery rate of the electroslag ingot is 96%; compared with the electroslag ingot, 10% Ce2O3 was added to the slag, and the Ce recovery rate was equivalent to the comparative example of Example 3, which was only 53.3%, indicating that the method of continuing to add Ce2O3 to the slag cannot make a qualitative improvement in the Ce recovery rate.

[0069] The above four embodiments illustrate that improving the Ce recovery rate in the electroslag process requires improvements in both the electrode and the slag system. Improvements made only in the slag system are unsuccessful.

Claims

1. A method for accurately controlling cerium in electroslag remelting of cerium-containing high-temperature alloys, characterized in that: The following method and process are adopted: (1) the following consumable electrode is used for smelting: a hole is punched in the center of the consumable electrode along the length direction, and a filler is filled in the hole; the filler composition and its weight ratio to the electrode are: Ce-Fe alloy 0.01% to 0.05%, MgO 0.1% to 0.5%, Na2SiO3 0.02% to 0.04%; the Ce content in the Ce-Fe alloy is 20% to 30wt%; (2) The composition and mass fraction of the slag system for electroslag remelting are: CaF2 44% to 48%, BaF2 15% to 17.5%, TiO2 1% to 2%, CaO 20% to 25%, Al2O3 10% to 15%, Ce2O3 2% to 5%; (3) The entire smelting process is protected by protective gas, and the oxygen content in the protective cover is controlled to be ≤0.01vol%.

2. The method for accurately controlling cerium in electroslag remelting of cerium-containing high-temperature alloy according to claim 1, characterized in that: The hole diameter is Φ1-3mm.

3. The method for accurately controlling cerium in electroslag remelting of cerium-containing high-temperature alloy according to claim 1, characterized in that: The consumable electrode is sintered at 450-550° C. for 3-4 hours.

4. The method for accurately controlling cerium in electroslag remelting of cerium-containing high-temperature alloy according to claim 1, characterized in that: The slag for electroslag remelting is pre-melted at 1500-1600°C, cooled, crushed, and then baked at 650-750°C.

5. The method for accurately controlling cerium in electroslag remelting of cerium-containing high-temperature alloy according to any one of claims 1 to 4, characterized in that: The target composition and mass fraction of the cerium-containing high-temperature alloy are: C≤0.10%, Si≤0.35%, Mn≤0.35%, P≤0.010%, S≤0.010%, Cr 32%-35%, W 4.3%-5.3%, Mo 2.3%-3.3%, Al 0.5%-1.1%, Ti0.5%-1.1%, Nb 0.5%-1.1%, Ce 0.005%-0.030%, and Ni balance.

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