阅读说明：本技术 一种大尺寸高铌高温706合金铸锭及其冶炼工艺 (Large-size high-niobium high-temperature 706 alloy ingot and smelting process thereof ) 是由 黄烁 赵光普 张北江 段然 秦鹤勇 李连鹏 丑英玉 齐超 于 2019-08-28 设计创作，主要内容包括：本发明公开了一种大尺寸高铌高温706合金铸锭及其冶炼工艺,用于解决现有冶炼工艺易出现Al、Ti元素烧损严重以及所制得的高铌高温706合金铸锭易出现黑斑和白斑的冶金缺陷。冶炼工艺包括：真空感应熔炼,制得多支成分相同的真空感应锭,进而制得相同数量的电渣电极,利用(CaF<Sub>2</Sub>-CaO-Al<Sub>2</Sub>O<Sub>3</Sub>-TiO<Sub>2</Sub>)四元渣,进行交换电渣重熔,再利用所得电渣锭制得自耗电极,然后以该自耗电极为起始原料,进行两次真空自耗重熔。采用该工艺能够实现锭重15吨以上、直径800mm以上的高铌高温706合金大尺寸铸锭的制备,最大限度地抑制黑斑和白斑冶金缺陷形成,减少Al、Ti元素烧损率。(The invention discloses a large-size high-niobium high-temperature 706 alloy ingot and a smelting process thereof, which are used for solving the metallurgical defects that the burning loss of Al and Ti elements is serious and the prepared high-niobium high-temperature 706 alloy ingot is easy to have black spots and white spots in the existing smelting process. The smelting process comprises the following steps: vacuum induction melting to obtain multiple vacuum induction ingots with the same components, and further to obtain electroslag electrodes with the same quantity, and utilizing (CaF) 2 ‑CaO‑Al 2 O 3 ‑TiO 2 ) And exchanging the quaternary slag, remelting the quaternary slag, preparing a consumable electrode by using the obtained electroslag ingot, and performing twice vacuum consumable remelting by using the consumable electrode as a starting material. The process can realize the ingot weight of more than 15 tonsAnd the preparation of the high-niobium high-temperature 706 alloy large-size cast ingot with the diameter of more than 800mm can inhibit the formation of black spots and white spots metallurgical defects to the maximum extent and reduce the burning loss rate of Al and Ti elements.)

1. The large-size high-niobium high-temperature 706 alloy ingot is characterized in that the diameter of the large-size high-niobium high-temperature 706 alloy ingot is more than 800mm, and the large-size high-niobium high-temperature 706 alloy ingot comprises the following chemical components in percentage by mass:

less than or equal to 0.02 wt% of C, 15.5-16.5 wt% of Cr, 40.0-43.0 wt% of Ni, 2.8-3.2 wt% of Nb, 1.5-1.8 wt% of Ti, 0.1-0.3 wt% of Al, less than or equal to 0.10 wt% of Si, less than or equal to 0.20 wt% of Mn, less than or equal to 0.015 wt% of P, less than or equal to 0.0013 wt% of S, less than or equal to 0.30wt% of Co, less than or equal to 0.20 wt% of Mo, less than or equal to 0.006wt% of B, less than or equal to 0.30wt% of Cu, less than or equal to 0.005 wt% of.

2. The process of smelting a large-size high-niobium high-temperature 706 alloy ingot according to claim 1, comprising the steps of:

vacuum induction melting: according to the designed alloy component requirements, pure metal raw materials and/or return materials are weighed according to elements required by alloy in unit weight as raw materials, vacuum induction melting is carried out, the Ni content in a melting mother solution is controlled to be 40.0-43.0 wt%, the Nb content is controlled to be 2.80-3.3 wt%, the Ti content is controlled to be 0.5-2.0 wt%, the Al content is controlled to be 0.2-0.5 wt%, and a plurality of vacuum induction ingots with the same components are poured;

exchange electroslag remelting: manufacturing the same number of electroslag electrodes by using the manufactured vacuum induction ingot; adopting all the prepared electroslag electrodes to carry out exchange electroslag remelting under the argon protection state, wherein the adopted slag system is (CaF)₂-CaO-Al₂O₃-TiO₂) Quaternary slag, (CaF)₂-CaO-Al₂O₃-TiO₂) CaF in quaternary slag₂60-75 wt% of CaO, 10-25 wt% of Al₂O₃8-13 wt% of TiO₂1-10 wt%; after the exchange electroslag remelting is finished, cooling and demolding to prepare an electroslag ingot:

primary vacuum consumable remelting: carrying out primary annealing, secondary annealing and forging drawing on the demoulded electroslag ingot to a preset size to obtain a primary consumable electrode, wherein the secondary annealing temperature is higher than the primary annealing temperature; then, carrying out primary vacuum consumable remelting by using a primary consumable electrode;

secondary vacuum consumable remelting: polishing and flatting a primary consumable remelting ingot obtained by primary vacuum consumable remelting to obtain a secondary consumable electrode; and then carrying out secondary vacuum consumable remelting by using a secondary consumable electrode to prepare a cast ingot with a target diameter.

3. The smelting process according to claim 1, wherein in the vacuum induction smelting step, the melting temperature is 1300-1550 ℃, after the raw materials are melted down, the raw materials are refined for 15-120 min under the action of electromagnetic stirring, and the refining temperature is 1350-1550 ℃; then cooling for 1-10 hours, and demolding to obtain a vacuum induction ingot; the vacuum induction melting process is repeated for a plurality of times to obtain a plurality of vacuum induction ingots with the same components.

4. The smelting process according to claim 1, wherein the electroslag electrode is prepared by performing direct stress relief annealing on each vacuum induction ingot, wherein during annealing, the temperature is raised to 600-800 ℃ in advance, then raised to 800-1000 ℃ at a speed of 5-45 ℃/h, and kept for 4-32 h, then cooled to 600-800 ℃ at a speed of 1-35 ℃/h, kept for 4-32 h, then air-cooled, and then polished and blunt-ended to obtain the electroslag electrode.

5. The process according to claim 1, wherein the slag system used in the exchange electroslag remelting is (CaF)₂-CaO-Al₂O₃-TiO₂) Quaternary slag, (CaF)₂-CaO-Al₂O₃-TiO₂) CaF in quaternary slag₂60-75 wt% of CaO, 10-25 wt% of Al₂O₃8-13 wt% of TiO₂1 to 5wt%.

6. The smelting process according to claim 5, wherein the steady-state melting rate of electroslag remelting is controlled to be 5 to 15 kg/min; before each electrode exchange, when the residual weight of the previous electrode is 500 kg-1000 kg, the melting speed is increased to 12-25 kg/min by a slope of 0.5-2 kg/min on the basis of the steady-state melting speed, the electrode is kept stable until the electroslag electrode is exchanged, the smelting parameters before the exchange are kept in the process of exchanging the electrode, and the exchange time is not more than 2 min; after electrode exchange is completed every time, after the next electrode is melted to 100 kg-500 kg, the melting speed is reduced to 5-15 kg/min of the steady-state melting speed by the slope of 0.5-2 kg/min, remelting is continued until 200-600 kg of the last electrode is remained, and then heat capping is started; and after the exchange electroslag remelting is finished, cooling for 2-10 h, and demolding to obtain an electroslag ingot.

7. The process of claim 1, wherein the step of vacuum consumable remelting is performed a plurality of times, and the step of performing primary annealing, secondary annealing, forging and drawing on the demolded electroslag ingot to a predetermined size to obtain the primary consumable electrode is performed in the following manner,

starting primary annealing for the electroslag ingot within 0.5-2 h after demoulding, specifically, preheating to 300-550 ℃, keeping the temperature for 12-32 h to realize temperature equalization, then heating to 600-750 ℃ at the speed of 1-25 ℃/h, keeping the temperature for 4-32 h, then heating to 800-1000 ℃ at the speed of 5-35 ℃/h, keeping the temperature for 4-32 h, then cooling to 550-750 ℃ at the speed of 1-35 ℃/h, keeping the temperature for 4-32 h, and then air cooling;

carrying out secondary annealing on the electroslag ingot after the primary annealing is finished, specifically, heating to 800-1000 ℃ at a speed of 5-35 ℃/h, then heating to 1050-1150 ℃ at a speed of 1-25 ℃/h, carrying out heat preservation for 4-32 h, then heating to 1150-1250 ℃ at a speed of 1-25 ℃/h, carrying out heat preservation for 24-72 h, then cooling to 800-950 ℃ at a speed of 1-35 ℃/h, carrying out heat preservation for 4-32 h, and then carrying out air cooling;

heating the electroslag ingot subjected to secondary annealing to 1100-1180 ℃ before forging, wherein the heating time before forging is 4-12 hours, free forging adopts a fast forging machine with the length being pulled out in one direction of more than 3000 tons, the single-side reduction amount of each pass is controlled to be 5-30 mm, and the final forging temperature is 850-1000 ℃;

and (4) polishing and flatly flattening the steel ingot after the free forging and drawing to obtain the primary consumable electrode.

8. The smelting process according to claim 1, wherein the steady-state melting speed is controlled to be 3.5-7.5 kg/min when the primary vacuum consumable remelting is carried out; starting helium cooling after smelting of 800-2000 kg; reducing the current to adjust the melting speed to 3.0-7.0 kg/min after 1500-5000 kg of the alloy is remained; and starting hot capping after 200-1000 kg of residual molten ingot is obtained, so as to obtain the one-time consumable remelting ingot.

9. The smelting process according to claim 1, wherein the steady-state melting speed is controlled to be 4.0-8.5 kg/min when secondary vacuum consumable remelting is carried out; introducing helium gas for cooling after 1000-3000 kg of smelting is started; after 2000-5500 kg of residual alloy is obtained, reducing the current to adjust the melting speed to 3.0-7.5 kg/min; and starting the hot sealing top after the rest 250-1500 kg.

10. The smelting process according to claim 1, wherein after the secondary consumable remelting is completed, the alloy is cooled in vacuum for 1-8 hours, and then stress relief annealing is started within 2 hours; during annealing, preheating to 300-750 ℃, preserving heat for 4-32 h to realize temperature equalization, then heating to 800-1000 ℃ at the speed of 5-50 ℃/h, preserving heat for 4-32 h, then cooling to 550-750 ℃ at the speed of 1-35 ℃/h, preserving heat for 4-32 h, and then air cooling to obtain the ingot with the target diameter.

Technical Field

The invention relates to the technical field of large-size high-niobium alloy, in particular to a large-size high-niobium high-temperature 706 alloy ingot and a smelting process thereof.

Background

706 superalloy is a special alloy that causes distortion of the matrix metal lattice by adding elements (chromium, tungsten, molybdenum, etc.) of different size than the matrix metal atoms (e.g., nickel) to the raw material, strengthening the matrix by adding elements (e.g., cobalt) that reduce the stacking fault energy of the alloy matrix and elements (tungsten, molybdenum, etc.) that slow the diffusion rate of the matrix elements. The steel ingot is subjected to aging treatment to precipitate second phases (γ', γ ", carbides, etc.) from the supersaturated solid solution, thereby strengthening the alloy. The structure of the gamma 'phase is the same as that of the matrix, the gamma' phase is of a face-centered cubic structure, the lattice constant is close to that of the matrix and the gamma 'phase is coherent with the crystal, so that the gamma' phase can be uniformly separated out in the form of fine particles in the matrix, the dislocation motion is blocked, and the obvious strengthening effect is generated. The gamma' phase is an intermetallic compound of A3B type, A represents nickel and cobalt, B represents aluminum, titanium, niobium, tantalum, vanadium and tungsten, and chromium, molybdenum and iron can be A and B. The typical gamma ' phase in the nickel-based alloy is Ni3(Al, Ti), the gamma ' phase is a body-centered tetragonal structure and comprises Ni3Nb, and the mismatching degree of the gamma ' phase and a matrix is high, so that the coherent distortion can be caused to a large extent, the alloy obtains high yield strength, but the strengthening effect is obviously reduced when the temperature exceeds 700 ℃, and the alloy needs to be treated by adopting a special treatment process. In addition, for 706 alloy containing Al and Ti, burning loss of Al and Ti is easy to occur in the electroslag remelting process, which is also an urgent problem to be solved in the preparation process.

In addition, for the high-temperature nickel-based 706 alloy with the Nb content exceeding 3%, the triple smelting process of vacuum induction smelting, electroslag remelting and vacuum consumable remelting is commonly adopted in the European and American production of high-temperature large ingots with the weight of more than 10 tons. For example, patent US20020170386a1 shows a triple smelting process for large ingots with an alloy diameter of 762mm or more. During the use of the triple smelting equipment, the diameters of the ingot shape and the electrode need to be matched, and several matching examples of the ingot shape and the electrode are given in the patent. However, for consumable high temperature alloy ingots weighing more than 15 tons, the vacuum induction ingot weighs more than 20 tons taking into account the loss between triple smelting ring joints (electrode polishing and flat head and tail), and the requirement for equipment capacity of the vacuum induction furnace and electroslag remelting furnace is higher. The main technical bottleneck of producing the high-temperature alloy large ingot with the capacity of more than 15 tons at home at present is that no vacuum induction melting equipment with the nominal capacity of more than 20 tons exists, and a single vacuum induction electrode ingot blank with the capacity of more than 20 tons cannot be prepared. In order to solve the problem, the method is suitable for domestic equipment conditions, 2 induction ingots of 10 tons are poured by a vacuum induction furnace, double-support-arm exchange electrodes are used for remelting, two short electrodes of small tonnage are used for preparing high-temperature alloy electroslag ingots of large tonnage, and the electrodes are forged for subsequent vacuum consumable remelting. However, when a method of remelting by using a double-arm exchange electrode is used to prepare a large-size electroslag ingot, a series of quality defects such as contact injection, steel flow, component fluctuation and inclusion are easily formed in the electrode exchange process, and the quality defects cannot be completely eliminated even through subsequent high-temperature diffusion annealing and electrode forging. In the subsequent vacuum consumable remelting process, when the consumable ingot is smelted to an electrode joint, the quality defects can cause fluctuation of smelting parameters of the consumable remelting process, 706 alloy with high alloying degree is very sensitive to the consumable remelting smelting process parameters, and smelting defects such as black spots, white spots and the like are easily caused by parameter fluctuation, so that the metallurgical quality of the consumable ingot is influenced.

Disclosure of Invention

Aiming at the defects in the prior art, the first purpose of the invention is to provide a large-size high-niobium high-temperature 706 alloy cast ingot, the weight of the obtained cast ingot can reach at least 15 tons, metallurgical defects such as black spots and white spots are avoided, Al and Ti elements are not obviously burnt, and bars forged by the cast ingot are subjected to nondestructive inspection to find that an electroslag remelting joint has no abnormal signal.

The second purpose of the invention is to provide the smelting process of the large-size high-niobium high-temperature 706 alloy ingot, which realizes the smelting of the large-size high-niobium high-temperature 706 alloy ingot with the ingot weight of more than 15 tons and the diameter of more than 800mm, has no obvious burning loss of Al and Ti elements in the smelting process, can effectively prevent the problem of heat cracking, furthest inhibit the formation of black spots and white spots metallurgical defects, reduce the element segregation degree and improve the thermoplasticity of the steel ingot.

In order to achieve the purpose, the invention provides the following technical scheme: the large-size high-niobium high-temperature 706 alloy ingot is characterized in that the diameter of the large-size high-niobium high-temperature 706 alloy ingot is more than 800mm, and the large-size high-niobium high-temperature 706 alloy ingot comprises the following chemical components in percentage by mass:

less than or equal to 0.02 wt% of C, 15.5-16.5 wt% of Cr, 40.0-43.0 wt% of Ni, 2.8-3.2 wt% of Nb, 1.5-1.8 wt% of Ti, 0.1-0.3 wt% of Al, less than or equal to 0.10 wt% of Si, less than or equal to 0.20 wt% of Mn, less than or equal to 0.015 wt% of P, less than or equal to 0.0013 wt% of S, less than or equal to 0.30wt% of Co, less than or equal to 0.20 wt% of Mo, less than or equal to 0.006wt% of B, less than or equal to 0.30wt% of Cu, less than or equal to 0.005 wt% of.

The invention provides a smelting process of a large-size high-niobium high-temperature 706 alloy ingot, which comprises the following steps of:

vacuum induction melting: according to the designed alloy component requirements, pure metal raw materials and/or return materials are weighed according to elements required by alloy in unit weight as raw materials, vacuum induction melting is carried out, the Ni content in a melting mother solution is controlled to be 40.0-43.0 wt%, the Nb content is controlled to be 2.80-3.3 wt%, the Ti content is controlled to be 0.5-2.0 wt%, the Al content is controlled to be 0.2-0.5 wt%, and a plurality of vacuum induction ingots with the same components are poured;

exchange electroslag remelting: manufacturing the same number of electroslag electrodes by using the manufactured vacuum induction ingot; adopting all the prepared electroslag electrodes to carry out exchange electroslag remelting under the argon protection state, wherein the adopted slag system is (CaF)₂-CaO-Al₂O₃-TiO₂) Quaternary slag, (CaF)₂-CaO-Al₂O₃-TiO₂) CaF in quaternary slag₂60-75 wt% of CaO, 10-25 wt% of Al₂O₃8-13 wt% of TiO₂1-10 wt%; after the exchange electroslag remelting is finished, cooling and demolding to prepare an electroslag ingot:

primary vacuum consumable remelting: carrying out primary annealing, secondary annealing and forging drawing on the demoulded electroslag ingot to a preset size to obtain a primary consumable electrode, wherein the secondary annealing temperature is higher than the primary annealing temperature; then, carrying out primary vacuum consumable remelting by using a primary consumable electrode;

secondary vacuum consumable remelting: polishing and flatting a primary consumable remelting ingot obtained by primary vacuum consumable remelting to obtain a secondary consumable electrode; then, secondary vacuum consumable remelting is carried out by utilizing a secondary consumable electrode to prepare a cast ingot with a target diameter

In the technical scheme of the invention, in order to overcome the problem of burning loss of Al and Ti, the Al content in the smelting mother liquor is controlled to be 0.2-0.5 wt%, the additionally added Al can be used as a deoxidizer to a certain extent, and (CaF) is adopted in the electroslag remelting process₂-CaO-Al₂O₃-TiO₂) Four-component slag of (CaF)₂-CaO-Al₂O₃-TiO₂) CaF in quaternary slag₂60-75 wt% of CaO, 10-25 wt% of Al₂O₃8-13 wt% of TiO₂1-10 wt%, based on the amount of additionally added Al, the composition of each part of the slag system, especially TiO₂Content of (2) TiO in the slag system₂The content of the Ti is controlled to be 1-10 wt%, so that the problem of burning loss of Ti elements at the head and the tail of the electroslag ingot can be solved, the Ti component in the electroslag ingot can be ensured to be uniform, and the burning loss of easily-oxidized elements can be reduced to the greatest extent; in order to overcome the problem of insufficient capacity of vacuum induction smelting equipment, a vacuum induction furnace with conventional tonnage (such as 12 tons) is adopted to prepare a plurality of induction ingots with the same components (so that the requirement on the weight of a single induction ingot is reduced), so that a plurality of electroslag electrodes are prepared, then electrode exchange remelting is adopted to prepare large-tonnage electroslag ingots, and then two times of true remelting are carried outAnd (3) empty consumable remelting, wherein the metallurgical quality at the electrode exchange joint can be improved by once vacuum consumable remelting, and the problem of metallurgical quality can be thoroughly solved by twice vacuum consumable remelting, so that a high-quality high-temperature alloy large-size consumable ingot which is free of metallurgical defects and at least reaches 15 tons can be prepared. Considering the loss, the weight of the plurality of vacuum induction ingots is 125-160% of the target weight of the ingots.

In a preferred embodiment, in the step of vacuum induction melting, the melting temperature is 1300-1550 ℃, after the raw materials are melted down, the raw materials are refined for 15-120 min under the action of electromagnetic stirring, and the refining temperature is 1350-1550 ℃; then cooling for 1-10 hours, and demolding to obtain a vacuum induction ingot; the vacuum induction melting process is repeated for a plurality of times to obtain a plurality of vacuum induction ingots with the same components.

In fact, when the diameter of the vacuum induction ingot exceeds 800mm and the single-support weight exceeds 10 tons, a large-size induction ingot made of high-niobium high-temperature alloy can generate large thermal stress in the solidification process after the casting is finished, particularly aging precipitation type alloy containing Al and Ti can precipitate strengthening phases to cause larger structural stress after being cooled to the strengthening aging precipitation temperature range, and the steel ingot can be directly burst in severe cases. However, the demoulding time is too short, the steel ingot is not completely solidified, and the steel ingot is easy to crack after being demoulded prematurely.

Therefore, in a preferred embodiment, the electroslag electrode is prepared by directly performing stress relief annealing on each vacuum induction ingot, wherein during annealing, the temperature is increased to 600-800 ℃ in advance, then is increased to 800-1000 ℃ at the speed of 5-45 ℃/h, is kept for 4-32 h, then is cooled to 600-800 ℃ at the speed of 1-35 ℃/h, is kept for 4-32 h, is air-cooled, and then is polished and flatheaded to obtain the electroslag electrode. Generally, the diameter of the obtained electroslag electrode should be adapted to the diameter of the matching crystallizer of the consumable vacuum arc furnace used in the consumable vacuum remelting step, i.e. the diameter of the matching crystallizer and the diameter of the electrode should be kept in a proper ratio, i.e. the filling ratio, is about 0.8-0.9.

By adopting the scheme, the direct stress relief annealing of the vacuum induction ingot has many advantages, and firstly, the excessive tissue stress formed when the temperature falls into the aging precipitation region due to air cooling after the steel ingot is demoulded can be avoided in time; secondly, the temperature of the steel ingot can be increased at a reasonable heating rate, and large thermal stress generated inside and outside the steel ingot is avoided aiming at the problem of low thermal conductivity of high-temperature alloy; thirdly, the steel ingot is kept at the temperature of 800-1000 ℃ for a certain time to ensure that the temperature of the steel ingot is fully uniform and the solidification internal stress is released; fourthly, the steel ingot can be effectively prevented from forming larger thermal stress and structural stress again through slow cooling at the speed of 1-35 ℃/h and heat preservation at the temperature of 600-800 ℃ for a certain time.

In a preferred embodiment, when exchange electroslag remelting is carried out, the slag system used is (CaF)₂-CaO-Al₂O₃-TiO₂) Quaternary slag, (CaF)₂-CaO-Al₂O₃-TiO₂) CaF in quaternary slag₂60-75 wt% of CaO, 10-25 wt% of Al₂O₃8-13 wt% of TiO₂1 to 5wt%.

In a more preferred embodiment, the steady-state melting speed of electroslag remelting is controlled to be 5-15 kg/min, and when the residual weight of the previous electrode is 500-1000 kg before each electrode exchange, the melting speed is increased to 12-25 kg/min at a slope of 0.5-2 kg/min on the basis of the steady-state melting speed, the electrode exchange is kept stable until the electroslag electrode exchange is started, the smelting parameters before the electrode exchange are kept in the electrode exchange process, and the exchange time is not more than 2 min; after electrode exchange is completed every time, after the next electrode is melted to 100 kg-500 kg, the melting speed is reduced to 5-15 kg/min of the steady-state melting speed by the slope of 0.5-2 kg/min, remelting is continued until 200-600 kg of the last electrode is remained, and then heat capping is started; and after the exchange electroslag remelting is finished, cooling for 2-10 h, and demolding to obtain an electroslag ingot.

By adopting the technical scheme, aiming at an ingot type with the diameter of more than 1000mm, the steady-state melting speed of electroslag remelting is controlled to be 5-15 kg/min, and the subsequent melting speed before and after the exchange electrode is adjusted, so that the depth of a molten pool during the exchange electrode can be reasonably increased, the problem of reduced fluidity of the molten pool caused by the suspension of melting during the exchange electrode process can be solved, the disturbance of the electrode instantly embedded into the molten pool to the molten pool is reduced, and the metallurgical quality problems of inclusion, injection connection and the like are reduced.

In a preferred embodiment, the specific implementation of primary annealing, secondary annealing, forging and drawing to a predetermined size of the demolded electroslag ingot to produce one such consumable electrode is as follows,

starting primary annealing for the electroslag ingot within 0.5-2 h after demoulding, specifically, preheating to 300-550 ℃, keeping the temperature for 12-32 h to realize temperature equalization, then heating to 600-750 ℃ at the speed of 1-25 ℃/h, keeping the temperature for 4-32 h, then heating to 800-1000 ℃ at the speed of 5-35 ℃/h, keeping the temperature for 4-32 h, then cooling to 550-750 ℃ at the speed of 1-35 ℃/h, keeping the temperature for 4-32 h, and then air cooling;

carrying out secondary annealing on the electroslag ingot after the primary annealing is finished, specifically, preserving heat for 4-24 hours at the temperature of 550-750 ℃, then heating to 800-1000 ℃ at the speed of 5-35 ℃/h, then heating to 1050-1150 ℃ at the speed of 1-25 ℃/h, preserving heat for 4-32 hours, then heating to 1150-1250 ℃ at the speed of 1-25 ℃/h, preserving heat for 24-72 hours, then cooling to 800-950 ℃ at the speed of 1-35 ℃/h, preserving heat for 4-32 hours, and then air cooling;

heating the electroslag ingot subjected to secondary annealing to 1100-1180 ℃ before forging, wherein the heating time before forging is 4-12 hours, free forging adopts a fast forging machine with the length being pulled out in one direction of more than 3000 tons, the single-side reduction amount of each pass is controlled to be 5-30 mm, and the final forging temperature is 850-1000 ℃;

and (4) polishing and flatly flattening the steel ingot after the free forging and drawing to obtain the primary consumable electrode. Generally, the diameter of the primary consumable electrode should be adapted to the diameter of the mating mold of the consumable vacuum arc furnace used for the primary consumable remelting.

The reason for adopting the technical scheme is that the thermal stress of the obtained electroslag ingot with the diameter of the high-niobium high-temperature alloy being more than 1000mm is extremely large in the solidification process, so that the electroslag ingot is very easy to crack; because the consumable electrode and the corresponding crystallizer require reasonable filling ratio, the large-size electroslag ingot cannot be directly used for one-time consumable remelting, and free forging and drawing needs to be utilized to reduce the diameter, for example, the diameter can be 800-900 mm; however, the diameter of the electroslag ingot is too large, so that solidification segregation is very serious, serious dendrite element segregation and a low-melting-point phase among dendrites exist, and the thermoplasticity is extremely poor.

In order to solve the problem of thermal stress of high-niobium high-temperature alloy electroslag ingots with the diameter of more than 1000mm, water is introduced into a water-cooled crystallizer in an adopted electroslag remelting furnace for cooling for 2-10 hours after electroslag remelting so as to ensure that steel ingots are fully solidified and cooled to be below an aging precipitation temperature, and primary annealing is started within 0.5-2 hours after demolding. During primary annealing, preheating to 300-550 ℃, avoiding excessive thermal stress generated by overhigh temperature, then preserving heat for 12-32 hours at 300-550 ℃ to realize temperature equalization, then heating to 600-750 ℃ at the speed of 1-25 ℃/h, preserving heat for 4-32 hours, then heating to 800-1000 ℃ at the speed of 5-35 ℃/h, preserving heat for 4-32 hours, then cooling to 550-750 ℃ at the speed of 1-35 ℃/h, preserving heat for 4-32 hours, and then air cooling. Through one-time annealing, the thermal stress formed by the temperature gradient in the solidification process of the electroslag ingot can be released, meanwhile, the strengthening phase is coarsened by utilizing overaging treatment to avoid forming structural stress, and further, the direct explosion cracking of the large-size high-temperature alloy electroslag ingot after demoulding is inhibited.

In order to improve the thermoplasticity of the high-niobium high-temperature alloy electroslag ingot with the diameter of more than 800mm, the electroslag ingot is subjected to secondary annealing, namely high-temperature diffusion annealing after the annealing is finished. In order to avoid overlarge thermal stress, the temperature rising speed is strictly controlled, therefore, the electroslag ingot is charged into a furnace and is kept warm for 4-24 hours at the temperature below 550-750 ℃, then the temperature rises to 800-1000 ℃ at the speed of 5-35 ℃/h, then the temperature rises to 1050-1150 ℃ at the speed of 1-25 ℃/h and is kept warm for 4-32 hours, then the temperature rises to 1150-1250 ℃ at the speed of 1-25 ℃/h and is kept warm for 24-72 hours, then the temperature is cooled to 800-950 ℃ at the speed of 1-35 ℃/h and is kept warm for 4-32 hours, and then air cooling is carried out. Through multi-stage slow temperature rise, explosive cracking caused by overlarge thermal stress formed in the steel ingot can be avoided, and in addition, through high-temperature long-time diffusion annealing, low-melting-point phases in the alloy can be redissolved, the segregation of dendritic crystal elements is weakened, the thermoplasticity of the steel ingot is further improved, and the high-plasticity steel ingot is provided for preparing a consumable electrode through subsequent forging.

In a preferred embodiment, the steady-state melting speed is controlled to be 3.5-7.5 kg/min during one-time vacuum consumable remelting; starting helium cooling after smelting of 800-2000 kg; reducing the current to adjust the melting speed to 3.0-7.0 kg/min after 1500-5000 kg of the alloy is remained; and starting hot capping after 200-1000 kg of residual molten ingot is obtained, so as to obtain the one-time consumable remelting ingot.

In the primary vacuum consumable remelting process, because the volume of the spindle is reduced in the solidification process and gaps are formed between the spindle and the wall of the crystallizer, the steel ingot and cooling water on the outer wall of the crystallizer cannot be in direct contact under the vacuum condition to realize heat dissipation, and helium is introduced for heat conduction; the steel ingot can dissipate heat through the bottom and the crystallizer in the early stage of smelting, the heat dissipation of the bottom is limited after the steel ingot is smelted to a certain stage, therefore, a proper amount of helium needs to be introduced after the steel ingot is smelted to a certain stage, too much helium breaks through a molten pool to be not beneficial to smelting stability, and too little helium cannot play a cooling effect; because the steel ingot is too large, the more the steel ingot is solidified, the larger the heat capacity is, the more difficult the heat transfer is, therefore, the melting speed needs to be properly reduced in the final stage of smelting, the depth of a molten pool is stabilized, and the formation probability of metallurgical defects is further reduced; the timing of heat capping is judged according to the residual weight of the consumable electrode, so that the cutting amount of the steel ingot can be saved, and the yield can be improved.

In a preferred embodiment, before secondary vacuum consumable remelting, polishing and flatting the tail of a primary consumable remelting ingot to obtain a secondary consumable electrode with the diameter matched with that of a crystallizer used for secondary vacuum consumable remelting; when secondary vacuum consumable remelting is carried out, the steady-state melting speed is controlled to be 4.0-8.5 kg/min; introducing helium gas for cooling after 1000-3000 kg of smelting is started; after 2000-5500 kg of residual alloy is obtained, reducing the current to adjust the melting speed to 3.0-7.5 kg/min; starting the heat sealing top after the rest of 250-1500 kg;

in the preferred embodiment, after the secondary consumable remelting is finished, the vacuum cooling is carried out for 1-8 hours, and then the stress relief annealing is started within 2 hours; during annealing, the annealing furnace is preheated to 300-750 ℃, the temperature is kept for 4-32 h to realize temperature equalization, then the temperature is raised to 800-1000 ℃ at the speed of 5-50 ℃/h, the temperature is kept for 4-32 h, then the annealing furnace is cooled to 550-750 ℃ at the speed of 1-35 ℃/h, the temperature is kept for 4-32 h, and then the annealing furnace is air-cooled.

In the process of primary vacuum consumable remelting, because the primary consumable electrode is forged by utilizing electroslag ingots prepared by exchanging and remelting electroslag by a plurality of vacuum induction ingots, metallurgical quality fluctuation exists at an electrode exchange joint, and the fluctuation can not be completely eliminated even through high-temperature diffusion and forging. Because the consumable remelting process is very sensitive to the quality of the electrode, abnormal problems such as melting speed fluctuation, electrode block falling and the like are easy to occur when remelting is carried out to the electrode exchange joint, metallurgical defects such as black spots, white spots and the like are easy to form, the metallurgical defects cannot be eliminated through subsequent high-temperature diffusion annealing, forging or heat treatment procedures, and the prepared bar or forge piece can be directly scrapped in severe cases. Therefore, the secondary consumable electrode is prepared by polishing and flatly facing the primary consumable remelting ingot, and then secondary consumable remelting is carried out. The diameter of the steel ingot subjected to secondary consumable remelting exceeds 800mm, and large thermal stress exists, so that after secondary consumable remelting is completed, vacuum cooling is performed, then the blank is broken, stress relief annealing is started within 2h, explosion and cracking of the steel ingot after demolding are avoided, the steel ingot is preheated to 300-750 ℃ for heat preservation for 4-32 h to realize temperature equalization during annealing, then the temperature is increased to 800-1000 ℃ for heat preservation for 4-32 h at the speed of 5-50 ℃/h, then the steel ingot is cooled to 550-750 ℃ for heat preservation for 4-32 h at the speed of 1-35 ℃/h, air cooling is performed, and then the mode is adopted subsequently, so that the thermal stress formed by temperature gradient in the solidification process of the primary consumable remelting ingot can be released, meanwhile, overaging treatment is utilized, a strengthening phase is coarsened, the formation of tissue stress is avoided, and further, and direct electroslag cracking of large-size high-temperature alloy after demolding.

The invention has the following advantages:

1. according to the method for preparing the large-size high-niobium high-temperature 706 alloy, the addition amount of Al in molten steel is reasonably controlled, and a specific quaternary slag system is adopted in the exchange electroslag remelting process, so that no Al and Ti elements are obviously burnt in the process.

2. The method can break through the tonnage limitation of an induction furnace and an atmosphere protection electroslag furnace, adopts a conventional tonnage (such as 12 tons) vacuum induction furnace to prepare 2 electrodes, then utilizes the electrode exchange of the electroslag furnace to smelt 2 induction ingots into 1 electroslag ingot, and then is used for manufacturing vacuum consumable ingots of at least 15 tons;

3. the method can utilize an electroslag furnace with limited tonnage of an electrode support arm to prepare a 20-ton-grade high-temperature alloy electroslag ingot by adopting an exchange electroslag remelting method;

4. electroslag ingots prepared by exchange electroslag remelting are subjected to high-temperature diffusion annealing to obtain certain thermoplasticity, and free forging cogging and drawing are utilized to prepare consumable electrodes with proper diameters, so that the smelting stability in the one-time consumable remelting process can be obviously improved;

5. the secondary consumable electrode prepared from the primary consumable remelting steel ingot is used for secondary consumable remelting, and further consumable remelting is carried out for multiple times when necessary, so that the problems of metallurgical defects such as inclusion and the like at the joint of an electroslag ingot exchange electrode in the exchange electroslag remelting process can be effectively solved, and the high-niobium high-temperature alloy consumable ingot without metallurgical defects, with the diameter of more than 800mm and the weight of more than 15 tons, can be prepared.

Detailed Description

The present invention will be described in further detail with reference to examples.