A method for controlling cracking defects of high-alloyed nickel-based wrought superalloy Φ508 mm specification ingot

Abstract

The application belongs to the technical field of metal materials, and particularly relates to a control method for cracking defects of high-alloyed nickel-based deformed high-temperature alloy ingot with a diameter of 508 mm. The method is a combination of VIM, installation of wedge-shaped riser, optimization of ingot solidification conditions, ESR slag optimization, power reduction method for feeding and VAR four-stage feeding, so as to reduce thermal stress and organizational stress generated in the melting process, thereby achieving the effect of improving the cracking defects of high-alloyed high-temperature alloy ingot. The high-alloyed high-temperature alloy ingot prepared by the method has good surface quality of triple ingot, and no cracking defects are found in the triple melting process, so that the effect of significantly reducing the cracking tendency of high-alloyed high-temperature alloy ingot can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, specifically relating to a method for controlling cracking defects in Φ508mm high-alloy nickel-based wrought high-temperature alloy ingots. Background Technology

[0002] With the rapid development of the aerospace industry, the thrust-to-weight ratio of aircraft is increasing, and the operating temperature of engine components is constantly rising, driving the research and application of wrought superalloys for turbine disks. To improve the service performance of these alloys and meet high-temperature strength requirements, a large amount of precipitation strengthening elements (Al, Ti, Nb) are added to high-performance wrought superalloys for turbine disks; these alloys are also known as highly alloyed wrought superalloys. Because of the high concentration of strengthening elements in highly alloyed wrought superalloys, compositional segregation and interdendritic eutectic precipitates inevitably occur, leading to a higher tendency for cracking.

[0003] The main causes of cracking in high-alloy high-temperature alloy ingots include: (1) External factors: During the alloy cooling process, the temperature difference between the center and the surface of the ingot causes uneven volume expansion and contraction, resulting in large thermal stress; (2) Internal factors: High-alloy high-temperature alloys have a high content of precipitation strengthening elements, and the micro-segregation of alloying elements is serious, resulting in large structural stress in the ingot. In order to improve the cracking defects of high-alloy high-temperature alloy ingots, the thermal stress and structural stress generated during the alloy cooling process should be reduced as much as possible. Existing technologies mainly optimize the process from the forging and heat treatment aspects of high-temperature alloy materials to prevent the alloy from cracking. However, in the field of alloy smelting, no effective method for controlling the cracking defects of high-alloy high-temperature alloy ingots has been proposed so far. Summary of the Invention

[0004] The technical problem to be solved by this invention is to provide a method for controlling cracking defects in Φ508mm high-alloy nickel-based wrought superalloy ingots. The method involves a three-stage melting process: vacuum induction melting (VIM), electroslag remelting (ESR), and vacuum arc remelting (VAR). In VIM melting, wedge risers are added and the ingot solidification conditions are optimized. In ESR melting, optimized pre-melted slag is used in combination with a power reduction method for feeding. In VAR melting, a four-stage feeding process is adopted. By combining the processes in each melting stage, the cracking tendency of the ingot in each melting step is reduced, so that the final high-alloy superalloy ingot does not crack.

[0005] To achieve the above objectives, the technical solution provided by this invention is a method for controlling cracking defects in Φ508mm high-alloy nickel-based wrought superalloy ingots, comprising the following steps:

[0006] (1) Vacuum induction melting: High-temperature alloy raw materials are vacuum induction melted. Before pouring, wedge-shaped heat-insulating risers are installed on the head of the ingot mold, and the temperature of the ingot mold is controlled. The alloy pouring temperature is 1420℃~1500℃. After pouring, the cooling time is determined according to the solidification time of the ingot. After cooling, the ingot is demolded. After demolding, the surface temperature of the ingot is measured and then hot annealing is carried out.

[0007] (2) Electroslag remelting: The ingot prepared in step (1) is subjected to electroslag remelting. In the later stage of remelting, the power is reduced in stages and the power is cut off at timed intervals to replenish the feed.

[0008] (3) Vacuum arc self-consuming remelting: Vacuum arc self-consuming remelting is carried out on the ingot prepared in step (2). During the steady-state remelting stage, the melting rate and droplet control are adopted. During the feeding stage, the current is reduced and the droplet control is increased. The cooling gas is linearly reduced and controlled.

[0009] Preferably, the composition of the high-alloyed nickel-based deformable superalloy, by mass percentage, is: Al 2.55%–3.90%, Ti 2.65%–5.20%, Nb 0%–3.40%, C 0.038%–0.07%, with the remainder being Ni.

[0010] Preferably, in step (1), before casting, the ingot mold is preheated to 400-600℃, and the time from loading the ingot mold into the mold chamber and evacuating it to casting is 30-90 minutes; wherein, the ingot mold is tapered, with a bottom inner diameter of Φ360±20mm and a top inner diameter of Φ340±20mm; the length of the wedge-shaped heat-insulating riser is 300-450mm, the thickness is 20-40mm, the inclination angle is 2-7°, the riser solidification time / ingot solidification time = 1.15-1.35; the ingot solidification time is the time when the solid phase volume fraction reaches ≥92%; the cooling time is the ingot solidification time ±10 minutes; and the ingot surface temperature is annealed at 600-800℃.

[0011] Preferably, in step (1), the power to the crucible is turned off in the early stage of casting, and the power of the crucible is increased to 20-50kW after the crucible tilt angle is greater than 60°.

[0012] Preferably, in step (2), the steady-state smelting power is set to 180-250kW, and the slag resistance is 4-10MΩ; the feeding is divided into 7 stages, and the feeding time is ≥70 minutes. The power P and time t of the feeding stage are set according to the following formula:

[0013] P n =P0*e (-a·t)

[0014] Where P0 is the steady-state smelting power, P nLet e ​​be the smelting power in the nth stage, e be the natural constant, and a be a coefficient. The ranges of a in each stage are 0.001–0.002, 0.002–0.004, 0.004–0.007, 0.0070–0.010, 0.010–0.013, 0.013–0.016, and 0.016–0.02, respectively.

[0015] After the power is reduced to the set value in the final stage, the power is immediately cut off and the furnace is cooled for 50±20 minutes. The cooling water temperature is set to 25~30℃ during furnace cooling. After exiting the furnace, hot annealing is performed.

[0016] Preferably, in step (2), the main components of the pre-melted slag, by weight percentage, are Al2O3 24.5±3.0%, TiO2 5.0±0.5%, CaO 23.0±3.0%, MgO 3.5±0.5%, and CaF2 44.0±3.0%; the pre-melted slag characteristic parameters are: moisture content ≤0.04%, which can reach ≤0.02% after baking; particle size 0~10mm, with slag material smaller than 1mm accounting for no more than 10% of the weight; electrical conductivity at 1700℃ ≥3.5Ω. -1 / cm, viscosity 0.010~0.020Pa·s.

[0017] Preferably, step (3) specifically includes: a steady-state smelting stage: the melting rate is set to 2.5–3.5 kg / min, and the droplet setting is 3.00–8.50 s. -1 The cooling gas flow rate is 0.1–0.2 L / min; the feeding stage is divided into four stages, with the current decreasing and the droplet increasing in stages, and the cooling gas flow rate decreasing linearly to below 0.02 L / min. The feeding time for each stage is 10–30 min.

[0018] Preferably, the process parameters for the four stages of the feeding process in step (3) are as follows:

[0019] First stage: The current is reduced to 75% to 85% of the stable melting current, the molten droplet is increased to 130% to 150% of the stable melting droplet, and the cooling gas flow rate is reduced to 90% to 95% of the stable melting flow rate;

[0020] Second stage: The current is reduced to 60% to 75% of the stable melting current, the molten droplet is increased to 150% to 160% of the stable melting droplet, and the cooling gas flow rate is reduced to 70% to 90% of the stable melting flow rate;

[0021] The third stage: the current is reduced to 30% to 60% of the stable melting current, the molten droplets are increased to 160% to 165% of the stable melting droplets, and the cooling gas flow rate is reduced to 30% to 70% of the stable melting flow rate;

[0022] Fourth stage: The current is reduced to 20% to 30% of the stable melting current, the molten droplet is increased to 165% to 170% of the stable melting droplet, and the cooling gas flow rate is reduced to 15% to 30% of the stable melting flow rate.

[0023] Preferably, in step (3), the cooling gas is helium.

[0024] Preferably, in step (2), the inner diameter of the electroslag crystallizer is Φ440±10mm.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] In VIM smelting, by adding wedge-shaped insulating risers and strictly controlling the pouring temperature and ingot mold preheating temperature, the solidification time of the riser and the solidification time of the ingot are kept at a fixed ratio. This optimizes the solidification process of the molten metal in the ingot mold, reduces the shrinkage cavity in the center of the ingot, and avoids cracking caused by large differences in solidification rates.

[0027] In ESR (Electroslag Remelting), a customized pre-melted slag with low moisture content and small particle size is used. This ensures uniform distribution of the pre-melted slag in the electroslag furnace, resulting in uniform heating of the molten pool and preventing macroscopic segregation caused by uneven temperature distribution in the alloy. High electrical conductivity improves the thermal efficiency of ESR, increases the temperature of the molten pool, ensures the stability of the electroslag remelting process, reduces parameter fluctuations, and decreases the probability of metallurgical defects. Moderate viscosity ensures good fluidity of the pre-melted slag, effectively adsorbing inclusions in the alloy and reducing the accumulation of crack initiation sites.

[0028] VAR melting, using a four-stage feeding process, can significantly reduce the size of the shrinkage cavity area at the head of the VAR ingot, reduce the stress in the head area, and decrease the risk of cracking in the VAR ingot.

[0029] By adding wedge risers to VIM and optimizing ingot solidification conditions, combined with ESR slag system optimization, power reduction feeding method, and VAR four-stage feeding method, the thermal stress and structural stress generated during the melting process are reduced, thereby improving the cracking defects of high-alloy high-temperature alloy ingots.

[0030] The high-alloyed high-temperature alloy ingots prepared by this method have good surface quality and no cracking defects were found during the triple melting process, which can significantly reduce the cracking tendency of high-alloyed high-temperature alloy ingots. Attached Figure Description

[0031] Figure 1 The figures show a comparison of the VIM ingot of Embodiment 1 and the VIM ingot of Comparative Example 1; wherein, Figure c is a physical image of Embodiment 1, and Figures a and b are physical images of Comparative Example 1.

[0032] Figure 2Figure 1 shows a comparison of the ESR ingots of Embodiment 1 and Comparative Example 2; wherein, Figure e is a physical image of Embodiment 1, and Figure d is a physical image of Comparative Example 2.

[0033] Figure 3 Figure 1 shows a comparison of the VAR ingot of Embodiment 1 and the VAR ingot of Comparative Example 3; Figure 2h is a physical image of Embodiment 1, and Figures 3f and 4g are physical images of Comparative Example 3. Detailed Implementation

[0034] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. The specific embodiments of the present invention will be further described in detail below. However, the present invention is not limited to these embodiments. Any improvement or substitution based on the basic spirit of the embodiments shall still fall within the scope of protection of the claims of the present invention.

[0035] It should be noted that: unless otherwise specified, the following examples shall be carried out under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples shall be commercially available.

[0036] The nickel-based superalloy composition of the present invention, by mass percentage, is: Al 2.55%–3.90%, Ti 2.65%–5.20%, Nb 0%–3.40%, C 0.038%–0.07%, with the remainder being Ni.

[0037] The method for controlling cracking defects in Φ508mm high-alloy nickel-based wrought superalloy ingots of the present invention includes the following steps:

[0038] (1) Vacuum induction melting:

[0039] High-temperature alloy raw materials are smelted in a vacuum induction furnace. The vacuum induction smelting includes charging, melting, refining, alloying and casting. The alloy casting temperature is 1420℃~1500℃. The crucible is powered off during the initial casting stage. After the crucible tilt angle exceeds 60°, the crucible power is increased to 20~50kW. Casting uses an ingot mold preheated to 400~600℃ and equipped with a wedge-shaped (narrower at the top, wider at the bottom) insulating riser. The time from loading the ingot mold into the vacuum induction melting furnace mold chamber to evacuation and casting is 30~90 minutes. The ingot mold is tapered, with a bottom inner diameter of Φ360±20mm and a top inner diameter of Φ340±20mm. The wedge-shaped insulating riser has a length of 300~450mm, a thickness of 20~40mm, and an inclination angle of 2~7°. The size of the wedge-shaped insulating riser is adjusted within the above range according to the ingot mold size and alloy solidification characteristics, ultimately achieving a riser solidification time / ingot solidification time = 1.15~1.35. The ingot solidification time is the time when the solid phase volume fraction reaches ≥92%. After vacuum cooling in the ingot mold chamber to achieve a solidification time of ±10 min, the ingot is demolded. After demolding, the surface temperature of the ingot is measured using a colorimetric infrared thermometer. When the temperature is 600-800℃, the ingot is placed in a resistance annealing furnace for annealing.

[0040] In step (1), installing a wedge-shaped insulating riser at the head of the ingot mold can reduce the shrinkage depth of the VIM ingot center, reduce the stress in the ingot, and reduce the crack-sensitive area. The size and shape of the wedge-shaped insulating riser will significantly affect the solidification time at the ingot riser. If the riser solidification time is too short, the molten metal at the riser cannot be well fed, resulting in a deeper shrinkage depth at the center of the ingot and increasing the overall stress of the ingot. If the riser solidification time is too long, too much molten metal remains at the riser, resulting in a larger shrinkage cavity at the riser and increasing the stress in the upper part of the ingot. Therefore, the size and shape of the insulating riser should be reasonably designed so that the riser solidification time is moderate, the molten metal at the riser can be properly fed, and the stress in the ingot is reduced. Based on domestic and foreign literature records and actual production experience, the length, thickness, and inclination angle of the insulating riser were constrained and appropriately adjusted within the constrained range so that the riser solidification time / ingot solidification time = 1.15~1.35. Under these conditions, a high-alloy high-temperature alloy VIM ingot with lower stress can be prepared.

[0041] Preheating the ingot mold can significantly reduce the thermal stress generated when molten metal enters the cold ingot mold. Selecting appropriate demolding time and temperature also helps to reduce thermal stress in the ingot. If the demolding time is too long, the ingot mold will become too cold, resulting in greater stress inside the ingot; if the demolding time is too short, the temperature of the ingot after demolding will be too high, and the surface temperature will drop rapidly after contact with cold air, resulting in greater stress on the ingot surface.

[0042] (2) Electroslag remelting:

[0043] The annealed VIM ingots are surface-machined, auxiliary electrodes are welded, and electroslag remelting is performed. Electroslag remelting includes a slag-forming stage, a stabilization melting stage, and a feeding stage. The inner diameter of the electroslag crystallizer used is Φ440±10mm. Before the slag-forming stage begins, uniformly mixed ESR pre-melted slag is added to the electroslag furnace. The ESR pre-melted slag of this invention has a low moisture content, small particle size, high electrical conductivity, and moderate viscosity. The pre-melted slag composition, by mass percentage, is Al2O3 24.5±3.0%, TiO2 5.0±0.5%, CaO 23.0±3.0%, MgO 3.5±0.5%, and CaF2 44.0±3.0%. The optimized pre-melted slag parameters meet the following requirements: ① Moisture content ≤0.04%, dried to ≤0.02% before entering the furnace; ② Particle size ≤4mm; ③ Electrical conductivity at 1700℃ ≥3.5Ω. -1 / cm; ④ Viscosity 0.010~0.020Pa·s. The steady-state smelting power setting is 180~250kW, and the slag resistance is 4-10MΩ. In the later stages of smelting, a seven-stage power reduction combined with timed power-off feeding process is adopted, with a total feeding time ≥70 minutes. The power (P) and time (t) settings for each feeding stage are calculated using the following formula:

[0044] P n =P0*e (-a·t)

[0045] Where P0 is the steady-state smelting power, P n Let be the smelting power of the nth stage, e be the natural constant, t be the feeding time, and a be a coefficient. The range of a for each stage is 0.001~0.002, 0.002~0.004, 0.004~0.007, 0.0070~0.010, 0.010~0.013, 0.013~0.016, and 0.016~0.02, respectively.

[0046] After the power is reduced to the set value in the final stage, the power is immediately cut off and the furnace is cooled for 50±20 minutes. The cooling water temperature is set to 25~30℃ during furnace cooling. After exiting the furnace, hot annealing is performed.

[0047] In step (2) above, the ESR pre-melted slag should have a low moisture content and small particle size to ensure uniform distribution in the electroslag remelting furnace, resulting in uniform heating of the molten pool and preventing macroscopic segregation of the alloy due to uneven temperature distribution. Higher electrical conductivity improves the thermal efficiency of ESR, increases the temperature of the molten pool, ensures the stability of the electroslag remelting process, reduces parameter fluctuations, and decreases the probability of metallurgical defects. Appropriate viscosity ensures good fluidity of the pre-melted slag, effectively adsorbing inclusions in the alloy and reducing the accumulation of crack initiation sites.

[0048] (3) Vacuum arc self-consumable remelting:

[0049] The ingot prepared in step (2) is subjected to vacuum self-consumption melting. During the steady-state melting stage, the melting rate and droplet control are adopted, the cooling gas (helium) is controlled by flow rate, and the feeding method is a four-stage feeding method.

[0050] During the steady-state smelting stage: the melting rate is set to 2.5–3.5 kg / min, and the droplet setting is 3.00–8.50 s. -1 The cooling gas flow rate is 0.1–0.2 L / min;

[0051] The feeding stage is controlled by current and droplet flow, and the helium flow rate is linearly reduced to below 0.02 L / min. The feeding time for each stage is 10–30 min, and the process parameters for each stage are as follows:

[0052] First stage: The current is reduced to 75% to 85% of the stable melting current, the molten droplet is increased to 130% to 150% of the stable melting droplet, and the helium flow rate is reduced to 90% to 95% of the stable melting flow rate;

[0053] Second stage: The current is reduced to 60% to 75% of the stable melting current, the molten droplet is increased to 150% to 160% of the stable melting droplet, and the helium flow rate is reduced to 70% to 90% of the stable melting flow rate;

[0054] The third stage: the current is reduced to 30% to 60% of the stable melting current, the molten droplet is increased to 160% to 165% of the stable melting droplet, and the helium flow rate is reduced to 30% to 70% of the stable melting flow rate;

[0055] Fourth stage: The current is reduced to 20% to 30% of the stable melting current, the molten droplet is increased to 165% to 170% of the stable melting droplet, and the helium flow rate is reduced to 15% to 30% of the stable melting flow rate.

[0056] The shrinkage cavity area at the head of the VAR ingot is the region where stress is most concentrated, making it a sensitive area for alloy cracking. A four-stage feeding process can significantly reduce the size of the shrinkage cavity area at the head of the VAR ingot, lower the stress in the head region, and reduce the risk of cracking in the VAR ingot.

[0057] The following describes a preferred embodiment in detail.

[0058] Example 1

[0059] (1) The high-temperature alloy raw materials are smelted in an 8-ton vacuum induction furnace. The vacuum induction smelting includes charging, melting, refining, alloying, and casting. The chemical composition of the alloy, in percentage, is: C 0.07%, Cr 18.00%, Co 15.00%, W 1.50%, Mo 3.20%, Al 3.10%, Ti 4.20%, Nb 2.10%, B 0.020%, Zr 0.045%, with the remainder being Ni. The alloy pouring temperature is 1480℃. The crucible is powered off before pouring. After the crucible tilt angle exceeds 60°, the crucible power is increased to 40kW. A preheated ingot mold with a wedge-shaped (narrower at the top, wider at the bottom) insulating riser is used. The time from loading the ingot mold into the vacuum induction melting furnace mold chamber to evacuation and pouring is 50 minutes. The ingot mold has a tapered shape with a bottom inner diameter of Φ360mm and a top inner diameter of Φ340mm. The insulating riser is 320mm long, 30mm thick, and tilted at 5°. The size of the insulating riser can be adjusted within the above range based on the ingot mold size and alloy solidification characteristics, ultimately achieving a riser solidification time / ingot solidification time = 1.20. The solidification time of the ingot is the time required when the solid volume fraction is ≥92%. After vacuum cooling in the ingot mold chamber to reach the solidification time ±10 min, the ingot is demolded. After demolding, the surface temperature of the ingot is measured by a colorimetric infrared thermometer. When the temperature is about 700℃, the ingot is placed in a resistance annealing furnace for annealing.

[0060] (2) The annealed VIM ingots were surface-machined, auxiliary electrodes were welded, and electroslag remelting was carried out. Electroslag remelting included a slag-forming stage, a stabilization melting stage, and a feeding stage. The electroslag crystallizer used had a size of Ф450mm and an inner diameter of Φ440mm. Before the slag-forming stage, uniformly mixed ESR pre-melted slag was added to the electroslag furnace, and the ESR slag system was optimized. The optimized slag system, by weight percentage, was Al2O3 22.5%, TiO2 5.0%, CaO 24.0%, MgO 4.0%, and CaF2 44.5%. The customized pre-melted slag had a low moisture content, small particle size, and suitable electrical conductivity and viscosity. The optimized pre-melted slag parameters met the following requirements: ① Moisture content 0.035%, dried to 0.02% before entering the furnace; ② Particle size 0-3mm; ③ Electrical conductivity at 1700℃ 3.8Ω. -1 / cm; ④ Viscosity 0.014 Pa·s. The steady-state melting power setting is 200kW, and the slag resistance is 5MΩ. In the later stage of melting, a seven-stage power reduction combined with timed power cut-off feeding process is adopted. The total feeding time is about 70 minutes. The power (P) and time (t) settings for the feeding stage are calculated according to the following formula:

[0061] P n =P0*e (-a·t)

[0062] Where P0 is the steady-state smelting power, P n Let be the smelting power of the nth stage, and 'a' be a coefficient. The range of 'a' for each stage is 0.001~0.002, 0.002~0.004, 0.004~0.007, 0.0070~0.010, 0.010~0.013, 0.013~0.016, and 0.016~0.02, respectively.

[0063] The power outputs for each stage of the feed rate reduction were 185kW, 160kW, 140kW, 110kW, 90kW, 70kW, and 55kW, respectively. After the power output in the final stage was reduced to the set value, the power was immediately cut off and the furnace was cooled for 50 minutes. The cooling water temperature during furnace cooling was set to 25℃. After exiting the furnace, hot annealing was performed.

[0064] (3) The ESR ingot was used as a VAR electrode for vacuum consumable remelting. Vacuum consumable remelting included an arc initiation stage, a stable melting stage, and a feeding stage. The crystallizer used was Ф508mm in size. During steady-state melting, melting rate and droplet size were controlled, and the cooling gas (He gas) was controlled by flow rate. The VAR ingot was fed in four stages, with the current gradually decreasing, the droplet size increasing, and the He gas flow rate decreasing. The feeding time for each stage was 25 minutes. After tapping, annealing was performed. The process parameters for each feeding stage are as follows:

[0065] Stable smelting stage: melting rate 2.8 kg / min, current 5.5 kA, molten droplets 6.5 / s, He gas flow rate 0.015 L / min.

[0066] First stage: Current 4.5kA, molten droplets 9.0 per second, He gas flow rate 0.014L / min.

[0067] Second stage: current 3.6kA, droplet count 10.0 / s, He gas flow rate 0.012L / min.

[0068] Third stage: Current 2.2kA, droplet count 10.5 / s, He gas flow rate 0.005L / min.

[0069] Fourth stage: current 1.2kA, droplet count 11.0 / s, He gas flow rate 0.003L / min.

[0070] The high-alloyed high-temperature alloy ingots prepared by the above method did not crack during the triple melting process, that is, no cracking defects were found in the VIM ingot, ESR ingot and VAR ingot.

[0071] Comparative Example 1

[0072] like Figure 1The VIM ingot shown is compared with the VIM ingot of Example 1. The method in Example 1 was followed, but the difference lies in the vacuum induction melting and casting steps: a mold preheated to 300°C and equipped with a straight cylindrical insulating riser was used for casting. The time from loading the mold into the vacuum induction melting furnace mold chamber to evacuation and casting was 50 minutes; the inner diameter of the mold was Φ350mm; the length of the insulating riser was 480mm and the thickness was 45mm. The calculated riser solidification time / ingot solidification time = 1.67. After vacuum cooling in the casting chamber for 120 minutes, the ingot was demolded and then cooled to room temperature. The high-alloyed high-temperature alloy VIM ingot prepared by this method exhibited transverse cracking and a large shrinkage cavity in the center of the ingot.

[0073] Comparative Example 2

[0074] like Figure 2 The ESR ingot shown is compared with the actual ESR ingot of Example 1. The method in Example 1 was followed, except that the electroslag remelting system composition was Al₂O₃ 30.0%, TiO₂ 3.0%, CaO 28.0%, MgO 2.5%, and CaF₂ 36.5%. The pre-melted slag parameters are as follows: ① Moisture content 0.06%, no drying treatment before entering the furnace; ② Particle size 0.1–10 mm; ③ Electrical conductivity at 1700℃ 3.0 Ω. -1 / cm; ④ Viscosity 0.03 Pa·s. The steady-state melting power setting was 200 kW, and the slag resistance was 3.5 MΩ. In the later stage of melting, a three-stage power reduction combined with timed power cut-off feeding process was adopted, with a total feeding time of about 60 minutes. The power of each feeding stage was 140 kW, 90 kW, and 50 kW, respectively. After the power was reduced to the set value in the final stage, the power was immediately cut off and the furnace was cooled for 40 minutes. The cooling water temperature during furnace cooling was set at 25℃. After tapping, hot annealing was performed. The high-alloyed high-temperature alloy ESR ingot prepared by this method showed longitudinal cracking.

[0075] Comparative Example 3

[0076] like Figure 3 The VAR ingot shown is compared with the actual VAR ingot of Example 1. The method in Example 1 was followed, except that the VAR ingot was fed in two stages, gradually reducing the current, increasing the droplet size, and decreasing the He gas flow rate. The feeding time for each stage was 50 minutes, and annealing was performed after tapping. The process parameters for each feeding stage are as follows:

[0077] Stable smelting stage: melting rate 2.8 kg / min, current 5.5 kA, molten droplets 6.5 / s, He gas flow rate 0.015 L / min.

[0078] First stage: current 4.8kA, droplet count 10.5 / s, He gas flow rate 0.012L / min.

[0079] Second stage: Current 2.6kA, droplet count 11.5 / s, He gas flow rate 0.006L / min.

[0080] The high-alloyed high-temperature alloy VAR ingots prepared by this method have large shrinkage cavities at the head and longitudinal cracks.

Claims

1. A method for controlling cracking defects in Φ508mm high-alloy nickel-based wrought superalloy ingots, characterized in that, The composition of the high-alloyed nickel-based wrought superalloy, by mass percentage, is: Al 2.55%~3.90%, Ti 2.65%~5.20%, Nb 0%~3.40%, C 0.038%~0.07%, with the remainder being Ni; the control method includes the following steps: (1) Vacuum induction melting: High-temperature alloy raw materials are vacuum induction melted. Before casting, wedge-shaped heat-insulating risers are installed on the head of the ingot mold, and the temperature of the ingot mold is controlled. The alloy casting temperature is 1420℃~1500℃. After casting, the cooling time is determined according to the solidification time of the ingot. After cooling, the ingot is demolded. After demolding, the surface temperature of the ingot is measured and then hot annealing is carried out. The wedge-shaped insulating riser has a length of 300-450mm, a thickness of 20-40mm, an inclination angle of 2-7°, and a riser solidification time / ingot solidification time = 1.15-1.35; the ingot solidification time is the time when the solid phase volume fraction reaches ≥92%; and the cooling time is the ingot solidification time ±10min. (2) Electroslag remelting: The ingot prepared in step (1) is electroslag remelted to optimize the slag system. In the later stage of smelting, the power is reduced in stages and the power is cut off at timed intervals to replenish the feed. The steady-state smelting power setting is 180~250kW, and the slag resistance is 4-10MΩ. Feeding is divided into 7 stages, with a feeding time ≥70 minutes. The power P and time t setting values ​​for each feeding stage are calculated using the following formula: Where P0 is the steady-state smelting power, P n Let be the smelting power of the nth stage, e be the natural constant, t be the feeding time, and a be a coefficient. The ranges of a for each stage are 0.001~0.002, 0.002~0.004, 0.004~0.007, 0.0070~0.010, 0.010~0.013, 0.013~0.016, and 0.016~0.02, respectively. After the power is reduced to the set value in the final stage, the power is immediately cut off and the furnace is cooled for 50±20 minutes. The cooling water temperature during furnace cooling is set to 25~30℃. After exiting the furnace, hot annealing is performed. (3) Vacuum arc self-consumption remelting: Vacuum arc self-consumption remelting is performed on the ingot prepared in step (2). During the steady-state melting stage, melting rate and droplet control are adopted. During the feeding stage, current reduction and droplet control are adopted. The cooling gas is controlled by linearly reducing the flow rate. During the steady-state smelting stage: the melting rate is set to 2.5~3.5 kg / min, and the droplet length is set to 3.00~8.50 s. -1 The cooling gas flow rate is 0.1~0.2L / min; the feeding stage is divided into four stages, with the current decreasing and the droplet increasing in stages, and the cooling gas flow rate decreasing linearly to below 0.02L / min. The feeding time for each stage is 10~30min.

2. The control method according to claim 1, characterized in that, In step (1), before casting, the ingot mold is preheated to 400~600℃, and the time from loading the ingot mold into the mold chamber and evacuating it to casting is 30~90min; wherein, the ingot mold has a taper, with a bottom inner diameter of Φ360±20mm and a top inner diameter of Φ340±20mm; the ingot surface temperature is annealed at 600~800℃.

3. The control method according to claim 1, characterized in that, In step (1), the power is turned off in the early stage of casting, and the heating power is increased to 20~50kW after the crucible tilt angle is greater than 60°.

4. The control method according to claim 1, characterized in that, In step (2), the main components of the pre-melted slag, by weight percentage, are Al2O3 24.5±3.0%, TiO2 5.0±0.5%, CaO 23.0±3.0%, MgO 3.5±0.5%, and CaF2 44.0±3.0%. The pre-melted slag's characteristic parameters are: moisture content ≤0.04%, which can reach ≤0.02% after baking; particle size 0~10mm, with slag particles smaller than 1mm accounting for no more than 10% of the total weight; and electrical conductivity ≥3.5Ω at 1700℃. -1 / cm, viscosity 0.010~0.020Pa·s.

5. The control method according to claim 1, characterized in that, The process parameters for the four stages of the feeding process in step (3) are as follows: First stage: The current is reduced to 75%~85% of the stable melting current, the molten droplet is increased to 130%~150% of the stable melting droplet, and the cooling gas flow rate is reduced to 90%~95% of the stable melting flow rate; Second stage: The current is reduced to 60%~75% of the stable melting current, the molten droplet is increased to 150%~160% of the stable melting droplet, and the cooling gas flow rate is reduced to 70%~90% of the stable melting flow rate; The third stage: the current is reduced to 30%~60% of the stable melting current, the molten droplet is increased to 160%~165% of the stable melting droplet, and the cooling gas flow rate is reduced to 30%~70% of the stable melting flow rate; Fourth stage: The current is reduced to 20%~30% of the stable melting current, the molten droplets are increased to 165%~170% of the stable melting droplets, and the cooling gas flow rate is reduced to 15%~30% of the stable melting flow rate.

6. The control method according to claim 1, characterized in that, Step (3), the cooling gas is helium.

7. The control method according to claim 1, characterized in that, In step (2), the inner diameter of the electroslag crystallizer is Φ440±10mm.

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