Large-size GH2070P alloy ingot and preparation method thereof

Abstract

The application discloses a large-size GH2070P alloy ingot and a preparation method thereof, and belongs to the field of high-temperature alloy preparation for ultra-supercritical power stations. The method is characterized in that the tail end face of a GH2070P electrode is baked in the arcing stage of vacuum arc consumable remelting, then the current value is increased to 13.0-15.0 kA at a rate of 0.4-0.6 kA / min, the cooling water flow is 1120-1300 L / min, the current value is reduced again to make the electrode continue to melt, the current value is increased to greater than or equal to 8.5 kA under 23.5-24.5 V, the melting is carried out at a constant melting rate in the stable melting stage, then the feeding is carried out, finally the power is turned off to cool, and the large-size GH2070P alloy ingot is obtained. The method solves the metallurgical risks of traditional sawing of the electrode head, and the problems of reduced production efficiency and material waste caused by the flat head, and the large-size and large-weight GH2070P alloy ingot is obtained, thereby meeting the demand of the large pipe of the ultra-supercritical power station.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloy preparation for ultra-supercritical power plants, specifically a large-size GH2070P alloy ingot and its preparation method. Background Technology

[0002] The core of 650-700℃ ultra-supercritical power generation technology is to enable water in the boiler to undergo phase change and perform work at higher temperatures and pressures above supercritical levels. This is currently a highly efficient and clean new coal-fired power technology. Ultra-supercritical generator units require high-temperature alloys to meet the stringent operating conditions of high temperature, high pressure, and corrosion. Considering cost, these alloys are typically nickel-based or iron-nickel-based high-temperature alloys. GH2070P is a new type of iron-nickel-based high-temperature alloy with advantages such as good high-temperature strength, corrosion and oxidation resistance, stable microstructure, and controllable cost, making it an ideal material for manufacturing large-scale pipelines in 650-700℃ ultra-supercritical units.

[0003] GH2070P alloy is typically produced into alloy ingots through vacuum induction melting followed by vacuum arc remelting, then forged into bars, and subsequently manufactured into power plant pipes through extrusion and machining. Since pipes require welding connections during unit construction, longer pipes require fewer weld joints, further reducing construction costs and simplifying construction. Therefore, the specifications of the alloy ingot are a crucial step in determining the length of pipes with a specific diameter. Due to the large material consumption, harsh operating conditions, and long length requirements of large-diameter pipes in power units, there is a demand for GH2070P alloy ingots that are large in size, heavy in weight, of excellent metallurgical quality, and low in cost.

[0004] Conventional high-temperature alloy ingot smelting processes include: vacuum induction melting (VIM) + vacuum arc remelting (VAR), vacuum induction melting (VIM) + electroslag remelting (ESR), and vacuum induction melting (VIM) + electroslag remelting (ESR) + vacuum arc remelting (VAR). Ingots typically range from Φ406 mm to Φ660 mm in diameter, with individual ingot weights generally ranging from 2 to 5 tons, suitable for forgings used in aerospace and aviation applications. Larger ingots, such as Φ840 mm, face challenges in controlling segregation, resulting in poor compositional uniformity and inconsistent metallurgical quality.

[0005] Vacuum induction melting (VIM), as the first step in high-temperature alloy smelting, produces ingots with severe shrinkage cavities and numerous inclusions at the head. Therefore, ESR or VAR is necessary to further refine the ingot to achieve a denser microstructure and fewer inclusions. Secondly, during VAR, to ensure the uniformity of composition and inclusion distribution between the ingot's head and tail, it is often necessary to reverse the melting process. That is, melting begins at the head of the VIM ingot, making the head the tail of the remelted ingot, and the tail of the VIM ingot the head of the remelted ingot. This is especially crucial for large-sized ingots with severe macroscopic compositional segregation.

[0006] VIM ingots often contain inclusions at the head. Direct melting would introduce many inclusions into the entire ingot. There are two conventional methods for handling this during production: one is to directly saw off the head, and the other is to melt a portion of the head during remelting before starting the formal melting process again—a method known as "flattening the head"—to ensure the metallurgical quality of the remelted ingot. However, sawing easily introduces inclusions, moisture, and oil into the porous core of the VIM ingot, causing contamination and leading to metallurgical risks. Flattening the head requires repeated furnace loading and unloading, electrode cleaning, and cooling operations, resulting in low production efficiency and complete waste of the melted material. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a large-size GH2070P alloy ingot and its preparation method. It solves the metallurgical risks caused by the introduction of inclusions, moisture, and oil contamination into the head of traditional sawing induction casting, as well as the reduced production efficiency and material waste caused by repeated furnace loading and unloading for melting, electrode cleaning, and cooling operations. The invention yields large-size, high-weight GH2070P alloy ingots with significant cost and metallurgical quality advantages, meeting the requirements of large pipelines in ultra-supercritical power plants.

[0008] This invention is achieved through the following technical solution: A method for preparing a large-size GH2070P alloy ingot, specifically including the following steps: Step 1: First, use the vacuum arc self-consumable remelting arc initiation process to bake the tail end face of the GH2070P electrode. Then, increase the current value to 13.0~15.0 kA at a rate of 0.4~0.6 kA / min, and the cooling water flow rate is 1120~1300 L / min. Then, decrease the current value to allow the electrode to continue melting. Step 2: Under a voltage of 23.5~24.5V, increase the current value to ≥8.5 kA to complete the transition from arc ignition to normal melting; Step 3: Melt at a constant melting rate, then feed the material back into the furnace, and finally cool after power is cut off to obtain a large-size GH2070P alloy ingot.

[0009] A further improvement of the present invention is that: Step 1: Weld the GH2070P electrode to the auxiliary electrode, and then place it in a vacuum arc furnace to bake the tail end face of the GH2070P electrode.

[0010] Step 1: The tail end face of the GH2070P electrode is baked under constant current and constant voltage conditions of 3.5~4.0kA and 23.5~25.0V.

[0011] The baking time T for the tail end face of the GH2070P electrode in step 1 satisfies the following relationship: T=a·w 2 +4.64, where T is in min, w is the weight of the GH2070P electrode in tons, and a is 0.315 in min / t. 2 .

[0012] After baking the tail end face of the GH2070P electrode in step 1, set the voltage to 24.0~25.0V.

[0013] In step 1, after increasing the current value to 13.0~15.0 kA, maintain it for 10~30 minutes, and then decrease the current value.

[0014] Step 1: Reduce the current value to 4.5-5.0 kA at a rate of 1-2 kA / min and maintain it for 10-30 min.

[0015] Step 2 increases the current value from 4.5-5.0 kA to the set current I for melting in step 3 at a rate of 0.3-0.5 kA / min, and then maintains it for 10-30 min, where I ≥ 8.5 kA, and I = b·R + 2.8, where b is 1.45 and the unit is (kA·min) / kg, and R is the melting rate in step 3 and the unit is kg / min.

[0016] The electrode mentioned in step 1 weighs 9.5~10.5t. When the electrode is melted to a remaining weight of 400~600kg in step 3, feeding begins. The feeding time is ≥150min. After power is cut off, the cooling time is ≥3min to obtain a large-size GH2070P alloy ingot.

[0017] A large-size GH2070P alloy ingot obtained by the preparation method of any one of the above-described large-size GH2070P alloy ingots.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: This invention discloses a method for preparing large-size GH2070P alloy ingots, specifically for the Φ840 size. It employs a vacuum arc remelting process with a self-consuming remelting electrode. By appropriately matching the current and voltage, the melting process of the electrode is controlled. Through the matching of bottom cooling conditions and electrode melting rate during the arc initiation stage, the ingot undergoes directional solidification under a high temperature gradient. This method cleverly fixes and controls the inclusions introduced from the induction casting head (tail of the remelting electrode) within a certain range at the tail of the remelted ingot and the edge of the molten pool. Simultaneously, the compositional segregation of the ingot during the arc initiation stage is controllable, thereby improving the overall metallurgical quality of the ingot. This method avoids the metallurgical risks introduced by traditional sawing induction casting into the ingot head, such as inclusions, moisture, and oil. It also avoids the reduced production efficiency and material waste caused by repeated furnace loading and unloading for melting, electrode cleaning, and cooling of the ingot head, as well as the risk of introducing numerous inclusions during conventional melting. Therefore, the resulting Φ840 GH2070P alloy ingot can weigh over 10 tons, offering significant cost and metallurgical quality advantages. When used to manufacture components for ultra-supercritical power plants, it meets the requirements of large pipelines in ultra-supercritical power plants, contributing to their safe operation. This method reduces the production cycle, increases the yield, and achieves an electrode utilization rate of over 98.5% during remelting. The area with high component segregation and inclusion content at the ingot tail is controllable, and the forging defect can be removed after subsequent bar forging, further reducing metallurgical risks. Attached Figure Description

[0019] Figure 1 A simplified diagram illustrating the arc initiation process of this invention.

[0020] Figure 2 The images show the side and front views of the tail of the ingot obtained in Example 1.

[0021] Figure 3 This is a diagram showing the slag formation in the molten pool during the arc initiation stage of Example 1.

[0022] Figure 4 Set up a curve for the arc initiation process of Comparative Example 1.

[0023] Figure 5 The slag in the molten pool during the arc initiation stage is shown in Comparative Example 1.

[0024] Figure 6 Photographs of the waste material on the flat-top and the scum on its surface, for comparison example 2. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0026] A method for preparing a Φ840 GH2070P alloy ingot specifically includes the following steps: Step 1: Weld the tail end of the GH2070P electrode to the auxiliary electrode, place it in a vacuum arc furnace, and evacuate it to below 1 Pa. The nominal diameter of the crystallizer used is Φ840 mm. The GH2070P electrode weighs 9.5~10.5t and is formed by vacuum induction melting and casting, followed by stress-relief annealing and surface treatment. The diameter of the surface-treated electrode is 710~740 mm, and the surface is free of pores and oxide scale defects.

[0027] Step 2, apply electricity to initiate an arc (e.g.) Figure 1 (as shown) The flow rate of cooling water at the bottom of the crystallizer is Q = c·I2-50, in L / min, where I2 is the peak current setting value of the second stage of the arc initiation period (13.0~15.0 kA), in kA, and c =90, in L / (min.kA). The first stage is the baking period, during which the electrode tail end face is heated at low power using constant current and constant voltage. The current setting range is 3.5~4.0kA, and the voltage setting range is 23.5~25.0V. The holding time is T=a·w. 2 +4.64, where T is the holding time in minutes, w is the electrode weight in tons (t), and a is a coefficient of 0.315 in minutes per t. 2 ; The second stage is the melting rate adjustment period. The voltage setting range is 24.0~25.0V, which allows the electrode to begin melting and reach a higher melting rate. During this period, the current is increased at a rate of 0.4~0.6 kA / min to a peak current of 13.0~15.0 kA, and then maintained for 10~30 minutes. Then, the melting rate is rapidly reduced to a certain value, specifically at a rate of 1~2 kA / min to 4.5~5.0 kA, and maintained for 10~30 minutes. The third stage is the transition period from arc ignition to normal melting. The voltage setting range is 23.5~24.5V, which allows the melting rate to rise slowly at a rate of 0.3~0.5 kA / min to the final set current (I3). I3 = b·R + 2.8, in kA, and I3 must be ≥ 8.5 kA. R is the set melting rate (target value) for the normal melting period in step 3, in kg / min, and b = 1.45, in (kA.min) / kg, which is close to the set value for the normal melting period. Then, this current is maintained for 10~30 min.

[0028] Step 3: Enter the normal melting period, using constant melting rate R control. When the electrode has 400~600kg remaining, start reducing the current to compensate for shrinkage. The compensation time is ≥150 minutes. After power is cut off, cool for ≥3 hours before unloading to obtain GH2070P alloy ingots with a specification of Φ840 mm.

[0029] Example 1: 1. The tail end of the GH2070P electrode is welded to the auxiliary electrode, and then placed in a vacuum arc furnace and evacuated to 0.5 Pa. The nominal diameter of the crystallizer used is Φ840 mm. The GH2070P electrode is formed by vacuum induction melting and casting, followed by stress-relief annealing and surface treatment. The diameter of the surface-treated electrode is 725±10 mm, and the surface is free of pores and oxide scale defects.

[0030] 2. Arc initiation upon energization: The cooling water flow rate at the bottom of the crystallizer is Q = 90 × 13.6 - 50 = 1174 L / min; The first stage of arc initiation uses constant current and constant voltage control, with the current set at 3.6kA and the voltage set at 23.8V. The holding time is T = a·w. 2 +4.64, where w=10t; The second stage uses current and voltage control, with the voltage set at 24.4V. First, the current is increased to a peak current of 13.6 kA at a rate of 0.5 kA / min, and then held for 20 min. Subsequently, the current is decreased to 4.6 kA at a rate of 1.5 kA / min and held for 20 min. The third stage voltage is set to 23.7 V, and the current is increased to I3 = 1.45·R + 2.8 = 8.6 kA at a rate of 0.33 kA / min, where R = 4 kg / min, and then the current is maintained for 20 min.

[0031] 3. During the normal melting period, a constant melting rate of R=4.2kg / min is used. When the electrode has 550kg remaining, the current is reduced to compensate for shrinkage. The compensation time is 200 minutes. After the power is cut off, the furnace is cooled for 3 hours to obtain a GH2070P alloy ingot with a specification of Φ840 mm.

[0032] Figure 2 The photo shows the tail end of the alloy ingot, where no obvious abnormalities can be seen on the surface.

[0033] Figure 3 The image shows the slag situation in the molten pool during the arc initiation stage. It can be seen that there is relatively little slag and no large pieces of slag.

[0034] Table 1 shows the slag and compositional uniformity data of the ingot smelting process using this method. The Cr and Ti element range requirements in the GH2070P alloy are relatively strict and the macroscopic segregation is relatively serious. The compositional range at the edge / center / center position of the ingot tail is used as the main evaluation index of compositional uniformity.

[0035] Table 1. Data on the uniformity of slag and ingot composition during the arc initiation stage in Example 1

[0036] Example 2: 1. The tail end of the GH2070P electrode is welded to the auxiliary electrode, and then placed in a vacuum arc furnace and evacuated to 0.4 Pa. The nominal diameter of the crystallizer used is Φ840 mm. The GH2070P electrode is formed by vacuum induction melting and casting, followed by stress-relief annealing and surface treatment. The diameter of the surface-treated electrode is 725±10 mm, and the surface is free of pores and oxide scale defects.

[0037] 2. Arc initiation upon energization: The cooling water flow rate at the bottom of the crystallizer is Q = 90 × 13.8 - 50 = 1192 L / min; The first stage of arc initiation uses constant current and constant voltage control, with the current set at 3.8 kA and the voltage set at 24.2 V. The holding time is T = a·w. 2 +4.64, where w = 10.5t; The second stage uses current-voltage control, with the voltage set at 24.5 V. First, the current is increased to a peak current of 13.8 kA at a rate of 0.5 kA / min, and then held for 20 min. Subsequently, the current is decreased to 4.5 kA at a rate of 2 kA / min and held for 20 min. The third stage voltage is set to 23.7 V, and the current is increased to I3 = 1.45·R + 2.8 = 9.325 kA at a rate of 0.4 kA / min, where R = 4.5 kg / min, and then the current is maintained for 20 min.

[0038] 3. During the normal melting period, a constant melting rate of R=4.5kg / min is used. When the electrode has 550kg remaining, the current is reduced to compensate for shrinkage. The compensation time is 200 minutes. After the power is cut off, the furnace is cooled for 3 hours to obtain a GH2070P alloy ingot with a specification of Φ840 mm.

[0039] Table 3 shows the slag and compositional uniformity data of the ingot smelting process using this method. The Cr and Ti element range requirements in the GH2070P alloy are relatively strict and the macroscopic segregation is relatively serious. The compositional range at the edge / center / center position of the ingot tail is used as the main evaluation index of compositional uniformity.

[0040] Table 2. Data on the uniformity of slag and ingot composition during the arc initiation stage in Example 2.

[0041] Example 3: 1. The tail end of the GH2070P electrode is welded to the auxiliary electrode, and then placed in a vacuum arc furnace and evacuated to 0.4 Pa. The nominal diameter of the crystallizer used is Φ840 mm. The GH2070P electrode is formed by vacuum induction melting and casting, followed by stress-relief annealing and surface treatment. The diameter of the surface-treated electrode is 725±10 mm, and the surface is free of pores and oxide scale defects.

[0042] 2. Arc initiation upon energization: The cooling water flow rate at the bottom of the crystallizer is Q = 90 × 14 - 50 = 1210 L / min; The first stage of arc initiation uses constant current and constant voltage control, with the current set at 3.9 kA and the voltage set at 24.3 V. The holding time is T = a·w. 2 +4.64, where w = 9.5t; The second stage uses current-voltage control, with the voltage set at 24.6 V; firstly, the current is increased to a peak current of 14.0 kA at a rate of 0.5 kA / min, and then held for 20 min; subsequently, it is decreased to 4.5 kA at a rate of 2 kA / min and held for 20 min. The third stage voltage is set to 23.8 V, and the current is increased to I3 = 1.45·R + 2.8 = 10.05 kA at a rate of 0.35 kA / min, where R = 5.0 kg / min, and then the current is maintained for 15 min.

[0043] 3. During the normal melting period, a constant melting rate of R=5.0kg / min is used. When the electrode has 480kg remaining, the current is reduced to compensate for shrinkage. The compensation time is 180 minutes. After the power is cut off, the furnace is cooled for 3 hours to obtain a GH2070P alloy ingot with a specification of Φ840 mm.

[0044] Table 3 shows the slag and compositional uniformity data of the ingot smelting process using this method. The Cr and Ti element range requirements in the GH2070P alloy are relatively strict and the macroscopic segregation is relatively serious. The compositional range at the edge / center / center position of the ingot tail is used as the main evaluation index of compositional uniformity.

[0045] Table 3. Data on the uniformity of slag and ingot composition during the arc initiation stage in Example 3.

[0046] Comparative Example 1: 1. The tail end of the GH2070P electrode is welded to the auxiliary electrode, and then placed in a vacuum arc furnace and evacuated to 0.5 Pa. The nominal diameter of the crystallizer used is Φ840 mm. The GH2070P electrode is 10t in length, formed by vacuum induction melting and casting, followed by stress-relief annealing and surface treatment. The diameter of the surface-treated electrode is 725±10 mm, and the surface is free of pores and oxide scale defects.

[0047] 2. Arc initiation upon power-on (process setting curve as shown) Figure 4 ): The cooling water flow rate at the bottom of the crystallizer is 700 L / min; The first stage of arc initiation uses constant current and constant voltage control, with the current set at 4.4 kA, the voltage set at 24.3 V, and the holding time at 20 min. The second stage uses current and voltage control; firstly, the current is increased from 4.4 kA to the peak current of 14.4 kA at a rate of 0.5 kA / min, and held for 20 min, at which time the voltage is set to 24.8 V; after 80 min, the current is reduced to 11.0 kA, and the voltage is set to 23.9 V.

[0048] 3. During the normal melting period, a constant melting rate of 5.0 kg / min is used. When the electrode has 400 kg remaining, the current is reduced to compensate for shrinkage. The compensation time is 220 minutes. After the power is cut off, the furnace is cooled for 3 hours to obtain a GH2070P alloy ingot with a diameter of 840 mm.

[0049] Figure 5 The image shows the slag in the molten pool during the arc initiation stage. It can be seen that there is a lot of slag and large inclusions, as indicated by the arrows, which poses a metallurgical quality risk.

[0050] Table 4 shows the slag and compositional uniformity data of the ingot smelting process using this method. The GH2070P alloy has strict requirements for the range of Cr and Ti elements and exhibits severe macroscopic segregation. The compositional range at the edge / center / tail end of the ingot is used as the main evaluation index for compositional uniformity. The amount of slag during the smelting process can serve as a semi-quantitative basis for evaluating metallurgical quality; a poorer slag content often results in more inclusions inside the ingot and a higher probability of metallurgical defects.

[0051] Table 4. Data on the uniformity of slag and ingot composition during the arc initiation stage in Comparative Example 1

[0052] Comparative Example 2: 1. The tail end of the GH2070P electrode is welded to the auxiliary electrode, and then placed in a vacuum arc furnace and evacuated to 0.5 Pa. The nominal diameter of the crystallizer used is Φ840 mm. The GH2070P electrode is 10t in length, formed by vacuum induction melting and casting, followed by stress-relief annealing and surface treatment. The diameter of the surface-treated electrode is 725±10 mm, and the surface is free of pores and oxide scale defects.

[0053] 2. Arc ignition melting, the process settings are as follows: The cooling water flow rate at the bottom of the crystallizer is 700 L / min; The first stage of arc initiation uses constant current and constant voltage control, with the current set at 4.4 kA, the voltage set at 24.3 V, and the holding time at 20 min. The second stage uses current and voltage control; firstly, the current is increased from 4.4 kA to the peak current of 14.4 kA at a rate of 0.5 kA / min, at which point the voltage is set to 24.8 V; after 80 minutes, the current is reduced to 11.0 kA, and the voltage is set to 23.9 V.

[0054] 3. During the normal melting period, a constant melting rate of 5.0 kg / min is used. When the electrode has 400 kg remaining, the current is reduced to compensate for shrinkage. The compensation time is 220 minutes. After power is cut off, the electrode is cooled for 3 hours.

[0055] 4. When melting 300kg, manually cut off the power, cool for 3 hours and remove from the furnace. Take out the melted flat-head material, clean the crystallizer and polish the electrode surface to remove splashes, and reload the furnace to start melting again. Repeat the same process when melting again to obtain GH2070P alloy ingots with a specification of Φ840mm.

[0056] Figure 6 The photos show the waste material and the slag on its surface. It can be seen that there is a lot of slag on the surface of the material, which proves that there is a lot of slag during the smelting process and it has not been properly removed. It is easy to carry it into the ingot and reduce the metallurgical quality.

[0057] Table 5 shows the slag and compositional uniformity data of the ingot smelting process using this method. The GH2070P alloy has strict requirements for the Cr and Ti element ranges and exhibits severe macroscopic segregation. The compositional range at the edge / center / tail end of the ingot is used as the main evaluation index for compositional uniformity. The amount of slag during the smelting process can serve as a semi-quantitative basis for evaluating metallurgical quality; a poorer slag content often results in more inclusions inside the ingot and a higher probability of metallurgical defects. Furthermore, in this comparative example, the time for finishing the ingot and re-preparing for smelting is approximately 6 hours longer than that for the non-finishing finishing process.

[0058] Table 5. Data on the uniformity of slag and ingot composition during the arc initiation stage in Comparative Example 2

Claims

1. A method for preparing a large-size GH2070P alloy ingot, characterized in that, Includes the following steps: S1. First, the tail end face of the GH2070P electrode is baked using the arc-starting process of vacuum arc self-consumption remelting. Then, the current value is increased to 13.0~15.0 kA at a rate of 0.4~0.6 kA / min, and the flow rate of cooling water is 1120~1300L / min. Then, the current value is reduced to allow the electrode to continue to melt. S2, at a voltage of 23.5~24.5V, increases the current value to ≥8.5 kA to complete the transition from arc initiation to normal melting; S3 is smelted at a constant melting rate, followed by feeding, and finally cooled after power is cut off to obtain a large-size GH2070P alloy ingot.

2. The method for preparing large-size GH2070P alloy ingots according to claim 1, characterized in that, S1 welds the GH2070P electrode to the auxiliary electrode, and then puts it into a vacuum arc furnace to bake the tail end face of the GH2070P electrode.

3. The method for preparing large-size GH2070P alloy ingots according to claim 1, characterized in that, S1 bakes the tail end face of the GH2070P electrode under constant current and constant voltage conditions of 3.5~4.0kA and 23.5~25.0V.

4. The method for preparing large-size GH2070P alloy ingots according to claim 3, characterized in that, The baking time T of the tail end face of the GH2070P electrode by S1 satisfies the following relationship: T=a·w 2 +4.64, where T is in min, w is the weight of the GH2070P electrode in tons, and a is 0.315 in min / t. 2 .

5. The method for preparing large-size GH2070P alloy ingots according to claim 3, characterized in that, After baking the tail end face of the GH2070P electrode in S1, set the voltage to 24.0~25.0V.

6. The method for preparing large-size GH2070P alloy ingots according to claim 1, characterized in that, In S1, after increasing the current value to 13.0~15.0 kA, maintain it for 10~30 minutes, and then decrease the current value.

7. The method for preparing large-size GH2070P alloy ingots according to claim 6, characterized in that, S1 reduces the current value to 4.5-5.0 kA at a rate of 1-2 kA / min and maintains it for 10-30 minutes.

8. The method for preparing large-size GH2070P alloy ingots according to claim 7, characterized in that, S2 increases the current value from 4.5~5.0 kA to the set current I for S3 melting at a rate of 0.3~0.5 kA / min, and then maintains it for 10~30 min, where I≥8.5 kA, and I=b·R+2.8, where b is 1.45 and the unit is (kA.min) / kg, and R is the melting rate of S3 and the unit is kg / min.

9. The method for preparing large-size GH2070P alloy ingots according to claim 1, characterized in that, The electrode mentioned in S1 is 9.5~10.5t. When S3 melts the electrode to a remaining weight of 400~600kg, feeding begins. The feeding time is ≥150min. After power is cut off, the cooling time is ≥3min to obtain a large-size GH2070P alloy ingot.

10. A large-size GH2070P alloy ingot obtained by the preparation method of the large-size GH2070P alloy ingot according to any one of claims 1 to 9.

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