A method for preparing high-niobium nickel-based corrosion-resistant alloy steel ingot

Abstract

The present invention relates to a method for preparing a high-niobium nickel-based corrosion-resistant alloy steel ingot. The preparation process comprises vacuum induction melting → finishing → ingot-drawing electroslag remelting → two-stage homogenization annealing → producing a high-purity, low-segregation steel ingot. The high-niobium nickel-based corrosion-resistant alloy steel ingot prepared using the present method effectively avoids problems such as severe segregation and coarse secondary phases caused by high niobium content. The steel ingot exhibits excellent forging plasticity, a total inclusion content of no more than 2.0, and is free of low-magnification defects such as black spots and white spots.

Description

Technical Field

[0001] The present invention relates to a method for preparing a nickel-based alloy, in particular to a method for preparing a high-niobium nickel-based corrosion-resistant alloy steel ingot. Background Art

[0002] Nickel-based corrosion-resistant alloys are widely used in fields such as oil drilling and chemical engineering. Nickel-based alloys are primarily prepared by casting, deformation, and powder metallurgy. Niobium-Cr-Fe-Nb-Mo-Ti-Al alloys are age-hardening alloys, and preliminary research has shown them to possess excellent mechanical properties. Niobium is an age-hardening element in nickel-based alloys, and niobium-containing nickel-based alloys can precipitate a fine γ″ strengthening phase. Increasing the niobium content is an effective method for improving alloy strength.

[0003] However, increasing niobium content leads to severe ingot segregation and the formation of large-scale eutectic Laves phases, making deformation difficult. Nickel-based alloys containing 5.0% or more niobium are prone to cracking during deformation. They are typically produced by casting or powder metallurgy, but cast alloys cannot fully realize the alloy's mechanical properties, while powder metallurgy alloys have lower purity and higher cost. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for preparing high-niobium nickel-based corrosion-resistant alloy steel ingots, wherein the alloy is of the Ni-Cr-Fe-Nb-Mo-Ti-Al system, and the preparation method is as follows: vacuum induction melting → finishing → ingot-drawing electroslag remelting → two-stage homogenization annealing → high-purity, low-segregation steel ingots. The method of the present invention aims to solve the problems of severe segregation and coarse second phase in high-niobium nickel-based alloys, improve the plasticity of alloy steel ingots, and lay a good foundation for subsequent deformation such as forging and hot rolling. It does not need to be prepared according to the casting and powder metallurgy processes, and ultimately obtains excellent comprehensive performance. The high-niobium nickel-based corrosion-resistant alloy steel ingots prepared by the method of the present invention have the advantages of deformability, high purity, and low segregation.

[0005] The technical solution of the present invention is:

[0006] A method for preparing a high-niobium nickel-based corrosion-resistant alloy steel ingot comprises the following steps:

[0007] 1) Vacuum induction melting:

[0008] ① First add Ni, Cr, Fe, Nb, and Mo, melt and stir, and keep the temperature at 1550-1600℃ and the pressure at 1-5Pa for ≥10 minutes;

[0009] ② Then add Ti, Al, Mn, C, Si, Mn, V, Zr, and Mg, and after all are melted, keep them at 1500-1550℃ and 1-2Pa for ≥15 minutes, stirring throughout the process;

[0010] ③Pouring: Let it stand for 5 to 10 minutes, adjust the temperature to 1450-1500℃, and pour to obtain a vacuum ingot;

[0011] The weight of the casting mold should be ≥3×the weight of the molten steel to be cast to ensure the cooling effect;

[0012] 2) Finishing;

[0013] 3) Electroslag remelting:

[0014] In the electroslag remelting of the withdrawing ingot type electroslag furnace, multiple skin breaking devices are evenly distributed on the lower edge of the crystallizer, and multiple electrodes are smelted into an electroslag ingot by exchanging electrodes;

[0015] ① Slag preparation and slag preparation:

[0016] After melting a pre-molten slag having a weight ratio of CaF2:Al2O3:CaO = 70:20:10, MgO and TiO2 are added to make a weight ratio of CaF2:Al2O3:CaO:MgO:TiO2 = 45-60:13-17:6.5-8.5:10-20:3-15;

[0017] ② Chemicals:

[0018] Gradually increase the current to stabilize the melting process and maintain the lowest current that stabilizes the melting process, or use a constant melting rate system to maintain a low melting rate;

[0019] ③ Ingot extraction:

[0020] The ingot is drawn out after the molten steel on the bottom 120-260mm surface solidifies;

[0021] ④Forced cooling:

[0022] After the bottom of the electroslag ingot is exposed to a height of ≥50mm, the slag skin is broken with a skin-breaking device to expose the metal surface. Water or water mist is sprayed on and around the broken slag skin. The spray angle and spray pressure are adjusted to ensure that more than 80% of the circumference is in contact with water and more than 50% of the slag skin falls off. Forced cooling significantly improves the cooling effect and solidification rate, reducing the depth of the molten steel pool.

[0023] ⑤Cooling after power failure:

[0024] Before the end of smelting, gradually reduce the current and feed the shrinkage. After all electrodes are melted, turn off the power and continue to keep the crystallizer cooling water and additional forced cooling water cooling. The cooling water holding time is ≥ crystallizer diameter (mm) × 0.2; in order to ensure the quality of the electroslag ingot and the uniformity of the product, the bottom of the electroslag ingot should be cut off by 100-300mm. The length of the electroslag ingot can be increased by exchanging electrodes, thereby reducing the proportion of the bottom cut-off part and improving the yield rate.

[0025] 4) Two-stage homogenization annealing:

[0026] ①Heat to 1135-1145℃ and keep warm for 12-24h;

[0027] ②Heating at a rate of 8-12℃ / h to 1190-1210℃, holding time = diameter of electroslag ingot (mm) × 0.15-0.3;

[0028] ③ Cool down quickly after coming out of the oven.

[0029] The weight percentage of each component of the alloy is: Cr: 20.0-25.0%, Fe: 3.0-15.0%, Nb: 5.5-8.0%, Mo: 2.0-6.0%, Ti: 0.8-1.2%, Al: 0.5-1.0%, Mn: 0.1-1.0%, the total amount of trace elements such as C, Si, Mn, V, Zr, Mg does not exceed 0.5%, and Ni is the balance.

[0030] The casting mold in step 1) is made of cast steel.

[0031] Step 1) the stirring time is ≥ 5 minutes.

[0032] Step 2) The finishing method is to polish away the defects of oxide scale, sagging and protrusion on the surface of the vacuum ingot.

[0033] Step 3) There are 3 to 5 skin-breaking devices and 2 to 4 exchange electrodes.

[0034] Step 3) also includes smelting one electrode into an electroslag ingot.

[0035] In step 3), the length of the broken slag skin is 100 to 300 mm.

[0036] The smelting process in step 3) is stabilized by using a constant melting rate system to maintain low melting rate smelting. Specifically, the melting rate of the chemical material in step 3) is 80% of the normal melting rate, and the melting rate is gradually increased to the normal melting rate when the ingot is withdrawn.

[0037] The unit of the holding time in step 3) is minutes, and the unit of the holding time in step 4) is hours.

[0038] The high-niobium nickel-based corrosion-resistant alloy steel ingot prepared by the above method effectively avoids problems such as severe segregation and coarse second phase caused by high niobium content. The steel ingot has good forging plasticity, the total inclusion amount is no more than level 2.0, and there are no low-magnification defects such as black spots and white spots.

[0039] The design ideas and functions of the main steps and parameters of the preparation method of the present invention are as follows:

[0040] The method of the present invention improves the cooling rate of vacuum ingots and electroslag ingots, increases the solidification rate, controls segregation and prevents the occurrence of coarse eutectic Laves phases for alloys with specific compositions through the design of each process step.

[0041] During the vacuum melting process, the purity and composition uniformity of the vacuum ingot are improved by designing processes such as refining temperature, vacuum degree and time, as well as increasing the cooling rate of the vacuum ingot.

[0042] During the electroslag remelting process, the slag formula and usage method are designed to improve the removal of harmful elements in steel and reduce inclusions, while controlling the slag skin thickness, thereby improving the cooling effect of the crystallizer; the present invention adopts a slag blending method of pre-melted slag + industrial pure oxide, which can flexibly adjust the slag composition, and more than 65% of the slag has been pre-melted, so no further pre-melting is required, reducing the slag cost.

[0043] Conventional electroslag remelting only has cooling capacity within the crystallizer. On this basis, adding direct forced water cooling greatly improves the cooling effect, thereby increasing the solidification rate during the electroslag remelting process, achieving the effect of significantly improving segregation and refining the eutectic second phase. This solves the problems of nickel-based alloys containing more than 5.5% niobium being prone to segregation, coarse second phase particles, and easy cracking during deformation.

[0044] Using 3 to 4 electrodes to smelt one electroslag ingot increases the length of the electroslag ingot, thereby reducing the proportion of the bottom resection and improving the yield rate.

[0045] Through double-stage homogenization annealing, the large-sized second phase is further homogenized and refined. The lower temperature (1135-1145℃) is used to first eliminate the low-melting-point phase to prevent it from melting and causing overburning. After the low-melting-point phase is dissolved into the matrix, it is quickly diffused and homogenized at ultra-high temperature (1190-1210℃) to ensure effect and efficiency.

[0046] The slag obtained by "① slag preparation and slag melting" in the third step can improve the effect of removing harmful elements in steel and reducing inclusions, while controlling the slag skin thickness to no more than 0.8 mm, thereby improving heat transfer efficiency and the cooling effect of the crystallizer cooling water. The slag finally obtained has the following characteristics: alkaline slag with good desulfurization effect; the slag has a good air isolation effect, which can reduce the burn-off of easily oxidized elements in the alloy; the addition of Al2O3 and TiO2 can establish a balance between the aluminum and titanium elements in the slag pool and the molten steel, reduce burn-off, and improve uniformity.

[0047] Beneficial effects of heat treatment of the ultra-high strength and toughness nickel-based corrosion-resistant alloy of the present invention:

[0048] (1) The preparation method of the present invention can effectively control the segregation and second phase size of high niobium nickel-based corrosion-resistant alloy steel ingots, greatly improving the forgeability of the steel ingots.

[0049] (2) The preparation method of the present invention effectively prevents the alloy elements from precipitating in the form of a large-sized second phase, creating conditions for controlling their finely dispersed precipitation in the subsequent preparation process.

[0050] (3) The larger the diameter of the electroslag ingot, the worse the cooling effect. For high-niobium nickel-based corrosion-resistant alloys, in order to obtain a good cooling effect so as to control segregation and the second phase, the diameter of the steel ingot prepared by conventional methods generally does not exceed 200 mm. The preparation method of the present invention, because it greatly improves the cooling effect during the solidification process, can meet the requirements for the preparation of larger-sized high-niobium nickel-based corrosion-resistant alloy steel ingots (the ingot diameter can reach more than 400 mm), forming a large-scale finished product preparation capability, and is more conducive to the mass production of high-niobium nickel-based corrosion-resistant alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is a high-magnification microstructure photograph of a conventionally cooled and rapidly solidified high-niobium nickel-based corrosion-resistant alloy;

[0052] Figure 2 This is a high-magnification microstructure photograph of a rapidly cooled and solidified high-niobium nickel-based corrosion-resistant alloy;

[0053] Figure 3 It is the macrostructure of high niobium nickel-based corrosion-resistant alloy steel ingot;

[0054] Figure 4 It is the macrostructure of high niobium nickel-based corrosion-resistant alloy steel ingot after forging and blanking. DETAILED DESCRIPTION

[0055] Example 1:

[0056] The composition of high niobium nickel-based corrosion-resistant alloy is as follows: Cr: 20.5%, Fe: 11.5%, Nb: 7.3%, Mo: 2.8%, Ti: 0.9%, Al: 0.5%, Mn: 0.2%, V: 0.2%, Ni is the matrix element, and the contents of other elements such as C, N, P, S, Si, Zr, Mg, Ca, Pb, Sn do not exceed 0.1%, and the total does not exceed 0.5%.

[0057] The first step is vacuum induction melting: ① First, add Ni, Cr, Fe, Nb, and Mo. After melting, stir for 5 minutes and maintain at 1550-1600°C and below 3 Pa for 15 minutes. ② Then, add the remaining raw materials. After melting, maintain at 1500-1550°C and below 2 Pa for 20 minutes, using electromagnetic stirring throughout the process. ③ Casting: After 5 minutes of stagnation, pour into a metal mold at 1460-1480°C to obtain a vacuum ingot. The vacuum ingot weighs 30 kg, and the mold weighs 100 kg.

[0058] The second step is finishing: polish away defects such as oxide scale, sagging, and protrusions on the surface of the vacuum ingot.

[0059] The third step, electroslag remelting, is performed using an ingot-drawing electroslag furnace. The mold has an inner diameter of 160mm and three evenly spaced slag-breaking devices along its lower edge. Three electrodes are exchanged to form an electroslag ingot. ① Slag Preparation and Slag Melting: After melting the pre-molten slag (CaF2:Al2O3:CaO = 70:20:10 by weight), industrial-grade MgO and TiO2 are added to ensure a CaF2:Al2O3:CaO:MgO:TiO2 ratio of 49:14:7:15:15 by weight. ② Beginning Melting: Gradually increase the current to stabilize the melting process, maintaining the minimum current required for a stable melting process. ③ Ingot Drawing: Ingot drawing begins after the bottom 150mm of the surface steel solidifies. ④ Additional Forced Cooling: After the bottom of the electroslag ingot is exposed to a height of 50mm, the slag skin is broken open using the slag-breaking device to expose the metal surface. Spray water mist onto and around the broken slag skin. Adjust the spray angle and pressure to ensure that more than 80% of the circumference is in contact with the water and more than 50% of the slag skin falls off. ⑤ Cooling after power failure: Gradually reduce the current to compensate for shrinkage before the end of smelting. After all electrodes have melted, power is turned off. Continue cooling with mold cooling water and additional forced cooling water for 40 minutes. The three electrodes are exchanged to form an electroslag ingot. 100mm of the bottom of the electroslag ingot is removed.

[0060] Step 4: Double-stage homogenization annealing: ① Raise the temperature to 1140°C and hold for 12 hours. ② Then raise the temperature to 1200°C at a rate of 12°C / h and hold for 30 hours. ③ Remove from the furnace and air cool.

[0061] Compared with the high niobium nickel-based corrosion resistant alloy steel ingot prepared by the above method, the second phase is more uniform and finer (see Figure 1 and Figure 2 ), the steel ingot has good forging plasticity, the total amount of inclusions is not more than 2.0 level, and there are no low-magnification defects such as black spots and white spots.

[0062] Example 2:

[0063] The composition of high niobium nickel-based corrosion-resistant alloy is as follows: Cr: 21.6%, Fe: 7.2%, Nb: 6.2%, Mo: 5.9%, Ti: 1.1%, Al: 0.8%, Mn: 0.2%, V: 0.1%, Ni is the matrix element, and the contents of other elements such as C, N, P, S, Si, Zr, Mg, Ca, Pb, Sn do not exceed 0.1%, and the total does not exceed 0.5%.

[0064] The first step is vacuum induction melting: ① First, add Ni, Cr, Fe, Nb, and Mo. After melting, stir for 5 minutes and maintain at 1550-1600°C and below 3 Pa for 20 minutes. ② Then, add the remaining raw materials. After melting, maintain at 1500-1550°C and below 2 Pa for 30 minutes, using electromagnetic stirring throughout the process. ③ Casting: Let stand for 5 minutes, then pour into a metal mold at 1480-1500°C to obtain a vacuum ingot. The vacuum ingot weighs 150 kg, and the mold weighs 500 kg.

[0065] The second step is finishing: polish away defects such as oxide scale, sagging, and protrusions on the surface of the vacuum ingot.

[0066] The third step, electroslag remelting, is performed using an ingot-drawing electroslag furnace. The mold has an inner diameter of 270mm and four evenly spaced slag-breaking devices along its lower edge. Three electrodes are exchanged to form an electroslag ingot. ① Slag Preparation and Slag Preparation: After melting the pre-molten slag (CaF2:Al2O3:CaO = 70:20:10 by weight), industrial-grade MgO and TiO2 are added to ensure a CaF2:Al2O3:CaO:MgO:TiO2 ratio of 56:16:8:10:10 by weight. ② Beginning Melting: Gradually increase the current to stabilize the melting process, maintaining the minimum current required for a stable melting process. ③ Ingot Drawing: Ingot drawing begins after the bottom 150mm of the surface steel solidifies. ④ Additional Forced Cooling: After the bottom of the electroslag ingot is exposed to a height of 50mm, the slag skin is broken using the slag-breaking device to expose the metal surface. Spray water onto and around the broken slag skin, adjusting the spray angle and pressure to ensure that over 80% of the circumference is in contact with the water and over 50% of the slag skin has fallen off. ⑤ Cooling after power failure: Gradually reduce the current to compensate for shrinkage before the end of smelting. After all electrodes have melted, power is turned off. Continue cooling with the mold cooling water and additional forced cooling water for 60 minutes. Three electrodes are exchanged to form an electroslag ingot, with 150mm of the bottom removed.

[0067] Step 4: Double-stage homogenization annealing: ① Raise the temperature to 1145°C and hold for 18 hours. ② Then raise the temperature to 1200°C at a rate of 10°C / h and hold for 48 hours. ③ Remove from the furnace and air cool.

[0068] The high niobium nickel-based corrosion-resistant alloy steel ingot prepared by the above method has a more uniform and fine second phase, good forging plasticity, a total inclusion content of no more than 2.0, and no low-magnification defects such as black spots and white spots (see Figure 3 、 Figure 4 ).

[0069] Figure 3 This is the macrostructure of high-niobium nickel-based corrosion-resistant alloy steel ingot. Although its grain size is coarse, there are no macroscopic defects such as black spots, white spots, and shrinkage cavities, indicating that the quality of the steel ingot has reached the expected effect. Figure 4This is the low-magnification structure of the high-niobium nickel-based corrosion-resistant alloy steel ingot after forging. Dynamic recrystallization occurs during the forging process to refine the grains, and coarse grains can no longer be observed. At the same time, no low-magnification defects such as black spots, white spots, shrinkage cavities, and cracks are seen, further proving the good quality of the steel ingot.

[0070] Example 3:

[0071] The composition of high niobium nickel-based corrosion-resistant alloy is as follows: Cr: 21.5%, Fe: 15.0%, Nb: 5.6%, Mo: 3.1%, Ti: 1.0%, Al: 0.5%, Mn: 0.2%, V: 0.1%, Ni is the matrix element, and the contents of other elements such as C, N, P, S, Si, Zr, Mg, Ca, Pb, Sn do not exceed 0.1%, and the total does not exceed 0.5%.

[0072] The first step is vacuum induction melting: ① First, add Ni, Cr, Fe, Nb, and Mo. After melting, stir for 5 minutes and maintain at 1550-1600°C and below 3 Pa for 20 minutes. ② Then, add the remaining raw materials. After melting, maintain at 1500-1550°C and below 2 Pa for 30 minutes, using electromagnetic stirring throughout the process. ③ Casting: Let stand for 10 minutes, then pour into a metal mold at 1480-1500°C to obtain a vacuum ingot. The vacuum ingot weighs 230 kg, and the mold weighs 700 kg.

[0073] The second step is finishing: polish away defects such as oxide scale, sagging, and protrusions on the surface of the vacuum ingot.

[0074] The third step, electroslag remelting, is performed using an ingot-drawing electroslag furnace. The mold has an inner diameter of 400mm and five evenly spaced slag-breaking devices along its lower edge. Four electrodes are exchanged to form an electroslag ingot. ① Slag Preparation and Slag Preparation: After melting the pre-molten slag with a ratio of CaF2:Al2O3:CaO of 70:20:10, industrial-grade MgO and TiO2 are added to ensure that the ratio of CaF2:Al2O3:CaO:MgO:TiO2 is 59.5:17:8.5:12:3. ② Starting the Melting Process: Gradually increase the current to stabilize the melting process, then maintain a low melting rate (80% of the normal melting rate) using a constant melting rate system. ③ Ingot Drawing: After the molten steel solidifies within the bottom 260mm, ingot drawing begins and the melting rate is gradually increased to the normal melting rate. ④ Additional Forced Cooling: After the bottom of the electroslag ingot is exposed to a height of 50mm, the slag skin is broken using the slag-breaking device to expose the metal surface. Spray water mist onto and around the broken slag skin. Adjust the spray angle and pressure to ensure that more than 80% of the circumference is in contact with the water and more than 50% of the slag skin falls off. ⑤ Cooling after power failure: Gradually reduce the current to compensate for shrinkage before the end of smelting. After all electrodes have melted, power is turned off. Continue cooling with mold cooling water and additional forced cooling water for 90 minutes. The four electrodes are exchanged to form an electroslag ingot. The bottom of the electroslag ingot is cut off by 200mm.

[0075] Step 4: Double-stage homogenization annealing: ① Raise the temperature to 1143°C and hold for 24 hours. ② Then raise the temperature to 1200°C at a rate of 10°C / h and hold for 72 hours. ③ Remove from the furnace and air cool.

[0076] The high niobium nickel-based corrosion-resistant alloy steel ingot prepared by the above method has a more uniform and fine second phase, good forging plasticity, a total inclusion content of no more than level 2.0, and no low-magnification defects such as black spots and white spots.

[0077] The present invention is not limited to the above embodiments. The above embodiments and descriptions in the specification are only for illustrating the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which all fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing a high-niobium nickel-based corrosion-resistant alloy steel ingot, characterized in that: The following steps are involved: 1) Vacuum induction melting: ① First add Ni, Cr, Fe, Nb, and Mo, melt and stir, and keep the temperature at 1550-1600℃ and the pressure at 1-5Pa for ≥10 minutes; ② Then add Ti, Al, Mn, C, Si, V, Zr, and Mg, and after all are melted, keep them at 1500-1550℃ and 1-2Pa for ≥15 minutes, stirring throughout the process; ③Pouring: Let it stand for 5 to 10 minutes, adjust the temperature to 1450-1500℃, and pour to obtain a vacuum ingot; The weight of the mold used for pouring is ≥3×the weight of the molten steel to be poured; 2) Finishing; 3) Electroslag remelting: In the electroslag remelting process of the withdrawable ingot electroslag furnace, multiple skin-breaking devices are evenly distributed along the lower edge of the crystallizer. Multiple electrodes are smelted into an electroslag ingot by exchanging electrodes. ① Slag preparation and slag preparation: After melting the pre-molten slag with a weight ratio of CaF2:Al2O3:CaO = 70:20:10, MgO and TiO2 are added to make the weight ratio of CaF2:Al2O3:CaO:MgO:TiO2 = 45-60:13-17:6.5-8.5:10-20:3-15; ② Chemicals: Increase the current gradually to maintain the lowest current for a stable melting process; ③ Ingot extraction: The ingot is drawn out after the molten steel on the bottom 120-260mm surface solidifies; ④Forced cooling: After the bottom of the electroslag ingot is exposed to a height of ≥50mm, use a skin-breaking device to break the slag skin to expose the metal surface; spray water or water mist on the position where the slag skin has been broken and the surrounding area, so that ≥80% of the circumference is in contact with water and ≥50% of the slag skin falls off; ⑤Cooling after power failure: Before the end of smelting, gradually reduce the current and feed the shrinkage. After all electrodes are melted, turn off the power and continue to cool the mold with cooling water and additional forced cooling water. The cooling water holding time should be ≥ mold diameter (mm) × 0.

2. The bottom of the electroslag ingot should be cut off by 100-300mm to ensure the uniformity of the electroslag ingot. The holding time is in minutes. 4) Double-stage homogenization annealing: ① Raise the temperature to 1135-1145°C and keep warm for 12-24 hours, where the unit of the holding time is hours; ②Heat to 1190-1210℃ at a rate of 8-12℃ / h. Holding time = diameter of electroslag ingot (mm) * 0.15-0.3; ③ Cool quickly after being taken out of the oven; The weight percentage of each component of the alloy is: Cr: 20.0-25.0%, Fe: 3.0-15.0%, Nb: 5.5-8.0%, Mo: 2.0-6.0%, Ti: 0.8-1.2%, Al: 0.5-1.0%, Mn: 0.1-1.0%, the total amount of trace elements C, Si, V, Zr, and Mg does not exceed 0.5%, and Ni is the balance.

2. The method according to claim 1, wherein: Step 1) The casting mold is made of cast steel.

3. The method according to claim 1, wherein: Step 1) The stirring time is ≥ 5 minutes.

4. The method according to claim 1, wherein: Step 2) The finishing method is to polish away the defects of oxide scale, sagging and protrusion on the surface of the vacuum ingot.

5. The method according to claim 1, wherein: Step 3) There are 3 to 5 skin-breaking devices and 2 to 4 exchange electrodes.

6. The method according to claim 1, wherein: Step 3) also includes smelting one electrode into an electroslag ingot.

7. The method according to claim 1, wherein: The smelting process in step 3) is stabilized by using a constant melting rate system to maintain low melting rate smelting. Specifically, the melting rate of the chemical material in step 3) is 80% of the normal melting rate, and the melting rate is gradually increased to the normal melting rate when the ingot is withdrawn.

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