Process for improving uniformity of tail part of vacuum consumable smelting cast ingot

Abstract

The invention discloses a process for improving the uniformity of the tail part of a vacuum consumable smelting cast ingot, the last smelting process of a high-quality deformed high-temperature alloy is vacuum consumable smelting (VAR), and the traditional smelting process can form relatively large composition segregation in a certain area of the tail part of the consumable cast ingot, so that the components are not uniform, and the defects of the traditional smelting process are overcome. Not only is the tail of a cast ingot easy to crack during forging, but also the tail structure of a bar is uneven and can be removed only through saw cutting at present, so that great waste of materials is caused. During vacuum consumable smelting, the arc striking plate with a certain size and specification is added during arc striking of vacuum consumable arc smelting, meanwhile, the consumable smelting arc striking process is optimized, the quality of a consumable electrode is controlled, the component uniformity of the tail of the high-temperature alloy consumable cast ingot is improved, and tail cracking in the forging process is avoided; and the uniformity of the tail structure of the bar is improved.

Description

Technical Field

[0001] The invention relates to the technical field of high-temperature alloy smelting, and in particular to a process for improving the uniformity of a tail of a vacuum consumable smelting ingot. Background Art

[0002] Among deformable high-temperature alloys, GH416, GH4169G, GH4169D and other alloys have a high Nb content, and Nb is an element that is easily segregated. During vacuum consumable melting, due to the strong cooling of the crystallizer base and the low melting rate in the arc starting stage, it is difficult to form a deep molten pool. This will result in the fallen metal blocks such as the grid, skirt and ingot crown being difficult to melt in the molten pool in the process of consumable melting, forming a steel liquid with uniform composition, thus forming local composition segregation; secondly, due to the strong cooling of the tail of the ingot, there is a repeated melting and solidification process of the molten metal at the tail of the ingot, and as the consumable melting process proceeds, the solidification rate of the molten metal at the front of the solid-liquid interface of the molten pool changes, which leads to a change in the concentration of the segregation element Nb in the liquid phase at the front of the solid-liquid interface, thereby solidifying to form a Nb-poor area, forming an area with uneven composition at the tail of the ingot, which makes it easy to crack during the forging process and forms an area with uneven structure at the tail of the bar.

[0003] At present, the method of cutting off the tail of the ingot is generally adopted to remove the influence of the tail of the ingot, but the amount of cutting off is large, resulting in a great waste of materials and increasing the cost of high-temperature alloys. Summary of the Invention

[0004] The object of the present invention is to provide a process for improving the uniformity of the tail of a vacuum consumable melting ingot, so as to solve the problems mentioned in the background technology.

[0005] To achieve the above object, the present invention provides the following technical solution: a process for improving the uniformity of the tail of a vacuum consumable melting ingot, specifically comprising the following steps:

[0006] S1. Vacuum induction melting: The alloy is prepared according to the composition requirements of GH4169 alloy and melted in a vacuum induction furnace. After refining and degassing, the molten steel is poured into an ingot mold with a diameter of Φ430mm and equipped with a heat-insulating riser after passing through a preheated launder and nozzle, and finally an induction cast ingot with a specification of Φ420mm is obtained;

[0007] S2. Preparation of consumable electrode: The induction ingot is prepared into a consumable electrode after stress relief annealing, surface treatment and head and tail removal;

[0008] S3. Vacuum consumable remelting: The prepared consumable electrode is welded, aligned, loaded into the furnace, and vacuumed. When the vacuum degree is ≤0.1 Pa and the leakage rate is ≤0.1 Pa / min, the process parameters are input for melting. The melting process is divided into three stages: arc starting stage, stable melting stage, and hot capping stage. The melting rate and droplet are controlled in the stable melting stage. After the melting is completed, it is cooled for a certain period of time and then removed from the furnace to obtain a consumable ingot with a diameter of Φ495 mm.

[0009] S4. High-temperature homogenization of ingots and preparation of bars: After two stages of high-temperature homogenization, the consumable ingots are forged into Ø270mm black-skinned bars using a fast forging machine. After peeling and cutting off the rotten heads, the finished Ø250mm bars are obtained.

[0010] Preferably, in step S1, the ingot mold with a diameter of Φ430 mm needs to be baked at ≥550°C for ≥3h, and when pouring the molten steel, the temperature of the ingot mold needs to be ≥400°C;

[0011] Preferably, in step S1, the ingot mold with a diameter of Φ430 mm uses a Φ410 insulation riser, the wall thickness of the insulation riser is required to be ≥20 mm, and the volume of the molten steel supported is 1 / 6 to 1 / 8 of the total volume of the induction casting ingot;

[0012] Preferably, in step S1, the temperature of the launder during pouring needs to be ≥1100°C, the nozzle diameter range is Φ15 to Φ30 mm, and when pouring molten steel, the flow rate of the molten steel through the nozzle is 5 to 6 kg / s;

[0013] Preferably, in the step S3, when loading the furnace, an arc starting plate of the same grade with a diameter of Φ430 to Φ500 mm and a thickness of ≥40 mm is used on the copper base of the consumable furnace crystallizer;

[0014] Preferably, in the step S3, when the consumable melting arc is started, the arc starting stage melting time is ≥60 min, no cooling gas is used in the arc starting stage, the arc starting stage is divided into 6 stages, and current and voltage control are used in all arc starting stages;

[0015] Phase 1: Duration: 15 to 20 minutes, current remains constant within the range of 3 to 4 kA, voltage remains constant within the range of 20 to 21 V, and melting rate is 0 kg / min.

[0016] The second stage: duration: 4 to 6 minutes, the current increases to 8 to 10 kA, the voltage increases to 22 to 23 V, and the melting rate increases to 2.0 to 3.0 kg / min.

[0017] The third stage: duration: 8 to 10 minutes, the current increases to 10 to 12 kA, the voltage range is 22 to 23 V, and the melting rate increases to 5.0 to 6.0 kg / min.

[0018] The fourth stage: duration: 10 to 15 minutes, the current remains constant within the range of 10 to 12 kA, the voltage remains constant within the range of 22 to 23 V, the melting rate range is 6.0 to 8.0 kg / min, and the highest point melting rate is at least twice that of the stable melting stage.

[0019] The fifth stage: duration: 4 to 6 minutes, the current is reduced to 8 to 8.5 kA, the voltage range is 22 to 23 V, and the melting rate range is 4.0 to 5.0 kg / min.

[0020] Stage 6: Duration: 15-20 minutes, current range 6-8kA, voltage range 20-21V, melting rate range 3.0-3.9kg / min.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The present invention proposes a process for improving the uniformity of the tail of a vacuum consumable melting ingot. In the high-temperature alloy double vacuum VIM+VAR melting process, the quality of the consumable electrode is improved and the chipping is reduced by controlling the insulation riser, pouring temperature, pouring speed, etc.; by optimizing the consumable melting arc starting process, an arc starting plate of the same brand as the consumable melting arc starting is added; the component segregation at the tail of the consumable ingot is reduced or eliminated, the amount of the consumable ingot tail removed is reduced, and the material utilization rate is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a low magnification of high temperature alloy (GH4169) rod;

[0024] Figure 2 It is the base of vacuum consumable arc furnace crystallizer and the arc starting plate of the same brand;

[0025] Figure 3 The head of the induction casting ingot of Example 1 was longitudinally dissected 300 mm (using a heat-insulating riser);

[0026] Figure 4 This is the low magnification of the tail of the rod in Example 1;

[0027] Figure 5 This is a high-magnification diagram of tissue sampling;

[0028] Figure 6 The head of the induction casting ingot of comparative example 1 was dissected 300 mm longitudinally (without using a heat-insulating riser);

[0029] Figure 7 It is lower than that of Comparative Example 1. DETAILED DESCRIPTION

[0030] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] A process for improving the uniformity of the tail of a vacuum consumable melting ingot, the specific scheme is as follows:

[0032] S1. Vacuum induction melting: The alloy is prepared according to the composition requirements of GH4169 alloy and melted in a vacuum induction furnace. After refining and degassing, the molten steel is poured into an ingot mold with a diameter of Φ430mm and equipped with a heat-insulating riser after passing through a preheated launder and nozzle, and finally an induction cast ingot with a specification of Φ420mm is obtained;

[0033] S2. Preparation of consumable electrode: The induction ingot is prepared into a consumable electrode after stress relief annealing, surface treatment and head and tail removal;

[0034] S3. Vacuum consumable remelting: The prepared consumable electrode is welded, aligned, loaded into the furnace, and vacuumed. When the vacuum degree is ≤0.1 Pa and the leakage rate is ≤0.1 Pa / min, the process parameters are input for melting. The melting process is divided into three stages: arc starting stage, stable melting stage, and hot capping stage. The melting rate and droplet are controlled in the stable melting stage. After the melting is completed, it is cooled for a certain period of time and then removed from the furnace to obtain a consumable ingot with a diameter of Φ495 mm.

[0035] S4. High-temperature homogenization of ingots and preparation of bars: After two stages of high-temperature homogenization, the consumable ingots are forged into Ø270mm black-skinned bars using a fast forging machine. After peeling and cutting off the rotten heads, the finished Ø250mm bars are obtained.

[0036] In step S1, the ingot mold with a diameter of Φ430 mm needs to be baked at 600±50°C for 4-5 hours. When pouring the molten steel, the temperature of the ingot mold must be ≥400°C.

[0037] In the step S1, the ingot mold with a diameter of Φ430 mm uses a Φ410 insulation riser, the wall thickness of the insulation riser is required to be 40-50 mm, and the volume of molten steel supported is 1 / 6-1 / 8 of the total volume of the induction casting ingot;

[0038] In step S1, the temperature of the launder during pouring must be ≥1100°C, the nozzle diameter range is Φ15 to Φ30 mm, and the flow rate of the molten steel through the nozzle during pouring is 5 to 6 kg / s.

[0039] In the step S3, when loading the furnace, an arc starter plate of the same grade with a diameter of Φ430-Φ500 mm and a thickness of 50-60 mm is used on the copper base of the consumable furnace crystallizer;

[0040] Wherein, in the step S3, when the consumable melting arc is started, the arc starting stage melting time is ≥60min, no cooling gas is used in the arc starting stage, the arc starting stage is divided into 6 stages, and the current and voltage control are used in the arc starting stage;

[0041] Phase 1: Duration: 15 to 20 minutes, current remains constant within the range of 3 to 4 kA, voltage remains constant within the range of 20 to 21 V, and melting rate is 0 kg / min.

[0042] The second stage: duration: 4 to 6 minutes, the current increases to 8 to 10 kA, the voltage increases to 22 to 23 V, and the melting rate increases to 2.0 to 3.0 kg / min.

[0043] The third stage: duration: 8 to 10 minutes, the current increases to 10 to 12 kA, the voltage range is 22 to 23 V, and the melting rate increases to 5.0 to 6.0 kg / min.

[0044] The fourth stage: duration: 10 to 15 minutes, the current remains constant within the range of 10 to 12 kA, the voltage remains constant within the range of 22 to 23 V, the melting rate range is 6.0 to 8.0 kg / min, and the highest point melting rate is at least twice that of the stable melting stage.

[0045] The fifth stage: duration: 4 to 6 minutes, the current is reduced to 8 to 8.5 kA, the voltage range is 22 to 23 V, and the melting rate range is 4.0 to 5.0 kg / min.

[0046] Stage 6: Duration: 15-20 minutes, current range 6-8kA, voltage range 20-21V, melting rate range 3.0-3.9kg / min.

[0047] The present invention is further described in detail below with reference to specific embodiments.

[0048] Example 1 comprises the following steps:

[0049] S1. Vacuum induction melting: The alloy is prepared according to the composition requirements of GH4169 alloy and melted in a vacuum induction furnace. After refining and degassing, the molten steel is poured into an ingot mold with a diameter of Φ430mm and equipped with a heat-insulating riser after passing through a preheated launder and nozzle, and finally an induction cast ingot with a specification of Φ420mm is obtained;

[0050] S2. Preparation of consumable electrode: The induction ingot is prepared into a consumable electrode after stress relief annealing, surface treatment and head and tail removal;

[0051] S3. Vacuum consumable remelting: The prepared consumable electrode is welded, aligned, loaded into the furnace, and vacuumed. When the vacuum degree is ≤0.1 Pa and the leakage rate is ≤0.1 Pa / min, the process parameters are input for melting. The melting process is divided into three stages: arc starting stage, stable melting stage, and hot capping stage. The melting rate and droplet are controlled in the stable melting stage. After the melting is completed, it is cooled for a certain period of time and then removed from the furnace to obtain a consumable ingot with a diameter of Φ495 mm.

[0052] S4. High-temperature homogenization of ingots and preparation of bars: After two stages of high-temperature homogenization, the consumable ingots are forged into Ø270mm black-skinned bars using a fast forging machine. After peeling and cutting off the rotten heads, the finished Ø250mm bars are obtained.

[0053] In step S1, the ingot mold with a diameter of Φ430 mm needs to be baked at 600±50°C for 4-5 hours. When pouring the molten steel, the temperature of the ingot mold must be ≥400°C.

[0054] In the step S1, the ingot mold with a diameter of Φ430 mm uses a Φ410 insulation riser, the wall thickness of the insulation riser is required to be 40-50 mm, and the volume of molten steel supported is 1 / 6-1 / 8 of the total volume of the induction casting ingot;

[0055] In step S1, the temperature of the launder during pouring must be ≥1100°C, the nozzle diameter range is Φ15 to Φ30 mm, and the flow rate of the molten steel through the nozzle during pouring is 5 to 6 kg / s.

[0056] In the step S3, when loading the furnace, an arc starter plate of the same grade with a diameter of Φ430-Φ500 mm and a thickness of 50-60 mm is used on the copper base of the consumable furnace crystallizer;

[0057] In the step S3, when the consumable melting arc is started, the arc starting stage has a melting time of 75 minutes, no cooling gas is used in the arc starting stage, and the arc starting stage is divided into 6 stages, all of which are controlled by current and voltage;

[0058] The first stage: duration: 20 minutes, the current is kept constant at 3kA, the voltage is kept constant at 21V, and the melting rate is 0kg / min.

[0059] The second stage: duration: 5 minutes, the current is increased to 9kA, the voltage is increased to 23V, and the melting rate is increased to 2.5-3.0kg / min.

[0060] The third stage: duration: 10 minutes, the current is increased to 12kA, the voltage is kept constant at 23V, and the melting rate is increased to 5.0-6.0kg / min.

[0061] The fourth stage: duration: 15 minutes, the current is kept constant at 12kA, the voltage is kept constant at 23V, the melting rate range is 7.0-8.0kg / min, and the highest point melting rate is at least twice the melting rate in the stable melting stage.

[0062] The fifth stage: duration: 5 minutes, the current is reduced to 8kA, the voltage is kept constant at 23V, and the melting rate range is 4.5 to 5.0kg / min.

[0063] Stage 6: Duration: 20 minutes, current reduced to 6kA, voltage kept constant at 23V, melting rate range 3.0~3.5kg / min.

[0064] Example 1, longitudinal dissection of the induction casting head 300mm, it can be seen that the shrinkage cavity of the ingot head is greatly reduced, such as Figure 3 As shown; the tail of the consumable ingot in Example 1 was not cut off, and a low-magnification test specimen and a high-magnification test specimen were cut 50 mm away from the tail of the bar (equivalent to the tail of the ingot). The low-magnification test specimen was subjected to standard heat treatment ((950-980℃)±10℃, kept warm for 10 hours, cooled to room temperature at a cooling rate equivalent to air cooling or faster, then kept warm at 720±10℃ for 8 hours, furnace cooled to 620℃±10℃ at a rate of 50±10℃ / h, kept warm for 8 hours, and air cooled), polished, and then corrosion tested to observe the uniformity of the structure. Figure 4 The image shows the low-magnification after corrosion. The low-magnification structure is uniform, without cracks and annual ring-shaped segregation bands. The high-magnification specimen is sampled in a "cross" shape, as shown in the figure below. Figure 5 As shown in Table 1, the test results show that the grain size is relatively uniform in the four directions, and the range is level 1.

[0065] Table 1 Example 1 High-magnification grain size

[0066]

[0067]

[0068] Comparative Example 1 comprises the following steps:

[0069] S1. Vacuum induction melting: The alloy is prepared according to the composition requirements of GH4169 alloy and melted in a vacuum induction furnace. After refining and degassing, the molten steel is poured into a preheated launder and nozzle and poured into an ingot mold with a diameter of Φ430mm without a heat-insulating riser to obtain an induction ingot with a specification of Φ420mm.

[0070] S2. Preparation of consumable electrode: The induction ingot is prepared into a consumable electrode after stress relief annealing, surface treatment and head and tail removal;

[0071] S3. Vacuum consumable remelting: The prepared consumable electrode is welded, aligned, loaded into the furnace, and vacuumed. When the vacuum degree is ≤0.1 Pa and the leakage rate is ≤0.1 Pa / min, the process parameters are input for melting. The melting process is divided into three stages: arc starting stage, stable melting stage, and hot capping stage. The melting rate and droplet are controlled in the stable melting stage. After the melting is completed, it is cooled for a certain period of time and then removed from the furnace to obtain a consumable ingot with a diameter of Φ495 mm.

[0072] S4. High-temperature homogenization of ingots and preparation of bars: After two stages of high-temperature homogenization, the consumable ingots are forged into Ø270mm black-skinned bars using a fast forging machine. After peeling and cutting off the rotten heads, the finished Ø250mm bars are obtained.

[0073] In step S1, the ingot mold with a diameter of Φ430 mm needs to be baked at 600±50°C for 4-5 hours. When pouring the molten steel, the temperature of the ingot mold must be ≥400°C.

[0074] In the step S1, the ingot mold with a diameter of Φ430 mm uses a Φ410 insulation riser, the wall thickness of the insulation riser is required to be 40-50 mm, and the volume of molten steel supported is 1 / 6-1 / 8 of the total volume of the induction casting ingot;

[0075] In step S1, the temperature of the launder during pouring must be ≥1100°C, the nozzle diameter range is Φ15 to Φ30 mm, and the flow rate of the molten steel through the nozzle during pouring is 5 to 6 kg / s.

[0076] In the step S3, when loading the furnace, an arc starter plate of the same grade with a diameter of Φ430-Φ500 mm and a thickness of 50-60 mm is used on the copper base of the consumable furnace crystallizer;

[0077] In the step S3, when the consumable melting arc is started, the arc starting stage has a melting time of 75 minutes, no cooling gas is used in the arc starting stage, and the arc starting stage is divided into 6 stages, all of which are controlled by current and voltage;

[0078] The first stage: duration: 20 minutes, the current is kept constant at 3kA, the voltage is kept constant at 21V, and the melting rate is 0kg / min.

[0079] The second stage: duration: 5 minutes, the current is increased to 9kA, the voltage is increased to 23V, and the melting rate is increased to 2.5-3.0kg / min.

[0080] The third stage: duration: 10 minutes, the current is increased to 12kA, the voltage is kept constant at 23V, and the melting rate is increased to 5.0-6.0kg / min.

[0081] The fourth stage: duration: 15 minutes, the current is kept constant at 12kA, the voltage is kept constant at 23V, the melting rate range is 7.0-8.0kg / min, and the highest point melting rate is at least twice the melting rate in the stable melting stage.

[0082] The fifth stage: duration: 5 minutes, the current is reduced to 8kA, the voltage is kept constant at 23V, and the melting rate range is 4.5 to 5.0kg / min.

[0083] Stage 6: Duration: 20 minutes, current reduced to 6kA, voltage kept constant at 23V, melting rate range 3.0~3.5kg / min.

[0084] Comparative Example 1: The longitudinal dissection of the induction casting head 300mm shows that the shrinkage cavity in the ingot head is relatively large. Figure 6 As shown, large pieces are likely to fall off, and they cannot be completely melted inside the molten pool, forming a component segregation area; in comparative example 1, the tail of the consumable ingot was not cut off, and low-magnification test specimens and high-magnification test specimens were cut at 50 mm and 100 mm from the tail of the bar (equivalent to the tail of the ingot). The low-magnification test specimens were subjected to standard heat treatment ((950-980°C) ± 10°C, kept warm for 10 hours, cooled to room temperature at a cooling rate equivalent to air cooling or faster, then kept warm at 720 ± 10°C for 8 hours, furnace cooled to 620°C ± 10°C at a rate of 50 ± 10°C / h, kept warm for 8 hours, and air cooled), polished, and then corrosion tested to observe the uniformity of the structure, as shown in FIG. Figure 4 The figure shows the low-magnification after corrosion. There are cracks in the center of the low-magnification image at 50mm. There are large areas of coarse grains in the low-magnification image at 100mm. The high-magnification specimen is sampled in the shape of a cross. Figure 5 As shown in Table 2, the test results show that in the coarse grain direction shown at low magnification, the grains are coarse, and the grain size in the four directions is uneven, with a range of 3.

[0085] Table 2 Comparative Example 1 High-magnification grain size

[0086] Location 1 2 3 4 Location A B C D 1 8 / / / 2 8 8.5 6 8.5 3 9 9 7 9

[0087] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A process for improving the uniformity of the tail of a vacuum consumable melting ingot, characterized in that: Specifically include the following steps: S1. Vacuum induction melting: The alloy is prepared according to the composition requirements of GH4169 alloy and melted in a vacuum induction furnace. After refining and degassing, the molten steel is poured into an ingot mold with a diameter of Φ430mm and equipped with a heat-insulating riser after passing through a preheated launder and nozzle, and finally an induction cast ingot with a specification of Φ420mm is obtained; S2. Preparation of consumable electrode: The induction ingot is prepared into a consumable electrode after stress relief annealing, surface treatment and head and tail removal; S3. Vacuum consumable remelting: The prepared consumable electrode is welded, aligned, loaded into the furnace, and vacuumed. When the vacuum degree is ≤0.1 Pa and the leakage rate is ≤0.1 Pa / min, the process parameters are input for melting. The melting process is divided into three stages: arc starting stage, stable melting stage, and hot capping stage. The melting rate and droplet are controlled in the stable melting stage. After the melting is completed, it is cooled for a certain period of time and then removed from the furnace to obtain a consumable ingot with a diameter of Φ495 mm. S4. High-temperature homogenization of ingots and preparation of bars: After two stages of high-temperature homogenization, the consumable ingots are forged into Ø270mm black-skinned bars using a fast forging machine. After peeling and cutting off the rotten heads, the finished Ø250mm bars are obtained.

2. The process for improving the uniformity of the tail of a vacuum consumable melting ingot according to claim 1, characterized in that: In the step S1, the ingot mold with a diameter of Φ430 mm needs to be baked at a temperature of ≥550°C for ≥3 hours. When pouring the molten steel, the temperature of the ingot mold must be ensured to be ≥400°C.

3. The process for improving the uniformity of the tail of a vacuum consumable melting ingot according to claim 1, characterized in that: In step S1, the ingot mold with a diameter of Φ430 mm uses a Φ410 insulation riser, the wall thickness of the insulation riser is required to be ≥20 mm, and the volume of molten steel it supports is 1 / 6 to 1 / 8 of the total volume of the induction casting ingot.

4. The process for improving the uniformity of the tail of a vacuum consumable melting ingot according to claim 1, characterized in that: In step S1, the temperature of the launder during pouring needs to be ≥1100°C, the nozzle diameter range is Φ15 to Φ30 mm, and when pouring molten steel, the flow rate of the molten steel through the nozzle is 5 to 6 kg / s.

5. The process for improving the uniformity of the tail of a vacuum consumable melting ingot according to claim 1, characterized in that: In the step S3, when loading the furnace, an arc starting plate of the same brand with a diameter of Φ430 to Φ500 mm and a thickness of ≥40 mm is used on the copper base of the consumable furnace crystallizer.

6. The process for improving the uniformity of the tail of a vacuum consumable melting ingot according to claim 1, characterized in that: In the step S3, when the consumable melting arc is started, the arc starting stage melting time is ≥60 minutes, no cooling gas is used in the arc starting stage, the arc starting stage is divided into 6 stages, and current and voltage control are used in the arc starting stage; Phase 1: Duration: 15 to 20 minutes, current remains constant within the range of 3 to 4 kA, voltage remains constant within the range of 20 to 21 V, and melting rate is 0 kg / min. The second stage: duration: 4 to 6 minutes, the current increases to 8 to 10 kA, the voltage increases to 22 to 23 V, and the melting rate increases to 2.0 to 3.0 kg / min. The third stage: duration: 8 to 10 minutes, the current increases to 10 to 12 kA, the voltage range is 22 to 23 V, and the melting rate increases to 5.0 to 6.0 kg / min. The fourth stage: duration: 10 to 15 minutes, the current remains constant within the range of 10 to 12 kA, the voltage remains constant within the range of 22 to 23 V, the melting rate range is 6.0 to 8.0 kg / min, and the highest point melting rate is at least twice that of the stable melting stage. The fifth stage: duration: 4 to 6 minutes, the current is reduced to 8 to 8.5 kA, the voltage range is 22 to 23 V, and the melting rate range is 4.0 to 5.0 kg / min. Stage 6: Duration: 15-20 minutes, current range 6-8kA, voltage range 20-21V, melting rate range 3.0-3.9kg / min.

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