Large ingot type electroslag remelting electrode structure and electroslag ingot remelting method

Abstract

The invention discloses a large ingot type electroslag remelting electrode structure and an electroslag ingot remelting method in the technical field of smelting technologies. The large ingot type electroslag remelting electrode structure comprises an electrode bar, and the electrode bar is arranged in a gradually shrinking mode from the top end to the bottom end; the electroslag ingot remelting method comprises the following steps that S1, an electrode is prepared, specifically, an electrode bar is machined into a gradually-shrunk shape in a machining mode; s2, a remelting stage, specifically, the prepared electrode bar is installed on an electroslag remelting furnace, an arcing stage is set, and voltage and current are preset; after the steady state stage, the melting speed is controlled to be gradually reduced to a first preset value; s3, in the feeding stage, the diameter shrinkage part of the top of the electrode bar is gradually molten to enter a slag bath, and a heating area of a molten bath gradually moves to the center; s4, a detection stage; and when the electroslag remelting process enters a feeding stage, a heating source of the molten pool gradually gets close to the center, so that the molten pool becomes smaller and shrinks to the center in the feeding process, the depth of a shrinkage cavity is effectively reduced, and the quality of a large ingot type electroslag remelting product is improved.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a large ingot-type electroslag remelting electrode structure and an electroslag ingot remelting method. Background Technology

[0002] In the electroslag remelting process of large ingots, the depth of shrinkage cavities is one of the key factors affecting product quality. The presence of shrinkage cavities leads to defects inside the ingot, reducing the density and mechanical properties of the material. Traditional electroslag remelting electrodes maintain a constant diameter throughout the remelting process. When the electroslag remelting process enters the feeding stage, because the electrode diameter remains unchanged, the current distribution is relatively stable, making it difficult for the heat source of the molten pool to effectively move towards the center. This prevents the molten pool from shrinking and contracting to the center in the ideal way during the feeding stage, resulting in a large shrinkage cavity depth, which seriously affects the quality and yield of large ingot products.

[0003] Therefore, developing an electroslag remelting electrode design method that can effectively control the location of the heat source in the molten pool and reduce the depth of the shrinkage cavity is of great practical significance. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is: how to improve the problem of large shrinkage depth in the electroslag remelting process of large ingots.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A large ingot-type electroslag remelting electrode structure is characterized by comprising an electrode rod, wherein the electrode rod is tapered from the bottom to the top.

[0007] Furthermore, the electrode rod comprises a cylindrical section and a tapered section connected sequentially from the bottom to the top, and the outer diameter of the joint between the cylindrical section and the tapered section is the same.

[0008] Furthermore, the outer diameter of the aforementioned tapering segment gradually changes linearly from the largest end to the smallest end.

[0009] Furthermore, the length of the tapered section is 500mm, and the outer diameters of the two ends of the tapered section are 860mm and 150mm, respectively.

[0010] A method for electroslag ingot remelting, characterized in that it employs a large ingot-type electroslag remelting electrode structure as described in any one of claims 1-4, and includes the following steps:

[0011] S1: Electrode preparation. The electrode rod is machined into a tapered shape. After machining, the machining marks and surface oxide layer on the outer wall of the electrode rod are removed.

[0012] S2: In the remelting stage, the prepared electrode rods are installed on the electroslag remelting furnace, using... The slag system has a slag volume of 400 kg. The arc-starting phase is set with preset voltage and current; after the steady-state phase, the melting rate is gradually reduced to the first preset value.

[0013] S3: During the feeding stage, the melting rate decreases from the first preset value to 0 kg / min, and the diameter shrinkage part of the top of the electrode rod gradually melts and enters the slag pool. The heating area of ​​the molten pool gradually moves towards the center.

[0014] S4: During the inspection stage, the obtained steel ingot is dissected to measure the depth of shrinkage cavity.

[0015] Furthermore, in step S1, the specific electrode rod processing process is as follows: Select a suitable mold steel material as the electrode rod base material, process it into a cylindrical electrode rod with a main body diameter of 860mm, and start from 500mm from the top of the electrode rod, use mechanical processing or design an ingot mold for die casting electrode rod to gradually shrink the diameter of the electrode rod by 150mm in a linear gradient manner; after processing, grind the surface of the electrode rod to remove processing marks and surface oxide layer.

[0016] Furthermore, in step S2, The minimum requirement for a mid-range configuration in a low-end system is 70%. and 30% .

[0017] Furthermore, in step S2, after the steady-state stage, the melting rate is controlled to decrease from 15 kg / min to a first preset value, which is 11 kg / min.

[0018] Furthermore, in step S2, the arc initiation stage is set to 120 minutes, the voltage is set to 50V, and the current is set to increase from 0kA to 30kA.

[0019] Furthermore, step S4 also includes performing a V-notch impact test on the steel ingot.

[0020] The beneficial effects of this invention are:

[0021] By designing the electrode structure in a tapered manner, the current in the electrode rod can gradually move closer to the center of the molten pool when the electroslag remelting process enters the feeding stage. This causes the heat source of the molten pool to gradually move closer to the center as well, so that the molten pool becomes smaller and shrinks to the center during the feeding process, effectively reducing the depth of the shrinkage cavity and improving the quality of large ingot electroslag remelted products. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the normal smelting stage of the present invention;

[0023] Figure 2 This is a schematic diagram of the feeding stage of the present invention;

[0024] The diagram is marked as follows: 1 - cylindrical segment, 2 - tapering segment. Detailed Implementation

[0025] The invention will be further described below with reference to the accompanying drawings.

[0026] like Figure 1 , Figure 2 As shown in the embodiment of this application, a large ingot-type electroslag remelting electrode structure is proposed, including an electrode rod, which is tapered from bottom to top. That is, the main body of the electrode rod is cylindrical, and its diameter gradually decreases from the direction upwards. The working principle is as follows: when the electroslag remelting process enters the feeding stage, as the diameter of the uppermost part of the electrode rod gradually decreases, the electrode rod continues to melt as the feeding stage continues. The diameter-shrinking part gradually moves downwards, causing the current in the entire electrode rod to gradually approach the center of the molten pool. Current is the source of Joule heating. During the electroslag remelting process, as the current approaches the center of the molten pool, the heat source in the molten pool also gradually approaches the center. This causes the temperature in the central region of the molten pool to rise relatively, while the temperature in the edge region decreases relatively. This promotes the molten pool to gradually shrink and contract to the center during the feeding process, thereby effectively reducing the depth of the shrinkage cavity.

[0027] The aforementioned electrode rod comprises a cylindrical section and a tapered section connected sequentially from bottom to top, with the outer diameter of the junction of the cylindrical and tapered sections being the same. That is, starting from the pre-set cylindrical section, the diameter of the electrode rod gradually shrinks, similar to a typical electroslag process during the normal smelting stage. However, upon entering the feeding stage, as the electrode diameter shrinks, the molten droplets of the electroslag move towards the center of the slag pool. Simultaneously, due to the reduced melting rate during the feeding stage, the molten pool gradually shrinks to the center of the electroslag ingot. This effectively reduces the size of the molten pool, thereby minimizing the shrinkage cavity in the electroslag ingot.

[0028] The diameter of the tapered section gradually decreases, reaching a value of d at the very end. If the diameter of the cylindrical section is D and its length is L, the diameter of the tapered section gradually decreases from D to d in a certain gradual manner. This gradual decrease can be linear, where the reduction in diameter per unit length remains constant along the electrode rod axis; or it can be nonlinear, such as optimizing the rate of diameter reduction based on current density and temperature field change models during electroslag remelting to achieve more precise control of current and heat source. The value of d is determined to ensure that the electrode can be stably welded onto the dummy electrode. L and d can be adjusted based on the actual diameter D of the cylindrical section and the current-voltage process curve of the electroslag ingot.

[0029] In this embodiment, the length of the tapered section is 500mm, and the outer diameters of the two ends of the tapered section are 860mm and 150mm, respectively, to ensure the best shrinkage compensation effect.

[0030] This embodiment also proposes a method for remelting electroslag ingots, including the following steps:

[0031] S1: Electrode preparation. The electrode rod is machined into a tapered shape. After machining, the machining marks and surface oxide layer on the outer wall of the electrode rod are removed. A suitable mold steel material is selected as the base material for the electrode rod, and it is machined into a cylindrical electrode rod with a main diameter of 860mm. Starting 500mm from the top of the electrode rod, the diameter of the electrode rod is gradually reduced by 150mm in a linear gradient, either by machining or by designing an ingot mold for die casting, from 860mm to 150mm. After machining, the surface of the electrode rod is polished to remove machining marks and surface oxide layer, ensuring a smooth surface to guarantee uniform current conduction during electroslag remelting.

[0032] S2: In the remelting stage, the prepared electrode rods are installed on the electroslag remelting furnace, using... The slag system has a slag volume of 400 kg. The arc-starting phase is set with preset voltage and current; after the steady-state phase, the melting rate is gradually reduced to the first preset value.

[0033] S3: During the feeding stage, the melting rate decreases from the first preset value to 0 kg / min. The diameter shrinkage portion at the top of the electrode rod gradually melts and enters the slag pool, and the heating area of ​​the molten pool gradually moves towards the center. The prepared electrode rod is then installed on the electroslag remelting furnace, using a 70%... - 30% The slag system consisted of 400 kg of slag. The arc initiation phase was set to 120 min, with a voltage of 50 V and a current increasing from 0 kA to 30 kA. During the steady-state phase, melting rate control was employed, decreasing from an initial 15 kg / min to 11 kg / min. Upon entering the feeding phase, the melting rate decreased from 11 kg / min to 0 kg / min. During the normal remelting phase, the electrode rod melted at a conventional rate, supplying molten metal to the molten pool. When the electroslag remelting process entered the feeding phase, it was observed that as the diameter of the electrode rod's top portion gradually melted and entered the slag pool, the heating area of ​​the molten pool gradually moved towards the center. Real-time monitoring of the molten pool surface temperature using an infrared thermometer revealed that the temperature at the center of the molten pool gradually increased, while the temperature at the edges relatively decreased.

[0034] S4: During the inspection phase, the obtained steel ingot is dissected to measure the shrinkage cavity depth. After remelting, the dissection and analysis of the resulting mold steel ingot revealed that the shrinkage cavity depth was significantly reduced compared to when using traditional constant-diameter electrode rods, decreasing from approximately 140mm to about 40mm. A V-notch impact test was performed on the steel ingot, yielding a result of 20J. Compared to steel ingots produced using traditional processes, the mechanical properties are significantly improved, and the product quality meets the requirements for high-end mold steel.

[0035] In summary, this invention proposes a large-ingot electroslag remelting electrode structure and an electroslag ingot remelting method. Through the electrode design method of this invention, ideal shrinkage of the molten pool can be achieved during the feeding stage, significantly reducing the shrinkage cavity depth. Actual testing shows that, under the same electroslag remelting process conditions, using the electrode designed in this invention reduces the shrinkage cavity depth of large-ingot products by 30%-50% compared to traditional electrode designs, greatly improving the internal quality and density of the product. The reduction in shrinkage cavity depth means a reduction in internal defects, resulting in a significant improvement in the mechanical properties of large-ingot electroslag remelted products. For example, when electroslag remelting a large mold steel ingot, using the electrode design of this invention increases the first-pass yield of impact energy by 15%-20%. Simultaneously, due to the reduction in internal defects, the yield rate is also improved by 10%-15%, reducing production costs and improving the economic benefits for enterprises.

Claims

1. A large ingot-type electroslag remelting electrode structure, characterized in that: It includes an electrode rod, which is tapered from the bottom to the top.

2. The large ingot-type electroslag remelting electrode structure according to claim 1, characterized in that: The electrode rod comprises a cylindrical section and a tapered section connected in sequence from the bottom to the top, and the outer diameter of the joint between the cylindrical section and the tapered section is the same.

3. The large ingot-type electroslag remelting electrode structure according to claim 2, characterized in that: The outer diameter of the tapering section changes linearly from the largest end to the smallest end.

4. The large ingot-type electroslag remelting electrode structure according to claim 3, characterized in that: The tapered section is 500mm long, and the outer diameters of its two ends are 860mm and 150mm, respectively.

5. A method for remelting electroslag ingots, characterized in that, The large ingot-type electroslag remelting electrode structure as described in any one of claims 1-3 includes the following steps: S1: Electrode preparation. The electrode rod is machined into a tapered shape. After machining, the machining marks and surface oxide layer on the outer wall of the electrode rod are removed. S2: In the remelting stage, the prepared electrode rods are installed on the electroslag remelting furnace, using... Scumbag system; Set the arc initiation stage, preset the voltage and current; after the steady state stage, control the melting rate to gradually decrease to the first preset value; S3: During the feeding stage, the melting rate decreases from the first preset value to 0 kg / min, and the diameter shrinkage part of the top of the electrode rod gradually melts and enters the slag pool. The heating area of ​​the molten pool gradually moves towards the center. S4: During the inspection stage, the obtained steel ingot is dissected to measure the depth of shrinkage cavity.

6. The electroslag ingot remelting method according to claim 5, characterized in that, In step S1, the specific electrode rod processing process is as follows: Select a suitable mold steel material as the base material for the electrode rod, process it into a cylindrical electrode rod with a main body diameter of 860mm, and start from 500mm below the top of the electrode rod, use mechanical processing or design an ingot mold for die casting to gradually reduce the diameter of the electrode rod by 150mm in a linear gradient manner; after processing, grind the surface of the electrode rod to remove processing marks and surface oxide layer.

7. The electroslag ingot remelting method according to claim 5, characterized in that, In step S2, The specific proportion in the slag mixture is: 70% and 30% .

8. The electroslag ingot remelting method according to claim 5, characterized in that, In step S2, after the steady-state stage, the melting rate is controlled to decrease from 15 kg / min to a first preset value, which is 11 kg / min.

9. The electroslag ingot remelting method according to claim 5, characterized in that, In step S2, the arc initiation stage is set to 120 minutes, the voltage is set to 50V, and the current is set to increase from 0kA to 30kA.

10. The electroslag ingot remelting method according to claim 5, characterized in that, Step S4 also includes performing a V-notch impact test on the steel ingot.

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