Electrode assembly for vacuum arc remelting and vacuum arc remelting method

Abstract

An electrode assembly for vacuum arc remelting, comprising a primary electrode (1) and a dummy electrode (2). The primary electrode (1) is a vacuum arc remelting electrode; one end of the primary electrode (1) is provided with a shrinkage cavity (3); the dummy electrode (2) is connected to the end of the primary electrode (1) with the shrinkage cavity (3) by means of soldering; an insulating material (4) is provided between the dummy electrode (2) and the primary electrode (1) with the shrinkage cavity (3); and the insulating material (4) covers the shrinkage cavity (3) of the primary electrode (1). By using the electrode assembly, the production cost of vacuum arc remelting ingots can be reduced, and a good inclusion level can be obtained.

Description

Electrode assembly for vacuum consumable remelting and vacuum consumable remelting method

[0001] This disclosure claims priority to a Chinese patent application filed with the Patent Office of China on July 21, 2023, with application number 202310901379.2 and invention name “Electrode assembly for vacuum consumable remelting and vacuum consumable remelting method”, the entire contents of which are incorporated by reference into this disclosure. Technical Field

[0002] The present invention relates to the technical field of alloy smelting, and in particular to an electrode assembly for vacuum consumable remelting and a vacuum consumable remelting method using the electrode assembly. Background Art

[0003] Vacuum Arc Remelting (VAR) involves the continuous remelting of consumable electrodes using an electric arc under vacuum conditions. Direct current is applied to generate an arc between the electrode and the base plate of a copper mold contained within a water jacket. The intense heat generated by the arc dissipates at the electrode tip, gradually forming a new ingot within the water-cooled mold. High vacuum is typically maintained throughout the remelting process. Under this intense water-cooling condition, the molten steel solidifies and crystallizes, resulting in a uniform, shrinkage-free, and dense ingot.

[0004] First, an arc is ignited between the lower end of the consumable electrode and the mold, forming an arc plasma zone between the lower end of the consumable electrode and the molten pool. This extremely high temperature causes the end of the consumable electrode to melt first. As non-metallic inclusions in the consumable electrode, such as oxides and nitrides, dissociate or are reduced by carbon under vacuum and high temperature conditions, further purification is achieved. Because the vacuum consumable arc furnace process removes gases and non-metallic inclusions, as well as certain low-melting-point harmful impurities, it significantly improves cold and hot working properties, plasticity, mechanical properties, and physical properties. In particular, the difference in longitudinal and transverse properties is reduced, which is crucial for ensuring the stability, consistency, and reliability of material properties.

[0005] Inclusions are inevitably generated during the remelting process. Some of these inclusions are removed by flotation during the remelting process, while the rest are broken up and evenly distributed across the cross-section of the solidified ingot.

[0006] In the production of primary electrodes for vacuum consumable remelting, the formation of electrode shrinkage cavities is unavoidable. In the area where the shrinkage cavities exist, the metal material is not dense and is mixed with a large number of inclusions. Without installing an insulating riser, the length of the shrinkage cavity area of ​​the cast electrode is usually 2-3 times the electrode diameter. When using electrodes with deeper shrinkage cavities for consumable remelting, if the shrinkage cavities melt downward during the remelting arc starting period, the removal rate of the primary electrode will be reduced, reducing production costs. However, the riser inclusions will be introduced into the remelting pool at an early stage, which is not conducive to the inclusion control of the remelting ingot. If the electrode shrinkage cavities are not removed and are arranged upward for consumable remelting, the arc will climb up the shrinkage cavities during the remelting feeding stage and melt the false electrode, causing the false electrode components to contaminate the remelting ingot.

[0007] Therefore, there is an urgent need for a method for reducing inclusions in vacuum consumable remelting ingots, so as to reduce the inclusions in the remelted ingots obtained by the vacuum consumable remelting smelting method and obtain high-quality alloys.

[0008] Summary of the Invention

[0009] In view of this, the present invention provides an electrode assembly for vacuum consumable remelting and a vacuum consumable remelting method using the electrode assembly, the main purpose of which is to improve the inclusion level of vacuum consumable remelting ingots at a lower cost and obtain high-quality alloys.

[0010] To achieve the above objectives, the present invention mainly provides the following technical solutions:

[0011] An embodiment of the present invention provides an electrode assembly for vacuum consumable remelting, wherein the electrode assembly includes a primary electrode and a dummy electrode, wherein the primary electrode is a consumable remelting electrode; one end of the primary electrode has a shrinkage hole, the dummy electrode is welded to the end of the primary electrode with the shrinkage hole, and an insulating material is arranged between the dummy electrode and the primary electrode with the shrinkage hole, and the insulating material covers the shrinkage hole of the primary electrode.

[0012] In some embodiments, the insulating material is mounted on a central portion of a transverse end surface of a dummy electrode for welding to the primary electrode with the shrinkage cavity.

[0013] In some embodiments, a groove is provided at the end of the dummy electrode facing the shrinkage hole of the primary electrode, and the insulating material is provided in the groove.

[0014] In some embodiments, the primary electrode used for remelting is not provided with a heat-insulating riser during the casting process, and shrinkage cavities are not removed during the remelting electrode preparation process.

[0015] In some embodiments, the insulating material is a high-temperature resistant insulating material.

[0016] In some embodiments, the high temperature resistant insulation material is made of asbestos fiber cement board or clay brick.

[0017] Another embodiment of the present invention provides a vacuum consumable remelting method using the aforementioned vacuum consumable remelting electrode assembly. During the vacuum consumable remelting process, the aforementioned electrode assembly is used. During the vacuum consumable remelting operation, the shrinkage cavity of the primary electrode points upward, meaning that the shrinkage cavity portion of the primary electrode melts at the end of the remelting process. Insulating material disposed between the dummy electrode and the primary electrode with the shrinkage cavity prevents the arc from climbing up the shrinkage cavity and melting the dummy electrode during the shrinkage feeding process, thereby reducing inclusions in the vacuum consumable remelting ingot.

[0018] In some embodiments, during the feeding phase, the smelting current is reduced from the current in the previous steady state phase to 1 / 8-1 / 4 of the original value within 0-2 minutes.

[0019] In some embodiments, the smelting current is reduced from the pre-steady-state current to 1 / 8-1 / 4 of the original value within 0-2 minutes, and is maintained at an actual melting rate of 0-0.3 kg / min for 20-70 minutes.

[0020] In some embodiments, the electrode position is locked while the smelting current decreases from the previous steady-state current to 1 / 8-1 / 4 of the original value within 0-2 minutes, and is maintained at an actual melting rate of 0-0.3 kg / min for 20-70 minutes; preferably, the electrode position is locked manually.

[0021] Compared with the prior art, the vacuum consumable remelting electrode assembly and the vacuum consumable remelting method using the electrode assembly of the present invention have at least the following beneficial effects:

[0022] (1) An electrode assembly for vacuum consumable remelting having a specific structure is provided: during the vacuum consumable remelting process, a primary electrode with a shrinkage hole at one end is used; during the vacuum consumable remelting operation, the shrinkage hole of the primary electrode points upward, that is, the shrinkage hole portion of the primary electrode melts at the end of the remelting; a dummy electrode is welded to the primary electrode with the shrinkage hole, and an insulating material is provided between the dummy electrode and the electrode with the shrinkage hole to prevent the arc from climbing up the shrinkage hole during the feeding period and melting the dummy electrode, thereby causing contamination of the remelting ingot composition;

[0023] (2) The primary electrode used for remelting is not provided with a heat-insulating riser during the casting process, and shrinkage cavities are not removed during the remelting electrode preparation process, thereby improving the metal yield and reducing production costs;

[0024] (3) Furthermore, an insulating material is assembled on the central portion of the transverse end face of the dummy electrode for welding to the primary electrode with the shrinkage cavity; preferably, the insulating material is a high-temperature resistant insulating material; further preferably, the high-temperature resistant insulating material is made of asbestos fiber cement board or clay brick; more preferably, the diameter of the insulating material is 10 mm larger than the diameter of the shrinkage cavity; by such an arrangement, it is possible to better avoid the arc climbing up the shrinkage cavity during the feeding period to melt the dummy electrode, thereby causing contamination of the remelted ingot components;

[0025] (4) Preferably, when entering the shrinkage feeding stage, the smelting current is reduced from the current in the previous steady state period to 1 / 8-1 / 4 of the original value within 0-2 minutes; preferably, the current is maintained at the actual melting rate of 0-0.3 kg / min for 20-70 minutes; more preferably, the smelting current is reduced from the current in the previous steady state period to 1 / 8-1 / 4 of the original value within 0-2 minutes, and the electrode position is locked (manual locking is optional), and the current is maintained at the actual melting rate of 0-0.3 kg / min for 20-70 minutes. In this way, on the one hand, electrodes with shrinkage cavities are used to improve the metal recovery rate, and on the other hand, short circuit accidents are avoided and inclusions are prevented from being trapped, which has a good promoting significance for the improvement of low-cost and high-quality vacuum consumable remelting process.

[0026] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG1 is a schematic diagram of an electrode of the present invention;

[0028] FIG2 is an example of a conventional feeding process curve and a feeding process curve of the present invention; FIG2(a) is an example of a conventional feeding process curve, in which, during the steady-state smelting stage, the current is adjusted to about 5000A by an automatic program; when entering the feeding period, the smelting current must be reduced to 2000A in 45 minutes and maintained at 2000A for 50 minutes; FIG2(b) is an example of a feeding process curve of the present invention, in which, during the steady-state smelting stage, the current is adjusted to about 5000A by an automatic program; when entering the feeding period, the smelting current must be reduced to 900A in 2 minutes and maintained at 900A for 70 minutes;

[0029] FIG3 shows the inclusions of 316 stainless steel after forging in vacuum consumable remelting according to Example 1 of the present invention; FIG3 (a) shows the inclusions at the head of the alloy prepared in Example 1; FIG3 (b) shows the inclusions at the middle of the alloy prepared in Example 1; and FIG3 (c) shows the inclusions at the tail of the alloy prepared in Example 1;

[0030] FIG4 shows the inclusions of the vacuum consumable remelting 316 stainless steel after forging in Example 2 of the present invention; FIG4 (a) shows the inclusions at the head of the alloy prepared in Example 2; FIG4 (b) shows the inclusions in the middle of the alloy prepared in Example 2; and FIG4 (c) shows the inclusions at the tail of the alloy prepared in Example 2;

[0031] FIG5 shows the inclusions of the vacuum consumable remelting 316 stainless steel after forging in Example 3 of the present invention; FIG5 (a) shows the inclusions at the head of the alloy prepared in Example 3; FIG5 (b) shows the inclusions in the middle of the alloy prepared in Example 3; and FIG5 (c) shows the inclusions at the tail of the alloy prepared in Example 3;

[0032] FIG6 shows the inclusions of the vacuum consumable remelting 316 stainless steel after forging in Comparative Example 1 of the present invention; FIG6 (a) shows the inclusions at the head of the alloy prepared in Comparative Example 1; FIG6 (b) shows the inclusions in the middle of the alloy prepared in Comparative Example 1; and FIG6 (c) shows the inclusions at the tail of the alloy prepared in Comparative Example 1;

[0033] Figure 7 shows the inclusion situation of the vacuum consumable remelting 316 stainless steel after forging in Comparative Example 2; wherein, Figure 7 (a) shows the inclusion situation of the head of the alloy prepared in Comparative Example 2, with Dfine=1.5; Figure 7 (b) shows the inclusion situation of the middle of the alloy prepared in Comparative Example 2, with Dfine=1.5; Figure 7 (c) shows the inclusion situation of the tail of the alloy prepared in Comparative Example 2, with Dfine=1.5; Figure 7 (d) shows the inclusion situation of the middle of the alloy prepared in Comparative Example 2, with Dcoarse=0.5; Figure 7 (e) shows the inclusion situation of the tail of the alloy prepared in Comparative Example 2, with Dcoarse=0.5.

[0034] The reference numerals indicate: 1. primary consumable electrode; 2. dummy electrode; 3. electrode shrinkage hole; 4. insulating material. DETAILED DESCRIPTION

[0035] To further illustrate the technical means and effects employed by the present invention to achieve its intended objectives, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention is provided in conjunction with the accompanying drawings and preferred embodiments. In the following description, different references to "one embodiment" or "embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0036] Primary electrodes used for remelting are slender rods with a height-to-diameter ratio greater than 3, making them extremely difficult to feed for shrinkage during the casting process. Unless an extremely large insulating riser, roughly the same size as the rod, is installed, it's impossible to produce compact, thin rod-shaped electrodes. To maximize the casting quality of the primary electrode, a fiber-cotton insulating riser with a height of 1.0-1.5 times the electrode diameter is typically installed during electrode casting. While electrodes cast using this method can produce an electrode end face with shallow shrinkage cavities after the riser is removed, it doesn't completely resolve the problem of residual shrinkage cavities (especially secondary shrinkage cavities). Furthermore, the assembled insulating riser requires very high-quality refractory fibers to achieve optimal insulation, inevitably increasing electrode production costs. Furthermore, the feed riser still contains a large amount of metal material, which reduces metal yield after removal, significantly increasing production costs. In summary, in order to improve the metal yield and reduce production costs, the present invention does not use a heat-insulating riser in electrode casting, so one end of the electrode has a shrinkage cavity, and the shrinkage cavity is not removed when the electrode is used for remelting, thereby avoiding waste of metal material and greatly reducing production costs.

[0037] An embodiment of the present invention provides an electrode assembly for vacuum consumable remelting, wherein the electrode assembly includes a primary electrode and a dummy electrode. The primary electrode is a consumable remelting electrode. One end of the primary electrode has a shrinkage cavity. The dummy electrode is welded to the end of the primary electrode with the shrinkage cavity, and an insulating material is provided between the dummy electrode and the primary electrode with the shrinkage cavity, and the insulating material covers the shrinkage cavity of the primary electrode. During the vacuum consumable furnace loading operation, the shrinkage cavity of the primary electrode points upward, and the electrode tip with the deeper shrinkage cavity is melted at the end of the consumable remelting. The dummy electrode is welded to the primary electrode with the shrinkage cavity, and an insulating material is provided between the dummy electrode and the primary electrode with the shrinkage cavity to prevent the arc from climbing up the shrinkage cavity and melting the dummy electrode during the shrinkage feeding period, thereby contaminating the components of the remelted ingot. Specifically, as shown in FIG1 , the dummy electrode 2 is welded to the primary consumable electrode 1, and the insulating material 4 covers the shrinkage cavity 3 of the primary consumable electrode 1.

[0038] In the specialty metallurgy industry, attempts have been made to reduce production costs by using primary electrodes without insulated risers and without excising shrinkage cavities for vacuum consumable remelting. However, these electrodes are invariably used with the shrinkage end of the primary electrode pointing downward, meaning that the portion of the electrode with the shrinkage cavities is used for arc starting during the consumable remelting process. While this process reduces the amount of cutting required in the shrinkage cavities, thus lowering production costs, this reduction comes at the expense of product quality (especially purity). First, the melting conditions during the arc starting phase of the consumable remelting process are extremely unstable, with intermittent current flow. The irregular shape of the shrinkage cavities in the electrode further complicates the control of stable melting. Instability in current and voltage control during the arc starting phase further degrades the stability of the subsequent steady-state melting phase, highly likely resulting in unsatisfactory melting throughout the entire consumable ingot melting process. Because the entire remelting process occurs under unstable conditions, the optimal conditions required for inclusion removal cannot be guaranteed, ultimately reducing the purity of the consumable remelted ingot. In addition, affected by the floating effect of inclusions, the inclusion level in the shrinkage area of ​​the primary electrode is higher than that in the middle and the other end of the electrode. Using this shrinkage area for arc melting will introduce a large number of inclusions into the alloy pool in the early stage of remelting. A large number of inclusions accompanied by an unstable melting state will introduce additional inclusions into the middle area of ​​the consumable ingot, which should be relatively pure. This shows that the use of electrodes with shrinkage holes for arc melting will worsen the quality of the consumable remelted ingot in terms of remelting stability and the amount of inclusions brought in. In order to circumvent the above-mentioned shortcomings, the present invention innovatively points the shrinkage end of the primary electrode upward during the vacuum consumable furnace loading operation, which not only saves metal raw materials and reduces production costs, but also avoids the shortcomings of arc starting in the shrinkage area, improves the stability of consumable remelting, and reduces the contamination of the metal in the intermediate steady-state area by additional inclusions.

[0039] Preferably, the insulating material is mounted on the center portion of the transverse end surface of the dummy electrode for welding to the electrode with the shrinkage hole. The diameter of the transverse end surface of the dummy electrode can be greater than, equal to, or smaller than the diameter of the end surface of the primary electrode with the shrinkage hole, as long as the dummy electrode can be welded to the primary electrode.

[0040] Preferably, the primary electrode used for remelting is not provided with a heat-insulating riser during the casting process, and shrinkage cavities are not removed during the remelting electrode preparation process.

[0041] In some embodiments, as shown in FIG1 , a groove is provided at the end of the dummy electrode facing the shrinkage hole of the primary electrode, and an insulating material is provided in the groove.

[0042] Preferably, the diameter of the insulating material is 10 mm larger than the diameter of the shrinkage cavity.

[0043] Furthermore, the insulating material is a high-temperature resistant insulating material with an operating temperature of 1200-1400° C.; preferably, the high-temperature resistant insulating material is made of asbestos fiber cement board or clay brick.

[0044] Asbestos fiber cement board is made of asbestos, glass fiber, clay and other materials according to a scientific formula. It has strong resistance to tension and pressure and can withstand temperatures of around 1400°C. Clay bricks use clay (including shale, coal gangue and other powders) as the main raw material. They are made through clay processing, molding, drying and roasting, and can withstand high temperatures.

[0045] Using electrode tips with shrinkage cavities for feeding consumable remelting has a natural disadvantage: near the end of feeding, the arc can creep up the shrinkage cavities and melt the exposed dummy electrode end face. In consumable remelting, dummy electrodes are typically made of carbon steel, which is both inexpensive and has low resistance, making it well-suited for use in a vacuum consumable environment. Since the carbon steel of the dummy electrode is unlikely to have the same composition as the remelted primary electrode, melting the dummy electrode and flowing into the underlying molten metal pool can contaminate the alloy composition, rendering the ingot scrapped. To prevent dummy electrode melting, two approaches are generally adopted: stopping smelting when a significant amount of primary electrode remains, or welding a dense transition metal section with the same composition as the primary electrode between the dummy electrode and the primary electrode. Both of these solutions have drawbacks: First, discontinuing the melting of excess metal reduces metal yield, hindering cost control; second, the added transition metal section increases welding difficulty, hindering the production of well-smoothed electrode components. Furthermore, requiring a specific transition metal section for each alloy grade increases production and operating costs. In order to avoid the above shortcomings, the present invention innovatively arranges insulating material between the welding dummy electrode and the electrode with shrinkage cavity to prevent the arc from climbing up along the shrinkage cavity to melt the dummy electrode during the shrinkage feeding period, thereby preventing the remelting ingot from being contaminated by the components; preferably, an insulating material is assembled at the center part of the transverse end face of the dummy electrode, as shown in FIG1 , and the insulating material is preferably a high-temperature insulating material, and a high-temperature resistant insulating material made of asbestos fiber cement board or clay brick can be selected. Further preferably, the diameter of the high-temperature resistant insulating material is 10 mm larger than the diameter of the shrinkage cavity, which effectively avoids the problem of the arc climbing up along the shrinkage cavity to melt the dummy electrode during the shrinkage feeding period, thereby realizing the use of the electrode with shrinkage cavity to reduce smelting costs without increasing product quality risks.

[0046] Preferably, after entering the remelting and feeding period, the smelting current is reduced from the previous steady-state current to 1 / 8-1 / 4 of its original value within 0-2 minutes; preferably, this is maintained for 20-70 minutes at an actual melting rate of 0-0.3 kg / min. More preferably, the smelting current is reduced from the previous steady-state current to 1 / 8-1 / 4 of its original value within 0-2 minutes, while the electrode position is locked, and this is maintained for 20-70 minutes at an actual melting rate of 0-0.3 kg / min. Locking the electrode position can be performed manually.

[0047] In conventional vacuum consumable operation, after the smelting enters the shrinkage feeding stage, the smelting current will gradually decrease to about 1 / 2-1 / 3 of the original steady-state smelting current at a relatively slow rate, and the decline usually lasts for more than 30 minutes, as shown in Figure 2(a). However, this type of operation is not suitable for application in the shrinkage feeding of electrodes with shrinkage cavities used in the present invention. Since the melting rate is affected by the smelting current, the actual melting rate also decreases at an extremely fast response speed when the smelting current decreases. Under actual working conditions, although the actual melting rate responds very quickly, the melting rate monitored by the weighing system of the consumable remelting furnace lags behind the actual melting rate by 10-20 minutes due to the limitations of equipment conditions (for example, the actual melting rate has begun to decline, but the melting rate displayed by the equipment needs to show a decline after 20 minutes). Under the condition that the actual melting rate has already dropped a lot and the corresponding melted electrode length has also decreased rapidly, the execution of the electrode movement speed by the smelting equipment is calculated based on the delayed measured melting rate. This results in the electrodes moving at a speed faster than the actual melting rate, which in turn reduces or even completely eliminates the arc spacing during melting. The loss of this arc spacing signals a short circuit. When a short circuit occurs, the smelting power drops to zero, the melt pool temperature also drops, and the process of inclusion removal is interrupted. In severe cases, this can lead to the entrapment of a large number of inclusions in the melt pool. Because the present invention utilizes a consumable remelting feeding electrode end with a shrinkage cavity, which contains a large number of inclusions, it is particularly disadvantageous in addressing the loss of arc spacing, power, and inclusion removal caused by the slow decline in melting rate during the feeding period. This can lead to even more inclusions being entrapped at the riser of the remelting ingot. Furthermore, the irregular shape and size of the shrinkage cavity remaining in the electrode makes it more difficult for the equipment operating program to accurately calculate the actual melted electrode length during the feeding phase. This makes it more likely that the smelting process will be interrupted by a short circuit and the entrapment of a large number of inclusions due to improper electrode lowering.

[0048] To circumvent the above shortcomings, the innovative process of the present invention is that: during the feeding phase, the smelting current is reduced from the pre-steady-state current to 1 / 8-1 / 4 of its original value within 0-2 minutes, so that the primary electrode essentially stops melting. Preferably, this is maintained for 20-70 minutes at an actual melting rate of 0-0.3 kg / min. More preferably, the smelting current is reduced from the pre-steady-state current to 1 / 8-1 / 4 of its original value within 0-2 minutes while the electrode position is locked (for equipment that can only manually control the electrode, manual locking can be selected) and maintained at an actual melting rate of 0-0.3 kg / min for 20-70 minutes, as shown in Figure 2(b). It is also possible to rapidly reduce the smelting current only during the feeding phase without locking the electrode, but instead slowly lowering it. If the electrode is not locked but slowly lowered, it is necessary to constantly monitor the electrode position to prevent contact with the remelting ingot and a short circuit. In this case, the distance between the electrode and the remelting ingot can be controlled to avoid the occurrence of short circuits. The innovative feeding process principle shifts from the traditional feeding mechanism, which relies on a combination of reduced heat input and a small amount of added hot metal flow, to one that relies solely on reduced heat input. By rapidly reducing the smelting current to a low level, the primary electrode essentially ceases to melt. A small amount of current still provides a certain amount of heat to the molten pool, preventing it from completely solidifying. Although no hot metal flow enters the molten pool, the solidus line at the bottom of the pool slowly moves upward, gradually reducing the pool volume and ultimately moving the shrinkage cavity to the upper end face of the consumable ingot or eliminating it completely. Since the electrode is essentially no longer melting during this stage, the electrode drive under automatic control could continue to lower the electrode, potentially leading to a short circuit. To mitigate this risk, it is preferable to lock the electrode drive, forcing it to remain in its original position to prevent a short circuit. In summary, the present invention adopts the method of rapidly reducing the current and continuously providing a small amount of energy to the upper part of the molten pool to feed the shrinkage of the consumable remelting ingot. On the one hand, electrodes with shrinkage holes are used to improve the metal yield. On the other hand, short-circuit accidents are avoided and the clamping of inclusions is avoided. It has a good promoting significance for the improvement of low-cost and high-quality vacuum consumable remelting process.

[0049] In the process provided by the present invention, the technical mechanism is as follows:

[0050] (1) Using a vacuum consumable remelting electrode assembly with a specific structure: During the vacuum consumable remelting process, a primary electrode with a shrinkage hole at one end is used; during the vacuum consumable remelting operation, the shrinkage hole of the primary electrode points upward, that is, the shrinkage hole of the primary electrode melts at the end of the remelting; the dummy electrode is welded to the primary electrode with the shrinkage hole, and an insulating material is provided between the dummy electrode and the electrode with the shrinkage hole to prevent the arc from climbing up the shrinkage hole during the feeding period and melting the dummy electrode, resulting in contamination of the remelting ingot composition;

[0051] (2) The primary electrode used for remelting is not provided with a heat-insulating riser during the casting process, and shrinkage cavities are not removed during the remelting electrode preparation process, thereby improving the metal yield and reducing production costs;

[0052] (3) Furthermore, an insulating material is assembled on the central portion of the transverse end face of the dummy electrode for welding to the primary electrode with the shrinkage cavity; preferably, the insulating material is a high-temperature resistant insulating material; further preferably, the high-temperature resistant insulating material is made of asbestos fiber cement board or clay brick; more preferably, the diameter of the insulating material is 10 mm larger than the diameter of the shrinkage cavity; by such an arrangement, it is possible to better avoid the arc climbing up the shrinkage cavity during the feeding period to melt the dummy electrode, thereby causing contamination of the remelted ingot components;

[0053] (4) Preferably, when entering the shrinkage feeding stage, the smelting current is reduced from the current in the previous steady state period to 1 / 8-1 / 4 of the original value within 0-2 minutes; preferably, the current is maintained at the actual melting rate of 0-0.3 kg / min for 20-70 minutes; more preferably, the smelting current is reduced from the current in the previous steady state period to 1 / 8-1 / 4 of the original value within 0-2 minutes, and the electrode position is locked (manual locking is optional), and the current is maintained at the actual melting rate of 0-0.3 kg / min for 20-70 minutes. In this way, on the one hand, electrodes with shrinkage cavities are used to improve the metal recovery rate, and on the other hand, short circuit accidents are avoided and inclusions are prevented from being trapped, which has a good promoting significance for the improvement of low-cost and high-quality vacuum consumable remelting process.

[0054] The present invention is further described below by means of specific embodiments:

[0055] Example 1

[0056] 316 stainless steel is smelted in a 1-ton vacuum consumable remelting furnace. No insulating risers are used during electrode casting, and shrinkage cavities are not removed. The remelting electrode has a diameter of Φ300 mm and weighs 935 kg. The inner diameter of the crystallizer is Φ355 mm. The primary electrode is placed into the furnace with its shrinkage cavity pointing upward. A clay brick is installed at the center of the transverse end face of the dummy electrode welded to the electrode with the shrinkage cavity. The clay brick diameter is 10 mm larger than the shrinkage cavity diameter. After the furnace is closed, the equipment is evacuated. A three-stage vacuum pump is used to reduce the vacuum to 0.13 Pa before arc melting is initiated. After the melt pool stabilizes, the melting current is gradually reduced, and the remelting enters the steady-state remelting phase. The vacuum level during the steady-state melting phase is maintained at 0.35 Pa. An automatic program adjusts the current to approximately 5000 A to maintain a steady-state melting rate of 3.0 kg / min. When the electrode weight remained at 33 kg, feeding was performed. The smelting current was reduced to 900 A within 2 minutes, and the electrode position was manually locked. The actual melting rate was maintained at 0.1 kg / min for 70 minutes. When the electrode weight remained at 25 kg, the power was turned off and the smelting was terminated.

[0057] The remelted consumable ingots were forged to a final size of 90 mm. 10 mm thick sections were cut from the head, tail, and center of the forged bars, with the head defined as 1 meter from the top and the tail defined as 1 meter from the end. Inclusion evaluation samples were taken at the 1 / 2 radius position, and inclusion levels at these three locations were inspected using the GB / T10561 standard. No Class A (sulfide), Class B (alumina), Class C (silicate), or Class DS (single spherical particle) inclusions were found. A small amount of Class D (spherical oxide) inclusions were found, resulting in a rating of 1.0 for the fine system.

[0058] Table 1. Inclusion ratings of vacuum consumable remelted 316 stainless steel after forging

[0059] Example 2

[0060] 316 stainless steel was smelted in a 1-ton vacuum consumable remelting furnace. During the electrode casting process, no insulating risers were used, and shrinkage cavities were not removed. The remelting electrode had a diameter of 300 mm and weighed 967 kg. The mold inner diameter was 355 mm. The primary electrode was placed into the furnace with its shrinkage cavity pointing upward. An asbestos fiber cement board was installed at the center of the transverse end face of the dummy electrode welded to the shrinkage cavity electrode. After the furnace was closed, the equipment was evacuated to a vacuum of 0.15 Pa using a three-stage vacuum pump before arc melting was initiated. After the melt pool stabilized, the melting current was gradually reduced, and the remelting entered the steady-state remelting phase. During this steady-state melting phase, the vacuum was maintained at 0.32 Pa. The current was automatically adjusted to approximately 5000 A to maintain a steady-state melting rate of 3.0 kg / min. When 33 kg of the electrode remained, shrinkage feeding was performed. At this point, the melting current was reduced to 625 A for 1 minute, and the electrode position was manually locked, maintaining the actual melting rate at zero for 20 minutes. When 32 kg of electrode remained, the power was turned off and the smelting was ended.

[0061] Consumable ingots obtained through remelting were forged to a final size of 90 mm. 10 mm thick sections were cut from the head, tail, and center of the forged bar, with the head defined as 1 meter from the top and the tail defined as 1 meter from the end. Inclusion evaluation samples were taken at the 1 / 2 radius position and the inclusion levels at these three locations were inspected using the GB / T10561 standard. No Class A, B, or C inclusions were found, though a small amount of Class D inclusions were detected, resulting in a rating of 1.0 for the fine system.

[0062] Table 2. Inclusion ratings of vacuum consumable remelted 316 stainless steel after forging

[0063] Example 3

[0064] 316 stainless steel is smelted in a 1t vacuum consumable remelting furnace. During the electrode casting process, no insulation riser is used and the shrinkage cavity is not removed. The remelting electrode has a diameter of Φ300mm, a weight of 984kg, and an inner diameter of the crystallizer is Φ355mm. The primary electrode is placed in the furnace with the shrinkage cavity pointing upward, and an asbestos fiber cement board is installed in the center of the horizontal end face of the dummy electrode welded to the electrode with the shrinkage cavity. After the furnace is closed, the equipment is evacuated and the vacuum degree is reduced to 0.14Pa using a three-stage vacuum pump before arc melting is started. After the molten pool is established and stabilized, the melting current is gradually reduced, and the remelting enters the steady-state remelting period. The vacuum degree is maintained at 0.31Pa during the steady-state melting stage. The current is adjusted to around 5000A through an automatic program to maintain a steady-state melting rate of 3.0kg / min. When the electrode weight was 35 kg, feeding was performed. At this time, the smelting current was reduced to 1250 A over 0.5 min, and the electrode position was manually locked. The actual melting rate was maintained at 0.3 kg / min for 30 min. When the electrode weight was 24 kg, the power was turned off and the smelting was terminated.

[0065] Consumable ingots obtained through remelting were forged to a final size of 90 mm. 10 mm thick sections were cut from the head, tail, and center of the forged bar, with the head defined as 1 meter from the top and the tail defined as 1 meter from the end. Inclusion evaluation samples were taken at the 1 / 2 radius position and the inclusion levels at these three locations were inspected using the GB / T10561 standard. No Class A, B, or C inclusions were found, though a small amount of Class D inclusions were detected, resulting in a rating of 1.0 for the fine system.

[0066] Table 3. Inclusion ratings of vacuum consumable remelted 316 stainless steel after forging

[0067] Comparative Example 1

[0068] 316 stainless steel is smelted in a 1t vacuum consumable remelting furnace. Insulated risers are used during the electrode casting process, and shrinkage cavities are removed. The remelting electrode has a diameter of Φ300mm, a weight of 843kg, and an inner diameter of the crystallizer of Φ355mm. After the furnace is closed, the equipment is evacuated, and a three-stage vacuum pump is used to reduce the vacuum to 0.13Pa before arc melting. After the molten pool is established and stabilized, the melting current is gradually reduced, and the remelting enters the steady-state remelting period. The vacuum level during the steady-state melting stage is maintained at 0.30Pa. The current is adjusted to around 5000A through an automatic program to maintain a steady-state melting rate of 3.0kg / min. When the electrode remains at 185kg, shrinkage is supplemented. At this time, the smelting current is reduced to 2000A after 45 minutes. When the electrode remains at 25kg, the power is turned off and the melting ends.

[0069] The consumable ingots obtained by remelting were forged, and the finished product size was Φ90mm. 1m from the top of the rod was the head, 1m from the tail of the rod was the tail, 10mm thick slices were cut from the head, tail and middle position of the forged finished rod, and inclusion evaluation samples were made at the 1 / 2 radius position. The inclusion levels at the three positions were checked using the GB / T10561 standard. No A, B, or C inclusions were found during the inspection, and a small amount of D inclusions were found, with a rating of 1.0 for the fine system. The inclusion levels obtained in this comparative example and the embodiment were the same, but the riser and shrinkage cavity were removed in the comparative example process, which reduced the metal yield and significantly increased the production cost.

[0070] Table 4. Inclusion rating of vacuum consumable remelted 316 stainless steel after forging

[0071] Comparative Example 2

[0072] 316 stainless steel is smelted in a 1t vacuum consumable remelting furnace. During the electrode casting process, no insulating risers are used, and shrinkage cavities are not removed. The remelting electrode has a diameter of Φ300mm, a weight of 969kg, and an inner diameter of the crystallizer of Φ355mm. The primary electrode is placed in the furnace with the shrinkage cavity pointing downward. After the furnace is closed, the equipment is evacuated, and a three-stage vacuum pump is used to reduce the vacuum to 0.14Pa before arc melting is started. After the molten pool is established and stabilized, the melting current is gradually reduced, and the remelting enters the steady-state remelting period. The vacuum degree during the steady-state melting stage is maintained at 0.34Pa. The current is adjusted to around 5000A through an automatic program to maintain a steady-state melting rate of 3.0kg / min. When the electrode remains at 190kg, shrinkage is supplemented. At this time, the smelting current is reduced to 2000A after 45 minutes. When the electrode remains at 30kg, the power is turned off and the melting ends.

[0073] The remelted consumable ingots were forged to a final size of 90 mm. 10 mm thick sections were cut from the head, tail, and middle of the forged bar, with the head defined as 1 meter from the top and the tail defined as 1 meter from the end. Inclusion evaluation samples were prepared at the 1 / 2 radius position and the inclusion levels at these three locations were inspected using the GB / T10561 standard. No Class A, B, or C inclusions were found, but a small amount of Class D inclusions were found. The inclusion levels were rated as 1.5 for fine at the head, 1.5 for fine and 0.5 for coarse at the middle, and 1.5 for fine and 0.5 for coarse at the tail. The inclusion levels obtained in this comparative example were significantly lower than those obtained in the previous examples.

[0074] Table 5. Inclusion rating of vacuum consumable remelted 316 stainless steel after forging

[0075] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiment based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A vacuum consumable remelting electrode assembly, characterized in that: The electrode assembly includes a primary electrode and a dummy electrode, the primary electrode is a consumable remelting electrode; one end of the primary electrode has a shrinkage hole, the dummy electrode is welded to the end of the primary electrode with the shrinkage hole, and an insulating material is arranged between the dummy electrode and the primary electrode with the shrinkage hole, and the insulating material covers the shrinkage hole of the primary electrode.

2. The vacuum consumable remelting electrode assembly according to claim 1, characterized in that: The insulating material is mounted on the central portion of the lateral end surface of the dummy electrode for welding connection to the primary electrode with the shrinkage cavity.

3. The vacuum consumable remelting electrode assembly according to claim 1, characterized in that: The end of the dummy electrode facing the shrinkage hole of the primary electrode is provided with a groove, and the insulating material is arranged in the groove.

4. The vacuum consumable remelting electrode assembly according to claim 1, characterized in that: The primary electrode used for remelting is not provided with a heat-insulating riser during the casting process, and shrinkage cavities are not removed during the remelting electrode preparation process.

5. The vacuum consumable remelting electrode assembly according to claim 1, characterized in that: The insulating material is a high temperature resistant insulating material.

6. The vacuum consumable remelting electrode assembly according to claim 5, characterized in that: The high temperature resistant insulating material is made of asbestos fiber cement board or clay brick.

7. A vacuum consumable remelting method, characterized in that: During the vacuum consumable remelting process, the electrode assembly according to any one of claims 1 to 6 is used. During the vacuum consumable furnace loading operation, the shrinkage hole of the primary electrode points upward, that is, the shrinkage hole part of the primary electrode melts at the end of remelting; the insulating material arranged between the dummy electrode and the primary electrode with the shrinkage hole prevents the arc from climbing up along the shrinkage hole to melt the dummy electrode during the shrinkage compensation period, so as to reduce the inclusions of the vacuum consumable remelting ingot.

8. The vacuum consumable remelting method according to claim 1, characterized in that: Entering the shrinkage compensation stage, the smelting current decreases from the previous steady-state current to 1 / 8-1 / 4 of the original value within 0-2 minutes.

9. The vacuum consumable remelting method according to claim 8, characterized in that: The smelting current is reduced from the current in the previous steady state period to 1 / 8-1 / 4 of the original value within 0-2 minutes, and is maintained at the level of an actual melting rate of 0-0.3 kg / min for 20-70 minutes.

10. The vacuum consumable remelting method according to claim 9, characterized in that: The smelting current is reduced from the previous steady-state current to 1 / 8-1 / 4 of the original value within 0-2 minutes, while the electrode position is locked and maintained at the level of an actual melting rate of 0-0.3 kg / min for 20-70 minutes.

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