A special slag system for inhibiting cracks and center segregation of steel ingot and electroslag remelting method

Abstract

The present application relates to the technical field of metal production and refining, and particularly relates to a special slag system for inhibiting cracks and center segregation of ingots and an electroslag remelting method. The special slag system comprises the following components: CaF2: 20%-33%, CaO: 35%-45%, Al2O3: 15%-25%, BaO: 3%-7%, B2O3: 2%-5%, and the total mass ratio is 100%. The technical scheme disclosed by the present application adds BaO and B2O3 into the electroslag remelting slag, can balance the alkalinity and viscosity of the slag, and fully play the synergistic effect of the two, that is, the strong desulfurization capacity of BaO is retained, the viscosity of the slag is adjusted through B2O3, the erosion of BaO on the refractory material is relieved, and the service life of the slag is prolonged; through adjusting the slag system, adding BaO and B2O3, and cooperating with the electroslag remelting dynamic process adjustment, the "flexible slag skin" formed can not only improve the purification efficiency of the slag, improve the stability of the remelting process, but also reduce the production cost, and can effectively reduce the center segregation and crack of the electroslag ingot in the electroslag remelting process.

Description

Technical Field

[0001] This invention belongs to the field of metal production and refining technology, specifically involving a special slag system and electroslag remelting method for suppressing cracks and center segregation in steel ingots, which can achieve root cause suppression of surface cracks and center segregation. Background Technology

[0002] Electroslag remelting (ESR) is a core process for achieving deep purification of molten steel. It involves resistance heating of the melting electrodes in a slag pool. As the molten metal droplets pass through the slag pool, they undergo desulfurization, deoxidation, and inclusion removal through the physicochemical action of the slag, ultimately yielding high-quality steel ingots with uniform composition and dense structure. The properties of the slag system (such as viscosity, melting point, basicity, and purification efficiency) are the core factors determining the quality of remelted steel. While traditional CaF2-based slag systems (such as CaF2-CaO-Al2O3) are widely used, they have significant drawbacks: First, their desulfurization capacity is limited by the amount of CaO added, as CaO has limited basicity, and excessive addition leads to a sharp increase in slag viscosity, hindering the smooth flow of molten metal droplets and reducing purification efficiency. Second, viscosity changes drastically with temperature; at high temperatures (1500-1700℃), the viscosity is low, easily causing slag pool fluctuations and affecting the stability of the remelting process. Third, the presence of Al2O3 may promote the formation of solid inclusions in the slag, increasing the inclusion content in the steel ingot.

[0003] Based on research and actual production practices, the electroslag remelting process currently faces two major bottlenecks:

[0004] (1) Surface cracks: Traditional slag systems (such as CaF2-CaO-Al2O3) form brittle slag skin after solidification. When the steel ingot solidifies and shrinks, the slag skin is prone to cracking and induces surface cracks in the steel ingot. The crack rate can reach 10%-20%. (2) Central segregation: The traditional constant power remelting mode results in a large melt pool depth (≥200mm), forming a V-shaped solidification front. Solute elements are easily enriched in the center, and the central segregation level can reach 2-3. Severe surface cracks in electroslag ingots are a major quality problem plaguing the high-end electroslag steel industry. Figure 1 As shown.

[0005] Existing technologies mostly alleviate the problems of surface cracks and central segregation by optimizing the basicity of the slag system or adjusting the cooling water volume, but they do not fundamentally solve the problems of slag skin brittleness and molten pool morphology, and the effects are limited.

[0006] In the traditional electroslag remelting process, the liquid slag solidifies on the inner wall of the crystallizer to form a solid slag skin. This slag skin is crucial for ensuring the surface quality of the steel ingot. Traditional slag skin (such as that using the CaF2-CaO-Al2O3 slag system) is usually composed of high-melting-point minerals (such as lanceolite 3CaO·2SiO2·CaF2), and is characterized by being hard, brittle, and thick.

[0007] Traditional ESR process parameters (such as current and voltage) and slag composition are typically set before smelting and remain largely unchanged during the process. However, in actual remelting of large steel ingots, the slag pool temperature, slag composition (especially the accumulation of oxides of easily oxidized elements such as Al and Ti), and molten pool morphology change dynamically as smelting progresses. The mismatch between a fixed process and a changing smelting environment can easily lead to deterioration of the ingot surface quality, unstable composition control, decreased purity, and even solidification defects. By monitoring electrical parameters and crystallizer water temperature in real time, the slag pool state and molten metal pool depth can be inferred. Based on this, the current or voltage can be dynamically adjusted to stabilize the molten pool morphology and control solidification quality.

[0008] Patent application CN202111251771.4 discloses "a novel slag-based heat-resistant steel hand-welding electrode for ultra-supercritical T / P91 steel and its production method." The core feature of this method is that the coating adopts a CaO-CaF2-SiO2-TiO2-BaO slag-based structure, and the coating is applied to the outer wall of the alloy core wire. The fully clad metal exhibits excellent mechanical properties after post-weld heat treatment, along with good high-temperature creep strength and creep resistance, meeting the requirements for high-temperature use. However, this technical solution only improves the mechanical properties of the metal after post-weld heat treatment and fails to apply it to the electroslag remelting process to improve the quality of electroslag ingots.

[0009] Patent application number CN201710404940.0 discloses "a fluorine-free protective slag for medium carbon steel". The core principle of this method is: by controlling the addition of a certain amount of BaO, the original Si is destroyed. O Si bond and B O B bonds promote the formation of granular calcium borosilicate (Ca). 11 Si4B2O 22 The crystalline mineral phase is obtained while the protective slag maintains a low viscosity; the crystalline phase of this slag is granular calcium borosilicate. However, this technical solution only addresses the deterioration of the crystallization and lubrication properties of the protective slag after fluorination, and cannot solve the problems that restrict the quality of electroslag remelting products, such as suppressing surface cracks and central segregation in steel ingots.

[0010] Patent application number CN202110346211.0 discloses "an ultra-low oxygen slag system for electroslag remelting and its preparation method." The core technical idea of ​​this patent is to rationally select and control the content of each component in the ultra-low oxygen slag system, resulting in extremely low levels of unstable oxides and thus low oxygen content generated during high-temperature decomposition. Simultaneously, during electroslag remelting, the ultra-low oxygen slag system can adsorb oxygen-containing inclusions, further reducing the oxygen in the molten steel to extremely low levels, effectively removing oxygen from the electrodes. From a practical application perspective, this process has significant operational limitations. The core problem lies in its narrow process control window and high stability requirements. Any air infiltration will oxidize and deactivate the active components in the slag, conversely increasing oxygen in the molten steel. Oxygen from the electrodes themselves will enter the molten pool, significantly reducing the effectiveness of the ultra-low oxygen slag system. In summary, this process method has a narrow process control window and significant operational limitations, resulting in a lack of universality in practical applications and hindering its large-scale promotion and application across the entire industry.

[0011] Patent application number CN202510720388.0 discloses "a slag material for electroslag remelting under high altitude and high humidity conditions and its preparation method." The components are as follows: calcium fluoride 20... 22%, aluminum oxide 25 28%, calcium oxide 20 25%, magnesium oxide 8 10%, silicon dioxide 8 10%, rare earth oxides 3 8%, Barium oxide 1 5%; For high-altitude (80% air pressure) environments, a low-hygroscopic, low-fluorine, and environmentally friendly slag material is provided, achieving improved slag pool stability, hydrogen and oxygen control, and reduced energy consumption. From a practical application perspective, this process has significant limitations. High humidity air greatly increases the risk of hydrogen increase in the slag system during remelting, while low air pressure lowers the boiling point of the slag pool, potentially triggering a "boiling" phenomenon. Both factors jointly undermine the stability of the metallurgical process, rendering traditional control methods based on fixed proportions and processes ineffective.

[0012] To optimize slag performance, research revealed that BaO, as a strongly alkaline oxide with significantly higher alkalinity than CaO, can significantly enhance the desulfurization capacity of the slag. It also disrupts the slag's network structure, lowers its melting point, and improves its fluidity. B2O3, by forming a low-melting-point glassy structure with alkaline oxides, adjusts the slag viscosity, maintaining suitable fluidity within the electroslag remelting temperature range. This facilitates the formation and passage of molten metal droplets, improving purification efficiency. Furthermore, B2O3 inhibits the volatilization of CaF2, reducing environmental pollution. However, adding either BaO or B2O3 alone has limitations: adding BaO alone leads to excessively high alkalinity in the slag, exacerbating erosion of refractory materials and shortening its service life; adding B2O3 alone reduces the slag's alkalinity, weakening its desulfurization capacity and failing to meet the requirements for deep purification. Summary of the Invention

[0013] The purpose of this invention is to provide a specialized slag system and electroslag remelting method for suppressing cracks and center segregation in steel ingots. This technology can suppress surface cracks and center segregation in steel ingots at their source. This scheme adds BaO and B2O3 to the electroslag remelting slag, achieving a balance between the slag's alkalinity and viscosity, fully leveraging the synergistic effect of both—preserving the strong desulfurization capacity of BaO while adjusting the slag viscosity through B2O3, and simultaneously mitigating the erosion of refractory materials by BaO, thus extending the slag's service life. By adjusting the slag system, adding BaO and B2O3, and coordinating with dynamic process adjustments in electroslag remelting, a "flexible slag skin" is formed. This not only improves slag purification efficiency and the stability of the remelting process but also reduces production costs and effectively reduces center segregation and crack formation in electroslag ingots during electroslag remelting.

[0014] According to one aspect of the present invention, a special slag system for suppressing cracks and center segregation in steel ingots is provided, the composition of which is as follows: CaF2: 20%-33%, CaO: 35%-45%, Al2O3: 15%-25%, BaO: 3%-7%, B2O3: 2%-5%, based on a total mass percentage of 100%.

[0015] The slag system designed in this invention is based on CaF2-CaO-Al2O3 (to ensure refining capacity), with the addition of BaO and B2O3 to adjust crystallization characteristics. After solidification, this slag system forms a "flexible slag skin." When the steel ingot shrinks, the slag skin buffers thermal stress through micro-plastic deformation, preventing cracking. The specific reasons for the slag system design are as follows: CaF2: 20%-33%, by destroying the tetrahedral structure of silicon and oxygen by fluoride ions, lowers the liquidus temperature of the slag system, keeps the slag in a liquid state at a lower temperature, reduces the tendency to solidify, significantly improves the flow properties of the slag, facilitates the separation of slag from metal and the coating of metal surface, and is a key component for adjusting the flowability of slag.

[0016] CaO: 35%-45%, as a basic oxide, increases the basicity of the slag system and increases the O content in the slag. 2- The concentration promotes the reaction of sulfides (such as FeS) in molten steel with CaO to form stable CaS, thereby enhancing desulfurization capacity and maintaining slag stability, thus avoiding a decrease in desulfurization efficiency due to excessive acidity.

[0017] Al2O3: 15%-25%, used to adjust viscosity by neutralizing acidic or alkaline components in the slag. Too low a content results in decreased slag viscosity and easy slag skin detachment; too high a content increases viscosity, affecting fluidity. Appropriate amounts of Al2O3 maintain suitable slag viscosity, ensuring a moderate slag skin thickness and effectively protecting the furnace lining.

[0018] BaO: 3%-7%, utilizing Ba 2+ The large radius characteristic disrupts the crystal structure in the slag, inhibits the formation and growth of brittle phases, reduces the crystallization rate of the slag system from 70%-80% to ≤60%, reduces the precipitation of brittle phases, improves the crack resistance of the slag, and prevents the slag skin from falling off due to brittle fracture.

[0019] B2O3: 2%-5%, forms a glassy structure, maintains good plasticity at high temperatures (such as 1200℃), and allows the slag skin to absorb energy through plastic deformation when subjected to temperature changes or mechanical impact, reducing the generation and propagation of cracks, improving the high-temperature plasticity of the slag skin (deformation rate ≥15%), and enhancing toughness.

[0020] According to another aspect of the present invention, an electroslag remelting method for suppressing cracks and center segregation in steel ingots is provided, comprising the following steps: Step 1, initial remelting stage: Add a basic slag system with the following composition to the electroslag furnace in one go: CaF2: 20%~33%, CaO: 35%~45%, Al2O3: 15%~25% to form a shallow molten pool, and then add B2O3; Step 2, mid-remelting stage: Ingot height 1 / 3H-2 / 3H, adjust power and cooling water flow rate again to form a molten pool with a depth of 100-150mm, add BaO, and control the slag basicity to 2.5-3.5; Step 3, final stage of remelting: At the ingot height of 2 / 3H-H, a multi-stage power reduction operation is adopted, the cooling water flow rate is adjusted, and B2O3 is added to obtain an electroslag ingot.

[0021] Based on the above technical solution, the initial stage of remelting specifically involves: using 50%-70% of the rated power and 1.2-1.5 times the rated flow rate of cooling water to form a shallow molten pool with a depth of ≤100mm. During the process of ingot height 1 / 4H-1 / 3H, 1%-2% B2O3 is added to reduce the viscosity and melting point of the slag, and to promote the rapid formation and homogenization of the slag pool.

[0022] Based on the above technical solution, the ratio of the depth to width of the molten pool in the initial stage of remelting is stabilized in a shallow and flat range of ≤0.5.

[0023] Based on the above technical solution, the intermediate remelting process specifically involves: increasing the power to 80%-90% of the rated power, reducing the cooling water flow rate to 0.8-1.0 times the rated flow rate, maintaining the molten pool depth at 100-150 mm and the surface flatness at ≤±10 mm, adding 3%-7% BaO, maintaining the high basicity and high reactivity of the slag, and reducing the precipitation of brittle phases.

[0024] Based on the above technical solution, the remelting process at the end is as follows: the power is reduced by 5%-10% every 10-15 minutes until the steel ingot is completely solidified, while the cooling water flow rate is maintained at 0.7-0.9 times the rated flow rate, and 1%-3% B2O3 is added to make the slag shell thickness 6-9 mm, thus obtaining an electroslag ingot.

[0025] Based on the above technical solution, the surface crack rate of the electroslag ingot is reduced by more than 80%, the level of central segregation is 0.5-1.0, and the target height H of the ingot body is 1500-2500mm.

[0026] Based on the above technical solution, by using infrared temperature measurement and molten pool depth sensor for real-time monitoring, when the molten pool depth is detected to exceed the axial temperature gradient > 30℃ / cm, power-cooling coordinated regulation is triggered: power is reduced by 5%-8% while cooling water flow is increased by 10%-15% to ensure the stability of the molten pool shape.

[0027] Based on the above technical solution, the rated power of the electroslag furnace used in the initial, middle, and later stages of remelting is 4500–5500 kVA, and the rated flow rate of the cooling water is 130–160 m³ / h. 3 / h.

[0028] In electroslag remelting, the solidification of a shallow, flat molten pool is key to improving the quality of steel ingots. It can reduce defects such as solute segregation and central porosity. As the ingot body gradually increases, the power gradually decreases (to avoid the electrodes melting too quickly and causing the molten pool to be too deep), while the cooling intensity increases accordingly (such as increasing the cooling water flow rate to match the heat dissipation requirements after the ingot body grows), ensuring that the ratio of the depth to width of the molten pool remains stable within a shallow, flat range of ≤0.5.

[0029] Under dynamic process conditions, flexible slag systems can form a uniform and resilient "flexible slag skin" on the surface of the ingot. This slag skin can effectively transfer cooling, keeping the solidification front gentle and avoiding directional solidification defects caused by excessively deep molten pools; it can also buffer thermal stress on the ingot surface, reducing stress concentration caused by abrupt temperature gradient changes and preventing surface cracks.

[0030] Synergistic effect of dynamic parameter adjustment and flexible slag system: The former maintains a shallow and flat molten pool through thermal balance control, while the latter promotes solidification uniformity through slag skin characteristics, ultimately achieving solidification of a shallow and flat molten pool, which significantly improves the density, microstructure uniformity and mechanical properties of steel ingots.

[0031] Compared with the prior art, the present invention has the following beneficial effects: 1. The technical solution disclosed in this invention is based on CaF2-CaO-Al2O3, with the addition of BaO and B2O3 to adjust the crystallization characteristics. Through the "flexible slag skin" slag system and dynamic process control, stress buffering and shallow flat molten pool solidification are achieved, thereby suppressing surface cracks and center segregation of steel ingots from the root.

[0032] 2. This invention proposes a "flexible slag skin" slag system and dynamic process control in the field of electroslag remelting to achieve stress buffering and shallow flat molten pool solidification, thereby suppressing surface cracks and center segregation of steel ingots from the root.

[0033] 3. The technical solution disclosed in this invention adjusts the slag system by adding BaO and B2O3, resulting in the formation of a mineral phase with a lower melting point, higher plasticity, and thinner thickness in the solidified slag skin. This slag skin is "flexible" and not easily brittle, hence the name "flexible slag skin." The "flexible slag skin" formed after the slag system solidifies inhibits surface cracks through physical buffering. The high plasticity and low crystallinity of the slag skin make it a "stress buffer layer," isolating stress from being transmitted to the steel ingot. When the steel ingot shrinks, the slag skin buffers thermal stress through micro-plastic deformation, preventing cracking and effectively reducing crack initiation and inhibiting crack formation.

[0034] In summary, the technical solution disclosed in this invention absorbs the solidification shrinkage stress of steel ingots through a physical buffering mechanism, and simultaneously adopts a dynamic power and cooling intensity control process based on the ingot height to construct a shallow and flat molten pool solidification morphology. The macroscopic segregation of solute elements is suppressed through temperature gradient optimization (the shallow and flat molten pool suppresses central segregation through morphological control). The synergistic effect of dynamic parameter adjustment and flexible slag system reduces the surface crack rate by more than 80%, reduces the molten pool depth to make the solidification front more planar, and ensures uniform distribution of solute elements, thereby reducing the central segregation level from level 3 to below level 1, significantly improving the internal and external quality of the steel ingot. This solution is suitable for the electroslag remelting production of high-quality steel. Attached Figure Description

[0035] Figure 1 The image shows surface cracks in high-end electroslag ingots (left image shows 30CrNiMoA alloy steel, right image shows 35CrMo alloy steel). Figure 2 The surface crack condition of the electroslag ingot described in Example 1; Figure 3 The surface crack condition of the electroslag ingot described in Example 3. Detailed Implementation

[0036] To make the objectives and technical solutions of this invention clearer, the following embodiments are provided for further explanation. However, the scope of protection of this invention is not limited to these embodiments; the embodiments are merely for illustrative purposes. Those skilled in the art should understand that any changes or equivalent substitutions that do not depart from the concept of this invention are included within the scope of protection of this invention.

[0037] Unless otherwise specified, all reagents and raw materials used in this invention are obtained through purchase.

[0038] In this embodiment of the invention, a 20-ton electroslag furnace is used for electroslag remelting of alloy steel, with a rated power of 4500-5500 kVA and a rated cooling water flow rate of 130-160 m³ / h. 3 / h, in specific implementation, the rated power is controlled at 5000kVA, and the rated flow rate of cooling water is controlled at 150m³ / h. 3 / h.

[0039] The present invention provides a special slag system for suppressing cracks and center segregation in steel ingots in the specific embodiments section. The composition of the special slag system is as follows: CaF2: 20%-33%, CaO: 35%-45%, Al2O3: 15%-25%, BaO: 3%-7%, B2O3: 2%-5%, based on a total mass percentage of 100%.

[0040] The present invention also provides a method for electroslag remelting to suppress cracks and center segregation in steel ingots in the specific embodiments section, comprising the following steps: Step 1, initial stage of remelting: Ingot height 0-1 / 3H, adjust power and cooling water flow rate to form a shallow molten pool, and then add B2O3; Step 2, mid-remelting stage: Ingot height 1 / 3H-2 / 3H, adjust power and cooling water flow rate again to form a molten pool with a depth of 100-150mm, add BaO, and control the slag basicity to 2.5-3.5; Step 3, final stage of remelting: At the ingot height of 2 / 3H-H, a multi-stage power reduction operation is adopted, the cooling water flow rate is adjusted, and B2O3 is added to obtain an electroslag ingot.

[0041] Based on the above technical solution, the initial stage of remelting specifically involves: using 50%-70% of the rated power and 1.2-1.5 times the rated flow rate of cooling water to form a shallow molten pool with a depth of ≤100mm. During the process of ingot height 1 / 4H-1 / 3H, 1%-2% B2O3 is added to reduce the viscosity and melting point of the slag, and to promote the rapid formation and homogenization of the slag pool.

[0042] Based on the above technical solution, the ratio of the depth to width of the molten pool in the initial stage of remelting is stabilized in a shallow and flat range of ≤0.5.

[0043] Based on the above technical solution, the intermediate remelting process specifically involves: increasing the power to 80%-90% of the rated power, reducing the cooling water flow rate to 0.8-1.0 times the rated flow rate, maintaining the molten pool depth at 100-150 mm and the surface flatness at ≤±10 mm, adding 3%-7% BaO, maintaining the high basicity and high reactivity of the slag, and reducing the precipitation of brittle phases.

[0044] Based on the above technical solution, the remelting process at the end is as follows: the power is reduced by 5%-10% every 10-15 minutes until the steel ingot is completely solidified, while the cooling water flow rate is maintained at 0.7-0.9 times the rated flow rate, and 1%-3% B2O3 is added to make the slag shell thickness 6-9 mm, thus obtaining an electroslag ingot.

[0045] Based on the above technical solution, the surface crack rate of the electroslag ingot is reduced by more than 80%, the level of central segregation is 0.5-1.0, and the target height H of the ingot body is 1500-2500mm.

[0046] Based on the above technical solution, by using infrared temperature measurement and molten pool depth sensor for real-time monitoring, when the molten pool depth is detected to exceed the axial temperature gradient > 30℃ / cm, power-cooling coordinated regulation is triggered: power is reduced by 5%-8% while cooling water flow is increased by 10%-15% to ensure the stability of the molten pool shape.

[0047] Based on the above technical solution, the rated power of the electroslag furnace used in the initial, middle, and later stages of remelting is 4500–5500 kVA, and the rated flow rate of the cooling water is 130–160 m³ / h. 3 / h.

[0048] The present invention discloses a special slag system for suppressing cracks and center segregation in steel ingots. Based on the requirements of the electroslag remelting process, the special slag system consists of a basic slag system added in one go during the initial stage of electroslag remelting, and components added at each stage of electroslag remelting. The specific description of the special slag system is as follows: 1. Basic slag system added in one go during electroslag remelting The basic slag system is a component that is added to the electroslag furnace in the initial stage of electroslag remelting, and no further additions are made during subsequent remelting processes. Its mass percentage (based on the total mass of the basic slag system being 100%) is as follows: Calcium fluoride (CaF2): 20%–33%; Calcium oxide (CaO): 35%–45%; Aluminum oxide (Al2O3): 15%–25%.

[0049] Explanation: The core function of the basic slag system is to lay the foundation for the slag in electroslag remelting, ensure the conductivity, fluidity and basic refining effect of the remelting process, and provide a stable matrix for subsequent staged addition of components and regulation of slag properties.

[0050] 2. A complete dedicated slag system formed after the entire electroslag remelting process is completed. The complete special slag system is composed of the aforementioned basic slag system and the components added at each stage of electroslag remelting, with a total mass percentage of 100%, i.e.: Calcium fluoride (CaF2): 20%–33%; Calcium oxide (CaO): 35%–45%; Aluminum oxide (Al2O3): 15%–25%; Barium oxide (BaO): 3%–7%; Boron trioxide (B2O3): 2%–5%.

[0051] 3. Correspondence between component additions and the complete slag system Barium oxide (BaO) and boron trioxide (B2O3) in the complete special slag system are added in stages through the electroslag remelting process. The specific addition method is matched with the electroslag remelting method to ensure that the composition of the slag after addition meets the above-mentioned proportion requirements of the complete special slag system. Boron trioxide (B2O3): It is added at the beginning of remelting (1 / 4H-1 / 3H of ingot height) and at the end of remelting. The total amount added in the two stages is the total proportion of B2O3 in the complete slag system (2% to 5%), of which 1% to 2% is added at the beginning and 1% to 3% is added at the end. Barium oxide (BaO): Added during the middle stage of remelting (1 / 3H-2 / 3H of ingot height), the amount added is the total proportion of BaO in the complete slag system (3%~7%). After addition, the basicity of the slag is controlled at 2.5-3.5 to ensure the refining and crack prevention effect of the slag.

[0052] Example 1 Taking electroslag remelted alloy structural steel (30CrNiMoA) as an example, the target ingot height H=2000mm.

[0053] 1. The composition of the slag system (wt%) is as follows: CaF2: 30%, CaO: 40%, Al2O3: 20%, BaO: 5%, B2O3: 5%, based on 100% total mass content of the slag system.

[0054] 2. Dynamic control process: (1) Initial stage of remelting (0-660mm): Add the basic slag system of CaF2: 30%, CaO: 40%, Al2O3: 20% to the electroslag furnace, power: 55% of the rated power; cooling water: 1.3 times the rated flow rate, and add 2% B2O3 when the ingot height is 500mm.

[0055] Control effects: A shallow, flat molten pool is quickly established, with a stable depth controlled at around 85 mm, and a depth-to-width ratio of 0.2. Strong cooling enables rapid slag formation, initially revealing the "flexible" characteristics, and resulting in a smooth bottom surface of the steel ingot.

[0056] (2) Mid-term remelting (660mm-1330mm): Power: linearly increase to 85% of rated power; Cooling water: gradually reduce to rated flow rate, add 5% BaO when the ingot height is 700mm, and adjust the basicity to 3.0.

[0057] Control effect: The molten pool depth is stabilized at 120-140mm. The effects of BaO and B2O3 are fully utilized, the slag skin is flexible, effectively lubricating the billet shell, and the heat flow is stable. Liquid level fluctuations are controlled within ±8mm.

[0058] (3) Remelting at the end (1330mm-2000mm): Power: Reduce the rated power by 7% every 12 minutes, with a total reduction of 35%. Cooling water: 0.8 times the rated flow rate. When the ingot height is 1350mm, add 3% B2O3. The surface quality, crack condition, central segregation condition, and slag skin condition of the resulting electroslag ingot are shown in Table 1. The thickness of the slag shell is 7mm. The surface crack condition of the electroslag ingot is shown in Table 1. Figure 2 .

[0059] Control effect: The molten pool solidifies upwards at a gentle slope, effectively avoiding "V-shaped shrinkage cavity" and macroscopic segregation at the end.

[0060] Example 2 Taking electroslag remelted alloy structural steel (35CrMo) as an example, the target ingot height H=2000mm.

[0061] 1. The slag composition (wt%) is as follows: CaF2: 28%, CaO: 38%, Al2O3: 22%, BaO: 7%, B2O3: 5%.

[0062] 2. Dynamic control process: (1) Initial stage of remelting (0-660mm): Power: Add the basic slag system of CaF2: 28%, CaO: 38%, Al2O3: 22% to the electroslag furnace, 50% of the rated power (lower starting power). Cooling water: 1.5 times the rated flow rate (stronger cooling), add 2% B2O3 when the ingot height is 500mm.

[0063] Control effect: The molten pool depth is extremely shallow, only about 80mm, and the depth-to-width ratio of the molten pool is 0.18. The high BaO / B2O3 content allows the slag skin to maintain good plasticity under strong cooling, completely eliminating initial surface longitudinal cracks.

[0064] (2) Mid-stage remelting (660mm-1330mm): Power: Increase to 90% of rated power. Cooling water: Reduce to 0.9 times the rated flow rate. When the ingot height is 700mm, add 7% BaO and adjust the basicity to 3.2.

[0065] Control effect: molten pool depth ~150mm. The slag system has excellent high-temperature performance and crystallization characteristics, forming a slag skin with uniform thickness and excellent flexibility, resulting in perfect surface quality in the middle of the steel ingot.

[0066] (3) Remelting at the end (1330mm-2000mm): Power: Reduce the rated power by 10% every 10 minutes, with a total reduction of 40% (steeper feeding slope). Cooling water: 0.7 times the rated flow rate. When the ingot height is 1350mm, add 3% B2O3. The surface quality, crack condition, central segregation condition, and slag skin condition of the resulting electroslag ingot are shown in Table 1. The thickness of the slag shell is 8mm.

[0067] Control effect: An extremely smooth solidification end was achieved, and the central porosity was controlled to the extreme.

[0068] Example 3 Taking electroslag remelted alloy structural steel (40CrNiMoA) as an example, the target ingot height H=2000mm.

[0069] 1. The slag composition (wt%) is as follows: CaF2: 33%, CaO: 42%, Al2O3: 18%, BaO: 3%, B2O3: 4%.

[0070] 2. Dynamic control process: (1) Initial stage of remelting (0-660mm): Add the basic slag system of CaF2: 33%, CaO: 42%, Al2O3: 18% to the electroslag furnace. Power: 70% of the rated power (higher starting power). Cooling water: 1.2 times the rated flow rate. When the ingot height is 500mm, add 2% B2O3.

[0071] Control effect: While ensuring that the depth of the molten pool does not exceed 95mm, the ratio of the depth to the width of the molten pool is controlled at 0.22, which shortens the start-up time and improves production efficiency.

[0072] (2) Mid-stage remelting (660mm-1330mm): Power: Maintain at 90% of rated power. Cooling water: Rated flow rate, add 3% BaO when the ingot height is 700mm, and adjust the basicity to 3.2.

[0073] Control effect: At higher power, relying on the excellent properties of the slag system itself, the depth of the molten pool can still be kept stable at about 130mm and the surface flatness is ±5mm, achieving high-speed remelting under high quality.

[0074] (3) Remelting at the end (1330mm-2000mm): Power: Reduce rated power by 5% every 15 minutes, with a total reduction of 30%. Cooling water: 0.9 times the rated flow rate. When the ingot height is 1350mm, add 2% B2O3. The surface quality, crack condition, central segregation condition, and slag skin condition of the resulting electroslag ingot are shown in Table 1. The thickness of the slag shell is 8mm. The surface crack condition of the electroslag ingot is shown in Table 1. Figure 3 .

[0075] Control effect: The feeding process was completed smoothly, and the smelting cycle was shortened as much as possible while ensuring quality.

[0076] Comparative Example Slag system: conventional CaF2-Al2O3-CaO ternary slag system (e.g., 60% CaF2, 20% Al2O3, 20% CaO).

[0077] Process: A conventional electroslag remelting process is used to produce 30CrNiMoA steel ingots with a stable power output. The cooling water flow rate is kept relatively constant (maintaining a power output of 5000 kVA and a cooling water flow rate of 150 m³ / h). 3 The surface quality, crack condition, central segregation condition, and slag skin condition of the obtained electroslag ingots are shown in Table 1.

[0078] Table 1. Surface quality, crack condition, central segregation, and slag skin condition of electroslag ingots.

[0079] As shown in Table 1, the technical solution disclosed in this invention improves the quality of electroslag ingots of high-requirement steel grades such as 30CrNiMoA to a new level through electroslag remelting and refining technology. Specifically, the surface crack rate is reduced by more than 80%, and the center segregation level is reduced from level 3 to below level 1, laying a solid ingot foundation for the subsequent forging of high-performance and high-quality forgings.

[0080] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A special slag system for suppressing cracks and center segregation in steel ingots, characterized in that, The composition of the special slag system is as follows: CaF2: 20%-33%, CaO: 35%-45%, Al2O3: 15%-25%, BaO: 3%-7%, B2O3: 2%-5%, based on a total mass percentage of 100%.

2. A method for electroslag remelting to suppress cracks and center segregation in steel ingots, characterized in that, Includes the following steps: Step 1, initial remelting stage: Add a basic slag system with the following composition to the electroslag furnace at one time: CaF2: 20%~33%, CaO: 35%~45%, Al2O3: 15%~25%. When the ingot height is 0-1 / 3H, adjust the power and cooling water flow rate to form a shallow molten pool with a depth ≤100mm, and then add B2O3. Step 2, mid-remelting stage: When the ingot height is 1 / 3H-2 / 3H, adjust the power and cooling water flow rate again to form a molten pool with a depth of 100-150mm. Add BaO and control the slag basicity to 2.5-3.

5. Step 3, final stage of remelting: The ingot height is 2 / 3H-H. Multi-stage power reduction operation is adopted and the cooling water flow rate is adjusted. B2O3 is added to make the slag shell thickness 6-9 mm, thus obtaining an electroslag ingot.

3. The electroslag remelting method according to claim 2, characterized in that, The initial stage of remelting specifically involves using 50%-70% of the rated power and 1.2-1.5 times the rated flow rate of cooling water to form a shallow molten pool with a depth of ≤100mm. During the process of ingot height 1 / 4H-1 / 3H, 1%-2% B2O3 is added.

4. The electroslag remelting method according to claim 2, characterized in that, In the initial stage of remelting, the ratio of the depth to width of the molten pool stabilizes in a shallow, flat range of ≤0.

5.

5. The electroslag remelting method according to claim 2, characterized in that, The remelting process specifically involves: increasing the power to 80%-90% of the rated power, reducing the cooling water flow rate to 0.8-1.0 times the rated flow rate, maintaining the molten pool depth at 100-150 mm and the surface flatness at ≤±10 mm, and adding 3%-7% BaO.

6. The electroslag remelting method according to claim 2, characterized in that, The remelting process at the end involves reducing the power by 5%-10% every 10-15 minutes until the steel ingot is completely solidified, while maintaining the cooling water flow rate at 0.7-0.9 times the rated flow rate and adding 1%-3% B2O3.

7. The electroslag remelting method according to claim 2, characterized in that, The surface crack rate of the electroslag ingot is reduced by more than 80%, the level of central segregation is 0.5-1.0, and the target height H of the ingot body is 1500-2500mm.

8. The electroslag remelting method according to claim 2, characterized in that, The rated power of the electroslag furnace used in the initial, middle, and later stages of remelting is 4500–5500 kVA, and the rated flow rate of the cooling water is 130–160 m³ / h. 3 / h.

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