Method for controlling shrinkage cavity depth of ingot crown of hot top sealing in electroslag remelting process

Abstract

The invention relates to the technical field of electroslag remelting, in particular to a control method for the ingot crown shrinkage cavity depth of hot top sealing in the electroslag remelting process, and the control method comprises the steps that S1, in the stable smelting stage, the length of a consumable electrode is 10% + / -2% of the initial length of the consumable electrode; s2, the current smelting power is reduced to 80%-90% of the smelting power in the stable smelting stage; s3, the current smelting power is reduced to 70%-75% of the smelting power of the stable smelting stage; s4, the current smelting power is reduced to 60%-65% of the smelting power of the stable smelting stage; s5, the current smelting power is reduced to 50%-55% of the smelting power in the stable smelting stage; and S6, the current smelting power is reduced to 40%-45% of the smelting power of the stable smelting stage, so that the consumable electrode is separated from the surface of the slag, and heat supply is stopped. The temperature near a metal molten pool is obtained by continuously measuring the temperature of the slag pool, the heat field input at the end of the consumable electrode and the temperature distribution characteristic in the crystallizer are accurately grasped, the solidification sequence of the ingot crown position is prevented from being disordered, the shrinkage cavity depth is reduced, and shrinkage cavity formation is inhibited.

Description

Technical Field

[0001] The present invention relates to the technical field of electroslag remelting, and in particular to a method for controlling the depth of shrinkage holes in an ingot crown during heat sealing during electroslag remelting. Background Art

[0002] Electroslag remelting (ESR) is a core smelting process for producing high-quality nickel-copper alloys. It relies on the resistance heat generated by an electric current passing through molten slag to melt the consumable electrode. The molten metal then solidifies into an ingot in a water-cooled mold. The slag serves as both a heat source and a heat insulator during the solidification process. The superheated slag remains above the liquid metal pool, ensuring a directional solidification sequence from bottom to top.

[0003] Because the surface of the ingot crown solidifies before its interior, it can trap isolated liquid metal, causing it to shrink during solidification and produce shrinkage cavities. This defect reduces the solidification quality of the ingot crown and must be removed, increasing scrap loss from head cutting. Therefore, before the end of nickel-copper alloy electroslag remelting, the metal pool needs to be hot-capped. The purpose is to continue the progressive solidification sequence of the alloy ingot, gradually shallowing the metal pool, reducing the depth of the shrinkage cavity, reducing the amount of head cutting of the ingot, and improving the ingot yield rate.

[0004] At present, the hot capping process for vacuum consumable melting of nickel-copper alloy generally adopts the method of reducing the current or reducing the melting rate, but the shrinkage cavity of the ingot cast by this method is still deep and the depth is uncontrollable. The reason is that reducing the current or melting rate is to adjust the thermal field near the end of the electrode. The end of the electrode is far away from the molten metal pool, and the heat transfer of the melt and the temperature change of the molten metal pool both require a long response time. The temperature distribution characteristics near the end of the electrode cannot reflect the temperature distribution characteristics of the molten metal pool in a timely manner, causing the solidification of the ingot to lag significantly compared to the melting of the electrode. Especially in the process of electroslag remelting of large ingots, the molten metal pool is deep V-shaped, the consumable electrode is far away from the bottom of the molten metal pool, and the lag is more obvious. This causes the temperature to drop below expectations, which ultimately affects the prediction of the solidification process of the ingot cast in the molten metal pool during the hot capping stage. Therefore, the existing hot capping process cannot avoid the formation of shrinkage cavities, the solidification quality is also unstable, and the process repeatability is poor.

[0005] To this end, the present invention provides a method for controlling the shrinkage cavity depth of a hot-capped ingot crown during electroslag remelting. Summary of the Invention

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for controlling the shrinkage cavity depth of the ingot crown during hot-capping in the electroslag remelting process, thereby solving the technical problem that the temperature distribution characteristics near the end of the consumable electrode cannot timely reflect the temperature distribution characteristics of the molten metal pool, resulting in a significant lag in the solidification of the ingot compared to the melting of the consumable electrode, causing the temperature to drop lower than expected, affecting the prediction of the solidification process of the molten metal pool in the hot-capping stage, and unable to avoid the formation of shrinkage cavities.

[0007] In order to achieve the above object, the present invention provides a method for controlling the shrinkage cavity depth of an ingot crown during hot-capping in an electroslag remelting process. The control method comprises: S1. In the stable smelting stage, the consumable electrode length is 10%±2% of the initial consumable electrode length. Entering the hot capping stage, the slag pool temperature T is continuously measured and the liquidus temperature of the nickel-copper alloy is calculated. and the solidus temperature of nickel-copper alloys ; S2. During the hot capping stage, the smelting power of the smelting stage will be stabilized. Reduce to current melting power , , ; for Power regulation coefficient when for Power when When the measured temperature meets , and the temperature drop for two consecutive temperature measurements meets the requirement of ≤1K / min, the slag temperature tends to be stable, and the current smelting power is maintained for 10min~20min; In step S2, the melting power of the smelting stage is stabilized for: ; Where, is the heat transfer from the slag pool to the consumable electrode, in W; is the heat transfer from the slag pool to the gas phase, unit is W; is the heat transfer from the slag pool to the crystallizer, unit is W; is the heat transfer from the slag pool to the ingot, unit is W; The heat transfer from the slag pool to the consumable electrode in the above formula is for:

[0008] Where, is the thermal conductivity of the slag, in units of ; T is the slag pool temperature, unit is K; is the solidus temperature of nickel-copper alloy, in K; The depth of the consumable electrode immersed in the slag pool, in m; is the radius of the consumable electrode, in m; Heat transfer from slag pool to gas phase for: ; Where, is the convective heat transfer coefficient between the slag and the gas phase, in units of ; T is the slag pool temperature, unit is K; is the gas phase temperature in the crystallizer, in K; is the mold radius, in m; is the radius of the consumable electrode, in m; Heat transfer from slag pool to crystallizer for: ; Where, is the convection heat transfer coefficient between the slag and the crystallizer, in units of ; T is the slag pool temperature, unit is K; is the liquid phase temperature in the crystallizer, in K; is the mass of slag in the slag pool, in kg; is the density of the slag, in units of ; is the mold radius, in m; Heat transfer from slag pool to ingot for: ; Where, is the thermal conductivity of the metal, in units of ; T is the slag pool temperature, unit is K; is the liquidus temperature of nickel-copper alloy, in K; is the depth of the metal pool, in m; is the mold radius, in m.

[0009] S3, reduce the current smelting power to , , ; for Power regulation coefficient when for Power when When the measured temperature meets , and the temperature drop for two consecutive temperature measurements meets the requirement of ≤1K / min, the slag temperature tends to be stable, and the current smelting power is maintained for 10min~20min; S4, reduce the current smelting power to , , ; for Power regulation coefficient when for Power when When the measured temperature meets , and the temperature drop for two consecutive temperature measurements meets the requirement of ≤1K / min, the slag temperature tends to be stable again, and the current smelting power is maintained for 10min~20min; S5. Reduce the current smelting power to , , ; for Power regulation coefficient when for Power when When the measured temperature meets , and the temperature drop in two consecutive temperature measurements meets the requirement of ≤1K / min, the slag temperature tends to be stable again, and the current smelting power is maintained for 10min~20min to make the liquid metal pool shrink toward the center of the ingot crown surface; In steps S2 to S5, the time interval between two consecutive temperature measurements is 0.5 min to 1 min; In steps S2 to S5, the temperature of the slag pool is measured at a position 0.85 to 0.95 times the depth of the slag pool.

[0010] S6. Reduce the current smelting power to , , When the melting rate of the consumable electrode is less than 5% to 10% of the melting rate of the consumable electrode in the stable smelting stage within 2 consecutive minutes, the consumable electrode is separated from the slag surface and the smelting power supply is turned off at the same time.

[0011] In steps S2 to S6, the adjustment time for reducing the current smelting power is less than 5s.

[0012] S7, keep the cooling water circulation running, and after 30 minutes, the hot capping stage ends; S8. The crystallizer is demoulded to obtain a solidified electroslag remelting ingot, and the electroslag remelting is completed.

[0013] The beneficial effects of the present invention are: The present invention provides a method for controlling the shrinkage cavity depth of the ingot crown during the electroslag remelting process by using an alternating strategy of decreasing and maintaining the melting power. By continuously measuring the slag pool temperature, the temperature near the molten metal pool is obtained, the thermal field input at the end of the consumable electrode and the temperature distribution state in the crystallizer are accurately grasped, and the solidification process of the ingot in the molten metal pool is grasped in real time, thereby controlling the melting power holding time and adjusting the thermal capping process in a timely manner. In addition, by maintaining the power for a longer period of time, the slag pool temperature is always higher than the surface of the molten metal pool. Compared with the traditional thermal capping process, this method ensures that the solidification sequence from bottom to top runs through the entire solidified ingot to the greatest extent, avoids the solidification sequence at the ingot crown position from being disrupted, thereby reducing the shrinkage cavity depth and inhibiting the formation of shrinkage cavity in the ingot crown.

[0014] Furthermore, by gradually controlling the smelting power and accurately controlling the input of slag pool heat, the problem of response time difference caused by the consumable electrode end being far away from the molten metal pool, the fast melting response time of the consumable electrode, and the slow response time of the slag pool temperature field is avoided, and the temperature distribution characteristics near the electrode end cannot reflect the temperature distribution characteristics of the molten metal pool in time. The hysteresis is significantly reduced, and the temperature drop is in line with expectations. Finally, the prediction of the ingot solidification process in the hot capping stage is achieved during the electroslag remelting process. DETAILED DESCRIPTION

[0015] In order to better understand the above technical solutions, exemplary embodiments of the present invention will be described in more detail below. It should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0016] This embodiment provides the melting power of the stable melting stage. The specific derivation process is: ; Where, is the heat transfer from the slag pool to the consumable electrode, in W; is the heat transfer from the slag pool to the gas phase, unit is W; is the heat transfer from the slag pool to the crystallizer, unit is W; is the heat transfer from the slag pool to the ingot, unit is W; During the electroslag remelting process, heat is generated by the Joule heat generated in the slag pool. When the furnace is in dynamic heat balance, this heat is mainly used for heat transfer from the slag pool to the consumable electrode, from the slag pool to the gas phase, from the slag pool to the crystallizer, and from the slag pool to the ingot.

[0017] Heat transfer from slag pool to consumable electrode for: ; Where, is the thermal conductivity of the slag, in units of ; T is the slag pool temperature, unit is K; is the solidus temperature of nickel-copper alloy, in K; The depth of the consumable electrode immersed in the slag pool, in m; is the radius of the consumable electrode, in m; When calculating the heat transfer from the slag pool to the consumable electrode The heat transfer from the slag pool to the consumable electrode is a heat conduction process. The depth of the consumable electrode immersed in the slag pool in the following embodiment is Take 0.001m.

[0018] Heat transfer from slag pool to gas phase for: ; Where, is the convective heat transfer coefficient between the slag and the gas phase, in units of , usually 5 ~50 ; T is the slag pool temperature, unit is K; is the gas phase temperature in the crystallizer, in K; is the mold radius, in m; is the radius of the consumable electrode, in m; The equivalent heat transfer coefficient is used to consider the convection heat transfer and radiation heat transfer between the slag pool and the high-temperature gas. Since the middle part is blocked by the consumable electrode, the contact area between the slag and the high-temperature gas is yes .

[0019] The heat transfer from the slag pool to the crystallizer in the above formula is for: ; Where, is the convection heat transfer coefficient between the slag and the crystallizer, in units of , usually 500 ~1200 ; T is the slag pool temperature, unit is K; is the liquid phase temperature in the crystallizer, in K; is the mass of slag in the slag pool, in kg; is the density of the slag, in units of ; is the mold radius, in m; Since there is convection heat transfer between the slag pool and the crystallizer wall, the slag pool releases heat to the crystallizer, and the contact area is ,Right now .

[0020] The heat transfer from the slag pool to the ingot in the above formula is for: ; Where, is the thermal conductivity of the metal, in units of ; T is the slag pool temperature, unit is K; is the liquidus temperature of nickel-copper alloy, in K; is the depth of the metal pool, in m; is the mold radius, in m; Since the metal molten pool and the paste area flow slowly, the heat is transferred between the slag pool and the ingot by heat conduction, and the temperature difference The temperature to be lowered to meet the power coefficient of this step; the molten metal pool is actually a cone when solidifying. During the calculation process, the molten metal pool covering the ingot is regarded as a cylinder, so the heat transfer from the slag pool to the ingot is required. The formula is modified, and the depth of the metal pool is Equivalent height equals , and then proceed Calculation.

[0021] From step S2 to step S6, there is a process of gradually decreasing the melting power, which is a process of gradually decreasing the melting power from the stable melting stage. The melting power gradually decreases at the beginning, that is, the melting power in the stable melting stage Gradually decrease to the current melting power to .

[0022] The present invention also provides two embodiments and four comparative examples of a method for controlling the shrinkage cavity depth of an ingot crown during hot capping during electroslag remelting, including Embodiment 1 and Embodiment 2, and Comparative Examples 1, 2, 3, and 4, as follows: Comparison of Example 1 with Comparative Example 1 and Comparative Example 2: In the electroslag remelting apparatus used in Example 1, the mold has a diameter of 0.73 m and a height of 2.8 m. The consumable electrode has a diameter of 0.59 m and a length of 3 m. The consumable electrode is made of Monel K500 nickel-copper alloy (chemical composition: C 0.075% wt, Si 0.01% wt, Mn 0.8% wt, Al 2.83% wt, Fe 0.82% wt, Cu 29.51% wt, Ti 0.52% wt, Ni 65.15%). The slag system used in this example is ESR 2037 (chemical composition: Al2O3 21% wt + CaO 20% wt + MgO2% wt + CaF2 57% wt). The total weight of the slag is 200 kg.

[0023] In this embodiment 1, the alternating current with a frequency of 50 Hz is used, and the density of the slag is 2460kg / m 3When the slag pool transfers heat to the consumable electrode, the slag pool temperature is T = 1750K, Q1 = 225028W; when the slag pool transfers heat to the gas phase, the slag pool temperature is T = 1750K, Q2 = 9988W; when the slag pool transfers heat to the crystallizer, the slag pool temperature is T = 1750K, Q3 = 348814W; when the slag pool transfers heat to the ingot, the slag pool temperature is T = 1750K, Q4 = 16504W; then the smelting power P0 in the stable smelting stage = Q1 + Q2 + Q3 + Q4 = 600kW. The specific process parameters and steps of the control method of this embodiment 1 are as follows: S1. When the consumable electrode length in the stable smelting stage of the electroslag remelting process reaches 0.3 m, the electroslag remelting process enters the hot capping stage, and the slag pool temperature T is continuously measured; S2. During the hot capping stage, the smelting power of the smelting stage will be stabilized. =600kW down to the current melting power P1=521kW (86.77% of P0), when the measured temperature meets , and the temperature drop in two consecutive temperature measurements meets ≤1K / min, the slag temperature tends to be stable, and the smelting power is continued to be maintained for 15 minutes to slowly reduce the temperature of the liquid metal molten pool; In step S2, the thermal conductivity of the slag 4.5 , the thermal conductivity of metal is 32 , the convection heat transfer coefficient between the slag and the crystallizer 540 , the convective heat transfer coefficient between slag and gas phase 50 , the liquid phase temperature in the crystallizer The gas phase temperature in the crystallizer is 300K. It is 373K.

[0024] In step S2, the thermal balance relationship is calculated to yield X1=P1 / P0≈0.8677.

[0025] S3, reduce the current smelting power to , P2=441kW (73.55% of P0), when the measured temperature meets , and the temperature drop in two consecutive temperature measurements meets ≤1K / min, the slag temperature tends to be stable, and then the smelting power is maintained for 15 minutes, so that the liquid metal molten pool slowly becomes shallower and the pure liquid phase area gradually disappears; In step S3, the thermal balance relationship is calculated to yield X2=P2 / P0≈0.7355.

[0026] S4, reduce the current smelting power to , P3=362kW (60.33% of P0), the measured temperature satisfies , and the temperature drop in two consecutive temperature measurements meets the requirement of ≤1K / min, the slag temperature tends to be stable again, and then the smelting power is maintained for another 15 minutes to allow the liquid metal pool to shrink toward the surface of the ingot crown; In step S4, the thermal balance relationship is calculated to yield X3=P3 / P0≈0.6033.

[0027] S5. Reduce the current smelting power to , P4=313kW (52.21% of P0), when the measured temperature meets , the temperature drop meets ≤1K / min for two consecutive temperature measurements, the slag temperature tends to be stable again, and then the smelting power is maintained to continue smelting for 15 minutes, so that the liquid metal pool shrinks to the center of the ingot crown surface; In step S5, the heat balance relationship is calculated to yield X4=P4 / P0≈0.5221.

[0028] S6. Reduce the current smelting power to , P5 = 240kW (40% of P0), after maintaining this power for 8 minutes, within 2 consecutive minutes, the consumable electrode melting rate is ≤ 0.9kg / min (10% of the consumable electrode melting rate in the stable smelting stage), the consumable electrode clamping device is driven to move upward to separate the consumable electrode from the slag surface, and the smelting power supply is turned off at the same time; S7, keep the cooling water circulation running, and after 30 minutes, the hot capping stage ends; S8. The crystallizer is demoulded to obtain a solidified electroslag remelting ingot, and the electroslag remelting is completed.

[0029] In step S2 to step S5, the time interval between two consecutive temperature measurements is 1 minute.

[0030] In steps S2 to S5, the temperature of the slag pool is measured at a position 0.9 times the depth of the slag pool, and the position and depth are fixed for multiple measurements.

[0031] The liquidus temperature of nickel-copper alloy is calculated from the composition of nickel-copper alloy consumable electrode. The solidus temperature of nickel-copper alloy is 1600K. is 1567K, here is about and The calculation of belongs to the existing technology and will not be described in detail here.

[0032] In step S2 to step S6, the adjustment time for reducing the current smelting power should be completed in a very short time. In this embodiment, the adjustment time is 3 seconds.

[0033] Continue to maintain the current melting power, and the melting power fluctuation is ≤1.5%.

[0034] The hot capping stage of the electroslag remelting process in Example 1 lasted 109 minutes (excluding the ingot cooling time), resulting in a steel ingot with a diameter of 0.73 m and a height of 1.95 m. The resulting ingot was longitudinally sectioned along its central axis, and the shrinkage cavity depth in the ingot crown was measured. The results are shown in Table 1, Example 1.

[0035] Comparative Example 1: All other conditions were the same as in Example 1, except that a current reduction strategy was employed during the hot capping phase, with the current continuously and slowly decreasing from 14 kA to 7 kA. This took 105 minutes (excluding the ingot cooling time), resulting in a steel ingot with a diameter of 0.73 m and a height of 1.95 m. The resulting ingot was longitudinally sectioned along its central axis, and the shrinkage cavity depth at the ingot crown was measured. The results are shown in Table 1 for Comparative Example 1.

[0036] Comparative Example 2: All other conditions were the same as in Example 1, except that a melt rate reduction strategy was employed during the hot capping stage. The melt rate was continuously and slowly reduced from 9 kg / min to 0.9 kg / min over a period of 105 minutes (excluding the ingot cooling time). A steel ingot with a diameter of 0.73 m and a height of 1.95 m was obtained. The resulting ingot was longitudinally sectioned along its central axis, and the shrinkage cavity depth in the ingot crown was measured. The results are shown in Table 1 for Comparative Example 2.

[0037] Table 1 Parameter comparison of Example 1, Comparative Example 1 and Comparative Example 2

[0038] Comparing Example 1 with Comparative Examples 1 and 2, it can be seen that, under the same process parameters during the stable smelting phase, and consistent remelting materials and slag, as shown in Table 1, the shrinkage cavity depth of the ingot crown in Example 1 was reduced by 100% and 100%, respectively, and the head cutting amount was reduced by 8.97% and 5.64%. In summary, Example 1 ensures that the slag pool temperature is always higher than the metal pool surface, and sequentially completes the processes of shallowing the liquid metal pool, shrinking the liquid metal pool toward the ingot crown surface, shrinking the liquid metal pool toward the center of the ingot crown surface, and solidifying the ingot crown surface, thereby obtaining a steel ingot with zero shrinkage cavity depth. The utilization rate of the steel ingot obtained in Example 1 is significantly improved.

[0039] However, Comparative Examples 1 and 2 cannot accurately grasp the temperature state near the molten metal pool, and the control parameter changes do not match the solidification process. For example, when the current or melting rate is too small, the temperature inside the molten metal pool is still relatively high, the slag pool temperature is lower than the molten metal pool temperature, the surface of the ingot crown solidifies before its interior, and the solidification order of the ingot crown from bottom to top is disrupted, resulting in shrinkage cavities of different depths.

[0040] Comparison of Example 2 with Comparative Example 3 and Comparative Example 4: The crystallizer in the electroslag remelting device used in this Example 2 has a diameter of 0.92 m and a height of 3.2 m. The consumable electrode has a diameter of 0.72 m and a length of 4 m. The consumable electrode is made of Monel K500 nickel-copper alloy (chemical composition: C 0.066% wt, Si 0.012% wt, Mn 0.76% wt, Al 2.9% wt, Fe 0.94% wt, Cu 29.68% wt, Ti 0.55% wt, Ni 65.32%). The slag system used in this example is ESR2027 (chemical composition: Al2O3 15% wt + CaO 18% wt + MgO 1% wt + CaF2 66% wt). The total weight of the slag is 200 kg.

[0041] In this embodiment 2, an alternating current with a frequency of 50 Hz is used, and the density of the slag is 2550kg / m 3 When the slag pool transfers heat to the consumable electrode, the slag pool temperature T is 1773K, Q1 = 256375W; when the slag pool transfers heat to the gas phase, the slag pool temperature T is 1773K, Q2 = 18024W; when the slag pool transfers heat to the crystallizer, the slag pool temperature T is 1773K, Q3 = 401841W; when the slag pool transfers heat to the ingot, the slag pool temperature T is 1773K, Q4 = 23572W; then the smelting power P0 in the stable smelting stage = Q1 + Q2 + Q3 + Q4 = 700kW. The specific process parameters and steps of the control method of this embodiment 2 are as follows: S1. When the consumable electrode length reaches 0.3 m in the stable melting stage of the ESR process, the ESR process enters the hot capping stage and the slag pool temperature T is continuously measured; S2. In the hot capping stage, reduce the melting power P0=700kW in the stable melting stage to the current melting power P1=585kW (83.54% of P0). When the measured temperature meets , and the temperature drop in two consecutive temperature measurements meets ≤1K / min, the slag temperature tends to be stable, and the smelting power is continued to be maintained for 15 minutes to slowly reduce the temperature of the liquid metal molten pool; In step S2, the thermal conductivity of the slag 3 , the thermal conductivity of metal is 32 , the convection heat transfer coefficient between the slag and the crystallizer 800 , the convective heat transfer coefficient between slag and gas phase 50 , the liquid phase temperature in the crystallizer The gas phase temperature in the crystallizer is 300K. It is 373K.

[0042] In step S2, the thermal balance relationship is calculated to yield X1=P1 / P0≈0.8354.

[0043] S3, reduce the current smelting power to P2=503kW (71.78% of P0), when the measured temperature meets , and the temperature drop in two consecutive temperature measurements meets ≤1K / min, the slag temperature tends to be stable, and then the smelting power is maintained for 15 minutes, so that the liquid metal molten pool slowly becomes shallower and the pure liquid phase area gradually disappears; In step S3, the thermal balance relationship is calculated to yield X2=P2 / P0≈0.7178.

[0044] S4, reduce the current smelting power to P3 = 420kW (60.03% of P0), and the measured temperature meets , and the temperature drop in two consecutive temperature measurements meets the requirement of ≤1K / min, the slag temperature tends to be stable again, and then the smelting power is maintained and smelting is continued for 15 minutes, so that the liquid metal pool shrinks toward the surface of the ingot crown; In step S4, the heat balance relationship is calculated to yield X3=P3 / P0≈0.6003.

[0045] S5, reduce the current smelting power to P4=360kW (51.42% of P0), when the measured temperature meets , the temperature drop meets ≤1K / min for two consecutive temperature measurements, the slag temperature tends to be stable again, and then the smelting power is maintained to continue smelting for 15 minutes, so that the liquid metal pool shrinks to the center of the ingot crown surface; In step S5, the thermal balance relationship is calculated to yield X4=P4 / P0≈0.5142.

[0046] S6, reduce the current smelting power to P5=300kW ( After maintaining this power for 6 minutes, the consumable electrode melting rate is ≤1.0kg / min (10% of the consumable electrode melting rate in the stable melting stage) within 2 consecutive minutes, the consumable electrode clamping device is driven to move upward to separate the consumable electrode from the slag surface, and the melting power is turned off at the same time; S7, keep the cooling water circulation running, and after 30 minutes, the hot capping stage ends; S8. The crystallizer is demoulded to obtain a solidified electroslag remelting ingot, thereby ending the electroslag remelting process.

[0047] In step S2 to step S5, the time interval between two consecutive temperature measurements is 1 minute.

[0048] In steps S2 to S5, the temperature of the slag pool is measured at a position 0.9 times the depth of the slag pool, and the position and depth of the temperature measurements are fixed for multiple times.

[0049] The liquidus temperature of nickel-copper alloy is calculated from the composition of nickel-copper alloy consumable electrode The solidus temperature of nickel-copper alloy is 1603K. It is 1563K.

[0050] In step S2 to step S6, the adjustment time for reducing the current smelting power should be completed in a very short time. In this embodiment, the adjustment time is 3 seconds.

[0051] While maintaining the current melting power, the melting power fluctuation is ≤1.5%.

[0052] The hot capping stage of the electroslag remelting process in this example lasted 128 minutes (excluding the ingot cooling time), resulting in a steel ingot with a diameter of 0.92 m and a height of 2.4 m. The resulting ingot was longitudinally sectioned along its central axis, and the shrinkage cavity depth in the ingot crown was measured. The results are shown in Example 2 in Table 2.

[0053] Comparative Example 3: Other conditions were the same as in Example 2, except that a current reduction strategy was employed during the hot capping phase. The current was continuously and slowly reduced from 16.5 kA to 8 kA over a period of 120 minutes (excluding the ingot cooling time). A steel ingot with a diameter of 0.92 m and a height of 2.4 m was obtained. The resulting ingot was longitudinally sectioned along its central axis, and the shrinkage cavity depth in the ingot crown was measured. The results are shown in Table 2 for Comparative Example 3.

[0054] Comparative Example 4: All other conditions were the same as in Example 2, except that a melting rate reduction strategy was employed during the hot capping stage. The melting rate was continuously and slowly reduced from 11 kg / min to 0.11 kg / min over a period of 120 minutes (excluding the ingot cooling time). A steel ingot with a diameter of 0.92 m and a height of 2.4 m was obtained. The resulting ingot was longitudinally sectioned along its central axis, and the shrinkage cavity depth at the ingot crown was measured. The results are shown in Table 2 for Comparative Example 4.

[0055] Table 2 Parameter comparison of Example 2, Comparative Example 3 and Comparative Example 4

[0056] Comparing Example 2 with Comparative Examples 3 and 4, it can be seen that, under the same process parameters during the stable smelting phase, and consistent remelting materials and slag, as shown in Table 2, the shrinkage cavity depth of the ingot crown in Example 2 was reduced by 79.0%, i.e., (205-43) / 205 = 79.0%; 71.7%, and (152-43) / 152 = 71.7%, respectively; and the amount of head cutting was reduced by 6.75% and 4.54%, respectively. In summary, Example 2 maximizes the slag pool temperature to always be higher than the metal pool surface, sequentially completing the processes of shallowing the liquid metal pool, shrinking the liquid metal pool toward the ingot crown surface, shrinking the liquid metal pool toward the center of the ingot crown surface, and solidifying the ingot crown surface, resulting in a steel ingot with extremely small shrinkage cavity depth. The utilization rate of the steel ingot obtained in Example 2 is significantly improved.

[0057] However, comparative examples 3 and 4 cannot grasp the temperature state near the molten metal pool, and the control parameter changes do not match the solidification process. For example, when the current or melting rate is too small, the temperature inside the molten metal pool is still high, the slag pool temperature is lower than the molten metal pool temperature, the surface of the ingot crown solidifies before its interior, and the solidification order from bottom to top of the ingot crown position is disrupted, resulting in shrinkage cavities with larger depths.

[0058] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for controlling the shrinkage cavity depth of an ingot crown during hot-capping during electroslag remelting, wherein the electroslag remelting process includes an arcing and slag-forming stage, a stable melting stage, and a hot-capping stage, characterized in that: The control method includes: S1. In the stable smelting stage, the consumable electrode length is 10%±2% of the initial consumable electrode length. Entering the hot capping stage, the slag pool temperature T is continuously measured and the liquidus temperature of the nickel-copper alloy is calculated. and the solidus temperature of nickel-copper alloys ; S2. During the hot capping stage, the smelting power of the smelting stage will be stabilized. Reduce to current melting power , , ; for Power regulation coefficient when for Power when When the measured temperature meets , and the temperature drop for two consecutive temperature measurements meets the requirement of ≤1K / min, the slag temperature tends to be stable, and the current smelting power is maintained for 10min~20min; S3, reduce the current smelting power to , , ; for Power regulation coefficient when for Power when When the measured temperature meets , and the temperature drop for two consecutive temperature measurements meets the requirement of ≤1K / min, the slag temperature tends to be stable, and the current smelting power is maintained for 10min~20min; S4, reduce the current smelting power to , , ; for Power regulation coefficient when for Power when When the measured temperature meets , and the temperature drop for two consecutive temperature measurements meets the requirement of ≤1K / min, the slag temperature tends to be stable again, and the current smelting power is maintained for 10min~20min; S5. Reduce the current smelting power to , , ; for Power regulation coefficient when for Power when When the measured temperature meets , and the temperature drop in two consecutive temperature measurements meets the requirement of ≤1K / min, the slag temperature tends to be stable again, and the current smelting power is maintained for 10min~20min to make the liquid metal pool shrink toward the center of the ingot crown surface; S6. Reduce the current smelting power to , , When the melting rate of the consumable electrode is less than 5% to 10% of the melting rate of the consumable electrode in the stable smelting stage within 2 consecutive minutes, the consumable electrode is separated from the slag surface and the smelting power supply is turned off at the same time.

2. The method for controlling the shrinkage cavity depth of the ingot crown during the electroslag remelting process according to claim 1, wherein: In step S2, the smelting power of the smelting stage is stabilized. for: ； Where, is the heat transfer from the slag pool to the consumable electrode, in W; is the heat transfer from the slag pool to the gas phase, unit is W; is the heat transfer from the slag pool to the crystallizer, unit is W; is the heat transfer from the slag pool to the ingot, unit is W; Heat transfer from slag pool to consumable electrode for: ； Where, is the thermal conductivity of the slag, in units of ; T is the slag pool temperature, unit is K; is the solidus temperature of nickel-copper alloy, in K; The depth of the consumable electrode immersed in the slag pool, in m; is the radius of the consumable electrode, in m; Heat transfer from slag pool to gas phase for: ； Where, is the convective heat transfer coefficient between the slag and the gas phase, in units of ; T is the slag pool temperature, unit is K; is the gas phase temperature in the crystallizer, in K; is the mold radius, in m; is the radius of the consumable electrode, in m; Heat transfer from slag pool to crystallizer for: ； Where, is the convection heat transfer coefficient between the slag and the crystallizer, in units of ; T is the slag pool temperature, unit is K; is the liquid phase temperature in the crystallizer, in K; is the mass of slag in the slag pool, in kg; is the density of the slag, in units of ; is the mold radius, in m; Heat transfer from slag pool to ingot for: ； Where, is the thermal conductivity of the metal, in units of ; T is the slag pool temperature, unit is K; is the liquidus temperature of nickel-copper alloy, in K; is the depth of the metal pool, in m; is the mold radius, in m.

3. The method for controlling the shrinkage cavity depth of the hot-capped ingot crown during electroslag remelting as claimed in claim 1, wherein in steps S2 to S5, the time interval between two consecutive temperature measurements is 0.5 min to 1 min.

4. The method for controlling the shrinkage cavity depth of the ingot crown during the electroslag remelting process according to claim 1, wherein: In the steps S2 to S5, the temperature of the slag pool is measured at a position 0.85 to 0.95 times the depth of the slag pool.

5. The method for controlling the shrinkage cavity depth of the ingot crown during the electroslag remelting process according to claim 1, wherein: In the steps S2 to S6, the adjustment time for reducing the current smelting power is less than 5s.

6. The method for controlling the shrinkage cavity depth of the ingot crown during the electroslag remelting process according to claim 1, wherein: In the steps S2 to S5, the current melting power is maintained, and the fluctuation of the melting power is less than 2%.

7. The method for controlling the shrinkage cavity depth of the ingot crown during the electroslag remelting process according to claim 1, wherein: After step S6, the method further includes: S7, keep the cooling water circulation running, and after 30 minutes, the hot capping stage ends; S8. The crystallizer is demoulded to obtain a solidified electroslag remelting ingot, and the electroslag remelting is completed.

Images