A method for controlling the shrinkage cavity depth of a hot-topped ingot crown in an electroslag remelting process

Abstract

The present application relates to the technical field of electroslag remelting, and particularly relates to a method for controlling shrinkage cavity depth of hot sealing top ing crown in electroslag remelting process, which comprises the following steps: S1, in the stable melting stage, the consumable electrode length is 10%+ / -2% of the initial consumable electrode length; S2, the current melting power is reduced to 80%-90% of the melting power in the stable melting stage; S3, the current melting power is reduced to 70%-75% of the melting power in the stable melting stage; S4, the current melting power is reduced to 60%-65% of the melting power in the stable melting stage; S5, the current melting power is reduced to 50%-55% of the melting power in the stable melting stage; S6, the current melting power is reduced to 40%-45% of the melting power in the stable melting stage, so that the consumable electrode is separated from the surface of the molten slag, and the heat supply is stopped. Through continuous measurement of the temperature of the slag pool, the temperature near the metal molten pool is obtained, the heat field input of the end of the consumable electrode and the temperature distribution characteristics in the crystallizer are accurately grasped, the solidification sequence of the ing crown position is avoided from being disturbed, the shrinkage cavity depth is reduced, and the shrinkage cavity formation is inhibited.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electroslag remelting, and particularly relates to a method for controlling shrinkage cavity depth of hot capping ingot crown in electroslag remelting process. BACKGROUND

[0002] Electroslag remelting is one of the core smelting processes for producing high-quality nickel-copper alloy. Electroslag remelting relies on the resistance heat generated by the current passing through the molten slag to melt the consumable electrode, and the molten metal solidifies into an ingot in a water-cooled mold. The molten slag plays a dual role of heat source and heat preservation during solidification. The overheated molten slag is always located above the liquid metal pool, thereby ensuring the directional solidification sequence of the liquid metal from bottom to top.

[0003] Because the ingot crown surface solidifies before its interior, it will trap isolated liquid metal, resulting in shrinkage cavity generated by solidification shrinkage. This defect will reduce the solidification quality of the ingot crown and must be cut off, increasing the waste loss of head cutting. Therefore, before the end of the electroslag remelting of the nickel-copper alloy, a hot capping process needs to be performed on the metal pool, which aims to continue the progressive solidification sequence of the alloy ingot, gradually shallow the metal pool, reduce the shrinkage cavity depth, reduce the amount of ingot cutting, and improve the ingot yield.

[0004] Currently, the hot capping process of the vacuum consumable smelting of the nickel-copper alloy generally adopts reducing current or reducing melting rate, but the shrinkage cavity of the ingot is still deep and the depth is uncontrollable. The reason is that reducing the current or the melting rate is to adjust the thermal field near the electrode end, and the electrode end is far away from the metal pool. The heat transfer of the melt and the temperature change of the metal pool all need a long response time, and the temperature distribution characteristics near the electrode end cannot timely reflect the temperature distribution characteristics of the metal pool, which makes the ingot solidification significantly lag behind the electrode melting. Especially in the process of large ingot electroslag remelting, the metal pool is in a deep V shape, and the distance between the consumable electrode and the bottom of the metal pool is far, so the lag is more obvious. This leads to a temperature drop lower than expected, which ultimately affects the prediction of the ingot solidification process in the metal pool during the hot capping stage. Therefore, the existing hot capping process cannot avoid the formation of shrinkage cavity, and the solidification quality is also unstable, and the repeatability of the process is poor.

[0005] Therefore, the present application provides a method for controlling shrinkage cavity depth of hot capping ingot crown in electroslag remelting process. SUMMARY

[0006] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present application provides a method for controlling shrinkage cavity depth of hot capping ingot crown in electroslag remelting process, thereby solving the technical problem that the temperature distribution characteristics near the electrode end cannot timely reflect the temperature distribution characteristics of the metal pool, which makes the ingot solidification significantly lag behind the electrode melting, leads to a temperature drop lower than expected, affects the prediction of the ingot solidification process in the metal pool during the hot capping stage, and cannot avoid the formation of shrinkage cavity.

[0007] In order to achieve the above object, the application provides a method for controlling the shrinkage cavity depth of a hot-capped ingot crown in an electroslag remelting process, which comprises the following steps:

[0008] S1. In a stable melting stage, the length of the consumable electrode is 10%±2% of the initial length of the consumable electrode, and the process enters a hot-capping stage, the temperature T of the slag pool is continuously measured, and the liquidus temperature of the nickel-copper alloy is calculated and the solidus temperature of the nickel-copper alloy ;

[0009] S2. In the hot-capping stage, the melting power in the stable melting stage is reduced to the current melting power , , , ; the power adjustment coefficient when ; the power when ;

[0010] When the measured temperature satisfies , and the temperature drop of the continuous two times satisfies ≤1K / min, the slag temperature tends to be stable, and the current melting power is maintained for 10-20 min;

[0011] In step S2, the melting power in the stable melting stage is :

[0012] ;

[0013] In the formula, is the heat transfer amount of the slag pool to the consumable electrode, with the unit of W; is the heat transfer amount of the slag pool to the gas phase, with the unit of W; is the heat transfer amount of the slag pool to the crystallizer, with the unit of W; is the heat transfer amount of the slag pool to the ingot, with the unit of W;

[0014] The heat transfer amount of the slag pool to the consumable electrode in the above formula is :

[0015]

[0016] In the formula, is the thermal conductivity of the slag, with the unit of ; T is the temperature of the slag pool, with the unit of K; is the solidus temperature of the nickel-copper alloy, with the unit of K; is the depth of the consumable electrode immersed in the slag pool, with the unit of m; is the radius of the consumable electrode, with the unit of m;

[0017] Heat transfer from the slag pool to the gas phase is:

[0018] ;

[0019] wherein, is the convective heat transfer coefficient between the molten slag and the gas phase, in W / m2K; ; T is the slag pool temperature, in K; is the gas phase temperature inside the crystallizer, in K; is the crystallizer radius, in m; is the consumable electrode radius, in m;

[0020] Heat transfer from the slag pool to the crystallizer is:

[0021] ;

[0022] wherein, is the convective heat transfer coefficient between the molten slag and the crystallizer, in W / m2K; ; T is the slag pool temperature, in K; is the liquid phase temperature inside the crystallizer, in K; is the mass of the molten slag in the slag pool, in kg; is the density of the molten slag, in kg / m3; ; is the crystallizer radius, in m;

[0023] Heat transfer from the slag pool to the ingot is:

[0024] ;

[0025] wherein, is the thermal conductivity of the metal, in W / mK; ; T is the slag pool temperature, in K; is the liquidus temperature of the nickel-copper alloy, in K; is the metal pool depth, in m; is the crystallizer radius, in m.

[0026] S3, the current smelting power is reduced to , , ; is the power adjustment coefficient when ; is the power when ;

[0027] When the measured temperature satisfies , and the temperature drop of the two consecutive temperature measurements satisfies ≤1K / min, the slag temperature tends to be stable, and the current smelting power is maintained for 10-20 min;

[0028] S4, the current smelting power is reduced to , , ; is the power adjustment coefficient when ; is the power when ;

[0029] When the measured temperature satisfies , and the temperature drop of the two consecutive temperature measurements satisfies ≤1K / min, the slag temperature tends to be stable again, and the current smelting power is maintained for 10-20 min;

[0030] S5, the current smelting power is reduced to , , ; is the power adjustment coefficient when ; is the power when ;

[0031] When the measured temperature satisfies , and the temperature drop of the two consecutive temperature measurements satisfies ≤1K / min, the slag temperature tends to be stable again, and the current smelting power is maintained for 10-20 min, so that the liquid metal bath shrinks to the center of the ingot crown surface;

[0032] In steps S2 to S5, the time interval of the two consecutive temperature measurements is 0.5-1 min;

[0033] In steps S2 to S5, the position of the slag pool temperature measurement is 0.85-0.95 times the depth of the slag pool.

[0034] S6, the current smelting power is reduced to , , When the consumable electrode melting rate is less than 5-10% of the stable smelting stage consumable electrode melting rate within 2 min, the consumable electrode is separated from the surface of the slag, and the smelting power is turned off.

[0035] In steps S2 to S6, the adjustment time of the current smelting power reduction is <5s.

[0036] S7, keep the cooling water circulation continue to run, after 30 min, the hot sealing top stage is finished;

[0037] S8, the crystallizer is demolded, and a solidified electroslag remelted ingot is obtained, and the electroslag remelting is finished.

[0038] The beneficial effects of the present application are:

[0039] The present application provides a method for controlling the shrinkage cavity depth of the hot-topped ingot crown in the electroslag remelting process, which adopts the strategy of alternating melting power reduction and keeping. By continuous measurement of the slag pool temperature, the temperature near the 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, the solidification process of the ingot in the metal pool is mastered in real time, and then the melting power keeping time is controlled, and the hot-topping process is adjusted in time. And through the power keeping for a long time, the slag pool temperature is always higher than the metal pool surface, compared with the traditional hot-topping process, the method maximizes the guarantee of the solidification sequence from bottom to top throughout the solidification ingot, avoids the solidification sequence at the ingot crown position being disturbed, thereby reducing the shrinkage cavity depth, and inhibiting the formation of the ingot crown shrinkage cavity.

[0040] Further, by decreasingly controlling the melting power, the heat input of the slag pool is accurately controlled, the problem that the temperature distribution characteristics near the electrode end cannot timely reflect the temperature distribution characteristics of the metal pool due to the slow response time of the slag pool temperature field and the fast response time of the consumable electrode melting caused by the far distance between the consumable electrode end and the metal pool is avoided, the hysteresis is significantly reduced, the temperature drop conforms to the expectation, and finally the solidification process of the ingot in the hot-topping stage in the electroslag remelting process is predicted. DETAILED DESCRIPTION

[0041] In order to better understand the above technical solutions, the exemplary embodiments of the present application will be described in more detail below. It should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided so that the present application can be more clearly, thoroughly understood and the scope of the present application can be completely conveyed to those skilled in the art.

[0042] The present embodiment gives the specific derivation process of the melting power in the stable melting stage .

[0043] ;

[0044] In the formula, Qs is the heat transfer amount of the slag pool to the consumable electrode, with the unit of W; Qg is the heat transfer amount of the slag pool to the gas phase, with the unit of W; Qc is the heat transfer amount of the slag pool to the crystallizer, with the unit of W; Qm is the heat transfer amount of the slag pool to the ingot, with the unit of W;

[0045] The heat in the ESR process is generated by Joule heat from the slag pool. When the dynamic heat balance in the furnace is reached, the heat is mainly used for heat transfer from the slag pool to the consumable electrode, heat transfer from the slag pool to the gas phase, heat transfer from the slag pool to the crystallizer, and heat transfer from the slag pool to the ingot.

[0046] Heat transfer from the slag pool to the consumable electrode is:

[0047] ;

[0048] wherein, is the thermal conductivity of the molten slag, and is ; T is the temperature of the slag pool, and is K; is the solidus temperature of the nickel-copper alloy, and is K; is the depth of the consumable electrode immersed in the slag pool, and is m; is the radius of the consumable electrode, and is m;

[0049] In 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, and the depth of the consumable electrode immersed in the slag pool in the following examples is 0.001 m.

[0050] Heat transfer from the slag pool to the gas phase is:

[0051] ;

[0052] wherein, is the convective heat transfer coefficient between the molten slag and the gas phase, and is , and is generally 5 ~ 50 ; T is the temperature of the slag pool, and is K; is the temperature of the gas phase in the crystallizer, and is K; is the radius of the crystallizer, and is m; is the radius of the consumable electrode, and is m;

[0053] The convective heat transfer and the radiative heat transfer between the slag pool and the high-temperature gas are considered by using an equivalent heat transfer coefficient. Since the middle part is blocked by the consumable electrode, the contact area between the molten slag and the high-temperature gas is .

[0054] The heat transfer from the slag pool to the crystallizer in the above formula is:

[0055] ;

[0056] wherein, is the heat transfer coefficient between the slag and the crystallizer, and the unit is 500 1200 ; T is the temperature of the slag pool, and the unit is K; is the temperature of the liquid phase in the crystallizer, and the unit is K; is the mass of the molten slag in the slag pool, and the unit is kg; is the density of the molten slag, and the unit is ; is the radius of the crystallizer, and the unit is m;

[0057] Since there is heat transfer by convection between the part of the slag pool in contact with the wall of the crystallizer, the slag pool releases heat to the crystallizer, and the contact area is , that is, .

[0058] The heat transfer amount of the slag pool to the ingot in the above formula is:

[0059] ;

[0060] In the formula, is the thermal conductivity of the metal, and the unit is ; T is the temperature of the slag pool, and the unit is K; is the liquidus temperature of the nickel-copper alloy, and the unit is K; is the depth of the metal pool, and the unit is m; is the radius of the crystallizer, and the unit is m;

[0061] Since the metal pool and the paste zone flow slowly, the heat transfer between the slag pool and the ingot is in the form of heat conduction, and the temperature difference is the temperature to be reduced to meet the power coefficient of this step; the metal pool is actually a cone when it solidifies, so the metal pool covering the ingot is regarded as a cylinder in the calculation process, and therefore the formula of the heat transfer amount of the slag pool to the ingot needs to be corrected, and then the depth of the metal pool is equivalent to , and the calculation of is performed.

[0062] Steps S2 to S6 are a process in which the smelting power gradually decreases, and the process is that the smelting power of the stable smelting stage is gradually decreased, that is, the smelting power of the stable smelting stage is gradually decreased to the current smelting power . .

[0063] This invention also provides two embodiments and four comparative examples of a method for controlling the shrinkage cavity depth of the ingot crown during hot sealing in electroslag remelting: Embodiment 1 and Embodiment 2, and Comparative Examples 1, 2, 3, and 4, as detailed below:

[0064] Comparison of Example 1 with Comparative Examples 1 and 2:

[0065] In Example 1, the crystallizer of the electroslag remelting apparatus has a diameter of 0.73m and a height of 2.8m. The consumable electrode has a diameter of 0.59m and a length of 3m. The material of the consumable electrode is 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 + MgO 2%wt + CaF2 57%wt). The total weight of the slag is 200kg.

[0066] In this embodiment 1, an AC current with a frequency of 50Hz is used, and the density of the molten slag is... 2460 kg / m 3 When heat is transferred from the slag pool to the consumable electrode, the slag pool temperature is T=1750K, and Q1=225028W; when heat is transferred from the slag pool to the gas phase, the slag pool temperature is T=1750K, and Q2=9988W; when heat is transferred from the slag pool to the crystallizer, the slag pool temperature is T=1750K, and Q3=348814W; when heat is transferred from the slag pool to the ingot, the slag pool temperature is T=1750K, and Q4=16504W; therefore, the smelting power in the stable smelting stage is P0=Q1+Q2+Q3+Q4=600kW. The specific process parameters and steps of the control method in this embodiment 1 are as follows:

[0067] S1. When the length of the consumable electrode in the stable melting stage of the electroslag remelting process is 0.3m, the electroslag remelting process enters the hot capping stage, and the slag pool temperature T is continuously measured.

[0068] S2. During the hot capping stage, the smelting power of the smelting stage will be stabilized. =600kW reduced to the current smelting power P1=521kW (86.77% of P0), when the measured temperature meets Furthermore, if the temperature drop meets the requirement of ≤1K / min in two consecutive temperature measurements, the slag temperature tends to stabilize. Continue to maintain the smelting power for 15 minutes to allow the temperature of the molten metal pool to decrease slowly.

[0069] In step S2, the thermal conductivity of the slag It is 4.5 thermal conductivity of the metal is 32 is 32 is 540 is 540 is 50 is 50 is 300K is 300K is 373K.

[0070] is 373K.

[0071] S3, the current smelting power is reduced to , P2=441kW (73.55% of P0), when the measured temperature satisfies , and the temperature drop of continuous two times of temperature measurement satisfies ≤1K / min, the slag temperature tends to be stable, and then the smelting power is kept for 15min, so that the liquid metal pool is slowly shallowed, and the pure liquid phase area gradually disappears;

[0072] In step S3, X2=P2 / P0≈0.7355 is calculated through the heat balance relationship.

[0073] S4, the current smelting power is reduced to , P3=362kW (60.33% of P0), the measured temperature satisfies , and the temperature drop of continuous two times of temperature measurement satisfies ≤1K / min, the slag temperature tends to be stable again, and then the smelting power is kept for 15min to continue smelting, so that the liquid metal pool shrinks to the surface of the ingot crown;

[0074] In step S4, X3=P3 / P0≈0.6033 is calculated through the heat balance relationship.

[0075] S5, the current smelting power is reduced to , P4=313kW (52.21% of P0), when the measured temperature satisfies , the temperature drop of continuous two times of temperature measurement satisfies ≤1K / min, the slag temperature tends to be stable again, and then the smelting power is kept for 15min to continue smelting, so that the liquid metal pool shrinks to the center of the surface of the ingot crown;

[0076] In step S5, X4=P4 / P0≈0.5221 is calculated through the heat balance relationship.

[0077] S6, the current smelting power is reduced to P5 = 240kW (40% of P0). After maintaining this power for 8 minutes, the melting rate of the consumable electrode is ≤0.9kg / min (10% of the melting rate of the consumable electrode during the stable melting stage) for 2 consecutive minutes. Drive the consumable electrode clamping device to move upward so that the consumable electrode is removed from the slag surface, and at the same time turn off the melting power supply.

[0078] S7. Keep the cooling water circulation running. After 30 minutes, the hot capping stage will end.

[0079] S8. The crystallizer is demolded to obtain a solidified electroslag remelted ingot, and the electroslag remelting process is completed.

[0080] In steps S2 to S5, the time interval between two consecutive temperature measurements is 1 minute.

[0081] In steps S2 to S5, the temperature measurement location in the slag pool is 0.9 times the depth of the slag pool, and the measurement location and depth remain unchanged for multiple measurements.

[0082] The liquidus temperature of the nickel-copper alloy was calculated from the composition of the consumable electrode. The solidus temperature of the nickel-copper alloy is 1600K. It is 1567K, here about and The calculations are all existing technologies and will not be described in detail here.

[0083] In steps S2 to S6, the adjustment time for reducing the current melting power should be completed in a very short time. In this embodiment, the adjustment time is 3 seconds.

[0084] Continue to maintain the current smelting power, with fluctuations in smelting power ≤1.5%.

[0085] In Example 1, the electroslag remelting process, specifically the hot capping stage, lasted 109 minutes (excluding ingot cooling time), yielding a steel ingot with a diameter of 0.73 m and a height of 1.95 m. The obtained steel ingot was longitudinally cut along its central axis, and the depth of the shrinkage cavity at the ingot crown was measured. The results are shown in Table 1, Example 1.

[0086] Comparative Example 1, with other conditions the same as Example 1, except that a current reduction strategy was adopted during the hot capping stage, with the current continuously and slowly decreasing from 14kA to 7kA over a period of 105 minutes (excluding ingot cooling time), resulting in a steel ingot with a diameter of 0.73m and a height of 1.95m. The obtained steel ingot was longitudinally cut along its central axis, and the depth of the shrinkage cavity at the ingot crown was measured. The results are shown in Comparative Example 1 in Table 1.

[0087] Comparative Example 2, with other conditions the same as Example 1, differs in that a decreasing melting rate strategy was adopted during the hot capping stage. The melting rate was continuously and slowly reduced from 9 kg / min to 0.9 kg / min, requiring 105 min (excluding ingot cooling time), resulting in a steel ingot with a diameter of 0.73 m and a height of 1.95 m. The obtained steel ingot was longitudinally cut along the central axis, and the depth of the shrinkage cavity at the ingot crown was measured. The results are shown in Comparative Example 2 in Table 1.

[0088] Table 1. Parameter comparison of Example 1, Comparative Example 1, and Comparative Example 2

[0089]

[0090] Comparing Example 1 with Comparative Examples 1 and 2, it can be seen from Table 1 that, under the same process parameters, remelting materials, and slag during the stable smelting stage, the ingot crown shrinkage depth of Example 1 was reduced by 100% and 100%, respectively, and the amount of cut-off material was reduced by 8.97% and 5.64%, respectively. In summary, Example 1 ensured that the slag pool temperature remained consistently higher than the surface of the molten metal pool, sequentially completing the processes of the molten metal pool becoming shallower, shrinking towards the ingot crown surface, shrinking towards the center of the ingot crown surface, and solidifying at the ingot crown surface, thus obtaining a steel ingot with zero shrinkage depth. The utilization rate of the steel ingot obtained in Example 1 was significantly improved.

[0091] Comparative Examples 1 and 2 could not accurately grasp the temperature state near the molten metal pool. The changes in control parameters did not match the solidification process. For example, when the current or melting rate was too low, the internal temperature of the molten metal pool was still high, the temperature of the slag pool was lower than the temperature of the molten metal pool, the surface of the ingot crown solidified before its interior, and the solidification sequence of the ingot crown from bottom to top was disrupted, resulting in shrinkage cavities of varying depths.

[0092] Comparison of Example 2 with Comparative Examples 3 and 4:

[0093] In this embodiment 2, the crystallizer of the electroslag remelting device has a diameter of 0.92m and a height of 3.2m. The consumable electrode has a diameter of 0.72m and a length of 4m. The material of the consumable electrode is 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 embodiment is ESR2027 (chemical composition: Al2O3 15%wt + CaO 18%wt + MgO 1%wt + CaF2 66%wt). The total weight of the slag is 200kg.

[0094] In this embodiment 2, an AC current with a frequency of 50Hz is used, and the density of the molten slag is... 2550kg / m3 When heat is transferred from the slag pool to the consumable electrode, the slag pool temperature T is 1773K, and Q1 = 256375W; when heat is transferred from the slag pool to the gas phase, the slag pool temperature T is 1773K, and Q2 = 18024W; when heat is transferred from the slag pool to the crystallizer, the slag pool temperature T is 1773K, and Q3 = 401841W; when heat is transferred from the slag pool to the ingot, the slag pool temperature T is 1773K, and Q4 = 23572W; therefore, the smelting power P0 in the stable smelting stage is P0 = Q1 + Q2 + Q3 + Q4 = 700kW. The specific process parameters and steps of the control method in this embodiment 2 are as follows:

[0095] S1. When the length of the consumable electrode in the stable melting stage of the electroslag remelting process is 0.3m, the electroslag remelting process enters the hot capping stage, and the slag pool temperature T is continuously measured.

[0096] S2. During the hot capping stage, the smelting power P0 = 700kW in the stable smelting stage is reduced to the current smelting power P1 = 585kW (83.54% of P0). When the measured temperature meets the requirements... Furthermore, if the temperature drop meets the requirement of ≤1K / min in two consecutive temperature measurements, the slag temperature tends to stabilize. Continue to maintain the smelting power for 15 minutes to allow the temperature of the molten metal pool to decrease slowly.

[0097] In step S2, the thermal conductivity of the slag 3 Thermal conductivity of metals 32 The convective heat transfer coefficient between the slag and the crystallizer For 800 The convective heat transfer coefficient between the slag and the gas phase 50 Liquid phase temperature inside the crystallizer The gas phase temperature inside the crystallizer is 300K. It is 373K.

[0098] In step S2, based on the thermal balance calculation, X1 = P1 / P0 ≈ 0.8354.

[0099] S3. Reduce the current smelting power to P2 = 503 kW (71.78% of P0), when the measured temperature meets the requirements. Furthermore, the temperature drop was ≤1K / min after two consecutive temperature measurements, and the slag temperature tended to stabilize. Then, the smelting power was maintained for 15 minutes, causing the liquid metal pool to slowly become shallower and the pure liquid phase region to gradually disappear.

[0100] In step S3, based on the thermal balance calculation, X2 = P2 / P0 ≈ 0.7178.

[0101] S4. Reduce the current smelting power to P3 = 420kW (60.03% of P0), and measure the temperature to meet the requirements. And after two consecutive temperature measurements, the temperature drop met the requirement of ≤1K / min, and the slag temperature stabilized again. Then, the smelting power was maintained and smelting continued for 15 minutes to allow the molten metal pool to shrink toward the surface of the ingot crown.

[0102] In step S4, based on the thermal balance calculation, X3 = P3 / P0 ≈ 0.6003.

[0103] S5. Reduce the current smelting power to P4 = 360kW (51.42% of P0), when the measured temperature meets the requirements. After two consecutive temperature measurements showed a temperature drop of ≤1K / min, the slag temperature stabilized again. The smelting power was then maintained for another 15 minutes to allow the molten metal pool to shrink toward the center of the ingot crown surface.

[0104] In step S5, based on the thermal balance calculation, X4 = P4 / P0 ≈ 0.5142.

[0105] S6. Reduce the current smelting power to P5=300kW ( (40% of the power), after maintaining this power for 6 minutes, within 2 consecutive minutes, the melting rate of the consumable electrode is ≤1.0 kg / min (10% of the melting rate of the consumable electrode in the stable melting stage), drive the consumable electrode clamping device to move upward, so that the consumable electrode is removed from the slag surface, and at the same time turn off the melting power.

[0106] S7. Keep the cooling water circulation running. After 30 minutes, the hot capping stage will end.

[0107] S8. The crystallizer is demolded to obtain a solidified electroslag remelted ingot, thus ending the electroslag remelting process.

[0108] In steps S2 to S5, the time interval between two consecutive temperature measurements is 1 minute.

[0109] In steps S2 to S5, the temperature measurement location in the slag pool is 0.9 times the depth of the slag pool, and the location and depth of the temperature measurement remain fixed for multiple measurements.

[0110] The liquidus temperature of the nickel-copper alloy was calculated from the composition of the nickel-copper alloy consumable electrode. The solidus temperature of the nickel-copper alloy is 1603 K. It is 1563K.

[0111] In steps S2 to S6, the adjustment time for reducing the current melting power should be completed in a very short time. In this embodiment, the adjustment time is 3 seconds.

[0112] While maintaining the current smelting power, the fluctuation in smelting power should be ≤1.5%.

[0113] The total heat sealing top stage of the electroslag remelting process of the example is 128 min (not including ingot cooling time), and a steel ingot with a diameter of 0.92 m and a height of 2.4 m is obtained. The steel ingot obtained is longitudinally split along the central axis, and the shrinkage cavity depth of the ingot crown is measured, and the results are shown in Example 2 of Table 2.

[0114] In Comparative Example 3, other conditions are the same as in Example 2, except that the heat sealing top stage adopts a current decreasing strategy, and the current is continuously and slowly reduced from 16.5 kA to 8 kA, and the required time is 120 min (not including ingot cooling time), and a steel ingot with a diameter of 0.92 m and a height of 2.4 m is obtained. The steel ingot obtained is longitudinally split along the central axis, and the shrinkage cavity depth of the ingot crown is measured, and the results are shown in Comparative Example 3 of Table 2.

[0115] In Comparative Example 4, other conditions are the same as in Example 2, except that the heat sealing top stage adopts a melt rate decreasing strategy, and the melt rate is continuously and slowly reduced from 11 kg / min to 0.11 kg / min, and the required time is 120 min (not including ingot cooling time), and a steel ingot with a diameter of 0.92 m and a height of 2.4 m is obtained. The steel ingot obtained is longitudinally split along the central axis, and the shrinkage cavity depth of the ingot crown is measured, and the results are shown in Comparative Example 4 of Table 2.

[0116] Table 2 Comparison of parameters of Example 2, Comparative Example 3 and Comparative Example 4

[0117]

[0118] Comparing Example 2 with Comparative Examples 3 and 4, under the condition that the process parameters are the same in the stable melting stage, the remelted materials and the molten slag are consistent, as shown in Table 2, the shrinkage cavity depth of the ingot crown of Example 2 is reduced by 79.0%, i.e. (205-43) / 205=79.0%; 71.7%, (152-43) / 152=71.7%; the cutting head amount is reduced by 6.75%, 4.54%. According to the above test results, Example 2 maximizes the guarantee that the temperature of the slag pool is always higher than the surface of the metal melt pool, and sequentially completes the process of the liquid metal melt pool becoming shallower, the liquid metal melt pool shrinking towards the surface of the ingot crown, the liquid metal melt pool shrinking towards the center of the surface of the ingot crown, and the surface of the ingot crown solidifying, to obtain a steel ingot with extremely small shrinkage cavity depth, and the utilization rate of the steel ingot obtained in Example 2 is significantly improved.

[0119] Comparative Examples 3 and 4 cannot grasp the temperature state near the metal melt pool, and the control parameter changes do not match the solidification process, for example, when the current or melt rate is too low, the temperature inside the metal melt pool is still relatively high, the temperature of the slag pool is lower than the temperature of the metal melt pool, the surface of the ingot crown solidifies before the inside of the ingot crown, and the solidification sequence from bottom to top of the ingot crown position is disrupted, resulting in a larger depth of shrinkage cavity.

[0120] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that modifications, substitutions, replacements and variations of the above-described embodiments can be made by those skilled in the art within the scope of the present application.

Claims

1. A method for controlling the depth of shrinkage cavity of a hot-topped ingot crown in an electroslag remelting process, the electroslag remelting process including an arc initiation slag phase, a stable melting phase, and a hot-topping phase, the method comprising: The control method comprises: ​ S1, in the stable melting stage, the consumable electrode length is 10%±2% of the initial consumable electrode length, into the hot sealing top stage, continuously measure the slag pool temperature T, and calculate the liquidus temperature of the nickel-copper alloy and the solidus temperature of the nickel-copper alloy ; S2, at the heat seal top phase, the smelting power of the stable smelting phase is reduced to the current smelting power , , ; power adjustment coefficient when S2 = 1; power when S2 = 0​​​ When the measured temperature satisfies , and the temperature drop of the two consecutive measurements satisfies ≤1 K / min, the slag temperature tends to be stable, and the current smelting power is maintained for 10-20 min. S3, Reduce the current smelting power to , , ; for Power regulation coefficient at that time; for Power at that time; When the measured temperature satisfies , and the temperature drop of the two consecutive measurements satisfies ≤1 K / min, the slag temperature tends to be stable, and the current smelting power is maintained for 10-20 min. S4. Reduce the current smelting power to , , ; for Power regulation coefficient at that time; for Power at that time; When the measured temperature meets , and the temperature drop of the two consecutive measurements meets ≤1 K / min, the slag temperature tends to be stable again, and the current smelting power is maintained for 10-20 min. S5. Reduce the current smelting power to , , ; for Power regulation coefficient at that time; for Power at that time; When the measured temperature meets , and the temperature drop of the two consecutive measurements meets ≤1 K / min, the slag temperature tends to be stable again, and the current smelting power is maintained for 10-20 min to make the liquid metal bath shrink to the center of the ingot crown surface. In the step S2 to step S5, the time interval of two consecutive temperature measurements is 0.5min~1min; S6, reduce the current melting power to , , In the next 2 minutes, when the consumable electrode melting rate is less than 5% to 10% of the stable melting stage consumable electrode melting rate, the consumable electrode is separated from the slag surface, and the melting power is turned off.

2. The method of controlling hot-topped ingot crown shrinkage cavity depth in an electroslag remelting process as claimed in claim 1, wherein, At said step S2, the melting power of the stable melting phase is increased is: ； wherein Qs is the heat transfer amount from the slag pool to the consumable electrode, and the unit is W; Qg is the heat transfer amount from the slag pool to the gas phase, and the unit is W; Qc is the heat transfer amount from the slag pool to the crystallizer, and the unit is W; Qi is the heat transfer amount from the slag pool to the ingot, and the unit is W; Amount of heat transferred from the slag pool to the consumable electrode Is: ； wherein is the thermal conductivity of the slag, in W / mK ; T is the bath temperature in K; T is the bath temperature in K; D is the depth of the consumable electrode submerged in the bath in m; R is the radius of the consumable electrode in m; Heat transfer from the slag pool to the gas phase Is: ； wherein is the convective heat transfer coefficient between the slag and the gas phase, in m2 / s ; T is the temperature of the slag bath, in K; is the temperature of the gas phase inside the crystallizer, in K; is the radius of the crystallizer, in m; is the radius of the consumable electrode, in m; Heat transfer from the slag pool to the crystallizer Is: ； wherein is the convective heat transfer coefficient between the slag and the crystallizer, in units of ; T is the temperature of the slag bath in K; T is the temperature of the slag bath in K; T is the temperature of the slag bath in K; T is the temperature of the slag bath in K; ; T is the temperature of the slag bath in K; Heat transfer from the slag pool to the ingot To: ； wherein K is the thermal conductivity of the metal, in units of T is the temperature of the slag bath, in units of K; T is the liquidus temperature of the nickel-copper alloy, in units of K; D is the depth of the metal bath, in units of m; R is the radius of the crystallizer, in units of m.

3. The method of controlling hot-topped ingot crown shrinkage cavity depth in an electroslag remelting process as claimed in claim 1, wherein, In the step S2 to step S5, the position of the slag pool temperature measurement is 0.85~0.95 times the depth of the slag pool.

4. The method of controlling hot-topped ingot crown shrinkage cavity depth in an electroslag remelting process of claim 1 wherein, In the step S2 to step S6, the adjustment time of the current smelting power reduction is <5s.

5. The method of controlling hot-topped ingot crown shrinkage cavity depth in an electroslag remelting process as claimed in claim 1, wherein, In the step S2 to step S5, the current smelting power is continuously maintained, and the fluctuation of the smelting power is <2%.

6. The method of controlling hot-topped ingot crown shrinkage cavity depth in an electroslag remelting process as claimed in claim 1, wherein, After the step S6, further comprising: S7, keep the cooling water circulation continue to run, after 30min, the hot sealing top stage is ended; S8, the crystallizer is demolded, and the solidified electroslag remelted ingot is obtained, and the electroslag remelting is ended.

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