Preparation method of retaining ring composite electroslag ingot

Abstract

The invention relates to a preparation method of a retaining ring composite electroslag ingot, belongs to the technical field of electroslag remelting smelting, and solves the problems that in the prior art, a retaining ring forge piece has forging cracks and is poor in surface quality, and an existing composite steel ingot has component difference and is complex in preparation process. According to the preparation method of the retaining ring composite electroslag ingot, the bottom, the main body part and the top of the composite electroslag ingot are made of different materials, and the preparation method comprises the following steps that 1, electrodes of the main body part of the composite electroslag ingot are prepared; step 2, preparing an electrode at the end part of the composite electroslag ingot; step 3, preparation before electroslag remelting of the composite electroslag ingot; 4, sequentially completing remelting of the bottom, the main body part and the top of the composite electroslag ingot in an electrode replacement mode; and 5, cooling solidification and demolding are conducted, specifically, after the steel ingot obtained after smelting is completed is subjected to mold cooling for 5-6 hours in a crystallizer, demolding is conducted, and the composite electroslag ingot with the end part and the main body part made of dissimilar materials is obtained. And the preparation of the retaining ring composite electroslag ingot with high metallurgical quality is realized.

Description

Technical Field

[0001] The invention relates to the technical field of electroslag remelting and smelting, and in particular to a method for preparing a guard ring composite electroslag ingot. Background Art

[0002] As one of the key basic components of thermal power and nuclear power steam turbine units, the working environment of the retaining ring is often subject to high-speed rotation, huge centrifugal force and additional stress generated by other uneven loads, alternating stress from the rotor, and thermal stress during assembly. Therefore, the retaining ring needs to have sufficient strength, toughness, and the ability to resist impact loads. For this reason, high content of Mn and N elements are added to the retaining ring steel. The addition of the above elements greatly improves the various mechanical properties and corrosion resistance of the retaining ring material.

[0003] Since the retaining ring material has a high N content, it is limited by the forging temperature and other factors during the forging process, and certain forging cracks usually appear, which seriously affects the surface quality of the retaining ring forging, and then has a certain impact on the net weight of the forging, hindering the production process of the retaining ring forging.

[0004] In order to avoid cracks at both ends of the forging during the forging process due to the particularity of the material, it is considered to compound a material close to the main material of the guard ring during the preparation of the electroslag ingot. The preparation of the composite electroslag ingot usually adopts the composite casting method, that is, the first molten steel is poured first, and then the second molten steel is poured. The mixed molten steel is cooled in the ingot mold for a period of time to realize the metallurgical interface of the two materials. Since the cooling speed of the ingot mold for the molten steel is relatively high, it takes a long time to realize the metallurgical interface. After the molten steel is mixed, a component gradient can be formed during this long period of time, resulting in a certain difference in the composition of the produced composite ingot; or the pre-processed ingot is preheated and combined with the ingot mold containing high-alloy molten steel to make the two metals composite together. This composite operation is complicated and has high requirements for high-alloy molten steel. At the same time, it is necessary to heat and process the ingot to be wrapped. Summary of the invention

[0005] In view of the above analysis, an embodiment of the present invention aims to provide a method for preparing a guard ring composite electroslag ingot, so as to solve at least one of the problems of forging cracks and poor surface quality in existing guard ring forgings, and composition differences, poor composite quality, and complex preparation process in existing composite steel ingots.

[0006] The embodiment of the present invention provides a method for preparing a composite electroslag ingot with a guard ring, wherein the bottom, the main body and the top of the composite electroslag ingot are made of different materials, and the method comprises the following steps:

[0007] Step 1, preparing the main part of the composite electroslag ingot electrode;

[0008] Step 2, preparing the end electrode of the composite electroslag ingot;

[0009] Step 3, preparation before electroslag remelting composite electroslag ingot: clean the inside of the crystallizer and the bottom water tank, and pre-lay a certain thickness of electrode slices on the bottom water tank as an ingot guide plate, then place the crystallizer on the bottom water tank, and fill the crystallizer with argon. Within 20 minutes after being filled with argon, start adding the initial slag into the crystallizer;

[0010] Step 4, completing the smelting of the bottom, main body and top of the composite electroslag ingot in sequence by replacing the electrodes;

[0011] Step 5, cooling, solidification and demoulding: After the smelting is completed, the steel ingot is cooled in the crystallizer for 5-6 hours, and then demoulded to obtain a composite electroslag ingot with different materials for the end and the main body.

[0012] Furthermore, the smelting process described in step 4 comprises the following steps:

[0013] Step 4-1, charging the furnace: a moment after adding the initial slag, the end electrode obtained in step 2 is welded to the dummy electrode;

[0014] Step 4-2, arcing and slag removal: connect the end electrode welded to the dummy electrode in step 4-1 to an AC power source, start arcing and slag removal, and after all the initial slag added in step 3 is melted, when the end electrode begins to melt, add the remaining slag in batches within 2 hours;

[0015] Step 4-3, bottom smelting of composite electroslag ingot: when the height of the composite electroslag ingot grows to a certain height, cut off the AC power supply, lift the furnace head to a certain height, replace the end electrode of the composite electroslag ingot with the main body electrode obtained in step 1, and lower the furnace head until the head of the main body electrode is immersed in the slag pool for a certain distance;

[0016] Step 4-4, melting the main part of the composite electroslag ingot: connect the AC power supply again to start melting the main part of the guard ring composite steel ingot. When the weight of the main part of the smelted composite steel ingot meets the subsequent material requirements, cut off the AC power supply, lift the furnace head to a certain height, replace the main part electrode with the end electrode, and then lower the furnace head until the head of the end electrode is immersed in the slag pool for a certain distance;

[0017] Step 4-5, top melting of composite electroslag ingot: connect the AC power supply again to start top melting of the guard ring composite ingot, that is, the shrinkage feeding process.

[0018] Specifically, the preparation method of the main electrode of the composite electroslag ingot in step 1 is to use the VOD+VD method to melt molten steel with a chemical composition of 1Mn18Cr18VN, then inject the smelted molten steel into the mold under atmospheric pressure, and demold the molten steel after cooling it in the ingot mold for 5 to 6 hours; send the ejected slender steel ingot with a circular cross-section to a sawing machine, and cut off the entire bottom and a certain distance from the top.

[0019] Exemplarily, the method for preparing the end electrode of the composite electroslag ingot in step 2 is to use the VOD+VD method to melt molten steel with a chemical composition of 304, then inject the molten steel into the mold under atmospheric pressure, and demold the molten steel after cooling in the ingot mold for 11 to 12 hours. Then, the ejected slender steel ingot with a circular cross-section is sent to a sawing machine to cut off the entire bottom and a certain distance from the top.

[0020] Furthermore, the material of the starter plate in step 3 is the same as that of the end electrode of the composite electroslag ingot, the thickness is 100-150 mm, and the diameter is equal to the electrode diameter.

[0021] Preferably, the weight of the initial slag added in step 3 is 30% of the total slag.

[0022] It should be noted that the crystallizer cooling system is turned on before the AC power is turned on in step 4-2. The crystallizer is cooled by water circulation, with an inlet water temperature of 24-26°C, an outlet water temperature of 30-35°C, and a circulating water flow rate of ≥5m 3 / h.

[0023] It is worth noting that the amount of the remaining slag added in batches in step 4-2 is controlled at 70kg to 80kg per time and completed within 2 hours.

[0024] Furthermore, in step 4, the current and voltage parameters during the three stages of smelting of the bottom, main body and top of the composite electroslag ingot are: the voltage is 63~67.5V and the current is 6~8KA in the bottom smelting stage of the composite electroslag ingot; the voltage is 76.5~90V and the current is 17~20KA in the main body smelting stage of the composite electroslag ingot; the voltage is 63~76.5V and the current is 5~16KA in the top smelting stage of the composite electroslag ingot.

[0025] Preferably, the top of the electrode to be smelted is preheated before replacing the electrode in step 4-3 and step 4-4. The conditions for preheating the top are a preheating temperature of 300 to 500° C. for 2 to 3 hours.

[0026] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0027] 1. The present invention uses materials of different materials to be composited at both ends of the guard ring electroslag ingot to prepare a new electroslag ingot, which effectively avoids cracks at both ends of the forging during the forging process of the guard ring forging due to the high content of Mn and N elements in the material, thereby accelerating the product development process;

[0028] The present invention prepares the bottom, main body and top electrodes respectively, and replaces the electrodes in sequence of bottom-main body-top for melting, and obtains a composite electroslag ingot with the end and the main body being of different materials after cooling and demolding; compared with welding a plurality of electrodes together before melting, the alternating melting electrodes heats and melts the metal more evenly, and the metallurgical quality of the product is higher, and the extra steps and material use in the welding electrode process and the waste of materials caused by welding errors are avoided, thereby effectively reducing costs and production complexity; the product research and development process is accelerated, and it is easy to implement and simple to operate; the weight and length of the two ends of the composite electroslag ingot can be adjusted independently, which greatly enriches the manufacturing process of the existing retaining ring forgings.

[0029] 2. The present invention optimizes the thickness of the starter plate and controls the thickness of the starter plate to be 100-150 mm, thereby improving the mechanical strength of the starter plate during the remelting process, while ensuring good thermal conductivity, electrical conductivity and melting uniformity, and maintaining temperature stability during the electroslag remelting process, ensuring uniform solidification of the slag ingot, and improving the metallurgical quality of the composite material;

[0030] The same material as the steel being produced is selected as the material of the ingot guide plate to ensure that the chemical composition of the bottom of the electroslag ingot is consistent with the target electroslag ingot composition, ensure good metallurgical compatibility, reduce interface reactions, and ensure good composite at the bottom of the composite electroslag ingot.

[0031] 3. The present invention optimizes the current and voltage during the three stages of smelting of the bottom, main body and top of the electroslag ingot according to the thickness of the ingot guide plate and the material characteristics of each part of the composite electroslag ingot: the voltage is 63-67.5V and the current is 6-8KA in the bottom smelting stage of the electroslag ingot; the voltage is 76.5-90V and the current is 17-20KA in the main body smelting stage of the electroslag ingot; the voltage is 63-76.5V and the current is 5-16KA in the top smelting stage of the electroslag ingot; the removal efficiency of gas and inclusions and the cleanliness of the composite electroslag ingot are improved.

[0032] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0034] Figure 1 This is a schematic diagram of the bottom of a composite electroslag ingot smelted according to an embodiment of the present invention;

[0035] Figure 2 This is a schematic diagram of the main part of the composite electroslag ingot smelting process according to an embodiment of the present invention;

[0036] Figure 3 It is a schematic diagram of the top of a composite electroslag ingot smelted according to an embodiment of the present invention.

[0037] Reference numerals:

[0038] 1-AC power supply; 2-bottom water tank; 3-crystallizer; 4-bottom of composite electroslag ingot; 5-metal molten pool; 6-slag pool; 7-end electrode; 8-guard ring metal; 9-main body electrode. DETAILED DESCRIPTION

[0039] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0040] A specific embodiment of the present invention discloses a method for preparing a composite electroslag ingot with a retaining ring, wherein the bottom, the main body and the top of the composite electroslag ingot are made of different materials, and the method comprises the following steps:

[0041] Step 1, preparing the main part of the composite electroslag ingot electrode;

[0042] Step 2, preparing the end electrode of the composite electroslag ingot;

[0043] Step 3, preparation before electroslag remelting composite electroslag ingot: clean the inside of the crystallizer 3 and the bottom water tank 2, and pre-lay a certain thickness of electrode slices on the bottom water tank as an ingot guide plate, then place the crystallizer 3 on the bottom water tank 2, and fill the crystallizer with argon. Within 20 minutes after being filled with argon, start adding the initial slag into the crystallizer;

[0044] Step 4-1, charging the furnace: a moment after adding the initial slag, the end electrode 7 obtained in step 2 is welded to the dummy electrode;

[0045] Step 4-2, arcing and slag removal: connect the end electrode 7 welded to the dummy electrode in step 4-1 to the AC power supply 1, start arcing and slag removal, and after all the initial slag added in step 3 is melted, when the end electrode begins to melt, add the remaining slag in batches within 2 hours;

[0046] Step 4-3, melting the bottom 4 of the composite electroslag ingot: when the height of the composite electroslag ingot grows to a certain height, cut off the AC power supply, lift the furnace head to a certain height, replace the end electrode of the composite electroslag ingot with the composite electroslag ingot main body electrode 9 obtained in step 1, and lower the furnace head until the head of the main body electrode is immersed in the slag pool 6 for a certain distance;

[0047] Step 4-4, melting the main part of the composite electroslag ingot: connect the AC power supply 1 again, start melting the main part of the guard ring composite steel ingot, when the weight of the main part of the smelted composite steel ingot meets the subsequent material requirements, cut off the AC power supply, lift the furnace head to a certain height, replace the main part electrode with the end electrode, and then lower the furnace head until the head of the end electrode is immersed in the slag pool 6 for a certain distance;

[0048] Step 4-5, top melting of composite electroslag ingot: connect the AC power supply again to start top melting of the guard ring composite steel ingot, i.e., the shrinkage feeding process;

[0049] Step 5, cooling, solidification and demoulding: After the smelting is completed, the steel ingot is cooled in the crystallizer for 5 to 6 hours, and then demoulded to obtain a composite electroslag ingot with different materials for the end and the main body.

[0050] Specifically, the preparation method of the main electrode of the composite electroslag ingot in step 1 is to use the VOD+VD method to melt molten steel with a chemical composition of 1Mn18Cr18VN, then inject the smelted molten steel into the mold under atmospheric pressure, and demold the molten steel after cooling in the ingot mold for 5-6 hours; send the ejected slender steel ingot with a circular cross-section to a sawing machine, cut off the entire bottom and a certain distance of the top, and then use it as the electrode of the main part of the composite electroslag ingot for use.

[0051] The preparation method of the composite electroslag ingot end electrode in step 2 is to use the VOD+VD method to melt molten steel with a chemical composition of 304, then inject the molten steel into the mold under atmospheric pressure, and demold the molten steel after cooling in the ingot mold for 11-12 hours. Then, the elongated steel ingot with a circular cross-section is sent to a sawing machine, and its entire bottom and a certain distance from the top are cut off to be used as the composite electroslag ingot end electrode.

[0052] The bottom of the slender steel ingot is the lower part that contacts the mold when the steel ingot solidifies. The tail cutting rate (the ratio of the weight of the cut-off part of the electrode bottom to the total weight of the electrode) is 1.8%, and the cutting length of the top of the steel ingot is 50-100mm. The purpose of the cutting is to remove the defective and poor quality blanks in the electrode blank water inlet and the electrode blank riser part. The less the cutting, the higher the utilization rate of the steel ingot. The actual cutting is determined according to the quality of the smelted electroslag ingot.

[0053] It should be noted that the diameter of the electrode of the main part of the composite electroslag ingot and the electrode at the end of the composite electroslag ingot in step 1 and step 2 are the same and match the size of the crystallizer.

[0054] In a possible design, the electrodes at the end of the composite electroslag ingot and the main part of the composite electroslag ingot are slender steel ingots with a circular cross-section of Ф440×3060mm.

[0055] Specifically, in step 3, a non-gas-protected electroslag furnace is used to melt the guard ring composite ingot, and is filled with argon gas to protect the remelting effect; the non-gas-protected electroslag furnace has the advantages of simple structure, strong versatility, low operation and maintenance costs, and easy operation. When combined with argon filling, it can effectively avoid the risk of air oxidation and pollution during the smelting process.

[0056] Furthermore, the electrode slice in step 3 is made of the same material as the circular slice of the end electrode of the composite electroslag ingot, and the thickness of the electrode slice is 100-150 mm, and the diameter is equal to the electrode diameter;

[0057] The electrode slice is used as a starter plate, and its thickness is 4 to 5 times that of the existing conventional electroslag remelting starter plate, which improves the mechanical strength of the starter plate during the remelting process, while ensuring good thermal conductivity, electrical conductivity and melting uniformity, and maintaining temperature stability during the electroslag remelting process, ensuring uniform solidification of the slag ingot, and improving the metallurgical quality of the composite material;

[0058] The same material as the steel being produced is selected as the material of the ingot guide plate to ensure that the chemical composition of the bottom of the electroslag ingot is consistent with the target electroslag ingot composition, ensure good metallurgical compatibility, reduce interface reactions, and ensure good composite at the bottom of the composite electroslag ingot.

[0059] It should be noted that the crystallizer cooling system must be turned on before the AC power is turned on in step 4-2. The crystallizer is cooled by water circulation, with an inlet water temperature of 24-26°C, an outlet water temperature of 30-35°C, and a circulating water flow rate of ≥5m 3 / h.

[0060] Preferably, the weight of the initial slag added in step 3 is 30% of the total slag amount; the amount of the remaining slag added in batches in step 4-2 is controlled to be 70kg-80kg / time, and is completed within 2 hours to accelerate slag melting and achieve rapid establishment of the slag pool;

[0061] The slag material composition is CaF2:Al2O3:MgO=70:25:5, wherein the melting point of the slag is 100-200°C lower than the melting point of the smelting steel, and the slag is ensured to have appropriate electrical conductivity, which can generate sufficient heat to ensure the melting, overheating and smelting of the metal, and improve the electrical efficiency of the electroslag remelting and reduce power consumption.

[0062] It is worth noting that during the steady-state smelting stages of step 4-3, step 4-4 and step 4-5, the argon protection device is placed at the upper mouth of the crystallizer for full argon protection until the end of smelting;

[0063] Furthermore, the current and voltage parameters during the three-stage melting process of the bottom, main body and top of the electroslag ingot in step 4-3, step 4-4 and step 4-5 are as follows: the voltage is 63-67.5V and the current is 6-8KA during the melting stage of the bottom of the electroslag ingot; the voltage is 76.5-90V and the current is 17-20KA during the melting stage of the main body of the electroslag ingot; the voltage is 63-76.5V and the current is 5-16KA during the melting stage of the top of the electroslag ingot. By optimizing the current and voltage during the three-stage melting process of the bottom, main body and top of the electroslag ingot, the removal efficiency of gas and inclusions and the cleanliness of the composite electroslag ingot are improved.

[0064] Exemplarily, before replacing the electrode in step 4-3 and step 4-4, the top of the electrode to be smelted is preheated, and the conditions for the top preheating are a preheating temperature of 300-500°C and a duration of 2-3 hours; the top of the electrode other than the first electrode is preheated to facilitate the exchanged electrode to enter the normal remelting state more quickly, thereby reducing the duration of a large temperature drop in the slag pool due to the lack of heat source input during the exchange of electrodes.

[0065] Specifically, the height of the composite electroslag ingot in step 4-3 increases to a certain height of 500 to 600 mm, which is determined according to the range requirements of the composite transition zone of the composite electroslag ingot product.

[0066] Furthermore, in step 4-3 and step 4-4, the end of the electrode is immersed in the slag pool to a depth of 5 to 10 mm; a suitable depth helps to improve the surface quality and internal quality of the electroslag ingot and reduce the accumulation of inclusions and gas.

[0067] In summary, the present invention adopts materials of different materials composited at both ends of the guard ring electroslag ingot to prepare a new electroslag ingot, which effectively avoids the crack phenomenon at both ends of the forging during the forging process of the guard ring forging due to the high content of Mn and N elements in the material; by optimizing the thickness of the ingot guide plate and controlling the thickness of the ingot guide plate to 100-150mm, the mechanical strength of the ingot guide plate during the remelting process is improved, while ensuring good thermal conductivity, electrical conductivity and melting uniformity, and maintaining temperature stability during the electroslag remelting process, ensuring uniform solidification of the slag ingot, and improving the metallurgical quality of the composite material.

[0068] The preparation method of the guard ring composite electroslag ingot of the present invention is described below with reference to specific embodiments.

[0069] Example 1

[0070] This embodiment provides a method for preparing a guard ring composite electroslag ingot, such as Figure 1 , Figure 2 , Figure 3 shown.

[0071] The specific process includes the following steps:

[0072] Step 1: Use a 40tLF furnace to smelt molten steel with a chemical composition of 0.085% C, 0.62% Si, 19% Mn, 0.015% P, 0.005% S, 18.5% Cr, 1.9% Ni, 0.65% N, and the rest is Fe, and cast it into a number of slender steel ingots with a circular cross-section of Ф440×3060mm. After cooling in the mold for 5 hours, demold the mold, and then process the slender steel ingots with a circular cross-section of Ф440×3060mm, with no obvious oxide layer on the surface, for use as the electrode 9 of the main part of the composite electroslag ingot.

[0073] Step 2: Use a 40tLF furnace to smelt molten steel with a chemical composition of 0.03% C, 0.5% Si, 1.6% Mn, 0.010% P, 0.002% S, 17.5% Cr, 12.3% Ni, 2.6% Mo, 0.12% N, and the rest is Fe. The tapping temperature is 1545°C, and the molten steel is cast into a number of slender steel ingots with a circular cross-section of Ф440×3060mm. After cooling in the mold for 12 hours, the slender steel ingots with a circular cross-section are demolded, and then the slender steel ingots with a circular cross-section are processed into Ф440×3060mm with no obvious oxide layer on the surface, and are used as the end electrode 7 of the composite electroslag ingot for standby use.

[0074] Step 3, preparation before electroslag remelting of composite electroslag ingot: clean the inside of the crystallizer and the bottom water tank, pre-lay 125mm thick slices on the bottom water tank 2, the material of which is the same as the end electrode 7 of the composite electroslag ingot, then sit the crystallizer 3 on the bottom water tank 2, and fill the crystallizer 2 with argon. After waiting for 20 minutes, start to add 750kg of initial slag, which weighs 30% of the total slag.

[0075] Step 4-1, a moment after adding the initial slag, welding the end electrode 7 obtained in step 2 to the dummy electrode;

[0076] Step 4-2, arcing and slag removal: connect the end electrode 7 welded to the dummy electrode in step 4-1 to the AC power supply 1, start arcing and slag removal, and add the remaining slag in batches after the initial melting, with the addition amount controlled at 70 kg / time, until all the slag is added. The whole process takes 2 hours, and a slag pool 6 is formed above the metal molten pool 5 to ensure the purity and quality of the guard ring metal 8;

[0077] Step 4-3, bottom melting of composite electroslag ingot: remelting with end electrode 7 until the height of electroslag ingot increases to 500mm; voltage of electroslag ingot bottom melting stage is 63~67.5V, current is 6~8KA;

[0078] Step 4-4, melting of the main part of the composite electroslag ingot: exchange the electrodes and continue remelting, using the main part electrode 9 to melt until the ingot height reaches 1500mm; the voltage of the electroslag ingot main body melting stage is 76.5~90V, and the current is 17~20KA;

[0079] Step 4-5, composite electroslag ingot top melting: perform the second electrode exchange, use the end electrode 7 to feed the top of the composite steel ingot, and when the ingot height reaches 2300mm, the electroslag remelting process is completed. The voltage of the electroslag ingot top melting stage is 63-76.5V, and the current is 5-16KA.

[0080] Step 5: The steel ingot begins to cool and solidify in the water-cooled crystallizer. After 5 hours, the ingot is demoulded to obtain a composite electroslag ingot with a guard ring having upper and lower parts made of 304 material and a middle part made of 1Mn18Cr18VN material.

[0081] After forging the produced composite steel ingot, the composite interface was cut open in the forging residue for observation. The composite interface was well fused without cracks and obvious stratification, thus achieving the remelting bonding of the composite guard ring electroslag ingot.

[0082] Comparative Example 1

[0083] This embodiment provides a method for preparing a guard ring composite electroslag ingot.

[0084] The specific preparation process is the same as that of Example 1, except that the thickness of the slices laid in step 3 and the voltage and current in the three melting stages are different:

[0085] The thickness of the slices laid in step 3 is 30 mm, the voltage in the bottom smelting stage of the electroslag ingot is 63-67.5 V, and the current is 5-6 KA; the voltage in the main body smelting stage of the electroslag ingot is 81-90 V, and the current is 15-17 KA; the voltage in the top smelting stage of the electroslag ingot is 67.5-76.5 V, and the current is 5-10 KA.

[0086] After the produced composite steel ingot was forged, cracks appeared, and when the composite interface in the forging residue was cut open for observation, stratification occurred at the composite interface.

[0087] Comparative Example 2

[0088] This embodiment provides a method for preparing a guard ring composite electroslag ingot.

[0089] The specific preparation process is as follows:

[0090] Steps 1 to 3 are the same as those in Example 1;

[0091] Step 4, after welding the three electrodes together in the order of end electrode-main electrode-end electrode, arcing and slag melting are started, and smelting is started;

[0092] Step 5: After smelting, the steel ingot begins to cool and solidify in a water-cooled crystallizer and is demolded after 5 hours.

[0093] After the produced composite steel ingot is forged, the composite interface in the forging residue is cut open for observation, and stratification is observed at the composite interface.

[0094] It can be seen from Example 1 and Comparative Example 1 that the thickness of the ingot plate does not meet the requirements of the present invention, resulting in poor metallurgical quality of the composite material and stratification. It can be seen from Example 1 and Comparative Example 2 that welding multiple electrodes together before smelting affects the uniformity of metal melting and reduces the metallurgical quality of the product.

[0095] In summary, the present invention performs electroslag remelting by replacing electrodes, and composites heterogeneous materials at both ends of the guard ring electroslag ingot to prepare a new electroslag ingot, effectively avoiding cracks at both ends of the forging during the forging process of the guard ring forging due to the high content of Mn and N elements in the material; by optimizing the thickness of the ingot guide plate and controlling the thickness of the ingot guide plate to 100-150 mm, the mechanical strength of the ingot guide plate during the remelting process is improved, while ensuring good thermal conductivity, electrical conductivity and melting uniformity, and maintaining temperature stability during the electroslag remelting process, ensuring uniform solidification of the slag ingot, and improving the metallurgical quality of the composite material.

[0096] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a ring-retaining composite electroslag ingot, characterized in that: The bottom, main body and top of the composite electroslag ingot are made of different materials, and include the following steps: Step 1, preparing the main part of the composite electroslag ingot electrode; Step 2, preparing the end electrode of the composite electroslag ingot; Step 3, preparation before electroslag remelting composite electroslag ingot: clean the inside of the crystallizer and the bottom water tank, and pre-lay a certain thickness of electrode slices on the bottom water tank as an ingot guide plate, then place the crystallizer on the bottom water tank, and fill the crystallizer with argon. Within 20 minutes after being filled with argon, start adding the initial slag into the crystallizer; Step 4, remelting the bottom, main body, and top of the composite electroslag ingot in sequence by replacing electrodes; Step 5, cooling, solidification and demoulding: After the smelting is completed, the steel ingot is cooled in the crystallizer for 5-6 hours, and then demoulded to obtain a composite electroslag ingot with different materials for the end and the main body.

2. The preparation method according to claim 1, characterized in that: The smelting process described in step 4 comprises the following steps: Step 4-1, charging the furnace: a moment after adding the initial slag, the end electrode obtained in step 2 is welded to the dummy electrode; Step 4-2, arcing and slag removal: connect the end electrode welded to the dummy electrode in step 4-1 to an AC power source, start arcing and slag removal, and after all the initial slag added in step 3 is melted, when the end electrode begins to melt, add the remaining slag in batches within 2 hours; Step 4-3, bottom smelting of composite electroslag ingot: when the height of the composite electroslag ingot grows to a certain height, cut off the AC power supply, lift the furnace head to a certain height, replace the end electrode of the composite electroslag ingot with the main body electrode obtained in step 1, and lower the furnace head until the head of the main body electrode is immersed in the slag pool for a certain distance; Step 4-4, melting the main part of the composite electroslag ingot: connect the AC power supply again to start melting the main part of the guard ring composite steel ingot. When the weight of the main part of the smelted composite steel ingot meets the subsequent material requirements, cut off the AC power supply, lift the furnace head to a certain height, replace the main part electrode with the end electrode, and then lower the furnace head until the head of the end electrode is immersed in the slag pool for a certain distance; Step 4-5, top melting of composite electroslag ingot: connect the AC power supply again to start top melting of the guard ring composite steel ingot, that is, the shrinkage feeding process.

3. The preparation method according to claim 1, characterized in that: The preparation method of the main electrode of the composite electroslag ingot in step 1 is to use the VOD+VD method to melt molten steel with a chemical composition of 1Mn18Cr18VN, then inject the smelted molten steel into the mold under atmospheric pressure, and demold the molten steel after cooling in the ingot mold for 5 to 6 hours; send the ejected slender steel ingot with a circular cross-section to a sawing machine, and cut off the entire bottom and a certain distance from the top.

4. The preparation method according to claim 1, characterized in that: The method for preparing the end electrode of the composite electroslag ingot in step 2 is to use the VOD+VD method to melt molten steel with a chemical composition of 304, then inject the molten steel into the mold under atmospheric pressure, and demold the molten steel after cooling in the ingot mold for 11 to 12 hours. Then, the slender steel ingot with a circular cross-section is sent to a sawing machine to cut off the entire bottom and a certain distance from the top.

5. The preparation method according to claim 1, characterized in that: The material of the starter plate in step 3 is the same as that of the end electrode of the composite electroslag ingot, with a thickness of 100 to 150 mm and a diameter equal to the electrode diameter.

6. The preparation method according to claim 5, characterized in that: The weight of the initial slag added in step 3 is 30% of the total slag amount.

7. The preparation method according to claim 2, characterized in that: Before turning on the AC power in step 4-2, turn on the crystallizer cooling system. The crystallizer is cooled by water circulation. The inlet water temperature is 24-26°C, the outlet water temperature is 30-35°C, and the circulating water flow rate is ≥5m 3 / h.

8. The preparation method according to claim 7, characterized in that: The amount of the remaining slag added in batches in step 4-2 is controlled at 70 kg to 80 kg per time and completed within 2 hours.

9. The preparation method according to claim 1, characterized in that: In step 4, the current and voltage parameters during the three stages of smelting of the bottom, main body and top of the composite electroslag ingot are: the voltage is 63~67.5V and the current is 6~8KA in the bottom melting stage of the composite electroslag ingot; the voltage is 76.5~90V and the current is 17~20KA in the main body melting stage of the composite electroslag ingot; the voltage is 63~76.5V and the current is 5~16KA in the top melting stage of the composite electroslag ingot.

10. The preparation method according to claim 2, characterized in that: In step 4-3 and step 4-4, the top of the electrode to be smelted is preheated before replacing the electrode. The conditions for the top preheating are a preheating temperature of 300-500° C. and a duration of 2-3 hours.

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