An electroslag remelting method for improving the surface quality of large ingot-shaped titanium-containing steel and controlling burnt elements

Abstract

The present invention belongs to the field of electroslag remelting. More specifically, it especially relates to an electroslag remelting method for improving the surface quality of large-ingot titanium-containing steel grades and controlling burn-out elements. The electroslag ingots produced by this method have no slag groove defects on the surface, and the Ti burn-out ratio at the head and tail of the electroslag ingot is low, meeting the Ti≥5(C+N) requirement; under the premise of meeting the product technical requirements, the product yield is greatly improved. This method uses graphite electrode slag to increase the slag current to 3000A and the voltage to 80V, which can increase the slag temperature to above 1600°C, and the slag pool is active, there is no slag at the bottom, and the slag temperature is high, which is beneficial to improving the surface quality of the electroslag ingot.

Description

Technical Field

[0001] The present invention belongs to the field of electroslag remelting, and more specifically, relates to an electroslag remelting method for improving the surface quality of large ingot-shaped titanium-containing steel and controlling burnt elements. Background Art

[0002] 321 stainless steel is an austenitic stainless steel with properties very similar to 304, but due to the addition of titanium, it has better resistance to intergranular corrosion and high-temperature strength. The addition of titanium effectively controls the formation of chromium carbide. 321 stainless steel has excellent high-temperature stress rupture performance, high-temperature creep resistance, and mechanical properties that are superior to 304 stainless steel. 321 stainless steel has the following characteristics: 1) Excellent resistance to intergranular corrosion; 2) Used for parts that cannot be heat treated after welding; 3) Excellent welding performance and good processing performance. 321 austenitic stainless steel has good corrosion resistance in the atmosphere and is widely used in industries such as petrochemicals, electric power, bridges, and automobiles. Specifically, it is used to manufacture acid-resistant transmission pipelines, large boiler superheaters, reheaters, steam pipes, petrochemical heat exchangers, etc. Summary of the Invention

[0003] The purpose of the present invention is to provide an electroslag remelting method for improving the surface quality of large-ingot titanium-containing steel grade 321 stainless steel and controlling burn-out elements in response to the above-mentioned problems. The electroslag ingots produced by this method have no slag groove defects on the surface, and the Ti burn-out ratio at the head and tail of the electroslag ingot is low, meeting the Ti≥5(C+N) requirement; while meeting the product technical requirements, the product yield is greatly improved.

[0004] The above technical objectives of the present invention are achieved through the following technical solutions:

[0005] An electroslag remelting method for improving the surface quality of large ingot titanium-containing steel and controlling burnt elements, characterized by:

[0006] Step 1. Electrode preparation: The electrode size is 660mm×2700mm. It is sawn and polished before remelting and smelting. It is baked at 550-610℃ for 3-5 hours before smelting.

[0007] Ensure that the electrode surface is free of defects such as severe cracks, heavy skin, flash, scars, etc., and free of impurities such as oxide scale, rust, oil, etc. Sawing and grinding before remelting are to ensure that the electrode rod is flat at both ends.

[0008] Step 2: Crystallizer preparation: Use a 950mm crystallizer and clean the inner wall of the crystallizer of dust and foreign matter before use.

[0009] Ensure that the inner wall of the crystallizer is dry and clean.

[0010] Step 3: Use polishing equipment to polish the copper bottom plate of the bottom water tank to remove surface adhesions, and polish both sides of the 15-20mm thick carbon steel plate clean to see the original color of the metal without any oxide scale;

[0011] Step 4: Place four pieces of arc starter at the center of the carbon steel plate. The arc starter content is 0.8-1.2% of the total slag. Start an arc to form a slag pool.

[0012] Step 5: Fill the crystallizer with argon gas at a flow rate of 28-32m 3 / h, maintain for 9-12 minutes, empty the air in the crystallizer, and adjust the argon flow rate to 8-12m 3 / h, until the smelting is completed;

[0013] Step 6: Prepare slag. Use pre-melted five-element slag. The slag composition is: CaF2 45%-55%, Al2O3 20%-25%, CaO 15%-25%, MgO 3%-7%, TiO2 2%-6%, and the slag amount is 400-500kg.

[0014] Step 7: Power on and start the arc. Use a 500mm graphite electrode for slagging. The slagging current is 1500-3000A and the voltage is 50-80V. Slagging is carried out in a step-by-step ascending mode, and the power of 3000A and 80V is maintained for more than 30 minutes. While powering on and starting the arc, add slag mixed with deoxidizer aluminum particles into the crystallizer. During the slagging period, reduce the opening of the bottom water tank inlet valve and control the outlet water temperature to be ≥40°C.

[0015] Reduce heat loss and ensure slag temperature.

[0016] Step 8: After slagging, enter the smelting stage: 2 hours before smelting, adopt the smelting mode of low current and high voltage, reduce the arc immersion depth of the electrode rod, and quickly increase the slag temperature;

[0017] Minimize steeling as much as possible to avoid the formation of slag grooves.

[0018] Step 9: During the smelting period, the melting rate is controlled at (0.80-0.85)D kg / h, where D is the mold diameter, and the unit of D is mm. Aluminum pellets are added during the smelting process for deoxidation. Depending on the Al and Ti composition of the original electrode, the addition method is as follows: add 0.2-0.3% of the slag to the slag, add 200-300g of aluminum pellets after the slag is finished, and then enter the smelting period; in the early stage of smelting: (200-400)g / 10min, time is 1-2h; in the middle and late stages of smelting: (200-300g) / h, until shrinkage is fed;

[0019] Step 10. Weigh the remaining electrodes using the automatic weighing system. When the weight reaches (0.5-0.6)Dkg, where D is the mold diameter and the unit of D is mm, start feeding. A high current and low voltage three-stage feeding process is used for feeding. The arc burial depth is appropriately increased to reduce the arcing phenomenon. At the same time, aluminum particles are added at a slag volume of 0.05-0.1% every 10 minutes to reduce the burning of Ti at the head of the electroslag ingot while ensuring the quality of feeding.

[0020] Step 11: When the electrode weight is 40-50 kg, the shrinkage feeding is completed, and after cooling for 120-150 minutes, the demoulding operation is performed.

[0021] The present invention has the following characteristics:

[0022] By using 500mm graphite electrodes to slag, increasing the slag current to 3000A and the voltage to 80V, the slag temperature can be raised to above 1600℃. The slag pool is active, there is no raw slag at the bottom, and the slag temperature is high, which is beneficial to improving the surface quality of the electroslag ingot.

[0023] By reducing the opening of the bottom water tank inlet valve during the slagging period, the outlet water temperature of the bottom water tank can be effectively controlled to be ≥40°C at the end of slagging, thereby reducing heat loss, being beneficial to raising the slag temperature, and improving the surface quality of the electroslag ingot;

[0024] By adopting a low current and high voltage smelting mode for 2 hours before smelting, the arc immersion depth of the electrode rod is reduced, the slag temperature is quickly raised, and the steel is minimized, thereby avoiding the formation of slag grooves;

[0025] Examples of setting the traditional current and voltage parameters and the current and voltage parameters of the present invention:

[0026]

[0027] Even if the current and voltage are increased in steps in the traditional process, the electrode rod is inserted into the slag pool to a great depth, the arc is buried deep, and the slag temperature is raised slowly, resulting in serious slag grooves on the bottom surface of the electroslag ingot.

[0028] The present invention adopts a relatively high voltage and low current mode, and the voltage is increased by 22-43V compared with the traditional voltage, which can greatly reduce the depth of the electrode rod inserted into the slag pool and the arc is shallow. Since the electrode rod is shallowly buried, the temperature drop when the slag is melted and the electrode is inserted into the smelting furnace is small, which can quickly increase the slag temperature. In addition, less steel is melted at this stage, thereby avoiding the formation of slag grooves.

[0029] By using pre-melted five-element slag, the slag system has the following components: CaF2 45%-55%, Al2O3 20%-25%, CaO 15%-25%, MgO 3%-7%, TiO2 2%-6%; this slag system is suitable for electroslag remelting of the titanium-containing steel and can ensure the recovery of titanium.

[0030] In order to improve the surface quality of the bottom of the electroslag ingot in the early stage of smelting, high voltage and low current smelting is adopted. The electrode rod is shallowly buried in the arc and the Ti burns seriously. Therefore, a suitable deoxidation system needs to be adopted in the slag and early stage of smelting to reduce the burn of titanium.

[0031] The deoxidation system combined with the pre-melted slag system in step six can ensure that the Ti content at the head and tail of the electroslag ingot meets the technical requirement of Ti≥5(C+N), and the deviation between the head and tail is small.

[0032] The present invention has the following beneficial effects:

[0033] 1. Using graphite electrodes during the slagging stage, operating in a relatively high-voltage, low-current mode during the slagging phase, and adjusting the bottom water tank inlet valve opening to maintain an outlet water temperature of ≥40°C effectively improves the surface quality of the bottom of the electroslag ingot. Conventional slagging and smelting methods for large-sized titanium-containing steels produce deep slag grooves at the bottom of electroslag ingots, making them difficult to properly grind and treat, severely impacting the forging yield, which hovers at 70%-75%. However, electroslag ingots smelted using this method exhibit no noticeable slag grooves below 800mm below the bottom, resulting in excellent surface quality. Simple grinding allows for forging, significantly improving the yield to over 85%, a 10% improvement.

[0034] 2. In the process of improving the surface of electroslag ingots, it is also necessary to consider the control of titanium burnout. Because increasing the melting rate, increasing the slag temperature, and shallowing the arc are all conducive to titanium burnout, in order to make titanium meet product requirements, a suitable deoxidation system must be adopted. The invention adopts the method of adding (0.2-0.3%) slag-amount aluminum particles with the slag, adding 200-300g aluminum particles after the slag is melted, and entering the smelting period; in the early stage of smelting: (200-400)g / 10min, the time is 1-2h; in the middle and late stages of smelting: (200-300g) / h, until shrinkage is fed; during shrinkage, (0.05-0.1%) slag-amount aluminum particles are added every 10min; the deoxidation system is combined with suitable pre-melted slag, and the slag system composition is: CaF2 45%-55%, Al2O3 20%-25%, CaO 15%-25%, MgO 3%-7%, TiO2 2%-6%; it can ensure that the Ti content at the head and tail of the electroslag ingot meets the requirement of Ti≥5(C+N), and the deviation at the head and tail is small. DETAILED DESCRIPTION

[0035] This specific embodiment is merely an explanation of the present invention and is not intended to limit the present invention. After reading this specification, those skilled in the art may make non-creative modifications to this embodiment as needed. However, as long as such modifications are within the scope of the claims of the present invention, they are protected by patent law.

[0036] Example 1

[0037] 1. Electrode preparation: The electrode size is 660mm*2700mm, and it is sawn and polished before remelting and smelting, and baked at 600℃ for 4 hours before smelting;

[0038] 2. Crystallizer preparation: Use 950mm specification crystallizer, and clean the inner wall of the crystallizer of dust and foreign matter before use;

[0039] 3. Use polishing equipment to polish the copper bottom plate of the bottom water tank to remove surface adhesions, and polish both sides of the 20mm thick carbon steel plate clean to see the original color of the metal without any oxide scale;

[0040] 4. Place four pieces of arc starter at the center of the carbon steel plate. The arc starter content is 1% of the total slag. Start an arc to form a slag pool.

[0041] 5. Fill the crystallizer with argon gas at a flow rate of 30m 3 / h, maintain for 10 minutes, empty the air in the crystallizer, and adjust the argon flow rate to 10m 3 / h, until the smelting is completed;

[0042] 6. Prepare slag. Use pre-melted five-element slag with the following composition: CaF2 50%, Al2O3 22%, CaO20%, MgO 5%, TiO2 3%, and the slag amount is 450kg.

[0043] 7. Power on and start the arc. Use a 500mm graphite electrode for slagging. The slagging current is 1500A and the voltage is 80V. Slagging is carried out in a step-by-step manner. The power of 3000A and 80V is maintained for 35 minutes. While starting the arc, add slag mixed with deoxidizer aluminum particles into the crystallizer. During the slagging period, reduce the opening of the bottom water tank inlet valve. After the slagging is completed, control the outlet water temperature at 41°C.

[0044] 8. After slagging is completed, enter the smelting stage: adopt the low current and high voltage smelting mode 2 hours before smelting, reduce the arc immersion depth of the electrode rod, and quickly increase the slag temperature;

[0045] IX. During the smelting period, the melting rate is controlled at 0.8D kg / h; where D is the mold diameter, and the unit of D is mm. At the same time, aluminum pellets are added during the smelting process for deoxidation. The addition method is: add 0.3% of the slag amount of aluminum pellets with the slag, add 200g of aluminum pellets after the slag is finished, and then enter the smelting period; in the early stage of smelting: 200g / 10min, time is 1.5h; in the middle and late stages of smelting: 300g / h, until feeding;

[0046] 10. Weigh the remaining electrodes according to the automatic weighing system.

[0047] When the weight reaches 0.5Dkg, where D is the mold diameter and the unit of D is mm, feeding begins. The three-stage feeding process of high current and low voltage is adopted to appropriately increase the arc immersion depth and reduce the arcing phenomenon. At the same time, aluminum particles are added at a slag volume of 0.05% every 10 minutes to reduce the burning of Ti at the head of the electroslag ingot while ensuring the quality of feeding.

[0048] 11. When the electrode weight is 40kg, stop feeding, cool for 120 minutes, and then perform demoulding.

[0049] Test results:

[0050]

[0051] Example 2

[0052] The difference from Example 1 is the deoxidation system:

[0053] At the same time, aluminum particles are added during the smelting process for deoxidation. The adding method is: add 0.2% of the slag amount of aluminum particles with the slag, add 300g of aluminum particles after the slag is melted, and enter the smelting period; in the early stage of smelting: 400g / 10min, time is 2h; in the middle and late stages of smelting: 200g / h, until shrinkage is compensated.

[0054] Test results:

[0055]

[0056] Example 3

[0057] The difference from Example 1 is the deoxidation system:

[0058] At the same time, aluminum pellets are added during the smelting process for deoxidation. The addition method is: add 0.25% of the slag amount of aluminum pellets with the slag, add 250g of aluminum pellets after the slag is melted, and enter the smelting period; in the early stage of smelting: 300g / 10min, time 1.8h; in the middle and late stages of smelting: 280g / h, until shrinkage is fed;

[0059] Test results:

[0060]

[0061] Example 4

[0062] The difference from Example 1 is the deoxidation system:

[0063] At the same time, aluminum pellets are added during the smelting process for deoxidation. The addition method is: add 0.23% of aluminum pellets to the slag, add 270g of aluminum pellets after the slag is melted, and enter the smelting period; in the early stage of smelting: 330g / 10min, time 1.2h; in the middle and late stages of smelting: 230g / h, until shrinkage is fed;

[0064] Test results:

[0065]

[0066] Example 5

[0067] The difference from Example 1 lies in the slag composition and slag amount: prepare slag material, use pre-melted five-element slag, the slag composition is: CaF2 48%, Al2O3 23%, CaO 20%, MgO 4%, TiO2 5%, and the slag amount is 470kg;

[0068] Test results:

[0069]

[0070] Comparative Example 1

[0071] The difference from Example 1 is the deoxidation system:

[0072] At the same time, aluminum particles are added during the smelting process for deoxidation. The adding method is: add 2% of the slag amount of aluminum particles with the slag, and add 100g / h during the smelting process.

[0073] Test results:

[0074]

[0075] Comparative Example 2

[0076] The difference from Example 1 is that the arc is started during power transmission:

[0077] Power is supplied to start the arc, and 500mm graphite electrodes are used for slagging. The slagging current is 8000A, the voltage is 120V, and the slagging time is 35min while maintaining the power of 8000A and 120V. Slag mixed with deoxidizer aluminum particles is added into the crystallizer at the same time as the power is supplied to start the arc. The opening of the bottom water tank inlet valve is reduced during the slagging period. The outlet water temperature is controlled at 35℃ after the slagging is completed.

[0078] Test results:

[0079]

[0080] The Ti content of the electroslag ingot head that was not prepared by the method of the invention was severely burned, which did not meet the product requirements, and the Ti content of the bottom was at the lower limit of the standard. In addition, due to the poor surface quality and large slag groove depth, the yield rate of the electroslag ingot after forging was low, at about 75%.

[0081] The Ti at both the head and tail of the electroslag ingots prepared by the method of the invention meet the product requirements, and the deviation between the head and tail is small; due to the good surface quality, the yield rate of the electroslag ingot after forging is significantly improved to more than 85%, an increase of at least 10%.

[0082] The contents illustrated in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. Without departing from the scope of the present invention, any improvements and modifications made should be within the scope of protection of the present invention.

Claims

1. An electroslag remelting method for improving the surface quality of large ingot-shaped titanium-containing steel and controlling burnt elements, characterized by: Step 1. Electrode preparation: The electrode size is 660mm×2700mm, and it is sawn and polished before remelting and smelting. It is baked at 550-610℃ for 3-5 hours before smelting. Step 2: Crystallizer preparation: Use a 950mm crystallizer and clean the inner wall of the crystallizer of dust and foreign matter before use; Step 3: Use polishing equipment to polish the copper bottom plate of the bottom water tank to remove surface adhesions, and polish both sides of the 15-20mm thick carbon steel plate clean to see the original color of the metal without any oxide scale; Step 4: Place four pieces of arc starter at the center of the carbon steel plate. The arc starter content is 0.8-1.2% of the total slag. Start an arc to form a slag pool. Step 5: Fill the crystallizer with argon gas at a flow rate of 28-32m 3 / h, maintain for 9-12 minutes, empty the air in the crystallizer, and adjust the argon flow rate to 8-12m 3 / h, until the smelting is completed; Step 6: Prepare slag. Use pre-melted five-element slag. The slag composition is: CaF245%-55%, Al2O3 20%-25%, CaO 15%-25%, MgO 3%-7%, TiO2 2%-6%, and the slag amount is 400-500kg. Step 7: Power on and start the arc. Use a 500mm graphite electrode for slagging. The slagging current is 1500-3000A and the voltage is 50-80V. Slagging is carried out in a step-by-step ascending mode, and the power of 3000A and 80V is maintained for more than 30 minutes. While powering on and starting the arc, add slag mixed with deoxidizer aluminum particles into the crystallizer. During the slagging period, reduce the opening of the bottom water tank inlet valve and control the outlet water temperature to be ≥40°C. Step 8: After slagging, enter the smelting stage: 2 hours before smelting, adopt the smelting mode of low current and high voltage, reduce the arc immersion depth of the electrode rod, and quickly increase the slag temperature; Step 9: During the smelting period, the melting rate is controlled at (0.80-0.85) D kg / h, where D is the diameter of the crystallizer, and the unit of D is mm; at the same time, aluminum particles are added during the smelting process for deoxidation. According to the Al and Ti components of the original electrode, the addition method is: add 0.2-0.3% of the slag amount of aluminum particles with the slag, add 200-300g of aluminum particles after the slag is finished, and then enter the smelting period; in the early stage of smelting: (200-400) g / 10min, time is 1-2h; in the middle and late stages of smelting: (200-300) g / h until shrinkage is fed; Step 10. Weigh the remaining electrodes using the automatic weighing system. When the weight reaches (0.5-0.6)D kg, where D is the mold diameter and the unit of D is mm, start feeding. A high current and low voltage three-stage feeding process is used for feeding. The arc burial depth is appropriately increased to reduce the arcing phenomenon. At the same time, aluminum particles are added at a slag volume of 0.05-0.1% every 10 minutes to reduce the burning of Ti at the head of the electroslag ingot while ensuring the quality of feeding. Step 11: When the electrode weight is 40-50 kg, the shrinkage feeding is completed, and after cooling for 120-150 minutes, the demoulding operation is performed.

2. The electroslag remelting method for improving the surface quality of large ingot titanium-containing steel and controlling burnt elements according to claim 1, characterized in that: Bake at 600℃ for 4 hours before melting.

3. The electroslag remelting method for improving the surface quality of large ingot titanium-containing steel and controlling burnt elements according to claim 1, characterized in that: The arc starter content is 1% of the total slag.

4. The electroslag remelting method for improving the surface quality of large ingot titanium-containing steel and controlling burnt elements according to claim 1 or 2, characterized in that: Fill the crystallizer with argon gas at a flow rate of 30m 3 / h, maintain for 10 minutes, empty the air in the crystallizer, and adjust the argon flow rate to 10m 3 / h until the smelting is completed.

5. The electroslag remelting method for improving the surface quality of large ingot titanium-containing steel and controlling burnt elements according to claim 1 or 2, characterized in that: Prepare slag. Use pre-melted five-element slag with the following composition: CaF2 50%, Al2O3 22%, CaO 20%, MgO 5%, TiO2 3%, and the slag amount is 450kg.

6. The electroslag remelting method for improving the surface quality of large ingot titanium-containing steel and controlling burnt elements according to claim 1 or 2, characterized in that: Prepare slag. Use pre-melted five-element slag. The slag composition is: CaF2 48%, Al2O3 23%, CaO 20%, MgO 4%, TiO2 5%, and the slag amount is 470kg.

7. The electroslag remelting method for improving the surface quality of large ingot titanium-containing steel and controlling burnt elements according to claim 1 or 2, characterized in that: Power was supplied to start the arc, and 500mm graphite electrodes were used for slagging. The slagging current was 1500A and the voltage was 80V. The slagging was carried out in a step-by-step ascending mode, and the power of 3000A and 80V was maintained for 35 minutes. Slag mixed with deoxidizer aluminum particles was added into the crystallizer at the same time as the arc was started. The opening of the bottom water tank inlet valve was reduced during the slagging period. The outlet water temperature was controlled at 41°C after the slagging was completed.

8. The electroslag remelting method for improving the surface quality of large ingot titanium-containing steel and controlling burnt elements according to claim 1 or 2, characterized in that: During the smelting period, the melting rate is controlled at 0.8D kg / h; where D is the diameter of the crystallizer, and the unit of D is mm; at the same time, aluminum particles are added during the smelting process for deoxidation, and the addition method is: 0.3% of the slag amount of aluminum particles is added with the slag, and 200g of aluminum particles are added after the slag is melted, and then the smelting period begins; in the early stage of smelting, the rate is 200g / 10min, the time is 1.5h; in the middle and late stages of smelting, the rate is 300g / h until shrinkage is fed.

9. The electroslag remelting method for improving the surface quality of large ingot titanium-containing steel and controlling burnt elements according to claim 1 or 2, characterized in that: At the same time, aluminum particles are added during the smelting process for deoxidation. The adding method is: add 0.2% of the slag amount of aluminum particles with the slag, add 300g of aluminum particles after the slag is melted, and enter the smelting period; in the early stage of smelting: 400g / 10min, time is 2h; in the middle and late stages of smelting: 200g / h, until shrinkage is compensated.

10. The electroslag remelting method for improving the surface quality of large ingot titanium-containing steel and controlling burnt elements according to claim 1 or 2, characterized in that: When the electrode weight is left at 40 kg, the shrinkage feeding is stopped and the mold is released after cooling for 120 minutes.

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