Method for utilizing ultra-low carbon steel casting residue straight return ladle

Abstract

The present application relates to a kind of utilization methods of ultra-low carbon steel casting residual straight return ladle, the method includes the following steps: step 1: converter blowing end temperature of molten steel ≥1660 ℃, blowing end [C]:0.02%~0.06%, ensure that molten steel enters furnace after argon station temperature ≥1620 ℃, use slide plate or stopper to stop slag during tapping process, control the thickness of ladle slag layer <100mm, ladle clearance is greater than 400mm;Step 2: molten steel argon blowing treatment: step 3: molten steel is transported to RH and is treated with vacuum decarburization, step 4: casting residue is poured before slag: after ladle pouring is finished, ladle casting residue is hoisted to slag turning position by crane, step 5: after slag pouring, ladle casting residue is poured into the next full ladle molten steel by crane, step 6: after molten steel is transported to RH and is treated with vacuum decarburization, step 7: after ladle pouring is finished, ladle casting residue is poured into the next full ladle molten steel after pouring before slag, repeat 4-6 steps can realize uninterrupted continuous casting residue straight return utilization.

Description

Technical Field

[0001] This invention relates to a method, specifically a method for utilizing ultra-low carbon steel casting residue directly returned to the ladle, which belongs to a refining process in the field of iron and steel metallurgy. Background Technology

[0002] In traditional steelmaking processes, ladle residue is typically poured into a slag basin and cooled for over 16 hours before being transported by ladle car to a slag treatment site. After being separated by a heavy hammer, the portion with a high iron content is magnetically separated and returned to the steel plant as scrap. This scrap is then added to a scrap trough via an electric suction cup and remelted into molten steel in a converter or electric furnace. Some steel plants also utilize ladle residue by returning it to the ladle. After 3-6 ladles of residue, it is mixed with molten iron and returned to the converter or electric furnace for remelting. Both of these methods result in long turnover cycles and increase the processing costs of the slag separation process and the burden on the converter. Direct ladle residue return involves adding the residue to the next full ladle of molten steel. After undergoing various ladle refining processes such as argon blowing, LF (Ladle Fluid), and vacuum refining, it is poured back onto the ladle. This method has the shortest process and lowest cost, overcoming the shortcomings of the aforementioned residue utilization methods. However, during the process of directly returning the casting residue to the ladle, the reuse of carbon and oxygen can easily cause foaming of the ladle slag, burn out the argon gas pipe, and cause personal injury accidents, especially for ultra-low carbon steel grades that have not been deoxidized.

[0003] A search of patent documents revealed that Chinese patent application number CN201210272881.3, "A Method for Hot Utilization of Stainless Steel Continuous Casting Residue," discloses the following steps: I. Transporting the ladle containing the residue to the electric furnace charging line, stopping the electric furnace power supply, and opening the electric furnace; II. Transporting and utilizing the ladle by pouring all the slag and molten steel from the ladle into a dephosphorized iron ladle, which is then added to the electric furnace along with the dephosphorized molten iron, serving as raw material for electric furnace smelting of stainless steel. The ratio of continuous casting residue to dephosphorized molten iron is: 2-5 tons of continuous casting residue; 80-120 tons of dephosphorized molten iron; III. Returning the electric furnace and smelting with electricity. This method has the following problems:

[0004] 1. The turnover cycle of casting waste heat returning to the electric furnace for smelting is long.

[0005] 2. Casting residue is used as scrap steel in electric arc furnace smelting, increasing the cost of electric arc furnaces.

[0006] Chinese Patent Application No. CN201210542865.1 discloses a method for treating and utilizing steel casting slag, including cyclical processing steps such as digestion, screening, and magnetic separation. Steam digestion of f-CaO in the casting slag promotes its expansion and pulverization, solving the problem of separating the casting slag from the casting vessel and reducing dust. This invention uses a combination of water-sprayed casting slag and hot-quenched steel slag as feed, leveraging the low f-CaO content of the hot-quenched steel slag to ensure that the final product's f-CaO content meets the needs of the cement and building materials industries. A rod mill process is also employed, resulting in good grinding effect and a relatively uniform and stable product particle size. The slag steel with a grade greater than 80% can be returned to steelmaking, the purified steel particles and magnetically separated powder with a grade greater than 42% can be used in the sintering process, and the steel tailings with an iron content of less than 2% and f-CaO of less than 3% can be used to produce steel slag powder, steel slag cement, building materials, and road materials. This method has the following problems:

[0007] 1. The casting residue needs to be digested, screened, and magnetically separated, which increases the cost of slag-steel separation.

[0008] 2. The processing cycle for recycling casting residues is long.

[0009] 3. Slag steel with 80% iron content is returned to steelmaking, increasing the burden on converter smelting.

[0010] Chinese Patent Application No. 201810207217.8 discloses a method for recovering molten steel from hot-state casting slag returned to the ladle. This method utilizes a holding furnace located in the molten steel receiving bay to receive and transfer multiple ladles of casting slag. The holding furnace's function is to reheat the casting slag, keeping it in a molten state. The slag is processed using mature and advanced drum technology. The remaining molten steel is received by a heated ladle, transported by a transfer trolley to the molten steel receiving bay for filling, desulfurization, and then fed into the converter, achieving hot recovery of the remaining molten steel from the casting slag. This method has the following problems:

[0011] 1. This method can reduce the burden on converter smelting by adding heat to the holding furnace to replenish the slag, but it increases the cost of heat replenishment in the holding furnace.

[0012] 2. After reheating, the casting residue is added to the ladle, desulfurized, and then smelted in the converter, resulting in a long turnover cycle.

[0013] Patent Application No.: 201510700821.0 A method for treating residual molten steel from a ladle discloses directly pouring the residual molten steel into a semi-steel ladle, then mixing the semi-steel, residual molten steel, and slag in the semi-steel ladle into a converter for smelting. This method saves the process of pouring the residual molten steel from the ladle into a slag pot for solidification and then cutting (or screening) it before returning it to the converter for reuse, thus reducing the treatment cost of residual molten steel from the ladle. Controlling the carbon content of the semi-steel in the semi-steel ladle to 2.0-3.5% can avoid violent reactions within the semi-steel ladle. However, this method has the following problems:

[0014] 3. This method reduces the processing cost of sorting casting residue slag, but increases the burden of converter smelting and also increases blowing losses.

[0015] 4. After the molten steel is added to the semi-steel ladle, it needs to be smelted in a converter, resulting in a long turnover cycle.

[0016] Patent application number 202010239300.0 discloses an energy-saving and emission-reduction method for recycling hot-state casting slag. Through a comprehensive review and summary of the feasibility analysis, process design, advantages and disadvantages analysis of recycling steps, process standard formulation, process operation formulation, and post-recycling effect analysis, a practical and feasible method for recycling hot-state casting slag has been developed. Recycling the casting slag improves the steel yield, reduces auxiliary material consumption, promotes rapid slag formation in refining, shortens refining time, and improves refining efficiency. Furthermore, before and after the slag recycling, the inclusions in the molten steel are essentially the same, the gas content decreases slightly, and the steel quality remains stable. Currently, our plant's casting slag recycling rate can reach over 60%. The adoption of casting slag recycling technology has significantly reduced costs, achieved remarkable energy-saving and emission-reduction effects, and yielded good economic and social benefits. However, this method has the following problems:

[0017] 1. This method does not specify the converter endpoint control temperature or endpoint oxygen content.

[0018] 2. This method requires LF refining after the molten steel is poured into the ladle, which increases processing costs for steel grades that do not require LF refining. Furthermore, this method does not treat the molten steel before pouring the molten steel, making it prone to carbon-oxygen reactions and slag overflow accidents. Therefore, a new solution is urgently needed to address these technical problems. Summary of the Invention

[0019] This invention addresses the problems existing in the prior art by providing a method for directly returning ultra-low carbon steel casting residue to the ladle. This technical solution offers a short-process method for directly utilizing ultra-low carbon steel casting residue in the ladle. The process involves converter tapping – ladle argon blowing station – vacuum treatment – ​​continuous casting – ladle casting residue slag removal – casting residue being added to the next full ladle of molten steel – vacuum treatment – ​​continuous casting. This method reduces the traditional ladle casting residue cooling and separation process and the subsequent return to the furnace, eliminating the problems of long ladle casting residue turnover, high slag separation and processing costs, and increased heat burden on the converter. Simultaneously, this method deoxidizes the ladle slag during tapping, removes slag before adding casting residue during the casting residue process, and treats the ladle slag exhaust during vacuum decarburization, reducing the risk of ladle residue loss during return to the furnace and slag overflow accidents.

[0020] To achieve the above objectives, the technical solution of the present invention is as follows: a method for utilizing ultra-low carbon steel casting residue directly returned to the ladle, characterized in that the method includes the following steps:

[0021] Step 1: The final temperature of the molten steel at the converter blowing point is ≥1660℃, and the final temperature [C] is 0.02%-0.06%. Ensure that the temperature of the molten steel when it enters the argon station after the furnace is ≥1620℃. Use a sliding plate or slag plug to block slag during the tapping process, control the slag layer thickness in the ladle to <100mm, and ensure that the ladle clearance is greater than 400mm.

[0022] Step 2: Argon blowing treatment of molten steel: When molten steel enters the station, it is strongly stirred for 3 minutes, and the argon flow rate is 200-400 L / min to ensure that the slag modifier added to the ladle is completely melted.

[0023] Step 3: The molten steel is transferred to RH for vacuum decarburization. During decarburization, the vacuum degree is controlled to be less than 0.27 kPa and the decarburization time is greater than 12 min. During the 5-8 min decarburization period, the slag surface of the ladle is covered by air mist spray. After decarburization, aluminum is added for deoxidation and alloying. The pure degassing time is guaranteed to be greater than 5 min. The molten steel is then continuously cast.

[0024] Step 4: Slag removal before casting: After the ladle pouring is completed, use a crane to lift the ladle of casting residue to the slag removal position.

[0025] Step 5: Use a crane to pour the slag residue into the next full ladle of molten steel, and control the slag residue time to within 8 minutes;

[0026] Step 6: After casting, the ladle of molten steel is transferred to an RH (Reverse Hydrocarbon) facility for vacuum decarburization treatment.

[0027] Step 7: After the ladle pouring is completed, the ladle residue is poured out before the slag is removed and then added to the next full ladle of molten steel. Repeating steps 4-6 can achieve uninterrupted and continuous direct return of the ladle residue.

[0028] As an improvement of this invention, in step 1, 5 kg / t of modified lime is added with the steel stream during the tapping process to thicken the slag. After tapping, 1.2 kg / t of high-alumina slag balls are added to the surface of the molten steel. Adding 5 kg / t of modified lime during tapping increases the basicity of the ladle slag, reduces its fluidity, and decreases oxygen transfer between the steel and slag. Adding 1.2 kg / t of high-alumina deoxidizer to the surface of the molten steel after tapping reduces the oxidizing properties of the ladle slag, preventing carbon-oxygen reactions due to high oxygen content during the casting process, which could lead to foaming and slag overflow.

[0029] As an improvement of the present invention, in step 4, the ladle of casting residue is tilted to a horizontal angle of 85 degrees. After the first casting residue furnace shows slag, wait 10 seconds before returning it to the right position. After the second casting residue furnace shows slag, wait 15 seconds before returning the ladle to the right position.

[0030] The slag removal before casting residue in step 4 of this invention is to avoid a large amount of slag in the molten steel and a thick slag layer after adding casting residue, which could lead to slag suction accidents during the RH vacuum treatment process. The initial 10-second wait before the ladle is returned to center after the casting residue is added, and the subsequent 15-second wait after the casting residue is returned to the furnace before the ladle is returned to center, are designed to control the total slag volume by adjusting the slag removal time based on the number of times the casting residue is used.

[0031] As an improvement of this invention, in step 6, the vacuum degree during decarburization is controlled to be less than 0.27 kPa, and the decarburization time is greater than 12 min. During the 5-8 min decarburization period, the ladle slag surface is covered by aerosol spray. After decarburization, aluminum is added for deoxidation and alloying, ensuring a pure degassing time of greater than 5 min before continuous casting of the molten steel. Covering the ladle slag surface with aerosol spray during the 5-8 min decarburization period promotes surface shrinkage and crack formation in the ladle slag, facilitating the removal of carbon-oxygen reaction products during decarburization and reducing the risk of slag layer foaming and damage to the circulating argon gas pipe.

[0032] Compared with the prior art, the present invention has the following advantages: 1) Through the above control steps, the present invention can ensure the safety of the process of returning the casting residue to the ladle and the RH vacuum treatment process, achieve the shortest recycling cycle of casting residue, the highest thermal efficiency, reduce the smelting burden of the converter, and at the same time, effectively reduce the consumption of steel materials; 2) By performing pre-slag removal operation on the ladle casting residue, the thickness of the ladle slag layer is reduced, eliminating the risk of slag suction accidents in the RH furnace. During the decarburization period of 5-8 minutes, the ladle slag surface is covered by aerosol spray for forced cooling and contraction, eliminating the risk of splashing due to the failure of gas generated by carbon-oxygen reaction to be discharged in time. After processing by this scheme, 5.3 tons of slag and steel can be recovered per furnace. Based on the calculation that the normal casting residue contains 60% molten steel, the consumption of steel materials can be reduced by 2.2 kg / ton of steel. Detailed Implementation

[0033] To enhance understanding of the present invention, the present invention will be described in detail below with reference to embodiments.

[0034] Example 1: A method for utilizing ultra-low carbon steel casting residue directly returned to the ladle, the method comprising the following steps:

[0035] Step 1: The final temperature of the molten steel at the converter blowing point must be ≥1660℃, and the final [C] concentration must be 0.02%-0.06%. Ensure that the temperature of the molten steel entering the argon station after the furnace is ≥1620℃. During the tapping process, use a sliding plate or slag plug to control the slag layer thickness in the ladle to <100mm, and ensure that the ladle clearance is greater than 400mm. In Step 1, 5kg / t of modified lime is added with the steel stream during the tapping process to thicken the slag. After tapping, 1.2kg / t of high-alumina slag balls are added to the surface of the molten steel. Adding 5kg / t of modified lime during the tapping process is to increase the basicity of the ladle slag, reduce its fluidity, and reduce oxygen transfer between the steel and slag. Adding 1.2kg / t of high-alumina deoxidizer to the surface of the molten steel after tapping is to reduce the oxidizing properties of the ladle slag and prevent carbon-oxygen reaction due to high oxygen content during the casting process, which could lead to foaming and slag overflow.

[0036] Step 2: Argon blowing treatment of molten steel: When molten steel enters the station, it is strongly stirred for 3 minutes, and the argon flow rate is 200-400 L / min to ensure that the slag modifier added to the ladle is completely melted.

[0037] Step 3: The molten steel is transferred to RH for vacuum decarburization. During decarburization, the vacuum degree is controlled to be less than 0.27 kPa and the decarburization time is greater than 12 min. During the 5-8 min decarburization period, the slag surface of the ladle is covered by air mist spray. After decarburization, aluminum is added for deoxidation and alloying. The pure degassing time is guaranteed to be greater than 5 min. The molten steel is then continuously cast.

[0038] Step 4: Slag removal before casting: After the ladle pouring is completed, use a crane to lift the ladle of casting residue to the slag removal position. In Step 4, tilt the ladle of casting residue to a horizontal 85-degree angle. After the first casting residue furnace shows slag, wait 10 seconds before returning it to the right position. After the second casting residue furnace shows slag, wait 15 seconds before returning the ladle to the right position.

[0039] The slag removal before casting residue in step 4 of this invention is to avoid a large amount of slag in the molten steel and a thick slag layer after adding casting residue, which could lead to slag suction accidents during the RH vacuum treatment process. The initial 10-second wait before the ladle is returned to center after the casting residue is added, and the subsequent 15-second wait after the casting residue is returned to the furnace before the ladle is returned to center, are designed to control the total slag volume by adjusting the slag removal time based on the number of times the casting residue is used.

[0040] Step 5: Use a crane to pour the slag residue into the next full ladle of molten steel, and control the slag residue time to within 8 minutes;

[0041] Step 6: After casting, the ladle of molten steel is transferred to the RH (Reverse Homogenization) system for vacuum decarburization. In Step 6, the vacuum level is controlled to be less than 0.27 kPa, and the decarburization time is greater than 12 minutes. During the 5-8 minute decarburization period, the ladle slag surface is covered with aerosol spray. After decarburization, aluminum is added for deoxidation and alloying, ensuring a pure degassing time of greater than 5 minutes. The molten steel is then continuously cast. Covering the ladle slag surface with aerosol spray during the 5-8 minute decarburization period promotes slag surface shrinkage and crack formation, facilitating the removal of carbon-oxygen reaction products during decarburization and reducing the risk of slag foaming and damage to the circulating argon gas pipe.

[0042] Step 7: After the ladle pouring is completed, the ladle residue is poured out before the slag is removed and then added to the next full ladle of molten steel. Repeating steps 4-6 can achieve uninterrupted and continuous direct return of the ladle residue.

[0043] Example 2: A method for utilizing ultra-low carbon steel casting residue directly returned to the ladle, the method comprising the following steps:

[0044] Step 1: The final temperature of the molten steel at the converter blowing point must be ≥1660℃, and the final temperature [C] at the blowing point must be 0.02%-0.06%. Ensure that the temperature of the molten steel entering the argon station after the furnace is ≥1620℃. During the tapping process, a sliding plate or slag-blocking plug is used to control the slag layer thickness in the ladle to <100mm, and the ladle clearance to be greater than 400mm. During the tapping process, 5kg / t of modified lime is added with the steel stream to thicken the slag. After tapping, 1.2kg / t of high-alumina slag balls are added to the surface of the molten steel.

[0045] Step 2: Argon blowing treatment of molten steel: When molten steel enters the station, it is strongly stirred for 3 minutes, and the argon flow rate is 200-400 L / min to ensure that the slag modification material added to the ladle is completely melted.

[0046] Step 3: The molten steel is transferred to RH for vacuum decarburization. During decarburization, the vacuum degree is controlled to be less than 0.27 kPa and the decarburization time is greater than 12 min. During the 5-8 min decarburization period, the slag surface of the ladle is covered by air mist spray. After decarburization, aluminum is added for deoxidation and alloying. The pure degassing time is guaranteed to be greater than 5 min. The molten steel is then continuously cast.

[0047] Step 4: Slag removal before casting: After the ladle pouring is completed, use a crane to lift the ladle of casting residue to the slag removal position, tilt the ladle of casting residue to a horizontal 85-degree angle. After the first casting residue heat shows slag, wait 10 seconds before returning it to the upright position. After the second or more casting residue heats show slag, wait 15 seconds before returning the ladle to the upright position.

[0048] Step 5: Use a crane to pour the slag residue into the next full ladle of molten steel, and control the slag residue time to within 8 minutes.

[0049] Step 6: After casting, the ladle of molten steel is transferred to RH for vacuum decarburization. During decarburization, the vacuum degree is controlled to be less than 0.27 kPa, and the deep decarburization time is greater than 12 min. During the 5-8 min decarburization period, the slag surface of the ladle is covered by air mist spray. After decarburization, aluminum is added for deoxidation and alloying. The pure degassing time is guaranteed to be greater than 5 min. The molten steel is then continuously cast.

[0050] Step 7: After the ladle pouring is completed, the ladle residue is poured out before the slag is removed and then added to the next full ladle of molten steel. Repeating steps 4-6 can achieve uninterrupted and continuous direct return of the ladle residue.

[0051] The converter in this embodiment of the invention is a 150t converter, and the steel grade is DN0140E1. The process parameters of this embodiment of the invention are shown in Table 1.

[0052] Table 1 Specific process parameters of the method embodiment of the present invention

[0053]

[0054] After adopting the above scheme, the molten steel surplus is directly cast after hot recycling, shortening the surplus processing cycle, reducing temperature drop, and greatly improving the billet yield. The reuse of surplus steel in the ladle enables the direct recycling of slag and steel generated during steelmaking, reducing processing costs and emissions, and has significant practical implications for improving the comprehensive recycling and utilization level of enterprise resources.

[0055] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention. Equivalent transformations or substitutions made based on the above technical solutions all fall within the scope of protection of the claims of the present invention.

Claims

1. A method for utilizing ultra-low carbon steel casting residue directly returned to the ladle, characterized in that, The method includes the following steps: Step 1: The final temperature of the molten steel at the converter blowing point is ≥1660℃, and the final temperature [C] at the blowing point is 0.02%-0.06%. Ensure that the temperature of the molten steel when it enters the argon station after the furnace is ≥1620℃. Use a sliding plate or slag plug to block slag during the tapping process, control the slag layer thickness in the ladle to <100mm, and ensure that the ladle clearance is greater than 400mm. Step 2: Argon blowing treatment of molten steel: When molten steel enters the station, it is strongly stirred for 3 minutes, and the argon flow rate is 200-400 L / min to ensure that the slag modifier added to the ladle is completely melted. Step 3: The molten steel is transferred to RH for vacuum decarburization. During decarburization, the vacuum degree is controlled to be less than 0.27 kPa and the decarburization time is greater than 12 min. During the 5-8 min decarburization period, the slag surface of the ladle is covered by air mist spraying. After decarburization, aluminum is added for deoxidation and alloying. The pure degassing time is guaranteed to be greater than 5 min. The molten steel is then continuously cast. Step 4: Slag removal before casting: After the ladle pouring is completed, use a crane to lift the ladle of casting residue to the slag removal position. Step 5: Use a crane to pour the slag residue into the next full ladle of molten steel, and control the slag residue time to within 8 minutes; Step 6: After casting, the ladle of molten steel is transferred to an RH (Reverse Hydrocarbon) facility for vacuum decarburization treatment. Step 7: After the ladle pouring is completed, the ladle residue is poured out before the slag is removed and then added to the next full ladle of molten steel. Repeating steps 4-6 can achieve uninterrupted and continuous direct return of the ladle residue.

2. The method for utilizing ultra-low carbon steel casting residue directly returned to the ladle according to claim 1, characterized in that, In step 1, 5 kg / t of modified lime is added along with the steel stream during the tapping process to thicken the slag. After tapping, 1.2 kg / t of high-alumina slag balls are added to the surface of the molten steel.

3. The method for utilizing ultra-low carbon steel casting residue directly returned to the ladle according to claim 2, characterized in that, In step 4, the ladle is tilted to a horizontal 85-degree angle. After the first casting of the ladle, wait 10 seconds after slag is seen and then return it to the upright position. After the second casting of the ladle, wait 15 seconds after slag is seen and then return the ladle to the upright position.

4. The method for utilizing ultra-low carbon steel casting residue directly returned to the ladle according to claim 3, characterized in that, In step 6, the vacuum degree is controlled to be less than 0.27 kPa during decarburization, and the decarburization time is greater than 12 min. During the 5-8 min decarburization period, the slag surface of the ladle is covered by air mist spraying. After decarburization, aluminum is added for deoxidation and alloying, ensuring that the pure degassing time is greater than 5 min, and the molten steel is continuously cast.

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