Method for improving niobium yield of niobium-containing austenite
By reasonably controlling the smelting conditions and the addition method of niobium iron niobium during the AOD converter smelting process, the problem of low niobium yield of austenitic stainless steel containing niobium is solved, and a significant increase in niobium yield and a reduction in smelting cost is achieved.
Patent Information
- Application Number
- CN202411405352.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-10
- Publication Date
- 2025-02-25
AI Technical Summary
The traditional niobium harvesting method of austenitic stainless steel containing niobium has high cost and is not ideal, resulting in high smelting costs and affecting the competitiveness of the company in the market.
By reasonably controlling the water temperature of the steel, slag alkalinity, slag alkalinity, desulfurization alkalinity during the AOD converter smelting process, and adding iron niobium in advance before steel discharge, performing steel discharge operations and LF ladle refining, and fine-tuning the niobium components to meet the casting requirements.
It significantly improves the niobium yield, from 85% of the traditional method to more than 95%, reduces smelting costs, improves the quality and performance of the product, and enhances the market competitiveness of the enterprise.
Smart Images
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Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of stainless steel smelting, and particularly relates to a method for improving the niobium recovery rate of niobium-containing austenite. Background Art
[0002] Niobium is a key grain refining element and a strength enhancing element in steel production. Adding niobium to austenitic stainless steel is beneficial to improving the resistance to intergranular corrosion and mechanical properties at high temperatures. At present, the overall stainless steel market is showing a volatile downward trend. Niobium, as a scarce resource, is not only expensive, but also my country's self-sufficiency in niobium is insufficient, so it has to purchase a large amount of niobium ore resources from overseas.
[0003] The traditional method of recovering niobium from niobium-containing austenitic stainless steel is to alloy niobium by adding ferroniobium and niobium into the LF furnace through steelmaking from the AOD converter. However, this method is not only too costly, but also has a low niobium recovery rate. Therefore, improving the niobium recovery rate of niobium-containing austenitic stainless steel through reasonable and effective methods can not only reduce smelting costs, but also help enterprises survive in the fiercely competitive market. Summary of the invention
[0004] The purpose of the present invention is to provide a method for improving the niobium recovery rate of niobium-containing austenitic stainless steel, so as to solve the problem of low recovery rate of niobium in the traditional method of recovering niobium from niobium-containing austenitic stainless steel.
[0005] The technical solution of the present invention is: a method for improving the yield of niobium-containing austenite, comprising the following steps: Step 1: After the AOD converter smelting of niobium-containing austenitic stainless steel enters the reduction stage, the binary basicity of the reduction slag is controlled to be 1.8-2.0, and the slag is poured after reduction; Step 2: After reduction, AOD converter smelting and desulfurization are carried out to control the binary basicity of AOD converter desulfurization slag, which is 2.2-2.5, and materials are added to ensure the fluidity of the slag; Step 3: After desulfurization, add the required ferroniobium to the bottom of the ladle in advance according to the AOD converter tapping amount and the target niobium composition, and perform tapping operations; Step 4: After steel is tapped, LF ladle refining is carried out. During LF furnace treatment, materials are added to adjust the slag according to the slag viscosity, and then the niobium composition of the molten steel is fine-tuned according to the incoming niobium content to make the molten steel composition meet the casting requirements.
[0006] As a further improvement of the present invention, in step 1, the temperature is controlled to be 1700-1720° C. before the AOD converter smelting of niobium-containing austenitic stainless steel enters the reduction stage.
[0007] As a further improvement of the present invention, in step 1, after the AOD converter smelting of niobium-containing austenitic stainless steel enters the reduction stage, the temperature of the molten steel is controlled to be 1650-1680°C.
[0008] As a further improvement of the present invention, in step one, the amount of slag remaining in the furnace is controlled when pouring the slag, and the amount of slag remaining in the furnace is controlled within 3t.
[0009] As a further improvement of the present invention, in step 2, the added materials are lime and fluorite, and the amount of fluorite added is 17-20% of the mass of the lime.
[0010] As a further improvement of the present invention, in step three, the steel tapping temperature is controlled during the steel tapping operation, and the steel tapping temperature is controlled to be 1630-1650°C.
[0011] As a further improvement of the present invention, in step 4, the material used for slag adjustment is lime or fluorite.
[0012] The beneficial effects of the present invention are as follows: by reasonably controlling the temperature of molten steel, slag basicity, slag retention amount, and AOD converter desulfurization basicity during the reduction stage of the AOD converter, the smelting process is optimized, the smelting efficiency and product quality can be significantly improved, and high-quality and high-performance products can be produced; the addition of lime and fluorite during desulfurization can promote the desulfurization reaction and improve the fluidity of the slag, and the synergistic effect of the two helps to improve the desulfurization efficiency of the AOD converter and the quality of the product; before the steel tapping operation after desulfurization, ferroniobium is added to the bottom of the ladle in advance according to the steel tapping amount of the AOD converter and the target niobium composition, which can ensure the effective addition of niobium elements in steel, thereby improving the performance of the product, optimizing the smelting process, reducing the production cost, and ultimately improving the performance and quality of the steel product; niobium is alloyed during the steel tapping process of the AOD converter, the niobium content is slightly adjusted to the target value after LF slag adjustment, and the slight adjustment of the niobium content during LF furnace treatment not only helps to improve the quality and performance of the product, but also can further optimize the mechanical properties of the alloy, thereby achieving an increase in the yield of niobium-containing austenite niobium.
[0013] This method utilizes the AOD converter steel-tapping operation to alloy niobium, thereby avoiding the influence of the slag layer on the niobium recovery rate. The method of adding ferroniobium is to add ferroniobium to the bottom of the ladle before the AOD converter steel-tapping, and niobium is alloyed during the AOD converter steel-tapping process. Only the niobium composition of the molten steel is fine-tuned in the LF, which effectively solves the problem of low niobium recovery rate of niobium-containing austenite, and avoids the problem of low niobium recovery rate caused by factors such as slag viscosity, stirring, and processing time during the LF furnace alloying process of ferroniobium. The niobium recovery rate is effectively increased from 85% in the previous traditional method to more than 95%, achieving stable and efficient production while effectively reducing the smelting cost of niobium-containing austenite. BRIEF DESCRIPTION OF THE DRAWINGS
[0014] Figure 1 Schematic diagram of the process of this method. DETAILED DESCRIPTION
[0015] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.
[0016] The present invention is further described in detail below with reference to the embodiments.
[0017] Embodiment 1, The first step is the AOD converter smelting reduction stage; Before entering the reduction stage of the AOD converter smelting niobium-containing austenitic stainless steel, temperature measurement and sampling are carried out to control the molten steel temperature at 1700℃; after entering the reduction stage, the molten steel temperature is controlled at 1650℃ after adding reducing materials, and the binary basicity of the reducing slag is controlled at 1.8. After reduction, the slag is poured, and the theoretical slag remaining in the furnace is 2.9t.
[0018] The second step is the AOD converter smelting and desulfurization stage; During the desulfurization stage of the AOD converter, 400 kg of lime and 68 kg of fluorite were added to control the binary basicity of the desulfurized slag to 2.2 and the steel-out temperature to 1630 °C.
[0019] The third step is tapping the AOD converter; The AOD converter smelts 347H steel with a steel output of 110t. Before smelting, 850kg of ferroniobium with a target niobium content of 0.5% is prepared and loaded into ton bags. When the AOD converter taps steel, an overhead crane is used to add 850kg of ferroniobium to the bottom of the ladle, and then the converter performs tapping operations.
[0020] The fourth step is LF ladle refining; First, 361 kg of fluorite was added to the LF to adjust the slag. Then, the composition of the molten steel was fine-tuned according to the incoming niobium content of 0.48%. 22 kg of ferroniobium was added to make the molten steel composition meet the casting requirements.
[0021] Embodiment 2, Before entering the reduction stage of the AOD converter smelting niobium-containing austenitic stainless steel, temperature measurement and sampling are carried out to control the molten steel temperature at 1710℃; after entering the reduction stage, the molten steel temperature is controlled at 1665℃ after adding reducing materials, and the binary basicity of the reducing slag is controlled at 1.9. After reduction, the slag is poured, and the theoretical slag remaining in the furnace is 2.85t.
[0022] The second step is the AOD converter smelting and desulfurization stage; During the desulfurization stage of the AOD converter, 400 kg of lime and 74 kg of fluorite were added to control the binary basicity of the desulfurized slag to 2.35 and the steel-out temperature to 1640 °C.
[0023] The third step is tapping the AOD converter; The AOD converter smelts 347H steel with a steel output of 112t. Before smelting, 880kg of ferroniobium with a target niobium content of 0.5% is prepared and loaded into ton bags. When the AOD converter taps steel, an overhead crane is used to add 880kg of ferroniobium to the bottom of the ladle, and then the converter performs tapping operations.
[0024] The fourth step is LF ladle refining; First, 315 kg of fluorite is added to the LF to adjust the slag, and then the composition of the molten steel is fine-tuned according to the incoming niobium content of 0.49%, among which 35 kg of ferroniobium is added to make the molten steel composition meet the casting requirements.
[0025] Embodiment 3, Before entering the reduction stage of the AOD converter smelting niobium-containing austenitic stainless steel, temperature measurement and sampling are carried out to control the molten steel temperature at 1720°C; after entering the reduction stage, the molten steel temperature is controlled at 1680°C after adding reducing materials, and the binary basicity of the reducing slag is controlled at 2.0. After reduction, the slag is poured, and the theoretical slag remaining in the furnace is 2.8t.
[0026] The second step is the AOD converter smelting and desulfurization stage; During the desulfurization stage of the AOD converter, 400 kg of lime and 80 kg of fluorite are added to control the binary basicity of the desulfurized slag to 2.5 and the steel-out temperature to 1650 °C.
[0027] The third step is tapping the AOD converter; The AOD converter smelts 347H steel with a steel output of 115t. Before smelting, 900kg of ferroniobium with a target niobium content of 0.5% is prepared and loaded into ton bags. When the AOD converter taps steel, an overhead crane is used to add 900kg of ferroniobium to the bottom of the ladle, and then the converter performs tapping operations.
[0028] The fourth step is LF ladle refining; First, add 100 kg of fluorite into LF to adjust the slag, and then fine-tune the composition of the molten steel according to the 0.5% niobium content entering the station, and add 38 kg of ferroniobium to make the molten steel composition meet the casting requirements.
[0029] The outgoing composition of the LF furnace, the amount of ferroniobium added, and the niobium recovery rate in Examples 1-3 are shown in Table 1.
[0030] Depend on Figure 1The comparison between the flow chart of the method and the data in Table 1 shows that the method optimizes the smelting conditions by reasonably controlling the molten steel temperature, slag basicity, slag retention, and AOD converter desulfurization basicity in the AOD converter reduction stage, which is beneficial to improving the niobium yield; according to the AOD converter steel output of 110-115t and the target niobium content of 0.5%, 850-900Kg of ferroniobium is added to the bottom of the ladle in advance, which can ensure the effective addition of niobium element in steel, thereby improving the performance of the product; at the AOD converter output, the niobium content is 0.5%, and the niobium content is 0.5%. During the steelmaking process, an appropriate amount of ferroniobium is added. By alloying niobium, the ferroniobium is prevented from being oxidized by free oxygen by taking advantage of the high steel-making temperature and small amount of slag in the converter, which can effectively increase the niobium recovery rate in niobium-containing steel. After the LF furnace adjusts the slag, the niobium composition of the molten steel is fine-tuned according to the incoming niobium content of 0.48-0.5%, and the niobium content is fine-tuned to the target value to avoid unqualified composition, further optimize the performance of the alloy, and effectively increase the niobium recovery rate of niobium-containing austenite, thereby improving the performance and economy of the material and reducing production costs.
Claims
1. A method for improving the yield of niobium-containing austenite, characterized in that: The following steps are involved: Step 1: After the AOD converter smelting of niobium-containing austenitic stainless steel enters the reduction stage, the binary basicity of the reduction slag is controlled to be 1.8-2.0, and the slag is poured after reduction; Step 2: After reduction, AOD converter smelting and desulfurization are carried out to control the binary basicity of AOD converter desulfurization slag, which is 2.2-2.5, and materials are added to ensure the fluidity of the slag; Step 3: After desulfurization, add the required ferroniobium to the bottom of the ladle in advance according to the AOD converter tapping amount and the target niobium composition, and perform tapping operations; Step 4: After steel is tapped, LF ladle refining is carried out. During LF furnace treatment, materials are added to adjust the slag according to the slag viscosity, and then the niobium composition of the molten steel is fine-tuned according to the incoming niobium content to make the molten steel composition meet the casting requirements.
2. The method for improving the niobium recovery rate of niobium-containing austenite according to claim 1, characterized in that: In step 1, the temperature of the niobium-containing austenitic stainless steel in the AOD converter is controlled at 1700-1720° C. before entering the reduction stage.
3. The method for improving the niobium yield of niobium-containing austenite according to claim 1, characterized in that: In step 1, after the AOD converter smelting of niobium-containing austenitic stainless steel enters the reduction stage, the temperature of the molten steel is controlled to be 1650-1680°C.
4. The method for improving the niobium yield of niobium-containing austenite according to claim 1, characterized in that: In step 1, the amount of slag remaining in the furnace is controlled when pouring slag, and the amount of slag remaining in the furnace is controlled within 3t.
5. The method for improving the yield of niobium-containing austenite according to claim 1, characterized in that: In step 2, the added materials are lime and fluorite, and the amount of fluorite added is 17-20% of the mass of the lime.
6. The method for improving the niobium yield of niobium-containing austenite according to claim 1, characterized in that: In step three, the tapping temperature is controlled during the tapping operation, and the tapping temperature is controlled to be 1630-1650°C.
7. The method for improving the niobium yield of niobium-containing austenite according to claim 1, characterized in that: In step 4, lime or fluorite is used as the material for slag adjustment.