A process for low cost smelting of duplex stainless steel

Abstract

The application discloses a low-cost smelting duplex stainless steel process, comprising: melting chromium-nickel pig iron in an electric furnace, dephosphorizing the chromium-nickel pig iron melt in the electric furnace, melting high-carbon chromium iron in an alloy melting furnace, mixing the high-carbon chromium iron melt melted in the alloy melting furnace with the dephosphorized molten nickel-containing iron in the electric furnace to prepare a duplex stainless steel mother liquid, AOD decarburization refining, argon blowing and nitrogen control, LF furnace refining and continuous casting. The process uses inexpensive chromium-nickel pig iron as raw material, replaces the expensive pure nickel + dephosphorized molten iron / low-phosphorus scrap steel in the prior art, significantly reduces the smelting cost of duplex stainless steel, effectively reduces the cost under the premise of meeting the product quality, meets the quality and performance requirements of duplex stainless steel products through the dephosphorization process of the electric furnace molten nickel-containing iron and the argon blowing and precise nitrogen control before AOD tapping, melts high-carbon chromium iron in an alloy melting furnace, reduces chromium loss in the electric furnace smelting process, and improves the chromium yield of the whole stainless steel smelting line.

Description

Technical Field

[0001] This invention belongs to the field of duplex stainless steel production technology, specifically relating to a low-cost process for smelting duplex stainless steel. Background Technology

[0002] With the development of laterite nickel ore application technology and the promotion of RKEF process, inexpensive chromium-nickel pig iron has become the main raw material for stainless steel smelting. However, the high content of residual elements such as C, P, S, and Si in nickel pig iron limits its application in stainless steel smelting. In particular, some stainless steel varieties with strict requirements for P and S have to use expensive pure nickel alloys in the smelting process. The price difference between pure nickel and nickel pig iron is 40,000 to 50,000 yuan per ton of nickel, which significantly increases the cost of stainless steel.

[0003] Duplex stainless steel is a ternary Fe-Cr-Ni alloy composed of ferrite (Q phase) and austenite (Y phase), combining the advantages of both ferritic and austenitic stainless steels, and exhibiting excellent resistance to chloride stress corrosion cracking. Because duplex stainless steel requires phosphorus (P) ≤ 0.030%, conventional smelting processes use low-phosphorus stainless steel raw materials and alloys. The main smelting methods are: one is hot metal dephosphorization pretreatment → electric furnace → AOD (Alternating Drying) → continuous casting, where blast furnace hot metal, after dephosphorization pretreatment, is added to the electric furnace, where high-carbon ferrochrome, pure nickel, and other alloys are added; the molten pre-melted liquid is then added to the AOD for smelting; the other is melting low-phosphorus stainless steel scrap in an electric furnace, while simultaneously adding high-carbon ferrochrome, pure nickel, and other alloys. Because existing duplex stainless steel processes all require pure nickel as one of the raw materials, the smelting cost of duplex stainless steel is extremely high. Moreover, because existing duplex stainless steel processes use electric furnaces to melt high-carbon ferrochrome, the chromium yield of the entire stainless steel smelting process is low. In addition, existing duplex stainless steel processes also have the problem of poor dephosphorization, which cannot meet the low phosphorus requirements of duplex stainless steel. Summary of the Invention

[0004] To address the aforementioned technical problems in the existing technology, this invention provides a low-cost process for smelting duplex stainless steel, comprising the following steps:

[0005] S1. Electric Furnace Melting of Chromium-Nickel Pig Iron and In-Furnace Dephosphorization of Molten Chromium-Nickel Pig Iron: High-phosphorus chromium-nickel pig iron raw materials are charged into the electric furnace for melting, and in-furnace dephosphorization is performed on the molten chromium-nickel pig iron to produce low-phosphorus, high-nickel nickel-containing molten iron. The amount of high-phosphorus chromium-nickel pig iron charged is controlled at 100%–120% of the nominal capacity of the electric furnace. The total power consumption of the electric furnace is controlled at 350 kWh–450 kWh per ton of high-phosphorus chromium-nickel pig iron. The basicity of the electric furnace is controlled at 1.9–2.2, and the total amount of lime added is determined based on this basicity. When the power supply to the electric furnace reaches 20%–25% of the total power consumption, lime is added at 15%–20% of the total lime amount. When the power supply to the electric furnace reaches 35%–40% of the total power consumption... When the electric furnace power supply reaches 45%–50% of the total power consumption, add lime at 25%–30% of the total lime supply, and simultaneously open the furnace door oxygen lance to inject oxygen into the molten pool inside the electric furnace; when the electric furnace power supply reaches 60%–65% of the total power consumption, add lime at 20%–30% of the total lime supply, and simultaneously add 8.0 kg–12.0 kg of carbon dust removal balls per ton of high phosphorus chromium nickel pig iron. The carbon dust removal balls are added in batches. During the dephosphorization process, samples are taken to analyze the composition of nickel-containing molten iron. When the P content is less than 0.02%, the electric furnace dephosphorization is completed. Then, add lime at 2%–5% of the total lime supply, and the electric furnace produces new slag before tapping steel.

[0006] S2. Melting high-carbon ferrochrome in an alloy melting furnace: High-carbon ferrochrome is melted in an alloy melting furnace, and the iron is tapped after it is completely melted.

[0007] S3. Preparation of duplex stainless steel mother liquor: The high-carbon ferrochrome melt molten in the alloy melting furnace is mixed with the nickel-containing molten iron after dephosphorization in the electric furnace to form duplex stainless steel mother liquor. The chemical composition of the duplex stainless steel mother liquor is controlled by mass percentage as follows: Cr: 20-26%, Ni: 4.0-6.0%, Si: 0.1-3.0%, C: 2.5-5%, P≤0.025%.

[0008] S4. AOD Decarburization Refining: The duplex stainless steel mother liquor is added to AOD for decarburization refining. Nitrogen gas is blown throughout the AOD smelting process. The slag basicity is controlled at 2.0-2.3, and based on this slag basicity, the total amount of lime added is determined to be 120-125 kg per ton of duplex stainless steel mother liquor. During the top lance blowing period, the amount of lime added is controlled at 30-35 kg per ton of duplex stainless steel mother liquor. After the temperature of the duplex stainless steel mother liquor reaches 1700℃, the remaining lime is added in batches, with the amount of lime added in each batch controlled at 30-35 kg per ton of duplex stainless steel mother liquor. At the end point, carbon samples are taken for analysis. If the carbon content is less than 0.03%, blowing continues for 25 minutes to end the AOD smelting.

[0009] S5. Argon and Nitrogen Control: Argon and nitrogen control are performed before AOD tapping. Argon blowing begins when the temperature reaches 1610–1650℃, with a total argon blowing volume of 4.3–4.7 Nm³ per ton of duplex stainless steel mother liquor. 3 control;

[0010] S6, LF furnace refining and continuous casting: AOD steel slag is discharged into the ladle, and after slag removal, it enters the LF furnace process for further refining. After refining, it is cast into duplex stainless steel billets in the continuous casting process.

[0011] Furthermore, in the above-mentioned low-cost smelting process for duplex stainless steel, in step S1, the total amount of lime added is determined to be 50-55 kg per ton of high-phosphorus chromium-nickel pig iron based on the electric furnace basicity of 1.9-2.2.

[0012] Furthermore, in the above-mentioned low-cost smelting process for duplex stainless steel, in step S1, the carbon content is controlled to be ≥2% and the chromium content to be ≤2% during the dephosphorization operation in the electric furnace, and the temperature of the nickel-containing iron water mother liquor is controlled to be 1400~1550℃.

[0013] Furthermore, in the above-mentioned low-cost process for smelting duplex stainless steel, in step S5, the argon blowing flow rate is set at 1500 m³ / h. 3 / h control, and the argon blowing rate is controlled according to the furnace age of the AOD furnace as follows: when the furnace age is ≤30 cycles, 4.3Nm 3 / t≤Argon blowing rate<4.5Nm 3 / t; When 30 < furnace age ≤ 60 cycles, 4.5 Nm 3 / t≤argon blowing rate<4.6Nm 3 / t; When furnace life > 60 cycles, 4.6 Nm 3 / t≤argon blowing rate≤4.7Nm 3 / t.

[0014] Furthermore, in the aforementioned low-cost process for smelting duplex stainless steel, the chemical composition of the high-phosphorus chromium-nickel pig iron is controlled by mass percentage as follows: C≤5.0%, Si≤5.0%, P≤0.050%, S≤0.20%, Cr≤3.5%, Ni: 3.0%~17.0%; the chemical composition of the high-carbon ferrochrome is controlled by mass percentage as follows: Cr: 48~55%, Si: 0.5~6.5%, C: 6~8%.

[0015] Furthermore, in the above-mentioned low-cost smelting process for duplex stainless steel, in step S4, if the carbon content is greater than 0.03%, the blowing continues, and then a new sample is taken until the carbon content is less than 0.03%, after which the blowing continues for 25 minutes to end the AOD smelting.

[0016] Furthermore, in the above-mentioned low-cost smelting process for duplex stainless steel, in step S1, after the dephosphorization of the electric furnace is completed, 80% of the dephosphorized slag is removed and then lime is added to create new slag for steel tapping.

[0017] Furthermore, in the above-mentioned low-cost smelting process for duplex stainless steel, in step S2, the high-carbon ferrochrome is tapped when the temperature is greater than 1650°C after being melted in the alloy melting furnace.

[0018] Furthermore, in the above-mentioned low-cost process for smelting duplex stainless steel, the alloy melting furnace is a medium-frequency furnace.

[0019] As one specific implementation method, in the above-mentioned low-cost process for smelting duplex stainless steel:

[0020] In step S1, 95 tons of high-phosphorus chromium-nickel pig iron are charged into an electric furnace with a nominal capacity of 90 tons. After melting, the molten chromium-nickel pig iron is dephosphorized in the electric furnace to produce low-phosphorus, high-nickel nickel-containing molten iron. The chemical composition of the high-phosphorus chromium-nickel pig iron is controlled by mass percentage as follows: C = 2.0%, Si = 0.3%, P = 0.040%, S = 0.10%, Cr = 1.7%, Ni = 9.5%. The total power consumption of the electric furnace is controlled at 38950 kWh, the basicity of the electric furnace is controlled at 2.0, and the total amount of lime added is controlled at 5050 kg. When the power supply of the electric furnace reaches 8000 kWh, lime is added. 700 kg of lime was added; when the electric furnace power supply reached 13000 kWh, 1300 kg of lime was added; when the electric furnace power supply reached 18000 kWh, 1500 kg of lime was added, and at the same time, the oxygen lance at the furnace door was opened to inject oxygen into the molten pool inside the electric furnace; when the electric furnace power supply reached 24000 kWh, 1300 kg of lime was added, and 900 kg of carbon dust removal balls were added at the same time, and then added in three batches of 200 kg, 300 kg and 400 kg respectively. After adding the carbon dust removal balls, slag was discharged in front of the furnace. After the slag was discharged, a sample was taken for analysis. The P content was 0.016%. Then 250 kg of lime was added to create new slag for steel tapping.

[0021] In step S2, a medium-frequency furnace is used to melt high-carbon ferrochrome, and the molten iron is tapped after melting.

[0022] In step S3, the high-carbon ferrochrome melt molten in the medium-frequency furnace is mixed with the nickel-containing molten iron after dephosphorization in the electric furnace to prepare duplex stainless steel mother liquor. The chemical composition of the duplex stainless steel mother liquor is controlled by mass percentage as C=3.1%, Si=0.1%, P=0.024%, S=0.07%, Cr=22.3%, and Ni=5.6%.

[0023] In step S4, duplex stainless steel mother liquor is added to AOD for decarburization refining. Nitrogen gas is blown throughout the AOD smelting process, the slag basicity is controlled at 2.2, the total amount of lime added is controlled at 123 kg per ton of duplex stainless steel mother liquor, the amount of lime added during the top lance blowing period is controlled at 33 kg per ton of duplex stainless steel mother liquor, after the temperature of duplex stainless steel mother liquor reaches 1700℃, the remaining lime is added in three batches, the amount of lime added in each batch is controlled at 30 kg per ton of duplex stainless steel mother liquor, the carbon sample is analyzed at the end point, the carbon content is C=0.026%, and the AOD smelting is ended after blowing for another 25 minutes.

[0024] In step S5, the temperature is measured before AOD tapping, and the temperature is 1630℃. The AOD furnace has been used for 39 cycles, and the total argon blowing volume is controlled at 4.5 Nm³. 3 / t;

[0025] In step S6, AOD steel slag is discharged into the ladle, and after slag removal, it enters the LF furnace process for further refining. After refining, it is cast into duplex stainless steel slabs in the continuous casting process.

[0026] The low-cost process for smelting duplex stainless steel of the present invention has the following advantages and beneficial effects:

[0027] 1. Using inexpensive chromium-nickel pig iron as raw material, instead of the expensive pure nickel + dephosphorized molten iron / low phosphorus scrap steel in the existing technology, significantly reduces the smelting cost of duplex stainless steel, and can effectively reduce costs while meeting product quality requirements;

[0028] 2. A dephosphorization process for nickel-containing molten iron in electric furnaces was developed, and nitrogen was precisely controlled by argon blowing before tapping using AOD (Alternating Oxygen Demand) to meet the quality and performance requirements of duplex stainless steel products.

[0029] 3. Use an alloy melting furnace to melt high-carbon ferrochrome to reduce chromium loss during electric furnace smelting and improve the chromium yield of the entire stainless steel smelting line;

[0030] 4. The dephosphorization pretreatment process for blast furnace hot metal has been reduced, thereby simplifying the process flow and improving thermal efficiency. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] The process route of the low-cost smelting method for duplex stainless steel of the present invention is as follows: melting chromium-nickel pig iron in an electric furnace → dephosphorizing the molten chromium-nickel pig iron in an electric furnace + melting high-carbon ferrochrome in an alloy melting furnace → mixing the molten high-carbon ferrochrome with the dephosphorized nickel-containing molten iron in an electric furnace and adding it to an AOD furnace → LF refining → continuous casting, including the following steps:

[0033] S1: Electric furnace melting of chromium-nickel pig iron and in-furnace dephosphorization of molten chromium-nickel pig iron. High-phosphorus chromium-nickel pig iron raw materials are charged into the electric furnace for melting, and the molten chromium-nickel pig iron undergoes in-furnace dephosphorization to produce low-phosphorus, high-nickel nickel-containing molten iron. The chemical composition of the high-phosphorus chromium-nickel pig iron is controlled by mass percentage as follows: C≤5.0%, Si≤5.0%, P≤0.050%, S≤0.20%, Cr≤3.5%, Ni: 3.0%~17.0%. The amount of high-phosphorus chromium-nickel pig iron charged is controlled at 100%~120% of the nominal capacity of the electric furnace. The total power consumption of the electric furnace is controlled at 350kWh~450kWh per ton of high-phosphorus chromium-nickel pig iron. The basicity of the electric furnace is controlled at 1.9~2.2, and the total amount of lime added is determined based on the basicity of the electric furnace. When the power supply of the electric furnace reaches 20%~25% of the total power consumption, 15%~20% of the total amount of lime is added. When the electric furnace power supply reaches 35%–40% of the total power consumption, add lime at 24%–28% of the total lime content. When the electric furnace power supply reaches 45%–50% of the total power consumption, add lime at 25%–30% of the total lime content, and simultaneously open the furnace door oxygen lance to inject oxygen into the molten pool inside the electric furnace. When the electric furnace power supply reaches 60%–65% of the total power consumption, add lime at 20%–30% of the total lime content, and simultaneously add 8.0 kg–12.0 kg of carbon dust removal balls per ton of high-phosphorus chromium-nickel pig iron. The carbon dust removal balls are added in batches. During the dephosphorization process, samples are taken to analyze the composition of nickel-containing molten iron. When the P content is less than 0.02%, the electric furnace dephosphorization is completed. Then, add lime at 2%–5% of the total lime content, and the electric furnace produces new slag before tapping steel.

[0034] S2: High-carbon ferrochrome is melted in an alloy melting furnace. The high-carbon ferrochrome is melted in an alloy melting furnace, and the molten iron is tapped after thorough melting. The chemical composition of the high-carbon ferrochrome is controlled by mass percentage as follows: Cr: 48–55%, Si: 0.5–6.5%, C: 6–8%.

[0035] S3: Preparation of duplex stainless steel mother liquor. The high-carbon ferrochrome molten liquid melted in the alloy melting furnace is mixed with nickel-containing molten iron after dephosphorization in the electric furnace to form the duplex stainless steel mother liquor. The chemical composition of the duplex stainless steel mother liquor is controlled by mass percentage as follows: Cr: 20–26%, Ni: 4.0–6.0%, Si: 0.1–3.0%, C: 2.5–5%, P≤0.025%.

[0036] S4: AOD Decarburization Refining. Duplex stainless steel mother liquor is added to AOD for decarburization refining. Nitrogen gas is blown throughout the AOD smelting process. The slag basicity is controlled at 2.0–2.3, and based on the slag basicity, the total amount of lime added is determined to be 120–125 kg per ton of duplex stainless steel mother liquor. During the top-lance blowing period, the amount of lime added is controlled at 30–35 kg per ton of duplex stainless steel mother liquor. After the temperature of the duplex stainless steel mother liquor reaches 1700℃, the remaining lime is added in batches, with each batch adding 30–35 kg per ton of duplex stainless steel mother liquor to ensure stable furnace temperature and prevent lime accumulation. At the endpoint, carbon samples are taken for analysis. If the carbon content is less than 0.03%, blowing continues for 25 minutes, ending the AOD smelting. If the carbon content is greater than 0.03%, blowing continues, and samples are taken again, until the carbon content is less than 0.03%, at which point blowing can continue for another 25 minutes before ending the AOD smelting.

[0037] S5: Argon and Nitrogen Control. Argon and nitrogen control are performed before AOD tapping. Argon blowing begins when the temperature reaches 1610–1650℃, with a blowing flow rate of 1500 m³ / h. 3 / h control, the total argon blowing volume is 4.3~4.7Nm per ton of duplex stainless steel mother liquor. 3 Control the argon blowing rate according to the furnace age of the AOD furnace as follows: when the furnace age is ≤30 cycles, 4.3 Nm³. 3 / t≤Argon blowing rate<4.5Nm 3 / t; When 30 < furnace age ≤ 60 cycles, 4.5 Nm 3 / t≤argon blowing rate<4.6Nm 3 / t; When furnace life > 60 cycles, 4.6 Nm 3 / t≤argon blowing rate≤4.7Nm 3 / t, which can meet the requirement that the N content in duplex stainless steel products is 1500ppm~1700ppm.

[0038] S6: LF furnace refining and continuous casting. AOD steel slag is discharged into the ladle, and after slag removal, it enters the LF furnace process for further refining. After refining, it is cast into duplex stainless steel billets in the continuous casting process.

[0039] Preferably, in the low-cost smelting process of duplex stainless steel of the present invention, the alloy melting furnace is a medium-frequency furnace.

[0040] Furthermore, in the above-mentioned low-cost smelting process for duplex stainless steel, in step S1, the total amount of lime added is determined to be 50-55 kg per ton of high-phosphorus chromium-nickel pig iron based on the electric furnace basicity of 1.9-2.2.

[0041] Furthermore, in the low-cost smelting process of duplex stainless steel of the present invention, during the dephosphorization operation in the electric furnace, the carbon content is controlled to be ≥2%, the chromium content to be ≤2%, and the temperature of the nickel-containing iron water mother liquor is controlled to be 1400~1550℃.

[0042] Furthermore, in the low-cost smelting process of duplex stainless steel of the present invention, after the dephosphorization of the electric furnace is completed, 80% of the dephosphorized slag is removed and then lime is added to create new slag for steel tapping.

[0043] Preferably, in the low-cost smelting process of duplex stainless steel of the present invention, the high-carbon ferrochrome is tapped when the temperature is greater than 1650°C after being melted in the alloy melting furnace.

[0044] Preferably, in the low-cost smelting process of duplex stainless steel of the present invention, the weight of the duplex stainless steel mother liquor is controlled to be 50-80% of the final smelting volume of the duplex stainless steel molten steel.

[0045] The following detailed description of the low-cost process for smelting duplex stainless steel according to the present invention, with reference to specific embodiments, is provided below.

[0046] Example 1

[0047] Example 1 of this invention is used to smelt and prepare duplex stainless steel of grade S32205. Its chemical composition, by mass percentage, is: C≤0.03%, Si≤1.0%, Mn≤2.0%, P≤0.030%, S≤0.020%, Cr: 21.00%~24.00%, Ni: 1.0%~10.0%, Mo: 0.3%~5.0%, N: 800ppm~3000ppm, with the balance being iron and unavoidable residual elements. The process route is: electric furnace melting of chromium-nickel pig iron → electric furnace dephosphorization of chromium-nickel pig iron molten liquid + alloy melting furnace melting of high-carbon ferrochrome → mixing of high-carbon ferrochrome molten liquid with nickel-containing molten iron after electric furnace dephosphorization and adding to AOD furnace → LF refining → continuous casting. Specifically, it includes:

[0048] S11: 95 tons of high-phosphorus chromium-nickel pig iron are charged into an electric furnace with a nominal capacity of 90 tons. After melting, the molten chromium-nickel pig iron is dephosphorized in the electric furnace to produce low-phosphorus, high-nickel nickel-containing molten iron. The chemical composition of the high-phosphorus chromium-nickel pig iron is controlled by mass percentage as follows: C=2.0%, Si=0.3%, P=0.040%, S=0.10%, Cr=1.7%, Ni=9.5%. The total power consumption of the electric furnace is controlled at 38950 kWh, the basicity of the electric furnace is controlled at 2.0, and the total amount of lime added is controlled at 5050 kg. When the power supply of the electric furnace reaches 8000 kWh, 8 kg of lime is added. 00kg; when the electric furnace power supply reaches 14000kwh, add 1300kg of lime; when the electric furnace power supply reaches 18000kwh, add 1400kg of lime, and at the same time open the furnace door oxygen lance to inject oxygen into the molten pool inside the electric furnace; when the electric furnace power supply reaches 24000kwh, add 1300kg of lime, and at the same time add 900kg of carbon dust removal balls, and add them in three batches of 200kg, 300kg and 400kg respectively. After adding the carbon dust removal balls, slag is discharged in front of the furnace. After slag discharge, a sample is taken for analysis. The P content is 0.016%. Then add 250kg of lime to create new slag for steel tapping.

[0049] S12: High-carbon ferrochrome is melted in a medium-frequency furnace, and the iron is tapped after melting.

[0050] S13: Mix the high-carbon ferrochrome melt molten in an induction furnace with the nickel-containing molten iron dephosphorized in an electric furnace to prepare duplex stainless steel mother liquor. The chemical composition of the duplex stainless steel mother liquor is controlled by mass percentage as follows: C = 3.1%, Si = 0.1%, P = 0.024%, S = 0.07%, Cr = 22.3%, and Ni = 5.6%.

[0051] S14: The duplex stainless steel mother liquor is added to AOD for decarburization and refining. Nitrogen gas is blown throughout the AOD smelting process. The slag basicity is controlled at 2.2. The total amount of lime added is controlled at 123 kg per ton of duplex stainless steel mother liquor. During the top lance blowing period, the amount of lime added is controlled at 33 kg per ton of duplex stainless steel mother liquor. After the temperature of the duplex stainless steel mother liquor reaches 1700℃, the remaining lime is added in three batches, with the amount of lime added in each batch controlled at 30 kg per ton of duplex stainless steel mother liquor to ensure stable furnace temperature and prevent lime accumulation. At the end point, carbon samples are taken for analysis, and the carbon content is C = 0.026%. After continuing blowing for 25 minutes, the AOD smelting is ended.

[0052] S15: Temperature measurement before tapping of AOD steel is 1630℃. The furnace life of AOD furnace is 39 cycles. The total argon blowing volume is controlled at 4.5Nm3 / t, which makes the N content in duplex stainless steel products 1650ppm.

[0053] S16: AOD steel slag is discharged into the ladle, and after slag removal, it enters the LF furnace process for further refining. After refining, it is cast into duplex stainless steel slabs in the continuous casting process.

[0054] Actual testing showed that the duplex stainless steel produced by the low-cost smelting process of this invention has a P content of ≤0.030% and a N content of 1500ppm to 1700ppm, which fully meets the requirements of duplex stainless steel.

[0055] In summary, compared with the prior art, the low-cost process for smelting duplex stainless steel of the present invention has the following advantages and beneficial effects:

[0056] 1. Using inexpensive chromium-nickel pig iron as raw material, instead of the expensive pure nickel + dephosphorized molten iron / low phosphorus scrap steel in the existing technology, the smelting cost of duplex stainless steel is significantly reduced. According to actual calculations, the cost reduction of duplex stainless steel is 2,600 to 5,200 yuan / ton, thus achieving effective cost reduction while meeting product quality requirements.

[0057] 2. A dephosphorization process for nickel-containing molten iron in electric furnaces was developed, ultimately achieving the goal of low phosphorus content in duplex stainless steel. By precisely controlling nitrogen through argon blowing before tapping with AOD, the N content in duplex stainless steel is ensured to be between 1500ppm and 1700ppm, meeting the quality and performance requirements of duplex stainless steel products.

[0058] 3. Using an alloy melting furnace to melt high-carbon ferrochrome reduces chromium loss during electric furnace smelting, increasing the chromium yield of the entire stainless steel smelting line by 2-3%.

[0059] 4. This method reduces the pretreatment steps for dephosphorization of blast furnace hot metal, simplifies the process flow, and improves thermal efficiency.

[0060] It should be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device.

[0061] It should also be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A low-cost process for smelting duplex stainless steel, characterized in that, Includes the following steps: S1. Electric furnace melting of chromium-nickel pig iron and in-furnace dephosphorization of molten chromium-nickel pig iron: High-phosphorus chromium-nickel pig iron raw materials are charged into the electric furnace for melting, and the molten chromium-nickel pig iron is dephosphorized in the electric furnace to produce low-phosphorus, high-nickel nickel-containing molten iron. The amount of high-phosphorus chromium-nickel pig iron charged is controlled at 100%–120% of the nominal capacity of the electric furnace. The total power consumption of the electric furnace is controlled at 350 kWh–450 kWh per ton of high-phosphorus chromium-nickel pig iron. The basicity of the electric furnace is controlled at 1.9–2.2, and the total amount of lime added is determined based on the basicity of the electric furnace. When the power supply of the electric furnace reaches 20%–25% of the total power consumption, lime is added at 15%–20% of the total lime addition. When the power supply of the electric furnace reaches 35%–40% of the total power consumption... When the electric furnace power supply reaches 45%–50% of the total power consumption, add lime at 25%–30% of the total lime supply, and simultaneously open the furnace door oxygen lance to inject oxygen into the molten pool inside the electric furnace; when the electric furnace power supply reaches 60%–65% of the total power consumption, add lime at 20%–30% of the total lime supply, and simultaneously add 8.0 kg–12.0 kg of carbon dust removal balls per ton of high phosphorus chromium nickel pig iron. The carbon dust removal balls are added in batches. During the dephosphorization process, samples are taken to analyze the composition of nickel-containing molten iron. When the P content is less than 0.02%, the electric furnace dephosphorization is completed. Then, add lime at 2%–5% of the total lime supply, and the electric furnace produces new slag before tapping steel. S2. Melting high-carbon ferrochrome in an alloy melting furnace: High-carbon ferrochrome is melted in an alloy melting furnace, and the iron is tapped after it is completely melted. S3. Preparation of duplex stainless steel mother liquor: The high-carbon ferrochrome melt molten in the alloy melting furnace is mixed with the nickel-containing molten iron after dephosphorization in the electric furnace to form duplex stainless steel mother liquor. The chemical composition of the duplex stainless steel mother liquor is controlled by mass percentage as follows: Cr: 20-26%, Ni: 4.0-6.0%, Si: 0.1-3.0%, C: 2.5-5%, P≤0.025%. S4. AOD Decarburization Refining: The duplex stainless steel mother liquor is added to AOD for decarburization refining. Nitrogen gas is blown throughout the AOD smelting process. The slag basicity is controlled at 2.0-2.

3. Based on the slag basicity, the total amount of lime added is determined to be 120-125 kg per ton of duplex stainless steel mother liquor. During the top lance blowing period, the amount of lime added is controlled at 30-35 kg per ton of duplex stainless steel mother liquor. After the temperature of the duplex stainless steel mother liquor reaches 1700℃, the remaining lime is added in batches, with the amount of lime added in each batch controlled at 30-35 kg per ton of duplex stainless steel mother liquor. At the end point, carbon samples are taken for analysis. If the carbon content is less than 0.03%, blowing continues for 25 minutes to end the AOD smelting. S5. Argon and Nitrogen Control: Argon and nitrogen control are performed before AOD tapping. Argon blowing begins when the temperature reaches 1610–1650℃, with a total argon blowing volume of 4.3–4.7 Nm³ per ton of duplex stainless steel mother liquor. 3 control; S6, LF furnace refining and continuous casting: AOD steel slag is discharged into the ladle, and after slag removal, it enters the LF furnace process for further refining. After refining, it is cast into duplex stainless steel billets in the continuous casting process.

2. The low-cost smelting process for duplex stainless steel as described in claim 1, characterized in that, In step S1, based on the electric furnace alkalinity of 1.9 to 2.2, the total amount of lime added is determined to be 50 to 55 kg per ton of high phosphorus chromium nickel pig iron.

3. The low-cost smelting process for duplex stainless steel as described in claim 1, characterized in that, In step S1, during the dephosphorization operation in the electric furnace, the carbon content is controlled to be ≥2% and the chromium content to be ≤2%, and the temperature of the nickel-containing iron water mother liquor is controlled to be 1400~1550℃.

4. The low-cost process for smelting duplex stainless steel as described in claim 1, characterized in that, In step S5, the argon blowing flow rate is set at 1500 m³ / s. 3 / h control, and the argon blowing rate is controlled according to the furnace age of the AOD furnace as follows: when the furnace age is ≤30 cycles, 4.3Nm 3 / t≤Argon blowing rate<4.5Nm 3 / t; When 30 < furnace age ≤ 60 cycles, 4.5 Nm 3 / t≤argon blowing rate<4.6Nm 3 / t; When furnace life > 60 cycles, 4.6 Nm 3 / t≤argon blowing rate≤4.7Nm 3 / t.

5. The low-cost process for smelting duplex stainless steel as described in claim 1, characterized in that, The chemical composition of the high-phosphorus chromium-nickel pig iron is controlled by mass percentage as follows: C≤5.0%, Si≤5.0%, P≤0.050%, S≤0.20%, Cr≤3.5%, Ni: 3.0%~17.0%; the chemical composition of the high-carbon ferrochrome is controlled by mass percentage as follows: Cr: 48~55%, Si: 0.5~6.5%, C: 6~8%.

6. The low-cost process for smelting duplex stainless steel as described in claim 1, characterized in that, In step S4, if the carbon content is greater than 0.03%, the blowing process continues, and then a new sample is taken until the carbon content is less than 0.03%. Then the blowing process continues for another 25 minutes to end the AOD smelting.

7. The low-cost process for smelting duplex stainless steel as described in claim 1, characterized in that, In step S1, after the dephosphorization of the electric furnace is completed, 80% of the dephosphorized slag is removed and then lime is added to create new slag for steelmaking.

8. The low-cost process for smelting duplex stainless steel as described in claim 1, characterized in that, In step S2, the high-carbon ferrochrome is tapped when the temperature is above 1650°C after being melted in the alloy melting furnace.

9. The low-cost process for smelting duplex stainless steel as described in claim 1, characterized in that, The alloy melting furnace is a medium-frequency furnace.

10. The low-cost process for smelting duplex stainless steel as described in claim 1, characterized in that: In step S1, 95 tons of high-phosphorus chromium-nickel pig iron are charged into an electric furnace with a nominal capacity of 90 tons. After melting, the molten chromium-nickel pig iron is dephosphorized in the electric furnace to produce low-phosphorus, high-nickel nickel-containing molten iron. The chemical composition of the high-phosphorus chromium-nickel pig iron is controlled by mass percentage as follows: C = 2.0%, Si = 0.3%, P = 0.040%, S = 0.10%, Cr = 1.7%, Ni = 9.5%. The total power consumption of the electric furnace is controlled at 38950 kWh, the basicity of the electric furnace is controlled at 2.0, and the total amount of lime added is controlled at 5050 kg. When the power supply of the electric furnace reaches 8000 kWh, lime is added. 700 kg of lime was added; when the electric furnace power supply reached 13000 kWh, 1300 kg of lime was added; when the electric furnace power supply reached 18000 kWh, 1500 kg of lime was added, and at the same time, the oxygen lance at the furnace door was opened to inject oxygen into the molten pool inside the electric furnace; when the electric furnace power supply reached 24000 kWh, 1300 kg of lime was added, and 900 kg of carbon dust removal balls were added at the same time, and then added in three batches of 200 kg, 300 kg and 400 kg respectively. After adding the carbon dust removal balls, slag was discharged in front of the furnace. After the slag was discharged, a sample was taken for analysis. The P content was 0.016%. Then 250 kg of lime was added to create new slag for steel tapping. In step S2, a medium-frequency furnace is used to melt high-carbon ferrochrome, and the molten iron is tapped after melting. In step S3, the high-carbon ferrochrome melt molten in the medium-frequency furnace is mixed with the nickel-containing molten iron after dephosphorization in the electric furnace to prepare duplex stainless steel mother liquor. The chemical composition of the duplex stainless steel mother liquor is controlled by mass percentage as C=3.1%, Si=0.1%, P=0.024%, S=0.07%, Cr=22.3%, and Ni=5.6%. In step S4, duplex stainless steel mother liquor is added to AOD for decarburization refining. Nitrogen gas is blown throughout the AOD smelting process, the slag basicity is controlled at 2.2, the total amount of lime added is controlled at 123 kg per ton of duplex stainless steel mother liquor, the amount of lime added during the top lance blowing period is controlled at 33 kg per ton of duplex stainless steel mother liquor, after the temperature of duplex stainless steel mother liquor reaches 1700℃, the remaining lime is added in three batches, the amount of lime added in each batch is controlled at 30 kg per ton of duplex stainless steel mother liquor, the carbon sample is analyzed at the end point, the carbon content is C=0.026%, and the AOD smelting is ended after blowing for another 25 minutes. In step S5, the temperature is measured before AOD tapping, and the temperature is 1630℃. The AOD furnace has been used for 39 cycles, and the total argon blowing volume is controlled at 4.5 Nm³. 3 / t; In step S6, AOD steel slag is discharged into the ladle, and after slag removal, it enters the LF furnace process for further refining. After refining, it is cast into duplex stainless steel slabs in the continuous casting process.