AOD rapid deep dephosphorization method for chromium-nickel pig iron melt

Abstract

The present invention discloses a method for rapid deep dephosphorization of a chromium-nickel pig iron melt by AOD, comprising: adding the chromium-nickel pig iron melt into an AOD furnace, performing desiliconization and dechromization operations, wherein the AOD top lance supplies oxygen, the side lances spray O2 and N2 gases, and lime is added in batches to form slag; after the desiliconization and dechromization are completed, the furnace slag is removed and an AOD deep dephosphorization operation is performed, wherein the AOD top lance supplies oxygen, the side lances supply O2 and N2 gases, and limestone is added to form slag during the deep dephosphorization process to produce an ultra-low-phosphorus chromium-nickel pig iron melt. The present invention solves the technical problem of the difficulty of AOD deep dephosphorization, achieves the purpose of using cheap chromium-nickel pig iron as the main raw material to prepare an ultra-low-phosphorus chromium-nickel pig iron melt through AOD rapid deep dephosphorization, and uses the ultra-low-phosphorus chromium-nickel pig iron melt as a stainless steel mother liquor to produce a low-phosphorus special stainless steel variety, simplifies the production process, reduces smelting costs, and develops a short-process, green, and low-cost process method for smelting low-phosphorus special stainless steel, which has good promotion value and economic benefits.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel production, and in particular relates to a method for rapid deep dephosphorization of a chromium-nickel pig iron melt by AOD. Background Art

[0002] The AOD (Argon Oxygen Decarburization) smelting process is an argon oxygen decarburization process and is currently the most commonly used process for producing stainless steel. Currently, approximately 75% of stainless steel is produced using the AOD process. The AOD process relies on the favorable kinetic conditions of side blowing to achieve decarburization and chromium preservation by increasing the process temperature and reducing the CO gas partial pressure. It has many advantages, such as simple equipment structure, easy operation, the use of inexpensive high-carbon ferrochrome and return stainless steel, and easy production of low-carbon and ultra-low-carbon stainless steel. However, since stainless steel smelting does not have the ability to dephosphorize, AOD smelting of stainless steel can only use pre-treated dephosphorized molten iron as the stainless steel mother liquor, which is a complex process and has high smelting costs.

[0003] With the widespread adoption of the RKEF (Rotary Klin Electric Furnace) process for producing chromium-nickel pig iron from laterite nickel ore, this relatively low-cost nickel pig iron has become a primary raw material for stainless steel. Its widespread use in conventional stainless steel production has reduced stainless steel smelting costs. However, nickel pig iron contains high levels of residual elements such as phosphorus, sulfur, silicon, and chromium, making it difficult to achieve deep dephosphorization of stainless steel.

[0004] Chinese patent application 201210212501.7, titled "A method for producing stainless steel mother liquor," discloses a method for dephosphorizing high-phosphorus chromium-nickel pig iron using an electric furnace. The resulting stainless steel mother liquor has a minimum phosphorus content of 0.020%. In Chinese patent application 201110220308.3, titled "A method for dephosphorizing high-phosphorus chromium-nickel pig iron," siliconization is performed in an electric furnace to a concentration of 0.05-1.0%, followed by the addition of AOD for dephosphorization, with the final AOD concentration being ≤0.04%. The chromium-nickel pig iron pre-melt produced using this prior art method cannot achieve deep AOD dephosphorization, making further dephosphorization difficult. Therefore, the chromium-nickel pig iron pre-melt cannot be used in large quantities as a stainless steel mother liquor to produce low-phosphorus specialty stainless steel grades. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems existing in the prior art, the present invention develops a method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD, which realizes the purpose of preparing ultra-low-phosphorus chromium-nickel pig iron melt by rapid deep dephosphorization of chromium-nickel pig iron pre-melt produced by RKEF through AOD, and using the ultra-low-phosphorus chromium-nickel pig iron melt as stainless steel mother liquor to produce low-phosphorus special stainless steel varieties.

[0006] The method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD of the present invention comprises the following steps:

[0007] Step 1: The chromium-nickel pig iron melt is added to the AOD furnace for desiliconization and dechromization operations. The AOD top gun supplies oxygen, the side guns blow O2 and N2 gases, and lime is added in batches to form slag.

[0008] Step 2: After desiliconization and dechromization, the slag is removed and the AOD deep dephosphorization operation is carried out. The AOD top gun supplies oxygen, and the side gun supplies O2 and N2 gases. Limestone is added to form slag during the deep dephosphorization process to produce ultra-low phosphorus chromium-nickel pig iron melt.

[0009] Furthermore, in the above-mentioned method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD:

[0010] During the desiliconization and dechromization operation in step 1, the oxygen flow rate of the AOD top gun is controlled to be 1.0-1.4 Nm / ton of steel. 3 / min, the oxygen lance position is controlled at 2300-2500mm, and the total flow rate of O2 and N2 gas supply per ton of steel is controlled at 0.6-0.8Nm 3 / min, the ratio of O2 and N2 is controlled to be O2:N2=3:1; lime is added in batches to make slag, the basicity of the desiliconized slag is controlled to be 1.3-1.5, and nickel pig iron is added during the desiliconization and dechromization process to adjust the molten steel temperature to 1350-1450℃;

[0011] In step 2, when Si≤0.03% and Cr≤0.50% in the molten steel, the desiliconization and dechromization operations are stopped, and after removing ≥75% of the desiliconized slag, the AOD deep dephosphorization operation is carried out;

[0012] In the AOD deep dephosphorization operation of step 2, the oxygen flow rate of the AOD top lance is controlled to be 1.2~1.5Nm 3 / min, the oxygen lance position is controlled at 2000-2300mm, and the total flow rate of O2 and N2 gas supply per ton of steel is controlled at 0.8-1.0Nm 3 / min, the ratio of O2 and N2 is controlled to be O2:N2=1:6; limestone is added in batches from a high position to make slag, and the basicity of the dephosphorization slag is controlled to be 5-8. The CO2 generated by the decomposition of limestone strengthens the stirring of the molten steel and decomposes and absorbs heat to control the molten steel temperature, which is controlled at 1500-1550℃;

[0013] In step 2, when P in the molten steel is less than or equal to 0.001%, the AOD deep dephosphorization operation is terminated, the top gun stops blowing oxygen, and the side guns all spray N2 gas for strong stirring. The N2 gas flow rate is controlled at 1.1 to 1.3 Nm per ton of steel. 3 / min, stir for 3 to 5 minutes, and remove ≥85% of the dephosphorized slag.

[0014] Furthermore, in the above-mentioned method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD, during the desiliconization and dechromization operation in step 1, the total oxygen blowing amount of the AOD top gun oxygen supply and the side gun O2 and N2 gas injection is controlled as follows: total oxygen blowing amount during desiliconization and dechromization = [weight of chromium-nickel pig iron melt × (Si% into furnace - 0.03%) × 0.8 + weight of chromium-nickel pig iron melt × (Cr% into furnace - 0.50%) × 0.323] / oxygen utilization rate % × 1000, wherein the unit of the total oxygen blowing amount during desiliconization and dechromization is Nm 3 The unit of weight of chromium-nickel pig iron melt is ton, and the oxygen utilization rate is 85%.

[0015] Furthermore, in the above-mentioned method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD, during the desiliconization and dechromization operation in step 1, the total amount of lime added in batches for slagging is controlled as follows: total amount of lime added = [weight of chromium-nickel pig iron melt × (Si% entering the furnace - 0.03%)] × 2.14 × 1.4 / CaO percentage content in lime, wherein the unit of the total amount of lime added is ton, the unit of the weight of the chromium-nickel pig iron melt is ton, and the CaO percentage content in the lime is 86%.

[0016] Furthermore, in the above-mentioned method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD, in the AOD deep dephosphorization operation of step 2, the total amount of limestone added in batches from a high position for slagging is controlled to be 80-90 kg per ton of steel.

[0017] Furthermore, in the above-mentioned method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD, in the AOD deep dephosphorization operation of step 2, the dephosphorization slag is a FeO-CaO-SiO2-MgO slag system, and its composition is controlled as follows: FeO: 20-25%, CaO: 45-55%, SiO2: 6-8%, MgO: 6-9%.

[0018] Furthermore, in the above-mentioned method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD, during the desiliconization and dechromization operation in step 1, the oxygen pressure of the AOD top gun oxygen supply is controlled to be 1.0 MPa.

[0019] Furthermore, in the above-mentioned method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD, in step 1, the chromium-nickel pig iron melt is a chromium-nickel pig iron melt produced by the RKEF process.

[0020] Furthermore, in the above-mentioned method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD, in step 1, the composition of the chromium-nickel pig iron melt is: C≤3.0%, Si: 0.5~2.5%, Cr≤3.5%, P≤0.060%, Ni: 6~18%, and the rest is iron and residual elements.

[0021] The method for deep dephosphorization of chromium-nickel pig iron melt by AOD of the present invention has the following advantages and beneficial effects: the present invention solves the technical problem of difficult deep dephosphorization by AOD, realizes the purpose of using cheap chromium-nickel pig iron as the main raw material to prepare ultra-low phosphorus chromium-nickel pig iron melt by rapid deep dephosphorization by AOD, and uses the ultra-low phosphorus chromium-nickel pig iron melt as stainless steel mother liquor to produce low-phosphorus special stainless steel varieties, simplifies the production process, reduces the smelting cost, develops a short-process, green, low-cost process method for smelting low-phosphorus special stainless steel, and has good promotion value and economic benefits. DETAILED DESCRIPTION

[0022] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0023] The present invention aims to solve the technical problem of difficult deep dephosphorization by AOD, and has developed a method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD. The specific process is as follows: the chromium-nickel pig iron melt is added into an AOD furnace, and desiliconization and dechromization operations are first performed, wherein the AOD top gun supplies oxygen, and the side guns spray O2 and N2 gases, and lime is added in batches to form slag; after the desiliconization and dechromization are completed, the slag is removed and deep dephosphorization is performed, and the AOD top gun supplies oxygen, and the side guns supply O2 and N2 gases. During the process, limestone is added to form slag, and high-alkalinity slag is formed for deep dephosphorization, so as to quickly produce ultra-low phosphorus stainless steel mother liquor.

[0024] Specifically, the method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD of the present invention comprises the following steps:

[0025] (1) A chromium-nickel pig iron melt is added to an AOD furnace. The composition of the chromium-nickel pig iron melt is: C ≤ 3.0%, Si: 0.5-2.5%, Cr ≤ 3.5%, P ≤ 0.060%, Ni: 6-18%, and the rest is iron and residual elements. The chromium-nickel pig iron melt can be, for example, a chromium-nickel pig iron melt produced by a RKEF process.

[0026] (2) Desiliconization and dechromization operations are carried out in the AOD. The AOD top gun supplies oxygen, the oxygen pressure is controlled at 1.0 MPa, and the oxygen flow rate per ton of steel is controlled at 1.0 to 1.4 Nm 3 / min, the oxygen lance position is controlled at 2300-2500mm, the side lances are used to spray O2 and N2 gases, and the total flow rate of O2 and N2 gas supply per ton of steel is controlled at 0.6-0.8Nm 3 / min, the ratio of O2 and N2 is controlled to be O2:N2=3:1, and the total oxygen blowing amount during the desiliconization and dechromization process is controlled as follows: total oxygen blowing amount during the desiliconization and dechromization process = [weight of chromium-nickel pig iron melt × (Si% into the furnace - 0.03%) × 0.8 + weight of chromium-nickel pig iron melt × (Cr% into the furnace - 0.50%) × 0.323] / oxygen utilization rate % × 1000, where the unit of total oxygen blowing amount during the desiliconization and dechromization process is Nm 3 The weight of the chromium-nickel pig iron melt is measured in tons, and the oxygen utilization rate is 85%. Lime is added in batches to form slag, and the total amount of lime added is controlled as follows: total amount of lime added = [weight of the chromium-nickel pig iron melt × (Si% entering the furnace - 0.03%)] × 2.14 × 1.4 / CaO percentage content in the lime, wherein the total amount of lime added is measured in tons, the weight of the chromium-nickel pig iron melt is measured in tons, and the CaO percentage content in the lime is 86%. By adding lime in batches to form slag, the basicity of the desiliconized slag is controlled to 1.3-1.5. Nickel pig iron is added during the process to adjust the molten steel temperature, and the molten steel temperature is controlled to 1350-1450°C.

[0027] (3) When Si≤0.03% and Cr≤0.50% in the molten steel, stop desiliconization and dechromization, and carry out AOD slag removal operation to remove most of the desiliconization slag, and the proportion of slag removal to the total slag volume is ≥75%.

[0028] (4) After the AOD slag removal is completed, the AOD deep dephosphorization operation is carried out, wherein the AOD top gun supplies oxygen, and the oxygen flow rate per ton of steel is controlled to be 1.2~1.5Nm 3 / min, the oxygen lance position is controlled at 2000-2300mm, the side lances are used to spray O2 and N2 gases, and the total flow rate of O2 and N2 gas supply per ton of steel is controlled at 0.8-1.0Nm 3 / min, the ratio of O2 and N2 is controlled to be O2:N2=1:6, limestone (CaCO3) is added in batches from a high position during the dephosphorization process, and the total amount of limestone added is controlled to be 80-90kg per ton of steel. Dephosphorization slag with an alkalinity of 5-8 is used for deep dephosphorization. The dephosphorization slag is a FeO-CaO-SiO2-MgO slag system, and its composition is controlled to be: FeO: 20-25%, CaO: 45-55%, SiO2: 6-8%, MgO: 6-9%. Limestone decomposes to produce CO2 (CaCO3=CaO+CO2↑), thereby enhancing the stirring of the molten steel, and at the same time decomposes to absorb heat to control the molten steel temperature, and the molten steel temperature is controlled at 1500-1550℃.

[0029] (5) When P in molten steel is less than or equal to 0.001%, dephosphorization is terminated, oxygen blowing from the top gun stops, and N2 gas is injected from all side guns for strong stirring to promote uniform temperature and composition of molten steel. The N2 gas flow rate is controlled at 1.1 to 1.3 Nm / ton of steel. 3 / min, stir for 3 to 5 minutes, remove most of the dephosphorization slag, the slag volume accounts for ≥85% of the total slag volume, and produce ultra-low phosphorus stainless steel mother liquor, which can be used for refining low-phosphorus special stainless steel in the AOD furnace later.

[0030] The method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD of the present invention will be described in detail below in conjunction with specific embodiments of the present invention.

[0031] Example 1

[0032] Example 1 of the present invention is used to perform AOD rapid deep dephosphorization of chromium-nickel pig iron melt using a 180-ton AOD furnace to produce ultra-low phosphorus stainless steel mother liquor. The specific implementation process is as follows:

[0033] (1) The chromium-nickel pig iron melt is added to the AOD furnace. The composition of the chromium-nickel pig iron melt is: C: 2.5%, Si: 1.5%, Cr: 3.0%, P: 0.050%, Ni: 12%, and the rest is iron and residual elements.

[0034] (2) Desiliconization and dechromization operations are carried out in the AOD, wherein the AOD top gun supplies oxygen with an oxygen pressure of 1.0 MPa and an oxygen flow rate of 240 Nm 3 / min, the oxygen lance position is 2500mm, the side lance blows O2 and N2 gases, and the total flow rate of O2 and N2 gas supply is 126Nm 3 / min, the ratio of O2 and N2 is O2:N2=3:1, and the total oxygen blowing amount in the desiliconization and dechromization process is controlled as follows: total oxygen blowing amount=[180×(1.5%-0.03%)×0.8+180×(3.0%-0.50%)×0.323] / 85%×1000=4200Nm 3 , add lime in batches to make slag, and the total amount of lime added is controlled as follows: total amount of lime added = [180×(1.5%-0.03%)]×2.14×1.4 / 86%=9.2 tons, and the basicity of the desiliconized slag is controlled to 1.4. Nickel pig iron is added during the smelting process to adjust the temperature of the molten steel, and the temperature of the molten steel is controlled at 1400-1450°C.

[0035] (3) When Si≤0.03% and Cr≤0.50% in the molten steel, stop desiliconization and dechromization, and perform AOD slag removal operation to remove 75% of the desiliconization slag.

[0036] (4) After the AOD slagging is completed, continue to blow oxygen for AOD deep dephosphorization operation, where the oxygen flow rate of the AOD top gun is 250Nm 3 / min, the oxygen lance position is 2100mm, the side lance blows O2 and N2 gases, and the total flow rate of O2 and N2 gas supply is 180Nm 3 / min, the ratio of O2 and N2 is O2:N2=1:6. During the dephosphorization process, limestone is added in batches from a high position. The limestone decomposes to produce CO2, thereby enhancing the stirring of the molten steel. At the same time, the decomposition absorbs heat to control the molten steel temperature. The molten steel temperature is controlled at 1500-1550℃. The total amount of limestone added is 15 tons. Dephosphorization slag with a basicity of 7 is made for deep dephosphorization. The dephosphorization slag is a FeO-CaO-SiO2-MgO slag system, and its composition is: FeO: 25%, CaO: 50%, SiO2: 7%, MgO: 9%.

[0037] (5) When P in the molten steel is less than or equal to 0.001%, dephosphorization is terminated, the top gun stops blowing oxygen, and the side guns all spray N2 gas for strong stirring to promote uniform temperature and composition of the molten steel. The N2 gas flow rate is 215Nm 3 / min, stirred for 5min, and 85% of the dephosphorization slag was removed to produce ultra-low phosphorus stainless steel mother liquor.

[0038] Using Example 1, 182 tons of ultra-low phosphorus chromium-nickel pig iron melt was finally prepared, and the steel composition was: C: 1.8%, Si: 0.01%, P: 0.001%, Ni: 13%, Cr: 0.06%. The ultra-low phosphorus chromium-nickel pig iron melt can be directly used as stainless steel mother liquor to continue refining low-phosphorus special stainless steel in an AOD furnace.

[0039] Example 2

[0040] Example 2 of the present invention is used to perform AOD rapid deep dephosphorization of chromium-nickel pig iron melt using a 90-ton AOD furnace to produce ultra-low phosphorus stainless steel mother liquor. The specific implementation process is as follows:

[0041] (1) The chromium-nickel pig iron melt is added to the AOD furnace. The composition of the chromium-nickel pig iron melt is: C: 2.0%, Si: 1.0%, Cr: 2.5%, P: 0.045%, Ni: 17%, and the rest is iron and residual elements.

[0042] (2) Desiliconization and dechromization operations are carried out in the AOD, wherein the AOD top gun supplies oxygen with an oxygen pressure of 1.0 MPa and an oxygen flow rate of 120 Nm 3 / min, the oxygen lance position is 2300mm, the side lance blows O2 and N2 gases, and the total flow rate of O2 and N2 gas supply is 66Nm 3 / min, the ratio of O2 and N2 is O2:N2=3:1, and the total oxygen blowing amount in the desiliconization and dechromization process is controlled as follows: total oxygen blowing amount = [90×(1.0%-0.03%)×0.8+90×(2.5%-0.50%)×0.323] / 85%×1000=1506Nm 3, add lime in batches to make slag, the total amount of lime added is controlled as follows: total amount of lime added = [90×(1.0%-0.03%)]×2.14×1.4 / 86%=3 tons, the basicity of the desiliconized slag is controlled to 1.5, nickel pig iron is added during the smelting process to adjust the temperature of the molten steel, and the temperature of the molten steel is controlled at 1420~1450℃.

[0043] (3) When Si≤0.03% and Cr≤0.50% in the molten steel, stop desiliconization and dechromization, and perform AOD slag removal operation to remove 75% of the desiliconization slag.

[0044] (4) After the AOD slagging is completed, continue to blow oxygen for AOD deep dephosphorization operation, where the oxygen flow rate of the AOD top gun is 130Nm 3 / min, the oxygen lance position is 2200mm, the side lance blows O2 and N2 gases, and the total flow rate of O2 and N2 gas supply is 90Nm 3 / min, the ratio of O2 and N2 is O2:N2=1:6. During the dephosphorization process, limestone is added in batches from a high position. The limestone decomposes to produce CO2, thereby enhancing the stirring of the molten steel. At the same time, the decomposition absorbs heat to control the molten steel temperature. The molten steel temperature is controlled at 1530-1550℃. The total amount of limestone added is 7.2 tons. Dephosphorization slag with an alkalinity of 6 is made for deep dephosphorization. The dephosphorization slag is FeO-CaO-SiO2-MgO slag system, and its composition is: FeO: 22%, CaO: 49%, SiO2: 7.5%, MgO: 8.5%.

[0045] (5) When P in the molten steel is less than or equal to 0.001%, dephosphorization is terminated, the top gun stops blowing oxygen, and the side guns all spray N2 gas for strong stirring to promote uniform temperature and composition of the molten steel. The N2 gas flow rate is 105Nm 3 / min, stirred for 4min, and 85% of the dephosphorization slag was removed to produce ultra-low phosphorus stainless steel mother liquor.

[0046] Using Example 2, 89 tons of ultra-low phosphorus chromium-nickel pig iron melt was finally prepared, and the steel composition was: C: 1.0%, Si: 0.01%, P: 0.001%, Ni: 17%, Cr: 0.08%. The ultra-low phosphorus chromium-nickel pig iron melt can be directly used as stainless steel mother liquor to continue refining low-phosphorus special stainless steel in an AOD furnace.

[0047] In summary, the method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD of the present invention uses chromium-nickel pig iron melt as raw material, and quickly produces ultra-low phosphorus chromium-nickel pig iron melt through desiliconization and dechromization in AOD and then AOD deep dephosphorization. The ultra-low phosphorus chromium-nickel pig iron melt has an AOD endpoint phosphorus content of P≤0.001%, and can be directly used as stainless steel mother liquor to continue to be refined in an AOD furnace for low-phosphorus special stainless steel.

[0048] Compared with the prior art, the method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD of the present invention has the following advantages and beneficial effects: the present invention solves the technical problem of difficult deep dephosphorization by AOD, realizes the purpose of using cheap chromium-nickel pig iron as the main raw material to prepare ultra-low phosphorus chromium-nickel pig iron melt through rapid deep dephosphorization by AOD, and uses the ultra-low phosphorus chromium-nickel pig iron melt as stainless steel mother liquor to produce low-phosphorus special stainless steel varieties, simplifies the production process, reduces the smelting cost, develops a short-process, green, low-cost smelting process method for low-phosphorus special stainless steel, and has good promotion value and economic benefits.

[0049] It should be noted that, in this article, the term "comprise" or any other variation thereof is intended to cover non-exclusive inclusion, so that an article or device that includes a series of elements includes not only those elements, but also includes other elements that are not explicitly listed, or also includes elements that are inherent to such article or device.

[0050] It should also be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD, comprising the following steps: Step 1: The chromium-nickel pig iron melt is added to the AOD furnace for desiliconization and dechromization operations, wherein: AOD top gun supplies oxygen, side guns spray O2 and N2 gases, and lime is added in batches to make slag; Step 2: After desiliconization and dechromization, the slag is removed and AOD deep dephosphorization is carried out. The AOD top gun supplies oxygen, and the side gun supplies O2 and N2 gases. Limestone is added to form slag during the deep dephosphorization process to produce ultra-low phosphorus chromium-nickel pig iron melt. Its characteristics are: During the desiliconization and dechromization operation in step 1, the oxygen flow rate of the AOD top gun is controlled to be 1.0-1.4 Nm / ton of steel. 3 / min, the oxygen lance position is controlled at 2300-2500mm, and the total flow rate of O2 and N2 gas supply per ton of steel is controlled at 0.6-0.8Nm 3 / min, the ratio of O2 and N2 is controlled to be O2:N2=3:1; lime is added in batches to make slag, the basicity of desiliconization slag is controlled to be 1.3-1.5, and nickel pig iron is added during the desiliconization and dechromization process to adjust the molten steel temperature and control the molten steel temperature at 1350-1450℃; In step 2, when Si≤0.03% and Cr≤0.50% in the molten steel, the desiliconization and dechromization operations are stopped, and after removing ≥75% of the desiliconized slag, the AOD deep dephosphorization operation is carried out; In the AOD deep dephosphorization operation of step 2, the oxygen flow rate of the AOD top lance is controlled to be 1.2~1.5Nm 3 / min, the oxygen lance position is controlled at 2000-2300mm, and the total flow rate of O2 and N2 gas supply per ton of steel is controlled at 0.8-1.0Nm 3 / min, the ratio of O2 and N2 is controlled to be O2:N2=1:6; limestone is added in batches from a high position to make slag, and the basicity of the dephosphorization slag is controlled to be 5-8. The CO2 generated by the decomposition of limestone strengthens the stirring of the molten steel and decomposes and absorbs heat to control the molten steel temperature, which is controlled at 1500-1550℃; In step 2, when P in the molten steel is less than or equal to 0.001%, the AOD deep dephosphorization operation is terminated, the top gun stops blowing oxygen, and the side guns all spray N2 gas for strong stirring. The N2 gas flow rate is controlled at 1.1 to 1.3 Nm per ton of steel. 3 / min, stir for 3 to 5 minutes, and remove ≥85% of the dephosphorized slag.

2. The method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD according to claim 1, characterized in that: During the desiliconization and dechromization operation in step 1, the total oxygen blowing amount of the AOD top gun oxygen supply and the side gun blowing of O2 and N2 gases is controlled as follows: Total oxygen blowing amount during desiliconization and dechromization = [weight of chromium-nickel pig iron melt × (Si% into furnace - 0.03%) × 0.8 + weight of chromium-nickel pig iron melt × (Cr% into furnace - 0.50%) × 0.323] / oxygen utilization rate % × 1000, where the unit of total oxygen blowing amount during desiliconization and dechromization is Nm 3 The unit of weight of chromium-nickel pig iron melt is ton, and the oxygen utilization rate is 85%.

3. The method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD according to claim 1, characterized in that: During the desiliconization and dechromization operation of step 1, the total amount of lime added in batches for slagging is controlled as follows: total amount of lime added = [weight of chromium-nickel pig iron melt × (Si% charged into furnace - 0.03%)] × 2.14 × 1.4 / CaO percentage content in lime, wherein the unit of the total amount of lime added is ton, the unit of the weight of the chromium-nickel pig iron melt is ton, and the CaO percentage content in the lime is 86%.

4. The method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD according to claim 1, characterized in that: In the AOD deep dephosphorization operation of step 2, the total amount of limestone added in batches from a high position for slagging is controlled to be 80-90 kg per ton of steel.

5. The method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD according to claim 1, characterized in that: In the AOD deep dephosphorization operation of step 2, the dephosphorization slag is a FeO-CaO-SiO2-MgO slag system, and its composition is controlled as follows: FeO: 20-25%, CaO: 45-55%, SiO2: 6-8%, MgO: 6-9%.

6. The method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD according to claim 1, characterized in that: During the desiliconization and dechromization operation in step 1, the oxygen pressure supplied by the AOD top gun is controlled to be 1.0 MPa.

7. The method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD according to claim 1, characterized in that: In step 1, the chromium-nickel pig iron melt is a chromium-nickel pig iron melt produced by the RKEF process.

8. The method for rapid deep dephosphorization of chromium-nickel pig iron melt by AOD according to claim 1, characterized in that: In step 1, the composition of the chromium-nickel pig iron melt is: C≤3.0%, Si: 0.5-2.5%, Cr≤3.5%, P≤0.060%, Ni: 6-18%, and the rest is iron and residual elements.