A high-purity iron ultra-low phosphorus smelting method

Abstract

This invention relates to the field of iron and steel metallurgy technology, specifically to a method for smelting high-purity iron with ultra-low phosphorus content. The method involves pre-treating molten iron to remove phosphorus, obtaining pre-treated molten iron, and then smelting the pre-treated molten iron with low-phosphorus scrap steel in a converter single-slag process. After the converter single-slag smelting is completed, slag washing and argon station stirring and refining are performed. Further LF refining is conducted as needed to enhance dephosphorization. The dephosphorized slag is removed to obtain ultra-low phosphorus steel, thus "liberating" the converter. The main task of dephosphorization in the converter is distributed among the molten iron pre-treatment, slag washing, argon station stirring and refining, and LF refining processes. This fully utilizes the dephosphorization potential of each smelting process, avoids dephosphorization failure due to improper converter operation, comprehensively improves the dephosphorization rate of molten iron, reduces converter slag consumption, and saves steelmaking costs. The high-purity iron ultra-low phosphorus smelting method can achieve a phosphorus content of ≤0.002wt% in molten steel.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a method for smelting high-purity iron with ultra-low phosphorus content. Background Technology

[0002] Pure iron is a primary material used in the production of neodymium nickel cobalt, low-carbon stainless steel, precision casting, high-temperature alloys, amorphous and nanocrystalline materials, iron-based alloys, neodymium iron boron magnetic materials, magnetic steel, electromagnetic brakes, electromagnetic clutches, and magnetic separators. These materials require high phosphorus content. However, the phosphorus content in molten iron used for pure iron smelting is generally between 0.12 wt% and 0.20 wt%, far exceeding the phosphorus content requirements for high-purity iron materials. Therefore, the vast majority of phosphorus needs to be effectively removed during the steelmaking process, which places high demands on the dephosphorization efficiency of steelmaking.

[0003] The dephosphorization reaction in steelmaking follows the thermodynamic conditions of "low temperature, high basicity, and strong oxidizing power." The reaction pathway is as follows: P in the molten iron is oxidized by FeO at the slag-metal interface to form P2O5, which then combines with CaO to form stable calcium phosphate Ca4P2O9 or Ca3P2O8, which enters the slag. Traditional long-process steelmaking typically concentrates the dephosphorization task in two stages: hot metal pretreatment and converter dephosphorization. However, in recent years, due to problems such as large temperature drops in hot metal pretreatment, conflicts between desulfurization and dephosphorization conditions, and high operating costs, most steel mills in China have cancelled pretreatment dephosphorization and switched to a "full converter" dephosphorization mode, leading to a series of technical bottlenecks. The converter single slag method is simple to operate and fast, but its dephosphorization efficiency is limited under the conditions of high phosphorus P≥0.15wt% and high silicon Si≥0.35wt% molten iron. The final P content is often higher than 0.010wt%, and the subsequent decarburization heating leads to obvious phosphorus return in the molten steel, making it difficult to stably obtain ultra-low phosphorus steel with P≤0.002wt%.

[0004] The converter double-slag method removes phosphorus-rich slag in a single slag-pouring operation, improving the initial dephosphorization rate. However, it requires extremely precise control over the timing and amount of slag pouring; pouring too early results in incomplete dephosphorization, while pouring too late exacerbates phosphorus reversion. When the slag basicity is too low, the viscosity is high, making slag pouring difficult; when the basicity is too high, a high-melting-point solid phase is formed, also hindering slag pouring. In actual operation, slag volume, iron loss, and temperature drop all increase significantly, resulting in poor process stability and large fluctuations in the final phosphorus content.

[0005] The dual-converter method involves setting up a dephosphorization converter and a decarburization converter. Although it can achieve a high dephosphorization rate, it requires two converter systems, resulting in high equipment investment, large land area, complex production scheduling, and stringent requirements for automation control, which is difficult for small and medium-sized steel mills to afford.

[0006] The impact of silicon content in molten iron: Silicon is more easily oxidized than phosphorus. In high-silicon molten iron with a Si content ≥0.35wt%, oxidants are consumed preferentially during pretreatment or early converter stages, delaying the dephosphorization reaction, increasing the molten pool temperature, and increasing the consumption of lime, oxygen, and slag. Existing technologies have not yet established a quantitative correspondence between Si in molten iron and the amount of dephosphorizing agent added and the slag-forming system, resulting in low dephosphorization efficiency and high cost of high-silicon molten iron.

[0007] It is difficult to stably control the phosphorus content at ≤0.002wt% by relying solely on the converter process: the temperature rise in the later stage of the converter is inevitable, and the P2O5 in the slag undergoes a reduction reaction and returns to the molten steel, resulting in the "phosphorus return" phenomenon; at the same time, the amount of converter slag is limited, the dephosphorization rate is limited, and the driving force for dephosphorization is insufficient when the phosphorus content is extremely low at ≤0.002wt%.

[0008] Existing hot metal pretreatment dephosphorization technologies, such as CN116891921A, do not consider the significant impact of Si in hot metal on the consumption of dephosphorizing agents, nor do they optimize the injection dynamics parameters, resulting in waste of dephosphorizing agents, long processing time, and large temperature drop. At the same time, their dephosphorizing agent formulation and injection method are difficult to achieve deep dephosphorization under high-silicon hot metal conditions.

[0009] Existing ultra-low phosphorus steel smelting processes, such as CN115044820A, adopt the route of "hot metal pretreatment → converter double slag → multiple LF slag removal". Although it can obtain steel with a P content ≤0.003wt%, the stringent requirement of P ≤0.13wt% in hot metal limits the adaptability of raw materials. Moreover, the process involves many steps, multiple slag removals, and large temperature drops, resulting in high energy consumption and metal yield losses. It does not provide quantitative control ranges for key parameters such as dephosphorized slag composition, basicity, and oxidizing properties, and its stability is insufficient after industrial scale-up.

[0010] Existing technologies generally face problems such as heavy load on converter dephosphorization, complex processes, narrow operating window, high risk of phosphorus reversion, poor raw material adaptability, and large fluctuations in final phosphorus content, making it difficult to achieve an economical and stable smelting process for ultra-low phosphorus steel with a phosphorus content of ≤0.002wt%. Summary of the Invention

[0011] To address the shortcomings of the existing technologies, the purpose of this invention is to provide a high-purity iron ultra-low phosphorus smelting method. This method, which takes "deep dephosphorization of molten iron pretreatment as the core, converter single-slag smelting as the link, converter tapping pre-melted slag washing and argon station stirring refining as the support, and LF refining enhanced dephosphorization as a supplement," "liberates" the converter by distributing the main task of converter dephosphorization to the molten iron pretreatment, converter tapping slag washing, argon station stirring refining, and LF refining processes. This fully utilizes the dephosphorization potential of each smelting process, avoids dephosphorization failure due to improper converter operation, comprehensively improves the dephosphorization rate of molten iron, reduces converter slag consumption, and saves steelmaking costs.

[0012] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for smelting high-purity iron with ultra-low phosphorus content includes the following steps: The Si content in the molten iron is determined. When the Si content is between 0.35wt% and 0.65wt%, the molten iron is pretreated for desiliconization, followed by pretreatment for dephosphorization. When the Si content in the molten iron is <0.35wt%, the molten iron is directly pretreated for dephosphorization to obtain pretreated molten iron. The P content in the pretreated molten iron is ≤0.03wt%, and the Si content is ≤0.05wt%.

[0013] The pretreated molten iron is then smelted with low-phosphorus scrap steel in a converter using single-slag smelting.

[0014] After the converter single-slag smelting is completed, the slag is washed and the argon station is used for stirring and refining.

[0015] Continue LF refining to enhance dephosphorization, remove the dephosphorization slag to obtain ultra-low phosphorus molten steel.

[0016] The phosphorus content of ultra-low phosphorus molten steel is ≤0.002wt%.

[0017] In a preferred embodiment of the present invention, the chemical composition of the molten iron is C≤4.80wt%, Si≤0.65wt%, Mn≤0.30wt%, P≤0.20wt%, S≤0.05wt%, N≤0.003wt%, Cu≤0.008wt%, Ni≤0.006wt%, Cr≤0.006wt%, with the balance being Fe, totaling 100%, and the temperature of the molten iron is 1300℃~1400℃.

[0018] In a preferred embodiment of the present invention, the desiliconization method for molten iron pretreatment involves blowing iron oxide scale powder into the molten iron ladle through a spray gun using air. The amount of iron oxide scale powder sprayed is (50wt%Si-7.0) kg / t to (50wt%Si-2.0) kg / t, which means that the amount of iron oxide scale powder sprayed per 1 t of molten iron is (50wt%Si-7.0) kg to (50wt%Si-2.0) kg, where 50wt%Si is 50 times the mass percentage of Si in the molten iron. The nozzle is 350mm to 550mm from the bottom of the ladle. After desiliconization until the Si content is ≤0.15wt%, the desiliconization slag is quickly skimmed off, with a slag skimming rate >85%.

[0019] The dephosphorization method for molten iron pretreatment involves injecting 25 kg / t to 36 kg / t of dephosphorizing powder using air as the carrier gas. This means adding 25 kg to 36 kg of dephosphorizing powder per ton of molten iron. The scale-up or scale-down can be adjusted accordingly. The final slag basicity is controlled to be 2.8 to 3.6. The dephosphorizing powder composition is: 38 wt% to 50 wt% active lime powder, 42 wt% to 55 wt% iron oxide scale powder, and 7 wt% to 13 wt% fluorite powder, totaling 100%.

[0020] In a preferred embodiment of the present invention, the direct hot metal pretreatment dephosphorization method involves directly injecting 30 kg / t to 50 kg / t of dephosphorization powder using air as the carrier gas. This means adding 25 kg to 36 kg of dephosphorization powder per 1 t of hot metal. The scale-up or scale-down can be adjusted accordingly. The final slag basicity is controlled to be 2.5 to 3.2. The dephosphorization powder composition is: 35 wt% to 53 wt% of active lime powder, 40 wt% to 57 wt% of iron oxide scale powder, and 7.0 wt% to 13 wt% of fluorite powder, totaling 100%.

[0021] In a preferred embodiment of the present invention, the conditions for converter single slag smelting are as follows: adding low-phosphorus scrap steel, wherein the phosphorus content is ≤0.03wt%, adding pretreated molten iron, and adding slag-forming agent in three batches totaling 50kg / t~75kg / t.

[0022] The specific method for adding slag-forming agents is as follows: In the early stage of smelting, add 12.0 kg / t to 16.0 kg / t of lime, 5.0 kg / t to 7.5 kg / t of lightly calcined dolomite, 4.0 kg / t to 6.0 kg / t of iron oxide scale, and 8.0 kg / t to 12.0 kg / t of quartz sand. This means that for every 1 t of molten iron, add 12 kg to 16 kg of lime, 5.0 kg to 7.5 kg of lightly calcined dolomite, 4.0 kg to 6.0 kg of iron oxide scale, and 8.0 kg to 12.0 kg of quartz sand. Scale-up or scale-down is appropriate. The binary basicity of the slag is 1.2 to 1.8, and the high-oxygen lance position is 2 in the early stage of smelting. From 0m to 2.4m, blowing for 4-7 minutes; during the middle stage of smelting, add 9.0kg / t to 13.0kg / t of lime and 3.0kg / t to 5.5kg / t of lightly calcined dolomite, with a slag binary basicity of 2.2-2.7, lower the oxygen lance position to 1.6m-2.0m, and blow for 5-8 minutes; in the later stage of smelting, add 3.2kg / t to 9.5kg / t of lime and 4.0kg / t to 6.0kg / t of iron oxide scale, with a low-oxygen lance position of 1.2m-1.6m, and blow for 5-9 minutes; at the final smelting point, the slag binary basicity is 3.0-3.6; the oxygen supply intensity is 2.3 Nm. 3 / min / t~2.9Nm 3 / min / t, blowing time 14min~24min, final steel liquid P content ≤0.004wt%, oxygen content 0.05wt%~0.09wt%, temperature 1590℃~1640℃; bottom blowing gas flow rate in the early and middle stages of smelting is 0.03Nm 3 / min / t~0.09Nm 3 / min / t, the bottom blowing gas flow rate in the later stage is 0.020Nm 3 / min / t~0.06Nm 3 / min / t.

[0023] In a preferred embodiment of the present invention, the slag washing operation is as follows: the slag discharge rate of the slag-blocking slide is <4.0 kg / t, and no deoxidation or alloying is performed during the slag discharge process.

[0024] When 10% to 20% of the steel is tapped, pre-melted slag is added at a rate of 2.0 kg / min / t to 3.5 kg / min / t until all pre-melted slag is added at the end of tapping. The total amount of pre-melted slag added is 10 kg / t to 15 kg / t. The composition of the pre-melted slag is FeO: 45wt% to 58wt%, CaO: 30wt% to 40wt%, SiO2: 6wt% to 10wt%, and Al2O3: 5wt% to 10wt%. It is mixed with the steel stream for slag washing and dephosphorization.

[0025] During the slag washing and argon station stirring refining process, a mixture of Ar and CO2 gas is blown into the ladle, with Ar accounting for 60%~100% of the volume and CO2 accounting for 0~40% of the volume. The total flow rate of the bottom-blown mixed gas during the tapping process is 3.0NL / min / t~7.0NL / min / t. After the tapping is completed, the flow rate of the bottom-blown mixed gas during the argon station stirring refining process is 2.0NL / min / t~5.0NL / min / t. The argon station stirring lasts for 4min~10min, during which the dephosphorization reaction of the molten steel occurs.

[0026] In a preferred embodiment of the present invention, the P content of the molten steel is detected before entering the LF refining and enhanced dephosphorization process: if the P content of the molten steel is ≤0.002wt%, the dephosphorization slag is directly removed; if the P content of the molten steel is >0.002wt%, slag is added for LF refining and enhanced dephosphorization.

[0027] In a preferred embodiment of the present invention, the LF refining and strengthening dephosphorization operation steps include: adding 1.5 kg / t to 3.5 kg / t of active lime and 0.5 kg / t to 1.5 kg / t of fluorite to dephosphorize the molten steel.

[0028] The electrodes are energized and heated to maintain the temperature of the molten steel at 1560℃~1600℃.

[0029] During dephosphorization, the bottom-blown Ar gas flow rate is 1.0 NL / min / t to 4.0 NL / min / t.

[0030] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention provides a method for smelting high-purity iron with ultra-low phosphorus content. This method is based on deep dephosphorization through hot metal pretreatment, linked by converter single-slag smelting, supported by slag washing of pre-melted slag from converter tapping and argon station stirring and refining, and supplemented by enhanced dephosphorization through LF refining. This method "liberates" the converter, distributing the main dephosphorization task across the hot metal pretreatment, tapping slag washing, argon station stirring and refining, and LF refining processes. It fully utilizes the dephosphorization potential of each smelting process, avoids dephosphorization failure due to improper converter operation, comprehensively improves the dephosphorization rate of molten iron, reduces converter slag consumption, and saves steelmaking costs.

[0031] 2. The high-purity iron ultra-low phosphorus smelting method of the present invention advances the main dephosphorization task to the molten iron, which can improve dephosphorization efficiency by utilizing the relatively low temperature of the molten iron during pretreatment. After pretreatment, the phosphorus content in the molten iron is ≤0.03wt%, breaking the limitation of blast furnace molten iron with a phosphorus content higher than 0.15wt% for smelting ultra-low phosphorus molten iron. By significantly reducing the phosphorus content of the molten iron entering the converter, it effectively inhibits phosphorus reversion in converter steelmaking. Only the converter single-slag method is required for smelting, and the blowing time is only 14 minutes. This process, lasting 24 minutes, significantly improves converter smelting efficiency and allows for stable control of the final phosphorus content in the molten steel to within 0.002 wt%. The dephosphorization process differs from demanganese dephosphorization; dephosphorization requires high slag basicity, while demanganese dephosphorization requires low slag basicity. It is difficult to achieve both simultaneously and perfectly. Therefore, this invention controls the binary basicity of the slag by adding slag-forming materials in batches during the converter single-slag smelting process. Specifically, at the beginning of blowing, 12.0 kg / t to 16.0 kg / t of lime and 5.0 kg / t to 7 kg / t of lightly calcined dolomite are added. The following additives are used in smelting: 0.5 kg / t of lime, 4.0 kg / t to 6.0 kg / t of iron oxide scale, and 8.0 kg / t to 12.0 kg / t of quartz sand. The binary basicity of the slag is 1.2 to 1.8. In the early stage of smelting, the high-oxygen lance position is 2.0 m to 2.4 m, and the blowing time is 4 min to 7 min. In the middle stage of smelting, 9.0 kg / t to 13.0 kg / t of lime and 3.0 kg / t to 5.5 kg / t of lightly calcined dolomite are added. The binary basicity of the slag is 2.2 to 2.7, and the oxygen lance position is 1.6 m to 2 m. 0m, blowing for 5min~8min; in the later stage of smelting, add 3.2kg / t~9.5kg / t of lime to molten iron and 4.0kg / t~6.0kg / t of iron oxide scale, oxygen lance position 1.2m~1.6m, blowing for 5min~9min; the slag binary basicity at the end of smelting is 3.0~3.6, which can not only flexibly control the slag basicity at different stages of converter, but also prevent the molten iron temperature from rising too quickly by adding cooling material iron oxide scale in the later stage of smelting, effectively inhibiting the return of phosphorus to molten steel.

[0032] 3. In this invention, silicon is oxidized before pre-dephosphorization of molten iron, which can significantly reduce the silicon content of molten iron entering the converter, thereby reducing converter slag and oxygen consumption. By adopting molten iron dephosphorization pretreatment, deep dephosphorization treatment of high silicon molten iron can be achieved, breaking the limitation that converters are difficult to efficiently dephosphorize high silicon molten iron.

[0033] 4. The pre-melted slag is used for dephosphorization during the tapping of the converter, which results in rapid slag formation and a fast dephosphorization reaction at the slag-steel interface. By bottom blowing a mixed gas containing CO2, not only can carbon emissions be reduced, but the oxidizing properties and decarburization endothermic characteristics of CO2 can also be used to enhance the dephosphorization effect of the argon station, further reducing the phosphorus content of the molten iron on the basis of the converter.

[0034] 5. After argon station stirring and dephosphorization, depending on whether the phosphorus content of the molten iron meets the standard, LF refining can be used to strengthen dephosphorization, stably achieving high-purity iron smelting with ultra-low phosphorus content ≤0.002wt%. Attached Figure Description

[0035] Figure 1 This is a process flow diagram of the high-purity iron ultra-low phosphorus smelting method of the present invention. Detailed Implementation

[0036] The following detailed description, in conjunction with embodiments of the present invention and accompanying drawings, provides a clear and complete illustration of the technical solutions in these embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] It should be noted that all technical terms used in this invention are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0038] Figure 1 The process flow diagram of the high-purity iron ultra-low phosphorus smelting method of the present invention is as follows: first, the molten iron is pretreated, then the converter single slag is smelted, the slag is washed, the argon station is stirred and refined, and finally the LF is refined.

[0039] Example 1 A method for smelting high-purity iron with ultra-low phosphorus content includes the following steps: (1) Initial molten iron: C: 4.3wt%, Si: 0.60wt%, Mn: 0.28wt%, P: 0.18wt%, S: 0.03wt%, N: 0.0020wt%, Cu: 0.007wt%, Ni: 0.0058wt%, Cr: 0.0045wt%, balance Fe, temperature 1300℃.

[0040] (2) Hot metal pretreatment: 25 kg / t of iron oxide scale powder is injected into the hot metal ladle with air as the carrier gas, and the nozzle is 450 mm away from the bottom of the ladle; at the end of the pre-desiliconization, the Si content is 0.13 wt% and the slag skimming rate is >85%; continue to inject 27.9 kg / t of dephosphorizing powder, which includes 11.8 kg / t of active lime powder, 13.6 kg / t of iron oxide scale powder and 2.5 kg / t of fluorite powder; the final slag binary basicity is 3.4, the iron liquid P content is 0.029 wt% and the Si content is 0.047 wt%.

[0041] (3) Converter single-slag smelting: Add low-phosphorus scrap steel P≤0.03wt%; oxygen supply intensity 2.5Nm 3 The blowing time was 18 minutes. The total amount of slag-forming agent added was 64.2 kg / t, added in three batches: 14 kg / t of lime, 7.5 kg / t of lightly calcined dolomite, 6 kg / t of iron oxide scale, and 10 kg / t of quartz sand in the early stage of smelting; 11.2 kg / t of lime and 4.5 kg / t of lightly calcined dolomite in the middle stage of smelting; and 6 kg / t of lime and 5 kg / t of iron oxide scale in the later stage of smelting. The blowing time was 5 minutes in the early stage, 6 minutes in the middle stage, and 7 minutes in the later stage. The oxygen lance position was controlled as follows: 2.2 m for high oxygen lance in the early stage, 1.8 m for medium oxygen lance in the middle stage, and 1.4 m for low oxygen lance in the later stage. The final slag basicity was 3.2, the final molten steel temperature was 1625℃, the oxygen content was 0.085 wt%, and the phosphorus content was 0.0039 wt%.

[0042] (4) Slag washing and argon station stirring and refining: 4 min after tapping, the amount of pre-melted slag added during the tapping process is 11 kg / t, the composition is FeO: 52 wt%, CaO: 35 wt%, SiO2: 8 wt%, Al2O3: 5 wt%; Ar gas is blown from the bottom to stir the molten steel during the slag washing and argon station stirring and refining process, and CO2 gas is not blown. The flow rate of Ar gas blown from the bottom is 5.7 NL / min / t. After the tapping is completed, the flow rate of Ar gas blown from the bottom is 2.8 NL / min / t during the argon station stirring and refining process, and the argon station stirring and refining process is 6 min; after the argon station refining is completed, the P content of the molten steel is 0.0023 wt%.

[0043] (5) LF refining: Add 2.4 kg / t of active lime and 0.8 kg / t of fluorite. Since the temperature is dynamically controlled, the temperature of the molten steel during dephosphorization is between 1562℃ and 1585℃. The flow rate of Ar gas blown from the bottom of the ladle is 2.9 NL / min / t. Refine until the P content of the molten steel is 0.0016 wt% at the end point, and remove the slag until the surface is smooth.

[0044] Example 2 A method for smelting high-purity iron with ultra-low phosphorus content includes the following steps: (1) Initial molten iron: C: 4.6wt%, Si: 0.32wt%, Mn: 0.28wt%, P: 0.13wt%, S: 0.045wt%, N: 0.0019wt%, Cu: 0.0067wt%, Ni: 0.0049wt%, Cr: 0.0041wt%, balance Fe, temperature 1350℃.

[0045] (2) Hot metal pretreatment: 42 kg / t of dephosphorizing powder was sprayed into the hot metal ladle using air as the carrier gas. The powder included 19.5 kg / t of active lime powder, 19.4 kg / t of iron oxide scale powder and 3.1 kg / t of fluorite powder. The nozzle was 430 mm from the bottom of the ladle. The final slag basicity was 3.0, and the final hot metal had a P content of 0.027 wt% and a Si content of 0.041 wt%.

[0046] (3) Converter single slag smelting: Add low-phosphorus scrap steel P≤0.03wt%; oxygen supply intensity 2.4Nm 3 The blowing time was 19 minutes. The total amount of slag-forming agent added was 65.1 kg / t, added in three batches: 15.8 kg / t of lime, 6.3 kg / t of lightly calcined dolomite, 5.7 kg / t of iron oxide scale, and 10.2 kg / t of quartz sand in the early stage of smelting; 10.2 kg / t of lime and 4.8 kg / t of lightly calcined dolomite in the middle stage of smelting; and 7.2 kg / t of lime and 4.9 kg / t of iron oxide scale in the later stage of smelting. The blowing time was 6 minutes in the early stage, 6 minutes in the middle stage, and 7 minutes in the later stage. The oxygen lance position was controlled as follows: 2.1 m for high oxygen lance in the early stage of smelting, 1.7 m for medium oxygen lance in the middle stage, and 1.4 m for low oxygen lance in the later stage. The final slag basicity was 3.3, the final steel temperature was 1618℃, the oxygen content was 0.082 wt%, and the phosphorus content was 0.0035 wt%.

[0047] (4) Slag washing and argon station stirring refining: The tapping time is 4 min, the amount of pre-melted slag added is 14 kg / t, and the composition is FeO: 50.5 wt%, CaO: 36.5 wt%, SiO2: 7.4 wt%, Al2O3: 5.6 wt%; the volume ratio of bottom-blown Ar and CO2 gas during the slag washing and argon station stirring refining process is 80%: 20%, the total flow rate of mixed gas during the tapping process is 4.5 NL / min / t, the total flow rate of bottom-blown mixed gas during the argon station stirring refining process after the tapping is 2.9 NL / min / t, and the argon station stirring refining is 7 min; the P content of the molten steel after the argon station refining is 0.0019 wt%.

[0048] Example 3 A method for smelting high-purity iron with ultra-low phosphorus content includes the following steps: (1) Initial molten iron: C: 4.5wt%, Si: 0.45wt%, Mn: 0.28wt%, P: 0.15wt%, S: 0.035wt%, N: 0.0021wt%, Cu: 0.0069wt%, Ni: 0.0055wt%, Cr: 0.0043wt%, balance Fe, temperature 1360℃.

[0049] (2) Hot metal pretreatment: 16 kg / t of iron oxide scale powder is injected into the hot metal ladle with air as the carrier gas, and the nozzle is 400 mm away from the bottom of the ladle; when the Si content is 0.145 wt% at the end of the pre-desiliconization, the slag skimming rate is >85%; continue to inject 27.1 kg / t of dephosphorizing powder, which includes 12.0 kg / t of active lime powder, 12.7 kg / t of iron oxide scale powder and 2.4 kg / t of fluorite powder; the final slag binary basicity is 3.3, the iron liquid P content is 0.027 wt% and the Si content is 0.035 wt%.

[0050] (3) Converter single slag smelting: Add low-phosphorus scrap steel P≤0.03wt%; oxygen supply intensity 2.8Nm 3 The blowing time was 17 minutes. The total amount of slag-forming agent added was 61.6 kg / t, added in three batches: 13.8 kg / t of lime, 5.6 kg / t of lightly calcined dolomite, 4.5 kg / t of iron oxide scale, and 10.3 kg / t of quartz sand in the first batch; 10.2 kg / t of lime and 4.6 kg / t of lightly calcined dolomite in the second batch; and 7.0 kg / t of lime and 5.6 kg / t of iron oxide scale in the third batch. The blowing time was 5 minutes in the first batch, 5 minutes in the second batch, and 7 minutes in the third batch. The oxygen lance position was controlled as follows: 2.2 m for high oxygen lance in the first batch, 1.8 m for medium oxygen lance in the second batch, and 1.5 m for low oxygen lance in the third batch. The final slag basicity was 3.1, the final steel temperature was 1619℃, the oxygen content was 0.085 wt%, and the phosphorus content was 0.0037 wt%.

[0051] (4) Slag washing and argon station stirring refining: 5 min after tapping, the amount of pre-melted slag added is 12 kg / t, the composition is FeO: 50 wt%, CaO: 35.8 wt%, SiO2: 8.7 wt%, Al2O3: 5.5 wt%; the volume ratio of bottom-blown Ar and CO2 gas during the slag washing and argon station stirring refining process is 75%: 25%, the total flow rate of mixed gas during the tapping process is 4.3 NL / min / t, the total flow rate of bottom-blown mixed gas during the argon station stirring refining process after the tapping is 2.5 NL / min / t, and the argon station stirring refining is 8 min; the P content of the molten steel after the argon station refining is 0.0026 wt%.

[0052] (5) LF refining: Add 2.3 kg / t of active lime and 0.6 kg / t of fluorite. Since the temperature of the refining process is dynamically controlled, the temperature of the molten steel is between 1565℃ and 1593℃. The flow rate of Ar gas blown from the bottom of the ladle is 3.4 NL / min / t. Refine to the point where the P content of the molten steel is 0.0018 wt% at the end of the refining process, and remove the slag until the surface is smooth.

[0053] Comparative Example 1 Traditional process: The smelting method of the converter double slag process includes the following steps: (1) Molten iron fed into the converter: C: 4.5wt%, Si: 0.53wt%, Mn: 0.25wt%, P: 0.12wt%, S: 0.027wt%, N: 0.0020wt%, Cu: 0.007wt%, Ni: 0.0058wt%, Cr: 0.0045wt%, balance Fe, temperature 1330℃.

[0054] (2) Converter double slag smelting: 50% of the decarburized slag from the previous furnace is retained for dephosphorization and demanganese removal in this furnace, and low-phosphorus scrap steel is added and mixed with molten iron, with an oxygen supply intensity of 2.9 Nm. 3 / min / t, blowing time 28min, oxygen lance position controlled at 2.0m; total slag-forming agent added 80.5kg / t, primary slag forming: add 25.9kg / t lime and 15.4kg / t lightly calcined dolomite. After blowing for 1min, adjust the oxygen lance position to 1.6m. After blowing for 4.2min, first slag removal, slag removal rate 60%; secondary slag forming: add 23.3kg / t lime and 15.9kg / t iron oxide scale. The final slag basicity is 4.4, the final steel liquid P content is 0.0079wt%, and the final steel liquid temperature is 1650℃.

[0055] Comparative Example 2 A smelting method without iron pretreatment includes the following steps: (1) Initial molten iron: C: 4.4wt%, Si: 0.51wt%, Mn: 0.28wt%, P: 0.128wt%, S: 0.039wt%, N: 0.0021wt%, Cu: 0.006wt%, Ni: 0.0056wt%, Cr: 0.0043wt%, balance Fe, molten iron temperature: 1350℃.

[0056] (2) Converter single-slag smelting: low-phosphorus scrap steel is added; oxygen supply intensity is 2.6 Nm 3The blowing time was 21 minutes. The total amount of slag-forming agent added was 75.6 kg / t, added in three batches: 16.4 kg / t of lime, 10.3 kg / t of lightly calcined dolomite, and 10.5 kg / t of iron oxide scale in the early stage of smelting; 12.7 kg / t of lime and 5.9 kg / t of lightly calcined dolomite in the middle stage of smelting; and 11.2 kg / t of lime and 8.6 kg / t of iron oxide scale in the later stage of smelting. The blowing time was 7 minutes in the early stage, 6 minutes in the middle stage, and 8 minutes in the later stage. The oxygen lance position was controlled as follows: 2.2 m for high oxygen lance in the early stage, 1.8 m for medium oxygen lance in the middle stage, and 1.4 m for low oxygen lance in the later stage. The final slag basicity was 4.1, the final molten steel temperature was 1613℃, the oxygen content was 0.071 wt%, and the phosphorus content was 0.015 wt%.

[0057] (3) Slag washing and argon station stirring refining: 4 min of slag washing, 11 kg / t of pre-melted slag was added during slag washing, with the composition being FeO: 52.3 wt%, CaO: 35.2 wt%, SiO2: 7.5 wt%, Al2O3: 5 wt%; the volume ratio of bottom-blown Ar and CO2 gas during slag washing and argon station stirring refining was 70%:30%; the total flow rate of mixed gas during slag washing was 4.7 NL / min / t; the total flow rate of bottom-blown mixed gas during argon station stirring refining was 3.2 NL / min / t after slag washing; 6 min of argon station stirring refining; the P content of molten steel was 0.0092 wt% after argon station refining.

[0058] (4) LF refining: Add 2.4 kg / t of active lime and 0.8 kg / t of fluorite, maintain the temperature at 1560℃~1583℃, and the Ar gas flow rate at the bottom of the ladle is 3.7 NL / min / t; the final P content of the molten steel is 0.0068 wt%, and the slag is removed to the mirror surface.

[0059] Results Analysis Table 1 shows the comparative data of the total dephosphorization rate of Examples 1 to 3, and Comparative Examples 1 and 2.

[0060] Table 2 shows the amount of slag used in each step of Examples 1-3, Comparative Examples 1 and 2.

[0061] Analysis of Comparative Example 2 and Example 2 shows that their initial phosphorus contents are similar. The final phosphorus content of Example 2 is 0.0019 wt%, but the final phosphorus content of Comparative Example 2 is 0.0068%. This demonstrates the importance of the dephosphorization step in the iron pretreatment powder spraying method.

[0062] Analysis of the smelting methods of Comparative Example 1 and Examples 1-3 shows that although the subsequent slag washing and LF refining processes are reduced, the double slag method itself has high requirements for converter operation level and precision. Moreover, even with a lower initial phosphorus content than other cases, the finished product phosphorus content (0.0079wt%) is much higher than that of Examples 1-3.

[0063] Analyzing Table 2, compared with the traditional dual-slag operation, the present invention distributes the slag-forming and dephosphorization pressure evenly throughout the entire process, reduces the converter smelting pressure and the amount of slag material used, and the phosphorus content of the finished product is ≤0.002wt%.

[0064] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, once they understand the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

[0065] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for smelting high-purity iron with ultra-low phosphorus content, characterized in that, Includes the following steps: The Si content in the molten iron was assessed. When the Si content was between 0.35 wt% and 0.65 wt%, pretreatment for desiliconization was performed, followed by pretreatment for dephosphorization. When the Si content was < 0.35 wt%, direct pretreatment for dephosphorization was performed to obtain pretreated molten iron. The pretreated molten iron had a P content ≤ 0.03 wt% and a Si content ≤ 0.05 wt%. The pretreated molten iron is then smelted with low-phosphorus scrap steel in a converter single-slag smelting process. After the converter single slag smelting is completed, the slag washing and argon station stirring and refining are carried out; Continue LF refining to enhance dephosphorization, remove dephosphorization slag to obtain ultra-low phosphorus steel liquid; The phosphorus content of ultra-low phosphorus molten steel is ≤0.002wt%.

2. The method for smelting high-purity iron with ultra-low phosphorus according to claim 1, characterized in that, The desiliconization method for molten iron pretreatment involves blowing iron oxide scale powder into the ladle through a spray gun using air. The blowing rate of the iron oxide scale powder is (50wt%Si-7.0) kg / t to (50wt%Si-2.0) kg / t, where 50wt%Si is 50 times the mass percentage of Si in the molten iron. The nozzle is 350mm to 550mm from the bottom of the ladle. After desiliconization until the Si content is ≤0.15wt%, the desiliconization slag is quickly skimmed off, with a slag skimming rate >85%. The dephosphorization method for molten iron pretreatment involves injecting 25 kg / t to 36 kg / t of dephosphorization powder using air as the carrier gas, controlling the final slag binary basicity to be 2.8 to 3.

6. The dephosphorization powder consists of 38 wt% to 50 wt% active lime powder, 42 wt% to 55 wt% iron oxide scale powder, and 7 wt% to 13 wt% fluorite powder, totaling 100%.

3. The method for smelting high-purity iron with ultra-low phosphorus according to claim 1, characterized in that, The direct hot metal pretreatment dephosphorization method involves directly injecting 30 kg / t to 50 kg / t of dephosphorization powder using air as the carrier gas, controlling the final slag binary basicity to be 2.5 to 3.

2. The dephosphorization powder composition is: 35 wt% to 53 wt% of active lime powder, 40 wt% to 57 wt% of iron oxide scale powder, and 7.0 wt% to 13 wt% of fluorite powder, totaling 100%.

4. The method for smelting high-purity iron with ultra-low phosphorus according to claim 1, characterized in that, The conditions for converter single slag smelting are as follows: add low-phosphorus scrap steel with a phosphorus content ≤0.03wt%, mix in pretreated molten iron, and add slag-forming agent in three batches totaling 50kg / t~75kg / t; The specific method for adding the slag-forming agent is as follows: In the early stage of smelting, add 12.0 kg / t to 16.0 kg / t of lime, 5.0 kg / t to 7.5 kg / t of lightly calcined dolomite, 4.0 kg / t to 6.0 kg / t of iron oxide scale, and 8.0 kg / t to 12.0 kg / t of quartz sand. The binary basicity of the slag is 1.2 to 1.

8. In the early stage of smelting, the high-oxygen lance position is 2.0 m to 2.4 m, and the blowing time is 4 min to 7 min. During the mid-smelting stage, add 9.0 kg / t to 13.0 kg / t of lime and 3.0 kg / t to 5.5 kg / t of lightly calcined dolomite, maintaining a slag basicity of 2.2 to 2.

7. Lower the oxygen lance position to 1.6 m to 2.0 m and blow for 5 to 8 minutes. During the late-smelting stage, add 3.2 kg / t to 9.5 kg / t of lime and 4.0 kg / t to 6.0 kg / t of iron oxide scale, maintaining a low-oxygen lance position of 1.2 m to 1.6 m and blowing for 5 to 9 minutes. At the final smelting point, the slag basicity should be 3.0 to 3.6, and the oxygen supply intensity should be 2.3 Nm³. 3 / min / t~2.9Nm 3 / min / t, blowing time 14min~24min, final steel liquid P content ≤0.004wt%, oxygen content 0.05wt%~0.09wt%, temperature 1590℃~1640℃; bottom blowing gas flow rate in the early and middle stages of smelting is 0.03Nm 3 / min / t~0.09Nm 3 / min / t, the bottom blowing gas flow rate in the later stage is 0.02Nm³ / min / t. 3 / min / t~0.06Nm 3 / min / t.

5. The method for smelting high-purity iron with ultra-low phosphorus according to claim 1, characterized in that, The operation of slag washing is as follows: the slag discharge rate of the slag-blocking slide is <4.0 kg / t, and no deoxidation or alloying is carried out during the slag washing process; When 10%~20% of the steel has been tapped, pre-melted slag is added at a rate of 2.0 kg / min / t to 3.5 kg / min / t until the end of tapping. The total amount of pre-melted slag added is 10 kg / t to 15 kg / t. The composition of the pre-melted slag is FeO: 45wt%~58wt%, CaO: 30wt%~40wt%, SiO2: 6wt%~10wt%, and Al2O3: 5wt%~10wt%. It is mixed with the steel stream for slag washing and dephosphorization. During the slag washing and argon station stirring refining process, a mixture of Ar and CO2 gas is blown into the ladle, with Ar accounting for 60%~100% of the volume and CO2 accounting for 0~40% of the volume. The total flow rate of the bottom-blown mixed gas during the tapping process is 3.0 NL / min / t~7.0 NL / min / t. After the tapping is completed, the flow rate of the bottom-blown mixed gas during the argon station stirring refining process is 2.0 NL / min / t~5.0 NL / min / t. The argon station stirring lasts for 4 min~10 min, during which the dephosphorization reaction of the molten steel occurs.

6. The method for smelting high-purity iron with ultra-low phosphorus according to claim 1, characterized in that, Before entering the LF refining and enhanced dephosphorization process, the phosphorus (P) content of the molten steel is tested: if the P content of the molten steel is ≤0.002wt%, the dephosphorization slag is removed directly; if the P content of the molten steel is >0.002wt%, slag is added for LF refining and enhanced dephosphorization.

7. The method for smelting high-purity iron with ultra-low phosphorus according to claim 6, characterized in that, The LF refining and enhanced dephosphorization operation steps include: adding 1.5 kg / t to 3.5 kg / t of active lime and 0.5 kg / t to 1.5 kg / t of fluorite to dephosphorize the molten steel; The electrodes are energized and heated to maintain the temperature of the molten steel at 1560℃~1600℃; During dephosphorization, the bottom-blown Ar gas flow rate is 1.0 NL / min / t to 4.0 NL / min / t.

8. The method for smelting high-purity iron with ultra-low phosphorus according to claim 1, characterized in that, The chemical composition of the molten iron is C≤4.8wt%, Si≤0.65wt%, Mn≤0.30wt%, P≤0.20wt%, S≤0.05wt%, N≤0.003wt%, Cu≤0.008wt%, Ni≤0.006wt%, Cr≤0.006wt%, with the balance being Fe, totaling 100%. The temperature of the molten iron is 1300℃~1400℃.

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