A method for accurately controlling silicon and sulfur contents in low-silicon and ultra-low-sulfur steel in an LF furnace

Abstract

The application discloses a method for precisely controlling the silicon and sulfur contents in low-silicon and ultra-low-sulfur steel in an LF furnace, and belongs to the field of steelmaking processes. The method comprises the following steps: desulfurization of molten iron, oxygen-laden tapping in a converter, LF slagging for desulfurization, slagging, LF slagging for desulfurization, and precise control of the silicon and sulfur contents in low-silicon and ultra-low-sulfur steel, so that the component requirements of S≤0.001% and Si≤0.02% are met.

Description

Technical Field

[0001] This invention relates to steelmaking processes, specifically to a method for precisely controlling the silicon and sulfur content in low-silicon ultra-low-sulfur steel using an LF furnace. Background Technology

[0002] Ladle refining (LF) is a crucial piece of equipment in ladle refining, possessing metallurgical functions such as desulfurization, deoxidation, heating, and inclusion removal. Low-silicon ultra-low-sulfur steel is a steel grade with Si ≤ 0.02% and S ≤ 0.001%. LF utilizes highly reducing top slag, easily reducing S in molten steel to ≤ 0.001% even with Si content > 0.1%. However, with the development of material applications, some new materials require Si ≤ 0.02% and S ≤ 0.001%. This is because in certain corrosive environments, Si may affect the formation or stability of the passivation film on the material surface, thereby reducing the material's corrosion resistance. However, when using existing LF processes to smelt steel grades with S ≤ 0.001%, Si ≤ 0.02% becomes a smelting challenge. LF desulphurization requires high reducing power, readily reducing Si from SiO2 in the slag into the steel. Generally, when smelting steel grades with S ≤ 0.001%, Si ≤ 0.05% is achieved. If the Si content in the steel is less than 0.02%, the steel needs to be deoxidized incompletely. The top slag of the steel does not meet the conditions for desulfurization. Generally, the S content in the steel reaches about 0.003%.

[0003] Gao Shengyong et al. applied for an invention patent entitled "A Smelting Method for Low-Silicon, Ultra-Low-Sulfur Steel", patent number CN201010622968.X. The invention adopts a process of hot metal pretreatment for deep desulfurization-dephosphorization converter dephosphorization and desiliconization-decarburization converter smelting-tap steel-LF refining. The invention is characterized by controlling the following technical parameters in the process steps: (1) Hot metal pretreatment for desulfurization is carried out using KR, and the [S] ≤ 0.003% after treatment, and the slag removal rate of hot metal is > 95%; (2) Desiliconization and dephosphorization are carried out in the dephosphorization converter, and the [Si] ≤ 0.01% after smelting; (3) Hot metal enters the decarburization converter, and lime is added. The amount is 18-25Kg / ton of steel, and the binary basicity of the slag is 4.0-5.0; (4) the decarburized converter is subjected to aluminum-iron deoxidation operation to make the acid-soluble aluminum content in the molten steel after tapping reach 0.03-0.05%; (5) after the LF enters the station, the steel composition is analyzed by sampling after the decarburized converter, and aluminum-iron adjustment operation is carried out according to the target acid-soluble aluminum content of 0.05%. Then, bottom blowing argon gas is used to stir, and the dissolved aluminum in the steel is used to remove the oxygen in the slag, so that the total iron content in the slag is less than 0.5%; the low silicon and ultra-low sulfur steel is based on the mass percentage [Si]≤0.03% and [S]≤0.003%. However, the above technical solution did not achieve the technical level of Si≤0.02% and S≤0.001%.

[0004] Li Zhanjun et al. applied for an invention patent entitled "A Method for Producing Low-Carbon, Low-Silicon, Ultra-Low-Sulfur Steel Using LF Single-Unit Process", patent number CN202110170421.9. The method involves pre-treating molten iron through desulfurization and slag removal to obtain pre-treated molten iron; then smelting the pre-treated molten iron, low-sulfur scrap steel, and auxiliary materials to obtain molten steel; the oxygen blowing time during the smelting process is controlled at 13-15 minutes, and the oxygen blowing rate is controlled at 46-52 Nm³ / t steel. The lance position is controlled at 1.5–1.7m; the molten steel is tapped to obtain tapped molten steel; the tapped molten steel is added to refining slag for refining to obtain low-carbon, low-silicon, ultra-low-sulfur refined molten steel and final refining slag; during the initial slag formation stage of the refining process, argon gas is bottom-blown at 600–800 NL / min; during the later heating stage of the refining process, argon gas is bottom-blown at 400–600 NL / min and the heating time is controlled to ≤15min; so that the carbon content of the steel is 0.030%. The required concentrations are 0.050%, silicon ≤0.050%, and sulfur ≤0.0020%. However, the above technical solution did not achieve the technical level of Si ≤0.02% and S ≤0.001%.

[0005] Li Zhanjun et al. applied for an invention patent entitled "A Low-Carbon, Low-Silicon, Ultra-Low-Sulfur Steel and Its Smelting Method," patent number CN202211176874.3. The invention involves desulfurizing molten iron to obtain pretreated molten iron; smelting the pretreated molten iron in a converter, followed by oxygen-retaining tapping to obtain refined molten steel; refining the molten steel using VD (Vacuum-Decarbonization) to obtain decarburized molten steel; and refining the decarburized molten steel using LF (Furnace-Refining) to obtain refined molten steel, thus completing the smelting process. This dual process of VD decarburization and LF furnace refining achieves the required control of low carbon, low silicon, and ultra-low sulfur content, with the carbon content in the steel below 0.016%, the silicon content below 0.030%, and the sulfur content stably controlled below 0.0015%. However, the above technical solution did not achieve the technical level of Si ≤ 0.02% and S ≤ 0.001%. Summary of the Invention

[0006] To address the problems of existing technologies, this invention provides a method for precisely controlling the silicon and sulfur content in low-silicon ultra-low-sulfur steel using an LF furnace. Under the condition that the S content is ≤0.001%, the Si content is precisely controlled to ≤0.02%, producing qualified products.

[0007] A method for precisely controlling the silicon and sulfur content in low-silicon ultra-low-sulfur steel using an LF furnace, comprising the following process route: hot metal pre-desulfurization - converter smelting - LF furnace refining - slag removal - LF furnace refining; including the following steps: (1) Pre-desulfurization of molten iron: Molten iron is pre-desulfurized by a pre-desulfurization device to obtain pre-desulfurized molten iron; the S content in the pre-desulfurized molten iron is ≤0.003%; (2) Converter smelting: using pre-desulfurized molten iron and scrap steel as raw materials, converter smelting is carried out. The steel is tapped with oxygen in the converter. The content of S in the molten steel is ≤0.005%. The amount of molten steel (mass of molten steel) is read when the steel is tapped. (3) LF furnace refining: After the molten steel enters the LF furnace, quicklime and slag-forming agent are added, and the temperature is raised to 1580-1620℃. After the temperature rise is completed, argon gas is stirred for 3-20 minutes, and the argon gas flow rate is not less than 60 m³ / min. 3 / h, stirring intensity is medium or above, P content is controlled ≤0.0020%, S content in molten steel is tested, and molten steel temperature is raised to the removal temperature of 1590-1625℃; The amount of quicklime added is 3.5-10 kg / t steel, and the amount of slag remover added is 0.35-2.5 kg / t steel. (4) Slag removal: Slag is removed from the molten steel until the slag surface is cleaned and the molten steel is exposed. SiO2 in the slag is removed to obtain the molten steel after slag removal. (5) LF furnace refining: After the molten steel is slag-removed, it is reintroduced into the LF furnace. The oxygen content is measured (fixed oxygen), quicklime and slagging agent are added, the amount of aluminum added is precisely controlled, and argon gas is used for desulfurization by stirring for 3-20 minutes. The argon gas flow rate is not less than 60 m³ / min. 3 / h, heating up to the outlet temperature of 1585-1610℃; The amount of quicklime added is 3.5-10 kg / t steel, and the amount of slag remover added is 0.35-2.5 kg / t steel. The aluminum includes aluminum used for removing oxygen from molten steel (deoxidized aluminum), aluminum used for removing oxygen from slag (deoxidized aluminum), aluminum used for alloying (alloyed aluminum), aluminum used for desulfurization stirring (stirred aluminum), and aluminum used for desulfurization (desulfurized aluminum). The amount of aluminum added for deoxygenating molten steel is determined based on the oxygen content and the amount of molten steel. The amount of aluminum added for deslag oxygenation is determined based on the amount of quicklime added and the amount of molten steel. The amount of aluminum added is determined based on the target amount of aluminum in the steel composition and the amount of molten steel. The amount of aluminum added for desulfurization stirring is determined based on the desulfurization stirring time and the amount of molten steel. The amount of aluminum added for desulfurization is determined based on the desulfurization amount (the S content in the molten steel detected in step (3)) and the amount of molten steel. The low-silicon ultra-low sulfur steel has an S content of ≤0.001% and a Si mass fraction of ≤0.02%.

[0008] Furthermore, in step (1), the mass fraction of S in the molten iron is ≤0.04%, and the mass fraction of Si is 0.2%-0.6%.

[0009] Furthermore, in step (1), CaO powder and Mg powder are added during the pre-desulfurization treatment. The amount of CaO powder added is 1.4-6.0 kg / t of molten iron, and the amount of Mg powder added is 0.25-1.5 kg / t of molten iron.

[0010] Furthermore, in step (2), in order to control the sulfur content in the tapped steel, the mass of scrap steel accounts for 5%-10% of the total amount of molten iron and scrap steel after pre-desulfurization. Furthermore, in step (2), the carbon content at the converter endpoint is less than 0.06%.

[0011] Furthermore, in step (3), the S content in the molten steel is not higher than 0.008%.

[0012] Furthermore, in steps (3) and (5), the slag-reducing agent is one or both of fluorite and bauxite.

[0013] Furthermore, in step (5), the oxygen content is ≤0.07%.

[0014] Furthermore, in step (5), the amount of aluminum added is precisely controlled to be 2-4 kg / t steel.

[0015] Furthermore, in step (5), the amount of aluminum oxide added during steel removal is determined (kg) according to formula 1 based on the oxygen content (0.0001%) and the amount of molten steel (t): Oxy-aluminum content in molten steel = a × oxygen content × molten steel quantity ---------- Formula 1 In Formula 1, a = 0.0010 - 0.0020, preferably 0.0015; The amount of alumina added for slag removal is determined using Formula 2 based on the amount of quicklime added (100 kg) and the amount of molten steel (t): Slag-removed alumina = b × amount of quicklime × amount of molten steel ---------- Formula 2 In Formula 2, b = 0.0335-0.0345, preferably 0.0337; Based on the target aluminum content (0.01%) in the steel composition and the amount of molten steel (t), the amount of alloying aluminum added (kg) is determined using Formula 3: Alloyed aluminum = c × steel grade aluminum composition × molten steel quantity ---------- Formula 3 In Formula 3, c = 0.1145 - 0.1155, preferably 0.115; The amount of aluminum added for stirring (kg) is determined using Formula 4 based on the desulfurization stirring time (min) and the amount of molten steel (t): Aluminum content = d × desulfurization stirring time × molten steel volume ---------- Formula 4 In Formula 4, d = 0.0315-0.0325, preferably 0.0318; The amount of desulfurized aluminum added (kg) is determined using Formula 5 based on the desulfurization rate (0.001%) and the amount of molten steel (t): Desulfurized aluminum = e × desulfurization amount × molten steel quantity ---------- Formula 5 In Formula 5, e = 0.0265-0.0275, preferably 0.0269.

[0016] Furthermore, the target amount of aluminum in the steel composition is ≤0.01%.

[0017] Furthermore, the carbon content in the low-silicon ultra-low sulfur steel is ≤0.04%.

[0018] Furthermore, the low-silicon ultra-low sulfur steel is of steel grade FBCT.

[0019] Furthermore, it also includes: (6) continuous casting.

[0020] The beneficial effects of this invention are: This invention reduces the sulfur content of steel tapped from the converter by desulfurizing molten iron and controlling the amount of scrap steel in the converter. Through oxygen-carrying tapping, LF slag formation for phosphorus removal, and slag skimming, the SiO2 content in the slag is reduced. LF slag formation for desulfurization yields a reducing slag with a sulfur capacity >50 and a binary basicity >7, achieving precise control of the silicon and sulfur content in low-silicon ultra-low-sulfur steel, meeting the composition requirements of S≤0.001% and Si≤0.02%.

[0021] This invention produces low-silicon, ultra-low-sulfur steel, providing high-quality raw materials for high-end steel products. Based on a profit of 1480 yuan / ton, an annual output of 2000 tons, and a technology contribution rate of 80%, the annual benefit is 1480 * 2000 * 0.8 = 2.368 million yuan. Detailed Implementation

[0022] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0023] Example 1 The target Si mass fraction for steel grade FBCT is ≤0.02%, the target S mass fraction is ≤0.001%, the target carbon mass fraction is ≤0.04%, and the target aluminum content is ≤0.01%. The molten iron contains 0.032% sulfur and 0.38% silicon. The molten iron is hoisted into the desulfurization station, where 910 kg of CaO powder and 280 kg of Mg powder are injected, resulting in a desulfurization level of 0.0014%. 272 ​​tons of molten iron and 20 tons of scrap steel are added to the converter, achieving a final carbon mass fraction of 0.025%. The steel output is 262 tons. 2606 kg of quicklime and 701 kg of fluorite are added to the LF (Fuel Processing Unit), and the temperature is raised to 1594℃. After heating, stirring is performed for 10 minutes, with an argon flow rate of 80 m³ / h. 3 / h. Sampling showed that the P content reached 0.0012% and the S content was 0.0045%. The temperature reached 1605℃, and the molten steel was poured out of the ladle and the slag was removed. The slag surface was cleaned to expose the molten steel. When the molten steel re-entered the LF, the oxygen content was determined to be 0.0423%. 3425 kg of quicklime and 1123 kg of fluorite were added. Based on the oxygen content (0.0423%) and the amount of molten steel (262t), the amount of deoxidized aluminum added was calculated using Formula 1: 423 × 262 × 0.0015 = 166 kg, and 166 kg of deoxidized aluminum was added. Based on the amount of quicklime (3425 kg) and the amount of molten steel (262t), the amount of deoxidized aluminum added was calculated using Formula 2: 34.25 × 262 × 0.0337 = 302 kg, and 302 kg of deoxidized aluminum was added. The target amount of aluminum content for the steel grade (0.01%) was calculated. Based on the molten steel volume (262t), the amount of alloyed aluminum added is calculated using Formula 3: 1 × 262 × 0.115 = 30kg, and 30kg of alloyed aluminum is added. Based on the desulfurization stirring time (12min) and the molten steel volume (262t), the amount of stirring aluminum added is calculated using Formula 4: 12 × 262 × 0.0318 = 100kg, and 100kg of stirring aluminum is added. Based on the desulfurization amount (0.0045%) and the molten steel volume (262t), the amount of desulfurized aluminum added is calculated using Formula 5: 4.5 × 262 × 0.0269 = , and 32kg of desulfurized aluminum is added. Argon gas is used for thorough stirring and desulfurization for 12min at a flow rate of 80m³ / min. 3 / h, the temperature of molten steel was measured at 1590℃, a sample was taken and poured onto the ladle. The mass fraction of carbon in the ladle was 0.035%, the mass fraction of silicon was 0.013%, the mass fraction of sulfur was 0.0008%, and the mass fraction of almand was 0.006%.

[0024] Example 2 The target Si mass fraction for steel grade FBCT is ≤0.02%, the target S mass fraction is ≤0.001%, the target carbon mass fraction is ≤0.04%, and the target aluminum content is ≤0.01%. The molten iron contains 0.030% sulfur and 0.34% silicon. The molten iron is hoisted into the desulfurization station, where 850 kg of CaO powder and 260 kg of Mg powder are injected, resulting in a desulfurization level of 0.0025%. 275 tons of molten iron and 20 tons of scrap steel are added to the converter, achieving a final carbon mass fraction of 0.032%. The steel output is 264 tons. 2475 kg of quicklime and 674 kg of fluorite are added to the LF (sulfurized iron / fouling) furnace, and the temperature is raised to 1586℃. After heating, stirring is performed for 10 minutes, with an argon flow rate of 80 m³ / h. 3 / h. Sampling showed that the P content reached 0.0011% and the S content was 0.0035%. The temperature reached 1602℃, and the molten steel was poured out of the ladle and the slag was removed. The slag surface was cleaned to expose the molten steel. When the molten steel re-entered the LF, the oxygen content was determined to be 0.0471%. 3536 kg of quicklime and 1016 kg of fluorite were added. Based on the oxygen content (0.0471%) and the amount of molten steel (264t), the amount of deoxidized aluminum added was calculated using Formula 1: 471 × 264 × 0.0015 = 187 kg, and 187 kg of deoxidized aluminum was added. Based on the amount of quicklime (3536 kg) and the amount of molten steel (264t), the amount of deoxidized aluminum added was calculated using Formula 2: 35.36 × 264 × 0.0337 = 315 kg, and 315 kg of deoxidized aluminum was added. The target amount of aluminum content for the steel grade (0.01%) was calculated. Based on the molten steel volume (264t), the amount of alloyed aluminum added is calculated using Formula 3: 1 × 264 × 0.115 = 30kg, and alloyed aluminum is added. Based on the desulfurization stirring time (15min) and the molten steel volume (264t), the amount of stirring aluminum added is calculated using Formula 4: 15 × 264 × 0.0318 = 126kg, and 126kg of stirring aluminum is added. Based on the desulfurization amount (0.0035%) and the molten steel volume (264t), the amount of desulfurized aluminum added is calculated using Formula 5: 3.5 × 264 × 0.0269 = 25kg, and 25kg of desulfurized aluminum is added. Argon gas is used for thorough stirring and desulfurization for 15min, with an argon gas flow rate of 80m³ / min. 3 / h, the temperature of molten steel was measured at 1585℃, a sample was taken and poured onto the ladle. The mass fraction of carbon in the ladle was 0.037%, the mass fraction of silicon was 0.016%, the mass fraction of sulfur was 0.0009%, and the mass fraction of almand was 0.007%.

Claims

1. A method for precisely controlling the silicon and sulfur content in low-silicon ultra-low-sulfur steel using an LF furnace, characterized in that, Includes the following steps: (1) Pre-desulfurization of molten iron: Molten iron is subjected to pre-desulfurization treatment to obtain pre-desulfurized molten iron; the S content in the pre-desulfurized molten iron is ≤0.003%; (2) Converter smelting: using pre-desulfurized molten iron and scrap steel as raw materials, converter smelting is carried out. Steel is tapped with oxygen in the converter. The S content in the molten steel is ≤0.005%. The amount of molten steel is read when tapping. (3) LF furnace refining: After the molten steel enters the LF furnace, quicklime and slag-forming agent are added, and the temperature is raised to 1580-1620℃. After the temperature rise is completed, argon gas is stirred for 3-20 minutes, and the argon gas flow rate is not less than 60 m³ / min. 3 / h, control the P content ≤0.0020%, detect the S content in the molten steel, and raise the molten steel temperature to the removal temperature of 1590-1625℃; The amount of quicklime added is 3.5-10 kg / t steel, and the amount of slag remover added is 0.35-2.5 kg / t steel. (4) Slag removal: Slag is removed from the molten steel until the slag surface is cleaned and the molten steel is exposed. SiO2 in the slag is removed to obtain molten steel after slag removal. (5) LF furnace refining: After the molten steel is slag-removed and re-enters the LF furnace, the oxygen content is measured, quicklime and slagging agent are added, the amount of aluminum added is precisely controlled, and argon gas is used for desulfurization by stirring for 3-20 minutes. The argon gas flow rate is not less than 60 m³ / min. 3 / h, heating up to the outlet temperature of 1585-1610℃; The amount of quicklime added is 3.5-10 kg / t steel, and the amount of slag remover added is 0.35-2.5 kg / t steel. The aluminum includes aluminum for removing oxygen from molten steel, aluminum for removing oxygen from slag, aluminum for alloying, aluminum for desulfurization stirring, and aluminum for desulfurization. The amount of aluminum added for deoxygenating molten steel is determined based on the oxygen content and the amount of molten steel. The amount of aluminum added for deslag oxygenation is determined based on the amount of quicklime added and the amount of molten steel. The amount of aluminum added for alloying is determined based on the target amount of aluminum in the steel composition and the amount of molten steel. The amount of aluminum added for desulfurization stirring is determined based on the desulfurization stirring time and the amount of molten steel. The amount of aluminum added for desulfurization is determined based on the S content and the amount of molten steel detected in step (3). In step (5), the amount of aluminum added for removing oxygen from the molten steel is determined using Formula 1, based on the oxygen content measured in units of 0.0001% and the amount of molten steel: Aluminum used for removing oxygen from molten steel = a × oxygen content × molten steel quantity ---------- Formula 1 In Formula 1, a = 0.0010 - 0.0020, the unit of molten steel quantity is t, and the unit of aluminum added for removing oxygen from molten steel is kg; Based on the amount of quicklime added in units of 100 kg and the amount of molten steel, the amount of aluminum added for slag removal is determined using Formula 2: Aluminum used for slag removal = b × amount of quicklime added × amount of molten steel --------- Formula 2 In Formula 2, b = 0.0335 - 0.0345, the unit of molten steel quantity is t, and the unit of aluminum added for slag removal oxygen is kg; Based on the target amount of aluminum in the steel grade composition (measured in units of 0.01%) and the amount of molten steel, the amount of aluminum to be added for alloying is determined using Formula 3: Aluminum used for alloying = c × target amount of aluminum in the aluminum composition of the steel grade × amount of molten steel ---------- Formula 3 In Formula 3, c = 0.1145 - 0.1155, the unit of molten steel is t, and the unit of aluminum added for alloying is kg; The amount of aluminum added for desulfurization stirring is determined using Formula 4, based on the desulfurization stirring time and the amount of molten steel: Aluminum used for desulfurization stirring = d × desulfurization stirring time × molten steel volume -------- Formula 4 In Formula 4, d = 0.0315 - 0.0325, the unit of molten steel quantity is t, the unit of desulfurization stirring time is min, and the unit of aluminum added for desulfurization stirring is kg; Following step (3) where the sulfur content and quantity of molten steel are measured in units of 0.001%, the amount of aluminum to be added for desulfurization is determined using formula 5: Aluminum used for desulfurization = e × S content × molten steel quantity ---------- Formula 5 In Formula 5, e = 0.0265 - 0.0275, the unit of molten steel quantity is t, and the unit of aluminum added for desulfurization is kg; The low-silicon ultra-low sulfur steel has an S content of ≤0.001% and a Si mass fraction of ≤0.02%.

2. The method according to claim 1, characterized in that, In step (1), the content of S in the molten iron is ≤0.04% and the content of Si is 0.2%-0.6%; CaO powder and Mg powder are added in the pre-desulfurization treatment, with the amount of CaO powder added being 1.4-6.0 kg / t of molten iron and the amount of Mg powder added being 0.25-1.5 kg / t of molten iron.

3. The method according to claim 1, characterized in that, In step (2), the mass of scrap steel accounts for 5%-10% of the total amount of molten iron and scrap steel after pre-desulfurization; the carbon content at the converter endpoint is less than 0.06%.

4. The method according to claim 1, characterized in that, In step (3), the S content in the molten steel is not higher than 0.008%.

5. The method according to claim 1, characterized in that, In steps (3) and (5), the slag-reducing agent is one or two of fluorite and bauxite.

6. The method according to claim 1, characterized in that, In step (5), the oxygen content is ≤0.07%, and the amount of aluminum added is precisely controlled to be 2-4 kg / t steel.

7. The method according to claim 1, characterized in that, The target amount of aluminum in the steel composition is ≤0.01%.

8. The method according to claim 1, characterized in that, The carbon content in the low-silicon ultra-low sulfur steel is ≤0.04%.

9. The method according to claim 1, characterized in that, Also includes: (6) Continuous casting.