Usage method of ladle slag modifier for silicon killed steel directly produced by converter

Abstract

The present invention relates to a method for using a converter direct-flow silicon-killed steel ladle slag modifier, and belongs to the field of smelting production technology in the metallurgical industry. The technical solution is: the converter blowing end temperature is 1620°C-1660°C; 2.0-5.0kg / t of lime, 0-1.0kg / t of fluorite and 0-1.0kg / t of quartz sand are added at the beginning of tapping; after tapping is completed, 1.5kg / t-3kg / t of pre-melted ladle slag modifier and 0-1.0 kg / t of ferrosilicon powder are added; argon gas is strongly blown from the bottom of the ladle to form slag; after the strong blowing is completed, the medium-intensity argon blowing time is 2-5min; after the medium-intensity argon blowing is completed, calcium treatment can be carried out according to the process requirements of the steel grade; after the calcium treatment is completed, it is switched to soft argon blowing to even out the composition, temperature and remove inclusions. The beneficial effects of the present invention are: achieving efficient desulfurization under the converter direct-flow process conditions of silicon-killed steel, and ensuring the castability of molten steel under the condition of low oxidizability of molten steel.

Description

Technical Field

[0001] The invention relates to a method for using a converter direct-load silicon-killed steel ladle slag modifier, and belongs to the technical field of smelting production in the metallurgical industry. Background Art

[0002] Silicon killed steel is generally produced using two processes: converter direct refining and LF refining, depending on the steel grade characteristics and quality requirements.

[0003] The converter direct-flow silicon-killed production process uses precipitation deoxidation during the tapping process, without slag washing or ladle slag modification. This results in relatively high oxygen content in the molten steel. To meet the required sulfur content for each steel grade, the incoming molten iron sulfur content must be strictly controlled or pretreated. Furthermore, if sulfur levels are high at the end of the converter blowing, additional slag blowing for desulfurization may be employed. This process results in high molten steel oxygen content and relatively poor product quality.

[0004] The LF refined silicon-killed steel production process places relatively loose requirements on the incoming hot metal. Deoxidation and desulfurization are achieved through the production of reducing slag during the refining process, resulting in relatively high production costs. For steel grades intended for drawing applications, a low-basicity ladle slag is required to maintain the deoxidation product as liquid silicates to ensure castability. However, due to the reduced alkalinity of the ladle slag's desulfurization capacity, hot metal pretreatment is still required to ensure that the sulfur content in the steel meets quality requirements.

[0005] Direct-converter aluminum-killed steel utilizes ladle slag modifiers to create high-basicity reducing slag, achieving efficient desulfurization and achieving a molten steel desulfurization rate of approximately 50%. This process is currently widely used in aluminum-killed steel production. To achieve rapid slagging, the refined slag, slag washes, or modifiers commonly used in aluminum-killed steel contain a certain amount of metallic aluminum. Using this in silicon-killed steel production can cause Al2O3 blockage in the steel's water outlets, failing to meet the castability requirements of silicon-killed steel.

[0006] CN 108570533 A discloses a deoxidizing slag suitable for silicon-killed steel. This low-aluminum, high-silicon, low-melting-point slag can rapidly deoxidize and produce foamed slag during the LF production process, shortening the time it takes to form white slag. However, the claims of this invention are limited to the preparation method for the deoxidizing slag; the LF refining process is required, which is costly. The specific implementation method does not clearly define the control of the ladle slag system, making it difficult to achieve desulfurization while ensuring the castability of the molten steel.

[0007] CN 116694865 A discloses a refined slag suitable for desulfurization of silicon-killed steel ladles and a method for its use. The refined slag contains 2% to 10% elemental Al and is not suitable for silicon-killed steel products that have special requirements for Al2O3 in the steel, especially the SWRH82B steel grade described in the embodiments. Since Al2O3 inclusions easily cause drawing fractures, such steel grades have strict requirements on the Al content of raw and auxiliary materials. The refined slag needs to be used in conjunction with the LF refining process to achieve the purpose of slag washing and desulfurization, which is relatively expensive.

[0008] CN 111041148 B discloses a process for continuous casting of medium-thin slabs of low-sulfur, medium-carbon structural steel directly from a converter. To ensure the final molten steel S content is ≤0.012%, this process requires molten iron pretreatment to control the incoming molten iron S content to ≤0.012%. High-temperature tapping is employed, with refined slag added for slag washing and a stirring desulfurization station using argon. While this process can control the molten steel S content to below 0.008%, it requires molten iron pretreatment, which is costly. Furthermore, the tapping temperature of 1670°C to 1680°C, which is too high to maintain the temperature loss during the argon blowing and stirring desulfurization process, increases the oxidizability of the molten steel, further increasing metal loss and causing severe erosion of the converter lining. Furthermore, the desulfurization capacity is only approximately 0.006%, resulting in poor desulfurization effectiveness. Summary of the Invention

[0009] The purpose of the present invention is to provide a method for using a converter direct-loaded silicon-killed steel ladle slag modifier, so as to achieve efficient desulfurization under the converter direct-loaded process conditions of silicon-killed steel, and ensure the castability of molten steel under the condition of low oxidation of molten steel, thereby solving the problems existing in the background technology.

[0010] The technical solution of the present invention is:

[0011] A method for using a converter direct-loaded silicon-killed steel ladle slag modifier, wherein the chemical composition of the silicon-killed steel is as follows: Si≤0.80%, S≤0.025%, and Al≤0.005%. The production process includes a converter, argon blowing, and continuous casting, and is controlled according to the following steps:

[0012] a. The S content of the molten iron in the furnace is ≤ 0.070%, and the final temperature of the converter blowing is 1620℃-1660℃;

[0013] b. Argon is blown from the bottom throughout the tapping process. Lime 2.0-5.0kg / t, fluorite 0-1.0kg / t and quartz sand 0-1.0kg / t are added at the beginning of tapping;

[0014] c. After tapping, add 1.5kg / t-3kg / t of pre-melted ladle slag modifier and 0-1.0 kg / t of ferrosilicon powder to the surface of the molten steel;

[0015] d. After the steel is tapped, argon is blown from the bottom of the ladle to form slag. The intensity of the strong blowing is based on the exposed diameter of the molten steel surface being greater than 500mm;

[0016] e. After the strong blowing is completed, dip the ladle slag. The color of the ladle slag should be white, grayish white or beige. If the slag color does not meet the requirements, add ferrosilicon powder and continue strong blowing to make slag;

[0017] f. After the slag sample color meets the requirements, desulfurization is carried out by blowing argon with medium intensity according to the sulfur content of the molten steel, and the medium intensity argon blowing time is 2-5 minutes;

[0018] g. After the medium-intensity argon blowing is completed, calcium treatment can be carried out according to the steel grade and process requirements;

[0019] h. After the calcium treatment is completed, the process is switched to soft argon blowing to even out the composition, temperature and remove inclusions. The soft argon blowing is based on the exposed diameter of the molten steel surface being ≤200mm. After the molten steel temperature and composition meet the process requirements of the steel grade, it enters the continuous casting process to cast qualified steel billets.

[0020] In the step c, the chemical composition weight percentage of the pre-melting ladle slag modifier is: SiO2≤15%, CaO≥35%, Si≥20%, Al<2%, Al2O3≤15%, MgO≤5%, C:3%-5%, S≤0.050%, P≤0.050%, and the rest are unavoidable impurities.

[0021] In the step e, the composition range of the ladle slag is: basicity (CaO / SiO2) 2.0-2.5; FeO+MnO<3%.

[0022] In the step d, the strong blowing intensity of the argon flow rate is ≥500 L / min, and the strong stirring time is 1-3 min.

[0023] In step f, the medium-intensity argon flow rate is ≥300 L / min.

[0024] In the step h, the soft blowing argon flow rate is 100±20 L / min, and the soft blowing argon time is 3-8 min.

[0025] The beneficial effects of the present invention are as follows: under conditions where the sulfur content of molten iron is relatively high, there is no need for molten iron pretreatment and LF refining. By producing low-alkalinity reducing slag, the sulfur content of molten steel can be controlled to 0.025% or below, thereby achieving efficient desulfurization under the conditions of direct-flow process of silicon-killed steel converter, and ensuring the castability of molten steel under conditions of low oxidizability of molten steel. DETAILED DESCRIPTION

[0026] A method for using a converter direct-loaded silicon-killed steel ladle slag modifier, wherein the chemical composition of the silicon-killed steel is as follows: Si≤0.80%, S≤0.025%, and Al≤0.005%. The production process includes a converter, argon blowing, and continuous casting, and is controlled according to the following steps:

[0027] a. The S content of the molten iron in the furnace is ≤ 0.070%, and the final temperature of the converter blowing is 1620℃-1660℃;

[0028] b. Argon is blown from the bottom throughout the tapping process. Lime 2.0-5.0kg / t, fluorite 0-1.0kg / t and quartz sand 0-1.0kg / t are added at the beginning of tapping;

[0029] c. After tapping, add 1.5kg / t-3kg / t of pre-melted ladle slag modifier and 0-1.0 kg / t of ferrosilicon powder to the surface of the molten steel;

[0030] d. After the steel is tapped, argon is blown from the bottom of the ladle to form slag. The intensity of the strong blowing is based on the exposed diameter of the molten steel surface being greater than 500mm;

[0031] e. After the strong blowing is completed, dip the ladle slag. The color of the ladle slag should be white, grayish white or beige. If the slag color does not meet the requirements, add ferrosilicon powder and continue strong blowing to make slag;

[0032] f. After the slag sample color meets the requirements, desulfurization is carried out by blowing argon with medium intensity according to the sulfur content of the molten steel, and the medium intensity argon blowing time is 2-5 minutes;

[0033] g. After the medium-intensity argon blowing is completed, calcium treatment can be carried out according to the steel grade and process requirements;

[0034] h. After the calcium treatment is completed, the process is switched to soft argon blowing to even out the composition, temperature and remove inclusions. The soft argon blowing is based on the exposed diameter of the molten steel surface being ≤200mm. After the molten steel temperature and composition meet the process requirements of the steel grade, it enters the continuous casting process to cast qualified steel billets.

[0035] In the step c, the chemical composition weight percentage of the pre-melting ladle slag modifier is: SiO2≤15%, CaO≥35%, Si≥20%, Al<2%, Al2O3≤15%, MgO≤5%, C:3%-5%, S≤0.050%, P≤0.050%, and the rest are unavoidable impurities.

[0036] In the step e, the composition range of the ladle slag is: basicity (CaO / SiO2) 2.0-2.5; FeO+MnO<3%.

[0037] In the step d, the strong blowing intensity of the argon flow rate is ≥500 L / min, and the strong stirring time is 1-3 min.

[0038] In step f, the medium-intensity argon flow rate is ≥300 L / min.

[0039] In the step h, the soft blowing argon flow rate is 100±20 L / min, and the soft blowing argon time is 3-8 min.

[0040] In the step b, the lime composition range is: CaO ≥ 90%, SiO2 ≤ 2.5%, S < 0.030%, MgO ≤ 2%, and the particle size is ≤ 20 mm;

[0041] Fluorite composition range is: CaF2 ≥ 80%, SiO2 ≤ 18.5%, S < 0.020%, P < 0.08%;

[0042] The composition range of quartz sand is: SiO2 ≥ 90%;

[0043] The composition range of ferrosilicon powder is: Si≥72%, P<0.045%, S<0.015%, Al≤2%;

[0044] The composition range of ladle slag is: basicity (CaO / SiO2) 2.0-2.5; FeO+MnO<3%;

[0045] Steel billets include: square billets, rectangular billets, slabs, round billets and H-beams. Example 1

[0046] The S content of the molten iron in the furnace is 0.062%, the final temperature of the converter blowing is 1634℃, the converter tapping volume is 120 tons, the final oxygen content of the converter is 558ppm, and the S content is 0.049%. When producing Q235B steel, 400kg of high-calcium lime and 50kg of fluorite are added at the beginning of tapping, and recarburizer, silicon-manganese alloy, ferrosilicon and silicon-aluminum-iron deoxidizer are added to 1 / 3 to 2 / 3 of the tapping. After tapping, 240kg of modifier and 40kg of ferrosilicon powder are added, and the mixture is stirred vigorously for 3 minutes. The argon flow rate is 550L / min. The color of the ladle slag sample is white. Color, medium intensity argon blowing for 5 minutes, argon flow rate 400L / min, feeding calcium line 150m, soft argon blowing for 4 minutes, argon flow rate 90L / min; ladle slag basicity (CaO / SiO2) = 2.4, (FeO+MnO) = 1.1%; outgoing molten steel Si: 0.13%, Al: 0.003%, S: 0.025%, desulfurization rate 48.98%; continuous casting produced 165mm×280mm cross-section rectangular billets, and there was no water blockage during the casting process; the total oxygen content of the billet was 41ppm. Example 2

[0047] The S content of the molten iron in the furnace was 0.036%, the final temperature of the converter blowing was 1645℃, the converter tapping volume was 116 tons, the final oxygen content of the converter was 310ppm, and the S content was 0.029%. When producing 45# steel, 400kg of high-calcium lime, 25kg of fluorite, and 50kg of quartz sand were added during the tapping process. Recarburizer, silicon-manganese alloy, ferrosilicon, and silicon-calcium-barium deoxidizer were added to 1 / 3 to 2 / 3 of the tapping volume. 350kg of modifier and 40kg of ferrosilicon powder were added at the end of tapping. The mixture was stirred vigorously for 3 minutes at an argon flow rate of 650L / min. The color of the ladle slag sample was beige. The mixture was blown with medium-intensity argon for 5 minutes at an argon flow rate of 350L / min. 80m of calcium wire was fed and soft argon was blown for 4 minutes at an argon flow rate of 120L / min. The basicity of the ladle top slag (CaO / SiO2) was 2.0. (FeO+MnO)=0.5%; Si: 0.22%, Al: 0.002%, S: 0.013% in the outgoing molten steel, with a desulfurization rate of 55.17%; continuous casting produced 150mm×150mm cross-section square billets, with no water blockage during the casting process; the total oxygen content of the billet was 28ppm. Example 3

[0048] The S content of the molten iron in the furnace is 0.027%, the final temperature of the converter blowing is 1652℃, the converter tapping volume is 166 tons, the final oxygen content of the converter is 403ppm, and the S content is 0.020%. When producing Q355B steel, 500kg of high-calcium lime and 80kg of fluorite are added during the tapping process. Recarburizer, silicon-manganese alloy, ferrosilicon, and silicon-aluminum-iron deoxidizer are added to 1 / 3 to 2 / 3 of the tapping. 350kg of modifier and 60kg of ferrosilicon powder are added at the end of tapping. The mixture is stirred vigorously for 2 minutes and the argon flow rate is 800L / min. The color of the ladle slag sample is off-white. The sample is blown with medium-intensity argon for 3 minutes at a flow rate of 300L / min. 200m of calcium wire is fed and soft argon is blown for 5 minutes at a flow rate of 100L / min. The basicity of the ladle top slag (CaO / SiO2) is 2.3. (FeO+MnO)=1.6%; Si: 0.30%, Al: 0.004%, S: 0.007% in the outgoing molten steel, with a desulfurization rate of 65%; continuous casting produced slabs with a cross-section of 210mm×1025mm, with no water blockage during the casting process; the total oxygen content of the slab was 33ppm.

Claims

1. A method for using a converter direct-loaded silicon-killed steel ladle slag modifier, characterized by: The chemical composition of silicon-killed steel is as follows: Si≤0.80%, S≤0.025%, Al≤0.005%. The production process includes converter, argon blowing and continuous casting, and is controlled according to the following steps: a. The S content of the molten iron in the furnace is ≤ 0.070%, and the final temperature of the converter blowing is 1620℃-1660℃; b. Argon is blown from the bottom throughout the tapping process. Lime 2.0-5.0kg / t, fluorite 0-1.0kg / t and quartz sand 0-1.0kg / t are added at the beginning of tapping; c. After tapping is completed, 1.5kg / t-3kg / t of pre-melted ladle slag modifier and 0-1.0kg / t of ferrosilicon powder are added to the surface of the molten steel. The chemical composition mass percentage of the pre-melted ladle slag modifier is: SiO2≤15%, CaO≥35%, Si≥20%, Al<2%, Al2O3≤15%, MgO≤5%, C:3%-5%, S≤0.050%, P≤0.050%, and the rest are unavoidable impurities; d. After the steel is tapped, argon is blown from the bottom of the ladle to form slag. The blowing intensity is based on the exposed diameter of the molten steel surface being greater than 500mm. The blowing intensity argon flow rate is ≥500L / min and the strong stirring time is 1-3min. e. After the strong blowing is completed, dip the ladle slag. The color of the ladle slag should be white, grayish white or beige. If the slag color does not meet the requirements, add ferrosilicon powder and continue strong blowing to make slag; f. After the slag sample color meets the requirements, desulfurization is carried out by blowing argon with medium intensity according to the sulfur content of the molten steel. The medium intensity argon flow rate is ≥300L / min and the medium intensity argon blowing time is 2-5min; g. After the medium-intensity argon blowing is completed, calcium treatment is carried out according to the steel grade and process requirements; h. After the calcium treatment is completed, switch to soft argon blowing to uniform the composition, temperature and remove inclusions. The soft argon blowing is based on the exposed diameter of the molten steel surface ≤ 200mm, the soft argon blowing flow rate is 100±20L / min, and the soft argon blowing time is 3-8min. After the molten steel temperature and composition meet the steel grade process requirements, it enters the continuous casting process to cast qualified steel billets.

2. The method for using the converter direct-loaded silicon-killed steel ladle slag modifier according to claim 1, characterized in that: In the step e, the composition range of the ladle slag is: basicity CaO / SiO2 2.0-2.5; FeO+MnO<3%.