A refining slag suitable for desulphurization of silicon killed steel ladle and a method of use

Abstract

The application discloses a refining slag suitable for desulfurization of a silicon killed steel ladle and a use method, and belongs to the technical field of refining slag. The chemical components of the refining slag include the following in mass percentage: CaO: 30-50%, Al2O3: 10-20%, SiO2: 0-10%, CaF2: 20-40%, elemental Al: 2-10%, S: less than or equal to 0.05%, N: less than or equal to 0.05%, Ti: less than or equal to 0.02%, and inevitable impurities; the refining slag is added after a silicon-containing deoxidizer is added during tapping of a converter and at the initial stage of LF refining, and can effectively improve the desulfurization capacity of the refining slag and shorten the slagging time.

Description

Technical Field

[0001] This invention belongs to the field of refining slag technology, and relates to a refining slag suitable for desulfurization of silicon killed steel ladles and its application method. Background Technology

[0002] Silicon-killed steel generally requires products with good drawing and fatigue properties, which necessitates low levels of impurities and high purity of molten steel. Sulfur, as one of the most significant impurities, is influenced by the deoxidation method, slag basicity, and performance requirements of the silicon-killed steel. Currently, the mainstream production process for silicon-killed steel relies on controlling the sulfur content of the molten iron to control the sulfur content of the finished product, resulting in high production costs. Furthermore, controlling the sulfur content of the molten iron is limited by the equipment and facilities of some enterprises, making desulfurization impossible. Additionally, with the increasing pursuit of steel purity and the stricter requirements for impurity content, simply controlling the sulfur content of the molten iron is no longer sufficient to meet the current demand for low-sulfur products.

[0003] In the LF refining process, a specially proportioned slag is added to the ladle. Under the physical heat of the molten steel and the action of the electrode arc, it melts into liquid slag, achieving purposes such as refining the molten steel and providing heat insulation. This slag is collectively referred to as refining slag. The basic functions of refining slag are to remove inclusions and elements such as sulfur and oxygen from the molten steel that can adversely affect steel quality, purify the molten steel, prevent the molten steel from absorbing air, and reduce heat loss. Existing silicon-killed steel refining slag has problems such as not desulfurizing, slow slag formation, and weak inclusion removal capacity during the smelting process. On the other hand, directly using aluminum-containing steel desulfurization slag systems can easily lead to an increase in Class B inclusions in steel grades, affecting the cleanliness of the molten steel. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides a refining slag and a method for desulfurizing silicon killed steel ladles, which can effectively solve the problems of slow slag formation and failure to desulfurize existing silicon killed steel refining production technology, while avoiding the "side effect" of increased inclusions.

[0005] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0006] A refining slag suitable for desulfurization of silicon-killed steel ladles, with the following chemical composition by mass fraction: CaO: 30%–50%, Al2O3: 10%–20%, SiO2: 0–10%, CaF2: 20%–40%, elemental Al: 2%–10%, S≤0.05%, N≤0.05%, Ti≤0.02%, with the remainder being unavoidable impurities.

[0007] The mass fractions of CaO, Al2O3, SiO2, CaF2, and elemental Al in the refining slag satisfy the following:

[0008] CaO: (SiO2+Al2O3)=1.0~5.0, CaO:CaF2=0.75~2.5, Al2O3:Al=1.0~10.0.

[0009] The particle size of the refining slag is 10mm to 40mm, with less than 10mm of screened material ≤10wt% and H2O ≤0.8wt%.

[0010] The raw materials for the refining slag include: lime, fluorite, aluminum ash, and binder.

[0011] The above-mentioned method of using refining slag includes the following steps:

[0012] Step (1): Add silicon-containing deoxidizer immediately after tapping the steel from the converter. When 1 / 3 of the steel has been tapped, start adding the refining slag. The amount of refining slag added is 2kg to 4kg per ton of steel.

[0013] Step (2): When LF refining is carried out, the refining slag is added in batches, and the amount of refining slag added is 2kg to 4kg per ton of steel.

[0014] In step (2), the refining residue is added at the initial stage of refining.

[0015] In step (2), after the refining slag is added, it is heated by electric arc for 2 to 5 minutes, during which the bottom blowing gas flow rate of the ladle is 100 to 300 NL / min.

[0016] The beneficial effects of adopting the above technical solution are as follows: 1. The components of the refining slag of the present invention work synergistically to effectively solve the problems of slow slag formation and lack of desulfurization in the existing technology; the specific process is as follows: the CaO / Al2O3 / SiO2 components form a matrix ternary slag system with a low melting point (SiO2 mainly comes from the deoxidation products of converter steelmaking), which has a fast slag formation speed and strong desulfurization capacity; the large amount of F element can not only rapidly reduce the melting point of the refining slag and improve the fluidity of the slag, providing more sufficient kinetic conditions for metallurgical reaction, but also, in conjunction with the CaO / Al2O3 / SiO2 matrix ternary slag system, further accelerate the slag formation speed; the use of elemental Al and other deoxidizers can quickly reduce the oxygen potential in the steel slag, thereby rapidly forming a highly efficient reducing refining slag with desulfurization and adsorption inclusions; at the same time, the CaO / Al2O3 / SiO2 matrix ternary slag system further improves the desulfurization efficiency.

[0017] 2. This invention utilizes the density difference between molten steel and slag to achieve deoxidation by using different types of deoxidizers in both materials. During the tapping process, a silicon-containing deoxidizer is first used to rapidly deoxidize the molten steel through sedimentation. Then, refining slag with a certain deoxidizing capacity is added, and the melting process of the refining slag deoxidizes the slag. This method significantly shortens the slag formation time of traditional steel slag diffusion deoxidation, relatively extending the flotation time of the deoxidation products. Furthermore, it achieves deoxidation by using different types of deoxidizers in both molten steel and slag, with the slag deoxidation products directly adsorbed within the slag, greatly reducing the impact of the slag deoxidation products on the molten steel.

[0018] 3. The refining slag in this invention uses conventional materials and materials such as lime, fluorite, and aluminum slag, which are widely available and have low manufacturing costs. Using this refining slag for smelting has the characteristics of fast slag formation, good desulfurization effect, high steel purity, simple smelting operation, and stable smelting quality. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the embodiments.

[0020] This invention provides a refining slag suitable for desulfurization of silicon-killed steel ladles. The chemical composition of this refining slag, by mass fraction, includes: CaO: 30%–50%, Al₂O₃: 10%–20%, SiO₂: 0–10%, CaF₂: 20%–40%, elemental Al: 2%–10%, S ≤ 0.05%, N ≤ 0.05%, Ti ≤ 0.02%, with the remainder being unavoidable impurities. Simultaneously, the mass fractions of CaO, Al₂O₃, SiO₂, CaF₂, and elemental Al in this refining slag satisfy the following:

[0021] CaO: (SiO2+Al2O3)=1.0~5.0, CaO:CaF2=0.75~2.5, Al2O3:Al=1.0~10.0.

[0022] The particle size of the refining slag is 10mm to 40mm, with less than 10mm of screened material ≤10wt% and H2O ≤0.8wt%.

[0023] The raw materials for the refining slag include: lime, fluorite, aluminum ash, and binder. The aluminum ash contains Al2O3, elemental Al, SiO2, Na2O, etc. Aluminum ash is a by-product of the aluminum smelting industry, including cast aluminum ash and electrolytic aluminum ash. The aluminum ash can also be replaced by aluminum scraps, aluminum powder, and a mixture of bauxite and soda ash in appropriate proportions.

[0024] Furthermore, the aluminum shavings and aluminum powder can also be replaced by silicon-calcium-barium-aluminum alloy, silicon-aluminum-iron, passivated magnesium, etc.

[0025] The above-mentioned method of using refining slag includes the following steps:

[0026] Step (1): Add silicon-containing deoxidizer immediately after tapping the steel from the converter. When 1 / 3 of the steel has been tapped, start adding the refining slag. The amount of refining slag added is 2kg to 4kg per ton of steel.

[0027] Step (2): When performing LF refining, the refining slag is added in batches at the beginning of refining. The amount of refining slag added is 2kg to 4kg per ton of steel, and the refining slag is dispersed on the steel slag surface as much as possible. After the refining slag is added, the electric arc heating is applied for 2 to 5 minutes, during which the bottom blowing gas flow rate of the ladle is 100 to 300 NL / min.

[0028] Example 1

[0029] This embodiment applies to the refining slag of silicon-killed steel ladle desulfurization. Its chemical composition by mass fraction includes: CaO: 41%, Al2O3: 16%, SiO2: 8%, CaF2: 26%, Al (elemental): 6%, S≤0.05%, N≤0.05%, Ti≤0.02%, and the remainder are unavoidable impurities.

[0030] CaO: (SiO2+Al2O3)=1.71, CaO:CaF2=1.58, Al2O3:Al=2.67.

[0031] The raw materials for refining slag include: lime, fluorite, aluminum ash, and binder. The aluminum ash contains Al2O3, elemental Al, SiO2, Na2O, etc. It is a by-product of the aluminum smelting industry, including molten aluminum ash and electrolytic aluminum ash. The aluminum ash can also be replaced by aluminum shavings or aluminum powder mixed with bauxite in appropriate proportions.

[0032] This embodiment describes the method for using refining slag in silicon-killed steel ladle desulfurization, which includes the following steps:

[0033] Step (1): Add silicon-containing deoxidizer immediately after the converter taps out steel. When 1 / 3 of the steel has been tapped, start adding the refining slag. The amount of refining slag added is 4 kg per ton of steel. The refining slag is added after the silicon-containing deoxidizer has been added.

[0034] Step (2): When performing LF refining, the refining slag is added in batches at the beginning of refining to ensure that the refining slag is dispersed on the steel slag surface as much as possible. The amount of refining slag added is 2 kg per ton of steel. After the refining slag is added, the electric arc heating is applied for 2 minutes to fully melt the refining slag. During the electric arc heating, the bottom blowing gas flow rate of the ladle is 300 NL / min.

[0035] Example 2

[0036] This embodiment is applicable to a new type of refining slag for desulfurization of silicon killed steel ladles. The chemical composition of the refining slag, by mass fraction, includes: CaO: 36%, Al2O3: 17%, SiO2: 9%, CaF2: 29%, Al (elemental): 7%, S≤0.05%, N≤0.05%, Ti≤0.02%, and the remainder being unavoidable impurities.

[0037] CaO: (SiO2+Al2O3)=1.38, CaO:CaF2=1.24, Al2O3:Al=2.43.

[0038] The raw materials for refining slag include: lime, fluorite, aluminum ash, and binder. The aluminum ash contains Al2O3, elemental Al, SiO2, Na2O, etc. It is a by-product of the aluminum smelting industry, including molten aluminum ash and electrolytic aluminum ash. The aluminum ash can also be replaced by aluminum shavings or aluminum powder mixed with bauxite in appropriate proportions.

[0039] This embodiment describes the method for using refining slag in silicon-killed steel ladle desulfurization, which includes the following steps:

[0040] Step (1): Add silicon-containing deoxidizer immediately after the converter taps out steel. When 1 / 3 of the steel has been tapped, start adding the refining slag. The amount of refining slag added is 3.5 kg per ton of steel. The refining slag is added after the silicon-containing deoxidizer is added.

[0041] Step (2): When performing LF refining, the refining slag is added in batches at the beginning of refining to ensure that the refining slag is dispersed on the steel slag surface as much as possible. The amount of refining slag added is 4 kg per ton of steel. After the refining slag is added, the electric arc heating effect lasts for 4.2 min to fully melt the refining slag. During the electric arc heating, the bottom blowing gas flow rate of the ladle is 260 NL / min.

[0042] Example 3

[0043] This embodiment is applicable to a new type of refining slag for desulfurization of silicon killed steel ladles. The chemical composition of the refining slag, by mass fraction, includes: CaO: 30%, Al2O3: 20%, SiO2: 10%, CaF2: 29%, Al (elemental): 8%, S≤0.05%, N≤0.05%, Ti≤0.02%, and the remainder being unavoidable impurities.

[0044] CaO: (SiO2+Al2O3)=1.0, CaO:CaF2=1.03, Al2O3:Al=2.5.

[0045] The raw materials for refining slag, by mass fraction, include: lime, fluorite, bauxite, aluminum shavings, and binder. The aluminum shavings may also be replaced by silicon-calcium-barium-aluminum alloy, silicon-aluminum-iron, passivated magnesium, etc.

[0046] This embodiment describes the method for using refining slag in silicon-killed steel ladle desulfurization, which includes the following steps:

[0047] Step (1): Add silicon-containing deoxidizer immediately after the converter taps out steel. When 1 / 3 of the steel has been tapped, start adding the refining slag. The amount of refining slag added is 2 kg per ton of steel. The refining slag is added after the silicon-containing deoxidizer has been added.

[0048] Step (2): When performing LF refining, the refining slag is added in batches at the beginning of refining to ensure that the refining slag is dispersed on the steel slag surface as much as possible. The amount of refining slag added is 4 kg per ton of steel. After the refining slag is added, the electric arc heating effect lasts for 4.6 min to fully melt the refining slag. During the electric arc heating, the bottom blowing gas flow rate of the ladle is 100 NL / min.

[0049] Example 4

[0050] This embodiment is applicable to a new type of refining slag for desulfurization of silicon killed steel ladles. The chemical composition of the refining slag, by mass fraction, includes: CaO: 50%, Al2O3: 10%, SiO2: 8%, CaF2: 20%, Al (elemental): 10%, S≤0.05%, N≤0.05%, Ti≤0.02%, and the remainder being unavoidable impurities.

[0051] CaO: (SiO2+Al2O3)=2.78, CaO:CaF2=2.5, Al2O3:Al=1.0.

[0052] The raw materials for refining slag, by mass fraction, include: lime, fluorite, bauxite, aluminum shavings, and binder. The aluminum shavings may also be replaced by silicon-calcium-barium-aluminum alloy, silicon-aluminum-iron, passivated magnesium, etc.

[0053] This embodiment describes the method for using refining slag in silicon-killed steel ladle desulfurization, which includes the following steps:

[0054] Step (1): Add silicon-containing deoxidizer immediately after the converter taps out steel. When 1 / 3 of the steel has been tapped, start adding the refining slag. The amount of refining slag added is 3.1 kg per ton of steel. The refining slag is added after the silicon-containing deoxidizer is added.

[0055] Step (2): When performing LF refining, the refining slag is added in batches at the beginning of refining to ensure that the refining slag is dispersed on the steel slag surface as much as possible. The amount of refining slag added is 3.8 kg per ton of steel. After the refining slag is added, the electric arc heating is applied for 5 minutes to fully melt the refining slag. During the electric arc heating, the bottom blowing gas flow rate of the ladle is 270 NL / min.

[0056] Example 5

[0057] This embodiment is applicable to a new type of refining slag for desulfurization of silicon killed steel ladles. The chemical composition of the refining slag, by mass fraction, includes: CaO: 30%, Al2O3: 20%, SiO2: 5%, CaF2: 40%, Al (elemental): 2%, S≤0.05%, N≤0.05%, Ti≤0.02%, and the remainder being unavoidable impurities.

[0058] CaO: (SiO2+Al2O3)=1.2, CaO:CaF2=0.75, Al2O3:Al=10.

[0059] The raw materials for refining slag, by mass fraction, include: lime, fluorite, bauxite, aluminum shavings, and binder. The aluminum shavings may also be replaced by silicon-calcium-barium-aluminum alloy, silicon-aluminum-iron, passivated magnesium, etc.

[0060] This embodiment describes the method for using refining slag in silicon-killed steel ladle desulfurization, which includes the following steps:

[0061] Step (1): Add silicon-containing deoxidizer immediately after the converter taps out steel. When 1 / 3 of the steel has been tapped, start adding the refining slag. The amount of refining slag added is 3.4 kg per ton of steel. The refining slag is added after the silicon-containing deoxidizer is added.

[0062] Step (2): When performing LF refining, the refining slag is added in batches at the beginning of refining to ensure that the refining slag is dispersed on the steel slag surface as much as possible. The amount of refining slag added is 3.2 kg per ton of steel. After the refining slag is added, the electric arc heating effect lasts for 3.4 min to fully melt the refining slag. During the electric arc heating, the bottom blowing gas flow rate of the ladle is 230 NL / min.

[0063] Example 6

[0064] This embodiment is applicable to a new type of refining slag for desulfurization of silicon killed steel ladles. The chemical composition of the refining slag, by mass fraction, includes: CaO: 50%, Al2O3: 10%, CaF2: 32%, Al (elemental): 5%, S≤0.05%, N≤0.05%, Ti≤0.02%, and the remainder being unavoidable impurities.

[0065] The raw materials for refining slag, by mass fraction, include: lime, fluorite, bauxite, aluminum shavings, and binder. The aluminum shavings may also be replaced by silicon-calcium-barium-aluminum alloy, silicon-aluminum-iron, passivated magnesium, etc.

[0066] CaO: (SiO2+Al2O3)=5.0, CaO:CaF2=1.56, Al2O3:Al=2.0.

[0067] This embodiment describes the method for using refining slag in silicon-killed steel ladle desulfurization, which includes the following steps:

[0068] Step (1): Add silicon-containing deoxidizer immediately after the converter taps out steel. When 1 / 3 of the steel has been tapped, start adding the refining slag. The amount of refining slag added is 2.9 kg per ton of steel. The refining slag is added after the silicon-containing deoxidizer is added.

[0069] Step (2): When performing LF refining, the refining slag is added in batches at the beginning of refining to ensure that the refining slag is dispersed on the steel slag surface as much as possible. The amount of refining slag added is 3.7 kg per ton of steel. After the refining slag is added, the electric arc heating effect lasts for 4.4 min to fully melt the refining slag. During the electric arc heating, the bottom blowing gas flow rate of the ladle is 300 NL / min.

[0070] Comparative Example 1

[0071] Comparing Comparative Example 1 with the above embodiments, the difference between Comparative Example 1 and the embodiments is as follows:

[0072] The conventional refining slag used has the following composition by mass fraction: CaO≤45%, Al2O3≤10%, SiO2≥30%, with the remainder being unavoidable impurities.

[0073] The conventional method of using refining slag is as follows:

[0074] Step (1): When the converter has tapped 1 / 2 of the steel, lime, quartz sand and other slag materials are added. The amount of slag materials added is 3.3 kg per ton of steel.

[0075] Step (2): When LF refining is carried out, lime, quartz sand and other slag materials are added at the beginning of refining, with an addition amount of 3.5 kg per ton of steel; after the slag materials are added, the electric arc heating is applied for 5.8 min to fully melt the refining slag; during the electric arc heating, the bottom blowing gas flow rate of the ladle is 200 NL / min.

[0076] Statistical example:

[0077] From August 2022 to May 2023, the refining slag from the example was used in SWRH82B steel in a 50t system, for a total of 450 heats. The composition content of the final slag from the LF heat of the example and Comparative Example 1, as well as the inclusions and composition content of the related heat products, were statistically analyzed, as shown in Tables 1 and 2.

[0078] Table 1. Composition and sulfur content of LF furnace final slag and products of Examples and Comparative Example 1

[0079]

[0080] Table 2. Inclusion levels in the billets of Examples and Comparative Examples 1

[0081]

[0082]

[0083] Note: ① The analysis of slag components in each embodiment and comparative example was performed according to the "Method for X-ray Fluorescence Spectroscopy Analysis of Slag" (YB / T 4177--2008);

[0084] ② The S content of the product shall be tested in accordance with the "Determination of Multi-element Content in Carbon Steel and Medium-low Alloy Steel by Spark Discharge Atomic Emission Spectroscopy (Conventional Method)" (GB / T 4336-2016); the inclusion detection and rating shall be carried out in accordance with the "Determination of Non-metallic Inclusion Content in Steel by Standard Rating Chart Microscopic Examination Method" (GB / T 10561-2005).

[0085] As shown in Tables 1 and 2, the refining slag used in the desulfurization of silicon-killed steel ladles of this invention exhibits a significant decrease in oxidizing power and an increase in slag basicity after use. Consequently, the sulfur capacity of the final slag increases significantly, resulting in a significant decrease in the sulfur content of the obtained product. Regarding inclusion control, compared to the conventional process (Comparative Example 1), the examples show a decreasing trend in type A inclusions and an increasing trend in the detection rate of type B inclusions. However, the type B inclusions can be controlled to ≤1.0 level, meeting the requirements of silicon-killed steel.

Claims

1. A refining slag suitable for desulfurization of silicon-killed steel ladles, characterized in that, The chemical composition of the refining slag, by mass fraction, is as follows: CaO: 30%–50%, Al₂O₃: 10%–20%, SiO₂: 0–10%, CaF₂: 20%–40%, elemental Al: 2%–10%, S≤0.05%, N≤0.05%, Ti≤0.02%, with the remainder being unavoidable impurities; the mass fractions of CaO, Al₂O₃, SiO₂, CaF₂, and elemental Al in the refining slag satisfy the following: CaO: (SiO2+Al2O3)=1.0~5.0, CaO:CaF2=0.75~2.5, Al2O3:Al=1.0~10.

0.

2. The refining slag suitable for desulfurization of silicon-killed steel ladles according to claim 1, characterized in that, The particle size of the refining slag is 10mm to 40mm, with less than 10mm of screened material ≤10wt% and H2O ≤0.8wt%.

3. The refining slag suitable for desulfurization of silicon-killed steel ladles according to claim 1 or 2, characterized in that, The raw materials for the refining slag include: lime, fluorite, aluminum ash, and binder.

4. A method for using refining slag according to any one of claims 1-3, characterized in that, Includes the following steps: Step (1): Add silicon-containing deoxidizer immediately after tapping the steel from the converter. When 1 / 3 of the steel has been tapped, start adding the refining slag. The amount of refining slag added is 2 kg to 4 kg per ton of steel. Step (2): When LF refining is carried out, the refining slag is added in batches, and the amount of refining slag added is 2kg to 4kg per ton of steel.

5. The method of using the refining slag according to claim 4, characterized in that, In step (2), the refining residue is added at the initial stage of refining.

6. The method of using the refining slag according to claim 5, characterized in that, In step (2), after the refining slag is added, it is heated by electric arc for 2 to 5 minutes, during which the bottom blowing gas flow rate of the ladle is 100 to 300 NL / min.

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