Method for improving desulfurization rate of LF treated low silicon steel

Abstract

The invention belongs to the field of steelmaking and continuous casting, relates to a method for improving the desulfurization rate of LF treated low silicon steel, and aims to solve the problems of low sulfur distribution coefficient and poor slag fluidity in the traditional LF desulfurization process during low silicon steel smelting. During converter tapping, table aluminum or high-aluminum iron is added for pre-deoxidation, and lime slag is added for washing desulfurization; before the molten steel enters the LF, argon blowing and oxygen determination are carried out at a CAS station, and an aluminum wire is fed to control the Als content; during LF treatment, lime is added to make high-alkalinity slag, and a ladle slagging agent is synchronously added to increase the flowability of top slag. According to the method, the KR desulfurization procedure is omitted, the technological process is simplified, the production cost is reduced, meanwhile, the desulfurization efficiency is improved, and the steel quality is guaranteed.

Description

Technical Field

[0001] The invention belongs to the field of steelmaking and continuous casting, and relates to a method for improving the desulfurization rate of low-silicon steel treated by LF. Background Art

[0002] Deep-drawing steel is a key steel product in the steelmaking and continuous casting industry, and controlling its chemical composition has a crucial impact on the steel's ultimate performance. Deep-drawing steel, in particular, typically requires an extremely low silicon (Si) content of 0.06% or less to ensure excellent deep-drawing performance and surface quality. However, this pursuit of low silicon content also places extremely stringent requirements on controlling sulfur (S) content in the steel, typically requiring a sulfur content of 0.010% or less to avoid adverse effects such as sulfur-induced hot brittleness.

[0003] In traditional steelmaking, silicon plays a vital role in molten steel as a strong deoxidizer. However, when the silicon content in molten steel is low, the residual dissolved oxygen ([O]) content can increase significantly, especially when insufficient deoxidation treatment is performed. This high dissolved oxygen content inhibits the transfer of sulfur from molten steel to slag, resulting in a lower sulfur distribution coefficient and making it difficult to further reduce the sulfur content in the steel.

[0004] To address this challenge, traditional LF (ladle refining furnace) desulfurization processes typically rely on the use of high-basicity slag. However, during the smelting of low-silicon steel grades, the source of SiO2 in the slag decreases, and to maintain high basicity, more basic oxides must be added. This often leads to increased slag viscosity and reduced fluidity. This reduced slag fluidity can severely hinder the mass transfer of sulfur between the molten steel and the slag, thereby compromising the desulfurization effect.

[0005] To overcome these issues, the current production of this type of low-silicon steel typically utilizes a process consisting of KR (hot metal pretreatment) + BOF (converter furnace steelmaking) + LF. However, this multi-stage process not only increases the complexity of the steelmaking process but also significantly raises production costs. While the KR desulfurization process can effectively reduce the sulfur content in hot metal, it requires significant equipment investment and is complex to operate. Furthermore, the necessity of KR desulfurization for hot metal with a low sulfur content has been questioned.

[0006] Therefore, how to simplify the steelmaking process and reduce production costs while ensuring the desulfurization effect of low-silicon steel has become a technical problem that needs to be urgently solved in the current steelmaking and continuous casting field. Summary of the Invention

[0007] In view of this, the object of the present invention is to provide a method for improving the desulfurization rate of low-silicon steel treated by LF, so as to solve the existing problems.

[0008] To achieve the above object, the present invention provides the following technical solution: a method for improving the desulfurization rate of low-silicon steel treated with LF, characterized in that it comprises the following steps:

[0009] When tapping the converter, add 300-500kg of Taiwan aluminum or high aluminum iron for pre-deoxidation, and add 600-800kg of lime for slag washing and desulfurization;

[0010] Before the molten steel enters the LF, argon is blown to determine oxygen and aluminum wire is fed at the CAS station to control the Als content in the molten steel to 0.040-0.055%;

[0011] During LF treatment, 500-700kg of lime is added to make slag, so that the slag basicity is controlled at 5-6.5;

[0012] During LF treatment, 50-100 kg of ladle slag remover is added simultaneously to increase the fluidity of the top slag.

[0013] Optionally, the basicity of the LF slag is regulated by adding lime, specifically adding 500-700 kg of lime per batch.

[0014] Optionally, the ladle slagging agent is added in an amount of 50-100 kg / heat to improve the fluidity of CaO-Al2O3-SiO2 slag.

[0015] Optionally, the CAS station accurately controls the dissolved aluminum content in the range of 0.040-0.055% through a constant oxygen aluminum feeding line.

[0016] Optionally, the slag washing and desulfurization in the converter tapping stage uses 600-800 kg of lime and aluminum deoxidizer to achieve an initial sulfur content of the molten steel of <0.030%.

[0017] Optionally, in the ultra-high basicity slag formed by the LF treatment, the CaO / SiO2 mass ratio is maintained in the range of 5.0-6.5.

[0018] Optionally, the ladle slagging agent comprises a mixture of fluorite and bauxite, the proportion of which ensures that the melting point of the slag system is ≤1350°C.

[0019] Optionally, the aluminum deoxidizer is Taiwan aluminum or high aluminum iron, and the amount added is dynamically adjusted according to the initial oxygen content of the molten steel.

[0020] Optionally, the process route eliminates the KR desulfurization step and directly adopts the short process of BOF converter-LF refining.

[0021] The beneficial effects of the present invention are:

[0022] Reducing steelmaking process costs: By optimizing the steelmaking process, the KR desulfurization process was eliminated and the original KR+BOF+LF process route was adjusted to a BOF+LF process route. This change significantly reduced the complexity and equipment required in the steelmaking process, thereby reducing the overall cost of the steelmaking process.

[0023] Improving desulfurization efficiency: By strengthening the deoxidation treatment of molten steel before entering the LF and adding a certain amount of ladle slag remover, the fluidity of the ladle top slag is effectively improved. This improvement measure improves the desulfurization rate when treating low-silicon steel in the LF, allowing the sulfur content in the molten steel to be more effectively reduced to below the target requirement.

[0024] Guaranteed steel quality: While ensuring desulfurization, this method also helps maintain stable control of the silicon content in the steel, ensuring good deep-drawing performance and surface quality. This is crucial for producing high-quality low-silicon steel.

[0025] Simplified process flow: Through process optimization, unnecessary steps and equipment are reduced in the steelmaking process, making the entire steelmaking process simpler and more efficient. This not only improves production efficiency but also reduces operational difficulty and error rates.

[0026] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. DETAILED DESCRIPTION

[0027] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] A method for improving the desulfurization rate of low-silicon steel treated with LF of the present invention comprises the following steps:

[0029] 1. Raw material preparation:

[0030] 1.1 Select molten iron with sulfur content ≤ 0.030% and directly feed it into the converter.

[0031] 1.2 Select high-quality scrap steel to reduce the sulfur brought into the scrap steel and ensure that the sulfur content at the converter end is less than 0.030%.

[0032] 2. Converter tapping process:

[0033] When tapping the converter, 300-500 kg of Taiwan aluminum or high aluminum iron is added for pre-deoxidation, and 600-800 kg of lime is added for slag washing and desulfurization to reduce the initial sulfur content in the molten steel to <0.030%.

[0034] 3.CAS station processing:

[0035] Before the molten steel enters the LF, argon is blown to determine the oxygen content at the CAS station, and aluminum wire is fed to accurately control the Als (dissolved aluminum) content in the molten steel within the range of 0.040-0.055%, so as to further reduce the dissolved oxygen content and promote sulfur transfer.

[0036] 4.LF treatment:

[0037] 4.1 In the LF treatment stage, 500-700 kg of lime is added to make slag so that the slag basicity (CaO / SiO2 mass ratio) is controlled in the range of 5-6.5 to form ultra-high basicity slag.

[0038] 4.2 At the same time, add 50-100kg of ladle slag agent to increase the fluidity of the top slag, improve the fluidity of the CaO-Al2O3-SiO2 slag, and promote the mass transfer process of sulfur between the molten steel and the slag.

[0039] 5. Process optimization:

[0040] The KR desulfurization process is eliminated and the short process of BOF converter-LF refining is directly adopted to simplify the steelmaking process and reduce production costs.

[0041] Example 1,

[0042] Raw materials: molten iron with sulfur content of 0.028%, high-quality scrap steel.

[0043] Converter tapping: add 400kg of Taiwan aluminum for pre-deoxidation and add 700kg of lime for slag washing and desulfurization.

[0044] CAS station: After blowing argon to determine the oxygen, aluminum wire is fed in and the AlS content is controlled at 0.045%.

[0045] LF treatment: add 600kg lime to make slag, control the slag basicity at 5.8, and add 80kg ladle slag agent.

[0046] Results: The sulfur content of LF outgoing from the station was 0.003%, the desulfurization rate reached 89.3%, and the sulfur content of molten steel reached the target requirement of ≤0.005%.

[0047] Example 2,

[0048] Raw materials: molten iron with sulfur content of 0.029%, high-quality scrap steel.

[0049] Converter tapping: add 350kg of high-aluminum iron for pre-deoxidation and add 650kg of lime for slag washing and desulfurization.

[0050] CAS station: After blowing argon to determine the oxygen, aluminum wire is fed in and the AlS content is controlled at 0.050%.

[0051] LF treatment: add 550kg lime to make slag, control the slag basicity at 6.2, and add 70kg ladle slag agent.

[0052] Results: The sulfur content of LF outgoing from the station was 0.004%, the desulfurization rate reached 86.2%, and the sulfur content of molten steel also reached the target requirement of ≤0.005%.

[0053] Through the above implementation methods and examples, it can be seen that the present invention optimizes the process, strengthens the deoxidation treatment of molten steel before entering LF, and adds a certain amount of ladle slag-removing agent, which effectively promotes the fluidity of the ladle top slag, improves the desulfurization rate of low-silicon steel treated by LF, and simplifies the steelmaking process and reduces production costs.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for improving the desulfurization rate of low silicon steel treated with LF, characterized in that: The following steps are involved: When tapping the converter, add 300-500kg of Taiwan aluminum or high aluminum iron for pre-deoxidation, and add 600-800kg of lime for slag washing and desulfurization; Before the molten steel enters the LF, argon is blown to determine oxygen and aluminum wire is fed at the CAS station to control the Als content in the molten steel to 0.040-0.055%; During LF treatment, 500-700kg of lime is added to make slag, so that the slag basicity is controlled at 5-6.5; During LF treatment, 50-100 kg of ladle slag remover is added simultaneously to increase the fluidity of the top slag.

2. The method for improving the desulfurization rate of low-silicon steel treated with LF according to claim 1, characterized in that: The basicity of the LF slag is regulated by the amount of lime added, specifically 500-700 kg of lime is added per batch.

3. The method for improving the desulfurization rate of low-silicon steel treated with LF according to claim 1, characterized in that: The amount of the ladle slag-reducing agent added is 50-100 kg / heat, and is used to improve the fluidity of the CaO-Al2O3-SiO2 slag.

4. The method for improving the desulfurization rate of low-silicon steel treated with LF according to claim 1, characterized in that: The CAS station accurately controls the dissolved aluminum content in the range of 0.040-0.055% through a constant oxygen feeding aluminum line.

5. The method for improving the desulfurization rate of low-silicon steel treated with LF according to claim 1, characterized in that: The slag washing and desulfurization in the converter tapping stage adopts 600-800 kg of lime and aluminum deoxidizer to work together to achieve an initial sulfur content of molten steel of less than 0.030%.

6. The method for improving the desulfurization rate of low-silicon steel treated with LF according to claim 1, characterized in that: In the ultra-high basicity slag formed by the LF treatment, the CaO / SiO2 mass ratio is maintained in the range of 5.0-6.

5.

7. The method for improving the desulfurization rate of low-silicon steel treated with LF according to claim 1, characterized in that: The ladle slagging agent comprises a mixture of fluorite and bauxite, and the proportion thereof ensures that the melting point of the slag system is ≤1350°C.

8. The method for improving the desulfurization rate of low-silicon steel treated with LF according to claim 1, characterized in that: The aluminum deoxidizer is selected from Taiwan aluminum or high aluminum iron, and its addition amount is dynamically adjusted according to the initial oxygen content of the molten steel.

9. The method for improving the desulfurization rate of low-silicon steel treated with LF according to claim 1, characterized in that: The process route eliminates the KR desulfurization step and directly adopts the short process of BOF converter-LF refining.