A clean steel and a method for its production

Abstract

The application provides a clean steel and a production method thereof, and comprises the following steps: S1, carrying out deoxidation treatment after converter tapping to obtain first molten steel; S2, carrying out LF refining on the first molten steel to obtain second molten steel; S3, carrying out desulfurization control on the second molten steel to obtain third molten steel; S4, controlling VD inlet slag composition and adjusting Al content in the molten steel after the end of the LF refining to control the VD inlet Al content, and obtaining fourth molten steel; S5, carrying out vacuum extraction after the VD inlet and carrying out strong bottom blowing stirring to obtain fifth molten steel; S6, carrying out soft bottom blowing stirring after the end of the VD pressure maintaining strong bottom blowing stirring to obtain sixth molten steel; and S7, carrying out soft blowing after the vacuum treatment of the sixth molten steel to obtain clean steel. The application can realize molten steel cleaning and inclusion miniaturization, and can finally control the total oxygen content in the steel to be less than 8ppm, the oxide inclusion size to be less than 10μm, and the number density to be 3 / mm 2 The following.

Description

[Technical Field]

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a clean steel and its production method. [Background Technology]

[0002] In existing technologies, clean steel produced using the BOF-LF-VD-CC process can achieve low sulfur content in the molten steel due to the sufficient reaction between steel and slag during the LF and VD refining stages. However, existing technologies struggle to control large-particle calcium aluminate inclusions in the molten steel, primarily due to the reaction:

[0003] Steel / slag interface:

[0004] 2[Al] + 3(MgO) = 3[Mg] + Al₂O₃

[0005] 2[Al] + 3(CaO) = 3[Ca] + (Al₂O₃)

[0006] Interface between molten steel and Al2O3 inclusions:

[0007] [Mg]+n / 3(Al2O3)=(MgO·(n-1) / 3Al2O3)+2 / 3[Al]

[0008] x[Ca]+[yMgO·zAl2O3]=[xCaO(yx)·MgO·zAl2O3]+x[Mg]

[0009] Inclusions in molten steel are transformed into calcium magnesium aluminate. In order to meet the requirements of castability, some steel grades adopt a calcium treatment process to control the inclusions to 12CaO·7Al2O3 and avoid nozzle blockage.

[0010] However, calcium aluminate inclusions have a large particle size, with some inclusions reaching hundreds of micrometers or more. During the steel rolling process, these inclusions can be rolled into Class B inclusions that exceed the standard, causing harm.

[0011] Therefore, it is necessary to study a clean steel and its production method to address the shortcomings of existing technologies and solve or mitigate one or more of the above-mentioned problems. [Summary of the Invention]

[0012] In view of this, the present invention provides a clean steel and its production method, which can achieve steel purification and inclusion miniaturization, ultimately controlling the total oxygen content in the steel to below 8 ppm, the oxide inclusion size to below 10 μm, and the number density to below 3 inclusions / mm. 2 the following.

[0013] On one hand, the present invention provides a method for producing clean steel using a BOF-LF-VD-CC process, the method comprising the following steps:

[0014] S1: After tapping from the converter, the steel undergoes deoxidation treatment to obtain the first molten steel;

[0015] S2: Preset slag composition, perform LF refining on the first molten steel to obtain the second molten steel;

[0016] S3: Desulfurize the second molten steel to obtain the third molten steel;

[0017] S4: Control the composition of VD slag entering the station and adjust the Al content in the third molten steel, control the aluminum content in VD entering the station, and obtain the fourth molten steel;

[0018] S5: After VD enters the station, a vacuum is drawn, and the fourth molten steel is strongly bottom-blown and stirred to obtain the fifth molten steel;

[0019] S6: After the VD pressure holding and strong bottom blowing agitation is completed, the fifth molten steel is stirred by soft bottom blowing to obtain the sixth molten steel;

[0020] S7: After vacuum treatment of the sixth molten steel, soft blowing is performed to obtain clean steel.

[0021] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the deoxidation treatment in S1 specifically involves: using Al deoxidation, and controlling the oxygen content in the molten steel to be ≤0.0010% after tapping.

[0022] In addition to the aspects described above and any possible implementation, a further implementation is provided in which the preset slag composition in S2 is specifically: MgO: 8-10%; Al2O3: 25-40%; CaO: 35-45%; SiO2≤10%.

[0023] In addition to the aspects and any possible implementations described above, an implementation is further provided in which, after desulfurization control in S3, the sulfur content in the third molten steel is ≤0.0010%.

[0024] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the composition of the VD slag entering the station is controlled in S4 as follows: after the LF refining is completed, bauxite and lightly calcined dolomite are added to the slag, the particle size of bauxite and lightly calcined dolomite being 2-5 mm; the composition of the VD slag entering the station is controlled as follows: MgO: 12-15%; Al2O3: 35-45%; CaO: 25-35%, SiO2≤10%, and CaO / Al2O3≤0.8.

[0025] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the aluminum content of VD entering the station in S4 is controlled at 0.03-0.05%.

[0026] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the stirring gas in S5 is CO2+Ar, the control time is 8-15 min, the volume ratio of CO2 to Ar is controlled at 0.2-0.4, and the bottom blowing flow rate is controlled at 100-300 Nl / min.

[0027] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the soft bottom blowing gas in S6 is CO2+Ar, the soft bottom blowing time is 3-5 min, the volume ratio of CO2 to Ar is controlled between 0.2 and 0.4, and the bottom blowing flow rate is controlled between 40-60 Nl / min.

[0028] In addition to the aspects and any possible implementations described above, a further implementation is provided in which the soft blowing gas in S7 is Ar gas, the soft blowing flow rate is controlled at 20-40 Nl / min, and the soft blowing time is 8-10 min.

[0029] In accordance with the aspects and any possible implementations described above, a clean steel is further provided, obtained by the production method of the clean steel, wherein the total oxygen content in the clean steel is below 8 ppm, the size of oxide inclusions is below 10 μm, and the number density is below 3 inclusions / mm².

[0030] Compared with the prior art, the present invention can achieve the following technical effects:

[0031] (1) Before the molten steel enters the VD, the slag is modified to significantly reduce the CaO content, thereby avoiding the full reaction between the aluminum in the molten steel and the CaO in the slag during the VD process, reducing the formation of large-particle calcium aluminate inclusions, while the Al2O3 and aluminum-magnesium spinel inclusions generated are more easily removed during the dynamic stirring process of the bottom-blown gas.

[0032] (2) Under vacuum and pressure conditions, the stirring gas is CO2+Ar, and the inclusions are transformed towards Al2O3·MgO to avoid the formation of large-particle calcium aluminate.

[0033] (3) The composition of the slag during the VD treatment process is controlled to be slag with high Al2O3 and high MgO content. The composition of the slag is controlled to be high melting point slag, which not only avoids excessive slag / steel reaction, but also avoids the entrapment of liquid slag droplets into the molten steel.

[0034] (4) Before VD enters the station, the slag is modified to reduce the CaO content. This avoids the full reaction between aluminum and CaO during the VD process, and avoids the formation of large-particle calcium aluminate inclusions. The generated Al2O3 and aluminum-magnesium spinel inclusions are more easily removed during the soft blowing process.

[0035] (5) Before VD enters the station, the slag is modified to increase the content of Al2O3 and MgO. The composition of the slag is controlled to be high-melting-point slag, which not only avoids excessive slag / steel reaction, but also avoids slag dripping into the molten steel.

[0036] (6) The stirring gas is CO2+Ar, and a strong + weak kinetic control method is matched to make full use of the competitive reaction between the metal elements Ca and Mg in the steel and CO2 in the bottom blowing gas, so as to promote the transformation of the inclusions towards Al2O3·MgO and avoid the formation of large-particle calcium aluminate.

[0037] Of course, any product implementing this invention does not necessarily need to achieve all of the technical effects described above at the same time. [Attached Image Description]

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart of a method for producing clean steel according to an embodiment of the present invention.

Detailed Implementation Methods

[0040] To better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0041] It should be understood that the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0042] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0043] like Figure 1As shown, this invention provides a method for producing clean steel using a BOF-LF-VD-CC process. The method for producing clean steel includes the following steps:

[0044] S1: After tapping from the converter, the steel undergoes deoxidation treatment to obtain the first molten steel;

[0045] S2: Preset slag composition, perform LF refining on the first molten steel to obtain the second molten steel;

[0046] S3: Desulfurize the second molten steel to obtain the third molten steel;

[0047] S4: Control the composition of VD slag entering the station and adjust the Al content in the third molten steel, control the aluminum content in VD entering the station, and obtain the fourth molten steel;

[0048] S5: After VD enters the station, a vacuum is drawn, and the fourth molten steel is strongly bottom-blown and stirred to obtain the fifth molten steel;

[0049] S6: After the VD pressure holding and strong bottom blowing agitation is completed, the fifth molten steel is stirred by soft bottom blowing to obtain the sixth molten steel;

[0050] S7: After vacuum treatment of the sixth molten steel, soft blowing is performed to obtain clean steel.

[0051] The deoxidation treatment in S1 specifically involves using Al deoxidation, and controlling the oxygen content in the molten steel to be ≤0.0010% after tapping.

[0052] The pre-set slag composition in S2 is as follows: MgO: 8-10%; Al2O3: 25-40%; CaO: 35-45%; SiO2 ≤ 10%.

[0053] After desulfurization control in S3, the sulfur content in the third molten steel is ≤0.0010%.

[0054] The specific steps for controlling the composition of the VD slag entering the station in S4 are as follows: after the LF refining is completed, bauxite and lightly calcined dolomite are added to the slag, with the particle size of bauxite and lightly calcined dolomite being 2-5 mm; the composition of the VD slag entering the station is controlled as follows: MgO: 12-15%; Al2O3: 35-45%; CaO: 25-35%, SiO2≤10%, and CaO / Al2O3≤0.8.

[0055] The aluminum content of VD entering the station in S4 is controlled at 0.03-0.05%.

[0056] In S5, the stirring gas is CO2+Ar, the stirring time is controlled at 8-15 min, the volume ratio of CO2 to Ar is controlled at 0.2-0.4, and the bottom blowing flow rate is controlled at 100-300 Nl / min.

[0057] In S6, the soft bottom blowing gas is CO2+Ar, the soft bottom blowing time is 3-5 min, the volume ratio of CO2 to Ar is controlled between 0.2 and 0.4, and the bottom blowing flow rate is controlled between 40-60 Nl / min.

[0058] In S7, the soft blowing gas is Ar gas, the soft blowing flow rate is controlled at 20-40 Nl / min, and the soft blowing time is 8-10 min.

[0059] The present invention also provides a clean steel, obtained by the aforementioned clean steel production method, wherein the total oxygen content in the clean steel is below 8 ppm, the oxide inclusion size is below 10 μm, and the number density is 3 inclusions / mm. 2 the following.

[0060] Example 1:

[0061] This invention provides a method for producing clean steel. Before the molten steel enters the VD (Vacuum-Deposition) process, bauxite and lightly calcined dolomite are added to increase the alumina content in the slag. This is combined with a VD bottom-blowing gas design using CO2 + Ar to promote the reaction between CO2 and Ca in the molten steel, reducing the Ca content in the steel. This reduces the formation of large-particle calcium aluminate in the steel / slag reaction, resulting in inclusions that are mostly small-sized magnesium aluminate spinels. Combined with soft blowing, this achieves both steel purification and inclusion refinement. Ultimately, the total oxygen content in the steel can be controlled to below 8 ppm, the average size of oxide inclusions to below 10 μm, and the number density to below 3 inclusions / mm. 2 the following.

[0062] The slag composition of the LF refining process of this invention is shown in Table 1, the slag composition of the VD inlet is shown in Table 2, the VD bottom blowing parameters are shown in Table 3, and the final control status is shown in Table 4. When producing clean steel using the BOF-LF-VD-CC process, the control is performed according to the following steps:

[0063] (1) Al deoxidation is used for steel tapping in the converter. After tapping, the oxygen content in the molten steel is controlled to be ≤0.0010%. This step is the usual control practice at the end of a clean steel converter. During the tapping process, the deoxidation task is completed, and the inclusions are continuously removed by steel / slag reaction, collision and floating during the subsequent refining process.

[0064] (2) The slag composition used in the LF refining process is: MgO: 8-10%; Al2O3: 25-40%; CaO: 35-45%; SiO2≤10%; The composition of this slag has a high sulfur capacity and high basicity, which is very beneficial for desulfurization. Combined with the high Al content in the molten steel, it can achieve a good desulfurization effect.

[0065] (3) After LF refining, the sulfur content of the molten steel is controlled to be ≤0.0010%. Thus, the task of removing sulfur from clean steel is achieved in the LF refining stage.

[0066] (4) After LF refining, bauxite and lightly calcined dolomite are added to the slag to control the composition of the VD slag entering the station as follows: MgO: 12-15%; Al2O3: 35-45%; CaO: 25-35%, SiO2≤10%, and CaO / Al2O3≤0.8. With this target composition, the MgO content in the slag is in a supersaturated state. Thus, under the intense VD stirring conditions, the aluminum in the molten steel mainly reacts with MgO to form spinel and Al2O3 inclusions, which can float to the surface in large quantities during the soft blowing process after vacuum treatment. This avoids the aluminum in the molten steel reacting with CaO to form Ca during the VD vacuum treatment process, ultimately forming calcium aluminate inclusions.

[0067] (5) After LF refining is completed, adjust the Al content in the molten steel and control the aluminum content of VD entering the station to be 0.03-0.05%;

[0068] (6) After VD enters the station, a vacuum is drawn, and strong bottom blowing and stirring are performed. The stirring gas is CO2 + Ar, and the stirring time is controlled at 8-15 min. The volume ratio of CO2 to Ar in the strong stirring gas is controlled between 0.2 and 0.4, and the bottom blowing flow rate is controlled at 100-300 Nl / min. Using CO2 + Ar as the stirring gas can utilize the reaction of CO2 with Ca in the molten steel to reduce the Ca content in the molten steel and reduce the CaO content in the inclusions. However, CO2 will also react with Mg in the molten steel, reducing the Mg content in the molten steel. The CaO and MgO content in the inclusions is significantly reduced. The Al2O3 content in the inclusions increases. (Because Ca reacts more easily with CO2, the CaO content in the inclusions decreases significantly, and the inclusions transform towards Al2O3·MgO).

[0069] (7) After the VD pressure holding and strong bottom blowing stirring is completed, soft bottom blowing stirring is adopted. The gas used is CO2 + Ar. The soft blowing time is 3-5 min. The volume ratio of CO2 to Ar is controlled between 0.2 and 0.4. The bottom blowing flow rate is controlled between 40-60 Nl / min. Here, there is a 3-5 min soft blowing under pressure holding conditions. The purpose is to prevent the slag caused by the strong stirring process from being entrained into the molten steel and promote the rapid separation of steel and slag.

[0070] (8) After vacuum treatment, perform soft blowing: Soft blowing time: 8-10 min, Ar gas is used for soft blowing, and the soft blowing flow rate is controlled at 20-40 Nl / min.

[0071] In existing technologies, slag refining with higher alkalinity is generally used to meet desulfurization requirements. However, during VD treatment of molten steel, due to the full reaction of steel and slag, the inclusions are mainly calcium aluminates. These inclusions have a large particle size and are more harmful to the steel.

[0072] This invention employs three main technical methods throughout the smelting process to control the composition of inclusions to be close to Al2O3·MgO spinel, resulting in relatively small inclusion particle sizes and minimal damage to the steel. The three main technical methods are summarized as follows:

[0073] (7) Before VD enters the station, the slag is modified to reduce the CaO content. This avoids the full reaction between aluminum and CaO during the VD process, and avoids the formation of large-particle calcium aluminate inclusions. The generated Al2O3 and aluminum-magnesium spinel inclusions are more easily removed during the soft blowing process.

[0074] (8) Before VD enters the station, the slag is modified to increase the content of Al2O3 and MgO. The composition of the slag is controlled to be high melting point slag, which not only avoids excessive slag / steel reaction, but also avoids the slag dripping into the molten steel.

[0075] (9) The stirring gas is CO2+Ar, and a strong + weak kinetic control method is used. The competitive reaction between the metallic elements Ca and Mg in the steel and CO2 in the bottom-blown gas is fully utilized to promote the transformation of inclusions towards Al2O3·MgO and avoid the formation of large-particle calcium aluminates.

[0076] Table 1

[0077]

[0078] Table 2

[0079]

[0080] Table 3

[0081]

[0082]

[0083] Table 4

[0084]

[0085] The clean steel and its production method provided in the embodiments of this application have been described in detail above. The description of the above embodiments is only for the purpose of helping to understand the method and core idea of ​​this application; at the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​this application. Therefore, the content of this specification should not be construed as a limitation of this application.

[0086] Certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that hardware manufacturers may use different names to refer to the same component. This specification and claims do not distinguish components based on differences in name, but rather on differences in function. The terms "comprising" and "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising / including but not limited to". "Approximately" means that within an acceptable margin of error, those skilled in the art can solve the technical problem and substantially achieve the technical effect within a certain margin of error. The following descriptions in the specification are preferred embodiments for carrying out this application; however, these descriptions are for the purpose of illustrating the general principles of this application and are not intended to limit the scope of this application. The scope of protection of this application shall be determined by the appended claims.

[0087] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a product or system comprising a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a product or system. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the product or system that includes said element.

[0088] It should be understood that the term "and / or" used in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this article generally indicates that the preceding and following related objects have an "or" relationship.

[0089] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A method for producing clean steel, using the BOF-LF-VD-CC process, characterized in that, The method for producing the clean steel includes the following steps: S1: After tapping from the converter, the steel undergoes deoxidation treatment to obtain the first batch of molten steel; S2: Preset slag composition, perform LF refining on the first molten steel to obtain the second molten steel; S3: Desulfurize the second molten steel to obtain the third molten steel; S4: Control the composition of VD slag entering the station and adjust the Al content in the third molten steel, control the aluminum content in VD entering the station, and obtain the fourth molten steel; S5: After VD enters the station, a vacuum is drawn, and the fourth molten steel is strongly bottom-blown and stirred to obtain the fifth molten steel; S6: After the VD pressure holding and strong bottom blowing agitation is completed, the fifth molten steel is stirred by soft bottom blowing to obtain the sixth molten steel; S7: After vacuum treatment of the sixth molten steel, soft blowing is performed to obtain clean steel; The pre-defined slag composition in S2 is as follows: MgO: 8-10%; Al2O3: 25-40%; CaO: 35-45%; SiO2 ≤ 10%. The specific steps for controlling the composition of the VD slag entering the station in S4 are as follows: after the LF refining is completed, bauxite and lightly calcined dolomite are added to the slag, with the particle size of bauxite and lightly calcined dolomite being 2-5mm; the composition of the VD slag entering the station is controlled as follows: MgO: 12-15%; Al2O3: 35-45%; CaO: 25-35%, SiO2≤10%, and CaO / Al2O3≤0.8; The aluminum content of VD entering the station in S4 is controlled at 0.03-0.05%; In S5, the stirring gas is CO2+Ar, the stirring time is controlled at 8-15 min, the volume ratio of CO2 to Ar is controlled at 0.2-0.4, and the bottom blowing flow rate is controlled at 100-300 Nl / min.

2. The method for producing clean steel according to claim 1, characterized in that, The deoxidation treatment in S1 specifically involves using Al deoxidation, and controlling the oxygen content in the molten steel to be ≤0.0010% after tapping.

3. The method for producing clean steel according to claim 1, characterized in that, After desulfurization control in S3, the sulfur content in the third molten steel is ≤0.0010%.

4. The method for producing clean steel according to claim 1, characterized in that, In S6, the soft bottom blowing gas is CO2+Ar, the soft bottom blowing time is 3-5 min, the volume ratio of CO2 to Ar is controlled between 0.2 and 0.4, and the bottom blowing flow rate is controlled between 40-60 Nl / min.

5. The method for producing clean steel according to claim 1, characterized in that, In S7, the soft blowing gas is Ar gas, the soft blowing flow rate is controlled at 20-40 Nl / min, and the soft blowing time is 8-10 min.

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