Clean steel and production and preparation method thereof

Abstract

The invention provides clean steel and a production and preparation method thereof.The production and preparation method comprises the steps that S1, deoxidation treatment is conducted after converter tapping, and first molten steel is obtained; s2, presetting slag composition, and performing LF refining on the first molten steel to obtain second molten steel; s3, performing desulfurization control on the second molten steel to obtain third molten steel; s4, after LF refining is finished, VD entering slag composition is controlled, the Al content in the molten steel is adjusted, the VD entering aluminum content is controlled, and fourth molten steel is obtained; s5, vacuum pumping is conducted after VD enters the station, strong bottom blowing stirring is conducted, and fifth molten steel is obtained; s6, after VD pressure maintaining strong bottom blowing stirring is finished, soft bottom blowing stirring is adopted, and sixth molten steel is obtained; and S7, after the sixth molten steel is subjected to vacuum treatment, soft blowing is conducted, and clean steel is obtained. By means of the method, molten steel cleaning and inclusion miniaturization can be achieved, finally, the total oxygen content in the steel can be controlled to be 8 ppm or below, the oxide inclusion size can be controlled to be 10 micrometers or below, and the number density is 3 pieces / mm < 2 > or below.

Description

[Technical field]

[0001] The present invention relates to the technical field of iron and steel metallurgy, and in particular to clean steel and a production method thereof. [Background technology]

[0002] In the prior art, the clean steel produced by the BOF-LF-VD-CC process can fully react between the steel and slag in the LF and VD refining stages, so that the sulfur content of the molten steel can be controlled at a low level. However, in terms of the control of inclusions, it is difficult to control the large-sized calcium aluminate inclusions in the molten steel with the prior art. The main reason is that:

[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] The inclusions in the molten steel are transformed into calcium magnesium aluminate, and some steel grades adopt calcium treatment process to meet the castability requirements, controlling the inclusions to 12CaO·7Al2O3 to avoid nozzle blockage.

[0010] However, calcium aluminate inclusions have a large particle size, and larger inclusions can reach more than several hundred microns. During the steel rolling process, they will be rolled into excessive Class B inclusions, causing harm.

[0011] Therefore, it is necessary to study a clean steel and a production method thereof to address the deficiencies of the prior art and to solve or alleviate one or more of the above problems. [Summary of the invention]

[0012] In view of this, the present invention provides a clean steel and a production method thereof, which can realize the purification of molten steel and the miniaturization of inclusions, and finally control the total oxygen content in the steel to be below 8ppm, the size of oxide inclusions to be below 10μm, and the number density to be 3 / mm 2 the following.

[0013] In one aspect, the present invention provides a method for producing clean steel, which is carried out using a BOF-LF-VD-CC process. The method for producing clean steel comprises the following steps:

[0014] S1: Deoxidation treatment is performed after the converter taps out steel to obtain the first molten steel;

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

[0016] S3: performing desulfurization control on the second molten steel to obtain the third molten steel;

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

[0018] S5: After the VD enters the station, it is vacuumed and the fourth molten steel is stirred by strong bottom blowing to obtain the fifth molten steel;

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

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

[0021] According to the above aspects and any possible implementation, an implementation is further provided, wherein the deoxidation treatment in S1 is specifically: Al deoxidation is adopted, and after the steel is tapped, the oxygen content in the molten steel is controlled to be ≤0.0010%.

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

[0023] According to the above aspects and any possible implementation, there is further provided an implementation, wherein after the desulfurization control in S3, the sulfur content in the third molten steel is ≤0.0010%.

[0024] According to the aspects and any possible implementation methods described above, an implementation method is further provided, in which the composition of the VD incoming slag is controlled in S4 as follows: after the LF refining is completed, bauxite and light-burned dolomite are added to the slag, and the particle size of the bauxite and the light-burned dolomite is 2-5mm; the composition of the VD incoming slag is controlled as follows: MgO: 12-15%; Al2O3: 35-45%; CaO: 25-35%, SiO2≤10%, and CaO / Al2O3≤0.8.

[0025] According to the above aspects and any possible implementation, an implementation is further provided, wherein the aluminum content of the VD inlet in S4 is controlled at 0.03-0.05%.

[0026] According to the aspects and any possible implementations described above, an implementation is further provided, wherein 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] According to the aspects and any possible implementation methods described above, an implementation method is further provided, wherein the soft bottom blowing gas in S6 adopts CO2+Ar, the soft bottom blowing time is 3-5min, the volume ratio of CO2 to Ar is controlled between 0.2-0.4; and the bottom blowing flow rate is controlled at 40-60Nl / min.

[0028] According to the above aspects and any possible implementation, an implementation is further provided, wherein 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] According to the aspects described above and any possible implementation methods, a clean steel is further provided, which is obtained by the production and preparation method of clean steel, 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 below 3 / 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 process, the slag is modified to significantly reduce the CaO content in it, so as to avoid the full reaction between the aluminum in the molten steel and the CaO in the slag during the VD process, reduce the formation of large-particle calcium aluminate inclusions, and the generated Al2O3 and aluminum-magnesium spinel inclusions are easier to remove during the dynamic stirring process of the bottom blowing gas;

[0032] (2) Under vacuum pressure, the stirring gas is CO2+Ar, and the inclusions are transformed into Al2O3·MgO, avoiding the formation of large-sized calcium aluminate;

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

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

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

[0036] (6) The stirring gas is CO2+Ar, and the 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 the CO2 in the bottom blowing gas, so as to promote the transformation of inclusions to Al2O3·MgO and avoid the formation of large-sized calcium aluminate.

[0037] Of course, any product implementing the present invention does not necessarily need to achieve all of the above-mentioned technical effects at the same time.

Brief Description of the Drawings

[0038] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0039] Figure 1 It is a flow chart of a method for producing clean steel provided by one embodiment of the present invention. [Specific implementation method]

[0040] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0041] It should be clear that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The singular forms "a", "said" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

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

[0044] S1: Deoxidation treatment is performed after the converter taps out steel to obtain the first molten steel;

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

[0046] S3: performing desulfurization control on the second molten steel to obtain the third molten steel;

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

[0048] S5: After the VD enters the station, it is vacuumed and the fourth molten steel is stirred by strong bottom blowing to obtain the fifth molten steel;

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

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

[0051] The deoxidation treatment in S1 is specifically as follows: Al deoxidation is adopted, and the oxygen content in the molten steel is controlled to be ≤0.0010% after the steel is tapped.

[0052] The preset slag composition in S2 is specifically: MgO: 8-10%; Al2O3: 25-40%; CaO: 35-45%, SiO2≤10%.

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

[0054] The composition of the VD incoming slag in S4 is specifically controlled as follows: after the LF refining is completed, bauxite and light-burned dolomite are added to the slag, and the particle size of the bauxite and the light-burned dolomite is 2-5mm; the composition of the VD incoming slag 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 in the S4 is controlled at 0.03-0.05%.

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

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

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

[0059] The present invention also provides a clean steel obtained by the production and preparation 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 3 / mm 2 the following.

[0060] Embodiment 1:

[0061] The present invention provides a production and preparation method of clean steel. Before the molten steel enters the VD process, bauxite and light-burned dolomite are added to increase the alumina content in the slag, and the VD bottom blowing gas is designed to be CO2+Ar, which promotes the reaction of CO2 gas with Ca in the molten steel and reduces the Ca content in the molten steel, thereby reducing the generation of a large number of large-particle calcium aluminates by the steel / slag reaction. The generated inclusions are mostly small-sized magnesium aluminum spinel, and the soft blowing operation is combined to achieve the purification of the molten steel and the miniaturization of the inclusions. Finally, the total oxygen content in the steel can be controlled to be below 8ppm, the average size of oxide inclusions to be below 10μm, and the number density to be 3 / mm 2 the following.

[0062] The slag composition of the LF refining process of the present invention is shown in Table 1 below, 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 situation is shown in Table 4. When the BOF-LF-VD-CC process is used to produce clean steel, the control is carried out according to the following steps:

[0063] (1) Al deoxidation is used in the converter, and the oxygen content in the molten steel is controlled to be ≤0.0010% after the tapping is completed. This step is the control habit of the end point of the general clean steel converter. During the tapping process, the deoxidation task is completed, and the inclusions continue to react with steel / slag and collide and float up to be removed during the subsequent refining process.

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

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

[0066] (4) After LF refining, bauxite and light-burned dolomite are added to the slag to control the composition of the VD slag to be: MgO: 12-15%; Al2O3: 35-45%; CaO: 25-35%, SiO2≤10%, and CaO / Al2O3≤0.8. The slag of this target composition has an MgO content in an oversaturated state, so that under the intense VD stirring conditions, the aluminum in the molten steel mainly reacts with MgO to generate spinel and Al2O3 inclusions, which can float up in large quantities during the soft blowing process after the vacuum treatment is completed; in order to avoid the aluminum in the molten steel reacting with CaO to generate Ca during the VD vacuum treatment, and finally generating calcium aluminate inclusions.

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

[0068] (6) After the VD enters the station, it is vacuumed and strong bottom blowing and stirring are performed. The stirring gas is CO2+Ar, and the control time is 8-15min. The volume ratio of strong stirring gas CO2 and Ar is controlled between 0.2-0.4, and the bottom blowing flow rate is controlled at 100-300Nl / min. The stirring gas is CO2+Ar, and CO2 can be used to react with Ca in the molten steel to reduce the Ca content of the molten steel and the CaO content in the inclusions. However, CO2 will also react with Mg in the molten steel to reduce the Mg content in the molten steel. The CaO and MgO contents in the inclusions are significantly reduced. The Al2O3 content in the inclusions is increased. (Since Ca reacts more easily with CO2, the CaO content in the inclusions is significantly reduced, and the inclusions are transformed to the direction of Al2O3·MgO)

[0069] (7) After the VD pressure-maintaining strong bottom blowing stirring is completed, soft bottom blowing stirring is adopted, and the gas is CO2+Ar, and the soft blowing time is: 3-5min; the volume ratio of CO2 to Ar is controlled between 0.2-0.4; the bottom blowing flow rate is controlled at 40-60Nl / min. Here, there is a 3-5min soft blowing under the pressure-maintaining condition, and its purpose is to cause the slag caused by the strong stirring process to be drawn into the molten steel and promote the rapid separation of the slag.

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

[0071] In the prior art, in order to meet the needs of desulfurization, slag with higher basicity is generally used for refining. However, in the VD process of treating molten steel, due to the full reaction of steel / slag, the inclusions are mainly calcium aluminates. Such inclusions have large particle sizes and are more harmful to steel.

[0072] The present invention adopts three main technical means in the whole smelting process to control the inclusions to be close to the composition of Al2O3·MgO spinel, the particle size of the inclusions is relatively small, and the harm to the steel is small. The three main technical means 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 of aluminum and CaO during the VD process and the formation of large calcium aluminate inclusions. The generated Al2O3 and aluminum-magnesium spinel inclusions are easier to remove 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 a high melting point slag, which not only avoids excessive slag / steel reaction, but also prevents liquid slag from dripping into the molten steel.

[0075] (9) The stirring gas is CO2+Ar, and the strong+weak kinetic control method is matched. The competitive reaction between the metal elements Ca and Mg in the steel and the CO2 in the bottom blowing gas is fully utilized to promote the transformation of inclusions to Al2O3·MgO, avoiding the formation of large-sized calcium aluminate.

[0076] Table 1

[0077]

[0078] Table 2

[0079]

[0080] Table 3

[0081]

[0082]

[0083] Table 4

[0084]

[0085] The above is a detailed introduction to a clean steel and its production method provided in the embodiment of the present application. The description of the above embodiment is only used to help understand the method and its core idea of ​​the present application; at the same time, for ordinary technicians in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

[0086] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different nouns to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. As mentioned throughout the specification and claims, "including" and "comprising" are open-ended terms, so they should be interpreted as "including / including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect. The subsequent description of the specification is a preferred embodiment of the present application, but the description is for the purpose of illustrating the general principles of the present application, and is not used to limit the scope of the present application. The scope of protection of the present application shall be determined by the definition of the attached claims.

[0087] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such a product or system. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the product or system including the elements.

[0088] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0089] The above description shows and describes several preferred embodiments of the present application, but as mentioned above, it should be understood that the present application is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the application concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present application, and should be within the scope of protection of the claims attached to the present application.

Claims

1. A method for producing clean steel, using a BOF-LF-VD-CC process, characterized in that: The production method of clean steel comprises the following steps: S1: Deoxidation treatment is performed after the converter taps out steel to obtain the first molten steel; S2: Preset the slag composition, perform LF refining on the first molten steel, and obtain the second molten steel; S3: performing desulfurization control on the second molten steel to obtain the third molten steel; S4: Control the composition of VD incoming slag and adjust the Al content in the third molten steel, control the aluminum content in the VD incoming station, and obtain the fourth molten steel; S5: After the VD enters the station, it is vacuumed and the fourth molten steel is stirred by strong bottom blowing to obtain the fifth molten steel; S6: After the VD pressure-maintaining strong bottom blowing stirring is completed, the fifth molten steel is stirred by soft bottom blowing to obtain the sixth molten steel; S7: After the sixth molten steel is vacuum treated, soft blowing is performed to obtain clean steel.

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

3. The method for producing clean steel according to claim 1, characterized in that: The preset slag composition in S2 is specifically: MgO: 8-10%; Al2O3: 25-40%; CaO: 35-45%, SiO2≤10%.

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

5. The method for producing clean steel according to claim 1, characterized in that: The composition of the VD incoming slag in S4 is specifically controlled as follows: after the LF refining is completed, bauxite and light-burned dolomite are added to the slag, and the particle size of the bauxite and the light-burned dolomite is 2-5mm; the composition of the VD incoming slag is controlled as follows: MgO: 12-15%; Al2O3: 35-45%; CaO: 25-35%, SiO2≤10%, and CaO / Al2O3≤0.

8.

6. The method for producing clean steel according to claim 1, characterized in that: The aluminum content of VD in the S4 is controlled at 0.03-0.05%.

7. The method for producing clean steel according to claim 1, characterized in that: The stirring gas in S5 is CO2+Ar, the control time is 8-15min, the volume ratio of CO2 to Ar is controlled at 0.2-0.4, and the bottom blowing flow rate is controlled at 100-300Nl / min.

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

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

10. A clean steel obtained by the production method of clean steel according to any one of claims 1 to 9, characterized in that: 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 / mm 2 the following.

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