Uniform modification method for IF steel ladle top slag

Abstract

The invention discloses a uniform modification method for IF steel ladle top slag, which comprises the following steps: adding lime through an overhead bunker when one third of converter tapping, and adding a modifier on the slag surface within 1min after tapping to modify the slag; after RH decarburization is finished, aluminum is added for molten steel deoxidation, and a modifier is added through a vacuum stock bin while aluminum is added for deoxidation; after RH treatment is finished, the steel ladle is conveyed to a modifier feeding position, and a modifier is added to the surface of the steel ladle through a spherical uniform distributor; the modifier comprises the following components in percentage by mass: 40-60% of Al, 20-30% of CaO, 15-25% of Al2O3 and less than or equal to 5% of SiO2; the Al adopts a cut aluminum sheet or an aluminum strip with the length of 3-10 mm; the CaO and the Al2O3 are prepared by mixing and pressing the pre-melted aluminate slag, the metal aluminum and the pre-melted slag into a spherical or ellipsoidal object with the diameter of 40-80mm; according to the method, the problem of uniform and deep modification of the IF steel top slag is well solved, TFe of the top slag is stably controlled within 5%, T.O can be stably controlled within 16 ppm, the quality of molten steel is improved, inclusion judgment change is reduced, and the percent of pass of slabs is stably increased.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for modifying IF steel ladle top slag. Background Art

[0002] During the IF steel production process, the highly oxidizing slag in the converter will inevitably be brought into the ladle by the molten steel. The oxidizing property of the refined slag entering the RH is generally more than 15%. During the refining process and subsequent steel pouring, the slag continuously transfers oxygen to the molten steel, causing Al and O in the molten steel to react to form Al2O3 inclusions, thereby deteriorating the quality of the molten steel. Therefore, in order to reduce the impact of the oxidizing property of the slag on the quality of the molten steel, the top slag of the automobile plate needs to be modified to reduce the oxidizing property of the top slag.

[0003] Top slag modification is to add a modifier containing metallic aluminum materials to the surface of the refined slag to reduce FeO in the refined slag, thereby reducing the oxidizability of the refined slag and improving the quality of the molten steel. Considering the cost and modification effect, the modification generally controls the top slag TFe within 5%, but there are two major problems in production: one is that the FeO reduction is not complete, the oxidizability is generally high, and the control is unstable. The oxidizability of the top slag depends on the amount of aluminum-containing modifier added. When the amount of steel-making modifier added is high, oxygen in the molten steel will be removed, resulting in insufficient oxygen for RH decarburization. RH needs to be blown for oxygen decarburization, which affects the purity of the molten steel; when the amount of steel-making modifier added is small, the modification effect cannot be achieved; and the top slag modification fluctuates greatly due to the influence of the slag flowability and the addition method. Second, the modification is uneven due to the influence of slag fluidity and the addition method. When the modifier is added to the ladle surface through the high-level silo, the addition position is relatively fixed, and accumulation will form after adding to the surface, which has a great influence on the uniformity of the modification, that is, the top slag oxidation in different parts of the ladle is different, which will also affect the cleanliness of the molten steel. In addition, in addition to reducing the oxidizability of the ladle top slag, the top slag modification also needs to increase and maintain the top slag's absorption capacity for Al2O3-type inclusions. Therefore, the top slag modification also needs to have the function of slag adjustment.

[0004] At present, the domestic use of 30-50% aluminum-containing modifiers to modify the top slag of IF steel ladle to reduce the secondary oxidation of molten steel. However, in actual production, due to the different composition, addition method, addition amount, and addition timing of the modifier, the top slag modification effect is also different, especially the uniformity and stability of the top slag modification effect of the ladle has always been a difficult problem in production. Summary of the invention

[0005] In view of the problems of high oxidizability, uneven modification and instability in the prior art of modifying the top slag of IF steel, the present invention provides a method for uniformly modifying the top slag of IF steel ladle to achieve stable control of the quality of automobile plates.

[0006] In order to achieve the above purpose, the technical solutions adopted are as follows:

[0007] A method for uniformly modifying IF steel ladle top slag comprises the following steps:

[0008] (1) When one third of the converter is tapped, lime is added through the high-level silo, and within 1 minute after the tapping, a modifier is added to the slag surface to modify the slag;

[0009] (2) After RH decarburization, aluminum is added to deoxidize the molten steel, and a modifier is added through a vacuum silo while adding aluminum for deoxidation;

[0010] (3) After the RH treatment is completed, the ladle is transported to the modifier feeding position, and the modifier is added to the ladle surface through the distributor.

[0011] According to the above scheme, the composition of the modifier is calculated by mass percentage: Al: 40-60%, CaO: 20-30%, Al2O3: 15-25%, SiO2≤5%.

[0012] According to the above scheme, the Al in the modifier adopts 3-10 mm long cut aluminum sheets or aluminum bars instead of powdered aluminum; CaO and Al2O3 adopt pre-melted aluminate slag, and the metallic aluminum and the pre-melted slag are mixed and pressed into a spherical or ellipsoidal object with a diameter of 40-80 mm.

[0013] According to the above scheme, the amount of lime added in step 1 is 1.0-2.0 kg / t steel.

[0014] According to the above scheme, the amount of modifier added in step 1 is 0.9 to 1.5 kg / t steel.

[0015] According to the above scheme, during the process of adding the modifier in step 1, the ladle car is moved back and forth to avoid the accumulation of the modifier.

[0016] According to the above scheme, the slag thickness is controlled to be ≤100mm during the steel-making process in step 1.

[0017] According to the above scheme, the amount of modifier added in step 2 is 0.4-0.8 kg / t steel.

[0018] According to the above scheme, the amount of modifier added in step 3 is 0.8 to 1.5 kg / t steel.

[0019] According to the above scheme, the distributor used in step 3 is spherical and evenly distributed with holes with a diameter of 100 to 120 mm. The diameter of the spherical surface of the distributor is 75% of the inner diameter of the upper part of the ladle.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] After the converter tapping is completed, a proper amount of modifier is added to the surface of the ladle to perform moderate surface deoxidation and modification, so as to avoid insufficient oxygen in RH decarburization caused by excessive slag; when aluminum alloying is performed after RH decarburization, a proper amount of modifier is added to perform slag-steel interface deoxidation and modification, and a liquid calcium aluminate protective layer is formed to reduce the oxygen transfer from the slag to the molten steel; after the RH is completed, a uniform distributor is used to add a proper amount of modifier to perform uniform depth modification on the slag surface, so as to avoid oxygen transfer from the top slag to the molten steel during the casting process.

[0022] The present modifier uses cut aluminum sheets or aluminum bars instead of powdered aluminum. On the one hand, it avoids the high Al2O3 due to the large specific surface area of ​​aluminum powder, which is easy to oxidize and affects the effective aluminum deoxidation in the modifier. On the other hand, it reduces the smoke caused by the addition of powdered aluminum to the slag surface. Since the CaO and Al2O3 in the modifier are low-melting-point pre-melted aluminate slag, they can be quickly melted and flow on the slag surface after being added to the slag surface, which plays a role in uniform modification. At the same time, after the RH refining is completed, a spherical or ellipsoidal modifier with a diameter of 40 to 80 mm is added to the slag surface through a uniform distributor, and the modifier is quickly and evenly distributed on the slag surface along the spherical distributor, which plays an effect of uniform modification of the slag surface.

[0023] The present invention solves the problem of uniform depth modification of IF steel top slag. The top slag TFe is stably controlled within 5%, the top slag components at different parts of the ladle are basically kept consistent, and the TO of the middle ladle can be stably controlled within 16ppm. This not only improves the quality of molten steel and reduces inclusion modification, but also steadily increases the qualified rate of slabs. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 : Schematic diagram of the distributor device used in the present invention. DETAILED DESCRIPTION

[0025] The following examples further illustrate the technical solution of the present invention, but are not intended to limit the scope of protection of the present invention.

[0026] The specific implementation method provides a uniform modification method of IF steel ladle top slag:

[0027] In order to ensure that the modifier added to the slag surface can be quickly melted and react with the oxygen in the slag, a high-efficiency and environmentally friendly modifier is used, and its weight composition is: Al: 40-60%, CaO: 20-30%, Al2O3: 15-25%, SiO2≤5%; wherein the aluminum in the modifier is a 3-10 mm long cut aluminum sheet or aluminum strip instead of powdered aluminum, CaO and Al2O3 are pre-melted aluminate slag, and the aluminum and pre-melted slag are mixed and pressed into a 40-80 mm spherical or ellipsoidal object;

[0028] (1) When one third of the converter is tapped, add lime (1.0-2.0 kg / t steel) through the high-level silo. Add a modifier to the slag surface within 1 minute after tapping to modify the slag. The amount of modifier added is 0.9-1.5 kg / t. During the process of adding the modifier, move the ladle car back and forth to avoid the accumulation of the modifier. During the tapping process, strictly control the amount of slag and control the slag thickness to ≤100 mm.

[0029] (2) After RH decarburization, aluminum is added to deoxidize the molten steel. At the same time, 0.4-0.8 kg / t of modifier is added through a vacuum silo to modify the top slag and form a reducing liquid calcium aluminate layer at the slag-steel interface to reduce the transfer of oxygen from the top slag to the molten steel.

[0030] (3) After the RH treatment is completed, the ladle is transported to the modifier feeding position, and 0.8-1.5 kg / t modifier is added to the ladle surface through a uniform distributor. The modifier is evenly added to the slag surface through the holes on the distributor to uniformly and deeply modify the top slag to prevent the top slag from transferring oxygen to the molten steel during the casting process.

[0031] The specific embodiment also provides a uniform distributor, and the schematic diagram of the device is shown in the attached Figure 1 As shown, the size of the spherical distributor 1 is 75% of the inner diameter of the upper part of the ladle, and is evenly covered with round holes with a diameter of 100 to 120 mm. The spherical distributor 1 is connected and fixed to the dust removal protective cover 3 through three distributor fixing hinges 2. After the modifier is added to the spherical distributor through the discharge port 4, it automatically slides down the spherical distributor and enters the slag surface of the ladle through the round holes on the surface, which plays a role of uniform addition.

[0032] The method of the present invention was applied to a 250t converter. The following are specific examples.

[0033] Example 1

[0034] The actual production process of the top slag modification of the automobile outer panel produced by the technical solution of the present invention is as follows:

[0035] (1) The weight composition of the modifier in this embodiment is: Al: 40%, CaO: 30%, Al2O3: 25%, SiO2: 5%; its diameter is 50mm spherical;

[0036] (2) When one third of the converter is tapped, lime (2.0 kg / t steel) is added through the high-level silo. Within 1 minute after the tapping, a modifier is added to the slag surface to modify the slag. The amount of modifier added is 0.9 kg / t. During the process of adding the modifier, the ladle car is moved back and forth to avoid the accumulation of the modifier. The tapping slag thickness is 60 mm.

[0037] (3) After RH decarburization, aluminum is added to deoxidize the molten steel. At the same time, 0.4 kg / t of modifier is added through the vacuum silo. After RH treatment, the ladle is transported to the modifier feeding position, and 1.5 kg / t of modifier is added to the surface of the ladle through a uniform distributor.

[0038] (4) After the addition of the modifier was completed, the slag was allowed to stand for 5 min, and slag oxygen was taken from four different parts of the ladle for composition analysis. See Table 1.

[0039] Table 1 Top slag composition after modification (%)

[0040] Location CaO <![CDATA[Al2O3]]> <![CDATA[SiO2]]> MgO TFe MnO 1 53.3 28.8 6.7 6.5 4.1 0.6 2 52.8 29.6 6.2 6.3 4.2 0.8 3 54.2 29.2 5.8 5.8 3.8 1.2 4 53.9 27.9 6.6 6.8 4.2 0.5

[0041] Example 2

[0042] The actual production process of the top slag modification of the automobile outer panel produced by the technical solution of the present invention is as follows:

[0043] (1) The weight composition of the modifier in this embodiment is: Al: 48%, CaO: 25%, Al2O3: 25%, SiO2: 2%; its diameter is 80mm spherical;

[0044] (2) When one third of the converter is tapped, lime (1.0 kg / t steel) is added through the high-level silo. Within 1 minute after the tapping, a modifier is added to the slag surface to modify the slag. The amount of modifier added is 1.5 kg / t. During the process of adding the modifier, the ladle car is moved back and forth to avoid the accumulation of the modifier. The tapping slag thickness is 100 mm.

[0045] (3) After RH decarburization, aluminum is added to deoxidize the molten steel. At the same time, 0.8 kg / t of modifier is added through a vacuum silo. After RH treatment, the ladle is transported to the modifier feeding position, and 0.8 kg / t of modifier is added to the surface of the ladle through a uniform distributor.

[0046] (4) After the addition of the modifier was completed, the slag was allowed to stand for 4 min, and slag oxygen was taken from four different parts of the ladle for composition analysis. See Table 2.

[0047] Table 2 Top slag composition after modification (%)

[0048] Location CaO <![CDATA[Al2O3]]> <![CDATA[SiO2]]> MgO TFe MnO 1 51.5 32.2 5.7 6.8 3.1 0.5 2 50.5 33.1 5.5 6.3 3.8 0.6 3 51.3 32.8 5.8 5.9 3.2 0.8 4 52 32.5 5.4 6.2 3.5 0.4

[0049] Example 3

[0050] The actual production process of the top slag modification of the automobile outer panel produced by the technical solution of the present invention is as follows:

[0051] (1) The weight composition of the modifier in this embodiment is: Al: 60%, CaO: 23%, Al2O3: 15%, SiO2: 2%; its diameter is 80mm spherical;

[0052] (2) When one third of the converter is tapped, 1.5 kg / t of lime is added through the high-level silo. Within 1 minute after the tapping, a modifier is added to the slag surface to modify the slag. The amount of modifier added is 1.0 kg / t. During the process of adding the modifier, the ladle car is moved back and forth to avoid the accumulation of the modifier. The tapping slag thickness is 80 mm.

[0053] (3) After RH decarburization, aluminum is added to deoxidize the molten steel. At the same time, 0.6 kg / t of modifier is added through the vacuum silo. After RH treatment, the ladle is transported to the modifier feeding position, and 1.2 kg / t of modifier is added to the surface of the ladle through a uniform distributor.

[0054] (4) After the addition of the modifier was completed, the slag was allowed to stand for 6 min, and slag oxygen was taken from four different parts of the ladle for composition analysis. See Table 3.

[0055] Table 3 Top slag composition after modification (%)

[0056] Location CaO <![CDATA[Al2O3]]> <![CDATA[SiO2]]> MgO TFe MnO 1 49.8 34.2 6.2 6.4 2.8 0.6 2 49.2 35.1 6.2 6 2.9 0.6 3 48.5 34.8 6.8 6.5 2.6 0.8 4 48.9 34.5 6.3 6.8 3 0.5

[0057] Example 4

[0058] The actual production process of the top slag modification of the automobile outer panel produced by the technical solution of the present invention is as follows:

[0059] (1) The weight composition of the modifier in this embodiment is: Al: 55%, CaO: 20%, Al2O3: 22%, SiO2: 3%; its diameter is 60mm spherical;

[0060] (2) When one third of the converter is tapped, 1.3 kg / t of lime is added through the high-level silo. Within 1 minute after the tapping, a modifier is added to the slag surface to modify the slag. The amount of modifier added is 1.25 kg / t. During the process of adding the modifier, the ladle car is moved back and forth to avoid the accumulation of the modifier. The tapping slag thickness is 70 mm.

[0061] (3) After RH decarburization, aluminum is added to deoxidize the molten steel. At the same time, 0.5 kg / t of modifier is added through the vacuum silo. After RH treatment, the ladle is transported to the modifier feeding position, and 1.3 kg / t of modifier is added to the ladle surface through a uniform distributor.

[0062] (4) After the addition of the modifier was completed, the slag was allowed to stand for 5.5 min, and slag oxygen was taken from four different parts of the ladle for composition analysis. See Table 4.

[0063] Table 4 Top slag composition after modification (%)

[0064] Location CaO <![CDATA[Al2O3]]> <![CDATA[SiO2]]> MgO TFe MnO 1 51.8 30.5 6.6 7.0 3.3 0.8 2 52.2 31.1 6.2 6.7 3.1 0.7 3 52 31.3 6.8 6.5 2.8 0.6 4 51.9 30.8 6.9 6.7 3 0.7

[0065] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for uniformly modifying IF steel ladle top slag, characterized in that The following steps are involved: (1) When one third of the converter is tapped, lime is added through the high-level silo, and within 1 minute after the tapping, a modifier is added to the slag surface to modify the slag; (2) After RH decarburization, aluminum is added to deoxidize the molten steel, and a modifier is added through a vacuum silo while adding aluminum for deoxidation; (3) After the RH treatment is completed, the ladle is transported to the modifier feeding position, and the modifier is added to the ladle surface through the distributor.

2. The uniform modification method of IF steel ladle top slag according to claim 1, characterized in that The composition of the modifier is calculated by mass percentage: Al: 40-60%, CaO: 20-30%, Al2O3: 15-25%, SiO2≤5%.

3. The uniform modification method of IF steel ladle top slag as claimed in claim 2, characterized in that The Al in the modifier is a 3-10 mm long cut aluminum sheet or aluminum bar; the CaO and Al2O3 are pre-melted aluminate slag, and the metal aluminum and the pre-melted slag are mixed and pressed into a spherical or ellipsoidal object with a diameter of 40-80 mm.

4. The uniform modification method of IF steel ladle top slag according to claim 1, characterized in that In step 1, the amount of lime added is 1.0-2.0 kg / t steel.

5. The uniform modification method of IF steel ladle top slag according to claim 1, characterized in that In step 1, the amount of modifier added is 0.9 to 1.5 kg / t steel.

6. The uniform modification method of IF steel ladle top slag according to claim 1, characterized in that During the process of adding the modifier in step 1, move the ladle car back and forth to avoid the accumulation of modifier.

7. The uniform modification method of IF steel ladle top slag according to claim 1, characterized in that In step 1, the slag thickness is controlled to be ≤100mm during the steel tapping process.

8. The uniform modification method of IF steel ladle top slag according to claim 1, characterized in that In step 2, the amount of modifier added is 0.4-0.8 kg / t steel.

9. The uniform modification method of IF steel ladle top slag according to claim 1, characterized in that In step 3, the amount of modifier added is 0.8-1.5 kg / t steel.

10. The uniform modification method of IF steel ladle top slag according to claim 1, characterized in that The distributor used in step 3 is spherical and evenly distributed with holes with a diameter of 100 to 120 mm. The diameter of the spherical surface of the distributor is 75% of the inner diameter of the upper part of the ladle.

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