Refining slag modifier for preventing oxygen return after RH (Ruhrstahl Heraeus) treatment and modification method thereof

Abstract

The invention discloses a refining slag modifier for preventing oxygen return after RH (Ruhrstahl Heraeus) treatment and a modification method thereof. The refining slag modifier comprises the following components in percentage by weight: 30 to 65 percent of Al, 3 to 30 percent of Fe, 5 to 20 percent of CaO, 5 to 20 percent of Al2O3, 2 to 7 percent of CaCO3, 5 to 15 percent of binder and the balance of inevitable impurities. According to the method, the problem that the refining slag transfers oxygen to the molten steel after RH treatment can be avoided, and the problem that the oxidizing property of the refining slag after RH treatment is high is fundamentally solved.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking and smelting, and in particular to a refined slag modifier for preventing oxygen return after RH treatment and a modification method thereof. Background Art

[0002] IF steel (interstitial free steel) is known as interstitial free steel. It is the main product of cold rolled automotive and household appliance plates. However, at the production site of the cold rolling production line and at the user end, IF steel is often found to have Al2O3 inclusion defects, in which Al2O3 presents a clustered and coarse morphology. The main reasons for the formation of Al2O3 are deoxidation products and secondary oxidation. The mechanism of deoxidation products is relatively clear, and they are basically produced by deoxidation in the refining process. However, there are relatively few studies on secondary oxidation. When FeO in the slag system oxidizes IF steel, it will lead to the formation of alumina.

[0003] Conventional means of reducing secondary oxidation are nothing more than reducing the oxidizability of slag. Therefore, relevant steel mills at home and abroad have made various technical improvements to the slag in the converter furnace and on the top of the ladle. For example, Chinese patent CN108504799B proposes a method for reducing the FeO content of the final slag during the reforming and smelting of molten converter slag. The method of reducing the FeO content in the furnace is used to add relevant reducing agent components into the furnace to reduce the FeO content in the furnace and reduce the oxidizability of the slag. Chinese Patent Publication No. CN110129512A proposes a final slag modifier and a method for modifying the final slag of converter semi-steel steelmaking, which belongs to the field of metallurgical technology. The final slag modifier includes: 50-55% MgO, 16% SiO2 and 12-18% C; it is said that this technology can deoxidize the final slag, adjust the content of MgO in the final slag and the viscosity of the final slag, reduce the oxygen content of molten steel, reduce the content of TFe in the final slag, increase the content of MgO in the final slag, increase the viscosity of the final slag, improve the fluidity of the final slag, and then improve the later slag splashing effect and increase the service life of the furnace lining. Chinese patent publication number CN109722501A proposes a ladle top slag modification method suitable for IF steel. No metallurgical lime is added during the converter tapping process. After the molten steel reaches the alloy fine-tuning station, aluminum particles are immediately added through a distributor, and then metallurgical lime is added through a distributor. The molten steel is left standing at the distribution position for 3 to 5 minutes before leaving the station. It is said that this method can solve the technical problems of the existing top slag modification process, such as serious environmental pollution, high oxygen consumption in the modification process, and high cost of the modifier, and achieve high-quality, green and economical production of IF steel.

[0004] Research has found that the oxidizability of the slag after RH treatment is higher than that before treatment. The above technology does not fundamentally solve the problem of oxidation of molten steel after RH treatment. In view of the above situation, it is urgent to develop a new technology that can prevent the refined slag from transferring oxygen to the molten steel after the RH treatment and solve the problem of high oxidizability of the refined slag after RH treatment. Summary of the invention

[0005] In view of the fact that the prior art cannot fundamentally solve the oxidation problem of molten steel after RH treatment, the purpose of the present invention is to provide a refined slag modifier and a modification method for preventing oxygen return after RH treatment, which can avoid the problem of oxygen transfer from refined slag to molten steel after RH treatment and fundamentally solve the problem of high oxidizability of refined slag after RH treatment.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] The invention provides a refined slag modifier for preventing reoxidation after RH treatment, comprising the following components by weight percentage: Al: 30-65%, Fe: 3-30%, CaO: 5-20%, Al2O3: 5-20%, CaCO3: 2-7%, binder: 5-15%, and the rest are inevitable impurities.

[0008] Preferably, among the unavoidable impurities, the content of SiO2 is ≤6wt%.

[0009] Preferably, the refined slag modifier for preventing reoxidation after RH treatment comprises 35-55% Al, 10-16% Fe, 12-18% CaO, 12-18% Al2O3, 3-5% CaCO3 and 7-11% binder.

[0010] Preferably, the binder is one of corn starch, potato starch and sweet potato starch.

[0011] The second aspect of the present invention provides a method for modifying refined slag to prevent reoxidation after RH treatment. After the RH treatment is completed, the refined slag modifier for preventing reoxidation after RH treatment as described in the first aspect of the present invention is added to the RH ladle before steelmaking. After the static reaction is completed, the ladle is covered and transported out to the next process.

[0012] Preferably, the addition amount of the refined slag modifier for preventing reoxidation after RH treatment is 60-100 kg / H steel.

[0013] Preferably, when the refined slag modifier for preventing reoxidation after RH treatment is used, the components of the refined slag modifier are mixed evenly and then pressed into a block-shaped modifier, and the density of the block-shaped modifier is 1.5 to 4.5 g / cm 3 .

[0014] Preferably, before the RH treatment, lime is added to the RH ladle when the steel is blown out of the converter, and the amount of lime added is 350-450 kg / H steel.

[0015] Preferably, after the static reaction is completed, the FeO content in the slag of the RH ladle is detected to be ≤2.5wt%.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] 1. Aiming at the problem of high oxidizability in slag after RH treatment, the present invention provides a slag modifier for preventing oxygen regeneration after RH treatment and a modification method thereof, which can prevent the slag from transferring oxygen to molten steel after RH treatment, fundamentally solve the oxidizability problem of slag, and improve the purity of IF steel molten steel;

[0018] 2. The refined slag modifier for preventing reoxidation after RH treatment and the modification method thereof of the present invention can fundamentally solve the problem of high oxidizability of refined slag after RH treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0020] Figure 1 It is a graph showing the change of FeO content in slag before and after RH treatment. DETAILED DESCRIPTION

[0021] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form.

[0022] In view of the fact that the domestic and foreign steel industries have not yet solved the problem of high oxidizability in the slag after RH treatment, the present invention provides a refined slag modifier and modification method for preventing oxygen return after RH treatment. After the RH treatment is completed, the refined slag in the RH ladle is prevented from transferring oxygen to the molten steel, thereby fundamentally solving the problem of high oxidizability of the top slag and improving the purity of IF steel molten steel.

[0023] From the perspective of metallurgical mechanism, firstly, using the metallurgical data manual, from the isoactivity curve (CaO+MgO+MnO)-(SiO2+P2O5)-FeO diagram, for a slag system of a certain component, the activity of FeO can be found out. For example, when the composition of RH ladle slag before RH refining treatment is as shown in Table 1, according to the weight ratio of 5% FeO, 46% CaO, 32% Al2O3, 6% SiO2, 4.5% MgO, and 1.3% MnO before refining treatment, a phase diagram is made based on the molar fractions of the three points (SiO2+P2O5+Al2O3), (CaO+MnO+MgO), and FeO, and the relevant FeO activity can be calculated and queried to be 0.15. The oxygen distribution coefficient is shown in formula (1):

[0024] (FeO) = [O] + [FeO] (1)

[0025] The equilibrium constant of the reaction is Where Kθ is the FeO activity, a [O] is the activity of oxygen, a [Fe] is the activity of iron. Activity is the effective concentration of mole fraction and has a dimension of 1.

[0026] Table 1 RH ladle slag composition before refining treatment

[0027] FeO CaO <![CDATA[Al2O3]]> <![CDATA[SiO2]]> MgO MnO <![CDATA[P2O5]]> 5％ 46％ 32％ 4.5％ 4.5％ 1.3％ 0.22％

[0028] When using pure substances, the activity of Fe is 1. When the oxygen in the molten steel is used as a dilute solution, a(O) = w[O], then the equilibrium constant K can be simplified to:

[0029] K=w [O] / a (FeO) (2)

[0030] Where K is the equilibrium constant, W [O] is the weight percentage of oxygen, a (FeO) is the FeO activity. Under pure oxide slag, lgw[O]=-6320 / T+2.734. Before IF refining treatment, the temperature is brought to 1610℃, and w [O] =0.2387, which is the distribution coefficient of oxygen between molten steel and FeO at this temperature. Substituting the activity of FeO 0.15 into formula (2), we get: [O] =0.03580, i.e. 358ppm.

[0031] The above calculation results show that at 1610°C, the free oxygen in the molten steel in equilibrium with 5% FeO is 358ppm; when the free oxygen in the molten steel is higher than 358ppm, the molten steel will transfer oxygen to the ladle slag. A base collected production data of 7273 furnaces before RH treatment. From the data, the average free oxygen in the molten steel is 472ppm. At this time, the oxygen potential of the molten steel is higher than the oxygen potential in the slag, so the oxygen in the molten steel will transfer toward the ladle slag. It can be seen that after the refining treatment in the above production process, the FeO in the slag increases. Combined with Figure 1 From the change of FeO content in the slag before and after RH treatment, it can be seen that after the RH treatment, the FeO content in the slag is higher than that before the treatment.

[0032] It can be seen that the reaction process of FeO in the slag at the slag / metal interface during the RH refining process has two directions. One is that the oxygen potential in the slag is lower than that in the molten steel (the FeO in the slag is 5-6%), and the molten steel transfers oxygen to the slag. When the molten steel is finished in the refining process, the oxygen potential in the slag is higher than that in the molten steel, and the slag will transfer oxygen to the molten steel. Therefore, from the completion of the refining process to the entire process of continuous casting ladle pouring, the oxygen transferred to the molten steel reacts with the acid-soluble aluminum dissolved in the molten steel as follows:

[0033] 2Al+3[O]=Al2O3 (3)

[0034] This is secondary oxidation caused by FeO in ladle slag. In order to control the oxidation of ladle slag, the FeO content in the slag needs to be reduced to less than 7% before RH treatment to prevent FeO in the slag from transferring oxygen to the molten steel. In the second stage, after RH treatment, in order to prevent oxygen in the slag from transferring to the molten steel, appropriate aluminum slag auxiliary materials that reduce FeO should be added to the top slag of the ladle to remove oxygen in the slag.

[0035] The present invention provides a refined slag modifier for preventing reoxidation after RH treatment, comprising the following components in weight percentage: Al: 30-65%, Fe: 3-30%, CaO: 5-20%, Al2O3: 5-20%, CaCO3: 2-7%, binder: 5-15%, and the rest are inevitable impurities; among the inevitable impurities, the content of SiO2 is ≤6%.

[0036] In a further preferred embodiment, the refined slag modifier for preventing reoxidation after RH treatment comprises 35-55% Al, 10-16% Fe, 12-18% CaO, 12-18% Al2O3, 3-5% CaCO3 and 7-11% binder.

[0037] In a specific embodiment, the binder can be corn starch, potato starch, sweet potato starch, etc.

[0038] The above-mentioned refining slag modifier for preventing oxygen reversion after RH treatment is mainly applicable to the metallurgical process field of changing the composition of ladle top slag in refining (RH) production to optimize product quality.

[0039] The design principle of the above-mentioned refined slag modifier for preventing oxygen reversion after RH treatment is as follows:

[0040] Al: Reduces the oxidizability of the ladle top slag, and uses the reducing agent metal aluminum to carry out redox reaction with FeO and MnO in the ladle slag. FeO and MnO react, and the reaction equation is:

[0041] 2Al+3FeO=Al2O3+3Fe

[0042] 2Al+3MnO=Al2O3+3Mn

[0043] Fe: Metallic Fe is the same component as that in molten steel. According to the principle of like dissolves like, although the atomic structures of Fe in slag and Fe in molten steel are solid and liquid respectively, the addition of metallic Fe increases the density of metallurgical slag and the Fe-slag-Fe-steel interface can contact each other, so that the smelting slag can be immersed in the ladle slag, promoting the reaction between metallic aluminum and FeO and MnO in the slag.

[0044] Al2O3: Al2O3 is the reaction product of metallic Al with FeO and MnO. When new Al2O3 is formed, it shows interfacial affinity with the existing Al2O3, that is, the new Al2O3 can be adsorbed by the same Al2O3 in the slag.

[0045] CaCO3: CaCO3 is easily decomposed when heated. The gas decomposed after heating becomes a protective atmosphere to avoid air burning of metallic aluminum. Due to the decomposition of CaCO3, the components in the slag system are stirred evenly, which promotes the uniformity of the reaction between FeO and metallic aluminum in the slag.

[0046] CaO: CaO is a common slag-forming agent and basicity controller in slag. By controlling the ratio of CaO and Al2O3, the melting point of metallurgical slag can be controlled at the same time. In the present invention, the weight ratio of CaO: Al2O3 can be controlled at 1:1 in the specific configuration to reduce the melting point in the slag, and the reaction is promoted by the lower melting point.

[0047] The present invention also provides a method for modifying refined slag to prevent reoxidation after RH treatment. After the RH treatment is completed and before steel is tapped, the refined slag modifier to prevent reoxidation after RH treatment is added to the RH ladle. After the static reaction is completed, the ladle is covered and transported out to the next process.

[0048] Specifically: After the RH treatment is completed and the vacuum tank rises, when the shiny slag surface leaks out, a refined slag modifier is added to the slag surface to prevent the re-oxidation after the RH treatment. It can be added by a mechanical distributor or manually. The amount of refined slag modifier added is 60-100kg / H steel, where H stands for heat, which means the furnace, that is, the amount of refined slag modifier added per furnace is 60-100kg. After the static reaction is completed, the FeO content in the slag of the RH ladle is detected to be ≤2.5wt%, which can meet the requirements of reducing the FeO content in the ladle top slag after the RH treatment is completed, so as to fundamentally eliminate the situation of oxidative contamination of molten steel in the slag, and then the ladle is covered and transported out to the next process.

[0049] When the above-mentioned refined slag modifier for preventing reoxidation after RH treatment is used, the components of the refined slag modifier can be fully mixed and then pressed into a block modifier (for example, the length, width and height are 10*10*20mm), and the density of the block modifier is 1.5-4.5g / cm 3 .

[0050] In IF steel smelting, it is generally believed that lime can increase alkalinity. Generally, 500-1000 kg / t of lime is added to adsorb acidic deoxidation products, which often causes a large number of CaO-Al2O3 inclusions in molten steel. Actual research has found that the purpose can be achieved by adding 350-450 kg / t of lime to the RH ladle when blowing steel from the converter. Therefore, before RH treatment, lime is added to the RH ladle when blowing steel from the converter. The amount added is 350-450 kg / H, where H stands for heat, which means heat, that is, the amount of lime added per heat is 350-450 kg. Here, the amount of free CaO is reduced to avoid the formation of spinel inclusions.

[0051] The following is a further introduction to a refined slag modifier and a modification method thereof for preventing oxygen return after RH treatment with reference to specific examples.

[0052] Table 2 Composition and content of refined slag modifier to prevent reoxidation after RH treatment

[0053] Al％ <![CDATA[Al2O3%]]> CaO% <![CDATA[CaCO3%]]> Fe% Binder % 1# 35 18 18 5 15 9 2# 40 15 15 3 16 11 3# 50 13 13 4 12 8 4# 55 12 12 4 10 7

[0054] Example 1

[0055] In this embodiment, the slag after RH treatment is modified by using 1# refined slag modifier for preventing re-oxygenation after RH treatment as shown in Table 2; corn starch is used as the binder.

[0056] The components of the refined slag modifier are fully mixed and pressed into a block shape, and then broken into a block modifier with a length, width and height of 10*10*20mm, and a density of 1.5-4.5g / cm 3 ;

[0057] On a certain day, IF steel was scheduled for production. After the converter blowing was completed, steel was tapped. During the tapping process, 350kg / t of lime was added to the ladle. After the RH treatment was completed, 1# refined slag modifier was added to the RH ladle to prevent the return of oxygen after the RH treatment. The added amount was 100kg / H steel. After the ladle was left to react, the FeO content in the slag was measured to be 2.3wt%. The ladle was then covered and hoisted by the RH trolley and crane to enter the next treatment process.

[0058] Example 2

[0059] In this embodiment, the 2# refined slag modifier shown in Table 2 is used to modify the slag after RH treatment for preventing re-oxygenation after RH treatment; and potato starch is used as the binder.

[0060] The components of the refined slag modifier are fully mixed and pressed into a block shape, and then broken into a block modifier with a length, width and height of 10*10*20mm, and a density of 1.5-4.5g / cm 3 ;

[0061] On a certain day, IF steel was scheduled for production. After the converter blowing was completed, steel was tapped. During the tapping process, 370kg / H of lime was added to the ladle. After the RH treatment was completed, 2# refined slag modifier was added to the RH ladle to prevent the return of oxygen after the RH treatment. The added amount was 80kg / H of steel. After the ladle was left to react, the FeO content in the slag was measured to be 1.9wt%. The ladle was then covered and hoisted by the RH trolley and crane to enter the next treatment process.

[0062] Example 3

[0063] In this embodiment, the 3# refined slag modifier shown in Table 2 is used to modify the slag after RH treatment to prevent re-oxygenation; the binder is sweet potato starch.

[0064] The components of the refined slag modifier are fully mixed and pressed into a block shape, and then broken into a block modifier with a length, width and height of 10*10*20mm, and a density of 1.5-4.5g / cm 3 ;

[0065] On a certain day, IF steel was scheduled for production. After the converter blowing was completed, steel was tapped. During the tapping process, 420kg / H of lime was added to the ladle. After the RH treatment was completed, 70kg / H of 3# refined slag modifier was added to the RH ladle to prevent the return of oxygen after the RH treatment. After the ladle was left to react, the FeO content in the slag was measured to be 2.2wt%. The ladle was then covered and hoisted by the RH trolley and crane to enter the next treatment process.

[0066] Example 4

[0067] In this embodiment, the 4# refined slag modifier shown in Table 2 is used to modify the slag after RH treatment; corn starch is used as the binder.

[0068] The components of the refined slag modifier are fully mixed and pressed into a block shape, and then broken into a block modifier with a length, width and height of 10*10*20mm, and a density of 1.5-4.5g / cm 3 ;

[0069] On a certain day, IF steel was scheduled for production. After the converter blowing was completed, steel was tapped. During the tapping process, 400kg / H of lime was added to the ladle. After the RH treatment was completed, 4# refined slag modifier was added to the RH ladle to prevent the return of oxygen after the RH treatment. The added amount was 60kg / H of steel. After the ladle was left to react, the FeO content in the slag was measured to be 2.1wt%. The ladle was then covered and hoisted by the RH trolley and crane to enter the next treatment process.

[0070] In summary, the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. 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 of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A refined slag modifier for preventing oxygen regeneration after RH treatment, characterized in that: The invention comprises the following components in weight percentage: Al: 30-65%, Fe: 3-30%, CaO: 5-20%, Al2O3: 5-20%, CaCO3: 2-7%, binder: 5-15%, and the rest are inevitable impurities.

2. The refined slag modifier for preventing reoxygenation after RH treatment according to claim 1, characterized in that: Among the inevitable impurities, the content of SiO2 is ≤6wt%.

3. The refined slag modifier for preventing reoxidation after RH treatment according to claim 1, characterized in that: The refined slag modifier for preventing reoxidation after RH treatment comprises 35-55% Al, 10-16% Fe, 12-18% CaO, 12-18% Al2O3, 3-5% CaCO3 and 7-11% binder.

4. The refined slag modifier for preventing reoxidation after RH treatment according to claim 1, characterized in that: The binder is one of corn starch, potato starch and sweet potato starch.

5. A method for modifying refined slag to prevent oxygen reversion after RH treatment, characterized in that: After the RH treatment is completed, the refined slag modifier for preventing the reoxidation after the RH treatment as claimed in any one of claims 1 to 4 is added to the RH ladle before steel is tapped. After the static reaction is completed, the ladle is covered and transported out to the next process.

6. The method for modifying refined slag to prevent reoxidation after RH treatment according to claim 5, characterized in that: The addition amount of the refined slag modifier for preventing reoxidation after RH treatment is 60-100 kg / H steel.

7. The method for modifying refined slag to prevent reoxidation after RH treatment according to claim 5, characterized in that: When the refined slag modifier for preventing reoxidation after RH treatment is used, the components of the refined slag modifier are mixed evenly, pressed into a shape, and then crushed into a block modifier, and the density of the block modifier is 1.5-4.5 g / cm 3 .

8. The method for modifying refined slag to prevent reoxidation after RH treatment according to claim 5, characterized in that: Before the RH treatment, lime is added to the RH ladle when blowing out steel in the converter, and the added amount is 350-450 kg / H steel.

9. The method for modifying refined slag to prevent reoxidation after RH treatment according to claim 5, characterized in that: After the static reaction is completed, the FeO content in the slag of the RH ladle is detected to be ≤2.5wt%.

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