Calcium aluminate-based composite refining slag as well as preparation method and application method thereof

Abstract

The invention discloses calcium aluminate-based composite refining slag as well as a preparation method and an application method thereof, and belongs to the technical field of ferrous metallurgy. The calcium aluminate-based composite refining slag comprises the following raw material components in percentage by mass: 15-25% of calcium aluminate pre-melting slag, 35-55% of low-nitrogen aluminum ash, 15-25% of aluminum particles, 4-6% of carbon powder, 10-20% of cryolite and 1-2% of a binder. The calcium aluminate-based composite refining slag prepared by the preparation method disclosed by the invention is applied to a refining process, so that the slag can be quickly formed, the slag state can be improved, the oxidability of the steel slag can be reduced, desulfurization and adsorption removal of steel inclusions are facilitated, and the problems of high energy consumption, high cost, poor smelting effect, low smelting cost and the like when the existing external refining slag is applied can be effectively solved. The production requirements of high-cleanliness steel or ultra-clean steel cannot be met, and adverse effects on the environment are easily caused.

Description

Technical Field

[0001] The invention belongs to the technical field of iron and steel metallurgy, relates to a steel slag modifier and an application technology thereof, and specifically relates to a calcium aluminate-based composite refined slag and a preparation method and an application method thereof. Background Art

[0002] At present, there are many types of slag agents used for off-furnace refining of molten steel in actual production. In response to the needs of different steel grades, metallurgical workers continue to develop and try various off-furnace refining slags, which generally include the following categories.

[0003] The first category is synthetic slag with lime, bauxite, wollastonite, fluorite slag and other raw materials; this type of slag is made by simply mechanically mixing the above raw materials after appropriate processing. Since the raw materials of this type of slag are almost all "raw materials", it has a slow slag formation rate, high impurity content, high slag consumption, and high energy consumption. At the same time, the fluorine content also aggravates the erosion of the furnace lining and the pollution to the environment. It cannot achieve the purpose of LF refining and slag making, especially when smelting high-grade steel grades, the quality pass rate is low and the cost is high.

[0004] The second type is pre-melted synthetic slag, which is obtained by high-temperature melting of limestone, dolomite, wollastonite, fluorite, bauxite, etc. Its main components are calcium aluminate series. This type of slag has a low melting point and strong desulfurization and removal capabilities, but the cost is extremely high. At the same time, the slag acquisition process puts great pressure on the environmental protection.

[0005] The third category is the recycled synthetic slag made from metallurgical waste slag as raw material, such as the reuse of CaO, SiO2, Al2O3 and MgO components contained in LF refined slag after desulfurization in the refining process. However, the multiple recycling of harmful elements such as P and S in the slag will lead to enrichment and increase, and the mineral structure of components such as CaO, SiO2, Al2O3 and MgO tends to be stable, and the activity decreases, which seriously affects the refining effect and makes it difficult to meet the production needs of high-cleanliness steel. In addition, the high energy consumption and serious environmental pollution in the recovery and treatment process of waste metallurgical slag also limit its large-scale application.

[0006] The fourth category is a refined slag powder composed of ultrafine powder of calcium carbonate, magnesium carbonate or a mixture of calcium carbonate and magnesium carbonate as the main raw material, and a mixture of calcium oxide and magnesium oxide + low melting point pre-melted slag + fluorite. Calcium carbonate and magnesium carbonate are used as in-situ generators of tiny bubbles to induce ultrafine bubbles in molten steel to remove inclusions. In addition, this slag agent can quickly melt in molten steel to form slag droplets and form low melting point calcium aluminate with Al2O3 inclusions in the molten steel, which is easy to float to the ladle slag, thereby reducing the number and size of Al2O3 inclusions produced by refining. However, after the surface of calcium oxide or magnesium oxide reacts with sulfur or Al2O3, its product is wrapped on the surface of calcium oxide or magnesium oxide particles, hindering its further reaction, resulting in high slag material consumption and low efficiency; at the same time, the slag material is ultrafine powder material, which will cause dust pollution and a large amount of slag waste during storage, transportation and use; the added CaO and MgO are ultrafine powders, which are very easy to absorb water and deteriorate, seriously affecting their performance.

[0007] Metallurgical work is based on the cleanliness requirements of different steel grades, and LF refining slag and its refining technology are constantly developed to meet the production needs of high-cleanliness or ultra-cleanliness steel. In order to maintain and give full play to the advantages of existing LF refining slag, suppress its adverse effects, and overcome the problems of high energy consumption, high inclusion content in steel products, poor shape or large size of inclusions, slow slag formation speed or insufficient foaming and short duration, slow desulfurization rate, weak inclusion adsorption capacity, and environmental pollution of slag during the refining process or after refining. Developing efficient and environmentally friendly LF refining slag to make it suitable for secondary refining slag system of molten steel, especially to meet the LF production of clean steel or ultra-clean steel refining slag, further improve the efficiency of removing desulfurization and adsorbing inclusions, reduce consumption and increase efficiency, and be more environmentally friendly has become an urgent problem to be solved by practitioners in the industry.

[0008] "CN200910164317.8 A steel slag modifier for off-furnace refining" discloses a steel slag modifier for off-furnace refining, the raw materials are composed of 50-70% active lime, 10-30% fluorite, and 10-30% calcium aluminate by weight percentage, and the chemical composition should meet the following requirements: active lime: CaO≥90%, MgO<8%, activity ≥300ml; fluorite: CaF2≥80%, SiO2<15%; calcium aluminate: 40%<CaO<60%, 25%<Al2O3≤45%, SiO2<5%, MgO<5%; the three raw materials are crushed to a particle size of ≤20mm, and then mixed with a mixer for 15-30 minutes, and the finished product is packaged after being evenly mixed. The modifier is added into the ladle with the steel flow during the converter steel tapping process, and the addition amount is 3-7kg / t steel. Advantages: After adding the modifier, liquid slag can be quickly generated, fully mixed with the ladle top slag, and the chemical composition of the ladle top slag can be changed, so that the composition of the ladle top slag is within the composition range that is conducive to desulfurization, thereby improving the refining desulfurization rate, reducing the refining cycle, improving production efficiency, and facilitating production continuity; at the same time, after adding the modifier, it will promote the floating removal of inclusions during the slag mixing process, and has a desulfurization rate of 30% to 60%, which is easy to operate and low in cost. Disadvantages: Different materials have different specific gravities, and there is an uneven phenomenon in the mixing process, which affects the control accuracy of the slag composition in the subsequent use process. The powder loss in the crushing and material preparation process is too much, which has a certain adverse effect on environmental protection.

[0009] "CN200610097700.2 Steel slag modified aluminum slag ball" discloses a steel slag modified aluminum slag ball used for improving the properties of steel slag during the refining treatment of pure steel and ultra-pure steel, which is conducive to the adsorption and removal of inclusions, reduces the total oxygen of the finished product, and has extremely low harmful impurity content. It contains metallic aluminum, aluminum oxide, calcium carbonate, calcium oxide and inevitable impurities. Advantages: ordinary and easy to obtain raw materials, simple and reliable balling process, no component segregation fluctuation, simple addition process, and excellent surface spreading and heat preservation performance of molten steel. Adding steel slag modified aluminum slag balls during refining treatment can improve the fluidity of slag in the furnace; reduce the total iron content in the slag, reduce the aluminum-calcium ratio, improve the performance of adsorbing Al2O3 in the refined slag, reduce the total oxygen of the finished product in the molten steel, and greatly reduce the inclusion of oxides in the molten steel. The product does not contain fluorine, which is beneficial to protecting the environment and equipment. Disadvantages: The materials are all "raw materials", the smelting process is slow to melt, and the energy consumption is high.

[0010] "CN201310433094.7 A production process of aluminum slag conditioning agent for LF refining furnace" discloses a method of preparing a refining slag agent using waste lining bricks and aluminum ash from aluminum electrolysis. When silicon carbide in the waste lining bricks and aluminum in the aluminum ash are added to the LF furnace, heat is released to create a reducing atmosphere, which is conducive to reducing the oxygen in the steel slag and achieving the purpose of steel slag modification. Advantages: Compared with other LF furnace deoxidation slag agents, waste lining bricks and aluminum ash from aluminum electrolysis are cheap, which reduces the production cost of LF furnace slag making, and the quality of LF furnace refining slag is stable, thereby achieving the recycling of waste lining bricks and aluminum ash waste from aluminum electrolysis and increasing the added value of solid waste. Disadvantages: The nitrogen content of aluminum ash containing metal aluminum electrolysis is extremely high, basically above 5%, which is extremely unfavorable for controlling the nitrogen content of liquid steel, especially high-quality low-nitrogen steel, which seriously restricts the application of the invention; in addition, the invention uses waste refractory materials, which have low activity and difficulty in melting, resulting in greatly weakened metallurgical effects and are not suitable for the development of high-quality steel.

[0011] "CN202410608315.8 A calcium aluminate synthetic slag and its preparation method and its application in the smelting method of high carbon steel" discloses a method of using calcium aluminate refining slag produced in the secondary refining process of aluminum-killed steel as the main raw material, and crushing and mechanically mixing a small amount of lime and bauxite to form a calcium aluminate synthetic slag with stable chemical composition and properties. Advantages: It realizes the secondary utilization of aluminum-killed steel refining slag, which not only greatly reduces the production cost of calcium aluminate synthetic slag, but also reduces the emission of refining waste slag from steel plants. The creative use of calcium aluminate synthetic slag for the refining and slag making of silicon-killed steel hard steel strands, and by designing a low-melting-point CaO-Al2O3-SiO2-MgO quaternary refining slag system and its slag-forming method, the use of refined fluorite is reduced, solving the problems of high production cost of traditional synthetic slag and high fluorite consumption in the smelting process of high carbon steel, resulting in high smelting cost and high pollution. Disadvantages: Multiple recycling of harmful elements such as P and S will lead to increased enrichment and pollution of molten steel; the mineral phase structure of components such as CaO, SiO2, Al2O3 and MgO tends to be stable and the activity decreases, which seriously affects the refining effect and makes it difficult to meet the production needs of high-cleanliness steel. Summary of the invention

[0012] The technical problem to be solved by the present invention is that the existing off-furnace refining slag has high energy consumption and cost when used, has poor smelting effect, cannot meet the production requirements of high-clean steel or ultra-clean steel, and is prone to adversely affect the environment. In order to solve the above technical problems, the present invention combines the advantages of the second and third types of refining slags from the perspectives of cost, metallurgical effect, and environmental protection, and proposes a composite refining slag with calcium aluminate pre-melted slag + low-nitrogen aluminum ash + reducing agent + flux (cryolith that cannot be reused by aluminum plants) and a preparation method and application technology.

[0013] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0014] In a first aspect, the present invention provides a calcium aluminate-based composite refined slag, the raw material components of which are as follows by mass percentage: 15-25% calcium aluminate pre-melted slag, 35-55% low-nitrogen aluminum ash, 15-25% aluminum particles, 4-6% carbon powder, 10-20% cryolite, and 1-2% binder.

[0015] The chemical composition of the calcium aluminate pre-molten slag is: 3CaO·Al2O3≥90%, and the rest are impurity elements.

[0016] The chemical composition of the above-mentioned low-nitrogen aluminum ash is: N≤1.0%, Al2O360~70%, and the rest are impurity elements.

[0017] The chemical composition of the aluminum particles is: aluminum ≥ 99%, and the rest are impurity elements.

[0018] The chemical composition of the above-mentioned carbon powder is: carbon ≥ 98%, and the rest are impurity elements.

[0019] The chemical composition of the above-mentioned cryolite is: F 38-42%, Al2O3 36-40%, Na2O 14-18%, and the rest are impurity elements.

[0020] The chemical composition of the above-mentioned binder is: 45% bentonite, 5% sodium carboxymethyl cellulose, 30% 425 cement, and 20% flour.

[0021] In a second aspect, the present invention provides a method for preparing the above-mentioned calcium aluminate-based composite refined slag, comprising the following steps:

[0022] A. preparing the raw material components of the calcium aluminate-based composite refined slag according to the above raw material components, and mixing the raw material components uniformly to obtain a mixed material;

[0023] B. The mixture obtained in step A is squeezed into balls, and the moisture content of the refined slag balls is reduced to less than 2.5% by drying and baking to obtain calcium aluminate-based composite refined slag.

[0024] In the above step A, the particle size of each raw material component is controlled to be ≤3 mm.

[0025] In the above step B, the specification of the refined slag balls is 20-40 mm; the refined slag balls are baked after the moisture content is controlled within 6% after drying; the baking temperature is 200-300° C., and the baking time is 3-5 hours.

[0026] In a third aspect, the present invention provides an application method of the calcium aluminate-based composite refined slag, comprising the following steps:

[0027] a. Add lime 3-5kg / t into the mixing process of converter steel tapping 钢 After steel is tapped, 1-3 kg / t 钢Add the above calcium aluminate based composite refined slag to the surface of the molten steel, and then soft blow for 3 to 5 minutes;

[0028] b. LF enters the station at 2~7kg / t 钢 Add calcium aluminate based composite refining slag to the surface of ladle slag, lime 3-10kg / t 钢 Add it to the surface of the ladle slag, and then heat it to deslagging, desulfurize it, etc. according to the conventional procedures.

[0029] In the above step a, the amount of lime added when smelting different steel grades is: 3kg / t for ordinary steel grades 钢 , general steel quantity 4kg / t 钢 , high-grade steel quantity 5kg / t 钢 ; The amount of calcium aluminate-based composite refined slag added when smelting different steel grades is: 3kg / t for ordinary steel grades 钢 , general steel quantity 4kg / t 钢 , high-grade steel quantity 5kg / t 钢 .

[0030] In the above step a, the soft blowing judgment standard is that the surface disturbance of the ladle slag and the diameter of the molten steel turning over are ≤20cm.

[0031] In the above step b, the amount of calcium aluminate-based composite refined slag added when smelting different steel grades is: 2-3 kg / t for ordinary steel grades 钢 , general steel 3~5kg / t 钢 , high-grade steel 5~7kg / t 钢 ; The amount of lime added is controlled at 1.0 to 1.5 times the amount of calcium aluminate-based composite refined slag added.

[0032] Furthermore, the above-mentioned ordinary steel grades are steels with P and S ≤0.045% in chemical composition, general steel grades are steels with P and S ≤0.025% in chemical composition, and high-grade steel grades are steels with P <0.015% and S ≤0.005% in chemical composition.

[0033] The beneficial effects of the present invention are as follows: the raw materials of the calcium aluminate-based composite refined slag of the present invention are simple and easy to obtain, and the low-nitrogen aluminum ash and industrial cryolite used are solid wastes from aluminum plants, which are in line with the national solid waste utilization policy and are conducive to alleviating the pressure of recycling metallurgical solid wastes; due to the use of partial pre-melted materials, the low-nitrogen aluminum ash is also treated at high temperature (electrode process) and is in powder form, and its melting speed in the steelmaking process is fast, which is significantly better than the first type of refined slag made entirely of raw materials and the refined slag made of refractory waste, and can basically achieve the melting effect of the second type of fully pre-melted refined slag. The application method of the calcium aluminate-based composite refined slag of the present invention can quickly form slag and effectively improve the slag state by adding the steel slag modifier during the refining process, while reducing the oxidizability of the steel slag, which is conducive to desulfurization and adsorption and removal of steel inclusions. DETAILED DESCRIPTION

[0034] The technical solution of the present invention can be specifically implemented in the following manner.

[0035] The present invention proposes a composite refining slag and application technology comprising calcium aluminate pre-melted slag + low-nitrogen aluminum ash + reducing agent + flux (cryolith that cannot be reused in aluminum plants), wherein the main functions of each component are as follows:

[0036] (1) Calcium aluminate pre-melted slag: mainly made of 3CaO·Al2O3, fast melting slag, and has strong Al2O3 adsorption and inclusion capacity;

[0037] (2) Low nitrogen aluminum ash: Rapid slag melting, adjusting the composition of ladle slag, mainly the proportion of Al2O3 in the ladle slag, to improve its ability to absorb inclusions;

[0038] (3) Reducing agent: Carbon powder helps submerged arc refining by removing oxygen from the slag and foaming during heating; aluminum metal mainly plays a role in reducing the oxygen in the slag;

[0039] (4) Cryolite: It has the ability to break the crystal structure of other components and lower the melting point. It mainly plays the role of fluxing and rapid slag formation. At the same time, its structure is stable at steelmaking temperature and will not decompose. It will not cause environmental pollution due to its fluorine content.

[0040] In the preparation method of the calcium aluminate-based composite refined slag of the present invention, the moisture content must be controlled within 6% before baking to avoid excessive moisture during the baking process, which may cause the balls to break.

[0041] The technical solution and effects of the present invention are further illustrated below through practical examples.

[0042] Example

[0043] The present invention provides three groups of application examples 1 to 3 using calcium aluminate-based composite refined slag; wherein example 1 is ordinary steel, example 2 is general steel, and example 3 is high-grade steel, specifically comprising the following steps:

[0044] S1: crush the calcium aluminate pre-melted slag into particles ≤3 mm, and mix them evenly with low-nitrogen aluminum ash, aluminum particles (≤3 mm), carbon powder, cryolite powder, and binder according to the proportions in Table 1;

[0045] Table 1 Refined slag formula of different examples, %

[0046] Calcium aluminate pre-melted slag Low nitrogen aluminum ash Toner Aluminum Granules cryolite Binder Example 1 19 40 5 20 15 1 Example 2 18 41 4 21 15 1 Example 3 20 39 6 19 14 2

[0047] S2: extruding the above mixture into balls, and then drying and baking to reduce the moisture content of the refined slag balls to less than 2.5%;

[0048] S3: lime is added in the mixed flushing process of the converter according to the amount shown in Table 2, and the above-mentioned refined slag balls are added to the surface of the molten steel after the tapping is completed, and then soft blowing is performed; the above-mentioned refined slag balls are added to the surface of the ladle slag when the LF enters the station, and lime is added to the surface of the ladle slag;

[0049] Table 2 Different example addition amount, kg / t 钢

[0050] Converter lime Converter Refining Slag LF furnace lime LF Refining Slag LF furnace fluorite Example 1 3 1 3 2 - Example 2 4 2 5 4 - Example 3 5 3 7 6 - Comparative Example 1 5 - 8 - 1.5 Comparative Example 2 4 - 9 - 2.0

[0051] S4: The heating slag, desulfurization and other processes are carried out, and the non-metallic inclusions in the steel after smelting are rated according to the national standard GB / T 10561-2023. The metallurgical effects are shown in Table 3.

[0052] Table 3 Metallurgical effects of different examples

[0053]

[0054]

[0055] As can be seen from Table 3, the slag forming speed of the example is faster than that of the comparative example. Due to the rapid slag forming and staged basicity control, the desulfurization rate is higher than that of the comparative example; at the same time, due to the fast slag forming speed, the removal effect of inclusions is better than that of the comparative example, and the T[O] of the tundish and the inclusion rating of the rolled product are better than those of the comparative example.

Claims

1. Calcium aluminate-based composite refined slag, characterized in that: The raw material components are as follows by mass percentage: 15-25% of calcium aluminate pre-melted slag, 35-55% of low-nitrogen aluminum ash, 15-25% of aluminum particles, 4-6% of carbon powder, 10-20% of cryolite, and 1-2% of binder.

2. The calcium aluminate-based composite refined slag according to claim 1, characterized in that: The chemical composition of calcium aluminate pre-melted slag is: 3CaO·Al2O3≥90%, the rest is impurity elements; The chemical composition of low nitrogen aluminum ash is: N ≤ 1.0%, Al2O3 60-70%, and the rest are impurity elements; The chemical composition of aluminum particles is: aluminum ≥ 99%, the rest are impurity elements; The chemical composition of carbon powder is: carbon ≥ 98%, the rest are impurity elements; The chemical composition of cryolite is: F 38-42%, Al2O3 36-40%, Na2O 14-18%, and the rest are impurity elements; The chemical composition of the binder is: 45% bentonite, 5% sodium carboxymethyl cellulose, 30% 425 cement, and 20% flour.

3. A method for preparing calcium aluminate-based composite refined slag, characterized in that: The steps include: A. preparing the raw material components of the calcium aluminate-based composite refined slag according to any one of claims 1 to 2, and uniformly mixing the raw material components to obtain a mixture; B. The mixture obtained in step A is squeezed into balls, and the moisture content of the refined slag balls is reduced to less than 2.5% by drying and baking to obtain calcium aluminate-based composite refined slag.

4. The method for preparing calcium aluminate-based composite refined slag according to claim 3, characterized in that: In step A, the particle size of each raw material component is controlled to be ≤3 mm.

5. The method for preparing calcium aluminate-based composite refined slag according to claim 3, characterized in that: In step B, the specification of the refined slag balls is 20-40 mm; the refined slag balls are baked after the moisture content is controlled within 6% after drying; the baking temperature is 200-300° C., and the baking time is 3-5 hours.

6. The application method of calcium aluminate-based composite refined slag is characterized by: The steps include: a. Add lime 3-5kg / t into the mixing process of converter steel tapping 钢 After steel is tapped, 1-3 kg / t 钢 Adding the calcium aluminate-based composite refined slag prepared by the preparation method according to any one of claims 3 to 5 to the surface of the molten steel, and then soft blowing for 3-5 minutes; b. LF enters the station at 2~7kg / t 钢 Add calcium aluminate based composite refining slag to the surface of ladle slag, lime 3-10kg / t 钢 Add it to the surface of the ladle slag, and then heat it to deslagging, desulfurize it, etc. according to the conventional procedures.

7. The application method of the calcium aluminate-based composite refined slag according to claim 6, characterized in that: In step a, the amount of lime added when smelting different steel grades is: 3kg / t for ordinary steel grades 钢 , general steel quantity 4kg / t 钢 , high-grade steel quantity 5kg / t 钢 ; The amount of calcium aluminate-based composite refined slag added when smelting different steel grades is: 3kg / t for ordinary steel grades 钢 , general steel quantity 4kg / t 钢 , high-grade steel quantity 5kg / t 钢 .

8. The application method of the calcium aluminate-based composite refined slag according to claim 6, characterized in that: In step a, the soft blowing judgment standard is that the surface disturbance of the ladle slag and the diameter of the molten steel turning surface are ≤20cm.

9. The application method of the calcium aluminate-based composite refined slag according to claim 6, characterized in that: In step b, the amount of calcium aluminate-based composite refined slag added when smelting different steel grades is: 2-3 kg / t for ordinary steel grades 钢 , general steel 3~5kg / t 钢 , high-grade steel 5~7kg / t 钢 ; The amount of lime added is controlled at 1.0 to 1.5 times the amount of calcium aluminate-based composite refined slag added.

10. The application method of the calcium aluminate-based composite refined slag according to claim 7 or 9, characterized in that: Ordinary steel grades are steels with chemical compositions of P and S ≤ 0.045%, general steel grades are steels with chemical compositions of P and S ≤ 0.025%, and high-grade steel grades are steels with chemical compositions of P < 0.015% and S ≤ 0.005%.

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