Preparation method and application method of silicon-calcium-based refining slag

Abstract

The invention discloses a preparation method and an application method of silicon-calcium-based refining slag, and belongs to the technical field of ferrous metallurgy. The preparation method comprises the following steps: ball-milling submerged arc furnace slag, magnetically separating to remove iron, and oxidizing, roasting and desulfurizing; the method comprises the following steps: uniformly mixing submerged arc furnace slag with silicon slag, carbon powder and a binder, extruding into balls, and controlling the water content to be within 2.5% to obtain the silicon-calcium-based refining slag. The application method comprises the following steps: adding the lime and the silicon-calcium-based refining slag to the surface of molten steel in a mixed flushing manner in a converter tapping process, and then softly blowing; and the silicon-calcium-based refining slag and lime are added to the surface of the ladle slag after the LF enters the station, then the ladle slag is heated to be molten and desulfurized, the silicon-calcium-based refining slag steel is added again to carry out slag adjusting treatment after desulfurization reaches the target, and soft blowing is carried out before the ladle leaves the station. The problems that existing refining slag is high in preparation and application cost, poor in sulfur control capacity, incapable of meeting the production requirements of high-clean steel or ultra-clean steel and prone to causing adverse effects on the environment can be effectively solved.

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 preparation method and an application method of silicon-calcium based refined slag. 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] "CN202410456200.1 A slag-forming agent for silicon-killed steel refining slag and its use method" provides a slag-forming agent for silicon-killed steel refining slag, including calcium aluminate, ferrosilicon powder and carbon powder, and the mass ratio of calcium aluminate, ferrosilicon powder and carbon powder is (45-49): (44-48): (2-10). Advantages: It can relatively reduce the use of fluorite in the steelmaking process, while reducing the melting point of the formed refined slag, promoting the slag-forming efficiency of LF refining, and obtaining a faster slag-forming rate, saving time to a certain extent, shortening the smelting cycle, improving the smelting efficiency, and ensuring the control of sulfur and molten steel cleanliness. Disadvantages: The amount of fluorite reduced is limited, and the cost of using ferrosilicon powder is relatively high.

[0008] "CN114075619A A slag-making method for fluorine-free CaO-SiO2 refined slag in steelmaking process" discloses a slag-making method for fluorine-free CaO-SiO2 refined slag in steelmaking process. Lime and industrial sodium carbonate are added as slag-making during and after the steel-making process to control the slag composition to 27-51% CaO, 25-32% SiO2, 8-31% Na2O, and the slag basicity to 1.1-1.6. Advantages: fluorine-free, beneficial to the environment; Disadvantages: The use of industrial sodium carbonate causes serious environmental pollution (the decomposition of sodium carbonate will produce a lot of dust), the ladle refractory material is seriously eroded, the basicity is low, and the sulfur control effect is poor.

[0009] "CN111926141A A refined slag for obtaining CaO-SiO2-MgO low melting point inclusions" is used for cord steel, and the mass percentage of each component of the refined slag is MgO 15-25%, Al2O3 <3%, and the rest is CaO and SiO2, and the basicity is 0.7-1.0. Advantages: Low melting point CaO-SiO2-MgO inclusions can be obtained, reducing the erosion of the refining slag on the ladle refractory. Disadvantages: This refined slag is only for cord steel, and its application range is limited. In addition, due to the low basicity, the sulfur control ability is poor.

[0010] "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.

[0011] For steels with strict requirements for Class B inclusions, such as heavy rails and steel for cords, these steels require strict control of the Al content in the molten steel. Therefore, there are certain requirements for Al2O3 in the slag. Generally, only CaO-SiO2-based slag systems with low Al2O3 can be used for these steels. However, this slag system also has some problems: 1) Poor desulfurization capacity. In order to ensure a certain desulfurization capacity, lime is generally added. At the same time, fluorite is added to help melt the slag to ensure the desulfurization effect; 2) After refining and sulfur control, in order to avoid the problem of excessive Class B and D inclusions caused by high basicity slag, SiO2 components (quartz sand) need to be added to adjust the basicity; 3) The slag-making process mostly uses "raw materials", which melts into slag slowly, and often requires the addition of fluorite and other slag-forming materials. Considering the pollution of fluorite to the environment and the decreasing mineral reserves, foreign steel and metallurgical industries basically no longer use fluorite or rarely use it. In China, due to this consideration, it is expected that relevant policies will also be introduced to limit or reduce the use of fluorite in the steel and metallurgical industry. Summary of the invention

[0012] The technical problem to be solved by the present invention is that the preparation and application cost of existing refined slag is high, the sulfur control ability is poor, it cannot meet the production requirements of high-clean steel or ultra-clean steel, and it is easy to cause adverse effects on the environment. In order to solve the above technical problems, the present invention takes the advantages of the second and third types of refined slags as the main material from the perspectives of cost, metallurgical effect, and environmental protection, and proposes a refining slag-making agent and application technology using vanadium-containing pig iron slag from a submerged arc furnace as the main material.

[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 method for preparing calcium-silicon-based refined slag, comprising the following steps:

[0015] A. After ball milling, the slag from the submerged arc furnace is magnetically separated to remove iron, so that TFe≤0.5%;

[0016] B. The slag from the ore-fired furnace after magnetic separation is desulfurized by oxidative roasting to make its final sulfur content ≤0.1%;

[0017] C. mixing the slag of the submerged arc furnace obtained in step B with silicon slag, carbon powder and a binder to obtain a mixture;

[0018] D. The mixture obtained in step C 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 silicon-calcium based refined slag.

[0019] In the above step A, the ore-fired furnace slag is vanadium-containing pig iron ore-fired furnace slag, and its chemical composition by mass percentage is: CaO 40-45%, SiO2 38-42%, S 0.3-0.5%, MgO 4-9%, TFe 1-3%, and the rest are inevitable trace impurities.

[0020] In the above step A, the particle size of the slag from the electric arc furnace after ball milling is ≤1 mm.

[0021] In the above step B, the temperature of the oxidative roasting is 1100-1200° C., and the roasting time is 1-2 hours.

[0022] In the above step C, at least one of the following is satisfied:

[0023] The silicon slag is industrial silicon ore thermal furnace silicon slag, with a particle size of ≤3mm, and its chemical composition by mass percentage is: 40-50% metallic silicon, 50-60% SiO2, and the rest are inevitable trace impurities;

[0024] The chemical composition of the carbon powder is as follows by mass percentage: carbon ≥ 98%, and the rest are impurity elements;

[0025] The chemical components of the binder are as follows by mass percentage: 45% bentonite, 5% sodium carboxymethyl cellulose, 30% 425 cement and 20% flour.

[0026] In the above step C, the mixture comprises, by mass percentage: 65-75% of slag from electric arc furnace, 15-25% of silicon slag, 5-10% of carbon powder, and 1-2% of binder.

[0027] In the above step D, the specification of the refined slag balls is 20-40 mm; the refined slag balls are baked after controlling the moisture content within 7% after drying; the baking temperature is 150-250° C. and the baking time is 4-6 hours.

[0028] In a second aspect, the present invention provides calcium-silicon-based refined slag produced by the above-mentioned preparation method.

[0029] In a third aspect, the present invention provides an application method of the above-mentioned calcium-silicon-based refined slag, comprising the following steps:

[0030] a. Add 3kg / t lime to the mixing process of converter steel tapping 钢 After steel is tapped, 2kg / t 钢 Adding the silicon-calcium based refined slag prepared by the above preparation method to the surface of the molten steel, and then soft blowing for 3 to 5 minutes;

[0031] b. LF enters the station at 2-3kg / t 钢 Add calcium-silicon based refined slag to the surface of ladle slag, lime 3-5kg / t 钢 Add to the surface of ladle slag, then heat to deslagging and desulfurize. After desulfurization reaches the target, add 1-2 kg / t of silicon-calcium based refined slag again 钢 Carry out slag adjustment and soft blowing for ≥7 minutes before leaving the station.

[0032] In the above application method, the soft blowing judgment standard is: the ladle slag surface is disturbed and the diameter of the molten steel turning over is ≤20cm.

[0033] In step b of the above application method, the amount of lime added during desulfurization is controlled at 1.5 to 2.4 times the amount of silicon-calcium based refining slag added when LF enters the station, and the alkalinity CaO / SiO2 is controlled at 2.8 to 3.5 during the period; after desulfurization, the alkalinity is adjusted to 2.0 to 3.0 by adding silicon-calcium based refining slag.

[0034] The beneficial effects of the present invention are as follows: the raw materials are simple and easy to obtain, and the price is very low (submerged arc furnace slag ≤ 20 yuan / t). At the same time, the submerged arc furnace slag and industrial silicon slag used are both secondary resources, which are in line with the national solid waste utilization policy and are conducive to alleviating the pressure of metallurgical solid waste recycling and utilization; since all pre-melted materials are used, the melting speed is fast in the steelmaking process, which is significantly better than the first type of refined slag made entirely of raw materials, and can achieve the melting effect of the second type of fully pre-melted refined slag; by adding the steel slag modifier during the refining process, slag can be quickly formed, the slag state can be effectively improved, and the oxidizability of the steel slag can be reduced, which is conducive to desulfurization and the adsorption and removal of steel inclusions. DETAILED DESCRIPTION

[0035] The technical solution of the present invention can be specifically implemented in the following manner.

[0036] The present invention proposes a refining slag-making agent and application technology with slag from smelting vanadium-containing pig iron in a submerged arc furnace as the main material, wherein the main functions of each component are as follows:

[0037] (1) Vanadium-containing pig iron ore hot furnace slag: This is pre-melted slag, which can accelerate the slag melting speed and has a strong ability to absorb inclusions;

[0038] (2) Industrial silicon slag from submerged arc furnace: metallic silicon can reduce the oxidizability of ladle slag; SiO2 can adjust the composition of ladle slag, mainly the binary basicity (CaO / SiO2) in ladle slag, to improve its ability to absorb inclusions;

[0039] (3) Carbon powder: The oxygen in the slag removal and the foaming during the heating process help submerged arc refining.

[0040] In the preparation method of silicon-calcium based refined slag of the present invention, the moisture content must be controlled within 7% before baking to avoid excessive moisture in the baking process causing ball breakage; lime and refined slag are added in a quantitative manner during the converter tapping process, which is convenient for standardized management and operation, and is also beneficial to the precise control of the slag composition (mainly the control of binary alkalinity).

[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 silicon-calcium based refined slag, which specifically include the following steps:

[0044] S1: Grind the vanadium-containing pig iron ore hot furnace slag into particles ≤1 mm by ball milling, and make its TFe≤0.5% by magnetic separation; desulfurize the slag after magnetic separation by oxidative roasting (temperature 1150°C), and finally the sulfur content is ≤0.1%; mix the treated slag with silicon slag (≤3 mm), carbon powder and binder according to the formula ratio in Table 1 to obtain a mixture;

[0045] Table 1 Refined slag formula, %

[0046]

[0047]

[0048] 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%, thereby obtaining silicon-calcium based refined slag;

[0049] S3: lime is added to the mixed flushing during the converter tapping process, and silicon-calcium based refined slag is added to the surface of the molten steel after tapping, and then soft blowing is performed; LF enters the station and adds refined slag balls to the surface of the ladle slag, lime is added to the surface of the ladle slag, and then the slag is heated and desulfurization is performed. After the desulfurization target is achieved, refined slag is added again for slag adjustment, and soft blowing is performed before leaving the station. The specific process parameters are shown in Table 2.

[0050] Table 2S3 Process parameters

[0051] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 <![CDATA[Converter lime kg / t 钢 > 3 3 3 2 4 <![CDATA[Converter refining slag kg / t 钢 > 2 2 2 - - Post-furnace soft blowing / min 3.2 3.8 4.6 5 3 <![CDATA[LF furnace lime kg / t 钢 > 4.5 3.9 4.3 3 5 <![CDATA[LF refining slag kg / t 钢 > 3+1 2+2 2.5+1.5 - - LF Fluorite - - - 2 3 LF soft blowing / min 8.1 9.2 8.6 8 9 Alkalinity during desulfurization period 3.1 2.8 3.5 - - Adjusted alkalinity 2.2 2.5 2.8 1.8 3.2

[0052] S4: 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.

[0053] Table 3 Metallurgical effects of different examples

[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. A method for preparing calcium-silicon based refined slag, characterized in that: The steps include: A. After ball milling, the slag from the submerged arc furnace is magnetically separated to remove iron, so that TFe≤0.5%; B. The slag from the ore-fired furnace after magnetic separation is desulfurized by oxidative roasting to make its final sulfur content ≤0.1%; C. mixing the slag of the submerged arc furnace obtained in step B with silicon slag, carbon powder and a binder to obtain a mixture; D. The mixture obtained in step C 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 silicon-calcium based refined slag.

2. The method for preparing calcium-silicon based refined slag according to claim 1, characterized in that: In step A, the ore-fired furnace slag is vanadium-containing pig iron ore-fired furnace slag, and its chemical composition by mass percentage is: CaO 40-45%, SiO2 38-42%, S0.3-0.5%, MgO 4-9%, TFe 1-3%, and the rest are inevitable trace impurities.

3. The method for preparing calcium-silicon based refined slag according to claim 1, characterized in that: In step A, the particle size of the slag from the electric arc furnace after ball milling is ≤1 mm.

4. The method for preparing calcium-silicon based refined slag according to claim 1, characterized in that: In step B, the temperature of oxidative roasting is 1100-1200° C., and the roasting time is 1-2 hours.

5. The method for preparing calcium-silicon based refined slag according to claim 1, characterized in that: In step C, at least one of the following is satisfied: The silicon slag is industrial silicon ore thermal furnace silicon slag, with a particle size of ≤3mm, and its chemical composition by mass percentage is: 40-50% metallic silicon, 50-60% SiO2, and the rest are inevitable trace impurities; The chemical composition of the carbon powder is as follows by mass percentage: carbon ≥ 98%, and the rest are impurity elements; The chemical components of the binder are as follows by mass percentage: 45% bentonite, 5% sodium carboxymethyl cellulose, 30% 425 cement and 20% flour.

6. The method for preparing calcium-silicon based refined slag according to claim 1, characterized in that: In step C, the mixture comprises, by mass percentage, 65-75% of slag from electric arc furnace, 15-25% of silicon slag, 5-10% of carbon powder, and 1-2% of binder.

7. The method for preparing calcium-silicon based refined slag according to claim 1, characterized in that: In step D, the specification of the refined slag balls is 20-40 mm; the refined slag balls are dried to control the moisture content within 7% and then baked; the baking temperature is 150-250° C. and the baking time is 4-6 hours.

8. The application method of calcium-silicon-based refined slag is characterized by: The steps include: a. Add 3kg / t lime to the mixing process of converter steel tapping 钢 After steel is tapped, 2kg / t 钢 Adding the silicon-calcium based refined slag prepared by the preparation method according to any one of claims 1 to 7 to the surface of the molten steel, and then soft blowing for 3 to 5 minutes; b. LF enters the station at 2-3kg / t 钢 Add calcium-silicon based refined slag to the surface of ladle slag, lime 3-5kg / t 钢 Add to the surface of ladle slag, then heat to deslagging and desulfurize. After desulfurization reaches the target, add 1-2 kg / t of silicon-calcium based refined slag again 钢 Carry out slag adjustment and soft blowing for ≥7 minutes before leaving the station.

9. The application method of calcium-silicon-based refined slag according to claim 8, characterized in that: Soft blowing judgment standard: the ladle slag surface is disturbed and the diameter of the molten steel turning over is ≤20cm.

10. The application method of calcium-silicon-based refined slag according to claim 8, characterized in that: In step b, the amount of lime added during desulfurization is controlled at 1.5 to 2.4 times the amount of silicon-calcium based refined slag added when LF enters the station, and the alkalinity CaO / SiO2 is controlled at 2.8 to 3.5 during the period; after desulfurization, the alkalinity is adjusted to 2.0 to 3.0 by adding silicon-calcium based refined slag.

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