Slag charge for rare earth steel electroslag remelting and preparation method

Abstract

The invention discloses a slag charge for rare earth steel electroslag remelting and a preparation method, the slag charge comprises the following components in percentage by mass: 40%-60% of CaF2, 20%-35% of Al2O3, 5%-10% of CaO, 10%-15% of a rare earth mixture and 3%-5% of Na2O, the rare earth mixture is a mixture of Ce2O3 and La2O3, and the mass ratio of Ce2O3 to La2O3 is 2: (0.5-1.5); the preparation method comprises the following steps: selecting and pretreating raw materials, proportioning and pelletizing, and packaging slag balls for later use; the rare earth oxide is added into the slag charge, so that oxidation of rare earth in the electroslag remelting process can be inhibited, the yield of the rare earth is increased, the yield of the rare earth in steel is increased to 80%-90% and is increased by 20%-30% compared with that of traditional slag charge, and therefore the content of the rare earth in the steel can be more accurately controlled, and the stability and consistency of the performance of the rare earth steel are guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of electroslag remelting metallurgical technology, specifically relating to a slag material for electroslag remelting of rare earth steel and its preparation method. Background Technology

[0002] In the production of rare earth steel, electroslag remelting (ESR) can effectively improve the uniformity of rare earth distribution in steel, increase the utilization rate of rare earths, and thus significantly improve the comprehensive performance of rare earth steel, such as strength, toughness, and corrosion resistance. However, existing ESR slag materials have some shortcomings when used in rare earth steel smelting. On the one hand, traditional slag materials have limited ability to maintain the stability of rare earth elements. During the remelting process, rare earth elements are easily burned off or react with other impurities, resulting in unstable rare earth yield in steel and difficulty in accurately controlling the rare earth content in the steel, affecting the consistency and stability of rare earth steel performance. On the other hand, some slag materials have insufficient metallurgical reactivity and cannot fully remove harmful impurities in molten steel, such as sulfur, phosphorus, and oxygen, making it difficult to meet the stringent purity requirements of high-end rare earth steel products. In addition, existing slag materials are difficult to match well with the electroslag remelting process of rare earth steel in terms of physicochemical properties such as melting point, viscosity, and electrical conductivity, resulting in high energy consumption, low production efficiency, and the need to improve the quality and surface finish of steel ingots. Therefore, developing a high-performance slag material and corresponding preparation method specifically for electroslag remelting of rare earth steel is of great practical significance for improving the quality and production efficiency of rare earth steel and giving full play to the excellent role of rare earth in steel.

[0003] Patent application number 202111293273.6 discloses a rare earth-specific electroslag remelting slag system and its production method and apparatus. The rare earth-specific electroslag remelting slag system includes electroslag remelting slag materials containing CaF2, CaO, MgO, Al2O3, SiO2, and Re. x O y To prevent rare earth element burn-off, a significant amount of rare earth oxides are added to this slag system. While this helps prevent rare earth burn-off and is beneficial for rare earth steel production, the SiO2 component added is an unstable oxide in the slag. At high temperatures, it is easily reduced by the rare earth elements in the steel, leading to rare earth burn-off. Furthermore, simply adding rare earth oxides does not guarantee effective inhibition of rare earth element oxidation in the steel. A high activity level of the rare earth oxides in the slag is necessary for them to be effective. Because rare earth oxides have very high melting points, excessive addition will inevitably result in the precipitation of solid rare earth oxides or their failure to dissolve in the slag, thus reducing their activity and failing to effectively inhibit the oxidation of rare earth elements in the steel.

[0004] CN 120425158A discloses a method for adding rare earth elements to plastic mold steel using electroslag remelting. This method employs rare earth pre-melted slag and a deoxidizer to stably add rare earth elements to the steel. It achieves stable addition of rare earth elements to plastic mold steel during electroslag remelting using a newly designed rare earth pre-melted slag + rare earth deoxidizer. The method exhibits good uniformity, ensuring stable control of rare earth content in the mold steel at 30ppm-50ppm, total oxygen content at ≤18ppm, and low inclusion content at ≤0.5%, solving the problem of re-oxidation and inclusion formation after rare earth element addition in existing methods. However, this patent has limited application scenarios, only applicable to plastic mold steel, and has not yet been extended to other rare earth steel types, resulting in poor versatility. In contrast, the slag material described in this patent can meet a wider range of rare earth steel electroslag remelting needs. Furthermore, this patent does not provide clear data on improving rare earth recovery rate, while this patent can increase the rare earth recovery rate to 80%-90%. In comparison, this patent does not demonstrate a similar significant effect. This patent does not employ a layered pressing pelletizing process, which may lead to uneven mixing of slag components, thus affecting the stability of metallurgical results. Furthermore, frequent addition of deoxidizers is required during the steady-state period, which can easily cause slag surface fluctuations.

[0005] CN113337727A discloses a slag material for preparing high-nitrogen steel using pressure electroslag remelting to suppress magnesium and rare earth element burn-off, and its application method. By using CaF2, CaO, and Al2O3 as the main components, and supplementing with MgO and rare earth oxides in a reasonable ratio, the concentration of MgO and rare earth oxides in the slag can be increased, and the oxygen activity in the molten steel can be balanced, thereby reducing the burn-off of magnesium and rare earth elements in the molten steel. This satisfies the high-temperature physical property requirements of electroslag remelting refining slag material, possessing strong refining and inclusion removal capabilities. It also effectively suppresses the oxidation and burn-off of magnesium and rare earth elements in the molten steel by controlling the reaction between the slag and the alloy, thus obtaining high-quality high-nitrogen stainless steel electroslag ingots containing magnesium and rare earth elements with qualified composition, good surface quality, and dense solidification structure. However, the application scenarios of this patent are relatively limited, only applicable to pressure electroslag remelting of high-nitrogen steel, failing to cover the scenario of ordinary rare earth steel, and thus having poor versatility. In contrast, the slag material of this patent is applicable to a wider range of rare earth steel electroslag remelting applications. The rare earth recovery rate is low, with a maximum recovery rate of only 70.9%, far lower than the 80%-90% of this patent, resulting in insufficient precision in controlling the rare earth content. The lack of a special pelletizing process, the absence of layered pressing, aluminum wire reinforcement, and alternative deoxidizing aluminum powder designs found in this patent, easily leads to problems such as slag surface fluctuations and uneven deoxidation, thus affecting the purity of the molten steel.

[0006] CN117089710A discloses an electroslag remelting process in which rare earth elements are added during the electroslag remelting process. The process involves baking the steel ingot according to steel ingot baking specifications before electroslag production; the slag system is formulated with a mass percentage ratio of 65% - CaF2:25%. Al2O3:10%-CaO, lanthanum-cerium rare earth wires are added to the above slag system at a mass ratio of 7:3. During remelting, downblown argon gas is used for protection, and the melting rate of the crystallizer is controlled at 380-450 kg / h. 2-3% silica is added with the slag material according to its mass percentage. After electroslag ingot molding and annealing in the furnace, a certain yield is obtained, providing important evidence for studying the influence of rare earth yield on the mechanical properties of materials. However, the rare earth yield of this patent is low, only about 3%, far lower than the high level of 80%-90% of this patent, making it difficult to accurately control the rare earth content in the steel, thus affecting the stability of the rare earth steel's properties. Furthermore, the slag system contains SiO2, which easily reacts with the rare earth in the steel at high temperatures, leading to oxidation and burn-off. This patent effectively suppresses this problem by using Na2O, but the process has not yet been solved. The slag preparation process has not been optimized and lacks key steps such as pretreatment and layered pressing to improve slag performance. This will affect the slag-steel reaction efficiency and the purity of molten steel, and easily lead to uneven deoxidation and slag surface fluctuations. Summary of the Invention

[0007] The purpose of this invention is to provide a slag material and preparation method for electroslag remelting of rare earth steel, aiming to solve the problems of unstable rare earth yield, insufficient removal of impurities in molten steel, and poor matching between physicochemical properties and process when existing electroslag remelting slag materials are used in rare earth steel smelting, so as to improve the quality and production efficiency of rare earth steel.

[0008] According to one aspect of the present invention, a slag material for electroslag remelting of rare earth steel is provided, the composition of which, by mass percentage, is as follows: CaF2 40%-60%, Al2O3 20%-35%, CaO 5%-10%, rare earth mixture 10%-15%, Na2O 3%-5%, wherein the rare earth mixture is a mixture of Ce2O3 and La2O3, and the mass ratio of Ce2O3 to La2O3 is 2:(0.5-1.5).

[0009] According to another aspect of the present invention, a method for preparing slag for electroslag remelting of rare earth steel is provided, comprising the following steps: raw material selection and pretreatment - batching and pelletizing - slag pellet packaging for later use; Raw material selection and pretreatment: Weigh a mixture of CaF2, Al2O3, CaO, Ce2O3 and La2O3 with a purity ≥98%, and Na2O powder as raw materials; place the weighed CaF2, CaO and Na2O powder in an oven for baking; and ball mill the weighed Al2O3, Ce2O3 and La2O3 mixture using a planetary ball mill at a speed of 300-600 r / min to obtain powder with a particle size of 5-10 μm. Ingredient preparation and pelletizing: Weigh the pretreated raw material powders according to the proportions. Put the pretreated CaO and Na2O powders into a high-speed mixer and mix (I). Press the mixture into 5-8mm particles in one step. Add the pretreated CaF2 powder and mix (II). Press the mixture into 10-15mm particles in a second step, which are composite material particles. Add the composite material particles to the mixture of pretreated Al2O3, Ce2O3 and La2O3 to form slag. Add aluminum wire segments and mix (III). Press the mixture into slag balls with a diameter of 20-30mm in a third step. The slag pellets are packaged for later use; after passing the inspection, the slag pellets are packaged in moisture-proof sealed bags.

[0010] Based on the above technical solution, the conditions for selecting raw materials and baking during pretreatment are as follows: The baking temperature is 500-800℃; Baking time is 2-3 hours; The ball milling process in the raw material selection and pretreatment takes 4-6 hours.

[0011] Based on the above technical solution, the mixing conditions for the ingredients and pelletizing process I are as follows: The mixing I was carried out in an argon atmosphere; The rotational speed of the mixing unit I is 300-500 r / min; The mixing time for I is 10-20 minutes.

[0012] Based on the above technical solution, the conditions for mixing the ingredients and pelletizing process II are as follows: The mixing II was carried out in an argon atmosphere; The rotational speed of the mixing II is 100-200 r / min; The mixing time for the second stage is 5-10 minutes.

[0013] Based on the above technical solution, the interior of the composite material particles in the batching and pelletizing process is composed of CaO and Na2O materials, and the exterior is composed of CaF2.

[0014] Based on the above technical solution, the aluminum wire segments are added at a mass ratio of aluminum to slag of 1:(50-80); The aluminum wire segment has a length of 5-10 mm and a diameter of 0.3-0.5 mm.

[0015] Based on the above technical solution, the conditions for mixing the ingredients and pelletizing process III are as follows: The rotational speed of the mixing III is 30-50 r / min; The mixing time for the third stage is 10-20 minutes.

[0016] Beneficial effects (1) By adding rare earth oxides to the slag, the oxidation of rare earth during electroslag remelting can be suppressed, the yield of rare earth can be increased, and the yield of rare earth in steel can be increased to 80%-90%, which is 20%-30% higher than that of traditional slag. This allows for more precise control of the rare earth content in steel and ensures the stability and consistency of rare earth steel performance.

[0017] (2) Through a special preparation process, the addition of aluminum powder for deoxidation to the slag pool during electroslag remelting can be eliminated, reducing problems such as slag surface fluctuation and uneven deoxidation caused by the addition of aluminum powder, effectively improving the purity of the molten steel and providing a guarantee for the production of high-quality rare earth steel. Attached Figure Description Figure 1 The following are flowcharts illustrating the slag preparation process in Examples 1-8 of this invention; Figure 2 This is a physical image of the slag material prepared in Example 2 of the present invention. Detailed Implementation

[0018] To make the objectives and technical solutions of this invention clearer, the following embodiments are provided for further explanation. However, the scope of protection of this invention is not limited to these embodiments; the embodiments are merely for illustrative purposes. Those skilled in the art should understand that any changes or equivalent substitutions that do not depart from the concept of this invention are included within the scope of protection of this invention.

[0019] Unless otherwise specified, all reagents and raw materials used in this invention are obtained through purchase.

[0020] The present invention provides a slag material for electroslag remelting of rare earth steel in the specific embodiments section. The composition of the slag material by mass percentage is as follows: CaF2 40%-60%, Al2O3 20%-35%, CaO 5%-10%, rare earth mixture 10%-15%, Na2O 3%-5%, wherein the rare earth mixture is a mixture of Ce2O3 and La2O3, and the mass ratio of Ce2O3 to La2O3 is 2:(0.5-1.5).

[0021] The functions of each component are as follows: CaF2: As the main slag-forming agent, it can lower the melting point of slag and improve the fluidity of slag, and promote full contact and reaction between slag and steel during electroslag remelting.

[0022] Al2O3: helps to adjust the viscosity and conductivity of slag, and also has the effect of adsorbing and removing inclusions in molten steel.

[0023] CaO: Participates in metallurgical reactions, effectively desulfurizing and dephosphorizing, and improving the purity of molten steel.

[0024] A mixture of Ce2O3 and La2O3 can interact with rare earth elements in molten steel during remelting, stabilizing the form of rare earth elements in steel and improving the rare earth yield.

[0025] The mass ratio of Ce2O3 to La2O3 is 2:(0.5-1.5), which is beneficial to mutually enhance the activity of rare earth oxides and play a role in further stabilizing rare earths in steel.

[0026] Na2O: Represents an alkali metal oxide that can reduce the activity of unstable impurity oxide SiO2 in liquid slag, inhibit the reaction between rare earth elements in steel and SiO2, and thus prevent the oxidation of rare earth elements in steel.

[0027] The present invention also provides a method for preparing slag for electroslag remelting of rare earth steel in the specific embodiments section, comprising the following steps: raw material selection and pretreatment - batching and pelletizing - slag pellet packaging for later use; Raw material selection and pretreatment: Weigh a mixture of CaF2, Al2O3, CaO, Ce2O3 and La2O3 with a purity ≥98%, and Na2O powder as raw materials. Place the weighed CaF2, CaO and Na2O powder in an oven and bake at 500~800℃ for 2~3 hours to remove moisture and volatile impurities, improve its purity and stability, and enhance its reactivity in the subsequent smelting process. The weighed mixture of Al2O3, Ce2O3 and La2O3 is ball-milled in a planetary ball mill at a speed of 300-600 r / min for 4~6 hours to refine the powder particle size to 5~10μm, increase its specific surface area, and improve its dispersibility in the slag.

[0028] Ingredient preparation and pelletizing: (1) Weigh the pretreated raw material powders according to the proportions; (2) Put the hygroscopic raw materials CaO and Na2O into a high-speed mixer and mix them at a speed of 300-500 r / min for 10-20 min. Argon gas is introduced as a protective gas during the process to prevent the raw materials from becoming damp or carbonized during the mixing process and to ensure that the components are mixed evenly. (3) Press the uniformly mixed CaO and Na2O material into 5-8 mm granules. (4) Add CaF2 powder to the granules mentioned in (3) and continue to mix them in a high-speed mixer at a speed of 100-200 r / min for 5-10 min. Argon gas is introduced as a protective gas during the process. Then, press the mixture into granules a second time. The particle size is controlled at 10-15 mm to form a composite material granule with CaO and Na2O as the main internal components and CaF2 as the external component. (5) Add the composite material particles described in (4) to the powder of the mixture of Al2O3, Ce2O3 and La2O3. Then, add aluminum wire segments with a length of 5-10 mm and a diameter of 0.3-0.5 mm according to the mass ratio of aluminum to slag of 1:50-80. Mix the mixture for 10-20 minutes at a speed of 30-50 r / min using a high-speed mixer. Then, press the mixture into slag balls three times, with the diameter controlled at 20-30 mm. The added aluminum wire segments mainly play two roles: first, as a strength-enhancing material for the final slag balls, improving the strength of the slag balls and preventing them from pulverizing before use; second, as a substitute for the aluminum powder added to the slag pool during the electroslag remelting process, it can play a role in deoxidation and prevent element loss.

[0029] Slag pellet packaging for later use: The prepared slag pellets undergo comprehensive quality testing, and the qualified slag pellets are packaged in moisture-proof sealed bags to complete the preparation of slag pellets.

[0030] Example The slag composition ratio (mass percentage) and rare earth recovery rate of this invention are shown in Table 1. Parameters related to raw material pretreatment are shown in Table 2. Parameters related to batching and pelletizing are shown in Table 3. After secondary pressing, composite particles (internal CaO, Na2O, external CaF2) are obtained. After tertiary pressing and passing quality inspection, the slag pellets are sealed in moisture-proof airtight bags. The slag preparation flow chart is shown below. Figure 1 See the physical image of the slag prepared in step 2. Figure 2 .

[0031] Table 1 shows the composition ratio of the slag and the rare earth recovery rate (wt.%).

[0032] Table 2 shows the parameters related to raw material pretreatment.

[0033] Table 3 lists the parameters related to ingredient preparation and pelleting.

[0034] Based on the above technical solutions, it can be seen that by adjusting the ratio of CaF2 and Al2O3, the proportion of rare earth oxides, and the amount of aluminum wire added, slag systems with different performance focuses can be formed. Example 1 focuses on the desulfurization of the slag (higher CaO content), Examples 2 and 3 focus on the exothermic properties of the slag (relatively less CaF2, low conductivity of the slag), Example 4 focuses on the yield of rare earth-containing steel (relatively high rare earth oxide content), and Examples 5 and 6 focus on the adsorption capacity of inclusions (higher CaF2 content). All of these can stabilize the rare earth form during electroslag remelting. Practical application verification shows that the rare earth yield is increased by 80%-90%.

[0035] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A slag material for electroslag remelting of rare earth steel, characterized in that, The composition of the slag by mass percentage is as follows: CaF2 40%-60%, Al2O3 20%-35%, CaO 5%-10%, rare earth mixture 10%-15%, Na2O 3%-5%, wherein the rare earth mixture is a mixture of Ce2O3 and La2O3, and the mass ratio of Ce2O3 to La2O3 is 2:(0.5-1.5).

2. The method for preparing slag for rare earth steel electroslag remelting according to claim 1, characterized in that, The process includes the following steps: raw material selection and pretreatment - batching and pelletizing - packaging slag pellets for later use; Raw material selection and pretreatment: Weigh a mixture of CaF2, Al2O3, CaO, Ce2O3 and La2O3 with a purity ≥98%, and Na2O powder as raw materials; place the weighed CaF2, CaO and Na2O powder in an oven for baking; ball mill the weighed mixture of Al2O3, Ce2O3 and La2O3 to obtain powder with a particle size of 5-10μm; Ingredient preparation and pelletizing: Weigh the pretreated raw material powders according to the proportions. Put the pretreated CaO and Na2O powders into a high-speed mixer and mix (I). Press the mixture into 5-8mm particles in one step. Add the pretreated CaF2 powder and mix (II). Press the mixture into 10-15mm particles in a second step, which are composite material particles. Add the composite material particles to the mixture of pretreated Al2O3, Ce2O3 and La2O3 to form slag. Add aluminum wire segments and mix (III). Press the mixture into slag balls with a diameter of 20-30mm in a third step.

3. The preparation method according to claim 2, characterized in that, The raw material selection and baking conditions during pretreatment are as follows: The baking temperature is 500-800℃; Baking time is 2-3 hours; The ball milling process in the raw material selection and pretreatment takes 4-6 hours.

4. The preparation method according to claim 2, characterized in that, The mixing conditions for the ingredients and pelletizing process I are as follows: The mixing I was carried out in an argon atmosphere; The rotational speed of the mixing unit I is 300-500 r / min; The mixing time for I is 10-20 minutes.

5. The preparation method according to claim 2, characterized in that, The conditions for mixing the ingredients with pelleting process II are as follows: The mixing II was carried out in an argon atmosphere; The rotational speed of the mixing II is 100-200 r / min; The mixing time for the second stage is 5-10 minutes.

6. The preparation method according to claim 2, characterized in that, The composite material particles in the batching and pelletizing process have CaO and Na2O inside and CaF2 outside.

7. The preparation method according to claim 2, characterized in that, The aluminum wire segments are added at a mass ratio of aluminum to slag of 1:(50-80); The aluminum wire segment has a length of 5-10 mm and a diameter of 0.3-0.5 mm.

8. The preparation method according to claim 2, characterized in that, The conditions for mixing the ingredients with pelleting process III are as follows: The rotational speed of the mixing III is 30-50 r / min; The mixing time for the third stage is 10-20 minutes.

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