A pre-melted slag and a method of preparing and using the same

Abstract

The application belongs to the technical field of alloys, and particularly relates to a pre-melted slag and a preparation method and application thereof. The application provides a pre-melted slag, which comprises the following components in percentage by mass: 40-55% CaF2, 15-20% CaO, 5-8% Al2O3, 7-9% MgO, and 15-25% rare earth oxides; and the mass ratio of the rare earth oxides to Al2O3 is greater than 2.5. The pre-melted slag provided by the application contains appropriate amounts of MgO and rare earth oxides, and has low impurity content, so that the reaction between rare earth, magnesium and SiO2 and other impurities in the electroslag remelting process can be reduced, thereby inhibiting the burning loss of rare earth and magnesium in the electroslag remelting process, and improving the yield of rare earth and magnesium in the alloy steel prepared by electroslag remelting.

Description

Technical Field

[0001] This invention belongs to the field of alloy technology, specifically relating to a pre-melted slag, its preparation method, and its application. Background Technology

[0002] For medium- and high-carbon alloy steels such as aerospace bearing steel, high-speed steel, and hot-work die steel, the service environment is often extremely harsh, thus requiring high strength and toughness. However, existing medium- and high-carbon alloy steels have high carbon and alloy content, often resulting in the precipitation of large-sized network eutectic carbides during solidification, which reduces the steel's toughness. Simultaneously, non-metallic inclusions in alloy steel typically deteriorate the strength and toughness of the material. Therefore, refining the carbides in medium- and high-carbon alloy steels and improving their cleanliness can extend their service life and reduce total life-cycle costs.

[0003] Rare earth elements (REs) have a strong affinity for oxygen, sulfur, and other harmful elements such as phosphorus and arsenic. Therefore, they are widely added to steel to achieve deep deoxidation and desulfurization, as well as to fix harmful elements segregated at grain boundaries. Rare earth elements can transform Al₂O₃ inclusions into rare earth inclusions such as RE₂O₃, RE₂O₃, and RE₂O₂S, and refine the size of these inclusions. Rare earth elements can also transform rod-shaped MnS sulfides in steel into spherical RE₂O₂S inclusions, greatly improving the toughness of the steel. Furthermore, rare earth treatment can refine eutectic carbides in medium- and high-carbon alloy steels, causing the continuous network of carbides in the ingot to fracture, ultimately improving the mechanical properties of the steel. Magnesium also has a very strong affinity for oxygen, but a weaker affinity for sulfur. Compared to rare earth elements, magnesium has a more significant effect on refining eutectic carbides in steel; even trace amounts of magnesium can have a significant effect.

[0004] Given the respective advantages of rare earth elements and magnesium, research and application of simultaneously incorporating them into steel have gradually increased in recent years. This aims to leverage the synergistic effect of rare earth and magnesium, improving the cleanliness of molten steel while refining eutectic carbides and enhancing the microstructure and properties of alloy steel. However, due to the high reactivity of both rare earth elements and magnesium, the use of traditional electroslag pre-melting slag for electroslag remelting of consumable electrodes containing rare earth elements and magnesium can lead to severe burn-off of rare earth elements and magnesium, negating their beneficial effects. Therefore, there is an urgent need to develop new electroslag remelting slags to significantly improve the yield of rare earth elements and magnesium during the electroslag remelting process. Summary of the Invention

[0005] In view of this, the present invention provides a pre-melted slag, its preparation method and application. The pre-melted slag provided by the present invention can improve the yield of rare earth and magnesium in alloy steel during electroslag remelting.

[0006]

[0007]

[0008] The mass ratio of the rare earth oxide to Al2O3 is greater than 2.5;

[0009] The mass percentage of impurities in the pre-melted slag is less than 0.5%, and the impurities include SiO2, FeO and MnO.

[0010] Preferably, the pre-melted slag comprises the following components in weight percentage:

[0011]

[0012] The present invention also provides a method for preparing the pre-melted slag described in the above technical solution, comprising the following steps:

[0013] Lime, fluorite, fused magnesia, rare earth oxides and alumina are mixed to obtain a mixture;

[0014] The mixture is melted and then mixed with an Fe-Al-C master alloy for a first refining process to obtain a first refined melt.

[0015] The first refined melt and the Fe-RE-C rare earth alloy are mixed and then refined a second time to obtain the second refined melt.

[0016] The second refined melt was allowed to stand and separate into layers to obtain pre-melted slag melt and ferroalloy melt, respectively.

[0017] The pre-melted slag liquid is cooled to obtain pre-melted slag.

[0018] Preferably, the melting temperature is 1420–1530°C.

[0019] Preferably, the Fe-Al-C master alloy has an Al content of 8-14% by mass and a C content of 5-6% by mass.

[0020] The amount of Fe-Al-C master alloy added is calculated according to Formula 1:

[0021] m1=a×M S ×(0.6w SiO2 +0.250w FeO +0.253w MnO ) / (w Al -0.02) Formula 1;

[0022] Where m1 is the mass of Fe-Al-C alloy added, in kg; a is a coefficient, ranging from 1 to 1.3; M S The mass of the mixture is expressed in kg; w SiO2The mass percentage of SiO2 in the mixture, expressed in %; w FeO The mass percentage of FeO in the mixture, expressed as %; w MnO The mass percentage of MnO in the mixture, expressed in %; w Al This represents the mass percentage of Al in the Fe-Al-C master alloy, expressed as a percentage.

[0023] Preferably, the temperature of the first refining is 1420-1530°C, and the holding time of the first refining is 10-20 minutes.

[0024] Preferably, the Fe-RE-C rare earth alloy contains 4-7% RE by mass and 5-6% C by mass.

[0025] The amount of Fe-RE-C rare earth alloy added is calculated according to Formula 2:

[0026] m2 = b / w RE ×M s Formula 2;

[0027] Where m2 is the mass of Fe-RE-C rare earth alloy added, in kg; b is a coefficient, b is 4 to 8, w RE M represents the mass percentage of RE in the Fe-RE-C rare earth alloy, expressed as %; S The mass of the mixture is expressed in kg.

[0028] Preferably, the temperature of the second refining is 1420-1530°C, and the holding time of the second refining is 20-30 minutes.

[0029] Preferably, the initial temperature for static stratification is 1420–1530°C, and the final temperature for static stratification is 40–70°C lower than the initial temperature for static stratification.

[0030] The present invention also provides the application of the pre-melted slag described in the above technical solution or the pre-melted slag prepared by the preparation method described in the above technical solution in the preparation of steel containing rare earth and magnesium by electroslag remelting.

[0031] This invention provides a pre-melted slag comprising the following components by mass percentage: 40-55% CaF2, 15-20% CaO, 5-8% Al2O3, 7-9% MgO, and 15-25% rare earth oxides; wherein the mass ratio of rare earth oxides to Al2O3 is greater than 2.5. The pre-melted slag provided by this invention contains a significant amount of MgO and rare earth oxides, while also containing a small amount of impurities. This reduces the reaction between rare earth elements, magnesium, and impurities such as SiO2 during electroslag remelting, thereby inhibiting the burn-off of rare earth elements and magnesium during electroslag remelting and improving the yield of rare earth elements and magnesium in the alloy steel prepared by electroslag remelting. Detailed Implementation

[0032] This invention provides a premelted slag comprising the following components in weight percentage:

[0033]

[0034] The mass ratio of the rare earth oxide to Al2O3 is greater than 2.5;

[0035] The mass percentage of impurities in the pre-melted slag is less than 0.5%, and the impurities include SiO2, FeO and MnO.

[0036] The pre-melted slag provided by this invention comprises 40-55% CaF2, preferably 45-52%, by mass percentage. By controlling the mass percentage of CaF2 in the pre-melted slag within the above range, this invention can control the melting point, viscosity, and surface tension of the pre-melted slag to a suitable range, which is not only beneficial for inclusion adsorption and desulfurization, but also beneficial for improving the surface quality of electroslag ingots.

[0037] The pre-melted slag provided by the present invention comprises 15-20% CaO, preferably 16-19%, by mass percentage. By limiting the mass percentage of CaO in the pre-melted slag to the above range, the present invention can improve the basicity of the pre-melted slag, improve the desulfurization efficiency, and further reduce the activity of SiO2, thus inhibiting the burn-off of active elements such as rare earth elements and magnesium in the steel during the electroslag remelting process.

[0038] The pre-melted slag provided by this invention comprises 5-8% Al2O3 by mass percentage, preferably 6-7%. By adding Al2O3 to the pre-melted slag and controlling its mass percentage within the above range, this invention can significantly reduce the electrical conductivity of the pre-melted slag, reduce power consumption, improve productivity, and further suppress the burn-off of rare earth and magnesium and other active elements in the steel during the electroslag remelting process.

[0039] The pre-melted slag provided by this invention comprises 7-9% MgO, preferably 7.5-8.5%, by weight percentage. By adding MgO to the pre-melted slag and controlling its weight percentage within the above range, this invention enables the formation of a semi-solidified film on the surface of the slag pool, which can prevent the slag pool from absorbing hydrogen, oxygen, and nitrogen. Furthermore, it can bring the MgO in the pre-melted slag to near saturation, thus inhibiting the loss of magnesium during the electroslag remelting process.

[0040] During the electroslag remelting process, magnesium in steel reacts chemically with unstable oxides such as SiO2. Taking SiO2 as an example, the reaction produces MgO and silicon, as shown in Equation 1:

[0041] 2Mg + SiO2 = 2MgO + Si (Equation 1)

[0042] When the MgO content in the pre-melted slag is within the above range, the chemical reaction can be inhibited from proceeding to the right, thereby inhibiting the loss of magnesium.

[0043] The pre-melted slag provided by this invention comprises 15-25% rare earth oxides (RE2O3), preferably 18-22%, by mass percentage. In this invention, the type of rare earth oxides is preferably consistent with the rare earth elements in the steel prepared by electroslag remelting. In this invention, the rare earth oxides preferably include Ce2O3 and / or La2O3, more preferably Ce2O3 or La2O3.

[0044] This invention, by adding rare earth oxide RE2O3 to the pre-melted slag and controlling its content within the above-mentioned range, can not only increase the activity of RE2O3 in the pre-melted slag, thereby inhibiting the burn-off of rare earth elements in the steel during the electroslag remelting process, but also avoid the deterioration of the surface quality of the electroslag ingot caused by excessive RE2O3 content, as well as the significant increase in the cost of the pre-melted slag.

[0045] During the electroslag remelting process, rare earth elements in steel will react chemically with unstable oxides such as SiO2. Taking SiO2 as an example, the reaction produces rare earth oxides and silicon. The reaction equation is shown in Equation 2:

[0046] 2RE + 1.5SiO2 = RE2O3 + 1.5Si (Equation 2)

[0047] RE represents rare earth elements, and RE2O3 represents rare earth oxides.

[0048] When the content of rare earth oxides in the pre-melted slag is within the above range, the chemical reaction can be inhibited from proceeding to the right, thereby inhibiting the burn-off of rare earth.

[0049] In this invention, the mass ratio of the rare earth oxide to Al2O3 is greater than 2.5, preferably greater than 3. By controlling the mass ratio of RE2O3 to Al2O3 within the above range, this invention can effectively suppress the loss of rare earth elements in steel during the electroslag remelting process due to excessively high relative Al2O3 content.

[0050] In this invention, the mass percentage of impurities in the pre-melted slag is less than 0.5%, preferably less than 0.35%. In this invention, the impurities include SiO2, FeO, and MnO. By limiting the total amount of impurities to the above range, this invention can effectively suppress the loss of rare earth and magnesium elements in the steel during the electroslag remelting process due to excessively high SiO2, FeO, and MnO content.

[0051] In this invention, the hemispherical melting temperature of the pre-melted slag is preferably 1250–1320°C, more preferably 1270–1300°C. By controlling the hemispherical melting temperature of the pre-melted slag within the above range, this invention enables the pre-melted slag to have suitable melting point, viscosity, and surface tension, which is not only beneficial for inclusion adsorption and desulfurization, but also for improving the surface quality of electroslag ingots.

[0052] The present invention also provides a method for preparing the pre-melted slag described in the above technical solution, comprising the following steps:

[0053] Lime, fluorite, fused magnesia, rare earth oxides and alumina are mixed to obtain a mixture;

[0054] The mixture is melted and then mixed with an Fe-Al-C master alloy for a first refining process to obtain a first refined melt.

[0055] The first refined melt and the Fe-RE-C rare earth alloy are mixed and then refined a second time to obtain the second refined melt.

[0056] The second refined melt was allowed to stand and separate into layers to obtain pre-melted slag melt and ferroalloy melt, respectively.

[0057] The pre-melted slag liquid is cooled to obtain pre-melted slag.

[0058] In this invention, unless otherwise specified, all raw materials are conventional commercially available products.

[0059] This invention involves mixing lime, fluorite, fused magnesia, rare earth oxides, and alumina to obtain a mixture. In this invention, the mass percentage of CaO in the lime is preferably greater than or equal to 93%, more preferably greater than or equal to 95%. In this invention, the mass percentage of CaO in the lime is preferably less than or equal to 1.5%, more preferably less than or equal to 1.2%; the total mass percentage of FeO and MnO in the lime is preferably less than or equal to 0.5%, more preferably less than or equal to 0.3%.

[0060] In this invention, the mass percentage of CaF2 in the fluorite is preferably greater than or equal to 97%, more preferably greater than or equal to 98%. In this invention, the mass percentage of SiO2 in the fluorite is preferably less than or equal to 1.2%, more preferably less than or equal to 1%; the total mass percentage of FeO and MnO in the fluorite is preferably less than or equal to 0.5%, more preferably less than or equal to 0.3%.

[0061] In this invention, the MgO content in the fused magnesia is preferably greater than or equal to 97%, more preferably greater than or equal to 98%. In this invention, the mass percentage of SiO2 in the fused magnesia is preferably less than or equal to 1.5%, more preferably less than or equal to 1%; the total mass percentage of FeO and MnO in the fused magnesia is preferably less than or equal to 0.5%, more preferably less than or equal to 0.3%.

[0062] In this invention, the rare earth oxide is preferably a rare earth oxide powder, and the average particle size of the rare earth oxide powder is preferably less than 3 mm, more preferably less than 1 mm. In this invention, the rare earth elements in the rare earth oxide are preferably the same as those in the alloy steel prepared by electroslag remelting. In this invention, the purity of the rare earth oxide is preferably greater than or equal to 96%, more preferably greater than or equal to 98%. In this invention, the mass percentage of SiO2 in the rare earth oxide is preferably less than or equal to 0.8%, more preferably less than or equal to 0.4%; the total mass percentage of FeO and MnO in the rare earth oxide is preferably less than or equal to 0.3%, more preferably less than or equal to 0.1%.

[0063] In this invention, the alumina is preferably alumina powder, and the average particle size of the alumina powder is preferably less than 3 mm, more preferably less than 1 mm. In this invention, the purity of the alumina is preferably greater than or equal to 96%, more preferably greater than or equal to 98%. In this invention, the mass percentage of SiO2 in the alumina is preferably less than or equal to 0.5%, more preferably less than or equal to 0.3%; the total mass percentage of FeO and MnO in the alumina is preferably less than or equal to 0.3%, more preferably less than or equal to 0.1%.

[0064] In this invention, the mass percentage of SiO2 in the mixture is preferably less than 1.5%, more preferably less than 1.0%; the mass percentage of FeO and MnO in the mixture is preferably less than 0.5%, more preferably less than 0.3%.

[0065] In this invention, the process prior to mixing preferably includes crushing the lime, fluorite, and fused magnesia. In this invention, the average particle size of the material after crushing is preferably less than or equal to 10 mm, more preferably less than or equal to 5 mm. This invention does not impose any particular limitation on the crushing process, as long as the desired average particle size is achieved. By controlling the average particle size of the lime, fluorite, and fused magnesia within the aforementioned range, this invention can accelerate the melting rate of the mixture, reduce energy consumption, and improve production efficiency.

[0066] The present invention has no special requirements for the mixing, as long as the mixing is uniform.

[0067] After obtaining the mixture, the present invention melts the mixture and mixes it with an Fe-Al-C master alloy for a first refining process to obtain a first refined melt. In this invention, the smelting is preferably carried out in an electric arc furnace, preferably a DC electric arc furnace. In this invention, the furnace lining of the electric arc furnace is preferably a carbonaceous refractory material. The present invention preferably adds the mixture to the electric arc furnace for smelting. The preferred feeding rate of the mixture into the electric arc furnace is 15–25 kg / min, more preferably 17–23 kg / min. By controlling the feeding rate within the above range, the present invention can prevent the mixture from clumping due to insufficient melting time, ensuring smooth production.

[0068] In this invention, the melting temperature is preferably 1420-1530°C, and more preferably 1450-1520°C.

[0069] In this invention, the Fe-Al-C master alloy is preferably Fe-Al-C master alloy particles; the average particle size of the Fe-Al-C master alloy particles is preferably less than 10 mm, more preferably less than 3 mm. By controlling the particle size of the Fe-Al-C master alloy particles within the above-mentioned range, this invention not only increases the total surface area of ​​the Fe-Al-C master alloy particles and improves the rate of the slag-metal reaction, but also inhibits the rapid settling of the Fe-Al-C master alloy particles to the bottom of the slag furnace before the slag-metal reaction reaches equilibrium, thereby promoting the slag-metal reaction.

[0070] In this invention, the Al content in the Fe-Al-C master alloy is preferably 8-14% by mass, more preferably 9-13%. The higher the Al content in the Fe-Al-C master alloy, the less the total amount of Fe-Al-C master alloy particles added, and the smaller the total surface area of ​​the Fe-Al-C master alloy particles, which is detrimental to improving the slag-metal reaction rate. By controlling the Al content of the Fe-Al-C master alloy particles within the above-mentioned range, this invention not only facilitates the full progress of the slag-metal reaction and yields a pre-melted slag with low impurity content, but also improves production efficiency.

[0071] In this invention, the mass percentage of C in the Fe-Al-C master alloy is preferably 5-6%, more preferably 5.2-5.8%. By controlling the C content in the Fe-Al-C master alloy particles within the above range, this invention not only inhibits the dissolution of the carbonaceous lining of the slag furnace and protects the lining energy, but also ensures that the Fe-Al-C master alloy particles are completely melted throughout the refining process, increasing the slag-metal reaction rate and further promoting the collision growth of Fe-Al-C master alloy droplets, thus facilitating slag-metal separation.

[0072] In this invention, the amount of Fe-Al-C master alloy added is preferably calculated according to Formula 1:

[0073] m1=a×M S ×(0.6w SiO2 +0.250w FeO +0.253w MnO ) / (w Al -0.02) Formula 1;

[0074] Where m1 is the mass of Fe-Al-C master alloy added, in kg; a is a coefficient, preferably 1 to 1.3, more preferably 1.1 to 1.2; M S The mass of the mixture is expressed in kg; w SiO2 The mass percentage of SiO2 in the mixture, expressed in %; w FeO The mass percentage of FeO in the mixture, expressed as %; w MnO The mass percentage of MnO in the mixture, expressed in %; w Al The percentage of Al in the Fe-Al-C master alloy is expressed as %. This invention, by controlling the amount of Fe-Al-C master alloy particles added within the above range, not only ensures sufficient reaction between Al and impurities such as SiO2, FeO, and MnO in the slag, effectively suppressing the loss of rare earth elements and magnesium in the steel during electroslag remelting, but also avoids excessive addition of Fe-Al-C master alloy, which would increase production costs.

[0075] In this invention, the preferred method of mixing the melted mixture with the Fe-Al-C master alloy is to sprinkle Fe-Al-C master alloy particles onto the surface of the melt obtained by melting.

[0076] In this invention, the temperature of the first refining is preferably 1420-1530°C, more preferably 1450-1520°C; the holding time of the first refining is preferably 10-20 min, more preferably 12-18 min.

[0077] In this invention, Al in the Fe-Al-C master alloy acts as an oxidant, reacting with impurities such as SiO2 in the first refining process to generate alumina and silicon, thereby reducing the content of impurities such as SiO2 in the pre-melted slag.

[0078] After obtaining the first refined melt, the present invention mixes the first refined melt with Fe-RE-C rare earth alloy for a second refining process to obtain the second refined melt.

[0079] In this invention, the Fe-RE-C rare earth alloy is preferably Fe-RE-C rare earth alloy particles; the average particle size of the Fe-RE-C rare earth alloy particles is preferably less than 10 mm, more preferably less than 3 mm. By controlling the particle size of the Fe-RE-C rare earth alloy particles within the above-mentioned range, this invention not only increases the total surface area of ​​the Fe-RE-C rare earth alloy particles and improves the rate of the slag-metal reaction, but also inhibits the rapid settling of the Fe-RE-C rare earth alloy particles to the bottom of the slag furnace before the slag-metal reaction reaches equilibrium, thereby promoting the slag-metal reaction.

[0080] In this invention, the mass percentage of RE in the Fe-RE-C rare earth alloy is preferably 4-7%, more preferably 4.5-6.5%. In this invention, the mass percentage of C in the Fe-RE-C rare earth alloy is preferably 5-6%, more preferably 5.2-5.8%.

[0081] In this invention, the amount of Fe-RE-C rare earth alloy added is preferably calculated according to Formula 2:

[0082] m2 = b / w RE ×M s Formula 2;

[0083] Where m2 is the mass of Fe-RE-C rare earth alloy added, in kg; b is a coefficient, preferably 4-8, more preferably 5-7; w RE M represents the mass percentage of RE in the Fe-RE-C rare earth alloy, expressed as %; S The mass of the mixture is expressed in kg.

[0084] This invention, by adding Fe-RE-C rare earth alloy and controlling its composition and amount within the above-mentioned range, not only ensures that the total amount of SiO2, FeO and MnO in the finished pre-melted slag is less than 0.5%, effectively suppressing the burn-off of rare earth and magnesium in the steel during the electroslag remelting process, but also avoids excessive addition of Fe-RE-C rare earth alloy, which would increase production costs.

[0085] In this invention, mixing the first refined melt and the Fe-RE-C rare earth alloy is preferably done by sprinkling Fe-RE-C rare earth alloy particles on the surface of the first refined melt.

[0086] In this invention, the temperature of the second refining is preferably 1420-1530°C, more preferably 1450-1520°C; the holding time of the second refining is preferably 20-30 min, more preferably 22-28 min.

[0087] In this invention, RE in the Fe-RE-C rare earth alloy acts as a reducing agent, which can react with impurities such as SiO2 in the second refining process to generate rare earth oxides and silicon, thereby reducing the content of impurities such as SiO2 in the pre-melted slag.

[0088] By controlling the first and second refining times within the aforementioned range, this invention ensures that impurities in the slag react fully with the Fe-Al-C master alloy and Fe-RE-C rare earth alloy, thereby ensuring that the total amount of SiO2, FeO, and MnO in the finished pre-melted slag is less than 0.5%, effectively suppressing the burn-off of rare earth and magnesium in the steel during the electroslag remelting process.

[0089] After obtaining the second refined molten liquid, the present invention allows the second refined molten liquid to stand and separate into layers, obtaining pre-melted slag and ferroalloy molten liquid respectively. In the present invention, the initial temperature of the standing and separating layer is preferably 1420-1530°C, and the ending temperature of the standing and separating layer is preferably 40-70°C lower than the initial temperature, more preferably 50-60°C lower. In the present invention, the system temperature at the end of the standing and separating layer is preferably 1370-1470°C, more preferably 1400-1450°C. By controlling the slag temperature within the above range at the end of the standing and separating layer, the present invention ensures a sufficiently long time for slag-metal separation, which is beneficial for obtaining a low-carbon finished pre-melted slag.

[0090] In this invention, after static stratification treatment, the pre-melted slag and ferroalloy melt naturally separate due to density differences. The Fe alloy melt, with its high density, will remain in the lower layer. In this invention, the mass fraction of Al in the Fe alloy melt is preferably 1.5–2.5%, more preferably 1.8–2.2%. By controlling the Al content in the Fe alloy solution within the above range, this invention not only improves the utilization rate of Al in the Fe-Al-C master alloy and reduces production costs, but also ensures that the total amount of SiO2, FeO, and MnO in the finished pre-melted slag is <0.5%, effectively suppressing the loss of rare earth elements and magnesium in the steel during electroslag remelting.

[0091] After settling and separating, the present invention preferably performs liquid separation on the settled and separated pre-melted slag-liquid system to obtain pre-melted slag-liquid. The present invention does not have any particular limitation on the liquid separation, and conventional methods in the art can be used; in the present invention, the liquid separation can be performed by direct pouring.

[0092] After obtaining the pre-melted slag liquid, the present invention cools the pre-melted slag liquid to obtain pre-melted slag. In the present invention, the cooling is preferably natural cooling. In the present invention, the cooling process further preferably includes: crushing the solid obtained after cooling to obtain pre-melted slag. In the present invention, the average particle size of the pre-melted slag is preferably 2-10 mm, more preferably 4-8 mm. By controlling the particle size of the pre-melted slag within the above range, the present invention can effectively suppress the deliquescence of the pre-melted slag, thereby reducing the loss of rare earth elements and magnesium in steel during the electroslag remelting process, as well as reducing hydrogenation in the electroslag ingot.

[0093] The preparation method provided by this invention involves first and second refining using a Fe-Al-C master alloy and a Fe-RE-C rare earth alloy, supplemented by a settling treatment to promote slag-metal separation, controlling the SiO2, FeO, and MnO content in the pre-melted slag to below 0.5%. The Fe-Al-C master alloy and Fe-RE-C rare earth alloy used in this invention have very low melting points, thus enabling efficient refining of the pre-melted slag at lower temperatures, significantly reducing energy consumption. Furthermore, low temperatures effectively reduce CaF2 volatilization, resulting in lower environmental pollution. The preparation method provided by this invention is simple, efficient, and safe.

[0094] This invention also provides the application of the pre-melted slag described in the above-described technical solutions or the pre-melted slag prepared by the preparation method described in the above-described technical solutions in the preparation of steel containing rare earth elements and magnesium using the electroslag remelting method. In this invention, the steel preferably includes gear steel, bearing steel, high-speed steel, or tool and die steel.

[0095] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0096] The raw materials used in the examples are as follows: Lime: CaO≥95%, SiO2≤1.3%, FeO+MnO≤0.4%, the remainder being impurities; Fluorite: CaF2≥97%, SiO2≤1.2%, FeO+MnO≤0.4%, the remainder being impurities; Fused magnesia: MgO≥98%, SiO2≤1.2%, FeO+MnO≤0.3%, the remainder being impurities; Rare earth oxides: RE2O3≥97%, SiO2≤0.6%, FeO+MnO≤0.1%, the remainder being impurities; Alumina: Al2O3≥98%, SiO2≤0.2%, FeO+MnO≤0.1%, the remainder being impurities; The particle size of the rare earth oxide powder is less than 1 mm, and the particle size of the alumina powder is less than 0.5 mm;

[0097] In this embodiment, the smelting is carried out in a DC electric arc furnace, and the furnace has a loading capacity of 450 kg.

[0098] Example 1

[0099] (1) Mixing: Lime, fluorite and fused magnesia are crushed separately to make the particle size of the crushed material less than 4 mm; the crushed lime, fluorite, fused magnesia, rare earth oxide powder (Ce2O3) and alumina powder are mixed evenly to obtain 450 kg of mixture; the mixture includes the following components in mass percentage: CaF2 51.78%, CaO 15.83%, Al2O3 5.74%, MgO 7.11%, Ce2O3 18.24%, SiO2 1.01%, FeO+MnO 0.29%;

[0100] (2) Melting and refining: The mixture was added to a DC electric arc furnace at a feeding rate of 18 kg / min; melting was carried out at 1450℃; after complete dissolution, 50.2 kg of Fe-Al-C master alloy particles with a particle size of less than 2 mm (the mass percentage of Al in the Fe-Al-C master alloy is 9% and the mass percentage of C is 5.5%) were evenly sprinkled on the surface of the melt, and the first refining was carried out at 1450℃ for 12 min; 49.1 kg of Fe-Ce-C rare earth alloy particles with a particle size of less than 3 mm (the mass percentage of Ce in the Fe-Ce-C rare earth alloy is 5.5% and the mass percentage of C is 5.1%) were evenly sprinkled on the surface of the melt after the first refining, and the second refining was carried out at 1450℃ for 29 min; the second refining melt was allowed to stand and separate into layers, and when the temperature of the melt was 1400℃, the liquid was separated to obtain pre-melted slag liquid and ferroalloy melt; the mass percentage of Al in the ferroalloy melt was 1.7%;

[0101] (3) Molding: Pour the pre-melted slag liquid into the slag hopper and let it cool naturally to obtain a solid. Crush the solid into particles with a particle size of less than 8 mm to obtain pre-melted slag.

[0102] Example 2

[0103] (1) Mixing: Lime, fluorite and fused magnesia are crushed separately to make the particle size of the crushed material less than 5 mm; the crushed lime, fluorite, fused magnesia, rare earth oxide powder (Ce2O3) and alumina powder are mixed evenly to obtain 450 kg of mixture; the mixture includes the following components in mass percentage: CaF2 40.87%, CaO 19.20%, Al2O3 7.58%, MgO 8.24%, rare earth oxides 22.91%, SiO2 0.92%, FeO+MnO 0.28%;

[0104] (2) Melting and refining: The mixture was added to a DC electric arc furnace at a feeding rate of 20 kg / min; melting was carried out at 1510℃; after complete dissolution, 37.3 kg of Fe-Al-C master alloy particles with a particle size of less than 1 mm (the mass percentage of Al in the Fe-Al-C master alloy is 11%, and the mass percentage of C is 5.8%) was evenly sprinkled on the surface of the melt, and the first refining was carried out at 1510℃ for 19 min; 50.0 kg of Fe-Ce-C rare earth alloy particles with a particle size of less than 2 mm (the mass percentage of Ce in the Fe-Ce-C rare earth alloy is 4.5%, and the mass percentage of C is 5.4%) was evenly sprinkled on the surface of the melt after the first refining, and the second refining was carried out at 1510℃ for 22 min; the second refined melt was allowed to stand and separate into layers, and when the melt temperature reached 1450℃, the liquid was separated to obtain pre-melted slag liquid and ferroalloy melt; the mass percentage of Al in the ferroalloy melt was 2.3%;

[0105] (3) Molding: Pour the pre-melted slag liquid into the slag hopper and let it cool naturally to obtain a solid. Crush the solid into particles with a particle size of less than 6 mm to obtain pre-melted slag.

[0106] Example 3

[0107] (1) Mixing: Lime, fluorite and fused magnesia are crushed separately to make the particle size of the crushed material less than 3mm; the crushed lime, fluorite, fused magnesia, rare earth oxide powder (Ce2O3) and alumina powder are mixed evenly to obtain 450kg of mixture; the mixture includes the following components in mass percentage: CaF2 46.03%, CaO 17.32%, Al2O3 6.66%, MgO 8.64%, rare earth oxide 20.1%, SiO2 0.95%, FeO+MnO 0.30%;

[0108] (2) Melting and refining: The mixture was added to a DC electric arc furnace at a feeding rate of 22 kg / min; melting was carried out at 1470℃; after complete dissolution, 29.0 kg of Fe-Al-C master alloy particles with a particle size of less than 3 mm (the mass percentage of Al in the Fe-Al-C master alloy is 13%, and the mass percentage of C is 5.2%) was evenly sprinkled on the surface of the melt, and the first refining was carried out at 1470℃ for 15 min; 48.5 kg of Fe-Ce-C rare earth alloy particles with a particle size of less than 1 mm (the mass percentage of Ce in the Fe-Ce-C rare earth alloy is 6.5%, and the mass percentage of C is 5.7%) was evenly sprinkled on the surface of the melt after the first refining, and the second refining was carried out at 1470℃ for 24 min; the melt after the second refining was allowed to stand and separate into layers, and when the temperature of the melt was 1420℃, the liquid was separated to obtain pre-melted slag liquid and ferroalloy melt; the mass percentage of Al in the ferroalloy melt was 2.1%;

[0109] (3) Molding: Pour the pre-melted slag liquid into the slag hopper and let it cool naturally to obtain a solid. Crush the solid into particles with a particle size of less than 4 mm to obtain pre-melted slag.

[0110] Comparative Example 1

[0111] The pre-melted slag was prepared according to the method of Example 1, except that a second refining was not performed.

[0112] Comparative Example 2

[0113] The pre-melted slag was prepared according to the method of Example 1, except that the Fe-Al-C master alloy in the first refining was replaced with a Fe-Al alloy, and the mass percentage of Al in the Fe-Al alloy was 9%.

[0114] Comparative Example 3

[0115] The pre-melted slag was prepared according to the method of Example 1, except that the static stratification was not performed, and the solution after the second refining was directly cooled and crushed to obtain the pre-melted slag.

[0116] Comparative Example 4

[0117] The pre-melted slag was prepared according to the method of Example 1, except that the mixture included the following components in mass percentage: CaF2 64.65%, CaO 15.76%, Al2O3 5.74%, MgO 5.02%, rare earth oxides (Ce2O3) 7.51%, SiO2 1.03%, and FeO+MnO 0.29%.

[0118] The content of SiO2 and the total content of FeO and MnO in the pre-melted slags prepared in Examples 1-3 and Comparative Examples 1-4 were detected by inductively coupled plasma mass spectrometry, and the results are listed in Table 1.

[0119] The pre-melted slags prepared in Examples 1-3 and Comparative Example 4 were applied to the electroslag remelting production of H13 steel containing rare earth elements and magnesium. The consumable electrode of the H13 steel contained 0.0257% Ce (rare earth), 0.0065% magnesium, 0.0021% oxygen, and 0.0009% sulfur by mass. The consumable electrode had a diameter of 75 mm and a weight of 80 kg. The crystallizer inner diameter was 120 mm. The remelting voltage was 37-38 V, and the current was 2300-2350 A. The yields of rare earth elements and magnesium after electroslag remelting are shown in Table 1.

[0120] Table 1. Impurity content and magnesium and rare earth yields in the pre-melted slags prepared in Examples 1-3 and Comparative Examples 1-4

[0121]

[0122]

[0123] As shown in Table 1, the mass percentage of SiO2 in the pre-melted slag prepared according to the embodiments of the present invention is between 0.31 and 0.39 wt.%, and the total mass percentage of FeO and MnO is between 0.011 and 0.017 wt.%. In Comparative Example 1, without the addition of Fe-RE-C rare earth alloy (without second refining), the total mass percentage of SiO2, FeO, and MnO is 0.0592 wt.%; in Comparative Example 1, using Fe-Al alloy instead of Fe-Al-C intermediate alloy, the total mass percentage of SiO2, FeO, and MnO is 0.853 wt.%; in Comparative Example 3, without settling treatment, the total mass percentage of SiO2, FeO, and MnO is 0.661 wt.%. The total amount of impurities SiO2, FeO, and MnO in the pre-melted slag obtained according to the preparation method provided by the present invention is controlled to be below 0.5 wt.%.

[0124] As shown in Table 1, the pre-melted slag prepared in Examples 1-3 can increase the rare earth recovery rate to 81.4%-85.3% and the magnesium recovery rate to 89.1%-92.4% when used in electroslag remelting. The pre-melted slag provided by this invention can significantly improve the recovery rate of rare earth and magnesium in steel during the electroslag remelting process.

[0125] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a pre-melted slag, characterized in that, Includes the following steps: Lime, fluorite, fused magnesia, rare earth oxides and alumina are mixed to obtain a mixture; The mixture is melted and then mixed with an Fe-Al-C master alloy for a first refining process to obtain a first refined melt. The first refined melt and the Fe-RE-C rare earth alloy are mixed and then refined a second time to obtain the second refined melt. The second refined melt was allowed to stand and separate into layers to obtain pre-melted slag melt and ferroalloy melt, respectively. The pre-melted slag liquid is cooled to obtain pre-melted slag; The pre-melted slag comprises the following components in weight percentage: CaF2 40~55%; CaO 15~20%; Al2O3 5~8%; MgO 7~9%; Rare earth oxides 15-25%; The mass ratio of the rare earth oxide to Al2O3 is greater than 2.5; The mass percentage of impurities in the pre-melted slag is less than 0.5%, and the impurities include SiO2, FeO and MnO.

2. The preparation method according to claim 1, characterized in that, The pre-melted slag comprises the following components in weight percentage: CaF2 45~52%; CaO 16~19%; Al2O3 6~7%; MgO 7.5~8.5%; Rare earth oxides: 18-22%.

3. The preparation method according to claim 1, characterized in that, The melting temperature is 1420~1530℃.

4. The preparation method according to claim 1, characterized in that, The Fe-Al-C master alloy contains 8-14% Al by mass and 5-6% C by mass.

5. The preparation method according to claim 1, characterized in that, The amount of Fe-Al-C master alloy added is calculated according to Formula 1: m1 = a × M S ×(0.6w SiO2 +0.250w FeO +0.253w MnO ) / (w Al -0.02) Official 1; Where m1 is the mass of Fe-Al-C alloy added, in kg; a is a coefficient, ranging from 1 to 1.3; M S The mass of the mixture is expressed in kg; w SiO2 The mass percentage of SiO2 in the mixture is expressed as %; w FeO The mass percentage of FeO in the mixture is expressed as %; w MnO The mass percentage of MnO in the mixture is expressed as %; w Al The mass percentage of Al in the Fe-Al-C master alloy is expressed in units of %.

6. The preparation method according to claim 1, 4, or 5, characterized in that, The temperature of the first refining process is 1420~1530℃, and the holding time for the first refining process is 10~20min.

7. The preparation method according to claim 1, characterized in that, The Fe-RE-C rare earth alloy contains 4-7% RE by mass and 5-6% C by mass. The amount of Fe-RE-C rare earth alloy added is calculated according to Formula 2: m2=b / w RE ×M s Formula 2; Where m2 is the mass of Fe-RE-C rare earth alloy added, in kg; b is a coefficient, b = 4~8, w RE M represents the mass percentage of RE in the Fe-RE-C rare earth alloy, expressed in %; S The mass of the mixture is expressed in kg.

8. The preparation method according to claim 1 or 7, characterized in that, The temperature of the second refining process is 1420~1530℃, and the holding time for the second refining process is 20~30 minutes.

9. The preparation method according to claim 1, characterized in that, The initial temperature for static stratification is 1420~1530℃, and the final temperature for static stratification is 40~70℃ lower than the initial temperature for static stratification.

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