Pre-melting slag charge for electroslag remelting as well as preparation method and application method of pre-melting slag charge

Abstract

The invention discloses a pre-melting slag material for electroslag remelting as well as a preparation method and an application method of the pre-melting slag material, and belongs to the technical field of smelting. The pre-melting slag material comprises the following components in percentage by mass: 40 to 60 percent of CaF2, 20 to 30 percent of CaO, 10 to 20 percent of Al2O3, 5 to 10 percent of SiO2, 1 to 5 percent of MgO and 0.5 to 2 percent of rare earth oxide. The preparation method comprises the steps of raw material mixing, smelting refining and crushing granulation. The pre-molten slag provided by the invention is wide in application range, can remarkably improve the purity and surface quality of electroslag ingots, and has the advantages of efficient desulfurization, low oxygen increment, controllable cost and the like. The problems of slag bath property fluctuation, cost increase and molten steel oxygenation caused by excessive introduction of rare earth in the prior art can be effectively solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of smelting, and relates to a premelted slag material for electroslag remelting, a preparation method thereof, and an application method thereof. Background Art

[0002] Electroslag Remelting (ESR) is a secondary metallurgical technology for refining metals through the resistance heat of molten slag, and is widely used in the preparation of high-end alloy steels, superalloys, and special materials. Its core lies in using the interfacial reaction between molten slag and metal to effectively remove non-metallic inclusions in steel and improve the solidification structure of ingots, thereby significantly enhancing the mechanical properties and purity of materials. With the continuous improvement of material performance requirements in fields such as aerospace, nuclear power, and military, how to precisely control the oxidation loss and uniform distribution of alloying elements (such as rare earth elements) during the electroslag remelting process has become a key difficult point in technology optimization.

[0003] Rare earth elements (such as La, Ce, Y, etc.) have multiple functions in steel, such as deoxidation, desulfurization, grain refinement, and improvement of inclusion morphology due to their unique physical and chemical properties. However, their high activity also makes them prone to oxidation loss during the smelting process, resulting in a low recovery rate. In order to fully utilize the metallurgical advantages of rare earth elements, in recent years, researchers have begun to explore the method of adding trace rare earth oxides to electroslag premelted slag. By optimizing the slag system design, rare earth oxides can not only reduce the melting point of the slag and improve fluidity, but also adjust the oxygen potential of the slag, inhibit the oxidation loss of rare earth elements, and increase their recovery rate.

[0004] Rare earth elements (such as La, Ce, Y, etc.) have been widely introduced into special steels due to their unique deoxidation, desulfurization, and grain refinement effects. However, the high chemical activity of rare earths causes them to easily react with the components of the slag system during the electroslag process, forming oxides or sulfides, resulting in low element recovery rate and composition segregation, directly affecting the mechanical properties and stability of steel. To solve this problem, existing technologies have tried to add rare earth oxides to the premelted slag to regulate the slag-metal reaction equilibrium. For example, CN116219186A discloses a premelted slag containing 15% - 25% rare earth oxides, which inhibits the burning loss of active elements through a high proportion of rare earth components. However, it has significant defects: high-content rare earth oxides easily lead to fluctuations in the melting point of the slag system and abnormal increase in viscosity, thereby causing a decline in the stability of the electroslag process; at the same time, excessive rare earth oxides may exacerbate the problem of oxygen absorption in the slag pool, increase the oxygen content of the molten steel, and instead reduce the material purity. In addition, the high proportion of rare earth addition leads to a significant increase in the cost of the slag material, limiting its application in industrial production.

[0005] Another limitation of the existing premelted slag system is that the component design does not fully balance the desulfurization efficiency and process stability. Although the traditional CaF2-Al2O3-based slag system has the characteristic of low melting point, its desulfurization ability is limited; while the high-alkalinity CaO-based slag system can improve the desulfurization effect, but it is prone to surface defects of electroslag ingots due to poor fluidity. In addition, although the introduction of components such as SiO2 and MgO can adjust the physical properties of the slag system, the influence mechanism of their mass transfer behavior on rare earth elements is not clear, and it is difficult to achieve efficient control of the slag-metal interface reaction.

[0006] Therefore, there is an urgent need to develop a new type of electroslag premelted slag material, which can ensure high desulfurization efficiency and process stability, and at the same time, through optimizing the content of rare earth oxides and the synergistic effect of slag system components, achieve the efficient utilization of rare earth elements, and solve the problems of slag pool property fluctuation, cost increase and steel liquid oxygen increase caused by excessive introduction of rare earth in the existing technology. Summary of the Invention

[0007] The present invention aims to provide a premelted slag material for electroslag remelting and a preparation method thereof, which can improve the desulfurization, deoxidation and inclusion removal abilities of the slag material by optimizing the slag material composition and preparation process, so as to obtain steel ingots with high purity and high uniformity.

[0008] To achieve the above application purpose, the technical solutions adopted in the present application are as follows:

[0009] In the first aspect, the present invention provides a premelted slag material for electroslag remelting, and its components by weight percentage include: 40-60% of CaF2, 20-30% of CaO, 10-20% of Al2O3, 5-10% of SiO2, 1-5% of MgO, and 0.5-2% of rare earth oxide.

[0010] In the components of the above premelted slag material, the rare earth oxide is La2O3 or Ce2O3.

[0011] In the second aspect, the present invention provides a preparation method of the above premelted slag material for electroslag remelting, which specifically includes the following steps:

[0012] S1-1. Prepare raw materials according to the components of the above premelted slag material, and then mix the raw materials evenly by dry mixing;

[0013] S1-2. The mixed materials are melted, and after complete melting, they are refined to obtain molten slag materials;

[0014] S1-3. After the molten slag material is cooled, it is crushed into particles to obtain a premelted slag material for electroslag remelting.

[0015] In the above step S1-1, the purity of the raw materials is controlled to be ≥95%, and the particle size of the raw materials is 50-200 mesh.

[0016] In the above step S1-2, the smelting temperature is 1400°C to 1600°C, and the refining time is 1 to 2 hours.

[0017] In the above step S1-3, the molten slag material is air-cooled to room temperature, and the particle size of the crushed particles is 1 to 10 mm.

[0018] Thirdly, the present invention provides an application method of the above pre-molten slag material for electroslag remelting, which specifically includes the following steps:

[0019] S2-1. Add the above pre-molten slag material, introduce argon, and start the electroslag furnace after monitoring that the oxygen partial pressure meets the standard. Melt the pre-molten slag material to form a slag pool, and at the same time adjust the current and voltage to ensure that the slag is completely melted and there is no obvious splash;

[0020] S2-2. Enter the steady-state smelting stage, adjust the current and voltage of smelting to make the melting rate stable, and ensure that the smelting process proceeds smoothly;

[0021] S2-3. When the electrode is consumed to near the bottom, enter the feeding stage, gradually reduce the melting rate to 0 within 10 minutes, and then cut off the power to complete the smelting.

[0022] In the above step S2-1, control the actual oxygen content in the furnace to be lower than 500 ppm.

[0023] In the above step S2-1, the addition amount of the pre-molten slag material is calculated according to the thickness of the slag layer after melting required for actual production. The calculation formula is: addition amount of the pre-molten slag material = radius of the electroslag ingot 2 ×3.14×required thickness of the slag layer after melting×density of the liquid slag.

[0024] Furthermore, in the conventional production process, the slag density of 2670 kg / m 3 is usually used, the slag layer thickness is 0.07 m to 0.2 m, and the addition amount of the pre-molten slag material is calculated therefrom.

[0025] In the above step 2-2, the steady-state smelting stage needs to maintain an argon atmosphere, and control the real-time oxygen content in the furnace to be lower than 1000 ppm.

[0026] In the above step 2-2, control the smelting melting rate to be 1.0 to 1.2 kg / min.

[0027] Advantages of the present invention: The premelted slag provided by the present invention realizes efficient desulfurization by optimizing the ratio of CaF2 and CaO, significantly enhancing the desulfurization efficiency of the slag. At the same time, in the composition of the premelted slag of the present invention, SiO2 is appropriately incorporated, and the introduction of this component effectively improves the fluidity of the slag, making the fluidity of the slag pool better during the electroslag process, thereby improving the surface quality of the electroslag ingot. Using the premelted slag formula and its preparation process designed by the present invention, the produced slag has uniform composition and appropriate melting point, which can ensure the stable progress of the electroslag remelting process. In addition, due to the addition of trace rare earth oxides in the premelted slag, a certain activity of rare earth elements in the slag phase is maintained in the slag-metal equilibrium reaction during the electroslag process, thereby inhibiting the burning loss of rare earth elements in the molten steel. At the same time, some rare earth elements can enter the metal phase in trace amounts, thus achieving the effect of adding trace rare earth elements to the steel, which is beneficial to improving the solidification microstructure of the electroslag ingot.

[0028] By precisely controlling the addition amount of rare earth elements, the present invention not only realizes the purpose of inhibiting the burning loss of rare earth elements in the steel and adding trace rare earth elements to the steel, but also cleverly avoids the problems of unstable slag pool properties during the electroslag process caused by excessive addition of rare earth elements, as well as problems such as oxygen increase in the steel due to the transfer of oxygen from variable valence oxides to the steel. This premelted slag is suitable for the electroslag remelting process of various steels and alloys, especially for steel grades containing rare earth elements, such as rare earth die steel, high-carbon die steel, stainless steel, superalloys, etc., and has more significant application effects. Description of the Drawings

[0029] Figure 1 is the premelted slag sample prepared in the embodiment of the present invention;

[0030] Figure 2 are 50 kg electroslag ingots smelted in the embodiment (right) and the comparative example (left);

[0031] Figure 3 are the as-cast microstructures of the electroslag ingots smelted in the embodiment (right) and the comparative example (left). Detailed Embodiments

[0032] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer, the present invention will be further described in detail below in conjunction with the embodiments. Those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art. For those not specified in the embodiments, the techniques or conditions described in the literature in the art or according to the product specifications are followed. The reagents or instruments used without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0033] I. Preparation of premelted slag materials for electroslag remelting, specifically including the following steps:

[0034] (1) Prepare raw materials according to the composition of the premelted slag materials below, ensuring that the purity of the raw materials is ≥95%, and the particle size of the raw materials is 50 - 200 mesh; put the raw materials of the examples and comparative examples into a mixer respectively, and then mix the raw materials evenly by dry mixing.

[0035] Example: CaF2 50%, CaO 25%, Al2O3 15%, SiO2 7%, MgO 2%, La2O3 1%.

[0036] Comparative example: CaF2 70%, Al2O3 30%.

[0037] (2) Put the mixed materials of the examples and comparative examples into an electric arc furnace respectively, and carry out smelting at 1500 °C. After complete melting, continue refining for 1.5 hours to obtain molten slag materials.

[0038] (3) Pour the molten slag materials into a cooling tank, air-cool to room temperature and then crush them into particles with a particle size of 1 - 10 mm to obtain the premelted slag materials for electroslag remelting.

[0039] Among them, the premelted slag materials for electroslag remelting prepared in the example are as Figure 1 shown, in the form of particles with a size of 1 - 10 mm.

[0040] II. Application of the premelted slag materials for electroslag remelting in a 50 kg - class electroslag furnace, specifically including the following steps:

[0041] (1) Process the H13 steel into an electrode, ensuring that the surface of the electrode is clean and free of oil; introduce a protective atmosphere (such as argon) into the electroslag furnace to prevent the molten slag and metal from oxidizing.

[0042] (2) Slag melting stage: Take 3 kg of the premelted slag prepared in the above - mentioned example and comparative example respectively, and add them into the crucible. Turn on the protective atmosphere, introduce argon into the furnace, and monitor the oxygen partial pressure in the furnace in real - time. When the actual oxygen content in the furnace is lower than 500 ppm, start the electroslag furnace, gradually increase the current and voltage to melt the premelted slag and form a stable molten slag pool. Adjust the current and voltage to ensure that the molten slag is completely melted and there is no obvious splashing.

[0043] (3) Steady - state smelting stage: When the molten slag is completely melted, enter the steady - state smelting stage, maintain the argon atmosphere, and require that the real - time oxygen content in the furnace ≤1000 ppm. Control the smelting current and voltage to keep the melting rate within the range of 1.0 - 1.2 kg / min. Maintain a stable melting rate to ensure the smooth progress of the smelting process.

[0044] (4) Feeding stage: When the electrode is consumed to near the bottom, it enters the feeding stage. Within 10 minutes, the melting rate is gradually reduced to 0, and then the power is cut off to complete the smelting.

[0045] The compositions, surface qualities, and as-cast microstructures of the electroslag ingots prepared in the examples and comparative examples were detected; among them, the composition comparison of the electroslag ingots smelted in the examples and comparative examples is shown in Table 1; among them, when the La content is lower than 0.0005%, it is regarded as below the detection limit and no longer detected.

[0046] Table 1 Composition of electroslag ingots (in mass percentage, %)

[0047] Element Original H13 steel Comparative example Example C 0.38～0.42 0.39 0.40 Si 0.80～1.20 0.85 0.92 Mn 0.20～0.50 0.25 0.28 Cr 4.80～5.20 4.95 5.05 Mo 1.20～1.50 1.35 1.38 V 0.80～1.20 0.95 0.98 P ≤0.015 0.008 0.006 S ≤0.005 0.003 0.001 Al ≤0.040 0.025 0.018 La - <0.0005 0.023 O (ppm) 30～50 18 12

[0048] It can be seen from Table 1 that in the examples, the high content of CaO increased the basicity of the slag material, resulting in a better desulfurization effect. At the same time, due to the introduction of rare earth elements, 0.023% of La element was detected in the electroslag ingots of the examples. The electroslag ingots smelted with the slag of the examples achieved the purpose of better desulfurization effect and trace addition of rare earth elements.

[0049] The electroslag ingots smelted in the examples (right) and comparative examples (left) are as Figure 2 shown. It can be seen from the figure that the surface of the electroslag ingots obtained in the examples eliminated small pits, and compared with the electroslag ingots obtained in the comparative examples, its surface quality was significantly improved.

[0050] The as-cast microstructures of the electroslag ingots smelted in the examples (right) and comparative examples (left) are as Figure 3 shown. It can be seen from the figure that there are a large number of eutectic carbides in the as-cast microstructure of the electroslag ingots smelted in the comparative examples, while in the as-cast microstructure of the electroslag ingots smelted in the examples, due to the introduction of trace rare earth elements through the slag system, the eutectic carbides in the electroslag ingots were significantly reduced, significantly improving the as-cast microstructure of H13 die steel.

Claims

1. The premelted slag material for electroslag remelting, characterized in that, Its composition by weight percentage includes: 40 - 60% of CaF₂, 20 - 30% of CaO, 10 - 20% of Al₂O₃, 5 - 10% of SiO₂, 1 - 5% of MgO, and 0.5 - 2% of rare earth oxide.

2. The premelted slag material according to claim 1, wherein: Among its composition components, the rare earth oxide is La₂O₃ or Ce₂O₃.

3. Preparation method of premelted slag material for electroslag remelting, characterized in that, It includes the following steps: S1 - 1. Prepare raw materials according to the composition components of the premelted slag material described in any one of claims 1 - 2, and then mix the raw materials evenly by dry mixing; S1 - 2. Melt the mixed materials, and refine them after complete melting to obtain molten slag material; S1 - 3. After the molten slag material cools, crush it into particles to obtain the premelted slag material for electroslag remelting.

4. The preparation method according to claim 3, characterized in that: In step S1 - 1, control the purity of the raw materials ≥95%, and the particle size of the raw materials is 50 - 200 mesh.

5. The preparation method according to claim 3, characterized in that: In step S1 - 2, the melting temperature is 1400°C - 1600°C, and the refining time is 1 - 2 hours.

6. The preparation method according to claim 3, wherein: In step S1 - 3, the molten slag material is air - cooled to room temperature, and the particle size of the crushed particles is 1 - 10 mm.

7. The application method of the premelted slag material according to any one of claims 1 to 2, or the premelted slag material prepared by the preparation method according to any one of claims 3 to 6 in electroslag remelting, characterized in that, It includes the following steps: S2 - 1. Add the premelted slag material, introduce argon, and start the electroslag furnace after monitoring that the oxygen partial pressure meets the standard. Melt the premelted slag material to form a slag pool, and at the same time adjust the current and voltage to ensure that the slag is completely melted and there is no obvious splashing; S2 - 2. Enter the steady - state melting stage, adjust the current and voltage of melting to make the melting rate stable, and ensure the smooth progress of the melting process; S2 - 3. When the electrode is consumed to be close to the bottom, enter the feeding stage, gradually reduce the melting rate to 0 within 10 minutes, and then cut off the power to complete the smelting.

8. The application method according to claim 7, characterized in that: In step S2 - 1, the addition amount of the premelted slag material is calculated according to the thickness of the slag layer after melting required by actual production; control the actual oxygen content in the furnace to be lower than 500 ppm.

9. The application method according to claim 8, wherein The calculation formula for the addition amount of the premelted slag material is: the addition amount of the premelted slag material = the radius of the electroslag ingot 2 × 3.14 × the required thickness of the molten slag layer × the density of the liquid slag.

10. The application method according to claim 7, characterized in that: In step 2 - 2, the steady - state melting stage needs to maintain an argon atmosphere, control the real - time oxygen content in the furnace to be lower than 1000 ppm; control the melting rate to be 1.0 - 1.2 kg / min.

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