Low-reactivity continuous casting protective slag for high-rare earth content rare earth steel and preparation method thereof

Abstract

The present application relates to the technical field of steel continuous casting, and particularly relates to a low-reactivity continuous casting protective slag for rare earth steel with high rare earth content and a preparation method thereof. The continuous casting protective slag of the present application comprises the following components in terms of mass fraction: CaO 16-22%, SiO2 22-28%, Al2O3 4-5%, MgO 1-2%, Na2O 9-12%, F ‑ 18-20%, Ce2O3 5-20%, and C 6-8%, and the rest is inevitable impurities. The continuous casting protective slag of the present application has suitable melting temperature, viscosity and surface tension, and the addition of rare earth oxide Ce2O3 can effectively inhibit the reaction between the Ce element in the molten steel and the components of the protective slag, and can be well applied to the rare earth steel with the Ce content in the range of 0.02-0.03%. After use, the physicochemical properties of the protective slag remain stable, and the continuous casting process is effectively ensured to run smoothly and the surface quality of the casting blank is ensured.

Description

Technical Field

[0001] This invention relates to the field of continuous casting technology for steel, specifically to a low-reactivity continuous casting protective slag for rare earth steel with high rare earth content and its preparation method. Background Technology

[0002] With the continuous advancement of metallurgical technology, rare earth elements are increasingly used in steel. Research has found that rare earths play five major roles in steel, mainly manifested in: purifying molten steel, modifying inclusions, microalloying, refining grains, and dispersion strengthening. Research on the application of rare earths in steel mainly focuses on the following aspects: (1) Rare earth weathering steel varieties, including 09CuPTiRE, have high strength, weather resistance, and fire resistance properties, and are mainly used in container and building structural steel. (2) Adding rare earths during the production of medium and heavy plates, pipeline steel, thin plates, and cold-rolled plates can develop low-cost, high-value-added, and stable products. (3) Adding rare earths to heat-resistant steel and stainless steel can replace 0Cr25Ni20, 0Cr21Ni32AlTi, and Inconel601, greatly improving the heat resistance, oxidation resistance, and corrosion resistance of the materials. (4) By utilizing the interaction between rare earth elements and microalloying elements in steel, rare earth elements can be added to steel separately or together with microalloying elements such as V, Ti, and B, thereby improving the comprehensive mechanical properties of steel. (5) In silicon-manganese cast steel, adding rare earth elements to replace some alloying elements such as Mn and Ni can improve the plasticity and toughness of the steel.

[0003] Continuous casting protective slag is a powdery or granular slag material that covers the surface of molten steel in the continuous casting mold and maintains normal casting. It is an essential material in the continuous casting production process. During continuous casting, the protective slag forms a powdery slag layer, a sintered layer, and a liquid slag layer from top to bottom. It has metallurgical functions such as heat insulation, preventing secondary oxidation of molten steel by isolating air, absorbing non-metallic inclusions, lubrication, and controlling heat transfer. It is of great significance for ensuring the smooth operation of the continuous casting process and the surface quality of the cast billet.

[0004] Traditional continuous casting protective slag is mainly based on a ternary slag system of CaO-SiO2-Al2O3. The components of CaO, SiO2, and Al2O3 are mainly located in the low-melting-point region of wollastonite in the ternary phase diagram, such as... Figure 1 As shown. The composition is 30%–50% CaO, 30%–60% SiO2, and less than 20% Al2O3. The melting point range is between 1300 and 1500℃. In addition, some fluxing agents (such as Na2O, CaF2, K2O, B2O3, etc.) and melting rate regulators (such as carbonaceous materials graphite or carbon black) are added to reduce the melting temperature of the protective slag and adjust the melting rate of the protective slag, respectively.

[0005] However, the traditional silicate-based continuous casting powder is not suitable for the continuous casting production of rare earth steel, mainly because the rare earth elements in the molten steel are very active, and the content of SiO2, Al2O3 and other components in the conventional continuous casting powder is relatively high, and the oxidation is relatively strong. The rare earth elements in the molten steel are prone to react with the slag-metal interface, such as Figure 2 As shown in the standard Gibbs free energy of the reaction of rare earth Ce with CaO, SiO2 and Al2O3. The intense slag-metal interface reaction will produce a large amount of rare earth oxides into the protective slag, and at the same time, the rare earth inclusions produced in the molten steel will float to the slag-metal interface. With the increase of continuous casting furnace times, the physical and chemical properties and the use performance of the protective slag will change, the melting temperature will increase, the viscosity will increase, the lubricating slag film between the casting blank and the crystallizer will become thin, and even there is no slag in the local area, which seriously deteriorates the lubricity of the protective slag, and further causes the increase of the surface cracks of the casting blank, and even the occurrence of the sticking leakage. From the above analysis, the intense slag-metal reaction will cause the deterioration of the performance of the protective slag, affect and limit the normal play of its metallurgical function, and seriously affect the smooth running of the continuous casting process and the stability of the casting blank quality. Therefore, it is one of the problems to be solved to develop a low-reactivity continuous casting protective slag suitable for high-rare-earth-content rare earth steel.

[0006] At present, many studies believe that since the rare earth elements mainly react with SiO2 in the protective slag, many patents design and develop continuous casting protective slag for rare earth steel by changing the content of SiO2. Patent CN200810039377.2 proposes to continue to increase the content of the easily-reactive component SiO2 in the traditional silicate-based continuous casting protective slag, so that SiO2 can still maintain a high content after the slag-metal reaction, that is, the overall component change ratio is small. However, the casting effect of this solution is not good, because increasing the content of SiO2 increases its reaction trend with rare earth.

[0007] Patents CN201510016163.3, 201610427406.7 and the like propose to increase the basicity and reduce the content of the easily-reactive component SiO2 as much as possible to effectively inhibit the slag-metal reaction. This scheme reduces the content of SiO2 to the range of 2-10%, but due to the high content of CaO and Al2O3, the basicity of the protective slag is also greatly increased. The nucleation activation energy of the protective slag gradually decreases with the increase of the basicity, and the glass state is more likely to be converted into a crystalline state, which increases the amount of crystals and the crystallization rate, resulting in an increase in the thermal resistance of the slag film and a deterioration in the lubricity, which increases the probability of continuous casting leakage. At the same time, greatly reducing the content of SiO2 will make the protective slag lose its glassiness, which seriously affects the lubricating function of the protective slag, and is not conducive to the continuous casting production.

[0008] In summary, the design of the continuous casting protective slag of the above invention has certain defects: either cannot inhibit the slag-gold reaction and the deterioration of the physical and chemical properties of the protective slag caused thereby; or inhibits the slag-gold reaction by reducing the content of SiO2, but this method cannot guarantee the lubricity of the protective slag at the same time, and seriously affects the quality of the casting blank. Therefore, so far, there is still no continuous casting protective slag that can solve the above technical problems. SUMMARY

[0009] (1) Technical problems to be solved

[0010] In view of the above-mentioned defects and deficiencies of the prior art, the present application provides a low-reactivity continuous casting protective slag for high-rare earth content rare earth steel and a preparation method thereof. Through the component design of the continuous casting protective slag and the synergistic effect of each component, not only is the slag-gold reaction inhibited and the deterioration of the physical and chemical properties avoided, but also the lubricity of the protective slag is guaranteed, thereby reducing the surface quality problems of the casting blank.

[0011] (2) Technical solutions

[0012] In order to achieve the above-mentioned purposes, the main technical solutions adopted by the present application include:

[0013] In a first aspect, the present application provides a low-reactivity continuous casting protective slag for high-rare earth content rare earth steel, which comprises the following components in terms of mass fraction: CaO 16-22%, SiO2 22-28%, Al2O3 4-5%, MgO 1-2%, Na2O 9-12%, F - 18-20%, Ce2O3 5-20%, and C 6-8%, and the rest is inevitable impurities.

[0014] Preferably, the melting point of the continuous casting protective slag is 1112-1154℃; the viscosity at 1300℃ is 0.08-0.13 Pa·S; and the surface tension at 1400℃ is 0.367-0.373 N / m.

[0015] Preferably, in the continuous casting protective slag, when the content of Ce2O3 increases from 5% to 20%, at 1450℃, the activity of SiO2 decreases from 2.47×10 -2 to 1.25×10 -2 , the activity of Al2O3 decreases from 2.28×10 -2 to 1.79×10 -2 , and the activity of Ce2O3 increases from 1.44×10 -3 to 7.10×10 -3 .

[0016] Preferably, in the continuous casting protective slag, when the content of Ce2O3 increases from 5% to 20%, at 1550℃, the activity of SiO2 in the protective slag decreases from 2.35×10 -2 to 1.27×10-2 The activity of Al2O3 is reduced from 1.93*10 -2 to 1.51*10 -2 The activity of Ce2O3 is increased from 2.03*10 -3 to 1.0*10 -2 .

[0017] Preferably, the low reactivity continuous casting protective slag is used for the rare earth steel with Ce content in the range of 0.02-0.03%.

[0018] The CaO content is 16-22%.

[0019] Because the molten steel contains high Al element, a large amount of Al2O3 inclusions appear in the slag, and CaO is a network-breaking oxide, therefore, increasing the CaO content in the protective slag can increase the basicity of the protective slag, obviously reduce the viscosity of the protective slag, and improve the capacity of the protective slag to absorb the oxide inclusions in the steel. The high basicity protective slag can improve the speed of dissolving and absorbing the inclusions in the steel, but the viscosity of the basic slag changes greatly with temperature, and when cooled to the liquidus temperature, the strong crystallization capacity causes continuous crystallization, which can seriously damage the glassiness of the molten slag, hinder the realization of the function of the protective slag, and cause serious defects of the casting blank. Therefore, in order to not produce a large amount of crystals during the continuous casting of the rare earth steel, the content of CaO is controlled in the range of 16-22%.

[0020] The SiO2 content is 22-28%.

[0021] In the protective slag, SiO2 acts as a network former and plays a key role in the protective slag. Higher SiO2 increases the glassiness of the protective slag, ensures the smooth progress of the continuous casting process and the surface quality of the casting blank, but when the SiO2 content in the protective slag is too low, although the reactivity of the protective slag is reduced, the glassiness of the protective slag is also reduced. Although the SiO2 content in the present application is 22-28%, as a whole, Ce2O3 can increase the activity of the reaction product and reduce the activity of SiO2, so the activity of SiO2 is not high.

[0022] The Al2O3 content is 4-5%.

[0023] A large amount of Al2O3 entering the molten slag can easily generate high-melting-point calcium aluminum yellow longite (2CaO*Al2O3*SiO2) and nepheline (NaAlSiO4), which deteriorate the lubrication, increase the viscosity of the slag, and reduce the capacity of the protective slag to absorb inclusions, but it can reduce the freezing point of the protective slag, thereby improving the lubrication of the slag. The Al2O3 content in the present application is finally determined as 4-5%, and because the Na2O content in the molten slag is high, in order to prevent the generation of a large amount of high-melting-point crystalline phase nepheline and calcium aluminum yellow longite, the network structure formation at this time is mainly completed by SiO2.

[0024] The content of Na2O is 9-12%.

[0025] Na2O belongs to network outer oxide, can destroy silicate structure, mainly plays the role of reducing melting temperature, improving the fluidity of the protective slag, and the addition of proper Na2O is beneficial to reduce the activity of SiO2, and the replacement of part of CaO by Na2O which is a strong alkaline oxide can effectively reduce the activity of CaO. At this time, the network structure is mainly formed by SiO2. In the system of the present application, the content of Na2O is controlled to be 9-12%.

[0026] The content of F - is 18-20%.

[0027] F - in the protective slag is added in the form of CaF2, and CaF2 is used as a fluxing agent in the protective slag. Fluoride has a very important regulating effect on the high temperature performance of the protective slag, and mainly plays the role of reducing the melting temperature and improving the fluidity of the protective slag in the slag system. The appropriate F ion in the molten slag can promote the disintegration of the silicon-oxygen polymer, and the control of the F ion in the range of 18-20% can reduce the viscosity of the protective slag without affecting the glassiness of the protective slag. The addition of F ion makes the slag film have good heat transfer, which is beneficial to the smooth progress of the continuous casting process.

[0028] The content of MgO is 1-2%.

[0029] MgO replaces part of CaO and is added to the protective slag, which not only inhibits the precipitation of crystals, but also has obvious fluxing effect. As a fluxing agent in the protective slag of the present application, MgO mainly plays the role of reducing the melting temperature and improving the fluidity of the protective slag in the slag system. MgO also increases the surface tension of the protective slag and reduces the interfacial tension between the molten slag and the inclusions, which is beneficial to the wetting of the molten slag to the inclusions. With the increase of the mass fraction, the melting temperature of the continuous casting protective slag is obviously reduced, but too high content is easy to produce high melting point crystalline mineral phase. The content of MgO is controlled in the range of 1-2% in the present application.

[0030] The content of C is 6-8%.

[0031] Carbonaceous materials such as graphite, carbon black and coke powder are used as melting rate adjuster to adjust the melting structure and melting rate of the protective slag, and the content of C is controlled at 6-8%. Carbon is a high-temperature resistant material, and the extremely fine carbon powder is adsorbed around the slag particles to separate the slag particles from each other, hinder the contact and fusion between the slag materials, and slow down the melting rate. If the amount of the added carbon powder is insufficient, the carbon particles are burnt out before the slag layer reaches the sintering temperature of the slag materials, and the sintering layer is developed and the melting rate is too fast, and the liquid slag layer is too thick. If the amount of the added carbon powder is excessive, some carbon particles exist after the slag materials are completely melted, and the sintering layer is shrunk and the thickness of the sintering layer is too thin. When the amount of the added carbon powder is moderate, some carbon particles are burnt out and the rest of the slag materials are effectively controlled by the carbon particles, and thus the sintering layer and the liquid slag layer with appropriate thickness are obtained.

[0032] In the second aspect, the application further provides a preparation method of the low-reactivity continuous casting protective slag for high-rare earth content rare earth steel, comprising the following steps:

[0033] S1, taking limestone, quartz sand, bauxite, magnesite, sodium carbonate, nepheline, ceria and carbonaceous material as raw materials, calculating the amount of each raw material according to the percentage content of the components of the protective slag, and weighing each raw material according to the calculated amount;

[0034] S2, mixing the weighed limestone, quartz sand, bauxite, magnesite, sodium carbonate, nepheline and ceria in S1, heating to 1410℃ for pre-melting, Na2CO3 is decomposed into Na2O, and then performing water quenching, drying and dehydrating, crushing and screening and other treatments to obtain a powdery water-quenched slag;

[0035] S3, mixing the carbonaceous material with the powdery water-quenched slag uniformly to obtain the low-reactivity continuous casting protective slag for high-rare earth content rare earth steel.

[0036] Preferably, in S1, each raw material meets the following requirements: CaCO3 in limestone > 95%; SiO2 in quartz sand > 95%; Al2O3 in bauxite > 75%, SiO2 < 4%; MgO in magnesite > 85%, SiO2 < 6%, Al2O3 < 2%; Na2CO3 in sodium carbonate > 95%; CaF2 88-90% in nepheline, SiO2 < 6.0%, S < 0.05%; Ce2O3 in ceria > 99%; C in carbonaceous material > 95%.

[0037] The technical principle of the component formula of the continuous casting protective slag of the application is as follows:

[0038] The content of CaO is controlled in 16-22%, which is used to provide basicity to absorb inclusions. The content of SiO2 is controlled in 22-28%, which is used as a network former and plays a key role in the protection slag. In the content range, the protection slag has good glassiness, which ensures the smoothness of the continuous casting process and the surface quality of the casting blank. MgO, Na2O and CaF2 are fluxing agents in the protection slag of the application, which mainly plays a role in reducing the melting temperature and improving the fluidity of the protection slag in the slag system. In addition, the addition of 5-20% Ce2O3 to the protection slag can increase the activity of the reaction product, reduce the activity of SiO2 and Al2O3, and make the Gibbs free energy of the reaction larger, thereby effectively reducing the reaction between rare earth and the protection slag. The reaction equation between the above-mentioned rare earth and SiO2 and Al2O3 in the protection slag is:

[0039] (1) [Ce]+3 / 4(SiO2)=1 / 2(Ce2O3)+3 / 4[Si]

[0040] ΔG1 is the Gibbs free energy of the reaction;

[0041] (2) [Ce]+1 / 2(Al2O3)=1 / 2(Ce2O3)+[Al]

[0042] ΔG2 is the Gibbs free energy of the reaction.

[0043] In the formula, a ce , a si , a Al are the activities of Ce, Si and Al in the molten steel respectively, a Ce2O3 , a SiO2 , a Al2O3 are the activities of Ce2O3, SiO2 and Al2O3 in the slag respectively. The present patent is based on the theory of coexistence of molecular ions of molten slag, and establishes the equilibrium constant equation of each reaction for the CaO-SiO2-Al2O3-Na2O-CaF2-MgO-Ce2O3 seven-component slag system. According to the law of conservation of mass, the activity calculation model of the protection slag is established, and then the nonlinear equation set is solved by Matlab programming. Through calculation, it is found that the activities of SiO2 and Al2O3 in the protection slag are low, the Gibbs free energy change of the reaction of Ce with SiO2 and Al2O3 is large, and the trend of reaction with rare earth Ce is obviously reduced.

[0044] (III) Beneficial effects

[0045] The beneficial effects of the application are:

[0046] (1), The protective slag of the present application has the characteristics of ensuring the glassiness and low activity of the protective slag, thereby being suitable for large batch continuous casting production of rare earth steel. Specifically, the SiO2 content in the protective slag is 22-28%, which can effectively ensure the glassiness of the protective slag, but as a whole, Ce2O3 can increase the activity of the reaction product and reduce the activity of SiO2, so the activity of SiO2 is not high, which effectively inhibits the slag-gold reaction.

[0047] (2), The effective cooperation of 4-5% Al2O3 and 9-12% Na2O in the protective slag can avoid the formation of a large amount of high-melting-point crystalline phase nepheline and calcium aluminum yellow long stone, and can also reduce the freezing point of the protective slag, thereby improving the lubrication of the slag.

[0048] (3), In the condition of mutual cooperation of multiple components, the content of Ce2O3 can increase the activity of the reaction product, reduce the activity of SiO2 and Al2O3, and make the Gibbs free energy change of rare earth and SiO2 and Al2O3 in the protective slag larger, thereby effectively reducing the reaction between rare earth and the protective slag, thereby inhibiting the rare earth burning loss caused by the reaction of the steel slag, and in this range, the physicochemical properties of the post-protective slag are good, the burning loss inhibition effect is good, the low-reactivity continuous casting protective slag for high-rare-earth-content rare earth steel is ensured to be continuous, the surface quality of the casting blank is good, and excellent technical effects are achieved. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 is the ternary system phase diagram of CaO-SiO2-Al2O3;

[0050] Figure 2 is the possible reaction of rare earth Ce and CaO-Al2O3-SiO2 system. DETAILED DESCRIPTION

[0051] In order to better explain the present application, the present application is described in detail below in combination with specific examples and comparative examples.

[0052] In the embodiment of the present application, a melting point and melting rate tester (hemisphere method) is used to test the melting point.

[0053] In the embodiment of the present application, a high-temperature melt physical property comprehensive tester (rotating cylinder method) is used to test the viscosity.

[0054] In the embodiment of the present application, a surface tension prediction model established by a modified Butler equation is used to calculate the surface tension.

[0055] In the embodiment of the present application, an activity calculation model established by a molecular ion coexistence theory and Matlab software are used to calculate the activity of the related components in the protective slag.

[0056] Table 1 is the content of each component of the protective slag of the specific embodiments 1-4 of the present application and the physical and chemical properties.

[0057] Table 1

[0058]

[0059] As shown in the above table, the melting point, viscosity and surface tension of the crystallizer protective slag of the present application are reasonable, which can make the protective slag have good lubricating effect in the crystallizer. The slags of Examples 1-4 in the table are applied to rare earth steel grades with Ce content in the range of 0.02-0.03%. The pouring temperature is 1550℃, and the results show that: the protective slags in Examples 1-4 have good liquid surface conditions in the crystallizer during the casting process, the continuous casting furnace number is ≥3, compared with Comparative Example 1, the rare earth yield of the steel liquid in Examples is increased by 4%, 6%, 9% and 11% respectively, at the same time, the physical and chemical properties of the protective slag remain stable, the surface quality of the casting blank is good, and the continuous casting process is effectively ensured.

[0060] In Example 1, the melting temperature is 1112℃, the viscosity at 1300℃ is 0.091 Pa·S; the surface tension at 1400℃ is 0.367 N / m, the activity of SiO2 of the protective slag at 1450℃ is 2.47×10 -2 , the activity of Al2O3 is 2.28×10 -2 , and the activity of Ce2O3 is 1.44×10 -3 ; the activity of SiO2 at 1550℃ is 2.35×10 -2 , the activity of Al2O3 is 1.93×10 -2 , and the activity of Ce2O3 is 2.03×10 -3 .

[0061] In Example 2, the melting temperature is 1124℃, the viscosity at 1300℃ is 0.098 Pa·S; the surface tension at 1400℃ is 0.369 N / m, the activity of SiO2 of the protective slag at 1450℃ is 2.01×10 -2 , the activity of Al2O3 is 2.14×10 -2 , and the activity of Ce2O3 is 3.05×10 -3 ; the activity of SiO2 at 1550℃ is 1.95×10 -2 , the activity of Al2O3 is 1.81×10 -2 , and the activity of Ce2O3 is 4.31×10 -3 .

[0062] The melting temperature thereof is 1138℃, the viscosity at 1300℃ is 0.11 Pa·S, the surface tension at 1400℃ is 0.371 N / m, the activity of SiO2 at 1450℃ is 1.60×10 -2 , the activity of Al2O3 is 1.97×10 -2 , and the activity of Ce2O3 is 4.90×10 -3 ; the activity of SiO2 at 1550℃ is 1.58×10 -2 , the activity of Al2O3 is 1.66×10 -2 , and the activity of Ce2O3 is 6.93×10 -3 .

[0063] The melting temperature thereof is 1154℃, the viscosity at 1300℃ is 0.12 Pa·S, the surface tension at 1400℃ is 0.373 N / m, the activity of SiO2 at 1450℃ is 1.25×10 -2 , the activity of Al2O3 is 1.79×10 -2 , and the activity of Ce2O3 is 7.10×10 -3 ; the activity of SiO2 at 1550℃ is 1.27×10 -2 , the activity of Al2O3 is 1.51×10 -2 , and the activity of Ce2O3 is 1.0×10 -2 .

[0064] Table 2 below is the content of each component and the physicochemical properties of the protective slag of Comparative Examples 1-4. In Comparative Example 1, no Ce2O3 is contained (blank comparison), in Comparative Example 2, the mass percentage of Ce2O3 is 4, in Comparative Example 3, the mass percentage of Ce2O3 is 22, and in Comparative Example 4, the mass percentage of Ce2O3 is 30.

[0065] Table 2

[0066]

[0067]

[0068] As shown in Table 2, the viscosity and melting temperature of the comparative examples 3 and 4 of the present application increase sharply, and the physical and chemical properties are unreasonable, which do not meet the requirements of continuous casting production. The slag of the comparative examples 1-4 in the table is applied to the rare earth steel with Ce content in the range of 0.02-0.03%. The pouring temperature is 1550℃, and the results show that: a large amount of solid condensate is generated at the slag-melt interface of the comparative examples 1 and 2, and the continuous casting process cannot proceed smoothly, and the surface quality of the casting blank is poor. Compared with comparative example 1, the rare earth yield of the molten steel in comparative example 2 is increased by 3%. The solid condensate at the interface of comparative examples 3 and 4 is less, and the continuous casting process is relatively smooth, and the surface quality of the casting blank is general and the physical and chemical properties are unstable. Compared with comparative example 1, the rare earth yield of the molten steel in comparative examples 3 and 4 is increased by 12%. Therefore, when the amount of Ce2O3 exceeds 20%, the inhibiting effect is no longer obvious. In summary, the mass percentage of Ce2O3 in the low-reactivity continuous casting protective slag for high-rare earth content rare earth steel of the present application is higher than 20% or lower than 5%, and the ideal technical effect cannot be obtained.

[0069] The protective slag of each of the above examples and comparative examples is prepared by the following method:

[0070] S1, limestone, quartz sand, bauxite, magnesia, sodium carbonate, nepheline, ceria, and carbonaceous material are used as raw materials, the amount of each raw material is calculated according to the percentage content of the components of the protective slag, and each raw material is weighed according to the calculated amount, wherein Na2CO3 is weighed according to the required amount of Na2O;

[0071] S2, the limestone, quartz sand, bauxite, magnesia, sodium carbonate, nepheline, and ceria materials weighed in S1 are mixed, heated to 1410℃ for pre-melting, Na2CO3 is decomposed into Na2O, and then the water-quenched slag is obtained after water quenching, drying and dehydrating, crushing and sieving, etc.

[0072] S3, the carbonaceous material is mixed with the powdered water-quenched slag to obtain the low-reactivity continuous casting protective slag for high-rare earth content rare earth steel.

[0073] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, but not to limit them; although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that: the technical solutions recorded in the above examples can still be modified, or some or all of the technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A low reactivity continuous casting protective slag for a high rare earth content rare earth steel, characterized by, comprising by mass fraction: CaO 16-22%, SiO2 22-28%, AI2O3 4-5%, MgO 1-2%, Na2O 9-12%, F - 18-20%, Ce2O3 5-20% and C 6-8%, the remainder being inevitable impurities.

2. The low reactivity continuous casting protective slag for high rare earth content rare earth steel according to claim 1, characterized by, The melting point range of the protective slag is 1112-1154℃; the viscosity range at 1300℃ is 0.08-0.13Pa·S; the surface tension at 1400℃ is 0.367-0.373N / m.

3. The low reactivity continuous casting protective slag for high rare earth content rare earth steel according to claim 1, characterized by, F in the protective slag - was added to the protective slag in the form of CaF2.

4. The low reactivity continuous casting protective slag for high rare earth content rare earth steel according to claim 1, characterized by, The activity of SiO2 in the protective slag is 2.47*10 -2 ~1.25*10 -2 at 1450℃, the activity of Al2O3 is 2.28*10 -2 ~1.79*10 -2 , the activity of Ce2O3 is 1.44*10 -3 ~7.10*10 -3 .

5. The low reactivity continuous casting protective slag for high rare earth content rare earth steels according to claim 1, characterized in that, The activity of SiO2 in the protective slag is 2.35 x 10 -2 ~ 1.27 x 10 -2 at 1550°C, the activity of Al2O3 is 1.93 x 10 -2 ~ 1.51 x 10 -2 , the activity of Ce2O3 is 2.03 x 10 -3 ~ 1.0 x 10 -2 .

6. The low reactivity continuous casting protective slag for high rare earth content rare earth steels according to claim 1, characterized in that, The low-reactivity continuous-casting protective slag is used for rare earth steel grades with Ce content in the range of 0.02-0.03%.

7. A method for producing a low-reactivity continuous casting protective flux for high-rare earth content rare earth steels as claimed in any one of claims 1 to 6, characterized in that, The method comprises the following steps: S1, taking limestone, quartz sand, bauxite, magnesia, sodium carbonate, nepheline, ceria, and carbonaceous material as raw materials, calculating the amount of each raw material according to the percentage content of the components of the protective slag according to any one of claims 1-6, and weighing each raw material according to the calculated amount; S2, mixing the weighed limestone, quartz sand, bauxite, magnesia, sodium carbonate, nepheline, and ceria materials in S1, heating to 1410℃ for pre-melting, decomposing Na2CO3 into Na2O, and then sequentially performing water quenching, drying and dehydrating, crushing and sieving to obtain a powdery water-quenched slag; S3, uniformly mixing the carbonaceous material with the powdery water-quenched slag to obtain the low-reactivity continuous-casting protective slag for rare earth steel with high rare earth content.

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