A rare earth-containing additive

Abstract

The invention discloses a rare earth-containing additive, which comprises rare earth metal and iron, wherein the content of the rare earth metal is 5wt% to 90wt%, and the content of the iron is 10wt% to 95wt%; the density of the additive is 6.3g / cm 3 ~8.4g / cm 3 , melting point is 850℃~1450℃, oxygen content is ≤150ppm, maximum size of inclusions is ≤35μm, total inclusions are ≤0.5wt%. By adjusting the density, melting point and shape of additives containing rare earth and iron, the applicable composition window of additives is increased, the speed of additives added to molten steel through the upper slag layer is increased, the viscous resistance of molten steel to additives is effectively reduced, the influence of slag layer is eliminated, the depth of rare earth additives is increased, and the depth of additives is effectively increased, thereby improving the rare earth yield and distribution uniformity.

Description

Technical Field

[0001] The invention relates to the technical field of metal material alloy preparation, and in particular to an additive containing rare earth. Background Art

[0002] Rare earths have the functions of purifying molten steel, refining grains, modifying inclusions and microalloying in steel. Adding rare earths to steel is an effective way to improve the quality of steel. However, because existing rare earth additives cannot meet application requirements, rare earths have not yet been widely used in the steel industry. The main reasons are as follows: (1) The active chemical properties of rare earths make it difficult to control the oxygen content in rare earth master alloy additives. Oxygen exists in the rare earth additives in the form of large-sized rare earth oxides. The above rare earth oxide inclusions will cause nozzle blockage during the casting process of rare earth steel, affecting the industrial continuous production of rare earth steel; (2) The melting point and density of the rare earth master alloy additives are very different from those of the molten steel. The rare earth master alloy can only be added to the upper part of the molten steel. After melting, the slag-metal reaction occurs, which greatly reduces the rare earth yield; (3) The shape of the rare earth master alloy additives is mostly regular rectangular or irregular blocks. Due to their own buoyancy and the viscous resistance of the molten steel, they cannot be added to the effective depth of the ladle away from the slag layer, affecting the uniformity of rare earth distribution and the yield.

[0003] In order to reduce the rare earth activity in rare earth additives and the difference between the melting point and density of rare earth additives and molten steel, the commonly used method is to increase the iron content in rare earth iron intermediate alloy additives. However, since its density and melting point cannot exceed that of molten steel, the yield and position depth of rare earth additives in molten steel have improved, but the effect is still not ideal, and there is a problem of too narrow applicable composition window. At the same time, a large increase in iron content will also lead to an increase in the amount of rare earth additives required, which will have an adverse effect on the temperature of molten steel and the compactness of various metallurgical links.

[0004] In order to improve the rare earth addition position, the ladle press method was invented. The above method uses steel plates to weld iron boxes, puts rare earth alloy additives in the box, and uses a crane to press it into the molten steel in the ladle. Although this method avoids the influence of the slag layer and makes the addition position controllable, it has problems such as complex equipment, cumbersome addition process, short life of the iron box and pollution to the molten steel. Summary of the invention

[0005] The purpose of the embodiment of the present invention is to provide a rare earth-containing additive. By regulating the density, melting point and shape of the additive containing rare earth and iron, the applicable composition window of the additive is increased, the speed at which the additive is added to the molten steel through the upper slag layer is increased, the viscous resistance of the molten steel to the additive is effectively reduced, the influence of the slag layer is eliminated, the input depth of the rare earth-containing additive is increased, the addition depth of the additive is effectively increased, and the rare earth yield and distribution uniformity are thereby improved.

[0006] To solve the above technical problems, a first aspect of an embodiment of the present invention provides a rare earth-containing additive, comprising: a rare earth metal and iron, wherein the content of the rare earth metal is 5wt% to 90wt%, and the content of the iron is 10wt% to 95wt%;

[0007] The density of the additive is 6.3 g / cm 3 ~8.4g / cm 3 , melting point is 850℃~1450℃, oxygen content is ≤150ppm, maximum size of inclusions is ≤35μm, and total amount of inclusions is ≤0.5wt%.

[0008] Further, the additive comprises: a first part and a second part formed integrally;

[0009] One end of the first part away from the second part is a hemispherical, cylindrical or parabolic structure;

[0010] The cross section of the connecting end of the second part and the first part is circular or elliptical;

[0011] The maximum dimension of any cross section of the second portion is smaller than the maximum dimension of the cross section of the connecting end of the first portion and the second portion.

[0012] Further, one end of the first part away from the second part is a hemispherical or parabolic structure;

[0013] The edge point coordinates of the axial cross section of the first part satisfy the following formula:

[0014]

[0015] Among them, x is the X-axis coordinate value of the first part along the axial direction, y is the Y-axis coordinate value perpendicular to the axial direction, the coordinate origin is the vertex of the first part away from the second part, n is the taper control factor of the first part of the additive, when n=0, the first part is a cylinder, when n=1, the first part is a cone, the value range of n is 0<n<1, and L is the length value of the additive along the axial direction.

[0016] Furthermore, the value range of n is 0.7<n<1.

[0017] Further, the ratio of the length L1 of the first portion along the axial direction of the cross section to the total length L of the additive is: 0.5≤L1 / L≤1;

[0018] The cross-sectional radius R of one end of the first part close to the second part has a value range of 1.5 cm to 24 cm, and the cross-sectional radius L has a value range of 3 cm to 48 cm.

[0019] Furthermore, a shell is provided outside the additive, and the shape of the shell matches the shape of the additive;

[0020] The iron content of the shell is greater than 95wt% and less than 99.9wt%, the thickness of the shell is 0.5cm to 4cm, the melting point is 1500℃ to 1538℃, and the density is 7.6g / cm 3 ~8.6g / cm 3 .

[0021] Furthermore, the additive further comprises: a transition metal, wherein the transition metal comprises: at least one of nickel, chromium, tungsten, molybdenum, cobalt, manganese, vanadium, niobium and titanium;

[0022] The content of the transition metal is 0.1wt% to 15wt%, the content of the rare earth metal is 15wt% to 70wt%, and the content of iron is 20wt% to 70wt%;

[0023] The density of the additive is 7.2 g / cm 3 ~8.2g / cm 3 , melting point is 1000℃~1300℃, oxygen content ≤100ppm, carbon content ≤300ppm, maximum size of inclusions ≤25μm, total amount of inclusions ≤0.1wt%.

[0024] Furthermore, the transition metal includes at least one of chromium, tungsten, molybdenum, vanadium, niobium and titanium.

[0025] Further, the rare earth metal includes at least one of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium;

[0026] Preferably, the rare earth metal includes at least one of lanthanum, cerium and yttrium.

[0027] The above technical solution of the embodiment of the present invention has the following beneficial technical effects:

[0028] 1. The additive prepared by this patent has the advantages of low oxygen, small total amount and size of inclusions, which can effectively reduce the introduction of foreign rare earth oxide inclusions in steel and alleviate nozzle blockage;

[0029] 2. Through the optimization of the composition design of rare earth, iron and transition group micro-alloying elements in the additive, the rare earth additive has a suitable density and melting point, and the rare earth and the main transition group micro-alloying elements in steel are added simultaneously and the depth of additive addition is effectively increased, thereby improving the rare earth yield and distribution uniformity;

[0030] 3. According to the melting point, density and other characteristics of rare earth additives, a reasonable rare earth additive shape is designed, which can effectively reduce the viscous resistance of molten steel to the additives, get rid of the influence of slag layer, increase the input depth of rare earth additives, promote a significant improvement in rare earth yield and uniformity indicators, and also increase the applicable composition window range of the intermediate alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a cross-sectional view of a rare earth-containing additive provided in an embodiment of the present invention.

[0032] Reference numerals:

[0033] 1. Part 1, 2. Part 2. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0035] Please refer to Figure 1 The first aspect of the embodiment of the present invention provides a rare earth-containing additive, comprising: a rare earth metal and iron, wherein the content of the rare earth metal is 5wt% to 90wt%, and the content of iron is 10wt% to 95wt%; the density of the additive is 6.3g / cm 3 ~8.4g / cm 3 , melting point is 850℃~1450℃, oxygen content is ≤150ppm, maximum size of inclusions is ≤35μm, and total amount of inclusions is ≤0.5wt%.

[0036] The above-mentioned additives are used to replace the existing rare earth iron additives, ladle blowing powder, ladle pressing method, and feeding rare earth wire method as additives used in steelmaking. By adjusting the density, melting point, and shape of the additives containing rare earths and iron, the speed at which the additives are added to the molten steel through the upper slag layer is increased, the viscous resistance of the molten steel to the additives is effectively reduced, the influence of the slag layer is eliminated, the input depth of the rare earth-containing additives is increased, the addition depth of the additives is effectively increased, and the rare earth yield and distribution uniformity are thereby improved.

[0037] Specifically, the rare earth metal in the additive includes at least one of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium; preferably, the rare earth metal includes at least one of lanthanum, cerium and yttrium. Lanthanum, cerium and yttrium have the advantages of modifying inclusions, refining grains, improving mechanical properties and corrosion resistance for steel materials.

[0038] Furthermore, the additive also includes: transition metals. The transition metals include: at least one of nickel, chromium, tungsten, molybdenum, cobalt, manganese, vanadium, niobium, and titanium; the content of the transition metals is 0.1wt% to 15wt%, the content of the rare earth metals is 15wt% to 70wt%, and the content of iron is 20wt% to 70wt%; the density of the additive is 7.2g / cm 3 ~8.2g / cm 3 , melting point is 1000℃~1300℃, oxygen content ≤100ppm, carbon content ≤300ppm, maximum size of inclusions ≤25μm, total amount of inclusions ≤0.1wt%.

[0039] The technical solution of the present invention optimizes the composition design of rare earth, iron and transition group microalloying elements in the additive, so that the rare earth additive has a suitable density and melting point, and realizes the simultaneous addition of rare earth and main transition group microalloying elements in steel.

[0040] Preferably, the transition metal includes at least one of chromium, tungsten, molybdenum, vanadium, niobium and titanium. Chromium, tungsten, molybdenum, vanadium, niobium and titanium have the best solid solution strengthening and precipitation strengthening effects on steel materials, and can effectively improve the room temperature / high temperature mechanical properties of steel materials.

[0041] In a specific embodiment of an embodiment of the present invention, the additive includes: a first part and a second part that are integrally formed; the end of the first part away from the second part is a hemispherical, cylindrical or parabolic structure; the cross-section of the connecting end of the second part and the first part is circular or elliptical; the maximum dimension D of any cross-section of the second part is smaller than the maximum dimension 2R of the cross-section of the connecting end of the first part and the second part.

[0042] According to the melting point, density and other inherent characteristics of rare earth additives, by adopting a hemispherical, cylindrical or parabolic structure, the shape of the additive is made more reasonable, effectively reducing the viscous resistance of molten steel to the additive, getting rid of the influence of the slag layer, increasing the input depth of the rare earth additive, promoting a significant improvement in the rare earth yield and uniformity indicators, and also increasing the applicable composition window range of the intermediate alloy.

[0043] It fundamentally solves the problem of effective addition of rare earths in the steelmaking process.

[0044] Furthermore, one end of the first part away from the second part is a hemispherical or parabolic structure; the edge point coordinates of the axial cross section of the first part satisfy the following formula:

[0045]

[0046] Among them, x is the X-axis coordinate value of the first part along the axial direction, y is the Y-axis coordinate value perpendicular to the axial direction, the coordinate origin is the vertex of the first part away from the end of the second part, n ranges from 0<n<1, and L is the length value of the additive along the axial direction.

[0047] Furthermore, the value range of n is 0.7<n<1. The ratio of the length L1 of the first part along the axial direction of the cross section to the total length L of the additive is: 0.5≤L1 / L≤1; the value range of the cross-sectional radius R of the end of the first part close to the second part is 1.5cm~24cm, and the value range of L is 3cm~48cm.

[0048] Under the above ratio, the first part of the additive becomes sharper and has a larger weight share. After the additive with this shape is added to the molten steel, due to its excellent fluid mechanics shape design, it has smaller viscous resistance and floating profit, and can quickly enter the middle and lower middle parts of the ladle, ensuring that the rare earth elements are added evenly and the yield is higher.

[0049] Furthermore, a shell is provided outside the additive, and the shape of the shell matches the shape of the additive; the iron content of the shell is greater than 95wt% and less than 99.9wt%, the thickness of the shell is 0.5cm to 4cm, the melting point is 1500℃ to 1538℃, and the density is 7.6g / cm 3 ~8.6g / cm 3 .

[0050] First, the outer iron alloy has a higher melting point and density than the internal rare earth and iron additives, which can better protect the internal rare earth additives and facilitate the storage and transportation of rare earth additives. In addition, the outer iron alloy can prevent the rare earth loss caused by the reaction between the internal rare earth additives and the slag layer on the surface of the molten steel. Secondly, according to the melting point, density and other inherent characteristics of the internal rare earth additives, the use of a suitable outer shell shape can effectively reduce the viscosity resistance of the molten steel to the additives, increase the depth of rare earth additives, promote a significant increase in rare earth yield and uniformity indicators, and also increase the applicable composition window range of the intermediate alloy.

[0051] The following describes the test values ​​obtained by the additive under different rare earth contents, different iron contents, different transition metal element contents, different shapes, and with or without a shell in several embodiments to determine the physical properties of the rare earth-containing additive, as shown in Table 1.

[0052] Table 1

[0053]

[0054]

[0055] Table 2 shows two comparative examples of commercially available ferrocerium alloy (Ce: 5wt%, Fe: 95wt) and ferroydtrium alloy (Y: 5wt%, Fe: 95wt), and their physical properties are shown in Table 2 below:

[0056] Table 2

[0057]

[0058] Correspondingly, an embodiment of the present invention further provides a method for preparing a rare earth-containing additive, which is used to prepare the above-mentioned rare earth-containing additive. Specifically, the additive can be prepared by the following three methods.

[0059] (1) Molten salt electrolysis

[0060] Iron and transition metal elements are made into alloy rods, which serve as high-melting-point iron alloy consumable cathodes.

[0061] Rare earth fluoride and lithium fluoride are placed inside the electrolytic cell as molten salt, and the high melting point iron alloy consumable cathode and graphite anode are conductive through the molten salt. During electrolysis, direct current is connected through the cathode and anode, and the electrolytic raw material rare earth oxide is added to the electrolytic molten salt through the upper opening of the electrolytic cell. The electrolysis temperature is (T m +50)℃~(T m +100)℃,T m The melting point of rare earth-containing additives. The cathode current density is less than 8A / cm 2 Under the action of direct current, an electrochemical reaction occurs, and the formed rare earth additive alloy drips from the cathode surface into the crucible at the bottom of the electrolytic cell.

[0062] (2) Thermal reduction method

[0063] The raw materials are rare earth fluoride, iron block, transition metal and reducing agent calcium particles, wherein the reducing agent dosage is 105% to 120% of the theoretical value. The raw materials are vacuum dehydrated at 400°C for 2 hours. The dehydrated raw materials are mixed by a mixer and then loaded into a heating furnace. Vacuum and wash the furnace with argon gas, and then pass argon gas to 20000Pa-80000Pa to reduce the volatilization of volatile elements. Heat to (T m +50)℃~(T m +150)℃,T m The melting point of the rare earth-containing additive is 2-10 hours of constant temperature, and then the slag is removed, and the power is turned off and the casting is cooled to room temperature with the furnace to obtain the rare earth-containing additive.

[0064] (3) Melt matching method

[0065] The raw materials are pure rare earth metals, iron blocks and transition metals, which are proportioned according to the target content of each element in the rare earth-containing additives. The iron blocks and transition elements are placed in the crucible of the medium frequency furnace, and the pure rare earth metals are placed in the medium frequency furnace feed trough. The medium frequency furnace is powered on and heated to the melting temperature (T m +50)~(T m +150)℃,T m The furnace atmosphere can be vacuum or atmosphere protection. The pressure in the furnace during vacuum melting is 10 -8 ~10Pa, and the pressure in the furnace during atmosphere melting is 10000Pa~110000Pa. After the iron and transition metal raw materials in the crucible are melted, the rare earth metal in the trough is added, and the rare earth-containing additive alloy melt is obtained after heat preservation and refining. The alloy solution is cast into a mold and cooled with the furnace to obtain a rare earth-containing additive.

[0066] The preparation process of the above additives is described in detail below with reference to several embodiments:

[0067] Embodiment 1:

[0068] Rare earth metal yttrium and pure iron are prepared according to the mass percentage of 5% and 95% respectively. Put the pure iron raw material into the crucible of the vacuum induction melting furnace, and put the rare earth metal yttrium into the material trough of the vacuum induction melting furnace; fill with high-purity argon gas, and when the vacuum degree in the furnace is maintained at 70000Pa, heat it to 1600℃. When the metal in the crucible is melted, add rare earth metal cerium to the molten metal through the material trough, and refine it for 10 minutes after it is melted. Finally, pour the alloy solution into a spherical mold with a radius of 10cm, and cool it with the furnace under the protection of the argon atmosphere in the furnace. The ferrocerium additive in this embodiment has a spherical shape with a radius of 10cm, a density of 7.7g / cm3, and a melting point of 1450℃.

[0069] Comparative Example 1:

[0070] Comparative Example 1 is a commercially available ferrocerium alloy (Ce: 5wt%, Fe: 95wt), which is in the shape of a square block with a side length of 10 cm, a density of 7.8g / cm3, and a melting point of 1500°C.

[0071] Comparative Example 2:

[0072] Comparative Example 2 is a commercially available yttrium-iron alloy (Y: 5wt%, Fe: 95wt), which has an irregular shape with an equivalent diameter of 10cm, a density of 7.7g / cm3, and a melting point of 1450°C.

[0073] The yttrium-iron alloy of Example 1 and the commercially available ferrocerium and yttrium-iron additives of Comparative Examples 1-2 were used as rare earth additives and added into a ladle with a molten steel depth of 3 m to smelt rare earth steel. The rare earth recovery rate, rare earth distribution uniformity and inclusion modification effect of the yttrium-iron alloy of Example 1 in the ladle were significantly better than those of Comparative Examples 1-2. The comparison results are shown in Table 3.

[0074] Embodiment 2:

[0075] The ratio and preparation method of the rare earth metal yttrium and pure iron raw materials are the same as those in Example 1. After refining, the alloy solution is poured into a cylindrical mold with a radius R of 10 cm and a height L of 20 cm, and cooled with the furnace under the protection of argon atmosphere in the furnace. The yttrium iron additive of this embodiment has a cylindrical shape with a radius of 10 cm and a height of 20 cm, a density of 7.7 g / cm3, and a melting point of 1450°C.

[0076] The yttrium-iron alloy of Example 2 and the commercially available ferrocerium and yttrium-iron additives of Comparative Examples 1-2 were used as rare earth additives and added into a ladle with a molten steel depth of 3 m to smelt rare earth steel. The rare earth yield rate, rare earth distribution uniformity and inclusion modification effect of the yttrium-iron alloy of Example 2 in the ladle were significantly better than those of Comparative Examples 1-2. The comparison results are shown in Table 3.

[0077] Embodiment 3:

[0078] The raw material ratio and preparation method of rare earth metal yttrium and pure iron are the same as those in Example 1. After refining, the alloy solution is poured into a parabola mold with a radius R of 10 cm, L1 of 10 cm, a height L of 20 cm, and n of 0.4, and cooled with the furnace under the protection of argon atmosphere in the furnace. The yttrium iron additive of this embodiment has a parabola shape with a radius R of 10 cm, L1 of 10 cm, a height L of 20 cm, and n of 0.4, a density of 7.7 g / cm3, and a melting point of 1450°C.

[0079] The ferrocerium yttrium alloy of Example 3 and the commercially available ferrocerium and ferroyttrium additives of Comparative Examples 1-2 were used as rare earth additives and added into a ladle with a molten steel depth of 3 m to smelt rare earth steel. The rare earth recovery rate, rare earth distribution uniformity and inclusion modification effect of the ferrocerium alloy of Example 3 in the ladle were significantly better than those of Comparative Examples 1-2. The comparison results are shown in Table 3.

[0080] Table 3

[0081]

[0082]

[0083] It can be seen from Table 1, Table 2 and Table 3 that the present invention has a wider applicable composition window of additives through rare earth, iron, transition metal composition regulation and shape optimization. The alloy additive of the present invention can effectively reduce the viscous resistance of molten steel to the additive, get rid of the influence of the slag layer, and add it to the appropriate depth of the molten steel. Compared with Comparative Examples 1-2, the inclusion size is smaller, the rare earth element yield is higher, and the distribution is more uniform.

[0084] The embodiment of the present invention is intended to protect an additive containing rare earth, the additive comprising: rare earth metal and iron, the content of rare earth metal is 5wt% to 90wt%, the content of iron is 10wt% to 95wt%; the density of the additive is 6.3g / cm 3 ~8.4g / cm 3 , melting point is 850℃~1450℃, oxygen content is ≤150ppm, maximum size of inclusions is ≤35μm, total amount of inclusions is ≤0.5wt%. The above technical solution has the following effects:

[0085] 1. The additive prepared by this patent has the advantages of low oxygen, small total amount and size of inclusions, which can effectively reduce the introduction of foreign rare earth oxide inclusions in steel and alleviate nozzle blockage;

[0086] 2. Through the optimization of the composition design of rare earth, iron and transition group micro-alloying elements in the additive, the rare earth additive has a suitable density and melting point, and the rare earth and the main transition group micro-alloying elements in steel are added simultaneously and the depth of additive addition is effectively increased, thereby improving the rare earth yield and distribution uniformity;

[0087] 3. According to the melting point, density and other characteristics of rare earth additives, a reasonable rare earth additive shape is designed, which can effectively reduce the viscous resistance of molten steel to the additives, get rid of the influence of slag layer, increase the input depth of rare earth additives, promote a significant improvement in rare earth yield and uniformity indicators, and also increase the applicable composition window range of the intermediate alloy.

[0088] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. A rare earth-containing additive, characterized in that: include: Rare earth metal and iron, the rare earth metal content is 5wt%~90wt%, and the iron content is 10wt%~95wt%; The density of the additive is 6.3 g / cm 3 ~8.4 g / cm 3 , melting point is 850℃~1450℃, oxygen content is ≤150ppm, maximum size of inclusions is ≤35μm, total amount of inclusions is ≤0.5wt%; The additive comprises: a first part and a second part formed in one piece; One end of the first part away from the second part is a hemispherical, cylindrical or parabolic structure; The cross section of the connecting end of the second part and the first part is circular or elliptical; The maximum dimension of any cross section of the second portion is smaller than the maximum dimension of the cross section of the connecting end of the first portion and the second portion; One end of the first part away from the second part is a hemispherical or parabolic structure; The edge point coordinates of the axial cross section of the first part satisfy the following formula: Wherein, x is the X-axis coordinate value of the first part along the axial direction, y is the Y-axis coordinate value perpendicular to the axial direction, the coordinate origin is the vertex of the first part away from the second part, n is the taper control factor of the first part of the additive, when n=0, the first part is a cylinder, when n=1, the first part is a cone, the value range of n is 0<n<1, and L is the length value of the additive along the axial direction; A shell is also provided outside the additive, and the shape of the shell matches the shape of the additive.

2. The rare earth-containing additive according to claim 1, characterized in that: The value range of n is 0.7<n<1.

3. The rare earth-containing additive according to claim 1, characterized in that: The ratio of the length L1 of the first portion along the axial direction of the cross section to the total length L of the additive is: 0.5≤L1 / L≤1; The cross-sectional radius R of one end of the first part close to the second part has a value range of 1.5 cm to 24 cm, and the cross-sectional radius L has a value range of 3 cm to 48 cm.

4. The rare earth-containing additive according to claim 1, characterized in that: The iron content of the shell is greater than 95wt% and less than 99.9wt%, the thickness of the shell is 0.5cm-4cm, the melting point is 1500℃-1538℃, and the density is 7.6g / cm 3 ~8.6 g / cm 3 .

5. The rare earth-containing additive according to claim 1, characterized in that: The additive further comprises: a transition metal, wherein the transition metal comprises: at least one of nickel, chromium, tungsten, molybdenum, cobalt, manganese, vanadium, niobium and titanium; The content of the transition metal is 0.1 wt% to 15 wt%, the content of the rare earth metal is 15 wt% to 70 wt%, and the content of iron is 20 wt% to 70 wt%; The density of the additive is 7.2-8.2 g / cm 3 , melting point is 1000~1300 ℃, oxygen content ≤100 ppm, carbon content ≤300 ppm, maximum size of inclusions ≤25 μm, total amount of inclusions ≤0.1 wt %.

6. The rare earth-containing additive according to claim 5, characterized in that: The transition metal includes at least one of chromium, tungsten, molybdenum, vanadium, niobium and titanium.

7. The rare earth-containing additive according to any one of claims 1 to 6, characterized in that: The rare earth metal includes at least one of lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium and yttrium.

8. The rare earth-containing additive according to claim 7, characterized in that: The rare earth metal includes at least one of lanthanum, cerium and yttrium.

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