Rare earth adding method for improving rare earth yield and microalloying effect

Abstract

The invention belongs to the technical field of metal material smelting, and particularly relates to a rare earth adding method for improving the rare earth yield and the microalloying effect, and the rare earth adding method comprises the following steps: S1, molten steel, Zr-Ti alloy and rare earth alloy are obtained, the Zr-Ti alloy is added into the molten steel for pre-deoxidation to obtain first molten steel, and the rare earth alloy comprises the first rare earth alloy and the second rare earth alloy; s2, the first rare earth alloy is added into the first molten steel for deep deoxidation, and second molten steel is obtained; and S3, a second rare earth alloy is added into the second molten steel for melting and continuous casting, and a continuous casting blank is obtained. According to the method, an ultra-low-oxygen environment is established through Zr-Ti pre-deoxidation and rare earth deep deoxidation, stable Zr-Ti-rare earth composite inclusions are formed by utilizing a composite inclusion structure, so that oxidation loss, slag adsorption loss and inclusion floating loss of rare earth are remarkably reduced, the yield of the rare earth is remarkably increased, and when the yield of the rare earth is increased in the smelting process, the yield of the rare earth is increased. The solid solubility in steel is synchronously increased along with the increase of the yield, and the rare earth microalloying effect can be improved.

Description

Technical Field

[0001] This application relates to the field of metal material smelting technology, specifically, to a method for adding rare earth materials to improve rare earth yield and microalloying effect. Background Technology

[0002] Rare earth elements (REs) are chemically highly reactive metallic elements, exhibiting strong affinity for oxygen and sulfur in the steelmaking environment. Therefore, effectively preventing excessive oxidation of rare earth elements during the smelting and casting of rare earth steel is crucial for determining rare earth yield, inclusion control, and the stability of subsequent mechanical properties. In actual production, if rare earth elements are rapidly oxidized on the surface of molten steel or at the slag interface, they form high-melting-point RE₂O₃ or complex RE–O–S oxysulfides. These products are not only difficult to dissolve and diffuse but also lead to a series of problems such as casting gate nodules, inclusion coarsening and aggregation, resulting in drastic fluctuations or even significant reductions in the strength and toughness of rare earth steel. These problems have long been considered the core bottlenecks restricting the large-scale production and stable performance improvement of rare earth steel.

[0003] In recent years, relying on my country's abundant rare earth resources, domestic research institutions and enterprises have achieved internationally leading technological advantages in the field of rare earth metallurgy. To reduce rare earth oxidation losses during smelting and improve rare earth yield, a delayed addition strategy is commonly adopted both domestically and internationally. This involves continuously feeding rare earth alloy wires into low-oxygen areas (such as near the crystallizer) as much as possible. However, this method itself still has significant drawbacks: First, the rare earth wires cannot completely melt and rapidly diffuse throughout the molten pool in a short time, causing local rare earth agglomeration, which is detrimental to uniform solidification. Second, if the oxygen content of the molten steel is high, even with a late-feeding method, the rare earths will still be rapidly oxidized, resulting in substantial losses. Therefore, although this technology improves some oxidation problems, it still cannot fundamentally improve the rare earth yield.

[0004] To address these issues, the team led by Li Dianzhong at the Institute of Metal Research, Chinese Academy of Sciences, proposed a "dual low-oxygen" control technology, namely a simultaneous control scheme of "low oxygen in molten steel + low oxygen in rare earth alloys." This involves creating a low-oxygen environment in the molten steel before the addition of rare earth elements and then subjecting the molten steel to low-oxygen treatment, allowing the rare earth elements to exist stably in the phase transformation reaction zone and maximize their microalloying effect. This strategy overcomes the limitations of the traditional "late addition of rare earth elements," enabling rare earth elements to participate in metallurgical processes such as inclusion modification, grain refinement, and grain boundary cleaning at an earlier stage. However, the "dual low-oxygen technology" places higher demands on the steel deoxidation operation, alloy preparation process, and logistics management in the steelmaking process, and correspondingly increases the production cost of rare earth steel, limiting its widespread application in some large-scale scenarios.

[0005] For my country's vast permafrost regions, the demand for low-cost, high-reliability steel is enormous for infrastructure projects such as highways, bridges, and utility tunnels. In order to achieve large-scale production while ensuring the comprehensive performance of materials (low-temperature resistance, freeze-thaw resistance, and corrosion resistance), it is necessary to find a smelting strategy that is cost-effective, easy to operate, and can effectively inhibit rare earth oxidation and significantly improve rare earth yield.

[0006] Therefore, research on process control related to rare earth yield has become a core scientific issue in upgrading rare earth steel smelting technology. The rare earth yield directly determines not only the microalloying efficiency of rare earths but also affects inclusion control behavior, grain structure evolution, steel cleanliness, and the dispersion of final service performance. Establishing a system to achieve a lower oxygen content upon rare earth addition by using Zr-Ti composite deoxidation before adding rare earths, thereby systematically improving the rare earth yield, will be a key path to achieving both high performance and low cost in rare earth steel. Summary of the Invention

[0007] To address the aforementioned technical problems, this application provides a rare earth addition method to improve rare earth yield and microalloying effect, comprising the following steps: S1, obtaining molten steel, Zr-Ti alloy, and rare earth alloy; adding the Zr-Ti alloy to the molten steel for pre-deoxidation to obtain a first molten steel, wherein the free oxygen content of the molten steel is 240-280 ppm; the mass ratio of the molten steel, the Zr-Ti alloy, and the rare earth alloy is 100:(0.01-0.045):(0.0015-0.01), and the rare earth alloy includes a first rare earth alloy and a second rare earth alloy, the mass ratio of the first rare earth alloy and the second rare earth alloy being (85-90):(10-15); S2, adding the first rare earth alloy to the first molten steel for deep deoxidation to obtain a second molten steel; S3, adding the second rare earth alloy to the second molten steel for melting and continuous casting to obtain a continuously cast billet.

[0008] As a preferred embodiment of the rare earth addition method for improving rare earth yield and microalloying effect described in this application, in step S1, the temperature of the molten steel is 1600-1700℃.

[0009] As a preferred embodiment of the rare earth addition method for improving rare earth yield and microalloying effect described in this application, step S1 further includes stirring the molten steel with micro-argon bubbles for 5-7 minutes before performing the pre-deoxidation.

[0010] As a preferred embodiment of the rare earth addition method for improving rare earth yield and microalloying effect described in this application, in step S1, the first molten steel includes a structure forming Zr-Ti composite inclusions, the Zr-Ti composite inclusions include ZrO2 and Ti2O3, and the free oxygen content of the first molten steel is ≤100ppm.

[0011] As a preferred embodiment of the rare earth addition method for improving rare earth yield and microalloying effect described in this application, step S2 further includes vacuuming. After vacuuming for 2-4 minutes, the first rare earth alloy is added to the first molten steel for deep deoxidation. Soft argon gas treatment is performed 4-10 minutes before the end of deep deoxidation.

[0012] As a preferred embodiment of the rare earth addition method for improving rare earth yield and microalloying effect described in this application, in step S2, the deep deoxidation time is 30-60 min, the temperature of the second molten steel is ≥1550℃, and the free oxygen content of the second molten steel is ≤20ppm.

[0013] As a preferred embodiment of the rare earth addition method for improving rare earth yield and microalloying effect described in this application, in step S2, the second molten steel forms a structure including Zr-Ti-rare earth composite inclusions.

[0014] As a preferred embodiment of the rare earth addition method for improving rare earth yield and microalloying effect described in this application, step S3 further includes circulating the second molten steel during the melting process for 8-20 minutes.

[0015] As a preferred embodiment of the rare earth addition method for improving rare earth yield and microalloying effect described in this application, in step S3, the rare earth yield is ≥34.5%.

[0016] As a preferred embodiment of the rare earth addition method for improving rare earth yield and microalloying effect described in this application, in step S3, the continuously cast billet includes Zr-Ti-rare earth composite inclusions and Zr-Ti composite inclusions, the rare earth in the continuously cast billet is uniformly distributed, the average size of the Zr-Ti-rare earth composite inclusions in the continuously cast billet is ≤2μm, the average grain size of the continuously cast billet is ≤10μm, and the mass ratio of the Zr-Ti-rare earth composite inclusions to the Zr-Ti composite inclusions is (80-90):(10-20).

[0017] This application proposes a rare earth addition method to improve rare earth yield and microalloying effect. By controlling the free oxygen concentration in molten steel, constructing a suitable inclusion nucleation system, and introducing rare earth in stages, the maximum effective retention of rare earth in molten steel is achieved, providing a new technical path for the smelting of high-performance rare earth steel.

[0018] Adding Zr-Ti alloy particles for pre-deoxidation of molten steel can rapidly reduce dissolved oxygen in the steel to below 100 ppm, weakening the thermodynamic driving force of rare earth oxidation reactions at the source. The deoxidation products of Zr and Ti are mainly ZrO2 and Ti2O3. These inclusions have higher melting points, densities closer to molten steel, and lower interfacial energies than traditional Al2O3 or CaO·Al2O3, making them dispersed in the molten steel and less prone to agglomeration. Under the action of bottom-blown Ar, large inclusions are effectively floated and removed, while the remaining small ZrO2 / Ti2O3 particles become ideal nucleation sites for subsequent deep deoxidation reactions of rare earths. This stage not only achieves low free oxygen construction in the molten steel but also pre-arranges "inclusion templates," laying the foundation for improving the utilization rate of rare earths and the efficiency of microalloying.

[0019] With the free oxygen in molten steel significantly reduced, the addition of rare earth alloys and deep deoxidation can further reduce the dissolved oxygen in the molten steel to below 20 ppm. Under this low-oxygen environment, the oxidation rate of rare earths is significantly lower than in traditional processes. Simultaneously, newly formed rare earth inclusions preferentially nucleate heterogeneously on ZrO2 / Ti2O3, forming fine and dispersed Zr-Ti-rare earth composite inclusions. This inclusion structure inhibits excessive growth and flotation of rare earth inclusions, effectively reducing rare earth losses caused by inclusion coarsening or aggregation. More importantly, due to reduced oxidation consumption, unoxidized rare earths can partially or even significantly enter the molten steel to achieve true solid solution, thereby significantly improving the rare earth yield.

[0020] Since the molten steel is already in an environment with extremely low free oxygen at this point, and the previously formed Zr-Ti-rare earth composite inclusions have effectively stabilized the inclusion system, the rare earth alloys added again are less prone to oxidation and adsorption, further increasing the yield. Because rare earths have consistent solid solubility in the same steel grade, as the rare earth yield increases during smelting, their solid solubility in the steel increases synchronously, enhancing the effect of rare earth microalloying. This allows rare earth addition to move beyond the traditional "late addition method," instead achieving high retention and efficient utilization of rare earths throughout the entire smelting process through graded control of free oxygen concentration.

[0021] The beneficial effects of this application are as follows:

[0022] Compared to the common method of adding rare earth elements in the crystallizer, this application successfully moves the rare earth element addition to the LF refining stage through Zr-Ti pre-deoxidation, avoiding the problem of insufficient melting and diffusion of rare earth alloys in the crystallizer stage, while effectively reducing the oxidation of rare earth elements.

[0023] The Zr-Ti composite deoxidation system preferentially consumes active oxygen in the molten steel and generates Zr-Ti composite inclusions with higher melting points and greater thermodynamic stability. This fundamentally reduces the free oxygen content in the molten steel, placing rare earth elements in a low-oxygen environment when they enter the molten steel. This effectively avoids the severe oxidation loss and uneven local diffusion that are common in the crystallizer stage, significantly increasing the actual amount of rare earth elements entering and the effective retention amount. As a result, the rare earth recovery rate in the steel eventually stabilizes at over 30%, a level that is difficult to achieve with traditional processes.

[0024] This application further utilizes the high-temperature stability of Zr-Ti composite inclusions, making them preferential adsorption cores for rare earth elements. This allows rare earth elements and Zr-Ti composite inclusions to synergistically form fine, dispersed, and thermally stable Zr-Ti-rare earth composite inclusions. These composite inclusions not only improve the mechanical properties of the finished steel but also reduce the oxygen content in the molten steel, effectively increasing the rare earth yield and ensuring that rare earth elements can better play their role as modified inclusions and grain refiners in the steel. Compared with the "dual low oxygen" control technology proposed by the Institute of Metal Research, Chinese Academy of Sciences, this application avoids the stringent requirements for ultra-low total oxygen control in molten steel and oxygen control in rare earth alloys while achieving an equivalent level of rare earth oxidation inhibition, thus avoiding a significant increase in smelting costs. Evaluation shows that the smelting process, raw material system, and energy consumption of this application are consistent with traditional Q-series bridge steel, with almost no increase in the cost per ton of steel plate, but a significant improvement in the effective utilization rate of rare earth elements in the steel, demonstrating outstanding economic advantages.

[0025] In the rare earth steel prepared using this application, the average size of inclusions is less than 2 μm. Simultaneously, the Zr-Ti-rare earth composite inclusions can serve as highly efficient heterogeneous nucleation sites during solidification. Their highly stable interface structure promotes austenite grain refinement and plays a role in grain boundary pinning and inhibiting grain growth in the subsequent weld heat-affected zone, significantly improving the strength-toughness balance of the steel plate and the structural stability of the weld zone. The high rare earth yield ensures sufficient formation of these composite inclusions, making the improvement of material microstructure and properties more stable and reliable.

[0026] This technology effectively overcomes three major bottlenecks caused by previous rare earth addition methods: 1. Severe rare earth oxidation loss, resulting in low and highly volatile yields. 2. Large and unstable inclusions, hindering their refining effect. 3. Significantly increased smelting costs due to intensified oxygen control. This application, through an innovative combination of the deoxidation system and the order of rare earth addition, can significantly improve rare earth yield and enhance the structural stability of fine composite inclusions. It exhibits good versatility, and its lower cost demonstrates its replicability and industrialization potential under large-scale, multi-steel grade production conditions.

[0027] In summary, this application establishes an ultra-low oxygen environment through Zr-Ti pre-deoxidation and rare earth deep deoxidation, and utilizes the composite inclusion structure to form stable Zr-Ti-rare earth composite inclusions. This significantly reduces rare earth oxidation losses, slag adsorption losses, and inclusion flotation losses, thereby significantly improving the rare earth yield. Since the solid solubility of rare earths is consistent in the same steel grade, as the rare earth yield increases during smelting, its solid solubility in the steel increases synchronously with the increase in yield, which can enhance the effect of rare earth microalloying. This technology not only improves the effective solid solubility and participation of rare earths in molten steel, but also promotes grain refinement and phase transformation control, which has important application value for improving the comprehensive performance of materials. It also has advantages such as simple process, controllable cost, and suitability for large-scale industrialization. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0029] Figure 1 This is a structural diagram of the Zr-Ti-rare earth composite inclusion in the continuously cast billet prepared in Example 1 of this application;

[0030] Figure 2 This is a microstructure image of the continuously cast billet prepared in Example 1 of this application.

[0031] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0032] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0033] This application provides a rare earth addition method to improve rare earth yield and microalloying effect, comprising the following steps:

[0034] S1. Obtain molten steel, Zr-Ti alloy, and rare earth alloy. Add the Zr-Ti alloy to the molten steel for pre-deoxidation to obtain a first molten steel, wherein the free oxygen content of the molten steel is 240-280 ppm; the mass ratio of the molten steel, the Zr-Ti alloy, and the rare earth alloy is 100:(0.01-0.045):(0.0015-0.01), and the rare earth alloy includes a first rare earth alloy and a second rare earth alloy, wherein the mass ratio of the first rare earth alloy and the second rare earth alloy is (85-90):(10-15).

[0035] The temperature of the molten steel is 1600-1700℃; before the pre-deoxidation, the molten steel is stirred with micro argon bubbles for 5-7 minutes; the first molten steel includes a structure that forms Zr-Ti composite inclusions, the Zr-Ti composite inclusions include ZrO2 and Ti2O3, and the free oxygen content of the first molten steel is ≤100ppm;

[0036] S2. Add the first rare earth alloy to the first molten steel and perform deep deoxidation to obtain the second molten steel.

[0037] A vacuum process is performed, and after 2-4 minutes of vacuuming, the first rare earth alloy is added to the first molten steel for deep deoxidation. 4-10 minutes before the end of the deep deoxidation, a soft-blowing argon process is performed. The deep deoxidation time is 30-60 minutes. The temperature of the second molten steel is ≥1550℃, and the free oxygen content of the second molten steel is ≤20ppm. The second molten steel forms a structure including Zr-Ti-rare earth composite inclusions.

[0038] S3. The second rare earth alloy is added to the second molten steel for melting and continuous casting to obtain a continuously cast billet;

[0039] The second molten steel is circulated during the melting process for 8-20 minutes; the rare earth yield is ≥34.5%; the continuous casting billet includes Zr-Ti-rare earth composite inclusions and Zr-Ti composite inclusions, the rare earth in the continuous casting billet is uniformly distributed, the average size of the Zr-Ti-rare earth composite inclusions in the continuous casting billet is ≤2μm, the average grain size of the continuous casting billet is ≤10μm, and the mass ratio of the Zr-Ti-rare earth composite inclusions to the Zr-Ti composite inclusions is (80-90):(10-20).

[0040] The technical solution of this application will be further described below with reference to specific embodiments.

[0041] Example 1

[0042] This application provides a rare earth addition method to improve rare earth yield and microalloying effect, comprising the following steps:

[0043] S1. Obtain molten steel, Zr-Ti alloy, and rare earth alloy. Add Zr-Ti alloy to molten steel for pre-deoxidation to obtain the first molten steel, wherein the free oxygen content of the molten steel is 266 ppm; the mass ratio of molten steel, Zr-Ti alloy, and rare earth alloy is 100:0.026:0.006, and the rare earth alloy includes a first rare earth alloy and a second rare earth alloy, wherein the mass ratio of the first rare earth alloy and the second rare earth alloy is 88:12.

[0044] The temperature of the molten steel was 1660℃; before pre-deoxidation, the molten steel was stirred with micro argon bubbles for 6 minutes; the first molten steel formed a Zr-Ti composite inclusion of highly stable ZrO2 and Ti2O3, and the free oxygen content of the first molten steel was 65ppm;

[0045] S2. Add the first rare earth alloy to the first molten steel and perform deep deoxidation to obtain the second molten steel.

[0046] Vacuuming was performed, and after 3 minutes of vacuuming, the first rare earth alloy was added to the first molten steel for deep deoxidation. 5.5 minutes before the end of deep deoxidation, soft blowing argon gas was applied. The deep deoxidation time was 42 minutes, the temperature of the second molten steel was 1580℃, and the free oxygen content of the second molten steel was 18ppm. The second molten steel formed a Zr-Ti-rare earth composite inclusion structure.

[0047] S3. The second rare earth alloy is added to the second molten steel for melting and continuous casting to obtain a continuously cast billet;

[0048] During the melting process, the second molten steel was circulated for 15 minutes; the rare earth recovery rate was 36.6%; please refer to [link / reference]. Figure 1 and Figure 2 , Figure 1 This is a structural diagram of the Zr-Ti-rare earth composite inclusion in the continuously cast billet prepared in Example 1 of this application; Figure 1 The composition of the Zr-Ti-rare earth composite inclusion shown in (a) is: O: 24.87wt%, S: 4.53wt%, Ti: 8.42wt%, Fe: 19.08wt%, Zr: 10.14wt%, La: 18.02wt%, Ce: 14.94wt%; Figure 1The composition of the Zr-Ti-rare earth composite inclusion shown in (b) is: O: 15.53 wt%, S: 3.07 wt%, Ti: 8.16 wt%, Fe: 44.53 wt%, Zr: 18.54 wt%, La: 4.69 wt%, Ce: 5.48 wt%; Figure 2 This is a microstructure image of the continuously cast billet prepared in Example 1 of this application; the continuously cast billet includes Zr-Ti-rare earth composite inclusions and Zr-Ti composite inclusions, the rare earth in the continuously cast billet is uniformly distributed, the average size of the Zr-Ti-rare earth composite inclusions in the continuously cast billet is 1.88 μm, the average grain size is 9.47 μm, and the mass ratio of Zr-Ti-rare earth composite inclusions to Zr-Ti composite inclusions is 85:15.

[0049] Example 2

[0050] This application provides a rare earth addition method to improve rare earth yield and microalloying effect, comprising the following steps:

[0051] S1. Obtain molten steel, Zr-Ti alloy, and rare earth alloy. Add Zr-Ti alloy to molten steel for pre-deoxidation to obtain the first molten steel, wherein the free oxygen content of the molten steel is 266 ppm; the mass ratio of molten steel, Zr-Ti alloy, and rare earth alloy is 100:0.040:0.009, and the rare earth alloy includes a first rare earth alloy and a second rare earth alloy, wherein the mass ratio of the first rare earth alloy and the second rare earth alloy is 90:10;

[0052] The temperature of the molten steel was 1660℃; before pre-deoxidation, the molten steel was stirred with micro argon bubbles for 6 minutes; the first molten steel formed a Zr-Ti composite inclusion of highly stable ZrO2 and Ti2O3, and the free oxygen content of the first molten steel was 56ppm;

[0053] S2. Add the first rare earth alloy to the first molten steel and perform deep deoxidation to obtain the second molten steel.

[0054] Vacuuming was performed, and after 3 minutes of vacuuming, the first rare earth alloy was added to the first molten steel for deep deoxidation. Soft argon gas was blown in 8 minutes before the end of deep deoxidation. The deep deoxidation time was 45 minutes, the temperature of the second molten steel was 1580℃, and the free oxygen content of the second molten steel was 16ppm. The second molten steel formed a Zr-Ti-rare earth composite inclusion structure.

[0055] S3. The second rare earth alloy is added to the second molten steel for melting and continuous casting to obtain a continuously cast billet;

[0056] During the melting process, the second molten steel was circulated for 15 minutes; the rare earth yield was 38.1%; the continuously cast billet included Zr-Ti-rare earth composite inclusions and Zr-Ti composite inclusions, and the rare earth was uniformly distributed in the continuously cast billet. The average size of the Zr-Ti-rare earth composite inclusions in the continuously cast billet was 1.84 μm, the average grain size was 9.13 μm, and the mass ratio of Zr-Ti-rare earth composite inclusions to Zr-Ti composite inclusions was 89:11.

[0057] Example 3

[0058] This application provides a rare earth addition method to improve rare earth yield and microalloying effect, comprising the following steps:

[0059] S1. Obtain molten steel, Zr-Ti alloy, and rare earth alloy. Add Zr-Ti alloy to molten steel for pre-deoxidation to obtain the first molten steel, wherein the free oxygen content of the molten steel is 266 ppm; the mass ratio of molten steel, Zr-Ti alloy, and rare earth alloy is 100:0.020:0.003, and the rare earth alloy includes a first rare earth alloy and a second rare earth alloy, wherein the mass ratio of the first rare earth alloy and the second rare earth alloy is 85:15;

[0060] The temperature of the molten steel was 1660℃; before pre-deoxidation, the molten steel was stirred with micro argon bubbles for 6 minutes; the first molten steel formed a Zr-Ti composite inclusion of highly stable ZrO2 and Ti2O3, and the free oxygen content of the first molten steel was 64ppm;

[0061] S2. Add the first rare earth alloy to the first molten steel and perform deep deoxidation to obtain the second molten steel.

[0062] Vacuuming was performed, and after 3 minutes of vacuuming, the first rare earth alloy was added to the first molten steel for deep deoxidation. Soft argon gas was blown in 8 minutes before the end of deep deoxidation. The deep deoxidation time was 40 minutes, the temperature of the second molten steel was 1600℃, and the free oxygen content of the second molten steel was 19ppm. The second molten steel formed a Zr-Ti-rare earth composite inclusion structure.

[0063] S3. The second rare earth alloy is added to the second molten steel for melting and continuous casting to obtain a continuously cast billet;

[0064] During the melting process, the second molten steel was circulated for 15 minutes; the rare earth yield was 34.5%; the continuously cast billet included Zr-Ti-rare earth composite inclusions and Zr-Ti composite inclusions, and the rare earth was uniformly distributed in the continuously cast billet. The average size of the Zr-Ti-rare earth composite inclusions in the continuously cast billet was 1.87 μm, the average grain size was 9.74 μm, and the mass ratio of Zr-Ti-rare earth composite inclusions to Zr-Ti composite inclusions was 83:17.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that no Zr-Ti alloy is added for pre-deoxidation; the other steps are the same as in Example 1.

[0067] The free oxygen content of the second molten steel was 266 ppm; the rare earth recovery rate was 10%. Due to the lack of Zr-Ti alloy for pre-deoxidation, there were a large number of large rare earth inclusions in the steel, and the average grain size of the continuously cast billet was 16.23 μm.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 1 is that the mass ratio of the first rare earth alloy to the second rare earth alloy is 95:5, while the other steps are the same as in Example 1.

[0070] The free oxygen content of the second molten steel is 17 ppm; the rare earth yield is 28.3%; the continuously cast billet includes Zr-Ti-rare earth composite inclusions and Zr-Ti composite inclusions; the average grain size of the continuously cast billet is 11.34 μm; and the mass ratio of Zr-Ti-rare earth composite inclusions to Zr-Ti composite inclusions in the continuously cast billet is 77:13.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that the mass ratio of the first rare earth alloy to the second rare earth alloy is 75:25, while the other steps are the same as in Example 1.

[0073] The free oxygen content of the second molten steel is 30 ppm; the rare earth yield is 26.9%; the continuously cast billet includes Zr-Ti-rare earth composite inclusions and Zr-Ti composite inclusions; the average grain size of the continuously cast billet is 12.15 μm; and the mass ratio of Zr-Ti-rare earth composite inclusions to Zr-Ti composite inclusions in the continuously cast billet is 73:27.

[0074] Comparative Example 4

[0075] The difference between this comparative example and Example 1 is that the first rare earth alloy and the second rare earth alloy are added to the first molten steel at the same time for deep deoxidation, while the other steps are the same as in Example 1.

[0076] The free oxygen content of the second molten steel is 17 ppm; the rare earth yield is 20.1%; the continuously cast billet includes Zr-Ti-rare earth composite inclusions and Zr-Ti composite inclusions; the average grain size of the continuously cast billet is 13.28 μm; and the mass ratio of Zr-Ti-rare earth composite inclusions to Zr-Ti composite inclusions in the continuously cast billet is 69:31.

[0077] As can be seen from the above examples and comparative examples: Example 1, combined with Comparative Example 1, shows that without Zr-Ti pre-deoxidation, the entire system is deoxidized by rare earths, which leads to a significant increase in the amount of rare earths added, a surge in cost, and the fact that all added rare earths participate in deoxidation, resulting in a significant decrease in yield, a decrease in their solid solubility in steel, a reduction in the effect of rare earth microalloying, and a large number of large-sized rare earth inclusions in the steel due to the lack of Zr-Ti alloy for pre-deoxidation; Example 1, combined with Comparative Example 2, shows that the efficiency of the first rare earth alloy in deep deoxidation of the first molten steel tends to stabilize with the excessive addition of the first rare earth alloy, with no significant improvement in deoxidation efficiency, while the loss of rare earths due to excessive addition increases. Although the second rare earth alloy has a higher yield, the amount added is too small, the amount of rare earths recovered is not significant, thus the total rare earth yield decreases, and its solid solubility in steel decreases accordingly, reducing the effect of rare earth microalloying; Example 1, combined with Comparative Example 3, shows that if the amount of the first rare earth alloy added is too small, the deoxidation of the second molten steel will be insufficient. The first rare earth alloy and the second rare earth alloy are added simultaneously, but the deoxidation efficiency of rare earth decreases sharply with the increase of their content. Furthermore, the rare earth is not added in a deep deoxidation environment with high yield. Most of the rare earth reacts with the free oxygen in the steel, resulting in a significant decrease in the overall rare earth yield and a decrease in the solid solubility of rare earth in the steel, thus affecting the rare earth microalloying effect. Examples 1-3 and Comparative Examples 1-4 show that this application achieves oxygen control throughout the smelting process through the synergistic effect of the Zr-Ti composite deoxidation mechanism and the two rare earth additions. This significantly improves the rare earth yield, increases the solid solubility of rare earth in the steel, enhances the rare earth microalloying effect, and has good repeatability, laying the foundation for high-efficiency, low-loss rare earth steel smelting technology.

[0078] This application provides a rare earth addition method to improve rare earth yield and microalloying effect. The method uses a Zr-Ti composite deoxidizer to create a low-free-oxygen environment in the molten steel. Combined with the introduction of rare earth elements that enhance reducing properties, this reduces the conversion of rare earth elements into coarse inclusions during melting and diffusion. This effectively avoids production risks such as low yield, casting nozzle clogging, and gate blockage caused by excessive rare earth oxidation. The industrial application of the composite deoxidizer described in this application allows rare earth inclusions to rapidly float into the slag in the early stages, significantly reducing the opportunity for rare earth elements to form ineffective inclusions in the molten steel. This ensures that rare earth elements are primarily retained in the steel in solid solution and microalloyed forms, achieving a significant transformation of rare earth resources from "depletion-oriented" to "utilization-oriented."

[0079] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for adding rare earth elements to improve rare earth yield and microalloying effect, characterized in that, Includes the following steps: S1. Obtain molten steel, Zr-Ti alloy, and rare earth alloy. Add the Zr-Ti alloy to the molten steel for pre-deoxidation to obtain a first molten steel, wherein the free oxygen content of the molten steel is 240-280 ppm; the mass ratio of the molten steel, the Zr-Ti alloy, and the rare earth alloy is 100:(0.01-0.045):(0.0015-0.01), and the rare earth alloy includes a first rare earth alloy and a second rare earth alloy, wherein the mass ratio of the first rare earth alloy and the second rare earth alloy is (85-90):(10-15). S2. Add the first rare earth alloy to the first molten steel and perform deep deoxidation to obtain the second molten steel. S3. The second rare earth alloy is added to the second molten steel for melting and continuous casting to obtain a continuously cast billet.

2. The rare earth addition method for improving rare earth yield and microalloying effect according to claim 1, characterized in that, In step S1, the temperature of the molten steel is 1600-1700℃.

3. The rare earth addition method for improving rare earth yield and microalloying effect according to claim 1, characterized in that, Step S1 further includes stirring the molten steel with micro argon bubbles for 5-7 minutes before performing the pre-deoxidation.

4. The rare earth addition method for improving rare earth yield and microalloying effect according to claim 1, characterized in that, In step S1, the first molten steel includes a structure that forms a Zr-Ti composite inclusion, the Zr-Ti composite inclusion includes ZrO2 and Ti2O3, and the free oxygen content of the first molten steel is ≤100ppm.

5. The rare earth addition method for improving rare earth yield and microalloying effect according to claim 1, characterized in that, Step S2 also involves vacuuming. After vacuuming for 2-4 minutes, the first rare earth alloy is added to the first molten steel for deep deoxidation. 4-10 minutes before the end of deep deoxidation, soft blowing argon gas is applied.

6. The rare earth addition method for improving rare earth yield and microalloying effect according to claim 1, characterized in that, In step S2, the deep deoxidation time is 30-60 minutes, the temperature of the second molten steel is ≥1550℃, and the free oxygen content of the second molten steel is ≤20ppm.

7. The rare earth addition method for improving rare earth yield and microalloying effect according to claim 1, characterized in that, In step S2, the second molten steel forms a structure including Zr-Ti-rare earth composite inclusions.

8. The rare earth addition method for improving rare earth yield and microalloying effect according to claim 1, characterized in that, Step S3 further includes circulating the second molten steel during the melting process for 8-20 minutes.

9. A rare earth addition method for improving rare earth yield and microalloying effect according to claim 1, characterized in that, In step S3, the rare earth recovery rate is ≥34.5%.

10. A rare earth addition method for improving rare earth yield and microalloying effect according to claim 1, characterized in that, In step S3, the continuously cast billet includes Zr-Ti-rare earth composite inclusions and Zr-Ti composite inclusions. The rare earth elements in the continuously cast billet are uniformly distributed. The average size of the Zr-Ti-rare earth composite inclusions in the continuously cast billet is ≤2μm, the average grain size of the continuously cast billet is ≤10μm, and the mass ratio of the Zr-Ti-rare earth composite inclusions to the Zr-Ti composite inclusions is (80-90):(10-20).

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