CN114700470B - Tundish covering agent for smelting rare earth steel and method for reducing rare earth loss - Google Patents
Tundish covering agent for smelting rare earth steel and method for reducing rare earth loss Download PDFInfo
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- CN114700470B CN114700470B CN202210243131.7A CN202210243131A CN114700470B CN 114700470 B CN114700470 B CN 114700470B CN 202210243131 A CN202210243131 A CN 202210243131A CN 114700470 B CN114700470 B CN 114700470B
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 143
- 229910052761 rare earth metal Inorganic materials 0.000 title claims abstract description 143
- 239000010959 steel Substances 0.000 title claims abstract description 143
- 150000002910 rare earth metals Chemical class 0.000 title claims abstract description 132
- 238000000034 method Methods 0.000 title claims abstract description 47
- 238000003723 Smelting Methods 0.000 title claims abstract description 22
- 238000009749 continuous casting Methods 0.000 claims abstract description 45
- 229910018072 Al 2 O 3 Inorganic materials 0.000 claims abstract description 30
- 229910021193 La 2 O 3 Inorganic materials 0.000 claims abstract description 15
- 229910004298 SiO 2 Inorganic materials 0.000 claims abstract description 10
- 239000002893 slag Substances 0.000 claims description 126
- 239000003795 chemical substances by application Substances 0.000 claims description 88
- 238000007670 refining Methods 0.000 claims description 61
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 29
- 239000001301 oxygen Substances 0.000 claims description 29
- 229910052760 oxygen Inorganic materials 0.000 claims description 29
- GSVIBLVMWGSPRZ-UHFFFAOYSA-N cerium iron Chemical compound [Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Fe].[Ce].[Ce] GSVIBLVMWGSPRZ-UHFFFAOYSA-N 0.000 claims description 15
- 230000000694 effects Effects 0.000 claims description 7
- NNLJGFCRHBKPPJ-UHFFFAOYSA-N iron lanthanum Chemical compound [Fe].[La] NNLJGFCRHBKPPJ-UHFFFAOYSA-N 0.000 claims description 7
- 229910001404 rare earth metal oxide Inorganic materials 0.000 claims description 6
- 238000007254 oxidation reaction Methods 0.000 claims description 5
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 4
- 238000005266 casting Methods 0.000 claims description 4
- 230000003647 oxidation Effects 0.000 claims description 4
- 238000001035 drying Methods 0.000 claims description 3
- 229910052786 argon Inorganic materials 0.000 claims description 2
- 239000012300 argon atmosphere Substances 0.000 claims description 2
- 239000012298 atmosphere Substances 0.000 claims description 2
- 238000002347 injection Methods 0.000 claims description 2
- 239000007924 injection Substances 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 abstract description 22
- 238000009851 ferrous metallurgy Methods 0.000 abstract description 2
- 238000002844 melting Methods 0.000 description 22
- 230000008018 melting Effects 0.000 description 22
- 230000000052 comparative effect Effects 0.000 description 15
- 239000000126 substance Substances 0.000 description 15
- 229910000640 Fe alloy Inorganic materials 0.000 description 14
- 239000000463 material Substances 0.000 description 12
- 239000010935 stainless steel Substances 0.000 description 8
- 229910010413 TiO 2 Inorganic materials 0.000 description 7
- 238000006213 oxygenation reaction Methods 0.000 description 6
- 238000004458 analytical method Methods 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 229910052684 Cerium Inorganic materials 0.000 description 3
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 238000006479 redox reaction Methods 0.000 description 3
- 238000011160 research Methods 0.000 description 3
- 238000012546 transfer Methods 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000007654 immersion Methods 0.000 description 2
- -1 low density Chemical class 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910001021 Ferroalloy Inorganic materials 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000010835 comparative analysis Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000007872 degassing Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 229910052746 lanthanum Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000014759 maintenance of location Effects 0.000 description 1
- 238000005272 metallurgy Methods 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000004064 recycling Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D1/00—Treatment of fused masses in the ladle or the supply runners before casting
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0006—Adding metallic additives
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/0087—Treatment of slags covering the steel bath, e.g. for separating slag from the molten metal
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
- C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
- C21C7/04—Removing impurities by adding a treating agent
- C21C7/076—Use of slags or fluxes as treating agents
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Abstract
The invention discloses a tundish covering agent for smelting rare earth steel and a method for reducing rare earth loss, belongs to the technical field of ferrous metallurgy, and solves the problem of low rare earth element yield in the existing rare earth steel smelting process. The tundish covering agent for smelting the rare earth steel comprises the following components in percentage by mass: 55-65, siO 2 ：5‑8，MgO：11‑15，Al 2 O 3 ：15‑24，FeO+MnO＜0.5，Ce 2 O 3 +La 2 O 3 ：0.1‑2.9，CaO/SiO 2 :8.0-11. Aiming at the characteristic that molten steel rare earth existing in a tundish is easy to oxidize in the continuous casting process of rare earth steel, the invention obtains the minimum rare earth loss by optimizing the components of the tundish covering agent. By adopting the tundish covering agent and the method, the yield in the refining-continuous casting process is more than 40%, which is improved by more than 8% compared with the existing rare earth yield, and the production cost is reduced by 50 yuan/ton of steel.
Description
Technical Field
The invention belongs to the technical field of ferrous metallurgy, and particularly relates to a tundish covering agent for smelting rare earth steel and a method for reducing rare earth loss.
Background
The action mechanism and action effect of rare earth in steel have been reported in a large number of documents, and the addition of rare earth in steel can obviously improve the structure of steel and improve the performance of steel. However, due to the special physical and chemical properties of rare earth metals, such as low density, easy volatilization, strong oxygen affinity and the like, the rare earth steel is seriously oxidized and burnt in the smelting process, and the rare earth yield is always lower. In laboratory or single furnace test, the rare earth yield is controllable, or the rare earth yield is not an essential and serious problem, but for continuously producing rare earth steel by adopting a continuous casting process, the stable addition of rare earth, the stable retention of rare earth in the steel and the like become key problems.
The rare earth yield in the rare earth steel production practice is about 30%, the fluctuation is large, and the rare earth components in the product are unstable. It is therefore highly desirable to provide a control method that reduces rare earth losses during the smelting of rare earth steels.
Disclosure of Invention
In view of the above analysis, the invention aims to provide a tundish covering agent for smelting rare earth steel and a method for reducing rare earth loss, aiming at overcoming the defects in the prior art, so as to solve the problem of low rare earth element yield in the existing rare earth steel smelting process.
The aim of the invention is mainly realized by the following technical scheme:
on one hand, the invention provides a tundish covering agent for smelting rare earth steel, which comprises the following components in percentage by mass: 55-65, siO 2 ：5-8，MgO：11-15，Al 2 O 3 ：15-24，FeO+MnO＜0.5，Ce 2 O 3 +La 2 O 3 ：0.1-2.9，CaO/SiO 2 ：8.0-11。
Further, the mass percentage of rare earth Ce and/or La in the rare earth steel is 0.002-0.05%.
On the other hand, the invention also provides a method for reducing rare earth loss, which comprises the following steps:
step 1, smelting in a converter or an electric furnace;
step 2, refining in an LF furnace or an LF furnace-RH furnace;
step 3, refining and then continuously casting;
in the step 3, molten steel enters a continuous casting crystallizer through a tundish, and is covered by a tundish covering agent to isolate air, wherein the tundish covering agent is used as the tundish covering agent.
Further, in the step 2, the ladle top slag components in the LF furnace refining are CaO in percentage by mass: 55-65, siO 2 ：5-8，MgO：11-15，Al 2 O 3 ：15-24，FeO+MnO＜0.5，Ce 2 O 3 +La 2 O 3 ：0.1-2.9，CaO/SiO 2 ：8.0-11；
Further, the thickness of the ladle top slag is 140-200mm.
Further, in step 2, rare earth is added in the final step of refining.
Further, rare earth is added in a cerium-iron and/or lanthanum-iron mode.
In step 2, before adding rare earth, the mass percentage of dissolved oxygen (O) in molten steel is controlled below 1.5 ppm.
Further, the tundish covering agent is used after the ladle top slag is ground to be below 200 meshes in refining and dried.
Further, the thickness of the tundish covering agent is 200-250 mm.
Compared with the prior art, the invention has the following beneficial effects:
1. by adopting the tundish covering agent and the method, the yield in the refining-continuous casting process is more than 40%, which is improved by more than 8% compared with the existing rare earth yield, and the production cost is reduced by 50 yuan/ton of steel.
2. Aiming at the characteristic that molten steel rare earth existing in a tundish is easy to oxidize in the process of continuous casting of rare earth steel, the minimum rare earth loss is obtained by optimizing the components of a tundish covering agent.
3. The top slag component of the refining ladle can be the same as that of the tundish covering agent, so that the tundish covering agent is manufactured by processing refining slag, the recycling of waste is realized, and the production cost is reduced to the greatest extent.
4. By the technical scheme of the invention, the utilization rate of rare earth metal, namely valuable resources, is improved, and an example is provided for the production of rare earth steel.
Drawings
FIG. 1 is a graph showing the oxygenation levels of various links from refining to continuous casting of rare earth steel before improvement;
fig. 2 shows the rare earth loss of the prior rare earth steel from refining to continuous casting.
FIG. 3 shows oxygenation amounts of various links from refining to continuous casting of the rare earth steel after tundish covering agent and ladle top slag improvement;
fig. 4 shows the rare earth loss of each link from refining to continuous casting of the rare earth steel after the tundish covering agent and ladle top slag are improved.
Detailed Description
The tundish covering agent for smelting rare earth steel and the method for reducing rare earth loss are described in further detail below with reference to specific examples, which are for illustrative purposes only, and the present invention is not limited to these examples.
The rare earth yield is about 30% in rare earth steel production practice, the fluctuation is large, the rare earth components in the product are unstable, the control method for reducing the rare earth loss in the process of smelting the rare earth steel is very necessary to be researched, and the factors influencing the rare earth yield are complex.
Therefore, the invention carries out deep research on rare earth loss in the process of smelting rare earth steel, and provides a tundish covering agent for smelting rare earth steel and a method for reducing rare earth loss.
The invention provides a tundish covering agent for smelting rare earth steel, and the mass percentage of the components is shown in table 1.
TABLE 1 tundish covering component wt./wt.%
| CaO | SiO 2 | MgO | Al 2 O 3 | FeO+MnO | Ce 2 O 3 +La 2 O 3 | CaO/SiO 2 |
| 56-65 | 5-8 | 11-15 | 15-24 | ＜0.5 | 0.1-2.9 | 8.0-11 |
In the research, it was found that the tundish covering agent is one of factors affecting the yield of rare earth. Accordingly, the present invention has been made in an intensive study on the following tundish covering agent. Specifically, the tundish covering agent comprises the following components: 26.91 percent of CaO; siO (SiO) 2 6.79％；Al 2 O 3 18.35％；MgO 16.91％；Fe 2 O 3 0.57％；C 0.01％；H 2 O0.33%; alkalinity: 3.96, ash content 25% and volatile content 5%.
Aiming at the tundish covering agent, the inventor obtains the oxygenation amount of each link in the process from refining to continuous casting of rare earth steel through thermodynamic equilibrium calculation, and obtains the relation diagrams shown in fig. 1 and 2. According to analysis, the rare earth loss of molten steel in the continuous casting process can be remarkably reduced through control optimization of tundish covering agent components, ladle top slag components, ladle lining materials, tundish materials, stopper rod materials, long nozzle materials, immersion nozzle materials and water feeding nozzle materials.
Specifically, as can be seen from fig. 1, the oxygenation of molten steel is related to the oxygenation of intake air, tundish covering agent component, ladle top slag component, ladle lining material, tundish material, stopper material, long nozzle material, immersion nozzle material, and water inlet material, wherein the oxygenation ratio of the intake air, tundish covering agent component and ladle top slag component is 80%. Accordingly, as can be seen from FIG. 2, at a rare earth addition of 50ppm, the total loss of rare earth metals in the process was 33.74ppm, which represents 67.5% of the rare earth addition, and the loss due to the neutralization suction air, the tundish covering agent component and the ladle top slag component was 21.07ppm, which represents 62.4% of the total loss, which represents 42% of the rare earth addition.
For the analysis, the melting temperature of the tundish covering agent is 1380-1450 ℃, so that the CaO content which is weakly reacted with rare earth is improved. The concentration of the rare earth oxide is increased, so that the activity of the rare earth oxide is improved, the rare earth element in molten steel is prevented from being transferred to the tundish covering agent, and the yield of the rare earth is improved.
Wherein Ce in the tundish covering agent 2 O 3 And La (La) 2 O 3 The content of (2) is related to the rare earth component in the molten steel, namely if the molten steel only contains Ce, the tundish covering agent only contains Ce 2 O 3 The method comprises the steps of carrying out a first treatment on the surface of the If the molten steel contains only La, the tundish covering agent contains only La 2 O 3 The method comprises the steps of carrying out a first treatment on the surface of the If the molten steel contains both Ce and La, the tundish covering agent contains Ce at the same time 2 O 3 And La (La) 2 O 3 。
Because the rare earth element has strong reducibility, the rare earth element is reduced at the temperature of molten steel>1500℃) will readily and readily cover SiO in the tundish covering agent 2 、Fe 2 O 3 Oxidation-reduction reaction occurs but is weak with CaO, so that the basicity (CaO/SiO) of the tundish covering agent is improved 2 ) From 3.96 to 8-11, siO 2 The amount of oxygen transfer is reduced, and the loss of rare earth is further reduced. Adding Ce into the tundish covering agent 2 O 3 +La 2 O 3 Then the activity of rare earth oxide in the tundish covering agent is increased, so that the oxidation of rare earth elements in steel is inhibited, and the yield is ensured.
The invention also provides a method for reducing rare earth loss, which comprises the following steps:
step 1, smelting in a converter or an electric furnace;
step 2, refining in an LF furnace or an LF furnace-RH furnace;
step 3, refining and then continuously casting;
specifically, in step 2, slag formation, that is, ladle top slag, is required in the LF refining process, and the above components of the tundish covering agent may be used, and the specific components are shown in table 1.
It is noted that ladle top slag is also one of factors affecting the yield of rare earth from the above. The invention researches the following ladle top slag. Specifically, ladle top slag: alkalinity is 5.5-6.0, caO is 55-60%; siO (SiO) 2 10-12％；Al 2 O 3 28-30％；MgO 6-8％；FeO 0.8-1.0％；MnO 0.8-1.0％；TiO 2 0.5-0.8%; the slag thickness is 138mm; the slag melting point was 1400 ℃.
By comparative analysis of the tundish covering agent of the present invention (see Table 1) and the above steel slag, it was found that the tundish covering agent increased the basicity, thus SiO 2 The content is relatively reduced, and the content of MgO is properly increased, so that the concentration of rare earth oxide is increased.
The rare earth element is known to have strong reducibility and is prepared at the temperature of refined molten steel>1500 ℃ C.) can be easily matched with SiO in the slag 2 The oxidation-reduction reaction of MnO and FeO is carried out, but the oxidation-reduction reaction of FeO is weak with CaO, if the alkalinity (CaO/SiO) 2 ) Increasing from below 6 to 8-11, siO 2 The amount of oxygen transfer is reduced, and the loss of rare earth is further reduced. Adding Ce 2 O 3 +La 2 O 3 Then the concentration and activity of rare earth oxide in the slag are increased, so that the oxidation of rare earth elements in the steel is inhibited, the transfer of the rare earth elements in the molten steel to the slag is prevented, and the yield is further ensured. Meanwhile, the melting temperature of the tundish covering agent is 1380-1450 ℃ which is lower than the temperature of refined molten steel>1500 ℃, so the alloy is in a liquid state during refining, and can play a good role in physical coverage and chemical metallurgy.
From the above analysis, it was found that the tundish covering agent of the present invention is equally applicable to ladle top slag in refining. Specifically, the ladle slag thickness in refining is 140-200mm.
The rare earth steel suitable for the invention is rare earth steel added with Ce and/or La, wherein the mass percentage of the rare earth Ce+La in the rare earth steel is between 0.002 and 0.05 percent, and the rare earth steel is added in a ferroalloy mode, such as cerium iron and/or lanthanum iron. The rare earth metal is added in the last step of refining in the step 2, namely, when the refining process is LF furnace-RH furnace, the rare earth metal is added in a vacuum chamber of the RH furnace, and is added in the final circulation degassing of RH vacuum, so that the rare earth yield is improved under the condition that the rare earth metal is not contacted with oxygen in air and has no slag reaction under vacuum; when the refining process is an LF furnace, refining is added in the LF furnace.
Before adding the rare earth alloy, the mass percentage of the dissolved oxygen (O) in the molten steel is controlled below 1.5 ppm.
The purpose of controlling the dissolved oxygen O in the molten steel before adding the rare earth alloy is to reduce the oxidation of free oxygen in the molten steel to rare earth, but in view of the limit of the current smelting technology level, the oxygen content can only be controlled to be 1.0ppm at the minimum, so the actual control level of the dissolved oxygen O in the molten steel is between 1.0 and 1.5 ppm.
After refining, the ladle is operated to a continuous casting pouring platform, molten steel enters a continuous casting crystallizer through a tundish, argon is blown into the tundish before rare earth steel is cast, the atmosphere of the tundish is kept to be inert, the tundish covering agent is used for covering the molten steel to isolate air, and conventional slag protection and/or argon atmosphere protection is adopted for molten steel injection.
Specifically, in step 3, the aforementioned tundish covering agent of the present invention is used as the tundish covering agent.
Since in practice the refining slag formation is preceded and followed by continuous casting, there is a possible embodiment in which the tundish covering agent is refined final slag.
However, since the slag is agglomerated after refining and the particle size is very large, good dispersibility is required as a tundish covering agent, and thus the refined slag is ground and sieved and used as the tundish covering agent.
The specific method is that the refined slag is ground to below 200 meshes (less than 0.075 mm), and is used after being dried, and the thickness of the tundish covering agent is controlled to be 200-250 mm. Through refining slag, the tundish covering agent has good dispersibility on the surface of molten steel, can isolate air and reduce air suction, thereby reducing oxygen in the air from entering the molten steel and generating oxidation reaction with rare earth elements.
In view of the above, if ladle top slag is used as a tundish covering agent, there are great restrictions in terms of process and operation, because the refining slag of the present furnace cannot be applied as a tundish covering agent of the present furnace, and the ladle top slag of the previous batch cannot be fully applied to the steel grade of the present batch due to the difference in smelting steel grades. Therefore, the tundish covering agent of the present invention needs to be manufactured separately according to the specific steel grade to be produced so as to meet the actual production needs.
By the method, compared with the oxygen increasing amount before improvement, the oxygen increasing amount is reduced by 18.7 percent as can be seen from the comparison of fig. 3 and fig. 1, and the rare earth loss amount is reduced by 8.56 percent from 67.48 percent to 58.92 percent as can be seen from the comparison of fig. 4 and fig. 2. Specifically, the loss amount caused by the tundish covering agent is reduced by 2.3%, the loss amount caused by ladle top slag is reduced by 3.92%, and the loss amount caused by air suction is reduced by 2.34%. The rare earth yield in the steel is improved from 32.52% to 41.08% in the refining-continuous casting process, 8.56% is improved, and the production cost is reduced by 50 yuan/ton of steel.
Comparative example
The 5-furnace wear-resistant steel NM400 is produced, and the production process comprises converter, LF furnace, RH furnace and continuous casting. The target components are as follows: c0.19-0.21%; si 0.55-0.65%; mn 1.45-1.60%; p is less than or equal to 0.015 percent; s is less than or equal to 0.005%; cr 0.35-0.45%; ti 0.01-0.02%; ce 0.02%.
Before adding cerium-iron alloy in RH furnace refining, the average mass percentage of dissolved oxygen (O) in molten steel is 1.43ppm.
After RH is out of station, the average component content in 5 furnaces of molten steel is as follows: c0.19%; si 0.62%; mn 1.50%; p0.013%; s0.004%; cr 0.41%; ti 0.016; ce 0.0357%.
The alkalinity of ladle top slag is 5.5-6.0, caO is 55-60%; siO (SiO) 2 10-12％；Al 2 O 3 28-30％；MgO 6-8％；FeO 0.8-1.0％；MnO 0.8-1.0％；TiO 2 0.5-0.8%; the slag thickness is 138mm; the slag melting point was 1400 ℃.
The tundish covering agent comprises the following components: 26.91 percent of CaO; siO (SiO) 2 6.79％；Al 2 O 3 18.35％；MgO 16.91％；Fe 2 O 3 0.57％；C 0.01％；H 2 O0.33%; alkalinity: 3.96, ash content 25% and volatile content 5%.
The average composition of the molten steel in 5 furnaces in the continuous casting crystallizer is as follows: c0.19%; si 0.60%; mn 1.52%; p0.014%; s0.002%; cr 0.38%; 0.015% of Ti and 0.0160% of Ce. The loss of rare earth is 0.0332 percent. The loss amount is 67.48% of the rare earth content after the RH furnace is out of the station.
Example 1
The produced steel is wear-resistant steel NM400, and the production flow is converter, LF furnace, RH furnace and continuous casting. The target components are as follows: c0.19-0.21%; si 0.55-0.65%; mn 1.45-1.60%; p is less than or equal to 0.015 percent; s is less than or equal to 0.005%; cr 0.35-0.45%; ti 0.01-0.02%; ce 0.02%.
Before adding cerium-iron alloy in RH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.45ppm.
After RH is out of the station, the chemical components of the molten steel are as follows: c0.19%; si 0.58%; mn 1.51%; p0.014%; s0.003%; cr 0.38%; ti 0.016; ce 0.0445%.
Controlling the alkalinity of ladle top slag furnace slag to be 5.5-6.0 and CaO to be 55-60%; siO (SiO) 2 10-12％；Al 2 O 3 28-30％；MgO 6-8％；FeO 0.8-1.0％；MnO 0.8-1.0％；TiO 2 0.5-0.8%; the slag thickness is 138mm; the slag melting point was 1400 ℃.
The alkalinity of the tundish covering agent is 11 and the CaO is 56%; siO (SiO) 2 5.1％；Ce 2 O 3 2.5％；Al 2 O 3 22%; mgO is 14; feO+MnO is 0.3% and the melting point is 1450 ℃. The granularity of the tundish covering agent is below 200 meshes<0.075 mm) and controlling the thickness of the tundish covering agent to be 210mm.
The molten steel in the continuous casting crystallizer comprises the following components: c0.19%; si 0.60%; mn 1.52%; p0.014%; s0.002%; cr 0.38%; 0.015% of Ti and 0.0165% of Ce. The loss of rare earth is 0.0280 percent. The loss amount is 62.88% of the rare earth content after the RH furnace is out of the station, and is reduced by 4.6% compared with the comparative example.
Example 2
The produced steel is corrosion resistant steel Q450NRQ1, and the production flow is converter-LF furnace-continuous casting. The target components are as follows: c is less than or equal to 0.12 percent; si is less than or equal to 0.75 percent; mn is less than or equal to 1.5 percent; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr 0.30-1.25%; cu 0.20-0.55%; ni 0.12-0.65%; la 0.02%.
In LH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.41ppm before lanthanum-iron alloy is added.
After LF goes out, the chemical components of molten steel are as follows: c0.047%; si 0.08%; mn 1.34%; p0.009%; s0.001%; cr 0.73%; cu 0.42%; ni 0.31%; la 0.0537%.
Controlling the alkalinity of ladle top slag furnace slag to be 5.5-6.0 and CaO to be 55-60%; siO (SiO) 2 10-12％；Al 2 O 3 28-30％；MgO 6-8％；FeO 0.8-1.0％；MnO 0.8-1.0％；TiO 2 0.5-0.8%; the slag thickness is 138mm; the slag melting point was 1400 ℃.
The alkalinity of the tundish covering agent is 11 and the CaO is 56%; siO (SiO) 2 5.1％；La 2 O 3 1.0％；Al 2 O 3 24%; mgO is 13%; feO+MnO is 0.4%; the slag thickness is 250mm; the slag melting point was 1445 ℃.
The molten steel in the continuous casting crystallizer comprises the following components: c0.047%; si 0.08%; mn 1.32%; p0.009%; s0.001%; cr 0.72%; cu 0.42%; ni 0.30%; la 0.0201%. The loss of rare earth is 0.0336 percent. The loss amount accounts for 62.6% of the rare earth content of the LF furnace after the LF furnace is out of the station, and is reduced by 4.9% compared with the comparative example.
Example 3
The produced steel is corrosion resistant steel Q450NRQ1, and the production flow is converter-LF furnace-continuous casting. The target components are as follows: c is less than or equal to 0.12 percent; si is less than or equal to 0.75 percent; mn is less than or equal to 1.5 percent; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr 0.30-1.25%; cu 0.20-0.55%; ni 0.12-0.65%; la+ce 0.0298%.
Before cerium-iron and lanthanum-iron alloy are added in LH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.35ppm.
After LF goes out, the chemical components of molten steel are as follows: c0.047%; si 0.08%; mn 1.34%; p0.009%; s0.001%; cr 0.73%; cu 0.42%; ni 0.31%; ce 0.0410%; la 0.0421%.
Controlling the alkalinity of ladle top slag furnace slag to be 5.5-6.0 and CaO to be 55-60%; siO (SiO) 2 10-12％；Al 2 O 3 28-30％；MgO 6-8％；FeO 0.8-1.0％；MnO 0.8-1.0％；TiO 2 0.5-0.8%; the slag thickness is 138mm; the slag melting point was 1400 ℃.
The alkalinity of the tundish covering agent is 11 and the CaO is 65 percent; siO (SiO) 2 5.9％；Ce 2 O 3 +La 2 O 3 1.0％；Al 2 O 3 16%; mgO is 12%; feO+MnO is 0.1%; the slag thickness is 230mm; the slag melting point was 1445 ℃.
The molten steel in the continuous casting crystallizer comprises the following components: c0.047%; si 0.08%; mn 1.32%; p0.009%; s0.001%; cr 0.72%; cu 0.42%; ni 0.30%; ce 0.0162; la 0.0148%. The loss of rare earth is 0.0521 percent. The loss amount accounts for 62.7% of the rare earth content of the LF furnace after the LF furnace is out of the station, and is reduced by 4.8% compared with the comparative example.
Example 4
The produced steel is wear-resistant steel NM400, and the production flow is converter, LF furnace, RH furnace and continuous casting. The target components are as follows: c0.19-0.21%; si 0.55-0.65%; mn 1.45-1.60%; p is less than or equal to 0.015 percent; s is less than or equal to 0.005%; cr 0.35-0.45%; ti 0.01-0.02%; ce 0.04%.
Before adding cerium-iron alloy in RH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.23ppm.
After RH is out of the station, the chemical components of the molten steel are as follows: c0.19%; si 0.62%; mn 1.50%; p0.013%; s0.004%; cr 0.41%; ti 0.016; ce 0.1056%.
Controlling the alkalinity of ladle top slag furnace slag to be 5.5-6.0 and CaO to be 55-60%; siO (SiO) 2 10-12％；Al 2 O 3 28-30％；MgO 6-8％；FeO 0.8-1.0％；MnO 0.8-1.0％；TiO 2 0.5-0.8%; the slag thickness is 138mm; the slag melting point was 1400 ℃.
The alkalinity of the tundish covering agent is 10 and the CaO is 60 percent; siO (SiO) 2 6％；Ce 2 O 3 2％；Al 2 O 3 19%; mgo=12%; feo+mno=0.4%; the slag thickness is 240mm; the slag melting point was 1434 ℃.
The molten steel in the continuous casting crystallizer comprises the following components: c0.20%; si 0.58%; mn 1.51%; p0.013%; s0.002%; cr 0.41%; ti 0.016; ce 0.0394%. The loss amount of rare earth is 0.0662%, the loss amount accounts for 62.7% of the rare earth content after the RH furnace is out of the station, and the loss amount is reduced by 4.8% compared with the comparative example.
Example 5
The produced steel is corrosion resistant steel Q450NRQ1, and the production flow is converter-LF furnace-continuous casting. The target components are as follows: c is less than or equal to 0.12 percent; si is less than or equal to 0.75 percent; mn is less than or equal to 1.5 percent; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr 0.30-1.25%; cu 0.20-0.55%; ni 0.12-0.65%; ce 0.008%.
Before adding cerium-iron alloy in LH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.47ppm.
After LF goes out, the chemical components of molten steel are as follows: c0.048%; si 0.08%; mn 1.31%; p0.01%; s0.004%; cr 0.39%; cu 0.33%; ni 0.036%; ce 0.0224%.
Controlling the alkalinity of ladle top slag furnace slag to be 5.5-6.0 and CaO to be 55-60%; siO (SiO) 2 10-12％；Al 2 O 3 28-30％；MgO 6-8％；FeO 0.8-1.0％；MnO 0.8-1.0％；TiO 2 0.5-0.8%; the slag thickness is 138mm; the slag melting point was 1400 ℃.
The alkalinity of the tundish covering agent is 9, caO is 63 percent, siO 2 7％，Ce 2 O 3 1.0％，Al 2 O 3 17%, mgO=11.5%, feO+MnO=0.35%, slag thickness 240mm, slag melting point 1458 ℃.
The molten steel in the continuous casting crystallizer comprises the following components: c0.048%; si 0.08%; mn 1.31%; p0.01%; s0.004%; cr 0.39%; cu 0.33%; ni 0.36%; ce 0.0083%. The loss of rare earth is 0.0141%. The loss amount accounts for 62.9% of the rare earth content of the LF furnace after the LF furnace is out of the station, and is reduced by 4.6% compared with the comparative example.
Example 6
The produced steel is corrosion resistant steel Q450NRQ1, and the production flow is converter-LF furnace-continuous casting. The target components are as follows: c is less than or equal to 0.12 percent; si is less than or equal to 0.75 percent; mn is less than or equal to 1.5 percent; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr 0.30-1.25%; cu 0.20-0.55%; ni 0.12-0.65%; ce 0.03%.
Before adding cerium-iron alloy in LH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.34ppm.
After LF goes out, the chemical components of molten steel are as follows: c0.047%; si 0.08%; mn 1.34%; p0.009%; s0.001%; cr 0.73%; cu 0.42%; ni 0.31%; ce 0.084%.
Controlling the alkalinity of ladle top slag furnace slag to be 8 and CaO to be 56%; siO (SiO) 2 7％；Ce 2 O 3 1.0％；Al 2 O 3 22%; mgO is 13%; feO+MnO is 0.4%; the thickness of the slag is 170mm; the slag melting point was 1477 ℃.
The tundish covering agent is the same as the comparative example, and comprises the following components: 26.91 percent of CaO; siO (SiO) 2 6.79％；Al 2 O 3 18.35％；MgO 16.91％；Fe 2 O 3 0.57％；C 0.01％；H 2 O0.33%; alkalinity: 3.96, ash content 25% and volatile content 5%.
The molten steel in the continuous casting crystallizer comprises the following components: c0.047%; si 0.08%; mn 1.32%; p0.009%; s0.001%; cr 0.72%; cu 0.42%; ni 0.30%; ce 0.0311%. The loss of rare earth is 0.0530%. The loss amount accounts for 63% of the rare earth content after the LF furnace is out of the station, and is reduced by 4.5% compared with the comparative example.
Example 7
The produced steel is wear-resistant steel NM400, and the production flow is converter, LF furnace, RH furnace and continuous casting. The target components are as follows: c0.19-0.21%; si 0.55-0.65%; mn 1.45-1.60%; p is less than or equal to 0.015 percent; s is less than or equal to 0.005%; cr 0.35-0.45%; ti 0.01-0.02%; ce 0.02%.
Before adding cerium-iron alloy in RH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.45ppm.
After RH is out of the station, the chemical components of the molten steel are as follows: c0.19%; si 0.58%; mn 1.51%; p0.014%; s0.003%; cr 0.38%; ti 0.016; ce 0.0401%.
Controlling the alkalinity of ladle top slag furnace slag to be 11 and CaO to be 56%; siO (SiO) 2 5.1％；Ce 2 O 3 2.5％；Al 2 O 3 22%; mgO is 14; feO+MnO is 0.3%; the slag thickness is 140mm; the slag melting point was 1450 ℃.
The tundish covering agent is ladle top slag in RH furnace refining, and the concrete method is that the RH refining slag is ground to below 200 meshes (< 0.075 mm), and is used after drying, and the thickness of the tundish covering agent is controlled to be 210mm.
The molten steel in the continuous casting crystallizer comprises the following components: c0.19%; si 0.60%; mn 1.52%; p0.014%; s0.002%; cr 0.38%; 0.015% of Ti and 0.0165% of Ce. The loss of rare earth is 0.0236 percent. The loss amount accounts for 58.9% of the rare earth content after the RH furnace is out of the station, and is reduced by 8.58% compared with the comparative example.
Example 8
The produced steel is wear-resistant steel NM400, and the production flow is converter, LF furnace, RH furnace and continuous casting. The target components are as follows: c0.19-0.21%; si 0.55-0.65%; mn 1.45-1.60%; p is less than or equal to 0.015 percent; s is less than or equal to 0.005%; cr 0.35-0.45%; ti 0.01-0.02%; ce 0.02%.
Before adding cerium-iron alloy in RH refining furnace, the mass percentage of dissolved oxygen (O) in molten steel is 1.41ppm.
After RH is out of the station, the chemical components of the molten steel are as follows: c0.19%; si 0.58%; mn 1.51%; p0.014%; s0.003%; cr 0.38%; ti 0.016; ce 0.0381%.
Controlling the alkalinity of ladle top slag furnace slag to be 11 and CaO to be 56%; siO (SiO) 2 5.1％；Ce 2 O 3 2.5％；Al 2 O 3 22%; mgO is 14%; feO+MnO is 0.3%; the slag thickness is 180mm; the slag melting point was 1450 ℃.
The tundish covering agent is ladle top slag in RH furnace refining, and the concrete method is that the RH refining slag is ground to below 200 meshes (< 0.075 mm), and is used after drying, and the thickness of the tundish covering agent is controlled to be 230mm.
The molten steel in the continuous casting crystallizer comprises the following components: c0.19%; si 0.55%; mn 1.52%; p0.014%; s0.002%; cr 0.38%; 0.015% of Ti and 0.0160% of Ce. The loss of rare earth is 0.0221 percent. The loss amount accounts for 58% of the rare earth content of the RH furnace after the RH furnace is out of the station, and is reduced by 9.48% compared with the comparative example.
Example 9
The produced steel is corrosion resistant steel Q450NRQ1, and the production flow is converter-LF furnace-continuous casting. The target components are as follows: c is less than or equal to 0.12 percent; si is less than or equal to 0.75 percent; mn is less than or equal to 1.5 percent; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr 0.30-1.25%; cu 0.20-0.55%; ni 0.12-0.65%; ce 0.03%.
Before adding cerium-iron alloy in LH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.34ppm.
After LF goes out, the chemical components of molten steel are as follows: c0.047%; si 0.08%; mn 1.34%; p0.009%; s0.001%; cr 0.73%; cu 0.42%; ni 0.31%; ce 0.0759%.
Controlling the alkalinity of ladle top slag furnace slag to be 8 and CaO to be 56%; siO (SiO) 2 7％；Ce 2 O 3 1.0％；Al 2 O 3 22%; mgO is 13%; feO+MnO is 0.4%; the slag thickness is 150mm; the slag melting point was 1477 ℃.
The tundish covering agent uses LF furnace refining slag, and the specific method is to grind the LF refining slag to below 200 meshes (< 0.075 mm), dry and use the LF refining slag, and control the thickness of the tundish covering agent to be 220mm.
The molten steel in the continuous casting crystallizer comprises the following components: c0.047%; si 0.08%; mn 1.32%; p0.009%; s0.001%; cr 0.72%; cu 0.42%; ni 0.30%; ce 0.0311%. The loss of rare earth is 0.0448%. The loss amount accounts for 59% of the rare earth content after the LF furnace is out of the station, and is reduced by 8.48% compared with the comparative example.
Example 10
The produced steel is corrosion resistant steel Q450NRQ1, and the production flow is converter-LF furnace-continuous casting. The target components are as follows: c is less than or equal to 0.12 percent; si is less than or equal to 0.75 percent; mn is less than or equal to 1.5 percent; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr 0.30-1.25%; cu 0.20-0.55%; ni 0.12-0.65%; la 0.02%.
In LH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.41ppm before lanthanum-iron alloy is added.
After LF goes out, the chemical components of molten steel are as follows: c0.047%; si 0.08%; mn 1.34%; p0.009%; s0.001%; cr 0.73%; cu 0.42%; ni 0.31%; la 0.0481%.
Controlling the alkalinity of ladle top slag furnace slag to be 11 and CaO to be 56%; siO (SiO) 2 5.1％；La 2 O 3 1.0％；Al 2 O 3 24%; mgO is 13%; feO+MnO is 0.4%; the slag thickness is 200mm; the slag melting point was 1445 ℃.
The tundish covering agent uses LF furnace refining slag, and the specific method is to grind the LF refining slag to below 200 meshes (< 0.075 mm), dry and use the LF refining slag, and control the thickness of the tundish covering agent to be 250mm.
The molten steel in the continuous casting crystallizer comprises the following components: c0.047%; si 0.08%; mn 1.32%; p0.009%; s0.001%; cr 0.72%; cu 0.42%; ni 0.30%; la 0.0201%. The loss of rare earth is 0.028%. The loss amount accounts for 58.2% of the rare earth content of the LF furnace after the LF furnace is out of the station, and is reduced by 9.28% compared with the comparative example.
Example 11
The produced steel is corrosion resistant steel Q450NRQ1, and the production flow is converter-LF furnace-continuous casting. The target components are as follows: c is less than or equal to 0.12 percent; si is less than or equal to 0.75 percent; mn is less than or equal to 1.5 percent; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr 0.30-1.25%; cu 0.20-0.55%; ni 0.12-0.65%; la+ce 0.0298%.
Before cerium-iron and lanthanum-iron alloy are added in LH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.35ppm.
After LF goes out, the chemical components of molten steel are as follows: c0.047%; si 0.08%; mn 1.34%; p0.009%; s0.001%; cr 0.73%; cu 0.42%; ni 0.31%; ce 0.0368%; la 0.0375%.
Controlling the alkalinity of ladle top slag furnace slag to be 11 and CaO to be 65%; siO (SiO) 2 5.9％；Ce 2 O 3 +La 2 O 3 1.0％；Al 2 O 3 16%; mgO is 12%; feO+MnO is 0.1%; the slag thickness is 190mm; the slag melting point was 1445 ℃.
The ladle covering agent uses LF furnace refining slag, and the specific method is to grind the LF refining slag to below 200 meshes (< 0.075 mm), dry and use the ladle covering agent, and control the thickness of the ladle covering agent to be 240mm.
The molten steel in the continuous casting crystallizer comprises the following components: c0.047%; si 0.08%; mn 1.32%; p0.009%; s0.001%; cr 0.72%; cu 0.42%; ni 0.30%; ce 0.0162; la 0.0148%. The loss of rare earth is 0.0433%. The loss amount accounts for 58.3% of the rare earth content of the LF furnace after the LF furnace is out of the station, and is reduced by 9.38% compared with the comparative example.
Example 12
The produced steel is wear-resistant steel NM400, and the production flow is converter, LF furnace, RH furnace and continuous casting. The target components are as follows: c0.19-0.21%; si 0.55-0.65%; mn 1.45-1.60%; p is less than or equal to 0.015 percent; s is less than or equal to 0.005%; cr 0.35-0.45%; ti 0.01-0.02%; ce 0.04%.
Before adding cerium-iron alloy in RH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.23ppm.
After RH is out of the station, the chemical components of the molten steel are as follows: c0.19%; si 0.62%; mn 1.50%; p0.013%; s0.004%; cr 0.41%; ti 0.016; ce 0.0961%.
Controlling the alkalinity of ladle top slag furnace slag to be 10 and CaO to be 60%; siO (SiO) 2 6％；Ce 2 O 3 2％；Al 2 O 3 19%; mgo=12%; feo+mno=0.4%; the slag thickness is 150mm; the slag melting point was 1434 ℃.
The ladle top slag in refining, which is used by an RH furnace, is used as a tundish covering agent, and the concrete method is that the RH refining slag is ground to below 200 meshes (less than 0.075 mm), and is used after being dried, and the thickness of the tundish covering agent is controlled to be 220mm.
The molten steel in the continuous casting crystallizer comprises the following components: c0.20%; si 0.58%; mn 1.51%; p0.013%; s0.002%; cr 0.41%; ti 0.016; ce 0.0394%. The loss amount of rare earth is 0.0567%, the loss amount accounts for 58.98% of the rare earth content after the RH furnace is out of the station, and the loss amount is reduced by 8.9% compared with the comparative example.
Example 13
The produced steel is corrosion resistant steel Q450NRQ1, and the production flow is converter-LF furnace-continuous casting. The target components are as follows: c is less than or equal to 0.12 percent; si is less than or equal to 0.75 percent; mn is less than or equal to 1.5 percent; p is less than or equal to 0.025%; s is less than or equal to 0.008 percent; cr 0.30-1.25%; cu 0.20-0.55%; ni 0.12-0.65%; ce 0.008%.
Before adding cerium-iron alloy in LH furnace refining, the mass percentage of dissolved oxygen (O) in molten steel is 1.47ppm.
After LF goes out, the chemical components of molten steel are as follows: c0.048%; si 0.08%; mn 1.31%; p0.01%; s0.004%; cr 0.39%; cu 0.33%; ni 0.036%; ce 0.0201%.
Controlling the alkalinity of ladle top slag furnace slag to be 9, caO 63% and SiO 2 7％，Ce 2 O 3 1.0％，Al 2 O 3 17%, mgO=11.5%, feO+MnO=0.35%, slag thickness 150mm, slag melting point 1458 ℃.
The tundish covering agent is refined slag used by an LF furnace, and the specific method is to grind the LF refined slag to below 200 meshes (< 0.075 mm), dry the LF refined slag and then use the LF refined slag, and control the thickness of the tundish covering agent to be 220mm.
The molten steel in the continuous casting crystallizer comprises the following components: c0.048%; si 0.08%; mn 1.31%; p0.01%; s0.004%; cr 0.39%; cu 0.33%; ni 0.36%; ce 0.0083%. The loss of rare earth is 0.0118%. The loss amount accounts for 58.78% of the rare earth content of the LF furnace after the LF furnace is out of the station, and is reduced by 8.7% compared with the comparative example.
From the above examples, it can be seen that the improvement of the tundish covering agent reduces the rare earth consumption by about 4%, and the use of the composition of the tundish covering agent for ladle top slag also reduces the rare earth consumption by about 4%. The improvement of the alkalinity of the tundish covering agent is beneficial to the improvement of the rare earth yield, but too high alkalinity can reduce the fluidity, has an influence on the covering effect of molten steel, and further increases the probability of sucking air. The thickness of the tundish covering agent and the ladle top slag is particularly important for slag with higher alkalinity, but exceeds a certain value, the effect is weakened, and the cost is increased.
Claims (5)
1. A method for reducing rare earth loss in smelting rare earth steel, which is characterized by comprising the following steps:
step 1, smelting in a converter or an electric furnace;
step 2, refining in an LF furnace or an LF furnace-RH furnace;
step 3, refining and then continuously casting;
the mass percentage of rare earth Ce and/or La in the rare earth steel is 0.002-0.05%;
in the step 2, the ladle top slag components in the LF furnace refining are CaO in percentage by mass: 55-65, siO 2 ：5-7，MgO：11-13，Al 2 O 3 ：17-24，FeO+MnO＜0.5，Ce 2 O 3 +La 2 O 3 ：0.1-2.9，CaO/SiO 2 :8.0-11, wherein the thickness of ladle top slag is 140-200mm; adding rare earth in the mode of cerium-iron and/or lanthanum-iron in the final refining step, and controlling dissolved oxygen (O) in molten steel before adding rare earth]The mass percentage of (2) is below 1.5 ppm;
in the step 3, molten steel enters a continuous casting crystallizer through a tundish, argon is blown into the tundish before rare earth steel casting, the atmosphere of the tundish is kept to be inert, the molten steel is covered by a tundish covering agent to isolate air, and slag protection and/or argon atmosphere protection are adopted for molten steel injection; the tundish covering agent comprises the following components in percentage by mass: 55-65, siO 2 ：5-7，MgO：11-13，Al 2 O 3 ：17-24，FeO+MnO＜0.5，Ce 2 O 3 +La 2 O 3 ：0.1-2.9，CaO/SiO 2 ：8.0-11，Ce 2 O 3 +La 2 O 3 The activity of rare earth oxide in the tundish covering agent is increased, the oxidation of rare earth element in steel is further inhibited, the tundish covering agent is prepared by grinding ladle top slag in refining to below 200 meshes, and the tundish covering agent is used after drying, and the thickness of the tundish covering agent is 200-250 mm.
2. The method according to claim 1, wherein in the step 2, the ladle top slag component in the LF furnace refining is CaO:55-65, siO 2 ：5-7，MgO：11-13，Al 2 O 3 ：17-24，FeO+MnO＜0.5，Ce 2 O 3 +La 2 O 3 ：0.1-2.9，CaO/SiO 2 ：8.0-10。
3. The method of claim 1, wherein the ladle top slag thickness is 140-190mm.
4. The method according to claim 1, wherein in the step 2, the mass percentage of the dissolved oxygen [ O ] in the molten steel is controlled to be 1.45ppm or less before the rare earth is added.
5. The method of claim 1, wherein the tundish covering agent has a thickness of 210 to 250mm.
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