Method for smelting rare earth-containing rack steel in vacuum induction furnace

Abstract

The application discloses a method for smelting rare earth-containing rack steel in a vacuum induction furnace, which comprises the following steps: raw material preparation, charging, vacuumizing and heating, refining, alloying, secondary charging, electromagnetic stirring and tapping and pouring; wherein the high-purity rare earth intermediate alloy block is added in the secondary charging; the tapping and pouring is directly poured into an ingot mold, the ingot mold is fixed with an iron-based rare earth intermediate alloy rod along the height direction of the ingot, and the ingot mold is placed in an electromagnetic stirrer in the vacuum induction furnace. The method can effectively reduce the contents of O, S and P in the steel, improve the inclusion morphology and size, fully play the micro-alloying effect of the rare earth elements, reduce the contact with the refractory material, effectively improve the rare earth yield, and the rare earth yield is greater than or equal to 80%.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy and manufacturing technology, and specifically relates to a method for smelting rare earth-containing rack steel in a vacuum induction furnace. Background Technology

[0002] Offshore platforms are marine engineering structures that provide a place for offshore operations and living quarters for the development and utilization of marine resources. With the rapid development of marine development, offshore platforms have been widely used in areas such as the exploration and development of seabed oil and gas, the laying of subsea pipelines, the utilization of ocean wave energy, and the construction of offshore airports and factories. Currently, the most widespread application of offshore platforms is in the exploration and development of offshore oil and gas resources.

[0003] By treating with rare earth microalloying elements, rack steel with well-matched properties can be obtained to meet the needs of different working conditions. Because rare earth metals easily form large-sized rare earth oxides during electrolytic preparation, these oxides, when added to the molten steel along with the rare earth metals or alloys, are difficult to float and remove, leading to fluctuations in the performance of rare earth steel. Therefore, high-purity rare earth iron-based master alloys are used, and the content of impurity elements such as O and S is strictly controlled. Only under extremely low oxygen conditions can rare earths play a crucial role in the purification, modification, and microalloying of steel.

[0004] The addition process of rare earth elements has an important impact on the alloy properties. There are two main methods for adding rare earth elements to molten steel in vacuum induction furnaces: one is to add them in the final stage of refining with rare earth intermediate alloy blocks or rare earth wires, and the other is to add them in the ingot mold. Chinese patent application CN 112831715 A discloses "a method for smelting ultra-high manganese steel with ultra-high purity containing rare earth elements". Before tapping the steel, a mixed La-Ce rare earth alloy is added. After adding rare earth elements in this way, (1) due to the reaction of rare earth elements with oxygen and inclusions dissolved in molten steel under vacuum conditions, RE2O3 and RE2O2S are generated. Their specific gravity is similar to or slightly higher than that of molten steel, and they are prone to forming cone segregation at the bottom; (2) secondary oxidation problems are prone to occur. Sulfur is reduced into molten steel, and it is possible that type I sulfides will appear during solidification. Rare earth elements after secondary oxidation no longer have a denaturing effect; (3) rare earth elements are prone to react with the refractory material in the crucible, which reduces the yield of rare earth elements. The composition of rare earth elements in steel fluctuates greatly. At the same time, the crucible wall is prone to nodule formation, which is difficult to clean. Chinese Patent CN1016499410A discloses "A method for adding rare earth elements to molten steel in a vacuum induction furnace". The method involves directly pouring molten steel into an ingot mold filled with rare earth wires. The rare earth element recovery rate is relatively high, (1) but the kinetic conditions are poor, and the rare earth elements do not have enough time to diffuse fully, resulting in segregation of rare earth elements in the steel ingot. (2) Most of the rare earth elements act as altered inclusions and are difficult to play a role in microalloying. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for smelting rare earth-containing rack steel in a vacuum induction furnace, which can not only modify inclusions, but also play a role in micro-alloying, and the inclusions are evenly distributed in the steel ingot.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for smelting rare earth-containing rack steel in a vacuum induction furnace includes raw material preparation, charging, vacuum heating, refining, alloying, secondary charging, electromagnetic stirring, and tapping / casting; wherein, the secondary charging involves adding high-purity rare earth intermediate alloy blocks; the tapping / casting is performed by direct casting, pouring molten steel into an ingot mold, wherein an iron-based rare earth intermediate alloy rod is fixed in the ingot mold along the height of the ingot, and the ingot mold is placed in an electromagnetic stirrer within the vacuum induction furnace.

[0008] Furthermore, the high-purity rare earth intermediate alloy block of the present invention is an Fe-La-Ce intermediate alloy with a uniformity test of ≤1%. The chemical composition and its mass percentage content are as follows: La: 10-12%, Ce: 20-22%, O≤50ppm, S≤10ppm, with the balance being Fe and unavoidable impurities. Moreover, the content of impurity elements is not harmful to the steel grade being smelted.

[0009] Furthermore, the iron-based rare earth master alloy rod of the present invention is an Fe-La-Ce master alloy with a uniformity test of ≤1%. The chemical composition and its mass percentage content are as follows: La: 10-12%, Ce: 20-22%, O≤50ppm, S≤10ppm, with the balance being Fe and unavoidable impurities. Moreover, the content of impurity elements is not harmful to the steel grade being smelted.

[0010] Furthermore, the raw materials used in the preparation of the raw materials described in this invention include pure iron rods, electrolytic manganese, electrolytic nickel, ferrosilicon, ferroboron, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, aluminum granules, high-purity rare earth master alloy blocks, and iron-based rare earth master alloy rods.

[0011] Furthermore, the charging process of this invention involves: first, cleaning the smelting crucible, placing a clean and dry pure iron rod into the crucible, and then placing C, electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, and aluminum granules into the hopper. The iron-based rare earth intermediate alloy rod is then fixed in the ingot mold along the height of the steel ingot, and the ingot mold is placed in the electromagnetic stirrer within the vacuum induction furnace. The furnace cover and furnace opening seal are cleaned with an alcohol cloth, and vacuum silicone grease is applied to prevent furnace leakage.

[0012] Furthermore, the vacuum heating method described in this invention involves closing the furnace lid and evacuating for 15 to 20 minutes. When the vacuum level is ≤3Pa, the furnace is purged with argon gas, and the vacuum process continues. After 10 minutes, the power is turned on for heating.

[0013] Furthermore, the refining process described in this invention is as follows: after all the iron rods and C have melted, refining begins, with the furnace pressure ≤1Pa and the refining time being 20-25 minutes;

[0014] Furthermore, the alloying process described in this invention involves: turning off the vacuum pump, introducing argon gas into the vacuum induction furnace, and after argon filling, ensuring the furnace pressure is >1 Pa. Electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, and aluminum granules are added to the hopper and smelted for 10-15 minutes; subsequently, ferroboron is added.

[0015] Furthermore, the secondary feeding method described in this invention involves adding high-purity rare earth intermediate alloy blocks to the molten steel, measuring the temperature of the molten steel using an infrared thermometer to reach 1580℃-1600℃, and holding the temperature for 2-4 minutes.

[0016] Furthermore, the electromagnetic stirring described in this invention maintains an electromagnetic inductor frequency of 20Hz, a current of 400A, a power of 70KW, and a magnetic induction intensity at the center of the electromagnetic stirrer >800Gs.

[0017] Furthermore, the temperature of the molten steel during the pouring process described in this invention is greater than 1580°C. o C, and use a slow-fast-slow method to pour molten steel into the ingot mold, with the maximum pouring speed of molten steel ≤ 1 / 8 of the maximum capacity of the crucible / s.

[0018] Furthermore, the electromagnetic stirrer of the present invention is ring-shaped, and its magnetic field distribution decreases sequentially from the center to the edge, with the magnetic field at the edge being no less than 400 Gs.

[0019] Furthermore, the chemical composition and mass percentage of the rare earth-containing rack steel of the present invention are as follows: C: 0.15-0.17%, Si: 0.18-0.26%, Mn: 0.96-1.0%, P≤0.006%, S≤0.003%, Ni: 1.7-1.9%, Al: 0.02-0.05%, Cr: 0.8-0.9%, Mo: 0.42-0.48%, B: 0.0012-0.0015%, Ti: 0.01-0.03%, V: 0.04-0.05%; Nb: 0.02-0.03%, La: 0.01-0.03%, Ce: 0.02-0.04%, with the balance being Fe and unavoidable impurities.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1) To stabilize and control the occurrence state of rare earth in steel, high-purity rare earth master alloy is added in two stages. The high-purity rare earth master alloy block is added at the end of refining, which effectively reduces the content of O, S and P in steel, improves the morphology and size of inclusions, and provides conditions for rare earth to play a micro-alloying role.

[0022] 2) A high-purity rare earth intermediate alloy rod is suspended in the height direction of the ingot mold. Under the protection of argon gas, the steel is tapped and poured. The heat of the molten steel is used to uniformly melt the rare earth intermediate alloy rod, giving full play to the micro-alloying effect of rare earth elements. At the same time, the contact with refractory materials is reduced, which effectively improves the rare earth yield and makes the rare earth yield not less than 80%.

[0023] 3) During the solidification process of molten steel, an electromagnetic stirrer is used to control the uniform distribution of rare earth elements, while improving the microsegregation of C, S, P, Si and Mn, controlling the crystallization process, inhibiting recrystallization growth during casting, realizing the controllable growth of inclusions and the homogenization of alloy composition, and obtaining steel ingots with low inclusion level and fine and uniform structure. Attached Figure Description

[0024] Figure 1 A schematic diagram of a method for adding rare earth elements to molten steel; wherein 1 is molten steel; 2 is an iron-based rare earth intermediate alloy rod; and 3 is an electromagnetic stirrer.

[0025] Figure 2 Rating of inclusions in rack steel in Example 1.

[0026] Figure 3 For comparison example 1, the rack steel inclusions are rated.

[0027] Figure 4 For comparison, the inclusion rating of the 3-tooth rack steel is performed.

[0028] Figure 5 Metallographic representation of rack steel in Example 1.

[0029] Figure 6 Metallographic features of rack steel for comparative example 1.

[0030] Figure 7 Metallographic features of rack steel for comparative example 2.

[0031] Figure 8 Metallographic features of rack steel for comparison. Detailed Implementation

[0032] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods. Example 1

[0033] The equipment used in this embodiment is a 50kg vacuum induction furnace with an ultimate vacuum of 0.1Pa, a power of 100KW, and a furnace charge of 45kg. The smelting method for rare earth-containing rack steel is as follows:

[0034] (1) Raw material preparation

[0035] The smelting raw materials include pure iron rods, electrolytic manganese, electrolytic nickel, ferrosilicon, ferroboron, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, aluminum granules, high-purity rare earth master alloy blocks, and iron-based rare earth master alloy rods; all raw materials are kept at 200°C in a vacuum drying oven before loading. o Baking at C for 2 hours; wherein, the uniformity of the high-purity rare earth intermediate alloy block and the iron-based rare earth intermediate alloy rod is ≤1%, and the chemical composition is: La: 10~12%, Ce: 20~22%, O≤50ppm, S≤10ppm, with the balance being Fe and unavoidable impurities.

[0036] (2) Loading

[0037] First, clean the smelting crucible thoroughly. Place a clean, dry pure iron rod into the crucible. Add C, electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, and aluminum granules to the hopper. Fix the iron-based rare earth intermediate alloy rod along the height of the steel ingot into the ingot mold. Place the ingot mold in the electromagnetic stirrer inside the vacuum induction furnace. Figure 1 As shown; clean the seal between the furnace cover and the furnace opening with an alcohol cloth, and apply vacuum silicone grease to prevent the furnace from leaking.

[0038] (3) Vacuum heating

[0039] Close the furnace lid and evacuate for 15 minutes. When the vacuum level reaches 3Pa, purge the furnace with argon gas and continue evacuating. After 10 minutes, turn on the power at 10KW and increase the power by 10KW every 5 minutes until it reaches 100KW.

[0040] (4) Refining

[0041] The furnace charge melts at a rate of 10 kg per hour. After the iron bars and carbon are completely melted, refining begins. The furnace pressure is 1 Pa, and the refining time is 20 minutes.

[0042] (5) Alloying

[0043] The vacuum pump was turned off, and argon gas was introduced into the vacuum induction furnace. After argon filling, the pressure inside the furnace was 0.5 atmospheres. Electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, and aluminum granules were added to the hopper and smelted for 10 minutes. Then, ferroboron was added. A process sample was taken and tested, and the contents of O, S, and P were found to be 0.0016%, 0.0036%, and 0.011%, respectively.

[0044] (6) Secondary feeding

[0045] Add high-purity rare earth intermediate alloy blocks to the molten steel and melt for 3 minutes; use an infrared thermometer to measure the temperature of the molten steel to reach 1595℃ and hold for 2 minutes.

[0046] (7) Electromagnetic stirring

[0047] Turn on the electromagnetic stirrer, keep the electromagnetic induction frequency at 20Hz, the current at 400A, and the power at 70KW. The magnetic field distribution in the electromagnetic stirrer decreases from the center to the edge, with the magnetic induction intensity at the center being 1200Gs and the magnetic induction intensity at the edge being 600Gs.

[0048] (8) Steel pouring

[0049] 1592 molten steel o C. Steel is poured into the ingot mold inside the electromagnetic stirrer by controlling the crucible tilting speed in a slow-fast-slow manner. The maximum pouring speed is ≤1 / 8 of the crucible's maximum capacity / s. The molten steel is injected into two molds through one injection pipe and two pipe bricks. Figure 1 As shown, rare earth elements are cast into thin-walled steel pipes. As the molten steel rises, the rare earth rods gradually dissolve. To prevent the oxidation of REM, Ar gas is blown in to regulate the atmosphere inside the mold. Example 2

[0050] The equipment used in this embodiment is a 50kg vacuum induction furnace with an ultimate vacuum of 0.1Pa, a power of 100KW, and a furnace charge of 45kg. The smelting method for rare earth-containing rack steel is as follows:

[0051] (1) Raw material preparation

[0052] The smelting raw materials include pure iron rods, electrolytic manganese, electrolytic nickel, ferrosilicon, ferroboron, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, aluminum granules, high-purity rare earth master alloy blocks, and iron-based rare earth master alloy rods; all raw materials are kept at 200°C in a vacuum drying oven before loading. o Baking at C for 2 hours; wherein, the uniformity of the high-purity rare earth intermediate alloy block and the iron-based rare earth intermediate alloy rod is ≤1%, and the chemical composition is: La: 10~12%, Ce: 20~22%, O≤50ppm, S≤10ppm, with the balance being Fe and unavoidable impurities.

[0053] (2) Loading

[0054] First, clean the smelting crucible thoroughly. Place a clean, dry pure iron rod into the crucible. Add C, electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, and aluminum granules to the hopper. Fix the iron-based rare earth intermediate alloy rod along the height of the steel ingot into the ingot mold. Place the ingot mold in the electromagnetic stirrer inside the vacuum induction furnace. Figure 1 As shown; clean the seal between the furnace cover and the furnace opening with an alcohol cloth, and apply vacuum silicone grease to prevent the furnace from leaking.

[0055] (3) Vacuum heating

[0056] Close the furnace lid and evacuate for 17 minutes. When the vacuum level reaches 2 Pa, purge the furnace with argon gas and continue evacuating. After 10 minutes, turn on the power at 10 KW and increase the power by 10 KW every 5 minutes until it reaches 100 KW.

[0057] (4) Refining

[0058] The furnace charge melts at a rate of 10 kg per hour. After the iron bars and carbon are completely melted, refining begins. The furnace pressure is 1 Pa, and the refining time is 22 minutes.

[0059] (5) Alloying

[0060] The vacuum pump was turned off, and argon gas was introduced into the vacuum induction furnace. After argon filling, the furnace pressure was 0.5 atmospheres. Electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, and aluminum granules were added to the hopper and smelted for 12 minutes. Then, ferroboron was added. Process samples were taken and tested to find that the O, S, and P contents were 0.0015%, 0.0035%, and 0.012%, respectively.

[0061] (6) Secondary feeding

[0062] Add high-purity rare earth intermediate alloy blocks to the molten steel and melt for 3 minutes; use an infrared thermometer to measure the temperature of the molten steel to reach 1590℃ and hold for 3 minutes.

[0063] (7) Electromagnetic stirring

[0064] Turn on the electromagnetic stirrer, keep the electromagnetic induction frequency at 20Hz, the current at 400A, and the power at 70KW. The magnetic field distribution in the electromagnetic stirrer decreases from the center to the edge, with the magnetic induction intensity at the center being 1100Gs and the magnetic induction intensity at the edge being 550Gs.

[0065] (8) Steel pouring

[0066] 1587 molten steel o C. Steel is poured into the ingot mold inside the electromagnetic stirrer by controlling the crucible tilting speed in a slow-fast-slow manner. The maximum pouring speed is ≤1 / 8 of the crucible's maximum capacity / s. The molten steel is injected into two molds through one injection pipe and two pipe bricks. Figure 1 As shown, rare earth elements are cast into thin-walled steel pipes. As the molten steel rises, the rare earth rods gradually dissolve. To prevent the oxidation of REM, Ar gas is blown in to regulate the atmosphere inside the mold. Example 3

[0067] The equipment used in this embodiment is a 50kg vacuum induction furnace with an ultimate vacuum of 0.1Pa, a power of 100KW, and a furnace charge of 45kg. The smelting method for rare earth-containing rack steel is as follows:

[0068] (1) Raw material preparation

[0069] The smelting raw materials include pure iron rods, electrolytic manganese, electrolytic nickel, ferrosilicon, ferroboron, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, aluminum granules, high-purity rare earth master alloy blocks, and iron-based rare earth master alloy rods; all raw materials are kept at 200°C in a vacuum drying oven before loading. o Baking at C for 2 hours; wherein, the uniformity of the high-purity rare earth intermediate alloy block and the iron-based rare earth intermediate alloy rod is ≤1%, and the chemical composition is: La: 10~12%, Ce: 20~22%, O≤50ppm, S≤10ppm, with the balance being Fe and unavoidable impurities.

[0070] (2) Loading

[0071] First, clean the smelting crucible thoroughly. Place a clean, dry pure iron rod into the crucible. Add C, electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, and aluminum granules to the hopper. Fix the iron-based rare earth intermediate alloy rod along the height of the steel ingot into the ingot mold. Place the ingot mold in the electromagnetic stirrer inside the vacuum induction furnace. Figure 1 As shown; clean the seal between the furnace cover and the furnace opening with an alcohol cloth, and apply vacuum silicone grease to prevent the furnace from leaking.

[0072] (3) Vacuum heating

[0073] Close the furnace lid and evacuate for 19 minutes. When the vacuum level reaches 1 Pa, purge the furnace with argon gas and continue evacuating. After 10 minutes, turn on the power at 10 KW and increase the power by 10 KW every 5 minutes until it reaches 100 KW.

[0074] (4) Refining

[0075] The furnace charge melts at a rate of 10 kg per hour. After the iron bars and carbon are completely melted, refining begins. The furnace pressure is 1 Pa, and the refining time is 25 minutes.

[0076] (5) Alloying

[0077] The vacuum pump was turned off, and argon gas was introduced into the vacuum induction furnace. After argon filling, the pressure inside the furnace was 0.5 atmospheres. Electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, and aluminum granules were added to the hopper and smelted for 15 minutes. Then, ferroboron was added. Process samples were taken and tested to find that the contents of O, S, and P were 0.0014%, 0.0036%, and 0.012%, respectively.

[0078] (6) Secondary feeding

[0079] Add high-purity rare earth intermediate alloy blocks to the molten steel and melt for 3 minutes; use an infrared thermometer to measure the temperature of the molten steel to reach 1587℃ and hold for 4 minutes.

[0080] (7) Electromagnetic stirring

[0081] Start the electromagnetic stirrer, keep the electromagnetic induction frequency at 20Hz, the current at 400A, and the power at 70KW. The magnetic field distribution in the electromagnetic stirrer decreases from the center to the edge, with a magnetic induction intensity of 1000Gs at the center and 500Gs at the edge.

[0082] (8) Steel pouring

[0083] 1582 molten steel o C. Steel is poured into the ingot mold inside the electromagnetic stirrer by controlling the crucible tilting speed in a slow-fast-slow manner. The maximum pouring speed is ≤1 / 8 of the crucible's maximum capacity / s. The molten steel is injected into two molds through one injection pipe and two pipe bricks. Figure 1 As shown, rare earth elements are cast into thin-walled steel pipes. As the molten steel rises, the rare earth rods gradually dissolve. To prevent the oxidation of REM, Ar gas is blown in to regulate the atmosphere inside the mold. Comparative Example 1

[0084] The difference between this comparative example and Example 1 is that the rare earth alloy block was not added through a secondary feeding method.

[0085] The equipment used in this comparative example is a 50kg vacuum induction furnace with an ultimate vacuum of 0.1Pa, a power of 100KW, and a furnace charge of 45kg. The smelting method for rare earth-containing rack steel is as follows:

[0086] (1) Raw material preparation

[0087] The smelting raw materials include pure iron rods, electrolytic manganese, electrolytic nickel, ferrosilicon, ferroboron, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, aluminum granules, high-purity rare earth master alloy blocks, and iron-based rare earth master alloy rods; all raw materials are kept at 200°C in a vacuum drying oven before loading. o Baking at C for 2 hours; wherein, the uniformity of the high-purity rare earth intermediate alloy block and the iron-based rare earth intermediate alloy rod is ≤1%, and the chemical composition is: La: 10~12%, Ce: 20~22%, O≤50ppm, S≤10ppm, with the balance being Fe and unavoidable impurities.

[0088] (2) Loading

[0089] First, clean the smelting crucible thoroughly. Place a clean and dry pure iron rod into the crucible. Add C, electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, and aluminum granules into the hopper. Fix the iron-based rare earth intermediate alloy rod along the height of the steel ingot into the ingot mold, and place the ingot mold in the electromagnetic stirrer inside the vacuum induction furnace. Clean the furnace cover and furnace opening seal with an alcohol cloth, and apply vacuum silicone grease to prevent the furnace from leaking.

[0090] (3) Vacuum heating

[0091] Close the furnace lid and evacuate for 16 minutes. When the vacuum level reaches 3Pa, purge the furnace with argon gas and continue evacuating. After 10 minutes, turn on the power at 10KW and increase the power by 10KW every 5 minutes until it reaches 100KW.

[0092] (4) Refining

[0093] The furnace charge melts at a rate of 15 kg per hour. After the iron bars and carbon are completely melted, refining begins. The furnace pressure is 1 Pa, and the refining time is 22 minutes.

[0094] (5) Alloying

[0095] The vacuum pump was turned off, and argon gas was introduced into the vacuum induction furnace. After argon filling, the pressure inside the furnace was 0.4 atmospheres. Electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, sponge titanium, and aluminum granules were added to the hopper and smelted for 13 minutes. Then, ferroboron was added. Process samples were taken and tested to find that the contents of O, S, and P were 0.0016%, 0.0032%, and 0.012%, respectively.

[0096] (6) Electromagnetic stirring

[0097] Turn on the electromagnetic stirrer, keep the electromagnetic induction frequency at 20Hz, the current at 400A, and the power at 70KW. The magnetic field distribution in the electromagnetic stirrer decreases from the center to the edge. The magnetic induction intensity at the center of the electromagnetic stirrer is 1000Gs, and the magnetic induction intensity at the edge is 500Gs.

[0098] (7) Steel pouring

[0099] 1595 molten steel o At time C, molten steel is poured, and by controlling the crucible tilting speed, a slow-fast-slow method is used to pour the molten steel into the ingot mold placed inside the electromagnetic stirrer. The maximum pouring speed of the molten steel is ≤1 / 8 of the crucible's maximum capacity / s. The molten steel is injected into two molds through one injection pipe and two pipe bricks. Figure 1 As shown. Comparative Example 2

[0100] The differences between this comparative example and Example 1 are: ① the rare earth alloy blocks were not added via a secondary feeding method; ② an iron-based rare earth intermediate alloy rod was fixed inside the ingot mold, but no electromagnetic stirrer was installed in the vacuum induction furnace. The amount of rare earth added in this comparative example is the same as the total amount of rare earth alloy blocks and rare earth intermediate alloy rods in Example 2. Comparative Example 3

[0101] The difference between this comparative example and Example 1 is that no rare earth alloy blocks and rare earth intermediate alloy rods were added.

[0102] The chemical composition of the rare earth-containing rack steels in each embodiment and comparative example is shown in Table 1.

[0103] Table 1. Chemical composition (wt%) of rare earth-containing rack steel in each embodiment.

[0104]

[0105] As can be seen from Table 1, after adding rare earth elements in each embodiment and Comparative Example 1, the O content in the rare earth-containing rack steel decreased from 0.0014%–0.0016% to 0.0003%–0.0005%, the S content decreased from 0.0035%–0.0036% to 0.0005%–0.0006%, and the P content decreased from 0.011%–0.012% to 0.005%–0.0006%. That is, the O, S, and P contents all decreased significantly, indicating that the O, S, and P contents were significantly reduced after adding rare earth elements in each embodiment. The O, S, and P contents in Comparative Example 1 and Comparative Example 2 did not decrease significantly, indicating that adding high-purity rare earth intermediate alloy blocks at the end of refining can effectively reduce the O, S, and P contents in the steel.

[0106] According to GB / T 10561-2023, the inclusions in Example 1, Comparative Example 1, and Comparative Example 3 were rated, and the results are as follows: Figure 2 , Figure 3 and Figure 4 As shown, Figure 2 The rating result is D category, sub-category 0.5. Figure 3 The rating result is Category B, subcategory 2.5. Figure 4 The rating result is Class B, Grade 1 (coarse series). A comparison between Example 1 and Comparative Example 1 demonstrates that adding rare earth elements at the end of refining can modify inclusions, thereby improving their morphology and size, and significantly improving metallurgical quality. A comparison between Comparative Example 1 and Comparative Example 3 shows that adding rare earth elements only to the hanging bar in the ingot mold failed to improve the morphology and size of inclusions in the steel.

[0107] The rare earth recovery rates of rare earth-containing rack steel ingots in each embodiment and Comparative Examples 1 and 2 are shown in Table 2.

[0108] Table 2. Rare earth recovery rate (%) of rare earth-containing rack steel ingots in each embodiment.

[0109]

[0110] As can be seen from Example 1 and Comparative Example 1 in Table 2, the yield of rare earth elements added twice, once at the end of refining and once in the ingot mold, was significantly higher than that of rare earth elements added only at the end of refining. As can be seen from Example 2 and Comparative Example 2, the yield of rare earth elements was significantly improved after using an electromagnetic stirrer, and the segregation of rare earth elements in the steel ingot was significantly reduced.

[0111] The metallographic structures of the rare earth-containing rack steels obtained in Example 1 and Comparative Example 1 are shown in the figures below. Figure 5 and Figure 6The metallographic structures of the rare earth-containing rack steels obtained in Comparative Examples 2 and 3 are shown in the figures below. Figure 7 and Figure 8 .from Figure 5 and Figure 6 As can be seen from the data, the rare earth-containing rack steel in Example 1 is predominantly composed of equiaxed crystals, and the grain size is significantly finer compared to Comparative Example 1, which has significantly coarser grains. This indicates that the rare earth addition method in Example 1 allows the rare earth to play a greater role in microalloying. Compared to Comparative Example 2, the rare earth-containing rack steel in Comparative Example 1 has a higher proportion of equiaxed crystals, indicating that electromagnetic stirring increases the equiaxed crystal ratio. In Comparative Example 3, dendrites are formed in the metallographic structure, and the dendrite spacing is significantly increased compared to Example 1 with added rare earth, indicating that the addition of rare earth increases the equiaxed crystal ratio and refines the dendrite spacing.

[0112] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for smelting rare earth-containing rack steel in a vacuum induction furnace, characterized in that, The process includes raw material preparation, charging, vacuum heating, refining, alloying, secondary charging, electromagnetic stirring, and steel casting. The secondary charging involves adding high-purity rare earth master alloy blocks. Steel casting is performed by direct casting, pouring molten steel into an ingot mold. The ingot mold has iron-based rare earth master alloy rods fixed along its height, and is placed within an electromagnetic stirrer in a vacuum induction furnace. The chemical composition and mass percentage of the rare earth-containing rack steel are: C: 0.15–0.17%, Si: 0.18–0.26%. %, Mn: 0.96~1.0%, P≤0.006%, S≤0.003%, Ni: 1.7~1.9%, Al: 0.02~0.05%, Cr: 0.8~0.9%, Mo: 0.42~0.48%, B: 0.0012~0.0015%, Ti: 0.01~0.03%, V: 0.04~0.05%; Nb: 0.02~0.03%, La: 0.01~0.03%, Ce: 0.02~0.04%, balance Fe and unavoidable impurities.

2. The method for smelting rare earth-containing rack steel in a vacuum induction furnace according to claim 1, characterized in that, The high-purity rare earth intermediate alloy block is an Fe-La-Ce intermediate alloy with a uniformity of ≤1%. Its chemical composition and mass percentage are: La: 10-12%, Ce: 20-22%, O ≤50ppm, S ≤10ppm, and the balance is Fe and unavoidable impurities.

3. The method for smelting rare earth-containing rack steel in a vacuum induction furnace according to claim 1, characterized in that, The iron-based rare earth master alloy rod is an Fe-La-Ce master alloy with a uniformity of ≤1%. Its chemical composition and mass percentage are as follows: La: 10-12%, Ce: 20-22%, O ≤50ppm, S ≤10ppm, and the balance is Fe and unavoidable impurities.

4. The method for smelting rare earth-containing rack steel in a vacuum induction furnace according to claim 1, characterized in that, Vacuum heating: Close the furnace cover and evacuate for 15 to 20 minutes. When the vacuum degree is ≤3Pa, purge the furnace with argon gas, continue evacuating, and turn on the power to heat after 10 minutes.

5. A method for smelting rare earth-containing rack steel in a vacuum induction furnace according to claim 1, characterized in that, The refining process begins after all the iron rods and carbon in the raw materials have melted. The furnace pressure is ≤1Pa and the refining time is 20-25 minutes. The alloying process involves: turning off the vacuum pump, introducing argon gas into the vacuum induction furnace, and ensuring the furnace pressure is >1 Pa after argon filling. Then, electrolytic manganese, electrolytic nickel, ferrosilicon, ferromolybdenum, ferrovanadium, ferroniobium, and sponge titanium are added to the hopper. After smelting for 10-15 minutes, ferroboron is added.

6. A method for smelting rare earth-containing rack steel in a vacuum induction furnace according to claim 1, characterized in that, The secondary feeding involves adding high-purity rare earth intermediate alloy blocks to the molten steel, measuring the temperature of the molten steel using an infrared thermometer to reach 1580℃-1600℃, and holding it at that temperature for 2-4 minutes. The temperature of the molten steel during the tapping and casting process is greater than 1580°C. o C, and use a slow-fast-slow method to pour molten steel into the ingot mold, with the maximum pouring speed of molten steel ≤ 1 / 8 of the maximum capacity of the crucible / s.

7. A method for smelting rare earth-containing rack steel in a vacuum induction furnace according to claim 1, characterized in that, The electromagnetic stirrer is ring-shaped, and its magnetic field distribution decreases from the center to the edge, with the magnetic field at the edge being no less than 400 Gs.

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