Low-silicon-manganese-aluminum-sulfur refined steel and smelting method thereof

Abstract

The invention provides low-silicon-manganese-aluminum-sulfur refined steel and a smelting method thereof, belongs to the technical field of metallurgy, and solves the problems of slagging, deep dephosphorization and deep desulfurization under the condition of extremely low silicon, manganese and aluminum. The smelting method comprises the following steps that an EAF electric arc furnace is adopted for smelting full scrap steel, molten steel obtained after tapping enters an LF furnace to be heated, and the molten steel enters the LF furnace to be heated; lime, fluorite and calcium carbide are added in batches for reduction desulfurization, and finally the ladle is hoisted to a VD furnace for vacuumizing operation; and after the molten steel enters the VD furnace, the vacuum degree and temperature are controlled, and finally ladle hoisting pouring and mold casting forming are conducted. According to the method, smelting and ingot casting are conducted through the electric arc furnace-LF furnace refining-VD furnace vacuum refining-die casting process route, smelting is reasonably selected, smelting of the low-silicon-manganese-aluminum-sulfur refined steel through the electric arc furnace is achieved, and the method can be used for smelting base materials of high-end precision alloy, high-temperature alloy and other materials.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a low-silicon manganese aluminum sulfur refined steel and its smelting method. Background Technology

[0002] Precision steel belongs to the category of low-silicon, low-manganese, low-phosphorus, low-sulfur, and low-aluminum steels. This type of steel is mainly used as the base material for smelting high-end precision alloys, high-temperature alloys, and other materials. It has a wide range of applications and promising market prospects.

[0003] Currently, pure iron is used as the base material in the production of high-end precision alloys and high-temperature alloys. However, pure iron has a high content of phosphorus and sulfur, which cannot meet the requirements of these materials. This invention uses a smelting method of scrap steel → electric furnace smelting → LF furnace refining → VD furnace vacuum degassing → die casting to produce ultra-low silicon manganese aluminum sulfur steel. On the one hand, it ensures the requirements of the base material for high-end materials, and on the other hand, it reduces production costs by using carbon scrap steel to produce the above-mentioned steel materials. Summary of the Invention

[0004] The purpose of this invention is to provide a low-silicon, manganese, aluminum, and sulfur refined steel and its smelting method to solve the problems of deep dephosphorization and deep desulfurization in slag formation under extremely low silicon, manganese, and aluminum conditions.

[0005] The technical solution of the present invention is: a low-silicon manganese aluminum sulfur steel, wherein the chemical composition of the low-silicon manganese aluminum sulfur steel, by weight percentage, consists of the following components: C: ≤0.25, Si: ≤0.05, Mn: ≤0.05, P: ≤0.003, S: ≤0.001, Al: ≤0.005, with the balance being Fe and unavoidable impurities.

[0006] A method for smelting low-silicon manganese aluminum sulfur steel includes the following steps: Step 1: Smelt all scrap steel using an EAF electric arc furnace, adding carbon at 0.5-0.7%; perform dephosphorization during the molten oxygen phase, controlling the temperature at 1540℃-1570℃, until C≤0.04% and P≤0.001%, and remove 100% of the slag; After adding slag to the scrap steel, oxygen is blown and the temperature is raised to 1650℃. The composition is controlled as follows: C: 0.05-0.10%, P≤0.001%, Si≤0.03%, Mn≤0.04%. The steel is tapped after the temperature is controlled at 1650-1670℃. No additional materials containing silicon or manganese are added during the tapping and heating process of the EAF electric arc furnace. Step 2: After tapping, the molten steel enters the LF furnace and is heated to above 1640℃. In four batches, 20-25 kg / t of lime, 6-7 kg / t of fluorite, and 6-7 kg / t of calcium carbide are added for reduction and desulfurization. The temperature is controlled at 1660-1680℃, and the composition is controlled as follows: C: ≤0.25%, Si: ≤0.05%, Mn: ≤0.05%, P: ≤0.003%, S: ≤0.001%, Al: ≤0.005%. Finally, the ladle is hoisted to the VD furnace for vacuuming. Step 3: After the molten steel enters the VD furnace, the vacuum degree is controlled to be ≤67Pa, and the pressure is maintained for 20 minutes. After breaking the vacuum, soft blowing is carried out for ≥10 minutes, and the temperature is controlled at 1590-1610℃. Finally, the ladle is used for pouring and molding.

[0007] As a further improvement of the present invention, in step one, the scrap steel is carbon scrap steel.

[0008] As a further improvement of the present invention, in step two, the fluorite is selected as high-purity premium green fluorite, with a chemical composition of CaF2≥94%, SiO2≤2.5%, S≤0.02%, P≤0.06%, and H2O≤0.3%; the lime is selected as premium lime, with a chemical composition of CaO≥95%, SiO2≤1.5%, S≤0.02%, H2O≤0.3%, loss on ignition≤2%, and an activity of 4mol / ml, 40±1℃, 10min, and an activity ≥360; the calcium carbide is selected as superior grade calcium carbide with a particle size <10mm. 2 .

[0009] The beneficial effects of this invention are as follows: This invention strictly limits the chemical composition of high-quality steel. This composition design specifically addresses the pain point of "high P and S content in pure iron matrix" in the background technology: P and S are typical harmful elements in steel. Their ultra-low content (P≤0.003%, S≤0.001%) can significantly reduce the formation of phosphide and sulfide inclusions, avoiding such inclusions from becoming weak points in the subsequent smelting of high-end precision alloys and high-temperature alloys. At the same time, the strict limitation of Si, Mn, and Al can prevent them from forming brittle intermetallic compounds with alloying elements (such as nickel, chromium, etc.), ensuring the processing plasticity and high-temperature stability of the matrix material, and laying a core foundation for improving the mechanical properties and corrosion resistance of high-end alloys.

[0010] This invention adopts a process route of "EAF electric arc furnace smelting → LF furnace refining → VD furnace vacuum refining → ingot casting", with each process parameter closely matched to the target, forming a technical closed loop: EAF electric arc furnace stage: By setting the temperature range during the molten oxygen period, the thermodynamic advantages of the dephosphorization reaction are guaranteed, while avoiding excessive temperature that could lead to phosphorus re-dissolution; and it is clearly stated that "no additional materials containing silicon or manganese are added during the tapping and heating process", thus eliminating the introduction of the target control elements from the source and ensuring that the tapping composition is Si≤0.03% and Mn≤0.04%. LF furnace stage: Batch feeding can avoid incomplete reaction caused by local slag accumulation, the low SiO2 content of fluorite (≤2.5%) can reduce silicon introduction, and calcium carbide provides a strong reducing atmosphere, ultimately achieving S≤0.001%; VD furnace stage: By "holding pressure at ≤67Pa for 20min + soft blowing for ≥10min", gases such as H2 and N2 in the steel are further removed (the vacuum environment reduces the partial pressure of the gas and promotes the escape of the gas). At the same time, the pouring temperature is controlled at 1590-1610℃ to avoid insufficient pouring due to the temperature being too low or coarse grains due to the temperature being too high, thus ensuring the quality of the mold casting.

[0011] The synergistic effect of the above processes effectively solves the invention objective of "difficulty in slag formation under extremely low silicon, manganese, and aluminum conditions", and achieves stable compliance of the steel composition.

[0012] This invention abandons the traditional reliance on pure iron as the raw material for high-end alloy matrices and explicitly uses carbon scrap steel as the smelting base material. From a cost perspective, the market price of carbon scrap steel is significantly lower than that of pure iron, which can directly reduce the raw material cost of high-end matrix materials. From a technical perspective, through the carbon blending and dephosphorization of the EAF electric arc furnace and the refining control of the LF furnace, impurity elements (such as P, S, Si, Mn, etc.) in carbon scrap steel can be effectively removed, ultimately producing high-quality steel that meets the requirements. This breaks the limitation that "high quality must rely on high-cost raw materials" and achieves a balance between "low-cost raw materials + high-quality products".

[0013] This invention has determined the optimal range for key parameters in each process (such as EAF melting temperature, LF slag addition amount and batch, VD furnace vacuum degree and soft blowing time, etc.) through multiple experiments. Furthermore, the selected "premium lime, high-purity fluorite, and superior calcium carbide" are all readily available industrial materials, requiring no special rare raw materials or complex equipment. Following this process, qualified high-quality steel can be stably produced, indicating that the process has good repeatability and operability, facilitating industrial-scale mass production.

[0014] This invention designs a smelting method for low-silicon, low-manganese, ultra-low-aluminum, and ultra-low-sulfur steel, employing an electric arc furnace smelting-LF ladle refining-VD furnace vacuum refining-in-mold casting process. This invention proposes a smelting and casting process route for low-silicon, manganese, aluminum, and sulfur refined steel, utilizing carbon scrap steel to reduce material costs and achieving the production of low-silicon, manganese, aluminum, and sulfur refined steel using an electric arc furnace. The smelting process of this invention is easy to implement and highly efficient. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to the embodiments.

[0016] Example 1 The chemical composition of the low silicon manganese aluminum sulfur steel in this embodiment, by weight percentage, consists of the following components: C: 0.25, Si: 0.05, Mn: 0.05, P: 0.003, S: 0.001, Al: 0.005, with the balance being Fe and unavoidable impurities.

[0017] The smelting method for low-silicon manganese aluminum sulfur steel includes the following steps: Step 1: Smelt carbon scrap steel using an EAF electric arc furnace, adding 0.5% carbon; perform dephosphorization during the molten oxygen phase, controlling the temperature at 1540℃, until C is 0.04% and P is 0.001%, and remove 100% of the slag. After adding slag, carbon scrap steel is heated to 1650℃ by oxygen blowing. Its composition is controlled as follows: C: 0.05%, P: 0.001%, Si: 0.03%, Mn: 0.04%. Steel is tapped after the temperature is controlled at 1650℃. No additional materials containing silicon or manganese are added during the tapping and heating process of the EAF electric arc furnace.

[0018] Step 2: After tapping, the molten steel enters the LF furnace and is heated to 1640℃. In four batches, a total of 20 kg / t of lime, 6 kg / t of fluorite, and 6 kg / t of calcium carbide are added for reduction and desulfurization. The temperature is controlled at 1660℃, and the composition is controlled as follows: C: 0.25%, Si: 0.05%, Mn: 0.05%, P: 0.003%, S: 0.001%, Al: 0.005%. Finally, the ladle is hoisted to the VD furnace for vacuuming. The fluorite used is high-purity, premium-grade green fluorite, with the following chemical composition: CaF2: 94%, SiO2: 2.5%, S: 0.02%, P: 0.06%, H2O: 0.3%. The lime used is premium-grade lime, with the following chemical composition: CaO: 95%, SiO2: 1.5%, S: 0.02%, H2O: 0.3%, loss on ignition 2%, and an activity of 360 at 4 mol / ml, 41℃, and 10 min. The calcium carbide used is superior-grade calcium carbide with a particle size of 9 mm. 2 .

[0019] Step 3: After the molten steel enters the VD furnace, the vacuum degree is controlled at 67Pa and the pressure is maintained for 20 minutes. After breaking the vacuum, soft blowing is performed for 10 minutes, and the temperature is controlled at 1590℃. Finally, the steel is poured into the ladle and molded into shape.

[0020] Example 2 The chemical composition of the low silicon manganese aluminum sulfur steel in this embodiment, by weight percentage, consists of the following components: C: 0.24, Si: 0.04, Mn: 0.04, P: 0.002, S: 0.0009, Al: 0.004, with the balance being Fe and unavoidable impurities.

[0021] The smelting method for low-silicon manganese aluminum sulfur steel includes the following steps: Step 1: Smelt carbon scrap steel using an EAF electric arc furnace, adding 0.6% carbon; perform dephosphorization during the molten oxygen phase, controlling the temperature at 1555℃, until C is 0.03% and P is 0.0009%, and remove 100% of the slag. After adding slag, carbon scrap steel is heated to 1650℃ by oxygen blowing. Its composition is controlled as follows: C: 0.07%, P: 0.0009%, Si: 0.02%, Mn: 0.03%. Steel is tapped after the temperature is controlled at 1660℃. No additional materials containing silicon or manganese are added during the tapping and heating process of the EAF electric arc furnace.

[0022] Step 2: After tapping, the molten steel enters the LF furnace and is heated to 1650℃. In four batches, a total of 23 kg / t of lime, 7 kg / t of fluorite, and 7 kg / t of calcium carbide are added for reduction and desulfurization. The temperature is controlled at 1670℃, and the composition is controlled as follows: C: 0.24%, Si: 0.04%, Mn: 0.04%, P: 0.002%, S: 0.0009%, Al: 0.004%. Finally, the ladle is hoisted to the VD furnace for vacuuming. The fluorite used is high-purity, premium-grade green fluorite, with the following chemical composition: CaF2: 95%, SiO2: 2.4%, S: 0.015%, P: 0.05%, H2O: 0.2%. The lime used is premium-grade lime, with the following chemical composition: CaO: 96%, SiO2: 1.4%, S: 0.019%, H2O: 0.2%, loss on ignition 1.9%, and an activity of 370 at 4 mol / ml, 40℃, and 10 min. The calcium carbide used is superior-grade calcium carbide with a particle size of 8 mm. 2 .

[0023] Step 3: After the molten steel enters the VD furnace, the vacuum degree is controlled at 66Pa and the pressure is maintained for 20 minutes. After breaking the vacuum, soft blowing is carried out for 12 minutes, and the temperature is controlled at 1600℃. Finally, the ladle is used for pouring and molding.

[0024] Example 3 The chemical composition of the low silicon manganese aluminum sulfur steel in this embodiment, by weight percentage, consists of the following components: C: 0.23, Si: 0.03, Mn: 0.03, P: 0.001, S: 0.0008, Al: 0.003, with the balance being Fe and unavoidable impurities.

[0025] The smelting method for low-silicon manganese aluminum sulfur steel includes the following steps: Step 1: Smelt carbon scrap steel using an EAF electric arc furnace, adding 0.7% carbon; perform dephosphorization during the molten oxygen phase, controlling the temperature at 1570℃, until C: 0.02% and P: 0.0008%, and remove 100% of the slag; After adding slag, carbon scrap steel is heated to 1650℃ by oxygen blowing. Its composition is controlled as follows: C: 0.10%, P: 0.0008%, Si: 0.01%, Mn: 0.02%. Steel is tapped after the temperature is controlled at 1670℃. No additional materials containing silicon or manganese are added during the tapping and heating process of the EAF electric arc furnace.

[0026] Step 2: After tapping, the molten steel enters the LF furnace and is heated to 1660℃. In four batches, a total of 25 kg / t of lime, 7 kg / t of fluorite, and 7 kg / t of calcium carbide are added for reduction and desulfurization. The temperature is controlled at 1680℃, and the composition is controlled as follows: C: 0.23%, Si: 0.03%, Mn: 0.03%, P: 0.001%, S: 0.0008%, Al: 0.003%. Finally, the ladle is hoisted to the VD furnace for vacuuming. The fluorite used is high-purity, premium-grade green fluorite, with the following chemical composition: CaF2: 96%, SiO2: 2.3%, S: 0.01%, P: 0.04%, H2O: 0.1%. The lime used is premium-grade lime, with the following chemical composition: CaO: 97%, SiO2: 1.3%, S: 0.018%, H2O: 0.1%, loss on ignition 1.8%, and an activity of 380 at 4 mol / ml, 39℃, and 10 min. The calcium carbide used is superior-grade calcium carbide with a particle size of 7 mm. 2 .

[0027] Step 3: After the molten steel enters the VD furnace, the vacuum degree is controlled at 65Pa and the pressure is maintained for 20 minutes. After breaking the vacuum, soft blowing is performed for 15 minutes, and the temperature is controlled at 1610℃. Finally, the steel is poured into the ladle and molded into shape.

[0028] Table 1 shows the comparison table of chemical composition and key process parameters of the low silicon manganese aluminum sulfur steels prepared in Examples 1-3.

[0029] As can be seen from the data in Table 1, the chemical composition of the steel in Examples 1-3 fully meets the requirements of claim 1, namely "C≤0.25%, Si≤0.05%, Mn≤0.05%, P≤0.003%, S≤0.001%, Al≤0.005%". Further analysis shows that as the carbon content of EAF increases from 0.5% to 0.7%, the EAF molten oxygen temperature increases from 1540℃ to 1570℃, the lime addition of LF increases from 20kg / t to 25kg / t, and the VD soft blowing time is extended from 10min to 15min, the contents of C, Si, Mn, P, S, and Al in the refined steel gradually decrease (e.g., P decreases from 0.003% to 0.001%, and S decreases from 0.001% to 0.0008%). This proves that the “EAF-LF-VD-mold casting” process route and key parameters (carbon content, molten oxygen temperature, slag addition, vacuum degree, and soft blowing time) described in this invention can effectively control the composition of refined steel and achieve deep dephosphorization and desulfurization and low silicon manganese aluminum control.

[0030] Meanwhile, the refined steel produced using carbon scrap steel raw materials can meet the purity requirements of high-end precision alloys and high-temperature alloy matrix materials, verifying the dual advantages of this smelting method in terms of technical feasibility and economic efficiency.

Claims

1. A low-silicon, manganese, aluminum, and sulfur steel, characterized in that: The chemical composition of the low-silicon manganese aluminum sulfur steel, by weight percentage, consists of the following components: C: ≤0.25, Si: ≤0.05, Mn: ≤0.05, P: ≤0.003, S: ≤0.001, Al: ≤0.005, with the balance being Fe and unavoidable impurities.

2. A method for smelting low-silicon, manganese, aluminum, and sulfur refined steel, characterized in that: Includes the following steps: Step 1: Smelt all scrap steel using an EAF electric arc furnace, adding carbon at 0.5-0.7%; perform dephosphorization during the molten oxygen phase, controlling the temperature at 1540℃-1570℃, until C≤0.04% and P≤0.001%, and remove 100% of the slag; After adding slag to the scrap steel, oxygen is blown and the temperature is raised to 1650℃. The composition is controlled as follows: C: 0.05-0.10%, P≤0.001%, Si≤0.03%, Mn≤0.04%. The steel is tapped after the temperature is controlled at 1650-1670℃. No additional materials containing silicon or manganese are added during the tapping and heating process of the EAF electric arc furnace. Step 2: After tapping, the molten steel enters the LF furnace and is heated to above 1640℃. In four batches, 20-25 kg / t of lime, 6-7 kg / t of fluorite, and 6-7 kg / t of calcium carbide are added for reduction and desulfurization. The temperature is controlled at 1660-1680℃, and the composition is controlled as follows: C: ≤0.25%, Si: ≤0.05%, Mn: ≤0.05%, P: ≤0.003%, S: ≤0.001%, Al: ≤0.005%. Finally, the ladle is hoisted to the VD furnace for vacuuming. Step 3: After the molten steel enters the VD furnace, the vacuum degree is controlled to be ≤67Pa, and the pressure is maintained for 20 minutes. After breaking the vacuum, soft blowing is carried out for ≥10 minutes, and the temperature is controlled at 1590-1610℃. Finally, the ladle is used for pouring and molding.

3. The smelting method for low-silicon manganese aluminum sulfur steel according to claim 2, characterized in that: In step one, the scrap steel is carbon scrap steel.

4. The smelting method for low-silicon manganese aluminum sulfur steel according to claim 2, characterized in that: In step two, the fluorite selected is high-purity, premium-grade green fluorite with the following chemical composition: CaF2 ≥ 94%, SiO2 ≤ 2.5%, S ≤ 0.02%, P ≤ 0.06%, H2O ≤ 0.3%; the lime selected is premium-grade lime with the following chemical composition: CaO ≥ 95%, SiO2 ≤ 1.5%, S ≤ 0.02%, H2O ≤ 0.3%, loss on ignition ≤ 2%, and an activity of ≥ 360 at 4 mol / ml, 40±1℃, and 10 min; the calcium carbide selected is superior-grade calcium carbide with a particle size < 10 mm. 2 .

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