To achieve true “high-purity steel,” induction furnace smelting must evolve from simple melting control to sophisticated độ chính xác interface chemistry control. Below is an in-depth expansion of three core technical pillars, covering thermodynamic principles, kinetic pathways, and practical operational parameters.
TÔI. A Guide to Composite Deoxidizers (Si-Ba, Si-Ca) in Induction Furnaces
The limitation of single-element deoxidizers (Và, Mn) lies in their deoxidation products, which are often high-melting-point solids (ví dụ., SiO2 melts at 1723°C). Given the relatively weak slag-metal reaction time in induction furnaces, these microscopic particles are extremely difficult to remove.
1. Thermodynamic Synergistic Effects of Composite Deoxidation
Composite deoxidizers (such as Si-Ca, Si-Ba, and Si-Al-Ba) are not merely a mixture of ingredients; they significantly enhance efficiency by lowering the activity of deoxidation products.
- Lowering the Oxygen Floor: According to thermodynamic equilibrium, the interaction of multiple elements can significantly reduce the equilibrium concentration of residual oxygen in molten steel.
- The Specific Role of Barium (Ba): With its high atomic weight, Barium effectively lowers the vapor pressure of Calcium (Ca), extending its residence time in the melt. Đồng thời, it allows the deoxidation product $BaO$ to combine with other oxides, forming higher-density liquid complexes that coalesce easily.
2. Kinetics of Inclusion “Growth and Flotation”
- Interfacial Tension Control: The liquid silicate inclusions produced by composite deoxidizers maintain high interfacial tension with the molten steel, making them easier to “squeeze out” of the melt.
- Collision Frequency: By utilizing the strong convection of induction electromagnetic stirring, the probability of microscopic liquid inclusions colliding to form larger particles increases, thereby overcoming the “radius bottleneck” defined by Stokes’ Pháp luật.
Ii. Controlling Alumina “Nozzle Clogging” in Induction Smelting
Aluminum deoxidation is the essential path to achieving deep deoxidized steel ([ồ] < 20trang/phút), but the cluster-like precipitation of Al2O3 is a nightmare for continuous casting nozzles.
1. Inclusion Modification
The core objective is to transform high-melting-point, polygonal Al2O3 into low-melting-point, spherical liquid calcium aluminates.
- Key Transformation: 2[Al] + 3[ồ] → Al2O3(S) +Ca → 12CaO · 7Al2O3(l).
- Liquid Window Control: The Ca/Al ratio in steel must be precisely controlled. According to the CaO-Al2O3 binary phase diagram, the product is fully liquid at 1600°C only when the CaO content is within the 45%–55% range.
2. Process Optimization
| Bước chân | Operational Key Points | Khách quan |
| Pre-deoxidation | Add Si-Mn first to reduce [ồ] to moderate levels. | Reduce Al burn-off and prevent mass formation of Al2O3. |
| Strong Deoxidation | Insert Al ingots or feed Al wire. | Rapidly reach target deoxidation depth. |
| Calcium Treatment | Feed Si-Ca wire 3–5 mins after final deoxidation. | Perform “spheroidization” modification on existing alumina particles. |
| Argon Bubbling/Standing | Weak stirring for 5–10 mins. | Allow modified liquid inclusions to float; avoid violent stirring to prevent secondary oxidation. |
Iii. Using a specific synthetic slag enables the induction furnace to dephosphorize
Phosphorus removal is the greatest technical weakness of induction furnaces because the slag layer relies on heat transfer from the melt (creating “cold slag”), whereas dephosphorization requires high basicity and high fluidity.
1. Các “Low Temperature – High Oxidation” Window
Dephosphorization is an exothermic reaction; theoretically, the lower the temperature, the higher the equilibrium constant.
- Melting Phase Dephosphorization: The optimal timing is when the charge has just melted, and the temperature is maintained around 1530°C–1580°C. Ở giai đoạn này, carbon oxidation is not yet intense, and the oxygen potential is sufficient to support phosphorus oxidation.
- Synthetic Slag Ratio: Recommended mix is 50%CaO + 25%Fe2O3 + 15%CaF2 + 10%MGO. Here, Fe2O3 provides oxygen, while CaF2 acts as a flux to solve the “cold slag” fluidity issue.
2. Enhanced Operational Path
The core logic is to complete dephosphorization before temperature ramping and deoxidation.
- Batch Slagging: Add synthetic slag early in the melting phase to maximize slag-metal contact via electromagnetic stirring.
- Forced Oxygen Blowing (Không bắt buộc): Use low-flow oxygen blowing to increase local slag temperature and oxygen potential.
- Thorough Slag Skimming: Phosphorus exists in slag as P2O5, which is highly unstable. Once the heating/reduction phase begins (adding deoxidizers), phosphorus will immediately revert to the steel. Vì thế, the dephosphorization slag must be completely removed before the reduction period starts.
Bản tóm tắt: The Process Chain for High-Purity Steel
Low-P phosphorus charge + Melting phase low-temp dephosphorization slag + Strong Al-deoxidation + Ca-treatment modification + Weak stirring flotation.
This workflow elevates the induction furnace from a simple melter to the status of a refining vessel.
