How to control Boron Content in Finished Steel

1, Boron Control in Induction Furnace

I. Boron Control in I nduction F urnace

Due to the smelting process of induction furnaces and the production cost control of steelmaking in induction furnaces, quartz sand is the main lining material for induction furnace smelting. Adding B2O3 The mechanism and advantages of using B₂O₃ as a sintering aid can be systematically summarized as follows:

Due to the smelting process of induction furnaces and the production cost control of steelmaking in induction furnaces, quartz sand is the main lining material for induction furnace smelting. The mechanism   theory and advantages of adding B₂O₃ as a sintering aid in quartz (rammed materials) for induction furnace s can be systematically summarized as follows:

1 ) . Reducing sintering temperature and promoting liquid phase formation

1. Reducing Sintering Temperature and Promoting Liquid Phase Formation

• Eutectic Effect ：B2O3 with SiO2 The binary system formed has a low eutectic point of only 372 ℃ , far lower than the refractoriness of pure quartz sand ( 1700 ℃ ), enabling the material to densify through liquid-phase sintering at low temperatures.
• Eutectic Effect : The binary system of B₂O₃ and SiO₂ has a low eutectic point of only 372°C, far lower than the refractoriness of pure quartz sand (1700°C), enabling the material to densify through liquid-phase sintering at low temperatures.
• Early Sintering ：372 ℃ The liquid phase generated during early sintering accelerates inter-particle bonding, forming initial strength and avoiding volume stress damage caused by quartz phase transformation (e.g., β→α quartz) at medium-low temperatures.
• Early Sintering : The liquid phase formed at 372°C accelerates inter-particle bonding, forming initial strength and avoiding volume stress damage caused by quartz phase transformation (e.g., β→α quartz) at medium-low temperatures.

2 ) . High-Temperature Viscous Layer Protection Mechanism

2. High-Temperature Viscous Layer Protection Mechanism

• Viscosity Regulation ：B2O3 As a glass network former, it SiO2 does not significantly reduce the high-temperature viscosity of the melt after integrating into the SiO₂ structure ( 1730 ℃ at this temperature the viscosity remains 2×10⁶ Pa·s ), forming a high-viscosity surface layer.
•  Viscosity Regulation : As a glass network former, B₂O₃ does not significantly reduce the high-temperature viscosity of the melt after integrating into the SiO₂ structure (viscosity remains as high as 2×10⁶ Pa·s at 1730°C), forming a high-viscosity surface layer
• Erosion Resistance The high-viscosity liquid layer effectively blocks the penetration and scouring of molten metal, reducing chemical erosion.
• Erosion Resistance: The high-viscosity liquid layer effectively blocks the penetration and scouring of molten metal, reducing chemical erosion
• Structural Stability Maintains the integrity of the glass phase network to prevent material softening or loss at high temperatures.
• Structural Stability: Maintains the integrity of the glass phase network to prevent material softening or loss at high temperatures..

3 ) . Inhibiting Damage of Quartz Phase Transformation

3) i Inhibiting   Damage of Quartz Phase Transformation  

• Volume Expansion Buffering Quartz undergoes rapid phase transformations near 573 ℃ （ β→α ）and 1200 ℃ （cristobalite formation）, accompanied by severe volume changes (e.g., β→α expansion +0.82% ).
•  Volume Expansion Buffering: Quartz undergoes rapid phase transformations near 573°C (β→α) and 1200°C (cristobalite formation), accompanied by severe volume changes (e.g., β→α expansion +0.82%).
• B2O3 B₂O₃ liquid phase fills the grain boundaries, relieving local stress and preventing bulging and cracking.
• B₂O₃ liquid phase fills the grain boundaries, relieving local stress and preventing bulging and cracking.
• Reduces porosity and improves structural densification in the medium-low temperature range.
• Reduces porosity and improves structural densification in the medium-low temperature range .

B2O3 Introduction through “ Low-temperature liquid-phase sintering - High-temperature high-viscosity protection ” The dual effects solve the contradiction between the vulnerability of silica rammed materials at low temperatures and insufficient high-temperature resistance, becoming a key technological path for optimizing induction furnace lining materials.

The introduction of B₂O₃ solves the contradiction between the vulnerability of silica rammed materials at medium-low temperatures and insufficient high-temperature resistance through the dual effect of "low-temperature liquid-phase sintering and high-temperature high-viscosity protection," making it a key technical path for optimizing induction furnace lining materials.

II. Regarding the quartz sand lining of the induction furnace Boron-free sintering agent The performance differences and process impacts are as follows:

II. Performance Differences and Process Impacts of Boron-Free Sintering Aids for Induction Furnace Quartz Sand Linings

1. Limitations of Boron-Free Sintering Aids

1. Limitations of Boron-Free Sintering Aids

（ 1 (1) Medium-low temperature sintering defects

(1) Medium-Low Temperature Sintering Defects

• High-temperature dependence Boron-free sintering agents need to be above 1450 ℃ to effectively promote sintering, resulting in: Primary sintering range ( 550-1200 ℃ ) failure Insufficient liquid phase formation in quartz sand results in weak particle bonding.
• High-Temperature Dependence : Boron-free sintering aids can only effectively promote sintering above 1450°C, which leads to: failure in the primary sintering zone (550-1200°C)---Insufficient liquid phase formation in quartz sand results in weak particle bonding;
• Thin semi-sintered layer Loose initial structure leads to poor resistance to mechanical impact.
•   Thin semi-sintered layer: Loose initial structure leads to poor resistance to mechanical impact.

（ 2 (2) Uncontrolled volume expansion:

(2 )Uncontrolled Volume Expansion:

• Quartz phase transformation stress concentration ：573 ℃ （ β→α (quartz) and 1200 ℃ (cristobalite formation), boron-free materials cannot buffer volume expansion through liquid phases >5% ).
•  Quartz Phase Transformation Stress Concentration: At 573°C (β→α quartz) and 1200°C (cristobalite formation), boron-free materials cannot buffer volume expansion (>5%) through liquid phases.
• Consequences: Lining bulging, spalling, increased porosity, and reduced erosion resistance.
• Consequences: Lining bulging, spalling, increased porosity, and reduced erosion resistance.

（ 3 (3) Melting risks caused by inadequate initial sintering ：

(3) Melting Risks Caused by Inadequate Initial Sintering

• Heavy scrap / Briquette impact Insufficiently sintered linings are easily broken by high-density charge materials (e.g., heavy scrap) or cause charge floating.
• Impact of heavy scrap/ briquettes: Insufficiently sintered linings are easily broken by high-density charge materials (e.g., heavy scrap) or cause charge floating

• Particle steel / Crushed material adaptability Lightweight charge materials have less impact on unsintered layers and can be preferred for the initial heat.
• Adaptability to particle steel/ crushed materials: Lightweight charge materials have less impact on unsintered layers and can be preferred for the initial heat.

2. Process compensation measures for boron-free linings

2.Process Compensation Measures for Boron-Free Linings

（ 1 When using boron-free materials, we need use process adjustments to compensate for defects:

（ 1）When using boron-free materials, we need use process adjustments to compensate for defects:

• Stepped heating Stepped baking before the initial heat ( 1200 ℃ 、 1400-1500 ℃ each holding 1 -2 hours) to force sintering.
• Stepped heating : we do stepped baking before the initial heat (1200°C, 1400-1500°C, each with 1-2 hours of holding) to force sintering.
• Charge selection Only crushed materials/ particle steel are used for the initial heat to avoid heavy scrap impact, then gradually add briquettes/ heavy scrap after the second heat. / particle steel, avoiding heavy scrap impact. Then gradually add briquettes / heavy scrap.
•  Charge selection: we use only crushed materials/ particle steel for the initial heat to avoid heavy scrap impact, then gradually add briquettes/ heavy scrap after the second heat.

(2) ， Ladle (Large Ladle) Lining Selection

(2) Selection of Ladle ( large ladle ) Linings

Since ladles do not undergo refining and have no heating process, the entire ladle does not allow for the sintering process of boron-free quartz sand lining materials. Boron-free quartz sand materials cannot be used for ladle rammed linings. Refractory bricks or refractory castables can be considered.

Since ladles do not undergo refining and have no temperature-raising process, the entire ladle does not allow for the sintering process of boron-free quartz sand lining materials. Quartz sand boron-free materials cannot be used for ladle rammed linings.  Instead,refractory bricks or refractory castables can be considered.

(3)   Selection of Tundish Linings

(3)Selection of Tundish Linings

The working temperature of tundishes is 1530-1580 °C. The tundish operating temperature is lower than that of ladles, and boron-free quartz sand ramming materials cannot complete the sintering process. Therefore, the tundish working layer needs to use resin-bonded materials because resins can 300 form carbon chains (harden) above 300°C, making them suitable for tundish working layers.

The working temperature of tundishes is 1530-1580°C, which is lower than that of ladles. Boron-free quartz sand rammed materials cannot complete the sintering process. Therefore, the tundish working layer should use resin-bonded materials. As resins can form carbon chains (hardening) above 300°C, they are suitable for tundish working layers.

Because resin-bonded rammed materials are resin-bonded, the hardened layer they form cannot be completely sintered. Therefore, after one cycle of operation, the tundish working layer needs to be completely replaced. Resin-bonded rammed materials cannot be reused.

   Since resin-bonded rammed materials form a hardened layer through resin bonding without complete sintering, the tundish working layer needs to be fully replaced after one cycle of operation. Resin-bonded rammed materials cannot be reused.