Five-Stage Lance Position Control (Low–High–Low–High–Low)
The five-stage lance position method is not a rigid rule but a guiding principle for BOF/LD blowing control, aimed at coordinating stirring, slag formation, temperature rise, FeO control, and carbon–oxygen reaction.
① Low (Initial strong stirring)
Lower the lance 100–200 mm below normal at blow start to intensify stirring, accelerate scrap melting, eliminate dead zones, and build early bath temperature. Use higher oxygen pressure (~0.9 MPa) for 60–90 s, then add slag materials in small, frequent batches. Early dolomite addition (MgO) promotes slag melting and early dephosphorization.
Lower the lance 100–200 mm below normal at blow start to intensify stirring, accelerate scrap melting, eliminate dead zones, and build early bath temperature. Use higher oxygen pressure (~0.9 MPa) for 60–90 s, then add slag materials in small, frequent batches. Early dolomite addition (MgO) promotes slag melting and early dephosphorization.
② High (Slag formation & heating)
Raise the lance to normal or slightly higher to promote slag melting and uniform heating. Maintain FeO at ~20–25% to ensure lime dissolution. This stage may be longer in low iron-consumption practice. Slag must be fully melted before adding the second batch; excessive lance height leads to low bath temperature, poor reactions, and high-FeO splashing.
Raise the lance to normal or slightly higher to promote slag melting and uniform heating. Maintain FeO at ~20–25% to ensure lime dissolution. This stage may be longer in low iron-consumption practice. Slag must be fully melted before adding the second batch; excessive lance height leads to low bath temperature, poor reactions, and high-FeO splashing.
③ Low (Suppress FeO & splashing)
As temperature and FeO rise, conditions for splashing emerge. Lowering the lance strengthens the carbon–oxygen reaction, consumes FeO, suppresses splashing, accelerates decarburization, and stabilizes bath stirring.
As temperature and FeO rise, conditions for splashing emerge. Lowering the lance strengthens the carbon–oxygen reaction, consumes FeO, suppresses splashing, accelerates decarburization, and stabilizes bath stirring.
④ High (Intense reaction control)
This is the most difficult stage. FeO is rapidly consumed, and improper lance adjustment can cause dry slag, violent splashing, phosphorus reversion, and equipment damage. Continuous flame observation is essential; adjust the lance before the flame turns vertical to maintain fluid slag without splashing.
This is the most difficult stage. FeO is rapidly consumed, and improper lance adjustment can cause dry slag, violent splashing, phosphorus reversion, and equipment damage. Continuous flame observation is essential; adjust the lance before the flame turns vertical to maintain fluid slag without splashing.
⑤ Low (End-point control)
Gradually lower the lance to carbon-blowing position for ≥40 s to homogenize temperature and composition and reduce slag FeO. Maintain a “soft” flame to avoid lance damage. Once endpoint carbon and temperature meet requirements, raise the lance and finish blowing.
Gradually lower the lance to carbon-blowing position for ≥40 s to homogenize temperature and composition and reduce slag FeO. Maintain a “soft” flame to avoid lance damage. Once endpoint carbon and temperature meet requirements, raise the lance and finish blowing.
Key Misconceptions & Operational Points
Defects are not simply due to insufficient slag amount
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Unmelted lime = ineffective lime → poor dephosphorization/desulfurization.
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Late melting of oversized or abnormal scrap introduces harmful elements at the end.
Typical 12-minute blow time allocation (reference only)
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Phase 1: 1.5–2 min
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Phase 2: 2–4 min
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Phase 3: 2–3 min
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Phase 4: ~3 min
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Phase 5: ~2 min
Actual timing must be adjusted by flame and furnace response.
Correct handling of splashing
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High-temperature splashing: add material briefly, then promptly lower the lance.
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Low-temperature splashing: do not raise the lance or add blindly; instead reduce oxygen pressure, add small batches, and stabilize the carbon–oxygen reaction
The blow is short but highly dynamic. Operators must understand flame–reaction relationships, make proactive adjustments, and use lance position to control the flame, not chase it. The five-stage method reflects a trend, not a rigid formula—skillful flexibility is the key to stable, high-quality steelmaking.
