BOF Steelmaking: How Is One Heat Made?

About 70% of world crude steel comes from converters (BOF). One heat takes just 30~40 minutes — faster than EAF. The secret is oxygen.

Principle: Top-Blown Oxygen

The converter is a tilting pear-shaped vessel with porous bottom bricks for Ar/N2 stirring. High-purity oxygen (>99.5%) is blown from a top lance; it oxidizes carbon, silicon, manganese and phosphorus in hot metal, releasing enormous heat.

That reaction heat alone heats the steel to 1600°C+ — no extra fuel needed. That's why it's fast and energy-efficient.

Standard Heat Sequence

1. Charging: scrap (coolant, 10~20%) then hot metal.

2. Blowing: oxygen blowing plus lime slag. Three phases: de-Si/de-Mn early, de-C middle, de-C + heating late. 12~18 minutes, from ~1300°C to ~1600°C.

3. Endpoint judgment: sublance measures temperature and oxygen activity to estimate carbon (e.g., 0.05~0.1%). Critical for endpoint control.

4. Tapping: tilt, tap into ladle, add alloys (FeSi, FeMn) and strong deoxidizer (Al).

5. Slag splashing: splash high-FeO slag on lining with nitrogen to extend campaign life to 10~20k heats.

Why Temperature Matters

Temperature climbs fast during blowing; endpoint temperature dictates refining and casting plans. Endpoint temperature/oxygen measurement is done nearly every heat — accuracy directly affects alloy cost and composition hit rate.

Summary

BOF speed comes from oxygen's self-heating; stability comes from precise endpoint judgment — the two eyes of which are temperature and composition, both relying on furnace-front measurement and sampling.