Understanding the Ladle Furnace in Secondary Refining

Understanding the Ladle Furnace in Secondary Refining

Secondary refining, also referred to as secondary metallurgy, encompasses various steel treatment processes conducted after primary melting and before casting—excluding standard alloying during furnace tapping. While definitions vary, secondary refining typically aims to:

- Homogenize or adjust temperature,

- Achieve precise chemical composition (e.g., carbon, sulfur, phosphorus, oxygen, and alloys),

- Control inclusions,

- Perform degassing and desulfurization.

These processes may occur at atmospheric pressure or under vacuum, with or without heating, stirring, or injection of solids/gases.

Role and Operation of a Ladle Furnace

A Ladle Furnace (LF) handles most secondary refining tasks, freeing the primary furnace for melting. Its core functions include:

1. Reheating liquid steel via graphite electrodes using electric power.

2. Homogenizing temperature and chemistry through inert gas stirring.

3. Forming a protective slag layer that:

   - Shields refractory lining from arc radiation,

   - Improves heat transfer to the steel,

   - Traps inclusions and metal oxides,

   - Enables desulfurization.

Additional LF capabilities may include:

- Alloy additions for bulk or fine-tuning of chemistry,

- Cored wire injection for trimming or inclusion modification,

- Deep desulfurization and dephosphorization,

- Buffering downstream steelmaking processes.

Stirring Mechanism

Stirring is normally achieved by injecting argon through porous plugs at the ladle bottom. A top lance serves as backup if bottom stirring is unavailable. The gas connection engages automatically once the ladle is positioned on the transfer car.

Emissions Control

Fumes and particulates generated during LF operations escape through openings in the water-cooled ladle roof. These are captured by a lateral draft hood installed above the roof, which draws in ambient air along with emissions. The roof itself is typically water-cooled with a refractory center section and designed to fully cover the ladle when lowered into operating position.

In summary, the Ladle Furnace is a versatile and critical station in secondary refining, enabling precise thermal and chemical conditioning of liquid steel prior to casting.

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