Secondary refining, also called ladle refining or ladle furnace refining, is an important process in modern steelmaking. After primary melting in an electric arc furnace (EAF) or induction furnace (IF), molten steel is transferred to a refining furnace for further treatment.
The purpose of secondary refining is to improve steel cleanliness, accurately control chemical composition and temperature, and optimize non-metallic inclusions. Modern refining technology can significantly reduce harmful elements and impurities such as sulfur, phosphorus, oxygen, hydrogen, and nitrogen, helping steel plants produce higher-quality steel products.
Main Functions of Secondary Refining
The secondary refining process mainly performs the following tasks:
- Homogenizing molten steel temperature and composition through stirring;
- Precise alloy adjustment and narrow composition control;
- Temperature control before continuous casting;
- Desulfurization, deoxidation, degassing, and inclusion removal;
- Inclusion modification to improve steel properties;
- Buffering and coordinating production between melting furnaces and continuous casting machines (CCM).
To achieve these goals, refining systems may use argon stirring, oxygen blowing, wire feeding, powder injection, heating, vacuum treatment, and slag refining technologies.
Typical EAF Secondary Refining Routes
In electric arc furnace steelmaking plants, common secondary refining configurations include:
EAF + LRF + CCM
This is a widely used configuration for producing alloy steel and general-quality special steel. The LRF is mainly responsible for temperature adjustment, deoxidation, alloy trimming, and steel cleanliness improvement before continuous casting.
EAF + LRF + VD + CCM
This process is suitable for cleaner steels with stricter gas and inclusion requirements, such as bearing steel, gear steel, and pipeline steel. VD treatment further improves degassing, desulfurization, and inclusion removal performance.
EAF + LRF + RH + CCM
The LRF + RH route is commonly applied in high-cleanliness steel production. LRF performs heating and slag refining, while RH treatment further reduces hydrogen and oxygen content and stabilizes casting temperature.
EAF + AOD/VOD + CCM
This route is mainly used for stainless steel production. AOD or VOD refining is used for decarburization and stainless steel refining after initial melting in the EAF.
Induction Furnace Secondary Refining Solutions
Compared with EAF steelmaking, the induction furnace (IF) itself has very limited refining capability. Therefore, raw material quality is especially important in IF steelmaking operations.
In practical projects, induction furnace steelmaking is commonly used under the following conditions:
- Availability of stable high-quality scrap resources;
- Recycling of return scrap from rolling mills or steel plants;
- Local power grids unsuitable for electric arc furnaces;
- Projects with relatively low budget;
When ordinary mixed scrap is used, secondary refining becomes increasingly important.
IF + LRF
This configuration mainly performs temperature adjustment and minor composition correction. However, it still requires relatively high-quality scrap materials.
IF + AOD + LRF
This process is mainly used for stainless steel production with induction furnaces.
IF + LOD + LRF
The LOD refining furnace developed by SME Group is designed to improve induction furnace steelmaking performance by supporting decarburization and dephosphorization. This solution helps reduce dependence on high-grade scrap while improving final steel quality and enhancing competitiveness in suitable regional markets.
