Ladle Metallurgy Furnace
A Ladle Metallurgy Furnace (LMF), is used to refine molten steel into specialty grades. This relieves the primary steelmaking furnace of most secondary refining operations. Ladle metallurgy is sometimes also called ladle refining or secondary steelmaking.[1]
Liquid steel tapped from a primary steelmaking furnace such as basic oxygen furnace, electric arc furnace, induction furnace, or energy optimization furnace, is subjected to further refining in a number of alternative processes collectively known as ladle metallurgy for high quality or specialty applications.[1]
The Process
A ladle furnace is one of the key components of ladle metallurgy processes. A ladle furnace consists of sampling and temperature manipulators, stirring equipment, multi-line wire feeders and modern automated systems. The ladle roof is typically of water-cooled design with a refractory centre or delta section and is configured to coordinate with existing ladles such that the roof covers completely cover the top portion of the ladle when in the operating (i.e., fully lowered) position.[1]
Molten steel is transferred into a ladle furnace and stirred by bubbling an inert gas such as argon up from the bottom of the ladle. The inert gas is introduced either by an opening in the bottom of the ladle or by bringing a lance or tube in from the top. The stirring and agitation produced by the inert gas bubbling up from the bottom ensures that the chemistry and temperature of the liquid steel is homogenized throughout the ladle, although some LMFs also use electromagnetic stirring. As the introduced argon bubbles float to the surface of the liquid steel, impurities like inclusions and metal oxides attach themselves to the bubbles and float to the surface of the molten steel. At the surface, they are absorbed into the slag layer which can then be tapped and separated, leaving the steel “clean” of impurities.[2]
The refining of steel in the ladle broadly comprises of operations like deoxidation, desulphurization, dephosphorization, controlled additions of alloying elements and inclusion modification. The steel is first deoxidized partially with silico-manganese, ferro-manganese, and / or ferro-silicon followed by a final deoxidation with aluminum. For steel grades with very low sulphur content desulphurization of steel is also done in the ladle in the presence of a calcium aluminate slag. Desulphurization achieved through powder injection is around 15 % faster than the desulphurization with a top slag only, combined with the gas rinsing. Dephosphorization in ladle is needed when the phosphorus content of input hot metal during primary steel making is high. Dephosphorization is achieved by treating steel with lime-based oxidizing slags containing iron oxide. Calcium treatment of liquid steel is normally adopted to modify the morphology of the inclusions. As a result of the treatment with calcium, the alumina and silica inclusions are converted to liquid calcium aluminates or calcium silicates. These liquid inclusions are globular in shape because of sulphur tension effects.[1]
Purpose
The main functions of a Ladle metallurgy are:
- homogenization of the chemical composition and temperature of liquid steel in the ladle,
- deoxidization of steel,
- adjustment of superheat, i.e., heating of the liquid steel to a temperature suitable for its continuous casting,
- additions of ferro-alloys and carburizer for making adjustments in the chemistry of liquid steel,
- vacuum degassing for the removal of dissolved hydrogen and nitrogen gases,
- decarburization for the removal of carbon for meeting the requirement of certain grades of steel,
- desulphurization for the reduction of sulphur concentrations to levels as low as 0.002 %,
- micro-cleanliness i.e., removal of undesirable non-metallic inclusions,
- inclusion morphology i.e., changing the composition of remaining non-metallic inclusions for improving the micro-structure of the steel, and
- improvement in the mechanical properties such as toughness, ductility, and transverse properties etc.[1]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 "Ladle Metallurgy – IspatGuru". www.ispatguru.com. Retrieved 2024-04-13.
- ↑ "Ladle Metallurgy Furnaces - Reibus International". reibus.com. Retrieved 2024-04-13.
