Causes analysis for damage of LF refining furnace lining

December 21, 2018

Causes analysis for damage of LF refining furnace lining

The LF ladle refining furnace is a refining equipment that uses arc heating technology. It refines the molten steel that is initially refined in a general steelmaking furnace in a special ladle. Because LF refining furnace has a series of advantages such as less investment, simple equipment, reasonable refining technology combination, flexible smelting process, low gas content in molten steel after refining, less harmful impurities, large reduction of inclusions, stable composition uniform temperature and so on, so it is an optimized metallurgical process to cooperate with high-power electric furnaces and continuous casting.

However, because LF refining furnace has high refining temperature, long heating time, and is subject to chemical reaction and corrosion, the damage mechanism of LF refining furnace lining is closely related to a series of factors, such as temperature, erosion etc. 

Mainly due to the following factors:

(1) Chemical reactions and erosion.

At high temperatures, molten steel and slag diffuse into the refractory materials, and at the same time, corrosion occurs. The slag is sometimes in contact with the brick surface for up to 90 minutes. The chemical reaction of CaO, SiO2 and CaF2 in the slag with the bricks causes the surface of the brick to form a slag permeable layer, and the matrix is filled with silicate. The low-melting silicate phase formed by the edge of the particle has C2S (melting point 2130℃) and decomposition, CMS (melting point 1450℃) and yellow feldspar solid solution (2CaO•MgO•2SiO2-2CaO•A12O3•2SiO2), etc. which cause discontinuous damage to the lining.

(2) Volatilization of refractory materials under high temperature vacuum.

According to the stability of alkaline refractories at high temperatures, C>CaO>CaO•MgO>MgO, calcium products in this order are the relatively best. Since the refractory materials can accelerate dissociation and volatilization under high temperature vacuum, the magnesia-based dolomite generally has the lowest volatilization rate under vacuum conditions.

(3) Erosion of slag and molten steel.

Due to the high permeability of CaO and CaF2 in the refining process, CaO and SiO2 in the slag migrate to the freezing point along the liquid channel formed by the pores, cracks and impurities of the brick matrix at high temperature, forming a low melting point mineral phase dominated by silicate, changing the structure of the brick and producing a metamorphic layer, which will form a structural flaking when the temperature changes sharply. Therefore, for the refining slag with high calcium content, the material of the slag may be magnesia-calcium refractory materials suitable for the slag composition to enhance slag resistance and durability.

(4)The thermal shock impact caused by intermittent operation will cause slag erosion on the surface of the brick billet to occur structural peeling, which will intensify the damage of the lining materials of the refining furnace.