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Research on LF (Ladle Furnace) refining technology began in 1968. At that time, it was found that the reduction and refining effect was remarkable by prefabricating the reduction slag in the electric arc furnace, mixing the steel slag, and blowing the ladle with argon. Therefore, the development of the ladle refining technology with the arc heating function was carried out for the purpose of omitting the reduction period of the electric arc furnace.
LF refining is one of the main methods of out-of-furnace refining, and its key is to quickly produce white slag. The purpose of LF slag making is to desulfurize, deoxidize, improve alloy yield, and remove inclusions. However, in the process of slag making of aluminum-controlled steel, there are certain contradictions in desulfurization, returning to silicon, increasing nitrogen, and removing inclusions, which need to be considered as a whole. In LF, it is necessary to produce fast and stable reducing white slag with good fluidity and certain emulsification, which is necessary for LF desulfurization, adsorption of inclusions and guarantee of molten steel quality.
The process of slag-changing after tapping commonly used in electric furnace process and converter process, namely: first tapping in electric arc furnace or converter, then ladle refining furnace refining (adding aluminum, adding slag, adding Ca-Si or adding slag modifier), and finally casting .
The LF is set up in an EAF steelmaking plant, reducing the EAF reduction time and ultimately eliminating the EAF reduction period. The smelting cycle of the electric arc furnace is shortened, the productivity of the electric arc furnace is improved, and the molten steel that meets the requirements of temperature, composition and cleanliness is provided for continuous casting within a certain period of time. It ensures the smooth operation of the electric arc furnace + LF refining + continuous casting process, so that the electric arc furnace develops into a high-efficiency short-flow steelmaking method that can produce ordinary steel grades from ordinary scrap and pig iron.
The first stage of electric arc furnace development is the traditional electric arc furnace including melting, oxidation and reduction. The second stage is due to the type of electric arc furnace (tapping slot type electric arc furnace), in order to avoid the oxidation slag polluting the molten steel and play the role of deoxidation and desulfurization of the steel slag, the reducing slag must be made in the electric arc furnace. The steel slag is mixed out, and the ladle refining furnace is used to complete the task of further reduction and refining. The third stage is due to the development of slag-free tapping technology, and the reduction period is all completed by LF refining, that is, the form of modern electric arc furnace steelmaking process EAF+LF+CC is formed.