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　　How can we improve the melting speed of medium-frequency induction furnaces?

　　Generally used for manufacturing alloy products, it is often employed in the refining of stainless steel plates. Electroslag furnaces capable of handling several dozen tons are available; medium-frequency induction furnaces, on the other hand, are typically not as large—very few exceed ten tons. Medium-frequency melting furnaces and electroslag remelting furnaces operate at different frequencies; the frequency of a medium-frequency melting furnace is higher than that of a DC furnace. The medium-frequency induction furnace uses this heat to heat and melt metals, thereby achieving the desired melting process. Its main characteristics are as follows:

　　1. The electromagnetic force acting on the molten metal causes significant stirring. This is a key feature of medium-frequency melting furnaces. The movement (stirring) of the liquid metal starts from the center of the melt pool and gradually spreads toward the sides of the induction coil. Due to the confinement exerted by the furnace bottom and the furnace opening, the final motion of the metal consistently moves upward, forming a camelback-shaped disturbance at the top of the melt pool.

　　2. Medium-frequency electric furnace The smelting process involves a series of staged operations, and all the metal charge to be melted consists of small batches of furnace charge. Due to issues such as the charging method, the packing density is only about one-third of the furnace’s capacity. At this stage, the furnace charge presents a very poor electrical load. When power is fed into the furnace, arcs tend to form between individual charge pieces, causing them to weld together. Once welding starts, the entire batch of charge effectively becomes a single large mass, thereby significantly improving furnace efficiency. The cost-effectiveness of high-frequency melting furnaces is 800 to 1,000 yuan higher than that of refining furnaces. This is mainly because medium-frequency induction furnaces are relatively inexpensive—typically costing just a few tens of thousands of yuan—and some used units are even cheaper. If favorable electricity tariffs can be secured, the cost of ironmaking using these furnaces could be further reduced. However, as economies of scale take effect and government regulations become more stringent, we believe that in the near future, high-frequency melting furnaces will gradually fade from the historical stage. Therefore, using medium-frequency induction furnaces for ironmaking places high demands on raw materials and makes it difficult to precisely control their chemical composition—this is especially evident in carbon content control. Since these furnaces cannot achieve the same vacuum conditions as AOD converters, even if the raw materials are perfectly controlled, it remains challenging to keep the carbon content below 0.03%. Moreover, without dedicated desulfurization and dephosphorization processes, it’s generally impossible to remove harmful elements like phosphorus from the raw materials. Consequently, when selecting grades such as 304L or 316L, medium-frequency induction furnaces are often ruled out—especially when producing export goods. For instance, galvanized flat bars and round bars produced by medium-frequency induction furnaces may frequently exceed the standard levels of P and S, though the extent of this issue varies from region to region: sometimes it’s quite noticeable, while at other times it’s less obvious. As we move on to subsequent processing steps, this shortcoming of high-frequency melting furnaces becomes even more apparent. Steel castings produced from the same batch of molten steel, after forging and pickling, often reveal subtle differences in material properties across various areas. This is hardly surprising, given that medium-frequency induction furnaces lack slag-removal capabilities. As a result, any surface treatments applied to the resulting products tend to expose existing defects even more clearly—such as porosity, cracks, and peeling.