Detailed Explanation of Arc Furnace Melting and External Refining Process

Detailed Explanation of Arc Furnace Melting and External Refining Process

The melting of tool steel often uses the core equipment of the electric arc furnace. During the arc furnace melting process, the scrap steel that has been carefully classified and managed is loaded into the furnace. Then, a hot arc is generated between the graphite electrode and the scrap steel, which is like a craftsman's fire, gradually melting the scrap steel. This is the charm of electric arc furnace melting. Its steelmaking scale is flexible and changeable, ranging from 5 tons to 200 tons, and it can handle it with ease.

The traditional arc furnace melting process should be fine-tuned by oxidation refining and then reduction refining. However, modern technology has quietly innovated. Today, the electric arc furnace mainly undertakes the heavy task of melting and oxidation refining, while the delicate work of reduction refining is completed by off-furnace refining. LF, RH, AOD and other refining methods are outstanding representatives of refining outside the furnace. They are like magic wands for steel processing, giving more possibilities to molten steel.

LF, or Ladle Furnace, is the crystallization of wisdom of Japan Special Steel (now Datong Special Steel) in the early 1970s. It transfers the molten steel from the electric furnace to the ladle, uses the power of graphite electrodes to keep it warm, and refines the slag at the same time, just like a careful craftsman, carving the quality of the molten steel. In addition, the argon gas introduced from the bottom of the furnace, like a gentle wind, stirs the molten steel and promotes the deepening of refining. The contribution of LF is that it can not only achieve ultra-low sulfur (S) and low oxygen (O) pure steel smelting, improve steel quality, but also omit the reduction step, improve productivity, and accurately control the casting temperature, making the pouring time more accurate.

The RH degassing method is another masterpiece of refining outside the furnace. It was jointly developed by West German Ruhr (now ThyssenKrupp) and Heraeus in 1959. After the molten steel is moved to the ladle, the vacuum chamber cover with an immersion pipe is cleverly used to pump the molten steel up and decompress it. At the same time, lifting gas is blown into the unidirectional immersion pipe to form a reflux of the molten steel, and it is efficiently degassed when passing through the vacuum chamber. The characteristics of the RH method are that the contact area between the molten steel and the vacuum is large, the degassing efficiency is high, and the composition control is easier. Today, the continuous matching refining technology of electric arc furnace-LF-RH degassing has become more mature, and it is seamlessly connected with the subsequent continuous casting process, and is widely used in the production of structural steel, etc.

AOD (Argon Oxygen Decarburizing), that is, argon oxygen decarburization refining method, is a leader in stainless steel refining. Since Union Carbide began research and development in 1950 and Jocelyn Steel (now Slater Steel) realized industrial application in 1968, it has become the mainstream method for stainless steel refining. The process of AOD is to load the molten steel into the AOD furnace, blow argon and oxygen from the side wall of the furnace bottom, so that carbon (C) is converted into CO gas for discharge, and effectively inhibit the oxidation of chromium, so as to achieve the goal of decarburization with extremely low carbon content. Subsequently, the advent of AOD-VCR refining method has provided strong support for the manufacture of stainless steel with extremely low carbon and nitrogen content. It realizes the decarburization process in the low-carbon range without oxygen blowing by adding the vacuum refining function to AOD, which has made an important contribution to the improvement of stainless steel quality.