Titanium alloy is a high-end, high value-added product in the special steel industry. At present, one of the topics of titanium alloy smelting is to develop a new process to significantly eliminate the defects of various inclusion forms in the ingot and ensure the chemical composition uniformity of the ingot. Vacuum consumable arc melting is conventionally used, but the inclusion problem cannot be completely solved. In recent years, the smelting method of the hearth has been newly developed and industrialized. There are mainly two types of methods:
Semi-continuous hearth smelting with independent heating source.
With this method, after the solid charge is melted, the metal remains liquid from the melting zone to the crystallizer path, and the cold bed furnace effectively separates and removes high specific gravity inclusions by the difference in specific gravity. It can be divided into plasma cold bed furnace and electron beam cold bed furnace.
It is more effective for removing low-density inclusion electron beam furnaces. The obvious advantage of the plasma cold bed furnace smelting system is that the alloy components can be maintained under different vapor pressures. During the smelting process, there is no obvious loss of easily evaporated elements such as Al, Cr, Mn, etc., and the crystallization rate can be significantly reduced. The β-stabilizing element is recombined in the liquid phase, thereby preventing the generation of β-spots.
Titanium alloys for General Electric engines in the United States have achieved significant results with this method. In recent years, the cold bed furnace smelting technology abroad is an important means to further improve the purity of metals and prevent the inclusion defects of titanium alloy compressor discs for aircraft engines.
Shell self-consumption electrode smelting
This type of hearth smelting is characterized by a large smelting current. It acts as a hearth by a cold metal crucible, and the molten metal flows into the crucible continuously, and is poured into the mold at the end of the melting.
Since the shell smelting is a variation of the smelting of the hearth, it has a high refining ability and can remove various inclusion defects, and the comprehensive smelting effect is equivalent to the first type.
Russia's Upper Salda Metallurgical Joint Enterprise smelts different grades of titanium alloys with a shell furnace. The actual experience of a large number of ingots proves that the shell smelting has a strong ability to refine and remove impurities. Under standard operation, no one case is caused by inclusions. Metal scrapped accident.
Comparing the two methods, if the hearth is smelted as a means for obtaining a consumable electrode for subsequent vacuum consumable arc melting, the former has obvious advantages compared with the hearth furnace. In the case of equivalent refining and impurity removal, the pre-stocking cost and metal treatment cost of the shell smelting are lower; the metals smelted before pouring into the ingot are all in a liquid state, and have the potential to make the ingot highly chemically uniform. In order to ensure the uniformity and safety of the alloy reinforcement.