One of the topics of titanium alloy smelting is to develop a new process to obviously eliminate the defects of various inclusions in the ingot and ensure the uniformity of the chemical composition of the ingot. Vacuum consumable arc melting is conventionally used, but the inclusion problem cannot be completely solved. In recent years, furnace hearth melting methods have been newly developed and industrialized. There are two main methods:
1. Semi-continuous hearth smelting with independent heating source.
When this method is adopted, after the solid charge is melted, the metal remains liquid on the route from the melting zone to the crystallizer, and the cold-bed furnace effectively separates and removes high-specific-gravity inclusions through 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 furnace. The obvious advantage of the plasma cold-bed furnace smelting system is that it can maintain different vapor pressures to obtain alloy components. During the smelting process, there is no obvious loss of easily vaporizable elements such as Al, Cr, Mn and so on. At the same time, the crystallization speed can be significantly reduced, The β stabilizing elements are concentrated in the liquid phase, so that the generation of β spots can be prevented.
Titanium alloys for General Electric engines in the United States have achieved significant results with this method. In recent years, cold-bed furnace smelting technology abroad is an important means to further improve metal purity and prevent defects in titanium alloy compressor disks for aircraft engines.
2. Smelting of consumable electrode
This type of hearth melting is characterized by a large melting current. It functions as a hearth by a cold metal crucible, and the molten metal continuously flows into the crucible, which is poured into a mold at the end of melting.
Hull smelting is a variant of hearth smelting, so it has high refining ability to remove impurities, and can remove various inclusion defects. Its comprehensive melting effect is equivalent to the first type.
A large amount of practical experience with ingots proves that smelting smelting has a strong ability to remove impurities. Under standard operation, there has been no incident of metal scrap due to inclusions.
For a comparison of the two methods, if furnace hearth melting is used as a method for making consumable electrodes for subsequent vacuum consumable arc melting, solid shell melting has obvious advantages compared with hearth furnaces. With the same refining and impurity removal capabilities, the initial preparation cost and metal processing cost of the smelting smelting are low; all the metal smelted before pouring into the ingot is in a liquid state, which has the potential to make the ingot obtain high chemical uniformity To ensure the uniformity and safety of alloy strengthening.