Methods for melting titanium rods and titanium alloy rod materials

Titanium alloy smelting methods: vacuum consumable electric arc furnace smelting method (referred to as VAR method), non-consumable vacuum arc furnace smelting method (Jianni NC method), cold hearth smelting method (referred to as CHM method), cold pot smelting method ( (referred to as CCM method), electroslag melting method (referred to as ESR method).
1. Vacuum consumable electric arc furnace melting method (referred to as VAR method)
With the development of vacuum technology and the application of computers, the VAR method has quickly become a mature industrial production technology for titanium. Most of today's titanium and its alloy ingots are produced using this method. The salient features of the VAR method are low power consumption, high melting speed and good quality reproducibility. The ingot melted by the VAR method has a good crystal structure and uniform chemical composition.
Technical features and advantages of modern advanced VAR furnaces:
(1) Full coaxial power input, which means complete coaxiality throughout the height of the furnace, is called coaxial power supply, which reduces the occurrence of segregation;
(2) The electric calibration inside the crucible can be fine-tuned in the X-axis/Y-axis direction.
(3) It has an accurate electrode weighing system to achieve constant speed melting. It not only ensures the melting quality, but also ensures the repeatability and consistency of each melting.
(4) Flexibility, that is, one furnace can produce a variety of ingot types and increase the size of ingots, which can greatly improve productivity.

(5) It has good economy.
The "coaxial power supply" method can avoid magnetic leakage caused by unbalanced supply current of the crucible, weaken or eliminate the adverse effects of the induced magnetic field on the smelting products, and improve the electrical efficiency, thereby obtaining ingots with stable quality.
Modern VAR furnaces can smelt large ingots with a diameter of 1.5m and a weight of 32t. There are technical problems to be solved: first, the electrode preparation method. The electrode preparation process is very cumbersome. An expensive press is required to melt sponge titanium and master alloy. And the returned residual material is pressed into a solid electrode or a single small electric wrench. The single electrode also needs to be welded into a consumable electrode. At the same time, in order to ensure the uniformity of the composition of the consumable electrode, it is also necessary to configure cloth, weighing, mixing, etc. Corresponding facilities. Second, there are occasional metallurgical defects such as segregation, such as composition segregation and solidification segregation. The former is caused by the uneven distribution of impurity elements or alloying elements in the electrode, which solidifies before the distribution can be balanced during smelting; the latter is caused by the occasional introduction of high-density inclusions (HDI) and low-density inclusions (HDI) into raw materials or processes. LDI), these inclusions cannot be completely dissolved during the smelting process, resulting in extremely harmful inclusions and other metallurgical defects.
2. Non-consumable vacuum electric arc furnace melting method (Jianmi NC method)
At present, water-cooled copper electrodes have replaced the tungsten-thorium titanium electrodes or graphite electrodes in the initial stage of the titanium industry, solving the problem of industrial pollution, making the NC method an important method for smelting titanium and titanium titanium. Several tons of NC The furnace is already operating in Europe and the United States.
The advantages of NC method smelting are:
(1)The process of pressing electrodes and welding electrodes can be omitted;
(2) It can make the arc stay on the material for a long time, thereby improving the uniformity of the ingot composition;
(3)Raw materials of different shapes and sizes can be used, and 100% residual materials can be added during the smelting process to realize titanium recycling. As a one-time smelting, the NC method is quite advantageous from the perspective of improving the recovery rate of residual materials and reducing costs. Usually, NC furnaces and VAR furnaces are used in conjunction to give full play to their respective advantages.
3. Cold hearth melting method (CHM method for short)
Metallurgical inclusion defects in titanium and titanium alloy ingots caused by raw material contamination and abnormal smelting processes have always affected the application of titanium and titanium alloy in the aerospace field. In order to eliminate metallurgical inclusions in titanium alloy aircraft engine rotating parts , cold hearth smelting technology came into being. The biggest feature of the CHM method is the separation of melting, refining and solidification processes, that is, the molten charge enters the cold hearth and is first melted, then enters the refining area of the cold hearth for refining, and finally solidifies into ingots in the crystallization area.