Technical specification for induction heating of tantalum and tantalum alloy before plastic deformation

Industrial pure tantalum can be deformed and processed at room temperature. Tantalum alloys must be deformed at high temperatures due to their high strength and resistance to deformation. Induction heating is mainly used for tantalum alloy ingot blooming. The billet recrystallizes the broken coarse original grains into fine new grains, which is conducive to subsequent plastic deformation. Under low or high temperature conditions, the billet is rolled and drawn to make tantalum sheet, tantalum strips, tantalum rods, tantalum tube, tantalum wire and other products, you can also receive various parts of different shapes through impact and energy.

There are two types of tantalum alloy ingot blooming, forging blooming and extrusion blooming. Free forging is mainly for the subsequent process of extruding pipes, bars or rolled plates, strips, and foil billets. Extrusion blanking is a commonly used blanking method for the production of blanks for plates, strips, rods, tubes, and wires.

(1) Induction heating industrial pure tantalum for forging billet can be cold forged (room temperature), and tantalum or alloy with high impurity content can be forged by warm (350~400℃) or high temperature forging.

(2) The induction heating tantalum alloy extrusion of extrusion billet requires high extrusion temperature and fast extrusion speed. The heating temperature of Ta-10W is 1450°C. From room temperature to 300°C, tantalum and its alloys are very stable in the air, starting to oxidize at 300°C, and oxidizing strongly above 400°C. Therefore, cold forging (room temperature) or warm forging (350~400°C) of tantalum and tantalum alloys generally, it is not necessary to take protective measures for the blank.

As a highly active metal, tantalum and its alloys at high temperatures are easily contaminated and oxidized by oxygen, hydrogen, and nitrogen. The heating temperature of tantalum alloy ingots before blooming is generally above 1000°C or even more than 1300°C. In the process of heating and plastic deformation processing, the surface of the tantalum alloy workpiece absorbs a large amount of oxygen and forms an oxide layer. The formation of the oxide layer will cause material loss. If the solid solution hardened layer is mechanically removed due to oxygen absorption, the material loss will be even greater. The surface of the blank is hardened by aeration, the surface grains are more difficult to deform, and the grain boundaries are easy to form cracks. The core of the bad material has low oxygen and high plasticity and the surface is hardened by oxidation to high oxygen. Pull crack.

Protective measures for blanks before induction heating of tantalum alloy:

(1) Protective atmosphere heating: Inert gas (generally argon) is passed through the inductor for protection, which can avoid oxidation and gas absorption during the heating of the billet. The gap between the inner diameter of the inductor coil lining and the blank is small, and less protective gas is needed. There are mature technologies to reduce the leakage of protective gas. Disadvantages of protective atmosphere heating: Leakage of argon gas will cause pollution of the production environment; the transfer process from the inductor to the plastic forming equipment, as well as the forging or extrusion process, cannot protect the blank.

(2) The outer metal sheath of the billet: the heating temperature of the alloy ingot is high, and it is difficult to have a heat-resistant metal material that can be fully qualified. When deformed, these metal sheath materials are easy to break or tear, which not only loses protection Function, and affect the operation of the processing process. After forging or extrusion, the sheath metal is pickled and cleaned. Therefore, this scheme is rarely used now. Moreover, the cladding metal sheath complicates the design of the sensor parameters, and the calculation of the sensor parameters is changed from a single tantalum alloy model to a superposition of tantalum and another metal hollow cylinder model. Due to the metal sheath, the heating time of the blank in the inductor is prolonged.

(3) Surface coating The surface and inner holes of the alloy are coated with protective coatings during forging and extrusion, which can be isolated from oxygen and other gases during heating, reducing high-temperature oxidation and inhalation. After exiting the sensor, in addition to isolating air, it also It can reduce the temperature loss during the transportation of the billet to the forging and extrusion equipment. During forging or extrusion, the coating acts as a lubricant between the die or extrusion cylinder wall and the bad material. The advantage of coating is that the subsequent processing of forged and extruded products is simple.

At present, the protection of tantalum and tantalum alloy ingots basically adopts a protective coating process.