Tantalum possesses exceptional chemical stability, exhibiting high resistance to various strong acids, strong alkalis, and aqua regia, maintaining its stability even at high temperatures. This gives tantalum tubes a unique advantage in chemical, medical, and other fields requiring contact with corrosive substances.
High Melting Point: Tantalum boasts a melting point as high as 2996℃, resulting in excellent high-temperature resistance. It can operate stably for extended periods in high-temperature environments, making it suitable for aerospace, electronics, and other fields with high temperature resistance requirements.
Moderate Hardness and Ductility: Tantalum's moderate hardness allows it to be drawn into fine wires or made into thin foils. This characteristic enables tantalum tubes to maintain good shape and dimensional accuracy during processing, facilitating various forming and joining operations. Low Coefficient of Thermal Expansion: This characteristic results in minimal dimensional changes in tantalum tubes under varying temperatures, contributing to stable performance in applications requiring high dimensional accuracy, such as precision instruments and electronic equipment. Production Methods: Powder metallurgy tantalum powder is pressed and sintered, then rolled or stretched into tubes. Electron beam melting of high-purity tantalum ingots is extruded and drawn into tubes. Surface treatments such as polishing or pickling are used to improve corrosion resistance and surface finish.
Tantalum tubes undergo work hardening during cold working processes such as rolling or drawing. Before further processing, they generally require annealing at a high temperature of 1000-1200℃ to eliminate internal stress, restore the tube's processing plasticity, and facilitate further processing such as diameter reduction and wall reduction to achieve the required dimensions. Finished tubes are mostly in a soft or semi-hard state and require complete annealing for recrystallization or incomplete annealing to eliminate internal stress before use. Because tantalum is highly chemically reactive at high temperatures, it reacts with oxygen, nitrogen, hydrogen, and other gaseous components in the air or heated atmosphere, as well as with processing lubricants and oils on the tube surface, causing the tantalum tube surface to absorb gases or oxidize, damaging its performance. According to current literature, for a long time, all tantalum tube annealing both internationally and domestically has been carried out using traditional vacuum annealing furnaces. In traditional vacuum annealing of tantalum tubes, resistance heating is used, which relies on radiation for heat transfer. This results in slow heating, gradually depleting the deformation energy stored in the tantalum lattice and weakening the nucleation ability for recrystallization. The annealed grains are relatively coarse, and the slow cooling rate further contributes to grain growth during cooling. This leads to relatively low strength and plasticity in the product.
Tantalum has a very high melting point, and its recrystallization annealing temperature is correspondingly high. Traditional vacuum annealing furnaces are limited by material properties, resulting in a relatively low temperature limit. Even with excessively extended holding times, it is difficult to achieve the desired recrystallization annealing for high-melting-point tantalum. Using traditional vacuum annealing, the tantalum tube exhibits a tensile strength of 210 MPa, a yield strength of 140 MPa, and an elongation of 25%.
Annealing is performed in a vacuum induction annealing furnace: An automatic conveyor feeds the tantalum tube at a speed of 10-50 cm/min through the induction coil heating section of the furnace. The heating section must reach the recrystallization temperature of the tantalum tube (1300-1600℃) within 3-5 seconds. The heat-resistant sleeve containing the tantalum tube continuously passes through the heating section of the induction coil, resulting in a stepped temperature distribution along the entire axial direction of the tube.
Under this temperature distribution, the crystal texture of the tube is regularly distributed along the axial direction. New crystal nuclei formed during the recovery process, without lattice distortion, are less likely to aggregate and recrystallize, thus preventing grain growth. Rapid cooling is then performed in the vacuum induction annealing furnace: The heat-resistant sleeve containing the tantalum tube exiting the heating section is uniformly fed into the cooling water jacket in the cooling section for rapid cooling. The tantalum tube cools to 300-600℃ within 1-2 minutes, at which point the vacuum induction annealing furnace stops heating. The tube then cools naturally to room temperature.
The tantalum tube enters the induction furnace through the induction coil and undergoes rapid cooling simultaneously and continuously. The main technical feature of this invention is that both the heating and rapid cooling of the tantalum tube are completed within the induction annealing furnace.
