Tantalum cannot be processed by ordinary methods for processing general metals. Generally, the initial process is forging heat treatment, which is made into flat billets or round small and medium-sized billets by hammering and stamping. Unlike general metals, tantalum cannot be heat-processed. The recrystallization temperature of tantalum exceeds 1000~C. If heated, even if a general protective layer is applied, excessive oxidation will occur. What is more serious is that if tantalum is exposed to such a high temperature, not only will excessive oxidation occur on the surface of tantalum, but oxygen will also invade between atoms inside the matrix, making tantalum brittle. Not only oxygen, but even nitrogen, carbon and hydrogen can make tantalum brittle. For the above reasons, tantalum is generally not heat-processed. When heat processing is necessary, a protective coating should be applied or it should be carried out in an inert gas atmosphere. Heat treatment Since tantalum reacts actively with oxygen, it is necessary to avoid heat treatment in an atmosphere where even a small amount of air is present. Therefore, almost all annealing is carried out in a high vacuum, and the airtightness of the heating furnace must also be very high. Usually, the heat treatment temperature of tantalum is generally between 950 and 1300℃. Tantalum and the commonly used tantalum alloys do not undergo phase changes within this temperature range. Heat treatment is only used for annealing, so the heating temperature and cooling rate are not important. In order to produce complete recrystallization, the heat treatment time should be slightly longer.
Commercially produced tantalum has a high purity. The grains become very large through annealing. The size of the crystal grains is determined by cold working, purity, temperature and process steps. Therefore, temperature control and process control are important means to determine the size of the crystal.
Unlike many other metals, tantalum must be very clean before heat treatment. If it is not cleaned very cleanly, surface contamination caused by hydrogen, oxygen, nitrogen and carbon will occur, resulting in brittle (hardened) structure. Because hydrogen, oxygen, nitrogen and carbon are very active invasive elements within the temperature range of tantalum annealing, once contaminated by these elements, there is no way to remove them except re-melting.
Tantalum plate manufacturing characteristics
Tantalum plates are almost all cold-processed. Generally, it starts with a 15-30cm tantalum ingot, cold forged into a slab about 8-10m thick, and then cold rolled from this slab, with a compression rate of more than 95%. In commercial production, the slab is usually rolled into a 0.63-1.2cm thick plate with a width of 51-102cm using a two-roller or a four-roller. The rolling is typically carried out at room temperature or near room temperature to prevent the formation of oxides on the surface. When hot rolling is required, the temperature rises to 1000℃ due to recrystallization and a fierce oxidation reaction occurs.
Almost all thick plates are heat treated and annealed in a vacuum. Since there is no phase change, the speed of heating and cooling is not important. Further rolling is carried out using an ordinary rolling mill, and a four-roller multi-roller is generally used at this time. Because tantalum is very soft, care should be taken to prevent scratches during processing and transportation.
Features of Tantalum Rod Manufacturing
To manufacture rod products, they are first forged or extruded into an intermediate moderate size, with a typical cross-sectional yield of 70%-90%, and then the material is annealed and heat treated. When further processed, forging, rolling, extrusion or drawing processes are usually used. Wires are processed using ordinary wire drawing machines. Since tantalum materials are very soft and easily scratched, surface problems are very serious during drawing, and manufacturers must pay special attention to surface conditions and lubrication.
Tantalum tube manufacturing features
Tantalum can be made into welded tubes and seamless tubes, and has a wide range of uses. Seamless tubes are manufactured by extrusion, tube reduction or deep drawing of plates. The welding manufacturing method is to first form the plate strip, then make it into a tube shape, and then weld the seam with gas tungsten arc (GTAW).