Tantalum

A high melting point ductile metal of grey-white color with high chemical resistance and high temperature tensile strength.

 

Ta

Symbol
Atomic number73
Atomic weight180.88
Specific weight at 20 °C16.6 g/cm3
Melting point3000 °C
Boiling point6100 °C
Melting heat174 kJ/kg
Specific thermal capacity at 20 °C0.143 kJ/(kg·K)
Thermal conductivity54 kJ/(m·K)
Therm. coefficient for linear expansion Coefficient for linear expansion6.6·10-6/K

Tantalum in steel

Solubility of tantalum in γ-iron is 6.5 %, and approx. 0.20 % in α-iron. Tantalum forms very resistant carbides (tantalum carbide, TaC) and increases the hardening properties of austenite by forming mixed crystals. Similar to niobium, tantalum constricts the γ-area but, compared to niobium, it has an increased affinity to oxygen.

In addition to niobium, tantalum is added to semi-killed structural steels with a low carbon content improving tensile strength and ductility due to grain refinement. In unalloyed steels, tantalum improves the creep resistance at moderately increased temperatures. Non-corroding steel types with approx. 18 % Cr and 8 % Ni can be stabilized with tantalum. During special annealing treatments, in particular tantalum carbides are released, while the formation of chromium carbides which trigger intercrystalline corrosion is almost completely prevented. For this purpose, niobium is preferred since lower amounts are required for complete stabilization due to the low atomic weight of niobium compared to tantalum.

In certain cases, tantalum was added to high-temperature resistant alloyed steel types instead of niobium; it turned out to be as effective with regard to ductility and strength at high temperatures.Compared to niobium, tantalum has an increased affinity to nitrogen. Therefore, tantalum nitride is formed considerably faster than niobium nitride. Due to this property, tantalum was added to nitriding steels in order to increase the formation of a hard surface layer.

Tantalum is used in hard metals for the production of cutting tools, matrixes and wear-resistant surfaces. Tantalum-containing tools feature wear-resistant cutting edges and low vulnerability to surface pitting. Tantalum carbide is more resistant than tungsten carbide and molybdenum carbide; together with niobium carbide, it is frequently used as a component of sintered carbide tools.

Tantalum in cast iron

Similar to niobium, tantalum can be found in cast iron as a trace element only.

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