Calcium

Calcium is a silvery white alkaline earth metal that oxidized very quickly in air.

SymbolCa
Atomic number20
Atomic weight40.08
Specific weight at 20 °C1.53 g/cm3
Melting point850 °C
Boiling point1350 °C
Melting heat326 kJ/kg
Specific thermal capacity at 20 °C0.65 kJ/(kg·K)
Thermal conductivity201 kJ/(m·K)
Therm. coefficient for linear expansion Coefficient for linear expansion22·10-6/K


Calcium in steel


Calcium and iron are completely insoluble within each other. Sources that report of traces of this element present in steel, probably only refer to non-metallic inclusions. Calcium has a lower melting point than iron and displays relatively high vapor pressure levels at temperatures as low as 850 °C so that addition of calcium to molten steel involves great difficulties. Moreover, calcium is extremely reactive and easily combines with oxygen, nitrogen, hydrogen, the halogen elements, carbon, silicon, and many other elements.

Therefore it is common practice to introduce calcium to a steel bath in the form of alloys, e.g. with silicon, manganese, and iron (see Ferro-alloy, Master alloy). Calcium-silicon is added to steel for deoxidation purposes. The deoxidation products rise to the surface and merge into the slag. The effect is that less and more harmless inclusions remain in the steel bath than with deoxidation using pure aluminum, silicon, or the like. The higher level of purity in steel deoxidized using calcium-silicon leads to improved mechanical properties.

Addition of calcium lowers the sulfur content, provided that the reducing conditions are maintained. In order to achieve good results, the addition of calcium to steel must be performed under strict compliance with prerequisites. Ground calcium-silicon is added to the deoxidation and desulfurization slag towards the end of the process. It is also added to non-corroding and other low-carbon steel types for slag reduction and as deoxidation agent.

In steels that have been treated with silicon, aluminum, or other deoxidation agents, addition of calcium can influence the type and distribution of non-metallic inclusions. Addition of 0.05 to 0.1 % Ca impedes formation of inclusions of eutectic nature at the grain boundaries. In this case, calcium is used in the form of calcium-silicon.

Calcium in cast iron

Cast iron in general does not contain calcium. If addition of large amounts of calcium is intended, special equipment must be used. A number of desulfurization processes take advantage of the fact that calcium has great affinity towards sulfur. With these processes, calcium is added as a metal, as calcium carbide or in the form of lime. Similar to magnesium, calcium also promotes formation of nodular graphite (see Nodular graphite cast iron). Some silicon-containing inocula (s. Inoculation) also contain calcium, which has a postive effect on nucleation conditions.

 

 

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