Selenium improves the machinability of steels. The “internal lubricant” properties of Selenium are retained in steels even when they are heat-­treated up to at least 1300 Mpa (200 ksi). High alloy steel castings inoculated with 0.02% Se will show less pinhole and porosity even at hydrogen concentrations of 8 to 11 ppm. Selenium is used for improving the transverse ductility and toughness by adding equal proportion to the steel’s sulphur content. Selenium alters the shape of sulphide inclusions, making them more globular and is thus similar to Calcium and Rare earth metals. Higher concentration of Selenium -­ 0.05% to 0.10% significantly reduces the rate of nitrogen absorption in liquid steel and thus will have better cold forming properties.

Chemical Composition:

Se 99% Min
Atomic Number 34
Atomic Weight 78.96
Density 4.85 g/cm3
Melting Point 220 C
Boiling Point 695 C

Addition Practice:

Selenium metal is added to the ladle for more even distribution. Being lighter than steel and highly volatile (boiling point below steel making temperature), recovery of around 60% only is achieved. However special techniques or Ferro Selenium can improve the Se recovery to 80/85%.


0.05 – 0.10% of Se is effective in Carbon and low alloy steels.
0.30% Se is needed in high alloy and Stainless Steels.