Ferro Sulphide (Iron Sulphide)

Ferro sulphide is a chemical compound that has been used for centuries in a wide range of industries, including chemical iron and streel industries. It is usually produced by the reduction of iron ore with sulfur or oxidation of ferro sulphide ores with air. Ferro sulphide is a key material used in foundries for a variety of critical processes. Its unique properties make it invaluable in the production of high-quality cast iron and steel components.

In foundries, during iron melting, sulphur levels decrease due to a widespread practice of using cleaner material, the use of low sulphur steel scrap, and the presence of manganese in the melt due to its strong affinity to sulphur, forming manganese sulphide. To inoculate the metal for cast iron production, iron does not readily respond if the sulphur content is below 0.04 %. Therefore, ferro sulphide is added to increase the sulphur content to the range of 0.05 – 0.12 %.

Ferro sulphide is preferred for such addition due to its higher melting point over pure sulphur. Pure sulphur has a low melting point resulting in easier formation of iron sulphide, which creates an interdendentric layer, increasing the possibility of cracking in the castings. Also, pure sulphur has a tendency to float over molten metal when exposed to air, resulting in sulphur dioxide, an undesirable gas that pollutes the environment.

In steel industries, Ferro Sulphide functions as a re-sulphurising agent to maintain suitable levels of sulphur in the metals and to promote sulphur reaction with residual hydrogen to avoid any chance of hydrogen embrittlement as shown in figure 1 below.

The correct level of sulphur also allows for the formation of manganese sulphide inclusions which act as lubricants during machining, reducing tool wear and improving cutting efficiency. It can also improve other properties positively, such as hardness and brittleness, in the production of white cast iron.