Almost all of the manganese produced is used in the manufacture of steel. During the Bessemer process, by which iron is converted into steel, manganese reacts with the sulphur which would otherwise form iron sulphide, and cause brittleness; it also reacts with the oxygen which would produce tiny holes and bubbles in the steel. Furthermore, manganese serves to harden the alloy. Such steels possess good shock and wear resistance, and are used in railway crossings.
Technetium is of less industrial importance than manganese, although its oxide has been used to promote corrosion-resistance in certain alloys, and technetium-99 can provide a source of radiation in medical research.
Rhenium too, because of its extreme rarity, is used on a far smaller scale than is manganese. Having a high melting point, and being resistant to corrosion, however, it is employed in thermocouples, electrical filaments and welding rods. It is also used as a catalyst.
