The most critical step in the production of steel today. This removes sulphur impurities from the metal. Sulfur is a common impurity in metal ores, and if not eliminated from them, sulfides can squeeze into the steel during rolling as foreign inclusions. These, because their composition differs greatly from that of the steel and they are prone to bite off in layers from the high-stress area under tension during time use、badly affect the steel's mechanical properties. The major purpose of desulphurization is to raise the quality and ductility of steel making it suitable for a wider range of uses. The issues for desulfurization are many and varied but all fixed firmly along this axis. The technique uses slag-forming materials, such as limestone or dolomite, to react with steel sulphur and form gas and slag, which are then removed. This process may be carried out in a converter, an electric furnace, or from ladle treatment stations for steelmaking purposes.In practice, the structure of desulphurized steel ranges from the construction materials and automotive industries to household electrical appliances such as air-conditioners and vacuum cleaners that run straight on electricity instead of gas backup systems.