Sulfur

Element, chemical symbol S. A yellow, nonmetallic element that resembles oxygen chemically but is less active and more acidic. Sulfur is a common residual element in steel originating during smelting where its presence is generally detrimental, with the exception of free machining steels. Below 0.05 percent content, its influence on the properties of the steel is slight, but beyond this limit it is liable to cause red-shortness.