Effect of Oxygen, Sulfur and Trace Elements on Cast Iron

Various properties of cast iron approximately determined by carbon and silicon, that is, physical, mechanical and other properties of cast iron can be estimated by the degree of saturation or the carbon equivalent. Effects of manganese and phosphorous on properties of cast iron are auxiliary and small compared with that of carbon and silicon. The detailed or final properties of cast iron are controlled and determined by oxygen, sulfur and trace elements contained in cast iron. In other words, oxygen, sulfur and trace elements finally determine the properties and qualities of cast irons with fixed contents of carbon, silicon, manganese and phosphorous. The following two facts show that this suggestion is valid. (1) In the case of cast irons having the same contents of carbon, silicon, manganese and phosphorous, their qualities vary with kinds of raw iron materials and kinds of melting furnace, melting technique and refractory materials of wall and bed(1) even in the furnace of the same type. (2) Spheroidal graphite cast iron is obtained only when a cast iron has extremely small contents of oxygen, sulfur and trace elements. Many researchers have been performed on oxygen, sulfur and minute elements in spheroidal graphite cast iron. As gray cast irons are obtained in a wide composition range of oxygen, sulfur and trace elements, effects of oxygen, sulfur and trace elements on gray cast irons have not been examined strictly until now. A special quantitative relation among oxygen, sulfur and trace elements, which give the best quality to gray cast iron, must exist in cast irons with fixed contents of carbon, silicon, manganese and phosphorous. The purpose of this paper is to show the relationship among the behaviours of oxygen, sulfur and trace elements on a structural diagram, and to determine the contents of oxygen and sulfur which give the best quality to gray cast iron. Effects of nitrogen and hydrogen on the graphitizing tendency of cast iron can be ignored. Nitrogen stabilizes pearlite and cementite, but does not effectively affect the graphitizing tendency. Hydrogen affects the