AFS Library

FORMATION OF SLAGS IN CAST IRON AND EFFECT ON CASTING

3333
Journal: Transactions of the American Foundrymen's Society V 70 P 612-621, 1962 (10 p)
Author: Dahlmann, A and Loehberg, K

Reactions between materials in close contact with metals and alloys occur easier when the latter are in the liquid. rather than in the crystalline slate. The possibilities for such reactions to take place are many, e.g., reactions between metal on the one hand and ceramics, molding materials or the atmosphere on the other hand. This paper deals with the reactions between liquid metals and oxygen. Investigations of reactions between liquid nonferrous metals and atmospheric oxygen, have alreadv been carried out on frequent occasions. Reactions between oxygen and metals, such as lead and zinc, have been studied with respect to the products formed and also the times taken for these reactions. It has been found that the latter are functions of the temperature and the composition of the allow and when plotted give either a linear or a parabolic graph. In contrast, reactions between liquid cast iron and oxygen of the air. have hardly been investigated. This may have stemmed from the belief that the slags encountered in castings were, in many cases, products of the reaction between melt and ceramic materials (in the widest sense). In the course of this investigation it was found that the observations published in the literature agreed with the authors' findings. These confirm that the slags appearing in spongy areas of castings arc developed bv the interaction of liquid iron and the air: this occurring in the ladle, in Ihe pouring stream or even in the mold. This preliminary contribution to the clarification of the problem of the kinetics of slag formation confirms the fact, known from the literature, that such reactions depend on the composition of the cast iron and especially on the silicon, managanese and sulfur contents. The author shows thai a close relationship exists between the composition of a cast iron, the temperature at which the oxide films are formed and the composition of the slags and their properties. In melts of cast iron that are rich in sulfur a sulfide slag is the first to develop, followed by a silicate slag. The temperature interval between the beginning of oxide film formation and the complete covering of the bath surface with slag is considerably smaller for melts low in manganese than for melts high in manganese. The possible cause of this may be a difference in wettability of metal and slag respectively. Summarizing, it is concluded that the formation of spongy areas in an iron casting is determined by the silicon, managanese and sulfur contents of the cast iron, by the pouting temperature and by the time during which the molten metal is exposed to the air.



$15.00 for members
$10.00 for corporate members
$30.00 for nonmembers


or Search again