Oxygen State Forms in Cast Iron and their Effect on Graphite Crystallization

Abstract

Oxygen influence on the structure and properties of cast iron is contradictory and depends on its state. It is supposed that the chemically combined oxygen exists into molten metal as Non-metallic inclusion, and it acts as a Graphite crystallization substrate and also increases graphitization degree of the cast iron. Dissolved oxygen deactivates the potential graphitization centers that are why cast iron chill tendency is increased. At the same time, according to experimental results, the more cast iron is saturated by oxygen, the higher its tendency for graphitization modification. In this study, the influence of the oxygen state on graphite forming process during the cast iron crystallization is considered and the details of its action on the graphite crystallization at different stages of casting solidification process are also represented. It is shown that oxygen, initially present in molten melt in chemically combined state, does not have a significant effect on the Cast Iron crystallization. At the same time, the dissolved oxygen in non-modified cast iron causes chill, but in modified Cast Iron the over-equilibrium dissolved Oxygen content promotes graphitizing crystallization by forming dispersed pre-crystallizing (“fresh”) non-metallic inclusions in liquid cast iron. On the basis of these concepts, the original interpretation of several well-known facts concerning graphitization modifying is presented. These facts have been widely discussed at the present time, and there is a great number of contraversal opinions on this account. Particularly, the new aspects of the damping effect of the graphitization modifying of the cast iron have been discussed. The causes of ferrosilicon graphitizing power increase by addition of the aluminum, calcium, barium, rare-earth metals and other powerful elements-deoxidizers to it are shown. The additional factors of high effectiveness of the in-mold graphitization modifying of cast iron are presented also