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Causes of Metal Penetration in Steel Castings

The objective of this project was to determine the effect of atmosphere at the mold/metal interface on chemical penetration. The research program was successful in identifying the major factors that influence steel penetration in sand molds. A case study of penetration samples revealed that both chemical and mechanical penetration were present in carbon and high manganese steels. It also found that only mechanical penetration is found in stainless steel samples. Sessile drop experiments were run to discover the effect of steel chemistry on the contact angle for different substrates. These experiments revealed the best substrate for each type of metal. Bauxite, magnesite and mullite were the best materials for resisting mechanical penetration. It was also shown that high manganese steels cannot be poured into silica molds and that stainless steel should not be poured in chromite molds. Mold/metal atmosphere tests were run to understand the effects of the atmosphere on chemical penetration. It was found that the chemistry affecting penetration has its greatest effect as the casting is just poured. This is because the interfacial gases are most oxidizing at this time. Chemical penetration of low carbon steels cannot be completely eliminated by adding carbon to green sand molds although a marked decrease is obtained in its severity. Solid state penetration can occur after the steel has solidified. This is caused by the extremely low diffusivity of carbon through solidified steel.
University of Alabama
Thomas Prucha
American Foundry Society
1695 Penny Lane
Schaumburg, IL  60173

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