Some Behaviors and Characteristicsof Decarburized Layer in Spheroidal Graphite Cast Iron

概要

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Spheroidal graphite cast irons are widely used for auto parts because they have large degrees of freedom in shape and are inexpensive. When they are welded, however, they show serious drawback of crack generation due to excess carbon at thehardened region of heat-affected zone. We have studied on decarburized spheroidal graphite cast iron which has a possibility of welding because of graphite free in the surface region. In the present study, some characteristics of the decarburized layer in the spheroidal graphite cast iron were investigated. The results obtained are as follows. Growth of decarburized layer is controlled by diffusion of carbon atoms toward the surface region in the iron during the heat-treatment and there is a critical temperature of 930 K for the decarburization, below which decarburization does not occur. When the area ratios of the decarburized layer to whole sectional area in the rod-shaped tensile test specimen was defined to be a ratio of decarburized layer, the tensile strength of the specimen scarcely influenced by the ratio of decarburized layer. However, when the overdecarburization was processed, the tensile strength showed a tendency to decrease. Therefore, it should be noted in practical use of the decarburized spheroidal graphite cast iron that the excessive decarburization makes the strength of thin parts of the iron to decrease.
秋田大学の論文