Some Behaviors and Characteristics of Decarburized Layer in Spheroidal Graphite Cast Iron

抄録

Spheroidal graphite cast irons are widely used for auto parts because they have large degrees of freedomin shape and are inexpensive. When they are welded, however, they show serious drawback of crackgeneration due to excess carbon at thehardened region of heat-affected zone. We have studied ondecarburized spheroidal graphite cast iron which has a possibility of welding because of graphite free in thesurface region. In the present study, some characteristics of the decarburized layer in the spheroidal graphitecast 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 theiron during the heat-treatment and there is a critical temperature of 930 K for the decarburization, belowwhich decarburization does not occur. When the area ratios of the decarburized layer to whole sectional areain the rod-shaped tensile test specimen was defined to be a ratio of decarburized layer, the tensile strengthof the specimen scarcely influenced by the ratio of decarburized layer. However, when theoverdecarburization 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 theexcessive decarburization makes the strength of thin parts of the iron to decrease.