Volumetric Changes During Freezing of Ductile Cast Iron

Abstract

The program was undertaken to develop a technique for measuring the volumetric changes occurring in graphitic ductile iron during solidification. It was desirable that the technique 1) permit cooling at a controlled rate, 2) minimize thermal gradients in the solidifying specimen and 3) provide capability of separating effects of the mold material from the expansion or contraction of the metal. Three techniques allowing unconstrained and near isothermal expansion were evaluated. The technique that appeared to offer the most precision consisted of cooling a sample of iron contained in a crucible while measuring the motion of a piston floating on the surface of the sample. The volumetric changes occurring during solidification of a hypereutectic ductile iron, a eutectic ductile iron and a eutectic gray iron were measured as a function of temperature using this technique. Marked differences were observed in both the amount and the temperature interval over which expansion occurred in the experimental irons. Proeutectic and eutectic expansion were observed during solidification of the hypereutectic ductile iron. The eutectic alloy exhibited a sharp expansion at the eutectic temperature and the amount of expansion observed was less than that of the hypereutectic alloy. The eutectic gray iron was found to expand less than the ductile iron of nearly the same composition.