Effect of Te on the Microstructural Changes during the Gray-to-White and White-to-Gray Transition in Directional Solidification of Fe-C-Si Alloys

摘要

The purpose of the present study is to understand the nature of the solidification of cast irons using the directional solidification technique. Cast irons can solidify directly by either the graphite-austenite or the iron carbide-austenite eutectic reactions. The existence of two eutectic systems is probably the most important fact to be considered in the study of the solidification of cast irons. Normally, the graphite eutectic, called a gray iron, is the more stable form and solidifies at a higher temperature than the carbide eutectic, called a white iron. Based on the fact that the addition of low levels of tellurium to a cast iron melt very strongly promotes the white iron structure at slower solidification rates, addition of tellurium to Fe-C-Si system was attempted in order to study the transition phenomenon within an acceptable range of the experimental solidification rates. The advantages of the directional solidification technique are that the temperature gradient, solidification rate, and the alloy composition can be varied independently. Varying the solidification rate with the temperature gradient and composition held constant will allow both the determination of the transition rates and the investigation of the continuous changes in structure, such as graphite morphology, accompanying the transition within a single sample. 20 refs., 57 figs., 3 tabs. (ERA citation 14:017742)