Growth of Cast Iron in Austenite Region

Abstract

During cyclic heating in the austenite-region grey cast irons increase their volume irreversibly without transformation and graphitization. In this study some experimental facts were obtained on the growth in air, but they could not be explained by the oxidation theory.
Therefore a new mechanism, suggested by the author, of the growth was applied to explain them. The results obtained are summarized as follows.
(1) Growth in austenite-region depends mainly on the difference in the temperature of cyclic heating.
(2) Even the hard grey cast iron that does not grow in the critical range may grow in austenite region.
(3) The dilatometer curves of nodular graphite cast iron show that this iron grows gradually in a loop in austenite-region during cyclic heating.
(4) Preheating in air promotes the growth in austenite region, but retards it in the cycle including transformation.
(5) Growth characteristics of cast iron may differ in critical-range and in austenite-region. And growth occurring in the cycle covering both regions is the sum of growth in individual regions.
(6) Growth by transformation can not be examined separately, and it is usually accompanied with growth in austenite region.
(7) Experimental facts on the growth in austenite region are not explainable by the earlier theories, and it is suggested that the migration of graphite carbon during cyclic heat treatment in austenite region may create irreversible volume changes.