The role of chromium during austempering of ductile iron

Abstract

The present work analyzes the effect of small additions of chromium in the final structure of a commercial Austempered Ductile Iron (ADI). The study is made with emphasis on the effect of this element on the processing window. The results indicate that chromium addition decreases the stability of austenite promoting the martensitic transformation during cooling which increases the hardness and reduces the elongation. Likewise the increase in chromium addition delays the rate of transformation to ausferrite (stage I) and accelerates the stage II reaction promoting the bainite formation narrowing the optimal processing window. However, this effect is markedly reduced when the material is subjected to a long process of homogenization, prior to austempering process. The results of this work are discussed in terms of the degree of chromium segregation during solidification.