Compacted graphite iron (GCI) is a cast iron grade that is engineered through graphite morphology modifications to achieve a combination of thermal and mechanical properties that are in between those of flake graphite iron and ductile iron. This chapter discusses the advantages of compacted graphite iron over gray iron and ductile iron. It presents examples of low- and high-frequency thermal cycling, both of which affect the thermal stresses that castings are exposed to during temperature fluctations. Information on optimum carbon and silicon ranges as well as mechanical property standards for CGI are provided. The chapter describes the critical factors that control CGI and discusses methods of CGI manufacturing.

This article discusses the composition and morphology of compacted graphite (CG) iron relative to that of gray and ductile iron. It explains that the graphite in CG iron is intermediate in shape between the spheroidal graphite found in ductile iron and the flake graphite in gray iron, giving it distinct advantages in a number of applications. The article also discusses the role of melt treatment elements and explains how alloying and heat treatment affect tensile strength, hardness, toughness, and ductility.

A spheroidized structure, which consists of spherically shaped cementite in a matrix of ferrite, is often desired in the production of steel, whether to improve properties, such as machinability and ductility, or accommodate subsequent hardening treatments. This chapter discusses the spheroidization of normalized and annealed steels by heating at subcritical temperatures. It explains how lamellar pearlite and proeutectoid cementite transform when heated and how deformation prior to heating affects both the mechanism and kinetics of spheroidization. It also explains how austenitizing contributes to the production of spheroidal transformation products and why secondary graphitization sometimes occurs.