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.

Iron and steel have been the most useful materials to meet the needs of several industries for many decades. Each iron and steel alloy offers unique attributes that make them the best choice for an application. This chapter provides an overview of each ferrous alloy—gray iron, malleable iron, compacted graphite iron (CGI), ductile iron, austempered ductile iron (ADI), and carbon steel and low-alloy steel; its versatile attributes; and its individual applications. A large section of the chapter covers the impact of electric vehicles on the future of the iron and steel castings industry, including discussion on electric vehicle categories and weights; impact of center of gravity on stability and steering; lightweighting incentives; and engineering for improved suspension.

The properties of cast iron are determined primarily by the form of carbon they contain, which in turn, is controlled by modifying compositions and cooling rates during casting. Certain alloys (such as Si, Al, Ni, Co, and Cu) promote graphite formation, while others (such as S, V, Cr, Sn, Mo, and Mn) promote the formation of cementite. This chapter examines the relative potencies of these alloys and their effect on microstructure. It covers the five most common commercial cast irons, including white, gray, ductile, malleable, and compacted graphite, describing their compositional ranges, distinguishing features, advantages, limitations, and applications.

The commercial relevance of cast irons is best understood in the context of the iron-carbon phase diagram, where their composition places them near the eutectic point, which sheds light on why they melt at lower temperatures than steel and why they can be cast into more intricate shapes. This chapter examines these unique properties and how they are derived. It begins by describing the basic metallurgy of cast iron, focusing on the eutectic reaction. It explains how to control the reaction and thus properties of cast iron by overcooling and inoculation. The chapter also discusses composition, microstructure, heat treatments, and the classification and casting characteristics of white, gray, ductile, malleable, compacted graphite, and special cast irons.

This chapter discusses the crystal structures of steel and cast iron, the iron-iron carbide equilibrium diagram, microconstituents or phases in the iron-iron carbide phase diagram, the iron-carbon carbide-silicon equilibrium diagram of cast irons, and the influence on microstructure by base elements and alloying elements. Graphitization, cooling rates, and heat treatment effects are covered. There also is discussion on inoculation benefits, flake graphite types and typical applications, evolution of cast iron types, ASTM specification A247 for graphite shapes, and selection of the best molding process. A large table lists typical material choices for various applications.

This chapter discusses the effect of composition and cooling rate on the microstructure and properties of cast irons and explains how they differ from steel. It describes the conditions under which white, gray, mottled (chilled), and nodular (ductile) cast irons are produced, and examines the growth mechanisms and structural details that set them apart. It also discusses the formation of compacted (vermicular) graphite and malleable iron, and compares and contrasts the composition, properties, and heat treatment of whiteheart and blackheart malleable types.