Ductile iron, also known as nodular iron or spheroidal graphite iron, is second to gray iron in the amount of casting produced. This article discusses the common grades of ductile iron that differ primarily by the matrix structure that contains the spherical graphite. The grades of ductile iron designated by their tensile properties in the specification ASTM A536 are presented in a table. The article various reviews factors, such as microstructure, composition, and section effect, affecting the mechanical properties of ductile iron. It discusses the hardness properties, tensile properties, shear and torsional properties, damping capacity, compressive properties, fatigue properties, and fracture toughness of ductile iron. The article concludes with information on the applications of austempered ductile iron.

This article discusses the stable and metastable three-phase fields in the binary Fe-C phase diagram. It schematically illustrates that austenite decomposition requires accounting for nucleation and growth of ferrite and then nucleation and growth of pearlite in the remaining untransformed volume. The article describes the austenite decomposition to ferrite and pearlite in spheroidal graphite irons and lamellar graphite irons. It provides a discussion on modeling austenite decomposition to ferrite and pearlite.

The main factors affecting the mechanical properties of compacted graphite irons both at room temperatures and at elevated temperatures are composition, structure (nodularity and matrix), and section size. This article presents a comparison between some properties of flake graphite (FG), compacted graphite (CG), and spheroidal graphite (SG) irons in a table. It discusses the effects of composition, structure, and section size on the mechanical properties of compacted graphite irons. The compressive and shear properties, modulus of elasticity, impact properties, fatigue strength, and elevated-temperature properties of compacted graphite irons are also reviewed.

The solidification of hypoeutectic cast iron starts with the nucleation and growth of austenite dendrites, while that of hypereutectic iron starts with the crystallization of primary graphite in the stable system or cementite in the metastable system. This article begins with a discussion on the nucleation and growth of austenite dendrites. It describes the nucleation of lamellar graphite, spheroidal graphite, and austenite-iron carbide eutectic. The article reviews three main graphite morphologies crystallizing from the iron melts during solidification: lamellar (LG), compacted or vermicular (CG), and spheroidal. It discusses the metastable solidification of austenite-iron carbide eutectic and concludes with information on gray-to-white structural transition of cast iron.

This article discusses the chemical composition, castability, mechanical properties at room temperature and elevated temperature, and physical properties of compacted graphite (CG) cast iron. The change in graphite morphology from the flake graphite (FG) in the base iron to the CG in the final iron is achieved by liquid treatment with different minor elements. CG irons have strength properties close to those of spheroidal graphite (SG) irons, at considerably higher elongations than those of FG iron, and with intermediate thermal conductivities. The main factors affecting the mechanical properties of CG irons both at room temperatures and at elevated temperatures are composition, structure (nodularity and matrix), and section size. The article also discusses the applications of CG irons that stem from their relative intermediate position between FG and SG irons. The tables in the article list the values for tensile properties, hardness, thermal conductivity, fatigue strengths, endurance ratios, and compressive properties of CG, FG, and SG irons.

Unlike gray iron, which contains graphite flakes, ductile iron has an as-cast structure containing graphite particles in the form of small, rounded, spheroidal nodules in a ductile metallic matrix. This article discusses the raw materials that are used for ductile iron production and outlines the most common and important requirements for controlling the composition of ductile iron. Treatment to produce ductile iron involves the addition of magnesium to change the form of the graphite, followed by or combined with inoculation of a silicon-containing material to ensure a graphitic structure with freedom from carbides. The article describes the methods of magnesium treatment, control of magnesium content, and inoculation. It concludes with a discussion on the metallurgical controls of ductile iron production.

Gray irons are a group of cast irons that form flake graphite during solidification, in contrast to the spheroidal graphite morphology of ductile irons. This article describes surface hardening of gray irons by flame and induction heating. It provides information on the classification of the gray irons in ASTM specification. The article presents examples that illustrate the use of stress relieving to eliminate distortion and cracking. It describes the three annealing treatments of gray iron: ferritizing annealing, medium (or full) annealing, and graphitizing annealing. The article discusses the parameters of the tensile strength and hardness of a normalized gray iron casting. These include combined carbon content, pearlite spacing, and graphite morphology. The article concludes with a discussion on the induction hardening of gray iron castings.

The transformation of austenite of cast irons represents a more complex and less studied subject. This article discusses the general features of the decomposition of austenite into bainite. It describes the heat treatment cycles of austempered cast iron microstructure. The article reviews several factors, such as presence of graphite and austenite grain size, which affect the transformation rate of austenite during austempering of free-graphite cast irons.

Gray irons are a group of cast irons that form flake graphite during solidification, in contrast to the spheroidal graphite morphology of ductile irons. The heat treatment of gray irons can considerably alter the matrix microstructure with little or no effect on the size and shape of the graphite achieved during casting. This article provides a detailed account of classes of gray iron, and heat treating methods of gray irons with examples. These methods include stress relieving, annealing, normalizing, transformation hardening, austenitizing, quenching, austempering, martempering, flame hardening, induction hardening, and nitriding.

Cast iron exhibits a considerable amount of eutectic in the solid state. This article discusses the structure of liquid iron-carbon alloys to understand the mechanism of the solidification of cast iron. It illustrates the nucleation of the austenite-flake graphite eutectic, austenite-spheroidal graphite eutectic, and austenite-iron carbide eutectic. The article provides a discussion on primary austenite and primary graphite. It also describes the growth of eutectic in cast iron in terms of isothermal solidification, directional solidification, and multidirectional solidification.

Compacted graphite iron (CGI) invariably includes some nodular (spheroidal) graphite particles, giving rise to the definition of the microstructure in terms of percent nodularity. This article discusses the graphite morphology and mechanical and physical properties of CGI. The mechanical and physical properties of CGI with ferritic and pearlitic matrix structures are summarized in a table. The article describes the standards for CGI, with the definition of the grades based on the minimum tensile strength. It also provides information on the applications of compacted graphite iron castings.

Machining of cast iron involves removing metal from the cast part, usually by cutting with a power-driven machine tool. This article discusses the factors that influence machinability, the methods used to evaluate machinability of cast irons, the effects of cast iron microstructure on cutting tool life, and the importance of as-cast surface integrity on the machining variation. It presents examples of cutting tool materials selection for different cast iron grades, and describes the effects of coolants on the machining of cast irons. A chart showing different cutting materials and cutting speed ranges for selected iron-carbon alloys is also presented. Different types of cutting tool wear observed during turning are schematically illustrated.

The ferrous metals are the most significant class of commercial alloys. This article describes the solidification structures of plain carbon steel, low-alloy steel, high-alloy steel, and cast iron, with illustrations. The formation of nonmetallic inclusions in the liquid before and during solidification is also discussed.

This article describes a method to predict mechanical properties of cast iron materials and illustrates how to use the predictions in computer-aided tools for the analysis of castings subjected to load. It outlines some ways to predict the hardness and elastic modulus of cast iron without going into dislocation theory. The article discusses modeling of hardness in cast iron based on a regular solution equation in which the properties of each phase depend on chemical composition and coarseness. It describes the evaluation of material parameters from the tensile stress-strain curve. The article concludes with an illustration of a finite-element method (FEM) model containing heterogeneous mechanical properties using local material definitions.

The appearance, morphology, and extent of the casting skin are the consequence of mold-metal interface interaction. This article discusses the classification of the mold-metal interaction based on severity: mild mold-metal interaction and severe mold-metal interaction. The casting surface exhibits some roughness, which depends on the molding materials used in the casting process. The article describes the effects of the casting skin in spheroidal graphite (SG) and compact graphite (CG) irons, as well as the mechanism of casting skin formation. It discusses the physics of liquid metal penetration in sand molds and concludes with information on the effect of sand additives and mold coatings.

Computational modeling assists in addressing the issues of solid/liquid interface dynamics at the microlevel. It also helps to visualize the grain length scale, fraction of phases, or even microstructure transitions through microstructure maps. This article provides a detailed account of the general capabilities of the various models that can generate microstructure maps and thus transform the computer into a dynamic microscope. These include standard transport models, phase-field models, Monte Carlo models, and cellular automaton models.

The microstructure that develops during the solidification stage of cast iron largely influences the subsequent solid-state transformations and mechanical properties of the cast components. This article provides a brief introduction of methods that can be used for simulating the solidification microstructure of cast iron. Analytical as well as numerical models describing solidification phenomena at both macroscopic and microscopic scales are presented. The article introduces macroscopic transport equations and presents analytical microscopic models for solidification. These models include the dendrite growth models and the cooperative eutectic growth models. The article provides some solutions using numerical models to simulate the kinetics of microstructure formation in cast iron. It concludes with a discussion on cellular automaton (CA) technique that can handle complex topology changes and reproduce most of the solidification microstructure features observed experimentally.

This article discusses criteria that can be used for the classification of cast iron: fracture aspect, graphite shape, microstructure of the matrix, commercial designation, and mechanical properties. It addresses the main factors of influence on the structure of cast iron, including chemical composition, cooling rate, and heat treatment. The article describes some basic principles of cast iron metallurgy. It discusses the main effects of the chemical composition of ductile iron and compacted graphite (CG) iron. The composition of malleable irons must be selected in such a way as to produce a white as-cast structure and to allow for fast annealing times. Some typical compositions of malleable irons are presented in a table. The article concludes with information on special cast irons.

This article discusses the classification schemes for cast irons and describes the characteristics of major categories, including gray iron, white iron, ductile iron, compacted graphite iron, mottled iron, malleable iron, and austempered ductile iron. It also discusses some of the basic principles of cast iron metallurgy. When discussing the metallurgy of cast iron, the main factors of influence on the structure include chemical composition, cooling rate, liquid treatment, and heat treatment. In terms of commercial status, cast irons can be classified as common cast irons and special cast irons. Special cast irons differ from the common cast irons mainly in the higher content of alloying elements. Alloying elements can be added in common cast iron to enhance some mechanical properties. They influence both the graphitization potential and the structure and properties of the matrix.

This article discusses the graphite morphology, chemical composition, mechanical and physical properties, and applications of compacted graphite (CG) irons. It compares the selected properties of gray, ductile and CG irons, and lists their property requirements as per ASTM A 842. A listing of tensile properties of various CG irons produced by different melt treatment methods is also provided.