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.

Austempered ductile iron (ADI) results from a specialty heat treatment of ductile cast iron. This article discusses the production of austempered ductile iron by heat treatment. The austempered ductile iron grades, according to ISO 17804 and EN 1564, are presented in a table. For economic reasons, or to avoid metallurgical problems, combinations of alloys are often used to achieve the desired hardenability in austempered ductile iron. The article provides information on the alloy combinations for austempered ductile iron. The mechanical properties, fracture toughness, fatigue, and abrasion resistance of the austempered ductile iron are discussed. The article concludes with information on the applications for austempered ductile iron.

Ductile cast irons are heat treated primarily to create matrix microstructures and associated mechanical properties not readily obtained in the as-cast condition. This article discusses the most important heat treatments of ductile irons and their purposes. International standards of ductile iron provided by ASTM International, the International Organization for Standardization (ISO), and SAE International are presented in a table. The article explains basic structural differences between the ferritic, pearlitic, martensitic, and ausferritic classes. It presents recommended practices for annealing ductile iron castings for different alloy contents and for castings with and without eutectic carbides. The article discusses the induction surface hardening and remelt hardening of ductile iron. It concludes with information on the effect of heat treatment on fatigue strength of 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.

Ductile cast irons are heat treated to create matrix microstructures and associated mechanical properties not readily obtained in the as-cast condition. This article provides a detailed account of the general characteristics of ductile irons. It discusses the most important heat treatments of ductile irons, namely, stress relieving, austenitizing, annealing, normalizing, quenching, martempering, austempering, and surface hardening. The article elucidates the effects of these heat treatments on the mechanical properties of the ductile irons.

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.

Cast irons, like steels, are iron-carbon alloys but with higher carbon levels than steels to take advantage of eutectic solidification in the binary iron-carbon system. This article introduces the solid-state heat treatment of iron castings and describes the various processes of heat treatment of cast iron. It provides information on stress relieving, annealing, normalizing, through hardening, and surface hardening of these castings. The article discusses general considerations for the heat treatment of cast iron. Cast irons are occasionally nitrided for various applications with the aim of enhancing surface hardness and corrosion resistance of the products. The article describes molten salt bath cyaniding and ion nitriding of cast iron.

Metallographic techniques for ductile irons are similar to those for other cast irons but more difficult than for steels, because graphite retention is a challenging task. This article presents recommended procedures to prepare ductile irons. It discusses three contemporary approaches for preparing ductile cast iron specimens with a wide range of phases and constituents as well as variations in graphite morphologies. A wide variety of matrix microstructures can be obtained in ductile irons. Examples are presented using a variety of etchants. Control of the nodularity of graphite in ductile irons is critical to their performance. The article presents details concerning the characterization of the graphite nodules.

The term cast iron designates a group of materials that contain more than one constituent in their microstructure due to excess carbon that result in unique characteristics such as the fracture appearance and graphite morphology. This article discusses the classification of cast iron and the various metallurgical aspects, such as the composition, alloying element, solidification, and graphite morphologies, of different types of cast iron. It describes the physical properties for various cast irons and the influence of microstructure and chemical composition on each property. The article provides a detailed account on thermal properties, conductive properties, magnetic properties, and acoustic properties of cast iron. It also examines heat treatment, namely, stress relieving, annealing, normalizing, through hardening, and surface hardening. The article presents a discussion on the welding, machining and grinding, and coating of the types of cast iron.

This article provides information on the salt baths used for a variety of heat treatments, including heating, quenching, interrupted quenching (austempering and martempering), case hardening, and tempering. It describes two general types of salt bath systems for steel hardening: the first type uses atmosphere austenitizing followed by salt quench and the second type employs austenitizing salt baths with rapid transfer to the quench salt. The article provides a detailed account on the construction, advantages and disadvantages, and limitations of isothermal quenching furnaces, submerged-electrode furnaces, immersed-electrode furnaces, and externally heated furnaces. It discusses the important applications of various furnace designs, including the austempering of ductile iron, the hardening of tool steels, and the isothermal annealing of high-alloy steels.

From the point of view of economics and ecology, thin-wall ductile iron (TWDI) castings can compete in terms of mechanical properties with the light castings made of aluminum alloys. This article discusses the effect of technological factors on the cooling rate and physicochemical state of the liquid metal for preparing thin-wall castings with good mechanical properties and performance while avoiding casting defects. It describes a variety of defects that may appear during the production of TWDI castings, such as casting skin anomalies (e.g., flake graphite, graphite segregation), graphite clusters, exploded graphite, slag inclusions, shrinkage porosity, eutectic chill and secondary carbides, and cold shuts. The article reviews the tensile, fatigue, impact, and wear properties of TWDI castings. It provides information on the production and applications of TWDI castings.

The mechanical properties of ductile cast irons are determined largely by the microstructure of the steel matrix in combination with the shape, size, and distribution of the graphite nodules. This article describes the designation of ductile cast irons according to the ASTM International designation system and reviews standard-grade ductile cast irons. An overview of the most commonly used standards related to designation and specification of ductile cast iron is presented in a table. This article discusses the use of low-alloy ductile cast irons at elevated temperatures and the chemical compositions and some mechanical properties of austenitic ductile cast irons. The article concludes with a discussion on heat treatment of austempered ductile iron.

Molten salt, including nitrite/nitrate salts, is the quenching medium most commonly used in austempering and marquenching of ferrous materials. This article describes the use of molten salts in the quenching of ferrous materials. It provides information on the processing and operation of salt quenching including considerations of time, temperature, environment, and safety, as well as critical characteristics such as the composition of the quenchant, agitation, and water additions.

This article begins with a description of the classes and grades of ductile iron. It discusses the factors affecting the mechanical properties of ductile iron. The article reviews the hardness properties, tensile properties, shear and torsional properties, compressive properties, fatigue properties, fracture toughness, and physical properties of ductile iron and compares them with other cast irons to aid the designer in materials selection. It concludes with information on austempered ductile iron.

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.

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 introduces the general principles and applications of heat treatment to iron castings. It provides a detailed discussion on the heat treatment processes, namely, stress relieving, annealing, normalizing, throughhardening, and surface hardening for various types of cast irons. These include gray iron, ductile iron, compacted graphite iron, white iron, malleable iron, and high-alloy iron. The article describes how to control temperature and atmosphere during the heat treatment of the iron castings.

This article is a compilation of color etchants that have been developed for a limited number of metals and alloys. It describes the optical methods for producing color, such as polarized light and differential interference contrast, with illustrations. The article discusses film formation and interference techniques such as anodizing, chemical etching, and tint etching. It provides a description of reagents that deposit sulfide films and molybdate films. The article concludes with a discussion on the thermal and vapor deposition methods to produce color.

This article describes the metallographic specimen preparation procedures for cast iron test samples, including mounting, grinding, polishing, and etching. It discusses the makeup and use of black-and-white and selective color etchants and where one might be preferred over the other. The article provides information on nearly 100 micrographs, discussing the microstructure of flake graphite in gray iron, nodular graphite in ductile iron, and temper graphite in malleable iron. It also examines the matrix microstructures of gray, ductile, compacted, and malleable cast iron samples.

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.