This article presents fractographs that show evidence of overload and fatigue in gray cast irons. The overload failure section illustrates a fractured motor housing, valve body, and bracket with microvoid coalescence (dimpled rupture) in the metal matrix between graphite flakes. The fractographs of fatigue failures illustrate a gearbox housing with fatigue striations and pearlitic microstructure.

The information provided in this article is intended for those individuals who want to determine why a casting component failed to perform its intended purpose. It is also intended to provide insights for potential casting applications so that the likelihood of failure to perform the intended function is decreased. The article addresses factors that may cause failures in castings for each metal type, starting with gray iron and progressing to ductile iron, steel, aluminum, and copper-base alloys. It describes the general root causes of failure attributed to the casting material, production method, and/or design. The article also addresses conditions related to the casting process but not specific to any metal group, including misruns, pour shorts, broken cores, and foundry expertise. The discussion in each casting metal group includes factors concerning defects that can occur specific to the metal group and progress from melting to solidification, casting processing, and finally how the removal of the mold material can affect performance.

Cast irons have been widely used by engineers in applications that require low cost, excellent castability, good damping capacity, ease of machining, and wear resistance. This article discusses the classification of wear for cast irons: adhesive wear, abrasive wear, and erosive wear. Typical wear applications for a variety of cast iron grades are listed in a table. The article reviews the general wear characteristics of gray irons, compacted graphite (CG) irons, and ductile irons. It discusses the typical compositions and properties of white and chilled iron castings. Gray cast iron is the dominant material for both brake drums and disk brake rotors. The article reviews brake lining chemistry effects, graphite morphology effects, and external abrasive effects on brake drums. It concludes with information on cast iron grinding balls.

Malleable iron is a type of cast iron that has most of its carbon in the form of irregularly shaped graphite nodules instead of flakes, as in gray iron, or small graphite spherulites, as in ductile iron. This article discusses the production of malleable iron based on the metallurgical criteria: to produce solidified white iron throughout the section thickness; and to produce the desired graphite distribution (nodule count) upon annealing. It describes the induction heating and quenching or flame heating and quenching for surface hardening of fully pearlitic malleable iron. Laser and electron beam techniques also have been used for hardening selected areas on the surface of pearlitic and ferritic malleable iron castings that are free from decarburization.

Foundry practices critical to the production of cast irons include melting, alloying, molten metal treatment, pouring, and the design of feeding systems (gating and risering) to allow proper filling of the casting mold. This article reviews these production stages of iron foundry casting, with particular emphasis on the melting practices, molten metal treatment, and feeding of molten metal into sand molds. It discusses the castability factors, such as fluidity, shrinkage, and resistance, of gray iron. Typical cupola charge compositions and the final analyses for class 30 and class 40 gray iron castings are presented in a table. The article describes the induction melting and arc furnace melting used in gray iron foundries. It also reviews the inoculation methods such as stream inoculation and mold inoculation, of gray iron.

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.

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 describes some examples of the different welding processes for gray, ductile, and malleable irons. These processes include fusion welding, repair welding, shielded metal arc welding, gas metal arc welding, flux cored arc welding, gas tungsten arc welding, submerged arc welding, oxyfuel welding, and braze welding. The article discusses various special techniques, such as groove-face grooving, studding, joint design modifications, and peening, for improving the strength of a weld or its fitness for service. The article describes other fusion welding methods such as electrical resistance welding and thermite welding. It reviews thermal spraying processes, such as flame spraying, arc spraying, and plasma spraying, of a cast iron.

This article describes the modification and inoculation of cast iron, and schematically illustrates the major effects of inoculation in gray cast irons. Inoculation could be considered as a common liquid-state treatment for all commercial cast irons (gray/compacted/ductile irons), while modification is essential to produce compacted graphite iron (intermediate level) and ductile iron. The article discusses the most important aspects of a gray cast iron inoculation treatment and the factors influencing its inoculation efficiency. It describes the modification and inoculation of ductile cast iron and compacted graphite cast iron.

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.

Thin-wall gray cast iron (TWGCI) can be seen as a potential material for the preparation of lightweight castings in automotive engineering applications. This article discusses the most important challenges for TWGCI: cooling rate, solidification, macrostructure, microstructure, and chilling tendency. It reviews the tensile properties and thermophysical properties of gray cast iron. The article describes the variables that influence molten iron preparation: charge materials, melting furnace thermal regime, chemical composition, modification and inoculation treatment, holding time/pouring procedure, mold properties (mold temperature, thermophysical properties of mold and mold coating), and casting design.

Gray cast iron is one of the most tolerant of metals when used with poorly designed filling systems. Good filling systems are necessary for the production of sound and acceptable ductile iron castings. This article presents an outline description of well-designed filling systems for all varieties of cast iron and all varieties of molds. It discusses the general conditions for the filling system layout, including the downsprue, sprue/runner junction, and runner. Both gray cast iron and compacted graphite iron exhibit a growth of graphite in direct contact with the liquid metal. The article concludes with a discussion on feeding of ductile iron.

This article presents typical wear applications for a variety of cast iron grades in a table. In general, wear is classified according to three major types: adhesive (frictional) wear (sliding and rolling) caused by contact of one metallic surface with another; abrasive wear caused by contact with metallic (shots, swarf) or nonmetallic abrasive materials; and erosive wear. The article discusses general wear characteristics of gray iron, compacted gray iron, and ductile iron. It provides information on the brake lining chemistry effects, graphite morphology effects, normal cast iron wear, local cast iron wear, and external abrasive effects on brake drums and disk brake rotors made of gray cast iron. The article concludes with a discussion on the application of cast iron for grinding balls.

A wide range of mechanical properties can be obtained with a given composition of cast iron, depending on the microstructural constituents that form during solidification and subsequent solid-state processing. This article discusses the mechanical properties of gray iron and provides some general property comparisons with malleable, ductile (nodular), and compacted graphite irons. The mechanical properties of gray iron are determined by the combined effects of its chemical composition, processing technique in the foundry, and cooling rates during solidification. The article provides information on the classification of gray irons based on ASTM International specification A48/A48M. It discusses the loading effect, surface effect, notch sensitivity, and environmental effect on the mechanical properties of gray iron. The chemical composition ranges of some of the more widely used heat-resistant gray irons suitable for elevated-temperature service are presented in a table.

Gray irons are commonly classified by their minimum tensile strength. This article describes properties used in the selection of gray irons and the factors that affect properties, particularly the effect of solidification. It discusses the three steps that its processing undergoes in the foundry: liquid metal preparation, solidification, and solid-state transformation. The article discusses the tensile properties of gray cast iron: tensile strength, yield strength, ductility, and modulus of elasticity. It describes hardness tests that are performed for determining the approximate strength characteristics and machinability of a gray iron casting. The article also presents typical mechanical properties of heat-resistant gray irons in a table. It concludes with information on the automotive application of alloy cast irons.

The metallographic specimen preparation process for microstructural investigations of cast iron specimens usually consists of five stages: sampling, cold or hot mounting, grinding, polishing, and etching with a suitable etchant to reveal the microstructure. This article describes the general preparation of metallographic specimens and the methods of macroscopic and microscopic examination. Usually, gray-scale (black-and-white) metallography is sufficient for microstructural analysis of cast irons. The article discusses the use of color metallography of gray irons and ductile irons. It also presents application examples of color metallography.

This article discusses the characterization of gray iron structures, following the sequence of structure formation, as it applies to unalloyed or low-alloyed gray iron. Austenite grains are the basic crystallographic entities of the metallic matrix in gray cast iron precipitated from the liquid melt. The article describes the macrostructure and dendrite morphology of primary austenite. Eutectoid transformation in the solid state causes the transformation of austenite to pearlite and/or ferrite, producing the as-cast structure. The article discusses the observations of the graphite and ferritic/pearlitic structure in as-cast gray iron.

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 International Committee of Foundry Technical Associations has identified seven basic categories of casting defects: metallic projections, cavities, discontinuities, defective surfaces, incomplete casting, incorrect dimension, and inclusions or structural anomalies. This article presents some of the common defects in each of the seven categories in a table. It discusses common defects determined during the examination of samples of ductile cast iron in Elkem's research facility in Norway. The article reviews common defects, such as shrinkage cavities, blowholes, hydrogen pinholes, nitrogen defects, and abnormal graphite morphology, found in gray iron. It concludes with a discussion on surface defects in compacted graphite iron.