This article reviews general trends in the cyclic response for representative commercial alloys to establish the spectrum of cyclic properties attainable through microstructural alteration. Individual alloy classes are examined in detail to assess the understanding of relationships between microstructure and fatigue resistance. These alloys classes include ferritic-pearlitic alloys, martensitic alloys, maraging steels, and metastable austenitic alloys. The article also discusses the role of internal defects and selective surface processing in influencing fatigue performance.

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 cast iron family includes several different groups, including gray iron, ductile iron, compacted graphite iron, malleable iron, white iron, and many different grades within each of these alloy groups. This article addresses issues specific to gray iron, but in many instances the discussion can be related to the other cast iron groups and the various grades within those groups. It discusses the usage of techniques and procedures in cast iron fractography. The article presents a list of common defects that can initiate failure.

The control of the solidification process of cast iron requires understanding and control of the thermodynamics of the liquid and solid phases and of the kinetics of their solidification, including nucleation and growth. This article addresses issues that allow for the determination of probability of formation and relative stability of various phases. These include the influence of temperature and composition on solubility of various elements in iron-base alloys; calculation of solubility lines, relevant to the construction of phase diagrams; and calculation of activity of various components. It discusses the role of alloying elements in terms of their influence on the activity of carbon, which provides information on the stability of the main carbon-rich phases of iron-carbon alloys, that is, graphite and cementite. The article reviews the carbon solubility in multicomponent systems, along with saturation degree and carbon equivalent.

Thermal analysis is used to analyze solidification processes by recording the temperature as a function of time during cooling or heating of a metal or alloy to or from a temperature above its melting point. This article describes the use of cooling curves for analyzing a solidification process, such as the solidification temperature, structure analysis, fraction of phases and heat of fusion with focus on solidification of cast iron, and the use of cooling curves to control and adjust the casting conditions. It discusses deviations from equilibrium that occur due to kinetic effects during solidification. The article also illustrates the evaluation of fraction of solid formed during the precipitation of austenite from heat balance.

Rapid solidification is a tool for modifying the microstructure of alloys that are obtained by ordinary casting. This article describes the fundamentals of the four microstructural changes, namely, microsegregation, identity of the primary phase, identity of the secondary phase, and the formation of noncrystalline phases. It considers three factors to understand the fundamentals of these changes: heat flow, thermodynamic constraints/conditions at the liquid-solid interfaces, and diffusional kinetics/microsegregation. These factors are described in detail.

Maraging steels are highly alloyed low-carbon iron-nickel martensite steels that possess an excellent combination of strength and toughness superior to that of most carbon-hardened steels. This article provides a detailed account of the formation of martensite in maraging steels. It discusses the heat treatment of these steels, namely, aging, solution annealing, age hardening, and nitriding. Their hardening during aging has been attributed to two different mechanisms: short-range ordering and precipitation. The article concludes with a discussion on the grain refinement using thermal cycling and transformation-induced plasticity maraging methods.

This article introduces basic physical metallurgy concepts that may be useful for understanding and interpreting variations in metallographic features and how processing affects microstructure. It presents some basic concepts in structure-property relationships. The article describes the use of equilibrium binary phase diagrams as a tool in the interpretation of microstructures. It reviews an account of the two types of solid-state phase transformations: isothermal and athermal. The article discusses isothermal transformation and continuous cooling transformation diagrams which are useful in determining the conditions for proper heat treatment (solid-state transformation) of metals and alloys. The influence of the mechanisms of phase nucleation and growth on the morphology, size, and distribution of grains and second phases is also described.

This article describes different methods by which the composition of cast iron can be analyzed. It provides particular emphasis on the methods for evaluating the graphitization potential of a melt with prescribed limits on carbon, silicon, and alloying elements. The article discusses the effect of cooling rate on the graphitization of a given composition by chill and wedge tests. Thermal analysis of cooling curves gives excellent information about the solidification and subsequent cooling of cast iron alloys. The article presents some applications of the cooling curve analysis and explains the evaluation of carbon-silicon contents, graphite shape, graphite nucleation, and contraction-expansion balance. It illustrates the use of an immersion steel sampling device for compacted graphite iron production and provides information on the ferrite-pearlite ratio in ductile iron.

The high-alloy irons can be categorized into two main groups: the high-alloy graphitic irons (covering both gray and ductile grades) and the high-alloy white irons. High-alloy irons are used in applications with demanding requirements, such as high resistance to wear, heat, and corrosion, or for combined properties. This article discusses the specification and selection of high-alloy irons. The common alloying elements and their effect on the stable and metastable eutectic temperatures are listed in a table. The article provides information on the compositions, properties and applications of high-alloy graphitic irons and high-alloy white irons.

Maraging steels comprise a special class of high-strength steels that differ from conventional steels in that they are hardened by a metallurgical reaction that does not involve carbon. Instead, these steels are strengthened by the precipitation of intermetallic compounds at temperatures of about 480 deg C. Commercial maraging steels are designed to provide specific levels of yield strength in the range of 1030 to 2420 MPa. However, some experimental maraging steels have yield strengths as high as 3450 MPa. These steels typically have very high nickel, cobalt, and molybdenum contents and very low carbon contents. This article outlines the processing of maraging steels: melting, hot working, cold working, machining, heat treating, surface treatment, and welding. It also covers mechanical and physical properties as well as tooling and aerospace applications, where maraging steels are extensively used.

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.

Cast irons primarily are iron alloys that contain more than 2% carbon and from 1 to 3% silicon. This article provides a description of iron-iron carbide-silicon system; and discusses the classification, composition, and characteristics of cast irons, such as gray, ductile, malleable, compacted graphite, and white cast iron. A table shows the correspondence between commercial and microstructural classification, as well as final processing stage in obtaining common cast irons.

Fracture mechanics is a multidisciplinary engineering topic that has foundations in both mechanics and materials science. This article summarizes the microstructural aspect of fracture resistance in structural materials. It provides a discussion on basic fracture principles and schematically illustrates the mechanism of crack propagation. The article describes the fracture resistance of high-strength steels, aluminum alloys, titanium alloys, and composites such as brittle matrix-ductile phase composites and metal-matrix composites. It also lists the effects of microstructural variables on fracture toughness of steels, aluminum alloys, and titanium alloys.

This article focuses on induction hardening process for heat treating operations specifically designed to result in proper microstructure/property combinations in either localized or in the final parts. It briefly reviews the heat treating basics for conventional heat treating operations of steels with iron-carbon phase and transformation diagrams. The article provides a summary of the important temperatures, definitions, and microstructural constituents associated with heat-treated steels. Basic transformation characteristics of heat-treated steels are reviewed. The article also discusses the various aspects of steel heat treatment by induction processing, and concludes with a description of steel alloys for induction processing.

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.

Alloy phase diagrams are useful for the development, fabrication, design and control of heat treatment procedures that will produce the required mechanical, physical, and chemical properties of new alloys. They are also useful in solving problems that arise in their performance in commercial applications, thus improving product predictability. This article describes different equilibrium phase diagrams (unary, binary, and ternary) and microstructures, description terms, and general principles of reading alloy phase diagrams. Further, the article discusses plotting schemes; areas in a phase diagram; and the position and shapes of the points, lines, surfaces, and intersections, which are controlled by thermodynamic principles and properties of all phases that comprise the system. It also illustrates the application of the stated principles with suitable phase diagrams.

This article reviews the factors influencing carburization to improve wear resistance of steel, such as operating temperature, cost, production volume, types of wear, and design criteria. It details the types of wear, namely abrasive wear and adhesive wear. The article discusses the characteristics of carburized steels that affect wear resistance, including hardness, microstructure, retained austenite, and carbides. It also describes the processing considerations for carburization of titanium.

Stainless steels are characterized as having relatively poor wear resistance and tribological properties, but they are often required for a particular application because of their corrosion resistance. This article describes the classification of stainless steels and wear. Stainless steels have been classified by microstructure and are categorized as austenitic, martensitic, ferritic, or duplex. The main categories of wear are related to abrasion, erosion, adhesive wear, and surface fatigue. The article presents a list that proposes the alloy family that could be the optimal selection for a particular wear mode. The corrosion modes include dry sliding, tribocorrosion, erosion, erosion-corrosion, cavitation, dry erosion, erosion-oxidation, galling and fretting.

This article focuses on the different parameters that influence the pitting corrosion of passive metals. The parameters are environment, metal composition, potential, temperature, surface condition, alloy composition, stochastic nature of the processes, and inhibitors. In addition, the article provides a detailed discussion on the various stages of pitting. These include passive film breakdown, metastable pitting, pit growth, and pit stifling or death.