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 processing of steel involves five distinct sets of texture development mechanisms, namely, austenite deformation, austenite recrystallization, gamma-to-alpha transformation, ferrite deformation, and static recrystallization during annealing after cold rolling. This article provides an introduction on crystallographic textures. It discusses the effects of austenite rolling and recrystallization on the texture and transformation behavior of recrystallized austenite and deformed austenite. The article illustrates the overall summary of the rolling and transformation behavior. It details cold-rolling textures, annealing textures, and recrystallization textures of steel samples. The article concludes with a summary of texture development during cold rolling and annealing.

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.

Austenitization refers to heating into the austenite phase field, during which the austenite structure is formed. This article highlights the purpose of austenitization, and reviews the mechanism and importance of thermodynamics and kinetics of austenite structure using an iron-carbon binary phase diagram. It also describes the effects of austenite grain size, and provides useful information on controlling the austenite grain size using the thermomechanical process.

Copper steels are precipitation-strengthened steels that are designed to have a unique combination of physical and mechanical properties. This article provides an overview of copper precipitate-strengthened steels and their applications, and discusses appropriate ASTM International standards. It describes the common phases and alloying elements present in copper precipitate-strengthened steels, and reviews the influences of alloying elements on processing, phase diagrams, microstructures, and mechanical properties. The article also discusses the thermomechanical process, solutionizing heat treatment, and isothermal aging in detail. It concludes with a review of the interrelationships between heat treatments, microstructures, and mechanical properties.

This article describes microstructures and microstructure-property relationships in steels. It emphasizes the correlation of microstructure and properties as a function of carbon content and processing in low-alloy steels. The article discusses the iron-carbon phase diagram and the phase transformations that change the structure and properties at varying levels of carbon content. Microstructures described include pearlite, bainite, proeutectoid ferrite and cementite, ferrite-pearlite, and martensite. The article depicts some of the primary processing steps that result in ferrite-pearlite microstructures. It shows the range of hardness levels which may be obtained by tempering at various temperatures as a function of the carbon content of the steel. To reduce the number of processing steps associated with producing quenched and tempered microstructures, new alloying approaches have been developed to produce high-strength microstructures directly during cooling after forging.

Thermomechanical processing (TMP) refers to various metal forming processes that involve careful control of thermal and deformation conditions to achieve products with required shape specifications and good properties. This article describes TMP methods in producing hot-rolled steel and reviews how improvements in the strength and toughness depend on the synergistic effect of microalloy additions and on carefully controlled thermomechanical conditions. It discusses TMP variables and the general distinctions between conventional hot rolling and common types of controlled-rolling schedules. The article describes the metallurgical processes in grain refinement of austenite steel by hot working, such as recovery and recrystallization and strain-induced transformation. The grain refinement in high strength low alloy steel by alloy addition is also discussed. The article provides an outline on the key stages of deformation, and the required metallurgical information at each of these stages.

Heat treating of stainless steel produces changes in physical condition, mechanical properties, and residual stress level and restores maximum corrosion resistance when that property has been adversely affected by previous fabrication or heating. This article focuses on annealing of different types of stainless steels such as austenitic, ferritic, duplex, martensitic, and precipitation-hardening, and on the heat treatment of superalloys and refractory metals. It discusses the recommended procedures for solution annealing, austenite conditioning, transformation cooling, and age tempering of precipitation-hardening stainless steels. The article also lists general recommendations for the annealing temperatures of tantalum, niobium, molybdenum, tungsten, and their alloys.

Magnetically soft materials are characterized by their low coercivity, an essential requirement for irons and steels selected for any application involving electromagnetic induction cycling. This article provides information on ferromagnetic material properties and how they are affected by impurities, alloying additions, heat treatment, residual stress, and grain size. It also describes classification and testing methods for magnetically soft materials such as high-purity iron, low-carbon steels, silicon steels, iron-aluminum alloys, nickel-iron alloys, iron-cobalt alloys, ferrites, and stainless steels. The article also addresses corrosion resistance and provides insights on the selection of alloys for power generation applications, including motors, generators, and transformers. A short note on the design and fabrication of magnetic cores is also included.

Surface hardening improves the wear resistance of steel parts. This article focuses exclusively on the methods that involve surface and subsurface modification without any intentional buildup or increase in part dimensions. These include diffusion methods, such as carburizing, nitriding, carbonitriding, and austenitic and ferritic nitrocarburizing, as well as selective-hardening methods, such as laser transformation hardening, electron beam hardening, ion implantation, selective carburizing, and surface hardening with arc lamps. The article also discusses the factors affecting the choice of these surface-hardening methods.

Solid-state transformations occurring in a weld are highly nonequilibrium in nature and differ distinctly from those experienced during casting, thermomechanical processing, and heat treatment. This article focuses on welding metallurgy of fusion welding of steels and highlights the fundamental principles that form the basis of many of the developments in steels and consumables for welding. Examples in the article are largely drawn from the well-known and relatively well-studied case of ferritic steel weldments to illustrate the special physical metallurgical considerations brought about by the weld thermal cycles and by the welding environment. The article provides information on welds in other alloy systems such as stainless steels and aluminum-base, nickel-base, and titanium-base alloys.

This article provides a detailed discussion on the effect of boron in heat-treated steel and thermomechanically-simulated steel. It describes the boron hardenability mechanism and the effect of composition and heat treatment parameters on boron hardenability. The article examines the hardening behavior of unalloyed boron steel and low-alloyed boron steel in heat treatment experiments by varying the austenitizing temperatures and cooling conditions. It also discusses the applications of boron steels.

This article aims to survey the factors controlling the weldability of carbon and low-alloy steels in arc welding. It discusses the influence of operational parameters, thermal cycles, and metallurgical factors on weld metal transformations and the susceptibility to hot and cold cracking. The article addresses the basic principles that affect the weldability of carbon and low-alloy steels. It outlines the characteristic features of welds and the metallurgical factors that affect weldability. It describes the common tests to determine steel weldability. There are various types of tests for determining the susceptibility of the weld joint to different types of cracking during fabrication, including restraint tests, externally loaded tests, underbead cracking tests, and lamellar tearing tests. Weldability tests are conducted to provide information on the service and performance of welds. The major tests that are discussed in this article are weld tension test, bend test, the drop-weight test, the Charpy V-notch test, the crack tip opening displacement test, and stress-corrosion cracking test.

This article provides general information on the definition, purposes, and quench equipment for direct-forge quenching (DFQ) and direct heat treatment (DHT) processes that are widely used in automotive and various other mechanical industries. It discusses the technological advances in these processes and their ability to produce high-quality components at low production cost from microalloyed steels. Further, the article describes the influence of carbon contents on toughness of microalloyed direct heat treated steels. It focuses on the DFQ and DHT steel technologies applied in continuous rolling mills to produce various DHT steels for machining and cold forming applications.

This article discusses the bulk formability or workability of steels. It describes their formability characteristics and presents procedures for various formability tests used for carbon and alloy steels. Tests for bulk formability can be divided into two main categories: primary tests and specialized tests. The article compares the processing of microalloyed plate and bar products. The article focuses on the use of torsion testing to evaluate the forgeability of carbon and alloy steels and presents information on measuring flow stress. The article discusses the metallurgy and thermomechanical processing of high-strength low-alloy (microalloyed) steels and the various parts of the rolling operation. The article summarizes some of the common tests for determining formability in open-die and closed-die forgings.

The heat treatment of steel is based on the physical metallurgical principles that relate to its processing, properties, and structure. The microstructures that result from the heat treatment of steel are composed of one or more phases in which the atoms of iron, carbon, and other elements in steel are associated. This article describes the phases of heat treated steel, and provides information on effect of temperature change and the size of carbon atoms relative to that of iron atoms during the heat treatment.

This article describes ironmaking and steelmaking practices (melt or liquid processing, including hot metal desulfurization) and discusses the evolution of these processes and their effects on steel properties. The physical chemistry of steelmaking may appear deceptively simple for integrated steel mill operations where ore from the ground is converted into steel. The various refining steps that occur in steelmaking are reviewed. The article also describes solid processing of steel, with emphasis on hot and cold rolling, thermomechanical processing, and annealing of flat steel products.

The properties of irons and steels are linked to the chemical composition, processing path, and resulting microstructure of the material. For a particular iron and steel composition, most properties depend on microstructure. Processing is a means to develop and control microstructure, for example, hot rolling, quenching, and so forth. This article describes the role of these factors in both theoretical and practical terms, with particular focus on the role of microstructure. It lists the mechanical properties of selected steels in various heat-treated or cold-worked conditions. In steels and cast irons, the microstructural constituents have the names ferrite, pearlite, bainite, martensite, cementite, and austenite. The article presents four examples that have very different microstructures: the structural steel has a ferrite plus pearlite microstructure; the rail steel has a fully pearlitic microstructure; the machine housing has a ferrite plus pearlite matrix with graphite flakes; and the jaw crusher microstructure contains martensite and cementite.

The properties of irons and steels are linked to the chemical composition, processing path, and resulting microstructure of the material. Processing is a means to develop and control microstructure by hot rolling, quenching, and so forth. This article describes the role of these factors in both theoretical and practical terms, with particular focus on the role of microstructure in various irons. These include bainite, pearlite, ferfite, martensite, austenite, ferrite-pearlite, ferrite-cementite, ferrite-martensite, graphite, and cementite. The article discusses the evolution of microstructural change in rail steels, cast iron, and steel sheet. It contains tables that list the mechanical properties and compositions of selected steels. The article also discusses the basis of material selection of irons and steels.

This article considers four types of high-strength structural steels: heat-treated low-alloy steels, as-rolled carbon-manganese steels, heat-treated (normalized or quenched and tempered) carbon steels, and as-rolled high-strength low-alloy (HSLA) steels (which are also known as microalloyed steels). The article places emphasis on HSLA steels, which are an attractive alternative in structural applications because of their competitive price per-yield strength ratios. HSLA steels are primarily hot-rolled into the usual wrought product forms and are furnished in the as-hot-rolled condition. In addition to hot-rolled products, HSLA steels are also furnished as cold-rolled sheet and forgings. This article describes the different categories of HSLA steels and provides a summary of characteristics and intended uses of HSLA steels described in the American Society for Testing and Materials (ASTM) specifications. The article also presents some applications of HSLA steels.