Alloy steels are alloys of iron with the addition of carbon and one or more of the following elements: manganese, chromium, nickel, molybdenum, niobium, titanium, tungsten, cobalt, copper, vanadium, silicon, aluminum, and boron. Alloy steels exhibit superior mechanical properties compared to plain carbonsteels as a result of alloying additions. This chapter describes the beneficial effects of these alloying elements in steels. It discusses the mechanical properties, nominal compositions, advantages, and engineering applications of various classes of alloy steels. They are low-alloy structural steels, SAE/AISI alloy steels, high-fracture-toughness steels, maraging steels, austenitic manganese steels, high-strength low-alloy steels, dual-phase steels, and transformation-induced plasticity steels.

This chapter discusses the fundamentals of heat treating of alloy steels. It begins with an overview of the designations of AISI-SAE grades of alloy steels, followed by a description of the purposes served by alloying elements. The effects of specific alloying elements on the heat treatment of alloy steels and of boron on hardenability of alloy steels are then discussed. Procedures for heat treating four specific alloy steels (4037, 4037H; 4140, 4140H; 4340, 4340; and E52100) are subsequently presented. The chapter concludes with a brief account of austempering and martempering treatments.

This chapter introduces the metallographer to the various types of steels and cast irons and explains how they are classified and defined. Classification and designation details are provided for plain carbon steels, alloy steels, and gray, white, ductile, and malleable cast irons.

This chapter presents the Unified Numbering System (UNS) for metals and alloys.

This chapter presents the early classes of stainless steel. These include martensitic alloys, austenitic alloys, and ferritic alloys. It also presents stainless steel trade names. The chapter describes standardized designation for type 304 stainless steel by various specification organizations.

Microstructures can be altered intentionally or unintentionally. In some cases, metallographers must diagnose what may have happened to the steel or cast iron based on the microstructural details. This chapter discusses how microstructure in steels and cast irons can be intentionally altered during heat treatment, solidification, and deformation (hot and cold working). Some specific examples are then shown to illustrate what can go wrong through unintentional changes in microstructure, for example, the loss of carbon from the surface of the steel by the process known as decarburization or the buildup of brittle carbides on the grain boundaries of an austenitic stainless steel by the process known as sensitization.

This chapter introduces the basic ferrous physical metallurgy principles that need to be understood by the metallographer. The discussion focuses on the variations in microstructures that are generated as a result of the phase transformations that occur during both heat treatment (as in steels) and solidification (as in cast irons). The chapter describes how the development of the iron-carbon phase diagram, coupled with the understanding of the kinetics of phase transformations through the use of isothermal transformation diagram, were breakthroughs in the advancement of ferrous physical metallurgy. Several examples of the morphological features of microstructural constituents in steels are also presented.

This chapter discusses the important aspects that a metallographer should understand in order to effectively reveal a microstructure. It begins by exploring etching response and how it can be a tool for revealing various microstructural features. The next part of the chapter discusses methods for revealing microstructure in the as-polished (unetched) specimen, then guidelines for selecting and using etchants when needed. The chapter discusses different types of etchants in terms of their ingredients, etching procedure, and major uses. The etchants discussed include basic etchants (nital and picral and their variations) and tint etchants for carbon and low-alloy steels and cast irons, and basic etchants for stainless steels. Finally, information is provided on different illumination methods (differential interference contrast and dark-field illumination) that can be used to highlight certain features in microstructures.

This chapter provides perspective on the physical dimensions associated with the microstructure of steel and the instruments that reveal grain size, morphology, phase distributions, crystal defects, and chemical composition, from which properties and behaviors derive. The chapter also reviews the definitions and classifications used to identify and differentiate commercial steels, including the AISI/SAE and UNS designation systems.

This chapter describes the designations of carbon and low-alloy steels and their general characteristics in terms of their response to hardening and mechanical properties. The steels covered are low-carbon steels, higher manganese carbon steels, boron-treated carbon steels, H-steels, free-machining carbon steels, low-alloy manganese steels, low-alloy molybdenum steels, low-alloy chromium-molybdenum steels, low-alloy nickel-chromium-molybdenum steels, low-alloy nickel-molybdenum steels, low-alloy chromium steels, and low-alloy silicon-manganese steels. The chapter provides information on residual elements, microalloying, grain refinement, mechanical properties, and grain size of these steels. In addition, the effects of free-machining additives are also discussed.

This chapter explains the definition of carbon steels and lists the Unified Numbering System designations and the compositions that are universally accepted by steel producers and fabricators. Compositions of higher hardenability carbon steels (higher manganese grades and/or boron treated steels) are also discussed, as well as those of free-machining carbon steels. Detailed heat treating procedures are presented for a representative group of carbon steels. The processes involved in tempering and austempering of carbon steels are also discussed.

This chapter first lists the compositions of typical steels that are suitable for nitriding. It then presents considerations for steel selection. The chapter also shows the influence of alloying elements on hardness after nitriding and the depth of nitriding. It provides a detailed discussion on plasma nitriding of type 422 stainless steel, nitriding of type 440A and type 630 (17-4 PH) stainless steel. The chapter also discusses plasma nitride case depths.

This chapter addresses some of the challenges involved in materials selection, providing context for much of the information presented in the book. It describes a typical four-step design scenario, noting material-related considerations and information needs. It explains how design decisions are complicated by the interconnected nature of material properties, design geometry, and manufacturing requirements and effects. The chapter also assesses the design impact of several materials and discusses codes, standards, and specifications.

This chapter discusses the important role of metallography and the metallographer in predicting and understanding the properties of metals and alloys. Examples are presented of a metallographer working as part of a team in a research laboratory of a large steel company and a metallographer working alone at a small iron foundry. The three basic areas in all metallography laboratories are discussed: the specimen preparation area, the polishing/etching area, and the observation/micrography area. Important safety issues in a metallographic laboratory are also considered.

The properties of martensite and the mechanisms that govern its formation are the key to understanding hardness and the hardenability of carbon steel. Martensite is a transformation product of austenite that requires rapid cooling to suppress diffusion-dependent transformation pathways. This chapter describes the conditions that must be met for martensite to form. It discusses the role of quenching and the factors that affect cooling rate, including heat transfer, thermal diffusivity, emissivity, and section size. It defines hardenability and explains how to quantify it using the Grossmann-Bain approach or Jominy end-quench testing. It also explains how hardenability can be improved through the addition of boron, phosphorus, and other alloys.

This chapter familiarizes readers with the methods used to quantify the effects of fatigue on component lifetime and failure. It discusses the development and use of S-N (stress amplitude vs. cycles to failure) curves, the emergence of strain-based approaches to fatigue analysis, and important refinements and modifications. It demonstrates the use of approximate equations, including the method of universal slopes and the four-point correlation technique, which provides reasonable estimates of elastic and plastic lines from information obtained in standard tensile tests. It also discusses high-cycle, low-cycle, and ultra-high cycle fatigue and presents several models that are useful for fatigue life predictions.

This article discusses the role of alloying in the production and use of carbon and low-alloy steels. It explains how steels are defined and selected based on alloy content and provides composition and property data for a wide range of designations and grades. It describes the effect of alloying on structure and composition and explains how alloy content can be controlled to optimize properties and behaviors such as ductility, strength, toughness, fatigue and fracture resistance, and resistance to corrosion, wear, and high-temperature creep. It also examines the effect of alloying on processing characteristics such as hardenability, formability, weldability, machinability, and temper embrittlement. In addition, the article provides an extensive amount of engineering data with relevance in materials selection.

This chapter provides a practical understanding of heat treatments and how to employ them to optimize the properties and structures of cast irons and steels. It discusses annealing, normalizing, quenching, tempering, patenting, carburizing, nitriding, carbonitriding, and nitrocarburizing. It describes the primary objectives of each treatment along with processing sequences, process parameters, and related phase transformations. The chapter contains more than 100 images, including time-temperature diagrams, transformation curves, data plots, and detailed micro- and macrographs. It also discusses the concepts of hardenability, critical diameter, quench severity, and Jominy testing.

Several specialized instruments are available for the metallographer to use as tools to gather key information on the characteristics of the microstructure being analyzed. These include microscopes that use electrons as a source of illumination instead of light and x-ray diffraction equipment. This chapter describes how these instruments can be used to gather important information about a microstructure. The instruments covered include image analyzers, transmission electron microscopes, scanning electron microscopes, electron probe microanalyzers, scanning transmission electron microscopes, x-ray diffractometers, microhardness testers, and hot microhardness testers. A list of other instruments that are usually located in a research laboratory or specialized testing laboratory is also provided.

Heat treatment of steel involves a number of processes to condition the microstructure and obtain desired properties. This includes various methods namely, annealing, normalizing, and hardening by quenching and tempering. This chapter focuses on general heat treatment procedures and the applications of particular types or grades of carbon and low-alloy steels. The discussion covers carbon steel classification for heat treating, tempering of quenched carbon steels, and austempering of steel. In addition, the chapter discusses the effects of alloying and hardenability on steel and provides information on martempering of steel.