This chapter discusses various processes involved in the production of steel from raw materials to finished mill products. The processes include hot rolling, cold rolling, forging, extruding, or drawing. The chapter provides a detailed description of two main furnaces used for making steel: the electric arc furnace and the basic oxygen furnace. It also provides information on the classification and specifications for various steels, namely, plain carbon steels, low-carbon steels, medium-carbon plain carbon steels, and high-carbon plain carbon steels. The chapter concludes with a general overview of the factors influencing corrosion in iron and steel and a brief discussion of corrosion-resistant coatings.

This chapter first examines the tempering behavior of plain carbon steels and then that of alloy steels. Next, some correlations are examined which allow estimations of the tempered hardness from the chemical compositions, tempering temperature and tempering time. The chapter then describes the effect of tempering on the mechanical properties of plain carbon steels and the microstructure of plain carbon steels. It shows examples of the structure of plain carbon steels. Additionally, the chapter explains the stages and kinetics of tempering in alloy steels and plain carbon steels. It also describes some methods of estimating the hardness. Finally, the chapter discusses the important problem of temper embrittlement.

Steel is broadly classified as plain-carbon steels, low-alloy steels, and high-alloy steels. This chapter begins by describing microconstituents of low- and medium-carbon steel, including bainite and martensite. This is followed by a section discussing the effect of alloying elements on steel. Then, it provides an overview of steel casting applications. Next, the chapter reviews engineering guidelines for steel castings and feeder design. The following section provides information on feeding aids. Further, the chapter describes the elements of gating systems for steel castings. It also describes the alloys, properties, applications, and engineering details of steel. Finally, the chapter explains defects in steel castings and presents guidelines for problem solving with examples.

The water-hardening steels are either essentially plain carbon steels or very low-alloy carbon steels. As a result, the water-hardening tool steels are the least expensive of tool steels and require strict control of processing and heat treatment to achieve good properties and performance. This chapter provides an overview of general processing and performance considerations of water-hardening tool steels. It describes the microstructural characteristics and hardenability of water-hardening tool steels. The chapter discusses the processes involved in the hardening and tempering of water-hardening tool steels.

Most quenched steels are tempered because the toughness of as-quenched steels is generally very poor. The tempering operation sacrifices strength for improvements in ductility and toughness. This chapter discusses the tempering process, the challenge of tempered martensite embrittlement, and the effect of wt% carbon on toughness. It also explains how alloying elements improve the hardenability and tempering response of plain carbon steels.

This appendix includes two annotated iron-carbon (Fe-C) phase diagrams. One is a poster-size diagram showing iron-carbon phases up to 7 wt% C along with representative microstructures. The other diagram is close-up view showing the phases that occur from 0 to 1.2 wt% C. It also includes labels identifying the microconstituents that form in plain carbon steels under rapid quenching conditions.

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.

The first step in the hardening of steel is getting it hot enough to form austenite, from which martensite can form upon quenching. Not all steels have the same austenitization requirements, however. High-carbon wear-resistant steels, such as bearing and tool steels, require the presence of carbides during austenitization; plain carbon and low-alloy steels do not. This chapter describes the austenitization process used in each of the two cases, namely single-phase austenitization (the accepted method for plain carbon low-alloy steels) and two-phase austenitization (required for high-carbon steels). It also addresses process-specific issues, explaining how the presence of carbides (in the two-phase process) produces significant changes, and how homogenization and austenite grain growth influence the single-phase process.

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 appendix is a compilation of terms and definitions related to the heat treatment of plain carbon and low-alloy steels.

Formation of the nitrided case begins through a series of nucleated growth areas on the steel surface. These nucleating growth areas will eventually become what is known as the compound layer or, more commonly, the white layer. This chapter discusses the influence of carbon on the compound zone. It explains how to control and calculate compound zone thickness. Compound zone thickness can be controlled by dilution, the two-stage Floe process, or by ion nitriding. The chapter describes the factors affecting surface case formation.

Steels contain a wide range of elements, including alloys as well as residual processing impurities. This chapter describes the chemical composition of low-alloy AISI steels, which are classified based on the amounts of chromium, molybdenum, and nickel they contain. It explains why manganese is sometimes added to steel and how unintended consequences, such as the development of sulfide stringers, can offset the benefits. It also examines the effect of alloying elements on the iron-carbon phase diagram, particularly their effect on transformation temperatures.

This chapter describes the two types of Time-Temperature-Transformation (TTT) diagrams used and outlines the methods of determining them. As a precursor to the examination of the decomposition of austenite, it first reviews the phases and microconstituents found in steels. This includes a presentation of the iron-carbon phase diagram and the equilibrium phases. The chapter also covers the common microconstituents that form in steels, including the nomenclature used to describe them. The chapter provides a comparison of isothermal and continuous cooling TTT diagrams. These diagrams are affected by the carbon and alloy content and by the prior austenite grain size, and the way in which these factors affect them is examined.

Martensitic stainless steels are essentially iron-chromium-carbon alloys that possess a body-centered tetragonal crystal structure (martensitic) in the hardened condition. Martensitic stainless steels are similar to plain carbon or low-alloy steels that are austenitized, hardened by quenching, and then tempered for increased ductility and toughness. This chapter provides a basic understanding of grade designations, properties, corrosion resistance, and general welding considerations of martensitic stainless steels. It also discusses the causes for hydrogen-induced cracking in martensitic stainless steels and describes sulfide stress corrosion resistance of type 410 weldments.

This chapter describes the metallurgy, composition, and properties of steels and other alloys. It provides information on the atomic structure of metals, the nature of alloy phases, and the mechanisms involved in phase transformations, including time-temperature effects and the role of diffusion, nucleation, and growth. It also discusses alloying, heat treating, and defect formation and briefly covers condenser tube materials.

This chapter addresses the concept of hardenability by first describing the basic hardening process for steel, starting with austenitization followed by quenching and tempering. The context also serves to clarify the difference between hardenability and hardness, which are often confused. Most of the information in the chapter is of a practical nature, covering application-oriented topics such as isothermal transformation (IT) and continuous transformation (CT) diagrams which are used to predict and control the rate of formation of ferrite, pearlite, and bainite. The chapter also discusses the effect of grain size and alloying elements and explains how Jominy end quench testing is used to evaluate the hardenability of steel.

Steel is made by adding carbon to iron, producing a solid solution defined by its crystalline structure. This chapter discusses the effect of carbon composition and temperature on the types of structures, or phases, that form. Using detailed phase diagrams, it explains how low-carbon (hypoeutectoid) and high-carbon (hypereutectoid) steels are made, how they are classified, and how they compare. It also describes eutectoid steels which, at 0.77 wt% C, form a separate class noted for its microstructure.

This chapter discusses the processes involved in the heat treatment of steel, namely austenitizing, hardening, quenching, and tempering. It begins with an overview of austenitizing of steels by induction heating, followed by a discussion on the processes involved in transformation of the soft austenite into martensite or lower bainite in the hardening operation. The chapter provides information on various quenching systems and a description of quenching techniques, namely austempering, martempering, and patenting. Difficulties associated with hardening of steel are discussed. Further, the chapter describes the equipment used for and principal variables of tempering. It discusses the causes for various forms of embrittlement due to tempering. Information on multiple tempering, protective-atmosphere tempering, and selective tempering are also provided, along with processes involved in selection of tempering temperature. The chapter ends with a section discussing various effects, advantages, and disadvantages of precipitation hardening.

Modern gears are made from a wide variety of materials. Of all these, steel has the outstanding characteristics of high strength per unit volume and low cost per pound. Although both plain carbon and alloy steels with equal hardness exhibit equal tensile strengths, alloy steels are preferred because of higher hardenability and the desired microstructures of the hardened case and core needed for the high fatigue strength of gears. This chapter provides an overview of the key considerations involved in the selection and application of heat treating processes for alloy steel gears and serves as an introduction to the subsequent chapters in this book.