The design stresses for most pressure-containing structural application, which are based upon minimum mechanical properties designated in the specifications published by the American Society for Testing and Materials (ASTM). This chapter reviews metallurgical characteristics and their influence on the properties and performance of structural carbon and low alloy steels and contains a summary of the relevant features of the ASTM product specifications.

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 article discusses the effect of alloying on high-strength low-alloy (HSLA) steels. It explains where HSLA steels fit in the continuum of commercial steels and describes the six general categories into which they are divided. It provides composition data for standard types or grades of HSLA steel along with information on available mill forms, key characteristics, and intended uses. The article explains how small amounts of alloying elements, particularly vanadium, niobium, and titanium, control not only the properties of HSLA steels, but also their manufacturability.

This chapter describes the classification of steels and the various compositional categories of commercial steel products. It explains how different alloying elements affect the properties of carbon and low-alloys steels and discusses strength, toughness, and corrosion resistance and how to improve them.

This chapter describes the heat treatments called annealing and normalizing for steels and examines the structures formed and the reasons for these treatments. It also provides a description of the special heat treatments, namely, martempering and austempering. Information on intercritical heat treatment is also included.

Structural steels are used for components such as I-beams and automobile frames. This chapter focuses on processing these steels to attain a fine primary ferrite grain size to develop high strength. It first reviews the concepts and principles of recrystallization in plastically deformed metals. The chapter reviews the concepts of annealing of cold worked metals. It then looks at hot working and the grain size associated with it. Additionally, the chapter reviews the methods of strengthening in the steels that rely mainly on reduction in the primary ferrite grain size. It discusses basic methods used to develop a small austenite grain size, and hence a small primary ferrite grain size. Then, the chapter covers the processes involved in the precipitation hardening of the ferrite. Finally, it examines some commercial thermomechanical processes used on structural steels, namely hot deformation and controlled cooling.

Most steels that are hardened are subjected to a subcritical heat treatment referred to as tempering. Tempering improves the toughness of as-quenched martensitic microstructures but lowers strength and hardness. This chapter describes the microstructural changes that occur during tempering and their effect on the mechanical properties of steel. It also discusses the effect of alloying elements and the formation of oxide colors.

Metallurgy, as discussed in this chapter, focuses on phases normally encountered in stainless steels and their characteristics. This chapter describes the thermodynamics and the three basic phases of stainless steels: ferrite, austenite, and martensite. Formation of the principal intermetallic phases is also covered. In addition, the chapter provides information on carbides, nitrides, precipitation hardening, and inclusions.

This chapter discusses the engineering significance of steel and briefly describes its chemical composition, crystal structure, Fe-C phases, and associated characterization techniques.

Advanced high-strength steels (AHSS) are best used for strong structural applications where lightweighting enhances the performance of a product. This chapter focuses on the applications of AHSS in the automotive industry. It explains the effect of automotive processing on AHSS components. The chapter also presents the nonautomotive applications of AHSS. It also provides the uses and trends of AHSS.

This chapter discusses the compositions, metallurgical phases, microstructure, heat treatment, grades, and structure-property relationships of steels. In addition, it describes the mechanisms involved in deformation, strengthening, and annealing of steels.

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 presents a discussion on the importance, types, applications, and advantages of advanced high-strength steel. It also provides a discussion on steelmaking technology.

When a metal is alloyed with another metal, either substitutional or interstitial solid solutions are usually formed. This chapter discusses the general characteristics of these solutions and the effects of several alloying elements on the yield strength of pure metals. It presents four rules that give a qualitative estimate of the ability of two metals to form substitutional solid solutions: relative size factor, chemical affinity factor, relative valency factor, and lattice type factor. The chapter provides information on alloys that form an ordered structure during heating. It describes the intermediate phases that are formed during solidification between the two extremes of substitutional solid solution on the one hand and intermetallic compound on the other. The chapter concludes with a section on strain aging in low-carbon steels that allows the interstitial atoms to diffuse to the dislocations and again form atmospheres that pin dislocation movement.

The formation of martensite is characterized by its athermal transformation kinetics, crystallographic features, and development of fine structure. This chapter describes the diffusionless, shear-type transformation of austenite to martensite and how it affects the morphology and microstructure of heat-treatable carbon steels. It also provides information on lath and plate martensite and how they differ in structure and deformation properties.

This chapter describes the various phases that form in tool steels, starting from the base of the Fe-C system to the effects of the major alloying elements. The emphasis is on the phases themselves: their chemical compositions, crystal structures, and properties. The chapter also provides general considerations of phases and phase diagrams and the determination of equilibrium phase diagrams. It describes the formation of martensite, characteristics of alloy carbides, and the design of tool steels.

All materials are susceptible to corrosion or some form of environmental degradation. Although no single material is suitable for all applications, usually there are a variety of materials that will perform satisfactorily in a given environment. The intent of this chapter is to review the corrosion behavior of the major classes of metals and alloys as well as some nonmetallic materials, describe typical corrosion applications, and present some unique weaknesses of various types of materials. It also aims to point out some unique material characteristics that may be important in material selection, and discuss, where appropriate, the characteristic forms of corrosion that attack specific materials. The materials addressed in this chapter include carbon steels, weathering steels, and alloy steels; nickel, copper, aluminum, titanium, lead, magnesium, tin, zirconium, tantalum, niobium, and cobalt and their alloys; polymers; and other nonmetallic materials, including rubber, carbon and graphite, and woods.

The existence of austenite and ferrite, along with carbon alloying, is fundamental in the heat treatment of steel. In view of the importance of structure and its formation to heat treatment, this chapter describes the various microstructures that form in steels, the various factors that determine the formation of microstructures during heat treatment processing of steel, and some of the characteristic properties of each of the microstructures. The discussion also covers the constitution of iron during heat treatment and the phases of heat-treated steel with elaborated information on iron phase transformation, hysteresis in heating and cooling, ferrite and austenite as two crystal structures of solid iron, and the diffusion coefficient of carbon.