This chapter covers a broad range of low-carbon steels optimized for structural applications. Low-carbon structural steels are generally considered the highest-strength steels that can be welded without undue difficulty, even in the field. They include mild steels, carbon-manganese and niobium- and vanadium-containing steels, and high-strength low-alloy steels. Chapter 5 discusses the composition, microstructure, and properties of these workhorse materials and explains how to identify the cause of production-related issues such as lamellar tearing and ferrite-pearlite banding. It also describes some of the alloying variations that have been developed to improve machinability and the mechanisms by which they work.

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.

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 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 discusses various alloying and processing approaches to increase the strength of low-carbon steels. It describes hot-rolled low-carbon steels, cold-rolled and annealed low-carbon steels, interstitial-free or ultra-low carbon steels, high-strength, low-alloy (HSLA) steels, dual-phase (DP) steels, transformation-induced plasticity (TRIP) steels, and martensitic low-carbon steels. It also discusses twinning-induced plasticity (TWIP) steels along with quenched and partitioned (Q&P) steels.

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.

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 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.

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.

Steels with martensitic and tempered martensitic microstructures, though sometimes perceived as brittle, exhibit plasticity and ductile fracture behavior under certain conditions. This chapter describes the alloying and tempering conditions that produce a ductile form of martensite in low-carbon steels. It also discusses the effect of tempering temperature on the mechanical behavior and deformation properties of medium-carbon steels.

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.

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 discusses the stress-strain response of ferritic microstructures and its influence on tensile deformation, strain hardening, and ductile fracture of carbon steels. It describes the ductile-to-brittle transition that occurs in bcc ferrite, the effects of aging and grain size on strength and toughness, continuous and discontinuous yielding behaviors, and dispersion and solid-solution strengthening processes.

This chapter examines the isothermal phase transformations of the iron-carbide system. The discussion includes the formation of ferritic, eutectoid, hypoeutectoid, hypereutectoid, bainitic, and martensitic microstructures as well as their properties, composition, and metallurgy. The use of time-temperature-transformation (TTT) diagrams in understanding the phase transformations and the changes in the isothermal transformation curves due to the addition of carbon and other alloying elements are also discussed.

The properties of steel are affected markedly as the percentage of carbon varies. This chapter describes the properties of alloys of iron and carbon, including a review of the iron-carbon phase diagram and, in particular, the portion of the diagram relevant to carbon steels. It addresses the processes involved in the transformation (decomposition) of austenite to achieve various 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.

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 ferrous metals, including low-carbon steels, stainless steels, and cast irons. It also provides information on hardening and hardenability and the tempering process.