This chapter discusses the properties and compositions of steels used in pressure vessels, piping, boilers, rebar, and other structural applications. It covers fine-grained steels, quenched and tempered steels, and controlled rolled (thermomechanical treatment) steels. It also compares and contrasts steels used for concrete reinforcement and in various types of pressure vessels, and presents a metallographic study of the effects of welding on the micro and macrostructure of steel.

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 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.

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.