This chapter describes heat treatments that produce uniform grain structures, reduce residual stresses, and improve ductility and machinability. It also discusses spheroidizing treatments that improve strength and toughness by promoting dispersions of spherical carbides in a ferrite matrix. The chapter concludes with a brief discussion on the mechanical properties of ferrite/pearlite microstructures in medium-carbon steels.

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.

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 examines the microstructure of special bar quality (or engineering) steels and how it is influenced by carbon content, tempering temperature, and prior austenitic grain size. It explains how some of the changes are difficult to detect and require special etching and/or measurement techniques. It provides information on many types of engineering steel, including medium and high-carbon steels used in rail applications. It also examines the effect of nickel-phosphorus coatings on stainless steel and phosphate coatings used to reduce friction during thread rolling and other such procedures.

This chapter covers the friction and wear behaviors of carbon, alloy, and tool steels. It begins a review of commercially available shapes and forms. It then describes the metallurgy and microstructure of various designations and grades of each type of steel and explains how it affects their performance in adhesive and abrasive wear applications and in environments where they are subjected to solid particle, droplet, slurry, and cavitation erosion and fretting damage.

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.

This chapter discusses the basic principles of friction and the factors that must be considered when determining its effect on moving bodies in contact. It provides an extensive amount of friction data, including static and kinetic friction coefficients for numerous combinations of engineering materials and coatings. It also describes the causes and effects of the most common forms of wear, the conditions under which they occur, the role of lubrication, and wear testing methods.

This appendix is a collection of isothermal diagrams for carbon steels, chromium-molybdenum steels, nickel-chromium-molybdenum steels, nickel-molybdenum steels, and chromium steels.

This chapter describes the causes of cracking, embrittlement, and low toughness in carbon and low-alloy steels and their differentiating fracture surface characteristics. It discusses the interrelated effects of composition, processing, and microstructure and contributing factors such as hot shortness associated with copper and overheating and burning as occur during forging. It addresses various types of embrittlement, including quench embrittlement, tempered-martensite embrittlement, liquid-metal-induced embrittlement, and hydrogen embrittlement, and concludes with a discussion on high-temperature hydrogen attack and its effect on strength and ductility.

This chapter covers the friction and wear behaviors of plastics and elastomers. It begins by describing the molecular differences between the two types of polymers and their typical uses. It then discusses the important attributes of engineering plastics and their suitability for applications involving friction, erosion, and adhesive and abrasive wear. It also discusses the tribology of elastomers and rubber along with their basic differences and the conditions under which they produce Schallamach waves. It includes information on polymer composites as well.

The microstructure of carbon steel is largely determined by the transformation of austenite to ferrite, cementite, and pearlite. This chapter focuses on the microstructures produced by diffusion-controlled transformations that occur at relatively low cooling rates. It describes the conditions that promote such transformations and, in turn, how they affect the structure of various phases and the rate at which they form. The chapter also discusses the concepts of transformation kinetics, minimum free energy, and nucleation and growth, and provides information on alloying, interphase precipitation, and various types of transformations.

This chapter describes cast steel features that may be identified or attributed to component failure during heat treatment or subsequent processing or service, namely porosity (generated by the presence of gas as well as by shrinkage pores), decarburization, cold joint, and inclusions.

This chapter explains how decarburization can occur during carburizing processes and how to limit the severity of its effects. It describes the reactions and conditions that result in a loss of carbon atoms and how they vary with changes in the physical metallurgy of the affected material and the processing environment. It examines the characteristic features of decarburized microstructures and assesses their influence on hardness, residual stresses, and fatigue and fracture behaviors. It also discusses corrective measures and practical considerations regarding their use.

Many companies conduct only metallurgical evaluations in the wake of failures, discovering nothing more than the physical mechanism by which the failure occurred. The origin of failures, however, is often complex, involving not only physical mechanisms, but also human behavior and latent factors. Failures may also involve multiple parts, entire machines, or processes of any size and shape. The chapter examines the unique aspects of many failures and explains how they can sometimes be traced to systemic issues. It also covers the reasons why products fail, including improper service or operation, improper maintenance, improper testing, assembly errors, fabrication or manufacturing errors, and design errors. The case of the Tacoma Narrows Bridge collapse is presented to illustrate the consequence of overlooked factors, in this case, wind dynamics, and the importance of identifying root causes to prevent repeat failures.

This chapter covers the friction and wear behaviors of cast irons. It describes the microstructure and metallurgy of gray, white, malleable, and ductile cast irons, their respective tensile properties, and their suitability for applications involving friction, various types of erosion, and adhesive and abrasive wear.

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.

Quenching is a critical step in the production of hardened steel. This chapter untangles some of the complexities of the quenching process and its effect on the microstructure and properties of various steels. Making extensive use of cooling curves, it sheds light on the transformations that occur at different cooling rates and the extent to which they can be changed by adjusting quench parameters. It discusses the role of quenching in martempering and austempering along with related problems such as cracking and distortion and the challenges posed by low-hardenability steels. It also discusses the use of various quenchants, including oil, polymer, and molten salt, and explains how to measure and compare their performance using a standard (ISO 9950) test.

Austenite is the key to the versatility of steel and the controllable nature of its properties. It is the parent phase of pearlite, martensite, bainite, and ferrite. This chapter discusses the importance of austenite, beginning with the influence of austenitic grain size and how to accurately measure it. It then describes the principles of austenite formation and grain growth and examines several time-temperature-austenitizing diagrams representing various alloying and processing conditions. The chapter concludes with a discussion on hot deformation and subsequent recrystallization.

This chapter discusses surface engineering treatments, including flame hardening, induction hardening, high-energy beam hardening, laser melting, and shot peening. It describes the basic implementation of each method, the materials for which they are suited, and their effect on surface metallurgy.

A pair of bearings mounted side by side in an aircraft engine failed in service. Photographs show that the inner rings were either broken or deformed, the balls were worn and flattened, and the cages severely damaged. The bearing races were damaged as well, but only on one side indicating a directional thrust. In addition to their examination, investigators also conducted metallographic studies and hardness tests, which indicated that the balls and inner rings reached temperatures above 825 °C (1520 °F). Based on their findings, investigators concluded that the bearings failed due to overheating, possibly as a result of misalignment compounded by insufficient lubrication and high speeds.