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.

Steel is an important material because of its tremendous flexibility in metal working and heat treating to produce a variety of mechanical, physical, and chemical properties. The purpose of this chapter is to present the metallurgical principles of heat treatment of steel in a generalized manner. The chapter provides a discussion on the constitution of commercially pure iron, subsequently leading to discussion on the iron-carbon alloy system. The chapter also describes the effect of carbon on the constitution of iron and of the solubility of carbon in iron. It provides information on transformations and on the classification of steels by carbon content. The chapter ends with a discussion on the effect of time on transformation and on the use of time-temperature-transformation diagrams.

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.

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.

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.

This chapter provides guidelines and insights on the selection of materials, coatings, and treatments for friction and wear applications. It begins with a review of the system nature of tribological effects, the subtleties of friction, and the selection idiosyncrasies of the material systems and lubricants covered in prior chapters. It then presents a systematic approach for selecting tribomaterials, using an automotive fan motor as an example.

Ductile iron has far superior mechanical properties compared to gray iron as well as significantly improved castability and attractive cost savings compared to cast steel. This chapter begins with information on graphite morphology and matrix type. It then discusses the advantages and applications of ductile iron. Next, the effects of various factors on the grades, chemistry, matrix, and mechanical properties of ductile iron are covered. This is followed by a section detailing the ductile iron treatment methods and the quality control methods used. Guidelines for gating and feeder design are then provided. Further, the chapter addresses the technology of ductile iron castings, including the performance and geometric attributes, molding and core-making processes used, material grades, mechanical properties, and chemical compositions of a few applications. Finally, it describes ductile iron casting defects and presents practical cases of problem-solving.

This chapter discusses the development of the nomenclature used to describe the constitution and structure of metals and alloys, particularly the phases observed in the microstructure of steel. It also points out some of the problems with current nomenclature and provides recommendations on how to avoid them.

Carbon and low-alloy steels in high-temperature service are vulnerable to the effects of hydrogen attack, which include severe loss in tensile and rupture strengths as well as ductility. As the chapter explains, when steel is in contact with hydrogen molecules at elevated temperatures, hydrogen atoms can be absorbed at the surface and then diffuse into the metal. Hydrogen atoms in the metal then react with iron carbide forming methane gas which can accumulate at grain boundaries and other interfaces. The chapter describes two applications, one in coal-fired boilers, the other in petroleum refining, where hydrogen attack was observed. It documents the extent of the damage in each case and identifies the source of the hydrogen.

Stainless steels derive their name from their exceptional corrosion resistance, which is attributed to their finely tuned compositions. This chapter discusses the alloying elements used in stainless steels and the some of the processing challenges they present. One of the biggest challenges is that stainless steels cannot be hardened by heat treatment. As a result, they are highly sensitive to processing-induced defects and the formation of detrimental phases. The chapter explains how alloy design, phase equilibria, microstructure, and thermomechanical processing can be concurrently optimized to produce high-quality austenitic, ferritic, and duplex stainless steels.

Unlike conventional quench and temper heat treatment, austempering is an iron and steel heat-treatment process that enhances mechanical properties through the isothermal transformation of austenite with a minimum amount of quenching stresses. This chapter begins with a discussion of austemperability requirements. Then outlines of austenitizing and austempering cycles and resultant microstructures are presented. This is followed by sections discussing the mechanical properties, advantages, limitations, machinability, process variants, and applications of austempered ductile iron (ADI). Information on the growth of premachined ADI components is also provided. Further, the chapter describes two slightly different systems for austempering: atmospheric-salt and salt-salt systems. Finally, it presents general guidelines for component designers, casting manufacturers, and heat treaters to apply ADI more widely and with improved success.

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.

Malleable iron has unique properties that justify its application in the metal working industry. This chapter discusses the advantages, limitations, and mechanical properties of malleable iron; provides a description of the malleabilization process; and presents manufacturing guidelines for malleable iron castings.

This chapter describes the phases and constituents present in iron-carbon steels in near-equilibrium conditions. It explains how to use phase diagrams to predict and manage the development of ferrite, austenite, cementite, and pearlite through controlled cooling. It discusses the transformations, grain structure, and properties associated with each phase and identifies the primary stabilizing elements. It includes several micrographs revealing various microstructural features and describes the processing route by which they were achieved. It explains how to estimate the volume fraction of iron-carbon phases in equilibrium and how to determine the amount of each phase that must be present to reach a desired composition. The chapter also discusses the phases associated with hypo- and hyper-eutectoid steels and presents more than a dozen micrographs, identifying important structural features along with cooling conditions and sample preparation procedures.

Tools steels are defined by their wear resistance, hardness, and durability which, in large part, is achieve by the presence of carbide-forming alloys such as chromium, molybdenum, tungsten, and vanadium. This chapter describes the alloying principles employed in various tool steels, including high-speed, water-hardening, shock-resistant, and hot and cold work tool steels. It discusses the influence of alloy design on the evolution of microstructure and properties during solidification, heat treating, and hardening operations. It also describes critical phase transformations and the effects of partitioning, precipitation, segregation, and retained austenite.

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 use of coating methods and materials and their impact on corrosion and wear behaviors. It provides detailed engineering information on a wide range of processes, including organic, ceramic, and hot dip coating, metal plating and cladding, and the use of weld overlays, thermal spraying, and various deposition technologies.

This chapter discusses the use of phase diagrams in alloy design, processing, and performance assessment. The examples cover both ferrous and nonferrous metals and a variety of goals and objectives. The chapter also identifies limitations and pitfalls associated with the use of phase diagrams.