Isothermal and continuous cooling transformation (CT) diagrams help users map out diffusion-controlled phase transformations of austenite to various mixtures of ferrite and cementite. This chapter discusses the application as well as limitations of these engineering tools in the context of heat treating eutectoid, hypoeutectoid, and proeutectoid steels. It also provides references to large collections of transformation diagrams and includes several diagrams that plot quenching and hardening transformations as a function of bar diameter.

This chapter provides a detailed discussion of salt bath nitrocarburizing. Process variations discussed include low-cyanide salt bath ferritic nitrocarburizing, salt bath nitrocarburizing plus post treatment, and the Kolene Nu-Tride process.

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.

Surface modification technologies improve the performance of tool steels. This chapter discusses the processes involved in oxide coatings, nitriding, ion implantation, chemical and physical vapor deposition processing, salt bath coating, laser and electron beam surface modification, and boride coatings that improve the performance of hot-work and high-speed tool steels.

Heat treatment is the most common way of altering the mechanical, physical, and even chemical properties of steels. This chapter describes the changes that occur in carbon and low-alloy steels during conventional heat treatments. It explains how austenite decomposition largely defines the final microstructure, and how the associated phase transformations are driven by nucleation and growth processes. It describes diffusionless and diffusive growth mechanisms and provides detailed information on the properties, structure, and behaviors of the transformation products produced, namely martensite and bainite. It also discusses the formation of austenite, the control and measurement of austenitic grain size, the characteristics of ferritic microstructures, and the methods used to classify ferrite morphology.