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This chapter introduces the principal heat treating processes, namely normalizing, annealing, stress relieving, surface hardening, quenching, and tempering. An overview of four of the more popular surface hardening treatments, namely carburizing, carbonitriding, nitriding, and nitrocarburizing, is provided.

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, a detailed account of furnaces and related equipment for heat treating, begins by describing three basic modes of heat transmission, namely conduction, convection, and radiation, followed by a discussion on the working principle, applications, advantages, and disadvantages of furnaces classified based on the heat transfer medium employed. The types of furnaces covered are batch-type, continuous-type, liquid bath, fluidized bed, and vacuum. The subsequent sections provide information on furnace parts, fixtures, quenching mediums, and quenching systems. The final section of the chapter describes the types of atmospheres available, emphasizing their applications and limitations.

The temperature and atmosphere conditions must be precisely controlled in order to achieve the desired metallurgical results during heat treating operations. In order to ensure the repeatability of operation, a heat treating system must have the necessary sensors, timers, and variable (temperature, atmosphere, etc.) controllers to hold the process within prescribed or specified limits. This chapter discusses temperature and atmosphere sensors used in a heat treating system. The temperature sensors covered are contact and noncontact types. The atmosphere sensors covered are oxygen probe, dew point, and infrared. The chapter concludes with an overview of the development of integrated control systems.

This chapter explains the definition of carbon steels and lists the Unified Numbering System designations and the compositions that are universally accepted by steel producers and fabricators. Compositions of higher hardenability carbon steels (higher manganese grades and/or boron treated steels) are also discussed, as well as those of free-machining carbon steels. Detailed heat treating procedures are presented for a representative group of carbon steels. The processes involved in tempering and austempering of carbon steels are also discussed.

This chapter discusses the fundamentals of heat treating of alloy steels. It begins with an overview of the designations of AISI-SAE grades of alloy steels, followed by a description of the purposes served by alloying elements. The effects of specific alloying elements on the heat treatment of alloy steels and of boron on hardenability of alloy steels are then discussed. Procedures for heat treating four specific alloy steels (4037, 4037H; 4140, 4140H; 4340, 4340; and E52100) are subsequently presented. The chapter concludes with a brief account of austempering and martempering treatments.

This chapter discusses the processes involved in heat treating of stainless steels, providing information on the classification, chemical compositions, and corrosion resistance of stainless steels and the effect of specific elements on the characteristics of iron-base alloys. Five groups of stainless steels are discussed: austenitic, ferritic, martensitic, precipitation-hardening, and duplex grades. The chapter also describes the heat treatment conditions that should be maintained for processing of stainless steels.

Tool steels represent a small, but very important, segment of the total production of steel. Their principal use is for tools and dies that are used in the manufacture of commodities. For the most part, the processes used for heat treating carbon and alloy steels are also used for heat treating tool steels, that is, annealing, austenitizing, tempering, and so forth. This chapter focuses on these heat treating processes of tool steels. Classification and approximate compositions and heating treating practices of some principal types of tool steels are provided. The steel types discussed include water-hardening; shock-resisting; oil-hardening cold-work; air-hardening, medium-alloy cold-work; high-carbon, high-chromium cold-work; low-alloy, special-purpose; mold; hot-work; and high-speed tool steels.

This chapter is a detailed account of heat treating techniques for cast irons (gray and ductile), providing the reader with a basic understanding of the differences among various types of cast irons and the concept of carbon equivalent. The types of heat treatments discussed are stress relieving, annealing, normalizing, surface hardening, quenching, martempering, austempering, and flame and induction hardening.

This chapter presents an overview of heat treating of nonferrous alloys. First, a brief discussion on the effects of cold work and annealing on nonferrous alloys is presented. This is followed by a discussion on the mechanisms involved in the more commonly used heat treating procedures for hardening or strengthening, namely solution treating and aging. Examples are presented for heat treating of two commercially important nonferrous alloys, one from the aluminum-copper system and one from the copper-beryllium system.

A successful heat treating operation is determined by the ability to satisfy the customer's quality requirements consistently and economically. This chapter reviews the steps that are important to produce quality parts in heat treating with a brief practical explanation of each. The steps include selecting proper material and design of the part being treated; determining whether the process is capable of heat treatment; using statistical process control, control charting, and in-process inspection and testing; and applying statistical quality control and final testing (sampling) to verify the results.

This chapter is a compilation of terms and definitions related to heat treating.

One of the primary advantages of steels is their ability to attain high strengths through heat treatment while still retaining some degree of ductility. Heat treatments can be used to not only harden steels but also to provide other useful combinations of properties, such as ductility, formability, and machinability. This chapter discusses various heat treatment processes, namely annealing, stress relieving, normalizing, spheroidizing, and hardening by austenitizing, quenching and tempering. It also discusses two types of interrupted quenching processes: martempering and austempering. The chapter concludes with a brief section on temper embrittlement.

All superalloys, whether precipitation hardened or not, are heated at some point in their production for a subsequent processing step or, as needed, to alter their microstructure. This chapter discusses the changes that occur in superalloys during heat treatment and the many reasons such changes are required. It describes several types of treatments, including stress relieving, in-process annealing, full annealing, solution annealing, coating diffusion, and precipitation hardening. It discusses the temperatures, holding times, and heating and cooling rates necessary to achieve the desired objectives of quenching, annealing, and aging along with the associated risks of surface damage caused by oxidation, carbon pickup, alloy depletion, intergranular attack, and environmental contaminants. It also discusses heat treatment atmospheres, furnace and fixturing requirements, and practical considerations, including heating and cooling rates for wrought and cast superalloys and combined treatments such as solution annealing and vacuum brazing.

This chapter discusses the processes involved in the calculation of cooling and heating curves and the estimation of austenitizing time. The chapter discusses the transformation of austenite, describing nucleation and growth rates. The chapter examines the calculation of the amount of martensite and retained austenite, and hardenability calculations. It reviews models for tempering of steels, estimation of mechanical properties, the hardness of martensite, and factors to consider to be able to calculate the residual stresses. It provides information on Kirkaldy’s model used for calculating Jominy curves. Tables for calculating the temperature distribution in steels as a function of time during heating and cooling are also included.

This chapter describes how the phases are arranged into desired microstructures during the heat treatment of tool steels. It describes the microstructural changes that are the objectives of the austenitizing, quenching, and tempering steps of tool steel hardening. The chapter covers austenite composition, retained austenite, and austenite grain size and grain growth. It provides information on the hardness and hardenability of tool steel. The chapter reviews some of these concepts and describes the microstructural appearance of the products of diffusion-controlled transformation of austenite. The role that diffusion-controlled phase transformations play relative to the hardenability of high-carbon and alloy tool steels is then emphasized. It presents general considerations of transformation diagrams, Jominy curves, and the hardenability of tool steels. The factors related to the kinetics and stabilization of martensite transformation are also covered. It briefly reviews selected aspects of the changes that evolve during tempering.

Furnaces for heat treatment of tool steels include ceramic-lined salt bath furnaces, vacuum furnaces, controlled-atmosphere furnaces, and fluidized-bed furnaces. This chapter describes the classification, operating principles, application, advantages, and disadvantages of each type of furnace.

This chapter provides an overview of the possible mechanisms of failure for heat treated steel components and discusses the techniques for examining fractures, ductile and brittle failures, intergranular failure mechanisms, and fatigue. It begins with a description of the general sources of component failure. This is followed by a section on the stages of a failure analysis, which can proceed one after the other or occur at the same time. These stages of analysis are collection of background data, preliminary visual examination, nondestructive testing, selection and preservation of specimens, mechanical testing, macroexamination, microexamination, metallographic examination, determination of the fracture mechanism, chemical analysis, exemplar testing, and analysis and writing the report. The chapter ends with a discussion on various processes involved in the determination of the fracture mechanism.