Carbonitriding introduces and diffuses atomic nitrogen into the surface steel during carburization. This chapter focuses on case composition of a carbonitrided case, case depth, case hardenability, hardness gradients, void formation, and applications of carbonitriding. The chapter discusses furnaces suitable for carbonitriding, atmosphere constituents, batch furnace atmospheres, continuous furnace atmospheres, safety, temperature selection, quenching, tempering, and hardness testing of a carbonitrided case.

The hardenability of steel is governed almost entirely by the chemical composition (carbon and alloy content) at the austenitizing temperature and the austenite grain size at the moment of quenching. This article introduces the methods to evaluate hardenability and the factors that influence steel hardenability and selection. The discussion covers processes involved in Jominy end-quench test for evaluating hardenability. The effect of carbon on hardenability data and the effect of alloys on hardenability during quenching and on the tempering response (after hardening) are also discussed. In addition, the article provides information on the hardenability limits of H-steels after a note on hardenability correlation curves and Jominy equivalence charts.

This chapter describes the designations of carbon and low-alloy steels and their general characteristics in terms of their response to hardening and mechanical properties. The steels covered are low-carbon steels, higher manganese carbon steels, boron-treated carbon steels, H-steels, free-machining carbon steels, low-alloy manganese steels, low-alloy molybdenum steels, low-alloy chromium-molybdenum steels, low-alloy nickel-chromium-molybdenum steels, low-alloy nickel-molybdenum steels, low-alloy chromium steels, and low-alloy silicon-manganese steels. The chapter provides information on residual elements, microalloying, grain refinement, mechanical properties, and grain size of these steels. In addition, the effects of free-machining additives are also discussed.

Heat treatment of steel involves a number of processes to condition the microstructure and obtain desired properties. This includes various methods namely, annealing, normalizing, and hardening by quenching and tempering. This chapter focuses on general heat treatment procedures and the applications of particular types or grades of carbon and low-alloy steels. The discussion covers carbon steel classification for heat treating, tempering of quenched carbon steels, and austempering of steel. In addition, the chapter discusses the effects of alloying and hardenability on steel and provides information on martempering of steel.

This chapter provides a practical understanding of heat treatments and how to employ them to optimize the properties and structures of cast irons and steels. It discusses annealing, normalizing, quenching, tempering, patenting, carburizing, nitriding, carbonitriding, and nitrocarburizing. It describes the primary objectives of each treatment along with processing sequences, process parameters, and related phase transformations. The chapter contains more than 100 images, including time-temperature diagrams, transformation curves, data plots, and detailed micro- and macrographs. It also discusses the concepts of hardenability, critical diameter, quench severity, and Jominy testing.

This chapter covers the fundamentals of heat treating. It begins with a review of the composition, classification, and properties of iron and steel, the phases of the iron-carbon system, and the basic types of heat treatments. It then discusses the topics of hardness and hardenability, the role of carbon in the hardening of steels, the process of austenitization, and the influence of cooling rate on subsequent transformations. The chapter also explains how induction heating affects residual stress, distortion, and grain size.

This appendix provides hardenability curves for several H-steels (1045H, 4130H, 4140H, 4142H, 4145H, 4340H, 5160H, 8620H) and one alloy steel (E52100).

The properties of martensite and the mechanisms that govern its formation are the key to understanding hardness and the hardenability of carbon steel. Martensite is a transformation product of austenite that requires rapid cooling to suppress diffusion-dependent transformation pathways. This chapter describes the conditions that must be met for martensite to form. It discusses the role of quenching and the factors that affect cooling rate, including heat transfer, thermal diffusivity, emissivity, and section size. It defines hardenability and explains how to quantify it using the Grossmann-Bain approach or Jominy end-quench testing. It also explains how hardenability can be improved through the addition of boron, phosphorus, and other alloys.

This chapter discusses the processes used in manufacturing to thermally alter the properties of metals and alloys. It begins with a review of the iron-carbon system, the factors that affect hardenability, and the use of continuous cooling transformation diagrams. It then explains how various steels respond to heat treatments, such as annealing, normalizing, spheroidizing, tempering, and direct and interrupted quenching, and surface-hardening processes, such as flame and induction hardening, carburizing, nitriding, and carbonitriding. It also addresses the issue of temper embrittlement and discusses the effect of precipitation hardening on aluminum and other alloys.

This chapter discusses ferrous metals, including low-carbon steels, stainless steels, and cast irons. It also provides information on hardening and hardenability and the tempering process.

This chapter provides information on various contributors to failure of carburized and carbonitrided components, with the primary focus on carburized components. The most common contributors covered include component design, selection of proper hardenability, increased residual stress, dimensional stability, and generation of quenching and grinding cracks. They also include insufficient case hardness and improper core hardness, influence of surface carbon content and grain size, internal oxidation, structure of carbides, and inclusion of noncarbide. Details on micropitting, macropitting, case crushing, pitting corrosion, and partial melting are also provided.

This chapter addresses the concept of hardenability by first describing the basic hardening process for steel, starting with austenitization followed by quenching and tempering. The context also serves to clarify the difference between hardenability and hardness, which are often confused. Most of the information in the chapter is of a practical nature, covering application-oriented topics such as isothermal transformation (IT) and continuous transformation (CT) diagrams which are used to predict and control the rate of formation of ferrite, pearlite, and bainite. The chapter also discusses the effect of grain size and alloying elements and explains how Jominy end quench testing is used to evaluate the hardenability of steel.

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.

This chapter discusses the general principles of measuring hardness and hardenability of steel. The discussion begins by defining hardness and exploring the history of hardness testing. This is followed by a discussion on the principles, applications, advantages, and disadvantages of commonly used hardness testing systems: the Brinell, Rockwell, Vickers, Scleroscope, and various microhardness testers that employ Vickers or Knoop indenters. The effect of carbon content on annealed steels and hardened steels is then discussed. A brief discussion on the concept of the ideal critical diameter and austenitic grain size of steels is also provided to understand how one can calculate and quantify hardenability. The processes involved in various methods for evaluating hardenability are reviewed, discussing the effect of alloying elements on hardenability.

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.

Carbonitriding is a modified form of gas carburizing. It is performed in a closed furnace chamber with an atmosphere enriched with a gaseous compound of carbon and nitrogen. This chapter provides information on the carbonitriding of steels, the applications of carbonitriding, the typical case depths, and the hardenability of carbonitrided parts. In addition, the chapter also discusses the processes involved in quenching, tempering, and distortion of carbonitrided steels.