Several specialized instruments are available for the metallographer to use as tools to gather key information on the characteristics of the microstructure being analyzed. These include microscopes that use electrons as a source of illumination instead of light and x-ray diffraction equipment. This chapter describes how these instruments can be used to gather important information about a microstructure. The instruments covered include image analyzers, transmission electron microscopes, scanning electron microscopes, electron probe microanalyzers, scanning transmission electron microscopes, x-ray diffractometers, microhardness testers, and hot microhardness testers. A list of other instruments that are usually located in a research laboratory or specialized testing laboratory is also provided.

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 operating mechanism, applications, advantages, and limitations of Brinell hardness testing, Rockwell hardness testing, Vickers hardness testing, Scleroscope hardness testing, and microhardness testing. In addition, the general precautions and selection criteria to be considered are described and details of equipment setup provided.

Hardness tests provide valuable information about the quality of materials and how they are likely to perform in different types of service. This chapter covers some of the most widely used hardness testing methods, including Vickers, Rockwell, and Brinell tests, Shore scleroscope and Equotip hardness tests, and microindentation tests. It describes the equipment and procedures used, discusses the factors that influence accuracy, and provides hardness conversion equations for different types of materials. It also explains how hardness testing sheds light on anisotropy, machinability, wear, fracture toughness, and tensile strength as well as temperature effects, residual stress, and quality control.

This chapter describes processes for evaluation of nitrided parts, including case depth and case hardness, and discusses the factors contributing to corrosion and distortion of parts after ferritic nitrocarburizing.

This chapter discusses the methods and procedures used for inspecting induction-hardened parts. It provides information on hardness and case depth measurements, nondestructive testing and surface analysis, the effect of various hardening errors, and relevant test standards.

This chapter reviews the tests and procedures used for measuring hardness of plastics and elastomers. The conventional testing methods (Rockwell, Vickers, Brinell, and Knoop) used for testing of metals are based on the idea that hardness represents the resistance against permanent plastic deformation of the material to be tested. However, elastic deformation must be considered in hardness measurement of elastomers. This chapter discusses the equipment and processes involved in the durometer (Shore) test, the International Rubber Hardness Degree test, and other specialized tests. It presents the criteria that can be used to select a suitable hardness testing method for elastomers or plastics and describes processes involved in specimen preparation and equipment calibration.

Nitriding is a case-hardening process used for alloy steel gears and is quite similar to case carburizing. Nitriding of gears can be done in either a gas or liquid medium containing nitrogen. This chapter discusses the processes involved in gas nitriding. It reviews the effects of white layer formation in nitrided gears and presents general recommendations for nitrided gears. The chapter describes the microstructure, overload and fatigue damage, bending-fatigue life, cost, and distortion of nitrided gears. Information on nitriding steels used in Europe and the applications of nitrided gears are also provided. The chapter presents case studies on successful nitriding of a gear and on the failure of nitrided gears used in a gearbox subjected to a load with wide fluctuations.

Nitriding is a surface hardening heat treatment that introduces nitrogen into the surface of steel while it is in the ferritic condition. Gas nitriding using ammonia as the nitrogen-carrying species is the most commonly employed process and is emphasized in this chapter. Nitriding produces a wear- and fatigue-resistant surface on gear teeth and is used in applications where gears are not subjected to high shock loads or contact stress. It is useful for gears that need to maintain their surface hardness at elevated temperatures. Gears used in industrial, automotive, and aerospace applications are commonly nitrided. This chapter discusses the processes involved in gas, controlled, and ion nitriding.

This chapter discusses the various factors influencing the evaluation of fatigue fracture of nitrided layers. It begins by describing the problems of enhancing the fatigue resistance of machine components. The significance and detailed assessment of the effect of a structural flaw are then explained, using investigations of the effect of variable core conditions on fatigue resistance as an example. This is followed by a discussion on the processes involved in the evaluation of fatigue properties of nitrided steels. The chapter also describes the determination of the fatigue characteristics of nitrided steels after the carbonitriding treatment.

The power generating industry has become proficient at predicting how long a component will last under a given set of operating conditions. This chapter explains how such predictions are made in the case of boiler tubes. It identifies critical damage mechanisms, progressive failure pathways, and relevant test and measurement procedures. It describes life assessment methods based on hardness, wall thickness, scale formation, microstructure, and creep. It also includes a case study on the determination of the residual life of a secondary superheater tube.