This chapter provides a discussion of nitriding furnace equipment and control systems. The discussion covers the essential design criteria of the furnace, types of nitriding furnaces, insulation for the reduction of furnace heat losses, and factors influencing furnace configuration and design. It also covers the processes involved in the construction and maintenance of retorts, methods for sealing a retort to prevent ammonia leaks, and safety precautions to be taken while using ammonia. Further, the chapter provides information on the factors for choosing a heating medium and discusses the processes involved in controlling temperature, gas dissociation, oxygen probes, and nitriding sensors.

This chapter covers the emerging practice of quantitative microscopy and its application in the study of the microstructure of metals. It describes the methods used to quantify structural gradients, volume fraction, grain size and distribution, and other features of interest. It provides examples showing how the various features appear, how they are measured, and how the resulting data are converted into usable form. The chapter also discusses the quantification of fracture morphology and its correlation with material properties and behaviors.

This chapter develops a corrosion model that accounts for solution potentials and the effects of coupling between cathodic and anodic reactions. It begins by examining potential differences at various points (in the solution) along a path from the anode to the cathode area. It then presents a simple model of a galvanically coupled electrode, in which the metal is represented as an array of anode and cathode reaction surfaces. The chapter goes on to develop the related theory of mixed electrodes, showing how it can be used to predict corrosion rates based on measured potentials and current densities, polarization characteristics, and physical variables such as anode-to-cathode area ratios and fluid velocity. It also discusses the effect of corrosion inhibitors, galvanic coupling, and external currents, making extensive use of polarization curves.

This chapter familiarizes readers with the basic concepts of corrosion, discussing chemical reactions, ion transfer mechanisms, electrochemical processes and variables, and the formation of solid corrosion products. It presents a simple but effective teaching tool, the elementary electrochemical corrosion circuit, using it to explain how electric potential differences drive the corrosion process and how corrosion rates vary in proportion to current density. The chapter concludes with a discussion on the importance of corrosion products, such as oxides and hydroxides, and how their formation can be a major factor in controlling corrosion.

This chapter discusses some of the more advanced methods and procedures used in failure analysis, including in-service material sampling, in situ microstructure analysis, and a form of punch testing that can determine the fracture toughness of any material from a tiny specimen. The chapter also covers quantitative fractography, fracture surface topography analysis, and the use of oxide dating as well as fault tree and failure modes and effects analysis (FMEA) and computational techniques.

This chapter provides a detailed account of cathodic protection. It begins by discussing the fundamentals of cathodic protection followed by a description of the various types of cathodic protection. It then describes the origins, types, and alleged failures of cathodic protection criteria. This is followed by a section providing information on anode materials that are used for cathodic protection applications. General guidelines for designing the cathodic protection systems are also listed. Finally, the chapter presents various examples on cathodic protection of steel structures. The examples are selected to familiarize the design engineer with the steps to follow in selecting a specific corrosion-control method.

A first-stage compressor blade failed prematurely in an aircraft engine, fracturing at the midpoint of the root transition region. An examination of the fracture surface revealed beach marks, striations, and pitting, indicating that the blade failed by fatigue due to a crack initiated by corrosion pits in the root transition region. The chapter recommends further investigations to determine the cause of pitting, which appears to be confined to the dovetail region.

A driven gear in the gear box of an aircraft engine fractured after a 40 h test run. The driving gear and gear shaft were also damaged. Based on the results of fractography, chemical analysis, metallography, and hardness testing, the fracture was caused by a fatigue crack initiating at the corner of the inner rim near an inclusion. The report recommends the use of a cleaner material and more carefully controlling case hardening process.

This chapter explains how metallography and hardness testing are used to evaluate the quality and condition of metal products. It also discusses the use of tensile testing, fracture toughness and impact testing, fatigue testing, and nondestructive test methods including ultrasonic, x-ray, and eddy current testing.

This appendix discusses in brief the sources of decarburization of steels as well as the effect of heat treatment on the process.

This chapter focuses on tensile testing of three types of engineering components that undergo significant loading in tension, namely, threaded fasteners and bolted joints; adhesive joints; and welded joints. It describes the standardized tensile test for externally threaded fasteners and provides a brief background on relationships among torque, angle-of-turn, tension, and friction. The chapter also describes the test methods covered in the ASTM F 606M standard, namely, product hardness; proof load by length measurement, yield strength, or uniform hardness; axial tension testing of full-sized products; wedge tension testing of full-sized products; tension testing of machined test specimens; and total extension at fracture testing. Finally, the chapter covers tensile testing of adhesive and welded joints.

This chapters discusses the considerations involved in the qualification and analysis of induction hardening treatments. The discussion covers material selection and prior heat treatment, hardness and case depth, frequency selection, power density and heating time, part and process tolerances, geometrical effects, quenchant selection, coil design, and work-handling equipment. The chapter also presents several examples, walking readers though each step, and discusses the development of setup instructions and operating procedures.

This chapter presents a relatively simple method for estimating forging loads and flow stresses. The method uses the slab analysis technique and accounts for material properties, friction and heat transfer, press ram speed, forging geometry, and billet and die temperatures. The chapter demonstrates the use of the method and compares the results with measured values.

This chapter discusses the thermally induced changes that occur on the surface of steel exposed to different environments. It explains how oxide scales form during heat treating and how factors such as temperature, composition, and surface finish affect growth rates, grain structure, and uniformity. It provides examples of oxides that form beneath the surface of steel and explains why it occurs. It describes the conditions associated with decarburization and explains how to determine the depth of decarburized layers in eutectoid, hypoeutectoid, and hypereutectoid steels. It also discusses the carburizing process, the factors that determine the depth and gradient of the carburized case, the effect of post-process treatments, and a variation on the process known as ferritic carbonitriding.

A turbine blade in an aircraft engine failed, fracturing at the root above the fir tree region. Fractography indicated that a fatigue crack initiated at the trailing edge of the blade and the final fracture occurred when the crack reached critical length. Although the exact cause of crack initiation could not be established, material defects, improper root loading, and high operating temperatures were ruled out. This chapter describes how investigators came to their conclusions and what they learned through visual and SEM examination and qualitative elemental analysis. It includes images of the microstructure and fracture surfaces and explains what some of the details reveal about the failure.

This chapter discusses equipment used for ferritic nitrocarburizing, including salt bath furnaces, atmosphere furnaces, and plasma furnaces. It also describes the processes involved in ferritic oxynitrocarburizing.