A fluidized-bed furnace system can be used for the gas nitriding process. This chapter focuses on fluidized-bed nitriding. It discusses the methods of heating a fluidized bed. The heating system can be electrical or gas, and internal or external. The chapter describes nitriding and oxynitriding processes in the fluidized-bed furnace. It also explains how to operate the fluid bed for nitriding. The chapter provides a discussion on the measurement of the gas dissociation.

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.

This chapters reviews the various process, material, and post-treatment problems that can occur in nitriding and how to troubleshoot them. The troubleshooting methods discussed relate to gas nitriding, salt bath nitriding, and ion nitriding.

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 process characteristics, advantages, disadvantages, and applications of various processes involved in surface hardening of steel. These include pack carburizing, liquid carburizing, gas carburizing, vacuum carburizing, plasma carburizing, gas nitriding, liquid nitriding, carbonitriding, and hardfacing. The chapter describes two surface hardening processes by localized heat treatment: flame hardening and induction hardening. It also briefly summarizes other surface hardening processes, namely, aluminizing, siliconizing, chromizing, titanium carbide coatings, and boronizing.

Stop-off coatings prevent nitriding of selected areas on components. This chapter discusses the processes, advantages, and disadvantages of stop-off techniques for gas nitriding, salt bath nitriding, and ion nitriding.

Several limitations in achieving optimal gear performance with conventional nitriding have led researchers to work on a variety of novel and improved nitriding processes. Of these, ion/plasma nitriding offers some promising results, which are reviewed in this chapter. The chapter concludes with a case history describing the application of ion nitriding to an internal ring gear of an epicyclic gearbox.

This chapter presents the salts used and the process advantages of salt bath nitriding. It describes bath testing and analysis including the materials and equipment, analysis procedure, and determination of sodium carbonate and sodium cyanate for titration testing of the nitriding salt bath. The chapter explains the procedures for maintenance of the salt bath and related equipment. It also discusses safety precautions and design parameters for furnace equipment.

This chapter discusses the metallurgical considerations and process requirements of nitriding. It presents the pioneering work of Adolph Machlet and Adolph Fry and presents early developments. One such development is the Floe process, a two-stage treatment used to reduce the formation of a compound layer on the surface of a nitrided steel.

Process gas control for plasma (ion) nitriding is a matter of estimating the flows necessary to accomplish the required surface metallurgy. This chapter reviews several studies aimed at better understanding process gas control in plasma nitriding and its influence on compound zone formation. Emphasis is placed on the effect of sputtering on the kinetics of compound zone formation. The discussion covers the processes involved in process gas control analysis by photo spectrometry and mass spectrometry and the difficulties associated with gas analysis.