Search Results for controlled nitriding

The nitriding process can be applied to various materials and part geometries. This chapter focuses on tool steels, pure irons, low-alloy steels, and maraging steels. Various considerations such as the surface metallurgy requirements of the die, including case depth, compound layer formation, and temperature, are also discussed in this chapter. The chapter also addresses steel selection and surface metallurgy of gears.

The compound zone that forms on the surface of nitrided steels is often called the white layer. When the nitrided sample is sectioned through the case, and then polished and etched with a standard solution of nital (2 to 5% nitric acid and alcohol), the immediate surface etches out as white in appearance above the nitrided case. This chapter focuses on the methods to control the compound zone, or white layer. It first provides information on a test to determine the presence of the white layer, and discusses the processes involved in the reduction of the compound zone by the two-stage process. Next, it describes other methods for controlling compound zone formation, and, finally, reviews the factors related to the determination of case depth in 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.

Formation of the nitrided case begins through a series of nucleated growth areas on the steel surface. These nucleating growth areas will eventually become what is known as the compound layer or, more commonly, the white layer. This chapter discusses the influence of carbon on the compound zone. It explains how to control and calculate compound zone thickness. Compound zone thickness can be controlled by dilution, the two-stage Floe process, or by ion nitriding. The chapter describes the factors affecting surface case formation.

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.

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 begins with an overview of the history of ion nitriding. This is followed by sections that describe how the ion nitriding process works, glow discharge characteristics, process parameters requiring good control, and the applications of plasma processing. The chapter explores what happens in the ion nitriding process and provides information on its gas ratios. It describes the reactions that occur at the surface of the material being treated during iron nitriding and defines corner effect and nitride networking. Further, the chapter provides information on the stability of surface layers and processes involved in the degradation of surface finish and control of the compound zone formation. Gases primarily used for ion nitriding and the control parameters used in ion nitriding are also covered. The chapter also presents the philosophies and advantages of the plasma generation technique for nitriding. It concludes with processes involved in oxynitriding.

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.

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.

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.

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.

Distortion is defined as an irreversible and usually unpredictable dimensional change in a component due to thermal processing or temperature variations and loading in service. This chapter describes two types of distortion: size distortion and shape distortion. It addresses how distortion can be managed by controlling certain factors. The chapter discusses the cause and effect of distortion during nitriding, the processes involved in stock removal prior to nitriding, and the criteria for post-machining operations.

Ion nitriding equipment can be categorized into two groups: cold-wall continuous direct current (dc) equipment and hot-wall pulsed dc equipment. This chapter focuses on these two categories along with other important considerations for ion (plasma) nitriding equipment and processing. Other important considerations discussed include the hollow cathode effect, sputter cleaning, furnace loading, pressure/voltage relationships, workpiece masking, and furnace configuration options. The chapter describes five methods of cooling parts from the process temperature to an acceptable exposure temperature after plasma nitriding. The chapter also presents some of the advantages of the pulsed plasma process.

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.

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.

The unique advantages of the nitriding process were recognized by German researchers in the early 1920s. It was used to treat steels for applications that required: high torque, high wear resistance; abrasive wear resistance; corrosion resistance; and high surface compressive strength. This chapter focuses on key process considerations and factors that helped nitriding gain acceptance. These factors include a low-temperature process, no quench requirement, minimal distortion, high hardness values, and resistance to oxidation.

This chapter details suitable steels for gas nitriding and discusses conventional gas nitriding, plasma (Ion) nitriding, the ferritic nitrocarburizing processes, gaseous ferritic nitrocarburizing, plasma nitrocarburizing, and the salt-bath ferritic nitrocarburizing processes.

Modern gears are made from a wide variety of materials. Of all these, steel has the outstanding characteristics of high strength per unit volume and low cost per pound. Although both plain carbon and alloy steels with equal hardness exhibit equal tensile strengths, alloy steels are preferred because of higher hardenability and the desired microstructures of the hardened case and core needed for the high fatigue strength of gears. This chapter provides an overview of the key considerations involved in the selection and application of heat treating processes for alloy steel gears and serves as an introduction to the subsequent chapters in this book.