This chapter provides a brief review of the scientific and technological developments leading to the widespread use of induction heat treating and its many applications in industry.

This chapter discusses the basic principles of induction heating and related engineering considerations. It describes the design and operation of induction coils, the magnitude and distribution of magnetic fields, and the forces that generate eddy currents in metals. It explains how induced electrical current causes metal to heat in proportion to their electrical resistance and how it affects temperature dependent properties such as resistivity and specific heat and, in turn, heating rates and efficiencies. It also discusses the effect of hysteresis and explains why eddy currents tend to be confined to the outer surface of the workpiece, a phenomenon known as the skin effect. The chapter includes several data plots showing how the depth of heating varies with frequency and how heating time, power density, and thermal conduction rate correspond with hardening depth.

This chapter discusses the basic components in an induction heat treating system. It describes the design and operating characteristics of power supplies, load-matching transformers, tuning capacitors, power regulators, controllers, process monitors, and diagnostic systems. It also provides information on fixtures and work-handling devices, quench systems, and load matching and tuning procedures.

This chapter discusses the design and operating principles of various types of electromagnetic coils. It explains how induction coils are classified based on the direction of the eddy currents they induce in the workpiece and the corresponding orientation, whether longitudinal or transverse, of the associated magnetic flux. It then discusses the factors that influence coil design and selection, including coupling efficiency, frequency, the number and spacing of turns, and the use of flux intensifiers. It also includes images and illustrations of various types of coils and coil geometries for basic as well as special purpose applications.

This chapter discusses the quenching process and its adaptation to induction heat treating. It describes the three stages of quenching, the cooling characteristics of various types of quenchants, and the details of nearly a dozen compatible quenching methods. It also explains how to verify whether a quenchant can cool a workpiece fast enough to achieve martensitic transformation without cracking or distortion.

Induction hardened steels are often tempered to increase their ductility and relieve quenching stresses. During tempering, martensitic microstructures supersaturated with carbon decompose into a more stable, ductile form. This chapter discusses the transformations associated with the tempering process and their effect on ductility as well as other properties. It describes the structural and compositional changes that occur during the four stages of tempering, the relative influence of time and temperature, and how tempering affects the hardness of various grades of steel. The chapter discusses the practice of both furnace and induction tempering, describing where and how they are used, their tempering characteristics, strengths and limitations, and operating parameters. It also discusses the use of residual heat tempering, a self-tempering process.

Induction heat treating is used in a wide range of applications. Typical uses, as described in this chapter, include the surface hardening of many types of shafts as well as gears and sprockets and the through-hardening of gripping teeth, cutting edges, and impact zones incorporated into various types of tools and track pins manufactured for off-highway equipment.

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 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 presents a step-by-step approach for analyzing the causes of nonconforming workpieces and determining potential solutions. The discussion covers a wide range of issues, including testing errors, latent and process-related defects, examination and testing techniques, defect characterization, and effective remedial actions.

This chapter discusses quality control programs and procedures for induction heat-treating systems and includes related forms and checklists.

This chapter discusses the maintenance needs of major components in induction heat-treating systems, including power supplies, heat stations, capacitors, high-frequency output stages, induction coils, water systems, quench systems, and fixturing.

This appendix illustrates the effect of various operating parameters on the case depth or thickness of scan hardened components.

This appendix provides practical information on induction coils and how they are made. It discusses soldering methods, preferred materials, design challenges, and best practices and procedures. It also discusses the design, construction, and application of magnetic flux concentrators and the growing use of computer simulation.

This appendix is a glossary of terms related to induction heat treating.

Mechanical components often require surface treatments to meet application demands. This chapter describes several surface hardening treatments for steel and their effect on microstructure, composition, and properties. It discusses flame hardening, induction heating, carburizing, nitriding, carbonitriding, and nitrocarburizing. The discussion on carburizing addresses several interrelated factors, including processing principles, alloying, surface oxidation, residual stresses, bending fatigue, contact fatigue, and fracture.

Induction heating, in most applications, is used to selectively heat only a portion of the workpiece that requires treatment. This chapter covers the basic principles, features, and metallurgical aspects of induction heating. The discussion includes the conditions required for induction heating and quenching, the use of magnetic flux concentrators to improve the efficiency of surface heating, and the quenching systems used for induction hardening. The discussion also provides information on time-temperature dependence in induction heating, workpiece distortion in induction surface hardening, residual stresses after induction surface hardening and finish grinding, and input and output control of steel for induction surface hardening of gears.

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.

This chapter discusses the processes involved in heat treating of stainless steels, providing information on the classification, chemical compositions, and corrosion resistance of stainless steels. Five groups of stainless steels are discussed: austenitic, ferritic, martensitic, precipitation-hardening, and duplex grades. The chapter also describes the heat treatment conditions that should be followed for processing of stainless steels.