Chapter 7: Tempering
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.