A spheroidized structure, which consists of spherically shaped cementite in a matrix of ferrite, is often desired in the production of steel, whether to improve properties, such as machinability and ductility, or accommodate subsequent hardening treatments. This chapter discusses the spheroidization of normalized and annealed steels by heating at subcritical temperatures. It explains how lamellar pearlite and proeutectoid cementite transform when heated and how deformation prior to heating affects both the mechanism and kinetics of spheroidization. It also explains how austenitizing contributes to the production of spheroidal transformation products and why secondary graphitization sometimes occurs.

This chapter describes heat treatments that produce uniform grain structures, reduce residual stresses, and improve ductility and machinability. It also discusses spheroidizing treatments that improve strength and toughness by promoting dispersions of spherical carbides in a ferrite matrix. The chapter concludes with a brief discussion on the mechanical properties of ferrite/pearlite microstructures in medium-carbon steels.