This chapter discusses the thermally induced changes that occur on the surface of steel exposed to different environments. It explains how oxide scales form during heat treating and how factors such as temperature, composition, and surface finish affect growth rates, grain structure, and uniformity. It provides examples of oxides that form beneath the surface of steel and explains why it occurs. It describes the conditions associated with decarburization and explains how to determine the depth of decarburized layers in eutectoid, hypoeutectoid, and hypereutectoid steels. It also discusses the carburizing process, the factors that determine the depth and gradient of...