This article provides a discussion on the transformations of various categories of bainite in ferrous systems. These include upper bainite, lower bainite, inverse bainite, granular bainite, and columnar bainite. The article also provides information on the bainite transformations in nonferrous systems.

The transformation of austenite of cast irons represents a more complex and less studied subject. This article discusses the general features of the decomposition of austenite into bainite. It describes the heat treatment cycles of austempered cast iron microstructure. The article reviews several factors, such as presence of graphite and austenite grain size, which affect the transformation rate of austenite during austempering of free-graphite cast irons.

This article provides a detailed discussion on the factors involved in the selection of steels for austempering, including section thickness limitations of steel parts and modifications of austempering practice. The selection of steel for an austempered component is based on the processing characteristics of the heat treating equipment employed. It is also based on the hardenability and transformation characteristics of the steel alloy as indicated by time-temperature-transformation and isothermal-transformation diagrams. The article contains tables that compare the dimensional changes that occur in stabilizer bars as a result of oil quenching and tempering with those that resulted from austempering. It also discusses the production applications of austempering and the problems encountered in austempering together with their solutions.

This article describes microstructures and microstructure-property relationships in steels. It emphasizes the correlation of microstructure and properties as a function of carbon content and processing in low-alloy steels. The article discusses the iron-carbon phase diagram and the phase transformations that change the structure and properties at varying levels of carbon content. Microstructures described include pearlite, bainite, proeutectoid ferrite and cementite, ferrite-pearlite, and martensite. The article depicts some of the primary processing steps that result in ferrite-pearlite microstructures. It shows the range of hardness levels which may be obtained by tempering at various temperatures as a function of the carbon content of the steel. To reduce the number of processing steps associated with producing quenched and tempered microstructures, new alloying approaches have been developed to produce high-strength microstructures directly during cooling after forging.

Steels are among the most versatile materials in modifying their microstructure and properties by heat treatment. This article outlines the basic concepts of physical metallurgy relating to the heat treatment of steel. It considers the phases and microstructures of steel together with the transformations observed and critical temperatures during heat treatment. Additionally, the different types of steels, heat treatments, and their purposes are also discussed.

The choice of heat treatment depends on the service requirements of a given bearing and how the bearing will be made. This article describes the design parameters, material characteristics required to sustain performance characteristics, metallurgical properties, and dimensional stability. It also provides a description of various extensively-used heat treatment processes, namely, carburizing, carbonitriding, induction surface hardening, and nitriding associated with various bearings. In addition, the article explores the factors to be considered in selecting a process and explains why it is optimum for a specific application.

Martempering and austempering processes may eliminate the need for conventional oil quenching and tempering. This article presents the suitability of steels for martempering and austempering. It discusses the compositions of oils suitable for marquenching and modified marquenching and also presents safety precautions recommended for the use of martempering oils. Finally, the article explains the effect of agitation and water in a molten salt bath.

This article introduces basic physical metallurgy concepts that may be useful for understanding and interpreting variations in metallographic features and how processing affects microstructure. It presents some basic concepts in structure-property relationships. The article describes the use of equilibrium binary phase diagrams as a tool in the interpretation of microstructures. It reviews an account of the two types of solid-state phase transformations: isothermal and athermal. The article discusses isothermal transformation and continuous cooling transformation diagrams which are useful in determining the conditions for proper heat treatment (solid-state transformation) of metals and alloys. The influence of the mechanisms of phase nucleation and growth on the morphology, size, and distribution of grains and second phases is also described.