Most materials of industrial significance consist of more than one atomic or molecular species, that is, they are not single component systems. For example, the basic components of steel are iron and carbon, although there are other components (elements) present. The components may be distributed throughout the material in a variety of ways and, even under equilibrium conditions, a material may be single- or multi-phase depending on the temperature and composition. In practice, the situation is further complicated by the fact that materials may exist in metastable conditions for long periods of time without changing to the equilibrium condition. A knowledge of the microstructure of a material, which is the number of phases present, their distribution, volume fraction, shape, and size, is essential since many properties are structure-sensitive, e.g., plastic and magnetic properties. This chapter is concerned with the understanding of the formation of phases, how the stability of phases may be represented in diagrams called equilibrium phase diagrams, and how we can use these diagrams to interpret microstructures. Finally, at the end of the chapter we will look at the structure and properties of some commercial materials. We begin by considering what happens when two components are mixed together.
KeywordsCast Iron Martensitic Transformation Equilibrium Phase Diagram Bainitic Transformation Plain Carbon Steel
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