Phase diagrams are graphical tools used to understand how metals and alloys behave under different temperature and composition conditions. By showing the phases—such as solid, liquid, or mixtures—that exist at various combinations of temperature and alloy composition, these diagrams help predict the structure and properties of a material as it cools or is heat-treated. Composition/temperature phase diagrams are particularly useful in metallurgy because they reveal how alloying elements affect melting points, phase transformations, and microstructure.
In this course, phase diagrams will provide a foundation for understanding alloy behavior, especially as we begin to study the iron-carbon system. This system is one of the most important in engineering, as it governs the properties of steels and cast irons—materials central to construction, manufacturing, and toolmaking. Through the iron-carbon diagram, we’ll explore critical concepts such as eutectoid and eutectic reactions, phase stability, and how different heat treatments produce desirable material characteristics.