A look into the simple iron-carbon equilibrium diagram (Fig.1) which is a graphical representation of different phases as a function of temperature and composition shows that a variety of steels with any desired combination of phases can be produced"by employing suitable techniques of heat treatments, mechanical processing or a combination of these. Thus, this diagram acts as a tool in producing the required degree of phases like ferrite, austenite cemen-tite etc in the micro-structure to give the expected prop-erties. Three horizontal lines in the diagram represents the three invariant transformations signifying the co-existence of phases in equilibrium at fixed temperature, of which the lower one is of our concern
