Steel hypo-eutectoid

Fig. 20.49 Schematic illustration of some of the ferritic/pearlitic microstructures observed in hypo-eutectoid steels after various heat treatments...

The higher the carbon content of a hypo-eutectoid steel, the more pearlite there will be in a ferritic/pearlitic structure and the greater will be the strength of the steel, other factors (grain-size, pearlite spacing, etc.) being equal. 

As noted above, most steels are, in practice, hypo-eutectoid. Consider, by way of example, a low-alloy steel containing 0 3%C. The Fe-C phase diagram (Fig. 20.44) indicates that as a steel of this composition is cooled below about 1 080K the equilibrium state is a two-phase structure containing primary, pro-eutectoid ferrite and austenite. On further cooling to below 996K the equilibrium structure consists of pro-eutectoid ferrite and pearlite. These differences are reflected in the rather more complicated T-T-T diagram used for this steel, shown in Fig. 20.48b. 

In terms of constituents, describe the microscopic (on an atomic scale) structures of tempered eutectoid, hypo-eutectoid, and hyper-eutectoid steel. 

Normalizing. This heat treatment is applied to obtain a uniform, fine-grained microstructure. The first step consists of heating the metal rapidly to, and holding it at a temperature 30-50 K above the (a + y)/y phase boundary (also referred to as the Ac3 line) for hypo-eutectoid steels, and heating rapidly to and holding at about 50 K above the eutectoid temperature (also referred to as Aci line). This step results in the formation of... 

---