For this reason, they are usually not specified for hot forging or for applications requiring uniformity. For other cold-forming applications, such as cold extrusion, killed steels are more suitable. This basic structure can be altered significantly by various heat treatments or by rolling techniques. A spheroidized annealed structure would consist of spheroids of iron and alloy carbides dispersed in a ferrite matrix for low hardness and maximum ductility, as might be required for cold-forming operations. Quenching and tempering provide the optimum combination of mechanical properties and toughness obtainable from steel.
Grain size can also be an important aspect of the microstructure.
Adjusting microstructure to optimize machinability.