Which is a common reason for performing heat treating on metals?

Heat treating is a crucial process in metallurgy that involves heating and cooling metals in a controlled manner to achieve desired physical and mechanical properties. One of the primary reasons for performing heat treating on metals is to enhance hardness.

When metals are subjected to heat treating processes such as quenching, tempering, or annealing, their internal structure is altered. During processes like quenching, the rapid cooling of heated metal can transform its microstructure into a harder form. For instance, in steel, the transformation of austenite to martensite through quenching significantly increases hardness.

This enhanced hardness improves the metal's resistance to wear and deformation, making it suitable for a variety of applications where strength and durability are critical. Therefore, the enhancement of hardness is a key objective in the heat treating process, allowing for improved performance in demanding environments.

The other options do not align with the objectives of heat treating, as increasing brittleness, encouraging corrosion, or reducing flexibility are generally undesirable outcomes in metal processing.