Which phase transformation occurs in metals when heated and then cooled slowly?

The process being described, where metals are heated and then allowed to cool slowly, corresponds to annealing. This phase transformation is important because it helps to reduce hardness, relieve internal stresses, and improve the ductility of the material. During annealing, the structure of the metal changes at a microscopic level, allowing for the rearrangement of atoms and the elimination of defects that may have formed during previous processing steps, such as cold working or casting.

By heating the metal to a specific temperature and holding it there for a period of time before allowing it to cool gradually, the resulting microstructure becomes more uniform and stabilized. The slow cooling rate is crucial; it avoids introducing new stresses and promotes the formation of softer phases within the metal, which ultimately enhances its mechanical properties for various applications.

This makes annealing a valuable process in metallurgy, contributing to the overall performance and workability of metallic materials.