Heat treatment places a finished part into an oven and exposes it to low or medium heat to achieve a greater internal structure. On a microscopic scale, metals form into an organized crystalline structure whereby the metal atoms naturally form into a perfectly spaced atomic structure. However, metals don’t usually form so perfectly, instead, they form into uneven groupings. When multiple groupings align with each other in the same general direction, that is called a “grain.”
When metal is cold, the grains in metal are set and cannot move naturally. Grains can only be moved or manipulated through the application of heat, force, or both. During the forging process, the grain structure is massively realigned to achieve greater strength and ideal internal forces, but the forged part may have some misaligned grains that compromise the structure of the part. To solve this, the part is heated again to allow the grains to realign themselves into a more desirable formation.