Reheating a hardened component to a temperature lower than the hardening temperature and then cooling it is known as __________.

Correct Answer: Option D — tempering

Tempering is a heat treatment process applied to ferrous alloys after hardening. By reheating the metal to a temperature below the critical transformation range and then cooling it, internal stresses are relieved, and the material's toughness is improved, effectively balancing hardness with the necessary ductility for structural applications.