ANS:C - annealing

The process described, heating hypoeutectoid steels to 30°C above the upper critical temperature line, soaking at that temperature, and then cooling slowly to room temperature to form a pearlite and ferrite structure, is called annealing. Annealing is a heat treatment process used to alter the microstructure of metals, particularly to achieve desired mechanical properties such as improved ductility, machinability, or softness. In the case of hypoeutectoid steels, annealing involves heating the material to a temperature slightly above the upper critical temperature, holding it at that temperature to allow for homogeneous austenitization, and then slowly cooling it to room temperature. This controlled cooling process allows for the formation of a fine pearlite and ferrite microstructure, which results in improved ductility and toughness in the steel. Annealing also relieves internal stresses and refines the grain structure, leading to a more uniform and stable material.