What does spheroidizing primarily achieve in the treatment of steel?

Spheroidizing is a heat treatment process that primarily aims to convert the carbide content in steel into a spherical form. This transformation enhances the machinability of the steel by reducing the hardness and allowing for easier cutting. In spheroidizing, steel is heated to a temperature just below critical and maintained for a long period, encouraging the carbon-rich alloy to form spherical carbide particles throughout the steel matrix. This results in a more ductile material, which is easier to work with in manufacturing processes.

The method does not focus on the formation of martensite, an allotropic form of iron that is typically hard but brittle, which occurs through a different quenching process. Additionally, spheroidizing does not aim primarily to increase tensile strength; rather, it actually reduces hardness for improved workability. The improvement of austenite structure is associated more with processes like normalizing or annealing rather than spheroidizing. Therefore, the conversion of carbide content into a spherical structure is the primary achievement of spheroidizing, making this the correct answer.