What does the term graphitization refer to in materials?

Graphitization specifically refers to the transformation that occurs in iron or low-alloy steel, where carbon is converted into graphite. This process can take place under certain conditions, particularly when the material is subjected to high temperatures over an extended period. The graphite formation can influence the material's properties, including improving its machinability and reducing brittleness.

In contrast, the other options do not accurately define graphitization. The conversion of metals to carbon, the strengthening of steel, and the development of corrosion all involve different processes unrelated to the specific formation of graphite in iron or low-alloy steels. Thus, focusing on the relationship between the heat treatment of these materials and the resultant formation of graphite clearly identifies why the correct answer is the formation of graphite in iron or low-alloy steel.