Which of the following is the most effective inhibitor of grain growth, when added in small quantity in steel ?

ANS:B - Vanadium

Vanadium is a transition metal that is commonly used as an alloying element in steel production. When added to steel in small quantities, typically less than 0.5%, vanadium has several beneficial effects on the microstructure and properties of the steel. One of the significant effects of vanadium in steel is its ability to inhibit grain growth. During the cooling process of steel from high temperatures, grains tend to grow larger, which can negatively impact the mechanical properties of the material. However, the addition of vanadium helps to restrict this grain growth by acting as a grain refiner. The mechanism by which vanadium inhibits grain growth involves its interaction with other elements in the steel, particularly carbon and nitrogen. Vanadium forms nitrides and carbides, which act as nucleation sites for new grains to form. This promotes the formation of a fine-grained microstructure in the steel, preventing the growth of large grains during cooling. Additionally, vanadium can also enhance the hardenability of steel, allowing it to be effectively hardened by heat treatment processes such as quenching and tempering. This is particularly advantageous in applications where high strength and toughness are required. Overall, the addition of vanadium to steel in small quantities is highly effective in improving its mechanical properties, including strength, toughness, and wear resistance, by inhibiting grain growth and refining the microstructure.