Vanadium tends to promote hardenability and a fine grain structure during heat treatment.

• A. It reduces hardness
• B. It increases ductility only
• C. It increases corrosion resistance
• D. It tends to promote hardenability and a fine grain structure during heat treatment

Answer: (D)

Vanadium acts as a carbide former in steels, forming stable vanadium carbides (VC) during heat treatment. These carbides precipitate at grain boundaries and within grains, pinning the boundaries and slowing grain growth. That pinning produces a finer austenite grain structure, and a finer grain size generally enhances strength and toughness. More importantly for heat treatment, the finer grains and the carbide pinning improve hardenability: the steel can transform to martensite more deeply under a given cooling rate, because the diffusion processes that drive other transformations are suppressed and the austenite grains don’t grow large enough to limit martensite formation. So vanadium helps both hardenability and grain refinement. It isn’t primarily about reducing hardness, increasing ductility alone, or boosting corrosion resistance in this context.