Silicon in steel has what primary effect regarding oxidation resistance and hardenability?

• A. 0.60%; Silicon improves oxidation resistance and hardenability
• B. 0.10%; Silicon reduces oxidation
• C. 1.5%; Silicon increases weldability
• D. 0.05%; Silicon improves magnetic characteristics

Answer: (B)

Silicon in steel mainly boosts oxidation resistance at high temperatures and increases hardenability when used in moderate amounts. It does this in two ways. First, silicon promotes the formation of a protective oxide layer on the surface (silicon oxide) during high-temperature exposure, which slows down the rate of oxidation compared with silicon-free steel. Second, silicon affects the transformation behavior of austenite during cooling: it slows carbon diffusion and shifts the transformation, making it easier for martensite to form in thicker sections, which enhances hardenability. In practice, roughly around 0.6% silicon is a common level that yields noticeable improvements in both oxidation resistance and hardenability, without introducing excessive brittleness or welding difficulties.