In steel, aluminum can be used up to 0.20% as a deoxidizer. What is another effect of aluminum in steel?

• A. Lessens grain growth by forming dispersed oxides or nitrides
• B. Increases electrical conductivity
• C. Up to 0.20% is used as a deoxidizer
• D. Always improves weldability

Answer: (C)

Aluminum in steel does more than deoxidize; it acts as a grain refiner by forming fine, stable oxide or nitride particles that stay dispersed in the metal. These dispersed particles pin grain boundaries during solidification and subsequent heat treatment, which slows grain growth and leads to a finer grain structure. A finer grain size typically improves toughness and can influence other properties, making aluminum’s secondary effect one of grain refinement through oxide or nitride dispersions.

Why the other ideas aren’t as fitting: electrical conductivity in steel isn’t enhanced by aluminum additions; the presence of oxides and impurities usually reduces conductivity. Saying that up to 0.20% is used as a deoxidizer describes its deoxidizing role, not an extra effect. And weldability isn’t universally improved by aluminum in all steels or welding conditions, so that claim isn’t dependable.