Question

Corrosion resistance of steel is increased by adding

• A. Chromium to nickel
• B. Nickel to molybdenum
• C. Aluminum to zinc
• D. Tungsten to sulphur

Hint:

Stainless steels contain at least \textbf{10.5\% chromium}, which forms a \textbf{passive oxide layer} that prevents rusting and oxidation, ensuring longer material lifespan in harsh environments.

Answer 1

The Correct Option is A

Corrosion resistance in steel is significantly enhanced by the inclusion of alloying elements that form protective oxide layers or improve passivation, a process where the material becomes less reactive. Step 1: Understanding Alloying for Corrosion Resistance - The combination of chromium and nickel is commonly used to make stainless steel, which exhibits enhanced resistance to corrosion. - Chromium, when added to steel, forms a thin, stable oxide layer on the surface, protecting the material from further oxidation (rusting). - Nickel further enhances this property by improving toughness, strength, and resistance to corrosion in various environments.


Step 2: Evaluating the Options - Option (A) - Correct: Stainless steel contains at least 10.5\% chromium and nickel to improve its corrosion resistance. - Option (B) - Incorrect: While nickel and molybdenum can improve hardness and strength, molybdenum is more effective at enhancing creep resistance rather than directly influencing corrosion resistance. - Option (C) - Incorrect: Aluminum and zinc are used for galvanization to protect steel from corrosion, but they are not added directly to enhance steel's inherent corrosion resistance. - Option (D) - Incorrect: Tungsten is used for increasing wear resistance, while sulfur tends to decrease toughness and make the material more brittle, hence not effective for corrosion protection.


Step 3: Conclusion By adding chromium to nickel, the corrosion resistance of steel is greatly enhanced, making option (A) the correct answer.