Stainless Steel – Reason for Corrosion Resistance Which element in stainless steel produces the protective passive film that gives the alloy its characteristic corrosion resistance?

Introduction:
Stainless steels are defined by their ability to resist rusting in many environments. This capability is tied to alloy chemistry. The question examines knowledge of the key element behind passivation.

Given Data / Assumptions:

• Typical stainless steels contain iron, chromium, and may include nickel, molybdenum, etc.
• Passivity arises from a very thin, adherent oxide film.
• We must identify the element primarily responsible.

Concept / Approach:

Chromium at around 10.5 percent or more enables formation of a stable chromium oxide film (Cr2O3) on the surface that self-repairs in the presence of oxygen, drastically reducing corrosion rates.

Step-by-Step Solution:

Verification / Alternative check:

Compare ferritic, austenitic, and martensitic grades: they all share chromium as the common backbone for corrosion resistance.

Why Other Options Are Wrong:

Carbon affects hardness but too much reduces corrosion resistance; sulphur promotes machinability but can harm corrosion behavior; vanadium and manganese play secondary roles unrelated to the primary passive film.

Common Pitfalls:

Confusing nickel's role (austenite stabilization) with the primary passivation role of chromium.

Final Answer:

Chromium