Metallurgy — crystal structure of austenitic stainless steels Austenitic stainless steels are characterized by which crystal structure at room temperature?

Introduction / Context:
Austenitic stainless steels (e.g., 304, 316) are widely used for their corrosion resistance and formability. Their mechanical and physical properties are directly influenced by their crystal lattice.

Given Data / Assumptions:

• Nickel-stabilized or nitrogen-stabilized stainless compositions.
• Room-temperature structure is considered.

Concept / Approach:
Austenite denotes the gamma phase of iron, which is FCC. Alloying with nickel and other elements stabilizes this FCC austenitic structure at room temperature in these stainless grades. FCC lattices typically provide good ductility and toughness.

Step-by-Step Solution:
Recall: ferritic stainless → BCC; martensitic → BCT; austenitic → FCC.Therefore, for austenitic stainless steel, the correct structure is FCC.

Verification / Alternative check:
Phase diagrams and X-ray diffraction data for 18-8 stainless steels confirm FCC (γ-Fe) at ambient temperature.

Why Other Options Are Wrong:

• Simple hexagonal: not applicable to austenitic stainless steels.
• BCC: corresponds to ferritic stainless steels, not austenitic.
• None of these: incorrect since FCC is correct.

Common Pitfalls:

• Confusing the terms “austenitic” with “martensitic” or “ferritic,” which have different lattices and properties.

Final Answer:
Face-centered cubic (FCC)