Stainless steel classification by chemistry — identify the grade from 16–18% Cr and ~0.12% C A steel containing approximately 16 to 18% chromium and about 0.12% carbon (with little or no nickel) is best described as which type of stainless steel?

Introduction / Context:
Stainless steels are grouped by metallurgical structure: ferritic (BCC), austenitic (FCC), martensitic (BCT/BCC), and duplex (mixed). Composition, especially chromium, carbon, and nickel, largely determines which family a given steel belongs to and therefore its properties and applications.

Given Data / Assumptions:

• Chromium content ~16–18%.
• Carbon about 0.12% (low to moderate).
• No explicit nickel addition.

Concept / Approach:
Ferritic stainless steels are chromium-only stainless grades (typically 11–30% Cr) with very low carbon, stabilizing the ferrite (BCC) phase at room temperature. Martensitic grades usually have 12–18% Cr but need higher carbon (often 0.15–1.2%) to form martensite and achieve hardenability. Austenitic grades (e.g., 18-8) require significant nickel (and sometimes manganese or nitrogen) to stabilize FCC; the prompt does not include nickel. Thus, a 16–18% Cr steel with about 0.12% C and little Ni fits the ferritic class.

Step-by-Step Solution:

Verification / Alternative check:
Common ferritic grades (e.g., Type 430) have ~16–18% Cr and low C, matching the description.

Why Other Options Are Wrong:

• Austenitic: would require Ni ~8–10% or more.
• Martensitic: generally higher carbon for quench hardening.
• Nickel steel: generic term, not a stainless classification here.
• Duplex: would list both Cr and significant Ni (and N), not implied.

Common Pitfalls:
Assuming any 16–18% Cr is austenitic because of the “18”; overlooking the nickel requirement.

Final Answer: