Stainless Steels: Passivity, Families and Selection
Distinguish stainless-steel families and connect composition, microstructure, fabrication and corrosion resistance.
Why stainless steel resists corrosion
Sufficient chromium forms a thin self-repairing passive oxide. Film stability depends on alloy chemistry and service environment.
Main families
Austenitic, ferritic, martensitic, duplex and precipitation-hardening grades combine different phase structures, strengths and fabrication characteristics.
Localised corrosion
Chlorides can destabilise passivity and cause pitting or crevice corrosion. Molybdenum, nitrogen and chromium improve resistance, but temperature and geometry remain decisive.
Fabrication effects
Welding, cold work, heat tint and contamination can alter phase balance or passive-film quality. Post-fabrication cleaning may be essential.
Engineering takeaway
Select stainless steel by environment, fabrication route and required properties—not by the word stainless.