Stainless Steel
Stainless Steel AISI/SAEIron-carbon alloy containing at least 10.5% chromium, which forms a passive oxide layer that resists corrosion and staining.
Stainless steels contain a minimum of 10.5% chromium, which forms a passive chromium oxide layer that resists corrosion. With over 150 grades in five metallurgical families — austenitic, ferritic, martensitic, duplex, and precipitation-hardening — stainless steels serve applications from kitchen sinks to nuclear reactor internals.
Designation Guide
The AISI 300 series (austenitic) includes the ubiquitous 304 (18Cr-8Ni) and 316 (with molybdenum for chloride resistance). The 400 series covers both ferritic (e.g., 430) and martensitic (e.g., 420, 440C) grades. Duplex grades use UNS numbers (S31803/S32205 for standard duplex, S32750/S32760 for super duplex). Precipitation-hardening grades (17-4PH, 15-5PH) combine corrosion resistance with high strength.
Selection Tips
Start with 304 for general corrosion resistance. Step up to 316L for chloride environments or welded constructions (L = low carbon, prevents sensitization). Consider duplex 2205 when you need double the yield strength of 304 in chloride service. For cutlery and surgical instruments requiring hardening, choose martensitic 420 or 440C. Always verify PREN (pitting resistance equivalent number) when selecting for seawater or chemical service.