Stainless grades.
304. 316. Duplex.
Corrosion resistance.
Stainless steel alloys — austenitic, ferritic, martensitic, duplex, precipitation-hardenable. Each suits different applications. Choose by corrosion environment, strength needs, fabrication requirements.
Key principles.
General-purpose
18-8 austenitic. General-purpose corrosion. Indoor and mild outdoor.
Marine grade
18-10-2 (Mo). Marine, food, mild chemical. Standard chemistry.
Severe service
22-5-3 duplex. 2× 316L strength. Severe marine, chemical.
Hardenable
Precipitation-hardenable. Strength to 1300 MPa. Aerospace, medical.
Hardenable martensitic
Heat-treatable. Cutlery, valves, surgical instruments.
Magnetic
Cheaper than austenitic. Appliance trim, decorative.
FAQ
304 vs 316L?
316L has 2-3% Mo, much better chloride/marine corrosion resistance. 304 sufficient for indoor, food, mild environments.
When duplex?
Severe marine (offshore, saltwater immersion), chloride process, where 316L pits. 30-50% premium over 316L.
Hardenable stainless?
Martensitic (410, 420) and PH (17-4) hardenable. Austenitic (304, 316L) cannot through-harden. Choose per strength needs.
Magnetic vs non-magnetic?
Austenitic (304, 316) non-magnetic. Ferritic (430) and martensitic (410) magnetic. Important for some applications.
Welding?
All weldable. L grades (304L, 316L) lower carbon, better welding. Duplex requires controlled heat input.
Cost ranking?
430 cheapest. 304 mid. 316L premium. Duplex/PH grades highest. Cost ratio approximately 1:2:3:4.