A practical map of stainless grades for buyers:

Austenitic (300 series) • 304 / 304L — general purpose, food equipment, architecture. 304L for welded parts. • 316 / 316L — molybdenum added; coastal, chemical, medical, food with chlorides. • 321 / 347 — titanium/niobium stabilised for high temperature. • 310S — high nickel/chromium for furnace and high-temperature service.

Ferritic (400 series) • 430 — decorative, appliances, dry indoor use; magnetic, lower cost. • 409 / 439 / 441 — automotive exhaust; 439/441 for hotter or more corrosive sections.

Martensitic • 410 / 420 / 440C — cutlery, blades, valves, bearings; hardenable, lower corrosion resistance.

Duplex • 2205 — high strength + chloride resistance; chemical, seawater, FGD. • 2507 — super duplex for severe seawater and oil & gas.

Precipitation hardening • 17-4PH (630) — high strength + moderate corrosion resistance; aerospace, medical, precision parts.

Nickel alloys / super-austenitic • 904L, 254SMO, 6% Mo — aggressive acids and high-chloride service.

How to use the chart: identify the environment first (chlorides, temperature, acid), then the mechanical requirement (strength, hardness), then the fabrication method (welding, deep drawing). Grade selection is a trade-off between corrosion, strength, weldability and cost — not a single "best" grade.