Stainless Steel Grades Chart: 304 vs 316, 410, 430

The key difference is that 316 contains 2.0–3.0% molybdenum, which 304 does not. Molybdenum dramatically improves resistance to chloride pitting and crevice corrosion, making 316 the standard choice for marine, coastal, chemical, and pulp/paper environments. Both grades have similar mechanical properties (304: 85,000 psi tensile, 35,000 psi yield; 316: 85,000 psi tensile, 35,000 psi yield in annealed condition), so the choice between them is driven by corrosion environment, not strength. 304 is generally less expensive than 316 because it lacks the molybdenum content. Use 304 for kitchen equipment, food processing, architectural trim, and dry indoor service. Use 316 for saltwater exposure, road salt, swimming pools, chemical handling, and any chloride-containing environment. Both are austenitic and nonmagnetic in the annealed condition.

It depends on the family. Austenitic grades (200 and 300 series — 304, 316, 321, 347, etc.) are nonmagnetic in the annealed condition but become slightly magnetic after cold working such as bending, drawing, or machining. Ferritic grades (405, 430, 446) and martensitic grades (410, 416, 420, 440-series, 431) are magnetic in all conditions. If a magnet sticks strongly to a stainless part, it is most likely a 400-series ferritic or martensitic grade. If it does not stick or sticks only weakly, it is most likely a 300-series austenitic grade. This magnetic test is a useful field indicator of family but not a definitive grade identification — only chemical analysis (XRF, optical emission spectroscopy, or full lab chemical analysis) can confirm a specific grade like 304 vs 316.

Only martensitic grades can be hardened by conventional heat treatment (austenitize, quench, temper). These include 410, 414, 416, 420, 431, and the 440-series (440A, 440B, 440C). The 440-series achieves the highest hardness — 440C reaches Rockwell C 60 and is used for bearings, ball valves, and surgical instruments. Austenitic grades (300 series) cannot be hardened by heat treatment but can be strengthened significantly by cold working — for example, 301 reaches 185,000 psi tensile in the full-hard condition. Ferritic grades (405, 430, 446) cannot be hardened by heat treatment — at their high chromium and low carbon, the alloy forms little or no austenite at high temperature, so there’s nothing to transform into martensite on quench. They gain modest strength from cold work but are normally used in the annealed condition.

Free-machining grades are designed to cut more easily by adding sulfur, selenium, or phosphorus to break chips. The most common are 303 (free-machining austenitic, sulfur-added — used for screw machine parts, shafts, valves, bolts, and bushings), 416 (free-machining martensitic — used for aircraft fittings, fasteners), 430F (free-machining ferritic — used for screw machine parts), and 420F (free-machining martensitic). Standard 304 and 316 are difficult to machine because they work-harden rapidly under cutting pressure. If your part requires extensive machining and the application allows it, specifying 303 instead of 304 substantially improves tool life and surface finish. Note that free-machining grades have reduced corrosion resistance and are not recommended for welded assemblies — the sulfur and selenium additions degrade weldability and chloride pitting resistance. For relative machinability ratings vs free-cutting B1112 steel, see our machinability chart.

For outdoor exposure away from saltwater, 304 is generally adequate. For coastal, marine, or chloride-rich environments (de-icing salt, pool chemistry, chemical processing, fertilizer handling), use 316 or 316L — the molybdenum content (2.0–3.0%) provides essential resistance to chloride pitting. For severe marine service such as sub-sea hardware or splash zones, 317 with 3.0–4.0% Mo offers further upgrade; for the most aggressive chloride environments engineers also specify duplex grades such as 2205 (UNS S32205, not listed in this chart — see ASTM A240). Avoid 400-series ferritic and martensitic grades for marine exposure — they have lower chromium and no nickel, and will rust readily in salt environments. 304L and 316L (low-carbon variants) should be specified when welding is involved to prevent intergranular corrosion.

304L has lower maximum carbon (0.03% vs 0.08% for standard 304). The lower carbon prevents chromium carbide precipitation at grain boundaries during welding — a phenomenon called sensitization that depletes chromium locally and causes intergranular corrosion in service. 304L has slightly lower strength (80,000 psi tensile vs 85,000 psi for 304 in the annealed condition). Specify 304L any time the part will be welded and exposed to a corrosive environment. The same logic applies to 316L vs 316 (0.03% C vs 0.08% C). For fabricated assemblies in food processing, chemical service, or marine use, the “L” grades are the safer specification.