304 vs 316 Stainless Steel: Which One Do You Need?

## Composition Both 304 (UNS S30400) and 316 (UNS S31600) are austenitic stainless steels in the 18-8 family, but their chemistry differs in one critical element. | Property | 304 | 316 | |----------|-----|-----| | Chromium | 18-20% | 16-18% | | Nickel | 8-10.5% | 10-14% | | Molybdenum | None | 2-3% | | Carbon (max) | 0.08% | 0.08% | | UNS | S30400 | S31600 | The 2-3% molybdenum in 316 is the defining difference. Molybdenum strengthens the passive film against chloride ion attack, raising the pitting resistance equivalent number (PREN) from approximately 18 for 304 to approximately 25 for 316. ## Mechanical Properties In the annealed condition, both grades have similar mechanical properties: | Property | 304 | 316 | |----------|-----|-----| | Tensile Strength (min) | 515 MPa | 515 MPa | | Yield Strength (min) | 205 MPa | 205 MPa | | Elongation (min) | 40% | 40% | | Hardness (max) | 92 HRB | 95 HRB | Both grades are non-magnetic in the annealed condition, though cold working can induce some martensite in 304 (making it slightly magnetic), while 316 is more stable due to its higher nickel content. ## Corrosion Resistance 304 performs well in mild atmospheric, freshwater, and many chemical environments. It resists oxidizing acids like nitric acid and most organic acids. However, 304 is vulnerable to pitting and crevice corrosion in chloride-containing environments, particularly warm seawater, brackish water, and de-icing salt solutions. 316 handles all the same environments as 304 plus chloride-bearing media. It resists pitting in coastal atmospheres, swimming pool environments, and dilute sulfuric acid. For marine hardware, pharmaceutical equipment, and chemical processing where chlorides are present, 316 is the standard choice. ### Low-Carbon Variants 304L (0.03% C max) and 316L (0.03% C max) resist sensitization during welding. For welded fabrications, specifying the L grade prevents intergranular corrosion in the heat-affected zone. ## Cost and Availability 316 typically costs 20-30% more than 304 due to the molybdenum and higher nickel content. Both are readily available in all product forms: sheet, plate, bar, tube, pipe, and fittings. 304 accounts for roughly 50% of all stainless steel production worldwide. ## When to Choose Each **Choose 304 when**: The environment is free of significant chlorides, the application is indoor or mild atmospheric, and cost is a factor. Common applications include kitchen equipment, food processing (non-saline), architectural trim, and general chemical equipment. **Choose 316 when**: Chlorides are present (coastal, marine, chemical processing with HCl or NaCl), the application involves pharmaceutical or medical equipment (316L is the standard surgical stainless), or the environment includes reducing acids like sulfuric or phosphoric acid.