Stainless steel 316

Mechanically almost identical to 304; the difference is 2-3% molybdenum, which is what resists chloride pitting. That single change is why 316 is specified for anything near salt water or swimming pools, where 304 develops brown pinprick stains within a season. It is not stainless in the absolute sense — stagnant salt water under a crevice will still pit it — so marine fittings are designed to drain and rinse.

Properties

Density

8,000 kg/m³ — 8.00 g/cm³

Melting range

1375–1400 °C

Tensile strength

485–680 MPa

Young's modulus

193 GPa

Thermal conductivity

16.3 W/(m·K)

Thermal expansion

15.9 µm/(m·K)

Floats in water

No

Magnetic

No

What it is used for

• Marine deck fittings and rigging
• Chemical and pharmaceutical plant
• Surgical instruments and implants
• Coastal architectural fixings

How it compares

Does it rust?

Not under normal conditions. The chromium content — at least 10.5% — forms a thin, self-repairing chromium oxide layer that seals the surface. It can still corrode where that layer is starved of oxygen or attacked: crevices, chloride exposure and contamination by ordinary steel particles all cause it. 316 resists chlorides considerably better than 304.

Is it magnetic?

Austenitic stainless — the 300 series — is not magnetic in its annealed state, because its crystal structure is face-centred cubic rather than body-centred. Cold working can make it slightly magnetic at bends and cut edges. This is why a fridge magnet cannot tell you whether something is stainless: the 400-series grades are strongly magnetic and equally stainless.