Stainless steel 304

The workhorse stainless: 18% chromium, 8% nickel, non-magnetic as supplied, and about 90% of the stainless you meet indoors. Its thermal conductivity is 16 W/(m·K) against mild steel's 50, which is why a stainless pan has hot spots and why stainless is slow and grabby to machine — the heat stays in the cutting edge. It expands about 45% more than carbon steel per degree, so mixed-metal assemblies and stainless-lined chimneys need that designed in.

Properties

Density

8,000 kg/m³ — 8.00 g/cm³

Melting range

1400–1455 °C

Tensile strength

515–750 MPa

Young's modulus

193 GPa

Thermal conductivity

16.2 W/(m·K)

Thermal expansion

17.3 µm/(m·K)

Floats in water

No

Magnetic

No

What it is used for

• Sinks, kitchen worktops and catering equipment
• Food and brewing vessels
• Balustrades and architectural trim
• Domestic cutlery and cookware

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.