Updated:
The key difference: molybdenum
| SUS304 | SUS316 | |
|---|---|---|
| Equivalent grades | AISI 304 · EN 1.4301 | AISI 316 · EN 1.4401 |
| Chromium (Cr) | ≈ 18–20% | ≈ 16–18% |
| Nickel (Ni) | ≈ 8–10.5% | ≈ 10–14% |
| Molybdenum (Mo) | None | ≈ 2–3% |
| Chloride resistance (sea water, salt, chemicals) | Moderate | Clearly better |
| Material cost | Lower | Higher |
Molybdenum gives 316 much better resistance to pitting and crevice corrosion where chloride ions are present. That is why 316 is used near the sea, in food processing with brine, in pharmaceuticals and chemical plants.
When to choose SUS304
- Dry indoor environments without salt or aggressive chemicals.
- Machine parts, fixtures, enclosures and frames in typical factories.
- A2 stainless fasteners for general assembly.
When to choose SUS316 / 316L
- Coastal outdoor equipment, marine and water-treatment applications.
- Food, beverage and pharmaceutical equipment exposed to brine or chlorinated cleaners.
- Welded parts: use 316L (low carbon) to reduce corrosion in the heat-affected zone.
- A4 stainless fasteners for harsh environments.
Does it matter for CNC machining?
Both are tough and work-harden during cutting, so they need sharp tools, an adequate feed and good coolant; 316 is usually slightly harder to machine. For parts that need only general rust resistance and heavy machining (threading, deep drilling), SUS303 – a free-machining grade – is worth considering, though it is less corrosion-resistant than 304 and not suitable for welding.
Is stainless steel magnetic?
Annealed 304 and 316 are essentially non-magnetic. After cold work (stamping, drawing, bending) they may become slightly magnetic – this is normal and does not mean the material is fake. The reliable way to confirm the grade is a mill test certificate or XRF/PMI analysis.
Duc Huy Intech machines parts and supplies fasteners in SUS303, SUS304 and SUS316/316L, with material certificates on request. Not sure which grade fits? Send us your drawing and operating environment – we will advise before quoting.