Article
Most stainless piping is austenitic: 304, 316 and their variants. The 400 series is different. These grades contain little or no nickel, are magnetic, and have properties that suit specific jobs better than any austenitic grade.
SS 410 – martensitic
- About 11.5–13.5% chromium, low nickel, carbon up to 0.15%.
- Can be hardened by heat treatment, giving high strength and wear resistance.
- Moderate corrosion resistance – good in mild atmospheres, steam and some petroleum service, but below 304.
- Used for pump shafts, valve trim, steam and gas turbine parts, refinery piping in mild service, and wear-resistant applications.
SS 446 – ferritic
- About 23–27% chromium, no significant nickel.
- Excellent resistance to oxidation and sulphur-bearing atmospheres at high temperature, up to roughly 1100 °C.
- Cannot be hardened by heat treatment; lower toughness, especially at low temperature and after long high-temperature exposure.
- Used for furnace parts, annealing boxes, burner nozzles, recuperators and glass and kiln equipment.
Comparison with 304
| Property | 410 | 446 | 304 |
|---|---|---|---|
| Structure | Martensitic | Ferritic | Austenitic |
| Magnetic | Yes | Yes | No (slightly when cold worked) |
| Hardenable | Yes | No | No (only by cold work) |
| Aqueous corrosion | Moderate | Good | Good |
| Sulphur atmospheres at high temperature | Fair | Excellent | Fair |
| Weldability | Needs preheat and PWHT | Limited, brittle HAZ | Excellent |
Fabrication cautions
410 needs preheat and post-weld heat treatment to avoid cracking. 446 develops a coarse, brittle grain in the heat-affected zone, so welding should be kept to a minimum and handled by experienced fabricators.
Ordering
Pipe 2" SCH 40, ASTM A268 TP446-1 / ASTM A268 TP410, seamless, annealed
Ferritic and martensitic tubing and pipe are commonly ordered to ASTM A268; confirm the specification required by your drawing.
Frequently asked questions
Is 410 stainless magnetic?
Yes. Both 410 and 446 are magnetic because of their martensitic and ferritic structures.
Why use 446 instead of 310S?
446 has very good resistance to sulphur-bearing atmospheres at high temperature and contains no nickel, which can make it more economical.
Can 410 be hardened?
Yes. 410 is martensitic and can be hardened and tempered.
Key takeaways
- 410 is hardenable and wear resistant with moderate corrosion resistance.
- 446 excels in hot oxidising and sulphur-bearing atmospheres.
- Both are magnetic and need care when welding.
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