Is 310 Stainless Steel Magnetic? Austenite Stability and Cold Working Effects
Apr 03, 2025
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Is 310 Stainless Steel Magnetic?
310 stainless steel (UNS S31000) is a fully austenitic grade containing approximately 24–26% chromium and 19–22% nickel. Its austenitic (face-centred cubic) microstructure is essentially non-magnetic in the annealed condition. In practice, however, magnetism can appear after cold working or welding, and understanding why helps engineers decide whether 310 is suitable for magnetism-sensitive applications.
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310 stainless steel plate
310 stainless steel pipe
310 stainless steel coil
Magnetic Behaviour in the Annealed Condition of 310 Stainless Steel
Effect of Cold Working of 310 Stainless Steel
Cold working - cold drawing, cold rolling or severe bending - can transform part of the austenite into strain-induced martensite, which has a body-centred cubic (BCC) structure and is weakly magnetic. The extent of this transformation depends on the austenite stability of the grade. Because 310 contains 19–22% nickel, its austenite is much more stable than that of 304 (8–10.5% Ni): strain-induced martensite forms only after heavy deformation, and the magnetism produced is usually weaker than that of 304 cold-worked to the same degree.
Effect of Welding or Heat Treatment of 310 Stainless Steel
The welding thermal cycle can locally change the crystal structure of the heat-affected zone, forming small amounts of ferrite or martensite and causing slight magnetism in and around the weld. This is a localised effect: the base material away from the weld remains non-magnetic. If required, the austenitic structure can be restored and the magnetism eliminated by solution annealing at about 1010–1120°C followed by rapid cooling (water or fast air cool), per the applicable specification.
310 vs 304: Comparison
| Property | 310 (UNS S31000) | 304 (UNS S30400) |
|---|---|---|
| Nickel content | 19–22% | 8–10.5% |
| Austenite stability | Very high | Moderate |
| Magnetism after cold working | Weak, only after heavy deformation | More pronounced (strain-induced martensite) |
| Typical relative permeability (annealed) | ≈ 1.02–1.05 | ≈ 1.02–1.08 (higher after cold work) |
| High-temperature resistance | Excellent (oxidation resistance to about 1000–1100°C in service) | Good (about 870°C continuous) |
| Cost position | Higher (Ni content) | Lower |
Values are typical; exact permeability depends on product form, processing history and measurement conditions.
High nickel content significantly enhances austenite stability. The austenite phase is resistant to decomposition at high temperatures, which suppresses the precipitation of ferrite and brittle sigma phase. Meanwhile, high chromium forms a dense oxide scale, enabling long‑term service up to 1050‑1100 ℃ in oxidizing atmospheres.
Practical Guidance of 310 Stainless Steel
For annealed plate, sheet, pipe or bar, 310 can be treated as non-magnetic in design.
After heavy cold forming (deep drawing, severe bending) or welding, verify the actual magnetic response if the application is magnetism-sensitive; a small magnet test is not a substitute for permeability measurement with a calibrated instrument.
Where absolute non-magnetism is required after fabrication, specify solution annealing after forming or welding, and verify by permeability measurement.
The presence of weak magnetism in a cold-worked or welded area is not a defect and does not reduce corrosion resistance or mechanical performance.
Summary
310 stainless steel is non-magnetic in the annealed condition, with a relative permeability near 1.0. Cold working can induce weak magnetism through strain-induced martensite, and welding can create small local amounts of ferrite or martensite - but both effects are weaker than in 304 because of 310's higher nickel content, and both can be eliminated by solution annealing. For magnetism-sensitive high-temperature applications, 310 is a suitable choice provided the fabrication history is controlled.
Applications of 310 Stainless Steel
1.Industrial Furnace & Heat‑Treatment Equipment (Primary Application)
Furnace liners, annealing covers, retorts, radiant tubes, furnace supports, kiln cars, burners, combustion chambers. Resists oxidation under repeated heating‑cooling thermal cycles.
2.Petroleum & Petrochemical Industry
Catalytic reformer furnace tubes, cracking units, high‑temperature reactors, furnace components, flare tips, tube hangers. Suitable for oxidizing and moderate carburizing atmospheres.
3.Power & Energy Generation
Boiler high‑temperature components, superheater hangers, coal‑gasifier internals, pulverized‑coal burners, high‑temperature flue‑gas piping, waste‑incinerator parts against hot flue‑gas corrosion.
4.High‑Temperature Chemical Process Units
High‑temperature reactor linings, process piping and heat exchangers for hot gas and sulfur‑bearing flue gas. Not recommended for brine or seawater service.
310 Radiant Tube
310 High-Temperature Heat Exchanger Piping
310 Boiler thermal pipelines
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FAQ
1.What is the difference between 310 and 310S stainless steel?
310S (UNS S31008) is low‑carbon version with C ≤0.08%. It minimizes intergranular carbide precipitation after welding, preferred for welded structures. Standard 310 has higher carbon content, delivers better creep‑rupture strength, suitable for non‑welded high‑temperature components. 310H (S31009) is high‑carbon grade for heavy‑duty high‑temperature pressure parts.
2.Can 310 / 310S resist chloride corrosion such as seawater?
No. 310 series is designed for high‑temperature oxidation resistance. Its resistance to chloride pitting and stress corrosion is poor. It shall not be used for seawater, brine or wet chloride‑containing environments. Choose 2205 / 2507 duplex steel for chloride service. 中文：不可以.
3.What information should I provide when ordering 310 series products?
Please specify grade (310 / 310S / 310H), product form (plate, pipe, tube, bar, forging), applicable standard (ASTM A240 / A310 / EN 10095), dimension, surface finish, quantity, and special testing requirements.
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