Understanding Magnetism in Stainless Steel
When engineers ask for non magnetic stainless steel, what they really care about is how the alloy behaves in a magnetic field and whether it will interfere with equipment. To choose the right grade, we have to start with the basics of magnetism in metals.
Ferromagnetic vs Paramagnetic vs Diamagnetic
In stainless steel and other metals, you’ll mainly see three magnetic behaviors:
- Ferromagnetic
- Strongly attracted to a magnet
- Can retain magnetism (can be permanently magnetized)
- Typical for carbon steel, ferritic stainless, martensitic stainless
- Paramagnetic
- Weakly attracted to a magnetic field
- Does not retain magnetism when the field is removed
- Typical for austenitic stainless steel in the fully annealed condition
- Diamagnetic
- Very weakly repelled by a magnetic field
- Effect is so small it’s usually irrelevant in stainless selection
- Seen in materials like copper, but not a design driver here
In practice, when buyers say “non-magnetic stainless,” they usually mean paramagnetic austenitic grades with very low magnetic permeability.
Crystal Structure: Austenitic vs Ferritic vs Martensitic
Magnetism in stainless steels is controlled mainly by crystal structure:
- Austenitic stainless steel (FCC structure)
- Examples: 304, 304L, 316, 316L, 904L
- Face-centered cubic (FCC) structure
- Inherently non-magnetic / low magnetic in solution-annealed condition
- Can pick up some magnetism after cold work or welding
- Ferritic stainless steel (BCC structure)
- Examples: 409, 430, 446
- Body-centered cubic (BCC) structure
- Strongly ferromagnetic
- Remains magnetic in all normal conditions
- Martensitic stainless steel (BCT structure)
- Examples: 410, 420, 440C
- Body-centered tetragonal (BCT) structure
- High hardness and strongly magnetic
- Used where wear and strength are more important than low magnetism
- Duplex stainless steel (mixed austenite + ferrite)
- Examples: 2205, 2507
- Mixed structure: typically ~50% ferrite, 50% austenite
- Moderately to strongly magnetic due to ferrite phase
If you need non magnetic stainless steel for MRI, electronics, or instruments, you should always start with an austenitic base grade.
Cold Working, Phase Transformation, and Magnetism
Even austenitic stainless steel can become partly magnetic after fabrication:
- Cold working (bending, deep drawing, forming, cold rolling)
- Deformation transforms some austenite (γ) into martensite (α’)
- This strain-induced martensite is ferromagnetic
- Result: increased magnetic response, especially on edges, bends, and highly worked zones
- Machining
- Heavy machining, threading, and cold-forming fasteners can raise local magnetism
- Bars, wires, and cold-drawn products will often show higher μr than annealed plate
- Welding
- Heat-affected zones and weld metal can have different phase balance
- Pick-up of δ-ferrite in welds can increase magnetism slightly
To keep stainless steel truly low-magnetic, we control alloy design, annealing, and cold work level very tightly.
Magnetic Permeability Ranges by Stainless Family
Magnetic behavior is best quantified by relative magnetic permeability (μr):
- μr = 1.0 → perfect vacuum (no magnetism)
- μr just above 1.0 → weak magnetic response (practically “non-magnetic”)
- Higher μr → stronger magnetic response
Typical μr ranges (guide values in annealed condition):
- Austenitic stainless steel (304, 316, 904L, etc.)
- Annealed, low cold work: μr ≈ 1.003 – 1.10
- For controlled low-magnetic grades: μr ≤ 1.05 or μr ≤ 1.01 can be specified
- Ferritic stainless steel (430, 446, etc.)
- Generally μr ≈ 500 – 2000+
- Strongly magnetic
- Martensitic stainless steel (410, 420, 440C)
- Typically μr ≈ 100 – 800
- Strongly magnetic
- Duplex stainless steel (2205, 2507)
- Mixed structure: μr ≈ 50 – 300
- Noticeably magnetic, not suitable where “non magnetic” is critical
When we supply non magnetic stainless steel coils, sheets, bars, pipes, and fasteners, we focus on austenitic grades and tightly controlled relative magnetic permeability so that the material behaves as required in your actual magnetic environment.
2. Truly Non‑Magnetic Stainless Steel Grades (2026 Update)
When people say “non magnetic stainless steel”, they usually mean austenitic stainless in a properly solution‑annealed condition, with relative magnetic permeability μr close to 1.00–1.02. That’s what we focus on and supply.
Key features of austenitic non‑magnetic stainless steel
- Crystal structure: FCC austenite = naturally non‑magnetic
- Nickel / N‑alloyed: Ni, N and sometimes Mn stabilize the austenite phase
- Low μr: In annealed condition typically μr ≈ 1.003–1.05
- Good combo: Non‑magnetic + high corrosion resistance + easy fabrication
- Warning: Cold‑working, bending, deep drawing, machining can locally raise μr (partial martensite formation)
Standard non‑magnetic stainless grades: 304, 304L, 316, 316L, 316Ti, 321
These are the global workhorses:
- 304 / 304L: General non‑magnetic stainless for equipment, structures, covers
- 316 / 316L: “Marine grade” with Mo, better pitting resistance, widely used around MRI and electronics
- 321 / 316Ti: Ti‑stabilized grades for higher temperatures and better control of carbides / magnetism after welding
We stock these as non‑magnetic stainless steel sheet, coil, pipe and bar in annealed condition, with controlled μr for technical users.
304 and 304L non‑magnetic properties and limits
- In theory: Annealed 304 / 304L is “practically non‑magnetic” (μr ≈ 1.02–1.10)
- In practice:
- Light magnet pull is common on heavily formed or cold‑rolled parts
- μr can jump above 1.10 after strong forming, bending, stamping
- Use 304L when:
- You weld a lot and want better corrosion + structure stability
- You need low carbon to keep properties stable near welds
If your project demands strict μr ≤ 1.05, 304/304L is acceptable but not ideal under heavy forming.
316 and 316L non‑magnetic behavior in real use
- Better corrosion resistance than 304 in marine, chemical, offshore
- In annealed condition:
- μr usually lower and more stable than 304, especially in 316L
- More reliable for electronics, MRI room fit‑out, medical frames
- After cold work:
- Still can pick up magnetism, but generally less than 304 for same deformation
For most non-magnetic stainless steel applications, 316L is the default upgrade when 304 is borderline.
Heat‑stabilized grades (316Ti, 321) for magnetism control
- 321 (Ti‑stabilized 304) / 316Ti (Ti‑stabilized 316):
- Designed to run at higher temperatures (e.g. 450–850 °C)
- Ti ties up carbon, reducing carbide precipitation and phase changes
- Help keep structure closer to austenitic after welding and thermal cycling
- Not “more non‑magnetic” on day one, but more stable against magnetism increase in high‑temp service.
Super‑austenitic non‑magnetic options
For harsh chemical or marine environments, high‑Ni, high‑Mo austenitic grades keep magnetism low and corrosion resistance high.
904L non‑magnetic performance
- High Ni (~24–26%) and Mo (~4.5%)
- Very low magnetic permeability in annealed condition
- Strong resistance to:
- Chloride pitting and crevice corrosion
- Sulfuric and phosphoric acids (within limits)
- Often used in:
- High‑end equipment, aggressive chemical lines
- Luxury products needing non‑magnetic + premium corrosion
254 SMO (S31254)
- Super‑austenitic with very high PREN (≥ 42)
- Excellent resistance in seawater, offshore, chlorinated process media
- Remains essentially non‑magnetic when properly annealed
- A good match for non-magnetic stainless steel for marine and offshore where duplex magnetism is unacceptable.
AL‑6XN and similar
- High Ni (~24%), Mo (~6%), N‑alloyed
- Designed for aggressive chloride + high purity environments
- μr very close to 1.0 in annealed state
- Common in semiconductor, pharma, ultra‑pure water systems needing non‑magnetic materials.
Nitronic non‑magnetic stainless alloys
The Nitronic family (austenitic, N‑strengthened) gives higher strength at still‑low μr.
Nitronic 50 (XM‑19)
- High strength austenitic with low magnetic permeability
- Much stronger than 316L, good corrosion resistance close to or above 316L
- Ideal for:
- Non-magnetic stainless steel fasteners, shafts, hardware
- Components needing strength + low μr (marine, lifting, subsea tools)
Nitronic 60
- Designed for galling and wear resistance
- Maintains low magnetism in annealed state
- Used in:
- Sliding parts, valve stems, wear rings, bushings where non‑magnetic + anti‑galling is needed.
Quick comparison table (typical ranges, not guaranteed values)
| Grade | Ni (%) | Mo (%) | PREN* (approx.) | Typical μr (annealed) | Common product forms |
|---|---|---|---|---|---|
| 304 / 304L | 8–11 | 0 | 18–19 | 1.02–1.10 | Sheet, coil, bar, pipe, fittings |
| 316 / 316L | 10–14 | 2–3 | 23–25 | 1.02–1.08 | Sheet, coil, bar, pipe, tube, fasteners |
| 321 | 9–12 | 0 | 18–19 | 1.02–1.10 | Sheet, tube, high‑temp parts |
| 316Ti | 10–14 | 2–3 | 23–25 | 1.02–1.08 | Sheet, pipe, high‑temp process |
| 904L | 24–26 | 4–5 | 33–36 | 1.005–1.05 | Sheet, coil, pipe, tank components |
| 254 SMO | 18–20 | 6–7 | 42–45 | 1.005–1.05 | Plate, bar, pipe for seawater/chemical |
| AL‑6XN | 23–25 | 6–7 | 44–46 | 1.005–1.03 | Tube, sheet, process equipment |
| Nitronic 50 | 11–13 | 1.5–3 | 28–30 | 1.005–1.05 | Bar, shafting, fasteners, chain, wire |
| Nitronic 60 | 8–9 | 0–0.75 | 20–22 | 1.01–1.05 | Wear parts, valves, nuts, bolts |
*PREN = Pitting Resistance Equivalent Number (higher = better chloride resistance).
How to choose between 304, 316L, 904L, Nitronic and others
Use this as a quick decision guide:
- Mild environment, light magnetism tolerance (μr ≤ ~1.10)
→ 304L (cost‑effective, widely available) - Marine, light chemical, MRI room fit‑out, better magnetism stability
→ 316L (global standard non‑magnetic stainless for serious jobs) - Aggressive chloride / chemical, premium equipment, strict low μr
→ 904L or AL‑6XN / 254 SMO (super‑austenitic non‑magnetic) - Need high strength + low magnetic permeability
→ Nitronic 50 (shafts, fasteners, lifting and marine hardware) - Need wear / galling resistance + low μr
→ Nitronic 60
If you need guaranteed low‑μr non‑magnetic stainless steel in coils, sheets, pipes or bars, you can check our dedicated non‑magnetic stainless steel product range or browse our wider stainless steel coil/strip/plate catalog and we’ll match a grade and condition to your μr target.
Magnetic Permeability & Non‑Magnetic Stainless Standards
What relative magnetic permeability (μr) means
Relative magnetic permeability (μr) tells you how a stainless steel reacts to a magnetic field compared with vacuum (μr = 1.0).
- μr ≈ 1.0 → practically non‑magnetic
- Higher μr → stronger magnetic response, more interference risk
For non magnetic stainless steel used in sensitive environments, μr is as critical as chemical composition.
Typical μr thresholds for non‑magnetic stainless
In real projects, engineers usually define “non‑magnetic” by μr limits, not by a magnet test:
- General low‑magnetic requirement: μr < 1.05
- High‑precision / MRI / instrumentation: μr ≤ 1.01
When you specify non-magnetic stainless steel grades (304L, 316L, 904L, Nitronic, etc.), you should always set a clear μr limit, not just “non‑magnetic”.
Why μr matters in MRI, electronics, precision tools
Low magnetic permeability stainless is critical when magnetic fields must stay stable and predictable:
- MRI and medical imaging: avoid image distortion, signal noise, and force on components
- Electronics, semiconductor, test rigs: prevent field disturbance around sensors, coils and precision circuits
- Navigation, aerospace, defense: protect compasses, gyros and guidance systems from bias and drift
In these cases, a small change in μr makes a big difference in performance.
ASTM A342 – how magnetic permeability is tested
Magnetic permeability for stainless steel is normally verified to ASTM A342. Common methods include:
- Permeability indicator / test bar method – quick screening of μr on finished components
- Magnetometer / fluxmeter / Helmholtz coil method – more accurate μr values for certification
- Gaussmeter‑based setups – measure magnetic induction under defined fields
If you need guaranteed μr ≤ 1.01, you should insist on ASTM A342 test results, not just a “non‑magnetic” note.
EN 10088‑2 and ISO 7153‑1 requirements
For global buyers, the main reference standards are:
- EN 10088‑2: defines grades, conditions, and typical magnetic behavior for flat stainless products
- ISO 7153‑1: specifies stainless steels for surgical instruments, including non‑magnetic austenitic grades and their expected magnetic response
We align our internal acceptance criteria with these standards when producing non-magnetic stainless steel sheet, coil, pipe and bar for medical, food, and industrial customers.
How MTCs show magnetic permeability
A professional Mill Test Certificate (MTC) should clearly state:
- Grade and condition (e.g. 316L, solution annealed)
- Test standard (e.g. ASTM A342 Method 3)
- Measured μr value or maximum μr range (e.g. μr ≤ 1.01 at 2 kA/m)
- Traceability to heat number and batch
If your current MTC only lists chemistry and tensile results, you are not yet controlling magnetism properly.
How Fullgreat Metal verifies μr for each batch
At Fullgreat Metal Limited, all non magnetic stainless steel coils, sheets, bars and pipes for MRI, electronics and precision tools go through μr control:
- 100% batch testing by calibrated magnetic permeability indicator
- Spot verification with Gaussmeter / magnetometer for critical projects
- Traceable reports attached to each shipment and linked to the MTC
Our QC system is built to the same discipline we use for our other precision products like high‑strength steel for automotive applications, with strict process and documentation control.
How to specify guaranteed low μr when ordering
To avoid disputes, you should lock the magnetic requirement directly into your PO or technical specification:
- State the maximum μr:
- Example: “Non‑magnetic stainless steel 316L, μr ≤ 1.01, tested to ASTM A342”
- Define product form & condition:
- Sheet, coil, bar, pipe; solution annealed; max cold work allowed
- Ask for:
- MTC with μr value
- Test method and calibration info
- Agreement that material outside the μr limit can be rejected or replaced
If you need help drafting a μr‑controlled spec for global sourcing or for your local MRI, semiconductor, food, or marine project, we can share standard clauses that our overseas customers already use successfully.
Key Advantages of Non‑Magnetic Stainless Steel
Why non‑magnetic stainless steel matters
Non‑magnetic stainless steel gives you stable performance anywhere magnetic fields are a problem. It combines low magnetic permeability with strong corrosion resistance and clean surface finish, so you can use one material across demanding sectors: medical, electronics, marine, food, aerospace, and more.
Benefits in sensitive electronic environments
In labs, cleanrooms, and semiconductor lines, magnetic noise kills accuracy. Low‑permeability austenitic and super‑austenitic grades keep instruments stable:
- Minimal distortion of weak signals and sensor readings
- Better stability for test fixtures, precision stages, and frames
- Safe to use near coils, transformers, and high‑frequency devices
Use non‑magnetic stainless steel sheet, coil, bar, and fasteners where you’d normally avoid steel because of magnetic pickup.
Zero interference in MRI and medical devices
For MRI and imaging rooms, magnetism is a hard stop. Non‑magnetic stainless steel is the go‑to structural and hardware material because it:
- Keeps image quality clean – no ghosting or distortion from ferromagnetic parts
- Allows safe fixtures, rails, tables, housings, and cabinets around MRI magnets
- Works well for surgical tools and medical device housings where both low μr and hygiene are critical
Most buyers here specify relative magnetic permeability μr ≤ 1.01 for key components.
Navigation, aerospace, and defense systems
Any system that relies on magnetic sensors or compasses needs non‑magnetic hardware:
- Structural frames and brackets near compasses and IMUs
- Fasteners, clamps, and connectors in avionics bays
- Submarine, UAV, and satellite parts where stray magnetism can shift readings
These applications typically use austenitic or super‑austenitic non‑magnetic stainless grades for both low μr and high strength-to-corrosion ratio.
Corrosion resistance: austenitic & super‑austenitic
Non‑magnetic usually means austenitic—and that’s a big plus for corrosion resistance:
- 304 / 304L – good general corrosion resistance, indoor and mild outdoor
- 316 / 316L – better pitting and crevice resistance in chloride and marine atmospheres
- 904L, 254 SMO, AL‑6XN – super‑austenitic, designed for aggressive chloride, acidic, and offshore environments
This lets you run non‑ferromagnetic hardware in places where standard stainless or coated carbon steel would fail early.
Marine, offshore, and chemical performance
For marine and process users, non‑magnetic stainless gives you both durability and stability around sensitive gear:
- Marine & offshore: deck hardware, winch components, pumps, non‑magnetic fasteners close to navigation systems
- Chemical processing: piping, heat exchangers, tanks, mixers exposed to chlorides, acids, and cleaning chemicals
Super‑austenitic options like 904L and 254 SMO bring very high PREN values, strong resistance to pitting, and reliable non‑magnetic behavior in annealed condition.
Low‑temperature toughness & impact
Austenitic non‑magnetic stainless steels keep their toughness at low temperatures:
- Excellent impact resistance down to cryogenic ranges
- No brittle fracture issues you see in ferritic or martensitic steels
- Good choice for LNG facilities, cold storage, and aerospace cryo lines needing non‑magnetic hardware
Hygiene and cleanability
Food, beverage, and pharma users pick non‑magnetic austenitic grades because they also meet hygiene and cleaning standards:
- Smooth surface, easy to polish and passivate
- Resistant to frequent CIP/SIP cycles, steam, and disinfectants
- Suitable for tanks, piping, conveyors, housings, and supports in hygienic design
You get food‑grade, corrosion‑resistant, non‑ferromagnetic performance in one material.
Lifecycle cost vs magnetic stainless
Non‑magnetic stainless often costs more upfront, but total cost usually drops over the life of the asset:
- Longer service life in corrosive or cleaned environments
- Fewer shutdowns from part replacement or coating failures
- No costly rework when magnetic interference shows up after installation
- Better resale and compliance in regulated industries (medical, aerospace, semiconductor, marine)
For some support structures that don’t need stainless, we also supply coated flat steels like our hot‑dip galvanized SGCC / SGCD / SGCE range when magnetism is not a concern and cost is the priority.
Quick comparison: why engineers choose non‑magnetic stainless
| Advantage | What you gain in real use |
|---|---|
| Low magnetic permeability (μr < ~1.05) | Stable measurements, safe use near MRI and sensors |
| Strong corrosion resistance | Longer life in marine, offshore, and chemical environments |
| Good toughness at low temperature | Safer performance in cryogenic and cold‑climate service |
| Hygienic and easy to clean | Compliance in food, beverage, and pharma plants |
| Flexible product forms | Sheet, coil, bar, pipe, and fasteners for full system builds |
| Lower lifecycle cost | Less downtime, fewer replacements, better long‑term value |
5. Industry Applications That Demand Non‑Magnetic Stainless Steel
Medical & MRI Equipment
Non magnetic stainless steel is standard in MRI and hospital environments because any magnetic pickup can distort images or pull parts toward the magnet.
We usually supply:
- 304L / 316L for MRI room structures, covers, cable trays, rails
- 316L / 904L / Nitronic 50 for MRI-compatible tables, brackets, cryogenic hardware
- 316L / 321 / ISO 7153‑1 grades for surgical tools and housings where low magnetism and easy cleaning matter
Result: stable images, no magnetic interference, and safe operation around high-field magnets.
Aerospace & Defense
Navigation and guidance systems must stay magnetically “quiet” so sensors stay accurate.
Typical non-magnetic stainless uses:
- Non-magnetic fasteners and fittings around compasses and magnetometers
- 316L / Nitronic 50 for satellite brackets, antenna parts, and structural hardware
- 904L / super-austenitic where both low magnetic permeability and harsh-environment resistance are required
This keeps heading data accurate and electronics stable, even in extreme conditions.
Electronics & Semiconductor
In high-precision electronics and semiconductor plants, stray magnetism can disturb beams, wafers, and test results.
We see strong demand for:
- Non-magnetic stainless steel sheet, coil, and bar for machine frames and cleanroom furniture
- 316L / 904L / Nitronic 50 for wafer handling tools, robot arms, precision fixtures
- Low μr (≤1.01) stainless for test fixtures, racks, vacuum chambers, and shielding
Non-magnetic stainless keeps instruments calibrated and yield rates high.
Test Fixtures, Racks & Vacuum Chambers
For labs, test houses, and vacuum systems, low magnetic permeability stainless is now a default spec.
Popular choices:
- 304L / 316L for frames, racks, and benches
- 316L / Nitronic 50 for ultra-low μr parts in magnetic test setups
- 904L / 254 SMO where test rigs also face corrosive or high-purity process gases
We can match non-magnetic stainless to standard carbon or cold-rolled steel frames when customers need mixed-material systems.
Food & Pharmaceutical Processing
Food, beverage, and pharma lines want hygiene + zero magnetic interference, especially near sensitive weighing and dosing equipment.
Use cases:
- 304L / 316L for tanks, conveyors, hoppers, and pipework
- 316L / 904L for CIP/SIP lines, high-chloride cleaning chemicals, and aggressive additives
- Non-magnetic stainless fasteners in mixer heads and filling machines to avoid metal pickup and contamination
Low magnetism also reduces the risk of “magnetic traps” in process flows.
Marine & Offshore
Marine and offshore customers need non-magnetic + corrosion-resistant hardware around navigation and communication gear.
We usually specify:
- 316L for non-magnetic deck hardware, rails, and housings
- 904L / 254 SMO / AL‑6XN for splash zones, high-chloride seawater, and chemical injection skids
- Nitronic 50 where strength, low μr, and seawater resistance must all be high
This keeps compass readings clean and hardware alive in salty, harsh service.
Luxury Watches & High‑End Consumer Products
Luxury brands use non magnetic stainless steel to meet anti-magnetic watch specs and premium feel.
Typical picks:
- 316L for most watch cases and bracelets
- 904L for high-end, corrosion-resistant watch bodies with excellent finish
- Special low‑μr austenitic or Nitronic grades for components around mechanical movements
Non-magnetic steels keep watches accurate near magnets, phones, and everyday electronics.
Real‑World Grade Choices (304L, 316L, 904L, Nitronic)
How global buyers usually match grades to applications:
- 304L
- Good for: non-critical frames, furniture, basic racks
- Limit: slightly higher magnetic pickup after heavy forming / welding
- 316L
- Good for: medical, marine, food, pharma, electronic frames
- Better chloride resistance, generally lower and more stable permeability in service
- 904L
- Good for: marine, offshore, luxury, chemical processing
- Used when both appearance and extreme corrosion resistance matter, while staying essentially non-magnetic in annealed condition
- Nitronic 50 / Nitronic 60
- Good for: high-load, wear, or highly sensitive low‑μr applications
- Nitronic 50 = high strength + very low permeability
- Nitronic 60 = better wear resistance with non-magnetic behavior
If you tell us your industry, μr target (for example, μr ≤ 1.01), and environment (chlorides, temperature, cleaning chemicals), we can narrow this down to one or two non-magnetic stainless steel grades that fit both technical and cost targets.
6. How to Test If Your Stainless Steel Is Really Non‑Magnetic
Quick magnet checks (but don’t stop here)
First filter test:
- Use a small strong magnet (not a weak fridge magnet).
- Non-magnetic stainless steel (austenitic, properly annealed) should show little to no attraction.
- If the magnet sticks strongly, you’re likely looking at ferritic, martensitic, or heavily cold‑worked austenitic steel.
Use this as a screening tool only, not as your final decision.
Limits of fridge magnet tests on 304 & 316
304, 304L, 316, 316L are designed to be non‑magnetic in the annealed condition, but in real life:
- Cold rolling, bending, deep drawing, and welding can transform some austenite to martensite.
- That martensite is magnetic, so a magnet may “slightly stick” even on true austenitic stainless.
- Result: a fridge magnet test can make good non‑magnetic stainless look “wrong” and get rejected for no reason.
If your project is critical (MRI, sensitive sensors, navigation instruments), never rely on this test alone.
Magnetic permeability indicator (on‑site test)
For proper on‑site verification, use a magnetic permeability indicator (Permeability Meter):
- Measures relative magnetic permeability (μr) directly, usually in the range 1.001–1.05.
- For “non-magnetic” stainless, most engineers target:
- General low‑magnetic use: μr < 1.05
- MRI / precision instruments: μr ≤ 1.01
- Fast, portable, easy to use on sheet, coil, bar, pipe, and finished parts.
When you buy non‑magnetic stainless from a supplier, this is the exact tool you want them to be using.
Laboratory Gaussmeter test (high accuracy)
For critical documentation and R&D, you can go to a lab and request:
- Gaussmeter / Teslameter testing to measure the magnetic field around the part.
- Combined with a calibrated magnet and fixture, labs can give you:
- Local magnetic field (Gauss or Tesla)
- Confirmation that parts meet μr limits under ASTM A342.
This is what many medical, aerospace, and semiconductor customers require in addition to mill certificates.
How cold working increases magnetism in austenitic stainless
Austenitic grades (304, 304L, 316, 316L, 904L, 254 SMO, AL‑6XN, Nitronic, etc.) start off nearly non‑magnetic when fully annealed. But:
- Cold rolling, bending, stamping, machining, threading, and forming can:
- Partially transform austenite → martensite.
- Increase magnetic permeability, sometimes above μr 1.05.
- The effect is strongest in high deformation zones: edges, bends, threads, deep draws.
So a coil can leave the mill non‑magnetic, then become “magnetic enough to fail spec” after processing at the fabricator.
How to reduce magnetic pickup during fabrication
If you want to keep your non‑magnetic stainless truly non‑magnetic, use these practices:
- Minimize cold work:
- Use larger bend radii.
- Avoid excessive forming in one hit; use multiple lighter passes.
- Go for machining rather than heavy cold forming when possible.
- Choose the right grade:
- 316L, 904L, 254 SMO, AL‑6XN, Nitronic 50 typically keep lower μr after forming than 304.
- Use proper tooling:
- Avoid contaminated tools and fixtures that may magnetize the surface.
- Demagnetize tools if needed.
Planning the process up front is cheaper than trying to fix magnetism at the end.
Annealing to restore low magnetic permeability
If your parts have picked up magnetism from cold work, solution annealing can help:
- Heat to the recommended solution anneal temperature (varies by grade, typically 1,040–1,120 °C for standard austenitic stainless).
- Hold to fully re‑austenitize the structure.
- Rapid water quench or fast cooling to avoid new precipitation.
- Result: martensite transforms back toward austenite, μr drops closer to 1.0–1.02.
Important:
- Full solution anneal is usually done at the mill or a certified heat treater, not in a normal workshop.
- Not all fabricated assemblies can be fully annealed (size, distortion, welds, surface finish limits), so again, it’s better to control cold work early.
Best practices for incoming inspection of non‑magnetic stainless
If you’re buying non‑magnetic stainless steel sheet, coil, bar, pipe, or fasteners, set a simple but strict incoming QC routine:
- Define the spec in the PO:
- Example: “Material must be austenitic stainless steel, solution annealed, with μr ≤ 1.01 (ASTM A342, Method 3).”
- Check documents:
- Mill Test Certificate (MTC) showing grade, heat treatment, chemistry (Ni, Cr, Mo), and magnetic permeability if available.
- Do quick shop tests:
- Magnet screening to catch obvious mix‑ups (ferritic/duplex instead of austenitic).
- Portable permeability meter spot checks, especially near edges or cold‑worked zones.
- Sample systematic batches:
- For high‑risk projects (MRI, aerospace, electronics), send periodic samples to a lab for Gaussmeter or full ASTM A342 testing.
By combining clear specs, proper paperwork, and simple on‑site tests, you can keep your non‑magnetic stainless supply chain under control and avoid expensive field failures.
Fullgreat Metal Limited – Non‑Magnetic Stainless Steel Supplier
Chinese Non‑Magnetic Stainless Steel Manufacturer
I run Fullgreat Metal as a focused non-magnetic stainless steel manufacturer in China. We specialize in austenitic and super-austenitic grades with controlled low magnetic permeability for MRI, medical, electronics, marine, and precision engineering projects worldwide.
- Location: China, serving Asia, Europe, North America, Middle East
- Focus: Non-magnetic stainless steel sheet, coil, pipe, bar, and precision parts
- Strength: Fast response for technical projects, flexible MOQs, stable quality
Factory Scale, Lines & Partnerships (Baosteel / TISCO)
We operate modern production and processing lines with stable raw material support:
- Strategic sourcing from Baosteel and TISCO for prime stainless slabs and coils
- Precision slitting, cutting, polishing, and machining workshops
- Independent finishing lines for low‑μr austenitic and super‑austenitic materials
For finished parts and hardware, we also supply custom components via our metal rods and bars production line.
Standard Stock Program – 304/304L, 316/316L, 904L
We keep regular stock of non‑magnetic stainless steel in common dimensions so you don’t wait:
- Grades: 304 / 304L, 316 / 316L, 904L (annealed, low‑magnetic condition)
- Forms: Sheet, plate, coil, strip, tube, pipe, round bar, flat bar
- Finish options: 2B, BA, No.4, HL, mirror, pickled & passivated
Non‑magnetic stainless steel coil, bar, and pipe are available for just‑in‑time shipments to OEMs.
Custom Melting, Rolling & Finishing
For tighter magnetic specs or special working conditions, we can tailor:
- Custom chemistry: Higher Ni / Mo / N for lower μr and higher corrosion resistance
- Rolling & annealing: Controlled solution annealing to reduce magnetic pickup
- Special finishes: Ultra-clean surfaces for semiconductor, vacuum, and medical users
If needed, we also deliver finished non‑magnetic metal parts through our in-house and partner metal parts manufacturing.
Quality Control & Third‑Party Certifications
Our quality system is built for export projects and critical installations:
- Certifications: ISO 9001, PED-compliant materials, DNV / ABS approvals on request
- Full heat traceability and batch records
- Chemical, mechanical, and microstructure testing in-house and via certified labs
Magnetic Permeability Testing & Documentation
For non‑magnetic stainless steel, we treat μr as a key parameter, not an afterthought:
- Batch testing of relative magnetic permeability (μr) using calibrated instruments
- Typical guarantees: μr ≤ 1.05, with μr ≤ 1.01 available for critical orders (on agreement)
- μr values clearly stated on Mill Test Certificates (MTC) and separate magnetism report if required
Global Shipping, Lead Times & Technical Support
We work directly with engineers, buyers, and project managers:
- Global shipping by sea or air, optimized packing for sheet, coil, bar, and pipe
- Standard sizes: short lead time from stock; specials: typically 2–6 weeks depending on spec
- Technical support on grade selection, μr requirement, fabrication tips, and documentation
How to Request Data Sheets, Samples & Prices
To move fast on your non-magnetic stainless project, you can:
- Send us your grade + product form + size + μr requirement (e.g. μr ≤ 1.01 or ≤ 1.05)
- Ask for material data sheets, MTC samples, and test reports for evaluation
- Request free small samples (where logistics allow) and a detailed price list / quotation
Share your drawing or spec, and I’ll match the right non‑magnetic stainless steel grade, delivery route, and testing package for your application.
8. Frequently Asked Questions on Non‑Magnetic Stainless Steel
Is 316 stainless steel completely non‑magnetic in all conditions?
No. Annealed 316 / 316L is “non‑magnetic” for most practical uses, but not absolutely zero.
After cold rolling, bending, deep drawing, or welding, some martensite can form and you’ll feel a light pull with a strong magnet. For strict low‑permeability jobs (MRI, instruments), I always recommend specifying 316L with μr ≤ 1.01 after final fabrication.
How does cold rolling or machining change magnetism in austenitic stainless?
Cold work is the main reason “non‑magnetic” stainless suddenly becomes magnetic:
- Cold rolling, forming, stamping → increases hardness and creates strain‑induced martensite → μr goes up.
- Heavy machining near edges → same effect in the surface layer.
- Solution annealing (proper heat treatment) after forming can bring μr back down close to 1.0.
If you need low magnetic permeability, always control cold work and ask for an annealed austenitic stainless steel condition.
Which non‑magnetic stainless grade has the lowest magnetic permeability?
Among commercial grades in normal supply:
- Super‑austenitic like 904L, 254 SMO (S31254), AL‑6XN
- Nitronic 50 (XM‑19)
These can typically be held in the range μr ≈ 1.003–1.01 when fully annealed and carefully processed. For ultra‑critical applications, Nitronic 50 is usually the go‑to low magnetic permeability stainless.
Can suppliers guarantee μr ≤ 1.01 and how is it tested?
Yes, but only if you specifically require it and the mill/factory is set up for it.
Typical testing:
- ASTM A342 – standard methods for measuring magnetic permeability
- Magnetic permeability indicator (handheld) – quick acceptance checks
- Lab tools like Gaussmeter/Permeability meter – for precise values
In my own factory, we test representative pieces from every low‑μr batch and record the relative magnetic permeability (μr) on the inspection report and MTC when customers ask for it.
304 vs 316 for non‑magnetic stainless – which should I choose?
It depends on environment and permeability requirement:
- 304 / 304L
- Cheaper, widely available
- Good “non‑magnetic” behavior when annealed
- Less corrosion resistance (not ideal for chloride or marine)
- 316 / 316L
- Better pitting/crevice corrosion resistance (Mo‑alloyed)
- More stable in marine, chemical, and food environments
- Better choice when you need non‑magnetic + corrosion resistance
If budget allows and conditions are even mildly aggressive, I recommend 316L non‑magnetic stainless over 304L.
Is 904L always non‑magnetic and when is it worth the extra cost?
904L is a high‑nickel, super‑austenitic grade. Properly annealed, it is very low magnetic and stays stable even after moderate forming. But:
- Extreme cold work can still create some magnetism.
- Cost is significantly higher than 316L.
It’s worth it when you need:
- Very strong corrosion resistance (chlorides, acids, seawater)
- Non‑magnetic stainless steel with long service life in harsh media
- Lower maintenance and longer uptime vs standard austenitic grades
For premium equipment or aggressive chemical/marine systems, 904L often pays back in lifecycle cost.
Are Nitronic 50 and Nitronic 60 better than 316L for non‑magnetic service?
In many demanding jobs, yes:
- Nitronic 50 (XM‑19)
- Very low magnetic permeability (μr near 1.0 when annealed)
- Much higher strength than 316L
- Excellent corrosion resistance, good for marine, offshore, shafts, fasteners
- Nitronic 60
- Designed for wear and galling resistance
- Low‑magnetic behavior plus outstanding sliding performance
- Ideal for non‑magnetic stainless fasteners, valves, and moving parts
If you need high strength + non‑magnetic + corrosion resistance, Nitronic 50 usually outruns 316L. For wear and anti‑galling, Nitronic 60 is the better pick.
What should I specify when ordering non‑magnetic stainless from a Chinese supplier?
If you want truly low‑magnetic material, be very clear in your PO:
- Grade & condition
- e.g. “316L, solution‑annealed, non‑magnetic stainless steel sheet/coil/bar”
- Magnetic permeability requirement
- e.g. “Relative magnetic permeability μr ≤ 1.01 after final annealing”
- Test standard
- “Magnetic permeability tested per ASTM A342”
- Product form & tolerance
- Sheet, coil, bar, pipe, fasteners, with thickness/size tolerances
- Certificates
- Mill Test Certificate (MTC) with chemistry, mechanicals, and μr values
- Third‑party inspection if needed (BV, SGS, etc.)
- Processing control
- “No heavy cold work after final annealing” when possible
If you need shaped or special profiles, you can also ask for custom non‑magnetic stainless steel bar, rod, or tube based on our special‑shaped steel and wire capabilities, and we’ll match the μr and mechanical requirements to your drawing.
