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Magnetic Stainless Steel Grades: The Complete 400-Series List & Why They Attract Magnets
When engineers and buyers talk about stainless steel, the assumption is often that it is non-magnetic — but that is only true for one family. There is a complete and widely used set of magnetic stainless steel grades that attract a magnet in every condition, and they are not a defect and not a lower-quality option. The 400 series — ferritic grades like 409, 430 and 439, and martensitic grades like 410, 420 and 440C — is the backbone of appliance trim, exhaust systems, magnetic latches, cutting tools and automated handling lines. This guide lists every common magnetic grade, explains the metallurgy behind why it is magnetic, and shows when to choose it over the non-magnetic austenitic family — with the global standard designations, the application logic and the sourcing checklist you need to buy it with confidence.
What Makes a Stainless Steel Magnetic? (BCC Structure in 30 Seconds)
Magnetism in stainless steel is controlled by crystal structure, not by quality or price. The magnetic grades have a body-centered cubic (BCC) atomic arrangement — the same structure as plain carbon steel — which allows magnetic domains inside the material to align under an external field and stay aligned once the field is removed. The non-magnetic austenitic grades (300 series) use a face-centered cubic (FCC) structure whose atoms do not support this alignment, so they remain paramagnetic with a relative permeability (μr) very close to 1.0.
The element that decides which structure a grade gets is nickel. Add enough nickel (roughly 8% or more, often combined with manganese and nitrogen) and the FCC austenite structure is stabilised at room temperature — the steel becomes non-magnetic. Remove the nickel and the BCC ferrite or martensite structure dominates — the steel is magnetic. This is why every 400-series grade is nickel-free or near-nickel-free, and why every 300-series grade contains 8% or more nickel. For the full metallurgy of the non-magnetic side — including the Schaeffler diagram and the role of austenite stabilisers — see our non-magnetic stainless steel definitive guide.
Two additional concepts matter on the shop floor. First, magnetic behaviour in the 400 series is not a surface effect — it runs through the full thickness of the material, so slitting, shearing and edge finishing do not remove it. Second, magnetic response can be strengthened by cold working: rolling, bending and stamping align the magnetic domains and refine the grain structure, so a hard-tempered 430 strip usually pulls a magnet more strongly than an annealed one. Neither effect ever makes a 400-series grade non-magnetic — it simply becomes “more magnetic”.
The 400-Series Family in Depth: Where Magnetism Comes From
The magnetic grades of stainless steel are divided into four sub-families, and each achieves its magnetic behaviour through a different microstructure.
Ferritic Grades: The Magnetic Workhorses
Ferritic stainless steels (409, 430, 439, 444) have a BCC ferrite structure at all temperatures. They are chromium-only alloys with little or no nickel, which keeps them magnetic in every condition — annealed, formed, welded or polished. Ferritic grades are the cheapest stainless steels, the most formable of the magnetic family, and the standard choice for decorative trim, automotive exhausts and magnetic assembly parts. Their main limitation is lower toughness in thick sections and a tendency to grain growth in the heat-affected zone of welds, which is why stabilised grades like 439 are preferred for welded assemblies.
Martensitic Grades: Magnetic and Hardenable
Martensitic stainless steels (410, 420, 440A/B/C) are also essentially chromium-only, but their higher carbon content allows them to be hardened by quench and tempering. In the annealed state they have a ferrite-like structure; after quenching they transform to a hard, strong martensite. Both structures are BCC or body-centered tetragonal (BCT), so the material is magnetic throughout. Martensitic grades trade formability for hardness — they cannot be deep-drawn like ferritic grades, but they can reach hardness levels of 50–60 HRC, which is why they dominate cutting tools, blades, bearings and wear parts.
Precipitation-Hardening Grades: Magnetic in Service
Precipitation-hardening grades such as 17-4 PH (SUS630, 1.4542) are austenitic or martensitic depending on condition. In the annealed condition 17-4 PH can appear weakly magnetic or even non-magnetic, but after the precipitation-hardening ageing treatment it transforms to martensite and becomes clearly magnetic. Buyers should never assume a PH grade is non-magnetic without verifying the specific heat treatment condition — a common source of field failures in aerospace and valve applications.
Duplex Grades: Magnetic Despite the Name
Duplex stainless steels (2205, 2507, 2304) contain roughly 50% austenite and 50% ferrite. The ferrite phase is ferromagnetic, so duplex grades are clearly magnetic even though they contain a large austenite fraction. This surprises many engineers who assume “contains austenite” equals “non-magnetic”. Duplex grades offer very high strength and excellent chloride stress-corrosion resistance, but they are not suitable for non-magnetic applications.
The Complete List of Magnetic Stainless Steel Grades
These are the grades that attract a magnet in all conditions, with their global standard designations so you can specify them correctly in any market:
| AISI / Grade | Family | JIS | EN / DIN | Key composition | Typical use |
|---|---|---|---|---|---|
| 409 | Ferritic | SUS409 | 1.4512 | ~11% Cr, Ti-stabilised | Exhaust systems, mufflers, heat shields |
| 430 | Ferritic | SUS430 | 1.4016 | 16–18% Cr, no nickel | Appliance trim, fridge doors, oven panels, decorative moulding |
| 439 | Ferritic | SUS439 | 1.4510 | 17–18% Cr, Ti-stabilised | Automotive, heat exchangers, welded kitchenware |
| 410 | Martensitic | SUS410 | 1.4006 | ~12% Cr, hardenable | Shafts, fasteners, valve parts, pump components |
| 420 | Martensitic | SUS420J2 | 1.4021 / 1.4028 | ~13% Cr, higher carbon | Cutlery, blades, moulds, dies, surgical instruments (non-implant) |
| 440C | Martensitic | SUS440C | 1.4125 | ~17% Cr, highest carbon | Bearings, cutting tools, knives, valve seats |
| 17-4 PH | Precipitation-hardening | SUS630 | 1.4542 | 17% Cr, 4% Ni, Cu + Nb | Aerospace, shafting, gears, chemical processing |
| 2205 | Duplex | SUS329J3L | 1.4462 | 22% Cr, 5% Ni, 3% Mo | Chemical, offshore, desalination, oil & gas |
Rule of thumb: if the grade number starts with 4 — 409, 410, 420, 430, 440 — it is magnetic in every condition. Duplex grades (2205, 2507) are also magnetic because their microstructure is roughly 50% ferrite, and ferrite is ferromagnetic. Only the 2-series and 3-series — 201, 304, 316, 310, 321, 904L — are non-magnetic in the annealed condition. For that side of the family, see our non magnetic stainless steel grades compared guide.
Within the 400 series, the ferritic grades are the most formable and the cheapest, making them the default for appliance and automotive trim. The martensitic grades trade formability for hardness — they can be quenched and tempered to reach hardness levels that austenitic grades cannot reach, which is why they dominate cutting tools, blades and bearings. Relevant standards for sheet, strip and plate include ASTM A240, EN 10088-2 and JIS G4304; for bars and shapes, ASTM A276 covers the same grades.
Why Buyers Deliberately Choose Magnetic Stainless Steel
In a surprising number of products, magnetism is a feature rather than a defect. Magnetic stainless steel is specified when the design needs the material to respond to a magnetic field — and the 400 series is the only stainless family that does this reliably and cheaply.
- Magnetic latches and closures — refrigerator doors, cabinet catches, appliance panels and display cases rely on a ferritic steel substrate that holds a permanent magnet. A 304 panel would not hold the latch closed.
- Sensor and switch actuation — reed switches, proximity sensors, door interlocks and flow meters detect a moving magnetic steel target. 430 is the standard target material because its magnetic response is consistent and repeatable across production batches.
- Automated handling and clamping — magnetic conveyors, robot grippers, press feeders and sheet separators pick up ferritic blanks by magnetism, eliminating mechanical clamps and reducing tooling cost on high-speed lines.
- Magnetic mounting systems — tool boards, signage, removable panels and temporary fixturing attach through magnetic contact with a steel substrate. 430 sheet is the standard backing material.
- Hardened wear parts — martensitic 420 and 440C give blades, springs, bearings and tools hardness and wear resistance that austenitic grades cannot reach through heat treatment.
- Cost stability — with zero nickel, ferritic grades cost a fraction of 304 and their price is far more stable when nickel markets swing. For components that do not need non-magnetic behaviour, 430 is often the most economical stainless choice.
For appliance trim and decorative moulding specifically, 430 is the industry workhorse — see our detailed guide to 430 stainless steel strip for automotive and appliance uses for grade chemistry, surface finishes and sourcing parameters.
Applications by Industry: Where Magnetic Stainless Is Specified
The magnetic stainless grades appear across a wider range of industries than most buyers realise, often in components that are never touched by a magnet during their working life.
Automotive and Commercial Vehicles
409 is the standard exhaust material — its combination of heat resistance, corrosion resistance and low cost makes it the default for mufflers, resonators and heat shields on most production vehicles. Ferritic 430 and 439 appear in trims, brackets and sensor targets. The magnetic response of these grades is actually relied upon by many vehicle systems: crankshaft position sensors, ABS wheel speed sensors and transmission speed sensors detect a magnetic steel target wheel, and the ferritic grades provide the consistent response those sensors need.
Home Appliances and White Goods
430 dominates refrigerator door panels, oven panels, washing machine drums and trim. The magnetic requirement is direct: refrigerator doors use magnetic gaskets, and the door panel must provide a ferromagnetic surface for the gasket to seal against. This is a textbook case where a non-magnetic grade would fail functionally — a fridge door in 304 would not seal properly.
Cutlery, Tools and Bearings
Martensitic grades rule this space. 420 and 440C are the standard materials for knives, scissors, surgical instruments (non-implant), cutting tools and precision bearings. Their hardness after heat treatment — up to 60 HRC — is the property that matters, and their magnetic behaviour is simply a consequence of the same structure that makes them hard.
Architecture and Interior Fit-Out
430 is widely used for interior cladding, lift panels, handrails and fixtures where a brushed stainless finish is wanted at a lower cost than 304. Magnetic mounting systems for removable signage and display panels use 430 as the backing substrate, allowing panels to be swapped without tools.
Renewable Energy and Electrical Enclosures
Ferritic grades are increasingly specified for solar mounting structures, battery cabinet panels and electrical enclosures where cost matters and magnetic response is harmless. The price stability of nickel-free grades is a major advantage in long-horizon infrastructure projects.
Magnetic 400-Series vs Non-Magnetic 300-Series: How to Choose
The decision between a magnetic 400-series grade and a non-magnetic 300-series grade comes down to four questions: does the part need to respond to magnetism, what is the corrosion environment, how hard does it need to be, and what is the budget?
| Decision factor | Choose 400-series (magnetic) | Choose 300-series (non-magnetic) |
|---|---|---|
| Magnetic behaviour needed | Yes — latch, sensor target, clamp, mounting | No — must stay magnet-free |
| Budget priority | Lower — no nickel content, stable pricing | Higher — nickel is the primary cost driver |
| Corrosion environment | Mild to moderate (430/439); indoor or sheltered | Severe — marine, chemical, chloride (316, 904L) |
| Hardness requirement | High — 420/440C hardenable by quench & temper | Cannot be hardened by heat treatment; only cold working |
| Forming complexity | Good for ferritic (430); lower for martensitic | Excellent deep-drawing and stretch-forming behaviour |
| Weldability | Good with stabilised grades (439); 430 needs care | Excellent across the austenitic family |
| Magnet-sensitive environment | Not suitable — will interfere | Required — μr < 1.01 standard |
Price is often the deciding factor for non-critical components. A 430 strip typically costs 30–50% less than 304 for the same dimensions, and because it contains no nickel, its price does not jump when nickel prices spike on the LME. For appliance trim, automotive decorative parts and indoor architectural panels, 430 delivers the corrosion resistance and formability needed at a materially lower cost. When corrosion risk is higher — coastal environments, chemical exposure, food contact with acidic products — the 300 series earns its premium and becomes the correct choice.
How to Test Magnetic Stainless Steel: What to Check on Receipt
Verifying a magnetic grade is simpler than verifying a non-magnetic one, but there are still three things worth checking on receipt.
- Magnet pull test — a strong neodymium magnet should clearly hold a ferritic or martensitic strip. If it does not, the grade may have been mislabelled — check the Mill Test Certificate rather than assuming.
- Consistency across the batch — magnetic response should be uniform across the coil or batch. If some pieces pull strongly and others weakly, question the heat and the processing history.
- Hardness and temper confirmation — for martensitic grades, confirm the hardness range (HRC or HV) on the certificate and, where practical, with a portable hardness tester. Hardness drift between batches is the most common cause of downstream performance failures in blades and bearings.
For the reverse case — confirming that a 300-series material is truly non-magnetic before it goes into a magnet-sensitive assembly — our guide to magnet testing and permeability verification explains both the simple magnet check and calibrated permeability measurement to ASTM A342.
The Trap: Magnetic Grades in Magnet-Sensitive Applications
The same property that makes 400-series useful becomes a serious problem near sensors, MRI equipment, electronics, gyroscopes, navigation systems or any calibrated magnetic environment. A magnetic 430 bracket mounted inside an instrument housing can shift calibration, trigger false sensor readings, or contaminate a clean magnetic environment. In MRI suites, even a small magnetic steel fastener can become a projectile hazard.
If your application cannot tolerate any magnetic response — medical devices, semiconductor equipment, aerospace instrumentation, sensor housings — use the austenitic grades and verify the incoming material before it reaches your production line. The permeability limit should be written into the specification (μr < 1.01, or μr < 1.005 for premium grades) and confirmed on the Mill Test Certificate, not assumed from the grade name.
Important: 300-Series Steel Can Become Magnetic Too
One source of confusion is worth naming directly: an austenitic 304 part that tests clean on receipt can attract a magnet after stamping, drawing, slitting or machining. Heavy cold work transforms some of the non-magnetic austenite into strain-induced martensite, and that martensite is magnetic. This is normal metallurgy, not a quality failure — and it is why stability under forming varies between grades. 304 (8–10.5% Ni) magnetises readily under cold work; 316/316L (10–14% Ni) is much more stable; 310S and 904L are essentially immune. We explain the full mechanism, the prevention strategies and the solution annealing fix in why austenitic stainless steel turns magnetic.
Common Myths About Magnetic Stainless Steel
Four misconceptions cause the most procurement friction, and they are worth addressing directly.
Myth 1: “If a magnet sticks, it is not real stainless steel.” False. 430, 410, 420 and 440C are all genuine stainless steels — they contain at least 10.5% chromium and resist corrosion. Magnetism and “stainlessness” are independent properties. A magnet test tells you the crystal structure, not the authenticity.
Myth 2: “Magnetic stainless steel is lower quality than non-magnetic.” False. The two families are optimised for different jobs. A magnetic 440C bearing outlasts a non-magnetic 304 bearing in wear applications; a magnetic 430 fridge door is the correct, industry-standard choice. Quality is about meeting the specification, not about which crystal structure the alloy has.
Myth 3: “All stainless steel is non-magnetic.” False. Only the austenitic 200/300 series is non-magnetic in the annealed condition. The ferritic, martensitic, duplex and most precipitation-hardening grades are magnetic — and together they represent a large share of total stainless steel production, especially in automotive and appliance markets.
Myth 4: “Ferritic stainless steel rusts, so it is only for cheap trim.” Partly false. 430 has good atmospheric corrosion resistance and is used outdoors in sheltered applications; 439 and 444 offer higher corrosion resistance for demanding environments. The limitation of ferritic grades is primarily in chloride-rich and acidic environments, where 316 or 904L are required. Matching the grade to the environment, not dismissing the family, is the correct approach.
Buying Magnetic 400-Series Stainless Steel Strip: What to Specify
When you source ferritic or martensitic strip for magnetic assemblies, hardened components or appliance trim, put these five points in writing on every enquiry:
- Grade + standard together — 430 (ASTM A240 / EN 10088-2 / JIS G4304) vs 409 vs 420 vs 440C are not interchangeable without confirming properties.
- Temper and hardness — annealed, half-hard, three-quarter-hard or full-hard; for martensitic grades, specify the HRC or HV range in writing.
- Magnetic response if it matters — for sensor targets and switch actuation, confirm the grade’s magnetic characteristics with your supplier rather than assuming all ferritic grades behave identically.
- Thickness tolerance and edge condition — precision slitting to ±0.01 mm with deburred or rounded edges keeps high-speed stamping and roll-forming stable and prevents tool wear.
- Mill Test Certificate with heat number — traceable chemistry and mechanical properties, documented coil by coil. If you are unfamiliar with what a 3.1 certificate should contain, see our MTC / EN 10204 3.1 explainer.
Fullgreat Metal — the Shenzhen branch of Hong Kong FGI Group — supplies ferritic stainless steel strip in 430, 409, 439 and custom grades alongside its non-magnetic austenitic range, with a monthly capacity of 50,000 tons, 10,000 tons of inventory and partnerships with 100+ mills in Japan, Korea, Germany, Taiwan and China. Since 2008 we have served more than 1,000 enterprises across 20+ countries under ISO 9001:2015, GRS and OEKO-TEX STANDARD 100 certification. Every coil ships with a heat-numbered Mill Test Certificate, and custom widths, tempers, surface finishes (2B, BA, 8K, polished) and edge conditions are available on request. For electronics-adjacent and sensor applications where non-magnetic behaviour is required, see our non-magnetic stainless steel for sensors and instruments guide.
Frequently Asked Questions
Q: Is 430 stainless steel magnetic?
A: Yes. 430 is a ferritic grade with a BCC structure and no nickel, so it is magnetic in all conditions — fully annealed, formed, welded or polished. It is the standard magnetic grade for appliance trim and decorative panels.
Q: Are all 400-series stainless steels magnetic?
A: Yes. Ferritic grades (409, 430, 439) and martensitic grades (410, 420, 440C) are all magnetic. The only stainless families that are non-magnetic are austenitic (200/300 series) — with the caveat that heavy cold work can make them partially magnetic too.
Q: Does magnetic stainless steel mean it is low quality?
A: No. Magnetism is determined by crystal structure; corrosion resistance is determined by chromium and molybdenum chemistry. A magnetic 430 part can outlast a non-magnetic 304 part in the right environment. Magnetic behaviour only matters when the application requires low magnetic permeability.
Q: What is the cheapest magnetic stainless steel?
A: 409 is typically the lowest-cost magnetic grade, followed by 430. Both are nickel-free, so their pricing is stable and independent of nickel market swings. 409 is widely used in exhaust systems; 430 is the standard for appliance trim.
Q: Can magnetic stainless steel be used near electronics or sensors?
A: Generally no — magnetic grades can interfere with sensors, coils, calibration and magnetic storage. For electronics-adjacent parts, specify austenitic non-magnetic grades and verify permeability on the Mill Test Certificate. See our non-magnetic stainless steel for sensors and instruments guide for application detail.
Q: Can a 304 part become magnetic after stamping?
A: Yes. Heavy cold work transforms some austenite into strain-induced martensite, which is magnetic. This is normal and more pronounced in 304 than in higher-nickel 316 or 310. If non-magnetic behaviour must survive forming, specify 316L or 310S and verify permeability after fabrication.
Q: What is the difference between 430 and 304 stainless steel?
A: 430 is ferritic, nickel-free, magnetic and cheaper; 304 is austenitic, contains 8–10.5% nickel, is non-magnetic in the annealed condition and costs more. For indoor trim and magnetic assemblies, 430 is often sufficient; for corrosion-critical and magnet-sensitive applications, 304 is the safer choice.
Q: Which stainless steel grades are non-magnetic?
A: The austenitic grades — 201, 304, 304L, 316, 316L, 310, 310S, 321, 347, 904L and 254 SMO — are non-magnetic in the annealed condition. For a grade-by-grade comparison of composition, stability and cost, see our non magnetic stainless steel grades compared guide.
Need magnetic 400-series strip — or non-magnetic austenitic strip — with traceable certification? Send your grade, dimensions and target properties to Bruce@fullgreat.com and we will confirm availability, temper and Mill Test Certificate documentation before you commit.
