Is stainless steel magnetic and how to identify the grade

At the same time, bent, drawn and welded 304 is noticeably more magnetic than annealed 304. That is why a magnet does not identify the grade — it gives only a rough hint.

Is 12Х18Н10Т magnetic or not: why one stainless steel is magnetic and another is not

The magnetic properties of steel are set by the crystal structure, not by the word "stainless" itself.

• Austenite has a face-centred cubic lattice. Such a structure is non-ferromagnetic, so annealed metal hardly attracts a magnet at all.
• Ferrite and martensite have a body-centred lattice. They are ferromagnetic, and a magnet is attracted to them in any state.

Which structure a composition turns into depends on the elements. Nickel retains austenite, which is why 304, 316, 321 and 12Х18Н10Т are weakly magnetic after annealing. Manganese and nitrogen also stabilise austenite, but more weakly. Without nickel, ferrite is obtained — that is how 430 is built, and it is always magnetic.

Deformation is a separate case. Bending, drawing, straightening, cutting and welding introduce internal stresses into austenitic steel, and part of the austenite turns into martensite. The metal starts to be magnetic. The more deformed the area, the more noticeable the effect: the magnet holds at a bend and lets go on a flat sheet.

Hence a simple conclusion: magnetism is a state of the metal, not its passport.

Austenitic and ferritic

Different classes of stainless steel behave predictably with a magnet.

Class	Structure	Magnetism	After deformation	Examples
Austenitic	face-centred	weak after annealing	grows	304, 316, 321, 12Х18Н10Т
Ferritic	body-centred	strong always	unchanged	430, 439
Martensitic	body-centred	strong always	unchanged	410, 420
Austenitic-ferritic	a mixture	noticeable	unchanged	duplex

Fasteners are marked separately: А2 is the austenitic group close to 304, А4 is close to 316. Both are weakly magnetic after annealing, but work-hardened fasteners can be noticeably attracted. More on the classes — in the analysis of steel grades.

What this means in practice:

• a magnet does not separate 304 from 316 — both are austenitic;
• a magnet does not separate annealed 304 from annealed 201 — both are weakly magnetic;
• a magnet reliably shows only one thing: you are dealing with ferritic or martensitic steel, if it is not deformed.

How to check the grade at home

There are no accurate home tests. There are quick techniques that help weed out obvious mistakes, but they do not replace analysis.

Method	What it shows	How reliable
Magnet	roughly divides austenite and ferrite	low accuracy
Appearance of the surface	nothing about the grade	does not work
Spark when grinding	very roughly, depends on skill	unreliable
Batch certificate	grade and composition	the main source
Spectral analysis	actual composition	an accurate method

If all you have is a magnet, use it like this. Take a known annealed area, not a bend and not a weld. If the metal is strongly attracted over the whole surface, it is most likely ferritic or martensitic steel. If it is weakly attracted or only at a bend, you may be looking at austenite.

Do not check the grade by spark, colour or weight: these signs depend on the state of the metal and on skill, not on composition. For food, medical and critical applications, the only correct path is to request the batch certificate or have a spectral analysis done.

Another household technique is to look at how the metal behaves in a wet environment. If rust spots appear after a few days, the metal is most likely not austenitic, or there is foreign iron on the surface. But this sign does not give the name of the grade either, so it is not suitable for acceptance.

What this does not prove

A magnet does not answer the main question — which grade you are looking at. Let us go through typical misconceptions.

1. "It is not magnetic, so it is good stainless steel." Annealed 201 is also weakly magnetic, although in resistance it is noticeably inferior to 304.
2. "It is magnetic, so it is not stainless steel." Bent 304 and a 316 weld seam attract a magnet while remaining austenitic.
3. "I will check 304 or 316 with a magnet." It will not work: both grades are austenitic, and they do not differ in magnetism. The difference between them is in molybdenum, not in structure.
4. "It is attracted more weakly, so the grade is higher." The force of attraction depends on the degree of deformation, not on the quality of the metal.
5. "If rust has appeared, the metal is the wrong one." Rust streaks are often caused by particles of ordinary steel that got onto the surface during processing or storage.

A magnet is suitable as a rough filter, but not as acceptance. If the batch goes into a critical assembly, check the documents.

Frequently asked questions

Is 12Х18Н10Т magnetic or not

After annealing it is weakly magnetic: the structure is austenitic. After bending, drawing and welding, part of the austenite turns into martensite, and the metal starts to attract a magnet noticeably more strongly.

Is AISI 304 magnetic or not

Annealed 304 is weakly magnetic. After cold deformation and in the weld seam zone, magnetism grows. That is exactly why a magnet cannot distinguish 304 from 316 or from 201.

Is AISI 316 magnetic or not

It behaves the same way as 304: weakly after annealing, more noticeably after deformation. It is impossible to distinguish 316 from 304 with a magnet — the difference between the grades is in molybdenum.

Stainless steel is not magnetic — which steel is it

Most likely austenitic in the annealed state: 304, 316, 321, 12Х18Н10Т or the economy 201. But the absence of magnetism guarantees neither the grade nor the quality.

Is A2 stainless steel magnetic or not

А2 is the austenitic group of fasteners, close to 304. In the annealed state it is weakly magnetic, but work-hardened fasteners (screws, studs) are attracted noticeably more strongly.

Is 430 magnetic

Yes, always. The ferritic structure is ferromagnetic, and heat treatment does not change that. More details — in the analysis of AISI 430.

Can the grade be determined with a magnet

No. A magnet only roughly divides steels into austenitic and ferritic and does not distinguish 304, 316 and 201 from one another. The grade is confirmed by a certificate or spectral analysis.

Place an order with a confirmed grade

A magnet will not replace documents, and the catalogue saves you from guesswork. Choose the required grade and size, specify the surface finish and the shipment week: no wording like "stainless steel in general" will remain in the order.

• Catalogue of stainless steel products
• AISI 304 or 316 — how the grades actually differ
• AISI 201 — the economy austenitic grade