Stainless Steel Rivets Ordered Non-Magnetic, Arrived Magnetic: Read Where the Magnet Pulls

Short answer: Austenitic stainless steel such as 304 is close to non-magnetic when it is annealed, but cold heading can make it magnetic. When rivets ordered as non-magnetic arrive magnetic, check where the magnet pulls before rejecting the delivery. The whole batch, only the head, or only the surface each point to a different production step.

SUS304 flat-head solid rivets. The head takes the heaviest deformation in cold heading.

Why a 304 rivet can turn magnetic

Cold working changes part of the austenite in 304 into martensite, and martensite is magnetic. A rivet head is upset from wire in a die, so it takes far more deformation than the shank. That is why the head is usually the first place a magnet sticks. Grades with more nickel, such as 305 or 316, keep their austenite better under cold work.

Four patterns and what they point to

This is the checklist our technical lead uses when a customer reports magnetic stainless rivets:

The whole batch is strongly magnetic. Either the raw material has too much ferrite, or the solution anneal was skipped.
The head is magnetic, the shank only weakly. The heading deformation was too large and there was no intermediate anneal.
Only the surface is slightly magnetic, and the inside is not after grinding. Look at the secondary cold work, such as polishing or sizing. Iron tooling in that step is the usual cause.
Still magnetic after annealing. The annealing temperature was too low, the hold time too short, or the cooling too slow.

SUS304 flat-head rivets with a through hole, from our product records. They are shown for the shape, not as a magnetism case.

How to check a batch you received

Test the head and the shank separately with the same magnet.
Grind a small spot on one or two pieces and test again, to separate a surface effect from the bulk.
Ask the supplier for the material certificate and whether the parts were solution annealed after heading.
If you still have the wire or a sample from an earlier good lot, test it the same way for comparison.

What to write in the RFQ

Write "non-magnetic" on the drawing, and say how it will be checked: a simple magnet test, or a permeability limit if your application needs one. State the stainless grade. For rivets with a large head, ask the supplier whether a higher-nickel grade or an anneal after heading is needed to meet it. Then the requirement is priced in from the start, not found at incoming inspection.

If you need stainless rivets with a non-magnetic requirement, send the drawing, grade and how you test through our RFQ form. We will say before quoting what it takes to meet it.

Related: what to specify for custom solid rivets · custom semi-tubular rivets

How this was written: the four patterns come from our internal product FAQ, reviewed by our technical lead in 2026. The general metallurgy (cold work forming martensite in 304) is standard knowledge. The rivets in the photos are from our product records and are not from a magnetism complaint.