"It sticks to a magnet, so it's not real stainless." Or the opposite: "It doesn't stick, so it must be 304." Both are common on site, and neither tells you the grade.
Why genuine 304 can be magnetic
Grades 304 and 316 are austenitic stainless steels. In the annealed (softened) condition, their structure is non-magnetic. But that structure changes when the metal is worked:
- Bending, forming and machining convert some of the structure to a magnetic form. A cold-formed elbow, a machined flange face or a threaded end can pull a magnet slightly, even when the grade is genuine.
- Castings are different again. Cast stainless such as CF8 (cast 304) and CF8M (cast 316) is deliberately made with a small amount of ferrite to resist cracking. So a genuine stainless valve body can be mildly magnetic straight from the foundry.
Why a cheap substitute can pass
The 200-series stainless steels, such as 201, are also austenitic. They save cost by replacing much of the nickel with manganese. They are non-magnetic, so they pass the magnet test, but they have lower corrosion resistance than 304. A magnet cannot catch this substitution.
Why a magnet can't separate 304 from 316
The difference between 304 and 316 is chemistry. Grade 316 contains about 2 to 3 percent molybdenum, which improves resistance to chlorides and pitting. Both behave the same way near a magnet, so the test says nothing about which one you have.
What does confirm the grade
| Method | What it tells you |
|---|---|
| PMI with a handheld XRF analyser | Alloy content in seconds: chromium, nickel, molybdenum, manganese |
| Spot test kits | Presence of molybdenum (316 vs 304) or nickel (304 vs 201) |
| EN 10204 3.1 certificate | The mill's chemical and mechanical results, if the heat number matches the part |
The strongest check is the combination: the part is marked with a heat number, the certificate matches it, and a test confirms the chemistry.
How we handle it at Al Juyushi
We check grade at intake instead of trusting a magnet. You can watch our material identification (PMI) and hydrostatic test clips on the home page.