How to test which type of stainless steel we have

A. If this is as frequent and serious problem as it sounds to be, you could invest in a alloy sorter / scrap sorter ⇦ this on eBay or Amazon [affil links] hand-held X-ray fluorescence machine. It will almost instantly identify the alloy.

But you must also institute a certification program where the seller promises in writing what the material is with every shipment. And then you have to blacklist any seller who proves to be a problem.

A. I use the copper sulphate ⇦ this on eBay or Amazon [affil links] test as a first level sorting, often with good results. Dissolve about 8 grams of copper sulphate in about 500 ml of water. Swab that onto your part. Carbon steel surfaces will immediately show a copper color as the iron dissolves and the copper replaces it. 300 series stainless shows no reaction, and 400 series USUALLY won't show a reaction, or it'll be very limited.

I don't use the variation of copper sulphate solution that contains 2 to 3 ml of sulfuric acid, as I consider that too aggressive for the 400 series stainless.

Realize that your results may vary depending on how clean your surface is, or if it is contaminated by embedded iron particulate, sometimes found on non-passivated stainless steels. Take a look at Method 102 in MIL-STD-753 [on DLA / cancelled] which you can find on Assist Quicksearch [Ed. note: replaced by AMSSTD753].

A. Hi Chris!

For the same reason that stainless steel is stainless. The chromium oxide layer at the surface renders the surface passive, and protects the metal.

A. Hi

I found this link and thought it might be helpful for You for quick stainless steel assessment:

www.engineeringtoolbox.com/identification-stainless-steel-d_383.html

Regards
Sebastian

A. The only stainless steel that is not attracted by magnet is austenitic grade: 304,316, 201,202. The others such as 400 series are magnetic. However, some austenitic grade could become magnetic when cold worked, especially 304.

I own a nickel and molybdenum test kit. This test kit is actually created to differentiate 304 and 316. however as I am kind of curious guy, I have tried it on several samples: carbon steel, series 200, and of course 400 series.

I purchased it from an Indonesian company. www.agp-supply.com

here is a link to their demo video :
www.youtube.com/watch?v=J7OmUeozO20

Here are my results:
carbon steel: Ni test show no reaction at all
Series 200: Ni test show dark brown color whereas for 300 series it should be yellow
Series 400: Ni test show positive result by showing yellow color

So you could use this test kit to sort carbon steel and 200 series. For 400 series you could easily use magnet as they are supposed to be magnetic.

In southeast asia, I never worried about supplier selling carbon steel as stainless steel as uncoated carbon steel rusts easily within a matter of days. It is more common for supplier to fake series 300 by supplying 200 series which is much cheaper.

A. Hi Naval. If there were a non-destructive AND simple AND non-expensive test that was accurate, we wouldn't need any others. Magnetic tests meet all three requirements, but don't tell you very much. So please keep in mind the aphorism "Two out of three ain't bad" :-)

a.) Non-destructive and simple is the x-ray fluorescence machines previously mentioned, but it's capital intensive (expensive).
b.) Non-destructive and non-expensive might be very carefully controlled spot tests and electrochemical tests such as the molybdenum spot test previously mentioned and the electrochemical tests available per the banner ad at the bottom of the page (not necessarily simple, and may involve careful tracking, and substituting test samples in lieu of your fabricated parts)
c). Simple and non-expensive include spot tests, spark tests, etc. But they may be destructive.

Describing all practical tests for differentiating every possible type of stainless steel would takes a good-sized book rather than a forum posting. If you can be more specific with your question, readers can probably be more specific with answers. Good luck!

Regards,

A. Hi Phil. Although people refer to a 400 or 4xx "series" of stainless steels, my understanding is that there is a "type 400" stainless steel. Are you sure the box says "400 series" rather than "type 400"? If the box says "type 400" it doesn't mean it might be 409 or 410 or whatever, it means it's 400.

Regards,

A. Hi Paul. According to the composition charts, ATS34 seems to have 5X as much molybdenum as 440C. It may be possible to do a molybdenum test. Koslow Scientific Testing Instruments [a finishing.com supporting advertiser] may be able to help.

Regards,

A. Hi Indrajit. We appended your inquiry to one of many threads on stainless steel testing. Yes, there are spot tests to determine certain characteristics of stainless steel, including composition and whether or not it has been passivated. But it is probably difficult for people to guess what chemical the dealer used and whether it actually revealed passivation vs. composition, let alone type 202 vs. type 304. Spot tests can be valid, but I don't know whether this particular one was. You might contact a supplier of such spot tests, like Koslow Scientific Testing Instruments [a finishing.com supporting advertiser], and see if you can get the test solutions and procedures yourself. Good luck.

Regards,

A. One of the common ones is a spot test for molybdenum, used to attempt to determine moly containing grades (e.g. 316) from non-moly containing grades (e.g. 304).

The only real foolproof method is to send a sample to a lab for analysis or have one of those very expensive handheld XRF units.

If the suppliers involved are reputable, typically just a material cert sheet is deemed sufficient.