How can you tell if 316 stainless is that and not 303 or 304 stainless

[WindyParticipant @windy30762]

Is there any home workshop way of checking if 316 stainless is that and not 303 or 304.

Reason an Ebayer is selling bar ends of various grade of stainless as having bought things that are not what they are advertised as I am cautious about Ebay sellers.

Please note this stainless bar end seller is probably OK. like the majority of sellers are.

[WindyParticipant @windy30762]

[Clive FosterParticipant @clivefoster55965]

Windy

This site :- **LINK** suggests that acid testing with either (or both) sulphuric and hydrochloric acid gives different results for the different stainless steels.

Whether acid testing counts as home workshop friendly is a whole 'nuther issue of course.

I imagine you'd need to do calibration tests with known samples first to be confident of your results. As described the differentiation seems very clear but personal experience with similar chemistry based visual colour change testing is that the real world is somewhat less precise than the description. Probably due to the technique being a bit more involved than a bald description suggests.

Clive

[Chris Evans 6Participant @chrisevans6]

303 machines nicely. 316 and 304 don't machine as well as 303 and tent to be harder to drill/tap.

[Brian WoodParticipant @brianwood45127]

Hello Chris,

The machining test does not seem to be definitive I'm afraid, I have no trouble at all machining 304, even to tapping 4BA threads in it; to me it is much like a decent steel to machine. I am using carbide but I do pretty much all my machining with that medium.

I have supplied a lot of machined bits to a local bespoke furniture maker, all in 304 and buy in 3 metre bars of it.

Regards

Brian

[John McNamaraParticipant @johnmcnamara74883]

316 is better for near the sea or marine use.

Regards
John

[Mick B1Participant @mickb1]

Take a look here to see whether you could make any of these practical tests:-

**LINK**

I'd say your application is fairly edgy if you really need to know…

[MuzzerParticipant @muzzer]

316 is a lot better at resisting salt corrosion than 303/304 and as John suggested, it's often called "marine grade" stainless. If you have known samples of each you could leave them in warm concentrated salt solution for a week or so and you should see the difference quite clearly. You'll almost certainly get red rust on the 303/304 by then and a lot more white rust but likely no red rust on the 316. Not massively scientific but the difference should be big enough for you to repeat the process with your mystery metal. 303/304 isn't actually very "stainless".

Murray

[Martin ConnellyParticipant @martinconnelly55370]

As well as the long wait (weight) and bucket of steam jokes we tell apprentices that you can tell 316L from 321 stainless by the smell. It does require cooperation from a few mates.

Martin C

[Martin 100Participant @martin100]

Try to drill say a 6mm hole with the wrong end of a drill bit. Press really hard, don't use cutting fluid and get the workpiece really hot . After a couple of minutes try to drill a hole in the same spot using the right end of the drill bit. If the hole drills ok it's 303, if it doesn't it's either 304 or 316 but probably 316.

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