welders, how do I tell stainless steel from aluminum?

[Elfmaze]

I would have though this was a stupid question untill today.  I salvaged some scrap metal off a grill going into the scrap yard.  But now that its home i'm looking at it.  and besides weighing it,  how do i know if its stainless or aluminum?   No magnetic signature,  and looks about the same. 

I was thinking just put the torch to a corner and see if it glows?

[CIG4R]

Use the corner of a hand file if it file cut's into it like "butter" it aluminum, if it the metal offers resistance stainless steel.

[soyjim]

I have items that are marked Stainless steel and they are magnetic.

[Pokey]

Magnet.

[GeeBeav]

I have items that are marked Stainless steel and they are magnetic.

Aren't some SS alloys "mildly magnetic"?

[usttobee50]

.....Elfmaze......most stainless metals will attract a magnet. Dairy Grade stainless, which is in the 200 grade, will not attract a magnet, also stainless should be noticeably
heavier..........      

[Boomer343]

Hit it with a grinder and you'll know pretty quick......

[B.D.F.]

Some have said that you can tell with a magnet but that is not correct- some stainless steel is not only non- magnetic, it is not even considered a ferrous material even though the major portion of the alloy is iron by far.

They really do not look the same but either could also be finished with almost anything.

As some have said trying to abrade the corner will show pretty quickly which is which as almost all aluminum alloys are much softer than stainless steel. In the end though it is weight which is usually obvious; steels, including stainless steels, are 3 times heavier than aluminum at least as a 'rule of thumb'.

And finally few items are made in both of those materials. They are really not direct competitors and depending on the process, one will be much easier to work with. Aluminum is much easier to cast due to its much lower melting temp (less than 1,100 F compared to over 2,000 F for S.S.). Stainless steel is much easier to weld and <usually > form as long as you can heat it a bit.

But if you really cannot tell and absolutely must know then a small sample and a propane torch will tell you; if it melts, it is not stainless steel and may be aluminum or some alloy of zinc (if a really cheap object). If it does not melt and is not magnetic, is some version of gray then it most likely is stainless steel. To determine the exact alloy will take laboratory analysis though.

Brian

I would have though this was a stupid question untill today.  I salvaged some scrap metal off a grill going into the scrap yard.  But now that its home i'm looking at it.  and besides weighing it,  how do i know if its stainless or aluminum?   No magnetic signature,  and looks about the same. 

I was thinking just put the torch to a corner and see if it glows?

[Elfmaze]

To determine the exact alloy will take laboratory analysis though.

An interesting point.   Can i join 316 to 304 stainless?

I hit it with the TIGs arc and it glows, so i'll go stainless with this one.  but I had a ton of thin bar stock I got out of an old fridge I though was stainless but has a strong magnetic signature.  I'm thinking a chromed steel now. 

 

Aren't some SS alloys "mildly magnetic"?

I didn't realize the magnet thing until I was playing with one of my brewery's kettles.  some parts of the kettle wall have barley any magnetic signature and other parts on the same kettle have a light magnetism...

[Mister Tee]

Also, if it's stainless, it's likely to be formed and welded sheet metal.  If it's aluminum, it's likely to be cast or die cast.

And yes you can weld 304 to 316.  304L and 316L are weldable grades, however.  Welding standard higher carbon 304 or 316 is problematic due to diffusion cracking.  To properly weld them, the welded parts should be heat treated all the way to phase dissolution.

[Cold Streak]

Generally 300 series sst is non-magnetic while the 400 series sst are magnetic.  It has to do with the alloys and the heat treatment they receive to give them their properties. 

[B.D.F.]

Yes, all stainless steel will TIG weld to all other stainless steels. S.S. will also weld to carbon (non- stainless) steel although as always with steel you have to be careful about the alloy, especially the carbon content (higher amounts of carbon mean less weldability). Welding stainless steel is usually easy and quite successful but there is a problem called 'hot - shortness' where the metal is brittle at very high temperatures. This can be a problem when welding S.S. because it shrinks rapidly when cooling from the liquid and can make micro- cranking, especially toward the center of the bead.

If you got the material hot enough to glow it was not aluminum.

Brian

An interesting point.   Can i join 316 to 304 stainless?

I hit it with the TIGs arc and it glows, so i'll go stainless with this one.  but I had a ton of thin bar stock I got out of an old fridge I though was stainless but has a strong magnetic signature.  I'm thinking a chromed steel now. 

 
I didn't realize the magnet thing until I was playing with one of my brewery's kettles.  some parts of the kettle wall have barley any magnetic signature and other parts on the same kettle have a light magnetism...

[B.D.F.]

The ability to heat- treat comes from the alloy rather than the other way around. Stainless steel that is magnetic is also heat treatable while the non- magnetic form is not. The 300 series can only be hardened by work hardening or a carbon additive process which makes the surface heat treatable (Kasenit, pack hardening, and similar processes).

400 series stainless is magnetic and heat treatable but also not as resistant to corrosion as the 300 series. Surgical cutting tools are typically made from 410 or 420 series stainless.

Brian

Generally 300 series sst is non-magnetic while the 400 series sst are magnetic.  It has to do with the alloys and the heat treatment they receive to give them their properties.