Is It Really Stainless Steel?

I'm sorry to say that there are also martensitic grades, and even duplex...

Magnet method will work only with austenitic variations. Luckly, this is the most likely to be found due to its higher corrosion resistance.

I never found hard to determine if it's stainless steel or not. Low carbon and low alloy do seem different. What's your exactly purpose with this issue? I mean, stainless steel is resistance to environments that are subject to oxidation, they may be subject to other means of attack.

Your question is worded too broadly, if you were to ask, "is there a way to determine if a piece of stainless steel is grade XYZ vs grade ABC?" then perhaps we could help you, using a variety of possible methods.

But to just declare the material is stainless, that i cannot do.

But to confirm it as a particular grade of stainless, that is likely quite possible. More specifics please.

milo

Hi...technically there is nothing like a stainless steel. All technical people may better call them as 'stain resistant steels'.

Fyi, all steels, stainless or otherwise rust. Because once the chromium % in steel goes up 5% or more it starts to exhibit stain resistant properties.

The word stainless is the discovery of some marketing genious. A simple way is to dip the sample piece in vinigar and leave it that way overnight. If you can't see stains next morning then you can call it stainless! Fyi, this steel was first discovered by this test!!

For specific applications you'll also have to determine whether it's been wrought or cast.

The story behind all this. I once bought a gear to use in a swimmingpool.

It was a gear with a hollow output shaft and an machined part to hold a toothwheel.

I wanted it to be made in stainless steel.

When I received the gear, the hollow shaft was non magnetic, but the machined part was magnetic.

I told to the vendor that I had the opinion that the machined part was not stainless steel. So six weeks later I got a new machined part and this was also magnetic.

This time I accepted the parts and sold it to my client.

Not me and not my vendor seem to know how to check it if it was really stainless ...

thanks for the advice

Sometimes, the working of a stainless steel component (lathe, milling machine, grinding etc) can lead to its magnetisation. Particularly if the tooling was magnetic too.

The suggestion of leaving a part of it in vinegar overnight sounds a good one. If it is carbon steel then it will have a thin layer of rust on it the next day. Perhaps best to put a test piece of carbon steel in a similar jug of vinegar next to it for comparison.

Finally, if the stainless steel has been worked with carbon steel tooling, then some contamination can occur and spots of rust may appear. These can be equally damaging in the long term depending on the environment in which they are used. A swimming pool environment is paricularly corrosive and these parts may require protection depending on the risk due to failure.

Has the stainless steel component been passivated? i.e. has it had its layer of chromium oxide activated by a chemical and then cleaned up?

Hi Rudy,

Funny you should mention this. I run into this problem all the time. We are a small manufacturer of stainless steel clamping systems (the clamps you see holding up street-signs in your local town) and primarily use AISI 304 (Austenitic) and 201 as raw material... This material starts out by being non magnetic. As part of the system we manufacture a buckle through a 5 stage press tool, and the 304 buckle comes out the other end slightly magnetic. Working the steel causes this, and I usually run into problems explaining this fact to end-customers (mostly engineers)...

All the best.

Stainless steel Banding Guy

www.stainlesssteelbanding.net

one simple test to sort stainless from non stainless is to use nitric acid. steel is quickly attacked while stainless is not attacked.

here you cand find how to perform the test and other interesting test:

http://www.atlasmetals.com.au/files/ASM_Tech_Notes/TN1-qualitative%20sorting%20tests%20rev%20Oct%202008.pdf

hope this can help u

S

corrosion prevention & protection

The easiest way is to ask your supplier to send proof with test reports. I like the ideas here. Having sold all these products for years these question come up from time to time. I like the nitric acid test. As a school science fair project for my son we used vineger and ot took longer than a night. So be careful

Remember it is stain 'less' steel. Given the variety of stainless steels and the considerable cost difference between them, I would use x-ray flourescence to semi-quantitative analysis of the alloy. Or ask the manufacturer for a certificate of grade.

One of the easiest ways I know is to see if you can cut the metal with an oxy acetylene torch. Being that stainless is resistant to oxidation it will not cut like carbon steel. It will get hot but when you mash the oxygen trigger to start cutting it will cool off immediately and not blow through. This will work on duplex stainless as well as others. I know it sounds destructive but it really does not take but a second to find out and if done correctly will not harm the metal.