Telling Stainless Steel from Other Metals 2

[Damineh]

My supervisor had taught me that I can check whether a piece of metal is stainless steel or not using a magnet. That’s all!
2 days ago, we had a rusted bearing and when he checked each and every component of the bearing with a magnet, he assured everyone none of the parts were stainless steel as the magnet attracted all of them.
We put all the components of a new bearing in water to see whether it would rust. It hasn’t yet. So we are clear that the bearing had been stainless steel and that the magnet test is not the correct way of stainless steel testing.
Now… I found out that magnet ofcourse attracts all magnetic materials such as nickel and monel and …. And that stainless steel at different grades has some percentage of Nickel.
Now… is there any other way to test for stainless steel?? How would I know what grade it is?? I don’t rely on the company that’s supplying us with the steel.

 

[MadMango]

The only real way to know is to get material certs from your suppliers.

Wanna Tip? faq731-376
"Probable impossibilities are to be preferred to improbable possibilities."

 

[Damineh]

What if the company doesn’t trust the supplier? They build us bearings and assemblies and sometimes they cheat! Is there any test that can identify the grade?

PS. Did I do anything wrong??? I have read that page before and don’t think my thread was a bad one . This is regarding the “Wanna Tip? FAQ731-376” comment.





Thank you.

Damineh

 

[automationbabe]

MadMango is correct.

If your company doesn't trust the supplier, or the supplier refuses to give certs, then you may want to look for a new supplier.

Another thing to check are you drawings for material specification. If it just calls out SST, the supplier will use whatever grade they get their hands on.

There are a lot of grades of SST. Magnets are not the most reliable way to tell. The finish could also make the part less magnetic.

Good luck!

 

[MadMango]

If you don't trust the supplier, then it's time to find a new supplier. Plain and simple.

But, you can go to

http://www.mcmaster.com

and search for a "metal/alloy identification kit" and you should be able to find what you are looking for.

As for the "Wanna Tip?", that's just part of my signature when I post. There was nothing wrong with anything you posted.

Wanna Tip? faq731-376
"Probable impossibilities are to be preferred to improbable possibilities."

 

[Metalguy]

*If* you're buying stainless steel ball/roller bearings, the common material is 440C--strongly magnetic.

 

[jbknudsen]

I agree with MadMango. The supplier should be able to produce MTR's (material trace records) or some type of certification on the material supplied. Within the documentaion, there should be the material composition and or grade of the material supplied. Meaning that your material should be disignated 316ss, 203, 203leaded, 17-4 PH, ect, ect. The list goes on. The nickel content should also be present in the documentation. If you cant get you vendor to send some type of certification on the material, I would find another vendor, fast.

Cheers,

Jay

 

[TVP]

Damineh,

You do not have to rely solely on your supplier for proper identification of an alloy. There are numerous methods that are used by test labs for identifying chemical composition of metals, which are quantitative, not qualitative like the kit sold by McMaster-Carr. I recommend you contact an independent test lab (certified by A2LA or a similar organization if not in the USA) and have some of your parts analyzed by a proper technique such as ICP-OES (ICP is also used with AES).

 

[ccw]

Hi Damineh,
The 3XX AISI series of stainless materials are non-magnetic, unless severely cold worked. Multi-strand stainless aircraft cable (severely cold worked by drawing) would be magnetic.

The 4XX AISI series of stainless materials, undoubtedly the material your bearing is made of, are magnetic.

There are instruments (spark spectrography, or nuclear backscatter) that can determine alloy content on a relative and non-destructive basis. You need certified samples to calibrate against.

 

[ijzer]

I would suggest you use PMI equipment to check the material composition. (e.g. "Texas nuclear analyzer" or "The Metallurgist&quot

 

[Ralph2]

We use copper sulphate as a quick and dirty check. Clean a section and place a drop on it. SS will not tarnish to a light copper color whereas any ferous metal will. As stated above some grades of SS are magnetic to various degrees. You can also check the hardness and compare it to known values.

 

[arto]

Try these guys:

http://www.spectro-ai.com/pdf/brochures/e/SpectroPORT_e.pdf

http://www.koslow.com/1542c.html

 

[Paskenell]

Hey Damineh - Lot of good suggestions you are receiving although I have to agree with TVP - the only sure way of knowing what you are getting is find a certified lab.

The training you received was wrong, although common. Your 300 series stainless are "generally" non magnetic unless, as ccw mentioned, they are severely cold worked or not properly passivated. Go to any hardware store and try to stick a magnet on a 18-8 or 304 stainless bolt and it probably wont show any noticeable magnetism. Take the same magnet to a 18-8 stainless lockwasher and you are likely to get a reaction. This is most often caused by microscopic tooling shavings left in the stainless, or the difference in 304 and whatever material (302?) was used in making the lockwasher. There are laymen tricks(which cannot offer anywhere near the reliability of a lab) - for instance Ralph 2 has shown the copper sulphate test, used comonly for testing passivation of stainless, can assist in determining if you have stainless or not. Putting most metals against a grinder and comparing the sparks to a piece you know is correct is another old trick - as different metals make different size sparks. I would give that old trick about a 10% reliability factor. :-(

While I am echoing the others who have already contributed to this post, please allow me one more. Find a supplier you can trust. There are too many ethical manufacturers out there and if you have concerns about this one, find someone reliable. Unreliable sources endanger not only you and your position, but also your company and its reputation, and your customer and their safety.

Nice friendly thread and I hope I didn't change the tone.

 

[Damineh]

Thank you all very much. Unfortunately, my supervisor who has a PhD and PEng, is so sure of himself that doesn't listen to what I suggest. I told him about magnetic strength of 300 and 400 series and that magnet wouldn't be the best method to examine stainlessness of steel, the first day he told me about the method. He never listened and say his words came from experience. I learned alot from what you suggested, all of you and I will learn more if you suggest more . I won't share my information with him anymore as he sees me as a fresh-out-of-school typa kid. Very sad!

Thank you.

Damineh

 

[CoryPad]

Damineh,

Does your supervisor have a PhD and PEng in Metallurgy/Materials? If so, he did not receive suitable education. Perhaps his degree and license are in another field, such as Mechanical Engineering? That would help explain the problem.





Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[diamondjim]

Damineh,
You mentioned that the bearing was stainless
steel. Just certain types of stainless steel
can be hardened which would limit the kinds
of stainless steel used by the manufacturer.
I think it would be up to him to supply a
good grade of stainless steel to meet your
requirements. Are you certain that stainless
steel is a requirement for the bearing? It
is hard to get the proper surface harness
with stainless steel and you may see early
failure if the original was steel with a
63Rc surface hardness. I would suppose your
supervisor was right about identifying the
orginal bearing as steel for the wrong reason
in that stainless steel can be magnetic.

 

[Timelord]

Damineh,

Being dinosaur who is a qualified tool maker in addition to being a P.E., I can tell you another method to tell stainless from steel and also determine the alloy with some accuracy. Find an old copy of Machinery's Handbook (My 17th edition has the info, but my 23rd edition doesn't). There is a section on how to discern what alloy you have by the spark pattern generated when you hold it against a grinding wheel. I have used this method all my life for non-critical identifications, but as MadMango says, the only way to be absolutely positive is get material certs from your vendor.

timelord

 

[Hippo41]

This is one of the oldest mis-conceptions I find in industry.

Stainless bearings for general consumption are made from 440C stainless, which a Martensitic stainless steel and IS magnetic. If you don't specify otherwise, your bearings will prbably be 440C.

You can get some deep groove ball bearings in 316 stainless which has some molybdenum in to improve corrosion resistance, but these bearigs will not have the same capacity as the 440C bearings. 316 bearings are usually ised in the photochemical industry, near printers inks, bleaches and dyes.

Some distributors wil offer stainless bearings in 316 stainless as they are usually CHEAPER than 440C (in my experience) so they get the business and think they are being clever.

You should inform your distroibutor what medium you want the bearings to run in and then get them to advise what bearings they can offer that will give you best performance.

Lester Milton
NBC Group Ltd, Telford, Shropshire, UK

 

[Maui]

Your boss sounds very much like a professor that we had in graduate school. She earned her Ph.D. from Berkely in Mechanical Engineering, and was accepted as a tenure track faculty member at the University of Rochester while I was a student there. One day while my friend was working in our lab, she knocked on the door. She was helping some students set up an experiment, but the piece of steel that she had in her hand was too long. My lab mate told her that he would just cut it to whatever length she needed. She looked at him and said, "This is steel. You can't cut it." Without saying another word he took the bar, put it in the vice, cut it with a hacksaw, and handed the pieces back to her. It sounds like your boss and she may have attended the same program.

By the way, the previous posts have all provided you with some good information. The most painless way to determine what type of steel the bearings are made from is to send one out to an independant testing laboratory for grade identification. They can perform this easily with a variety of equipment including x-ray diffraction, optical emmission analysis, or an EDAX scanner on an SEM, etc. Most stainless steel bearings are made from 400 series martensitic stainless steels. This is because the 400 series stainless grades can be heat treated to a relatively high hardness which is what a bearing application often requires. Since they are martensitic in the heat treated condition, they are also magnetic.


Maui

 

[Damineh]

Yes I have learned a lot from this one question I had. I am very pleased to have joined this forum as I learn things I wouldn’t learn from books.

Heh yeah that lady and my supervisor must have the same background!

I have taken all the material courses offered at school including electives such as ceramics, ferrous and non-ferrous metals. I might still be an undergrad. That doesn’t indicate I might know things a PhD doesn’t. It’s very unfortunate that not much credit is given to undergrads. I don’t know about educational system back in the 70’s. I think students had less projects and labs. We even have to work during out studies. It’s a must to graduate to have 5 workterms. I am not saying I know lots. It’s just that it’s frustrating when he doesn’t listen to me even though I might be right.

By the way, does a steel rod (very thin around 2mm in diameter) melt if I leave it on fire?

Thank you.

Damineh