Inconel or Stainless Steel?

I hope this helps but is not a scientific test

depending on what type of stainless steel you are looking at

if 304 or 316 it has a nice shiny appearance

inconel is a dull grey and forms a redish oxide

Use a magnet. If it sticks it's steel, if does not than it's something else.

Hope it helps.

W R O N G

What is WRONG?

What is wrong is that Carbon steel and Stainless steel are two very different animals. Some stainlesses, mainly in the 400 series, are magnetic, most stainlesses in the 300 series, and some in the 400 series are not (or at least not to a great degree and then only when cold worked.). Therefore your test is not at all conclusive.

I've got a Inconel or Incoloy turbine wheel friction weld to a SS shaft. The shaft it's magnetic the turbine it's not.

the shaft may be 420 stainless or one of the other ferritic iron/chromium stainlesses in the 400 series. If you add nickel to the alloy it looses virtually all of it's magnetism. you can cold work it and get a little back, but if it is used in an application that is at elevated temp, you will anneal the part and the additional strength you get from cold-work will go away causing the part to fail. Also cold worked stainlesses are more susceptible to corrosion and cracking.

Inconnel is not magnetic - it has more nickel than stainless.

Stainless steel frequently does not contain enough ferric compounds to be magnetic so this test won't necessarily prove anything

Unfortunately, neither of the answers given in Posts 1&2 are reliable. The surface finish depends on the rollers used to form the sheet; quite commonly one side is much shinier than the other. There are many varieties of Stainless Steel; some are magnetic, while some are not.

Effectively, if you don't have the certification sheet that came with the bellows, then you can't be sure what it is made of, and certainly should not attempt to sell it except as scrap! If you are going to use it yourself, assume it is cheap stainless. If stainless is adequate for your job, inconel will probably last longer. If you require inconel, and don't have certs, don't use it! Safety First!

have to agree with dkwarner on the safety first issue. If you are not sure you must accept the worst case.

On a side note you will probably find that inconel is magnetic, however this does not prove your sample is inconel, it only proves that it is not 304 or 316 stainless.

I just double-checked two pieces of Inconel 625. Neither was magnetic!

316 SS does have some magnetic properties to it.

Only when it is cold-worked to a great degree. But such cold-work eliminates it for use in most pressure vessel applications.

I understand.

Can you give me an example of what you mean by pressure vessel?

We purchase it as pump shaft.

Anything that must be manufactured per ASME pressure vessel codes. Tanks, boilers, chemical reactor vessels, Nuclear reactor vessels. Any fabricated container that must withstand internal pressure and temperature.

Inconel is readily welded where as SS is a horse of a different color at the least without critical specification.

The inconel and the SS (most of them) are welded with the same rods.

Why don't you go the simple way (depending on quantity) any lab will do a spark chemical analysis for you on a small test piece.

These people do stainless steel test kits, might be worth speaking to.

Can you tell me the name of the handheld digital unit to analyze the material?

Thanks

Probably something like this though there are several makes. As has been said before many scrap yards use these to classify materials although the guns are very expensive.

I don't have a quick way to determine if a material is inconel or stainless, but these links can be helpful:

https://www.steelforge.com/metaltidbits/inconel.htm

https://www.thomasnet.com/products/inconelr-39900550-1.html

https://en.wikipedia.org/wiki/Inconel

Best regards,

John Sijs

With the temperatures in mind, then what kind of temperatures are these bellows exposed too? Are they actually left in the heat for long periods?

If it's something that is applied intermittently then I couldn't see a need for something manufactured from inconel.

I'm not very familiar with inconel but from what I gather with it being nickel based material it would be more costly then stainless steel. As such if it isn't constantly being exposed to extreme heat for long durations then I can't see any company shelling out the extra money for inconel when stainless steel will suffice.

It is all about the Nickel content. The stainless is Iron based and the Inconel's are Nickel based. We use a Inovex chem gun to take actual chemistries in order to distinguish the differences between different Inconel's. You could grind the alloys using a angle grinder. The one that produces a very fine and dull spark will be the Inconel. The Stainless will produce a brighter and more pronounced spark. The chem test kits are iffy due to the fact that some stainless alloys also contain Chrome and Nickel. You need to look for the Iron.

A NDE (non-destructive-examination) testing company will most likely have a portable alloy analyzer. You can find these companies under inspection services / testing services.

Serveral kinds of alloy analyzers exist, but they operate in the same basic way. The material is irradiated (isotope source or x-ray) and the analyzer looks at the reflected radiation pattern and determines the alloy content from that. Each element (Cr, Ni, Fe, Mo etc...) reflects the radiation differently. These cannot detect lighter elements (from Oxygen down to Hydrogen). Usually these devices have an alloy library, so it will report your material as alloy 625, 825, 800, 304, 316 etc.... It can also be set to report weight percent composition of all detected elements.

If you want to use the expansion joint, hire somebody to analyze the material.

If this part is already ASME stamped, you are merely verifying that it is what it's manufacturer says it is. However, if you are trying to stamp the part yourself and you have lost material traceability it is scrap regardless of what an alloy analyzer tells you. The alloy analyzer report is not an acceptable substitute for a material test report.

Most Incolloys have large amounts of iron in them too. Even the Inconels have measurable amounts of iron.

Thanks everyone for great replies. I figured I would have to get a chemical analysis done, but sometimes there are simple and cheaper alternatives that get overlooked so one always has to ask.

Gosh.

Color is one way. weight is another. malleability is another. Hardness yet another. Machining characteristics another.

There clearly are differences in all the properties you have mentioned, but I certainly would not want to install a part (except in some home-made contraption where safety is of no concern) based on any, or even al, of those factors.

Most of the places I have seen Inconel specified do involve human safety to a significant degree. I would not want my name associated with any part so chosen!

Inconel is commonly used in sub sea drilling applications where heat wear and pressure as well as a corrosive environment exist. It is also used in engine cylinders and similar components.

Clearly our OP is not using this material often. I suspect he is also having trouble with work hardening and tool fracture - just a guess.

Since the material has clearly become seperated from it's MTR then it should in fact be resubmitted for analysis. That would remove ALL doubt.

Hi raggededgge - Assuming you could take a sample, have you considered a Charpy-Impact test: http://en.wikipedia.org/wiki/Charpy_impact_test? We used to do these at the lab I worked at. Low-technology but does the job. Much luck. - Larry

WOrking from memory I would say no to this.

You must have the MTR for at least one of the materials as a reference. And then it must be within an allowable acceptable deviation range.....

...on second thought I say no altogether as the 2 could be too close to diff. by this test alone.

Just an opinion.

I worked with a tube furnace and we had to use Inconel because it wouldn't oxidize around 800C and all stainless steels would because the chromium layer would evaporate off.

I think that the only way is to make a chemical analisys. There are so many different types of SS and Inconel with so different chemical composition. You need at least to know which types of SS (austenitic, ferritic...) and which Inconel you're trying to sort..

here you can find a lot of test to sort SS from other materials :

On-site methods for stainless steel grade product sorting

http://www.bssa.org.uk/topics.php?article=175

hope this help u

S

corrosion prevention & protection

Stainless steel - is well known for its quality of corrosion resistant and it is widely used for food handling and cutlery among many other applications. Stainless steel does not lose its quality when it comes in contact with water or rust, in shot it does not corrode while other normal steel does.

To learn about Inconel alloys prefer this link: http://super-metals.com/alloy/inconel-600/