Nitronic 40 vs 21-6-9 5

[TominBoulder]

My customer wants to minimize magnetic permeability for a small diameter shaft. He has chosen Nitronic 40 and is getting good results. Apparently, Nitronic 40 is a trademarked material of AK Steel. The "generic" equivlaent of Nitronic 40 is 21-6-9. I would gain some supply flexibility if I could also use 21-6-9. Is there a difference in these materials?

 

[EdStainless]

Most of this material is actually made to S21904, a tighter chemistry than the original Nit40.
This is fairly available (we make a lot of tubing in this alloy).

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Plymouth Tube

 

[TVP]

If you are specifying the raw material on a drawing for production in North America, I suggest you use the UNS designation for the grade and an appropriate ASTM standard for the product form:

bar--> UNS S21900 (Type XM-10) according to ASTM A276 or UNS S21904 (Type XM-11) according to ASTM A276 for 0.04% max Carbon

wire--> UNS S21900 (Type XM-10) according to ASTM A580 or UNS S21904 (Type XM-11) according to ASTM A580


Nitronic 40 is a tradename from Armco, but they don't even produce bar and wire anymore, so you are not gaining anything by specifying this on a drawing.

 

[mfgenggear]

Tom

Make it optional

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[TominBoulder]

TVP,
Thanks for your response. With some additional reserarch we found that Armco was bought by AK Steel and that AK Steel licenses Electralloy to produce their Nitronic materials here in the US. I am unclear if Electralloy's Nitronic 40 is in anyway superior (or even different) from steel made to UNS S21904 (Type XM-11) according to ASTM A276 for 0.04% max Carbon. Electralloy does specify that carbon is .04 max.

I have found other mills that produce materials that are similar that do not use the Nitronic 40 trademark. For example, we purchased a small amount from one mill that designates their material as N40 (21-6-9). They do produce to ASTM A276-10 (XM-11 Condition A). The chemistry and phyical properties all match up nicely. Unfortunately, the property that my customer is most interested in (low magnetic permeability) is not addressed in the mill certs from these other mills. And, I don't know what factors influence magnetic permeability. My customer is reluctant to move away from something that works. Testing is an option, but for right now, the burden of proof is on us to make a change.

Thanks again for your help. If you have any other insight, I would appreciate it.

 

[jwhit]

I'm not certain how the igh Mn content influences the accuracy of the calculation, but, you could estimate ferrite content based on the Schoeffer Diagram (ASTM A800). Ferrite is the source of magnetism in the austenitic alloys, the lower the ferrite number the lower the permeability. I ran some quick calcs and found that with the Cr equivalent elements on the high side and the Ni equivalent elements on the low side you would see about 5-6% ferrite, enough to give it a little magnetic permeability. If you swing the numbers in the opposite direction you will be at <0% ferrite. I have looked for a chart or formula that equates ferrite to permeability without any luck. This may give you a start on knowing what permeability to expect.

 

[EdStainless]

If people are sticking near the middle of the S21904 chemistry then it will be nonmagnetic.
If they haven't shaved the Ni and Mn too low then it will stay nonmagnetic even when heavily cold worked.
We buy sheep from Allegheny (ATI Ludlum).

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Plymouth Tube

 

[TVP]

Tom,

Ed has expert level knowledge about this, so I concur with his assessment. I also think that jwhit provided some useful information relative to phase stability and the Schaeffler diagram. You can make some comparisons among the various heats that you have received to see if any of them have theoretically produced ferrite. Botttom line, I doubt that specifying the material according to the ASTM designation is going to change the final performance-- specifying Nitronic 40 on your drawing isn't guaranteeing anything relative to magnetic properties.

 

[EdStainless]

Sheep???? Sheet is what I was after, should have called it strip, harder to mess up.
I wish that I could blame spell check

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Plymouth Tube

 

[dgallup]

I was wondering when Allegheny Ludlum got into the livestock business.

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