Change of magnetic properties of steel by thermal treatment! 1

[UweErnst]

Hello,

Does stainless steel loose its non-ferromagnetic properties when exposed to temperatures up to 850°C (Brazing) for a period of several hours.

Final use will be at low temperature. The steels we are looking in are 304, 310, 316, 321.

Thanks

 

[mcguire]

This thermal cycle will precipitate (Fe,Cr)carbides if you don't use L grades ( except for the 321 ). The remaining matrix will be of a leaner composition. In the 304 this could raise the Ms temperature sufficiently to cause martensite transformation at your cryogenic temperature. In the 316 and the 310, the alloys are rich enough to avoid danger of martensite, but you may get sigma which isn't ferromagnetic but it is brittle. The 321 will not be affected.

 

[CadAndy]

I just found this out from FSU and from brazing
300 Series Stainless with Alumina and Beryllium.
Brazing should only take about 1 minute once you
get it to the temperature you want Our brazing
process took about 12 hours and we didn't have any
change in magnetic properties or any other properties.
We also used a vacuum braze to do our brazing.

On the other hand if you use 304 and 321 in a cryogenic
environment it will become magnetic. Depending on the
time involved and the seriosness of the product
Superconducting magnets could only be made out of 316
or 316L. I do not know about 310. Unless you know
somebody that works in the cryogenic field that data
is hard to find.

 

[mcguire]

21-6-9, one of the nitronics, is excellent at cryogenic temeratures. It is anti-ferro magnetic. It was to be the magnet of the super-colliding super conducting accelerator in Texas. No martensite worries at all.

 

[UweErnst]

Thank you for your replies.

Best regards

 

[mcguire]

I need to clarify a remark I made. The 321 won't be affected by the thermal treatment, but it is fairly unstable and prone to martensite formation at cryogenic temperatures.