Magnetic Austenitic SS??? 1

[LanaCarrie]

I have a component that is spec'ed as 304 SS. However, it was brought to my attention that it is magnetic so I had PMI done to confirm that it is 304. The chemistry checks out. How is is possible for an austenitic to be magnetic??

 

[LanaCarrie]

I found a vague reference saying austenitics can be magnetized by forming operations. Does anyone know how this works?

 

[NickE]

One Thing: Cold work...

Not sure as to the mechanism, I think that the Austenintic structure undergoes a deformation induced transformation to martensite. I know this happens in 301ss and also 17-7, I think that its possible to work any austenitic steel to martensite if enough carbon is present. Though there may be another controlling factor that determines the amount of cold work necessary to produce a martensitic structure out of the metastable RT austenites.

nick

 

[unclesyd]

A very short reply.

You can get magnetic austenitic S/S several different ways.
Cold working, especially small parts like fasteners will become very magnetic. This can be removed by heating above 1150̊F and air cooling. This is any easy way to see if you have Austenitic S/S. Being magnetic from cold work doesn't appreciably hurt the corrosion rate of the material. The work-hardening property of Austenitic S/S is used to improve the strength of some fasteners. The process that allows this to happen is very complex.

One other fabrication process that creates a magnetic Austenitic S/S is from welding where you form Ferrite which is magnetic. This can only be removed by quench annealing. This is a very complicated subject and is usually taken care by welding procedures. It is not unusual for welds in Austenitic S/S, especially 316 S/S to be very magnetic. Casting and forgings may also show some magnetism based on their thermal history. The degree of magnetism is measurable and is usually left as is unless the enviroment that it will be exposed to requires that it addressed.

The magnetic properties of stainless welds are used by the salvage people to try to down grade scrap. They will tell the material has to much iron therefore it is mixed scrap.

 

[LanaCarrie]

Thank you both for your responses. The component is heavily cold worked so your information definitely makes sense. Much appreciated!

 

[BobUXL]

I have seen many bundles of 303, 304, and 316 get a demag at shipping and come into the customers plant magnitized. Just putting the alloy near a magnetic source can magnetize the material. Even the bouncing of the material during truck tranmsport to the customer can induce a slight magnetic property. But, this condition is more prevalent with cold worked material than fully annealed material. And to complicate this further, ASTM and AMS specs state that condition A austenitic materials can have tensile strengths in the 115 to 125 ksi region. Far above the 90/95 ksi tensile in fully annealed material. But, producers are allowed to sell this as annealed material. So one needs to beware of the certifications and the mechanical properties of the material to determine the true metallurgical condition.