Can CF8M cast valve disc be magnetic

[insproh]

Can a CF8M (SS-316) cast valve disc be magnetic by any means.
I was a little shocked to see austenitic SS magnetic

 

[arunmrao]

No,it is difficult for it to be magnetic, unless there is some shop floor contamination. An out of the context remark, the casting looks to be a poor one.


"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[Gilmiril]

If it was cold-worked after casting, then it could be magnetic, but otherwise I'd agree that it shouldn't be magnetic.

 

[weldstan]

Yes. Ferrite contents can be quite high (> 10%). While they are not highly ferromagnetic, they will very likely exhibit some. Check with a Severn gage or equivalent to determine ferrite level

 

[jwhit]

CF8M castings will usually have a small degree of magnetism, the ferrite content is usually controlled to fall in a range of about 5 to as high as 20% with ~8-15% being preferred. The ferrite is slightly magnetic. In castings the presence of ferrite helps to prevent weld cracking due to hot shortness sometimes found in fully austenitic alloys. For cryogenic applications the austenite/ferrite ratio is shifted to less than 5% by controlling the chemistry, usually below 2% since the ferritic portion of the alloy can undergo a ductile to brittle transition and thus reduces notch toughness at low temperatures (think <-320F). If you need a fully non-magnetic casting, be prepared to pay a premium for the additional chemistry controls required.

 

[moltenmetal]

You're probably checking it with a very strong rare earth magnet and getting a weak attraction that feels fairly strong to your fingers. Castings and weld metal in austenitic stainless steels are often designed to contain a fair bit of ferrite, which if I dust off a memory which may not be accurate, has something to do with reducing the risk of solidification cracking. So no, you can't use a rare earth magnet ferromagnetism pass-fail test as a proxy for alloy content for these materials.