Is 316 Stainless Steel Magnetic?

[Canopy Locked]

Just had some new parts sent to me by the boat dealer from whom I purchased a new boat last year. There has been significant amount of rusting, especially on things like ball catches. The dealer has told me that there was a batch of catches used in the factory that did not have stainless steel balls and they have sent me 2 new catches.

My magnet is currently stuck to the side of the catch just over where the ball is located inside..

I thought that stainless was not magnetic?

Can anyone confirm?

Ta

 

[Norman_E]

316 is not attracted by a magnet. It is an austenitic stainless steel, as is grade 304. Martensitic stainless steels are attracted, but austenitic stainless steels are not.
EDIT: Are you sure it is the ball that is holding the magnet, and not the spring, which is probably carbon steel?

 

[vyv_cox]

Not much to add to what Norman_E has written. You will sometimes read that 304 can become magnetic due to cold work but it is a very faint effect.

However, don't write off martensitic/ferritic stainless steels entirely, they can be pretty good in corrosion, especially the 13% chromium ones. Most stainless steel cutlery is made from it, the cheaper stuff from only 5% chromium, and it remains corrosion free in domestic situations. Some Jeanneau prop shafts are made from it, photos on my website. I would not be surprised if your rusty bits are chromium plated steel.

 

[ReefMagnet]

Cutlery is martensitic s/steel, and in the old days a lot of automotive chrome trim was actually ferritic s/steel. I'd suspect the balls themselves would probably be bearings made of the harder martensitic stuff.

 

[sailinglegend420]

316 is not attracted by a magnet. It is an austenitic stainless steel, as is grade 304. Martensitic stainless steels are attracted, but austenitic stainless steels are not.
EDIT: Are you sure it is the ball that is holding the magnet, and not the spring, which is probably carbon steel?

Interesting answers. Some more questions.

So if the magnetic ball is removed then 316 S/S should not retain any magnetism - is that correct? Unless, as I understand from Google, it has been partly changed by martensitic stress induced transformation (MSIT) - or cold working!

I have received a replacement Clarke Pump for my watermaker which appears to be very highly magnetic. I'm assured it's all 316 by the dealer who took one to bits and found very larger steel springs - not in contact with the sea water - they were causing the problem. There was some loose swarf in one of the in/out threads that was still magnetic when removed. Is cutting a thread MSIT?

 

[Plevier]

I have a Lewmar Pro windlass. Lewmar say the cast casing is 316. However it holds a magnet quite firmly. It isn't cold worked other than a bit of drilling/boring for screws and bearings. So can it be 316?

 

[colhel]

Under no circumstances can you make 316 magnettic. As Vyv says 304 can magnetise slithly and us machinists can usually only detect this in the swarf. 400 series ie 431 413 or in old money EN57 is magnetic

 

[Tradewinds]

Another view here.

A consultant metallurgist from OZ and another says 316 can be!

http://www.finishing.com/112/70.shtml

 

[colhel]

Another view here.

A consultant metallurgist from OZ and another says 316 can be!

http://www.finishing.com/112/70.shtml

I think that's b*ll*cks. But I'm only a machinist

 

[rogerthebodger]

Any one know of or used the moly test to check the grade of stainless 304 /316

http://www.stainlesspickling.co.uk/moly-drop-test-960

 

[sailinglegend420]

Another view here.

A consultant metallurgist from OZ and another says 316 can be!

http://www.finishing.com/112/70.shtml

Here's my link that says MSIT can cause magnetism in 316 S/S. It certainly seems to have done so on my swarf.

http://www.fastenal.com/web/en/75/magnetism-in-stainless-steel-fasteners

 

[vyv_cox]

Here's my link that says MSIT can cause magnetism in 316 S/S. It certainly seems to have done so on my swarf.

http://www.fastenal.com/web/en/75/magnetism-in-stainless-steel-fasteners

I think the article is somewhat theoretical. In a decent 316 with a nickel content above 8%, which most are to avoid exactly the conditions described in the article, magnetism is not going to occur unless there is heavy cold working, such as turning. It is not unusual to see retained ferrite in the microstructure of a 304 because the nickel content is kept to the bare minimum.

Martensite is transformed from ferrite when the quench rate is very high, which would be difficult to arrange under normal circumstances in a fitting (e.g. red hot plunged into cold water). Again, martensite would be more likely in swarf due to its small volume.

 

[chrisclin]

Surely in the examples quoted above - water pump, windlass etc - there are electric motors involved. I would expect them to respond to a magnet as that's how electric motors work (or so my physics teacher taught me many years ago!).

 

[sailinglegend420]

Surely in the examples quoted above - water pump, windlass etc - there are electric motors involved. I would expect them to respond to a magnet as that's how electric motors work (or so my physics teacher taught me many years ago!).

A Clark Pump doesn't have a motor, it's a energy recovery device that boost the pressure from 150 PSI to 650 PSI - all done by magic! I'm sure your physics teacher had never heard of one either.

 

[chrisclin]

A Clark Pump doesn't have a motor, it's a energy recovery device that boost the pressure from 150 PSI to 650 PSI - all done by magic! I'm sure your physics teacher had never heard of one either.

Well that's educational. Even after a Google I can't say I understand how it works but surely there has to be some form of input power to raise the pressure. It doesn't seem to work like a garden hose with your finger over the end!
Anyway, my point about the windlass still applies - unless it's a manual one

 

[Graham_Wright]

Under no circumstances can you make 316 magnettic. As Vyv says 304 can magnetise slithly and us machinists can usually only detect this in the swarf. 400 series ie 431 413 or in old money EN57 is magnetic

Up until yesterday, I would have agreed wholeheartedly with that (save for the cold working and battering situations).

However, I have just received some neodymium for a HiFi project I am working on.

All my 316 material, bar, square, round and tube, is quite noticeably attracted to these magnets.

303 is slightly less strongly attracted than 304 (and mild steel is damn near impossible to detach!)

Before anyone asks, all my material is supplied with certificates of conformity and mechanical and chemical analyses.

(……and now, on today's news, I hear a new magnetic wonder material has been discovered.)