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Magnetic "stainless steel"


Davey-T
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Purchased some 12mm stainless steel rod recently from an EBay site and just discovered it's magnetic and an offcut that's been out in the rain has started to show signs of rust.

It looks like stainless steel ie: the right colour

Tested some other 10mm stainless steel rod and that shows no sign of being magnetic.

Anyone come across this before ?

Dave

Edited by Davey-T
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Some stainless steel is slightly magnetic, some isn't.   I have some 40+ year old stainless steel spanners that are slightly magnetic.

But I thought the definition of stainless steel was that it was a chrome steel that does not rust under normal conditions.    The aforementioned spanners still do not have a spot of rust on them, despite being kept in slightly damp garages for most of their life.

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As above  :icon_biggrin:

http://www.bssa.org.uk/faq.php?id=24

Is stainless steel non-magnetic?

It is commonly stated that “stainless steel is non-magnetic”. This is not strictly true and the real situation is rather more complicated. The degree of magnetic response or magnetic permeability is derived from the microstructure of the steel. A totally non-magnetic material has a relative magnetic permeability of 1. Austenitic structures are totally non-magnetic and so a 100% austenitic stainless steel would have a permeability of 1. In practice this is not achieved. There is always a small amount of ferrite and/or martensite in the steel and so permeability values are always above 1. Typical values for standard austenitic stainless steels can be in the order of 1.05 – 1.1. See Composition effects on the magnetic permeability of austenitic stainless steels

It is possible for the magnetic permeability of austenitic steels to be changed during processing. For example, cold work and welding are liable to increase the amount of martensite and ferrite respectively in the steel. A familiar example is in a stainless steel sink where the flat drainer has little magnetic response whereas the pressed bowl has a higher response due to the formation of martensite particularly in the corners.

In practical terms, austenitic stainless steels are used for “non-magnetic” applications, for example magnetic resonance imaging (MRI). In these cases, it is often necessary to agree a maximum magnetic permeability between customer and supplier. It can be as low as 1.

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Thanks for all the quick responses guys, this is A2 stainless steel is A4 "better".

This is for studs to be chemically fixed in concrete to bolt down my pier so don't want them rusting away anytime soon :grin:

Also purchased a selection of nuts and washers and none of these are magnetic

Dave

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31 minutes ago, Tinker1947 said:

Have read of this, might explain the A2 to A4 difference...

https://en.wikipedia.org/wiki/Stainless_steel

Yes, had a browse around a few things now.

Just looked at the stuff I've already made and this bit hasn't even been outside

Dave

SS-rust.png

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Some years ago we bought a LX200 gps for my wife to use in the observatory.  Whilst modifications were made in the observatory we set it up on the tripod. 

The compass that comes with the mount would not point north, until we took it off and moved away, when it was fine. Bringing it back to the mount showed that it was the tripod legs that were throwing it off.

Nice one Meade - magnetic tripod legs under a compass! 

Rob 

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From what I remember A4, also known as 316 stainless is somewhat more resistant than A2 / 302.

Found 316 studding in RS, at a price http://uk.rs-online.com/web/c/fasteners-fixings/threaded-rods-studs/threaded-rods-studs/#esid=4294477011&applied-dimensions=4293623087

When I was researching stainless steel for a demo fusor (Don't ask!) I found that 316 / 316L was the prefered option by a long way. The fittings I sourced from Edwards Vacuum were all 316L. I even had a base-plate mad up in 316 SS for the job to have fittings mIG welded on.

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Don't want to risk it so I've ordered some A4 threaded rod from what appears to be a more reputable source ie: not EB, as it will be outside in all weathers, mostly rain :grin:

Dave

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Just received replacement threaded rod from a different source and there is not a hint of magnetism.

Sent a query to the original supplier but not had a reply.

Dave

Edited by Davey-T
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I generally find that you can tell if it is a decent grade of stainless steel...

1) Very little, if any magnetism (using a strong neodymium magnet). This isn't always true, but generally the good stuff isn't magnetic, or is only very slightly magnetic whereas the not so good stuff is usually very magnetic.
2) It doesn't look/feel cheap. It is shiny, but not too shiny like it is chrome plated.

Of course number 2 is very subjective. If you buy from a reputable source and want it to last for as long as possible then some form of 316 (as mentioned above) will be your best bet but it will be more expensive.

Most of the Chinese junk is precisely that regardless of claimed grade.

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Quite a bit of the stainless steel family is magnetic and it has no bearing on the quality of the material. Austenitic stainless is the only one out of the group that doesn't have magnetic properties because of the other elements used in it's production. Also the way the stainless is worked can have a bearing on the magnetism. If it is say hot or cold rolled.

I could say most of the junk comes from china, but it is untrue as some others are much worse offenders in quality control and certification saying it meets or exceeds a certain composition. 

Stainless has generally a lower tensile strength than High carbon steel but on a pier it's not exactly stressed unless it's a several ton telescope mounted on top :wink:

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16 hours ago, mapstar said:

Quite a bit of the stainless steel family is magnetic and it has no bearing on the quality of the material. Austenitic stainless is the only one out of the group that doesn't have magnetic properties because of the other elements used in it's production. Also the way the stainless is worked can have a bearing on the magnetism. If it is say hot or cold rolled.

I could say most of the junk comes from china, but it is untrue as some others are much worse offenders in quality control and certification saying it meets or exceeds a certain composition. 

Stainless has generally a lower tensile strength than High carbon steel but on a pier it's not exactly stressed unless it's a several ton telescope mounted on top :wink:

Sorry Damian, but all types of Stainless Steel exhibit some magnetic qualities. Some are just mostly not of any real detriment for most purposes. I have seen some very high quality S/S ruined because a technician tried to show me it was not magnetic by touching it with a strong magnet. You can only test it with a magnetometer, nothing else!

 

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13 hours ago, Physopto said:

Sorry Damian, but all types of Stainless Steel exhibit some magnetic qualities. Some are just mostly not of any real detriment for most purposes. I have seen some very high quality S/S ruined because a technician tried to show me it was not magnetic by touching it with a strong magnet. You can only test it with a magnetometer, nothing else!

 

Hi Derek, are you returned or still on holiday ?

I only enquired about this because quite by chance I discovered that the stainless steel threaded rod that I bought was rather strongly magnetic and an off cut that was out in the rain was showing signs of rust, I was a bit concerned as I intended burying them in the concrete patio.

None of the sundry stainless steel washers and nuts I purchased showed any sign of being magnetic and some more threaded rod from a different supplier is also non magnetic.

Obviously sticking an ordinary magnet on it is hardly a rigorous test but it satisfies me, standard galvanised rod would probably see me out anyway :grin:

Dave

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21 hours ago, Physopto said:

I have seen some very high quality S/S ruined because a technician tried to show me it was not magnetic by touching it with a strong magnet. You can only test it with a magnetometer, nothing else!

Hmmm? Very confused now. How on earth do you 'ruin' stainless steel by touching it with a magnet? 

Regards, Hugh

 

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Even more confused! How does magnetising stainless steel ruin it?

Many grades of stainless steel ARE ferromagnetic and can will inevitably become magnetised to some degree just from handling in the Earth's magnetic field.  Even the austenitic grades can pick up an appreciable degree of magnetism. The presence (or absence) of some magnetism has no effect on the mechanical or chemical properties of the alloy.

If the absence of any magnetic field is a requirement, as may be the case for the materials used to fabricate some types of scientific instruments such as magnetometers, then stainless steel is not the right material to use. Aluminium or titanium would be preferable.

Regards, Hugh 

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