How magnetic is A2/304 stainless?

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GHA

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These came off ebay - https://www.ebay.co.uk/itm/M12-HEX-...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

Says A2(304) but seems awfully magnetic - before I start with the supplier,does this look wrong? It's a strong magnet, little bit of force with the flat bar which is stamped as 304.

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GHA

I've accused a supplier of sending me non stainless steel cupboard hinges and asked for a refund. He contacted me and asked how I knew they weren't stainless and I told him they were magnetic. He went back to the factory and complained but they assured him they were 100% stainless steel

I did some research and found ss will become slightly magnetic when it is "worked".

"There is a myth in the stainless steel industry that stainless steel is not magnetic. Or that if it is magnetic, the stainless steel is not stainless.

Magnetism and corrosion resistance are not connected. Corrosion resistance depends on how much chromium and (sometimes) molybdenum is in the stainless steel. The higher the chromium and molybdenum, the better corrosion resistance".

The magnetism myth is because the common magnetic grades of stainless steel, 409 and 430, don’t resist corrosion as well as the common non-magnetic grades, 304 and 316. You can’t expect them to. Grade 409 has 11% of chromium, which is plenty for automotive muffler systems".

http://www.australwright.com.au/stainless-steel-magnetism-corrosion-resistance/

https://greenwoodmagnetics.com/resource/what-is-the-difference-between-304-and-316-stainless-steel/

Maybe do a bit more research? I know I had better reference a while back.

Clive
 
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Yes. I bought some s/s washers from a reputable supplier of s/s fastenings and I found they were slightly magnetic.
 
coopec said:
GHA

I've accused a supplier of sending me non stainless steel cupboard hinges and asked for a refund. He contacted me and asked how I knew they weren't stainless and I told him they were magnetic. He went back to the factory and complained but they assured him they were 100% stainless steel

I did some research and found ss will become slightly magnetic when it is "worked".

"There is a myth in the stainless steel industry that stainless steel is not magnetic. Or that if it is magnetic, the stainless steel is not stainless.

Magnetism and corrosion resistance are not connected. Corrosion resistance depends on how much chromium and (sometimes) molybdenum is in the stainless steel. The higher the chromium and molybdenum, the better corrosion resistance".

The magnetism myth is because the common magnetic grades of stainless steel, 409 and 430, don’t resist corrosion as well as the common non-magnetic grades, 304 and 316. You can’t expect them to. Grade 409 has 11% of chromium, which is plenty for automotive muffler systems".

http://www.australwright.com.au/stainless-steel-magnetism-corrosion-resistance/

https://greenwoodmagnetics.com/resource/what-is-the-difference-between-304-and-316-stainless-steel/

Maybe do a bit more research? I know I had better reference a while back.

Clive
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I did do a fair bit of research on google, these are "really " magnetic, not just a bit. If they really are 304 then the difference between the conn nuts & the 304 flat bar is very surprising. Your quote says it as well - "the common non-magnetic grades, 304 and 316. "

And from your link - "[FONT=&quot]304 stainless steel contains chromium (min. 18%), and nickel (min. 8%). It is an austenite steel and is only slightly responsive to magnetic fields". These don't seem like 304. [/FONT]

I've ground off some surface on one and it's now half submerged in some concentrated sea water to see what happens before chopping of a couple which are already attached to the boat. Maybe in dryish areas with a load of epoxy on top they'll be OK.
 
GHA

Maybe I was careless with my selected quote from the article but the article does go on to say:

"The strength of the magnetism depends on how much the metal has been deformed. Even when these grades are cut (cold, by shearing) the deformation in the edge of the metal causes magnetism.
Stainless steel bolts are made by cold forging the head, and cold rolling or machining the thread. They are often quite strongly magnetic.

How were those small bits cut: by shear?

In my case I found the leaves of the hinge were not magnetic, just the pin.
 
coopec said:
GHA

Maybe I was careless with my selected quote from the article but the article does go on to say:

"The strength of the magnetism depends on how much the metal has been deformed. Even when these grades are cut (cold, by shearing) the deformation in the edge of the metal causes magnetism.
Stainless steel bolts are made by cold forging the head, and cold rolling or machining the thread. They are often quite strongly magnetic.

How were those small bits cut: by shear?

In my case I found the leaves of the hinge were not magnetic, just the pin.
Click to expand...

The 304 flat bar was cut with a grinder - barely magnetic , none of the other nuts/bolts A2 or A4 are anything like as magnetic as the ebay ones, which certainly rings some alarm bells. Not sure it's worth getting in a ruck with the supplier though, they look like some sort of stainless and being in the wrong country would make returning a pain, maybe just take it on the chin. Would be interesting to hear from those in the know though. A4 M12 conn nuts are not the cheapest up the hardware store! Least they've got some so the work can continue.
 
I've used a certain amount of 300 series stainless in my home workshop over the years, turning, drilling, milling, sawing etc.
I don't recall any becoming anywhere near as magnetic as your items appear to be.
 
GHA

I share your attitude on this matter. Why get excited about a bit of magnetism in a cupboard hinge! Mind you if it was in salt water I would demand the best.

I don't know why a Chinese bolt would be more magnetic than one made in the UK (if in fact they are): maybe the method of manufacture?

Roger (Shaw) posted the link to a very interesting video clip on how they make bolts. Maybe the Chinese use a different technique?

Maybe this is the link Roger posted

https://www.youtube.com/watch?v=SxEN5wXV-gU

Clive
.
 
300 series stainless steels are nominally austenitic and therefore contain no ferrite. Ferrite is magnetic, austenite is not. Cheap 300 series may have less nickel than it should, 8%, and thus there may be some ferrite content. Considerable working, such as drilling, can be quite magnetic due to transformation by heat, but flat bar should definitely not be as magnetic as the video shows.

400 series stainless steel is ferritic or martensitic, both of which are magnetic. As the quote above says, they are less corrosion resistant but may well be stronger.
 
But, but, but the flat bar has been worked so it surely would be magnetic?

The strength of the manetism depends on how much the metal has been deformed. Even when these grades are cut (cold, by shearing) the deformation in the edge of the metal causes magnetism

AND

Cold work

Wrought, austenitic stainless steels, such as 304 and 316, are generally regarded as non-magnetic in the annealed condition, ie they are not attracted significantly by a magnet. However, if they are cold worked they will be attracted to a permanent magnet. The change occurs because the cold work deformation induces a transformation of the microstructure from austenite to martensite.



This is an interesting article re new developments in S

https://www.assda.asn.au/technical-...ion/70-low-nickel-austenitic-stainless-steels
 
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The magnetism induced by cold work is very minor, nowhere near equivalent to a ferritic steel. Test it on your swaged fittings and shroud wires, both of which are heavily cold worked.

Duplex is magnetic. Some prop shafts and rudder posts are made in it, notably by Jeanneau.
 
Well the culprits have only been soaking in seawater and hot sun for a day but don't show any tarnish yet, think they'll be allowed to stay and put to light dry duties as and when the need arises.

Though in future I think stainless will only be purchased when I can be there with a strong magnet double checking...
 
Neeves said:
Just out of interest - where does duplex stainless fit into this - magnetic or not.

Jonathan
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Duplex, Super Duplex, are magnetic and commonly used for marine applications as they're far superior to 316 in terms of strength. 17-4 is magnetic and less corrosion resistant than 316 and Duplex but stronger, often found in shackles etc.
 
I use a lot of 316. This is sourced from an attested supplier and comes with certificates. I can make it magnetic by working.

In respect of nuts, the one I use have always been marked A2 or A4 (save for Nylocs) not to say that all are.
 
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