Stainless steel magnetic?

Hi all,
I've an issue on stainless steel. I've got some product, that my supplier claims is stainless steel. However, a magnet sticks strongly to
it: the material obviously is magnetic. So that indicates normal iron/steel instead! According to my friend, no stainless steel attracts magnets. I really don't know if this is the case. Manufacturer claims it is stainless steel type 304.
So the question is: will a magnet stick to a stainless steel 304 sheet?
Wouter.
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Your friend is wrong: 400 series stainless and many duplex stainless steels are strongly ferromagnetic (i.e., a permanent magnet will stick to it).
300 series stainless steel is generallly not ferromagnetic, but will change when machined or plastically deformed. The amount of work done on the part determines magnetic strength.
A 304 stainless steel part will hold a magnet if it was machined or cold rolled. If the magnetism is a problem, it'll have to be heat treated to remove the magnetic phase.
If you doubt the material, the only way to know for sure is to send it out for chemical analysis. A magnetic test is not sufficient.
Mike

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Interesting. My son has a refrigerator that is the new look with stainless steel. He's annoyed as his magentic trinkets don't stick to it.
Al
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Al wrote:

Hello Al,
A "typical" refrigerator magnet is not very strong, it is unlikely to have much holding force on a stainless steel refrigerator. In addition, the magnet usually has some decorative cover that adds weight, this'll also reduce the holding power.
A NdFeB magnet will likely hold onto one of those stainless steel fridges (I've never tried), but don't expect a lot of holding power. I suppose the designers of those fridges prefer the clean, uncluttered look of a magnet-free refrigerator door.
Mike
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We use the magnets we extract from old hard drives. They are very powerful and still don't stick. I have processed dozens of hard drives I have obtained at the town's recycling center.
I've also taken the tiny magnets out of old CD-ROM drives. They are about 1/8 by 1/4 inch or so in size. I glue one to a ball point pen and stick it on the frig. Now I always have a pen available. He ain't having no luck ;-)
Al
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The magnetism is not a problem at all. We're talking about gas barbecues here; the problem is they are rusting. And that should not happen, at least not within a few weeks after arrival in our warehouse, a single cleaning session after assembly (I don't know really what they used, but it won't be anything aggressive or so). It is thin sheet (presumably rolled, no idea whether hot or cold), and after that bent in shape. The flat surfaces apparently also show the ferromagnetism.
Heat treatment: I suppose you mean like red hot for quite some time?
But indeed we do not really trust the material. I'll ask my friend to make some photos and have a look; if it's chrome plated steel that should be obvious as I expect the chrome layer to peel off where it's rusting.
Wouter.

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SS 304 should not be rusting even if it was cold rolled enough to be magnetic. There is a thin corrosion resistant layer on the surface 304. As long as the layer is intact, the material will not rust. Trouble is, the layer can be compromised by mechanical or chemical means. If you scratch a piece of 304 with a carbon steel nail in packaging or use a wire brush to clean the surface, you leave behind enough "free iron" to initiate the corrosion. Certain cleaning solutions (Chlorine Bleach, for example) are aggressive enough to break down the layer and expose the base material. Without air to reform the protective layer, the attack begins. Once begun, it will not stop.
The nature of the contamination will dictate the solution to the issue but ,in each case, the rust will have to be arrested and removed and the surface allowed to reform its protective layer. Your manufacturing partner should have sufficient experience with these issues to provide some assistance.
Wouter van Marle wrote:

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Send it to the testing lab. It will cost you less than 200$ for grade identyfication.
--
melon



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Dear all,
Thanks for the fast and constructive answers. I've come to the conclusion that the manufacturer is probably right, and that for future production we will certainly ask them to use a better grade stainless steel (they offer to use grade 410 instead; at higher price of course). That should certainly do away with our rusting problems.
Wouter.
On Sun, 2006-06-11 at 21:53 -0500, melon wrote:

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1) 410 is definitely magnetic 2) 302B may be more suited than plain 302, if oxidation is an issue, 304 and 302 are generic stainless grades
WHAT are your service conditions? You need to choose a stainless for the specific conditions you expect. If corrosion resistance is the primary issue, then look to 316, 317 or 446 -- 302 and 304 are used a lot, but if exposure to marine conditions, even including ocean air (sometimes for a mile or more inland), is an issue then you need 316 instead.
(Data drawn from Allegheny-Ludlum "Stainless Steel Handbook" 1956.)
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On Tue, 2006-06-13 at 12:50 +0000, Kevin G. Rhoads wrote:

The product I'm talking about is gas barbecues, the bigger ones. They're made from stainless steel plates - no added coating or paint.
Service condition: gardens. So rain (may be acid of course), and food. Sauces, hamburgers, fat, garlic sauce, well you get the idea :) It has to be generally weather and cleaning resistant.
Wouter.
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Stainless plate for gas barbecues would have two special service issues that I can see: heat exposure and chloride exposure.
Chloride ion is problematic for most stainless steels, which is why marine and FOOD SERVICE applications often specify special stainlesses. Whether there is enough food exposure depends I would suppose on where in the product the steel is being used. Barbecue sauce is typically loaded with salt, and that is your chloride source.
Similarly, heat exposure would not be the whole barbecue but only certain areas.
I am presuming that appearance is an issue, you want something that will continue to look good.
From Stainless Steel Handbook, p7: "... the low alloy steels such as Type 410, 12% chromium, being less corrosion resistant that those steels having higher alloy content such as Types 316, 317 or 446. This variation in corrosion resistance appears to be related to the amount of chromium contained in the steel, and the resistance can be improved by the addition of nickel or molybdenum."
It is worth noting that standard flatware stainless is typically 18/8 at least 18% chromium and 8% nickel. The addition of nickel improves the resistance to chloride ions. Some cookware uses 18/10.
From Stainless Steel Handbook, p7, further on: "Consider the use of a steel for resistance to the corrosive elements in an industrial atmosphere. Type 410 or any of the 122% chromium steels would develop a superficial rust after several weeks' exposure. The film formed acts as a barrier to further corrosive action, but the resultant part is objectionable from an appearance standpoint. Type 430, 17% chromium, will take several months to form the superficial rust film. The additionm however, of 8% nickel to Type 430 produces a steel, Types 301, 302, or 304, which will not form a rust film and will remain free of corrsosive deposits. In some atmospheres even Types 302 or 304 are not satisfactory, particularly coastal installations, and a steel having higher corrosion resistance such as Type 316 must be used."
Type 301 is only 17/7, whereas 302 is 18/8. 302 is the minimum likely to work well, and if it does not suffice, then 302B, 316 or 317 or 314 would be canditates. However, if 302 does not suffice, 401 will be horrible. 304 is very similar to 302B, (not quite as much silicon) so I think that if you've had issues with that, you may need to upscale to 316 or similar. However, 304 and 302B have better heat resistance. 302B should be better than 304 for most high temp applications.
Is there any patterning to the corrosion that would correlate to either heat exposure, food juice exposure or both?
Another thing to consider is that stainless steels form a surface passivation layer which protects them. The presence of small amounts of certains things in that surface can seriously degrade it. Some people recommend hot nitric acid treatments to passivate the surface after cleaning and degreasing. Such treatments may allow you to use steels that would not suffice without the treatments. I suggest you get the advice of a real, honest to G-d metallurgist to help with your steel selection. Otherwise you will likely get a grade that is more than needed, with corresponding high cost.
HTH Kevin
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If rust is the real problem, don't waste your money on the material upgrade. SS410 will also rust. You will need to specify some variant of 18-8 stainless (SS304) which, according to your earlier post, was what you thought you were getting.
Wouter van Marle wrote:

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Hi
There are two classes of stainless steel, one is ferritic stainless steel and another is austenitic stainless steel......so coming to the point, ferritic is magnetic and austenitic is non-ferromagnetic....the curie temp for Iron is 768 deg. celsius......so below that ferrite structure exists (so only called as ferritic stainless steel)...above that austenite structure exists (so only austenitic)..How ever the structure of austenite can be stabilized at room temperature by adding alloying elements...
You can't tell that if a stainless is not magnetic that doesn't mean that it is not stainless steel.......
Regards Prakash
Wouter van Marle wrote:

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Hi
There are two classes of stainless steel, one is ferritic stainless steel and another is austenitic stainless steel......so coming to the point, ferritic is magnetic and austenitic is non-ferromagnetic....the curie temp for Iron is 768 deg. celsius......so below that ferrite structure exists (so only called as ferritic stainless steel)...above that austenite structure exists (so only austenitic)..How ever the structure of austenite can be stabilized at room temperature by adding alloying elements...
You can't tell that if a stainless is not magnetic that doesn't mean that it is not stainless steel.......
Regards Prakash
Wouter van Marle wrote:

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Most experts use three: austenitic, ferritic and martensitic. Ferritic is as magnetic as regular steels, austenitic and martensitic are not very magnetic.
BUT 1) they are not totally non-magnetic in the sense that brass is. amd 2) both can develop magnetism with cold-work and other treatments by generating ferritic phase as some fraction of the whole. Even a small amount of ferritic phase renders them far from non-magnetic.
If you need truely non-magnetic stuff, don't depend on stainless, use titanium or aluminum or brass (depending on other needs).
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