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Stainless Steel That is Magnetic?

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Q. We are considering the purchase of a high-end stainless steel appliance. To be sure that it was stainless, and not brushed chrome, we tested it with a magnet and found it to be magnetic. The manufacturer says it's definitely stainless, and not brushed chrome. Can anyone explain this? And is a magnetic stainless a good quality metal for kitchen appliances? Thanks very much for anyone's response to this. Carly

Carling Ldeleted
- Philadelphia, Pennsylvania, USA


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A. Hi Carling. Check your stainless knives, forks, and spoons with a magnet and you may discover the same situation, with some or all magnetic. The '400' series stainless steels that are often used in a kitchen are magnetic. It's the '300' series stainless steels that are non-magnetic. Magnetic stainless is probably good enough for a kitchen.

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


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A. Type 400 series stainless contains no nickel (one of the most expensive element in stainless alloy), therefore is cheaper in price. Some of the better flatware products are type 304 or (18-8) stainless.

Type 304 stainless offers better corrosion resistance than the 400 series. Most architectural stainless is done in the 300 series.

Michael Liu Taylor
   specialty stainless steel distributor
Dallas, Texas


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A. Carling,

As the above people have said, the series 400 stainless is magnetic and the 300 series for practical kitchen purposes it is non magnetic.

The 400 series knives etc keep a nice sharp edge, the 300 series don't corrode so easily and they are softer, due to the nickel, one assumes.

HOWEVER, strictly speaking, series 300 ARE magnetic. If one were towing a magnetometer behind an aircraft to measure ground magnetism, the instrument will fail were stainless used ... something to do with magnetic flux. Instead, one makes the instrument from aluminium.

... in the 60's we used to make plastic 'birds', as they were called, for towing behind aircraft (for Barringer Research's magnetometers) and aerodynamically one had to be very careful otherwise these 'birds' would swing around crazily and chase the aircraft! That's when they and we learned about about stainless and magnetism. End of boring story.

Cheers !

freeman newton portrait Freeman Newton
- White Rock, British Columbia, Canada

freeman newton died


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A. All of the above is correct, but probably not the answer to your question. My guess is that the side panels of your stainless steel kitchen appliances are probably made from cold-rolled 300 series stainless steel - probably type 301 or 302. These alloys have very similar chemical composition (18 Cr and 8 Ni) and corrosion resistance to type 304, which was mentioned above. These are all nominally austenitic alloys (nonmagnetic), but some of the austenite transforms to martensite (magnetic) when the material is deformed, as in cold rolling. This martensite transformation causes the 300-series to be magnetic when cold formed.

The cold-rolled condition is much harder than annealed material, which helps to keep the panels stiff and resistant to denting, even when very thin. An annealed 304 stainless steel panel would dent easily and would soon be not very pretty from normal wear and tear.

The magnetic response for the appliance panels is similar to that for kitchen flatware, which is mostly made from 18-8 stainless steel. Cutlery (knives), scissors, and the like are often made from 400 series alloys, which can be heat treated to high hardness for sharpening. The 300 series alloys cannot be hardened by heat treating.

I hope that this makes sense. If you really want to know how the panels are made, I bet that you could contact the manufacturer and track down a materials engineer that would set things straight.

hanke Larry Hanke
  materials testing laboratory
Minneapolis, Minnesota



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thumbsup2Thanks so very much for this info. We will go ahead and purchase this item and not be worried about getting inferior stainless.

We appreciate the time you, and all the others who replied, have taken to write.

Carly

Carly Ldeleted
- Philadelphia, Pennsylvania USA


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Don't leave this book with the last page ripped out, though, Carly. Give us the manufacturer and model no. after you buy it, and we'll try to get their materials engineer to chime in as Mr. Hanke suggested.

 

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

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A. Sir,

There are magnetic and non-magnetic alloys and formations of stainless steel however, if you will take a magnet and compare the strength of pull against ASTM steel, you will find that the pull of a magnet toward "any" stainless steel is quite a bit less than that for mild steel.

Norman B. Czerski
- Eagle River, Alaska, USA



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Q. I would like to put stainless panels in my built-in refrigerator, but I would like them to be magnetic. These are custom made/cut. I am wondering if I can use the 400 series stainless steel for this purpose or if there's a functional reason that I would need to use the 300 series.

Thank you.

Giselle Gdeleted
- San Francisco, California, USA


++++ appended here by the editor in lieu of spawning a duplicative thread

Q. I just purchased stainless steel exhaust pipes for my auto, I checked with a magnet and it sticks! Markings on pipe are (2", 14 ga) ALUM 02243 BL AT 23-29-14, can anyone tell from these markings if pipe is stainless? I would like to know what I'm talking about before I call and try to return.

Thanks,

Matt DiPietrantonio
Service Tech - Ocean View, New Jersey


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A. Stainless steel 300 series are slightly magnetic since they can contain from 0 to 8% ferrite formed after solidification depending of the chemistry of the steel batch. The second cause of magnetic response is martensitic transformation upon cold working or machining (alloy 301 work hardens and respond the most that way).

In order to have a soft response to magnet the Ni/Cr ratio must be high. Also to maintain magnetic response to minimum a solution anneal treatment can be done 1095 °C then rapid quench. A stress relieve treatment on non-sensitizing grades like 304L can be done at 700-800 °C (this cannot be done on 304 or 316 because carbides will precipitate and the part will corrode.

Guy Morin
- Trois-Rivières, QC, Canada


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Q. I recently bought a barbeque, made by Charmglow from Home Depot; listed materials in construction are stainless steel and aluminum. I tried the magnet test and found that it adhered to most of the grill (excepting the side panels of the cover, cast aluminum). The only part the magnet would not adhere to was the lifting handle on the cover on the grill. If it's not brushed/polished finish, to me it looks like paint on steel -- is there a way to determine if the flat panels and frame are stainless or aluminum or just painted steel before I return it?
Also, if the side panels are 400 series stainless, how will their corrosion resistance be in the salt air of the Fla. keys? ... but it looks soooooooo pretty :(

R Patton
- Key Largo, Florida, USA


May 31, 2008

Q. ARE MANUFACTURERS PASSING OFF STEEL USED ON REFRIGERATORS AS 'STAINLESS', WHEN IT STAINS LIKE WATER MARKS AND IS NON-MAGNETIC?

COLSTER SOUL
CONSUMER - UK


June 2, 2008

A. Hi, Colster. Yes, some of them.

Plain steel is magnetic. The best grades of stainless steel are non-magnetic, but some grades of stainless steel are magnetic (the grades that don't have nickel in them). Plain steel does not corrode with white water marks, it corrodes with red rust. Water marks are usually from using a cleaner that is not compatible with the stainless.

To make a confusing situation even more confusing, many manufacturers now coat the stainless steel with some kind of organic clearcoat (a clear paint); and others ("Clean Steel" style) paint plain steel to make it look like stainless.

Regardless, don't consider the finish on stainless steel appliances as robust; it may look "industrial strength" but it is anything but. Painted appliances are far more robust, as hundreds of sob stories about disappointment with stainless appliances on this site attest.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

June 16, 2008

thumbsup2Thank you Ted for your informative message. I wish I had contacted you before choosing my "stainless steel" fridge/freezer. I am very disappointed with its appearance after only three months' use. A liquid appears to have dripped down the lower door leaving grey marks. I had explained to the salesperson that I wanted a labour-saving kitchen owing to my weak hands and mobility problem. A note with the appliance warned not to use harsh cleaners but that now recommended contains citric acid. I should have stuck to white, but already had a Neff s/s oven which is easy to keep clean. I think there should be a warning notice on 'stainless steel' which is not stainless. Again thanks.

Dorothy Sawle
- Solihull, England


October 8, 2010

A. To put everyone at rest, stainless steel sometimes becomes magnetic if it has been worked with or casted. We sell Stainless Steel Fittings and always have this issue with clients and their silly magnets and who don't understand the physics behind metal.

Christopher Europa
Stainless Steel Fittings Supplier - Cape Town, South Africa

October 2010

Thanks, Christopher.

You are right that magnets don't tell the whole story. But the reason that people try a magnet to check whether something is a stainless or not isn't mindless curiosity, it's because its performance proved unsatisfactory. When a consumer spends $1000+ for what is promoted as stainless steel, they shouldn't have to "understand the physics behind metal" to avoid being deceived by a manufacturer, some of whom are working hard to do just that. Before we dismiss people as "silly" for using the limited tools at their disposal, I think we should examine what we may be doing that is delivering performance that they are unsatisfied with.

As one example, flatware manufacturers like Oneida have cheapened their patterns by converting them from 18/8 (type 300) to 18/0 (type 400). When people experience rusting, they test and find that the new pieces that are rusting are magnetic, unlike their old pieces that didn't rust. As another example, we may sometimes call a cast stainless steel item "type 316" even though it will rust under conditions where people know that real 316 shouldn't rust; so they test it with a magnet and find that it is magnetic. Are we perhaps wrong in calling it 316 if it is far more prone to rusting than people should expect from such a label? br>
Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

March 14, 2012

Q. Can I do magnetic test to SA 240 Gr 321
Thanks,

Abdelkrim Boulfiza
- Algeria

March 15, 2012

A. Hi, Abdelkrim. There are dozens of grades of stainless steel that are magnetic and dozens that aren't. So, while a strongly magnetic sample is probably not type 321, unfortunately a non-magnetic type is not necessarily 321.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey

March 17, 2012

Q. We have received from a local vendor M6x10 set screws in duplex steel of grade 1.4410. The supplies are supported by a Compliance letter stating that the material grade is 1.4410.However, the screws are found to be Non-magnetic.

Is our Rejection stating that "Material of screws is not "Duplex steel", but appears to be "Stainless steel" justified based on testing with a magnet.

Madan Mohan
- Saudi Arabia


July 26, 2012

A. 1.4410 is a super duplex stainless steel with a microstructure of 50:50 Austenite & Ferrite.

Madan Mohan
- Saudi Arabia


May 10, 2012

A. There are two types of 400 series steels, Martensitic and Ferritic. Martensitic is magnetic; Austentic (300 series) and Ferritic are not, from my understanding.

Thanks

Randy Butternubs
- Hopkinsville, Kentucky, USA


April 9, 2014

A. Austenitic stainless (300 series) is what the industry calls non-magnetic, while martensitic and ferritic are magnetic.

The fact that an appliance such as a dishwasher is stained does not mean it isn't stainless steel, but may be a result of calcium or other substance in hard water being deposited on a not-mirror-smooth surface. Stainless steel is not absolutely stain-proof as the name might imply, but much more resistant to corrosives than non-stainless steels with less chromium and nickel.

If you want to see the difference, buy a small piece of mild steel plate from your local hardware supplier and put it in an out-of-the-way place in your dishwasher for six months... Then compare to the inside walls of the dishwasher.

Jon Roesler
- Layton, Utah, USA

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