Stainless Steel That is Magnetic?

A. Hi Carling. Check your stainless knives, forks, and spoons with a magnet and you may discover the same situation, with some or all of them magnetic. The '400' series stainless steels (about 18% chrome, but no nickel in them) that are often used in a kitchen are magnetic. It's the '300' series stainless steels (18% chrome plus 8-10% nickel) that are non-magnetic (even then, cold rolling the panels can make them magnetic). Magnetic stainless is probably good enough for a kitchen, but it is less expensive (and not as good) as the non-magnetic stainless steels.

A. Type 400 series stainless contains no nickel (one of the most expensive elements 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.

A. Carling,

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

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 who would set things straight.

Thanks 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

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.

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.

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 responds 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.

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 than stainless steel, as hundreds of sob stories about disappointment with stainless appliances on this site attest.

Regards,

A. To put everyone at rest, stainless steel sometimes becomes magnetic if it has been worked with or cast. 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.

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October 2010

Thanks, Christopher. You are right that magnets don't tell the whole story; one simple test almost never does.

opinion! But the reason that people try a magnet to check whether something is stainless or not isn't silliness, it's because the performance of magnetic stainless steel has proven so 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 the manufacturer, some of whom are working very hard to do just exactly 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 justifiably disgusted with. My non-magnetic Frigidaire fridge, Maytag microwave, and Kenmore range all look fine ... whereas my newer Bosch magnetic stainless dishwasher is a disgrace -- which is a shame because, other than aesthetically, it's a good appliance. Am I "silly" when I decide I'll bring a magnet next time?

As another example, flatware manufacturers like Oneida have cheapened their patterns by converting them from 18/8 (type 3xx) to 18/0 (type 4xx). When people experience rusting, they test and find that their new pieces which are rusting are magnetic, unlike their old pattern pieces that didn't rust. Damn magnets, how can we let consumers be so unfair to Oneida? As another example, we may sometimes label a cast stainless steel fitting "type 316" even though metallurgists tell us that castings are not actually type 316, and even though they will rust under conditions where people know that rolled or wrought 316 would not rust; so the buyer tests it with a magnet and finds that the casting is magnetic. Are they misunderstanding the physics of metal, or are we wrong in trying to call it 316 when it is actually a casting and is far more prone to rusting than people have come to expect from a "316 stainless steel" label?
Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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,

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

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

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.

 Hi John, I appreciate the input, but my magnetic Bosch dishwasher did not succumb to calcium staining which my non-magnetic appliances were not exposed to ... it's 'stainless' material is grossly inferior, period.

Regards,

A. That's easy Marino, buy painted appliances! My painted Weber B-B-Q grill is 3 years old, never covered, and fine.

But my Kenmore stove/oven is non magnetic stainless steel and is fine too. Call me a "silly magnets guy who doesn't understand the physics behind metal", but the magnetic stainless steel of my Bosch dishwasher, which is much newer than the stove, and sitting right next to it, is very stained and discolored.

You might try to solve the grill problem by cleaning with citric acid and then clearcoating it. And be careful that you are not splashing from a hose with fertilizer onto your grill; that accelerates rusting.

Regards,

Stainless IS just that ... Stain LESS! Many manufacturers are turning to SS430 metal due to cost and availability. As well, a good test for rust-resistance is a magnet. If it holds a magnet then it is more susceptible to rust as less passive.

adv.
Either case, Scratch-B-Gone will quickly and safely remove this damage and restore your finish.

Good grilling.

 Hi Don. Remember that magnetic induction cookware must be magnetic :-)

Regards,