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Why is stainless steel non-magnetic?

Q. I am a grade 6 science teacher. I teach that steel is a magnetic metal, and the question comes up, "why isn't stainless steel, such as is found on the sink faucet, attracted to a magnet? I am at a loss to answer. HELP!

Thomas Sdeleted
- Kingsville, Maryland


 

A. I'm no expert on this myself, Thomas, but magnetism does not actually work on the individual elements of the alloy; it works on materials that allow the alignments of electrons to be pulled into a particular preferred orientation. The short answer is that some stainless steels, because of the way the nickel combines with the iron, produce a crystal structure that has the electrons aligned randomly and precludes the atoms from being free to move into the orientation that we identify as magnetic.

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

Stainless Steel for Design Engineers


 

A. Hello Thomas!

Some stainless steels are magnetic: those whose atomic arrangement is in a body centered cubic or body centered tetragonal orientation can be strongly ferromagnetic. The stainless steel in your sink is usually in a face centered cubic orientation, and it isn't ferromagnetic.

That said, I think your question remains, and my best answer is "Heck, I don't know, and I've got a BS in Metallurgy". Guess I slept through that part of my solid state physics classes that covered the question, and explained then why pure nickel (FCC) and cobalt (Hexagonal Close Packed, which is close to FCC) ARE ferromagnetic.

I guess I'm also saying that the answer isn't obvious, by any means, and that it'd be difficult to give a full explanation to sixth grade students. I'd stick with Ted's answer.

Good luck!

Lee Gearhart
metallurgist
East Aurora, New York



May 30, 2008

Q. A lot of welders will tell you to check a metal with a magnet to see if its iron/steel. This obviously doesn't seem foolproof?

drew MANN
DIY - UK


July 2, 2008

A. Hi, Drew. I'd say that being non-magnetic warns the welder that the item is not plain steel, so s/he must give it up or at least proceed differently. But being magnetic is not ironclad proof (bad pun) that it is plain steel that will be easily welded.

Regards,

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

August 13, 2008

A. All stainless is not the same. Different types and ingredients. Different properties. There are tables to tell you this.

Look up "passivation".
This is a process that "lines up" the nonferrous molecules on the surface so the stainless does not rust and is nonmagnetic.

Old (more than 20 yrs) 304 stainless is usually nonmagnetic as they all did this extra step so the product didn't corrode. Try it on some old flatware sometime, and then on new. New 304 stainless is usually magnetic-most producers have cut the passivation step as a cost saving measure. Old stainless is usually NON magnetic.

C Laza
plumbing - Milwaukee,Wisconsin



October 30, 2008

Q. I would like to know if a magnet can stick to stainless steel jewelry, if it does is that piece of jewelry a FAKE?

Clarence Anderson
- McDonough, Georgia


November 6, 2008

A. Hello, C. Laza, thanks for your reply which is somewhat accurate, but not fully. Passivation does not have to do with magnetism; it is a chemical process that dissolves iron from the surface so as to deter rusting. 304 stainless steel is still (mostly) non-magnetic (but can become attracted to a magnet as a result of cold working). Stainless which is strongly magnetic is a different type of stainless -- not 3xx series but 4xx series. It is cheaper because it contains no nickel, but there are occasions where it's actually better like knife blades (304 cannot hold an edge).

Hi, Clarence. Some stainless steel is magnetic, some is not. In either case, stainless steel is not a precious metal like gold, nor even a semi-precious metal like silver. So I don't know exactly what meaning you have in mind when you ask whether it's "fake".

Regards,

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

May 18, 2011

A. I can shed some light on the question about stainless steel, jewelry and the "fake" question as its the exact reason I followed links to get to this site. I just ordered a fairly expensive watch on line that is purported to be stainless steel, but my curiosity led me to the internet when I noticed a magnet would not stick to either the watch or the ss bracelet. From the reading I've done here, I'm content with new information regarding the molecular arrangements possible and the reasons some stainless isn't magnetic. Thank you!

Michael Williams
- Detroit, Michigan, USA


December 1, 2009

Q. Some people around the planet produce stainless steel foil in a form that is thin enough to handle, like aluminum foil. If stainless is a chemical process on the top of magnetic material, like steel. How is it possible to obtain a non magnetic material like foil when steel itself has to be thick enough to attract a magnet. Yet the foil is made in order of 0.05 mm thick.

Gilbert Sambolin Sr.
- Hallandale, Florida


December 2009

A. Hi, Gilbert. Stainless steel is not a "chemical process on the top of magnetic material". Stainless steel is a solid material where chrome and/or nickel and some other materials are mixed in with steel to produce an alloy that has different characteristics, including a resistance to rusting.

Regards,

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


Hematite vs. Magnetite

April 30, 2011

Q. I was under the understanding that stainless has hematite (non magnetic ore) and magnetic steel is made with magnetite ore. Obviously there are nickel/chrome ext. But I'm just referring to magnetic properties.

henry vachon
- gwinn, Michigan usa

wikipedia
Hematite
Magnetite


April 30, 2011

Hi, Henry.

I'd say partial credit on that one :-)

You are correct that hematite (Fe2O3) is non-ferromagnetic and magnetite (Fe3O4) is ferromagnetic. But I think you'll find that once the materials are smelted into iron, it doesn't matter which oxidation state the iron was originally in, and both can be made into steel, magnetic grades of stainless steel, and non-magnetic grades of stainless steel.

Regards,

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

September 8, 2011

Q. I have come across the problem of non magnetic stainless steel a lot over the last 12 months, as the firm I am contracting with want all there stainless steel m/c parts to be non magnetic, but I have found this not to be possible . As the part have a lot of different machining processes done to them. We have used different grades, i.e., 303 & 304 etc, but at then end of the day there is alway some magnetic attraction. 302 grade is meant to be non magnetic but you can't get hold of it in any real material sizes.

Paul Nobbs
- Stevenage, Herts, UK

October 5, 2011

A. Austenitic Stainless steels are generally non-magnetic (face centered cubic structure) but Ferritic and Martensitic Stainless? steels usually are. A fairly graphic demonstration can be given by heating a piece of Carbon Steel with a magnet attached, when the steel reaches the Austenitic transformation temperature the magnet will fall off.

George Waite
welding engineer - Totnes Devon UK

October 7, 2011

Q. So, if hematite (Fe2O3) is a non-ferromagnetic and can made into Steel or Stainless steel, does the raw Steel type, before any processes (cold or hot), exhibit any magnetic properties. Or, is it still non-magnetic with less corrosion resistance and less tensile strength?

Thank you

Samuel Monroe
- Sarasota, Florida


Stainless Steel Armature Plates for Maglocks

October 12, 2011

Q. I have an armature plate from a maglock. It appears to be stainless steel of some sorts. I cut a piece of the plate off with a hacksaw and could see that the metal was uniform throughout. In other words, it is not mild steel that has been plated. I thought stainless steel was non-magnetic.

My need to know is based on the following. I have been approached to make Maglocks for a customer. It would be helpful if I could bypass the learning curve of finding out what materials need to be used.

Adrian Carboni
Product Designer - Johannesburg South Africa

October 12, 2011

A. Hi, Adrian.

I don't know what the item is made of, and I suspect that just cutting it in half and observing with the naked eye won't give enough info. But, as mentioned, some stainless steels including the 4xx series are magnetic, not much different from plain steel. The 3xx series are theoretically non-magnetic (although cold working may make them slightly magnetic). Good luck.

Regards,

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


December 17, 2011

thumbsup2Thanks for the interesting thread. I was also under the impression that stainless was non-magnetic, but that myth has been busted.
Q. I do have a question regarding stainless steel appliances. I am curious whether one stainless is better than another. It appears that on this thread the non magnetic stainless goes thru an extra process and with the added nickel would seem more expensive to make and has better "healing" properties. I could then conclude that manufacturer spent more money for better quality? Or is that stretching it?

Erik Visser
- British Columbia, Canada


December 2011

A. Hi, Erik. No, I don't think that is stretching it at all.

18/8 (8% nickel) or 18/10 (10% nickel) is not only more expensive than 18/0 (0% nickel) because of the cost of the nickel, but it is more corrosion resistant. Yes, the manufacturer spent more on 18/8 or 18/10 and it is a better material for appliances.

If the appliance is magnetic it is not necessarily true that it is not stainless, so the manufacturer isn't necessarily misleading you -- but I personally would bring a magnet to the appliance store and not buy any appliance that a magnet sticks to.

Regards,

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

April 29, 2012

A. Dear Sir
We have been manufacturing magnetic 302 stainless steel wires with tensiles in excess of 3000MPA for decades. This is simply a property characteristic that results from producing zero stress relaxation arch wires for Orthodontics. It is commonly known as Australian Light Wire or A J Wilcock Orthodontic Wire. Initially, the raw material is Austenitic and non magnetic, however, after the processes of thermo-mechanical work hardening and repetitive dynamic strain aging it becomes Martensitic and highly magnetic. Some wires have been known to have yields in excess of 3000MPA in the straightened condition! We have made tons of the stuff over the last 65 years. Sincerely

Arthur Wilcock
- Strasbourg France



September 17, 2012

Q. Hi my problem is I'm trying to weld 316 stainless down-hole electric motor that is full of magnets that give me really bad arc blow.

I was wondering what my best welding process would be? SMAW DC will not work at all; GMAW works somewhat, but we are getting porosity and we need a seal weld.
Thank you for your time.
Sheldon

Sheldon Martin
- Edmonton,Alberta,Canada

ACRONYMS:

SMAW = Shielded Metal Arc Welding
DC = Direct Current
GMAW = Gas Metal Arc Welding

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