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Stainless Steel and Magnets

Frankie | Posted in General Discussion on July 4, 2006 08:38am

I am finishing up a stainless steel vent hood and duct installation over a garland range. The back panel of the range is also stainless steel.

I needed to level and plumb the vertcal duct and thought of using my stabila, cool modified torpedo level. It won’t stick to the duct or the hood but it does stick to the fridge and rear stainless steel panel of the garland range.

Why does some stainless work with magnets while others don’t? A month ago I was finishing up another kitchen project and the mgnets would not stick to the fridge door even though it was ss. It was a new fridge so I thought it was clad in a ss electroplated Formica. Maybe it really is ss!

So can anyone tell me why this is happening?

Frankie

Exasperate your vegetables until exhausted; disturb your chestnuts in milk until queasy, then disappoint.

Arabella Weir as Minty Marchmont – Posh Nosh

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Replies

  1. User avater
    IMERC | Jul 04, 2006 09:08am | #1

    with true SS it's the higher percentage of nickle that makes it magnetic...

    on the low end of SS it's all the "filler" metals that make it magnetic...

    IIRC it take at least 5% nickle to qualify it as SS...

    some SS is called SS even though it is stretching the definition a bit...

     

    so real quality SS as for trash level SS are magnetic.. middle road isn't...

     

    Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming

    WOW!!! What a Ride!

    Forget the primal scream, just ROAR!!!



    Edited 7/4/2006 2:10 am by IMERC

  2. User avater
    Sphere | Jul 04, 2006 02:07pm | #2

    Ig IMERC has a nickle magnet I want one too..it'd probably work with copper.

    here is why...

    The three main types of stainless steels are austenitic, ferritic, and martensitic. These three types of steels are identified by their microstructure or predominant crystal phase.

    Austenitic:
    Austenitic steels have austenite as their primary phase (face centered cubic crystal). These are alloys containing chromium and nickel (sometimes manganese and nitrogen), structured around the Type 302 composition of iron, 18% chromium, and 8% nickel. Austenitic steels are not hardenable by heat treatment. The most familiar stainless steel is probably Type 304, sometimes called T304 or simply 304. Type 304 surgical stainless steel is an austenitic steel containing 18-20% chromium and 8-10% nickel.

    Ferritic:
    Ferritic steels have ferrite (body centered cubic crystal) as their main phase. These steels contain iron and chromium, based on the Type 430 composition of 17% chromium. Ferritic steel is less ductile than austenitic steel and is not hardenable by heat treatment.

    Martensitic:
    The characteristic orthorhombic martensite microstructure was first observed by German microscopist Adolf Martens around 1890. Martensitic steels are low carbon steels built around the Type 410 composition of iron, 12% chromium, and 0.12% carbon. They may be tempered and hardened. Martensite gives steel great hardness, but it also reduces its toughness and makes it brittle, so few steels are fully hardened.

    There are also other grades of stainless steels, such as precipitation-hardened, duplex, and cast stainless steels. Stainless steel can be produced in a variety of finishes and textures and can be tinted over a broad spectrum of colors.

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    Spheramid Enterprises Architectural Woodworks

    There is no cure for stupid. R. White.

    1. Frankie | Jul 04, 2006 02:50pm | #3

      Holy Crap!Quite the tech and well stated response! However - It does not, as far as I can read and in layman's terms, explain how the three types affect magnetism. I went to the About Site and read a few of their other articles. None address magnetism. I do now know how to clean ss, why spots are left and how NOT to clean ss.Interesting reading.Nickel is not magnetic? Never really even considered thinking about it. Arg! More thinking!Frankie

      Exasperate your vegetables until exhausted; disturb your chestnuts in milk until queasy, then disappoint.

      Arabella Weir as Minty Marchmont - Posh Nosh

      1. User avater
        BillHartmann | Jul 04, 2006 03:14pm | #4

        http://www.physlink.com/Education/AskExperts/ae546.cfm"QuestionIs stainless steel magnetic? Does it depend on the amount of chromium, or nickel alloy?Asked by: James McGuiganAnswerStainless steels are a very broad group of metals. The name was adopted as a generic term for steel alloys with a minimum of 10.5% chromium. The chromium gives the steel its 'stainless' properties - essentially corrosion resistance. On the surface of the metal, a very thin chromium-rich oxide layer is formed which is inert - i.e. it prevents the steel from rusting. The advantage of stainless steels over plated steels is that, if scratched or damaged, the steel will 'self-repair' as a new oxide layer is formed. In plated steels, scratches in the plate will often lead to corrosion of the steel underneath.Stainless steel wrenchIn general, the higher the proportion of chromium, the stronger the corrosion resistance of the steel. In addition to chromium, other metals are added to give the steel particular properties such as strength and malleability. Specifically nickel is used to strengthen the oxide layer.As for whether they are magnetic, the answer is that it depends. There are several families of stainless steels with different physical properties. A basic stainless steel has a 'ferritic' structure and is magnetic. These are formed from the addition of chromium and can be hardened through the addition of carbon (making them 'martensitic') and are often used in cutlery. However, the most common stainless steels are 'austenitic' - these have a higher chromium content and nickel is also added. It is the nickel which modifies the physical structure of the steel and makes it non-magnetic.So the answer is yes, the magnetic properties of stainless steel are very dependent on the elements added into the alloy, and specifically the addition of nickel can change the structure from magnetic to non-magnetic."Also;http://www.azom.com/details.asp?ArticleID=1140

      2. User avater
        Sphere | Jul 04, 2006 03:38pm | #5

        The short answer is that the cladding is SS on a reefer not the frame inside..otherwise the kids pics won't stick.

        Spheramid Enterprises Architectural Woodworks

        There is no cure for stupid. R. White.

      3. WorkshopJon | Jul 04, 2006 03:47pm | #6

        Holy Crap!

        Quite the tech and well stated response!"

        Frankie,

        I think that was a cut and paste on Duane's part, albeit a good one, and he did take the time to track down a site with good info.

        WSJ 

        1. Frankie | Jul 04, 2006 05:43pm | #7

          Yup! And I much appreciate(d) it. I was just commenting that though I was better informed - never knew there was more than one type of ss - I remained confused. It was still a very generous and well researched response which I had not found/ known.Internet posting allow us at times to become familiar and write to/ address each other in an informal/ casual way - a way which we may not use if we were face to face. This is often forgotten, disregarded, or misinterpreted. Please do not understand any of my posts to be flipant or disrespectful. This site and its members are an important part of my life and learning adventures. I have the highest regard for each - well, at least most of the members.Frankie

          Exasperate your vegetables until exhausted; disturb your chestnuts in milk until queasy, then disappoint.

          Arabella Weir as Minty Marchmont - Posh Nosh

  3. Egg | Jul 04, 2006 06:21pm | #8

    Easy to see that metallurgy is a science.

    Magnets are attracted to iron Fe.

    More basically 300 series stainless steels do not have iron, also called non-magnetic stainless.

    400 series stainless contain a small percentage of iron.  Therefore, they can "rust" usually more of a staining, they can however be more formable, more weldable and easier to topcoat since the iron will accept a phosphate pretreatment.

    1. User avater
      BillHartmann | Jul 04, 2006 06:37pm | #9

      "More basically 300 series stainless steels do not have iron, also called non-magnetic stainless."If it does not have iron in it then it is STEEL, stainless or not.

    2. moltenmetal | Jul 04, 2006 08:21pm | #10

      Sorry but I have to correct that point:  austenitic stainless steels (304, 316 etc.) are still STEELS, and they have large quantities of iron in them.  Indeed 304 and 316SS are each over 70% IRON!  They also contain significant amounts of nickel- in fact, more than 8%.  The difference is that the iron in the stainless steel is embedded in a different crystal structure (austenite) than the ferrite, martensite etc. that is found typically in carbon steel.  The same goes for the nickel- it too is bound up in the austenite crystals.

      Austenite crystals do not attract a magnet.  So 304 or 316SS will not "stick to" a magnet- unless something has been done to create another crystal phase in the metal.  Cold work (i.e. like threading or forming) will cause some ferrite or martensite to form.  Welding can do so too, especially if it's done with a filler metal designed to have some additional ferrite content so the weldments don't crack as easily.   The same goes for some of the cast grades like CF8M (the material the commodity stainless ball valves and 150# threaded fittings are made from, even when they're stamped "316"):  this material too will sometimes weakly attract a magnet, since it contains some ferrite to impart crack resistance etc.  So sometimes, even 304 or 316 SS threaded rod or welded articles will weakly attract a magnet.  

      Stainless steels which must be hardened or maintain an edge, such as for knives etc., are usually not made of austenitic stainless steels.  They're made from ferritic or preferrably martensitic grades, because these are superior for the job relative to 304 or 316 grades.  These materials attract a magnet very strongly.  I'm just guessing, but I suspect that the cladding on refrigerators etc. where aesthetics are more important than corrosion resistance, and where some hardness will impart some scratch and dent resistance to the material, might be made of ferritic or martensitic grades too.

      To make things even more complex, there are also "duplex" ferritic/austenitic grades of stainless steel.  These have SUPERIOR corrosion resistance to that of 316SS for seawater etc., yet these too are fairly strongly attracted to a magnet because they may contain up to 50% ferrite crystal content.  They're also a b*tch to weld, because every time you heat the stuff up you have a tendency to produce more ferrite.  Too much ferrite and the corrosion resistance is greatly reduced.

      So- whether a material (strongly) sticks to a magnet or not is a poor gauge of whether the material is stainless steel or not, and is a very poor gauge of whether the material will have the corrosion resistance you want even if you KNOW it's stainless steel.  If you know the material to be a steel, all a magnet will tell you is if the material is an austenitic stainless steel, or something else.

       

      1. chrisjohns | Jul 05, 2006 10:18pm | #11

        A "ferrite gauge" is a calibrated series of magnets used to measure ferrite content. 

        I have used ferrite gauges to measure % ferrite in "austenitic stainless steels" which had a range of % ferrite of 0 to about 25%.  The minimum increment that I recall was .5%.

        Ferrite is a magnetic metalurgical phase. 

        Ferrite in stainless steel is like chocolate chips in a cookie.

        These observations may help some to get a feel for how some stainless steel can be "magnetic" while others, even in the same category, are not.

  4. CJM | Jul 05, 2006 10:48pm | #12

    "Why does some stainless work with magnets while others don't?"

    Well, Aluminum is non-magnetic...

    1. JohnSprung | Jul 06, 2006 02:56am | #13

      Each iron atom has its own tiny little bit of magnetism.  The crystal structure determines whether these all line up and make the object magnetic, or cancel each other and make it non-magnetic. 

      As for a quick and dirty home magnet test, if it isn't magnetic, it's probably some kind of stainless, or maybe a plated non-ferrous part.  If it is magnetic, in most cases it's just plain old cold rolled rustable steel.  But there's a chance it could be stainless. 

      It also helps to consider what kind of part it is.  Nails, for instance, will almost always be either magnetic ordinary steel, or non-magnetic 304 or 316 stainless.  The more exotic the part, like shoulder screws with fancy heads, the less the magnet test means. 

      The other wild card is the influx of cheap stuff from the second and third worlds.  Metalurgy QC can be really bad there.  

       

      -- J.S.

       

    2. WorkshopJon | Jul 07, 2006 12:45am | #14

      Well, Aluminum is non-magnetic..."

      A trip to the Boston Museum of Science will prove that statement wrong, as they have a display that magnetically hovers an aluminum disk.  You drop the disk in and press a button.   The aluminum disk hovers.......

      WSJ

      1. User avater
        Sphere | Jul 07, 2006 01:09am | #15

        I recall that some of the Ele MAg "rails" on a MAGLEV train were Al too..funny how that is.

        Spheramid Enterprises Architectural Woodworks

        There is no cure for stupid. R. White.

      2. CJM | Jul 07, 2006 08:25pm | #16

        Aluminium is nontoxic (as the metal), non-magnetic, and non-sparking. The Mag-lev devices work with an aluminum guideway. The guideway has aluminum loops at normal temperature; their loop currents are generated by magnetic induction as vehicle loops move past them. The induced currents in “figure-8” guideway loops levitate and vertically stabilize the vehicle. So the magnetic field is not an intrinsic property of the aluminum.
        As far as the floating aluminum disc, well any object can be made to levitate in a strong (>16 Tesla) field. Here's a link to a frog made to levitate: http://www.hfml.ru.nl/froglev.html
        The same was once done to a Sumo wrestler. The point is, one possible reason a magnet may not stick to ductwork or a refrigerator, is that some quantity of aluminum may have been used in the product, therefore a magnet will not stick to it. And there are aluminum based products, such as refrigerators and duct work made from aluminum, although they are not in widespread use.The first principle is that you must not fool yourself and you are the easiest person to fool.
        Richard P. Feynman

      3. DanH | Jul 07, 2006 09:11pm | #18

        That's an induction effect -- the same for any conductor.
        If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison

        1. moltenmetal | Jul 08, 2006 04:07am | #19

          You can demonstrate this effect by dropping a rare earth magnet down a piece of copper tubing.  Aluminum tubing will do too, but copper's more conductive so the effect is more pronounced.   It'll take a surprisingly long time for the magnet to fall out.  No more mysterious than dropping a rock in a glass full of glycerine, but it's still pretty cool.

  5. DanH | Jul 07, 2006 09:07pm | #17

    Generally SS is not strongly magnetic, though it varies from alloy to alloy. When I was in the testing biz it was sometimes used for test fixtures precisely because of its non-magnetic properties.

    If Tyranny and Oppression come to this land, it will be in the guise of fighting a foreign enemy. --James Madison

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