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Why isn't my SS cookware magnetic?

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E_M Feb 16, 2011 05:12 PM

So I have 2 old Faberware pots that say "Aluminum Clad Stainless Steel" on the bottom. Since I plan on switching to induction, I have been running around with a magnet taking stock of my equipment. These pots are not magnetic. Does anyone know why?

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  1. Chemicalkinetics Feb 16, 2011 05:20 PM

    Because not all stainless steels are magnetic. For example, 18/10 stainless steel is non-magnetic (if you investigate really hard, it is, but very faint)

    http://www.ssina.com/faq/index.html#5

    4 Replies
    1. re: Chemicalkinetics
      e
      E_M Feb 16, 2011 05:28 PM

      Oh.

      Are they a lesser quality?

      1. re: E_M
        Chemicalkinetics Feb 16, 2011 05:32 PM

        .... actually these non-magnetic stainless steel are/were considered HIGHER quality for flatware as well as cookware. Unless, of course, if the person is looking for an induction cooking, then they are inferior -- as in your case.

        http://www.foodservicewarehouse.com/e...

        1. re: Chemicalkinetics
          paulj Feb 16, 2011 09:09 PM

          It is common to use 18/10 for the body of the pot, and bond a magnetic layer on the base.

          1. re: paulj
            Chemicalkinetics Feb 17, 2011 07:54 AM

            You are right. Thanks.

    2. Sarah Feb 16, 2011 05:26 PM

      That's why s/s fridge doors are magnet-free.

      1. kaleokahu Feb 16, 2011 07:15 PM

        E_M: It's all in the alloy and the detection circuitry of your new induction top.

        If you plan to keep your cookware, take it all to a showroom that has a demonstration model of your make & model, and TEST them. This is the only way to be sure of compatibility. I suppose if you wanted to be thorough about it, you'd also compare your stuff to a known reference that works *well* on your intended cooktop.

        I really think the induction manufacturers could increase sales and minimize uncertainty and hard feelings if they simply included a converter disk with every stovetop. Seems like common sense to me...

        11 Replies
        1. re: kaleokahu
          paulj Feb 16, 2011 09:07 PM

          Are you implying that some non-magnetic SS cookware works on one brand of Induction cooktop and not on another?

          The usual claim is that if the pan is magnetic (a modest size magnet, such as a kitchen door one, will stick to it), then it will work on an Induction stove.

          I have a partial counter example - a nonmagnetic SS mixing bowl that works just fine on an induction burner.

          Anyways, for the OP. Most induction compatible SS cookware has an extra layer of steel bonded to the base, one the does react to the burner. That layer often has a sharp corner (as opposed to rounded like the inside of a pan), though I'm sure that's not a requirement. It will also say induction-compatible and/or have a symbol such as a coil. European designed pots are more likely to have this.

          1. re: paulj
            kaleokahu Feb 17, 2011 08:47 AM

            paulj: What I am saying and implying is that the different manufacturers of the cooktops have different designs, electronics and sensors. There are cases like yours reported here where pans that will not respond to a household magnet will work (read: with the poster's cooktop). Likewise, it's reported that some pans that do attract the same magnet will not work (same proviso).

            I'd also like to observe that it may not be as binary an analysis as these discussions suggest. That is, I doubt that it is as simple as works/doesn't work. Yes, the pan has to trip the detection circuitry to persuade the cooktop to energize the coil in the first place. But as we round first base, I think we have to look at whether all degrees of magnetism in the materials alloys produce heat equally well. Your counterexample suggests so, since I think your bowl is in fact very weakly magnetic. But I am not sure that a more ferromagnetic alloy bowl that is otherwise the same would perform exactly the same.

            What I'm pondering here is that, when a manufacturer claims "Induction Compatible" for a ware, what does that really mean? That it will or is likely to be detected? That if detected it will heat? That it will heat to a certain % of the theoretical output of the hob? What latitude is there between tripping the detector and maximum energy transfer? If someone knows if the EU or the Cookware Manufacturer's Assn. or other body has standards for these claims, I'd like to read them.

            1. re: kaleokahu
              paulj Feb 17, 2011 09:32 AM

              My guess is that the detection circuit is there, primarily to protect the cooktop itself. Some electronics can damage themselves if run without a load. But I'm quite rusty on the subject.

              Secondarily the detection circuits should reduce user frustration. You don't want to put a pan on the burner, and then wonder why it isn't hot after 5 minutes of use.

              As far as I know manufacturers are not making claims about how much heat their burners produce in specific pans. The 'heat' ratings are for the power consumed by the unit(s), not BTUs in the pan. Heat production in a pan may be depend on material (carbon steel, SS, etc), thickness, pan shape or area; but I haven't detected any obvious patterns. Cheap enameled steel heats just as well as cast iron or layered SS. That weakly magnetic SS bowl gave me the fastest boil times, though bowl shape may have more to do with that than material.

              Plus, except for limited tasks like boiling water, heat distribution is more important than heat output. And for that, it's hard to beat cast aluminum with a steel insert.

              For the OP, old American SS probably will not work on an induction burner. I have such a pan from around 1990 that does not work on my burner. It wasn't made with that use in mind.

              1. re: paulj
                Chemicalkinetics Feb 17, 2011 09:48 AM

                "My guess is that the detection circuit is there, primarily to protect the cooktop itself. Some electronics can damage themselves if run without a load"

                I believe you are right.

                1. re: Chemicalkinetics
                  kaleokahu Feb 17, 2011 05:11 PM

                  Chem and Paul: "...the detection circuit is there, primarily to protect the cooktop itself."

                  There is something to this, yes, but there is also the liability aspect of a magnetic utensil (or ring, watch, toy, etc.) left on the hob. No safety feature, no UL listing, no insurance, no stove business.

                  "[M]anufacturers are not making claims about how much heat their burners produce in specific pans." Yep, and someone should look at this, and we should all wonder why not. The touted 90% efficiency rating is the theoretical max, and if it turns out that it drops significantly with some/all "compatible" cookware, oops, guess we oughtn't say anything. Seems the induction manufacturers are getting a bye, since it is the *pan* that gets hot, not the hob.

                  "...old American SS... 1990" Dang I'm old. The Revereware I'm sending to Lucy is 1950s, and my coffeemaker is c1840!

                  1. re: kaleokahu
                    paulj Feb 17, 2011 05:53 PM

                    Exactly how is the 90% efficiency rating measured? 90% of the max power consumption of the whole unit? 90% of the power applied when using that pot?

                    Lets say the magnetic field sets up a weak current in the pan, and thus produce just a small amount heat. What does that do to the current consumption in the burner? If that current is high and generates a lot of heat in the coil, it would be waste heat, and mean low efficiency. But if the current in the coil is also low, then the efficiency can still be high, even though the overall power consumption is less than the rate maximum.

                    On the other hand if you use a converter disk, which gets hot, but the heat transfer from disk to pot is poor, you would end up with a poor efficiency. When efficiency is low, look for heat loss.

                    Compare an incandescent bulb with an LED. A 100w (1750 lm) incandescent may produce more light than a 10W (700lm) LED, but will also be a lot less efficient. You can tell by the amount of heat given off by the two bulbs, as well as the ratio of lm/w

                    To test the efficiency of a burner and pot combination you need to plug the burner into a watt meter, and measure the power consumed while doing a known amount of work, such as raising the temperature of a known mass of water x degrees. The speed at which that is done (boil time) is a measure of power, but not efficiency.

                    1. re: paulj
                      kaleokahu Feb 17, 2011 07:35 PM

                      paulj: I don't know how it's measured. It's pretty opaque in the DOE study that originated it and pretty much every induction zealot parrots this 90% number. All I know is that it is a theoretical max. In an earlier thread, I pondered whether the measurement takes into account real-world factors, such as the comparative efficiencies of Induction+SS (or CI) vs. Radiant+Cu--or even Induction+Converter+Cu. No one here knows, and I'm on my way to concluding NO ONE knows, even the boys & girls at DOE. A friend of mine in cookware manufacturing has told me that the CMA (comprised/funded 93% by SS clad corps) don't want this tested.

                      "To test the efficiency of a burner and pot combination you need to plug the burner into a watt meter, and measure the power consumed while doing a known amount of work..."

                      Amen, Brother! My efforts to interest a university applied physics lab in doing such a thing have--so far--come to naught. I might try a crude version of some tests if I could lay hands on a 220VAC watt meter. I have an induction appliance dealer lined up who is willing to let me play on their demonstration units.

                      Oh, and I checked with a couple induction top manufacturers, and they won't tell you the wattage and current numbers for lower hob settings. All they will give you is the max wattage rating.

                      1. re: kaleokahu
                        paulj Feb 17, 2011 08:03 PM

                        There's some mention of efficiency studies about half way down this page
                        http://theinductionsite.com/how-induc...

                        1. re: paulj
                          kaleokahu Feb 17, 2011 08:13 PM

                          paulj: Are you meaning the link that is underscored "established"? I believe that's the original DOE study that keeps getting repeated. I remember no methodology specifics from reading it, but maybe I dozed off... Did you find any?

                          1. re: kaleokahu
                            paulj Feb 17, 2011 09:29 PM

                            I was thinking of the 'take a closer look' section, which ends:
                            "In fact, Panasonic states for several of its units that efficiency is 90%, noting that: Heating-efficiency measurements were taken based on standards of the Japanese Electrical Manufacturers' Association and using a Panasonic standard enamelled iron pot. Also: a University of Hong Kong research product showed induction efficiencies from 83.3% to 87.9%, numbers clearly in line with 84% as a minimum and 90% as possible."

                            Of course even if you had reliable efficiency numbers for different stoves, it wouldn't tell you which is cheaper to run - unless you factor in the costs of natural gas and electricity. One is measured in cubic feet (I think - I haven't had gas for a couple of decades), the other KwHr.

                            For me, efficiency matters primarily in the summer when I'd rather not heat up the kitchen more than necessary. Then the induction burner wins hands down over the electric coil stove. I can tell that just by feeling the excess heat radiating from the coil burners.

                            Otherwise, induction is nice because of its responsiveness and control.

                            1. re: paulj
                              kaleokahu Feb 17, 2011 09:53 PM

                              paulj: Great. Now I have to chase down the JEMA standards and a "standard" Panasonic pot.

                              You may remember that I live where I actually LIKE a little added kitchen heat most of the year. But I'm still interested in understanding and testing these efficiency claims.

        2. e
          E_M Feb 17, 2011 01:54 AM

          Just to go on a tangent, yes, I have heard that occasionally a magnetic pot (Le Creuset) would not work on an induction (Wolf?) cooktop. Wouldn't this fault lie with the cooktop, since LC works on others? And I believe that Wolf fixed this in subsequent versions, but still. The cooktop has an equal responsibility to work with the pots.

          3 Replies
          1. re: E_M
            SanityRemoved Feb 17, 2011 05:02 AM

            I would imagine that many manufacturers of induction stove tops go for a range of required magnetism that allows for a similar response across the different cookware they have tested. They could probably make a wider range of pans/materials work but if that results in one pan on a low setting responding appropriately and another pan set at low but responding like it was on a high setting then we move away from what they are trying to replicate. By eliminating certain metals and alloys they can achieve results that are similar to what is expected using gas or electric stove tops. We can accept differences between materials we cook with but no matter what we cook on we expect somewhat similar results.

            Without limitations imagine all the cook books that would need revision. "Note: If using Bovine Impression or Whackology 3000 cookware on a Quadraquirk or Vapid Industries induction stove top, set heat to medium-low"

            1. re: SanityRemoved
              paulj Feb 17, 2011 07:55 AM

              I imagine the burner applies some power (may be not full) to the induction coil, and senses its response. Without a pan it will respond one way; with a good cooking pot (material, size, etc) another way. If the response is in spec, it moves on to full power; if not, error message.

              1. re: paulj
                SanityRemoved Feb 17, 2011 08:53 AM

                That makes sense to me. I also wonder at what point the amount of power used for a less suitable pan would cause the electric meter to spin faster. In the end it could be cheaper to buy a disc or even induction rated pans.

          2. s
            slopfrog Feb 17, 2011 05:30 PM

            Magnetism in stainless steels is often misunderstood by most people. I am not a metallurgist, but I will do my best to explain the reason for the various magnetic behaviors in stainless steels.

            All stainless steel may look pretty much the same to the naked eye. However, on a microscopic level they are quite different. There are lots of little crystals, each with their own structure of how they are put together. There are three main types of these structures in stainless steel. They are called austenite, ferrite, and martensite.

            By far the most common stainless steel is "austenitic." This just means it has mostly austenite in it. When you see 18/8 or 18/10 listed for the steel, it is telling you how much Chromium / Nickel is in the steel. The first number means 18% chromium, and the second means 8% or 10% nickel. The nickel is the key to making austenite. Both of those common steels are therefore austenitic. (You may have heard of types 304 and 316 steel... they are pretty much the same thing as 18/8 and 18/10.)

            Austenite is quite soft, at least as far as steels go, and is paramagnetic. That just means it doesn't get magnetized or a magnet won't stick to it. On the plus side, austenite is very tough (hard to break, it doesn't shatter, it bends and smooshes) and is extremely resistant to corrosion.

            Ferrite isn't really all that important when worrying about stainless steels found in the kitchen. But it is stronger than austenite, less corrosion resistant, and is ferromagnetic. That just means it gets magnetized and a magnet will stick to it.

            Martensite is an extremely hard phase of stainless steel. It is very hard, but also very brittle and not very tough. (Think of it sort of like glass. It is very hard -- thats why it dulls your knives on a glass cutting board -- but will shatter if you hit it.) It is very susceptible to corrosion. Most kitchen knives are made from martensitic stainless steel. They do this so that the knife gets sharp and stays sharp. If you were to try to make an austenitic kitchen knife, it would never get very sharp and would be dull after a short while. But as you probably know, a kitchen knife rusts much easier than an 18/10 stainless pot. Martensite is ferromagnetic, so the magnet sticks to it.

            So that explains why a magnet will stick to your stainless steel knife but not to your stainless steel pot.

            That begs the question: why do some austenitic steels have a magnet weakly get attracted to them? It's because the metal is never made up of just one phase. It's a mix of different ones. The more ferrite and martensite that is present, the more the magnet will stick. You can also form ferrite and martensite from "cold working" austenite. If you sat and hammered on your 18/8 pot for a long time, you would notice that your magnet sticks to the hammered area better than it first did. You would also notice that the area you hammered would be more susceptible to corrosion. Since nickel is what stabilizes austenite, it would be harder to do with an 18/10 pot than your 18/8 pot.

            Since the more magnetic the stainless steel is, the more susceptible to corrosion it is, if you go shopping for pots you can see what is attracted to a magnet and what's not. Even amongst pots that claim to be of the same alloy, you will see that some are more magnetic. That is because they were cold worked when they were made. They are more likely to get corroded over time.

            1 Reply
            1. re: slopfrog
              paulj Feb 17, 2011 05:38 PM

              So a good induction compatible SS probably will have a corrosion resistant, nonmagnetic body, a magnetic base, and conductive aluminum core. An example is my Fagor pressure cooker.

            2. s
              slopfrog Feb 17, 2011 05:48 PM

              I'll also try to answer a little bit about the induction heating issues. I am not an electrical engineer either, but this is it as I understand it:

              An induction "burner" creates a rapidly changing electromagnetic field. The changing back and forth of this field induces an electric current in conductors like metal. This is the principle by which generators work. You spin a magnet within a coil of wire, and you get electricity out of it.

              When have an electric current flowing, you will create heat. If you've ever felt the cord of your vacuum cleaner after using it a while, you will notice it is warm. The electricity flowing through the metal in the wire is making heat because the wire has resistance to the current. This is also how an electric burner element works, except it has a very high resistance intentionally to make heat -- your vacuum cleaner's manufacturer was just cheap and used a thin wire.

              So any metal will get warm from the rapid changing of an electromagnetic field around it. But that's not the whole story either. A magnetic field forming, collapsing, and reforming within the metal creates heat by something called magnetic hysteresis. This can only occur in materials with a high magnetic permeability (to keep it simple for us, that just means a magnet will stick to it.)

              So a pan that has a lot of martensite, ferrite, or other magnetic material in it will get heated both by the current and by the hysteresis -- creating a pan that heats quickly and gets hot on an induction range. An aluminum pan, on the other hand, will only be heated by the current, so it won't get as hot as fast. Of course, a manufacturer could put a layer of carbon steel surrounded by an austenitic stainless steel to get the corrosion resistance of austenite while still getting a pan that heated very nicely over an induction range.

              2 Replies
              1. re: slopfrog
                kaleokahu Feb 17, 2011 07:18 PM

                slopfrog: I am no metallurgist either, but I have read that hysteresis losses contribute something <10% of the heat from an induction appliance. Do you know otherwise?

                1. re: kaleokahu
                  s
                  slopfrog Feb 18, 2011 12:34 PM

                  I couldn't say one way or the other. I would assume that the percent of heat coming from hysteresis vs. inducted currents is a complex function of the appliance's metallic makeup, geometry, and also of the frequency and intensity of the AC inductor. To determine how they all play together to make what percentage of heat would require a specialized engineer.

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