00:00A magnet shouldn't stick to stainless steel, is that really true?
00:03And if the magnet sticks to stainless steel, does that mean it's fake?
00:13Hey, Detailed Engineering, have you heard people claim that good stainless steel isn't magnetic?
00:19Or even tests done here on the internet trying to show that if a magnet sticks to stainless steel, then
00:25it's fake.
00:26Well, not all stainless steel is the same.
00:29And the interaction with magnets depends on the microstructure of the material, not its quality or whether it's real or
00:37fake.
00:37There are families of stainless steels that are naturally magnetic and others that, under typical conditions, are not.
00:44So, why does this happen and what really defines if stainless steel is good?
00:49But let's get to it, why are some metals attracted to magnets and others not?
00:53This has to do with the arrangement of the atoms and how the magnetic moments align,
00:58practically speaking, for stainless steel.
01:00If the microstructure is austenitic, with a face-centered cubic crystal structure,
01:06the material is typically non-magnetic or only weakly paramagnetic.
01:11Now, if it is ferritic or body-centered cubic or martensitic, which is a tetragonal form derived from iron,
01:20it is ferromagnetic and will attract a magnet.
01:23In other words, the phenomenon is related to the steel phases present after manufacturing and treatment.
01:29And what are the stainless steel families and how does this affect the magnet?
01:32The stainless steels?
01:34Austenitic like those from the 300 series, for example.
01:38The AISI-304 in annealed conditions normally does not attract magnets, unlike ferritic ones like AISI-430
01:47and martensitic ones like AISI-410 and AISI-420.
01:52They are magnetic.
01:54Duplex steels like SAF-2205, which combine austenite and ferrit, tend to be partially magnetic.
02:03Therefore, the behavior in relation to a magnet is a reflection of the microstructure,
02:07where austenite, in general, is not magnetic.
02:11Ferritic and martensitic steels are magnetic, and when you have a mixture, it has intermediate magnetism.
02:18But I've heard that nickel is the secret to stainless steel that doesn't stick to a magnet.
02:22Is that true?
02:23In part, yes.
02:24Nickel is an austenite stabilizer in AC-304, for example.
02:29The typical composition is around 18% chromium and 8% nickel,
02:35which favors the non-magnetic austenitic phase.
02:39In AISI-316, in addition to chromium and nickel, there is molybdenum,
02:43typically 2% to 3% to improve pitting corrosion resistance in chloride environments.
02:50AISI-430, a common ferritic stainless steel, has about 16% to 18% chromium and little or no nickel,
02:59making it naturally magnetic.
03:01AISI-410 martensitic has around 11.5 to 13.5% chromium,
03:07and a carbon content that allows hardening, also exhibiting magnetism.
03:12But why does an AISI-304 sometimes attract a magnet only on the bent edges or deformed areas?
03:20The answer lies in martensite, which is induced by deformation when 304 undergoes cold working,
03:28such as bending, drawing, or stamping.
03:31Part of the austenite can transform into martensite, which is ferromagnetic.
03:36The practical result is a 304 that remains barely magnetic in the areas that weren't worked,
03:43and shows noticeable attraction where it was deformed.
03:46This doesn't mean that the material is fake or of low quality.
03:50It's a well-known metallurgical effect in austenitic steels, with certain combinations of chromium and nickel.
03:57Did you notice how even a simple magnet test actually hides super complex materials engineering behind it?
04:03Uncovering the truth behind myths, and deeply understanding every technical detail,
04:07is what sets a good engineer apart.
04:09In weld beads of austenitic steels, it's common to have a fraction of delta ferrite in the weld metal
04:16to reduce susceptibility to solidification cracking.
04:20This ferrite is ferromagnetic, so a magnet can stick to the weld bead area or the heat affected zone,
04:28even if the main body of the material is mostly austenitic and non-magnetic.
04:32Again, this doesn't indicate counterfeiting, it just shows the presence of a magnetic phase locally,
04:39due to the welding design.
04:41But hold on, does a magnetic stainless steel mean it's worse against corrosion,
04:45and non-magnetic means it's better?
04:47Not necessarily.
04:49Corrosion resistance depends on the composition and the environment, not on magnetism.
04:54There is ferritic stainless steel in refrigerators and panels,
04:57which works very well in indoor and dry environments, even though it's magnetic.
05:03In marine environments or those with chlorine, AIC 316 is usually preferred because of the presence of molybdenum.
05:10On the other hand, 430, although useful and economical for indoor applications,
05:14has lower resistance to pitting corrosion in chloride environments.
05:18So, does it stick or not?
05:20A magnet does not determine corrosion resistance performance and there is fake stainless steel.
05:26Unfortunately, there are cases of poorly specified or incorrectly labeled materials,
05:32but using a magnet to detect counterfeiting is a misleading shortcut.
05:36The difference between material that is unsuitable for the application and counterfeit material is significant,
05:42and the magnet does not distinguish this.
05:45And how can you really check what the alloy is?
05:48For reliable grade identification, PMI methods or positive material identification are used,
05:55such as X-ray fluorescence spectrometry or optical emission spectrometry,
06:00which measure the chemical composition and confirm the levels of elements like chromium, nickel and molybdenum.
06:08Material certificates from the supplier with traceability and the applicable standard are also essential.
06:14Specific corrosion tests or criteria such as PREN help compare performance in chloride environments.
06:22None of this is replaced by a magnet and you can use a magnet for some quick screening in daily
06:28routines.
06:29Well, yes, but only as a screening tool and with caution.
06:32If a component is strongly magnetic, you might suspect it's ferritic or martensitic.
06:38If it's practically non-magnetic, it could be annealed austenitic.
06:43And if it's somewhere in between, it's likely deformed austenitic.
06:48But this is just a preliminary indication and isn't suitable for testing quality,
06:52authenticity or suitability for the application.
06:55For responsible design, purchasing and specification, ask for the grade,
06:59check standards and use suppliers with technical documentation and a reliable track record.
07:04So, what's the final message?
07:06For those who associate good stainless steel with not being attracted to a magnet,
07:10the message is, magnetism is not a quality criterion for stainless steel,
07:14it just reveals something about it. At most, it shows which metallurgical phase is present
07:19and this varies with the alloy family, processing and composition.
07:23What defines if a stainless steel is good is whether it is suitable for the environment and its function.
07:29And the magnet doesn't tell the whole story if you saw a video using the magnet test as a verdict
07:35of authenticity.
07:37It is worth asking what family the stainless steel belongs to,
07:40what the manufacturing process was and what the environment of use is.
07:44These three answers explain pretty much every case where a magnet sticks to stainless steel
07:49and at the same time, debunk the idea that if it sticks, then it's fake.
07:54In engineering, context is everything and when it comes to stainless steel,
07:57context means microstructure, composition and environment.
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08:29So, had you ever seen this magnet test with stainless steel?
08:33Were you someone who believed that stainless steel couldn't attract a magnet?
08:37Let me know in the comments, I want to hear from you.
08:39Right here on the side, there are two interesting video options that you need to watch to expand your knowledge
08:43and explore your curiosity.
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08:52That's it, engineering enthusiasts, take care and I'll see you in the next video.
