Difficulties magnetizing plain steel flat bar

[IDNeon]

Well I figured while getting an answer to the title problem, I'll go all in and see how best an answer I can get on several things!

Basically I thought (seemingly wrong) that you could take a magnet, magnetize a magnetic metal, and repeat this process and compound magnets together eventually to create a compound magnet strong enough to saturate any magnetic metal...

Well I could magnetize weird steel:iron objects like files but they barely compound and they could only get so strong...so I went an bought a plainsteel bar, and had it cut to nice lengths, and wouldn't I be damned if the thing barely magnetized at all!

So what I'm trying to discover is:

Can a magnetic metal left in even a weak field long enough become saturated? If not why not?

Must a magnetic field be strong enough to over come anything such as magnetic domain? Is this or it's low permeability the reason the steel is not magnetizing?

Or did I get unlucky and get an Ausentitic piece of low-carbon steel and it can barely magnetize because of it's microstructure?

A bonus question, if the domains are random such that an object were not polar, if you were to align a fraction of the domains so that you had some retained magnetism, but not enough of the domains would the other random domains pull the aligned domains back out of alignement?

I've noticed my bars tend to lose magnetism and are painful to align the more I work them.

Hope these questions are clear as a layman...I hope they are not pretty dumb too

 

[IRstuff]

I suggest you read some of the articles in Wikipedia, starting with:

http://en.wikipedia.org/wiki/Magnetic_domains

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[IDNeon]

Well I did read that but it isn't clear to me why the plain steel is difficult to magnetize. As far as I can tell it is either the steel is austenite, the magnet is too hard to magnetize with my weaker magnets, or I'm not leaving it in a field long enough to change enough domains.

Also wiki didn't make it clear how domains effect each other in partial alignments. For instance why won't partially aligned domains favor full alignment based on the majority of strongest alignments? 51% same alignment means the 49% gradually align with the majority?

But for now the first paragraph is my focus.

 

[MagMike]

If your plain steel flat bar is carbon steel, your bar isn't austenitic.

Plain steel doesn't have a high enough coercivity to retain much magnetism after the magnetizing force is removed. That's why they are not considered permanent magnets.

You need to use a permanent magnet, not plain steel.

BTW: What are you trying to do?

 

[IDNeon]

I want to build an old school magneizer as a hobby and go through basically the steps taken by Gowan Knight to do it. It wold help then to know where to get some iron bars instead of a plain steel? I don't want to just buy bar magnets, the hobby's goal is to take a weak magnet like a lodestone and build more magnets. I don't want alloys made for magnetizing purposes... I'd love just hard plain iron bars but where could I get that? Everything is steel at hardware stores.

Based on that what would you recommend for this hobby lol?

 

[IDNeon]

Also I'd like help better understanding those processes...so feel free to get technical.

 

[IRstuff]

This is not an education site; it's a work-related site, for people to ask questions about work-related problems. In any case, a weak magnet cannot create a stronger magnet; consider it analogous to conservation of energy.

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[RyreInc]

A few points:

Not all domains have the same coercivity--when only a portion of the domains are aligned, the ones with the lowest coercivity align first.

Time is not a factor in magnetizing (it is, but only on the micro/millisecond scales, to overcome eddy currents).

The shape of the object affects its ability to retain magnetization (look up "permeance coefficient").

 

[dgallup]

Your plain steel is too soft. It demagnetizes as soon as you remove the source magnetic field. That's what the other posters are referring to when they say it has low coercivity. You need a hardened steel. That is why your files worked, they are ferromagnetic and hard.

You will have a much easier time using a coil and battery to magnetize things than just rubbing them with a magnet. Note that you need a lot of amp-turns to get a strong enough field.

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[MagBen]

Gowan Knight's experiment makes no much sense and not at all secret NOW. The consept was to put two permanet magnets on both end of bar to be magentized, and magnetize the bar.

The concept of a "compound" magnet makes more sense. The idea to keep the polarity from multiple magents at the same direction is to keep the magnetic field as strong as possible when the distance increases. In the air, B=H, so the largest strength field close to the surface is steel's the Br, so in case of square loop, the highest H could be 20,000Oe, surfficient to fully magentize any soft magnetic alloy if the bar is short enough and field between the two compound magnets keep a contant at 2T. This is theoritically possible.

 

[IDNeon]

I now have a better understanding of what I want, like martensitic steel or 430 steel since that should be available (though oddly not easy to find in flats).

But strangely I can't seem to put two and two together why a low carbon steel is softly magnetic when structurally it should be ferrite, or pearlite or cementite, all of which should be magnetic hard magnetic?

Am I mistaken about the microstructure of plain steel/low carbon steel?

Or am I mistaken about ferrite being hard magnetic material?

 

[ndsram]

Dear IDNeon,

Well there are nuemerous replies, but I can suggest you to improve the magnetism in plain steel. Now that you make some heat treatment process to change the microstructure, you'll see improvement. If you've some cobalt powder, heat treat to red hot and sprinkle the powder on the red hot metal, you'll see improvement. Moreover if you could improve the hysteresis area of the steel, your steel would be magnet.
Impart some heating and quenching process will magnetism in steel

To explain on the magnetization, the magnetic domain on the material (plain steel) doesnot sufficiently have the capacity to pin the domain wall on the grain boundaries during the magnetization process. The pinning of domain wall will induce magnetism in the material. However the domain wall pinning is strong in case of hard magnetic material (permanent magnets)

Steel has higher permeability. To saturate the magnetic metal, the applied field should be morethan that of the Hc of the material.

regards
n d senthil ram

 

[dgallup]

In very general terms if the material is soft mechanically it will be soft magnetically. Soft materials may be strongly ferromagnetic but will not retain much magnetism. Low carbon steel and 430 are both examples of soft magnetic materials. Neither will make a decent permanent magnet. You need hardened high carbon steels or martensitic stainless steel like 440C. These will still not be nearly as good as the materials typically used to make permanent magnets.

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[IDNeon]

Yes, I understand modern permanents are either special alloys or sintered ferrites, I could over time work with making an anisotropic ferrite bar magnet as Gowan sort of did with his iron filings pulverized to dust then fixed into a linseed matrix.

But let me then just clarify. All ferrite (pure) is soft? How does Magnetite retain magnetism? Is it based on the several physical properties which restrict domain movement?

If ferrite is generally soft it makes sense then all that makes a hard magnet are those alloys which make a BCC or BCT structure and make domain movement difficult?

If Ferrite can be hard...then what is causing it to be soft in low carbon steels? Mg,Mn,Cu,Zn,Li alloys make soft ferrite...

But Co,Sr and some others make hard ferrite?

How is the low carbon/high carbon effecting coercive force?

 

[IDNeon]

Just going back to the basics...I'm trying to duplicate some of the early magnetic experiments. How were these gentlemen 400-300 years ago making permanent magnets like Gowan knight's magnetic machine? They weren't using neodymium or cobalt alloys, even Alnico is from 1930s and they weren't even using hardened steels but just plain iron right?

My plain steel bars don't even retain enough magnetism to lift a nail!

These guys were making out of rudamentary materials magnets that could lift 20 times their weight!

What am I missing? -.-

 

[dgallup]

Carbon.

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[MagBen]

you are mentioning too many things at the same time.

To be a permanent magnet (so-called magnetic), the material needs to either have magnetocrystalline anisotropy, or shape anisotropy. the former refers to L10 (ordered fcc) or other asystemic cystilliine sturcuture (fcc, or bcc does not work), examples are NbFeB, FePt, MnAl, hard ferrites etc. The latter refers to elongated structure, say L/D ratio>1. examples are AlNiCo, FeCoCr (Arnokrome). To take advantage of shape anisotropy, it will also need to be nano-or micro-structure (in other words, single domain structure), such that the magentic domain can be held when the external field is removed. The elongated structure also needs to be seperated by non-magnetic structure to decrease exchange coupling. In Gowan's experiment, filings were single domain particle seperated by paste, when aligned in an earth magnetic field, this structure was held.

If one can make such a structure, you will get a strong magnet: pure iron nano-sized elongated particles with L/D ratio of 5-10/1, the particles are seperated by any nonmagnetic material (peopele tried silver).

carbon and alloy elements could pin the domain movement which make the alloy a little "harder", but basically hgih carbon, high alloy steel is still soft magnetically, if the fcc or bcc structure is not drastically changed to have obviously crystalline anisotropy. as a rule of thumb: coercivity (Hc) <10 Oe is soft magnet; Hc>100Oe is permanent magnet; 10-100Oe, semi-hard magent.