Difficulties magnetizing plain steel flat bar
Difficulties magnetizing plain steel flat bar
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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
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
RE: Difficulties magnetizing plain steel flat bar
http://en.wikipedia.org/wiki/Magnetic_domains
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RE: Difficulties magnetizing plain steel flat bar
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.
RE: Difficulties magnetizing plain steel flat bar
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?
RE: Difficulties magnetizing plain steel flat bar
Based on that what would you recommend for this hobby lol?
RE: Difficulties magnetizing plain steel flat bar
RE: Difficulties magnetizing plain steel flat bar
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RE: Difficulties magnetizing plain steel flat bar
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").
RE: Difficulties magnetizing plain steel flat bar
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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RE: Difficulties magnetizing plain steel flat 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.
RE: Difficulties magnetizing plain steel flat bar
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?
RE: Difficulties magnetizing plain steel flat bar
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
RE: Difficulties magnetizing plain steel flat bar
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RE: Difficulties magnetizing plain steel flat bar
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?
RE: Difficulties magnetizing plain steel flat bar
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? -.-
RE: Difficulties magnetizing plain steel flat bar
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RE: Difficulties magnetizing plain steel flat bar
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.