magnetism, or you just happy to see me?

B

Billbo66

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Nov 19, 2008
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While packing for a trip this a.m., I noticed a strange happening. I placed a new Swamp Rat HC (154CM) near a compass....and it moved the needle toward it. Hmmmm.....so I waved it back and forth, and confirmed that yes, the blade must be magnetized. Then I got out a knife in S30V, and it actually repelled the needle. So I tried the RC-6 (1095), which acted like the S30V, slightly repelling the needle of the compass.

I don't think this will make any difference in the big picture, other than a bit of concern over storing the compass and Swamp Rat next to each other in gear over a period of time. I did think it was interesting. Can anyone explain this phenomenon to me? I seem to remember reading something about heat treating to demagnetize steel. Interesting.
 
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Steel can be charged either positively or negatively. If it's grounded it'll decharge. This can happen to any kind of steel no matter if it's been hardened. It's just a matter of electrons jumping over to the blade.

Nothing weird.
 
I have found that polishing a blade on a linen wheel will charge it with static electricity, which isn't permanent. However, a "charged blade" is a bit of an annoyance when sharpening as it holds the metal "filings" along the edge of the blade making me have to wipe more often. I prefer my filings to be held in the oil creating a "slurry" which sometimes helps in the sharpening process. When stropping the final edge micro-filings are a detriment and I don't like them at all. They tend to contaminate the abrasive on the strop.
 
Hi,

I don't know their manufacturing process, but the residual magnetism you are seeing is most likely caused by a less than perfect de-mag from grinding your blade.

During the grinding process, the blade is held by a magnet allowing a clear work surface. These electro-magnets are very strong. Strong enough to almost permanently alter the magnetic properties of the steel. After the work is done, the magnetic chuck has it's field flip-flopped quickly a time or two. This is to de-mag the part. Tool steels are notorious for being hard to de-mag. They always seem to hold a bit of magnetism no matter what.

Eventually, your knife blade will lose most of it's strong magnetic attraction. It will take awhile though.

dalee
 
dalee100 said:
Hi,

I don't know their manufacturing process, but the residual magnetism you are seeing is most likely caused by a less than perfect de-mag from grinding your blade.

During the grinding process, the blade is held by a magnet allowing a clear work surface. These electro-magnets are very strong. Strong enough to almost permanently alter the magnetic properties of the steel. After the work is done, the magnetic chuck has it's field flip-flopped quickly a time or two. This is to de-mag the part. Tool steels are notorious for being hard to de-mag. They always seem to hold a bit of magnetism no matter what.

Eventually, your knife blade will lose most of it's strong magnetic attraction. It will take awhile though.

dalee
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This is pretty accurate. Steel primarily achieves its macroscopic magnetic properties (e.g., magnetism WE would notice) via the alignment of smaller magnetic domains by means such as those dalee mentions above.

The domains will slowly randomize over time. There are other ways to demagnetize using degaussing systems ... this can also be done through heating, though most of us simply choose to wait.

It will fade.
 
Well, the compass needle is a magnet, after all. It will deflect toward a nearby piece of steel whether it is magnetized or not. The fact that the compass deflects near the knife is not a certain indication that the knife steel is magnetized.
 
oooh the joys of land naving a half mile with a bayonet in your hand next to the compass thinking your spot on only to find that your a frickin idiot :D
 
gibbyx said:
Might make a difference in EOD work.
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Would never use any steel blade for EOD work, titanium or bronze only. For setting charges it is ok as the steel should never come near the caps but quite often in EOD you can be dealing with magnetic triggers. Mission Knives makes some nice titanium blades designed for EOD personnel.
 
Billbo66 said:
While packing for a trip this a.m., I noticed a strange happening. I placed a new Swamp Rat HC (154CM) near a compass....and it moved the needle toward it. Hmmmm.....so I waved it back and forth, and confirmed that yes, the blade must be magnetized. Then I got out a knife in S30V, and it actually repelled the needle. So I tried the RC-6 (1095), which acted like the S30V, slightly repelling the needle of the compass.

I don't think this will make any difference in the big picture, other than a bit of concern over storing the compass and Swamp Rat next to each other
Click to expand...

You do of course realize that because the other steels repelled the needle, they are magnetically charged too, just in the opposite polarity.
 
MikeH said:
Well, the compass needle is a magnet, after all. It will deflect toward a nearby piece of steel whether it is magnetized or not. The fact that the compass deflects near the knife is not a certain indication that the knife steel is magnetized.
Click to expand...

That's what I was thinking.

Kind regards,

Jos
 
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