Hardening the cutting edge of a knife with graphite

I will tell you and show you a simple way to harden any knife at home. And then, I will not harden the entire knife, but only its cutting edge, which greatly simplifies the task.
Hardening the cutting edge of a knife with graphite

If we go into detail, it will most likely not be hardening, but carburization, which aims to increase the hardness and wear resistance of the metal.

Hardening the cutting edge of a knife


We take a knife.
Hardening the cutting edge of a knife with graphite

We go along the edge with a file, while paying attention to the dull sound and slight grinding of the metal. Everything indicates that the knife is made of ordinary steel and has not been previously hardened.
Hardening the cutting edge of a knife with graphite

For hardening you need graphite. It is best to obtain graphite from graphite brushes of a generator or brushed electric motor. Of course, I haven’t tried it, but you can also get graphite rods from AA batteries or simple pencils.
In general, we grind this graphite into powder in any way. There is no need to grind it too much, without fanaticism.
Hardening the cutting edge of a knife with graphite

Next, I need a metal base on which the graphite powder will lie. I took a piece of galvanized drywall profile.
Hardening the cutting edge of a knife with graphite

The knife edge hardening process also requires a power source.Ideally, this is a pulsed DC welding machine set to minimum. You can also try to repeat the process using another source, 30-60 volts AC or DC. There is another dangerous option: using a 220 V network directly, in series with an incandescent lamp, but this is already fraught, so I do not recommend it.
Hardening the cutting edge of a knife with graphite

Hardening the cutting edge of a knife with graphite

Pour in graphite. We connect the plus of the welding machine to the base of the substrate, and the minus to the knife.
We set the inverter to minimum settings and turn it on.
We begin the process of hardening the edge. To do this, very carefully run the edge of the knife along the graphite pile.
Our task is: first, to prevent the blade from touching the base. And the second thing is to prevent the graphite from burning. In both cases the blade will be damaged.
Hardening the cutting edge of a knife with graphite

Hardening the cutting edge of a knife with graphite

Hardening the cutting edge of a knife with graphite

Ideally, the blade should be moved slowly, and the graphite should sparkle and flicker. Naturally, you don’t need to lower the knife too much.
As soon as you notice the contact area heating up, immediately lift the knife.
Hardening the cutting edge of a knife with graphite

Hardening the cutting edge of a knife with graphite

The whole process does not last long, about 5 minutes. During this time I managed to walk along the entire length of the blade several times.

Knife hardening result


Hardening the cutting edge of a knife with graphite

We take the file and shuffle the blade like the first time. A ringing sound is immediately audible, indicating the high hardness of the metal. Plus, the edge is practically impossible to process.
Hardening the cutting edge of a knife with graphite

We cut a glass jar.
Hardening the cutting edge of a knife with graphite

Leaves notches, be healthy!
We knock on a steel nail.
Hardening the cutting edge of a knife with graphite

The result is excellent - not a scratch on the knife.
Hardening the cutting edge of a knife with graphite

Finally, I cut the nail with a knife by hitting it with a hammer.
Hardening the cutting edge of a knife with graphite

The knife was not damaged!
I'm not a big expert in steel hardening, but the method really clearly works. Local craftsmen say that such hardening increases the hardness of a section of metal to almost 90 units.I can’t disagree or refute, since I don’t have a hardness tester. If you have questions or suggestions, as well as comments, write in the comments. Good luck to all!

Watch a video of the knife hardening process


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Comments (10)
  1. feelloff
    #1 feelloff Guests 23 November 2017 14:16
    7
    I do not recommend using mains voltage -

  2. Oltaviro Oltaviro
    #2 Oltaviro Oltaviro Guests November 24, 2017 12:04
    1
    “Ideally, the blade should be moved slowly, and the graphite should sparkle as it flickers” - how exactly should graphite sparkle?
    1. Valentine
      #3 Valentine Guests 24 November 2017 13:04
      7
      I always wondered where such pseudo-clever people come from. Everyone understands - to spark without burning an arc.
  3. Vladimir
    #4 Vladimir Guests November 26, 2017 11:59
    5
    If it works, then it’s possible. The problem is that the powder does not conduct low voltage current. Even metal filings (Popov’s experiments with a baretter) Rather, not all the powder, but individual pieces for priming the arc. The polarity is correct - the anode dissolves. Cemented steel is brittle with great hardness; in production, the depth is 1-3 mm for subsequent processing, hardening and grinding.
    1. Guest Andrey
      #5 Guest Andrey Guests December 4, 2017 12:44
      4
      It’s just that 90 units won’t work, the maximum is 60-63 according to HRC. It's just carbon, albeit cemented
  4. Rozakhusainov
    #6 Rozakhusainov Guests December 22, 2017 07:45
    3
    Super! Exactly what is needed.
  5. Guest Yuri
    #7 Guest Yuri Guests 25 May 2019 12:39
    2
    This is not graphite, but carbon powder. Graphite is gray and slippery to the touch, so you need to look for graphite brushes. They leave a mark on paper no worse than a pencil. Pencil lead will not work, there is a lot of clay there. Or, if possible, go to the nearest foundry, they have an abundance of ground graphite for molding.
  6. Skeptic
    #8 Skeptic Guests 17 July 2019 14:54
    1
    What the hell is hardening - the product is clearly cemented, and not of the highest quality...
  7. ripped
    #9 ripped Guests February 8, 2020 00:39
    4
    Is the sharpness of the edge lost when carburizing or will carburizing not affect the sharpness?
  8. Max
    #10 Max Guests March 3, 2020 04:21
    3
    The process of saturating the blade with carbon is described, but not a word about hardening! That is, just this is not enough, after that you need to heat the knife again and put it in water, only then will it give hardness.