Thread: How to heat treat a file?

Hi Shaggy,

The best method to establish the temperature to reharden at is by using a magnet. The steel will become non magnetic once the bottom end of the critical temperature zone is reached. If you go above this by around 200 degrees you will obtain the full hardness without the guess work. To soften the steel is basically the same without quenching. If you have access to a heat treating furnace you will be able to ring the steel up to temperature in it then allow it to cool in the furnace.

It's already been menioned that some files are only case hardened and it is a good idea to cut off a small test piece to save the heart ache of putting in a lot of work for nothing. This has happened to me nn the past.

If it does turn out to be case hardened it can be used for damascus projects down the track.

I hope this helps.

Keith.

Thanks for the info.

Yesterday I got another file from the same brand. I have an uncle who works in the metal industry and he is going to get me specific data on the metal composition and the way to soften and harden it to factory specs. The files I'm using now are tested this week at 70HRC, so that's pretty hard, but brittle. But I don't mind, the edge is so fine it should sharpen up nicely.

If you are going to heat treat it, you're not going to hit 70 HRc.
And that's a good thing. The adjective for a 70 HRc razor would be 'defective'.
Extremely brittle, and extremely hard to hone.

People here have honed razors at HRc 64 and 65. It's very tedious and time consuming, and has a high risk of micro chipping.
I don't even know how you;d get a file to 70 HRc using normal heat treatment methods. But even if you could, it would just mean you created a useless razor

I'll double up on that!!

I recently had a full hollow 440c blade that was around 61-63. I accidentally forgot to put it through its second temper cycle. It wouldn't get through one shave then the edge would be so chipped out it was like it was never honed. It took a little while to figure out what was wrong, but an additional temper cycle and now its shaving like a champ. I think (depending on steel and profile) that 57-60 is where its at as far as razor edges go!

HI Shaggy,

70 HRC is unbelievably hard. this would only be obtainable under very controlled conditions. I'd recommend quenching the blade in oil even if this steel turns out to be a water quench steel also. The cross section of a razor compared to a file as you can understand is significantly different and a blade would more than likely not survive a quench that violent.

a blade hardness of around 60HRC would give the best overall performance whilst keeping a measure of toughness to prevent micro chipping and accidental knocks on the basin ect. as previously mentioned.

I know that having a razor with 70hrc is much to hard/brittle. It should be in the neighbourhood of 60-63 now. The original files are 70hrc, the one I am doing now is hardend to that 60ish figure.

Just curious, how are you testing the hardness & coming up with conclusive numbers?

My uncle who gave me the files is a metalworker milling/turning etc. and has the equipment to test this, and so he did.

Originally Posted by Shaggy8675

My uncle who gave me the files is a metalworker milling/turning etc. and has the equipment to test this, and so he did.

That is certainly very convenient. Most of us have to devise all sorts of tests to get some idea of what is happening.
A rockwell tester is something I want to buy some day.

Well, we come from a family of metalworkers here. Me, my uncles, my brother, nephews all got their feet in turning, milling, grinding, welding etc. So it has got it's perks